Engine Speed Recording
Engine Speed Recording
Engine speed recording
The crankshaft sensor is required for exact engine speed recording. This also enables misfire detection and rough road detection.
The smooth idle speed evaluation only works when the engine is running at idle (cold or warm). Individual cylinders with a bad combustion performance are pinpointed. The rough road detection detects rough road driving on a poor-quality road surface.
Brief component description
The following components are described for the engine speed recording:
Crankshaft sensor
The crankshaft sensor records the position of the crankshaft with the aid of a sensor wheel screwed to the crankshaft. The DME uses this to calculate the engine speed. The crankshaft sensor is required in order to achieve fully sequential fuel injection (individual fuel injection for each cylinder at optimum ignition point).
The increment gear has 58 teeth as well as a reference gap of 2 teeth. The reference gap enables detection of the upper dead centre of the 1st cylinder. By monitoring the individual teeth, the Hall effect sensor delivers a certain number of signal jumps to the engine control system.
The signal from the crankshaft sensor means that the DME also evaluates the crankshaft acceleration. The crankshaft acceleration provides an indication of the combustion quality of individual cylinders.
Voltage is supplied by the DME with 5 Volts and ground.
System functions
The following system functions are described:
Misfire detection
The operational smoothness values of the individual cylinders are displayed for troubleshooting purposes. The engine must be operated at idle speed for at least 3 minutes to produce useful values. The smooth idle speed evaluation only works when the engine is running at idle (cold or warm). Individual cylinders with a bad combustion performance are pinpointed. Random fluctuations in the smooth-running value of individual cylinders can only be detected through close observation of the value. If combustion in the engine is theoretically even, the operational smoothness values will be 0 (averaged over all cylinders). An increase in the smooth-running values may be caused by various factors (e.g. misfiring, excess air, mixture deviations, faults in fuel supply, low compression). For this reason, exact control limits cannot be specified. The engine speed is measured at the increment wheel assisted by the crankshaft sensor. As well as recording the engine speed, smooth running of the engine (= misfire detection) is monitored. For misfire detection, the increment gear in the DME control unit is divided into 2 segments according to the firing interval (between 2 ignition operations). Within the DME control unit, the periodic duration of the individual segments is measured and statistically evaluated. For each mapped value on the characteristic map, the maximum permissible values for irregular running are stored (as a function of engine speed, load and engine temperature). If these values are exceeded for a specific number of combustion cycles, a fault entry is stored for each faulty cylinder detected.
Rough road detection
The poor-road-surface detection detects poor-road operation on bad surfaces (stony surfaces, gravel or potholes) by means of the communicated wheel acceleration. If a rough section of road is detected, a fault is stored and the misfire detection is briefly suppressed. This is necessary as the vibrations in the drive train caused by poor road surfaces can lead to erroneous misfire detection. Conversely, it is also possible that the rough road detection comes into effect too late (once misfiring has already been erroneously detected). in which case incorrectly diagnosed misfiring is identified with the assistance of the rough road detection.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.