A transmission (21) as a power transmission device for a vehicle comprises an input shaft (22), an output shaft (23), a planetary continuously variable transmission mechanism (31), a direct connecting mechanism (27), and an idler gear (29). The direct connecting mechanism (27) comprises a direct connecting clutch (30). The planetary continuously variable transmission mechanism (31) comprises a planetary gear mechanism (32), a pump side clutch (33), a hydraulic pump (36), a hydraulic motor (38), and a motor side clutch (40). The hydraulic pump (36) and the hydraulic motor (38) are connected via a pair of main lines (37A, 37B). An electromagnetic on-off valve (41) capable of switching between a communicating state and a blocking state between the pair of main lines (37A, 37B) is provided between the pair of main lines (37A, 37B).

A control mechanism for a hydrostatic transmission includes a piston rod, a neutral biasing spring, a piston, a cylinder case provided with a first fluid chamber and a second fluid chamber, a solenoid valve capable of selectively supplying pressurized fluid to the first fluid chamber and the second fluid chamber, a pivot shaft configured to swingably support the cylinder case, and a first relief valve configured to flow the hydraulic fluid from the first fluid chamber to the second fluid chamber when a hydraulic pressure in the first fluid chamber exceeds a set pressure, and a second relief valve configured to flow the hydraulic fluid from the second fluid chamber to the first fluid chamber when a hydraulic pressure in the second fluid chamber exceeds a set pressure.

A control mechanism for a hydrostatic transmission includes a piston rod, a neutral biasing spring, a piston, a cylinder case provided with a first fluid chamber and a second fluid chamber, a solenoid valve capable of selectively supplying pressurized fluid to the first fluid chamber and the second fluid chamber, a pivot shaft configured to swingably support the cylinder case, and a first relief valve configured to flow the hydraulic fluid from the first fluid chamber to the second fluid chamber when a hydraulic pressure in the first fluid chamber exceeds a set pressure, and a second relief valve configured to flow the hydraulic fluid from the second fluid chamber to the first fluid chamber when a hydraulic pressure in the second fluid chamber exceeds a set pressure.

A neutral valve includes a spool inserted in a housing so as to be movable in a predetermined direction, the spool configured to move to a neutral position set such that a first and second port are connected to each other through a valve passage, a first offset position located at neutral position's first side in the predetermined direction and set such that second port and valve passage are disconnected from each other, and a second offset position located at neutral position's second side in the predetermined direction and set such that first port and valve passage are disconnected from each other. The spool's outer peripheral portion includes a first pressure receiving surface receiving first port's fluid pressure to be pushed toward the first side in the predetermined direction and a second pressure receiving surface receiving second port's fluid pressure to be pushed toward second side in the predetermined direction.

A neutral valve includes a spool inserted in a housing so as to be movable in a predetermined direction, the spool configured to move to a neutral position set such that a first and second port are connected to each other through a valve passage, a first offset position located at neutral position's first side in the predetermined direction and set such that second port and valve passage are disconnected from each other, and a second offset position located at neutral position's second side in the predetermined direction and set such that first port and valve passage are disconnected from each other. The spool's outer peripheral portion includes a first pressure receiving surface receiving first port's fluid pressure to be pushed toward the first side in the predetermined direction and a second pressure receiving surface receiving second port's fluid pressure to be pushed toward second side in the predetermined direction.

A hydraulic system for actuating an interlocking shifting element of a transmission which comprises two piston chambers and a piston element that delimits the piston chambers. The piston element can be acted upon in one piston chamber by a pressure to open the shifting element and, in the other piston chamber, by another pressure to close the shifting element. Pressure can be delivered by a valve to two piston chamber and the valve can be actuated by an actuator by a pilot pressure. The valve and the electro-hydraulic actuator are designed and functionally connected to one another such that, in the event of a pressure drop, a total hydraulic force, acting to close the shifting element, is applied to the piston element and, if the current supply to the actuator fails, a total hydraulic force acting, in the opening direction of the shifting element, acts upon the piston element.

A hydraulic system for actuating an interlocking shifting element of a transmission which comprises two piston chambers and a piston element that delimits the piston chambers. The piston element can be acted upon in one piston chamber by a pressure to open the shifting element and, in the other piston chamber, by another pressure to close the shifting element. Pressure can be delivered by a valve to two piston chamber and the valve can be actuated by an actuator by a pilot pressure. The valve and the electro-hydraulic actuator are designed and functionally connected to one another such that, in the event of a pressure drop, a total hydraulic force, acting to close the shifting element, is applied to the piston element and, if the current supply to the actuator fails, a total hydraulic force acting, in the opening direction of the shifting element, acts upon the piston element.

A process for start-up of a propulsion system for a vehicle displacement component. The propulsion system includes a hydraulic pump, a hydraulic motor fed by the hydraulic pump via a closed-loop hydraulic circuit, and an electric motor. The process for start-up includes the following steps, given a configuration when the propulsion system is at a standstill, in which the electric motor, the hydraulic pump and the feed pump are at a standstill, and the hydraulic motor is disengaged: start-up of the feed pump, starting up of the electric motor, setting in rotation of the hydraulic pump, adjustment of the displacement of the hydraulic pump and/or of the rotational speed of the electric motor for providing a flow rate corresponding to a setpoint on the hydraulic motor, start-up of the hydraulic motor.