A method for controlling a work vehicle includes driving a first hydraulic pump and a second hydraulic pump by an engine to supply hydraulic fluid to a first hydraulic motor and a second hydraulic motor, respectively, to drive a first traveling device and a second traveling device, respectively. An operation state of a direction input device to operate a traveling direction of the work vehicle is detected. Based on the operation state detected, whether or not a traveling state of the work vehicle is a turning state. When it is determined that the traveling state is the turning state, a rotation command to decrease a target rotational speed of the engine from a first rotational speed to a second rotational speed is output.

A hydraulic system for controlling a pair of steerable caster wheels includes a left side actuator and a right side actuator. A rear steering control valve is moveable between a first state for disabling direct control of the left and side actuators and a second state for enabling direct control the left and right side actuators to provide a steer response. A fluid connection continuously connects the pressure source and the fluidic tie rod fluid circuit in fluid communication when the rear steering control valve is disposed in one of the first state and the second state to continuously supply the pressurized fluid to the fluidic tie rod fluid circuit.

A vehicle includes a rear steering system and a front differential hydraulic drive system. A first front drive control valve is operable to output a defined fluid flow in response to a steering command input. A second front drive control valve is operable to selectively divert a portion of the defined fluid flow output from the first front drive control valve. When the vehicle is operating in a pre-defined condition, a steering controller may control the second front drive control valve to divert a portion of the defined fluid flow from the first front drive control valve to define a reduced fluid flow, which is communicated to the front differential hydraulic drive system, to reduce a steering ratio of the front differential hydraulic drive system relative to the rear steering system, to desensitize steering provided by the front differential hydraulic drive system.

A hydrostatic traction drive has a steering function, which is implemented via two laterally acting secondary units (traction motors), which are supplied by a common primary unit (pump) in the open circuit. The primary unit is pressure-controlled. The two secondary units are torque-controlled. The affected vehicle is steerable as a function of a steering command by different torque specifications for the two secondary units. Furthermore, a hydrostatic drive for a mobile work machine has working hydraulics in addition to the traction drive. The working hydraulics are also supplied by the primary unit in parallel to the two secondary units.

A variable ratio hydraulic steering device with two or more orbit displacers ensures steering with low actuating forces even in the event of a total or partial failure of the oil flow supply. In the event of a total or partial failure of the oil flow supply, the device is capable of switching from one orbit displacer to another, if necessary, independently of the pressure at the inlet connection of the steering device.

A hydraulic system for controlling a pair of steerable caster wheels includes a left steering command valve, a right steering command valve, and a rear steering control valve. A supply pressure fluid circuit interconnects a pressure source and the rear steering control valve. A command valve supply fluid circuit interconnects the rear steering control valve with both the right steering command valve and the left steering command valve. A left side steering fluid circuit interconnects a left side actuator and the left steering command valve. A right side steering fluid circuit interconnects a right side actuator and the right steering command valve. A fluidic tie rod fluid circuit interconnects both the left side actuator and the right side actuator with the rear steering control valve. A tank return fluid circuit interconnects the rear steering control valve, the left and right steering command valves, and a tank.

An excavator includes a lower travelling body; an upper turning body mounted on the lower travelling body; a hydraulic pump installed in the upper turning body; a travelling hydraulic motor that is a variable displacement type motor configured to move the lower travelling body by being driven by hydraulic oil discharged by the hydraulic pump; and a control device configured to control a motor capacity of the travelling hydraulic motor so as to be switchable between a plurality of levels. The control device switches the motor capacity to a low rotation setting upon detecting that an operation for changing a travelling direction of the lower travelling body is performed.

A working machine includes a controller configured or programmed to perform an automatic deceleration for automatically decelerating a left traveling motor and a right traveling motor rotated at a second speed by shifting from the second speed to the first speed, and to determine a deceleration threshold that is used for judging whether the automatic deceleration has to be performed or not.

A working machine includes a controller configured to determine a first deceleration threshold corresponding to each of a first traveling pressure, a second traveling pressure, a third traveling pressure, and a fourth traveling pressure, to perform automatic deceleration to reduce rotation speeds of a left traveling motor and a right traveling motor, and to judge whether to perform the automatic deceleration based on the determined first deceleration threshold, the first traveling pressure, the second traveling pressure, the third traveling pressure, and the fourth traveling pressure.

Each of left and right direction switching valves includes: a pump port connected to a pump; a first compensation port connected to an upstream side of a corresponding pressure compensation valve; a second compensation port connected to a downstream side of the corresponding pressure compensation valve; a pair of supply/discharge ports connected to a corresponding travel motor; and a communication port. The communication ports of the left and right direction switching valves are connected by a communication line. When a spool shifts from a neutral position by the travel operation device, the pump port communicates with the first compensation port and the second compensation port communicates with one of the supply/discharge ports and the communication port. Each direction switching valve is configured wherein a degree of communication between the second compensation port and communication port increases in a shifting amount of the spool from the neutral position.