Control device for internal combustion engine

Abstract

To reduce an emission during a cold start-up.SOLUTION: An internal combustion engine 1 comprises: an intake side electric variable valve mechanism 13 which changes a valve timing of an intake valve 9; and an exhaust side hydraulic variable valve mechanism 16 which changes a valve timing of an exhaust valve 10. A CPU 120 of a control device 100 executes processes to advance the valve timing of the intake valve 9 until a lapse of predetermined time since commencement of a cold start-up and to retard the valve timing of the exhaust valve 10 after the lapse of the predetermined time.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine.

Background Art

[0002] For example, Patent Document 1 describes an internal combustion engine provided with a hydraulic variable valve mechanism that changes the valve timing of an exhaust valve. In this internal combustion engine, the valve timing of the exhaust valve is retarded at cold start to improve emissions at cold start.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, until the oil pressure rises after starting the engine, the hydraulic variable valve mechanism cannot be driven. Therefore, it is difficult to improve emissions by retarding the valve timing of the exhaust valve until a predetermined time required after starting cold start until the oil pressure rises has elapsed.

Means for Solving the Problems

[0005] The control device for an internal combustion engine that solves the above problems is applied to an internal combustion engine including 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 after starting 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.

[0006] Unlike a hydraulic variable valve mechanism, an electric variable valve mechanism can start driving immediately after the engine starts. Therefore, in this configuration, until the valve timing of the exhaust valve can be retarded during cold start, the electric variable valve mechanism is driven to advance the valve timing of the intake valve. When the valve timing of the intake valve is advanced in this way, valve overlap occurs in which both the exhaust valve and the intake valve are in the open state. When valve overlap occurs, internal EGR increases, reducing the NOx emissions. Therefore, the NOx emissions are reduced even before the valve timing of the exhaust valve is retarded. As a result, emissions can be further reduced during cold start.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0008] Hereinafter, an embodiment in which a control device for an internal combustion engine is embodied will be described. <Regarding the Internal Combustion Engine and the Control Device> As shown in Fig. 1, in the internal combustion engine 1, air is inhaled into the combustion chamber 2 through the intake passage 3 and the intake port 3a, and the fuel injected from the fuel injection valve 4 is supplied to the combustion chamber 2. When the air-fuel mixture composed of air and fuel is ignited by the spark plug 5, the air-fuel mixture burns and the piston 6 reciprocates, and the crankshaft 7, which is the output shaft of the internal combustion engine 1, rotates. The air-fuel mixture after combustion is discharged from the combustion chamber 2 to the exhaust passage 8 as exhaust gas. A catalyst 50 for purifying the exhaust gas is provided in the exhaust passage 8.

[0009] The internal combustion engine 1 is provided with an oil pump 90 that is rotationally driven by the crankshaft 7, and the exhaust-side variable valve mechanism 16 described later is driven by utilizing the pressure of the hydraulic oil pumped from this oil pump 90.

[0010] A throttle valve 29 for measuring the intake air amount 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 the intake port 3a connected to the intake passage 3. An exhaust valve 10 is provided in the exhaust port 8a connected to the exhaust passage 8. These intake valve 9 and exhaust valve 10 open and close respectively as the intake-side camshaft 11 and the exhaust-side camshaft 12, to which the rotation of the crankshaft 7 is transmitted, rotate.

[0011] The intake-side camshaft 11 is provided with an intake-side 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-side camshaft 11 with respect to the crankshaft 7. This intake-side variable valve mechanism 13 is an electric variable valve mechanism that is driven by an electric motor that rotates by receiving power supply from a battery (not shown).

[0012] 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 by utilizing the pressure of the hydraulic oil fed from an oil pump 90 rotated by the crankshaft 7. Therefore, the exhaust-side variable valve mechanism 16 is driven when the hydraulic pressure P of the hydraulic oil pressure-fed from the oil pump 90 is equal to or higher than a specified threshold value Pref.

[0013] The control device 100 performs various controls of the internal combustion engine 1 by controlling the throttle valve 29, the fuel injection valve 4, the ignition plug 5, the intake-side variable valve mechanism 13, the exhaust-side variable valve mechanism 16, etc. This control device 100 includes a CPU 120 and a memory 130 composed of a ROM and a RAM, etc., and the CPU 120 executes the program stored in the memory 130 to perform various controls.

[0014] 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. Further, the control device 100 refers to the cooling water temperature THW detected by the water temperature sensor 33 and the engine rotational speed NE calculated from the output signal Scr of the crank angle sensor 34. Further, the control device 100 refers to the output signal Scai of the intake-side cam angle sensor 35 that detects the rotational angle of the intake-side camshaft 11 and the output signal Scae of the exhaust-side cam angle sensor 36 that detects the rotational angle of the exhaust-side camshaft 12. Further, the control device 100 refers to the output signal of the accelerator position sensor 28 that 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.

[0015] <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 of the crank angle sensor 34 and the output signal Scai of the intake-side cam angle sensor 35. Incidentally, in the present embodiment, the state where the intake valve timing is at the most retarded timing is set as the initial value "0", and the valve timing of the intake valve 9 is grasped by the amount of valve timing advance from this initial value.

[0016] Also, the control device 100 calculates the exhaust-side timing VTexr, which is the actual valve timing of the exhaust valve 10, based on the output signal Scr of the crank angle sensor 34 and the output signal Scae of the exhaust-side cam angle sensor 36. Incidentally, in the present embodiment, the state where the exhaust valve timing is at the most advanced timing is set as the initial value "0", and the valve timing of the exhaust valve 10 is grasped by the amount of valve timing retard from this initial value.

[0017] The control device 100 also calculates the engine load ratio KL. The engine load ratio KL is a parameter that determines the amount of air filled in the combustion chamber 2, and is the ratio of the amount of air flowing in per combustion cycle of one cylinder to the reference inflow air amount. Note that the reference inflow air amount may be variably set according to the engine rotational speed NE.

[0018] 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 rotational speed NE, the engine load ratio KL, and the like. The intake-side target value VTint is the amount of valve timing advance of the intake valve from the above-described initial value. When this intake-side target value VTint is calculated, the control device 100 controls the drive of the intake-side variable valve mechanism 13 so that the intake-side timing VTinr coincides with the intake-side target value VTint. Note that the intake valve timing at engine startup is set to the timing of the above-described initial value.

[0019] In addition, the control device 100 performs valve timing control of the exhaust valve 10. That is, the control device 100 calculates an exhaust-side target value VText, which is the target value of the valve timing of the exhaust valve 10, based on the engine rotational speed NE, the engine load factor KL, and the like. The exhaust-side target value VText is the amount of retard of the exhaust valve timing from the above-described initial value. When this exhaust-side target value VText is calculated, the control device 100 controls the drive of the exhaust-side variable valve mechanism 16 so that the exhaust-side timing VTexr matches the exhaust-side target value VText. Note that the exhaust valve timing at the time of engine start is set to the timing of the above-described initial value.

[0020] FIG. 2 shows a processing procedure executed by the control device 100 at the time of cold start. The processing shown in this FIG. 2 is implemented by the CPU 120 executing a program stored in the memory 130 of the control device 100 at predetermined intervals. Note that the control device 100 determines that the current engine start is a cold start when, for example, the coolant temperature THW when starting the engine is equal to or lower than a predetermined temperature. In the following, step numbers are represented by numbers with "S" attached at the beginning.

[0021] When starting this processing, the CPU 120 determines whether or not the current elapsed time Taf after start is equal to or greater than a determination value Tafref (S100). The elapsed time Taf after start is the elapsed time since starting the engine and is measured by the CPU 120. In addition, a predetermined time, that is, the oil pressure rise time, which is the time required for the oil pressure P of the hydraulic oil to become equal to or higher than the above-described threshold value Pref after starting the engine, is set in advance as the determination value Tafref.

[0022] When it is determined that the elapsed time Taf after startup is less than the determination value Tafref (S100: NO), the CPU 120 executes a process of advancing the intake valve timing (S110). In the process of S110, a predetermined 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 predetermined value that becomes an appropriate valve overlap period VOR for reducing NOx with respect to the valve overlap period during which both the exhaust valve 10 and the intake valve 9 are in the open state.

[0023] Then, the CPU 120 repeatedly executes the processes of S100 and S110 until an affirmative determination is made in S100. On the other hand, when it is determined in S100 that the elapsed time Taf after startup is equal to or greater than the determination value Tafref (S100: YES), that is, when the drive of the hydraulic exhaust side variable valve mechanism 16 becomes possible, the CPU 120 executes the processes after S120.

[0024] In the process of S120, the CPU 120 executes a process of retarding the exhaust valve timing. In the process of S120, a predetermined exhaust side target value VTex1 is set as the exhaust side target value VText, and the drive of the exhaust side variable valve mechanism 16 is controlled toward the exhaust side target value VTex1. The exhaust side target value VTex1 is a predetermined value that makes the valve overlap period an appropriate period for reducing NOx. Specifically, in the present embodiment, when the intake valve timing is set to the initial value of "0", it is a value at which the above-described valve overlap period VOR is obtained. Here, in the process of S130 described later, a process of setting the initial value of "0" as the intake side target value VTint is executed. Therefore, the same value as the intake side target value VTin1 is set for the exhaust side target value VTex1.

[0025] Next, the CPU 120 executes a process of retarding the intake valve timing (S130). In this S130, an initial value of "0" is set as the intake side target value VTint, and the drive of the intake side variable valve mechanism 13 is controlled toward that initial value.

[0026] Next, the CPU 120 determines whether or not the warm-up of the catalyst 50 is completed (S140). The determination of the completion of the warm-up of the catalyst 50 can be made as appropriate. For example, the completion of the warm-up can be determined based on the integrated intake air amount becoming equal to or greater than a predetermined value after the engine start, the elapsed time Taf after the start becoming equal to or greater than a predetermined value, the estimated or detected temperature of the catalyst 50 becoming equal to or greater than a predetermined value, and the like.

[0027] When it is determined that the warm-up of the catalyst 50 is not 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 the control for calculating the intake side target value VTint and the exhaust side target value VText based on the engine rotation speed NE, the engine load factor KL, and the like as described above.

[0028] When the process of S150 is executed, the CPU 120 ends this process. <Operation> The operation of this embodiment will be described.

[0029] FIG. 3 shows the intake valve timing and the exhaust valve timing when the process of S110 shown in FIG. 2 is executed. As shown in FIG. 3, when the intake valve timing is advanced from the initial valve timing by the execution of the process of S110, the valve opening timing IVO of the intake valve becomes a timing on the advanced side compared to the initial valve opening timing IVOs. As a result, a valve overlap period VOR is formed in which the valve opening timings of both the intake valve 9 and the exhaust valve 10 overlap. When the valve overlap period VOR is generated in this way, in the internal combustion engine 1, the internal EGR increases, so that the NOx emission amount is reduced.

[0030] 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 the execution of the process of S120, the valve closing timing EVC of the exhaust valve becomes a timing on the retarded side compared to the initial valve closing timing EVCs. Also, the intake valve timing advanced by the process of S110 is retarded by the execution of the process of S130. As a result, the valve opening timing IVO of the intake valve is returned to the initial valve opening timing IVOs. By such a retardation process of the exhaust valve timing and the intake valve timing, the same valve overlap period VOR as the valve overlap period VOR shown in FIG. 3 is maintained. When the valve overlap period VOR is generated in this way, in the internal combustion engine 1, the internal EGR increases, so that the NOx emission amount is reduced.

[0031] Also, when the exhaust valve timing is retarded by the process of S120, the valve opening timing EVO of the exhaust valve 10 becomes a timing on the retarded side compared to the initial valve opening timing EVOs. When the valve opening timing EVO of the exhaust valve 10 becomes late in this way, the period of the expansion stroke becomes long. When the period of the expansion stroke becomes long, the amount of HC (hydrocarbon) contained in the combustion gas burned in the expansion stroke increases. That is, since the afterburning of HC is promoted, the amount of HC discharged to the exhaust passage 8 decreases.

[0032] <Effect> The effect of the present embodiment will be described. The electric intake-side variable valve mechanism 13, unlike the hydraulic exhaust-side variable valve mechanism 16, can start driving immediately after the engine starts. Therefore, in this embodiment, until the affirmative determination is made in the process of S100 shown in FIG. 2, that is, until the valve timing of the exhaust valve can be retarded during cold start, the process of S110 is executed. That is, by driving the electric intake-side variable valve mechanism 13 to advance the valve timing of the intake valve 9, valve overlap is generated. When valve overlap is generated in this way, as described above, the NOx emission amount is reduced. Therefore, the NOx emission amount is reduced before the valve timing of the exhaust valve 10 is retarded. Therefore, it becomes possible to further reduce emissions during cold start.

[0033] In addition, this embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non-conflicting range. · The valve overlap period VOR formed by the process of S100 shown in FIG. 2 and the valve overlap period VOR formed by the processes of S120 and S130 shown in FIG. 2 may be made different. In the case of this modification example, for example, as the exhaust-side target value VTex1, a value different from the intake-side target value VTin1 may be set. Also, as the intake-side target value VTint set in the process of S130 shown in FIG. 2, a value larger than the initial value "0" and smaller than the intake-side target value VTin1 may be set.

[0034] · When the valve overlap period formed by retarding the exhaust valve timing may be made longer than the valve overlap period VOR, the process of S130 shown in FIG. 2 may be omitted.

[0035] · In the process of S100 shown in FIG. 2, the elapsed time Taf after startup was referred to determine whether or not the hydraulic pressure P of the hydraulic oil is equal to or higher than the threshold value Pref, but other values may be referred to. For example, the total number of rotations of the crankshaft 7 after the start of engine startup may be referred to.

[0036] · At the time of cold startup, the valve timing control shown in FIG. 2 and the cold warm-up control for warming up the catalyst 50 etc. by raising the temperature of the exhaust gas discharged from the combustion chamber 2 may be used in combination. Note that examples of such cold warm-up control include retard correction of the ignition timing. Further, when the internal combustion engine 1 is provided with an in-cylinder injection valve for directly injecting fuel into the combustion chamber 2, it is possible to raise the exhaust temperature by performing so-called divided injection in which the fuel injected from the in-cylinder injection valve is injected in a plurality of times.

[0037] · The control device 100 is not limited to one including the CPU 120 and the memory 130 and executing software processing. For example, it may include a dedicated hardware circuit (for example, 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 includes 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 includes a processing device and a program storage device that execute a part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) It includes a dedicated hardware circuit that executes all of the above processing. Here, there may be a plurality of software processing circuits and dedicated hardware circuits including a processing device and a program storage device. That is, the above processing may be executed by a processing circuit including at least one of one or a plurality of software processing circuits and one or a plurality of dedicated hardware circuits.

Explanation of Signs

[0038] 1... Internal combustion engine 2... Combustion chamber 3... Intake passage 8…Exhaust passage 9…Intake valve 10…Exhaust valve 11…Intake-side camshaft 12…Exhaust-side camshaft 13…Intake-side variable valve mechanism 16…Exhaust-side 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-side cam angle sensor 36…Exhaust-side cam angle sensor 50…Catalyst 90…Oil pump 100…Control device 120…CPU 130…Memory

Claims

1. A control device for an internal combustion engine, comprising 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, performing a process of advancing the valve timing of the intake valve until a predetermined time has elapsed since the start of cold start of the internal combustion engine, and performing a process of retarding the valve timing of the exhaust valve after the predetermined time has elapsed, wherein the predetermined time is preset as the time required for the hydraulic pressure of the hydraulic oil pumped to the hydraulic variable valve mechanism to become equal to or higher than a predetermined threshold value since the start of the internal combustion engine. A control device for an internal combustion engine.

2. When the coolant temperature at the start of 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. The control device for an internal combustion engine according to Claim 1.

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