Abstract:
A parking lock device comprises a parking lock mechanism ( 12 ) which locks an output shaft ( 1 A) of a vehicle automatic transmission ( 1 ) when a shift lever ( 18 ) is changed over to a parking range, and an automatic brake device ( 14 ) which brakes the vehicle. When the shift lever ( 18 ) is changed over to the parking range at a vehicle speed is not less than a predetermined vehicle speed VSP 1,  a control unit ( 15 ) first operates the automatic brake device ( 14 ) to decelerate the vehicle and then operates the parking lock mechanism ( 12 ) after the vehicle speed has dropped to less than the predetermined vehicle speed VSP 1.  By this deceleration, the shock given to the vehicle by locking the output shaft ( 1 A) while the vehicle is running is suppressed. The load of the parking lock mechanism due to the locking of the output shaft ( 1 A) is also alleviated.

Description:
FIELD OF THE INVENTION 
     This invention relates to a parking lock mechanism which locks an output shaft of an automatic transmission of a vehicle when a parking range is selected by a driver. 
     BACKGROUND OF THE INVENTION 
     In a vehicle provided with an automatic transmission, a so-called shift by wire parking lock mechanism is known which locks the output shaft of the automatic transmission by the action of an actuator such as a motor according to the movement of a shift lever to a parking range. If the driver unexpectedly moves the shift lever to the parking range while the vehicle is running, however, a shock occurs due to sudden locking of the output shaft of the transmission which may give a discomfort to driver or passenger of the vehicle. Further, sudden locking of the output shaft may give damage to the parking lock mechanism. 
     In this connection, Tokkai Hei 5-280637 published by the Japanese Patent Office in 1993 discloses a parking lock mechanism wherein, when a certain predetermined vehicle speed condition is satisfied while the vehicle is running, operation of the parking lock mechanism is permitted after emitting an alarm sound, and when the vehicle speed condition is not satisfied, the operation of the parking lock mechanism is ineffectual. 
     SUMMARY OF THE INVENTION 
     In this parking lock mechanism, as the transition to the parking lock state is notified in advance to the driver, the driver is not startled by an unintended shock, but there is no difference from the state where there is a transition to the parking lock state when the vehicle is running. 
     In other words, all the kinetic energy of the vehicle is stopped by the parking lock mechanism alone, so a large shock nevertheless occurs, and the parking lock mechanism must also be strong enough to stop the kinetic energy of the vehicle. 
     The output shaft is restricted by the engaging of a locking pawl with a parking gear which rotates together with the output shaft of the automatic transmission. When the vehicle speed exceeds a predetermined value, the locking pawl does not enter the teeth of the locking gear as the teeth of the rotating parking gear push aside the locking pawl. However, the driver or passengers hear an unpleasant noise when the parking gear pushes aside the locking pawl. 
     Further, when the shift lever is moved to the parking range before the driver stops the vehicle, the parking mechanism does not operate if the vehicle speed condition is not satisfied. If the intended parking lock operation is not performed, it may even occur that the driver mistakenly considers the vehicle has a fault, and hastily operates the shift lever repeatedly. 
     It is therefore an object of this invention to mitigate the shock due to the operation of a parking lock mechanism on a vehicle when the vehicle is running. 
     It is another object of this invention to mitigate the load on the parking lock mechanism due to the operation of the parking lock mechanism when the vehicle is running. 
     It is yet another object of this invention to prevent an unpleasant noise due to the operation of the parking lock mechanism when the vehicle is running. 
     It is yet another object of this invention to perform a parking lock operation intended by the driver while still achieving the above objects. 
     In order to achieve the above objects, this invention provides a parking lock device which locks an output shaft of an automatic transmission of a vehicle according to a change-over of a shift lever to a parking range. The parking lock device comprises a parking lock mechanism which locks a rotational movement of the output shaft, a sensor which detects a vehicle speed, a sensor which detects the change-over of the shift lever to the parking range, a braking device which brakes the vehicle, and a microprocessor. The microprocessor is programmed to determine whether or not the vehicle speed is less than a first predetermined vehicle speed, activate the braking device to decelerate the vehicle when the shift lever has changed over to the parking range at a vehicle speed not less than the first predetermined vehicle speed, and prevent the parking lock mechanism from locking the rotation of the output shaft until the vehicle speed becomes less than the first predetermined speed. 
    
    
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a controller of an automatic transmission for a vehicle provided with a parking lock mechanism according to this invention. 
     FIG. 2 is a perspective view of a range change-over mechanism and the parking lock mechanism according to this invention. 
     FIG. 3 is a flowchart describing a main routine for parking lock control and speed change control performed by a control unit according to this invention. 
     FIG. 4 is a flowchart describing an automatic brake force computing routine performed by the control unit. 
     FIGS. 5A-5C are diagrams describing a relation between a vehicle speed and a vehicle deceleration according to this invention. 
     FIG. 6 is an enlarged lateral view of a parking lock mechanism according to a second embodiment of this invention. 
     FIG. 7 is an enlarged transverse view of a cam of the parking lock mechanism according to the second embodiment of this invention. 
     FIG. 8 is an enlarged transverse view of a locking pawl of the parking lock mechanism according to a third embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, an automatic transmission  1  comprises a control module  2  containing an oil pressure circuit for speed ratio control. 
     The transmission  1  is connected to an engine of a vehicle, not shown. The control module  2  comprises a range selection actuator  4  such as a motor which strokes a manual valve  3  shown in FIG. 2 according to a selection range of a shift lever  18  and shift solenoid valves  5 ,  6  which change a power transmission path inside the automatic transmission  1 . The shift solenoid valves  5 ,  6  operate according to input signals, and vary a speed ratio by operating a clutch or brake of a planetary gear mechanism of the automatic transmission  1  using the oil pressure supplied from the manual valve  3 . 
     Referring to FIG. 2, the manual valve  3  and range selection actuator  4  are joined via a worm  4 A formed on the output shaft of the range selection actuator  4 , a gear  7  which engages with the worm A, a sector piece  8  engaged with a shaft  7 A of the gear  7 , a pin  8 A fixed to the sector piece  8 , and a rod  3 A engaging with the pin  8 A. The manual valve  3  comprises a spool that works as a valve body, and the rod  3 A is joined to the spool. 
     When the range selection actuator  4  rotates the worm  4 A, the pin  8 A displaces the spool in the axial direction via the rod  3 A. The manual valve  3  supplies the oil pressure of an oil pressure source to the shift solenoid valves  5 ,  6  according to the displacement position of the spool. 
     The displacement position of the rod  3 A is defined by a detent mechanism comprising plural notches  8 B formed in the sector material  8 , and a roller  9 A engaging with the notches  8 B. The notches  8 B are formed for each selection range. The roller  9 A is supported on a case of the manual valve  3  via a plate spring  9 . 
     The automatic transmission  1  has an output shaft  1 A to drive the drive wheels and a parking lock mechanism  12  to lock the rotation of the output shaft  1 A. The parking lock mechanism  12  comprises a parking gear  10  rotating with the output shaft  1 A, a locking pawl  11 A that can engage with the parking gear  10 , and a parking lock actuator  11 . The parking lock actuator  11  is an actuator that moves the locking pawl  11 A towards and away from the parking gear  10  so as to cause the locking pawl  11 A to engage with and disengage from the parking gear  10 . In the state where the locking pawl  11 A is engaged with the parking gear  10 , the rotation of the output shaft  1 A is locked. In the state where the locking pawl  11 A is disengaged from the parking gear  10 , the rotation of the output shaft  1 A is not locked. 
     The speed ratio of the transmission is determined by combinations of ON and OFF of the input signal to the shift solenoid valve  5  and ON and OFF of the input signal to the shift solenoid valve  6 . These signals are controlled by a control unit  15 . 
     The control unit  15  controls the parking lock mechanism  12  by a signal output to the parking lock actuator  11 , and performs brake control together with the operation of the parking lock of the parking lock mechanism  12  by supplying a braking pressure from brake actuators  14  to wheel cylinders  13  which apply a braking force on the wheels of the vehicle. 
     Here, the brake actuator  14  is an actuator which can supply a brake pressure to the wheel cylinder  13  according to a signal from the control unit  15  without depending on the operation of a brake pedal of the vehicle. 
     An automatic brake mechanism of this type is known from U.S. Pat. No. 5,206,808. 
     Specifically, pilot cylinders  9 F,  9 R, pump  15 , reservoir  17 , solenoid change-over valve  18  and pressure control valves  13 R,  13 L,  14 R,  14 L in U.S. Pat. No. 5,206,808 correspond to the brake actuator  14  of this embodiment. Further. the oil cylinders  5 R,  5 L,  6 R,  6 L disclosed in U.S. Pat. No. 5, 206,808 correspond to the wheel cylinder  13  of this embodiment. 
     In order to control the parking lock mechanism  12  and the brake actuators  14 , signals are respectively input to the control unit  15  from a throttle opening sensor  16  which detects a throttle opening TVO of the engine, a vehicle speed sensor  17  which detects a vehicle speed VSP, and a shift lever switch  19  which detects a selection range RNG of the shift lever  18 . 
     The control unit  15  comprises a microprocessor having a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM) and an input/output interface (I/O interface). 
     The control unit  15  performs parking lock control and transmission control by performing a routine shown in FIG. 3 and a related subroutine shown in FIG. 4 based on these input signals. 
     The routine and the subroutine are performed at an interval of ten milliseconds while the vehicle is running. 
     In a step S 21 , the vehicle speed VSP is compared with a predetermined vehicle speed VSP 2  for determining a stationary state. A new vehicle speed VSP is detected each time the routine is performed. The predetermined vehicle speed VSP 2  is for distinguishing vehicle speeds which are unsuitable for parking lock operation by any means, and vehicle speeds at which parking lock operation is possible if it is combined with a deceleration operation of the vehicle. The predetermined vehicle speed VSP 2  is set to, for example, 20 km/hr. 
     When the vehicle speed VSP is less than the predetermined vehicle speed VSP 2 , it may be considered that the vehicle is in a range wherein a parking lock operation is possible. In this case, the routine proceeds to a step S 23 . 
     In the step $ 23 , it is determined whether or not the selection range RNG is a parking range (P). When the selection range RNG is the parking range (P), the routine proceeds to a step S 25 . 
     In the step  825 , the vehicle speed VSP is compared with another predetermined vehicle speed VSP 1 . The predetermined vehicle speed VSP 1  is set in order to determine whether or not the vehicle deceleration is necessary when the parking lock operation is performed. Therefore, the predetermined speed VSP 1  is set smaller than the predetermined speed VSP 2 , for example to 8 km/hr. 
     When the vehicle speed VSP is equal to or greater than the predetermined vehicle speed VSP 1 , the routine proceeds to a step  326 . When the vehicle speed VSP is less than the predetermined vehicle speed VSP 1 , the routine proceeds to a step S 27 . 
     The routine proceeds to the step S 27  when the vehicle is hardly moving. In this case, the parking lock operation is performed. Specifically, the parking lock actuator  11  is driven so that the locking pawl  11 A is engaged with the parking gear  10 , and the rotation of the output shaft  1 A of the automatic transmission  1  is locked. After the processing of the step  827 , the routine is terminated. 
     On the other hand, when the vehicle speed VSP is equal to or greater than the predetermined vehicle speed VSP 1 , an automatic braking operation is first performed in the step S 26  to decrease the vehicle speed VSP. The automatic brake operation is an operation where the required braking pressure is supplied to the wheel cylinders  13  by the braking actuators  14  without depending on the depression of the brake pedal by the driver. In the following description, for the purpose of showing a difference, depression of the brake pedal by the driver will be referred to as intentional braking. 
     The processing of the step S 26  is performed using the routine shown in FIG.  4 . 
     Describing this subroutine, first in a step S 31 , a real vehicle deceleration G is computed based on the variation of the vehicle speed VSP. Herein, deceleration is computed as a negative acceleration. 
     In a following step S 32 , by looking up a prestored map, a target deceleration Gt is calculated from the vehicle speed VSP. 
     In a following step S 33 , the real vehicle deceleration G and a target deceleration at are compared, and the larger of their absolute values is selected as a final target deceleration GtA. 
     In a next step S 34 , a difference between the final target deceleration GtA and the real vehicle deceleration G is computed, and the required pressure of the wheel cylinders  13  is calculated so that this difference Is zero. A signal corresponding to this required pressure is then output to the brake actuators  14 , and the subroutine is terminated. 
     Here, referring to FIGS. 5A-5C, when an intentional brake operation is not performed, the target deceleration at is achieved purely by an automatic brake operation. 
     On the other hand, when the brake pedal is largely depressed by an intentional brake operation, there is no need to operate the automatic brake unless tile vehicle speed VSP is in a very low speed range, as shown in FIG.  5 C. 
     When an intentional, moderate degree of braking is performed, the deceleration G due to the intentional brake operation does not reach the target deceleration, so the difference between the target deceleration GtA and the deceleration G due to an intentional brake operation is compensated by an automatic brake operation. 
     Now, in the step S 26 , the control unit  15  terminates the routine after an automatic brake operation is performed using the subroutine of FIG.  4 . Even on the next and subsequent occasions when the routine is performed, provided that the vehicle speed VSP is not less than the predetermined vehicle speed VSP 1 , the automatic brake operation is again performed in the step S 26 . 
     On the other hand, when the selection range RNG shows a range other than the parking range (P) in the step S 23 , the parking lock operation is unnecessary. In this case, in a step S 24 , the routine is terminated after performing ordinary control of the automatic transmission  1  based on the selected range RNG. The ranges other than the parking range (P) comprise a drive range (D), low speed ranges such as first gear (1), second gear (2) and third gear (3), a reverse range (R) and a neutral range (N). 
     Ordinary control of the automatic transmission  1  means that neither parking lock nor braking is performed, and that only operation of the shift solenoid valves  5 ,  6  is performed. 
     In the step S 21 , when the vehicle speed VSP is equal to or greater than the predetermined vehicle speed VSP 2 , it means that the vehicle is running at a speed which is unsuitable for parking lock operation. 
     In this case, in a step S 22 , the routine determines whether or not the selection range RNG shows the parking range (P), as in the step S 23 . 
     When the selection range RNG shows a range other than the parking range (P), the routine performs ordinary control of the automatic transmission  1  based on the selection range RIG in the step S 24 , as in the case where an identical determining result is obtained in the step S 23 , and the routine is terminated. 
     On the other hand, when tile selection range RNG shows the parking range (P) in the step S 22 , the routine proceeds to a step S 28 . 
     Here, control of the automatic transmission  1  is performed based on the selection range RNG prior to selecting the parking range (P), and the routine is terminated. Specifically, if the drive range (D) is selected prior to selecting the parking range (P), speed ratio control in the drive range (D) is performed, and if the reverse range (R) is selected prior to selecting the parking range (P). speed ratio control in the reverse range (R) is performed. 
     In other words, even if the parking range (P) is selected, parking lock operation and drive of the brake actuators  14  based on the parking range (P) are not performed, and control of the automatic transmission  1  prior to the selection of the parking range (P) is performed instead. 
     After performing the step S 28 , the routine is terminated. 
     Due to the execution of the routine, when the vehicle speed VSP is equal to or greater than VSP 2 , the operation is ignored even if the shift lever  18  is moved to the parking range (P), and control of the automatic transmission  1  is performed based on the range RNG before the changeover to the parking range (P). 
     Under the condition that the vehicle speed VSP is less than VSP 2  and equal to or greater than VSPS, when the shift lever  18  is operated to the parking range (P), automatic braking is first performed until the vehicle speed VSP becomes equal to VSP 1 , then a parking lock operation is performed. 
     When the vehicle speed VSP is less than VSP 1 , and the shift lever  18  is moved to the parking range, a parking lock operation Is immediately performed. In this region, even if a parking lock operation is performed wherein the locking pawl  11 A is engaged with the parking gear  10 , an unpleasant shock or noise is not produced, and the force exerted by the locking pawl  11 A on the parking gear  10  can be suppressed low. 
     By setting a deceleration range between the vehicle speeds VSP 2  and VSP 1 , performing a parking lock operation in a relatively high speed range is made possible. 
     At the same time, by performing an automatic brake operation prior to locking up the parking gear  10 , the load on the parking lock members such as the locking pawl  11 A and parking gear  10  when the parking lock operation is performed can be suppressed to the same level as the parking lock operation performed below the vehicle speed VSP 1 . Further, a parking lock operation is not performed until deceleration to the vehicle speed VSP 1 , so an unpleasant noise due to the lipping off of the locking pawl  11 A from the teeth of the parking gear  10  is not produced. 
     If the vehicle speed VSP is less than VSP 2 , a parking lock operation will definitely be performed due to the movement of the shift lever  18  to the Parking range (P) even if the vehicle is not in the stationary state. Hence, there is no reason for the driver to repeatedly operate the shift lever  18  due to misunderstanding that the vehicle has a fault. 
     According to tins embodiment, an automatic brake comprising the brake actuators  14  and the wheel cylinders  13  was used, but another brake may be used instead. 
     U.S. Pat. No. 5,993,351 discloses a hybrid vehicle wherein an engine is combined with an electric motor, and regenerative braking that has a similar effect to engine braking is performed by making the motor generate electricity using the rotation energy of the drive wheels. 
     When this invention is applied to such a hybrid vehicle, the automatic brake operation of the step S 26  may be performed by using the regenerative braking mechanism comprising the motor  4 , inverter and battery  14  of U.S. Pat. No. 5,993,351. 
     Referring to FIGS. 6 and 7, a second embodiment of this invention relating to the parking lock mechanism  12  will now be described. 
     According to this embodiment, instead of the locking pawl  11 A and parking lock actuator  11  of the first embodiment, the parking lock mechanism  12  comprises a locking pawl  41 A, lever  41 , conical cam  44  and parking lock actuator  45 . 
     Referring to FIG. 6, the locking pawl  41 A is formed at one end of the lever  41 . A lever  41  is supported free to rotate on the case of the manual valve  3  via a pin  42 , and is pushed in a direction tending to separate it from the parking gear  10  by a return spring  43 . A pair of rollers  46  that can engage with the teeth of the parking gear  10  are attached at one end of the locking pawl  41 A. The lower end of the lever  41  comes in contact with the conical cam  44 . 
     Referring to FIG. 7, the conical cam  44  has a conical surface which comes in contact with the lever  41 . 
     The conical cam  44  is attached to a tip of the parking lock actuator  45  and as the parking lock actuator  45  elongates, the lever  41  is pushed up against the return spring  43  by the conical surface of the conical cam  44 , and the roller  46  is engaged with the teeth of the parking gear  10 . For this purpose, the contact surface of the lever  41  with the conical cam  44  is formed in a concave shape which fits the cam surface of the conical cam  44 . 
     In this way, by attaching the roller  46  to the locking pawl  41 A, engaging with and disengaging from the teeth of the parking gear  10  is rendered smooth by the rolling action of the roller  46 , and the drive force of the parking lock actuator  45  can be made small. According to research performed by the inventors, it is desirable to set the pressure angle of the teeth of the parking gear  10  to 0°±5°. 
     Referring to FIG. 8, a third embodiment of this invention relating to the locking pawl  11 A will now be described. 
     According to this embodiment, instead of providing the pair of rollers  46  on either side of the locking pawl  11 A as in the second embodiment, a U-shaped groove  41 B is formed at the tip of the locking pawl  41 A, and a single roller  46  is housed In this groove  41 B. In this case also, as in the second embodiment, engaging and disengaging of the locking pawl  41 A with the teeth of the parking gear  10  is rendered smooth by the roller  46 . 
     The contents of Tokugan Hei 11-333915, with a filing date of Nov. 25, 1999 in Japan, U.S. Pat. No. 5,206,808 and U.S. Pat. No. 5,993,351 are hereby incorporated by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. 
     The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: