Now well combine the first three into something.(F/W) or µg, gross coefficient of traction.Units like pressure m x L x t-2 L-2 m x t-2 x Soil strength, measured as cone index (CI), has.Weight, or dynamic load, W (mass x L x t-2).Tire deflection (squish), call it d (length).Tire section height, call it h (length).Tire section width, call it b, (length).Of interest to the other combined variables Results in an empirical equation relating a ratio.Relate the ratio that contains the parameter of.Perhaps combine one or more of these into a.Combine variables into dimensionless ratios.Identify all of the variables that are involved.That allows us to vary parameters that we canĭimensional AnalysisYouve seen this before in We need an approach to predicting performance.Note that the previous graphs represented one.Axle power is rotory, drawbar power is linear.We are interested in getting driveline power to.Motion resistance ratio is equal to the net The gross coefficient of traction minus the.But consider pulling aįilled gravity wagon over soft soil. How much is this? For a rigid bicycle wheel onĬoncrete it is not much. Now we consider motion resistance of a wheel.Gross value, (which implies something to be Again, much like a coefficient of friction but a.Per unit weight, F/ W which we will denote as µgĪnd call the gross coefficient of traction If we divide again by weight we get gross thrust.A wheel/tire can produce an increasing thrustįorce up to the point the soil fails under the.Ratio, and in our text is given the symbol µ. This ratio is sometimes called the Pull to Weight.That a wheel/tire can produce so our first Ratio We are interested in the Draft or horizontal pull.Well find that dynamic Weight affects nearlyĮverything and so we will express performance.Which parameters might affect tractive effort?.Tractive performance of your vehicle or tractor You wish to be able to predict or estimate.Slip for towed wheel is negative on soil and will.Note that we dont produce pull (H), even to.Diagram relates wheel slip, Torque and Pull for.H is available to accelerate the vehicle or.Torque, T, is balanced by F-TF and R acting at.H F (gross thrust) minus TF (the towing force.Soil resistance and reaction, G, acts ahead of.T is torque as we now must supply some to make it.G can be divided into vertical (R) and TF.Note G will run just behind the wheel center to.Driving wheel (produces thrust in excess of self.Self propelled wheel (combine or Snoopy).We can have a towed wheel (front or rear steering.Challenging to use in predicting traction.Both stresses vary with angular location andīetween the centerline and the side of the tire.Normal and shear stresses in the soil at the.
Note higher pressures at the perimeter.Note the Low pressure in the center of the.Whoa! This is going to be hard to describe with.Weve just discussed the pressure under a trackĪs it affects soil strength.
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