Input Signals/Components
INPUT SIGNALS/COMPONENTS
CAMSHAFT POSITION SENSORS
Located on the upper timing case covers, the camshaft position sensors monitor the position of the camshafts to establish start of ignition tiring order, set up sequential fuel injection triggering and for accurate camshaft advance-retard (VANOS) timing feedback.
Each intake camshaft's advance-retard angles are adjusted simultaneously yet independently. For this reason ME 7.2 requires a camshaft position sensor on each cylinder bank for accurate feedback to monitor the VANOS controlled camshaft positioning.
The sensors are provided with operating power from the ECM main relay. The sensors produce a unique asymmetrical square-wave signal representative of the impulse wheel shape. The sensors are new in the fact that they are "active" hall effect sensors. Active hall sensors provide:
- low signal when a tooth of the camshaft impulse wheel is located in front of the sensor
- high signal when an air gap is present.
The active hall sensors supply a signal representative of camshaft position even before the engine is running. The ME 7.2 determines an approximate location of the camshafts positions prior to engine start up optimizing cold start injection (reduced emissions.)
HOT FILM AIR MASS SENSOR (HFM 5)
The M62 TU is equipped with a new Hot Film Air Mass Sensor identified as HFM 5. It is a combined air mass/intake air temperature sensor. The separate intake air temperature sensor is no longer used on the M62 TU.
The HFM 5 is provided with operating power from the ECM main relay. Based on calculated intake air mass, the HFM 5 generates a varying voltage between 0.5 and 4.5 volts as an input signal to the ME 7.2
An additional improvement of the HFM 5 is that the hot film element is not openly suspended in the center bore of the sensor as with previous HFMs. It is shrouded by a round fronted plastic labyrinth which isolates it from intake air charge pulsations.
This feature allows the HFM to monitor and calculate the intake air volume with more accuracy. This feature adds further correction for calculating fuel injection "on" time (ti) which reduces emissions further.
INTEGRATED AMBIENT BAROMETRIC PRESSURE SENSOR
The ME 7.2 Control Module contains an integral ambient barometric pressure sensor. The sensor is part of the SKE and is not serviceable. The internal sensor is supplied with 5 volts. In return it provides a linear voltage of approx. 2.4 to 4.5 volts representative of barometric pressure (altitude).
The ME 7.2 monitors barometric pressure for the following reasons:
- The barometric pressure signal along with calculated air mass provides an additional correction factor to further refine injection "on" time.
- Provides a base value to calculate the air mass being injected into the exhaust system by the secondary air injection system. This correction factor alters the secondary air injection "on" time optimizing the necessary air flow into the exhaust system.
- Recognition of altitude above the accepted criteria postponing DM-TL activation for evaporative emission leak diagnosis.
RADIATOR OUTLET TEMP SENSOR
First seen on the MS 42.0 control system, the ME 7.2 uses an additional water temperature sensor located on the radiator outlet.
ME 7.2 requires this signal to monitor the water temperature leaving the radiator for precise activation of the IHKA auxiliary fan.
DSC III ROAD SPEED SIGNAL
ME 7.2 receives the road speed signal directly from the DSC III control module for maximum vehicle speed management. The DSC control module provides a processed output of the right rear wheel speed sensor as a digital square wave signal. The frequency of the signal is proportion- alto the speed of the vehicle (48 pulses per one revolution of the wheel).
The cruise control function (FOR) of the ME 7.2 also monitors vehicle speed from the redundant vehicle speed CAN bus signal. The CAN bus speed signal is provided by the DSC III control module and based on the combined average of both front wheel speed signals.
Additionally, ME 7.2 monitors all four wheel speed signals via CAN bus signalling to detect abrupt fluctuations in vehicle speed signals for the purpose of detecting rough road surfaces. This is continuously monitored as part of the OBD II emission requirements providing a correction factor for misfire detection plausibility. Earlier systems only monitored the right rear speed signal input from DSC.
ACCELERATOR PEDAL SENSOR (PWG)
The driver's application of the accelerator pedal is monitored by a PWG sensor in the driver's footwell as with previous non-bowden cable EML systems.
The PWG provides two separate variable voltage signals to the ME 7.2 control module for determining the request for operating the Electric Throttle Valve (EDK) as well as providing a kickdown request with automatic transmission vehicles.
The ME 7.2 monitors the changing signal ranges of both circuits as the pedal is pressed from LL to VL.
- In vehicles equipped with an automatic transmission (A5S 440Z), the ME 7.2 recognizes the max pedal value (4.5V) as a kickdown request and signals the AGS via CAN bus.
PWG SIGNAL MONITORING & PWG FAILSAFE OPERATION:
- If the monitored PWG potentiometer signals are not plausible, ME 7.2 will only use the lower of the two signals as the driver's pedal request input providing failsafe operation. Throttle response will be slower and maximum throttle position will be reduced.
- When in PWG failsafe operation, ME 7.2 sets the EDK throttle plate and injection time to idle (LL) whenever the brake pedal is depressed.
- When the system is in PWG failsafe operation, the instrument cluster matrix display will post "Engine Emergency Program" and PWG specific fault(s) will be stored in memory.
EDK THROTTLE POSITION FEEDBACK SIGNALS
The EDK throttle plate position is monitored by two integrated potentiometers. The potentiometers provide DC voltage feedback signals as input to the ME 7.2 for throttle and idle control functions.
Potentiometer signal 1 is the primary signal, Potentiometer signal 2 is used as a plausibility cross-check through the total range of throttle plate movement.
EDK FEEDBACK SIGNAL MONITORING & FAILSAFE OPERATION:
- If plausibility errors are detected between Pot 1 and Pot 2, ME 7.2 will calculate the inducted engine air mass (from HFM signal) and only utilize the potentiometer signal that closely matches the detected intake air mass.
- The ME 7.2 uses the air mass signalling as a "virtual potentiometer" (pot 3) for a comparative source to provide failsafe operation.
- If ME 7.2 cannot calculate a plausible conclusion from the monitored pots (1 or 2 and virtual 3) the EDK motor is switched off and fuel injection cut out is activated (no failsafe operation possible).
- The EDK is continuously monitored during all phases of engine operation. It is also briefly activated when KL 15 is initially switched on as a "pre-flight check" to verify it's mechanical integrity (no binding, appropriate return spring tension) by monitoring the motor control amperage and the reaction speed of the EDK feedback potentiometers.
If faults are detected the EDK motor is switched off and fuel injection cut off is activated (no failsafe operation possible). The engine does however continue to run extremely rough at idle speed.
MFL CRUISE CONTROL DATA SIGNAL
The ME 7.2 control module provides the FGR cruise control function. Throttle activation is provided by ME 7.2 automatic control of the EDK and monitoring of the throttle plate position feedback potentiometer signals.
All of the familiar driver requested cruise control function requests are provided to the ME 7.2 control module via the MFL control module on a single FOR data signal wire.
BRAKE LIGHT SWITCH
The Electronic Brake Switch (Hall effect) provides brake pedal position status to the ME 7.2. The control module monitors both the brake light and a separate brake light test switch circuits for plausibility.
When the brake pedal is pressed the brake light segment of the switch provides a high signal. Simultaneously, the brake light test switch (located in the same housing) provides a ground signal.
CAN BUS
- The CAN bus consists entirely of a twisted pair wire set. This configuration eliminates the need for a ground shield.
- The Engine Control Module has two CAN bus communication ports, one dedicated to AGS and the other for the balance of the vehicle's CAN bus control modules.
- This configuration improves the reliability of CAN bus signalling. If an open occurs in one area, the other control systems can still communicate on either side of the open.
- However, signals not reaching their intended recipients will cause CAN bus faults to be stored in the affected systems.