What is a knock sensor on a car engine for?

The combustion of the engine is very complicated, so it needs to have a very precise design and control. A little control error or abnormality will cause abnormal combustion, and "knock" is a kind of abnormal combustion. Simply put, knocking is abnormal pressure in the combustion chamber caused by abnormal combustion.

When the engine is working, due to the influence of excessive ignition timing (ignition advance angle), engine load, temperature, and fuel quality, engine knocking will be caused. When knocking occurs, due to the combustion of gas before the piston moves to the top dead center, the light one will generate noise and reduce the power of the engine, and the heavy one will damage the mechanical parts of the engine. In order to prevent the occurrence of knocking, the knock sensor is an indispensable and important component, so that the ignition advance time can be adjusted by the electronic control system.

Because the engine has a knocking phenomenon, there is also a knock sensor. The knock sensor is installed in the middle of the engine block. Taking a four-cylinder engine as an example, it is installed between the 2 and 3 cylinders, or one in the middle of 1 and 2 cylinders, 3, the middle one of 4 cylinders. Its function is to measure the degree of engine jitter. When the engine knocks, the knock sensor converts the mechanical vibration of the engine into a signal voltage and sends it to the ECU. According to the ignition and other data stored in advance, the ECU calculates and corrects the ignition advance angle in time to adjust the ignition time to prevent the occurrence of knocking.

Engine knocking caused by low-grade fuel, premature ignition, etc. can cause engine damage. The function of the knock sensor is to transmit the engine knock to the electronic control module in the form of an electrical signal, which is an important basis for the control module to adjust the ignition timing to prevent further knocking. Knock sensors are generally of piezoelectric ceramic type. When the engine vibrates, the ceramic inside is squeezed to generate an electrical signal.

There are many kinds of knock sensors, such as magnetostrictive knock sensors, piezoelectric ceramic knock sensors, piezoelectric resonance sensors, etc.