GB2249605A

GB2249605A - Bicycle speed change mechanism

Info

Publication number: GB2249605A
Application number: GB9024086A
Authority: GB
Inventors: Tsyr-Shin Chen; Cheng-Wen Chen
Original assignee: ROOTS ENTERPRISE CO Ltd
Current assignee: ROOTS ENTERPRISE CO Ltd
Priority date: 1990-11-06
Filing date: 1990-11-06
Publication date: 1992-05-13
Also published as: GB9024086D0

Abstract

A bicycle speed change mechanism, characterized in that, a stop ring 303 is installed at the front end of a speed change support 305, the stop ring is bent to one side to form a positioning plate 303C that is bent outwardly. One end of a C-type snap ring 302 is installed next to the stop ring 303 and extends outwardly to form a handle 302a. The handle is bent to one side to form an angle plate 302b on which two tapped holes 302c, 302d are formed. When two bolts 301a, 301b mounted in the tapped holes are adjusted, the torsion force of the spring mounted inside the speed change support is accordingly adjusted. Thus, after the speed change mechanism is used for a long period of time, the bicycle chain can still be maintained at a fixed tension. <IMAGE>

Description

IMPROVEMENTS IN BICYCLE SPEED CHANGE MECHANISMS The present invention relates to an improved form of bicycle speed change mechanism for bicycles and particularly to a speed change device in which there is an adjusting mechanism provided.

A conventional speed change mechanism as shown in Fig. 1 is well known wherein a speed change mechanism 100 is mounted at the rear of a bicycle, a torsion spring being mounted in a speed change support 101 to press a flange thereof against a baffle angle of the bicycle frame. When the rider pulls all adjusting cable 102 to change the riding speed. a double connecting lever sliding mechanism produces a parallel sliding action and moves a chain guider 103 connected to the other end of the double connecting lever horizontally. A bicycle chain 104 is then moved to the next rear transmission gear accordingly.During this procedure, as the radius of the rear transmission gear changes, the whole speed changer must move backwards to compensate the difference resulting from such change so as to keep the bicycle chain 104 at the same tension; the force necessary for maintaining the chain tension comes from the torsion spring which is installed in the speed change support 101.

Fig. 2 shows the structure of the common speed change mechanism, in which a support shaft 206 is installed in a support body 203 and then fixed in a tapped hole 200a on the bottom end of a bicycle frame 200. Also mounted on the support shaft there is a cover 205, a spring 204, a sleeve tube 202 and a C-type snap ring 201, in which the right hand side outer rim of the cover 205 is fixed at the end of the support shaft 206, the step-type outer rim of the other side of the cover 205 presses the spring 204 into the support body 203 and onto the sleeve tube 202. The right hand end bent part of the spring 204 is fixed in a groove 203a of support body 203 the left hand end bent part of the spring 204 being fixed into a guide hole 202b formed on the left hand side stepped part of the sleeve tube 202.A threaded part 206b of the support shaft 206 extrudes from the sleeve tube 202, and a C-type snap ring 201 is put onto the gap 206a to prevent the sleeve tube from dropping out of support body 203 and the thread 206b of the support shaft 206 is locked into the tapped hole 200a of the bicycle frame 200. To change the riding speed, a bicycle rider must pull the adjusting cable very often to move the chain guide horizontally so as to move the chain to the next rear transmission gear. After a long period of use, the elastic fatigue phenomenon will easily occur in the torsion spring 204. As it is impossible to adjust the spring coefficient or modify the spring S torsion force1 the time necessary to change riding speed becomes longer and longer, furthermore, the tension force of the chain maintained by the chain guide becomes weaker.These are the common defects which occur in usual bicycle speed change mechanisms.

According to the present invention a speed change mechanism for a bicycle comprises a bicycle frame on which there is a tapped hole to fit a support body of the speed change mechanism, a stop ring adapted to press a spring into the support body and cause the spring to rotate in order to regulate the force produced by the spring, a Ctype snap ring located in the gap between a support shaft to prevent the support shaft from dropping out of the support body in which a torsion spring is mounted, one end of the support body being connected to a chain guide, one end of the torsion spring being fixed in a guide hole of the stop ring whilst the other end is fixed in a guide hole of a step-type inner rim of the support body, the spring producing the force necessary for the speed change mechanism to keep a bicycle chain at a fixed tension, is characterized in that the stop ring mounted at the front end of the support body is adapted to bend outwardly on one side to form a positioning plate and the C-type snap ring inserted in the gap of the support shaft prevents the stop ring from being loose, one end of the C-type snap ring extends outwardly to form a handle, one side of the handle bending along the axial direction of the support shaft to form an angle plate on which two aligned guide holes are formed, one of the two bolts in the guide holes of the angle plate can keep the positioning plate of the stop ring at a fixed distance and angle from the C-type snap ring, whilst the other bolt can keep the angle plate of C-type snap ring at a fixed distance and angle from the baffle angle of the bicycle frame where the speed change mechanism is located, adjustment of the length of the two bolts extruding from the guide holes of the angle plate, controls the angle of rotation of the stop ring with respect to the baffle angle of the bicycle frame and consequently change the force produced by the torsion spring which is dragged by the stop ring, after a long period of use, adjustment of the two bolts so that the stop ring drags the spring produces a compensatory spring force so as to make up the spring force lost due to elastic fatigue thereby keeping the tension of bicycle chain fixed.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagramatic view showing a prior art bicycle speed change mechanism; (already described) Fig. 2 is an exploded perspective view showing components of the common bicycle speed change mechanism of Fig. 1 (already described) Fig. 3 is an exploded perspective view showing the components of the present invention; and Fig. 4 is a side view of the speed change mechanism of the present invention.

Referring to Fig. 3, there is shown the component parts of the present invention. A threaded part of a support shaft 307 is locked into a tapped hole 300a located at the bottom end of a bicycle frame 300. The support shaft 307 is mounted and fixed inside a support body 305, comprising a washer 306 and a torsion spring 304. The two ends of the spring 304 are bent in the axial direction of the support body 305, the right hand end of the spring being inserted into a guide hole 305a formed on the step-type outer rim of support body 305, whilst the other end of the spring is inserted into a guide hole.303a formed on the step-type inner rim of a stop ring 303. The stop ring 303 is adapted to adhere to the outer end of the support body 305 to press and retain the spring 304 therein. The threaded part of support shaft 307 passes through the support body 305 and through the stop ring 303.A C-type snap ring 302 is then put over a gap 307a of the support shaft to prevent the stop ring 303 and the spring 304 from leaving the support body 305. The outer rim of the stop ring 303 is bent outwardly to form a flange 303b. The flange 303b is arrested by a stop member 305b of the support body 305.

This makes the stop ring 303 stop at a fixed point when it rotates as the result of the force from the torsion spring 304. A positioning plate 303c, adapted to receive a bolt 301a installed in the C-type snap ring 302 is provided on the upper end of the flange 303b.

Thus, the positioning plate 303c on the stop ring is kept away from the C-type snap ring at a fixed distance when rotating, which means that the torsion force produced by the torsion spring 304, dragged by the stop ring 303, can be adjusted accordingly. One end of the Ctype snap ring 302 extends outwardly to form a handle 302a. One side of the handle is bent in the axial direction of the support shaft to form an angle plate 302b. Two aligned tapped holes 302c and 302d are formed on the angle plate. Two bolts 301a and 301b are separately screwed into the two tapped holes. The function of the bolt 301a is to keep the positioning plate 303c of the stop ring and the angle plate 302b of the C-type snap ring at a fixed distance and the function of the bolt 301b is to keep the angle plate 302b of the C-type snap ring and the baffle angle of the bicycle frame at a fixed distance. So, by adjusting the length of bolts 301a and 301b that extrude out of the tapped holes of the angle plate 302b, the torsion spring 304, dragged by the stop ring 303, can be moved to compensate the spring force and to clear the phenomenon of elastic fatigue occurring in the spring 304 after a long period of use.

Referring to Fig. 4, it can be seen that on the angle plate 302b of the C-type snap ring 302 which is mounted in the bicycle frame 300, the two bolts 301a and 301b are mounted in opposing directions.

The bolt 301a passes through the lower part of the angle plate 302b and reaches the positioning plate 303c of the stop ring 303, whilst the bolt 301b passes through the upper part of the angle plate 302b and reaches the baffle angle 300b of bicycle frame 300. Thus, by adjusting the length of the bolts 301a and 301b extruding through the angle plate 302b of the C-type snap ring, the distance between the positioning plate 303c of the stop ring 303 and the baffle angle 300b of bicycle frame 300 can be controlled to adjust the spring force produced by the torsion spring 304 which is dragged by the stop ring 303. Meanwhile, by adjusting the two bolts 301a and 301b on the angle plate 302b, a bigger range of adjustment of the spring 304 dragged by stop ring 303 can be achieved to move the stop ring 303 to drag the spring 304 to compensate the spring force and thereby keep the spring tension at a fixed value so as to clear the phenomenon of elastic fatigue occurring in the spring 304 after a long period of use.

Claims

A speed change mechanism for a bicycle comprising a bicycle frame on which there is a tapped hole to fit a support body of the speed change mechanism, a stop ring adapted to press a spring into the support body and cause the spring to rotate in order to regulate the force produced by the spring, a C-type snap ring located in the gap between a support shaft to prevent the support shaft from dropping out of the support body in which a torsion spring is mounted, one end of the support body being connected to a chain guide, one end of the torsion spring being fixed in a guide hole of the stop ring whilst the other end is fixed in a guide hole of a step-type inner rim of the support body, the spring producing the force necessary for the speed change mechanism to keep a bicycle chain at a fixed tension, characterized in that the stop ring mounted at the front end of the support body is adapted to bend outwardly on one side to form a positioning plate and the C-type snap ring inserted in the gap of the support shaft prevents the stop ring from being loose, one end of the C-type snap ring extends outwardly to form a handle, one side of the handle bending along the axial direction of the support shaft to form an angle plate on which two aligned guide holes are formed, one of two bolts in the guide holes of the angle plate can keep the positioning plate of the stop ring at a fixed distance and angle from the C-type snap ring, whilst the other bolt can keep the angle plate of C-type snap ring at a fixed distance and angle from the baffle angle of the bicycle frame where the speed change mechanism is located, adjustment of the length of the two bolts extruding from the guide holes of the angle plate, controls the angle of rotation of the stop ring with respect to the baffle angle of the bicycle frame and consequently change the force produced by the torsion spring which is dragged by the stop ring, after a long period of use, adjustment of the two bolts so that the stop ring drags the spring produces a compensatory spring force so as to make up the spring force lost due to elastic fatigue thereby keeping the tension of bicycle chain fixed.
2. A bicycle speed change mechanism constructed and arranged to operate substantially as herein described with reference to and as illustrated in Figs 3 and 4 of the accompanying drawings.