Combustion monitoring system for fuel injected engines

A method for detecting force waves in solid metal objects comprising the steps of:

• (a) forming a cylindrical cavity in the metal such that the axis of the cavity is substantially perpendicular to the movement of the force wave to be detected;
• (b) placing at the inner end of said cavity a flat piece of piezoelectric material having a first face in electrical contact with the inner end of said cavity and the second and opposite face facing outward from said cavity;
• (c) inserting into said cavity from its outer end an element comprising an inner core of an elastic, conductive material within an outer sleeve of insulating material which surrounds said conductive material except for the forward and rearward ends thereof, the forward end of said conductive material being uninsulated and adapted to be pressed against the outward facing portion of said piezoelectric element;
• and
• (d) positioning in said cavity a coaxial fitting of the type having a protruding central conductor shaft supported in spaced insulated relation to an outer cylindrical conductor, the central shaft of said coaxial fitting being adapted to conductively engage the rearward end of the conductive core upon positioning of said coaxial end fitting into said cavity, whereby said conductive core is compressed between the outward face of said piezoelectric element and said central conductor shaft of the coaxial fitting so as to provide an output terminal for the signal which develops in the piezoelectric material in response to the force waves.

A transducer for developing electrical signals in response to pressure in a chamber in a housing having a port from the outside of the housing to the chamber, comprising a body in engagement with the housing at the port having

• a first surface thereon serving as a pressure-sensing face extending into the port;
• a second surface thereon for at least partially seating against the housing at the port therein;
• a cavity in said body extending from outside the chamber toward said pressure-sensing face and having an inner surface which is in proximity with said seating surface and is transverse to said port;
• a piezoelectric element on the inner surface of said cavity for developing an electrical signal responsive to flexing of said housing due to pressure changes in the chamber;
• a compressible plug disposed in said cavity and having a core of conductive elastomeric material and an outer sheath of insulating material, said sheath being open on opposing ends so that on one end the conductive material is adapted to contact the piezoelectric element;
• means for compressing said plug within said cavity so that the conductive core contacts with said piezoelectric element;
• and
• output terminal means coupled to the conductive core at the opposing end of said plug for receiving the electrical signal from said piezoelectric element.

A method for detecting force waves in solid metal objects comprising the following steps:

• (a) forming a cylindrical cavity in the metal such that the axis of the cavity is substantially perpendicular to the movement of the force wave to be detected;
• (b) placing at the inner end of said cavity a flat piece of piezoelectric material having a first face in electrical contact with the inner end of said cavity and the second and opposite face facing outward from said cavity;
• (c) inserting into said cavity from its outer end an element comprising an inner core of elastic, conductive material within an outer sleeve of insulating material which surrounds said conductive material except for the forward and rearward ends thereof, the forward end of said conductive material being uninsulated and adapted to be pressed against the outward facing portion of said piezoelectric element;
• (d) compressing said element against said piezoelectric material to stress said material;
• and
• (e) contacting the rearward end of the conductive core to provide an output terminal for the signal which develops in the peizoelectric material in response to the force waves.

For use in a diagnostic system for a diesel engine of the type having a combustion chamber associated with each cylinder and a threaded port extending from each combustion chamber to the outer surface of the engine which is adapted to accept a glow plug, a transducer assembly comprising a metal housing having a shank portion threaded for a screw-type engagement with said threaded port and a head portion external to said shank portion and having a recessed cavity extending along the axis of said port, said shank portion having a forward end for extending into said port and acting as a pressure face within the cylinder and closing the inside surface of said cavity transverse to the axis of the port, said metal housing at least partially seating against said engine at said head portion and a piezoelectric element coupled to the inner end of the cavity so as to develop an electrical signal during flexure of said housing resulting from pressure changes against said pressure face, an element comprising an inner core of an elastic, electrically conductive material within an outer sleeve of insulating material which surrounds said conductive material except for the ends thereof, said element being inserted into said cavity and having one end in contact with said piezoelectric element, and an electrical output means coupled to the other end of said element for compressing said element against said piezoelectric element and for transmitting the electrical signal generated by said piezoelectric element.