1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8512 FAX: (724) 776-0243TO PLACE A DOCUMENT
3、 ORDER: (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http:/www.sae.orgCopyright 1999 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.A.SURFACEVEHICLE400 Commonwealth Drive, Warrendale, PA 15096-0001RECOMMENDEDPRACTICESubmitted for recognition as an American National Sta
4、ndardJ2452:ISSUEDJUN1999Issued 1999-06Stepwise Coastdown Methodology for Measuring Tire Rolling ResistanceForewordThis SAE Recommended Practice establishes a laboratory method for determination of tire rollingresistance of Passenger Car and Light Truck tires. The method provides a standard for colle
5、ction and analysis ofrolling resistance data with respect to vertical load, inflation pressure, and velocity. The primary intent is forestimation of the tire rolling resistance contribution to vehicle force applicable to SAE Vehicle Coastdownrecommended practices J2263 and J2264.1. ScopeThis SAE Rec
6、ommended Practice is applicable to pneumatic Passenger Car “P” Type, Light TruckMetric, and Light Truck High Flotation tires, or similar tires approved by bodies other than Tire 17-20-1995 by S. H. Bordelon and S. M. Padula. “An Analytical Model for Transient Rolling Resistance Behavior of Tires,” M
7、ars, Will V.; Luchini, John R.;Journal of Tire Science and Technology, v27#4, 1999.3. Definitions3.1 Rolling ResistanceRolling resistance is the energy consumed per unit distance and is equivalent to thescalar sum of all contact forces tangent to the test surface and parallel to the wheel plane of t
8、he tire. Units areNewtons (lbf).3.2 Rolling Resistance CoefficientRolling resistance coefficient is the ratio of the rolling resistance to the tireload. Units are Newtons per 1000 N of applied load. (Pounds per 1000 lbs of applied load or kg/ton (1000 kg)3.3 Loaded RadiusLoaded radius is the perpend
9、icular distance from the axis of rotation of the loaded tire to thesurface on which it is rolling. Units are mm (in).COPYRIGHT Society of Automotive Engineers, Inc.Licensed by Information Handling ServicesSAE J2452: Issued JUN1999-3-3.4 Maximum LoadMaximum load is molded in the sidewall and is liste
10、d as load limit in the tire load tables ofthe current Tire & Rim Association, Inc. (TRA) Yearbook, or in corresponding tables published by similarorganizations concerned with standardization. For Light Truck tires, the maximum load is defined as themaximum load (or load limit) given for single tire
11、operation. This is given in mass units (kg) which must beconverted to units of force (N) unless the load scale is calibrated in kg (lbf). A mass of 1 kg results in a verticalforce of 9.80665 N because of the acceleration due to gravity (g=9.80665 m/s2).3.5 Base Inflation PressureFor this document, t
12、he base inflation pressure is determined from the InflationPressure as marked on the tire sidewall and revised to reflect actual tire inflation pressure usage. Baseinflation pressure for Passenger Car “P” Type tires is defined in Table 1.For Light Truck (LT metric and High Flotation) tires, the base
13、 inflation pressure is defined as the inflationpressure corresponding to the maximum load for single tire operation (see 3.4). Units are kPa (psi).3.6 Regulated Inflation PressureThe state of regulated inflation pressure is achieved by inflating the tire to therequired pressure independent of its te
14、mperature and maintaining this inflation pressure during testing. This isnormally done by the use of a rotating union.3.7 Ambient TemperatureThe term ambient temperature refers to the temperature of the air measured during arolling resistance test at a fixed location near the cooler part of the tire
15、/wheel assembly. Units are C (F).3.8 Ambient Reference TemperatureAll rolling resistance data are referenced to an ambient temperature of24C (75 F).3.9 Tire Rolling Resistance EquilibriumA tire is said to have achieved equilibrium when its rolling resistancedoes not change with time under constant o
16、perating conditions. In context of this laboratory test, equilibrium isattained when the tire operating temperature has stabilized for a given load, pressure, speed, and ambienttemperature, resulting in a relatively constant rolling resistance.3.10 Standard Reference ConditionA single value of tire
17、load, regulated inflation pressure, and speed specifiedsuch that tires can be compared at a single condition. For this method, standard reference conditions are asfollows:3.10.1 PASSENGER CAR “P” TYPE TIRESa. Tire Load: 70% of T&RA 240 kPa loadb. Inflation Pressure: 260 kPa (38 psi)c. Speed: 80 km/h
18、 (50 mph)3.10.2 LIGHT TRUCK - METRIC TIRESa. Tire Load: 70% of T&RA 350 kPa load b. Inflation Pressure: 370 kPa (54 psi)c. Speed: 80 km/h (50 mph)TABLE 1BASE INFLATION PRESSURE - “P” TYPEInflation Pressure(marked on sidewall)kPa (psi)Base InflationPressurekPa240 (35) Standard Load 240300 (44) Standa
19、rd Load 240350 (51) Standard Load 350280 (41) Extra Load 280340 (49) Extra Load 340COPYRIGHT Society of Automotive Engineers, Inc.Licensed by Information Handling ServicesSAE J2452: Issued JUN1999-4-3.10.3 LIGHT TRUCK - HIGH FLOTATION TIRESa. Tire Load: 70% of T&RA load at 35 psi b. Inflation Pressu
20、re: 260 kPa (38 psi)c. Speed: 80 km/h (50 mph)3.11 Machine MeasurementsTire spindle force (Fx) or torque measurements which are obtained at the machineprior to any compensation for crosstalk, parasitic losses, or ambient temperature. For the force method, unitsare N (lbf). For the torque method, uni
21、ts are N-m (in-lbf).3.12 Crosstalk (Force Method)The error in the machine spindle force reading due to load misalignment andinteractions between load and spindle force transducers. This applies only to the force method. Units are N(lbf).3.13 Gross Tire Spindle ForceNet tire spindle force plus parasi
22、tic loss forces. It is obtained by subtracting theappropriate crosstalk from the machine measurements. Units are N (lbf).3.14 Parasitic lossesThe errors in the machine readings due to machine friction. For the force method, thisincludes spindle bearing friction. Units are N (lbf). For the torque met
23、hod, this includes both flywheel andspindle bearing friction. Units are N-m (in-lbf). For this work, aerodynamic losses of the tire/wheel/machineassembly are considered to be negligible.3.15 Net Tire Spindle Force (Force Method)The force at the machine spindle due to tire-rolling resistance only.It
24、is obtained by applying the appropriate crosstalk corrections to machine measurements and subtractingparasitic losses. For force machines where rolling resistance is in the vertical plane, tire, wheel, and spindleweight must also be accounted for. Units are N (lbf).3.16 Net Input Torque (Torque Meth
25、od)The torque at the roadwheel input shaft due only to tire rollingresistance. It is obtained by subtitling the appropriate parasitic losses from the machine measurements. Unitsare N-m (in- lbf).3.17 Mean Equivalent Rolling Force (MERF)The average rolling resistance of a tire, at a given load/inflat
26、ioncondition, over a driving cycle with a specified speed-time profile. This implicitly weights the rolling resistancefor each speed using the length of time spent at that speed during the cycle. For the purpose of this document,MERF is a combined weighting of MERFs calculated using the standard EPA
27、 urban and highway drivingcycles. Specifically, this weighting is 55% for the EPA Urban (FTP) Cycle and 45% for the EPA Highway FuelEconomy Cycle.3.18 Standard Mean Equivalent Rolling Force (SMERF)For any tire is the MERF for that tire under standardload/inflation conditions defined in 3.10. For thi
28、s document, the final SMERF is also calculated by weightingthe SMERF obtained for the EPA urban and highway cycles, as discussed previously for MERF calculation.4. SymbolsSee specific section where in use.5. Conversion FactorsTABLE 2CONVERSION FACTORSQuantity UnitSI Multiply By UnitsVelocity Km/h 0.
29、62137 mphPressure Kilo-Pascal 0.145037 pounds/in2 (psi)Vertical Load Kg 9.80665 Newtons (N)Force Newton (N) 0.224809 pound-force (lbf)Torque Newton-meter (N-m) 8.850748 inch-pound-force (in-lbf)Temperature Degrees Celsius (C) C*9/5 + 32 degrees Fahrenheit (F)Energy Joule (J) 0.73756 foot-pound-force
30、 (ft-lbf)COPYRIGHT Society of Automotive Engineers, Inc.Licensed by Information Handling ServicesSAE J2452: Issued JUN1999-5-6. Test EquipmentThe equipment most commonly used for this procedure is the laboratory test wheel.6.1 Test Surface6.1.1 TEST SURFACE DIAMETERThe minimum diameter of the test s
31、urface is recommended to be 1.219 m (48 in).A 1.707 m (67.23 in) surface is most commonly used.6.1.2 WIDTHThe width of the test surface must exceed the loaded contact width of the test tire. Common testsurface width is at least 0.30 m (11.8 in).6.1.3 TEXTUREThe surface shall be textured with a mediu
32、m grit (80 grit) particulate size. The recommendedsurface is aluminum oxide resin bound to a cotton cloth fabric backing and grained at 80 grit. Periodicrenewal of the surface is recommended as contamination or wear adds variability to test results. Break-in ofthe surface may be required in order to
33、 stabilize its effect on rolling resistance. The acceptability of newsurfaces should be verified using an appropriate control tire or monitoring process. See Appendix B foradditional information on surface conditioning.6.2 Test RimsThe test rims must have an approved contour and width for the size o
34、f the tire tested as specifiedby the Tire & Rim Association, Inc. or similar organizations for the size of the tire tested. The normal rim fortesting is the measuring rim for a particular tire, although other approved rims may be used. The rim width andcontour used must be reported with the test res
35、ults. Typical radial/lateral runout should be less than 1.3 mm(0.05 in) total reading.6.3 TemperatureAn overall ambient room temperature representing air temperatures throughout the test roomis difficult to define and measure. Therefore, the location of ambient temperature is to be fixed at a latera
36、ldistance 0.4 m (16 in) from a point on either rim flange farthest from the test surface, as depicted in Figure 1.Measurements can be made at other locations if demonstrated to result in the same temperature as thisspecified location.FIGURE 1AMBIENT TEMPERATURE MEASUREMENT POINTCOPYRIGHT Society of
37、Automotive Engineers, Inc.Licensed by Information Handling ServicesSAE J2452: Issued JUN1999-6-6.4 Alignment AccuraciesThe following alignment accuracies are specified such that the effect on rollingresistance does not surpass 0.5 N (0.1 lb). This does not cover systematic errors which must be elimi
38、nated bycareful calibration and proper data processing. Accuracies should be maintained in the loaded condition, up tothe operating load of tests to be run.a. Tire Load Fore-Aft Offset: 0.2 mm (0.01 in)b. Tire Load Angular Offset: 0.3 degreec. Tire Slip Angle: 0.1 degreed. Tire Inclination Angle: 0.
39、2 degree6.4.1 CROSSTALK COMPENSATION (FORCE METHOD)Using the force method, load misalignment as well asinteractions between load and spindle force transducers can introduce large errors in the spindle forcereading. Such errors must be quantified and eliminated by subtracting them from machine measur
40、ements toobtain gross spindle force. Two commonly used methods for accomplishing this are described as follows,although other methods may be used if their technical validity can be demonstrated.6.4.1.1 Forward and Reverse RunsA stepwise coastdown is run in the forward direction of rotation, thenrepe
41、ated in the reverse direction. The tire-rolling resistance and parasitic loss forces reverse with directionof rotation, but crosstalk and load misalignment do not. Forward and reverse spindle force measurementsare subtracted and divided by two, resulting in gross spindle force (net spindle force plu
42、s parasitic spindleforce losses). For analysis purposes, other measured parameters such as tire load, inflation pressure,speed, and ambient temperature should be averaged for the forward and reverse stepwise coastdownruns. A graphical example of this method of crosstalk compensation is provided in F
43、igure 2.6.4.1.2 Machine CharacterizationCrosstalk and load misalignment are characterized as a function of test loadand test speed. This is usually accomplished by experiment, allowing a calculated correction to besubtracted from machine spindle force readings to obtain gross spindle force (net spin
44、dle force plusparasitic spindle force loss).6.5 Instrumentation AccuraciesThe instrumentation used for the reading and recording of test data must besufficiently accurate and precise to provide rolling resistance measurements with a standard deviation of 0.5 N(0.1 lb) or less. To achieve this accura
45、cy, measurements common to both methods of rolling resistancedetermination must be maintained within the following accuracies:a. Tire Load: The greater of 10 N (2 lb) or 0.5%b. Inflation Pressure: 1 kPa (0.1 psi)c. Speed: 1 km/h (0.5 mph)d. Temperature: 0.2 C (0.5 F)e. Force Method - In addition to
46、the common accuracies specified previously, the use of this methodrequires the following accuracies:1. Spindle Force: The greater of 0.1 N (0.02 lb) or 0.5%2. Loaded Radius: 1 mm (0.04 in)f. Torque MethodIn addition to the common accuracies specified previously, the use of this methodrequires Input
47、Torque Accuracy of: the greater of 0.1 N*m (0.9 in-lb) or 0.5%.COPYRIGHT Society of Automotive Engineers, Inc.Licensed by Information Handling ServicesSAE J2452: Issued JUN1999-7-FIGURE 2CROSSTALK COMPENSATION EXAMPLE6.6 Control AccuraciesTest conditions must be maintained at their specified values
48、such that the overallvariability of the rolling resistance measurement is minimized. The standard deviation of the test shall notexceed 0.5 N (0.1 lbf) as quantified by a suitable gage repeatability and reproducibility method. To meet thisrequirement, the average value of measurement taken during th
49、e rolling resistance data collection period mustbe within the accuracies stated as follows:a. Tire Load: The greater of 20 N (5 lb) or 0.5%b. Inflation Pressure: 1.5 kPa (0.2 psi)c. Test Surface Speed: 1.5 km/h (1.0 mph)d. Ambient Temperature: 4 C (7 F)6.7 StabilityThe test should maintain speed, tire load, inflation pressure, and ambient temperature at stablevalues within the limits stated in 6.6 to the greatest extent possible as rolling resistance data is collected.Generally, data should be collected over a period o
