FIGURE 4-18 Fuel savings with respect to conventional cycles on standard drive cycles under (left) a 50 percent load and (right) a 100 percent load. SOURCE: ANL (2009).

FIGURE 4-19 Percentage of braking energy recovered at the wheels under (left) a 50 percent load and (right) a 100 percent load. SOURCE: ANL (2009).

FIGURE 4-20 Percentage average engine efficiency of conventional and hybrid trucks for (left) a 50 percent load and (right) a 100 percent load on standard cycles. SOURCE: ANL (2009).

cant improvement since start-stop is the only main feature in it to aid in engine efficiency. The full hybrid gains in the transient and urban cycles as the engine can be completely switched off in electric-only mode.

The drive cycle or duty cycle plays an important role in determining the following: type of hybrid technology to be used, level of hybridization and sizing of components, and power management strategy.

Since the HHDDT cycle is short and does not represent the real highway cycle, a new cycle was formulated with original acceleration followed by a cruising part and finally a deceleration part. Figure 4-21 shows how the new drive cycle was obtained from the HHDDT cycle. The results of removing stops from the HHDDT cycle have been grouped in Figure 4-22. In every other bar the hybrids are compared with the conventional vehicle, hence the values are greater.

When the breaks are removed from the highway cycle, there is a significant drop in fuel savings in the hybrid con-