Patent Description:
A shaft member such as a crankshaft, an intermediate shaft, a propulsion shaft, or the like for a ship is slidably supported by a bearing member such as a slide bearing or the like. Furthermore, a lubricating liquid is supplied to a gap between the shaft member and the bearing member. The lubricating liquid forms a lubricating film between the shaft member and the bearing member to inhibit seizure therebetween. Meanwhile, if surface roughnesses of the shaft member and the bearing member are high relative to a thickness of the lubricating film, seizure is likely to occur between these members.

As a technique for inhibiting seizure of a sliding member, a method of smoothing a sliding face, e.g., a surface, of the shaft member is known. For example, Patent Document <NUM> discloses a combined sliding member having surface characteristics adaptable to a reduction in friction of an internal combustion engine.

Patent Document <NUM> describes that the reduction in friction can be achieved by setting a surface roughness Rz of a sliding face of a piston ring to <NUM> to <NUM>, the surface roughness Rz of a sliding face of a cylinder liner to <NUM> to <NUM>, an initial wear height Rpk to <NUM> to <NUM>, an effective load roughness Rk to <NUM> to <NUM>, and an oil sump depth Rvk to <NUM> to <NUM>. <CIT>, which is a document according to Article <NUM>(<NUM>) EPC, discloses a sliding member comprising: a shaft member having a shaft diameter of greater than or equal to <NUM>; and a bearing member having an inner peripheral face which slidably supports an outer peripheral face of the shaft member.

Patent Document <NUM>: <CIT> Patent Document <NUM>: <CIT>.

In manufacture of a large sliding member for a ship, deflection of the shaft member or the like during mechanical processing may make it difficult to increase accuracy of roundness and cylindricity of the shaft member. Therefore, it may be difficult for the sliding member to achieve sufficient dimensional accuracy by mechanical processing alone.

In view of the foregoing circumstances, in the manufacture of the large sliding member for a ship, manual polishing of the sliding face after the mechanical processing can be considered. However, in light of manufacturing cost and the like, it is not realistic to precisely control a surface shape of the sliding face of such a large sliding member in such a manner as described in Patent Document <NUM>. Furthermore, in the sliding member for a ship or the like, hardness of the bearing member is not high in some cases, making polishing processing itself of a sliding face of the bearing member difficult.

The present invention was made in view of the foregoing circumstances, and an object of the present invention is to provide a sliding member which enables inhibition of seizure between a shaft member and a bearing member, while an increase in manufacturing cost is suppressed.

A sliding member according to the present invention made to solve the aforementioned problems is disclosed in claim <NUM>.

The sliding member according to the one aspect of the present invention enables inhibition of the seizure between the shaft member and the bearing member while an increase in manufacturing cost is suppressed.

Firstly, embodiments of the present invention are listed and described.

A sliding member according to one aspect of the present invention includes: a shaft member having a shaft diameter of greater than or equal to <NUM>; and a bearing member having an inner peripheral face which slidably supports an outer peripheral face of the shaft member, wherein in a case in which an arithmetic mean roughness of the outer peripheral face is denoted by Rai [µm], a contact rate Aat between the outer peripheral face and the inner peripheral face satisfies the following formula <NUM>.

In general, in a case in which the contact rate between the outer peripheral face of the shaft member and the inner peripheral face of the bearing member is high, the bearing pressure applied to the inner peripheral face of the bearing member decreases; thus, seizure between these members is easily inhibited. By satisfying the above formula <NUM>, the sliding member enables controlling the contact rate to be greater than or equal to a limit value at which the seizure can be inhibited. Furthermore, due to using the above formula <NUM>, the sliding member does not require precise control of the surface shape of the sliding face, and thus an increase in manufacturing cost can be inhibited.

The arithmetic mean roughness Rai is preferably less than or equal to <NUM>. Thus, owing to the arithmetic mean roughness Rai being less than or equal to the upper limit, the seizure between the shaft member and the bearing member can be more surely inhibited.

The shaft member is preferably a crank journal or a crankpin of a crankshaft. The crankshaft has sites which are eccentric to each other, and thus deflection is likely to occur in mechanical processing. Therefore, it is difficult to increase the dimensional accuracy by mechanical processing alone, and manual polishing is especially likely to be required after the mechanical processing. On the other hand, due to using the above formula <NUM>, the sliding member does not require precise control of the surface shape of the sliding face; thus, in the case in which the shaft member is a crank journal or a crankpin of a crankshaft, an increase in manufacturing cost can be effectively inhibited.

Another aspect of the present invention is a method for manufacturing a sliding member including: a shaft member having a shaft diameter of greater than or equal to <NUM>; and a bearing member having an inner peripheral face which slidably supports an outer peripheral face of the shaft member, the method including: a polishing step of manually polishing the outer peripheral face such that in a case in which an arithmetic mean roughness of the outer peripheral face is denoted by Rai [µm], a contact rate Aat between the outer peripheral face and the inner peripheral face satisfies the above formula <NUM>.

According to the method for manufacturing a sliding member, by manually polishing the outer peripheral face in the polishing step such that the above formula <NUM> is satisfied, the contact rate can be controlled to be greater than or equal to the limit value at which the seizure can be inhibited. Furthermore, due to using the above formula <NUM> in the polishing step, the method for manufacturing a sliding member does not require precise control of the surface shape of the sliding face, and thus an increase in manufacturing cost can be inhibited.

It is to be noted that in the present invention, the "shaft diameter" means a diameter of the outer peripheral face of the shaft member, and the "arithmetic mean roughness" means a value measured according to JIS-B0601 (<NUM>) at a high-frequency cut-off value (λc) of <NUM> and a low-frequency cut-off value (λs) of <NUM>.

In the present invention, the "contact rate" means a proportion of an area of a part which has come into contact with the bearing member, in the total sliding area of the outer peripheral face of the shaft member in a case in which the shaft member is rotated around a central axis thereof while the outer peripheral face of the shaft member is pressed against the inner peripheral face of the bearing member at an arbitrary angle in a radial direction of the shaft member.

Hereinafter, embodiments of the present invention are described in detail with reference to the drawings.

The sliding member in <FIG> includes: a shaft member <NUM> having a shaft diameter D of greater than or equal to <NUM>; a bearing member <NUM> having an inner peripheral face <NUM> which slidably supports an outer peripheral face <NUM> of the shaft member <NUM>; and a lubricating oil <NUM>. A central axis P of the shaft member <NUM> extends in a horizontal direction (a Y direction in <FIG>). The inner peripheral face <NUM> of the bearing member <NUM> surrounds the outer peripheral face <NUM> of the shaft member <NUM> along a circumferential direction. The lubricating oil <NUM> is supplied to a gap between the outer peripheral face <NUM> of the shaft member <NUM> and the inner peripheral face <NUM> of the bearing member <NUM>. Furthermore, the lubricating oil <NUM> forms an oil film <NUM>. The inner peripheral face <NUM> slidably supports the outer peripheral face <NUM> by thus facing the outer peripheral face <NUM> with the oil film <NUM> interposed therebetween.

According to the problem posed for the invention in the shaft member <NUM> having the shaft diameter of greater than or equal to <NUM>, it is difficult to increase the dimensional accuracy of the outer peripheral face <NUM> by mechanical processing alone; therefore, according to the invention a part not the entirety of the outer peripheral face <NUM> is manually polished after the mechanical processing. As referred to herein, to "manually polish" means manually polishing with sandpaper or the like.

In a case in which an arithmetic mean roughness of the outer peripheral face <NUM> (more specifically, an arithmetic mean roughness of the outer peripheral face <NUM> after manual polishing thereof) is denoted by Rai [µm], the contact rate Aat between the outer peripheral face <NUM> and the inner peripheral face <NUM> satisfies the following formula <NUM>. It is to be noted that as the "arithmetic mean roughness Rai", a value determined by the following procedure can be employed. Firstly, four circumferential positions are decided at intervals of <NUM> deg along the circumferential direction of the outer peripheral face <NUM>. Next, for each of these circumferential positions, two measurement points which differ in position in the axial direction are set. Then, arithmetic mean roughnesses measured at the measurement points at an evaluation length <NUM> are averaged, and the resulting average value is determined as the arithmetic mean roughness Rai of the outer peripheral face <NUM>. Furthermore, the evaluation length can be set along a direction orthogonal to a direction of the manual polishing. For example, in a case in which the outer peripheral face <NUM> is polished along the circumferential direction, the evaluation length can be set along the axial direction of the shaft member <NUM>.

The upper limit of the contact rate Aat is not particularly limited and is, for example, preferably <NUM>, more preferably <NUM>, and still more preferably <NUM>. When the contact rate Aat is greater than the upper limit, a polishing amount in the case of the manual polishing increases, and thus there may be a possibility that the manufacturing cost cannot be suppressed. It is to be noted that the "contact rate Aat" can be determined, for example, by using a straight edge having a plane which extends parallel to the axial direction of the shaft member <NUM>, or a shell-shaped bearing model having an inner peripheral face which partly surrounds the outer peripheral face <NUM> of the shaft member <NUM>. In these methods for measuring the contact rate Aat, ink is applied to the plane or the inner peripheral face, and then the plane or the inner peripheral face is pressed against the entirety of the outer peripheral face <NUM> of the shaft member <NUM> to transfer the ink thereonto. After that, a part onto which the ink has been transferred is defined as a contact part which comes into contact with the inner peripheral face <NUM>, the contact part being in the outer peripheral face <NUM>, and the contact rate Aat is determined by a transfer rate of the ink. In implementation of the method using the straight edge or the method using the bearing model, ink diluted with a diluent is preferably used. For example, it is preferred to use Red Touch Paste, available from Daizo Corporation, by diluting such that consistency as defined in JIS-K2220 (<NUM>) is greater than or equal to <NUM> and less than or equal to <NUM>. The consistency can be controlled by adjusting a concentration of the ink in accordance with a temperature of the ink in measurement of the contact rate Aat. Specifically, the consistency can be controlled in the following manner: in a case in which the temperature of the ink during the measurement is higher than or equal to <NUM> and lower than or equal to <NUM>, the concentration of the ink is set to <NUM>%; in a case in which the temperature is higher than <NUM> and lower than or equal to <NUM>, the concentration of the ink is set to <NUM>%; and in a case in which the temperature is higher than <NUM> and lower than or equal to l40 °C, the concentration of the ink is set to <NUM>%. Applying the ink which has been thus diluted to the straight edge or the bearing model facilitates determining microscopic unevenness of the outer peripheral face <NUM> when the ink has been transferred.

The shaft member <NUM> is a rotating body which rotates in the circumferential direction with respect to the bearing member <NUM>. The shaft member <NUM> is exemplified by a crankshaft, an intermediate shaft, a propulsion shaft, and the like for a ship, each of which is to be disposed in a ship. Examples of a material of the shaft member <NUM> include carbon steel, low-alloy steel, an aluminum alloy, and the like.

The shaft member <NUM> is preferably a crank journal or a crankpin of a crankshaft. The crankshaft has a large number of sites which are eccentric to each other, and thus deflection is likely to occur in mechanical processing. Therefore, it is difficult to increase the dimensional accuracy by mechanical processing alone, and manual polishing of the outer peripheral face <NUM> of the shaft member <NUM> is especially likely to be required after the mechanical processing. On the other hand, due to using the above formula <NUM>, the sliding member does not require precise control of surface characteristics of the sliding face. Accordingly, in the case in which the shaft member <NUM> is a crank journal or a crankpin of a crankshaft, the sliding member enables effective inhibition of an increase in manufacturing cost.

The lower limit of the shaft diameter D of the shaft member <NUM> is <NUM> as described above, may be <NUM>, and may be <NUM>. In a case in which the shaft diameter D of the shaft member <NUM> is greater than or equal to the lower limit, it is difficult to increase the dimensional accuracy by mechanical processing alone, and manual polishing of the outer peripheral face <NUM> of the shaft member <NUM> is likely to be required after the mechanical processing. Meanwhile, in light of the manufacturing cost and the like, to strictly control the surface shape of the outer peripheral face <NUM> of the shaft member <NUM> having a large diameter by manual polishing is far from realistic. With regard to this point, due to using the above formula <NUM>, the sliding member does not require precise control of the surface shape of the sliding face. Therefore, even when the shaft diameter D of the shaft member <NUM> is greater than or equal to the lower limit, an increase in manufacturing cost can be inhibited.

The upper limit of the shaft diameter D of the shaft member <NUM> is preferably <NUM>,<NUM>, more preferably <NUM>,<NUM>, and still more preferably <NUM>,<NUM>. When the shaft diameter D is greater than the upper limit, the sliding member may become too large, which may be contrary to a demand for, e.g., a reduction in device size.

The lower limit of a Young's modulus of the shaft member <NUM> is preferably <NUM> GPa, more preferably <NUM> GPa, and still more preferably <NUM> GPa. When the Young's modulus of the shaft member <NUM> is less than the lower limit, deflection of the shaft member <NUM> may increase at the time of the mechanical processing. As a result, time required for the manual polishing increases, and thus it may be difficult to sufficiently suppress the manufacturing cost. On the other hand, the sliding member exhibits especially superior effects in a case in which deflection of the shaft member <NUM> occurs to some degree. In light of this, the upper limit of the Young's modulus of the shaft member <NUM> is not particularly limited and may be, for example, <NUM> GPa.

The upper limit of the arithmetic mean roughness Rai of the outer peripheral face <NUM> is preferably <NUM>, more preferably <NUM>, and still more preferably <NUM>. When the arithmetic mean roughness Rai is greater than the upper limit, it may be difficult to inhibit the seizure between the outer peripheral face <NUM> and the inner peripheral face <NUM>. Meanwhile, the lower limit of the arithmetic mean roughness Rai can be set to <NUM> in light of enabling easily adjusting the surface shape of the outer peripheral face <NUM> by the manual polishing, and may be <NUM>.

The shaft member <NUM> may have contact-free parts on both ends in the axial direction thereof, the contact-free parts not coming into contact with the bearing member <NUM>. That is to say, on the both ends in the axial direction, the outer peripheral face <NUM> of the shaft member <NUM> may be provided with non-contact parts at which no contact occurs in the above-described method for measuring the contact rate Aat. In the case in which the shaft member <NUM> is a crank journal or a crankpin as described above, the contact-free parts are likely to be generated. The sliding member having a configuration in which the shaft member <NUM> has such contact-free parts enables easy inhibition of the seizure between the shaft member <NUM> and the bearing member <NUM>.

On the outer peripheral face <NUM> of the shaft member <NUM>, a plurality of roughness projection apices may be present, wherein the roughness projection apices are calculated by the following procedure. Firstly, based on a roughness curve with a measured length of <NUM>, the roughness curve being measured at a cut-off value of <NUM> according to JIS-B0601 (<NUM>), an average line of the roughness curve is set according to JIS-B0601 (<NUM>). With the average line as a reference, heights of measurement points above the average line are defined as positive values, while heights of measurement points below the average line are defined as negative values. An average value of the heights of all the measurement points having positive values is denoted by Thr0. Next, of the measurement points on the roughness curve, a measurement point which is higher than measurement points adjacent thereto on both sides and has a height of greater than -Thr0 is defined as a temporary apex. Of measurement points between temporary apices adjacent to each other, a measurement point having a smallest height (having a largest depth from the temporary apices adjacent to each other) is defined as a valley. Then, for all the temporary apices, height differences between a temporary apex and each of valleys adjacent to the temporary apex on both sides are respectively determined, and apices in which the larger value of these height differences is less than <NUM> × Thr0 are excluded. As a result, remaining temporary apices are determined as roughness projection apices.

In a case in which the roughness projection apices are present on the outer peripheral face <NUM> of the shaft member <NUM>, the lower limit of a radius of curvature of roughness projections on the outer peripheral face <NUM> may be <NUM>, and may be <NUM>. When the manual polishing is performed, the radius of curvature of roughness projections is likely to increase. When the radius of curvature of roughness projections is large, seizure is likely to occur between the outer peripheral face <NUM> and the inner peripheral face <NUM>. Even with such a configuration, the sliding member enables easy inhibition of the seizure between the outer peripheral face <NUM> and the inner peripheral face <NUM>.

It is to be noted that the "radius of curvature of roughness projections" as referred to herein means a value calculated by the following procedure. Firstly, straight lines are drawn toward the roughness projection apex from all measurement points between the roughness projection apex and valleys adjacent to the roughness projection apex on both sides, and the measurement point for which the slope of the straight line is the largest is defined as an end of the roughness projection. The radius of curvature of each roughness projection is determined by -<NUM>/a, wherein a denotes a quadratic coefficient of a quadratic function obtained by approximating a roughness curve between both ends of each roughness projection by the method of least squares. A median of the radii of curvature of all the roughness projections on the roughness curve is determined as the radius of curvature of the roughness projections.

When the manual polishing is performed, the outer peripheral face <NUM> of the shaft member <NUM> is likely to have a large radius of curvature of roughness projections as described above. Furthermore, with regard to other roughness characteristics of the outer peripheral face <NUM>, the degree of roughness is also likely to increase. In this case, by using sandpaper having a sufficiently large grit number, the arithmetic mean roughness Rai of the outer peripheral face <NUM> can be reduced. For example, by polishing with sandpaper having roughness of a grit number of greater than or equal to <NUM>, the arithmetic mean roughness Rai can be reduced to less than or equal to <NUM>. The grit number of the sandpaper may be greater than <NUM>, and may be greater than <NUM>. A procedure for polishing with the sandpaper is exemplified by a method in which the sandpaper is pressed with the hand against the outer peripheral face <NUM> while rotating the shaft member <NUM>, thereby polishing the outer peripheral face <NUM> along the circumferential direction of the outer peripheral face <NUM>. Furthermore, in a case in which it is difficult to polish while rotating the shaft member <NUM>, e.g., in case of a crankshaft for a ship or the like, a method may be employed in which the outer peripheral face <NUM> is manually rubbed with the sandpaper along the circumferential direction of the outer peripheral face <NUM>.

The bearing member <NUM> is exemplified by a crank bearing, an intermediate bearing, a propulsion bearing, and the like for a ship, each of which is to be disposed in a ship. Examples of a material of the bearing member <NUM> include white metal, an aluminum alloy, trimetal, kelmet, and the like.

A hardness H<NUM> [HV] of the shaft member <NUM> is preferably higher than a hardness H<NUM> [HV] of the bearing member <NUM>. In general, since the hardness H<NUM> of the bearing member <NUM> is low, it is difficult to intentionally control the surface roughness of the inner peripheral face <NUM> by mechanical processing and/or the like. Even in such a case, by setting the hardness H<NUM> of the shaft member <NUM> to be higher than the hardness H<NUM> of the bearing member <NUM>, the inner peripheral face <NUM> of the bearing member <NUM> can be polished owing to the sliding with the shaft member <NUM>. As a result, the surface roughness of the inner peripheral face <NUM> of the bearing member <NUM> is reduced, and thus the contact rate Aat between the outer peripheral face <NUM> and the inner peripheral face <NUM> is easily controlled. The lower limit of a ratio (H<NUM>/H<NUM>) of the hardness H<NUM> of the shaft member <NUM> to the hardness H<NUM> of the bearing member <NUM> is preferably <NUM>, more preferably <NUM>, still more preferably <NUM>, and particularly preferably <NUM>. When the above ratio is less than the lower limit, it may be difficult to reduce the surface roughness of the inner peripheral face <NUM> by rotation of the shaft member <NUM>. Conversely, the upper limit of the above ratio is not particularly limited and may be, for example, <NUM> in light of ease of selection of materials of the shaft member <NUM> and the bearing member <NUM>, and the like.

The lubricating oil <NUM> is exemplified by paraffin base oil and the like. By forming the oil film <NUM>, the lubricating oil <NUM> facilitates maintaining a fluid lubrication state between the outer peripheral face <NUM> and the inner peripheral face <NUM>.

The lower limit of a viscosity of the lubricating oil <NUM> is preferably <NUM> × <NUM>-<NUM> Pa sec, and more preferably <NUM> × <NUM>-<NUM> Pa sec. When the viscosity is less than the lower limit, there may be a possibility that the seizure between the outer peripheral face <NUM> and the inner peripheral face <NUM> cannot be sufficiently inhibited. Conversely, the upper limit of the viscosity of the lubricating oil <NUM> is preferably <NUM> × <NUM>-<NUM> Pa sec, and more preferably <NUM> × <NUM>-<NUM> Pa·sec. When the viscosity is greater than the upper limit, there may be a possibility that a friction loss between the outer peripheral face <NUM> and the inner peripheral face <NUM> cannot be sufficiently inhibited. It is to be noted that the viscosity as referred to herein means a viscosity calculated based on a temperature of the oil film <NUM> during steady driving of the shaft member <NUM>. Furthermore, "during steady driving" as referred to herein means a point of time at which the rotation of the shaft member <NUM> is kept constant except for the start and end of the rotation of the shaft member <NUM>.

Due to satisfying the above formula <NUM>, the sliding member enables controlling the contact rate Aat to be greater than or equal to the limit value at which the seizure can be inhibited. Furthermore, due to using the above formula <NUM>, the sliding member does not require precise control of the surface shape of the sliding face, e.g., does not require controlling roughness characteristics other than the arithmetic mean roughness Rai to fall within predetermined ranges, controlling the contact rate Aat to be excessively large, etc. Thus, the sliding member enables inhibition of the seizure between the shaft member <NUM> and the bearing member <NUM> as well as inhibition of an increase in manufacturing cost.

By the method for manufacturing a sliding member in <FIG>, the sliding member in <FIG> is manufactured. The method for manufacturing a sliding member includes a polishing step S1 of manually polishing the outer peripheral face <NUM> of the shaft member <NUM>.

In the polishing step S1, the outer peripheral face <NUM> is manually polished such that the contact rate Aat between the outer peripheral face <NUM> and the inner peripheral face <NUM> satisfies the above formula <NUM>. In the polishing step S1, the outer peripheral face <NUM> is polished to satisfy the above formula <NUM> in such a manner that the contact rate Aat is increased or the arithmetic mean roughness Rai of the outer peripheral face <NUM> is reduced.

A method for increasing the contact rate Aat is exemplified by a method in which a contact part of the outer peripheral face <NUM> is specified using the above-mentioned straight edge or shell-shaped bearing model, and then the contact part is partly polished such that the total contact rate between the outer peripheral face <NUM> and the inner peripheral face <NUM> can be increased.

A method for reducing the arithmetic mean roughness Rai of the outer peripheral face <NUM> is exemplified by polishing the outer peripheral face <NUM> with sandpaper having a large grit number. The grit number of the sandpaper is preferably greater than or equal to <NUM>, more preferably greater than or equal to <NUM>, and still more preferably greater than or equal to <NUM>. By thus using the sandpaper having a large grit number, the arithmetic mean roughness Rai of the outer peripheral face <NUM> is easily reduced to satisfy the above formula <NUM>.

According to the method for manufacturing a sliding member, by manually polishing the outer peripheral face <NUM> in the polishing step S <NUM> such that the above formula <NUM> is satisfied, the contact rate Aat can be controlled to be greater than or equal to the limit value at which the seizure can be inhibited. Furthermore, due to using the above formula <NUM> in the polishing step S <NUM>, the method for manufacturing a sliding member does not require precise control of the surface shape of the sliding face. Thus, the method for manufacturing a sliding member enables inhibition of the seizure between the shaft member <NUM> and the bearing member <NUM> as well as inhibition of an increase in manufacturing cost.

The above-described embodiments do not limit the configuration of the present invention. Therefore, in the above-described embodiments, the components of each part of the above-described embodiments can be omitted, replaced, or added based on the description in the present specification and general technical knowledge. The present invention is limited by the scope of the appended claims.

In the above-described embodiments, the central axis of the shaft member extends in the horizontal direction; however, the central axis of the shaft member may be inclined to the horizontal direction.

In the above-described embodiments, the lubricating oil is supplied to the gap between the outer peripheral face of the shaft member and the inner peripheral face of the bearing member; however, a lubricating liquid other than the lubricating oil may be used for the sliding member. For example, it is possible to use seawater or the like as the lubricating liquid.

Hereinafter, the present invention is described in detail by way of Examples; the present invention should not be construed as being limited to description in the Examples. In the Examples, a seizure test and a simulation test were performed.

A shaft member and a bearing member having an inner peripheral face which surrounded the entire periphery of an outer peripheral face of the shaft member were fixed to a frictional wear tester available from KOBELCO MACHINERY ENGINEERING Co. The seizure test of each of No. <NUM> to No. <NUM> was performed using the frictional wear tester in such a manner that the shaft member was rotated while the inner peripheral face of the bearing member was pressed against the outer peripheral face of the shaft member under the following configuration conditions and operating conditions. A load from the bearing member to the shaft member was increased in stages from the start of the test to a maximum load. When seizure occurred between the shaft member and the bearing member, the frictional wear tester was stopped, and the load at a stage immediately before that of the load at that point of time was defined as a limit load. In this seizure test, the outer peripheral face of the shaft member was manually polished by pressing sandpaper with the hand against the outer peripheral face of the shaft member while rotating the shaft member. By the manual polishing, the arithmetic mean roughness Rai of the outer peripheral face of the shaft member, and the contact rate between the shaft member and the bearing member were controlled. In this seizure test, owing to the shaft member having a relatively shaft diameter being used for the test, with regard to each of the following No. <NUM> to No. <NUM>, the contact rate between the shaft member and the bearing member could be improved to substantially <NUM>%. Table <NUM> shows whether seizure occurred and the limit load in the seizure test.

In No. <NUM>, carbon steel having a Young's modulus of <NUM> GPa and a Poisson's ratio of <NUM> was used as the shaft member, and the shaft diameter was set to <NUM> (tolerance: -<NUM> to -<NUM>). The arithmetic mean roughness of the outer peripheral face of the shaft member was controlled to be <NUM>. It is to be noted that in No. <NUM> to No. <NUM>, the arithmetic mean roughness of the outer peripheral face of the shaft member was determined by the above-described method for measuring the arithmetic mean roughness Rai in such a manner that the evaluation length was set along the axial direction of the outer peripheral face of the shaft member. As the bearing member, a slide bearing, available from DAIDO METAL CO. , constituted by a combination of an upper half member and a lower half member was used. With regard to the slide bearing, white metal corresponding to WJ1 as defined in JIS-H5401 (<NUM>) is used, the Young's modulus being <NUM> GPa and the Poisson's ratio being <NUM>; a diameter of the inner peripheral face is <NUM> (tolerance: <NUM> to +<NUM>); and an axial direction length of the inner peripheral face (bearing width) is <NUM>. The arithmetic mean roughness of the inner peripheral face of the bearing member was set to <NUM>. A rotation speed of the shaft member was set to a constant value of <NUM>,<NUM> rpm. Furthermore, at the time of rotating the shaft member, "FBK OIL RO32", available from ENEOS Corporation, was supplied as the lubricating oil between the outer peripheral face of the shaft member and the inner peripheral face of the bearing member. A supply temperature of the lubricating oil was set to <NUM>, and circulating oil supply was employed as a supply method. The load from the bearing member to the shaft member was set to <NUM> kN at the start of the test and increased in stages by <NUM> kN at intervals of <NUM> minutes to the maximum load of <NUM> kN.

In No. <NUM>, low-alloy steel in which the Young's modulus was <NUM> GPa and the Poisson's ratio was <NUM> was used as the shaft member, and the shaft diameter was set to <NUM> (tolerance: -<NUM> to -<NUM>). The arithmetic mean roughness of the outer peripheral face of the shaft member was controlled to be <NUM>. The bearing member was the same as in No. <NUM>. The rotation speed of the shaft member was set to a constant value of <NUM>,<NUM> rpm. Furthermore, as in No. <NUM>, the lubricating oil was supplied between the outer peripheral face of the shaft member and the inner peripheral face of the bearing member. The load from the bearing member to the shaft member was set to <NUM> kN at the start of the test and increased in stages by <NUM> kN at intervals of <NUM> minutes to the maximum load of <NUM> kN.

The configuration conditions and the operating conditions of No. <NUM> were similar to those of No. <NUM> except that the arithmetic mean roughness of the outer peripheral face of the shaft member was controlled to be <NUM>.

As shown in Table <NUM>, the limit load of No. <NUM>, in which the arithmetic mean roughness of the outer peripheral face of the shaft member is <NUM>, is <NUM> kN. This means that seizure occurred at the point of time when the load was <NUM> kN. Furthermore, the limit load of No. <NUM>, in which the arithmetic mean roughness of the outer peripheral face of the shaft member is <NUM>, is <NUM> kN. This means that seizure occurred at the point of time when the load was <NUM> kN. No. <NUM> to No. <NUM>, in which no seizure occurred, satisfy the above formula <NUM>. On the other hand, No. <NUM> and No. <NUM>, in which seizure occurred, do not satisfy the above formula <NUM>.

In the simulation test, EXCITE Power Unit (EXCITE <NUM> R1, available from AVL List GmbH) was used as software, and the following configuration conditions and operating conditions were set to confirm a sliding state between the shaft member and the bearing member. As an analysis model of each of the following No. <NUM> to No. <NUM>, a single bearing model (joint: EHD2) was used. The lubricating oil was supplied between the outer peripheral face of the shaft member and the inner peripheral face of the bearing member by circulating oil supply. <FIG> shows the relationship between a minimum film thickness ratio A and the bearing pressure applied to the inner peripheral face in each of No. <NUM> to No. <NUM>; <FIG> shows the relationship between the minimum film thickness ratio A and the bearing pressure applied to the inner peripheral face in each of No. <NUM>, No. <NUM>, and No. <NUM>; <FIG> shows the relationship between the minimum film thickness ratio A and the bearing pressure applied to the inner peripheral face in each of No. <NUM>, No. <NUM>, and No. <NUM>; and <FIG> shows the relationship between the minimum film thickness ratio A and the maximum contact pressure in each of No. <NUM> to No. <NUM>. It is to be noted that the "minimum film thickness ratio" as referred to herein means a value calculated according to the following formula <NUM> in a case in which a minimum oil film thickness of the lubricating oil is denoted by hmin [µm], the arithmetic mean roughness of the outer peripheral face of the shaft member is denoted by Rai [µm], and the arithmetic mean roughness of the inner peripheral face of the bearing member is denoted by Ra<NUM> [µm]; and the "maximum contact pressure" as referred to herein means a maximum pressure at a time of solid contact between the outer peripheral face of the shaft member and the inner peripheral face of the bearing member.

In No. <NUM>, a shaft member <NUM> in <FIG> was used, and the following configuration conditions and operating conditions were set.

Shaft member: as the shaft member <NUM>, steel in which an axial direction length L<NUM> was <NUM>, a shaft diameter D<NUM> was <NUM>, a stiffness was <NUM>,<NUM> N/mm<NUM>, and the Poisson's ratio was <NUM> was used. The arithmetic mean roughness Rai of an outer peripheral face of the shaft member <NUM> was set to <NUM>, and a root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>. As roughness parameters (Summit Roughness, Mean Summit Height, and Elastic Factor) to be input to the software, values obtained by converting the arithmetic mean roughness Rai by the following procedure were employed. Firstly, six small shaft members (shaft diameter: <NUM>; axial direction length: <NUM>) were prepared, and each outer peripheral face was manually polished such that the arithmetic mean roughness Ra of the outer peripheral face varied in a range from approximately <NUM> to <NUM>. The arithmetic mean roughness Ra was determined by the above-described method for measuring the arithmetic mean roughness Rai in such a manner that the evaluation length was set along the axial direction of the outer peripheral face of the small shaft member. Furthermore, based on waveform data acquired in the measurement of the arithmetic mean roughness Ra, the roughness parameters were determined according to definitions in the manual of the software. Then, regression equations representing relationships between the arithmetic mean roughness Ra and the respective roughness parameters were derived, and according to these regression equations, the predetermined arithmetic mean roughness Rai was converted to the corresponding roughness parameters. Also in the following No. <NUM> to No. <NUM>, values converted by the above-described method were employed as the roughness parameters of the shaft member to be input to the software. The outer peripheral face of the shaft member <NUM> has one ring-shaped concave portion extending in the circumferential direction thereof. The concave portion has a rectangular cross section with a width (length in the axial direction of the shaft member <NUM>) of LA1 [mm] and a depth of d<NUM> [mm]. In the axial direction of the shaft member <NUM>, distances from both ends of the shaft member <NUM> to the concave portion are equal. The depth d<NUM> of the concave portion was set to <NUM>. The concave portion is a contact-free part which does not come into contact with the bearing member at the time of rotating the shaft member <NUM>. Thus, the contact rate Aat between the shaft member <NUM> and the bearing member is calculated by (L<NUM> - LA1) / L<NUM>. The width LA1 of the concave portion was set to a value at which the contact rate Aat was <NUM>.

Bearing member: as the bearing member, white metal in which the axial direction length of the inner peripheral face (bearing width) was <NUM>, a radial gap with the shaft member was <NUM>, the stiffness was <NUM>,<NUM> N/mm<NUM>, and the Poisson's ratio was <NUM> was used. The arithmetic mean roughness Ra<NUM> of the inner peripheral face of the bearing member was set to <NUM>, and a root mean square roughness Rq<NUM> was set to <NUM>, obtained by multiplying the arithmetic mean roughness Ra<NUM> by <NUM>. As the roughness parameters to be input to the software, values obtained by converting, according to the above-mentioned regression equations, the arithmetic mean roughness Ra<NUM> to the corresponding roughness parameters were employed. Also in the following No. <NUM> to No. <NUM>, values converted by the above-described method were employed as the roughness parameters of the bearing member to be input to the software.

Rotation speed: the rotation speed of the shaft member <NUM> was set to <NUM>,<NUM> rpm.

Load: the load applied to the inner peripheral face of the bearing member was increased in stages from <NUM> kN to <NUM> kN.

Lubricating oil: a lubricating oil having a density of <NUM>/m<NUM> and a specific heat of <NUM>,<NUM> J/(kg·K) was used. Furthermore, the viscosity of the lubricating oil was fixed to <NUM> × <NUM>-<NUM> Pa·sec. This viscosity corresponds to the viscosity of FBK OIL RO32, available from ENEOS Corporation, at <NUM>.

Model at the time of solid contact: at the time of solid contact between the shaft member and the bearing member, a perfect elasto-plastic body having a yield stress of <NUM> MPa was used as a plastic deformation model of surface roughness projections.

In No. <NUM>, the shaft member <NUM> in <FIG> was used, and the following configuration conditions were set. Furthermore, the operating conditions were similar to that of No. <NUM>.

Shaft member: the configuration was similar to that of No. <NUM> except that the arithmetic mean roughness Rai of the outer peripheral face was set to <NUM>, the root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>, and the width LA1 of the concave portion was set to a value at which the contact rate Aat was <NUM>.

Bearing member: the configuration was similar to that of No. <NUM> except that the arithmetic mean roughness Ra<NUM> of the inner peripheral face was set to <NUM>, and the root mean square roughness Rq<NUM> was set to <NUM>, obtained by multiplying the arithmetic mean roughness Ra<NUM> by <NUM>.

In No. <NUM>, the shaft member <NUM> in <FIG> was used, and the following configuration conditions were set. Furthermore, the operating conditions were similar to those of No. <NUM>.

Shaft member: the configuration was similar to that of No. <NUM> except that the arithmetic mean roughness Rai of the outer peripheral face was set to <NUM>, the root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>, and the width LA1 of the concave portion was set to the value at which the contact rate Aat was <NUM>.

In No. <NUM>, the shaft member <NUM> in <FIG> and the same bearing member as in No. <NUM> were used. Furthermore, the operating conditions were similar to those of No. <NUM>.

Shaft member: the configuration was similar to that of No. <NUM> except that the width LA1 of the concave portion was set to the value at which the contact rate Aat was <NUM>.

In No. <NUM>, the following configuration conditions were set. Furthermore, the operating conditions were similar to those of No. <NUM>.

Shaft member: as the shaft member, steel in which the axial direction length was <NUM>, the shaft diameter was <NUM>, the stiffness was <NUM>,<NUM> N/mm<NUM>, and the Poisson's ratio was <NUM> was used. The arithmetic mean roughness Rai of the outer peripheral face of the shaft member was set to <NUM>, and the root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>. The outer peripheral face of the shaft member did not have a concave portion, and the contact rate Aat was <NUM>.

Shaft member: the configuration was similar to that of No. <NUM> except that the arithmetic mean roughness Rai of the outer peripheral face was set to <NUM>, and the root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>.

Bearing member: the same bearing member as in No. <NUM> was used.

In No. <NUM>, a shaft member <NUM> in <FIG> was used, and the following configuration conditions were set. Furthermore, the operating conditions were similar to those of No. <NUM>.

Shaft member: as the shaft member <NUM>, steel in which an axial direction length L<NUM> was <NUM>, a shaft diameter D<NUM> was <NUM>, the stiffness was <NUM>,<NUM> N/mm<NUM>, and the Poisson's ratio was <NUM> was used. The arithmetic mean roughness Rai of an outer peripheral face of the shaft member <NUM> was set to <NUM>, and the root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>. The outer peripheral face of the shaft member <NUM> has three ring-shaped concave portions extending in the circumferential direction thereof. These concave portions have rectangular cross sections which have widths (lengths in the axial direction of the shaft member <NUM>) of LA21 [mm], LA22 [mm], and LA23 [mm], respectively, and each of which has a depth of d<NUM> [mm]. The widths LA21, LA22, and LA23 of the concave portions are equal to each other. In the axial direction of the shaft member <NUM>, the concave portions are arranged at regular intervals. The depth d<NUM> of each of the concave portions was set to <NUM>. The concave portions are contact-free parts which do not come into contact with the bearing member at the time of rotating the shaft member <NUM>. Thus, the contact rate Aat between the shaft member <NUM> and the bearing member is calculated by (L<NUM> - LA21 - LA22 - LA23) / L<NUM>. Each of the widths LA21, LA22, and LA23 of the concave portions was set to a value at which the contact rate Aat was <NUM>.

Shaft member: an axial direction length of the shaft member <NUM> is controlled to be smaller than an axial direction length L<NUM> of the inner peripheral face of the bearing member (bearing width L<NUM>). That is to say, the axial direction length of the shaft member <NUM> is, at both ends thereof, shorter than that of the inner peripheral face by LA31 [mm] and LA32 [mm], respectively. The amounts LA31 and LA32 by which the axial direction length has been shortened are equal. The shaft member <NUM> simulates a shaft member having contact-free parts on both ends thereof. As the shaft member <NUM>, steel in which the axial direction length was L<NUM> - LA31 - LA32 [mm], a shaft diameter D<NUM> was <NUM>, the stiffness was <NUM>,<NUM> N/mm<NUM>, and the Poisson's ratio was <NUM> was used. The arithmetic mean roughness Rai of the outer peripheral face of the shaft member <NUM> was set to <NUM>, and the root mean square roughness Rqi was set to <NUM>, obtained by multiplying the arithmetic mean roughness Rai by <NUM>. The contact rate Aat between the shaft member <NUM> and the bearing member is calculated by (L<NUM> - LA31 - LA32) / L<NUM>. Furthermore, each of LA31 and LA32 was set to a value at which the contact rate Aat was <NUM>.

Bearing member: the configuration was similar to that of No. <NUM> except that the arithmetic mean roughness Ra<NUM> of the inner peripheral face was set to <NUM>, and the root mean square roughness Rq<NUM> was set to <NUM>, obtained by multiplying the arithmetic mean roughness Ra<NUM> by <NUM>. That is to say, the axial direction length L<NUM> of the inner peripheral face of the bearing member was set to <NUM>.

As shown in <FIG>, when comparing No. <NUM> to No. <NUM>, in which the contact rate Aat is <NUM> and equal, at the same bearing pressure, the lower the arithmetic mean roughness Rai is, the higher the minimum film thickness ratio A is. Also in <FIG>, at the same bearing pressure, the minimum film thickness ratio A of No. <NUM>, in which the arithmetic mean roughness Rai is low, is high as compared with that of No. <NUM> and No. <NUM>, in which the arithmetic mean roughness Rai is high. Furthermore, at the same bearing pressure, the minimum film thickness ratio A of No. <NUM>, in which the contact rate Aat is <NUM>, is higher than that of No. <NUM>, in which the contact rate Aat is <NUM>. When comparing No. <NUM>, No. <NUM>, and No. <NUM>, which are equal in terms of the contact rate Aat and the arithmetic mean roughness Rai in <FIG>, it is found that the minimum film thickness ratio A varies owing to the difference in the disposition of the contact-free part(s).

<FIG> shows a tendency for the maximum contact pressure to be uniquely determined by the minimum film thickness ratio A, regardless of the contact rate Aat, the arithmetic mean roughness Ra<NUM>, and the disposition of the contact-free part(s). Therefore, the magnitude of the minimum film thickness ratio A can be used as an indicator that shows resistance to the seizure between the shaft member and the bearing member. Furthermore, as described above, since the minimum film thickness ratio A increases as the arithmetic mean roughness Rai decreases and the contact rate Aat increases, the sliding member in this simulation test has superior seizure resistance when the arithmetic mean roughness is lower and the contact rate Aat is higher.

In the seizure test, the limit load of No. <NUM> is <NUM> kN, and this limit load is converted to the bearing pressure of <NUM> MPa. Accordingly, it is considered that in No. <NUM>, seizure occurs under the condition of the bearing pressure of approximately <NUM> MPa. Meanwhile, the condition of No. <NUM> corresponds to that of No. <NUM>, in which the arithmetic mean roughness Rai of the shaft member is <NUM> and the contact rate Aat is <NUM>. According to <FIG>, in No. <NUM>, the minimum film thickness ratio A at the bearing pressure of <NUM> MPa is <NUM>. The minimum film thickness ratio A of <NUM> satisfies a range of the minimum film thickness ratio A of less than <NUM>, in which it is generally possible for seizure to occur. Furthermore, referring to <FIG>, the maximum contact pressure is generated at the minimum film thickness ratio A of around <NUM>. Accordingly, in this simulation test, it was concluded that seizure occurred at the bearing pressure at which the minimum film thickness ratio A was <NUM>. That is to say, the bearing pressure at which the minimum film thickness ratio A was <NUM> was defined as a seizure limit bearing pressure Plim [MPa].

<FIG> shows a plot obtained by reading, as the seizure limit bearing pressure, the bearing pressure at which the minimum film thickness ratio A was <NUM> in each of <FIG>, wherein the horizontal axis represents the arithmetic mean roughness and the vertical axis represents the seizure limit bearing pressure Plim. Furthermore, each curve in <FIG> means a power approximation of the plotted values. In the conditions in which the shaft member <NUM> was used and the contact rate Aat was <NUM>, in the case in which the arithmetic mean roughness of the outer peripheral face of the shaft member is denoted by Rai [µm], the seizure limit bearing pressure Plim was approximated by Rai raised to the power of -<NUM>. On the other hand, in the conditions in which the shaft member <NUM> was used and the contact rate Aat was <NUM>, the seizure limit bearing pressure Plim was approximated by Rai raised to the power of -<NUM>. This indicates that the seizure limit bearing pressure Plim is proportional to the arithmetic mean roughness Rai raised to the power of approximately -<NUM>, without being influenced by the contact rate Aat.

<FIG> shows a plot obtained by reading, as the seizure limit bearing pressure, the bearing pressure at which the minimum film thickness ratio A was <NUM> in each of <FIG>, wherein the horizontal axis represents the contact rate Aat and the vertical axis represents the seizure limit bearing pressure Plim. Furthermore, each curve in <FIG> means a power approximation of the plotted values. In the conditions in which the shaft member <NUM> was used and the arithmetic mean roughness Rai was <NUM>, the seizure limit bearing pressure Plim was approximated by Rai raised to the power of <NUM>. In the conditions in which the shaft member <NUM> was used and the arithmetic mean roughness Rai was <NUM>, the seizure limit bearing pressure Plim was approximated by Rai raised to the power of <NUM>. In the conditions in which the shaft member <NUM> was used and the arithmetic mean roughness Rai was <NUM>, the seizure limit bearing pressure Plim was approximated by Rai raised to the power of <NUM>. This indicates that the seizure limit bearing pressure Plim in the case of using the shaft member <NUM> is proportional to the contact rate Aat raised to the power of approximately <NUM>, without being influenced by the arithmetic mean roughness Ra<NUM>.

On the other hand, in the conditions in which the shaft member <NUM> was used and the arithmetic mean roughness Rai was <NUM>, the seizure limit bearing pressure Plim was approximated by Rai raised to the power of <NUM>. Furthermore, in the conditions in which the shaft member <NUM> was used and the arithmetic mean roughness Rai was <NUM>, the seizure limit bearing pressure Plim was approximated by Rai raised to the power of <NUM>.

According to the above discussion regarding <FIG>, it is considered that the arithmetic mean roughness Rai [µm] and the contact rate Aat independently contribute to the seizure limit bearing pressure Plim [MPa]. Hence, it was presumed that the seizure limit bearing pressure Plim was calculated according to the following formula <NUM>. It is to be noted that in the following formula <NUM>, α, β, and γ denote constants determined by the shape of the shaft member.

Based on the values of the seizure limit bearing pressure Plim in the simulation test, values of α, β, and γ in the above formula <NUM> were derived. As a result, in the case of using the shaft member <NUM>, α = <NUM>, β = -<NUM>, and γ = <NUM> can be assigned to the above formula <NUM>; in the case of using the shaft member <NUM>, α = <NUM>, β = -<NUM>, and γ = <NUM> can be assigned to the above formula <NUM>; and in the case of using the shaft member <NUM>, α = <NUM>, β = -<NUM>, and γ = <NUM> can be assigned to the above formula <NUM>.

It is considered that the seizure between the shaft member and the bearing member is inhibited under the condition in which the seizure limit bearing pressure Plim in the above formula <NUM> is sufficiently high. For example, by using <NUM> MPa, obtained by converting the maximum load of <NUM> kN in the seizure test to the bearing pressure, Plim ≥ <NUM> can be employed as a condition for inhibiting the seizure. This condition is obtained as the following formula <NUM> by using the above formula <NUM>.

In a manufacturing process of a crankshaft of a vessel, in a case in which the contact condition between the shaft member and the bearing member becomes poor after mechanical processing, contact-free parts are often generated at both ends of the shaft member. Thus, the above formula <NUM> was obtained by substituting α = <NUM>, β = -<NUM>, and γ = <NUM>, which are the parameters in the case of using the shaft member <NUM>, into the above formula <NUM>.

Claim 1:
A sliding member comprising:
a shaft member (<NUM>, <NUM>, <NUM>, <NUM>) having a shaft diameter (D) of greater than or equal to <NUM>; and
a bearing member (<NUM>) having an inner peripheral face (<NUM>) which slidably supports an outer peripheral face (<NUM>) of the shaft member (<NUM>, <NUM>, <NUM>, <NUM>),
wherein the outer peripheral face (<NUM>) of the shaft member (<NUM>, <NUM>, <NUM>, <NUM>) is polished in part and not in its entirety by manual polishing after mechanical processing,
wherein
in a case in which an arithmetic mean roughness of the outer peripheral face (<NUM>) is denoted by Rai [µm], a contact rate Aat between the outer peripheral face (<NUM>) and the inner peripheral face (<NUM>) satisfies formula <NUM>: <MAT>
wherein the contact rate Aat and the arithmetic mean roughness Rai of the outer peripheral face (<NUM>) of the shaft member (<NUM>, <NUM>, <NUM>, <NUM>) are determined in accordance with the methods defined respectively in paragraphs [<NUM>] and [<NUM>] in the description.