TRANSMISSION PARK CONTROL SYSTEM

A park valve performs a multi-plexing function in which an out-of-park circuit is connected to line pressure when the valve is in an out-of-park position and is vented when the valve is in a park position. When particular clutches are released, the out-of-park circuit biases the park valve toward the out-of-park position. To initiate engagement of park, a controller commands a low line pressure, reducing the forces that bias the park valve toward the out-of-park position. Once the valve reaches an intermediate position in which the line pressure circuit is no longer fluidly connected to the out-of-park circuit, the controller commands an increase in line pressure, increasing the forces that bias the park valve toward the park position. 驻车阀执行多重功能，其中脱离驻车档回路在所述阀处于脱离驻车档位置时连接到管路压力，并在所述阀处于驻车档位置时通气。当释放特定的离合器时，所述脱离驻车档回路将所述驻车阀偏向所述脱离驻车档位置。为了引起接合驻车档，控制器命令低管路压力，从而减小将所述驻车阀偏向所述脱离驻车档位置的力。一旦所述阀到达所述管路压力回路不再流体连接到所述脱离驻车档回路的中间位置，所述控制器便命令增加管路压力，从而增加将所述驻车阀偏向所述驻车档位置的力。