Abstract: To obtain higher current yield from ion current measurable across the electrodes of a spark plug upon application of a biasing potential thereto, occurring immediately after an ignition event due to ionization of burning hydrocarbons within the combustion chamber of an internal combustion engine (ICE), the polarity of the circuit including a spark plug is so selected that the smaller one of the electrodes, typically the center electrode of the spark plug, has a positive measuring voltage and positive ignition voltage applied thereto so that the positively charged ions, which have a substantially greater mass than the electrons, will be caused to flow to the negatively charged substantially greater electrode, thus resulting in an enhanced ion current. A standard automotive ignition circuit can be used, with the battery connected, as customary, with negative-ground (FIG.

Abstract: A light guide element, secured in a spark plug-like housing and positioned, for example, within a metallic tube forming a spark plug connector, is coated at the end facing the combustion chamber with a light-impervious material viz: graphite, the graphite emitting radiation upon influence of heat arising within the combustion chamber, which radiation is transmitted to the optical pick-up for subsequent photo-electric evaluation thereof. The optical pick-up is, for example, a quartz glass rod coupled to a light guide cable, or directly coupled to an opto-electrical transducer.

Abstract: In order to eliminate from an ion current sensor signals which are not derived from knocking of an engine, the ion current sensor signal is evaluated by a high-pass - low-pass filter to filter out signals of frequencies extraneous to knocking frequencies, using, preferably, a digital filter including two timing stages (11, 13) connected to a counter; to inhibit response of the circuit, an interrupter switch (8) is included in the evaluation circuit, which is opened upon sensing of disturbance signals due to ignition events, for example upon occurrence of ignition, by setting a timing stage (20) which maintains the switch open, and thus inhibits evaluation of oscillatory signals from the ion current sensor (1) for the timing duration thereof.

Abstract: The knock sensing equipment has a control circuit which generates gating signals for dividing the operation into a measuring phase and a test phase. In the latter, the possible malfunction of the sensor is determined. During the test phase, the sensor responds either to background noise or to a test voltage and the sensing output signals are compared to a predetermined minimum and/or maximum level. Malfunction is indicated if the signals furnished by the sensor are outside of the indicated range.

Abstract: The leading edge of each pulse of an incoming signal sequence starts a first monostable multivibrator whose period is equal to the period of the pulse sequence when the pulse sequence has the desired frequency. The input signal sequence and the output signal from the multivibrator are applied to two inputs of an exclusive OR gate. The latter furnishes an output signal corresponding to the difference in pulse width between the signal applied to the two inputs. The leading edge of the difference signal then starts a second monostable multivibrator whose pulse width corresponds to the maximum allowable frequency deviation. The output signal of the second monostable multivibrator is applied to an inverting input of an AND gate. The direct input of the AND gate receives the difference signal. The AND gate, therefore, only furnishes an output signal when the difference signal has a greater pulse width than the output signal of the second multivibrator, i.e.

Abstract: In order to suppress the train of detector oscillations after the disappearance of the engine knock phenomenon, the invention provides a piezoelectric oscillator which is set into vibration by engine knock and includes circuitry for applying signals of opposite polarity to the oscillator at times when no engine knock is expected. Accordingly, the output of the piezoelectric engine knock detector is used only in a relatively narrow time interval during the combustion cycle. In the remaining interval, the circuit switches over to a configuration where the oscillations of the piezoelectric oscillator are damped. The construction of the invention makes it possible to discriminate between different cylinders of a multi-cylinder engine and to assign the knock phenomenon to particular engine cylinders. A number of embodiments is presented.