As discussed last month, the Bosch ME-Motronic engine management system is a radical departure from current systems which control fuel injection and ignition timing. The relationship between the accelerator pedal position and the opening angle of the throttle valve is no longer fixed - there is no accelerator cable.
Instead the Electronic Control Unit (ECU) determines how much engine torque is required and then opens the throttle valve to the appropriate angle.
Fig.1: unlike a conventional management system, in the ME-Motronic system there are multiple torque request inputs, rather than a system that indirectly responds to the driver's request by sensing increased intake airflow or changes in manifold pressure. The driver and external systems make the External Torque Requests, while the Internal Torque Requests are pre-programmed internal ECU factors. Actual developed torque is determined by control of the throttle valve angle, intake charge pressure (turbo cars), ignition advance angle, injection cut and injection pulse width. [Audi]
The chosen throttle opening is based on complex software that models the engine’s instantaneous torque output and compares this with the required torque output, as requested not only by the driver but also by other in-car systems.
Torque control logic
The ME-Motronic system coordinates the various torque demands in order that it can implement an overall torque control strategy.
Torque requests are categorised as “Internal” or “External”. External torque requests include those made by the driver, cruise control system and driving dynamics systems like Automatic Stability Control.
