he quality of our environment is not improving." This was how, in November 1999, EU Environment Commissioner Margot Wallström summed up the result of the EU's Fifth Environment Action Programme, which was just ending.
Traffic growth is at the top of the list of causes. Unleaded fuel and catalytic converters have cut the amount of some pollutants emitted by new cars. But the big picture remains grim. From 1990 to 1995, for example, the total amount of the greenhouse gas carbon dioxide produced by road transport in the EU went up by 120%.
Despite low consumer awareness, the EMS could play a major part in emissions control for as long as the internal combustion engine rules the roads. Its function is to control engine combustion. Dr Tony Truscott of Ricardo Consulting Engineers, the lead partner in the Aeneas Innovation project(1), points out that in doing so, it must strike a balance between three competing objectives - optimum performance, maximum fuel economy and minimum emissions. With a microprocessor at its heart, it can strike that balance more precisely than is possible with electromechanical means alone.
Innovative sensors and advanced control algorithms are the basis for an Engine Management System which is more flexible, more reliable and more cost-effective than current technologies. |
Maps to models
In an ordinary spark-ignition petrol engine, a basic EMS works by controlling two output variables - the amount of air and fuel admitted to the cylinders for combustion, and the timing of the ignition sparks. It continually adjusts each in response to changes in key input variables such as air and engine temperatures and accelerator position.
The appropriate values for the output variables have to be determined by the EMS itself. A conventional EMS does this very simply. It just looks them up in tables, or 'maps', stored in its digital memory. But this established technique has its drawbacks. Many maps are needed, making EMS calibration expensive, especially as it has to be redone for almost every variant of every vehicle model to which the EMS is fitted.
The EMS now fitted to the engine on the Aeneas consortium's test bed is different. It is a model-based EMS. The idea is to replace some of the maps with equations describing the behaviour of the engine. As Truscott puts it, "What we're doing is developing algorithms which actually incorporate the laws of physics in the engine."
The crucial advantage is flexibility. With clever programming, the model-based engine-control algorithm can adapt to inevitable but unpredictable changes in the engine. Wear is a prime example. Engine behaviour is affected by wear, but in ways too complex for a map-based system to handle. As a result, engine performance deteriorates gradually over its lifetime. Flexibility also means transferability - model-based EMSs can be easily transferred from ordinary gasoline engines to other types, such as Gasoline Direct Injection engines.
Measuring pressure directly
Until recently, the model-based EMS has been an unrealistic proposition for mass-produced vehicles. The sensors available for monitoring key engine variables, especially cylinder pressure, have been unsuitable. "Fortunately, there have been improvements in sensor technology, with very robust material systems like silicon on insulator and silicon carbide on insulator," Truscott points out.
Sensors based on these materials are being developed by Ricardo's two consortium partners, Kistler, a sensor company, and DaimlerChrysler, the vehicle manufacturer. They measure cylinder pressure directly, unlike the sensors that have been tried in the past. Thus, as Truscott explains, the EMS "really takes the internal combustion engine to its limits because the sensors provide information of exactly what is going on at the heart of the engine".
Smart algorithms
The other factor critical to the Aeneas EMS is the set of intelligent control algorithms that will process that information. An algorithm developed by DaimlerChrysler uses the precise cylinder-pressure measurements from the new sensors to calculate another key engine variable, the mass of air flowing into the engine. The Aeneas system can thus do without the transducer used by conventional EMSs to measure mass airflow, saving cost and improving reliability.
Control algorithms are currently being developed for the Aeneas EMS. Some have already been tested using data obtained from a test bed engine fitted with new cylinder-pressure sensors. The next step is to complete the development and testing on a vehicle demonstrator to validate the Aeneas technology.
While the demonstrator is the objective of the Aeneas Innovation project, the long-term plan goes further. After validation, DaimlerChrysler will take on the task of bringing the system into production, while Ricardo will be responsible for the marketing. In the meantime, interested parties can register for updates on the project's progress by joining the Aeneas Club through its website.
(1) IN301056I - Application and evaluation of a novel engine management system based on intelligent control algorithms and utilising innovative sensor technology (Aeneas).
Contact
| 
AUTOMOTIVE MICROSYSTEMS
