Patent Description:
A coil spring obtained by forming a spring wire into a helical shape that axially extends from one side toward the other side is widely used as a valve spring for an internal combustion engine, a spring for a high-pressure pump, and the like.

This coil spring is a component intended to axially exert elastic force when axially compressed, and is known to also produce, in addition to the elastic force in the axial direction, force (lateral force) in the direction perpendicular to the axial direction when compressed.

Desirably, production of lateral force is prevented as much as possible.

That is to say, for example, when lateral force is produced in the case of using the coil spring as a pressing member for pressing a reciprocating plunger, frictional force produced between the plunger and the guide surface where the plunger is reciprocally accommodated is increased.

An increased frictional force leads to increased wear and frictional heat due to sliding resistance to the plunger, and may result in operational problems of an apparatus such as a high-pressure pump where the plunger is used.

In this regard, the first-listed applicant of the present application has proposed a coil spring for reducing lateral force (see Patent Literature <NUM> cited below).

The coil spring described in Patent Literature <NUM> is designed such that the number of active coils between the set height and the maximum height during use is an integer, and thus the coil spring is capable of reducing lateral force compared with coil springs that do not have an integer or near-integer number of active coils.

Meanwhile, the coil spring has end coil parts located at the respective axial ends and a central coil part located between the end coil parts, and the region where there is a space between axially adjacent coils (a space between coils) corresponds to the active coil part.

Patent Literature <NUM> discloses the concept of designing a spring such that the number of coils in the active coil part is an integer, but does not describe a specific configuration that does not allow the number of coils in the active coil part to change during use.

The present invention has been conceived in view of such conventional art, and an object of the present invention is to provide a coil spring capable of preventing production of lateral force as much as possible.

In order to achieve the object, the present invention provides a coil spring according to claim <NUM>. Document <CIT> is considered to represent the closest prior art and discloses the preamble of claim <NUM>.

The coil spring according to the present invention includes a first end coil part having a first bearing surface that is arranged on one side in the axial direction of the coil spring and faces one side in the axial direction of the coil spring, a second end coil part having a second bearing surface that is arranged on the other side in the axial direction of the coil spring and faces the other side in the axial direction of the coil spring, and a central coil part between the first and second end coil parts.

The first end coil part is configured to include a first end coil part edge region that extends from a first end on one side in the longitudinal direction of the spring wire to a part forming the first reference point, and a first end coil part transitional region that extends from the first end coil edge region to the central coil part. The first end coil part edge region is bent toward one side in the axial direction of the coil spring as compared with the first end coil part transitional region.

The first bearing surface is configured to extend from the first end coil part edge region to the first end coil part transitional region across a border between the first end coil part edge region and the first end coil part transitional region.

Preferably, the second end coil part is configured to include a second end coil part edge region that extends from a second end on the other side in the longitudinal direction of the spring wire to a part forming the second reference point, and a second end coil part transitional region that extends from the second end coil edge region to the central coil part. The second end coil part edge region being bent toward the other side in the axial direction of the coil spring as compared with the second end coil part transitional region.

The second bearing surface is configured to extend from the second end coil part edge region to the second end coil part transitional region across a border between the second end coil part edge region and the second end coil part transitional region.

In any one of the above configurations, preferably, the number of turns of helical space from the first reference point to the second reference point is an integral multiple.

Below, one embodiment of the coil spring according to the present invention will now be described with reference to the attached drawings.

<FIG> and <FIG> show a perspective view and a front view, respectively, of a coil spring 1A according to the present embodiment in a natural length state.

As shown in <FIG> and <FIG>, the coil spring 1A according to the present embodiment is obtained by forming a spring wire <NUM> into a helical shape axially extending from one side to the other side, and is suitably used as a valve spring for an internal combustion engine, a spring for a high-pressure pump, and the like.

In reference to the coiling of the spring wire <NUM>, the coil spring 1A has a first end coil part <NUM> including a first end <NUM> on one side in the longitudinal direction of the spring wire <NUM> and having a first bearing surface <NUM> facing one side in the axial direction of the coil spring 1A; a second end coil part <NUM> including a second end <NUM> on the other side in the longitudinal direction of the spring wire <NUM> and having a second bearing surface <NUM> facing the other side in the axial direction of the coil spring 1A; and a central coil part <NUM> between the first and second end coil parts <NUM>, <NUM>.

In the coil spring 1A, the region where there is a space between the coils of the spring wire <NUM> adjacent in the axial direction of the coil spring 1A acts as an active coil part that exerts elastic force.

Hereafter, the space between the axially adjacent coils of the spring wire <NUM> will now be described in detail.

On one side in the axial direction, the space between coils is increased from a first reference point <NUM>, where the space between coils in the natural length state is zero, helically toward the other side in the axial direction; in the central coil part <NUM>, the space between coils is at a reference value L (L><NUM>, see <FIG> below) that is set according to the required elastic force of the coil spring 1A; and on the other side in the axial direction, the space between coils is reduced helically toward the other side in the axial direction and is zero at a second reference point <NUM>.

That is to say, as shown in <FIG>, the helical shape (hereinafter referred to as helical space) formed by the space between coils has, on one side in the axial direction, a first end region <NUM> wherein the space between coils in the natural length state is increased from the first reference point <NUM>, where the space between coils in the natural length state is zero, circumferentially toward the other side in the axial direction along the helical shape; a reference region <NUM> located closer to the other side in the axial direction than the first end region <NUM> is, wherein the space between coils in the natural length state is at the reference value L; and a second end region <NUM> located closer to the other side in the axial direction than the reference region <NUM> is, wherein the space between coils is reduced circumferentially toward the other side in the axial direction along the helical shape, and the space between coils in the natural state is zero at the second reference point <NUM>.

<FIG> is a graph showing the relationship between the number of turns of helical space and the distance of space between coils in the coil spring 1A.

As shown in <FIG>, in the coil spring 1A according to the present embodiment, the first end region <NUM> is configured such that the number of turns of the helical space is greater than <NUM> and the distance of space between coils in the natural length state in a terminal position 61E is greater than the reference value L.

In the present embodiment, as shown in <FIG>, the terminal position 61E of the first end region <NUM> is located at a position corresponding to about <NUM> turns of the helical space from the first reference point <NUM> toward the other side in the axial direction; the reference value L is set at <NUM>; and the distance of space between coils in the natural length state in the terminal position 61E is set at <NUM> (reference value Lx <NUM>).

Moreover, as shown in <FIG>, the coil spring 1A is configured such that the helical space has a first transitional region <NUM>(<NUM>) between the first end region <NUM> and the reference region <NUM>.

The first transitional region <NUM>(<NUM>) is configured such that the distance of space between coils is reduced from the terminal position 61E of the first end region <NUM> along the helical shape of the helical space toward the other side in the axial direction and becomes the reference value L.

This configuration makes it possible to effectively prevent the space between coils from becoming zero in the first end region <NUM> when the coil spring 1A is compressed from the natural length state, and it is thus possible to effectively suppress production of lateral force during compressional operation.

That is to say, in the coil spring 1A, the distance of space between coils at the terminal position 61E of the first end region <NUM> provided on one side in the axial direction is greater than the reference value L.

Accordingly, it is possible to effectively prevent compressional operation of the coil spring 1A as shown in <FIG> from resulting in a change in the number of active coils on one side in the axial direction, and it is thereby possible to effectively suppress production of lateral force during compressional operation.

As shown in <FIG>, in the coil spring 1A according to the present embodiment, the second end region <NUM> is configured such that the number of turns of helical space is greater than <NUM> and the distance of space between coils in the natural length state in the starting position <NUM> is greater than the reference value L.

In the present embodiment, the second end region <NUM> has a configuration substantially identical to the first end region <NUM>.

That is to say, as shown in <FIG>, the starting position <NUM> of the second end region <NUM> is located at a position corresponding to about <NUM> turns of the helical space from the second reference point <NUM> toward one side in the axial direction; and the distance of space between coils in the natural length state at the starting position <NUM> is set at <NUM> (reference value L x <NUM>), which is identical to the distance of space between coils at the terminal position 61E of the first end region <NUM>.

Moreover, as shown in <FIG>, the coil spring 1A is configured such that the helical space has a second transitional region <NUM>(<NUM>) between the reference region <NUM> and the second end region <NUM>.

The second transitional region <NUM>(<NUM>) is configured such that the distance of space between coils is increased from the reference value L as it extends from a terminal position 65E of the reference region <NUM> along the helical shape of the helical space toward the other side in the axial direction until the starting position <NUM> of the second end region <NUM>.

This configuration makes it possible to effectively prevent the space between coils from becoming zero in the second end region <NUM> when the coil spring 1A is compressed from the natural length state, and it is thus possible to effectively suppress production of lateral force during compressional operation.

The coil spring 1A can be manufactured with, for example, a manufacturing apparatus <NUM> shown in <FIG>.

As shown in <FIG>, the manufacturing apparatus <NUM> has feed rollers <NUM> for feeding the spring wire <NUM>; a guide member <NUM> for guiding the spring wire <NUM> conveyed by the feed rollers <NUM>; first and second coiling tools <NUM>(<NUM>), <NUM>(<NUM>) provided downstream in the conveying direction of the spring wire <NUM> that is conveyed by the feed rollers <NUM> while being guided by the guide member <NUM>, wherein the first and second coiling tools <NUM>(<NUM>), <NUM>(<NUM>) forming the helical coil spring 1A from the linear spring wire <NUM>; a core metal member <NUM> for guiding the coil spring 1A formed into a helical shape by the first and second coiling tools <NUM>(<NUM>), <NUM>(<NUM>); a pitch tool <NUM> for adjusting the pitch of the coil spring 1A; and a cutting tool <NUM> for cutting the spring wire <NUM> in cooperation with the core metal <NUM>.

The positions of the first and second coiling tools <NUM>(<NUM>), <NUM>(<NUM>) can be adjusted in the radial direction with reference to the center of the coil spring 1A to be formed, and the coil diameter of the coil spring 1A is changed in accordance with the change of the radial positions of the first and second coiling tools <NUM>(<NUM>), <NUM>(<NUM>).

The position of the pitch tool <NUM> can be adjusted in the radial direction with reference to the center of the coil spring 1A, and the pitch of the coil spring 1A is changed in accordance with the change of the radial position of the pitch tool <NUM>.

The cutting tool <NUM> is radially reciprocable with reference to the center of the coil spring 1A, and is movable between a cutting position for cutting the spring wire <NUM> in cooperation with an engagement surface <NUM> of the core metal <NUM> and a retreated position away from the core metal <NUM>.

Preferably, as shown in <FIG>, the first end region <NUM> has a constant pitch angle of the space between coils from the first reference point <NUM> to the terminal position 61E, and the pitch angle of the space between coils is set such that the displacement of the space between coils per turn of the helical space toward the other side in the axial direction is L.

This configuration facilitates the positioning control of the pitch tool <NUM>.

Likewise, preferably, as shown in <FIG>, the second end region <NUM> has a constant pitch angle of the space between coils from the starting position <NUM> to the second reference point <NUM>, and the pitch angle of the space between coils is set such that the displacement of the space between coils per turn of the helical space toward the other side in the axial direction is -L.

Hereafter, the results of experiments concerning lateral force performed on the coil spring 1A according to the present embodiment and a conventional coil spring will now be described.

As an example (a working example) of the coil spring 1A according to the present embodiment, a coil spring 1a having the following configuration was provided.

Lateral force produced by the coil spring 1a of the working example was measured with a side force spring tester (SFT Series, manufactured by Japan Instrumentation System Co.

As an example (a comparative example) of a conventional coil spring, a coil spring having the following configuration was provided, and a similar experiment was conducted.

Lateral force produced by the comparative example was also measured with the side force spring tester (SFT Series, manufactured by Japan Instrumentation System Co.

As shown in <FIG>, in the working example 1a wherein the number of turns of helical space in the first and second end regions <NUM>, <NUM> is greater than <NUM>, and the distance of space between coils in the terminal position 61E of the first end region <NUM> and in the starting position <NUM> of the second end region <NUM> is greater than the distance of space between coils L in the reference region <NUM>, production of lateral force is significantly suppressed as compared with the comparative example.

This result means that with the coil spring 1a according to the working example, it is possible to effectively prevent the space between coils from becoming zero in the first and second end regions <NUM>, <NUM> during compressional operation.

Preferably, the coil spring 1A is configured such that the number of turns of helical space from the first reference point <NUM> to the second reference point <NUM> is an integral multiple.

That is to say, the coil spring 1A is configured such that the first reference point <NUM> and the second reference point <NUM> are located in circumferentially the same positions.

This configuration makes it possible to more effectively prevent production of lateral force during compressional operation.

Preferably, a region of the first end coil part <NUM>, which is located closer to the end side than the first reference point <NUM> is, can be bent toward one side in the axial direction.

<FIG> shows a partial front view of a modification 1B wherein a region of the first end coil part <NUM>, which is located more toward the end side than the first reference point <NUM> is, is bent toward one side in the axial direction.

As shown in <FIG>, in the modification 1B, the first end coil part <NUM> includes a first end coil part edge region <NUM> extending from a first end <NUM> on one side in the longitudinal direction of the spring wire <NUM> to a part that forms the first reference point <NUM>, and a first end coil part transitional region <NUM> extending from the first end coil edge region <NUM> to the central coil part <NUM>.

The first end coil part edge region <NUM> is bent toward one side in the axial direction of the coil spring 1B as compared with the first end coil part transitional region <NUM>, and the first bearing surface <NUM> is formed so as to cross the border shared with the first end coil part transitional region <NUM> from the first end coil part edge region <NUM> and reach the first end coil part transitional region <NUM>.

The modification 1B having this configuration makes it possible to provide a thick first end coil part <NUM> while ensuring the flatness of the first bearing surface <NUM> by sufficiently securing the amount by which the first bearing surface <NUM> can be polished, and thus makes it possible to further reduce production of lateral force during compressional operation.

Naturally, the same configuration is also applicable to the second end coil part <NUM>.

Claim 1:
A coil spring (1B) having a spring wire (<NUM>) formed into a helical shape axially extending from one side to the other side so as to include a first end coil part (<NUM>) having a first bearing surface (<NUM>) that is arranged on one side in the axial direction of the coil spring (1B) and faces one side in the axial direction of the coil spring (1B), a second end coil part (<NUM>) having a second bearing surface (<NUM>) that is arranged on the other side in the axial direction of the coil spring (1B) and faces the other side in the axial direction of the coil spring (1B) and a central coil part (<NUM>) between the first and second end coil parts (<NUM>, <NUM>), wherein the first end coil part (<NUM>) includes a first end coil part edge region (<NUM>) that extends from a first end (<NUM>) on one side in the axial direction of the coil spring (1B) to a part forming a first reference point (<NUM>) on one side in the axial direction where a space between coils (<NUM>) that are adjacent to each other in an axial direction is zero in the natural length state, and a first end coil part transitional region (<NUM>) that extends from the first end coil edge region (<NUM>) to the central coil part (<NUM>),
the first end coil part edge region (<NUM>) is bent toward one side in the axial direction of the coil spring (1B) as compared with the first end coil part transitional region (<NUM>); the coil spring (1B) being characterized in that,
the first bearing surface (<NUM>) extends from the first end coil part edge region (<NUM>) to the first end coil part transitional region (<NUM>) across a border between the first end coil part edge region (<NUM>) and the first end coil part transitional region (<NUM>).