Digital Motor Electronic (DME)
Digital Motor Electronics (DME M1.2, 12-cylinder M 70):��Fig. 52b Motronic System Diagram (Typical):
Interconnected System of Signals to the Drive Control Units:
Abbreviations:
Notes:
The following description refers to the digital motor electronics DME M1.2 for the 12-cylinder M 70 engine (5.0 I).
Functional Description:
Two DME control units operate independently each with six cylinders. If not otherwise specified, the explanations, therefore, refer to only one row of cylinders.
The DME control unit I supplies the cylinders 1...6, the identical control unit II the cylinders 7...12. To differentiate between them during diagnostic procedures, Pin 40 of the control unit II is connected to ground. The associated components are mainly provided double. Exceptions are:
- Relay for oxygen sensor heating and
- engine temperature sensor.
The oxygen sensor heating relay is assigned to the DME control unit I. The two engine temperature sensors are mounted together in one common housing.
The DME enables exact control of fuel injection and ignition also under variable operating conditions.
The DME can also operate in conjunction with the following systems:
- Electronic transmission control EGS
- Electronic throttle control EML
- Automatic stability control ASC
- Engine drag torque control MSR
- Instrument cluster
- Antitheft system DWA
- ON-BOARD computer BC
Corresponding to requirements, these systems can influence the entire engine management system.
The digital motor electronics system undertakes the functions which are listed below on brief and which are described in more detail in the following.
- Injection control
- Ignition timing control
- Dwell angle control
- Adaptive emission control
- Adaptive idle speed control
- Adaptive tank ventilation
- Idle speed control
- Maximum engine speed limitation
- Cold start control
- Acceleration enrichment
- Dynamic deceleration fuel cut~ut
- Emergency (limited) operation control
- Characteristic map switchover for EH transmission
- Relay control
- Drive-away protection
- Self-Diagnosis with defect code storage
Input Signals:
Input Signals:
Input Signals:
Output Signals:
Output Signals:
Ignition Timing Control:
The DME control unit determines the ignition timing (ignition angle) on the basis of the engine speed and load signals which are output via the ignition output stages. This function also takes into consideration other input signals such as the engine temperature, intake air temperature, position of the throttle valve and signals from the electronic throttle control EML, automatic stability control ASC, engine drag torque control MSR and from the electronic transmission control EGS.
Dwell Angle Control:
The engine speed and the battery or system voltage are the decisive factors with respect to the time available to build up the primary voltage in the ignition coil. From these variables, the digital motor electronics determines the necessary dwell angle, thus ensuring sufficient ignition voltage under all operating conditions.
Injection Control:
The DME control unit calculates the correct ignition timing on the basis of the engine speed, air flow or air mass, throttle position, oxygen sensor voltage, engine temperature and intake air temperature. The change in the fuel/air mixture is achieved by the opening duration of the injector valves. The battery voltage or voltage of the vehicle electrical system is also taken into consideration in calculating the injection timing since the pull-up and dropout times of the injector valves are extended as the voltage drops.
Types of Injection:
Each injector valve group is activated by one output stage (power amplifier). This arrangement makes it possible to divide the injection cycle into cylinder groups (semisequential injection).
Arrangement of injector valve groups:
12-cylinder: Cylinders 1+3+5 and 2+4+6 or
Cylinders 7+9+11 and 8+10+12
Semisequential Injection:
As of an engine speed of 600 rpm, fuel is injected only once per 7200 crank angle into one cylinder group. This facilitates precise metering of the quantity of fuel since the injector valves need not be activated so often. It also enables restricted engine operation in the event of failure of one group.
Semisequential injection is only active when the DME control unit has received a signal from the pulse generator for the cylinder reference point. If this signal is not received during engine operation, the control system remains set to semisequential injection.
The cylinder reference point sensor is mounted on the injection lead of cylinder No.6 at the distributor.
Parallel Injection:
Parallel injection refers to simultaneous activation of all injector valves and takes place only when the cylinder reference point sensor (pulse generator) has supplied no signal since starting the engine. As soon as a signal is applied, the system switches over to semisequential injection after the next deceleration phase.
Emission Control on Models With Catalytic Converter:
To maintain the optimum degree of efficiency of the catalytic converters, this system aims at achieving an ideal air-fuel ratio (Lamda = 1) for combustion. The heated oxygen sensor is used for this purpose which measures the residual oxygen content in the exhaust gas and sends a corresponding voltage signal to the control unit. Here, the mixture composition is corrected if necessary by changing the injection timing. In the case of failure of the oxygen sensor, the DME control unit controls the system with a substitute value (0.45 V) preprogrammed in the control unit.
Since a temperature of approx. 300 °C is necessary for efficient operation of the oxygen sensor, power is supplied via a relay to a heating resistor in the oxygen sensor. The relay is activated by the DME control unit.
On 12-cylinder engines, both heating resistors in the oxygen sensor are supplied with voltage via one relay. The relay is activated by the DME control unit I.
This relay will be phased out of series production. On models without oxygen sensor heating relays, the sensor heating is activated directly by the EKP relay.
CO Potentiometer:
On models not equipped with a catalytic converter, the CO setting can be corrected by means of a potentiometer (on the air mass meter). Particular care must be taken to ensure that the plug connection for the CO potentiometer is connected in the wiring harness.
Idle Speed Control:
On the 12-cylinder engine, the idle speed is not controlled by the digital motor electronics but rather by the electronic throttle control system. The idle speed is controlled directly by the position of the throttle valve.
Maximum Engine Speed Limitation:
On the 12-cylinder engine, the maximum engine speed is limited by the electronic throttle control EML. The maximum speed is limited directly by reducing the throttle angle.
Cold Start Control:
During the start phase, fuel is injected several times for each cylinder group per crankshaft revolution. The quantity of fuel is adapted dependent on the engine temperature and the engine speed.
In addition, the ignition timing is shifted in the retard direction the higher the temperature and the lower the start engine speed.
During the initial period after engine start, the initially injected quantity is reduced depending upon the temperature and engine speed in order to avoid and excessively rich mixture. If start is repeated within one minute, the complete initial quantity is no longer injected.
After starting (as of approx. 600 rpm), fuel is injected only once for each cylinder group per crankshaft revolution. This means that fuel is injected in the cylinders 2-4-6 and during the first revolution and in the cylinders 1-3-5 during the second revolution. The cylinders 8-10-12 and 7-9-11 are also supplied in the same way but offset by 60° crank angle.
During the warm-up phase, the injection timing and the ignition timing are correspondingly varied also dependent on engine speed and temperature.
These measures are intended to ensure a lower fuel consumption, good throttle response and smooth engine operation.
Deceleration Fuel Cut-out:
To reduce fuel consumption, the deceleration fuel cut-out is activated when the throttle valve is closed and the engine speed is above approx. 1000...1200 rpm. The DME cuts out the injection and shifts the ignition timing in the retard direction until the engine speed has dropped below the cut-in speed. Below this engine speed, fuel injection cuts in once again and the ignition timing moves towards the advance direction once again. The cut-in speed is dependent upon the engine temperature and the drop in engine speed.
Acceleration Adaptation:
In the case of a sudden change in the throttle position towards the full load direction, the digital motor electronics increases the quantity of injected fuel for the duration of the acceleration procedure and shifts the ignition timing in the advance direction. This function takes into account the criteria such as maximum torque, clean exhaust gas and no acceleration knocking.
Air Mass Measurement:
During operation, a heated platinum wire is subjected to the flow of intake air in the inner tube of the hot-wire air mass meter (HLM). Heat is dissipated from the hot wire by the flow of air. This heat is compensated by controlling the heating current. At the same time, the supplied current also flows via a precision resistor whose voltage drop represents a direct measure for the air mass which is drawn in. Air-temperature fluctuations are detected by way of a compensation resistor and taken into account in the measurement. After switching oft the engine, an increased current surge is applied to the hot wire for approx. 1 second in order to burn the wire clean of impurities.
The advantages offered by the air mass meter can be found in the fact that, in this case, the air mass is measured and not the air flow (volume). Fluctuations in the air density (different air pressure due to differences in altitude and weather situation) are already taken into account during initial measurement. In addition, less resistance is offered to the flow of air in the air mass meter since it is not equipped with an air sensor plate which needs to be pressed down.
The voltage value of the air mass meter in conjunction with the engine speed is a direct measure for the engine load.
Fuel Evaporation Control on Models With Catalytic Converter:
The fuel evaporation control line of the fuel tank is connected to the activated carbon filter, in which the fuel vapors which accumulate in the tank are collected. The activated carbon filter is linked by means of a further line to the air manifold. A fuel evaporation control valve is installed in every line. When the fuel evaporation control valve is open, the vacuum in the air manifold draws in fresh air to the activated carbon filter.The fresh air flushes out the fuel collected in the filter and routes it to the engine to the combustion process.
Since this additionally supplied mixture influences combustion to a considerable extent, the fuel evaporation control valve consists of a no~ return valve and an electrically operated valve. Due to the non-return valve, the fuel evaporation control valve is closed initially when no power is applied. The no~return valve prevents fuel collecting in the air manifold when the vehicle is parked. The non-return valve opens as the vacuum in the air manifold increases. Electrical activation for both rows of cylinders takes place dependent on engine speed and load. The venting cycle (flushing phase) begins as soon as the emission (lambda) control system is active. On completion of one cycle, the valve is closed for approx. 1 minute (rest phase).
Adaptations:
The fuel-air mixture formed in the intake tract requires a certain period of time until it 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 control system is also dependent on load and engine speed. Mixture deviation detected by the oxygen sensor result in storage of adaptation values (learned correction values). By way of these adaptations, the injection can be set close to the normal value in advance, thus achieving a reduction in the response time.
For instance, if the basic injection values for the DME characteristic map are too low during idling in order to maintain the ideal fuel-air mixture, the emission control system would have to constantly increase the injection timing. In this case, an adaptation value is learned 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:
Fuel Evaporation Control Adaptation:
When the fuel evaporation control valve is open, an additional combustible mixture or air is supplied to the engine from the activated carbon filter. The shift in the air-fuel ratio detected by the oxygen sensor is almost completely compensated by way of the fuel evaporation control adaptation value.
Idle Air Adaptation:
The EML undertakes idle air adaptation. By way of the throttle valve, it ensures constant idle speeds.
Idle Mixture Adaptation:
If the idle signal is applied during the rest phase of the fuel evaporation control system, idle mixture adaptation takes place at certain intervals.
Part Load Mixture Adaptation:
Also in the part load range, mixture adaptation takes place at certain intervals. The determined adaptation value is taken into account in all part load ranges.
Relay Control:
The DME main relay is activated by the DME control unit as of ignition ON. After shutting down the engine, the relay remains on for a further 3 5 in order to avoid post-ignition.
The EKP relay is activated as of ignition ON as soon as the DME control unit receives engine speed signals from the crankshaft pulse generator. The oxygen sensor heating relay is activated as of ignition ON. It is switched oft dependent on engine speed and load.
Emergency Operation Control:
In the case of failure of sensors, substitute values are made available which enable further yet restricted engine operation. Further engine operation is no longer possible if the engine speed sensor fails.
Transmission Intervention in EH Transmission:
During the shift procedure, the EGS control unit sends the DME control unit a signal which has the effect of retarding the ignition timing and reducing the torque. This ensures smooth transmission to the next drive range.
As soon as the torque converter clutch has engaged, the DME control units switch over to another injection timing characteristic map.
Drive-away Protection:
When the drive-away protection function is activated on the on-board computer (code entered) or when the antitheft system DWA is armed, a signal (>10 V) is sent to the DME control units which consequently switch off the ignition and injection.
This function can only be activated below an engine speed of approx. 500 rpm.
Automatic Stability Control ASC:
The ASC controller is integrated in the ABS control unit. It operates in conjunction with the DME and EML.
The peripheral speeds of the wheels are monitored by the wheel sensors. An excessive speed difference between the driven and non~riven (idle) wheels is detected as wheel slip. Consequently, the EML control unit is instructed to reduce the throttle opening. If excessively high wheel slip still occurs, the DME control unit is instructed to retard the ignition timing. The ignition and the injection can be temporarily switched off as a further measure.
Engine Drag Torque Control MSR:
In the same way as the ASC, the MSR is integrated in the ABS control unit. The engine is influenced via the DME and EML.
A signal is sent to the DME control unit when increased slip occurs at the drive wheels when the vehicle is coasting. Consequently, the deceleration fuel cut-out function is deactivated. In addition, the EML control unit is instructed to adapt the throttle position until the wheel slip is once again within the permissible range.
This function can only be activated at an engine speed below approx. 500 rpm.
Catalytic Converter Protection Function (Ignition Circuit Monitoring):
In the DME M1.2, the cylinder reference point sensors serve to monitor the ignition circuits. If the cylinder reference point sensor on the ignition lead 6 (or 12) fails to detect an ignition signal, the fuel supply is shut oft by switching oft the electrical fuel pump relay.
The cylinder reference point sensor therefore monitors the entire primary side and the cylinder 6 or 12 on the secondary side.
Self-diagnosis:
The task of the self-diagnosis feature is to detect and store malfunctions in DME components, the associated lines or in the memory of the control unit (ROM, RAM).
The DME control unit makes available substitute values in the event of sensor failure. These substitute values are cancelled once again when normal operation can be resumed.
To facilitate fast and convenient troubleshooting, the stored defect codes or current values can be monitored from the DME control unit with the aid of the BMW DIAGNOSTIC SYSTEM.
Testing and Inspection