FR2742408A1 - Crankset with no neutral position - Google Patents

Abstract

The crankset comprises two coaxial crank spindles mounted in a crank tube (2). The external spindle (8) rotates around a first axis (10) in crank tube bearings and is fixed to the first crank (11). The internal spindle (9) rotates in second bearings in the external spindle and is connected to the second crank (13). Each spindle has a radial arm (20,22) adjacent to one or more chain wheels driving a chain transmission. The axis (25) of the chain-wheel carrier (15) is moved forward relative to the spindles and the carrier is coupled to each radial arm by a hinged connecting rod. Seals (42,46,53) are placed inside the crankset tube to protect the spindle bearings (45,48,51) from the environment.

Description

CRANKSET WITHOUT DEAD POINT
The present invention relates to a crankset without dead center, in particular for a bicycle, comprising: a fixed bottom bracket tube, a hollow outer shaft mounted for rotation about a first axis by first bearings in the bottom bracket tube and integral with a first crank, an inner shaft rotatably mounted by first bearings coaxially in the outer shaft and secured to a second crank, sealing means for ensuring leaktight protection of said bearings vis-à-vis the outside of the crankset, an output element mounted for rotation about a second parallel axis and offset with respect to the first axis on an eccentric element fixed to the bottom bracket tube, the output element being intended to drive a mechanical transmission, and two articulated connections connecting the 'output element respectively to each crank or each shaft.

 The invention applies in particular to bicycle cranksets, but also to any other case of use of a crankset driven by muscular force, for example for propelling any vehicle or for actuating a machine, a fan, a electric generator, etc.

 In a conventional crankset, the vertical position of the cranks in the same radial plane constitutes a neutral position, because the weight of the pedaler cannot produce a torque on either of the two cranks in this position.

To eliminate this drawback, it has been proposed for more than 60 years to center the toothed plate which drives the chain of a bicycle forwards, to separate the cranks from one another and from the plate to allow them a reciprocal angular play, and to connect each crank or its shaft to the plate by an articulated connection capable of absorbing the radial movements due to the eccentricity. Patent documents FR 763'303,
FR 905'476, FR 984'583, FR 2'526'392, FR 2'584'671,
US 4'159'652 and US 5'067'370 describe such bottomless pedalboards. However none of these pedalboards has imposed itself commercially, probably because of problems of realization and resistance to the effects of water and dirt, because sealing is difficult to ensure due to the multiplicity of moving parts.

 In a crankset of the kind indicated in the preamble, described in document WO 86/05459, each of the two articulated connections between the corresponding shaft and the plate serving as an output element comprises a radial arm made in one piece with the shaft and oriented in the same direction as the corresponding crank. To transmit an approximately tangential force and therefore a torque to the plate, the connection comprises either a roller carried by the plate and engaged in a radial slide of the arm, or an oscillating disc housed in the arm and provided with an eccentric pin engaged in the tray. This articulated mechanism is protected, on the outside of the plate, by a circular casing fixed to the plate, having a front flange provided with a central opening to let pass the internal shaft carrying the crank on this side. This opening is large enough to allow the oscillating rotary movement of the housing relative to the shaft, because of the eccentricity; it is closed internally by a flange integrated in the shaft, a seal in the form of an annular disc being placed between the two flanges so as to slide on one of them. Part of the sliding surface on this flange is thus sometimes covered by the lining, sometimes exposed to the open air. Soiling that reaches it can therefore get into the joint, quickly deteriorate the seal, reach the bearings and damage them, which led to abandon the marketing of this type of crankset. the transverse size of the casing containing the two radial arms between the plate and the corresponding crank, requiring also to move the other crank away to maintain symmetry with respect to the median plane of the bicycle.

 The present invention relates to a crankset capable of avoiding the aforementioned drawbacks, while ensuring a lasting seal of the bearings of the shafts, which are generally bearings, and allowing a compact and light construction. An additional aim is to arrange the articulated connection in a simple, effective form which withstands the external ambient conditions.

 In its general form, the invention relates to a crankset of the kind indicated in the preamble, characterized in that the sealing means comprise first sealing means, disposed around the outer shaft in the bottom bracket tube and protecting the first bearings vis-à-vis the outside of this tube, and second sealing means, arranged in the outer shaft and protecting the second bearings vis-à-vis the outside of this shaft.

 Thus the rolling bearings of the crank shafts, which are the most sensitive to dirt, can be protected by seals located entirely inside the bottom bracket tube, radially between coaxial rotating parts, especially between cylindrical surfaces of these parts. These linings can be of a known and proven type, occupying little space and giving satisfaction in conventional cranksets. There is no need for an external casing, each articulation of the articulated connections can easily be produced by a sealed bearing, commercially available.

 In a particularly advantageous embodiment of a crankset according to the invention, each of said articulated links comprises a link having an end connected to the output element by a first articulation, the other end of said link is connected to the corresponding shaft or to the corresponding crank by a second articulation, and said first articulation is located near a radial plane passing through the first and the second axis when the corresponding crank is in a horizontal downward position. This results in ease of construction and an improvement in the efficiency of the crankset.

Other characteristics and advantages of the invention will appear in the following description of a preferred embodiment of a bicycle crankset, presented by way of example with reference to the accompanying drawings, in which
FIG. 1 is a perspective view of the bicycle crankset according to the invention,
FIG. 2 is a side elevation view of the bottom bracket,
FIG. 3 is a sectional view of the crankset in the plane of its two parallel axes, this plane being for example horizontal, and
FIG. 4 is a diagram in elevation showing eight successive positions of the cranks of the crankset,
FIG. 5. represents the evolution of the torque transmitted to the chainrings on a turn of the pedal, when the cyclist exerts only a downward vertical force on the pedals,
- Figure 6 shows the evolution of the speed of rotation of each crank on a turn of the pedal, for a constant speed of the chainrings.

 Referring to Figures 1 to 3, the bottom bracket 1 has a bottom bracket tube 2 which is incorporated into a bicycle frame 3, this frame comprising tubes 4, 5, 6 and 7, one end of each tube being welded to tube 2 An outer shaft 8 and an inner shaft 9 are mounted in the tube 2 in a rotary and coaxial manner, to rotate around a first axis 10. A left crank 11 provided with a pedal 12 is removably fixed on the outer shaft 8, and a right crank 13 provided with a pedal 14 is removably attached to the inner shaft 9. On the right side of the bicycle, the crankset 1 has a chainring 15 on which, in a conventional manner , are mounted three removable plates 16, 17 and 18 intended to drive the rear wheel of the bicycle by a chain transmission. The plates are fixed by means of screws 19. In a radial plane located between the plate holder 15 and the right crank 13, the outer shaft 8 has a radial arm 20 whose free end is connected to the plate holder by an articulated link 21. Similarly, the inner shaft 9 has a radial arm 22 whose free end is connected to the tray holder by an articulated link 23. The arms 20 and 22 extend in respective directions approximately opposite, but oscillating angularly with respect to each other during the rotation of the crankset, as well as the cranks.

 In FIGS. 2 and 3, it can be seen that the plate carrier 15 is mounted eccentrically with respect to the crank shafts 8 and 9, its axis of rotation 25 having an eccentricity E with respect to the axis 10 of the shafts. The tray holder 15 is mounted on a stationary eccentric 26 by means of a pair of ball bearings 27 centered on the axis 25. The eccentric 26 has a cylindrical end piece 28 centered on the axis 10 and provided with a external thread enabling it to be screwed into a corresponding thread on the bottom bracket tube 2. The end piece 28 also carries a lock nut 29 which is blocked by screwing against the tube 2 to block the angular position of the eccentric 26. Thus, by loosening the lock nut 29, it is possible to rotate the eccentric 26 to orient the eccentricity E in any desired direction. This direction is horizontal towards the front in the example shown. In known manner, it follows that when one of the cranks 11, 13 is in the vertical plane passing through the axis 10, that is to say at its neutral point, the other crank is located in front of this plane and can produce a torque, as will be explained with reference to Figure 4.

 In Figure 3, the links 21 and 23 are not shown, to clarify the drawing and reveal the construction of their joints.

The articulation of each link 21, 23 on the corresponding arm 20, 22 is produced by a sealed rotary roller 31 whose axis 32 is fixed in the arm by means of a locking screw 33. The roller 31 is driven into a corresponding hole in the link. The articulation of each link on the tray holder 15 is produced by another sealed rotary roller 34 whose axis 35 is threaded and held in an orifice of the tray holder by means of a threaded clamping bush 36. The rollers 31 and 34 may for example be of the KR19C.DZ type from the company
FAG. The two links 21 and 23 have the same dimensions, and their articulations formed by the two rollers 34 on the tray holder 15 are diametrically opposite with respect to the axis 25.

 Figure 3 also shows the construction inside the bottom bracket tube 2, which is internally threaded at its two ends to receive respectively the eccentric 26 on the right and, on the left, an externally threaded bush 38 capable of being blocked at the by means of a lock nut 39 similar to the lock nut 29. The socket 38 has three inner bearing surfaces of staggered diameters to center respectively a first tubular spacer 40, a pair of ball bearings 41 carrying the outer shaft 8, and a gasket sealing ring 42 of the same type as those used in conventional bicycle pedals. The shaft 8 is fixed axially on the bearings 41 by means of a circlip 43 and a washer 44 taken between the inner ring of one of the bearings 41 and a shoulder of the shaft. The outer ring of the same bearing 41 axially abuts the first spacer 40, the other end of which abuts the end piece 28 of the eccentric 26. To the right, the outer shaft 8 is supported in the eccentric 26 by another bearing, formed by a bearing with needles 45 closed externally by an annular seal 46 similar to the seal 42.

 The outer shaft 8 is hollow, its inner bore having three successive staggered diameters, the smallest of which constitutes an access hole 54 allowing the passage of a screwdriver. In service, this hole is closed by a removable waterproof plug 47. The rest of the bore of the outer shaft contains the inner shaft 9 and its bearings. These are formed by a pair of ball bearings 48 whose inner rings are locked by tightening by means of an inner washer 49 and a screw 50, and on the other hand by two needle bearings 51 separated by a second spacer 52 and protected from the outside by an annular seal 53 closing the gap between the two shafts.

 Thus, the two shafts 8 and 9 are mounted in a perfectly rigid manner inside the bottom bracket tube 2, while the sealing of their bearings is entirely ensured by the tight annular seals 42, 46 and 53 radially between two coaxial cylindrical surfaces. These seals have relatively small diameters and are well protected in the bottom bracket tube, which gives them a long service life.

In addition, the construction described above makes it possible to assemble the crankset in advance, out of the tube 2, then to assemble it in a block in this tube. The assembly is carried out as follows
- Drive out each roller 31 in the corresponding link 21, 23.

 - engage the axis 32 of each roller 31 in the corresponding arm 20, 22 and block it by means of the screw 33.

 - drive the two bearings 27 out of the eccentric 26.

 - drive out the tray holder 15 on the bearings 27.

 - fix the large plate 18 and the medium plate 17 to the plate holder 15.

 - fix the two rollers 34 on the tray holder 15.

 - fix the small plate 16 on the plate holder 15.

 - in the outer shaft 8, insert the washer 49, then drive out the two bearings 48.

 - drive out the first needle bearing 51, introduce the spacer 52, drive out the other needle bearing 51, then the seal 53.

 - hold the outer shaft 8 vertically and insert the screw 50 placed on a screwdriver in the hole 54.

 - insert the inner shaft 9 into the outer shaft 8. Tighten the screw 50 fairly tightly and place the plug 47.

 - Introduce the spacer 40 into the eccentric 26, then drive the needle bearing 45 into the eccentric until it touches the spacer.

Also remove the seal 46. Pull out the spacer 40.

 - screw the lock nut 29 against the eccentric 26.

 - introduce the two shafts in the eccentric 26.

 - introduce the spacer 40 into the eccentric 26.

 - place the washer 44, the width of which has been previously adjusted, on the outer shaft 8, then the bearings 41 and the circlip 43.

 - screw the assembly fully into the bottom bracket tube 2.

- unscrew the assembly until the eccentricity
E of the eccentric 26 is directed in the desired position, for example horizontally forward.

 - unscrew the lock nut 29 to block the eccentric 26 on the tube 2.

 - insert the seal 42 into the socket 38.

 - screw the sleeve 38 into the tube 2 and tighten fairly tightly.

 - put the chain on one of the plates 16 to 18.

 - mount the pedals on the cranks 11 and 13.

 - mount the cranks 11 and 13 on the profiled heads 55 and 56 of the shafts 8 and 9.

 A particularly advantageous characteristic of the crankset 1 is that the two diametrically opposite rollers 34, forming the articulations of the links 21, 23 on the chainring 15, are each arranged substantially opposite the corresponding crank 11, 13. This means that each radial arm 20, 22 is angularly offset relative to the corresponding crank, by an angle which is determined by the lengths of the link and of the arm. This offset is preferably forward in the normal direction of rotation of the crankset, in order to exert traction on the link, but it could also be in the other direction. The advantage of this position of the anchor points on the plate carrier is that, when the crank is directed forward and therefore produces the greatest driving torque, the direction of the link is approximately perpendicular to the direction of the eccentricity E, which allows the maximum torque to be transmitted optimally to the tray holder, as will be seen below.

This advantage is largely preserved if the eccentricity is given a direction other than horizontal, provided that it is directed forward.

FIG. 4 represents eight successive positions ah of the right crank 13, with its radial arm 22, its link 23 and the rollers 31 and 34 forming the articulations of the link, for eight successive positions spaced 450 from the tray holder 15. Si it is assumed that the bicycle is traveling at a constant speed and that the angular speed of the chainring is therefore constant, the eight positions are regularly spaced over time. In Figure 4, the angles of rotation 6 of the chainring and O of the crank originate from the vertical passing through the corresponding axis of rotation 25, 10. The figure is drawn for the following dimensions
Length of each arm 20.22: R1 = 60 mm
Anchor point radius 34
on the tray holder: R2 = 55 mm
Eccentricity (horizontal): E = 5 mm
Length of each link 21, 23: B = 28 mm
Arm-crank offset Ç = 270
We notice that E = R1 - R2, so that the two corresponding circles 57 and 58 are tangent. As a result, in the vicinity of position a, where the crank is directed forward and produces the maximum torque, the rod is substantially perpendicular to the radii of the two circles and therefore transmits the torque in an optimal manner, with minimal radial forces.

 The opposite positions a-e, b-f, c-g and d-h represent respective simultaneous positions of the two cranks. The angle between the two cranks is maximum in the position c-g close to the vertical, therefore perpendicular to the direction of the eccentricity E, which eliminates the dead center in a known manner. During the upward trajectory of each crank, corresponding to the positions d, e and f, the rod 23 is not perpendicular to the radii R1 and R2, but this does not matter since it then does not transmit d significant effort. On the other hand, the rod is substantially perpendicular to the spokes in the downward trajectory of the crank (positions g, h, a and d), which makes it possible to modify the direction of eccentricity by pivoting the eccentric 26, for example to adapt the crankset to the morphology of the cyclist or to his personal position on the bicycle, without affecting the performance of the crankset.

 FIG. 4 also makes it possible to understand that the arrangement of the rollers 34, that is to say the anchoring points of the links 21 and 23 on the plate holder 15 opposite each crank 11 and 13, can be changed under certain conditions while retaining the same kinematic and dynamic advantages. From the diagram in FIG. 4, suppose that the crank 13 is mounted in another orientation on its shaft 9, which amounts to choosing another value for the angle 4 between the crank and the corresponding radial arm 22. example, let us admit that in position a of the mechanism, we disassemble the crank 13 horizontal and we reassemble it vertically upwards, by proceeding also symmetrically with the other crank, this amounts to adding 90 "to Ç and removing 90" to O without changing anything to the other parameters.

The change in O changes the direction of application of the forces by the cyclist relative to the pedal. It then suffices to pivot the whole of the crankset 900 forward in its tube 2 around the axis 10 to restore the kinematic and dynamic conditions of FIG. 4.

The eccentricity E then becomes vertical downwards, the axis 25 being placed below the axis 10. The general condition relating to the preferred position of the articulations formed by the rollers 34 is therefore that, when the crank is located in the horizontal position towards the front, the articulation 34 of the corresponding link on the tray holder 15 must be near the radial plane passing through the two axes 10 and 25, therefore in the same general direction as the eccentricity E .

 FIG. 5 represents the torque M applied to the plate carrier 15 as a function of the angle 8 of rotation thereof, assuming that the cyclist exerts only a vertical downward force of 600 N on the descending crank, the cranks having a standard length of 175 mm. Curve 60 represents the torque in a traditional crankset, where the two cranks are integral with the chainring. The curve 61 represents the torque in the crankset 1 according to the invention, in the arrangement of FIG. 4, that is to say with the horizontal eccentricity E towards the front. This curve is flatter than curve 60, that is to say that the torque is more uniform over one turn of the pedal. The minimum torque 63, in the neutral zone where the torque 60 of the traditional crankset falls to zero, represents approximately 20% of the maximum torque. In practice, we know that the minimum torque will often be a little higher, because an experienced cyclist still applies certain horizontal or rising forces to the pedals.

 The curve 64 represents the torque in the crankset 1 when the eccentricity E is directed forwards at 300 from below the horizontal. It is noted that it is very close to the curve 61 and has the same maximum and minimum values, that is to say that such a pivoting of the eccentric 26 does not affect the performance of the crankset when the forces applied the pedals are vertical. On the other hand, it makes it possible to adapt the kinematics of the crankset, in particular the position of the zone where the cranks are offset, to the morphology of the cyclist and to his position on the bicycle.

 The diagram in FIG. 6 represents the evolution of the angular speed o of the cranks as a function of the angle e of the right crank 13 for a constant speed of the chainring 15 (1 revolution per second) and therefore of the bicycle, when the eccentricity E is in the horizontal direction, therefore under the conditions of curve 61 in FIG. 5. Curve 65 concerns the right crank 13 and curve 66 relates to the left crank 11. The right 67 represents the speed of the plate carrier 15 .

We see that each crank turns more slowly when it goes down, and faster when it goes up. The speed of each crank varies gradually, smoothly, and the minimum speed is approximately 86% of the maximum speed. This is important for the comfort of the cyclist and protects his endurance by avoiding imposing on his legs sensitive accelerations and decelerations;
In view of the above description, those skilled in the art will understand that the invention makes it possible to produce a crankset perfectly protected against external conditions, in particular, water and dirt, without the use of bulky accessories such as a outer casing. In addition, the bottom bracket can be completely assembled before it is inserted into the bottom bracket tube, which guarantees safe and easy mounting and also facilitates possible dismantling. The offset position of the arms 20 and 22 relative to the cranks, unlike the prior art according to document FR 2 584 671 where these arms are located opposite the cranks, allows advantageous kinematics and optimal transmission of the torque from the cranks to the chainrings , without increasing the dimensions and weight of the construction. If necessary, this arrangement also makes it possible to produce the right crank and the arm associated therewith in a single piece, thereby allowing a substantial gain in the total width of the crankset. This arm is then not necessarily radial and can in particular extend in the circumferential direction from the crank.

Claims (10)

 1. Crankset without neutral, especially for a bicycle, comprising  - a fixed bottom bracket tube (2),  a hollow outer shaft (8) rotatably mounted about a first axis (10) by first bearings in the bottom bracket tube and secured to a first crank (11),  an inner shaft (9) rotatably mounted by first bearings coaxially in the outer shaft and secured to a second crank (13),  sealing means for ensuring leakproof protection of said bearings vis-à-vis the outside of the bottom bracket,  - an output element (15) rotatably mounted about a second axis (25) parallel and offset with respect to the first axis on an eccentric element (26) fixed to the bottom bracket, the output element being intended to drive mechanical transmission, and  - two articulated connections (20-23, 31-36) connecting the output element respectively to each crank or to each shaft,  characterized in that the sealing means comprise first sealing means (42, 46), arranged around the outer shaft (8) in the bottom bracket tube (2) and protecting the first bearings (41, 45) vis-à-vis the outside of this tube, and second sealing means (47, 53), arranged in the outer shaft (8) and protecting the second bearings (48, 51) vis-à-vis from outside this tree.  2. Crankset according to claim 1, characterized in that the first and second sealing means comprise annular sealing packings (42, 46, 53) each arranged radially between two rotary elements.  3. Crankset according to claim 1, characterized in that the eccentric element (26) is adjustable by pivoting around the first axis (10) to adjust the direction of its eccentricity (E).  4. Crankset according to claim 3, characterized in that the eccentric element (26) is screwed into the bottom bracket tube (2) and carries a lock nut (29) arranged to block it against said tube.  5. Crankset according to one of the preceding claims, characterized in that each of said articulated connections comprises a link (21, 23) having one end connected to the output element by a first articulation (34-36), in that the other end of said link is connected to the corresponding shaft (8, 9) or to the corresponding crank (13) by a second articulation (31-33), and in that said first articulation (34-36) located near a radial plane passing through the first and second axes (10, 25) when the corresponding crank (11, 13) is in a horizontal downward position (a).  6. Crankset according to claim 5, characterized in that the first articulation (34-36) is located substantially opposite the corresponding crank (11, 13).  7. Crankset according to claim 5, characterized in that each shaft (8, 9) is provided with a radial arm (20, 22) disposed outside opposite the outlet element (15) and carrying said second articulation, said arm being angularly offset relative to the corresponding crank.  8. Crankset according to claim 7, characterized in that each crank (11, 13) is removably mounted on the corresponding shaft.  9. Crankset according to one of claims 5 to 8, characterized in that, in view in a vertical plane, the circles (57, 58) representing the trajectories of the first and second articulation of each link (21, 23 ) are tangent.  10. Crankset according to one of the preceding claims, characterized in that the output element (15) is a chainring on which one or more toothed chainrings (16-18) are removably mounted.