Gear for a bicycle transmission

Abstract

A gear (10) for a bicycle transmission (20) is described, having an external contour (11) with teeth (12a, 12b) formed thereon, wherein the external contour (11) is defined by a maximum pitch diameter (.sub.max) and a minimum pitch diameter (.sub.min), does not have any axes of symmetry and is formed exclusively with point symmetry with respect to its centre of symmetry (M). The invention was therefore based on the problem of developing a gear (10) which improves the pedaling feel of a bicycle transmission (20). The problem is solved in that the external contour (11) exhibits a change in its curvature at every point.

Claims

1. A gear for a bicycle transmission, the gear comprised of a body having an outer contour with teeth, wherein the outer contour is defined by a maximum pitch diameter .sub.max and a minimum pitch diameter .sub.m, has no axes of symmetry, and is formed exclusively with point symmetry with respect to its center of symmetry, and has a curvature that changes at each point.

2. The gear as in claim 1, wherein the gear has four segments each segment of a same size, wherein the maximum pitch diameter .sub.max and the minimum pitch diameter .sub.min run through a first and third segment and the first and third segments are aligned point-symmetrically around the center of symmetry.

3. The gear as in claim 2, wherein the second and fourth segments have exclusive pitch diameters whose lengths are between the maximum pitch diameter .sub.max and the minimum pitch diameter .sub.min.

4. The gear as in claim 2, wherein there is an angle between the maximum pitch diameter .sub.max and the minimum pitch diameter .sub.min of the first and third segments which is at least one of between 50 and 70, between 55 and 65 and between 58 and 62.

5. The gear as in claim 3, wherein there is an angle between the maximum pitch diameter .sub.max and the minimum pitch diameter .sub.min of the first and third segments which is at least one of between 50 and 70, between 55 and 65 and between 58 and 62.

6. The gear as in claim 1 wherein the adjacent teeth each have a different pitch diameter .

7. The gear as in claim 1, wherein a ratio of maximum pitch diameter .sub.max to minimum pitch diameter .sub.min is greater than 1.30.

8. A combination of a bicycle transmission and a gear, the bicycle transmission comprising: a central shaft supported with respect to a fixed frame element so that the central shaft rotates around a central bearing axis, a first sun gear, positioned concentrically to the central shaft and connected rigidly to the frame element, and at least one first gearing assembly that rotates with respect to the frame element in the gearing assembly, the gearing assembly comprising a carrier plate having a first section connected rigidly to the central shaft, and a planet gear supported on the carrier plate so that the planet gear rotates around a planet gear bearing axis, wherein the planet gear engages the first sun gear, a crank arm rigidly engaging the planet gear, a swing arm, and a pedal crank on which the crank arm is supported so that the pedal crank swivels and which is held against the carrier plate by the swing arm, wherein the swing arm is attached to the carrier plate and the pedal crank so that the swing arm swivels, and the gear attached to the carrier plate, the gear comprising a body having an outer contour with teeth, wherein the outer contour is spanned by a maximum pitch diameter .sub.max and a minimum pitch diameter .sub.min, has no axes of symmetry, and is formed exclusively with point symmetry with respect to its center of symmetry, and has a curvature that changes at each point, wherein the gear is in a fixed position on the central shaft.

9. The combination as in claim 8, wherein the minimum pitch diameter .sub.min in a rotation direction is offset by an angle from a connecting line running between a central bearing axis and a planet gear bearing axis.

10. The combination as in claim 9, wherein the angle is at least one of between 1 and 15, between 3 and 7, and between 4 and 6.

11. The combination as in claim 8, wherein a position of the pedal crank on the gear changes during one rotation of the gear.

12. The combination as in claim 8, also comprising: a second sun gear, a second gearing assembly with which the second sun gear interacts, the second gearing assembly able to rotate with respect to the frame element, wherein the second gearing assembly is offset by 180 from the first gearing assembly, the second gearing assembly comprising a planet gear, a carrier plate having a first section connected rigidly to the central shaft and a second section on which the planet gear is supported so that the planet gear rotates, the planet gear engaging the second sun gear, a crank arm that rigidly engages the planet gear, a pedal crank, on which the crank arm is supported so that the crank arm swivels and which is held against the carrier plate by a swing arm, wherein the swing arm is attached to the carrier plate and the pedal crank so that the swing arm swivels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side view of a gear according to the invention;

(2) FIG. 2 is a partially cut away side view of the gear shown in FIG. 1 installed in a bicycle transmission; and

(3) FIG. 3 is a lengthwise section through the bicycle transmission shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) FIG. 1 shows a side view of a gear 10 having a body with an oval outer contour 11. The outer contour 11 fully encircles the circumference of the gear 10 and is the path of a power transmission means (not shown here) such as a chain or toothed belt. All around the outer contour 11 there are teeth 12a, 12b that allow an installed gear 10 to engage with the power transmission means. For illustrative purposes, the outer contour 11 in FIG. 1 is shifted inward equidistantly at all points, but its curvature pattern corresponds to the pattern through an individual pitch diameter of adjacent teeth 12a, 12b.

(5) The gear 10 has four fastener openings 25 equally spaced around its circumference, by means of which the gear 10 can be attached with a carrier plate 31 to a gearing assembly 30 in a bicycle transmission 20 (see FIG. 2).

(6) The bicycle transmission 20 comprises a central shaft 21, attached coaxially inside a fixed sun gear 24 so that the sun gear rotates around the central bearing axis 23. The central shaft 21 thereby extends through a fixed frame element 22, by means of which the bicycle transmission 20 can be solidly attached to a bicycle frame 40.

(7) The gearing assembly rotates around the sun gear 24 and comprises the carrier plate 31 and a planet gear 32 attached rotatably to a first section 31a. The planet gear 32 is permanently engaged with the sun gear 24 and rotates together with the carrier plate 31 around its periphery. A crank arm 34 is attached to the planet gear 32. The crank arm rotates rigidly together with the planet gear 32 and is fastened with a swivel connection to a pedal crank 35 extending upward (see FIG. 3). The pedal crank 35 is also connected to the carrier plate 31 by a swing arm 36 in the direction of its free end. The swing arm 36 engages both the pedal crank 35 and a second section 31b of the carrier plate 31 with a swivel connection.

(8) On the back, which is covered by the frame element 22, there is another sun gear 24 that is also connected to an associated gearing assembly 30 and allows the rider to pedal on both sides. The only part of the back gearing assembly that can be seen in FIG. 2 is the pedal crank 35 extending downward. The two gearing assemblies 30 are identical in configuration and placed at 180 to each other, as shown in FIG. 3.

(9) As can be seen in FIG. 1, the gear 10 is divided into four segments 13a, 13b, 13c, and 13d, each spanning a 90 angle around a center of symmetry M. The segments 13a, 13b, 13c, and 13d are divided by an x-axis running horizontally through the image plane, oriented to the ground or road surface, and a vertical y-axis running perpendicular to it. The alignment of the x-axis and y-axis is represented by the position of the central shaft 21 shown in FIGS. 2 and 3, wherein the center of symmetry M aligns with the central bearing axis 23 of the central shaft 21. The gear 10 rotates together with the segments 13a, 13b, 13c, and 13d when it is moved to engage synchronously with the central shaft 21.

(10) The first segment 13a is shown at the upper right of the image plane in FIG. 1. It is followed, counterclockwise, by the second segment 13b, the third segment 13c, and the fourth segment 13d. Because of the point-symmetrical configuration of the outer contour 11, the segments 13a, 13b, 13c, and 13d are arranged point-symmetrically to each other.

(11) The first segment 13a and the third segment 13b are configured respectively with a maximum pitch diameter .sub.max and a minimum pitch diameter .sub.min. The maximum pitch diameter .sub.max and the minimum pitch diameter .sub.min therefore are not at right angles to each other, as they would be in an ellipse, but rather intersect at an angle of <90. In the invention example shown in FIG. 1, angle =61.25. This results in a lower maximum pedal speed V.sub.max around the x-axis, especially compared to a circular gear. However, the maximum pedal speeds V.sub.max indicated in FIG. 2 are still nearly twice as high as the minimum pedal speeds V.sub.min.

(12) In addition to reducing the maximum pedal speed V.sub.max, the goal is to increase the minimum pedal speed .sub.max around the y-axis of the minimum pitch diameter .sub.min offset from the connecting line 37 by an angle in the rotation direction 14 of the gear 10. In the illustrated vertical position of the pedal cranks 35 according to FIG. 2, the central bearing axis 23 and a planet gear bearing axis 33 are exactly on top of each other and aligned with the y-axis. The connecting line 37 runs precisely through the central bearing axis 23 and the planet gear bearing axis 33 and serves as the reference size for the angle to be created there.

(13) The outer contour 11 in the area of the second segment 13b and the fourth segment 13d has a changing pitch diameter between adjacent teeth 12a and 12b, with a length between the maximum pitch diameter .sub.max and the minimum pitch diameter .sub.min of the first and third segments 13a and 13c.

(14) The lengthwise section shown in FIG. 3 identifies the first and second sun gears 24, fixed with respect to the frame element 22, which are located on both outer sides of the frame element 22. Both sun gears 24 are attached solidly by a hollow cylinder 26 to form a one-piece integral assembly unit. A complete one-piece assembly is understood to involve a connection that cannot be separated other than by destroying it.

(15) The central shaft 21 runs concentrically inside the hollow cylinder 26 and is supported so that it can rotate contiguously to sun gear 24 by means of a central shaft bearing 27. Due to the central shaft bearing 27 that is placed axially as far to the outside of the central shaft 21 as possible and coaxially inside of the sun gears 24, effective pull-out torques can be applied especially well to the central shaft 21.

(16) The carrier plate 31 is mounted rigidly on each axial end section of the central shaft 21, and it rotates in a circle together with the central shaft 21 when the bicycle transmission is in operation. The connection between the carrier plate 31 and the central shaft 21 is made in the centrally located first section 31a of the carrier plate 31. In the radial direction of the carrier plate 31 there is an outer second section 31b, in which the planet gear 32 is held rotatably against the carrier plate 31.

(17) On the outer end of a planet gear shaft 32a of the planet gear 32 with respect to the frame element 32, a crank arm 34 is either attached rigidly or formed as a complete one-piece component. The crank arm 34 extends in a radial direction with respect to the planet gear shaft 32a and engages rotatably with the pedal crank 35.

(18) Power is provided to the bicycle transmission 20 through its two pedal cranks 35 on the respective gearing assemblies 30, located axially to the central shaft 21 on the outsides of the bicycle transmission. FIG. 3, like FIG. 2, shows the pedal cranks 35 and the gearing assembly 30 associated with each in an extended position, in which the crank arm 34 extends from the planet gear shaft 32a of the planet gear 32 radially inward toward the central shaft 21. This puts the free end of the pedal crank 35 in its farthest outward position. In order to achieve the most uniform pedaling feel with the most constant pedal speed possible, in this extended position the gear 10 effectively engages its power transmission means (not shown), with a minimum pitch diameter .sub.min offset by the angle , and thereby increases the existing minimum pedal speed V.sub.min in this area.

(19) The lengthwise cut in FIG. 3 also clearly shows that the crank arm 34 can also move to a position rotated 180, thereby placing the free end of the pedal crank 35 in a powered position. In this powered position (not shown here), the gears 12a, 12b effectively engage the power transmission means within angle , which reduces the existing maximum pedal speed V.sub.max in this area.

(20) On the free end of each pedal crank 35, as shown in FIG. 3, for example, a pedal 38 is attached that can rotate with respect to the associated pedal crank 35 by means of a pedal bearing 39. The pedal bearing 39 has a bearing axis that is fixed with respect to the pedal crank 35.