Environmental Engineering Reference
In-Depth Information
Chapter 11
Hybrid vehicle test and validation
Development of hybrid propulsion systems requires knowledge of the vehicle
attributes in terms of mass, frontal area, tyre rolling radius and rolling resistance,
plus its aerodynamic drag coefficient. The accepted procedure for obtaining these
data comes from vehicle coast down testing. This chapter illustrates the coast down
process on two very different vehicles seen often on highways in North America
and Europe: the sports utility vehicle (SUV) and tractor-trailers (semis).
Before engaging in coast down testing it is necessary to know the vehicle mass,
frontal area and tyre rolling radius. The procedure to obtain these data, if not known
from manufacturer's specifications, is to weigh the vehicle and calculate the frontal
area and tyre rolling radius according to (11.1):
A
¼
c
a
HW
(m
2
,m)
ð
11
:
1
Þ
1
;
609
2
p
N
w
r
w
¼
where the vehicle track,
W
, and height from ground to roof,
H
, are used to approximate
the frontal area. The factor
c
a
(~0.9) is a coefficient in (11.1) to make provision for
nominal ground clearance and aerodynamic styling (body contours). The tyre rolling
radius is best obtained by noting the number of revolutions made per set distance, such
as a kilometre or mile. In (11.1) the number of tyre revolutions per mile is used to
compute the dynamic rolling radius on the road surface for which the vehicle attributes
are being evaluated. The static rolling radius has been described earlier in this topic,
and will be compared here to dynamic rolling radius to validate the factor of 0.95-0.99
used in that discussion. The procedure for the derivation of tyre dynamic rolling radius
from the tyre manufacturer code is repeated here for clarity. For example, the P235/70
R16 tyre manufactured by Continental Group has a section width of 235 mm, an aspect
ratio (section height as percentage of section width of 70%) and a rim diameter of 16
00
(406.4 mm). Using these data the dynamic rolling resistance is calculated using (11.2):
c
r
ð
d
rim
þ
2
ð
70
=
100
Þ
w
s
Þ
2
r
w
¼
ð
11
:
2
Þ
where
d
rim
is the rim diameter (convert inches to mm),
w
s
is the tyre section width
in mm and
c
r
is a coefficient to down adjust static rolling radius to dynamic rolling
