Hydraulic controller for working machine

Abstract

A hydraulic controller for working machine according to the present invention, which presupposes an electronic control system where an integrated bleed-off valve common to hydraulic actuators is used for bleed-off control and the bleed-off valve is controlled by the secondary pressure of a proportional solenoid valve controlled by a controller, is constituted to compensate supply of a pressure oil for the hydraulic actuators even if the secondary pressure of the proportional solenoid valve is stopped, by providing, at the bleed-off valve, a fail-safe position with a fail-safe path which opens with an opening having smaller area than an unload opening.

1 . A hydraulic controller for working machine comprising: 
 hydraulic actuators;    a hydraulic pump as a hydraulic pressure source for said hydraulic actuators;    control valves for controlling motion of each of said hydraulic actuators based on operation of an operating means;    a bleed-off valve for putting a surplus of pressure oil discharged from said hydraulic pump back to a tank;    a control means for controlling said bleed-off valve; and    a compensating means for assuring an opening amount of said bleed-off valve in such a manner of compensating supply of the pressure oil from said hydraulic pump to each of said hydraulic actuators in a condition that said control means can not control said breed-off valve so that supply of the pressure oil from said hydraulic pump to each of said hydraulic actuators can not be compensated.    
   
   
       2 . The hydraulic controller for working machine according to  claim 1 , wherein said compensating means is provided at said bleed-off valve, said compensating means being a fail-safe path adapted to be openable with an opening having smaller area than an unload path in an operation halting condition of said bleed-off valve.  
   
   
       3 . The hydraulic controller for working machine according to  claim 1 , wherein said bleed-off valve is a hydraulic pilot valve for operating between an unload position and a block position according to an amount of pilot pressure, said hydraulic pump is a capacity variable hydraulic pump, the discharge amount thereof being controlled by a pump regulator, and said control means comprises a proportional solenoid valve for sending a pilot pressure to said bleed-off valve and a controller for sending a control signal to said proportional solenoid valve, wherein said control means is adapted to control said pump regulator in such a manner that the discharge amount of said hydraulic pump increases as an operation amount of said operating means increases, wherein said compensating means is a pilot pressure switching valve provided between said proportional solenoid valve and said bleed-off valve, and wherein a switching means for switching its operating position is provided with said pilot pressure switching valve which, by said switching means under a failure condition, switches from a normal position for providing a secondary pressure of said proportional solenoid valve as pilot pressure with said bleed-off valve to a fail-safe position for providing a pump controlling pressure supplied to said pump regulator as pilot pressure with said bleed-off valve.