Not only are these events the most prevalent deceleration events
encountered during most driving styles, they also offer the
opportunity to recapture braking energy, which allows for
i
mproved fuel economy.
Within the context of these negative tractive force events,
two distinct vehicle behaviors can be observed for
conventional vehicles. Figure 2 shows the fueling rates for
two vehicles during a fairly nominal deceleration event from
the UDDS cycle. The Ford Fusion shown in blue shows
behavior that would be consistent with the estimated
deceleration fuel rate discussed in Equation 1. In contrast, the
VW Jetta TSI shown in red shows
no fueling during the
entire deceleration event. This deceleration without engine
fueling is frequently referred to as
Decel. Fuel Cut-off
(DFCO)