Environmental Engineering Reference
In-Depth Information
radius is
e
= 0.955. Equation 3.2 defines the derivation of section height from the
given section width and tyre aspect ratio:
r
w
¼
0
:
5
eð
OD
rim
þ
2
H
section
Þ
ð
3
:
1
Þ
c
100
W
section
H
section
¼
ð
3
:
2
Þ
From the data given in Table 3.3 and from (3.1) and (3.2) the tyre rolling radius
is found to be
r
w
= 284.6 mm. For the given data the 1.8 L Zetec is modelled as
a torque source with breakpoint at 85 kW corresponding to a vehicle speed of
26.2mph according to the definitions in (3.3), where driveline efficiency is the
composite of automatic transmission efficiency, propeller shaft plus CV joints, and
final drive, all approximately equal to 0.85:
h
dl
P
e
G
r
T
e
w
a
¼
G
r
¼
z
1
z
FD
ð
3
:
3
Þ
h
dl
¼
h
AT
h
prop
h
FD
w
a
r
w
0
:
447
V
¼
When these data are plugged into the vehicle dynamic simulation model to
account for driveline tractive effort and road load, the chart shown in Figure 3.4
results. In this chart aerodynamic drag is taken at the standard 200 m elevation, still
air and level grade.
Vehicle acceleration
111.085664
150
112.5
1
0.447
V
n
,1
75
37.5
0
0
0
10
20
30
40
50
60
70
80
0
V
n
,0
80
Time (s)
Figure 3.4 Vehicle performance on level grade, no headwind and 500 W
accessory load
In Figure 3.4 the vehicle accelerates to 60mph in just under 10 s, very close to
the listed elapsed time. The vehicle's maximum speed is realistic at 112mph with
the driver as the only occupant.
