ME-SFI ignition system function

P07.61-0374-09

Example of ME-SFI ignition system

A16 Knock sensors

B2/5 Hot film mass air flow sensor

B6/1 Camshaft Hall sensor

B11/4 Coolant temperature sensor

B17 Intake air temperature sensor
(on engine 104, 111, 112, 113 integrated in hot film mass air flow sensor)

B37 Accelerator pedal sensor

K40 Relay module model 170, 210 up to 2/97

K40/4 Fuse and relay module Model 202, 208,
Model 210 as of 3/97, Model 163 designation F1

L5 Crankshaft position sensor

M16/1 Electronic accelerator EA/CC/ISC actuator

N3/10 ME-SFI [ME] control unit

N15/3 ETC [EGS] control unit

N16/1 Base module model 129, 140

N47-1 ASR/SPS control unit

N47-5 ESP / SPS [PML] / BAS control unit

N54 RCL control unit

R4 Spark plugs

T1/1 Ignition coils Engine
104, 111: a two-spark ignition coil
for two cylinders
Engine 119, 120: one ignition coil for each cylinder

Engine 112, 113: a double ignition coil for each cylinder

X11/4 Data link connector

CAN Data bus

P07.61-0217-05

Signal assignment

Shown on engine 119

1 Crank angle
2 Cylinder ignition TDC
3 Signal from crankshaft position sensor (L5)

4 Signal from camshaft Hall sensor (B6/1)
5 Rpm signal TNA

a Recognition of cylinder 1

Function

When the crankshaft is rotating, an alternating voltage is generated in the crankshaft position sensor by the teeth of the driven plate. In this case, each tooth generates an alternating voltage signal. No voltage is generated through the gap of 2 missing

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teeth. The ME-SFI control unit detects the TDC position of the crankshaft with the 2nd negative slope after the gap.

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If the signal from the camshaft Hall sensor is at 0 V ("low") at this moment, the ME control unit processes this in order to detect ignition TDC. This is used for actuating the ignition coils and the fuel injectors.

The high voltage is distributed rotorlessly. Advantages of the rotorless high voltage distribution are:

- significantly reduced electromagnetic interference level (no naked sparks)

- no rotating parts

- reduction in noise

- reduced high voltage connections.

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1. Determine ignition angle according to input signals,
actuate ignition coils and release ignition spark .

The ME-SFI control unit essentially analyzes the following signals for determining the ignition angle:

- Engine load

- Crankshaft position sensor

- Camshaft Hall sensor

- Coolant temperature sensor

- Intake air temperature sensor/charge air.

Coil ignition: The ME control unit interrupts at the point of ignition timing at the ground end the ignition coil primary circuit of the ignition coil.

ECI ignition system (engine 137): The ME control unit actuates the output stages in the ECI ignition modules.

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The ignition angle can only be checked with the HHT/STAR DIAGNOSIS.

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2. Ignition angle adaptation

2.1 Catalytic converter heating-up (warming-up)

The ignition angle is continuously retarded for about 20 seconds in order to more rapidly warm up the catalytic converter to its operating temperature if:

- coolant temperature at start > 15 °C and < 40 °C

- Selector lever position P or N

At the same time idle speed is increased by the idle speed control.

2.2 Idle speed

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

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

2.3 Deceleration fuel shutoff

The ignition angle is briefly retarded when combustion is resumed (fuel injectors actuated) in order to prevent a sudden increase in torque.

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2.4 Intake air temperature/coolant temperature

The ignition angle is retarded under load, as a function of the intake air temperature and coolant temperature, in order to prevent any knocking tendency at high intake air and coolant temperatures. The ignition angle is "Retarded" if:

- Intake air temperature > 35 °C

- Coolant temperature > 105 °C

In supercharged engines the charge air temperature is used as information for the ignition timing adjustment in place of the intake air temperature.

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The values of the retardation of the ignition angle of intake air temperature and coolant temperature are added together.

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2.5 Transmission overload protection

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

2.6 ESP/ASR control mode

In order to reduce the engine troque as rapidly as possible in the ESP/ASR control mode, the ignition angle is retarded by the throttle valve actuator (opening angle reduced) prior to the control mode being activated. The information from the ESP/ASR control unit is supplied over the CAN databus to the ME-SFI control unit.

2.7 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".

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2.8 Smooth engine running analysis

To restrain the three way catalytic converter from thermal overload through combustion misfiring and in order to keep the exhaust emission values, the smooth operation of the engine is continuously monitored.

If combustion misfiring is identified at one or several cylinders, the corresponding fuel injection valves are no longer actuated after a certain number of misfires.

Engine 104, 111, 112, 113, 119, 120: Smooth operation evaluation is performed through the signals of the crankshaft position sensor.

Engine 137: Identification of combustion misfiring by means of ionic current signal, see ECI ignition system function.

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2.9 Double ignition engine 112, 113, 137

Two spark plugs 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 by the ME-SFI control unit through its own ignition coil. On engine 112, 113 both ignition coils of a cylinder are combined to form a dual ignition coil.

In the lower part load range up to approx. 2000 rpm both ignition sparks of a cylinder are triggered simultaneously. At moderate and high engine loads, the ignition sparks are triggered offset by as much as 10° crank angle. In this case,

The sequence of actuation is constantly varied in order to achieve a uniform wear of both spark plugs and to avoid deposits on only one side of the combustion chamber.

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