Environmental Engineering Reference
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point made earlier in reference to Figure 10.11. The key finding now is that once
lithium ion chemistries trend below approximately 0 C, their power capability
becomes dramatically reduced just as it does in NiMH systems.
Two significant aspects of advanced chemistry battery performance are
revealed in these charts. First, vehicle fuel economy at 10 C is reduced to 50% of
its 25 C normalized value. Second, the ability of the battery pack to accept charge
decreases strongly for both cold and hot temperatures in the Camry and very dra-
matically for cold temperatures in the Escape hybrid. The differences in battery
pack performance between these two vehicles are not known, but speculated to be
associated with their respective thermal management systems and energy man-
agement strategies (EMS). Regardless, the fact remains that at cold temperature the
vehicle performance and economy will be dramatically restricted due to limitations
on the energy storage battery.
1.6
Poly. (Camry)
Poly. (Esc)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-15
-5
5
15
25
35
45
Battery (NiMH) temperature ( ç C)
350
Camry
Esc
300
250
200
150
100
50
0
-15
-5
5
15
25
35
45
Battery (NiMH) temperature (
ç
C)
Figure 10.12 Fuel economy and brake energy recuperation versus battery
temperature
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