Hydraulic Drive System

摘要

A hydraulic drive system (1) including a meter-in compensator (37) and a bleed-off compensator (42) comprises a plurality of sensors (64 to 68), a controller (62), and an outlet pressure switching valve (61) The controller (62) determines whether or not the state of a wheel loader (2) which is detected based on the signals output from the sensors (64 to 68) meets a predetermined steering limiting condition. When the controller (62) determines that the state of the wheel loader (2) meets the steering limiting condition, it outputs a command signal to the outlet pressure switching valve (61). The outlet pressure switching valve (61) reduces the flow rate of the hydraulic oil flowing to steering cylinders (18L, 18R), in response to the command signal in such a manner that the flow rate becomes lower than that corresponding to the operation amount of a handle of a steering device (35).

主权项

1. A hydraulic drive system comprising:
a hydraulic pump to which a steering actuator for switching a traveling direction of a vehicle and a work machine actuator for moving a work machine are connected in parallel; a steering device for operating the steering actuator; a steering control valve which includes a spool which is movable according to an operation of the steering device and is configured to move the spool to adjust an opening degree of the spool to flow hydraulic oil from the hydraulic pump to the steering actuator at a flow rate corresponding to an amount of the operation of the steering device; an actuator control valve configured to control the flow rate of the hydraulic oil flowing from the hydraulic pump to the work machine actuator; a meter-in compensator which is provided in a meter-in passage connecting the hydraulic pump to the steering control valve, and is configured to adjust an opening degree of the meter-in passage in such a manner that the opening degree of the meter-in passage is increased as the opening degree of the spool of the steering control valve is increased by the operation of the steering device; a bleed-off compensator which is provided in a bleed-off passage connecting the hydraulic pump to the actuator control valve and is configured to adjust an opening degree of the bleed-off passage in such a manner that the opening degree of the bleed-off passage is reduced with an increase in a pressure of the hydraulic oil flowing to the steering actuator; a vehicle state detecting unit configured to detect a state of the vehicle; a controller configured to determine whether or not the state of the vehicle which is detected based on a signal output from the vehicle state detecting unit meets a predetermined steering limiting condition, and output a flow rate limiting command when the controller determines that the state of the vehicle meets the predetermined steering limiting condition; and a flow rate control mechanism configured to reduce the flow rate of the hydraulic oil flowing to the steering actuator in such a manner that the flow rate of the hydraulic oil flowing to the steering actuator becomes lower than the flow rate of the hydraulic oil corresponding to the amount of the operation of the steering device, in response to the flow rate limiting command received as an input from the controller.