TORQUE LIMITER

Abstract: Torque limiter comprises: a bottomed cylinder formed of a magnetic material; an end plate fixedly and coaxially fitted in the open end of the cylinder; a rotary shaft coaxially and rotatably supported in bearings fitted in the bottom wall of the cylinder and the end plate, respectively; two rotors formed of a magnetic material and coaxially secured to the rotary shaft; a permanent magnet disposed between and contiguously to the rotors and coaxially secured to the rotary shaft; an annular core formed of a magnetic material and coaxially fitted in the cylinder contiguously to the end plate; magnetic powder filled in the gap between the core and one of the rotors disposed opposite to the core; and sealing members disposed between the bottom surface of the cylinder and one of the rotors on the side of the bottom surface of the cylinder and between the inner end surface of the end plate and the other rotor on the side of the end plate. In filling the magnetic powder in the gap, the cylinder is placed upright with the open end thereof turned up, then the magnetic powder is distributed over the outer end surface of the rotor, and then the annular core and the end plate are fitted in the open end of the cylinder in that order. Since the rotor is magnetized by the permanent magnet, the magnetic powder is attracted to the rotor, and hence will not fall off, which facilitates filling the magnetic powder in the gap.

Description: The present invention relates to a torque limiter according to the preamble of Claim 1. The torque limiter includes a magnetic powder clutch which yields to a torque exceeding a specific magnitude, for use in the transmission line of general industrial machines, such as copying machines and wire winding machines, for limiting the torque acting on the transmission line to a specific magnitude. A torque limiter of that kind comprising a magnet assembly and an outer housing, rotatable to one another, with magnetable particles in a gap between them is known from GB-A-2 029 126. Furthermore, a conventional torque limiter for the above purposes is known with the construction and functions as described with reference to Fig. 7 showing the upper half of the torque limiter in a longitudinal section. Shown in Fig. 7 are a rotary shaft 1, bearings 2, a cylinder made of a magnetic material, end plates 4 and 5 made of a nonmagnetic material such as brass or a stainless steel and fixedly fitted in the opposite ends of the cylinder 3, respectively, rotors 6 and 7 made of a magnetic material and coaxially secured to the rotary shaft 1, a permanent magnet 8 disposed between the rotors 6 and 7, and coaxially secured to the rotary shaft 1, magnetic powder P such as iron powder filled in a space A within the cylinder 3, and sealing members 9 such as oil seal elements or felt rings for preventing the entrance of the magnetic powder P into the bearings 2. The rotary shaft 1 is supported rotatably in the bearings 2 on the end plates 4 and 5. The rotor 6, the magnetic powder P, the cylinder 3, the magnetic powder P and the rotor 7 forms a magnetic circuit  indicated by a broken line followed by the magnetic flux of the permanent magnet 8. The torque of the rotary shaft 1 is transmitted to the cylinder 3 or the torque of the cylinder 3 is transmitted to the rotary shaft 1 by the agency of the magnetic flux. When the torque to be transmitted exceeds a specific magnitude, the magnetic flux is unable to transmit the torque and allows the rotary shaft 1 and the cylinder 3 to move relative to each other, so that the torque capable of being transmitted by the torque limiter is limited below the specific magnitude. The conventional torque limiter has the following drawbacks: (1) In filling the magnetic powder P in the cylinder 3, the magnetic powder P is liable to stagnate in a space B between the outer end surface of the rotor 7 and the inner end surface of the end plate 5 and between the outer end surface of the rotor 6 and the inner end surface of the end plate 4, and hence it is difficult to fill the magnetic powder P satisfactorily in the normal space A between the outer circumferences of the rotors 6 and 7, and the inner circumference of the cylinder 3. (2) The magnetic powder P is liable to stay in the space B while the torque limiter is stopped and starts gradually migrating to the normal space A after the torque limiter has started rotating, and hence the torque limiter is unable to transmit torque satisfactorily in the initial period of operation. Accordingly, an object of the present invention is to provide a torque limiter of a construction allowing easily filling the magnetic powder in an effective space therein. Another object of the present invention is to provide a torque limiter capable of stably transmitting torque from the beginning of operation. A further object of the present invention is to provide a torque limiter capable of effective torque transmission. Still a further object of the present invention is to provide a torque limiter capable of varying in torque transmission capacity. These objects are achieved by the features of Claim 1. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. Fig. 1 is a half-side longitudinal sectional view showing the upper half of a torque limiter, in a first embodiment, according to the present invention; Fig. 2 is a half-side longitudinal sectional view showing the upper half of a torque limiter, in a second embodiment, according to the present invention; Fig. 3 is a half-side longitudinal sectional view showing the upper half of a torque limiter, in a third embodiment, according to the present invention; Fig. 4 is a half-side longitudinal sectional view showing the upper half of a torque limiter, in a fourth embodiment, according to the present invention; Fig. 5 is a half-side longitudinal sectional view showing the upper half of a torque limiter, in fifth embodiment, according to the present invention; Fig. 6 is a half-side longitudinal sectional view showing the upper half of a torque limiter, in a sixth embodiment, according to the present invention; and Fig. 7 is a half-side longitudinal sectional view showing the upper half of a conventional torque limiter. In the drawings, like reference characters designate like or corresponding parts throughout. First Embodiment (Fig. 1): Referring to Fig. 1, there are shown a rotary shaft 1, bearings 2, sealing members 9, a bottomed magnetic cylinder 15 having a bottom wall 16 and formed of a magnetic material, magnetic rotors 11R and 11L formed of a magnetic material and coaxially secured to the rotary shaft 1, a permanent magnet 13 disposed between the rotors 11R and 11L and coaxially secured to the rotary shaft 1, an end plate 14 formed of a nonmagnetic material, such as brass or stainless steel, or a magnetic material, such as steel, a magnetic core 10 attached to the inner end surface of the end plate 14, and magnetic powder P filled in the gap between the outer end surface of the rotor 11R and the inner end surface of the magnetic core 10. The rotary shaft 1 is supported rotatably in the bearings 2 fitted in the end plate 14 and the bottom wall 16 of the cylinder 15, respectively. The sealing members 9 prevents the entrance of the magnetic powder P into the bearings 2. In this torque limiter, a magnetic circuit  is formed from the permanent magnet 13 via the rotor 11L, the cylinder 15, the magnetic core 10, the magnetic powder P and the rotor 11R to the permanent magnet 13 as indicated by a broken line. Torque is transmitted from the rotary shaft 1 to the cylinder 15 or from the cylinder 15 to the rotary shaft 1 by the agency of magnetic flux following the magnetic circuit . When the torque exceeds a specific magnitude, the rotary shaft 1 and the cylinder 15 slip circumferentially relative to each other to limit the torque to be transmitted. In filling the magnetic powder P in the torque limiter, the cylinder is placed upright with the open end thereof turned up, then the magnetic powder P is distributed over the outer end surface, namely, the upper end surface in this situation, of the rotor 11R through the open end of the cylinder, and then the end plate 14 is fitted in the open end of the cylinder 15. Since the rotor 11R is magnetized by the permanent magnet 13, the magnetic powder P stays over the outer end surface of the rotor 11R, which facilitates filling the magnetic powder P in the torque limiter. Since the magnetic powder P is attracted to the rotor 11R and always stays in place, the torque limiter is able to function normally and stably from the beginning of operation without delay. Second Embodiment (Fig. 2): Referring to Fig. 2, the members 1, 2, 9, 10R, 11R, 11L, 13 and 14R of the second embodiment are identical in disposition, material and construction to the members 1, 2, 9, 10, 11R, 11L, 13 and 14 of the first embodiment, respectively. The second embodiment employs a cylinder 15 which is open at the opposite ends. The end plate 14R is fixedly fitted in one open end of the cylinder 15, while another end plate 14L is fixedly fitted in the other open end of the cylinder 15. Another magnetic core 10L is attached to the inner end surface of the end plate 14L. Magnetic powder P is filled in the gap between the outer end surface of the rotor 11R and the inner end surface of the magnetic core 10R. A magnetic circuit  is formed from the permanent magnet 13, the rotor 11L, the magnetic core 10L, the cylinder 15, the magnetic core 10R, the magnetic powder P and the rotor 11R to the permanent magnet 13 as indicated by a broken line in Fig. 2. Torque is transmitted from the rotary shaft 1 to the cylinder 15 or from the cylinder 15 to the rotary shaft 1 by the agency of magnetic flux following the magnetic circuit . When the torque exceeds a specific magnitude, the rotary shaft 1 and the cylinder 15 slip circumferentially relative to each other to limit the torque to be transmitted. The second embodiment is the same as the first embodiment in facility of assembling, functions and effects. Third Embodiment (Fig. 3): The members 1, 2, 9, 10R, 14 and 15 of the third embodiment are the same as the members 1, 2, 9, 10, 14 and 15 of the first embodiment, respectively. The third embodiment has only one rotor 11 coaxially secured to the rotary shaft 1, and an additional magnetic core 10L. The first and second embodiments each employs the disk-shaped permanent magnet 13, while the third embodiment employes an annular permanent magnet 13. The annular permanent magnet 13 is fitted in the cylinder 15 and attached to the inner surface of the bottom wall 16 of the cylinder 15, and the additional magnetic core 10L is attached to the inner end surface of the annular permanent magnet 13. The direction of magnetization of the permanent magnet 13 is parallel to the axis of the rotary shaft 1. Magnetic powder P is filled in the gap between the rotor 11 and the magnetic core 10L. Thus, a magnetic circuit  is formed from the permanent magnet 13 through the cylinder 15, the magnetic core 10R, the rotor 11, the magnetic powder P and the magnetic core 10L to the permanent magnet 13 as indicated by a broken line in Fig. 3. Torque is transmitted from the rotary shaft 1 to the cylinder 15 or from the cylinder 15 to the rotary shaft 1 by the agency of the magnetic flux following the magnetic circuit . When the torque exceeds a specific magnitude, the rotary shaft 1 and the cylinder 15 slip circumferentially relative to each other to limit the torque to be transmitted. In filling the magnetic powder P in the torque limiter, the cylinder is placed upright with the open end, i.e., the right-hand end as viewed in Fig. 3, turned up, and then the magnetic powder P is distributed over the inner end surface of the magnetic core 10L. Since the magnetic core 10L is magnetized by the permanent magnet 13, the magnetic powder P stays over the inner surface of the magnetic core 10L, which facilitates filling of the magnetic powder P. After the magnetic powder P has been distributed over the inner surface of the magnetic core 10L, the rotor 11 is fixedly mounted on the rotary shaft 1, and then the assembly of the magnetic core 10R and the end plate 14 is fitted in the open end of the cylinder 15. The magnetic powder P can be easily poured over the inner end surface of the magnetic core 10L through the open end of the cylinder 15. Since the magnetic poweder P is attracted to the magnetic core 10L and always stays in place, the torque limiter is able to function stably and normally from the beginning of operation without delay. Fourth Embodiment (Fig. 4): The fourth embodiment is substantially the same as the third embodiment in construction and assembling procedure. The fourth embodiment is different from the third embodiment in that an annular permanent magnet 13 is fitted in the cylinder 15, held between the inner circumference of the cylinder 15 and an annular magnetic core 10L, and is radially magnetized. Magnetic powder P is filled in the gap between the rotor 11 and the magnetic core 10L. A magnetic circuit  is formed from the permanent magnet 13 through the cylinder 15, the magnetic core 10R, the rotor 11, the magnetic powder P and the magnetic core 10L to the permanent magnet 13 as indicated by a broken line in Fig. 4. Torque is transmitted from the rotary shaft 1 to the cylinder 15 or from the cylinder 15 to the rotary shaft 1 by the agency of the magnetic flux following the magnetic circuit . When the torque exceeds a specific magnitude, the rotary shaft 1 and the cylinder 15 slip circumferentially relative to each other to limit the torque to be transmitted. In filling the magnetic powder P in the gap between the rotor 11 and the magnetic core 10L, the cylinder is placed upright with the open end thereof turned up, and then the magnetic powder P is distributed over the inner end surface of the magnetic core 10L. Since the magnetic core 10L is magnetized by the permanent magnet 13, the magnetic powder P is attracted to and stays over the inner end surface of the magnetic core 10L without falling from the end surface of the magnetic core 10L, which facilitates filling the magnetic powder P. After filling the magnetic powder P, the torque limiter is assembled in the same assembling procedure as that of the third embodiment. The fourth embodiment is the same as the third embodiment in the facility of assembling, functions and effects. Fifth Embodiment (Fig. 5): The fifth embodiment is similar to the foregoing embodiments, except that the torque transmission capacity of the fifth embodiment is greater than those of the foregoing embodiments. The fifth embodiment employs two permanent magnets to enhance the magnetic flux following the magnetic circuit . Referring to Fig. 5, there are shown a rotary shaft 1, bearings 2, a cylinder 15 coaxially receiving the rotary shaft 1 therethrough, end plates 14R and 14L fitted in the opposite open ends of the cylinder 15, respectively, and rotatably supporting the rotary shaft 1 in the bearings 2, a rotor 11 coaxially secured to the rotary shaft 1, sealing members 9, annular permanent magnets 13R and 13L coaxially attached to the respective inner end surfaces of the end plates 14R and 14L, respectively, annular magnetic cores 10R and 10L coaxially attached to the respective inner end surfaces of the end plates 14R and 14L, respectively, annular magnetic cores 10R and 10L coaxially attached to the respective inner end surfaces of the permenent magnets 13R and 13L, respectively, and magnetic powder P filled in gaps between one end surface of the rotor 11 and the inner end surface of the magnetic core 10R and between the other end surface of the rotor 11 and the inner end surface of the magnetic core 10L. The permanent magnets 13R and 13L are disposed so that the respective directions of magnetization are the same and are parallel to the axis of the rotary shaft 1. Thus, a magnetic circuit  is formed from the permanent magnet 13 R through the magnetic core 10R, the magnetic powder P, the rotor 11, the magnetic powder P, the magnetic core 10L, the permanent magnet 13L, the end plate 14L, the cylinder 15 and the end plate 14R to the permanent magnet 13R as indicated by a broken line in Fig. 5. Torque is transmitted from the rotary shaft 1 to the cylinder 15 or from the cylinder 15 to the rotary shaft 1 by the agency of the magnetic flux following the magnetic circuit . When the torque exceeds a specific magnitude, the rotary shaft 1 and the cylinder 15 slip circumferentially relative to each other to limit the torque to be transmitted. The enhanced magnetic flux produced by the two permanent magnets 13R and 13L enhances the torque transmission capacity of the torque limiter. Sixth Embodiment (Fig. 6): The torque transmitting capacity of a torque limiter is dependent on the type of the permanent magnet, and the type and amount of the magnetic powder. However, in some cases, the torque transmission capacity of the torque limiter needs to be adjusted minutely. The sixth embodiment is constructed so that the adjustment of the torque transmission capacity is possible. Referring to Fig. 6, there are shown a rotary shaft 1, bearings 2, sealing members 9R and 9L, a bottomed cylinder 15 formed of a magnetic material and coaxially receiving the rotary shaft 1 therethrough, an annular magnetic core 10 formed of a magnetic material and fitted in the cylinder 15, rotors 11R and 11L formed of a magnetic material and coaxially secured to the rotary shaft 1, a permanent magnet 13 disposed between the rotors 11R and 11L and coaxially secured to the rotary shaft 1, an end plate 14 formed of a nonmagnetic material, such as brass or a stainless steel, or a magnetic material, such as steel, and firmly fitted in the open end of the cylinder 15 so as to be contiguous to the magnetic core 10, a spacer 17 interposed between the sealing member 9L on the side of the bottom wall 16 of the cylinder 15 and the rotor 11L on the side of the bottom wall 16 of the cylinder 15, and magnetic powder P filled in the gap between the inner end surface of the magnetic core 10 and the outer end surface of the rotor 11R on the side of the open end of the cylinder 15. The rotary shaft 1 is supported rotatably in the bearings 2 on the bottom wall 16 of the cylinder and the end plate 14 fixedly fitted in the open end of the cylinder 15. The sealing members 9R and 9L prevents the entrance of the magnetic powder P into the bearings 2. The direction of magnetization of the permanent magnet is parallel to the axis of the rotary shaft 1. A magnetic circuit  is formed form the permanent magnet 13 through the cylinder 15, the magnetic core 10, the magnetic powder P, and the rotor 11R to the permanent magnet 13. Torque is transmitted from the rotary shaft 1 to the cylinder 15 or from the cylinder 15 to the rotary shaft 1 by the agency of the magnetic flux following the magnetic circuit . When the torque exceeds a specific magnitude, the rotary shaft 1 and the cylinder 15 slip circumferentially relative to each other to limit the torque to be transmitted. The size of the gap between the inner end surface of the magnetic core 10 and the outer end surface of the rotor 11R filled with the magnetic powder P, hence, the torque transmission capacity of the torque limiter, is dependent on the thickness t of the spacer 17. That is, the size G₁ of the gap when t = 0, namely, when the space 17 is not provided, is reduced to a size G₂ = G₁ - t when the spacer 17 is interposed between the sealing member 9L and the rotor 11L, so that the torque transmission capacity of the torque limiter is enhanced. Thus, the torque transmission capacity of the torque limiter can be easily adjusted by selectively determining the thickness t of the spacer 17. The spacer 17 may be interposed between the bottom surface of the cylinder 15 and the sealing member 9L disposed near the bottom surface of the cylinder 15. It is also possible to adjust the size of the gap between the inner end surface of the magnetic core 10 and the outer end surface of the rotor 11R to be filled with the magnetic powder P, hence, the torque transmission capacity of the torque limiter, by adjusting the depth of entrance of the end plate 14 from the open end of the cylinder 15, hence the distance of the inner end surface of the magnetic core 10 from the open end of the cylinder 15. As apparent from the foregoing description, according to the present invention, the magnetic powder P is filled in the gap between the end surface of the rotor secured to the rotary shaft and the end surface of the magnetic core disposed opposite to the rotor instead of filling the magnetic powder P in the gap between the inner circumference of the cylinder and the outer circumference of the rotor or the outer circumferences of the rotors. Therefore, in filling the magnetic powder P in the gap between the inner end surface of the magnetic core and the outer end surface of the rotor, the magnetic powder P is attracted to the outer end surface of the rotor which is magnetized by the permanent magnet disposed contiguously to the same rotor, and is prevented from falling off the rotor, which facilitates filling the magnetic powder P in the gap. Furthermore, since the magnetic powder P always stays in place over the end surface of the rotor, the torque limiter is able to function normally and stably from the beginning of operation. Still further, according to the present invention, the torque transmission capacity of the torque limiter can be easily enhanced by providing two permanent magnets instead of one, and can be easily adjusted by providing a spacer having an appropriate thickness so as to adjust the size of the gap to be filled with the magnetic powder P properly.

Claims: A torque limiter comprising: a cylinder (15) formed of a magnetic material and closed on both ends; at least one end plate (14) fixedly and coaxially fitted in one end of said cylinder (15), a rotary shaft (1) coaxially and rotatably supported in bearings (2, 2), at least one rotor (11) coaxially secured to said rotary shaft (1), at least one permanent magnet (13) coaxially secured to said rotary shaft (1) or to said cylinder (15), magnetic powder (P) filled in a space within the cylinder (15), and sealing members (9, 9) disposed between said end plate (14) said at least one rotor (11, to prevent the entrance of said magnetic powder (P) into said bearings (2, 2); characterised in that at least one annular core (10) formed of a magnetic material is provided within the cylinder (15), and the magnetic powder (P) is filled in a gap between said at least one annular core (10) and said at least one rotor (11). A torque limiter according to claim 1, characterised in that one rotor (11) is provided, and said at least one permanent magnet (13) is annular shaped and fitted in said cylinder to the inner surface of said bottom wall (16). A torque limiter according to claim 1, characterised in that two rotors (11L, 11R) are secured to said rotary shaft (1) with a space therebetween, and said permanent magnet (13) is disk shaped and coaxially secured to said rotary shaft (1) between said rotors (11L, 11R). A torque limiter according to claim 2 or claim 3, characterised in that said cylinder (15) comprises one bottom wall (16) and one end plate (14). A torque limiter according to claim 2 or claim 3, characterised in that said cylinder (15) comprises two end plates (14L, 14R). A torque limiter according to claim 4 in connection with claim 3, characterised in that two annular cores (10L, 10R) formed of a magnetic material are fixedly fitted in said cylinder (15) contiguously to said end plates (14L, 14R) and opposite to and at a distance from said rotors (11L, 11R). A torque limiter according to claim 4 in connection with claim 1, characterised in that said annular permanent magnet (13) is fixedly and coaxially fitted contiguously to the inner surface of said bottom wall (16) of said cylinder (15) and magnetised in a direction parallel to the axis of said rotary shaft (1), and two annular cores (10R, 10L) are fitted in said cylinder (15) contiguously to said permanent magnet (13) and to the inner end surface of said end plate (14), respectively. A torque limiter according to claim 2, characterised in that said permanent magnet (13) is radially magnetised and coaxially fitted in said cylinder (15) contiguously to the inner surface of the bottom wall (16) of said cylinder (15), and a first annular core (10L) is fixedly fitted in said permanent magnet (13) contiguously to the inner surface of the bottom wall (16) of said cylinder (15), and a second annular core (10L) is fixedly and coaxially fitted in said cylinder (15) contiguously to the inner surface of said inner end plate (14). A torque limiter according to claim 2, characterised in that two annular permanent magnets (13L, 13L) magnetised in the same direction parallel to the axis of said rotary shaft (1) are coaxially fitted in said cylinder (15) contiguously to the inner end surfaces of said end plates (14L, 14R), respectively, and two annular cores (10L, 10R) formed of a magnetic material are coaxially fitted in said cylinder (15) contiguously to the inner end surfaces of said permanent magnets (13L, 13R), respectively. A torque limiter according to claim 2, characterised in that a spacer (17) is provided between one of said sealing members (9L, 9R) disposed contiguously to the bottom surface of said cylinder (15) and one of said rotors (11L, 11R) on the side of the inner surface of the bottom wall (16) of said cylinder (15). A torque limiter according to claim 10, characterised in that the torque transmission capacity can be varied by changing the spacer (17) for another spacer having a thickness different from that of the former (17). A torque limiter according to one of the preceding claims, characterised in that the torque transmission capacity can be varied by adjusting a depth of entrance of said end plate (14) from the open end of said cylinder (15). A torque limiter according to one if the preceding claims, characterised in that said rotor (11) is formed of a magnetic material. A torque limiter according to any of the preceding claims, characterised in that said end plate (14) or end plates (14L, 14R) are formed of a magnetic material. A torque limiter according to any of the claims 1 to 14, characterised in that said end plate (14) or end plates (14L, 14R) are formed of a nonmagnetic material.

Inventors: MAJI, HIROSHI C/O ISE FACTORY, OI, SUKEHACHI C/O ISE FACTORY
Applicants: SHINKO ELECTRIC CO. LTD.
Application year: 1987
Main classification: F16D37
IPC codes: F16D37