Spark generating apparatus having strain gage cylinder pressure measurement feature

Abstract

An ignition coil, spark plug, and pressure sensor for an internal combustion engine are, in a preferred embodiment, integrated into a single assembly and mounted directly on a plug hole of an internal combustion engine. A hard spark plug shell serves as a pressure member and on which a strain gage is affixed. Changes in the pressure in the combustion chamber deform the shell, causing a corresponding change in the resistance of the strain gage. A bridge circuit or the like is used to measure the resistance change thereby providing a direct indication of cylinder pressure.

1 . A spark generating assembly for initiating combustion and detecting a pressure in a cylinder of an internal combustion engine, said assembly comprising: 
 an outer housing;    a control circuit interface portion coupled to a first end of said outer housing;    a central electrode having a main axis and a first end configured for connection to a relatively high voltage source;    an insulator radially outwardly of said central electrode, said central electrode further having a second, exposed end axially opposite said first end;    a conductive shell outwardly of said insulator and coupled to a second end of said outer housing, said shell having a center portion and an engagement portion, said engagement portion being having threads and configured to engage a corresponding aperture of said engine that is in communication with said combustion cylinder;    a second electrode spaced apart from said second end of said central electrode to define a spark gap therebetween, said second electrode being electrically connected to said shell;    a strain gage directly affixed to said center portion of said conductive shell whereby the strain gage strains with the shell due to direct affixation, said strain gage configured to detect deformations of said shell indicative of said pressure;    said assembly further comprising an ignition coil disposed within said outer housing configured to be connected to a low voltage source through said control circuit interface to selectively energize said ignition coil, said ignition coil being coupled to said first end of said central conductor and further configured to generate said relatively high voltage;    said assembly further comprising a bridge circuit electrically connected to said strain gage configured to generate a pressure signal indicative of said pressure;    wherein said outer housing, said control circuit interface portion, said ignition coil, said conductive shell and said strain gage are formed as an integrated assembly, and said strain gage and electrical connections to said bridge circuit are formed in a flex circuit comprising a multi-layer circuit including a ground plane layer and subsequent outer layers having leads disposed thereon sandwiched between insulating layers, all of which provide electromagnetic interference (EMI) shielding.    
   
   
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