Importance

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Abstract

An improved timing control mechanism is provided for an engine-driven fuel injection pump of the type having plungers actuated by an adjustable cam. The cam is adjusted by the linear displacement of a timing piston operating in a cylinder. A pressurized hydraulic fluid admitted to a pressure chamber at one end of the cylinder provides a force against one end of the timing piston which is opposed by a biasing element, such as a spring. A rotary servo valve extends into an axial bore in one end of the timing piston for controlling the flow of hydraulic fluid through a control orifice formed in the wall of the piston bore and connecting with the cylinder's pressure chamber. The servo valve is axially fixed and includes an inclined, typically helical, control edge. Upon rotation of the valve, as by an electric rotary stepper motor, the control edge effectively moves 'axially' relative to the control orifice to vary flow therethrough and thus cause the piston to track that 'axial' positioning of the control edge. The valve's control edge is so positioned relative to its flow-occluding surface as to compensate for destabilizing forces transmitted to the timing piston through the cam.

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First Claim