Overload protection device

Abstract

To provide an overload protection device which has a simple structure and a low processing cost, can increase transmission torque, enhances accuracy of allowable torque to be set, and enables continuous use even in an overload state by returning torque to normal.SOLUTION: An overload protection device includes a torque transmission mechanism for performing torque transmission of an inner ring 120 and an outer ring 110 coaxially provided in a mutual rotatable manner. Cam slide surfaces 111, 121 of the inner ring 120 and the outer ring 110 have a cylindrical shape. The torque transmission mechanism has: a plurality of cams 130 provided in a circumferential direction between the cam slide surfaces 111, 121 of the inner ring 120 and the outer ring 110; and energization means 140 for energizing the plurality of cams 130 in an auto-rotation direction. The cams 130 have a plurality of minimum radial portions and a plurality of maximum radial portions which are alternately arranged, and are formed in a rotation symmetry shape relative to the auto-rotation center.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an overload protection device that includes an inner ring and an outer ring that are rotatable relative to each other coaxially, and a torque transmission mechanism that transmits torque between the inner ring and the outer ring, and is capable of blocking torque transmission against torque above a tolerance.

Background Art

[0002] An overload protection device that includes a torque transmission mechanism for transmitting torque between two shafts and is capable of blocking torque transmission against torque above a tolerance is well known. For example, as in Patent Document 1, there is known an overload protection device that includes a torque transmission mechanism for transmitting torque between an inner ring and an outer ring that are rotatable relative to each other coaxially, and is capable of blocking torque transmission against torque above a tolerance.

[0003] The overload protection device described in Patent Document 1 is configured such that a plurality of engaging portions (221) having a concave arc shape are provided on the inner peripheral surface of the outer ring (second main body 20), and torque is transmitted by urging a driving member (30) from the inner ring (first main body 10) to the outer peripheral side and pressing it against the engaging portion (221). Against torque above a tolerance, the driving member (30) moves toward the inner ring side against the biasing force to block torque transmission.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The overload protection device described in Patent Document 1 is configured by a torque transmission mechanism between the inner ring and the outer ring and can be miniaturized, but there is a problem in that both the inner ring and the outer ring have a complicated shape and the processing cost is high. In addition, since there is only one torque transmission point on the circumference and it is impossible to provide more torque transmission points than the maximum number of engagement parts (221), it has been difficult to increase the transmitted torque. Furthermore, there are also restrictions on the pressing force of the elastic member that biases the drive member (30), making it difficult to increase the transmitted torque. Also, since the elastic member applies a large pressing pressure with a short stroke in a small space, there has been a problem that it is difficult to increase the accuracy of the allowable torque to be set.

[0006] In order to obtain a large transmitted torque, it is also conceivable to use the limit of the allowable torque of a one-way clutch with a general cam as an overload protection device. However, when the cam clutch exceeds the limit of the allowable torque, since torque transmission remains blocked and it is impossible to return to the torque transmission state again, it can be used as an emergency overload protection device, but there has been a problem that it cannot be applied to uses where it can be continuously used if it returns to normal torque even in an overload state.

[0007] The present invention solves these problems, has a simple structure, low processing cost, can increase the transmitted torque, can increase the accuracy of the allowable torque to be set, and can be continuously used if it returns to normal torque even in an overload state, and an object thereof is to provide an overload protection device.

Means for Solving the Problems

[0008] The present invention comprises an inner ring and an outer ring that are rotatable relative to each other coaxially, and a torque transmission mechanism that transmits torque between the inner ring and the outer ring, and is an overload protection device capable of blocking torque transmission against torque above a tolerance. The outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring are cylindrical. The torque transmission mechanism has a plurality of cams provided in the circumferential direction between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring, and biasing means for biasing the plurality of cams in their rotation direction. The cams are formed in a rotationally symmetric shape with respect to their rotation center, with a plurality of minimum radius portions and a plurality of maximum radius portions arranged alternately. When the minimum radius portion faces the inner peripheral surface of the outer ring, the diameter including the minimum radius portion is formed smaller than the interval between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring. When the maximum radius portion faces the inner peripheral surface of the outer ring, the diameter including the maximum radius portion is formed larger than the interval between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring, thereby solving the above problems.

Advantages of the Invention

[0009] According to the invention according to claim 1, since the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring are cylindrical, and the cams are formed in a rotationally symmetric shape with respect to their rotation center, with a plurality of minimum radius portions and a plurality of maximum radius portions arranged alternately, it has a simple structure, low processing cost, and can be continuously used if it returns to normal torque even in an overload state. Also, a large number of cams can be arranged in the circumferential direction, and the cams rotate and engage between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring by slight elastic deformation of the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring to transmit torque, so it is possible to transmit a large torque.

[0010] According to the configuration described in claim 2, since the minimum diameter connecting the two minimum radius portions and the maximum diameter connecting the two maximum radius portions are arranged so as to form an angle other than 90°, it can be used as a one-way clutch that transmits torque only in one direction. According to the configuration described in claim 3, the biasing means has a spring wound around a pressing portion provided on the cam to bias the pressing portion in the direction of the inner ring. The pressing portion provided on the cam is formed so as to be pressed by the spring at a position eccentric with respect to the rotation center of the cam. In a state where the minimum radius portion faces the inner peripheral surface of the outer ring, the diameter including the minimum radius portion is formed smaller than the distance between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring, so that it is possible to operate as a one-way clutch during rotation in the direction opposite to overload protection. According to the configurations described in claims 4 and 5, it is possible to increase the amount of engagement due to the rotation of the cam with respect to the transmitted torque, and it is possible to accurately set the allowable torque with a small torque.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0012] Examples of the present invention will be described with reference to FIGS. 1 to 3. However, the present invention is not limited to these embodiments.

Examples

[0013] As shown in FIG. 1, an overload protection device 100 according to an embodiment of the present invention includes an inner ring 120 and an outer ring 110 that are provided coaxially and rotatable relative to each other, and a torque transmission mechanism that transmits torque between the inner ring 120 and the outer ring 110. The outer peripheral surface of the inner ring 120 and the inner peripheral surface of the outer ring 110 are each cylindrical, and have a plurality of cams 130 provided in the circumferential direction between the outer peripheral surface of the inner ring 120 and the inner peripheral surface of the outer ring 110, and a spring 140 which is a biasing means for biasing the plurality of cams 130 in their rotation directions. The outer peripheral surface of the inner ring 120 and the inner peripheral surface of the outer ring 110 are respectively used as cam sliding surfaces 121 and 111 to constitute a torque transmission mechanism.

[0014] As shown in FIGS. 2 and 3, the cam 130 is formed in a rotationally symmetric shape with respect to its rotation center with two minimum radius portions and two maximum radius portions alternately arranged. The diameter including the two minimum radius portions constitutes a minimum diameter 132, and the diameter including the two maximum radius portions constitutes a maximum diameter 133. Further, the minimum diameter 132 is formed smaller than the interval D between the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110, and the maximum diameter 133 is formed larger than the interval D between the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110. It should be noted that FIGS. 2 and 3 are drawn with the size and shape of the cam emphasized for the purpose of explanation.

[0015] The cam 130 has a contact diameter 134 having the same dimension as the interval D between the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110. By winding the spring 140 around the pressing portion 131, the cam 130 is biased to rotate, and the portion of the contact diameter 134 is in contact with both the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110. The relative rotation of the inner ring 120 and the outer ring 110 in one direction (the outer ring 110 rotates in the clockwise direction shown in the figure) is allowed and the transmission of the rotational torque is blocked. The relative rotation of the inner ring 120 and the outer ring 110 in the other direction (the outer ring 110 rotates in the counterclockwise direction shown in the figure) is blocked by the cam 130 rotating in the direction of the arrow in FIG. 3 and wedging between the cam sliding surfaces 111 and 121 of the inner ring 120 and the outer ring 110, and the rotational torque is transmitted.

[0016] The operation of the overload protection device 100 configured as described above will be described based on FIGS. 2 to 4. The state where the portion of the contact diameter 134 of the cam 130 shown in FIG. 2 contacts both the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110 is defined as the rotation angle 0° of the cam 130. As shown in FIG. 4, the contact diameter 134 is the same dimension as the interval D between the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110. In the state of 0°, there is no expansion of the interval D (expressed as "flexure" in the figure) due to slight elastic deformation of the inner ring 120 and the outer ring 110, and the transmissible torque is also zero. When the outer ring 110 attempts to rotate relative to the inner ring 120 in the counterclockwise direction shown in the figure from this state, as the transmissible torque increases, the cam 130 rotates while meshing and the flexure also increases.

[0017] In this section, the transmissible torque is the sum of the tangential force (the force due to the wedge angle) generated by the angular displacement in the circumferential direction of the force application points between the cam 130 and the cam sliding surface 121 of the inner ring 120 and between the cam 130 and the cam sliding surface 111 of the outer ring 110 due to the shape of the cam 130, and the force generated by the static friction between the cam 130 and the cam sliding surfaces 111 of the inner ring 120 and the outer ring 110. Therefore, when the maximum diameter 133 of the cam 130 shown in FIG. 3 intersects the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110 at a right angle (about 110° in the illustrated embodiment), the flexure is maximum and the force due to static friction is maximum. However, since the force due to the wedge angle is maximum slightly before that, the rotation angle of the cam 130 at which the maximum allowable torque is reached is slightly before the rotation angle at which the flexure is maximum (about 100° in the illustrated embodiment).

[0018] When the maximum allowable torque is exceeded, slipping occurs between the cam 130 and the cam sliding surface 121 of the inner ring 120 or the cam sliding surface 111 of the outer ring 110, and the inner ring 120 and the outer ring 110 start relative rotation, and the transmitted torque rapidly decreases. Thus, damage and adverse effects due to overload are prevented. Even after exceeding the maximum allowable torque, the deflection remains while decreasing until the minimum diameter 132 of the cam 130 intersects the cam sliding surface 121 of the inner ring 120 and the cam sliding surface 111 of the outer ring 110 at a right angle (about 150° in the illustrated embodiment). Therefore, the cam 130 further rotates by kinetic friction. After the position where the deflection becomes zero, the transmission torque becomes zero. However, since the cam 130 is urged by the spring 140 to rotate, the cam 130 further rotates by 180°, that is, up to 0° shown in FIG. 2, and the transmission of torque starts again.

[0019] In the present embodiment, the engagement of the cam 130 expands the interval D by slight elastic deformation of the inner ring 120 and the outer ring 110. However, the interval D may be expanded by incorporating elastic members into the inner ring or the outer ring. For example, as schematically shown in FIG. 5, an elastic member is arranged in the circumferential direction between each of the cam sliding surfaces of the inner ring divided into a plurality in the circumferential direction (a), an elastic member is arranged in the circumferential direction between each of the cam sliding surfaces of the outer ring divided into a plurality in the circumferential direction (b), an elastic member that presses each of the cam sliding surfaces of the inner ring divided into a plurality in the circumferential direction in the radial direction is arranged (c), an elastic member that presses each of the cam sliding surfaces of the outer ring divided into a plurality in the circumferential direction in the radial direction is arranged, and the like may be provided. Also, as shown in FIG. 5(e), an elastic member may be incorporated into the cam itself to generate engagement by deformation of the cam itself.

[0020] As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the present invention described in the claims. In the above embodiment, the cam 130 has a shape that is rotationally symmetric twice (180°). However, it may have a shape that is rotationally symmetric an even number of times, such as four times (90°) or more. In the above embodiment, it is assumed to act as a one-way clutch in which the torque transmission direction is only in one direction of rotation and the reverse rotation is free. However, cams arranged to act on the reverse rotation may be mixed so that torque can be transmitted in both directions and overload protection can be provided.

[0021] Also, in the above embodiment, when the minimum radius portion faces the inner peripheral surface of the outer ring, the diameter including the minimum radius portion is formed smaller than the interval between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring, and it is configured to provide overload protection against relative rotation in one direction and be free for relative rotation in the other direction. However, when considering relative rotation in the other direction is not considered, the biasing means may be omitted by always keeping the cam in contact with the outer peripheral surface of the inner ring and the inner peripheral surface with the diameter including the minimum radius portion being the interval between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring. Furthermore, by adopting a cam shape in which a wedging angle force is generated in both directions, overload protection may be enabled for relative rotation in both directions.

Explanation of Reference Numerals

[0022] 100 ··· Overload protection device 110 ··· Outer ring 111 ··· Cam sliding surface 120 ··· Inner ring 121 ··· Cam sliding surface 130 ··· Cam 131 ··· Pressing portion 132 ··· Maximum diameter 133 ··· Minimum diameter 134 ··· Contact diameter 140 ··· Spring (biasing means) D ··· Interval

Claims

1. An overload protection device that includes an inner ring and an outer ring that are coaxially arranged so as to be rotatable relative to each other, and a torque transmission mechanism that transmits torque between the inner ring and the outer ring, and that can cut off transmission of torque when a torque exceeds an allowable value, an outer peripheral surface of the inner ring and an inner peripheral surface of the outer ring are cylindrical, the torque transmission mechanism includes a plurality of cams provided in a circumferential direction between an outer peripheral surface of the inner ring and an inner peripheral surface of the outer ring, The cam has a plurality of minimum radius portions and a plurality of maximum radius portions alternately arranged and is formed in a rotationally symmetric shape with respect to its rotation center, an overload protection device characterized in that, when the maximum radius portion faces the inner circumferential surface of the outer ring, a diameter including the maximum radius portion is formed larger than the distance between the outer circumferential surface of the inner ring and the inner circumferential surface of the outer ring.

2. The cam has two minimum radius portions at 180° positions and two maximum radius portions at 180° positions, 2. The overload protection device according to claim 1, characterized in that the minimum diameter connecting the two minimum radius portions and the maximum diameter connecting the two maximum radius portions are arranged to form an angle other than 90°.

3. the torque transmission mechanism has a biasing means for biasing the plurality of cams in the rotation direction thereof, when the minimum radius portion faces the inner circumferential surface of the outer ring, a diameter including the minimum radius portion is smaller than a distance between the outer circumferential surface of the inner ring and the inner circumferential surface of the outer ring, the biasing means has a spring that is wound around a pressing portion provided on the cam and biases the pressing portion toward the inner ring, 2. The overload protection device according to claim 1, wherein the pressing portion provided on the cam is formed so as to be pressed by the spring at a position eccentric to the center of rotation of the cam.

4. 2. The overload protection device according to claim 1, wherein at least one of the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring is configured to be movable in the radial direction and is biased in a direction approaching each other.

5. 2. The overload protection device according to claim 1, wherein the cam is made of an elastic material or includes an elastic member, and the radius of the maximum radius portion is configured to be variable.

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