210 may be made of a soft magnetic material.

FIG. 5 is a cross-sectional view perpendicular to the top-bottom direction of the movable element according to Example 1 and a movable element according to Comparative Example. FIG. 6 is a diagram illustrating load characteristics applied to the piston with respect to the position of the piston of the compressor. FIG. 7 is a diagram illustrating results of comparison of thrust generated in the movable element 2 when an alternating current is applied to the windings 5 and when an alternating current is not applied to the windings 5 with respect to the position of the movable element in Example 1 and Comparative Example.

In FIG. 5, the movable element 2 according to Example 1 includes one primary magnet 211 and one secondary magnet 212, and a distance (length) between the bearing shafts 600 in the front-rear direction (relative displacement direction) is L1. On the other hand, in the movable element 2 according to Comparative Example, one primary magnet 211 and two secondary magnets 212 are provided, and a distance (length) between bearing shafts 600 in a front-rear direction (relative displacement direction) is defined as L2. As can be seen from FIG. 5, L1<L2, and in the present Example, the distance (length) between the bearing shafts 600 in the front-rear direction can be shortened, the moment force applied to the movable element 2 can be reduced, and the load applied to each of the bearings can be reduced. As a result, the service life of the bearings can be improved.

As can be seen from FIG. 6, at the time of pushing of the piston, the load increases as the pressure inside the cylinder increases, and when the pressure reaches a desired pressure and a discharge valve 900 is opened, the load becomes constant. On the other hand, at the time of withdrawal of the piston, the load decreases as the pressure inside the cylinder decreases, and when the pressure inside the cylinder matches the pressure on the suction side, a suction valve 910 is opened and the load becomes 0. As described above, the load applied to the piston of the compressor is mainly in a direction in which the piston is pushed, and is asymmetric with respect to the front-rear direction.

As can be seen from FIG. 7, in a case where three magnets according to Comparative Example are provided, since field element poles 210 are arranged symmetrically in the front-rear direction, a thrust average value when a current is not applied is 0, and the magnitude of the thrust when a current is applied is symmetrical in the front-rear direction. Therefore, in order to cope with the above-described asymmetric load in the front-rear direction, it is necessary to reduce the thrust at the time of withdrawal of the piston, and special control or a circuit for applying a current asymmetric in both directions of a stroke has been required.

On the other hand, in a case where the two magnets according to the present Example are provided, since the field element poles 210 are arranged asymmetrically in the front-rear direction, a thrust average value when a current is not applied is positive in the front direction, and the magnitude of the thrust when a current is applied is asymmetrical in the front-rear direction. Therefore, special control or a specific circuit is unnecessary in order to cope with the load asymmetric in the front-rear direction described above, and a current symmetric in both directions of a stroke can be passed.

According to the present Example, the service life of the bearings can be improved, and the overall length of the system can be reduced.

Example 2

A linear motor according to Example 2 of the present invention will be described with reference to FIGS. 8 to 11. FIG. 8 is a diagram illustrating a waveform of thrust when a direct current is applied to windings to move a movable element in a front-rear direction (relative displacement direction) when a length of a secondary magnet is changed in Example 2. In FIG. 8, the length of the secondary magnet in the front-rear direction is changed to 14 mm, 20 mm, and 26 mm. As illustrated in FIG. 8, a zero-cross point at which the thrust crosses a zero-level axis in the front direction differs depending on the length of the secondary magnet in the front-rear direction, and the longer the length, the longer the zero-cross point extends in the front direction. When the thrust exceeds the zero-cross point, the thrust acts in the rear direction, and thus the stroke in the front direction can be limited by the zero-cross point.

The above description will be explained with reference to FIGS. 9 to 11. FIG. 9 is a schematic diagram of thrust generated in each movable element magnetic pole when a current is applied to the windings and the movable element is located at the center in the front-rear direction in Example 2, and corresponds to a position B in FIG. 8. FIG. 10 is a schematic diagram of thrust generated in each movable element magnetic pole when the movable element is located at the foremost portion in the front-rear direction in Example 2, and corresponds to a position C in FIG. 8. FIG. 11 is a schematic diagram of thrust generated in each movable element magnetic pole when the movable element is located at the rearmost portion in the front-rear direction in Example 2, and corresponds to a position A in FIG. 8.

In FIG. 9, a pitch between poles of magnetic pole teeth 301 in the front-rear direction is τp1, a pitch between poles of field element poles 210 in the front-rear direction is τp2, the distance from the center of the magnetic pole tooth 301 on the front side to the center of a primary magnet 211 is τp1/2, the distance from the center of the magnetic pole tooth 301 on the rear side to the center of the secondary magnet 212 is τx, and the distance from an end of a piston 7 to an inner wall of a cylinder is Su. In this case, when a current is applied to the windings, as illustrated in the drawing, an N pole and an S pole are excited at ends of each of the magnetic pole teeth 301, and the thrust in the front direction indicated by arrows is generated in each magnet by the interaction between the magnetic poles by the primary magnet 211 and the secondary magnet 212.

FIG. 10 illustrates a position to which the movable element is advanced by τu in the front direction, and that corresponds to the position C in FIG. 8. The center of the primary magnet 211 and the center of the secondary magnet 212 are located between the centers of the two magnetic pole teeth 301, and the thrust generated in each magnet is offset in opposite directions, so that the thrust becomes 0. The position of the movable element at this time is expressed by the following equation.

τ
⁢
u

=

(

τ
⁢
p
⁢

1
/
2

+

τ
⁢
x

)

/
2

(
1
)

In the compressor, when a position where the piston collides with a wall surface of the cylinder, that is, a stroke upper limit position is Su, u is set to be larger than a thrust generation upper limit position τu, so that the effect of avoiding the collision of the piston and preventing the damage of the piston can be obtained. That is, the following may be used.

Su>(τp1/2+τx)/2 . . . (2) Solving this for τx gives:

τ
⁢
x

<

2
⁢
Su

-

τ
⁢
p
⁢

1
/
2

(
3
)

The length of each secondary magnet 212 with respect to a desired stroke can be determined by the above equation. Here,

τ
⁢
p
⁢
2

=

τ
⁢
p
⁢

1
/
2

+

τ
⁢
x

(
4
)

The following relationship is derived from Equations (3) and (4).

τ
⁢
p
⁢
2

<

2
⁢
S
⁢
u

(
5
)

That is, the pitch τp2 between poles of the field element poles 210 in the front-rear direction may be less than twice the stroke upper limit position Su.

FIG. 11 illustrates a state where the movable element is located at the rearmost portion in the front-rear direction, and corresponds to the position A in FIG. 8. Since the secondary magnet 212 extends outside the magnetic pole tooth 301, the thrust is affected only by the primary magnet 211 and does not depend on the length of the secondary magnet 212.

According to the present Example, it is possible to suppress the effect of the secondary magnet on the thrust when the movable element is located at the rearmost portion in the front-rear direction.

Example 3

A linear motor according to Example 3 of the present invention will be described with reference to FIGS. 12 to 14. FIG. 12 is a schematic diagram of thrust generated in a movable element when a current is applied to windings and the movable element is located at the center in a front-rear direction in a case where three magnets according to Conventional Example are provided. FIG. 13 is a schematic diagram of thrust generated in a movable element when a current is applied to windings and the movable element is located at the center in a front-rear direction in Example 3. FIG. 14 is a graph illustrating the transition of the magnitude of thrust generated with respect to the ratio of lengths of a primary magnet and a secondary magnet in Example 3 and Conventional Example.

In FIGS. 12 and 13, a pitch between poles of magnetic pole teeth 301 in the front-rear direction is τp1, a pitch between poles of the primary magnet 211 is τm1, and a pitch between poles of the secondary magnet is τm2. Here, τp1=23.5. FIG. 14 illustrates the transition of the magnitude of the thrust when the ratio of the lengths τm1 and τm2 is changed.

In a case where three magnets according to Comparative Example are provided, the thrust becomes maximum when τm1=23.5 and τm2=20, and there is a relationship of τm1=τp1 in this case. On the other hand, in a case where the two magnets according to the present Example are provided, the thrust is maximized when τm1=25.5 and τm2=19, and in this case, the pitch τm1 between the poles of the primary magnet 211 is longer than the pitch τp1 between poles of a plurality of armature magnetic poles (τm1>τp1). Therefore, the thrust can be maximized by setting τm1=τp1 in a case where three magnets according to Comparative Example are provided, whereas the thrust can be maximized by setting τm1>τp1 in a case where the two magnets according to the present Example are provided.

According to the present Example, the thrust in the front direction can be increased, and the length of the linear motor in the front-rear direction can be shortened.

Example 4

A linear motor according to Example 4 of the present invention will be described with reference to FIGS. 15 to 16. FIG. 15 is a cross-sectional view perpendicular to a top-bottom direction of a movable element according to Example 4. FIG. 16 is a cross-sectional view perpendicular to a left-right direction of the linear motor according to Example 4.

A configuration according to Example 4 is the same as that in Example 1 except for the following points, and the configuration described in Example 1 can be used except for the following configuration according to the present Example.

A neck part 202 of the movable element 2 according to the present Example includes a gap 203 to which a second secondary magnet 213 having a length in the left-right direction shorter than those of a primary magnet 211 and a secondary magnet 212 is fitted. The second secondary magnet 213 is disposed in the gap (fitting portion) 203 so as to fill the gap (fitting portion) 203, thereby preventing positional displacement in the left-right direction and the front-rear direction. Further, an adhesive is applied to a contact surface between the secondary magnet 212 and the gap (fitting portion) 203, thereby preventing positional displacement in the top-bottom direction. The secondary magnet 212 and the second secondary magnet 213 are provided asymmetrically with respect to the position of the center of the primary magnet 211 in the front-rear direction (relative displacement direction).

The second secondary magnet 213 can improve the thrust when the movable element 2 is driven in the rear direction, and can be applied to a case where a load is also applied in the rear direction. For example, as illustrated in FIG. 16, by arranging pistons 7 and cylinders 8 on both sides of the movable element 2 in the front-rear direction, the pistons 7 and the cylinders 8 can be used as a so-called two-stage compressor in which one of the cylinders compresses to an intermediate pressure and the other of the cylinders compresses to the highest pressure.

The diameters of the piston 7 and the cylinder 8 disposed in the rear direction are smaller than the diameters of the piston 7 and the cylinder 8 disposed in the front direction.

Example 5

FIG. 17 is a perspective view illustrating a compressor using a linear motor according to Example 5 of the present invention. FIG. 18 is a cross-sectional view illustrating a main part of the compressor in FIG. 17.

The compressor 1000 according to the present Example can be used as a gas compressor that compresses air or a refrigerant, and includes a resonant spring 400 provided on one side of an armature 3 in a reciprocating direction of a movable element 2 and a piston (disposed in a cylinder 8, not shown) provided on the other side of the armature 3, the cylinder 8, electromagnetic valves 1400 (1400A, 1400B), an exhaust valve 1500, a dryer 1600, and an inverter 1700.

In the compressor 1000 according to the present Example, a drive motor for the piston is constituted by the linear motor, and the movable element 2 has a flat plate shape (flat plate shape). The movable element 2 further protrudes rearward from a rear end of an end member 4. As the linear motor, any one of the linear motors according to Examples 1 to 4 is used.

A casing 1800 that houses the armature 3 and the resonant spring 400 is attached to the cylinder 8. In the present embodiment, the end member 4 is used as a front surface of the casing 1800, but a member constituting the front surface of the casing 1800 may be provided on the front side of the end member 4. That is, instead of using the end member 4 as the front surface member of the casing 1800, a front surface member may be provided separately from the end member 4.

In the casing 1800, a cylindrical side surface (side surface member) 1810 and a rear surface (rear surface member, bottom surface member) 1820 are configured separately, and the rear surface 1820 is fixed to the cylinder 8 via a base plate 1900 by an insertion member 1830 extending in the front-rear direction. As a result, the side surface 1810 is sandwiched between the rear surface 1820 and the cylinder 8.

An electrode protrudes forward from the casing 1800 side, and each of extended ends of the windings 5 is electrically connected to one end of the electrode. The other end of the electrode is inserted into the inverter 1700 through a through hole (not illustrated) formed in the base plate 1900, and is electrically connected to an internal inverter circuit.

The base plate 1900 is provided with a gas suction/discharge port 1910. The two electromagnetic valves 1400A and 1400B are attached to the base plate 1900, and two through-holes (gas passages) 1920a and 1920b through which gas flows are provided corresponding to the electromagnetic valves 1400A and 1400B. The electromagnetic valves 1400A and 1400B are three-way valves and constitute a gas suction/discharge valve. When the one electromagnetic valve 1400A is in the suction state, the other electromagnetic valve 1400B is in the discharge state. The one electromagnetic valve causes 1400A gas sucked from the suction/discharge port 1910 in the suction state to flow into the casing 1800 through the through hole 1920a. At this time, the other electromagnetic valve 1400B is in the discharge state, and blocks the flow of the gas through the through hole 1920b.

The gas flowing into the casing 1800 through the electromagnetic valve 1400A flows through a gap between the movable element 2, and the end member 4 and the base plate 1900, flows into the cylinder 8, and flows to the dryer 1600 through the cylinder 8. Furthermore, the gas is discharged from the dryer 1600 through the other electromagnetic valve 1400B. When the suction and discharge states of the electromagnetic valve 1400A and the electromagnetic valve 1400B are switched, the gas flows following the reverse of the above-described path. The cylinder 8 compresses the entered gas as necessary. A suction/discharge port (not illustrated) is provided at a position corresponding to the suction/discharge port 1910 on the side where the through hole 1920b of the base plate 1900 is provided.

The dryer 1600 is attached to a cylinder head 8A of the cylinder 8 so as to be communicable with the inside of the cylinder 8.

According to the present Example, it is possible to provide a compressor capable of increasing the thrust in the front direction and reducing the length of the linear motor in the front-rear direction to suppress an increase in size.

Example 6

FIG. 19 is a configuration diagram of a refrigerator according to Example 6. The refrigerator 2001 includes a double refrigerating compartment door 2002a divided into left and right parts on a front surface side of a refrigerating compartment 2002, and includes a drawer-type ice-making compartment door 2003a, an upper freezing compartment door 2004a, a lower freezing compartment door 2005a, and a vegetable compartment door 2006a on front surfaces of an ice-making compartment 2003, an upper freezing compartment 2004, a lower freezing compartment 2005, and a vegetable compartment 2006, respectively.

A machine compartment 2020 is provided on a rear side of the vegetable compartment 2006, and a compressor 2024 is disposed in the machine compartment