Vehicular shift control apparatus

A vehicular shift control apparatus for a vehicle provided with a parking lock device selectively switched to a locking position in which rotation of wheels of the vehicle is prevented and a non-locking position in which the rotation of the wheels is not prevented, by an operation of an electrically operated actuator, the vehicular shift control apparatus being configured to perform a failure diagnosis to determine whether the actuator is operable or not, the vehicular shift control apparatus includes: the vehicular shift control apparatus permits the operation of the actuator if a supply voltage to the actuator is raised from a value lower than a predetermined threshold supply voltage value to a value not lower than the threshold supply voltage value after a determination that the actuator is inoperable is obtained in the failure diagnosis.

TECHNICAL FIELD

The present invention relates to a control performed to deal with a failure of a shift-by-wire system.

BACKGROUND ART

There is well known a vehicular shift control apparatus adopting a so-called “shift-by-wire (SBW) system configured to electrically change a shift position associated with a manner of running of a vehicle, by operating an electrically operated actuator such as an electric motor. Patent Document 1 discloses an example of a SBW control apparatus provided in a shift range switching device. This SBW control apparatus is configured such that in the event of power application to the SBW control apparatus after instantaneous power removal therefrom, a position of an output shaft (an angular position of the output shaft) of the above-described electrically operated actuator, which output shaft position is memorized before the instantaneous power removal and kept in memory after the power removal is recognized as the output shaft position after the power application, if the above-described actuator was not operated before the instantaneous power removal.

PRIOR ART DOCUMENT

Patent Documents

Patent Document 1: JP-2006-336840 A

Patent Document 2: JP-2003-034157 A

SUMMARY OF THE INVENTION

Object Achieved By The Invention

The vehicle may have a failure that disables the above-described electrically operated actuator to be operated, after the power application to the SBW control apparatus after the power removal therefrom, for instance. Possible causes for such a failure of the vehicle include a failure of the electrically operated actuator per se, and a drop of a supply voltage to the electrically operated actuator below a lower limit value above which the electrically operated actuator is operable.

If the above-described SBW control apparatus once determines that the above-described electrically operated actuator is inoperable after the power application, the above-described SBW control apparatus is usually configured to deem the electrically operated actuator to be inoperable since the determination and to perform a fail-safe control to prevent an operation of the electrically operated actuator. For example, the fail-safe control is performed to prevent a transition to a state in which the vehicle can be run.

Where the above-described electrically operated actuator is not operable due to a drop of the above-described supply voltage, namely, due to an excessively low value of the supply voltage, however, this supply voltage may be possibly raised to a value equal to or higher than the above-indicated lower limit value, enabling the actuator to be operated. In this case where the above-described electrically operated actuator becomes operable as a result of the rise of the supply voltage, it is adequate to recognize the electrically operated actuator to be operable and to cancel the fail-safe control and perform a normal control to be performed when the electrically operated actuator is normally operable. However, the SBW control apparatus is not configured to perform the normal control in the above-indicated case, but is configured to maintain the determination that the actuator is still inoperable. In this respect, it is noted that this problem is not recognized in the prior art.

The present invention was made in view of the background art described above. It is an object of this invention to provide a vehicular shift control apparatus configured to perform an adequate control processing with respect to the electrically operated actuator in consideration of a possibility that the actuator becomes operable after the actuator is once determined to be inoperable.

Means For Achieving The Object

The object indicated above is achieved according to the present invention, which provides a vehicular shift control apparatus for (a) a vehicle provided with a parking lock device selectively switched to a locking position in which rotation of wheels of the vehicle is prevented and a non-locking position in which the rotation of said wheels is not prevented, by an operation of an electrically operated actuator, the vehicular shift control apparatus being configured to perform a failure diagnosis to determine whether said actuator is operable or not, and (b) characterized in that the above-described vehicular shift control apparatus permits the operation of the above-described actuator if a supply voltage to the above-described actuator is raised from a value lower than a predetermined threshold supply voltage value to a value not lower than the threshold supply voltage value after a determination that the above-described actuator is inoperable is obtained in said failure diagnosis.

Advantages Of The Invention

If the supply voltage to the above-described electrically operated actuator is raised from the value lower than the above-indicated threshold supply voltage value to the value not lower than the threshold supply voltage value, the above-described actuator which was determined to be inoperable prior to this rise of the supply voltage is considered to become inoperable due to an excessive drop of the supply voltage. Further, the actuator is considered to be operable after the rise of the supply voltage. According to the present invention described above, therefore, an adequate control processing can be performed with respect to the actuator, in consideration of a possibility that the actuator becomes operable, more specifically, a possibility that the above-described supply voltage is raised to a sufficiently high value, after the previous determination that the actuator is inoperable. For example, the adequate control processing is a normal control of the actuator to be implemented where the actuator is normally operable on the premise that the actuator is operable. On the other hand, an inadequate control processing with respect to the actuator may be a control of the actuator to be implemented in the event of a failure of the above-described actuator, for instance, a control to inhibit an operation of the actuator, based on an incorrect recognition that the actuator is inoperable, while in fact the actuator is operable.

According to a preferred form of the present invention, the above-described threshold supply voltage value is a lower limit of the supply voltage to the above-described actuator. In this preferred form of the invention, it is possible to more adequately determine that the above-described actuator which was determined to be inoperable become inoperable due to an excessive drop of the above-described supply voltage.

According to another preferred form of the invention, the vehicular shift control apparatus performs the above-described failure diagnosis as a second failure diagnosis if the supply voltage to the above-described actuator is raised from the value lower than the above-described predetermined threshold supply voltage value to the value not lower than the threshold supply voltage value after the determination that the above-described actuator is inoperable is obtained in the first failure diagnosis, and permits the operation of the above-described actuator only if the determination that the above-described actuator is operable is obtained in the above-described second failure diagnosis. In this preferred form of the invention, it is possible to permit the operation of the actuator after it is confirmed that the actuator becomes operable as a result of the rise of the supply voltage to the above-described actuator.

According to a further preferred form of the invention, the vehicular shift control apparatus permits the operation of the above-described actuator under a condition that a predetermined manual operation has been performed by a vehicle passenger after a rise of the above-described supply voltage to the above-described actuator from the value lower than the above-described threshold supply voltage value to the value not lower than the threshold supply voltage value, if the rise of above-described supply voltage to the value not lower than threshold supply voltage value occurs after the determination that the above-described actuator is inoperable is obtained in the above-described failure diagnosis. In this preferred form of the invention, the above-described actuator is operated after the manual operation by the vehicle passenger, preventing a discomfort that would otherwise be felt by the vehicle passenger upon operation of the actuator while the vehicle passenger recognizes that the actuator is inoperable.

According to still another preferred form of the invention, the above-described predetermined manual operation by the vehicle passenger is an operation that enables the above-described vehicle to be ready for running. This preferred form of the invention has an advantage that the vehicle passenger is not required to perform a special operation to permit the operation of the above-described actuator, since the operation that enables the vehicle to be ready for running is an operation required to start running of the vehicle.

According to a further preferred form of the invention, (a) the vehicle shift control apparatus inhibits the operation of the above-described actuator if the determination that the above-described actuator is inoperable is obtained in the above-described failure diagnosis, and (b) the shift control apparatus cancels an inhibition of the operation of the above-described actuator, before permitting the operation of the actuator after the inhibition if above-described vehicle shift control apparatus permits after the operation of above-described actuator is inhibited. In this preferred form of the invention, it is possible to avoid commanding the above-described actuator to be operated when the actuator is inoperable. In addition, it is possible to avoid a complicated control of permitting and inhibiting the operation of the above-described actuator.

According to yet another preferred form of the invention, the above-described vehicle is provided with a vehicle drive power transmitting system in a power transmitting path between its vehicle drive power source and its drive wheels. Although the vehicle drive power source preferably includes a gasoline or diesel engine or any other internal combustion engine operable to generate a drive power by combustion of a fuel, but may use any other type of drive power source such as an electric motor or electric motors, alone, or in combination of the internal combustion engine. Namely, the above-described vehicle may be: an engine-drive vehicle using only an engine as the drive power source; an electric vehicle using only an electric motor or electric motors; a hybrid vehicle using both of an engine and an electric motor or electric motors; a vehicle using any drive power source other than the engine and electric motors; or a vehicle using three or more different types of drive power source.

According to a still further preferred form of the invention, the above-described vehicle drive power transmitting system is constituted, for example, by: a transmission alone; a torque converter and a transmission having a plurality of speed ratios; or this latter transmission, a speed reducing portion and a differential mechanism portion. For example, this transmission is constituted by: a speed reducing device such as a planetary gear set to which the above-described electric motor or motors is/are connected in the above-described electric vehicle; one of various types of planetary gear type automatic transmission having a plurality of gear positions (speed positions), for example, four, five, six or more forward drive speed positions, which are selectively established by selectively connecting rotary elements of a plurality of planetary gear sets through coupling devices; a synchronous meshing type parallel-two-axes automatic transmission having a plurality of pairs of permanently meshing shifting gears disposed on two axes, which are selectively brought into a power transmitting state by synchronizing devices which are operated by hydraulic actuators to automatically shift the automatic transmission; a so-called belt type continuously variable transmission which has a transmission belt functioning as a power transmitting member connecting a pair of variable-diameter pulleys effective diameters of which are variable to continuously change the speed ratio; a so-called traction type continuously variable transmission having a pair of cones rotatable about a common axis, and a plurality of rollers which are rotatable about respective axes intersecting the axis of the cones and which are squeezed between the pair of cones such that an angle of intersection of the axes of the rollers with respect to the axis of the cones is changed to change the speed ratio of the transmission; an automatic transmission functioning as an electrically controlled continuously variable transmission having a differential mechanism constituted by a planetary gear device configured to distribute a drive force from an engine to a first electric motor and its output shaft, and a second electric motor disposed on the output shaft of the differential mechanism, and wherein the differential mechanism performs a differential operation to mechanically transmit a major portion of the drive force of the engine to the vehicle drive wheels, and to electrically transmit the remaining portion of the drive force through an electric path from the first electric motor to the second electric motor, for thereby electrically changing the speed ratio of the automatic transmission; or an automatic transmission designed to be installed on a so-called parallel type hybrid vehicle wherein an electric motor is operatively connected to an engine shaft or an output shaft.

According to a yet further preferred form of the invention, the above-described parking lock device is configured to establish a locking state in the above-described locking position by engagement of a locking pawl with a locking gear rotating with the above-described wheels in the above-described locking position, and establish a non-locking state in the above-described non-locking position by canceling the locking state. The above-described locking gear may be fixed to an output rotary member of a transmission connected to the above-described wheels, or alternatively to any other rotary member directly connected to the wheels.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail by reference to the drawings.

Embodiment

FIG. 1is the view schematically showing an arrangement of a power transmitting path from an engine12of a vehicle10to which the present invention is applicable, to drive wheels14of the vehicle10, and is also the block diagram showing major elements of a control system provided on the vehicle10to control a parking lock device16and other devices. As shown inFIG. 1, the vehicle10is provided with the parking lock device16, a transmission18, and a manually operable shift operating device30, and adopts a shift-by-wire (SBW) system configured to electrically change a shift position associated with a manner of running of the vehicle10, that is, a shift position (shift range) of the transmission18. The transmission18is arranged so as to be suitably used on a transverse FF (front-engine front-drive) type of vehicle10, so that a drive force of the engine12which is a vehicle drive power source in the form of an internal combustion engine is transmitted from an output rotary member of the transmission18in the form of an output gear22that is one of two gears of a counter gear pair20, to a pair of drive wheels14through a power transmitting device in the form of the counter gear pair20, a final gear pair24, a differential gear device26, and a pair of axles (drive shafts (D/S))28, in this order of description. A transaxle (TA) is constituted by the above-described transmission18, counter gear pair20, final gear pair24, differential gear device26, and other elements. While the present invention will be described as applied to a hybrid vehicle provided with the drive power source in the form of the engine12and electric motors M, it is to be understood that the invention is equally applicable to any type of vehicle such as an ordinary engine-driven vehicle, hybrid vehicle, an electric vehicle and a fuel-cell vehicle, provided that the vehicle adopts the shift-by-wire system.

The vehicle10is also provided with an electronic control apparatus100including a vehicular shift control apparatus configured to control an operation state of the parking lock device16, and the other devices. For example, the electronic control apparatus100is principally constituted by a so-called microcomputer incorporating a CPU, a RAM, a ROM, and an input-output interface. The CPU performs signal processing operations according to control programs preliminarily stored in the ROM while utilizing a temporary data storage function of the RAM, to implement: hybrid drive controls such as an output control of the engine12and a drive control of the electric motors M; a shifting control of the transmission18; a shift position switching control of the transmission18using the shift-by-wire system; and a switching control to control the operation state of the parking lock device16.

The electronic control apparatus100is arranged to receive signals such as: shift lever position signals indicative of operating positions PSHand generated from a shift sensor36and a select sensor38(shown inFIG. 2) which are position sensors for detecting the operating positions PSHof a shift lever32; a P-switch signal generated from a P switch34which is operable by a user to change the shift position of the transmission18to a parking position (P position) from any non-P position other than the P position; a P-position signal indicative of an operating state of P-lock in the parking lock device16provided to switch the shift position of the transmission18between the P position and the non-P position by establishing or canceling a parking lock (P lock); a power switch signal indicative of an operating state of a vehicle power switch40operable by the user to apply and remove power to and from the vehicle10; wheel speed pulse signals generated from rotation speed sensors in the form of wheel speed sensors42and indicative of rotating speeds Nwof the wheels (drive wheels14and driven wheels) which correspond to a vehicle speed V; a brake operation signal generated from a brake switch44and indicative of a brake-on state BONrepresenting an operated state of a foot brake pedal (not shown) provided to operate a primary vehicle brake system; a signal indicative of a charging current or a discharging current ICDof an electric-energy storage device46; a signal indicative of a voltage VBATof the electric-energy storage device46; and a signal indicative of a state of charging (stored electric energy amount) SOC of the electric-energy storage device46.

The electronic control apparatus100is further arranged to generate signals such as: hybrid control command signals including engine output control command signals for controlling an output of the engine12, motor control command signals for controlling operations of the electric motors M provided in the transmission18, and shifting control command signals for controlling shifting operations of the transmission18; shift position switching control command signals for changing the shift position of the transmission18; a vehicle speed indication control command signal for controlling a speedometer58to indicate the present vehicle speed V, the speedometer58being provided in a display device in the form of a known combination meter56configured to provide the user with vehicle information relating to a running state of the vehicle; a shift position indication control command signal for controlling a shift position indicator (shift position display device)60provided in the combination meter56, to indicate the selected shift position of the transmission18; a parking lock indication control command signal (P-lock indication control command signal) for controlling a P-position indicator light62provided as a locking indicator light to indicate an operation of a P-lock (parking lock state; P-lock state), i.e. to indicate the shift position is P-position by lighting; and a P switching control command signal for switching the parking lock device16. It is noted that the P-position indicator light62is a display light which is operated without synchronization of an operating state (illuminated/non-illuminated state) of the combination meter56, and which is built in the P switch34, for instance.

Described more specifically, the electronic control apparatus100is provided with a power source and hybrid control computer (hereinafter referred to as “PM-HV-ECU”)104, a parking control computer (hereinafter referred to as “P-ECU”)106, and a meter control computer (hereinafter referred to as “meter ECU”)108. It is noted that the above-indicated P-ECU106corresponds to the vehicular shift control apparatus according to this invention.

For example, the PM-HV-ECU104is configured to change a power supply state of the vehicle10, on the basis of the power switch signal received from the vehicle power switch40manually operable by the user. In the present embodiment, the power supply state may be changed to a selected one of: a power-off state (ALL-OFF state; IGACC-OFF state) in which the vehicle10cannot be run; a partial power-on state (ACC-ON state; IG-OFF state) in which the vehicle10cannot be run but some of the functions of the vehicle10can be performed in an off state of the combination meter56; a power-on state (IG-ON state) in which a power supply relating to the vehicle running is available in an on state of the combination meter56; and a vehicle-run-ready state (READY-ON state) in which the vehicle running can be controlled according to the hybrid control command signals relating to the vehicle running, and in which the vehicle10can be started and run by an operation of an accelerator pedal. The above-indicated some functions of the vehicle10that can be performed include a function of power application to permit operations of a navigating system and an audio device64, and power application to a power source receptacle (not shown) for connection to a battery. The above-indicated IG-ON state is the above-indicated power-on state in which the functions other than the functions for controlling the vehicle running according to the hybrid control command signals can be performed (for instance, the shift position of the transmission18can be changed), and in which the engine12and the electric motors M cannot be started or operated, that is, the vehicle10cannot be started and run even with an operation of the accelerator pedal. The READY-ON state can be established by an operation of the above-described vehicle power source switch40, under the condition that a failure does not take place in an initial processing operation of the P-ECU106and an initial drive control of the parking lock device16, which are performed or implemented before transition to the READY-ON state. Namely, even if the vehicle power switch40has been operated to switch the power supply state to the READY-ON state, the power supply state is not switched to the READY-ON state in the event of an occurrence of such a failure as described above, but is switched to the other state such as the IG-ON state in this event.

For instance, the PM-HV-ECU104is configured to permit the power supply state to the READY-ON state from any one of the other states, if an input of the above-indicated power switch signal is detected in the P position and in the brake-on state BON. The PM-HV-ECU104is further configured to switch the power supply state to the ALL-OFF state if the vehicle speed V is lower than a predetermined threshold value V′ and the input of the power switch signal is detected, in the P position and in the IG-ON or READY-ON state. The PM-HV-ECU104is also configured to switch the power supply state of the vehicle10such that the ALL-OFF state, ACC-ON state and IG-ON state are sequentially established, repeatedly in this order of description each time the power switch signal is received in the P position and not in the brake-on state BON. The PM-HV-ECU104is further configured to apply to the P-ECU106an automatic P switching command signal for operating the parking lock device16to automatically switch the shift position to the P position, if the vehicle speed V is lower than the predetermined threshold value V′ and the input of the power switch signal is detected in the non-P position and in the IG-ON state. In this case, the PM-HV-ECU104switches the power supply state of the vehicle10to the ALL-OFF state after the P position has been established. (This series of operations to establish the P position is referred to as “automatic P-lock operation”.) The above-indicated predetermined threshold value V′ is a vehicle-stop-state judging vehicle speed obtained by experimentation and stored in memory, below which it is determined that the vehicle is stationary.

The PM-HV-ECU104is also configured to implement an overall control of the operation of the transmission18, for instance. After the power supply state of the vehicle10has been switched to the READY-ON state, for example, the PM-HV-ECU104starts the hybrid system for permitting the vehicle running, and applies hybrid control commands relating to the vehicle running, to the engine12, electric motors M and transmission18, for controlling the vehicle running. Further, the PM-HV-ECU104is configured to apply shift position switching control commands to the transmission18for changing its shift position, on the basis of the shift lever position signals which are received from the shift sensor36and select sensor38and which relate to the operating position PSH. If the shift position of the transmission18is the P position at this point of time, the PM-HV-ECU104applies a P canceling command signal to the P-ECU106, on the basis of the above-indicated shift lever position signals, for switching the shift position of the transmission18from the P position to one of the non-P positions. Further, the PM-HV-ECU104applies a P-lock switching command signal to the P-ECU106, on the basis of the P-switch signal received from the P switch34, for switching the shift position of the transmission18from the non-P position to the P position. Further, the PM-HV-ECU104applies a shift position indication signal to the meter ECU108, for indicating the present shift position. In addition, the PM-HV-ECU104applies a parking lock indication control command signal (P-lock indication control command signal) to the P switch34, on the basis of a P-lock state signal received from the P-ECU106and indicative of the P-lock state (P position), for illuminating the P-position indicator light62in the P switch34, to indicate the P-lock state.

The electric-energy storage device46is a chargeable and dischargeable direct current power source, which is constituted by a secondary battery such as a nickel hydrogen battery or a lithium ion battery, for example. An electric energy stored in the electric-energy storage device46is supplied to the electric motor M through the inverter48, for accelerating the vehicle or for driving the vehicle with the electric motor M, for instance. When a regenerative brake is applied to the vehicle under deceleration, tan electric energy generated by the electric motor M is stored in the electric-energy storage device46through the inverter48.

The P-ECU106is configured to control the operation of the parking lock device16to establish or cancel the parking lock, for switching the shift position between the P position and the non-P positions, on the basis of the automatic P switching command signal and P switching command signals (P-lock switching command signal and P switching canceling command signal) received from the PM-HV-ECU104. The P-ECU106is further configured to make a determination as to whether the transmission18is placed in the P position or any one of the non-P positions, on the basis of the P-position signal received from the parking lock device16and indicative of its operating state, and to apply the P-lock state signal indicative of a result of the determination, to the PM-HV-ECU104, and the other control devices.

When the power supply state of the vehicle10is switched from the ALL-OFF state or ACC-ON state to the IG-ON state or READY-ON state, the P-ECU106implements the initial drive control of the parking lock device16, for controlling the detection of a P-wall position and a non-P-wall position for adequately obtaining the P-position signal and a non-P-position signal, as described below. Prior to implementing the series of initial control operations of the above-indicated parking lock device16upon switching of the power supply state of the vehicle10is switched from the ALL-OFF state or ACC-ON state to the IG-ON state or READY-ON state, the P-ECU106implements its own initial processing operation. It is noted that the P-ECU106is held in its power-off state when the present power supply state of the vehicle10is the ALL-OFF or ACC-ON state, and in its power-on state when the present power supply state of the vehicle10is the IG-ON or READY-ON state. The above-indicated power-off state of the P-ECU106is a state in which power is removed from the P-ECU106, while the above-indicated on-state of the P-ECU106is a state in which power is applied to the P-ECU106.

The meter ECU108is configured to apply a vehicle speed indication control command signal to the speedometer58in the combination meter56, for indicating the present vehicle speed V. For example, the meter ECU108determines a meter indication vehicle speed signal V by counting the number of rectangular waves of a vehicle speed pulse signal obtained on the basis of the wheel speed pulse signals received from the wheel speed sensors42. Then, the meter ECU108controls the speedometer58so as to illuminate the appropriate segments for indicating the present vehicle speed V, on the basis of the determined meter indication vehicle speed signal V. The meter ECU108is further configured to apply a shift position indication control command signal to the shift position indicator60in the combination meter56, on the basis of the shift position indication signal received from the PM-HV-ECU104, so that the shift position indicator60indicates the present shift position. For instance, the present shift position is indicated by illuminating an area of the shift position indicator60in which an indicium representative of the present shift position is located.

FIG. 2is the view showing an example of the shift operating device30provided as a switching device (manipulator) manually operable to select one of a plurality shift positions of the transmission18. This shift operating device30is provided with the shift lever32, which is a manually operable member which is disposed near a vehicle operator's seat and which is momentarily operable to the plurality of operating positions PSH. Namely, the manually operable member is of an automatic return type which is automatically returned to an original position (initial position) upon removal of an operating force from the member. The shift operating device30provided in the present embodiment is also provided with the separate P switch34which is disposed near the shift lever32and which is a manually operable member momentarily operable to place the shift position of the transmission18into the parking position (P position) for establishing the parking lock.

As shown inFIG. 2, the shift lever32has the three operatingpositions PSHconsisting of an operating position R, an operating position N and an operating position D which are arranged along a line extending in a front-rear direction or a vertical direction of the vehicle, that is, a longitudinal direction of the vehicle, and the two operating positions PSHconsisting of an operating position M and an operating position B which are arranged along another line parallel to the above-indicated line. The shift lever position signals indicative of the respective operating positions PSHare applied to the PM-HV-ECU104. The shift lever32is operable from one of the operating positions R, N and D to another in the longitudinal direction, and between the operating positions M and B in the longitudinal direction, and is further operable between the operating positions N and B in a direction orthogonal with the longitudinal direction, i.e., in a lateral direction of the vehicle.

The P switch34is a pushbutton of a momentary operation type, for example, and generates the P-switch signal to be generated to the PM-HV-ECU104each time the pushbutton is pressed by the user. When the P switch34is pressed while the shift position of the transmission18is placed in one of the non-P positions, for instance, the P-ECU106operates to switch the shift position to the P position, on the basis of the P switching command signal received from the PM-HV-ECU104, if predetermined conditions are satisfied. These conditions include a condition that the vehicle speed V is not higher than a P-lock permission value Vp. This P position is a parking position in which the power transmitting path in the transmission18is cut off, while at the same time the parking lock device16is placed in a parking lock state in which the rotation of the drive wheels14is mechanically prevented. The P switch34incorporates the P-position indicator light62, which is illuminated under the control of the PM-HV-ECU104, when the P-lock state signal received from the P-ECU106indicates the P position.

The operating position M of the shift lever32of the shift operating device30is the initial position (home position) of the shift lever32. The shift lever32placed in any operating position PSH(operating position R, N, D or B) other than the operating position M is returned to the operating position M by a mechanism such as a spring device, when the vehicle operator releases the shift lever32, that is, when the operating force acting on the shift lever32is removed. When the shift operating device30is operated to one of the operating positions PSH, the PM-HV-ECU104operates to establish the shift position corresponding to that operating position PSH, on the basis of the shift lever position signals indicative of the operating position PSHin question, and to command the shift position indicator60to indicate the present operating position PSH, that is, the established shift position of the transmission18.

The shift positions will be described. The R position established when the shift lever32is operated to the operating position R is a reverse-drive position in which a drive force is transmitted to the drive wheels14to drive the vehicle in the reverse direction. The N position established when the shift lever32is operated to the operating position N is a neutral position in which the power transmitting path in the transmission18is cut off. The D position established when the shift lever32is operated to the operating position D is a forward-drive position in which a drive force is transmitted to the drive wheels14to drive the vehicle in the forward direction. When the PM-HV-ECU104determines on the basis of the shift lever position signals that the shift lever32has been operated to one of the operating positions PSH(more specifically, operating position R, N or D) in which the parking lock of the vehicle should be canceled, while the shift position is P position, the PM-HV-ECU104applies the P canceling command signal to the P-ECU106to cancel the parking lock, if predetermined conditions are satisfied. These conditions include a condition that the vehicle is placed in the brake-on state BON. On the basis of the P canceling command signal received from the PM-HV-ECU104, the P-ECU106applies the P switching control command signal to the parking lock device16to cancel the parking lock. Then, the PM-HV-ECU104operates to establish the shift position corresponding to the presently established operating position PSH.

The B position established when the shift lever32is operated to the operating position B is a forward-deceleration-drive position (engine braking range) in which the drive wheels14are decelerated with an engine braking effect provided by a regenerative braking torque generated by the electric motor M during running of the vehicle in the D position, for example. The PM-HV-ECU104invalidates an operation of the shift lever32to the operating position B if the presently established shift position is other than the D position, and validates this operation of the shift lever32to the operating position B only if the presently established shift position is the D position. If the shift lever32is operated by the vehicle operator to the operating position B when the P position is presently established, for instance, the presently established P position is maintained.

In the shift operating device30according to the present embodiment, the shift lever32is returned to the operating position M upon removal of the operating force from the shift lever32. Accordingly, the presently established shift position cannot be recognized by visual observation of the operating position PSHof the shift lever32. For this reason, the shift position indicator60is disposed at a position for easy observation by the vehicle operator, so that the presently established shift position (which may be the P position) is indicated by the shift position indicator60.

In the shift operating device30of the present embodiment which adopts the so-called “shift-by-wire (SBW)” system, the shift lever is operated two-dimensionally in a first direction P1which is the above-indicated longitudinal direction, and a second direction P2which is the lateral direction intersecting the first direction P1(perpendicular to the first direction P1in the present example ofFIG. 2). Accordingly, the shift operating device30is provided with the shift sensor36as a first-direction detecting portion for detecting an operation of the shift lever in the above-indicated first direction P1, and the select sensor38as a second-direction detecting portion for detecting an operation of the shift lever in the above-indicated second direction P2, in order to supply the electronic control apparatus100with position sensor signals indicative of the presently established operating position PSH. Each of the shift sensor36and select sensor38applies a voltage signal as its output signal (a signal indicating the position of the shift lever) corresponding to the operating position PSHto the electronic control apparatus100, so that the electronic control apparatus100recognizes (determines) the operating position PSHon the basis of a voltage represented by the voltage signal. Namely, it is considered that the above-described first-direction detecting portion (shift sensor36) and second-direction detecting portion (select sensor38) cooperate with each other to constitute an operating-position detecting portion for detecting the operating position PSHof the shift operating device30.

An example of a manner of recognizing the operating position PSHwill be described. An output signal voltage VSFof the shift sensor36has different levels at respective first-direction first, second and third positions P1_1, P1_2and P1_3that are respectively the R operating position, the M and N operating positions and the B and D operating positions (, which levels fall within respective low, medium and high ranges, for example), and an output signal voltage VSLof the select sensor38has different levels at respective second-direction first and second positions P2_1and P2_2that are respectively the M and B operating positions and the R, N and D operating positions (, which levels fall within respective low and high ranges, for example). The PM-HV-ECU104detects the above-described different levels of the above-indicated output signal voltages VSFand VSL, and recognizes the operating positions PSH(R, N, D, M and B) on the basis of respective different combinations of the levels of the two output signal voltages.

FIG. 3is the view showing an arrangement of the parking lock device16provided to mechanically prevent rotation of the drive wheels14. As shown inFIG. 3, the parking lock device16is provided with a P-lock mechanism (parking-lock mechanism)66, an electrically operated actuator in the form of a P-lock drive motor (parking-lock drive motor)68, and an encoder70, and is operated to prevent a movement of the vehicle10, on the basis of control signals from the electronic control apparatus100.

The P-lock drive motor68, which corresponds to the electrically operated actuator provided according to the present invention, is a switched reluctance motor (SR motor), for instance, and is operated to operate the P-lock mechanism66, in the shift-by-wire system according to commands (control signals) received from the P-ECU106. The P-lock drive motor68is provided with a P-motor power source relay (not shown), so that an electric power is applied and removed to and from the P-lock drive motor68. The P-motor power source relay is configured to cut off the electric power to the P-lock drive motor68for inhibiting an operation of the P-lock drive motor68, when a supply voltage VMRapplied to the P-lock drive motor68is not higher than a predetermined relay switching value. On the other hand, the P-motor power source relay applies the electric power to the P-lock drive motor68for permitting the operation of the P-lock drive motor68, when the supply voltage VMRapplied to the P-lock drive motor68is higher than the predetermined relay switching value. The above-indicated relay switching value is preliminarily obtained by experimentation to determine whether the above-indicated supply voltage VMRis sufficiently high to enable the P-lock drive motor68to generate a torque sufficient to rotate or pivot a detent plate74with a high degree of stability.

The encoder70is a rotary encoder configured to generate A-phase, B-phase and Z-phase signals, for example, and is rotated together with the P-lock drive motor68. The encoder70detects a rotary motion of the SR motor and generates a signal representative of the rotary motion, that is, a pulse signal for obtaining a count (encoder count) corresponding to an amount of motion (angle of rotation) of the P-lock drive motor68. The pulse signal generated by the encoder70is applied to the P-ECU106, so that the P-ECU106recognizes the rotary motion of the SR motor, and controls energization of the SR motor to drive.

The P-lock mechanism66is provided with: a shaft72rotated by the P-lock drive motor68; the detent plate74rotated or pivoted by a rotary motion of the shaft72; a rod76moved by a rotary or pivotal motion of the detent plate74; a parking gear78rotated together with the drive wheels14; a parking lock pawl80for preventing a rotary motion of (for locking) the parking gear78; a detent spring82provided to limit the rotary or pivotal motion of the detent plate74for locking the shift position; and a roller84. A location at which the parking gear78is disposed is not limited, provided that the drive wheels14are locked when the parking gear78is locked. For instance, the parking gear78may be coaxially fixed to the output gear22of the transmission18(seeFIG. 1).

The detent plate74is operatively connected to a drive shaft of the P-lock drive motor68through the shaft72, and cooperates with the rod76, detent spring82, roller84, etc. to function as a parking lock positioning member which is operated by the P-lock drive motor68for switching between the parking lock position corresponding to the P position and the non-parking lock position corresponding to the shift positions other than the P position (corresponding to the non-P positions). The shaft72, detent plate74, rod76, detent spring82and roller84cooperate to function as a parking lock switching mechanism.

FIG. 3shows a state in which the non-parking lock position is established, that is, any one of the non-P positions is established as the shift position. In this state, the parking gear78is not locked by the parking lock pawl80, the rotation of the drive wheels14is not prevented by the P-lock mechanism66. A rotary or pivotal motion of the shaft72by the P-lock drive motor68in a direction indicated by an arrow C inFIG. 3from the position of this state causes the rod76to be pressed through the detent plate74in a direction indicated by an arrow A inFIG. 3, so that the parking lock pawl80is pivoted upwards in a direction indicated by an arrow B inFIG. 3by a tapered member86provided at one end of the rod76. As a result of the pivotal motion of the detent plate74, the roller84of the detent spring82is moved from one of two recesses formed in an upper end portion of the detent plate74, namely, moved from a non-parking lock position90(hereinafter referred to as a “non-P position90”: indicated inFIG. 4), along a crest88into the other of the two recesses, namely, to a parking-lock position92(hereinafter referred to as a “P position92”: indicated inFIG. 4). The roller84is provided on the detent spring82such that the roller84is rotatable about its axis. When the detent plate74has been rotated or pivoted to cause the roller84to be moved to the P position92, the parking lock pawl80has been pivoted upwards into meshing engagement with the parking gear78. Thus, the drive wheels14with which the parking gear78is rotated are mechanically locked, and the shift position is switched to the P position. For reducing a load acting on the P-lock mechanism66of the parking lock device16including the detent plate74, detent spring82and shaft72, upon switching of the shift position between the P position and the non-P position, the P-ECU106controls the amount of rotation of the P-lock drive motor68so as to reduce an impact which acts on the roller84of the detent spring82has been moved downwards along the crest88into each of the above-indicated two recesses. The parking lock device16is considered to have a locking position (P position) in which the roller84is located at the P position92for inhibiting the rotation of the drive wheels (vehicle wheels)14, and a non-lock position (non-P position) in which the roller84is located at the non-P position90for permitting the rotation of the drive wheels (vehicle wheels)14.

As described above, the parking lock device16is selectively switched to the above-indicated locking position or the above-indicated non-locking position, by the operation of the P-lock drive motor68on the basis of the command from the P-ECU106. In other words, the parking lock device16is switched according to a manual operation by the vehicle operator, between a locking state (P-lock state) in which a locking tooth in the form of the parking lock pawl80is in meshing engagement with rotary teeth in the form of the parking gear78rotated with the vehicle wheels (drive wheels14), and a non-locking state (non-P lock state) in which the locking state is canceled.

FIG. 4is the view showing an arrangement of the detect plate74. In each of the two recesses, one of two surfaces of the two recesses which is remote from the crest88is called a “wall”. Namely, the wall of each recess is positioned such that the wall comes into abutment on the roller84of the detent spring82when the roller84has been moved downwards along the crest88into the corresponding recess while the P-ECU106does not execute the following control. The wall at the P position92is called a “P wall”, while the wall at the non-P position90is called a “non-P wall”. When the roller84is moved from the P position92to the non-P position90, the P-ECU106controls the P-lock drive motor68so as to prevent the non-P wall94from abutting on the roller84. Described more specifically, the P-ECU106stops the rotary motion of the P-lock drive motor68before the non-P wall94comes into abutment on the roller84. An angular position at which the rotary motion of the P-lock drive motor68is stopped as described above is called a “target non-P angular position”. When the roller84is moved from the non-P position90to the P position92, the P-ECU106controls the P-lock drive motor68so as to prevent the P wall96from abutting on the roller84. Described more specifically, the P-ECU106stops the rotary motion of the P-lock drive motor68before the P wall96comes into abutment on the roller84. An angular position at which the rotary motion of the P-lock drive motor68is stopped as described above is called a “target P angular position”. With the P-lock drive motor68being thus controlled by the P-ECU106, the load acting on the P-lock mechanism66including the detent plate74, detent spring82and shaft72upon switching of the shift position can be considerably reduced. The reduction of the load makes it possible to reduce the size and cost of manufacture of the P-lock mechanism66.

FIG. 5is the view indicating a relationship between an angle of rotation of the P-lock drive motor68, that is, the encoder count, and the shift positions. The angle of rotation of the P-lock drive motor68provided to rotate the detent plate74is limited by the non-P wall94and the P wall96.FIG. 5schematically indicates the position of the P wall96(P-wall position) and the position of the non-P wall94(non-P-wall position), in connection with the control of the rotary motion of the P-lock drive motor68. The P-wall position and the non-P-wall position define a maximum angle of rotation of the P-lock drive motor68. A P-judgment position and a non-P-judgment position indicated inFIG. 5are predetermined angular positions of the detent plate74at which a judgment of the switching of the shift position is made. That is, an angular range from the P-judgment position to the P-wall position is a P-position range, while an angular range from the non-P-judgment position to the non-P-wall position is a non-P-position range. When the angle of rotation of the P-lock drive motor68detected by the encoder70is held within the P-position range, it is judged that the P position is established as the shift position. When the angle of rotation of the P-lock drive motor68is held within the non-P-position range, it is judged that the non-P position is established as the shift position. When the angle of rotation of the P-lock drive motor68is held within a range from the P-judgment position to the non-P-judgment position, it is judged that the shift position has not been established, or that the shift position is being switched. The above-described judgments are made by the P-ECU106.

As also indicated inFIG. 5, a target P angular position is set within the P-position range, and a target non-P angular position is set within the non-P-position range. The target P angular position is a position at which the P wall96does not abut on the roller84of the detent spring82during switching from the non-P position to the P position. This target P angular position is set with a predetermined amount of margin with respect to the P-wall position. This amount of margin is determined by taking account of an error due to a chronological change. The thus determined margin can absorb the chronological change after a considerably large number of operations of the parking lock device, making possible to avoid a mutual abutting contact of the P wall96and the roller84during switching of the shift position from the non-P position to the P position. Similarly, the target non-P angular position is a position at which the non-P wall94does not abut on the roller84of the detent spring82during switching from the P position to the non-P position. This target non-P angular position is set with a predetermined amount of margin with respect to the non-P wall position. This amount of margin is determined by taking account of an error due to a chronological change. The thus determined margin can absorb the chronological change after a considerably large number of operations of the parking lock device, making possible to avoid a mutual abutting contact of the non-P wall94and the roller84during switching of the shift position from the P position to the non-P position. The amounts of margin with respect to the non-P-wall position and the P-wall position need not be equal to each other, and may be determined to be different values depending upon a geometric configuration of the detent plate74, for instance.

In the parking lock device16arranged as described above, the P-ECU106obtains the encoder count corresponding to the angle of rotation of the P-lock drive motor68, on the basis of the pulse signal generated from the encoder70. Further, the P-ECU106resets the encoder count when the power supply state of the vehicle10is the ALL-OFF state or the ACC-ON state, for example, and updates the encoder count on the basis of the output signal of the encoder70when the power supply state is switched from the ALL-OFF or ACC-ON state to the IG-ON or READY-ON state. In the present embodiment, the encoder count is reduced when the rotation takes place in the direction toward the P-wall position (in the direction indicated by the arrow C inFIG. 3). Further, the P-ECU106controls the P-lock drive motor68such that the obtained encoder count coincides with predetermined target encoder counts (target count values). These target count values are preliminarily obtained by experimentation, for instance, as target values at which the target P angular position and target non-P angular position of the P-lock drive motor68are established.

The relationship between the angle of rotation of the P-lock drive motor68and the shift positions has been described. By the way, it is noted that the encoder70is a relative angular position sensor, and that the P-ECU106loses information on an absolute angular position of the P-lock drive motor68, for example, information on the above-described P-wall position and the above-described non-P-wall position when the P-ECU106is placed in the power-off state. Therefore, the P-ECU106is required to obtain the absolute angular position of the P-lock drive motor68when the P-ECU106is switched from the power-off state to the power-on state. A method of controlling the angular position of the P-lock drive motor68by using the encoder70which obtains the relative positional information will be described in detail.

FIG. 6is the state transition view indicating a series of initial controls of the parking lock device16upon switching of the P-ECU106from its power-off state to its power-on state as a result of an operation of the vehicle power switch40to change the power supply state of the vehicle10from the ALL-OFF state or ACC-ON state to the IG-ON state. When the PM-HV-ECU104switches the power supply state of the vehicle10from the ALL-OFF state or ACC-ON state to the IG-ON state [STATE A], as indicated inFIG. 6, the P-ECU106is switched from the power-off state to the power-on state, and implements an initial standby until a relay (P-motor power source relay) of the P-lock drive motor68has been closed [STATE B]. In this STATE B, the P-ECU106implements its own initial processing operation. Successively, the P-ECU106implements an initial drive control of the P-lock drive motor68, such as an excitation matching (phase matching) operation of the P-lock drive motor68, so as to assure an adequate control of the operation of the P-lock drive motor68[STATE C]. Then, the P-ECU106detects the above-described P-wall position or non-P-wall position to set a reference position [STATE D]. After the reference position has been set, the P-ECU106implements a normal control for establishing or canceling the parking lock on the basis of an operation of the P switch34or a shifting operation by the user [STATE E]. It is noted that the power supply state of the vehicle10cannot be switched to the READY-ON state in the event of an occurrence of a failure (for example, a failure of the P-lock drive motor68) in the process of transition to the above-indicated STATE E when the vehicle power switch40is operated to switch the power supply state to the READY-ON state. This aspect will be described by reference toFIGS. 11,12, etc. A method of control of the above-described detection of the P-wall position and non-P-wall position (in the above-indicated STATE D) will be described.

FIG. 7is the view for explaining the method of control to detect the P-wall position. In a P-wall position detecting control executed by the P-ECU106, the P-lock drive motor68is initially operated to rotate or pivot the detent plate74in the direction indicated by the arrow C inFIG. 3, that is, in the direction to cause the P wall96to move toward the roller84of the detent spring82, until the P wall96comes into abutting contact with the roller84. The P wall96functions as a member to limit the rotary motion of the P-lock drive motor68in the predetermined direction indicated by the arrow C inFIG. 3, at the P position92, namely, at a predetermined shift position in the form of the P position92. It is noted that the P wall96may be configured to cooperate with the detent spring82and roller84to constitute the above-indicated member to limit the rotary motion. Arrows F1, F2and F3inFIG. 7respectively indicate a torque generated by the P-lock drive motor68, a biasing force of the detent spring82, and a pressing force generated by the rod76and acting against the torque. Broken line indicates the position of the detent plate74′ at which the P wall96and the roller84abut on each other. Accordingly, the position of the P wall96can be detected by detecting this position of the detent plate74′.

After the P wall96abuts on the roller84, the detent plate74is pivoted from the position indicated by the broken line, by the torque F1of the P-lock drive motor68, in the direction indicated by the arrow C inFIG. 3, against the biasing force of the detent spring82. Consequently, the detent spring82is deflected, causing an increase of the biasing force F2and an increase of the pressing force F3generated by the rod76. The pivotal motion of the detent plate74is stopped when the torque F1becomes equal to a sum of the biasing force F2and the pressing force F3.

The P-ECU106determines a moment of stopping of the pivotal motion of the detent plate74on the basis of the obtained encoder count. For example, the P-ECU106determines that the pivotal motion of the detent plate74and the rotary motion of the P-lock drive motor68is stopped, if the smallest or largest value of the encoder count is kept unchanged for a predetermined length of time. Which one of the smallest and largest values is monitored is selected depending upon the encoder70. Irrespective of which one of the smallest and largest value is monitored, a fact that the smallest or largest value is kept unchanged for the predetermined length of time indicates that the detent plate74is kept stationary.

The P-ECU106detects, as a provisional P-wall position, the angular position of the detent plate74at which the rotary motion is stopped, and calculates an amount or angle of deflection of the detent spring82. For instance, this amount or angle of deflection is calculated according to a map which is preliminarily stored in the P-ECU106and which represents a relationship between the amount or angle of deflection and the voltage (supply voltage VMR) applied to the P-lock drive motor68. The P-ECU106calculates the amount or angle of deflection on the basis of the voltage applied to the P-lock drive motor68upon detection of the provisional P-wall position, and according to the map. It is noted that a map using the voltage VBATof the electric-energy storage device46in place of the applied voltage of the P-lock drive motor68may be used. The voltage VBATof the electric-energy storage device46is monitored by the P-ECU106and can be easily detected. In this case, the map must be prepared by taking account of an amount of drop of the voltage due to wire harness, etc. in a power supply line from the electric-energy storage device46to the P-lock drive motor68.

The P-ECU106compensates the provisional P-wall position on the basis of the amount or angle of deflection calculated according to the above-indicated map, and determines the compensated provisional P-wall position as the final P-wall position. The P-ECU106sets the encoder value at the final P-wall position, as a CNTP value. Then, the P-ECU106operates the P-lock drive motor68to rotate or pivot the detent plate74in the direction indicated by the arrow D inFIG. 3, that is, in the direction causing the P wall96to move away from the roller84of the detent spring82, until the encoder count is zeroed, so that the detent plate74is brought to the predetermined P position. This predetermined P position, which is set within the P-position range, is set such that a difference between the encoder counts at the P position and the final P-wall position is equal to the CNTP value. The predetermined P position may be set as the target P angular position. Thus, the target P angular position can be set by determining the final P-wall position. It is noted that the map representative of the relationship between the applied voltage and the amount or angle of deflection may be replaced by a map representative of an output torque of the P-lock chive motor68and the amount or angle of deflection. Instead of calculating the amount or angle of deflection with the map, a sensor may be used to detect the amount or angle of deflection.

FIG. 8is the view for explaining a method of control to detect the non-P-wall position. In a non-P-wall position detecting control executed by the P-ECU106, the P-lock drive motor68is initially operated to rotate or pivot the detent plate74in the direction indicated by the arrow D inFIG. 3, that is, in the direction to cause the non-P wall94to move toward the roller84of the detent spring82, until the non-P wall94comes into abutting contact with the roller84. The non-P wall94functions as a member to limit the rotary motion of the P-lock chive motor68in the predetermined direction indicated by the arrow D inFIG. 3, at the non-P position90, namely, at a predetermined shift position in the form of the non-P position90. It is noted that the non-P wall94may be configured to cooperate with the detent spring82and roller84to constitute the above-indicated member to limit the rotary motion. Arrows F1, F2and F3inFIG. 8respectively indicate a torque generated by the P-lock drive motor68, a biasing force of the detent spring82, and a tensile force generated by the rod76and acting against the torque. Broken line indicates the position of the detent plate74″ at which the non-P wall94and the roller84abut on each other. Accordingly, the position of the non-P wall94can be detected by detecting this position of the detent plate74″.

After the non-P wall94abuts on the roller84, the detent plate74is pivoted from the position indicated by the broken line, by the torque F1of the P-lock drive motor68, in the direction indicated by the arrow D inFIG. 3, against the biasing force F2of the detent spring82. Consequently, the detent spring82is tensioned, causing an increase of the biasing force F2and an increase of the tensile force F3generated by the rod76. The pivotal motion of the detent plate74is stopped when the torque F1becomes equal to a sum of the biasing force F2and the tensile force F3.

The P-ECU106determines a moment of stopping of the pivotal motion of the detent plate74on the basis of the obtained encoder count. For example, the P-ECU106determines that the pivotal motion of the detent plate74and the rotary motion of the P-lock drive motor68is stopped, if the smallest or largest value of the encoder count is kept unchanged for a predetermined length of time.

The P-ECU106detects, as a provisional non-P-wall position, the angular position of the detent plate74at which the rotary motion is stopped, and calculates an amount of elongation of the detent spring82. For instance, this amount of elongation is calculated according to a map which is preliminarily stored in the P-ECU106and which represents a relationship between the amount of elongation and the voltage applied to the P-lock drive motor68. The P-ECU106calculates the amount of elongation on the basis of the voltage applied to the P-lock drive motor68upon detection of the provisional non-P-wall position, and according to the map.

The P-ECU106compensates the provisional non-P-wall position on the basis of the amount of elongation calculated according to the above-indicated map, and determines the compensated provisional non-P-wall position as the final non-P-wall position. The P-ECU106sets the encoder value at the final non-P-wall position, as a CNTCP value. Then, the P-ECU106operates the P-lock drive motor68to rotate or pivot the detent plate74in the direction indicated by the arrow C inFIG. 3, that is, in the direction causing the non-P wall94to move away from the roller84of the detent spring82, until the encoder count is reduced by a predetermined value to a value CP, so that the detent plate74is brought to the predetermined non-P position. This predetermined non-P position, which is set within the non-P-position range, is set such that a difference between the encoder counts at the non-P position and the final non-P-wall position is equal to a predetermined value. The predetermined non-P position may be set as the target non-P angular position. Thus, the target non-P angular position can be set by determining the final non-P-wall position. It is noted that the map representative of the relationship between the applied voltage and the amount of elongation may be replaced by a map representative of the output torque of the P-lock drive motor68and the amount of elongation. Instead of calculating the amount of elongation with the map, a sensor may be used to detect the amount of elongation.

As described above, the reference position can be set by detecting the wall position corresponding to the shift position to be established, on the basis of the obtained encoder count during a rotary motion (operation) of the P-lock drive motor68in the direction of limitation of the rotary motion, while the P-ECU106is placed in the power-on state in which the IG-ON state is established as the power supply state of the vehicle10.

FIG. 9is the view for explaining waveforms of an energization command pulse applied to the P-lock drive motor68. In a normal control of switching of the shift position, an energization command pulse having a relatively long period of a high (ON) state is applied to the P-lock drive motor68. On the other hand, an energization command pulse to be applied to the P-lock drive motor68in the wall position detecting controls executed by the P-ECU106is formulated so that an output of the P-lock drive motor68per unit time in the wall position detecting controls is smaller than that in the normal control of switching of the shift position. Described more specifically, the energization command pulse to be applied to the P-lock drive motor68has a relatively short period of an ON state. An impact upon abutting contact between the wall (non-P wall94or P wall96) and the roller84can be reduced by reducing the operating speed of the P-lock drive motor68in the wall position detecting controls. It is noted that each of three U, V and W phases of the P-lock drive motor68is energized when an energization command for each phase is in the ON state while the energization command pulse indicated inFIG. 9is in the ON state.

As described above, the P-ECU106is configured to first implement its own initial processing operation and then implement the initial control to detect the wall positions of the parking lock device16, when the vehicle power switch40is operated to switch the power supply state of the vehicle10to the IG-ON state or READY-ON state, that is, when the P-ECU106is switched from its power-off state to its power-on state. Namely, the initial control for the parking lock device16includes the initial drive control of the P-lock drive motor68, and the following detection of the above-indicated P-wall position and non-P-wall position to set the reference positions. That is, the practical maximum angle of rotation of the P-lock drive motor68which is defined by and between the detected P-wall position and non-P-wall position can be measured by implementing the wall position detecting controls to detect the wall position corresponding to one of the two shift positions and then the wall position corresponding to the other shift position. The absolute angular position of the P-lock drive motor68can be obtained by detecting the wall positions, so that the target angular positions can be set.

If the P-ECU106detects that the P-lock drive motor68is not operable in the above-described initial drive control of the P-lock drive motor68implemented prior to the above-described wall position detecting controls, for instance, the P-ECU106which has recognized a failure of the drive motor68does not, as a principle, implement the above-described wall position detecting controls that require an operation of the P-lock drive motor68and inhibits the transition of the power supply state of the vehicle10to the READY-ON state. The failure of the P-lock drive motor68may be a hardware defect of the P-lock drive motor68per se, or a drop of the supply voltage VMRof the P-lock drive motor68(hereinafter referred to as “P-motor supply voltage VMR”) below the lowest value (for example, the above-indicated relay switching value”) required to enable the drive motor68to be operated. An example of the failure of the P-lock drive motor68due to the drop of the P-motor supply voltage VMRdetected by the P-ECU106will be described by reference toFIG. 10.

FIG. 10is the time chart for explaining the case where a battery voltage which is the P-motor supply voltage VMRis gradually lowered from 12V as a result of continuation of the power-on state of the P-ECU106while the engine12is kept at rest. It is noted that the “P-motor” indicated inFIG. 10is the P-lock drive motor68.

At a point of time t1indicated inFIG. 10, the P-motor supply voltage VMRhas been lowered to the above-indicated relay switching voltage (e.g., 6.6V). After this point of time t1, therefore, the above-described P-motor power source relay cuts off a power supply to the P-lock drive motor68, so that the P-lock drive motor68is inoperable.

The P-motor supply voltage VMRis further lowered after the point of time t1, and an instantaneous power removal due to a noise, for instance, causes a drop of the P-motor supply voltage VMRat a point between points of time t2and t3, below an ECU stop voltage (e.g., 5.8V) which is the lowest voltage value above which the P-ECU106can be placed in the power-on state. As a result, the P-ECU106is temporarily placed in the power-off state (ECU stop state) between the points of time t2and t3. After the point of time t3, the P-motor supply voltage VMRis raised above the above-indicated ECU stop voltage, so that the P-ECU106is restored to its power-on state.

At a point of time t4after the P-ECU106is switched from the power-off state back to the power-on state, the P-motor supply voltage VMRis higher than a diagnostic voltage (e.g., 6.0V) for diagnosis of the P-lock drive motor68which is set higher than the above-indicated ECU stop voltage and lower than the above-indicated relay switching value, so that the P-ECU106implements a diagnosis of the P-lock drive motor68, namely, determines whether the P-lock drive motor68is operable or not. In the example ofFIG. 10, after the point of time t4the P-motor supply voltage VMRis kept below the above-indicated relay switching voltage value, and the P-lock drive motor68is not operable, so that the P-ECU106determines that the P-lock drive motor68fails to operate. Namely, if the P-motor supply voltage VMRafter the P-ECU106is switched from the power-off state to the power-on state is held in a range (indicated by a hatched area A01inFIG. 10) between the above-indicated diagnostic voltage and the above-indicated relay switching voltage value, the P-ECU106determines that the P-lock drive motor68is not operable due to the drop of the P-motor supply voltage VMR, even in the absence of a hardware defect of the P-lock drive motor68.

Where the P-lock drive motor68is not operable due to the drop of the P-motor supply voltage VMR, as described above, the P-lock drive motor68may be made operable with a rise of the P-motor supply voltage VMR, as a result of external charging of the battery. In the present embodiment, the P-ECU106can be switched to the READY-ON state if the P-motor supply voltage VMRis raised after the P-ECU106once determines that the P-lock drive motor68is not operable. Major control functions of the P-ECU106will be described.

FIG. 11is the functional block diagram showing the major functions of the P-ECU106. As shown inFIG. 11, the P-ECU106is provide with supply voltage detection determining means130, actuator operation determining means132, passenger operation determining means134, actuator operation permitting means136, wall position detection controlling means138and vehicle run permitting means140.

The supply voltage detection determining means130is configured to detect the P-motor supply voltage VMRfrom time to time after the P-ECU106is switched from the power-off state to the power-on state. The supply voltage detection determining means130determines whether the detected P-motor supply voltage VMRis equal to or higher than a predetermined threshold supply voltage value V1MR, in other words, whether the P-motor supply voltage VMRis lower than the threshold supply voltage value V1MR. The threshold supply voltage value V1MRis a lower limit of the P-motor supply voltage VMR, which may be, for instance, a guaranteed lower limit voltage value (e.g., 8V) which is higher than the above-indicated relay switching value and above which a normal operation of the P-lock drive motor68is guaranteed.

When the P-motor supply voltage VMRis lower than the above-indicated threshold supply voltage value V1MR, for example, the supply voltage detection determining means130determines that the P-motor supply voltage VMRis lower than the above-indicated threshold supply voltage value V1MR. If the P-motor supply voltage VMRis raised from a value lower than the above-indicated threshold supply voltage value V1MR, to a value not lower than threshold supply voltage value V1MR, the supply voltage detection determining means130determines that the P-motor supply voltage VMRis raised from the value lower than the above-indicated threshold supply voltage value V1MR, to the value not lower than threshold supply voltage value V1MR.

The actuator operation determining means132is configured to perform a failure diagnosis to determine whether the P-lock drive motor68is operable or not. Described more specifically, the actuator operation determining means132performs the above-described failure diagnosis in the STATE C indicated inFIG. 6, for example, when the P-ECU106is switched from the power-off state to the power-on state. The actuator operation determining means132performs the above-described failure diagnosis also when the P-motor supply voltage VMRis raised from a value lower than the above-described threshold supply voltage value V1MR, to a value not lower than the threshold supply voltage value V1MR, after the determination that the P-lock drive motor68is inoperable is obtained in the above-described failure diagnosis. The determination as to whether the P-motor supply voltage VMRis raised from the value lower than the above-described threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MRis made by the above-described supply voltage detection determining means130. To perform the above-described failure diagnosis, the actuator operation determining means132commands the P-lock drive motor68to be operated by a predetermined angle in the directions indicated by the arrows C and D inFIG. 3, and determines that the P-lock drive motor68is not operable, if a pulse signal is not generated by the encoder70while the P-lock drive motor68is commanded to be operated in both of the above-indicated directions. The determination as to whether the P-lock drive motor68is operable may be made by any other method or by using a sensor, for instance.

The passenger operation determining means134is configured to determine whether a predetermined manual operation has been performed by a vehicle passenger. Described more specifically, the predetermined manual operation is an operation to enable the vehicle10to be ready for running, that is, an operation (hereinafter referred to as a “vehicle run permitting operation”) to switch the power supply state of the vehicle10to the above-described vehicle-run-ready state (READY-ON state). Information as to whether this operation has been performed is obtained from the PM-HV-ECU104.

The actuator operation permitting means136is configured to permit an operation of the P-lock drive motor68when the actuator operation determining means132obtains, in the above-described failure diagnosis, the determination that the P-lock drive motor68is operable. This permission makes it possible to operate the P-lock drive motor68. When the actuator operation determining means132obtains, in the above-described failure diagnosis, the determination that the P-lock drive motor68is not operable, on the other hand, the actuator operation permitting means136inhibits an operation of the P-lock drive motor68. This inhibition makes it impossible to operate the P-lock drive motor68.

The actuator operation permitting means136may permit an operation of the P-lock drive motor68even when the actuator operation determining means132obtains in the above-described failure diagnosis the determination that the P-lock drive motor68is not operable. Described more specifically, the actuator operation permitting means136permits an operation of the P-lock drive motor68when the P-motor supply voltage VMRis raised from a value lower than the threshold supply voltage value V1MRto a value not lower than the threshold supply voltage value V1MR, after the actuator operation determining means132obtains in the above-described failure diagnosis the determination that the P-lock drive motor68is not operable. In this case, the actuator operation permitting means136permits the operation of the P-lock chive motor68after the inhibition of the operation, that is, the actuator operation permitting means136first cancels the inhibition and then gives the permission to avoid being complicated.

As described above, the actuator operation permitting means136permits the operation of the P-lock drive motor68if the P-motor supply voltage VMRis raised from the value lower than the threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MR, after the actuator operation determining means132obtains in the failure diagnosis the determination that the P-lock drive motor68is not operable. However, an additional condition may be used by the actuator operation permitting means136to permit the operation. For instance, the actuator operation permitting means136may permit the operation of the P-lock drive motor68only if the actuator operation determining means132obtains the determination that the P-lock drive motor68is operable, on the basis of the failure diagnosis performed after the P-motor supply voltage VMRis raised from the value lower than the threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MR. The actuator operation permitting means136may permit the operation of the P-lock drive motor68under an additional condition that the above-indicated vehicle run permitting operation has been performed, after the P-motor supply voltage VMRis raised from the value lower than the threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MR. The actuator operation permitting means136may permit the operation of the P-lock drive motor68under a condition of combination of the above-described conditions. The determination as to whether the P-motor supply voltage VMRis raised from the value lower than the threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MRis made by the above-described supply voltage detection determining means130, and the determination as to whether the above-indicated vehicle run permitting operation has been performed is made by the above-described passenger operation determining means134.

The wall position detection controlling means138is configured to implement the above-described P-wall position detecting control and non-P-wall position detecting control, for detecting the above-indicated P-wall position and non-P-wall position, when the actuator operation permitting means136permits an operation of the P-lock drive motor68after the P-ECU106is switched from the power-off state to the power-on state. When the actuator operation permitting means136inhibits an operation of the P-lock drive motor68, on the other hand, the wall position detection controlling means138does not implement the above-described P-wall position detecting control and non-P-wall position detecting control.

The vehicle run permitting means140is configured to permit the PM-HV-ECU104to switch the power supply state of the vehicle10to the above-indicated vehicle-run-ready state (READY-ON state), after the wall position detection controlling means138has detected the above-indicated P-wall position and non-P-wall position. With this permission given by the vehicle run permitting means140, the PM-HV-ECU104switches the power supply state of the vehicle10to the above-indicated vehicle-run-ready state (READY-ON state) when the above-described vehicle run permitting operation is performed or if the vehicle run permitting operation has been performed. Namely, the power supply state of the vehicle10is switched to the above-indicated vehicle-run-ready state (READY-ON state) when the above-indicated vehicle run permitting operation has been performed after the actuator operation permitting means136permits an operation of the P-lock drive motor68.

When the actuator operation permitting means136inhibits an operation of the P-lock drive motor68, on the other hand, the vehicle run permitting means140does not permit the PM-HV-ECU104to switch the power supply state of the vehicle10to the above-indicated vehicle-run-ready state (READY-ON state). Without the permission given by the vehicle running permitting means140, the PM-HV-ECU104does not switch the power supply state of the vehicle10to the above-indicated vehicle-run-ready state (READY-ON state). If the above-indicated vehicle run permitting operation has been performed, the PM-HV-ECU104switches the power supply state to the above-indicated power-on state (IG-ON state) rather than the above-indicated vehicle-run-ready state (READY-ON state).

FIG. 12is the flow chart illustrating a major control operation of the P-ECU106of the present embodiment, that is, a control operation to inhibit and permit an operation of the P-lock drive motor68. This control operation is performed alone, or concurrently with other control operations, when the P-ECU106is switched from the power-off state to the power-on state. For example, the P-ECU106is switched from the power-off state to the power-on state, when the power supply state of the vehicle10is switched from the ALL-OFF state or ACC-ON state to the IG-ON state by operating the vehicle power switch40, or when the P-motor supply voltage VMRis raised to a value not lower than the above-indicated ECU stop voltage (indicated in the time chart ofFIG. 10) after instantaneous power removal from the P-ECU106due to a noise while the P-motor supply voltage VMRis lower than the ECU stop voltage, as illustrated inFIG. 13. The “optional device voltage” indicated inFIG. 13is a voltage applied to optional devices such as an air conditioner and the audio device64. In the present embodiment, the optional device voltage is equal to the above-indicated battery voltage, and is therefore equal to the above-indicated P-motor supply voltage VMR.

When the P-ECU106is switched from the power-off state to the power-on state, step SA1(hereinafter “step” being omitted) of the control operation inFIG. 12is implemented. In SA1, the P-motor supply voltage VMRis detected and stored from time to time. Namely, an operation to detect and store the P-motor supply voltage VMRis initiated in SA1, and continued during implementation of the following steps. SA1is followed by SA2. SA1corresponds to the supply voltage detection determining means130.

SA2is provided to perform the above-described failure diagnosis as to whether the P-lock drive motor68is operable. If an affirmative determination is obtained in SA2, that is, if the P-lock drive motor68is operable, the control flow goes to SA3. If a negative determination is obtained in SA2, the control flow goes to SA7. SA2corresponds the actuator operation determining means132.

SA3is provided to permit an operation of the P-lock drive motor68. SA3is followed by SA4. SA3corresponds to the actuator operation permitting means136.

SA4is provided to implement the above-described P-wall position detecting control and the above-described non-P-wall position detecting control, for detecting the above-indicated P-wall position and the above-indicated non-P-wall position. After the detection of the above-indicated P-wall position and non-P-wall positions (wall abutment learning) is completed, the control flow goes to SA5. SA4corresponds to the wall position detection controlling means138.

SA5is provided to determine whether the operation to switch the power supply state of the vehicle10to the READY-ON state (vehicle run permitting operation) has been performed by the vehicle passenger, that is, a start switch has been operated by the passenger. An affirmative determination in SA5is made also when the above-indicated start switch is operated upon switching of the P-ECU106to its power-on state. The control flow goes to SA6when the affirmative determination is made in SA5, i.e., the start switch is operated. SA5corresponds to the passenger operation determining means134.

SA6is provided to permit the PM-HV-ECU104to switch the power supply state of the vehicle10to the above-described vehicle-run-ready state (READY-ON state). According to this permission, the PM-HV-ECU104switches the above-indicated power supply state to the above-described vehicle-run-ready state (READY-ON state). SA6corresponds to the vehicle run permitting means140.

SA7is provided to determine that the P-lock drive motor68is in an abnormal state (fails to operate), and inhibit the operation of the P-lock drive motor68. SA7corresponds to the actuator operation permitting means136. SA7is followed by SA8.

SA8is provided to determine whether the P-motor supply voltage VMRis excessively low, more specifically, whether the P-motor supply voltage VMRis lower than the above-indicated threshold supply voltage value V1MR. If an affirmative determination is obtained in SA8, that is, if the P-motor supply voltage VMRis lower than the above-indicated threshold supply voltage value V1MR, the P-lock drive motor68which was determined in SA2to become inoperable is considered to become inoperable due to an excessive drop of the P-motor supply voltage VMR. In this case, the control flow goes to SA9. If a negative determination is obtained in SA8, the inoperable state is not considered to be caused by the above-indicated P-motor supply voltage VMR, but is considered to be caused by a hardware defect of the P-lock drive motor68per se. In this case, the control flow goes to SA16. SA8corresponds to the supply voltage detection determining means130.

SA9is provided to memorize “an occurrence of abnormality (a failure) of the P-lock drive motor68due to an excessive low supply voltage”. SA9is followed by SA10.

SA10is provided to determine whether the P-motor supply voltage VMR(=optional device voltage) is raised to a value not lower than the threshold supply voltage value V1MR. If the P-motor supply voltage VMR(=optional device voltage) is raised to a value not lower than the threshold supply voltage value V1MR, the control flow goes to SA11. SA10corresponds to the supply voltage detection determining means130.

SA11is provided to determine whether the above-indicated start switch has been operated (the vehicle run permitting operation has been performed) by the vehicle passenger after the affirmative determination is obtained in SA10, that is, after the P-motor supply voltage VMRis raised to a value not lower than the threshold supply voltage value V1MR. If an affirmative determination is obtained in SA11, that is, if the above-indicated start switch has been operated after the affirmative determination is obtained in SA10, the control flow goes to SA12. SA11corresponds to the passenger operation determining means134.

SA12is provided to cancel (clear) the determination of abnormality of the P-lock drive motor68in SA7, and to cancel the inhibition of an operation of the P-lock drive motor68. SA12corresponds to the actuator operation permitting means136. SA12is followed by SA13.

SA13is provided to perform the above-described failure diagnosis as to whether the P-lock drive motor68is operable. Since the failure diagnosis was once performed in SA2, the failure diagnosis in SA13is the second failure diagnosis. If an affirmative determination is obtained in SA13, that is, if the P-lock drive motor68is operable, the control flow goes to SA14. If a negative determination is obtained in SA13, the control flow goes to SA16. SA13corresponds to the actuator operation determining means132.

SA14is provided to permit an operation of the P-lock drive motor68. SA14is followed by SA15. SA14corresponds to the actuator operation permitting means136.

SA15is provided to implement the above-described P-wall position detecting control and the above-described non-P-wall position detecting control, for detecting the above-indicated P-wall position and the above-indicated non-P-wall position. After the detection of the above-indicated P-wall position and non-P-wall positions (wall abutment learning) is completed, the control flow goes to SA6. SA15corresponds to the wall position detection controlling means138.

SA16is provided to determine that the P-lock drive motor68per se suffers from a hardware defect, that is, fails to operate, and to inhibit an operation of the P-lock drive motor68, or maintain the inhibition of the operation if the operation has already been inhibited. SA16corresponds to the actuator operation permitting means136. SA16is followed by SA17. [0101] SA17is provided to inhibit the PM-HV-ECU104to switch the power supply state of the vehicle10to the above-described vehicle-run-ready state (READY-ON state). According to this inhibition, the PM-HV-ECU104does not switch the power supply state of the vehicle10to the vehicle-run-ready state (READY-ON state). For instance, the PM-HV-ECU104maintains the power-on state (IG-ON state). SA17corresponds to the vehicle run permitting means140.

FIG. 14is the flow chart illustrating a major control operation of a prior art P-ECU, for comparison with that illustrated in the flow chart ofFIG. 12. Like the control operation of the flow chart ofFIG. 12, the control operation of this flow chart is performed when the P-ECU is switched from the power-off state to the power-on state, as illustrated inFIG. 13.

In SB1ofFIG. 14, the determination is made as to whether the P-lock drive motor68is operable. If the P-lock drive motor68is operable, SB2-SB4are implemented. If the P-lock drive motor68is not operable, SB5-SB7are implemented.

SB2is provided to implement the wall abutment learning, as in SA4ofFIG. 12. After the wall abutment learning is completed, SB3is implemented to make the determination as to whether the above-indicated start switch has been operated, as in SA5ofFIG. 12. If an affirmative determination is obtained in SB3, SB4is implemented to permit the PM-HV-ECU104to switch the power supply state of the vehicle10to the READY-ON state. According to this permission, the PM-HV-ECU104switches the power supply state to the READY-ON state.

On the other hand, SB5is provided to determine that the P-lock drive motor68is abnormal (fails to operate), as in SA7ofFIG. 12. Then, the control flow goes to SB6to determine that the motor failure takes place, as in SA16ofFIG. 12. Then, the control flow goes to SB7to inhibit the PM-HV-ECU104to switch the power supply state of the vehicle10to the READY-ON state. According to this inhibition, the PM-HV-ECU104does not switch the power supply state of the vehicle10to the READY-ON state, even when the above-indicated start switch is operated. For example, the PM-HV-ECU104maintains the IG-ON state.

As described above, the prior art control operation illustrated inFIG. 14has a problem that once the P-lock drive motor68is determined to be inoperable, the power supply state of the vehicle10cannot be switched to the READY-ON state even after the P-lock drive motor68becomes operable again as a result of a rise of the P-motor supply voltage VMRto a sufficiently high value, unless the P-ECU is switched back to the power-on state. The control operation according to the present embodiment illustrated inFIG. 12does not suffer from the prior art problem described above.

The present embodiment is configured such that the actuator operation determining means132performs the failure diagnosis as to whether the P-lock drive motor (actuator)68is operable or not, and the actuator operation permitting means136permits an operation of the P-lock drive motor68if the P-motor supply voltage VMRis raised from a value lower than the above-indicated threshold supply voltage value V1MRto a value not lower than the threshold supply voltage value V1MRafter the actuator operation determining means132obtains, in the failure diagnosis, the determination that the P-lock drive motor68is inoperable. If the P-motor supply voltage VMRis raised from the value lower than the above-indicated threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MR, the P-lock drive motor68which was determined to be inoperable prior to this rise of the P-motor supply voltage VMRis considered to become inoperable due to an excessive drop of the P-motor supply voltage VMR. Further, the P-lock drive motor68is considered to be operable after the rise of the P-motor supply voltage VMR. Accordingly, an adequate control processing can be performed with respect to the P-lock drive motor68, in consideration of a possibility that the P-lock drive motor68becomes operable, more specifically, a possibility that the P-motor supply voltage VMRis raised to a sufficiently high value, after the previous determination that the P-lock drive motor68is inoperable. The adequate control processing reduces a loss of a vehicle operating comfort felt by the vehicle operator. For example, the adequate control processing is a normal control of the P-lock drive motor68to be implemented where the P-lock drive motor68is normally operable. On the other hand, an inadequate control processing with respect to the P-lock drive motor68may be a control of the P-lock drive motor68to be implemented in the event of a failure of the P-lock drive motor68, for instance, a control to inhibit an operation of the P-lock drive motor68, based on an incorrect recognition that the P-lock drive motor68is inoperable, while in fact the P-lock drive motor68is operable.

The present embodiment is further configured such that the threshold supply voltage value V1MRis a lower limit of the P-motor supply voltage VMR, so that it is possible to more adequately determine that the P-lock drive motor68which was determined to be inoperable become inoperable due to an excessive drop of the P-motor supply voltage VMR.

The present embodiment is also configured such that the actuator operation determining means132performs the above-described failure diagnosis as a second failure diagnosis if the P-motor supply voltage VMRis raised from the value lower than the above-described threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MRafter the determination that the P-lock drive motor68is inoperable is obtained in the first failure diagnosis, and such that the actuator operation permitting means136may permit the operation of the P-lock drive motor68only if the actuator operation determining means132obtains in the second failure diagnosis the determination that the above-described P-lock drive motor68is operable. Accordingly, it is possible to permit the operation of the P-lock drive motor68after it is confirmed that the P-lock drive motor68becomes operable as a result of the rise of the P-motor supply voltage VMRto the value not lower than the threshold supply voltage value V1MR.

The present embodiment is further configured such that the actuator operation permitting means136permits the operation of the P-lock drive motor68under a condition that the above-described vehicle run permitting operation has been performed by the vehicle passenger after the rise of the P-motor supply voltage VMRfrom the value lower than the threshold supply voltage value V1MRto the value not lower than the threshold supply voltage value V1MRafter the actuator operation determining means132obtains in the above-described failure diagnosis the determination that the P-lock drive motor68is inoperable. Accordingly, the P-lock drive motor68is operated after the operation by the vehicle passenger, preventing a discomfort that would otherwise be felt by the vehicle passenger upon operation of the P-lock drive motor68while the vehicle passenger recognizes that the P-lock drive motor68is inoperable.

In the present embodiment, the predetermined manual operation by the vehicle passenger detected by the passenger operation determining means134is the operation (vehicle run permitting operation) to switch the power supply state of the vehicle10to the above-indicated vehicle-run-ready state (READY-ON state). The detection of the vehicle run permitting operation has an advantage that the vehicle passenger is not required to perform a special operation to permit the operation of the P-lock drive motor68, since the vehicle run permitting operation is an operation required to start running of the vehicle.

The present embodiment is also configured such that the actuator operation permitting means136inhibits the operation of the P-lock drive motor68if the actuator operation determining means132obtains in the above-described failure diagnosis the determination that the P-lock drive motor68is inoperable. The actuator operation permitting means136cancels an inhibition of the operation of the P-lock drive motor68, before permitting the operation of the P-lock drive motor68after the inhibition. Accordingly, it is possible to avoid a complicated control of permitting and inhibiting the operation of the P-lock drive motor68.

The present embodiment is also configured to implement SA8ofFIG. 12for making the determination as to whether the P-motor supply voltage VMRis excessively low, after the determination in SA2that the P-lock drive motor68is inoperable, so that it is possible to correctly determine whether the inoperable state of the P-lock drive motor68determined in SA2is caused by an excessive drop of the P-motor supply voltage VMRor a hardware defect of the P-lock drive motor68per se.

The present embodiment is further configured to implement SA13ofFIG. 12for making the second failure diagnosis after the determination in SA10that the P-motor supply voltage VMRis raised to a value not lower than the threshold supply voltage value V1MR, so that the load of the P-lock drive motor68, etc. is reduced, as compared with the load where the failure diagnosis is performed at a regular interval irrespective of the P-motor supply voltage VMR, for determining whether the P-lock drive motor68is operable or not.

The present embodiment is also configured to use the same value V1MRas the threshold for diagnosing the P-motor supply voltage VMRin both of SA8and SA10ofFIG. 12, eliminating a need for setting different threshold values to be used in the respective two steps.

While the embodiment of this invention has been described in detail by reference to the drawings, it is to be understood that the invention may be otherwise embodied.

For example, the battery for supplying an electric energy to the P-lock drive motor68in the illustrated embodiment may be provided in the electric-energy storage device46, or provided as an electric power source separate from the electric-energy storage device46in the vehicle10.

While the threshold supply voltage value V1MRused in the illustrated embodiment is set to be the above-indicated guaranteed lower limit voltage value of the P-lock drive motor68, the threshold supply voltage value V1MRmay be set otherwise. For instance, the threshold supply voltage value V1MRmay be set to be the above-indicated relay switching voltage value which is a lower limit when electric power is supplied to the P-lock drive motor68, above which the P-lock drive motor68is operable.

Although the predetermined manual operation by the vehicle passenger which is detected by the passenger operation determining means134in the illustrated embodiment is the above-indicated vehicle run permitting operation, the predetermined manual operation is not limited to this vehicle run permitting operation, and may be other manual operations performed by the vehicle passenger.

In the illustrated embodiment, the PM-HV-ECU104switches the power supply state of the vehicle10to the READY-ON state from any other state, when the PM-HV-ECU104receives the above-described power switch signal in the brake-on state BONwhile the P position is established. However, the power supply state may be switched to the READY-ON state when another operation by the vehicle passenger other than the operation performed to generate the power switch signal is performed, or when such another operation is performed concurrently with the operation to generate the power switch signal.

Although SA11is implemented prior to SA14in the flow chart ofFIG. 12in the illustrated embodiment, the flow chart may be modified such that SA11is not implemented prior to SA14, but is implemented between SA14and SA6.

In the illustrated embodiment, the flow chart ofFIG. 12includes SA13. However, the flow chart may be modified so as to eliminate SA13so that SA12is followed by SA14.

In the illustrated embodiment, the flow chart ofFIG. 12includes SA9. However, SA9may be eliminated.

In the illustrated embodiment, the actuator operation determining means132is configured to perform the failure diagnosis when the P-ECU106is switched from the power-off state to the power-on state, for instance. However, the failure diagnosis may be performed in other cases, for example, when the PM-HV-ECU104or P-ECU106detects any failure. Alternatively, the failure diagnosis may be performed at a predetermined time interval.

It is to be understood that the foregoing embodiment and modifications have been described for illustrative purpose only, and that the present invention may be embodied with various other changes and improvements which may occur to those skilled in the art.

NOMENCLATURE OF REFERENCE SIGNS

16: Parking lock device