A knock sensor (DD, knock sensor) is a sensor for determining the knock level during an internal combustion engine operation, a member of the electronic engine control system (ECM) sensors group. The installation location of the specified sensor is the cylinder block. The presence of a knock sensor makes it possible to obtain the maximum power of the internal combustion engine to achieve the best fuel efficiency without compromising the engine.
Engine detonation is an uncontrolled explosive process of combustion of a fuel-air mixture, during which the mixture ignites spontaneously in the combustion chamber.
Detonation in the engine can occur for several reasons, among which the main ones are:
- use of fuel with low detonation resistance;
- the tendency of the engine to detonate due to individual design features ( engine compression ratio, combustion chamber device, spark plug installation location );
- disturbances in the processes of mixture formation and preparation of an inappropriate working mixture of fuel and air;
- incorrectly set ignition timing ( fuel injection timing for a diesel engine );
- engine operation under heavy load at low speeds;
- overheating of the power unit, glow ignition due to a large number of carbon deposits, etc.
Detonation combustion of the mixture is accompanied by an increased noise of the internal combustion engine, an increase in engine temperature and resonant metal knocks. The appearance of detonation causes a significant increase in shock and temperature loads on the main elements of the CPG and KShM, which significantly reduces the service life of a gasoline or diesel engine.
DD is usually divided into two types:
- resonant knock sensor;
- broadband sensor;
The knock sensor is needed to timely transmit to the ECU a signal about the appearance of a knock in the engine, which has exceeded the permissible threshold.
The knock sensor device is based on a special piezoelectric plate. Some voltage is generated on said piezoelectric sensor plate as a result of engine detonation. The height of the voltage depends on what the amplitude of the oscillations will be, as well as their frequency. In other words, the sensor detects knocks and vibrations inside the engine.
Reaching the maximum voltage threshold at the output of the knock sensor serves as a signal to the ECU that the knock has reached an unacceptable limit. Based on the output signal of the knock sensor, the electronic control unit dynamically adjusts the ignition timing (IOP) in the ignition system, shifting this angle downward.
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