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 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.

Abstract: A transmission includes a selectable one-way clutch with active and passive states. Successful transition from the active state to the passive state is only possible when there is no torque tending to cause overrunning. After commanding a transition from the active state to the passive state, a controller partially engages a first friction clutch to induce a torque tending away from overrunning until a lash crossing is detected. Then, the controller releases the first clutch and partially applies a second clutch to induce a torque toward overrunning. When slip is detected, indicating successful achievement of the passive state, the second clutch is released.

Abstract: A transmission includes a selectable one-way clutch with an active state and a passive state. To avoid occupant discomfort and hardware damage, transitions from the passive state to the active state must only be commanded when no or very little slip is present across the selectable one-way clutch. Several methods are presented to eliminate slip, depending on vehicle speed. When the vehicle is stationary, full engagement of a clutch that causes slip to be proportional to vehicle speed eliminates slip. When the vehicle is moving backwards, partial engagement of the above clutch eliminates slip. When the vehicle is moving forwards, full engagement of all but one clutch of a tie-up condition and partial engagement of the remaining clutch of the tie-up condition brings the vehicle to a stop and eliminates slip.

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 a selectable one-way clutch with an active state and a passive state. To avoid occupant discomfort and hardware damage, transitions from the passive state to the active state must only be commanded when no or very little slip is present across the selectable one-way clutch. Several methods are presented to eliminate slip, depending on vehicle speed. When the vehicle is stationary, full engagement of a clutch that causes slip to be proportional to vehicle speed eliminates slip. When the vehicle is moving backwards, partial engagement of the above clutch eliminates slip. When the vehicle is moving forwards, full engagement of all but one clutch of a tie-up condition and partial engagement of the remaining clutch of the tie-up condition brings the vehicle to a stop and eliminates slip.

Abstract: A transmission includes a selectable one-way clutch with active and passive states. Successful transition from the active state to the passive state is only possible when there is no torque tending to cause overrunning. After commanding a transition from the active state to the passive state, a controller partially engages a first friction clutch to induce a torque tending away from overrunning until a lash crossing is detected. Then, the controller releases the first clutch and partially applies a second clutch to induce a torque toward overrunning. When slip is detected, indicating successful achievement of the passive state, the second clutch is released.

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 a transmission having a torque converter, a device configured to generate line pressure, and at least one fluid path connecting the device in fluid communication with the torque converter. A controller is programmed to, responsive to an engine-off time exceeding a threshold and a parameter indicative of departure being present, command the device to generate line pressure so that fluid is supplied to the torque converter. The device may be a transmission pump or an accumulator.

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 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.

Abstract: A vehicle includes a transmission having a torque converter, a device configured to generate line pressure, and at least one fluid path connecting the device in fluid communication with the torque converter. A controller is programmed to, responsive to an engine-off time exceeding a threshold and a parameter indicative of departure being present, command the device to generate line pressure so that fluid is supplied to the torque converter. The device may be a transmission pump or an accumulator.

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 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.