JP7613237B2 - Engine Control Unit - Google Patents

Description

The present invention relates to a control device applied to an engine that has cylinders, an output shaft that rotates by receiving energy from combustion in the cylinders, an intake passage through which intake air introduced into the cylinders flows, an exhaust passage through which exhaust gas discharged from the cylinders flows, and an EGR passage that connects the intake passage and the exhaust passage.

One example of the above control device is disclosed in Patent Document 1 below. The engine control device described in Patent Document 1 includes a throttle valve provided in the intake passage, an EGR valve (EGR control valve) provided in the EGR passage, and a control unit that controls the throttle valve and EGR valve. When there is a request to automatically stop the engine, the control unit opens the EGR valve while stopping fuel injection into the cylinder, and fully closes the throttle valve and EGR valve when the engine stops due to the injection stop (fuel cut).

JP 2004-100497 A

According to the engine control device described in Patent Document 1, when restarting a stopped engine, intake air containing EGR gas is introduced into the cylinder, which is expected to have the effect of suppressing the amount of NOx generated by combustion during restart. However, depending on the operating state immediately before fuel cut is performed, it is expected that the engine will stop with an excessively large amount of EGR gas trapped in the intake passage. In such a case, the proportion of fresh air introduced into the cylinder during restart may be too low, which may reduce the combustibility of the mixture. In addition, depending on the control after the engine is stopped, a large amount of fresh air that has passed through the throttle valve may be introduced into the cylinder when the engine is restarted, which may reduce the effect of suppressing the amount of NOx generated.

The present invention was made in consideration of the above circumstances, and aims to provide an engine control device that can suppress the amount of NOx produced while ensuring startability when restarting the engine.

In order to solve the above-mentioned problems, the present invention provides a control device that is applied to an engine having a cylinder, an output shaft that rotates by receiving energy from combustion in the cylinder, an intake passage through which intake air introduced into the cylinder flows, an exhaust passage through which exhaust gas discharged from the cylinder flows, and an EGR passage that connects the intake passage and the exhaust passage, and the control device includes an injector that supplies fuel to the cylinder, an EGR valve that is provided in the EGR passage so as to be able to open and close, a throttle valve that is provided in the intake passage upstream of a connection between the EGR passage and the intake passage so as to be able to open and close, and a control unit that controls each part of the engine including the injector, the throttle valve, and the EGR valve, and the control unit is configured to automatically execute a fuel cut that stops the supply of fuel by the injector when a predetermined automatic stop condition is established. and a restart control unit that restarts the supply of fuel by the injector when a predetermined restart condition is met, the automatic stop control unit executes oxygen concentration adjustment control that adjusts the opening of the throttle valve and the opening of the EGR valve so that the oxygen concentration in the intake passage downstream of the connection portion becomes a predetermined target value lower than the oxygen concentration in the atmosphere between the execution of the fuel cut and the stop of the rotation of the output shaft, and maintains the throttle valve in a fully closed state after the execution of the oxygen concentration adjustment control, and the restart control unit opens the throttle valve after the restart condition is met and increases the opening of the EGR valve between the stop of the rotation of the output shaft and the opening of the throttle valve (claim 1).

According to the present invention, the oxygen concentration adjustment control is executed between the time when the fuel cut is executed and the time when the rotation of the output shaft stops, so that the oxygen concentration in the intake passage downstream of the connection and the EGR passage communicating with it can be set to a target value lower than the oxygen concentration in the atmosphere. In addition, by maintaining the throttle valve in a fully closed state after the execution of the oxygen concentration adjustment control and opening the throttle valve after the restart condition is satisfied, the introduction of fresh air through the throttle valve is prohibited for at least the period from the time when the rotation of the output shaft stops until the restart condition is satisfied, so that the oxygen concentration in the intake passage downstream of the connection and the oxygen concentration in the EGR passage can be maintained at approximately the target value.

Moreover, the opening of the EGR valve is increased after the rotation of the output shaft stops, and then the throttle valve is opened after the restart condition is satisfied. Therefore, when the engine is restarted in response to the satisfaction of the restart condition, the gas in the EGR passage can be reliably introduced into the cylinder before the fresh air that has passed through the throttle valve reaches the cylinder, and the gas introduced into the cylinder can be mainly composed of the gas in the intake passage downstream of the connection portion and the gas in the EGR passage, which has a target oxygen concentration. Therefore, according to the present invention, it is possible to prevent the oxygen concentration in the cylinder from becoming excessively low or high when the engine is restarted, and it is possible to reduce the amount of NOx generated while ensuring the combustibility of the mixture when combustion of the mixture in the cylinder is resumed, and thus the startability of the engine. In addition, after combustion in the cylinder is resumed, the fresh air that has passed through the throttle valve reaches the cylinder, so that the necessary oxygen can be introduced into the cylinder after combustion is resumed.

In the above configuration, preferably, the throttle valve opening after the restart condition is satisfied is set to a position closer to the closed side than the full opening (claim 2).

This configuration reliably keeps the amount of fresh air introduced into the cylinder through the throttle valve low when the engine begins to restart, thereby reliably suppressing increases in the oxygen concentration in the cylinder and increases in the amount of NOx produced.

In the above configuration, the oxygen concentration adjustment control preferably includes a first control for opening the throttle valve so that the oxygen concentration in the intake passage downstream of the connection portion rises to the target value, and a second control for fully closing the throttle valve when the oxygen concentration rises to the target value (claim 3).

According to this configuration, by opening the throttle valve after fuel cut (first control), oxygen-rich fresh air can be introduced into the intake passage downstream of the throttle valve to increase the oxygen concentration in the intake passage downstream of the throttle valve. Here, before fuel cut, the oxygen concentration in the intake passage downstream of the connection is significantly lower than the oxygen concentration in the atmosphere due to the recirculation of burnt gas through the EGR passage. Therefore, according to this configuration, the oxygen concentration in the intake passage downstream of the connection can be increased toward the target value by implementing the first control. In addition, when the oxygen concentration rises to the target value, the throttle valve is closed (second control) and then maintained in a fully closed state, and the introduction of fresh air through the throttle valve is stopped. Therefore, according to this configuration, the oxygen concentration in the intake passage downstream of the connection and the oxygen concentration in the EGR passage can be reliably maintained at the target value after the rotation of the output shaft is stopped.

As described above, the engine control device of the present invention can suppress the amount of NOx produced.

1 is a schematic system diagram showing a preferred embodiment of an engine to which a control device of the present invention is applied; FIG. 2 is a functional block diagram showing a control system of the engine. 5 is a flowchart showing the first half of an automatic stop/restart control executed when the engine is automatically stopped or restarted. 5 is a flowchart showing the latter half of the automatic stop/restart control. 4 is a time chart showing an example of time changes of each state quantity when the automatic stop/restart control is executed.

<Overall engine configuration>
Fig. 1 is a schematic system diagram showing a preferred embodiment of an engine to which the control device of the present invention is applied. The engine E shown in this figure is a four-stroke diesel engine mounted on a vehicle as a power source for running. The engine includes an engine body 1 driven by a supply of fuel containing diesel oil, an intake passage 30 through which intake air introduced into the engine body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, a supercharger 50 driven by the exhaust gas passing through the exhaust passage 40, and a high-pressure EGR device 60 and a low-pressure EGR device 70 for recirculating a part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30.

The engine body 1 is an in-line multi-cylinder type having multiple cylinders 2 (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the paper surface of FIG. 1. The engine body 1 comprises a cylinder block 3 in which multiple cylinders 2 are formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the upper end opening of each cylinder 2, and multiple pistons 5 housed in each cylinder 2 so as to be able to slide back and forth. Note that in this embodiment, the side from the cylinder block 3 toward the cylinder head 4 is treated as the top and the opposite is treated as the bottom, but this is for convenience of explanation and is not intended to limit the installation posture of the engine.

A combustion chamber 6 is formed above the piston 5 of each cylinder 2. Each combustion chamber 6 is a space defined by the underside of the cylinder head 4, the side surface (cylinder liner) of the cylinder 2, and the crown surface 5a of the piston 5. Fuel is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. The mixture of the supplied fuel and air is burned in the combustion chamber 6, and the piston 5, which is pushed down by the expansion force caused by the combustion, reciprocates up and down.

A crankshaft 7, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 3 (below the pistons 5). The crankshaft 7 is connected to the pistons 5 of each cylinder 2 via connecting rods 8, and rotates around a central axis in response to the reciprocating motion (up and down movement) of the pistons 5.

The crankshaft 7 is connected to the motor M via the clutch C. The clutch C connects the crankshaft 7 and the motor M in a manner that allows them to be connected and disconnected. When the engine is started, the crankshaft 7 is forcibly rotated by the motor M. Specifically, when the engine is started, the clutch C is engaged, and the crankshaft 7 and the motor M are connected by the clutch C in a state in which torque is transmitted between them. This allows the torque of the motor M to be transmitted to the crankshaft 7, and the crankshaft 7 is rotated and driven by the motor M to crank the engine.

A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 7, and the engine speed, which is the rotation speed of the crankshaft 7. The water temperature sensor SN2 detects the temperature of the cooling water flowing inside the cylinder block 3 and the cylinder head 4, i.e., the engine water temperature.

The cylinder head 4 has an intake port 9 and an exhaust port 10 that communicate with the combustion chamber 6, each formed for each cylinder 2. The cylinder head 4 is also equipped with a combination of an intake valve 11, an exhaust valve 12, and an injector 15 for each cylinder 2. The intake valve 11 is a valve that opens and closes the opening of the intake port 9 on the combustion chamber 6 side. The exhaust valve 12 is a valve that opens and closes the opening of the exhaust port 10 on the combustion chamber 6 side. The injector 15 is an injection valve that injects fuel (diesel) into the combustion chamber 6, and is attached to the cylinder head 4 so that it injects fuel from the center of the ceiling surface of the combustion chamber 6 toward the crown surface 5a of the piston 5, for example.

The cylinder head 4 is fitted with a valve mechanism 13 that drives the intake valves 11 to open and close, and a valve mechanism 14 that drives the exhaust valves 12 to open and close. The combination of these valve mechanisms 13, 14 includes, for example, a pair of camshafts linked to the crankshaft 7, and drives the intake valves 11 and exhaust valves 12 of each cylinder 2 to open and close in conjunction with the rotation of the crankshaft 7.

The intake passage 30 is a tubular member that forms a flow passage for intake air introduced into the combustion chamber 6 of each cylinder 2. The intake passage 30 has an intake manifold 30a (including multiple branch pipes arranged in a direction perpendicular to the paper surface of FIG. 1) that branches out corresponding to the multiple cylinders 2 in the downstream portion close to the engine body 1. This intake manifold 30a is connected to the cylinder head 4 so as to communicate with the intake port 9 of each cylinder 2. The portion of the intake passage 30 other than the intake manifold 30a is a single tubular member that forms a common passage connected to the intake manifold 30a.

In the intake passage 30, an air cleaner 31, a throttle valve 32, an intercooler 33, and a surge tank 34 are arranged in this order from the upstream side. The air cleaner 31 is a filter that removes foreign matter from the intake air. The throttle valve 32 is an electric butterfly valve that can adjust the flow rate of the intake air flowing through the intake passage 30. The intercooler 33 is a heat exchanger that cools the intake air compressed by the turbocharger 50 (compressor 51, described in detail later). The surge tank 34 is a tank that provides space for evenly distributing the intake air to each cylinder 2, and is connected to the upstream end of the intake manifold 30a.

An airflow sensor SN3 and an intake pressure sensor SN4 are arranged in the intake passage 30. The airflow sensor SN3 is arranged in a portion of the intake passage 30 downstream of the air cleaner 31, and detects the flow rate of the intake air passing through that portion, i.e., the intake air flow rate. The intake pressure sensor SN4 is arranged in the surge tank 34, and detects the pressure of the intake air passing through the surge tank 34, i.e., the intake pressure.

The exhaust passage 40 is a tubular member that forms a flow passage for exhaust gas discharged from the combustion chamber 6 of each cylinder 2. The exhaust passage 40 has an exhaust manifold 40a (including multiple branch pipes arranged in a direction perpendicular to the paper surface of FIG. 1) that branches out corresponding to the multiple cylinders 2 in the upstream portion close to the engine body 1. This exhaust manifold 40a is connected to the cylinder head 4 so as to communicate with the exhaust port 10 of each cylinder 2. The portion of the exhaust passage 40 other than the exhaust manifold 40a is a single tubular member that forms a common passage connected to the exhaust manifold 40a.

The exhaust passage 40 is provided with a catalytic converter 41 that purifies the exhaust gas. The catalytic converter 41 incorporates an oxidation catalyst 42 that oxidizes and detoxifies the CO and HC in the exhaust gas, and a DPF (diesel particulate filter) 43 that collects particulate matter contained in the exhaust gas.

An exhaust _O2 sensor SN5 is attached to the exhaust passage 40. The exhaust _O2 sensor SN5 is provided in a portion of the exhaust passage 40 between the turbine 52 and the catalytic device 41, and detects the concentration of oxygen contained in the exhaust gas passing through this portion, i.e., the exhaust oxygen concentration.

The turbocharger 50 includes a compressor 51 arranged in the intake passage 30, a turbine 52 arranged in the exhaust passage 40, and a turbine shaft 53 connecting the compressor 51 and the turbine 52.

The turbine 52 is an impeller that rotates by receiving the energy of the exhaust gas flowing through the exhaust passage 40. The turbine 52 is disposed in the exhaust passage 40 between the downstream end (exhaust collection section) of the exhaust manifold 40a and the catalytic device 41. The rotation of the turbine 52 is transmitted to the compressor 51 via the turbine shaft 53.

The compressor 51 is an impeller that rotates in conjunction with the rotation of the turbine 52 to compress and send out (supercharge) the intake air. The compressor 51 is disposed in the intake passage 30 between the air cleaner 31 and the throttle valve 32.

The high-pressure EGR device 60 is a recirculation device for recirculating a portion of the relatively high-pressure exhaust gas before it flows into the turbine 52 to the intake passage 30 as EGR gas. The high-pressure EGR device 60 includes a first EGR passage 61 that connects the exhaust passage 40 and the intake passage 30, and a first EGR valve 62 and a first EGR cooler 63 provided in the first EGR passage 61. The first EGR valve 62 is an electrically operated valve that can adjust the flow rate of the EGR gas flowing through the first EGR passage 61. The first EGR cooler 63 is a heat exchanger that cools the EGR gas flowing through the first EGR passage 61. The first EGR passage 61 and the first EGR valve 62 correspond to the "EGR passage" and "EGR valve" in the present invention, respectively.

The location where the upstream end (exhaust passage 40 side) of the first EGR passage 61 is connected to the exhaust passage 40 is the first EGR inlet portion 61a, and the location where the downstream end (intake passage 30 side) of the first EGR passage 61 is connected to the intake passage 30 is the first EGR outlet portion 61b. In this case, the first EGR inlet portion 61a is located between the turbine 52 in the exhaust passage 40 and the downstream end (exhaust collection portion) of the exhaust manifold 40a. Also, the first EGR outlet portion 61b is located between the throttle valve 32 and the surge tank 34 in the intake passage 30. In other words, the first EGR passage 61 connects the exhaust passage 40 upstream of the turbine 52 and the intake passage 30 downstream of the throttle valve 32 to each other. The first EGR outlet portion 61b corresponds to the "connection portion between the EGR passage and the intake passage" in the present invention.

The low pressure EGR device 70 is a recirculation device for recirculating a portion of the exhaust gas having a relatively low pressure after passing through the turbine 52 to the intake passage 30 as EGR gas. The low pressure EGR device 70 includes a second EGR passage 71 that connects the exhaust passage 40 and the intake passage 30, and a second EGR valve 72 and a second EGR cooler 73 provided in the second EGR passage 71. The second EGR valve 72 is an electrically operated valve that can adjust the flow rate of the EGR gas flowing through the second EGR passage 71. The second EGR cooler 73 is a heat exchanger that cools the EGR gas flowing through the second EGR passage 71.

The location where the upstream end (exhaust passage 40 side) of the second EGR passage 71 is connected to the exhaust passage 40 is the second EGR inlet portion 71a, and the location where the downstream end (intake passage 30 side) of the second EGR passage 71 is connected to the intake passage 30 is the second EGR outlet portion 71b. In this case, the second EGR inlet portion 71a is located downstream of the turbine 52 and the catalytic device 41 in the exhaust passage 40. The second EGR outlet portion 71b is located between the air cleaner 31 and the throttle valve 32 in the intake passage 30 (more specifically, between the air cleaner 31 and the compressor 51). In other words, the second EGR passage 71 connects the exhaust passage 40 downstream of the turbine 52 and the intake passage 30 upstream of the throttle valve 32.

<Control system>
2 is a functional block diagram showing the engine control system. The ECU 100 shown in the figure is a device for controlling the engine in an integrated manner, and is composed of a microcomputer including a processor (CPU) for performing various arithmetic operations, memories such as ROM and RAM, and various input/output buses.

Information detected by each of the engine sensors is input to the ECU 100. For example, the ECU 100 is electrically connected to the crank angle sensor SN1, water temperature sensor SN2, air flow sensor SN3, intake pressure sensor SN4, and exhaust _O2 sensor SN5. Information detected by each of the sensors SN1 to SN5, that is, information such as the crank angle, engine speed, engine water temperature, intake air flow rate, intake pressure, and exhaust oxygen concentration, is sequentially input to the ECU 100.

In addition, ECU 100 also receives detection information from various sensors equipped in the vehicle. In this embodiment, the vehicle is equipped with a vehicle speed sensor SN6, an accelerator sensor SN7, and a brake sensor SN8. Vehicle speed sensor SN6 is a sensor that detects the vehicle speed, which is the traveling speed of the vehicle, accelerator sensor SN7 is a sensor that detects the accelerator opening, which is the opening of an accelerator pedal equipped in the vehicle, and brake sensor SN8 is a sensor that detects whether or not the brake pedal equipped in the vehicle is being operated (brake operation). Detection information (vehicle speed, accelerator opening, and brake operation information) from each of the sensors SN6 to SN8 is also sequentially input to ECU 100.

The ECU 100 controls each part of the engine while executing various judgments and calculations based on the input information from the above sensors SN1 to SN8. For example, the ECU 100 is electrically connected to the injector 15, the throttle valve 32, the first EGR valve 62, and the second EGR valve 72, and outputs control signals to each of these devices based on the results of the above calculations. The ECU 100 also outputs control signals to the clutch C and the motor M.

The ECU 100 functionally includes a judgment unit 101, an automatic stop control unit 102A, and a restart control unit 102B. The judgment unit 101 performs various judgments such as whether the automatic stop condition and the restart condition are met. The automatic stop control unit 102A controls the injector 15, the throttle valve 32, the first EGR valve 62, etc. when the automatic stop condition is met. For example, when the automatic stop condition is met, the automatic stop control unit 102A executes a fuel cut to stop fuel injection (fuel supply) by the injector 15 in order to stop the engine. The restart control unit 102B controls the injector 15, the throttle valve 32, the first EGR valve 62, etc. when the restart condition is met. For example, when the restart condition is met, the restart control unit 102B resumes fuel injection (fuel supply) by the injector 16. Hereinafter, the automatic stop control unit 102A and the restart control unit 102B are collectively referred to as the automatic stop/start control unit 102.

The engine of this embodiment is configured to be capable of automatically stopping and restarting. In other words, the ECU 100 has the function of automatically stopping and restarting the engine under predetermined conditions. The above-mentioned automatic stop conditions are conditions that permit the engine to be automatically stopped, and the above-mentioned restart conditions are conditions that permit the engine to be automatically restarted after the engine is automatically stopped due to the automatic stop conditions. Various conditions can be set for the automatic stop conditions and restart conditions depending on the vehicle model, etc.

For example, in a vehicle whose only driving power source is essentially an engine (a so-called engine vehicle), the automatic stop condition may be satisfied when multiple conditions are met, including (i) the vehicle is substantially stopped, (ii) the accelerator pedal is in the OFF state, and (iii) the brake pedal is in the ON state (depressed). In addition, in this vehicle, after the engine is automatically stopped after the automatic stop condition is satisfied, the restart condition may be satisfied when multiple conditions are met, including (i) the vehicle is substantially stopped, (ii) the accelerator pedal opening is greater than 0 (depressed), and (iii) the brake pedal is in the OFF state (not depressed). In this case, the ECU 100 (determination unit 101) determines whether the automatic stop condition and the restart condition are satisfied based on information input from the vehicle speed sensor SN6, the accelerator sensor SN7, and the brake sensor SN8, etc.

On the other hand, in a vehicle that also uses a motor M as a power source for driving, i.e., a so-called hybrid vehicle that can run as an EV using only the motor M, there are cases where the driving force of the engine is not required even while the vehicle is running, and when such a situation occurs, the automatic stop condition may be established. In this case, the ECU 100 calculates the target torque of the driving source including the engine and the motor M from the vehicle speed detected by the vehicle speed sensor SN6 and the accelerator opening detected by the accelerator sensor SN7, and determines whether or not engine output (positive output torque that contributes to driving) is required based on various conditions including the calculated target torque. If it is determined that engine output is not required, it is determined that the automatic stop condition is established. In this vehicle, if it is determined that engine output is required when the engine is automatically stopped after the automatic stop condition is established, it is determined that the restart condition is established.

<Automatic stop/restart control>
Next, the automatic stop/restart control executed by the ECU 100 when the engine in operation is automatically stopped and then restarted will be described in detail. Figures 3 and 4 are flowcharts showing a specific procedure of the automatic stop/restart control. Here, the automatic stop/restart control includes a control for adjusting the oxygen concentration in the intake air present in the intake passage 30 downstream of the first EGR outlet 61b, and hereinafter, the oxygen concentration to be adjusted, i.e., the oxygen concentration in the intake air present in the intake passage 30 downstream of the first EGR outlet 61b, will be referred to as the "final intake oxygen concentration."

When the control according to the flowchart in FIG. 3 starts, the ECU 100 (determination unit 101) first determines whether the automatic stop condition is met (step S1).

When step S1 returns YES and it is confirmed that the automatic stop condition is met, the ECU 100 (automatic stop/start control unit 102) executes a fuel cut to stop fuel injection from the injector 15 of each cylinder 2 (step S2). When the fuel cut is executed, combustion in each cylinder 2 is stopped, and the engine speed gradually decreases.

Here, the load of the engine is not high just before the automatic stop condition is satisfied. In this state, the engine is operated with at least one of the first EGR valve 62 and the second EGR valve 72 open. That is, as a prerequisite for the automatic stop condition to be satisfied, the engine is performing EGR, which recirculates exhaust gas from the exhaust passage 40 to the intake passage 30, and the EGR rate (the proportion of EGR gas in the intake air) is relatively high. Therefore, when the automatic stop condition is satisfied, the oxygen concentration in the intake passage 30 is significantly lower than the oxygen concentration in the atmosphere at least in the vicinity of the engine body 1 (more specifically, the portion downstream of the first EGR outlet 61b), and the value is lower than the target value Dx of the oxygen concentration used in step S5 described later.

Next, the ECU 100 (automatic stop/start control unit 102) sets the opening of the throttle valve 32 to the stop throttle opening and sets the opening of the first EGR valve 62 to the stop EGR opening (step S3). The stop throttle opening and the stop EGR opening are neither fully closed (0%) nor fully open (100%), that is, intermediate openings. These stop openings are preset and stored in the ECU 100. In this embodiment, the stop throttle opening and the stop EGR opening are set to approximately the same value (for example, about 30%). The opening of the second EGR valve 72 can be set to an appropriate value, for example, it can be set to a specific intermediate opening determined separately from the throttle valve 32 and the first EGR valve 62.

With the throttle valve 32 open, fresh air is introduced into the intake passage 30. Although the first EGR valve 62 is open, the oxygen concentration of the EGR gas increases as combustion in the cylinder 2 is stopped after fuel cut. This causes the oxygen concentration in the intake passage 30 and the oxygen concentration in the first EGR passage 61 to increase. Furthermore, with combustion in the cylinder 2 stopped, the components of the gas introduced into the cylinder 2 and the gas discharged from the cylinder 2 become almost equal, and the oxygen concentration in the intake passage 30 downstream of the first EGR outlet 61b, i.e., the final intake oxygen concentration, becomes equal to the oxygen concentration in the first EGR passage 61.

Next, the ECU 100 (automatic stop/start control unit 102) controls the throttle valve 32 and the first EGR valve 62 so that their openings change in conjunction with the engine speed (step S4). Specifically, the ECU 100 gradually reduces the openings of the throttle valve 32 and the first EGR valve 62 as the engine speed gradually decreases, within a range in which the throttle valve 32 and the first EGR valve 62 are maintained in an open state. In this embodiment, the openings of the throttle valve 32 and the first EGR valve 62 are gradually reduced while being maintained at substantially the same value.

Next, the ECU 100 (determination unit 101) determines whether the estimated value of the final intake oxygen concentration has reached or exceeded a predetermined target value Dx (step S5). The target value Dx is preset and stored in the ECU 100. The target value Dx is set to a value smaller than the oxygen concentration of the atmosphere, that is, the intake oxygen concentration when all the intake air is fresh air. The target value Dx is also set to a value larger than the final intake oxygen concentration that can be reached when a fuel cut is performed, and in step S5, it is determined whether the estimate of the final intake oxygen concentration has risen to the target value Dx.

The ECU 100 continues to control the throttle valve 32 and the first EGR valve 62 to gradually decrease their openings in accordance with the engine speed (step S4), while waiting for the determination in step S5 to become YES. Then, when the ECU 100 (automatic stop/start control unit 102) determines YES in step S5 and confirms that the final intake oxygen concentration has increased to the target value Dx, it fully closes the throttle valve 32 (step S6).

Next, the ECU 100 (automatic stop/start control unit 102) adjusts the opening of the first EGR valve 62 so that the intake pressure does not fall below a predetermined reference pressure Px (see FIG. 5(f)) (step S7). The reference pressure Px is the pressure in the surge tank 34 detected by the intake pressure sensor SN4, i.e., the reference value of the intake pressure, and is a pressure equivalent to a weak negative pressure slightly below atmospheric pressure.

Now, since the introduction of new intake air is basically stopped by closing the throttle valve 32 in step S6, in order to keep the intake pressure at a weak negative pressure in this state, it is necessary to increase the opening of the first EGR valve 62 to promote the recirculation of EGR gas through the first EGR passage 61. Therefore, in step S7, the ECU 100 drives the first EGR valve 62 in the opening direction. Specifically, the ECU 100 determines the basic opening of the first EGR valve 62 from the engine speed while referring to a map, etc., and calculates the target opening of the first EGR valve 62 by correcting the determined basic opening using the pressure detected by the intake pressure sensor SN4. In step S7, the opening of the first EGR valve 62 is controlled according to the target opening calculated in this way.

Next, the determination unit 101 determines whether the engine speed has fallen below a predetermined reference speed Nx (step S8). This determination is made based on the detection value of the crank angle sensor SN1. The reference speed Nx is a value smaller than the engine speed at the time of fuel cut in step S2, and is preset to a value that can adjust the future negative pressure of the intake air pressure to an appropriate level and is stored in the ECU 100. Specifically, the reference speed Nx is set to a value that causes the minimum value Py (see FIG. 5(f)) of the intake air pressure that is significantly negatively pressurized after step S9 described later to fall within a predetermined target range Z. The target range Z can be set to include, for example, 50 kPa, and the reference speed Nx can be set to, for example, about 700 to 800 rpm.

The ECU 100 continues to adjust the opening of the first EGR valve 62 (step S7) while waiting for the determination in step S8 to become YES. Then, when the ECU 100 (automatic stop/start control unit 102) determines YES in step S8 and confirms that the engine speed is less than the reference speed Nx, it fully closes the first EGR valve 62 (step S9). Here, the throttle valve 32 is already in a fully closed state through the control of step S10. Therefore, from step S9 onwards, both the throttle valve 32 and the first EGR valve 62 are fully closed. As a result, the intake pressure is made negative from step S9 onwards.

Next, the ECU 100 (determination unit 101) determines whether the engine has completely stopped (step S10). The ECU 100 determines that the engine has completely stopped when the engine speed detected by the crank angle sensor SN1 drops to substantially zero.

The ECU 100 waits for the judgment of step S10 to become YES while maintaining both the first EGR valve 62 and the throttle valve 32 in a fully closed state. Then, when the ECU 100 (automatic stop/start control unit 102) judges YES in step S10 and confirms that the engine has completely stopped, it opens the first EGR valve 62 and sets the opening degree of the first EGR valve 62 to a predetermined starting EGR opening degree (step S11). At this time, the throttle valve 32 is not opened, and the first EGR valve 62 is opened while the throttle valve 32 is maintained in a fully closed state. The above starting EGR opening degree is an intermediate opening degree, which is preset and stored in the ECU 100. The starting EGR opening degree is set to, for example, about 50%. Note that step S11 may be performed a predetermined time after the engine has completely stopped, but in this embodiment, it is performed immediately after the determination in step S10 becomes YES.

Next, the ECU 100 (determination unit 101) determines whether the restart condition is satisfied (step S12). The ECU 100 waits for the determination in step S12 to become YES while keeping the throttle valve 32 in a fully closed state and the opening degree of the first EGR valve 62 at the start EGR opening degree. Then, when the ECU 100 (automatic stop/start control unit 102) determines that the restart condition is satisfied in step S12 as YES, it starts the start control to start the engine (step S13). Specifically, the ECU 100 switches the clutch C from an open state (a state in which torque is not transmitted between the crankshaft 7 (engine E) and the motor M) to an engaged state (a state in which torque is transmitted between the crankshaft 7 (engine E) and the motor M via the clutch C). In addition, the ECU 100 drives the motor M when the motor M is stopped. As a result, the engine starts cranking and the engine restart is started. Then, when cranking begins and the engine speed reaches or exceeds a predetermined speed, the ECU 100 (automatic stop/start control unit 102) resumes fuel injection from the injector 15 into the combustion chamber 6 of each cylinder 2.

When step S13 is started, that is, when start control is started, the ECU 100 (automatic stop/start control unit 102) opens the throttle valve 32 and sets the opening of the throttle valve 32 to the start throttle opening (step S14). The start throttle opening is an intermediate opening that is set in advance and stored in the ECU 100. The start throttle opening is set to, for example, about 30%, which is smaller than the start EGR opening.

The above step S14, i.e., opening of the throttle valve 32, is performed almost simultaneously with the start of the start control. In this embodiment, the throttle valve 32 is opened almost simultaneously with the ECU 100 issuing a command to the clutch C to switch from the open state to the engaged state.

Next, the ECU 100 (determination unit 101) determines whether or not the engine start has been completed (step S15). Specifically, the ECU 100 determines that the engine start has been completed when the engine speed detected by the crank angle sensor SN1 becomes equal to or greater than a predetermined determination speed.

While continuing the start control, the ECU 100 waits for the determination in step S15 to become YES. Then, when the ECU 100 determines YES in step S15 and confirms that the engine start is complete, it transitions to control of normal operation (operation other than operation after the automatic stop condition is satisfied and operation from the satisfaction of the restart condition to the completion of engine start). For example, the ECU 100 calculates the torque required for the engine based on the accelerator opening, etc., and controls the injector 15, the first EGR valve 62, and the throttle valve 32 so that the torque is realized and so that an EGR rate corresponding to the torque and the engine speed, etc. is realized.

<Example of operation of each part with automatic stop/restart control>
FIG. 5 is a time chart showing an example of the change over time of each state quantity when automatic stop/restart control is executed, in which (a) is a flag indicating whether the automatic stop condition is met, (b) is a flag indicating whether the restart condition is met, (c) is the state of the clutch C, (d) is a flag indicating whether fuel injection from the injector 15 is required, (e) is the engine speed, (f) is the intake pressure (pressure in the surge tank 34), (g) is the opening degree of the throttle valve 32, (h) is the opening degree of the first EGR valve 62, and chart (i) shows the change over time of the final intake oxygen concentration (intake oxygen concentration in the surge tank 34).

In FIG. 5, the time when the automatic stop condition is satisfied is set to t1. When the automatic stop condition is satisfied, fuel cut is executed. Furthermore, immediately after fuel cut, the opening of the throttle valve 32 is set to the stop throttle opening α%, and the opening of the first EGR valve 62 is set to the stop EGR opening α%. In the example of FIG. 5, the opening of the throttle valve 32 before time t1 is smaller than the stop throttle opening α%, so the opening of the throttle valve 32 is increased immediately after time t1. On the other hand, the opening of the first EGR valve 62 before time t1 is larger than the stop EGR opening α%, so the opening of the first EGR valve 62 is reduced immediately after time t1.

As fuel cut is performed, the engine speed begins to substantially decrease from time t2. As a result, from time t2 onwards, the openings of the throttle valve 32 and the first EGR valve 62 are gradually reduced from their respective stop openings.

As described above, since fuel cut is performed and the throttle valve 32 is open, the final intake oxygen concentration gradually increases from time t1 onwards. Then, at time t3, the final intake oxygen concentration increases to the target value Dx.

When the final intake oxygen concentration rises to the target value Dx at time t3, the opening of the throttle valve 32 is immediately reduced to 0% and the throttle valve 32 is fully closed. By fully closing the throttle valve 32, the inflow of fresh air into the intake passage 30 is stopped. As a result, the increase in the final intake oxygen concentration essentially stops around time t3, and the final intake oxygen concentration is maintained near the target value Dx after time t3. As described above, after fuel cut, the final intake oxygen concentration and the oxygen concentration in the first EGR passage 61 become equal. As a result, the oxygen concentration in the first EGR passage 61 is also maintained near the target value Dx after time t3.

In addition, immediately after time t3, the opening of the first EGR valve 62 is increased by adjusting the intake pressure so that it does not fall below the reference pressure Px, thereby maintaining the intake pressure at a value that does not fall below the reference pressure Px.

At time t4 after time t3, when the engine speed drops to the reference speed Nx, the opening of the first EGR valve 62 is reduced to 0%. This control causes both the first EGR valve 62 and the throttle valve 32 to be fully closed.

With both the first EGR valve 62 and the throttle valve 32 in a fully closed state, the intake pressure drops rapidly after time t4, and the intake pressure reaches its minimum value Py some time after time t3. Here, as described above, the reference rotation speed Nx is set to a value that causes the minimum value Py of the intake pressure to fall within a predetermined target range Z, and the minimum value Py of the intake pressure that is achieved some time after time t3 falls within the target range Z.

At time t5, which is delayed from time t4, the engine speed drops to zero and the engine comes to a complete stop. Then, the first EGR valve 62 opens and its opening is increased from 0% to the starting EGR opening β%. In the example of FIG. 5, the starting EGR opening β% is set to an opening larger than the stopping EGR opening α% described above.

When the first EGR valve 62 opens, gas flows from the first EGR passage 61 into the intake passage 30. This increases the intake pressure to close to atmospheric pressure. Meanwhile, the throttle valve 32 is closed, so the flow of fresh air into the intake passage 30 is kept stopped. Furthermore, because of the above, the oxygen concentration in the first EGR passage 61 is close to the target value Dx. Therefore, the final intake oxygen concentration is maintained at a value close to the target value Dx even after time t5.

In the example of FIG. 5, the restart condition is met at time t6, some time after time t5. In response to this, the clutch C is switched to the engaged state (switched from OFF to ON) at time t7, which is delayed from time t6. By switching the clutch C to the engaged state at time t7, torque is transmitted from the motor M to the engine (crankshaft 7). As a result, engine cranking begins immediately after time t7, and the engine speed increases. As described above, if the motor M is stopped at time t6, the motor M begins to be driven at time t7.

Also, at time t7, i.e., at approximately the same timing as when the clutch C is switched to the engaged state, the throttle valve 32 is opened and its opening is increased from 0% to the starting throttle opening γ%. In the example of FIG. 5, the starting throttle opening γ% is set to an opening larger than the stopping throttle opening α%.

Here, the throttle valve 32 opens at time t7, allowing the introduction of fresh air into the intake passage 30 downstream of the throttle valve 32. However, there is a drive delay in the throttle valve 32, and there is a distance between the throttle valve 32 and the surge tank 34, so the fresh air does not reach the surge tank immediately. Also, when the engine starts cranking, a flow of intake air toward the cylinder 2 occurs, but since the connection part (first EGR outlet part) 61b between the first EGR passage 61 and the intake passage 30 is arranged in a position closer to the surge tank 34 than the throttle valve 32, the gas in the first EGR passage 61 is preferentially introduced into the surge tank 34 over the intake air upstream of the throttle valve 32, that is, the fresh air, for a while even after the engine starts cranking. And, as described above, the oxygen concentration in the first EGR passage 61 is a value close to the target value Dx, which is almost equal to the final intake oxygen concentration. As a result, even if the throttle valve 32 is opened at time t7, the oxygen concentration in the surge tank 34 does not increase, and this oxygen concentration, i.e., the final intake oxygen concentration, is maintained at a value close to the target value Dx.

When the engine starts cranking at time t7, fuel injection from the injector 15 is resumed at a later time t8. At this time, intake air from the surge tank 34 is introduced into cylinder 2. As described above, the oxygen concentration in the surge tank 34 is set to a value close to the target value Dx. As a result, the fuel injected from the injector 15 burns in an atmosphere where the oxygen concentration is the target value Dx.

Now, some time after time t7, the fresh air that has passed through the throttle valve 32 reaches the surge tank 34. However, the oxygen concentration of the EGR gas decreases as the combustion of the mixture in cylinder 2 resumes. Therefore, the mixture of the EGR gas and the fresh air suppresses the increase in the oxygen concentration in the surge tank 34, and even after time t8, the oxygen concentration in the surge tank 34, i.e., the final intake oxygen concentration, and ultimately the oxygen concentration in cylinder 2, remains close to the target value Dx.

At time t9, some time after time t8, the engine speed becomes equal to or higher than the reference speed Ny. Engine control then switches to normal control, and the openings of the throttle valve 32 and first EGR valve 62 are set to openings corresponding to the accelerator opening, etc. In the example of FIG. 5, after time t9, the opening of the throttle valve 32 is set to an opening greater than the starting throttle opening γ%, and the opening of the first EGR valve 62 is set to an opening smaller than the starting EGR valve opening β%.

In the example operation shown in FIG. 5, the control for opening both the throttle valve 32 and the first EGR valve 62 between time t1 and time t3 corresponds to the "first control" in the present invention, the control for fully closing the throttle valve 32 at time t3 corresponds to the "second control," and the control including the first control and the second control corresponds to the "oxygen concentration adjustment control."

<Action and effect>
As described above, in the above embodiment, in response to the establishment of the automatic stop condition, a fuel cut (step S3 in FIG. 3) is executed to stop the fuel injection from the injector 15, and the throttle valve 32 and the first EGR valve 62 are controlled so that the final intake oxygen concentration, which is the oxygen concentration in the intake passage 30 downstream of the first EGR outlet 61b, becomes a target value Dx lower than the oxygen concentration in the atmosphere during the period from the fuel cut to the complete stop of the engine, and the throttle valve 32 is maintained fully closed until the restart condition is established. Then, after the complete stop of the engine, the first EGR valve 62 is first opened and its opening is increased from 0% to the start EGR opening, and then the throttle valve 32 is opened after the restart condition is established. Therefore, according to the above embodiment, when the engine is restarted, the amount of NOx generated can be suppressed while ensuring the combustibility of the mixture and thus the startability of the engine. In addition, after the combustion of the air-fuel mixture is restarted, fresh air can be introduced into the cylinder 2, thereby preventing the oxygen concentration in the cylinder 2 from becoming excessively low, and combustibility can be ensured.

Specifically, after the final intake oxygen concentration reaches the target value Dx, the throttle valve 32 is maintained in a fully closed state until the restart condition is satisfied, thereby stopping the inflow of fresh air into the intake passage 30 through the throttle valve 32 during this period. As a result, the final intake oxygen concentration, i.e., the oxygen concentration in the intake passage 30 downstream of the first EGR outlet 61b and the first EGR passage 61 communicating therewith, can be maintained near the target value Dx until the restart condition is satisfied. Then, by opening the throttle valve 32 after the restart condition is satisfied after the first EGR valve 62 is opened, as described above, at the start of the engine restart, the gas in the first EGR passage 61 can be preferentially introduced into the surge tank 34 over the intake air upstream of the throttle valve 32, i.e., fresh air. As a result, when the combustion of the mixture in the cylinder 2 is resumed, the gas in that cylinder 2 can be composed mainly of gas that has been retained in the portion of the intake passage 30 downstream of the throttle valve 32 and in the first EGR passage 61 that communicates with this portion, and the gas has an oxygen concentration maintained at the target value Dx. Therefore, when the engine is restarted, the mixture can be burned with an appropriate oxygen concentration, and the generation of NOx can be suppressed while ensuring the combustibility of the mixture.

In particular, the target value Dx is set to a concentration lower than the oxygen concentration in the atmosphere. This ensures that NOx generation is suppressed. In addition, in the above embodiment, the target value Dx is set to a value higher than the final intake oxygen concentration that can be achieved when fuel cut is performed. This ensures that oxygen deficiency is prevented when the combustion of the air-fuel mixture resumes, ensuring good combustibility.

In addition, by opening the throttle valve 32 after the restart condition is satisfied, fresh air that has passed through the throttle valve 32 after the combustion of the mixture is resumed can be introduced into the cylinder 2. Therefore, the mixture can be stably burned in the cylinder 2. Here, in the above embodiment, the first EGR 62 is maintained in an open state even after the restart condition is satisfied. Therefore, as described above, the EGR gas with a reduced oxygen concentration due to the restart of the combustion of the mixture and the fresh air that has passed through the throttle valve 32 can be mixed and introduced into the cylinder 2. Therefore, even after the combustion of the mixture is resumed, the oxygen concentration in the cylinder 2 can be prevented from becoming excessively low or high.

In addition, in the above embodiment, the opening of the throttle valve 32 that is realized after the restart condition is satisfied is set to a starting opening that is closer to the closed side than fully open. This makes it possible to more reliably prevent a large amount of fresh air from being introduced into the cylinder 2 through the throttle valve 32 when the engine is restarted, and reliably reduces the oxygen concentration in the cylinder 2 and therefore the amount of NOx produced.

In the above embodiment, the throttle valve 32 is closed when the final intake oxygen concentration reaches the target value Dx, while the opening of the first EGR valve 62 is controlled to increase. Then, the first EGR valve 62 is closed when the engine speed becomes less than the reference speed Nx. Therefore, it is possible to prevent the intake pressure from becoming an excessive negative pressure between the closing of the first EGR valve 62 and the complete stop of the engine. For example, as described above, it is possible to prevent the minimum value Py of the intake pressure from becoming excessively small, and to increase the probability that the minimum value Py falls within the target range Z. If the minimum value Py of the intake pressure falls below the target range Z, that is, if the intake pressure falls to an excessively strong negative pressure, the speed at which the engine speed decreases becomes excessively fast, and as a result, the shock (shock transmitted to the vehicle body due to the reaction of the sudden stop) that occurs when the engine is completely stopped is likely to increase, and the occupant may feel uncomfortable. In contrast, in this embodiment, the closing timing of the first EGR valve 62 is relatively delayed (later than the closing timing of the throttle valve 32), so the amount of decrease in intake pressure can be kept within an appropriate range, and shock when the engine is stopped can be reduced. In addition, some engines perform stop position control to adjust the stop position of the piston 5 of each cylinder 2 to a position that is favorable for restarting. In such an engine, when control that relatively delays the closing of the first EGR valve 62 is adopted as in this embodiment, the speed at which the engine speed decreases can be adjusted to an appropriate range, so that the accuracy of the above-mentioned piston 5 stop position control can be prevented from decreasing, and the restartability of the engine can be improved.

<Modification>
In the above embodiment, the throttle valve 32 is opened at the same time as issuing a command to the clutch C to switch to the engaged state when restarting the engine, but the timing of opening the throttle valve 32 is not limited to this. That is, in the above embodiment, the start timing of the start control is set to the timing of issuing a command to the clutch C, but other timings may be used as the start timing of the start control, such as the timing when engine cranking starts or the timing when the restart condition is satisfied.

In addition, in the above embodiment, the first EGR valve 62 is opened immediately after the engine is completely stopped. However, the timing for opening the first EGR valve 62 after the engine is completely stopped may be any time between when the engine is completely stopped, that is, when the rotation of the crankshaft 7 stops, and when start control is started, and this timing is not limited to immediately after the engine is completely stopped.

In the above embodiment, the final intake oxygen concentration, which is the oxygen concentration in the intake air present in the intake passage 30 downstream of the first EGR outlet 61b, is estimated by calculation, and the throttle valve 32 is fully closed when the estimated final intake oxygen concentration rises to the target value Dx. However, the final intake oxygen concentration may be directly detected by a sensor. For example, a sensor capable of detecting oxygen concentration may be attached to the surge tank 34, and the final intake oxygen concentration may be detected by the sensor.

In the above embodiment, in addition to the high-pressure EGR device 60 including the first EGR passage 61 connecting the exhaust passage 40 upstream of the turbine 52 and the intake passage 30 downstream of the throttle valve 32, the engine is provided with a low-pressure EGR device 70 including a second EGR passage 71 connecting the exhaust passage 40 downstream of the turbine 52 and the intake passage 30 upstream of the throttle valve 32, but the low-pressure EGR device 70 is not essential and may be omitted.

In the above embodiment, an example of applying the present invention to a diesel engine that burns fuel containing diesel oil by pressure ignition has been described, but the engine to which the present invention can be applied is any engine that is capable of EGR operation that recirculates exhaust gas from the exhaust passage to the intake passage, and the present invention may be applied to engines other than diesel engines. For example, the present invention can also be applied to a gasoline engine that is capable of burning fuel containing gasoline by spark ignition and is equipped with an EGR device.

1: Engine body 2: Cylinder 7: Crankshaft (output shaft)
15: injector 30: intake passage 32: throttle valve 40: exhaust passage 61: first EGR passage (EGR passage)
61b: First EGR outlet (connection between the EGR passage and the intake passage)
62: First EGR valve (EGR valve)
102A: Automatic stop control unit 102B: Restart control unit

Claims (3)

A control device is applied to an engine having a cylinder, an output shaft that rotates by receiving energy of combustion in the cylinder, an intake passage through which intake air introduced into the cylinder flows, an exhaust passage through which exhaust gas discharged from the cylinder flows, and an EGR passage connecting the intake passage and the exhaust passage,
an injector for supplying fuel to the cylinder;
an EGR valve provided in the EGR passage so as to be capable of opening and closing;
a throttle valve provided in an intake passage upstream of a connection portion between the EGR passage and the intake passage so as to be capable of opening and closing;
a control unit that controls each part of the engine including the injector, the throttle valve, and the EGR valve,
the control unit includes an automatic stop control unit that executes a fuel cut to stop the supply of fuel by the injector when a predetermined automatic stop condition is satisfied, and a restart control unit that restarts the supply of fuel by the injector when a predetermined restart condition is satisfied,
the automatic stop control unit executes an oxygen concentration adjustment control for adjusting an opening degree of the throttle valve and an opening degree of the EGR valve so that the oxygen concentration in the intake passage downstream of the connection portion becomes a predetermined target value lower than the oxygen concentration in the atmosphere during the period from when the fuel cut is executed until the rotation of the output shaft stops, and maintains the throttle valve in a fully closed state after the execution of the oxygen concentration adjustment control;
the restart control unit opens the throttle valve after the restart condition is satisfied, and increases an opening degree of the EGR valve during a period from when rotation of the output shaft stops to when the throttle valve is opened. 2. The engine control device according to claim 1,
The engine control device according to claim 1, wherein the restart control unit sets an opening degree of the throttle valve to a closing degree rather than a full opening degree after the restart condition is satisfied. The engine control device according to claim 1 or 2,
an intake passage provided on a downstream side of the connection portion and configured to open the throttle valve so that the oxygen concentration in the intake passage downstream of the connection portion increases to the target value; and a second control configured to fully close the throttle valve when the oxygen concentration in the intake passage downstream of the connection portion increases to the target value.

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