|
Vehicle 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 Speed Critical speed and standing waves Force variations Inflation pressure and the road surface Diameter Rolling resistance coefficient “f” Road surface roughness Water, slush and snow 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
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 Aerodynamic 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 |
|
Determination of Vehicle Road Loads Kinetic Energy K energy of motion Coastdown process & sequence Determination of resistance forces for a speed interval Determination of average decelerations for a speed interval Choosing the coastdown speed intervals Maximum and minimum coastdown speeds Speedometer calibration Vehicle weight Road surface requirements Plotting the road loads Road Loads in Terms of Work and Power
The vehicle road load map Adding boundaries to the road load map Road loads in term of horsepower
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
Basics of Energy Conversion and Fuel Efficiency of Vehicle Powerplants The US Vehicle Park Hydrocarbon fuels Combustion of hydrocarbon fuels and air mixtures Heat of Combustion Advantages and disadvantages of common automotive fuels Flammability limits for gasoline/air mixtures Heat release vs. fuel/air ratios Throttling the torque/power output of gasoline engines Throttling the torque/power output of diesel engines
Fuel Efficiency of Internal Combustion Engines Ideal torque/power output characteristics of automotive powerplants Torque/power characteristics of gasoline engines Torque/power characteristics of diesel engines Effect of torque/speed modifying transmissions Brake mean effective pressure (bmep) Brake specific fuel consumption (bsfc) BSFC speed/load contours (or islands) Full-throttle bsfc Part-throttle bsfc Torque/power requirements to meet the road load demands Electric vehicles Gas-electric hybrid powertrain vehicles Batteries The turbocharged powertrain solution
APPENDICES · Conversion factors · Torque/power speed relationships · SAE vehicle axis system · SAE tire axis system |
