Motor electronics (ME) ignition system - function - GF07.61-P-3008SM

ENGINE 113.986 

ENGINE 113.987 

ENGINE 113.988 

ENGINE 113.989 

Fig 1: Motor Electronics Ignition System - Function Diagram - Engine 113.986/987/988/989

Courtesy of MERCEDES-BENZ USA

1. Determine ignition angle and actuate ignition coils 

   The ME-SFI [ME] control unit (N3/10) essentially analyzes the following signals for determining the ignition angle:

   • Crankshaft position,
   • Camshaft position,
   • Coolant temperature,
   • Air mass,
   • Intake air pressure,
   • Intake air temperature,
   • Knocking signal,
   • Torque request via CAN

   and interrupts the ignition coil primary circuit for ignition coils at the ground end in the moment of ignition timing.

2. Ignition angle adaptation 
   1. Catalytic converter heating up (warming-up phase) 

      The ignition angle is continuously retarded for about 20 seconds in addition to increasing the idling speed in order to more rapidly heat up catalytic converters to operating temperature if:

      • Coolant temperature at start > -10°C < 40°C
   2. Idling speed 

      To assist idling speed control, the ignition angle can be retarded by as much as a 36° crank angle or advanced by as much as a 20° crank angle.

      

      Altering the ignition angle provides more rapid control than altering the position of the throttle valve (idling speed control).

   3. Inertia fuel shutoff 

      The ignition angle is briefly retarded in order to prevent a sudden increase in torque when combustion is resumed (by actuating the fuel injection valves (Y62).

   4. Intake air temperature/coolant temperature 

      The ignition angle is set to retarded at higher loads according to a performance map in order to avoid the tendency to knock at increased intake air and coolant temperatures.

      The ignition angle adjustment to retarded takes place if:

      • Intake air temperature > 35°C
      • Coolant temperature > 50°C
   5. Transmission overload protection 

      In order to protect the shift elements of the automatic transmission from excessive thermal stresses during powershifts (1-2, 2-1), the ignition angle is briefly retarded during the gearshift and the engine torque is thus reduced. The ME-SFI control unit is supplied with a signal over the CAN databus by the ETC control unit (N15/3) for this purpose.

   6. ESP/ASR control mode 

      In order to reduce the engine torque as rapidly as possible in the ESP/ASR control mode, the ignition angle is retarded by the throttle valve (opening angle reduced) before the commencement of the control cycle. The ME control unit receives information concerning reduction of the engine torque via the CAN data bus from the ESP control unit.

   7. Smooth engine running analysis 

      Smooth engine running is constantly monitored in order to protect the catalytic converters from excessive thermal stresses if combustion misfiring exists.

      If the smooth engine running analysis detects combustion misfiring, the appropriate fuel injector or injectors is/are no longer operated after a certain number of combustion misfirings.

   8. Anti-knock control (AKC) 

      If uncontrolled combustion (knocking) occurs at one or several cylinders, the ignition angle at the relevant cylinder or cylinders is "Retarded".

   9. Double ignition 

      Two spark plugs (R4) for each cylinder are beneficial because of the arrangement of the valves for achieving optimal emission levels and smooth engine running. Each spark plug is actuated separately via its own ignition coil by the ME control unit. Both ignition coils of a cylinder are combined to form a dual ignition coil.

      Both ignition sparks of one cylinder are released simultaneously and always with optimal power.

      The high voltage distribution is performed smoothly (i.e. without mechanical ignition distributor).

      

      For troubleshooting in the double ignition system, it is possible to switch off one ignition circuit each with the STAR DIAGNOSIS.

      The ignition angles can be tested using the STAR DIAGNOSIS.