A hydraulic pump is driven by an engine. A hydraulic motor is driven by hydraulic fluid discharged from the hydraulic pump thereby causing a vehicle to travel. A controller controls a rotation speed of the engine and a displacement of the hydraulic pump. The controller acquires a tractive force of the vehicle. The controller changes the rotation speed of the engine to a low speed side in accordance with a reduction in the tractive force.

A device for varying the swept volumes of first and second hydraulic machines, whose swept volumes depends upon pivoting positions of adjustable axes thereof which can be connected to one another by first and second lines. The axes can be coupled to a piston-cylinder device which is adjustable by a control valve unit for pivoting the axes. Pressures in the area of the hydraulic machines can be limited by the control valve unit. The control valve unit can be coupled to a respective first or second line with the highest pressure. A device for determining an existing actual pressure is located upstream of the control valve unit, at least in the area of one of the first and the second lines that connects with the first and the second hydraulic machines. The control valve unit can be actuated based on the actual pressure value determined by the device.

A device for varying the swept volumes of first and second hydraulic machines, whose swept volumes depends upon pivoting positions of adjustable axes thereof which can be connected to one another by first and second lines. The axes can be coupled to a piston-cylinder device which is adjustable by a control valve unit for pivoting the axes. Pressures in the area of the hydraulic machines can be limited by the control valve unit. The control valve unit can be coupled to a respective first or second line with the highest pressure. A device for determining an existing actual pressure is located upstream of the control valve unit, at least in the area of one of the first and the second lines that connects with the first and the second hydraulic machines. The control valve unit can be actuated based on the actual pressure value determined by the device.

A driving stage of a servo valve, including a hydraulic ejector and a hydraulic receiver able to be moved relative to each other, one of the two hydraulic units being integral with a mobile unit, movable relative to a body of the servo valve through actuation means, characterized in that the actuation means comprise two piezoelectric actuators connected in series. Control device comprising a servo valve comprising such a driving stage.

A driving stage of a servo valve, including a hydraulic ejector and a hydraulic receiver able to be moved relative to each other, one of the two hydraulic units being integral with a mobile unit, movable relative to a body of the servo valve through actuation means, characterized in that the actuation means comprise two piezoelectric actuators connected in series. Control device comprising a servo valve comprising such a driving stage.

A transmission device (1) with secondarily coupled power splitting in which part of an applied torque can be conducted, in a first power branch (3) at least by way of a hydrostatic system (4), and the other part of the torque can be conducted in a second power branch (5) via mechanical system (6), located between a transmission input (7) and a transmission output (8). The hydrostatic system (4) of the first power branch (3) includes at least one pump (12) and at least one motor (13) that is functionally connected to the pump by way of a hydraulic circuit, and both of the pump and motor are adjustable. The two power paths (3, 5) can be summed by a summing gear system (9). The pump (12) is made smaller than the motor (13).

A transmission device (1) with secondarily coupled power splitting in which part of an applied torque can be conducted, in a first power branch (3) at least by way of a hydrostatic system (4), and the other part of the torque can be conducted in a second power branch (5) via mechanical system (6), located between a transmission input (7) and a transmission output (8). The hydrostatic system (4) of the first power branch (3) includes at least one pump (12) and at least one motor (13) that is functionally connected to the pump by way of a hydraulic circuit, and both of the pump and motor are adjustable. The two power paths (3, 5) can be summed by a summing gear system (9). The pump (12) is made smaller than the motor (13).

A control method for a work vehicle, includes: calculating a speed ratio indicating a ratio between a rotation speed of an input shaft connected to an engine and a rotation speed of an output shaft connected to a traveling device; and outputting a capacity command for changing at least one of a capacity of a first hydraulic pump motor and a capacity of a second hydraulic pump motor based on correlation data indicating a relationship between the speed ratio and the capacities of the first and second hydraulic pump motors, wherein the correlation data is set so that both the capacity of the first hydraulic pump motor and the capacity of the second hydraulic pump motor are changed with a change in the speed ratio in a predetermined speed ratio range between a first speed ratio and a second speed ratio higher than the first speed ratio.

A work vehicle includes an engine, a hydrostatic transmission, a storage device storing leakage flow rate data defining a relationship between a differential pressure of hydraulic fluid between the first drive circuit and the second drive circuit and a leakage flow rate of the hydraulic fluid in the hydraulic circuit in stalling, and a controller in communication with the storage device. The hydrostatic transmission includes a traveling pump, a hydraulic circuit with first and second drive circuits, and a traveling motor. The controller is configured to determine a target traction force of the work vehicle, determine a target differential pressure that is a target value of the differential pressure from the target traction force, determine the leakage flow rate from the target differential pressure with reference to the leakage flow rate data, and determine a target flow rate of the traveling pump from the leakage flow rate.

A work vehicle includes an engine, a hydrostatic transmission, a storage device storing leakage flow rate data defining a relationship between a differential pressure of hydraulic fluid between the first drive circuit and the second drive circuit and a leakage flow rate of the hydraulic fluid in the hydraulic circuit in stalling, and a controller in communication with the storage device. The hydrostatic transmission includes a traveling pump, a hydraulic circuit with first and second drive circuits, and a traveling motor. The controller is configured to determine a target traction force of the work vehicle, determine a target differential pressure that is a target value of the differential pressure from the target traction force, determine the leakage flow rate from the target differential pressure with reference to the leakage flow rate data, and determine a target flow rate of the traveling pump from the leakage flow rate.