Pressure spring, pressure spring structure, and method for manufacturing pressure spring

Abstract

This pressure spring comprises a first plate spring and a second plate spring that extend in the length direction. Both ends of the first plate spring in the length direction are configured as fixed parts that are laminated and joined to the second plate spring in the plate thickness direction. Respective intermediate parts of the first plate spring and the second plate spring in the length direction face each other in a state of being separated from each other in the plate thickness direction. The length of the intermediate part of the second plate spring along the surface of the second plate spring as viewed from the plate width direction is less than the length of the intermediate part of the first plate spring along the surface of the first plate spring when viewed from the plate thickness direction. In the intermediate part of the first plate spring, a residual stress is applied to the outer surface side, which is on the opposite side to the second plate spring along the plate thickness direction, in the direction of pulling in the direction along the outer surface of the first plate spring as viewed from the plate width direction, and the intermediate part of the second plate spring is in a no-load state in the length direction.

Description

Compression spring, compression spring structure, and method for manufacturing compression spring

[0001] The present invention relates to a compression spring, a compression spring structure, and a method for manufacturing a compression spring. This application claims priority to Japanese Patent Application No. 2023-117133, filed on July 18, 2023, the contents of which are incorporated herein by reference.

[0002] BACKGROUND ART Conventionally, as shown in, for example, Patent Document 1 below, a compression spring has been known in which a pressure target is sandwiched between the apexes of a curved first leaf spring and a curved second leaf spring in the thickness direction and pressed against the spring.

[0003] Japanese Patent No. 5040228

[0004] Conventional compression springs tend to require a large amount of space to output a high load, making it difficult to output a high load in a small space.

[0005] The present invention provides a compression spring, a compression spring structure, and a method for manufacturing a compression spring that can output a high load in a small space.

[0006] A compression spring according to one aspect of the present invention comprises a first leaf spring and a second leaf spring extending in the longitudinal direction, wherein both longitudinal ends of the first leaf spring are fixed portions stacked and joined to the second leaf spring in the plate thickness direction, the longitudinal middle portions of the first leaf spring and the second leaf spring face each other while being spaced apart in the plate thickness direction, the length of the middle portion of the second leaf spring along the surface of the second leaf spring as viewed in the plate width direction is shorter than the length of the middle portion of the first leaf spring along the surface of the first leaf spring as viewed in the plate width direction, and residual stress is applied to the outer surface of the middle portion of the first leaf spring, which is opposite the second leaf spring in the plate thickness direction, in a direction that pulls the middle portion of the second leaf spring in the direction along the outer surface of the first leaf spring as viewed in the plate width direction, and the middle portion of the second leaf spring is in an unloaded state in the longitudinal direction.

[0007] The device includes a first leaf spring and a second leaf spring. Therefore, when the compression spring is sandwiched between a pair of pressure-receiving bodies in the thickness direction and a compression load from the second leaf spring along the thickness direction is applied to the middle portion of the first leaf spring, a tensile force in the longitudinal direction is applied to the second leaf spring via the fixed portion of the first leaf spring. In this case, the length of the middle portion of the second leaf spring along the surface of the second leaf spring as viewed in the width direction is shorter than the length of the middle portion of the first leaf spring along the surface of the first leaf spring as viewed in the width direction. Therefore, regardless of the material of the second leaf spring, the second leaf spring suppresses deformation of the first leaf spring, allowing the spring constant of the compression spring to be increased, enabling a high load to be output in a small space.

[0008] Furthermore, a residual stress is applied to the outer surface of the intermediate portion of the first leaf spring in a direction that tensiles the outer surface of the first leaf spring when viewed from the leaf width direction (hereinafter referred to as the first specific direction). Therefore, the compressive stress in the first specific direction that occurs when a compressive load from the second leaf spring along the thickness direction is applied to the outer surface of the intermediate portion of the first leaf spring is alleviated. This makes it possible to suppress the load that occurs in the intermediate portion of the first leaf spring, even if the compression spring undergoes significant compressive deformation in the thickness direction, thereby improving durability. The aforementioned residual stress is applied to the intermediate portion of the first leaf spring, and the intermediate portion of the second leaf spring is in an unloaded state in the longitudinal direction. Therefore, when joining both longitudinal ends of the first leaf spring to the second leaf spring, it is not necessary to, for example, join one of the first and second leaf springs to the other leaf spring while elastically deforming the other leaf spring, and then apply the elastic restoring force of one leaf spring to the other leaf spring, thereby generating a tensile stress in the first specific direction on the outer surface of the middle portion of the first leaf spring. Simply joining both longitudinal ends of the first leaf spring to the second leaf spring is therefore sufficient. This allows both longitudinal ends of the first leaf spring to be joined to the second leaf spring easily and accurately, and reduces the load on the second leaf spring when the compression spring is compressed and deformed in the thickness direction, thereby improving durability.

[0009] The intermediate portion of the first leaf spring, when viewed in the plate width direction, is curved in the plate thickness direction so as to present a protruding curve facing away from the intermediate portion of the second leaf spring, and in the intermediate portion of the first leaf spring, a residual stress is imparted on the inner surface side, which is the second leaf spring side along the plate thickness direction, in a direction that compresses the inner surface of the first leaf spring when viewed in the plate width direction, and the fixed portion may extend straight in the longitudinal direction when viewed in the plate width direction.

[0010] The inner surface of the intermediate portion of the first leaf spring is imparted with residual stress in a direction compressing the first leaf spring's inner surface as viewed in the leaf width direction (hereinafter referred to as the second specific direction). Therefore, when a second leaf spring indentation load along the thickness direction is applied to the outer surface of the intermediate portion of the first leaf spring, the tensile stress in the second specific direction generated on the inner surface of the intermediate portion of the first leaf spring is alleviated. This makes it possible to suppress the load generated on the intermediate portion of the first leaf spring, even if the compression spring undergoes significant compressive deformation in the thickness direction, thereby improving durability. The outer surface of the intermediate portion of the first leaf spring is imparted with residual stress in a direction tensile in the first specific direction, while the inner surface is imparted with residual stress in a direction compressing in the second specific direction. Therefore, a first leaf spring having a curved intermediate portion due to the residual stresses described above can be easily formed. For example, the first plate spring can be obtained by deforming a flat plate material for a first plate spring, which extends straight over its entire length, by bending it within the plastic region so that the outer surface of the portion intended to form the intermediate section becomes a protrusion, by subjecting the inner surface of the portion of the flat plate material for a first plate spring intended to form the intermediate section to shot blasting, or by irradiating the inner surface of the portion of the flat plate material for a first plate spring intended to form the intermediate section with a laser.

[0011] The spring may further include a third leaf spring having an intermediate portion provided on the opposite side of the first leaf spring, sandwiching the intermediate portion of the second leaf spring in the thickness direction, as viewed in the width direction.

[0012] When viewed from the plate width direction, the middle portion of the third leaf spring is provided on the opposite side of the first leaf spring, which sandwiches the middle portion of the second leaf spring in the plate thickness direction. Therefore, the middle portions of the first leaf spring and the third leaf spring are sandwiched in the plate thickness direction by the pair of pressed bodies, making it possible to apply a pressing load from the pair of pressed bodies to the first leaf spring and the third leaf spring with little variation, and making it possible to stabilize the posture of the pressing spring between the pair of pressed bodies.

[0013] The first leaf spring and the third leaf spring may be included in an integral plate material, the plate material may have two or more slits extending in the longitudinal direction, the third leaf spring may be located at a different position from the first leaf spring in the plate width direction, and the plate material may have a total of three or more first leaf springs and third leaf springs formed therein.

[0014] The first leaf springs and the third leaf springs may be provided alternately in the plate width direction on the plate material.

[0015] The first and third leaf springs may be arranged symmetrically with respect to the center of the plate width direction.

[0016] The compression spring may further have a fourth leaf spring whose intermediate portion in the longitudinal direction faces the intermediate portion of the third leaf spring while being spaced apart in the plate thickness direction, and whose intermediate portion is in an unloaded state in the longitudinal direction, and both longitudinal ends of at least one of the third leaf springs may be joined to both longitudinal ends of the fourth leaf spring.

[0017] The first leaf spring and the third leaf spring may be symmetrical in shape with respect to a center line of the second leaf spring in the thickness direction, and both ends of the third leaf spring in the longitudinal direction may be joined to both ends of the second leaf spring in the longitudinal direction.

[0018] The first leaf spring and the third leaf spring have continuous outer peripheries when viewed from the leaf width direction, and the inner peripheral surfaces of both longitudinal ends of the first leaf spring and the inner peripheral surfaces of both longitudinal ends of the third leaf spring may be joined to both longitudinal ends of the second leaf spring.

[0019] The first leaf spring and the second leaf spring may be formed from an integral plate material.

[0020] In one aspect of the present invention, the compression spring structure has two compression springs arranged in a state where they are inverted in the plate thickness direction, and the second leaf springs of each of the two compression springs are arranged in a state where they are stacked in the plate thickness direction.

[0021] A method for manufacturing a compression spring according to one aspect of the present invention includes a deformation step of plastically deforming a flat plate material for a first leaf spring so that the outer surface side of a portion intended to form a middle portion becomes a protrusion, thereby imparting residual stress to the outer surface side of the middle portion of the first leaf spring in a tensile direction along the outer surface of the first leaf spring as viewed in the leaf width direction, and imparting residual stress to the inner surface side of the middle portion of the first leaf spring in a compressive direction along the inner surface of the first leaf spring as viewed in the leaf width direction; and a joining step of stacking and joining both longitudinal ends of the first leaf spring to the second leaf spring in the plate thickness direction, while maintaining the middle portion of the second leaf spring in an unloaded state in the longitudinal direction.

[0022] The method includes the deformation step and the joining step, and therefore, a compression spring can be reliably obtained in which the outer surface of the intermediate portion of the first leaf spring is subjected to residual stress in a direction that tensiles the intermediate portion in the first specific direction, and the inner surface of the intermediate portion is subjected to residual stress in a direction that compresses the intermediate portion in the second specific direction, such that the intermediate portion of the second leaf spring is in an unloaded state in the longitudinal direction.

[0023] A method for manufacturing a compression spring according to another aspect of the present invention includes a slit forming step of forming two or more slits in a flat plate material, each slit extending in the length direction, leaving at least one end, to form three or more first regions and two or more second regions in total; and a step of plastically deforming the first regions so that the outer surface side of a portion to form a middle portion of the first leaf spring is protruding, thereby imparting residual stress to the outer surface side of the middle portion of the first leaf spring in a tensile direction along the outer surface of the first leaf spring as viewed in the leaf width direction, and imparting residual stress to the inner surface side of the middle portion of the first leaf spring in a compressive direction along the inner surface of the first leaf spring as viewed in the leaf width direction, and deforming the second regions. The method includes a deformation step of plastically deforming the third leaf spring in the direction opposite to the portion of the first leaf spring where the intermediate portion is to be formed so that the outer surface side of the portion where the intermediate portion is to be formed becomes a protrusion, thereby imparting residual stress to the outer surface side of the intermediate portion of the third leaf spring in a direction that tensiles the outer surface of the third leaf spring in a direction along the outer surface of the third leaf spring as viewed in the leaf width direction, and imparting residual stress to the inner surface side of the intermediate portion of the third leaf spring in a direction that compresses the inner surface of the first leaf spring as viewed in the leaf width direction; and a joining step of stacking and joining both longitudinal ends of the first leaf spring to both longitudinal ends of the second leaf spring in the plate thickness direction while maintaining the intermediate portion of the second leaf spring in an unloaded state in the longitudinal direction.

[0024] A method for manufacturing a compression spring according to another aspect of the present invention includes a slit forming step of forming two or more slits in a flat plate material, the slits extending in the length direction except for at least one end, thereby forming three or more first regions and second regions in total; a plastic deformation step of the first region such that an outer surface side of a portion intended to form an intermediate portion of the first leaf spring becomes a protrusion, imparting residual stress to the outer surface side of the intermediate portion of the first leaf spring in a tensile direction along the outer surface of the first leaf spring as viewed in the plate width direction, and imparting residual stress to the inner surface side of the intermediate portion of the first leaf spring in a compressive direction along the inner surface of the first leaf spring as viewed in the plate width direction, and deforming the second region such that an outer surface side of a portion intended to form an intermediate portion of the first leaf spring becomes a protrusion. a deformation step of plastically deforming the third leaf spring in a direction opposite to the fixed portion thereof, thereby imparting a residual stress to the outer surface side of the intermediate portion of the third leaf spring in a tensile direction along the outer surface of the third leaf spring as viewed in the leaf width direction, and imparting a residual stress to the inner surface side of the intermediate portion of the third leaf spring in a compressive direction along the inner surface of the first leaf spring as viewed in the leaf width direction; and a joining step of stacking and joining both longitudinal ends of the first leaf spring to both longitudinal ends of the second leaf spring on one side in the plate thickness direction while maintaining the intermediate portion of the fourth leaf spring in an unloaded state in the longitudinal direction.

[0025] In another aspect of the present invention, a method for manufacturing a compression spring includes plastically deforming a first flat plate material for a leaf spring so that an outer surface side of a planned intermediate portion forming portion becomes a protrusion, imparting a residual stress in a tensile direction along the outer surface of the first leaf spring as viewed in the leaf width direction to the outer surface side of the intermediate portion of the first leaf spring, and imparting a residual stress in a compressive direction along the inner surface of the first leaf spring as viewed in the leaf width direction to the inner surface side of the intermediate portion of the first leaf spring; and plastically deforming a third flat plate material for a leaf spring so that an outer surface side of a planned intermediate portion forming portion becomes a protrusion, imparting a residual stress in a tensile direction along the outer surface of the first leaf spring as viewed in the leaf width direction to the outer surface side of the intermediate portion of the third leaf spring. The method includes a deformation step of applying a residual stress in a direction that tensiles the third leaf spring in a direction along the outer surface thereof and applying a residual stress in a direction that compresses the third leaf spring in a direction along the inner surface thereof as viewed in the leaf width direction to the inner surface side of the middle portion of the third leaf spring; and a joining step of stacking the first leaf spring, the second leaf spring, and the third leaf spring protruding on the side opposite the first leaf spring in the thickness direction while maintaining the middle portion of the second leaf spring in an unloaded state in the longitudinal direction, and joining both longitudinal ends of the first leaf spring and both longitudinal ends of the third leaf spring to both longitudinal ends of the second leaf spring.

[0026] A method for manufacturing a compression spring according to another aspect of the present invention includes a molding step in which a tubular material is crushed using a mold, thereby continuously forming the first leaf spring and the third leaf spring so that both end sides in a predetermined radial direction of the tubular material are flat and the central portions are spaced apart to form protruding curved shapes, and the shapes of the first leaf spring and the third leaf spring are symmetrical with respect to the one direction of the tubular material; an inserting step in which the second leaf spring is inserted between the first leaf spring and the third leaf spring; and a joining step in which both longitudinal end portions of the second leaf spring are joined to the flat portions of the first leaf spring and the third leaf spring.

[0027] A method for manufacturing a compression spring according to another aspect of the present invention includes a molding process in which a tubular material is crushed using a mold, so that when viewed from the axial direction of the tubular material, one side of the tubular material in a predetermined direction that is along the radial direction of the tubular material is formed flat, and the other side in the one direction is formed so that the central portion in an orthogonal direction perpendicular to the one direction presents a curved shape that protrudes toward the other side of the one direction and both end portions in the orthogonal direction are flat, thereby forming the first leaf spring and the second leaf spring as an integrated unit in which the flat portion of the first leaf spring and the flat portion of the second leaf spring are continuous.

[0028] According to the above aspect of the present invention, it is possible to output a high load in a small space.

[0029] 1A is a perspective view of a pressure spring of a first embodiment; FIG. 1B is a view of the pressure spring of FIG. 1A seen from the plate width direction; FIG. 1C is a flowchart of a method for manufacturing a pressure spring of the first embodiment; FIG. 1D is a perspective view of a pressure spring of a second embodiment; FIG. 3 is a view of the pressure spring of FIG. 3 seen from the plate width direction; FIG. 1E is a flowchart of a method for manufacturing a pressure spring of the second embodiment; FIG. 1F is a view explaining a slit forming step in the method for manufacturing a pressure spring of the second embodiment; FIG. 1G is a perspective view of a pressure spring of a third embodiment; FIG. 1H is a perspective view of a pressure spring of a fourth embodiment; FIG. 8A is a view of the pressure spring of FIG. 8A seen from the plate width direction; FIG. 1H is a flowchart of a method for manufacturing a pressure spring of the fourth embodiment; FIG. 1J is a perspective view of a pressure spring of a fifth embodiment; FIG. 10A is a view of the pressure spring of FIG. 10A seen from the plate width direction; FIG. 1J is a view explaining a method for manufacturing a pressure spring of the fifth embodiment ... 12A is a view of the compression spring of FIG. 12A seen from the plate width direction. FIG. 13 is a view explaining a method for manufacturing a compression spring of a sixth embodiment. FIG. 14 is a view explaining a method for manufacturing a compression spring of a sixth embodiment. FIG. 15 is a view explaining a method for manufacturing a compression spring of a sixth embodiment. FIG. 16 is a perspective view of a compression spring structure of a seventh embodiment. FIG. 17 is a view of the compression spring structure of FIG. 14A seen from the plate width direction.

[0030] First Embodiment A compression spring 1 according to a first embodiment of the present invention will be described below with reference to FIGS. 1A and 1B . As shown in FIGS. 1A and 1B , the compression spring 1 of this embodiment includes a first leaf spring 11 and a second leaf spring 12 extending in the longitudinal direction X, and is sandwiched between a pair of pressed bodies in the plate thickness direction Z. The first and second leaf springs 11 and 12 have their respective ends in the longitudinal direction X stacked in the plate thickness direction Z and joined by, for example, brazing, bonding, welding, ultrasonic bonding, or the like. The first and second leaf springs 11 and 12 have their respective ends in the longitudinal direction X extending straight in the longitudinal direction X. Hereinafter, the ends of the first leaf spring 11 in the longitudinal direction X will be referred to as first fixing portions (fixing portions) 21, and the ends of the second leaf spring 12 in the longitudinal direction X will be referred to as second fixing portions (fixing portions) 22.

[0031] The intermediate portions 23, 24 of the first leaf spring 11 and the second leaf spring 12 in the longitudinal direction X face each other while being spaced apart in the plate thickness direction Z. The length of the intermediate portion 24 of the second leaf spring 12 along the surface of the second leaf spring 12 as viewed from the plate width direction Y is shorter than the length of the intermediate portion 23 of the first leaf spring 11 along the surface of the first leaf spring 11 as viewed from the plate width direction Y.

[0032] When viewed from the plate width direction Y, the intermediate portion 23 of the first plate spring 11 is curved in the plate thickness direction Z so as to present a protruding curved shape away from the intermediate portion 24 of the second plate spring 12. When viewed from the plate width direction Y, the second plate spring 12 extends straight in the longitudinal direction X over its entire length in the longitudinal direction X. Note that the intermediate portion 24 of the second plate spring 12 may be curved, when viewed from the plate width direction Y, so as to present a protruding curved shape in a direction approaching the plate thickness direction Z or in a direction away from the intermediate portion 23 of the first plate spring 11 in the plate thickness direction Z.

[0033] In the intermediate portion 23 of the first leaf spring 11, a residual stress F1 is applied to the outer surface 23a side, which is the opposite side of the second leaf spring 12 along the plate thickness direction Z, in a direction that tensiles the first leaf spring 11 in a direction along the outer surface 23a as viewed from the plate width direction Y. In the intermediate portion 23 of the first leaf spring 11, a residual stress F2 is applied to the inner surface 23b side, which is the second leaf spring 12 side along the plate thickness direction Z, in a direction that compresses the first leaf spring 11 in a direction along the inner surface 23b as viewed from the plate width direction Y.

[0034] The aforementioned residual stress F1 applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11 decreases along the thickness direction Z toward the inner surface 23b of the intermediate portion 23 of the first leaf spring 11. The aforementioned residual stress F2 applied to the inner surface 23b of the intermediate portion 23 of the first leaf spring 11 decreases along the thickness direction Z toward the outer surface 23a of the intermediate portion 23 of the first leaf spring 11. The intermediate portion of the intermediate portion 23 of the first leaf spring 11 in the thickness direction Z includes a region with no residual stress.

[0035] The middle portion 24 of the second leaf spring 12 has no residual stress in the longitudinal direction X over the entire area, and no force is applied in the longitudinal direction X from the first leaf spring 11. In other words, the middle portion 24 of the second leaf spring 12 is in an unloaded state in the longitudinal direction X.

[0036] Next, a method for manufacturing the compression spring 1 configured as above will be described with reference to Fig. 2. The method for manufacturing the compression spring 1 of this embodiment includes a deformation step and a joining step.

[0037] First, in the deformation process, a flat plate material for the first leaf spring 11, which extends straight over the entire length in the longitudinal direction X, is plastically deformed so that the outer surface 23a of the portion where the intermediate portion 23 is to be formed becomes a protrusion (step S11). During this process, in the flat plate material for the first leaf spring 11, each portion where the first fixing portion 21 is to be formed is supported so as to maintain a shape extending straight in the longitudinal direction X, and moves so as to contract in the longitudinal direction X as the portion where the intermediate portion 23 is to be formed is plastically deformed into a convex shape. This imparts residual stress as described above, resulting in a first leaf spring 11 having a curved intermediate portion 23.

[0038] Next, in the joining process, the plastically deformed first leaf spring 11 is stacked on top of the second leaf spring 12, which extends straight over its entire length in the longitudinal direction X and is in an unloaded state in the longitudinal direction X (step S12). Then, the second fixing portions 22 of the second leaf spring 12 (both ends of the second leaf spring 12 in the longitudinal direction X) are joined to the first fixing portions 21 of the first leaf spring 11 (both ends of the first leaf spring 11 in the longitudinal direction X) (step S13). At this time, no force is applied to the first leaf spring 11 and the second leaf spring 12 in the longitudinal direction X, and the middle portion 24 of the second leaf spring 12 is maintained in an unloaded state in the longitudinal direction X. The first fixing portions 21 of the first leaf spring 11 and the second fixing portions 22 of the second leaf spring 12 are simply stacked and joined in the plate thickness direction Z. Here, since the fixing portions 21 and 22 are end regions having a certain range, when joining the fixing portions 21 and 22, the entire flat portion of the fixing portions 21 and 22 may be joined, or only a part of the fixing portions 21 and 22, such as a strip-shaped or frame-shaped portion, may be joined.

[0039] Therefore, the shapes of the first leaf spring 11, which has a curved intermediate portion 23 due to the residual stress as described above, and the second leaf spring 12, which extends straight over the entire length in the longitudinal direction X, remain the same before and after the first fixing portion 21 of the first leaf spring 11 and the second fixing portion 22 of the second leaf spring 12 are joined to each other.

[0040] As described above, the compression spring 1 according to this embodiment includes a first leaf spring 11 and a second leaf spring 12 extending in the longitudinal direction X. Both end portions of the first leaf spring 11 in the longitudinal direction X are formed as first fixing portions 21 that are stacked and joined to the second leaf spring 12 in the plate thickness direction Z. The intermediate portions 23, 24 of the first leaf spring 11 and the second leaf spring 12 in the longitudinal direction X face each other while being spaced apart in the plate thickness direction Z. The length of the intermediate portion 24 of the second leaf spring 12 along the surface of the second leaf spring 12 as viewed in the plate width direction Y is shorter than the length of the intermediate portion 23 of the first leaf spring 11 along the surface of the first leaf spring 11 as viewed in the plate width direction Y. In the intermediate portion 23 of the first leaf spring 11, a residual stress is applied to the outer surface 23a, which is the opposite side of the second leaf spring 12 in the thickness direction Z, in a direction that tensiles the first leaf spring 11 in the direction along the outer surface 23a as viewed from the width direction Y. The intermediate portion 24 of the second leaf spring 12 is in an unloaded state in the longitudinal direction X. The compression spring 1 according to this embodiment includes a first leaf spring 11 and a second leaf spring 12. Therefore, when the compression spring 1 is sandwiched between a pair of pressed bodies in the thickness direction Z and a pressing load from the second leaf spring 12 in the thickness direction Z is applied to the intermediate portion 23 of the first leaf spring 11, a tensile force in the longitudinal direction X is applied to the second leaf spring 12 via the first fixed portion 21 of the first leaf spring 11. In this case, the length of the intermediate portion 24 of the second leaf spring 12 along the surface of the second leaf spring 12 as viewed in the leaf width direction Y is shorter than the length of the intermediate portion 23 of the first leaf spring 11 along the surface of the first leaf spring 11 as viewed in the leaf width direction Y. Therefore, regardless of the material of the second leaf spring 12, the second leaf spring 12 suppresses deformation of the first leaf spring 11, making it possible to increase the spring constant of the compression spring 1 that is developed, and to output a high load in a small space.

[0041] Furthermore, residual stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11 in a tensile direction along the outer surface 23a as viewed from the plate width direction Y (hereinafter referred to as the first specific direction). Therefore, the compressive stress in the first specific direction that occurs when a compressive load from the second leaf spring 12 along the plate thickness direction Z is applied to the outer surface 23a of the intermediate portion 23 is alleviated. As a result, even if the compression spring 1 is significantly compressed and deformed in the plate thickness direction Z, it is possible to suppress the load that occurs in the intermediate portion 23 of the first leaf spring 11, thereby improving durability.

[0042] The aforementioned residual stress is applied to the intermediate portion 23 of the first leaf spring 11, and the intermediate portion 24 of the second leaf spring 12 is in an unloaded state in the longitudinal direction X. Therefore, when joining both ends of the first leaf spring 11 in the longitudinal direction X to the second leaf spring 12, it is not necessary to, for example, join one of the first and second leaf springs 11 and 12 to the other leaf spring in an elastically deformed state, and then apply the elastic restoring force of one leaf spring to the other leaf spring, thereby generating tensile stress in the first specific direction on the outer surface 23 a of the intermediate portion 23 of the first leaf spring 11; it is sufficient to simply join both ends of the first leaf spring 11 in the longitudinal direction X to the second leaf spring 12. Therefore, both ends of the first leaf spring 11 in the longitudinal direction X can be joined to the second leaf spring 12 easily and with high precision, and when the compression spring 1 is compressed and deformed in the plate thickness direction Z, the load on the second leaf spring 12 is reduced, thereby improving durability.

[0043] Furthermore, when viewed from the plate width direction Y, the intermediate portion 23 of the first plate spring 11 is curved in the plate thickness direction Z so as to present a protruding curved line facing away from the intermediate portion 24 of the second plate spring 12. In the intermediate portion 23 of the first plate spring 11, a residual stress is applied to the inner surface 23b side, which is the second plate spring 12 side along the plate thickness direction Z, in a direction compressing the inner surface 23b of the first plate spring 11 when viewed from the plate width direction Y. When viewed from the plate width direction Y, the first fixing portion 21 extends straight in the longitudinal direction X.

[0044] A residual stress is applied to the inner surface 23b of the intermediate portion 23 of the first leaf spring 11 in a compressive direction along the inner surface 23b as viewed from the plate width direction Y (hereinafter referred to as the second specific direction). Therefore, when a compressive load from the second leaf spring 12 along the plate thickness direction Z is applied to the outer surface 23a of the intermediate portion 23, the tensile stress in the second specific direction generated on the inner surface 23b is alleviated. This makes it possible to suppress the load generated on the intermediate portion 23 of the first leaf spring 11 even if the compression spring 11 is significantly compressed in the plate thickness direction Z, thereby improving durability.

[0045] A residual stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11 in a direction that tensiles the intermediate portion 23 in the first specific direction, and a residual stress is applied to the inner surface 23b in a direction that compresses the intermediate portion 23 in the second specific direction. Therefore, it is easy to form a first leaf spring 11 having a curved intermediate portion 23 due to the residual stress applied. For example, the first leaf spring 11 can be obtained by deforming a flat plate material for the first leaf spring 11, which extends straight over the entire length of the longitudinal direction X, by bending the flat plate material for the first leaf spring 11 within a plastic region so that the outer surface 23a of the portion where the intermediate portion 23 will be formed becomes a protrusion, by subjecting the flat plate material for the first leaf spring 11 to shot blasting, or by irradiating the inner surface 23b of the portion where the intermediate portion 23 will be formed with a laser.

[0046] The manufacturing method of the compression spring 1 according to this embodiment includes a deformation step of plastically deforming a flat plate material for the first leaf spring 11 so that the outer surface 23a of the portion where the intermediate portion 23 will be formed becomes a protrusion, thereby imparting a residual stress to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11 in a tensile direction along the outer surface 23a of the first leaf spring 11 as viewed in the leaf width direction Y and imparting a residual stress to the inner surface 23b of the intermediate portion 23 of the first leaf spring 11 in a compressive direction along the inner surface 23b of the first leaf spring 11 as viewed in the leaf width direction Y, and a joining step of stacking and joining both ends of the first leaf spring 11 in the longitudinal direction X to the second leaf spring 12 in the plate thickness direction Z while maintaining the intermediate portion 24 of the second leaf spring 12 in an unloaded state in the longitudinal direction X. The manufacturing method of the compression spring 1 includes the deformation step and the joining step. Therefore, a residual stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11 in a direction that pulls it in the first specific direction, and a residual stress is applied to the inner surface 23b in a direction that compresses it in the second specific direction, thereby reliably obtaining a compression spring 1 in which the intermediate portion 24 of the second leaf spring 12 is in an unloaded state in the longitudinal direction X.

[0047] Second Embodiment Next, a pressure spring 2 according to a second embodiment of the present invention will be described with reference to Figures 3 and 4. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0048] 3 and 4, the compression spring 2 of this embodiment includes a third leaf spring 13 having an intermediate portion 28 provided on the opposite side of the intermediate portion 23 of the first leaf spring 11A, which sandwiches the intermediate portion 24 of the second leaf spring 12 in the plate thickness direction Z, as viewed in the plate width direction Y. As viewed in the plate width direction Y, the intermediate portions 24, 28 of the second leaf spring 12 and the third leaf spring 13 are spaced apart in the plate thickness direction Z.

[0049] In the illustrated example, the third leaf springs 13 are provided separately on both sides of the first leaf spring 11A in the plate width direction Y. Both ends of the third leaf spring 13 in the longitudinal direction X extend straight in the longitudinal direction X, are formed integrally with the first fixing portion 21 of the first leaf spring 11A, and protrude from the first fixing portion 21 in the plate width direction Y. The first leaf spring 11A and the third leaf spring 13 are formed from a single plate material 30 that has the same thickness throughout. Both ends of the third leaf spring 13 in the longitudinal direction X are flat portions 27 that extend straight in the longitudinal direction X when viewed from the plate width direction Y.

[0050] The intermediate portions 28 of the third leaf springs 13 connect the flat portions 27 located at both ends in the longitudinal direction X in the longitudinal direction X. When viewed from the plate width direction Y, the intermediate portions 28 of the third leaf springs 13 are curved in the plate thickness direction Z so as to present a protruding curved shape toward the side away from the intermediate portions 23 of the first leaf springs 11A. When viewed from the plate width direction Y, the center of the intermediate portions 28 of the third leaf springs 13 in the longitudinal direction X is located on the opposite side from the intermediate portions 23 of the first leaf springs 11A, sandwiching the intermediate portions 24 of the second leaf springs 12 in the plate thickness direction Z.

[0051] When viewed from the plate width direction Y, the intermediate portions 28, 23 of the third plate spring 13 and the first plate spring 11A are symmetrical with respect to a line that passes through the center of the first fixing portion 21 and the flat portion 27 in the plate thickness direction Z and extends in the longitudinal direction X. The sizes of the intermediate portions 28, 23 of the third plate spring 13 and the first plate spring 11A are the same.

[0052] In the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, respectively, a residual stress F1 is applied to the outer surfaces 23a, 28a, which are opposite the second leaf spring 12 along the plate thickness direction Z, in a direction that tensiles the outer surfaces 23a, 28a as viewed from the plate width direction Y. In the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, a residual stress F2 is applied to the inner surfaces 23b, 28b, which are on the second leaf spring 12 side along the plate thickness direction Z, in a direction that compresses the inner surfaces 23b, 28b as viewed from the plate width direction Y.

[0053] The aforementioned residual stress F1 applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A decreases along the thickness direction Z toward the inner surface 23b of the intermediate portion 23 of the first leaf spring 11A. The aforementioned residual stress F2 applied to the inner surface 23b of the intermediate portion 23 of the first leaf spring 11A decreases along the thickness direction Z toward the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A. A region without residual stress is included in the intermediate portion of the intermediate portion 23 of the first leaf spring 11A in the thickness direction Z.

[0054] The residual stress F1 imparted to the outer surface 28a of the intermediate portion 28 of the third leaf spring 13 decreases along the thickness direction Z toward the inner surface 28b of the intermediate portion 28 of the third leaf spring 13. The residual stress F2 imparted to the inner surface 28b of the intermediate portion 28 of the third leaf spring 13 decreases along the thickness direction Z toward the outer surface 28a of the intermediate portion 28 of the third leaf spring 13. The intermediate portion 28 of the third leaf spring 13 in the thickness direction Z includes a region free of residual stress. The residual stress distributions and magnitudes in the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13 are the same. However, the residual stress distributions and magnitudes in the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13 may differ from each other.

[0055] There is no residual stress in the longitudinal direction X throughout the entire intermediate portion 24 of the second leaf spring 12, and no force is applied in the longitudinal direction X from the first leaf spring 11A and the third leaf spring 13. In other words, the intermediate portion 24 of the second leaf spring 12 is in an unloaded state in the longitudinal direction X.

[0056] The first leaf spring 11A and the third leaf spring 13 are included in an integrated plate material 30. The plate material 30 has two or more slits 31 extending in the longitudinal direction X. The third leaf spring 13 is located at a different position from the first leaf spring 11A in the plate width direction Y. The plate material 30 has a total of three or more first leaf springs 11A and third leaf springs 13. In the illustrated example, the plate material 30 has two slits 31 and a total of three first leaf springs 11A and third leaf springs 13. However, the present invention is not limited to this. There may be three or more slits 31, and a total of four or more first leaf springs 11A and third leaf springs 13.

[0057] The plate material 30 has the first leaf springs 11A and the third leaf springs 13 arranged alternately in the plate width direction Y. Note that in the illustrated example, the first leaf springs 11A and the third leaf springs 13 are arranged alternately. However, the present invention is not limited to this. The first leaf springs 11A and the third leaf springs 13 do not have to be arranged alternately in the plate material 30. For example, if the plate material 30 has three slits 31 and two first leaf springs 11A and two third leaf springs 13, the order in the plate width direction Y may be, for example, the first leaf springs 11A, the third leaf springs 13, the third leaf springs 13, and the first leaf springs 11A.

[0058] The first leaf springs 11A and the third leaf springs 13 are arranged symmetrically with respect to the center in the plate width direction Y (i.e., the center line CL1 shown in FIG. 3 , which is a straight line that passes through the center of the pressure spring 2 in the plate width direction Y and extends in the longitudinal direction X). Note that FIG. 3 shows an example in which the first leaf spring 11A is provided between two third leaf springs 13, so that the first leaf springs 11A and the third leaf springs 13 are arranged symmetrically with respect to the center in the plate width direction Y. For example, if there are five slits 31 in the plate material 30, and a total of six first leaf springs 11A and third leaf springs 13 are formed, it is preferable that the arrangement of the first leaf springs 11A, third leaf spring 13, first leaf spring 11A, first leaf spring 11A, third leaf spring 13, first leaf spring 11A is symmetric with respect to the center in the plate width direction Y.

[0059] Furthermore, when the compression spring 2 presses the pressed body, the arrangement of the first leaf spring 11A and the third leaf spring 13 does not have to be symmetrical with respect to the center in the plate width direction Y when viewed from the length direction X. As long as the moment about the length direction X is balanced when the compression spring 2 is sandwiched between the pressed body, the arrangement of the first leaf spring 11A and the third leaf spring 13 may be asymmetrical. "The moment being balanced" does not necessarily mean a perfect balance, but may include general industrial tolerances.

[0060] Furthermore, it is preferable that the total dimension of the first leaf spring 11A in the leaf width direction Y and the total dimension of the third leaf spring 13 in the leaf width direction Y are (approximately) the same dimension.

[0061] In this embodiment, residual stress is applied to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, respectively, in a direction that tensiles the intermediate portions 23 a, 28 a in a direction along the outer surfaces 23 a, 28 a as viewed in the plate width direction Y (hereinafter referred to as the first specific direction). Therefore, compressive stress in the first specific direction that occurs when a compressive load from the second leaf spring 12 in the plate thickness direction Z is applied to the outer surfaces 23 a, 28 a of these intermediate portions 23, 28 is alleviated. As a result, even if the compression spring 2 is significantly compressed and deformed in the plate thickness direction Z, it is possible to suppress the load that occurs in the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, respectively, and durability can be improved.

[0062] The aforementioned residual stress is applied to the intermediate portion 23 of the first leaf spring 11A, and the intermediate portion 24 of the second leaf spring 12 is in an unloaded state in the longitudinal direction X. Therefore, when joining both ends of the first leaf spring 11A in the longitudinal direction X to the second leaf spring 12, it is not necessary to, for example, join one of the first leaf spring 11A and the second leaf spring 12 to the other leaf spring in an elastically deformed state, and then apply the elastic restoring force of one leaf spring to the other leaf spring, thereby generating tensile stress in the first specific direction on the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A. Simply joining both ends of the first leaf spring 11A in the longitudinal direction X to the second leaf spring 12 is sufficient. Therefore, both ends of the first leaf spring 11A in the longitudinal direction X can be joined to the second leaf spring 12 easily and with high precision, and when the compression spring 2 is compressed and deformed in the plate thickness direction Z, the load on the second leaf spring 12 is reduced, thereby improving durability.

[0063] Residual stress is applied to the inner surfaces 23b, 28b of the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, respectively, in a direction compressive in a direction along the inner surfaces 23b, 28b as viewed from the plate width direction Y (hereinafter referred to as the second specific direction). Therefore, when a compressive load from the second leaf spring 12 along the plate thickness direction Z is applied to the outer surfaces 23a, 28a of these intermediate portions 23, 28, the tensile stress in the second specific direction generated on the inner surfaces 23b, 28b is alleviated. As a result, even if the compression spring 2 is significantly compressed and deformed in the plate thickness direction Z, it is possible to suppress the load generated on the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, respectively, thereby improving durability.

[0064] In the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, residual stress is applied to the outer surfaces 23a, 28a in a direction that tensiles the intermediate portions in the first specific direction, and residual stress is applied to the inner surfaces 23b, 28b in a direction that compresses the intermediate portions in the second specific direction. Therefore, the first leaf spring 11A and the third leaf spring 13 having the intermediate portions 23, 28 that are curved due to the residual stress applied as described above can be easily formed. For example, the first leaf spring 11A and the third leaf spring 13 can be obtained by bending the flat plate material for the first leaf spring 11A and the flat plate material for the third leaf spring 13, which extend straight over the entire length in the longitudinal direction X, within the plastic region so that the outer surfaces 23a, 28a of the portions where the intermediate portions 23, 28 are to be formed are protruding, by subjecting the inner surfaces 23b, 28b of the portions where the intermediate portions 23, 28 are to be formed of the flat plate material for the first leaf spring 11A and the flat plate material for the third leaf spring 13, respectively, to shot blasting, or by irradiating the inner surfaces 23b, 28b of the portions where the intermediate portions 23, 28 are to be formed of the flat plate material for the first leaf spring 11A and the flat plate material for the third leaf spring 13, respectively, with a laser.

[0065] When viewed from the plate width direction Y, the intermediate portion 28 of the third plate spring 13 is provided on the opposite side of the intermediate portion 23 of the first plate spring 11A, which sandwiches the intermediate portion 24 of the second plate spring 12 in the plate thickness direction Z. Therefore, the intermediate portion 23 of the first plate spring 11A and the intermediate portion 28 of the third plate spring 13 are sandwiched in the plate thickness direction Z by the pair of pressed bodies, making it possible to apply a pressing load from the pair of pressed bodies to the first plate spring 11A and the third plate spring 13 with little variation, and making it possible to stabilize the posture of the pressing spring 2 between the pair of pressed bodies.

[0066] In the example shown in FIG. 3 , the second leaf springs 12 are provided only in portions overlapping the first leaf springs 11A when viewed from the plate thickness direction Z, and do not extend outward from the first leaf springs 11A in the plate width direction Y. However, the present invention is not limited to this. Both ends of the second leaf springs 12 in the length direction X may extend outward in the plate width direction Y so as to face the flat portions 27 of the third leaf springs 13. In other words, both ends of the second leaf springs 12 in the length direction X may extend so as to overlap the flat portions 27 of the third leaf springs 13 when viewed from the plate thickness direction Z. In this case, it is preferable that the extending portions of the second leaf springs 12 are joined to the flat portions 27 of the third leaf springs 13.

[0067] A method for manufacturing the compression spring 2 according to the second embodiment will be described with reference to Figures 5 and 6. The method for manufacturing the compression spring 2 according to this modification includes a slit forming step, a deformation step, and a joining step.

[0068] First, in the slit forming step, as shown in FIG. 6 , two or more slits 31 extending in the longitudinal direction X, leaving both ends, are formed in a flat plate material 30, thereby forming a total of three or more first regions A1 and second regions A2 (step S21). The first region A1 and the second region A2 are regions in the plate material 30 divided in the plate width direction Y by the slits 31 as boundaries. The first region A1 is the region that will become the first leaf spring 11A, and the second region A2 is the region that will become the third leaf spring 13. Note that, although the above description has been given of forming the slits 31 extending in the longitudinal direction X, leaving both ends, in the plate material 30, the present invention is not limited thereto. It is sufficient that the slits 31 extending in the longitudinal direction X, leaving at least one end, are formed in the plate material 30.

[0069] Next, in the deformation step, the first region A1 is plastically deformed so that the outer surface 23a of the portion where the intermediate portion 23 of the first leaf spring 11A is to be formed protrudes, and the second region A2 is plastically deformed in the opposite direction from the portion where the intermediate portion 23 of the first leaf spring 11A is to be formed so that the outer surface 28a of the portion where the intermediate portion 28 of the third leaf spring 13 is to be formed protrudes (step S22). As a result, residual stress is imparted to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A in a tensile direction along the outer surface 23a of the first leaf spring 11A as viewed from the leaf width direction Y, and residual stress is imparted to the inner surface 23b of the intermediate portion 23 of the first leaf spring 11A in a compressive direction along the inner surface 23b of the first leaf spring 11A as viewed from the leaf width direction Y. Furthermore, a residual stress is applied to the outer surface 28a of the intermediate portion 28 of the third leaf spring 13 in a tensile direction along the outer surface 28a of the third leaf spring 13 as viewed in the plate width direction Y, and a residual stress is applied to the inner surface 28b of the intermediate portion 28 of the third leaf spring 13 in a compressive direction along the inner surface 28b of the third leaf spring 13 as viewed in the plate width direction Y. During this process, the planned formation portions of the first fixing portion 21 and the flat portion 27 in the flat plate material are supported so as to maintain a shape extending straight in the longitudinal direction X. Therefore, the planned formation portions of the first fixing portion 21 and the flat portion 27 move so as to contract in the longitudinal direction X in accordance with the convex plastic deformation of the planned formation portions of the intermediate portion 23 and the planned formation portions of the intermediate portion 28. As a result, the first leaf spring 11A and the third leaf spring 13 having curved intermediate portions 23, 28 due to the aforementioned residual stresses applied thereto are obtained from a single sheet of plate material 30.

[0070] Next, in the joining process, the second leaf spring 12 is stacked on one side (upper side) or the other side (lower side) of the first leaf spring 11A in the plate thickness direction Z (step S23). Thereafter, while maintaining the intermediate portion 24 of the second leaf spring 12 in an unloaded state in the longitudinal direction X, both ends of the first leaf spring 11A in the longitudinal direction X are joined to both ends of the second leaf spring 12 in the longitudinal direction X (step S24). That is, in the joining process, while maintaining the intermediate portion 24 of the second leaf spring 12 in an unloaded state in the longitudinal direction X, both ends of the first leaf spring 11A in the longitudinal direction X are stacked and joined to both ends of the second leaf spring 12 in the plate thickness direction Z. Therefore, the shapes of the first leaf spring 11A and the third leaf spring 13, which have curved intermediate portions 23, 28 due to the residual stresses described above, and the second leaf spring 12, which extends straight over the entire length in the longitudinal direction X, remain the same before and after the first fixing portion 21 of the first leaf spring 11A and the second fixing portion 22 of the second leaf spring 12 are joined to each other.

[0071] The manufacturing method of the compression spring 2 includes the deformation step and the joining step, and therefore, the compression spring 2 can be reliably obtained in which the outer surface 23 a of the middle portion 23 of the first leaf spring 11A is subjected to residual stress in a direction that tensiles the middle portion 23 in the first specific direction, and the inner surface 23 b of the middle portion 23 is subjected to residual stress in a direction that compresses the middle portion 24 in the longitudinal direction X.

[0072] Third Embodiment Next, a pressure spring 3 according to a third embodiment of the present invention will be described with reference to Fig. 7. In the third embodiment, the same components as those in the second embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0073] As shown in Figure 7, the compression spring 3 of this embodiment further includes fourth leaf springs 14. When viewed from the plate width direction Y, the fourth leaf springs 14 extend straight in the longitudinal direction X over the entire length of the longitudinal direction X. Two fourth leaf springs 14 are provided facing two third leaf springs 13, respectively. An intermediate portion 33 of each fourth leaf spring 14 in the longitudinal direction X faces the intermediate portion 28 of the third leaf spring 13 while being spaced apart in the plate thickness direction Z. The intermediate portion 33 of each fourth leaf spring 14 is in an unloaded state in the longitudinal direction X. Both end portions (flat portions 27) of the third leaf spring 13 in the longitudinal direction X are joined to both end portions 34 of the fourth leaf spring 14 in the longitudinal direction X.

[0074] Both end portions 34 of the two fourth leaf springs 14 in the length direction X are connected in the plate width direction Y via connecting portions 35. The two fourth leaf springs 14 and the two connecting portions 35 are provided on an integral plate material 36. In other words, the two fourth leaf springs 14 and the two connecting portions 35 form a rectangular frame-shaped plate material 36. In this embodiment, both end portions of the second leaf spring 12A in the length direction X have protruding portions 29 that extend outward in the plate width direction Y so as to face the flat portions 27 of the third leaf spring 13. The second leaf spring 12A has an H-shape.

[0075] As described above, the compression spring 3 according to this embodiment further includes a fourth leaf spring 14 whose intermediate portion 33 in the longitudinal direction X faces the intermediate portion 28 of the third leaf spring 13 while being spaced apart in the plate thickness direction Z, and whose intermediate portion 33 is in an unloaded state in the longitudinal direction X. Both ends in the longitudinal direction X of at least one third leaf spring 13 are joined to both ends 34 in the longitudinal direction X of the fourth leaf spring 14. According to the compression spring 3 according to this embodiment, the provision of the fourth leaf spring 14 makes it possible to increase the spring constant of the compression spring 3 and stabilize the posture of the compression spring 3 between a pair of pressed bodies.

[0076] When manufacturing the compression spring 3 according to this embodiment, in step S23 of the manufacturing method according to the second embodiment shown in Fig. 5, the second leaf spring 12A is stacked on one side (upper or lower side) of the first leaf spring 11A in the plate thickness direction Z, and the fourth leaf spring 14 is stacked on the other side (lower or upper side) of the third leaf spring 13 in the plate thickness direction Z. Furthermore, in the joining step, in addition to joining both ends of the first leaf spring 11 and the second leaf spring 12A, both ends of the third leaf spring 13 and both ends of the fourth leaf spring 14 are joined.

[0077] Fourth Embodiment Next, a pressure spring 4 according to a fourth embodiment of the present invention will be described with reference to Figures 8A and 8B. In the fourth embodiment, the same components as those in the first to third embodiments are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0078] 8A and 8B , in this embodiment, the first leaf spring 11B, the second leaf spring 12B, and the third leaf spring 13B have the same size in the leaf width direction Y. The first leaf spring 11B, the second leaf spring 12B, and the third leaf spring 13B are separate bodies and arranged at the same position in the leaf width direction Y. The second fixing portion 22 is sandwiched in the leaf thickness direction Z between the first fixing portion 21 and the flat portion 27. The intermediate portions 24, 23 of the second leaf spring 12B and the first leaf spring 11B face each other in the leaf thickness direction Z, and the intermediate portions 24, 28 of the second leaf spring 12B and the third leaf spring 13B face each other in the leaf thickness direction Z.

[0079] As shown in FIG. 8B , the first leaf spring 11B and the third leaf spring 13B are symmetrical in shape with respect to the center line CL2 in the thickness direction Z of the second leaf spring 12B (i.e., a straight line passing through the center of the second leaf spring 12B in the thickness direction Z and extending in the longitudinal direction X, as shown in FIG. 8B ). The symmetry of the shape does not necessarily mean a perfect symmetry, but may include industrially common shape and dimensional errors. Both ends (flat portions 27) of the third leaf spring 13B in the longitudinal direction X are joined to both ends (second fixing portions 22) of the second leaf spring 12B in the longitudinal direction X. The first leaf spring 11B, the second leaf spring 12B, and the third leaf spring 13B are located at approximately the same position in the width direction Y and overlap each other. The compression spring 4 of this embodiment can have a higher spring constant than the compression spring 1 of the first embodiment shown in FIG. 1 .

[0080] A method for manufacturing the pressure spring 4 according to the fourth embodiment will be described with reference to Fig. 9. The method for manufacturing the pressure spring 4 according to this embodiment includes a deformation step and a joining step.

[0081] In the deformation process, the flat plate material for the first leaf springs 11B is plastically deformed so that the outer surface 23a of the portion where the intermediate portion 23 is to be formed becomes a protrusion, and the flat plate material for the third leaf springs 13B is plastically deformed so that the outer surface 28a of the portion where the intermediate portion 28 is to be formed becomes a protrusion (step S31). As a result, residual stress is imparted to the outer surface 23a of the intermediate portion 23 of the first leaf springs 11B in a tensile direction along the outer surface 23a of the first leaf springs 11B as viewed in the plate width direction Y, and residual stress is imparted to the inner surface 23b of the intermediate portion 23 of the first leaf springs 11B in a compressive direction along the inner surface 23b of the first leaf springs 11B as viewed in the plate width direction Y. In addition, a residual stress is applied to the outer surface 28a of the middle portion 28 of the third leaf spring 13B in a direction that pulls the spring in a direction along the outer surface 28a of the third leaf spring 13B when viewed from the plate width direction Y, and a residual stress is applied to the inner surface 28b of the middle portion 28 of the third leaf spring 13B in a direction that compresses the spring in a direction along the inner surface 28b of the third leaf spring 13B when viewed from the plate width direction Y.

[0082] Next, in the joining process, the second leaf spring 12B and the plastically deformed first leaf spring 11B are stacked in this order in the plate thickness direction Z on top of the plastically deformed third leaf spring 13B (step S32). Then, while maintaining the middle portion 24 of the second leaf spring 12B in an unloaded state in the longitudinal direction X, both ends of the first leaf spring 11B in the longitudinal direction X and both ends of the third leaf spring 13B in the longitudinal direction X are joined to both ends of the second leaf spring 12B in the longitudinal direction X (step S33). That is, in the joining process, while maintaining the intermediate portion 24 of the second leaf spring 12B in an unloaded state in the longitudinal direction X, the first leaf spring 11B, the second leaf spring 12B, and the third leaf spring 13B protruding opposite the first leaf spring 11B are stacked in the plate thickness direction Z, and both ends in the longitudinal direction X of the first leaf spring 11B and both ends in the longitudinal direction X of the third leaf spring 13B are joined to both ends in the longitudinal direction X of the second leaf spring 12B. Therefore, the shapes of the first leaf spring 11B and the third leaf spring 13B, which have curved intermediate portions 23, 28 due to the aforementioned residual stress, and the second leaf spring 12B, which extends straight over the entire length in the longitudinal direction X, remain unchanged before and after joining the first fixed portion 21 of the first leaf spring 11B and the second fixed portion 22 of the second leaf spring 12B to each other.

[0083] Fifth Embodiment Next, a pressure spring 5 according to a fifth embodiment of the present invention will be described with reference to Figures 10A and 10B. In the fifth embodiment, the same components as those in the first to fourth embodiments are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0084] 10A and 10B , in this embodiment, the outer peripheries of the first leaf spring 11C and the third leaf spring 13C are continuous when viewed in the plate width direction Y. The inner circumferential surfaces of both ends of the first leaf spring 11C in the length direction X and the inner circumferential surfaces of both ends of the third leaf spring 13C in the length direction X are joined to both ends of the second leaf spring 12B in the length direction X.

[0085] The first and third leaf springs 11C and 13C are formed continuously so that both ends in the longitudinal direction X are flat and the intermediate portions 23, 28 in the longitudinal direction X are spaced apart and curved. The outermost ends 21a of the flat portions (first fixing portions 21) located at both ends in the longitudinal direction X of the first leaf spring 11C and the outermost ends 27a of the flat portions 27 located at both ends in the longitudinal direction X of the third leaf spring 13C are continuous in the plate thickness direction Z. The first and third leaf springs 11C and 13C are symmetrical in shape with respect to the center line CL2 of the second leaf spring 12B in the plate thickness direction Z. The symmetry of the shapes does not necessarily mean perfect symmetry, but may include industrially common shape and dimensional errors.

[0086] 11A to 11D, a method for manufacturing the compression spring 5 according to the fifth embodiment will be described. The method for manufacturing the compression spring 5 according to the present embodiment includes a molding step, a fitting step, and a joining step.

[0087] In the molding process, as shown in FIGS. 11A and 11B , a mold M1 is used to crush the tubular material 40, thereby continuously forming the first and third leaf springs 11C and 13C such that both ends in a predetermined direction (corresponding to the longitudinal direction X) along the radial direction of the tubular material 40 are flattened and the central portions are spaced apart to form protruding curved shapes. At this time, the shapes of the first and third leaf springs 11C and 13C are symmetrical with respect to the one direction. In the fitting process, as shown in FIG. 11C , the second leaf spring 12B is fitted between the first and third leaf springs 11C and 13C. In the joining process, as shown in FIG. 11D , both ends of the second leaf spring 12B in the longitudinal direction X are joined to the flat portions of the first and third leaf springs 11C and 13C.

[0088] In this embodiment, since the first leaf spring 11C and the third leaf spring 13C are continuous, there is no need to position the first leaf spring 11C and the third leaf spring 13C when the first leaf spring, the second leaf spring, and the third leaf spring are stacked and joined in three layers, and the compression spring 5 can be easily manufactured.

[0089] Sixth Embodiment Next, a pressure spring 6 according to a sixth embodiment of the present invention will be described with reference to Figures 12A and 12B. In the sixth embodiment, the same components as those in the first to fifth embodiments are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0090] 12A and 12B, in this embodiment, the first leaf spring 11D and the second leaf spring 12D are continuous when viewed in the plate width direction Y. In other words, the first leaf spring 11D and the second leaf spring 12D are formed from an integral plate material.

[0091] The second leaf spring 12D is planar. That is, when viewed from the plate width direction Y, the second leaf spring 12D extends straight in the longitudinal direction X over the entire length of the second leaf spring 12D in the longitudinal direction X. The first leaf spring 11D has a shape in which an intermediate portion 23 in the longitudinal direction X is curved to present a protruding curve, and both end portions in the longitudinal direction X are flat. The flat portions located at both ends of the first leaf spring 11D in the longitudinal direction X and both end portions of the planar second leaf spring 12D in the longitudinal direction X are continuous in the plate thickness direction Z. Furthermore, it is preferable that the inner circumferential surfaces of the flat portions located at both ends of the first leaf spring 11D in the longitudinal direction X and the inner circumferential surfaces of both end portions in the longitudinal direction X of the second leaf spring 12D are joined.

[0092] 13A to 13C, a method for manufacturing the compression spring 6 according to this embodiment will be described. The method for manufacturing the compression spring 6 according to this embodiment includes a molding step.

[0093] In the molding process, the tubular blank 50 is flattened using a mold M2, so that, when viewed from the axial direction of the tubular blank 50 (corresponding to the plate width direction Y), one side of the tubular blank 50 in a predetermined radial direction (corresponding to the plate thickness direction Z) is flattened, and the other side of the tubular blank 50 in the predetermined direction is curved so that its central portion in the orthogonal direction (corresponding to the longitudinal direction X) perpendicular to the one direction exhibits a curved shape that protrudes toward the other side of the one direction, and both end portions in the orthogonal direction are flat. This results in the formation of an integrated first leaf spring 11D and second leaf spring 12D in which the flat portions of the first leaf spring 11D and the flat portions of the second leaf spring 12D are continuous. In the molding process, to mold the second leaf spring 12D into a flat shape, the portion of the tubular blank 50 that will become the second leaf spring 12D may be deformed using the mold M2 so that it protrudes in the opposite direction to the protrusion of the cylindrical tubular blank 50, taking springback into consideration. As a result, after removing the mold M2, it is possible to obtain the compression spring 6 having the desired shape. Furthermore, after the molding process, both ends of the first leaf spring 11D in the orthogonal direction and both ends of the second leaf spring 12D in the orthogonal direction may be joined together.

[0094] In this embodiment, since the first leaf spring 11D and the second leaf spring 12D are continuous, there is no need to position the first leaf spring 11D and the second leaf spring 12D in relation to the shape in which the first leaf spring and the second leaf spring are stacked and joined in two layers, and the compression spring 6 can be easily manufactured.

[0095] Seventh Embodiment Next, a compression spring structure 7 according to a seventh embodiment of the present invention will be described with reference to Figures 14A and 14B. In the seventh embodiment, the same components as those in the sixth embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0096] As shown in FIGS. 14A and 14B , in the compression spring structure 7 of this embodiment, two compression springs 6 according to the sixth embodiment are provided, inverted in the plate thickness direction Z. The second leaf springs 12D of each of the two compression springs 6 are provided stacked in the plate thickness direction Z. Both end portions in the length direction X of the two second leaf springs 12D are joined. Alternatively, both end portions in the length direction X of all of the two first leaf springs 11D and two second leaf springs 12D may be joined in the plate thickness direction Z. In this embodiment, the compression spring structure 7 is formed by combining compression springs 6, which are a single component, and therefore the compression spring structure 7 can be manufactured efficiently and at low cost. Furthermore, in the compression spring structure 7, by joining the second leaf springs 12D of the two compression springs 6 at both ends in the longitudinal direction X, it is possible to increase the spring constant of the compression spring compared to when they are not joined, and it is possible to stabilize the posture of the compression spring structure 7 between a pair of pressed bodies. Note that in the compression spring structure 7, the second leaf springs 12D of the two compression springs 6 may also be connected by adhesively bonding them in a planar manner. Furthermore, in this embodiment, the second fixing portion (fixing portion) 22 may be provided on a portion of the second leaf spring 12D other than both ends in the longitudinal direction X.

[0097] (Modification) Two compression springs 1 according to the first embodiment may be provided with the second leaf springs 12 facing each other to form a compression spring structure. In this case, by joining the second leaf springs 12 of the two compression springs 1 at both ends in the longitudinal direction X, it is possible to increase the spring constant of the compression springs that are developed compared to when they are not joined, and it is possible to stabilize the posture of the compression spring structure between a pair of pressed bodies. Note that the second leaf springs 12 of the two compression springs 1 may also be connected by adhesively bonding them together in a planar manner.

[0098] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0099] For example, it is not necessary to impart residual stress compressing the inner surfaces 23b, 28b of the intermediate portions 23, 28 of the first leaf spring 11 and the third leaf spring 13 in a direction along the inner surfaces 23b, 28b when viewed from the plate width direction Y.

[0100] In the above embodiment, the compression springs 1, 2, 3, 4, 5, and 6 and the compression spring structure 7 are configured such that the length direction X is longer than the plate width direction Y. However, the compression springs 1, 2, 3, 4, 5, and 6 and the compression spring structure 7 may be configured such that the length direction X is longer than the plate width direction Y.

[0101] In the above embodiment, a single pressure spring 1, 2, 3, 4, 5, 6 or pressure spring structure 7 is provided on the pressed body. However, a plurality of pressure springs 1, 2, 3, 4, 5, 6 or pressure spring structures 7 may be arranged side by side in the length direction X or the plate width direction Y. Furthermore, when a plurality of pressure springs 1, 2, 3, 4, 5, 6 or a plurality of pressure spring structures 7 are provided, they may be arranged with a 90-degree offset between the length direction X and the plate width direction Y.

[0102] In addition, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, without departing from the spirit of the present invention, and the above-described embodiments and variations may be combined as appropriate.

[0103] According to the present invention, it is possible to provide a pressure spring, a pressure spring structure, and a method for manufacturing a pressure spring that can output a high load in a small space.

[0104] DESCRIPTION OF SYMBOLS 1, 2, 3, 4, 5, 6 Compression spring 7 Compression spring structure 11, 11A, 11B, 11C, 11D First leaf spring 12, 12A, 12B, 12D Second leaf spring 13, 13B, 13C Third leaf spring 14 Fourth leaf spring 21 First fixing portion (fixing portion, both ends) 22 Second fixing portion (fixing portion, both ends) 23 Intermediate portion of first leaf spring 23a Outer surface 23b Inner surface 24 Intermediate portion of second leaf spring 27 Flat portion (both ends) 28 Intermediate portion of third leaf spring 33 Intermediate portion of fourth leaf spring 34 Both ends X Length direction Y Plate width direction Z Plate thickness direction

Claims

1. It comprises a first leaf spring and a second leaf spring extending in the longitudinal direction, The longitudinal ends of the first leaf spring are fixed portions that are laminated and joined to the second leaf spring in the thickness direction. The intermediate portions in the longitudinal direction of the first leaf spring and the second leaf spring face each other with a distance between them in the thickness direction. The length of the middle portion of the second leaf spring along the surface of the second leaf spring, as viewed from the width direction of the leaf, is shorter than the length of the middle portion of the first leaf spring along the surface of the first leaf spring, as viewed from the width direction of the leaf. In the middle portion of the first leaf spring, a residual stress is applied to the outer surface opposite to the second leaf spring, along the thickness direction, in a direction that tensilely pulls along the outer surface of the first leaf spring when viewed from the width direction. The middle section of the second leaf spring is a compression spring that is unloaded in the longitudinal direction.

2. The intermediate portion of the first leaf spring is curved in a way that, when viewed from the width direction of the leaf, protrudes in the direction toward the side away from the intermediate portion of the second leaf spring along the thickness direction. In the middle portion of the first leaf spring, a residual stress is applied to the inner surface side, which is the second leaf spring side along the thickness direction, in a direction that compresses it in a direction along the inner surface of the first leaf spring when viewed from the width direction. The compression spring according to claim 1, wherein the fixing portion extends straight in the longitudinal direction when viewed from the plate width direction.

3. The compression spring according to claim 1 or 2, further comprising a third leaf spring having an intermediate portion provided on the opposite side of the first leaf spring that sandwiches the intermediate portion of the second leaf spring in the thickness direction when viewed from the width direction of the leaf spring.

4. The first leaf spring and the third leaf spring are included in a single plate material. The aforementioned plate material has two or more cuts formed in it that extend in the longitudinal direction. The third leaf spring is located in a different position from the first leaf spring in the width direction of the leaf, The compression spring according to claim 3, wherein three or more of the first leaf springs and the third leaf springs are formed in the plate material.

5. The compression spring according to claim 4, wherein the plate material is alternately provided with the first leaf spring and the third leaf spring in the width direction of the plate.

6. The compression spring according to claim 4, wherein the arrangement of the first leaf spring and the third leaf spring is symmetrical with respect to the center in the width direction of the leaf.

7. The present invention further comprises a fourth leaf spring, the intermediate portion of which in the longitudinal direction is opposed to the intermediate portion of the third leaf spring at a distance in the thickness direction from the intermediate portion of the third leaf spring, and the intermediate portion of the fourth leaf spring is unloaded in the longitudinal direction. At least one of the longitudinal ends of the third leaf spring is joined to the longitudinal ends of the fourth leaf spring. The compression spring according to claim 4.

8. The compression spring according to claim 3, wherein the first leaf spring and the third leaf spring are symmetrical in shape with respect to the center line in the thickness direction of the second leaf spring, and both ends of the third leaf spring in the longitudinal direction are joined to both ends of the second leaf spring in the longitudinal direction.

9. The compression spring according to claim 3, wherein the outer circumferences of the first leaf spring and the third leaf spring are continuous when viewed from the width direction of the leaf, and the inner circumferential surfaces of both ends of the first leaf spring in the longitudinal direction and the inner circumferential surfaces of both ends of the third leaf spring in the longitudinal direction are joined to both ends of the second leaf spring in the longitudinal direction.

10. The compression spring according to claim 1, wherein the first leaf spring and the second leaf spring are formed from a single plate material.

11. Two of the compression springs described in claim 10 are provided in a state where they are reversed in the plate thickness direction. A compression spring structure in which the second leaf springs of each of the two compression springs are arranged in a stacked manner in the thickness direction.

12. A method for manufacturing a compression spring according to claim 1 or 2, A deformation step is performed in which a flat plate material for the first leaf spring is plastically deformed so that the outer surface of the portion to be formed in the intermediate part becomes a protrusion, a residual stress is applied to the outer surface of the intermediate part of the first leaf spring in a tensile direction along the outer surface of the first leaf spring when viewed from the width direction, and a residual stress is applied to the inner surface of the intermediate part of the first leaf spring in a compressive direction along the inner surface of the first leaf spring when viewed from the width direction. A method for manufacturing a compression spring, comprising: a joining step of joining the ends of the first leaf spring in the longitudinal direction to the second leaf spring by stacking them in the thickness direction, while maintaining the middle portion of the second leaf spring in an unloaded state in the longitudinal direction.

13. A method for manufacturing a compression spring according to claim 4, A cut-forming step involves forming two or more cuts in a flat material that extend in the length direction, leaving at least one end intact, thereby forming a total of three or more first and second regions. A deformation step comprising: plastically deforming the first region such that the outer surface side of the planned intermediate portion of the first leaf spring protrudes, thereby imparting a residual stress on the outer surface side of the intermediate portion of the first leaf spring in a tensile direction along the outer surface of the first leaf spring when viewed from the plate width direction, and imparting a residual stress on the inner surface side of the intermediate portion of the first leaf spring in a compressive direction along the inner surface of the first leaf spring when viewed from the plate width direction, and plastically deforming the second region on the opposite side from the planned intermediate portion of the first leaf spring such that the outer surface side of the planned intermediate portion of the third leaf spring protrudes, thereby imparting a residual stress on the outer surface side of the intermediate portion of the third leaf spring in a tensile direction along the outer surface of the third leaf spring when viewed from the plate width direction, and imparting a residual stress on the inner surface side of the intermediate portion of the third leaf spring in a compressive direction along the inner surface of the third leaf spring when viewed from the plate width direction, A method for manufacturing a compression spring, comprising: a joining step of joining the ends of the first leaf spring in the longitudinal direction to the ends of the second leaf spring in the longitudinal direction by stacking them in the thickness direction, while maintaining the middle portion of the second leaf spring in an unloaded state in the longitudinal direction.

14. A method for manufacturing a compression spring according to claim 7, A cut-forming step involves forming two or more cuts in a flat material that extend in the length direction, leaving at least one end intact, thereby forming a total of three or more first and second regions. A deformation step comprising: plastically deforming the first region such that the outer surface side of the planned intermediate portion of the first leaf spring protrudes, thereby imparting a residual stress on the outer surface side of the intermediate portion of the first leaf spring in a tensile direction along the outer surface of the first leaf spring when viewed from the plate width direction, and imparting a residual stress on the inner surface side of the intermediate portion of the first leaf spring in a compressive direction along the inner surface of the first leaf spring when viewed from the plate width direction, and plastically deforming the second region on the opposite side from the planned intermediate portion of the first leaf spring such that the outer surface side of the planned intermediate portion of the third leaf spring protrudes, thereby imparting a residual stress on the outer surface side of the intermediate portion of the third leaf spring in a tensile direction along the outer surface of the third leaf spring when viewed from the plate width direction, and imparting a residual stress on the inner surface side of the intermediate portion of the third leaf spring in a compressive direction along the inner surface of the third leaf spring when viewed from the plate width direction, A method for manufacturing a compression spring, comprising: a joining step of joining the ends of the first leaf spring in the longitudinal direction by stacking them on one side in the thickness direction with the ends of the second leaf spring in the longitudinal direction, while maintaining the middle portion of the second leaf spring in an unloaded state in the longitudinal direction; and joining the ends of the third leaf spring in the longitudinal direction by stacking them on the other side in the thickness direction with the ends of the fourth leaf spring in the longitudinal direction, while maintaining the middle portion of the fourth leaf spring in an unloaded state in the longitudinal direction.

15. A method for manufacturing a compression spring according to claim 8, A deformation step is performed in which a flat plate material for the first leaf spring is plastically deformed so that the outer surface of the portion to be formed in the intermediate section becomes a protrusion, and a residual stress is applied to the outer surface of the intermediate section of the first leaf spring in a tensile direction along the outer surface of the first leaf spring when viewed from the plate width direction, and a residual stress is applied to the inner surface of the intermediate section of the first leaf spring in a compressive direction along the inner surface of the first leaf spring when viewed from the plate width direction, and a flat plate material for the third leaf spring is plastically deformed so that the outer surface of the portion to be formed in the intermediate section becomes a protrusion, and a residual stress is applied to the outer surface of the intermediate section of the third leaf spring in a tensile direction along the outer surface of the third leaf spring when viewed from the plate width direction, and a residual stress is applied to the inner surface of the intermediate section of the third leaf spring in a compressive direction along the inner surface of the third leaf spring when viewed from the plate width direction, A method for manufacturing a compression spring, comprising: a joining step of stacking the first leaf spring, the second leaf spring, and the third leaf spring protruding on the opposite side from the first leaf spring in the thickness direction while maintaining the middle portion of the second leaf spring in an unloaded state in the longitudinal direction, and joining the longitudinal ends of the first leaf spring and the longitudinal ends of the third leaf spring to the longitudinal ends of the second leaf spring.

16. A method for manufacturing a compression spring according to claim 9, A molding process is performed in which a cylindrical material is crushed using a mold, thereby forming the first leaf spring and the third leaf spring in a continuous manner such that both ends in a predetermined direction along the radial direction of the cylindrical material become flat, and the central portions are spaced apart from each other, forming a curved projection, and the shapes of the first leaf spring and the third leaf spring are symmetrical with respect to the aforementioned direction of the cylindrical material. The process involves inserting the second leaf spring between the first leaf spring and the third leaf spring, A method for manufacturing a compression spring, comprising a joining step of joining both longitudinal ends of the second leaf spring to the flat portions of the first leaf spring and the third leaf spring.

17. A method for manufacturing a compression spring according to claim 10, A method for manufacturing a compression spring, comprising: a molding step of using a mold to crush a cylindrical material, thereby forming one side of the cylindrical material in a predetermined direction along the radial direction of the cylindrical material into a flat shape when viewed from the axial direction of the cylindrical material, and shaping the other side in the same direction so that the central part in a direction perpendicular to the same direction exhibits a curved shape with a projection toward the other side in the same direction, and both ends in the same direction are flat, thereby forming an integrated first leaf spring and second leaf spring in which the flat portion of the first leaf spring and the flat portion of the second leaf spring are continuous.