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Vehicle Axle Loads depend on

Vehicle Axle Loads depend on. Hitch loads Aerodynamic drag Inertia Force ( a x W/g ) Slope/grade ( θ ) Rolling resistance Vehicle geometry (towing/towed) L, c, b, h, h h, h b, h a. Fundamental rule of vehicle dynamics.

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Vehicle Axle Loads depend on

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  1. Vehicle Axle Loads depend on • Hitch loads • Aerodynamic drag • Inertia Force ( ax W/g) • Slope/grade (θ) • Rolling resistance • Vehicle geometry (towing/towed)L, c, b, h, hh, hb, ha

  2. Fundamental rule of vehicle dynamics Control forces act on the tires’ contact patches (i.e. accelerate, brake, turn)

  3. DA x ha Wsinθ Wcosθ W/g ax W B h Rxf z Fxf Rhx θ A Rxr b hh Rhz c Fxr Wf L dh Wr Find Axle Loads Wr and Wf

  4. Solving for Axle Load Wf Taking moments about point B, we can similarly find Wr • What happens to axle loads for changes in: • Grade? • Hitchloads? • Acceleration? • Drag?

  5. DAb Wbsinθ hab Rhx Wb/g ax Wbcosθ hh Rhz Wb Wt Trailer (with boat/ATV/payload) FBD x hb z θ Rxtr e A f

  6. Solving the system of eqn’s Let’s rearrange the equations… Solve this eqnfirst To obtain: Two steps: 1. Calculate Rhx and Rhz , then2. Substitute Rhx and Rhz into axle load formulas for Wr , Wf

  7. Gradeability… ability to climb grades Ability to climb is a function of: Need friction between towing tires and surface Traction forces = f(μ, axle weights) Traction force ≥ downhill weight = Wtotal sinө

  8. Forces in x-direction Assume no hitch and drag forces, constant velocity, then But remember maximum traction is limited by friction available at surface!

  9. Vehicle towing trailer uphill at constant velocity Let drag, rolling, & inertia forces = 0 4WD FWD RWD Let’s do some examples…

  10. What grade can a vehicle climb? Friction limited Power limited Anything else? http://www.youtube.com/watch?v=OS5b_cuDVhs

  11. First, what is “slope and grade?” Slope: Angle θ Slope: Grade (%)

  12. Vehicle towing trailer uphill at constant velocity Will a 4WD, FWD or RWD have enough traction to climb grade?

  13. Which drive will be “grade-able?” (4WD, FWD or RWD) Recall…force to overcome…. 824 lbs. FWD and RWD will slip!

  14. Automate calculations with a spreadsheet…. Connect ot course website at: http://coen.boisestate.edu/reggert/ME485/ME485.htm Click on… GradeabilityS09 (*.xls)

  15. Gradeability (Ford E150 plus ATV and trailer)

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