Dual-clutch transmission parking brake disengaging method of a vehicle

Abstract

A method for disengaging a parking lock of a dual-clutch transmission of a motor vehicle with at least one drive unit is provided. The method includes, upon detection of an absolute value of a road inclination along a longitudinal axis of the motor vehicle exceeding a predetermined threshold and upon actuation of a selector lever for disengaging the parking lock prior to disengagement of the parking lock, issuing a torque request to the drive unit and closing a power-shifting clutch of the dual-clutch transmission with an engaged gear in a sub-transmission to which the power-shifting clutch is allocated. A torque transferred by the power-shifting clutch as a consequence of closing the power-shifting clutch and the torque request to the drive unit is a relief torque. The torque request to the drive unit and the closed power-shifting clutch are selected to counteract a torque, supported by a parking lock pawl, applying with an engaged parking lock by drive wheels on an output side at the transmission.

Claims

1. A method for disengaging a parking lock of a dual-clutch transmission of a motor vehicle with at least one drive unit, the method comprising: upon detection of an absolute value of a road inclination along a longitudinal axis of the motor vehicle exceeding a predetermined threshold and upon actuation of a selector lever for disengaging the parking lock prior to disengagement of the parking lock, issuing a torque request to the at least one drive unit and closing a power-shifting clutch of the dual-clutch transmission with an engaged gear in a sub-transmission to which the power-shifting clutch is allocated; wherein a torque transferred by the power-shifting clutch as a consequence of closing the power-shifting clutch and the torque request to the drive unit is a relief torque, and wherein the torque request to the drive unit and the closed power-shifting clutch are selected to counteract a torque supported by a parking lock pawl, and wherein the torque supported by the parking lock pawl is applied with an engaged parking lock by drive wheels on an output side at the transmission.

2. The method of claim 1, further comprising disengaging the parking lock upon reaching a torque threshold of the relief torque transferred by the power-shifting clutch in order to account for a physical dead time of a hydraulic system.

3. The method of claim 1, wherein the relief torque is applied by the at least one drive unit at a constant rotational speed of the at least one drive unit.

4. The method of claim 1, wherein the at least one drive unit comprises an internal combustion engine such that the relief torque is applied by the internal combustion engine.

5. The method of claim 1, wherein the at least one drive unit comprises an electric motor such that the relief torque is applied by the electric motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The FIGURE shows chronological progressions of various vehicle and dual-clutch transmission conditions in accordance with an exemplary embodiment of the invention

DETAILED DESCRIPTION

(2) Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

(3) In the following, the invention is more specifically described by way of example based on the attached FIGURE, which shows the progressions of the road inclination, the vehicle speed, the accelerator pedal travel, the engine rotational speed, the rotational speed of the input shafts of the sub-transmission of the dual-clutch transmission, the roll-back prevention function (hill holder), the selector lever position, the gears engaged in the sub-transmissions, the clutch torque of the two power-shifting clutches and the signals of the parking lock sensor as a function of time.

(4) In the attached FIGURE, curve A represents the chronological progression of the road inclination, curve B represents the chronological progression of the vehicle speed, curve C represents the chronological progression of the accelerator pedal travel, curve D represents the chronological progression of the engine rotational speed, curve E represents the chronological progression of the rotational speed of the input shaft of the first sub-transmission of the dual-clutch transmission and curve F represents the chronological progression of the input shaft of the second sub-transmission of the dual-clutch transmission. Furthermore, curve G represents the chronological progression of the roll-back prevention function, curve H represents the chronological progression of the selector lever position, curve I represents the chronological progression of the current travel gear, curve J represents the chronological progression of the predicted gear (that is, of the gear that is engaged in the sub-transmission not connected to the drive), curve K represents the chronological progression of the clutch torque of the power-shifting clutch allocated to the second sub-transmission, curve L represents the chronological progression of the clutch torque of the power-shifting clutch allocated to the first sub-transmission, and curve M represents the chronological progression of the signals of the parking lock sensor.

(5) At the point in time t_0, the road inclination exceeds a predetermined threshold, for example five percent (5%), whereas this is detected by a sensor and is transmitted to a controller, whereas, at the same point in time, the roll-back prevention function is transferred from the inactive status to the ready status. Thereby, with a constant accelerator pedal position and lever position, the vehicle speed, the engine rotational speed and the rotational speeds of the input shafts of the sub-transmission are reduced based on the inclination; the travel gear corresponds to the first gear and is engaged in the second sub-transmission.

(6) At the point in time t_1, with a further declining engine rotational speed, the driver steps off the accelerator pedal, whereas the vehicle is stationary, the roll-back prevention function is transferred from ready status to active status and the rotational speed of the input shafts of the sub-transmission is zero, whereas, at the point in time t_2, at an inclination that exceeds a predetermined threshold, the selector lever for engaging the position P is actuated and the engagement of the parking lock is requested. The predicted gear, which is engaged in the first sub-transmission, corresponds to the reverse gear at such point in time, whereas, in the second sub-transmission, the first gear is engaged. Due to the dead time of the hydraulic system, for displacing the locking pawl for engaging the parking lock, the parking lock is engaged after the point in time t_2.

(7) At the point in time t_3, the selector lever for engaging the position D is actuated and the disengagement of the parking lock is requested, whereas, in accordance with exemplary aspects of the invention, prior to the disengagement of the parking lock, a torque request is issued and a power-shifting clutch of the dual-clutch transmission with an engaged gear in the sub-transmission, to which the power-shifting clutch is allocated, is closed, whereas the power-shifting clutch to be closed and the torque request to the at least one drive unit are selected in such a manner that a torque transferred by the power-shifting clutch counteracts a torque applied to the transmission on the output side by the drive wheels when the parking lock is engaged, the torque transferred by the power-shifting clutch is supported by the parking lock pawl and serves as a relief torque. In this manner, a damping is achieved. In the present case, the power-shifting clutch allocated to the second sub-transmission, in which the first gear is engaged, is closed, because the vehicle is on an inclination.

(8) In the event that the vehicle is on a gradient, the power-shifting clutch allocated to the first sub-transmission, in which the reverse gear is engaged, is closed to provide a relief torque, whereas the gear is subsequently engaged in accordance with the driver command.

(9) In order to optimize the response time upon the disengagement of the parking lock, already upon reaching a torque threshold, which, in the example shown, amounts to 30 Nm and is achieved at the point in time t_4, the disengagement process of the parking lock is carried out, by which the physical dead time of the hydraulic system is taken into account. The torque is then increased up to a predetermined maximum value. The parking lock is completely disengaged shortly prior to the point in time T_5, whereas, at the point in time T_5, the carrying out of the method in accordance with exemplary aspects of the invention is completed, and, at the subsequent point in time T_6, at which the roll-back prevention function is transferred from active status to ready status, the vehicle is accelerated as a response to the actuation of the accelerator pedal, the travel gear is the second gear in the first sub-transmission and, as a predicted gear, the first gear remains engaged in the second sub-transmission.

(10) Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims.

REFERENCE SIGNS

(11) A chronological progression of the road inclination B chronological progression of the vehicle speed C chronological progression of the accelerator pedal travel D chronological progression of the engine rotational speed E chronological progression of the rotational speed of the input shaft of the first sub-transmission F chronological progression of the rotational speed of the input shaft of the second sub-transmission G chronological progression of the roll-back prevention function H chronological progression of the selector lever position I chronological progression of the travel gear J chronological progression of the predicted gear K chronological progression of the clutch torque of the power-shifting clutch allocated to the second sub-transmission L chronological progression of the clutch torque of the power-shifting clutch allocated to the first sub-transmission M chronological progression of the signals of the parking lock sensor