Problem

A FWD vehicle has the following data:

Front axle weight: 1750 lb

Center of gravity height: 15 in.

Air drag coefficient: 0.30

Tire radius: 11.40 in.

Max. power @6000 RPM: 138 HP

Powertrain efficiency: 0.96

Rear axle weight: 1200 lb

Wheelbase: 105 in.

Frontal projected area: 22.0 square feet

Roll resistance coefficient: 0.02

Max. torque @4500 RPM: 132 ft.lb

Final drive ratio: 3.143

A six-speed manual transmission is used for the vehicle and the gear ratios from 1st to

4th gears are: 1st gear (3.92), 2nd gear (2.76), 3rd gear (1.85), 4th gear (1.35). The engine

WOT output plot is as given in Figure 1.3.

a) The vehicle runs in the 5th gear at a speed of 55 mph with the engine speed at 2450

RPM. The driver then makes a 5-6 upshift and the engine RPM drops by 500 RPM

immediately after the shift. Determine the 5th and the 6th gear ratios.

Automotive Engine Matching 27

b) Determine the engine torque and work done by the engine when the vehicle cruises

for 1.5 miles at a constant speed of 65 mph on level ground in the 6th and 5th gears

respectively.

c) The driver floors the gas pedal and simultaneously makes a 6-5 downshift when the

vehicle runs on a 3% slope at a speed of 65 mph. Determine the vehicle acceleration

immediately after the 6-5 downshift.

d) What is the steepest percentage slope the vehicle can negotiate at a speed of 70 mph?