 Proceedings of Engineering and Technology Innovation , vol. 4, 2016, pp. 43 - 45 43 Structural Analysis of Existing Multi-Speed Transmission Hubs of Bicycles Yi-Chang Wu * Department of Mechanical Engineering, National Yunlin University of Science & Technology, Yunlin, Taiwan. Received 01 February 2016; received in revised form 10 March 2016; accept ed 02 April 2016 Abstract This paper presents the analysis of topological structure of multi-speed transmission hubs for bicycles . Three existing transmission hubs with 8-speed, 11-speed and 12-speed are introduced. The topological structure of each gear mechanism, which is the main body of a transmission hub, is analyzed. The degrees -of-freedom (DOF) of the transmission hub is calculated by the Kutzbach’s equation. The related clutching sequence table for each transmission hub is also listed . Keywor ds : structural analysis, multi-speed, transmission hub, bicycle 1. A Sturmey-Archer 8-Speed Transmission Hub (a) Cross -section ABC abc 1 234 91011 678 5 第一組第二組第三組 InputOutput (b) Sketch diagram (c) Clutching sequence table Fig. 1 Sturmey-Archer 8-speed transmission hub Figs. 1(a) and 1(b) show the cross -section and sketch diagram of the Sturmey-Archer 8-speed transmission hub [1], respectively. It is a gear mechanism consists of 11 links, 6 gear pairs and 10 turning pairs. According to the Kutzbach’s criterion, the degrees -of-freedom (DOF) of this gear mechanism is: DOF = 3(N-1)-2J1-1J2 = 3(11-1)-2*10-1*6 = 4. Because it is a 4-DOF mechanism, four constraints are required for precise controlling this mechanism. Except for an input constraint, three additional constraints should be provided, which can be achieved by controlling the engagement of mechanical clutches within the gear mechanism. As can be seen in the clutching sequence table shown in Fig. 1(c), three mechanical c lutches are activated at each gear stage. 2. A Shimano 11-Speed Transmission Hub Figs. 2(a) and 2(b) show the cross -section and sketch diagram of the Shimano 11-speed trans- mission hub [2], respectively. It consists of three sets of compound planetary gear trains, which is a 12-link gear mechanism with 7 gear pairs and 11 turning pairs. According to the Kutzbach’s crite- rion, the DOF of this gear mechanism is: DOF = 3(N-1)-2J1-1J2 = 3(12-1)-2*11-1*7 = 4. For this * Corresponding aut hor. Email: wuyc@yuntech.edu.tw Proceedings of Engineering and Technology Innovation , vol. 4, 2016, pp. 43 - 45 44 Copyright © TAETI transmission hub, 8 mechanical clutches are in- stalled for controlling the power-flow path at each gear stage. Fig. 2(c) depicts the clutching se- quence table of this transmission hub. (a) Cross -section ABC ab c d 12345 6 7 8 9 10 11 12 第一組第二組第三組 InputOutput e (b) Sketch diagram (c) Clutching sequence table Fig. 2 Shimano 11-speed transmission hub 3. A Sachs 12-Speed Transmission Hub Figs . 3(a ) and 3(b) show the cross -section and sketch diagram of the Sachs 12-speed transmission hub [3], respectively. It consists of two sets of compound planetary gear trains as transmission units and one basic planetary gear train as a d ifferentia l unit. Th is is a 14-link gear mechanis m with 9 gear pairs and 13 turning pairs. According to the Kutzbach’s criterion, the DOF of this gear mechanis m is: DOF = 3(N-1)-2J1-1J2 = 3(14-1)-2* 13-1*9 = 4. For this transmission hub, 8 mechanical clutches are installed for controlling the power-flo w paths of the two sets of transmission units. Fig. 3(c ) shows the clutching sequence table of this transmission hub. (a) Cross -section 23456 9 7 8 14 1 12 13 11 Output a bc d ABCDE Input 10 \ (b) Sketch diagram (c) Clutching sequence table Fig. 3 Sachs 12-speed transmission hub 4. Conclusions Based on the above analysis, we can con- clude that the ma in body of a mult i-speed transmission hub used for b icycles is usually a comple x planetary gear train for provid ing with several forwa rd gears. Mechanical clutches, Proceedings of Engineering and Technology Innovation , vol. 4, 2016, pp. 43 - 45 45 Copyright © TAETI especially for one-way c lutches, are emp loyed on coaxia l links, i.e., the sun gears, carriers and ring gears, for correctly guiding the powe r-flo w path at each gear stage. The number of activated clutches at each gear stage is related to the DOF of the planetary gear mechanism. Acknowledgment The author is grateful to the Ministry of Sci- ence & Technology (Taiwan, R.O.C) for sup- porting this research under Grants No. MOST 104-2628-E-224-001-M Y3. References [1] Ricke ls & SRAM, A mu lti-speed hub gear, World Patent, 01/92094, 2001. [2] Shimano Inc., Bicycle hub transmission, U. S. Patent, 2009/0023542, 2009. [3] M. Gerhard, Mult i-speed hub for bicycles, U. S. Patent, 5527230, 1996.