0090 - Description of design and function General, Brief description, Components and arrangement, Function details Engine 102 - 2 E-E Carburetor

The throttle valve actuator is an electropneu-

matic actuator with two electromagnetic valves,

a diaphragm, a logarithmic potentiometer and a plunger.

The potentiometer protects the position of the plunger at that moment and inputs this signal to the electronic control unit.

By admitting or releasing air to or from the diaphragm chamber, the desired engine speed is reached. The two electromagnetic valves are controlled by the electronic control unit.

A filter is integrated in the air admission port (atmospheric side) and a check valve in the evacuation port (vacuum side).

The needle control is connected to the choke. In view of the low air throughput in the idling and near-idling range, it is not possible to control the mixture via the main nozzle system.

In these ranges, the mixture is controlled by a correction needle which is more or less immersed in the idle air nozzle and which influences the idle air quantity.

The throttle valve potentiometer (R24) is a rotary potentiometer with an integrated torsion return spring which is connected to the 1st stage throttle valve shaft by a loose-fitting sleeve coupling.

The control unit performs the following functions:

 Controlling start and warming-up mixture

 Controlling idle speed

 Acceleration enrichment

 Map control

 Decel fuel cutoff

 Engine stop

 Lambda control

 Heating intake manifold and bypass

 Limiting maximum engine speed

 Control of ignition in the event of faults at throttle valve actuator

Control unit input signals

 Coolant temperature.

 Engine speed (TD signal).

 Position and sequence of movement of throttle valve via throttle valve potentiometer.

 Plunger position of throttle valve actuator via potentiometer of throttle valve actuator.

 Gear detection of automatic transmission via starter lockout switch.

 A/C compressor cut-in signal via A/C compressor control unit.

 Lambda signal via oxygen sensor.

 Resistance trimming plug detection (KAT or ECE map plug).

Control unit output signals

 Choke actuator.

 Throttle valve actuator.

 Idle signal for control unit of ignition system.

 Lambda test signal for diagnostic socket.

 Intake manifold and bypass heater.

 Fault signal for ignition control unit in the event of faults in throttle valve actuator.

Basic setting of resistance trimming plugs

The basic setting of the resistance trimming plug for the electronic control unit of catalytic converter or retrofit cars is position "1".

The remaining intermediate positions of the resistance trimming plug up to "7" permit the mixture maps to be individually adapted should customer complaints be received (refer to Test and adjustment work 07.2-114).

Oxygen sensor

Refer to Group 14 for description of design
and function of the oxygen sensor.

Description of function
Function sequences which are identical or differ only insignificantly in comparison to previous carburetors, are not described. The operations involved in electronic carburetor control are dealt with in detail so that they are understood.

Float device

The float device operates according to the already known principle. The float needle (58) is "automatically opened" by the float, thus avoiding the float needle jamming. The float travel down the way is limited by the stop (60).

The float level is fixed by the press-fitted depth of the float needle seat, and therefore cannot be varied.

Fuel cutoff

(Limiting engine maximum speed)

The electronic control unit is supplied with the engine speed signal through contact 25. If an engine speed of 615050 rpm is exceeded, the current flow direction for the choke actuator is reversed (poles reversed) in the control unit, the choke (6) opens and moves into the vertical position.

The closing plate (45) is now pulled against the nozzle assy by means of lever (35), actuating rod (61), thus blocking the fuel supply to all the fuel-conveying systems. Once the engine speed has dropped below approx. 6100 rpm, the fuel supply is restored.

When the ignition is switched off, the float chamber vent valve (Y18) is de-energized and switches to "external venting". The fuel vapours are drawn through the external vent port (37) to atmosphere or passed into a charcoal canister where they are stored. When the engine is running, the stored fuel vapours are drawn off and combusted.

When the ignition is switched on, the float chamber vent valve (Y18) is energized, the solenoid picks up, the valve switches to "internal venting". A link is created between float chamber and clean air side of air filter.

A voltage (via terminal 30a battery+) exists constantly at contact 1 of the control unit, even when the ignition is switched off. The choke (6) is opened fully by the force of the compression spring (32).

When the ignition is switched on, the control unit is supplied additionally with voltage via contact 13 (= terminal 15 ignition), it is activated and allows a 100 Hz clocked current to flow to the choke actuator. The choke moves slightly into the closed position.

The plunger of the throttle valve actuator is fully extended and has moved the throttle valve (42) into the start position.

Start procedure at coolant temperature
>+20 °C

When the engine is started, the control unit is supplied with the engine speed signal (TD signals) through contact 25 and allows a current, determined by engine temperature and the mixture map stored in the control unit, to flow to the choke actuator. The coolant temperature signal is input to the control unit through contact 21.

The current existing at the choke actuator now closes the choke to a certain position (start position). After the engine has started, the control unit detects engine self-running through contact 25 (TD signal), reduces the current, and the choke moves back to the matching warming-up map position.

Start procedure at coolant temperature
<+18 °C

If the coolant temperature is below+18 °C, the choke actuator is supplied immediately with a relatively high current when the ignition is switched on, the choke (6) is fully closed to ensure that the engine starts immediately even at low temperatures.

After the engine has started (engine self-running), the current existing at the choke actuator is reduced and the choke moves back to the matching warming-up map position.

Repeat start

If a repeat start is performed, the choke closes in line with the particular coolant temperature, and the plunger of the throttle valve actuator moves back into start position.

Automatic opening of choke

If the starting mixture is over-enriched when starting the engine from cold, the choke can be opened fully electrically by applying full throttle to produce a leaner starting mixture.

To ensure that the mixture is not too rich when the engine is started at a coolant temperature <+18 °C, the control unit reduces the current supply to the choke actuator after the starting speed is exceeded (=self-running), the choke (6) opens slightly, the mixture is leaned to the warming-up mixture.

At the same time, as engine speed increases and exceeds the specified idling speed (at
-20 °C approx. 1000 rpm), the idle speed control is activated (refer to Section "L" for function of idle speed control).

The throttle valve actuator is now activated by the control unit and pulls the plunger back far enough for the engine to run at an idle speed corresponding to the coolant temperature.

The warming-up mixture in the idling and near-idling range is influenced by the needle control of the idle correction air dependent on the choke position.

Up to normal engine operating temperature, the warming-up mixture is controlled in line with the warming-up mixture map stored in the control unit as a function of the coolant temperature. At normal engine operating temperature, the choke is not vertical but is moved against the closing position.

The idle speed control continuously compares actual idle speed with set idle speed according to a map stored in the control unit. Variations in engine speed of >40 rpm are corrected with the throttle valve actuator (Y22/2). The idle speed detection is formed from the potentiometer signal of the throttle valve actuator and the signal of the throttle valve potentiometer.

Idle speed is constantly maintained at a certain level over the entire temperature range dependent on the coolant temperature, selector lever of automatic transmission in drive position or A/C compressor switched on.

The gear engaged in the automatic transmission is detected via contact 16 of the control unit and terminal 50 of the starter lockout switch. A/C compressor on is detected via contact 19 of the control unit.

After the engine starts, engine speed is slightly higher for a short time.

If the set idling speed is exceeded, current pulses are supplied to the "evacuation valve" (96) through connector 3 of the throttle valve actuator from contact 9 of the control unit (N45). The valve opens, the engine vacuum acts in the diaphragm chamber, the plunger (101) is pulled back far enough for the set idle speed to be reached.

If engine speed drops below set idle speed, current pulses are supplied to the "air admission valve" (97) through connector 8 of the throttle valve actuator from contact 3 of the control unit (N45). Air is admitted to the diaphragm chamber, the plunger (101) extends far enough for the set idle speed to be reached.

The acceleration mixture map is stored in the control unit. Enrichment of the mixture when accelerating is performed by closing the choke (6) to a defined position as a function of coolant temperature, engine speed, throttle valve angle and throttle valve opening speed.

The last two influencing parameters are detected by the throttle valve potentiometer and input to the control unit via contacts 7, 11, 18.

Acceleration enrichment is not activated when the car accelerates slowly. The transition enrichment until the main nozzle comes into play is performed solely via the slot bypass system (40).

When the car accelerates, the control unit supplies more or less current to the choke actuator depending on the intensity of acceleration (speed of change in angle at throttle valve potentiometer).

Sharp acceleration = large current, choke closes more

Slight acceleration = small current, choke closes less

The vacuum in mixing chamber increases and fuel is now supplied via the idle, bypass and main nozzle system. Once acceleration is completed, the choke moves back with a time delay to a position corresponding to the mixture map for constant operation.

Part load

At constant operation in part load range, the mixture is controlled by a mixture map stored in the control unit.

The control unit constantly scans the information regarding coolant temperature, engine speed, throttle valve angle or throttle valve stationary.

These data form the basis for determining a current from the mixture map, which is supplied to the choke actuator. The choke adopts the corresponding position.

Transition to 2nd stage main nozzle system

The throttle valve (46) of the 2nd stage is operated with vacuum through the aneroid cell (3) of the 2nd stage in line with the opening angle of the throttle valve of the 1st stage, as well as the air throughput.

The design of the lever system ensures that the 2nd stage opens progressively only after the throttle valve of the 1st stage has opened two-thirds. When the 1st stage throttle valve is closed, the 2nd stage is automatically closed mechanically by the lever (81) (forced return).

To ensure lag-free transition from the 1st stage to the moment where the main nozzle system of the 2nd stage comes into play, a bypass slot (47) is provided below the 2nd stage throttle valve (46).

When the 2nd stage throttle valve opens, the fuel mixture flows through the transition fuel nozzle (55), mixing pipe (50) and passage (73) (refer to Section "O").

The correction air flows in through the port in the mixing pipe (50).

The mixing pipe has a retraction passage (76) to ensure that no fuel can flow on out of the bypass slot if the engine is switched off when hot.

Decel fuel cutoff is operational provided the following conditions are met:

 Engine speed higher than deceleration speed threshold, e. g.: engine at normal operating temperature:

> 1400 rpm for manual transmission

> 1100 rpm for automatic transmission

 Decel fuel cutoff (accelerator not depressed).

The throttle valve potentiometer (R24) is operated through contact 2 by a voltage of approx. 5 Volts from contact 18 of the control unit. As a result of a change in the resistance at the rotary potentiometer, the control unit detects the position (angle setting) of the throttle valve and, by the change in the direction of rotation at the potentiometer, that the accelerator is being released.

As soon as the accelerator has been fully released, the throttle valve lever (27) is resting against the plunger (101) of the throttle valve actuator (Y22/2). The control unit (N45) now detects idling with deceleration from the two potentiometer signals (throttle valve actuator and throttle valve potentiometer). Decel fuel cutoff is now activated.

The evacuation valve (96) is supplied with voltage at contact 3 from contact 9 of the control unit. The diaphragm chamber is now pressurized with vacuum with a slight time delay, the plunger (101) is pulled back, likewise with a time delay (damped closing) far enough for the idle mixture outlet (41) and the bypass slot (40) to be in the atmospheric range. The fuel delivery is thus interrupted.

When engine speed drops below the resume speed of 1400 rpm or 1100 rpm respectively, decel fuel cutoff is cancelled and the idle speed control activated; fuel is again supplied to the engine.

Engine stop (running-on safeguard)

When the ignition is switched off, contact 13 of the control unit (terminal 15 of ignition) is deenergized, the control unit detects "engine stop" and activates through contact 9 after a time function the evacuation valve (96) through connector 3 of the throttle valve actuator. The valve opens for approx. 3 seconds and the diaphragm chamber is pressurized with vacuum. The remaining function sequence is identical to that for decel fuel cutoff (evacuation valve).

The plunger (101) takes only a few seconds to retract (time function) to reliably prevent any running-on. After the retraction period has elapsed, the air admission valve (97) is actuated for a few seconds through connector 8 of the throttle valve actuator by contact 3 of the control unit and air admitted to the diaphragm chamber. The plunger now moves fully forward again into the start position.

Engine stop function on cars with control unit 006 545 51 32 (enlarged fault detection program).

If the plunger (101) of the throttle valve actuator (Y22/2) does not retract when the engine is switched off (engine stop), this is detected by the control unit (N45) through the throttle valve actuator potentiometer signal.

To prevent the engine running-on, the choke actuator (Y22/1) is energized with reversed polarity for approx. 3 seconds, as for limiting maximum engine speed, and the fuel supply to all the fuel nozzles shut off by the closing plate (45) (refer to limiting engine maximum speed for remaining function).

The lambda mixture map stored in the electronic control unit (N45) is activated by the resistance trimming plug with the inscription "KAT". The map is designed to maintain lambda=1.

The lambda control is not activated in the following operating states:

 Starting at coolant temperatures <+17 °C. The control is not activated until approx. +70 °C.

 Starting at coolant temperature between +17 °C to +30 °C. The control is inhibited for approx. one minute.

 When accelerating, provided the acceleration enrichment is activated.

 When decelerating.

 At full load.

In the operating condition listed above, the electronics (control unit) switches to "open-loop controlled mode", the closed-loop control is deactivated. Only the data permanently stored in the control unit are then used for the open-loop control, these being dependent on the various parameters (coolant temperature, engine speed, throttle valve position, speed of change in angle at throttle valve).

The signals of the oxygen sensor are input

through contact 8 to the control unit. With a rich

mixture (l=<1) the control unit is supplied with

a voltage >450 millivolts, with a lean mixture

a voltage <450 millivolts.

The oxygen sensor signal is converted in the control unit, the choke actuator is supplied with a greater or smaller current. The choke opens or closes only until the mixture ratio is always oscillating around lambda 1.

Only this oscillating of the mixture composition around lambda 1 enables the three pollutants CO, HC and NOx to be optimally reduced in the three-way catalytic converter.

Detection characteristics for control unit with fault detection

a) 1st version

With the engine running and the coolant temperature sensor connector detached, the connected lambda control tester indicates 30 %.

b) 2nd version

With the ignition switched on, the connected lambda control tester indicates 70 %.

The control unit with fault detection monitors the following signals and parts:

 Throttle valve potentiometer.

 Throttle valve actuator potentiometer and malfunctions (leaks, valves sticking).

 Coolant temperature signal.

 Oxygen sensor signal.

 Engine speed signal (TD).

 Solenoid coils of throttle valve actuator.

 Control line for inlet manifold heater relay.

 Control line for ignition control unit if fault occurs in throttle valve actuator.

 Resistance trimming plug for 2 E-E carburetor control unit.

Fault readout with on/off ratio, possible causes

of faults remedy according to test table (see

07.2-114, Section "F").

If a fault occurs at the throttle valve actuator of the carburetor, the control unit of the 2 E-E carburetor passes a fault signal to the ignition control unit.

Standard implementation: 09/88

The firing point is retarded to maximum 12° after TDC in line with the coolant temperature and engine speed. The firing point is only retarded if the throttle valve lever is resting against the plunger of the throttle valve actuator.

The fault control is activated if:

 Fault exists at throttle valve actuator potentiometer or in electric wiring (interrupt/short-circuit). Fault exists at evacuation or air admission valve (valves sticking, leak).

 If short-circuit exists at throttle valve actuator valves or in electric wiring.

The fault circuit is deactivated:

When driving as soon as a throttle valve lever is no longer touching the plunger of the throttle valve actuator, i. e. has moved away from it (part load, accelerating, full load). In addition, if the throttle valve actuator plunger jams in the near-idling range, in order to achieve stable engine running.

Function description

a) Normal mode: If the engine is operating normally, the control unit of the 2 E-E carburetor switches connector 4 of the ignition control unit to ground through contact 15, the voltage drops to <0.5 Volts.

b) Fault mode: If a fault exists, the ground in the control unit of the carburetor is interrupted, the voltage rises to 11 - 14 Volts, and the firing point is retarded to maximum 12° after TDC in line with the coolant temperature.