Creep-inhibiting device for an automotive vehicle equipped with an automatic transmission

Claim 1

In a creep-inhibiting device for use in an automotive vehicle equipped with an engine, a fluid coupling, a transmission mechanism coupled in series to said fluid coupling and having a frictionally engaging element, and an operating fluid source for supplying an operating fluid to said frictionally engaging element, said device including: engine load sensor means for producing a signal fluid having a pressure proportionate to load applied on said engine; and control means interposed between said frictionally engaging element and said operating fluid source, wherein said control means is adapted to control the power transmission capacity of said frictionally engaging element within a range from substantially zero to a predetermined value in dependence on the pressure of said signal fluid supplied thereto, to inhibit creeping of said vehicle when said engine is in a no-load state, the improvement wherein said control means comprises: an input fluid line connected to said operating fluid source; an output fluid line connected to said frictionally engaging element; a valve body disposed to selectively connect and disconnect said input fluid line to and from asid output fluid line and having: first and second end faces, a first pressure chamber defined in part by said first end face of said valve body always connected to said output fluid line to be supplied with an operating fluid pressure in said output fluid line, a second pressure chamber defined in part by said second end face of said valve body and disposed to be supplied with the pressure of said signal fluid; a third fluid line having a restriction located between said operating fluid source and said valve body and disposed to always connect said input fluid line to said output fluid line; resilient means arranged in said second pressure chamber and urging said valve body in a direction of connecting said input fluid line to said output fluid line counteracting the pressure in said first pressure chamber; and a drain line disposed to be opened and closed by said valve body so that said input fluid line is connected to and disconnected from a zone under a lower pressure via said drain line, said drain line escaping said operating fluid pressure in said output fluid line to said zone under a lower pressure when said valve body is biased in a direction of disconnecting said input fluid line from said output fluid line, by an amount corresponding to the amount by which said valve body is biased in the last-mentioned direction; said input fluid line. said output fluid line, and said drain line being so located relative to said valve body that said valve body connects said input fluid line to said output fluid line when said valve body is displaced toward said first pressure chamber, and said valve body disconnects said input fluid line from said output fluid line and at the same time connects said drain line to said zone under a lower pressure when said valve body is displaced toward said second pressure chamber; said valve body being displaceable in response to a difference between the operating fluid pressure in said first pressure chamber and the pressure of said signal fluid in said second pressure chamber to assume an equilibrated position wherein the operating fluid pressure in said output fluid line is maintained at a pressure slightly lower than an engaging pressure at which said frictionally engaging element engages, when the engine is in said no-load state.