Chassis Test Cycles for Assessing Emissions from Heavy Duty Trucks 941946
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.