Variable rate EGR valve with step motor control and method therefor

Claim 1

A variable flow rate valve comprising; a housing defining a pressure chamber, a flexible diaphragm secured to said housing and defining an end of said pressure chamber, said diaphragm movable in one direction in response to decreases in the pressure within the pressure chamber and movable in an opposite direction in response to increases in the pressure within said pressure chamber; means independent of said diaphragm for providing a variable mechanical position limit or stop for said diaphragm in said one direction including an axially extending member; means for selectively varying the pressure within said pressure chamber for causing said diaphragm to move in response to the pressure differential thereacross for engagement with said stop means; wherein said varying means comprises; an opening through said diaphragm, valve means including a valve, positioned opposite said member proximate another side of said diaphragm for closing off communication through said opening, said valve means further including means for biasing said valve to close said opening wherein when said valve seals said opening pressure within said pressure chamber is permitted to decrease thereby moving said diaphragm in said one direction into engagement with said member and wherein when said valve is apart from said opening pressure within said chamber is permitted to increase moving said diaphragm in said opposite direction apart from said member, wherein said member includes a nut threadably and axially movable relative to a lead screw, said lead screw rotated by a step motor in response to control signals input thereto.