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Different realizations of adaptive cruise control systems (ACC) have been tested. Firstly, only throttle access has been realized. In addition to this, the second realization utilizes access to the automatic transmission ECU. Finally, the third realization includes access to the brakes. Essentially, the first two versions are characterized by different states (e.g. acceleration, hold speed, deceleration), while the third version is based on continuous longitudinal vehicle control, e.g. using fuzzy methods [1]. Practical results showed high system stability for all three ACC versions. Advantages and disadvantages of each realization have been worked out based on simulated and measured results. Measurements showed that the first two solutions are sufficient to handle many traffic situations. However, in comparison with these versions, the third realization turned out to be the most powerful one.

The center of the Siemens LEV/ULEV-solution is an electronic control unit with a high potential processor, which fulfills all requirements for high calculation accuracy and OBDII-diagnostics. Several new functions were designed on this platform to make sure that the vehicle emissions are low in every operating condition and over the vehicle lifetime. The paper describes the emission benefits of selected new functions and components. Improved fuel preparation with air assisted injectors decreases the engine out emissions and allows a higher spark retardation and a leaner engine mixture without driveability degradation in the catalyst heat up phase. A transient function includes a physical intake manifold model for the calculation of the air amount which enters the cylinder and also a 2nd order wall wetting compensation model. An electrical heated catalyst (EHC) combined with secondary air injection and a multi brick cascade catalyst system.

Due to stringent emission requirements, such as Californian “Low Emission Vehicle - Ultra Low Emission Vehicle” or European “EURO2000”, as well as increased mileage requirement for vehicle emission durability, the catalyst aging process needs to be better understood. Beside contamination (by silicon, phosphorus, lead,…), a concern for catalyst durability is thermal stress due, for instance, to engine misfiring, poor air-fuel mixture distribution or poor cylinder combustion during deceleration mode. Uncontrolled lambda during engine acceleration mode gives alternately lean and rich mixtures. This will increase the concentration of oxygen and carbon monoxide in the exhaust gas. Deceleration modes are generally calibrated for efficient engine braking with spark retard. This may lead to poor combustion when the pedal is released, with an increase of hydrocarbons and oxygen concentration in the exhaust. The emitted pollutants will be oxidized in the catalyst.