Electric Throttle System (EML) Functional Description

INTEGRAL ELECTRIC THROTTLE SYSTEM (EML)

FUNCTIONAL DESCRIPTION







When the accelerator pedal is moved, the PWG provides a change in the monitored signals. The ME 7.2 compares the input signal to a programmed map and appropriately activates the EDK motor via proportionally high/low switching circuits. The control module self-checks it's activation of the EDK motor via the EDK feedback potentiometers.

Requirements placed on the Electric Throttle System:
- Regulate the calculated intake air load based on PWG input signals and programmed mapping.
- Control idle air when LL detected with regard to roadspeed as per previous systems.
- Monitor the driver's input request for cruise control operation.
- Automatically position the EDK for accurate cruise control (FGR) operation.
- Perform all DSC III throttle control interventions.
- Monitor and carryout max engine and roadspeed cutout.

PWG SIGNAL MONITORING & PWG FAILSAFE OPERATION:
- As a redundant safety feature the PWG provides two separate signals from two integral potentiometers (Pot 1 and Pot 2) representing the driver's request for throttle activation.
- 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 FEEDBACK SIGNAL MONITORING & EDK FAILSAFE OPERATION:
- The EDK provides two separate signals from two integral 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, 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, 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 (no failsafe operation possible). The engine does however continue to run extremely rough at idle speed.
- When a replacement EDK is installed, the ME 7.2 adapts to the new component (required amperage draw for motor control, feedback pot tolerance differences, etc). This occurs immediately after the next cycle of KL 15 for approximately 30 seconds. During this period of adaptation, the maximum opening of the throttle plate is 25%.