Shock absorber and method for manufacturing shock absorber

Abstract

A shock absorber (20) includes: an outer cylinder (21); a first bushing (41) and a second bushing (42) in the interior of the outer cylinder (21); an inner cylinder (22) of which, with respect to the outer cylinder (21), a portion (51) is inserted into the outer cylinder (21) and a remaining portion (52) is exposed from the outer cylinder (21); and a first coating (71) and a second coating (72) formed on an outer circumferential surface (22c) of the inner cylinder (22). The second bushing (42) is located farther on an open end (21b) side of the outer cylinder (21) than the first bushing (41). The first coating (71) is located in a first sliding region (61) of the outer circumferential surface (22c) that slides on the first bushing (41). The second coating (72) is formed in at least a part of an exposed portion (52) exposed from the outer cylinder (21) and a second sliding region (62) that slides on the second bushing (42) in the outer circumferential surface (22c), and is different in material than the first coating (71).

Description

Shock absorber and method for manufacturing the same

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[0001] The present invention relates to an improved technique for a shock absorber and a method for manufacturing the same.

[0002] A so-called telescopic shock absorber in which an inner cylinder is inserted through an outer cylinder so as to be relatively movable is widely used in, for example, front forks of saddle-riding vehicles such as motorcycles. In some cases, two major conditions are required for the outer peripheral surface of the inner cylinder. The first condition is to ensure the slidability and wear resistance of the portion of the outer peripheral surface of the inner cylinder that slides against the outer cylinder. The second condition is to ensure the hardness, strength, wear resistance, and aesthetics of the portion of the outer peripheral surface of the inner cylinder that is exposed from the outer cylinder. Therefore, the outer peripheral surface of the inner cylinder is subjected to a surface treatment. As a conventional technique for surface treatment, for example, Patent Document 1 is known.

[0003] The technique known from Patent Document 1 is to form a titanium nitride film (coating) on the outer peripheral surface of the inner cylinder and form a titanium oxide film (coating) on the surface of this titanium nitride film.

[0004] Japanese Patent Application Laid-Open No. 2005-282589

[0005] Since the technique known from Patent Document 1 forms a titanium film over the entire outer peripheral surface of the inner cylinder, the manufacturing cost increases, so there is room for improvement.

[0006] An object of the present invention is to provide a technique that can satisfy the usage conditions required for the coating formed on the outer peripheral surface of the inner cylinder while suppressing the manufacturing cost of the shock absorber.

[0007] As a result of intensive studies, the present inventor focused on the fact that the usage conditions required for the coating formed on the outer peripheral surface of the inner cylinder, the usage conditions required for the coating inside the outer cylinder, and the usage conditions required for the coating exposed from the outer cylinder are different. And it was found that the coating materials should be selected respectively in consideration of the usage conditions of each part of the outer peripheral surface of the inner cylinder. The present invention has been completed based on this finding.

[0008] According to one example of the present disclosure, a buffer is provided comprising: an outer cylinder having one end as a closed end and the other end as an open end; an annular first bush provided inside the outer cylinder; an annular second bush provided inside the outer cylinder on the open end side of the first bush; an inner cylinder having a portion inserted through the outer cylinder, the first bush, and the second bush so as to be relatively movable in the axial direction of the outer cylinder, with the remainder exposed from the outer cylinder; a first coating formed on the outer circumferential surface of the inner cylinder in a first sliding region that slides against the first bush; and a second coating formed on the outer circumferential surface of the inner cylinder in a second sliding region that slides against the second bush and on at least a portion of the exposed portion exposed from the outer cylinder, the second coating being made of a different material from the first coating.

[0009] Another example of the present disclosure provides a method for manufacturing a shock absorber comprising: an outer cylinder; an annular first bush provided inside the outer cylinder; an annular second bush provided inside the outer cylinder at a position axially different from the first bush; and an inner cylinder having one end inserted into the outer cylinder and the other end protruding from the outer cylinder, and being movable relative to the outer cylinder, the method comprising: a first coating forming step of applying a first coating to a portion of the outer circumferential surface of the inner cylinder that slides relative to the first bush; and a second coating forming step of applying a second coating of a material different from the first coating to at least a portion of the outer circumferential surface of the inner cylinder that slides relative to the second bush and an exposed portion exposed from the outer cylinder.

[0010] This disclosure provides a technology that can satisfy the required operating conditions for the coating formed on the outer surface of the inner cylinder while suppressing the manufacturing cost of the buffer.

[0011] This is a side view of a motorcycle equipped with a front fork containing a shock absorber according to Example 1. This is a cross-sectional view of the shock absorber shown in Figure 1. This is an enlarged view of the area around the first and second bushings of the shock absorber shown in Figure 2. This is a cross-sectional view showing the relationship between the outer cylinder and inner cylinder of the shock absorber shown in Figure 2. This is an external cross-sectional view of a part of the inner cylinder shown in Figure 4. This is a process diagram showing the surface treatment of the inner cylinder shown in Figure 5. This is an external cross-sectional view of a part of the inner cylinder of the shock absorber according to Example 2.

[0012] Embodiments of the present invention will be described below with reference to the attached drawings. Note that the forms shown in the attached drawings are examples of the present invention, and the present invention is not limited to these forms. In the description, left and right refer to left and right relative to the occupants in the vehicle, and front and rear refer to front and rear relative to the direction of travel of the vehicle. Also, in the drawings, Up indicates up, Dn indicates down, Fr indicates front (direction of travel, direction of driving), Rr indicates rear (opposite direction to the direction of travel), Li indicates left, and Ri indicates right.

[0013] <Example 1> The buffer 20 of Example 1 will be described with reference to Figures 1 to 6.

[0014] As shown in Figure 1, the shock absorber 20 is provided, for example, on the front fork 13. This front fork 13 is used in a motorcycle 10, which is a type of saddle-type vehicle in which the rider straddles the vehicle. Hereafter, the motorcycle 10 may be referred to as a "saddle-type vehicle 10".

[0015] The motorcycle 10 comprises a body 11, an engine 12 supported at the lower center of the body 11, a front fork 13 located at the front of the body 11, a front wheel 14 supported by the front fork 13, and a steering handle 15 connected to the front fork 13. A passenger seat 16 is provided at the upper center of the body 11. Furthermore, the motorcycle 10 comprises a wheel support mechanism 17 extending from the rear of the body 11 toward the rear and capable of swinging vertically, a rear wheel 18 supported by this wheel support mechanism 17, and a rear suspension 19 spanning between the body 11 and the wheel support mechanism 17.

[0016] The front fork 13 is equipped with two shock absorbers 20 (fork units 20) located on both sides of the front wheel 14. The stroke in which the shock absorber 20 compresses along the center line CL is called the compression stroke, and the stroke in which the shock absorber 20 extends along the center line CL is called the extension stroke.

[0017] As shown in Figure 2, in Embodiment 1, the shock absorber 20 is an inverted hydraulic shock absorber filled with oil. In other words, this shock absorber 20 has a telescopic configuration and comprises a cylindrical outer tube 21 positioned on the upper side to be supported by the vehicle body 11, and a cylindrical inner tube 22 positioned on the lower side to support the front wheel 14.

[0018] The outer tube 21 is sometimes referred to as the "outer cylinder 21" or "first cylinder 21," and the inner tube 22 is sometimes referred to as the "inner cylinder 22" or "second cylinder 22." The centerline CL of the shock absorber 20 may be referred to as the "centerline CL of the outer cylinder 21" or the "centerline CL of the inner cylinder 22" as appropriate. The centerline CL of the outer cylinder 21 coincides with the centerline CL of the inner cylinder 22. Also, the axial direction of the shock absorber 20 may be referred to as the "axial direction of the outer cylinder 21" or the "axial direction of the inner cylinder 22" as appropriate.

[0019] One end 21a (upper end 21a) of the outer cylinder 21 is a closed end, closed by a cap member 23. The other end 21b (lower end 21b) of the outer cylinder 21 is an open end. The inner cylinder 22 is made up of a straight pipe with both ends 22a and 22b open. A portion of the upper part of the inner cylinder 22 is inserted through the outer cylinder 21 so as to be movable relative to it in the axial direction, while the rest is exposed from the outer cylinder 21.

[0020] One end 21a of the outer cylinder 21 is sometimes called the "closed end 21a of the outer cylinder 21," and the other end 21b of the outer cylinder 21 is sometimes called the "open end 21b of the outer cylinder 21." Of the inner cylinder 22, one end 22a (upper end 22a) that is inserted into the outer cylinder 21 is sometimes called the "inserted end 22a of the inner cylinder 22," and the other end 22b (lower end 22b) of the inner cylinder 22 that is exposed from the outer cylinder 21 is sometimes called the "exposed end 22b of the inner cylinder 22."

[0021] The lower end portion 22d of the outer circumferential surface 22c of the inner cylinder 22, which is exposed from the outer cylinder 21, is fitted into a recess 24a of the axle holder 24 in a sealed manner and is screw-connected. In other words, a screw-connected portion 22e, consisting of a male screw that can be screw-connected to the axle holder 24, is formed on the lower end portion 22d. The axle holder 24 can be connected to the axle 14a for the front wheel 14 shown in Figure 1.

[0022] The outer cylinder 21 and the inner cylinder 22 are biased by a compression coil spring 25 in a direction that separates them from each other in the axial direction. The upper end of the compression coil spring 25 is supported by a pipe-shaped spring support portion 26 that extends downward from the cap member 23 at the upper end of the outer cylinder 21. The lower end of the compression coil spring 25 is supported by the inside of the axle holder 24.

[0023] Furthermore, the shock absorber 20 includes a cylindrical cylinder 27 extending from the axle holder 24 into the inner cylinder 22, a piston rod 28 extending from the cap member 23 into the cylinder 27, and a piston 29 provided at the tip of the piston rod 28. This piston 29 is capable of reciprocating motion within the cylinder 27.

[0024] As shown in Figure 3, the outer cylinder 21 is provided with a first sealing member 31 and a second sealing member 32, and a first bush 41 and a second bush 42, all located on the center line CL of the inner cylinder 22.

[0025] The first sealing member 31 is located at the open end 21b of the inner circumferential surface 21c of the outer cylinder 21. This first sealing member 31 is a dust seal that can prevent dust from entering the outer cylinder 21 from the outside. The sealing lip 31a of this first sealing member 31 faces outward in the longitudinal direction of the outer cylinder 21 and is in slidable contact with the outer circumferential surface 22c of the inner cylinder 22.

[0026] The second sealing member 32 is located on the closed end 21a (see Figure 2) side of the inner circumferential surface 21c of the outer cylinder 21, rather than the open end 21b, and is in slidable contact with the outer circumferential surface 22c of the inner cylinder 22. This second sealing member 32 is configured as an oil seal that can prevent oil leakage from inside the outer cylinder 21. The second sealing member 32 may also serve as a dust seal that can prevent dust from entering the outer cylinder 21 from the outside.

[0027] Figures 2 to 4 show the shock absorber 20 in its most extended state along the center line CL. As shown in Figures 3 and 4, the first bush 41 and the second bush 42 are annular members integrally provided on the inner circumferential surface 21c of the outer cylinder 21, and slidably support the outer circumferential surface 22c of the inner cylinder 22. The first bush 41 is positioned to support the outer circumferential surface 22c of the inner cylinder 22 when the shock absorber 20 is in its most extended state. The second bush 42 is located inside the outer cylinder 21, closer to the open end 21b (towards the second seal member 32) than the first bush 41.

[0028] As is clear from the above description, the inner cylinder 22 has a portion 51 (storage portion 51) inserted through the outer cylinder 21, the first bush 41 and the second bush 42 so as to be movable relative to the outer cylinder 21 in the axial direction, while the remaining exposed portion 52 (exposed area 52) is exposed from the outer cylinder 21. This exposed portion 52 is the range from the open end 21b of the outer cylinder 21 to the exposed end 22b of the inner cylinder 22.

[0029] As shown in Figure 4, the area 61 on the outer circumferential surface 22c of the inner cylinder 22 that can slide axially with respect to the first bush 41 is called the "first sliding region 61". The base end 61a of this first sliding region 61 and the axial length of the first sliding region 61 are preferably set taking into account the error of the relative expansion and contraction of the inner cylinder 22 in the axial direction with respect to the outer cylinder 21.

[0030] The area 62 on the outer circumferential surface 22c of the inner cylinder 22 that is capable of sliding axially with respect to the second bush 42 is called the "second sliding region 62". The base end 62a of this second sliding region 62 and the axial length of the second sliding region 62 are preferably set taking into account the error of the relative expansion and contraction of the inner cylinder 22 in the axial direction with respect to the outer cylinder 21.

[0031] The area 63 on the outer circumferential surface 22c of the inner cylinder 22 between the first sliding area 61 and the second sliding area 62 is called the "non-sliding area 63". In this non-sliding area 63, the outer circumferential surface 22c of the inner cylinder 22 does not slide against either the first bush 41 or the second bush 42. The axial intermediate position 64 within this non-sliding area 63 is called the "intermediate point 64".

[0032] The inner cylinder 22 has at least one hole 65 that extends radially inward and outward. This hole 65 is located between the portion of the inner cylinder 22 supported by the first bush 41 and the portion supported by the second bush 42. Preferably, this hole 65 is located on the side of the second sliding region 62 (opposite to the first sliding region 61) with respect to the midpoint 64 of the non-sliding region 63 of the inner cylinder 22. As shown in Figure 3, this hole 65 allows oil inside the inner cylinder 22 to be guided into the gap 66 between the inner circumferential surface 21c of the outer cylinder 21 and the outer circumferential surface 22c of the inner cylinder 22. The oil in this gap 66 lubricates the sliding surfaces of the inner cylinder 22 relative to the respective sealing members 31, 32 and the respective bushes 41, 42.

[0033] As shown in Figures 4 and 5, the first coating 71 is formed (applied) around the entire circumference of the first sliding region 61 on the outer circumferential surface 22c of the inner cylinder 22. The second coating 72 is formed (applied) around the entire circumference of the second sliding region 62 and around at least a portion of the exposed portion 52 on the outer circumferential surface 22c of the inner cylinder 22.

[0034] The axial boundary 73 between the first coating 71 and the second coating 72 on the outer circumferential surface 22c of the inner cylinder 22 is in contact with each other (including configurations where they are slightly spaced apart). This boundary 73 is positioned so as not to slide with respect to both the first bush 41 and the second bush 42. This boundary 73 is located on the second bush 42 side (the opposite side in the axial direction from the first sliding region 61) with respect to the midpoint 64. Furthermore, the boundary 73 is located on the second bush 42 side (the opposite side in the axial direction from the first sliding region 61) with respect to the hole 65. The exposed region 52 (the portion 52 exposed from the outer cylinder 21) of the outer circumferential surface 22c of the inner cylinder 22 has only the screw connection portion 22e and includes an uncoated region 74 where the second coating 72 is not formed.

[0035] As shown in Figure 5, more preferably, the first coating 71 is formed over the entire circumference of the outer circumferential surface 22c of the inner cylinder 22, generally in the upper half from the insertion end 22a to the boundary 73. The second coating 72 is formed over the entire circumference of the outer circumferential surface 22c of the inner cylinder 22, generally in the lower half from the boundary 73 towards the exposed end 22b. However, the screw connection portion 22e of the outer circumferential surface 22c of the inner cylinder 22 is an uncoated region 74 where the second coating 72 is not formed. In other words, the second coating 72 is formed over the outer circumferential surface 22c of the inner cylinder 22, in the range from the lower end of the first coating 71 to the upper end 22f of the screw connection portion 22e.

[0036] Next, the materials of the first coating 71 and the second coating 72 will be described in detail. When a bending load (road surface reaction force) is applied from the axle 14a (see Figure 1) to the inner cylinder 22, this bending load acts on the first bush 41 and the second bush 42 shown in Figure 4. In this case, according to the concept of a cantilevered beam on one side, the second bush 42 receives a larger load than the first bush 41. In other words, the sliding portion of the outer circumferential surface 22c of the inner cylinder 22 with the second bush 42 is more prone to bending stress than the sliding portion with the first bush 41. Furthermore, the exposed portion 52 of the outer circumferential surface 22c of the inner cylinder 22 that is exposed to the outside from the outer cylinder 21 is susceptible to damage such as scratches from flying stones from the road surface while a motorcycle 10 (see Figure 1) is in motion. Taking this into consideration, the present invention has selected the materials for the first coating 71 and the second coating 72.

[0037] Specifically, the first coating 71 is a film formed by nickel hard chromium plating. Generally, decorative chromium plating involves applying a thin chromium plating with a thickness of less than 1 μm to a metal surface after nickel plating, while hard chromium plating (hard chromium plating) involves directly applying chromium plating with a thickness of 1 μm or more to a metal surface. Here, the process of applying chromium plating with a thickness of 1 μm or more after nickel plating is called "nickel hard chromium plating."

[0038] In contrast, a second coating 72 with high hardness (high wear resistance) is formed on the sliding portion of the outer circumferential surface 22c of the inner cylinder 22 with the second bush 42. For example, the second coating 72 is one of the following: a film containing titanium components, a film formed by diamond-like carbon coating, or a film formed by SiCN (silicon nitride). Titanium components include titanium oxide and titanium nitride. In this way, by appropriately selecting the material, the color of the second coating 72 can be made different from the color of the first coating 71.

[0039] Next, a method for manufacturing the buffer 20 with the above configuration will be described with reference to Figures 5 and 6. Here, an example will be described in which the first coating 71 is formed on the outer surface 22c of the inner cylinder 22 by "nickel hard chromium plating", and the second coating 72 contains "titanium components".

[0040] As shown in Figure 6, an example of a method for manufacturing the inner cylinder 22 of the shock absorber 20 is as follows. First, in the inner cylinder preparation step S01, the inner cylinder 22 is prepared. This inner cylinder 22 has a screw joint portion 22e and a hole portion 65 that have been machined, and the outer surface 22c has been mechanically polished to make it smooth. In the next step S02, the first coating formation step, the first coating 71 is applied to the portion of the outer surface 22c of the inner cylinder 22 that slides relative to the first bush 41 (see Figure 4) (from the insertion end 22a to the boundary 73). In the next step, S03, the second coating formation step, a second coating 72 made of a different material from the first coating 71 is applied to at least a portion of the outer peripheral surface 22c of the inner cylinder 22, specifically the second sliding region 62 that slides relative to the second bush 42 (see Figure 4) and the exposed portion 52 exposed from the outer cylinder 21 (from the boundary 73 to the upper end 22f of the screw joint portion 22e). In this second coating formation step (step S03), the portion of the inner cylinder 22 to be coated with the second coating 72 is placed in a furnace 80 such as an electric furnace, while the portion coated with the first coating 71 is removed from the furnace 80 and the second coating 72 is applied. This completes the manufacturing of the inner cylinder 22.

[0041] <Example 2> The buffer 120 of Example 2 will be described with reference to Figure 7. Figure 7 shows the outer surface of the inner cylinder 22 of the buffer 120 of Example 2, and corresponds to Figure 5 which describes the inner cylinder 22 of Example 1. The buffer 120 of Example 2 is characterized in that the first coating 71 and the second coating 72 of Example 1 shown in Figure 5 are changed to the first coating 171 and the second coating 172 shown in Figure 7. Other basic configurations are the same as the buffer 20 of Example 1. For parts common to the buffer 20 of Example 1 and its manufacturing method, the reference numerals are reused and detailed explanations are omitted.

[0042] On the outer peripheral surface 22c of the inner cylinder 22 of the second embodiment, a first coating 171 and a second coating 172 are formed. The first coating 171 is formed including the range where the second coating 172 is formed on the outer peripheral surface 22c of the inner cylinder 22. That is, the first coating 171 is formed from the insertion end 22a of the inner cylinder 22 to the upper end 22f of the screw coupling portion 22e. The second coating 172 is formed on the lower half of the outer peripheral surface 171a (coating outer peripheral surface 171a) of the first coating 171. The range of this second coating 172 corresponds to the range of the second coating 72 of the first embodiment shown in FIG. 5. That is, the second coating 172 is indirectly formed on the range from the boundary 173 to the upper end 22f of the screw coupling portion 22e of the outer peripheral surface 22c of the inner cylinder 22 via the first coating 171. This boundary 173 corresponds to the position of the boundary 73 of the first embodiment shown in FIG. 5. In other words, by forming the second coating 172 on the coating outer peripheral surface 171a of the first coating 171, it is indirectly formed on the portion that slides with respect to the second bush 42 (see FIG. 4) of the outer peripheral surface 22c of the inner cylinder 22.

[0043] For example, the first coating 171 is formed on the outer peripheral surface 22c of the inner cylinder 22, the coating outer peripheral surface 171a of this first coating 171 is smoothed by mechanical polishing, and the second coating 172 is formed on this coating outer peripheral surface 171a. The shock absorber 120 of the second embodiment exhibits the same effects as the shock absorber 20 of the first embodiment.

[0044] Summarizing the shock absorbers 20; 120 and their manufacturing methods described above, it is as follows.

[0045] Refer to Figures 3 to 5 and Figure 7. According to this embodiment, firstly, the buffer 20;120 comprises an outer cylinder 21 with one end as a closed end 21a and the other end as an open end 21b, an annular first bush 41 provided inside the outer cylinder 21, an annular second bush 42 provided inside the outer cylinder 21 on the open end 21b side of the first bush 41, and a portion of the outer cylinder 21, the first bush 41 and the second bush 42 being inserted so as to be relatively movable in the axial direction of the outer cylinder 21, with the remainder being on the outside The device includes an inner cylinder 22 exposed from the cylinder 21, a first coating 71;171 formed on a first sliding region 61 of the outer circumferential surface 22c of the inner cylinder 22 that slides against the first bush 41, and a second coating 72;172 formed on a second sliding region 62 of the outer circumferential surface 22c of the inner cylinder 22 that slides against the second bush 42, and on at least a part of the exposed portion 52 (exposed region 52) exposed from the outer cylinder 21, and made of a different material from the first coating 71;171.

[0046] Thus, the first bush 41 is provided inside the outer cylinder 21. The first sliding region 61 of the outer circumferential surface 22c of the inner cylinder 22 that slides against the first bush 41 is located inside the outer cylinder 21. A first coating 71;171 is formed on this first sliding region 61. On the other hand, the second bush 42 is provided inside the outer cylinder 21, closer to the open end 21b than the first bush 41. The second sliding region 62 of the outer circumferential surface 22c of the inner cylinder 22 that slides against the second bush 42, and at least a portion of the exposed portion 52 that is exposed from the outer cylinder 21, are covered with a second coating 72;172. The material of the second coating 72;172, which is exposed from the outer cylinder 21 in at least a portion, is different from the material of the first coating 71;171 located inside the outer cylinder 21. In other words, the material required for the first coating 71;171 located inside the outer cylinder 21 is different from the material required for the second coating 72;172 exposed from the outer cylinder 21. By using different materials for each coating 71, 72;171, and 172, it is possible to use a less expensive material for one of them than the other. Therefore, the manufacturing cost of the buffer 20;120 can be reduced while satisfying the respective operating conditions required for the first coating 71;171 and the second coating 72;172.

[0047] Refer to FIGS. 3 to 5 and FIG. 7. Second, preferably, the shock absorber 20; 120 described first, wherein the hardness of the second coating 72; 172 is greater than the hardness of the first coating 71; 171. Thus, by increasing the hardness of the portion 52 (exposed region 52) of the outer peripheral surface 22c of the inner cylinder 22 that is exposed to the outside from the outer cylinder 21, for example, damage such as scratches on the inner cylinder 22 can be suppressed by flying stones from the driving road surface during the running of the motorcycle 10 (see FIG. 1). Furthermore, in the sliding portion 62 (second sliding region 62) of the inner cylinder 22 with the second bush 42, bending stress is more likely to occur than in the sliding portion 61 (first sliding region 61) with the first bush 41. In contrast, in the present invention, a second coating 72; 172 having a high hardness (high wear resistance) is formed on the sliding portion 62 of the outer peripheral surface 22c of the inner cylinder 22 with the second bush 42. Therefore, the durability of the outer peripheral surface 22c of the inner cylinder 22 can be enhanced, and the appearance of the portion 52 of the outer peripheral surface 22c of the inner cylinder 22 that is exposed from the outer cylinder 21 can be maintained. Moreover, since the second coating 72 having a high hardness (high wear resistance) is formed on a part of the outer peripheral surface 22c of the inner cylinder 22, the cost can be reduced compared to the case where it is formed on the entire surface.

[0048] Refer to FIGS. 3 to 5 and FIG. 7. Third, preferably, the shock absorber 20; 120 described second, wherein the second coating 72; 172 contains a titanium component. Thus, since the second coating 72; 172 contains a titanium component, it has a high hardness and is excellent in wear resistance and toughness. Moreover, since it is the second coating 72; 172 containing a titanium component, it is generally golden in color and thus has excellent appearance. Therefore, it is possible to achieve both an improvement in the appearance and high hardness of the outer peripheral surface 22c of the inner cylinder 22.

[0049] Refer to Figures 3 to 5 and Figure 7. Fourth, preferably, the shock absorber 20;120 as described in the third, wherein the first coating 71;171 is a film formed by nickel hard chromium plating. Since the first coating 71;171 is located inside the outer cylinder 21, it is not a problem if its wear resistance is lower than that of the second coating 72;172. For this reason, the first coating 71;171 is formed by inexpensive nickel hard chromium plating, compared to the second coating 72;172 which contains titanium components. A low-cost shock absorber 20;120 can be obtained.

[0050] Refer to Figures 3 to 5 and Figure 7. Fifth, preferably, the shock absorber 20;120 described second, wherein the second coating 72;172 is a film formed by a diamond-like carbon coating (DLC). By forming the second coating 72;172 with diamond-like carbon, the hardness of the portion 52 (exposed area 52) of the outer peripheral surface 22c of the inner cylinder 22 that is exposed to the outside from the outer cylinder 21 can be increased, thereby suppressing damage such as scratches to the inner cylinder 22 caused by flying stones from the road surface while the motorcycle 10 is in motion. This makes it possible to increase the durability of the outer peripheral surface 22c of the inner cylinder 22 and maintain the appearance of the portion 52 of the outer peripheral surface 22c of the inner cylinder 22 that is exposed to the outside from the outer cylinder 21. Furthermore, since the second coating 72;172, which is highly hard (highly wear-resistant), is formed only on a portion of the outer circumferential surface 22c of the inner cylinder 22, the cost can be reduced compared to forming it on the entire surface.

[0051] Refer to Figures 3 to 5 and Figure 7. Sixth, preferably, the buffer 20;120 described in the first description, wherein the color of the second coating 72;172 is different from the color of the first coating 71;171. This improves the appearance of the portion 52 (exposed region 52) of the outer peripheral surface 22c of the inner cylinder 22 that is exposed from the outer cylinder 21.

[0052] Refer to Figures 3 to 5 and Figure 7. Seventh, preferably, the buffer 20;120 described in sixth, wherein the second coating 72;172 is a film formed of SiCN (silicon nitride). By forming the second coating 72;172 with SiCN, various colors can be set by adjusting the interference color of light.

[0053] Refer to Figures 3 to 5 and Figure 7. Eighth, preferably, the shock absorber 20;120 described in the first description, wherein the boundary 73;173 between the first coating 71;171 and the second coating 72;172 is set at a position 63 (non-sliding region 63) on the outer peripheral surface 22c of the inner cylinder 22 that does not slide with respect to both the first bush 41 and the second bush 42. Therefore, the boundary 73;173 between the first coating 71;171 and the second coating 72;172 is not located with respect to either the first bush 41 or the second bush 42. Accordingly, the sliding properties of the first coating 71;171 with respect to the first bush 41 and the sliding properties of the second coating 72;172 with respect to the second bush 42 can be sufficiently maintained. Moreover, the durability of the first coating 71;171 and the second coating 72;172 can be sufficiently ensured.

[0054] Refer to Figures 3 to 5 and Figure 7. Ninth, preferably, the shock absorber 20;120 described in the eighth, wherein the axial sliding range of the first coating 71;171 with respect to the first bush 41 is defined as the first sliding region 61. The axial sliding range of the second coating 72 with respect to the second bush 42 is defined as the second sliding region 62. The range axially separated between the first sliding region 61 and the second sliding region 62 is defined as the non-sliding region 63. The axial intermediate position 64 within the non-sliding region 63 is defined as the midpoint 64. The boundary 73;173 is located on the opposite side of the axial direction from the midpoint 64 to the first sliding region 61. Therefore, the formation range of the second coating 72;172 can be shortened, and as a result, the formation cost of the second coating 72;172 can be reduced.

[0055] Refer to Figures 3 to 5 and Figure 7. Tenth, preferably, the shock absorber 20;120 described in ninth, wherein the inner cylinder 22 has a hole 65 that penetrates radially inward and outward. The hole 65 is located in the non-sliding region 63 and is located on the opposite side in the axial direction from the first sliding region 61 with respect to the midpoint 64. The boundary 73;173 is located on the opposite side in the axial direction from the first sliding region 61 with respect to the hole 65. For this reason, the hole 65 does not overlap with the second coating 72;172, but overlaps only with the first coating 71;171. If the hardness of the second coating 72;172 is greater than the hardness of the first coating 71;171, the hole 65 can be made in the lower-hardness first coating 71;171, thereby improving the workability of drilling.

[0056] Refer to Figures 4 and 7. Eleventh, preferably, the shock absorber 120 described in the first example (Example 2), wherein the first coating 171 is formed on the outer peripheral surface 22c of the inner cylinder 22, including the area on which the second coating 172 is formed. The second coating 172 is formed on the outer peripheral surface 171a of the first coating 171, and is formed on the portion of the outer peripheral surface 22c of the inner cylinder 22 that slides against the second bush 42. In the invention shown in Figure 5 (Example 1), it is necessary to accurately perform surface treatment so that there is no gap at the boundary 73 between the first coating 71 and the second coating 72. In contrast, in the invention shown in Figure 7 (Example 2), no gap occurs at the boundary 173 of the second coating 172. Therefore, it is easy to set the position of the boundary 173.

[0057] Refer to Figures 4, 5, and 7. Twelfth, preferably, the shock absorber 20;120 described in the first description, wherein the portion 52 (exposed region 52) of the outer peripheral surface 22c of the inner cylinder 22 that is exposed from the outer cylinder 21 has only a screw connection portion 22e that is screw-connected to the axle holder 24 and includes an uncoated region 74 where the second coating 72;172 is not formed. In this way, the second coating 72;172 is not formed on the portion of the outer peripheral surface 22c of the inner cylinder 22 where the screw connection portion 22e is located. Therefore, the processability of the second coating 72;172 is good.

[0058] Refer to Figures 3 to 6. In this embodiment, the thirteenth buffer 20 comprises an outer cylinder 21, an annular first bush 41 provided inside the outer cylinder 21, an annular second bush 42 provided inside the outer cylinder 21 at a different axial position relative to the first bush 41, and an inner cylinder 22 having one end 22a (insertion end 22a) inserted into the outer cylinder 21 and the other end 22b (exposed end 22b) protruding from the outer cylinder 21, and being movable relative to the outer cylinder 21. The manufacturing method for the buffer 20 includes a first coating forming step of applying a first coating 71 to a portion of the outer circumferential surface 22c of the inner cylinder 22 that slides relative to the first bush 41, and a second coating forming step of applying a second coating 72 made of a material different from the first coating 71 to at least a portion of the second sliding region 62 of the outer circumferential surface 22c of the inner cylinder 22 that slides relative to the second bush 42, and to the exposed portion exposed from the outer cylinder 21.

[0059] In other words, the material required for the first coating 71 located inside the outer cylinder 21 is different from the material required for the second coating 72 exposed from the outer cylinder 21. By using different materials for each coating 71 and 72, it is possible to use a less expensive material for one of them than the other. Therefore, the manufacturing cost of the buffer 20 can be reduced while satisfying the respective usage conditions required for the first coating 71 and the second coating 72. In this way, the aesthetic appearance of the parts exposed to the outside can be changed while keeping costs down.

[0060] Refer to Figures 5 and 6. Fourteenth, preferably, the method for manufacturing the buffer 20 as described in the thirteenth, wherein the first coating 71 is formed by nickel hard chromium plating. The second coating 72 contains titanium. In the second coating formation step, the portion of the inner cylinder 22 to be coated with the second coating 72 is placed in the furnace 80, while the portion to which the first coating 71 has been applied is removed from the furnace 80 and the second coating is applied. Thus, in the second coating formation step, the portion of the inner cylinder 22 to be coated with the second coating 72 is placed in the furnace 80, but the portion to which the first coating 71 has been applied is not placed in the furnace 80. Compared to the case in which the second coating 72 is applied to the entire surface of the inner cylinder 22, the cycle time for manufacturing the inner cylinder 22 is shortened.

[0061] Furthermore, the buffers 20;120 and the method for manufacturing the buffers 20;120 according to the present invention are not limited to the above embodiments, as long as they achieve the functions and effects of the present invention.

[0062] The shock absorbers 20;120 of the present invention are suitable for application to front forks mounted on saddle-type vehicles.

[0063] 20...buffer, 21...outer cylinder, 21a...closed end, 21b...open end, 22...inner cylinder, 22a...insertion end, 22b...exposed end, 22c...outer surface, 22d...lower end exposed from the outer cylinder, 22e...screw joint, 24...axle holder, 41...first bush, 42...second bush, 51...part of the inner cylinder (storage area), 52...remaining exposed part (exposed area), 61...first sliding area, 62...second sliding area, 63...non-sliding area, 64...midpoint, 65...hole, 71...first coating, 72...second coating, 73...boundary, 74...uncoated area, 80...furnace, 120...buffer, 171...first coating, 171a...outer surface 172...Second coating.

Claims

1. A buffer comprising: an outer cylinder having one end as a closed end and the other end as an open end; an annular first bush provided inside the outer cylinder; an annular second bush provided inside the outer cylinder on the open end side of the first bush; an inner cylinder having a portion inserted through the outer cylinder, the first bush and the second bush so as to be relatively movable in the axial direction of the outer cylinder, with the remainder exposed from the outer cylinder; a first coating formed on a first sliding region of the outer circumferential surface of the inner cylinder that slides against the first bush; and a second coating formed on at least a portion of the second sliding region of the outer circumferential surface of the inner cylinder that slides against the second bush and the exposed portion exposed from the outer cylinder, the second coating being made of a different material from the first coating.

2. The shock absorber according to claim 1, wherein the hardness of the second coating is greater than the hardness of the first coating.

3. The buffer according to claim 2, wherein the second coating contains a titanium component.

4. The buffer according to claim 3, wherein the first coating is a film formed by nickel hard chromium plating.

5. The buffer according to claim 2, wherein the second coating is a film formed by a diamond-like carbon coating.

6. The buffer according to claim 1, wherein the color of the second coating is different from the color of the first coating.

7. The buffer according to claim 6, wherein the second coating is a film formed of SiCN.

8. The buffer according to claim 1, wherein the boundary between the first coating and the second coating is set at a position on the outer surface of the inner cylinder that does not slide against both the first bush and the second bush.

9. The shock absorber according to claim 8, wherein the sliding range of the first coating in the axial direction relative to the first bush is defined as the first sliding region, the sliding range of the second coating in the axial direction relative to the second bush is defined as the second sliding region, the range separated in the axial direction between the first sliding region and the second sliding region is defined as the non-sliding region, the midpoint of the axial direction within the non-sliding region is defined as the midpoint, and the boundary is located on the opposite side of the axial direction from the midpoint to the first sliding region.

10. The shock absorber according to claim 9, wherein the inner cylinder has a hole that penetrates radially inward and outward, the hole is located in the non-sliding region and is located on the opposite side in the axial direction from the first sliding region with respect to the midpoint, and the boundary is located on the opposite side in the axial direction from the first sliding region with respect to the hole.

11. The shock absorber according to claim 1, wherein the first coating is formed on the outer surface of the inner cylinder including the area on which the second coating is formed, and the second coating is formed on the outer surface of the first coating, thereby forming on the portion of the outer surface of the inner cylinder that slides against the second bush.

12. The shock absorber according to claim 1, wherein the portion of the outer surface of the inner cylinder that is exposed from the outer cylinder has only a screw connection portion that is screw-connected to the axle holder and includes an uncoated region where the second coating is not formed.

13. A method for manufacturing a shock absorber comprising: an outer cylinder; an annular first bush provided inside the outer cylinder; an annular second bush provided inside the outer cylinder at a position axially different from the first bush; and an inner cylinder having one end inserted into the outer cylinder and the other end protruding from the outer cylinder, and being movable relative to the outer cylinder, the method comprising: a first coating forming step of applying a first coating to a portion of the outer circumferential surface of the inner cylinder that slides relative to the first bush; and a second coating forming step of applying a second coating of a material different from the first coating to at least a portion of the outer circumferential surface of the inner cylinder that slides relative to the second bush and an exposed portion exposed from the outer cylinder.

14. The method for manufacturing a buffer according to claim 13, wherein the first coating is formed by nickel hard chromium plating, the second coating contains a titanium component, and the second coating formation step involves placing the portion of the inner cylinder to be coated with the second coating into a furnace, and applying the second coating to the portion that has the first coating applied while it is removed from the furnace.

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