CEE 320 Spring 2008 Vehicle Dynamics Example Problems

CEE 320 Spring 2008 Problem 2.2 A vehicle manufacturer is considering an engine for a new sedan (C D = 0.25, A f = 17 ft 2 ). The car will be tested at 100 mph maximum speed on a concrete paved surface at sea level (ρ = slugs/ft 3 ). The car currently weights 2100 lb, but the designer selected an under- powered 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?

CEE 320 Spring Answer

CEE 320 Spring 2008 Problem 2.8 A car is traveling on a paved road with C D = 0.35, A f = 21 ft 2, W = 3000 lb, ρ = slugs/ft 3. Its engine is running at 3000 rpm and is producing 250 ft-lb of torque. The car’s 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 car’s maximum acceleration be under these conditions on a level road? (assume the available tractive effort is the engine-generated tractive effort)

CEE 320 Spring 2008 Example 1 You are driving a 1989 Ford 5.0L Mustang Convertible up a snow- covered Crystal Mountain Blvd. on your way to go snowboarding with 3 friends (120 lbs each). Traffic on the road forces you temporarily stop on a 6% uphill grade. Assuming the coefficient of road adhesion is 0.15 (no chains), can you get moving again? If yes, How? 1989 Ford 5.0L Mustang Convertible 4000 rpm 3200 rpm Curb Weight3640 Weight DistributionFront 57% Rear 43% Wheelbase100.5 in Tire SizeP225/60R15

CEE 320 Spring 2008 Example 2 Same situation but now you are in a 1993 Honda Civic EX sedan rpm 4800 rpm Curb Weight2520 Weight DistributionFront 59% Rear 41% Wheelbase103.2 in Tire SizeP185/70R Honda Civic EX sedan

CEE 320 Spring 2008 Example 3 Same situation but now you are in a 2003 Honda Element EX 4WD. Does the Element have to use its on-demand 4WD? 2003 Honda Element EX 4WD 5500 rpm 4500 rpm Curb Weight3595 Weight DistributionFront 56% Rear 44% Wheelbase101.4 in Tire SizeP215/60R16

Mass factor (γ b )1.04 Gravity (g)32.2 ft/sec 2 Coefficient of road adhesion (μ)0.90 (good, dry) Coefficient of rolling resistance (f rl )0.012 Grade (θ)0 (flat) Air density (ρ) slugs/ft 3 ValuePalmer (Caravan) Turkiyyah (X5) Mahoney (Explorer) Mackenzie (Focus) Arduino (Accord) Weight3764 lb4519 lb4078 lb2677 lb2855 lb Drag coefficient (C D ) Braking efficiency ( η b )0.95 Vehicle height68.9”67.2”68.4”56.8”55.1” Vehicle width78.6”73.7”70.2”66.7”70.1” Max torque210 ft-lb (4000 rpm) 315 ft-lb (2600 rpm) 237 ft-lb (3000 rpm) 133 ft-lb (4500 rpm) 139 ft-lb (4000 rpm) Max power180 hp (5000 rpm) 324 hp (5200 rpm) 203 hp (5250 rpm) 136 hp (6000 rpm) 130 hp (5200 rpm) Gas Mileage18/2413/1716/2126/3523/31

CEE 320 Spring 2008 Professor Braking Distance Braking from 60 mph to a stop –Rick Palmer (Dodge Caravan) –George Turkiyyah (VW Golf) –Joe Mahoney (Ford Explorer) –Pedro Arduino (Honda Accord) –Steve Muench (Honda Element)

CEE 320 Spring 2008 Professor Max Acceleration Same contenders –Scott Rutherford (Lexus RX 300) –George Turkiyyah (VW Golf III) –Laura Lowes (Toyota Forerunner Ltd.) –Joe Mahoney (Ford Explorer Sport) –Steve Muench (Honda Element)

Driveline efficiency ( η d )85% Gravity (g)32.2 ft/sec 2 Coefficient of road adhesion (μ)0.90 (good, dry) ValueRutherford (RX 300) Turkiyyah (Golf) Lowes (4Runner) Mahoney (Explorer) Muench (Element) 4WD?YESNOYES Weight4065 lb3174 lb4055 lb4078 lb3578 lb Wheel base (L)103”98.9”109.8”101.8”101.4” lrlr 58.8”62.3”56.8” lflf 44.2”36.6”44.6” h27”20”28”30” Gear reduction ratio Tire radius16”15”16” Maximum torque242 ft-lb (3600 rpm) 122 ft-lb (2600 rpm) 282 ft-lb (3800 rpm) 237 ft-lb (3000 rpm) 161 ft-lb (4500 rpm) Maximum power230 hp (5600 rpm) 115 hp (5200 rpm) 245 hp (5200 rpm) 203 hp (5250 rpm) 160 hp (5500 rpm)