Transmission shifting with speed dither and torque dither

A method of disengaging a transmission of a series hydraulic hybrid system having an input shaft for receiving power from a prime mover, an output drive shaft, at least one primary hydraulic pump/motor, and at least one secondary hydraulic pump/motor connected to the primary hydraulic pump/motor via a high pressure manifold and selectively connectable to the output drive shaft of the transmission, the method comprising the steps of:

• entering a disengagement stage;
• calculating a desired torque of the output shaft of the at least one secondary pump/motor via a controller,
• operating the at least one secondary pump/motor at a target torque that is the desired torque plus a desired torque dither;
• disengaging the output shaft of the at least one secondary pump/motor with the output drive shaft of the transmission via power transmission components when the target torque is commanded;
• wherein the operating includes regulating a flow of fluid to and from an accumulator that stores pressurized fluid to the at least one secondary pump/motor to achieve the target torque, and
• wherein after disengagement of the output shaft of the pump/motor and the output drive shaft is confirmed, the controller exits from the disengagement stage.

A hybrid system for a vehicle comprising:

• a power drive unit having:
• an input shaft for receiving power from a prime mover;
• an output drive shaft;
• a primary hydraulic pump/motor having an output shaft;
• a secondary hydraulic pump/motor connected to the primary hydraulic pump/motor via a high pressure manifold and having an output shaft;
• and
• power transmission components for selectively coupling the input shaft to at least one of the primary hydraulic pump/motor and the output drive shaft and for selectively coupling the secondary hydraulic pump/motor to the output drive shaft;
• an accumulator for storing pressurized fluid connected to both the primary and secondary pump/motors via the high pressure manifold;
• and
• a controller calculating a desired speed of the output shaft of the secondary pump/motor, operating the secondary pump/motor at a target speed that is the desired speed plus a desired speed dither, and engaging the output shaft of the secondary pump/motor with the output drive shaft unit when the target speed is reached within a prescribed speed error threshold;
• wherein the controller controls the high pressure manifold to supply fluid from the accumulator to the secondary pump/motor for operating the secondary pump/motor at the target speed.

A hybrid system for a vehicle comprising:

• a power drive unit having:
• an input shaft for receiving power from a prime mover;
• an output drive shaft;
• a primary hydraulic pump/motor having an output shaft;
• a secondary hydraulic pump/motor connected to the primary hydraulic pump/motor via a high pressure manifold and having an output shaft;
• and
• power transmission components for selectively coupling the input shaft to at least one of the primary hydraulic pump/motor and the output drive shaft and for selectively coupling the secondary hydraulic pump/motor to the output drive shaft;
• an accumulator for storing pressurized fluid connected to both the primary and secondary pump/motors via the high pressure manifold;
• and
• a controller calculating a desired torque of the output shaft of the secondary pump/motor, operating the secondary pump/motor at a target torque that is the desired torque plus a desired torque dither, and disengaging the output shaft of the secondary pump/motor from the output drive shaft of the transmission when the target torque is commanded;
• wherein the controller regulates the high pressure manifold to supply fluid to and from an accumulator to the pump/motor to achieve the target torque.