A valve for controlling the flow of hydraulic fluid to a hydraulic motor. The valve includes a sleeve and a spool. The sleeve includes a first fluid flow port for receiving hydraulic fluid from the supply line; a second fluid flow port for supplying hydraulic fluid to a second valve; a third fluid flow port for receiving hydraulic fluid from a first control line; a fourth fluid flow port for receiving hydraulic fluid from a second control line; and a fifth fluid flow port in fluid communication with the return line. The valve is arranged to be actuated to move the spool between a first position and a second position. When the spool is in the second position, the fifth fluid flow port is in fluid communication with the second, third and fourth fluid flow ports and the first fluid flow port is closed by the spool.

A bi-directional pump connected to a motor by a pair of supply/discharge lines; a regulator changes the bi-directional pump tilting angle; and a controller controls the regulator based on a turning signal outputted from a turning operation valve. At the turning acceleration, at which the signal increases, the controller calculates a motor flow rate passing through the motor and an instruction flow rate determined based on the turning signal. If the instruction flow rate is greater than a reference flow rate obtained by adding a predetermined value to the motor flow rate, the controller controls the regulator so the bi-directional pump tilting angle is adjusted to a tilting angle realizing the reference flow rate. If the instruction flow rate is not greater than the reference flow rate, the controller controls the regulator so the bi-directional pump tilting angle is adjusted to a tilting angle realizing the instruction flow rate.

A hydrostatic drive system is disclosed which allows for simpler and more robust control of hydraulic vibration. The system comprises first and second hydraulic drive units and a variable damping device. At least the first hydraulic drive unit is a variable displacement type and comprises a displacement control. The variable damping device comprises at least one variable element. The system comprises a first linkage apparatus between the displacement control and the variable element and is operable to control the variable element in accordance with the displacement of the displacement control.

A hydrostatic drive system is disclosed which allows for simpler and more robust control of hydraulic vibration. The system comprises first and second hydraulic drive units and a variable damping device. At least the first hydraulic drive unit is a variable displacement type and comprises a displacement control. The variable damping device comprises at least one variable element. The system comprises a first linkage apparatus between the displacement control and the variable element and is operable to control the variable element in accordance with the displacement of the displacement control.

An adaptive automatic transmission control system responds to stopping of a vehicle for reducing torque absorption by an automatic transmission and movement of and range to obstructions forward from a vehicle for reengaging the automatic transmission after a stop. The torque converter is released from its reduced torque absorption mode under one of three circumstances: 1) the brake pedal is released; 2) the detected obstruction moves outside a first predefined maximum range; and, 3) the detected obstruction moves outside a second predefined maximum range and at greater than a predefined minimum speed.

An adaptive automatic transmission control system responds to stopping of a vehicle for reducing torque absorption by an automatic transmission and movement of and range to obstructions forward from a vehicle for reengaging the automatic transmission after a stop. The torque converter is released from its reduced torque absorption mode under one of three circumstances: 1) the brake pedal is released; 2) the detected obstruction moves outside a first predefined maximum range; and, 3) the detected obstruction moves outside a second predefined maximum range and at greater than a predefined minimum speed.

A fluid pressure drive device includes a flushing circuit configured to discharge a working fluid from one of the pair of main passages to a tank. The flushing circuit has a low pressure selection valve provided between the pair of main passages and configured to be switched by a pressure difference between the pair of main passages, the low pressure selection valve being configured to select the main passage on the low pressure side; and a flushing passage configured to lead the working fluid passing through the low pressure selection valve to the tank. The flushing passage has a first orifice and a bent portion formed on the downstream side of the first orifice.

A fluid pressure drive device includes a flushing circuit configured to discharge a working fluid from one of the pair of main passages to a tank. The flushing circuit has a low pressure selection valve provided between the pair of main passages and configured to be switched by a pressure difference between the pair of main passages, the low pressure selection valve being configured to select the main passage on the low pressure side; and a flushing passage configured to lead the working fluid passing through the low pressure selection valve to the tank. The flushing passage has a first orifice and a bent portion formed on the downstream side of the first orifice.

Torque reduction control is executed for temporarily reducing a torque capacity of a reaction engagement device during a transition of a shift. The reaction engagement device is maintained in an engaged state from before the shift to after the shift such that a predetermined rotating element in an automatic transmission bears a reaction caused by progress of the shift resulting from a change of an engaging-side engagement device into an engaged state. Therefore, without delaying a change of the engaging-side engagement device into the engaged state, transmission of torque that is generated as a result of rattling during a transition of a shift is reduced. Thus, in shift control over the automatic transmission, shock at the time of rattling is reduced while a stop of a shift due to a delay in change of the engaging-side engagement device into the engaged state is prevented.

Torque reduction control is executed for temporarily reducing a torque capacity of a reaction engagement device during a transition of a shift. The reaction engagement device is maintained in an engaged state from before the shift to after the shift such that a predetermined rotating element in an automatic transmission bears a reaction caused by progress of the shift resulting from a change of an engaging-side engagement device into an engaged state. Therefore, without delaying a change of the engaging-side engagement device into the engaged state, transmission of torque that is generated as a result of rattling during a transition of a shift is reduced. Thus, in shift control over the automatic transmission, shock at the time of rattling is reduced while a stop of a shift due to a delay in change of the engaging-side engagement device into the engaged state is prevented.