Elsevier

Tribology International

Volume 152, December 2020, 106568
Tribology International

The dynamic wedging and friction characteristics of one-way clutch under transient loads from stator

https://doi.org/10.1016/j.triboint.2020.106568Get rights and content

Highlights

  • Blade-row interaction or the switch of conditions would lead to continuous transient unsteady loads in the transmission system.

  • The dynamic wedge process can cause about 25% overshoot of the contact force.

  • The frictional force in the outer ring is larger than those in the inner ring at first, causing the slide near the outer ring’s contact area.

  • The self-lock performance of the one-way clutch has a close relationship with the wedge angle, material’s frictional coefficient and the spring loads.

Abstract

The frictional characteristics, as well as its self-lock mechanism of the one-way clutch under working conditions were further explored. First of all, the wedge and friction characteristics of the one-way clutch under the corresponding working conditions were explored and analyzed by combining the transient-flow simulation and explicit dynamics. The results show that the loads transmitted by the stator and the one-way clutch are typical transient unsteady loads; during wedge process, both the transmission force and the contact stress of the one-way clutch are transient with an overshoot and finally converge. As for the wedging process, the self-lock characteristics turn out to be determined by the wedge angle and frictional coefficient, and influenced by the spring force.

Introduction

It is well known that in a hydraulic transmission system, the Hydrodynamic torque converter (HTC) can not only automatically vary the speed and multiply the torque, but also absorb shock loads or vibration energy, leading to a great improvement in the transmission performance. However, it also causes a decrease in the transmission efficiency comparing to those without it. The utilization of the one-way clutch (Fig. 1) can alleviate such disadvantages: it can not only keep the torque converter’s basic function at low speed ratio but also maintain relatively high efficiency in high speed ratio by introducing a coupling condition.

Among the one-way clutch currently used for hydraulic transmission, those with rollers and logarithmic spiral profile [1] have the feature to maintain the same wedge angle for different contact positions, therefore, it has its advantage in self-locking feature in wedging process and sensitive separation performance in reverse-rotatory condition, besides, it can offer relative high load performance. As a result, this type of one-way clutch has been wildly used with a good application prospects.

Wei Wei [2] and his colleges carried out detailed two-dimensional and three-dimensional numerical simulation on the design and self-locking mechanism, their results show that both wedging and separating process are dynamic processes with oscillation and rebound, which has been verified by the three-dimensional explicit dynamic simulation, besides, it also indicated that the axial stress distribution of the contact surface is nonuniform, but reducing the three-dimensional problem down to the two-dimensional problem in the aspect of strength design is feasible.

Noted that during this process, it is the preload of spring on the rollers that the rollers can always keep in contact with the inner and outer rings and offer pre-stress, which can be helpful to accelerate the wedging process, but during the separation, this preload will hinder the separation of rollers and inner or outer rings, and make it a process of continuous friction and slip, which would increase the resistance torque [3], resulting in energy loss and efficiency drop.

Since the torque converter is a typical multi-element hydrodynamic turbomachinery, which can be significantly affected by the rotor–stator and rotor–rotor interactions in the internal flow field. The most obvious feature is that there is obvious fluctuation in the torque results of the blade and its corresponding wheel. Those unsteady loads would directly transfer to the stator, as well as the component that directly connected with it, like the one-way clutch, therefore, those related components would suffer those unsteady loads instead of the steady static one [4], [5]. This result would show its obvious difference with the previous research results that basically based on the static loads.

Furthermore, under the influence of such unsteady loads, it is still worth knowing whether the roller of the one-way coupling can still maintain close contact with the inner and outer rings and keep the wedging process steady by its self-lock function. In this way, the relative research can not only be helpful for the design and optimization of the one-way clutch, but it also means a lot for the research to steadily self-lock or reduce the influence of the sliding of the stator on the torque performance. Besides, it also has its role and significance for enhancing the stability of the transmission system, as well as energy loss reduction and efficiency improvement.

All in all, due to that the change of the working state or working loads of the one-way clutch is directly related to the stator loads or internal flow characteristics, it is necessary to explorer the dynamic characteristics of the one-way clutch while combining the unsteady transient loads from the flow field of torque converter, by means of this, an advanced dynamic analysis of the wedge characteristics is further studied.

Section snippets

Theoretical aspect

As is known to us all that the torque converter is a typical multi-element turbomachinery [6], the blade flutter as well as the wheel torque flutter is closely related to the rotor-rotor or rotor-stator interaction [7], [8] of the internal flow field, therefore, it is necessary to obtain those internal transient flow fields state and its induced loads pulsations first.

Since the stator shaft is fastened to the stationary housing of the gearbox via one-way clutch, the blade torque, as well as the

Mechanics analysis of the one-way clutch

The one-way clutch has a close relationship with torque converter, especially for the stator, and its geometry structure and the basic components can be seen from Fig. 5:

From Fig. 5, we can clearly see that the stator’s inner ring has bonded with the outer ring of the one-way clutch, which means that the stator loads can be regarded as those of the one-way clutch. The torque converter’s working results show that the stator would suffer the torque loads with anticlockwise direction (Fig. 5) at

Explicit dynamics based on the CFD results

The basic wedging process for one-way clutch goes as the previous chapter describes, however, since the loads of the stator comes from the pressure difference of the stator blades, which is fully transient one with pulsation, this indicates that the loads of the outer ring should be TS(t) (Fig. 3 is a typical example for loads during the wedging process) instead of the average steady torque TS. From this point of view, the explicit dynamic based on the transient CFD results would be more

Conclusion

About all, by combining hydrodynamic transient analysis and structural explicit dynamic method, the wedging dynamic process is compared with the structural mechanic analysis based on balanced/quasi-balanced state, or the explicit results with both steady and transient loads, some useful relationship between the loads and the contact force was promoted, and some more differences in this transient dynamic process were compared, the following conclusions can be drawn:

  • 1.

    The blade torque, as well as

CRediT authorship contribution statement

Zhifang Ke: Data curation, Methodology, Writing - original draft, Editing, Validation. Wei Wei: Conceptualization, Writing - review & editing, Supervision. Cheng Liu: Visualization, Validation, Writing - review & editing. Meng Guo: Formal analysis, Validation. Qingdong Yan: Supervision, Resources, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (NSFC) [Grant Nos. 51475041 and 51805027]; National Ministry’s Basic Product Innovation Program, China [Grant237099000000170009]; National Key Lab of Vehicular Transmission Foundation, China [Grant No. 614221304040517]; Zhifang Ke was supported by the China Scholarship Council (CSC) for 18 months study at the University of Virginia.

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