Hydraulic control system for transmission of vehicle

Claim 1

An hydraulic control system for the transmission of an automotive vehicle having a driving engine comprising in combination, a drive shaft adapted to be driven by the engine; a driven shaft adapted to drive the vehicle, means for providing multi-ratio power trains between said drive shaft and driven shaft and having friction engaging mechanisms including fluid pressure actuated servo-means for engagement thereof for completing said power trains when engaged, a source of fluid pressure, a line pressure conduit for connecting said pressure source to said servo-means, pressure regulating valve means including a pressure reducing chamber for controlling line pressure within said conduit to and from a predetermined high valve and a predetermined low value respectively, manual selector valve means disposed between said pressure regulating valve means and said servo-means for selectively connecting said line pressure conduit to said servo-means, flow regulating means interposed between the said selector valve means and said servomeans for regulating fluid pressure supplied into said servomeans, and sensing means for comparing the pressures in said line pressure conduit and servo-means, said sensing means including a housing, a spool valve defining a bore of said housing into a first pressure chamber connected to both said servo-means and said flow regulating means and a second pressure chamber normally connected to said line pressure conduit through said selector valve means, and a resilient member disposed within said first chamber, said second chamber being selectively connected to said pressure reducing chamber of the regulating valve means when said spool valve operates because of the difference between fluid pressure within said second pressure chamber and the total pressure produced by said resilient member and fluid pressure within said first chamber, whereby as said line pressure is applied to said servo-means through said selector valve means and said flow regulating means and to said second pressure chamber of said sensing means, said spool valve starts operation to lead line pressure into said pressure reducing chamber so as to cause said pressure regulating valve means to control said line pressure down to a low value, and to return the line pressure of low value to a high value as the line pressure supplied into said servo-means reaches a predetermined value.