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Exhaust/Consumption Type Testing

Determining consumption by CO2-measuring

When governments want to introduce the CO2 tax, they need accurate and reproducible data obtained either about the consumption or CO22 emissions. Both amount to the same thing. Indeed, because e.g., in an injection system with flow-back, the exact measuring is difficult and the exhaust gas portion is measured at the same time anyhow, the CO2 content in the exhaust gases will be used as a yardstick for the fuel-consumption when type-testing is done.

Driving according to precise legal requirements (cycles)

The above graph shows it clearly. On the roller test-bench, the vehicle must absolve a very definite cycle. Thereby, speeds, acceleration- and gear-changing behaviour are precisely laid out. The individual gear- speeds are marked in colours for better orientation. The idling speed (green) is always selected at the end of a cycle, at a certain speed. The roller test-bench basically has only a GS (electric motor) for simulating the inertial masses or drag of the vehicle (e.g., in coasting down tests), the recording of the vehicle performance is regulated by means of an eddy-current-brake.

Urban four times 50 km/h, open roads up to 120 km/h

The, just about 200 seconds long first part, is repeated three times, thus showing the urban traffic (medium blue). This is the first shown consumption value given in the brochure. 400 seconds are needed for the open-road value (light blue). In this case, all the gear-speeds are used and the vehicle is taken up to 120 km/h. As opposed to an inspection within the scope of the safety standards authority, the exhaust gases are collected and precisely analysed.

The vehicle must first be brought up to the specified temperature

Indeed, the exhaust gas- and consumption test is still not sufficiently described. The regulations for testing a vehicle on the roller test-bench are enough to fill several box files. Two important aspects are mentioned here. Firstly, the temperature of the vehicle is crucial. With the introduction of more stringent laws the temperatures are becoming lower and lower. What we actually need, not only in summer, is one whole night in a suitably tempered room, to bring all the parts to the required temperature. In addition, if the slightest error crops up with the, in the meantime warmed up engine, the next attempt can only be made after many hours.

The rolling-test-bench requires vehicle-specific data

Almost even more important, is the simulation of the load on the rollers. The electric motors must give an exact impression of the situation of the vehicle and particularly the drives on the road, thus with at least, a force which is staggered, depending on the speed. Nowadays, this can only be done with the help of computers. They record the data taken in a coasting down test at high speed on the test-track, with which the test- bench is then fed. Therefore, the same engine in a SUV must work distnictly more than in an estate car. Accordingly, the exhaust gases are formed.

The freewheeling test provides a picture of the roll- and the air resistance

Coasting down tests are nothing out of the ordinary for earlier students of automotive technology. At that time, not every institute had a dynamometer. If one choses the correct test track, such a test can be very informative. Nowadays, the computer can even make a distiction between the various running resistances. If, in the upper speed range, the vehicle loses speed rapidly, then the air resistance is quite high. At low speeds, the quality of the rolling resistance is apparent.

The NEDC (New European Driving Cycle) test shown here, is valid only in Europe and above all, only for motor cars and light delivery vehicles. Globally seen, there are also other cycles (e.g., FTP 75 in America or the 10-15 mode in Japan). Basically, the mentioned vehicles are already taxed in Germany using this method. E.g., the Euro III to Euro IV classifications are based on this, the Euro I and Euro II on a similar (almost the same) cycle. A taxation according to CO2 would thus mean, simply a changing of the thresholds.

Utility vehicles are also tested, but on an engine test-bench

There is also a similar stage plan for the exhaust gas limits of utility vehicles. They however, will not be tested on the rollers, but on the engine, on a suitable test-bench. Accordingly, the utility vehicle exhaust gases will be shown in g/kWh, similar to the specific fuel consumption. The pollutant emission of motorcycles is also limited and is slowly becoming comparable with that valid for motor cars.

Statistical information regarding failed exhaust gas tests is compulsory

The necessity for examination is proved by a so-called fault-statistic. This also means, that all possible vehicles are registered before a repair is made. Indeed, demands are also made on the vehicle manufacturer. He must guarantee the function of exhaust gas relevant parts for 100.000 kms (previously 80.000 kms) or for 5 years and, must also prove this in the type-testing. If possible, any malfunctions in the electronic error-control should also be included. 08/08