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Besides the legally controlled components carbon monoxide, total hydrocarbons, oxides of nitrogen and particulate matter (vehicles with diesel engines), there are many other components in the exhaust gas of motor vehicles, which are not explicitly controlled by law, and are therefore classified as unregulated exhaust gas components. This does not mean that these components are not subject to environmental legislation, but rather the opposite is the case. For more than ten years, US legislation has been calling for constant proof from vehicle manufacturers that the exhaust gas treatment systems, which are built into vehicles to reduce the legally controlled emissions, do not release other (unregulated) components in such concentrations as to represent an unjustifiably high health risk.

The purpose of this paper is to discuss the complex problem area of inspection and maintenance and to show a possible way out of this problem. The main difficulty of inspection and maintenance results from the high variability of exhaust emission values. Therefore only cars with very high emissions far beyond the production distribution curve, so-called outliers, can be identified in an emission test. For the detection of such outliers a new measurement procedure for catalyst equipped passenger cars is presented. The basic idea is to determine the conversion rate of the catalytic system with regard to the exhaust emission components HC, CO and NOX using the new test procedure (“component check/catalyst”) which is suitable also for routine checks. It is important to check the catalytic system under dynamic engine conditions. On the other hand the procedure should operate without a chassis dynamometer - because of cost reasons.

The effects of the total exhaust emission with its hundreds of different compounds and potential coergisms resulting therefrom, with special reference to a potential carcinogenic or cocarcinogenic effect on the respiratory tract, can only be established using experiments which consider the exhaust with all its gaseous components and particulate matter as a whole. Long-term diesel and gasoline engine exhaust inhalatin studies with rats, hamsters and mice which have already been accomplished or are still running at the Fraunhofer-Institut für Toxikologie und Aerosolforschung, aim to investigate the chronic-toxic effects, as well as the potential carcinogencity or cocarcinogenicity of exhaust emissions.

The legislation to limit the exhaust gas emissions of motor vehicles has led to the evolvement of a variety of measuring and testing procedures which differ from country to country. Our investigations of the mandatory exhaust test procedures existing in the US and in Europe result in proposals which could be a reliable basis of a world-wide harmonized legislation. The recommendations include an improved driving schedule, standardized sampling systems and the introduction of standard test equipment for matching the test cells. Furthermore, modifications of the current evaluation of certification, assembly-line, and in-use compliance testing are given.

Distribution functions of repetitive exhaust measurement results on the same vehicles and of single measurement results on many vehicles from the assembly line are investigated. The correlation between mass emission components is also analyzed. The probabilities for passing or failing certification tests are calculated using a Monte Carlo-method under consideration of the standard deviations of test data. From the results of these statistical and experimental investigations, proposals for the improvement of certification- and assembly line test procedures for the USA and Europe are deduced.

Our investigations have shown that the current calibration procedures for dynamometers do not suffice to obtain a good conformity between different dynamometers. As a criterion for dynamometer calibration, we use in two different ways the torque which is measured on the drive shaft of a test car. The static method yields the complete dynamometer characteristic: torque versus car speed. The dynamic method uses the averaged time integral of the torque measured over a driving cycle. Both methods supplement each other. In order to achieve a good reproducibility, a mechanized driver has been developed. Test results are discussed.