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.

The present invention provides a work machine including a steering device that is very responsive to switching operations. The work machine includes: a proportional solenoid valve for outputting a first pilot pressure oil with a pressure responding to a steering signal; a solenoid valve for outputting a second pilot pressure oil with a predetermined pressure while the steering signal is outputted from the steering device; a switching valve capable of switching to a first state of outputting the first pilot pressure oil to a directional control valve and a second state of outputting the second pilot pressure oil to the directional control valve, while the first pilot pressure oil is outputted from the proportional solenoid valve and the second pilot pressure oil is outputted from the solenoid valve in parallel; and a controller to switch the switching valve from the first state to the second state in a case where a malfunction is detected in a main circuit ranging from the steering device to the directional control valve via the proportional solenoid valve and the switching valve of the first state.

A hydraulic control device includes: a hydraulic pump connected in parallel to steering and boom cylinders; a steering control valve that controls the direction of operating oil flowing through the steering cylinders; a boom control valve that connects the hydraulic pump to a tank when the valve is at a neutral position and controls the direction of the oil flowing through the boom cylinders when the valve is at an offset position; a meter-in pressure compensator that increases flow rate of the oil flowing through a variable restrictor of the steering control valve in accordance with pressure in front of and behind the restrictor; and a bleed-off pressure compensator that decreases flow rate of the oil flowing through the boom control valve in accordance with the increase in pressure of the oil flowing through the steering cylinders to maintain the predetermined pressure of the oil in the steering control circuit.

A hydraulic system for a work machine includes a hydraulic bump to output an operation fluid, a hydraulic switch valve to be switched among switching positions in accordance with a pressure of the operation fluid, a proportional valve to change the pressure of the operation fluid applied to the hydraulic switch valve, a travel hydraulic device to change a thrust power in accordance with the switching positions of the hydraulic switch valve. And, the hydraulic system includes a controller to control the proportional valve in accordance with a state of the travel hydraulic device.

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.

A working machine includes a controller to perform an automatic deceleration operation to automatically decelerate from a second speed to a first speed when a value calculated based on a first traveling pressure, a second traveling pressure, a third traveling pressure, and a fourth traveling pressure becomes equal to or more than a deceleration threshold in a state where a left traveling motor and a right traveling motor are being driven at the second speed. The controller determines the deceleration threshold based on any one of a first cross-differential pressure acquired by subtracting the fourth traveling pressure from the first traveling pressure, a second cross-differential pressure acquired by subtracting the third traveling pressure from the second traveling pressure, a third cross-differential pressure acquired by subtracting the second traveling pressure from the third traveling pressure, and a fourth cross-differential pressure acquired by subtracting the first traveling pressure from the fourth traveling pressure.

A hydraulic system (40) for a work machine comprising a priority circuit (41) including at least a first priority actuator (47, 48) and a priority control valve (58) for controlling the supply of hydraulic fluid to the first priority actuator (47, 48) and for providing a load sense signal indicative of the load acting on the first priority actuator (47, 48); an auxiliary circuit (42) including at least a first auxiliary actuator (51) and at least a first auxiliary control valve (80) for controlling the supply of hydraulic fluid to the first auxiliary actuator (51); at least a first pump (46) for producing a flow of hydraulic fluid; and a priority valve (74) for distributing the flow from the pump (46) to the priority circuit (41) and auxiliary circuit (42) for operating the respective actuators thereof, with priority being given to the priority circuit (41) as a function of the load sense signal.

Power machines, power sources for power machines, and methods which provide a hydraulic signal from a hydraulic system, through the swivel joint or swivel, to control a tensioning cylinder coupled to the undercarriage without requiring a modification to the swivel. In exemplary embodiments, the same hydraulic signal provided to at least one other hydraulic component on the undercarriage to control another machine function is also provided to control one or more tensioning cylinders. For example, exemplary disclosed embodiments provide the same hydraulic signal to tension a tensioning cylinder as is provided to shift one or more two-speed drive motors. This prevents or reduces the likelihood of de-tracking without requiring a change or redesign of the swivel.

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.