Spark Plug Combustion Ionization Sensor

Abstract

A spark plug combustion ionization sensor for measuring ion current inside the cylinder of an internal combustion engine. The sensor measures ion current which flows when the energy released during combustion ionizes the air inside the cylinder, and thus can detect combustion and emission parameters. The spark plug combustion ionization sensor generally includes an insulated, dedicated sensing electrode, separate from the sparking electrode of a spark plug. The sensing electrode may also be shielded to further reduce interference such as electromagnetic interference (EMI). The use of a dedicated electrode allows for ion current measurement with less electromagnetic noise from the ignition process, and also eliminates the need for circuitry that is typically necessary when the sparking electrode is also used to sense ion current.

I claim: 
     
         1 . A spark plug, comprising:
 a sparking electrode;   an electrically insulating body having a first end and a second end, wherein the electrically insulating body surrounds at least a portion of the sparking electrode, and wherein the sparking electrode exposed at the first end of the electrically insulating body;   a housing surrounding a portion of the electrically insulating body, wherein the housing is adapted for mounting the spark plug in an engine cylinder head;   a ground electrode connected to the housing, wherein the ground electrode is positioned to create a spark gap between the sparking electrode and the ground electrode; and   a sensing electrode extending through either the housing or the electrically insulating body, wherein the sensing electrode is electrically isolated from the sparking electrode, wherein a portion of the sensing electrode is exposed near the ground electrode.   
     
     
         2 . The spark plug of  claim 1 , wherein the sensing electrode is electrically isolated from the ground electrode. 
     
     
         3 . The spark plug of  claim 1 , wherein the sensing electrode extends through the electrically insulating body, further comprising:
 insulating material substantially surrounding the sensing electrode along its length; and   an electrically conductive shield substantially surrounding the insulating material along its length, the electrically-conductive shield being electrically isolated from the sensing electrode and the sparking electrode, wherein the electrically-conductive shield substantially reduces electromagnetic interference in the sensing electrode.   
     
     
         4 . The spark plug of  claim 3 , wherein the electrically conductive shield is configured to be conductively coupled to ground. 
     
     
         5 . The spark plug of  claim 4 , wherein the housing comprises a metal and wherein the electrically conductive shield is conductively coupled to the metal. 
     
     
         6 . The spark plug of  claim 1 , further comprising at least a second sparking electrode exposed at the first end of the electrically insulating body. 
     
     
         7 . The spark plug of  claim 1 , further comprising at least a second sensing electrode, wherein the second sensing electrode is electrically isolated from the sparking electrode and wherein a portion of the second sensing electrode is exposed at the first end of the electrically insulating body. 
     
     
         8 . The spark plug of  claim 1 , wherein the sensing electrode is substantially tubular and substantially surrounds the sparking electrode along its length, further comprising:
 an insulating material disposed between the sparking electrode and the sensing electrode along the length of the sparking electrode.   
     
     
         9 . The spark plug of  claim 1 , wherein the housing comprises a metal and wherein the sensing electrode extends through the housing, further comprising:
 insulating material substantially surrounding the sensing electrode along at least part of its length.   
     
     
         10 . The spark plug of  claim 9 , wherein the sensing electrode is electrically isolated from the ground electrode. 
     
     
         11 . The spark plug of  claim 9 , further comprising at least a second sensing electrode, the second sensing electrode extending through the metal and comprising a conductive element exposed at the first end of the spark plug, further comprising:
 insulating material substantially surrounding the second sensing electrode along its length.   
     
     
         12 . The spark plug of  claim 10 , wherein the sensing electrode comprises a single conductive element. 
     
     
         13 . The spark plug of  claim 10 , wherein the sensing electrode comprises a plurality of conductive elements. 
     
     
         14 . The spark plug of  claim 13 , wherein the plurality of conductive elements include a conductive rod and a resistor. 
     
     
         15 . The spark plug of  claim 1 , wherein the sensing electrode comprises a conductive land on the electrically insulating body. 
     
     
         16 . The spark plug of  claim 15 , wherein the sensing electrode comprises a plurality of sensing electrodes configured as conductive lands. 
     
     
         17 . The spark plug of  claim 15 , wherein the at least one sensing electrode is electrically isolated from the ground electrode. 
     
     
         18 . The spark plug of  claim 16 , further comprising conductive leads coupled to the conductive lands and extending through the electrically insulating body. 
     
     
         19 . The spark plug of  claim 17 , wherein the housing is threaded and comprises a metal. 
     
     
         20 . The spark plug of  claim 1 , further comprising:
 insulating material substantially surrounding the sparking electrode along its length; and   an electrically conductive shield substantially surrounding the insulating material along its length, the electrically-conductive shield being electrically isolated from the sensing electrode and the sparking electrode, wherein the electrically-conductive shield substantially reduces electromagnetic interference in the sensing electrode.   
     
     
         21 . The spark plug of  claim 20 , further comprising:
 an insulating layer substantially surrounding the electrically conductive shield along its length, wherein the sensing electrode is substantially tubular and is disposed between the insulating layer and the electrically insulating body.