Vehicle Dynamics Example Problems - University of Washington
Vehicle Dynamics Example Problems Example problems Calculate value of resistive forces Aerodynamic Rolling Gravity
Power required to overcome resistive forces Problem 2.1 A new sports car has a drag coefficient of 0.29 and a frontal area of 20 ft2, and is traveling at 100 mi/h. How much power is required to overcome aerodynamic drag if =0.002378 slugs/ft3?
Problem 2.2 A vehicle manufacturer is considering an engine for a new sedan (C D = 0.25, Af = 17 ft2). The car will be tested at 100 mph maximum speed on a concrete paved surface at sea level ( = 0.002378 slugs/ft3). The car currently weights 2100 lb, but the designer selected an underpowered engine because he did not account for aerodynamic and rolling resistances. If 2 lb of additional vehicle weight is added for each unit of horsepower needed to overcome the neglected resistance, what will be the final weight of the car if it is to achieve its
100 mph speed? Balance forces Calculate available tractive effort Maximum tractive effort Engine generated tractive effort Acceleration Calculate maximum speed
Available engine power Resistive forces Maximum speed Problem 2.8 A car is traveling on a paved road with CD = 0.35, Af = 21 ft2, W = 3000 lb, = 0.002378 slugs/ft3. Its engine is running at 3000 rpm and is producing 250 ft-lb of torque. The cars gear reduction ratio is 3.5 to 1, driveline efficiency is 90%, driveline slippage is 3.5%, and the road-wheel
radius is 15 inches. What will the cars maximum acceleration be under these conditions on a level road? (assume the available tractive effort is the engine-generated tractive effort) Problem 2.10 A 2500-lb car has a maximum speed of 150 miles/hour with 14 inch radius wheels, a gear reduction of 3 to 1, and a driveline efficiency of 90%. It is known that at the
cars top speed the engine is producing 200 ft-lb of torque. If the cars frontal area is 25 ft2, what is its drag coefficient? Braking and stopping Braking Braking force Brake force ratio
Theoretical stopping distance Practical stopping distance Driver perception/reaction Problem 2.20 A driver is traveling at 110 miles/hour down a 3% grade on good, wet pavement. An accident investigation team noted that braking skid marks started 590 ft before a
parked car was hit at an estimated 55 mi/h. Ignoring air resistance, and using theoretical stopping distance, what was the braking efficiency of the car? Problem 2.23 A car is traveling at 75 mi/h down a 3% grade on poor, wet pavement. The cars braking efficiency is 90%. The brakes were applied 300
ft before impacting a object. The car had an antilock braking system, but the system failed 200 ft after the brakes had been applied (wheels locked). What speed was the car traveling at just before it impacted the object? (Assume theoretical stopping distance, ignore air resistance, and let frl=0.015.)
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