08-17-2017, 12:12 AM
A speedometer or speedometer is an indicator that measures and shows the instantaneous speed of a vehicle. Now universally adapted to motor vehicles, they began to be available as options in the 1900, and as standard equipment from around 1910 on wards. Speedometers for other vehicles have specific names and use other means to detect speed. For a boat, this is a pit log. For an airplane, this is a speed indicator.Charles Babbage is credited with creating an early type of a speedometer, which usually fitted locomotives.The electric speedometer was invented by Croatian Josip Belu i in 1888, and was originally called a speedometer.
Operation
Originally patented by Otto Schultze on October 7, 1902, it uses a flexible rotating cable usually driven by the gear connected to the output of the vehicle's transmission. The Volkswagen Beetle early and many motorcycles, however, use a cable driven from a front wheel. When the car or motorcycle is in motion, a set of speedometer gear converts a speedometer cable, which then turns the speedometer mechanism itself. A small permanent magnet attached to the speedometer cable interacts with a small aluminum cup (called speedcup) attached to the axis of the instrument's analog speedometer instrument. As the magnet rotates near the cup, the changing magnetic field produces eddy currents in the cup, which themselves produce another magnetic field. The effect is that the magnet exerts a torque on the cup, "dragging" it, and thus the speedometer pointer, in the direction of its rotation without mechanical connection between them.
The axis of the pointer is held to zero by means of a fine torsion spring. The torque in the cup increases with the speed of rotation of the magnet. Therefore, an increase in the speed of the automobile will rotate the cup and the speedometer pointer against the spring. The cup and pointer will rotate until the pair of eddy currents in the cup is balanced by the opposite pair of spring and then stopped. Since the torque in the cup is proportional to the speed of the car, and the spring deflection is proportional to the torque, the angle of the pointer is also proportional to the speed, so that equally spaced markers on the dial can be used For speed gaps. At a given speed, the pointer will remain stationary and pointing to the appropriate number on the speedometer dial.
The return spring is calibrated in such a way that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including the ratios of the rear axle gears driving the flexible cable, the final drive ratio in the differential and the diameter of the driven tires.
One of the main disadvantages of the eddy current speedometer is that it can not display the speed of the vehicle when running in reverse as the cup rotates in the opposite direction - in this scenario the needle would be driven against its mechanical pin in position zero .