Environmental Engineering Reference
In-Depth Information
Having calculated the vehicle's average velocity and deceleration over the two
measurement intervals provides the information needed to solve the road load
expressions simultaneously. Writing the road load expression for both intervals,
and noting that vehicle mass can also be obtained from the manufacturer's model
plate that is riveted to the vehicle's B-pillar, one obtains for the high speed test
data:
m
v
a
1
¼
m
v
gR
0
þ
0
:
5
r
C
d
AV
1
ð
N
Þ
ð
11
:
7
Þ
The road load expression for the low speed test data is given by (11.8):
m
v
a
2
¼
m
v
gR
0
þ
0
:
5
r
C
d
AV
2
ð
N
Þ
ð
11
:
8
Þ
The drag coefficient is easily obtained by subtracting (11.8) from the high
speed test data (11.7) as follows:
2
m
v
ð
a
1
a
2
Þ
r
A
ð
V
1
V
2
Þ
C
d
¼
ð
#
Þ
ð
11
:
9
Þ
Even though the high speed test data are dominated by aerodynamic drag, it is
more accurate to separate out the rolling resistance component as done in (11.9).
The coefficient for static rolling resistance,
R
0
, is obtained in a similar fashion to
(11.9). First, multiply (11.7) by
a
2
, then multiply (11.8) by
a
1
and add the two.
Solving for
R
0
:
a
2
V
1
a
1
V
2
g
ð
V
1
V
2
Þ
R
0
¼
(kg
=
kg)
ð
11
:
10
Þ
The coefficient of static rolling resistance has units of tangential force (N) to
normal force (N). Rolling resistance can be computed for the entire vehicle (all four
tyres), by axle if the front and rear loading differ from 50 to 50, which is generally
the case, or by individual corner (one-fourth of car mass).
In the remaining sections some specific vehicle testing is performed to illus-
trate the procedure and the impact of trailer towing on propulsion power.
11.2 Sports utility vehicle test
The Ford Motor Co. Escape SUV is tested for rolling resistance and aerodynamic
drag coefficient. The Escape hybrid based on a single mode electronic continuously
variable transmission (eCVT) has been in production since June 2004. The eva-
luation Escape is equipped with a 2.4 L V6 engine, 4-speed automatic transmission
and automatic four wheel drive. Specification data are listed in Table 11.1.
