Hydraulic fluid pressure control device for a continuously variable

Abstract

A control device for a continously variable belt transmission device, including driving and driven pulley assemblies with an endless belt assembly fitted in a power transmitting manner around them in V-shaped grooves thereof to provide power transmission therebetween at a speed change ratio, the driving and driven pulley assemblies having respective first and second pressure chambers, each of which according to supply of hydraulic fluid pressure to it alters the effective pulley radius of its pulley assembly. The control device supplies a line pressure to the second pressure chamber for the driven pulley assembly, and includes: a control pressure generating valve which generates a control pressure which decreases along with increase in the speed change ratio; a line pressure generating valve, which receives supply of the control pressure from the control pressure generating valve, and which generates the line pressure and supplies it to the second pressure chamber for the driven pulley assembly, this line pressure decreasing along with increase in the control pressure generated by the control pressure generating valve; and a cutoff valve which, when a sudden increase of the speed change ratio is required, prevents transmission of the control pressure from the control pressure generating valve to the line pressure generating valve. Thereby, in these circumstances of sudden speed change ratio increase, the line presure is made to be maximum, and accordingly is well able to power the driven pulley assembly, at its pressure chamber, to quickly alter the speed change ratio.