Hydraulic control circuits

Claim 1

A single hydraulic control device for a self propelled lifting truck such as a fork lift truck having hydraulically power operated steering means, hydraulically operated mast tilt means and hydraulically operated means for raising and lowering the load carrying forks on the mast, the hydraulic control device comprising a hydraulic fluid reservoir, a fluid supply line from the reservoir to a first circuit incorporating the hydraulic power assisted steering means, a fluid flow restrictor in said first circuit to said steering means, a relief valve between said restrictor and said hydraulically power operated steering means downstream of said restrictor to maintain a predetermined pressure in said steering means, a second fluid supply line supplied by fluid from said restrictor and incorporating said hydraulically operating mast tilt means, and said hydraulically operated fork raising and lowering means through separate valve means, a pump for pumping fluid around circuits connected to both of said supply lines, a prime mover drivingly connected to said pump, and a control unit responsive to fluid pressure in said mast tilt and fork raising and lowering means to vary the pump output to maintain a substantially constant fluid pressure to said steering means and to supply fluid from said restrictor to said hydraulically actuated mast tilt means and fork raising and lowering means in response to signals from said control unit.