Throttle Valve (DK) Motors
The throttle valve assembly consists of the DK housing with the throttle valve plate, return spring, drive motor and feedback potentiometers. In contrast to the M70 - EML system, the EML IIIs throttle valve plate is driven directly by the motor shaft. The gear drive is eliminated which allows for a more precise control of the throttle plate positioning.
A dual stepper motor configuration is used to drive the throttle plate. Both stepper motors are controlled through separate final stages in the EML control module and operate on the one armature. The final stages for one stepper motor windings are controlled by one micro processor while the second motor windings are controlled by the second processor. The control of the stepper motors takes place simultaneously by each processor.
The dual feedback potentiometers signal the movement and position of the throttle plate to each processor. The two potentiometers have separate power and ground circuits to ensure the reliability of their operation.
This dual redundancy system allows the EML IIIs to continue operation, without driver inconvenience, if one stepper motor or control circuit malfunctions. If the self diagnosis of the EML IIIs detects a fault with one of the stepper motor controls, it will switch off the affected circuit and continue operation from one motor control circuit. The fault will be logged and the EML fault warning will be displayed in the cluster matrix.
If a fault occurs that cannot allow continued operation of the throttle valve, the control for that bank of cylinders will be switched off as with the previous EML system.
STEPPER MOTOR CONTROL
A digital square wave signal is used to drive the stepper motor of the DK assembly. The duty cycle of the frequency and trigger of the signal are changed to produce the magnetic field required to move the stepper motor rotor.
Each set of stepper motor windings are controlled by four final stages. Each final stage has the ability to switch between power and ground to reverse the direction of current flow through the windings (trigger). This switching allows the magnetic field of the coils to be reversed allowing the rotor to be driven in either direction to position the throttle plate at the precise setting called for by the PWG input request.
The final stage control varies the duty cycle to control the speed of movement and position of the throttle plate.
Self Diagnosis: The scope of EML's self diagnosis for stepper motor operation includes:
- Checking - Both throttle valves are checked dynamically prior to engine starting (part of pre-start check with KL 15 on).
- All eight final stage controls per stepper motor when KL 15 is switched on.
- Monitoring - The supply voltages for all potentiometers.
- Throttle valve set position with the feedback potentiometers position.
- Comparing the two potentiometer signals.
- Comparing the set points calculated by each individual processor
- The throttle valve operation for OBD II checking requirements.
CONDITIONS OF STEPPER MOTOR CONTROL
Starting: The EML IIIs control module will position the throttle valves to the optimum opening for engine start when it receives the KL 50 input over the CAN line.
Idle: The EML IIIs programming will maintain a stable idle by adjusting the opening of the throttle valves when the vehicle is at a standstill. The EML receives the engine RPM signal from the DME control module over the CAN line.
The idle will be stabilized for A/C compressor activation to compensate for the load of the compressor.
The EML receives TD and AC on signals over the can line.
Decel Fuel Cutoff: Decel fuel cutoff is activated based on the input from the pedal position sensor and the engine RPM signals. A high signal is supplied from the EML control module to the DME control modules for the purpose of activating decel fuel cut off.
These input signals to the DME control modules are separate hard wire lines that are also used for the "safety fuel cut off" feature of the EML control.