Environmental Engineering Reference
In-Depth Information
Table 4.3 Manual transmission gear step selection by
accelerated geometric ratio
Gear select
Low
Mid
High
6
x
6
5
4
3
2
1
z
x
0.7
0.861
1.178
1.709
2.59
4.07
The gear shift ratio coverage,
G
src
=
z
6
/
z
1
= 5.81, which is typical of a 6-speed
box. When this transmission is used in a vehicle driveline (e.g. 3.0-4.0 L V6), the
engine torque and power are mapped to the road load as shown in Figure 4.2.
Vehicle tractive effort and road load
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
0
0
50
100
150
200
250
300
350
Vehicle speed (kph)
Figure 4.2 Driveline matching with downsized V6 and 6-speed transmission
In Figure 4.2 the tractive effort is shown as the composite of the engine torque
versus speed overlaid on the vehicle speed and road load plots. The steps in engine
supplied torque as magnified by the transmission gear selected are shown as being
stepped by the geometric gear step ratio. At high vehicle speeds where the torque
envelope is stretched over a wider speed region, the smaller gear steps act to
minimize the abruptness of a shift.
Road load curves for 0% up to 7% grade and finally 30% grade are super-
imposed on the chart in Figure 4.2. The intersection of the traction hyperbola with
the corresponding road load determines the top vehicle speed on grade.
Example 2:
Using (4.4), find the approximate gear scaling factor,
z
0
, the geometric
ratio,
r
, and the acceleration factor,
a
, for the Camaro SS with Hydramatic 6L80
automatic and the Aisen Warner AY6 manual transmissions.
