Control apparatus for a vehicle

Providing a control apparatus for a vehicle having a parking lock device 50 which is placed in its released state with a hydraulic pressure generated by an oil pump 58 operated by an engine 26, which control apparatus permits reduction of a risk of unintended releasing of the parking lock device 50 upon occurrence of an operating failure of an ON-OFF switching valve 72 or a switching valve 70 of a hydraulic device 69 provided to supply the hydraulic pressure.Engine start restricting means 92 is configured to restrict starting of the engine 26 when a component of the hydraulic device 69 provided to operate the parking lock device 50 has an operating failure that causes the parking lock device 50 to be held in its released state, as compared with the starting when the component does not have the operating failure, so that the engine start restricting means 92 reduces a risk of releasing of the parking lock device 50 due to application of the hydraulic pressure from the hydraulic device 69 to the parking lock device 50, which application would be caused by the starting of the engine 26.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2009/052059 filed Feb. 6, 2009, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a control apparatus for a vehicle, and more particularly to a manner of control of a vehicle having a parking lock device hydraulically placed in a locking state and an unlocking state.

BACKGROUND ART

There is available a vehicular automatic transmission provided with a hydraulic control unit configured to perform a switching operation depending upon a selected shift lever position to effect a shifting operation, according to an electric command signal fed through a wire (electric wire) called a shift by wire (SBW). A rotary motion of such an output shaft of an automatic transmission is inhibited by an actuator of a parking lock device, which is operated on the basis of a command signal generated by a shift lever operation to a parking position (P). Patent Document 1 discloses a technique wherein the actuator of the parking lock device is hydraulically operated.

According to the technique disclosed in Patent Document 1, the parking lock device is brought into its locking state by a biasing force of a spring, to inhibit the rotation of the output shaft, while the parking lock device placed in the locking state is brought into its unlocking state, by a force produced by a hydraulically operated valve, to permit the rotation of the output shaft.Patent Document 1: JP-2002-533631

DISCLOSURE OF THE INVENTION

Object to be Achieved by the Invention

In the parking lock device configured to be hydraulically placed in the locking and unlocking states, as described above, the valve, a cylinder or any other member of a hydraulic device may fail to normally operate, with a result of sticking (positional locking) of a spool of the valve or a piston in a given position, for example. In such an event, the hydraulic pressure generated by the hydraulic device corresponds to the position in which the member in question is stuck. If the member in question of the hydraulic device operating the parking lock device is stuck in the position for generating the hydraulic pressure to place the parking lock device in the unlocking state, for instance, the hydraulic pressure generated by the hydraulic device is kept at a level for placing the parking lock device in the unlocking state.

In a vehicle, a hydraulic pressure is generally generated by an oil pump driven by a drive power source. While the drive power source is at rest, the oil pump is also at rest, so that the hydraulic pressure is not generated by the oil pump. In the parking lock device which is placed in the locking state not by the hydraulic pressure but by the biasing force of the spring, and in the unlocking state by the hydraulic pressure, according to the technique as disclosed in Patent Document 1, therefore, the parking lock device can be placed into the locking state by the biasing force of the spring when the hydraulic pressure is not available with the drive power source being at rest, even while the member in question of the hydraulic device is stuck in the position for generating the hydraulic pressure to place the parking lock device in the unlocking state.

Although the parking lock device is placed in the locking state while the drive power source is at rest, however, there is a risk that the parking lock device is placed into the unlocking state when the drive power source is started again.

The present invention was made in view of the background art described above. It is therefore an object of the present invention to provide a control apparatus for a vehicle wherein a parking lock device is placed in a unlocking state by a hydraulic pressure generated by an oil pump driven by a drive power source, which control apparatus is configured to reduce the risk of the parking lock device being placed into the unlocking state while a member of the hydraulic device to generate the hydraulic pressure fails to normally operate.

Means for Achieving the Object

The object indicated above is achieved according to the first aspect of the present invention, which provides a control apparatus for a vehicle (a) having a drive power source, a power transmitting device for transmitting a drive force generated by the above-described drive power source to drive wheels, and a parking lock device for locking an output shaft of the above-described power transmitting device when the above-described power transmitting device is placed in a power disconnecting state, (b) the above-described parking lock device being placed in a released state with a hydraulic pressure generated by an oil pump operated by the drive power source, the control apparatus being characterized by comprising (c) drive-power-source start restricting means for restricting starting of the above-described drive power source when a component of a hydraulic device provided to operate the above-described parking lock device has an operating failure that causes the above-described parking lock device to be held in the released state, as compared with the starting when the component does not have the above-described operating failure.

According to the third aspect of the invention, there is provided a control apparatus for a vehicle (a) having a drive power source, a power transmitting device for transmitting a drive force generated by said drive power source to drive wheels, and a parking lock device for locking an output shaft of said power transmitting device when said power transmitting device is placed in a power disconnecting state, (b) the above-described parking lock device being placed in a released state with a hydraulic pressure generated by an oil pump operated by the drive power source, the control apparatus being characterized by comprising: (c) drive-power-source stop restricting means for restricting stopping of said drive power source when a component of a hydraulic device provided to operate said parking lock device has an operating failure that causes said parking lock device to be held in the released state.

Advantages of the Invention

According to the first aspect of the invention, the above-described drive-power-source start restricting means restricts starting of the above-described drive power source when a component of the hydraulic device provided to operate the above-described parking lock device has an operating failure that causes the parking lock device to be held in the released state, as compared with the starting when the component does not have the above-described operating failure, so that the drive-power-source start restricting means reduces a risk of releasing of the above-described parking lock device due to application of the hydraulic pressure from the above-described hydraulic device to the above-described parking lock device, which application would be caused by the starting of the above-described drive power source.

In one preferred form of the invention described above, the above-described drive-power-source start restricting means inhibits the starting of the above-described drive power source when braking means provided to apply a brake to the vehicle is not operated to apply the brake to the vehicle. In this preferred form of the invention wherein the starting of the above-described drive power source is inhibited when the braking means is not operated to apply the brake to the vehicle, there is a reduced risk of insufficiency of the vehicle braking force due to releasing of the above-described parking lock device which would be caused by the starting of the above-described drive power source.

According to the third aspect of the invention, the above-described drive-power-source stop restricting means restricts stopping of the above-described drive power source when a component of the hydraulic device provided to operate the above-described parking lock device has an operating failure that causes the parking lock device to be held in the released state, so that the drive-power-source stop restricting means reduces a risk of releasing of the above-described parking lock device due to application of the hydraulic pressure from the above-described hydraulic device to the above-described parking lock device in accordance with starting of the drive power source, which application would be caused by the re-starting of the above-described drive power source after the drive power source is stopped.

In one preferred form of the former aspect of the invention described above, the above-described drive-power-source stop restricting means inhibits the stopping of the above-described drive power source when braking means provided to apply a brake to the vehicle is not operated to apply the brake to the vehicle. In this preferred form of the invention wherein the stopping of the above-described drive power source is inhibited when the braking means is not operated to apply the brake to the vehicle, there is a reduced risk of insufficiency of the vehicle braking force due to releasing of the above-described parking lock device which would be caused by the re-starting of the above-described drive power source after the above-described drive power source is stopped.

EXPLANATION OF REFERENCE SIGNS

10: Automatic transmission (Power transmitting device)24: Output shaft of power transmitting device26: Engine (Drive power source)50: Parking lock device52: Parking brake (Braking means)58: Oil pump64: Drive wheels90: Engine stop restricting means (Drive-power-source stop restricting means)92: Engine start restricting means (Drive-power-source start restricting means)100: Electronic control device (Control apparatus for a vehicle)

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of this invention will be described in detail by reference to the drawings.

FIG. 1is a block diagram for explaining one example of a construction of a vehicle controlled according to the present invention, illustrating major portions of a control system according to the invention. As shown inFIG. 1, a drive force produced by a drive power source in the form of an engine26is transmitted to an input shaft22of an automatic transmission10through a torque converter28, for example. The automatic transmission10which is a power transmitting device is constructed to transmit a rotary motion of the input shaft22to an output shaft24with a speed change. In the present embodiment, the input shaft22is a turbine shaft of the torque converter28, for example. A rotary motion of the output shaft24is transmitted to drive left and right drive wheels64through a differential gear device (final speed reducing device)60and a pair of axles62, for example.

An electronic control device100includes a so-called “microcomputer” incorporating a CPU, a RAM, a ROM and an input and output interface. The CPU performs signal processing operations according to control programs stored in the ROM while utilizing a temporary data storage function of the RAM, to control an output of the engine26and a shifting operation of the automatic transmission10. The CPU consists of independent control sections such as an engine control section, and a shifting control section configured to control linear solenoid valves for operating hydraulically operated frictional coupling devices (not shown) in the automatic transmission10.

As indicated inFIG. 1, the electronic control device100receives signals from sensors and switches (not shown), for instance, an output signal of a crank position sensor indicative of a crank position, such as a crank angle (angular position) ACR(°) and an operating speed NEof the engine26, an output signal of a turbine speed sensor indicative of a rotating speed NTof the turbine shaft of the torque converter28(namely, a rotating speed NINof the input shaft22of the automatic transmission10), an output signal of an output shaft speed sensor indicative of a rotating speed NOUTof the output shaft24corresponding to a running speed V of the vehicle, an output signal of an intake air quantity sensor indicative of an intake air quantity QAIRof the engine26, an output signal of a shift position sensor42indicative of a selected operating position PSHof a manual shifting device in the form of a shift lever40, an output signal of a parking position switch41provided to select a parking position P, an output signal of an accelerator sensor indicative of an accelerator operating amount ACCof an accelerator pedal, an output signal of a throttle position sensor indicative of an angle θTHof opening of an electronic throttle valve, an output signal of a brake switch indicative of an operated state BONof a normally used braking device in the form of a foot brake device, an output signal of a parking brake switch54indicative of an operated state PBONof a parking brake device, an output signal of an AT oil temperature sensor indicative of a temperature TOILof a working oil within a hydraulic control unit76, an output signal of an acceleration sensor indicative of an acceleration value (deceleration value) G of the vehicle, and a start/stop switch56provided to start and stop the engine.

The electronic control device100generates engine output control command signals SEfor output control of the engine26, such as a drive signal to drive a throttle actuator for opening and closing the electronic throttle valve, a fuel injection signal for controlling an amount of injection of a fuel from a fuel injecting device, and an ignition timing signal for controlling an ignition timing of the engine26by an igniter. The electronic control device100further generates shifting control command signals SPfor shifting control of the automatic transmission10, such as a valve command signals for energizing and de-energizing the linear solenoid valves provided within the hydraulic control unit76to perform the shifting operation of the automatic transmission10, and a drive signal for controlling a linear solenoid valve provided to control a line pressure PL. Described in detail, the automatic transmission10is a step-variable automatic transmission, for instance, which includes a differential gear device and which has a plurality of gear positions having respective different speed ratios, which are selectively established by respective combinations of engaged and released states of the hydraulically operated frictional coupling devices in the form of clutches and brakes connected to respective rotary elements of the differential gear device and other members of the automatic transmission10. The plurality of those hydraulically operated frictional coupling devices are selectively engaged and released by hydraulic pressures supplied from the linear solenoid valves within the hydraulic control unit76.

When the parking position switch41is operated to select the parking position P, or when the shift lever40is operated to any one of its operating positions to cancel the parking position P, the electronic control device100generates a parking lock command signal SPKfor operating an ON-OFF switching valve72to generate a hydraulic pressure for actuating a parking lock device50(described below) to execute a parking lock for inhibiting a rotary motion of the output shaft24or to cancel the parking lock.

The shift lever40is disposed near an operator's seat, for example, and has three positions, that is, positions R, N and D arranged in a front-rear (longitudinal) direction of the vehicle, and manual positions “+”, B and “−” arranged parallel to a line of arrangement of those positions R, N and D, so that the shift lever40is movable to a desired one of the positions in an H pattern. In the present embodiment, the parking position switch41is provided independently of the shift lever40, to select the parking position P for executing the parking lock.

The above-indicated position R is a reverse drive position selected to reverse the direction of rotation of the output shaft24of the automatic transmission10, and the position N is a neutral position selected to disconnect a power transmitting path through the automatic transmission10, while the position D is a forward drive position selected to permit the shifting operation of the automatic transmission10within a drive range, to establish one of forward drive gear positions consisting of a first gear position (1st) through an eighth gear position (8th). The position B is a manual forward drive position in which the shifting operation takes place within different ranges having respective different numbers of the forward drive gear positions are available, with the relatively higher-speed gear position or positions being unavailable. The parking position P selected by operating the parking position switch41is a parking lock position in which the automatic transmission10is placed in the neutral state for disconnecting the power transmitting path in the automatic transmission10, and in which the rotary motion of the output shaft24is mechanically inhibited by a mechanical parking mechanism.

The shift lever40placed in the position B is movable to the position “+” and the position “−”, so that the number of the forward drive gear positions available is increased each time the shift lever40is moved to the position “+”, and is reduced each time the shift lever40is moved to the position “−”. When the shift lever40is moved to the position “+” or “−”, the automatic transmission10is shifted from the presently selected forward drive gear position to another, for example.

The position D is considered to be a position for selecting an automatic shifting mode in which the automatic transmission10is automatically shiftable to any one of the forward drive gear positions available, while the position B is considered to be a position for selecting a manual shifting mode in which the automatic transmission10is automatically shiftable to one of the forward drive gear positions the number of which is smaller than in the automatic shifting mode, and from which the shift lever40is manually movable to change the number of the forward drive gear positions available (to change the highest-speed forward drive gear position).

Referring back toFIG. 1, the parking lock device50is operated to inhibit the rotary motion of the output shaft24of the automatic transmission10when the parking position switch41is operated to select the parking position P, as described below in detail.

A parking brake lever52is provided to operate and release the parking brake device (not shown), and is connected to the parking brake device through a cable (not shown). When the parking brake lever52is pivoted upwards, for instance, the parking brake device is operated to apply a parking brake to the vehicle, and this operation of the parking brake lever52is detected by a parking brake switch54, so that a signal indicating the operation of the parking brake device is fed to the electronic control device100. The parking brake lever52has, for example, a ratchet mechanism, which can hold the parking brake lever52in its pivoted state, i.e. the parking brake device in its operated state and permits it to be returned to its released state.

A start/stop switch56is a so-called “ignition switch”, for example, which is operated by the vehicle operator to supply the electronic control device100with a signal to start and stop the drive power source in the form of the engine26.

FIG. 3is a view for explaining a construction of the parking lock device50for executing the parking lock when the parking position switch41is operated to select the parking position P, and an arrangement of a hydraulic device for operating the parking lock device50.

The parking lock device50has: a shaft102rotated by a pivotal member48as described below; a detent plate120fixed to and pivoted by the shaft102; a rod104movable in its longitudinal direction by a pivotal motion of the detent plate120; a parking gear108fixed to the output shaft24of the automatic transmission10; a parking lock pawl106pivotably connected to a casing (not shown) to lock the parking gear108; a detent spring110provided to hold, with its biasing force, the detent plate120in a selected one of angular positions described below; and a rotatable pin112supported at a distal end portion of the detent spring110.

The detent plate120is operatively connected through the shaft102to the pivotal member48of a crank mechanism47described below, and cooperates with the rod104, detent spring110, rotatable pin112and other members to function as a shift positioning member operated by the crank mechanism47to change the shift position of the transmission. The shaft102, detent plate120, rod104, detent spring110and rotatable pin112cooperate with each other to function as a shift position changing mechanism.

As shown inFIG. 5, the detent plate120has four recesses formed in its upper end portion, between a pair of inner wall surfaces126,128. These four recesses correspond to the respective shift positions P, R, N and D. The four recesses include an outer recess124corresponding to the position P. Those shift positions P, R, N and D of the detent plate120correspond to the respective shift positions P, R, N and D selected by the shift lever40and the parking position switch41. The shift positions R, N and D are called non-P positions.

Referring back toFIG. 3, the parking lock device50shown therein is placed in a state in which the shift position P is selected. In this state, the parking lock pawl106locks the parking gear108to prevent rotary motions of drive shafts of the vehicle. In this embodiment, this state is called the operated state of the parking lock device50. When the parking lock command signal PSKto return the parking lock device50from this operated state to its released state is generated from the electronic control device100, the crank mechanism47is operated to rotate the shaft102in a direction indicated by an arrow C shown inFIG. 3, so that the rod104is moved by the detent plate120in a direction indicated by an arrow A shown inFIG. 3, whereby a tapered member114provided at one end of the rod104permits the parking lock pawl106to be pivoted downwards in a direction indicated by an arrow B shown inFIG. 3. As the detent plate120is pivoted, the rotatable pin112of the detent spring110is moved from the outer recess124of the four recesses formed in the upper end portion of the detent plate120and corresponding to the respective positions P, R, N and D, namely, from the position P (124) (indicated inFIG. 5to one of the other recess, namely, to one of the non-P positions121(indicated inFIG. 5), while clearing the tooth122. This rotatable pin112is provided on the detent spring110such that the rotatable pin112is rotatable about its axis. When the rotatable pin112has been moved into one of the non-P positions121with a pivotal motion of the detent plate120in the direction C until rotatable pin112, the parking lock pawl106has been pivoted downwards to a position in which the parking lock pawl106does not mesh with the parking gear108. As a result, the mechanical locking of the output shaft24and the vehicle drive wheels64is released, and the detent plate120is pivoted to the above-indicated non-P position. When the shaft102is rotated in a direction D by a crank mechanism47, the detent plate120is pivoted to the shift position P with reversal of the motions described above.

A rotary encoder46generates a pulse signal for counting the number (encoder counts) indicative of an amount of operation of the crank mechanism47, that is, an amount of the pivotal motion of the pivotal member48. The electronic control device100determines whether the position P or non-P position is selected, on the basis of the output pulse signal of the rotary encoder46. The amount of the pivotal motion of the pivotal member48corresponds to an amount of rotation of the shaft102of the parking lock device50. The above-described position P is determined by experimentation or simulation, as a position in which the parking gear108is securely locked by the parking lock pawl106. Namely, the rotary encoder46functions as a parking lock sensor for detecting whether the parking lock device50is placed in its operated or released state.

FIG. 3also shows a hydraulic circuit showing one example of an arrangement of a hydraulic device69for operating the above-described parking lock device50. This hydraulic circuit is provided by the hydraulic control unit76(shown inFIG. 1).

A mechanical oil pump58is driven by the engine26, to generate a hydraulic pressure, which is regulated to a desired line pressure PPK(parking lock releasing line pressure PPK), by a pressure regulating valve68of a relief type.

An ON-OFF switching valve72is a solenoid-operated valve, for instance, and is operated according to the parking lock command signal SPKfrom the electronic control device100, to apply a pilot pressure PSPto a switching valve70described below. In the present embodiment, the ON-OFF switching valve72is configured to generate the pilot pressure PSPwhen an input control signal in the form of the parking lock command signal SPKis in an on state, and not to generate the pilot pressure PSPwhen the parking lock command signal SPKis in an off state. It is noted here that the parking lock command signal SPKis turned on when the electronic control device100determines that the parking lock device50should be placed in the operated state, and is turned off when the electronic control device100determines that the parking lock device50should be placed in the released state.

The switching valve70has an input port, a drain port and an output port. When the switching valve70is not supplied with the pilot pressure PSP, a spool disposed within the switching valve70is held in a position for communication between the input port communicating with the pressure regulating valve68and the output port communicating with a hydraulic cylinder74described below, under a biasing force of a spring disposed within the switching valve70, for example. When the switching valve70is supplied with the pilot pressure PSP, on the other hand, the spool is moved to a position for communication between the above-described output port and the drain port EX communicating with a drain line.

The hydraulic cylinder74serving as a hydraulic actuator has an oil chamber77receiving a hydraulic pressure from the above-described switching valve70, a piston75, and a spring78for biasing the piston75in a direction opposite to a direction in which the hydraulic pressure in the oil chamber77acts on the piston75. When the hydraulic pressure PPKis supplied from the switching valve70to the oil chamber77, the piston75is moved to a position of equilibrium between the above-described hydraulic pressure PPKand a biasing force of the spring78. The crank mechanism47includes a crank rod49connected to the piston75, and functions to convert linear motions of the piston75input thereto via the crank rod49, that is, motions of the piston75in directions E and F indicated inFIG. 3, into pivotal motions of the pivotal member48, that is, motions of the pivotal member48in the directions C and D indicated inFIG. 3. The pivotal member48and the shaft102of the parking lock device50are fixed to each other such that the pivotal member48is pivoted about the axis of the shaft102.

The hydraulic device69and the parking lock device50are constructed as described above. To place this parking lock device50in its operated state, the parking lock command signal SPKgenerated from the electronic control device100is initially turned on, to enable the ON-OFF switching valve72to generate the pilot pressure PSP. As a result, the switching valve70is placed in the state for communication between the drain port EX and the output port communicating with the oil chamber77of the hydraulic cylinder74, so that the pressurized oil in the oil chamber77of the hydraulic cylinder74is discharged from the drain port EX of the switching valve70, whereby the piston75in the hydraulic cylinder74is moved in the direction F indicated inFIG. 3, under the biasing force of the spring78. Consequently, the shaft102of the parking lock device50is rotated through the crank mechanism47, in the direction D indicated inFIG. 3. Thus, the detent plate120is pivoted to locate the rotatable pin112in the position P, so that the parking pawl106is pivoted upwards to lock the parking gear108. Thus, the parking lock device50is placed in its operated state in which the output shaft24of the automatic transmission10is locked.

To place the parking lock device50in its released state, the parking lock command signal SPKgenerated from the electronic control device100is turned off, to disable the ON-OFF switching valve72to generate the pilot pressure PSP. As a result, the switching valve70is placed in the state for applying the hydraulic pressure PPKreceived from the pressure regulating valve68to the oil chamber77of the hydraulic cylinder74, so that the piston75is moved in the direction E indicated inFIG. 3, by a pressing force which acts on the piston75based on the hydraulic pressure PPKin the oil chamber77, which pressing force is larger than the biasing force of the spring78. This motion of the piston75is converted by the crank mechanism47into a rotary motion of the shaft102in the direction C indicated inFIG. 3. The detent plate120is pivoted so that the rotatable pin112located in the position P is moved to one of the non-P positions121, so that the parking pawl106is pivoted downwards in the direction B indicated inFIG. 3, to a position for disengagement from the parking gear108. Thus, the parking lock device50is placed in its released state.

The valves and other components of the hydraulic device may suffer from operating failures or abnormalities such as wire disconnection, short circuiting and spool sticking of the solenoid-operated valves, which may cause a failure to apply the hydraulic pressure to the desired locations.

Described in detail, such operating failures include, for example, sticking of the spool of the ON-OFF switching valve72, which disables this valve72to generate the pilot pressure PSPirrespective of the on or off state of the parking lock command signal SPK, and a failure of the switching valve70, which causes permanent communication of its output port with the input port communication with the pressure regulating valve68, even when the pilot pressure PSPis applied to the switching valve70. These operating failures cause the hydraulic pressure regulated by the pressure regulating valve68to be applied to the oil chamber77of the hydraulic cylinder74, irrespective of the on or off state of the parking lock command signal SPK, so that the parking lock device50is kept in its released state.

In the present embodiment wherein the oil pump58is driven by the drive power source, the oil pump58fails to generate a hydraulic pressure while the drive power source in the form of the engine26is held at rest. Consequently, the parking lock releasing line pressure PPKis not applied to the oil chamber77of the hydraulic cylinder74, and the oil is discharged from the oil chamber77, irrespective of whether the switching valve70is placed in the state for communication of its drain port EX with the oil chamber77, or in the state for communication between the pressure regulating valve60and the oil chamber77during the engine26at rest. Namely, the parking lock device50is placed in its operated state when the engine26is at rest.

In the arrangement described above, the parking lock device50which has been placed in the operated state while the engine26is at rest may be placed in the released state when the engine26is started again, if the oil chamber77of the hydraulic cylinder74is held in communication with the pressure regulating valve68due to the operating failure of the ON-OFF switching valve72or the switching valve70described above, for example.

FIG. 4is the functional block diagram for explaining major control functions of the above-described electronic control device100, that is, the major control functions performed when the engine26is stopped and started, if the oil chamber77of the hydraulic cylinder74is held in communication with the pressure regulating valve68due to an operating failure of any component of the hydraulic device69provided to operate the parking lock device50.

Shift control means80is provided and configured to determine the gear position of the automatic transmission10to be established, on the basis of control parameters including: the presently selected operating position PSHof the shift lever40detected by the shift position sensor42; the output signal of the parking position switch41indicating whether the parking position P is selected; the vehicle speed V; and the operating amount ACCof the accelerator pedal, and according to a shifting map stored in memory. The shift control means80is further configured to controlling the solenoid-operated valves incorporated in the hydraulic control unit76, to generate the hydraulic pressures required to establish the selected gear position of the automatic transmission10.

Parking lock executing means82is provided and configured to place the parking lock device50in its operated state, according to the output signal of the parking position switch41indicative of the selection of the parking position P, and to place the parking lock device50in its released state, according to the output signal of the shift position sensor42indicative of the selecting of any one of the above-indicated positions R, N and D other than the parking position P. Described in detail, the parking lock device50is configured to generate the parking lock command signal SPKfor operating the ON-OFF switching valve72incorporated in the hydraulic control unit76, to control the hydraulic device69for selectively placing the parking lock device50in the operated or released state.

Abnormality detecting means84is provided and configured to detect an abnormality of the hydraulic device69, more specifically, a failure of the hydraulic device69to place the parking lock device50in its operated state, in spite of generation of a command signal from the parking lock executing means82to execute the parking lock. In the present embodiment, this failure is caused by an operating failure of the ON-OFF switching valve72or switching valve70as a component of the hydraulic device69, which operating failure causes the communication of the oil chamber77of the hydraulic cylinder74with the pressure regulating valve68.

Described in detail, the abnormality detecting means84determines whether the parking lock device50cannot be placed in the operated state, in spite of generation of the command signal from the parking lock executing means82to execute the parking lock. This determination is made on the basis of the output signal of the parking position switch41indicative of the selection of the above-described parking position P, and the output signal of the rotary encoder46indicative of the amount of rotation of the above-described shaft102of the parking lock device50. That is, the abnormality detecting means84detects this abnormality if a determination that the parking lock device50has been placed in the operated state is not obtained on the basis of the output signal of the above-described rotary encoder46, within a predetermined length of time after the output signal of the parking position switch41indicative of the selection of the above-described parking position P is generated. For example, the determination that the parking lock device50is placed in the operated state can be obtained when the output signal of the rotary encoder46indicates that the shaft102has been rotated by an amount required to pivot the detent plate120to locate the rotatable pin112in the position P (124). The above-indicated predetermined length of time may be determined to be a sum of an average time from a moment of generation of the output signal of the parking position switch41indicative of the selection of the parking position P to a moment at which the parking lock device50is placed in the operated state, in the absence of the above-indicated abnormality, and a predetermined additional time. The average time is obtained by experimentation or simulation.

If the abnormality detecting means84detects the above-indicated abnormality, the abnormality detecting means84turns on a parking-switching-valve abnormality diagnosis flag indicating that the abnormality has occurred. On the basis of this diagnosis flag set in the on state, emergency drive-power-source control means86described below recognizes that the abnormality in question has occurred. The abnormality detecting means84is also configured to command indicating means94described below to inform the vehicle operator of the fact that the abnormality has occurred when the abnormality is detected. For instance, the indicating means94informs the vehicle operator of a possibility of the operating failure of the parking lock device50, or prompts the vehicle operator to operate the parking brake lever52before operating the start/stop switch56to stop the engine26.

Engine control means96is provided and configured to start and stop the engine26on the basis of respective command signals generated by the start/stop switch56for starting and stopping the engine26. Described in detail, the engine control means96starts the engine26by a starter motor not shown, when the command signal for starting the engine26is generated by the start/stop switch56, and stops the engine26by stopping ignition of the engine26, for example, when the command signal for stopping the engine26is generated by the start/stop switch56.

Emergency drive-power-source control means86is provided and configured to execute stopping and starting controls of the drive power source upon detection of an abnormality by the abnormality detecting means84, which controls are different from those executed without detection of the abnormality. The emergency drive-power-source control means86includes engine stop restricting means90and engine start restricting means92.

The engine stop restricting means90is configured to command the engine control means96to execute the following controls of the engine26when the command signal to stop the engine26is generated by the start/stop switch56and before the operation of controlling the engine26to stop by the engine control means96, while an abnormality is detected by the abnormality detecting means84. Namely, the engine stop restricting means90commands the engine control means96to stop the engine26if the parking brake switch54detects that the parking brake lever52for operating braking means in the form of the parking brake device is placed in its operated position, and to inhibit the stopping of the engine26if the parking brake switch54does not detect that the parking brake lever52is placed in its operated position. This engine stop restricting means90corresponds to drive-power-source stop restricting means.

The engine start restricting means92is configured to command the engine control means96to execute the following controls of the engine26when the command signal to start the engine26is generated by the start/stop switch56and before the operation of controlling the engine26to start by the engine control means96, while an abnormality is detected by the abnormality detecting means84. Namely, the engine start restricting means92commands the engine control means96to start the engine26if the parking brake switch54detects that the parking brake lever52for operating braking means in the form of the parking brake device is placed in its operated position, and to inhibit the starting of the engine26and command the indicating means94to provide the vehicle operator with suitable information as described below, if the parking brake switch54does not detect that the parking brake lever52is placed in its operated position. For example, the indicating means94provides information prompting the vehicle operator to operate the parking brake lever52before starting the engine26. This engine start restricting means90corresponds to drive-power-source start restricting means.

The indicating means94is configured to command outputting means98such as a display device or a voice generating device to provide the vehicle operator with suitable information, according to the commands generated by the abnormality detecting means84and engine start restricting means92described above. Described in detail, the outputting means98provides an indication that there is a possibility of occurrence of any abnormality of the parking lock device50, or information prompting the vehicle operator to operate the parking brake lever52before operating the start/stop switch56before stopping the engine26, if an abnormality is detected by the abnormality detecting means84, and provides information prompting the vehicle operator to operate the parking brake lever52before starting the engine26, if the starting of the engine26is inhibited by the above-described engine start restricting means92.

FIG. 6is a flow chart for explaining major control functions of the above-described electronic control device100, more specifically, control functions to be performed when the command signal for stopping the engine26is generated by the start/stop switch56during an operation of the engine26.

SA1and SA2are steps corresponding to the abnormality detecting means84. SA1is implemented to determine whether the parking lock device50is not placed in the operated state, that is, the parking lock is not executed, within the above-described predetermined length of time after the parking position P has been selected by the parking position switch41. For example, this determination is made on the basis of the output of the rotary encoder46. If the parking lock device50is not placed in the operated state within the above-described predetermined length of time, an affirmative determination is obtained in the present step, and SA2is then implemented. If the parking lock device50is placed in the operated state within the above-described predetermined length of time, on the other hand, it is determined that the hydraulic device69is normal, so that a negative determination is obtained in the present step, whereby the present cycle of operation of the flow chart is terminated.

SA2is the step implemented if the affirmative determination is obtained in SA1, that is, if the parking lock device50is not placed in the operated state within the above-described predetermined length of time. In this case, it is determined that any component of the hydraulic device69for operating the parking lock device50may fail to normally operate to execute the parking lock, so that the parking-switching-valve abnormality diagnosis flag is turned on.

SA3corresponding to the indicating means94etc. is implemented to command the outputting means98to inform the vehicle operator that there is a possibility of occurrence of an abnormality of the parking lock device50, or to provide information prompting to operate the parking brake lever52before operating the start/stop switch56to stop the engine26.

SA4is a step corresponding to the engine stop restricting means90etc. SA4is implemented to determine on the basis of the output of the parking position switch54, whether the parking brake lever52is placed in the operated position, when the command signal to stop the engine26is generated by the start/stop switch56during the engine26running. If the parking brake lever52is placed in the operated state when the command signal to stop the engine26is generated, an affirmative determination is obtained in SA4, and SA5is then implemented. If it is determined on the basis of the output of the parking position switch54that the parking braking brake lever52is placed in the released state when the command signal to stop the engine26is generated, a negative determination is obtained in this step, and SA6is then implemented.

SA5corresponding to the engine control means96is implemented to stop the engine26which has been operating. Described in detail, the engine control means96stops the engine26by stopping the ignition by ignition plugs not shown, or stopping the supply of a fuel by a fuel supply valve not shown, for example. It is noted that the present embodiment is configured such that the oil pump58is not operated to generate the hydraulic pressure when the engine26is at rest, so that the parking lock device50is brought into its operated state by the biasing force of the spring78, as described above.

SA6implemented when the negative determination is obtained in SA4corresponds to the engine stop restricting means90. In SA6, the stopping of the engine26is inhibited in spite of generation of the command signal to stop the engine26in SA4.

FIG. 7is a flow chart for explaining other major control functions of the above-described electronic control device100, more specifically, control functions to be performed when the command signal for starting the engine26is generated by the start/stop switch56while the engine26is at rest.

Initially, SB1is implemented to determine whether the command signal by the start/stop switch56to start the engine26has been detected during the engine26stopping. If the command signal to start the engine26has been detected, an affirmative determination is obtained in this step, and SB2is then implemented. If the command signal to start the engine26has not been detected, on the other hand, a negative determination is obtain in the present step, and the present of operation of the flow chart is terminated.

The following SB2-SB4correspond to the engine starting restricting means92. SB2is implemented to determine whether the parking-switching-valve abnormality diagnosis flag is placed in the on state. This parking-switching-valve abnormality diagnosis flag is turned on in SA2of the flow chart ofFIG. 6, for example, during the operation of the engine26before the engine26is stopped. If the parking-switching-valve abnormality diagnosis flag is placed in the on state, an affirmative determination is obtained in SB2, and SB3is then implemented. If the parking-switching-valve abnormality diagnosis flag is not placed in the on state, a negative determination is obtained in SB2, and SB5is then implemented.

SB3is implemented to determine whether the parking brake lever52is placed in the released state. For example, this determination is made on the basis of the output of the parking position switch54. If the parking brake lever52is placed in the released state, an affirmative determination is obtained in the present step, and SB4is then implemented. If the parking brake lever52is placed in the operated state, on the other hand, SB5is implemented.

SB4is a step implemented when an affirmative determination is obtained in SB3, that is, when the parking brake lever52is placed in the released state while the parking-switching-valve abnormality diagnosis flag is placed in the on state. In this step, the starting of the engine26is inhibited, in spite of detection in SB1of the command signal to start the engine26. Described in detail, a cranking operation to start the engine26is inhibited, for example. The present step SB4also corresponding to the indicating means94is implemented to command the outputting means98such as an optical display device or a voice generating device to provide information prompting to operate the parking brake lever52for starting the engine26.

On the other hand, SB5is a step which corresponds to the engine control means96and which is implemented if a negative determination is obtained in SB2or SB3, that is, when the parking-switching-valve abnormality diagnosis flag is placed in the off state, or when the parking brake lever52is placed in the operated state while the parking-switching-valve abnormality diagnosis flag is placed in the on state. In this step, the engine26is started on the basis of the command signal to start the engine26, which has been detected in SB1.

In the embodiment described above, the engine start restricting means92restricts starting of the engine26when the ON-OFF switching valve72, switching valve70or any other component of the hydraulic device69provided to operate the parking lock device50has an operating failure that causes the parking lock device50to be held in the released state, as compared with the starting when the component does not have the operating failure, so that the engine start restricting means92reduces a risk of releasing of the parking lock device50due to application of the hydraulic pressure from the hydraulic device69to the parking lock device50, which application would be caused by the starting of the engine26.

The above-described embodiment is further arranged such that the engine start restricting means92inhibits the starting of the engine26when the parking brake lever52for operating the parking brake device is not operated. Since the starting of the engine26is inhibited when the parking brake device is not operated to apply the brake to the vehicle, there is a reduced risk of insufficiency of the vehicle braking force due to releasing of the parking lock device50which would be caused by the starting of the engine26.

The above-described embodiment is also arranged such that the engine stop restricting means90restricts stopping of the engine26when the ON-OFF switching valve72, switching valve70or any other component of the hydraulic device92provided to operate the parking lock device50has an operating failure that causes the parking lock device50to be held in the released state, so that the engine stop restricting means90reduces a risk of releasing of the parking lock device50due to application of the hydraulic pressure from the hydraulic device69to the parking lock device50in accordance with starting of the engine26, which application would be caused by the re-starting of the engine26after the engine26is stopped.

The above-described embodiment is further arranged such that the engine stop restricting means90inhibits the stopping of the engine26when the parking brake lever52for operating the parking brake device is not operated. Since the stopping of the engine26is inhibited when the parking brake is not operated to apply the brake to the vehicle, there is a reduced risk of insufficiency of the vehicle braking force due to releasing of the parking lock device52in accordance with starting of the engine26which would be caused by the re-starting of the engine26after the engine26is stopped.

While the preferred 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 above-described embodiment uses the step-variable automatic transmission10as the power transmitting device. However, the use of the step-variable automatic transmission10is not essential. For instance, the automatic transmission10may be replaced by a continuously-variable automatic transmission the speed ratio of which is continuously variable over a predetermined range.

The above-described embodiment is arranged such that the shift lever40to select the gear positions other than the parking position, and the parking position switch41to select the parking position are provided as devices operated by the vehicle operator to select the shift positions. However, this arrangement is not essential. Namely, the shift lever40may be modified to select all shift positions including the parking position.

The above-described embodiment is further arranged such that the parking lock hydraulic pressure PPKis kept applied to the oil chamber77of the hydraulic cylinder74in the hydraulic device69, for biasing the rod102of the parking lock device50in a direction to hold the parking lock device50in its released state. However, this arrangement is not essential. For example, the piston76of the hydraulic cylinder74, or the crank rod49of the crank mechanism47is locked with a ratchet mechanism or a magnet, for instance, after the parking lock device50is once placed in its released state, and the locking of the piston76or crank rod49is released when the parking lock device50is again placed into its operated state. In this case, the hydraulic device69need not be kept operated to generate the hydraulic pressure for holding the parking lock device50in the released state.

Although the above-described embodiment uses the hydraulic cylinder74as the hydraulic actuator, any other type of hydraulic actuator such as a hydraulic motor or a diaphragm type hydraulic actuator may be used.

In the above-described embodiment, the parking brake device operated by the parking brake lever52is used to apply a parking brake to the vehicle. However, any other parking brake device may be used, provided the parking brake device is capable of applying a parking brake to the vehicle, irrespective of the operating state of the drive power source of the vehicle, that is, irrespective of whether the drive power source is in operation or at rest.

The sticking of the spools of the ON-OFF switching valve72and switching valve70is described as examples of the operating failure or abnormality of the hydraulic device69, with respect to the above-described embodiment. However, the operating failure of the hydraulic device69includes any other failure such as the sticking of the piston77of the hydraulic cylinder74.

While the engine26is used as the drive power source in the above-described embodiment, any other drive power source may be used. For example, the drive power source includes both an engine and an electric motor.

The engine stop restricting means90in the above-described embodiment is configured to permit and inhibit stopping of the engine26depending upon whether the parking brake lever52is placed in the operated state or not (SA4) when a command signal to stop the engine26is output, that is, to permit stopping of the engine26(in SA5) when the parking brake lever52is placed in the operated state, and not to permit stopping of the engine26(in SA6) when the parking brake lever52is placed in the released state. However, this configuration is not essential. For example, the engine stop restricting means90may be modified to inhibit stopping of the engine irrespective of whether the parking brake lever52is placed in the operated or released state when an abnormality is detected by the abnormality detecting means84(when the affirmative determination is obtained in SB1). This modification provides some degree of advantage.

The engine start restricting means90in the above-described embodiment is configured to inhibit and permit starting of the engine26depending upon whether the parking brake lever52is placed in the released state or not (SB3), when an abnormality is detected by the abnormality detecting means84(when the affirmative determination is obtained in SB2) while the command signal to start the engine26is detected (while the affirmative determination is obtained in SB1), that is, to inhibit starting of the engine26(in SB4) when the parking brake lever52is placed in the released state, and to permit starting of the engine26(in SB5) when the parking brake lever52is placed in the operated state. However, this configuration is not essential. For example, the engine start restricting means90may be modified to inhibit starting of the engine irrespective of whether the parking brake lever52is placed in the operated or released state, when an abnormality is detected by the abnormality detecting means84(when the affirmative determination is obtained in SB2) while the command signal to start the engine26is detected (while the affirmative determination is obtained in SB1). This modification provides some degree of advantage.

It is to be understood that various other changes not specifically described herein may be made in the present invention, without departing from the spirit of the invention.