Rpm request, basic function

Overview

This document contains information on:

 General

 Function requirements

 Function

General

The combustion engine control unit continuously requests the engine speed as a basis for calculating numerous control procedures. The crankshaft Hall sensor generates voltage signals and forwards them to the combustion engine control unit. The combustion engine control unit calculates an engine speed signal on the basis of the voltage signals and forwards it to the connected control units via the bus system.

Function requirements

 Engine management ON (circuit 87M)

 Engine in operation

Function

A sensor rotor with magnetic terminal fields that differ in terms of their polarity is located on the crankshaft. The rotation of the sensor rotor allows the crankshaft Hall sensor to generate square wave signals. The combustion engine control unit evaluates the square wave signals and calculates the engine speed and crankshaft position. Depending on the number of terminal fields, one terminal field or one square wave signal specifies a particular change of the crankshaft angle. The absolute position of the crankshaft can be determined on the basis of an irregularity of the sensor rotor, e.g. in the case of missing terminals.

 In the event of an engine stop, the engine may change its direction of rotation shortly before it comes to a standstill. The combustion engine control unit detects the reversal of the direction of rotation on the basis of the pulse width of the square wave signal and can still detect the exact crankshaft position. This information is required when quickly starting the engine in ECO start/stop mode.

 If the voltage signal from the crankshaft Hall sensor fails, the voltage signals from the intake camshaft or exhaust camshaft Hall sensor are used for limp-home mode as a substitute.