JP2902584B2 - Compressor and method of designing coil spring used in compressor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compressor and a method of designing a coil spring for the compressor, and more particularly to a technique of a compressor having a long-life coil spring.

[0002]

2. Description of the Related Art A compressor is used, for example, incorporated in a Stirling refrigerator or the like. Stirling refrigerators are used, for example, for cooling sensors of infrared cameras. Such infrared sensors are used for inspection of products such as semiconductor circuits, and for confirming safety of facilities such as a pipeline of a complex.

[0003] A compressor incorporated and used in a Stirling refrigerator reciprocates a piston inserted into a cylinder to supply a pulsating compressed gas to the refrigerator.
The method of reciprocating the piston includes a method of converting the rotational motion of the motor into a reciprocating motion by a cam mechanism, and a method of directly reciprocating the electromagnetic force by supporting the piston at a neutral point in the cylinder with a coil spring. Since the direct reciprocating drive method is more advantageous for downsizing the compressor, a Stirling refrigerator usually incorporates a compressor that drives a piston using this method.

In a compressor in which a piston is supported by a coil spring, the piston has a resonance frequency determined by a spring constant defined by a gas spring formed by the coil spring and a compressed gas in a cylinder and the mass of the piston. This resonance frequency is matched with the frequency of the reciprocating drive of the piston, and the piston is driven more efficiently.

[0005]

The life of a compressor is a factor that affects the life of an infrared camera. In order to extend the life of the device in which the compressor is incorporated, it is desired to extend the life of the compressor.

An object of the present invention is to provide a technique capable of extending the life of a coil spring and, consequently, the life of a compressor.

[0007]

The compressor of the present invention has an internal
A cylinder having a cavity, inserted into the cylinder,
A cavity communicating with the outside is defined between the inside of the cylinder and the outside.
Reciprocating drive at a fixed stroke to compress the gas in the cavity
A piston for supplying compressed gas to the outside, and the piston
And a coil spring supporting the neutral point in the cylinder.
Having half of the stroke L [mm]
The effective number of turns of the spring is n, the diameter of the material is d [mm], and the coil
The average diameter is D [mm] and the transverse elastic modulus of the spring material is G [kg
f / mm ^Two], The tensile strength is σ_B[Kgf / mm^Two]
When the force correction coefficient is κ,

[0008]

ΚLGd / (πnD ² σ _B ) ≦ 0.12.

The method for designing a coil spring for a compressor according to the present invention compresses the gas in the cylinder by reciprocating a piston inserted in the cylinder and supported at a neutral point by the coil spring at a predetermined stroke to compress the gas in the cylinder. Determining the number of durable reciprocating operations of the compressor, supplying N to the outside, the number of durable reciprocating operations N, half of the stroke L [mm], the effective number of turns of the coil spring n, and the diameter of the material d [m
m], the average coil diameter is D [mm], the transverse elastic modulus of the spring material is G [kgf / mm ² ], and the tensile strength is σ _B [kgf /
mm ² ], and when the stress correction coefficient is κ,

[0010]

## EQU4 ## κLGd / (πnD ² σ _B ) ≦ −0.0125
× log (N) +0.2375 to design the coil spring.

When the upper limit stress coefficient of 1 × 10 ⁹ durable reciprocating drive of the coil spring is obtained from JIS B 2704, it is about 0.24. However, when a coil spring designed to have an upper limit stress coefficient of about 0.24 is used for a compressor to perform reciprocating driving, 1 × 10 ⁹ durable reciprocating driving times cannot be obtained.

[0012] The JIS standard specifies the standard of the upper limit stress coefficient under the condition that only one of compression and tension stress is applied to a coil spring. Because both compression and tension stresses are applied to the coil spring of a compressor, JIS
It is considered that the standard cannot be applied as it is. When designed to have an upper limit stress coefficient of about 0.12, 1 × 10
It could withstand more than ⁹ reciprocating drives.

Further, by designing the coil spring so that the upper limit stress coefficient is about 1/2 of the upper limit stress coefficient obtained from the JIS standard corresponding to the target number of durable reciprocating driving, the desired number of durable reciprocating driving can be obtained. Can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a compressor will be described with reference to FIG. FIG. 1 is a sectional view of a compressor opposed to a piston.
A concave portion 19 having a circular cross section is formed from the left and right end surfaces of the yoke 5 toward the center in the drawing, and a conduit 2 connecting the bottom surface of the concave portion and the side surface of the yoke 5 is formed. The yoke 5 has a symmetrical structure with respect to a plane including the pipe 2. The inner peripheral surface of the concave portion 19 functions as a cylinder. The piston 7 is inserted into the cylinder constituted by the yoke 5,
A compression chamber 4 is defined by the cylinder and the piston.
The compression chamber 4 is continuous with the pipe 2, and the compressed gas is supplied to the outside through the pipe 2.

On the left and right end surfaces of the yoke 5, grooves 3 are defined along the circumferential direction so as to surround the periphery of the concave portion 19. The outer peripheral side surface of the groove 3 is defined by the inner peripheral surface of the annular permanent magnet 17 attached to the yoke 5 and the inner peripheral surface of the open end of the cylindrical case 1 attached to the permanent magnet 17. . The other end of case 1 is closed.

A U-shaped magnetic path is formed by the yoke 5, the permanent magnet 17, and the vicinity of the opening end of the case 1, and a magnetic field in the thickness direction is generated in the groove 3. The end of the piston 7 outside the cylinder is formed in a flange shape, and the movable coil 1 engaging with the groove 3 is formed.
6 is attached to this flange-like part. The piston 7 is elastically attached to the end face on the closed end side of the case 1 via a coil spring 8, and is supported at a neutral point in the cylinder.

On the outside of the case 1, a cylindrical pressure holding container 18 having one end closed is arranged. The open end of the pressure holding container 18 is connected to the yoke 5 to keep the inside airtight. A current terminal 6 that penetrates the pressure holding container 16 from the inside to the outside is attached, and current is supplied to the movable coil 16 through the current terminal 6. When an alternating current is applied to the movable coil 16, the movable coil 16 receives a lateral force in the drawing by the magnetic field of the permanent magnet 17, and reciprocates the piston.

When the piston 7 is displaced in the axial direction, it receives a restoring force from the coil spring 8, but also receives a restoring force due to the compression and expansion of the gas sealed in the compression chamber 4. That is, the piston 7 includes a gas spring and a coil spring 8.
And a unique resonance frequency determined from the mass of the movable part. This resonance frequency is
By designing so as to synchronize with the frequency of the current flowing through 6, the piston can be efficiently driven.

Next, a method of designing the coil spring 8 will be described. Assuming that the composite spring constant is kc and the mass of the movable part is m, the resonance frequency fr is

[0020]

[Mathematical formula-see original document] fr = ( ^1/2 [pi]) (kc / m) ^1/2 (1) From the equation (1), when the drive frequency (usually the frequency of the commercial power supply) and the mass of the movable part are determined, an appropriate composite spring constant kc is determined. The gas spring constant is determined by the amount of gas sealed in the compression chamber 4. The appropriate coil spring constant may be a value obtained by subtracting the gas spring constant from the composite spring constant.

Assuming that the diameter of the coil spring material is d [mm], the transverse elastic constant is G [kgf / mm ² ], the effective number of turns is n, and the average coil diameter is D [mm], the spring constant k of the coil spring is

[0022]

K = G × d ⁴ / (8 × n × D ³ ) (2) Therefore, once the spring constant of the coil spring is determined, the coil spring may be designed so as to satisfy Expression (2).

Next, with reference to FIG. 2, the number of serviceable reciprocating drive of the coil spring will be described. FIG. 2A shows the JIS
The upper limit stress coefficient shown as a reference diagram in B2704,
6 is a graph showing a relationship between a lower limit stress coefficient and the number of serviceable reciprocating drives. The horizontal axis represents the lower limit stress coefficient τ _min / σ _B , and the vertical axis represents the upper limit stress coefficient τ _max / σ _B. Where τ _min , τ _max
Represents the minimum value and the maximum value of the torsional correction stress τ [kgf / mm ² ], respectively, and σ _B represents the tensile strength inherent to the material.

The torsional correction stress τ is

[0025]

Τ = 8κDP / (πd ³ ) (3) Here, κ is a corrected stress coefficient, and c = D
As / d

[0026]

Κ = (4c−1) / (4c−4) + 0.615 / c (4) P [kgf] is the load applied to the spring,
The displacement from the natural length of the spring is x [mm],

[0027]

P = kx (5)

The straight line extending to the upper right from the origin in FIG. 2A shows a line in which the ratio γ between the upper limit stress coefficient and the lower limit stress coefficient is constant. A straight line extending from the upper right end to the lower left indicates a line in which the number of durable reciprocating drives is constant.

Since the coil spring used in the compressor is displaced in both the compression and extension directions around the natural length of the spring, the minimum value of the load P applied to the spring is when the spring has the natural length. The value is 0. Since the torsional correction stress coefficient τ at this time becomes 0 from the equation (3), the lower limit stress coefficient τ _min / σ _B is also 0.

Therefore, the number of durable reciprocating drivings is shown in FIG.
It is sufficient to pay attention to the straight line of γ = 0 (the vertical line at the left end of the figure).
The upper limit stress coefficient is determined from the intersection of the straight line of γ = 0 and the straight line indicating the number of times of durable reciprocation. In this way, the relationship between the number of serviceable reciprocating drives and the upper limit stress coefficient when the lower limit stress coefficient is 0 can be obtained.

FIG. 2B shows the relationship between the number of durable reciprocating drives and the upper limit stress coefficient when the lower limit stress coefficient is 0. The horizontal axis represents the number of serviceable reciprocating drives, and the vertical axis represents the upper limit stress coefficient. In order to obtain the desired number of serviceable reciprocating drives, it is necessary to design the upper limit stress coefficient to be smaller than the upper limit stress coefficient shown by the curve in the figure.

When the spring is displaced by the same amount in both the compression and extension directions about the natural length of the spring, the maximum load _Pmax applied to the spring is given by the maximum displacement of the spring being L (the stroke is 2 × L). From equation (5),

[0033]

P _max = k × L (6) Therefore, the upper limit stress coefficient τ _max / σ _B is given by the following equations (2), (3), and (6).

[0034]

Τ _max / σ _B = κLGd / (πnD ² σ _B ) (7) Note that κ is uniquely determined if the average diameter D of the coil and the diameter d of the material are determined from Equation (4).

The durable number of reciprocal driving of a coil spring manufactured under various conditions was measured by experiments. As a spring material, a piano wire having a lateral elastic modulus G of 8000 kgf / mm ² was used.

The spring constant k of a coil spring having a material diameter d of 1.0 mm, an effective number of turns n of 10, and an average coil diameter D of 5.5 mm is 0.601 kgf / mm from equation (2). The tensile strength σ _B of a piano wire having a diameter d of 1.0 mm is about 225 kgf / mm ² . When the coil spring is repeatedly compressed and extended so that the half stroke L is 5 mm around the natural length, the upper limit stress coefficient τ _max / σ _B is
From equation (7), it is about 0.239.

When the upper limit stress coefficient is 0.239, FIG.
From (B), the number of durable reciprocating drives is obtained as 1 × 10 ⁹ times.
When this coil spring was actually driven back and forth with a half stroke of 5 mm, the coil spring was broken by driving 1.8 × 10 ⁷ times. FIG.
The value was almost two orders of magnitude smaller than the number of reciprocating drives expected from (B).

Next, the diameter d of the material is 0.8 mm,
A coil bar having a number n of 12 times and an average coil diameter D of 5.5 mm
Ne was produced. The spring constant k of this spring is about 0.205
kgf / mm. For a piano wire with a diameter d of 0.8 mm
Tensile strength σ_BIs about 235kgf / mm^TwoIt is. This
When the Ilspring was driven back and forth under the same conditions as above,
1.4 × 10⁹It did not break even when driven back and forth twice. this
Upper limit stress coefficient τ _max/ Σ_BIs about 0.120
Yes, about 1/2 of the upper limit stress coefficient shown by the curve in FIG.
It is.

As shown in the first experimental example, FIG.
The reason why the durable reciprocating drive count determined from the solid line in (1) was not obtained is considered as follows. The number of durable reciprocating drivings specified in JIS B2704 is a value in a case where any one of compression strain and tensile strain is applied to the coil spring. On the other hand, the coil spring used in the compressor is
It is displaced both in compression and in tension around its natural length.
Therefore, both compressive strain and tensile strain are periodically applied. As described above, since both the compressive strain and the tensile strain are applied, FIG.
It is considered that the life is shorter than the service reciprocating drive count predicted from the solid line (B). Therefore, the above 2
When designing a coil spring for a compressor as in the second experimental example, it is preferable to allow a safety factor of about twice as much.

From this consideration, it can be seen that the upper limit stress coefficient is as shown in FIG.
It is considered that if the design is made to be approximately 1/2 of the upper limit stress coefficient indicated by the curve, the desired number of durable reciprocating driving can be obtained. That is, when the desired number N of serviceable reciprocating drives is determined, the spring may be designed so that the upper limit stress coefficient is lower than the broken line in FIG.

That is,

[0042]

The design may be made so as to satisfy τ _max / σ _B ≦ −0.0125 × log (N) +0.2375 (8) Equation (8) is obtained by using equation (7).

[0043]

ΚLGd / (πnD ² σ _B ) ≦ −0.0125 × log (N) +0.2375 (9)

When the compressor is driven by a commercial power supply (50/60 Hz), a coil spring having a durable driving frequency of about 1 × 10 ⁹ times is usually required. From the broken line in FIG. 2B, it is understood that it is desirable to design the upper limit stress coefficient to be equal to or less than 0.12 in order to obtain about 1 × 10 ⁹ durable driving times.

When an actual coil spring is designed, the spring constant and the mass of the movable part are determined so that the piston resonates at the same frequency as the drive frequency. When the spring constant is determined, the coil spring is designed so as to satisfy Expression (2). At this time, design is made so as to simultaneously satisfy Expression (9). If an appropriate condition cannot be found, the spring constant and the mass of the movable portion may be reviewed.

A compressor using a coil spring designed to satisfy the above conditions can be used as a compressor for cooling gas such as a Stirling refrigerator or a pulse tube refrigerator. As a result, the life of the refrigerator can be extended.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0048]

As described above, according to the present invention,
It is possible to extend the life of the coil spring used in the compressor. If the life of the compressor is prolonged, the replacement cycle of the compressor in an apparatus using the compressor is prolonged, leading to labor saving in maintenance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a compressor opposed to a piston.

FIG. 2 is a graph showing a relationship between an upper limit stress coefficient and a lower limit stress coefficient of a coil spring and the number of times of durable reciprocating drive, and a relationship between the upper limit stress coefficient and the number of times of durable reciprocation when the lower limit stress coefficient is 0.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Pipeline 3 Groove 4 Compression chamber 5 Yoke 6 Current terminal 7 Piston 8 Coil spring 16 Moving coil 17 Permanent magnet 18 Pressure holding container 19 Depression

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F04B 17/04 F04B 19/22 F16F 1/04 F25B 9/14 520 B21F 35/00

Claims (1)

(57) [Claims] 1. A durable reciprocating compressor for supplying a compressed gas to the outside by compressing a gas in the cylinder by reciprocating a predetermined stroke of a piston inserted into the cylinder and supported at a neutral point by a coil spring. A step of determining the number of times of drive;
[Mm], the effective number of turns of the coil spring is n, the material diameter is d [mm], the average coil diameter is D [mm], the transverse elastic coefficient of the spring material is G [kgf / mm ² ], and the tensile strength is σ.
_B [kgf / mm ² ] and the stress correction coefficient is κ, κLGd / (πnD ² σ _B ) ≦ −0.0125
And a step of designing the coil spring so as to satisfy × log (N) +0.2375.