JP2021001639A - Double-row thrust needle roller bearing - Google Patents

Abstract

To provide a double-row thrust needle roller bearing capable of achieving a long service life even under a severe lubrication condition.SOLUTION: A double-row thrust needle roller bearing 1 includes a pair of raceway rings 2, 3, a plurality of needle rollers 5, and a retainer 4 for retaining the needle rollers 5. The plurality of needle rollers 5 is arranged in a radial direction of the bearing in a plurality of rows, the needle rollers 5 are made from an iron-based material, and a hard film 8 is a film having a structure comprising: a base layer directly formed on rolling surfaces of the needle rollers 5 and made of mainly Cr and WC; a mixture layer of a gradient composition formed thereon and made from mainly WC and DLC; and a surface layer formed thereon and made from mainly DLC. A surface formed with the base layer has arithmetic average roughness Ra of a roughness curve is 0.3 μm or less, and root-mean-square gradient RΔq is 0.05 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a double-row thrust needle roller bearing, and more particularly to a double-row thrust needle roller bearing used in a compressor for an automobile air conditioner, an automatic transmission, an electric brake, and the like.

Thrust needle roller bearings are generally composed of a raceway ring, a plurality of needle rollers, and a cage, and are known as bearings capable of achieving high load capacity and high rigidity while having a simple structure. There is. Further, the thrust needle roller bearing has advantages such as a small axial thickness, and is therefore widely used in applications such as compressors where space saving is required.

Due to the basic structure of thrust needle roller bearings, differential slip occurs between the rollers and the raceway wheels. Specifically, in a thrust needle roller bearing, a cylindrical roller is arranged on a raceway ring having a flat raceway surface, and the roller and the raceway ring are in line contact with each other. And the center of the revolving movement of the time coincides. The rollers have a predetermined length in the radial direction of the bearing, but the peripheral speeds on the rolling surface of the rollers are the same. On the other hand, the peripheral speed of the raceway ring that rolls and comes into contact with the roller increases from the center of rotation of the bearing toward the outer diameter. Therefore, the difference in peripheral speed between the roller and the raceway ring is maximum at both ends of the roller. Theoretically, the pure rolling motion is performed only on the pitch circle of the bearing, and the difference in peripheral speed between the roller and the raceway ring increases from the point on the pitch circle toward both ends of the roller, and the differential slip increases. This differential slip increases in proportion to the length of the rollers.

The differential slip in thrust needle roller bearings is large compared to other types of bearings. Therefore, due to the differential slip, edge stress is likely to occur between the edge portion of the roller and the raceway ring, and surface-origin type peeling is likely to occur at the edge portion of the roller rolling portion of the raceway ring. .. As a measure to mitigate the influence of differential slip between the roller and the raceway surface of the raceway ring, it is conceivable to shorten the roller length, but if the roller length is simply shortened, the roller contact Since the area becomes smaller, the contact surface pressure of the rollers increases, which may cause problems such as premature peeling on the outer surface of the rollers.

As a solution to this problem, double-row thrust needle roller bearings have been proposed (see Patent Documents 1 to 3). In double-row thrust needle roller bearings, the contact surface pressure acting on the rollers is reduced while reducing the effect of differential slip by arranging multiple rollers in the radial direction of the bearing while shortening the roller length. Can be kept low.

In Patent Document 1, by forming crowning on the rolling surface of at least one roller of a plurality of roller rows, differential slip is reduced, and further reduction of load capacitance and increase of rolling contact surface pressure are suppressed. ing. Further, in Patent Document 2, the double-row thrust needle roller bearing is provided with a single-row crowned roller and a raceway ring having a predetermined high-density carbide distribution on the surface layer to reduce differential slip. While suppressing the increase in rolling contact surface pressure, the wear of the raceway ring is reduced to improve the surface damage resistance. Further, in Patent Document 3, the end face of the roller is set to the F end face and the end face accuracy is set to a predetermined value or less, so that drilling wear is less likely to occur and the bearing sound is reduced.

Japanese Unexamined Patent Publication No. 2003-97562 Japanese Unexamined Patent Publication No. 2003-156050 Japanese Unexamined Patent Publication No. 2004-156744

In recent years, compressors for automobile air conditioners, automatic transmissions, electric brakes, and the like have been miniaturized and increased in output. Along with this, the usage environment tends to have a high load and a high temperature, such as a decrease in the viscosity of the lubricating oil. The lubrication environment is becoming more severe than ever for bearings.

When the lubrication conditions are severe, peeling due to rolling fatigue (peeling starting from the inside) does not occur, but peeling occurs starting from the surface layer (surface). Unlike radial bearings, thrust bearings rotate with slippage, so the oil film tends to break off due to the effects of heat generated by sliding friction. In recent years, in order to reduce fuel consumption, the viscosity of lubricating oil has been reduced, the lubrication conditions for bearings have become stricter, and the oil film has become more likely to break.

Thrust needle roller bearings have a large slip and a low oil film forming ability, so the life of the bearing is often shortened due to surface-origin peeling. In double-row thrust needle roller bearings, although slippage is reduced by double-rowing the rollers, further extension of life is required in order to cope with the harsher lubrication environment in recent years.

The present invention has been made to address such a problem, and an object of the present invention is to provide a double-row thrust needle roller bearing capable of obtaining a long life even under severe lubrication conditions.

The double-row thrust needle roller bearing of the present invention comprises a pair of race wheels, a plurality of needle rollers rotatably arranged between the pair of race wheels, and a cage for holding the needle rollers. A double-row thrust needle roller bearing in which the plurality of needle rollers are arranged in a plurality of rows in the radial direction of the bearing, the needle rollers are made of an iron-based material, and the hard film is the needle rollers. A base layer mainly composed of chromium (hereinafter referred to as Cr) and tungsten carbide (hereinafter referred to as WC) formed directly on the rolling surface of the bearing, and a base layer formed on the base layer. A film having a structure composed of a mixed layer mainly composed of WC and diamond-like carbon (hereinafter referred to as DLC) and a surface layer mainly composed of DLC formed on the mixed layer, and the above-mentioned mixed layer. Is a layer in which the content of the WC in the mixed layer decreases and the content of the DLC in the mixed layer increases continuously or stepwise from the base layer side to the surface layer side. It is characterized in that the arithmetic average roughness Ra of the roughness curve on the surface on which the base layer is formed is 0.3 μm or less, and the squared average square root inclination RΔq is 0.05 or less.

The skewness Rsk obtained from the roughness curve on the surface on which the base layer is formed is −0.2 or less.

The maximum mountain height Rp obtained from the roughness curve on the surface on which the base layer is formed is 0.4 μm or less.

The plurality of needle-shaped rollers have an outer roller located on the outer side in the radial direction and an inner roller located on the inner side in the radial direction, and the cage has a plurality of pockets provided at intervals in the circumferential direction. It is characterized in that the outer roller and the inner roller are housed in each of the plurality of pockets.

The plurality of needle-shaped rollers have an outer roller located on the outer side in the radial direction and an inner roller located on the inner side in the radial direction, and the cages are provided at positions on the outer side in the radial direction at intervals in the circumferential direction. It has a plurality of outer pockets provided and a plurality of inner pockets provided at radial inner positions at intervals in the circumferential direction, and the outer rollers are housed in each of the plurality of outer pockets. It is characterized in that the inner roller is housed in each of the inner pockets of the.

The double-row thrust needle roller bearing of the present invention is formed by forming a hard film having a predetermined film structure including DLC on the rolling surface of the needle roller. The WC used for the mixed layer has an intermediate hardness and elastic modulus between Cr and DLC, and the concentration of residual stress after film formation is unlikely to occur. Further, by forming the mixed layer of WC and DLC into an inclined composition, the structure is such that WC and DLC are physically bonded.

Further, since the base layer formed directly on the rolling surface of the needle-shaped roller contains Cr, it is compatible with iron-based materials and has excellent adhesion as compared with W and Si. Further, the arithmetic average roughness Ra of the roughness curve indicating the surface roughness of the surface (roller surface) on which the base layer is formed is 0.3 μm or less, and the root mean square slope RΔq is 0.05 or less. Therefore, the roughness is sufficiently small, the roughness protrusions are not sharpened, and the stress concentration due to the protrusion contact is reduced. As a result, the peel resistance of the hard film itself is excellent, and the aggression against the mating material can be suppressed. In double-row thrust needle roller bearings that suppress differential slip and extend the service life, the service life can be extended even under stricter lubrication conditions by using needle rollers with a hard film formed. ..

It is sectional drawing which shows an example of the double-row thrust needle roller bearing of this invention. It is a top view which shows another example of the arrangement form of a plurality of needle-shaped rollers. It is a top view which shows another example of the arrangement form of a plurality of needle-shaped rollers. It is an enlarged view of the cage of FIG. It is a figure which shows another example of a cage. It is a figure which shows another example of a cage. It is a schematic cross-sectional view which shows the structure of a hard film. It is a schematic diagram which shows the film formation principle of the UBMS method. It is a schematic diagram of a UBMS apparatus. 2 It is a mock drawing of a cylindrical tester.

The double-row thrust needle roller bearing of the present invention will be described with reference to FIGS. 1 to 6. In these figures, the same reference numbers indicate the same or equivalent elements. FIG. 1 (a) is an axial sectional view of a double-row thrust needle roller bearing, and FIG. 1 (b) is a partial plan view of a cage in which the needle rollers are held.

As shown in FIG. 1A, the double-row thrust needle roller bearing 1 has a pair of raceway wheels 2 and 3 facing each other in the axial direction and needle rollers rotatably arranged between the raceway wheels. It includes a (rolling element) 5 and a cage 4 for holding the needle roller 5. The needle-shaped rollers 5 are arranged in a plurality of examples (two rows in FIG. 1) in the radial direction of the bearing, and have an inner roller 5a located on the inner side in the radial direction and an outer roller 5b located on the outer side in the radial direction. In FIG. 1, each of the pair of raceway rings 2 and 3 has an annular raceway surface, one of which is a fixed side raceway ring and the other of which is a rotation side raceway ring. The thrust needle roller bearing 1 does not necessarily have a fixed side raceway ring and a rotation side raceway ring, and may have a rolling surface directly on the mating side of the member to be incorporated.

FIG. 1B shows an example of the arrangement form of the inner roller 5a and the outer roller 5b. As shown in FIG. 1 (b), the cage 4 has a plurality of pockets 6 provided at intervals in the circumferential direction. The inner roller 5a and the outer roller 5b are housed in each pocket 6. In the form of FIG. 1, the number of inner rollers 5a and the number of outer rollers 5b are the same, and one inner roller 5a and one outer roller 5b are accommodated in one pocket. The plurality of pockets 6 are provided at equal intervals in the circumferential direction. This interval is the interval between the lines passing through the substantially center of the circumferential direction of each pocket. The arrangement of the inner rollers 5a and the outer rollers 5b is not limited to the form shown in FIG. 1, and for example, the forms shown in FIGS. 2 and 3 can be adopted.

The cage 4 of FIG. 2 has a plurality of inner pockets 7a provided at radial inner positions at circumferential intervals, and a plurality of outer pockets 7a provided at radial outer positions at circumferential intervals. It has a pocket 7b. The inner roller 5a is housed in each of the plurality of inner pockets 7a, and the outer roller 5b is housed in each of the plurality of outer pockets 7b. In the form of FIG. 2, the number of inner rollers 5a and the number of outer rollers 5b are the same. The plurality of inner pockets 7a and the plurality of outer pockets 7b are provided at equal intervals in the circumferential direction.

Similar to the cage of FIG. 2, the cage 4 of FIG. 3 has a plurality of inner pockets 7a for accommodating the inner rollers 5a and a plurality of outer pockets 7b for accommodating the outer rollers 5b. In the form shown in FIG. 3, the number of the inner rollers 5a and the number of the outer rollers 5b are different, and the number of the outer rollers 5b is larger than that of the inner rollers 5a. The number of inner rollers 5a may be larger than that of outer rollers 5b.

In the embodiment shown in FIGS. 1 to 3, two needle-shaped rollers are arranged in the radial direction, but three or more needle-shaped rollers may be arranged in the radial direction. In that case, the number of rollers in each column may be the same as each other or different from each other.

FIG. 4 shows an enlarged view of the cage of FIG. In FIG. 4, the cage 4 is composed of a plate-shaped first member 4a and a second member 4b which are vertically overlapped and joined. In the cage 4 of the form of FIG. 4, the outer peripheral portion of the first member 4a is bent so as to be crimped and sandwiched by the outer peripheral portion of the second member 4b, and the inner peripheral portion of the second member 4b is bent to hold the first member 4a. I try to hold it by caulking it on the inner circumference of the.

The cage used for the double-row thrust needle roller bearing of the present invention is not limited to the form shown in FIG. 4, and the cage shown in FIGS. 5 and 6 can be used. For example, in the cage 4 of FIG. 5, the outer peripheral portion and the inner peripheral portion of the ring-shaped first member 4a are bent toward the second member 4b side, and the outer peripheral portion and the inner peripheral portion of the second member 4b are the first member. It is bent toward the 4a side. The bent outer peripheral portion and inner peripheral portion of the first member 4a are fitted into the bent outer peripheral portion and inner peripheral portion of the second member 4b. On the other hand, the cage 4 of FIG. 6 is formed as a single component by a synthetic resin or the like.

The present invention is characterized in that a hard film having a predetermined structure is formed on the needle rollers of a double-row thrust needle roller bearing. Specifically, as shown in FIGS. 1 to 6, a hard film 8 is formed on the rolling surface of the needle-shaped rollers 5 (including the inner rollers 5a and the outer rollers 5b). By forming a hard film on the inner and outer rollers, the thrust needle roller bearing can have a long life even under severe lubrication conditions. In the double-row thrust needle roller bearing of the present invention, it is sufficient that a hard film is formed at least on the rolling surface of the needle roller, and the hard film is applied to the entire roller surface (including the axial end face) of the needle roller. It may be formed. Further, in the form of FIGS. 1 to 6, the hard film is formed on all the needle-shaped rollers, but it is sufficient that the hard film is formed on at least one or more needle-shaped rollers. For example, a hard film may be formed on each of the inner and outer rollers. Further, a hard film may be formed on the rolling surface of the raceway ring that makes rolling contact and sliding contact with the needle-shaped roller.

In the double-row thrust needle roller bearing, the roller to be formed of a hard film is made of an iron-based material. As the iron-based material, any steel material generally used as a bearing member can be used, and examples thereof include high carbon chrome bearing steel, carbon steel, tool steel, and martensitic stainless steel. Further, it is preferable that the pair of raceway rings are also made of the same iron-based material.

The hardness of the rolling surface on which the hard film is formed is preferably Vickers hardness of Hv650 or more. By setting the Hv to 650 or higher, the difference in hardness with the hard film (underlayer) can be reduced and the adhesion can be improved.

On the rolling surface on which the hard film is formed, it is preferable that the nitrided layer is formed by nitriding treatment before forming the hard film. As the nitriding treatment, it is preferable to perform a plasma nitriding treatment on the roller surface, which does not easily form an oxide layer that hinders adhesion. Further, it is preferable that the hardness of the surface after the nitriding treatment is Hv1000 or more in terms of Vickers hardness in order to further improve the adhesion to the hard film (underlayer).

In the present invention, the rolling surface on which the hard film is formed, that is, the surface on which the underlying layer is formed, has an arithmetic average roughness Ra of 0.3 μm or less and a root mean square inclination RΔq of 0.05 or less. Is. Ra is preferably 0.2 μm or less. Further, the rolling surface on which the hard film is formed may be a mirror-finished surface. The lower limit of Ra is not particularly limited, and is, for example, 0.005 μm or more. Since mirror surface processing is disadvantageous in terms of productivity and manufacturing cost, Ra is preferably 0.05 μm or more, and more preferably 0.1 μm or more, from the viewpoint of manufacturing. RΔq is preferably 0.03 or less, more preferably 0.02 or less. The arithmetic mean roughness Ra and the root mean square slope RΔq are numerical values calculated in accordance with JIS B 0601, and are measured using a contact type or non-contact type surface roughness meter or the like. Specific measurement conditions are a measurement length of 4 mm and a cutoff of 0.8 mm. By setting the root mean square slope RΔq of the rolling surface to 0.05 or less, the peak in the roughness curve becomes gentle, the radius of curvature of the protrusion becomes large, and the local surface pressure can be reduced. Further, at the time of film formation, it is possible to suppress the concentration of electric fields at a micro level due to roughness, prevent local changes in film thickness and hardness, and improve the peeling resistance of the hard film.

The maximum mountain height Rp obtained from the roughness curve of the rolling surface on which the base layer is formed is preferably 0.4 μm or less. The maximum mountain height Rp is calculated in accordance with JIS B 0601. The relationship between the maximum mountain height Rp obtained from the roughness curve and the arithmetic mean roughness Ra is preferably 1 ≦ Rp / Ra ≦ 2, and more preferably 1.2 ≦ Rp / Ra ≦ 2.

Further, the skewness Rsk obtained from the roughness curve of the rolling surface on which the base layer is formed is preferably negative. Rsk is an index of the degree of distortion, and is more preferably −0.2 or less. Skewness Rsk is a quantitative expression of the vertical symmetry of the amplitude distribution curve centered on the average line, that is, an index showing the bias of the surface roughness with respect to the average line. Skewness Rsk is calculated according to JIS B 0601. When the skewness Rsk is negative, it means that the roughness shape is convex downward (valley), and there are many flat portions on the surface. As a result, it can be said that the surface has few protrusions and stress concentration due to the protrusions is unlikely to occur. In addition, there is a method to reduce the roughness by removing the surface protrusions by collision with the polishing media such as barrel polishing, but be careful because new protrusions may be formed depending on the processing conditions and the Rsk may turn positive. is necessary.

The structure of the hard film in the present invention will be described with reference to FIG. As shown in FIG. 7, the hard film 8 is formed of (1) a base layer 8a mainly composed of Cr and WC formed directly on the rolling surface 5c of the roller 5, and (2) a base layer 8a. It has a three-layer structure including a mixed layer 8b mainly composed of WC and DLC formed on the film, and (3) a surface layer 8c mainly composed of DLC formed on the mixed layer 8b. Here, in the mixed layer 8b, the content of WC in the mixed layer decreases continuously or stepwise from the base layer 8a side to the surface layer 8c side, and the content of DLC in the mixed layer is reduced. This is the layer where the rate is high. In the present invention, the film structure of the hard film has a three-layer structure as described above, so that sudden changes in physical properties (hardness, elastic modulus, etc.) are avoided.

Since the base layer 8a contains Cr, it has good compatibility with needle-shaped rollers made of cemented carbide materials and iron-based materials, and has better adhesion to needle-shaped rollers than when W, Ti, Si, Al, etc. are used. Excellent for. Further, the WC used for the base layer 8a has an intermediate hardness and elastic modulus between Cr and DLC, and concentration of residual stress after film formation is unlikely to occur. Further, it is preferable that the base layer 8a has an inclined composition in which the Cr content is small and the WC content is high from the roller 5 side to the mixed layer 8b side. As a result, the adhesion between the needle roller 5 and the mixed layer 8b on both sides is excellent.

The mixed layer 8b is an intermediate layer interposed between the base layer and the surface layer. As described above, the WC used for the mixed layer 8b has an intermediate hardness and elastic modulus between Cr and DLC, and the concentration of residual stress after film formation is unlikely to occur. Since the mixed layer 8b has an inclined composition in which the WC content is small and the DLC content is high from the base layer 8a side to the surface layer 8c side, both sides of the base layer 8a and the surface layer 8c Has excellent adhesion. Further, the structure is such that the WC and the DLC are physically bonded in the mixed layer, and damage in the mixed layer can be prevented. Further, since the DLC content is increased on the surface layer 8c side, the adhesion between the surface layer 8c and the mixed layer 8b is excellent. The mixed layer 8b is a layer in which a highly non-adhesive DLC is bonded to the base layer 8a side by WC by an anchor effect.

The surface layer 8c is a film mainly composed of DLC. In the surface layer 8c, it is preferable to have an inclined layer portion 8d whose hardness increases continuously or stepwise from the mixed layer 8b side on the side adjacent to the mixed layer 8b. This is a part obtained by continuously or stepwise changing (increasing) the bias voltage in order to avoid a sudden change in the bias voltage when the bias voltage is different between the mixed layer 8b and the surface layer 8c. By changing the bias voltage in this way, the hardness of the inclined layer portion 8d is inclined as described above. The hardness increases continuously or stepwise because the composition ratio of the graphite structure (sp ² ) and the diamond structure (sp ³ ) in the DLC structure is biased toward the latter as the bias voltage increases. As a result, the sudden difference in hardness between the mixed layer and the surface layer is eliminated, and the adhesion between the mixed layer 8b and the surface layer 8c is further excellent.

The film thickness of the hard film 8 (total of the three layers) is preferably 0.5 to 5.0 μm. If the film thickness is less than 0.5 μm, the wear resistance and mechanical strength may be inferior, and if it exceeds 5.0 μm, it may be easily peeled off. Further, the ratio of the thickness of the surface layer 8c to the film thickness of the hard film 8 is preferably 0.8 or less. If this ratio exceeds 0.8, the inclined structure for physical bonding of WC and DLC in the mixed layer 8b tends to be a discontinuous structure, and the adhesion may be deteriorated.

By forming the hard film 8 into a three-layer structure including a base layer 8a, a mixed layer 8b, and a surface layer 8c having the above composition, peeling resistance is excellent.

In thrust needle roller bearings, differential slip occurs between the raceway ring and the needle roller. Due to this differential slip, heat is generated on the contact surface, and the oil film forming property is lowered. When the oil film breaks and becomes boundary lubrication, surface damage such as wear of rollers and raceway rings and surface peeling due to shear stress is likely to occur. Further, under boundary lubrication, the surface of the rollers and the raceway is roughened, and the oil film forming property is further deteriorated. In the thrust needle roller bearing of the present invention, by forming a hard film having the above structure and physical properties on the rolling surface of the needle roller, heat generation is suppressed due to the low friction characteristics of the DLC, and wear and roughness on the roller side are achieved. It can be expected to have effects such as prevention of surface formation and flattening of track surface roughness due to the polishing effect of the mating material of DLC. As a result, even in a harsh lubrication state, there is little damage to the raceway surface and rolling surface, and the service life is long. Further, under grease lubrication, when the metal new surface is exposed due to damage to the raceway ring or the like, grease deterioration is promoted by catalytic action, but in the double-row thrust needle roller bearing of the present invention, the raceway surface due to metal contact due to the hard film Since damage to the rolling surface can be prevented, this grease deterioration can also be prevented.

Further, since the hard film according to the present invention is formed on the rolling surface having a predetermined roughness parameter, the hard film itself has excellent peel resistance and can suppress aggression against the mating material. Therefore, the original characteristics of DLC can be exhibited, and the double-row thrust needle roller bearing of the present invention has excellent seizure resistance, wear resistance, and corrosion resistance, and is long with little damage to the raceway surface even in a harsh lubrication state. It will reach the end of its life.

Hereinafter, the film forming process of the hard film of the present invention will be described. In this film forming step, a surface finishing process is performed on the surface on which the base layer 8a is formed, a step of forming a film of the base layer 8a and the mixed layer 8b, and the surface layer 8c is used as a sputtering gas. It includes a step of forming a film using a UBMS apparatus using Ar gas. The hard film is obtained by forming a base layer 8a, a mixed layer 8b, and a surface layer 8c in this order on the film-forming surface of the bearing member that has been surface-finished.

In the step of forming the film of the base layer 8a and the mixed layer 8b, it is preferable to use a UBMS apparatus using Ar gas as the sputtering gas. The film forming principle of the UBMS method using the UBMS apparatus will be described with reference to the schematic diagram shown in FIG. In the figure, the base material 12 is a rolling element (roller) to be formed, but is schematically shown as a flat plate. As shown in FIG. 8, inner magnets 14a and outer magnets 14b having different magnetic characteristics are arranged in the central portion and the peripheral portion of the round target 15, and the magnets 14a, while forming a high-density plasma 19 in the vicinity of the target 15. A part 16a of the magnetic field lines 16 generated by 14b reaches the vicinity of the base material 12 connected to the bias power supply 11. The effect of diffusing Ar plasma generated during sputtering along the magnetic field lines 16a to the vicinity of the base material 12 can be obtained. In such a UBMS method, along the magnetic field lines 16a reaching the vicinity of the base material 12, Ar ions 17 and electrons are caused by the ion assist effect of causing more ionized targets 18 to reach the base material 12 as compared with ordinary sputtering. , A dense film (layer) 13 can be formed.

In the step of forming the base layer 8a, the Cr target and the WC target are used together as the target 15, and in the step of forming the mixed layer 8b, the WC target and the graphite target are used together as the target 15. In the step of forming the base layer 8a, the film is formed while continuously or stepwise increasing the sputtering power applied to the WC target and decreasing the power applied to the Cr target. As a result, a layer having a structure in which the Cr content is low and the WC content is high toward the mixed layer 8b side can be obtained.

In the step of forming the mixed layer 8b, the sputtering power applied to the graphite target as the carbon supply source is increased continuously or stepwise, and the electric power applied to the WC target is decreased. As a result, a layer having a gradient composition in which the WC content is low and the DLC content is high toward the surface layer 8c side can be obtained.

In the step of forming the surface layer 8c, it is preferable to use a UBMS apparatus using Ar gas as the sputtering gas. More specifically, in this step, using this apparatus, a graphite target and a hydrocarbon-based gas are used in combination as a carbon supply source, and the amount of the hydrocarbon-based gas introduced into the apparatus is 100. It is a step in which the ratio of the introduced amount is 1 to 10, the degree of vacuum in the apparatus is 0.2 to 0.8 Pa, and carbon atoms generated from the carbon supply source are deposited on the mixed layer 8b to form a film. Is preferable.

As a hard film used for the rollers of the double-row thrust needle roller bearing of the present invention, a hard film was formed on a predetermined base material (test piece), and the physical characteristics of the hard film were evaluated. In addition, the wear of the mating material was evaluated by a rolling slip test using a two-cylindrical tester. These will be described below as examples and comparative examples.

The test pieces, UBMS equipment, sputtering gas, etc. used for the evaluation of the hard film are as follows.
(1) Test piece physical characteristics: SUJ2 quenching and tempering product 750Hv
(2) Test piece: With respect to the sliding surface of the SUJ2 ring (φ40 × L12 subcurvature 60) polished (arithmetic mean roughness Ra, root mean square slope RΔq, maximum peak height Rp, skewness Rsk are shown in Table 1). (3) UBMS equipment: manufactured by Kobe Steel Co., Ltd .; UBMS202
(4) Sputtering gas: Ar gas

The conditions for forming the base layer will be described below. Vacuum the inside of the film formation chamber to about 5 × 10 ^-3 Pa, bake the base material with a heater, etch the base material surface with Ar plasma, and then apply it to the Cr target and WC target by the UBMS method. The electric power was adjusted and the composition ratio of Cr and WC was inclined to form a Cr / WC inclined layer having a large amount of Cr on the base material side and a large amount of WC on the surface side.

The conditions for forming the mixed layer will be described below. A film was formed by the UBMS method in the same manner as the base layer. Here, for the mixed layer, while supplying methane gas, which is a hydrocarbon gas, the sputter power applied to the WC target and the graphite target is adjusted, the composition ratio of WC and DLC is inclined, and the WC on the base material side. A WC / DLC inclined layer with a large amount of DLC was formed on the surface side.

In each test piece, the arithmetic mean roughness Ra and the root mean square slope RΔq are changed by changing the surface finishing conditions. Various roughness parameters on the surface of the test piece were measured with a surface roughness measuring instrument (Taylor Hobson: Foam Talisurf PGI830). Table 1 shows the average value of the values measured 5 times with a reference length of 0.8 mm and a number of sections of 5 according to JIS B 0601.

FIG. 9 is a schematic view of the UBMS apparatus. As shown in FIG. 9, the sputter evaporation source material (target) 22 is applied to the base material 21 arranged on the disk 20 by a non-equilibrium magnetic field to increase the plasma density in the vicinity of the base material 21 and increase the ion assist effect. It is a device having a UBMS function capable of controlling the characteristics of the coating film deposited on the base material by doing so (see FIG. 8). With this device, a composite coating film in which a plurality of UBMS coating films (including composition gradients) are arbitrarily combined can be formed on the base material. In this embodiment, the base layer, the mixed layer, and the surface layer are formed as a UBMS film on the ring as the base material.

Examples 1-7, Comparative Examples 1-3
The substrates shown in Table 1 were ultrasonically cleaned with acetone and then dried. After drying, the base material was attached to the UBMS apparatus, and the base layer and the mixed layer were formed under the above-mentioned formation conditions. A DLC film, which is a surface layer, was formed on the film to obtain a test piece having a hard film. The conditions for forming the surface layer are that the degree of vacuum in the film forming chamber in the above device is 0.8 Pa, the bias voltage with respect to the substrate is 50 V, and the ratio of the amount of methane gas introduced into the above device is the amount of Ar gas introduced 100 (volume part). ) Is 1 (volume part). The results are also shown in Table 1. The film thickness in the table is the total film thickness of the three layers (underlayer, mixed layer, and surface layer).

<Rolling and slip test using a 2 cylindrical tester>
The obtained test piece was tested for wear of the mating material due to rolling and slipping using the two-cylindrical tester shown in FIG. This two-cylindrical tester includes a drive-side test piece 23 and a driven-side test piece 24 that rolls and slides into contact with each other. Each test piece (ring) is supported by a support bearing 26, and a load is applied by a load spring 27. It is loaded. In the figure, 25 is a drive pulley and 28 is a non-contact tachometer. Slip was generated with a difference in rotation, and the aggression of the opponent was evaluated from the wear depth of the cylinder on the mating material side. The specific test conditions are as follows. The wear depth of the mating material-side cylinder was determined using a surface roughness measuring instrument (Taylor Hobson: Foam Talisurf PGI830) with respect to the reference surface.
(Test condition)
Mating material: Grinded finish (0.02 μmRa) SUJ2 ring (φ40 × L12 subcurvature 60)
Lubricating oil: VG320 equivalent oil (containing additives) Felt pad refueling Maximum contact surface pressure: 1.5 GPa
Rotation speed: (test piece side) 127min ^-1
(Mating material side) 126min ^-1
Relative slip rate: 0.8%
Cutoff time: 72h

Table 1 shows the results of the two-cylinder rolling slip test. The film forming conditions of the base material and the surface layer used are the same, and the hardness of the surface layer is about 23 GPa on average. When the arithmetic average roughness Ra of the roughness curve indicating the surface roughness of the surface on which the hard film is formed is 0.3 μm or less and the root mean square slope RΔq is 0.05 or less (Examples 1 to 7). In the two-cylinder rolling slip test, the mating material wear tends to be small, and the mating aggression is reduced. In particular, in Example 3, although Ra, Rsk, and Rp were similar to those in Comparative Example 3, the result was that the opponent's aggression was significantly different due to the difference in RΔq. It is considered that this is because the tip radius of the protrusion is blunted and the stress concentration is relaxed.

In Example 6, Ra and RΔq are similar to those in Example 3, but the opponent's aggression is different. It is considered that this is because Rsk became a positive value and the number of upward protrusions increased. Further, from the result of Example 5, it is considered that the smaller the Rsk, the larger the wear of the mating material is not, and it is important to suppress the aggression of the mating material that the Rsk does not become 0 or more.

From the above, in the present invention, in order to alleviate the stress concentration of the protrusions at the time of contact between the hard film and the mating material and suppress the wear of the mating material, the arithmetic mean roughness Ra of the roughness curve and the root mean square slope RΔq are used. The condition of the surface of the base material is specified.

Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and changes can be made to the illustrated embodiment within the same range as the present invention or within the same range.

In the double-row thrust needle roller bearing of the present invention, a DLC film is formed on the rolling surface of the needle roller, and the DLC film is excellent in peeling resistance even when operated under severe lubrication, and the characteristics of the DLC main body are excellent. It is excellent in seizure resistance, abrasion resistance, and corrosion resistance. In addition, the aggression against the partner material is suppressed. Therefore, the double-row thrust needle roller bearing of the present invention can be applied to various applications including applications under harsh lubrication conditions, and is particularly used for compressors for automobile air conditioners, automatic transmissions, electric brakes, and the like. Can be advantageously applied to double row thrust needle roller bearings.

1 Double row thrust needle roller bearing 2 Track ring 3 Track ring 4 Cage 5 Needle roller 5a Inner roller 5b Outer roller 6 Pocket 7 Pocket 7a Inner pocket 7b Outer pocket 8 Hard film 11 Bias power supply 12 Base material 13 film (layer) )
14 Magnet 15 Target 16 Magnetic line 17 Ar ion 18 Ionized target 19 High-density plasma 20 Disk 21 Base material 22 Spatter evaporation source material (target)
23 Drive side test piece 24 Driven side test piece 25 Drive pulley 26 Support bearing 27 Load spring 28 Non-contact tachometer

Claims (5)

A pair of raceway wheels, a plurality of needle-shaped rollers rotatably arranged between the pair of raceway rings, and a cage for holding the needle-shaped rollers are provided, and the plurality of needle-shaped rollers have a bearing diameter. Double-row thrust needle roller bearings arranged in multiple rows in the direction.
The needle-shaped roller is made of an iron-based material, and the hard film is formed on a base layer mainly composed of chromium and tungsten carbide, which is directly formed on the rolling surface of the needle-shaped roller, and on the base layer. It is a film having a structure composed of a mixed layer mainly composed of tungsten carbide and diamond-like carbon formed on the film, and a surface layer mainly composed of diamond-like carbon formed on the mixed layer.
In the mixed layer, the content of the tungsten carbide in the mixed layer decreases continuously or stepwise from the base layer side to the surface layer side, and the diamond-like carbon in the mixed layer becomes smaller. It is a layer with a high content rate,
A double-row thrust needle roller characterized in that the arithmetic average roughness Ra of the roughness curve on the surface on which the base layer is formed is 0.3 μm or less, and the root mean square slope RΔq is 0.05 or less. bearing. The double-row thrust needle roller bearing according to claim 1, wherein the skewness Rsk obtained from the roughness curve on the surface on which the base layer is formed is −0.2 or less. The double-row thrust needle roller bearing according to claim 1 or 2, wherein the maximum mountain height Rp obtained from the roughness curve on the surface on which the base layer is formed is 0.4 μm or less. The plurality of needle-shaped rollers have an outer roller located on the outer side in the radial direction and an inner roller located on the inner side in the radial direction.
The cage has a plurality of pockets provided at intervals in the circumferential direction, and the outer roller and the inner roller are housed in each of the plurality of pockets, according to claim 1. The double row thrust needle roller bearing according to any one of claims up to 3. The plurality of needle-shaped rollers have an outer roller located on the outer side in the radial direction and an inner roller located on the inner side in the radial direction.
The cage has a plurality of outer pockets provided at radial outer positions at circumferential intervals and a plurality of inner pockets provided at radial inner positions at circumferential intervals. However, any one of claims 1 to 3, wherein the outer roller is housed in each of the plurality of outer pockets, and the inner roller is housed in each of the plurality of inner pockets. Double row thrust needle roller bearings as described in the section.