A travel control device is provided with hydraulic pumps of a variable capacity type that are driven by an engine; hydraulic motors that are driven by discharged oil from the hydraulic pumps; traveling devices that are rotation-driven by the hydraulic motors; a travel operation lever that is operated so as to instruct a traveling operation; a first control valve for generating a charged hydraulic pressure by adjusting the discharged oil from a charge pump and a second control valve for generating a capacity control hydraulic pressure in accordance with the operation of the travel operation lever. The first control valve is designed to pressure-adjust and generate a charged hydraulic pressure in accordance with the rotation speed of the engine, and the hydraulic pump is subjected to a variable capacity control process by a capacity control hydraulic pressure that is pressure-adjusted and generated by the second control valve.

There is provided a working machine which is capable of vehicle speed control through accelerator pedal operation even during execution of work under a condition where engine rotational speed is maintained constant. The working machine has the normal mode for exercising vehicle speed control by controlling engine rotational speed on the basis of the amount of depression of the accelerator pedal and by controlling the swash plate of the HST pump on the basis of the engine rotational speed, and the attachment mode for exercising vehicle speed control by controlling the swash plate of the HST pump on the basis of the amount of depression of the accelerator pedal irrespective of engine rotational speed.

The invention relates to a method for monitoring a functional state of a pressure-driven actuator which comprises an actuator compartment defined at least in portions by a flexibly deformable wall, the actuator being actuated by applying pressure to the actuator compartment by means of an operating pressure supply, a work process being carried out to actuate the actuator, which process is accompanied by the actuator transitioning from a starting configuration to an end configuration. The pressure the pressure applied to the actuator compartment is measured depending on time by means of a sensor apparatus during the transition from the starting configuration to the end configuration. The invention also relates to a pressure-driven actuator.

The invention relates to a method for monitoring a functional state of a pressure-driven actuator which comprises an actuator compartment defined at least in portions by a flexibly deformable wall, the actuator being actuated by applying pressure to the actuator compartment by means of an operating pressure supply, a work process being carried out to actuate the actuator, which process is accompanied by the actuator transitioning from a starting configuration to an end configuration. The pressure the pressure applied to the actuator compartment is measured depending on time by means of a sensor apparatus during the transition from the starting configuration to the end configuration. The invention also relates to a pressure-driven actuator.

An obstacle detector of a construction vehicle includes a brake mechanism which includes: a first hydraulic closed circuit including a pump for rolling, which is equipped with a swash plate, and a motor for rolling, which is connected with the pump for rolling; a second hydraulic closed circuit including a first hydraulic passage communicating with one side of the pump for rolling and a second hydraulic passage communicating with another side of the pump for rolling, to actuate the swash plate; and a neutral valve provided in the second closed circuit. When an emergency brake is activated, at least one of a compressive returning force to compress a low-pressure side of the tilted swash plate for returning the swash plate to a neutral position and a decompressive returning force to decompress a high-pressure side of the swash plate for returning the swash plate to the neutral position is generated.

An obstacle detector of a construction vehicle includes a brake mechanism which includes: a first hydraulic closed circuit including a pump for rolling, which is equipped with a swash plate, and a motor for rolling, which is connected with the pump for rolling; a second hydraulic closed circuit including a first hydraulic passage communicating with one side of the pump for rolling and a second hydraulic passage communicating with another side of the pump for rolling, to actuate the swash plate; and a neutral valve provided in the second closed circuit. When an emergency brake is activated, at least one of a compressive returning force to compress a low-pressure side of the tilted swash plate for returning the swash plate to a neutral position and a decompressive returning force to decompress a high-pressure side of the swash plate for returning the swash plate to the neutral position is generated.

A working machine includes a prime mover, a traveling pump driven by a power of the prime mover to deliver operation fluid, a traveling motor rotated by the operation fluid delivered from the traveling pump to have a rotation speed stage shiftable between a first speed stage and a second speed stage higher than the first speed stage, a traveling switching valve shiftable between a first state where the rotation speed stage of the traveling motor is set to the first speed stage and a second state where the rotation speed stage of the traveling motor is set to the second speed stage, an actuation valve configured to change a pilot pressure of a pilot fluid to control a flow of operation fluid delivered from the traveling pump, and a controller configured to control the pilot pressure of the pilot fluid output from the actuation valve so that a value of the pilot pressure differs depending on whether the set rotation speed stage of the traveling motor is the first speed stage or the second speed stage.

A hydraulic system for a work machine includes a tank to store an operation fluid, a hydraulic device to be operated by the operation fluid, a control valve to control the hydraulic device, a first fluid tube connecting the hydraulic device and the control valve, the first fluid tube being to supply the operation fluid from the control valve to the hydraulic device, a second fluid tube branching from the first fluid tube and connected to the tank, a switch valve provided to the second fluid tube, the switch valve being to control a flow rate of the operation fluid, and an oil cooler provided to the second fluid tube between the switch valve and the tank.

A hydraulic system in a work machine includes a travel operation device provided in a pilot oil path between a hydraulic pump a travel pump and including an operation member and configured to generate a pilot pressure supplied via the pilot oil path and an additional pilot pressure in accordance with an operation amount of the operation member. The travel pump is to control a flow direction of hydraulic oil supplied to a travel motor based on the pilot pressure and the additional pilot pressure. A pressure selection valve is provided in a first coupling oil path to select a selected pressure from the pilot pressure and the additional pilot pressure to apply the selected pressure to the pilot hydraulic oil in the second coupling oil path. A pressure adjustment valve is provided in a second coupling oil path to control the selected pressure to be an adjusted pilot pressure.

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.