MODEL | 909 |
Shown at left front wheel |
L6/1 | Left front rpm sensor |
L6/2 | Right front rpm sensor |
N42.45-2050-04
Shown at left rear wheel |
L6/3 | Left rear rpm sensor |
L6/4 | Right rear rpm sensor |
D42.45-0023-11
Location
The left front rpm sensor and the right front rpm sensor are attached to the respective steering knuckle of the front axle.
The left rear rpm sensor and the right rear rpm sensor are located at the respective wheel carrier of the rear axle.
Task
The rpm sensor detects the rotational speed and rotational direction of the wheel. The rpm sensor also detects air gap faults. The rpm sensor sends this information to the ESP® control unit (N30/4).
Body
The rpm sensor consists of a housing, a sensor element with auxiliary magnet to generate a magnetic field, and an electronic analysis system.
1 | Initialization |
2 | Speed pulse |
A | Information bits |
D42.45-0040-11
Function
The change in the strength of the magnetic field is caused by a change in resistance in the sensor. An electronic analysis system inside the rpm sensor generates signals which are sent as current pulses along the supply line to the ESP® control unit. The interval between the speed pulses is the dimension for the rotational speed.
Between the speed pulses, 8 information bits for rotational direction, strength of the magnetic field and air gap fault are sent to the ESP® control unit. The ESP® control unit uses the current pulses to calculate the vehicle speed and for monitoring purposes.
The wheel speeds and wheel rotation directions are made available to other control units in the vehicle via the engine CAN (CAN C) (e.g. to display the vehicle speed in the instrument cluster (P15)).
The sensor functions according to the principle of magnetostriction.