Principle of Operation
Principle of Operation
Air flow into the engine is regulated by the Valvetronic system controlling valve lift adjustment. The intake air flow is set by adjusting the valve lift while the throttle valve is fully opened. This further improves cylinder filling and reduces fuel consumption. All of the ECM monitoring, processing and output functions are a result of regulated air flow.
The Accelerator Pedal Position is monitored by the ECM for pedal angle position and rate of movement. As the accelerator is moved, a rising voltage signal from the Hall sensors requests acceleration (and at what rate).
The ECM will request the Valvetronic control module to increase the intake valve "lift". As a result of the increased air flow, the ECM will increase the volume of fuel injected into the engine and advance the ignition timing. The "full throttle" position indicates maximum acceleration to the ECM, and in addition to the functions just mentioned, this will have an effect on the air conditioning compressor (covered in Performance Controls).
As the accelerator pedal is released (integral springs), the decrease in voltage signals the ECM to activate fuel shut off if the rpm is above idle speed (coasting). The Valvetronic control module will decrease the valve lift to maintain idle speed. The ECM monitors the engine idle speed in addition to the accelerator pedal position and Valvetronic position.
The pedal position sensor consists of two separate Hall sensors with different voltage characteristics and independent ground and voltage supply. Sensing of the accelerator pedal position is redundant. The pedal position sensor is monitored by checking each individual sensor channel and comparing the two pedal values. Monitoring is active as soon as the sensors receive their voltage supply (KL15).
The Electronic Throttle valve is operated by the ECM (supplying voltage and ground) for opening and closing based on the accelerator pedal position, engine load and intake manifold vacuum.
When the throttle valve is operated, the ECM monitors feedback potentiometers located on the actuator shaft for position/plausibility. These two sensors operate inversely (voltage values) with throttle plate actuation.
The tasks of the throttle valve are:
Starting the engine
During the starting procedure at a temperature between 20 °C and 60 °C, airflow is controlled by the throttle valve.
If the engine is at operating temperature, it will be switched to non-throttle mode approximately 60 seconds after start up. In cold conditions, however the engine is started with the throttle valve fully opened, which has a positive effect on the starting characteristics.
Ensuring a constant vacuum of 50 mbar in the intake manifold
This vacuum is needed to exhaust the blow-by gases from the crankcase and the fuel vapors from the activated charcoal filter
The backup running function
If the Valvetronic system should fail, the throttle valve implements the engine's backup running function (conventional load control).
The Hot-Film Air Mass Meter (HFM) varies voltage monitored by the ECM representing the measured amount of intake air volume. This input is used by the ECM to determine the amount of fuel to be injected.
The heated surface of the hot-film in the intake air stream is regulated by the ECM to a constant temperature of 180° above ambient air temperature. The incoming air cools the film and the ECM monitors the changing resistance which affects current flow through the circuit. The hot-film does not require a "clean burn" it is self cleaning due to the high operating temperature for normal operation.
The Air Temperature signal allows the ECM to make a calculation of air density. The varying voltage input from the NTC sensor indicates the larger proportion of oxygen found in cold air as compared to less oxygen found in warmer air. The ECM will adjust the amount of injected fuel because the quality of combustion depends on oxygen sensing ratio
The ignition timing is also affected by air temperature. If the intake air is hot the ECM retards the base ignition timing to reduce the risk of detonation. If the intake air is cooler the base ignition timing will be advanced. The ECM uses this input as a determining factor for Secondary Air Injection activation (covered in the Emissions section), VANOS, Valvetronic, Knock adaptation and exhaust flap operation.
The Valvetronic System is operational when activation of terminal 15 switches the ECM main relay to supply voltage. The Valvetronic module reduces the voltage supply to the internal electronics and the sensors (5 volts). The system carries out a pre-drive check. The relays (in the IVM) are activated after a delay (approx. 100 ms) which supplies the load circuit for the Valvetronic motors. From this stage on, the ECM and the Valvetronic control module communicate via the LoCAN bus.
The ECM determines the intake valve lift for starting based on engine and ambient temperature (large lift when cold, minimum lift when warm). The ECM also determines the intake valve lift based on the acceleration requested by the driver. The Valvetronic control module converts the ECM command by operating the motors until the actual value from the eccentric shaft position sensor corresponds with the target value. The Valvetronic control module transmits the exact position of the eccentric shaft to the ECM via the LoCAN bus. When the Valvetronic modui1e detects a fault, ft is also transmitted on the LoCAN bus to the ECM for storage in fault memory.
A Redundant Position Control Hard Wire is between the ECM and the Valvetronic control module. Only two messages can be transmitted using this wire:
- Test function
- Maximum valve lift
A signal with a frequency of 100 Hz is placed on this wire to transmit these two messages. The test function is carried out during the pre-drive check. The pulse width rate is 50%.
- The maximum valve lift command is given if the LoCAN bus is faulty. In this case, the pulse width rate is 80%.
- If there is a fault (backup running Junction) when running with maximum valve lift, the operating motors are supplied with 30% power. This drives the motors softly to the limit slop which prevents additional mechanical tau Its. The load control is now operated conventionally by using the throttle valve.
The Bank Alignment function adjusts the distribution of load between the two cylinder banks. This alignment runs continuously during the engine operation to assure an equal load distribution to both cylinder banks.
The values of the individual cylinders are determined by the load request and the crankshaft reference/rpm signal. The ECM compares these actual values with stored limit values. As soon as the values are recognized, the ECM increases the lift of the intake valves on each bank.
After deletion of the adaptation values, the bank alignment is automatically performed by the ECM (or the DISplus can be used). The eccentric shafts are adjusted in steps (1 degree of rotation increments) until both bank outputs are equal. The following conditions must be present for the bank alignment:
ECM
- No load on the engine
- coolant Temperature > 85 degrees C
- No Faults Present
- All Auxiliary consumers Switched Off
- Minimum Valve Lift Detected
If faults relative to bank alignment are present, the following should also be considered during diagnosis:
Faults Related to Bank Alignment
- Damaged Valves
- Defective HVA Elements
- Misfire - Related functions and components (injection, ignition, compression, etc.)
The Valvetronic control module is assigned (programming) to the appropriate engine and ECM by the DISplus.
The Idle Speed Control is also regulated by the Valvetronic system. Reduced valve lift when the engine is idling ensures that the engine receives the appropriate airflow. When the Valvetronic system is in use, the idle speed control and intake manifold vacuum is also regulated using the electronic throttle valve.
During the starting procedure at a temperature of between 20 °C and 60 °C, airflow is controlled by the throttle valve. If the engine is at operating temperature, it will be switched to non-throttle mode approximately 60 seconds after it is started up.
At temperatures below 20 °C, the engine is started with the throttle valve fully opened using the Valvetronic for idle speed control (this has a positive effect on the starting characteristics).
NOTE: If the idle speed control is faulty, the engine must be checked for vacuum leaks because leaking air has an immediate effect on idling (unmetered air leaks).