Why Is Fuel Economy Important - Literature review Example

In the figure above, the rolling resistance appearing at the tire-road interface is shown as Curve A and is almost independent of speed. The aerodynamic resistance is shown as Curve B and it is proportional to the square of velocity. Curve C, which is the sum of Curve A and Curve B, is defined as the road load resistance and it represents the total force necessary for maintaining a steady speed on an even road. The product of the weight of the vehicle with the sine of the slope of the road is the grade-resistant force, different values of which correspond to different values of inclination, as shown in the figure under discussion. The percent slope, called grade is the tangent of the road grade angle. A schematic representation of the tractive force which is generated at the rear wheels of an internal combustion engine-powered vehicle with a three-speed standard shift transmission is also shown in the above diagram. When the transmission is changed to a higher gear, there is a decrease in speed reduction ratio and a consequent decrease in transmission output torque and hence the tractive force also comes down. The force available for driving the vehicle forward is the difference between the tractive force and the road load resistance and is called the free-tractive effort. The combination of the vehicle resistance forces along with the combined performance of the engine and power drive train gives the ultimate fuel economy potential of an IC engine-powered vehicle while the total of the resistance forces at any operating point has to match the tractive force delivered by the drive train (Hilliard & Springer, 1984, p.9).
The aerodynamic drag or the air drag of an automobile is decided by the shape of the vehicle and its frontal area and is proportional to the square of its speed. The resistance offered by air can be expressed as (Pundir, 2008, p.18):
F_w=C_w A (ρV^2)/2
where:
F_w is the air resistance
A is the frontal area of the vehicle
ρ is the air density
V is the vehicle speed
C_w is the air drag coefficient