Digital Motor Electronics

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Digital Motor Electronics (DME) is a microprocessor based system that controls the ignition, fuel injection, oxygen sensor and numerous ancillary functions. 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 distance you can still cover with fuel in the tank, an average speed, outside temperature and more.

In the 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 DDE (Digital Diesel Electronics) 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 the altitude. DME then literally fine-tunes 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).

How it works: The two main tasks DME has to perform are (1) injecting the right amount of fuel and (2) providing a spark at the correct time. In order to do this, the system needs to know things about the engine's current state. DME can track dozens of different sensors, but every system needs to know three basic things:

1.) how much air is coming in

2.) the position of the throttle, and

3.) 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 DME can diagnose itself for quick and efficient trouble-shooting.

Circuit diagram of early DME system

The core of a DME application are microprocessors. Microprocessors work at astonishing speeds. 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.