Principle of Operation
Principle of Operation
Air flow into the engine is regulated by the Throttle Valve and/or the Idle Air Actuator. Both of these air "passages" are necessary for smooth engine operation from idle to full load. On the MS45 system, the Throttle Valve and the Idle Air Actuator are electrically controlled. All of the ECM monitoring, processing and output functions are a result of regulated air flow.
The Accelerator Pedal Position (PWG) is monitored by the ECM for pedal angle position and rate of movement. As the accelerator is moved, a rising voltage signal from the potentiometers/Hall sensors requests acceleration and at what rate. The ECM will increase the volume of fuel injected into the engine, advance the ignition timing and open the Throttle Valve and/or Idle Air Actuator.
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), a decrease in voltage signals the ECM to activate fuel shut off if the RPM is above idle speed (coasting). The Throttle Valve will be closed and Idle Air Actuator Valve will open to maintain idle speed.
The ECM monitors the engine idle speed in addition to the accelerator pedal position and throttle position voltage. If the voltage values have changed (mechanical wear of throttle plate or linkage), the ECM will adjust the Idle Air Actuator to maintain the correct idle speed.
The potentiometers/Hall sensors are nonadjustable because the ECM learns the throttle angle voltage at idle speed. If the throttle housing/accelerator pedal module is replaced, the adaptations must be cleared and adaptation procedure must be performed using the DlSplus/MoDlC. If this is not performed, the vehicle win not start, or run in Fail-safe mode.
If this input is defective, a fault code will be stored and the Malfunction Indicator and/or EML Light will be illuminated. Limited engine operation will be possible.
The MS45 PWG pedal position sensor consists of two separate Hall sensors with different voltage characteristics and independent power supply (located in the accelerator pedal module).
The pedal position sensor is monitored by checking each individual sensor circuit and comparing the two pedal values. Monitoring is active as soon as the sensors receive voltage (KL15). The ECM decides what operating mode the pedal position sensor is to assume.
^ Mode = Pedal position sensor fully operable.
^ Mode 1 = Failure of one pedal position sensor (maximum engine speed is limited).
^ Mode 2 = Failure of both pedal position sensors (engine speed limited to 1500 rpm).
The Idle Air Actuator is controlled by the ECM modulating the ground signals (PWM at 100 Hz) to the valve. By varying the duty cycle applied to the windings, the valve can be progressively opened, or held steady to maintain the idle speed.
The ECM controls the Idle Air Actuator to supply the necessary air to maintain idle speed. When acceleration is requested and the engine load is low (<15%), the actuator will also supply the required air.
The basic functions of the idle speed control are:
^ Control the initial air quantity (air temp <0° C, EDK is simultaneously opened).
^ Variable preset idle based on load and inputs.
^ Monitor RPM range intake for each preset position.
^ Vacuum Limitation
^ Smooth out the transition from acceleration to deceleration.
Under certain engine operating parameters, the EDK throttle control and the Idle Air Actuator are operated simultaneously. This includes all idling conditions and the transition from off idle. As the request for load increases, the idle valve will remain open and the EDK will supply any additional air volume required to meet the demand.
Backup Operation of Idle Air Actuator:
If a fault is detected with the Idle Air Actuator, the ECM will initiate fail-safe measures depending on the effect of the fault (increased air flow or decreased air flow). If there is a fault in the Idle Air Actuator/circuit, the EDK will compensate to maintain idle speed. The "Malfunction Indicator and/or EML" Light will be illuminated to inform the driver of a fault.
If the fault causes increased air flow (actuator failed open), VANES and Knock Control are deactivated which noticeably reduces engine performance.
The MS45 EDK Feedback Signal Monitoring/Backup Operation when a fault is detected in the system is as follows:
^ The EDK provides two separate signals from two integrated potentiometers (Pot 1 and Pot 2) representing the exact position of the throttle plate.
^ EDK Pot 1 provides the primary throttle plate position feedback. As a redundant safety feature, Pot 2 is continuously cross checked with Pot 1 for signal plausibility.
^ If plausibility errors are detected between Pot 1 and Pot 2, MS45 will calculated the inducted engine air mass rom HEM signal) and only utilize the potentiometer signal that closely matches the detected intake air mass.
- The MS 43.0 uses the air mass signaling as a virtual potentiometer (Pot 3) for a comparative source to provides fail-safe operation.
- If MS 43.0 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 (Fail-safe operation if not possible).
^ The EDK is continuously monitored during all phases of engine operation. It is also briefly activated/adapted when KL 15 is initially switched on as a "preflight check" to verify its mechanical integrity (no binding, appropriate return spring tension, etc). This is accomplished by monitoring both the motor control amperate and the reaction speed of the EDK feedback potentiometers. If faults are detected the EDK motor is switched off and the fuel injection cut off is activated Fail-safe operation is not possible). The engine does however continue to run extremely rough at idle speed.
^ When in emergency operation, the engine speed is always limited to 130 RPM by fuel injector cutout, and activation of the "EML" light to alert the driver of a fault.
^ When in emergency operation, the engine speed is always limited to 1300 RPM by fuel injector cutout, and activation of the "EML" light to alert the driver of a fault.
^ When a replacement EDK is installed, the MS45 adapts to the new component (required amperage draw for motor control, feedback pot tolerance difference, etc). This occurs immediately after the next cycle of KL15 for approximately 60 seconds. During this period of adaptation. the maximum opening of the throttle relate its 25%
The Total Intake Air Flow Control is performed by the ECM simultaneously operating the EDK throttle control and the Idle Air Actuator.
The ECM detects the drivers request from the potentiometers/Hall Sensors monitoring the accelerator pedal position. This value is added to the Idle Air control value and the total is what the ECM uses for EDK activation. The ECM then controls the Idle Air Actuator to satisfy the idle air "fill". In addition, the EDK will also be activated = precontrol idle air charge. Both of these functions are utilized to maintain idle RPM.
The EDK is electrically held at the idle speed position, and all of the intake air is drawn through the Idle Air Actuator. Without a load on the engine (<15%), the EDK will not open until the extreme upper RPM range. If the engine is under load (>15%), the Idle Air Actuator is open and the EDK will also open.
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° C above intake 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.
If this input is defective, a fault code will be set and the Malfunction Indicator Light will illuminate when the OBD II criteria is achieved. The ECM will maintain engine operation based on the Throttle Position Sensors and Crankshaft Position/Engine Speed Sensor.
The Air Temperature signal allows the ECM to make a calculation of intake air temperature. 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).
If this input is defective, a fault code will be set and the Malfunction Indicator Light will illuminate when the OBD II criteria is achieved. The ECM will maintain engine operation based on the HEM and Engine Coolant Temperature sensor.