|Publication number||USRE39159 E1|
|Application number||US 10/402,410|
|Publication date||Jul 11, 2006|
|Filing date||Mar 27, 2003|
|Priority date||Jan 25, 1995|
|Publication number||10402410, 402410, US RE39159 E1, US RE39159E1, US-E1-RE39159, USRE39159 E1, USRE39159E1|
|Inventors||James B. Klassen, Jamie W. Calon|
|Original Assignee||Santa Cruz Bicycles, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Referenced by (33), Classifications (5), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation-in-part of U.S. Ser. No. 08/724,303, filed Sep. 19, 1996, abandoned Apr. 22, 1999; which is a continuation-in-part of U.S. Ser. No. 08/558,162, filed Nov. 15, 1995 (U.S. Pat. No. 5,628,524, issued May 13, 1997); which is a continuation-in-part of U.S. Ser. No. 08/377,931, filed Jan. 25, 1995 (U.S. Pat. No. 5,553,881, issued Sep. 10, 1996). This application claims benefit of provisional application Ser. No. 60/040,702 filed Mar. 13, 1997.
The present invention relates generally to bicycles, and more particularly to a rear suspension system which provides efficient energy transmission but still provides compliant suspension action when the bicycle is ridden over rough terrain.
Shock absorbing rear suspensions for bicycles are known. In general, however, these have not proven entirely satisfactory in practice.
In most rear suspension assemblies, the rear axle pivots about a single point when subjected to bump forces, as when traversing rough terrain. In these designs, the pedaling forces which are extended by the rider tend to either compress or extend the spring/damper assembly of the rear suspension. In this respect, the spring/damper assembly of the rear suspension is affected by the pedal force and some of the rider's energy is needlessly wasted.
This effect manifests itself by the common tendency of rear suspension systems to either lock up or “squat” when the rider pedals. Since most of these systems have a single lever arm which pivots about a single axis, the lock up or squat generally occurs as a result of chain tension action on the single lever arm. If the single pivot line is above the chain line, the suspension will typically lock up and/or “jack”, thereby providing compliance only when the shock or bump force exceeds the chain tension. Conversely, if the single pivot point of the suspension system is below the chain line, the system will typically squat, since the chain tension is acting to compress the spring/damper assembly of the rear suspension system, similar to a shock or bump force.
The present invention has solved the problems cited above. Broadly, this is a bicycle comprising: a chain drive in which the distance from the axis of a drive sprocket to the axis of a rear wheel hub is represented by a variable value CSL; and a compressible rear suspension having a linkage for moving the hub along a controlled wheel travel path as the suspension is compressed, the controlled wheel travel path having an arc radius which is greater towards a lower end of the path and smaller towards an upper end of the path.
The wheel travel path may comprise (a) a preferred pedaling position at a predetermined position Dp which is located along the rear travel path; (b) a lower curve segment below the position Dp in which there is an increasing rate of chainstay lengthening with increasing compression of the suspension system, such that the first derivative relationship
is a curve having a generally positive slope, so that the second derivative relationship
is generally positive; and (c) an upper curve segment above the position Dp in which there is a decreasing rate of chainstay lengthening with increasing compression of the suspension system, such that the first derivative relationship
is a curve having a generally negative slope, so that the second derivative relationship
is generally negative.
The linkage may comprise upper and lower link members which connect a rear frame section to a forward frame section. The link members are pivotally mounted to the frame sections, with the upper link member extending in a downward and forward direction when the suspension is in an uncompressed position, and the lower link member extending in a downward and rearward direction in this position. The link members are mounted so as to rotate in opposite directions as the suspension is compressed.
A shock absorber may be mounted between the lower link member and the forward frame section so as to be compressed with compression of the rear suspension. The lower end of the shock absorber may be mounted to a second arm of the lower link member.
The present invention provides a rear suspension system which effectively absorbs forces which are received due to irregular terrain, but which minimizes the compression/extension of the suspension by forces which are applied by the rider during vigorous and/or uneven pedaling. This is accomplished by means of a dual eccentric crank mechanism which moves the rear wheel along a predetermined path as the suspension is compressed, so that the chain tension works to counteract the downward forces on the frame during selected phases of the compression cycle.
Although, as was noted above, the frame assembly which has thus far been described is generally conventional in configuration, and therefore has the advantage of being suitable for use with more-or-less standardized components such as saddles, handlebar stems, and so forth, it will be understood that the suspension system of the present invention may also be employed with bicycle frames which have configurations other than the generally conventional one which is shown herein.
The rear suspension system 12 of the present invention comprises three interconnected subassemblies: (1) a lower pivot assembly 30, (2) an upper pivot assembly 32, and (3) a rear swinging arm assembly 34, the rear wheel being mounted at the apex of the latter, in axle notches (dropouts) 35a, 35b.
As will be described in greater detail below, the lower pivot assembly 30 comprises a framework 36 which is pivotally mounted to the forward frame section by front and rear eccentric crank members 38a, 38b. The upper pivot assembly 32, in turn, comprises a rocker frame 40 which is pivotally mounted to the seat tube of the frame section by a spindle 42. The rocker frame 40 extends both forwardly of and behind the seat tube 14, and at its forward end is pivotally mounted to the upper end of a spring/shock absorber 44, the lower end of the shock member being pivotally mounted to a bracket 46 in the seat tube. The rearward end of the rocker frame is attached at pivot pins 48a, 48b to the upper end of the upper control arm member 50 of the swinging arm assembly. The control arm member is bifurcated so as to form first and second rearwardly extending legs 52a, 52b which correspond somewhat to conventional seat stays in general orientation. At their lower ends, the two leg portions 52a, 52b are attached at pivot points 54a, 54b to the rearward ends of the two leg portions 56a, 56b of the lower arm member 58, the forward ends of which are fixedly mounted to the framework of lower pivot assembly 30.
The actual wheel travel path which is provided by the system of the present invention is relatively complex, and will be described in detail below. However, the general direction of the suspension motions will be summarized here for the purposes of this overview. As the bicycle is ridden over rough terrain, impact loading which is received at the rear wheel causes the rearward end of the swinging arm assembly 34 to move up and down and along a curved path, as is indicated by arrow 60. Simultaneously, the joint between the arm member 50 and the rearward end of the upper pivot assembly 32 moves up and down and along an arcuate path, as indicated by arrow 62, causing the rocker frame of the upper pivot assembly to pivot around spindle 42. This in turn compresses and unloads the shock absorber 44, between the end of the upper pivot assembly 32 and fixed frame bracket 46.
Simultaneously with these motions, the framework of the lower pivot assembly 30 pivots about the bottom bracket shell on the eccentric crank members 38a, 38b, as indicated by arrows 66, 68. As will be described in greater detail below, this movement prescribes the curve which the wheel axle follows as the suspension is compressed, and this motion fails generally into three phases; during the first phase, the combined motion of the eccentrics is such that the effective pivot point of the assembly is near the rear eccentric member; during the second phase both eccentrics move together so as to add a rearward component to the motion of the assembly, the pivot point moving to a point above the bottom bracket; during the final phase, the pivot point moves toward the front eccentric member.
The result is that these combined motions provide a “virtual pivot point” which shifts so as to define a complex curve which is followed by the rear wheel as the suspension is compressed. As will be described in greater detail below, this allows the system to employ what is known as a “chainstay lengthening effect” (i.e., an effective increase in the distance between the bottom bracket shell 23 and the axle of the rear wheel at 35) at selected points in the compression cycle. In those phases where the chainstay lengthening effect increases, tension on the drive chain causes the suspension assembly to provide an upward force on the frame in response to the application of downward force on the pedals. Below the position (referred to herein as the “preferred pedaling position”) to which the suspension is compressed by the mass of the rider resting on the seat tube, there is a lesser chainstay lengthening effect, with the result that there is a lesser or minimal effect of chain tension on the suspension below the preferred pedaling position so that it remains compliant to unpowered vertical inputs by the rider (i.e., rider weight) and to bump forces caused by the terrain. The net effect of this is that the system is able to “isolate” pedal inputs from terrain inputs, i.e., the suspension will not compress/extend due to pedal forces which are exerted by the rider, but will remain compliant to irregularities of the terrain.
Having provided an overview of the system of the present invention, each of the subassemblies will now be described in greater detail, and this will be followed by a description of the motion which these elements cooperate to provide.
The rearward ends of the two side plate members 70a, 70b are fixedly mounted to the forward end of the lower control arm member 58, which is provided with a mounting block 76 which fits between the side plate members. The two leg portions 56a, 56b of the lower arm member extend rearwardly from this, more or less parallel to the side plate members, so as to form an open area 78 which accommodates the rear wheel.
Circular openings 80a, 80b are provided proximate the forward and rearward ends of each side plate member 70 to receive the ends of the eccentric crank members 38a, 38b and their associated bearings 82a, 82b; in the embodiment which is illustrated, the ends of the eccentric crank members and the bearings are retained in the framework by pinch bolts 84a, 84b. The main spindles of the eccentric crank members are supported for pivoting motion in forward and rear frame lugs 86, 88 (see also
ii. Upper Pivot Assembly
In a middle portion of the framework, the side plate members are provided with openings 94 which accommodate the axle or spindle 42 and its associated bearing 96, these being retained in the plate members by pinch bolts 98. The spindle 42 extends through a cooperating bore in a frame lug 100 on the seat tube. However, unlike the eccentrics of the lower pivot assembly, spindle 42 is a straight axis member which provides a single axis of rotation.
The rearward end of framework 40 is pivotally mounted to the upper end of upper control arm member 50. In the embodiment which is illustrated, the upper ends of the two leg portions 52a, 52b are joined by a crossbar 102, from which first and second plates, 104 extend into the gap between the two side plate members 90a, 90b. The extension plates 104 are provided with cooperating bores (not shown) for the inner ends of the two pivot pins 48a, 48b, the outer ends of the pins and their associated bearings 106 being retained in openings 108 by pinch bolts 110.
As the forward end of the framework, the two side plate members 90a, 90b are provided with bores 112 which receive a pivot pin 114 which extends through a bore (not shown) formed in the end 116 of the shock absorber. The lower end 118 of the shock absorber is mounted to the frame tube by a second pivot pin 120 which extends through a bore 122 formed in the protruding end of frame bracket 46.
Spindle 42 and the pivot pins 48, 114, and 120 are arranged so that their axes all lie parallel to one another.
Shock absorber 44 is preferably of a conventional type, such as a Fox™ or Risse™ bicycle rear spring and damper unit. Other shock absorbing mechanisms having suitable spring and damping characteristics may be substituted for the exemplary type which has been described above.
iii. Swinging Arm Assembly
The forwardly extending tang portions 134a, 134b of the axle mount brackets (dropouts) are received in and fixedly mounted to the leg portions 56a, 56b of lower arm member 58. The upper corners 136a, 136b, in turn, are received in the forked lower ends 138a, 138b of the legs 52a, 52b of upper arm member 50, and are mounted thereto by pivot pints 140a, (not shown) and 140b. The pivot axis provided by pins 140a, 140b lies parallel to those of the other pivot points in the system.
In a suspension system which causes the chainstay length to increase when the wheel is moved vertically, a downward force will develop on the wheel when the chain is tensioned, i.e., by the powered inputs at the pedals, this being referred to as a “chainstay lengthening effect”. The greater the increase in chainstay length for a given vertical wheel displacement, i.e., the greater the rate of chainstay lengthening, the greater the downward force on the wheel when the chain is tensioned. Chainstay lengthening which develops indiscriminately throughout the range of suspension travel (as is the case with many prior suspensions), is undesirable because it causes the bicycle to “back-pedal” when the wheel is moved virtually by the terrain; also, such systems require an excessively long chain and rear deraileur so that were will be enough slack to make up for the change in distance. With no chain tensioning at all, on the other hand, it is not possible to provide any upward force on the frame to oppose the downward pedaling force of the rider. However, by providing the controlled path for movement of the rear wheel which is described herein, the present invention is uniquely able to apply varying degrees of “chain lengthening effect” are provided only where these are necessary to balance out the forces which are applied by the rider.
The basic forces which are applied to the suspension are as follows: (1) Mass of the rider, or “un-powered” input (vertically downward force on seat and/or bottom bracket center axis); (2) Pedal force applied by the rider, or “powered input” (vertically downward force and/or turning moment about bottom bracket spindle axis which applies a forward force to the rear wheel as a result of chain tension); (3) Combined force of spring and damper (upward on frame and downward on rear wheel center axis); and (4) Vertical terrain input (slightly backward and/or upward on rear wheel center axis). The present invention selectively applies the chainstay lengthening effect to balance the first three of these forces, so that they can be isolated from the fourth; this has been achieved by determining which segments of the wheel travel path correspond with the greatest compressive force on the suspension from pedal inputs, and configuring the wheel path so that the counteracting chainstay lengthening effect occurs only at those points where it is needed.
The first segment of the path is that which is traversed as the mass of the rider causes the suspension to compress or “sag”, bringing the wheel to the optimum position for pedaling, this being referred to herein as the “preferred pedaling position”. The wheel travel path of the present invention is configured to apply an increase in chainstay lengthening at this point (i.e., at about the preferred peadling position), so that the downward force on the frame is opposed by a downward force on the wheel as a result of chain tension; directly above the preferred pedaling position is where the greatest degree of chainstay lengthening is applied in most embodiments, to oppose vigorous downward pedal inputs which would otherwise cause the suspension to compress.
As the wheel moves over the next segment of the path, above the preferred pedaling position, the increasing resistance of the suspension spring unit (e.g., the shock absorber) assists the chainstay lengthening effect in opposing rider pedal inputs. For this reason, progressively less chainstay lengthening is required as the wheel moves toward the top of its path, so that the final segment of the path is designed so that minimal chainstay lengthening effect occurs towards is top, where the opposing spring force is the greatest.
This wheel path can be contrasted with those which are provided by prior art systems. Low pivot suspensions, for example, in which the pivot point at or near the bottom bracket, employ very little chainstay lengthening and therefore allow undesirable movement of the suspension at wheel positions above the preferred pedaling position resulting in a loss of pedaling efficiency. High pivot designs, in turn, employ chainstay lengthening to oppose the vertical rider inputs, but cause too much lengthening, especially when used in long travel (e.g., over three inches) suspensions. Furthermore, high pivot systems tend to “over-control” the rear wheel under hard pedaling, forcing it toward the bottom of the suspension stroke when the wheel is below the preferred pedaling position. It might seem from this that a pivot point halfway between the high and low positions would result in optimized characteristics, but this is not feasible in practice because of the many variations in riding position and pedaling techniques (e.g., sitting or standing, “spinning” or “pounding”, and so forth). The present invention achieves a more encompassing solution by employing a “shifting” pivot point which provides characteristics resembling those of to a low pivot system at the top and bottom of the wheel path, and resembling those of a high pivot system when the wheel is located directly above the preferred pedaling position where the greatest chainstay lengthening effect is needed.
ii. Dual Eccentric Linkage
The dual eccentric linkage which defines the wheel travel path of the present invention makes up part of the bottom pivot assembly 30. This assembly and the general orientation of the forward and rear eccentrics 38a, 38b can be seen in
Thus, as the suspension is compressed, the spindle portions rotate within the frame section, and the offset lobe portions 154 swing through arcuate paths, as indicated by arrows 156a, 156b. In the exemplary embodiment which is illustrated, the spacings between the primary and secondary axes is approximately 7 inches, with the range of possible spacings being from about 1″ or less to about 23″.
iii. Interaction of the eccentric crank members during the phases of wheel travel
In the schematic views of
The final phase of motion is shown in
With further reference to
d. Description of wheel travel curve
i. Basic configuration
It is also important to note that the primary desirable characteristics of the suspension are provided by the pronounced chainstay lengthening effect (focus “B”) at the preferred pedaling position, followed by the“tapering off” of the chainstay lengthening effect in the next phase above this (focus “C”). The lower third of the defined wheel travel path (i.e., focus “A”) may therefore be regarded as somewhat optional (and may consequently be deleted in some embodiments), in that the enhancements which it provides are incremental as compared to those which are provided by the next two segments of the path. Also, the radius of the lower portion of the S-shaped path may be selected to approximate infinity, with the result that this part of the path may be virtually straight.
The preferred pedaling position is preferably (although not necessarily in all embodiments) located proximate or slightly below the inflection point or zone between the upper two segments, so that there is an increase in the chainstay lengthening effect (i.e., an increase in the rate of chainstay lengthening) as the axle moves upwardly above the preferred pedaling position, and then a decrease in the chainstay lengthening effect (i.e., a decrease in the rate of increase) as the axle moves into the upper portion of the curve. In short, immediately above the preferred pedaling position, or “sag” position (at approximately 1 inch of wheel travel in the illustrated embodiment), the rate of chainstay lengthening increases significantly; then after a predetermined amount of rear wheel travel which has been optimized for the particular bicycle (e.g., 1-2 inches), the rate slows or decreases.
The slowing or reduction of the chainstay lengthening effect is most important for high-travel suspensions: as was noted above, the reason for this is that as the wheel moves toward the upper end of its travel the spring will be providing increasing resistance, and an excessive rate of chainstay lengthening in this area will cause undesirable pedal feedback and strain on the drive train. In the case of bicycles having relatively modest (e.g., approximately 3 inches or less) amounts of rear wheel travel, it may not be necessary to significantly reduce the chemstay lengthening effect at the upper end of the wheel travel path: Due to the limited amount of suspension travel, a relatively simple curve may suffice without developing excessive pedal kickback; for example; a wheel travel path which describes a simple concave arc (relative to the bottom bracket axis) may be suitable for a road bicycle where large amounts of suspension travel are not needed.
A degree of chainstay lengthening effect is also desirable below the preferred pedaling position. This is because when the rider stands up on the pedals, the weight transfers from the seat, which is almost directly above the rear wheel, to the bottom bracket, which is located well forward of the rear wheel. As a result, the load on the rear suspension decreases, so that the suspension decompresses slightly and tends to bring the wheel axis to a point which is below that of the preferred pedaling position. Accordingly, it is desirable to provide a wheel travel path in which the bottom portion of the curve extends downwardly and forwardly from the preferred pedaling position in a relative straight line (or a shallowly concave curve), so that when the wheel drops as the rider stands up, the axis will still be at a point along the curve where an opposing force is generated in response to the pedal inputs.
For example, assume that the preferred pedaling position at a 1 inch sag point with the rider seated, then as the rider stands up and his weight shifts towards the front of the bicycle, with the result that the axis of the rear wheel shifts downwardly along the wheel travel path approximately ⅔ inch; with a forwardly sloping “straight line” bottom part curve, the slope of the curve at the first point, i.e., when the rider is standing, is similar to that when the rider is sitting.
ii. Curve variations
The exemplary “S-shaped” curve described above is highly advantageous for many applications, notably extreme off-road riding conditions. It will be understood, however, that the present invention may be embodied throughout a range of curves, and which may be particularly suited to other specific applications, such as road bicycles or bicycles for light-duty trail riding, for example.
As is illustrated by
Accordingly, at the far right,
As was noted above,
iii. General analysis
Specifically, plot 240 in
As can be seen in
The plot of the derivative CSL′ produces the curve 252 which is shown in FIG. 15C. As can be seen, the peak rate of chainstay lengthening occurs at a point 254 approximately 5 units of travel along the curve which is approximately at the 1 inch sag point (vertical displacement). The plot of CSL & CSL′ vs. D thus clearly demonstrates the increasing rate of chainstay lengthening which occurs proximate the preferred pedaling position.
As can seen in
As can be seen in
iv. Mathematical description of curves
As shown above, the shape of the curve or path which is provided by the person invention can be described in terms of two relevant parameters, i.e., the chainstay length (CSL) and a distance (D) along the path which is traversed by the hub, beginning at the lowest position of the suspension. As previously noted, the chainstay length parameter CSL is simply the distance from the centerline of the pedal sprocket shaft to the center of the rear wheel hub. The distance D, in turn, can be defined by selecting a series of closely spaced points along the path and adding up the incremental arc lengths to define a total distance along the curve that the hub has moved from its initial position.
The first derivative of CSL with respect to D, (which may also be called the slope of the curve CSL vs. D) represents the rate of change of the CSL parameter with respect to the distance D along the curve. AS the wheel hub moves along its path, beginning from the lowest position and moving generally upward, this rate first exhibits and increase as D increases, reaches a maximum value, and then exhibits a decrease with a further increase in the distance D. Therefore, both an increase and a decrease of the rate of change of the CSL parameter must be present in order to provide the advantages of the present invention.
In mathematical terms, the rate of change, i.e., the first derivative of CSL with respect to the distance D, is defined by:
The increasing and decreasing of the rate, in turn, can be described in terms of the second derivative of CSL with respect to D, i.e.:
where the term CSL″ is positive as the hub moves upwardly along the path, goes through zero, and then becomes negative as the hub moves further upwards.
Thus, the wheel travel path which is provided by the present invention can be described as comprising the following, wherein D1, is normally located proximate to, but not necessarily immediately at, the junction of the upper and lower curve portions:
The lower swing arm member 314, and the upper swing arm member 316 are generally similar to the corresponding elements which have been described above, although the forging/castings have been simplified for economy of manufacture and enhanced strength.
As can be seen in
As is shown in
The lower, non-bifurcated ends 342, 344 of the crank links have bores 346, 348 which provide support for the middle portions of the lower pivot pins 350, 352. The outer ends of the two lower pivot pins are supported in recesses in forward end of the lower swing arm member by bearings 345a-d. The pivot pins are provided by hardened bolts, with bolt heads 356, 358 on one end and lock nuts 360, 362 on the other which engage the outer surfaces of the bearings 354a-d so as to provide a predetermined amount of preload. The inner surfaces of the bearings, in turn, engage thrust washers 364a-d which abut the outer surfaces of the two pivoting links 320, 322. To exclude dirt and water from the bearings, the recesses in the swing arm member are covered by removable dust caps 366a-d.
In this embodiment, the eccentrics are positioned closer together on the frame than in the configuration which was described above. As a result, the difference between the angles of the eccentrics must be significantly less; for example, in the particular embodiment which is illustrated, in which the spacing between the axes of the two eccentrics is approximately 2.5 inches, the initial angle between them may be only about 30°, e.g., 135° and 160° forward of TDC.
The advantages of the embodiment which is shown in
The embodiment which is illustrated in
The simplified assembly 300 is also relatively less sensitive to bearing and bushing tolerances, inasmuch as the primary force on the bearings in this embodiment is linear rather than radial. The thrust washer bushings can be interference fit between the eccentrics, mounting bracket, and chainstay assembly to avoid play. Also, while the embodiment which is illustrated uses bolts to provide the necessary preload on the eccentric shafts, it is possible to machine the desired preload for the thrust washers into the parts themselves, thus eliminating the need for bolts and allowing for the use of simple and inexpensive shafts and spring clips.
As yet another advantage, the suspension assembly 300 which is illustrated in
f. Additional Configurations
i. Friction Bushing System
It will be understood that substantially identical friction bushing assemblies are employed at the rearward crank link, although for the sake of clarity these are not shown in FIG. 24.
The advantage of the friction bushing configuration relative to the more “efficient” ball bearing system which has been described above is that the plain bushings will provide a slight amount of friction which serves to minimize wheel movement during normal riding, while allowing the suspension to remain sufficiently compliant to absorb any significant bump forces which are encountered. As a result, excessive compliance (or “jiggling”) which may occur with the more efficient ball bearing construction is minimized or eliminated.
Moreover, increased pedaling forces are accomplished by an increase in the horizontal forces on the bushings, as a result of chain tension and the opposing force which is generated due to the wheel travel path of the present invention. The net effect of this is to increase the resistance which is offered by the friction bushings under these conditions, which in turn renders the suspension less compliant and consequently more efficient at times of increased pedaling effort.
Still further, if relatively higher friction bushings are used on the rearward eccentric, the friction which is offered by the bushings will manifest itself to the greatest degree as the wheel approaches the top portion of its travel, in other words, as the suspension approaches the limit of its compression. This is due to the fact that a greater rotation of the rearward eccentric occurs as the wheel hub moves toward the upper end of the curve. Thus, by providing a higher coefficient of friction on the rearward bushings, an increased friction damping effect is provided at the top of the wheel travel path. This “stimulates” the variable dampening action of a shock absorber, so that models using the friction bushing system may employ much cheaper springs without viscous dampening, or a simple urethane bumper or a cross frame, without development of excessive rebound force of the spring at full compression.
Any bushings which provide the desired degree of friction may be employed in this construction. However, lead-teflon impregnated porous bronze bushings are particularly suited for this purpose, bushings of this type being available from Garlock, Inc. 1666 Division St. Palmyra, N.Y. 14522 and Permaglide bushings from INA Bearing Co. Ltd. 2200 Vauxhall Place, Richmond, B.C. Canada V6V 1Z9.
ii. Eccentric Crank Members
iii. Bottom Pivot Arms
iv. Eccentric Bearing Mechanism
As can be seen in
A forward eccentric crank member such as those which have been described above can be used in conjunction with the eccentric bearing assembly 540. Alternatively,
V. Cam Slot and Follower Mechanism
In particular, in the construction which is shown in
The cam follower 574, in turn, is formed by a transversely extending roller pin 282; this fits closely within the cam slot 578 in engagement with the cam surfaces thereof, so that the follower follows the path which is prescribed by the cam faces when the pin travels in a vertical direction through slot 578. Rearwardly of the cam follower but still towards its forward end, the lower swing arm member 576 is supported by a connecting arm 584 which is pivotally mounted to the swing arm member at its lower end (pivot pin 586), and to a frame bracket 587 on the seat tube at its upper end (pivot pin 588).
Accordingly, as the rearward end of the lower spring arm members is displaced vertically in the directions generally indicated by arrow 589, the roller pin 574 is driven vertically up and down through the slot 578 in the cam plate, so that the cam surface forces the rear axle to follow the desired wheel travel path.
vi. Counter-rotating link mechanism
Accordingly, as can be seen in
The pivoting rear frame section 612, in turn, is another triangular assembly, which includes chain and seat stays 622, 624, and somewhat vertically extending front stays 626; although only one of each of these stays is visible in the side view of
A pair of dropouts 628 are mounted at the apexes of the chain and seat stays 622, 624, for carrying the rear wheel axle as described above. Also somewhat similar to the embodiments which have been described above, the forward ends of the chainstays 622 (at the bottom front corner of the triangular rear frame section) are mounted to the first eccentric link member 604. However, in the embodiment which is shown in
The pivot connection 630 at which the rear frame section is mounted to the upper link 602 is positioned a spaced distance d, below and slightly forward of the pivot connection 632 at which the link is mounted to the forward frame section. As can be seen in
Similarly, there is a spaced distance d2 between the lower pivot connection 638 at which the lower front corner of the rear frame section is joined to the lower link member 604, and the joint 640 which joins this link to the front frame section. With respect to the forward frame section, the lower link member 604 is mounted adjacent to and behind the bottom bracket shell 642, on a rearwardly extending bracket 644.
As can also be seen in
In the exemplary embodiment which is illustrated, suitable dimensions for the members include the following:
Upper link dpivot center spacing d1
Lower link member pivot center
Pivot spacing h1 between link member forward frame
Spacing h2 between link member rear frame pivot
Initial chainstay length l1 (between bottom
bracket center and rear axle)
Moreover, the counter-rotating action of the spaced apart upper and lower link members 602, 604 produces a rotational motion in the rear frame section, as indicated schematically by arrow 670, which has the desirable result of producing a effective reduction of unsprung weight/mass in the system, i.e., the rear frame section goes through rotational motion, as opposed to reciprocating motion, as the wheel works up and down. Moreover, braking forces generated by the rear brakes, whether against the seat stays 612 as by caliper brakes acting in a direction indicated by arrow 672 in
Suitable, both upper and lower links 602 and 604 may be fabricated of high strength aluminum alloy. Also, the vertical forward stays 626 should be constructed to have comparatively high strength so as to be able to bear the fairly high tension forces which are generated during operation of the system under competition conditions.
As was noted above, the graph in
This subset of wheel travel paths (i.e., those curves which have a significantly larger radius at the bottom of the path than at the top) has the particular advantage of providing a high degree of pedal force cancellation at the bottom of the range of travel, without causing too much chainstay lengthening at the top of the travel, where it is not needed. This is particularly desirable in the case of those bicycles which use only a single front chain ring but still require a high-travel rear suspension, such as “downhill only” racing bikes. By providing a curve with the large radius at the bottom of the wheel path, the present invention provides a stable position for the wheel in order to counter movement of the suspension due to chain torque; by way of analogy, if the chain were to pull against a curve having a small radius, this would be like trying to balance a ball on top of a strongly convex surface, whereas the larger radius arc (which the present invention provides at the beginning of the wheel travel path) acts more like balancing a ball on a comparatively flat surface, i.e., it is more stable. In order for this large radius to balance the forces correctly, it must have a focus point located at some height above the line from the drive gear axis to the driven wheel axis. However, if this large arc were to continue all the way to the upper part of the wheel path, this would cause too much chainstay lengthening effect at the upper limits of suspension compression and result in severe bipacing or pedal feedback when the wheel encounters bump forces. The present invention avoids this problem by forming a wheel travel path in which the radius of the arc becomes smaller as the wheel moves to the top of its travel, which in turn keeps the wheel from moving to far away from the drive gear in this phase of the travel.
In short, for these type of bicycles, the present invention has the advantage of providing a wheel path curve which has greater arc radius for the first part of the wheel travel and a smaller radius further along the wheel travel path. In addition to single driver-gear bicycles (including commuter cruiser, and BMX bikes, in addition to the “downhill only” bicycles mentioned above), the advantages discussed in the preceding paragraph also benefit bicycles which use conventional, multiple drive-gears, although the benefits may not be quite as dramatic as in the case of a single drive gear.
It is clear from the foregoing that the present invention provides a unique wheel travel path having a lower curved portion in which there is an increasing rate of chainstay lengthening as the suspension compresses toward the preferred pedaling position, and a second curved portion above the preferred pedaling position in which there is a decreasing rate of chainstay lengthening, which yields the advantages which have been discussed above. The inventors have disclosed several embodiments of the present invention in which various mechanisms which are employed to generate the controlled wheel travel path; it will be understood that numerous modifications to and variations on these mechanisms will occur to those having ordinary skill in the art, and it should be understood that such will fall within the scope of the present invention. Moreover, in the illustrative embodiments which have been described herein, generation of the wheel path is principally a function of the lower pivot assembly; as a result, it will be understood that these and other lower pivot mechanisms which provide the prescribed path may be used in combination with other types of suitable upper suspension mechanisms. In addition to those which have been shown herein.
It is therefore to be recognized that these and many other modifications may be made to the illustrative embodiments of the present invention which are shown and discussed in this disclosure without departing from the spirit and scope of the invention. As just one example, in some embodiments the bearings of the pivot assemblies may be mounted to the eccentrics themselves, rather than to the supporting members.
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|U.S. Classification||280/284, 280/283|
|Oct 6, 2008||REMI||Maintenance fee reminder mailed|
|Nov 26, 2008||FPAY||Fee payment|
Year of fee payment: 8
|Nov 26, 2008||SULP||Surcharge for late payment|
Year of fee payment: 7
|May 9, 2012||FPAY||Fee payment|
Year of fee payment: 12
|Apr 9, 2013||AS||Assignment|
Free format text: SECURITY AGREEMENT;ASSIGNOR:SANTA CRUZ BICYLCES, INC.;REEL/FRAME:030183/0254
Owner name: COMERICA BANK, CALIFORNIA
Effective date: 20130328