JP2019156337A - Bicycle crank assembly with built-in torque transmission mechanism - Google Patents

Abstract

To provide a bicycle crank assembly which is excellent in torque transmission property from a crank to a sprocket, and which has high durability with a simple structure.SOLUTION: A bicycle crank assembly comprises: a crank shaft with an internal space, provided with an opening part at one end part; a crank arm mounted to the end part of the crank shaft; a torque transmission mechanism which includes a slide shaft built in the internal space of the crank shaft and provided with a plurality of rows of groove parts extending in the axial direction of the crank shaft on an outer peripheral surface, and which includes a plurality of rolling bodies accommodated in the respective plurality of rows of groove parts of the slide shaft; and a sprocket mounted around the slide shaft in the torque transmission mechanism. In the bicycle crank assembly, the number of the rows is five or less in the rows of groove parts extending on the outer peripheral surface of the slide shaft in the torque transmission mechanism.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a bicycle crank assembly, and more particularly, to a bicycle crank assembly incorporating a torque transmission mechanism suitable for use in a bicycle that travels using a speed change mechanism.

  A bicycle including the speed change mechanism includes a single front sprocket, a plurality of rear sprockets, a chain connecting the front sprocket and a desired rear sprocket, and a rear derailleur that changes the rear sprocket engaged with the chain. Then, shifting is performed by changing the rear sprocket engaged with the chain by operating the rear derailleur. A bicycle equipped with such a transmission mechanism is usually called a bicycle with a transmission.

  In a bicycle with a transmission, depending on the position of the rear sprocket that engages with the chain during shifting, the chain that connects the front sprocket and the rear sprocket may be arranged obliquely with respect to the front sprocket. Since the chain holding force of the front sprocket is reduced, the chain may fall off the front sprocket due to vibration during traveling.

  As a bicycle equipped with a speed change mechanism for avoiding troubles that may occur when the bicycle is traveling, Patent Document 1 discloses that the front sprocket moves so that the front sprocket can move along the center axis of rotation. A crank assembly with a mechanism has been proposed. In the crank assembly moving mechanism, a plurality of shaft bodies are arranged between the peripheral portion of the front sprocket and the crank arm, and the front sprocket changes the distance from the crank arm via the plurality of shaft bodies. It is configured to be movable.

  Patent Document 2 discloses a front sprocket that is configured so that the front sprocket can be moved along the center axis of rotation, which is effective in avoiding the above-described trouble that may occur during shifting operation or bicycle traveling. A crank assembly with a sliding mechanism is disclosed. The sliding mechanism of the crank assembly disclosed in Patent Document 2 has a hollow inside the rotating shaft of the crank arm (that is, the crankshaft) and slides in the hollow portion in the axial direction of the rotating shaft. The sliding mechanism has a shaft inserted therein, and a front sprocket is attached to one end of the sliding mechanism. As an example of this sliding mechanism, a rolling element such as a ball bearing is arranged around the sliding shaft, and the axis of the sliding shaft in the rotating shaft using the rolling of the rolling element is used. A configuration is disclosed in which smooth sliding in the direction and transmission of torque of the rotating shaft generated by rotation of the crank arm to the front sprocket through the sliding mechanism are disclosed.

US2013 / 0008282A1 JP 2017-109529 A

  As described above, in Patent Document 2, a crankshaft having an internal space with an opening at one end; a crank attached to the one end of the crankshaft; built in the internal space of the crankshaft A sliding shaft having a plurality of rows of grooves extending in the axial direction of the crankshaft on the outer peripheral surface; and a torque transmission mechanism including a plurality of rolling elements housed in each of the plurality of rows of grooves of the sliding shaft; A bicycle crank assembly is disclosed that includes a sprocket mounted around a sliding shaft of a torque transmission mechanism.

  The sliding mechanism of the front sprocket disclosed in Patent Document 2 has a smooth axial direction of the sliding shaft in the outer cylinder by interposing a rotating body such as a ball bearing between the outer cylinder and the sliding shaft. It is understood that it is a mechanism that realizes a simple movement, and generally uses a configuration called “linear motion bearing”. In the sliding mechanism specifically described in Patent Document 2, a hollow rotating shaft (crankshaft) coupled to the crank arm is shaped like an outer cylinder of a linear motion bearing, and the inside is represented by a ball bearing. A rotating shaft (same as a rolling element holder) that accommodates and holds a rotating body (same as a rolling element) is inserted into a sliding shaft with a front sprocket attached to one end. . The sliding mechanism specifically disclosed in Patent Document 2 has a hexagonal cross section as a sliding shaft (a hexagonal shape seen as a regular hexagon is shown in the drawing). A total of six rows of grooves extending in the axial direction are formed at each corner, and a plurality of rolling elements are accommodated and held in each of the grooves of each row.

  As a result of the study of the inventor of the present invention, that is, the inventor of the present invention, when the bicycle with a transmission provided with the speed change mechanism disclosed in Patent Document 2 is run for a long period of time, Although it depends on the severity, etc., it has been found that there may be a problem in smooth torque transmission from the crank arm to the front sprocket.

  The present inventor conducted further studies to investigate the cause of the problem of smooth torque transmission that is likely to occur after the above-mentioned long-term traveling or severe traveling, and as a specific example in Patent Document 2 The described sliding mechanism using a sliding shaft having hexagonal cross sections with six rows of grooves is very useful for smooth sliding of the sliding shaft within the crank arm rotation shaft. Although it can be said to be a preferable sliding mechanism, it has been found that the mechanism for transmitting the torque generated by the rotation of the crank arm to the front sprocket is not necessarily optimal.

  Following the above findings, the present inventor continued to further study, and as a result of the study, surprisingly, a sliding shaft provided with five or three rows of grooves at each corner of a polygon having a cross section of a pentagon or a triangle. Or a sliding mechanism using a sliding shaft provided with two rows of grooves at the position of the axis relative to the central axis of the sliding shaft. It is possible to ensure smooth sliding of the drive shaft, and smooth the torque generated by the rotation of the crank arm to the front sprocket despite the long-term and / or severe driving of the bicycle with a transmission. It was found that a decrease in transmission function is less likely to appear.

Based on the above-described novel findings found by the inventors, the present invention provides a bicycle crank assembly having the following configuration.
A crankshaft having an internal space with an opening at one end;
A crank attached to the one end of the crankshaft;
A sliding shaft provided in the outer space with a plurality of rows of grooves extending in the axial direction of the crankshaft, and a plurality of rollers housed in each of the plurality of rows of grooves on the sliding shaft. A torque transmission mechanism including a moving body, and a sprocket mounted around the sliding shaft of the torque transmission mechanism,
A bicycle crank assembly comprising:
A crank assembly for a bicycle, wherein a groove extending on the outer peripheral surface of the sliding shaft of the torque transmission mechanism has five rows or less.

  The phrase “a plurality of rolling elements accommodated in contact with the inner peripheral surface of the crankshaft” means that all of the plurality of rolling elements accommodated in the groove are in contact with the inner peripheral surface of the crankshaft. The term includes both the configuration and a configuration in which most of the plurality of rolling elements (for example, 80% or more based on the number of rolling elements) are in contact with the inner peripheral surface of the crankshaft.

  In addition, the sliding mechanism using the sliding shaft provided with the hexagonal cross section of each of the six rows of grooves described in Patent Document 2 is, as described above, after the above-mentioned long-term bicycle running or severe The cause of the occurrence of troubles in smooth torque transmission during smooth driving has not necessarily been confirmed at this time. However, according to the present inventors' previous studies, a sliding mechanism for torque generated by rotation of a crank arm from a sliding mechanism using a sliding shaft having hexagonal cross-sectional corners in six rows of grooves. The transmission to the front sprocket attached to the sliding shaft is through the contact area between the rolling elements such as a total of six sets of ball bearings and the inner peripheral surface of the crankshaft. If it is transmitted, but even if one of those rolling elements is unevenly worn or partially damaged as a result of long-term or severe driving of the bicycle, Alternatively, when the crankshaft is deformed, it is estimated that the torque transmission described above will be non-uniform, which will result in non-uniform torque transmission to the front sprocket. Furthermore, even if slight non-uniformity of symmetry occurs during machining of the crank arm rotation shaft, sliding shaft, and grooves disposed around the sliding shaft, torque generated by rotation of the crank arm It is also conceivable that non-uniformity occurs in the transmission of the sliding mechanism to the sliding shaft.

  On the other hand, the inventor of the present invention, in the bicycle crank assembly according to the present invention, the grooves extending on the outer peripheral surface of the sliding shaft constituting the torque transmission mechanism from the rotating shaft of the crankshaft have a plurality of rows of five rows or less. Therefore, the number of rolling elements that are likely to be unevenly worn or partially damaged due to long-term or severe running of the bicycle is reduced, and the rotation axis, sliding axis, and sliding of the crank arm are reduced. It is estimated that the number of locations where slight non-uniformity of symmetry, which is likely to occur during machining of the groove portions arranged around the shaft, will also decrease. On the other hand, it is presumed that smooth sliding in the axial direction within the crankshaft (crank rotating shaft) of the sliding shaft is sufficiently ensured by the action of the rolling elements housed in a plurality of rows of grooves not more than five rows. .

Preferred embodiments of the bicycle crank assembly according to the present invention are described below.
(1) A recess extending in the axial direction of the crankshaft (preferably in the axial direction) is formed on the inner peripheral surface of the crankshaft that is in contact with the rolling elements housed in a plurality of rows of grooves provided on the outer peripheral surface of the sliding shaft. A section cut along a vertical plane has an arc shape). Due to the formation of the axial recesses (particularly the recesses having an arcuate cross section) of the crankshaft inner peripheral surface, the contact area between the plurality of rolling elements housed in the groove and the crankshaft inner peripheral surface is increased. The transmission efficiency of the torque generated by the rotation of the crankshaft to the front sprocket is improved.

(2) The groove portions extending on the outer peripheral surface of the sliding shaft of the torque transmission mechanism are in a triple row, and each groove portion is positioned at each vertex of a triangle centering on the position of the central axis of the sliding shaft. . By positioning the groove provided on the outer peripheral surface of the sliding shaft at each vertex of the triangle centering on the position of the central axis of the sliding shaft, smooth sliding in the axial direction of the sliding shaft in the crankshaft is achieved. The simplification of the sliding mechanism is realized without loss. Furthermore, the balance of the contact between the rolling elements housed in the three rows of grooves and the inner peripheral surface of the crankshaft is improved.
Such an improvement in the balance of contact between the rolling elements housed in each of the three rows of grooves and the inner peripheral surface of the crankshaft can be achieved by sliding the grooves provided on the outer peripheral surface of the sliding shaft, as described below. It appears prominently when it is placed at each vertex of an equilateral triangle whose center point is the position of the center axis of the dynamic axis. The “equilateral triangle” referred to in this specification does not mean an “equilateral triangle” in a mathematically strict sense, but as an evaluation of an article manufactured by ordinary machining, ”Means a shape that is determined to be.
(3) The groove portions extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism are in a triple row, and each groove portion is at each vertex of an equilateral triangle centering on the position of the central axis of the sliding shaft. positioned.

(4) The groove portions extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism are two rows, and each groove portion is in a symmetric position with the position of the central axis of the sliding shaft as a center point. Even with such two rows of grooves, the sliding mechanism can be simplified without impairing smooth sliding in the axial direction of the sliding shaft in the crankshaft. In addition, the term “symmetric position” described here does not mean “symmetric position” in a mathematically exact sense, and is manufactured by ordinary machining. It means a positional relationship that is determined to be a “symmetrical position” as the evaluation of an article.

(5) A rolling element holder for holding the rolling element is included in the torque transmission mechanism. Mounting of the rolling element cage in the linear bearing is generally performed for the reliable accommodation and holding of the rolling element, and its use is also preferable in the sliding mechanism of the bicycle crank assembly of the present invention. .

(6) A plurality of rows of grooves extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism have an arc-shaped cross section, and a straight line connecting both ends of the arc-shaped section of the arc-shaped cross section is larger than the diameter of the rolling element. small. By making the groove part formed in the outer peripheral surface of a sliding shaft into such a shape, it is easy to ensure the smooth rolling of the rolling element accommodated in the groove part.
(7) One end portion of both ends of the arc-shaped portion of the arc-shaped cross section of the groove portion extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism is a central axis of the sliding shaft rather than the other end portion. The bicycle crank assembly according to claim 6, wherein the bicycle crank assembly extends to a position remote from the position. The groove formed on the outer peripheral surface of the sliding shaft and the periphery thereof have such a shape, so that the rolling element can be smoothly rolled and held in the groove of the rolling element at the time of rolling. The dynamic shaft rigidity is also improved.

(8) The inner peripheral surface of the crankshaft and the plurality of rolling elements housed in the plurality of rows of grooves of the sliding shaft of the torque transmission mechanism are in contact with each other to form a torque transmission surface.

(9) A plurality of rows of groove portions of the sliding shaft of the torque transmission mechanism are arranged at equal intervals along the outer periphery of the sliding shaft. By arranging the grooves on the outer peripheral surface of the sliding shaft in this manner, smoother sliding of the sliding shaft can be ensured and smoother torque transmission can be realized.

(10) The plurality of rolling elements have a diameter that is ½ or less of the inner diameter of the crankshaft (crank rotation shaft).
(11) Recesses extending in the axial direction of the crankshaft are formed on the inner peripheral surface of the crankshaft, which is in contact with a rotating body housed in a plurality of rows of grooves provided on the outer peripheral surface of the sliding shaft. The length between both end portions of the cross section is larger than the diameter of the rolling element.

  In the crank assembly for a bicycle according to the present invention, the weight can be reduced with a simple structure, and smooth sliding in the axial direction within the crankshaft (crank rotating shaft) of the sliding shaft is ensured. Furthermore, the use of the bicycle crank assembly according to the present invention makes it difficult for the torque transmission efficiency from the crank to the sprocket to appear even when the bicycle is run for a long time or severely.

It is a perspective view which shows the external appearance of the crank assembly for bicycles of this invention. It is front sectional drawing which shows the internal structure of the crank assembly for bicycles of FIG. It is the front view (a) of the sliding mechanism of the crank assembly for bicycles of this invention, and side sectional drawing in alignment with CC line. They are a front sectional view (a) and a right side view of the sliding mechanism of the bicycle crank assembly of the present invention. FIG. 4 is an enlarged view of a side sectional view (b) of the sliding mechanism of the bicycle crank assembly of FIG. 3. It is an assembly drawing which shows each component which comprises the sliding mechanism of the crank assembly for bicycles of this invention. They are a front view (a), perspective views (b), (c), a left side view (d), and a right side view (e) of the sliding shaft of the sliding mechanism of the bicycle crank assembly of the present invention. FIG. 4 is a perspective view (a), a front view (b), and a side view (c) of a rotating body holder preferably used for the configuration of the sliding mechanism of the bicycle crank assembly of the present invention.

  The bicycle crank assembly of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view showing an appearance of a bicycle crank assembly 10 of the present invention, and FIG. 2 is a front sectional view showing an internal structure of the bicycle crank assembly 10 of FIG.

  The bicycle crank assembly 10 shown in FIGS. 1 and 2 has a hollow crankshaft (crank rotating shaft) 11 in the shape of a tubular body with one end closed and the other end open. A crank arm 13 a mounted on one end of the shaft 11, a crank arm 13 b mounted on the other end of the crank shaft 11, a sliding shaft 12 housed in the inner space of the crank shaft 11, and a sliding shaft A rolling element 14 such as a ball bearing disposed around the front end of the sliding shaft 12 is fixed to one end of the sliding shaft 12 (an end protruding toward the other end of the crankshaft 11) via a fixing tool 15. The sprocket 16 is a main component. In the bicycle crank assembly of FIG. 2, the groove portions extending on the outer peripheral surface are arranged in three rows, and each groove portion is located at each vertex of an equilateral triangle centering on the position of the central axis of the sliding shaft. A sliding mechanism using a sliding shaft is employed. Here, “the grooves in the three rows are located at the vertices of an equilateral triangle centered on the position of the central axis of the sliding shaft” means that the center of each rolling element accommodated in each groove or each groove When the cross-sectional shape of is approximated to a circle, it is formed by line segments that connect the centers of the circles, and line segments that connect the centers and points (center points) representing the position of the center axis of the sliding shaft. It means that the polygon is an equilateral triangle. A specific example will be described later with reference to FIG.

  3 shows a front view (a) of the crankshaft of the bicycle crank assembly of the present invention shown in FIG. 2, and a side cross-sectional view (b) taken along line CC of the front view (a). The side sectional view (b) shows a sectional view of the sliding mechanism employed in the bicycle crank assembly of the present invention. 4 is a front sectional view (a) and a right side view (b) of the sliding mechanism of the crank assembly for a bicycle of the present invention shown in FIG. The front cross-sectional view (a) of FIG. 4 is shown as a cross-section along the line D-D entered in the right side view (b).

  3 and 4, spline for mounting and fixing the crank arms 13a and 13b is provided at one end 11a and the other end 11b of the crankshaft as shown in FIGS. 1 and 2, respectively. Is formed. The closed end portion 11a is preferably closed in order to prevent dust and dirt from entering the internal space of the crankshaft. However, depending on the traveling conditions of the bicycle, a part or the entire surface thereof is opened. However, there is a case where the operation of the sliding mechanism employed in the present invention is not greatly affected.

  In the side cross-sectional view (b) of FIG. 3 and the side view (b) of FIG. 4, as in FIG. 2, balls are formed in the grooves of each row of the sliding shaft 12 in which three rows of grooves are formed on the peripheral surface. A drawing in which a plurality of rolling elements 14 such as bearings are accommodated side by side is shown. The rolling elements 14 are held by the rolling element holder 17 in a state of being reliably accommodated inside the grooves of the sliding shaft 12.

  FIG. 5 is an enlarged view of a side cross-sectional view (b) of the sliding mechanism of the bicycle crank assembly of FIG. 3, which is a representative configuration of the bicycle crank assembly of the present invention. The groove portions extending in the axial direction on the outer peripheral surface of the sliding shaft are arranged in three rows, and each groove portion is located at each vertex of an equilateral triangle centering on the position of the central axis of the sliding shaft. '' FIG. 4 is an enlarged view illustrating the positional relationship of each component and the meaning of “regular triangle” referred to herein. Of course, the “regular triangle” shown in FIG. 5 is a virtual diagram.

  As shown in FIG. 5, a recess extending in the axial direction of the crankshaft is formed on the inner peripheral surface of the crankshaft 11 with which the rolling elements 14 accommodated in the plurality of rows of grooves 18 provided on the outer peripheral surface of the sliding shaft 12 are in contact. 11a is preferably formed.

  Further, as shown in FIG. 5, a plurality of rows of groove portions 18 extending in the axial direction on the outer peripheral surface of the sliding shaft 12 of the torque transmission mechanism have an arc-shaped cross section, and both end portions of the arc-shaped portion of the arc-shaped cross section. It is preferable that the straight line L1 connecting the two is smaller than the diameter of the rolling element 14. Further, one end E1 of both ends of the arc-shaped section of the arc-shaped cross section of the groove 18 extending in the axial direction on the outer peripheral surface of the sliding shaft 12 of the torque transmission mechanism slides more than the other end E2. It is preferable to extend to a position far from the center axis position C of the shaft.

  The inner peripheral surface of the crankshaft 11 and the plurality of rolling elements 14 accommodated in the plurality of rows of grooves of the sliding shaft 12 of the torque transmission mechanism are in contact with each other to form a torque transmission surface TT. It is preferable.

  The plurality of rows of groove portions 18 of the sliding shaft 12 of the torque transmission mechanism are preferably arranged at equal intervals along the outer periphery of the sliding shaft 12.

  It is preferable that the plurality of rolling elements 14 have a diameter that is 1/2 or less of the inner diameter L2 of the crankshaft 11 (meaning the inner diameter of the portion having the largest inner diameter) L2.

  And the dent 11a extended in the axial direction of a crankshaft is formed in the inner peripheral surface of the crankshaft which the rolling element 14 accommodated in the groove part 18 accommodated in the outer peripheral surface of the sliding shaft 12 contacts, It is preferable that the length L2 between both ends of the cross section of each recess 11a is larger than the diameter of the rolling element 14.

  FIG. 6 is an assembly view showing each part constituting the sliding mechanism of the bicycle crank assembly of the present invention. As can be understood from the correspondence with FIGS. 3 and 4, the bicycle crank assembly of the present invention functions as an outer cylinder from the viewpoint of the linear motion bearing. The sliding shaft 11 around which a rolling element holder 17 for holding the rolling element 14 is mounted is accommodated in the internal space of the crank rotation shaft 11. Also in FIG. 6, the sliding shaft 11 includes three rows of groove portions 18 that extend in the axial direction around the shaft 11 and are arranged in parallel at a uniform interval. These three rows of grooves 18 are preferably formed at three corners of a cross section of a triangular (preferably equilateral triangle) shape forming the sliding shaft 11 groove forming region. The other parts are accessory parts mounted inside the crankshaft to limit the sliding area of the sliding shaft 11 and the rolling element cage 17 inside the crankshaft 11.

  FIG. 7 is a front view (a), perspective views (b) and (c), a left side view (d) and a right side view (e) of the sliding mechanism of the bicycle crank assembly according to the present invention. ). Also in FIG. 7, the sliding shaft 11 includes three rows of groove portions 18 arranged in the axial direction around the sliding shaft 11 and in parallel with each other at a uniform interval.

  FIG. 8 is a perspective view (a), a front view (b), and a side view (c) of a rolling element holder preferably used for the structure of the sliding mechanism of the bicycle crank assembly of the present invention. In the rolling element cage of FIG. 8, the groove portions extending on the outer peripheral surface of the sliding shaft of the torque transmission mechanism are arranged in three rows, and each groove portion is a positive point centered on the position of the central axis of the sliding shaft. Although shown in the example which has the rolling element holder 17 used for the bicycle crank assembly of the structure located in each vertex of a triangle, and the rolling element 14 accommodated and held by the rolling element holder 17, it is sliding It goes without saying that the configuration and shape change depending on the shape of the shaft and the number and shape of the grooves formed on the peripheral surface of the sliding shaft. Of course, the number of rolling elements accommodated in the rolling element holder 17 can be changed as desired.

  As the rolling element, a ball bearing generally used in a linear motion bearing is used, but if necessary, a rolling element having a different shape such as a “roller” -shaped rolling element or a “俵” -shaped rolling element is used. You can also.

  The above description of the sliding mechanism of the bicycle crank assembly according to the present invention includes three rows of grooves extending in the axial direction in the periphery and arranged in parallel at a uniform interval as shown in the accompanying drawings. Although the cross section of the groove region was made by referring to a sliding mechanism using a (equivalent) triangular sliding shaft, as described above in this specification, the sliding mechanism of the bicycle crank assembly of the present invention is: A sliding shaft provided at the top of a polygonal corner having a cross section of a pentagonal or less polygonal section having a grooved section having five or less rows of grooves extending in the axial direction at the periphery and arranged in parallel with each other at a uniform interval, or It is also possible to use a sliding shaft in which the groove portions extending in the axial direction on the outer peripheral surface of the sliding shaft are two rows and each groove portion is symmetrical with respect to the position of the central axis of the sliding shaft.

DESCRIPTION OF SYMBOLS 10 Crank assembly 11 Crankshaft 11a Recessed part 12 Sliding shaft 13a, 13b Crank arm 14 Rolling body 15 Fixing tool (sprocket fixing tool)
16 Front sprocket 17 Rolling element cage 18 Groove C Center axis position of sliding shaft E1, E2 Each end of arc section of arc section of groove section L1 Straight line connecting both ends of arc section of arc section of groove section L2 Crank Shaft inner diameter TT Torque transmission surface

Claims (11)

A crankshaft having an internal space with an opening at one end;
A crank attached to the one end of the crankshaft;
A sliding shaft with a plurality of rows of grooves extending in the axial direction of the crankshaft built in the inner space of the crankshaft on the outer peripheral surface, and a plurality of rows of grooves on the sliding shaft on the inner peripheral surface of the crankshaft. A torque transmission mechanism including a plurality of rolling elements housed in contact with each other;
And a sprocket attached around the sliding shaft of the torque transmission mechanism,
A bicycle crank assembly comprising:
A crank assembly for a bicycle, wherein a groove extending on the outer peripheral surface of the sliding shaft of the torque transmission mechanism has five rows or less.   The dent extended in the axial direction of a crankshaft is formed in the internal peripheral surface of the crankshaft which the rolling element accommodated in the groove part of the multiple rows provided in the outer peripheral surface of the said sliding shaft contacts. Bicycle crank assembly.   The groove portions extending on the outer peripheral surface of the sliding shaft of the torque transmission mechanism are arranged in three rows, and each groove portion is located at each vertex of a triangle centering on the position of the central axis of the sliding shaft. The crank assembly for a bicycle according to 1 or 2.   The groove portions extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism are arranged in three rows, and each groove portion is located at each vertex of an equilateral triangle centering on the position of the central axis of the sliding shaft. The bicycle crank assembly according to claim 1 or 2.   The bicycle crank assembly according to any one of claims 1 to 4, wherein the torque transmission mechanism includes a rolling element holder that holds the rolling elements.   A plurality of rows of grooves extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism have an arc-shaped cross section, and a straight line connecting both ends of the arc-shaped section of the arc-shaped cross section is smaller than the diameter of the rolling element. Item 6. The bicycle crank assembly according to any one of items 1 to 5.   One end of both ends of the arc-shaped section of the arc-shaped cross section of the groove extending in the axial direction on the outer peripheral surface of the sliding shaft of the torque transmission mechanism is farther from the center axis position of the sliding shaft than the other end. The bicycle crank assembly of claim 6, wherein the bicycle crank assembly extends to a position.   The inner peripheral surface of the crankshaft and a plurality of rolling elements housed in a plurality of rows of grooves of the sliding shaft of the torque transmission mechanism are in contact with each other to form a torque transmission surface. The bicycle crank assembly according to any one of items 7 to 7.   The bicycle crank assembly according to any one of claims 1 to 8, wherein a plurality of rows of grooves of the sliding shaft of the torque transmission mechanism are arranged at equal intervals along the outer periphery of the sliding shaft. Solid.   The bicycle crank assembly according to any one of claims 1 to 9, wherein the plurality of rolling elements have a diameter of ½ or less of an inner diameter of a crankshaft.   A recess extending in the axial direction of the crankshaft is formed on the inner peripheral surface of the crankshaft that is in contact with the rolling elements accommodated in the plurality of rows of grooves provided on the outer peripheral surface of the sliding shaft, and the cross section of each recess is The bicycle crank assembly according to any one of claims 1 to 10, wherein a length between both end portions is larger than a diameter of the rolling element.

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