Determining engine compression from starter motor current
First Claim
1. Apparatus for testing compression in an internal combustion engine having a starter motor and a source of current therefore, comprisingmeans for detecting the starter motor current waveform when the engine is cranked with the ignition inhibited, the waveform having cycles corresponding with compression cycles in individual cylinders,means for generating a starter motor current signal corresponding with the amplitude of cycles of said current waveform,means for transducing the intake manifold absolute pressure to a corresponding measured intake absolute pressure electrical signal,a source of a reference signal corresponding with the starter motor current in a reference good engine operated at a given intake manifold absolute pressure,means to adjust said reference signal in the ratio of the measured intake absolute pressure signal to the given intake absolute pressure, andmeans to compare said measured starter motor current signal with said adjusted starter motor current reference signal.
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Abstract
Satisfactory or unsatisfactory engine compression is diagnosed by comparing the amplitude of the starter motor current, when cranking an engine having its ignition inhibited, with a reference value. The reference value is adjusted in accordance with the intake manifold absolute pressure, as determined from measurements during the test of ambient pressure and intake manifold vacuum.
17 Citations
10 Claims
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1. Apparatus for testing compression in an internal combustion engine having a starter motor and a source of current therefore, comprising
means for detecting the starter motor current waveform when the engine is cranked with the ignition inhibited, the waveform having cycles corresponding with compression cycles in individual cylinders, means for generating a starter motor current signal corresponding with the amplitude of cycles of said current waveform, means for transducing the intake manifold absolute pressure to a corresponding measured intake absolute pressure electrical signal, a source of a reference signal corresponding with the starter motor current in a reference good engine operated at a given intake manifold absolute pressure, means to adjust said reference signal in the ratio of the measured intake absolute pressure signal to the given intake absolute pressure, and means to compare said measured starter motor current signal with said adjusted starter motor current reference signal.
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6. The method of determining the mechanical conditions in an engine which affect compression, comprising the steps of
measuring the amplitude of the starter motor current when cranking the engine with ignition inhibited, measuring the intake manifold absolute pressure, multiplying a known value of starter motor current when cranking a good engine operating with a given intake manifold absolute pressure by the ratio of said measured intake manifold absolute pressure divided by said given intake manifold absolute pressure, to provide an adjusted value, and comparing said measured starter motor current with said adjusted value of starter motor current.
Specification