Speedometer(Odometer) Magnet

Speedometer(Odometer) magnet

Motorcycle speedometer magnets have been one of the largest users of cast AlNiCo magnets over the last few decades, and the majority of speedometer magnets are now exported to the Indian market.

AlNiCo Odometer magnet is a magnet manufactured by AlNiCo that is used in automobile odometers. It consists of an outer AlNiCo magnet ring and a magnetic injection molded body with a shaft hole that is fitted into the outer magnetic ring's hole. The outer magnetic ring is an interference fit, the magnetic injection molding body and the outer magnet ring are cylindrical bodies, the outer magnet ring is an AlNiCo permanent magnet, and the diameter of the hole in the outer magnet ring corresponds to the magnetic injection molding body's diameter. The diameter of the injection body's shaft hole is three times that of the injection molded body.The production process of the AlNiCo Odometer magnet is simple and easy, the raw material AlNiCo is relatively cheaper than rare earth Neodymium or SmCo, and the product's use performance is equal to or better than that of existing similar products, thereby reducing production costs and saving a lot of expensive rare earth permanent magnet materials.

Working Principle

A flexible shaft connects the speedometer's drive shaft to the driving gears inside the front wheel. The AlNiCo magnet is attached to the drive shaft and rotates with it. A metallic cup covers AlNiCo coils, and there is a small gap between the AlNiCo magnet and the cup. The lower end of the speedometer needle is connected to a hair spring by a metallic cup. Hair springs will keep the needle swing steady and reset it on time. When the motorcycle is running, the front wheel rotates the gears, which then turn the magnet on the drive shaft. At this point, the flux lines between the magnet and the metallic cup will be cut, resulting in an induced current and magnetic field. Because of the interaction between the induced magnetic field and the magnetic field of the magnet, the metallic cup will rotate. The damping effect of the hair spring affects the rotation of the metallic cup, and the needle will rest at a specific speed when the torque of the cup equals the damping torque of the hair spring. Higher speed produces more torque, resulting in a wider swing angle. The counter is made up of three worm gear pairs and a drum. When the flexible shaft rotates 1000 times, it drives the end worm gear, and the gear turns a circle, then raised claw will stir digits on the drum.

How a purely electronic Odometer works?

The pure electronic odometer sensor is not in direct contact with the mechanical parts, and there is a small gap between the sensor probe and the target wheel, which is usually kept to 1.4+0.6mm. When the car is in motion, the odometer rotor rotates in tandem with the transmission output shaft. When a specific tooth of the odometer rotor rotates to the position corresponding to the sensor probe, the sensitive device in the probe is affected by the odometer rotor's magnetic field and outputs a low level.The odometer rotor's teeth are not aligned with the sensor probe, and the sensitive device in the probe is not affected by the magnetic field and outputs a high level, so that every time the transmission's output shaft rotates one revolution, the odometer sensor outputs a square wave pulse signal, which is transmitted through the connecting wire harness. The magnetoelectric pulse signal sent by the sensor can be processed by the microcomputer inside the meter and displayed on the display screen for the speedometer.The computer processes the odometer to calculate and display the mileage based on the vehicle speed and total running time.

When the AlNiCo magnet magnet is demagnetized, the speedometer pointer swings only slightly when driving at high speeds. At medium and low speeds, it frequently points to zero, or the pointer index is too large, and the indication value is incorrect.

Solution: Remove the speedometer, remove the rotor, and re-magnetize.