Crankshaft Hall Sensor, Basic Function - GF07.04-P-2004A

Engine all (CAR) 

Overview 

This document contains information on:

• General 
• Structure 
• Location 

General 

The crankshaft Hall sensor contactlessly detects the increment structure (perforated plate) on the starter ring gear and forms an electrical signal (impulse pattern) based on this. The combustion engine control unit uses this signal as a basis on which to calculate the rotational speed and current angular position of the crankshaft.

Example illustration on engine M272 

Courtesy of MERCEDES-BENZ USA

Function 

The crankshaft Hall sensor and its electronics are cast into a plastic housing with a 3-pin plug connection. The distance to the sensor rotor is determined by the installation position and is approx. 0.3 to 1.3 mm. The crankshaft Hall sensor scans the perforated plate with the 58 teeth and a gap of 2 teeth (60-2).

Each of the 4 mm wide teeth generates a signal change at the crankshaft Hall sensor. The signal changes from approx. 5 V (high) to approx. 0 V (low) depending on the rotational speed.

If the engine turns backward shortly before coming to a standstill, this is recognizable through a change to the pulse width (differentiation of the direction of rotation by the crankshaft Hall sensor). The signal change is triggered by the teeth passing in front of the Hall sensor. There is no further signal change when passing the gaps or the long gaps with 2 missing teeth. By passing the gap with 2 missing teeth, the top dead center of cylinder 1 is recognized.

The falling signal edge of the signal is evaluated. For a frequency measurement, the gap between two negative edges must be measured.

The signal from the rising signal edge is not used for determination of the RPM or rotational angle. Together with the falling signal edge, it delivers information about the pulse width, which allows a statement to be made about the direction of rotation.