|
This book is essentially Part 1 of the Fuel Efficiency Book. It is an introduction to the forces that resist the motion of a vehicle for any driving condition, and define its Road Load. It is offered separately as this subject is basic to other automotive subjects such as performance, dynamics, steering and suspension, braking, etc. |
|
TABLE OF CONTENTS
VEHICLE MOTION RESISTANCE FORCES
ROLLING RESISTANCE Tire rolling resistance Pneumatic tire construction Tire spring rate Tire footprint Tire crawl Mechanisms of tire rolling resistance Tire developed length Tire revolutions per mile Tire effective radius Re Tire elasticity and hysteresis Factors that affect tire rolling resistance Tire speed Critical speed and standing waves Force variations Inflation pressure and the road surface Tire diameter Rolling resistance coefficient “f” Road surface roughness Water, slush and snow Tire section Distribution of the energy loss Tire load and speed ratings Magnitude of the tire resistance forces Tire friction and tractive effort limits Road adhesion coefficient μ (mu) Tire slip Tractive force vs. longitudinal slip
MECHANICAL ROLLING RESISTANCE The power-on and power-off conditions Hypoid gearset friction loses Universal and constant velocity joints Universal cross type joints Double cardan joints CV joint assemblies Ball and trunnion Tripod joints
AIR RESISTANCE Properties of air Standard air Air resistance Components of air resistance Form drag Internal flow drag Lift drag Interference drag Surface drag The air resistance force RA Calculation of the air resistance force Effect of air density on RA Vehicle frontal area (A) Drag coefficient (Cd) Range of Cd values for ground vehicles CdA Simplified expression for RA Lateral wind forces – yaw angle ϕ (epsilon) Center of pressure CP pitching, yawning and rolling moments |
|
GRADE RESISTANCE RG Measurements of road grades Range of road grades in the USA Calculation of grade resistance force The downhill grade pull problem
INERTIA RI Inertia force defined Determination of acceleration level Determination of vehicle mass Effective vehicle mass Mass factor γ (gamma) Determination of inertia force
THE VEHICLE ROAD LOAD MAP Adding boundaries to the road load map Road loads in term of horsepower
DRIVE TORQUE VS. TRACTIVE EFFORT REQUIREMENTS Tractive effort requirements vs. vehicle speed Ideal torque/power characteristics of automotive powerplants Typical torque/power characteristics of gasoline engines Typical torque/power characteristics of Diesel engines
ROLE OF TORQUE/SPEED MODIFYING TRANSMISSION Gear ratio selection Geometric series Advantages of geometric series
THE VEHICLE PERFORMANCE ENVELOPE Vehicle performance constraints & Boundaries The level, hard surfaced road boundary Maximum speed The Tractive Effort boundary Defining tractive effort limitations The “Right Side” boundary Performance objectives/boundaries set by the vehicle engineer The “Left Side” boundary Gradeability and acceleration requirements Constant maximum horsepower Vehicle power-on and power-off conditions
THE VEHICLE PERFORMANCE ENVELOPE Vehicle performance constraints & Boundaries The level, hard surfaced road boundary Maximum speed The Tractive Effort boundary Defining tractive effort limitations The “Right Side” boundary Performance objectives/boundaries set by the vehicle engineer The “Left Side” boundary Gradeability and acceleration requirements Constant maximum horsepower Vehicle power-on and power-off conditions |
