A vehicle including a control valve to lift and lower a boom. The vehicle further includes a control circuit to control a speed of the boom lowering via a pressure compensator that balances a first pressure signal downstream of a control valve during the boom lowering and a second pressure signal from a hydraulic user interface so that, upon increasing of the first pressure signal during the boom lowering, the control valve progressively closes.

A vehicle including a control valve to lift and lower a boom. The vehicle further includes a control circuit to control a speed of the boom lowering via a pressure compensator that balances a first pressure signal downstream of a control valve during the boom lowering and a second pressure signal from a hydraulic user interface so that, upon increasing of the first pressure signal during the boom lowering, the control valve progressively closes.

A hydraulic drive system includes: a first hydraulic pump of the variable capacitance type; a first regulator including a first proportional valve; a second hydraulic pump that dispenses operating oil; a switch valve; a control device; and a malfunction detection device. The switch valve can switch to a third valve position in which the switch valve allows the operating oil dispensed from both the first hydraulic pump and the second hydraulic pump to be supplied to first and second traveling hydraulic motors and first and second hydraulic actuators. The control device controls the operation of the first proportional valve by outputting a first flow rate command signal to the first proportional valve, and when the malfunction detection device detects a malfunction of an electrical system related to the first proportional valve, the control device switches the switch valve to the third valve position.

A hydraulic drive system includes: a first hydraulic pump of the variable capacitance type; a first regulator including a first proportional valve; a second hydraulic pump that dispenses operating oil; a switch valve; a control device; and a malfunction detection device. The switch valve can switch to a third valve position in which the switch valve allows the operating oil dispensed from both the first hydraulic pump and the second hydraulic pump to be supplied to first and second traveling hydraulic motors and first and second hydraulic actuators. The control device controls the operation of the first proportional valve by outputting a first flow rate command signal to the first proportional valve, and when the malfunction detection device detects a malfunction of an electrical system related to the first proportional valve, the control device switches the switch valve to the third valve position.

A braking device may include a brake casing rotatably assembled with respect to a shaft along an axis of rotation, first braking elements and second braking elements, forming a stack, an elastic return element configured to exert an application force on the first and second braking elements, and a brake release actuator, adapted to bias the elastic return element along a direction opposing the application direction. The braking device a may include a diffusion wedge and a pressure wedge positioned respectively to bear against the stack and against the elastic return element. The diffusion wedge and the pressure wedge may have contact surfaces defining an annular linear contact about the axis of rotation.

A braking device may include a brake casing rotatably assembled with respect to a shaft along an axis of rotation, first braking elements and second braking elements, forming a stack, an elastic return element configured to exert an application force on the first and second braking elements, and a brake release actuator, adapted to bias the elastic return element along a direction opposing the application direction. The braking device a may include a diffusion wedge and a pressure wedge positioned respectively to bear against the stack and against the elastic return element. The diffusion wedge and the pressure wedge may have contact surfaces defining an annular linear contact about the axis of rotation.

Problem to be solved: To provide a hydraulic circuit for the construction machine which enables to use the relief valve of low capacity in the work tool circuit. Solution: The hydraulic circuit 2 for a construction machine has: a hydraulic pump 4 of variable capacity, a work tool 6 operated by hydraulic oil delivered by the hydraulic pump 4, a work tool operating device 10 to output a signal for operating the work tool 6, a control valve 14 allowing the hydraulic pump 4 to supply the hydraulic oil to the work tool 6 based on the signal output from the work tool operating device 10, a tool's relief valve 44 to release the hydraulic oil flowing between the control valve 14 and the work tool 6, a pressure sensor 46 to detect a pressure of hydraulic oil flowing into the work tool 6, and a controller 48 to reduce a delivery rate from the hydraulic pump 4 when the pressure detected by the pressure sensor 46 exceeds a predetermined value.

Problem to be solved: To provide a hydraulic circuit for the construction machine which enables to use the relief valve of low capacity in the work tool circuit. Solution: The hydraulic circuit 2 for a construction machine has: a hydraulic pump 4 of variable capacity, a work tool 6 operated by hydraulic oil delivered by the hydraulic pump 4, a work tool operating device 10 to output a signal for operating the work tool 6, a control valve 14 allowing the hydraulic pump 4 to supply the hydraulic oil to the work tool 6 based on the signal output from the work tool operating device 10, a tool's relief valve 44 to release the hydraulic oil flowing between the control valve 14 and the work tool 6, a pressure sensor 46 to detect a pressure of hydraulic oil flowing into the work tool 6, and a controller 48 to reduce a delivery rate from the hydraulic pump 4 when the pressure detected by the pressure sensor 46 exceeds a predetermined value.

Disclosed are a novel rotation control system and method for an excavator. The novel rotation control system comprises a controller, an electrical control handle, an instrument, a rotating motor, a rotating valve trim, a main pump, a first electromagnetic valve, a second electromagnetic valve, a first pilot pressure sensor, a second pilot pressure sensor, an overflow valve and a one-way valve, and further comprises a rotation sensor used for detecting whether an excavator is rotating, a regulator used for controlling the displacement of the main pump, and a temperature sensor used for monitoring the temperature of hydraulic oil in real time.

Disclosed are a novel rotation control system and method for an excavator. The novel rotation control system comprises a controller, an electrical control handle, an instrument, a rotating motor, a rotating valve trim, a main pump, a first electromagnetic valve, a second electromagnetic valve, a first pilot pressure sensor, a second pilot pressure sensor, an overflow valve and a one-way valve, and further comprises a rotation sensor used for detecting whether an excavator is rotating, a regulator used for controlling the displacement of the main pump, and a temperature sensor used for monitoring the temperature of hydraulic oil in real time.