JP7711525B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for an internal combustion engine.

For example, Patent Document 1 describes an internal combustion engine equipped with a hydraulic variable valve mechanism that changes the valve timing of the exhaust valve. In this internal combustion engine, the valve timing of the exhaust valve is retarded during cold start to improve emissions during cold start.

JP 2005-147015 A

However, the hydraulic variable valve mechanism cannot be driven until the hydraulic pressure builds up after the engine starts. Therefore, during the time required for the hydraulic pressure to build up after the start of a cold start has elapsed, it is difficult to improve emissions by retarding the valve timing of the exhaust valve.

The control device for an internal combustion engine that solves the above problem is applied to an internal combustion engine that includes an electric variable valve mechanism that changes the valve timing of an intake valve, and a hydraulic variable valve mechanism that changes the valve timing of an exhaust valve. This control device executes a process of advancing the valve timing of the intake valve until a predetermined time has elapsed since the start of a cold start of the internal combustion engine, and a process of retarding the valve timing of the exhaust valve after the predetermined time has elapsed.

Unlike hydraulic variable valve mechanisms, electric variable valve mechanisms can start operating immediately after engine start. Therefore, in this configuration, the electric variable valve mechanism is operated to advance the intake valve timing until it becomes possible to retard the exhaust valve timing during cold start. When the intake valve timing is advanced in this way, valve overlap occurs in which both the exhaust valve and the intake valve are open. When valve overlap occurs, internal EGR increases, reducing NOx emissions. Therefore, NOx emissions are reduced even before the exhaust valve timing is retarded. This makes it possible to further reduce emissions during cold start.

1 is a schematic diagram showing an internal combustion engine and a control device according to an embodiment; 4 is a flowchart showing a procedure of a process executed by the control device of the embodiment. 11A to 11C are diagrams illustrating the operation of the embodiment. 11A to 11C are diagrams illustrating the operation of the embodiment.

Hereinafter, a specific embodiment of a control device for an internal combustion engine will be described.
<Regarding the internal combustion engine and the control device>
As shown in Fig. 1, in an internal combustion engine 1, air is drawn into a combustion chamber 2 through an intake passage 3 and an intake port 3a, and fuel injected from a fuel injection valve 4 is supplied to the combustion chamber 2. When an air-fuel mixture made up of air and fuel is ignited by an ignition plug 5, the mixture is combusted, causing a piston 6 to reciprocate and rotate a crankshaft 7, which is an output shaft of the internal combustion engine 1. The combusted air-fuel mixture is discharged from the combustion chamber 2 to an exhaust passage 8 as exhaust gas. A catalyst 50 for purifying the exhaust gas is provided in the exhaust passage 8.

The internal combustion engine 1 is equipped with an oil pump 90 that is driven and rotated by the crankshaft 7, and the pressure of the hydraulic oil pumped from this oil pump 90 is used to drive the exhaust side variable valve mechanism 16, which will be described later.

A throttle valve 29 for adjusting the amount of intake air is provided in the intake passage 3 of the internal combustion engine 1. The opening degree of this throttle valve 29 is adjusted by an electric motor.
An intake valve 9 is provided in an intake port 3a connected to the intake passage 3. An exhaust valve 10 is provided in an exhaust port 8a connected to the exhaust passage 8. The intake valve 9 and the exhaust valve 10 open and close in accordance with the rotation of an intake camshaft 11 and an exhaust camshaft 12 to which the rotation of the crankshaft 7 is transmitted.

The intake camshaft 11 is provided with an intake variable valve mechanism 13 that changes the valve timing (opening and closing timing) of the intake valve 9 by changing the relative phase of the intake camshaft 11 with respect to the crankshaft 7. This intake variable valve mechanism 13 is an electric variable valve mechanism that is driven by an electric motor that rotates by receiving power from a battery (not shown).

The exhaust side camshaft 12 is provided with an exhaust side variable valve mechanism 16 that changes the valve timing (opening and closing timing) of the exhaust valve 10 by changing the relative phase of the exhaust side camshaft 12 with respect to the crankshaft 7. This exhaust side variable valve mechanism 16 is a hydraulic variable valve mechanism that is driven using the pressure of hydraulic oil sent from an oil pump 90 that is rotated by the crankshaft 7. Therefore, the exhaust side variable valve mechanism 16 is driven when the hydraulic pressure P of the hydraulic oil pumped from the oil pump 90 is equal to or higher than a specified threshold value Pref.

The control device 100 performs various controls of the internal combustion engine 1 by controlling the throttle valve 29, the fuel injector 4, the spark plug 5, the intake variable valve mechanism 13, the exhaust variable valve mechanism 16, etc. This control device 100 is equipped with a CPU 120 and a memory 130 composed of a ROM, a RAM, etc., and performs various controls by the CPU 120 executing the programs stored in the memory 130.

When performing various controls, the control device 100 refers to the intake air amount GA detected by the air flow meter 31 and the throttle opening TA, which is the opening of the throttle valve 29 detected by the throttle sensor 30. The control device 100 also refers to the cooling water temperature THW detected by the water temperature sensor 33 and the engine rotation speed NE calculated from the output signal Scr of the crank angle sensor 34. The control device 100 also refers to the output signal Scai of the intake side cam angle sensor 35, which detects the rotation angle of the intake side camshaft 11, and the output signal Scae of the exhaust side cam angle sensor 36, which detects the rotation angle of the exhaust side camshaft 12. The control device 100 also refers to the output signal of the accelerator position sensor 28, which detects the operation amount (accelerator operation amount ACCP) of the accelerator pedal 27 operated by the driver of the vehicle equipped with the internal combustion engine 1.

<Processing Executed by the Control Device>
The control device 100 calculates the intake side timing VTinr, which is the actual valve timing of the intake valve 9, based on the output signal Scr from the crank angle sensor 34 and the output signal Scai from the intake side cam angle sensor 35. In this embodiment, the state in which the intake valve timing is most retarded is set to an initial value of "0", and the valve timing of the intake valve 9 is grasped by the amount of advancement of the valve timing from this initial value.

The control device 100 also calculates the exhaust side timing VTexr, which is the actual valve timing of the exhaust valve 10, based on the output signal Scr from the crank angle sensor 34 and the output signal Scae from the exhaust side cam angle sensor 36. Incidentally, in this embodiment, the state in which the exhaust valve timing is at the most advanced timing is set to an initial value of "0", and the valve timing of the exhaust valve 10 is grasped by the amount of retardation of the valve timing from this initial value.

The control device 100 also calculates the engine load factor KL. The engine load factor KL is a parameter that determines the amount of air filled in the combustion chamber 2, and is the ratio of the amount of inflow air per combustion cycle of one cylinder to a reference amount of inflow air. The reference amount of inflow air may be an amount that is variably set according to the engine speed NE.

The control device 100 performs valve timing control of the intake valve 9. That is, the control device 100 calculates the intake side target value VTint, which is the target value of the valve timing of the intake valve 9, based on the engine speed NE, the engine load factor KL, etc. The intake side target value VTint is the amount of advance of the intake valve timing from the initial value described above. After calculating this intake side target value VTint, the control device 100 controls the drive of the intake side variable valve mechanism 13 so that the intake side timing VTinr matches the intake side target value VTint. Note that the intake valve timing at engine start is set to the initial value timing described above.

The control device 100 also controls the valve timing of the exhaust valve 10. That is, the control device 100 calculates an exhaust side target value VText, which is a target value for the valve timing of the exhaust valve 10, based on the engine speed NE, the engine load factor KL, and the like. The exhaust side target value VText is the amount of retardation of the exhaust valve timing from the initial value described above. After calculating this exhaust side target value VText, the control device 100 controls the drive of the exhaust side variable valve mechanism 16 so that the exhaust side timing VTexr coincides with the exhaust side target value VText. Note that the exhaust valve timing at engine start is set to the initial value timing described above.

Figure 2 shows the processing procedure executed by the control device 100 during a cold start. The processing shown in Figure 2 is performed by the CPU 120 executing a program stored in the memory 130 of the control device 100 at a predetermined cycle. Note that the control device 100 determines that the current engine start is a cold start, for example, if the cooling water temperature THW at the time the engine start is initiated is equal to or lower than a predetermined temperature. In the following, step numbers are represented by numbers preceded by "S."

When this process starts, the CPU 120 judges whether the current elapsed time after start-up Taf is equal to or greater than the judgment value Tafref (S100). The elapsed time after start-up Taf is the time elapsed since the engine start-up has begun, and is measured by the CPU 120. The judgment value Tafref is preset with a predetermined time required for the hydraulic oil pressure P to reach or exceed the threshold value Pref after the engine start-up has begun, that is, the so-called hydraulic pressure rise time.

If it is determined that the time since starting Taf is less than the reference value Tafref (S100: NO), the CPU 120 executes a process to advance the intake valve timing (S110). In the process of S110, a default intake side target value VTin1 is set as the intake side target value VTint, and the drive of the intake side variable valve mechanism 13 is controlled toward the intake side target value VTin1. The intake side target value VTin1 is a default value that is an appropriate valve overlap period VOR for reducing NOx, for the valve overlap period during which both the exhaust valve 10 and the intake valve 9 are open.

Then, the CPU 120 repeatedly executes the processes of S100 and S110 until a positive determination is made in S100.
On the other hand, when it is determined in S100 that the elapsed time since starting Taf is equal to or greater than the reference value Tafref (S100: YES), that is, when the hydraulic exhaust side variable valve mechanism 16 becomes operable, the CPU 120 executes the process from S120 onwards.

In the process of S120, the CPU 120 executes a process to retard the exhaust valve timing. In this process of S120, a default exhaust target value VTex1 is set as the exhaust target value VText, and the drive of the exhaust variable valve mechanism 16 is controlled toward the exhaust target value VTex1. The exhaust target value VTex1 is a default value that provides an appropriate valve overlap period for reducing NOx. Specifically, in this embodiment, the value is a value that provides the above-mentioned valve overlap period VOR when the intake valve timing is set to the initial value "0". Here, in the process of S130 described later, a process is executed to set the intake target value VTint to the initial value "0". Therefore, the exhaust target value VTex1 is set to the same value as the intake target value VTin1.

Next, the CPU 120 executes a process to retard the intake valve timing (S130). In this S130, the intake side target value VTint is set to an initial value of "0", and the drive of the intake side variable valve mechanism 13 is controlled toward the initial value.

Next, the CPU 120 determines whether or not the warm-up of the catalyst 50 has been completed (S140). The determination of the completion of the warm-up of the catalyst 50 can be performed as appropriate. For example, the completion of the warm-up can be determined based on the fact that the cumulative intake air volume since the start of the engine becomes equal to or exceeds a preset value, the elapsed time after start-up Taf becomes equal to or exceeds a preset value, or the estimated or detected temperature of the catalyst 50 becomes equal to or exceeds a preset value.

When it is determined that the warm-up of the catalyst 50 has not been completed (S140: NO), the CPU 120 repeatedly executes the processes of S120, S130, and S140.
On the other hand, when it is determined that the warm-up of the catalyst 50 is completed (S140: YES), the CPU 120 shifts the intake valve timing and the exhaust valve timing to normal control (S150). This normal control is a control in which the intake side target value VTint and the exhaust side target value VText are calculated based on the engine rotation speed NE, the engine load factor KL, and the like, as described above.

After executing the process of S150, the CPU 120 ends this process.
<Effect>
The operation of this embodiment will be described.

FIG. 3 shows the intake valve timing and the exhaust valve timing when the process of S110 shown in FIG. 2 is executed.
3, when the intake valve timing is advanced from the initial valve timing by executing the process of S110, the intake valve opening timing IVO becomes more advanced than the initial valve opening timing IVOs. This creates a valve overlap period VOR in which the opening timings of the intake valve 9 and the exhaust valve 10 overlap. When the valve overlap period VOR occurs in this way, the internal EGR in the internal combustion engine 1 increases, thereby reducing the amount of NOx emissions.

FIG. 4 shows the intake valve timing and the exhaust valve timing when the processes of S120 and S130 shown in FIG. 2 are executed.
As shown in Fig. 4, when the exhaust valve timing is retarded from the initial valve timing by executing the process of S120, the exhaust valve closing timing EVC becomes more retarded than the initial valve closing timing EVCs. Also, the intake valve timing that was advanced by the process of S110 is retarded by executing the process of S130. As a result, the intake valve opening timing IVO is returned to the initial valve opening timing IVOs. By retarding the exhaust valve timing and the intake valve timing in this way, the valve overlap period VOR is maintained to be the same as the valve overlap period VOR shown in Fig. 3. When the valve overlap period VOR occurs in this way, the internal EGR increases in the internal combustion engine 1, thereby reducing the amount of NOx emissions.

In addition, when the exhaust valve timing is retarded by the processing of S120, the opening timing EVO of the exhaust valve 10 becomes more retarded than the initial opening timing EVOs. In this way, when the opening timing EVO of the exhaust valve 10 is retarded, the period of the expansion stroke becomes longer. When the period of the expansion stroke becomes longer, the amount of HC (hydrocarbons) contained in the combustion gas that is burned during the expansion stroke increases. In other words, the afterburning of HC is promoted, and the amount of HC discharged into the exhaust passage 8 decreases.

＜Effects＞
The effects of this embodiment will be described.
Unlike the hydraulic exhaust side variable valve mechanism 16, the electric intake side variable valve mechanism 13 can start driving immediately after the engine is started. Therefore, in this embodiment, the process of S110 is executed until the determination in the process of S100 shown in FIG. 2 is affirmative, that is, until the valve timing of the exhaust valve can be retarded during cold start. In other words, the electric intake side variable valve mechanism 13 is driven to advance the valve timing of the intake valve 9, thereby causing valve overlap. When valve overlap occurs in this way, the amount of NOx emissions is reduced as described above. Therefore, the amount of NOx emissions is reduced even before the valve timing of the exhaust valve 10 is retarded. Therefore, it is possible to further reduce emissions during cold start.

This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.
The valve overlap period VOR formed by the process of S100 shown in Fig. 2 may be different from the valve overlap period VOR formed by the processes of S120 and S130 shown in Fig. 2. In this modified example, for example, the exhaust side target value VTex1 may be set to a value different from the intake side target value VTin1. Also, the intake side target value VTint set in the process of S130 shown in Fig. 2 may be set to a value larger than the initial value "0" and smaller than the intake side target value VTin1.

- If the valve overlap period formed by retarding the exhaust valve timing can be made longer than the valve overlap period VOR, the process of S130 shown in FIG. 2 can be omitted.

- In the process of S100 shown in FIG. 2, the time since start Taf is referenced to determine whether the hydraulic oil pressure P is equal to or greater than the threshold value Pref, but other values may also be referenced. For example, the total number of rotations of the crankshaft 7 since the engine start-up has begun may also be referenced.

- During cold start, the valve timing control shown in FIG. 2 may be used in combination with cold warm-up control, which warms up the catalyst 50 and other components by increasing the temperature of the exhaust gas discharged from the combustion chamber 2. An example of such cold warm-up control is retarding the ignition timing. In addition, if the internal combustion engine 1 is equipped with an in-cylinder injection valve that directly injects fuel into the combustion chamber 2, it is also possible to increase the exhaust temperature by performing a so-called split injection, in which the fuel is injected from the in-cylinder injection valve in multiple separate injections.

The control device 100 is not limited to having a CPU 120 and a memory 130 and executing software processing. For example, it may have a dedicated hardware circuit (e.g., ASIC, etc.) that processes at least a part of the software processing executed in the above embodiment. That is, the control device 100 may have any of the following configurations (a) to (c). (a) It has a processing device that executes all of the above processing according to a program, and a program storage device such as a memory that stores the program. (b) It has a processing device and a program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) It has a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software processing circuits and dedicated hardware circuits that include a processing device and a program storage device. That is, the above processing may be executed by a processing circuit that includes at least one of one or more software processing circuits and one or more dedicated hardware circuits.

DESCRIPTION OF SYMBOLS 1 internal combustion engine 2 combustion chamber 3 intake passage 8 exhaust passage 9 intake valve 10 exhaust valve 11 intake camshaft 12 exhaust camshaft 13 intake variable valve mechanism 16 exhaust variable valve mechanism 28 accelerator position sensor 29 throttle valve 30 throttle sensor 31 air flow meter 33 water temperature sensor 34 crank angle sensor 35 intake cam angle sensor 36 exhaust cam angle sensor 50 catalyst 90 oil pump 100 control device 120 CPU
130…Memory

Claims (2)

A control device for an internal combustion engine including an electric variable valve mechanism that changes valve timing of an intake valve and a hydraulic variable valve mechanism that changes valve timing of an exhaust valve,
A process of advancing the valve timing of the intake valve until a predetermined time has elapsed since the start of a cold start of the internal combustion engine;
and delaying the valve timing of the exhaust valve after the predetermined time has elapsed .
The predetermined time is preset as a time required from the start of the internal combustion engine until the hydraulic pressure of the hydraulic oil pumped to the hydraulic variable valve mechanism becomes equal to or higher than a predetermined threshold.
A control device for an internal combustion engine. 2. The control device for an internal combustion engine according to claim 1, wherein if a cooling water temperature at the time of starting the internal combustion engine is equal to or lower than a predetermined temperature, it is determined that the current start of the internal combustion engine is a cold start.