Digital Motor Electronics DME M5.2
Digital motor electronics DME M5.2
Introduction
The digital motor electronics DME M5.2 from Bosch as already used in the M73 is now used on the M62 engine. It replaces the DME M3.3 of the M60 engine.
This new version of the DME has been developed to meet the objectives specified in the introduction and to comply with new American legislation (e.g. OBD II). The Californian standards in particular stipulate very stringent requirements with regard to exhaust emission values.
These CARB functions (Californian Air Resource Board) are realized in the DME M5.2.
The vehicles designated for the American market are equipped with an on-board diagnosis (OBD) interface which is standardized for all vehicle manufacturers. This interface makes it possible for the state traffic supervisory authority to read out OBD-relevant information from the DME fault code memory at any time. Access to this limited scope of fault code memory information is enabled by internal coding in the DME control unit.
The most important features of the DME M5.2 are:
- Operation of all 8 cylinders with one control unit
- Static high-voltage distribution
- Fully sequential cylinder-individual fuel injection
- Integrated adaptive knock control
- Stereo emission (lambda) control
- Self-diagnosis and emergency operation characteristics
- CAN-bus link
- OBD II functions
- Vehicle immobilization via EWS II (electronic vehicle immobilization)
- Automatic start function
- Control of characteristic map thermostat
OBD II (US only)
In order to monitor compliance with exhaust emission limit values, the Californian and US legislation require monitoring of all emission-related components during vehicle operation. This made more effective self-diagnosis necessary which, among other things, includes a misfiring detection function. If an emission-related fault occurs, the DME activates the 'check engine' lamp in the instrument cluster on US vehicles. This signals to the driver that a fault has occurred in the engine management system which influences exhaust emission and must therefore be eliminated immediately in a specialist workshop.
The most important OBD II diagnosis functions are:
- Misfiring detection
- Catalytic convener monitoring (oxygen sensor monitor)
- Fuel supply
- Fuel tank ventilation system
A further component part of the OBD II system is an interface which is standardized for all vehicle manufacturers and which can be used by US traffic supervisory authorities to read out emission-related faults stored in the control unit with the aid of a scan tool. Access to the data in the fault code memory is restricted for these authorities to emission-related faults.
With the exception of the functions
- Activation of 'check engine' lamp
- Oxygen sensor monitor downstream of catalytic converters
All OBD II-relevant monitoring functions which are not designated for the US market are also realized in the DME 5.2 control units. The standardized OBD II interface which permits supervisory authorities access to the fault code memory is also installed only in US vehicles.
Misfiring detection
The rotary speed of the engine is measured at the increment wheel with the aid of the inductive pulse generator. In addition to measuring the engine speed, misfiring is also detected on the M62 (same as M73).
To facilitate misfiring detection, the increment wheel is now subdivided internally in the control unit into four segments corresponding to the ignition interval (on 8-cylinder engine, 4 ignition cycles per crankshaft revolution).
The period duration (T) of the individual increment wheel segments is measured in the control unit. If the combustion sequence is OK in all cylinders, the period duration of all increment segments will be of the same length (T1 = T2 = T3 = T4).
If a fault (misfiring) now occurs at one cylinder, the period duration allocated to this cylinder is extended by fractions of milliseconds (see Fig.: T3>T1, T2, T4). These segment times are evaluated statically in the control unit.
Principle of misfiring detection
1 Engine operation OK.
2 Misfiring in section T3
The maximum permissible irregularity values, i.e. the deviation of the period duration of one segment are stored for each characteristic map point as a function of engine speed, load and engine temperature.
On exceeding these permissible values, the cylinders detected as faulty are stored in the fault code memory. In this case, the 'check engine' lamp is activated on US vehicles.
As a further measure, fuel injection to the faulty cylinders is switched off in order to protect the catalytic converter from overheating.
Adaptation
Manufacture-related tolerances of the increment wheel can lead to malfunctions of the misfiring detection system. For this reason, the DME automatically carries out adaptation.
The manufacture-related tolerances of the increment wheel are adapted in coasting phases of the engine without ignition and injection as the engine produces no irregularities due to the combustion procedure in these phases.
Service note:
After replacing a flywheel, increment sensor or DME control unit, particular care must be taken as part of the subsequent test run to ensure that a longer engine cruising phase (approx. 10 sec) is maintained to make it possible for the DME control unit to adapt the flywheel.
CAN-bus link
Digital data transfer between the following control units takes place via the CAN-bus link:
- DME
- AGS
- ABS/ASC
Fuel injector valves
Conical jet valves (as on M60) from Bosch and Lucas are used for both engine capacity variants.
Air mass meter
As on the M60, a hot-film air mass meter is used on the M62.
Idle speed control
As on the M60, the idle speed is controlled on the M62 engine by means of a two- winding rotary actuator (ZWD 5). The air drawn in by the ZWD 5 at idling speed is routed to the mixing chamber of the throttle valve.
Oxygen sensors
An oxygen sensor is arranged upstream of each of the two catalytic converters. The M62 models designated for the US market are additionally equipped with a second oxygen sensor (monitor) downstream of the catalytic converter in order to comply with OBD II regulations. The oxygen sensors are of identical design to those on the M73 engine. (Type designation: Bosch LSH 25).
Knock control / knock sensors
The M62 also features a knock control system. The knock control prevents knocking engine operation. For this purpose, if there is a risk of knocking, the control retards the ignition timing of the corresponding cylinder(s) as far as necessary.
The 4 knock sensors are mounted on the water jacket of the engine block between the two rows of cylinders. They are arranged such that one sensor monitors the two adjacent cylinders. The design and function of the knock sensors are identical to those of the M60.
Coolant temperature sensor
A dual temperature sensor is used on the M62 (as on M52). It serves the purpose of registering the coolant temperature both for the engine management system as well as for the remote thermometer in the instrument cluster. For this purpose, two galvanically isolated NTC pellets with different resistance characteristic curves are integrated in the sensor.
The dual temperature sensor is mounted on the end face of the engine in the water pump housing.
Automatic start function
The automatic start function serves to improve driver comfort during the starting procedure. In order to start the engine, it is only necessary to turn the ignition key into the 'start' position for a short time (terminal 50). After the DME control unit has received the input signal from terminal 50, the starter motor is activated until the engine starts up. All E38 vehicles with M73 engine are already equipped with this function.
Now all E38 and E39 vehicles with M62 engine are equipped with the automatic start function in conjunction with the special option automatic transmission.
Function
The starter relay is no longer activated directly via terminal 50 with the automatic start function. Terminal 50 now only serves as an input signal for the DME 5.2.
When the DME 5.2 control unit receives the incoming start signal (terminal 50) and the EWS control unit detects the correct change code at the same time, the DME activates the starter relay via the 'automatic start' output. The prerequisite for this is that the gear selector lever is in 'P' or 'N' position.
The starter motor is activated by the starter relay until 'engine running' is detected by the crankshaft sensor.
'Engine running' is detected when the engine speed
- nMot> 920 rpm when the engine is cold or
- nMot> 680 rpm when the engine is at operating temperature is temporarily exceeded during the starting procedure.
On detecting the 'engine running' signal, the DME control unit switches off the starter relay. If starting the engine is unsuccessful, the automatic start procedure is terminated after 20 sec by a ground signal output by the DME.
Function Diagram 'Automatic Start':
1 Crankshaft sensor
2 Starter relay
3 With automatic transmission (L2)
ASC functions
All vehicles with M62 engine are equipped with ASC+T as standard. In order to implement the ASC functions, the M62 engine is equipped with a choke (as on the M60) which is controlled by the ADS II actuator as required in conjunction with a bowden operating cable assembly.
The ABS II actuator is controlled by the ABS/ASC control unit. Other ASC interventions such as ignition timing adjustment as well as ignition and injection cutout are controlled by the DME control unit.
The idle speed actuator (ZWD 5) is also used on the M62 engine to realize the engine drag torque control function (MRS). The idle speed actuator opens specifically when the engine drag torque control (MSR) is activated. It receives a pulse width modulated signal from the DME for this purpose.
The information necessary to control the ASC functions in the DME control unit is transferred via the CAN-bus.