JP7845902B2 - Plain bearing - Google Patents

Description

This invention relates to a sliding bearing for slidably supporting a shaft member, and more particularly to a sliding bearing having a cylindrical sliding member and a resin housing formed by injection molding on the outer circumferential surface of the sliding member.

A cylindrical sliding bearing 101 having a resin housing 140 formed by injection molding is known (Figures 8-9). The sliding bearing 101 has an inner circumferential surface 142 that functions as a sliding surface supporting the shaft member, and an outer circumferential surface 144 that functions as a fixed surface fixed to the mating member.

Conventionally, methods for imparting sliding properties to resin housings include adding additives such as solid lubricants to the resin, or integrating the sliding surface with the resin housing by constructing it as a separate component. However, methods involving the addition of additives make it difficult to achieve both the housing's function (mechanical properties) and the bearing's function (sliding characteristics). Furthermore, this method also makes it difficult to obtain high internal diameter dimensional accuracy and cylindricity due to the anisotropy of resin molding shrinkage.

Patent Document 1 proposes a method for insert molding a sliding bearing in which a thin-walled cylindrical metal split bush with an axial slit is used as the sliding member, and this sliding member is integrated with a resin housing. Reference Document 1 also mentions the need to prevent the resin from flowing out onto the sliding surface of the split bush in order to achieve high precision on the inner circumferential surface of the sliding bearing. Therefore, in insert molding, the split bush is first mounted on the core pin of the injection molding device with the slit tightly sealed, and then the resin is injected into the cavity of the injection molding device (paragraphs 0016-0019 and 0070, etc.).

Japanese Patent Publication No. 2020-085243

The sliding bearing described in Patent Document 1 uses a metal split bushing. However, when the sliding surface is metal, the sliding characteristics are insufficient in lubrication environments where solid contact occurs, such as boundary lubrication. Patent Document 1 also proposes applying a coating (such as PTFE coating) to the sliding surface to improve its sliding properties (paragraph 0020, etc.), but the coating does not provide sufficient bonding force when subjected to high loads.

Furthermore, in the sliding bearing described in Patent Document 1, in order to ensure the joint between the resin housing and the metal split bush, it is necessary to increase the holding force of the split bush by the housing by filling the resin at high pressure during injection molding. However, if the rigidity of the split bush is insufficient, deformation occurs and the sliding performance is impaired. On the other hand, if the rigidity of the split bush is too high, it becomes difficult to conform to the shape of the mold, resulting in an unstable shape for the sliding bearing.

Therefore, the object of the present invention is to provide a sliding bearing having a sliding member and a resin housing, wherein the sliding member has sufficient sliding characteristics even when subjected to high loads, the bonding between the sliding member and the resin housing is high, and the inner diameter accuracy and roundness of the sliding member are high.

According to the present invention, a sliding bearing for slidably supporting a shaft member is provided, comprising a cylindrical sliding member and a resin housing formed on the outer circumferential surface of the sliding member. The sliding member has a coiled bushing with a mating surface extending in the axial direction. The coiled bushing has a multilayer structure including at least a resin layer located on the inner diameter side and forming a sliding surface, an intermediate layer located on the outer diameter side of the resin layer, and a backing plate located on the outer diameter side of the intermediate layer. Furthermore, the resin material of the resin housing flows at the mating surface, with 10-90% of the coiled bushing's wall thickness flowing from the outer circumferential surface toward the inner circumferential surface.

According to one embodiment of the present invention, the wall thickness of the coiled bushing can be set to 5-20% of the inner diameter of the coiled bushing.

Furthermore, according to one embodiment of the present invention, the coiled bushing can have a three-layer structure consisting of a resin layer, an intermediate layer, and a backing plate.

In this invention, the resin layer of the coiled bushing may contain a resin material and additives added to the resin material, and the resin material may contain polytetrafluoroethylene (PTFE).

Furthermore, the intermediate layer of the coiled bushing may include a porous metal material and a resin material impregnated into the porous metal material.

In the sliding bearing of the present invention, by using a multi-layered wrapped bushing having a resin layer on the inner diameter side, and particularly a three-layered wrapped bushing consisting of a resin layer, an intermediate layer, and a backing plate, a highly adhesive resin sliding layer is provided while improving sliding characteristics. With this configuration, the sliding layer is bonded by a physical anchoring effect, which is particularly effective when using a low-tack resin material such as PTFE for the resin layer.

Furthermore, although the coiled bushing is integrally formed with the resin housing by injection molding, by allowing resin material to flow into the joint of the coiled bushing, particularly by setting the flow rate to 10-90%, the holding force of the coiled bushing can be improved, preventing the coiled bushing from coming loose or rotating together with the housing.
Furthermore, the inflow rate of resin material into the joint of a coiled bushing represents the ratio of the length of resin material inflow extending from the outer surface to the inner surface of the coiled bushing to the wall thickness (radial thickness) of the coiled bushing. Therefore, an inflow rate of 0% means that no resin material has flowed from the outer surface to the joint, and an inflow rate of 100% means that the resin material has flowed into the joint from the outer surface to the inner surface, across the entire wall thickness of the coiled bushing.
Unlike the present invention, if the resin material inflow rate is less than 10%, the inflow amount is insufficient, and improvement in the holding force of the coiled bushing cannot be expected. Furthermore, if the resin material inflow rate exceeds 90%, the joint of the coiled bushing will open up, and the inner diameter accuracy will deteriorate. Moreover, if the resin material inflow rate exceeds 100% and flows into the inner circumferential surface, the sliding characteristics will be impaired.

Furthermore, according to the present invention, the rigidity of the coiled bushing may be appropriately adjusted by setting the wall thickness of the coiled bushing to 5 to 20% of the inner diameter. This makes it possible to achieve sufficient holding force for the coiled bushing and a coiled bushing shape with excellent sliding properties.
The rigidity of a coiled bushing is determined by the ratio of its wall thickness to its inner diameter (wall thickness/inner diameter). If this ratio is 5% or higher, rigidity can be efficiently increased, making the coiled bushing less prone to deformation even under pressure during injection molding. If this ratio is 20% or lower, rigidity is high and the conformability to the mold does not decrease, resulting in a stable shape (and therefore higher roundness).

The configuration and advantages of the present invention will be described in more detail below with reference to the accompanying drawings. It should be understood that the drawings illustrate non-limiting embodiments for illustrative purposes only.

This is a front view of a sliding bearing according to one embodiment of the present invention, as seen from the axial direction. This is a cross-sectional view of the sliding bearing shown in Figure 1, taken along line A-A. Figure 2 is an enlarged view of a part B of the sliding bearing, showing a detailed cross-section of the coiled bushing. Figure 1 is an enlarged view of a part C of the sliding bearing, showing a detailed view of the joint of the coiled bushing. This figure corresponds to Figure 4 of a sliding bearing according to another embodiment of the present invention, and shows in detail another configuration of the joint of the coiled bushing. This is a diagram illustrating an example of the manufacturing process for a sliding bearing. This is a diagram illustrating an example of the manufacturing process for a sliding bearing. This is a front view of a conventional sliding bearing, seen from the axial direction. Figure 8 is a cross-sectional view taken along line D-D of a conventional sliding bearing.

A sliding bearing 1 according to one embodiment of the present invention will be described in detail below.

(Structure of a sliding bearing)
Figure 1 is a front view of the sliding bearing 1 as seen from the axial direction, and Figure 2 is an axial cross-sectional view of the sliding bearing 1. The sliding bearing 1 has a cylindrical shape and consists of a coiled bushing 20 as a sliding member located on the inner diameter side and a resin housing 40 located on the outer diameter side thereof. The resin housing 40 is joined to the outer circumferential surface 24 of the coiled bushing 20 so as to hold the coiled bushing 20. The outer circumferential surface 44 of the resin housing 40 functions as a fixing surface for fixing the sliding bearing 1 to a mating member (not shown), and the inner circumferential surface 22 of the coiled bushing 20 functions as a sliding surface for slidably supporting a shaft member (not shown).

Figure 3 is an enlarged view of a part B of the sliding bearing 1 shown in Figure 2, and in particular shows in detail the axial cross-section of the coiled bushing 20. As can be seen from Figure 3, the coiled bushing 20 is formed by shaping a cylindrical thin plate with a three-layer structure consisting of a resin layer (sliding layer) 32 located on the innermost diameter side and forming the inner circumferential surface (sliding surface) 22, a backing plate 36 located on the outermost diameter side, and an intermediate layer 34 between the resin layer 32 and the backing plate 36. The intermediate layer 34 includes a porous metal material 34a formed on the backing plate 36 and a resin material 34b, the same as the resin layer 23, impregnated inside it.
Although the coiled bushing in this embodiment has a three-layer structure, it may also have a four-layer structure, for example, by further having a plating layer on the outer circumferential surface side of the backing plate 36. The plating layer can be formed from, for example, copper, tin, zinc, etc. Alternatively, a five-layer structure can be formed by also forming a plating layer on the inner circumferential surface side of the backing plate 36. In this case, a porous metal material 34a is sintered on the plating layer on the inner circumferential surface side and impregnated with a resin material 34b. Furthermore, the inner circumferential surface side of the resin layer 32 can also be surface-treated.

As shown in detail in Figure 4, the coiled bushing 20 has a joint 26 that extends axially and is the abutting portion between the circumferential end faces of three-layer thin plates. In this embodiment, the joint 26 has a gap extending radially with a constant width W in the radial cross-section (Figure 4). The resin material constituting the resin housing 40 flows into the joint from the outer circumferential surface 24 to the inner circumferential surface 22 of the coiled bushing 20, up to 10-90% of the wall thickness (radial thickness) t of the coiled bushing 40.

The inner diameter d of the coiled bushing 20 can be, for example, 3 to 50 mm. Generally, when the inner diameter exceeds 50 mm, it becomes a bearing that can withstand higher loads. In this case, the wall thickness t of the coiled bushing 20 can be, for example, 0.5 to 2.5 mm in 0.5 mm increments, and the width W of the joint can be 0.1 to 0.3 mm. It is preferable that the ratio of the wall thickness to the inner diameter of the coiled bushing 20 be 5 to 20%, and in this case, the upper and lower limits of the inner diameter for each wall thickness in 0.5 mm increments are as shown in Table 1.

Furthermore, in other embodiments of the present invention, the joint of the coiled bushing 20 does not necessarily have to extend radially with a constant width W in the radial cross-section of the coiled bushing 20. Instead, as shown in Figure 5, the joint 26' may have a predetermined width W on the outer circumferential surface 24 of the coiled bushing 20, but gradually decrease in width toward the inner circumferential surface 22, closing approximately in the center of the wall thickness. Such a joint 26' makes it easier to obtain a configuration in which the resin material flows into the coiled bushing 40 up to 10-90% of its wall thickness (radial thickness) t. The joint does not necessarily have to be a stepped or dovetail shape, or any other shape that gradually decreases in width toward the inner circumferential surface 22. The width may also be varied in the axial direction.

(Material of the sliding bearing)
The resin material constituting the resin housing 4 can be any material that is injection moldable, for example, glass fiber-filled plant-derived polyamide 10T can be used. Alternatively, as a thermoplastic resin, general-purpose plastics (PP, PE, PS, ABS, PMMA, PVC, PLA), engineering plastics (PA, POM, PC, PBT, PVDF), and super engineering plastics (PPS, PEEK, LCP, PFA, FEP, PEI, PAR, PSF, PES, PI, PAI) can be used, and thermosetting resins (PF, UF, MF, EP, PUR) may also be used. Furthermore, the resin layer 32 of the coiled bushing 20 can be made of a base resin mixed with additives. The base resin can be, for example, PTFE, POM, PEEK, PA, etc., and the additives can include, for example, solid lubricants such as graphite and _MoS2 , and wear-resistant agents such as alumina and carbon fiber. The backing plate 36 of the coiled bushing 20 is made from, for example, iron or carbon steel. The intermediate layer 34 of the coiled bushing 20 can be obtained by impregnating a resin material that constitutes the resin layer 32 with, for example, sintered copper and copper alloy powder.

(Manufacturing method for sliding bearings)
The sliding bearing 1 can be manufactured, for example, by the following injection molding method.
First, as shown in Figure 6, a first mold 60 is provided having a core pin 61 and a cylindrical cavity 62 formed around it, and an insert material 20' (wound bushing 20) is fitted onto the core pin 61. Next, as shown in Figure 7, a second mold 64 is clamped onto the first mold 61, and resin material is filled into the cavity 62 through a sprue 65 formed in the second mold 64. After cooling and setting, the molded product is removed from the mold, thereby providing a sliding bearing with a resin housing 40 formed around the wound bushing 20.
In this embodiment, the shape of the joint of the insert material 20' was made straight, its opening width was adjusted to 0.6 mm, and the injection pressure (holding pressure) was adjusted to 40 MPa, resulting in a resin material inflow ratio of 50% relative to the wall thickness of the coiled bushing 40. However, the inflow ratio will vary depending on the shape and type of the resin housing to be molded, so the desired inflow ratio can be achieved by adjusting the shape of the joint of the insert material, the opening width, the pressure applied to the resin being molded, etc.

(Performance evaluation test)
To evaluate the bushing retention force and roundness of the sliding bearing according to the present invention, performance evaluation tests were conducted on Examples 1 to 8 and Comparative Examples 1 to 2.
The three-layer coiled bushing was formed by sintering a porous intermediate layer onto a backing plate and impregnating it with a resin sliding layer (PTFE). The housing was molded using Unitika Ltd.'s XecoT® XG510A30D injection molding machine (FANUC ROBOSHOT α-S50iA). The inflow rate of resin material into the joint of the coiled bushing was determined by measuring a cross-section perpendicular to the axial direction.

(Test results)
Table 2 below summarizes the test results for measuring bushing retention force and roundness when the inflow rate of resin material into the joint of the wrapped bushing was changed using Examples 1 to 5 and Comparative Examples 1 to 2.
Furthermore, the bushing retention force was determined by measuring the force required to push the coiled bushing out of the housing in the axial direction using an autograph, and the roundness was determined by measuring the roundness of the inner diameter of the bushing using a roundness measuring instrument.

(Test results)
Furthermore, Table 3 below summarizes the test results for measuring bushing retention force and roundness when the ratio of wall thickness to inner diameter of the coiled bushing was changed using Examples 3 and 6-8.

The test results in Table 2 confirm that a sliding bearing with a good balance of bushing retention force and roundness can be obtained when the resin material inflow ratio is between 10% and 90%. In particular, it can be seen that the retention force decreases when the resin material inflow ratio is low, as in Comparative Example 1, while the roundness deteriorates when the resin material inflow ratio is too high, as in Comparative Example 2.
Furthermore, the test results in Table 3 confirm that the roundness can be improved while maintaining the bushing retention force by adjusting the ratio of the wall thickness to the inner diameter of the coiled bushing.

While embodiments and examples of the present invention have been described in detail above with reference to the drawings and in relation to performance evaluation tests, the specific configurations are not limited to these, and modifications that do not depart from the gist of the invention as described in the claims are included in the present invention.

1. Plain bearing 20. Wrapped bushing 22. Inner surface 24. Outer surface 26. Joint 32. Resin layer (sliding layer)
34 Intermediate layer 34a Porous metal material 34b Resin material 36 Backing plate 40 Resin housing 44 Outer surface 20' Insert material (wound bushing 20)
60 First mold 61 Core pin 62 Cavity 64 Second mold 65 Sprue

Claims (7)

A sliding bearing for slidably supporting a shaft member, comprising a cylindrical sliding member and a resin housing formed on the outer circumferential surface of the sliding member,
The sliding member has a coiled bushing with a joint extending in the axial direction, the coiled bushing has a multilayer structure including at least a resin layer located on the inner diameter side and forming a sliding surface, an intermediate layer located on the outer diameter side of the resin layer, and a backing plate located on the outer diameter side of the intermediate layer, the joint has a gap extending radially from the outer circumferential surface of the coiled bushing toward the inner circumferential surface, the resin material of the resin housing flows into the gap toward the inner circumferential surface of the coiled bushing at a rate of 10 to 90% of the wall thickness of the coiled bushing, the coiled bushing is fixed to the resin housing and does not move in the axial direction, and is characterized as a sliding bearing. The sliding bearing according to claim 1, wherein the wall thickness of the coiled bushing is 5 to 20% of the inner diameter of the coiled bushing. The sliding bearing according to claim 1, wherein the coiled bushing has a three-layer structure consisting of the resin layer, the intermediate layer, and the backing plate. The sliding bearing according to claim 1, wherein the resin layer comprises a resin material and an additive added to the resin material. The sliding bearing according to claim 1, wherein the resin material of the resin layer contains polytetrafluoroethylene. The sliding bearing according to claim 1, wherein the intermediate layer comprises a porous metal material and a resin material impregnated in the porous metal material. The sliding bearing according to claim 1, wherein, in the radial cross-section of the coiled bushing, the width of the gap gradually decreases from the outer circumferential surface to the inner circumferential surface of the coiled bushing, and closes at a position of 10-90% of the wall thickness.