Environmental Engineering Reference
In-Depth Information
duration of braking events illustrated in Figure 1.20, it is possible to then build a
histogram of hybrid propulsion and braking energy. The energy distribution over
the same FUDC has been included in Figure 1.22.
60
Percent time
spent at
power level
Percent energy
at power level
50
40
30
20
10
0
-10
-20
-20
-10
0
10
20
30
Power (kW)
Figure 1.22 Distribution of power and energy in a drive cycle
Two things should now be clear from Figure 1.22: (1) a 20 kW regeneration
capability captures virtually all of the available kinetic energy of a mid-sized pas-
senger vehicle, assuming of course that the hybrid M/G is on the front axle; and
(2) vehicle tractive effort is supplied with a motoring power level of 30 kW. This
seems to indicate that hybrid traction power plants in excess of 30 kW are neces-
sary primarily to deliver acceleration performance customers expect. More will be
said of this power plant sizing in later chapters. One example of the mild hybrid
discussed here, the Ford Motor Co. P2000 low storage requirement (LSR) vehicle,
is described in more depth in Reference 11. The P2000 is a 2,000 kg, 5-passenger
mid-sized sedan with a 1.8 L CIDI engine and an 8 kW S/A rated at 300 Nm of
peak cranking torque from a 300 V NiMH battery pack. The vehicle is low storage
because the battery pack energy is less than 1 kWh.
It was noted above that real world customer usage is modelled with a revised
drive cycle known as ATDS. This cycle has much more aggressive acceleration and
deceleration than other standard drive cycles and yields more accurate fuel econ-
omy predictions for North American drivers. An illustration of the ATDS cycle is
given in Figure 1.23, where acceleration (and deceleration levels are in ft/s
2
) and
vehicle speed is in mph. Also, this drive cycle is a combined city-highway in the
proportion of 2:1 to better reflect real world usage.
In Figure 1.23 the acceleration axis is mid-chart at 0 with extremes of
25 ft/s
2
.
Vehicle speed has its axis at the bottom of the plot and registers 10 mph/division up
to 80 mph. The vehicle speed trace shown in Figure 1.23 is representative of most
city stop and go driving patterns in which the vehicle accelerates to some modest
speed and then encounters either other traffic or the next stop light. The highway
portion of the vehicle speed trace is representative of more restricted access high-
ways such as city beltways or expressway driving.
