Torque limiter

Abstract

Provided is a novel torque limiter capable of preventing, as much as possible, lubricant flowing out of an external device from entering the inside of an outside member. A circular recessed portion 10, or an annular recessed groove 210b extending continuously in the circumferential direction, is formed in the center of both end surfaces in the axial direction of an inside member 4, and cylindrical blocking walls 42, 48 that enter the recessed portion 10 or the recessed groove 210b are formed on a pair of supporting walls 26, 46, respectively.

Description

Torque limiter

[0001] The present invention relates to a torque limiter.

[0002] An example of a torque limiter is disclosed in Patent Document 1 below. The torque limiter disclosed in Patent Document 1 below includes an inner member, an outer member that houses the inner member and shares a central axis with the inner member, and a braking member that is engaged with the outer member so as not to rotate relative to the inner member and is made of a coil spring that is in close contact with the outer peripheral surface of the inner member and applies a braking torque. The outer member is composed of a cylindrical main body and a shield that closes the open end of the main body. The main body and the shield each have an annular support wall that extends radially and supports the inner member from both axial sides. When a rotational torque about the central axis that rotates the inner member and the outer member relative to each other is applied, the braking torque is overcome and the inner member and the outer member rotate relative to each other if the rotational torque is greater than a predetermined value.

[0003] Torque limiters are commonly used as components that protect a drive source, such as a motor, by disconnecting the load when the motor is overloaded, i.e., as a component that limits the transmitted torque. Furthermore, torque limiters are also used as devices for maintaining the angular position of a vehicle hatchback when the vehicle is rotated by a driving means such as an electric motor, for example. By fixing the hatchback at a desired angle without using an electromagnetic brake, the hatchback can be swung open and closed by applying extra torque from the electric motor. In either case, the torque limiter is a mechanical component that transmits or cuts off the rotational power of an external device, and is therefore arranged adjacent to the external device in the axial direction (i.e., in series).

[0004] Japanese Patent Application Publication No. 10-110739

[0005] As described above, torque limiters are mechanical components that transmit and interrupt the rotational power of external equipment. Therefore, lubricants such as grease and oil are applied to the interior of the torque limiter and the external equipment. Such lubricants can leak out due to vibrations, shocks, and other factors during operation. Because the torque limiter is positioned axially adjacent to the external equipment, lubricants leaking from the external equipment tend to infiltrate the inside of the torque limiter from the axial end of the torque limiter. In the torque limiter disclosed in Patent Document 1, the support wall on the main body side and the support wall on the shield side are both annular. Therefore, lubricants leaking from the external equipment can easily infiltrate the inside of the torque limiter by simply passing through the inner circumferential surfaces of the support walls of the main body and the shield. If lubricants leaking from the external equipment infiltrate the inside of the torque limiter and mix with the lubricants originally applied to the inside of the torque limiter, the lubricants originally applied to the inside of the torque limiter may become abnormal, potentially preventing the torque limiter from performing its intended function.

[0006] The present invention has been made in consideration of the above facts, and its main technical object is to provide a new and improved torque limiter that can prevent as much as possible lubricant that has leaked from an external device from entering the inside of the outer member.

[0007] As a result of extensive research, the inventors have found that the above-mentioned main technical problem can be solved by forming a circular recess or an annular groove extending continuously in the circumferential direction in the center of both axial end faces of the inner member, and by forming a cylindrical blocking wall in each of the pair of support walls that enters the recess or groove.

[0008] That is, according to the present invention, there is provided a torque limiter that solves the above-mentioned main technical problem, comprising an inner member, an outer member that houses the inner member and has a common central axis with the inner member, and a braking member that applies a braking torque in close contact with the outer peripheral surface of the inner member and / or the inner peripheral surface of the outer member, wherein the outer member is composed of a cylindrical main body and a shield that closes the open end of the main body, and the outer member has a pair of annular support walls that extend radially and support the inner member from both axial sides, and when a rotational torque about the central axis that rotates the inner member and the outer member relatively is applied, the inner member and the outer member rotate relatively to each other overcoming the braking torque if the rotational torque is greater than a predetermined value, wherein a circular recess or annular groove that extends continuously in the circumferential direction is formed in the center of both axial end faces of the inner member, and each of the pair of support walls is formed with a cylindrical blocking wall that enters the recess or the groove.

[0009] Preferably, the outer peripheral surface of the blocking wall radially supports the inner peripheral surface of the recess or groove in the inner member, and the axial end surface of the blocking wall axially supports the bottom surface of the recess or groove in the inner member. Preferably, each of the pair of support walls has an annular support groove into which an axial end of the inner member is fitted. The inner member is preferably composed of a connecting member made of synthetic resin or soft metal and provided with a connecting portion for connecting to an external device, and a metal acting member attached to the outer peripheral surface of the connecting member and non-rotatable relative to the connecting member. Preferably, one of the pair of support walls is disposed on the main body, and the other is disposed on the shield. The braking member is preferably a coil spring, non-rotatably engaged with the outer member and in close contact with the outer peripheral surface of the inner member. The outer member can be fixed and connected to an external device to be used as an angular position maintaining device.

[0010] In the torque limiter constructed according to the present invention, a circular recess or an annular groove extending continuously in the circumferential direction is formed in the center of both axial end faces of the inner member, and a cylindrical blocking wall that enters the recess or groove is formed in each of the pair of support walls, so that lubricant leaking from the external device must overcome the blocking wall to enter the inside of the outer member. In other words, the blocking wall functions as a dam, so that the torque limiter constructed according to the present invention prevents lubricant leaking from the connected external device from entering the inside of the outer member as much as possible.

[0011] Fig. 5 is a diagram showing the configuration of a preferred embodiment of a torque limiter configured according to the present invention. Fig. 6 is an exploded perspective view of the torque limiter shown in Fig. 1. Fig. 7 is a diagram showing the inner member of the torque limiter shown in Fig. 1 alone. Fig. 8 is a diagram showing the main body and shield constituting the outer member of the torque limiter shown in Fig. 1 alone. Fig. 9 is a diagram showing the configuration of a first modified example of a torque limiter configured according to the present invention. Fig. 10 is a perspective view showing the inner member of the torque limiter shown in Fig. 5. Fig. 11 is a diagram showing the configuration of a second modified example of a torque limiter configured according to the present invention.

[0012] A more detailed description will be given below with reference to the accompanying drawings showing preferred embodiments of a torque limiter constructed according to the present invention. In the following description, unless otherwise specified, "one side" and "the other side" in the axial direction refer to the left side and "the other side" in the state shown in the A-A cross section of Figure 1 as the reference.

[0013] 1 and 2, the torque limiter generally designated by the numeral 2 comprises an inner member 4, an outer member 6, and a braking member 8. The inner member 4 and the outer member 6 share a common central axis o. For ease of understanding, the braking member 8 is indicated by light ink in the cross-sectional view taken along line A-A in FIG. 1 (the same applies to FIGS. 5 and 7 described below).

[0014] The inner member 4 will be described with reference to Figures 1 and 2 as well as Figure 3. In the illustrated embodiment, the inner member 4 has a cylindrical shape that is integrally molded by powder metallurgy, and the cross section of the outer circumferential surface of the inner member 4 is circular. Circular recesses 10 are formed in the centers of both axial end faces of the inner member 4. The two recesses 10 have the same diameter and depth. The inner diameter of an intermediate portion 14 defined between both axial end portions 12 where the recesses 10 are formed is slightly smaller than the inner diameter of the end portions 12, and an annular bottom surface 16 perpendicular to the axial direction is defined at the bottom of the recess 10. Serrations 18 are formed on the inner circumferential surface of the intermediate portion 14.

[0015] Next, the outer member 6 will be described with reference to Figures 1, 2, and 4. The outer member 6 is composed of a cylindrical main body 20 and a shield 22 that closes the open end of the main body 20. In the illustrated embodiment, the outer member 6 includes one main body 20 and one shield 22, both of which are molded from an appropriate synthetic resin. Referring primarily to Figure 4(a), the main body 20 includes a cylindrical outer wall 24 that extends linearly in the axial direction and a ring-shaped one-side support wall 26 that extends radially inward from the inner circumferential surface of the outer wall 24 at an axially intermediate portion of the outer wall 24. A one-side retaining portion 28 of a required shape is formed on the inner circumferential surface of one axial end of the outer wall 24. Four arc-shaped notches 30, locally displaced axially to one side, are formed at equiangular intervals in the circumferential direction on the other axial end of the outer wall 24. A pair of slits 32a and 32b extending linearly toward one axial side and penetrating radially are formed in the circumferential center of each of the bottom surfaces (i.e., the surfaces facing the other axial side) of the four notches 30. A locking projection 34 projecting radially inward is formed at the other axial end of the inner circumferential surface of the outer peripheral wall 24 between the pair of slits 32a and 32b. The inner circumferential surface of the outer peripheral wall 24 further includes a pair of auxiliary walls 36a and 36b extending from the other axial side of the one-side support wall 26 to the axial end of each of the pair of slits 32a and 32b. Each of the pair of auxiliary walls 36a and 36b has an arc shape and is disposed at equal angular intervals in the circumferential direction, defining spaces 38a and 38b between the pair of auxiliary walls 36a and 36b. A lightening portion 40 is appropriately provided in each of the pair of auxiliary walls 36a and 36b. A cylindrical one-side blocking wall 42 is formed on the inner peripheral edge of the other axial side surface of the one-side support wall 26. A circular one-side support groove 44 is also formed on the other axial side surface of the one-side support wall 26, surrounding the outer peripheral edge of the one-side blocking wall 42.

[0016] Referring primarily to FIG. 4( b), the shield 22 includes an annular other-side support wall 46 extending perpendicular to the axial direction, and thus radially. A cylindrical other-side blocking wall 48 is formed on the inner peripheral edge of one axial side of the other-side support wall 46. A cylindrical auxiliary wall 50 is also formed on one axial side of the other-side support wall 46, and an annular other-side support groove 52 is defined between the auxiliary wall 50 and the other-side blocking wall 48. A required-shaped other-side retaining portion 54 is formed on the other axial side of the other-side support wall 46. Four arc-shaped engagement pieces 56 are arranged equiangularly around the periphery on the other axial side of the outer peripheral surface of the other-side support wall 46, extending beyond the other axial end edge of the other-side support wall 46. The inner diameter of each of the four engagement pieces 56 is locally increased at the circumferential center of the inner peripheral surface, forming a recess 58 penetrating in the axial direction. A recess 60 is formed on the outer peripheral surface of the other-side support wall 46 that faces the recess 58 when viewed in the axial direction. Referring to the cross-sectional view taken along line A-A in Figure 4(b), the recess 60 extends from the other axial end surface of the other-side support wall 46 to one axial end, and a locking projection 62 is provided at this one axial end.

[0017] The main body 20 and the shield 22 are combined by fitting the engaging pieces 56 of the shield 22 into the notches 30 of the main body 20 and allowing the locking projections 34 of the main body 20 to elastically ride over and lock onto the locked projections 62 of the shield 22. Prior to combining the main body 20 and the shield 22, the inner member 4 is housed inside the outer member 6. At this time, as can be understood by referring to the A-A cross-sectional view in Figure 1, the one-side blocking wall 42 of the main body 20 enters the recess 10 formed in one axial end face of the inner member 4, and the other-side blocking wall 48 of the shield 22 enters the recess 10 formed in the other axial end face of the inner member 4. The one-side blocking wall 42 and the other-side blocking wall 48 are both cylindrical, and in the illustrated embodiment, the outer peripheral surfaces of the one-side blocking wall 42 and the other-side blocking wall 48 radially support the inner peripheral surface of the recess 10 of the inner member 4, while the axial end surfaces of the one-side blocking wall 42 and the other-side blocking wall 48 axially support the bottom surface 16 of the recess 10 of the inner member 4. Furthermore, in the illustrated embodiment, one axial end of the inner member 4 is fitted into the one-side support groove 44 of the main body 20, and the other axial end is fitted into the other-side support groove 52 of the shield 22. Thus, the outer member 6 supports the inner member 4 for rotation about the central axis o.

[0018] The braking member 8 will be described with reference to Figures 1 and 2. In the illustrated embodiment, the braking member 8 is a coil spring made of a metal wire, and includes a winding portion 64 in which the wire is wound in a spiral shape, and a pair of hook portions 66a and 66b in which the wire is linearly extended radially outward at both axial ends of the winding portion 64. The cross section of the wire is rectangular. In a free state, i.e., when no external force is applied to the pair of hook portions 66a and 66b, the inner diameter of the winding portion 64 is smaller than the outer diameter of the inner member 4. The braking member 8 is attached to the outer peripheral surface of the inner member 4 with the winding portion 64 elastically expanded in diameter, and the inner peripheral surface of the winding portion 64 is in close contact with the outer peripheral surface of the inner member 4. 1, the braking member 8 is housed inside the outer member 6, and as shown in the A-A cross-sectional view and the B-B cross-sectional view of FIG. 1, the outer peripheral surface of the wound portion 64 closely faces the inner peripheral surfaces of the auxiliary walls 36a and 36b of the main body 20 of the outer member 6. As shown in the B-B cross-sectional view, the pair of hook portions 66a and 66b are both disposed in the space 38a of the main body 20. As a result, when the braking member 8 together with the inner member 4 is rotated relative to the outer member 6, one of the pair of hook portions 66a and 66b comes into contact with the circumferential end surface of the auxiliary wall 36a or 36b in the space 38a of the outer member 6. In this way, the braking member 8 is locked to the outer member 6 so as not to rotate relative to it, and is in close contact with the outer peripheral surface of the inner member 4, thereby applying the required braking torque by frictional force. Since the braking member 8 slides against the inner member 4, the braking member 8 is coated with a fluorine-based lubricant such as grease or oil.

[0019] Referring to FIG. 1 , in the illustrated embodiment, the torque limiter 2 is used as an angular position maintaining device for a hatchback. To this end, the outer member 6 is fixed to a vehicle (not shown) by a one-side retaining portion 28 provided on the main body 20 and a second-side retaining portion 54 provided on the shield 22. The inner member 4 is connected to a drive shaft S (shown by a two-dot chain line) inserted inside the outer member 4 by serrations 18. When the drive shaft S is rotated by a drive source such as an electric motor, the inner member 4 rotates integrally with the drive shaft S relative to the outer member 6, causing the hook portion 66 a or 66 b of the coil spring (brake member 8) attached to the inner member 4 to abut against the circumferential end surface of the auxiliary wall 36 a or 36 b of the outer member 6, thereby pushing the spring in a direction that loosens it. Which of the two hook portions 66 a or 66 b is pushed depends on the direction of rotation of the drive shaft S. When the rotational torque applied to the drive shaft S is greater than a predetermined value, the inner member 4 and the outer member 6 rotate relative to each other, overcoming the required braking torque from the braking member 8. In the illustrated embodiment, one axial end of the inner member 4 is fitted into one-side support groove 44 formed in the main body 20 of the outer member 6, and the other axial end is fitted into the other-side support groove 52 formed in the shield 22 of the outer member 6, so that the inner member 4 can rotate stably with respect to the outer member 6. Because the drive shaft S can rotate in both forward and reverse directions, the torque limiter 2 in the illustrated embodiment functions as a so-called bidirectional torque limiter.

[0020] Here, external devices such as a gearbox and a spindle are connected to both ends of the drive shaft S, and these external devices are arranged axially adjacent to the torque limiter 2. Because the gearbox, spindle, etc. are mechanical components that transmit rotational power, lubricants such as grease and oil are applied to their interiors. This lubricant may leak out due to vibrations, shocks, etc. during operation. Since the torque limiter 2 is arranged axially adjacent to the external devices, the lubricant leaked from the external devices tends to infiltrate into the inside of the torque limiter 2, i.e., the inside of the outer member 6, from the axial end of the torque limiter 2. In the illustrated embodiment, the lubricant can move axially along the outer peripheral surface of the drive shaft S, and therefore tends to infiltrate into the inside of the outer member 6 from the inner peripheral surfaces of the one-side support wall 26 and the other-side support wall 46. However, in the torque limiter constructed according to the present invention, a circular recess 10 is formed in the center of both axial end faces of the inner member 4, and the one-side support wall 26 and the other-side support wall 46 are respectively formed with cylindrical one-side blocking walls 42 and other-side blocking walls 48 that enter the recess 10, so that the lubricant leaking from the external equipment must overcome the one-side blocking walls 42 and other-side blocking walls 48 in order to enter the inside of the outer member 6. In other words, the one-side blocking wall 42 and the other-side blocking wall 48 function as a weir, so the torque limiter constructed according to the present invention prevents as much as possible the lubricant leaking from the connected external equipment from entering the inside of the outer member 6. Furthermore, both the one-side blocking wall 42 and the other-side blocking wall 48 are cylindrical in shape, and in the illustrated embodiment, the outer surfaces of the one-side blocking wall 42 and the other-side blocking wall 48 radially support the inner surface of the recess 10 of the inner member 4, and the axial end surfaces of the one-side blocking wall 42 and the other-side blocking wall 48 axially support the bottom surface 16 of the recess 10 of the inner member 4, thereby preventing misalignment between the inner member 4 and the outer member 6.

[0021] Figure 5 shows a first modified example of a torque limiter constructed in accordance with the present invention. Comparing the torque limiter shown in Figure 5 with the torque limiter shown in Figure 1, the only difference is the configuration of the inner member, and the other configurations are substantially the same. Therefore, in the following explanation, only the above differences will be explained, and the same components will be numbered 100 and will not be explained in detail.

[0022] In the torque limiter 102 shown in FIG. 5 , the inner member 104 is composed of a connecting member 104a made of synthetic resin or soft metal and provided with a connecting portion (serrations 118) for connecting to an external device, and a metal acting member 104b attached to the outer peripheral surface of the connecting member 104a and unable to rotate relative to the connecting member 104a. Referring also to FIG. 6 , the connecting member 104a is integrally molded from a relatively high-strength synthetic resin such as PPS and has an overall cylindrical shape. Recesses 110 are formed on both axial end surfaces of the connecting member 104a. A plurality of engaging ridges 168, each with an arc-shaped cross section and extending linearly in the axial direction, are arranged equiangularly around the circumferential direction on the outer peripheral surface of the connecting member 104a. Meanwhile, the acting member 104b is integrally molded by powder metallurgy and has an overall cylindrical shape. The outer peripheral surface of the acting member 104b has a circular cross section, and the braking member 108 is attached to this outer peripheral surface. A plurality of engaging grooves 170, each having an arc-shaped cross section and extending linearly in the axial direction, are arranged at equal angular intervals on the inner peripheral surface of the acting member 104b in correspondence with the plurality of engaging ridges 168 arranged on the outer peripheral surface of the connecting member 104a. The engaging ridges 168 are fitted into the engaging grooves 170, thereby engaging the connecting member 104a and the acting member 104b so that they cannot rotate relative to each other.

[0023] In this embodiment, the inner member 104 is composed of a connecting member 104a made of synthetic resin and a metal acting member 104b. The connecting member 104a, on which the serrations 118 serving as the connecting portion are formed, and the acting member 104b, on which the braking member 108 acts, are molded separately. This provides advantages over an inner member that is integrally molded by powder metallurgy in the following respects. Because the braking member 108 is in close contact with the outer peripheral surface of the inner member to apply the required braking torque, the outer peripheral surface of the inner member that is in close contact with the braking member 108 is subjected to centerless polishing followed by barrel polishing to ensure that the required braking torque is stably generated. Here, if connecting portions such as serrations are formed during barrel polishing, this is undesirable because the connecting portions may be damaged by the barrel polishing. However, in this embodiment, the working member 104b to be barrel polished and the connecting member 104a on which the serrations 118 forming the connecting portion are formed are molded separately. Therefore, by performing barrel polishing only on the working member 104b, it is possible to avoid damaging the serrations 118 forming the connecting portion. Furthermore, when the connecting member 104a is made of synthetic resin, resin molding allows for higher precision molding than powder metallurgy, so the connecting portion can be molded with high precision. Even when the connecting member 104a is made of a soft metal such as aluminum or zinc, the connecting portion can be molded with high precision by die casting.

[0024] Figure 7 shows a second modified example of a torque limiter constructed in accordance with the present invention. Comparing the torque limiter shown in Figure 7 with the torque limiter shown in Figure 1, the only difference is the configuration of the inner member, and the other configurations are substantially the same. Therefore, in the following explanation, only the above differences will be explained, and the same components will be numbered 200 and will not be explained in detail.

[0025] In the torque limiter 202 shown in Figure 7, the inner member 204 is integrally molded by powder metallurgy. The inner member 204 has a shaft portion 270 that penetrates the center of the shield 222 and extends to the other axial direction (therefore, the shaft portion 270 extends along the central axis o), and serrations 218 serving as connecting portions are formed on the outer peripheral surface of the shaft portion 270. In this embodiment, a circular recess 210a is formed in the center of one axial end face of the inner member 204, and an annular groove 210b is formed in the other axial end face surrounding the outer peripheral edge of the base end of the shaft portion 270. An other-side blocking wall 248 formed in the shield 222 extends into the groove 210b.

[0026] Although the torque limiter constructed according to the present invention has been described above in detail with reference to the accompanying drawings, the present invention is not limited to the above-described embodiment, and appropriate modifications and variations are possible within the scope of the present invention. For example, in the illustrated embodiment, the brake member 8 is a coil spring having a pair of hook portions 66a and 66b. However, the brake member 8 may have only a single hook portion. If the coil spring has only a single hook portion, the torque limiter functions as a one-way torque limiter. The coil spring may be locked to the inner member so as not to rotate relative to the inner member and be in close contact with the inner circumferential surface of the outer member. Furthermore, the brake member does not necessarily have to be a coil spring; it may be a leaf spring, annular spring, tolerance ring, or the like. Furthermore, the main body of the outer member may penetrate in the axial direction, and both axial ends of the main body may be closed by a pair of shields. In this case, a support wall is provided on each of the pair of shields located on both axial sides. The torque limiter of the present invention is not limited to use as an angular position maintaining device and can be used for various purposes.

[0027] 2: Torque limiter 4: Inner member 6: Outer member 8: Braking member 10: Recess 20: Main body (of outer member) 22: Shield (of outer member) 26: One-side support wall 42: One-side blocking wall 46: Other-side support wall 48: Other-side blocking wall

Claims

1. A torque limiter comprising an inner member, an outer member that houses the inner member and has a common central axis with the inner member, and a braking member that applies a braking torque in close contact with the outer peripheral surface of the inner member and / or the inner peripheral surface of the outer member, wherein the outer member is composed of a cylindrical main body and a shield that closes the open end of the main body, and the outer member has a pair of annular support walls that extend radially and support the inner member from both axial sides, and when a rotational torque about the central axis that rotates the inner member and the outer member relatively is applied, the inner member and the outer member rotate relatively overcoming the braking torque if the rotational torque is greater than a predetermined value, wherein a circular recess or annular groove that extends continuously circumferentially is formed in the center of both axial end faces of the inner member, and each of the pair of support walls is formed with a cylindrical blocking wall that enters the recess or groove.

2. A torque limiter as described in claim 1, wherein the outer peripheral surface of the blocking wall radially supports the inner peripheral surface of the recess or groove in the inner member, and the axial end surface of the blocking wall axially supports the bottom surface of the recess or groove in the inner member.

3. A torque limiter according to claim 1, wherein each of said pair of support walls is formed with an annular support groove into which an axial end of said inner member is fitted.

4. A torque limiter as described in claim 1, wherein the inner member is composed of a connecting member made of synthetic resin or soft metal and provided with a connecting portion for connecting to an external device, and a metal acting member attached to the outer surface of the connecting member and unable to rotate relative to the connecting member.

5. A torque limiter according to claim 1, wherein one of said pair of support walls is disposed on said main body and the other is disposed on said shield.

6. A torque limiter according to claim 1, wherein said braking member is a coil spring that is locked to said outer member so as not to rotate relative to said outer member and that is in close contact with the outer peripheral surface of said inner member.

7. The torque limiter according to claim 1, wherein the outer member is fixed and the inner member is connected to an external device, and is used as an angular position maintaining device.

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