Hydraulic control system for working machine

Abstract

A hydraulic control system for a working machine according to the present invention includes a regulator control valve for controlling an operation of a pump regulator and a controller for sending a control signal for changing a discharge quantity of the pump to the regulator control valve in accordance with an operation amount of an operating means. On the basis of the control signal, a secondary pressure in the regulator control valve is fed to the pump regulator. This system further includes a fail-safe valve disposed in a control line joining the pump regulator and the regulator control valve. The fail-safe valve has an ordinary position for sending the secondary pressure to the pump regulator and a fail-safe position for sending an oil pressure from a path other than the regulator control valve to the pump regulator in such a manner that a predetermined discharge amount is ensured. The fail-safe valve is configured so as to switch from the ordinary position to the fail-safe position in accordance with a failure signal indicative of failure in the regulator control valve. According to this, while adopting an electronic control system for the pump, it is possible to continue a work even in the failed condition of the system.

1 . A hydraulic control system for a working machine, comprising: 
 hydraulic actuators;    a variable capacity hydraulic pump as an oil pressure source for said hydraulic actuators;    a pump regulator for controlling a discharge amount of said hydraulic pump;    an electromagnetic proportional regulator control valve for controlling an operation of said pump regulator;    a controller adapted to send a control signal for changing the discharge amount of said hydraulic pump to said regulator control valve in accordance with an operation amount of an operating means, wherein a secondary pressure in said regulator control valve being fed as a controlling oil pressure to said pump regulator in accordance with said control signal; and    a fail-safe valve disposed in a pump control line joining said pump regulator and said regulator control valve, said fail-safe valve having an ordinary position for sending the secondary pressure in said regulator control valve as a controlling oil pressure to said pump regulator and a fail-safe position for sending an oil pressure from a path other than said regulator control valve as a pump controlling oil pressure to said pump regulator in such a manner that a predetermined pump discharge amount is ensured, said fail-safe valve being configured so as to switch from said ordinary position to said fail-safe position in accordance with a failure signal indicative of failure in operation of said regulator control valve;    wherein an electromagnetic switching valve is used as said fail-safe valve, a failure detector is further provided for detecting an output failure of the control signal outputted from said controller to said regulator control valve, and when the output failure is detected by said failure detector, said controller switches said fail-safe valve to said fail-safe position.    
   
   
       2 . The hydraulic control system for a working machine according to  claim 1 , wherein said fail-safe valve is configured as a hydraulic pilot switching valve with a hydraulic pilot port adapted to switch between said ordinary position and said fail-safe position on the basis of a pilot pressure introduced into said hydraulic pilot port and a spring force resisting said pilot pressure, the secondary pressure in said regulator control valve is introduced into the hydraulic pilot port of said fail-safe valve, a signal is issued as the failure signal when said secondary pressure drops below a preset value, and in accordance with said signal the fail-safe valve switches from said ordinary position to said fail-safe position by said spring force.  
   
   
       3 . The hydraulic control system for a working machine according to  claim 1 , wherein an electromagnetic switching valve is used as said fail-safe valve, a failure detector is further provided for detecting an output failure of the control signal outputted from said controller to said regulator control valve, and when the output failure is detected by said failure detector, said controller switches said fail-safe valve to said fail-safe position.  
   
   
       4 . The hydraulic control system for a working machine according to  claim 1 , further comprising an auxiliary hydraulic pump, pressure oil from said auxiliary hydraulic pump being fed as a primary pressure to said regulator control valve and also fed as a controlling oil pressure to said pump regulator in a switched state of said fail-safe valve to said fail-safe position.  
   
   
       5 . The hydraulic control system for a working machine according to  claim 1 , wherein bleed-off path is formed respectively in each of control valves for controlling operations of said hydraulic actuators independently, a throttle is provided on the most downstream side of a center bypass line for connecting said bleed-off path in each of said control valves tandem to a tank, and said controller being configured so as to send a control signal for changing the discharge amount of said hydraulic pump to said regulator control valve in accordance with a negative control pressure developed by said throttle and being configured so that said negative control pressure is fed as a controlling oil pressure to said pump regulator in a switched state of said fail-safe valve to said fail-safe position.