Research on a novel configuration synthesis method of no-spin traction continuously variable transmission

https://doi.org/10.1016/j.mechmachtheory.2020.103963Get rights and content

Abstract

The no-spin design methodology of the traction continuously variable transmission (CVT) is the latest achievement in the field of CVT mechanism research. According to this methodology, four basic no-spin traction CVT mechanisms are acquired. In order to obtain more no-spin traction CVT mechanism topologies, a novel Configuration Factor Table (CFT) method for the configuration synthesis of basic no-spin traction CVT mechanisms is proposed, of which the main idea is from the basic law of separation and free combination of genes. Then the five main steps of configuration synthesis using this CFT method are described in detail. Based on this method, the configuration synthesis case studies of logarithmic CVT and conical CVT are carried out. The results show that 14 variant mechanisms of logarithmic CVT and 10 variant mechanisms of conical CVT are obtained. Among them, the swing-logarithmic CVT, rolling-logarithmic CVT, swing-conical CVT and rolling-conical CVT are considered to have the potential to become the new generation of high-power transmitting and high-efficiency traction CVTs.

Introduction

Traction continuously variable transmission (CVT) is an ideal mechanical transmission device to reduce vehicle emissions, improve vehicle efficiency, and achieve energy saving and environmental protection [1,2]. The working principle of the traction CVT is that a certain thickness of oil film is formed between the driving component and the driven component, and the oil film generates a solidification effect under high pressure to realize the power transmission [3]. Traction CVT has been extensively studied, mainly focusing on the contact problem [4,5], speed ratio control and modeling [6], [7], [8], [9], structure and parameter optimization [10], [11], [12], innovative CVT design and research [1,[13], [14], [15], [16], [17], efficiency analysis [1,[18], [19], [20], [21] and so on. For a traction CVT, there are three main types of power losses in the contact area, including creep (slip) losses, side slip losses, and spin losses [19]. The spin is in fact a power loss caused by the uneven distribution of velocity on the surface of the contact area, which is determined by a geometrical relation of the driving and driven components [5]. However, when the rotational axes of two traction components are parallel with the tangential line of the contact area, spin is zero. When these two rotational axes intersect the tangential line of the contact area at one point, spin also can be eliminated. Hence, these special conditions are always called no-spin conditions or zero-spin conditions [22]. Lots of researches show that spin is one of the important factors affecting the traction performance of traction CVT. In other words, reducing spin can improve the reliability and life [23], increase the bearing capacity [1,3,24] and significantly improve transmission efficiency [18,[25], [26], [27] of traction CVTs.

Therefore, scholars have been paying attention to reduce or eliminate the spin in the traction CVTs. William and Daniel [28] firstly designed a zero-spin traction CVT based on the Half Toroidal CVT by redesigning the parameters and disk curve. Narita et al. [29] proposed a novel CVT mechanism using a zero-spin disk, called Shaft Drive CVT, which was proved that the spin decreased to less than 1% at all speed ratio range, then the efficiency and power density are consequently improved. Novellis et al. [1] designed a new type of double roller Full-Toroidal CVT, which has a higher efficiency than that of the original Full-Toroidal CVT, and it mainly because the new structure could decrease the magnitude of the spin losses. Li [30] designed a self-rotation-free traction type stepless speed changer, which has the no-spin transmission characteristics. However, the most representative research is the no-spin design methodology of traction CVT developed recently. Firstly, Li et al. [25,26] optimized the no-spin disk generatrix for the Half Toroidal CVT based on the no-spin conditions, and a novel logarithmic CVT is obtained, which has an averagely 2%-3% higher transmission efficiency than that of the Half Toroidal CVT. Subsequently, on the basis of this optimization, Li et al. [22] systematically proposed a no-spin design methodology for transmission components generatrix in traction CVTs. The main idea of this method is to redesign the transmission parts or the transmission generatrix so that the contact area satisfies the no-spin conditions, then the no-spin traction CVT is finally achieved. Using this method to redesign the FU-type CVT and the tapered-roller and ring-disk CVT (TRCVT), the integral CVT and the Lambert CVT were obtained respectively [22]. Afterwards, a novel no-spin conical CVT was also acquired with this design method used to redesign the roller disk CVT by the author of this paper [22]. In addition, Li et al. [31] proposed another method based on the envelope theorem to optimize the shapes of disks and rollers of Half Toroidal CVT to get the outer cone and inner cone CVTs. However, the outer cone CVT is quite similar to the conical CVT mechanism, and this similarity will be verified in the Section 3.2. Therefore, there are already four basic no-spin traction CVT mechanisms obtained by using the no-spin CVT design methodology, as shown in Table 1, where the coordinate system established during the no-spin design process and the obtained basic mechanism solution are all described.

It is worth noting that these four types of no-spin traction CVTs are only basic mechanism by replacing the original transmission parts with the no-spin redesigned parts, which have not been considered synthetically from the structural feathers, transmission characteristics and carriable speed characteristics. In order to promote the practical application of these no-spin traction CVT mechanisms, it is quite necessary to find more topological configurations for different engineering applications. However, it is found that when considering the structural symmetry of the conical CVT mechanism, three more no-spin mechanisms can be obtained, and if both the structural symmetry and the number of movable parts involved in shifting motion are considered, much more no-spin mechanisms can be obtained [27]. This finding reminds us of the laws of gene separation and free combination in genetics, of which more progenies can be obtained from crossing two parent generations, as shown in Fig. 1.

Therefore, following the clue of gene separation and free combination law, a novel configuration synthesis method is proposed in this paper, which is called “configuration factor table (CFT) method”. Further, five steps for the use of this method to the configuration synthesis of no-spin traction CVTs are described in detail. In order to verify the practicality and effectiveness of this method, the configuration synthesis case studies of logarithmic CVT and conical CVT are carried out, and more generalized no-spin mechanisms are obtained finally, which also effectively provides practical examples for using this method to conduct the configuration synthesis for other types of traction CVT mechanisms.

Section snippets

CFT method

In the field of genetics, Mendel's pea hybridization experiments tell us that genes have the principle of separation and free combination, and the freely combined progeny will show different traits. This gives us a strong inspiration. Can we separate and reorganize the configuration features of a particular basic mechanism to find more family mechanisms when conducting a study of configuration synthesis for no-spin traction CVTs? Guided by this idea, the following hypotheses for the traction

Case studies on configuration synthesis for no-spin traction CVTs

In this section, the case studies on the configuration synthesis of the basic logarithmic CVT mechanism and conical CVT mechanism are carried out to obtain more no-spin traction CVT mechanisms. The synthesis of other no-spin traction CVT mechanisms, such as the integral CVT and Lambert CVT, can be studied by taking these as examples.

Conclusions

Based on the idea of gene separation and free combination, the configuration synthesis of no-spin traction CVTs are studied in this paper, and a novel CFT method is proposed. Further, the configuration synthesis case studies of logarithmic CVT and conical CVT mechanisms are carried out to verify the practicality and effectiveness of this novel CFT method. Therefore, the following conclusions can be drawn:

  • (1)

    The main idea of the CFT method is that the basic mechanisms have different configuration

Acknowledgments

This work was supported by the Starting Fund for Teacher Development and Research of Chengdu University of Technology [Grant numbers 10912-KYQD2019_07733].

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