Digital Motor Electronics
From Wikipedia, the free encyclopedia
Digital Motor Electronics (DME) is a microprocessor based system that controls the ignition, fuel injection, oxygen sensor, and numerous ancillary functions of an automobile. The DME provides raw data to an on-board computer that uses an alphanumeric display to provide you with information such as the average fuel consumption, the driving distance available with the fuel in the tank, average speed, outside temperature, etc.
In the automotive industry, DME is often referred to as the Engine Control Unit (ECU), under the heading of Electronic Engine Management Systems. BMW also uses the term Digital Diesel Electronics (DDE) for diesel engine models instead of DME.
DME operates by continually monitoring such factors as engine temperature, speed, intake airflow, exhaust gas composition, and even altitude. DME can fine-tune the engine hundreds of times a second to provide maximum performance and efficiency. DME has a fail-safe program in the event of certain electrical faults. Current DME versions also have on-board diagnostics (OBD).
[edit] Operation
The two main tasks DME performs are (1) the injecting of the proper amount of fuel and (2) providing a spark at the correct time. In order for this to happen, the system requires information about the engine's current state. DME can track dozens of different sensors, however, every system needs to know three basic things:
- How much air is coming into the engine.
- The position of the throttle.
- How fast the engine is running.
Using the information about how much air is flowing through the engine and how fast it's turning, DME uses a fuel map to determine how long each injector should stay open each cycle to inject the right amount of fuel. During part-throttle operation, the injector pulse-width is also modified by the readings from the oxygen sensor, a device that sits in the exhaust collector and determines how much oxygen is left over in the exhaust. Each cylinder is constantly adjusted to maximum operating efficiency under virtually all conditions.
In the event of an electrical fault, DME can reconfigure itself to bypass the problem and it can diagnose itself for quick and efficient trouble-shooting.
The core of a DME application are microprocessors. The core of central engine management in the current BMW M3 executes nearly twenty million instructions per second (20 MIPS). Microprocessors also have a reputation for being extremely reliable. They are designed for a lifespan of at least 150,000 active hours. A car, by comparison, is expected to survive 4,000 hours of use.[citation needed]
