Speed Sensor
Rod-shaped speed sensors (impulse transmitters) measure wheel speeds. Three speed sensors measure wheel speed of each front wheel and both rear wheels. Speed sensors for front axle are on steering knuckles. Speed sensor for rear axle is on axle housing. Drive pinion serves to measure rear wheel speed.
Speed sensor measures wheel speed by sensing rotor teeth movement. On front axle, rotor teeth are machined into front wheel hub. See Fig 1.
On rear axle, toothed rotor is pressed on drive pinion. Axles with different ratios have gear wheels with different number of teeth. Speed sensors consist of magnetic core and coil. Rotation of rotor, set specific distance from sensor, causes alternating voltage in coil.