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Smart Science ISSN: (Print) 2308-0477 (Online) Journal homepage: https://www.tandfonlinecom/loi/tsma20 Design of a Gear-Shifting Control Mechanism for 8Speed Bicycle Drive Hub Li-An Chen, Pei-Wun Ren & Yi-Chang Wu To cite this article: Li-An Chen, Pei-Wun Ren & Yi-Chang Wu (2013) Design of a GearShifting Control Mechanism for 8-Speed Bicycle Drive Hub, Smart Science, 1:2, 94-98, DOI: 10.1080/23080477201311665593 To link to this article: https://doi.org/101080/23080477201311665593 Published online: 04 Jan 2016. Submit your article to this journal Article views: 539 View related articles Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonlinecom/action/journalInformation?journalCode=tsma20 Smart Science Vol. 1, No 2, pp 94-98(2013) Design of a Gear-Shifting Control Mechanism for 8-Speed Bicycle Drive Hub Li-An Chen1, Pei-Wun Ren1, and Yi-Chang Wu1,* 1Department of Mechanical Engineering, National

Yunlin University of Science and Technology, Yunlin, Taiwan, ROC * Corresponding Author / E-mail: wuyc@yuntech.edutw KEYWORDS: Drive hub; Tansmission mechanism; Gear-shifting control mechanism The multi-speed drive hub stored on the rear wheel of a bicycle is an important speed-changing device to adjust the pedaling force and driving speed. This paper proposes a feasible gear-shifting control mechanism of an 8-speed distributed-flow-type transmission mechanism. A transmission mechanism consisting of two parallel-connected transmission units and one differential unit is introduced first. Then, based on the clutching sequence table, the embodiment design of a gear-shifting control mechanism is presented to selectively control the engagement of pawl-and-ratchet clutches and slot-with-block clutches as well as govern the power-flow path. The power-flow path at each speed-stage of this 8-speed drive hub is analyzed to verify the feasibility of the proposed design. Manuscript received:

October 19, 2013 / Accepted: November 19, 2013 1. Introduction actuation and power transmission path of each clutch, so as to validate the rationality of the design proposed. The multi-speed hub is an important variable driving gear for bicycles, mounted inside the rear wheel hub. The hub transmission consists of a speed shifting mechanism and a set of speed adjusting gear. The speed shifting mechanism consists of planetary gear train, providing multiple speed ratio values. The speed adjusting gear consists of clutch and connecting parts, controlling the gear shift fittingly. The speed shifting mechanism and speed adjusting gear of the hub transmission are embedded in the hub shell for protection, thus, the hub transmission has longer life cycle than current derailleur external gear-shaft. In addition, the hub transmission does not displace the chain to different chain wheels for gearshift anymore, overcoming the chain disengagement in gearshift effectively. The patents of bicycle

hub transmission are mostly possessed by foreign bicycle factories. The number of patents and the ability to develop key technologies of Taiwanese bicycle factories lag behind relatively. However, under the efforts of scholars and experts, specific design proposals and R&D achievements are accumulated, but most of studies focus on the design of speed shifting mechanism of hub transmission [1-3]. Few literatures aim at the design of speed adjusting gear, obstructing the practical development of hub transmission. This paper designs the speed adjusting gear of bicycle hub transmission specifically, and takes the 8-speed split transmission hub of literature [4] as object to design the translational speed adjusting gear. The speed adjusting gear is implemented by the layout of ratchet type coupling clutch and spline keyway fixed clutch and the specific design of translational control lever. The rotation speed of various machine members at each gear is tested to confirm the 2. An

8-speed split transmission hub Fig. 1 shows the 8-speed split transmission hub, it consists of one differential unit and two variable units. The split transmission hub means the power is imported by the chain wheel and split into two parts, which flow through variable unit I and variable unit II respectively. They are merged into the differential unit III at last The power is exported from the hub shell. The gear mechanism has 12 turning pairs and 8 gear pairs, the degree of freedom of the mechanism is 4. For constrained motion of the speed shifting mechanism, there must be four independent constraint conditions. The planet arm 5 is connected to the chain wheel, providing an input constraint. The other three constraint conditions are implemented by the actuation of three clutches. Fig 2 (a) is the sectional view of the split transmission hub. Fig 2 (b) shows the clutch actuation sequence list and the speed ratio values of various gears. Table 1 shows the parts list of the transmission

hub and the tooth number of gear assembly. 3. Design of a translational speed adjusting gear The function of speed adjusting gear is to actuate the dead lever, input lever and output lever corresponding to various gears of speed shifting mechanism properly. The translational speed adjusting gear is Smart Science 94 Smart Science Vol. 1, No 2, pp 94-98(2013) 8 Rear wheel hub 12 7C Variable unit (PGT ) C Differential unit (PGT ) 4R 6R 7R Output end 4S B 11 10 9 3 2 Cf3 A Input end 5 6C 1 Variable unit (PGT ) Fig. 4 Size planning of translational control lever 0 Cf2 (PGT -2) (PGT -1) Fig. 1 Schematic of 8-speed split transmission hub [4] (a) Sectional view Gear One-way clutch A B C S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 Cf1 Cf2 Speed ratio Cf3 value 1.18 1.00 Clutch Fixed clutch 0.87 0.76 0.68 0.62 0.53 0.49 Fig. 5 Schematic diagram of gear shifting of translational control lever Symbol “ “

represents clutch actuation (b) Clutch actuation sequence list Fig. 2 Sectional view of 8-speed transmission hub and clutch actuation sequence list Fig. 3 Translational control lever configuration the design subject in this paper, combined with the clutch actuation sequence list to design the speed adjustment assembly, so that it can shift gears in sequence. The control lever shifts axially, the main shaft of the control device is hollowed for mounting the translational control lever, and there is an internal spline in the internal surface of sun gear, so that the translational control lever can shift axially in the internal spline of sun gear, as shown in Fig. 3 The teeth of translational control lever engage with or disengage from the internal spline of sun gear during gearshift. The sun gear acts as dead lever in engagement, and it idles in disengagement. Therefore, the teeth of control lever and the internal spline of sun gear form the three fixed clutches, Cf1, Cf2 and Cf3. As

the packaging space width for the rear wheel of bicycle is about 180mm, each tooth is designed in width of 3 mm, the clearance on both sides is 0.5 mm to avoid interference in Smart Science 95 Smart Science Vol. 1, No 2, pp 94-98(2013) Table 1 Parts list and tooth number of gears Basic assemblies No. Designation No. Designation Ring gear 6R (32 teeth) 0 Main shaft 6 coupling Planet arm 6C Ring gear 7R (120 teeth) Sun gear 1 1 7 (32 teeth) coupling Planet arm 7C Ring gear 8 Sun gear 2 2 8 (120 teeth) (24 teeth) and hub shell Planet gear 9 Sun gear 3 3 9 (48 teeth) (40 teeth) Ring gear 4R (112 teeth) Planet gear 10 10 4 coupling (48 teeth) Sun gear 4S (76 teeth) Planet gear 10 5 Planet gear 5 11 (36 teeth) Designation 12 Planet arm 12 Ci Regulating ring 13 Chain wheel A Coupling clutch A 14 Chain wheel seat B Coupling clutch B 15 Right side cover C Coupling clutch C Cf1 Fixed clutch Cf1 Cf2 Fixed clutch Cf2 Cf3 Fixed clutch Cf3 16 gearshift, as shown in Fig.

4 The control lever is pulled in turn rightwards to complete gearshift, as shown in Fig. 5 The face width of tooth of sun gear increases by 4 mm with each unit of pulling the control lever in gearshift. As the gear is changed by axial translation in sequence by the translational control lever, in order to reset the translational control lever, there must be a return spring, a compression spring is mounted on its left side, and an extension spring is mounted on its right side. The layout is shown in Fig. 6 In addition, the coupling clutches A, B and C consist of pawl and ratchet, as shown in Fig. 7 The clutch actuation is adjusted by extra speed automatically. When the pawl speed is higher than the ratchet speed, the clutch is actuated, the power is transmitted by the coupling clutch. On the contrary, when the pawl speed is lower than the ratchet speed, the clutch is not actuated. Based on this extra speed, it is unnecessary to control the actuation of coupling clutch, reducing the

assembly number of speed adjusting gear effectively. Speed adjustment assembly No. Designation No. Left side cover Fig. 7 Coupling clutch 4. Power transmission path testing The hub transmission slides on the main shaft by the translational control lever, the fixed clutch uses different sun gears as fixed parts, and the speed difference determines the actuation of coupling clutch. Eight gears can be shifted only by controlling the relative position of translational control lever on the main shaft. Take gear I as an example, the power transmission path is described below: The translational control lever is in the leftmost of slideway inside the main shaft, the power is transmitted from chain wheel 13 to the member 5. The power split is described below: (i) Split 1: the teeth of translational control lever seize the sun gear 1 to actuate the fixed clutch Cf1, so the first set of variable unit PGT I is actuated, and the member 4R of PGT I is shifted. At this point, the ratchet speed

of member 4S is higher than the pawl speed of member 5, the coupling clutch A is not actuated, so the power is transmitted to the differential unit PGT III as the shifted Fig. 6 Schematic diagram of mounting springs for translational control lever Smart Science 96 Smart Science Vol. 1, No 2, pp 94-98(2013) member 4R drives the stationary planet gear 12, the power flow direction is shown as the solid line in Fig. 8 (ii) Split 2: the sun gears 2 and 3 are not fixed, so the coupling clutch B is actuated. The pawl on the member 5 drives the ratchet of stationary member 6, and then the coupling clutch C is actuated, namely, the pawl of member power is transmitted to the variable unit PGT II-2, the 6 drives the ratchet of stationary part 7, then the power is transmitted to the differential unit PGT III. The power flow direction is shown as the dotted line in Fig. 8 (iii) Merge: ω4S and ω7 are merged into differential unit PGT III, exported from ring gear 8 to the hub at last. In

addition, the power transmission paths of Gear 2 and Gear 8 are shown in Fig.s 9 to 15 respectively According to the analysis of power transmission paths of eight gears, under the control of translational speed adjusting gear, the clutches can be actuated exactly according to the gears, so that the ring gear 8 at the output end generates correct rotation speed, so the proposed speed adjusting gear is a feasible design proposal. Fig. 12 Power transmission path of Gear 5 Fig. 13 Power transmission path of Gear 6 Fig. 14 Power transmission path of Gear 7 Fig. 8 Power transmission path of Gear 1 Fig. 15 Power transmission path of Gear 8 Fig. 9 Power transmission path of Gear 2 5. Conclusions This paper proposed a design proposal of translational speed adjusting gear for bicycle hub transmission, an 8-speed transmission hub is taken as object, the actuation of clutch is controlled by configuring ratchet type coupling clutch and spline keyway fixed clutch and specific design of

translational control lever, as well as its relative position in axial direction of main shaft, so as to shift the gear. The translational speed adjusting gear needs a large axial packaging space to mount machine members, when the gear number of hub transmission is larger than eight, the translational speed adjusting gear is inapplicable to the limited rear wheel axle space of bicycles, a rotary or rotary translational speed adjusting gear must be designed, so as to solve the problem of insufficient axial packaging space. Fig. 10 Power transmission path of Gear 3 Fig. 11 Power transmission path of Gear 4 Smart Science 97 Smart Science Vol. 1, No 2, pp 94-98(2013) ACKNOWLEDGEMENT The authors are grateful to the National Science Council (Taiwan, R.OC) for supporting this research under grant NSC 102-2221-E224-016-MY2 REFERENCES [1] [2] [3] [4] C. H Hsu, Y C Wu, “Enumeration of Planetary Gear Trains for Multi-Speed Bicycle Drive Hubs,” Proceedings of National Science

Council (Republic of China) Part A, Vol. 22, No. 5, pp 670-676, (1998) C. H Hsu, T C Wen, “Creative Design Methodology for Split-Power Multi-Speed Drive Hubs of Bicycles (in Chinese),” Proceedings of the 11th National Conference on the Design of Mechanisms and Machines, Hsinchu, Taiwan, Paper No. A1N-51943, 2008 Y. C Wu, S L Lin, “Conceptual Design of a 16-Speed Bicycle Drive Hub,” Applied Mechanics and Materials, 5254, 279-284 (2011) Y. C Wu, P W Ren, “Design of an Eight-Speed Transmission Hub for Bicycles (in Chinese),” Proceedings of the 15th National Conference on the Design of Mechanisms and Machines, Tainan, Taiwan, Paper No. A-018, 2012 Smart Science 98