• 한국자동차공학회논문집
• /
• 제16권4호
• /
• pp.103-109
• /
• 2008

Semi-spherical CVT(SS-CVT) is one of friction drives, which transmits power via the friction force between a spherical shaped variator and output disks. The variator varies the speed ratio of SS-CVT continuously as well as transmits input power into the output shaft. Therefore two friction forces are normally applied on the variator; one is the longitudinal friction force for power transmission and the other is the lateral for shifting. In order to investigate the dynamic behavior of SS-CVT, we introduced a numerical model of 2-dimensional friction force using a function of slip ratio and slip angle. And a dynamic model, which describes the shifting mechanism of SS-CVT, is developed through 3-dimensional vector analysis. Finally we presented numerical results of the shift characteristics focused on the transient behavior of the variator's slip ratio and slip angle. The numerical results also show the typical CVT shifting characteristics of SS-CVT and stable shifting behaviors of the variator.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집A
• /
• pp.690-695
• /
• 2000

This article deals with the analytic results on the development and application of the Spherical CVT. The Spherical CVT is marked by its simple configuration, the infinite torque multiplication characteristic, and the smooth transitions between forward/neutral/reverse states of output speed. In this study, we describe the conceptual principles behind the Spherical CVT and some applications of it, which we developed recently. And, we propose the shifting algorithm based on the analytic consideration of CVT powertrain system. Contrary to conventional shifting algorithms using the OOL(optimal operating line) of the power source, the proposed shifting algorithm is represented as a $2^{nd}$ order equation in an explicit form, and it reveals the possibility of theoretic design of all optimal controller. As an example, we present numerical results that demonstrate the energy saving possible and the proposed shifting algorithm from the use of the Spherical CVT over standard reduction gear unit, using an ideal dc motor model.

• 동력기계공학회지
• /
• 제13권4호
• /
• pp.18-23
• /
• 2009

구면무단변속기(SS-CVT)는 구조가 간단하여 변속기구의 부피와 무게를 기존의 변속기구에 비하여 줄일 수 있으며, 별도의 클러치 없이 출력축의 정회전, 역회전 그리고 중립상태 등을 구현할 수 있다. 본 연구에서는 이러한 구면무단변속기의 기구적 특징과 변속메카니즘을 이용하여 직류모터와 가솔린엔진을 장착한 병렬형 하이브리드차량의 동력전달계를 제안하고자 한다. 이를 위하여 먼저 구면무단변속기의 작동원리에 대해 설명하고 전용 실험장치를 제작하여 무단변속성능을 검증하였다. 또한 직류모터를 보조 동력원으로 사용하는 병렬형 하이브리드차량 동력전달계의 설계를 위해 연결기어비와 구면무단변속기의 변속비를 차량주행성능에 맞추어 설정하였으며, 이를 차량가속성능의 수치 시뮬레이션을 통하여 분석하였다. 시뮬레이션 결과를 바탕으로 구면무단변속기의 하이브리드차량 동력전달계의 적용가능성을 검증하였으며, 연구결과로 선정된 구성요소의 설계파라미터를 이용하여 시작차량을 제작하였다.

• International Journal of Automotive Technology
• /
• 제4권4호
• /
• pp.165-172
• /
• 2003

This article deals with the spin loss analysis of friction drive CVTs, especially for the cases of S-CVT and SS-CVT. There are two main sources of power loss resulting from slippage in the friction drive CVT, spin and slip loss. Spin loss, which is also a main design issue in traction drives, results from the elastic contact deformation of rotating bodies having different rotational velocities. The structure and operating principles of the S-CVT and SS-CVT are first reviewed briefly. And to analyze the losses resulting from slippage, we reviewed previous analyses of the friction mechanism. A modified classical friction model is proposed, which describes the friction behavior including Stribeck (i.e., pre-sliding) effect. It is also performed an in-depth study for the velocity fields generated at the contact regions along with a Hertzian analysis of deflection. Hertzian results were employed to construct the geometric parameters and normal pressure distributions of the contact surface with respect to elastic and plastic deformations. With analytic formulations of the relative velocity field, deflection, and friction mechanism of the S-CVT and SS-CVT, quantitative analyses of spin loss for each case are carried out. As a result, explicit models of spin loss were developed.

• 한국자동차공학회논문집
• /
• 제13권5호
• /
• pp.134-141
• /
• 2005

Semi-Spherical Continuously Variable Transmission(SS-CVT) is the CVT which transmits power by rolling friction between dry metals, and its outstanding advantage is the ability of realizations of neutral, forward and reverse states without relying on any other devices. A spherical shaped variator transmits power and also changes gear ratio where keeping contact with a output disk. The frictional direction to transmit power and the other direction to change gear ratio are perpendicular to each other, so we can describe that two dimensional rolling friction is occurred in the contact point between the variator and the disk. Since magnitudes or relations of the two forces are completely unknown, they were analyzed by the experiments in this study. We determined the variables related with the friction phenomena by the dimensional analysis, and manufactured the SS-CVT test bench which could measure the related variables. Finally, the empirical formula for evaluating the two friction forces was proposed based on the experimental results.