77 Vehicle Architectures and Design 3.7.2 s Tandard d riVe c ycles The standard drive cycles are used by the governmental agencies and automotive industry for per- formance evaluation of a vehicle, which includes certification of vehicle fuel economy. A drive cycle may have both speed and road grade components, although typically one is held constant while the other is varied. Two commonly used standard drive cycles are the urban dynamometer driving schedule (UDDS) and the highway fuel economy test (HWFET), simulating urban and highway driving, respectively. The two drive cycles are shown in Figures 3.20 and 3.21.
The UDDS drive cycle runs a distance of 7.5 miles in 1,369 s with frequent stops and has an average speed of 19.6 mph. The HWFET drive cycle runs a distance of 10.26 miles in 765 s and has an average speed of 48.3 mph. Another standard drive cycle is the US06 drive cycle, which is used to test the effectiveness of the vehicle control strategy under extreme driving conditions. The drive cycle is shown in Figure 3.22. The US06 drive cycle is the most aggressive of the three drive cycles shown so far. It features rapid acceleration and hard braking, and has top speeds just over 80 mph.
The Japanese technical standard drive cycle J1015, shown in Figure 3.23, is also useful in simulating urban driving with frequent stops. The section will conclude describing the standard J227a driving cycle recommended by the Society of Automotive Engineers (SAE) to evaluate the performance of EVs and energy sources fol- lowed by an example EV simulation. This short drive cycle is useful for hand calculations needed to develop the concepts of electric and hybrid vehicle fundamentals. The SAE J227a has three sched- ules designed to simulate the typical driving patterns of fixed-route urban, variable-route urban and variable-route suburban travels.
These three patterns are the SAE J227a driving schedules B, C and D, respectively. Each schedule has five segments in the total driving period: (i) acceleration time t a to reach the maximum velocity from start-up; (ii) cruise time t cr at a constant speed; (iii) coast time t co when no energy is drawn from the source; (iv) brake time t b to bring the vehicle to stop and (v) 30 25 20 Cycle Speed (m/s) 15 10 5 0 200 400 600 800 1000 1200 1400 0 Time (s) FIGURE 3.20 Urban dynamometer driving schedule (UDDS).