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

Abstract

Provided is a method for manufacturing a pressure spring comprising a first plate spring and a second plate spring that extend in a length direction, wherein both end parts in the length direction of the first plate spring are stacked in a plate thickness direction on and joined to both end parts in the length direction of the second plate spring, intermediate parts in the length direction of the respective first plate spring and second plate spring face each other in a state of being separated from each other in the plate thickness direction, a length of the intermediate part of the second plate spring along a surface of the second plate spring as viewed from a plate width direction is shorter than a length of the intermediate part of the first plate spring along a surface of the first plate spring as viewed from the plate width direction, and, in the intermediate part of the first plate spring, a stress in the direction of stretching along an outer surface of the first plate spring as viewed from the plate width direction is applied to the outer surface side that is the opposite side to the second plate spring along the plate thickness direction. The method performs a joining step for joining both end parts in the length direction of the first plate spring to a long second plate spring material configured by integrally connecting a plurality of second plate springs in the length direction, and a cutting step for cutting at least the second plate spring material to obtain a pressure spring, in this order.

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. 2023-172633, filed on October 4, 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 third 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 second leaf spring in an unloaded state in the longitudinal direction, and stacking and joining both longitudinal ends of the third leaf spring to both longitudinal ends of the fourth leaf spring on the other 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] A method for manufacturing a compression spring according to one aspect of the present invention includes a first leaf spring and a second leaf spring extending in a longitudinal direction, wherein both longitudinal end portions of the first leaf spring are stacked and joined in a thickness direction to both longitudinal end portions of the second leaf spring, and wherein intermediate portions of the first leaf spring and the second leaf spring in the longitudinal direction face each other while being spaced apart in the thickness direction, and the length of the intermediate portion of the second leaf spring along the surface of the second leaf spring as viewed in the width direction is equal to or longer than the length of the first leaf spring along the surface of the first leaf spring as viewed in the width direction. A method for manufacturing a compression spring in which a stress is applied to the outer surface of the intermediate portion of the first leaf spring, the outer surface being shorter than the length of the intermediate portion of the first leaf spring in the thickness direction, on the opposite side of the second leaf spring, in a direction that pulls the spring in the direction along the outer surface of the first leaf spring as viewed in the width direction. The method includes a joining step of joining both longitudinal ends of the first leaf spring to a long second leaf spring material formed by connecting a plurality of second leaf springs together in the longitudinal direction, and a cutting step of cutting at least the second leaf spring material to obtain the compression spring, in this order.

[0029] The compression spring 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 longitudinal tensile force is applied to the second leaf spring via both longitudinal ends 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.

[0030] In the middle portion of the first leaf spring, a stress is applied to the outer surface side, which is the opposite side of the second leaf spring along the plate thickness direction, in a direction along the outer surface of the first leaf spring as viewed from the plate 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 plate thickness direction is applied to the outer surface side of the middle portion of the first leaf spring is alleviated, and even if the compression spring is significantly compressed in the plate thickness direction, it is possible to suppress the load generated in the middle portion of the first leaf spring, thereby improving durability.

[0031] The method for manufacturing a compression spring includes a joining step of joining both longitudinal ends of a first leaf spring to a long second leaf spring material, and a cutting step of cutting at least the second leaf spring material to obtain compression springs, in that order. Therefore, multiple compression springs can be manufactured more efficiently than, for example, a case in which a first leaf spring cut to a specified length is joined to a second leaf spring cut to a specified length.

[0032] During the joining process, both longitudinal ends of the first leaf spring may be joined to the second leaf spring material while applying a stress to the outer surface of the middle portion of the first leaf spring in a direction that pulls the outer surface of the first leaf spring in the direction along the outer surface of the first leaf spring when viewed from the leaf width direction.

[0033] During the joining process, stress is applied to the outer surface of the middle part of the first leaf spring in the first specific direction, and then both longitudinal ends of the first leaf spring are joined to the second leaf spring material, so that a compression spring can be easily obtained.

[0034] Before the joining step, residual stress may be applied to the outer surface side of the middle portion of the first leaf spring in a direction that pulls the first leaf spring in a direction along the outer surface of the first leaf spring when viewed in the leaf width direction.

[0035] Prior to the joining step, residual stress is applied to the outer surface of the intermediate portion of the first leaf spring in the direction of tension of the first specific direction, so that during the joining step, the force applied to the first leaf spring to generate stress in the outer surface of the intermediate portion of the first leaf spring in the direction of tension of the first specific direction can be eliminated or at least reduced, making it possible to easily obtain a compression spring.

[0036] The joining step may include joining both longitudinal ends of the first leaf spring to the second leaf spring material while the first leaf spring is elastically deformed so that the longitudinal size of the first leaf spring is reduced.

[0037] In the joining process, both longitudinal ends of the first leaf spring are joined to the second leaf spring material while the first leaf spring is elastically deformed so that the size of the first leaf spring in the longitudinal direction is reduced. This eliminates the need for the process of pre-imparting residual stress.

[0038] During the joining step, both longitudinal ends of the first leaf spring may be joined to the second leaf spring material while the second leaf spring material is stretched in the longitudinal direction.

[0039] During the joining process, both longitudinal ends of the first leaf spring are joined to the second leaf spring material while the second leaf spring material is stretched in the longitudinal direction. Therefore, a restoring force is generated in the second leaf spring cut from the second leaf spring material during the cutting process, and a stress in the first specific direction is applied to the outer surface of the middle portion of the first leaf spring. Therefore, during the joining process, it is possible to eliminate or at least reduce the force applied to the first leaf spring to generate a stress in the first specific direction on the outer surface of the middle portion of the first leaf spring, making it easy to obtain a compression spring.

[0040] The compression spring further includes a third leaf spring having an intermediate portion provided on the opposite side of the first leaf spring with the intermediate portion of the second leaf spring sandwiched in the thickness direction when viewed from the leaf width direction, the first leaf spring and the third leaf spring are arranged symmetrically with respect to the center of the second leaf spring in the thickness direction, both ends of the third leaf spring in the length direction are stacked and joined to both ends of the second leaf spring in the length direction on the opposite side of the first leaf spring in the thickness direction, and the intermediate portions of the first leaf spring, the second leaf spring, and the third leaf spring in the length direction face each other while being spaced apart in the thickness direction, a length of the intermediate portion of the second leaf spring along the surface of the second leaf spring, as viewed from the plate width direction, that is shorter than the length of the intermediate portion of the first leaf spring along the surface of the first leaf spring and the length of the intermediate portion of the third leaf spring along the surface of the third leaf spring, as viewed from the plate width direction; and a stress is applied to the outer surface side of the intermediate portion of the third leaf spring, which is opposite the second leaf spring along the plate thickness direction, in a direction that pulls the outer surface of the third leaf spring as viewed from the plate width direction; and in the joining step, both longitudinal ends of the first leaf spring and both longitudinal ends of the third leaf spring may be joined to the second leaf spring material.

[0041] The compression spring further includes a third leaf spring having an intermediate portion located on the opposite side of the first leaf spring and sandwiching the intermediate portion of the second leaf spring in the plate thickness direction, when viewed from the plate width direction, the first leaf spring and the third leaf spring are included in a single plate material, the third leaf spring is located at a different position from the first leaf spring in the plate width direction, and a stress is applied to the intermediate portion of the third leaf spring on the outer surface side opposite the outer surface side of the first leaf spring in a direction that pulls the third leaf spring in a direction along the outer surface of the third leaf spring when viewed from the plate width direction, and the joining step may include a slit forming step, prior to the joining step, of forming two or more slits in the flat plate material extending in the length direction, leaving at least one end, to form three or more first regions and second regions in total, and in the joining step, both longitudinal ends of the first leaf spring of the flat plate material may be joined to the second leaf spring material.

[0042] The compression spring further includes a third leaf spring having an intermediate portion provided on the opposite side of the first leaf spring with the intermediate portion of the second leaf spring sandwiched in the plate thickness direction when viewed from the plate width direction, and a fourth leaf spring having an intermediate portion in the longitudinal direction opposed to the intermediate portion of the third leaf spring while being spaced apart in the plate thickness direction, the first leaf spring and the third leaf spring are included in an integral plate material, the third leaf spring is located at a different position from the first leaf spring in the plate width direction, and a stress is applied to the intermediate portion of the third leaf spring on an outer surface side opposite to the outer surface side of the first leaf spring in a direction pulling the third leaf spring in a direction along the outer surface of the third leaf spring when viewed from the plate width direction, The joining step may be preceded by a slit forming step in which two or more slits extending in the length direction, leaving at least one end, are formed in the flat plate material, thereby forming a total of three or more first regions and second regions; in the joining step, both longitudinal ends of the first leaf spring of the flat plate material are joined to the second leaf spring material, and both longitudinal ends of the third leaf spring of the flat plate material are joined to a long fourth leaf spring material formed by connecting a plurality of the fourth leaf springs integrally in the length direction; and in the cutting step, at least the second leaf spring material and the fourth leaf spring material are cut to obtain the compression springs.

[0043] Between the slit forming step and the joining step, there may be a deformation step of 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 leaf width direction, and imparting 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 in the opposite direction to the first leaf spring.

[0044] During the joining step, a plurality of the first leaf springs are joined to the second leaf spring material along the longitudinal direction, and during the cutting step, the two joint portions of the second leaf spring material that are located outermost in the longitudinal direction among the joint portions with the plurality of first leaf springs are cut, and then the remaining joint portions are cut to obtain a plurality of the compression springs.

[0045] During the joining process, multiple first leaf springs are joined to the second leaf spring material along the length. This allows multiple first leaf springs to be joined to the second leaf spring material while the same longitudinal position of the second leaf spring material remains fixed. This allows multiple pressure springs to be manufactured more efficiently than, for example, a cutting process being performed each time a first leaf spring is joined to a second leaf spring material. During the cutting process, the second leaf spring material is cut at the two outermost joints in the length direction among the joints with the multiple first leaf springs as the first cut, and then the remaining joints are cut as the second cut to obtain multiple pressure springs. This allows the connected pressure springs, including the second leaf spring material to which the multiple first leaf springs have been joined and from which the cut second leaf spring material has been removed, to be transferred from the joining machine used during the joining process to a cutting machine used during the second cut. This allows the joining step and the second cutting in the cutting step to be performed in parallel, for example, and thus makes it possible to efficiently manufacture a plurality of pressure springs.

[0046] The joining step may involve joining both longitudinal ends of the first leaf spring included in a long first leaf spring material formed by connecting a plurality of the first leaf springs together in the longitudinal direction to the second leaf spring material, and the cutting step may involve cutting the second leaf spring material together with the first leaf spring material.

[0047] In the cutting step, the second leaf spring material is cut integrally with the first leaf spring material to obtain the compression spring, so that a plurality of compression springs can be manufactured efficiently.

[0048] According to the above aspect of the present invention, it is possible to output a high load in a small space.

[0049] 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 pressure spring of FIG. 12A as seen from the plate width direction. FIG. 14A is a view illustrating a manufacturing method of a pressure spring of a sixth embodiment. FIG. 14B is a view illustrating a manufacturing method of a pressure spring of a sixth embodiment. FIG. 14C is a view illustrating a manufacturing method of a pressure spring of a sixth embodiment. FIG. 14D is a perspective view of a pressure spring structure of a seventh embodiment. FIG. 14A is a view of the pressure spring structure of FIG. 14A as seen from the plate width direction. FIG. 14D is a view illustrating a joining step of a manufacturing method of an eighth embodiment. FIG. 14E is a view illustrating a cutting step of a manufacturing method of an eighth embodiment. FIG. 14F is a view illustrating a joining step of a manufacturing method of a ninth embodiment. FIG. 14G is a view illustrating a cutting step of a manufacturing method of a ninth embodiment. FIG. 14H is a view illustrating a state immediately before joining in a joining step of a manufacturing method of a tenth embodiment. FIG. 14H is a view illustrating a joining step of a manufacturing method of an eleventh embodiment. FIG. 14H is a view illustrating a joining step of a manufacturing method of a twelfth embodiment. FIG. 14H is a view illustrating a joining step of a manufacturing method of a thirteenth embodiment. FIG. 14H is a view illustrating a joining step of a manufacturing method of a fourteenth embodiment. FIG. 14H is a view illustrating a first cut in a cutting step of a manufacturing method of a fifteenth embodiment. FIG. 14H is a view illustrating a second cut in a cutting step of a manufacturing method of a fifteenth embodiment. FIG. 14H is a view illustrating a cut line forming step of a manufacturing method of a sixteenth embodiment. FIG. 14H is a view illustrating a state immediately before joining in a joining step of a manufacturing method of a sixteenth embodiment. 23A and 23B are diagrams illustrating the state immediately before bonding in the bonding step of the manufacturing method according to the seventeenth embodiment.

[0050] 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.

[0051] The first and second leaf springs 11 and 12 have the same size in the longitudinal direction X. Both end edges of the first and second leaf springs 11 and 12 in the longitudinal direction X are connected without a step in the plate thickness direction Z. The sizes of the first and second leaf springs 11 and 12 in the longitudinal direction X may be different from each other, or both end edges of the first and second leaf springs 11 and 12 in the longitudinal direction X may be connected via a step in the plate thickness direction Z. The middle portions 23 and 24 of the first and second leaf springs 11 and 12 in the longitudinal direction X face each other while being spaced apart in the plate thickness direction Z. The length of the middle 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 middle 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.

[0052] The intermediate portion 23 of the first leaf spring 11 is curved in the thickness direction Z as viewed from the width direction Y, so as to present a protruding curved shape away from the intermediate portion 24 of the second leaf spring 12. The intermediate portion 23 of the first leaf spring 11 may be bent in the thickness direction Z as viewed from the width direction Y, so as to present a protruding shape, such as a trapezoidal, rectangular, or triangular shape (each of which may have rounded corners), that protrudes away from the intermediate portion 24 of the second leaf spring 12. The second leaf spring 12 extends straight in the length direction X as viewed from the width direction Y. The intermediate portion 24 of the second leaf spring 12 may be curved in the thickness direction Z as viewed from the width direction Y, so as to present a protruding curved shape toward or away from the intermediate portion 23 of the first leaf spring 11.

[0053] In the intermediate portion 23 of the first leaf spring 11, a residual stress F1 is applied to the outer surface 23a, which is the opposite side of the second leaf spring 12 along the plate thickness direction Z, in a direction that pulls the first leaf spring 11 in the direction along the outer surface 23a as viewed in the plate width direction Y. Note that the stress applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11 in the direction that pulls the first leaf spring 11 in the direction along the outer surface 23a as viewed in the plate width direction Y may be a tensile stress that occurs on the outer surface 23a of the intermediate portion 23 when the first leaf spring 11 is compressed and deformed within its elastic range in the longitudinal direction X. In the intermediate portion 23 of the first leaf spring 11, a residual stress F2 is applied to the inner surface 23b, which is the side of the second leaf spring 12 along the plate thickness direction Z, in a direction that compresses the first leaf spring 11 in the direction along the inner surface 23b as viewed in the plate width direction Y. In addition, the stress 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 when viewed from the plate width direction Y may be a compressive stress generated on the inner surface 23b of the intermediate portion 23 when the first leaf spring 11 is compressed and deformed within its elastic range in the longitudinal direction X.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] In each of the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13, a residual stress F1 is applied to the outer surfaces 23a, 28a, which are opposite the second leaf spring 12 in the thickness direction Z, in a direction that pulls the intermediate portions 23a, 28a in the direction along the outer surfaces 23a, 28a as viewed in the width direction Y. The stress applied to the outer surfaces 23a, 28a of the intermediate portions 23, 28 of the first leaf spring 11A and the third leaf spring 13 in the direction that pulls the intermediate portions 23a, 28a in the direction along the outer surfaces 23a, 28a as viewed in the width direction Y may be a tensile stress that occurs on the outer surfaces 23a, 28a of the intermediate portions 23, 28 when the first leaf spring 11A and the third leaf spring 13 are compressed and deformed within their elastic range in the length direction X. In each of 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 compressing the inner surfaces 23b, 28b as viewed from the plate width direction Y. Note that the stress 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 in a direction compressing the inner surfaces 23b, 28b as viewed from the plate width direction Y may be a compressive stress generated on the inner surfaces 23b, 28b of the intermediate portions 23, 28 when the first leaf spring 11A and the third leaf spring 13 are compressed and deformed within their elastic range in the longitudinal direction X.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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. Note that the sizes of the first leaf spring 11, the second leaf spring 12, and the third leaf spring 13 in the leaf width direction Y may be different from one another. For example, the dimensions of the first leaf spring 11 and the third leaf spring 13 in the plate width direction Y may be the same and different from the dimension of the second leaf spring 12 in the plate width direction Y.

[0099] 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 .

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] (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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] The method for manufacturing a single compression spring has been described above with reference to Figures 2, 5, 6, 9, 11A to 11D, and 13A to 13D. However, with respect to the compression springs according to the first, second, third, and fourth embodiments, it is possible to efficiently manufacture multiple compression springs in succession. Below, methods for manufacturing multiple consecutive compression springs will be described as the eighth to seventeenth embodiments.

[0123] Eighth Embodiment A method for manufacturing a compression spring 1 according to an eighth embodiment of the present invention will be described with reference to Figures 15 and 16. In this manufacturing method, a plurality of continuous compression springs 1 are manufactured from the compression springs 1 of the first embodiment shown in Figures 1A and 1B. The manufacturing method for the compression spring 1 of this embodiment involves performing a joining process and a cutting process in this order.

[0124] 15 , in the joining process, the first fixing portion 21 of the first leaf spring 11 is joined to a long second leaf spring material 132 configured by connecting a plurality of second leaf springs 12 together in the longitudinal direction X. The second leaf spring material 132 is wound in a roll, and during the joining process, it is unwound to a certain length that allows the plurality of second leaf springs 12 to be cut out, and its tip is fixed in a state where it is stretched straight in the longitudinal direction X.

[0125] In the illustrated example, during the joining process, the first leaf spring 11 is elastically deformed so that the size of the first leaf spring 11 in the longitudinal direction X is reduced, and the first fixing portion 21 is joined to the second leaf spring material 132 by a joining machine 126 while applying a stress to the outer surface 23a of the middle portion 23 of the first leaf spring 11 in a direction along the outer surface 23a of the first leaf spring 11 as viewed from the leaf width direction Y (hereinafter referred to as the first specific direction).

[0126] At this time, two pressing jigs 125, spaced apart in the length direction X, are brought into contact with the outer surface of the first leaf spring 11 facing the opposite side of the second leaf spring 12 along the plate thickness direction Z, and the relative movement between the pressing jigs 125 and the first leaf spring 11 is restricted by, for example, frictional force. In this state, the two pressing jigs 125 are moved relatively closer to each other in the length direction X, causing the first leaf spring 11 to elastically deform as described above. In the illustrated example, the frictional force generated between the pressing jigs 125 and the first leaf spring 11 is greater than the frictional force generated between the second leaf spring material 132 and the first leaf spring 11.

[0127] Prior to the joining step, residual stress in the first specific direction may be applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11. In this case, the first leaf spring 11 may or may not be elastically deformed during the joining step, as described above. Furthermore, the second leaf spring material 132 may be pulled in the longitudinal direction X during the joining step.

[0128] In the illustrated example, the joining step is an example in which the first fixing portions 21 of the first leaf springs 11 included in an elongated first leaf spring material 131 configured by integrally connecting a plurality of first leaf springs 11 in the longitudinal direction X are joined to the second leaf spring material 132. Alternatively, the joining step may use individual first leaf springs 11 without employing the elongated first leaf spring material 131.

[0129] The first leaf spring material 131 is formed in a wave shape that curves in the plate thickness direction Z and extends in the length direction X. When viewed from the plate width direction Y, the first leaf spring material 131 has a curved shape that protrudes in the plate thickness direction Z toward the side away from the second leaf spring material 132, and is configured by alternatingly connecting in the length direction X curved portions 131a that become the intermediate portion 23 in the compression spring 1 and flat portions 131b that extend straight in the length direction X and become the first fixed portion 21 in the compression spring 1.

[0130] During the joining process, the holding jig 125 is brought into contact with the two flat portions 131b of the first leaf spring material 131 located on both sides of the curved portion 131a in the longitudinal direction X while restricting relative movement, and the two holding jigs 125 are moved closer to each other in the longitudinal direction X, thereby elastically deforming the curved portion 131a so that the radius of curvature when viewed from the plate width direction Y becomes smaller.

[0131] Next, in the cutting process, the second leaf spring material 132 is cut integrally with the first leaf spring material 131 to obtain the compression spring 1. At this time, as shown in FIG. 16 , the holding jig 125 and the joining machine 126 are moved away from the first leaf spring material 131 in the plate thickness direction Z. In this state, the second leaf spring material 132 is fed out, and the portion joined in the joining process described above is moved away from the holding jig 125 and the joining machine 126 in the length direction X and moved to a position where the cutting machine 129 is installed, where it is cut by the cutting machine 129. Here, the portions of the first leaf spring material 131 and the second leaf spring material 132 adjacent to the rear side of the portion cut integrally in the cutting process in the feeding direction along the length direction X are joined in the plate thickness direction Z. This prevents the relative positions of the first leaf spring material 131 and the second leaf spring material 132 from shifting during cutting.

[0132] 16 shows an example in which the portions of the first leaf spring material 131 and the second leaf spring material 132 adjacent to the portion cut in the cutting process on both sides in the longitudinal direction X are joined. However, the portions of the first leaf spring material 131 and the second leaf spring material 132 adjacent to the portion cut in the cutting process on both sides in the longitudinal direction X that are sandwiched between the first fixing portions 21 do not have to be joined.

[0133] Ninth Embodiment A method for manufacturing a compression spring according to a ninth embodiment of the present invention will be described with reference to Figures 17 and 18. In the manufacturing method of this embodiment, a plurality of continuous compression springs 4 are manufactured using the compression springs 4 of the fourth embodiment shown in Figures 8A and 8B. The manufacturing method of the compression spring 4 of this embodiment involves performing a joining step and a cutting step in this order.

[0134] In the joining process, the first fixing portion 21 of the first leaf spring 11B and the flat portion 27 of the third leaf spring 13B are joined to a long second leaf spring material 132 configured by connecting a plurality of second leaf springs 12B together in the longitudinal direction X. The second leaf spring material 132 is wound in a roll, and during the joining process, it is unwound to a certain length that allows the plurality of second leaf springs 12B to be cut out, and its tip is fixed in a state where it is stretched straight in the longitudinal direction X.

[0135] In the illustrated example, during the joining process, the first leaf spring 11B and the third leaf spring 13B are elastically deformed so that the size of each of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X is reduced, and the first fixing portion 21 and the flat portion 27 are joined to the second leaf spring material 132 by the joining machine 126 in a state in which a stress is applied to the outer surfaces 23a, 28a of the intermediate portions 23, 28 of each of the first leaf spring 11B and the third leaf spring 13B in a direction along the outer surfaces 23a, 28a of each of the first leaf spring 11B and the third leaf spring 13B as viewed from the leaf width direction Y (hereinafter referred to as the first specific direction).

[0136] At this time, two pressing jigs 125, spaced apart in the longitudinal direction X, are placed in contact with the outer surfaces of the first leaf spring 11B and the third leaf spring 13B, facing away from the second leaf spring 12B in the thickness direction Z, respectively, to restrict relative movement between the pressing jigs 125 and the first leaf spring 11B and between the pressing jigs 125 and the third leaf spring 13B, for example, by frictional force. In this state, the two pressing jigs 125 are moved relatively closer to each other in the longitudinal direction X, causing the first leaf spring 11B and the third leaf spring 13B to elastically deform as described above. In the illustrated example, the frictional forces generated between the pressing jigs 125 and the first and third leaf springs 11B and 13B are greater than the frictional forces generated between the second leaf spring material 132 and the first and third leaf springs 11B and 13B.

[0137] Prior to the joining process, residual stress in the first specific direction may be applied to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B. In this case, the first leaf spring 11B and the third leaf spring 13B may or may not be elastically deformed during the joining process. Furthermore, the second leaf spring material 132 may be pulled in the longitudinal direction X during the joining process.

[0138] In the illustrated example, the joining process joins the first fixing portion 21 of the first leaf spring 11B included in the long first leaf spring material 131, which is formed by connecting multiple first leaf springs 11B together in the longitudinal direction X, to the second leaf spring material 132, and also joins the flat portion 27 of the third leaf spring 13B included in the long third leaf spring material 133, which is formed by connecting multiple third leaf springs 13B together in the longitudinal direction X, to the second leaf spring material 132.

[0139] The first leaf spring material 131 and the third leaf spring material 133 are formed in a wave-like shape that curves in the plate thickness direction Z and extends in the length direction X. When viewed in the plate width direction Y, the first leaf spring material 131 and the third leaf spring material 133 have a curved shape that protrudes in the plate thickness direction Z toward the side away from the second leaf spring material 132, and are configured by alternating in the length direction X curved portions 131 a and 133 a that become the intermediate portions 23 and 28 in the compression spring 4 and flat portions 131 b and 133 b that extend straight in the length direction X and become the first fixed portion 21 and the flat portion 27 in the compression spring 4. When viewed in the plate width direction Y, the first leaf spring material 131 and the third leaf spring material 133 have a symmetrical shape to the second leaf spring material 132.

[0140] During the joining process, the holding jig 125 is brought into contact with the two flat portions 131b, 133b located on both sides of the curved portions 131a, 133a in the longitudinal direction X of each of the first leaf spring material 131 and the third leaf spring material 133 while restricting relative movement, and the two holding jigs 125 are moved closer to each other in the longitudinal direction X, thereby elastically deforming the curved portions 131a, 133a so that the radius of curvature when viewed from the plate width direction Y becomes smaller.

[0141] Next, in the cutting process, the second leaf spring material 132 is cut integrally together with the first leaf spring material 131 and the third leaf spring material 133 to obtain the compression spring 4. At this time, as shown in FIG. 18 , the holding jig 125 and the joining machine 126 are moved away from the first leaf spring material 131 and the third leaf spring material 133 in the plate thickness direction Z. In this state, the second leaf spring material 132 is fed out, and the portion joined in the joining process described above is moved away from the holding jig 125 and the joining machine 126 in the longitudinal direction X, moved to a position where the cutting machine 129 is provided, and cut by the cutting machine 129. Here, in the first leaf spring material 131, the second leaf spring material 132, and the third leaf spring material 133, the portions adjacent to the rear side of the portions cut integrally in the cutting process in the feeding direction along the longitudinal direction X are joined in the plate thickness direction Z. This makes it possible to prevent the relative positions of the first leaf spring material 131, the second leaf spring material 132, and the third leaf spring material 133 from shifting when they are cut.

[0142] As described above, the compression spring 4 according to this embodiment includes the first leaf spring 11B and the second leaf spring 12B. Therefore, when the compression spring 4 is sandwiched between a pair of pressed bodies in the plate thickness direction Z and a compressive load from the second leaf spring 12B along the plate thickness direction Z is applied to the intermediate portion 23 of the first leaf spring 11B, a tensile force in the longitudinal direction X is applied to the second leaf spring 12B via the first fixed portion 21 of the first leaf spring 11B. In this case, the length of the intermediate portion 24 of the second leaf spring 12B along the surface of the second leaf spring 12B, as viewed in the plate width direction Y, is shorter than the length of the intermediate portion 23 of the first leaf spring 11B along the surface of the first leaf spring 11B and the length of the intermediate portion 28 of the third leaf spring 13B along the surface of the third leaf spring 13B, as viewed in the plate width direction Y. Therefore, regardless of the material of the second leaf spring 12B, the second leaf spring 12B suppresses deformation of the first leaf spring 11B, making it possible to increase the spring constant of the compression spring 4 that is generated, and enabling high loads to be output in a space-saving manner.

[0143] Since a stress in a pulling direction is applied to the outer surfaces 23a, 28a of the intermediate portions 23, 28 of each of the first and third leaf springs 11B and 13B, respectively, the compressive stress in the first specific direction that occurs when a pressing load from the second leaf spring 12B along the plate thickness direction Z is applied to the outer surfaces 23a, 28a of the intermediate portions 23, 28 of each of the first and third leaf springs 11B and 13B is applied, is alleviated.As a result, even if the compression spring 4 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 each of the first and third leaf springs 11B and 13B, thereby improving durability.

[0144] The method for manufacturing the compression spring 4 according to this embodiment involves, in this order, a joining step of joining the first fixing portion 21 and the flat portion 27 to the long second leaf spring material 132, and a cutting step of cutting at least the second leaf spring material 132 to obtain the compression spring 4. Therefore, a plurality of compression springs 4 can be manufactured more efficiently than, for example, a case in which the first leaf spring 11B and the third leaf spring 13B cut to a specified length are joined to the second leaf spring 12B cut to a specified length.

[0145] With stress applied in the first specific direction to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, respectively, the first fixing portion 21 and the flat portion 27 are joined to the second leaf spring material 132. In this case, the compression spring 4 can be easily obtained.

[0146] During the joining process, the first fixing portion 21 and the flat portion 27 are joined to the second leaf spring material 132 in a state in which the first leaf spring 11B and the third leaf spring 13B are elastically deformed so that the size of each of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X is reduced. In this case, the step of previously applying residual stress can be omitted.

[0147] In the cutting step, the second leaf spring material 132 is cut integrally with the first leaf spring material 131 and the third leaf spring material 133 to obtain the compression spring 4, so that a plurality of compression springs 4 can be manufactured efficiently.

[0148] Tenth Embodiment Next, a method for manufacturing a compression spring 4 according to a tenth embodiment of the present invention will be described with reference to Fig. 19. In the manufacturing method of this embodiment, a plurality of linked compression springs 4 are manufactured using the compression springs 4 of the fourth embodiment shown in Figs. 8A and 8B. In this tenth embodiment, the same components as those in the ninth embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0149] In the manufacturing method of the compression spring 4 of this embodiment, prior to the joining step, residual stress is applied to the outer surfaces 23a, 28a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, respectively, in a direction that pulls them in the first specific direction. Then, during the joining step, with the second leaf spring material 132 being pulled in the longitudinal direction X, the first fixing portion 21 of the first leaf spring 11B and the flat portion 27 of the third leaf spring 13B are joined to the second leaf spring material 132 by a joining machine 126 shown in FIG. 17 . During this joining, the two pressing jigs 125 are not moved toward each other in the longitudinal direction X, but rather abut against the two flat portions 131b, 133b of the first leaf spring material 131 and the third leaf spring material 133, respectively, located on both sides of the curved portions 131a, 133a in the longitudinal direction X, with their relative movement restricted.

[0150] After the joining step, as in the ninth embodiment, the holding jig 125 and the joining machine 126 are moved away from the first leaf spring material 131 and the third leaf spring material 133 in the plate thickness direction Z. In this state, the second leaf spring material 132 is fed out, and the portion joined during the joining step described above is moved away from the holding jig 125 and the joining machine 126 in the longitudinal direction X, moved to a position where a cutting machine is provided, and cut by the cutting machine to obtain the compression spring 4 (cutting step). Alternatively, multiple compression springs 4 may be obtained by the following procedure. That is, during the joining step, multiple first leaf springs 11B are joined to the second leaf spring material 132 along the longitudinal direction X, and multiple third leaf springs 13B are joined to the second leaf spring material 132 along the longitudinal direction X. Then, during the cutting step, as a first cut, in the second leaf spring material 132, of the joints between the plurality of first leaf springs 11B and the plurality of third leaf springs 13B, two joints 134 located outermost in the longitudinal direction X are cut to obtain a series of pressure springs 4. Then, as a second cut, the remaining joints in this series of pressure springs 4 are cut with a cutter to obtain a plurality of pressure springs 4.

[0151] In this embodiment, as long as the second leaf spring material 132 is pulled in the longitudinal direction X during the joining process, it is not necessary to apply any stress, including residual stress, in the direction pulling the second leaf spring material 132 in the first specific direction to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B. Also, as long as stress in the direction pulling the second leaf spring material 132 in the first specific direction is applied to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B during the joining process, it is not necessary to pull the second leaf spring material 132 in the longitudinal direction X.

[0152] As described above, according to the method for manufacturing the compression spring 4 of this embodiment, prior to the joining step, residual stress in a direction pulling the first specific direction is applied to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B. Therefore, during the joining step, it is possible to eliminate or at least keep low the force applied to the first leaf spring 11B and the third leaf spring 13B in order to generate stress in a direction pulling the first specific direction on the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, and the compression spring 4 can be easily obtained.

[0153] During the joining step, while the second leaf spring material 132 is being pulled in the longitudinal direction X, the first fixing portion 21 of the first leaf spring 11B and the flat portion 27 of the third leaf spring 13B are joined to the second leaf spring material 132. Therefore, a restoring force is generated in the second leaf spring 12B cut from the second leaf spring material 132 during the cutting step, and a stress is applied in a pulling direction in the first specific direction to the outer surfaces 23a, 28a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, respectively. Therefore, during the joining process, it is possible to eliminate or at least keep low the force applied to the first leaf spring 11B and the third leaf spring 13B in order to generate stress in the first specific direction on the outer surfaces 23a, 28a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, respectively, and the compression spring 4 can be easily obtained.

[0154] Next, a method for manufacturing the pressure springs 4 according to the eleventh to fourteenth embodiments of the present invention will be described with reference to FIGS.

[0155] The eleventh to fourteenth embodiments differ from the ninth and tenth embodiments in that, in the joining process, individual first leaf springs 11B are used instead of the elongated first leaf spring material 131, and individual third leaf springs 13B are used instead of the elongated third leaf spring material 133. That is, in the eleventh to fourteenth embodiments, only the elongated second leaf spring material 132 is cut during the cutting process. The eleventh to fourteenth embodiments are common in that, in the joining process, the first fixing portion 21 of the first leaf spring 11B and the flat portion 27 of the third leaf spring 13B are joined to the second leaf spring material 132 while the first leaf spring 11B and the third leaf spring 13B are elastically deformed so that the dimensions of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X are reduced. In the eleventh to fourteenth embodiments, the joining machine 126 is not shown. In the eleventh to fourteenth embodiments, the form (method) of elastically deforming the first leaf spring 11B and the third leaf spring 13B is different so that the size of each of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X is reduced during the joining process.

[0156] Eleventh Embodiment A method for manufacturing a pressure spring 4 according to an eleventh embodiment of the present invention will be described with reference to Fig. 20. In this eleventh embodiment, the same components as those in the ninth embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0157] In the manufacturing method of the compression spring 4 of this embodiment, during the joining process, two pressing jigs 125A, which are provided apart in the longitudinal direction X, are brought into contact with not only the outer surfaces of the first leaf spring 11B and the third leaf spring 13B facing the opposite side of the second leaf spring 12B in the plate thickness direction Z, but also the end edges 11a, 13a facing the longitudinal direction X. In this state, the two pressing jigs 125A are moved toward each other in the longitudinal direction X, elastically deforming the first leaf spring 11B and the third leaf spring 13B so that the sizes of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X are reduced. The pressing jigs 125A are formed with recesses 125a into which the first fixing portions 21 or the flat portions 27 are inserted. During the joining step, one of the two pressing jigs 125A may be fixed, and the other pressing jig 125A may be moved in the length direction X.

[0158] As described above, according to the manufacturing method of the compression spring 4 of this embodiment, during the joining step, the pressing jig 125A supports not only the outer surfaces of the first leaf spring 11B and the third leaf spring 13B that face the opposite side of the second leaf spring 12B along the plate thickness direction Z, but also the end edges 11 a, 13 a that face the length direction X. Therefore, the first leaf spring 11B and the third leaf spring 13B can be elastically deformed with precision as described above.

[0159] Twelfth Embodiment A method for manufacturing a pressure spring 4 according to a twelfth embodiment of the present invention will be described with reference to Fig. 21. In this twelfth embodiment, the same components as those in the eleventh embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0160] In the manufacturing method of the compression spring 4 of this embodiment, during the joining step, the first fixing portion 21 and the flat portion 27 of each of the first leaf spring 11B and the third leaf spring 13B are supported by the support member 141. In this state, the inner surfaces 23b, 28b of the intermediate portions 23, 28 are pressed toward the opposite side of the second leaf spring 12B along the plate thickness direction Z, thereby elastically deforming the first leaf spring 11B and the third leaf spring 13B so that the size of each of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X is reduced.

[0161] Two support members 141 are provided for each of the first fixing portion 21 and the flat portion 27, spaced apart in the longitudinal direction X, and supported to be slidable in the longitudinal direction X. The two support members 141 move toward each other in the longitudinal direction X as the first leaf spring 11B and the third leaf spring 13B elastically deform. The support members 141 are formed with recesses 141a into which the first fixing portion 21 or the flat portion 27 is inserted. The support members 141 contact not only the outer surfaces of the first leaf spring 11B and the third leaf spring 13B facing away from the second leaf spring 12B in the thickness direction Z, but also the end edges 11a, 13a facing in the longitudinal direction X. As described above, the manufacturing method of the compression spring 4 according to this embodiment allows the first leaf spring 11B and the third leaf spring 13B to be elastically deformed with precision as described above.

[0162] A method for manufacturing a pressure spring 4 according to a thirteenth embodiment of the present invention will be described with reference to Fig. 22. In this thirteenth embodiment, the same components as those in the twelfth embodiment are denoted by the same reference numerals, and a description thereof will be omitted, with only the differences being described.

[0163] In the manufacturing method of the compression spring 4 of this embodiment, during the joining step, portions of the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, located on both sides of the center portion in the longitudinal direction X, are supported. In this state, the center portions in the longitudinal direction X of the inner surfaces 23 b, 28 b of the intermediate portions 23, 28 are pressed toward the opposite side of the second leaf spring 12B along the plate thickness direction Z, elastically deforming the first leaf spring 11B and the third leaf spring 13B so that the size of each of the first leaf spring 11B and the third leaf spring 13B in the longitudinal direction X is reduced.

[0164] As described above, in the manufacturing method of the compression spring 4 according to the present embodiment, during the joining step, with the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B, respectively, portions located on both sides of the central portion in the longitudinal direction X in the longitudinal direction X are supported, and the central portions in the longitudinal direction X of the inner surfaces 23 b, 28 b of the intermediate portions 23, 28 are pressed toward the opposite side of the second leaf spring 12B in the plate thickness direction Z using a deformation jig. Therefore, the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B are bent at three points, and the compression spring 4 can be easily and accurately manufactured, in which the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B are subjected to tensile stress in the first specific direction.

[0165] Fourteenth Embodiment A method of manufacturing a pressure spring 4 according to a fourteenth embodiment of the present invention will be described with reference to Fig. 23. In this fourteenth embodiment, the same components as those in the eleventh embodiment will be denoted by the same reference numerals, and a description thereof will be omitted, with only the differences being described.

[0166] In the manufacturing method of the compression spring 4 of this embodiment, during the joining process, the inner surfaces 23b, 28b of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B are supported by a support mold 142. In this state, the pressing mold 143 presses the outer surfaces of the intermediate portions 23, 28 facing away from the second leaf spring 12B in the thickness direction Z toward the second leaf spring 12B along the thickness direction Z over the entire area, elastically deforming the first leaf spring 11B and the third leaf spring 13B so that the dimensions of the first leaf spring 11B and the third leaf spring 13B in the length direction X are reduced. As described above, the manufacturing method of the compression spring 4 of this embodiment allows the first leaf spring 11B and the third leaf spring 13B to be elastically deformed with precision as described above.

[0167] In the eleventh to fourteenth embodiments, during the joining step, the second leaf spring material 132 may or may not be pulled in the longitudinal direction X. In the eleventh to fourteenth embodiments, prior to the joining step, residual stress in a direction pulling the second leaf spring material 132 in the first specific direction may be imparted to the outer surfaces 23 a, 28 a of the intermediate portions 23, 28 of the first leaf spring 11B and the third leaf spring 13B.

[0168] The manufacturing methods of the above-described eleventh to fourteenth embodiments may be applied to the manufacturing method of the compression spring 1 according to the eighth embodiment. That is, in the manufacturing method of the compression spring 1 according to the eighth embodiment, the long first leaf spring material 131 may not be used in the joining step, and individual first leaf springs 11 may be used. In this case, only the long second leaf spring material 132 is cut in the cutting step.

[0169] Fifteenth Embodiment Next, a method for manufacturing a compression spring 4 according to a fifteenth embodiment of the present invention will be described with reference to Figures 24 and 25. In the manufacturing method of this embodiment, a plurality of linked compression springs 4 are manufactured for the compression springs 4 of the fourth embodiment shown in Figures 8A and 8B. In the fifteenth embodiment, the same components as those in the ninth embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0170] In the manufacturing method of the compression spring 4 of this embodiment, during the joining step, a plurality of first leaf springs 11B and a plurality of third leaf springs 13B are joined to a second leaf spring material 132 along the longitudinal direction X. In the second leaf spring material 132, the joint portions with the first leaf springs 11B and the joint portions with the third leaf springs 13B are located at the same position in the longitudinal direction X. Then, during the cutting step, as a first cut, two joint portions 134 that are located outermost in the longitudinal direction X among the joint portions with the plurality of first leaf springs 11B and the plurality of third leaf springs 13B are cut off in the second leaf spring material 132. Then, the connected body of compression springs 4 having the second leaf spring material 132 joined with the plurality of first leaf springs 11B and the plurality of third leaf springs 13B, respectively, is transferred from the joining machine used during the joining step to a cutting machine 129 used during the cutting step. Thereafter, as a second cutting step, the remaining joint portion is cut by a cutter 129 to obtain a plurality of pressure springs 4.

[0171] As described above, according to the method for manufacturing the compression spring 4 of this embodiment, during the joining step, the first fixing portions 21 of the plurality of first leaf springs 11B are joined to the second leaf spring material 132 along the longitudinal direction X, and the flat portions 27 of the plurality of third leaf springs 13B are joined to the second leaf spring material 132 along the longitudinal direction X. Therefore, it is possible to join the plurality of first fixing portions 21 and the plurality of flat portions 27 to the second leaf spring material 132 while keeping the same positions in the longitudinal direction X of the second leaf spring material 132 fixed. For example, compared to a case where a cutting step is performed each time one first leaf spring 11B and one third leaf spring 13B are joined to the second leaf spring material 132, it is possible to efficiently manufacture the plurality of compression springs 4.

[0172] During the cutting process, the first cut is made by cutting the two outermost joint portions 134 in the longitudinal direction X of the joint portions of the second leaf spring material 132 with the plurality of first leaf springs 11B and the plurality of third leaf springs 13B, and the second cut is made by cutting the remaining joint portions to obtain the plurality of pressure springs 4. Therefore, the connected body of pressure springs 4 having the second leaf spring material 132 to which the plurality of first leaf springs 11B and the plurality of third leaf springs 13B have been joined and cut off can be transferred from the joining machine used in the joining process to the cutting machine 129 used in the second cutting. This allows the joining process and the second cut of the cutting process to be performed in parallel, for example, thereby efficiently manufacturing the plurality of pressure springs 4.

[0173] In the ninth, tenth, and fifteenth embodiments, in the joining process, the long first leaf spring material 131 may not be used, but individual first leaf springs 11 may be used, and the long third leaf spring material 133 may not be used, but individual third leaf springs 13 may be used.

[0174] Sixteenth Embodiment Next, a method for manufacturing a compression spring 2 according to a sixteenth embodiment of the present invention will be described with reference to Figures 26 and 27. In the manufacturing method of this embodiment, a plurality of continuous compression springs 2 are manufactured for the compression springs 2 of the second embodiment shown in Figures 3 and 4. The manufacturing method of the compression spring 2 of this embodiment involves performing a slit forming step, a joining step, and a cutting step in this order.

[0175] The compression spring 2 includes a first leaf spring 11A, a second leaf spring 12, and a third leaf spring 13. When viewed from the leaf width direction Y, the third leaf spring 13 has an intermediate portion 28 provided on the opposite side of the first leaf spring 11A, sandwiching the intermediate portion 24 of the second leaf spring 12 in the plate thickness direction Z. The first leaf spring 11A and the third leaf spring 13 are included in an integrated plate material 30. The third leaf spring 13 is located at a different position from the first leaf spring 11A in the plate width direction Y. A stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A in a pulling direction along the outer surface 23a of the first leaf spring 11A when viewed from the plate width direction Y. In the middle portion 28 of the third leaf spring 13, a stress is applied to the outer surface 28a side opposite to the outer surface 23a side of the first leaf spring 11A in a direction pulling the spring in the direction along the outer surface 28a of the third leaf spring 13 when viewed from the plate width direction Y.

[0176] The slit forming step is performed before the joining step. In the slit forming step, as shown in Fig. 26 , in a flat plate material 150 formed by integrally connecting a plurality of plate materials 30 in the longitudinal direction X, two or more slits 31 are formed in each plate material 30, leaving at least one end of each plate material 30, extending in the longitudinal direction X, thereby forming a total of three or more first regions A1 and second regions A2.

[0177] 27 , in the joining step, both ends (first fixing portions 21) of the first leaf spring 11A of the flat plate material 150 (plate material 30) in the longitudinal direction X are joined to a long second leaf spring material 132 formed by integrally connecting a plurality of second leaf springs 12 in the longitudinal direction. At this time, similar to the joining step in the manufacturing method of the eighth embodiment, a pressing jig 125 and a joining machine 126 are used to join both ends of the first leaf spring 11A in the longitudinal direction X to the second leaf spring material 132.

[0178] In the cutting step, the second leaf spring material 132 is cut integrally together with the flat plate material 150 to obtain the compression spring 2. At this time, similar to the cutting step in the manufacturing method of the eighth embodiment, the pressing jig 125 and the joining machine 126 are moved away from the flat plate material 150 in the plate thickness direction Z. In this state, the second leaf spring material 132 is fed out, and the portion joined in the joining step described above is moved away from the pressing jig 125 and the joining machine 126 in the length direction X and moved to a position where the cutting machine 129 is provided, and is cut by the cutting machine 129.

[0179] In this embodiment, an example is shown in which a long flat plate material 150 on which a plurality of first flat springs 11A and a plurality of third flat springs 13 are formed in the longitudinal direction X is joined to the second flat spring material 132. However, instead of employing the long flat plate material 150, an individual plate material 30 on which the first flat springs 11A and two third flat springs 13 are formed may be used as the flat plate material.

[0180] Furthermore, in this embodiment, as in the tenth embodiment, it is particularly preferable to include a deformation step before the joining step (between the slit forming step and the joining step). In the deformation step, residual stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A in a direction that tensiles the outer surface 23a of the first leaf spring 11A as viewed in the leaf width direction Y, and residual stress is applied to the outer surface 28a of the intermediate portion 28 of the third leaf spring 13 in a direction that tensiles the outer surface 28a of the third leaf spring 13 as viewed in the leaf width direction Y. The deformation step may be the same as the deformation step in the manufacturing method of the second embodiment.

[0181] Furthermore, during the joining process, both ends of the first leaf spring 11A in the longitudinal direction X may be joined to the second leaf spring material 132 while applying a stress to the outer surface 23a of the middle portion 23 of the first leaf spring 11A in a direction that pulls the outer surface 23a of the first leaf spring 11A in a direction along the outer surface 23a of the first leaf spring 11A when viewed from the leaf width direction Y.

[0182] Alternatively, this embodiment may not include the deformation step, and deformation and joining of first leaf spring 11A may be performed simultaneously. Specifically, as in the ninth and eleventh to fourteenth embodiments, during the joining step, both ends of first leaf spring 11A in the longitudinal direction X may be joined to second leaf spring material 132 in a state in which first leaf spring 11A and third leaf spring 13 are elastically deformed so that the size of first leaf spring 11A in the longitudinal direction X is reduced.

[0183] Furthermore, during the joining step, both longitudinal ends of the first leaf spring 11A may be joined to the second leaf spring material 132 while the second leaf spring material 132 is pulled in the longitudinal direction X.

[0184] Furthermore, in this embodiment, the second leaf spring material 132 may be cut in the cutting step, generally in order from one end. Alternatively, the following procedure similar to that of the fifteenth embodiment may be adopted. That is, in the joining step, a plurality of first leaf springs 11A are joined to the second leaf spring material 132 along the longitudinal direction X. Then, of the joint portions of the second leaf spring material 132 with the plurality of first leaf springs 11A, the two joint portions located outermost in the longitudinal direction are cut. Then, in the cutting step, the remaining joint portions are cut.

[0185] Seventeenth Embodiment Next, a method for manufacturing a compression spring 3 according to a seventeenth embodiment of the present invention will be described with reference to Fig. 28. In the manufacturing method of this embodiment, a plurality of continuous compression springs 3 are manufactured for the compression spring 3 of the third embodiment shown in Fig. 7. The manufacturing method of the compression spring 3 of this embodiment involves performing a slit forming step, a joining step, and a cutting step in this order.

[0186] The compression spring 3 includes a first leaf spring 11A, a second leaf spring 12A, a third leaf spring 13, and a fourth leaf spring 14. When viewed from the leaf width direction Y, the third leaf spring 13 has an intermediate portion 28 provided on the opposite side of the first leaf spring 11A, sandwiching the intermediate portion 24 of the second leaf spring 12A in the plate thickness direction Z. An intermediate portion 33 of the fourth leaf spring 14 in the length direction X faces the intermediate portion 28 of the third leaf spring 13 while being spaced apart in the plate thickness direction Z. The first leaf spring 11A and the third leaf spring 13 are included in an integrated plate material 30. The third leaf spring 13 is located at a different position in the plate width direction Y from the first leaf spring 11A. A stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A in a direction that pulls the spring in a direction along the outer surface 23a of the first leaf spring 11A when viewed from the plate width direction Y. A stress is applied to the outer surface 28a of the intermediate portion 28 of the third leaf spring 13, on the side opposite to the outer surface 23a of the first leaf spring 11A, in a direction that pulls the spring in a direction that pulls the spring in a direction that pulls the spring in a direction that pulls the spring in a direction along the outer surface of the third leaf spring 13 when viewed from the plate width direction Y.

[0187] The slit forming step is performed before the joining step. In the slit forming step, as in the sixteenth embodiment, in the flat plate material 150 formed by integrally connecting a plurality of plate materials 30 in the longitudinal direction X, two or more slits 31 extending in the longitudinal direction are formed in each plate material 30, leaving at least one end, to form a total of three or more first regions A1 and second regions A2.

[0188] In the joining step, both ends (first fixing portions 21) of the first leaf spring 11A of the flat plate material 150 (plate material 30) in the longitudinal direction X are joined to a long second leaf spring material 132A formed by connecting a plurality of second leaf springs 12A together in the longitudinal direction, and both ends (flat portions 27) of the third leaf spring 13 of the flat plate material 150 (plate material 30) in the longitudinal direction X are joined to a long fourth leaf spring material 151 formed by connecting a plurality of fourth leaf springs 14 together in the longitudinal direction. At this time, as in the joining step in the manufacturing method of the eighth embodiment, a holding jig 125 and a joining machine 126 are used to join both ends (in the longitudinal direction X) of the first leaf spring 11A to the second leaf spring material 132A, and both ends (in the longitudinal direction X) of the third leaf spring 13 to the fourth leaf spring material 151.

[0189] In the cutting step, at least the second leaf spring material 132A and the fourth leaf spring material 151 are cut to obtain the compression spring 2. At this time, similar to the cutting step in the manufacturing method of the eighth embodiment, the holding jig 125 and the joining machine 126 are moved away from the flat plate material 150 in the plate thickness direction Z. In this state, the second leaf spring material 132A is fed out, and the portion joined in the joining step described above is moved away from the holding jig 125 and the joining machine 126 in the length direction X and moved to a position where the cutting machine 129 is provided, and cut by the cutting machine 129.

[0190] In this embodiment, it is particularly preferable to include a deformation process before the joining process (between the slit forming process and the joining process), as in the tenth embodiment. In the deformation process, residual stress is applied to the outer surface 23 a of the intermediate portion 23 of the first leaf spring 11A in a direction that tensiles the outer surface 23 a of the first leaf spring 11A as viewed in the leaf width direction Y, and residual stress is applied to the outer surface 28 a of the intermediate portion 28 of the third leaf spring 13 in a direction that tensiles the outer surface 28 a of the third leaf spring 13 as viewed in the leaf width direction Y.

[0191] Furthermore, during the joining process, both ends of the first leaf spring 11A in the longitudinal direction X may be joined to the second leaf spring material 132A while a stress is applied to the outer surface 23a of the intermediate portion 23 of the first leaf spring 11A in a direction that pulls the spring in a direction that follows the outer surface 23a of the first leaf spring 11A when viewed from the plate width direction Y, and both ends of the third leaf spring 13 in the longitudinal direction X may be joined to the fourth leaf spring material 151 while a stress is applied to the outer surface 28a of the intermediate portion 28 of the third leaf spring 13 in a direction that pulls the spring in a direction that follows the outer surface 28a of the third leaf spring 13 when viewed from the plate width direction Y.

[0192] Alternatively, this embodiment may not include the deformation step, and deformation and joining of the first leaf spring 11A and the third leaf spring 13 may be performed simultaneously. Specifically, as in the ninth and eleventh to fourteenth embodiments, during the joining step, both ends of the first leaf spring 11A in the longitudinal direction X may be joined to the second leaf spring material 132A while the first leaf spring 11A and the third leaf spring 13 are elastically deformed so that the size of the first leaf spring 11A in the longitudinal direction X is reduced. During the joining step, both ends of the third leaf spring 13 in the longitudinal direction X may be joined to the fourth leaf spring material 151 while the first leaf spring 11A and the third leaf spring 13 are elastically deformed so that the size of the third leaf spring 13 in the longitudinal direction X is reduced.

[0193] Furthermore, during the joining process, while the second leaf spring material 132A and the fourth leaf spring material 151 are pulled in the longitudinal direction X, both ends of the first leaf spring 11A in the longitudinal direction may be joined to the second leaf spring material 132A, and both ends of the third leaf spring 13 in the longitudinal direction X may be joined to the fourth leaf spring material 151.

[0194] Furthermore, in this embodiment, the second leaf spring material 132A and the fourth leaf spring material 151 may be cut in the cutting step, generally in order from the end. Alternatively, the following procedure similar to that of the fifteenth embodiment may be adopted. That is, in the joining step, a plurality of first leaf springs 11A are joined to the second leaf spring material 132A along the longitudinal direction X, and a plurality of third leaf springs 13 are joined to the fourth leaf spring material 151 along the longitudinal direction X. Then, of the joint portions between the second leaf spring material 132A and the fourth leaf spring material 151 and the plurality of first leaf springs 11A and the plurality of third leaf springs 13, the two joint portions located outermost in the longitudinal direction are cut. Then, in the cutting step, the remaining joint portions are cut.

[0195] 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.

[0196] 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.

[0197] 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 in the longitudinal direction of the first leaf spring) 22 Second fixing portion (fixing portion, both ends in the longitudinal direction of the second leaf spring) 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 in the longitudinal direction of the third leaf spring) 28 Intermediate portion of third leaf spring 33 Intermediate portion of fourth leaf spring 34 Both ends X Longitudinal direction Y Plate width direction Z Plate thickness direction

Claims

1. A compression spring comprising 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 thickness direction, wherein the longitudinal middle portions of the first leaf spring and the second leaf spring face each other while being spaced apart in the thickness direction, wherein 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, wherein a residual stress is applied to the outer surface side of the middle portion of the first leaf spring that is opposite the second leaf spring in the thickness direction in a direction that pulls the middle portion of the second leaf spring along the outer surface of the first leaf spring as viewed in the width direction, and wherein the middle portion of the second leaf spring is in an unloaded state in the longitudinal direction.

2. A compression spring as claimed in claim 1, wherein the intermediate portion of the first leaf spring is curved in the thickness direction so as to present a protruding curve facing away from the intermediate portion of the second leaf spring when viewed in the width direction, the intermediate portion of the first leaf spring has residual stress applied to the inner side of the intermediate portion of the first leaf spring that is the second leaf spring side along the thickness direction in a direction compressing the intermediate portion in a direction along the inner surface of the first leaf spring when viewed in the width direction, and the fixed portion extends straight in the length direction when viewed in the width direction.

3. A compression spring as described in claim 1 or 2, further comprising 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 plate thickness direction, when viewed in the plate width direction.

4. The compression spring according to claim 3, wherein the first leaf spring and the third leaf spring are included in an integral plate material, the plate material has two or more slits extending in the longitudinal direction, the third leaf spring is located at a different position from the first leaf spring in the plate width direction, and a total of three or more of the first leaf spring and the third leaf spring are formed on the plate material.

5. The compression spring according to claim 4, wherein the first leaf springs and the third leaf springs are alternately provided on the plate in the plate width direction.

6. The compression spring according to claim 4, wherein the first leaf spring and the third leaf spring are arranged symmetrically with respect to the center of the leaf width direction.

7. The compression spring as claimed in claim 4, further comprising a fourth leaf spring, the intermediate portion of which faces the intermediate portion of the third leaf spring while being spaced apart in the plate thickness direction, the intermediate portion being in an unloaded state in the longitudinal direction, and both ends of at least one of the third leaf springs in the longitudinal direction being joined to both ends of the fourth leaf spring in the longitudinal direction.

8. A compression spring as described in claim 3, wherein the first leaf spring and the third leaf spring are symmetrical in shape with respect to a 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. A compression spring as described in claim 3, wherein the first leaf spring and the third leaf spring have continuous outer peripheries when viewed in the leaf width direction, and the inner circumferential surfaces of both end portions in the longitudinal direction of the first leaf spring and the inner circumferential surfaces of both end portions in the longitudinal direction of the third leaf spring are joined to both end portions in the longitudinal direction of the second leaf spring.

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

11. A compression spring structure comprising two compression springs according to claim 10, the two compression springs being provided in a state where they are inverted in the plate thickness direction, and the second leaf springs of the two compression springs being provided in a state where they are stacked in the plate thickness direction.

12. A method for manufacturing a compression spring as claimed in claim 1 or 2, comprising: a deformation step of plastically deforming a flat 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 a residual stress in a pulling direction along the outer surface of the first leaf spring as viewed in the plate width direction to the outer surface side of the middle 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 plate width direction to the inner surface side of the middle portion of the first leaf spring; 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.

13. A method for manufacturing a compression spring according to claim 4, comprising the steps of: forming two or more slits in a flat plate material, leaving at least one end, extending in the length direction, thereby forming a total of three or more first regions and second regions; a deformation process of plastically deforming the first region so that an outer surface side of a portion intended to form a middle portion of the first leaf spring 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 middle portion of the first leaf spring and 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 middle portion of the first leaf spring, and plastically deforming the second region in a direction opposite to the portion intended to form a middle portion of the first leaf spring so that an outer surface side of a portion intended to form a middle portion of the third leaf spring becomes a protrusion, imparting a residual stress in a tensile direction along the outer surface of the third leaf spring as viewed in the leaf width direction to the outer surface side of the middle portion of the third leaf spring and 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 middle portion of the third leaf spring; 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 a plate thickness direction while maintaining an intermediate 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, comprising the steps of: forming two or more slits in a flat plate material, leaving at least one end, extending in the length direction, thereby forming a total of three or more first regions and second regions; a deformation process of plastically deforming the first region so that an outer surface side of a portion intended to form a middle portion of the first leaf spring becomes a protrusion, imparting a residual stress in a direction that tensilely extends along the outer surface of the first leaf spring as viewed in the leaf width direction to the outer surface side of the middle portion of the first leaf spring and a residual stress in a direction that compresses the inner surface of the first leaf spring as viewed in the leaf width direction to the inner surface side of the middle portion of the first leaf spring, and plastically deforming the second region in a direction opposite to the portion intended to form a middle portion of the first leaf spring so that an outer surface side of a portion intended to form a middle portion of the third leaf spring becomes a protrusion, imparting a residual stress in a direction that tensilely extends along the outer surface of the third leaf spring as viewed in the leaf width direction to the outer surface side of the middle portion of the third leaf spring and a residual stress in a direction that compresses the inner surface of the third leaf spring as viewed in the leaf width direction to the inner surface side of the middle portion of the third leaf spring; 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 of the plate thickness direction while maintaining an intermediate portion of the second leaf spring in an unloaded state in the longitudinal direction, and stacking and joining both longitudinal ends of the third leaf spring to both longitudinal ends of the fourth leaf spring on the other side of the plate thickness direction while maintaining an intermediate portion of the fourth leaf spring in an unloaded state in the longitudinal direction.

15. A method for manufacturing a compression spring as claimed in claim 8, comprising the steps of: plastically deforming a first flat leaf spring material so that an outer surface side of a portion intended to form a middle section becomes a protrusion, imparting a residual stress in a direction tensile along the outer surface of the first leaf spring as viewed in the plate width direction to the outer surface side of the middle section of the first leaf spring, and imparting a residual stress in a direction compressive along the inner surface of the first leaf spring as viewed in the plate width direction to the inner surface side of the middle section of the first leaf spring; and plastically deforming a third flat leaf spring material so that an outer surface side of a portion intended to form a middle section becomes a protrusion, imparting a residual stress in a direction tensile along the outer surface of the third leaf spring as viewed in the plate width direction to the outer surface side of the middle section of the third leaf spring, and imparting a residual stress in a direction compressive along the inner surface of the third leaf spring as viewed in the plate width direction to the inner surface side of the middle section of the third leaf spring; 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 a plate thickness direction while maintaining an intermediate 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.

16. A method for manufacturing a compression spring as claimed in claim 9, comprising: a molding step of crushing a tubular material using a die to continuously form the first and third leaf springs so that both end sides in a predetermined radial direction of the tubular material are flattened and central portions are spaced apart to present a protruding curved shape, and the first and third leaf springs have shapes symmetrical with respect to the one direction of the tubular material; an inserting step of inserting the second leaf spring between the first and third leaf springs; and a joining step of joining both longitudinal end portions of the second leaf spring to the flat portions of the first and third leaf springs.

17. A method for manufacturing a compression spring as described in claim 10, comprising a molding step of crushing a tubular material using a mold to mold one side of the tubular material in a predetermined radial direction of the tubular material into a flat shape when viewed in the axial direction of the tubular material, and to mold the other side in the one direction so that its central portion in a direction perpendicular to the one direction presents a curved shape protruding toward the other side in 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 one integrated unit in which the flat portion of the first leaf spring and the flat portion of the second leaf spring are continuous.

18. A method for manufacturing a compression spring, comprising a first leaf spring and a second leaf spring extending in a longitudinal direction, both longitudinal ends of the first leaf spring being joined to both longitudinal ends of the second leaf spring by stacking in the thickness direction, the longitudinal middle portions of the first leaf spring and the second leaf spring facing each other while being spaced apart 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 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, and a stress is applied to the outer surface side of the middle portion of the first leaf spring that is opposite the second leaf spring in the thickness direction in a direction pulling the middle portion of the first leaf spring along the outer surface of the first leaf spring as viewed in the width direction, the method comprising the steps of: joining both longitudinal ends of the first leaf spring to a long second leaf spring material formed by connecting a plurality of the second leaf springs together in the longitudinal direction; a cutting step of cutting at least the second leaf spring material to obtain the compression spring, in this order.

19. A method for manufacturing a compression spring as described in claim 18, wherein during the joining process, both longitudinal ends of the first leaf spring are joined to the second leaf spring material while applying a stress to the outer surface side of the middle portion of the first leaf spring in a pulling direction along the outer surface of the first leaf spring when viewed in the leaf width direction.

20. A method for manufacturing a compression spring as described in claim 19, wherein prior to the joining process, residual stress is imparted to the outer surface side of the middle portion of the first leaf spring in a direction pulling the spring in a direction along the outer surface of the first leaf spring when viewed in the leaf width direction.

21. A method for manufacturing a compression spring as described in claim 19 or 20, wherein the joining step joins both longitudinal ends of the first leaf spring to the second leaf spring material while the first leaf spring is elastically deformed so that the longitudinal size of the first leaf spring is reduced.

22. A method for manufacturing a compression spring as described in any one of claims 18 to 20, wherein during the joining step, both longitudinal ends of the first leaf spring are joined to the second leaf spring material while the second leaf spring material is stretched in the longitudinal direction.

23. The compression spring further comprises 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 when viewed from the leaf width direction; the first leaf spring and the third leaf spring are arranged symmetrically with respect to the center of the second leaf spring in the thickness direction; both ends of the third leaf spring in the length direction are stacked and joined to both ends of the second leaf spring in the length direction on the opposite side to the first leaf spring in the thickness direction; the intermediate portions of the first leaf spring, the second leaf spring, and the third leaf spring in the length direction face each other while being spaced apart in the thickness direction; the length of the intermediate portion of the second leaf spring along the surface of the second leaf spring when viewed from the leaf width direction is shorter than the length of the intermediate portion of the first leaf spring along the surface of the first leaf spring and the length of the intermediate portion of the third leaf spring along the surface of the third leaf spring when viewed from the leaf width direction; 19. The method for manufacturing a compression spring according to claim 18, wherein a stress is applied to an outer surface side of an intermediate portion of the third leaf spring, which is opposite the second leaf spring in the plate thickness direction, in a direction pulling the third leaf spring in a direction along the outer surface of the third leaf spring as viewed from the plate width direction, and in the joining step, both end portions in the longitudinal direction of the first leaf spring and both end portions in the longitudinal direction of the third leaf spring are joined to the second leaf spring material.

24. The method for manufacturing a compression spring as set forth in claim 18, wherein the compression spring further comprises a third leaf spring having an intermediate portion provided on the opposite side of the first leaf spring and sandwiching an intermediate portion of the second leaf spring in the plate thickness direction when viewed in the plate width direction, the first leaf spring and the third leaf spring are included in an integral plate material, and the third leaf spring is located at a different position from the first leaf spring in the plate width direction, and a stress is applied to the intermediate portion of the third leaf spring on an outer surface side opposite to the outer surface side of the first leaf spring in a direction pulling the third leaf spring in a direction along the outer surface of the third leaf spring when viewed in the plate width direction, and the method further comprises a slit forming step, prior to the joining step, of forming two or more slits in the flat plate material extending in the length direction, leaving at least one end, to form three or more first regions and second regions in total, and in the joining step, both longitudinal ends of the first leaf spring of the flat plate material are joined to the second leaf spring material.

25. The compression spring further comprises 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 plate thickness direction when viewed in the plate width direction, and a fourth leaf spring having an intermediate portion in the longitudinal direction opposed to the intermediate portion of the third leaf spring while being spaced apart in the plate thickness direction; the first leaf spring and the third leaf spring are included in an integral plate material, and the third leaf spring is located at a position different from that of the first leaf spring in the plate width direction; a stress is applied to the intermediate portion of the third leaf spring on the outer surface side opposite to the outer surface side of the first leaf spring in a direction pulling the third leaf spring in a direction along the outer surface of the third leaf spring when viewed in the plate width direction; and a slit forming process is carried out prior to the joining process, in which two or more slits are formed in the flat plate material extending in the longitudinal direction, leaving at least one end, to form a total of three or more first regions and second regions; 19. The method for manufacturing a compression spring according to claim 18, wherein in the joining step, both longitudinal ends of the first leaf spring of the flat plate material are joined to the second leaf spring material, and both longitudinal ends of the third leaf spring of the flat plate material are joined to a long fourth leaf spring material constituted by a plurality of the fourth leaf springs connected together in the longitudinal direction, and in the cutting step, at least the second leaf spring material and the fourth leaf spring material are cut to obtain the compression spring.

26. A method for manufacturing a compression spring as set forth in claim 24 or 25, comprising a deformation process between the slit forming process and the joining process, for imparting a residual stress in a pulling 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 for imparting a residual stress in a pulling direction along the outer surface of the third leaf spring as viewed in the leaf width direction and in the opposite direction to the first leaf spring to the outer surface side of the intermediate portion of the third leaf spring.

27. A method for manufacturing a compression spring as described in any one of claims 18 to 20, wherein during the joining step, a plurality of the first leaf springs are joined to the second leaf spring material along the longitudinal direction, and during the cutting step, of the joints between the second leaf spring material and the plurality of first leaf springs, two joints that are located outermost in the longitudinal direction are cut, and then the remaining joints are cut to obtain a plurality of the compression springs.

28. A method for manufacturing a compression spring as described in any one of claims 18 to 20, wherein the joining step joins both longitudinal ends of the first leaf spring included in a long first leaf spring material formed by connecting a plurality of the first leaf springs together in the longitudinal direction to the second leaf spring material, and the cutting step cuts the second leaf spring material integrally together with the first leaf spring material.

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