Environmental Engineering Reference
In-Depth Information
14
1st gear
2nd gear
3rd gear
4th gear
5th gear
6th gear
12
10
8
6
4
0
0
50
100
150
200
-1
speed [km*h ]
Fig. 8.1
Influence of the gear choice on the fuel consumption in a mid-size car
8.2 Operating Functions of the Propulsion
The most important operating functions of the propulsion system are:
• Starting and steering the vehicle;
• Interrupting the running engine;
• Changing the torque;
• Adjusting the speed of the driving wheels; and
• Operating the transmission system
0
s elements [
2
].
Not only the engine technology, and internal and external resistances, but also
the propulsion system significantly influences route fuel consumption:
:
RFC
ð
1
Þ
¼
fSFC
;
PE
ð
2
Þ
;
DR
ð
3
Þ
ð
8
:
1
Þ
(1)
RFC Route fuel consumption
(2)
Propulsion efficiency
(3)
Driving resistances
There is a strong relationship between the propulsion efficiency and resistances
while driving. Driving resistances mainly depend on the rolling, the air, the
acceleration, the slope and the brake resistance [
3
].
8.2.1 Gear Choice
Independently from the gear technology, fuel consumption can be reduced by
1-3% through increasing the number of gears due to increasing the transmission
ratio in the final gear because the operating point of the engine is thereby shifted
towards higher efficiency.
For example with 7/8 gears instead of 6 gears in an automatic transmission, fuel
savings of between 5 and 6% can be achieved (see Fig.
8.1
)[
4
].
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