DIS Direct Ignition System
Description of system
In the C 14 SE engine, the conventional distributor is replaced by the DIS. The DIS module has two dual ignition coils. Each coil has two outputs and can thus supply high voltage to two spark plugs. The DIS module receives two sequential electronic ignition signals (EST) from the control unit. The EST A signal contains the ignition information for coil 1 and EST B the information for coil 2, which are stored as characteristic maps in the control unit EEPROM.
The ignition signal phases are displaced by 180°.
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DIS Direct Ignition System (continued)
Block diagram
The DIS module contains two ignition voltage amplifiers, each of which supplies one coil with primary current. A current limiter circuit protects against overload.
D 8150 shows the block diagram.
The control unit starts ignition via two signal outputs. Each lead (EST A and EST B) supplies one coil. EST A ignites cylinders 1 and 4, EST B cylinders 2 and 3. When the ignition signal actuates EST A (terminal C-1/4 is pulsed to ground), coil 1 induces a high voltage pulse according to Lenz's law. Each coil simultaneously ignites one cylinder with combustible mixture and one with combusted mixture.
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1 Control unit 5 Coil 2/3
2 Current limiter 6 EST A
3 "Darlington" circuit 1) 7 EST B
4 Coil 1/4 8 Crankshaft sensor
1) A Darlington circuit is a special cascade connection of transistors to amplify output.
DIS Direct Ignition System (continued)
DIS module
This module is a part of the distributorless ignition system which, together with the two dual ignition coils, form the DIS.
The DIS module receives two sequential electronic ignition signals (EST). Signal EST A contains ignition information for coil 1 and signal EST B the information for coil 2.
This information is stored in the control unit characteristic map.
It is thus the regulating unit of the DIS.
DIS Direct Ignition System (continued)
Installation
The DIS module is installed as a unit. Conventional high voltage cables are used.
The three DIS module fastening bolts are tightened to a torque of 8 Nm/6 lbf. ft.
Coil Parameters
| Primary resistance; | 0,56 W+/- 0.05 W |
|---|---|
| Engine speed range: | 30 to 8000 rpm |
| Secondary resistance: | 6 kW+/- 0.05 kW |
DIS Direct Ignition System (continued)
Electronic ignition signals
The EST input receives a voltage signal from the control unit.
EST signal
The two dual ignition coils are supplied with the necessary ignition energy by the dual ignition coil driver module. This primary current builds up a magnetic field in the primary winding. When the control unit has determined the point at which ignition must occur using the ignition map, the primary current (EST signal) is switched off (dwell angle algorithm). The magnetic field, which has flowed through the primary and the secondary winding collapses.
The resulting high voltage is forwarded via the two high voltage cables of the DIS module and the spark plug electrodes to the engine ground.
Up to MY '92, the EST switch level was 0 V and 12 V. This is altered as of MY '93.
The Transistor-Transistor-Logic (TTL) now supplies the typical voltage values of 0 V and 5 V.
The dwell angle algorithm of the control unit has two different modi:
Starting mode and operating mode
In the starting mode, the dwell period (EST on) is dependent on a fixed angle in °CA and battery voltage. In the operating mode, the dwell period is based on the relationship between engine speed and battery voltage as stored in the dwell angle map.
The transition from the starting mode to the operating mode occurs at approx. 400 rpm.
Dwell period in starting mode
| Battery voltage | Magnetic field starts to build up at |
|---|---|
| greater than 12 V | 18° to 24 °CA before ignition point |
| less than 10 V | 36° to 42 °CA before ignition point |
DIS-Direct Ignition System (continued)
Primary Current as a Function of the Battery Voltage in Operating Mode
If the battery voltage is higher than 9 V, the primary current will not sink below 6.5 A. This will only change when the engine speed is greater than 3000 rpm. In this case, the amount of time that the EST signal is switched on is not sufficient to attain this value.
Voltage limitation
The operating range of the DIS lies between 6 V and 16 V. However, overvoltage of up to 24 V or reversal of the supply voltage and ground leads will not lead to damage, as long as it does not persist for longer than 60 s.
Diagnosis
As of MY '93, the engine control unit is able to recognize short circuits to ground and short circuit to battery voltage in the EST leads in the entire engine speed range. As soon as a fault is recognized, the engine control unit activates the telltale.
As of MY '93, an ignition Actuator Test is possible for the EST B and A leads.