Spring plunger and manufacturing method therefor

Abstract

A spring plunger (1) has a cylindrical shape that extends along an axis (L), is open at least on a second direction side (X2), and is rotationally symmetrical with respect to the axis (L). The spring plunger comprises: a protrusion (2) which comprises a tip (21) positioned on a first direction side (X1) and a rear end (22) connected to the second direction side (X2) of the tip (21) and having an inner diameter larger than that of the tip (21); and a spring (3) having a compression spring structure extending coaxially with the protrusion (2) and being integrated with the protrusion (2) with the end of the spring on the first direction side (X1) inserted into the tip of the protrusion (2) in a lightly press-fitted state, the second direction side (X2) protruding, in a non-compressed state, from the rear end (22) of the protrusion (2). This spring plunger (1) is easily incorporated into a device, enables fine adjustment of the spring load, and makes the spring (3) less likely to tilt.

Description

Spring plunger and method of manufacturing the same

[0001] The present invention relates to a spring plunger and a method for manufacturing the same.

[0002] In order to obtain a good clicking sensation when operating a switch device or the like, a spring plunger is used, which includes a spring having a compression spring structure and a protrusion such as a ball, pin, or cap that is biased by the spring (see, for example, Patent Document 1).

[0003] The switch device disclosed in Patent Document 1 includes a case (31), a cam (37) that rotates at a position facing the bottom of the case (31), and a spring plunger disposed in a hollow portion (37d) of the cam (37) so as to be in sliding contact with the bottom of the case (31). The spring plunger is composed of a spring (41) and a hollow cap-shaped protrusion (40) biased by the spring (41). In the switch device disclosed in Patent Document 1, the spring plunger fits into a detent valley (31d) that sandwiches a detent ridge (31c) formed on the bottom of the case (31), thereby determining the rotational position of the cam (37), resulting in a good operating feel.

[0004] Furthermore, in the spring plunger used in the switch device disclosed in Patent Document 1, the protrusion (40) and the spring (41) are not integrated, and their relative positions are fixed only after they are incorporated into the device, making handling them until assembly difficult. However, spring plungers that make handling easier until assembly have also appeared (see, for example, Non-Patent Document 1).

[0005] The spring plunger disclosed in Non-Patent Document 1 consists of a hollow cap-shaped protrusion and a spring inserted into the protrusion. This spring plunger has a protrusion (dowel) formed at one location on the inner peripheral surface by striking the peripheral wall of the protrusion from the outer periphery inward with a punch or the like, and the spring inserted into the protrusion is caught on this protrusion and does not come out, thereby integrating the protrusion and spring. As a result, when incorporating the spring plunger disclosed in Non-Patent Document 1 into a device, the protrusion and spring can be handled as a single unit without being separated, making it easy to incorporate into the device.

[0006] Japanese Patent Application Publication No. 9-134641

[0007] http: / / konishi-mfg.com / goods / plun / gn31.php

[0008] However, in the spring plunger disclosed in Non-Patent Document 1, the spring is caught on a protrusion on the inner peripheral surface of the protrusion, fixing the spring to the protrusion, so that overall length adjustment (spring projection adjustment) can only be made in increments of the winding pitch of the spring, which can result in poor load accuracy. Also, in the spring plunger disclosed in Non-Patent Document 1, the spring is fixed by a protrusion that protrudes laterally from one point on the inner peripheral surface, so that in particular when the gap (clearance) between the inner diameter dimension of the protrusion and the outer diameter dimension of the spring is large, the spring can be fixed at an angle to the protrusion, resulting in poor movement accuracy.

[0009] In view of the above, an object of the present invention is to provide a spring plunger that is easy to incorporate into a device, allows fine adjustment of the spring load, and is less likely to tilt, and also to provide a method for manufacturing such a spring plunger.

[0010] In order to solve the above problem, the spring plunger of the present invention is characterized by comprising: a protrusion that extends along an axis extending from a first direction side to a second direction side, that is open at least on the second direction side and has a cylindrical shape that is rotationally symmetrical about the axis, that has a tip portion located on the first direction side and a rear end portion that is connected to the second direction side of the tip portion and has an inner diameter dimension larger than that of the tip portion; and a spring that has a compression spring structure that extends coaxially with the protrusion, that has an end on the first direction side that is lightly pressed into the inside of the tip portion of the protrusion and is integrated with the protrusion, and that has a spring that protrudes on the second direction side from the rear end portion of the protrusion when not compressed.

[0011] In the spring plunger according to the present invention, the end face of the projection on the first direction side is hemispherical.

[0012] In addition, in the spring plunger according to the present invention, a gap is secured between the rear end of the projection and the spring.

[0013] In addition, the spring plunger according to the present invention may be configured so that the inner diameter of the tip portion is constant or gradually increases as it goes toward the second direction.

[0014] In addition, in the spring plunger according to the present invention, one or more crimping grooves may be formed at the tip portion, recessed around the outer circumferential surface so that the inner circumferential surface is pushed out and protruded around the entire periphery.

[0015] The method for manufacturing a spring plunger according to the present invention is characterized by comprising: a protrusion setting step of setting a protrusion that extends along an axis extending from a first direction side to a second direction side, has a cylindrical shape that is rotationally symmetrical with respect to the axis, and has a tip portion located on the first direction side and a rear end portion that is connected to the second direction side of the tip portion and has an inner diameter dimension larger than that of the tip portion; and a light press-fitting step of applying a compressive force from the second direction side to the protrusion set in the protrusion setting step, and lightly press-fitting and fitting the end portion on the first direction side to integrate a spring having a compression spring structure with the protrusion.

[0016] The method for manufacturing a spring plunger according to the present invention may further include an overall length adjustment step of releasing the compressive force applied in the light press-fitting step, causing the second direction side of the spring to protrude from the rear end of the projection, and applying compressive or tensile force to the protruding portion of the spring as needed to keep the overall length within a predetermined range.

[0017] The method for manufacturing a spring plunger according to the present invention may further include, after the light press-fitting step, a crimping step in which one or more outer peripheral surfaces of the tip end of the protrusion are pressed inward along the entire circumference to push out and protrude the inner peripheral surface of the protrusion along the entire circumference.

[0018] In the method for manufacturing a spring plunger according to the present invention, in the light press-fitting step, the spring may be lightly press-fitted into the plunger while checking the reaction force of the spring.

[0019] According to the present invention, it is possible to provide a spring plunger that is easy to incorporate into a device, allows fine adjustment of the spring load, and is less likely to tilt, and also to provide a method for manufacturing such a spring plunger.

[0020] Fig. 1 is an external view of a spring plunger according to embodiment 1. Fig. 2 is a longitudinal cross-sectional view of the spring plunger of Fig. 1. Fig. 3 is a flowchart showing a method for manufacturing the spring plunger according to embodiment 1. Fig. 4 is a longitudinal cross-sectional view of a spring plunger according to embodiment 2. Fig. 5 is a longitudinal cross-sectional view of a spring plunger according to embodiment 3. Fig. 6 is a flowchart showing a method for manufacturing the spring plunger according to embodiment 3. Fig. 7 is an external view showing a modified example of a protrusion.

[0021] A spring plunger according to an embodiment of the present invention will be described below with reference to the drawings. Note that the drawings do not necessarily reflect the actual dimensions.

[0022] [Embodiment 1] (Configuration of spring plunger 1) Fig. 1 is an external view showing the appearance of spring plunger 1 of embodiment 1, and Fig. 2 is a longitudinal cross-sectional view thereof. The spring plunger 1 of embodiment 1 is used to constitute a positioning mechanism, a click mechanism, a stopper mechanism, etc. by sliding against a mating part having a ridge, groove, hole, etc. in an intermittent switch such as a dial switch or a slide switch, or a moving mechanism, for example.

[0023] As shown in Figures 1 and 2, the spring plunger 1 includes a cylindrical projection 2 extending along an axis L extending from a first direction side X1 to a second direction side X2, and a spring 3 having a compression spring structure, with at least the end portion on the first direction side X1 fitted into the cylindrical projection 2.

[0024] The protrusions 2 are made of metal or resin, and have a hemispherical end face on the first direction side X1, an open end on the second direction side X2, and a cylindrical shape with a bottom that is rotationally symmetrical with respect to the axis L. The protrusions 2 have thin, uniformly thick side walls. The protrusions 2 each have a tip end 21 located on the first direction side X1, and a rear end 22 that connects to the tip end 21 on the second direction side X2.

[0025] The tip portion 21 is composed of a hemispherical portion 21a on the first direction side X1 and a cylindrical portion 21b with a constant inner diameter that extends straight from the end of the hemispherical portion 21a toward the second direction side X2 for a predetermined length. The cylindrical portion 21b of the tip portion 21 has a specified inner diameter so that a spring 3 (described later) can be lightly press-fitted into it, and a specified length so that the spring 3 can be held when lightly press-fitted.

[0026] The rear end 22 comprises a tapered portion 22a that is connected to the front end 21 and gradually increases in diameter toward the second direction X2, and a cylindrical portion 22b that has a constant inner diameter and extends straight from the end of the tapered portion 22a toward the second direction X2 for a predetermined length. The inner diameter of the cylindrical portion 22b of the rear end 22 is set so that it is larger than the inner diameter of the cylindrical portion 21b of the front end 21 and the outer diameter of the spring 3 (described below). The length of the rear end 22 is set appropriately based on the installation location, the amount by which the spring 3 is desired to enter the protrusion 2 when compressed, how the spring 3 is to be restricted from collapsing, etc. The rear end portion 22 may have chamfered corners on the inner diameter side of the mouth to make it easier to guide the spring 3 when press-fitting it, or may have chamfered corners on the outer diameter side of the mouth to make it easier to slide against the mating side when in use, or may have protrusions arranged rotationally symmetrically around the periphery to make it harder to turn against the mating side when in use.

[0027] The spring 3 is a so-called coil spring having a compression spring structure, and extends coaxially with the projection 2. The spring 3 is wound at an equal pitch with a constant diameter, and its end on the first direction side X1 is lightly press-fitted into the inside of the tip end 21 of the projection 2, making it one with the projection 2. When the spring 3 is not compressed, its second direction side X2 protrudes from the rear end 22 of the projection 2. A gap is secured between the inner wall surface of the rear end 22 of the projection 2 and the spring 3, allowing the spring 3 to smoothly expand and contract within the rear end 22 of the projection 2.

[0028] The spring plunger 1 configured in this manner, in which the protrusion 2 and the spring 3 are integral, is installed in, for example, a blind hole formed in a member to be incorporated, and is used. In the installed spring plunger 1, when the tip 21 of the protrusion 2 is pressed toward the second direction side X2 with the second direction side end face of the spring 3 abutting against a fixed surface of the member to be incorporated, the portion of the spring 3 located toward the second direction side relative to the tip 21 of the protrusion 2 bends and its overall length becomes shorter, and a biasing force (reaction force) that tries to push the tip 21 of the protrusion 2 back toward the first direction side X1 is generated in accordance with the amount of bending.

[0029] (Manufacturing Method of Spring Plunger 1) Figure 3 is a flowchart showing a manufacturing method of the spring plunger 1 according to the first embodiment. Next, the manufacturing method of the spring plunger 1 will be described with reference to Figure 3. As shown in Figure 3, the spring plunger 1 is manufactured through a thrust setting process ST1, a light press-fitting process ST2, a total length adjustment process ST3, a reaction force measurement process ST4, and an appearance inspection process ST5, in that order.

[0030] First, in the protrusion setting step ST1, the protrusion 2 is set in the manufacturing equipment with the hemispherical portion 21a of the tip 21 facing the first direction side X1.

[0031] Next, in the light press-fitting step ST2, the spring 3 is set in a position coaxial with the second direction side X2 of the projection 2 set in the projection setting step ST1, and a compressive force is applied to the spring 3 from the second direction side X2 to lightly press-fit the end of the spring 3 on the first direction side X1 into the tip 21 of the projection 2, thereby integrating the spring 3 with the projection 2.

[0032] Next, in the overall length adjustment process ST3, the compressive force applied in the light press-fitting process ST2 is released, and the second direction side X2 of the spring 3 is caused to protrude from the rear end 22 of the projection 2. Then, the overall length of the spring plunger 1 or the extension of the spring 3 from the projection 2 is measured, and if it is longer than specified, a compressive force is applied to the spring 3 from the second direction side X2, or if it is shorter than specified, a tensile force is applied to the spring 3 toward the second direction side X2, thereby adjusting the overall length of the spring plunger 1 to fall within a predetermined range.

[0033] Next, in the reaction force measuring step ST4, the spring plunger 1 whose overall length has been adjusted in the overall length adjusting step ST3 is deflected, and an inspection device including a pressure gauge is used to measure whether the reaction force is within a predetermined range.

[0034] Next, in the appearance inspection process ST5, the final appearance is inspected visually or using an inspection device including a camera to check whether the spring 3 has fallen off, whether the spring 3 is installed at an angle, whether the overall length is within a predetermined range, whether the outer diameter is within a predetermined range, whether there are any scratches or dents that would result in a defect, etc. The spring plunger 1 is completed through the above processes.

[0035] (Operations and Effects) The spring plunger 1 of the first embodiment has a cylindrical shape that is rotationally symmetrical about the axis L, and includes a protrusion 2 having a tip end 21 located on the first direction side X1 and a rear end 22 that is connected to the tip end 21 on the second direction side X2 and has a larger inner diameter than the tip end 21, and a spring 3 that is lightly press-fit into the inside of the tip end 21 of the protrusion 2 and is integrated with the protrusion 2, and whose second direction side X2 protrudes from the rear end 22 of the protrusion 2 in an uncompressed state. In other words, in the spring plunger 1, the spring 3 is lightly press-fit into the tip end 21 of the protrusion 2, and a portion of the outer peripheral surface of the spring 3 on the first direction side X1 is held evenly, thereby integrating the protrusion 2 and the spring 3. Therefore, since the protrusion 2 and the spring 3 are integrated, the spring plunger 1 is easy to handle and to incorporate into a device. Furthermore, with the spring plunger 1, the outer peripheral surface of the spring 3 is held by light press-fitting onto the tip 21 of the projection 2, so the projection 2 and the spring 3 can be shifted in the axial direction without separating them. Furthermore, with the spring plunger 1, the outer peripheral surface of the spring 3 is held evenly onto the tip 21 of the projection 2, so the spring 3 is less likely to tilt relative to the projection 2. Therefore, the spring plunger 1 is easy to incorporate into a device, allows fine adjustment of the spring load, and is a spring plunger that is less likely to tilt.

[0036] Furthermore, according to the spring plunger 1, the end face of the protrusion 2 on the first direction side X1 is hemispherical, so when the spring plunger 1 is incorporated into a device, it can smoothly slide into contact with a mating part that has ridges, grooves, holes, etc.

[0037] Furthermore, according to the spring plunger 1, a gap is secured between the rear end portion 22 of the protrusion 2 and the spring 3, so that the spring 3 can move smoothly when expanding and contracting.

[0038] The manufacturing method of the spring plunger 1 of the first embodiment includes a projection setting step ST1 in which the projection 2 is set, and a light press-fitting step ST2 in which the spring 3 is lightly press-fitted into the projection 2 to be integrated with the projection 2. According to this manufacturing method, it is possible to manufacture the spring plunger 1 in which the projection 2 and the spring 3 are integrated, which achieves the above-mentioned effects.

[0039] Furthermore, in the manufacturing method of the spring plunger 1 of embodiment 1, the compressive force applied in the light press-fitting step ST2 is released, the spring 3 is protruded from the protrusion 2, and an overall length adjustment step ST3 is performed in which a compressive force or a tensile force is applied to the protruding portion of the spring 3 as necessary to keep the overall length within a predetermined range, so that a spring plunger 1 with good overall length accuracy can be manufactured.

[0040] Furthermore, in the manufacturing method of the spring plunger 1 of embodiment 1, a reaction force measurement process ST4 is performed in which the spring plunger 1 is bent and the reaction force is measured to see if it is within a predetermined range, so that a spring plunger 1 with good accuracy in the spring force of the protrusion 2 can be manufactured.

[0041] [Embodiment 2] Figure 4 is a longitudinal cross-sectional view of a spring plunger 101 according to embodiment 2. The spring plunger 101 according to embodiment 2 has the same basic configuration as the spring plunger 1 according to embodiment 1, but the shape of the protrusion is slightly different from that of the spring plunger 1 according to embodiment 1. The spring plunger 101 according to embodiment 2 will be described below. Note that the shape of the spring 3 is the same as that of embodiment 1, and therefore the same reference numerals in Figure 4 as in Figure 2 are used, and description thereof will be omitted.

[0042] In the spring plunger 101, the protrusion 102 has a hemispherical end face on the first direction side X1, an open end on the second direction side X2, and a cylindrical shape with a bottom that is rotationally symmetrical with respect to the axis L. The protrusion 102 has a thin, uniformly thick side wall. The protrusion 102 comprises a tip end 121 located on the first direction side X1 and a rear end 122 that connects to the tip end 121 on the second direction side X2.

[0043] The tip portion 121 is composed of a hemispherical portion 121a on the first direction side X1 and a tapered cylindrical portion 121b whose inner diameter gradually increases from the end of the hemispherical portion 121a toward the second direction side X2, unlike in embodiment 1. The tapered cylindrical portion 121b of the tip portion 121 has a tapered inner diameter dimension that is specified so that the spring 3 can be lightly press-fitted into it.

[0044] The rear end portion 122 has a constant inner diameter and extends straight a predetermined length toward the second direction side X2 from the end of the tapered cylindrical portion 121b of the front end portion 121. The rear end portion 122 has an inner diameter that is set larger than the inner diameter of the front end portion 121 and the outer diameter of the spring 3.

[0045] In the spring plunger 101, the inner diameter of the tip portion 121 gradually increases toward the second direction side X2, but similar to the spring plunger 1 of embodiment 1, the spring 3 is lightly press-fitted into the tip portion 121 of the protrusion 102, and part of the outer circumferential surface of the spring 3 on the first direction side X1 is held uniformly, thereby integrating the protrusion 102 and the spring 3. Therefore, the spring plunger 101 has the same effects as the spring plunger 1 of embodiment 1 described above.

[0046] [Embodiment 3] Figure 5 is a longitudinal cross-sectional view of a spring plunger 201 according to embodiment 3, and Figure 6 is a flowchart showing a method for manufacturing the spring plunger 201. The spring plunger 201 according to embodiment 3 has the same basic configuration as the spring plunger 1 according to embodiment 1, but the shape of the protrusion is slightly different from that of the spring plunger 1 according to embodiment 1, and the manufacturing method is also slightly different to form this different shape. The spring plunger 201 according to embodiment 3 will be described below. Note that the shape of the spring 3 is the same as that of embodiment 1, and therefore the same reference numerals in Figure 5 as in Figure 2 are used, and description thereof will be omitted.

[0047] In the spring plunger 201, the protrusion 202 has a hemispherical end face on the first direction side X1, an open end on the second direction side X2, and a cylindrical shape with a bottom that is rotationally symmetrical with respect to the axis L. The protrusion 202 has a thin, uniformly thick side wall. The protrusion 202 comprises a tip end 221 located on the first direction side X1 and a rear end 222 that connects to the tip end 221 on the second direction side X2.

[0048] The tip portion 221 is composed of a hemispherical portion 221a on the first direction side X1 and a cylindrical portion 221b extending a predetermined length from the end of the hemispherical portion 221a toward the second direction side X2. The cylindrical portion 221b of the tip portion 221 has an inner diameter dimension that is specified so that the spring 3 can be lightly press-fitted, and a length dimension that is specified so that the spring 3 can be held when the spring 3 is lightly press-fitted, similar to the cylindrical portion 21b of the tip portion 21 of embodiment 1. However, the cylindrical portion 221b of the tip portion 221 has a different shape from the cylindrical portion 21b of the tip portion 21 of embodiment 1 in that the cylindrical portion 221b has a plurality of crimping grooves 221c that are recessed around the outer circumferential surface so that the inner circumferential surface is extruded and protruded around the entire periphery.

[0049] The rear end portion 222 is made up of a tapered portion 222a that is connected to the front end portion 221 and gradually increases in diameter toward the second direction X2, and a cylindrical portion 222b that has a constant inner diameter and extends straight from the end of the tapered portion 222a toward the second direction X2 for a predetermined length. The rear end portion 222 has the same shape as the rear end portion 22 of the first embodiment.

[0050] As shown in FIG. 6, the spring plunger 201 is manufactured through a thrust setting process ST1, a light press-fitting process ST2, a total length adjusting process ST3, a reaction force measuring process ST4, a crimping process ST6, and an appearance inspection process ST5.

[0051] The thrust setting process ST1, the light press-fitting process ST2, the overall length adjustment process ST3, the reaction force measurement process ST4, and the appearance inspection process ST5 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0052] In the crimping process ST6, after the light press-fitting process ST2, after the compressive force is released in the full length adjustment process ST3, or after the reaction force is measured in the reaction force measurement process ST4 (shown as after the reaction force measurement process ST4 in FIG. 6 as an example), the outer circumferential surface of the tip end 221 of the protrusion 202 is pressed inward along the entire circumference, thereby pushing out multiple protrusions along the entire periphery of the inner circumferential surface of the protrusion 202. Crimping grooves 221c are formed on the outer circumferential surface of the tip end 221 of the protrusion 202, and the spring 3 is held by the protrusions formed on the inner circumferential surface so that it is more difficult for it to come out.

[0053] The spring plunger 201 has a crimping groove 221c formed in the tip portion 221, which is recessed around the outer periphery so that the inner periphery is pushed out and protruded all around, and similarly to the spring plunger 1 of embodiment 1, the spring 3 is lightly press-fitted into the tip portion 221 of the protrusion 202 to adjust its overall length, and then a portion of the outer periphery of the spring 3 on the first direction side X1 is evenly held by the crimped protrusion, thereby more firmly integrating the protrusion 202 and the spring 3. Therefore, the spring plunger 201 has the same effects as the spring plunger 1 of embodiment 1 described above.

[0054] Although the present invention has been described based on the above embodiment, the present invention is not limited to the above embodiment and can be embodied in various forms without departing from the spirit of the present invention, and for example, the following modifications are also possible.

[0055] (1) The materials, thicknesses, dimensional relationships, tip shapes, etc. described in the above embodiments are merely examples and can be changed within the scope that does not impair the effects of the present invention.

[0056] (2) In the above embodiment, the spring 3 is described as being wound at an equal pitch, but the present invention is not limited to this. The winding method of the spring may be set as appropriate, such as an equal pitch, an unequal pitch, a pitch that allows partial contact, the number of turns of the seat, the shape of the seat, etc., depending on the design specifications that reflect the requirements of use and the efficiency of manufacturing.

[0057] (3) In the above-described first and second embodiments, the protrusions 2, 102 are described as having thin, uniformly-thick side walls, but the present invention is not limited to this. The protrusions may be rotationally symmetrical cylindrical, have a tip end and a rear end whose inside diameter is larger than that of the tip end, and may be thick-walled or have uneven thickness.

[0058] (4) In the third embodiment described above, a plurality of crimping grooves 221c are formed. However, only one crimping groove may be formed.

[0059] (5) In the above embodiment, the light press-fitting step ST2, the total length adjustment step ST3, and the reaction force measurement step ST4 are described as being performed separately, but the present invention is not limited to this. These steps can also be performed simultaneously (e.g., the light press-fitting step ST2 can incorporate the steps performed in the total length adjustment step ST3 or the reaction force measurement step ST4). Depending on the specifications, the order of the total length adjustment step ST3 and the reaction force measurement step ST4 can be reversed. Depending on the specifications, at least one of the total length adjustment step ST3 and the reaction force measurement step ST4 can be omitted. For example, a pressure gauge can be attached to the press tool used to apply a compressive force in the light press-fitting step ST2, and the spring 3 can be lightly press-fitted into the protrusion 2 while monitoring the reaction force of the spring 3, thereby incorporating the steps performed in the reaction force measurement step ST4 into the light press-fitting step ST2. Also, for example, if the free length is not important during use but the spring force of the protrusion 2 is, the overall length adjustment process ST3 may be omitted, and conversely, if the free length is important during use but the spring force of the protrusion 2 is not, the reaction force measurement process ST4 may be omitted.

[0060] (6) In the above-described embodiment, the protrusions 2, 102, and 202 have been described as having different shapes, but the shape of the protrusions is not limited to these as long as they are rotationally symmetrical about the axis L, the spring is lightly press-fitted, and the outer circumferential surface of the spring is held evenly. The protrusions can also be modified, for example, as follows:

[0061] 7A and 7B are external views showing modified examples of the protrusion, with FIG. 7A showing a first modified example and FIG. 7B showing a second modified example.

[0062] The protrusion 302 in the first modified example shown in FIG. 7( a) has a cylindrical shape with a bottom that is rotationally symmetrical with respect to the axis L, similar to the embodiment, and is composed of a tip portion 321 located on the first direction side X1 and a rear end portion 322 that connects to the tip portion 321 on the second direction side X2. The tip portion 321 has a shape similar to the tip portion 21 in the first embodiment, and is composed of a hemispherical portion 321a on the first direction side X1 and a cylindrical portion 321b that has a constant outer diameter and extends in a straight line from the end of the hemispherical portion 321a toward the second direction side X2 for a predetermined length. The cylindrical portion 321b of the tip portion 321 has a specified inner diameter so that a spring can be lightly press-fitted. The rear end portion 322 has a cylindrical shape that has a constant outer diameter and extends in a straight line toward the second direction side X2. The rear end portion 322 has an outer dimension slightly larger than that of the cylindrical portion 321b of the front end portion 321, and is connected to the front end portion 321 by a step. The rear end portion 322 has an inner diameter dimension that is larger than the inner diameter dimension of the cylindrical portion 321b of the front end portion 321 and the outer diameter dimension of the spring 3.

[0063] The protrusion 402 in the second modified example shown in FIG. 7( b) has a cylindrical shape with a bottom that is rotationally symmetrical about the axis L, similar to the embodiment. It includes a tip portion 421 located on the first direction side X1 and a rear end portion 422 that connects to the tip portion 421 on the second direction side X2. The tip portion 421 has a shape similar to the tip portion 21 in the first embodiment, and includes a hemispherical portion 421a on the first direction side X1 and a cylindrical portion 421b that has a constant inner diameter and extends straight from the end of the hemispherical portion 421a toward the second direction side X2 for a predetermined length. The cylindrical portion 421b of the tip portion 421 has an inner diameter that is specified so that the spring can be lightly press-fitted. The rear end portion 422 has a tapered shape that connects to the tip portion 421 and gradually expands in diameter toward the second direction side X2. The inner diameter of the rear end portion 422 is specified so that it is larger than the outer diameter of the spring 3.

Claims

1. A spring plunger, comprising: a protrusion extending along an axis extending from a first direction side to a second direction side, having a cylindrical shape that is rotationally symmetric with respect to the axis and at least the second direction side is open, including a tip portion located on the first direction side and a rear end portion connected to the second direction side of the tip portion and having an inner diameter larger than that of the tip portion; and a spring having a compression spring structure extending coaxially with the protrusion, wherein an end portion on the first direction side is fitted into the inside of the tip portion of the protrusion in a lightly press-fitted state and integrated with the protrusion, and in a non-compressed state, the second direction side protrudes from the rear end portion of the protrusion.

2. The spring plunger according to claim 1, wherein the protrusion has a hemispherical end face on the first direction side.

3. The spring plunger according to claim 1, wherein a gap is provided between the rear end portion of the protrusion and the spring.

4. The spring plunger according to claim 1, wherein the inner diameter dimension of the tip portion is constant or gradually increases toward the second direction side.

5. The spring plunger according to claim 1, wherein at the tip portion, one or more caulking grooves are formed so as to surround the entire outer peripheral surface and recessed so that the inner peripheral surface protrudes over the entire circumference.

6. A method for manufacturing a spring plunger, comprising: a protrusion setting step of setting a protrusion that extends along an axis extending from a first direction side to a second direction side, has a cylindrical shape that is rotationally symmetric with respect to the axis, includes a tip portion located on the first direction side, and a rear end portion connected to the second direction side of the tip portion and having an inner diameter larger than that of the tip portion; and a lightly press-fitting step of applying a compressive force from the second direction side to the spring having a compression spring structure set in the protrusion setting step and press-fitting the end portion on the first direction side to integrate it with the protrusion.

7. In the method for manufacturing a spring plunger according to claim 6, a full-length adjustment step is further included, in which the compressive force applied in the light press-fitting step is released, the second-direction side of the spring is protruded from the rear end portion of the protrusion, and a compressive force or a tensile force is applied to the protruded portion of the spring as necessary to keep the overall length within a predetermined range.

8. In the method for manufacturing a spring plunger according to claim 6, a caulking step is further included, in which after the light press-fitting step, one or a plurality of outer peripheral surfaces of the tip end portion of the protrusion are pushed inward over the entire circumference to extrude and project the inner peripheral surface of the protrusion over the entire circumference.

9. In the method for manufacturing a spring plunger according to any one of claims 6 to 8, in the light press-fitting step, the spring is lightly press-fitted into the protrusion while checking the reaction force of the spring.

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