contd...

The vehicle speed –time and normalized torque -time curves for the ETC are shown in Fig. 4.6. The cycle was derived from the data collected on different road types i.e., highway, urban and rural roads, under varying traffic density, road gradients and distance between stopping points. The data were collected for different types of vehicles such as trucks, buses and city buses. The normalized figures are integrated in three sub-cycles of
10 minutes each. For establishing limits, emissions from the three sub- parts of the cycle may be measured separately and later combined using weighting factors.

US Heavy Duty Test Procedure

In the USA until 1984, a steady state test cycle consisting of 13 different engine speed and load combinations was used for measurement of gaseous exhaust emissions from the heavy-duty vehicle engines. Emissions were measured under engine idling, and at rated and maximum torque engine speeds as in European R-49 cycle but at different engine loads and the engine operating modes had different weighting factors than the European test procedure. From 1985, a transient mode test replaced the 13-mode test. This test cycle was developed from the driving pattern data measured in New York and Los Angeles. The cycle represents driving pattern only for the city operation. It contains the traffic characteristics of congested urban, uncongested urban and city expressway driving. The US transient cycle test is run over a full range of load and speed conditions with equal weighing factor to each operation point of the cycle. The total test consists of three phases, cold start cycle, hot soak and hot start cycle; each phase of 20 minutes duration. Data on engine speed, load and gaseous emissions are monitored once per second. Computer controlled engine test bed and data acquisition are used. The emission results are integrated over the test cycle. The weighting factors for the cold start and hot start cycles are 1/7 and 6/7, respectively.