US Patent 7191658 Pressure-detecting device and method of manufacturing the same

One end of a rod-like pressure-conveying member is disposed in a sensing unit, and the other end extends into and through an insertion hole of an engine. A combustion pressure, to which the other end of the rod-like member is exposed, is conveyed to the sensing unit through the pressure-conveying member for the detection of the combustion pressure. The pressure-conveying member resonates at a knocking frequency fn of the engine and the knocking frequency fn is detected based on the resonance of the pressure-conveying member.