Torque limiter

Abstract

Provided is a novel torque limiter in which an inner member (6a to 6d) does not shake in the axial direction in an inner space (16a to 16d) having a side in the axial direction closed by a shield member (10a to 10d) even if the length of the inner space (16a to 16d) in the axial direction is longer than the length of the inner member (6a to 6d) in the axial direction. The inner member (6a to 6d) or a braking member (8a to 8d) in close contact with the inner member (6a to 6d) is biased in the axial direction against an outer member (4a to 4d) and the shield member (10a to 10d).

Description

Torque limiter

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

[0002] Patent Document 1 listed below discloses a torque limiter including an outer member having an inner space that is closed on one axial side and open on the other side, an inner member and a braking member (coil spring) housed in the inner space, and a shield member that is combined with the outer member after the inner member and the braking member are housed in the inner space and closes the other side of the inner space, the outer member and the inner member being rotatable relative to each other, and the braking member being disposed between the outer member and the inner member and applying a required braking torque to the relative rotation. Because the other side of the inner space is closed by the shield member after the inner member and the braking member are housed in the inner space, the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member.

[0003] In the torque limiter disclosed in Patent Document 1, both the outer member and the inner member are rotatable, but one of them may be fixed. When one of them is fixed, the torque limiter may be used, for example, as an angular position maintaining device when a vehicle hatchback is rotated by a driving means such as an electric motor. Such angular position maintaining devices typically use electromagnetic brakes, but because electromagnetic brakes are complex and expensive, it is desirable to use a mechanical torque limiter with a simpler and less expensive configuration. In this case, the outer member is fixed to the vehicle as a housing, and the inner member is coupled to a shaft connecting the electric motor and the hatchback. Furthermore, as disclosed in Japanese Patent Publication No. 7035254, which was filed by the applicant of the present application and has already been granted a patent, the inner member may also be used as a coupling member connecting a shaft extending from an electric motor to a shaft extending from the hatchback.

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

[0005] In the torque limiter disclosed in Patent Document 1, the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member, so the inner member has axial play in the inner space, and there is a risk that undesirable noise will be generated during operation due to this play.

[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 in which the inner member does not rattle in the axial direction in the inner space, even if the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member.

[0007] As a result of extensive research, the inventors have found that the above-mentioned main technical problem can be solved by axially biasing the inner member or a braking member that is in close contact with the inner member against the outer member and the shield member.

[0008] That is, according to a first aspect of the present invention, there is provided a torque limiter that solves the above-mentioned main technical problem, comprising: an outer member having an inner space that is closed on one axial side and open on the other side; an inner member and a braking member that are housed in the inner space; and a shield member that is combined with the outer member after the inner member and the braking member are housed in the inner space and closes the other side of the inner space, wherein the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member, the outer member and the inner member are rotatable relative to each other, and the braking member is disposed between the outer member and the inner member to apply a required braking torque to the relative rotation, characterized in that the inner member is axially biased against the outer member and the shield member by a biasing means.

[0009] In this case, the biasing means is preferably a wave washer housed in the inner space.

[0010] According to a second aspect of the present invention, there is provided a torque limiter that solves the above-mentioned main technical problem, comprising: an outer member having an inner space that is closed on one axial side and open on the other axial side; an inner member and a braking member that are housed in the inner space; and a shield member that is combined with the outer member after the inner member and the braking member are housed in the inner space and closes the other side of the inner space, wherein the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member, the outer member and the inner member are rotatable relative to each other, and the braking member is disposed between the outer member and the inner member to apply a required braking torque to the relative rotation, characterized in that the braking member is in close contact with the inner member and is axially biased against the outer member and the shield member.

[0011] In this case, the braking member may be a compression coil spring compressed from both axial sides by the outer member and the shield member, the compression coil spring including a winding portion around which a wire is wound and a hook portion where the wire extends in a direction away from the winding portion, the inner member having a cylindrical outer peripheral surface to which the winding portion of the compression coil spring is attached, the diameter of the outer peripheral surface being larger than the inner diameter of the winding portion when the compression coil spring is in a free state, or the braking member may be a coil spring including a winding portion around which a wire is wound and a hook portion where the wire extends in a direction away from the winding portion, the inner member having a cylindrical outer peripheral surface to which the winding portion of the coil spring is attached, the diameter of the outer peripheral surface being larger than the inner diameter of the winding portion when the coil spring is in a free state, and the shield member and / or the outer member may be integrally formed with a biasing means for biasing the coil spring in the axial direction. Furthermore, the braking member may be a coil spring having a winding portion around which wire is wound and a hook portion where the wire extends in a direction away from the winding portion, the outer surface of the inner member may be cylindrical, the winding portion of the coil spring may be attached to the outer surface, the diameter of the outer surface may be larger than the inner diameter of the winding portion when the coil spring is in a free state, and the inner space may also contain a biasing means for biasing the coil spring in the axial direction.

[0012] In both the first and second aspects of the present invention, the outer member is a fixed housing, and the inner member is connected to an external device, so that the device can be used as an angular position maintaining device.

[0013] In a torque limiter constructed according to the first aspect of the present invention, the inner member is urged in the axial direction relative to the outer member and the shield member by the urging means, and therefore, in the inner space whose other axial side is closed off by the shield member, both axial ends of the inner member are simultaneously supported by the urging means and either the axial side surface of the outer member or the axial side surface of the shield member, or by the urging means arranged on both axial sides, thereby preventing the generation of abnormal noise due to axial rattle.

[0014] In a torque limiter constructed according to a second aspect of the present invention, the brake member is biased in the axial direction relative to the outer member and the shield member, so that in the inner space whose other axial end is closed by the shield member, both axial ends of the brake member are simultaneously supported by the axial side surface of the outer member and the axial side surface of the shield member, by one of the axial side surface of the outer member or the axial side surface of the shield member and the biasing means, or by the biasing means arranged on both axial sides. Because the inner member is in close contact with the brake member, both axial ends of the brake member are simultaneously supported in the inner space, and the inner member is also supported in the inner space without any axial rattle. In other words, the inner member is supported via the brake member. Since the inner member is not biased in the axial direction, there is no change in the so-called contact strength between the inner member and the outer member or the shield member, i.e., the magnitude of the resistance due to friction between the inner member and the outer member or the shield member. Furthermore, since the required braking torque is set between the inner member and the brake member, the magnitude of the required braking torque also does not change. Therefore, variations in required braking torque between individual units are suppressed.

[0015] Fig. 1 is a diagram showing the configuration of a preferred embodiment of a torque limiter configured according to a first aspect of the present invention. Fig. 2 is a diagram showing the outer member of the torque limiter shown in Fig. 1 alone. Fig. 3 is a diagram showing the inner member of the torque limiter shown in Fig. 1 alone. Fig. 4 is a diagram showing the shield member of the torque limiter shown in Fig. 1 alone. Fig. 5 is a diagram showing the configuration of a first embodiment of a torque limiter configured according to a second aspect of the present invention. Fig. 6 is a diagram showing the configuration of a second embodiment of a torque limiter configured according to the second aspect of the present invention. Fig. 7 is a diagram showing the configuration of a third embodiment of a torque limiter configured according to the second aspect of the present invention.

[0016] 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.

[0017] Figure 1 shows the configuration of a preferred embodiment of a torque limiter constructed according to a first aspect of the present invention. The torque limiter, generally designated by the numeral 2a, comprises an outer member 4a, an inner member 6a, a braking member 8a, and a shield member 10a, and they share a common central axis o. In the cross-sectional view B-B of Figure 1, the braking member 8a is indicated by light ink for ease of understanding.

[0018] Referring to Figures 1 and 2, the synthetic resin outer member 4a has a circular end plate 12a arranged perpendicular to the axial direction and a cylindrical outer wall 14a extending from the outer periphery of the end plate 12a toward the other axial direction. An inner space 16a is formed inside the outer wall 14a. That is, one axial side of the inner space 16a is closed and the other is open. A circular through-hole 18a is formed in the center of the end plate 12a, penetrating it in the axial direction. Four arc-shaped recesses 20a having a required circumferential width are formed circumferentially spaced apart on the outer periphery of one axial side of the end plate 12a. A circular support recess 22a is formed in the center of the other axial side of the end plate 12a, and a ring-shaped support ridge 24a is formed on the bottom surface of the support recess 22a, surrounding the outer periphery of the through-hole 18a. Six grooves 26a with an arc-shaped cross section are formed on the outer peripheral surface of the outer peripheral wall 14a at equal angular intervals in the circumferential direction, extending linearly over the entire axial length. A pair of locking walls with an arc-shaped cross section (designated 28a1 and 28a2) are provided on the inner peripheral surface of the outer peripheral wall 14a at circumferential intervals and extending a required amount in the axial direction from the other axial side surface of the end plate 12a, with a pair of gaps 30a1 and 30a2 between the pair of locking walls 28a1 and 28a2. A ring-shaped locking groove 32a extending circumferentially is formed at the other axial end of the inner peripheral surface of the outer peripheral wall 14a.

[0019] 1 and 3, the metal inner member 6a is cylindrical. In the illustrated embodiment, the outer circumferential surface of the inner member 6a is cylindrical. A ring-shaped supported ridge 34a is formed on the outer circumferential edge of one axial side of the inner member 6a. A female engaging portion 36a made of serrations is formed on the inner circumferential surface of the inner member 6a except for the other axial end, and a female locking portion 38a made of splines is formed on one axial end.

[0020] Referring to FIG. 1 , in the illustrated embodiment, the braking member 8a is a coil spring (hereinafter, the coil spring may be referred to as 8) and includes a winding portion 40a in which a metal wire is wound in a spiral shape and a pair of hook portions 42a1 and 42a2 in which the wire extends radially outward from the winding portion 40a. The winding portion 40a is attached to the outer circumferential surface of the inner member 6a. The coil spring 8a may be either a compression coil spring or an extension coil spring. In a free state in which no load is applied to the coil spring 8a, the inner diameter of the winding portion 40a is smaller than the diameter of the outer circumferential surface of the inner member 6a (in other words, the diameter of the outer circumferential surface of the inner member 6a is larger than the inner diameter of the winding portion 40a when the coil spring is in a free state). The coil spring 8a is attached in close contact with the outer circumferential surface of the inner member 6a with the inner diameter of the winding portion 40a expanded. The pair of hook portions 42a1 and 42a2 are formed by both ends of the wire rod, and are therefore provided at both axial ends of the wound portion 40a.

[0021] Continuing with the explanation with reference to FIG. 1 , the inner member 6a and the coil spring 8a (brake member) are housed in the inner space 16a of the outer member 4a. At this time, the outer peripheral surface of one axial end of the inner member 6a is supported from the radially outer side by the inner peripheral surface of the outer member 4a, which defines the support recess 22a of the outer member 4a, and the inner peripheral surface of the supported rib 34a of the inner member 6a is supported from the radially inner side by the outer peripheral surface of the support rib 24a of the outer member 4a. The outer surface of the wound portion 40a of the coil spring 8a faces the inner peripheral surfaces of the pair of locking walls 28a1 and 28a2, and the pair of hook portions 42a1 and 42a2 are commonly fitted into the gap 30a1. Thus, the coil spring 8a is supported in a non-rotatable state relative to the outer member 4a.

[0022] 1 and 4, the synthetic resin shield member 10a includes a circular shield plate 44a arranged perpendicular to the axial direction. A circular through-hole 46a is formed in the center of the shield plate 44a, penetrating in the axial direction. A ring-shaped support wall 48a is formed on one axial side of the shield plate 44a, surrounding the outer periphery of the through-hole 46a. A cylindrical mounting wall 50a is formed on the other axial side of the shield plate 44a, extending axially from the outer periphery. A ring-shaped circumferential groove 52a, which is open toward the other axial side, is formed in the mounting wall 50a, and six ribs 54a are arranged at equal angular intervals in the circumferential direction in the ring-shaped groove 52a. A circumferentially extending, annular locking protrusion 56a is formed on the outer peripheral surface of the mounting wall 50a. The locking protrusion 56a is engaged with a locking groove 32a formed on the inner peripheral surface of the outer peripheral wall 14a of the outer member 4a, thereby fitting the shield member 10a to the outer member 4a and closing the other axial side of the inner space 16a. As shown in the cross-sectional view taken along line A-A in FIG. 1 , one axial side surface of the shield plate 44a axially supports the other axial side surface of the inner member 6a, and the inner peripheral surface of the support wall 48a radially supports the outer peripheral surface of the other axial end of the inner member 6a. However, the axial length of the inner space 16a, the other axial side of which is closed by the shield member 10a, is longer than the axial length of the inner member 6a. The above-mentioned "axial length of the inner space 16a whose other axial side is closed by the shield member 10a" refers to the length from the bottom surface of the support recess 22a of the outer member 4a to one axial side surface of the shield plate 44a of the shield member 10a, and in the illustrated embodiment, it is the axial length from the part excluding the support protrusion 24a on the other axial side surface of the support recess 22a to the part excluding the support wall 48a on one axial side surface of the shield plate 44a.

[0023] In the torque limiter constructed according to the first aspect of the present invention, it is important that the inner member 6a is axially biased against the outer member 4a and the shield member 10a by a biasing means. In the illustrated embodiment, the biasing means is a wave washer 58a housed in the inner space 16a, which is disposed inside the support ribs 24a of the outer member 4a to bias the inner member 6a in the other axial direction. If desired, the wave washer 58a may be disposed outside the support ribs 24a.

[0024] In the torque limiter constructed according to the first aspect of the present invention, the inner member 6a is axially biased against the outer member 4a and the shield member 10a by the wave washer 58a, which serves as a biasing means. Therefore, in the inner space 16a, the other axial side of which is closed by the shield member 10a, both axial ends of the inner member 6a are simultaneously supported by the wave washer 58a and the axial side surfaces of the shield member 10a, thereby preventing noise due to axial rattle. In this aspect, the braking member may be of any type, as long as the inner member 6a is axially biased against the outer member 4a and the shield member 10a by the biasing means. In other words, the coil spring 8a may be in close contact with the inner circumferential surface of the outer member 4a rather than the outer circumferential surface of the inner member 6a. When the coil spring 8a is in close contact with the inner circumferential surface of the outer member 4a, the gap (30a1) into which the pair of hook portions 42a1 and 42a2 fit is formed in the outer circumferential surface of the inner member. Furthermore, since the braking member only needs to apply a braking torque to the relative rotation between the outer member 4a and the inner member 6a, other means such as a leaf spring or a tolerance ring may be used instead of a coil spring. Furthermore, the biasing means may be disposed between the inner member 6a and the shield member 10a, in which case both axial ends of the inner member 6a are simultaneously supported by the biasing means and the axial side surfaces of the outer member 4a. Furthermore, the biasing means may be disposed on both axial sides of the inner member 6a, i.e., between the inner member 6a and the outer member 4a (more specifically, its end plate 12a) and between the inner member 6a and the shield member 10a, in which case both axial ends of the inner member 6a are simultaneously supported by the biasing means.

[0025] In the illustrated embodiment, the outer member 4a is a fixed housing held via the recess 20a and the recessed groove 26a, and the inner member 6a is connected to an external device and used as an angular position maintaining device. A male locking portion 102 formed of a spline on a connecting member 100, shown by a two-dot chain line in FIG. 1, is engaged with the female locking portion 38a of the inner member 6a, so that the inner member 6a and the connecting member 100 rotate integrally. The connecting member 100 further includes a male engaging portion 104 coaxially formed with the female engaging portion 36a of the inner member 6a. In the illustrated embodiment, the male engaging portion 104 of the connecting member 100 is connected to an input device such as an electric motor (not shown), and the housing 4a is connected to an output device such as a vehicle hatchback (not shown). Therefore, when rotational torque is applied from the input device, the inner member 6a attempts to rotate together with the coil spring 8a. At this time, since the coil spring 8a cannot rotate relative to the outer member 4a as described above, one of the pair of hook portions 42a1 and 42a2 is pushed by the circumferential side surface of one of the pair of locking walls 28a1 and 28a2 within the gap 30a1 formed in the outer member 4a in a direction that loosens the coil spring 8a, and the inner member 6a rotates relative to the coil spring 8a against the required braking torque due to the tightening force of the coil spring 8a. In other words, the rotational torque from the input side device is transmitted to the output side device to drive it. On the other hand, when rotational torque from the input side device is not input, the inner member 6a is held in place by the required braking torque due to the coil spring 8a. Thus, the angular position of the output side device is maintained. If desired, the housing 4a may be connected to the input side device, and the male engaging portion 104 of the connecting member 100 may be connected to the output side device.

[0026] Next, a torque limiter constructed according to a second aspect of the present invention will be described. In the torque limiter constructed according to the first aspect of the present invention described above, the inner member is axially biased against the outer member and the shield member by a biasing means. However, in the torque limiter constructed according to the second aspect of the present invention described below, a braking member that is in close contact with the inner member is axially biased against the outer member and the shield member. This is the point where the torque limiter constructed according to the second aspect of the present invention differs from the torque limiter constructed according to the first aspect of the present invention. Figures 5 to 7 show first to third embodiments of the torque limiter constructed according to the second aspect of the present invention, respectively. The overall configurations of the illustrated torque limiters according to the first to third embodiments are the same as those of the torque limiter shown in Figure 1 . Therefore, in the following description, the same components will be designated by the same reference numerals followed by one of the letters b to d (b in the first embodiment, c in the second embodiment, and d in the third embodiment), and detailed description will be omitted. Only the different components will be described. In the illustrated first to third embodiments, a coil spring is also used as the braking member, and therefore, when the coil spring is in a free state, the inner diameter of the wound portion is smaller than the outer diameter of the inner member, and the coil spring is attached to the inner member with the inner peripheral surface of the wound portion in close contact with the outer peripheral surface of the inner member. Note that in Figures 5 to 7, the shield members 10b to 10d are shown separated from the outer members 4b to 4d, but this is for the sake of convenience, and in reality they are assembled by engaging with the locking protrusions 56b to 56d and the locking grooves 32b to 32d.

[0027] In the torque limiter 2b shown in FIG. 5, the braking member 8b is a compression coil spring. Therefore, in a free state, the wire constituting the wound portion 40b has a gap in the axial direction. After the inner member 6b and the compression coil spring 8b are accommodated in the inner space 16b, when the other axial side of the inner space 16b is closed by the shield member 10b, the compression coil spring 8b is compressed from both axial sides by the outer member 4b (more specifically, its end plate 12b) and the shield member 10b. In the illustrated embodiment, the other axial side of the compression coil spring 8b is pressed to one axial side by the support wall 48b of the shield member 10b. Thus, both ends of the compression coil spring 8b are simultaneously supported from both axial sides by the axial side surfaces of the outer member 4b (i.e., the end plate 12b) and the axial side surfaces of the shield member 10b.

[0028] In the torque limiter 2c shown in Fig. 6, a biasing means 58c that biases the coil spring 8c in the axial direction is formed integrally with the shield member 10c. In the illustrated embodiment, the coil spring 8c is a tension coil spring, but it may also be a compression coil spring. The biasing means 58c is a wave-shaped elastic piece formed on one axial side surface of the shield plate 44c. When the inner member 6c and the coil spring 8c are accommodated in the inner space 16c and the other axial side of the inner space 16c is closed by the shield member 10c, the biasing means 58c abuts against the other axial end of the coil spring 8c and presses it to one axial side. Both axial ends of the coil spring 8c are simultaneously supported from both axial sides by the other axial side surface of the end plate 12c of the outer member 4c and the biasing means 58c. If desired, in this embodiment, the biasing means 58c may be integrally formed on the other axial side surface of the end plate 12c of the outer member 4c rather than on the shield member 10c, in which case both axial ends of the coil spring 8c are simultaneously supported from both axial sides by the biasing means and one axial side surface of the shield member. Also, the biasing means 58c may be integrally formed on the other axial side surface of the end plate 12c of the outer member 4c rather than on the shield member 10c, in which case both axial ends of the inner member 6c are simultaneously supported from both axial sides by the biasing means 58d.

[0029] In the torque limiter 2d shown in Fig. 7, a biasing means 58d that biases a coil spring 8d in the axial direction is housed in the inner space 16d. In the illustrated embodiment, the coil spring 8d is a tension coil spring, but it may also be a compression coil spring. The biasing means 58d is a rubber ring disposed between the other axial side surface of the end plate 12d of the outer member 4d and the coil spring 8d. When the other axial side of the inner space 16d is closed by the shield member 10d after the inner member 6d and the coil spring 8d are housed in the inner space 16d, the biasing means 58d abuts against one axial end of the coil spring 8d and presses it toward the other axial side. Both axial ends of the coil spring 8d are simultaneously supported from both axial sides by the biasing means 58d and one axial side surface of the support wall 48d of the shield member 10d. If desired, in this embodiment, the biasing means 58d may be disposed between the axial side surface of the support wall 48d of the shield member 10d and the coil spring 8d, in which case both axial ends of the coil spring 8d are simultaneously supported from both axial sides by the other axial side surface of the outer member (i.e., the end plate 12d) and the biasing means. Also, the biasing means 58d may be disposed on both axial sides of the inner member 6d, i.e., between the inner member 6d and the end plate 12d of the outer member 4d and between the inner member 6d and the shield member 10d, in which case both axial ends of the inner member 6d are simultaneously supported by the biasing means 58d.

[0030] In the torque limiter configured according to the second aspect of the present invention, the braking members 8b to 8d are urged in the axial direction against the outer members 4b to 4d and the shield members 10b to 10d, so that in the inner spaces 16b to 16d whose other axial sides are closed by the shield members 10b to 10d, both axial ends of the braking member 8b are simultaneously supported by the axial side surface of the outer member 4b (i.e., the end plate 12b) and the axial side surface of the shield member 10b, and both axial ends of the braking members 8c and 8d are simultaneously supported by either the axial side surfaces of the outer members 4c and 4d (i.e., the end plates 12c and 12d) and the axial side surfaces of the shield members 10c and 10d and the urging means 58c and 58d, or by the urging means 58c and 58d arranged on both axial sides. Because the inner members 6b to 6d are in close contact with the braking members 8b to 8d, both axial ends of the braking members 8b to 8d are simultaneously supported in the inner spaces 16b to 16d, and the inner members 6b to 6d are also supported in the inner spaces 16b to 16d without any axial rattle. In other words, the inner members 6b to 6d are supported via the braking members 8b to 8d. Because the inner members 6b to 6d are not axially biased, there is no change in the so-called contact strength between the inner members 6b to 6d and the outer members 4b to 4d and the shield members 10b to 10d, i.e., the magnitude of resistance due to friction between the inner members 6b to 6d and the outer members 4b to 4d and the shield members 10b to 10d. Furthermore, because the required braking torque is set between the inner members 6b to 6d and the braking members 8b to 8d, the magnitude of the required braking torque also does not change. Therefore, variation in the required braking torque between individual components is suppressed. In the second and third embodiments of this aspect, the braking members may be of any type as long as they are in close contact with the inner members 6b to 6d, and therefore may be leaf springs, tolerance rings, or the like.

[0031] Although the torque limiter configured 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 changes are possible within the scope of the present invention. For example, in the illustrated embodiment, the torque limiter is used as an angular position maintaining device, that is, the outer member is fixed, but there are also cases in which the outer member rotates.

[0032] 2a to 2d: Torque limiters 4a to 4d: Outer members 6a to 6d: Inner members 8a to 8d: Braking members 10a to 10d: Shield members 16a to 16d: Inner spaces 58a, 58c, 58d: Urging means

Claims

1. A torque limiter comprising an outer member having an inner space which is closed on one axial side and open on the other axial side, an inner member and a braking member housed in the inner space, and a shield member which is combined with the outer member after the inner member and the braking member are housed in the inner space and closes the other side of the inner space, wherein the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member, the outer member and the inner member are rotatable relative to each other, and the braking member is disposed between the outer member and the inner member to apply a required braking torque against the relative rotation, characterized in that the inner member is axially biased against the outer member and the shield member by a biasing means.

2. The torque limiter according to claim 1, wherein said biasing means is a wave washer housed in said inner space.

3. A torque limiter comprising an outer member having an inner space which is closed on one axial side and open on the other side, an inner member and a braking member housed in the inner space, and a shield member which is combined with the outer member after the inner member and the braking member are housed in the inner space and closes the other side of the inner space, wherein the axial length of the inner space whose other side is closed by the shield member is longer than the axial length of the inner member, the outer member and the inner member are rotatable relative to each other, and the braking member is disposed between the outer member and the inner member to apply a required braking torque against the relative rotation, characterized in that the braking member is in close contact with the inner member and is axially urged against the outer member and the shield member.

4. A torque limiter as described in claim 3, wherein the braking member is a compression coil spring compressed from both axial sides by the outer member and the shield member, and comprises a winding portion around which wire is wound and a hook portion in which the wire extends in a direction away from the winding portion, the outer peripheral surface of the inner member is cylindrical, the winding portion of the compression coil spring is attached to the outer peripheral surface, and the diameter of the outer peripheral surface is larger than the inner diameter of the winding portion when the compression coil spring is in a free state.

5. A torque limiter as claimed in claim 3, wherein the braking member is a coil spring, comprising a winding portion around which a wire is wound and a hook portion in a direction in which the wire extends away from the winding portion, the outer circumferential surface of the inner member is cylindrical, the winding portion of the coil spring is attached to the outer circumferential surface, and the diameter of the outer circumferential surface is larger than the inner diameter of the winding portion when the coil spring is in a free state, and the shield member and / or the outer member are integrally formed with biasing means for biasing the coil spring in the axial direction.

6. A torque limiter as claimed in claim 3, wherein the braking member is a coil spring, comprising a winding portion around which a wire is wound and a hook portion in a direction in which the wire extends away from the winding portion, the outer circumferential surface of the inner member is cylindrical, the winding portion of the coil spring is attached to the outer circumferential surface, the diameter of the outer circumferential surface is larger than the inner diameter of the winding portion when the coil spring is in a free state, and the inner space also contains biasing means for biasing the coil spring in the axial direction.

7. A torque limiter according to any one of claims 1 to 6, wherein the outer member is a fixed housing and the inner member is connected to an external device and used as an angular position maintaining device.

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