Abstract: Ideally, when a transmission is in Neutral, no torque should be exerted on the vehicle wheels by the powertrain. However, even with all clutches in a gearbox disengaged, some torque may be transmitted from a turbine shaft to the transmission output due to clutch drag and transmission component inertia. To avoid transmitting torque, a subset of clutches may be engaged to produce an input tie-up state, this holding the turbine shaft against rotation while permitting rotation of the output element.

Abstract: Air ingestion into a transmission hydraulic system may lead to a number of issues. For example, the time to engage a hydraulically actuated parking mechanism may be excessive. As another example, the pump may not prime properly on a subsequent engine start. The air ingestion issue may be detected based on variability of transmission line pressure. When the line pressure variability exceeds a threshold, actions are taken to mitigate the potential issues.

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 vehicle includes an engine, a transmission, and a controller. The transmission has clutches, a circuit configured to transport fluid to the clutches, a pump configured to circulate the fluid through the circuit, and an accumulator disposed along the circuit. The controller is programmed to, responsive to an engine start and a fluid temperature being less than a temperature threshold, discharge the accumulator to prime the pump.

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 vehicle includes an engine, a transmission, and a controller. The transmission has clutches, a circuit configured to transport fluid to the clutches, a pump configured to circulate the fluid through the circuit, and an accumulator disposed along the circuit. The controller is programmed to, responsive to an engine start and a fluid temperature being less than a temperature threshold, discharge the accumulator to prime the pump.

Abstract: Air ingestion into a transmission hydraulic system may lead to a number of issues. For example, the time to engage a hydraulically actuated parking mechanism may be excessive. As another example, the pump may not prime properly on a subsequent engine start. The air ingestion issue may be detected based on variability of transmission line pressure. When the line pressure variability exceeds a threshold, actions are taken to mitigate the potential issues.

Abstract: Ideally, when a transmission is in Neutral, no torque should be exerted on the vehicle wheels by the powertrain. However, even with all clutches in a gearbox disengaged, some torque may be transmitted from a turbine shaft to the transmission output due to clutch drag and transmission component inertia. To avoid transmitting torque, a subset of clutches may be engaged to produce an input tie-up state, this holding the turbine shaft against rotation while permitting rotation of the output 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 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: A park valve includes a slidable end-cap. Under normal circumstances, the end-cap is held in a nominal position by a spring, such as a Belleville spring. The 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. In an intermediate position, a hydraulic lock condition may potentially occur. When engaging park, the hydraulic lock condition is prevented by the slidable end-cap.

Abstract: A transmission park mechanism is hydraulically actuated. Specifically a controller releases the parking pawl by commanding engagement of particular shift elements at an elevated line pressure. The process of transitioning from Park to a Drive or Reverse condition may involve several sequential steps. To reduce the delay between driver selection of Drive or Reverse and completion of the engagement, it is advantageous to raise the line pressure in response to depression of a brake pedal, prior to movement of the shift lever. To limit the adverse fuel economy impact of increased line pressure, the line pressure is lowered again if the driver does not move the shift lever soon after depressing the brake pedal.

Abstract: A park valve includes a slidable end-cap. Under normal circumstances, the end-cap is held in a nominal position by a spring, such as a Belleville spring. The 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. In an intermediate position, a hydraulic lock condition may potentially occur. When engaging park, the hydraulic lock condition is prevented by the slidable end-cap.

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: 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 park mechanism is hydraulically actuated. Specifically. a controller releases the parking pawl by commanding engagement of particular shift elements at an elevated line pressure. The process of transitioning from Park to a Drive or Reverse condition may involve several sequential steps. To reduce the delay between driver selection of Drive or Reverse and completion of the engagement, it is advantageous to raise the line pressure in response to depression of a brake pedal, prior to movement of the shift lever. To limit the adverse fuel economy impact of increased line pressure, the line pressure is lowered again if the driver does not move the shift lever soon after depressing the brake pedal.