Abstract:
A bicycle is equipped with a rear wheel suspension having a swing arm with one or more generally cantilevered side arms, which are capable of withstanding bending and torsional loads and isolating said loads from the rider. A bottom portion of the bicycle frame includes a pedal sleeve. A pedal or crank assembly rotates within the pedal sleeve about a rotational axis with a fixed location relative to the frame. The swing arm is pivotally secured to the frame for movement about the rotational axis. A shock-absorbing element is connected between the swing arm and the frame.

Description:
This patent claims the benefit under 35 USC 119(e) of U.S. Provisional Application Ser. No. 60/457,626 filed Mar. 26, 2003, which is incorporated in full herein by this reference to it. 
    
    
     FIELD OF THE INVENTION 
     The subject invention is generally related to bicycles, and is specifically related to a rear suspension system for a bicycle. 
     BACKGROUND OF THE INVENTION 
     Bicycles have been utilized as a means of transportation for over a hundred years and continue to grow in popularity. The mountain bike is one type of bike that has become more and more popular in recent years. These types of bikes are often used in rough terrain, leading to an uncomfortable ride. Therefore, some recently designed bicycle frames include a rear suspension system. Bicycles equipped with suspension attempt to provide increased rider comfort, enhanced wheel contact and control, and less net rolling resistance without significantly increasing the cost, complexity or maintenance requirements of the bicycle. 
     However, no prior art suspension system meets all of these goals. Some systems are heavy, complex or require frequent maintenance. Some systems also cause adverse effects on other parts of the bicycle. For example, the distance between the crank axis, the axis that the pedals rotate around, and the axle of the rear wheel may vary with compression of the suspension system, forcing the transmission components to deal with increasing and decreasing amounts of chain slack. Some systems also create undesired reactions. For example, a rear suspension may cause “pogoing”, or movement of the axle through the rear wheel up or down relative to the rest of the frame as a reaction to pedaling forces. A rear suspension may also cause “biopacing” whereby movement of the crank arms accelerate or decelerate as a reaction to compression or decompression of the suspension. Pogoing and biopacing effects are particularly present in suspension systems where the chain slack varies as the suspension system compresses. 
     In particular, some rear suspension systems have multiple pivot points. These systems are generally complex and therefore expensive to manufacture. They also are subject to wear in multiple locations. U.S. Pat. No. 4,789,174, for example, describes a system having many pivot points including two pivot points directly above and below the rear wheel axle. These pivot points add significant complexity to the system and cause the distance between crank axis and rear axle to vary as the suspension system compresses. 
     U.S. Design Pat. No. 368,880 discloses another rear suspension system. In this system, a chain stay assembly pivots on the opposed ends of a bottom bracket tube. A pair of spring units connect the chain stays to the seat tube in about the location where the seat stays would normally be. The distance between the crank axis and rear axle remains constant, but this design requires two long stroke spring units, thereby increasing cost, complexity and maintenance. 
     U.S. Pat. No. 5,685,553 discloses another suspension system having a rear triangle that pivots on a frame. A bottom bracket and a rear wheel are both contained in the rear triangle. In this way, a fixed chain length is provided. However, pivoting of the rear triangle also moves the bottom bracket relative to the frame, causing the distance and angle between the seat and pedals to change while riding. 
     SUMMARY OF THE INVENTION 
     The subject invention provides a rear wheel suspension system for a bicycle. The suspension has a main frame for holding the seat and front forks. The main frame also has a bottom portion including a pedal sleeve. A pedal or crank assembly rotates within the pedal sleeve about a rotational axis which may be called a crank axis. The crank axis has a fixed location relative to the frame. A swing or trailing arm is pivotally secured to the frame for movement about the rotational axis. The swing arm may have one or two generally cantilevered side arms. The axle of the rear wheel has a fixed location relative to the swing arm. A shock-absorbing element is connected between the swing arm and the frame. The shock-absorbing element may be centrally located, that is located near a line between the front and back tires, or with some or all of the shock-absorbing element within the width of the tires. A rear wheel suspension system for a bicycle may have a frame, a pedal sleeve attached to and rotatable relative to the frame about a rotational axis having a fixed location relative to the frame, a pedal assembly secured and rotatable within the pedal sleeve, a trailing arm fixed for rotation with the pedal sleeve, and a shock absorbing element connecting the trailing arm to the frame to resist rotation of the trailing arm. A suspension system for a bicycle may comprise, a frame having a bottom portion with two sides, a pedal assembly secured for rotation to the bottom portion of the frame and rotatable about a rotational axis, a trailing arm secured to the bottom portion of the frame between the two sides of the frame and pivotable about the rotational axis, and a shock absorbing element connecting the swing arm to the frame. 
     The invention may provide a number of desirable characteristics. For example, the bearings for the swing arm have a single pivot point and may have a large surface area. This tends to reduce unwanted play, particularly after extended use. Since the rotation axis of the trailing arm is coaxial with the crank axis, the chain length required to connect the front and rear sprockets remains constant regardless of the position of the rear suspension. Therefore, biopacing or pogoing may be reduced and the stress on a chain tensioner is reduced, such that a chain tensioner is no longer required, in some cases. The position of the crank axis remains fixed relative to the seat and the suspension has a small number of pieces to reduce fabrication and assembly costs. The suspension may also allow the rear suspension to swing forward so that the bicycle can be arranged into a compact shape for storage. 
     The invention also provides various additional aspects or features. In one such aspect, the swing arm is attached to the frame through a lever arm. The lever arm may extend from the pedal sleeve and rotate about the rotational axis of the crank assembly at a fixed angular displacement from the swing arm. For example, the lever arm may extend upwards from the pedal sleeve. This allows the lever arm and shock-absorbing element to be hidden between the sides of a monocoque frame. 
     In another aspect, the pedal sleeve may rotate relative to the frame about the rotational axis of the crank assembly. In this case, the swing arm is fixed to the pedal sleeve and rotates with the pedal sleeve. A lever arm may also be fixed to the pedal sleeve and rotates with the pedal sleeve. The pedal sleeve thus provides a structure for connecting sides of a swing arm together or to the lever arm, even through these various parts may be separated by parts of the frame. For example, the lever arm may be located between two sides of a frame, as described above, while the swing arm has a side arm located outside of the shell. 
     In another aspect, the bottom portion of the frame may have two sides with the trailing arm secured to a point between the two sides. A lever arm, as described above, may also be provided between the two sides. The sides may be part of a stressed shell, for example a monocoque or semi-monocoque shell. 
     In other aspects, the swing arm may have a single side arm. The single side arm may be adapted to hold or include a rear wheel hub body. A side arm on the chain side may comprise a portion having a channeled cross-section or having one or more covers to enclose a portion of the chain. The side arm and covers may be configured to provide a torsion box. Hydraulic pumps and motors may be used to dispense with chains and sprockets. 
     The description above is intended only to introduce the reader to the invention. Aspects of the invention may reside in a combination or sub-combination of elements described above or in other parts of this patent, or be described in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages or aspects of the present invention will become apparent in the following detailed description of exemplary embodiments which will be discussed in connection with the accompanying drawings wherein: 
         FIG. 1  is a right side elevational view of a bicycle showing the design of the frame and the suspension system of the first embodiment of the invention; 
         FIG. 2A  is a left perspective view of the suspension system of the first embodiment, with components in exploded form; 
         FIG. 2B  is a left perspective view of the suspension system of the first embodiment; 
         FIG. 3  is a left perspective view of the suspension system of the second embodiment, illustrating a different form of swing arm; and 
         FIG. 4  is a left perspective view of the suspension system of the third embodiment, illustrating a bicycle with hydraulic drive means and single-sided swing arm. 
         FIG. 5  is a partial cross-section of the first embodiment. 
         FIG. 6  is a left perspective exploded view of the frame of the first embodiment. 
         FIG. 7  is a left side view of parts of the suspension system of a fourth embodiment. 
         FIG. 8  is a right side pictorial view of the components of  FIG. 7 , but with a cover removed to show inner components. 
         FIG. 9  is a top view of the components of  FIG. 7  further including a rear wheel and parts of a frame. 
         FIG. 10  is a right side pictorial view of the components of  FIG. 7  with a rear wheel attached. 
         FIG. 11  is a side view of the complete bicycle of the fourth embodiment. 
         FIG. 12  is a side view of the bicycle of  FIG. 11  compacted for storage. 
         FIG. 13  is a cross-section A—A from  FIG. 7 . 
         FIG. 14  is a cross-section B—B from  FIG. 7 . 
         FIG. 15  is a cross-section C—C from  FIG. 7 . 
         FIG. 16  is an enlarged pictorial view corresponding to the front part of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  shows a bicycle  100  according to an embodiment of the invention, comprising a main frame indicated in its entirety by the reference number  12 . The frame  12  may have a top frame part  12 A and a bottom frame part  12 B. The frame  12  has two sides which include stressed walls of a monocoque or semi-monocoque shell, although other frame designs may also be used. The frame  12  supports a saddle-bearing tube or seat post  22 , an attachment or head tube  23  for the handlebars and a fork  24  to which the front wheel  110  is associated in a conventional manner. The frame  12  is part of a suspension assembly  50  which supports the rear wheel  111 . A transmission assembly is of the conventional chain and sprocket type, whereby rotary motion from the pedals  25 , acting through crank arms  2 , is transmitted to the rear wheel  111  via a chain  20  that is wrapped around a front sprocket  11  and rear sprocket  14 , more clearly visible in  FIGS. 2A and 2B . 
     The various components of the suspension assembly  50  are shown in an exploded view in  FIG. 2A  and an assembled view in  FIG. 2B . Coupled to frame  12  is a shock absorber element  7 . The shock absorber element  7  may be any device that resists or controls movement of the suspension assembly  50  and may have a spring or other elastomer and a dampener. The shock absorber element  7  is located within the frame  12  which allows a reasonable length for it. The shock absorber element is attached to the frame via a frame pivot pin  15 . At the other end of the shock absorber element  7 , a second pivot pin  8  is inserted through hole  13  in order to connect the shock absorber to a lever arm  4 . The lever arm  4  is fixed to a trailing or swing arm  5  by welding, bonding, bolting or another suitable method. The lever arm  4  and swing arm  5  are also attached to or comprise a pedal sleeve  36 . The pedal sleeve  36  may also be called a bottom bracket since it performs the functions of a conventional bottom bracket in that it holds the axle and bearings that the pedals  25  rotate on. The lever arm  4  and swing arm  5  may be attached to each other through the pedal sleeve  36  and the lever arm  4  or pedal sleeve  36  or both may also be formed as integral parts of the swing arm  5 . The lever arm  4  can be pointed in any direction or even omitted in favor of attaching the shock absorbing element  7  directly to the swing arm  5 , for example to a bar placed between the side arms. However, if the lever arm  4  is pointed in a generally upward direction, for example at an angular displacement of 60 degrees or more from the swing arm  5 , it can be located within the frame  12  with the shock absorber element  7 , and can have a reasonable length, i.e. greater than the distance between the center of the crank axle and the front of the rear wheel  11 , and can be oriented within about 30 degrees of normal to the shock absorber element  7 . Further, if the frame  12  is of a clamshell design or monocoque design, then the lever arm  4  and shock absorber  7  can be hidden from view within the frame shell. 
     The swing arm  5  illustrated in  FIGS. 2A and 2B  has two side arms that attach to either side of the rear hub  6  that forms part of the rear wheel  111 . In an alternate embodiment illustrated in  FIG. 3 , a single sided swing arm  205 , having only one side arm, is employed instead of the two-sided swing arm  5 . The single sided swing arm  205  has higher bending and torsional rigidity, sufficient to support the rear hub  6  without the need for a mating arm. 
     The swing arms  5 ,  205  are generally cantilevered in that all or most of their length, for example 75% or more, is unsupported by any other frame or suspension component. The ends of the swing arms  5 ,  205  receive in full all vertical forces applied to the rear wheel  111  since they are in the only path for load to travel from the rear wheel  111  to the shock absorber  7  or frame  12 . A bottom bracket cartridge assembly  9  is attached to the swing arm  5 ,  205  and provides a rotation pivot for the crank arm  2 , pedal  25  and front sprocket  11 . In particular, the bottom bracket cartridge assembly  9  comprises a housing containing bearings and an axle rotating around a crank axle rotational axis, or crank axis,  44 . The bottom bracket cartridge assembly  9  screws into the pedal sleeve  36 . Optionally, a separate axle, which may be integral with the crank arms, and bearing parts can be attached to the pedal sleeve  36  according to known techniques for conventional bottom brackets. 
     The pedal sleeve  36  and thus the swing arm  5 ,  205  and lever arm  4 , are held in the frame  12  through a rotational connection provided by swing arm bearings  3 . Swing arm bearings  3  are coaxial with and reside around the bottom bracket cartridge assembly  9 . As shown in  FIGS. 2A ,  5  and  6 , the swing arm bearings  3  are held in openings  34  in a bottom portion  30  of the frame  12 . The openings  34  are defined in part by, and accessed through, one or more removable caps  32 . A step  38  in each opening  34  locates the swing arm bearings  3  laterally. A retaining ring or other structure may also be used. To attach the swing arm  5  to the frame  12 , the swing arm bearings  3  are press fit onto the ends of the pedal sleeve  36 . The swing arm  5  and swing arm bearings  3  are then placed into the half of the openings  34  provided in the main part of the frame  12 . Caps  32  are then screwed to the main part of the frame  12  to complete and close the openings  34  around the swing arm bearings  3 . The pedal sleeve  36  and caps  32  or other parts of the openings  34  may optionally have various splines, abutments or other features of shape to withstand lateral forces between the swing arm  5  and the frame  12  in addition to or in place of the features described above. 
     Hence, a single pivot axis for the swing arm  5  exists that is coaxial with the axle for the pedals  25  and crank arms  2 . In operation, when the bicycle encounters bumps in the road or terrain, the rear wheel  111  will act on the rear hub  6 , driving it upward and downward. This motion will cause the swing arm  5 ,  205  to rotate about the bottom bracket rotational axis via bearings  3 . Since the lever arm  4  is fixed to the swing arm  5 ,  205 , it will rotate about the bottom bracket rotational axis at an angle equal to that of the swing arm  5 ,  205 . The outer end of the lever arm  4 , which is rotationally attached to the shock absorber element  7  via pivot pin  8 , will activate the shock absorber  7  by pushing against it. Reaction forces from the shock absorber  7  will serve to return the lever arm  4  and hence the swing arm  5 ,  205  back to their original positions. In this manner, the swing arm  5 ,  205  can absorb shock loads experienced by the rear of the bicycle  100 . 
     In an alternate embodiment, a hydraulic drive replaces the conventional chain and sprocket arrangement. As illustrated in  FIG. 4  for another single-sided swing arm  305 , a hydraulic pump, details not shown, incorporates a modified button bracket assembly  309  and is located in or near the pedal sleeve  36 , and a hydraulic motor, details not shown, is located adjacent to, or inside, a modified rear hub  306 . Hydraulic lines, not shown, join the hydraulic pump to the hydraulic motor, such that there is a hydraulic connection between the two. This hydraulic drive system can be used to propel the bicycle in a manner such as that described in patent US Pat. No. 5,938,224, which is incorporated in full herein by this reference to it, for example. The hydraulic drive system illustrated in  FIG. 4  can be used with a two-sided swing arm  5 . Other drive mechanisms such as belts or rotating shafts may also be used. Other forms of multi-speed transmissions may also be used. For example, front or rear derailleurs may by attached to the trailing arm  5 ,  205  to allow for shifting between multiple sprockets of a set. 
     Optionally, the back of the frame  12  may be left open to a point above the top of the lever arm  4 . This allows the swing arm  5 ,  205 ,  305  to rotate forward once the shock absorber element  7  is disconnected. With the front wheel  110  removed, the rear wheel  111  is able to move forward and occupy a space under the front of the frame  12  including much of the space where the front wheel  110  was prior to removal. This enables the bicycle  100  to be put into a more compact form, which facilitates storage in a smaller area. 
     In a fourth embodiment, shown in  FIGS. 7 through 16 , a generally cantilevered, single sided, compound trailing arm  600  is constructed from two components, a trailing arm inner member  55  and an outer cover  70 . The trailing arm inner member  55  and outer cover  70  can be made of various materials, for example cast magnesium. A quick release lever arm  54  engages the shock absorber element  7  in a lever arm slot  89 . The shock absorber element  7  is releasably held in the lever arm slot  89  by a flip lever  91  which can be flipped to release the shock absorber element  7 . The chain  20  is looped over the front sprocket  11  and rear sprocket  14  in the conventional manner. An idler wheel  48  can be used to tension the chain  20  such that a conventional means for adjusting the location of a rear hub relative to the chain stay is not required. The idler wheel  48  also decreases the area occupied by the chain  20 . A pedal assembly  46 , consisting of a front sprocket  11 , crank arms  2  and a crank axle and bearings, is attached to the pedal sleeve  36  in various ways, such as those known in the industry. 
     Referring to  FIG. 13 , the rear sprocket  14  is joined to a transmission hub  83  by screwing, welding or other joining technology. The transmission hub  83  is of a type commonly available and sometimes called an internal rear hub mechanism because it has a cable operated shift mechanism  79  for changing gear ratios within the transmission hub  83 . The cable travels to the shift mechanism  79  through the back part of the compound trailing arm  600  but is omitted from the drawings for clarity. A wheel hub  77 , replacing the hub body found around a conventional transmission hub  83 , is joined to the transmission hub  83  by pressing, welding, or other joining means. One side of the transmission hub  83  is attached to the outer cover  70  of the compound trailing arm  600  by nut  80  and washers  78 ,  81 . The other side of the transmission hub  83  is held by rear wheel bearings  76  which hold the wheel hub  77  relative to the rear portion of the trailing arm inner member  55  but allow the rear wheel hub  77  to rotate. Bearing preload nut  87  is used to preload rear wheel bearings  76 . Lock-nut  86  is used to keep bearing preload nut  87  from loosening. A three-spoke composite rear wheel  71  is joined to the wheel hub  77  via screws (not shown), but can be joined by other methods. The rear tire  72  is joined to the composite rear wheel  71  using methods that are common in the industry. 
     Referring to  FIG. 14 , screws  75  keep the outer cover  70  attached to the trailing arm inner member  55 . The screws  75  pass through holes  69  in the trailing arm inner member  55  and outer cover  70  to make a casing for the chain  20 . The outer cover  70  adds structural strength to the trailing arm inner member  55  to help make the compound trailing arm  600  stiff in both bending and torsional twisting modes to provide for a precise ride and strong enough so that it will not break during normal riding. The chain  20  may also be completely enclosed by the composite swing arm  600 , thus improving the visual appearance of the bicycle  100  and ensuring that the greasy chain  20  does not soil the rider. This arrangement also provides for a more clean appearance and protects the chain  20  from the elements. Optionally, the trailing arm inner member  55  and outer cover  70  may be assemblies of sub-components. For example, the outer cover  70  may be made in two parts so that the chain  20  can be exposed without removing the crank arms  2 . Further optionally, the trailing arm inner member  55  may be designed to withstand all expected loads by itself, so that the outer cover  70  can be designed as a protective or decorative cover only. 
       FIGS. 15 and 16  show the construction around the pedal assembly  46 . A bottom bracket cartridge assembly  9  provides an axle supported by bearings in a housing for rotation about the crank axis  44 . Other means of supporting an axle may also be used. The crank arms  2  are joined to a bottom bracket cartridge assembly  9 , for example, by one of the methods commonly used in the bicycle industry. The bottom bracket cartridge assembly  9  is held in the pedal sleeve  36  by press fit, screwing together or another method. The compound trailing arm  600  is pivotably attached to the pedal sleeve  36  through bushings  90  located around the outside of the pedal sleeve  36  but inside of the end of the compound trailing arm  600 . Compound trailing arm  600  may rotate around the pedal sleeve  36  in bushings  90  at least through a selected degree of movement. This rotation may be oriented about the crank axis  44  through the center of the bottom bracket cartridge assembly  9 . 
     To assemble the bicycle  100 , the pedal sleeve  36  is placed into a semicircular recess in the bottom of each of two opposed sides of the frame  12 . The sides of the frame  12  are spaced far enough apart to admit the quick release lever arm  54 , shock absorber element  7  and bushings  90 . A bottom portion  30  of the frame  12  is also open between the sides to allow the compound trailing arm  600  to exit through the back of the frame. A recess on one side of the frame has a ridge that fits into a groove  35  in one side of the pedal sleeve  36  to locate the pedal sleeve laterally within the frame  12 . Bottom bracket caps  96 ,  97  having a semi-circular recess in their upper edges, are put in place against to capture the pedal sleeve  36  within the recesses of the frame  12  and caps  96 ,  97 . The pedal sleeve  36 , with its attached compound trailing arm  600  and pedal assembly  46  is then bolted to the bicycle  100  via cap holes  95  using bolts, not shown. 
     As described above, the crank axis  44  is fixed in position relative the frame. The bushings  90  allow the swing arm inner member  55  to rotate independently of the bottom bracket caps  96 ,  97  which are fixed to the bicycle  100 . The compound trailing arm  600  can rotate independently of the bicycle  100  and the pedal cranks  2  can rotate independently of the compound trailing arm  600 . The compound trailing arm  600  is pivotably attached to the frame  12  of the bicycle  100 , but the frame  12  does not interfere with rotation of the compound trailing arm  600  through its expected range of motion. The frame  12  illustrated is a clamshell or monocoque frame  12  but other frames  12 , such as a frame made of tubes, may be used. Optionally, the frame  12  may be left sufficiently open between the sides in the bottom portion  30  to allow the quick release lever arm  54  and compound trailing arm to rotate as required to make the bicycle more compact for storage, as will be described below. 
     The fourth embodiment, as for any of the previous embodiments, can be adapted to other drives. For example, a hydraulic drive, as described above, may be used. Shafts or belt drives may also be adapted for use with the compound trailing arm  600 . Other forms of multi-speed transmissions may also be used. For example, front or rear derailleurs may by attached to the compound trailing arm  600  to allow for shifting between multiple sprockets of a set. 
     When the fourth embodiment is being ridden and encountering bumps in the road, the composite rear wheel  71  will act on the rear hub  77 , driving it upward and downward. This will cause the trailing arm inner member  55  to rotate about the pedal sleeve  36  over bushings  90 . Since the quick release lever arm  54  is fixed to the compound trailing arm  600 , it will also rotate about the pedal sleeve  36  through an angle equal to the angular movement of the compound trailing arm  600 . The upper end of the quick release lever arm  54 , which is rotationally attached to the shock absorber element  7 , will move in such a way as to activate the shock absorber element  7 . Reaction forces from the shock absorber element  7  will dampen movement of the quick release lever arm  54  and return quick release lever arm  54  and compound swing arm  600  back to their original positions. In this manner, the compound swing arm  600  can provide for suspension of the rear of the bicycle  100 . Pedaling function is the same as on a conventional rear hub transmission bicycle. 
     The bicycle  100  of the fourth embodiment may be easily made more compact for storage. As shown in  FIG. 7 , the shock absorber element  7  is engaged into lever arm slot  89  in quick release lever  54  and held in place by flip lever  91 . With the shock absorber element  7  engaged, the bicycle  100  appears as in  FIG. 11 . Referring to  FIG. 12 , if the flip lever  91  is released, and the composite front wheel  73  and front tire  74  are removed, then the compound trailing arm  600  may be rotated forward, for example by  135  degrees or more. The end of compound trailing arm  600  and rear composite wheel  71  then occupy a location under the front of the frame  12  of the bicycle  100  where the composite front wheel  73  and front tire  74  were previously located. This allows the bicycle  100  to be stored in more confined or compact spaces, particularly if the seat is also removed, as is shown in  FIG. 12 . 
     While various exemplary embodiments of the invention have been described above, the invention is not limited to the embodiments disclosed. For example, but without limitation, parts of the various embodiments may be mixed together. Any of the first, second or third embodiments could have their trailing arms  5 ,  205 ,  305  modified to shaped with a channel, have a cover  70 , or hold a transmission hub  83  as for the compound trailing arm  600 . The first, second or third embodiments could also be modified so that their trailing arms  5 ,  205 ,  305  rotate in a bushing  90  around a non-rotating pedal sleeve  36  as for the fourth embodiment. Similarly, the compound trailing arm  600  could be fixed to a pedal sleeve  36  held by swing arm bearings  3  to rotate relative to the frame  12  as for the first, second and third embodiments. In the fourth embodiment, the compound trailing arm  600  could also be modified to have two side arms or to hold a rear hub  6 ,  306  as in the first, second and third embodiments. Other or modified embodiments may be made within the scope of the invention protected by this patent which is defined by the following claims.