Information Technology Reference
In-Depth Information
The energy consumed on a segment is given by an equation of the form:
E = Pt + Wd
(1)
Where:
E = The energy consumed
P = The power consumed by accessory loads
W = The work done on the vehicle based on distance traveled
t = time
d = distance traveled
Power is the sum of the time dependent terms consisting primarily of accessory loads.
A model is needed to predict those loads based on factors such as climate control
requirements, lighting requirements, windshield wipers, etc. Lacking that model we
use different levels of accessory loads to create scenarios.
The prior results demonstrate that speed and gradient are major factors in work,
and to a lesser extent the road type. We take work to be the sum of gradient factors B
and speed factors A. An equation for B is developed for each road type in Fig. 8
where s is the slope of the road in degrees.
The speed (V) component (C) of work is given by:
C = A
aero
V
2
+ B
aero
V + C
aero
(2)
Substituting (B+C) for W and A for P, energy consumption can be computed as:
E = At + (B+C)d (3)
The factors A
freeway
, C
freeway
, A
highway
, C
highway
, A
street
, C
street
, D are fit functions primari-
ly related to the road, and the factors A
aero
, B
aero
, C
aero
are fit factors related to the
aerodynamics of the vehicle.
This equation was plotted for a set of 150 routes generated at a mapping website
assuming no gradient. The results are plotted in Fig. 10 where it is seen that under
high accessory loads there is a minimum energy speed at about 20 MPH. In the case
where there is low accessory load the energy consumption appears to asymptotically
approach zero energy consumption. In fact, in the low accessory load cases there is
also an optimal energy consumption speed, but at a much lower speed than vehicles
are ordinarily driven.
Fig. 10.
The meta-model results applied to routes through 20 different cities in the US
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