Wheel RPM sensor, component description - GF42.45-P-5134MCC
MODEL 451.3/4
Location
The left front RPM sensor and right front RPM sensor are mounted on the steering knuckles of the front axle.
The left rear RPM sensor and right rear RPM sensor are mounted on the wheel carriers of the rear axle.
Task
The RPM sensors generate a square wave signal which the ESP control unit (N47-5) uses to detect the current wheel speed and other additional information.
Design
The RPM sensor consists of the RPM sensor head and an electrical line.
The display shows the current curve through the active RPM sensor during an acceleration phase.
Function
A change in internal resistance inside the RPM sensor is caused by the strength and direction of an external magnetic field. This change generates a square wave signal, whose frequency is dependent on the rotational speed. The amplitude height remains constant. The direction of travel is detected by a different signal representation when the wheel is running to the left or right. This signal is read directly by the ESP control unit.
The width of the square wave pulse provides various additional information (e.g. direction of travel and installation position) and the distance between the square wave pulses indicates the current wheel speed.
When the vehicle or the corresponding wheel is at a standstill, the RPM sensor transmits a standstill pulse every second.
The external magnetic field is produced by a multipole ring. This consists of an elastomer plastic containing metallic particles. These are aligned by a special magnetization method so as to produce various magnets whose polarity at the circumference alternates from north to south.
Advantages compared with a passive (inductive) RPM sensor:
- Sensing of vehicle speed right down to standstill.
- Improvement in signal quality (digital signal).
- Signal largely insensitive to vibrations and temperature differences.
- Lower weight and smaller design than induction-type pulse generator.