Quantity control during starting - function

W07.15-1243-71

A Temperature-dependent starting injection amount

B Initial start time

C Max. time for start quantity enrichment

D Max. start quantity (temperature-dependent)

t Time

VE Injection quantity per pump stroke

Determination of the injection or fuel delivery quantity takes place irrespective of the accelerator pedal position in order to achieve a secure engine start with the lowest possible pollutant emission:

The selected injection quantity for the starting procedure is oriented primarily on the engine temperature which is detected by the MR/PLN control unit based on the mean value of the coolant and the charge air temperature.

The resulting delivery quantity can, however, be limited to reduce the pollutant emission:

A smoke limitation function operates over a smoke limitation performance map because the smoke emission increases with increasing loads or engine speed and, on the other hand, an altitude correction function prevents too much fuel being injected at great heights which causes increased smoke emission.

 There is an atmospheric pressure sensor for altitude correction in the MR/PLN control unit over which the air pressure of the ambient air is detected and the current altitude of the vehicle is deduced.

This primarily temperature-dependent start injection amount (A) is the basis to start the engine. If the engine does not start immediately, the injection quantity is increased continuously until the engine fires or the limit value for the maximum start injection amount (D) is reached.

The maximum start injection amount (D) is maintained until actuation of the starter and the solenoid valves in the unit pumps is broken off after about 40 seconds to protect the engine, the starter and the battery.

If the engine has started, the injection quantity in the idling speed control is exceeded by the start control system at a particular rotational speed. This is known as the starter cut-off but has nothing to do with the starter cut-off speed at the starter. The starter cut-off can be above or below the starter cut-off speed depending on the temperature conditions and causes a change of calculation methods.