Abstract: A closed loop knock control system integrates a knock signal comprising knock intensity indicating knock pulses from an engine mounted knock sensor into a retard voltage in an integrating amplifier normally provided with a fixed reference voltage through a series pair of resistors. The junction of the series pair of resistors is connected through another resistor and a semiconductor switch, when the switch is actuated, to a second constant reference voltage greater in the retard direction than the first. An open loop knock anticipating system responds to a detected knock anticipating event by actuating the semiconductor switch means for a predetermined time duration to produce a step change in the retard direction for the predetermined time duration in the retard voltage and thus in the spark timing. If voltage limiting means is provided in the closed loop system for the output of the integrator, the summed combination of the closed and open loop retard voltages is also limited thereby.

Abstract: A vehicle mounted, spark ignited, internal combustion engine subject to bursts of ringing knock vibration of varying duration corresponding to knock of varying intensity includes apparatus effective to generate pulses in response to the bursts and of corresponding duration. Further apparatus delays the trailing edge of each pulse by a common predetermined duration to favorably reduce the ratio of the durations of such pulses before application to apparatus effective to control a knock reducing parameter of the engine. The reduced ratio of duration between short and long pulses provides more uniform control over the total range of knock intensity. The engine may also include apparatus to delay the leading edge of each pulse by a common predetermined duration to eliminate short noise pulses and improve the knock signal to noise ratio. If so, this apparatus is inserted prior to the trailing edge delay apparatus and the common predetermined duration of the latter is greater than that of the former.