Overview
This document contains information on:
General
Function requirements
Function
General
The glow system consists of the glow output stage and the electrically heated glow plugs, which are inserted in the combustion chambers. The glow plugs are preheated in the startup phase. This ensures that the requisite ignition temperature of the fuel/air mixture is reached. After engine start, the glow plugs continue to heat up for a little while. This serves to reduce pollutants as a result of unburnt hydrocarbons in the exhaust gas.
Function requirements
Engine management ON (circuit 87M)
Glow system functional
Colder temperatures
Function
The glow system implements the glow request from the combustion engine control unit.
In the process, the glow plugs are energized. The electrical energy is largely turned into heat. After heating up has taken place, the voltage to the glow plugs is gradually reduced.
With the glow system, a differentiation is made between the following processes:
Preglowing
Start-ready glowing
Start-glowing
Afterglowing
Diagnostic glowing
Particle filter glowing
Emergency glowing
Preglowing
The glow plugs are preheated during preglowing. This ensures that the requisite ignition temperature of the fuel/air mixture is reached.
To this end, the combustion engine control unit reads in the engine oil temperature and subsequently actuates the glow output stage and the preglowing indicator lamp in the instrument cluster, depending on the coolant temperature. The glow output stage actuates the glow plugs. Once the specified temperature has been reached the effective voltage is gradually reduced.
Start-ready glowing
Start-ready glowing maintains the temperature necessary for engine start in the combustion chamber. This takes place independently from the engine oil temperature.
Once the start-ready temperature of 1250 °C is reached, the preglow indicator lamp in the instrument cluster goes out.
Start-glowing
Additional function requirements:
Engine in operation
Startup glowing is used to stabilize the cold start engine speed.
Here, startup glowing supports the first power strokes of the engine and its run up at cold start speed.
Afterglowing
Additional function requirements:
Engine in operation
Afterglowing improves smooth running characteristics after a cold start and the engine warm-up characteristics. To this end, the combustion engine control unit monitors the engine oil temperature and, depending on this, actuates the glow output stage, e.g. after a cold start.
Diagnostic glowing
In diagnostic glowing, the combustion engine control unit checks the functioning of the glow plugs. To perform the diagnosis, the glow plugs are energized at a low temperature level. Diagnostic glowing is activated during troubleshooting or if the preglow system has not been activated for an extended period of time, e.g. in high ambient temperatures.
Particle filter glowing
Additional function requirements:
Engine in operation
Particle filter glowing supports the regeneration of the diesel particulate filter. To this end, the engine load is increased through glowing and the burning of the particles in the diesel particulate filter is supported.
Emergency glowing
Emergency glowing is activated for 180 s if one of the following cases arises:
Glow output stage detects no activity 2 s after activation by circuit 87M.
Communication with the glow output stage drops out for more than 250 ms during glowing.
If a new glow request is not received by the combustion engine control unit, the emergency glowing is ended after 180 s.