coupling

Abstract

Clutch comprising: a clutch bell (1) having a cylindrically shaped receiving chamber (2) containing several clutch shoes (70) and rotating about an axis of the receiving chamber (2); a rotating bearing part (71) within the receiving chamber (2) which rotates about an axis of the receiving chamber (2) due to a power transmitted by a drive shaft (100) and which supports an end part of each of the several clutch shoes (70) in a manner that allows rotation about an axis parallel to the axial center of the receiving chamber (2);and a preloading element (46) that preloads the clutch shoes (70) towards the axial center of the receiving chamber (2), wherein the clutch shoes (70) are provided along a circumferential surface of the receiving chamber (2), characterized in that at least a part of the drive shaft (100) is arranged in the receiving chamber (2) and is connected coaxially to the receiving chamber (2), a connecting part (80) forming a ring shape is provided, which is fitted onto the drive shaft (100) in such a way that rotation inside the receiving chamber (2) is possible, and which is connected to a drive shaft (100), a projecting detent tooth (81) is provided on an outer circumferential surface of the connecting part (80), wherein the projecting detent tooth (81) and the clutch shoes (70) form a ratchet mechanism, and the preloading element (46) preloads the clutch shoes (70) with a force that is at most equal to their own weight the clutch shoe (70).;

Description

[Field of Invention]The present invention relates to a clutch which is disposed in a transmission path for a driving force and which performs connection or disconnection of the transmission path.[General Art]In a small drive device such as a small motorcycle, a chainsaw, or a remote engine drive helicopter, a centrifugal clutch that does not require clutch operation is generally used (for example, see Patent Documents 1 and 2).Patent Document 1 describes a centrifugal clutch. This centrifugal clutch includes: a cylindrically shaped clutch drum connected to an output shaft; a hub (a rotating bearing part) accommodated in the clutch drum, connected to a drive shaft, and rotating about the axial center of the clutch drum; two arc-shaped clutch shoes supported by the hub in such a manner as to be able to rotate about an axis parallel to the axial center of the clutch drum; and a spring biasing the clutch shoes toward the axial center of the clutch drum.When the hub rotates at a speed at least as high as a predetermined speed in conjunction with rotation of the drive shaft, the clutch shoes resist the biasing force of the spring to approach and engage the inner circumferential surface of the clutch bell. The clutch drum rotates, thereby rotating the output shaft.Patent Document 2 describes a centrifugal clutch including: a cylindrically shaped clutch drum connected to an output shaft; a boss (a rotating bearing part) inside the clutch drum, connected to an input shaft and rotating about the axial center of the clutch drum; four arc-shaped clutch shoes disposed between the boss and the clutch drum; and a coil spring biasing the clutch shoes toward the axial center of the clutch drum.In this centrifugal clutch, as well, when the boss rotates at a rotation speed at least as high as a predetermined rotation speed in conjunction with rotation of the drive shaft, the clutch shoes resist the biasing force of the coil spring so as to approach and engage the inner circumferential surface of the clutch cup. The clutch drum rotates, thereby rotating the output shaft.In recent years, an electromagnetic clutch has also been proposed in which the clutch can be electromagnetically connected or disconnected based on the rotational speed of the drive shaft (see, for example, Patent Document 3).Other relevant prior art related to the present invention is described in Patent Documents 4-7.[Prior Art Documents][Patent Documents][Patent Document 1] Japanese Patent Application Laid-Open JP H07-190 100A[Patent Document 2] Japanese Patent Application Laid-Open JP H06-280 901A[Patent Document 3] Japanese Patent Publication JP 3 688 973 B2[Patent Document 4] WO 2004 / 106 762 A1[Patent Document 5] DE 33 24 355 A1[Patent Document 6] DE 15 50 764 B[Patent Document 7] JP S59-186 533 U[Summary of the Invention][Problems underlying the Invention]In the centrifugal clutch described in Patent Documents 1 and 2, when the rotational speed of the hub or the boss, in other words, the rotational speed of the drive shaft, is lower than a predetermined rotational speed (for example, 1000 1 / min), the biasing force of the spring prevents the clutch shoes from engaging the clutch cup.Depending on the necessary specifications, it is necessary for the clutch shoes to engage the clutch bell at a rotational speed which is lower than a predefined rotational speed. In order to meet this need, it is possible to proceed, for example, by setting the biasing force of the spring low, that is, setting the predetermined rotational speed low.In a case where the predetermined rotation speed is set low (e.g., set to 100 1 / min), the centrifugal force acting on the clutch shoe also becomes small. In a case where the centrifugal force acting on the clutch shoe becomes substantially equal to the dead weight of the clutch shoe or, alternatively, becomes smaller than the dead weight, the clutch shoe resists the force of the spring due to its dead weight even when the rotation is performed at a rotation speed at which the input shaft and the output shaft would be expected to be separated from each other (e.g., below 100 1 / min) so as to approach and engage the inner circumferential surface of the clutch cup. As a result, there arises a problem that the input shaft and the output shaft are connected to each other although the rotation is at a rotation speed at which disconnection should be realized.It could be expected that the above-described problem can be solved when the electromagnetic clutch is used. However, when the electromagnetic clutch is used, in addition to the electromagnetic clutch itself, a controller that controls the electromagnetic clutch, a sensor that detects the rotation speed of the drive shaft, a power source, and the like are required. This causes an increase in the number of components and thus causes a complex structure. Further, in an apparatus including the electromagnetic clutch, the controller, the sensor, the power source, and the like, an increase in size is inevitable.The present invention has been devised in view of these circumstances. An object thereof is to provide a clutch with a simple configuration in which even in a case where the rotational speed at which the clutch shoes start to engage with the clutch bell is set to a lower rotational speed, a situation that the clutch shoes engage with the clutch bell can be avoided when the input shaft rotates at a rotational speed at which the input shaft and the output shaft are expected to be separated from each other.[Means for Solving the Problem]The present invention is defined in the independent claims. According to the present invention, there is provided a clutch including: a clutch bell including a cylindrical-shaped accommodation chamber that contains a plurality of clutch shoes and that rotates about an axis of the accommodation chamber; a rotating bearing part inside the accommodation chamber that rotates about the axis of the accommodation chamber due to power transmitted from a drive shaft and that supports an end part of each of the plurality of clutch shoes in a manner that allows rotation about an axis parallel to the axial center of the accommodation chamber; and a biasing member that biases the clutch shoes toward the axial center of the receiving chamber, the clutch shoes being provided along a circumferential surface of the receiving chamber, characterized in that a converting part that converts an own weight of one of the clutch shoes into a force in a direction that causes disengagement with the output shaft and that then causes the converted force to act on the other clutch shoes is provided.In the present invention, for example, the dead weight of one clutch shoe is converted into a force in a direction that causes disengagement from the output shaft and that then acts on the other clutch shoes. That is, the dead weight of the one clutch shoe is converted into a force that causes the other clutch shoes to be released from the output shaft. Thus, even if the biasing force of the biasing member is made small, a situation that the other clutch shoes engage with the output shaft due to the self-weight is avoided.According to the present invention, the clutch is characterized in that the clutch bell is connected to the output shaft, and the converting part converts the dead weight of one of the clutch shoes into a force directed to the axial center of the receiving chamber and then causes the converted force to act on the other clutch shoes.In the present invention, for example, the dead weight of one clutch shoe is converted into a force directed to the axial center of the accommodation chamber and then acts on the other clutch shoes. That is, the dead weight of the one clutch shoe is converted into a force that causes the other clutch shoes to separate from the inner circumferential surface of the clutch cup. Thus, even if the biasing force of the biasing member is made small, a situation that the other clutch shoes engage the inner circumferential surface of the clutch bell due to the dead weight is avoided.According to the present invention, the clutch is characterized in that the clutch shoe is provided with a friction material formed to be in contact with the circumferential surface of the accommodation chamber.In the present invention, when only one (any) of the clutch shoes is provided with the friction material, a one-way clutch is realized, and when both the clutch shoes are provided with the friction material, a two-way clutch is realized.According to the present invention, the clutch is characterized in that at least a part of the input shaft is disposed in the accommodation chamber and connected coaxially to the accommodation chamber, a connection part is provided which is set on the input shaft in such a manner as to allow rotation inside the accommodation chamber and which is connected to the output shaft, and the conversion part converts the dead weight of one of the clutch shoes into a force directed to the circumferential surface of the accommodation chamber and then causes the converted force to act on the other clutch shoes.According to the present invention, the clutch is characterized in that the biasing member biases the clutch shoes with a force that is at most as large as the self-weight of the clutch shoe.In the present invention, the biasing force of the biasing member is set to be at most as high as the dead weight of the clutch shoe, so that the rotation speed at which the clutch shoe starts approaching the inner circumferential surface can be made remarkably low.According to the present invention, there is provided a clutch including: a clutch bell having a cylindrical-shaped accommodation chamber containing a clutch jaw and connected to an output shaft and then rotating about an axis of the accommodation chamber; a rotating support part inside the accommodation chamber, which rotates about the axis of the accommodation chamber due to power transmitted from a drive shaft and supports an end part of the clutch jaw in a manner allowing rotation about an axis parallel to the axial center of the accommodation chamber; and a biasing member that biases the clutch shoes toward the axial center of the accommodation chamber, the clutch shoes being provided along a circumferential surface of the accommodation chamber, characterized in that the rotating bearing part includes a rotating shaft that supports the one end part of the clutch shoe, and an angle formed between a first line segment connecting a contact point between the other end part of the clutch shoe and the circumferential surface of the accommodation chamber and a rotation center of the rotating shaft and a second line segment connecting the contact point and a rotation center of the driving shaft satisfies tan θ<μ (where μ is a friction coefficient).In the present invention, a so-called frictional engagement is generated between the other end portion of the clutch shoe and the clutch bell so that the clutch shoe engages the clutch bell. Further, when the biasing force of the biasing member is adjusted, the clutch shoe engages the clutch bell only when necessary.According to the present invention, the clutch is characterized in that the other end part of the clutch shoe is provided with a friction material formed to be in contact with the circumferential surface of the receiving chamber, and the friction material is constructed to be engaged with the circumferential surface of the receiving chamber without slipping.In the present invention, a so-called frictional connection is generated between the friction material and the clutch bell so that the clutch jaw engages the clutch bell substantially without slipping.[Effect of the Invention]In the clutch according to the present invention, for example, the self-weight of one clutch shoe is converted into a force that is at the axial center of the accommodation chamber and then acts on the other clutch shoes. That is, the dead weight of the one clutch shoe is converted into a force that causes the other clutch shoes to separate from the inner circumferential surface of the clutch cup. Thus, even if the biasing force of the biasing member is made small, a situation that the other clutch shoes engage the inner circumferential surface of the clutch bell due to the dead weight is avoided. Thus, a connection between the input shaft and the output shaft at a rotational speed at which disconnection is to be achieved can be avoided.[Brief Description of Drawings]FIG. 1 is a front partial sectional view schematically illustrating an internal structure of a clutch according to Embodiment 1. FIG. 2 is an exploded perspective view schematically illustrating an internal structure of a clutch. FIG. 3 is an explanatory diagram describing a relationship between a friction coefficient μ between a friction material and a clutch drum and a strut angle θ. FIG. 4 is an explanatory diagram describing a clutch in the stopped state. FIG. 5 is an explanatory diagram describing a clutch in a state where a drive shaft rotates in a normal direction at or above an engagement start speed. FIG. 6 is an explanatory diagram describing a clutch in a state where an input shaft has an engagement start speed or more and torque in a normal rotational direction is input from an output shaft. FIG. 7 is a graph schematically illustrating a relationship between a pressing force and a friction coefficient in a friction material made of a material and a rotational speed of a drive shaft. FIG. 8 is a graph schematically illustrating a relationship between a pressing force and a friction coefficient in a friction material made of another material and a rotational speed of a drive shaft. FIG. 9 is an explanatory diagram describing a relationship between an own weight of a clutch shoe and a biasing force of a spring in a clutch not provided with an engagement mechanism. FIG. 10 is a diagram illustrating another device that biases clutch shoes in a direction of being separated from a receiving chamber. FIG. 11 is a diagram illustrating another device that biases clutch shoes in a direction of being separated from a receiving chamber. FIG. 12 is a front view schematically illustrating an internal structure of a clutch according to Embodiment 2. FIG. 13 is an exploded perspective view schematically illustrating a coupling. FIG. 14 is an exploded perspective view schematically illustrating a first modification in which a configuration of a clutch has been partially changed. FIG. 15 is a front view schematically illustrating a second modification in which a configuration of a clutch has been partially changed. FIG. 16 is a perspective view schematically illustrating a third modification in which a configuration of a clutch has been partially changed. FIG. 17 is an exploded perspective view schematically illustrating a fourth modification in which a configuration of a clutch has been partially changed. FIG. 18 is a front view schematically illustrating a clutch according to Embodiment 3.[Implementation mode of the invention](Embodiment 1)The present invention will be described in detail below with reference to the drawings illustrating a clutch according to Embodiment 1. FIG. 1 is a front partial sectional view schematically illustrating the internal structure of a clutch, and FIG. 2 is an exploded perspective view schematically illustrating the internal structure of the clutch. In this case, a clutch bell 1 is not shown in FIG. 2.A clutch includes a flat clutch cup 1 having a closed-end cylindrical shape. In a radial direction center portion in the lower part of the clutch drum 1, an output shaft fitting hole 2 a, into which an output shaft (not shown) is fitted, is provided. A cylindrically shaped receiving chamber 2 is formed in the interior of the clutch bell 1, which receiving chamber contains a first clutch jaw 10 and a second clutch jaw 20.Inside the accommodation chamber 2, there is provided a rotating support part 30 that rotates about the axis of the accommodation chamber due to power transmitted from a drive shaft (not shown) and supports each of both an end part of the first clutch shoe 10 and the second clutch shoe 20 in such a manner as to allow rotation about an axis that is parallel to the axial center of the accommodation chamber 2, the rotating support part 30 includes: a coupling plate 31 that has an elliptical shape and is coupled to the drive shaft; a protruding part 32 that protrudes at one end part in the longitudinal direction of the coupling plate on the side of one surface of the coupling plate 31; and a counter plate 33 that is provided in a front part of the protruding part 32 and that is opposed to the one surface of the coupling plate 31. The rotating bearing member 30 is contained in the accommodation chamber 2 in such a manner that the other surface of the coupling plate 31 is opposed to the bottom surface of the accommodation chamber 2.The central part on the one surface side of the coupling plate 31 is funnel-shaped and stepped-recessed. Further, an input shaft fitting hole 31b into which the input shaft is fitted is provided in the lower part of the recess. Here, the position of the center of rotation of the input shaft and the position of the center of rotation of the output shaft are substantially the same. An annular part 31 dprotrudes from the one surface of the coupling plate 31 so as to surround the recessed portion. A groove part 31 chaving an L-shaped cross section is formed at the other end part in the longitudinal direction of the coupling plate 31.The one end part in the longitudinal direction of the coupling plate 31, the protruding part 32, and the counter plate 33 form a recessed insertion part 34 into which the first clutch shoe 10 and the second clutch shoe 20 are inserted. The bottom surface of the recessed insertion part 34 (the side surface of the protruding part 32) is provided with two bearing holes 32 aand 32 bin which springs described later are received and supported. Each of the bearing holes 32 aand 32 bhas a closed-end cylindrical shape, and the axial centers of the bearing holes 32 aand 32 bangulate the bottom surface of the recessed insertion part 34. More specifically, the lines on which the respective axial centers of the two bearing holes 32 aand 32 brun do not intersect each other on the drive shaft fitting hole 31 bside, as illustrated in FIG. 1 in a front view.In the counter plate 33, two insertion holes 33 aand 33 a, into which a first rotation shaft 17 and a second rotation shaft 27 described later are inserted, are provided in a direction perpendicular to the longitudinal direction of the coupling plate 31 in parallel with each other. Further, also in the coupling plate 31, two insertion holes 31a and 31a corresponding to the insertion holes 33a and 33a, respectively, are provided. Each of the two insertion holes 33 aand 33 aprovided in the counter plate 33 and each of the two insertion holes 31 aand 31 aprovided in the coupling plate 31 are arranged coaxially with each other.The first clutch shoe 10 has a semi-circular arc shape along the circumferential surface of the accommodation chamber 2, and then an end part of the first clutch shoe 10 is inserted into the recessed insertion part 34. An end part of the first clutch shoe 10 is provided with a rotation shaft hole 13 into which the first rotation shaft 17 is inserted. The rotation shaft hole 13 is disposed coaxially with an insertion hole 33 aprovided in the counter plate 33 and an insertion hole 31 aof the coupling plate 31 corresponding to the one insertion hole 33 a. The first rotary shaft 17 is inserted into the two insertion holes 31 aand 33 aand the rotary shaft hole 13, and then the first clutch shoe 10 rotates about the first rotary shaft 17.In a portion corresponding to the bearing hole 32 ain the one end part of the first clutch shoe 10, a spring hole 14 into which a spring 41 is inserted is provided. The spring hole 14 has a closed-end cylindrical shape. The helical spring 41 is inserted into the bearing hole 32a with one end part first, and then is inserted into the spring hole 14 with the other end part first. The spring 41 biases the first clutch shoe 10 in a direction separating it from the accommodation chamber 2 (counterclockwise in FIG. 1 ). The amount of biasing force of the spring 41 is substantially equal to the dead weight of the first clutch shoe 10, or alternatively is less than the dead weight.A friction material 12 is fixed to the other end portion of the first clutch shoe 10 with a fixing portion 11 therebetween. The circumferential surface portion of the other end part of the first clutch shoe 10 is formed to be thicker than the other portion of the first clutch shoe 10 in the axial longitudinal direction, so that the fixing part 11 is formed. The friction material 12 is provided on the outer circumferential surface of the fixing part 11 and is integrated therewith. Here, the fixing part 11 and the friction material 12 protrude toward the rotating bearing part 30. However, they are disposed at a position corresponding to the position of the groove part 31c, and therefore they do not interfere with the rotary bearing part 30, and at this time, the portion where the groove part 31c is provided on the coupling plate 31 does not need to be provided.The second clutch shoe 20 has a semi-circular arc shape along the circumferential surface of the accommodation chamber 2, and then an end part of the second clutch shoe 20 is inserted into the recessed insertion part 34. In the accommodation chamber 2, the second clutch shoe 20 is located on a side opposite to the first clutch shoe 10 so as to form a C-shape together with the first clutch shoe 10. The one end part of the second clutch shoe 20 is provided with a rotation shaft hole 23 into which the second rotation shaft 27 is inserted. The rotation shaft hole 23 is disposed coaxially with the other insertion hole 33 aprovided in the counter plate 33 and with an insertion hole 31 aof the coupling plate 31 corresponding to the other insertion hole 33 a. The second rotary shaft 27 is inserted into the two insertion holes 31 aand 33 aand the rotary shaft hole 23, and then the second clutch shoe 20 rotates about the second rotary shaft 27.In a portion corresponding to the bearing hole 32 bin the one end part of the second clutch shoe 20, a spring hole 24 into which a spring 42 is inserted is provided. The spring hole 24 has a closed-end cylindrical shape. The helical spring 42 is inserted into the bearing hole 32b with one end part thereof first, and then is inserted into the spring hole 24 with the other end part thereof first. The spring 42 biases the second clutch shoe 20 in a direction to separate it from the accommodation chamber 2 (clockwise in FIG. 1 ). The magnitude of the biasing force of the spring 42 is substantially equal to the dead weight of the second clutch shoe 20, or alternatively is less than the dead weight.Here, the design may be changed such that the lines on which the respective axial centers of the two bearing holes 32 aand 32 brun intersect each other on the drive shaft fitting hole 31 bside. Then, the design of the spring holes 14 and 15 can be changed accordingly.A friction material 22 is fixed to the other end portion of the second clutch shoe 20 with a fixing portion 21 therebetween. The circumferential surface portion of the other end part of the second clutch shoe 20 is formed to be thicker than the other portion of the second clutch shoe 20 in the axial longitudinal direction, so that the fixing part 21 is formed. The friction material 22 is provided on the outer circumferential surface of the fixing part 21 and is integrated therewith. Here, the fixing part 21 and the friction material 22 protrude toward the rotating bearing part 30. However, they are disposed at a position corresponding to the position of the groove part 31c, and therefore they do not interfere with the rotary bearing part 30.The individual respective end portions of the first clutch shoe 10 and the second clutch shoe 20 are opposed to each other in the circumferential direction of the accommodation chamber 2. Then, an engaging mechanism 50 is provided in the opposing portion. The engagement mechanism 50 includes: a protruding part 15 that protrudes from the first front surface of the one end part of the first clutch shoe 10 toward the second clutch shoe 20 in the vicinity of the rotation shaft hole 13; and a recessed part 25 that is formed in the front surface of the one end part of the second clutch shoe 20 in the vicinity of the rotation shaft hole 23 and with which the protruding part 15 engages.Recesses 16 and 16 are formed at right and left sides of the protruding part 15, respectively. Then, two protruding parts 26 and 26 corresponding to the recesses 16 and 16 are formed to the right and left of the recessed part 25. The two recesses 16 and 16 allow the protruding part 15 to have a length necessary for engagement with the recess part 25. Further, the two recesses 26 and 26 allow the recess part 25 to have a depth necessary for receiving the protruding part 15. The protruding parts 26 do not engage with the recesses 16, and the protruding parts 26 are separated from the recesses 16.FIG. 3 is an explanatory diagram describing a relationship between a friction coefficient μ between the friction material 12 and the clutch drum 1 and a strut angle θ. Here, the second clutch bell 20 is not shown in FIG. 3.As illustrated in FIG. 3, the positional relationship between the friction material 12 and the first rotating shaft 17 is configured such that an angle (a strut angle θ) formed between a line segment AB connecting a contact point A of the friction material 12 fixed to the first clutch shoe 10 and the clutch cup 1 (the inner circumferential surface of the accommodation chamber) and a rotation center B of the first rotating shaft 17 and a line segment AC connecting the contact point A and a rotation center C of the input shaft (the rotation center of the output shaft) can satisfy the following condition: tan θ<μ. Here, the strut angle θ is changed depending on the contact position of the friction material 12 and the clutch bell 1. However, the positional relationship between the friction material 12 and the first rotating shaft 17 is designed so that the above-described condition can be satisfied even when the friction material 12 comes into contact with the clutch drum 1 at any point.Further, similarly, an angle (a strut angle θ) formed between a line segment connecting a contact point between the friction material 22 fixed to the second clutch shoe 20 and the clutch cup 1 and a rotation center of the second rotation shaft 27 and a line segment connecting the contact point and the rotation center of the input shaft (the rotation center of the output shaft) also satisfies the above-described condition.When this condition is satisfied, the friction materials 12 and 22 serve as braces so that a so-called frictional connection is generated between the friction material 12 or 22 and the clutch bell 1. Due to this, the friction materials 12 and 22 substantially engage the clutch drum 1 without slipping when the friction materials 12 and 22 come into contact with the clutch drum 1. In other words, the friction materials 12 and 22 are arranged according to the friction coefficient μ so that the above-described condition can be satisfied.However, as described above, the friction coefficient μ varies greatly depending on the friction materials 12 and 22 in some cases, depending on conditions such as the pressing pressure and the temperature. When such friction materials 12 and 22 in which the friction coefficient μ varies greatly are used, the above-described condition is not always satisfied. When the friction coefficient becomes smaller depending on the state of the clutch, so that the above-described condition is no longer satisfied, the frictional engagement does not occur.FIG. 4 is an explanatory diagram describing the clutch in the stopped state. FIG. 5 is an explanatory diagram describing the clutch in a state where the input shaft rotates in a normal direction at or above an engagement start speed. FIG. 6 is an explanatory diagram describing the clutch in a state where the input shaft has or exceeds the engagement start speed and torque in a normal rotational direction is input from the output shaft. Here, it is assumed that the first clutch shoe 10 is disposed at the top and the second clutch shoe 20 is disposed at the bottom.As illustrated in FIG. 4, in a stopped state, a downward own weight F 2 acts on the second clutch shoe 20, and thus the second clutch shoe 20 tends to approach the clutch shoe 1. On the other hand, a downward dead weight F 1 acts on the first clutch shoe 10 in a similar manner, and the first clutch shoe 10 and the second clutch shoe 20 have substantially the same dead weight.The own weight F 1 is converted by the first rotation shaft 17 into a rotational force F 3 (a counterclockwise force in FIG. 4 ) acting around the first rotation shaft 17. The rotational force F 3 is then transmitted to the engagement mechanism 50 so that the protruding part 15 engaged with the recess part 25 rotates counterclockwise and the second clutch shoe 20 rotates clockwise about the second rotation shaft 27. That is, due to the engagement mechanism 50, the rotational force F 3 is converted into a rotational force F 4 acting around the second rotational shaft 27 (a clockwise force in FIG. 4 ).The rotational force F 4 is converted by the second rotation shaft 27 into an upward force F 5 (opposite to the own weight F 2). Since the first clutch shoe 10 and the second clutch shoe 20 have substantially the same own weight, the own weight F 2 and the force F 5 are substantially the same. Thus, a force balance is achieved between the own weight F 2 and the force F 5. This avoids a situation in which the second clutch jaw 20 arranged at the bottom comes into contact with the clutch bell 1 due to its own weight.Biasing forces 41 and 42 act on the first clutch shoe 10 and the second clutch shoe 20, respectively. The biasing force F 6 acting on the first clutch shoe 10 is converted into a counterclockwise force by the first rotation shaft 17, and then acts as a force causing the first clutch shoe 10 to separate from the clutch bell 1. The biasing force F 6 acting on the second clutch shoe 20 is converted into a clockwise force by the second rotation shaft 27 and then acts as a force that causes the second clutch shoe 20 to separate from the clutch cup 1.The first clutch shoe 10 and the second clutch shoe 20 separate from the circumferential surface of the accommodation chamber 2 due to the biasing forces F 6, thus there is a gap between the friction material 12 or 22 present in the first clutch shoe 10 or the second clutch shoe 20 and the circumferential surface of the accommodation chamber 2, thus allowing the clutch cup 1 to freely rotate.As described above, in a stopped state, a force balance is achieved between the dead weight F 2 of the second clutch shoe 20 and the force F 5 (the force obtained by converting the dead weight of the first clutch shoe 10). In other words, the dead weights of the first clutch shoe 10 and the second clutch shoe 20 cancel each other. Also, when the biasing force F 6 of the spring 42 provided in the second clutch shoe 20 is substantially equal to or alternatively less than the dead weight F 2 of the second clutch shoe 20, a situation that the second clutch shoe 20 comes into contact with the clutch cup 1 by the dead weight is avoided.The biasing force F 6 of the spring 42 provided in the second clutch shoe 20 is not cancelled by the dead weight F 2 of the second clutch shoe 20, and thus acts on the second clutch shoe 20 as a force that causes it to separate from the clutch bell 1.Here, in a case where the first clutch shoe 10 is disposed at the bottom and the upper clutch shoe 20 is disposed at the top, the directions of the acting forces are reversed. However, similar to the second clutch shoe 20 described above, a situation that the lower-disposed first clutch shoe 10 comes into contact with the clutch bell 1 due to the self-weight is avoided.Although an external force is caused to the first clutch shoe 10 and the second clutch shoe 20 by vibration or the like, operation is similar to that described above. For example, in a situation where the clutch is brought into a horizontal orientation, even if an external force acts on the clutch, a situation that the first clutch shoe 10 or the second clutch shoe 20 comes into contact with the clutch bell 1 due to the external force is avoided.As illustrated in FIG. 5, centrifugal force acts on the first clutch shoe 10 and the second clutch shoe 20 when the drive shaft rotates in a normal direction (see an unshaded arrow in FIG. 5 ). Then, when the centrifugal force becomes larger than the biasing force of the spring 41 (for example, when the rotational speed of the drive shaft 100 reaches 1 / min or more), the first clutch shoe 10 and the second clutch shoe 20 approach the clutch drum 1. the friction material 12 provided in the first clutch shoe 10 and the friction material 22 provided in the second clutch shoe 20 come into contact with the circumferential surface of the accommodation chamber 2, so that the first clutch shoe 10 causes a frictional engagement to engage with the circumferential surface. The clutch shoe 1 rotates so that a rotation center is transmitted from the input shaft to the output shaft (see the shaded arrow in FIG. 5 ). At this time, no frictional coupling of the second clutch shoe 20 to the clutch bell 1 takes place.At this time, when the biasing force F 6 of the spring 41 of the biasing member is set to be at most as high as the dead weight of the first clutch shoe 10, the rotational speed at which the first clutch shoe 10 starts to engage the inner circumferential surface of the clutch drum 1 can be made remarkably low.When the friction material 22 provided in the second clutch shoe 20 is in contact with the clutch drum 1 as illustrated in FIG. 6 (when the rotational speed of the input shaft is at least 100 1 / min, for example), and a torque in the normal rotational direction is applied from the output shaft (see an unshaded arrow in FIG. 6 ), the friction material 22 provided in the second clutch shoe 20 and the clutch drum 1 frictionally engage each other. The torque from the output shaft is transmitted to the input shaft (see a shaded arrow in FIG. 6 ).In this case, for example, when the clutch according to Embodiment 1 is used as a clutch for power transmission in a vehicle equipped with an internal combustion engine, so-called engine brake can be realized. The clutch according to Embodiment 1 can be used as a two-way clutch.In a case where no friction material 22 is present on the second clutch shoe 20, the torque from the output shaft is not transmitted to the input shaft, and thus the clutch is used as a one-way clutch. The presence or absence of the torque transmission from the output shaft to the input shaft may be changed according to necessary specifications. Thus, the user can select from among a one-way clutch and a two-way clutch.The friction materials 12 and 22 are selected according to necessary specifications. Generally, the friction coefficient of the friction materials 12 and 22 varies depending on the pressing pressure. However, depending on the material used in the friction materials 12 and 22, some friction materials 12 and 22 are strongly dependent on the nip pressure, and other friction materials 12 and 22 are not strongly dependent on the nip pressure.As described above, in the relationship between the friction coefficient μ between the friction material 12 or 22 and the clutch drum 1 and the strut angle θk, the condition necessary for establishing non-slip engagement between the friction material 12 or 22 and the clutch drum 1 is tan θ<μ (see FIG. 3 ). On the other hand, the condition for causing slippage between the friction material 12 or 22 and the clutch drum 1 is tan θ>μ.The strut angle θ is determined by the positional relationships between the first rotating shaft 17 or the second rotating shaft 27, the friction material 12 or 22, and the input shaft or the output shaft. When the positional relationships are set, tan θ has a fixed value α. When μ>α, non-slip engagement is established (the "non-slip engagement" is hereinafter referred to as "coupling"). Further, when μ<α, slipping engagement is established.FIG. 7 is a graph schematically illustrating the relationship between the pressing pressure and the friction coefficient in the friction materials 12 and 22 made of one material and the rotational speed of the drive shaft. FIG. 8 is a graph schematically illustrating the relationship between the nip pressure and the coefficient of friction in the friction materials 12 and 22 made of another material and the rotational speed of the drive shaft. Here, the pressing force generated by the centrifugal force acting on the first clutch jaw 10 or the second clutch jaw 20, and thus the magnitude of the pressing force, corresponds to the magnitude of the rotational speed.As illustrated in FIG. 7, in the friction materials 12 and 22 using the one material, the friction coefficient μ is larger than α regardless of the magnitude of the pressing pressure. In a case where the friction material 12 using the one material is fixed to the first clutch shoe 10, the friction material 12 couples to the clutch drum 1 so that the torque of the input shaft is directly transmitted to the output shaft when the rotational speed of the input shaft is at least as high as the rotational speed at which engagement starts (the engagement start rotational speed) (see FIG. 5 ).On the other hand, in a case where the friction material 22 using the one material is fixed to the second clutch shoe 20, the friction material 22 couples to the clutch cup 1 so that the torque of the output shaft is directly transmitted to the input shaft when the rotation speed of the output shaft is at least as high as the engagement start rotation speed (see FIG. 6 ). In other words, the engagement start speed is substantially equal to the lowest speed at which the friction material 12 or 22 and the clutch drum 1 are coupled to each other (the coupling speed).As illustrated in FIG. 8, in the friction materials 12 and 22 using another material, the magnitude of the friction coefficient μ varies depending on the magnitude of the pressing pressure. In the friction materials 12 and 22 using the other material, the coupling rotational speed is higher than the engagement start rotational speed.In a case where the friction material 12 using the other material is fixed to the first clutch shoe 10, the friction coefficient μ is smaller than α when the rotation speed of the input shaft is a value between the engagement start rotation speed and the coupling rotation speed, and thus the friction material 12 slidably engages the clutch shoe 1 to transmit power to the output shaft. On the other hand, when the rotational speed of the input shaft is higher than the coupling rotational speed, the friction coefficient μ is higher than α, and thus the friction material 12 couples with the clutch drum 1 (see FIG. 5 ).In a case where the friction material 22 using the other material is fixed to the second clutch shoe 20, the friction coefficient μ is smaller than α when the rotation speed of the input shaft is a value between the engagement start rotation speed and the coupling rotation speed, and thus the clutch drum 1 and the friction material 22 transmit the power to the output shaft in a slipping manner. On the other hand, when the rotational speed of the output shaft is higher than the coupling rotational speed, the friction coefficient μ is higher than α, and thus the friction material 22 couples with the clutch drum 1 (see FIG. 6 ).Here, when the rotational speed of the input shaft is less than the engagement start rotational speed, the first clutch shoe 10 and the second clutch shoe 20 separate from the clutch drum 1, and thus the friction materials 12 and 22 do not come into contact with and do not engage with the clutch drum 1.When the friction materials 12 and 22 are selected from a plurality of friction materials each consisting of different materials according to a specification, the clutch may be configured such that the friction materials 12 and 22 can engage the clutch bell 1 without slipping, or alternatively, the clutch may be configured such that the friction materials 12 and 22 can engage the clutch bell 1 slipping.In a case where the friction materials 12 and 22 are engaged with the clutch drum 1 without slipping, at a time when the friction materials 12 and 22 are started to be engaged with the clutch drum 1, the rotational speed of the output shaft at the start time immediately becomes substantially equal to the rotational speed of the input shaft, and thus a quick coupling can be realized.In a case where the friction materials 12 and 22 are slidably engaged with the clutch drum 1, in association with an increase in the rotational speed of the drive shaft, in a state where the friction materials 12 and 22 are slid on the circumferential surface of the accommodation chamber 2, the pressing pressure on the circumferential surface of the accommodation chamber 2 gradually increases. Thus, coupling is established between the input shaft and the output shaft without a large impact force occurring.Here, when the friction material 12 of the first clutch shoe 10 and the friction material 22 of the second clutch shoe 20 are respectively made of different materials, the coupling rotational speed may be respectively made different in a case where a torque in the normal rotational direction is input from the input shaft and in a case where a torque in the normal rotational direction is input from the output shaft. For example, one of the friction materials 12 and 22 engages the clutch drum 1 without slipping, and the other engages the clutch drum 1 with slipping.In the clutch according to Embodiment 1, the self-weight of the clutch shoe 10 is converted by the engagement mechanism 50 into a force directed to the axial center of the accommodation chamber 2 and then acting on the other clutch shoe 20. That is, the dead weight of the first clutch shoe 10 is converted into a force that causes the other clutch shoe 20 to separate from the inner circumferential surface of the clutch drum 1. Thus, even if the biasing force of the spring 42 is made smaller than the dead weight, a situation that the second clutch shoe 20 engages with the inner circumferential surface of the clutch drum 1 due to the dead weight is avoided. Thus, a connection between the input shaft and the output shaft at a rotational speed at which disconnection is to be achieved can be avoided. Further, an increase in magnitude is avoidable, and torque can be transmitted from the input shaft to the output shaft even at a low speed.In a case where the engagement mechanism 50 is not provided, a small configuration does not allow a situation that torque is transmitted from the input shaft to the output shaft at a low speed. The reasons for this are as follows.FIG. 9 is an explanatory diagram describing a relationship between an own weight of the clutch shoe and the biasing force of the spring in a clutch not provided with the engagement mechanism 50.A centrifugal force F c, which acts on the clutch drum, is expressed as F c= mrω 2 here, m is the mass (kg) of the clutch drum, r is the distance (m) from the rotation center of the rotation shaft to the center of gravity, and ω is the angular velocity (rad / s).The force that presses the clutch shoe against the clutch drum 1 is the difference between the centrifugal force F c and the biasing force F s of the spring. Thus, the transmission torque T of the clutch is expressed by the following formula. Here, μ is the friction coefficient, and R is the inner diameter of the clutch bell 1.In order to increase the transmission torque at a low speed, the biasing force of the spring needs to be decreased, the clutch shoe needs to be made heavier, the inner diameter of the clutch shoe 1 needs to be increased, or some other method needs to be adopted as apparent from the above formula.In a case where the clutch shoe is made heavy or the inner diameter of the clutch shoe 1 is increased, an increase in the clutch weight or an increase in the clutch size is caused. Thus, this method is not advantageous. Thus, in order to avoid the increase in weight and the increase in size, one operable way is to reduce the biasing force of the spring.However, in a case where the biasing force of the spring is excessively reduced, even if the rotation speed of the input shaft is at a rotation speed at which the input shaft and the output shaft would be expected to separate from each other, the clutch shoe approaches the circumferential surface of the accommodation chamber 1 due to the dead weight mg, so that a friction material comes into contact with and engages the clutch cup 1, and thus an undesirable force is transmitted to the output shaft (see FIG. 9 ). Thus, the biasing force F s of the spring needs to be set to a level that allows the clutch shoe's own weight to be supported.That is, F s > mg is necessary. When the biasing force F s of the spring is set to the smallest force that allows the clutch shoe's own weight mg to be supported, the transmission torque T becomesThe conditions necessary to ensure that the transmission torque has a positive value areAlso, at a low rotation speed (in a case where ω is set to a small value), for an increase in transmission torque, an increase in the distance between the center-of-gravity position of the clutch shoe and the position of the rotation center (an increase in r) is indispensable. This causes an increase in size of the clutch. That is, a situation that a clutch having a small size generates transmission torque at a low rotation speed is not achievable as long as the engagement mechanism 50 is not used.In the clutch according to Embodiment 1, due to the use of the engagement mechanism 50, in a state where an increase in size is avoided, torque can be transmitted from the input shaft to the output shaft even at a low rotation speed.Here, in the clutch according to Embodiment 1, the engagement mechanism 50 has been provided. However, instead of the engagement mechanism 50, another mechanism that converts the dead weight of the first clutch shoe 10 into a force directed to the axial center of the accommodation chamber 2 and then applies the converted force to the second clutch shoe 20 may be used. For example, a member made of a raw material having a high friction coefficient (e.g., a member made of rubber) may be fixed to both an end part of the first clutch shoe 10 and the second clutch shoe 20. Then, these members are brought into contact with each other, so that the dead weight of the first clutch shoe 10 can be converted into a force directed to the axial center of the accommodation chamber 2 and then applied to the second clutch shoe 20. Alternatively, a gear may be provided in both an end part of the first clutch shoe 10 and the second clutch shoe 20, and then these gears may mesh with each other. Further, a sprocket or a pulley may be provided in both an end part of the first clutch shoe 10 and the second clutch shoe 20, and then a chain or a belt in the form of 8 may be wound.Further, the number of the clutch shoes is not limited to two. For example, four may be used. When the number of clutch shoes is increased, the load acting on the clutch shoes or the friction materials 12 and 22 can be dispersed, and thus the durability can be improved. Further, the shape of the clutch shoe is not limited to an arc shape, and may be formed in a straight shape.In the above-mentioned embodiment, the spring and the spring hole serve as an example of the means that biases the clutch shoe in a direction to be separated from the accommodation chamber 2. Thus, another device may be used. FIGS. 10 and 11 are diagrams illustrating another device that biases the clutch shoe in a direction to be separated from the accommodation chamber 2.As illustrated in FIG. 10, the first clutch shoe 10 and the second clutch shoe 20 may be coupled to each other by a spring 43. Alternatively, the first clutch shoe 10 and the bearing rotating member 30 may be coupled to each other by a spring 44, as illustrated in FIG. 11, and then the first clutch shoe 20 and the bearing rotating member 30 may be coupled to each other by a spring 44. The springs 43 and 44 bias the first clutch shoe 10 and the second clutch shoe 20 in a direction to be separated from the receiving chamber 2.Further, the clutch shoe and the rotating shaft may be connected by a spring, or alternatively, an annular spring may be disposed before the clutch. Then the coupling jaws can be connected to each other.(Embodiment 2)The present invention will be described below with reference to the drawings illustrating a clutch according to Embodiment 2. FIG. 12 is a front view schematically illustrating the internal structure of a clutch, and FIG. 13 is an exploded perspective view schematically illustrating the clutch. In this case, the clutch bell 1 is not illustrated in FIG. 13.A bearing rotating part 30 includes: a coupling plate 31; two protruding parts 32 and 32; and counter plates 33 provided respectively in upper and front parts of each protruding part 32 and opposing one surface of the coupling plate 31. In the coupling plate 31, an insertion hole 31a is provided at the right and left. In the coupling plate 33, an insertion hole 33a is provided coaxially with the insertion hole 31a. From the central part of one surface of the coupling plate 31, a bearing ring 38 athat supports a bearing gear 38 described later protrudes in the axial longitudinal direction. The bearing ring 38a is provided in the peripheral edge of the drive shaft fitting hole 31b.The bearing gear 38 (a rotating member) is seated on the bearing ring 38a in such a manner as to allow rotation. The bearing gear 38 has an annular part 37 provided on the peripheral edge of the drive shaft. A recess part 35 is provided in both a portion of the outer circumferential surface of the annular part 37 and the other portion which is offset from the one portion by about 180 degrees. Then, two protruding parts 36 and 36 are provided on both sides in the vicinity of the recess part 35.Two clutch shoes 60 and 60 are provided inside the clutch bell 1. The clutch shoe 60 has a semicircular arc shape along the circumferential surface of the accommodation chamber 2. An end part of the clutch shoe 60 is provided with a rotation shaft hole 63 into which a rotation shaft 67 is inserted. The rotation shaft hole 63 is disposed coaxially with the insertion hole 31 aand the insertion hole 33 a. The rotation shaft 67 is inserted into the insertion hole 31 a, the insertion hole 33 a, and the rotation shaft hole 63. Then, the clutch shoe 60 rotates about the rotation shaft 67.The one end part of the clutch shoe 60 is provided with: a protruding part 65 inserted into the recess part 35; and two recesses 66 and 66 formed on both sides in the vicinity of the protruding part 65 and into which the protruding parts 36 and 36 are inserted. The two recesses 66 and 66 allow the protruding part 65 to have a length necessary for engagement with the recess part 35. Further, the two recesses 36 and 36 make it possible for the recess part 35 to have a depth necessary for receiving the protruding part 65. The protruding parts 36 do not engage with the recesses 66, and the protruding parts 36 are separated from the recesses 66.Similarly to the first clutch shoe 10 and the second clutch shoe 20 according to Embodiment 1, the clutch shoe 60 is provided with a spring hole 64, and then a spring 45 is inserted into the spring hole 64. The spring 45 biases the clutch shoe 60 in a direction to be separated from the receiving chamber 2. The magnitude of the biasing force of the spring 45 is substantially equal to the dead weight of the clutch shoe 60, or alternatively is less than the dead weight.A friction material 62 is fixed to the other end portion of the clutch shoe 60 with a fixing portion 61 therebetween. The circumferential surface portion of the other end part of the clutch shoe 60 is formed to be thicker than the other portion of the clutch shoe 60 in the axial longitudinal direction, so that the fixing part 61 is formed. The friction material 62 is provided on the outer circumferential surface of the fixing part 61 and integrated therewith. Here, the friction material 62 has the same characteristics as the friction materials 12 and 22 described in Embodiment 1.In the clutch according to Embodiment 2, the own weights of one clutch shoe 60 (the clutch shoe 60 on the lower side in FIG. 12 ) and the other clutch shoe 60 (the clutch shoe 60 on the upper side in FIG. 12 ) cancel each other similarly to Embodiment 1. Even if the biasing force of the spring provided in the one clutch shoe 60 is substantially equal to or alternatively less than the own weight, a situation that the one clutch shoe 60 comes into contact with the clutch shoe 1 by the own weight is avoided. Here, the clutch according to Embodiment 2 is a so-called one-way clutch.FIG. 14 is an exploded perspective view schematically illustrating a first modification in which the configuration of the clutch according to Embodiment 2 has been partially changed. As illustrated in FIG. 14, a configuration may be used where the bearing ring 38 ais not used. In this case, the bearing gear 38 is fitted on the drive shaft.FIG. 15 is a front view schematically illustrating a second modification in which the configuration of the clutch according to Embodiment 2 has been partially changed. The number of the clutch shoes 60 is not limited to two, and thus may be three or more. For example, three clutch shoes 60 may be disposed inside the clutch bell 1, as shown in FIG. 15. Then, a recess part 35 and two protruding parts 36 and 36 may be provided in each of the portions of the outer circumferential surface of the annular part 37, and then the protruding part 65 of the clutch shoe 60 may engage with the recess part 35. In this case, the positions of the recess part 35 and the two protruding parts 36 and 36 in the circumferential direction and, among other things, the positions and the dimensions for the length of the clutch shoe 60 in the circumferential direction are suitably determined, so that in a stopped state, a balance of forces is achieved between the clutch shoes 60.Further, the configuration of the rotary bearing part 30 is appropriately changed according to the number of the clutch shoes 60, the dimensions, and the like. Further, in Embodiment 2, the recess part 35 was provided in the annular part 37, and the protruding part 65 was provided in the clutch shoe 60. Instead, the protruding part may be provided in the annular part 37, and the recess part may be provided in the clutch shoe 60. In this case, the protruding part of the annular part 37 is inserted into the recessed part of the clutch shoe 60.The recess part 35 of the bearing gear 38 and the protruding part 65 serve as examples of the means that transmits a torque about the rotating shaft generated by gravity of one clutch shoe to the other clutch shoes. As another means, for example, a member made of a raw material having a high friction coefficient may be fixed to an end portion of the clutch shoe and the annular portion 37. Then, these members can be brought into contact with each other, so that the dead weight of the clutch shoe can be converted into a force directed to the axial center of the receiving chamber and then acting on the other clutch shoes. Alternatively, the bearing gear 38 may not be provided, and then a sprocket or a pulley may be fixed to the one end part of each clutch shoe. Then, a torque may be transmitted through a chain or a belt.FIG. 16 is a perspective view schematically illustrating a third modification in which the configuration of the clutch according to Embodiment 2 has been partially changed. FIG. 17 is an exploded perspective view schematically illustrating a fourth modification in which the configuration of the clutch has been partially changed.The clutch according to Embodiment 2 may be a two-way clutch. As shown in FIGS. 16 and 17, two bearing gears 38 and 38 are set on the bearing ring 38 aand allowed to align with each other in the axial direction. Two clutch shoes 60 and 60 engage each bearing gear 38. Between the coupling plate 31 and the counter plates 33, the two coupling shoes 60 and 60 are arranged such that the rotation shaft holes 63 and 63, the insertion hole 31a, and the insertion hole 33a are arranged coaxially with each other. The rotating shaft 67 is inserted into the insertion hole 31 a, the insertion hole 33 a, and the two rotating shaft holes 63 and 63, and then the clutch shoes 60 and 60 rotate about the rotating shaft 67.When the drive shaft rotates in the normal direction, centrifugal force acts on the clutch shoe 60, and when the centrifugal force becomes larger than the biasing force of the spring 45, the clutch shoe 60 approaches the clutch cup 1, the friction material 62 provided in the clutch shoe 60 comes into contact with the circumferential surface of the accommodation chamber 2, so that the clutch shoes 60 and 60 engaging a bearing gear 38 (the clutch shoes located on a side opposite to the rotating bearing part 30 in the axial longitudinal direction as illustrated in FIGS. 16 and 17 ) frictionally engage. The clutch shoe 1 rotates so that the center of rotation is transmitted from the input shaft to the output shaft. Here, at this time, the friction materials 62 provided in the clutch shoes 60 and 60 that mesh with the other bearing gear 38 (the clutch shoes disposed on the side of the rotating bearing part 30 in the axial direction as illustrated in FIGS. 16 and 17 ) come into contact with the clutch cup 1, but do not frictionally mesh. When the friction material 62 provided in the clutch shoe 60 comes into contact with the clutch drum 1 and a rotational center in the normal rotational direction is input from the drive shaft, the friction materials 62 provided in the clutch shoes 60 and 60 engaging with the other bearing gear 38 frictionally engage the clutch drum 1. The torque from the output shaft is transmitted to the input shaft. That is, this clutch serves as a two-way clutch.Among the configurations in Embodiment 2, configurations similar to those of Embodiment 1 are denoted by like reference numerals, and detailed description thereof is omitted.Here, in Embodiments 1 and 2, a configuration in which the dead weights of one and the other clutch shoes cancel each other was used. However, the biasing force of the biasing member may be increased (for example, made larger than the clutch's own weight), and then the configuration that the own weights of the one and the other clutch shoes cancel each other may not be provided. In this case, in a stopped state or in a state where the clutch shoes rotate at a rotational speed at which the input shaft and the output shaft would be expected to separate from each other, the biasing force of the biasing member prevents the clutch shoes from coming into contact with the clutch bell.Further, a configuration may be employed where a single clutch shoe is provided and the clutch shoe then engages the clutch cup 1 in such a manner as to satisfy tan θ<μ, that is, without slipping. In this case, the configuration where the clutch dead weights are not provided.(Embodiment 3)The present invention will be described below with reference to the drawings illustrating a clutch according to Embodiment 3. FIG. 18 is a front view schematically illustrating a clutch according to Embodiment 3. In the clutch bell 1 a drive shaft 100 is provided coaxially. At least a part of the drive shaft 100 is disposed within the accommodation chamber 2.A plurality of recessed receiving portions 2 bare provided on the inner circumferential surface of the receiving chamber 2. Each recessed receiving part 2 bincludes a biasing member such as a spring 46, and a plurality of rotating shafts (rotating bearing parts) 71 are provided in parallel to the drive shaft 100 inside the receiving chamber 2.An annular member 75 which can rotate about the axis of the accommodation chamber 2 is provided along the inner circumferential surface of the accommodation chamber 2. A plurality of recess parts (conversion parts) 75 aare provided on the inner circumferential surface of the annular part 75. An end part of the clutch shoe 70 having an arc shape is provided on each rotating shaft 71 in such a manner as to allow rotation. The other end part of the clutch shoe 70 is provided with a protruding part 70 a(a converting part) fitted into the recessed part 75 a.The spring 46 contained in the recessed receiving portion 2b presses the outer circumferential surface of the annular portion 75 so that the clutch shoe 70 can be biased toward the axial center of the receiving chamber 2. That is, in FIG. 18, the spring 46 presses the annular part 75 in the clockwise direction, and then the annular part 75 presses the protruding part 71 in the clockwise direction around the rotation shaft, so that the clutch shoe 70 is biased toward the axial center of the accommodation chamber 2. Here, the spring 46 biases the clutch shoe 70 with a force that is at most as large as the dead weight of the clutch shoe 70.In the accommodation chamber 2, an annular connection part 80 connected to the output shaft (not illustrated) is fitted on the input shaft 100 in a manner allowing rotation. In the outer circumferential surface of the connecting part 80, a plurality of protruding ratchet teeth 81 obliquely protruding in the radially outward direction are provided in parallel to each other in the circumferential direction. The protruding ratchet teeth 81 and the clutch shoes 70 form a ratchet mechanism.Now, an engagement between the clutch shoes 70 and the connecting part 80 will be described. When the clutch is in a stopped state, each of the clutch shoes 70 is biased toward the axial center by the spring 46, and thus engages with the protruding ratchet tooth 81 of the connecting part 80. When power is transmitted from a drive source (not shown), the input shaft 100 starts rotating clockwise, so that the connection part 80 and the output shaft rotate. When the rotational speed of the drive shaft 100 increases to or above a predetermined rotational speed (for example, 900 1 / min), the other end part of the clutch shoe 70 rotates toward the circumferential surface side of the accommodation chamber 2 due to centrifugal force so as to separate from the protruding ratchet tooth 81 of the connection part 80. As a result, the connecting part 80 does not rotate.The spring 46 biases the clutch shoe 70 with a force that is at most as large as the dead weight of the clutch shoe 70, that is, with a relatively small force. When the drive shaft 100 rotates at a low or medium speed (e.g., below 900 1 / min), the clutch jaw 70 engages the protruding ratchet tooth 81. Then, as the centrifugal force becomes larger, the clutch shoe 70 separates from the protruding ratchet tooth 81.When the rotational speed of the input shaft 100 decreases below the predetermined rotational speed, the clutch shoe 70 engages with the connecting part 80 again due to the biasing force of the spring 46.As shown in FIG. 18, due to the characteristic, a force directed to the side of the input shaft 100 (i.e., toward the axial center of the accommodation chamber 2) acts on the clutch shoe 70 located on the upper side when the clutch is brought into a vertical orientation and the rotation occurs at or above the predetermined rotational speed. For example, in FIG. 18, a force directed to the side of the drive shaft 100 acts on the clutch shoe 70 disposed on the upper side.On the other hand, due to the dead weight, a force F 7 acting on the circumferential surface side of the accommodation chamber 2 acts on the clutch shoe 70 disposed on the lower side. The force F 7 is converted into a force F 8 by the protruding part 70 aof the clutch shoe 70 disposed on the lower side and the recess part 75 athat fits into the protruding part 70 a, which causes the annular part 75 to rotate counterclockwise. The force F 8 is converted into a force F 9 directed to the circumferential surface side of the accommodation chamber 2 by the protruding part 70 aof the clutch shoe 70 disposed on the upper side and the recess part 75 athat fits into the protruding part 70 a.When the clutch is brought into a vertical orientation and the rotation takes place at or above the predetermined rotational speed, a situation can be avoided where the clutch jaw 70 moves toward the axial center of the receiving chamber 2 due to the dead weight and then engages with the protruding ratchet tooth.The embodiments disclosed herein are to be considered illustrative and not restrictive in any point. The technical features described in the individual embodiments can be combined with one another. Further, the scope of the present invention should be considered to include all modifications within the scope of the claims and the range equivalent to the scope of the claims.[Description of Reference Numerals]1 Clutch shoe 2 Accommodation chamber 10 First clutch shoe 12, 22 Friction material 15 Protruding part 20 Second clutch shoe 25 Recessed part 30 Rotating bearing part 35, 75 a Part (conversion part) 36 Protruding part (conversion part) 37 Annular part 38 Bearing gear (rotating part) 41, 42, 46 Spring (biasing member) 50 Engagement mechanism (conversion part) 65 Protruding part (conversion part) 66 Recess (conversion part) 70 a Part (conversion part) 75 Annular part 71 Rotating shaft (rotating bearing part)

Claims

A clutch comprising: a clutch cup (1) having a cylindrically shaped accommodation chamber (2) that contains a plurality of clutch shoes (70) and rotates about an axis of the accommodation chamber (2); a rotating bearing part (71) within the accommodation chamber (2) that rotates about an axis of the accommodation chamber (2) due to power transmitted from a drive shaft (100) and that supports an end part of each of the plurality of clutch shoes (70) in a manner that allows rotation about an axis parallel to the axial center of the accommodation chamber (2); and a biasing member (46) that biases the clutch shoes (70) toward the axial center of the accommodation chamber (2), the clutch shoes (70) being provided along a circumferential surface of the accommodation chamber (2), characterized in that, that at least a part of the drive shaft (100) is disposed in the accommodation chamber (2) and connected coaxially to the accommodation chamber (2), a connection part (80) forming a ring shape is provided, which is fitted on the drive shaft (100) in a manner allowing rotation inside the accommodation chamber (2) and which is connected to a drive shaft (100), a protruding ratchet tooth (81) is provided on an outer circumferential surface of the connection part (80), the protruding ratchet tooth (81) and the clutch shoes (70) form a ratchet mechanism, and the biasing member (46) biases the clutch shoes (70) with a force that is at most as large as the self weight of the clutch shoe (70).Clutch according to Claim 1, characterized in that the clutch jaw (10, 20, 60) is provided with a friction material (12, 22, 62) which is designed in such a way that it is in contact with the circumferential surface of the receiving chamber (2).A clutch comprising: a clutch cup (1) including a cylindrically shaped accommodation chamber (2) that contains a clutch shoe (10, 20) and that is connected to an output shaft and that then rotates about an axis of the accommodation chamber (2); a rotating bearing part (30) that rotates inside the accommodation chamber (2) about the axis of the accommodation chamber (2) due to power transmitted from a drive shaft and that supports an end part of the clutch shoe (10, 20) in a manner that allows rotation about an axis parallel to the axial center of the accommodation chamber (2); and a biasing member (41, 42, 43, 44) that biases the clutch shoes toward the axial center of the receiving chamber (2), the clutch shoes (10, 20) being provided along a circumferential surface of the receiving chamber (2), characterized in that the rotating bearing part (30) has a rotating shaft (17, 27) that supports an end part of the clutch shoe (10, 20), and satisfies an angle (θ) formed between a first line segment (AB) connecting a contact point (A) between the other end part of the clutch shoe (10, 20) and the circumferential surface of the receiving chamber (2) and a rotation center point (B) of the rotating shaft (17, 27) and a second line segment (AC) connecting the contact point (A) and a rotation center point (C) of the driving shaft, tan θ<μ, where μ is a friction coefficient.A clutch according to claim 3, characterized in that the other end portion of the clutch shoe (10, 20) is provided with a friction material (12, 22) formed in contact with the circumferential surface of the receiving chamber (2).

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