Variable rate spring for a fuel injector

Abstract

A fuel injector for use in a diesel engine which is equipped with an engine brake governed by a hydraulic circuit includes an injector body with a hollow interior, a plunger located within the injector body, a moveable coupling positioned within the injector body, a nozzle for the dispensing of fuel, and a variable rate return spring which is positioned between the injector body and the moveable coupling. The variable return spring is designed with a variable pitch between adjacent coils such that the pitch between coils near the end(s) of the spring is reduced over that near the center of the spring. The use of the variable rate spring is intended to address the problem of premature fatigue failures caused by the return spring oscillating at or above its natural frequency. The oscillations are induced due to the exhaust valve opening and closing events and are transmitted directly through the engine brake hydraulic circuit to the injectors by way of the injector push tube. With the variable rate spring, if resonance occurs at one harmonic, the end coils close and open up, thus changing the natural frequency of the spring and tending to throw it out of resonance. In this manner, the spring will not oscillate at its natural frequency since the natural frequency is changing.