Environmental Engineering Reference
In-Depth Information
shift ratio coverage (ratio of low to high gear) for constant power speed range
decreases dramatically.
In summary, Figure 3.2 highlights a very important fact in propulsion system
sizing and driveline matching: As power plant rating increases for the same appli-
cation, the need for large gear shift ratio coverage decreases, fewer gear steps are
necessary, and power plant torque is sufficient to meet vehicle acceleration targets to
very substantial speeds. Figure 3.3 illustrates the acceleration performance for vehi-
cles equipped with these large engines. Data for Figure 3.3 are taken from a vehicle
simulation using fourth-order Runge-Kutta integration of the net tractive force
available at the driven wheels while accounting for all road load conditions.
Figures 3.2 and 3.3 convey a strong message about setting vehicle propul-
sion targets. For the conventional vehicle listed and for three very different high
performance engines, it can be seen that vehicle acceleration is only loosely
connected to gross power plant rating but very intimately tied to powertrain
matching. A huge engine does not even require a transmission - simply connect it
to the wheels and it has sufficient torque to launch the vehicle with more than
202.807781
Vehicle acceleration
300
225
1
0.447
V
n
,1
150
75
0
0
0
10
20
30
40
V
n
,0
50
60
70
80
0
80
(a)
Time (s)
Vehicle acceleration
165.86241
200
150
1
0.447
V
n
,1
100
50
0
0
0
10
20
30
40
50
60
70
80
V
n
,0
0
80
(b)
Time (s)
Figure 3.3 Vehicle acceleration performance for three engine types: (a) vehicle
with V10 engine, 0-60 time 8.6 s and maximum speed 200 mph;
(b) vehicle with V12 engine, 0-60 time 7.2 s and maximum speed
162 mph; (c) vehicle with V16 engine, 0-60 time 8.4 s and maximum
speed 260 mph
