A bicycle transmission

Abstract: A bicycle transmission comprises a sprocket assembly (14,16) rotatably coupled to the frame (12) of a bicycle for receiving a chain (18), a front and rear sprocket selector for causing the sprocket assembly to shift the chain from one sprocket to another, a sliding bracket for retractably mounting the sprocket selector to the bicycle frame, adjustment brackets for finely adjusting the front and rear sprocket selectors to correspond to the path of the sprocket assembly, and a compensator (20) for engaging and following the chain as it is shifted between sprockets to eliminate any free chain between the compensator (20) and the sprocket and for reentraining the chain in the event of complete derailment. The bicycle transmission includes a sprocket assembly comprising a stationary sector (22), a swinging sector (26) hingedly coupled to the stationary sector, and a plurality of load bearing surfaces (140,142,144) extending radially outwardly of the stationary sector for taking the load from the swinging sector.

Description: The invention relates to a bicycle transmission comprising a sprocket assembly. US-4,580,997 discloses a bicycle transmission comprising a front sprocket assembly for holding a chain. A large sprocket comprises a stationary sector coupled to the axle of a pedal crank. The stationry sector has a plurality of sprockets and defines a generally V-shaped, open area, the V-shaped area being defined by a hinged side and a parting side of the stationary sector. A swinging sector is hingedly coupled to the stationary sector at the hinged side of the V-shaped area and is spring biased to the driving position. In the driving position the hinge supports the load and the chain acts as a latch between the sprocket and the swing sector, and, when the sector is not in contact with a chain, by a spring. As the chain bears a part of the load of the swinging sector in the shift position, the chain has to withstand lateral forces although it is rather constructed to bear the forces in its actual length. This is not advantageous for a smooth run of the chain The transition between hinged and parting side of the V-shaped area is curved similarly to the load-bearing surfaces of the invention, but is unable to bear loads at least in the swung state. However a main difference to the embodiment of the invention consists in that several sprockets are provided with a cut-out. Attempts to take the load by the stationary sector of the parting side, as compared to the hinged side, have been proven unsuccessful as the periphery of the swinging sector at the parting side would have to be at least as thick as the most extreme position of the periphery of the stationary sector. Of course, any additional thickness of the sprocket assembly adds weight to the bicycle and makes the sprocket assembly more difficult to manufacture. It is the object of the invention to provide an improved bicycle transmission of the above-mentioned type enabling a smoother run of the chain if the swinging sector is in the shifted position with an improved distribution of the load taken by the swinging sector, but with a simple, light construction which is easy to manufacture. This object is attained by a bicycle transmission with the featrues of claim 1. The load bearing surfaces generally take most of the load of the swinging sector, relieving the load on the hinged side and the parting side. This load is transmitted to the load bearing surfaces by means of the engagement phases in a position when they abut to the flanges. Advantageous features and embodiments are cited in the dependent claims. Brief Description of the Drawings Figure 1 is an isometric view of a bicycle including the transmission of the present invention; Figure 2 is an enlarged isometric view of the sprocket shifting assembly of the present invention including the compensator, adjustment bracket, and sliding bracket; Figure 3 is an exploded isometric view of the compensator portion of the sprocket shifting assembly; Figure 4 is an exploded isometric view of the sprocket selector for the rear sprocket assembly, including the corresponding double-plated adjustment bracket, sliding bracket, and mounting bracket; Figure 5 is a cross-sectional side view taken along the line 5-5 of Figure 4 of the double-plated adjustment bracket; Figure 6 is an end elevational view of the inventive sprocket shifting assembly including the compensator; Figure 7 is a side elevational view of the sprocket shifting assembly with the chain entrained around the outer sprocket; Figure 8 is a side elevational view of the sprocket shifting assembly with the chain entrained around the second middle sprocket; Figure 9 is an exploded side elevational view of the inventive sprocket assembly showing the swinging sector separated from the stationary sector, exposing the load-bearing surfaces; Figure 10 is an end elevational view of the stationary sector of the inventive sprocket assembly; Figure 11 is a partial isometric view of the inventive sprocket assembly showing the swinging sector pivoted relative to the stationary sector; Figure 12 is an enlarged isometric view of an alternative embodiment of the compensator, the jockey wheel, and the compensator mounting bracket of the present invention; Figure 13 is an alternative embodiment of the frame mounting bracket for securing the sliding bracket and the compensator mounting bracket to the bicycle frame; Figure 14 is a side elevational view of an alternative embodiment of the tensioning arm; Figure 15 is an end elevational view of the tensioning arm of Figure 14; Figure 16 is an enlarged side elevational view of a sprocket selector for the front sprocket assembly and corresponding adjustment bracket; Figure 17 is a top view of the front sprocket selector and adjustment bracket of Figure 16; Figure 18 is a sectional side elevation view, taken along the line 18-18 of Figure 17, of the front sprocket selector and adjustment bracket; Figure 19 is a partial rear elevational view of the front sprocket selector and adjustment bracket of Figure 16; Figure 20 is a rear isometric view of the sprocket selector and adjustment bracket of Figure 16; and Figure 21 is an isometric view, partly in section, of the front sprocket selector and front sprocket assembly of Figure 14. Detailed Description of the Invention With reference to Figure 1, the present invention is generally intended for a bicycle 10 which includes a frame 12, a front sprocket assembly 14, a rear sprocket assembly 16, and a chain 18 entrained around both the front sprocket assembly 14 and the rear sprocket assembly 16. A compensator 20 is coupled to the frame 12 at one end and entrained by the chain 18 at the opposite end to take up slack in the chain 18 that may result when the chain is shifted between the sprockets of the rear sprocket assembly 16. The compensator 20 also urges the chain 18 in an upward direction to maintain as much of the chain as possible entrained around the sprocket holding the chain. The bicycle transmission of the present invention is intended for use with all types of cycles, regardless of the number of wheels involved, and for use with all kinds of bicycles, including street bicycles, mountain bicycles, racing bicycles, and any other type of bicycle. Figure 2 shows a preferred embodiment of the rear sprocket assembly 16, including the compensator 20, a rear sprocket selector 42, a double-plated adjustment bracket 46, a sliding bracket 48, and a mounting bracket 60. The rear sprocket assembly 16 comprises a stationary sector 22 coupled to the rear axle 24 of the bicycle 10, and a swinging sector 26 hingedly coupled to the stationary sector 22. Both the stationary sector 22 and the swinging sector 26 include a plurality of sprockets, including a large, outer sprocket 28, a first middle sprocket 30, a second middle sprocket 32, and an inner sprocket 34. When the chain 18 is not being shifted between sprockets, the stationary sector 22 and the swinging sector 26 remain aligned so that each of the sprockets has a 360° outside diameter which lies in a single plane. While the embodiment of Figure 2 shows four sprockets of varying diameters, it is understood that the invention is equally suitable for sprocket assemblies having more or fewer sprockets. The stationary sector 22 defines a generally V-shaped open area into which a corresponding V-shaped swinging sector 26 is mounted. The V-shaped opening, shown in greater detail in Figures 9-11, is defined by a hinged side 36 and a parting side 38 of the stationary sector 22. A pawl 40 extends radially outward from the outer sprocket 28 of the swinging sector 26. The pawl 40 travels in a circular path and is deflected in a direction transverse to the planes of the sprockets to pivot the swinging sector 26 relative to the stationary sector 22 in order to shift the chain 18 from a holding sprocket to a receiving sprocket. As shown in Figure 2, the sprocket selector 42 is mounted to the bicycle frame 12 in close proximity to the rear sprocket assembly 16 to cause the chain to shift from one sprocket to another. The sprocket selector includes an arc-shaped pawl guide housing 44, the arc of which corresponds to the circular path of the pawl 40. The pawl guide housing 44 must be positioned close enough to the sprocket assembly 16 to allow the pawl 40 to pass through the pawl guide housing 44, yet the housing 44 cannot be mounted so close that it interferes with the rotation of the sprocket assembly 16. The sprocket selector 42 is coupled to the frame 12 by way of a double-plated adjustment bracket 46 which finely adjusts the position of the pawl guide housing 44. The adjustment bracket 46 is coupled to the sliding bracket 48, which is in turn mounted to the bicycle frame 12. Each of the above-mentioned elements shown in Figure 2 will be discussed later in greater detail. The compensator 20 generally comprises an articulated arm 50 having a proximal and distal end, the proximal end being pivotally coupled to the sliding bracket 48, and a tensioning arm 56 pivotally connected to the distal end of the articulated arm 50. A jockey wheel 52 is also coupled to the distal end of the articulated arm 50 to engage the chain 18 and maintain as much of the chain 18 entrained around the particular sprocket as possible. The tensioning arm 56 is coupled to the distal end of the articulated arm 50 adjacent the jockey wheel 52 and a spring housing 54. A tensioning wheel 58 is rotatably coupled to the end of the tensioning arm 56 opposite the articulated arm 50. The spring housing 54 encloses a means for biasing the tensioning arm 56 away from the articulated arm 50 and for biasing the compensator 20 as a whole in an upward direction so that the compensator 20 follows the chain 18 and takes up any slack created by shifting the chain 18 between sprockets. With reference to Figure 3, one embodiment of the compensator 20 is shown in an exploded isometric view. The articulated arm 50 of the compensator 20 is mounted to the bicycle frame 12 (Figure 1) by means of a mounting bracket 60. A vertical pin 62 having a threaded end extends upwardly of the proximal side of the articulated arm 50. A dust cover 64 is inserted over the vertical pin 62 which allows the articulated arm 50 to pivot freely in a horizontal plane. The end of the pin is inserted through an aperture 66 defined by the mounting bracket 60 and secured in place with a threaded nut 68. An upper parallelogram linkage 70 and a lower parallelogram linkage 72 are coupled to the proximal end of the articulated arm 50 to maintain the jockey wheel 52 parallel to the planes of the sprockets and allow the jockey wheel 52 to follow the chain 18 from sprocket to sprocket. The upper parallelogram linkage 70 comprises an upper base arm 74 hingedly coupled to the proximal end of the articulated arm 50 by a pin 76, and an upper extension arm 78 hingedly coupled to the distal end of the articulated arm 50 by a pin 80. The upper extension arm 78 defines an elongated slot 82 which allows the extension arm 78 to move relative to the upper base arm 74 to change the length of the upper parallelogram linkage 70 as needed to properly position the jockey wheel 52 in place against a given sprocket. The upper base arm 74 and the upper extension arm 78 are coupled together by a nut and bolt arrangement as shown in Figure 3. The lower parallelogram linkage 72 is assembled essentially the same as the upper parallelogram linkage 70. A lower base arm 84 is hingedly coupled to the distal end of the articulated arm 50 by means of a pin 86. The lower extension arm 88 is hingedly coupled to the proximal end of the articulated arm 50 by way of a pin 90. Similar to the upper parallelogram linkage, the lower extension arm 88 includes an elongated slot 92 which allows the lower extension arm 88 to move relative to the lower base arm 84 so the lower parallelogram linkage 72 can be adjusted to an appropriate length. The lower base arm 84 is coupled to the lower extension arm also by a nut-and-bolt connection through the slot 92, as shown in Figure 3. Although the foregoing describes a preferred embodiment of the articulated arm 50, it is to be understood that the specific manner of constructing and assembling articulated arm 50, including the parallelogram linkage, could vary according to what is known by persons skilled in the art. A lever spring 94 is rotatably coupled to the pin 90 of the lower extension arm 88 in such a way that the lever spring 94 extends between the upper parallelogram linkage 70 and the lower parallelogram linkage 72. The lever spring 94 biases the parallelogram linkage upwardly to urge the jockey wheel 52 into engagement with the chain 18 and acts in conjunction with the parallelogram linkage to maintain the jockey wheel 52 parallel to the planes of the sprockets. Use of the lever spring 94 is, however, optional and is not an absolute requirement to carry out the present invention. A cylindrical button connection 96 having an enlarged circular head 98 and a circumferential slot 100 is integrally formed on the distal end of the articulated arm 50. The coil spring housing 54 is inserted over the button connection 96 and set screws 102 may be tightened into the circumferential slot 100 to securely couple the spring housing 54 to the articulated arm 50. A similar type of connection may be used at the proximal end of the articulated arm 50. It should be noted that the button connection 96 is but one method of connecting the spring housing 54 to the articulated arm 50, and that other means for securing the housing 54, such as welding or other permanent coupling means, could be used. The spring housing 54 defines a small, cylindrical aperture 104 through which a connecting bolt 106 may be inserted to secure the tensioning arm 56 to the distal end of the articulated arm 50. The spring housing 54 also defines a larger aperture (not shown) having a bottom 108 into which a coil spring 110 is inserted. The coil spring 110 has oppositely-extending ends 112 which may be inserted into alternative cavities 114 to prevent the coil spring 110 from rotating relative to the spring housing when the compensator 20 is in operation. The coil spring 110 is the primary and may be the only means for providing an upward bias to the compensator 20. In addition, the coil spring 110 biases the tensioning arm 56 away from the articulated arm 50 in order to maintain tension in the chain 18 and keep the chain 18 entrained around the sprocket. The tensioning arm 56 includes a dust cover 116 within which an end of the coil spring 110 is housed. The dust cover 116 is placed over one end of the spring housing 54 to keep foreign substances away from the spring. Plate 56a holds the coil spring 110 in place. A portion of the tensioning arm 56 surrounded by the dust cover 116 defines an aperture 118 through which the connecting bolt 106 is inserted to rotatably mount the tensioning arm 56 to the articulated arm 50. The tensioning arm 56 comprises a pair of plates 56a, 56b which extend side-by-side and parallel to one another and are coupled to the articulated arm 50 at one end and provide a means for rotatably mounting a tensioning wheel 58 at the opposite end. The connecting bolt 106 is inserted through the spring housing 54, the coil spring 110, the plate 56a, the tensioning wheel 58, and into a threaded bore 120 defined by the plate 56b to secure the distal of the articulated arm together. Referring again to Figures 1 and 2, as the chain 18 leaves the front sprocket assembly 14 it becomes entrained around the tensioning wheel 58, between the plates 56a, 56b, around the jockey wheel 52, around the sprocket assembly 16, and finally back around the front sprocket assembly 14. Referring now to Figure 6, the compensator 20 holds the chain 18 firmly against the outer sprocket 28 so that no gap exists between the sprocket, the chain 18, and the jockey wheel 52. That is, there is no lead chain between the jockey wheel 52 and the holding sprocket. The parallelogram linkage and the vertical pin 62 allow the jockey wheel 52 to remain in a plane parallel to the plane of the sprockets at all times. As shown in solid lines in Figure 6, the jockey wheel 52 lies in the same vertical plane as the outer sprocket 28. When the chain is shifted down to the inner sprocket 34 (shown in phantom) the compensator 20 follows the chain automatically so that the jockey wheel 52 remains continually engaged with the chain 18. The chain 18 itself provides transverse stability to the jockey wheel 52 to keep the chain 18 engaged with the jockey wheel 52. The parallelogram linkage and the vertical pin 62 allow the jockey wheel 52 and the tensioning wheel 58 to remain parallel to the planes of the sprockets when the chain 18 is entrained any of the sprockets, including the small, inner sprocket 34. Figures 7 and 8 show how the articulated arm 50 moves relative to the tensioning arm 56 when the chain 18 is shifted from one sprocket to another. Figure 7 shows the chain 18 (in phantom) entrained around the outer sprocket 28 which takes up more chain and thus causes the tensioning arm 56 to move toward the articulated arm 50 against the bias of the coil spring 110 (not shown) in the spring housing 54 to shorten the distance between the tensioning wheel 58 and the front sprocket assembly 14 (Fig. 1). Therefore, when the chain is entrained around the outer sprocket 28, a small angle () is formed between the articulated arm 50 and the tensioning arm 56. Figure 8 shows the chain 18 (in phantom) entrained around the inner sprocket 34. At this position, the coil spring 110 (not shown) within the spring housing 54 causes the tensioning arm 56 to rotate relative to the articulated arm 50 to form a large angle () between the articulated arm 50 and the tensioning arm 56 and take up slack in the chain 18 resulting from shifting from a large diameter sprocket to a small diameter sprocket. With reference to Figures 4 and 5, the mounting bracket 60, which mounts the compensator 20 and sprocket selector 42 to the bicycle frame 12 (shown in phantom), is secured to the bicycle frame 12 by machine screws 126. The mounting bracket 60 also includes a pair of bolts 122 which extend downwardly of the mounting bracket 60 for securing the sliding bracket 48 to the bicycle frame 12. The bolts 122 are inserted through elongated slots 124 of the sliding bracket 48 and secure the bracket 48 to the frame 12 by corresponding nuts (not shown). The rear sprocket selector 42 is mounted to the bicycle frame 12 by way of the sliding bracket 48. The elongated slots 124 allow the entire sprocket selector 42 to be positioned closely to and retracted away from the path of the pawl 40 and the rear sprocket assembly 16 so that the bicycle wheel and sprocket assembly 16 may be removed from the bicycle frame without interfering with the sprocket selector 42. The sprocket selector 42 must be positioned so that the pawl 40 travels in a circular path through a slot 128 in the pawl-guide housing 44 without interference during normal operation when no shifting takes place. Therefore, fine adjustments to the sprocket selector 42 are commonly required in order for the pawl-guide housing 44 to be properly positioned. A positioning screw 125 may be used to move the sliding bracket 48 relative to the mounting bracket 60 upon initial installation. Thereafter, the positioning screw 125 acts as a reference point when the sliding bracket 48 is retracted and later repositioned. The double-plated adjustment bracket 46 is provided to align the pawl guide housing 44 to allow the pawl 40 to pass through the slot 128 without interference. A pair of plates 46a, 46b are coupled together by an allen-head machine screw 130 which is inserted through a vertical extension 131 of the sliding bracket 48 and threadably received by the plate 46a. A resilient washer 132 is placed between the screw 130 and the vertical extension 131 to ensure that the allen-head machine screw 130 remains tightened. As shown in Figure 5, the double-plated adjustment bracket 46 encases spherical heads 135 of adjustment screws 134 having ends which are threadably received by the pawl guide housing 44. The spherical heads 135 allow the adjustment screws 134 to rotate within the adjustment bracket 46 while the treaded ends adjust the position of the pawl guide housing 44. The principal advantage of the adjustment bracket 46 is that the pawl-guide housing 44 can be finely adjusted after the sprocket selector 42 has been coupled to the bicycle frame 12. The sprocket selector 42 also includes a vertical screw 139 which rides in a slot 136 defined by a horizontal extension 138 of the sliding bracket 48 for adjusting the position of the pawl guide housing 44. Once the proper position is achieved, the vertical screw 139 is secured in the slot 136 by a corresponding nut (not shown). With reference to Figures 9-11, the present invention also involves a plurality of flanges with load-bearing surfaces 140, 142, 144 extending from the stationary section 22 of the sprocket assembly 16 for transmitting the load of the swinging sector 26 imparted by the chain 18 to the stationary sector 22. With reference to Figure 9, the stationary sector 22 defines a generally V-shaped opening bounded by a hinged side 36 and a parting side 38. Within the area of the V-shaped opening, a load-bearing surface extends outwardly from the stationary sector 22 for each sprocket: an outer load-bearing surface 140 which corresponds to the outer sprocket 28, a first middle load-bearing surface 142 which corresponds to the first middle sprocket 30, and a second middle load-bearing surface 144 which corresponds to the second middle sprocket 32. The inner sprocket 34 does not require a load-bearing surface, since the inner sprocket 34 comprises a continuous 360° ring. As shown in Figure 9, the swinging sector 26 provides an outer engagement face 146 which corresponds to the outer load-bearing surface 140, a first middle engagement face 148 which corresponds to the first middle load-bearing surface 142, and a second middle engagement face 150 which corresponds to the second middle load-bearing surface 144. Each of the load bearing surfaces 140, 142, 144 extends parallel to the plane of the parting side 38. Because the load bearing surfaces 140, 142, 144 are relatively short in radial length, and therefore provide short moment arms, they do not have to be unnecessarily thick to withstand the magnitude of torque imparted by the chain 18 to the swinging sector 26. The load bearing surfaces 140, 142, 144 generally take most of the load of the swinging sector 26, relieving the load on the hinged side 36 and the parting side 38. With reference to Figure 10, a spring clip 152 is coupled to both sides of the stationary sector 22 for engaging a portion of the swinging sector 26 so that after the swinging sector 26 has caused the chain 18 to shift to a different sprocket, the swinging sector 26 automatically returns to its normal position in alignment with the stationary sector 22. Figure 11 shows link members 154, 156, 158 pivotally connecting the sprockets of the swinging sector 26. The link members 154, 156, 158 maintain the spacing between the sprockets and limit the range of movement of the swinging sector 26 about hinged side 36. The location of the load-bearing surfaces 140, 142, 144 as shown in Figures 9-11 allows the stationary sector 22 to take the load imparted by the chain 18 onto the swinging sector 26, rather than the load being taken at hinged side 36 or the parting side 38 of the swinging sector 26. If the load-bearing surfaces were located at the parting side 38 of the stationary sector 22, the width of the swinging sector 26 at its periphery would have to be as wide as the full range of articulation required for a shift from a smaller to a larger sprocket. The shift from a larger to smaller sprocket puts no load on the hinge. Therefore, because the load-bearing surfaces are located close to the center axis of the stationary sector 22, the sprockets can be manufactured in a single width, which is cheaper than manufacturing sprockets with a peripheral thickness to correspond to the fall range of articulation of the swinging sector 26. Figure 12 shows an exploded perspective view of an alternative embodiment of a compensator 220. An articulated arm 250 of the compensator 220 is mounted to a bicycle frame 12 (not shown) by means of a compensator mounting bracket 260. A vertical pivot pin 262 extends vertically through the top and bottom of the proximal side of the articulated arm 250 and is received by apertures 263 of the mounting bracket 260. The pivot pin 262 allows the articulated arm 250 to pivot in a horizontal direction. The compensator mounting bracket 260 is secured to the frame 12 through apertures 269. An upper parallelogram linkage member 270 and a lower parallelogram linkage assembly 272 are coupled to the proximal end of the articulated arm 250 and serve to maintain a jockey wheel 252 aligned in a parallel orientation with respect to the planes of the sprockets at all times during shifting. This allows the jockey wheel 252 to follow the chain 18 (not shown) from sprocket to sprocket and take up any slack in the chain. The upper parallelogram linkage member 270 is hingedly coupled to the proximal end of the articulated arm 250 by a pin 276, and is hingedly coupled to the distal end of the articulated arm 50 by a pin 280. In one embodiment, the pins 276, 280 allow the linkage member 270 to pivot along a plane corresponding to the angle required to shift the chain 18 between sprockets. The length of the linkage member 270 is fixed according to the range of articulation required to properly position the jockey wheel 252 in place against a given sprocket. The lower parallelogram linkage assembly 272 comprises a lower base arm 284 hingedly coupled to the distal end of the articulated arm 250 by means of a pivot pin 286. The lower extension arm 288 is hingedly coupled to the proximal end of the articulated arm 250 by way of a pivot pin 290. The pins 286, 290 allow the parallel linkage assembly 272 to rotate in a plane corresponding to the angle required to shift the chain between the sprockets. The lower base arm 284 includes an elongated slot 292 into which the lower extension arm 288 is inserted to enable the lower extension arm 288 to ride in the slot 292 and move relative to the lower base arm 284. This movement allows the lower parallelogram linkage 272 to be adjusted to an appropriate length, according to the vertical range of motion required. The length of the lower base arm 284 is moved relative to the lower extension arm 288 by an adjustment screw 293, as shown in Figure 12. A lever spring 294 is rotatably coupled to the pin 290 of the lower extension arm 288 in such a way that the lever spring 94 extends between the upper parallelogram linkage member 270 and the lower parallelogram linkage assembly 272. The purpose of the lever spring 294 is the same as described above with respect to the embodiment of Figure 3. The compensator mounting bracket 260 also includes a threaded setscrew 264 which passes completely through the mounting bracket 260. The purpose of setscrew 264 is to adjust the range of horizontal movement of the articulated arm 250. For example, when less articulation is desired, the setscrew 264 is turned to increase the distance it extends toward the apertures 263. Upon extreme articulation, a pocket 267 journaled into the proximal end of the articulated arm 250 engages the setscrew 264, which acts as a fence such that the jockey wheel 252 cannot drift out of the plane corresponding to the angle required to shift the chain 18 between the sprockets. The range of articulation may be set so as to not exceed the horizontal position of the inner sprocket 34 so the chain has less chance of becoming completely derailed from the sprocket assembly. Another aspect of the present invention involves a stop piece 278 having a pair of mounting apertures 282 and being mounted to the proximal end of the articulated arm 250 through apertures 283. The stop 278 engages the upper parallelogram linkage member 270 to limit the upward range of motion of the articulated arm 250. The stop 278 thus also helps prevents the jockey wheel 252 from moving excessively in a vertical direction, which otherwise might cause the jockey wheel to pass vertically upwardly beyond the vertical location of the inner sprocket. In combination, the setscrew 264 and the stop piece 278 set vertical and horizontal movement limits on the chain 18 so that the chain 18 remains constantly entrained around one of the sprockets. This prevents the chain from moving excessively in vertical direction, from skipping indiscriminately from one sprocket to another, and from becoming completely derailed. The jockey wheel 252 includes an annular hollowed-out portion 255 located between the outermost periphery of the wheel 252 and the axis about which the wheel rotates. The hollowed-out portion 255 gives the wheel a shock-absorbing capability, which prevents the chain 18 from bouncing up and down relative to the wheel 50. The hollowed-out portion 255 tends to flex or "dish" when experiencing a shock which effectively absorbs the shock. On the opposite side, the jockey wheel includes a wide shoulder 257 which also helps maintain the chain 18 entrained on the teeth of the jockey wheel 52. Figure 13 shows an alternative embodiment of a frame mounting bracket 261 having mounting screws 222 which correspond to the apertures 269 of the mounting bracket 260 (Figure 12) for securing the mounting bracket 260 to the bicycle frame 12. The sliding bracket 48 (Figure 4) is also secured to the frame 12 by the frame mounting bracket 261 such that the bracket 48 is sandwiched between the frame mounting bracket 261 and the bracket 260 on the mounting screws 222. Figures 14 and 15 show an alternative embodiment of the jockey wheel 252 and the tensioning arm 256. A plurality of helical ridges 160 are formed in one side of the jockey wheel 252. The ridges 160 are curved in such a way as to urge the chain 18 (not shown) back onto the jockey wheel 252 in the event the chain derails from the jockey wheel. A deflector guard 162 is coupled to the tensioning arm 256 at mounting point 163 and acts in combination with the ridges 160 to reentrain the chain in the event of derailment. Further, the guard 162 acts as a shield to prevent the chain from becoming wedged between the jockey wheel 252 and the arm 256, which might break the chain. Referring now to Figures 16-21, another aspect of the invention includes a mounting bracket 172 for securing the front sprocket selector 166 to the bicycle frame 12. The front sprocket assembly 14 (Figure 1) is secured to the bicycle frame 12 through pedal shaft 164. The front sprocket selector 166 must be coupled to the frame 12 to ensure that the pawl 170 (Figure 21), traveling in a path 168, passes unimpededly through slot 168 of the sprocket selector 166 when no shifting takes place. This type of front sprocket selector is described in U.S. Patent No. 4,894,046. Proper adjustments of the front sprocket selector 166 must be made in a radial direction, with respect to the pedal shaft axis 164, and in a transverse direction (in and out of the page as shown in Figure 16). The radial orientation of the sprocket selector path 168 is primarily established by mounting the bracket 172 about the pedal shaft 164. A perpendicular protrusion piece 175 of the bracket 172 is inserted into a corresponding aperture in the pedal shaft housing 176 to ensure that the bracket 172 is properly oriented. Fine adjustments in the radial direction are made by a radial adjustment screw 178. With respect to transverse adjustments, the selector 166 is coupled to the bracket 172 through a dove tail extension piece 180 which is inserted into a transverse channel 182 of the bracket 172 (see Figures 16 and 19). A transverse adjustment screw 184 is threadably received by the dovetail piece 180 which adjusts the position of the sprocket selector in the transverse direction, A pair of attachment studs 186 (shown in hidden lines in Figure 16) allow the sprocket selector 166 to be removably secured to the bicycle frame 12. Thus, the sprocket selector 166 can be removed and serviced without the need of removing the bracket 172 from the pedal shaft 164. A chain guard 188, which prevents the chain 18 from accidentally derailing to the inside, is mounted to the bracket 172 by screws 190, 192 and must normally be removed prior to removing the sprocket selector 166. A major benefit of the adjustment bracket 172 is that the front sprocket selector 166 can first be firmly secured to the frame 12; subsequently, the adjustments can be made to allow the pawl 170 to pass through the pawl path 168 without obstruction. This eliminates the need to preadjust the sprocket selector 166 before securing it to the frame and hence the burdensome trial-and-error guessing that would otherwise be required. The front sprocket selector bracket 172 thus provides a secure, reliable, efficient means for adjusting the front sprocket selector 166 to correspond to the path of pawl 170. While the preferred embodiments of the present invention have been illustrated and described, it is to be understood that variations will be apparent to one of ordinary skill in the art without departing from the principles described herein. Accordingly, the invention is not to be limited to the specific embodiments illustrated in the drawings, but by the scope of the claims.

Claims: A bicycle transmission comprising a sprocket assembly (16) coupled to an axle (24) of a bicycle wheel for holding a chain (18), the sprocket assembly (16) comprising a stationary sector (22) coupled to the axle (24) of the bicycle wheel, the stationary sector (22) having a plurality of sprockets (28, 30, 32, 34) and defining a generally V-shaped, open area, the V-shaped area being defined by a hinged side (36) and a parting side (38) of the stationary sector (22), and a swinging sector (26) being hingedly coupled to the stationary sector (22) at the hinged side of the V-shaped area, a plurality of flanges extending outwardly of the stationary sector (22) within the V-shaped area, each flange having a load bearing surface (140, 142, 144) that lies in a plane corresponding to a sprocket (28, 30, 32, 34) of the stationary sector (22); and the swinging sector (22) having a plurality of engagement faces (146, 148, 150) corresponding to the load bearing surfaces (140, 142, 144), the engagement faces (146, 148, 150) imparting the load transmitted to the swinging sector by the chain to the load bearing surfaces. A bicycle transmission according to claim 1, characterized in that the load bearing surfaces (140, 142, 146) lie in a plane parallel to the plane of the parting side (38) of the swinging sector (26). A bicycle transmission according to one of the claims 1 or 2, characterized in that the load bearing surfaces (140, 142, 144) take a substantial portion of the load imparted from the swinging sector (26) to the stationary sector (22). A bicycle transmission according to one of the claims 1 to 3, characterized in that the flanges are of a thickness substantially equal to the thickness of the corresponding sprocket. A bicycle transmission according to one of the claims 1 to 4, characterized in that the swinging sector (26) has a pawl (40) extending beyond the periphery of the sprocket assembly (16) and travelling in a circular path as the sprocket assembly (16) rotates; and a sprocket selector (42) coupled to a bicycle frame (12) for shifting between sprockets (28, 30, 32, 34) of the sprocket assembly (16) by deflecting the pawl (40) and causing the swinging sector (26) to pivot relative to the stationary sector (22) to shift the chain (18) from one sprocket to another. A bicycle transmission according to claim 5, characterized in that the sprocket selector (42) can be removed from the bicycle frame (42) with removing the mounting bracket (60). A bicycle transmission according to one of the claims 1 to 6, characterized in that it further comprises retracting means (126, 48) for retractably securing the sprocket selector (42) to a bicycle frame (12) adjacent the sprocket assembly (16) to allow the pawl (40) to pass through the sprocket selector (42), the retracting means (124) allowing the sprocket selector (42) to be moved away from the sprocket assembly (16) while sprocket selector (42) remains attached to the bicycle frame (12) so the sprocket assembly (16) can be removed from the bicycle frame (12) without interference with the sprocket selector (42). A bicycle transmission according to claim 7, characterized in that the retracting means (124, 48) comprises a sliding bracket (48) coupled to the bicycle frame (12) for securing the sprocket selector (42) in close proximity to the sprocket assembly (16) and for retracting the sprocket selector (42) away from the sprocket assembly (16) so that the sprocket assembly (16) can be removed from the bicycle frame (12). A bicycle transmission according to one of the claims 1 to 8, characterized in that it further comprises means (48, 124) for releasably securing the sprocket selector to the bicycle frame; and means (134, 46) for finely adjusting the sprocket selector (42) after the sprocket selector (42) has been secured to the bicycle frame (12) such that the pawl (40) passes unimpededly through a slot (136) in the sprocket selector (42) when no shifting between sprockets (28, 30, 32, 34) occurs. A bicycle transmission according to claim 9, characterized in that the fine adjustment means (134, 46) comprises an adjustment bracket (46) encasing a spherical end (135) of an adjustment screw (134), the adjustment screw (134) being threadably received by the sprocket selector (42) such that when the screw (134) is rotated the spherical end (135) rotates within the adjustment bracket (46) and the sprocket selector (42) moves relative to the adjustment bracket (46). A bicycle transmission according to one of the claims 9 or 10, characterized in that the fine adjustment means (134, 46) is capable of adjusting the sprocket selector (42) in the radial and transverse directions. A bicycle transmission according to one of claims 9 to 11, characterized in that the means for releasably securing (48, 124) the sprocket selector (42) to the bicycle frame (12) comprises a sprocket selector mounting bracket (60). A bicycle transmission according to one of the claims 1 to 12, characterized in that it further comprises a compensator (20, 220) having a proximal end and a distal end, the distal end having an engagement means (58, 52) for engaging and holding the chain, the proximal end is privotally coupled to the bicycle frame (12) and the compensator (20, 220) includes biasing means (110) for urging the engagement means (52) toward the sprocket (28, 30, 32, 34) such that engagement means (52) forces the chain (18) to be entrained around the sprocket (28, 30, 33, 34), wherein the compensator (20, 220) functions independently of the shifting means (42) and automatically follows the chain (18) when shifted between sprockets (28, 30, 32 34). A bicycle transmission according to claim 13, characterized in that the rear sprocket assembly (16) comprises a stationary sector (22) and a parting sector (26), the shifting means (42) causing the parting sector (26) to move relative to the stationary sector (22) to shift the chain (18) from one sprocket (28, 30, 32, 34) to another, the compensator (20, 220) freely following the chain (18) from one said sprocket to another said sprocket to take up any slack in the chain (18) caused by shifting. A bicycle transmission according to claim 13 or 14, characterized in that the biasing means (110) urges the engagement means (52, 252) toward the sprocket (28, 30, 32, 34) with sufficient force to eliminate any free chain between the engagement means (52) and the sprocket (28, 30, 32, 34). A bicycle transmission according to one of the claims 13 to 15, characterized in that the compensator (20, 220) comprises: an articulated arm (50, 250) having a proximal end and a distal end, the proximal end being pivotally coupled to the bicycle frame (12); a jockey wheel (52, 252) rotatably mounted to the distal end of the articulated arm (50, 250) for engaging and urging the chain (18) into engagement with the sprocket (28, 30, 32, 34); a tensioning arm (56) pivotally mounted to the distal end of the articulated arm (50); a tensioning wheel (58) rotatably coupled to the tensioning arm (56) opposite the jockey wheel (52, 252) for maintaining tension in the chain (18) and receiving the chain (18) after the chain (18) leaves the front sprocket (14); and biasing means (110) for biasing the jockey wheel (52, 252) toward the sprocket (28, 30, 32, 34) to urge the chain (18) into engagement with the sprocket (28, 30, 32, 34) and for biasing the tensioning arm (56) away from the articulated arm (50, 250) to constantly maintain tension in the chain (18). A bicycle transmission according to claim 16, characterized in that it further comprises means (70, 72, 62, 262, 270, 272) for maintaining the jockey wheel (52, 252) substantially parallel to the planes of the sprockets (28, 30, 32, 34) regardless of which sprocket holds the chain (18). A bicycle transmission according to claim 16 or 17, characterized in that the biasing means (110) comprises a coil spring (110) mounted in a spring housing (54) coupled to the distal end of the articulated arm (50, 250). A bicycle transmission according to one of the claims 16 to 18, characterized in that the articulated arm (50, 250) includes a means (70, 270, 72, 272, 62, 262) for maintaining the jockey wheel (52, 252) substantially parallel to the planes of the sprockets (28, 30, 32, 34) regardless of which sprocket holds the chain (18). A bicycle transmission according to one of the claims 16 to 19, characterized in that the articulated arm (50, 252) comprises a parallelogram linkage (70, 270, 72, 272) coupled to the bicycle frame (12) by a vertical pin (62, 262), the parallelogram linkage (70, 270, 72, 272) and the pin (62, 262) allowing the jockey wheel (52, 252) to follow the chain (18) as the chain (18) is shifted from one sprocket (28, 30, 32, 34) to another and to remain parallel to the planes of the sprockets (28, 30, 32, 34). A bicycle transmission according to one of the claims 16 to 20, characterized in that the jockey wheel (52, 252) comprises means (160, 162) for re-entraining the chain (18) around the jockey wheel (52, 252) in the event the chain (18) becomes derailed from the jocket wheel (52, 252). A bicycle transmission according to one of the claims 16 to 21, characterized in that the jockey wheel (52, 252) comprises a plurality of helical grooves (160) notched into one side and a shield (162), the helical grooves (160) causing the chain (18) to ride back onto the jockey wheel (52, 252) in the event the chain (18) becomes derailed from the jockey wheel (52, 252), the shield (162) preventing the chain (18) from becoming lodged between the jockey wheel (52, 252) and the tensioning arm (56). A bicycle transmission according to one of the claims 16 to 22, characterized in that the jockey wheel (52, 252) comprises means (255) for absorbing shock experienced by the bicycle to prevent the jockey wheel (52, 252) and chain (18) from bouncing up and down relative to the sprocket. A bicycle transmission according to claim 23, characterized in that the means (252) for absorbing shock comprises an annular groove (255) formed in the periphery of the jockey wheel (52, 252), the groove (255) allowing the jockey wheel (52, 252) to compress upon experiencing shock from the bicycle and thus absorb the shock. A bicycle transmission according to one of the claims 16 to 24, characterized in that it further comprises means (278) for restricting the movement of the articulated arm (50, 250) in the vertical direction to prevent the chain (18) from becoming derailed from the sprocket assembly (16). A bicycle transmission according to claim 25, characterized in that the means (278) for restricting vertical movement comprises a stop piece (278) coupled to the proximal end of the articulated arm (50, 250) for engaging the articulated arm (50, 250) and preventing movement of the articulated arm (50, 250) beyond a predetermined vertical distance. A bicycle transmission according to one of the claims 16 to 26, characterized in that it further comprises means (260, 264, 267) for limiting the horizontal movement of the articulated arm (50, 250) to prevent the chain (18) from becoming derailed from the sprocket assembly (16). A bicycle transmission according to claim 27, characterized in that the means (260, 264, 267) for limiting horizontal movement comprises a setscrew (264) secured to a compensator mounting bracket (260), the articulated arm (50, 250) engaging the setscrew (264) to prevent the articulated arm (50, 250) from moving horizontally beyond a predetermined position.

Inventors: BROWNING BRUCE W, BROWNING MARC S, BROWNING, BRUCE W., BROWNING, MARC S.
Applicants: BROWNING AUTOM TRANSMISSION, BROWNING AUTOMATIC TRANSMISSIONS LIMITED PARTNERSHIP
Application year: 1991
Main classification: B62M9
IPC codes: B62M9