SAE J 345A-1969 Wet or Dry Pavement Passenger Car Tire Peak and Locked Wheel Braking Traction.pdf

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: (412) 772-8512 FAX: (412) 776-0243TO PLACE A DOCUMENT

3、 ORDER; (412) 776-4970 FAX: (412) 776-0790http:www.sae.orgCopyright 1969 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 StandardJ345aREV.MAR

4、69Issued 1968-06Revised 1969-03Superseding J345a JUN68(R) WET OR DRY PAVEMENT PASSENGER CAR TIREPEAK AND LOCKED WHEEL BRAKING TRACTIONForewordThis Document has not changed other than to put it into the new SAE Technical Standards BoardFormat.1. ScopeThis SAE Recommended Practice defines the best kno

5、wn techniques for evaluating peak and lockedwheel braking traction. It covers an important phase of tire braking traction, namely, the wet or dry pavementstraight ahead conditions. However, this is but a small portion of the whole field of tire traction. As testprocedures are established for other p

6、hases of this complex study, additional supplementary procedures willbe written. A discussion of this entire subject is contained in Appendix B to this recommended practice.1.1 ObjectThe object of this SAE Recommended Practice is to provide a general test procedure for measuringthe braking traction

7、of passenger car tires on wet or dry pavement.2. ReferencesThere are no referenced publications specified herein.3. Preparation of Tire(s) for TestsNew tires, both control and design tires to be tested, shall be trimmed toremove all protuberances in the tread area caused by mold air vents or flashes

8、 at mold junctions. Tires shallbe mounted on Tire and Rim Association (T inflated to 24 psi; loaded to (80100%)T and run on a passenger car for 100 miles at 6070 mph on dry roads,50miles on front wheels and 50 miles on rear wheels. This is a break-in run to remove mold lubricant andmold sheen from t

9、he tread surface. Excessive acceleration, braking, and cornering that might result inabnormal tread surface wear are to be avoided.4. EquipmentA suitable test device designed to measure tire braking forces and meeting requirementsoutlined in Appendix A.Control reference tires of specified design, co

10、mpounds, and construction.5. Test Procedure5.1 Test ConditionsLoad: 100% T&RA load limit at 24 psi 25 lbInflation Pressure: 24 psi cold 1/2 psiTest Speed: 20, 40, 60 1 mphSAE J345a Revised MAR69-2-5.2 Test SurfaceTest surface shall be any clean, level surface for which tire-surface braking coefficie

11、ntinformation is required. In tests requiring vehicle provided watering, the test surface shall be watered at a rateproportional to speed to provide a 0.020 in. 25% calculated film depth independent of test speed. Externalwatering may be provided to fulfill any specific test condition.5.3 Testing Pr

12、ocedureBring test device up to test speed prior to reaching test site. Apply brakes on testwheel(s) until wheels are locked. Hold wheels locked for a minimum of two seconds. Hold test vehicle atrequired test speed 1 mph. Record tire braking traction force, vehicle speed, and all other desiredparamet

13、ers, starting a minimum of 1 sec before initiation of lockup to 1 sec after unlocking the test tire.For each specific test, a minimum of ten readings, five each in opposite directions, are to be made for each tire.The sequence of testing to be as follows:a. Control test tire.b. Tests of tire(s) to b

14、e evaluated (no more than two).c. Repeat of control test tire.d. Repetition of steps (b) and (c) to complete all required test tires.For each test, record the following information:a. Tire description (make, type, size, cord material, etc.)b. Tire static load.c. Tire cold inflation pressure.d. Date.

15、e. Time.f. Ambient temperature.g. Surface temperature.h. Water temperature.i. Speed.j. Surface description.k. Water depth.l. Whether force or torque.m. General remarks.6. Data Reduction and Analysis6.1 Raw Data ReductionPeak and locked wheel sliding force shall be read for each specific test run. Th

16、esliding value shall be the average value between 0.2 and 1.2 sec after the test wheel lockup. The dataprocessor should note any unusual anomalies appearing in the data.6.2 Data ReductionEach separate peak and sliding coefficient should be reduced to a braking coefficient bydividing the force by the

17、 applicable tire vertical load corresponding to the force. If the test equipment used is atrailer which does not measure the tire load, changes in tire load due to weight transfer must be compensatedfor by calculating coefficient according to the following formula:(Eq. 1)Braking Coefficient ()FW hL-

18、 F-=SAE J345a Revised MAR69-3-where:F = friction force, lb (per wheel)W = static trailer weight, lb (per wheel)h = trailer hitch height, in.L = trailer wheel base length, center of axle to center of hitch, in.All 10 individual coefficients are to be averaged. Calculate the standard deviation to prov

19、ide an index of datavariance by the following formula:(Eq. 2)where:Xi = individual data pointsX = average of data pointsn = total number of data points6.3 Data AnalysisEach averaged data point for a test tire at a test condition provides a measure of the brakingtraction value of the specific tire an

20、d surface combination under the conditions at the time of that test.7. Notes7.1 Marginal IndiciaThe change bar (l) located in the left margin is for the convenience of the user in locatingareas where technical revisions have been made to the previous issue of the report. An (R) symbol to the leftof

21、the document title indicates a complete revision of the report.PREPARED BY THE SAE TIRE COMMITTEEStandard DeviationXi X()2i 1=nn 1-=SAE J345a Revised MAR69-4-APPENDIX APERFORMANCE SPECIFICATIONS FOR A TIRE BRAKING TRACTION COEFFICIENT TEST DEVICEA.1 ScopeThis specification is designed to provide nee

22、ded performance specifications for a device to evaluatetire braking traction coefficients. Specifications are provided for force measuring as well as torque measuringtransducers. However, torque transducers are not recommended for tire testing and should be considered as atemporary expediency. Consu

23、lt Appendix B for further discussion.A.2 SpecificationsThe following specification assumes design conforming to good engineering practice toprovide those requirements dictated by experience which are necessary to produce the most repeatable,accurate, and significant data. This specification is writt

24、en, in general, for a trailer type device. However, allbasic design criteria are relevant for any type of equipment.A.3 Trailer (if device is of trailer type)A.3.1 Suspension system shall provide adequate load carrying capabilities and be of such a design as to isolatesuspension resonance.A.3.2 Trai

25、ler shall be designed to allow loading to at least 100% of 24 psi T&RA loads for all listed passenger car tiresizes.A.3.3 Trailer shall be designed to allow the hitch height to be no higher than loaded tire radius and the length fromhitch ball to axle centerline to be no less than 10 times hitch hei

26、ght.A.3.4 Trailer shall be designed to accommodate all T&RA passenger car rim sizes.A.3.5 Location of center of gravity height should be as close as possible to trailer hitch height.A.3.6 Hitch vertical load should be 150 50 lb.A.3.7 It is desirable to have a trailer hitch arrangement such that the

27、trailer can be towed in line or offset with thetowing vehicle tires. For external watering, the trailer hitch on the towing vehicle shall be so arranged that thetrailer tires will run in tracks separate from the tire tracks of the towing vehicle.A.4 TransducersA.4.1 Force MeasuringThe tire force mea

28、suring transducer should be designed to measure tire force withminimum inertial effects. Transducer should have an output directly proportional to force with less than 1%hysteresis and less than 1% nonlinearity. It should have less than 1% sensitivity to any expected cross axisloading or torque load

29、ing. The transducer shall be suspended in such a manner as to experience less than 1deg angular rotation with respect to its measuring plane at the maximum expected loading.A.4.2 Torque MeasuringA torque measuring transducer is not recommended for tire testing. If requirementsdictate use of a device

30、 of this type, the transducer must meet the following performance specifications:Transducer shall provide an output directly proportional to torque with less than 1% hysteresis and less than1% nonlinearity. It should have less than 1% sensitivity to any expected cross axis loading.A.4.3 Additional t

31、ransducer outputs for measuring quantities, such as vertical load, etc., must meet requirementsstated in A4.1.SAE J345a Revised MAR69-5-A.4.4 Vehicle speed measuring transducers, such as “fifth wheel,“ etc., shall provide speed resolution better than0.5 mph over the expected range of operation. Outp

32、ut should be directly viewable by operator and alsorecorded.A.5 Signal Conditioning and Recorder SystemA.5.1 All transducers measuring parameters subject to inertia loading should be designed and/or located in such amanner as to minimize this effect. If the foregoing is not practical, data correctio

33、n must be made for theseeffects if they exceeded 2% of actual data based on expected operation. All signal conditioning and recorderare to be capable of providing linear output with necessary gain to allow better than 2% data readingresolution. All systems must provide a minimum band width of at lea

34、st 020 Hz (flat 2%).A.5.2 All strain gage transducers must be equipped with resistance shunt calibration resistors which can be appliedbefore and after test sequences.A.5.3 Vehicle speed, tire friction force, and a time base signal must be recorded in phase (020 Hz 5 deg). Anyadditional desired inpu

35、ts, such as vertical load, wheel speed, torque, etc., must meet these requirements aswell as the requirements in 5.1.A.5.4 All cabling and system design to follow good engineering practice with respect to environment protection. Asignal-to-noise ratio of at least 20/1 is desirable on all recorded ch

36、annels.A.6 Towing VehicleA.6.1 Towing vehicle and trailer must comply with all legal requirements applicable to state or states when operatedon public roads.A.6.2 Vehicle should have sufficient engine capacity to provide an adequate speed range and to allow 60 mphmeasurements with a speed loss of no

37、t greater than 1 mph.A.7 Watering SystemA.7.1 Either a self-contained watering system or a method for wetting a test pad to a uniform prescribed depth maybe used.A.7.2 A self-contained watering system, if deemed necessary, shall water at a rate to provide a uniform calculatedfilm thickness of 0.020

38、25%, regardless of speed, and at least as wide as the test tire.A.7.3 Adequate water storage should be supplied to meet individual needs.A.7.4 A water nozzle system for trailer shall be of such a design as to meet the requirements of A7.2.A.8 CalibrationA.8.1 Each wheel of the assembled unit with it

39、s own instrumentation should be placed on a suitable calibrationplatform and loaded vertically to the test load and with the correct tire pressure. The entire trailer should beleveled. The calibration platform should utilize air bearings (or equivalent) so that the platform is not able toinduce any

40、lateral or fore and aft forces. Care must be taken to assure applied load is in plane of transducersensitivity.Incremental loading should be applied up to a fore-aft force of at least 70% of T&RA load at 24 psi.SAE J345a Revised MAR69-6-A.8.2 The foregoing technique is suitable for calibrating all o

41、ther transducers, including brake torque devices. Acalibration of torque transducers by this method is accurate only for the tire used at the load, pressure, andenvironment at the time of test calibration. While this provides a partial correction for footprint center pointrelocation, it in no way re

42、duces the inherent errors explained in Appendix B unless each and every tire iscalibrated at test load and pressure. Pure torque arm calibration is suitable assuming calibrations arecorrected for individual test tire static loaded radius. This method does not give any correction for footprintcenter

43、point location.A.8.3 Test EquipmentReference load cells, instrumentation, etc. should have an accuracy and sensitivity of atleast twice that of the object system. This will insure reasonable accuracy and resolution during calibration.A.8.4 Sound engineering practices and judgment should be used thro

44、ughout the calibration process.SAE J345a Revised MAR69-7-APPENDIX BTIRE TRACTION TESTINGB.1 The term tire traction would describe a quality of tire performance. No single evaluation of tractionperformance describes a tires overall traction capabilities. Any measurement of tire traction is a measurem

45、entof the tire-road surface combination. Tire performance is affected by many factors. Most prominent aresurface variations, speed, and load, followed by tire variables such as tread design, tread compound, and tireconstruction.Comparative tire traction performance testing is usually conducted by te

46、sting different tires on the samesurface under the same conditions. There is no surface which remains constant, since individual surfacecoefficients are affected by many variables, such as wear, temperature, fluid depth, etc. There is no knownmethod of defining and constructing duplicate fixed textu

47、re surfaces with accurately maintained control oftraction variables. Because of these problems, the control tire technique has been developed to provide amethod for evaluating comparative traction data. The control tire data evaluation assumes that the changesexperienced by the control tire affect t

48、he test tire in the same way and proportionately.The foregoing information implies that there is some minimum degree of confidence within which differencesbetween individual tires cannot be termed significant. The procedures in this SAE Recommended Practice fortire braking traction evaluation repres

49、ent the best known techniques. The equipment specified is capable ofaccurately measuring what occurs at a given instant in time. The influence of uncontrolled parameters createsa degree of variation in results dependent upon the particular test conditions. When future knowledge allowscontrol or compensation for these variables, one will be able to measure smaller significant differences in tiretraction.Appendix A defines a basic set of performance criteria for the development of a braking traction t