Note
Sensor wheel adaptation must be carried out after replacing a DME control unit or increment wheel. If only the increment wheel is replaced, the sensor-wheel adaptation must first be deleted (disconnect control unit from power supply for 5 minutes). Sensor wheel adaptation is implemented automatically as soon as the engine is operated in overrun condition for at least 10 seconds. See sensor-wheel adaptation.
Note
After conducting repairs on the pedal position sensor or EML control unit it is possible that the vehicle does not respond to the throttle control system. In this case, pedal position sensor adaptation must be carried out (see EML).
M1.7 M70 |
M5.2 M73 |
|---|---|
No knock control |
2 knock sensors per row of cylinders |
1 inductive pulse generator (cylinder reference sensor) at ignition lead, cylinder 6 |
1 Hall sensor (camshaft sensor) on camshaft of cylinder row cyl. 1...6 |
2 air mass meters |
2 hot-film air mass meters |
1 intake air temperature sensor per row of cylinders |
1 intake air temperature sensor (for cylinder row, cyl. 7...12) |
2 engine temperature sensors in one joint housing |
1 engine temperature sensor on cylinder row, cyl. 1...6 |
1 tank ventilation valve per row of cylinders "open with no power applied" as soon as vacuum builds up in intake system and the mechanical non-return valve opens |
1 tank ventilation valve per row of cylinders "closed with no power applied". |
1 oxygen sensor per row of cylinders ahead of catalytic converter |
4 oxygen sensors: 1 oxygen sensor per row of cylinders before and after the catalytic converter |
- |
New spark plugs and smaller, lighter ignition coils |
Speed signal from instrument cluster |
Speed signal from ABS/DSC control unit |
No secondary air pump |
1 secondary air pump to improve exhaust gas at cold start |
1 fuel pump and one EKP relay per row of cylinders |
1 fuel pump and 1 EKP relay activated by both DME control units |
No CAN-bus |
Data exchange between DME control units via CAN-bus |
No automatic start |
Automatic start. If the DME detects a signal from terminal 50, the starter relay is activated directly by the DME control unit. The relay is triggered once the engine has started (detection via speed signal). |
2 DME control units operate in this system. The DME control unit I supplies the row of cylinders 1 (cylinders 1...6), the identical control unit supplies the row of cylinders II (cylinders 7...12). For the purpose of differentiation in diagnosis mode, Pin 48 on control unit II is connected to ground. Relevant components are mostly installed in duplicate. Exceptions are:
The DME control unit calculates the correct injection timing on the basis of the engine speed, air mass, throttle position, oxygen sensor voltage, engine and intake air temperature. A change in the fuel-air mixture is achieved on the basis of the opening duration of the fuel injectors. The battery or system voltage is also included in the calculation for the injection timing since the pickup and dropout times of the fuel injectors are extended as the voltage drops.
Each fuel injector is activated by its own output stage. This facilitates precise metering of the injection quantity and rapid response to load change.
Once the start procedure has been initiated, fuel is injected cylinder-selective 1 x per working cycle (2 crankshaft revolutions).
The injection timing (ti) is derived from the programmed basic start injection quantity and the correction variables from the input signals of the coolant and intake air temperature. Cylinder activation is based on the reference mark generator signal (crankshaft signal generator).
The DME M5.2 features cylinder-individual fuel injection (CIFI). CIFI involves the individual activation of each cylinder. The system ensures that fuel injection of each cylinder is completed before the inlet valve opens. An optimum fuel-air mixture and thus improved combustion with low fuel consumption is achieved in this way.
Injection of each cylinder can be deactivated individually if a fault occurs in the ignition or injection system. These faults are then also stored in the defect code memory.
The ignition timing (ignition angle) is determined by the DME control unit on the basis of the engine speed and load signals and output via the ignition output stages. This procedure also takes into account other input signals such as the engine temperature, intake air temperature, throttle valve position and signals from the electronic throttle control EML, dynamic stability control DSC and adaptive transmission control AGS.
The engine speed and battery or system voltage are decisive with regard to the time available to build up the primary voltage in the ignition coil. From these variables, the digital motor electronics then determines the necessary dwell angle thus ensuring adequate ignition voltage under all operating conditions.
Misfiring causes irregularities in the rotational speed of the crankshaft. These irregularities can be detected by way if changes in the segment time.
Segment times (time, in which a certain number of teeth on the increment wheel move past the sensor) are constantly determined via the reference mark sensor (= crankshaft sensor). These segment times are constantly checked during engine operation. In the event of a fault, a defect code is stored and injection of the corresponding cylinder is deactivated.
Note
Sensor wheel adaptation must be carried out after replacing a DME control unit or increment wheel. If only the increment wheel is replaced, the sensor-wheel adaptation must first be deleted (disconnect control unit from power supply for 5 minutes). Sensor wheel adaptation is implemented automatically as soon as the engine is operated in overrun condition for at least 10 seconds. See sensor-wheel adaptation.
Misfiring below an engine speed of 3000 rpm is detected by the misfiring detection system. Above 3000 rpm misfiring is detected by the ignition circuit monitoring (self-diagnosis) and prevents damage to catalytic converters.
The secondary circuit monitoring operates with a "shunt" (resistor in secondary ground line).
If, after successful ignition, the threshold voltage for misfiring detection is not reached, a defect code is stored, the fault lamp activated (US models only) and the corresponding row of cylinders deactivated.
If the throttle is closed and the engine speed is above approx. 800 rpm, the deceleration fuel cutout is activated in order to reduce consumption. The DME blanks out the fuel injection and shifts the ignition timing (angle) in retard direction until the engine speed has dropped to below the cut-in speed. Below this speed, the injection is reactivated and the ignition timing drifts back in advance direction. The cut-in speed is dependent on the engine temperature and the drop in engine speed.
A sudden change in the throttle position in full load direction causes the digital motor electronics to increase the injection quantity for the duration of the acceleration procedure. This process takes into consideration the criteria of maximum torque, clean exhaust gas and no acceleration knocking.
Operation of an engine with knocking combustion over a prolonged period can lead to serious damage. Knocking tendency is increased by:
The compression ratio can also reach excessively high values due to deposits or production-related scatter.
On engines without knock control, these unfavourable influences must be taken into consideration in the ignition design by providing a safety distance to the knock limit. However, this results in unavoidable losses in efficiency in the upper load range.
The knock control can prevent knocking engine operation. For this purpose, if there is an imminent risk of knocking, the control retards the ignition timing of the corresponding cylinder(s) (cylinder-selective) as far as necessary. This makes it possible to adapt the ignition characteristic map to the consumption-optimum values without having to take the knock limit into consideration. A safety distance is no longer necessary.
The knock control system carries out all knock-related corrections to the ignition timing and enables perfect operation also with regular grade fuel (minimum RON 91).
The knock control provides:
The M73 is equipped with a cylinder-selective, adaptive knock control system. Two knock sensors per row of cylinders detect knocking combustion. The sensor signals are evaluated in the DME control units.
The compression ratio can also reach excessively high values due to deposits or production-related scatter.
On engines without knock control, these unfavourable influences must be taken into consideration in the ignition design by providing a safety distance to the knock limit. However, this results in unavoidable losses in efficiency in the upper load range.
The knock control can prevent knocking engine operation. For this purpose, if there is an imminent risk of knocking, the control retards the ignition timing of the corresponding cylinder(s) (cylinder-selective) as far as necessary. This makes it possible to adapt the ignition characteristic map to the consumption-optimum values without having to take the knock limit into consideration. A safety distance is no longer necessary.
The knock control system carries out all knock-related corrections to the ignition timing and enables perfect operation also with regular grade fuel (minimum RON 91).
The knock control provides:
The knock sensor is a piezo-electric structure-borne noise microphone. It picks up the structure-borne noise and converts it into voltage signals.
If knocking occurs, the ignition is retarded for a certain number of working cycles and then gradually approaches the original value.
A defect is stored in the defect code memory of the DME control unit in the event of a knock sensor failing. In this case, both rows of cylinders are always protected by constant retard setting of the ignition timing (knock protection function in DME control unit I and II) .
The 4 knock sensors are secured with 8 mm screws on the cylinder heads of the engine block between the two rows of cylinders. They are arranged in such a way that one sensor monitors three adjacent cylinders.
Only screw locking compound may be used to lock the screws. Washers, spring washers or serrated lock washers must under no circumstances be used.
Self-diagnosis of the knock control system includes following checks:
The knock control system is switched off if a fault is found during the course of one of these checks. The emergency program adopts the task of controlling the ignition timing. At the same time, a defect code is stored in the defect code memory. The emergency program ensures damage-free operation as from minimum RON 91. It depends on the engine load, speed and temperature.
The diagnosis procedure cannot detect whether the plug connectors of the sensors have been interchanged. The engine can be damaged if the sensors are interchanged. Particular care must therefore be taken during service work to ensure that the sensors are connected correctly (see repair instructions).
In order to maintain optimum efficiency of the catalytic converters, the system endeavours to provide the ideal air-fuel mixture ratio (Lambda = 1) for combustion. 2 heated oxygen sensors (in front and behind the catalytic converter) serve as the sensors which measure the residual oxygen in the exhaust gas and transfer corresponding voltage values to the control unit. Here, if necessary, the mixture composition is corrected accordingly in that the injection timing is varied. The operability of the catalytic converter (conversion efficiency) is monitored via the oxygen sensor behind the catalytic converter.
The heating resistors in the oxygen sensors are supplied with a voltage since a temperature of approx. 300 °C is necessary for effective operation of the oxygen sensors.
A heated surface of the hot-film air mass sensor in the flow of intake air is controlled to a constant temperature with respect to the intake air. The intake air flowing past this surface cools this heated surface and thus changes its resistance. The heating current which is necessary in order to maintain the constant temperature is the measurement variable for the air mass drawn in. The DME control unit uses this variable to calculate the injection timing.
Important advantages:
The hot-film air mass meter renders unnecessary clear-burning of the sensor after the engine has been shut down. Any dirt deposits on the surface do not influence the sensor signals directly since the protective film cleans itself due to the constant overtemperature.
The ventilation line of the fuel tank is connected to an activated carbon filter (carbon canister), in which the fuel vapours produced in the tank are collected. The activated carbon filter is connected by a further line to the air manifold. A tank ventilation valve is integrated in this line.
When the tank ventilation valve is open, fresh air is drawn in via the activated carbon filter due to the vacuum in the air manifold. The fresh air flushes out the fuel collected in the filter and feeds it to the engine for combustion.
Since this additionally supplied fuel-air mixture has a considerable effect on combustion, the tank ventilation valve is designed as an electrically controlled valve. The tank ventilation valve is closed when no power is applied.
After starting, the first flushing phase is initiated in that the tank ventilation valve is activated for approx. 6 minutes (348 seconds). The valve is then closed for 100 seconds in order to implement basic adaptation. Once basic adaptation has been completed successfully, the subsequent flushing phase has a duration of 90 minutes (5400 seconds). Otherwise a further short flushing phase (approx. 6 minutes) takes place. In order to conclude basic adaptation successfully, the engine must idle and run in the part-load range.
Correction can be carried out by a compensating value in the DME control unit. This CO-correction can be carried out solely via the corresponding diagnosis program with DIS or MoDiC.
The fuel-air mixture formed in the intake tract requires a certain period of time until is reaches the oxygen sensor in the form of exhaust gas. This time decreases as load and engine speed increase. For this reason, the response time of the emission (lambda) control system is also dependent on load and engine speed. Fuel-air mixture deviations detected by the oxygen sensor result in adaptation values (learned correction values) being stored. By way of the adaptations, the injection can be brought close to the nominal value in advance. A reduction in the response time is achieved in this way.
For instance, if the basic injection values of the DME characteristic map are too low during idling or in order to maintain the ideal fuel-air mixture, the emission (lambda) control system would have to constantly increase the injection timing. In this case, an adaptation value is learnt which corrects the basic injection value. The emission (lambda) control then only needs to undertake the fine adjustment.
Following adaptations are performed during engine operation:
When the tank ventilation valve is open, an additional combustible mixture is supplied from the carbon canister to the engine. The shift in mixture detected by the oxygen sensor is completely corrected out by means of the tank ventilation adaptation value.
The task of idle air adaptation is carried out by the idle actuator. On the basis of the air volume it ensures a constant idle speed.
If idling is detected on the basis of the throttle position during the rest phase of the tank ventilation system, idle mixture adaptation takes place at certain intervals.
Also in the partial load range, mixture adaptation takes place at certain intervals. The determined adaptation value is taken into consideration in all partial load ranges.
Misfiring causes irregularities in the rotational speed of the crankshaft. These irregularities can be detected by way of changes in the segment time.
Segment times (time, in which a certain number of teeth on the increment wheel move past the sensor) are constantly determined via the reference mark sensor (= crankshaft sensor). These segment times are constantly checked during engine operation. In the event of a fault, a defect code is stored and injection of the corresponding cylinder is deactivated. Refer to misfiring detection.
In order to avoid incorrect evaluation, sensor-wheel adaptation must be carried out after replacing a DME control unit or increment wheel. If only the increment wheel is replaced, the sensor-wheel adaptation must first be deleted (disconnect control unit from power supply for 5 minutes).
The sensor wheel adaptation determines the irregularity of the increment wheel and takes it into consideration when evaluating the segment times. Sensor wheel adaptation is implemented automatically as soon as the engine is operated in overrun condition for at least 10 seconds.
The intake air temperature sensor is mounted in the clean air bowl of the air cleaner. A precision NTC resistor is used to convert the "temperature" into a measurement value "resistance" which can be evaluated electrically by the DME control unit.
The intake air temperature sensor is not required for correction of the injection timing since the intake air temperature is taken into consideration automatically during air mass measurement. The intake air temperature sensor (NTC-I) is required during the start procedure in conjunction with the coolant temperature sensor (NTC-II). The resistance values of both sensors supply exact information for calculating the injection timing. In this way hot start problems in particular are avoided.
The input of the driving speed signal (V-signal) is required in the DME control unit for several functions.
The dynamic stability control is integrated in the ABS/DSC control unit. The rotational speeds of the wheels are monitored by sensors. Too high a speed difference between driven and non-driven wheels is detected as wheel slip. In addition, the system detects whether the vehicle is oversteered or understeered with the aid of the steering angle sensor.
Depending on the severity of the necessary intervention, the DSC initiates following measures:
For drive slip control:
For engine drag torque control:
An electrical secondary air pump which ensures rapid heating of the catalytic converter is used to subsequently treat the exhaust gas during the start phase. During the start phase, the secondary air pump pumps air via the shut-off valve into the manifolds of both rows of cylinders. The two shut-off valves are activated by a pneumatically operated electrical switchover valve. Depending on the engine temperature the valve is operated for a duration of approx. 20 seconds (warm start) up to approx. 100 seconds (cold start). The secondary air pump is also switched off as soon as an engine speed greater than 3000 rpm or full load is reached.
The CAN-bus (Controller Area Network) is a serial bus system, in which all connected stations are equally entitled, i.e. each control unit can both send as well as receive. In other words, the connected control units can "communicate" and exchange information via the lines.
Due to the linear structure of the network, the bus system is fully available for all other stations in the event of one station failing. The connection consists of two data links (CAN-L and CAN-H) which are protected against interference by shielding (CAN-S).
At present, the control units adaptive transmission control AGS, digital motor electronics DME, electronic throttle control EML and dynamic stability control DSC are interconnected with this system.
The connected control units must all have the same CAN status. The CAN status can be checked via the diagnosis interface. The CAN status (bus index) is specified on the identification of the relevant control unit connected to the CAN-bus.
A large number of information items such as CAN statuses or operating variables such as engine speed and temperature, are exchanged between the control units via the CAN-bus.
In the event of sensors failing, substitute values are made available which enable continued, restricted engine operation. In the event of the speed sensor failing, engine operation is no longer possible on the corresponding row of cylinders.
Component |
Substitute measures |
|---|---|
Intake temperature sensor |
Substitute values active |
Engine temperature sensor |
Substitute values active |
Hot-film mass meter |
Substitute value from position of throttle valve (EML information via CAN) |
During the shift procedure, the EGS control unit sends a signal to the DME control unit resulting in the ignition timing been set in retard direction and thus a reduction in torque. This measure ensures a smooth transition to the next drive stage.
As soon as the torque converter clutch is closed, the DME control units switch over to a different ignition characteristic map.
With the aid of the electronic vehicle immobilizer EWS of the multi-information display MID or of the antitheft system DWA, DME ignition and injection can be blanked out and the fuel pump prevented from being switched on.
The automatic start is an improvement in comfort for the start procedure. It keeps start operation and the resulting noise emission as short as possible. The starter is triggered by briefly turning the ignition key into the start position (momentary touch function).