The throttle valve is a component part of the air intake system of the engine and controls the quantity of air required to combust the fuel.
In the EMLIIIS system, the 2 throttle valves for the 2 rows of cylinders are not opened and closed as in conventional systems by means of an operating cable but rather by actuator motors.
Stepper motors are used to drive the throttle valves which, in contrast to the DC motors used in the previous EML system, require no gear mechanism and therefore feature better dynamics.
Potentiometers which constantly signal the current position of the throttle valves to the EMLIIIS control unit are connected directly to the throttle valves.
In view of the fact that the throttle position has a direct influence on the engine output, for safety reasons, 2 stepper motors are installed per throttle valve and 2 potentiometers to signal their position.
Each throttle valve is driven simultaneously by 2 stepper motors mounted on the same drive shaft with one controlled by the computer MC1 and the other by computer MC2 so that the function of both throttle valves can be maintained by the other computer in the event of a computer failing.
Each stepper motor consists of a sine winding and a cosine winding, each of which are controlled via shielded, separate supply lines by its own stepper IC. If one stepper IC fails the function is adopted by the other stepper IC.
If, despite the integrated redundancy, perfect operation of the throttle valve can no longer be ensured due to a fault in a throttle valve, this throttle valve and thus the relevant row of cylinders is shut down. Restricted operation with the remaining row of cylinders is possible.
Each throttle valve features 2 independent potentiometers to signal the current position of the valve to the EMLIIIS control unit. The 2 potentiometers are operated with 2 voltage supplies which are decoupled from each other so that in the event of one voltage supply or one potentiometer failing the other potentiometer can still ensure correct position feedback.
As part of the self-diagnosis function, the throttle valves are checked exactly in a large number of tests: