Bicycle frame with passive seat tube pivot joint

A bicycle frame assembly that includes an upper frame member and a lower frame member that each extend between a head tube and a dropout. A seat tube extends between the upper frame member and the lower frame member. The seat tube is preferably connected to a bottom bracket of the lower frame member and is connected by a pivot to the upper frame member so that the seat tube can deflect from a rest position without altering an orientation of a top tube to a bottom tube of the upper and lower frame members, respectively.

BACKGROUND OF THE INVENTION

The present invention relates to bicycles and, more particularly, to a bicycle frame assembly wherein the seat tube is connected at an overlapping intersection of a top tube and the seat stays by a passive pivot that allows the seat stay to deflect from a generally linear at-rest orientation to improve the vertical compliance of the bicycle frame.

The primary structural component of a conventional two-wheel bicycle is the frame. On a conventional road bicycle, the frame is typically constructed from a set of tubular members assembled together to form the frame. For many bicycles, the frame is constructed from members commonly referred to as the top tube, down tube, seat tube, seat stays and chain stays, and those members are joined together at intersections commonly referred to as the head tube, seat post, bottom bracket and rear dropout. The top tube usually extends from the head tube rearward to the seat tube. The head tube, sometimes referred to as the neck, is a short tubular structural member at the upper forward portion of the bicycle which supports the handlebar and front steering fork, which has the front wheel on it. The down tube usually extends downwardly and rearward from the head tube to the bottom bracket, the bottom bracket usually comprising a cylindrical member for supporting the pedals and chain drive mechanism which powers the bicycle. The seat tube usually extends from the bottom bracket upwardly to where it is joined to the rear end of the top tube. The seat tube also usually functions to telescopically receive a seat post for supporting a seat or saddle for the bicycle rider to sit on.

The chain stays normally extend rearward from the bottom bracket. The seat stays normally extend downwardly and rearward from the top of the seat tube. The chain stays and seat stays are normally joined together with a rear dropout for supporting the rear axle of the rear wheel. The portion of the frame defined by the head tube, seat post and bottom bracket and the structural members that join those three items together can be referred to as the main front triangular portion of the frame, with the seat stays and chain stays defining a rear triangular portion of the frame. The foregoing description represents the construction of a conventional bicycle frame which of course does not possess a suspension having any shock absorbing characteristics.

Although the increased popularity in recent years of off-road cycling, particularly on mountains and cross-country, has made a shock absorbing system in many instances a biking necessity. An exemplary rear wheel suspension system is disclosed in U.S. Pat. No. 7,837,213. Generally, bicycle suspension systems intended for off-road riding conditions include a number of links that are connected and movable or pivotable to allow the bicycle frame to absorb a portion of the energy associated with aggressive riding over uneven terrain. However, such robust suspension systems do not particularly lend themselves to extended rides over paved terrain. The robust nature of such systems increases the weight attributable to the bicycle assembly. During rides intended to test rider stamina, endurance, and conditioning, such robust suspension systems would detrimentally affect rider time performance.

Fixed shape forward and rear triangle frame shapes are generally well accepted as the preferred configuration for many road bicycles due to their collective light weight and robust frame. However, even paved surfaces can present discontinuities wherein most riders would prefer some degree of bicycle suspension to limit or reduce the forces communicated to the rider from payment discontinuities. The ever increasing capabilities of bicyclists have created a sub-set of the road bicycle termed an endurance bicycle. Endurance bicycles are generally understood as race-ready road bicycles with added comfort to allow riders to complete rides of ever increasing duration and/or distance. Many endurance bicycles maintain a fixed forward and rear triangle frame and provide impact dampening with suspension seat posts and/or vibration dampening handlebar assemblies.

An alternate approach to an endurance bicycle is disclosed in U.S. Pat. No. 6,932,371. U.S. Pat. No. 6,932,371 discloses a bicycle assembly wherein the seat tube forms a passive suspension element via the elimination of the seat stays and providing a second set of chain stays that are located in closer proximity to the bottom bracket that to the top tube. The frame assembly of U.S. Pat. No. 6,932,371 includes a number of gusset members that are required to provide the desired non-vertical stiffness of the frame assembly. In achieving the desired vertical compliance, the bicycle frame of U.S. Pat. No. 6,932,371 includes a number of supplemental structures that, in improving vertical compliance, detrimentally affect the overall weight of the underlying bicycle assembly.

Accordingly, there is a desire to provide a bicycle frame assembly that includes a passive suspension element but does not appreciably detrimentally affect the weight of the overall bicycle frame assembly.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a bicycle frame assembly having a deflectable seat tube that overcomes one or more of the aforementioned drawbacks. One aspect of the invention discloses a bicycle frame assembly having an upper frame member and a lower frame member. The upper frame member includes a top tube and a pair of seat stays and extends between a dropout and a head tube in a generally continuous manner. The lower frame member includes a bottom tube, a bottom bracket, and a chain stay and extends between the dropout and the head tube. A seat tube extends from the lower frame member toward the upper frame member and passes beyond the top tube. The seat tube is connected to the upper frame member by a pivot so that more of the seat tube is located between the pivot and the bottom bracket than extends beyond the upper frame member. Preferably, an opening is formed through the top tube or a lug that connects the seat stays with the top tube. The seat tube preferably passes through the opening in the upper frame member. Alternatively, the seat tube could be perforated or otherwise contoured to pass generally around the more horizontal structure of the top tube and/or the seat stays. As another alternative, the seat tube could pass rearward relative to the top tube so as to be positioned in the space generally flanked by the seat stays.

Another aspect of the invention that is useable with one or more of the above aspects discloses a bicycle frame assembly that includes a forward frame triangle that includes a top tube and a bottom tube. The top tube includes a first end that is connected to a head tube and a second end. The bottom tube includes a first end that is connected to the head tube and a second end. A bottom bracket is connected to the second end of the bottom tube. A seat tube extends in an upward direction from the bottom bracket and a pair of seat stays is connected to the top tube and extends in a rearward direction beyond the forward frame triangle. A pivot connects the seat tube to the forward frame triangle proximate the top tube at a location nearer a bicycle seat than the bottom bracket. The pivot allows that portion of the seat tube disposed between the pivot and the bottom bracket to deflect from an at rest position during vertical loading of the seat tube.

Another aspect of the invention that is useable with one or more of the above aspects discloses a bicycle frame assembly having an upper frame member that includes a top tube and a pair of seat stays. The upper frame member extends between a dropout associated with a rear wheel and a head tube. An opening is formed in the upper frame member. A lower frame member that includes a bottom tube, a bottom bracket, and a chain stay extends between the dropout and the head tube. A seat tube extends from the lower frame member toward the upper frame member and passes through the opening in the upper frame member. A pivot connects the seat tube to the upper frame member proximate the opening so that more of the seat tube is located between the pivot and the bottom bracket than extends beyond the upper frame member.

Another aspect of the invention that is useable with one or more of the above aspects discloses a method of allowing deflection of a seat tube. A seat tube is connected to a bottom bracket. The seat tube is connected to an upper frame member with a pivot that is located at an overlapping intersection of the seat tube and the upper frame member so that the seat tube can deflect from alignment along a line between the bottom bracket and the pivot.

These and various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows a bicycle10having a frame assembly12according to the present invention. Bicycle10includes a seat16and handlebars18that are attached to frame assembly12. A seat post20is connected to seat16and slidably engages a seat tube22of frame assembly12. A top tube24and a down tube26extend forwardly from seat tube22to a head tube28of frame12. Handlebars18are connected to a stem or steer tube30that passes through head tube28and is connected or integrally formed with a fork crown32. Understandably, handlebar18may include a stem that is constructed to slidably engage an interior cavity of steer tube30. It is appreciated that one or more of the structures of bicycle10and frame assembly12can be constructed from similar materials, a variety of different materials, and various combinations thereof. Preferably, frame assembly12and seat tube22are formed of metal-type materials, such as aluminum-type materials, carbon fiber materials, and/or materials that are sufficiently formable and robust enough to support the rider of bicycle10.

Fork assembly14includes a pair of fork blades or fork legs34that extend from generally opposite ends of fork crown32and are constructed to support a front wheel assembly36at an end thereof or dropout38. Dropouts38engage generally opposite sides of an axle40constructed to engage a hub42of front wheel assembly36. A number of spokes44extend from hub42to a rim46of front wheel assembly36. A tire48is engaged with rim46such that rotation of hub42and rim46, relative to fork legs34, rotates tire48.

Bicycle10includes a front brake assembly50having an actuator52attached to handlebars18and a pair of brake pads53positioned on generally opposite sides of front wheel assembly36. Brake pads53are constructed to engage a brake wall54of rim46thereby providing a stopping or slowing force to front wheel assembly36. A rear wheel assembly56includes a brake assembly58similar to front wheel brake assembly50but it is appreciated that one or both of front and rear wheel brake assemblies50,58could be provided in other brake configurations such as a disk brake assembly wherein a rotor and a caliper are positioned proximate one or more of front wheel axle40or a rear axle64, respectively. A rear wheel66is positioned generally concentrically about rear axle64.

A pair of seat stays62,68(FIG. 2) and a pair of chain stays70,71(FIG. 2) extend rearward relative to seat tube22and offset rear axle64from a crankset72. Crankset72includes a set of pedals74that is operationally connected to a flexible drive member such as a chain76via one or more variable diameter chain gears or a chain ring or sprocket78. Rotation of chain76communicates a drive force to a gear cluster80positioned proximate rear axle64. Gear cluster80is generally concentrically orientated with respect to rear axle64and includes a number of variable diameter gears.

Gear cluster80is operationally connected to a hub82of rear wheel66. A number of spokes84extend radially between hub82and a rim86of rear wheel66of rear wheel assembly56. As is commonly understood, rider operation of pedals74drives chain76thereby driving rear wheel66which in turn propels bicycle10. Fork assembly14is constructed to support a forward end88of bicycle10above a ground surface90. Handlebar18is connected to frame12and fork assembly14such that operator manipulation of handlebar18is communicated to fork assembly14to facilitate rotation of front wheel assembly36relative to frame assembly12along a longitudinal axis, indicated by arrow175, of bicycle10. As is commonly understood, such manipulation of handlebar18steers bicycle10during riding.

Understandably, the construction of bicycle10shown inFIG. 1is merely exemplary of a number of bicycle configurations. That is, whereas bicycle10is shown as what is commonly understood as a street or road bike, it is appreciated that the present invention is applicable to a number of bicycle configurations including those bicycles with more aggression suspension systems commonly found in off-road or mountain bike frame configurations, and/or hybrids, cross-over or multi-purpose bicycle frame configurations.

Referring toFIGS. 1 and 2, top tube24and seat stays68extend in a fairly continuous manner to form an upper frame member100that extends from head tube28to a pair of dropouts102,103that support rear axle64. Upper frame member100can be formed as one piece and/or assembled from a distinct top tube24, seat stays68, and/or an optional lug104that is disposed between the top tube24and the seat stays68. It is appreciated that seat stays62,68and top tube24of upper frame member100could be formed as a unitary structure, a number of discrete permanently connected elements, or connected to one another via an optional lug104associated with an overlap area105of seat tube22and upper frame member100. In a similar manner, it is also appreciated that down tube26, bottom bracket110, and chain stays70,71, whose assemblies collectively define a lower frame member that extends from head tube28to one or more dropouts102,103could be formed as a unitary assembly wherein bottom bracket110is formed with down tube26or chain stays70,71, or an assembly wherein the chain stays70,71and down tube26can be permanently affixed to a discrete bottom bracket lug or simply bottom bracket110. Once assembled, as plainly shown inFIG. 1, bicycle10includes a forward frame triangle that is a generally defined by the triangular shape of the direction of extension of the seat tube, the top tube, and the down tube of frame assembly12regardless of the methodology or number of discrete elements used to form the frame assembly.

As shown inFIG. 2, seat tube22includes a first end108that is secured to bottom bracket110of bicycle frame12and a second end112that extends in a generally upward direction beyond the location of the lug or overlap area105with upper frame member100. Preferably, seat post20(FIG. 1) telescopically cooperates with seat tube22of frame assembly12. A passive pivot assembly120connects an upper portion of seat tube22to bicycle frame assembly12proximate overlap area105such that more of seat tube22extends between pivot assembly120and bottom bracket110than extends in an upward direction relative to the intersection of seat tube22and upper frame member100.

Passive pivot assembly120completes the linkage between upper frame member100, which includes top tube24and the structures associated with seat stays62,68. A lower end of seat tube22is secured to lower frame member101, which includes the down tube26and bottom bracket110and preferably one of more chain stays70,71. As explained above, seat tube22, top tube24and down tube25collectively generally define the forward triangle of frame assembly12. Frame assembly12has a fairly robust and stable feel during use but is also constructed to provide impact dampening performance in a manner that does not allow changing of the relative connection points of any of the respective members of the forward frame triangle. As described further below with respect toFIG. 6, the non-bonded rigid yet pivotable connection of seat tube22with upper frame member100allows deflection of seat tube22in a vertical plane and in a direction along the longitudinal length of the seat tube22so as to allow the frame assembly12to provide a limited degree of suspension performance or vertical compliance without altering the orientation of the connection points of any of the frame members relative to one another.

As shown inFIGS. 3-5, overlap area105includes a passage130that is shaped to allow seat tube22to pass therethrough. An opening132(FIG. 5) is formed laterally through seat tube22and shaped to rotationally cooperate with pivot assembly120. As mentioned above, it is envisioned that seat tube22merely pass over an axis or longitudinal area associated with one or more of the top tube, the seat stays, and/or a fabrication lug being formed therebetween. It is envisioned that the seat tube could be perforated or otherwise contoured to pass generally around the more horizontal structure of the top tube and/or the seat stays associated with upper frame member100. As another alternative, the seat tube could pass rearward relative to the closed structure of top tube24so as to be positioned in the space generally flanked by the seat stays. Each configuration allows limited passive pivoting between seat stays70,71and the adjacent structure of upper frame member100of bicycle frame assembly12.

As shown inFIG. 3, passage130is bounded on a forward side131by an end wall associated with top tube24or a portion of the respective frame lug104. A first optional gasket134is disposed between forward side131of overlap area105and top tube24and generally surrounds a forward side136, and opposite lateral sides138,140of seat tube22. Optional gasket134prevents moisture and/or dirt and/or debris from entering the pivot area associated with passage130and the passage of seat tube22therethrough but does not otherwise interfere with the flexion of seat tube22during use of bicycle10as described further below with respect toFIG. 6. Passage130is bounded on opposite lateral sides by side walls142,144of upper frame member100. An optional rear web wall146completes the definition of passage130such that upper frame member100completely surrounds seat tube22with web wall146extending laterally between seat stays62,68.

As shown inFIGS. 4 and 5, pivot assembly120includes a first bolt or other fastener150, a second bolt or other fastener152, a guide sleeve154, and first and second bearings or bushings156,158. Each of fasteners150,152includes a threaded portion160, a stem portion162, and a head portion164. The radial diameter of each fastener150,152gradually increase from the respective threaded portion160to the stem portion162to the head portion164. One or each of head portions164includes a drive surface166that is shaped to cooperate with a driving tool, such as a hex driver or the like for securing each of first and second fasteners150,152relative to pivot assembly120. Although shown as being formed on an interior radial surface of fasteners150,152, it is appreciated that driving surface166could have any number of shapes and/or be provided on a radial exterior surface of the corresponding fastener150,152. It is further appreciated that one of fasteners150,152could formed integrally with sleeve154such that operation of one respective fastener secures pivot assembly120relative to bicycle frame assembly12.

Each bushing156,158includes an outer radial surface170, an inner radial surface172, an outboard lateral surface174, and an inboard lateral surface176. As used herein, the inboard and outboard lateral directions associated with surfaces174,176of each bushing156,158refers to the orientation of surfaces170,174relative to a longitudinal vertical plane that contains longitudinal axis175of bicycle10and the relative position of the respective surfaces and/or structures relative to the same. For example, surfaces176of bushings156,158are nearer a longitudinal axis, indicated by line178, of upper frame member100. Accordingly, surfaces174are further outboard and surfaces176are further inboard relative to one another and longitudinal axis178of upper frame member100along a longitudinal axis, indicated by line180, of pivot assembly120. As shown inFIG. 5, the longitudinal axis180of pivot assembly120is oriented in a crossing direction relative to, and is preferably normal to, longitudinal axis178of upper frame member100.

Still referring toFIGS. 4 and 5, a first opening184and the second opening186are formed in each of the respective sidewalls142,144of upper frame member100and centered along axis180of pivot assembly120. A seat188extends circumferentially about at least one of openings184,186in the lateral outboard facing surface of the respective sidewall142,144. Seat188is defined by a lip190that extends circumferentially about the corresponding opening184,186and is shaped to cooperate with sleeve154and a corresponding bushing156,158.

Sleeve154includes a stem portion194, the head portion196, and an opening198formed therethrough. Sleeve154is constructed to slidably cooperate with openings184,186in a direction aligned with axis180. When assembled, head portion196of sleeve154traverses an overlapping area between opening184and a seat199associated with opening132of seat tube22as well as opening200associated with optional gasket134. Optional gasket134includes a second opening202that, when assembled, is also concentrically oriented with respect axis180of pivot assembly120and cooperates with the other of fasteners150,152. Opening132of seat tube22circumferentially cooperates with stem portion194of sleeve154when the longitudinal axis of opening132is aligned axis180of pivot assembly120. As explained further below with respect toFIG. 6, the axis of opening132of seat tube22is formed along a plane, indicated by line204, that is offset in a forward direction relative to longitudinal axis175of bicycle10and with respect to a longitudinal axis206of seat tube22.

Threaded portions160of each fastener150,152operatively cooperate with a threaded surface210(FIG. 4) formed on an inner radial surface of sleeve154. Bushings156,158rotatably cooperate with stem portion162of each of fasteners150,152and cooperate with seats188defined by upper frame member100. As shown inFIGS. 4 and 5, pivot assembly120can include another optional gasket214that cooperates with the laterally outboard directed sides of pivot assembly120. Gasket214includes a first arm216and a second arm218that extend in a generally upward direction relative to a web wall220. The laterally inboard facing side of each arm216,218includes a lip221that is shaped to snuggly cooperate with a radially outboard directed surface of head portion164of a respective fastener150,152. Preferably, upper frame member100includes a recess222that is shaped to mimic the shape of gasket214such that when assembled, gasket214provides a generally smooth contour along the exterior surface of upper frame member100associated with pivot assembly120.

When assembled, pivot assembly120provides a secure connection between upper frame member100and seat tube22and does so in a manner that prevents lateral, longitudinal, and vertical movement of seat tube22relative to upper frame member100but allows rotation of seat tube22about axis180associated with opening132which is collinear with pivot assembly120relative to upper frame member100. Such a connection allows only flexion or flexing movement of seat tube22relative to the other structural members of bicycle frame assembly12during use of bicycle10.

As mentioned above, other interactions between seat tube22and frame assembly12are envisioned that allow similar deflection of the seat tube22. For instance, seat tube22could include a passage like passage130or otherwise be contoured so that the seat tube passed around the top tube/seat stays/lug and/or such that the top tube/seat stays/lug pass through the seat tube. Still another alternative includes connecting the seat stays to the upper frame member or top tube at a location forward of the seat tube such that the seat tube would be positioned in an area generally flanked by the seat stays. Referring toFIG. 6, although an axis, indicated by line180, of pivot assembly120is offset in an forward direction relative to the longitudinal axis206of seat tube22, is appreciated that axis180could be oriented to intersect axis206or offset in a rearward direction relative thereto so as to alter the deflection performance of seat tube22and/or to better suit the preferences of a given rider or class of users.

Referring toFIG. 6, during normal use of frame assembly12, seat tube22maintains a generally “at rest” configuration as represented by seat tube22shown inFIG. 6. Preferably, seat tube22has a fairly linear at rest orientation. Understandably, during normal use, some initial deflection of seat tube22may occur depending on the weight and preferred orientation of the rider during normal use over relatively smooth terrain. During an impact event, indicated by arrow230, a downward and rearward bending moment is imparted to seat tube22by the interaction of the rider with the rear portion of a saddle, which is commonly offset to the rear of the longitudinal centerline206of seat tube22. Such loading of the seat tube allows seat tube22to pivot in a passive manner about pivot assembly120and results in a rearward deflection of an upper portion232of seat tube22positioned above pivot assembly120and a forward deflection of a lower portion234of seat tube22that is positioned between pivot assembly120and bottom bracket110relative to the at-rest orientation.

The deflection of seat tube22relative to upper frame member100and lower frame member101is shown graphically inFIG. 6by line236. Such a configuration allows near the entirety of seat tube22to deflect from an at rest position to a “bent” orientation, represented by line236to improve the vertical compliance of frame assembly12. Supporting an upper end of seat tube22proximate the intersection of seat tube22with upper frame member100provides a fairly rigid feel of frame assembly12during all riding conditions but mitigates the communication of undampened travel surface discontinuities to the rider via rider interaction with the bicycle seat. Such performance improves rider comfort and decreases rider discomfort commonly associated with extended rides. Preferably, seat tube22deflects no more than 15 degrees from an at rest orientation and more preferably, seat tube22deflects no more than 7 degrees from a rest position in response to rider interaction with seat16. Such a configuration has been shown to provide a desired degree of responsiveness to rider interaction with the bicycle frame and does so in a manner that improves the vertical compliance of the bicycle frame assembly without unduly detracting from the same. However, it is appreciated that any desired range of deflection can be provided. Preferably, the greatest deflection value is associated with a deflection that a rider will tolerate and still feel comfortable on the bicycle during most riding conditions to a near unperceivable deflection during most riding conditions.

As shown in the experimental data below, frame assembly12provides greater longitudinal deflection of the seat tube with comparable lateral stiffness for bicycle frames having similar shapes and with nearly negligible contribution to the overall weight of the bicycle frame assembly. It is further envisioned that the forward and/or rearward orientation of the pivot axis relative to the longitudinal axis of the seat tube can be manipulated to satisfy a wide variety of rider performance preferences and/or to alter the deflection performance of the seat tube. It is further appreciated that the construction of the seat tube can be manipulated to further alter the vertical compliance of the frame assembly while providing a robust bicycle frame assembly.

As shown in the data provided above, configuring a bicycle frame with the passive pivot connection between the seat tube and the upper frame member provides improved vertical compliance of the seat tube of approximately 60% with an increase in frame assembly weight of approximately 48 grams or only approximate 5% of the overall weight of the frame assembly. Accordingly, bicycle frame assembly12provides a bicycle frame have acceptable frame responsiveness with improved vertical compliance for improving rider comfort.

Therefore, one embodiment of the invention includes a bicycle frame assembly having a forward frame triangle that includes a top tube and a bottom tube. The top tube includes a first end that is connected to a head tube and a second end. The bottom tube includes a first end that is connected to the head tube and a second end. A bottom bracket is connected to the second end of the bottom tube. A seat tube extends in an upward direction from the bottom bracket. A pair of seat stays are connected to the top tube and extend in a rearward direction beyond the forward frame triangle. A pivot connects the seat tube to the forward frame triangle proximate the top tube at a location nearer a bicycle seat than the bottom bracket.

Another embodiment of the invention that includes one or more features combinable with the above embodiment includes a bicycle frame assembly having an upper frame member that includes a top tube and a pair of seat stays. The upper frame member extends between a dropout associated with a rear wheel and a head tube. An opening is formed in the upper frame member. A lower frame member that includes a bottom tube, a bottom bracket, and a chain stay extends between the dropout and the head tube. A seat tube extends from the lower frame member toward the upper frame member and passes through the opening in the upper frame member. A pivot connects the seat tube to the upper frame member proximate the opening so that more of the seat tube is located between the pivot and the bottom bracket than extends beyond the upper frame member.

Another embodiment of the invention that is useable with one or more of the aspects of the above embodiments discloses a method of allowing deflection of a seat tube. A seat tube is connected to a bottom bracket. The seat tube is connected to an upper frame member with a pivot that is located at an overlapping intersection of the seat tube and the upper frame member so that the seat tube can deflect from alignment along a line between the bottom bracket and the pivot.