This paper describes work carried out to predict and improve the fatigue life of arduous turbocharger applications by means of detailed measurements on a vehicle, linked to test bed measurements and modification of the turbocharger match. The turbocharger speed is highly cyclic when used on buses operating in cities due to the close spacing of bus stops and the heavy traffic conditions encountered. Each of the major speed cycles is a fatigue event for the compressor wheel, and an incorrectly applied turbo will surfer Low Cycle Fatigue failures at unacceptably low mileage. The life of the impeller is dictated by the difference between maximum and minimum turbo speed in any significant fatigue event and the frequency of their occurrence. For the MAN application in question, using a cast aluminium impeller, it was recommended that the maximum turbo speed on the engine test bed should not exceed 105,000 rpm. The turbo wastegate setting and engine control unit were changed accordingly for production engines. The changes did not alter the acceleration times of the vehicle, hut turbo impeller life will most certainly be improved. Some of these parameters cannot be controlled, such as traffic conditions or vehicle weight. However, the wastegate setting and gearbox (which have the most significant effects) are parameters which we can control. The other factors must be measured in the field and accommodated accordingly. The turbo speed during bus operation must not exceed 104,000 rpm to achieve a life of 500,000 km. For wastegated turbochargers, this means a limit of 105,000 rpm on the test bed when specifying a turbo match. For fixed geometry, the turbo speed set on the test bed can be higher, but it is recommended that it should not exceed 109,000 rpm within the engine speed range used during gearshifts. The paper describes datalogging to gather field data from a variety of bus applications, and the analysis thereof to predict impeller life. Further analysis is described, correlating turbo conditions on the vehicle to performance test bed conditions by considering the vehicle system as a whole. This enables the performance engineers to predict turbo fatigue life from test bed performance data without the need for vehicle testing.
Turbo matching techniques for highly cyclic bus applications
Anpassung von Abgasturboladern zyklisch hochbeanspruchte Motoren von Bussen
2002
10 Seiten, 8 Bilder, 1 Tabelle, 3 Quellen
Conference paper
English
Turbo matching techniques for highly cyclic bus applications
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