Environmental Engineering Reference
In-Depth Information
10
9
Avg. = 8.1
HEV
8
Mild
Medium
7
Avg. = 6.74
6
Non-HEV
5
4
3
2
1
0
800
900
1,000
1,100
1,200
1,300
1,400
1,500
1,600
Vehicle weight (kg)
Peak engine + electric ratio
Engine-only ratio
Non-HEV engine-only
Figure 1.18 Peak power to weight of hybrids versus conventional vehicles
(Delphi Automotive, with permission)
size relative to curb weight. In other words, the hybrids retain the size and cabin
volume of their heavier CVs but are far lighter. The Honda Insight is the lowest
mass vehicle in the study at 890 kg (virtually the PNGV mass target).
In Figure 1.18 the three hybrid vehicles labelled mild are the DaimlerChrysler
ESX3, Ford Prodigy and Honda Insight. Each of these vehicles has a relatively
small electric machine mounted to the engine crankshaft. The two vehicles labelled
medium hybrids are the GM Precept and Toyota Prius. These latter two hybrids
have a twin M/G architecture and very different transmissions than the mild
hybrids. The mild hybrids have downsized engines, but not nearly so downsized as
the medium hybrids when compared to their CV engine-only points. In fact, the
mild hybrids in Figure 1.18 have engine displacements relatively close to three of
the CVs listed as non-HEVs.
A convenient metric for ICE powered vehicles to meet performance targets is
an engine peak power rating of 10 kW/125 kg of vehicle mass. This is roughly 8
kW/100 kg and close to the trend line drawn in Figure 1.18 for the CVs. The
hybrids, on the other hand, are able to meet performance targets with significantly
lower rated engines plus electric power of 6.74 kW/100 kg. The difference is 1.36
kW/100 kg. Recalling from Table 1.3 that the Prius (rightmost of the five hybrid
vehicle points in Figure 1.18) has a mass of 2,765 lb (1,256 kg) and a rated engine
power of 70 hp (52 kW), we calculate an engine plus electric power of
1
;
256
¼
84
:
6
kW
100 kg
E
þ
P
¼
6
:
74
ð
1
:
1
Þ
E
E
þ
P
¼
33
84
:
6
¼
39%
E
P
¼
