WO2010019999A1

WO2010019999A1 - Improved bicycle drive assembly

Info

Publication number: WO2010019999A1
Application number: PCT/AU2009/001062
Authority: WO
Inventors: William Andrews
Original assignee: William Andrews
Priority date: 2008-08-22
Filing date: 2009-08-14
Publication date: 2010-02-25
Also published as: TW201026556A

Abstract

A pedal drive assembly for a bicycle, the assembly including; a primary drive shaft mounted on a bicycle frame and having respective first and second ends extending beyond the frame; the first and second ends receiving and retaining thereon respective first and second crank arms; said first and second crank arms engaging respective first and second ends of said shaft via a coupling on each crank arm; the crank arms each comprising at a distal free end an off set coupling assembly including a first shaft which engages the free end of the pedal and includes a formation offset relative to the first shaft and which receives and retains a pedal connection.

Description

IMPROVED BICYCLE DRIVE ASSEMBLY

BACKGROUND

The invention relates to an improved drive assembly for push bicycles. The invention further relates to improvements in drive systems for bicycles and specifically drive pedal crank systems. The invention further relates to a drive pedal crank system which can generate increased torque and energy for a given energy input provided by the rider. The invention further relates to a pedal drive assembly for a bicycle which increases mechanical advantage compared to existing pedal drive assemblies .

PRIOR ART

Push bicycles are propelled by the action of a rider applying load via pedals attached to a crank arm which extends to a primary drive shaft. The drive shaft is connected to a primary sprocket which imparts drive to at least one rear wheel sprocket via a drive chain. When the rider applies load to a pedal this induces a moment or torque at the primary drive shaft which load is then transferred via the drive chain to rear wheel drive. Torque is the product of a load applied at one point and the distance from that load point to a rotation axis. As the load increases the torque increases for the same moment arm distance. As the moment arm increases, a reduced load can generate the same torque or an increased load will generate more torque. The loading applied to the pedal required to impart drive will be affected by such parameters as ground contour, wind, the weight of the rider and drag between the wheels and the surface on which the bicycle is travelling. In a conventional bicycle, the distance between the pedal connection axis of the crank arm and the primary drive shaft is fixed by the length of the pedal arm. The length of the crank arm is limited by the distance between a ground surface and the primary drive shaft to ensure that on a down stroke, the pedal is well clear of the ground surface. The objective is to maximize the mechanical advantage within the constraints of the operating space. Many attempts have been made in the past to increase the mechanical advantage in bicycle drive systems. Attempts have included extending the pedal arm to gain more torque for the same load or in other words, to increase the mechanical advantage. Whilst there have .been a number of varying attempts to increase the torque of a bicycle crank system, nearly all have involved a mechanism that axially the length of the crank arm to provide greater torque to the primary shaft of the drive system. Other systems employed an externally mounted lever and pivot system that induced greater forces into the drive system. The known drive assemblies in which attempts have been made to increase mechanical advantage and thus torque have a number of disadvantages The mechanisms attempting to increase torque involved in the prior art fall into a number of categories:

1 Mechanisms which cause a crank arm length variation during rotation.

2 mechanisms which induce greater force to the drive system during rotation.

3 mechanisms that allow a crank arm to vary its length to selected fixed lengths.

Variable length crank arms have included internal mechanisms, designed to control and order various aspects of the prior art drive systems to cause crank arm variation. These mechanisms are generally complex, involving many moving parts subject to particularly high stresses. Bearing in mind that the components are relatively small, one of the main problems with variable length crank arms, has been the compromise between parts being large enough to withstand the high stresses experienced by the various drive mechanisms and also support structure, but small enough to provide an acceptable alternative drive system. Another significant problem with these variable length systems is that whilst on paper they show significant crank arm extension to impart much greater rotation and therefore torque to the drive system, in practice they experience significant mechanical energy losses in operation occasioned by the action of the crank arm retracting in a generally upwards direction whilst the rider is attempting to force the pedal arm in a generally downwards direction during the last quarter of the crank arm rotation to a vertical down position. As a result of the opposing forces experienced during the rotation, they significantly negate the gains of a longer crank arm. Another significant problem with the extendible crank arms is noise generated by the various drive mechanisms loading and unloading during the course of a rotation under high stresses. The above described systems are bulky and heavy compared to traditional crank systems. They also require significant lubrication of moving parts and are also subject to dust and grit invasion of those moving parts.

Mechanisms having external components such as levers and pivots that interact with the crank arms also experience significant problems. They are cumbersome and bulky and when compared to traditional solid rigid crank arm systems, they can experience unwanted movement and noise due to the additional pivot points. They also suffer from unwanted structural flexing whilst also experiencing irregular pedal rotational paths.

The prior art also teaches the use of crank arms that can be adjusted during operation , moving to various fixed lengths. Also known is a system where a rider's feet control a mechanism that causes a variation in the crank arm length during rotation of the arm.

^• In this example the rider is able to locate spring loaded retaining pins in various locating holes along the crank arm to select and retain various crank arm lengths using the feet of the user. In operation without some form of indicating system to acknowledge the various length positions and a suitable pin to hole alignment position, this task would require a significant amount of practice and skill.

One of the problems with the prior art assemblies attempting to increase the crank length is that they are often physically bulky to house the necessary components as a result of which the crank arm dimensions are significantly greater. The pedals are spaced significantly further apart than traditional fixed length pedal arms to avoid interference with the back wheel of the bicycle frame, this causes the rider's feet often to be placed unacceptably further apart than usual.

In summary the known prior art inventions individually or collectively as described all experience significant problems even though they attempt to provide a more efficient alternative to the traditional fixed length arm. There is a long felt want in the industry to provide improvements in bicycle drive systems which increase mechanical advantage with a minimum of parts and which is relatively economic to manufacture and simple to operate.

THE INVENTION

The present invention seeks to ameliorate the shortcomings of the prior art by providing an improved drive system for push bicycles. The present invention provides an improved drive assembly for push bicycles and specifically drive pedal crank systems. The invention further provides a pedal drive system which can generate increased torque and energy for a given energy input provided by the rider. The invention further provides a pedal drive assembly for a bicycle which increases mechanical advantage compared to existing pedal drive assemblies .

The invention to be described herein provides an alternate bicycle drive system which augments the traditional fixed length crank arm but which does not suffer from the many deficiencies of the prior art.

The invention further provides a drive pedal crank system which can generate increased torque and energy for a given energy provided by the rider.

In its broadest form the present invention comprises:

a bicycle drive assembly including a pedal arm having a proximal end which is mounted on a primary drive shaft and distal end which receives and retains thereon a coupling member, the coupling member having a shaft which engages the distal end of the pedal arm and a formation which is offset relative to and is capable of rotation about an axis of the coupling member shaft; wherein, the rotation of the coupling member extends beyond the distal end of the pedal arm during drive rotation of the pedal arm thereby increasing torque transmitted to the primary drive shaft. In another broad form the present invention comprises:

a pedal drive assembly for a bicycle, the assembly including; a primary drive shaft mounted on a bicycle frame and having respective first and second ends extending beyond the frame; the first and second ends receiving and retaining thereon respective first and second crank arms; said first and second crank arms engaging respective first and second ends of said shaft via a coupling on each crank arm; the crank arms each comprising at a distal free end an off set coupling assembly including a first shaft which engages the free end of the crank arm and includes a formation offset relative to the first shaft and which receives and retains a pedal connection.

Preferably the first shaft of the offset coupling member is fixed to the free end formation in the crank arm so that the eccentric formation is capable of rotation relative to an axis through the first shaft of the coupling member. Preferably, the. eccentric formation rotates as the crank arm rotates. The pedal includes a threaded connection member which attaches to the formation of the coupling member. The coupling member allows the threaded connection member of the pedal to rotate about an axis through said free end of the said pedal when the connection member of the pedal is connected to the formation. Preferably, the formation is integral with a rotatable plate.

Preferably, the formation is arranged on the plate so that as the crank arm rotates, the formation rotates through a circle which is concentric with the axis through the shaft, of the coupling member. A circumferential location of the formation in the circle during rotation is relative to the circumferential position of the crank arm as it rotates about the primary drive shaft.

The crank arm rotates about the drive axis, the coupling member moves between a first location in which at least part of the coupling member extends distally beyond the axis through the first shaft to a maximum extent in a direction along a longitudinal axis of the crank arm and a second location in which the coupling member extends proximally along the longitudinal axis of the crank arm. The pedal is preferably connected to the formation of the coupling member via a threaded shaft. The formation preferably comprises a threaded recess and rotates in a circle having a first radial size. The pedal arm rotates simultaneously with the rotation of the first radial arm.

In another broad form the present invention comprises:

a crank arm for a bicycle drive assembly, the crank arm having a proximal end which is mounted on a primary transversely disposed drive shaft and distal end which receives and retains thereon a coupling member, the coupling member having a shaft which engages the distal end of the crank arm and a formation which is offset relative to and is capable of rotation about an axis of the coupling member shaft; wherein, the rotation of the coupling member extends beyond the distal end of the crank arm during drive rotation of the crank arm thereby increasing torque transmitted to the primary drive shaft.

The crank arm is mounted on the drive shaft via a bearing within a bearing retaining hole on the crank arm.

In another broad form the present invention comprises:

a pedal drive assembly for a bicycle, the assembly including a pair of crank arms each attached via a proximal end to a primary transverse drive shaft and each having at an opposite distal end an opening capable of receiving and retaining a coupling member; each coupling member including a shaft which engages said distal end opening and a formation which is capable of rotation about the coupling member shaft as the pedals rotate about the primary transverse drive shaft.

Preferably the shaft of the coupling member which engages the distal end of a pedal is disposed normally to the plane of rotation of the crank arms. The coupling member receives a pedal via a formation in the coupling member and allows the pedal to rotate about an axis of the shaft of the coupling member as the crank arm rotates about the primary drive shaft. As a result, the coupling member and crank arms rotate simultaneously. Preferably, the pedal locates in a threaded recess on the coupling member located eccentric to the coupling member shaft.

The arrangement including the coupling member, allows the crank arms to rotate in a 360 degree plane about primary drive shaft and simultaneously allows the pedal to rotate about the shaft of the coupling,

Throughout the specification a reference to crank arm will be taken to be a reference to the member of a bicycle drive assembly in which a proximal end is connected to a primary transverse drive shaft and a distal end supporting a pedal via a swing or rotatable coupling. Throughout the specification a reference to coupling, coupling swing arm or swing arm may be taken as a reference to a coupling which joins the pedal to the crank arm and which is capable of at least partial rotation relative to the crank arm in the clockwise or anticlockwise directions and which is capable of that rotation about an axis offset from an axis through a distal opening in the crank arm.

The present invention provides an alternative to the known prior art and the shortcomings identified. The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying representations, which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. In the accompanying illustrations, like reference characters designate the same or similar parts throughout the several views. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. It will be convenient to hereinafter describe the invention in relation to a metal section in the present exemplary application. However, it is to be appreciated that the invention may be constructed from other materials.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described in more detail according to a preferred but non limiting embodiment and with reference to the accompanying illustrations, wherein:

Figure 1 shows a bicycle drive assembly including bicycle frame, drive sprockets and according to one embodiment an exploded crank arm connection assembly.

Figure 2 shows an exploded view of the pedal arm of figure 1 according to one embodiment isolated from the drive assembly.

Figure 3 shows a side elevation of a the pedal arm of figure 2 including the coupling swing arm according to a preferred embodiment.

Figure 4 shows a radial crank arm according to one embodiment, positioned in a horizontal position during the course of a rotation.

Figures 5 shows in individual radial positions a crank arm which is rotated 360 degrees in increments about a primary drive axis,

Figure 6 shows in individual radial positions a crank arm which is rotated 360 degrees in increments about a primary drive axis,

Figure 7 shows a primary drive assembly attached to a bicycle frame and various radial crank arm positions during 360 degree rotation of the crank arm.

Figure 8 shows a bicycle drive assembly including bicycle frame, drive sprockets and according to an alternative embodiment an exploded crank arm connection assembly. DETAILED DESCRIPTION

The present invention to be described below in more details provides an alternative to the known prior art and the shortcomings identified. The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying representations, which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. In the accompanying illustrations, like reference characters designate the same or similar parts throughout the several views.

It is to be appreciated that the invention is not limited to the particular assembly described . The examples referred to herein are illustrative and are not to be regarded as limiting the scope of the invention. While various embodiments of the invention have been described herein, it will be appreciated that these are capable of modification, and therefore the disclosures herein are not to be construed as limiting of the precise details set forth, but to avail such changes and alterations as fall within the purview of the description .

Figure 1 shows an exploded view of a bicycle drive assembly 1 including a bicycle frame 2 ( abbreviated) terminating in sleeve 3 which receives and retains therein a primary drive shaft 4 having first and second ends 5 ( partly obscured) and 6. Second end 5 receives drive sprockets 7, 8 and 9 which are usually manufactured in one piece. Sprockets 7, 8 or 9 engage a conventional drive chain (not shown) which transmits drive to rear wheel sprockets known in the prior art.

Crank arm 10 attaches to tapered end 6 of shaft 4 via opening 11 in proximal end 12. Opening 11 has a corresponding taper which engages tapered end 6 of shaft 4. Pedal arm 13 which retains pedal 14 engages opposite end 5 of drive shaft 4 in a similar manner. Crank arms 10 and 13 are known in the prior art bicycle drive assemblies and are typical of pedal arm geometry. Crank arm 10 terminates in distal end 15 which includes bearing retaining opening 16.

Opening 16 includes retaining groove 17 which receives and retains retaining circlip 18. Circlip 18 retains double row bearing 19 which fits within opening 16. Bearing 19 is trapped between circlip 18 and retaining shoulder 20 of crank arm 10. Assembly 1 further comprises a coupling swing arm 21 which includes a body which retains on one face spigot 23 and on an opposite face a threaded opening 24 which receives and retains therein shaft 25 of pedal 26. Spigot 23 is fitted to bearing retaining opening 22 when bearing 19 is located within opening 16. Coupling swing arm 21 is fitted to bearing 19 by way of spigot 23 by fitting spigot 23 to inner bearing opening 22 of bearing 19. Spigot 23 is retained by circlip 18 which engages groove 27 on the leading end of spigot 23. In line with threaded opening 24 of coupling swing arm 21 is threaded spigot 25 of pedal 26. Pedal 26 is attached to swing arm 21 by screw fitting of spigot 25 of pedal 26 into opening 24. Pedal 14 engages pedal arm 13 in a similar manner that that described above for the engagement of pedal 26 to crank arm 10. The following detailed description of the coupling swing arm 21 and its co operation with crank arm 10 is applicable to the manner of engagement of pedal 14 to pedal arm 13.

Figure 2 shows with corresponding numbering for corresponding parts an exploded view of the crank arm 10 of figure 1 according to one embodiment isolated from the drive assembly. Proximal end 12 of crank arm 10 receives shaft 4 ( see figure 1) in opening 11. Distal end 15 includes bearing retaining opening 16 and retaining groove 17 which receives and retains retaining circlip 18 as shown in figure 1. Bearing 19 fits within opening 16. Bearing 19 is trapped between circlip 18 and retaining shoulder 20 of crank arm 10. Assembly 1 further comprises a coupling swing arm 21 which includes a body 22 which retains on one face spigot 23 and on an opposite face a threaded opening 24 which receives and retains therein shaft 25 of pedal 26. Spigot 23 is fitted to bearing retaining opening 22 when bearing 19 is located within opening 16. Coupling swing arm 21 is fitted to bearing 19 by way of spigot 23 by fitting spigot 23 to inner bearing opening 22 of bearing 19. Spigot 23 is retained by circlip 18 ( see figure 1) which engages groove 27 on the leading end of spigot 23.

Figure 3 shows with corresponding numbering for corresponding parts, a side elevation of a the crank arm of figure 2 including the coupling swing arm 21 according to a preferred embodiment. According to a preferred embodiment, one compact double row bearing 19 is housed within pedal arm 10. Bearing 19 is capable of, accommodating the forces induced by a rider in swing arm 21 through its full range of rotation. It will be appreciated by persons skilled in the art that the double row bearing 19 has an optimal size to strength ratio, allows it to be of particularly compact dimensions when compared to the very high and varying forces a bearing of this type can withstand. According to figure 3, the concept of utilizing only one double row bearing 19 housed within crank arm 10, allows the dimensions of crank arm 10 to be relatively narrow as a result of the narrowness of bearing 19 indicated by distance line 30. Furthermore, swing arm 21 is positioned immediately beside crank arm 10 and is also harrow relative to pedal arm 10 indicated by distance 31. Crank arm 10 need only be of sufficient width dimension to accommodate the spigot 25 of pedal 26.

In light of this, the combined features of a compact double row bearing 19 in conjunction with a compact coupling swing arm 21 effectively allows the present invention overall components of the invention to conform closely to that of a traditional fixed length pedal arm assemblies. As may be seen in figure 3, swing arm 21 rotates about axis 32 which passes through spigot 23. As crank arm 10 is rotated by application of rider force to pedal 26 ( figure 1), and since pedal 26 is connected to threaded recess 24 this will cause swing arm 21 and crank 10 to rotate simultaneously . Pedal 26 will rotate about axis 33 which is offset from axis 32 by a distance d. Radial distance d which is the maximum displacement distance between axes 33 and 32 may vary depending upon the length of swing arm 21 selected, The relative distance. between axes 32 and 33 represents an increased moment arm between axis 33 and axis 34 through radial distance 1. Swing arm 21 operates in a manner which enables a co incidence between the location during rotation of the crank arm 10 when applied load is at a maximum and a location of swing arm 21 at which distance 1 is at a maximum. This co incidence will occur when the crank arm 10 is at or hear 90 degrees of clockwise rotation in a 360 degree arc of rotation. This operational geometry is further illustrated with reference to figures 4-7.

Figure 4 shows a radial pedal arm 10 according to one embodiment, positioned in a horizontal attitude during the course of a pedal induced rotation in the direction of arrow 41 about shaft 4 (axis 43), which engages opening 1 1. According to another aspect of the overall invention, the invention identifies and has taken into consideration the overall geometry of the bicycle, and in particular the seat position of the bicycle in relationship to the drive system and more particularly the crank arm 10 as being an integral aspect of the invention to cause swing arm 21 according to figure 3 to experience maximum movement away from primary drive shaft 4.

In practice the seat of the bicycle is oriented above and somewhat behind the crank arms and primary drive assembly. This orientation causes the rider's legs to push away from the seat with a resultant force which has a forward and downward components. As a result of this the rider imparts forces to the primary drive assembly crank system at an angle from the hip of the rider according to figure 7. • The angle of force line 30 according to figure 4 shows that by the involvement of the overall geometry of the bicycle it forces pedal connection point 19 to follow a pedal track path 48, being of an increased distance from main shaft / when compared to the axis track 47 of bearing 19 and distance marker 32 without the overall geometrical affect of the seat to crank orientation. To highlight the significance of this feature figure 4 shows angle of forced line 50 intersecting at the axis of pedal connection point 33 and distance marker 33 shows a significant increase in pedal arm length between axis 32 and axis 33 in comparison to distance 1 between axis 32 and axis 42. However upon further marginal rotation of crank arm 10 to markers 32 and 33, the increased moment distance is substantially increased. To add further significance to this, in practice the marker points of 32 and 33 during rotation are also at an advantage point where the legs of the rider begin to straighten being at their strongest to further take advantage of the crank arm in a most extended position of the crank rotation. Figure 5 shows in individual radial positions crank arm 10 which is rotated 360 degrees in 45 degree increments about primary drive axis 4. According to figure 5 the invention facilitates a mechanism involving the integration of crank arm 10 and secondary coupling swing arm 21 to rotational Iy interact during rotation of the drive assembly to effectively cause an extension of crank arm 10, to maintain a generally vertical orientation according to the axis points 34 and 35 of figure 5.

For swing arm 21 according to figure 5, the connection of swing arm 21 to pedal arm 10 is by way of bearing 19 of crank arm 10 that in turn allows swing arm 21 to experience a 360 degree rotation without restriction relative to crank arm 10 during the course of its rotation. Without taking into consideration any forces that may be imparted from the rider and according to rotational arrow 29 of figure 5, crank arm 10 when rotating from the vertical position (being preferably that of a traditional fixed length pedal arm) to the horizontal position being a travel of 90 degrees, causes secondary swing arm 21 to naturally swing out whilst maintaining a generally vertical orientation according to the individual swing arm 21 positions of the assembly of figure 6 to cause pedal connection threaded hole 19 of swing arm 21 to progressively increase its distance from main shaft 1 according to distance marker 31 and pedal track 46 at the horizontal position. The increase distance experienced by pedal connection to opening 16 of swing arm 21 effectively provides a progressively, extending crank arm 10 being of greater leverage to cause increased rotational forces to main shaft 1 of the crank system. Upon further rotation of crank arm 10, pedal track 48 shows a continuing progressive increase in distance from main shaft 4 whilst progressing to its vertical down position. Upon full rotation of crank arm 10 pedal track 48 shows a progressive decrease from drive shaft 4 whilst maintaining a generally vertical orientation when traveling from the vertical down position.

Figure 6 shows in individual radial positions crank arm 10 rotated 360 degrees in increments about primary drive axis 4. As shown pedal arm 10 and coupling swing arm 21 mutually co operate during rotation of crank arm 10 in the direction of arrow

44 to place a pedal during rotation of the crank arm 10 is a location for at least part of the rotation which effectively extends the moment arm of crank arm 10. When crank arm 10 is rotated as shown, even in the absence of a pedal load applied by a rider, rotation of crank arm 10 starting from a vertical orientation and heading to a horizontal orientation, will cause swing arm 21 to naturally swing out and forward while a pedal remains in a generally horizontal attitude. This is best shown in figure 3.

Threaded opening 24 of swing arm 21 progressively increases its distance from main drive shaft 4 during rotation of crank arm 10 as shown by distance marker 45 and pedal track 48 at the horizontal position. The increase distance experienced by pedal connection opening 24 of coupling swing arm 21 effectively provides a progressively extending crank arm with greater moment leverage to increase torque force to main drive shaft 4. Upon further rotation of crank arm 10, pedal track 48 shows a continuing progressive increase in distance of opening 24 from main shaft 4 whilst progressing to a vertical down position at 6 o'clock. Upon full rotation of pedal arm 10 pedal track 48 shows a progressive decrease in distance of opening 24 from crank ^•shaft 4 whilst maintaining a generally vertical orientation when traveling from the 6 o'clock position.

Due to the nature of the coupling of swing arm 21 to crank arm 10 by way of bearing 19 of crank arm 10, swing arm 21 maintains a generally vertical orientation according to the axis points 34 and 35 ( see figure 5) and is allowed a 360 degree rotation without restriction relative to pedal arm 10 during the course of its rotation.

Figure 7 shows a primary drive assembly attached to a bicycle frame 49 and pedal arm 10 various radial positions during 300 degree rotation about drive shaft 4. Figure 7 shows a relationship between a rider seat position 80 and location of swing arm 21 during rotation of crank arm 10. The use of swing arm 21 takes into consideration the overall geometry of the bicycle, and in particular the relationship of a seat position of the bicycle relative to the crank arm rotation allowing swing arm 21 to increase the moment arm applied through a pedal back to drive shaft 4 at during a down stroke on the pedal. The seat location 80 of the bicycle is preferably oriented above and rear of shaft 4 .This orientation results in a resultant rider force on a pedal having vertical and horizontal components. As a result the rider imparts forces to the drive shaft at an angle from the hip of the rider according to figure 7. The angle of force line 50 ( see also figure 4) shows that pedal connection point opening 24 follows a pedal track path 48, which is a greater distance away from shaft 4 compared to the axis track 47 of opening bearing 19 and distance marker 32 ( see figures 4 and 5).

Figure 8 shows an exploded view of a bicycle drive assembly 50 including a bicycle frame 51 ( abbreviated) terminating in sleeve 52 which receives and retains therein a primary drive shaft 53. In the embodiment of figure 8, the view of the bicycle frame is opposite to that shown in figure 1 in that crank arm 54 is mounted on the same side as drive sprocket 55 unlike figure 1 which shows crank arm 10 mounted on the opposite side to drive sprockets 7, 8 and 9. Sprocket 55 receives a conventional drive chain (not shown) which transmits drive to rear wheel sprockets in an arrangement known in the prior art. Crank arm 54 attaches to shaft 53 via opening 56 in proximal end 57. Opening 56 has a taper which engages a corresponding taper on shaft 53. Crank arm 54 terminates in distal end 58 which includes threaded opening 59. Opening 59 receives and retains connection assembly 60 which retains pedal 61 via threaded arm 62. Assembly 60 allows arm 62 of pedal 61 to rotate relative to pedal arm 54 during rotation of crank arm 54. Assembly 60 comprises, according to the non limiting embodiment of figure 8, a mounting member 63 having a housing 64 defining an internal space 65. Extending from housing 64 is a threaded connector 66 which is received and retained in opening 59 of crank arm 54. Internal space 65 of mounting member 63 receives and retains bearing 67 which is connected to collar 68 via circlip 69. Circlip 69 is retained in groove 70 which allows bearing 67 to rotate freely relative to collar 68. Collar 68 is tightly retained in space 65 by friction fitting against internal wall 71 of housing 64. Bearing 67 and collar 68 are locked into housing 64 by locking ring 72 which includes an internal 73 thread which engages a corresponding external thread 74 on housing 64. Once locking ring 72 secures bearing 67 inside housing 64 , bearing 67 can freely rotate relative to collar 68. Arm 62 of pedal 61 is connected to threaded opening 75 in bearing 67 via threaded arm 62. An alternative connection regime to that described above may be employed provided it allows opening 75 to rotate relative to and during rotation of crank arm 54. Crank, arm 54 rotates about drive shaft 53 in a conventional manner. Crank arm rotates through 0- 360 degrees. A longitudinal central axis 76 extends through threaded connector 66 and a -second longitudinal axis 77 extends through threaded arm 62. Axes 76 and 77 are parallel but axis 77 is offset relative to axis 76. In a conventional bicycle a longitudinal axis through threaded arm 62 of pedal 61 coincides with axis 76 through crank arm 54. Axes 76 and 77 are not co linear in the embodiment of figure 8 so an eccentricity is maintained. The distance between axes 76 and 77 provides an addition to the moment arm of crank arm 54 as pedal arm rotates. Using the clock compass as a reference, the crank arm 54 rotates from 12 O' clock to 12' O clock. In a typical rotation of the crank arm 54 as the crank arm 54 approaches 3 o clock, threaded pedal arm 62 is located at a limit of distance distally beyond axis 76. A rider usually places maximum load on the pedal 61 when pedal arm 54 is between 3 o' clock and 6 O clock. During this arc of rotation and due to the eccentricity of pedal arm 62 and increased moment arm during that arc of travel, increased torque is generated about drive shaft 53 compared to that which would be generated by the same load applied to a pedal of a conventional bike. Opening 75 of bearing 67 is free to rotate through - 360 degrees.

An advantage of the invention is that the mechanical advantage of an increased crank 1 arm length is achieved with a minimum of parts, with an assembly taking up a relatively small space, which is lightweight, simple and inexpensive to manufacture. The increased pedal arm length obtained by the assembly of the invention increase torque during rotation of the crank arm and through an arc of crank arm rotation when rider applied load is at a maximum thereby increasing torque compared to the same load applied to a conventional pedal and fixed length crank arm. Also, using the connection assembly according to the embodiments of the invention described, ground clearance is not compromised on the down stroke of the pedal even though there is a slight reduction in clearance. The natural extension provided by the rotation of threaded pedal arm 62 of pedal 61 during rotation of the crank arm 54 causes the diameter of the pedal arm arc to increase marginally when the crank arm 54 is oriented vertically. As a result of this the legs of the rider during the crank arm rotation reach further down compared to a conventional fixed length pedal arm. marginally reduced. Preferably the crank arm 54 when in a vertical position the is identical to a corresponding pedal position of a standard traditional pedal arm. A riders seat can be adjusted to select a preferred knee height during rotation. Most rider's legs are capable of accommodating the increased vertical down position of the crank arm incorporating the present invention. Furthermore the ground clearance of the average bicycle is more than adequate to allow for the marginally increased down travel caused by the connection assembly. Bicycles which are manufactured to accommodate the rotating pedal connection assembly may be provided with a slightly elevated drive shaft. Nevertheless, the assembly which increase the moment arm can be retrofitted to existing bicycles.

It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention as broadly described herein without departing from the overall spirit and scope of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1 A pedal drive assembly for a bicycle, the assembly including; a primary drive shaft mounted on a bicycle frame and having respective first and second ends extending beyond the frame; the first and second ends receiving and retaining thereon respective first and second crank arms; said first and second crank arms engaging respective first and second ends of said shaft via a coupling on each crank arm; the crank arms each comprising at a distal free end an off set coupling assembly including a first shaft which engages the free end of the crank arm arid includes a formation offset

. relative to the first shaft and which receives and retains a pedal connection.

2 A drive assembly according to claim 1 wherein the first shaft of the offset coupling assembly is fixed to an opening in the free end of the crank arm.

^• 3 A drive assembly according to claim 2 wherein the offset formation is capable of rotation relative to an axis through the first shaft of the coupling member.

4 A drive assembly according to claim 3 wherein the offset formation in the coupling member rotates as the crank arm rotates.

5 A drive assembly according to claim 4 wherein the pedal includes a threaded connection arm which attaches to the formation of the coupling assembly.

6 A drive assembly according to claim 5 wherein the coupling assembly allows the threaded connection arm of the pedal to rotate about an axis through said free end of the said crank arm when the connection member of the pedal is connected to the formation.

7 A drive, assembly according to claim 6 wherein the formation is integral with a rotatable bearing.

8 A drive assembly according to claim 7 wherein the formation is a threaded opening arranged on the bearing so that as the crank arm rotates, the opening also rotates through a circle which is concentric with the axis through the shaft of the coupling member. 9 A drive assembly according to claim 8 wherein the crank arm connector has a thread which engages a corresponding thread in the opening in the rotatable bearing.

10 A drive assembly according to claim 9 wherein during rotation of the crank arm and bearing, a circumferential location of the opening in the bearing is relative to a circumferential position of the crank arm as it rotates about the primary drive shaft.

11 A drive assembly according to claim 10 wherein as the crank arm rotates about the drive axis, the coupling assembly moves between a first location in which at least part of the coupling member extends distally beyond the axis through the first shaft to a maximum extent in a direction along a longitudinal axis of the crank arm and a second location in which the coupling assembly extends proximally along the longitudinal axis of the crank arm.

12 A drive assembly according to claim 11 wherein the opening in the bearing rotates in a circle having a first radial size.

13 A drive assembly according to claim 12 wherein the crank arm rotates in a circle having a second radial size. 4 A drive assembly according to claim 13 wherein the crank arm and coupling assembly bearing rotate simultaneously. 5 A bicycle drive assembly including a crank arm having a proximal end which is mounted on a primary drive shaft and distal end which receives and retains thereon a coupling assembly, the coupling assembly including a shaft which engages the distal end of the crank arm and a formation which is offset relative to and is capable of rotation about an axis of the coupling assembly shaft; wherein, the rotation of the coupling assembly extends beyond the distal end of the crank arm during drive rotation of the crank arm thereby increasing torque transmitted to the primary drive shaft.

6 A pedal drive assembly for a bicycle, the assembly including a pair of crank arms each attached via a proximal end to a primary transverse drive shaft and each having at an opposite distal end an opening capable of receiving and retaining a coupling member; each coupling assembly including a shaft which engages said distal end opening and a formation which is capable of rotation about the coupling assembly shaft as the pedals rotate about the primary transverse drive shaft.

7 A pedal drive assembly for a bicycle, the assembly including; a primary drive shaft mounted on a bicycle frame and having respective first and second ends extending beyond the frame; the first and second ends receiving and retaining thereon respective first and second crank arms; said first and second crank arms engaging respective first and second ends of said shaft via a coupling on each crank arm; the crank arms each comprising at a distal free end an off set coupling assembly including a first shaft which engages the free end of the pedal and a bearing which includes a formation offset relative to the first shaft and which receives and retains a pedal connection. 18 A drive assembly according to claim 17 wherein the first shaft of the offset coupling assembly is fixed to an opening in the free end of the crank arm.

19 A drive assembly according to claim 18 further comprising a bearing which rotates to allow rotation of the offset formation relative to an axis through the first shaft of the coupling member.

20 A drive assembly according to claim 19 wherein the offset formation in the coupling member rotates as the crank arm rotates.

21 A drive assembly according to claim 20 wherein the pedal includes a threaded connection arm which attaches to the formation of the coupling assembly.

22 A drive assembly according to claim 22 wherein the coupling assembly allows the threaded connection arm of the pedal to rotate about an axis through said free end of the said crank arm when the connection member of the pedal is connected to the formation.

23 A drive assembly according to claim 22 wherein the formation is a threaded opening arranged on the bearing so that as the crank arm rotates, the opening also rotates through a circle which is concentric with the axis through the shaft of the coupling member.

24 A drive assembly according to claim 23 wherein the threaded connection arm of the pedal has a thread which engages a corresponding thread in the opening in the bearing.

25 A drive assembly according to claim 24 wherein during rotation of the crank arm and bearing, a circumferential location of the opening in the bearing is adopted relative to a circumferential position of the crank arm as it rotates about the primary drive shaft.

26 A drive assembly according to claim 25 wherein, the coupling assembly includes a housing which receives and retains the bearing.

27 A drive assembly according to claim 29 wherein the bearing is retained in the housing by a locking collar connected to the housing via co operating threads.

28 A crank arm for a pedal drive assembly for a bicycle; the crank arm comprising at a distal free end an offset coupling assembly including a first shaft which engages the free end of the crank arm and includes a formation offset relative to the first shaft and which receives and retains a pedal connection.

29 A crank arm according to claim 28 wherein the first shaft of the offset coupling assembly is fixed to an opening in the free end of the crank arm.

30 A crank arm according to claim 29 wherein the offset formation is capable of rotation relative to an axis through the first shaft of the coupling member.

31 A crank arm according to claim 30 wherein the offset formation in the coupling member rotates as the crank arm rotates.

32 A crank arm according to claim 31 wherein the pedal includes a threaded connection arm which attaches to the formation of the coupling assembly.

33 A crank arm according to claim 32 wherein the coupling assembly allows the threaded connection arm of the pedal to rotate about an axis through said free end of the said crank arm when the connection member of the pedal is connected to the formation.

34 A crank arm according to claim 33 wherein the formation is integral with a rotatable bearing.

35 A crank arm according to claim 34 wherein the formation is a threaded opening arranged on the bearing so that as the crank arm rotates, the opening also rotates through a circle which is concentric with the axis through the shaft of the coupling member. 36 A crank arm according to claim 35 wherein the crank arm connector has a thread which engages a corresponding thread in the opening in the rotatable bearing.

37 A crank arm according to claim 36 wherein during rotation of the crank arm and bearing, a circumferential location of the opening in the bearing is relative to a circumferential position of the crank arm as it rotates about the primary drive shaft.

38 A pedal drive bicycle including a primary transverse drive shaft mounted on a bicycle frame and having respective first and second ends extending beyond the frame; the first and second ends receiving and retaining thereon respective first and second crank arms; said first and second crank arms engaging respective first and second ends of said shaft via a coupling on each crank arm; the crank arms each comprising at a distal free end an off set coupling assembly including a first shaft which engages the free end of the crank arm and includes a formation offset relative to the first shaft and which receives and retains a pedal connection.