English 
digital speedometer for motorcycles
The digital speedometer displays the driving speed of the automobile through the swing of the pointer. In short, there is a system in the speedometer (rotary table with pointer shaft, rotating shaft with permanent magnet, bearing, hairspring and other parts) to control the swing of pointer. The swing amplitude of the pointer is finally determined by the speed output by the transmission (that is, the rotating shaft of the speedometer is driven by the flexible shaft, which is connected with the worm gear in the worm transmission pair on the output shaft of the automobile transmission or transfer case). Due to the manufacturing process and assembly error of these parts, as well as the natural wear in the process of use and the magnetic change of magnetic components, the indication error of speedometer will be caused.
Another important reason for the error is related to the automobile tire, because the displayed number of the speedometer is only related to the speed output by the transmission, but the actual speed is related not only to the speed, but also to the rolling radius of the tire. Automobile tires wear gradually with the increase of mileage, and its rolling radius decreases gradually. The tire pressure also affects the rolling radius. Therefore, there will be an error between the indicated value of the speedometer and the actual vehicle speed. According to the regulations, the allowable error range of speedometer is + 20% - 5%. That is, when the actual speed is 40km / h, the indicated value of the speedometer should be between 38 ~ 48km / h, or when the indicated value of the speedometer is 40km / h, the actual speed should be between 33.3 ~ 42.1km/h.
At present, the calibration methods of speedometer mainly include road experiment and indoor bench experiment. The road experiment method is that the vehicle passes through a test road of a predetermined length at the same speed according to the different speeds on the speedometer, measures the time of passing through the road section, then calculates the actual speed, and then compares it with the speedometer to calculate the indication error of the exit speedometer at different speeds. The indoor bench test method is mainly tested by the roller speedometer test-bed.
In order to prevent the error between the actual speed and the value displayed by the speedometer from being too large and affecting the driving safety, the owner is required to regularly identify the speedometer in the corresponding safety regulations
Get a Quote / Info