Control method for internal combustion engine and control device for internal combustion engine

Abstract

This internal combustion engine (1) has a hydraulically driven variable valve timing mechanism (8) capable of changing the valve timing of an engine valve. To change the valve timing of the engine valve, the internal combustion engine (1) temporarily increases the working hydraulic pressure supplied to the variable valve timing mechanism (8) to a target hydraulic pressure (Pt) at the time of switching. To change the valve timing of the engine valve, when the working hydraulic pressure becomes equal to or higher than a predetermined control-permission hydraulic pressure (Pc) lower than the target hydraulic pressure (Pt) at the time of switching, the internal combustion engine (1) starts control of the variable valve timing mechanism (8) to change the valve timing of the engine valve.

Description

Control method and control device for internal combustion engine

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

[0002] For example, Patent Document 1 discloses an engine (internal combustion engine) having a cam switching mechanism that switches between multiple cams having cam profiles with different output characteristics by operating or deactivating a hydraulic actuator, and transmits the movement of the cams to at least one of the intake valves or exhaust valves.

[0003] In Patent Document 1, the cam switching mechanism is capable of changing the valve timing of the intake valve or the exhaust valve.

[0004] In Patent Document 1, the cam switching mechanism switches the cam by controlling the switching of a hydraulic switching valve provided in a hydraulic path to the hydraulic actuator, which requires high hydraulic pressure to improve the responsiveness of the hydraulic actuator.

[0005] In Patent Document 1, an accumulator that stores oil generated by an oil pump is connected to a hydraulic path to a hydraulic actuator, and the oil pump is operated only when necessary.

[0006] However, a high pressure is required to operate the hydraulic actuator with good response, and a high oil pressure must be supplied to the hydraulic actuator in order to increase the response of the cam switching mechanism.

[0007] In other words, there is room for further improvement in achieving both improved responsiveness when changing the valve timing and improved energy efficiency (energy saving) of the mechanism that changes the valve timing by optimizing (reducing) the hydraulic oil pressure supplied to the mechanism that changes the valve timing.

[0008] Japanese Patent Application Publication No. 5-195735

[0009] The internal combustion engine includes a hydraulically driven variable valve timing mechanism capable of changing the valve timing of an engine valve, a hydraulic pressure supply unit that raises the hydraulic pressure supplied to the variable valve timing mechanism to a predetermined first control hydraulic pressure by hydraulic pressure increase control that temporarily raises the hydraulic pressure supplied to the variable valve timing mechanism when changing the valve timing, a hydraulic pressure detection unit that detects the hydraulic pressure supplied to the variable valve timing mechanism, and a valve timing detection unit that detects the valve timing. When changing the valve timing, the internal combustion engine starts control of the variable valve timing mechanism to change the valve timing when the hydraulic pressure reaches or exceeds a predetermined second control hydraulic pressure that is lower than the first control hydraulic pressure.

[0010] The internal combustion engine of the present invention can achieve both improved responsiveness when changing valve timing and improved energy efficiency (energy saving) by efficiently controlling the hydraulic pressure.

[0011] The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine having an internal combustion engine control system, a method for controlling an internal combustion engine, and a method for controlling an internal combustion engine.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Figure 1 is an explanatory diagram showing a schematic system configuration of an internal combustion engine 1 to which the present invention is applied.

[0013] The internal combustion engine 1 is mounted on a vehicle such as an automobile to drive a generator (not shown) mounted on the vehicle. The internal combustion engine 1 has an oil pump 2 as a hydraulic pump, an oil passage 3 through which oil discharged from the oil pump 2 flows, an oil cooler 4 and an oil filter 5 provided in the oil passage 3, a main gallery 6 located downstream of the oil filter 5, a variable valve timing mechanism 8 to which oil in the main gallery 6 is supplied via a solenoid valve 7, and an on-board control unit 9 that controls the solenoid valve 7.

[0014] The oil pump 2 is a well-known electronically controlled vane-type variable displacement pump that can vary the oil discharge pressure, and pumps up and discharges oil from the oil pan 10. The oil pump 2 has a solenoid valve (pump solenoid valve) 2a that operates when the discharge pressure is changed. The solenoid valve 2a is controlled to open and close by the control unit 9. The oil pump 2 can limit the discharge pressure of the oil pump 2 to a relatively low pressure by fully opening a drain passage (not shown) with the solenoid valve 2a.

[0015] The main gallery 6 is formed in the cylinder block of the internal combustion engine 1. Oil that passes through the main gallery 6 is supplied to the lubrication parts of the internal combustion engine 1.

[0016] The solenoid valve 7 is a valve timing control solenoid valve that controls the supply of oil in the main gallery 6 to the variable valve timing mechanism 8. The solenoid valve 7 is located on the oil (hydraulic oil pressure) supply path between the main gallery 6 and the variable valve timing mechanism 8. The solenoid valve 7 is capable of switching between a state in which the oil in the main gallery 6 is supplied to the variable valve timing mechanism 8 and a state in which the oil in the main gallery 6 is not supplied to the variable valve timing mechanism 8.

[0017] The variable valve timing mechanism 8 is a hydraulically driven variable valve mechanism that is driven using the hydraulic pressure of the oil supplied to the main gallery 6, and is capable of changing the valve timing of the intake valve or exhaust valve, which are engine valves.

[0018] The variable valve timing mechanism 8 in this embodiment is a variable phase control (VTC) mechanism that continuously advances or retards the phase of the central angle of the lift of the engine valve (phase relative to the crankshaft). The variable phase control mechanism is already known, for example, from Japanese Patent Application Laid-Open No. 2002-89303, and retards the phase of a camshaft (not shown) that drives the opening and closing of the engine valve relative to the crankshaft (not shown).

[0019] The control unit 9 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input / output interface. The control unit 9 receives detection signals from various sensors, such as an oil pressure sensor 11 that detects the oil pressure (hydraulic oil pressure) in the main gallery 6, a cam angle sensor 12 that detects the angle of the camshaft of the engine valve, and a crank angle sensor 13 that detects the crank angle of the crankshaft.

[0020] The oil pressure sensor 11 corresponds to an oil pressure detection unit and detects the hydraulic oil pressure supplied to the variable valve timing mechanism 8. The crank angle sensor 13 is capable of detecting the engine speed of the internal combustion engine 1.

[0021] The control unit 9 is capable of detecting the valve timing of the engine valves using the detection signals of the cam angle sensor 12 and the crank angle sensor 13. That is, the control unit 9 is capable of detecting the operating angle (VTC operating angle) of the variable valve timing mechanism 8 using the detection signals of the cam angle sensor 12 and the crank angle sensor 13. In other words, the control unit 9 corresponds to a valve timing detection section.

[0022] The control unit 9 controls the discharge pressure of the oil pump 2 in accordance with the engine speed and load of the internal combustion engine 1. For example, the control unit 9 performs predetermined low oil pressure control so that the discharge pressure of the oil pump 2 becomes a first oil pressure P1, which is a predetermined low oil pressure, when the internal combustion engine 1 is operated in a low-speed, low-load operating range. For example, the control unit 9 performs predetermined medium oil pressure control so that the discharge pressure of the oil pump 2 becomes a second oil pressure P2, which is a predetermined medium oil pressure higher than the first oil pressure P1, when the internal combustion engine 1 is operated in a low-speed, high-load operating range. For example, the control unit 9 performs predetermined high oil pressure control so that the discharge pressure of the oil pump 2 becomes a third oil pressure P3, which is a predetermined high oil pressure higher than the second oil pressure P2, when the internal combustion engine 1 is operated in a high-speed, high-load operating range. Here, the first oil pressure P1 is set, for example, so that the operating angle of the variable valve timing mechanism 8 can be maintained (maintained) and the valve timing of the engine valves can be maintained (maintained).

[0023] FIG. 2 is an explanatory diagram that schematically shows the relationship between the hydraulic pressure (hydraulic pressure) that is the discharge pressure of the oil pump 2 and the engine speed of the internal combustion engine 1.

[0024] As shown by the thick solid line in Figure 2, the hydraulic pressure is controlled to a first hydraulic pressure P1 when the internal combustion engine 1 is operated in a low-speed, low-load operating range, and is controlled to a third hydraulic pressure P3 when the internal combustion engine 1 is operated in a high-speed operating range regardless of the load. Also, as shown by the dashed line in Figure 2, the hydraulic pressure is controlled to a second hydraulic pressure P2 when the internal combustion engine 1 is operated in a low-speed, high-load operating range.

[0025] Here, since the internal combustion engine 1 is installed for generating electricity to drive a generator, it is basically operated at a first operating point for warming up the catalyst, such as during a cold start, and a second operating point that prioritizes fuel efficiency after warm-up is complete. The first and second operating points are operating points determined by the engine speed and load of the internal combustion engine 1, and in this embodiment, both belong to the low-speed, low-load operating range. Therefore, the hydraulic pressure required to maintain the current valve timing at both the first and second operating points is the first hydraulic pressure P1. The second operating point has a higher engine speed than the first operating point.

[0026] The variable valve timing mechanism 8 requires a higher hydraulic pressure to responsively switch the valve timing of the engine valve from the current valve timing to another valve timing than the minimum hydraulic pressure required to stably maintain the valve timing of the engine valve at the current valve timing. In other words, the variable valve timing mechanism 8 can change the valve timing of the engine valve (the operating angle of the variable valve timing mechanism 8) with good responsiveness when the hydraulic pressure is equal to or higher than a predetermined control allowable hydraulic pressure Pc.

[0027] When the internal combustion engine 1 is stopped, the operating angle of the variable valve timing mechanism 8 is at the initial position A0, and the valve timing of the engine valve corresponds to the initial position A0. When the internal combustion engine 1 is operating at a first operating point, the operating angle of the variable valve timing mechanism 8 is at the initial position A0, and the valve timing of the engine valve corresponds to the initial position A0. When the internal combustion engine 1 is operating at a second operating point, the operating angle of the variable valve timing mechanism 8 is at the first advance position A1, and the valve timing of the engine valve corresponds to the first advance position A1. The valve timing of the engine valve when the operating angle of the variable valve timing mechanism 8 is at the first advance position A1 is more advanced than the valve timing of the engine valve when the operating angle of the variable valve timing mechanism 8 is at the initial position A0. The first advance position A1 is the operating angle of the variable valve timing mechanism 8 at which the fuel efficiency of the internal combustion engine 1 is improved compared to the initial position A0.

[0028] The variable valve timing mechanism 8 is capable of stably maintaining the valve timing of the engine valve as long as the operating oil pressure is the first oil pressure P1. In other words, the first oil pressure P1 is set to the minimum operating oil pressure at which the valve timing of the engine valve (the operating angle of the variable valve timing mechanism 8) can be stably maintained. Furthermore, when the operating oil pressure is greater than the first oil pressure P1 but less than the control allowable oil pressure Pc, the variable valve timing mechanism 8 can stably maintain the valve timing of the engine valve at the current valve timing, but cannot responsively switch the valve timing of the engine valve from the current valve timing to another valve timing.

[0029] Therefore, when the valve timing of the engine valve (the operating angle of the variable valve timing mechanism 8) is maintained at the current valve timing, the control unit 9 controls the hydraulic pressure to a low first hydraulic pressure P1. When the target value of the valve timing of the engine valve (the target value of the operating angle of the variable valve timing mechanism 8) is changed and the valve timing of the engine valve (the operating angle of the variable valve timing mechanism 8) is switched from the current valve timing to another valve timing, the control unit 9 determines that there is a request to change (drive) the variable valve timing mechanism 8, and performs hydraulic pressure increase control to temporarily increase the hydraulic pressure so that the hydraulic pressure reaches a predetermined switching target hydraulic pressure Pt. The switching target hydraulic pressure Pt is a value equal to or higher than the control permissible hydraulic pressure Pc, which ensures responsiveness.

[0030] Furthermore, when the control unit 9 performs hydraulic pressure increase control, it performs a fault diagnosis (diagnosis #1) of the hydraulic system (oil pump 2) that supplies hydraulic pressure to the main gallery 6, assuming that predetermined diagnosis permission conditions are met. If the control unit 9 determines that the system is not normal as a result of diagnosis #1, it performs a predetermined cleaning control, and after the cleaning control, it performs a fault diagnosis (diagnosis #2) of the oil pump 2 again. The names of diagnosis #1 and diagnosis #2 are merely different for convenience's sake to distinguish between the fault diagnosis performed before the cleaning control and the fault diagnosis performed after the cleaning control, but the diagnostic content is the same. If the control unit 9 determines that the system is not normal as a result of diagnosis #2, it determines that there is a fault (abnormality) in the hydraulic system that supplies hydraulic pressure to the main gallery 6.

[0031] Furthermore, if the result of diagnosis #2 indicates that the system is normal but the variable valve timing mechanism 8 is unable to change the valve timing of the engine valve, the control unit 9 determines that there is a malfunction in the solenoid valve 7 located between the main gallery 6 and the variable valve timing mechanism 8 or in the variable valve timing mechanism 8. In other words, if the result of diagnosis #2 indicates that the system is normal but the variable valve timing mechanism 8 is unable to change the valve timing of the engine valve, the control unit 9 determines that there is a malfunction in the variable valve timing mechanism 8. In other words, even if the hydraulic system (oil pump 2) is determined to be normal, if the valve timing of the engine valve does not reach a predetermined control target value, the control unit 9 determines that there is a malfunction in the variable valve timing mechanism 8.

[0032] The control unit 9 determines that there is a request to change the valve timing of the variable valve timing mechanism 8 (a request to drive the variable valve timing mechanism 8), for example, when the target value of the valve timing of the engine valve (the target value of the operating angle of the variable valve timing mechanism 8) changes by a predetermined value or more, or when the difference between the target value of the valve timing of the engine valve (the target value of the operating angle of the variable valve timing mechanism 8) and the actual valve timing of the engine valve (the actual operating angle of the variable valve timing mechanism 8) becomes a predetermined value or more.

[0033] The control unit 9 performs a fault diagnosis (diagnosis #1 and diagnosis #2) of the hydraulic system (oil pump 2) when, for example, the following diagnosis permission conditions are met: the vehicle ignition switch is turned on, devices related to the control of the oil pump 2, such as the oil pressure sensor 11 and the crank angle sensor 13, are normal, there is a request to change the valve timing of the engine valves, etc.

[0034] When the control unit 9 determines that there is a request to change the valve timing of the engine valve when the hydraulic pressure is at the first hydraulic pressure P1, it performs tests #1 and #2 while performing hydraulic pressure increase control, which temporarily increases the hydraulic pressure. Tests #1 and #2 determine (diagnose) the presence or absence of a malfunction (abnormality) based on whether the hydraulic pressure reaches the control allowable hydraulic pressure Pc within a predetermined time. Test #1 determines that there is a risk of a malfunction (abnormality) in the hydraulic system (oil pump 2) if the hydraulic pressure does not reach the control allowable hydraulic pressure Pc within the predetermined time. Test #2 determines that there is a malfunction (abnormality) in the hydraulic system (oil pump 2) if the hydraulic pressure does not reach the control allowable hydraulic pressure Pc within the predetermined time. In other words, test #2 determines whether there is a malfunction (abnormality) in the hydraulic system (oil pump 2).

[0035] Cleaning control involves reciprocating the movable part of the solenoid valve 2a of the oil pump 2, and is carried out to remove foreign matter (contamination) that has become lodged in the movable part of the solenoid valve 2a, thereby restoring the movable part of the solenoid valve 2a to its intended operating state.

[0036] When cleaning control is performed after diagnosis #1, which is performed as a result of determining that there is a request to change the valve timing of the engine valve when the operating oil pressure is the first oil pressure P1, cleaning control is performed for a predetermined time (e.g., several seconds) while oil pressure increase control is being performed.

[0037] The control unit 9 immediately terminates the cleaning control when the hydraulic pressure becomes equal to or higher than the control allowable hydraulic pressure Pc during the cleaning control. In other words, the cleaning control terminates when the hydraulic pressure drop is corrected before a predetermined time has elapsed after the start of the cleaning control. Note that the cleaning control may be continued for a predetermined time even after the hydraulic pressure drop is corrected.

[0038] FIG. 3 is a timing chart showing the behavior of various parameters when a fault diagnosis (hydraulic system diagnosis) of the hydraulic system is performed.

[0039] Time t0 is the timing at which the internal combustion engine 1 starts. At time t0, the internal combustion engine 1 is in a cold state, and is operated at a first operating point for warming up the catalyst until time t1.

[0040] Time t1 is the timing when the warm-up of the internal combustion engine 1 is completed and the operating point of the internal combustion engine 1 is switched from the first operating point to the second operating point. As shown by the thin solid line, the target value of the operating angle of the variable valve timing mechanism 8 is switched instantaneously (stepwise) from the initial position A0 to the first advance position A1 at time t1. Also, at time t1, hydraulic pressure increase control is started. Therefore, as shown by the thin solid line, the target value of the working hydraulic pressure (hydraulic pressure) is switched instantaneously (stepwise) from the first hydraulic pressure P1 to the switching target hydraulic pressure Pt, which is higher than the control allowable hydraulic pressure Pc. If there is no malfunction in the hydraulic system, the detected value (actual hydraulic pressure) of the working hydraulic pressure (hydraulic pressure) begins to rise toward the switching target hydraulic pressure Pt from time t1, as shown by the thick solid line.

[0041] Time t2 is the timing when the working oil pressure (hydraulic pressure) reaches the control allowable oil pressure Pc. The variable valve timing mechanism 8 starts switching (changing) its operating angle at time t2. Therefore, if there is no malfunction in the hydraulic system or malfunction of the variable valve timing mechanism 8, the detected value of the operating angle (VTC operating angle) of the variable valve timing mechanism 8 will change from time t2 toward the first advance position A1, as shown by the thick solid line.

[0042] Time t3 is the timing when the detected value of the operating angle (VTC operating angle) of variable valve timing mechanism 8 reaches the first advance angle position A1, which is the target value. The oil pressure increase control ends after a predetermined time has elapsed from time t3.

[0043] Here, diagnosis #1 is performed from time t1 to time t3. If the result of diagnosis #1 indicates that the hydraulic system is normal, then the hydraulic system is determined to be normal at time t3, as shown by the solid line. If the result of diagnosis #1 indicates that there is a risk of a malfunction (abnormality) in the hydraulic system, cleaning control is performed following diagnosis #1. Cleaning control is performed for a predetermined period of time, for example, from time t3. Diagnosis #2 is performed after cleaning control is completed.

[0044] Time t4 is the timing when test #2 ends. If test #2 does not determine that the hydraulic system is normal, it is determined that there is a fault (abnormality) in the hydraulic system, as indicated by the dashed line.

[0045] Time t5 is the timing when a request to stop the internal combustion engine 1 is issued, and also the timing when the hydraulic pressure increase control is started. The variable valve timing mechanism 8 starts switching (changing) the operating angle (VTC operating angle) at time t5 without waiting for the operating hydraulic pressure to reach the control permissible hydraulic pressure Pc.

[0046] Time t6 is the timing when the internal combustion engine 1 stops.

[0047] Time t7 is the timing to restart the internal combustion engine 1. At time t7, the internal combustion engine 1 is in a warm-up state, and the internal combustion engine 1 resumes operation at the second operating point.

[0048] Time t8 is the timing when the working oil pressure (hydraulic pressure) reaches the control allowable oil pressure Pc. At time t8, variable valve timing mechanism 8 begins switching (changing) the operating angle (VTC operating angle). Therefore, if there is no malfunction in the hydraulic system or no malfunction of variable valve timing mechanism 8, the detected value of the operating angle (VTC operating angle) of variable valve timing mechanism 8 will change from time t8 toward the first advance position A1, as shown by the thick solid line.

[0049] If cleaning control has been completed for the current trip, diagnosis #2 begins at time t8. Note that a trip is defined as the period from when the ignition switch (power source for the hybrid system) is turned on until the ignition switch (power source for the hybrid system) is turned off.

[0050] Time t9 is the timing when the detected value of the operating angle (VTC operating angle) of variable valve timing mechanism 8 reaches the first advance angle position A1, which is the target value. The oil pressure increase control ends after a predetermined time has elapsed from time t9.

[0051] Time t10 is the timing at which test #2 ends.

[0052] Time t11 is the timing when a request to stop the internal combustion engine 1 is issued, and also the timing when the hydraulic pressure increase control is started. The variable valve timing mechanism 8 starts switching (changing) the operating angle (VTC operating angle) at time t11 without waiting for the operating hydraulic pressure to reach the control permissible hydraulic pressure Pc.

[0053] Time t12 is the timing when the internal combustion engine 1 stops.

[0054] FIG. 4 is a flowchart showing the flow of control of the internal combustion engine 1 in the above-described embodiment.

[0055] In step S1, it is determined whether the malfunction determination flag is "0." If the malfunction determination flag is "0" in step S1, the process proceeds to step S2. If the malfunction determination flag is not "0" in step S1, the current routine is terminated.

[0056] In step S2, it is determined whether or not there is a request to change the valve timing of the engine valve. If it is determined in step S2 that there is a request to change the valve timing of the engine valve, the routine proceeds to step S3. If it is determined in step S2 that there is no request to change the valve timing of the engine valve, the current routine is terminated. The routine proceeds to step S3.

[0057] In step S3, it is determined whether the cleaning flag is "1." If it is determined in step S3 that the cleaning flag is "1," the process proceeds to step S4. If it is determined in step S3 that the cleaning flag is not "1," the process proceeds to step S12.

[0058] In step S4, the target value of the hydraulic pressure (oil pressure) is changed. That is, in step S4, the hydraulic pressure is changed from the first hydraulic pressure P1 to a switching target hydraulic pressure Pt that is greater than the control allowable hydraulic pressure Pc.

[0059] In step S5, it is determined whether the actual oil pressure is equal to or greater than the control allowable oil pressure Pc. If it is determined in step S5 that the actual oil pressure is equal to or greater than the control allowable oil pressure Pc, the process proceeds to step S6. If it is determined in step S5 that the actual oil pressure is less than the control allowable oil pressure Pc, the process proceeds to step S11.

[0060] In step S6, the target value of the valve timing of the engine valve is changed. That is, in step S6, the target value of the operating angle (VTC operating angle) of the variable valve timing mechanism 8 is changed from the initial position A0 to the first advance position A1.

[0061] In step S7, it is determined whether the valve timing of the engine valve has reached a target value. That is, in step S7, it is determined whether the operating angle (VTC operating angle) of variable valve timing mechanism 8 has reached first advance position A1. If it is determined in step S7 that the valve timing (VTC operating angle) has reached first advance position A1, the process proceeds to step S8. If it is determined in step S7 that the valve timing (VTC operating angle) has not reached first advance position A1, the process proceeds to step S9.

[0062] In step S8, it is determined that there is no malfunction in the hydraulic system (oil pump 2) and that the system is normal.

[0063] In step S9, it is determined that the failure is due to malfunction of the variable valve timing mechanism 8.

[0064] In step S10, the failure determination flag is set to "1." When the failure determination flag becomes "1," the variable valve timing mechanism 8 transitions to a fail-safe mode, and the operating angle (VTC operating angle) is fixed to, for example, the initial position A0. When the failure determination flag becomes "1," the variable valve timing mechanism 8 transitions to the fail-safe mode, and the valve timing of the engine valve is fixed. Furthermore, when the failure determination flag becomes "1," the control unit 9 notifies the driver by, for example, turning on a warning light. For example, when repairs are completed at a repair shop, the failure determination flag is switched from "1" to "0."

[0065] In step S11, it is determined that there is a malfunction in the hydraulic system (oil pump 2).

[0066] In step S12, the target value of the hydraulic pressure (oil pressure) is changed. That is, in step S4, the hydraulic pressure is changed from the first hydraulic pressure P1 to a switching target hydraulic pressure Pt that is greater than the control allowable hydraulic pressure Pc.

[0067] In step S13, it is determined whether the actual oil pressure is equal to or greater than the control allowable oil pressure Pc. If it is determined in step S13 that the actual oil pressure is equal to or greater than the control allowable oil pressure Pc, the process proceeds to step S14. If it is determined in step S13 that the actual oil pressure is less than the control allowable oil pressure Pc, the process proceeds to step S19.

[0068] In step S14, the target value of the valve timing of the engine valve is changed. That is, in step S14, the target value of the operating angle (VTC operating angle) of the variable valve timing mechanism 8 is changed from the initial position A0 to the first advance position A1.

[0069] In step S15, it is determined whether the valve timing of the engine valve has reached a target value. That is, in step S15, it is determined whether the operating angle (VTC operating angle) of variable valve timing mechanism 8 has reached first advance position A1. If it is determined in step S15 that the valve timing (VTC operating angle) has reached first advance position A1, the process proceeds to step S16. If it is determined in step S15 that the valve timing (VTC operating angle) has not reached first advance position A1, the process proceeds to step S17.

[0070] In step S16, it is determined that there is no failure in the hydraulic system (oil pump 2) and that the system is normal.

[0071] In step S17, it is determined that the failure is due to malfunction of the variable valve timing mechanism 8.

[0072] In step S18, the failure determination flag is set to "1".

[0073] In step S19, cleaning control is carried out.

[0074] In step S20, it is determined whether a predetermined time has elapsed since the start of cleaning control. If it is determined in step S20 that the predetermined time has elapsed since the start of cleaning control, the process proceeds to step S21. If it is determined in step S20 that the predetermined time has not elapsed since the start of cleaning control, the process proceeds to step S13.

[0075] In step S21, the cleaning flag is set to "1." The cleaning flag is initialized to "0" for each trip. That is, the cleaning flag is set to "0" when the ignition switch (power source for the hybrid system) is turned off.

[0076] In the flowchart of FIG. 4, the flow from step S3 to step S4 corresponds to diagnosis #2, the flow from step S3 to steps S12 and S13 corresponds to diagnosis #1, and the flow from step S13 to step S19 corresponds to cleaning control.

[0077] In the internal combustion engine 1 of the above-described embodiment, when there is a request (drive request) to change the operating angle (VTC operating angle) of the variable valve timing mechanism 8 while the operating oil pressure is at the first oil pressure P1, oil pressure increase control is performed. As a result, the target value of the operating oil pressure is switched to the switchover target oil pressure Pt. When the operating oil pressure reaches or exceeds the control allowable oil pressure Pc, the control unit 9 as a control section starts control of the variable valve timing mechanism 8 to change the valve timing of the engine valve. When the oil pressure increase control ends, the operating oil pressure drops to the first oil pressure P1.

[0078] In other words, when changing the valve timing, if the hydraulic pressure supplied to the variable valve timing mechanism 8 is lower than the control allowable pressure Pc as the second control hydraulic pressure, the oil pump 2 as a hydraulic pressure supply unit increases the hydraulic pressure supplied to the variable valve timing mechanism 8 to the switching target hydraulic pressure Pt, and when the change in valve timing is complete, decreases the hydraulic pressure to the first hydraulic pressure P1 as the fourth control hydraulic pressure which is lower than the control allowable pressure Pc. Furthermore, when the hydraulic pressure becomes equal to or higher than the control allowable pressure Pc as the second control hydraulic pressure, the internal combustion engine 1 starts controlling the variable valve timing mechanism 8 to change the valve timing of the engine valve.

[0079] The internal combustion engine 1 can efficiently control the hydraulic pressure because it is possible to lower the hydraulic pressure except when changing the valve timing of the engine valve. Furthermore, when the hydraulic pressure reaches the control permissible hydraulic pressure Pc and control of the variable valve timing mechanism 8 begins, the valve timing of the engine valve can be quickly changed. In other words, the internal combustion engine 1 can simultaneously improve responsiveness when changing the valve timing of the engine valve and improve energy efficiency (energy saving) by efficiently controlling the hydraulic pressure without requiring an accumulator.

[0080] If the internal combustion engine 1 cannot start changing the valve timing of the engine valve, it determines that a failure has occurred, and can take appropriate fail-safe measures.

[0081] The internal combustion engine 1 may determine that a malfunction has occurred if the operating oil pressure does not reach the control allowable oil pressure Pc as the third control oil pressure within a predetermined time period after starting oil pressure increase control to raise the operating oil pressure to the switching target oil pressure Pt as the first control oil pressure.

[0082] If the hydraulic pressure does not reach a control allowable pressure Pc as a third control pressure that is equal to or lower than the switching target pressure Pt as the first control pressure within a predetermined time after starting hydraulic pressure increase control that increases the hydraulic pressure to a switching target pressure Pt as the first control pressure, the internal combustion engine 1 interrupts the increase in the hydraulic pressure (interrupts hydraulic pressure increase control) and performs a predetermined cleaning control that reciprocates the movable portion of the solenoid valve 2 a multiple times. Then, if the hydraulic pressure does not reach a control allowable pressure Pc as the third control pressure within a predetermined time after restarting hydraulic pressure increase control after performing the cleaning control, the internal combustion engine 1 determines that a malfunction has occurred.

[0083] When the increase in the hydraulic pressure is interrupted, that is, when cleaning control is performed, the hydraulic pressure may be returned to the first hydraulic pressure P1, or may be maintained at the hydraulic pressure that was increased by the hydraulic pressure increase control.

[0084] By performing cleaning control, the internal combustion engine 1 can remove foreign matter and the like that has become lodged in the solenoid valve 2a of the oil pump 2, thereby improving the reduction in operating oil pressure caused by the solenoid valve 2a.

[0085] If the change in the valve timing of the engine valve cannot be started, the internal combustion engine 1 performs cleaning control, and if the hydraulic pressure still does not increase, it determines that a failure has occurred, thereby linking it to a necessary fail-safe as appropriate. Specifically, for example, the internal combustion engine 1 is controlled with the valve timing fixed at an initial position A0 or the like.

[0086] The effect of improving oil pressure due to removal of foreign matter by cleaning control does not increase as the number of cleaning controls performed during the same trip increases.

[0087] In other words, the effect of improving oil pressure by removing foreign matter through cleaning control from the second time onwards during one trip is small.

[0088] Therefore, if the internal combustion engine 1 has already performed cleaning control in the same trip (if it has already been performed), it can determine that there is a failure without performing cleaning control again, thereby quickly taking the necessary fail-safe measures as appropriate.

[0089] The hydraulic pressure increase control involves maintaining the operating hydraulic pressure at the switching target hydraulic pressure Pt as the first control hydraulic pressure for a predetermined period (predetermined time), and then reducing (returning) the operating hydraulic pressure to the value before (just before) the hydraulic pressure increase control was started.

[0090] In the internal combustion engine 1, the hydraulic pressure increase control maintains (holds) the operating hydraulic pressure at the target hydraulic pressure Pt at the time of switching, thereby stabilizing the valve timing of the engine valve in a transient state such as immediately after a movement (change) in the valve timing of the engine valve.

[0091] Even if the operating oil pressure reaches the control allowable oil pressure Pc as the third control oil pressure, the internal combustion engine 1 determines that a malfunction has occurred if the valve timing of the engine valve does not reach a predetermined control target value.

[0092] The internal combustion engine 1 can determine a malfunction related to the valve timing of the engine valve even when the operating oil pressure is normal.

[0093] The oil pump 2 performs oil pressure increase control in an operating range where the internal combustion engine 1 is operating at low revolutions and low load. Therefore, in an operating range where the internal combustion engine 1 is operating at low revolutions and low load, oil pressure increase control is not performed except when the valve timing of the engine valve is changed. Furthermore, in an operating range where the internal combustion engine 1 is operating at high revolutions or high load, the working oil pressure is controlled to a level that does not require oil pressure increase even when the valve timing is changed, and oil pressure increase control can be performed only in an operating range where the internal combustion engine 1 is operating at low revolutions and low load.

[0094] This allows the internal combustion engine 1 to lower the operating oil pressure in a specific operating range, that is, an operating range where the engine speed is low and the load is low.

[0095] In the internal combustion engine 1, when the change in valve timing of the engine valve is to the advance side by changing the operating angle of the valve timing variable mechanism 8 from the initial position A0 to the first advance position A1 as a fuel economy position, the valve timing of the engine valve is advanced from the current valve timing after the operating oil pressure reaches the control allowance oil pressure Pc as the second control oil pressure through oil pressure increase control.

[0096] When the internal combustion engine 1 changes the valve timing of the engine valve to the advance side, it uses the force of hydraulic oil pressure to overcome the reaction force of the cam of the internal combustion engine 1 and the tension of the chain to drive the variable valve timing mechanism 8.

[0097] In the case where the change in valve timing of the engine valve is a change to the retard side by changing the operating angle of the valve timing variable mechanism 8 from the first advance position A1 as a fuel economy position to the initial position A0, the internal combustion engine 1 starts changing the valve timing of the engine valve at the timing when hydraulic pressure increase control is started.

[0098] When changing the valve timing of the engine valve to the retard side, the internal combustion engine 1 can use the tension of the chain to drive the variable valve timing mechanism 8 so that the valve timing of the engine valve is retarded with good responsiveness, even when the hydraulic oil pressure is low. Therefore, when retarding the valve timing of the engine valve, the internal combustion engine 1 can immediately drive the variable valve timing mechanism 8 without waiting for the hydraulic oil pressure to increase.

[0099] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0100] For example, cleaning control may be performed on the solenoid valve 7 located between the main gallery 6 and the variable valve timing mechanism 8 on the hydraulic pressure supply path.

[0101] For example, Test #1 and Test #2 may be configured to determine (diagnose) the presence or absence of a failure (abnormality) based on whether or not the hydraulic oil pressure reaches the target oil pressure at switching Pt within a predetermined time.

[0102] For example, diagnosis #1 and diagnosis #2 may be configured to determine (diagnose) whether or not there is a malfunction (abnormality) based on whether or not the operating oil pressure reaches a predetermined third control oil pressure set between the control allowable oil pressure Pc and the target oil pressure at switching Pt within a predetermined time period.

[0103] For example, the internal combustion engine 1 may be configured to perform cleaning control if the operating oil pressure does not reach the switching target oil pressure Pt as the third control oil pressure within a predetermined time period after the start of the oil pressure increase control.

[0104] For example, the internal combustion engine 1 may be configured to determine that a failure has occurred if the operating oil pressure does not reach the switching target oil pressure Pt as the third control oil pressure within a predetermined time after the cleaning control is performed and the oil pressure increase control is resumed.

[0105] For example, the internal combustion engine 1 may determine that a malfunction has occurred when the operating oil pressure does not reach a third control oil pressure, which is a value equal to or greater than the control permissible oil pressure Pc.

[0106] This makes it possible to ensure that the internal combustion engine 1 can obtain at least the control allowable oil pressure Pc as the operating oil pressure when it is determined that no failure has occurred.

[0107] For example, the internal combustion engine 1 may set the target oil pressure at switching Pt as the third control oil pressure to a value equal to the control allowable oil pressure Pc as the second control oil pressure. In this case, the internal combustion engine 1 sets the target oil pressure at switching Pt to the minimum value in the selectable range (a range equal to or greater than the control allowable oil pressure Pc), thereby minimizing the time required for failure determination and enabling cleaning control and predetermined fail-safe measures to be implemented promptly.

[0108] For example, the above-mentioned tests #1 and #2 may be configured to determine (diagnose) whether or not there is a malfunction (abnormality) based on whether or not the hydraulic oil pressure reaches the target oil pressure at switching Pt within a predetermined time.

[0109] The above-described embodiment relates to a control method for the internal combustion engine 1 and a control device for the internal combustion engine 1 .

Claims

1. A control device for an internal combustion engine comprising: a hydraulically driven variable valve timing mechanism capable of changing the valve timing of an engine valve; a hydraulic pressure supply unit that raises the hydraulic pressure to a predetermined first control hydraulic pressure by hydraulic pressure increase control that temporarily raises the hydraulic pressure supplied to the variable valve timing mechanism when changing the valve timing; a hydraulic pressure detection unit that detects the hydraulic pressure; and a valve timing detection unit that detects the valve timing, wherein when changing the valve timing, the control device starts control of the variable valve timing mechanism to change the valve timing when the hydraulic pressure reaches or exceeds a predetermined second control hydraulic pressure that is lower than the first control hydraulic pressure.

2. A control method for an internal combustion engine as described in claim 1, wherein if the operating oil pressure does not reach a predetermined third control oil pressure that is lower than the first control oil pressure within a predetermined time after the start of the oil pressure increase control, it is determined that a failure has occurred.

3. A control method for an internal combustion engine as set forth in claim 1, wherein the hydraulic pressure supply unit is a hydraulic pump capable of changing its discharge pressure, the hydraulic pump having a solenoid valve that operates when changing the discharge pressure, and if the operating oil pressure does not reach a predetermined third control oil pressure that is lower than the first control oil pressure within a predetermined time after the hydraulic pressure increase control is started, a predetermined cleaning control is carried out in which a movable part of the solenoid valve is moved back and forth multiple times, and if the operating oil pressure does not reach the third control oil pressure within the predetermined time after the hydraulic pressure increase control is resumed after the cleaning control is carried out, a failure is determined to have occurred.

4. A control method for an internal combustion engine as described in claim 3, wherein the internal combustion engine is mounted on a vehicle, and when the oil pressure increase control is started with the cleaning control already performed during one trip between when the vehicle's ignition switch is turned on and when it is turned off, if the operating oil pressure does not reach the third control oil pressure within the specified time after the oil pressure increase control is started, it is determined that a failure has occurred.

5. The control method for an internal combustion engine according to claim 3, wherein the third control oil pressure is equal to or greater than the second control oil pressure.

6. The control method for an internal combustion engine according to claim 3, wherein said third control oil pressure is equal to said second control oil pressure.

7. A control method for an internal combustion engine as described in claim 3, wherein the hydraulic pressure increase control maintains the operating hydraulic pressure at the first control hydraulic pressure for a predetermined period of time, and then reduces the operating hydraulic pressure to the value before the hydraulic pressure increase control was started.

8. A control method for an internal combustion engine according to claim 3, wherein even if the operating oil pressure reaches the third control oil pressure, if the valve timing does not reach a predetermined control target value, a malfunction is determined.

9. A control method for an internal combustion engine according to claim 3, wherein the oil pressure increase control is performed in an operating range where the internal combustion engine is operating at low speed and low load.

10. A control method for an internal combustion engine as described in claim 3, wherein in an operating range where the internal combustion engine is operating at high speeds or under high load, the operating oil pressure is controlled to a level that does not require an increase in oil pressure even when the valve timing is changed, and the oil pressure increase control is performed only in an operating range where the internal combustion engine is operating at low speeds and under low load.

11. A control method for an internal combustion engine as described in claim 1, wherein, when the change in the valve timing is a change to the advance side by changing the operating angle of the variable valve timing mechanism from a predetermined initial position to a predetermined fuel efficiency position at which the fuel efficiency of the internal combustion engine is improved compared to the initial position, the valve timing is advanced after the operating oil pressure reaches the second control oil pressure through the oil pressure increase control.

12. A control method for an internal combustion engine as described in claim 11, wherein, when the change in valve timing is a change to the retard side by changing the operating angle of the variable valve timing mechanism from the fuel economy position to the initial position, the change in valve timing is started at the timing when the hydraulic pressure increase control is started.

13. A control device for an internal combustion engine comprising: a hydraulically driven variable valve timing mechanism capable of changing the valve timing of an engine valve; a hydraulic pressure supply unit that raises the hydraulic pressure to a predetermined first control hydraulic pressure by hydraulic pressure increase control that temporarily raises the hydraulic pressure supplied to the variable valve timing mechanism when changing the valve timing; a hydraulic pressure detection unit that detects the hydraulic pressure; a valve timing detection unit that detects the valve timing; and a control unit that starts control of the variable valve timing mechanism to change the valve timing when the hydraulic pressure reaches or exceeds a predetermined second control hydraulic pressure that is lower than the first control hydraulic pressure.

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