Further Monitoring Concepts

The MDK safety concept can detect a jammed or binding throttle valve as well as a broken link spring. This fault is detected by the ECM monitoring the feedback potentiometers from the MDK in relation to the pulse width modulation to activate the MDK motor.

Emergency operation functions if the throttle valve is jammed:

Activation of the "EML" Light to alert the driver of a fault.
MDK is deactivated, the throttle valve is compensated for by closing the idle speed actuator and retarding the ignition (engine power reduction).
To maintain vehicle control, the MDK opening is compensated for by closing the idle speed actuator and retarding the ignition (engine power actuator).
Engine power is further limited by fuel injector cutout.

In the event of a fault, the DISplus or MoDIC must be used to interrogate the fault memory, and clear the fault once the proper repair has been performed.

The MS43 EDK Feedback Signal Monitoring/Failsafe 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 monitoring feature, Pot 2 is continuously cross checked with Pot 1 for signal plausibility.
If plausibility errors are detected between Pot 1 and Pot 2, MS 43.0 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 MS 43.0 uses the air mass signalling as a "virtual potentiometer" (pot 3) for a comparative source to provide failsafe 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 (failsafe operation is 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 "pre-flight check" to verify it's mechanical integrity (no binding, appropriate return spring tension, etc). This is accomplished by monitoring both 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 (failsafe 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 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 MS 43.0 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 30 seconds. During this period of adaptation, the maximum opening of the throttle plate is 25%.

The Total Intake Air Flow Control is performed by the ECM simultaneously operating the MDK/EDK throttle control and the Idle Air Actuator.

The ECM detects the driver's 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 MDK/EDK activation. The ECM then controls the Idle Air Actuator to satisfy the idle air "fill". In addition, the MDK/EDK will also be activated = pre-control idle air charge. Both of these functions are utilized to maintain idle RPM.

The MDK/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 MDK/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 MDK/EDK will also open.

MDK: In the upper PWG range (approximately <60%), the MDK is switched off. The throttle valve is opened wider exclusively by the pulley via the spring linkage.

At the full throttle position, "kickdown" is obtained by depressing the accelerator pedal fully. This will overwind the pulley, but the spring linkage will not move the throttle plate past 90 degrees of rotation.

Fig 1: Identifying Graph

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 300° 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.

The Suction Jet Pump is regulated by the ECM to provide sufficient vacuum for the brake booster under all operating conditions. The ECM controls the Suction Jet Pump Solenoid to allow vacuum flow through. The additional vacuum compensation is activated by the ECM when the idle air actuator is regulated for:

A/C Compressor "on"
Vehicle in gear and the clutch is released (driving under load)
Engine in warm-up phase >70° C

Additional vacuum compensation is applied to the brake booster when the circuit is "deactivated" (Solenoid sprung open). Vacuum enhancement is limited to the brake booster when the control circuit is "activated" (Solenoid powered closed).