Problem:

The gear ratios of a 5-speed manual transmission are given as 1" (3.25), 2nd (1.96), 3rd (1.24), 4th (0.75), 5th

(0.58), final drive (3.94). The engine fuel map is shown below, where the horizontal axis is the engine RPM

and the vertical axis is the engine torque (ft.lb). The transmission is used for a FWD car with the following

data:

Front axle weight: 1450 lbs

Center of gravity height: 14 inch

Air drag coefficient: 0.30

Tire radius: 10.0 in.

Powertrain efficiency: 0.93

Rear axle weight: 1250 lbs

Wheel base: 102 in.

Frontal projected area: 21.00 square feet

Roll resistance coefficient: 0.02

Road adhesion coefficient: 1.0

a) How much the engine speed will drop (in terms of RPM) when a 3-4 upshift is made at a vehicle speed

of 40 mph.

b)

Determine the gas mileage when the car is cruising at a contact speed of 65 mph on level ground in 5th

gear and in 4th gear respectively.

c)

As shown in the fuel map, the point (2300, 58) is approximately the most fuel efficient point.

Determine the gear ratio if the engine is to operate at the status defined by this point and the

corresponding vehicle speed.