Controlling apparatus for bulldozer blade

Claim 1

A controlling apparatus for the operation of a bulldozer blade, comprising: (a) a hydraulic circuit connected between a hydraulic power source and cylinder means including a hoist cylinder for hoisting and lowering the bulldozer blade and a tilt cylinder for tilting the same, said hydraulic circuit including electromagnetic valve means for controlling said cylinder means; (b) an electric circuit electrically connected between an electric power source supply for supplying an electric signal into said electric circuit and said electromagnetic valve means, to effect manual and automatic operations of the bulldozer blade said electric circuit including a main switch, first switching means for selectively changing said electric circuit into a circuit for the manual operation or a circuit for the automatic operation, a safety relay connected with said first switching means adapted to be actuated only when said first switching means is maintained in a position where said electric circuit is changed into the manual operation circuit thereby preventing unexpected operation of said blade, a manual operation preferential relay connected with said safety relay, a load reading relay connected with said safety and manual operation preferential relays and adapted to be actuated by a signal fed from a load detecting circuit so as to send the electric signal from said manual operation preferential relay to one of the solenoids of said electromagnetic valve means, and second switching means manually controlled by the operation of an operating lever and adapted to turn off said manual operation preferential relay with the result of opening the automatic operation circuit when said second switching means is turned off in response to the operation of the operating lever for effecting the manual operation of the bulldozer blade; and (c) means for detecting a load applied to the bulldozer blade, said load detecting means being mounted on a push arm for supporting the bulldozer blade and being electrically connected with said load detecting circuit.