Hydraulic driving apparatus for working machine

摘要

Provided is an apparatus to lower a load, comprising a hydraulic pump, a hydraulic actuator having first and second ports, a manipulation device, a hydraulic circuit including meter-in and meter-out flow passages for the first and second ports respectively and a regeneration flow passage with a check valve, a control valve, a meter-out flow controller adjusting a meter-out flow rate according to the manipulation device, a back pressure valve, and a non-regeneration operation relief valve whose set pressure is not less than a sum of a minimum set pressure of the back pressure valve, an inlet-outlet pressure difference of the meter-out flow controller when the meter-out flow rate is maximum and a discharge flow rate of the hydraulic pump is maximum, and an actuator pressure difference for driving the hydraulic actuator with no load, and not less than a maximum set pressure of the back pressure valve.

主权项

1. A hydraulic driving apparatus for a working machine, the hydraulic driving apparatus being designed to drive a load in a lowering direction equal to a self-weight falling direction of the load by means of hydraulic pressure and comprising:
a hydraulic pump; a driving power source for driving the hydraulic pump to cause the hydraulic pump to discharge hydraulic fluid therefrom; a hydraulic actuator having a first port and a second port, the hydraulic actuator being adapted to drive the load in the lowering direction by receiving a supply of hydraulic fluid discharged from the hydraulic pump through the first port and discharging the hydraulic fluid from the second port; a manipulation device adapted to be manually operated to designate an operating speed of the hydraulic actuator; a hydraulic circuit for work including a meter-in flow passage for leading the hydraulic fluid from the hydraulic pump into the first port of the hydraulic actuator during a mode for driving the load in the lowering direction, a meter-out flow passage for leading the hydraulic fluid discharged from the second port of the hydraulic actuator into a tank during the mode for driving the load in the lowering direction, and a regeneration flow passage communicating the meter-out flow passage with the meter-in flow passage; a control valve for changing a state of the supply of the hydraulic fluid from the hydraulic pump to the hydraulic actuator so as to operate the hydraulic actuator at a speed designated by the manipulation device; a meter-out flow controller provided in the meter-out flow passage to adjust a meter-out flow rate, which is a flow rate of hydraulic fluid in a region of the meter-out flow passage upstream of a position where the regeneration flow passage is connected to the meter-out flow passage, to a flow rate corresponding to a speed designated by the manipulation device, the meter-out flow controller including a meter-out orifice having a flow passage area variable accordingly to a manual operation of the manipulation device, and a meter-out flow regulation valve receiving inputs of respective pressures on upstream and downstream sides of the meter-out orifice and changing the meter-out flow rate to allow an inlet-outlet pressure difference of the meter-out orifice to become a predetermined value, the inlet-outlet pressure difference being a difference between the pressures on the upstream and downstream sides of the meter-out orifice; a back pressure valve provided in the meter-out flow passage at a position downstream of the position where the regeneration flow passage is connected to the meter-out flow passage, to produce a predetermined back pressure; a check valve provided in the regeneration flow passage to limit a flow direction of hydraulic fluid in the regeneration flow passage to a direction from the meter-out flow passage to the meter-in flow passage; and a non-regeneration operation relief valve adapted to be opened, when a pressure of the meter-in flow passage becomes equal to or greater than a set pressure thereof, to let out the hydraulic fluid flowing through the meter-in flow passage into the tank and thereby determine an upper limit of the pressure of the meter-in flow passage, wherein the set pressure of the non-regeneration operation relief valve is set to a value which is equal to or greater than a sum of a minimum value of a set pressure of the back pressure valve, an inlet-outlet pressure difference of the meter-out flow controller when the meter-out flow rate adjusted by the meter-out flow controller has a maximum value and a discharge flow rate of the hydraulic pump has a maximum value, and an inlet-outlet actuator pressure difference required for driving the hydraulic actuator with no load, and is set to a value equal to or greater than a maximum value of the set pressure of the back pressure valve.