A pump operation piston biased by a neutral spring mechanism and a larger volume operation spring biased by a larger volume operation spring in a larger volume direction operatively move pump and motor volume adjusting members, respectively, is provided. A first pressure control valve commonly controls supply-discharge of pressure oil that presses the pump operation piston in a first slide direction and the motor operation piston in a smaller volume direction. A second pressure control valve controls supply-discharge of pressure oil that presses the pump operation piston in a second slide direction. Biasing forces of the neutral spring mechanism and the larger volume operation spring are so set that, after the pump operation piston is moved in the first slide direction by a predetermined distance, the motor operation piston starts moving.

A pump operation piston biased by a neutral spring mechanism and a larger volume operation spring biased by a larger volume operation spring in a larger volume direction operatively move pump and motor volume adjusting members, respectively, is provided. A first pressure control valve commonly controls supply-discharge of pressure oil that presses the pump operation piston in a first slide direction and the motor operation piston in a smaller volume direction. A second pressure control valve controls supply-discharge of pressure oil that presses the pump operation piston in a second slide direction. Biasing forces of the neutral spring mechanism and the larger volume operation spring are so set that, after the pump operation piston is moved in the first slide direction by a predetermined distance, the motor operation piston starts moving.

Methods and systems for a hydromechanical transmission in a vehicle are provided herein. In one example, the transmission system includes a hydrostatic assembly with a hydraulic pump in fluidic communication with a hydraulic motor. The transmission system further includes a controller configured to selectively transition between a torque control mode and a speed control mode of the hydrostatic assembly while the vehicle is on a slope.

Methods and systems for a hydromechanical transmission in a vehicle are provided herein. In one example, the transmission system includes a hydrostatic assembly with a hydraulic pump in fluidic communication with a hydraulic motor. The transmission system further includes a controller configured to selectively transition between a torque control mode and a speed control mode of the hydrostatic assembly while the vehicle is on a slope.

Provided is a work vehicle capable of reducing the fuel consumption while maintaining the working efficiency. A wheel loader 1 comprising a vehicle body controller 5, 5A for controlling an engine 41, wherein the vehicle body controller 5, 5A limits an upper limit rotational speed of the engine 41 based on an accelerator pedal step-on amount α, a brake pedal step-on amount β, a torque converter speed ratio e which is a ratio of a rotational speed of a torque converter 42, a discharge pressure P1 of a loading hydraulic pump 44, and a stroke amount S1 of lift arm cylinders 22 or a stroke amount S2 of a bucket cylinder 24.

Provided is a work vehicle capable of reducing the fuel consumption while maintaining the working efficiency. A wheel loader 1 comprising a vehicle body controller 5, 5A for controlling an engine 41, wherein the vehicle body controller 5, 5A limits an upper limit rotational speed of the engine 41 based on an accelerator pedal step-on amount α, a brake pedal step-on amount β, a torque converter speed ratio e which is a ratio of a rotational speed of a torque converter 42, a discharge pressure P1 of a loading hydraulic pump 44, and a stroke amount S1 of lift arm cylinders 22 or a stroke amount S2 of a bucket cylinder 24.

Methods and systems for controlling a hydromechanical transmission are proposed. In one example, a control method for a hydrostatic unit of a hydromechanical variable transmission (HVT) is presented, comprising controlling the hydrostatic unit via a feedforward control architecture including a non-linear, multi-coefficient model, wherein the hydrostatic unit comprises a hydrostatic pump and a hydrostatic motor. A desired differential pressure of the hydrostatic unit or a desired hydraulic pump displacement may be used as inputs for the model, where the model's output is a pressure difference for a pump control piston coupled to a swash plate of the hydrostatic unit. Use of the non-linear model permits the hydrostatic unit to be controlled based on load, speed, and/or torque, thereby increasing the adaptability of the control system.

In a hydraulic control device switchable between a first state in which a first oil is supplied from a first pump to a hydraulic operation part via a bypass valve and a second state in which the first oil supplied from the first pump is pressurized by using the second pump and the pressurized first oil is supplied, as a second oil, to the hydraulic operation part, control that adds a correction hydraulic pressure of a predetermined amount to the hydraulic pressure of the oil discharged from a valve for adjusting the pressure of the oil supplied to the hydraulic operation part is performed when the second state is switched to the first state due to a stop or a low rotation state of the second pump.

In a hydraulic control device switchable between a first state in which a first oil is supplied from a first pump to a hydraulic operation part via a bypass valve and a second state in which the first oil supplied from the first pump is pressurized by using the second pump and the pressurized first oil is supplied, as a second oil, to the hydraulic operation part, control that adds a correction hydraulic pressure of a predetermined amount to the hydraulic pressure of the oil discharged from a valve for adjusting the pressure of the oil supplied to the hydraulic operation part is performed when the second state is switched to the first state due to a stop or a low rotation state of the second pump.

A hydrostatic transmission system includes a hydraulic motor and at least one proportional control valve and at least one pump connected to the hydraulic motor to provide fluid to operate the hydraulic motor. The at least one pump includes at least one fluid driver having a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from the pump inlet to the pump outlet. The hydrostatic transmission system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover and concurrently establishes an opening of the at least one proportional control valve to adjust at least one of a flow and a pressure in the hydrostatic transmission system to an operational set point.