Abstract: A transmission includes a gearing arrangement configured to shift speed ratios by disengaging an off-going shift element and engaging an oncoming shift element and an electrohydraulic valve having an actuatable valve element configured to control an engagement state of the oncoming shift element. A controller is programmed to, during a shift of the transmission, in response to the off-going shift element disengaging and an expected ratio change not initiating, monotonically increase current to the valve to a maximum value to overcome frictional resistance on the valve element, and programmed to, in response to expiration of a timer and the ratio change still not initiating, send a repeating pattern of high and low current signals according to a duty cycle to overcome frictional resistance of the valve element.

Abstract: A transmission includes a gearing arrangement configured to shift speed ratios by disengaging an off-going shift element and engaging an oncoming shift element and an electrohydraulic valve having an actuatable valve element configured to control an engagement state of the oncoming shift element. A controller is programmed to, during a shift of the transmission, in response to the off-going shift element disengaging and an expected ratio change not initiating, monotonically increase current to the valve to a maximum value to overcome frictional resistance on the valve element, and programmed to, in response to expiration of a timer and the ratio change still not initiating, send a repeating pattern of high and low current signals according to a duty cycle to overcome frictional resistance of the valve element.

Abstract: A transmission includes an accumulator to hold one of more shift elements in an engaged state while an engine is off. The transmission also includes a hydraulic park system that disengages park in response to engagement of two shift elements. In some circumstance, draining the accumulator in an uncontrolled manner in the presence of a failed valve may lead to unintentionally disengaging park. To avoid this, the accumulator is discharged in a controlled manner. Fluid is first transferred from the accumulator to a shift element apply chamber. Then, the fluid is vented from the shift element apply chamber.

Abstract: A transmission assembly including a clutch system, an accumulator, and a controller is provided. The clutch system may include a flow source. The accumulator may be selectively in communication with the flow source via a solenoid valve. The controller may be programmed to, responsive to detection of a vehicle stop and the accumulator charged below a predetermined threshold, output a command to open the solenoid valve to rapidly charge the accumulator from the flow source. The predetermined threshold may be an accumulator pressure between 700 kPa and 900 kPa. The controller may be further programmed to, responsive to detection of the accumulator being charged to or above the predetermined threshold, output a shut down command to an engine in communication with the transmission assembly and to output a close command to the solenoid valve. The flow source may be a pump out circuit or a line pressure circuit.

Abstract: In a special operating mode, a controller is programmed to disengage a hydraulically actuated park mechanism without use of engine power. The starter motor is used to rotate the engine-driven pump at sufficient speed to command disengagement of Park. Once park is disengaged, a holding pin is used to maintain the out of park condition without hydraulic pressure or flow.

Abstract: 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 engage park, a controller commands a low line pressure, reducing the forces that bias the park valve toward the out-of-park position. To accelerate the pressure decay in the line pressure circuit, thereby decreasing the time required to achieve park, the controller commands engagement of one or more shift elements.

Abstract: A transmission assembly including a clutch system, an accumulator, and a controller is provided. The clutch system may include a flow source. The accumulator may be selectively in communication with the flow source via a solenoid valve. The controller may be programmed to, responsive to detection of a vehicle stop and the accumulator charged below a predetermined threshold, output a command to open the solenoid valve to rapidly charge the accumulator from the flow source. The predetermined threshold may be an accumulator pressure between 700 kPa and 900 kPa. The controller may be further programmed to, responsive to detection of the accumulator being charged to or above the predetermined threshold, output a shut down command to an engine in communication with the transmission assembly and to output a close command to the solenoid valve. The flow source may be a pump out circuit or a line pressure circuit.

Abstract: A transmission includes an accumulator to hold one of more shift elements in an engaged state while an engine is off. The transmission also includes a hydraulic park system that disengages park in response to engagement of two shift elements. In some circumstance, draining the accumulator in an uncontrolled manner in the presence of a failed valve may lead to unintentionally disengaging park. To avoid this, the accumulator is discharged in a controlled manner. Fluid is first transferred from the accumulator to a shift element apply chamber. Then, the fluid is vented from the shift element apply chamber.

Abstract: 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.

Abstract: In order to pre-stage a clutch piston in preparation for clutch engagement, a controller commands a high current to a Casting Integrated Direct Acting Solenoid (CIDAS) valve. This staging is performed in two distinct phases wherein the current is higher in the first phase than in the second phase. Staging the piston in this manner reduces the staging time and reduces the variability of the staging time. The duration of the first phase may be adjusted based on a number of parameters including, the length of a preceding engine off period, the number of clutch applications since the engine off period, a fluid temperature, and a length of time since a preceding engagement of the clutch.

Abstract: 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.

Abstract: In a special operating mode, a controller is programmed to disengage a hydraulically actuated park mechanism without use of engine power. The starter motor is used to rotate the engine-driven pump at sufficient speed to command disengagement of Park. Once park is disengaged, a holding pin is used to maintain the out of park condition without hydraulic pressure or flow.

Abstract: 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 engage park, a controller commands a low line pressure, reducing the forces that bias the park valve toward the out-of-park position. To accelerate the pressure decay in the line pressure circuit, thereby decreasing the time required to achieve park, the controller commands engagement of one or more shift elements.

Abstract: In order to pre-stage a clutch piston in preparation for clutch engagement, a controller commands a high current to a Casting Integrated Direct Acting Solenoid (CIDAS) valve. This staging is performed in two distinct phases wherein the current is higher in the first phase than in the second phase. Staging the piston in this manner reduces the staging time and reduces the variability of the staging time. The duration of the first phase may be adjusted based on a number of parameters including, the length of a preceding engine off period, the number of clutch applications since the engine off period, a fluid temperature, and a length of time since a preceding engagement of the clutch.

Abstract: A control strategy and method for controlling friction element engagement and disengagement time for an automatic transmission when the transmission is operating at cold ambient temperatures. During drive-to-reverse or reverse-to-drive friction element engagements with power on, the strategy compensates for a tendency of an oncoming friction element to gain capacity before an off-going clutch loses capacity, thereby avoiding a potential friction element tie-up condition when the transmission is operated with intermediate or high levels of engine torque as the friction elements are sequentially engaged and disengaged during cold rock cycling.

Abstract: A control strategy and method for controlling friction element engagement and disengagement time for an automatic transmission when the transmission is operating at cold ambient temperatures. During drive-to-reverse or reverse-to-drive friction element engagements with power on, the strategy compensates for a tendency of an oncoming friction element to gain capacity before an off-going clutch loses capacity, thereby avoiding a potential friction element tie-up condition when the transmission is operated with intermediate or high levels of engine torque as the friction elements are sequentially engaged and disengaged during cold rock cycling.