Environmental Engineering Reference
In-Depth Information
According to (1.1), the Prius has 84.6 kW peak electric plus engine power and
52 kW of engine-only power (Table 1.3), leaving 32.6 kW of electric M/G power.
The second part of (1.1) shows that this corresponds to an electric fraction of 39%.
The 2010 Prius IV, for example, has a 1.8 L, L4 engine rated 73 kW at 5,200 rpm, a
main electric traction motor (MG1) rated 60 kW and a battery pack (NiMH) rated
27 kW. The Toyota specification on the Prius IV shows a net power of 100 kW. The
Prius IV net power is therefore peak engine power plus peak battery power or
P
net
=
P
e
+
P
b
= 73 kW + 27 kW = 100 kW. The electric fraction, according to (1.1), is 27/
(73+27) = 27%. This is a distinct case of lower electrification compared to the 2003
Prius. In Chapter 2 the electronic continuously variable transmission (eCVT) used in
the Prius hybrids will be discussed. For the case at hand the traction motor, MG1, is
rated 60 kW because it must have peak capability to sum peak battery power and
peak generator power. The Prius single mode eCVT splits engine power to the
generator and circulates this power electrically via back-to-back power inverters to
the traction motor. This traction motor sums circulating electric power with battery
power and therefore must be rated for this.
Most internal combustion engines develop approximately 50 kW/L of dis-
placement. The electric fraction of 39% for the Toyota Prius means that 32.6 kW of
engine power has been offset by electric propulsion. A 32.6 kW reduction in engine
power means that the ICE power plant may be reduced by 0.65 L. In other words,
the production Camry's 2.4 L, 157 hp engine could be downsized to a 1.75 L
engine, all things equal. Weight reduction permits further reduction to a production
1.5 L engine. The classical relation of engine thermal efficiency to weight reduc-
tion [4] is shown in Figure 1.19 where the design space has been highlighted.
Power plants capable of even 40% thermal efficiency include CIDI
5
engines
50
40
CIDI
X
30
20
10
X
FCEV
0
30
40
50
60
Power plant thermal efficiency (%)
Figure 1.19 Design space of vehicle weight reduction versus power plant thermal
efficiency
5
Compression Ignition Direct Injected (CIDI) or, as commonly known, a diesel engine.
