Transmission hydraulic control system

摘要

An automatic transmission uses 6 shift elements applied in combinations of four to establish ten forward speed ratios and a reverse speed ratio. The automatic transmission uses a hydraulic control system to control engagement of the six elements, control engagement of a torque converter bypass clutch, control engagement of a parking pawl, and to provide fluid for a hydrodynamic torque converter and for lubrication. The parking pawl is disengaged in response to engagement of two of the six shift elements and remains disengaged in response to engagement of other shift elements. A single valve controls several different functions associated with the two-pass torque converter. Pressurized fluid is provided by a variable displacement engine driven pump and also by an electric pump. A priority valve reduces lubrication flow when other fluid demands are high as indicated by the pump displacement control circuit.

主权项

1. A transmission comprising:
first, second, and third shift elements engageable in combination to establish a reverse transmission ratio; a fourth shift element engageable in combination with the first and second shift elements to establish a forward launch transmission ratio; first, second, third, and fourth hydraulic circuits configured to engage the first, second, third, and fourth shift elements respectively in response to pressurization of the respective hydraulic circuit; a parking pawl engageable to hold a transmission output shaft against rotation; and a park valve configured to disengage the parking pawl in response to simultaneous pressurization of the first and second hydraulic circuits and then to maintain the parking pawl in a disengaged state in response to pressurization of either of the second or third hydraulic circuits.