CA2194029A1 - Tandem bicycle propulsion system utilizing a shared footpedal and crank assembly - Google Patents
Tandem bicycle propulsion system utilizing a shared footpedal and crank assemblyInfo
- Publication number
- CA2194029A1 CA2194029A1 CA002194029A CA2194029A CA2194029A1 CA 2194029 A1 CA2194029 A1 CA 2194029A1 CA 002194029 A CA002194029 A CA 002194029A CA 2194029 A CA2194029 A CA 2194029A CA 2194029 A1 CA2194029 A1 CA 2194029A1
- Authority
- CA
- Canada
- Prior art keywords
- rider
- footpedal
- seat
- pedal
- bicycle
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62K—CYCLES; CYCLE FRAMES; CYCLE STEERING DEVICES; RIDER-OPERATED TERMINAL CONTROLS SPECIALLY ADAPTED FOR CYCLES; CYCLE AXLE SUSPENSIONS; CYCLE SIDE-CARS, FORECARS, OR THE LIKE
- B62K3/00—Bicycles
- B62K3/12—Tandems
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62M—RIDER PROPULSION OF WHEELED VEHICLES OR SLEDGES; POWERED PROPULSION OF SLEDGES OR SINGLE-TRACK CYCLES; TRANSMISSIONS SPECIALLY ADAPTED FOR SUCH VEHICLES
- B62M1/00—Rider propulsion of wheeled vehicles
- B62M1/36—Rider propulsion of wheeled vehicles with rotary cranks, e.g. with pedal cranks
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62M—RIDER PROPULSION OF WHEELED VEHICLES OR SLEDGES; POWERED PROPULSION OF SLEDGES OR SINGLE-TRACK CYCLES; TRANSMISSIONS SPECIALLY ADAPTED FOR SUCH VEHICLES
- B62M3/00—Construction of cranks operated by hand or foot
- B62M3/08—Pedals
Abstract
A kit of detachable parts which modify a single rider bicycle such that it accommodates two riders. Each rider applies propulsive force to a common crank-arm and chainwheel assembly by means of two shared footpedal assemblies which transmit both riders' foot pressure onto the same pedal bearing spindles.
Each of said footpedal assemblies is comprised of upper and lower footpedal members upon which the front and rear riders respectively apply propulsive foot pressure. The upper footpedal member is non-rotateably affixed to the lower footpedal member, said lower pedal member being concentric to and rotateable about the crank assembly's pedal bearing spindle. Fixation of the upper pedal to the lower pedal is by means of vertical compression members disposed such that the rear tandem rider can insert the forepart of each foot in between the two footpedal members to exert foot pressure onto the lower, rotateable footpedal member. Said member has a rearward protrusion used by the rear rider to exert heel pressure thereby stabilizing the pedal assembly against forward torque induced by the front rider's eccentric point of pressure application. The front tandem rider places the rear portion of each foot onto the upper footpedal member and exerts heel pressure, thereby transmitting additional propulsive force onto the lower footpedal member. The rear tandem rider's seat is adjustably affixed onto a support rail member at a location behind and substantially lower than the front rider's seat. Said rear seat support rail member is affixed to the bicycle frame using appropriate bracket members. An adjustable support mechanism with two degrees of freedom permits the front rider's seat to be both raised and advanced with respect to its single rider location such that the legs of the two closely coupled riders do not interfere with each other during pedaling activity.
Each of said footpedal assemblies is comprised of upper and lower footpedal members upon which the front and rear riders respectively apply propulsive foot pressure. The upper footpedal member is non-rotateably affixed to the lower footpedal member, said lower pedal member being concentric to and rotateable about the crank assembly's pedal bearing spindle. Fixation of the upper pedal to the lower pedal is by means of vertical compression members disposed such that the rear tandem rider can insert the forepart of each foot in between the two footpedal members to exert foot pressure onto the lower, rotateable footpedal member. Said member has a rearward protrusion used by the rear rider to exert heel pressure thereby stabilizing the pedal assembly against forward torque induced by the front rider's eccentric point of pressure application. The front tandem rider places the rear portion of each foot onto the upper footpedal member and exerts heel pressure, thereby transmitting additional propulsive force onto the lower footpedal member. The rear tandem rider's seat is adjustably affixed onto a support rail member at a location behind and substantially lower than the front rider's seat. Said rear seat support rail member is affixed to the bicycle frame using appropriate bracket members. An adjustable support mechanism with two degrees of freedom permits the front rider's seat to be both raised and advanced with respect to its single rider location such that the legs of the two closely coupled riders do not interfere with each other during pedaling activity.
Description
,~ 21 94~29 BACKGROUND AND PRIOR~ ART:
This invention relates to bicycles and more particularly to a means for modifying a ~vllv~-"iu-lal bicycle configuration so as to d,CUlllll~Od.li~, two actively pedaling riders.
Heretofore, various efforts have been made to devise means for accommodating tworiders upon the same bicycle such that they can both contribute energy towards propulsion of the vehicle. The prior art reveals three relevant categories of vehicle.
I) The first are those tandem bicycles essentially composed of two conventional, single rider bicycles detachably affixed to each other in a side by side configuration. While no longer a true bicycle, this four wheeled vehicle configuration does have the advantage of permitting two existing, single rider bicycles to be Lldl~fulllled into a tandem rider apparatus. However, the cost of ,uch a vehicle is at least double that of a single rider bicycle and the safety of such a vehicle on public roads is ~u~ Jlull is~d by both its width and its handling ~,h-.a~
This invention relates to bicycles and more particularly to a means for modifying a ~vllv~-"iu-lal bicycle configuration so as to d,CUlllll~Od.li~, two actively pedaling riders.
Heretofore, various efforts have been made to devise means for accommodating tworiders upon the same bicycle such that they can both contribute energy towards propulsion of the vehicle. The prior art reveals three relevant categories of vehicle.
I) The first are those tandem bicycles essentially composed of two conventional, single rider bicycles detachably affixed to each other in a side by side configuration. While no longer a true bicycle, this four wheeled vehicle configuration does have the advantage of permitting two existing, single rider bicycles to be Lldl~fulllled into a tandem rider apparatus. However, the cost of ,uch a vehicle is at least double that of a single rider bicycle and the safety of such a vehicle on public roads is ~u~ Jlull is~d by both its width and its handling ~,h-.a~
2) The prior art also reveals a second and more prevalent category of tandem bicycle which d~ ~ulllluuddLt:s its riders, one in front of the other, upon an elongated frame while each rider actuates separate pedal and crank assemblies, said assemblies being rotatively coupled through an auxiliary drive chain. This tandem configuration affords a considerable gain in mechanical e~fficiency with respect to two riders pedaling separate bicycles. Said efficiencies result :from decreased wind resistance on the rear rider as well as the weight and friction economies inherent to sharing wheels, steering ~ U1II~UIIL~
brakes, some frame l;Ulll~/On~ and some transmission ~UIIII)UII.,.IL~. However, the elongated tandem configuration still n~cP s the duplication of certain heavy andexpensive UUIII~JUII~,.lt~. two separate pairs of pedals, crank arms and main bearing assemblies together with the auxiliary chain required to couple the front and rear drive UUlll,UUll~,llt:~. Furthermore, the elongated frame structure nPrPi~;tA~PC additional frame members to extend and support the two main triangles which make up a ~;ullv~llLiulldl bicycle frame. These additional fi ame members also add si~nificantly to the cost and weight of the vehicle. Furthermole, if no second rider is available to contribute pedaling energy, the elongated tandem con~ïguration is too heavy and unwieldy for efficient propulsion by a single rider, thereby limiting the vehicle's versatility as a means of Lldlls~UI LdLiUII.
brakes, some frame l;Ulll~/On~ and some transmission ~UIIII)UII.,.IL~. However, the elongated tandem configuration still n~cP s the duplication of certain heavy andexpensive UUIII~JUII~,.lt~. two separate pairs of pedals, crank arms and main bearing assemblies together with the auxiliary chain required to couple the front and rear drive UUlll,UUll~,llt:~. Furthermore, the elongated frame structure nPrPi~;tA~PC additional frame members to extend and support the two main triangles which make up a ~;ullv~llLiulldl bicycle frame. These additional fi ame members also add si~nificantly to the cost and weight of the vehicle. Furthermole, if no second rider is available to contribute pedaling energy, the elongated tandem con~ïguration is too heavy and unwieldy for efficient propulsion by a single rider, thereby limiting the vehicle's versatility as a means of Lldlls~UI LdLiUII.
3) A third category of prior art exists which is the most relevant to the present invention.
This prior art modifies the conveniional single rider configuration by adding a second seat assembly as well as footpedals that are modified to A~cornnno/' the feet of the rear rider upon the same footpedal assemblies as those used by the first rider. In theory, this approach permits the second rider to sit behind the first rider and apply pedaling energy directly to the shared pedals. Sharing suitably modified pedals affixed to the crank of a single rider bicycle has a number of advantages with respect to conventional tandem bicycles:
I) An existing bicycle can be easily be converted to serve in either a single rider or tandem mode.
2 1 94~29 2) The cost of the special pedals and seating means are far less than the cost of a dedicated tandem bicycle.
3) Since almost all mechanical parts are shared by both riders, the gross vehicle weight is less than that of a dedicated tandem bicycle.
Various attempts to implement sLlch a scheme have been proposed by Liljenberg (2,706,418), Sykes (3,457,803), Kelly (2,337,246), Raba (2,361,708) and Ridgeway(2,715,342). However, none of the prior art has resulted in a viable solution due to one or both of the following drawbacks:
Drawback #1: The means for accommodating the rear rider' s feet on the pedals extended the normal dimensions of the rotateable pedal assembly such that the pedal can occasionally hit the road during u se, thereby causing loss of power to the vehicle and possible injury to the riders. The "side by side" foot placement configuration proposed within this prior art caused pedal grounding during tums. . The "over/under" foot placement configuration proposed within this prior art did not provide adequate road clearance for the rear rider's feet (the rear rider's feet being located under the pedal assembly's bearing spindle).
Drawback #2: The seating a~vll~u~vdaiillg for the rear rider was such that the two riders experience ergonomic fatigue while pedaling due to illlrl rr.,e. c between their legs.
It is therefore the objective of the present invention to provide a tandem bicycle propulsion system which eliminates the ~rv.rlll~lltivllrd drawbacks inherent to the prior art. The present invention achieves this objective by providing a kit of three sub-assemblies that are attachable to a conventional, single rider bicycle and which together modify said bicycle such that:
I) Both riders can direc~dy actuate the same footpedal assemblies while continuously mrin~Aining adequate clearance between the road and pedal assemblies.
2) A second rider can sit comfortably upon the modified bicycle at an optimal location behind and below the first rider.
3) The front rider can adjust the location of the front seat both forwards and upwards with respect to its normal location, thereby providing adequate leg clearance between the two riders during all phases of crank rotation.
DESCRIPTION OF THE KIT'S THREE SUB-ASSEMBLIES:
Sub-assembly #1:
Both conventional single rider bicycles and conventional tandem bicycles, employ a footpedal design comprised essentially of a rotateable, footpedal member substantially symmetric about the crank arm's pedal bearing spindle. The present invention rrcr,mmr ' the feet of both the front and rear riders upon the same footpedal assembly by providing the front rider with a non-rotateable upper footpedal member . ccrntrirAlly affixed to and supported somewhat above the concentrically rotateable footpedal member.
The lower (concentric) footpedal member is used by the rear rider during tandem operation of the vehicle. By placing both rider's feet above the pedal assembly's bearing spindle, the present invention insures that adequate ground clearance is maintained at essentially the same distance as when the vehicle is operated in the single rider mode (when the front rider occupies the rotateable footpedal members). Each of the dual-tiered footpedal assemblies receives botlh the front and rear rider's feet, one above the other, such that they are as close to each other as rnArrmir~lly possible. It does so by supporting the front rider's heel in front of, and immediately above, the upper surface of the rear rider's foot such that the front rider's heel fits as closely as possible into the crotch of the rear riders ankle without actually touching it.
To enable correct relative positio:ning of the two riders' feet, the upper footpedal member is non-rotateably affixed to the rotateable, lower footpedal member by means of substantially vertical compression members affixed at their upper and lower ends to the sides of the upper and lower fooq~edal members. In a preferred clllbudilllclll, the spacing between the upper and lower footpedal members as well as the dihedral angle between the plane of the two footpedal members is adjustable by means of a multiplicity of fixation points near each end of the compression members w hich can be used to adjust the effective length of each l,Ulll~)lCi~ iUII member. The compression members are disposed along the sides of the upper and lower footpedal members such that the rear tandem rider can insert the forepart of each foot onto the lower, concentric footpedal member and thereby apply propu]lsive foot pressure to the bicycle's crank and chainwheel assembly.
In a preferred clllbudilllcllL, the upper fooqpedal surface is flared upwards along its rearmost edge to form a more ~~ mic ~lly correct receptacle for receiving the rear rider's foot. This same flared lip also serves as a tactile aid to help the front rider feel when the heel of each foot is positioned on the upper footpedal in its optimal location (i.e.: as far back as possible without actually contacting the crotch formed by the rear rider's foot and shin bone).
When using the present invention in single nder mode, the lone rider pedals in the conventional manner by applying propulsive force to the lower, rotateable footpedal members. However, during tandem mode operation, the lower footpedal members become occupied by the rear rider, therefore the front rider must pedal using the upper footpedal members. Tandem pedaling action is a, culll~l;shcd by first placing the rear portion of each of the front rider's feet onto the upper footpedal member of each of the bi-level footpedals. The front rider then applies propulsive force by exerting heel pressure onto the assembly. The front rider's heel pressure is transmitted down the ~,UllllJlC~iUII
members and into the lower footp,edal members, thereby augmenting the rear riders pedaling force already being applied to the bicycle's crank and transmission assembly.
Foot pressure exerted by the rear rider onto the lower footpedal members is transferred directly to the pedal assembly's bearing spindle with virtually no eccentric offset or turning moment (i.e.: the ball of the foot applies force symmetrically, both fore and aft of the bearing spindle). However, pressure applied by the front rider onto the upper footpedal member is applied at a point that is substantially eccentric to the assembly's axis of rotation. If the force vector of the front rider's applied pressure does not pass exactly through the assembly's axis of rotation, the pedal member's eccentricity creates an unstable turning moment about the assembly's bearing spindle. The instability of this force geometry is proportional to the ec~_cllLli_i~y of the upper footpedal member (i.e.
proportional to the distance between the planes of the two footpedal members). Since the present invention forces the front r ider to apply only heel pressure to the footpedal assembly, slight variations in natu:ral foot movement during pedaling tend to produce a force vector which often passes somewhat forward of the assembly's axis of rotation, 2~ 9~29 thereby inducing a ~.sfAhilizing ~Forward torque. If left uncontrolled, this rotational instability could easily cause the entire footpedal assembly lo rapidly spin forwa}d when a strong pedaling force is exerted by the front rider. Such highly unstable forward rotation would quickly dislodge both riders' feet from the pedal assembly, causing loss of power to the vehicle and possible injury to the riders.
To address this problem, the present invention provides two mechanical means to achieve a dynamic balance of rotational forces about the pedal assembly's axis. The first means for uuullLcld~,Lillg the unstable rotational force is simply to position the two riders' feet on the pedal assembly as close together as physically possible. This close proximity between the two riders' feet minimizes the lever-arm effect caused by upper pedal member's e.~,..LIi~iLy. 1~ .h~g the upper pedal member's lever-arm effect help5 to minimizes the unstable rotational force however it cannot completely eliminate the danger caused by rotational instability. Unless great care is exercised by the front rider, the natural variability of foot attitude inherent to natural pedaling motion still causes brief forward torque surges in the whole footpedal assembly.
The present invention therefore provides a second means of ~ uuLcld~L;Ilg the unstable forward torque produced by the front rider's eccentric application of force onto the pedal assembly. This innovation is based on harnessing an equal and opposite "~ oly torque generated by the rear rider's pedaling force. The rear rider naturally can apply the required uulll~cll~dtu~y torque to the pedal assembly by shifting the location of foot pressure application towards the r ear of the lower footpedal member, thereby inducing the Culll~cll~dLuly torque required to prevent forward rotation of the pedal assembly. This rearward ,1;~l,l,1. c",. .,1 of the force vector on the lower footpedal member could conceivably be accomplished by moving the rear rider's feet backwards and forwards as required to counteract the variable forward torque produced by i,l~."l.~i~l. .I('ir~ in the front rider's pedaling motion. However, given the rapidity with which the ~ l y torque must be applied, the rear rider would quickly tire of continually shifting foot placement fore and aft on the lower footpedal.
The most natural and relaxing muscular action that applies brief periods of ~ulu~cul~dLuly torque occurs when the rear rider simply applies downward heel pressure. This heel pressure creates instant counter-rotative force to counteract the front rider's eccentric force vector. However, heel pressure can only have effect if the rear rider's entire foot and pedal member are disposed so that the foot is fully supported from heel to toe. The present invention therefore provides a modified lower footpedal member which is constructed a~yllllllcLIi~a]]y so as to provide the necessary foot support. This support is provided by a rear projection of the lower footpedal such that the lower footpedal member is asymmetric about the bearing spindle. The rear footpedal extension provides heel support for the rear rider, thereby permitting the rider' s heel pressure to modulate the required counter-rotative torque into the pedal assembly.
To avoid fabricating a large and heavy pedal assembly, the rear extension of each lower footpedal member may be truncated shorter than required to fully support the rear rider's heel. If this is the case, any overhang of the rider's heel past the end of the rearward pedal extension creates a bending force which will tend to lift the r ider's toe off the pedal member (thereby defeating the desired uulll~ dLuly torque modulation). Therefore, the 2~ 94029 .
present invention optionally hluul~ul~Lcs a conventional bicycle toe-clip on the front edge of the lower pedal member which insures that all of the heel pressure induced corrective torque is actually transferred into the rotateable pedal assembly.
S~b-assembly ~2:
The second of the three functional sub-assemblies which constitute this invention provides a means for the second rider to sit comfortably on the modified bicycle at a location behind and below the front rider. This function is provided by a seconduul~vc;uLiu~al, bicycle seat together with the appropriate support members that affix it to the bicycle in the correct ergonormic location. The rear seat is adjustably supported and positioned along a substantially horizontal rail member, affixed at its front end to the upper seatstay members of the cullvellLiullal bicycle frame. Rear support for said horizontal rail member is provided by two UUIII~ iiiUII members affixed at their upper ends to said rail and at their lower ends to each side of the bicycle frame near the location of the rear axle. The rear rider's bicycle seat is adjustably positioned on said support rail, to a location behind the front rider's seat.
For optimal ergonomic interaction with the front rider, the rear seat support rail must be kept as low as possible on the bicycle's structure. The compression members supporting said rail therefore have multiple fixation points which permit the rail to be vertically positioned on the bicycle such that it just clears the rear tire. A clamping device is also provided to adjustably affix the rear rider's seat at a point along the horizontal support rail member at the location which provides comfortable leg extension to the rear rider' s (lower) footpedals. Additional vertical leg clearance between the riders is created by rnmfigllring the internal support structure of the rear seat as well as the clamping device used to adjustably affix it to the support rail member in a manner that positions the rear seat as close to its support rail as possible.
Many existing bicycles are fitted with cantilever style brakes affixed to the seat-stay frame members which protrude outwards from the frame such that they could contact the rear rider's inner thighs during pedaling activity. To eliminate this ergonomic problem, the present invention provides me~ans for re-locating the existing brake assembly behind the rear rider's legs such that no hl~ with the brake assembly is experienced during pedaling. This clearance is established by providing an additional pair of cantilever brake pivots affixed to the two vertical compression members which support the rear seat assembly. These pivot pins are located on said members such that the existing brake cantilever assemblies can be transferred from the seat-stays to their new locations and maintain correct frictional ~ g~ with the rear wheel-rim. The existing brake actuation cable is replaced with a longer one which can reach from the handlebar brake lever to the new brake location on the rear seat supports. To accommodate the brake cable, a standard cable ferule is affixed to the rear of the seat support rail such that the cable's outer sheath is correctly positioned and restrained with respect to the re-positioned rear brake cantilever assemblies.
As an altemate means of providing adequate side clearance between the rear rider's inner legs and the existing rear brake assembly is to eliminate the rim-friction rear brake altogether and replace it with a disk brake or internal expansion hub brake. In fact, since the bicycle's gross vehicle weighl: will be approximately doubled by the addition of a 2~ 94~2q .
second rider, it would be a prudent safety measure to improve the vehicle's braking power in this manner.
The support rail assembly may optionally incorporate a backrest structure which provides two functions:
The first function of the backrest is to provide a more restful seating position for the rear rider during slow, relaxed cycling activity.
The second function of the backr,est is to prevent the rear rider from sliding backwards during hard pedaling.
The support rail assembly may optionally incorporate a pair of handholds located behind the rear seat. These handholds can be used by rear rider to maintain a stronger hold on the bicycle during hard maneuvers. They can also be used to lift the rear rider's body off the seat, thereby momentarily relieving pressure on the buttocks.
Sub-assembly #3:
The third of the three functional sub-assemblies which constitute the present invention provides a means for adjustably re-positioning the front rider's seat forward and upward with respect to its normal position. This re-positioning is required to insure adequate vertical clearance between the front and rear riders' legs at all angles of crank rotation.
During tandem pedaling, the rear rider's legs must move in close proximity behind and beneath the front rider's legs without any mutual interference. Given the geometry and seat location of the typical single rider bicycle, when both rider's feet are at the top of the pedaling stroke, the vertical separation between the front and rear seats would not be great enough to establish sufficient clearance between the top of the rear rider's thigh and the bottom of the front rider's thi,gh. The present invention already provides means to seat the rear rider as low as possible with respect to the front rider. Despite these attempts to optimally position the rear seat to provide maximum clearance between the riders, the dimensions and geometry of the typical bicycle and the leg size of typical riders, will still preclude adequate clearance between the riders.
To achieve the necessarv vertical clearance, the front rider's seat location must also be moved upwards from its normal, single rider location. Since, when converting from the single rider mode of operation to the tandem rider mode of operation, the front rider moves from the lower to the upper footpedal members, in order to retain the correct leg extension distance between the front rider's seat and the upper footpedal member, the front seat must also be raised by a distance approximately equal to the distance between the upper and lower foot pedal m~ mbers. The required amount of vertical seat adjustment could be accomplishe~ simply extending the existing seatpost A~jnctm,nt ullr~ ~ Aly the bicycle's existing seatpost is often not long enough to permit the required amount of additional vertical movement. More importantly, simply extending the existing seatpost actnally moves the front seat backwards into the abdomen of the rear rider. Therefore, the present invention must provide a specialized mechanism forincreasing both vertical and horizontal separation between the front and rear riders.
To provide this function, the present invention uses an adjustable cantilever mPAhArlism with two degrees of freedom which enables the operator to adjustably raise and move 2 ~ 94029 forward front seat. The front seat adjustment mPch~nicm is a cantilever that's ai'fixed between the bicycle's existing seatpost and existing (front) seat by means of the existing seat clamp. In a preferred embocliment, standard bicycle seat clamps are used at each end of the cantilever to connect it to the seat and seatpost.
A standard bicycle seat clamp pn~vides both angular adjustment and longitudinal adjustment for the seat by means of two pivoting clamps that affix to the two support rail members which are integral to the under-structure of standard bicycle seats. In a preferred embodiment of the present invention, the adjustable cantilever mechanism consists of two straight seat extension rods, each having the same cross sectional diameter and spacing as the two horizontal seat support members which are integral to the under-structure of standard bicycle seatis. The rear end of each seat extension rod can thus be securely engaged by the bicyclehi existing seat clamp such that each is cantilevered forward and upward from the top of the seatpost. The two seat extension rods are thus held parallel to each other at a distance equal to the distance between the seat support members fabricated into the lowc,r structure of typical bicycle seats. The length of cantilever in the two seat extension rods can be adjusted to the desired length by sliding them in the seat clamp prior to tightening the clamp's fixation screw. A second seat clamp IIIP. h.111;~111 is affixed to the other (upper) end of the two cantilevered members thereby enabling the seat to be ac justably affixed to the upper end of the cantilevered members. When the clamp assemblies at both ends of the seat extension rods are loosened, the seat extension rods are adjustable both angularly and longitudinally thereby permitting the user to re-position the front seat both above and forward of its single rider location.
This same seat adjustment mecha,nism also serves to provide a cantilevered suspension for the front seat by deforming under load to absorb some road shock before it reaches the rider.
This same seat adjustment mP~hi~ni~im also provides a hand hold which can be used by the rear rider to stabilize upper body movement on the bicycle.
A.' ' ' ' Design C ' I
The present invention is intended primarily for converting existing single rider bicycles to tandem operation however the inventive elements can also be i-~,bl~ d~ed into the design and fabrication of new single/tandem bicycles. In the case of such newly fabricated bicycles, the frame geometry would be optimized for a more balanced weight distribution by lPngthPning the bicycle's, horizontal chainstay frame members with respect to their conventional, single rider proportions. Fork geometry would also be modified to provide greater strength and high speed stability. Components such as wheels, brakes and frame tubing would also be upgraded to improve durability under the greater loads imposed by dual rider operation.
T .~ngihPning the chainstays would place the rear rider's weight further forward with respect to the rear axle and thus help to control any tendency for the front wheel to leave the ground during hard ~rcplpr~i nn or when climbing steep grades. However, in the case of converting an existing single rider bicycle to provide tandem capability, lengthening of the chainstay frame members would be prohibitively expensive. In such cases, the 2~ 9432q tendency towa}ds front end lightness is effectively controlled by simply moving the front rider's seat somewhat forward of its normal location, thereby re-distributing the front rider's weight onto the front wheel.
Optionally, "bar-end" handlebar risers can be purchased and added to the kit. These auxiliary handholds can then be adjusted to displace the front riders hand grips along the same vector as the front rider's seat and pedal positions have been displaced. The handlebar adjustment would then3by establish the front rider's posture to a~lulu~illlàL~ly the same position as before the footpedal position was moved to the upper footpedals and the front seat was displaced to ~comm. ~P the rear rider.
The rear rider may hand aid the Frocess of pedaling the tandem bicycle by using hand pressure on his or her knees to more fully utilize the additional muscular force of the upper body to augment that of the legs.
In addition to the vehicular application described above, the present invention can also serve as a bicycle stand. To accomplish this mode of operation, the operator simply rotates the crank such that either pedal is h~ .e.lk.'~,ly aft of its lowest point.
Gravitational force naturally rotates the pedal assembly so as to present the upper pedal member at lowest to the ground. This contact point with the ground serves as a bicycle stand by virtue of the fact that the gravitational force of the bicycle onto the pedal imparts a forward motion to the vehicle (~:hrough the llall~llu~iun). This forward force is countered-acted by the frictional contact of the pedal assembly has with the ground. The resulting dynamic balance of forc:es enables the bicycle to be directly supported by the pedal assembly.
With respect to the prior art:
By eliminating the additional crank and pedal assembly normally required by the rear tandem rider, the present invention provides a significantly lighter vehicle. Weight savings are also achieved by eliminating the additional drive chain normally required to link dual crank assemblies as well as the additional frame members needed to form the elongated frame inherent to previous tandem bicycle designs.
Furthermore, mechanical friction in the vehicle's drive train is significantly reduced by eliminating the second pair of footpedal bearings, the second crank bearing and the second drive chain and sprocket assembly required by previous tandem bicycle designs.
Furthermore, due to the rear rider's seating position being situated more fully within the slipstream created by the front rider, the vehicle's wind resistance is reduced compared to conventional tandem bicycle designs.
Ful Lhcillllul~, by eliminating the n:eed for a second crank and pedal assembly, a second drive chain and chainwheel assembly as well as the additional frame members needed to form an elongated frame, the cost of fabrication of the present invention is significantly reduced compared to previous tandem bicycle designs 2l 9402~
Furthermore, since the present invention is of similar size and weight as a single rider bicycle, the sarne vehicle can still be efficiently propelled by a single front rider when no second rider is available to help pedal.
F~l~thcllllulc, the present invention permits an existing single rider bicycle to be quickly converted into a tandem bicycle and back to a single rider bicycle.
Furthermore, when not in service as a vehicle, the present invention acts as a bicycle stand.
2~ 9402q -DRAWINGS AND DETAILED DESCRIPTION:
In drawings illustrating an embodiment of the invention:
FIG. 1 is an elevational view of a conventional single rider bicycle having tandem rider modifications mounted thereon which are constructed in accordance with and embodying the present invention: said bicycle being illustrated as occupied and actuated by two riders.
FIG. 2 is an elevational view sirrlilar to figure I except that the bicycle is illustrated being unoccupied by riders and the pedal assemblies are rotated to their support stand locations whereby the upper foot support surface contacts the ground when the vehicle is leaned over.
FIG. 3 is an enlarged view of F]:G. 1 illustrating details of the pedal assembly with the riders' feet correctly positioned.
FIG. 4 is an enlarged view of F]:G. 1 illustrating details of the rear seat support assembly and modified rear brake assembly.
FIG. 5 is an enlarged view of F]~G. 1 illustrating details of the front seat support assembly.
The present invention is compnsed of three sub-assemblies:
I) - The dual level pedals.
2) - The rear seat and its attendant support structure.
3) - The front seat raising and a~b~a~ ..L mechanism.
When affixed to a conventional single rider bicycle structure, these three sub-assemblies operate in concert to effect its conversion to tandem operation.
Referring to the working ~Illbodi~ illustrated in FIG. 1 which illustrates the relationship between the present invention's three main sub-assemblies: the front rider places the rear part of each foot onto the upper pedal surface member ## of each of the dual level pedal assemblies. The front rider's foot is thus displaced vertically upward with respect to its normal, single rider location on the rotateable lower surface member, by a distance equal to the distance between the upper and lower pedal surface members.
To ~,UIII~)~ ' for this change in reach to the pedals, the front seat is also displaced upward the same distance by adjostably re-positioning the seat adjustment members ##.
The seat adjustment members also permit the seat to be adjusted forward of its lliulldl location so as to prc,vide clearance for the rear rider and transfer weight onto the front wheel. The rear rider sil:s on the rear seat ## and places the front part of each foot on the rotateable, lower pedal surfaces ## and adjustably positions the rear seat ##
along the support rail ##
Referring to the workable embodiment illustrated in FIG. 3 each of the two upperfootpedal surface members ## is adjustably affixed to and supported substantially above its Cullc ~olldillg rotateable, lower footpedal surface member assembly ## by means of a series of substantially vertical compression members ##.
The upper footpedal surface member ## has a series of drilled tab members ## bent downwards along its sides so as to provide fixation points for the compression members ##. Each lower footpedal surface is comprised of a hub ## which rotates around the pedal's bearing spindle ## which in turn is affixed to the crank arm ## of the bicycle's 21 9402~
existing L .~ llliiX~iUII m~ h~nicn I Two U shaped members comprised of a central section ## and two drilled end tab sections ## bent at 90 degrees to the central member are affixed to the front and rear of ea.ch pedal hub ##. The two central sections ## affixed to the pedal hub ## serve as foot support surfaces for the rear rider. The drilled tab members ## provide lower fixation points for the vertical compression members ##supporting the upper footpedal member ##.
The upper end of each compression member ## is rotateably affixed to its respective upper footpedal tab ## using matching holes and a tightening fastener ## which serves to prevent rotation once a CUIIII'UI Idl11C angular adjustment is set. The lower end of each UUIIIUlU~:~iUn member ## is affixed to the lower footpedal surface member using a similar rotateable fixation means as is ernployed at the upper end, however it has multiple fixation holes ## to permit the length of each compression member to be adjusted to suit both rider's pedaling comfort. Depending on the anatomical configuration of each rider, the upper footpedal member ## is fixed at a greater or lesser angle and separation with respect to the lower footpedal me mber ##.
Referring to the workable embodiment illustrated in FIG. 4, the main support rail member ## for the rear rider' s seat ## is adjustably affixed Lo the frame of the host bicycle at both of its ends so as to maintain the support rail in a substantially horizontal position, aligned with the axis of the bicycle and immediately above the bicycle's rear tire. The m.~h?ni.cm for affixing the front of the seat support rail to the host bicycle is comprised of a angled bracket #~ which is bolted through the front of the support rail member on one end and at the other end through the hole in the bicycle's seat stay brace ## normally provided to mount the rear brake assembly. The mechanism for affixing the rear of the seat support rail to the host bicycle is comprised of two rail support struts ##.
The top of each of the two rail support struts is bolted to the left and right side respectively of the rear seat support rail using a bolt ##. Spacer elements ## may be inserted between the seat support rail and the rail support stluts to provide adequate clearance between the rail support struts and the rear tire. The seat support rail may be of any cross sectional shape however a preferred clllbodilllcllL employs a circular cross-section as this minimizes fabrical:ion costs and also permits the use of a seat fixation device described below.
The rear bicycle seat ## is adjustably affixed at a point along the seat support rail ## such that it affords the rear rider a comfortable reach to the lower footpedals. The seat fixation device ## is a clamp which is affixed at its upper extremity to the underside of the rear rider's seat and at its lower extremity to the seat support rail. In a preferred clulJudilllcllL, the seat fixation device is the standard commercially available seat post clamp ## used to affix a bicycle seat to the substantially vertical seat post of a UUllV~,IlLiUllcl] bicycle. These inexpensive and cullllllcll,;dlly available seat clamps are comprised of a ~u~ c~ible clamping band ## which secures to the seatpost said band being rotateably coupled to a pair of pincer clamps ## which secure to the standard dual frame members ## which are integral to the bicycle seat. A single bolt ## through the rotation point of the clamping assembly simnlt?~ollcly secures the pincer clamps to the seat frame and the compressible band clamp to the seatpost. Tightening bolt ## also fixes the angle between the two clamping elements. Typically the clamping assembly permits at least 180 21 q4~29 degrees of rotation between said elements, thereby permitting the clamps for the rear rider's seat ## of the present invention to be rotated 90 degrees from its normal configuration with respect to a vertical seatpost such that the seat can be adjustably affixed to the horizontal seat support rail ##.
Referring to the workable embodiment illustrated in FIG 5, the front rider's seat ## is adjustably re-affixed to a position both forward and above it's normal position by means of a seatpost clamp ##, two 1/4 inch rod members ## and a seat fixation clamp ##. The seatpost clamp is the same mechanism described above that is used to secure the rear seat ## to the seat support rail ## however instead of be affb~ed to the two standard frame rails ## integral to the seat ##, its two upper clamping jaws ## are affixed to the lower ends of two seat extension rods ##. The seat extension rods are of suitable diameter to engage the seat clamp jaws. The seat extension rods ## are ra~lulc~d of sufficiently rigid and resilient material to support the c~antilevered weight of the fiont rider. The upper clamping assembly is comprised of two swivel clamp assemblies identical to those used both to secure the rear seat to the support stlucture. When the clamp assemblies at both ends of the seat extension rods are loosened, seat extension rods are adjustable both angularly and loneih~in~lly with respect to the clamp mechanism thereby permitting the user to re-position the front seat both above and forward of its single rider location.
Materials for fabricating the bi-le vel footpedal apparatus, the rear seat support structure and the front seat raising and ad~ ancement mechanism are typically aluminum and steel however other metal alloys and even some reinforced plastics can provide the strength, resilience and light weight that are required. Although the invention has been described with reference to a particular illustrative ehample, it is recognized that various minor mechanical modifications are possible when implementing this inventive concept.
This prior art modifies the conveniional single rider configuration by adding a second seat assembly as well as footpedals that are modified to A~cornnno/' the feet of the rear rider upon the same footpedal assemblies as those used by the first rider. In theory, this approach permits the second rider to sit behind the first rider and apply pedaling energy directly to the shared pedals. Sharing suitably modified pedals affixed to the crank of a single rider bicycle has a number of advantages with respect to conventional tandem bicycles:
I) An existing bicycle can be easily be converted to serve in either a single rider or tandem mode.
2 1 94~29 2) The cost of the special pedals and seating means are far less than the cost of a dedicated tandem bicycle.
3) Since almost all mechanical parts are shared by both riders, the gross vehicle weight is less than that of a dedicated tandem bicycle.
Various attempts to implement sLlch a scheme have been proposed by Liljenberg (2,706,418), Sykes (3,457,803), Kelly (2,337,246), Raba (2,361,708) and Ridgeway(2,715,342). However, none of the prior art has resulted in a viable solution due to one or both of the following drawbacks:
Drawback #1: The means for accommodating the rear rider' s feet on the pedals extended the normal dimensions of the rotateable pedal assembly such that the pedal can occasionally hit the road during u se, thereby causing loss of power to the vehicle and possible injury to the riders. The "side by side" foot placement configuration proposed within this prior art caused pedal grounding during tums. . The "over/under" foot placement configuration proposed within this prior art did not provide adequate road clearance for the rear rider's feet (the rear rider's feet being located under the pedal assembly's bearing spindle).
Drawback #2: The seating a~vll~u~vdaiillg for the rear rider was such that the two riders experience ergonomic fatigue while pedaling due to illlrl rr.,e. c between their legs.
It is therefore the objective of the present invention to provide a tandem bicycle propulsion system which eliminates the ~rv.rlll~lltivllrd drawbacks inherent to the prior art. The present invention achieves this objective by providing a kit of three sub-assemblies that are attachable to a conventional, single rider bicycle and which together modify said bicycle such that:
I) Both riders can direc~dy actuate the same footpedal assemblies while continuously mrin~Aining adequate clearance between the road and pedal assemblies.
2) A second rider can sit comfortably upon the modified bicycle at an optimal location behind and below the first rider.
3) The front rider can adjust the location of the front seat both forwards and upwards with respect to its normal location, thereby providing adequate leg clearance between the two riders during all phases of crank rotation.
DESCRIPTION OF THE KIT'S THREE SUB-ASSEMBLIES:
Sub-assembly #1:
Both conventional single rider bicycles and conventional tandem bicycles, employ a footpedal design comprised essentially of a rotateable, footpedal member substantially symmetric about the crank arm's pedal bearing spindle. The present invention rrcr,mmr ' the feet of both the front and rear riders upon the same footpedal assembly by providing the front rider with a non-rotateable upper footpedal member . ccrntrirAlly affixed to and supported somewhat above the concentrically rotateable footpedal member.
The lower (concentric) footpedal member is used by the rear rider during tandem operation of the vehicle. By placing both rider's feet above the pedal assembly's bearing spindle, the present invention insures that adequate ground clearance is maintained at essentially the same distance as when the vehicle is operated in the single rider mode (when the front rider occupies the rotateable footpedal members). Each of the dual-tiered footpedal assemblies receives botlh the front and rear rider's feet, one above the other, such that they are as close to each other as rnArrmir~lly possible. It does so by supporting the front rider's heel in front of, and immediately above, the upper surface of the rear rider's foot such that the front rider's heel fits as closely as possible into the crotch of the rear riders ankle without actually touching it.
To enable correct relative positio:ning of the two riders' feet, the upper footpedal member is non-rotateably affixed to the rotateable, lower footpedal member by means of substantially vertical compression members affixed at their upper and lower ends to the sides of the upper and lower fooq~edal members. In a preferred clllbudilllclll, the spacing between the upper and lower footpedal members as well as the dihedral angle between the plane of the two footpedal members is adjustable by means of a multiplicity of fixation points near each end of the compression members w hich can be used to adjust the effective length of each l,Ulll~)lCi~ iUII member. The compression members are disposed along the sides of the upper and lower footpedal members such that the rear tandem rider can insert the forepart of each foot onto the lower, concentric footpedal member and thereby apply propu]lsive foot pressure to the bicycle's crank and chainwheel assembly.
In a preferred clllbudilllcllL, the upper fooqpedal surface is flared upwards along its rearmost edge to form a more ~~ mic ~lly correct receptacle for receiving the rear rider's foot. This same flared lip also serves as a tactile aid to help the front rider feel when the heel of each foot is positioned on the upper footpedal in its optimal location (i.e.: as far back as possible without actually contacting the crotch formed by the rear rider's foot and shin bone).
When using the present invention in single nder mode, the lone rider pedals in the conventional manner by applying propulsive force to the lower, rotateable footpedal members. However, during tandem mode operation, the lower footpedal members become occupied by the rear rider, therefore the front rider must pedal using the upper footpedal members. Tandem pedaling action is a, culll~l;shcd by first placing the rear portion of each of the front rider's feet onto the upper footpedal member of each of the bi-level footpedals. The front rider then applies propulsive force by exerting heel pressure onto the assembly. The front rider's heel pressure is transmitted down the ~,UllllJlC~iUII
members and into the lower footp,edal members, thereby augmenting the rear riders pedaling force already being applied to the bicycle's crank and transmission assembly.
Foot pressure exerted by the rear rider onto the lower footpedal members is transferred directly to the pedal assembly's bearing spindle with virtually no eccentric offset or turning moment (i.e.: the ball of the foot applies force symmetrically, both fore and aft of the bearing spindle). However, pressure applied by the front rider onto the upper footpedal member is applied at a point that is substantially eccentric to the assembly's axis of rotation. If the force vector of the front rider's applied pressure does not pass exactly through the assembly's axis of rotation, the pedal member's eccentricity creates an unstable turning moment about the assembly's bearing spindle. The instability of this force geometry is proportional to the ec~_cllLli_i~y of the upper footpedal member (i.e.
proportional to the distance between the planes of the two footpedal members). Since the present invention forces the front r ider to apply only heel pressure to the footpedal assembly, slight variations in natu:ral foot movement during pedaling tend to produce a force vector which often passes somewhat forward of the assembly's axis of rotation, 2~ 9~29 thereby inducing a ~.sfAhilizing ~Forward torque. If left uncontrolled, this rotational instability could easily cause the entire footpedal assembly lo rapidly spin forwa}d when a strong pedaling force is exerted by the front rider. Such highly unstable forward rotation would quickly dislodge both riders' feet from the pedal assembly, causing loss of power to the vehicle and possible injury to the riders.
To address this problem, the present invention provides two mechanical means to achieve a dynamic balance of rotational forces about the pedal assembly's axis. The first means for uuullLcld~,Lillg the unstable rotational force is simply to position the two riders' feet on the pedal assembly as close together as physically possible. This close proximity between the two riders' feet minimizes the lever-arm effect caused by upper pedal member's e.~,..LIi~iLy. 1~ .h~g the upper pedal member's lever-arm effect help5 to minimizes the unstable rotational force however it cannot completely eliminate the danger caused by rotational instability. Unless great care is exercised by the front rider, the natural variability of foot attitude inherent to natural pedaling motion still causes brief forward torque surges in the whole footpedal assembly.
The present invention therefore provides a second means of ~ uuLcld~L;Ilg the unstable forward torque produced by the front rider's eccentric application of force onto the pedal assembly. This innovation is based on harnessing an equal and opposite "~ oly torque generated by the rear rider's pedaling force. The rear rider naturally can apply the required uulll~cll~dtu~y torque to the pedal assembly by shifting the location of foot pressure application towards the r ear of the lower footpedal member, thereby inducing the Culll~cll~dLuly torque required to prevent forward rotation of the pedal assembly. This rearward ,1;~l,l,1. c",. .,1 of the force vector on the lower footpedal member could conceivably be accomplished by moving the rear rider's feet backwards and forwards as required to counteract the variable forward torque produced by i,l~."l.~i~l. .I('ir~ in the front rider's pedaling motion. However, given the rapidity with which the ~ l y torque must be applied, the rear rider would quickly tire of continually shifting foot placement fore and aft on the lower footpedal.
The most natural and relaxing muscular action that applies brief periods of ~ulu~cul~dLuly torque occurs when the rear rider simply applies downward heel pressure. This heel pressure creates instant counter-rotative force to counteract the front rider's eccentric force vector. However, heel pressure can only have effect if the rear rider's entire foot and pedal member are disposed so that the foot is fully supported from heel to toe. The present invention therefore provides a modified lower footpedal member which is constructed a~yllllllcLIi~a]]y so as to provide the necessary foot support. This support is provided by a rear projection of the lower footpedal such that the lower footpedal member is asymmetric about the bearing spindle. The rear footpedal extension provides heel support for the rear rider, thereby permitting the rider' s heel pressure to modulate the required counter-rotative torque into the pedal assembly.
To avoid fabricating a large and heavy pedal assembly, the rear extension of each lower footpedal member may be truncated shorter than required to fully support the rear rider's heel. If this is the case, any overhang of the rider's heel past the end of the rearward pedal extension creates a bending force which will tend to lift the r ider's toe off the pedal member (thereby defeating the desired uulll~ dLuly torque modulation). Therefore, the 2~ 94029 .
present invention optionally hluul~ul~Lcs a conventional bicycle toe-clip on the front edge of the lower pedal member which insures that all of the heel pressure induced corrective torque is actually transferred into the rotateable pedal assembly.
S~b-assembly ~2:
The second of the three functional sub-assemblies which constitute this invention provides a means for the second rider to sit comfortably on the modified bicycle at a location behind and below the front rider. This function is provided by a seconduul~vc;uLiu~al, bicycle seat together with the appropriate support members that affix it to the bicycle in the correct ergonormic location. The rear seat is adjustably supported and positioned along a substantially horizontal rail member, affixed at its front end to the upper seatstay members of the cullvellLiullal bicycle frame. Rear support for said horizontal rail member is provided by two UUIII~ iiiUII members affixed at their upper ends to said rail and at their lower ends to each side of the bicycle frame near the location of the rear axle. The rear rider's bicycle seat is adjustably positioned on said support rail, to a location behind the front rider's seat.
For optimal ergonomic interaction with the front rider, the rear seat support rail must be kept as low as possible on the bicycle's structure. The compression members supporting said rail therefore have multiple fixation points which permit the rail to be vertically positioned on the bicycle such that it just clears the rear tire. A clamping device is also provided to adjustably affix the rear rider's seat at a point along the horizontal support rail member at the location which provides comfortable leg extension to the rear rider' s (lower) footpedals. Additional vertical leg clearance between the riders is created by rnmfigllring the internal support structure of the rear seat as well as the clamping device used to adjustably affix it to the support rail member in a manner that positions the rear seat as close to its support rail as possible.
Many existing bicycles are fitted with cantilever style brakes affixed to the seat-stay frame members which protrude outwards from the frame such that they could contact the rear rider's inner thighs during pedaling activity. To eliminate this ergonomic problem, the present invention provides me~ans for re-locating the existing brake assembly behind the rear rider's legs such that no hl~ with the brake assembly is experienced during pedaling. This clearance is established by providing an additional pair of cantilever brake pivots affixed to the two vertical compression members which support the rear seat assembly. These pivot pins are located on said members such that the existing brake cantilever assemblies can be transferred from the seat-stays to their new locations and maintain correct frictional ~ g~ with the rear wheel-rim. The existing brake actuation cable is replaced with a longer one which can reach from the handlebar brake lever to the new brake location on the rear seat supports. To accommodate the brake cable, a standard cable ferule is affixed to the rear of the seat support rail such that the cable's outer sheath is correctly positioned and restrained with respect to the re-positioned rear brake cantilever assemblies.
As an altemate means of providing adequate side clearance between the rear rider's inner legs and the existing rear brake assembly is to eliminate the rim-friction rear brake altogether and replace it with a disk brake or internal expansion hub brake. In fact, since the bicycle's gross vehicle weighl: will be approximately doubled by the addition of a 2~ 94~2q .
second rider, it would be a prudent safety measure to improve the vehicle's braking power in this manner.
The support rail assembly may optionally incorporate a backrest structure which provides two functions:
The first function of the backrest is to provide a more restful seating position for the rear rider during slow, relaxed cycling activity.
The second function of the backr,est is to prevent the rear rider from sliding backwards during hard pedaling.
The support rail assembly may optionally incorporate a pair of handholds located behind the rear seat. These handholds can be used by rear rider to maintain a stronger hold on the bicycle during hard maneuvers. They can also be used to lift the rear rider's body off the seat, thereby momentarily relieving pressure on the buttocks.
Sub-assembly #3:
The third of the three functional sub-assemblies which constitute the present invention provides a means for adjustably re-positioning the front rider's seat forward and upward with respect to its normal position. This re-positioning is required to insure adequate vertical clearance between the front and rear riders' legs at all angles of crank rotation.
During tandem pedaling, the rear rider's legs must move in close proximity behind and beneath the front rider's legs without any mutual interference. Given the geometry and seat location of the typical single rider bicycle, when both rider's feet are at the top of the pedaling stroke, the vertical separation between the front and rear seats would not be great enough to establish sufficient clearance between the top of the rear rider's thigh and the bottom of the front rider's thi,gh. The present invention already provides means to seat the rear rider as low as possible with respect to the front rider. Despite these attempts to optimally position the rear seat to provide maximum clearance between the riders, the dimensions and geometry of the typical bicycle and the leg size of typical riders, will still preclude adequate clearance between the riders.
To achieve the necessarv vertical clearance, the front rider's seat location must also be moved upwards from its normal, single rider location. Since, when converting from the single rider mode of operation to the tandem rider mode of operation, the front rider moves from the lower to the upper footpedal members, in order to retain the correct leg extension distance between the front rider's seat and the upper footpedal member, the front seat must also be raised by a distance approximately equal to the distance between the upper and lower foot pedal m~ mbers. The required amount of vertical seat adjustment could be accomplishe~ simply extending the existing seatpost A~jnctm,nt ullr~ ~ Aly the bicycle's existing seatpost is often not long enough to permit the required amount of additional vertical movement. More importantly, simply extending the existing seatpost actnally moves the front seat backwards into the abdomen of the rear rider. Therefore, the present invention must provide a specialized mechanism forincreasing both vertical and horizontal separation between the front and rear riders.
To provide this function, the present invention uses an adjustable cantilever mPAhArlism with two degrees of freedom which enables the operator to adjustably raise and move 2 ~ 94029 forward front seat. The front seat adjustment mPch~nicm is a cantilever that's ai'fixed between the bicycle's existing seatpost and existing (front) seat by means of the existing seat clamp. In a preferred embocliment, standard bicycle seat clamps are used at each end of the cantilever to connect it to the seat and seatpost.
A standard bicycle seat clamp pn~vides both angular adjustment and longitudinal adjustment for the seat by means of two pivoting clamps that affix to the two support rail members which are integral to the under-structure of standard bicycle seats. In a preferred embodiment of the present invention, the adjustable cantilever mechanism consists of two straight seat extension rods, each having the same cross sectional diameter and spacing as the two horizontal seat support members which are integral to the under-structure of standard bicycle seatis. The rear end of each seat extension rod can thus be securely engaged by the bicyclehi existing seat clamp such that each is cantilevered forward and upward from the top of the seatpost. The two seat extension rods are thus held parallel to each other at a distance equal to the distance between the seat support members fabricated into the lowc,r structure of typical bicycle seats. The length of cantilever in the two seat extension rods can be adjusted to the desired length by sliding them in the seat clamp prior to tightening the clamp's fixation screw. A second seat clamp IIIP. h.111;~111 is affixed to the other (upper) end of the two cantilevered members thereby enabling the seat to be ac justably affixed to the upper end of the cantilevered members. When the clamp assemblies at both ends of the seat extension rods are loosened, the seat extension rods are adjustable both angularly and longitudinally thereby permitting the user to re-position the front seat both above and forward of its single rider location.
This same seat adjustment mecha,nism also serves to provide a cantilevered suspension for the front seat by deforming under load to absorb some road shock before it reaches the rider.
This same seat adjustment mP~hi~ni~im also provides a hand hold which can be used by the rear rider to stabilize upper body movement on the bicycle.
A.' ' ' ' Design C ' I
The present invention is intended primarily for converting existing single rider bicycles to tandem operation however the inventive elements can also be i-~,bl~ d~ed into the design and fabrication of new single/tandem bicycles. In the case of such newly fabricated bicycles, the frame geometry would be optimized for a more balanced weight distribution by lPngthPning the bicycle's, horizontal chainstay frame members with respect to their conventional, single rider proportions. Fork geometry would also be modified to provide greater strength and high speed stability. Components such as wheels, brakes and frame tubing would also be upgraded to improve durability under the greater loads imposed by dual rider operation.
T .~ngihPning the chainstays would place the rear rider's weight further forward with respect to the rear axle and thus help to control any tendency for the front wheel to leave the ground during hard ~rcplpr~i nn or when climbing steep grades. However, in the case of converting an existing single rider bicycle to provide tandem capability, lengthening of the chainstay frame members would be prohibitively expensive. In such cases, the 2~ 9432q tendency towa}ds front end lightness is effectively controlled by simply moving the front rider's seat somewhat forward of its normal location, thereby re-distributing the front rider's weight onto the front wheel.
Optionally, "bar-end" handlebar risers can be purchased and added to the kit. These auxiliary handholds can then be adjusted to displace the front riders hand grips along the same vector as the front rider's seat and pedal positions have been displaced. The handlebar adjustment would then3by establish the front rider's posture to a~lulu~illlàL~ly the same position as before the footpedal position was moved to the upper footpedals and the front seat was displaced to ~comm. ~P the rear rider.
The rear rider may hand aid the Frocess of pedaling the tandem bicycle by using hand pressure on his or her knees to more fully utilize the additional muscular force of the upper body to augment that of the legs.
In addition to the vehicular application described above, the present invention can also serve as a bicycle stand. To accomplish this mode of operation, the operator simply rotates the crank such that either pedal is h~ .e.lk.'~,ly aft of its lowest point.
Gravitational force naturally rotates the pedal assembly so as to present the upper pedal member at lowest to the ground. This contact point with the ground serves as a bicycle stand by virtue of the fact that the gravitational force of the bicycle onto the pedal imparts a forward motion to the vehicle (~:hrough the llall~llu~iun). This forward force is countered-acted by the frictional contact of the pedal assembly has with the ground. The resulting dynamic balance of forc:es enables the bicycle to be directly supported by the pedal assembly.
With respect to the prior art:
By eliminating the additional crank and pedal assembly normally required by the rear tandem rider, the present invention provides a significantly lighter vehicle. Weight savings are also achieved by eliminating the additional drive chain normally required to link dual crank assemblies as well as the additional frame members needed to form the elongated frame inherent to previous tandem bicycle designs.
Furthermore, mechanical friction in the vehicle's drive train is significantly reduced by eliminating the second pair of footpedal bearings, the second crank bearing and the second drive chain and sprocket assembly required by previous tandem bicycle designs.
Furthermore, due to the rear rider's seating position being situated more fully within the slipstream created by the front rider, the vehicle's wind resistance is reduced compared to conventional tandem bicycle designs.
Ful Lhcillllul~, by eliminating the n:eed for a second crank and pedal assembly, a second drive chain and chainwheel assembly as well as the additional frame members needed to form an elongated frame, the cost of fabrication of the present invention is significantly reduced compared to previous tandem bicycle designs 2l 9402~
Furthermore, since the present invention is of similar size and weight as a single rider bicycle, the sarne vehicle can still be efficiently propelled by a single front rider when no second rider is available to help pedal.
F~l~thcllllulc, the present invention permits an existing single rider bicycle to be quickly converted into a tandem bicycle and back to a single rider bicycle.
Furthermore, when not in service as a vehicle, the present invention acts as a bicycle stand.
2~ 9402q -DRAWINGS AND DETAILED DESCRIPTION:
In drawings illustrating an embodiment of the invention:
FIG. 1 is an elevational view of a conventional single rider bicycle having tandem rider modifications mounted thereon which are constructed in accordance with and embodying the present invention: said bicycle being illustrated as occupied and actuated by two riders.
FIG. 2 is an elevational view sirrlilar to figure I except that the bicycle is illustrated being unoccupied by riders and the pedal assemblies are rotated to their support stand locations whereby the upper foot support surface contacts the ground when the vehicle is leaned over.
FIG. 3 is an enlarged view of F]:G. 1 illustrating details of the pedal assembly with the riders' feet correctly positioned.
FIG. 4 is an enlarged view of F]:G. 1 illustrating details of the rear seat support assembly and modified rear brake assembly.
FIG. 5 is an enlarged view of F]~G. 1 illustrating details of the front seat support assembly.
The present invention is compnsed of three sub-assemblies:
I) - The dual level pedals.
2) - The rear seat and its attendant support structure.
3) - The front seat raising and a~b~a~ ..L mechanism.
When affixed to a conventional single rider bicycle structure, these three sub-assemblies operate in concert to effect its conversion to tandem operation.
Referring to the working ~Illbodi~ illustrated in FIG. 1 which illustrates the relationship between the present invention's three main sub-assemblies: the front rider places the rear part of each foot onto the upper pedal surface member ## of each of the dual level pedal assemblies. The front rider's foot is thus displaced vertically upward with respect to its normal, single rider location on the rotateable lower surface member, by a distance equal to the distance between the upper and lower pedal surface members.
To ~,UIII~)~ ' for this change in reach to the pedals, the front seat is also displaced upward the same distance by adjostably re-positioning the seat adjustment members ##.
The seat adjustment members also permit the seat to be adjusted forward of its lliulldl location so as to prc,vide clearance for the rear rider and transfer weight onto the front wheel. The rear rider sil:s on the rear seat ## and places the front part of each foot on the rotateable, lower pedal surfaces ## and adjustably positions the rear seat ##
along the support rail ##
Referring to the workable embodiment illustrated in FIG. 3 each of the two upperfootpedal surface members ## is adjustably affixed to and supported substantially above its Cullc ~olldillg rotateable, lower footpedal surface member assembly ## by means of a series of substantially vertical compression members ##.
The upper footpedal surface member ## has a series of drilled tab members ## bent downwards along its sides so as to provide fixation points for the compression members ##. Each lower footpedal surface is comprised of a hub ## which rotates around the pedal's bearing spindle ## which in turn is affixed to the crank arm ## of the bicycle's 21 9402~
existing L .~ llliiX~iUII m~ h~nicn I Two U shaped members comprised of a central section ## and two drilled end tab sections ## bent at 90 degrees to the central member are affixed to the front and rear of ea.ch pedal hub ##. The two central sections ## affixed to the pedal hub ## serve as foot support surfaces for the rear rider. The drilled tab members ## provide lower fixation points for the vertical compression members ##supporting the upper footpedal member ##.
The upper end of each compression member ## is rotateably affixed to its respective upper footpedal tab ## using matching holes and a tightening fastener ## which serves to prevent rotation once a CUIIII'UI Idl11C angular adjustment is set. The lower end of each UUIIIUlU~:~iUn member ## is affixed to the lower footpedal surface member using a similar rotateable fixation means as is ernployed at the upper end, however it has multiple fixation holes ## to permit the length of each compression member to be adjusted to suit both rider's pedaling comfort. Depending on the anatomical configuration of each rider, the upper footpedal member ## is fixed at a greater or lesser angle and separation with respect to the lower footpedal me mber ##.
Referring to the workable embodiment illustrated in FIG. 4, the main support rail member ## for the rear rider' s seat ## is adjustably affixed Lo the frame of the host bicycle at both of its ends so as to maintain the support rail in a substantially horizontal position, aligned with the axis of the bicycle and immediately above the bicycle's rear tire. The m.~h?ni.cm for affixing the front of the seat support rail to the host bicycle is comprised of a angled bracket #~ which is bolted through the front of the support rail member on one end and at the other end through the hole in the bicycle's seat stay brace ## normally provided to mount the rear brake assembly. The mechanism for affixing the rear of the seat support rail to the host bicycle is comprised of two rail support struts ##.
The top of each of the two rail support struts is bolted to the left and right side respectively of the rear seat support rail using a bolt ##. Spacer elements ## may be inserted between the seat support rail and the rail support stluts to provide adequate clearance between the rail support struts and the rear tire. The seat support rail may be of any cross sectional shape however a preferred clllbodilllcllL employs a circular cross-section as this minimizes fabrical:ion costs and also permits the use of a seat fixation device described below.
The rear bicycle seat ## is adjustably affixed at a point along the seat support rail ## such that it affords the rear rider a comfortable reach to the lower footpedals. The seat fixation device ## is a clamp which is affixed at its upper extremity to the underside of the rear rider's seat and at its lower extremity to the seat support rail. In a preferred clulJudilllcllL, the seat fixation device is the standard commercially available seat post clamp ## used to affix a bicycle seat to the substantially vertical seat post of a UUllV~,IlLiUllcl] bicycle. These inexpensive and cullllllcll,;dlly available seat clamps are comprised of a ~u~ c~ible clamping band ## which secures to the seatpost said band being rotateably coupled to a pair of pincer clamps ## which secure to the standard dual frame members ## which are integral to the bicycle seat. A single bolt ## through the rotation point of the clamping assembly simnlt?~ollcly secures the pincer clamps to the seat frame and the compressible band clamp to the seatpost. Tightening bolt ## also fixes the angle between the two clamping elements. Typically the clamping assembly permits at least 180 21 q4~29 degrees of rotation between said elements, thereby permitting the clamps for the rear rider's seat ## of the present invention to be rotated 90 degrees from its normal configuration with respect to a vertical seatpost such that the seat can be adjustably affixed to the horizontal seat support rail ##.
Referring to the workable embodiment illustrated in FIG 5, the front rider's seat ## is adjustably re-affixed to a position both forward and above it's normal position by means of a seatpost clamp ##, two 1/4 inch rod members ## and a seat fixation clamp ##. The seatpost clamp is the same mechanism described above that is used to secure the rear seat ## to the seat support rail ## however instead of be affb~ed to the two standard frame rails ## integral to the seat ##, its two upper clamping jaws ## are affixed to the lower ends of two seat extension rods ##. The seat extension rods are of suitable diameter to engage the seat clamp jaws. The seat extension rods ## are ra~lulc~d of sufficiently rigid and resilient material to support the c~antilevered weight of the fiont rider. The upper clamping assembly is comprised of two swivel clamp assemblies identical to those used both to secure the rear seat to the support stlucture. When the clamp assemblies at both ends of the seat extension rods are loosened, seat extension rods are adjustable both angularly and loneih~in~lly with respect to the clamp mechanism thereby permitting the user to re-position the front seat both above and forward of its single rider location.
Materials for fabricating the bi-le vel footpedal apparatus, the rear seat support structure and the front seat raising and ad~ ancement mechanism are typically aluminum and steel however other metal alloys and even some reinforced plastics can provide the strength, resilience and light weight that are required. Although the invention has been described with reference to a particular illustrative ehample, it is recognized that various minor mechanical modifications are possible when implementing this inventive concept.
Claims (14)
1) A tandem bicycle propulsion system utilizing a single pedal crank assembly, said crank being directly actuated by means of rotateable footpedal assemblies shared by both front a rear riders, said footpedal assemblies being comprised of a lower load-bearing surface member substantially symmetric to the pedal's bearing spindle which receives pressure from the rear rider's foot together with an upper load-bearingsurface member which receives pressure from the front rider's foot, said upper member being affixed to and supported substantially above the lower footpedal member such that the force vector of both rider's pedaling effort can be exerted so as to pass downwards through the center of the pedal assembly's bearing spindle.
2) INSERT SEPARATE CLAIM FOR REAR EXENTSION OF LOWER PEDAL TO
COUNTERACT TORQUE INSTABILITY CAUSED BY ECCENTRICITY OF
FRONT RIDER'S POINT OF PRESSURE APPLICATION.
COUNTERACT TORQUE INSTABILITY CAUSED BY ECCENTRICITY OF
FRONT RIDER'S POINT OF PRESSURE APPLICATION.
3) INSERT SEPARATE CLAIM TO COVER ADJUSTMENT OF ANGLE AND DIST
BETWEEN PEDAL'S UPPER AND LOWER MEMBERS
BETWEEN PEDAL'S UPPER AND LOWER MEMBERS
4) INSERT SEPARATE CLAIM TO COVER HEEL STOP ON UPPER PEDAL
MEMBER TO CORRECTLY POSITION FRONT RIDER'S HEEL
MEMBER TO CORRECTLY POSITION FRONT RIDER'S HEEL
5) INSERT SEPARATE CLAIM TO COVER TOE CLIP TO PROVIDE SOLID
FIXATION TO LOWER PEDAL MEMBER
FIXATION TO LOWER PEDAL MEMBER
6) A bicycle configured in accordance with claim 1 to which a rear rider's seat is affixed at a location immediately behind and substantially lower than the front rider's seat such that, when both rider's feet are engaged onto the bi-level footpedal assemblies, their legs do not interfere with each other when applying pedaling force to the pedal crank, for all angles of pedal crank rotation.
7) INSERT SEPARATE CLAIM FOR REAR BRAKE RE-POSITIONING
MECHANISM
MECHANISM
8) INSERT SEPARATE CLAIM TO COVER BACKREST ON REAR SEAT
ASSEMBLY
ASSEMBLY
9) INSERT SEPARATE CLAIM TO COVER REAR RIDER HAND HOLDS (BOTH
ON FRONT SEAT RISER AND REAR SEAT SUPPORT)
ON FRONT SEAT RISER AND REAR SEAT SUPPORT)
10) INSERT SEPARATE CLAIM TO COVER HAND AIDING OF REAR LEGS
11) A bicycle configured in accordance with claim 1 and claim 2 to which a front seat position adjustment device is affixed between the seat and seatpost, said adjustment device comprised of a rail member detachably affixed to the top of the seatpost, said rail member being horizontally cantilevered forward from the upper extremity of the seatpost and engaging a sliding fixation device which in turn engages the standard seat support members integral to the lower structure of standard bicycle seats, thereby permitting the front seat to be adjustably re-positioned somewhat forward of itsnormal location.
12) INSERT ADDITIONAL CLAIM TO COVER STAND FUNCTION OF
INVENTION
INVENTION
13) INSERT CLAIM TO INTEGRATE THE THREE MAJOR COMPONENTS INTO A
KIT SUCH THAT IMPROVEMENTS TO ONE OF THE ELEMENTSDOESN'T
CONSTITUTE A NEW INVENTION.
KIT SUCH THAT IMPROVEMENTS TO ONE OF THE ELEMENTSDOESN'T
CONSTITUTE A NEW INVENTION.
14) INSERT SEPARATE CLAIM TO COVER BOTH CASES:
-KIT TO CONVERT EXISTING BICYCLES
-NEWLY CONSTRUCTED BICYCLES INCORPORATING THE SAME DESIGN
PRINCIPALS BUT WITH OPTIMISED FRAME GEOMETRY AND
STRENGTHENED COMPONENTS.
-KIT TO CONVERT EXISTING BICYCLES
-NEWLY CONSTRUCTED BICYCLES INCORPORATING THE SAME DESIGN
PRINCIPALS BUT WITH OPTIMISED FRAME GEOMETRY AND
STRENGTHENED COMPONENTS.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002194029A CA2194029A1 (en) | 1996-12-27 | 1996-12-27 | Tandem bicycle propulsion system utilizing a shared footpedal and crank assembly |
| CA002199997A CA2199997A1 (en) | 1996-12-27 | 1997-03-14 | Tandem bicycle propulsion system utilizing a shared footpedal and crank assembly |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002194029A CA2194029A1 (en) | 1996-12-27 | 1996-12-27 | Tandem bicycle propulsion system utilizing a shared footpedal and crank assembly |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2194029A1 true CA2194029A1 (en) | 1998-06-27 |
Family
ID=4159556
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002194029A Abandoned CA2194029A1 (en) | 1996-12-27 | 1996-12-27 | Tandem bicycle propulsion system utilizing a shared footpedal and crank assembly |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2194029A1 (en) |
-
1996
- 1996-12-27 CA CA002194029A patent/CA2194029A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |