Method and apparatus for nesting a suspension bicycle frame

The present invention is a swingarm suspension bicycle frame that is designed to allow nesting of the swingarm within the main frame of the bicycle frame, thereby allowing the bicycle frame to be packed and shipped in a smaller package than prior art bicycles of similar frame and wheel size, and a method for nesting such a suspension bicycle frame. In one or more embodiments, the pivot bearing to which the pivot point of the swingarm is attached is positioned along the seat support member of the main frame at a distance from the bottom of the bracket mount of the seat support member that is at least as great as the distance from the pivot point of the swingarm to the shock absorber mounting point of the swingarm. Such a location allows the swingarm to be nested within the main frame of the bicycle frame.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of and priority to and from U.S. Provisional Patent Application No. 63/233,277 filed Aug. 15, 2021, which is incorporated in its entirety by reference herein.

FIELD OF THE INVENTION

The present invention relates to the field of suspension frames for bicycles.

BACKGROUND OF THE INVENTION

FIG. 1shows a traditional prior art rigid (non-suspension) bicycle frame100. Prior art bicycle frame100has two generally triangular portions. The front triangular portion, sometimes referred to as the “main triangle,” includes a down tube110, a seat tube120, a top tube130, and a head tube140to which a front fork150is mounted. The rear triangular portion, sometimes referred to as the “rear triangle,” includes the seat tube120, left and right chain stays160, and left and right seat stays170.

FIG. 2shows an example of a prior art suspension bicycle frame200. Prior art suspension bicycle frame200, like prior art rigid frame100ofFIG. 1, includes a main triangle that includes a down tube210, a seat tube220, a top tube230, and a head tube240. Instead of a rear triangle, however, bicycle frame200includes a swingarm250that is pivotably mounted to down tube210, typically using a pivot bearing, at a pivot point260. The movement of swingarm250around pivot point260is restrained and dampened by a shock absorber270. Commercial examples of bicycles that include a swingarm suspension like bicycle frame200include the “Five” models from Orange Mountain Bikes Limited of West Yorkshire, England and the “Atroz” models from Diamondback Bicycles of Kent, Wash.

FIG. 3shows a perspective view of the swingarm250ofFIG. 2. The construction of swingarm250is typical of swingarms used in swingarm suspension bicycle frames. It includes right and left arms300and310, respectively, which are typically approximately mirror images of each other. Arms300and310are typically made of metal, such as aluminum, or of a composite material, such as a carbon fiber composite. They may me solid, or have hollow or partially hollow cores. Arms300and310each include front bearing mount openings340and350, respectively, and rear wheel mount openings370and380, respectively. Arms300and310are rigidly connected to one another by connection structure330to form a rigid integrated unit. In the embodiment ofFIG. 3, connection structure330is implemented as a round rod whose ends are fixedly attached to each of arms300and310, for example by welding if arms300and310are constructed of metal or by bonding if they are constructed of a composite material. In other prior art embodiments, connecting structure330may include additional structures joining arms300and310, such as, for example, a metal or composite plate across the front portions of arms300and310. Arms300and310must be joined by connection structure330into a rigid integrated unit to prevent flexing and resulting undesirable wheel wobble that would occur if each arm300and310could move independently of each other about front pivot point260ofFIG. 2. Further, connecting structure330must be located towards the front of arms300and310so as not to interfere with the rear wheel when it is mounted to wheel mount openings370and380.

In the embodiment ofFIG. 3, connecting structure330includes a shock absorber mount360for attaching to one end of shock absorber270ofFIG. 2.

In prior art swingarm suspension bicycle frames, as shown in the embodiment ofFIG. 2, pivot point260around which swingarm250pivots is placed at approximately the same vertical height as the center290of rear wheel280. This is so that, when rear wheel280moves up and down in response to road shocks, center290of rear wheel280moves approximately vertically up and down, thereby minimizing chain stretch and an effect sometimes referred to as “pedal jerk” that can occur if the movement of center290is such that it moves in a manner that significantly changes the spacing between center290of wheel280and the center axis of chain wheel295.

FIG. 4is an image generated by a publicly available software program called “Linkage” available at www.bikechecker.com. Linkage is bicycle analysis and design software that models, analyses and calculates movements and forces of different bicycle suspension geometries. Linkage allows a user to model and analyze a wide variety of bicycle suspension frame geometries. Linkage models for over 1500 bicycle suspension frame geometries are available at the Linkage website.

FIG. 4shows part of one of the output images of the Linkage program for a Linkage model of the “Orange Five” bicycle. The Orange Five bicycle has a swingarm frame geometry similar to that of the swingarm suspension frame embodiment shown inFIGS. 2 and 3. The Linkage model400of the Orange Five bicycle shown inFIG. 4includes a swingarm410pivotably attached to down tube415of front frame triangle405at pivot point420. Movement of swingarm410about pivot point420is restrained by shock absorber450mounted between swingarm410and down tube415. As in the embodiment ofFIG. 2, the height of pivot point420is close to the height of center460of wheel430when wheel430is mounted to swingarm410. Arc440is the path of movement of the center460of wheel430as swingarm410pivots about pivot point420as calculated by the Linkage program. As shown inFIG. 4, arc440is approximately vertical, so that the distance between center460of wheel430and the center of rotation of chainwheel425does not greatly change as swingarm410moves to absorb shocks within the range of movement permitted by shock absorber450.

Persons of ordinary skill in the art of bicycle suspension frame design have long sought to design suspension frames so as to limit chain stretch and pedal jerk. See, for example, the teaching of U.S. Pat. Nos. 5,332,246, 5,509,679, 7,521,743, 7,909,347, 8,066,297, 8,272,657, 9,302,732 and 10,377,442. Heretofore, persons of ordinary skill in the art have not recognized any benefit in purposefully designing a suspension bicycle frame in a configuration that causes an increase in chain stretch and resulting pedal jerk.

SUMMARY OF THE INVENTION

The present invention is a swingarm suspension bicycle frame that is not designed to minimize chain stretch and pedal jerk as in the prior art, but instead is designed to allow nesting of the swingarm within the main frame (e.g. the main triangle) of the bicycle frame, thereby allowing the bicycle frame to be packed and shipped in a smaller package than prior art bicycles of similar frame and wheel size, and a method for nesting such a suspension bicycle frame. In one or more embodiments, the pivot bearing to which the pivot point of the swingarm is attached is positioned along the seat support member of the main frame at a distance from the bottom of the bracket mount of the seat support member that is at least as great as the distance from the pivot point of the swingarm to the shock absorber mounting point of the swingarm. Such a location results in increased chain stretch and pedal jerk as compared to swingarm suspension bicycle frames of the prior art, but allows the swingarm to be nested within the main frame of the bicycle frame.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth to provide a thorough description of the invention. However, it will be apparent to those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.

One of the disadvantages of full size prior art rigid and suspension bicycle frames is the size of box or other container needed to ship them (“full size” as used herein means bicycle frames that are made to accept wheels 26 inches and larger). Even though use of materials such as aluminum and carbon fiber composites has allowed the construction of light weight bicycle frames, shipping costs remain high because of the bulky shipping containers that are required. That has resulted in high shipping costs when a bicycle is transported, for example when shipped from a manufacturer to a dealer or customer, or by the owner after purchase. That is a particular disadvantage when a bicycle owner desires to take the bicycle along on an airline trip. Prior art full-size bicycle frames have heretofore not been able to fit into a container that meets the checked-luggage size limitation of 62 inches (sum of length, width, and depth), even when easily removable components such as the seat, wheels, handlebars, pedals, and in some cases cranks, have been removed. As a result, a bicycle owner who seeks to take a full size bicycle of the prior art along on an airplane trip is forced to pay oversize baggage surcharges that can amount to several hundred dollars per trip.

Full size bicycles of the prior art that have swingarm suspension bicycle frames can be shipped in somewhat smaller containers than bicycles with rigid frames because the swingarm can be rotated up and forward around the pivot bearing by which the swingarm is mounted to the frame's main triangle after the rear wheel and the shock absorber mounting bolt are removed. However, because the swingarm pivot point is positioned low on the main triangle in the prior art to reduce chain stretch and resulting pedal jerk, the range of such rotation is limited by the connecting structure that connects the left and right swingarms together. As shown inFIG. 5, for example, swingarm250of swingarm suspension bicycle frame200ofFIG. 2can only be rotated about 30 to 40 degrees (indicated by arrow510inFIG. 5) about pivot point260before the shock absorber mount360of swingarm250hits down tube210, preventing further movement.

FIG. 6shows an embodiment of a bicycle frame600of the invention. The embodiment ofFIG. 6was created by modifying the computer model of the Orange Five bicycle frame shown inFIG. 4using the Linkage software, which allows a user to edit a model to modify the linkage geometry of the modeled frame. ComparingFIG. 6toFIG. 4, it can be seen that one of the changes made to the computer model of the Orange Five bicycle frame400ofFIG. 4includes moving the pivot point420of the swingarm410from a location low on the down tube415to a location on a swingarm bearing mount structure625mounted to seat tube610(for example by welding or composite bonding) about midway along seat tube610. Another change made from bicycle frame400ofFIG. 4is mounting the fixed end455of shock absorber450to a mounting structure mounted to top tube620instead of to down tube415. Finally, the shape and dimensions of swingarm650of the embodiment ofFIG. 6differ from those of swingarm410ofFIG. 4. The front short leg670of swingarm650is shorter than the front short leg470of swingarm410to accommodate the shorter distance between pivot point615and shock absorber mounting point680, as compared to the distance between pivot point420and shock absorber mounting point480. In addition, the angle between front short leg670and rear long leg675of swingarm650is smaller than the angle between front short leg470and rear long leg475of swingarm410. Also, the length of rear long leg675is appropriate to accommodate the distance between shock absorber mounting point680and rear wheel mounting point630.

Arc660shows the path of movement of rear wheel mounting point630when swingarm650moves upward as road shocks are absorbed by the suspension system formed by swingarm650and shock absorber640. Arc660is not approximately vertical like arc440ofFIG. 4, but is angled toward the rear of bicycle frame600. This has the result of increasing the distance between rear wheel mounting point630and the center645of chain wheel685when the suspension moves upward, causing chain stretch and pedal jerk.FIG. 7is an image generated by the Linkage software program showing the chain stretch resulting from upwards travel of 100 mm of rear wheel mounting point630of swingarm675of bicycle frame600. The chain stretch is substantial, as indicated by nearly horizontal orientation of rear derailleur chain tensioner690, compared to the more vertical orientation when the suspension is not compressed shown inFIG. 6. To reduce chain stretch for the embodiment ofFIGS. 6 and 7, the spring force of shock absorber640can be increased, which will effectively reduce chain stretch, but also reduce the amount of suspension travel.

The advantages of the swingarm suspension frame of the present invention are shown inFIGS. 8 and 9.FIG. 8shows how swingarm650of swingarm suspension frame600of the invention can be rotated so as to nest within the outside perimeter of main triangle800(which includes seat tube610, top tube620and down tube695of the embodiment ofFIG. 6) after the wheels, shock absorber, and crankset have been removed. In the embodiment ofFIG. 8, as indicated by arrow810, swingarm650can be rotated around pivot point615approximately 180 degrees before the connecting structure of swingarm650contacts down tube820of main triangle800, preventing further movement.

FIG. 9shows the resulting configuration of frame600after swingarm650has nested within main triangle800. In addition, inFIG. 9, front fork825has been rotated so as to face backwards and has been compressed to its maximum amount of suspension travel, which is easiest if front fork825is an air suspension fork that whose effective spring force is reduced once the air pressure is released. As shown by outline900, in the embodiment ofFIG. 9, nesting swingarm suspension bicycle frame600can fit within a rectangular enclosure having dimensions L by H, In one or more embodiments, the dimensions of main triangle800are selected such that L and H are each less than 26 inches, which allows frame600to be packed into a case having 26×26×10 inches, which meets typical airline non-oversize checked baggage size requirements (length plus width plus thickness less than 62 inches).

FIG. 10shows a schematic representation of main triangle800and swingarm615that is useful for illustrating relevant parameters of embodiments of the swingarm suspension frame of the invention that include a main triangle, like main triangle800of the embodiment ofFIG. 6. InFIG. 10, triangle1000schematically represents the inside perimeter of main triangle800, and triangle1010schematically represents swingarm615, the vertices of triangle1010being pivot point615, rear wheel mounting point630, and shock absorber mounting point680. Triangle1010is thus a generic representation of a swingarm, which can have a variety of shapes and forms, but which must provide a rigid supporting structure for the three features that form the vertices of triangle1010, namely pivot point615, rear wheel mounting point630, and shock absorber mounting point680.

FIG. 11separately depicts the schematic representations of main triangle1000and swingarm triangle1010ofFIG. 10. As shown inFIG. 11, main triangle1000includes a line segment1020that schematically represents swingarm bearing mount structure625. Swingarm bearing1110is disposed at the end of line segment1020. The length of line segment1020thus represents the distance that pivot point615is offset from seat tube610in the embodiment ofFIG. 6. In other embodiments, pivot point615may be disposed on seat tube610itself, in which case the length of line segment1020would be zero.

FIG. 12is a schematic representation of a general embodiment of a main triangle1200of the invention which demonstrates some of the criteria required to construct a nesting swingarm suspension bicycle frame according to the invention. Main triangle1200includes top tube1210, down tube1220and seat tube1230. Main triangle1200also includes a pivot bearing support1240mounted to seat tube1230and a pivot bearing1250mounted to pivot bearing suppont1240. Main triangle1200, in the same way as main triangle of bicycle frames of the prior art, can have any of a variety of sizes and shapes, depending on the size of the wheels to be used, the size of the rider for which the frame is intended, etc.

Item1260inFIG. 12is a circular arc centered is at pivot bearing1250. It has a radius R1, which is the maximum radius of arc1260that fits inside main triangle1200.

FIG. 13is a schematic representation of a general embodiment of a swingarm1300of the invention. Swingarm1300is depicted as a triangle whose vertices are shock absorber mounting point1310, pivot point1320, and rear wheel mounting point1330. Although the schematic representation of swingarm1300is depicted as a triangle, those of skill in the art will appreciate that swingarm1300can have any shape or configuration that encompasses those three points, including, for example, configurations similar to those of swingarm250ofFIG. 2or swingarm475ofFIG. 4.

For certain configurations of swingarm1300, shock absorber mounting point1310will be the part of the front part of swingarm1300(the part that faces towards the front wheel of the bicycle when mounted to the pivot bearing of the main triangle) that would first contact the main triangle when swingarm1300pivots forwards about the pivot bearing of the main triangle. That is, for the embodiment of swingarm1300ofFIG. 13, shock absorber mount1310is the point of first contact with the main triangle. That means, for example, if pivot point1320of swingarm1300were mounted to pivot bearing1250of main triangle1200ofFIG. 12, the distance R2between pivot point1320and shock absorber mounting point1310of swingarm1300ofFIG. 13(i.e. the point of first contact) should not be greater than radius R1ofFIG. 12for swingarm1300to be able to rotate the maximum extent around pivot bearing1250so as to nest within main triangle1200according to the invention.

FIG. 14shows a schematic representation of an embodiment of a swingarm1400in which the configuration of swingarm1400is such that there is a different point of first contact1405than shock absorber mounting point1410that first contacts the main triangle when swingarm1400pivots about the main triangle's pivot bearing. Point of first contact1405may for example be a portion of the connecting structure that connects the left and right portions of swingarm1400. Thus, if pivot point1420of swingarm1400were mounted to pivot bearing1250of main triangle1200ofFIG. 12, the distance R3between pivot point1420and point of first contact1405of swingarm1400ofFIG. 14should not be greater than radius R1ofFIG. 12for swingarm1400to be able to rotate the maximum extent around pivot bearing1250so as to nest within main triangle1200according to the invention.

In general, for a swingarm to be able to nest within a main triangle according to the invention, the distance between its pivot point at which it is mounted to the pivot bearing of the main triangle and the swingarm's point of first contact (whether it is the shock absorber mounting point or some other point) should be less than the maximum radius of an arc, centered at the pivot bearing of the main triangle to which the swingarm is mounted, that can inscribe the top tube and down tube of the main triangle. This distance will be referred to hereinafter as the “first contact distance.”

Looking again atFIG. 12, it is apparent that the radius R1of inscribed arc1260in the embodiment of main triangle1200ofFIG. 12would be greater if pivot bearing1250were mounted closer to, and in the limiting case mounted directly to, seat tube1230.

FIG. 15shows a schematic representation of a main triangle1500in which pivot bearing1550is mounted directly to seat tube1530of main triangle1500. Comparison withFIG. 12shows that the radius R4of inscribed arc1560of the embodiment ofFIG. 15is greater than radius R1of inscribed arc1260of the embodiment ofFIG. 12.

Another aspect that is apparent fromFIG. 15is that R4has a maximum value when the perpendicular distance between down tube1520and pivot bearing1550is approximately equal to the distance between pivot bearing1550and the intersection of top tube1510with seat tube1530. That point can be easily identified from the geometry of any particular main triangle of a bicycle frame.

Looking back atFIG. 6, it can be seen that swingarm650acts as a lever arm that transmits the generally upward force exerted by rear wheel605into the more horizontal force transmitted by shock absorber mounting point680to shock absorber640. Because the distance DS between pivot point615and shock absorber mounting point680is shorter than the distance DW between rear wheel mounting point630and pivot point615, the force FS on shock absorber640is greater than the force FW exerted by rear wheel605on rear wheel mounting point630, the ratio of FS/FW being proportional to DW/DS. The response of the suspension formed by swingarm650and shock absorber640is dependent among other things on the spring rate of shock absorber640and force FS. It is at times desirable that force FS not exceed a certain limit, dependent for example on the spring rate of shock absorber640. For that to occur, there is a minimum desired value of distance DS, which, for a given configuration of a swingarm such as swingarm1400ofFIG. 14, determines a minimum desired value for the first contact distance of the swingarm (referred to herein as “the minimum desired value” or “MDV”), which may be greater than DS depending on where on a particular swingarm the point of first contact is located.

Depending on the specific dimensions of a particular main frame, the MDV may be less than, equal to, or greater than the radius of the maximum radius of the largest inscribed arc centered at the pivot bearing of a particular main frame (e.g. R4in the embodiment ofFIG. 15).

Considering again main frame1500ofFIG. 15, if the MDV is greater than R4, that desired value cannot be achieved with the existing main triangle geometry, and either the seat tube length needs to be increased or a stiffer shock absorber used.

If the MDV is equal to R4, then pivot bearing1550would need to be mounted to seat tube1530at the location shown inFIG. 15, i.e. such that the perpendicular distance between down tube1520is approximately equal to the distance between pivot bearing1550and the intersection of top tube1510with seat tube1530.

If the MDV is less than to R4, then pivot bearing1550can be mounted either higher or lower on seat tube1530than the location shown inFIG. 15. It will be recalled that it in a swingarm bicycle suspension system, chain stretch and pedal jerk increase with increased height of pivot bearing1550on seat tube1530. Accordingly, if the MDV is less than R4, it is desirable to lower the position of pivot bearing1550as compared to the position shown inFIG. 15.

FIG. 16shows an embodiment of a main triangle1600for which the MDV is less than R4. In the embodiment ofFIG. 16, pivot bearing1650is mounted to seat tube1630at the approximate location at which the perpendicular distance from down tube1620to pivot bearing1650is approximately equal to the MDV. That is the lowest location at which pivot bearing1650can be mounted to allow a swingarm having a distance from its pivot point to its point of first contact equal to the MDV to nest within main triangle1600according to the invention.

The term “main triangle” has been used herein to refer to the main part of a swingarm suspension bicycle frame to which the front fork and swingarm are mounted. A more generic term for that portion of a bicycle frame is “main frame,” which includes both what has been referred to as “main triangles” that feature a generally triangular arrangement of a top tube, seat tube, and down tube, as well as alternative configurations, for example, frames that do not feature a down tube, but instead feature enlarged and strengthened top and seat tubes. Such main frames may, for example, be formed of metal or of composite materials, such as a carbon fiber composite.

FIG. 17shows how the nesting swingarm of the present invention can be implemented on a main frame1700that does not include a down tube. In the embodiment ofFIG. 17, main frame1700includes a top member1710(which may or may not be in the form of a tube) and a seat support member1730(which also may or may not be in the form of a tube). A bottom bracket mount1765is disposed at the bottom of seat support member1730. A pivot bearing1750is also mounted to seat support member1730.

For a main frame like main frame1700of the embodiment ofFIG. 17, the limiting boundaries for inscribed arc1740are the bottom1715of top member1710and the bottom1770of bottom bracket mount1765. As shown inFIG. 17, the radius R5of the largest inscribed arc centered at pivot bearing1750for main frame1700is generally half the distance between the bottom1715of top member1710and the bottom1770of bottom bracket mount1765, and the location of pivot bearing along seat support member1730is halfway between the bottom1715of top member1710and the bottom1770of bottom bracket mount1765. Thus the maximum first contact distance for a swingarm to be used with main frame1700to allow the swingarm to nest within main frame1700according to the invention is R5. Swingarm1780is an example of such a swingarm that has a first contact distance of R5.

FIG. 18shows how swingarm1780can pivot around pivot bearing1750to nest within main frame1700according to the invention.

FIG. 19shows an inscribed arc1910for main frame1700for a swingarm for which the MDV is less than R5ofFIG. 17. As shown inFIG. 19, for a swingarm with a first contact distance of MDV, pivot bearing1750can be lowered to a location on seat support member1730whose distance from bottom1770of bottom bearing1765is approximately equal to the MDV.

Thus, a novel swingarm suspension bicycle frame has been presented. Although the invention has been described using specific example embodiments, those of ordinary skill in the art will understand that the invention is not limited to the specific example embodiments described herein. Other embodiments will be apparent to those of ordinary skill in the art.