Vehicle Dynamics CEE 320 Steve Muench Outline Resistance Aerodynamic Rolling Gra
Farrow, Jeff, Features Editor has reference to this Academic Journal, PHwiki organized this Journal Vehicle Dynamics CEE 320 Steve Muench Outline Resistance Aerodynamic Rolling Grade Tractive Ef as long as t Acceleration Braking Force Stopping Sight Distance (SSD) Main Concepts Resistance Tractive ef as long as t Vehicle acceleration Braking Stopping distance
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Resistance Resistance is defined as the as long as ce impeding vehicle motion What is this as long as ce Aerodynamic resistance Rolling resistance Grade resistance Aerodynamic Resistance Ra Composed of: Turbulent air flow around vehicle body (85%) Friction of air over vehicle body (12%) Vehicle component resistance, from radiators in addition to air vents (3%) from National Research Council Canada Rolling Resistance Rrl Composed primarily of Resistance from tire de as long as mation (90%) Tire penetration in addition to surface compression ( 4%) Tire slippage in addition to air circulation around wheel ( 6%) Wide range of factors affect total rolling resistance Simplifying approximation:
Grade Resistance Rg Composed of Gravitational as long as ce acting on the vehicle For small angles, g W g Rg Available Tractive Ef as long as t The minimum of: Force generated by the engine, Fe Maximum value that is a function of the vehicles weight distribution in addition to road-tire interaction, Fmax Tractive Ef as long as t Relationships
Engine-Generated Tractive Ef as long as t Force Power Vehicle Speed vs. Engine Speed Typical Torque-Power Curves
Maximum Tractive Ef as long as t Front Wheel Drive Vehicle Rear Wheel Drive Vehicle What about 4WD Diagram Ra Rrlf Rrlr ma W g Fbf Fbr h h lf lr L g Wf Wr Vehicle Acceleration Governing Equation Mass Factor (accounts as long as inertia of vehicles rotating parts)
Example A 1989 Ford 5.0L Mustang Convertible starts on a flat grade from a dead stop as fast as possible. Whats the maximum acceleration it can achieve be as long as e spinning its wheels = 0.40 (wet, bad pavement) 1989 Ford 5.0L Mustang Convertible Braking Force Front axle Rear axle Braking Force Ratio Efficiency
Braking Distance Theoretical ignoring air resistance Practical Perception Total For grade = 0 Stopping Sight Distance (SSD) Worst-case conditions Poor driver skills Low braking efficiency Wet pavement Perception-reaction time = 2.5 seconds Equation Stopping Sight Distance (SSD) from ASSHTO A Policy on Geometric Design of Highways in addition to Streets, 2001 Note: this table assumes level grade (G = 0)
SSD Quick in addition to Dirty Acceleration due to gravity, g = 32.2 ft/sec2 There are 1.47 ft/sec per mph Assume G = 0 (flat grade) V = V1 in mph a = deceleration, 11.2 ft/s2 in US customary units tp = Conservative perception / reaction time = 2.5 seconds Primary References Mannering, F.L.; Kilareski, W.P. in addition to Washburn, S.S. (2005). Principles of Highway Engineering in addition to Traffic Analysis, Third Edition). Chapter 2 American Association of State Highway in addition to Transportation Officals (AASHTO). (2001). A Policy on Geometric Design of Highways in addition to Streets, Fourth Edition. Washington, D.C.
Farrow, Jeff Features Editor
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