Since adoption of a knock control system (KCS) on Toyota Crown (2.0ℓ. OHC with Turbo-charger) in autumn 1980, Toyota has continued development and application of various resonance-type and non-resonance-type knock sensors using piezoelectric elements (piezoceramics), with the aim of obtaining stabilization of characteristics and a high degree of reliability for our KCSs.The new resonance-type knock sensor introduced in the 1986 model Toyota Supra (3.0ℓ DOHC) is characterized by its remarkably expanded knock detecting frequency bandwidth. This knock sensor's knock detecting part has a disc center support structure. The sensor has a piezoceramic with enlarged surface causing an output voltage increase which results in a decrease in computer input impedance. As a result, it provides a decrease of quality factor (Q) at resonance time, expansion of the knock detecting frequency bandwidth, improvement of response and an increase in the S/N ratio regarding electrical noise. Furthermore, a reduction in number of the parts has permitted improvement of productivity and reliability, as well as cost reduction.