HK1069022B - Structure for fixing a ring-shaped permanent magnet - Google Patents

Description

Fixing structure of ring-shaped permanent magnet

Technical Field

The present invention relates to a fixing structure of a ring-shaped permanent magnet having a permanent magnet in a support body, which is used for a driving device such as a linear motor.

Background

Conventionally, for example, a stirling cycle engine disclosed in patent document 1 is known in which a piston and a displacer are slidably inserted into a cylinder provided in a casing and the piston is reciprocally driven by a drive mechanism. The driving mechanism for driving the piston to reciprocate is composed of the following three parts: the electromagnetic valve includes a ring-shaped permanent magnet fixed to one end of a short cylindrical support body connected to the top of a piston, a magnetic conductive portion disposed on the inner periphery of the permanent magnet with a magnetic field gap therebetween and disposed opposite to the inner periphery, and an electromagnetic coil wound around a core disposed on the outer periphery of the permanent magnet with the magnetic field gap therebetween and disposed opposite to the outer periphery. When the piston is driven by the driving mechanism to move in the cylinder in a direction approaching the displacer, the gas in a compression chamber formed between the piston and the displacer is compressed and reaches an expansion chamber formed between the top end of the displacer and the top end of the casing through a heat sink, a regenerator, and a heat sink, thereby pressing down the displacer to have a predetermined phase difference with respect to the piston. When the piston moves in a direction away from the displacer, a negative pressure is formed in the compression chamber, and the gas in the expansion chamber flows back to the compression chamber through the heat absorbing plate, the regenerator, and the heat radiating plate, thereby pushing up the displacer with a predetermined phase difference with respect to the piston. By performing a reversible cycle of 2 isothermal changes and an equal volume change in such a process, the vicinity of the expansion chamber becomes a low temperature, and the vicinity of the compression chamber becomes a high temperature.

The drive mechanism for such a stirling cycle engine causes an alternating current to flow through an electromagnetic coil, which generates an alternating magnetic field that axially reciprocates an annular permanent magnet fixed to a support body, and axially reciprocates a piston connected to the support body to which the permanent magnet is fixed within a cylinder.

Heretofore, the permanent magnet used in such a drive mechanism is fixed to a cylindrical support by an adhesive. At this time, as shown in fig. 3, the permanent magnet M is fixed to the support body B by an adhesive by placing the permanent magnet M on a dedicated fixing tool a, applying the adhesive to the permanent magnet M, and then placing the support body B on the tool a so as to adhere to the permanent magnet M. However, in the method of fixing the permanent magnet M in the support body B using the fixing tool a, since the support body B and the permanent magnet M are first required to be attachable to and detachable from the fixing tool a, a gap is required between the outer periphery of the fixing tool a and the inner peripheries of the support body B and the permanent magnet M; further, since the permanent magnet M is fixed to the support B by an adhesive, when the support B and the permanent magnet M are radially overlapped as shown in fig. 3, the support B and the permanent magnet M must be bonded to each other. In this way, since the support body B and the permanent magnet M have a gap with the dedicated fixture a and the support body B and the permanent magnet M need to be bonded, there is a problem that eccentricity is likely to occur between the pistons to which the permanent magnet M and the support body B are connected, and the coaxiality between the pistons and the permanent magnet M is likely to be deviated, and it is difficult to ensure accuracy. Further, when the ring-shaped permanent magnet M expands and contracts due to the influence of temperature or the like, the permanent magnet M may be separated from the support B due to the difference in thermal expansion coefficient between the permanent magnet M and the support B, and the quality of the product may not be stabilized. Further, the use of an adhesive requires a step such as curing, and the workability of assembly is not good.

[ patent document 1 ]

Japanese patent laid-open No. 2001-355513

Disclosure of Invention

Accordingly, an object of the present invention is to provide a fixing structure of a ring-shaped permanent magnet, which can reliably fix a support body and a permanent magnet together without using an adhesive when the permanent magnet is mounted, and can improve output characteristics of a driving mechanism by coaxially supporting the permanent magnet on the support body with high accuracy.

A first structure of the present invention is a fixing structure of a ring-shaped permanent magnet, which is composed of a ring-shaped permanent magnet and a cylindrical support body supporting the ring-shaped permanent magnet, and is characterized in that a permanent magnet having a negative thermal expansion coefficient in a direction perpendicular to a magnetic flux is used as the ring-shaped permanent magnet, and the ring-shaped permanent magnet is embedded in an inner peripheral surface of the cylindrical support body molded from a synthetic resin, thereby firmly fixing the ring-shaped permanent magnet to the cylindrical support body.

With the first configuration, the work and the members required for the insertion, adhesion, and other fixing of the permanent magnet are not necessary, and the accuracy of the coaxial alignment of the permanent magnet to the support body is determined only by the accuracy of the mold formed by the insertion.

In addition, according to the second configuration of the present invention, the material of the ring-shaped permanent magnet is Nd-Fe-B magnetic material.

In the second configuration, since the permanent magnet is formed of an Nd — Fe — B magnetic material, the permanent magnet has a property that the thermal expansion coefficient in the magnetic flux direction is positive and the thermal expansion coefficient in the direction perpendicular to the magnetic flux is negative, and the synthetic resin support contracts after cooling, the support and the permanent magnet can be more firmly pressed together when the support and the permanent magnet contract after molding.

Further, according to the third configuration of the present invention, the ring-shaped permanent magnet is magnetized in the radial direction so that the polarities of the inside and the outside are opposite to each other.

In the third configuration, since the thermal expansion coefficient of the permanent magnet formed of the Nd — Fe — B based magnetic material in the magnetic flux direction is positive and the thermal expansion coefficient thereof in the direction perpendicular to the magnetic flux direction is negative, the support body made of the synthetic resin is expanded and deformed in the plane direction perpendicular to the magnetic flux direction after cooling to increase the diameter thereof, and is contracted and deformed after cooling, so that the support body and the permanent magnet are pressed against the outer surface of the permanent magnet more firmly if they are cooled after molding.

Drawings

FIG. 1 is a sectional view showing a state where a support according to an embodiment of the present invention is coupled to a permanent magnet

FIG. 2 shows an overall cross-sectional view of an embodiment of the invention incorporated into a Stirling cycle engine

FIG. 3 is a sectional view showing a conventional example

Detailed Description

One embodiment of the present invention will be described below by way of example for use in a stirling cycle engine with reference to the accompanying drawings. In fig. 1 to 2, reference numeral 1 denotes a housing including a cylindrical portion 2 formed in a substantially cylindrical shape and a main body 3. The cylindrical portion 2 is made of stainless steel or the like, and is integrally formed of a root portion 4, a middle portion 5, and a top portion 6.

The cylinder part 2 is provided with a cylinder 7 coaxially inserted into the cylinder part 2 and extending into the main body 3. The top 6 side of the cylinder 7 is coaxially followed by an elongated cylinder 7A separated from the cylinder 7. The cylinder 7 on the side of the main body 3 is formed by casting such as die casting using a metal such as aluminum, and is formed integrally with the later-described mounting portions 26 and 27 and the connecting arm portion 30, and is formed by cutting the inner and outer peripheries of the cylinder 7 after casting. The displacer 8 is housed in the top side of the cylinder 7 and the inside of the extension cylinder 7A and is slidable in the axial direction. An expansion chamber E is formed between the top of the displacer 8 and the top 6 of the cylindrical portion 2, and the inside and outside of the extension cylinder 7A communicate with each other through a gap 9. In the intermediate portion 5, a regenerator 10 is provided between the inner periphery of the cylindrical portion 2 and the outer periphery of the cylinder 7, and a communication hole 11 for communicating the inside and the outside of the cylinder 7 is formed in the root portion 4 in the cylinder 7 itself. Heat absorbing fins 12 are provided between the inner periphery of the top portion 6 of the cylindrical portion 2 and the outer periphery of the top portion of the extension cylinder 7A, and heat radiating fins 13 are provided between the inner periphery of the cylindrical portion 2 and the outer periphery of the cylinder 7 between the regenerator 10 and the communication hole 11. A passage 14 is formed from the inner top of the extended cylinder 7A to the compression chamber C in the cylinder 7 through the gap 9, the heat absorbing fins 12, the regenerator 10, the heat dissipating fins 13, and the communication hole 11. Further, in the main body 3, a piston 15 is housed inside the cylinder 7 on the base side thereof so as to be slidable in the axial direction. The base of the piston 15 is coaxially connected to a drive mechanism 16. The drive mechanism 16 is constituted by a short cylindrical support 17 connected to the base of the piston 15 via a connecting body 15A and coaxially extended to the outer periphery of the base side of the cylinder 7, a short cylindrical permanent magnet 18 fixed to the inner peripheral surface of the top of the support 17, an annular electromagnetic coil 19 provided near the outer periphery of the permanent magnet 18, and a magnetic permeable part 20 provided near the inner periphery of the permanent magnet 18.

The support 17 is made of synthetic resin, and the ring-shaped permanent magnet 18 fixed to the inner peripheral surface of the top portion thereof is made of Nd-Fe-B sintered magnetic material. When the support 17 is formed, a molding material of the support 17 in a state in which the permanent magnet 18 before magnetization is assembled is filled in a mold (not shown) for forming the support 17, and the permanent magnet 18 is integrally insert-molded on the inner peripheral surface of the top of the support 17. After the molding is completed, the permanent magnet 18 is magnetized in the radial direction.

A first leaf spring 21 for controlling the operation of the piston 15 is connected to a connecting body 15A for connecting the support body 17 to the piston 15. One end of a rod 22 for controlling the operation of the displacer 8 is connected to the root of the displacer 8, and the other end of the rod 22 is connected to a second leaf spring 23. The rod 22 extends through the piston 15. The pair of leaf springs 21, 23 are disposed outside the root portion of the cylinder 7 in the main body 3, and the second leaf spring 23 is disposed at a position farther from the root portion of the cylinder 7 than the first leaf spring 21. The electromagnetic coil 19 is provided by winding a core 24, and the core 24 is integrated with the electromagnetic coil 19 and the like.

A mounting portion 26 projecting coaxially with the cylinder 7 is formed integrally with the outer peripheral surface of the middle portion of the cylinder 7, and a flange-like mounting portion 27 is formed integrally with the cylinder 7 at a position closer to the base of the cylinder 7 than the mounting portion 26. A pair of such attachment portions 26 and 27 are formed with a space therebetween, and the attachment portion 26 is in contact with the root portion 4 of the cylindrical portion 2 with an O-ring 26A interposed therebetween, thereby fixing the cylinder 7 to the cylindrical portion 2 of the housing 1. The mounting portion 27 is configured such that one side surface 27A thereof is brought into contact with the mounting portion 3A inside the main body 3 and is fixed to the mounting portion 3A by a screw, and one end of the core 24 constituting the driving mechanism 16 is brought into contact with the other side surface 27B thereof. The other end of the core 24 is abutted by a fixing ring 28, the core 24 is sandwiched between the fixing ring 28 and the mounting portion 27, and the core 24 and the electromagnetic coil 19 integrated with the core 24 are fixed to the mounting portion 27 by screws 29. A plurality of connecting arm portions 30 are provided to protrude from the other side surface 27B of the mounting portion 27 so as to be substantially parallel to the axial direction of the cylinder 7. The connecting arm portion 30 is formed integrally with the mounting portion 27 at a root portion 30A. The first leaf spring 21 is attached to the tip end of the connecting arm 30 with the spacer 31, and the second leaf spring 23 is attached to the spacer 31 with the screw 32.

In the figure, reference numeral 33 denotes a vibration absorbing unit provided at the other end of the housing 1, and a plurality of leaf springs 34 are arranged so as to be coaxially overlapped with the balance weight 35 via a connecting portion arranged on the axis of the cylinder 7.

Therefore, the mounting portion 26 is brought into contact with the inside of the root portion 4 of the cylindrical portion 2 via the O-ring 26A, one side surface 27A of the mounting portion 27 is brought into contact with the mounting portion 3A inside the main body 3, and the mounting portion 3A is fixed by a screw, and the cylinder 7 is fixed to the housing 1 in the manner described above. At this time, the mounting portion 26 is brought into contact with the inner surface of the cylindrical portion 2 via the O-ring 26A, whereby the cylinder 7 can be coaxially disposed in the cylindrical portion 2. The cylinder 7 is provided with a magnetically permeable part 20 on the outer periphery of the cylinder 7 on the base side, and the electromagnetic coil 19 and the core 24 constituting the drive mechanism 16 are fixed to a mounting part 27 formed integrally with the cylinder 7 by the fixing ring 28 and the screws 29. The displacer 8, the piston 15, and the like are assembled into the cylinder 7, and a first plate spring 21 attached to a connecting body 15A at the root of the piston 15 is held and fixed between the arm 30 and a spacer 31, and a second plate spring 23 connected to the other end of a rod 22 connected to the displacer 8 is fixed to the other end of the spacer 31. Then, the main body 3 and the cylindrical portion 2 are connected, and the vibration absorbing unit 33 assembled in advance is attached to the main body 3.

Therefore, with the above configuration, if an alternating current is caused to flow through the electromagnetic coil 19, the electromagnetic coil 19 generates an alternating magnetic field that generates a force that reciprocates the permanent magnet 18 in the axial direction and concentrates on the core 24. By this force, the piston 15 connected to the support 17 to which the permanent magnet 18 is fixed reciprocates in the axial direction in the cylinder 7. Therefore, when the piston 15 moves in a direction approaching the displacer 8, the gas in the compression chamber C formed between the piston 15 and the displacer 8 is compressed, passes through the communication hole 11, the fin 13, the regenerator 10, the heat absorbing plate 12, and the gap 9, reaches the expansion chamber E formed between the top of the displacer 8 and the top 6 of the cylinder part 2, and presses down the displacer 8 with a predetermined phase difference from the piston 15. When the piston 15 moves in a direction away from the displacer 8, a negative pressure is formed in the compression chamber C, and the gas in the expansion chamber flows back from the expansion chamber E to the compression chamber C through the gap 9, the heat absorbing plate 12, the regenerator 10, the heat dissipating plate 13, and the communication hole 11, thereby pushing up the displacer 8 with a predetermined phase difference with respect to the piston 15. By performing a reversible cycle of 2 isothermal changes and an equal volume change in this process, the vicinity of the expansion chamber E becomes a low temperature, and the vicinity of the compression chamber C becomes a high temperature.

Therefore, the driving device 16 used in the stirling cycle engine is a device that generates a force for reciprocating the permanent magnet 18 in the axial direction by the alternating magnetic field generated by the electromagnetic coil 19, and reciprocates the piston 15 connected to the support body 17 for fixing the permanent magnet 18 in the axial direction in the cylinder 7 by the force, and therefore it is important to mount the support body 17 and the permanent magnet 18 coaxially with the piston 15, but according to the present embodiment, since the permanent magnet 18 is integrally embedded in the support body 17, the work and material required for insertion, adhesion, and other fixing of the permanent magnet 18 are not necessary, and the accuracy of the coaxiality of the permanent magnet 18 to the support body 17 is determined only by the accuracy of the mold formed by the embedding, and therefore the accuracy of the coaxiality of the permanent magnet 18 with respect to the support body 17 is improved.

In the present embodiment, the annular permanent magnet 18 fixed to the inner peripheral surface of the support 17 is formed of an Nd-Fe-B sintered magnetic material. The permanent magnet 18 made of an Nd — Fe — B based sintered magnetic material has a characteristic of having a positive thermal expansion coefficient in a direction parallel to a magnetic flux (magnetization direction) and a negative thermal expansion coefficient in a direction perpendicular to the magnetic flux. That is, when the ring-shaped permanent magnet is magnetized in the radial direction, the direction of the magnetic flux, that is, the thickness direction of the permanent magnet has a positive expansion coefficient, and the permanent magnet perpendicular to the magnetic flux has a negative expansion coefficient in the planar direction. Therefore, after the ring-shaped permanent magnet is cooled, the ring-shaped permanent magnet is contracted in the thickness direction of the permanent magnet and expanded and deformed in the plane direction of the permanent magnet, and as a result, the entire permanent magnet is expanded and deformed in the radial direction and the axial direction. On the other hand, since the synthetic resin constituting the support 17 has a positive expansion coefficient, it contracts and deforms upon cooling. Therefore, in the present embodiment in which the annular permanent magnet 18 is formed by fitting the annular permanent magnet 18 into the support 17 by a method such as injecting molten resin into a mold in which the annular permanent magnet 18 is arranged in advance, such that the support 17 is radially outward and the annular permanent magnet 18 is radially inward, the support 17 is deformed to be contracted inward as indicated by an arrow a in fig. 1 after molding, and the annular permanent magnet 18 is deformed to be radially expanded as indicated by an arrow b in fig. 1. This makes it possible to more firmly fix the permanent magnet 18 to the support 17 without generating a gap between the support 17 and the permanent magnet 18, and thus, the accuracy of coaxiality between the support 17 and the permanent magnet 18 can be ensured. Therefore, the piston 15 can be accurately attached coaxially with the permanent magnet 18, and the overall coaxial accuracy of the piston 15, the support 17, and the permanent magnet 18 can be improved, thereby improving the performance of the drive mechanism 16 and the stirling cycle engine. Further, since no adhesive is used except for the work and material required for fixing the permanent magnet M by adhesion or the like, the permanent magnet M is less susceptible to the use environment conditions such as temperature, and the assembling property can be improved while the change over a long period of time is small.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, although the driving device for the stirling cycle engine is exemplified in the above embodiment, the present invention is also applicable to driving devices used for other devices and can also be applied to various electric motors.

According to the first aspect of the present invention, since the annular permanent magnet is fixed to the tubular support body by providing the fixing structure of the annular permanent magnet, the annular permanent magnet is constituted by the annular permanent magnet and the tubular support body supporting the annular permanent magnet, and the annular permanent magnet having a negative thermal expansion coefficient in a direction perpendicular to the magnetic flux is used as the annular permanent magnet, and the annular permanent magnet is embedded and formed in the inner peripheral surface of the tubular support body molded from the synthetic resin, the work and material required for the insertion, adhesion, and other fixing of the permanent magnet are not required at all, and the accuracy of the coaxiality of the permanent magnet with respect to the support body is determined only by the accuracy of the mold formed by the embedding, and therefore the accuracy of the coaxiality of the permanent magnet with respect to the support body. Further, the permanent magnet has a property that the coefficient of thermal expansion in the direction of magnetic flux is positive and the coefficient of thermal expansion in the direction perpendicular to the magnetic flux is negative, and the synthetic resin support contracts after cooling, so that the support and the permanent magnet can be more firmly pressed together when the support and the permanent magnet contract after molding.

Further, according to the second configuration of the present invention, since the material of the annular permanent magnet is Nd — Fe — B based magnetic material, the permanent magnet has a property that the coefficient of thermal expansion in the magnetic flux direction is positive and the coefficient of thermal expansion in the direction perpendicular to the magnetic flux is negative, and the support made of synthetic resin contracts after cooling, the support and the permanent magnet can be more firmly pressed together when the support and the permanent magnet contract after molding.

Further, according to the third configuration of the present invention, since the support body and the annular permanent magnet are arranged in a positional relationship in the radial direction so that the annular permanent magnet is inside and the support body is outside, the annular permanent magnet is magnetized in the radial direction so that the polarities of the inside and the outside are opposite, if the support body and the permanent magnet are cooled after molding, the support body made of the synthetic resin contracts, and the permanent magnet made of the Nd — Fe-B based magnetic material expands and deforms in the direction perpendicular to the magnetic flux direction, and the diameter increases, so that the support body is pressed against the outer surface of the permanent magnet more firmly, and the permanent magnet can be fixed to the support body more firmly.

As a technical effect of the above embodiment, the radial positional relationship between the support and the annular permanent magnet is such that the annular permanent magnet is on the inside and the support is on the outside, whereby the shrinkage rate of the support made of synthetic resin is larger than that of the permanent magnet. Further, by arranging the ring-shaped permanent magnet radially inside and the support radially outside, the support is pressed against the outer surface of the permanent magnet by cooling the support and the permanent magnet after molding, so that not only can the coaxial accuracy be ensured without generating a gap at the bonding surface of the support and the permanent magnet, but also the permanent magnet can be firmly fixed to the support.

Claims (3)

1. A fixing structure of a ring-shaped permanent magnet is composed of a ring-shaped permanent magnet and a cylindrical support body supporting the ring-shaped permanent magnet, and is characterized in that the ring-shaped permanent magnet is made of a permanent magnet having a negative thermal expansion coefficient in a direction perpendicular to a magnetic flux, and the ring-shaped permanent magnet is embedded in an inner peripheral surface of the cylindrical support body molded by synthetic resin, so that the ring-shaped permanent magnet is firmly fixed to the cylindrical support body.

2. The fixing structure of a ring-shaped permanent magnet according to claim 1, wherein: the material of the ring-shaped permanent magnet is Nd-Fe-B magnetic material.

3. The fixing structure of a ring-shaped permanent magnet according to claim 1 or 2, wherein: the ring-shaped permanent magnet is magnetized in the radial direction so that the polarities of the inside and the outside are opposite.