CHEN Bao, LEI Gang

1.School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China；2.Chongqing Institute of Automobile, Chongqing University of Technology, Chongqing 400054, China

SuspensionRubberMount’sImpactonEvaluationofVehiclePerformance

CHEN Bao1, 2*, LEI Gang2

1.SchoolofMechanicalEngineering,SouthwestJiaotongUniversity,Chengdu610031,China；2.ChongqingInstituteofAutomobile,ChongqingUniversityofTechnology,Chongqing400054,China

Toeffectivelystudyhowthesuspensionrubbermounttoaffectvehicleperformance,thispaperintroducedsomeuptodateresearcheswhichfocusonrubbermountanditsimpact.Differentmodelingandcalculationtheorieswereadoptedtocomparetheadvantagesanddisadvantagesfortheseresearchesinthispaper.Somepreviousresearchresultsofauthors’teamwereusedtoshowthechangeofvehicleperformanceundertheconditionsofdifferentinfluencefactorsofrubbermount.AconclusioncouldbedrawnthattherelativetolerancesoftotalweightedRMSaccelerationforacarmodelwithorwithoutrubbermountscouldchangeobviouslywhenthethreemainfactorsareused.Basedontheconclusionsofthispaperandotherresearchresults,ameaningfulresearchplanisproposedfortherubbermountanditsimpact.

rubbermount，vehicleperformance，multi-bodydynamicmodel，roadroughness，driving-speed，stiffness，weightedRMSacceleration

1.Introduction

Vehicle technology of 21 century has made greater progress than before, at the same time, as people share the happiness brought by super vehicle technology, more people set some higher demands on vehicle performance such as ride comfort and handling stability. Suspension system, as one of important vehicle assemblies, has a greater impact on vehicle performance than other vehicle assemblies. Rubber mount is especially important as a type of part for suspension system to isolate vibration and reduce road shocks during high-speed driving. Once the rubber mount is installed into any one vehicle, the multi-nonlinear characteristic always impacts the vehicle performance due to the material, geometry, and contact.

Firstly, the researches about influence of rubber mount on vehicle performance were reviewed to show the present study situation in this paper, and some insufficient research areas were put forward. And then, some modeling and calculation theories for vehicle performance were presented to describe the advantages and disadvantages, respectively. Secondly, some previous research results of present authors’ team were listed to show a more detailed study of rubber mount influence on the vehicle performance than the other researches as mentioned before. Based on the consideration of influence importance for rubber mount on vehicle performance, the present research achievements are not enough. Therefore, some new research areas will be put forward in the next study plan for the authors’ team.

2.Present research situation on rubber mount and its impact

Currently, many literatures from domestic and overseas often focus on the characteristic of any one rubber mount. A kind of method to select a suitable constitutive equation to get good stiffness curves as compared with experiments data is introduced in “Selection of Constitutive Models in Rubber Bushing Simulation” of a SAE paper[1], and in another SAE paper “Parameters Identification of Constitutive Models of Rubber Bushing”, the focus is to deduce the torsion stiffness by using the axial and radial stiffness[2]. The other literatures mainly are interested in rubber mount’s impact to suspension performance, these are discussed in two master theses, i.e., “Analysis on Suspension K&C Character and Automobile Stable Steering Performance Affected by Rubber Bushing Stiffness”[3] and “The Influence of Rubber Bushing Stiffness to Suspension K&C Characteristics and Full Vehicle handing and stability”[4]. Some researcher conducted the other study works on vehicle performance impacted by rubber mount, these research results can be found in literatures [5-7].

The research achievements mentioned above have promoted to a certain extent for auto parts design and automotive manufacture. However, some deeper study about rubber mount and its impact actually could be done in the future.

3.Review of research results from the authors’ team

3.1.Twotypesofsimulationmodels

In order to perform some numerical simulations, some better simulation models must be established, and when the kinematics & compliance of a car would be studied, any one kind of multi-body dynamics simulation system must be selected. At least two simulation systems are popular in the world, one is ADAMS, another is SIMPACK, although there are some differences between each other. Fig.1 is a comparison of a car model from these two simulation systems [8].

A four link mechanism is presented as an example; two topology diagrams of four link mechanism can be built to obtain Fig.2. For a multi-body system including some closed-loops, there are the following expressions about the number of degrees of freedom (DOFsystem) and the number of first order states(FOSsystem):

DOFsystem=DOFjoint-constraint

(1)

FOSsystem=2DOFjoint+constraint

(2)

2DOFjointrepresents the number of Ordinary Differential Equations (ODEs), constraint represents the number of algebraic equations[9].

“Bad” model is as follows:

DOFsystem=DOFjoint-constraint=18-17=1

FOSsystem=2DOFjoint+constraint=2×18+17=53

“Good” model is as follows:

DOFsystem=DOFjoint-constraint=3-2=1

FOSsystem=2DOFjoint+constraint=2×3+2=8

Fig.1 Multi-body car model with rubber mounts

Fig.2 Two topology diagrams of four link mechanism

From the above mentioned example, the number of differential equations based on generalized coordinates (“Good” model from SIMPACK) is much smaller than those based on absolute coordinates (“Bad” model from ADAMS). Therefore, the solution speed will be faster for a “Good” model. When a multi-body system has more than one body, and the number of constraints becomes bigger, the superiority of a model based on generalized coordinates will be particularly evident.

The integration of the differential equations can be done either off- or on-line[10]. It is called on-line integration in SIMPACK animating the model whilst performing the integration process; this is also called real time simulation. Otherwise for ADAMS, the integration time is defined by the duration between a start and end time, and the animation of the model is performed later by ADAMS. Normally, off-line integration is selected in a real application.

3.2.Vehicleperformanceimpactedbyrubber

mounts

3.2.1.Scenarios and simulating conditions

Human’s ride comfort is an important performance to any kind of vehicle according to the standard of GB/T4970—2009[11], and some special scenarios were set up in the other research results from the authors’ team. The first scenario had the same driving speed (70 km/h) and different road roughness (first road: Good Asphalt, second road: Medium Asphalt, third road: Bad Pavement). The second scenario had the same road roughness (Good Asphalt) and different driving speeds (80 km/h, 85 km/h, and 90 km/h). The last scenario was to study how extent about effectiveness of each direction’s stiffness impact on vehicle performance when any one of six direction’s stiffness was put out of action and the other five direction’s stiffness were remained.

In order to analyze the impact of suspension rubber mount on ride comfort, the total weighted RMS acceleration (av) of the seat surface was used as an evaluation index. The following two assumptions about rubber mounts were made in each scenario:① Model of front & rear suspensions without rubber mounts.② Model of front & rear suspensions with rubber mounts.

In order to obtain the other simulation conditions, for example, the selection & design of road roughness, the calculation methods of the total weighted RMS acceleration and so on, the readers could refer to some literatures[12-13].

Evaluation of the results for any scenario of this paper was done by using the relative difference. And the relative difference is defined as a percentage deviation betweenav,without_mountsof a car model without rubber mounts andav,with_mountsof the car model with rubber mounts.

(3)

3.2.2.Analysis of simulation results based on scenarios

The analyses were performed under three special scenarios.

For the first scenario, the Good asphalt is adopted and the relative difference is 6.24%. however, the relative differences of the Medium asphalt and the Bad pavement are 3.84% and 2.70%, respectively.

For the second scenario, the relative differences of 70 km/h and 80 km/h are 6.24% and 6.46%, respectively. However, the relative differences of 85 km/h and 90 km/h are 47.31% and 64.93%, respectively.

For the third scenario, if the translational stiffness inXandZare hided, the relative differences are 5.58% and 2.93%, respectively; if the translational stiffness inYand rotational stiffness inYare hided, the relative differences are 0.44% and -0.31%, respectively; if the rotational stiffness inXandZare hided, the relative differences are all zero.

Tab.1 shows the ultimate values of relative differences under a special impact factor for every scenario.

Tab.1 Ultimate values of relative difference

In the second scenario, the acceleration-time histories with or without rubber mounts are presented in Fig.3 and Fig.4, respectively, for two driving speeds of 80 km/h and 85 km/h. When the driving speed is higher than 80 km/h, the rubber mounts have a greater impact on the acceleration-time histories, and beyond the speed of 85 km/h, the impact of the rubber mounts will be more obvious from Fig.4.

Fig.3 Acceleration-time histories of 80 km/h

Fig.4 Acceleration-time histories of 85 km/h

4.Conclusions

According to the research achievements about rubber mount and its impact from the literatures, some important conclusions can be drawn:

With the gradual deterioration of road roughness, the relative difference gets smaller and smaller. In other words, the better the road, the greater impact of rubber mount. Therefore, a suggestion could be given that a driver should try to select a better road to drive.

With the increase of the driving speed, the relative difference becomes greater and greater. When the driving speed is higher than 85 km/h, especially in the direction ofYaxis, the impact of rubber mount on ride comfort becomes more important and obvious.

Any one direction’s stiffness of rubber mount has different impact on vehicle performance, in this paper, the translational stiffness inXhas dominant affect on the total weighted RMS acceleration of human’s ride comfort.

For the future research plan about rubber mount and its impact, the material, the geometry and the contact conditions of rubber mount will be considered and the parameters and the installing direction of rubber mount will be optimized to analyze the suitable matching of ride comfort and handling stability.

[1] Yuan Qu,Lin-bo Zhang.Parameters Identification of Constitutive Models of Rubber Bushing[J].SAE Technical Paper,2011(1):95.

[2] YUANG Qu,SHEN Wu.Selection of Constitutive Models in Rubber Bushing Simulation[J].SAE Technical Paper,2012(1):761.

[3] JIANG dong.Analysis on Suspension K&C Character and Automobile Stable Steering Performance Affected by Rubber Bushing Stiffness[D].Zhengjiang:Jiangsu University,2011.

[4] LI linhua.The Influence of Rubber Bushing Stiffness to Suspension K&C Characteristics and Full Vehicle handing and stability[D].Changsha:Hunan University,2011.

[5] HUI Xiaodan.Simulation Research of Vehicle Handling StabilityBased on SIMPACK Software[J].Technology & Application,2010,14(4):36-37.

[6] DU Zixue,WANG Xingcong.Research on Modeling and Simulation of Microbus Ride Comfort Based on SIMPACK Software[J].Agricutural Equipment & Vehicle Engineering,2008(12):31-33.

[7] WANG Mingrong,SONG Yongzeng.Modeling and Simulation Analysis of Automotive Ride Performance[J].Automotive Technology,2005(4):7-10.

[8] CHEN Bao,TANG Aihua.Research for Evaluation of Ride Comfort Based on Generalized Road Surface Profiles and Normal Driving Speed[J].Journal of Southwest China Normal University:Natural Science Edition,2012,37(7):70-74.

[9] Documentation of SIMPACK 8.9: Analysis and design of general mechanical systems[EB/OL].[2013-03-08].http://ol.cadfamily.com/simpack/index.html.

[10] MIAO Bingrong,XIAO Shoune,JIN Dingchang.Research on modeling and analysis of a complex multibody system by using SIMPACK[J].Mechanical Science and Technology,2006(25):813-816.

[11] GB/T 4970—2009,Method of random input running test-automotive ride comfort[S].Beijing: Chinese Standard Publishing house,2010.

[12] CHEN Bao,ZHANG Yong,LEI Gang.Research for effectiveness of suspension rubber bushings on subjective reactions of human’s ride comfort[J].Modern Manufacturing Engineering,2012(5):44-49.

[13] CHEN Bao,KE Jian.Double Scenarios Analysis for Impact of Suspension Rubber Bushings on Ride Comfort[J].Modern Manufacturing Engineering,2012,34(5):134-140.

悬架橡胶衬套对车辆性能评价的影响

陈 宝1,2*,雷 刚2

1.西南交通大学 机械工程学院， 成都 610031；2.重庆理工大学 重庆汽车学院， 重庆 400054

为进一步深入研究悬架橡胶衬套对车辆性能评价的影响，介绍了当前有关橡胶衬套及其影响的研究热点，同时用不同的建模与计算理论比较说明各自的优缺点。一些前期研究结论也被引入，以说明在不同影响因子的作用下橡胶衬套对车辆性能改变的影响。结果表明，当3种主要的影响因子被使用时，对有无衬套的轿车模型的总加权加速度均方根值的相对变化率改变极为明显。最后对橡胶衬套及其影响提出下一步研究计划。

橡胶衬套；车辆性能；多体动力学模型；路面不平度；行驶车速；刚度；加权加速度均方根

U461.6

2012-11-18

*CHEN Bao,Assistant professor.E-mail: chenbao@cqut.edu.cn

10.3969/j.issn.1001-3881.2013.06.010