Knock sensor

A knock sensor for mounting on a vibration generating part comprising:

• a base including a cylindrical part to be mounted on the vibration generating part, and a flange part provided at a part of the cylindrical part;
• an annular piezoelectric element fitted to the cylindrical part and for converting a knocking vibration of the vibration generating part into an electric signal to detect the knocking vibration, said piezoelectric element having a pair of axial end surfaces;
• annular electrodes respectively provided to be in contact with both of said surfaces of the piezoelectric element, each of said annular electrodes covering less than the entire respective surfaces of the piezoelectric element;
• terminal plates disposed to be in contact with the respective electrodes and for extracting an output of the piezoelectric element;
• and
• a hold unit for pressure holding the piezoelectric element, the electrodes and the terminal plates to the flange part,
• wherein an electric insulating material having an almost equal thickness to the electrodes is provided on a respective portion of each of said piezoelectric element surfaces which is not in contact with the electrodes.