Patent ID: 7305821

Claim:
A hydraulic control apparatus, comprising: a variable capacity pump; a first change over valve group including at least one change over valve connected with a first delivery line branched from a delivery line of the variable capacity pump and arranged to have a load sensing function; a delivery flow control means for adjusting a delivery flow rate of the variable capacity pump by receiving a hydraulic oil pressure signal from a load sensing line arranged in accordance with the change over valve having the load sensing function; a second change over valve group including at least one change over valve connected with a second delivery line branched from the delivery line of the variable capacity pump; an open and close motion valve connected with the second delivery line at a upstream side of the second change over valve group and having functions of open and close, and throttle in accordance with a hydraulic operation pressure signal applied to the change over valve belonging to the second change over valve group; and a compensation valve arranged at a downstream side of the open and close motion valve; an outlet side of the compensation valve being connected with the second change over valve group, wherein one side of the compensation valve is forced through force caused by hydraulic oil pressure at an outlet port of the open and close motion valve and a spring with a given spring force, and the opposite side of the compensation valve is forced through force caused by hydraulic oil pressure on the second delivery line, wherein the compensation valve is acted in the direction of opening by hydraulic oil pressure supplied from the outlet of the open and close motion valve due to the force on the one side, and is acted in the direction of closing by hydraulic oil pressure supplied from the inlet of the open and close motion valve due to the force on the opposite side, and wherein said compensation valve is provided with a bleed off passage which is connected with the outlet side of the open and close motion valve, and hydraulically communicates with a tank side when the force on said one side is greater than the force on said opposite side.