Generally, the speed sensor of automobile engine is on the vane flywheel, and the sensor also has a kind of information collection and feedback information of mechanical parts: 1. The speed sensor on the engine is a Hall sensor, which works through the signal teeth on the flywheel and converts the magnetic signal into an electrical signal through the semiconductor element, so the sensor can work without contacting the measured object. 2. The speed sensor on the tachometer directly converts the mechanical signal into an electrical signal, and the sensor is meshed with the main reduction gear of the gearbox through a gear, and the rotation of the main reduction gear drives the sensor gear to rotate, thereby outputting a speed signal; 3. Sensors are equivalent to people's eyes, nose, ears and even skin, and can transmit information to the car brain, and the information received by the car brain will make judgments like people.