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VEHICLE MOTION RESISTANCE FORCES (PART 1)
ROLLING RESISTANCE Tire rolling resistance Pneumatic tire construction Tire spring rate Tire footprint Tire crawl Mechanisms of tire rolling resistance 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
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
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
VEHICLE PROPULSION (PART 2)
The Internal Combustion Engine Electric and hybrid powerplants Other vehicle propulsion systems
DRIVE TORQUE 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
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VEHICLE PROPULSION FUELS Hydrocarbon fuels Alcohols Ethanol Methanol Corrosion considerations of alcohol The Brazilian alcohol program Heat of Combustion High and Low heating values Advantages and disadvantages of common fuels
IMPACT OF DISTRIBUTION/REFUELING INFRASTRUCTURE Transportation and distribution Alcohols Natural gas Shale gas/methane Electricity Hydrogen
COMBUSTION OF AIR/FUEL MIXTURES Stoichiometric air/fuel ratio Open – close loop air/fuel control Heat release vs. air/fuel ratio Flammability limits Burn rate Charge density Air/fuel ratio vs. exhaust emissions
BASIC CHARACTERISTICS OF RECIPROCATING ENGINES The slider-crank mechanism Gas pressure vs. crank arm torque output Actual pressure and crank arm torque output Spark advance
FOUR STROKE OTTO CYCLE Valve events Pressure-time diagram for gas engine Pressure-volume diagram for gas engine Throttling the gasoline engine Fuel metering Pumping loses due to throttling
FOUR STROKE DIESEL CYCLE Throttling the diesel engine Pressure-time diagram for the diesel engine Pressure-volume diagram for the diesel engine
OVER-EXPANDED/MODIFIED ATKINSON CYCLE Pressure-volume diagram for Atkinson cycle
NORMALIZED ENGINE PARAMETERS Brake mean effective pressure (bmep) Horsepower per square inch of piston area Brake specific fuel consumption (bsfc) BSFC speed/load contours (or islands) Piston speed Engine load factor Normalized BSFC map for gasoline engine Part throttle BSFC
CAM PHASERS, VARIABLE VALVE TIMING, LIFT DURATION AND OVERLAP Variable valve timing (VVT) Cam timing change Variable valve lift and duration VVT and fuel consumption and emissions VVT and the overexpanded cycle
VVT STRATEGIES Discrete two position phase shifters, fixed lift Continuously variable phase shifters, fixed lift and unmodified lift curve Continuously variable phase shifters, fixed lift and modified lift curve Variable lift, duration and phasing, mechanical Variable lift, duration and phasing, electromagnetic Variable lift, duration and phasing, hydraulic
SOME VVT EXAMPLES Honda VTEC BMW VANOS Toyota VVTL-i FIAT MultiAir
DIRECT FUEL INJECTION
BASICS OF GAS-ELECTRIC HYBRID POWERTRAINS Motivation/drivers for electric & hybrid vehicles Electric Drive vehicles Stop-start mild hybrids Light hybrids Regenerative braking Plug-in hybrid electric vehicles (PHEV) Electric drive only vehicles Gas-electric hybrids
GAS-ELECTRIC HYBRID ARCHITECTURES Series gas-electric hybrids Series charge depleting hybrids Series charge sustaining hybrids Parallel gas-electric hybrids Series-parallel hybrids Charge depleting parallel hybrids Charge sustaining parallel hybrids The 2010 MY Toyota Prius III The 2010 MY Chevy Volt The 2010 Honda Insight
BATTERIES Electric energy measurements Battery types, Ratings Lead-acid batteries Nickel Metal Hydride batteries Lithium Ion batteries Service life, replacement costs
THE GRID
PATH TO INCREASES IN FUEL EFFICIENCY NHTSA – NAS Report Summary Gasoline engine approach Diesel engine approach Hybrid-electric powerplant Summary chart
THE US VEHICLE PARC Demographics Fleet fuel economy EPA MPG estimates
APPENDICES ☼ Petroleum statistics ☼ Conversion factors ☼ Torque/power speed relationships ☼ Definitions for engine terms ☼ SAE vehicle and tire axis system |
