Method for disengaging hydraulic park
AssigneeFord Global Technologies, LLC
InventorTimothy Fedullo
Life of this patent
Estimating the term…
Abstract
A hydraulically controlled park system disengages a parking pawl in response to engagement of particular shift elements. When the vehicle is one a grade, greater force may be required to dis-engage the pawl, potentially leading to a failure to dis-engage. The controller avoids this failure by engaging an uphill gear ratio and controlling the transmission input torque to transfer load from the parking pawl to the gearing prior to engaging the shift elements that dis-engage the pawl. Following dis-engagement of the parking pawl, the transmission is in a tie-up condition in which the output shaft is held stationary by shift elements. The controller transitions from this tie-up condition to the selected gear ratio by releasing shift elements.
Claims20
A method of operating a vehicle comprising:
- in response to de-selection of Park via a shift selector while the vehicle is on a grade,
- engaging a first shift element to establish a first gear ratio selected to propel the vehicle up the grade,
- in response to engaging the first shift element, controlling transmission input torque to a first value that corresponds with unloading a parking pawl, pawl and maintaining a position of the vehicle on the grade while the first gear ratio is established,
- in response to controlling the transmission input torque to the first value, engaging a second shift element to disengage the parking pawl and create a transmission tie-up,
- in response to creating the transmission tie-up, adjusting the torque at the transmission input during the tie-up to a second value that corresponds with an idle torque, and
- in response to selection of a second gear ratio based on the shift selector and the transmission tie-up, gradually releasing one of the first and second shift elements to establish the second gear ratio.
A method of operating a vehicle comprising:
- in response to de-selection of Park,
- engaging a first shift element to establish a first gear ratio,
- in response to engaging the first shift element, controlling transmission input torque to a first value that corresponds with unloading a parking pawl and maintaining a position of the vehicle on a grade while the first gear ratio is established,
- in response to controlling the transmission input torque to the first value, engaging a second shift element to disengage the parking pawl and create a transmission tie-up,
- in response to creating the transmission tie-up, adjusting the torque at the transmission input during the tie-up to a second value that corresponds with an idle torque, and
- in response to selection of a second gear ratio and the transmission tie-up, gradually releasing one of the first and second shift elements to establish the second gear ratio.
A transmission comprising:
- a plurality of shift elements;
- a park system configured to engage and disengage a parking pawl;
- and
- a controller programmed to, in response to a command to de-select Park,
- engage a first subset of the plurality of shift elements to establish a first gear ratio,
- in response to establishing the first gear ratio, control a transmission input torque to a first value that corresponds with unloading the parking pawl and maintaining a position of the vehicle on a grade while the first gear ratio is established,
- in response to controlling the transmission input torque to the first value, engaging a second subset of the plurality of shift elements to disengage the parking pawl and create a transmission tie-up,
- in response to creating the transmission tie-up, adjusting the torque at the transmission input during the tie-up to a second value that corresponds with an idle torque, and
- in response to selection of a second gear ratio and the transmission tie-up, gradually releasing one of the first and second subsets of the plurality of shift elements to establish the second gear ratio.
Dependencies are inferred from the claim text.