Environmental Engineering Reference
In-Depth Information
BSA Street Rider data
Parameter
Description Rating
Parameter
Description
Rating
3S
1P
22 Ah
VRLA
Battery pack
48 V, 1 kWh Aerodynamic
C
d
(#)
0.32
Battery mass Kg
38
Rolling
resistance
R
0
(kg/kg)
0.008
Vehicle mass Kg
75
Rolling radius P205/50R16V (
r
w
)
0.203 m
A
f
(m
2
)
ICE power
kW
0.75
Frontal area
1.12
11.1 Vehicle coast down procedure
The coast down test procedure is now explained. Vehicle attributes of mass, frontal
area and tyre dynamic rolling radius have been explained in the previous section.
Vehicle test mass must be adjusted for occupant and cargo. In the coast down
testing reported below there are two occupants: a driver and a time keeper. Coast
down testing is necessary in order to extract the vehicle's aerodynamic drag coef-
ficient and tyre rolling resistance. By taking measurements of elapsed time between
two closely spaced speeds when the vehicle is rolling fast and again when the
vehicle has nearly stopped rolling, it is possible to determine these two coefficients
with a fair accuracy. Higher resolution could be obtained by wind tunnel testing, for
example, but coast down testing is a very accepted method.
During coast down the vehicle decelerates naturally according to its road load,
consisting primarily of aerodynamic drag at higher speeds and rolling resistance at
low speeds. The procedure used is to solve the simultaneous equations of road load
for the two distinct speed regimes as explained by a review of Figure 11.1. In this
figure the vehicle is shown to be travelling at some speed higher than the fastest test
speed,
V
a
1
, when it is shifted into neutral and allowed to coast. The test is per-
formed on a level road surface - asphalt in this case - and when the wind is calm.
The vehicle coasts through speeds
V
a
1
and
V
a
2
that are 5 to 10 kph apart,
resulting in an elapsed time of
t
1
seconds as noted by a stopwatch or data logger if
available. The vehicle continues to coast down through the second set of speeds,
V
b
1
and
V
b
2
, that are again 5 to 10 kph separated. From the measured data as shown
in Figure 11.1, the average speed in both the high and low speed test regimes is
calculated along with average acceleration in that interval. For this reason it is good
practice to keep the vehicle speed separation close, and not exceed 10 kph for the
measurement. The average velocity and acceleration are then
V
a
1
V
a
2
2
V
1
¼
(m
=
s)
ð
11
:
5
Þ
V
b
1
V
b
2
2
V
2
¼
