IMPROVED WHEEL PERFORMANCE ON SAND BY CONTROLLED CIRCUMFERENTIAL RIGIDITY

AN ANALYSIS OF EXPERIMENTALLY DETERMINED NORMAL STRESS DISTRIBUTIONS BENEATH TIRES ON SAND REVEALED A STRONG TENDENCY FOR THE NORMAL STRESSES TO BE GREATER IN AREAS OF HIGHER-THAN-AVERAGE TIRE RIGIDITY. THIS PHENOMENON WAS MOST PRONOUNCED WHEN THE SOIL WAS STRONG AND THE INFLATION PRESSURE WAS LOW. SINCE WHEEL PERFORMANCE IS DETERMINED ULTIMATELY BY THE STRESSES AT THE SOIL-TIRE INTERFACE, THE QUESTION AROSE AS TO WHETHER THE OBSERVED PHENOMENON COULD BE USED ADVANTAGEOUSLY IN OFF-ROAD MOBILITY RESEARCH. IF THE STRESS DISTRIBUTION AT THE INTERFACE DEPENDED LARGELY ON THE RIGIDITY DISTRIBUTION, THEN A CONTROL OF THE INTERFACE RIGIDITY PATTERN SHOULD PERMIT A FAVORABLE INFLUENCE ON THE STRESS DISTRIBUTION, AND THUS AN INCREASE IN THE PERFORMANCE OF THE WHEEL. TO EXAMINE THIS HYPOTHESIS, AN EXPERIMENTAL WHEEL WAS BUILT; ITS PERFORMANCE IS DESCRIBED IN THIS REPORT. THE CONTROL OF LOCAL TIRE RIGIDITY WAS ACHIEVED BY A SYSTEM OF SIX NONROTATING HYDRAULIC JACKS INSIDE THE WHEEL ACTING AGAINST A FIXED FLEXIBLE SHOE, ALONG WHICH THE INNER SURFACE OF THE TIRE SLID AS IT ROTATED. BY LOADING THE JACKS INDIVIDUALLY IN A GIVEN PATTERN, AN INTERFACE RIGIDITY DISTRIBUTION SIMILAR TO THIS LOADING PATTERN WAS ACHIEVED. STRESS CONCENTRATIONS AT THE REAR END OF THE CONTACT PATCH ARE OBVIOUSLY FAVORABLE, WHILE THOSE AT THE FRONT END ARE UNFAVORABLE. WHEN THE LOADING PATTERN OF THE HYDRAULIC JACKS WAS ARRANGED ACCORDINGLY IN A ROUGHLY LINEAR MANNER, TESTS WITH SAND AT TWO STRENGTH LEVELS SHOWED THAT THE WHEEL WITH FAVORABLE RIGIDITY DISTRIBUTION (HIGH INTERNAL PRESSURE AT THE REAR OF THE SOIL-WHEEL INTERFACE) DEVELOPED UP TO 25 PERCENT MORE PULL THAN THE WHEEL WITH UNFAVORABLE RIGIDITY DISTRIBUTION. THE GREATER PULL WAS PARALLELED BY AN EFFICIENCY INCREASE OF THE SAME ORDER. AN ANALYSIS OF THE INTERFACE GEOMETRY, WHICH VARIES WITH THE INTERNAL PRESSURE DISTRIBUTION, SHOWED THAT THE PERFORMANCE VARIATION WAS ACCOUNTED FOR BY THE INTERFACE RIGIDITY PATTERN ALONE; NO INFLUENCE OF THE INTERFACE GEOMETRY ITSELF COULD BE DETECTED. ANOTHER IMPORTANT RESULT OF THE TESTS WAS THAT ONLY A SLIGHT RIGIDITY VARIATION WAS FOUND NECESSARY FOR MAXIMUM PERFORMANCE IMPROVEMENT. A RIGIDITY VARIATION BEYOND A GIVEN LIMIT WAS INEFFECTIVE. HOWEVER, THE RATHER CRUDE TEST DEVICE DID NOT ALLOW A QUANTITATIVE ASSESSMENT OF THIS THRESHOLD. ACCORDINGLY, A SCHEMATIC DRAWING OF A MULTICOMPARTMENT TIRE OPERATING UPON THIS PRINCIPLE IS PRESENTED HEREIN. /AUTHOR/

  • Supplemental Notes:
    • Tech Rpt M-69-2, 63 PP, 28 FIG, 13 TAB, 11 REF, 1 APP
  • Authors:
    • Wiendieck, K W
  • Publication Date: 1969

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Filing Info

  • Accession Number: 00232953
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 26 1970 12:00AM