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what kind of speed is registered by an automobile speedometer?
It is technically easy to accurately display speed. Today's vehicle speed signal is generally obtained from the wheel speed sensor on the wheel and then transmitted to the trip computer. After calculation, it is displayed on the instrument panel. Because the wheel speed signal is very accurate, the speed calculated by the computer is also very accurate. As long as these data are directly displayed on the instrument panel, the speed displayed by the speedometer is accurate. However, the final speed displayed on the dashboard is the modified data, which is higher than the actual speed.
On the expressway with a speed limit of 100 km, the actual speed is between 88 km / h and 100 km / h, which will never exceed 100 km / h. If the instrument panel displays the actual speed, the actual speed is 100 km / h, and the speedometer also displays 100 km / h. therefore, it is difficult for the driver to control and it is easy to cause overspeed.
How do we know the actual speed of the car?
One method is to use the vehicle inspection computer to directly read the data in the driving computer, which is absolutely accurate. The calculation of vehicle mileage is based on this data; Another method is to use auxiliary equipment, such as mobile phone navigation and vehicle navigation. It is very convenient and accurate to calculate the vehicle speed by using GPS signal, but the speed displayed by navigation will be delayed. The speed we see is actually the speed one second ago, not real-time speed.
Why can't the speedometer of the car accurately display the actual speed?
0-16km / h is within the allowable error range.The indicated speed of the speedometer shall not be lower than the actual speed, and the error between the indicated speed and the actual speed shall comply with the following formula: "0 ≤ indicated speed, actual speed ≤ actual speed / 104KM / h". According to this formula, when the actual vehicle speed is 120km / h, 120km / h ≤ indicated vehicle speed ≤ 120km / h, 12km / h 4km / h, that is, the vehicle speed displayed on the instrument panel is between 120km / h and 136km / h, which meets the standard. The traditional speedometer is mechanical. A typical mechanical odometer is connected to a flexible shaft. There is a wire rope in the flexible shaft. The other end of the flexible shaft is connected to the gear of the transmission. The rotation of the gear drives the steel cable to rotate. The wire and cable drives the magnet in the odometer cover ring to rotate. The cover ring is connected with the pointer, and the pointer is placed at the zero position through the hairspring. The rotation speed of the magnet causes the change of the magnetic line of force, and the balance is broken, so the pointer is driven. This speedometer is simple and practical, and is widely used in various models. With the development of electronic technology, many automobile instruments use electronic speedometer. The common method is to obtain the signal from the speed sensor on the transmission and deflect the pointer or display the number by changing the pulse frequency.
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