The invention relates to a chainwheel for a bicycle, a home trainer, a go-cart or a like human-powered device provided with a crank assembly.

BACKGROUND

From practice, of course, the circular chainwheel of bicycles is known. Also from practice, different non-circular chain wheels are known as front gear of a bicycle.

US-5,549,314 describes a non-circular chainwheel most accurately. In this publication a chainwheel is provided which is point symmetrical relative to an imaginary central point and whose circumference can be divided into a first half and a second half, each extending over a segment of arc of 180°. In turn, each half is subdivided into five different zones. As indicated in column 2, lines 23-24 of the U.S. patent publication, the underlying principle of the chainwheel described therein is that "the force to be provided is proportional to the muscular force that the user may provide". The underlying principle of the chainwheel known from the patent publication can be summarized as follows. First, with a circular chainwheel, the course of drive torque is measured as a function of the angular position of the crank. This drive torque is not constant as there are different factors that influence the force to be exerted by a cyclist on a pedal. Moreover, the angular position of the cranks and the direction of the force exerted by the user on the pedals are, of course, of great influence on the drive torque exerted by the user on the crankshaft and this, in the end, determines the tensile force on the chain. For instance, if the force exerted on the pedal were directed exactly vertically downwards and the crank were also in the vertical position, the drive torque that is exerted, and hence the driving force the chainwheel exerts on the chain, is nil. Conversely, if the crank, given a force being exerted exactly vertically on the pedal, is in a horizontal position, the exerted drive torque is at a maximum. However, a cyclist does not exert a constant force, and this variable force is certainly not always directed vertically, either. Also the weight of the legs, the dynamic forces that occur as a result of acceleration and deceleration of the mass of the upper and lower legs, and the position of the legs at the different angular positions of the cranks lead to variation in the resulting drive torque. In other words, in some positions of a crank arm, in the case of a circular chainwheel, a lesser drive torque is provided than in other positions of this crank arm. By varying the radius of the chainwheel, it is possible, given a variable drive toque exerted by the cyclist, yet to exert a more or less constant force on the chain. Hence, when in a particular position of the crank arm the drive torque to be exerted by the user is small, then, when it is chosen to apply the principle of the U.S. patent publication, the radius of the chainwheel in the point of application of the chain should be chosen to be small, whereas, when in a particular position of the crank arm the drive torque to be exerted by the user is great, the radius of the chainwheel in the point of application of the chain will have to be chosen to be relatively great. This choice by principle leads to a particular chainwheel which has different zones and with the crank arms oriented at a particular angle to these zones. These zones are defined in the U patent.

SUMMARY OF THE INVENTION

The present invention starts from a different principle in the design of the non-circular chainwheel. For a given number of rotations per minute, a chainwheel shape was sought with which two goals are realized, namely:

1. starting from a specific power to be provided, the peak loads of the hip and knee joints and muscles were determined and the design of the chainwheel and the position of the crank relative to the chainwheel were optimized to minimize these peak loads; and

2. starting from particular peak loads of the hip and knee joints which occur with a circular chainwheel at 90 rotations per minute, the design of the chainwheel and the position of the crank relative to the chainwheel were optimized so as to optimize the average power that is provided per rotation.

According to the invention, on the basis of these criteria, a chainwheel is provided intended for a crank assembly of a bicycle, home trainer, go-cart or like human-powered device provided with a crank assembly, wherein the front chainwheel is non-circular and is

point-symmetrical about an imaginary central point, and comprises:

• fastening means for fastening the chainwheel to a crank of a crank assembly, wherein the crank has an imaginary crank axis which extends in a longitudinal direction of the crank and runs from a rotation axis of the crank, on which also the imaginary central point is located, in the direction of a free end of the crank where a pedal can be connected to the crank.

The chainwheel is characterized

· by four successive, different zones, to be referred to as, viewed in

circumferential direction, successively, a first zone A, a second zone B which adjoins the first zone A, a third zone C which adjoins the second zone B, and a fourth zone D which adjoins the third zone C, the first through fourth zones A-D extending through an angular range of 180 degrees; and

• by four successive, different zones, to be referred to as, viewed in

circumferential direction, successively, a fifth zone A which adjoins the fourth zone D, a sixth zone B' which adjoins the fifth zone A', a seventh zone C which adjoins the sixth zone B' and an eighth zone D' which by one end adjoins the seventh zone C and by the other end adjoins the first zone A, the fifth through eighth zones A'-D' corresponding to the first through fourth zones A-D, respectively, in that these fifth through eighth zones A'-D' are point-symmetrical relative to those first through fourth zones A-D about the imaginary central point;

in that the third and seventh zones C and C are each formed by a circular segment having a radius R which defines the maximum diameter of the chainwheel, wherein a large axis of the chainwheel extends from the middle of the circular segment-shaped, third zone C to the middle of the circular segment-shaped, seventh zone C, and wherein the middle of the large axis is the imaginary central point and also forms the midpoint of the circular segments defining the third and seventh zones C, C, these circular segments each passing through an angular range of 42° ± 3°;

in that the fourth zone D passes through an angular range of 19° ± 3°, and wherein the curve of that zone D is defined by a function which is known as an Archimedean spiral, wherein the radial increase which the fourth zone D passes through, viewed from the fifth zone A to the third zone C, is 31%, such that the distance to the imaginary central point at the transition from the fourth zone D to the fifth zone A is 0.76 times the radius R mentioned;

in that the second zone B passes through an angular range of 79° ± 3°, and wherein the curve of this zone B is defined by a function which is known as an Archimedean spiral, wherein the radial increase the second zone B passes through, viewed from the first zone A to the third zone C, is 31%, such that the distance to the imaginary central point at the transition from the second zone B to the first zone A, is 0.76 times the radius R mentioned;

in that the first zone A passes through an angular range of 40° ± 3°, wherein the first zone A is formed by a straight line, wherein a small axis of the chainwheel is formed by a perpendicular to the straight line defining the zone A and which has as one endpoint the imaginary central point and as other endpoint the intersection with the straight line, wherein the small axis (SA) includes an angle with the part of the large axis that extends between the imaginary central point and the third zone C, which angle is in the range of 112° ± 3°;

• in that the fastening means for fastening the crank to the chainwheel are designed such that in at least one fastened condition of the chain gear on the crank, the imaginary crank axis includes an angle with the part of the large axis that extends between the imaginary central point and the third zone C, which angle is 67° ± 3°; and

• in that the part of the small axis that extends from the imaginary central point to the first zone A includes an angle with the crank axis of 45° ± 3°.

With a thus designed chainwheel which is oriented relative to the crank in the above defined manner, at a given average crank power that is provided per rotation, the peak load in the knee extensor muscles (these are the muscles that are most prone to injury when cycling) is reduced by 9.2 % relative to a circular chainwheel with which the same average crank power per rotation is provided. Moreover, with a chainwheel according to the invention, given equal loading of the joints, i.e., when by a user the same joint moments as in the case of a circular chainwheel are produced in the case of a non-circular chainwheel, 2.7 % more crank power is provided than with a circular chainwheel. In the case of the chainwheel known from the U.S. patent publication, the peak load of the knee extensor muscles is reduced relative to the circular chainwheel by a few per cents less than in the case of the chainwheel according to the invention. The crank power gain relative to the circular chainwheel is also smaller with the chainwheel from the U.S.patent than with the chainwheel according to the invention.

Therefore, with the chainwheel according to the invention, on average, a higher power is produced than with a circular chainwheel and also a higher average power than with the chainwheel known from the above mentioned U.S. publication. Moreover, the peak load of the most injur -prone muscles which occurs in the case of the chainwheel according to the invention is considerably less than in the case of a circular chainwheel and is also significantly less than in the case of the chainwheel known from the U.S. publication.

Further elaborations are described in the subclaims and will be further clarified hereinafter on the basis of an exemplary embodiment which is shown in the Figures.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a side view of an exemplary embodiment according to the invention;

Fig. 2 shows a schematic side view of a chainwheel with crank, in which the different zones and the various angles are shown;

Fig. 3 shows a graph in which the crank power of a circular chainwheel is shown as weU as the crank power of a chainwheel according to the invention, given equal moments in the joints of the user;

Fig. 4 shows a graph in which the loading of the hip and the knee with a circular chainwheel and with a chainwheel according to the invention is plotted, given an equal total crank power provided per rotation;

Fig. 5 shows a perspective view of an exemplary embodiment of a crank having mounted thereon a chainwheel with chain guide; and

Fig. 6 shows the chainwheel at the location of the chain guide, viewed from a rear side.

DETAILED DESCRIPTION

Figures 1 and 2 show an exemplary embodiment of a chainwheel according to the invention. Figure 1 shows a practical exemplary embodiment and Figure 2 schematically shows in what manner the chainwheel 12 is provided with different zones and in what manner the crank is oriented relative to these zones. The chainwheel 12, which is provided at its circumference with a toothing, is intended for a crank assembly 10 of a bicycle, home trainer, go-cart or like human-powered device provided with a crank assembly. The chainwheel 12 is non-circular and is point-symmetrical about an imaginary central point M. The chainwheel 12 is provided with fastening means 14, 16, 18, 20, 22 for fastening the chainwheel 12 to a crank 24 of a crank assembly 10. The crank 24 has an imaginary crank axis CA which extends in a longitudinal direction of the crank 24 and runs from a rotation axis of the crank 24, on which also the imaginary central point M is located, in the direction of a free end 24a of the crank 24 where a pedal 26 can be connected to the crank 24. The chainwheel 12 is characterized:

• by four successive, different zones, to be referred to as, viewed in

circumferential direction, successively, a first zone A, a second zone B which adjoins the first zone A, a third zone C which adjoins the second zone B, and a fourth zone D which adjoins the third zone C, the first through fourth zones A-D extending through an angular range of 180 degrees; and

• by four successive, different zones, to be referred to as, viewed in

circumferential direction, successively, a fifth zone A which adjoins the fourth zone D, a sixth zone B' which adjoins the fifth zone A, a seventh zone C which adjoins the sixth zone B' and an eighth zone D' which by one end adjoins the seventh zone C and by the other end adjoins the first zone A, the fifth through eighth zones A-D' corresponding to the first through fourth zones A-D, respectively, in that these fifth through eighth zones A'-D' are point-symmetrical relative to those first through fourth zones A-D about the imaginary central point M; in that the third and seventh zones C and C are each formed by a circular segment having a radius R which defines the maximum diameter of the chainwheel 12, wherein a large axis LA of the chainwheel 12 extends from the middle CM of the circular segment- shaped, third zone C to the middle CM of the circular segment- shaped, seventh zone C, and wherein the middle of the large axis LA is the imaginary central point M and also forms the midpoint of the circular segments defining the third and seventh zones C, C, the third and seventh zones C, C each passing through an angular range of 42° ± 3°;

in that the fourth zone D passes through an angular range of 19° ± 3°, and wherein the curve of that zone D is defined by a function which is known as an Archimedean spiral, wherein the radial increase which the fourth zone D passes through, viewed from the fifth zone A to the third zone C, is 31%, such that the distance to the imaginary central point at the transition from the fourth zone D to the fifth zone A is 0.76 times the radius R mentioned;

in that the second zone B passes through an angular range of 79° ± 3°, and wherein the curve of this zone B is defined by a function which is known as an Archimedean spiral, wherein the radial increase which the second zone B passes through, viewed from the first zone A to the third zone C, is 31%, such that the distance to the imaginary central point at the transition from the second zone B to the first zone A, is 0.76 times the radius R mentioned;

in that the first zone A passes through an angular range of 40° ± 3°, wherein the first zone A is formed by a straight line, wherein a small axis SA of the chainwheel 12 is formed by a perpendicular to the straight line defining the zone A and which has as one endpoint the imaginary central point M and as other endpoint the intersection with the straight line, wherein the small axis SA includes an angle with the part of the large axis LA that extends between the imaginary central point M and the third zone C, which angle is in the range of 112° ± 3°;

• in that the fastening means 14-22 for fastening the crank 24 to the chainwheel 12 are designed such that in at least one fastened condition of the chainwheel 12 on the crank 24, the imaginary crank axis CA includes an angle with the part of the large axis LA that extends between the imaginary central point M and the third zone C, which angle is 67° ± 3°; and

· in that the part of the small axis SA that extends from the imaginary central point M to the first zone A includes an angle with the crank axis CA of 45° ± 3°.

In an embodiment, of which an example is shown in Figure 1, the fastening means 14-22 can be designed for mounting the chainwheel 12 on the crank 24 in at least two different rotational positions, so that the chainwheel 12, and hence also the zones A-D and A'-D' thereof, can be fastened at different angles to the crank axis CA.

In an embodiment, of which an example is shown in Figure 1, the at least two different rotational positions can provide an angular

displacement of the chainwheel 12 relative to the crank axis CA of 8°.

In an embodiment, of which an example is shown in Figure 1, the fastening means 14-22 can provide five different positions. As is known, the right-hand crank of a bicycle is generally provided with a number of radially extending gear mounting arms 28, 30, 32, 34, 36. A conventional chainwheel or chain gear is generally provided with five mounting openings

corresponding to the chain gear mounting arms 28, 30, 32, 34, 36. In the exemplary embodiment, instead, the chainwheel 12 is provided with five series of, each, five mounting openings 14-22, each series of five mounting opening 14-22 being associated with a corresponding chain gear mounting arm 28, 30, 32, 34, 36. Neighboring mounting openings 14-22 within a series of five mounting openings are staggered 8° relative to each other, viewed in circumferential direction.

In the exemplary embodiment shown in Figure 1, the angles between the crank axis CA and the part LAi of the large axis LA that extends between the imaginary central point M and the third zone C, in the different rotational positions in which the chainwheel 12 can be mounted on the crank 24, are chosen as follows: 67°, 75°, 83°, 91° and 99°.

The invention relates not only to a chainwheel 12 but also to a crank assembly 10 comprising at least one chainwheel 12 according to the invention and a crank 24 which is connected to the chainwheel 12 with the aid of the fastening means 14-22 of the chainwheel 12.

The invention further relates to a bicycle, a home trainer, a go-cart or like human-powered device provided with a crank assembly according to the invention.

Figure 3 shows a graph in which the crank power of a circular chainwheel is shown as well as the crank power of a chainwheel according to the invention, given equal moments in the joints of the user. On the horizontal axis, time is plotted, the period of time represented being 0.66 s, which corresponds to one rotation when the rotational speed of the crank assembly is 90 rpm (rotations per minute). On the vertical axis, the crank power is plotted. The curve 38 shows the course of the crank power of the circular chainwheel and the curve 40 the course of the crank power of the non-circular chainwheel 12 during one rotation. The average crank power that is provided when using the circular chainwheel is 104 W, while the average crank power that is provided by the non-circular chainwheel is 106.8 W.

Figure 4 shows a graph plotting the power that must be provided by the hip and the knee with a circular chainwheel and with a non-circular chainwheel according to the invention, respectively, given an equal total crank power supplied per rotation. On the horizontal axis, time is plotted, the period of time represented being 0.66 s, which corresponds to one rotation when the rotational speed of the crank assembly is 90 rpm

(rotations per minute). On the vertical axis, the power that is to be supplied by the knee joint and the hip joint is plotted. Curve 42 shows the course of the power to be supplied by the hip when using a circular chainwheel. Curve 44 shows the course of the power to be supplied by the knee when using a circular chainwheel. Curve 46 shows the course of the power to be supplied by the hip when using a non-circular chainwheel according to the invention. Curve 48 shows the curve of the power to be supplied by the knee when using a non-circular chainwheel according to the invention. The joint which is most prone to injury when cycling is the knee joint. It appears from the graph that the peak power at the knee joint, which peak power occurs in the graph shown after 0.1 s, is 90.8% of the peak power that must be supplied with a circular chainwheel. The risk of injuries when using a non-circular chainwheel according to the invention has thus been considerably reduced, while at the same time the average power supplied has increased relative to the circular chainwheel. Both positive results mentioned, for that matter, also hold true with respect to the chainwheel described in the above mentioned U.S. patent.

Figures 5 and 6 show an example of a chainwheel 12 according to an embodiment in which on the chainwheel at least one chain guide 50, 50' is provided. The at least one chain guide 50, 50' extends in any case along the first zone A and the fifth zone A'. In practical tests, it has appeared that in some cases the chain may run off the rectilinear first and fifth zones A, A. This is prevented by the at least one chain guide 50, 50', which

considerably increases the safety of the crank assembly comprising a chainwheel 12 according to the invention.

In a further elaboration, the at least one chain guide can comprise two chain guides 50, 50' which are designed as a substantially plate-shaped part having an outer circumference 52, 52' which runs parallel to a line connecting the tops of the chain teeth 54 of the chainwheel 12 with each other. The outer circumferences 52, 52' of the chain guides 50, 50' are at a distance from the imaginary central point M that is a few millimeters gr eater than the corresponding distance of the connecting line mentioned.

In an alternative further elaboration, the at least one chain guide can comprise one chain guide 50 which is designed as a substantially plate- shaped part having an outer circumference which runs parallel to a line connecting the tops of the chain teeth 54 of the chainwheel 12 with each other. The outer circumference 52, 52' is at a distance from the imaginary central point M that is a few milhmeters greater than the corresponding distance of the connecting line mentioned. The single chain guide 50 extends throughout the circumference of the chainwheel 12.

In a still further elaboration, the at least one chain guide 50, 50' can be mounted on the side of the chainwheel which is directed to the crank 24 and pedal 26 associated with the chainwheel. For it is precisely in that direction that under some circumstances the chain runs off the chainwheel and this is prevented by the presence of the at least one chain guide 50, 50'.

Although the invention is represented and described in detail with reference to the drawing, this drawing and the description are to be regarded as an example only. The invention is not limited to the

embodiments described. Features that are described in dependent claims can be combined with each other. The reference numerals in the claims and the description of the drawings should not be construed as limitations of the embodiments to just the examples shown in the Figures, but are for clarification only. Different combinations of embodiments are possible.