WO2008142555A2

WO2008142555A2 - Drive mechanism diagnostic apparatus and diagnostic method

Info

Publication number: WO2008142555A2
Application number: PCT/IB2008/001311
Authority: WO
Inventors: Tokiji Ito
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-05-24
Filing date: 2008-05-23
Publication date: 2008-11-27
Also published as: WO2008142555A3; JP2008291747A

Abstract

A diagnostic method for a drive mechanism that is driven such that an actual drive state comes to match a target drive state which is variably set, determines that the drive mechanism is operating normally when it has been determined that the drive mechanism is not sticking and a target operating angle (Rt) is changed from a previous target operating angle, and suspends making a determination as to whether the drive mechanism is operating normally when the target operating angle (Rt) is not changed. This avoids to determine erroneously that the mechanism is operating normally when the actuel drive state matches the target drive state or when no attempt is being made -to change the actuel drive state.

Description

DRIVE MECHANISM DIAGNOSTIC APPARATUS AND DIAGNOSTIC METHOD

BACKGROUND OF THE INVENTION

1 . Field of the Invention The invention relates to a diagnostic apparatus and diagnostic method for a drive mechanism.

2, Description of the Related Art

When driving various drive mechanisms, a target drive state of the drive mechanism is variably set and the drive mechanism is driven by a motor or the like so that the actual drive state of the drive mechanism comes to match the target drive state. A variable valve timing mechanism that variably changes a valve characteristic of an engine valve in an internal combustion engine, for example, is one such drive mechanism that is driven in this way.

Also, there is a possibility that the drive mechanism may stick. Accordingly, a diagnostic apparatus can be used that detects whether the drive mechanism is sticking based on the actual drive state of the drive mechanism that is driven so that the actual drive state comes to match the target drive state, A determination that the drive mechanism is sticking can be made in one of the two following ways, for example. [1 ] It is determined that the drive mechanism is sticking when the difference between the actual drive state and the target drive state is large (see Japanese Patent Application Publication No. 2006-70789 (JP-A-2006-70789)). [2] It is determined that the drive mechanism is sticking when, in a case in which the drive mechanism is driven by a motor, a drive command value and drive current of the motor, which are parameters indicative of the actual drive state of the drive mechanism, are abnormal values when an attempt is made to make the actual drive state match the target drive state.

The diagnostic apparatus also determines whether the drive mechanism is operating normally. One conceivable way to do this is to make the determination based on whether or not the drive mechanism is sticking. For example, it can be determined that the drive mechanism is operating normally when it has been determined that the drive mechanism is not slicking,

However, when the determination that the drive mechanism is operating normally is made in this way. that determination may be erroneous in the following situation, That is, if the determination in [1 ] above is used and the drive mechanism is sticking when the actual drive state matches the target drive state, it will erroneously be determined that the drive mechanism is not sticking because the difference between the actual drive state and the target drive state is not large. Based on this determination then, it will erroneously be determined that the drive mechanism is operating normally.

Also, if the determination in [2] above is used and the drive mechanism is sticking when no attempt is being made to change the actual drive state of the drive mechanism, the drive command value and the drive current of the motor, which are parameters indicative of the actual drive state of the drive mechanism, will not be abnormal values so it will erroneously be determined that the drive mechanism is not sticking. Based on this determination then, it will erroneously be determined that the drive mechanism is operating normally.

Incidentally, the problem of erroneously determining that the drive mechanism is operating normally is not limited to a variable valve timing mechanism that can change the valve characteristics of engine valves, but is also generally common in other types of drive mechanisms as well.

SUMMARY OF THE INVENTION

This invention thus provides a drive mechanism diagnostic apparatus and diagnostic method for suppressing a determination that the drive mechanism is operating normally from being made erroneously when determining whether the drive mechanism is operating normally.

A first aspect of the invention relates to a diagnostic apparatus for a drive mechanism that is driven such that an actual drive state comes to match a target drive state which is variably set. This diagnostic apparatus includes a sticking determining portion and a normal operation determining portion. The sticking determining portion determines whether the drive mechanism is slicking based on the actual drive state of the drive mechanism. The normal operation determining portion i) determines that the drive mechanism is operating normally when it has been determined by the sticking determining portion that the drive mechanism is not sticking and the current target drive stale of the drive mechanism is changed from a previous target drive state, and ii) suspends making a determination as to whether the drive mechanism is operating normally when the current target drive state of the drive mechanism is not changed from the previous target drive state.

According to this structure, the drive mechanism is determined to be operating normally when it has been determined by the sticking determining portion that the drive mechanism is not sticking and the current target drive state of the drive mechanism is changed from a previous target drive state, and suspends making a determination as to whether the drive mechanism is operating normally in any other case. When the current target drive state of the drive mechanism changes from a previous target drive state in this case, it means that an attempt is being made to change the actual drive state of the drive mechanism, Accordingly, it is possible to inhibit a determination that the drive mechanism is operating normally from being made based on a determination that the drive mechanism is not sticking when no attempt is being made to change the actual drive state of the drive mechanism. Hence, it is possible to inhibit an erroneous determination that the drive mechanism is operating normally from being made based on that determination.

In the foregoing aspect, the drive mechanism may be a variable valve timing mechanism that changes a valve characteristic of an engine valve in an internal combustion engine. In a variable valve timing mechanism that changes a valve characteristic of an engine valve in an internal combustion engine, at times such as when the internal combustion engine is warming up or operating steadily, for example, the target drive state of the variable valve timing mechanism is fixed at a target drive state appropriate for the operating state of the engine at that time, and the actual drive state of the variable valve timing mechanism is fixed at that target drive state so often no attempt is made to change the actual drive state from that state. As a result, the likelihood that there will be an erroneous determination that the drive mechanism is operating normally increases. However, the foregoing structure makes it possible to inhibit a determination that the drive mechanism is operating normally from being made based on a determination that the drive mechanism is not sticking when no attempt is being made to change the actual drive state of the drive mechanism. Hence, it is possible to inhibit an erroneous determination that the drive mechanism is operating normally from being made based on that determination.

In the foregoing aspect, the norma] operation determining portion may determine that the drive mechanism is operating normally when the amount of change in the current target drive state of the drive mechanism from the previous target drive state is equal to or greater than a first predetermined value.

When the amount of change in the current target drive state of the drive mechanism from the previous target drive state is equal to or greater than the first predetermined value and it has been determined that the drive mechanism is not sticking, it means that an attempt is being made to change the actual drive state by changing the target drive state and it has been determined that the drive mechanism is not sticking. According to this structure, it is determined that the drive mechanism is operating normally when it has been determined that the drive mechanism is not sticking and the amount of change in the current target drive state of the drive mechanism from the previous target drive state is equal to or greater than the first predetermined value. Therefore, that determination can be made more accurately.

In the foregoing structure, the normal operation determining portion may determine that the driving mechanism is operating normally when i) it has been determined by the sticking determining portion that the driving mechanism is not sticking, ii) the current target drive state of the drive mechanism is changed from the previous target drive state of the drive mechanism, and iii) the current actual drive state of the drive mechanism is changed from a previous actual drive state.

According to this structure, it is determined that the drive mechanism is operating normally when i) it has been determined that the drive mechanism is not sticking, ii) the target drive slate is changed from the previous target drive state, and iii) the actual drive state is changed from a previous actual drive state. When the target drive stale of the drive mechanism changes from a previous target drive state, it means that an attempt is being made to change the actual drive state of the drive mechanism. Moreover, when the actual drive state of the drive mechanism changes from a previous actual drive state, it means that the actual drive state has actually changed in response to a • change in the target drive state. Accordingly, it will not be determined that the drive mechanism is operating normally based on a determination that the drive mechanism is not sticking when no attempt is being made to change the actual drive state of the drive mechanism and the actual drive state is not actually changed, Therefore, it is possible to inhibit an erroneous determination that the drive mechanism is operating normally from being made based on that determination. Hence, a determination that the drive mechanism is operating normally can be made more accurately. In the foregoing structure, the normal operation determining portion may determine that the drive mechanism is operating normally when the amount of change in the current actual drive state of the drive mechanism from the previous actual drive state is equal to or greater than a second predeteπnined value.

When the actual drive state has changed by a predetermined value or more from the previous actual drive state and it has been determined that the drive mechanism is not sticking, it means that the actual drive state has changed in response to a change in the target drive state and it has been determined that the drive mechanism is not sticking. According to the foregoing structure, the determination that the drive mechanism is operating normally can be made more accurately when it is made based on the fact that i) it has been deteπnined that the drive mechanism is not sticking, ii) it has been determined that the target drive state is changed from the previous target drive state, and iii) it has been determined that the actual drive state is changed from the previous actual drive state. BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is an enlarged sectional view of a variable valve timing mechanism of an engine to which a diagnostic apparatus according to an example embodiment of the invention is applied, together with the structure of the area around a cylinder head of the engine; FIG. 2 is a fractured perspective view of the internal structure of the variable valve timing mechanism shown in FIG. 1 ;

FIG. 3 is a fractured perspective view of the internal structure of an input arm and an output arm shown in FIG. I ;

FIG. 4 is a simplified diagram of an actuator that drives the variable valve timing mechanism shown in FIG. 1 , and a control apparatus that controls (i.e., drives) the actuator; and

FIG. 5 is a flowchart illustrating a routine for performing a diagnostic on the variable valve timing mechanism.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An example embodiment in which the diagnostic apparatus of the invention is applied to a variable valve timing mechanism of an automotive engine will now be described with reference to FIGS. 1 to 5. FIG. 1 is an enlarged sectional view of variable valve timing mechanism of an engine 1 to which the diagnostic apparatus of the invention is applied, together with the structure of the area around a cylinder head 2 of the engine 1. In the engine 1 , a combustion chamber 6 is defined by the cylinder head 2, a cylinder block 3, and a piston 5, An intake passage 7 and an exhaust passage 8 are connected to the combustion chamber 6. Communication between the intake passage 7 and the combustion chamber 6 is controlled by opening and closing an intake valve 9. Similarly, communication between the exhaust passage 8 and the combustion chamber 6 is controlled by opening and closing an exhaust valve 10.

An intake camshaft 1 1 and an exhaust camshaft 12 for driving the intake valve 9 and the exhaust valve 10, respectively, are provided on the cylinder head 2. The intake camshaft I l and the exhaust camshaft 12 are rotated by rotation transmitted from a crankshaft (i.e.. an output shaft) of the engine 1. Also, the intake camshaft 1 1 is provided with an intake cam 1 I a and the exhaust camshaft 12 is provided with an exhaust cam 12a. The intake cam H a rotates together with the intake camshaft 1 1 , and as it doe^'s so, it causes the intake valve 9 to open and close. Similarly, the exhaust cam 12a rotates together with the exhaust camshaft 12. and as it does so. it causes the exhaust valve 10 to open and close.

Also, the engine 1 is also provided with a variable valve timing mechanism that can change the valve characteristics of engine valves such as the intake valve 9 and the exhaust valve 10. In this example embodiment, this variable valve timing mechanism is a variable valve timing mechanism 14 that can change the maximum lift amount and the operating angle of the intake valve 9 and is thus provided between the intake cam 1 Ia and the intake valve 9. This variable valve timing mechanism 14 is controlled to increase the maximum lift amount and operating angle of the intake valve 9 as the operating state of the engine requires more intake air, for example. This is because air is more efficiently drawn into the combustion chamber 6 from the intake passage 7 when the maximum lift amount and operating angle are large, thereby enabling the necessary amount of intake air to be supplied.

Next, the structure of the variable valve timing mechanism 14 will be described in detail. The variable valve timing mechanism 14 includes an input arm 17 and an output arm 18. The input arm 17 is pushed against by the rotating intake cam 1 1 a and pivots (i.e., rocks) about the axis of a rocker shaft 15 and a control shaft 16 which extend parallel to the intake camshaft 11. As the input arm 17 pivots or rocks, it causes the output arm 18 to also pivot or rock about the axis. A roller 19 is rotatably mounted to the input arm 17. The input arm 17 is urged to the intake cam 11a side by a coil spring 20 such that the roller 19 is pressed against the intake cam 1 1 a. Also, when the output arm 18 pivots or rocks, it presses against a rocker arm 21 so as to lift the intake valve 9 via the rocker arm 21.

A base end portion of the rocker arm 21 is supported by a lash adjuster 22, and a tip end portion of the rocker arm 21 contacts the intake valve 9. Also, the rocker ami 21 is urged toward the output arm 18 side by a valve spring 24 of the intake valve 9. As a result, a roller 23 that is rotaiably supported between the base end portion and the tip end portion of the rocker arm 21 is pressed against the output arm 18. Accordingly, as the input arm 17 and the output arm 18 pivot or rock as the intake cam 1 I a rotates, the output ami 18 lifts the intake valve 9 via the rocker arm 21 such that the intake valve 9 opens and closes.

The variable valve timing mechanism 14 enables the relative positions of the input arm 1 7 and the output aim 18 in the rocking direction to be changed by axially displacing the control shaft 16 arranged in the pipe-shaped rocker shaft 15. In this way, when the relative positions of the input arm 17 and the output arm 18 in the rocking direction are changed, the maximum lift amount and the operating angle of the intake valve 9 are able to be changed. That is, the maximum lift amount and the operating angle of the intake valve 9 simultaneously become smaller as the input arm 17 and the output arm 18 come closer together in the rocking direction. Conversely, the maximum lift amount and the operating angle of the intake valve 9 simultaneously become larger as the input arm 17 and the output arm 18 become farther apart from one another in the rocking direction.

Next, the internal structure of the variable valve timing mechanism 14 will be described with reference to FIGS. 2 and 3. FIG, 2 is a fractured perspective view of the internal structure of the input arm 17 and the output arm 18 of the variable valve timing mechanism 14.

As shown in FIG, 2, the variable valve timing mechanism 14 is provided with a cylindrical slider 26 arranged inside the input arm 17 and the output arm 18. The rocker shaft 15 is inserted through the slider 26 and the control shaft 16 is inserted through the rocker shaft 15. When the control shaft 16 moves in the axial direction, this movement is transmitted to the slider 26 via an engaging member, not shown, provided on the control shaft 16 such that the slider 26 is also displaced in the axial direction. An input gear 27a having helical splines 27 is fixed to the center portion in the length direction of the outer wall of the slider 26. and an output gear 29a having helical splines 29 is fixed to both end portions in the length direction of the outer wall of the slider 26.

Meanwhile, as shown in FIG 3, an annular gear 28a with internal teeth (hereinafter simply referred to as "internal gear 2Sa^") that has helical splines 28 is formed on the inner wall of the input arm 1 7. and an annular gear 30a with internal teeth (hereinafter simply referred to as ^■"internal gear 3Oa'^') that has helical spines 30 is formed on the inner wall of the outer arm 18. The internal gear 28a of the input arm 17 is in mesh with the input gear 27a of the slider 26 (see FIG. 2). and the internal gear 30a of the outer ami 18 is in mesh with the outer gear 29a of the slider 26 (see FIG 2). Incidentally, the helical splines 27 and 28 have a different helix angle than the helical splines 29 and 30, and in this example embodiment, the directions of the angles of the tooth traces are opposite.

When the slider 26 is displaced in the axial direction by the movement of the control shaft 16 in the axial direction, the relative positions of the input arm 17 and the output arm 18 in the rocking direction change according to the mating of the helical splines 27 and 29 with the helical splines 28 and 30, More specifically, the relative positions of the input arm 17 and the output arm 18 in the rocking direction change in such a way that the input arm 17 and the output arm 18 move closer together as the slider 26 is displaced in the direction of arrow L in FIG. 2, and move farther apart from one another as the slider 26 is displaced in the direction of arrow H. Hence, the maximum lift amount and the operating angle of the intake valve 9 when the output arm 18 pivots (i.e., rocks) as the intake cam 11a rotates can be changed by changing the relative positions of the input arm 17 and the output arm 18 in the rocking direction in this way.

Next, an actuator that displaces the control shaft 16 in the axial direction in order to operate the variable valve timing mechanism 14, and a control apparatus that controls thai actuator will be described with reference to FIG. 4.

As shown in FIG. 4. the actuator includes a motor 47 that is connected via a converting mechanism 48 to a base end portion (i.e., the right end portion in the drawing) of the control shaft 16. The converting mechanism 48 is used to convert rotary motion of the motor 47 into linear motion in the axial direction of the control shaft 16. The control shaft 16 is then axially displaced by driving the motor 47 within a predetermined rotational angle range, for example, within a rotational angle range (O to 3600°) of 10 rotations of the motor 47, thereby driving the variable valve timing mechanism 14.

When the motor 47 is driven in reverse, the control shaft 16 is displaced in the direction of arrow L and the relative positions of the input arm 17 and the output arm 18 in the rocking direction change such that the input arm 17 and the output arm 18 move closer together. Also, when the motor 47 is driven in the forward direction, the control shaft 16 is displaced in the direction of arrow H and the relative positions of the input arm 17 and the output arm 18 in the rocking direction change such that the input arm 17 and the output arm 18 move farther apart from one another. Thus, the maximum lift amount and operating angle of the intake valve 9 when the output arm 18 pivots (i.e., rocks) as the intake cam 11a rotates can be changed by changing the relative positions of the input arm 17 and the output arm 18 in the rocking direction by driving the motor 47 in this way. The control apparatus that controls the actuator (i.e., the motor 47) includes an electronic control unit (ECU) 50 that controls various aspects of the engine 1 , such as controlling the valve characteristics, i.e., maximum lift amount and operating angle, of the intake valve 9. This ECU 50 includes a CPU that executes calculations and processing related to the various controls, ROM in which programs and data necessary for those controls are stored, RAM in which calculation results of the CPU are temporarily stored, an input port for receiving signals from other devices, and an output port for sending signals to other devices, and the like.

Various sensors are connected to the input port of the ECU 50. Some of these sensors include an accelerator position sensor 51 , a throttle position sensor 52, an airflow meter 53. a crank position sensor 54. a coolant temperature sensor 55, position sensors 56 and 57, and a current sensor 58.

The accelerator position sensor 51 detects the depression amount of an accelerator pedal (i.e., accelerator depression amount) that is depressed by a driver of the vehicle.

The throttle position sensor 52 detects the opening amount of a throttle valve provided in the intake passage 7 of the engine 1 (i.e., the throttle opening amount). The airflow meter 53 detects the amount of air that is drawn into the combustion chamber 6 through the intake passage 7. The crank position sensor 54 outputs a signal indicative of the rotation of an output shaft of the engine 1 and is used to detect the engine speed and the like.

The position sensors 56 and 57 output pulse signals having different phases according to the magnetism of a multipolar magnet that rotates together with a rotor of the motor 47 when that rotor rotates. The current sensor 58 detects the drive current of the motor 47.

Also, drive circuits of the motor 47 and the like are connected to the output port of the ECU 50. The ECU 50 ascertains the operating state of the engine based on detection signals received from the various sensors described above. Then the ECU 50 controls the valve characteristics of the intake valve 9 by operating the variable valve timing mechanism 14, which is done by driving the motor 47 and axially displacing the control shaft 16 based on the operating state of the engine that was ascertained. The valve characteristics of the intake valve 9, i.e., the maximum lift amount and the operating angle of the intake valve 9, correspond to the axial position of the control shaft

16, that is, the rotational angle within the predetermined rotational angle range of the motor 47.

Incidentally, the rotational angle of the motor 47 can be obtained based on pulse signals output from the two position sensors 56 and 57 when the rotor is rotating. That is, an edge of the pulse signal output from the position sensors 56 and 57 when the rotor is rotating is counted and the actual rotational angle within the rotational angle range of the motor 47 is then obtained based on the counted value. The maximum lift amount and the operating angle of the intake valve 9 at that time can then be obtained based on the actual rotational angle of the motor 47 that was obtained in this way.

To precisely control the maximum lift amount and the operating angle of the intake valve 9 by operating the variable valve timing mechanism 14 by driving the motor 47. the actual maximum lift amount and operating angle are detected based on the rotational angle of the motor 47, and the motor 47 is driven so that the detected maximum lift amount and operating angle come to match a target maximum lift amount and operating angle, respectively. Because the maximum lift amount and operating angle of the intake valve 9 change simultaneously, an actual operating angle Rr which is a value that corresponds to the actual maximum lift amount and operating angle will be used as one parameter, and a target operating angle Rt which is a value corresponding to the target maximum lift amount and operating angle will be used as another parameter,

The actual operating angle Rr is a value that indicates the actual driving state of the variable valve timing mechanism 14. and is detected based on the operating angle of the motor 47 obtained from the edge count value of the pulse signals output from the position sensors 56 and 57. Also, the target operating angle Rt is a value that indicates the target driving state of the variable valve timing mechanism 14, and is variably set according to the operating state of the engine 1 ascertained based on the detection signals received from the various sensors. When the target operating angle Rt changes according to the operating state of the engine 1, the motor 47 is driven so that the actual operating angle Rr comes to match the target operating angle Rt.

Also, the motor 47 is driven so that the driving speed of the motor 47 when the actual operating angle Rr is brought closer to the target operating angle Rt can be changed according to a drive command value that is determined according to the difference between the actual operating angle Rr and the target operating angle Rt. That is, the drive command value is set larger to increase the driving speed of the motor 47 when the actual operating angle Rr is brought closer to the target operating angle Rt, the larger the difference between the actual operating angle Rr and the target operating angle Rt is. Conversely, the drive command value is set smaller to reduce the driving speed of the motor 47 when the actual operating angle Ri' is brought closer to the target operating angle Rt. the smaller the difference between the actual operating angle Rr and the target operating angle Rt is. Also, the drive command value is gradually increased when the actual operating angle Rr is not able to match the target operating angle Rt even if the motor 47 is driven in an attempt to bring the actual operating angle Rr close to the target operating angle Rt.

Accordingly, the drive command value of the motor 47 is a parameter that indicates the actual drive state of the variable valve timing mechanism 14 which is operated by driving the motor 47. Incidentally, the value of the drive current of the motor 47 becomes larger as the drive command value increases to increase the driving speed of the motor 47. Accordingly, the drive current of the motor 47 is a parameter that indicates the actual drive state of the variable valve timing mechanism 14 that is operated by driving the motor 47, Next, an outline of the diagnostic of the variable valve timing mechanism 14, that is, a routine for determining whether the variable valve timing mechanism 14 is sticking and whether the variable valve timing mechanism 14 is operating normally will be described. When determining whether the variable valve timing mechanism 14 is sticking, a determination that the variable valve timing mechanism 14 is sticking is made using at least one of the following two methods [1] and [2].

[1] It is determined that the variable valve timing mechanism 14 is sticking when the difference between the actual operating, angle Rr and the target operating angle Rt is greater than a preset determining value. [2] It is determined that the variable valve timing mechanism 14 is sticking when the drive command value and the drive current of the motor 47 when attempting to make the actual operating angle Rr match the target operating angle Rt are abnormal values.

Also, it is possible to make a determination that the variable valve timing mechanism 14 is operating normally, for example, when it is not determined that the variable valve timing mechanism 14 is sticking, i.e., when it is determined that the variable valve timing mechanism 14 is not slicking. However, if the determination that the variable valve timing mechanism 14 is operating normally is made in this way. it is possible that the determination may be erroneous when no attempt to change the actual operating angle Rr is being made, as may be the case when the actual operating angle Rr matches the target operating angle Rt and the target operating angle Rt is constant.

That is, when making the determination of [1 ] above, if the variable valve timing mechanism 14 is sticking while the actual operating angle Rr matches the target operating angle Rt it is determined that the variable valve timing mechanism 14 is not sticking because the difference between the actual operating angle Rr and the target operating angle Rt is not equal to or greater than the determining value. As a result, it is erroneously determined, based on that determination, that the variable valve timing mechanism 14 is operating normally. Also, when making the determination of [2] above, if the variable valve timing mechanism 14 is sticking while no attempt is being made to change the actual operating angle Rr by changing the target operating angle Rt. for example, it is determined that the variable valve timing mechanism 14 is not sticking because the drive command value and the drive current of the motor 47 are not abnormal values. As a result, it is erroneously determined, based on that determination, that the variable valve timing mechanism 14 is operating normally.

In particular, when the engine 1 is warming up or operating steadily and the like, the target operating angle Rt is fixed for that particular engine operating state and the actual operating angle Rr is fixed to that target operating angle Rt so often no attempt is made to change the actual operating angle Rr from that state. As a result, the likelihood that there will be an erroneously determination that the variable valve timing mechanism 14 is operating normally increases. Thus, in this example embodiment, it is determined that the variable valve timing mechanism 14 is operating normally when i) it is determined that the variable valve timing mechanism 14 is not sticking, ii) the target operating angle Rt is changed from the previous target operating angle, and iii) the actual operating angle Ri is changed from the previous actual operating angle. Furthermore, when the target operating angle Rt and the actual operating angle Rr are not changed, the determination as to whether the variable valve timing mechanism 14 is operating normally is suspended. As a result, it is possible to inhibit a determination that the variable valve timing mechanism 14 is operating normally from being made based on a determination that the variable valve timing mechanism 14 is not sticking when no attempt to change the actual operating angle Rr is being made, such as when the actual operating angle Rr matches the target operating angle Rt and that target operating angle Rt is constant. Thus it is possible to inhibit an erroneous determination that the variable valve timing mechanism 14 is operating normally from being made based on that determination. Next, a routine for determining whether the variable valve timing mechanism 14 is sticking and whether the variable valve timing mechanism is operating normally will be described with reference to the flowchart in FIG. 5 which shows a diagnostic routine. This diagnostic routine is executed cyclically at predetermined time intervals, for example, by the ECU 50. In step SlOl of the routine, the target operating angle Rt that can be variably set and the actual operating angle Rr that is detected are stored in the RAM of the ECU 50 at predetermined time intervals. Incidentally, this predetermined time is longer than the execution cycle of the diagnostic routine (e.g., one second). In step S 102, it is determined whether the variable valve timing mechanism 14 is sticking using at least one of the methods [1] and [2] described above. If the determination in step S 102 is no, then it is determined that the variable valve timing mechanism 14 is sticking (step S 107). If, on the other hand, the determination in step S 102 is yes, then it is determined whether the variable valve timing mechanism 14 is operating normally so steps S 103 and thereafter are executed. First in step S 103 of this series of steps, it is determined whether determining conditions for determining whether the variable valve timing mechanism 14 is operating normally are satisfied, Examples of the determining conditions include i) that the voltage of a battery which is used as the power supply for driving the motor 47 be at least an appropriate value (such as 8 volts), and ϋ) that a learning process for learning a learning value which is a value corresponding Io the deviation of the rotational angle of the motor 47 from the appropriate value not be in the middle of being executed. When all of these conditions are satisfied, it is determined in step S 103 that the determining conditions are satisfied. Then it is determined whether the target operating angle Rt is changed from the previous target operating angle (step S 104), If so. it is determined whether the actual operating angle Rr is changed from the previous actual operating angle (step Sl 05).

In step S 104, it is determined whether the difference between the current target operating angle Rt and the target operating angle Rt stored in the RAM (i.e.. the absolute value of the difference between the two) is equal to or greater than a predetermined value α (α > 0). When the difference is equal to or greater than the predetermined value α. which is a value greater than 0. it means that an attempt is being made to change the actual operating angle Rr by changing the target operating angle Rt and it has been determined in step S 102 that the variable valve timing mechanism 14 is not sticking. Incidentally, the predetermined value α is set to a value that enables it to be determined that the variable valve timing mechanism 14 is operating normally when it is determined that the variable valve timing mechanism 14 is not sticking at this time.

In step S 105, it is determined whether the difference between the current actual operating angle Rr and the actual operating angle Rr stored in the RAM (i.e., the absolute value of the difference between the two) is equal to or greater than a predetermined value β (β > 0). When the difference is equal to or greater than the predetermined value β, which is a value greater than 0, it means that the actual operating angle Rr is actually changed in response to a change in the target operating angle Rt and it has been determined in step S 102 that the variable valve timing mechanism 14 is not sticking. Incidentally, the predetermined value β is set to a value that enables it to be determined that the variable valve timing mechanism 14 is operating normally when it is determined that the variable valve timing mechanism 14 is not sticking at this time.

Then it is determined that the variable valve timing mechanism 14 is operating normally when both of the determinations in steps S104 and S105 are yes, i.e., when the target operating angle Rt has changed and the actual operating angle Rr has changed in response to that change in the target operating angle Rt when it has been determined that the variable valve timing mechanism 14 is not sticking (step S 106). If. on the other hand, the determination in step S 104 is no or the determination in step S 104 is yes but the determination in step S 105 is no. a determination as to whether the variable valve timing mechanism 14 is operating normally is suspended,

This example embodiment yields the following effects.

(1 ) The variable valve timing mechanism 14 is determined to be operating normally when it has been determined that the variable valve timing mechanism 14 is not sticking and the target operating angle Rt is changed from the previous target operating angle, i.e.. there is an attempt being made to change the actual operating angle Rr. Also. the determination as to whether the variable valve timing mechanism 14 is operating normally is suspended when the target operating angle Rt is not changed. Accordingly, it is possible to inhibit a determination that the variable valve timing mechanism 14 is operating normally from being made based on a determination that the drive mechanism is not sticking when no attempt is being made to change the actual operating angle Rr. Hence, it is possible to inhibit an erroneous determination that the variable valve timing mechanism 14 is operating normally from being made based on that determination,

Incidentally, when the engine 1 is warming up or operating steadily, the target operating angle Rt is fixed in a target drive state appropriate for that operating state of the engine, and the actual operating angle Rr is fixed to that target operating angle Rt so often no attempt is made to change the actual operating angle Rr from that state. As a result, the likelihood that there will be an erroneous determination that the variable valve timing mechanism 14 is operating normally increases. However, despite this tendency, it possible to inhibit a determination that the variable valve timing mechanism 14 is operating normally from being made based on a determination that the variable valve timing mechanism 14 is not sticking when no attempt is being made to change the actual operating angle Rr, Hence, it is possible to inhibit an erroneous determination that the variable valve timing mechanism 14 is operating normally from being made based on that determination.

(2) The determination that the target operating angle Rt is changed from the previous target operating angle (i.e.. YES in step S 104 in FlG. 5) is made based on the fact that the amount of change when target operating angle Rt changes is equal to or greater than the predetermined value α. i.e.. based on the fact that the difference between the current target operating angle Rt and the target operating angle Rt stored in the RAM is equal to or greater than the predetermined value α. This predetermined value α is set to a value that enables it to be determined that the variable valve timing mechanism 14 is operating normally when it has been determined that the variable valve timing mechanism 14 is not sticking (i.e.. YES in step S 102 in FIG. 5). Accordingly, the determination that the variable valve timing mechanism 14 is operating normally can be made more accurately when it is made based on the fact that i) it has been determined that the variable valve timing mechanism 14 is not sticking, and ii) it has been determined that the target operating angle Rt is changed from the previous target operating angle. (3) With regard to whether the variable valve timing mechanism 14 is operating normally, more specifically, it is determined that the variable valve timing mechanism 14 is operating normally when i) it has been determined that the variable valve timing mechanism 14 is not sticking, ii) the target operating angle Rt is changed from the previous target operating angle, and iii) the actual operating angle Rr is changed from the previous actual operating angle. Also, if the actual operating angle Rr is not changed, the determination as to whether the variable valve timing mechanism 14 is operating normally is suspended. When the actual operating angle Rr changes from the previous actual operating angle in this case, it means that the actual operating angle Rr has actually changed in response to a change in the target operating angle Rt. Accordingly, it is possible to inhibit a determination that the variable valve timing mechanism 14 is operating normally from being made based on a determination that the variable valve timing mechanism 14 is not sticking when no attempt is being made to change the actual operating angle Rr by changing the target operating angle Rt and the actual operating angle Rr is not actually changed. Hence, it is possible to inhibit an erroneous determination that the variable valve timing mechanism 14 is operating normally from being made based on that determination so the determination that the variable valve timing mechanism 14 is operating normally can be made more accurately.

(4) The determination that the actual operating angle Rr is changed from the previous actual operating angle (i.e.. YES in step S 105 in FIG. 5) is made based on the fact that the amount of change in the actual operating angle Rr at that time is equal to or greater than the predetermined value β. i.e.. based on the fact that the difference between the current actual operating angle Rr and the actual operating angle Rj' stored in the RAM is equal to or greater than the predetermined value β. This predetermined value β is set to a value that enables it to be determined that the variable valve timing mechanism 14 is operating normally when it has been determined that the variable valve timing mechanism 14 is not sticking (i.e.. YES in step S 102 in FIG 5). Accordingly, the determination that the variable valve timing mechanism 14 is operating normally can be made more accurately when it is made based on the fact that i) it has been determined that the variable valve timing mechanism 14 is not sticking, ii) it has been determined that the target operating angle Rt is changed from the previous target operating angle, and iii) it has been determined that the actual operating angle Rr is changed from the previous actual operating angle.

Incidentally, the example embodiment described above may also be modified as follows, for example.

The actual operating angle Rr does not have to change from the previous operating angle for it to be determined that the variable valve timing mechanism 14 is operating normally (i.e., step S 105 in FIG. 5 may be omitted).

It may be determined that the variable valve timing mechanism 14 is sticking using only one of the determinations from among [1] and [2] above.

The invention may also be applied to a variable valve timing mechanism that variably changes the opening and closing timing of the intake valve 9, as valve characteristics of the intake valve, by variably changing the relative rotational phase of the intake camshaft 11 with respect to the crankshaft. When a variable valve timing mechanism that variably changes a valve characteristic of the exhaust valve 10 is provided, the invention may also be applied to that variable valve timing mechanism,

The invention may also be applied to a drive mechanism other than the variable valve timing mechanism 14.

While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the example embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including move, less or only a single element, are also within the spirit and scope of the invention.

Claims

CLAIMS:

1 . A diagnostic apparatus for a drive mechanism that is driven such that an actual drive state comes lo match a target drive state which is variably set, comprising: a sticking determining portion that determines whether the drive mechanism is sticking based on the actual drive state of the drive mechanism; and a normal operation determining portion which i) determines that the drive mechanism is operating normally when it has been determined by the sticking determining portion that the drive mechanism is not sticking and the current target drive state of the drive mechanism is changed from a previous target drive state, and ii) suspends making a determination as to whether the drive mechanism is operating normally when the current target drive state is not changed from the previous target drive state.

2. The diagnostic apparatus according to claim 1 , wherein the drive mechanism is a variable valve timing mechanism that changes a valve characteristic of an engine valve in an internal combustion engine.

3. The diagnostic apparatus according to claim 1 or 2, wherein the normal operation determining portion determines that the drive mechanism is operating normally when the amount of change in the current target drive state of the drive mechanism from the previous target drive state is equal to or greater than a first predetermined value.

4. The diagnostic apparatus according to any one of claims 1 to 3, wherein the normal operation determining portion determines that the driving mechanism is operating normally when i) it has been determined by the sticking determining portion that the driving mechanism is not sticking, ii) the current target drive state of the drive mechanism is changed from the previous target drive state, and iii) a current actual drive state of the drive mechanism is changed from a previous actual drive state.

5. The diagnostic apparatus according to any one of claims 1 to 4, wherein the normal operation determining portion determines that the drive mechanism is operating normally when the amount of change in the current actual drive slate of the drive mechanism from the previous actual drive state is equal to or greater than a second predetermined value.

6. The diagnostic apparatus according to claim 1 , further comprising: a storing portion that stores the previous target drive state of the drive mechanism.

7. The diagnostic apparatus according to claim 6. wherein: the storing portion stores the actual drive state of the drive mechanism in addition to storing the previous target drive state,

8. A diagnostic method for a drive mechanism that is driven such that an actual drive state comes to match a target drive state which is variably set, comprising: determining whether the drive mechanism is sticking based on the actual drive state of the drive mechanism; and determining whether the current target drive state of the drive mechanism is changed from a previous target drive state when it has been determined that the driving mechanism is not sticking, and determining that the drive mechanism is operating normally when the current target drive state is changed from the previous target drive state, and suspending making a determination as to whether the drive mechanism is operating normally when the current target drive state is not changed from the previous target drive state.