The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jul. 22, 1986
Filed:
Jul. 12, 1985
Gerald T Fattic, Anderson, IN (US);
David S Dennis, Anderson, IN (US);
William J Ricketts, Anderson, IN (US);
General Motors Corporation, Detroit, MI (US);
Abstract
Apparatus for sensing the timing of peak combustion pressure in an internal combustion engine includes a capacitive piezoelectric element adapted for flexure in response to variations in combustion chamber pressure and connected in parallel with a first resistance, a constant current generator connected to establish a predetermined voltage across the first resistance and thereby across the piezoelectric element when the capacitance of the latter remains constant, a second resistance, a source of the predetermined voltage, and an operational amplifier effective to compare the voltage across the piezoelectric element with the predetermined voltage and source or sink current through the second resistance to maintain the predetermined voltage across the piezoelectric element. The output voltage of the operational amplifier is an analog of the current through the second resistance and thus of the rate of change of capacitance of the piezoelectric element. The crankshaft angle after ignition at which this voltage crosses the predetermined reference corresponds to the timing of peak combustion pressure. In order to reduce noise in the 6 to 9 kilohertz range, the first and second resistances may be reduced, the second resistance bypassed at high frequencies and the output voltage amplified with low pass filtering.