Deceleration based compression test

Claim 1

Apparatus for measuring compression in a vehicle mounted internal combustion engine having ring gear teeth which are spaced at crankshaft intervals and which rotate at engine speed, and having an accelerator and a transmission clutch for controlling engine speed above idle and for engaging and disengaging the engine from the vehicle load, respectively, in response to operator control, the apparatus comprising: tooth sensor means for sensing rotation of the ring gear tooth and providing a ring gear tooth (RGT) signal having periodic pulses spaced at the same crankshaft angle intervals as the teeth, and having a pulse frequency proportional to engine speed; converter means for converting said RGT signal pulse frequency into a corresponding speed signal having an amplitude representative of the engine's sub-cyclic speed resulting from the sub-cycle intervals of the engine cylinders; transmission sensor means; for sensing the vehicle tranmission setting and providing a transmission signal indicative of disengagement of the engine from the vehicle; and signal processing means, responsive to said RGT signal, said sub-cyclic speed signal, and said transmission signal, and including memory means for storing signals, for sampling and storing in said memory means said sub-cyclic speed signal values occurring at each RGT signal pulses during deceleration of the engine from a cruise speed to the idle speed, in the presence of said transmission signal, said processing means summing said stored sub-cyclic speed samples to calculate a deceleration increment associated with the compression interval of each cylinder and for comparing said deceleration increments of all cylinders to provide an indication of cylinder compression.