A phenomenological friction model of tripod constant velocity (CV) joints

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Abstract

Constant velocity (CV) joints have been favored for automotive applications, compared to universal joints, due to their superiority of constant velocity torque transfer and plunging capability. High speed and sport utility vehicles with large joint articulation angles, demand lower plunging friction inside their CV joints to meet noise and vibration requirements, thus requiring a more thorough understanding of their internal friction characteristics. In this paper, a phenomenological CV joint friction model was developed to model the friction behavior of tripod CV joints by using an instrumented CV joint friction apparatus with tripod-type joint assemblies. Experiments were conduced under different operating conditions of oscillatory speeds, CV joint articulation angles, lubrication, and torque. The experimental data and physical parameters were used to develop a physics-based phenomenological CV joint dynamic friction model. It was found that the proposed friction model captures the experimental data well, and the model was used to predict the external generated axial force, which is the main source of force that causes vehicle vibration problems.

Introduction

Constant velocity (CV) joints are an integral part of modern vehicles exhibiting superior vibration performance compared to universal joints as they eliminate uneven rotating torque via their self-centering ability. When connected to the driveshaft, CV joints provide plunging capabilities to compensate for length changes due to steering motion, wheel bouncing, and engine movement. In this research, the emphasis is on a class of plunging CV joints called tripod CV joints, which have been favored in automatic transmission vehicles, due to their noise and vibration advantages as they offer lower plunging resistance, compared to ball-type joints [1].

Even though CV joints are standard design components attached to torque transmitting shafts in vehicles, there are aspects of their friction and contact dynamics that are not understood or modeled. For example, a main CV joint-related problem in vehicles is the so-called “take off shudder,” which occurs when a vehicle moves abruptly. This problem is related to the internal CV joint friction, which consequently generates an axial force known as generated axial force (GAF). Another problem causing undesirable vehicle vibration is what is referred as “idle boom” that occurs because the plunging joint is directly connected to the transmission, which is excited by the engine, and thus transfers vibration to the driveshafts via the CV joints [2].

Extensive testing with all new model vehicles is typically undertaken to minimize or avoid potential vehicle problems, which lead to longer and costly development periods. Better understanding of the non-linear dynamic friction behavior of CV joints and the development of a CV joint friction model can provide powerful design tools and shorter development efforts. Current research in modeling CV joint effects on vehicle performance assumes constant empirical friction coefficient values [3]. Such models, however, are long known to be inaccurate, especially under dynamic conditions, which is the case for CV tripod joints [4].

In this paper, a phenomenological CV joint friction model is developed to predict the friction behavior of tripod CV joints. Using a prototype well instrumented CV joint friction apparatus with tripod-type joint assemblies, experiments were conducted under different operating conditions of oscillatory speeds, CV joint articulation angles, lubrication, and applied torque. The experimental data and basic physical parameters were used to develop a physics-based semi-empirical CV joint internal friction model. The proposed friction coefficient model was then used to develop a practical GAF model. Based on both the friction and GAF models, one can establish a better understanding of CV joint friction and use these models for designing vehicle components with improved performance.

Section snippets

Apparatus and instrumentation

The test apparatus and instrumentation used in this work, are shown in Fig. 1 and is described in detail in Lee and Polycarpou [5]. The apparatus uses complete CV joint assemblies and consists of dynamic sliding and height adjustment mechanisms and a static torque generator. The apparatus is capable of conducting controlled experiments to measure the internal friction of CV joint assemblies. The instrumented CV joint apparatus enables measurements of key performance parameters, such as CV joint

Slip-to-roll ratio

As discussed in the introduction, in addition to pure CV joint sliding friction, there is also rolling friction during CV joint operation. For rolling friction, the slip-to-roll ratio between roller and housing is very important since (a) at β=0°, GAF is zero because the slip-to-roll ratio is zero (which means that all friction is due to rolling friction); and (b) as the CV joint angle increases, the GAF and the possibility for “shudder” increases. Based on the above argument, the slip-to-roll

Semi-empirical phenomenological friction model

The CV joint total friction includes both static (stationary) and dynamic (stroking) components and the proposed model specifically includes both terms. Static friction arises from the applied torque without any stroking action and dynamic friction arises from the stroking action under the applied torque. Note that one could directly curve-fit the experimental data of Fig. 3 to obtain an empirical friction model. However, the physics of the problem will not be captured, as the individual

Conclusion

A physics-based semi-empirical CV joint internal friction model has been proposed based on both experiments and physical parameters. To measure the internal CV joint friction forces, a CV joint friction apparatus was designed and constructed and includes an embedded tri-axial force transducer inside the CV joint. Experiments were performed under different articulation angles, rotational phase angles, lubrication conditions and applied torque values. It was found that there is both static

Acknowledgments

The authors would like to thanks Delphi Saginaw Steering Systems for funding this project. Special thanks to William P. Skvarla and Dave Litter for coordinating the project and supplying the samples, and to Mark W. McPherson for providing useful advice and information in the design of the CV joint friction apparatus.

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1

Currently with the Department of Mechanical Engineering, Inha University, Korea.

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