WO2008012521A1

WO2008012521A1 - Bicycle pedal crank drive unit

Info

Publication number: WO2008012521A1
Application number: PCT/GB2007/002810
Authority: WO
Inventors: Andrew James Smith
Original assignee: Andrew James Smith
Priority date: 2006-07-26
Filing date: 2007-07-24
Publication date: 2008-01-31
Also published as: WO2008012521B1

Abstract

An improved bicycle pedal crank assembly that allows a longer lever arm between the foot pedal and the crank assembly bottom bracket centre line during the power stroke; on the return stroke the lever arm distance is shortened. A linear bearing or similar device is mounted onto the end of the bottom bracket assembly, the crank itself reciprocating in and out of said bearing. Cams that optimize the pedal motion are located at both ends of the bottom bracket housing.

Description

BICYCLE PEDAL CRANK DRIVE UNIT

FIELD OF THE INVENTION

[002] The present invention relates to the drive unit of a bicycle or the like, and more particularly relates to an improved pedal crank mechanism.

BACKGROUND OF THE INVENTION

[003] Bicycles to date use a pedalling action whose crank length is fixed and whose motion is circular about a central axis, the longer the crank the more torque generated but at the expense of a larger pedal orbit.

[004] Bicycles have gearing to allow the rider to decide which gear ratio is appropriate for a given application; this consequentially determines the distance that the bike moves forward with each pedal stroke. For example, a normal chain driven bicycle has wheels that are 66cm(26inch) in diameter. The "lowest" gear ratio might be a front chain wheel with 22 teeth and a rear gear having 30 teeth That means that the gear ratio is 0.73-to-l. For each pedal stroke, the rear wheel turns 0.73 times. In other words, for each pedal stroke, the bicycle moves forward 151.5cm that is equivalent to 5.4 km/h at a 60 rpm pedalling rate). The "highest" gear ratio on the bike might be a front chain wheel with 44 teeth and a rear gear having 11 teeth That creates a 4-to-l gear ratio. With the same 66cm diameter wheels, the bicycle moves forward 830cm with each pedal stroke. At a 60-rpm pedalling rate, the speed of the bike is 29.9 km/h. By doubling the pedalling rate to 120 rpm, the bike has a maximum speed of 59.8 km/h This speed range (5.4 - 59.8 km/h) allows the rider to climb the steepest hill very slowly or enables him to go faster when the terrain or conditions are appropriate.

SUMMARY OF THE INVENTION

[005] The present invention has been made to facilitate the conventional cycling operation by creating a longer crank arm lever on the power stroke. This crank arm moves radially in and out during each crank arm revolution and by design advantageously limits the height to which the leg thigh raises during this rotational movement thereby reducing the effort required to complete the rotational movement of the crank arm and additionally magnifying the power stroke at the same time. [006] In this embodiment the crank shaft reciprocating guide device is shown as being preferably a linear bearing and is mounted onto the end of the bottom bracket axle and guides the linear motion of the crank arm during rotation about the bottom bracket centre line.

[007] Most pedal motions associated with similar cam controlled designs have had circular movements having the same constant diameter and whose centres are offset from the bottom bracket centre line. As a result of the present invention's cam profile path here specifically and preferably anon-circular pedal motion is obtained as shown as an example in this embodiment, but not limited to being, an elliptical movement. The cam itself can be either a male with outer profiled faces as shown in FIG 9 or female and here in this embodiment the female cam profile has been used as the example to demonstrate the principle of the invention. [008] The preferred embodiment utilises a 'chainless' shaft-driven drive system (FIG

1) that transmits the rotational movement of the pedal orbit through 90 degrees, along a drive shaft and then returns the drive 90 degrees to directly drive the back wheel; said back wheel incorporating an internally geared rear hub.

[009] Another embodiment of the invention uses a conventional chain driven bicycle as shown in FIG 2.

[010] Another embodiment of the invention incorporates a hydraulic drive system located in the place of the normal bottom bracket.

[011] Both the shaft-driven drive system, the internally geared rear hub and the hydraulic drive are known to those in the art.

ADVANTAGES

[012] The present invention improves upon the current art by enabling the bicycle to move Easier, Faster or Further ΕFF' for the same energy input.

DRAWING EXPLANATION

[013] Some of the objects and advantages of the present invention having been stated, others will appear as the description proceeds when taken in conjunction with the accompanying drawings, which are not necessarily drawn to scale, wherein;

FIG 1 is a fragmentary plan view, with the front of the bicycle facing left, of the preferred shaft-driven pedal crank mechanism, whereby (1) is the pedal showing the pedal centre line, (2) is the generic number for the cam, (3) are the cam strengthening/bracing pins, (4) is the bottom bracket housing, (5) is the bottom bracket axle, (6) is the bottom bracket centre line (7) is the pedal crank shaft, (8) is the crank shaft reciprocating guidance system shown here in this embodiment as being a linear bearing, (9) is the cam follower, (10) is the chainless shaft-driven drive, (11) is a general representation of the rear wheel side frame supports, (12) is the bottom bracket and cam clamping nut, (13) is the linear bearing adaption clamp for the bottom bracket axis, and (22) is the cam follower connection shaft. FIG 2 is a fragmentary plan view, with the front of the bicycle facing left, of the pedal crank mechanism for another embodiment of the invention illustrating a conventional chain driven bicycle where (20) is a representation of a chain wheel sprocket.

FIG 3 is a fragmentary left leg side view of the pedal crank mechanism and in particular the cam profile path, the rotational movement and orbit path of the pedal, the legs forward and back lateral range, whereby (14) is the pedal orbit path and the 3,6,9 & 12 o'clock pedal positions are shown in italic font around the orbit path, the same descriptive orbit is applied to the right leg whereby the power stroke would occur at 3 o'clock when looking at the right side of the bicycle with the front wheel facing to the right.

FIG 4 is a fragmentary view of the cam profile including cross section view, whereby (2a) is the inner cam track, (2b) is the outer cam track, (15) is the removable outer cam segment used to install the cam follower/crank arm, (16) are the cam support arms, (17) are the cam support struts (18) is an example of the recessed hole for the bracing struts, (19) is the square hole for cam unit assembly to the bicycle bottom bracket / bottom bracket housing & (26) are the cam unit support and bracing strut spacers.

FIG 5 is a fragmentary cross section of the cam profile's V-shape with matching cam follower.

FIG 6 shows a fragmentary view of another embodiment of the invention and illustrates the necessary modification required to a conventional chain driven bicycle where (20) is the chain wheel sprocket representation and (21) is the cam follower reciprocating clearance slot.

FIG 7 shows the difference between the leg movement of a conventional leg trajectory for a 175mm crank and of that from the present invention.

FIG 8 is a fragmentary view of an another embodiment of the invention illustrating an alternative cam unit and cam follower configuration where (23) is an example of a cam unit whose cam follower is mounted between the bottom bracket centre line and the pedal centre line, (24) is a representation of a crank shaft sleeve and (25) is a representation of a crank shaft for said configuration.

FIG 9 is a fragmentary left leg side view of another embodiment of the invention illustrating a male cam (27) with a varying width cross section and with a plurality of cam followers, in this diagram shown as having two, mounted at the end of crank shaft (7) and at the opposite end from the pedal orbit. Said cam is not limited to having a varying width cross section and could also be of uniform width.

The same can be said of the embodiment illustrated in FIG 8 where a similar male cam could also be fitted in place of the female cam shown.

FIG 10 shows a fragmentary side view of a typical bicycle fitted with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[014] The present invention now will be described more fully hereinafter with reference to the accompanying drawings in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[015] The principle of levers is used in all common bicycle power strokes whereby the lever action comes from the pedal as it rotates at a given distance from a central point called the bottom bracket centre line. This crank length is not just a function of the riders own physical leg dimensions where typically a 20% ratio of crank to leg length is a general guide but also the intended activity such as speed trials where shorter cranks are preferred and longer endurance based activities where longer cranks are the norm.

[016] Leverage itself is a combination of the force exerted and the distance from which the force is applied. The longer the distance about the fulcrum the higher the leverage. [017] The pedalling operation for a cyclist using the current invention is the same as for a normal bicycle; the difference is that the pedal motion is controlled by the cam profile resulting preferably in a non-circular pedal orbit.

[018] As the pedal rotates the reciprocating crank shaft (T) slides back and forth held in position by the above mentioned linear guiding system (8) and follows an orbit (14) guided by the cam units profile (2) and cam followers (9).

[019] Said system is advantageously of use to any type of bicycle or similar device using a rotary pedal motion whereby the improvement is to be one of increased ease in pedalling, and/or for the same power input as a conventional bicycle, faster bicycle speed or an increase in the distance covered.

[020] Another embodiment using a cam unit to define the pedal orbit, as shown in

FIG 8, can be having a crank arrangement whereby the cam follower is mounted between the bottom bracket centre line and the pedal centre line where a sliding sleeve (24), guided by some linear means, is mounted over a fixed crank shaft (25); said sleeve connected to a cam follower which in turn follows the cam unit's (23) profile and consequently guides the reciprocating motion of the sleeve and therefore pedal position as the crank shaft rotates.

[021] There are limits in terms of ones leg capability in turning too large a pedal diameter whereby a larger diameter due to crank length causes a higher thigh movement and has a consequential larger pedal orbit. A small diameter allows a faster cadence but has a reduced lever effect.

[022] Most adult bicycles are fitted with a crank length in the 165 to 175mm range depending on the particular use intended.

[023] The present invention has, as an example in this embodiment, an effective crank length on the power stroke of 200mm so by increasing the leverage for a 165mm crank by 21.2% and for a 175mm crank by 14.3%. The preferred effective crank length for the power stroke for the current invention (defined as the horizontal distance from the bottom bracket centre line to the 9 o'clock position as shown in FIG

3) lies for a bicycle incorporating the features of the current invention in a range between 150 and 380mm.

[024] By using the preferred shaft-driven drive system (FIG 1) and lengthening the effective crank length the applied torque on the power stroke can be increased, when compared to the above mentioned normal 165/175 mm cranks, greater than 30%.

Advantageously by combining the above mentioned increased torque due to the longer leverage with an appropriate cam design which enables a smaller pedal orbit than the said 165/175mm cranks, the resulting power output can be additionally increased for the same given pedalling effort.

[025] At the same time due to the cam units profile design there are two additional benefits with the leg movement. First is that advantageously it is limited in terms of pedal orbit and consequential thigh maximum movement (FIG 7) reducing by about

10 degrees the height that the thigh raises when compared to a 175mm crank and secondly the legs lateral range in movement, as an example in this embodiment having 325 mm and which is defined as the linear horizontal distance between the 9 and 3 o'clock positions of the pedal orbit (FIG 3) and which can for a bicycle incorporating the features of the current invention be in a range of 170 and 400 mm, is in so doing kept in this example advantageously less than the equivalent distance for an even smaller 165 mm crank thereby making the cycling operation both more comfortable due to the reduced height the thigh has to travel and orbit time faster while yielding more torque on the power stroke. Optimisation of the various dimensional factors depending on the intended use of the bicycle and the rider's physical characteristics and preferences.

[026] As also shown in the example in FIG 3 the pedal motion is advantageously smooth and elliptical but can be any non circular form.

[027] One problem that is overcome by the present invention with respect to long cranks is during bicycle cornering as the rider leans into the corner whereby the end of the pedal can touch the floor at its lowest rotative position. On the current invention the anti-clockwise pedal motion shown for the left leg example (FIG 3) for the return pedal orbit from 6 to 12 o'clock is concentric, but not limited to being due to an appropriate cam unit profile design, about the bottom bracket centre line and here in the current embodiment this distance as an example is 125 mm about the bottom bracket centre line but preferably for a bicycle incorporating the features of the current invention operates in a range from 20 up to 190mm. Another advantageous consequence is that it is therefore possible to have a lower centre of gravity by reducing the bottom bracket centre line distance to the ground which improves the bicycles stability whilst still achieving the same vertical leg profile at the 6 o'clock position and at the same time allowing the rider to be able to touch the floor more comfortably with ones foot when the bicycle stops. [028] There are in this embodiment two cam units (2) as can be seen in FIG 1. Each cam unit has its profiled face facing outward from the bicycle bottom bracket frame housing whereby the right leg side cam unit is connected in a given position directly onto the shaft driven drive shaft housing which in turn is securely mounted to the bicycle bottom bracket frame housing and in a manner so as not to rotate. The left cam unit is mounted in a given position on the opposite outside edge of the bottom bracket housing (4) and preferably has a square section outer form machined at the end of said housing to ensure an accurate cam unit fit and to avoid rotation, this part mating with the cams support central axis which has a corresponding square hole to ensure positive location, with final securing to the machine frame done by means of an internally threaded clamping ring (12) or similar securing device which clamps both the cam unit and bottom bracket to the bicycle. It is of course possible to mount only one cam unit specifically for a single leg to benefit from the inventions improvements.

[029] Each cam unit is preferably supported by a plurality of finger supports in this embodiment shown with a three finger support (16) mounted at 120 degrees as shown in FIG 4, the purpose of which is three fold, to give rigidity, to reduce weight and to reduce dirt accumulation areas.

[030] As shown in FIG 4 the inner cam profile (2a) and outer cam profile (2b) profiles are additionally supported by a plurality of bracing struts (17) in this embodiment shown with three, said support fingers and bracing struts preferably connect to the inner and outer cam profiles by means of spacers (26) which reduce weight and dirt accumulation areas. In another embodiment using a male cam the bracing struts are no longer necessary.

[031] As shown in FIG 1 the cam units (2) are joined preferably by a plurality of strengthening phis (3) hi this embodiment shown having five whose purpose is to stabilize the whole cam structure in such a way as render it free from any lateral torsion or vibration. Each strengthening pin preferably locates in a recessed hole (18) located either at the rear of the cam units profile finger supports (16) or the rear of the bracing struts (17) to magnify the stability of said cam unit. In another embodiment using a male cam the use of strengthening pins is also preferred. In another embodiment it is of course possible to secure the cams by some means direct onto the bicycle frame.

[032] The cam profile has preferably a formed shape which could be square, rounded, 'V shaped or any other form and for the current embodiment is illustrated as having an angular 'V form on the inner (2a) and outer (2b) sides with correspondingly formed cam follower in the centre as shown in FIG 5. Dirt ingress into the cam profile track is inevitable and is treated in this design by having as few as possible dirt collection points in the cam unit construction to avoid contamination and secondly having the cam units design, due to its 'V shape, made to dispel dirt outwards away from the cam follower (9) and cam profile face.

[033] The cam follower (9) can for each left and right leg cam unit, each unit comprising said inner (2a) and outer (2b) cam profiles as shown in FIG 4, be either singular as shown in FIG 5 or can incorporate two cam followers for each cam unit, where said purpose is to follow the respective cam profile and to allow for the change in the working rotation of the cam follower as the cam followers orbit their respective working cam profile face. In another embodiment as shown in FIG 9 using a male cam there would be a plurality of cam followers for each cam unit. [034] Also shown in this embodiment in FIG 4 incorporated on each of the left and right leg outer cam unit profiles (2b) is a removal cam segment (15) to allow the cam follower to be fitted into the cam profile track. Said segment can be located either on the inner (2a) or outer (2b) cam profiles and can occupy any portion of the cams periphery.

[035] Mounted onto each of the two bottom bracket crank shafts (7) is the crank guiding system the preferred embodiment being a linear bearing (8) but can be a bush and shaft or any similar low friction unit that allows a guided reciprocating crank shaft motion.

[036] The above mentioned said linear bearing (8) is shown in this embodiment as having an additional adaption piece (13) that allows the bottom bracket crank shaft axle (5) to be connected to said linear bearing, however with the benefit of high volume production of the invention the adaption piece can be incorporated in the design of the preferred linear bearing so that the bearing clamps directly onto the bottom bracket axle.

[037] As shown in FIG 1 at one end of each crank shaft (7), the pedal (1) is attached and at the other end is the cam follower connection shaft (22), both the pedal shaft and cam follower connection shaft are to be securely fitted with recessed lugs or other means onto the crank shaft to enable a robust and solid fitting. The connection shaft (22) supports the cam follower (9). On the power stroke, as can be seen in FIG 1 where the right leg is at the power stroke position, the respective cam follower's (9) centre line is positioned as close as possible to the bottom bracket centre line (6) and in a range between 20 to 100 mm from said bottom bracket centre line, consequently said guide units physical centre can be offset from that of the bottom bracket centre line and in a direction toward the pedal (1). In another embodiment using a male cam this range applies to the cam follower closest to the bottom bracket centre line. [038] The drive system to the rear wheel has, as previously mentioned, at least three variations the preferred embodiment being the shaft-driven drive system (FIG 1) coupled to an internally geared rear hub in the rear wheel to those known in the art. Alternatively another example of the embodiment is using a conventional chain drive where the chain wheel sprocket (20) has a slot cut (21) in it to provide clearance for the reciprocating motion of the cam follower connection shaft (22) as shown in FIG 6. Another embodiment of the invention incorporates a hydraulic drive system located in the place of the normal bottom bracket.

[039] Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. For example, any device that would utilize the above mentioned cam units profile contour in order to (1) maximize the leverage principle in order to magnify the torque on the effective power stroke for whatever reason or (2) to have a faster return movement back to the power stroke position in its rotational cycle or (3) to have an effective increase in the number of revolutions for the same energy input (or any combination of the three) where the rotating power source be generated either manually or mechanically or electrically is encompassed by the current invention and any of the claims therein. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A bicycle pedal crank drive unit comprising a cam unit whose profile predetermines the pedal motion about the bottom bracket centre line; a system for effectively varying the length of the crank shaft to enable a longer crank arm on the power stroke.

2. A bicycle pedal crank drive unit according to claim I₅ which has a cam unit (2) whose profile creates a pedal motion which is non circular (14) about the bottom bracket centre line (6)

3. A bicycle pedal crank drive unit according to claim 2, where said pedal orbit (14) can have an effective crank length at the power stroke, which is defined as the horizontal distance between the pedal centre line (1) and the bottom bracket centre line (6) with the crank shaft (7) fully extended, for a bicycle incorporating the features of the current invention of between 150 to 380 mm.

4. A bicycle pedal crank drive unit according to claim 2, where the return pedal orbit, which is defined as the pedal orbit path opposite the power stroke and is for the left leg example between the 6 to 12 o'clock positions about the said bottom bracket centre line and in an anti-clockwise direction as shown in FIG 3 (with the same logic extrapolated to the right leg where the return pedal stroke would be between 12 and 6 o'clock in a clockwise direction), of between 20 and 190mm from the bottom bracket centre line, with said orbit in this area not limited to being concentric about the bottom bracket centre line.

5. A bicycle pedal crank drive unit according to claim 4, where it is possible to lower the centre of gravity of the bicycle and hence rider by reducing the bottom bracket centre line distance to the ground.

6. A bicycle pedal crank drive unit according to claim 1, which have the cam followers (9) preferably mounted at the end of the crank shaft (7) as shown in this embodiment in FIG 1.

7. A bicycle pedal crank drive unit according to claim 2, who in another embodiment using a cam unit profile to define the pedal orbit, as shown in FIG 8, can have a crank arrangement whereby the cam followers are mounted between the bottom bracket centre line and the pedal centre line where a sliding sleeve (24), guided by some linear means, is mounted over a fixed crank shaft (25); said sleeve is subsequently connected to the cam followers which follow the cam unit's (23) profile and consequently guides the reciprocating motion of the sleeve and therefore pedal position as the crank shaft rotates.

8. A bicycle pedal crank drive unit according to claim 1, which has a crank shaft reciprocating guide unit preferably as shown in this embodiment as being a linear bearing (8) but can be a bush and shaft or any similar low friction unit that allows a guided reciprocating crank shaft motion and is effectively mounted directly onto the bottom bracket tapered square or splined axle (5) thereby rotating and reciprocating in a fixed orbit path about the bottom bracket centre line.

9. A bicycle pedal crank drive unit according to claim 1, which on the power stroke, as can be seen in FIG 1 where the right leg is at the power stroke position, has the cam follower's (9) centre line positioned as close as possible to the bottom bracket centre line (6) and in a range between 20 to 100 mm from said bottom bracket centre line, said cam follower/s secured to the crank shaft (7) and positioned at the opposite end of the crank shaft to the power stroke, consequently said guide units physical centre can be offset from that of the bottom bracket centre line and in a direction toward the pedal (1).

10. A bicycle pedal crank drive unit according to claim 1, which have a plurality of cam units in this embodiment shown as having two cam units (2) as shown in FIG 1 mounted in a given position effectively at either end of the bottom bracket housing (4) and fixed in a manner so as not to rotate.

11. A bicycle pedal crank drive unit according to claim 1, which has an inner (2a) & outer cam profile face (2b) with corresponding cam follower whose form is preferably 'V shaped as shown in FIG 5 but could be any other form.

12. A bicycle pedal crank drive unit according to claim 7, that incorporates a removable segment (15) either in the inner (2a) or outer (2b) cam unit profiles to allow the cam follower (9) to be fitted into said cam profile track.

13. A bicycle pedal crank drive unit according to claim 1, who in another embodiment has a male cam (27), as shown in FIG 9, preferably with a varying width cross section and with a plurality of cam followers, in this diagram shown as having two, mounted at the end of crank shaft (7) and at the opposite end from the pedal orbit. Said cam is not limited to having a varying width cross section and could also be of uniform width.

14. A bicycle pedal crank drive unit according to claim 1, which, when compared to normal 165/175 mm cranks, reduces the height to which the leg thigh raises during the cranks rotational movement as a direct result of the cam profile design, as shown in FIG 7.

15. A bicycle pedal crank drive unit according to claim 1, which has a horizontal linear distance as shown in FIG 3 between the 3 o'clock and 9 o'clock positions of the pedal orbit that can preferably for a bicycle incorporating the features of the current invention of between 170 mm and maximum of 400 mm.

16. A bicycle pedal crank drive unit according to claim 1, who in this preferred embodiment incorporates a 'no chain' shaft-driven drive (FIG 1) with rear wheel incorporating an internally geared rear hub.

17. A bicycle pedal crank drive unit according to claim 1, who in another embodiment when incorporated into a conventional chain driven bicycle (FIG 2 and FIG 6) incorporates a slot (21) that is either machined into or falls in an open segment of the chain wheel sprocket to allow the cam follower connection shaft (22) reciprocal movement.

18. A bicycle pedal crank drive unit according to claim 1, who in another embodiment can be combined with a hydraulically driven drive to either the front or rear wheel.