Dynamic combustion characteristic sensor for internal combustion engine

A dynamic combustion characteristic sensor for an internal combustion engine having a block and a head defining a combustion chamber therebetween and high voltage spark generating apparatus effective to initiate combustion of a combustible charge within said combustion chamber, the sensor comprising, in combination:

• a headbolt comprising a threaded shank adapted for engagement with the engine block adjacent the combustion chamber and further comprising a head having a bottom peripheral surface adapted to engage the engine head with a predetermined preload force and a flat upper surface substantially normal to the shank, the head being adapted for engagement with torque generating apparatus for the achievement of said preload force;
• a piezoelectric disc affixed to the upper surface of the headbolt so as to partake of flexure of the headbolt head due to combustion related strains between the engine block and engine head;
• inner electrical terminal means in electrical contact with one side of the piezoelectric disc so as to provide an output electrical signal therefrom;
• outer electrical terminal means in electrical contact with the other side of the piezoelectric disc for a ground connection thereto and forming, with said headbolt head, an electrostatic shield for said piezoelectric disc and inner electrical terminal;
• and
• electrical circuit means effective to receive the shielded signal from said inner electrical terminal, said electrical circuit including high pass filter means effective to pass signals having frequency content typical of combustion pressure variations but to block signals having frequency content typical of thermally induced strains in the engine.

A dynamic combustion characteristic sensor for an internal combustion engine having a block and a head defining a combustion chamber therebetween and high voltage spark generating apparatus effective to initiate combustion of a combustible charge within said combustion chamber, the sensor comprising, in combination:

• a headbolt comprising a threaded shank adapted for engagement with the engine block adjacent the combustion chamber and further comprising a head having a bottom peripheral surface adapted to engage the engine head with a predetermined preload force, a flat upper surface substantially normal to the shank and an annular vertical portion rising from said flat upper surface, the head being adapted for engagement with torque generating apparatus for the achievement of said preload force;
• an insulator member;
• an outer electrical terminal member surrounding said insulator member and engaged, along with said insulator member, around its lower periphery, by said annular vertical wall;
• an inner electrical terminal member projecting through said insulator member and insulated thereby from said outer electrical terminal member, said inner electrical terminal member being electrostatically shielded by said outer electrical terminal member;
• a piezoelectric disc having one side affixed to the upper surface of the headbolt so as to partake of flexure of the headbolt head due to combustion related strains between the engine block and engine head, said one side further being in electrical contact with said upper surface;
• and
• spring contact means engaging said inner electrical terminal means and said other side of the piezoelectric disc so that electrical signals generated by the latter are provided to the inner electrical terminal means uncontaminated by noise from said high voltage spark generating apparatus when said sensor engages the engine head and block with said predetermined preload force.