Patent Application
20130305863
The present disclosure relates generally to a vehicle parking brake or lock system and more particularly to a method of operating a park lock mechanism.
Vehicles transmissions have a park setting or gear in which the transmission may be locked and the vehicle turned off. When a vehicle is parked on a hill or other grade, gravitational forces on the vehicle provide a load on the vehicle park lock system. With such a load on the park lock system, disengagement of the park lock system to permit the transmission to be shifted out of park may be difficult or noisy or have a harsh movement.
A method of operating a park lock mechanism in a vehicle includes determining a force acting on a vehicle park lock mechanism when the vehicle is in park, and providing an offsetting force to counteract the force on the park lock mechanism before the vehicle is shifted out of park. In doing so, harshness and noise that may be associated with shifting a vehicle out of park, especially when the vehicle is parked on an incline, can be reduced or eliminated.
In at least one implementation, a method of providing an offsetting force to a park lock system in a vehicle includes providing an offsetting force on a transmission output shaft in a direction opposite to the force on the transmission output shaft due to the force of gravity on the vehicle. The offsetting force, in at least one example, can be applied without first determining the magnitude of the force needed, and the offsetting force can be applied until the net force on the park lock mechanism, or on the output shaft, is below a threshold.
Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings provided hereinafter. It should be understood that the summary and detailed description, including the disclosed embodiments and drawings, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the invention, its application or use. Thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the invention.
Referring in more detail to the drawings,
In more detail, as shown in
The park lock system 10 includes the lock mechanism 12 and an actuator 24 for selectively engaging the lock mechanism 12 with the park gear 14. In the example shown, the lock mechanism 12 includes a pawl 26 pivoted at a first end about a pin 28 to move a second end including a lock tab 30 toward and away from the park gear 14. This permits the pawl 12 to be moved between disengaged (
The actuator 24 may include a motor 32 and a drive member 34 driven by the motor 32 to move the pawl 26 from its disengaged position to its engaged position. The motor 32 may be any suitable reversible electric motor 32. The motor 32 is coupled to a threaded spindle 36 to rotate the spindle in forward and reverse directions and thereby move the drive member 34. The drive member 34 travels along the spindle 36 in a direction dictated by the direction of rotation of the spindle 36. In the implementation shown, the drive member 34 moves toward the motor 32 when the spindle 36 is rotated in the forward direction and the drive member 34 moves away from the motor 32 when the spindle 36 is rotated in the reverse direction.
In use, to engage the park lock system 10 the motor 32 is driven in its forward direction. This moves the drive member 34 toward the motor 32 along the spindle 36 until the drive member 34 engages the park pawl 26. If the lock tab 30 of the pawl 26 is aligned with a gap 22 between adjacent teeth 20 in the park gear 14, the pawl 26 is moved to its engaged position with the lock tab 30 received between adjacent teeth 20 as shown in
To shift the vehicle out of park, the park pawl 26 must be moved to its disengaged position. To do this, the motor 32 is driven in its reverse direction and the drive member 34 moves away from the motor 32 and the pawl 26. As the drive member 34 disengages from the pawl 26, the return spring biasing the pawl 26 moves the pawl 26 toward its disengaged position until the lock tab 30 is free and clear of the park gear 14 and the park gear can rotate without interference from the park pawl.
At least when the vehicle is parked on an incline, the force of gravity on the vehicle will tend to rotate the park gear 14 against and firmly into engagement with the lock tab 30 of the park pawl 26. This can provide a significant force on the park pawl 26 such that when the park pawl 26 is moved to its disengaged position, the park pawl 26 may abruptly move out of its engaged position and a loud noise and abrupt (but usually slight) movement of the vehicle may occur. Noise may also be attributed to the sudden movement of the park gear 14 upon release of the park pawl 26. The noise and vehicle movement can be startling or unsettling to some people.
To reduce or eliminate the noise and/or sudden movement of the vehicle upon disengagement of the park pawl 26 from the park gear 14, a counterforce is provided to lessen (potentially reduce to zero) the force the park gear 14 places on the lock tab 30 at least when the vehicle is parked on a grade or incline above a threshold magnitude. The counterforce may be provided by an electric motor coupled to the output shaft 16. The electric motor may provide a torque that counters the force tending to rotate the shaft 16 such that the force the park gear 14 provides on the lock tab 30 is reduced. In this way, the park lock system 10 is readily adaptable to an electric vehicle application where such an electric motor coupled to the output shaft 16 is already available. Of course, the counterforce could be provided in other vehicles including those using a combustion engine where the offsetting torque could be provided by the engine itself, or by another prime mover including an electric motor, if desired.
Accordingly, the park lock system 10 in operation may utilize any method of applying a counterforce or offsetting torque to lessen the force acting on the park lock mechanism 12 before the park lock mechanism 12 is disengaged from the park gear 14. In operation, one method of applying a counterforce is shown in the flow chart of
In more detail, the method of
Then, if there is a request 46 to shift the vehicle out of park and to another gear, the motor may be energized to provide the desired counteracting torque to the shaft 16. The counteracting torque applied can be sensed at 48, and when the desired counteracting torque, or a greater torque, has been applied to the shaft 16, the counteracting torque is no longer applied and the vehicle may then be shifted out of park at 50 and into another gear. A suitable controller, which may be a stand alone unit or part of an existing vehicle controller or control system, may be used to determine the offsetting force needed to be applied to the output shaft 16, and to control and monitor the application of the offsetting force to the output shaft 16.
Another way to determine the force on the park pawl 26 is to actually sense the force acting on the park pawl 26, such as with a strain gauge or other sensor. Such a force sensor 60 is shown diagrammatically in
Other steps may be included or substituted for steps identified in the representative flow chart and described method. For example, before beginning the method a determination can be made at 52 as to whether the vehicle is stationary and in park. If not, then no counteracting torque should be applied so the method should not be performed. Another step 54 may be to determine if the vehicle is parked on an incline that is greater than a threshold incline. The threshold incline can be chosen so that on inclines less than the threshold, the force on the pawl 26 will be within an acceptable range without any offsetting force applied to the output shaft 16 such that disengagement of the park pawl 26 will not cause unacceptable noise or vehicle movement. In this way, if the vehicle is not parked on a greater than threshold incline, then no offsetting force need be applied to the output shaft 16 and the method can be stopped.
Also, a system check may be provided at 56 before the counteracting torque is applied. The system check may include one or more steps designed to prevent application of the counteracting torque in certain conditions. For example, the system check may verify one or more of the following: 1) that the park lock is not already disengaged; 2) the vehicle currently is on a grade; 3) there is an operator request to disengage park; 4) the vehicle brake pedal has been/is applied (perhaps by sensing brake pedal switch(es) or receiving an indication from the system or vehicle ECU); 5) a signal indicative of the vehicle grade that was stored from the previous ignition cycle (e.g. when the vehicle engine or motor was shutoff) is within a threshold value of the current signal regarding the grade the vehicle is currently on; 6) the integrity of the indicated/signaled grade is verified (perhaps through a Controller Area network (CAN), Cyclic Redundancy Check (CRC) and/or Rolling Counter (RC) check; 7) a traction motor angular displacement is less than a threshold; and 8) that the counteracting torque applied (achieved torque) is within a threshold of the desired or calculated torque intended to be applied. In at least some implementations, the counteracting torque would not be applied if any of the above conditions were not satisfied. The system check could also verify that sufficient brake system pressure exists to hold the vehicle stationary if the park lock is disengaged, and that a hand brake has been applied before disengaging the park lock, if desired.
Of course, other method steps may be added or substituted for the steps shown in
Further, while a particular park lock mechanism 12 and system 10 are described, the method of providing an offsetting force to the transmission output shaft 16 could be used with any park lock mechanism 12 and system 10. That is, the electric motor driven system, including the drive member 34, pawl 26, etc, are not needed. The force on any type of vehicle park lock system 10 could be reduced by providing a counteracting or offsetting force or torque to the transmission output shaft 16 or park gear 14.
