Quantity control starting, function

W07.15-1243-71

A Temperature dependent start injection quantity

B Initial start time

C Max. time for start quantity enrichment

D Max. start injection quantity (temperature-dependent)

t Time

VE Injection quantity per pump stroke

Determination of the injection or delivered fuel volume independently of the accelerator pedal position in order to achieve a secure engine start with the lowest possible emission of pollutants:

The injection quantity selected for the start process depends primarily on the engine temperature which is determined by the MR/PLD control unit as the average value of the coolant and the charge air temperature.

The resulting fuel quantity can, however, be limited to reduce pollutant emissions:

On the one hand the smoke limiter reduces smoke emissions with increasing load or as the engine speed increases by using the smoke limiting characteristic and on the other hand altitude correction prevents too much fuel being injected at greater altitudes leading to increased smoke emissions.

 There is an atmospheric pressure sensor in the MR/PLD control unit for altitude correction purposes over which the air pressure of the ambient air is determined and the current height above sea level of the vehicle derived.

The engine starts with this initial, primarily temperature-dependent, start injection quantity (A). The injected quantity will be continuously increased until the engine fires if the engine does not fire immediately or until the limit value for the maximum start injection quantity (D) has been reached.

The maximum start injection quantity (D) will be maintained until such time as actuation of the starter and the solenoid valves in the unit pumps is interrupted after about 40 s to protect the engine, starter and battery.

Once the engine has fired, the injection quantity will be regulated to the idling speed condition at a particular engine speed by the start control. This changeover is known as starter break-off, but has nothing to do with the starter break-off speed at the starter. The starter break-off can lie above or below the starter break-off speed depending on the temperature conditions and leads to a change in the method of calculation.