Chassis Test Cycles for Assessing Emissions from Heavy Duty Trucks

Paper #:
  • 941946

Published:
  • 1994-10-01
Citation:
Clark, N., McKain, D., Messer, J., and Lyons, D., "Chassis Test Cycles for Assessing Emissions from Heavy Duty Trucks," SAE Technical Paper 941946, 1994, https://doi.org/10.4271/941946.
Pages:
14
Abstract:
Recent interest in the effect of engine life on vehicle emissions, particularly those from alternately fueled engines, has led to a need to test heavy duty trucks in the field over their lifetime. West Virginia University has constructed two transportable laboratories capable of measuring emissions as a vehicle is driven through a transient test schedule. Although the central business district (CBD) cycle is well accepted for bus testing, no time-based schedule suited to the testing of class 8 trucks with unsynchronized transmissions is available. The Federal Test Procedure for certifying heavy duty engines can be translated with some difficulty into a flat road chassis cycle although original data clearly incorporated unpredictable braking and inclines. Two methods were attempted for this purpose, but only an energy conservation method proved practical. A chassis cycle was developed for the case of a 261 kW (350 hp) 9-speed tractor with a specified torque curve and rear end ratio operated at 18,180 kg (40,000 lb.) weight. However, it is evident that the range of engines and transmissions in service render a test of this type to be vehicle specific, so that a more geometric cycle, in the spirit of the CBD, was sought. Field Data show that power to weight ratios have a profound effect on vehicle emissions. A simulation including a simple shift time compensation was used to assess the acceleration ability of class 8 trucks. In addition, it is proposed that trucks be tested at 70% of gross vehicle weight (GVW) up to a GVW of 27,270 kg (60,000 lb.) above which the testing weight should be set at 19,090 kg (42,000 lb.). The proposed cycle consists of five accelerations, each to a steady state speed (8.94, 11.18, 13.41, 15.64 and 17.88 m/s) (20, 25, 30, 35, 40 mph), each followed by a deceleration and an idle period. Acceleration was based on the ability of the truck to accelerate to 8.94 m/s (20 mph) in 25 see, which test data from a chassis dynamometer show to be generous. The shape of the acceleration curve was set using a cubic equation for velocity in time, developed from an acceleration simulation. Braking rate was set at 0.595 m/s2 (1.33 mph/sce) and the whole test was completed in 8 km (5 miles). This new test, termed the WVU 5 peak 5 mile truck cycle, is now being used in gathering data by the West Virginia University Transportable Emissions Testing Laboratories.
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