BICYCLE TRANSMISSION

Abstract: An automatic transmission for a bicycle in which actuators (20) responsive to the speed of the bicycle relocate a multi-sprocket assembly (16) carried by the drive wheel for selectively engaging each of the sprockets of the sprocket assembly with drive chain. A one-direction clutch (28) rotatably connects the pedal crank and an associated front sprocket to disengage when the rider holds the pedal crank against turning with the chain.

Description: BICYCLE TRANSMISSION DESCRIPTION Technical Field The present invention relates to bicycle transmissions and, more particularly, to automatic transmissions for bicycles. Background Prior Art To facilitate bicycling over changing terrain, road conditions and weather conditions, bicycles commonly have multi-speed transmissions. One of the most common types of transmission systems for bicycles is the derailleur-type transmission in which the rear wheel and, in many cases, the pedal crank have associated multi-sprocketed assembli whereby the gear ratio may be selectively adjusted by laterally moving the chain to engage with sprocket of varying diameter. In almost all commercial systems, the cyclist selects the gear ratio by manually operating one or more levels operably connected to the derailleur system. For a variety of reasons as outlined in U.S. Patent No. 3-,929,925, it would be desirable to have an automatic shifting device which adjusts the speed of the bicycle. OMPI While several automatic shifting devices have been proposed for bicycles or the like, see U.S. Patent Nos. 4,201,094 and 2,956,443, no automatic shifting device has as yet achieved widespread commercial success. The need continues for automatic shifting device which are sufficiently simple and reliable to gain commercial acceptance. Summary of the Invention Accordingly, it is a primary object of the invention to provide an improved bicycle transmis&.v*n system in which the gear ratio is adjusted to the speed of the bicycle. An automatic variable-speed bicycle transmission system is provided in which " a front sprocket driven by the pedal crank is connected to a multi-sprocket assembly associated with the rear axle by a continuous chain. The sprocket assembly is actuated by an actuator weight mounted on the rear wheel responsive to the speed of the bicycle to move laterally relative to the chain to determine the sprocket which engages the chain. In order to permit the bicycle to coast, the pedal crank is connected or linked to the front sprocket by a one-way clutch which transfers driving torque from the pedal to the sprocket when the rider pedals in a forwardly- oving direction, but disengages when the rider holds the crank against turning with the chain and the cran -driven sprocket. Brief Description of Several Views of Drawings Other objects and advantages of the invention will become apparent from the following detailed description in reference to the accompanying drawings, in which: OMPI FIG. 1 is an elevation view of a bicycle with an automatic transmission system embodying various features of the present invention; FIG. 2 is an elevation view, partially cut away, of the rear axle and associated transmissi apparatus in the high gear position of the bicycle shown in FIG. 1; FIG. 3 is a view similar to that of FIG. 2 showing the transmission apparatus in the low gear position; FIG. 4 is a fragmentary elevation view of the rear wheel of the bicycle shown in FIG. 1 illustrating an actuator which responds to the speed of the bicycle and shifts the engagement of the chain with the respective sprockets of the assembly with the chain; FIG. 5 is a front elevation view of the rear sprocket assembly and associated pivoted pulleys for maintaining tension of the chain; FIG. 6 is a side elevation view of the pivoted pulleys of FIG. 5; and, FIG. 7 is an elevation view, partially cut away, of a pedal crank-sprocket assembly includin a one-direction clutch which connects the pedal crank to the front sprocket. Detailed Description In accordance with the present invention, an automatic variable-speed transmission is provided for a bicycle 10 (FIG. 1) or similar vehicle in which a crank-driven front sprocket 12 is connected by a drive chain 14 to a driven multi-sprocketed assembly 16 carried by the rear drive wheels axle with selective engagement of the chain with the various diameter sprockets 18 of the sprocket assembly being accomplished automatically with substantial variations in the speed of the vehicle. This is achieved by weighted speed actuators 20 responsive to the centrifugal force of the rotating bicycle wheel 22 to actuate the sprocket assembly 16 laterall relative to the chain 14 when the centrifugal force increases. Preferably, the sprocket assembly 16 is biased in the opposite direction by a spring 24 (FIG. 2) so that, for example, when the centrifugal force decreases, the spring shifts the sprocket assembly 16 relative to the chain 14. In order to allow the bicycle rider to stop pedaling and allow wheels 22 to continue to rotate, i.e., for the rider and bicycle to coast as down a hill, a one-direction clutch is used at the pedal crank 26 with the clutch 28 (FIG. 7) being disengaged while the bicycle 10 is coasting. When the rider pedals, the clutch is engaged. So that the invention may be more fully understood, the derailleur and transmission mechanism is now described in greater detail. The rear axle assembly shown in FIG. 2 includes a hub shaft 30 attachable to the bicycle frame as by a nut 32 at either end thereof and a hub shell 34 which rotates therearound. At either end of the hub shaft 30, ball holders 36 with bearding surfaces 40 cooperating with bearing surfaces 41 of complementary cylindrical end portions 44 of the hub shell 34 to hold standard bicycle bearings 37 therebetween to permit free rotation of the hub shell around the non-rotating hub shaft 30. The bicycle wheel rim 22 is attached by spokes 38 to annular hub shell flanges 40a and 40b. In standard derailleur transmission systems, a sprocket assembly is secured to the hub shell to rotate therewith and is laterally fixed thereto, and the chain is laterally moved to selectively engage with the various sprockets of the sprocket system. In the present invention, the chain 14 connecting the front sprocket 12 to the rear sprocket assembly 16 is laterally fixed in a single plane, and the sprocket assembly 16 is movable inward and outward to reposition itself relative to the chain, whereby engagement of the chain with the various sprockets is selected. The respective sprockets 44a-44e.,are carried and shifted laterally by a sleeve or shell 42 which is telescoped over one end of the hub shell 34 outwardly of the hub flange 40b to which the spokes 38 are attached. The sleeve 42 has a first or large diameter portion 46 carrying the large diameter sprockets 44a,- 44b and 44c which are keyed by a key (not shown) to the sleeve 42 to turn the sleeve and the hub shell. Herein, the small diameter sprockets 44d and 44e are drivingly secured to the sleeve 42 to turn the same by being screw- threaded onto a threaded small diameter portion 48 of the sleeve 42. Mounted on the sleeve's larger smaller diameter portions between adjacent sprockets are spacer rings 50 which provide the desired separation between the sprockets 44 which is sufficient that the chain 14 does not rub against adjacent sprockets but small enough so that the chain does not become caught between sprockets. It will be appreciated that to slide the sprocket assembly automatically in a lateral direction while the bicycle rider is applying a driving force to the chain 14 and a driving torque to one of the sprockets 44 requires a good sliding friction and drive mechanism between the hub shell 34 and the sprocket assembly. Herein, a bearing means is provided between the sprocket assembly and the hub also acts to transfer the driving torque from the sprocket assembly to the rear wheel hub. Herein, the bearing means comprises ball bearings 56 slideab longitudinally in races defined by aligned grooves in respectively facing portions of the hub shell 34 and the sleeve 42. More specifically, at various evenly-spaced circumferential positions, complement arcuate grooves 52 and 54 (FIG. 3) are provided in the inside parameter of the sprocket shell 42 and in the complementary outside diameter of the hub shell 34 which define cylindrical keyways there¬ between which are parallel to the hub shaft axis. The cylindrical keyways each carry a plurality of ball bearings 56 with diameters slightly less than the keyway diameter. The bearings 56 key the hub shell 34 to the sprocket shell 42 at about three to four locations about the hub. An annular ring 58 is secured around the end of the lesser diameter portion 48 of the sprocket shell to close off the end of the keyway races and retain the ball bearings 56 in the cylindrical keyway races from their outer ends. The biasing spring 24 which shifts the sprocket assembly in one lateral direction which is to increase the size of the driving sprocket 44, in this instance, is carried in an encircling cup-like portion 60 of the hub shell 34. The cup portion 60 has a closed end 62 generally midway between the hub shell flanges 40a and 40b and extends through the right-hand hub shell flange 40b where its open end 64 overlies the inner open end 66 of a protective cup 68 extending inward from the inner end 70 of the sprocket shell. The closed - TTLEmXfr 70 of the sprocket shell 42 closes off the inner end of the sprocket shell grooves 54 to retain the ball bearings 56 in the keyways. The hub shaft- encircling compressed coil spring 24 is enclosed within the interengaging cup portions 60 and 68 of the hub shell 34 and sprocket shell 70 and extends between the closed ends 62 and 72 thereof to bias the sprocket shell 72 outward. When the compression spring 24 is expanded to the maximum length permitted (as in FIG. 2) -to shift the sprocket assembly to where the sprocket 44a engages the chain 14, the retainer ring 58 abuts a C-ring 76 disposed in an annular groove closely adjacent the outer end of the hub shell 34. When the sprocket assembly 16 is moved inward, of course, the chain 14 engages with progressively small sprockets 44 to change the rotation ratio between crank 26, and the sprocket assembly shifts to progressively higher gears. To shift the sprocket assembly 16 against the force of the spring 24, the centrifugal actuators 20 are disposed at diametrically opposed locations, on the rear drive wheel assembly are each operably connected to the sprocket assembly 16 by a connecting means in the form of a chain 78. Herein, the chain is connected to a guide in the hub by hollow tubes 88 with ends of the chains fastened to the sprocket sleeve 42. More specifically, each bead chain 78 has an end extending through a reduced-in-diameter bore portion 82 to an enlarged spherical stop 84 in an enlarged diameter bore 80. The stop 84 on the end of the chain abuts the end of the bore 80 to transfer the pulling force of the bead chain to the sprocket assembly 16. In order to change directions, each bead chai 78 is threaded through a J tube 88 which guides the head chain around a right angle bend, the J tube having a horizontal leg : 90 along the outside of the cup portion 60 of the hub shell 34 coaxial with the bore 80 and extending through the right-hand hub shell flange 40b, and a leg - 92 disposed midway between the left-hand and right- hand hub shell flanges 40a and 40b directed toward the bicycle wheel rim 22. The other end of each bead chain 78 is connected to the corresponding actuator 20 to be pulled thereby with a force propor¬ tional to the speed of the rear drive wheel to exert a pull on the sprocket assembly 16 in oppositio to the biasing force of the spring 24. Each centrifugal weight actuator 20, as best seen in FIG. 4, includes a rod- 94 having a weight- 96 at one end and pivotally mounted at its other end- 98 on a bracket- 99 secured by a screwed clamping plate to a pair of the wheel spokes 38. The rod- 94 and weight are mounted generally in the plane of the bicycle wheel between the left- hand and right-hand spokes. A plurality of radially- spaced holes 100 are provided in rod- 94 which extends about one-half the distance from the pivot end • 98 to the weight 96, and the end of the bead chain 78 is connected through one of the holes- The tension on the bead chain 78, resulting from the outward biasing of the sprocket assembly 16 by the hub shell spring 24, and an adjustable torsion spring (not shown) at the sensor pivot end- ' 98, maintain the actuator 20 in its rest position shown in solid in FIG. 4 with the rod- 94 generally transvers to a radius of the wheel 22. When the bicycle 10 move the centrifugal force of the wheel 22 tends to swing the weight- 96 outward, overcoming the force of the pivot torsion spring and the hub shell spring 24. As the weight 96 swings outward, as shown in phantom line in FIG. 4, the rod' 94 pulls the bead chain 78 which, in turn, pulls the sprocket assembly 16 inward. As the sprocket assembly 16 is pulled inward, the chain 14 is deformed out of plane until a portion of the chain catches on the next adjacent sprocket 44 and jumps thereto. As the speed increas the transmission moves through successively higher gears as the chain 14 jumps to successively smaller sprockets 44 until, as shown in FIG. 3, the inner end 66 of the sprocket shell 42 abuts the outer end 62 of the hub shell cup portion 60. When the bicycle 10 slows, the process is reversed, and the hub shaft spring 24 progressively overcomes the decreasing pulling force of the actuator 22 to bias the sprocket assembly 16 outward, causing ' the chain 14 to jump progressively to lower gear sprockets 44 until in the low gear, with the drive chain on the largest sprocket 44a, the ball retaining ring 58 at the end of the sprocket shell 42 abuts the C-ring 76. Typically, each actuator 20 will have a six-inch long rod 94 with a disc-shaped weight at the end thereof which is about two-inches in diameter and 1/4-inch thick. The weight- 96 will typically travel about three inches between its rest (low gear) position and its high gear position. While automatic bicycle transmission systems have been described in which the gear ratio is adjusted according to pedal pressure, a system in which the gear ratio is adjusted according to bicycle speed more appropriately determines the correct gear ratio. Whenever the bicycle 10 comes OMPI to a stop, the transmission shifts to its lower gear position which is most appropriate for start¬ up. On the other hand, when the bicycle 10 is moving rapidly, e.g., coasting down a steep hill, the transmission remains in a high gear despite the fact that, no pressure at all is being exerted on the pedal. From time-to-time, it may be necessary to adjust the tension so that the swinging outward of the weights.96 effect changing of the gears. This may be achieved by adjusting the torsion spring at the actuator pivot end- 98 and by repositioning the actuator 20 on the spokes 38 to achieve tautness of the bead chain 78. By selection of the rod shaft hole 100 to which the bead chain 78 is attached the speed range in which the transmission goes through its full range of gear changes may be adjuste A protecting bellows 104 is secured to the outer end of the hub shell 34 and to the outer end of the sprocket shell 42 by annular rings 106 to keep dirt out of the transmission mechanism, particularly the hub shell grooves 52 which are open at their outer ends. A close interfit of the hub shell cup portion 60 and the sprocket shell protective cup portion 68 keeps dirt from entering. In a derailleur transmission system where the drive chain jumps between different diameter sprockets 44 resulting in varying amounts of free chain, it is necessary to maintain chain tension with each of the engages sprockets 44a-44e of the sprocket assembly 16 so that a loose chain 14 does not jump off the gear mechanism entirely. Similar to derailleur systems commonly in use, the present invention utilizes a chain tension mechanism indicate generally at 110 in FIG. 5. An arm 112 is pivotally OMPI mounted at its upper end 114 from the frame closely adjacent the outer end of the hub shaft 30 and an adjustable torsion spring 116 (FIG. 6) at the pivot point biases the arm so that its lower end 118 tends to swing backwards. Pivotally mounted at the lower end of the arm 112 is a cross-arm 120 having sprockets 122a and 122b rotatably mounted at either end thereof. A torsion spring 124 at the pivot point of the cross-arm 120 tends to bias the cross-arm to a horizontal position. The arm 112 from the hub shaft 30 is appropriately deformed out of plane, at best seen in FIG. 6, to locate the sprockets 122 of the cross-arm 120 generally in the plane of the drive chain 14. The portion of the drive chain 14 extending rearward from the lower side of the crank sprocket 12 winds below and up over the rear cross-arm pulley 122a, winds forwards below and up over the front cross-arm pulley 122b, and backward below and up over the sprocket assembly 16. In the high gear position (FIG. 3) , the arm 112 from adjacent the hub shaft 30 is biased toward its backward position and the cross-arm 120 is biased toward its horizontal positio to effectively increase the distance which the drive chain 144 winds around the cross-arm pulley 122 When the chain 14 is engaged with larger sprockets 44 in the lower gear positions, the chain which winds a greater distance around the larger sprockets pulls the hub shaft arm 112 forward and pulls the cross-arm 120 vertically to correspondingly shorten the travel of the chain around the cross-arm pulleys 122. Thus, the drive chain 14 is maintained at all times under generally slack-free tension. A particular advantage of the present invention in which the chain 14 is laterally fixed is that OMPI the tesnion adjusting sprockets 122 may be laterally fixed. The advantages of a laterally-fixed chain- adjusting mechanism 110 may best be appreciated by those who have tediously adjusted conventional bicycle transmission systems in which the lateral movement of the tension-adjusting mechanism must be coordinated with the lateral movement of the chain. In conventional derailleur systems, a one-direction clutch is incorporated in the rear axle assembly which engages to transfer torque from the sprocket assembly to the hub shaft. In the present invention, the rear sprocket assembly is not clutched by a one-way clutch to the hub. in order to allow the bicycle 10 to coast so that the drive wheel may continue to move without the pedals being turned as when the rider holds the pedals stationary while coasting downhill, the one-direction clutch 28 is provided which connects the pedal crank 26 to the associated sprocket 28. Illustrated in FIG. 7 is a freewheel assembly 128 in which the horizontal segment 130 of the pedal crank 26 is mounted for rotation through the drum portion 132 at the lower end of the bicycle frame. Ball holders 134 are secured to the pedal crank 26 by locknut 136 at either end of the drum 132 to rotate therewith and maintain standard bicycle beardLngs 138 between the ball holder bearing surfaces 140 and complementary bearing surfaces 142 of the drum 132. The clutch-sprocket free wheel assembly 128 is spaced by a spacer 144 from the right-hand end of the drum 132 to align the front sprocket 12 with the sprocket assembly 16. A crank shell 146 is secured to the crank 26 to rotate therewith and include an inner annular bearing race 153 for outer bearings 151. An outer sprocket sleeve 154 is disposed about the crank shell and has outer bearing surfaces engaging the respective ball bearin 148 and 151 to permit independent rotation of the sprocket shell relative to the crank. The front sprocket 12 is keyed to the sprocket sleeve 154 to rotate the sleeve. The clutch mechanism for clutching the pedal crank 26 and crank shell 146 to the sprocket sleeve 154 and the sprocket 12 comprises a clutch similar to that used conventionally for the rear wheels. Such know one-way clutches comprise a ring of ratchet teeth 156 disposed on the interior surface of the sprocket sleeve 154 between its bearing surfaces 152, and a plurality of pawls 158 on the outer surface of the crank shell 146. The pawls 158 are biased outward by individual springs 160 to engage the ratchet teeth 156 in a single direction only, i.e., when the crank 26 is providing forward torque to transfer torque from the crank 26 to the sprocket 12. Herein, the teeth slide over the pawls without engaging them when the crank 26 is held stationary and the sprocket 12 and sprocket sleeve 154 continue to turn with the chain 14. Thus, the bicycle continues to travel during coasting without the crank being turned by the sprocket 12 which is continuing to turn with the front sprocket 12 and the engaged rear sprocket 44. While the invention has been described in terms of a preferred emboddL ent, modifications obvious to one skilled in the arm may be made without departing from the scope of the present invention. While the invention has been described in terms of a five-speed bicycle, the invention could be adapted to a ten- or fifteen-speed bicycle by providin mechanisms whereby a multi-sprocketed crank freewheel may be moved manually dLnward and outward of the frame hub so that the bicycle may be operated in a selected register according to the fatigue of the cycler with the gear sprocket assembly automatical going through its range of gears according to the speed of the cycle. The automatic transmission, described herein, is, of course, applicable to other chain-driven vehicles such as tricycles of the type popular with older people. The pivoted speed actuator described in conjunction with the invention might be replaced with a radially-moving weight on the order of the weight adjusters described in U.S. Patent No. 3,885,814 Various features of the invention are set forth in the following.Claims. OMPI

Claims: CLAIMS 1. An automatic transmission system for a chain-driven vehicle, comprising: a crank (26) and a crank-driven sprocket (12) ; a shiftable multi-sprocket assembly (16) carried by the drive wheel having a plurality of sprockets (44) ; a continuous drive chain (14) engaging said crank-driven sprocket and for engaging each of the sprockets of said sprocket assembly to drive said drive wheel at different speeds depending upon which one of said sprockets is engaged; and, actuating means (20) responsive to the speed of said vehicle operable to shift the operative engagement between the respective sprockets of said assembly with said chain. 2. A transmission system for a chain- driven vehicle, comprising: a crank (26) and a crank-driven sprocket (12) ; a shiftable multi-sprocket assembly (16) carried by the drive wheel having a plurality of sprockets (44) . a continous drive chain (14) engaging said crank-driven sprocket and for engaging each of the sprockets of said sprocket assembly to drive said drive wheel at different speeds depending upon which one of said sprockets is engaged, said chain being fixed in a plane, and in which said sprocket assembly shifts laterally relative to said chain to place the respective sprockets in alignment with said chain. 3. A transmission system according to Claim 1 where said continous chain is fixed in a plane and in which said sprocket assembly shifts laterally relative to said chain to place the respective sprockets in alignment with said chain. 4. A transmission system according to Claim 3, including means (24) to bias said sprocke assembly in a first lateral direction and wherein said actuating means shifts said sprocket assembly in an.opposite direction according to the speed of the vehicle. 5. A transmission system according to Claim 1 wherein said actuating means is mounted on a wheel of said vehicle and is actuated by the centrifugal force of said rotating wheel. 6. A transmission system according to CladL 5 wherein said actuating means comprises a weighted member (94) pivotably mounted on said wheel, said member being moved outwardly by the centrifugal force generated by said wheel rotation. 7. A transmission system according to Claim 6 wherein the actuating means is positioned outwardly along spokes (38) of a drive wheel and wherein a cable-like member (78) extends from said weighted member to said sprocket assembly. 8. A transmission system according to Claims 1 or 2 also including tension means (110) to tension said drive* chain to maintain the chain tensioned with each of the engaged sprockets of said sprocket assemblv. 9. A transmission system according to Claims 1 or 2 wherein a one-direction clutch (28) connects said crank-driven sprocket and said crank to transfer torque between said crank, and said sprocket when the rider pedals in a forwardly- moving direction and which disengages when the rider holds the crank against turning with the chain and crank-driven sprocket. 10. A transmission system according to Claims 1 or 2 wherein said sprocket assembly includes a inner hub member (34) carried by said drive wheel and a sprocket-carrying member (42) disposed therearound; groove means (52 and 54) between said sprocket-carrying member and said hub member parallel to the axis or the drive wheel; and, 'ball bearings .(56) disposed in said groove means rotatably keying said hub member to said sprocket member while .facilitating lateral movement therebetween. 11. ■ An automatic transmission system for a chain-driven vehicle comprising: a crank (26) and a crank-driven sprocket (12); a sprocket assembly (16) carried by said drive wheel; a continuous chain (14) engaging said crank-driven sprocket and said sprocket assembly; means (24 . , 42 and 60) for changing the rotation ratio between said crank-driven sprocket and said sprocket assembly; acutating means (20) responsive to the speed of said vehicle operable to select said rotation ratio; and, OMPI a one-direction clutch (28) connecting said crank and said crank-driven sprocket to transfer torque between said crank and said sprocket when the rider pedals in a forwardly-moving direction and which disengages when the rider holds the crank against turning with the chain and crank-driven sprocket. 12. An automatic transmission system according to Claim 11 wherein said sprocket assembly has a plurality of sprockets (44) and said actuating means is operable to shift the operative engagement between the respective sprockets of said assembly with said chain. 13. A transmission system according to Claim 12 wherein said •continuous chain is fixed in a plane -and in which said sprocket assembly shifts laterally relative to said chain to place the respective sprockets in alignment with said chadLn.

Inventors: BREDEN C, DANIELCZYK Z
Applicants: DANIEL CORP
Application year: 1981
Main classification: B62M25
IPC codes: B62M9, B62M25