Control device for an engine

In an engine having a variable valve timing mechanism to which an intermittent operation control is applied, appropriate execution of a foreign object removal process for the variable valve timing mechanism is enabled. An engine control device (16) which can execute intermittent operation control for an engine (12) having a variable valve timing mechanism (80) comprises a judging part which judges an abnormality in the variable valve timing mechanism (80) (step S10), a foreign object removal process executing part which causes a foreign object removal process to be executed for the variable valve timing mechanism (80) when the judging part judges that there is an abnormality in the variable valve timing mechanism (80) during an engine operation (step S12), and an intermittent operation control prohibiting part which prohibits the intermittent operation control of the engine (12) during execution of the foreign object removal process of the variable valve timing mechanism (80) (step S16).

RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2009-217691, filed on Sep. 18, 2009, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a control device of a hybrid vehicle, and particularly to a control device of a hybrid vehicle which intermittently starts and stops an engine.

BACKGROUND ART

Conventionally, an engine is known which comprises a variable valve timing (VVT) mechanism in which an open/close timing of a suction valve is set to be variable. Such an engine is used as a running power source of an automobile.

In the variable valve timing mechanism, an engine power and a gas exhaust capability are optimized according to the number of rotations of the engine, by setting a rotational phase angle of a cam shaft to which a cam for opening or closing the suction valve is fixed to be variable such as advancing (advance angle) or delaying (lag angle) the rotational phase angle of the cam shaft with respect to the rotational phase angle of a crankshaft. In such a variable valve timing mechanism, when hydraulic control is used for changing the phase angle of the cam shaft, in many cases, lubricant oil which is used for lubricating a piston or power transmission system in the engine is also used as the operation oil for the hydraulic control. In this case, a foreign object contained in the operation oil, such as metal powder, may be clogged in the portion which is movable by the hydraulic control, and the variable valve timing mechanism may not be normally operated.

For example, JP 2001-254637 A discloses a valve characteristic control device of an internal combustion engine in which, when it is judged that there is abnormality in the variable valve timing mechanism, the variable valve timing mechanism is forcefully driven, for a foreign object removal process.

JP 2005-220759 A discloses a lift amount variable control device of an internal combustion engine in which, when the lift amount of a suction valve is fixed at a low lift side due to failure of a variable valve mechanism, a target number of idle rotations is corrected and increased, to avoid occurrence of stalling of the engine.

When the engine having the variable valve timing mechanism as described above is equipped in a hybrid vehicle which has a motor as a separate running power source which is driven by electrical power from a battery, even during running of the vehicle, an intermittent operation control is executed in which the operation of the engine is stopped during EV running in which the vehicle is run with the motor power. If the operation of the engine is stopped in the middle of the foreign object removal process as disclosed in JP 2001-254637 A when abnormality occurs in the variable valve timing mechanism in such a hybrid vehicle, the foreign object removal process cannot be properly executed. Because of this, problems are expected in which a user who is notified by the vehicle that failure has occurred in the variable valve timing mechanism may complain, and cost for solving such occurrence of the failure may be increased.

In addition, because the above-described foreign object removal process is control involving degradation of exhaust, in particular countries, laws require that the failure judgment of the variable valve timing mechanism be established by completing the foreign object removal process within a predetermined time period (for example, 10 seconds). In such a case, if the engine is stopped in the middle of the foreign object removal process as described above, the possibility of judgment of failure of the variable valve timing mechanism is high even through the abnormality can be solved by executing, to the maximum possible extent within the predetermined time period, the foreign object removal process.

Moreover, in JP 2005-220759 A, as described above, the target number of idling rotations is corrected and increased when the variable valve mechanism is fixed, to avoid stalling of the engine. However, although such a configuration has an advantage of inhibiting passive stopping of the engine operation during idling, this configuration cannot be applied to a vehicle which executes the intermittent operation control to actively stop the engine operation, in cases not limited to the time of idling, in order to improve the fuel consumption.

SUMMARY OF THE INVENTION

An advantage of the present invention is that an engine control device is provided which enables suitable execution of a foreign object removal process for a variable valve timing mechanism, in an engine having the variable valve timing mechanism to which an intermittent operation control is applied.

According to one aspect of the present invention, there is provided an engine control device which can execute an intermittent operation control of an engine having a variable valve timing mechanism, the engine control device comprising a judging part which judges an abnormality of the variable valve timing mechanism, an abnormality recovery process executing part which executes an abnormality recovery process for the variable valve timing mechanism when the judging part judges that there is an abnormality in the variable valve timing mechanism during an engine operation, and an intermittent operation control prohibiting part which prohibits the intermittent operation control of the engine during execution of the abnormality recovery process of the variable valve timing mechanism.

According to another aspect of the present invention, it is preferable that, in the engine control device, the judging part judges that there is an abnormality in the variable valve timing mechanism when a difference between an actual phase angle of a cam shaft of the variable valve timing mechanism detected by a cam angle sensor and a target phase angle is greater than a predetermined angle.

According to another aspect of the present invention, it is preferable that, in the engine control device, the variable valve timing mechanism comprises a rotor which is connected to an end of a cam shaft to which a cam which opens and closes at least one of a suction valve and an exhaust valve of the engine is fixed, a housing which stores in its inside the rotor in a rotatable state by hydraulic control and which rotates with the rotor in synchronization with a crankshaft of the engine, and a control valve which controls supply and exhaust of operation oil in the housing to rotate the angular position of the rotor with respect to the housing to an advance angle side or a lag angle side, and the abnormality recovery process is an operation to rotate the rotor so that the angular position of the rotor with respect to the housing alternately changes in a predetermined time interval to the advance angle side or the lag angle side.

In this case, it is preferable that, during the execution of the abnormality recovery process, a hydraulic pressure of the operation oil supplied to the control valve is set higher than that during a normal operation.

According to another aspect of the present invention, it is preferable that, in the engine control device, when the judging part does not judge that the abnormality of the variable valve timing mechanism has been resolved even after the abnormality recovery process has continued for a predetermined time period, the abnormality of the variable valve timing mechanism is displayed on a display part.

According to other aspect of the present invention, it is preferable that the engine control device is equipped in a hybrid vehicle which is equipped with a motor which is driven by receiving supply of electrical power from a battery as a running power source in addition to the engine which is a running power source.

According to further other aspect of the present invention, there is provided a vehicle comprising the engine control device according to any one of the above-described aspects of the present invention.

According to the engine control device of various aspects of the present invention, in the engine having the variable valve timing mechanism, when it is judged that there is abnormality in the variable valve timing mechanism during engine operation, and the abnormality recovery process is being executed, the intermittent operation control of the engine is prohibited. Because of this, it is possible to prevent stopping of the engine in the middle of the abnormality recovery process, and to reliably execute the abnormality recovery process. As a result, it is possible to inhibit judgment of failure of the variable valve timing mechanism even when the variable valve timing mechanism can be returned to the normal operation by removing the foreign object through the abnormality recovery process.

DETAILED DESCRIPTION OF THE EMBODIMENT

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. In this description, the specific shape, material, numerical value, direction, etc. are provided merely as exemplary, to facilitate understanding of the present invention, and may be suitably changed according to the usage, objective, specification, etc.

In the following description, the engine control device according to the preferred embodiment of the present invention will be described exemplifying a hybrid vehicle comprising a motor which is driven by electrical power from a battery as a running power source, in addition to an engine to which the intermittent operation control is applied. However, the present invention is not limited to such a configuration, and may be applied to a vehicle such as an automobile having, as the running power source, only the engine to which the intermittent operation control is applied.

FIG. 1is a diagram schematically showing a structure of a hybrid vehicle10including an engine control device according to a preferred embodiment of the present invention. InFIG. 1, a mechanical power transmission system is shown with a solid line, an electric power line is shown with a dot-and-chain line, and a signal line is shown with a dotted line. The hybrid vehicle10comprises an engine12which can output mechanical power for running, two three-phase alternating current synchronization motor generators (hereinafter simply referred to as “motor”) MG1and MG2, and a mechanical power distributing and integrating mechanism14.

The engine12is an internal combustion engine which uses gasoline, light oil, etc. as fuel. The engine12is electrically connected to an ECU (Electronic Control Unit) for the engine (hereinafter simply referred to as “engine ECU”)16, and is configured such that a control signal is received from the engine ECU16to adjust the fuel injection, ignition, amount of intake air, timing of the suction valve, etc., and operations or actions, including start and stop, are controlled. A crank angle sensor11which detects a rotational angle θcr of the crankshaft is placed close to a power shaft13connected to the crankshaft of the engine12. A detection result of the crank angle sensor11is input to the engine ECU16, for use in calculation and monitoring of the rotational speed Ne of the engine, change of timing of the suction valve by the variable valve timing mechanism, etc. The variable valve timing mechanism included in the engine12will be described later in detail. The engine ECU16corresponds to the engine control device in the present invention.

The mechanical power distributing and integrating mechanism14comprises a planetary gear mechanism having a sun gear18placed at a center portion, a ring gear20placed concentrically with the sun gear18and having an internal tooth at an internal periphery of a ring, and a plurality of planetary gears22which engage both the sun gear18and the ring gear20. The plurality of planetary gears22are attached to the end of a carrier26in a rotatable manner.

In the mechanical power distributing and integrating mechanism14, the power shaft13of the engine12is connected to the carrier26via a damper24for reducing torque impact, a rotational shaft30connected to the rotor29of the motor MG1is connected to the sun gear18, and a decelerator or reduction gear unit34is connected to the ring gear20via a ring gear shaft32. With this structure, in the mechanical power distributing and integrating mechanism14, when the motor MG1functions as a power generator, the mechanical power from the engine12which is input from the carrier26is distributed to the side of the sun gear18and the side of the ring gear20according to the gear ratio, and when the motor MG1functions as a motor, the mechanical power from the engine12which is input from the carrier26and the mechanical power from the motor MG1which is input from the sun gear18are integrated, and the integrated mechanical power is input from the ring gear20via the ring gear shaft32to the decelerator34having a gear array having a predetermined deceleration ratio.

A rotational shaft38connected to a rotor36of the motor MG2is also connected to the decelerator34, and when the motor MG2functions as a motor, mechanical power from the motor MG2is input to the decelerator34.

The mechanical power which is input from at least one of the ring gear shaft32and the rotational shaft38of the motor MG2is transmitted to a car shaft40via the decelerator34, causing a wheel42to be rotationally driven. When, on the other hand, the mechanical power is input from the wheel42and the car shaft40to the rotational shaft38via the decelerator34during regenerative control, the motor MG2functions as a power generator. The regenerative braking is not limited to a case where the driver executes a braking operation to decelerate the vehicle, and also includes cases where the driver releases pressing of the acceleration pedal to stop acceleration of the vehicle and where the vehicle is running down a slope by the action of gravity.

The motors MG1and MG are electrically connected to corresponding inverters44and46, respectively, and the inverters44and46are electrically connected to a battery50which functions as a power supply device, via a DC/DC converter (hereinafter simply referred to as “converter”)48. For the battery50, a secondary battery such as a lithium ion battery is preferably used. Alternatively, in place of the battery, a capacitor which can be charged without a chemical reaction or a fuel cell which generates power using hydrogen as fuel may be used as the power supply device.

When the motors MG1and MG2function as a motor, a direct current voltage Vb which is a battery voltage is supplied to the converter48from the battery50through a smoothing capacitor52. The converter48has a function to boost the input voltage Vb to a predetermined value Vc and output the boosted voltage. The converter48generally comprises a reactor, two switching elements for electric power (such as, for example, IGBT), and two diodes connected in a parallel head-to-tail manner to these switching elements. However, the structure of the converter is not limited to such a structure, and a convertor of any structure having a voltage boosting and reducing function of a direct current voltage may be used.

The direct current voltage Vc which is output from the converter48is input to the inverters44and46through an smoothing capacitor54. The inverters44and46convert the input direct current voltage Vc into a three-phase alternate current voltage, and apply the converted voltage to the motors MG1and MG2, so that the motors MG1and MG2are rotationally driven as motors. As described, the converter output voltage Vc is the inverter input voltage, and will hereinafter also be called a system voltage VH.

Each of the inverters44and46comprises a U-phase arm, a V-phase arm, and a W-phase arm, each of which comprises two switching elements for electric power (for example, IGBT), in which diodes are connected in a parallel head-to-tail manner, connected in series. Intermediate points of the phase arms of the U-phase, V-phase, and W-phase are connected to the phase coils of the motors MG1and MG2. However, the structure of the inverter is not limited to that described above, and any structure having a direct current/alternate current conversion function may be used.

Because the motor MG1is connected to the engine12via the mechanical power distributing and integrating mechanism14, the motor MG1may be driven as the motor and used as a cell motor for start of the engine, or may alternatively be driven as motor and subjected to torque control, to be used as a gearbox for changing the rotational speed Ne of the engine12.

When the motors MG1and MG2function as power generators, on the other hand, a three-phase alternate current voltage which is output from the motors MG1and MG2is converted to direct current by the inverters44and46, the voltage is reduced by the converter48, and the battery50is charged. Because the inverters44and46share the power lines56and58connected to the converter48, it is also possible to supply the power generated by one of the motors MG1and MG2to the other motor without passing through the converter48, to rotationally drive the other motor.

The inverters44and46are electrically connected to an ECU for a motor (hereinafter also referred to as “motor ECU”)60, and the operations of the inverters44and46are controlled based on an ON/OFF control signal of the switching element for power, transmitted from the motor ECU60. In addition, the motors MG1and MG2comprise rotational angle sensors31and37which detect rotational angles of rotors29and36, respectively. The rotational angle sensors31and37are preferably formed with, for example, a resolver or the like. The detected values of the rotational angle sensors31and37are input to the motor ECU60and used for calculation or the like of the rotational speeds Nm1and NM2of the motors.

The motor ECU60controls the converter48and inverters44and46so that a mechanical power demanded based on a torque instruction Tr* which is input from a hybrid ECU66to be described below is output from the motor MG1and/or MG2. In addition, when the motor ECU60receives a regeneration instruction from the hybrid ECU66, the motor ECU60controls the converter48and the inverter46to charge the generated power which is output from the motor MG2to the battery50.

The battery50comprises an SOC sensor62for detecting a state of charge or remaining capacity (State Of Charge or SOC). The SOC sensor62may be formed with a current sensor which detects a charge/discharge current of the battery50. A value detected by the SOC sensor62is input to an ECU for battery (hereinafter also referred to as “battery ECU”)64. In addition, a battery voltage Vb detected by a voltage sensor and a battery temperature detected by a temperature sensor (not shown) or the like are also input to the battery ECU64. The battery ECU64monitors and controls the battery remaining capacity SOC to be maintained at an appropriate range based on an integrated value of the charge/discharge current detected by the SOC sensor62, and outputs a charge limiting signal or a discharge limiting signal to the ECU for hybrid (hereinafter also referred to as “hybrid ECU”)66according to the remaining battery capacity SOC.

The hybrid ECU66is electrically connected to the engine ECU16, the motor ECU60, and the battery ECU64, and has a function to integrally control the operations of the engine12and the motors MG1and MG2, and to manage the battery50. The hybrid ECU66may be formed preferably with a microcomputer comprising a CPU which executes various programs for vehicle control, a ROM which stores a control program, a control map, etc. in advance, and a RAM to and from which various detected values can be stored and read at any time, etc. In the map stored in the ROM, an engine intermittent operation control program and a program to prohibit the engine from starting for a heater are stored in advance.

The hybrid ECU66transmits an engine control signal to the engine ECU16as necessary, and receives data related to the engine operation state (such as, for example, the rotational speed Ne of the engine) from the engine ECU16as necessary. In addition, the hybrid ECU66transmits the demand torque instruction Tr* to the motor ECU60as necessary, and receives data (such as, for example, rotational speeds of the motors Nm1and Nm2, motor current, etc.) related to the motor operation state as necessary. Moreover, the hybrid ECU66receives from the battery ECU64data necessary for managing the battery such as the remaining battery capacity SOC, a battery voltage, a battery temperature, the charge/discharge limiting signals, etc.

A vehicle velocity sensor68and an acceleration opening sensor70are electrically connected to the hybrid ECU66and a vehicle velocity Sv which is the running velocity of the hybrid vehicle10and acceleration opening information Ac corresponding to an amount of pressing of the acceleration pedal (not shown) are input, respectively.

In addition, a display lamp (corresponding to display part)71which is placed at a location which can be easily viewed by the driver is electrically connected to the hybrid ECU66. The display lamp71is switched ON and displayed based on a signal from the engine ECU16indicating that an abnormality judgment of the variable valve timing mechanism of the engine12is determined, and is provided for notifying the driver or a repair person of the abnormality or failure of the variable valve timing mechanism. The display unit for notifying the driver or the like of the abnormality of the variable valve timing mechanism is not limited to a display lamp, and may be, for example, a display unit of other display forms such as a display of a navigation system. Alternatively, the driver or the like may be notified of the abnormality of the variable valve timing mechanism using an automated voice along with a visual notification using light and text.

Next, primary portions of a variable valve timing mechanism80provided in the engine12will be described with reference toFIGS. 2 through 4.FIG. 2is a perspective view showing a controller82of the variable valve timing mechanism80,FIG. 3is a front view of the controller82viewed from a direction of arrow A, andFIG. 4is a cross sectional diagram along a B-B line of the controller82shown inFIG. 3.

As shown inFIG. 2, the controller82is connected along with a sprocket85to one end of a cam shaft84to which a cam83for opening and closing a suction valve (not shown) is fixed. The sprocket85is connected, along with a sprocket of a cam shaft for an exhaust valve provided in parallel to the cam shaft84, to a sprocket fixed on the crankshaft of the engine12, via an endless chain. With this structure, the cam shaft84is configured to rotate in synchronization with the crankshaft13when the engine12is operated.

In addition, a cam angle sensor86is provided opposing an outer peripheral surface of the camshaft84. The cam angle sensor86detects one or a plurality of detection target sections87(only one of which is shown inFIG. 2) formed on a surface of the cam shaft84, to detect a rotational angle θcam of the cam shaft84. The value detected by the cam angle sensor86is input to the engine ECU16.

In the present embodiment, a configuration is described in which the controller82which is apart of the variable valve timing mechanism80is provided on the cam shaft84for a suction valve, but the present invention is not limited to such a configuration, and a similar controller may be provided on at least one of the cam shafts for the suction valve and an exhaust valve.

The controller82comprises a rotor90, and a housing92which stores the rotor90inside. As shown inFIG. 4, the rotor90is fixed on an end of the cam shaft84with a bolt94, and rotates with the cam shaft84. The housing92which stores the rotor90in a rotatable state, on the other hand, is fixed to a side surface of the sprocket85by a plurality of bolts95, and rotates with the sprocket85. With this structure, the rotational driving force which is input via the chain to the sprocket85is transmitted from the housing92to the rotor90, and rotates the cam shaft84.

As shown inFIG. 3, the rotor90comprises a center portion96having an approximately circular cylinder shape and a plurality (in the present embodiment, four) of vane portions98which protrude from an outer peripheral surface of the center portion96to the outside in a radial direction and which are uniformly provided with respect to the circumferential direction. The housing92, on the other hand, comprises an outer peripheral portion100having an approximately circular tube shape, and a plurality (in the present embodiment, four) of partition wall portions102which protrude from an inner peripheral surface of the outer peripheral portion100toward the inside in the radial direction and which are uniformly provided with respect to the circumferential direction.

An outer peripheral end surface of the vane portion98of the rotor90and an inner peripheral wall surface of the outer peripheral portion100of the housing92are in contact with each other in a slidable manner. In addition, an inner peripheral end surface of the partition wall portion102of the housing92and an outer peripheral wall surface of the center portion96of the rotor90are in contact with each other in a slidable manner. With the rotor90and the housing92placed in this manner, with respect to the rotation direction of the cam shaft84and the sprocket85shown with an arrow R, an advance angle chamber104is formed between a downstream-side side surface of the vane portion98and an upstream-side side surface of the partition wall portion102, and a lag angle chamber106is formed between an upstream-side side surface of the vane portion98and a downstream-side side surface of the partition wall portion102.

In the present embodiment, four advance angle chambers104and four lag angle chambers106are closed in an airtight state by a cover member108fixed on the housing92by the bolt95. In addition, in order to secure airtightness between the advance angle chamber104and the lag angle chamber106which are adjacent to each other in the circumferential direction, a sealing member110is provided on the outer peripheral end surface of the vane portion98of the rotor90and the inner peripheral end surface of the partition wall portion102of the housing92.

Through each advance angle chamber104, an advance angle operation oil passage114formed in an end of the cam shaft84is opened and connected. With this structure, the operation oil which enters or exits the advance angle chamber104through the advance angle operation oil passage114from and to an advance angle operation oil supply and exhaust port115formed on an outer peripheral surface of an end of the cam shaft84is supplied to or exhausted from the advance angle chamber104with a uniform pressure.

Similarly, through each lag angle chamber106, a lag angle operation oil passage116formed in an end of the cam shaft84is opened and connected. With this structure, the operation oil which enters or exits the lag angle chamber106through the lag angle operation oil passage116from or to a lag angle operation oil supply and exhaust port117formed on an outer peripheral surface of an end of the cam shaft is supplied to or exhausted from the lag angle chamber106with a uniform pressure.

Next, hydraulic control of the controller82including the advance angle chamber104and the lag angle chamber106as described above will be described with reference toFIGS. 5 through 7.FIG. 5is a diagram for explaining an operation to advance the phase angle of the cam shaft84(that is, cam83; similarly in the following description) in the variable valve timing mechanism80,FIG. 6is a diagram for explaining an operation to delay the phase angle of the cam shaft84in the variable valve timing mechanism80, andFIG. 7is a diagram for explaining an operation to maintain the phase angle of the cam shaft84in the variable valve timing mechanism80.

With reference toFIG. 5, the advance angle chamber104and the lag angle chamber106of the controller82are respectively connected to openings122and124formed in a tubular valve housing121of an oil control valve (OCV) via the advance angle operation oil passage114and the lag angle operation oil passage116. In the valve housing121of the oil control valve120, a spool valve element126is stored in a movable manner, and a position of the spool valve element126is determined by, for example, an electromagnetic actuator. The electromagnetic actuator is completely magnetized, intermediately magnetized, or demagnetized according to a signal from the engine ECU16. In addition, in the valve housing121, an operation oil supply port132through which the operation oil is supplied with a predetermined pressure from an operation oil reservoir (not shown) as shown by an arrow130, and operation oil exhaust ports134and136through which the operation oil is exhausted from the oil control valve120to the operation oil reservoir, are formed.

When the electromagnetic actuator is demagnetized, the spool valve element126is positioned at a position shown inFIG. 5. In this configuration, the spool valve element126connects, in the valve housing121, the operation oil supply port132and the opening122to which the advance angle operation oil passage114is connected, and connects the operation oil exhaust port136and the opening124to which the lag angle operation oil passage116is connected. With this configuration, the operation oil enters through the advance angle operation oil passage114to expand the advance angle chamber104, and exits through the lag angle operation oil passage116to contract the lag angle chamber106. As a result, in the controller82, the angular position of the rotor90with respect to the housing92is rotated in a rotational direction (direction of arrow R), and the cam shaft84is advanced.

With reference toFIG. 6, when the electromagnetic actuator is completely magnetized, the spool valve element126connects, in the valve housing121, the operation oil supply port132and the opening124to which the lag angle operation oil passage116is connected, and connects the operation angle exhaust port134and the opening122to which the advance angle operation oil passage114is connected. With this configuration, the operation oil enters through the lag angle operation oil passage116to expand the lag angle chamber106, and exits through the advance angle operation oil passage114to contract the advance angle chamber104. As a result, in the controller82, the angular position of the rotor90with respect to the housing92is rotated in a direction opposite to the rotation direction (direction of arrow R), and the cam shaft84is delayed.

With reference toFIG. 7, on the other hand, when the electromagnetic actuator is intermediately magnetized, the spool valve element126is positioned, in the valve housing121, at a position to close both of the two openings122and124. With this configuration, the entrance and exiting of the operation oil to and from both the advance angle chamber104and the lag angle chamber106are stopped, and the angular position of the rotor90with respect to the housing92is maintained. As a result, the advance angle or lag angle of the cam shaft84is constantly maintained at a target phase angle.

Next, with reference toFIG. 8, control executed by the engine ECU16will be described.FIG. 8is a flowchart showing processing steps for prohibiting intermittent operation control of the engine12during the foreign object removal process executed by the controller82of the variable valve timing mechanism80. The process shown inFIG. 8is periodically executed during an engine operation every predetermined time (for example, every few msecs).

The engine ECU16continuously monitors the crank angle θcr detected by the crank angle sensor11(refer toFIG. 1), and the cam angle θcam detected by the cam angle sensor86(refer toFIG. 2), during the operation of the engine12. The cam angle θcam is set to a target phase angle θcam* by hydraulic control of the oil control valve120described above, based on an operation state of the engine, for example, the rotational speed Ne of the engine. For the target phase angle θcam*, a value which is stored in the ROM included in the engine ECU16in advance in the form of a table or a map or the like is read and used.

When the process ofFIG. 8is started, first, in step S10, it is provisionally judged whether or not a fixation abnormality of the variable valve timing mechanism80has occurred. The fixation abnormality of the variable valve timing mechanism80in many cases is caused by a foreign object such as metal powder included in the operation oil being clogged between movable portions of the variable valve timing mechanism80, for example, between the spool valve element126of the oil control valve120and the valve housing121or between the rotor90of the controller82and the housing92, resulting in an operation deficiency.

In the step S10described above, when a state where a difference between an actual cam angle θcam detected by the cam angle sensor86and the target phase angle θcam* is greater than a predetermined angle range (for example, ±5 degrees) is continued for a predetermined period (for example, 10 seconds), it is provisionally judged that there is a fixation abnormality in the variable valve timing mechanism80. When this is not the case, on the other hand, it is judged that there is no fixation abnormality, and the end process is executed.

When it is provisionally judged in step S10that there is a fixation abnormality in the variable valve timing mechanism80, the process proceeds to step S12, and a foreign object removal process (abnormality recovery process) is executed. In the foreign object removal process, the position of the spool valve element126of the oil control valve120moves alternately between the position shown inFIG. 5and the position shown inFIG. 6in a short time period. With this process, the rotor90alternately rotates to the advance angle side or the lag angle side with respect to the housing92, and as a result, the foreign object causing the operation deficiency may be removed.

In the above-described foreign object removal process, it is also possible to supply operation oil130at a hydraulic pressure higher than that during the normal operation. In order to do so, the control to increase the rotational speed of the oil pump which supplies the operation oil130to the oil control valve120may be executed. With this process, the effect of the foreign object removal process can be further improved.

In subsequent step S14, it is judged whether or not the foreign object removal process is being executed. In this step, if the foreign object removal process is being executed, in the next step S16, the intermittent operation control of the engine12is prohibited. With this process, it is possible to prevent stopping of the engine12during the foreign object removal process which is programmed to be continuously executed for only a predetermined period (for example, 9 seconds), and to reliably complete the foreign object removal process. As a result, it is possible to inhibit failure judgment of the variable valve timing mechanism80in a case where the variable valve timing mechanism80can be recovered to the normal operation with the foreign object being removed by the foreign object removal process.

With the steps S14and S16described above, the intermittent operation control of the engine is prohibited during the predetermined period in which the foreign object removal process is executed, and when the foreign object removal process is completed (NO in step S14), the intermittent operation control of the engine12is permitted in step S18, and the engine returns to the normal engine control state.

After the foreign object removal process is executed for the predetermined time period as described above, the hydraulic control by the oil control valve120is executed so that the cam shaft84is set at the target phase angle θcam*. If the angle difference between the actual cam angle θcam detected by the cam angle sensor86and the target phase angle θcam* is within a predetermined angle range (for example, ±5 degrees), it is judged that the fixation abnormality of the variable valve timing mechanism80is resolved and the engine has returned to the normal operation. When, on the other hand, the angle difference is out of the predetermined angle range, the fixation abnormality of the variable valve timing mechanism80is determined, and the determination signal is transmitted from the engine ECU16to the hybrid ECU66. The hybrid ECU66receives this determination signal, and causes the display lamp to emit light, to notify the driver that an abnormality has occurred in the variable valve timing mechanism80.

In the above-described embodiment, a configuration is described in which the engine ECU16executes the process to prohibit the intermittent operation control of the engine during the foreign object removal process, but alternatively, the hybrid ECU66may executes a similar process in place of the engine ECU16.