JP7796763B2 - Engine control device and engine control method - Google Patents

Description

The present invention relates to an engine control device and an engine control method for controlling an engine equipped with a variable valve timing control mechanism mounted on a hybrid vehicle.

In recent years, hybrid systems using an engine and a motor as the drive source have become mainstream for automotive powertrains. In hybrid vehicles, the engine is stopped and restarted more frequently than in conventional vehicles with internal combustion engines. Normally, when the engine is running, burned gases (exhaust gases) flow into the exhaust pipe. Gasoline-powered vehicles are equipped with a three-way catalyst in the exhaust pipe, which has the advantage of being the most efficient at purifying burned gases during stoichiometric air-fuel combustion.

However, when the engine is stopped and restarted, fresh air flows into the exhaust pipe during the fuel cut period, causing the oxygen storage capacity inside the three-way catalyst to become excessive, resulting in a deterioration in the purification efficiency of nitrogen oxides. As a result, enriched fuel injection is required to restore purification efficiency to an appropriate level when the engine is restarted after being stopped. In other words, to prevent enriched fuel injection when the engine is restarted, it is necessary to suppress the outflow of fresh air during the engine's fuel cut period.

Variable valve timing control mechanisms that change the phase of a camshaft that drives an intake valve or exhaust valve are known. For example, a variable valve timing control mechanism includes an engine with two intake valves for each cylinder, an inner camshaft with an inner cam integrally attached to its outer periphery that drives one of the intake valves, and an outer camshaft that is rotatable relative to the inner camshaft and has an outer cam integrally attached to its outer periphery that drives the other intake valve. A hydraulic actuator rotates the inner camshaft and outer camshaft relative to each other using supplied hydraulic pressure, thereby changing the operating angle of the intake valve or exhaust valve for each cylinder and controlling the timing of the opening and closing of the intake valve or exhaust valve.

Patent document 1 discloses an internal combustion engine system that allows air to flow back from the exhaust pipe to the intake pipe by changing valve timing based on information from an air-fuel ratio sensor in order to control gas flow during a fuel cut.

Japanese Patent Application Laid-Open No. 2020-169606

However, because hydraulic variable valve timing control mechanisms increase hydraulic pressure based on engine speed, they cannot change valve timing at low engine speeds. Therefore, when the engine in a hybrid vehicle is stopped, valve timing control must be completed before a certain engine speed is reached in order to start the next engine start from the desired valve timing phase.

Also, hybrid vehicles can be equipped with an idling stop function while the vehicle is in motion, which is expected to improve fuel efficiency. In recent years, to further reduce fuel consumption, fuel injection is cut off during periods when torque is not required when stopping the engine. However, frequent engine stops and restarts can also have negative effects. When the engine rotates by inertia with fuel cut, unburned air (fresh air) is drawn into the engine cylinders and discharged in that state. When the fresh air is discharged into the exhaust pipe and reaches the three-way catalyst installed in the exhaust pipe, the oxygen contained in the fresh air is stored in the three-way catalyst, creating an oxygen surplus. Similarly, when the engine is restarted, fresh air is discharged between the start of engine rotation and the first combustion. In particular, hybrid vehicles have a higher engine speed at the first combustion compared to conventional vehicles, and there is a longer time until the first combustion. As a result, a larger amount of fresh air flows from the engine's combustion chamber into the three-way catalyst installed in the exhaust pipe.

When a three-way catalyst falls into an oxygen-excess state, its efficiency in purifying nitrogen oxides (NOx) decreases. Therefore, the next time the engine is restarted, enriched fuel injection is implemented to remove excess oxygen from the three-way catalyst by increasing the amount of fuel injected and supplying excess fuel so that the air-fuel ratio is lower than the stoichiometric mixture ratio. However, enriched fuel injection consumes excess fuel, leading to worse fuel economy. Furthermore, because combustion occurs in an excess fuel state, emissions also worsen compared to combustion at the stoichiometric mixture ratio.

One method that has been adopted to solve these problems is to advance the phase of the intake valve in order to reduce the amount of fresh air discharged into the exhaust pipe during fuel cut. However, even if the discharge of fresh air into the exhaust pipe is suppressed after the intake valve phase is switched, the fresh air discharged into the exhaust pipe during the phase switch will reach the three-way catalyst, causing oxygen to be stored in the three-way catalyst. For this reason, it is not possible to completely eliminate the discharge of fresh air.

Furthermore, even when restarting the engine, there is a risk of misfire due to insufficient intake air volume depending on the amount of intake valve advance. For this reason, the intake valve phase must be changed to a valve timing that allows combustion between the start of engine rotation and the first combustion, and fresh air is discharged into the exhaust pipe during this phase change.

Thus, once the intake valve phase has been shifted to the target position, it is possible to prevent fresh air from being discharged into the exhaust pipe, but during the transitional period during the phase change, fresh air is discharged and oxygen is stored in the three-way catalyst. As a result, enriched fuel injection is ultimately required when the engine is restarted, which inevitably leads to a deterioration in both fuel economy and emissions.

However, the method described in Patent Document 1 requires that the variable valve timing control mechanism be capable of phase change at low engine speeds, a high phase change speed, and a wide phase change angle. To meet these requirements, a high-performance variable valve timing control mechanism, in other words, a substantially electric variable valve timing control mechanism, is essential.

Given the above situation, there was a demand for a method to prevent fresh air from flowing into the three-way catalyst when the fuel injection pulse is stopped between the engine stop process and engine restart in a hybrid vehicle, without using a high-performance variable valve timing control mechanism.

In order to solve the above problem, one aspect of the present invention is an engine control device that controls an engine mounted on a hybrid vehicle and includes a fuel injection device that injects fuel into air drawn into a cylinder of an internal combustion engine, an intake valve phase variable mechanism that changes the phase of an intake valve provided in an intake pipe of the internal combustion engine, an exhaust valve phase variable mechanism that changes the phase of an exhaust valve provided in an exhaust pipe of the internal combustion engine, a motor generator connected to the crankshaft of the internal combustion engine, and a crank angle sensor that detects the rotation of the crankshaft .
the engine control device includes a state determination unit that determines the engine speed from a signal from the crank angle sensor, determines whether an engine start flag from a vehicle control device of the hybrid vehicle is on or off , and determines whether a fuel cut command is on or off ; a control unit that controls fuel injection pulses of the fuel injection device, and controls the intake valve phase variable mechanism and the exhaust valve phase variable mechanism ; and a phase change information storage unit that stores the engine speed when the fuel injection pulse is stopped, which is obtained when the fuel injection pulse is stopped, an intake reference phase that is the phase of the intake valve for drawing air from the intake pipe into the cylinders of the internal combustion engine, an exhaust reference phase that is the phase of the exhaust valve for discharging air from inside the cylinders to the exhaust pipe, an exhaust target phase that sets the phase of the exhaust valve to a position advanced from the exhaust reference phase in accordance with the engine speed when the fuel injection pulse is stopped in order to cause air in the exhaust pipe to flow back into the cylinders, and an intake target phase that sets the phase of the intake valve to a position retarded from the intake reference phase in accordance with the engine speed when the fuel injection pulse is stopped in order to cause air in the cylinders to flow back into the intake pipe .
And the control unit
When the engine start flag is in an off state and the fuel cut command changes from off to on, a process is performed in which the fuel injection pulse stop is started and the value of the engine speed detected by the state determination unit is stored in the phase change information storage unit as the engine speed when the fuel injection pulse is stopped;
When the engine start flag is in an OFF state and the fuel cut command is in an ON state, the intake valve phase is controlled using the intake target phase, the exhaust valve phase is controlled using the exhaust target phase, and the fuel injection pulse is stopped;
When the engine start flag changes from off to on, if the engine speed detected by the state determination unit has not reached the initial combustion speed that is the timing for the initial combustion when the engine is restarted, motoring is performed to rotate the crankshaft using the motor generator, and the intake valve phase is controlled using the intake target phase, the exhaust valve phase is controlled using the exhaust target phase, and the fuel injection pulse is stopped.
When the engine start flag is on and the engine speed detected by the state determination unit has reached the initial combustion speed, the intake valve phase is controlled using the intake reference phase, the exhaust valve phase is controlled using the exhaust reference phase, and the fuel injection pulse is stopped until both controls are completed: the intake valve phase reaches the intake reference phase using the intake valve phase variable mechanism, and the exhaust valve phase reaches the exhaust reference phase using the exhaust valve phase variable mechanism.

In addition, an engine control device in another aspect of the present invention controls the phase of the intake valve and exhaust valve before and after a change in engine condition by using the oxygen storage capacity of a three-way catalyst installed in the exhaust pipe, instead of the engine speed at the time the fuel injection pulse is stopped in the engine control device of the above-mentioned aspect.

An engine control device according to at least one aspect of the present invention changes the phases of the intake valves and exhaust valves during engine stop processing of a hybrid vehicle in accordance with the engine state (engine speed or oxygen storage capacity of a three-way catalyst) when fuel injection pulses are stopped. This generates a backflow of burned gas in the intake pipe and exhaust pipe, preventing fresh air from flowing into the exhaust pipe until the first explosion when the engine is restarted. Therefore, it is possible to prevent fresh air from flowing into the three-way catalyst during the fuel injection pulse stop state between the engine stop processing and engine restart of the hybrid vehicle.
Furthermore, by using not only the intake valve but also the exhaust valve to generate backflow, the performance requirements for the variable valve timing control mechanism are relaxed, making it possible to prevent fresh air from entering the three-way catalyst without using a high-performance variable valve timing control mechanism.
Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

1 is a schematic configuration diagram showing an example in which an engine control device mounted on a hybrid vehicle according to a first embodiment of the present invention is applied to a series hybrid vehicle. 1 is a schematic diagram showing an example of the configuration of an engine according to a first embodiment of the present invention. FIG. FIG. 2 is a control block diagram showing an example of the internal configuration of an ECU according to the first embodiment of the present invention. FIG. 4 is a diagram showing an example of profiles of an intake valve and an exhaust valve during power generation operation when the engine is driven according to the first embodiment of the present invention. 4 is a diagram showing an example of the engine speed, fuel injection request, and intake valve/exhaust valve profiles at the start of fuel cut during engine operation according to the first embodiment of the present invention; FIG. 3A to 3C are diagrams showing examples of profiles of intake valves and exhaust valves that cause backflow in an engine cylinder according to the first embodiment of the present invention, and the state inside the engine cylinder; 4A and 4B are diagrams showing examples of profiles of the engine speed, fuel injection request, and intake valve/exhaust valve from the start of fuel cut to engine stop when the engine is running according to the first embodiment of the present invention. 5 is a graph showing an example of a target intake phase of an intake valve and a target exhaust phase of an exhaust valve according to the engine speed during a fuel cut according to the first embodiment of the present invention. 5 is a graph showing an example of an intake valve phase change speed of an intake valve and an exhaust valve phase change speed of an exhaust valve according to engine speed during fuel cut according to the first embodiment of the present invention. 10A and 10B are diagrams showing examples of engine speed, fuel injection request, and intake valve/exhaust valve profiles from engine start to before phase change when restarting the engine according to the first embodiment of the present invention. 10A and 10B are diagrams showing examples of engine speed, fuel injection request, and intake valve/exhaust valve profiles from the start of phase change to the first combustion when restarting the engine according to the first embodiment of the present invention. 4 is a flowchart showing an example of a procedure for variable valve timing control during engine stop processing according to the first embodiment of the present invention. 4 is a flowchart showing an example of a procedure for variable valve timing control at the time of restarting the engine according to the first embodiment of the present invention. 10 is a flowchart showing an example of a procedure for variable valve timing control during engine stop processing using an oxygen storage amount as a control trigger according to a second embodiment of the present invention.

Hereinafter, examples of embodiments of the present invention will be described with reference to the accompanying drawings. Components having substantially the same function or configuration in this specification and the accompanying drawings will be designated by the same reference numerals, and duplicate descriptions will be omitted.

First Embodiment
[General configuration of a series hybrid vehicle]
FIG. 1 is a schematic diagram showing an example in which an engine control device according to a first embodiment of the present invention is applied to a series hybrid vehicle.
The hybrid vehicle 100 according to this embodiment is an example of a series hybrid vehicle that includes a traction motor for running the vehicle and uses the engine only for generating electricity.

The navigation device 111 ("NAVI" in the figure) receives GPS signals transmitted via satellite radio waves from multiple GPS (Global Positioning System) satellites above the hybrid vehicle 100, which is equipped with an engine 113 as its power source, to determine its current location, and is able to display the current location of the hybrid vehicle 100 superimposed on a map displayed on a display device within the hybrid vehicle 100. The navigation device 111 may also use mobile phone base stations, Wi-Fi (registered trademark) access points, etc. to determine the current location. Information on the current location of the hybrid vehicle 100 determined by the navigation device 111, as well as map information including the surrounding area in which the hybrid vehicle 100 is traveling and the route to the destination, are output to the vehicle control device, i.e., the VCU (Vehicle Control Unit) 101.

An accelerator pedal position sensor 106 and a brake switch 107 are provided inside the cabin of the hybrid vehicle 100. The accelerator pedal position sensor 106 detects the amount of depression of the accelerator pedal, i.e., the accelerator pedal position. The brake switch 107 detects whether the brake pedal is depressed.

Engine 113 is an in-line three-cylinder gasoline engine for an automobile that uses spark ignition combustion and is an example of an internal combustion engine. This engine 113 is equipped with a starter 112 for starting engine 113. The crankshaft of engine 113 is equipped with a crank angle sensor 110 for detecting its rotation angle, and the other end of the crankshaft is connected to motor generator 114.

The generator control device, i.e., GCU (Generator Control Unit) 103, controls the operation of the motor generator 114 via the inverter 115 so that the inverter 115 can charge the battery 116 at a predetermined voltage. The motor generator 114 is driven by the engine 113 to generate electricity, which charges the battery 116 via the inverter 115.

The battery control device, i.e., BCU (Battery Control Unit) 104, controls the charging and discharging of the battery 116 based on the battery output requirement from the VCU 101. The battery 116 is equipped with a battery voltage sensor 109 that measures the internal voltage of the battery 116, and the VCU 101 constantly checks the voltage of the battery 116.

The motor control device, i.e., MCU (Motor Control Unit) 105, controls the inverter 117 and motor 118 (traction motor) based on the motor output requirement from the VCU 101. The inverter 117 is supplied with power from the electrically connected battery 116. The inverter 117 then converts the DC power discharged from the battery 116 into AC power and supplies the AC power to the motor 118. The motor 118 is connected to the wheels 120 via a reduction gear 119. In addition, a vehicle speed sensor 108 is provided on the drive shaft of the wheels 120.

The signals output from the vehicle speed sensor 108, battery voltage sensor 109, and crank angle sensor 110 are sent to the VCU 101. In addition, the signals output from the accelerator opening sensor 106 and brake switch 107 are also sent to the VCU 101.

The VCU 101 is mounted on a vehicle (hybrid vehicle 100) that runs on the output of at least one of an internal combustion engine (engine 113) and an electric drive unit (motor 118). The VCU 101 calculates the driver's requested torque based on the output signal of the accelerator pedal position sensor 106. That is, the accelerator pedal position sensor 106 is used as a requested torque detection sensor that detects the requested torque for the engine 113 and the motor 118. The VCU 101 also determines whether the driver has requested deceleration based on the output signal of the brake switch 107. The VCU 101 also calculates the remaining power of the battery 116 based on the output signal of the battery voltage sensor 109. The VCU 101 also calculates the rotational speed of the engine 113 based on the output signal of the crank angle sensor 110. The VCU 101 then calculates the optimal operating amounts of each device, such as the requested engine output, requested motor output, and requested battery output, based on the driver's request obtained from the outputs of the various sensors and the operating state of the hybrid vehicle 100.

The engine required output calculated by the VCU 101 is sent to the engine control device, i.e., ECU (Engine Control Unit) 102. The engine control device (ECU 102) controls the engine 113 installed in a hybrid vehicle that is driven by the coordination of the output of the engine (engine 113) and the output of the electric motor (motor 118).

The ECU 102 controls the engine 113 based on the required output from the VCU 101. Specifically, in addition to controlling the starter 112, the ECU 102 also controls the intake cam 11, exhaust cam 12, injector 13, spark plug 14, ignition coil 15 shown in FIG. 2 (described later), throttle valve 26 shown in FIG. 2, and variable valve timing control mechanism (hereinafter referred to as "VTC") 50 shown in FIG. 3. The VTC (Valve Timing Control) 50 includes an intake valve phase variable mechanism 51 and an exhaust valve phase variable mechanism 52.

The motor required output calculated by the VCU 101 is sent to the MCU 105. The battery required output calculated by the VCU 101 is sent to the BCU 104. The motor required output calculated by the VCU 101 is sent to the GCU 103.

[Engine Overview]
FIG. 2 is a schematic diagram showing an example of the configuration of the engine 113 according to the first embodiment.
In a series hybrid vehicle, when the charge capacity of the battery 116 (referred to as "battery capacity") falls below a specified value, the engine 113 is started to charge the battery 116. Conversely, when the charge capacity of the battery 116 exceeds the specified value, the engine 113 is stopped.

The engine 113 shown in Figure 2 is configured as, for example, a naturally aspirated in-line three-cylinder engine with each cylinder having a displacement of 400 cc. The engine 113 has a cylinder head 1, a cylinder block 2, and a piston 3 inserted into the cylinder block 2, which form a combustion chamber. The piston 3 is connected to the crankshaft 5 via a connecting rod 4. A crank angle sensor 110 located near the crankshaft 5 detects the engine speed.

For each cylinder, the intake pipe 7 and exhaust pipe 8 each branch into two and connect to the combustion chamber. Each cylinder has two openings at the connection between the intake pipe 7 (intake manifold) and the combustion chamber, and two openings at the connection between the exhaust pipe 8 (exhaust manifold) and the combustion chamber. A pair of intake valves 9 and a pair of exhaust valves 10 are provided to open and close the openings of the combustion chamber. Figure 2 shows only one intake valve 9, one exhaust valve 10, and one associated cam. In the following explanation, only the operation of one of the pair of intake valves 9 will be described, and the explanation of the other intake valve 9 will be omitted. Regarding the exhaust valves 10, only the operation of one exhaust valve 10 will be described, and the explanation of the other exhaust valve 10 will be omitted.

An intake cam 11 is provided above the intake valve 9, and an exhaust cam 12 is provided above the exhaust valve 10. The intake valve 9 opens and closes as the intake cam 11 rotates. The exhaust valve 10 opens and closes as the exhaust cam 12 rotates.

Although not shown, an intake cam pulley connected to the intake cam 11, an exhaust cam pulley connected to the exhaust cam, and a crank pulley connected to the crankshaft 5 are provided on the side of the engine 113 and are connected via a timing belt. As a result, when the engine 113 is operating, the crankshaft 5 rotates, causing the intake cam 11 and exhaust cam 12 to rotate. The intake cam pulley and exhaust cam pulley are set so that the intake cam 11 and exhaust cam 12 rotate once for every two rotations of the crankshaft 5.

The intake cam 11 is also provided with an intake valve phase variable mechanism 51 (see Figure 3 described later) that can change the phase of the intake valve (intake valve 9) provided in the intake pipe (intake pipe 7). The exhaust cam 12 is also provided with an exhaust valve phase variable mechanism 52 (see Figure 3 described later) that can change the phase of the exhaust valve (exhaust valve 10) provided in the exhaust pipe (exhaust pipe 8).

The intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 are electrically driven, and the ECU 102 can advance or retard the phase of the intake valve 9 and the exhaust valve 10 by rotating the motors provided in the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52. The speed at which the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 change the phase of the intake valve 9 and the exhaust valve 10 (referred to as the "phase change speed") is, for example, 300 degrees CA (Crank Angle) per second. An intake cam angle sensor 31 is installed on the intake cam 11, and detects changes in the angle of the intake cam 11, i.e., the rotation speed of the intake cam 11. Similarly, an exhaust cam angle sensor 32 installed on the exhaust cam 12 detects changes in the angle of the exhaust cam 12, i.e., the rotation speed of the exhaust cam 12.

In addition, the crankshaft 5 is provided with a motor generator 114 that acts as a generator when generating electricity and as a motor when the engine 113 is started or stopped.

An injector 13 is provided on the intake side of the combustion chamber, and a spark plug 14 and ignition coil 15 are provided above the combustion chamber. Fuel is stored in a fuel tank 16 and is sent to a high-pressure fuel pump 18 via a fuel pipe by a feed pump 17. The high-pressure fuel pump 18 is driven by an exhaust cam 12, and pressurized fuel is sent to a common rail 19. A fuel pressure sensor 20 is installed in the common rail 19 so that the fuel pressure can be detected. The common rail 19 and the injectors 13 provided in each cylinder are connected by fuel pipes.

A collector 21 is provided upstream of the intake pipe 7. The intake pipe 7 is connected to each cylinder from this collector 21. A throttle valve 26 is provided upstream of the collector 21, which can change the amount of air flowing into the collector 21. An air flow meter 28 is provided upstream of the throttle valve 26, which detects the flow rate of air flowing through the intake pipe 7 upstream of the throttle valve 26. A pressure sensor 27 is provided in the collector 21, which detects the air pressure inside the collector 21.

Meanwhile, a three-way catalyst 22 is provided at the end of the exhaust pipe 8. An air-fuel ratio sensor 25 is provided upstream of the three-way catalyst 22, and an oxygen sensor 24 is provided downstream of the three-way catalyst 22. A temperature sensor 23 is provided in the three-way catalyst 22 to measure the temperature of the three-way catalyst 22. A water temperature sensor 29 is provided in the cylinder block 2 to measure the temperature of the water flowing around the cylinder block 2.

Signals for water temperature and engine speed are input to ECU 102. ECU 102 controls the on/off of fuel injection and the phase of VTC 50 based on various information obtained from signals input from each sensor.

[Internal configuration and operation of ECU]
Next, an example of the internal configuration and operation of the ECU 102 will be described.
FIG. 3 is a control block diagram showing an example of the internal configuration of the ECU 102.

The engine control unit (ECU 102) controls the engine 113 equipped with a VTC 50 (intake valve phase variable mechanism 51, exhaust valve phase variable mechanism 52) that can change the phase of the intake valve 9 and the exhaust valve 10. The ECU 102 executes the engine control method according to this embodiment to control the engine 113 equipped with the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52.

The ECU 102 includes a CPU (Central Processing Unit) 40, a RAM (Random Access Memory) 41, and a ROM (Read Only Memory) 42. The ECU 102 receives input signals such as the primary voltage detected by a voltage sensor (not shown) of the ignition coil 15, the secondary current detected by a current sensor (not shown) of the ignition coil 15, accelerator depression information (accelerator opening) detected by the accelerator opening sensor 106, angle information (crank angle) and engine speed 113 detected by the crank angle sensor 110, throttle valve opening from the throttle valve 26, and battery voltage (battery capacity) detected by the battery voltage sensor 109.

Input information from each sensor input to the ECU 102 is temporarily stored in RAM 41 and processed by the CPU 40 in accordance with a predetermined control program. Variables and parameters generated during the CPU 40's calculations are temporarily written to RAM 41, and these variables and parameters are read out by the CPU 40 as appropriate. However, an MPU (Micro Processing Unit) may be used instead of the CPU 40.

ROM 42 permanently stores programs, data, etc. necessary for the operation of CPU 40, and is used as an example of a computer-readable, non-transitory recording medium that stores programs executed by ECU 102. A control program describing the contents of the arithmetic processing performed by CPU 40 is written in ROM 42 in advance, and is read and executed by CPU 40 as appropriate.

The ROM 42 also stores map information 421 (phase change information storage unit) used to select the phase change method. The phase change information storage unit (map information 421) configured in the ROM 42 stores the reference phase (current phase) of the intake valve 9 before a state change in the engine 113 and the target phase of the intake valve 9 after a state change in the engine 113 as phase change information for the intake valve 9. Similarly, for the exhaust valve 10, the phase change information storage unit (map information 421) stores phase change information including the reference phase and target phase. The reference phase and target phase are information representing the opening and closing timings of the intake valve 9 and exhaust valve 10. However, the ECU 102 may be provided with non-volatile storage, and the map information 421, which is updated via a network, may be stored in the non-volatile storage. The maximum achievable phase change speed of the intake valve 9 and exhaust valve 10 of the VTC 50 is determined by the specifications.

The VTC 50 may be configured to hold the intake valve 9 and exhaust valve 10 at an intermediate phase between the reference phase and the target phase for a predetermined time when changing the intake valve 9 and exhaust valve 10 from their respective reference phases (current phases) to their target phases, in order to generate backflow more efficiently. In this case, the phase change information storage unit (map information 421) may store, as phase change information for the intake valve 9 and exhaust valve 10, the reference phase, target phase, intermediate phase, and the duration (intermediate hold period) for which the intake valve 9 and exhaust valve 10 are held near the intermediate phase within a predetermined range including the intermediate phase.

The control program executed by the CPU 40 realizes the functions of the ECU 102, including the state determination unit 401 and control unit 402 shown in the figure. The control unit 402 has an intake valve phase change unit 403 and an exhaust valve phase change unit 404.

For example, when the VCU 101 (Figure 1) instructs the ECU 102 to stop the engine 113, the ECU 102 according to this embodiment controls to cut off the fuel supplied to the engine 113. The fuel cut is initiated before the engine 113 is stopped when the charge capacity (remaining battery capacity) of the battery 116 used to drive the vehicle (hybrid vehicle) reaches or exceeds a specified charge value.

Furthermore, if the driver presses the accelerator while the engine 113 is stopped and fuel is cut, the ECU 102 restarts the engine 113. Therefore, the state determination unit 401 determines a change in the state of the engine 113 and outputs the determination result. A change in the state of the engine 113 includes a cut in the fuel supplied to the engine 113 as the engine 113 stops. A change in the state of the engine 113 also includes a restart of the engine 113 after a state in which fuel was continuously cut.

The control unit 402 controls the VTC 50 (intake valve phase variable mechanism 51, exhaust valve phase variable mechanism 52) that can change the phase of the intake valve 9 provided in the intake pipe 7 of the engine 113 and the phase of the exhaust valve 10 provided in the exhaust pipe 8. This control unit 402 includes an intake valve phase change unit 403 and an exhaust valve phase change unit 404. The control unit 402 changes the phase of at least one of the intake valve 9 and the exhaust valve 10, and changes the valve opening and closing timing, based on, for example, battery capacity, in response to changes in the state of the engine 113, such as when the ECU 102 starts a fuel cut to stop the engine 113 or when the engine 113 is restarted.

The intake valve phase change unit 403 outputs an instruction to change the phase of the intake valve 9 of the engine 113 through the intake valve phase variable mechanism 51 of the VTC 50 of the engine 113 based on changes in the state of the engine 113 and map information 421 (phase change information). For example, when the intake valve phase change unit 403 changes the relative rotational phase of the intake camshaft with respect to the crankshaft using the VTC 50 after a fuel cut, it changes the phase of the intake valve 9 based on the relationship between the current phase of the intake camshaft and the target phase described in the map information 421.

In addition, the exhaust valve phase change unit 404 outputs an instruction to change the phase of the exhaust valve 10 through the exhaust valve phase variable mechanism 52 of the VTC 50 based on changes in the state of the engine 113 and the map information 421 (phase change information). For example, when the VTC 50 changes the relative rotational phase of the exhaust camshaft with respect to the crankshaft after a fuel cut, the exhaust valve phase change unit 404 changes the phase of the exhaust valve 10 based on the relationship between the current phase of the exhaust camshaft and the target phase described in the map information 421.

In addition, the control unit 402 may be configured to combine the functions of the intake valve phase change unit 403 and the exhaust valve phase change unit 404 into one, and the control unit 402 may control the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52.

The VTC 50 includes an intake valve phase variable mechanism 51 and an exhaust valve phase variable mechanism 52 .
The intake valve phase variable mechanism 51 opens and closes the intake valve 9 at a predetermined time by variably controlling the phase of the intake valve 9 based on instructions from the intake valve phase change unit 403. The intake valve phase variable mechanism 51 can change the phase of the intake valve 9 to advance or retard by driving the intake cam 11 based on instructions from the intake valve phase change unit 403. In the following description, it is assumed that the intake valve phase change unit 403 advances or retards the phase of the intake valve 9.

The exhaust valve phase variable mechanism 52 variably controls the phase of the exhaust valve 10 based on instructions from the exhaust valve phase change unit 404, thereby opening and closing the exhaust valve 10 at a predetermined time. The exhaust valve phase variable mechanism 52 can change the phase of the exhaust valve 10 to advance or retard by driving the exhaust cam 12 based on instructions from the exhaust valve phase change unit 404. In the following explanation, it is assumed that the exhaust valve phase change unit 404 advances or retards the phase of the exhaust valve 10.

[Variable valve timing control mechanism]
Next, the variable valve timing control mechanism (VTC) 50 will be described.
In the engine 113, the VTC 50 changes the timing of opening and closing the intake valve 9 and the exhaust valve 10 to improve intake efficiency and exhaust efficiency and ensure smooth combustion in the engine cylinders. The timing of opening and closing the intake valve 9 and the exhaust valve 10 is also referred to as "valve timing." The rotation speed signals of the crankshaft 5, intake cam 11, and exhaust cam 12 detected by the crank angle sensor 110, intake cam angle sensor 31, and exhaust cam angle sensor 32 are input to the ECU 102, whereby the relative phase difference between the crankshaft 5 and the intake camshaft/exhaust camshaft is calculated. In the configuration of the engine 113 of this embodiment, for example, the crank angle sensor acquires angles (rotation speed signals) every 6 degrees CA, and the intake cam angle sensor 31 and exhaust cam angle sensor 32 acquire angles (rotation speed signals) every 180 degrees CA.

The VTC 50 provided on the intake cam 11 and exhaust cam 12 is electrically operated. While the engine 113 of this embodiment is described as being equipped with an electrically operated VTC 50, the present invention does not rely on the VTC drive system, such as electric or hydraulic. The VTC system may also be different for the intake valve 9 side and the exhaust valve 10 side. For example, the VTC on the intake valve 9 side may be electrically operated and the VTC on the exhaust valve 10 side may be hydraulic, or vice versa.

The intake valve phase change unit 403 and the exhaust valve phase change unit 404 change the phase of the intake valve 9 and the exhaust valve 10 from the reference phase described below through the VTC 50 (intake valve phase variable mechanism 51 and exhaust valve phase variable mechanism 52) based on the phase change information read from the phase change information storage unit (map information 421) and the change in the state of the engine 113 determined by the state determination unit 401.

The intake valve phase change unit 403 and the exhaust valve phase change unit 404 issue instructions to the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52, respectively, to change the phase of the intake valve 9 and the exhaust valve 10 in response to changes in the state of the engine 113, such as when the ECU 102 starts a fuel cut to stop the engine 113 or when the engine 113 is restarted, based on, for example, battery capacity. At this time, the intake valve phase change unit 403 and the exhaust valve phase change unit 404 read map information 421 from the ROM 42 and perform control such as switching the opening and closing timing (target phase) of the intake valve 9 and the exhaust valve 10 and/or switching the phase change speed of the intake valve 9 and the exhaust valve 10.

The intake valve phase variable mechanism 51 is configured to rotate the shaft of the intake cam 11 based on instructions from the intake valve phase change unit 403, and is capable of continuously or stepwise controlling the phase of the intake valve 9 to any phase, either advanced or retarded. The exhaust valve phase variable mechanism 52 is configured to rotate the shaft of the exhaust cam 12 based on instructions from the exhaust valve phase change unit 404, and is capable of continuously or stepwise controlling the phase of the exhaust valve 10 to any phase, either advanced or retarded. The intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 can be configured using well-known technology, so detailed explanations will be omitted.

In the following explanation, it is assumed that the intake valve phase change unit 403 changes the phase of the intake valve 9, and the exhaust valve phase change unit 404 changes the phase of the exhaust valve 10 to the advance or retard side.

In this embodiment, the ECU 102 is configured to include the state determination unit 401, intake valve phase change unit 403, exhaust valve phase change unit 404, and map information 421, but this configuration is not limited to this. For example, some or all of the state determination unit 401, intake valve phase change unit 403, exhaust valve phase change unit 404, and map information 421 may be implemented in a device separate from the ECU 102.

Next, the timing for changing the phase of the intake valve 9 and exhaust valve 10 (valve opening/closing timing) and examples of the changed phase of the intake valve 9 and exhaust valve 10 will be explained with reference to Figures 4 to 7. Note that the horizontal axis of Figures 4 to 7 shows how the strokes within the engine cylinder change in the order of expansion stroke, exhaust stroke, intake stroke, and compression stroke, and the vertical axis shows the successive lift amounts [mm] of the intake valve 9 and exhaust valve 10.

Figure 4 is a diagram showing an example of the profiles of the intake valve 9 and exhaust valve 10 during power generation operation when the engine is driven in the first embodiment. In the following, each profile of the intake valve 9 and exhaust valve 10 shown in the diagram represents the opening/closing timing and lift amount of the intake valve 9 and exhaust valve 10.

In Figure 4, the change in lift amount of intake valve 9 is represented by profile 9a, and the change in lift amount of exhaust valve 10 is represented by profile 10a. For example, the maximum lift amount of intake valve 9 is set to 6 mm, and the operating angle is set to 190 deg. CA. The maximum lift amount of exhaust valve 10 is set to 8 mm, and the operating angle is set to 200 deg. CA. The closing timing of intake valve 9 is set near bottom dead center (BDC), and the closing timing of exhaust valve 10 is set near top dead center (TDC).

As shown in Figure 4, when the engine 113 is running, the profile 10a of the exhaust valve 10 changes during the exhaust stroke, and the profile 9a of the intake valve 9 changes during the intake stroke. Profiles 10a and 9a barely overlap, and the period during which they overlap and both valves are lifted is very short. The phase of the intake valve 9 indicated by profile 9a and the phase of the exhaust valve 10 indicated by profile 10a are each referred to as the "reference phase."

[Profile switching during engine stop processing]
FIG. 5 is a diagram showing an example of the engine speed, fuel injection request, and profiles of the intake valve 9 and the exhaust valve 10 at the start of fuel cut when the engine is running according to the first embodiment.
The upper and middle sections of Figure 5 show an example of the relationship between the engine speed [rpm] and the fuel injection request (fuel injection pulse) related to fuel cutoff. The lower section of Figure 5 shows an example of the profiles of the intake valve 9 and the exhaust valve 10 at the point indicated by the "▼" in the upper and middle sections of Figure 5 (start of fuel cutoff). The relationship between the horizontal and vertical axes in the lower section of Figure 5 is the same as that in Figure 4. That is, the profiles 9a and 10a of the intake valve 9 and the exhaust valve 10 shown in the lower section of Figure 5 are the same as the profiles of the power generation operation before the engine 113 transitions to fuel cutoff operation. As shown in Figures 4 and 5, it is assumed that the phases of the intake valve 9 and the exhaust valve 10 during combustion in the engine 113 are controlled to the reference phase.

When the battery capacity reaches its upper limit, the ECU 102 performs control (engine stop processing) to stop the engine 113. Therefore, before stopping the engine 113, the ECU 102 transitions to fuel cut operation, which stops fuel injection. At this time, because the engine 113 rotates by inertia, unburned air, or so-called fresh air, flows into the exhaust pipe 8 in the states of profiles 9a and 10a. Therefore, the intake valve phase change unit 403 and the exhaust valve phase change unit 404 (Figure 3) change the phases of the intake valve 9 and the exhaust valve 10 to the phases indicated by profiles 9b and 10b, as shown by the solid lines in the upper part of Figure 6.

Here, examples of profiles of the intake valve 9 and the exhaust valve 10 that cause backflow in the engine cylinder and the state inside the engine cylinder will be described with reference to FIG.
6 is a diagram showing an example of profiles of the intake valve 9 and the exhaust valve 10 that cause backflow in the engine cylinder according to the first embodiment, and the situation inside the engine cylinder. The upper part of Fig. 6 shows an example of profiles before and after changing the phases of the intake valve 9 and the exhaust valve 10, and the lower part of Fig. 6 shows the situation inside the engine cylinder for each stroke.

As shown in the upper part of Figure 6, the phase of the intake valve 9 is retarded from profile 9a to the stop position of profile 9b, and the phase of the exhaust valve 10 is advanced from profile 10a to the stop position of profile 10b. At this time, profile 9b of the intake valve 9 is retarded by 90 degrees CA relative to profile 9a during power generation operation. Also, profile 10b of the exhaust valve 10 is advanced by 90 degrees CA relative to profile 10a during power generation operation.

For this reason, as shown in profiles 9b and 10b of the intake valve 9 and exhaust valve 10 after fuel cut in the engine 113, the phases of the intake valve 9 and exhaust valve 10 during engine stop processing are in a so-called negative overlap state, where the opening timing of the intake valve 9 provided in the intake pipe 7 during the compression stroke is significantly different from the opening timing of the exhaust valve 10 provided in the exhaust pipe 8 during the expansion stroke. The phase of the intake valve 9 represented by profile 9b is called the "intake target position," and the phase of the exhaust valve 10 represented by profile 10b is called the "exhaust target position."

When the intake valve 9 is controlled to the intake target position and the exhaust valve 10 is controlled to the exhaust target position, a flow (backflow) occurs in which gas is drawn into the cylinder of the engine 113 from the exhaust pipe 8 during the expansion stroke (1), passes through the exhaust stroke (2) and intake stroke (3), and returns to the intake pipe 7 during the compression stroke (4). As an example, the opening timing of the intake valve 9 is retarded by 90° CA from the intake stroke to the compression stroke, and the opening timing of the exhaust valve 10 is advanced by 90° CA from the exhaust stroke to the expansion stroke. However, it is desirable to change the phase change angle depending on the engine 113 rotational speed during fuel cut. The phase change angles of the intake valve 9 and exhaust valve 10 according to the engine rotational speed during fuel cut are explained with reference to Figures 7 and 8.

Figure 7 shows an example of the engine speed, fuel injection request, and intake valve 9/exhaust valve 10 profiles from the start of fuel cutoff to engine stop when the engine is running in the first embodiment. The top and middle sections of Figure 7 are graphs showing an example of the relationship between the engine speed [rpm] and fuel injection request (fuel injection pulse) related to fuel cutoff, and are the same as the graphs shown in the top and middle sections of Figure 5. The bottom section of Figure 7 shows the profiles 9b and 10b of the intake valve 9 and exhaust valve 10 after the phase change at the points indicated by "▼" in the top and middle sections of Figure 7 as solid lines, and the profiles 9a and 10a of the intake valve 9 and exhaust valve 10 before the phase change as dashed lines. The profile shown in the bottom section of Figure 7 is the same as the profile shown in the top section of Figure 6.

[Target phase of intake valve and exhaust valve according to engine speed]
Fig. 8 is a graph showing an example of the target intake phase (intake valve timing) of the intake valve 9 and the target exhaust phase (exhaust valve timing) of the exhaust valve 10 according to the engine speed during fuel cut according to the first embodiment. The horizontal axis of Fig. 8 represents the engine speed [rpm] during fuel cut, and the vertical axis represents the phase change angle [deg. CA] in the retard direction of the intake valve 9 and the phase change angle [deg. CA] in the advance direction of the exhaust valve 10. Information on the phase change angle of each valve shown in Fig. 8 is stored as map information 421 (phase change information storage unit) in the ROM 42 of the ECU 102 shown in Fig. 3.

As shown in FIG. 8 , the phase change information storage unit (map information 421) in this embodiment specifies that the higher the engine speed of the engine 113 when fuel cut is initiated, the more the intake valve 9 is retarded relative to the reference position (reference phase) and the more the exhaust valve 10 is advanced relative to the reference position (reference phase). Therefore, the intake valve phase change unit 403 and the exhaust valve phase change unit 404 obtain the retard amount of the intake valve 9 and the advance amount of the exhaust valve 10 corresponding to the engine speed at the time of fuel cut based on the map information 421 read from the ROM 42. The intake valve phase change unit 403 and the exhaust valve phase change unit 404 then control the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 based on the obtained retard amount of the intake valve 9 and the advance amount of the exhaust valve 10. In this embodiment, the phase change speed of the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 is 180 [deg. CA/sec].

Under the above conditions, a flow of gas is generated from the exhaust pipe 8 toward the intake pipe 7 between 0.5 [sec] and 2.5 [sec] as shown in the upper and middle sections of Figure 7. As shown in Figure 7, by retarding the intake valve 9 by 90 [deg. CA] and advancing the exhaust valve 10 by 90 [deg. CA], as described above, a flow is established in which gas is drawn in from the exhaust pipe 8 during the expansion stroke (1) and discharged to the intake pipe 7 during the compression stroke (4), i.e., a reverse flow.

At this time, during the period from fuel cut to engine stop (during engine stop processing), the amount of gas flowing back from the exhaust pipe 8 to the intake pipe 7 changes depending on the number of cycles that the engine 113 idles while maintaining the above valve timing. Therefore, it becomes necessary to control the amount of gas flowing back from the exhaust pipe 8 to the intake pipe 7 depending on the engine speed at the time of fuel cut. In this embodiment, the explanation will be given assuming that by applying the present invention (map information 421 in Figure 8) during the period from fuel cut to engine 113 stop, a substantially constant amount of gas flowing back is generated regardless of the engine speed at the time of fuel cut.

In addition, in this embodiment, the method (Figure 8) is used to change the intake target phase of the intake valve 9 and the exhaust target phase of the exhaust valve 10 depending on the engine speed at the start of fuel cut. However, there are also methods that vary the phase change speed of each of the intake valve 9 and exhaust valve 10. An example of switching the phase change speed of each valve during the period from the start of fuel cut until the engine restart depending on the engine speed at the time of fuel cut will be described with reference to Figure 9.

[Intake valve and exhaust valve phase change speed according to engine speed]
Fig. 9 is a graph showing an example of the phase change speed of the intake valve 9 and the phase change speed of the exhaust valve 10 according to the engine speed during fuel cut according to the first embodiment. The horizontal axis of Fig. 9 represents the engine speed [rpm] during fuel cut, and the vertical axis represents the phase change speed [deg. CA/s] of the intake valve 9 and the phase change speed in the advance direction [deg. CA/s] of the exhaust valve 10. Information on the phase change speed of each valve shown in Fig. 9 is stored as map information 421 (phase change information storage unit) in the ROM 42 shown in Fig. 3.

When the engine speed is low when fuel is cut, the time until the engine stops is short and the number of cycles is small, so the backflow volume is secured by increasing the phase change speed, as shown in Figure 9. On the other hand, when the engine speed is high when fuel is cut, there is a margin of time until the engine stops, so the phase change speed is reduced.

Furthermore, in this embodiment, a method is used in which the target phase position or phase change speed is adjusted according to the engine speed during fuel cut. However, the map information 421 inside the ECU 102 may be established by combining these two parameters. By performing variable valve timing control using such map information 421, more accurate backflow amount adjustment is possible.

Alternatively, the phase change rate can be fixed and the rate at which the engine speed decreases can be changed by the motor generator 114, allowing the amount of backflow to be adjusted based on the relative relationship between the two.

[Profile switching when restarting the engine]
Next, a sequence for the next restart of the engine 113 will be described with reference to FIGS.
10 and 11 show the profiles of the intake valve 9 and the exhaust valve 10 in each stroke when the engine 113 is restarted.

As described above, to eliminate enriched injection when restarting the engine 113, the amount of fresh air discharged into the exhaust pipe 8 must be set to zero. However, in the profiles 9b and 10b of the intake valve 9 and exhaust valve 10 during engine stop processing shown in the lower part of Figure 7, the amount of fresh air during the intake stroke is insufficient (decompression). For this reason, when the ECU 102 starts the engine 113, the intake valve phase change unit 403 must control the intake valve 9 and exhaust valve 10 by switching to a profile that allows combustion before the first explosion. In this embodiment, the profiles of the intake valve 9 and exhaust valve 10 when the ECU 102 starts the engine 113 are the same as the profiles 9a and 9b during engine stop processing shown in Figure 7.

FIG. 10 is a diagram showing an example of the engine speed, fuel injection request, and intake valve 9/exhaust valve 10 profiles from the engine start to before the phase change when the engine is restarted according to the first embodiment.
The upper and middle figures of Fig. 10 show an example of the relationship between the engine speed [rpm] from engine start to first combustion and the fuel injection request (fuel injection pulse). The lower figure of Fig. 10 shows an example of the profile of the intake valve 9 and the exhaust valve 10 at the point indicated by "▼" in the upper and middle figures of Fig. 10 (start of engine start). The relationship between the horizontal and vertical axes in the lower figure of Fig. 5 is the same as that in Fig. 4.

The lower part of Figure 10 shows the profiles of the intake valve 9/exhaust valve 10 from engine start to 0.5 seconds using dashed lines. For example, when the ECU 102 receives a start signal from the VCU 101 at the point indicated by the "▼", it gradually increases the engine speed of the engine 113 by motoring. In this embodiment, the state in which fuel is not injected at engine start and the engine 113 is forcibly rotated by the motor-generator 114 is referred to as "motoring." As described above, the profile of the intake valve 9 is profile 9b, and the profile of the exhaust valve 10 is profile 10b. 0.5 seconds after the start of the engine 113, the profiles of the intake valve 9 and exhaust valve 10 are changed to combustible profiles 9a and 10a by controlling the intake valve 9 to advance and the exhaust valve 10 to retard (see Figure 11).

In this embodiment, the trigger for changing the profiles of the intake valve 9 and exhaust valve 10 when the engine is restarted is determined, for example, by the engine speed during fuel cutoff or the phase of the intake valve 9 and exhaust valve 10 during engine start-up. The phase of the intake valve 9 and exhaust valve 10 during engine start-up assumes that the time required for the VTC 50 to complete the phase change varies depending on the amount of phase change. The start time of the phase change (profile change) is determined by the relationship between the amount of phase change and the speed of the phase change. As described above, the amount of phase change from the reference phase (Figure 8) and the speed of the phase change (Figure 9) vary depending on the engine speed during fuel cut-off. However, the trigger for the profile change is not limited to the above example. For example, other triggers may include the elapsed time since the engine start command was turned on, or the backflow amount reaching a predetermined cycle of cylinder capacity.

Figure 11 is a diagram showing an example of the engine speed, fuel injection request, and intake valve 9/exhaust valve 10 profiles from the start of phase change to the first combustion when restarting the engine in the first embodiment. The upper and middle sections of Figure 11 are graphs showing an example of the relationship between the engine speed [rpm] and the fuel injection request (fuel injection pulse) from engine start to the first combustion, and are the same as the graphs shown in the upper and middle sections of Figure 10.

In the lower part of Figure 11, the profiles 9a and 10a of the intake valve 9 and exhaust valve 10 after the phase change at the point indicated by "▼" in the upper and middle parts of Figure 11 (at the time of initial explosion) are shown by solid lines, and the profiles 9b and 10b of the intake valve 9 and exhaust valve 10 before the phase change are shown by dashed lines. The profiles 9a and 10a of the intake valve 9 and exhaust valve 10 shown in the lower part of Figure 11 are the same as the profiles 9a and 10a in Figure 5. Here, the ECU 102 changes (returns) the phases of the intake valve 9 and exhaust valve 10 to the reference phase, i.e., switches the profiles of the intake valve 9 and exhaust valve 10 from profiles 9b and 10b to profiles 9a and 10a, respectively, by the time the elapsed time reaches 1.0 seconds, with the engine starting time being 0 seconds.

In this embodiment, the phase change speed of the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 at this time is 180 [deg. CA/sec]. Therefore, as shown by "▽" in Figure 11, the ECU 102 calculates backward the timing of starting the phase change from the initial combustion timing (1.0 [sec]) indicated by "▼" and the phase change speed. For example, if the phase change speed is 180 [deg. CA/sec], the phase change of the intake valve 9 and the exhaust valve 10 by the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 must start at least 0.5 [sec] earlier.

By using the above-mentioned sequences during engine stop processing and engine restart, the ECU 102 can eliminate the discharge of fresh air from the intake pipe 7 to the exhaust pipe 8 during one cycle during fuel-cut idling, thereby preventing deterioration of exhaust emissions when the engine is restarted due to excess oxygen in the three-way catalyst 22.

Here, a major difference in the behavior of the engine 113 during engine stop processing and engine restart is the number of idle revolutions of the engine 113 when fuel is cut off. Basically, the initial combustion revolution speed when the engine restarts often takes on a roughly constant value. Therefore, the number of idle revolution cycles when the engine restarts takes on a fairly constant value. However, this value will fluctuate depending on the outside temperature and the remaining battery charge.

On the other hand, the engine speed during fuel cut during engine stop processing depends on the driving state of the engine 113. Therefore, the number of idling cycles during engine stop processing is often not uniquely determined. Therefore, in this embodiment, the amount of backflow air from the exhaust pipe 8 to the intake pipe 7 is controlled by adjusting the profiles (target phase position, phase change speed) of the intake valve 9 and exhaust valve 10 during engine stop processing. However, in addition to control by the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 during engine start (motoring before initial combustion), a similar backflow air amount adjustment effect can also be achieved by methods such as controlling the engine speed at initial combustion or the rate of change when the engine 113 speed increases.

For example, Figure 11 shows an example in which the engine speed threshold Rth is set as the trigger for starting the phase change of the intake valve 9 and exhaust valve 10. In this example, the engine speed threshold Rth coincides with the phase change start timing of 0.5 [sec] calculated backward from the initial combustion timing. When the engine speed during motoring reaches the threshold Rth, the phase change to profiles 9a and 10a of the intake valve 9 and exhaust valve 10 begins. In this way, by appropriately setting the engine speed threshold Rth, the backflow occurrence period of the engine 113 can be minimized and the amount of backflow can be suppressed.

Similarly, the amount of backflow in the engine 113 can be suppressed by controlling the rate at which the engine speed increases during engine shutdown processing, engine restart, or both. Alternatively, the amount of backflow can be adjusted by changing the engine speed at the time of initial combustion during engine restart.

[Explanation of variable valve timing control]
Next, an example of a procedure for variable valve timing control by the ECU 102 from engine stop processing to engine restart will be described with reference to FIGS.

12 is a flowchart showing an example of the procedure of variable valve timing control during engine stop processing according to the first embodiment. Fig. 12 shows a series of steps from when the ECU 102 generates a fuel cut command to the injector 13 to when the engine is stopped.
Fig. 13 is a flowchart showing an example of the procedure for variable valve timing control when restarting the engine according to the first embodiment. Fig. 13 shows the flow from an engine start request (restart) from the ECU 102 through the initial engine combustion to a normal operating state.

The procedures shown in the flowcharts of Figures 12 and 13 are realized by the CPU 40 (Figure 3) reading and executing a control program recorded in the ROM 42. As described above, an example has been described in which the target phase position or phase change speed is changed depending on the engine speed during fuel cut, but the flowcharts shown in Figures 12 and 13 show an example of a method for changing the target phase position.

(Variable valve timing control during engine shutdown)
12 will be described below for each processing step. In this flowchart, the start condition is that the engine is running, and the end condition is when the ECU 102 confirms that the engine has completely stopped.

<Step S1>
In the control of VTC 50 while the engine is running, as normal control, CPU 40 (control unit 402) within ECU 102 outputs profiles of intake valve 9 and exhaust valve 10 corresponding to the engine speed and required torque (e.g., profiles 9a and 10a in FIG. 5 ) to intake valve phase changing unit 403 and exhaust valve phase changing unit 404, respectively, based on map information 421 ( FIG. 3 ) in ROM 42. Then, intake valve phase changing unit 403 and exhaust valve phase changing unit 404 within control unit 402 control VTC 50 to achieve optimal operation of intake valve 9 and exhaust valve 10 based on the profiles of intake valve 9 and exhaust valve 10 (e.g., profiles 9a and 10a).

<Step S2>
Next, the control unit 402 determines whether the engine stop condition flag is satisfied based on the determination result of the state determination unit 401. For example, the state determination unit 401 checks the battery charge capacity of the battery 116 ( FIG. 1 ). If the state determination unit 401 determines that the battery charge capacity has reached the upper limit or a predetermined threshold (Yes in S2), the control unit 402 stores the engine stop condition flag in the RAM 41, completes preparations for engine stop, and proceeds to step S3. On the other hand, if the battery charge capacity has not reached the upper limit or the predetermined threshold (No in S2), the control unit 402 returns to step S1 and continues normal control. The control unit 402 does not stop the engine unless the key is turned off, even if the hybrid vehicle is stopped due to a traffic light, traffic congestion, or the like. If the key is turned off, the control unit 402 terminates the processing of this flowchart. Other engine stop conditions include idle stop, non-use of air conditioning equipment, or catalyst temperature reaching a threshold.

<Step S3>
Next, the state determination unit 401 determines whether a fuel cut command is ON in the ECU 102. If the fuel cut command is ON (Yes in S3), the process proceeds to step S4. If the fuel cut command is OFF (No in S3), the process returns to step S1, and the control unit 402 continues normal control. Before stopping the engine 113, the ECU 102 goes through a process of transitioning to fuel cut operation to stop fuel injection. At this time, because engine torque is not required, the engine 113 enters a fuel cut operation mode, and the ECU 102 turns off the fuel injection signal (fuel injection pulse) to the injector 13, stopping fuel supply to the combustion chamber (fuel cut). During the fuel cut operation period after fuel cut (during the engine stop processing in FIG. 5), the engine 113 rotates by inertia, and the engine speed eventually reaches zero. Therefore, confirmation that fuel injection has been stopped is used as one of the flags for determining that the engine is stopped.

<Step S4>
Next, after the determination in step S3 is Yes (the engine stop condition flag is present and the fuel cut command is ON), the state determination unit 401 acquires the engine speed at the time of transition to the fuel cut operation.

<Step S5>
Furthermore, the control unit 402 (intake valve phase changing unit 403, exhaust valve phase changing unit 404) refers to map information 421 for engine stop behavior, and determines a target intake phase (e.g., the reference phase plus the phase change amount in the upper part of FIG. 8 ) for the intake valve 9 and a target exhaust phase (e.g., the reference phase plus the phase change amount in the lower part of FIG. 8 ) for the exhaust valve 10, which correspond to the engine speed at the start of fuel cutoff, obtained by the state determination unit 401. At this time, the phase change speed is a fixed value within the range of the specifications of the VTC 50, but as shown in FIG. 9 , the phase change speed may be variable depending on the engine speed at the time of fuel cutoff. For example, the phase change speeds for the intake valve 9 and the exhaust valve 10 may be determined, and the target phases (the amount of phase change from the current position) may be transmitted to the intake valve phase changing unit 403 and the exhaust valve phase changing unit 404, respectively.

<Step S6>
Next, the intake valve phase changing unit 403 controls the intake valve phase variable mechanism 51 to retard the phase of the intake valve 9 based on the target intake phase, simultaneously with the start of fuel cut of the engine 113. Furthermore, the exhaust valve phase changing unit 404 controls the exhaust valve phase variable mechanism 52 to advance the phase of the exhaust valve 10 based on the target exhaust phase. The target phase of the intake valve 9 after fuel cut is set to the target intake position (profile 9b in FIG. 7 ), and the target phase of the exhaust valve 10 is set to the target exhaust position (profile 10b in FIG. 7 ). Through this processing, the intake valve phase changing unit 403 and the exhaust valve phase changing unit 404 switch, for example, the profile 9a of the intake valve 9 to the retarded profile 9b and the profile 10a of the exhaust valve 10 to the advanced profile 10b. Completion of the phase change to the target profile by each of the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 can be used as one of the flags for determining engine stop.

<Step S7>
Next, the control unit 402 (intake valve phase changing unit 403) determines whether the intake valve 9 (intake cam 11) has reached the designated intake target phase, based on the detection result of the intake cam angle sensor 31 obtained by the state determination unit 401. If it is determined that the intake valve 9 has reached the intake target phase (Yes in S7), the process proceeds to the determination process of step S8. On the other hand, if it is determined that the intake valve 9 has not reached the intake target phase (No in S7), the intake valve phase changing unit 403 returns to step S6 and continues changing the phase of the intake valve 9 to the retard side.

<Step S8>
Next, the control unit 402 (exhaust valve phase changing unit 404) determines whether the exhaust valve 10 (exhaust cam 12) has reached the designated exhaust target phase, based on the detection result of the exhaust cam angle sensor 32 acquired by the state determination unit 401. If it is determined that the exhaust valve 10 has reached the exhaust target phase (Yes determination in S8), the process proceeds to the determination processing of step S9. On the other hand, if it is determined that the exhaust valve 10 has not reached the exhaust target phase (No determination in S8), the exhaust valve phase changing unit 404 returns to step S6 and continues changing the phase of the exhaust valve 10 to the advance side.

In steps S7 and S8, whether the intake valve 9 has reached the specified intake target phase and whether the exhaust valve 10 has reached the specified exhaust target phase are set as flags, and it is confirmed whether the phase of each valve is at the target phase based on the flags. Note that steps S7 and S8 may be performed in parallel, or the processing order may be reversed.

<Step S9>
After the determination of Yes in step S8, the state determination unit 401 determines that the engine 113 has stopped. The CPU 40 (state determination unit 401) also calculates the phase of the intake valve 9 and the phase of the exhaust valve 10 at the final time when the engine is stopped from the detection results of the intake cam angle sensor 31 and the exhaust cam angle sensor 32, and stores each phase value in the RAM 41 of the ECU 102. After the processing of step S9, the processing of this flowchart ends.

For example, in this embodiment, the conditions for determining that the engine has stopped are the AND conditions (logical product) of the following four items: the fuel injection signal from the CPU 40 to the injector 13 is off (Yes in S3), the pulse signal (rotation speed signal) from the crank angle sensor 110 is not input to the CPU 40, the phase of the intake valve 9 is controlled to the target phase position (Yes in S7), and the phase of the exhaust valve 10 is controlled to the target phase position (Yes in S8).

Basically, the engine speed will not reach zero before the intake valve 9 profile reaches the intake target phase (profile 9a) and the exhaust valve 10 profile reaches the exhaust target phase (profile 10a). In other words, the control unit 402 calculates the phase change speed of the intake valve 9 and the exhaust valve 10 so that the intake valve 9 and the exhaust valve 10 are not controlled when the pulse input from the crank angle sensor 110 is discontinued. However, if the engine stops first, the CPU 40 (state determination unit 401) stores the phases of the intake valve 9 and the exhaust valve 10 at that time in the RAM 41. Alternatively, a phase change method such as forcibly driving the engine 113 using a generator provided in the hybrid mechanism when the engine stops can be considered.

(Variable valve timing control when restarting the engine)
Next, an example of a procedure for variable valve timing control by the ECU 102 when the engine is restarted will be described with reference to FIG.

<Step S11>
In this embodiment, the engine stop period before the engine is restarted is designated as step S11. The state determination unit 401 of the CPU 40 stores the phases of the intake valve 9 and the exhaust valve 10 at the moment (or immediately before) the engine is stopped in the RAM 41 of the ECU 102 (see step S9 in FIG. 12 ). Furthermore, if the phases of the intake valve 9 and the exhaust valve 10 fluctuate during the engine stop period due to a subsequent disturbance or the like, the state determination unit 401 calculates the amount of phase fluctuation from the phase at the time the engine was stopped, taking into account the phase fluctuation, and updates the phase values stored in the RAM 41 when the engine was stopped.

<Step S12>
Next, the control unit 402 of the CPU 40 checks the requirements for engine restart. First, the control unit 402 determines whether the engine start condition flag is satisfied based on the determination result of the state determination unit 401. For example, the state determination unit 401 checks the battery charge capacity of the battery 116 ( FIG. 1 ) and stores the engine start condition flag in the RAM 41 when the remaining battery charge falls below a threshold. In this embodiment, a series hybrid vehicle is targeted, and the engine is driven based on the remaining charge of the battery 116. If the state determination unit 401 determines that the remaining battery charge is less than the threshold (Yes in S12), the control unit 402 proceeds to step S13. On the other hand, if the remaining battery charge is equal to or greater than the threshold (No in S12), the control unit 402 continues the determination process of step S12. Other engine start conditions include the end of idle stop, the use of an air conditioning system, or the catalyst temperature falling below a threshold. Alternatively, multiple engine start conditions may be combined. Here, it is assumed that the remaining capacity of the battery 116 falls below a threshold value and the VCU 101 issues a request to the ECU 102 to restart the engine.

<Step S13>
Next, the control unit 402 of the CPU 40 determines whether the engine start flag acquired by the ECU 102 from the VCU 101 is ON. If the engine start flag is ON (Yes in S13), the process proceeds to step S14, and if the engine start flag is OFF (No in S13), the process returns to step S12.

In this embodiment, the flag information for two conditions is checked when restarting the engine, and the engine is started based on the logical AND output of both flag information, but this is not necessarily the case. In step S12, if all engine start conditions are met, the engine start condition flag may be set. Furthermore, in step S13, if the engine start condition flag is set, the ECU 102 sends the engine start flag to each component. That is, the control unit 402 considers engine start preparation to be complete based on the determination result of step S12, furthermore, when the engine start flag is set to ON and the phases of the intake valve 9 and exhaust valve 10 are stored, and an engine start signal is sent to each component in the hybrid vehicle. Here, components are controlled by the ECU 102, such as the injector 13, ignition coil 15, and motor-generator 114.

<Step S14>
This step and step S15 show control of the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 when the engine is restarted. In step S14, the control unit 402 calls from the RAM 41 the phases of the intake valve 9 and the exhaust valve 10 (e.g., profiles 9b and 10b) that reflect the phase fluctuations that occurred when the engine was stopped or after that.

<Step S15>
Next, the control unit 402 obtains the phase change amount (target phase) of the intake valve 9/exhaust valve 10 from the phase of the intake valve 9/exhaust valve 10 (e.g., profiles 9b, 10b) read in step S14 by referring to map information 421 stored in ROM 42. For example, the map information 421 defines the relationship between the phase of the intake valve 9/exhaust valve 10 (or including the phase change amount) when the engine is stopped and the target phase of the intake valve 9/exhaust valve 10 when the engine is restarted. Here, the target phase of the intake valve 9/exhaust valve 10 when the engine is restarted corresponds to the reference phase of the intake valve 9/exhaust valve 10 (e.g., profiles 9a, 10a). At this time, the phase change speed is a fixed value within the specification range of the VTC 50. However, as in FIG. 9 , the phase change speed may be variable depending on the engine speed at the time of first combustion.

Furthermore, in this embodiment, map information 421 related to the control of the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 is defined, but the same effect of adjusting the backflow amount can also be achieved by using the motor generator 114 to change the rate of increase in engine speed during engine stop processing, engine restart, or both. Alternatively, the backflow amount can be adjusted by changing the engine speed at the time of initial combustion during engine restart.

<Step S16>
Next, after confirming that all the conditions in steps S12 to S15 are satisfied, the control unit 402 starts rotating the engine 113 (motoring) by the motor generator 114.

Steps S17 and S18
This step shows how the phases of the intake valve 9 and the exhaust valve 10 are maintained as the engine speed increases during engine start. After the process of step S16, the control unit 402 maintains the phases of the intake valve 9 and the exhaust valve 10 at the phases at the time of engine start (S17). That is, the control unit 402 maintains the phases of the intake valve 9 and the exhaust valve 10 based on profiles 9b and 10b (FIG. 10) and repeats this phase maintenance until the engine speed reaches a predetermined speed (S18). When the engine speed reaches the predetermined speed, the repeated process ends. Then, triggered by the engine speed passing the predetermined speed, the control unit 402 changes the phases of the intake valve 9 and the exhaust valve 10 using the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52. That is, the control unit 402 switches the profiles of the intake valve 9 and the exhaust valve 10 from profiles 9b and 10b to profiles 9a and 10a (FIG. 11).

In this embodiment, the engine speed is set as a fixed value and the phase change start flag is set to ON as the timing for starting the phase change of the VTC 50. However, when controlling the amount of air backflow from the exhaust pipe 8 to the intake pipe 7 during the engine start sequence, in addition to controlling the valve timing, a method such as storing the timing information for turning the phase change flag ON as a variable engine speed in the ECU 102 can be considered. In other words, the profile may be switched in stages depending on the engine speed. For example, in the example of this embodiment described above, the phase control of the intake valve 9 and exhaust valve 10 was two-stage control based on profiles 9a, 10a and profiles 9b, 10b, but it may also be three or more stages.

<Step S19>
This step shows the control and behavior of the intake valve phase variable mechanism 51 and the exhaust valve phase variable mechanism 52 after the engine speed reaches a predetermined speed in steps S17 and S18. After processing in step S18, the control unit 402 causes the intake valve phase variable mechanism 51 to advance the phase of the intake valve 9 at a specified phase change rate so that the phase becomes the target phase specified in step S15. The control unit 402 also causes the exhaust valve phase variable mechanism 52 to retard the phase of the exhaust valve 10 at a specified phase change rate so that the phase becomes the target phase specified in step S15. For example, in this embodiment, the profile 9b of the intake valve 9 is switched to the advance profile 9a ( FIG. 11 ), and the profile 10b of the exhaust valve 10 is switched to the retard profile 10a ( FIG. 11 ). It is assumed that the target values of the phase change amounts at this time are determined from the map information 421 in step S15.

<Step S20>
This step and step S21 indicate the engine initial combustion conditions. The control unit 402 determines whether the engine speed has reached the initial combustion speed based on the detection result of the crank angle sensor 110 obtained by the state determination unit 401. If it is determined that the engine speed has reached the initial combustion speed (Yes in S20), the process proceeds to the determination process of step S21. On the other hand, if it is determined that the engine speed has not reached the initial combustion speed (No in S20), the determination of the engine speed in this step continues.

<Step S21>
Next, the control unit 402 (intake valve phase changing unit 403, exhaust valve phase changing unit 404) determines whether the intake valve 9 (intake cam 11) and the exhaust valve 10 (exhaust cam 12) have reached their designated target phases, based on the detection results of the intake cam angle sensor 31 and the exhaust cam angle sensor 32 obtained by the state determination unit 401. If it is determined that the intake valve 9 and the exhaust valve 10 have reached their target phases (Yes in S21), the process proceeds to step 22. On the other hand, if it is determined that the intake valve 9 or the exhaust valve 10 has not reached its target phase (No in S21), the intake valve phase changing unit 403 or the exhaust valve phase changing unit 404 continues to determine the phase of the intake valve 9 or the exhaust valve 10, respectively, in this step.

In steps S20 and S21 described above, the engine speed and the phases of the intake valve 9 and exhaust valve 10 are listed as conditions for initial combustion. In the case of a typical series-type hybrid vehicle, the engine speed at the time of initial combustion is often set to approximately 1000 to 1500 rpm. In this embodiment, the condition for the phases of the intake valve 9 and exhaust valve 10 is that they have converged to within, for example, ±3° CA of the target phase angles specified in steps S15 and S19. While conditions such as engine speed and components other than the variable valve timing control mechanism 50 are not listed in this flowchart, it is assumed that they have been determined by the ECU 102.

<Step S22>
Next, after the preparation for the initial combustion is completed by steps S20 and S21, the CPU 40 (control unit 402) turns on the fuel injection flag and sends a fuel injection pulse to the injector 13, thereby starting combustion in the engine 113 (initial combustion).

<Step S23>
After that, the complete combustion determination flag is set, and the CPU 40 (control unit 402) confirms that complete combustion has been achieved, and then transitions to normal engine control (normal control). After the processing of step S23, the processing of this flowchart ends.

By going through the engine stop processing and engine restart sequence shown in Figures 12 and 13 above, it is possible to prevent fresh air from flowing into the three-way catalyst 22 when fuel is cut, and to prevent deterioration of exhaust quality the next time the engine is restarted.

As described above, the engine control device (ECU 102) according to the first embodiment is an engine control device that controls an engine mounted on a hybrid vehicle that is driven by the cooperation of the output of the engine (engine 113) and the output of the electric motor (motor 118). The engine control device includes a state determination unit (state determination unit 401) that determines the state of the engine, an intake reference phase (profile 9a, reference position in FIG. 8) that is the phase of the intake valve provided in the engine's intake pipe before a change in the engine's state, an exhaust reference phase (profile 10a, reference position in FIG. 8) that is the phase of the exhaust valve provided in the engine's exhaust pipe, the engine speed when the fuel injection pulse is stopped (when fuel is cut off) during engine stop processing, and the intake target phase of the intake valve after the fuel injection pulse is stopped (profile 11b). and a control unit (402) that performs control to change the phase of the intake valve through the intake valve phase variable mechanism (intake valve phase variable mechanism 51) and change the phase of the exhaust valve through the exhaust valve phase variable mechanism (exhaust valve phase variable mechanism 52) between the engine stop process and the engine restart process, thereby causing a backflow of burned gas in the engine. The control unit is configured, when a fuel injection pulse stop is detected as a change in the engine state, to change the intake valve from the intake reference phase (profile 9a) to the intake target phase (profile 9b) through the intake valve phase variable mechanism and to change the exhaust valve from the exhaust reference phase (profile 10a) to the exhaust target phase (profile 10a) through the exhaust valve phase variable mechanism, based on the engine speed when the fuel injection pulse stopped and the phase change information (FIG. 8) stored in the phase change information storage unit.

In addition, in the engine control device (ECU 102) of the first embodiment, the phase change information (contents of map information 421) is set so that the higher the engine speed when the fuel injection pulse is stopped (when fuel is cut), the more the intake target phase is set to the retard side relative to the intake reference phase, and the more the exhaust target phase is set to the advance side relative to the exhaust reference phase (Figure 8).

The engine control device (ECU 102) of this embodiment, configured as described above, changes the phase of the intake valve and exhaust valve depending on the engine state (engine speed) when the fuel injection pulse is stopped during the engine stop process of a hybrid vehicle. This creates a backflow of burned gas in the intake and exhaust pipes, preventing fresh air from flowing into the exhaust pipe until the first explosion when the engine is restarted. Therefore, during the fuel injection pulse stop state between the engine stop process of a hybrid vehicle and the engine restart, the forward flow rate from the intake pipe to the exhaust pipe and the reverse flow rate from the exhaust pipe to the intake pipe are controlled depending on the engine speed, preventing fresh air from flowing into the three-way catalyst. Therefore, in this embodiment, enriched fuel injection is prevented when the engine is restarted, improving fuel efficiency and preventing deterioration of exhaust emissions.

Furthermore, according to this embodiment, by using not only the intake valve but also the exhaust valve to generate a backflow of burned gas, the performance requirements of the variable valve timing control mechanism are relaxed. Therefore, it is possible to prevent fresh air from flowing into the three-way catalyst without using a high-performance variable valve timing control mechanism.

In addition, in the engine control device (ECU 102) of the first embodiment, after the engine stop processing is completed, the control unit (control unit 402) is configured to change the intake valve from the intake target phase to the intake reference phase through the intake valve phase variable mechanism (intake valve phase variable mechanism 51) in accordance with the timing of the initial explosion when the engine is restarted, and to change the exhaust valve from the exhaust target phase to the exhaust reference phase through the exhaust valve phase variable mechanism (exhaust valve phase variable mechanism 52).

In the engine control device (ECU 102) of this embodiment, configured as described above, during the engine restart process after the engine stop process is completed, the intake valve and exhaust valve phases (profiles 9b, 10b) are returned to the reference phases (profiles 9a, 10a) of the original engine state (before fuel cut) in time with the timing of the first explosion (see Figure 11). This allows the engine to switch from a state in which the reverse flow of burned gas is maintained to a forward flow at the appropriate timing and resume power generation operation. Therefore, even before the first explosion when the engine is restarted, the amount of fresh air flowing into the exhaust pipe and, therefore, into the three-way catalyst can be reduced.

In addition, in the engine control device (ECU 102) according to the first embodiment, the phase change information storage unit (map information 421) further stores, as phase change information, the relationship (Figure 9) between the engine speed when the fuel injection pulse is stopped (during fuel cut) during the engine stop process, the intake phase change rate of the intake valve by the intake valve phase variable mechanism, and the exhaust phase change rate of the exhaust valve by the exhaust valve phase variable mechanism. When a fuel injection pulse stop is detected, the control unit (control unit 402) is configured to change the intake valve from the intake reference phase (profile 9a) to the intake target phase (profile 9b) at the intake phase change rate through the intake valve phase variable mechanism, and to change the exhaust valve from the exhaust reference phase (profile 10a) to the exhaust target phase (profile 10b) at the exhaust phase change rate through the exhaust valve phase variable mechanism, based on the engine speed when the fuel injection pulse is stopped and the phase change information stored in the phase change information storage unit.

In addition, in the engine control device (ECU 102) of the first embodiment, the phase change information (contents of map information 421) is set so that the higher the engine speed when the fuel injection pulse is stopped (when fuel is cut), the lower the intake phase change speed and exhaust phase change speed (Figure 9).

In the engine control device (ECU 102) of this embodiment configured as described above, the intake valve and exhaust valve are changed from the reference phase to the target phase at a phase change speed corresponding to the engine speed when the fuel injection pulse is stopped, thereby generating a backflow of burned gas, thereby enabling more accurate adjustment of the backflow amount.

Furthermore, in the engine control device (ECU 102) of the first embodiment, the control unit (control unit 402) is configured to continue stopping the fuel injection pulses during the engine stop process until the intake valve phase variable mechanism has reached the intake target phase, or the exhaust valve phase variable mechanism has reached the exhaust target phase, or both of these controls have been completed (Figure 7).

The engine control device (ECU 102) of this embodiment, configured as described above, can gradually reduce the engine speed while preventing backflow of burned gases during the engine stop process.

Furthermore, in the engine control device (ECU 102) according to the first embodiment, the control unit (control unit 402) may control the rate of change of the engine speed during engine stop processing, engine restart, or both, in conjunction with the phase control of the intake valve of the variable intake valve phase mechanism and the phase control of the exhaust valve of the variable exhaust valve phase mechanism. The control unit may also control the engine speed at the time of initial combustion during engine restart.

Second Embodiment
The second embodiment is an example in which the phases of the intake valve 9 and the exhaust valve 10 are controlled based on the oxygen storage capacity (OSC) of the three-way catalyst 22 instead of the engine speed as in the first embodiment.

[Applicable engine configuration]
The basic configuration of the engine and its peripheral devices in the second embodiment is the same as that of the first embodiment, as shown in Figures 1, 2, and 3. In this embodiment, a method is shown in which the profiles of the intake valve 9 and the exhaust valve 10 when the engine is stopped are switched depending on the oxygen storage capacity (oxygen storage amount) of the three-way catalyst 22, rather than the engine speed, as the condition when the engine is stopped.

Here, an example of a procedure for variable valve timing control during engine stop processing according to the second embodiment will be described with reference to FIG.
FIG. 14 is a flowchart showing an example of the procedure of variable valve timing control during engine stop processing using the oxygen storage amount as a control trigger according to the second embodiment.

The engine 113 according to this embodiment includes a means for detecting the oxygen storage capacity (OSC) of the three-way catalyst 22, and the ECU 102 is capable of constantly acquiring the oxygen storage amount, which is an indicator of the oxygen storage capacity. Methods for calculating the oxygen storage amount are described in, for example, Japanese Patent Application Laid-Open Nos. 2007-126982 and 2011-149337. For example, the state determination unit 401 calculates a calculation formula expressed as "intake air amount x (actual air-fuel ratio - center air-fuel ratio)" based on the air flow meter 28, which measures the intake air amount of the engine 113, and the output (actual air-fuel ratio) of the air-fuel ratio sensor 25 installed upstream of the three-way catalyst 22. The center air-fuel ratio is an air-fuel ratio that can purify the three components of HC, CO, and NOx with high efficiency and in a balanced manner, and is estimated from the oxygen sensor 24 downstream of the three-way catalyst 22 and the oxygen storage amount.

The flowchart shown in Figure 14 will be explained below, with each processing step separated. In this flowchart, as in the first embodiment, the start condition is that the engine is running, and the end condition is when the ECU 102 confirms that the engine has completely stopped. Also, in this flowchart, steps S31 to S33 and steps S36 to S39 have the same control and behavior as in the first embodiment (see the flowchart in Figure 12), so the explanation will focus on the processing in steps S34 and S35.

In this embodiment and flowchart, a method of adjusting the backflow amount by varying the target phase position (opening/closing timing) of the intake valve 9 and the exhaust valve 10 according to the oxygen storage capacity of the three-way catalyst 22 during fuel cut is described. However, as with the first embodiment, this embodiment is also capable of achieving the same backflow amount adjustment effect by switching the phase change speed of the intake valve 9 and the exhaust valve 10 according to the oxygen storage capacity. In other words, the variable valve timing control of the intake valve 9 and the exhaust valve 10 in this embodiment adjusts the backflow of air from the exhaust pipe 8 to the intake pipe 7 by varying the target phase position, varying the phase change speed, or combining both.

Furthermore, when oxygen storage capacity is used, map information 421 can be obtained by replacing the intake valve timing (target phase position) and exhaust valve timing (target phase position) shown on the horizontal axis of Figure 8 with oxygen storage capacity [%]. For example, oxygen storage capacity [%] is expressed as the ratio of the current oxygen storage capacity to the maximum oxygen storage capacity of the three-way catalyst 22. If the target phase position is replaced with oxygen storage capacity, the slope of the graph in Figure 8 will be reversed. For example, in the case of the intake valve 9, the larger the oxygen storage capacity, the more retarded the target phase position is set, since it is desirable not to allow fresh air to flow into the exhaust pipe 8. On the other hand, in the case of the exhaust valve 10, the larger the oxygen storage capacity, the more advanced the target phase position is set.

As with the target phase position, the phase change speed can also be determined by using map information 421, which replaces the intake valve timing (phase change speed) and exhaust valve timing (phase change speed) shown on the horizontal axis of Figure 9 with oxygen storage capacity [%]. Even when the phase change speed is replaced with oxygen storage capacity, the slope of the graph in Figure 9 will be reversed. For example, in the case of intake valve 9, the phase change speed is set to a higher value as the oxygen storage capacity increases, since it is desired to generate backflow earlier. Similarly, in the case of exhaust valve 10, the phase change speed is set to a higher value as the oxygen storage capacity increases.

<Step S34>
Step S34 in Fig. 14 shows the control performed by the CPU 40 (control unit 402) of the ECU 102 at the start of engine stop processing. It is assumed that, in the normal control of step S31, the engine stop processing is started through the determinations of steps S32 and S33, and fuel cut is executed. The state determination unit 401 of the CPU 40 calculates the oxygen storage capacity (oxygen storage amount) of the three-way catalyst 22 at the moment (or immediately before) the fuel cut is started. After processing step S34, the process proceeds to step S35.

<Step S35>
Next, the control unit 402 (intake valve phase changing unit 403) determines a target phase (e.g., profile 9b) for the intake valve 9 during engine stop processing based on the map information 421 in the ROM 42, in accordance with the oxygen storage capacity (OSC) of the three-way catalyst 22 during fuel cut. Similarly, the control unit 402 (exhaust valve phase changing unit 404) determines a target phase (e.g., profile 10b) for the exhaust valve 10 during engine stop processing based on the map information 421 in the ROM 42, in accordance with the oxygen storage capacity of the three-way catalyst 22 during fuel cut. At this time, the control unit 402 may determine not only the target phase for the engine stop processing but also the phase change speed from the map information 421. After processing step S35, the process proceeds to step S36.

The profiles of the intake valve 9 and exhaust valve 10 selected here vary depending on the oxygen storage amount, but when the oxygen storage amount is relatively large, a large amount of oxygen is already stored in the three-way catalyst 22, and a larger backflow amount is required. Therefore, the control unit 402 increases the retard amount of the intake valve 9 and the advance amount of the exhaust valve 10. On the other hand, when the oxygen storage amount is relatively small, the control unit 402 decreases the retard amount of the intake valve 9 and the advance amount of the exhaust valve 10. In this embodiment, it is desirable to use the variable valve timing control described above to keep the final oxygen storage amount at the time the engine is stopped the same.

In the first embodiment described above, the target phase (profile) of the intake valve 9 and exhaust valve 10, or the phase change speed of each valve, during the subsequent engine stop process and engine restart was specified based on the engine speed at the moment of fuel cut.However, in the second embodiment, a similar backflow adjustment effect is achieved based on the state of the oxygen storage capacity of the three-way catalyst 22.

In addition, the map information 421 held within the ECU 102 can also be created by combining the engine speed and oxygen storage capacity during fuel cut. In other words, a target phase position and phase change speed are set for each combination of engine speed and oxygen storage capacity. Using map information that combines these two makes it possible to adjust the backflow amount more accurately.

The present invention is not limited to the first and second embodiments described above, and of course, various other applications and modifications are possible as long as they do not deviate from the gist of the present invention as set forth in the claims. For example, the first and second embodiments described above provide detailed and specific descriptions of the configuration of the engine and ECU (engine control unit) in order to clearly explain the present invention, and are not necessarily limited to those that include all of the components described. Furthermore, it is also possible to add, replace, or delete other components from part of the configuration of each embodiment.

Furthermore, some or all of the above-mentioned configurations, functions, processing units, etc. may be implemented in hardware, for example by designing them as integrated circuits. Broad processor devices such as FPGAs (Field Programmable Gate Arrays) and ASICs (Application Specific Integrated Circuits) may also be used as hardware.

In addition, in the flowcharts describing the chronological processing shown in Figures 12 to 14, multiple processes may be executed in parallel or the processing order may be changed as long as it does not affect the processing results.

In addition, in each of the above-described embodiments, the control lines and information lines shown are those considered necessary for explanation, and not all control lines and information lines in the product are necessarily shown. In reality, it can be assumed that almost all components are interconnected.

7...intake pipe, 8...exhaust pipe, 9...intake valve, 9a...(intake valve during power generation operation) profile, 9b...(intake valve when engine is stopped) profile, 10...exhaust valve, 10a...(exhaust valve during power generation operation) profile, 10b...(exhaust valve when engine is stopped) profile, 11...intake cam, 12...exhaust cam, 13...intake cam angle sensor, 22...three-way catalyst, 24...oxygen sensor, 25...air-fuel ratio sensor, 40...CPU, 50...variable valve Valve timing control mechanism (VTC), 51... intake valve phase variable mechanism, 52... exhaust valve phase variable mechanism, 100... hybrid vehicle, 102... ECU, 109... battery voltage sensor, 110... crank angle sensor, 113... engine, 114... motor generator, 116... battery, 118... motor, 401... state determination unit, 402... control unit, 403... intake valve phase change unit, 404... exhaust valve phase change unit, 421... map information

Claims (4)

An engine control device for controlling an engine mounted on a hybrid vehicle, the engine control device comprising: a fuel injection device that injects fuel into air drawn into a cylinder of an internal combustion engine; an intake valve phase variable mechanism that changes the phase of an intake valve provided in an intake pipe of the internal combustion engine; an exhaust valve phase variable mechanism that changes the phase of an exhaust valve provided in an exhaust pipe of the internal combustion engine; a motor generator that is connected to a crankshaft of the internal combustion engine ; and a crank angle sensor that detects rotation of the crankshaft,
a state determination unit that determines an engine speed from a signal of the crank angle sensor, determines whether an engine start flag from a vehicle control device of the hybrid vehicle is on or off , and determines whether a fuel cut command is on or off ;
a control unit that controls a fuel injection pulse of the fuel injection device, and controls the intake valve phase variable mechanism and the exhaust valve phase variable mechanism ;
a phase change information storage unit that stores: an engine speed when a fuel injection pulse is stopped, which is acquired when a fuel injection pulse is stopped; an intake reference phase, which is a phase of the intake valve for drawing the air from the intake pipe into a cylinder of the internal combustion engine; an exhaust reference phase , which is a phase of the exhaust valve for discharging the air from inside the cylinder to the exhaust pipe; an exhaust target phase, which sets the phase of the exhaust valve to a position advanced from the exhaust reference phase in accordance with the engine speed when a fuel injection pulse is stopped in order to cause the air in the exhaust pipe to flow back into the cylinder; and an intake target phase, which sets the phase of the intake valve to a position retarded from the intake reference phase in accordance with the engine speed when a fuel injection pulse is stopped in order to cause the air in the cylinder to flow back into the intake pipe ;
The control unit
when the engine start flag is in an off state and the fuel cut command changes from off to on, the fuel injection pulse stop is started, and the value of the engine speed detected by the state determination unit is stored in the phase change information storage unit as the engine speed when the fuel injection pulse is stopped;
When the engine start flag is in an off state and the fuel cut command is in an on state, the intake valve phase is controlled using the intake target phase, the exhaust valve phase is controlled using the exhaust target phase, and the fuel injection pulse is stopped;
When the engine start flag changes from off to on, if the engine speed detected by the state determination unit has not reached the initial combustion speed that is the timing for initial combustion when the engine is restarted, motoring is performed by using the motor generator to rotate the crankshaft, and the intake valve phase is controlled using the intake target phase, the exhaust valve phase is controlled using the exhaust target phase, and the fuel injection pulse is stopped;
When the engine start flag is in an on state and the engine speed detected by the state determination unit has reached the initial explosion speed, the intake valve phase is controlled using the intake reference phase, the exhaust valve phase is controlled using the exhaust reference phase, and the fuel injection pulse is stopped until the intake valve phase reaches the intake reference phase by the intake valve phase variable mechanism and the exhaust valve phase reaches the exhaust reference phase by the exhaust valve phase variable mechanism are both controlled.
Engine control device. an intake valve phase variable mechanism that changes the phase of an intake valve provided in an intake pipe of the internal combustion engine; an air flow meter that is provided in the intake pipe and measures an intake air amount; an exhaust valve phase variable mechanism that changes the phase of an exhaust valve provided in an exhaust pipe of the internal combustion engine ; a three-way catalyst that is provided downstream of an exhaust valve in the exhaust pipe; an oxygen sensor that is provided in the exhaust pipe; a motor generator that is provided and connected to a crankshaft of the internal combustion engine; and a crank angle sensor that detects rotation of the crankshaft ,
a state determination unit that determines an engine speed from a signal of the crank angle sensor, determines an oxygen storage capacity of the three-way catalyst from signals of the air flow meter and the oxygen sensor, and determines whether an engine start flag from a vehicle control device of the hybrid vehicle is on or off , and determines whether a fuel cut command is on or off ;
a control unit that controls a fuel injection pulse of the fuel injection device, and controls the intake valve phase variable mechanism and the exhaust valve phase variable mechanism;
a phase change information storage unit that stores an oxygen storage capacity when a fuel injection pulse is stopped that is acquired when a fuel injection pulse is stopped, an intake reference phase that is a phase of the intake valve for drawing the air from the intake pipe into a cylinder of the internal combustion engine, an exhaust reference phase that is a phase of the exhaust valve for discharging the air from inside the cylinder to the exhaust pipe, an exhaust target phase that sets the phase of the exhaust valve to a position advanced from the exhaust reference phase in accordance with the oxygen storage capacity when the fuel injection pulse is stopped in order to cause the air in the exhaust pipe to flow back into the cylinder, and an intake target phase that sets the phase of the intake valve to a position retarded from the intake reference phase in accordance with the oxygen storage capacity when the fuel injection pulse is stopped in order to cause the air in the cylinder to flow back into the intake pipe ,
The control unit
When the engine start flag is in an off state and the fuel cut command changes from off to on, the fuel injection pulse stop is started, and the value of the oxygen storage capacity of the three-way catalyst detected by the state determination unit is stored in the phase change information storage unit as the oxygen storage capacity when the fuel injection pulse is stopped,
When the engine start flag is in an off state and the fuel cut command is in an on state, the intake valve phase is controlled using the intake target phase, the exhaust valve phase is controlled using the exhaust target phase, and the fuel injection pulse is stopped;
When the engine start flag changes from off to on, if the engine speed detected by the state determination unit has not reached the initial combustion speed that is the timing for initial combustion when the engine is restarted, motoring is performed by using the motor generator to rotate the crankshaft, and the intake valve phase is controlled using the intake target phase, the exhaust valve phase is controlled using the exhaust target phase, and the fuel injection pulse is stopped;
When the engine start flag is in an on state and the engine speed detected by the state determination unit has reached the initial explosion speed, the intake valve phase is controlled using the intake reference phase, the exhaust valve phase is controlled using the exhaust reference phase, and the fuel injection pulse is stopped until the intake valve phase reaches the intake reference phase by the intake valve phase variable mechanism and the exhaust valve phase reaches the exhaust reference phase by the exhaust valve phase variable mechanism are both controlled.
Engine control device. An engine control method by an engine control device that controls an engine mounted on a hybrid vehicle, the engine including a fuel injection device that injects fuel into air drawn into a cylinder of the internal combustion engine, an intake valve phase variable mechanism that changes the phase of an intake valve provided in an intake pipe of the internal combustion engine, an exhaust valve phase variable mechanism that changes the phase of an exhaust valve provided in an exhaust pipe of the internal combustion engine, a motor generator that is connected to a crankshaft of the internal combustion engine, and a crank angle sensor that detects rotation of the crankshaft,
a state determination process for determining whether an engine rotation speed is obtained using the crank angle sensor, determining whether an engine start flag from a vehicle control device of the hybrid vehicle is on or off , and determining whether a fuel cut command is on or off ;
a process of storing in a phase change information storage unit the engine speed when fuel injection pulses are stopped, which is acquired when a fuel injection pulse is stopped, an intake reference phase which is the phase of the intake valve for drawing the air from the intake pipe into the cylinder of the internal combustion engine , an exhaust reference phase which is the phase of the exhaust valve for discharging the air from inside the cylinder to the exhaust pipe, an exhaust target phase which sets the phase of the exhaust valve to a position advanced from the exhaust reference phase in accordance with the engine speed when fuel injection pulses are stopped in order to cause the air in the exhaust pipe to flow back into the cylinder, and an intake target phase which sets the phase of the intake valve to a position retarded from the intake reference phase in accordance with the engine speed when fuel injection pulses are stopped in order to cause the air in the cylinder to flow back into the intake pipe;
a process of starting to stop the fuel injection pulses when the engine start flag is in an off state and the fuel cut command changes from off to on, and storing the value of the engine speed detected in the state determination process in the phase change information storage unit as the engine speed when the fuel injection pulses are stopped;
a process of controlling the phase of the intake valve using the target intake phase, controlling the phase of the exhaust valve using the target exhaust phase, and stopping the fuel injection pulse when the engine start flag is in an off state and the fuel cut command is in an on state;
and when the engine start flag changes from off to on, if the engine speed detected by the state determination process has not reached an initial combustion speed that is the timing for initial combustion when the engine is restarted, performing motoring to rotate the crankshaft using the motor generator, controlling the phase of the intake valve using the intake target phase, controlling the phase of the exhaust valve using the exhaust target phase, and stopping the fuel injection pulse,
When the engine start flag is in an on state and the engine speed detected in the state determination process has reached the initial explosion speed, the intake valve phase is controlled using the intake reference phase, the exhaust valve phase is controlled using the exhaust reference phase, and the fuel injection pulse is stopped until the intake valve phase reaches the intake reference phase by the intake valve phase variable mechanism, and the exhaust valve phase reaches the exhaust reference phase by the exhaust valve phase variable mechanism are both controlled.
Engine control method. an engine control method using an engine control device that controls an engine mounted on a hybrid vehicle, the engine including: a fuel injection device that injects fuel into air taken into a cylinder of the internal combustion engine; an intake valve phase variable mechanism that changes the phase of an intake valve provided in an intake pipe of the internal combustion engine; an air flow meter that is provided in the intake pipe and measures an intake air amount; an exhaust valve phase variable mechanism that changes the phase of an exhaust valve provided in an exhaust pipe of the internal combustion engine; a three-way catalyst that is provided downstream of an exhaust valve in the exhaust pipe; an oxygen sensor that is provided in the exhaust pipe; a motor generator that is connected to a crankshaft of the internal combustion engine; and a crank angle sensor that detects rotation of the crankshaft ,
a state determination process for determining an engine speed from a signal of the crank angle sensor, determining an oxygen storage capacity of the three-way catalyst from signals of the air flow meter and the oxygen sensor, determining whether an engine start flag from a vehicle control device of the hybrid vehicle is on or off , and determining whether a fuel cut command is on or off ;
a process of storing in a phase change information storage unit the oxygen storage capacity when the fuel injection pulse is stopped, which is acquired when the fuel injection pulse is stopped, an intake reference phase which is the phase of the intake valve for drawing the air from the intake pipe into the cylinder of the internal combustion engine , an exhaust reference phase which is the phase of the exhaust valve for discharging the air from inside the cylinder to the exhaust pipe, an exhaust target phase which sets the phase of the exhaust valve to a position advanced from the exhaust reference phase in accordance with the oxygen storage capacity when the fuel injection pulse is stopped in order to cause the air in the exhaust pipe to flow back into the cylinder, and an intake target phase which sets the phase of the intake valve to a position retarded from the intake reference phase in accordance with the oxygen storage capacity when the fuel injection pulse is stopped in order to cause the air in the cylinder to flow back into the intake pipe;
a process of starting to stop the fuel injection pulses when the engine start flag is in an off state and the fuel cut command changes from off to on, and storing the value of the oxygen storage capacity of the three-way catalyst detected in the state determination process in the phase change information storage unit as the oxygen storage capacity when the fuel injection pulses are stopped;
a process of controlling the phase of the intake valve using the target intake phase, controlling the phase of the exhaust valve using the target exhaust phase, and stopping the fuel injection pulse when the engine start flag is in an off state and the fuel cut command is in an on state;
and when the engine start flag changes from off to on, if the engine speed detected by the state determination process has not reached an initial combustion speed that is the timing for initial combustion when the engine is restarted, performing motoring to rotate the crankshaft using the motor generator, controlling the phase of the intake valve using the intake target phase, controlling the phase of the exhaust valve using the exhaust target phase, and stopping the fuel injection pulse,
When the engine start flag is in an on state and the engine speed detected in the state determination process has reached the initial explosion speed, the intake valve phase is controlled using the intake reference phase, the exhaust valve phase is controlled using the exhaust reference phase, and the fuel injection pulse is stopped until the intake valve phase reaches the intake reference phase by the intake valve phase variable mechanism, and the exhaust valve phase reaches the exhaust reference phase by the exhaust valve phase variable mechanism are both controlled.
Engine control method.