Journal of Materials Science and Engineering A 1(20 1 1)6 1 6-626 Formerly part ofJournal of Materials Science and Engineering,ISSN 1934-8959 ……瓣龋 Design,Construction and Validation of a Portable Tire Test Rig 一 Brad Hopkins ,Derek Fox ,Josh Caffee ,Bryan Sides ,William Burke5Michael Craft and Saied Taheri ,l Department 0j Mechanical Engineering,Virginia Polytechnic Institute and State University,Blacksburg,VA USA 2 Magneti Marelli.Sanford,NC USA 3 General Motors,MilJord,M1,USA 4 Force Protection Industries 1nc. Ladsot7.SC.USA 5 Marine Advanced Research Inc Richmond,CA USA Received:March 04,201 1/Accepted:April 12,201 I/Published:October 10,201 1 Abstract:Tire force and moment testing is a valuable way of quantifying the performance of a tire.The data collected from such testing is also used by many researchers for vehicle dynamic simulation studies as wel1 as chassis control system development. Although various studies have claimed correlation between data from rolling road type machines and road testing trailers,the claim only extends for on.road conditions.Many military vehicles as well as agricultura1 vehicles operate in an environment which requires new levels of tire test data.This paper will discuss the design and testing of a portable trailer tire test rig.This rig was conceived and constructed for use on both on.and off-road driving surfaces and is also fitted for wet.road testing.The rig will eventually be used to collect tire data on various tire sizes both on and off-road on various road surfaces,such as grass,asphalt,concrete,and gravel tor varying speeds,pressures,loads,and slip angles.The data will be used to develop a modiifed Paccjka Magic Formula Tire Model that can be used for conducting simulation in both on and off-road conditions. Key words:Portable tire test rig,Pacejka magic formula,tire force and moment testing 1.IntrOductiOn of the non-inertiaI forces that direct the motion of the vehicle.This can be helpful for developing vehicle The primary objective of this work is to develop an accurate method for conducting vehicle dynamics studies using empirical tire test data gathered from on— and off-road testing.This is essential in correct representation of the tire—road interaction during stability control algorithms and testing them in an accurate simulation environment[8]. The Pacejka Magic Formula has proven to be a hi ly accurate tire mode1.The only downfall is that it requires extensive testing since it is a semi-empirical simulation studies concerning severe steering and braking maneuvers.There are many tire models in model[9,1 0].However,if the proper test equipment is available,suficientf data can be collected and the tire model can be developed with a curve fiting routine existence,including the semi—empirical Pacejka Magic Formula[1,2】,the friction—based LuGre tire model[3], and models that account for the differences in tire behavior in the adhesion,transition,and saturation [1 1].The Magic Formula is also capable of accounting or diffferent driving surfaces as well,including both regions[4].These tire models are a powerful and necessary tool for accurate vehicle dynamics studies on—and off-road surfaces[1 2】.In this respect,a portable tire test rig was designed and constructed to 【5—7】,as the forces in the tire contact patch provide all Corresponding author:Brad Hopkins,Ph.D.candidate collect data to develop a Pacejka based tire mode1. Other tire test rigs are in existence,such as the two vehicle setup proposed by Pottinger[131,which is used research ifeld:tire mechanics.E-mail:bradhopkins@vt.edu. for the specific purpose of collecting tire force and Design,Construction and Validation of a Portable Tire Test Rig 6l7 moment data on ice or snow.The tire test rig proposed in this paper is capable of being driven on both on。and off-road driving surfaces and does not necessarily require a closed road to perform testing. The remainder of this PaDer proceeds as follows. First the tire test rig overall design and operation is presented.The speciifc hardware used to develop the trailer is described.Speciifc attention is given to the design and operation of the steer and camber controls. The tire measuring device,a specially designed dynamometer hub that measures the lateral, longitudinal and vertical forces,as well as the aligning, rolling nad overturning moment will be discussed.The LabView Virtual Instrument program that controls the tire movement and records all data will be shown. Lateral force versus slip angle data that was collected f0r a Michelin Hydroedge P2 1 5/60R1 6 tire will be presented Lastly,the Magic Formula tire model will be presented and validated against third—party data. 2.Experiment This research involved the design,construction,and validation of a portable tire test rig for developing a Pacejka Magic Formula tire mode1.The following Experimental Setup section will present the design and construction of the rig,followed by the Experimental Procedure section.which wil1 explain the experiments that were performed to validate the operation of the portable tire test rig. 2.1 Experimental Setup The following sections will explain the i various components of the portable tire test rig,including rig housing and transportation,application of forward speed,vertical load and slip angle control,application of camber nagle,and force and moment measurement. 2.1.1 Portable Tire Test Rig Design The Intelligent Transporttaion Laboratory has developed a unique method for measuring the forces and moments of tires within an enclosed cargo trailer. The trailer is a 2.4 meter by 9.75 meter。three—axle cargo trailer made by Covenant Cargo,and has a loading capacity of 5,900 kilograms.The trailer is pulled behind a tow vehicle using a bumper-pull style hitch. A Miller gasoline generator provides single—phase,1 20 Volt and three—phase,480 Volt Alternating Current power to the trailer that powers the equipment,including extra outlets for accessories such as computers and lights.The power to all equipment is controlled through two breaker boxes—one for single-phase equipment and one for three‘phase equipment.The trhee-phase power is conditioned through a transformer in order to achieve proper equipment voltages.During testing the Miller generator is placed and transported in the bed of the tow vehicle to isoltae the test trailer from vibrtaions during testing.The tow vehicle used for this testing was a 2005 Ford F.3 50 crew—cab dually.AIl personnel nad monitoring equipment and emergency equipment are located inside the truck during testing.A wireless camera is mounted inside the trailer and projected to a monitor inside the truck.An emergency stop switch is also run from the testing equipment to the truck cab in order to stop testing immediately if a problem were to arise.Fig.1 shows the test setup of the tow vehicle, with the generator in the truck bed and trailer attached to the bumper hitch. A section of the lfoor in rfont of the traiier axles was removed to allow the tire test rig to access the road surface.The open section runs the width of the trailer, excluding the outermost steel flame of the trailer,and 1.2 meters longitudinally.A safety door was constructed Fig.1 The tire test trailer attached to the towing vehicle with generator setup shown. 6l8 Design,Construction and Validation of a Portable Tire Test Rig to cover the open floor section when traveling to the test site.The tire test rig is supported by a load frame, which is a reinforced steeI frame that runs laterally across the trailer.The force hub on which the tire mounts is connected to a mounting plate by an upper and lower control arm.The mounting plate is connected to the steel 1oad flame of the trailer on two vertical slide rails.The plate mounted to these rails allows the entire hub assembly to be vertically raised and lowered.It can be raised completely inside the trailer for safe travel to the test site,and then lowered down to the road surface when testing is to be performed.A Duff-Norton worm screw actuator is used to raise and lower the hub and tire assembly.The screw actuator is rated to safely handle 1,800 kilograms of 1oad on its in—plane axis and has a 24:1 reduction gear in the screw actuator housing,so minimal torque is required to raise and lower the assembly.F ig.2 shows a model ofthe Ioad lfame on the left and close up ofthe mounting plate and hub configuration on the right. 2.1.2 Vertical Load Application The tire and hub assembly is loaded using a Firestone‘Airstroke’airspring filled with nitrogen gas. The airspring is mounted rigidly to the upper lfame of the movable mounting plate.When pressure is applied, the airspring execs a downward force onto the servo motor mounting structure which applies the vertical load through the steering fork.Fig.3 shows how the airspring is mounted.Once the test assembly is lowered to the road surface using the screw actuator,the nitrogen tank forces nitrogen into the airspring until the desired vertical load is achieved.The Firestone airspring is capable of applying up to 44.5 kilonewtons offorce.The nitrogen tank can hold 3.4 cubic meters of nitrogen and store up to 1 6,500 kilopascals.Nitrogen gas was chosen over compressed air because it can maintain average pressure more efifciently and it is not as readily affected by temperature changes.The nitrogen gas is controlled through a pressure regulator on the tank as welI as an electronic pressure transducer. The regulator on the pump is adjusted to the maximum pressure required for testing in order to prevent damage to the pressure transducer and airspring.The pressure transducer is controlled by a LabView Vitrual Instrument,which adjusts the airspring to the pressure required ofr the user’s desired vertical load. 2.1.3 Steering and Camber Parker servo motors and controllers are used to adj ust both steer and camber angle.Parker brushless servo motors were used since they are capable of high continuous torque.Both servo motors are powered using Parker Compax3 controllers and driven by a Lal:IView Virtual Instrument.The servo controllers are connected to a National Instruments Data Acquisition setup and connected to the computer through a Universal Serial Bus connection. The steering servo is connected to the steering fork by a 1 53:l planetary gear set,and requires a robust, trhee.phase powered motor.This servo motor iS rated up t0 49.5 kilogram—centimeters of continuous torque and has a strong planetary gear reduction in order to withstand steer angle sweeps at high longitudinal velocities.With the assumption that the trailer is towed in a straight line,the tire slip angle is equal to the steer angle.The test setup allows for slip angle sweeps between一20 and+20 degrees.A 1inear potentiometer is used to measure the slip angle.A LabView Virtual Instrument sends a signal to the Compax3 controller which controls the servo motor with its built—in functions. The camber servo motor is used to drive a separate Duff-Norton worm screw actuator.This servo motor is smaller,only requiring single—phase power,with a continuous torque rating of 7 kilogram—centimeters. The screw actuator iS connected to the top ofthe Kistler hub and acts as the mounting point of the upper control arm.As the worm gear is extended or retracted the upper portion of the hub is pushed out and pulled in, causing the tire to camber.The camber angle is set to discrete angles and held constant for each test run.A LabView Virtual Instrument sends a signal to the Compax3 controller which controls the servo motor Design,Construction and Validation of a Portable Tire Test Rig 6l9 Steer|Load Forks Fig.2 Computer animated drawing of load frame inside trailer with hub assembly(1eft),close up computer animated drawing of mounting plate and hub assembly on slide rails(right).(Note:Some components removed from model for clarity). Acquisition setup and transmits the data to a LabView Vitualr Instrument.The LabView program is able to continuously show the three forces (1ateral, longitudinal,and vertica1)and the three moments (aligning,overturning,and rolling)acting on the tire and simultaneously save the data to an Excel spreadsheet.The photograph on the right of Fig.4 shows the Kistler hub. 2.1.5 Data Acquisition and Control A LabView Virtual Instrument code has been written to control t[ae steering of the tire,monitor the Fig.3 Air spring mounted between rigid top plate and vertical loading structure. pressure in the airbag to ensure proper vertical load, and collect force and moment datfl rom tfhe force hub. The ComPax3 servo controllers,Kistler amplifier, with its built-in functions.The photograph on the left of Fig.4 shows a picture of the upper control arlYl with camber gear setup as mounted to the hub. 2.1.4 Tire Force and Moment Measurement A Kistler force hub is used to measure the dynamic pressure transducer,and linear potentiometer are connected to a National Instruments Data Acquisition pad nd acontrolled by the LabView Vitualr Instrument program by a Universal Serial Bus connection.The front panel of the Vitualr Instrument is designed SO that and quasi-static forces and moments acting at the spindle.The Kistler hub is able to measure the applied longitudinal,lateral and vertical forces as well as calculate the aligning,overturning and rolling the user Can input the desired maximum slip angle and requency ffor a sinusoidal slip angle sweep.Fig.5 shows the data rom fa sample test event. 2.1.6 Dry and Wet Testing In order to achieve a variety of dry and wet surface moments acting on the tire.The dynamometer has a high degree of rigidity that allows for the measurement of minute dynamic changes in large forces.The Kistler hub is connected to a Kistler charge ampliifer that outputs the signal to a NationaI Instruments Data conditions,a 1.9 cubic meter water tank with pump and spray nozzles was installed in the front of the trailer. When weather permits,dry testing can be performed on Design,Construction and Validation of a Portable Tire Test Rig 621 the Data Acquisition pad.The Data Acquisition pad is then connected to the laptop using a Universal Serial Bus connection.The safety door is removed from the lfoor opening,the hub assembly is lowered,and the tire is mounted to the Kistler hub. The hub assembly is adjusted to the correct camber angle using the camber servo motor.An emergency stop switch is run from the steer servo controller to the cab of the truck.A wireless camera is set up with a monitor in the cab of the turck so that the user can monitor the test and shut down the steer motor with the emergency stop switch in case of emergency. Once the equipment is prepped,the desired vertical load is set by filling the air bag with nitrogen.The standard warm—up procedure,as determined by Intelligent Transportation Laboratory,is to drive the trailer in a straight.1ine for 1 0 minutes at 50 kilometers per hour and 1/2 of the tires rated vertical load.The desired maximum slip angle for the slip angle sweep and the frequency of the slip angle sweep are then speciifed by the user using the LabView Vitrual Instrument. Once the process is activated,the slip angle sweep will begin.The steer servo will execute one period of a sine sweep using the maximum slip angle and rfequency as specified by the user.All testing is performed with straight-line driving of the trailer,so that the steer nagle ofthe tire can be assumed to be the slip angle.The trailer side slip angle is not measured and no compensation is considered in generating the mode1.This will be addressed in future work.The Virtual Instrument records the three forces(1ateral, longitudinal,and vertica1)and the three moments (aligning,overturning,and rolling)acting on the Kistler hub into a ifle that the user can access later.This procedure is then repeated for each desired combination of vertical load and camber angle. The validation testing was performed on dry asphalt at Danville Regional Ai ̄ort in Danville,Virginia using the Michelin Hydroedge P2 1 6/60R1 6 tire.Table l shows the properties of this tire.The tire was first warmed up by driving the tire at 1/2 its rated vertical load ofr ten minutes.During testing,the tire was driven at a ofrward speed of 50 kilometers per hour.The tire was tested at three different vertical loads:l/2 rated. 3/4 rated,and rated,and tested at four discrete camber angles:0,2,4 and 6 degrees.A combination of each vertical load and camber angle required l 2 total test runs.For each run,a slip angle sine sweep with amplitude of 1 5 degrees and frequency of 0.05 Hertz was performed.All forces and moments acting on the tire were recorded with particular interest on the lateral force.The vertical load was also measured for use in the development of the tire mode1. 3.Results and Diseussion This section presents the results of the dry asphalt tire testing that was described in the previous section. The collected lateral force versus slip angle data will ifrst be compared to an existing accurate third party model ofthe same tire to validate the tire test rig.Then, the collected data will be used to develop a IateraI force Magic Formula tire mode1. 3. Validation.’Comparison to ThirdParty Model The data collected from the tire was compared to results from a third party modeI to validate the tire t6st trailer.The third party model was developed by testing the Michelin Hyrdroedge P2 l 5/60R 1 6 at 24 l kilopascals inflation pressure,and 50 kilometers per hour forward speed on a fita track test machine.The model consists of a set of Pacejka coefficients to be used in the Pacejka’s Magic Formula to produce a steady state tire mode1.The following plots compare lateral force versus slip angle ofr a third party tester and the results from the tire test trailer,for the Michelin Table 1 Test tire properties. Model Michelin hydroedge Size P2l5/60R16 Load index 94(1477 lbs) Speed index T(118mph) Inflation pressure 24l kPa(35 psi) 622 Design,Construction and Validation of a Portable Tire Test Rig Hydroedge tire,taken at vertical loads of 2 kilonewtons, 【_ 'l≥ Z _)享 一I{ 苫l1 increments as shown i:_【【_(1_1. ̄、 Z u n Fig.6-9.In these fg-!王一 一 igures,the I3.5 kilonewtons,and 6 kilonewtons with increasing camber angles from 0 to 6 degrees at 2 degrees dotted points are the tire test trailer data and the lines are the third party Magic Formula model at the …………-_““L ◆data 2 0kilonewtons —1_’l~ ●… ●▲data 3 5 kilonewtons data 6 0 kilonewtons 一 一一。’。●II-i . — . —………一一一一。TImdPar Model 2 0 kilonewtons ThirdPart、.Mode1.3 5 kilonewtons ThirdPartyModd 6.0kilonewtons J ,V 2 ・8 -4 、… { .一 ’’’_----- 一…… 8Up AI埘etdl 耐》 Fig・6 Lateral force versus slip angle for different vertical loads,0 degrees camber angle. U ◆—data 3 07 kilonewkms data4 39kilonewtons data 6 59 kilonewtons 一 ■●■●-~.一—’■■● ▲~ —_1●■●■=●百 1”… … —………ThircIPartyMode1 3 07 kilonewtons 一1r●■■-=,■■●日■ ThirdparI_vModel 4 39 kilonewtons一 ’ 。一。ThirdPar Mode1 6 59 kilonewtons . 2 -8 -4 … { '.一 .. 。 ’・III- ’ …一一一一一一一.…一~ .!!一一一…一… 一一-▲^▲▲^■^■●l■● Fig・7 Lateral force versus slip angle or differentf vertical loads,2 degrees camber angle. ●data3 01 kilolleWtons 一一~・I‘ 一_…,。一 _…一一・ 罩窨 一… … ■da▲dta 4 81kilonewtons ata 5 65 kjlonewtons 一一一一・一 一 暑 一 一 … 《 —Th………ThirddP Par Mo1.vMode1 34 08 1 kilonewtonnss "IllirdPartvModel 5 65 kilonewtols 2 -8 —4 —●—●‘_ _’■~ _1一 =! 二二~……1-'- ●--一~…一_2- ::~~’ Fig.8 Lateral force versus slip angle or differentf vertical loads,4 degrees camber angle. Design,Construction and Validation of a Portable Tire Test Rig 玄Il三享 Z :0 一 缸 623 ◆data2 2 kilonewtons — ~………一 一::: ’、 — 一…■d▲ data 36 637k ikliolnonewewttonons s —………-一 ThirdPartyModel,2 2 kilonewtons ThirdPar哆Modd 3 3 kilonewtons一 ThirdPar Model,6,67 kiIolle ̄lons . , 2 -8 .4 … ( ●一- 一.一.-’.-1. —1.--_1 .‘ 一 . 跚ip 脚eId 唧 Fig・9 Lateral force versus slip angle for different vertical loads,6 degrees camber angle. respective vertical loads.The data displayed in the plots has been processed through Fast Fourier Transform filtering and correction of offsets using OriginPro ̄software in order to produce a set Of steady—state data. The figures show that the collected data matches the Hertz for three different vertical loads and four different camber angles was used to determine the Pacejka coeficifents for lateral force.Eq.(1)shows Pacejka’s Magic Formula for lateral force.The main coeficifents B.C.D.E.SH and S are defined in Eqs. (2)・(9).The coeficifents ao,a ..,al7 are the Pacejka coeficifentsfo lateralforce F isthelateralforce.F,is the vertical load, camber angle. third party model within 1 0%or better for 0,2 and 6 degrees of camber with a worst case average error is the slip angle,and is the experienced at 4 degrees of camber at 1 4%.There are slight discrepancies between the collected data and the :Dsin【C ctan(Ba 一E 一arctan(Bcty))))+Sv(1) v=t2,+S C=a0 third party fit,which may be present due to several factors.These factors include the difference in the coe伍cient of friction between the flat track and the asphalt road that the tire was tested on.and the fact that the flt tarack remains even the entire test while the asphalt road that the tire was tested on contains iregularities,such divots. 3.2ForceandMomentEreModel A Matlab script has been writen that is able to receive the data collected from the test trailer and as bumps and (2) (3) D=a +a2 Il-al5Y ) E= 6 +07 x1— l6 +a17)Sign JJ (4) (5) BCD=a3 sin(2arctan /a4)X1一口5 B=BCD/(CD) SH:a8 +a9+aloY (6) (7) (8) Sv=allC+口12+a13 +a14 lo (9) The collected data will display a hysteresis loop due to carcass and tread compliance because of the slip angle sweep.OriginPro ̄and Matlab ̄were used to ilfter each set of data in order to produce a steady-state force or moment versus slip angle curve that the Matlab calculte Paceajka coefficients for uSe in the Pacejka Magic Formula.The Magic Formula model gives a steady state characterization of the tire—road force and moment interactions for a given combination of vertical load,camber angle,and slip angle.A set of data consisting of 1 5 degrees slip angle sweeps at 005 .script is able to interpret.The Matlab script uses a curve fiting routine that globally fits the raw data and produces Pacejka coeficifents.The Pacejka coe讯cients for the Michelin Hydroedge P2 1 5/60R1 6 are shown in Table 2.Fig.10—13 show plots ofthe 624 Design,Construction and Validation of a Portable Tire Test Rig collected data and the Magic Formula generated curves displayed as lines.The Magic Formula model matches based on the Pacejka coeficifents determined from the curve fitting routine.In the plots,the collected data is the collected data within 1 0%or better at 0,2 and 6 degrees with a maximum average error of 1 4% experienced at 4 degrees of camber. 专 g.I事 Z ]lIL1 l。 l1 Idisplayed as dots and the Magic Formula fit is Table 2 Pacejka coeficifents for Michelin Hydroedge P215/60RI6. UVVu ◆l1—■ —一data 2 0 kilonewtons data 3 5 kilonewtons data 6 0 kilonewtons /via cFormula 2 0 kilonewtoas Ma e Fonnula 3 5 kilonewtons Innn 一■▲………。 一・一一一Ma e Formula 6 0 kilonewtons . 2 .8 -4 f 、 .一 ’ 一一’一…一一一…一二 —I—-一 …。 ~.  ̄iipAI堪亡(dl蝉懈) .Fig.10 Lateral force versus slip angle for different vertical loads,0 degrees camber angle. …v 一”‘.‘ ^.… ‘‘‘--▲●・-… … ◆tinIa 3 07 kilonewIL)II ̄ ■data 4 39 kilonewtons data 6 59 kilonewtons Ma西cFornmla、3 0了kilonewton ̄ 、一 一墨 。 … ▲—一-一・・一・______-_0■■■■■ ’’……… ’…__,'■'-■‘ —■■ . 。一 ………Ma eFormula4 39kilonewtons 】 FOIlnula 6 59kilouewllmls 2 -8 -4 … l . 1’ ’l ~~-一-・一_…_ ~‘‘一一一~一 一一--▲▲▲▲▲▲▲▲▲▲ Fig.I 1 Lateral force versus slip angle for different vertical loads,2 degrees camber angle. Design,Construction and Validation of a Portable Tire Test Rig 一 _【_IL1- Z~ u'IL1 _【I:lI t}l1 II三^ ̄ Z :t)陶_【I;缸 一 625 ●■一一一一一一一一一一data3 01 kilonewtons data 4 81 kilonewtoils data5 65 kilonewtons Ma CFormtlla 3 0I kilonewtons 一~ 摹 … ●U口I一 一’ . ▲—一一--一。一一一 ………MarcFornmla.4。81kilonewtons Ma西cFormula 5 65kilollewtotis 2 .8 -4 …,、( -- 一1■- —。 鼍 _●--.-~一 一…………….… q嘲目嚆 二二—。-… Fig.12 Lateral force versus slip angle for different vertical loads,4 degrees camber angle・ ■■■■■■■■●●●-▲-^…一 一—一 一'- 。 II-III・・・・・・…一一 za_一’’ ▲ data 2.2 kilonewtons data3 3kilollewtons data 6.67 kilon ̄vtons —Ma cFormula 2 2kilonewtons ………Ma西eFornmla。3 3 kilonewtons ◆■▲— 2 .8 -4 …F ■ 一一一一一Ma西eFofmllla.6 67kilonewtons 《 1'_ ~~一。 。 : —一一■■■I--_m' . mMlmmm .t ̄ipAl e( 靠 Fig.13 Lateral force versus slip angle for different vertical loads,6 degrees camber angle・ Conclusions This paper presented the design and validation of a tire test trailer capable of collecting tire force and moment data on various driving surfaces.By Acknowledgments This project was supported in part by a grant from the Tank and Automotive Command of the United States Army,with Dr.Alexander Reid as Program Manager.The views expressed in this paper are those of the authors,and not the United States Govemment, comparing the collected data to a third party lateral orce model of fthe same tire.it was shown that the tire test rig is capable of collecting accurate data.An in house curve fitting routine was then used with the me United States Army,or Tank and Automotive Command. collected data to generate a Pacejka Magic Formula tire mode1 that ift the data within 1 O%total error.In order References to validate the portable tire test rig f0r off-road accuracy,extensive testing would need to be performed 川1 H.B.Pacejka,E.Bakker,The magic formula tyre model, Vehicle System Dynamics 21(1992)1-I8. on a variety of off-road driving surfaces.Additionally, in the future the rig will also be validated for larger tires, H.B.Pacejka,Tire and Vehicle Dynamics,2nd ed.,SAE International,2006. 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