The invention of the present application intends to provide a work machine that can ensure high operability by preventing abrupt actuation of an actuator and a shock to a machine body by use of a bleed-off function at the time of starting of the actuator and that can improve the energy-saving performance by reducing a bleed-off flow rate after the starting of the actuator. For this purpose, a controller opens a bleed-off valve at a timing at which an operation device is being operated and before a flow rate of a hydraulic pump starts increasing, and closes the bleed-off valve at a timing at which the operation device is being operated and after the flow rate of the hydraulic pump has started increasing.

A relief circuit is operable between a first state and a second state to allow different functions of a hydraulic system to relieve at different pressures. In the first state of the relief circuit, the relief circuit is configured so that each of the functions of the hydraulic system relieve at the same pressure. In the second state of the relief circuit, the relief circuit is configured so different functions of the hydraulic system can operate simultaneously while also relieving at different pressures. In particular, a first function relieves at a first pressure and a second function relieves at a second pressure that is higher than the first pressure.

A relief circuit is operable between a first state and a second state to allow different functions of a hydraulic system to relieve at different pressures. In the first state of the relief circuit, the relief circuit is configured so that each of the functions of the hydraulic system relieve at the same pressure. In the second state of the relief circuit, the relief circuit is configured so different functions of the hydraulic system can operate simultaneously while also relieving at different pressures. In particular, a first function relieves at a first pressure and a second function relieves at a second pressure that is higher than the first pressure.

A work vehicle includes a valve for switching between a merging position for causing a first oil passage for driving a bucket and a second oil passage for driving an arm to communicate with each other, and a diverging position for separating the first oil passage and the second oil passage. The work vehicle is adapted to switch the valve from the merging position to the diverging position, when one of a pump pressure in the first pump and a pump pressure in the second pump comes to be equal to a predetermined value during an excavation operation. The work vehicle is adapted to control both pumps, such that the amount of the oil discharged from the first pump is larger than the amount of the oil discharged from the second pump, when the pump pressure in the first pump is equal to or more than the predetermined value.

A shovel according to an embodiment of the present invention includes a lower traveling body, an upper turning body pivotally mounted on the lower traveling body, a hydraulic pump mounted on the upper turning body, a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump, an operating device used to operate the actuator, and a control device configured to control an acceleration/deceleration characteristic of the hydraulic actuator in response to an operation of the operating device depending on a work mode.

A turn-drive apparatus capable of securing high acceleration at the time of turning start with a reduced relief loss includes a hydraulic pump of a variable capacity type, a turning motor, a turning control device, a relief valve, and a flow rate control device that controls a pump flow rate. The flow rate control device calculates a relief-cut-control target pump flow rate on the basis of the sum of a minimum relief flow rate and a turning-speed flow rate, and inputs a pump capacity command to the variable capacity-type hydraulic pump based thereon. The flow rate control device makes the relief-cut-control target pump flow rate larger than the sum of the minimum relief flow rate and the turning-speed flow rate at the time of turning start.

A turn-drive apparatus capable of securing high acceleration at the time of turning start with a reduced relief loss includes a hydraulic pump of a variable capacity type, a turning motor, a turning control device, a relief valve, and a flow rate control device that controls a pump flow rate. The flow rate control device calculates a relief-cut-control target pump flow rate on the basis of the sum of a minimum relief flow rate and a turning-speed flow rate, and inputs a pump capacity command to the variable capacity-type hydraulic pump based thereon. The flow rate control device makes the relief-cut-control target pump flow rate larger than the sum of the minimum relief flow rate and the turning-speed flow rate at the time of turning start.

A hydraulic-pump flow-rate calibration system includes: a variable capacitance type hydraulic pump that supplies an operating fluid to a hydraulic actuator; a regulator that changes the dispense flow rate of the hydraulic pump according to a flow rate command signal; a flow rate detection device that detects the flow rate of the operating fluid; a control device that outputs the flow rate command signal to the regulator to control the regulator; and a calibration device that calculates an actual measurement characteristic of the dispense flow rate for the flow rate command signal, and performs, on a preset reference characteristic, calibration based on the actual measurement characteristic. The actual measurement characteristic is calculated as a result of the flow rate of the operating fluid being detected by the flow rate detection device during output of a predetermined flow rate command signal from the control device to the regulator.

A hydraulic-pump flow-rate calibration system includes: a variable capacitance type hydraulic pump that supplies an operating fluid to a hydraulic actuator; a regulator that changes the dispense flow rate of the hydraulic pump according to a flow rate command signal; a flow rate detection device that detects the flow rate of the operating fluid; a control device that outputs the flow rate command signal to the regulator to control the regulator; and a calibration device that calculates an actual measurement characteristic of the dispense flow rate for the flow rate command signal, and performs, on a preset reference characteristic, calibration based on the actual measurement characteristic. The actual measurement characteristic is calculated as a result of the flow rate of the operating fluid being detected by the flow rate detection device during output of a predetermined flow rate command signal from the control device to the regulator.

A drive device for driving a fluid pressure cylinder has an air supply source which supplies air, a switching valve which switches between the supply and discharge of the air to and from the fluid pressure cylinder, bypass piping which connects the head-side cylinder chamber and rod-side cylinder chamber of the fluid pressure cylinder, and a bypass switching valve which switches between the states of flow of air through the bypass piping. Air in the head-side cylinder chamber is supplied to the rod-side cylinder chamber through the bypass piping by setting the bypass switching valve to an open state in a return stroke of the fluid pressure cylinder.