Magnetic encoder and rolling bearing unit including magnetic encoder

Abstract

To provide an environment-friendly magnetic encoder which achieves heat shock resistance, heat resistance and high temperature stability required for the magnetic encoder, and to provide a rolling bearing unit including the magnetic encoder.SOLUTION: A magnetic encoder 20 is attached to a fixing member (slinger) 17 which can be attached to a rotary member (inner ring) 12, and a substantially annular magnet portion (magnetic pole forming ring) 21 which is multipolar-magnetized in a circumferential direction is made of a magnet material containing a ferrite-based magnetic powder and a thermoplastic-resin, and is integrally joined to the fixing member, wherein the thermoplastic-resin contains PA10T in which a hard segment is made of plant-derived 110 decanediamine and petroleum-derived terephtalic acid and a PA10T thermoplastic-elastomer in which a soft segment is made of plant-derived dimer acid and plant-derived dimer diamine. Further, the composition contains PA10T composed of plant-derived 110 - decanediamine and petroleum-derived terephtalic acid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic encoder and a rolling bearing unit equipped with a magnetic encoder. [Background technology]

[0002] Conventionally, magnetic encoders used in rolling bearings for wheels and the like have used plastic magnet binders that have been given flexibility in order to meet strict heat shock resistance specifications, specifically thermoplastic resins containing polyamide 12-based thermoplastic elastomers, which are block copolymers having hard segments of polyamide 12 and soft segments of polyether components, as disclosed in Patent Document 1 by the present applicant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4238933 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the polyamide 12-based thermoplastic elastomers that have been used until now are derived from petroleum and are not environmentally friendly. Furthermore, although polyamide 12-based thermoplastic elastomers are actually used in mixtures with polyamide 12, there is little room for improvement in terms of heat resistance and high-temperature stability due to the increasing specifications of automobiles and harsh environmental conditions.

[0005] The present invention has been made in light of these circumstances, and aims to provide an environmentally friendly magnetic encoder and a rolling bearing unit equipped with a magnetic encoder that achieves the heat shock resistance, heat resistance, and high-temperature stability required of a magnetic encoder. [Means for solving the problem]

[0006] The magnetic encoder of the first invention is a magnetic encoder comprising a fixed member that can be attached to a rotating body, and a substantially annular magnet portion that is attached to the fixed member and magnetized with multiple poles in the circumferential direction, wherein the magnet portion is made of a magnetic material containing ferrite magnetic powder and a thermoplastic resin, the magnet portion is integrally joined to the fixed member made of a magnetic material, and the thermoplastic resin of the magnet portion includes PA10T, whose hard segment is made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, and a PA10T-based thermoplastic elastomer whose soft segment is made of plant-derived dimer acid and plant-derived dimer diamine. The second invention is a magnetic encoder according to the first invention, characterized in that the thermoplastic resin contains PA10T, which is made from plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid. A third invention is the magnetic encoder according to the first or second invention, characterized in that the fixing member is made of a surface-roughened iron-based magnetic material. A magnetic encoder according to a fourth aspect of the present invention is characterized in that the magnetic powder according to either the first or second aspect of the present invention contains at least strontium ferrite. The fifth invention is characterized in that, in the magnetic encoder described in the first invention, the magnet portion is integrally joined to the fixing member made of a magnetic material by an adhesive, and the adhesive is at least one selected from the group consisting of phenolic resin-based adhesives and epoxy resin-based adhesives. The sixth invention is a rolling bearing unit characterized by comprising a fixed ring, a rotating ring, a plurality of rolling elements arranged to be freely rollable in the circumferential direction between the fixed ring and the rotating ring, and a magnetic encoder described in the first or second invention fixed to the rotating ring. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an environmentally friendly magnetic encoder and a rolling bearing unit equipped with a magnetic encoder that achieves the heat shock resistance, heat resistance, and high-temperature stability required of a magnetic encoder.

[0008] Specifically, by applying polyamide 10T-based thermoplastic elastomer, which has excellent heat resistance, low water absorption, and flexibility, to the resin material used as the binder for the magnetic material of a magnetic encoder, it is possible to provide a magnetic encoder that has excellent heat shock resistance, is highly reliable, and can be used in a variety of environments, while also being low cost.

[0009] Furthermore, since the polyamide 10T-based thermoplastic elastomer of the present invention has a bio-content of 50% or more, it can be used to create a magnetic encoder that is more environmentally friendly than conventional polyamide 12-based thermoplastic elastomers that are made solely from petroleum-derived components and have a bio-content of 0%. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a rolling bearing unit equipped with a magnetic encoder. [Figure 2] FIG. 2 is a cross-sectional view showing the periphery of the magnetic encoder of FIG. [Figure 3] FIG. 2 is a schematic diagram showing an example of a magnet portion magnetized in multiple poles in the circumferential direction. [Figure 4] FIG. 10 is a cross-sectional view showing another example of a rolling bearing unit equipped with a magnetic encoder. [Figure 5] FIG. 10 is a cross-sectional view showing yet another example of a rolling bearing unit equipped with a magnetic encoder. [Figure 6] FIG. 6 is a cross-sectional view showing the periphery of the magnetic encoder of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a magnetic encoder used in a rolling bearing for a wheel or the like, and more particularly to a plastic magnet used in a magnetic encoder. The following description will be made with reference to the accompanying drawings. Note that these embodiments are merely one embodiment of the present invention and should not be construed as limiting in any way, and appropriate design modifications are possible within the scope of the present invention.

[0012] Fig. 1 is a cross-sectional view showing an example of a rolling bearing to which a magnetic encoder 20 is assembled, and Fig. 2 is an enlarged view of the area around the magnetic encoder. The illustrated rolling bearing 10 comprises an outer ring 11 which is a fixed ring, an inner ring 12 which is a rotating body, a plurality of balls 13 which are rolling bodies that are rollably disposed in an annular gap defined by the outer ring 11 and the inner ring 12 and are held at equal intervals in the circumferential direction by a cage 14 and are rollably arranged, a sealing device 15 disposed at the open end of the annular gap, and a magnetic encoder 20 fixed to the inner ring 12.

[0013] The sealing device 15 comprises a seal member 16 fixed to the inner peripheral surface of the outer ring 11, and a slinger 17 located outside the open end of the seal member 16 and fixed to the outer peripheral surface of the inner ring 12. The sealing device 15 closes the open end of the annular gap by sliding contact between the seal member 16 and the slinger 17, preventing foreign matter such as dust from entering the inside of the bearing and preventing the lubricant filled inside the bearing from leaking out of the bearing.

[0014] The sealing member 16 is constructed by reinforcing a rubber seal 19, which is also formed in an annular shape with a roughly L-shaped cross section, with a core metal 18 formed in an annular shape with a roughly L-shaped cross section. The tip of the rubber seal 19 is branched into multiple seal lips 19a, 19b, 19c, which are brought into sliding contact with the surface of the slinger 17.

[0015] The magnetic encoder 20 includes a fixed member (hereinafter also referred to as a slinger) 17 that can be attached to the rotating body (hereinafter also referred to as an inner ring) 12, and a substantially annular magnet portion (hereinafter also referred to as a magnetic pole-forming ring) 21 that is attached to the slinger 17 and magnetized with multiple poles in the circumferential direction. As shown in FIG. 3, the magnetic pole-forming ring 21 is a multi-pole magnet, and N and S poles are formed alternately in the circumferential direction. Thus, the magnetic encoder 20 is configured with the slinger 17 and the magnetic pole-forming ring 21 that is attached to the outer surface (magnet joint surface) of the slinger 17 and is made of the above-mentioned magnetic material, and the magnetic pole-forming ring 21 is fixed to the inner ring 12 using the slinger 17 as a fixed member.

[0016] The slinger 17 is made of a roughened iron-based magnetic material. This does not reduce the magnetic properties of the encoder magnet, and can be selected based on the operating environment, corrosion resistance, and cost, depending on the installation position of the slinger. The most preferred iron-based magnetic materials are ferritic stainless steel (e.g., SUS430) and martensitic stainless steel (e.g., SUS410, SUS420), which have a certain level of corrosion resistance.

[0017] The slinger 17 is made of a thin plate of ferritic stainless steel (such as SUS430) or martensitic stainless steel (such as SUS410), and has a cylindrical portion 17a that is fitted onto the inner ring 12, and a brim-like flange portion 17c that is connected to the axial end of the cylindrical portion 17a via a curved portion 17b and is formed to extend radially outward.

[0018] 3, the magnetic pole forming ring 21 is a multi-pole magnet with N poles and S poles alternately formed in the circumferential direction. The number of poles in the magnetic pole forming ring 21 is approximately 70 to 130, and preferably 90 to 120. A magnetic sensor (not shown) is disposed opposite the magnetic pole forming ring 27.

[0019] Next, another example of a rolling bearing unit equipped with a magnetic encoder is shown in Fig. 4. Fig. 4 is a partial cross-sectional view showing an example of application to a wheel supporting rolling bearing unit 100 for supporting a driven wheel in an independent suspension.

[0020] The inner ring 107 of the rolling bearing unit 100 is fitted onto a small-diameter step 106 formed on the inner end of the hub 103 and is fixed to the hub 103 by a crimped portion 109 formed by crimping the inner end of the hub 103 radially outward. The hub 103 and inner ring 107 form a rotating ring (rotating body) 102. The wheel is fixedly connected to the outer end of the hub 103 by studs 105 planted at predetermined intervals in the circumferential direction on a mounting flange 104 formed on a portion protruding from the outer end of the outer ring 101, which serves as the fixed ring. In contrast, the outer ring 101 is fixedly connected to a knuckle (not shown) or other component of a suspension system by a connecting flange 111 formed on its outer periphery. A plurality of balls 112, which serve as rolling elements, are arranged between the outer ring 101, hub 103, and inner ring 107 and are guided by a cage 113 so as to roll freely in the circumferential direction.

[0021] Furthermore, sealing devices 15, 115 are provided between the inner peripheral surfaces of both ends of the outer ring 101 and the outer peripheral surface of the middle portion of the hub 103 and the outer peripheral surface of the inner end of the inner ring 106, respectively. These sealing devices 15, 115 isolate the space in which the balls 112 are provided from the outside space, between the inner peripheral surface of the outer ring 101 and the outer peripheral surfaces of the hub 103 and inner ring 106. A magnetic pole-forming ring 21 is attached to the outer surface of a slinger 17 that constitutes this sealing device 15, and similar to the embodiment in FIG. 1, this forms a magnetic encoder 20. A magnetic sensor 114 is disposed axially outward of the magnetic encoder 20, facing it, and can detect changes in magnetic flux density to determine the rotational speed of the wheel.

[0022] Next, we will show another example of a rolling bearing unit equipped with a magnetic encoder. Fig. 5 is a partial cross-sectional view showing an example of application to a wheel support rolling bearing unit 100 for supporting a driven wheel in an independent suspension, and Fig. 6 is an enlarged view of the magnetic encoder and its surroundings. Note that the same members as those in the wheel support rolling bearing unit 100 shown in Fig. 4 are given the same reference numerals and their explanations will be omitted.

[0023] The wheel support rolling bearing unit 100 shown in the figure has the sealing device 15 removed from the wheel support rolling bearing unit 100 shown in Figure 4, and instead the entire unit is sealed with a sensor cap 115. The sensor cap 115 is a resin lid member that is attached to cover the opening surrounded by the outer ring 101, and the sensor 114 is fixed to this sensor cap 115.

[0024] The magnetic pole-forming ring 21 is made of a magnetic material containing ferrite magnetic powder and a thermoplastic resin, and is integrally joined to a fixed member, a slinger 17, made of a magnetic material. The thermoplastic resin of the magnetic pole-forming ring 21 is a PA10T-based thermoplastic elastomer whose hard segments are made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, and whose soft segments are made of plant-derived dimer acid and plant-derived dimer diamine. The magnetic encoder further includes PA10T made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid as the thermoplastic resin.

[0025] The magnetic pole-forming ring 21 is bonded to the fixed member made of a magnetic material with an adhesive, and the adhesive is at least one selected from the group consisting of a phenolic resin adhesive and an epoxy resin adhesive. In other words, adhesives that can be diluted with a solvent and undergo a nearly two-stage curing reaction are preferred, taking into account their heat resistance, chemical resistance, and ease of handling.

[0026] The phenolic resin adhesive is preferably one used as a rubber vulcanization adhesive, and although there are no particular limitations on the composition, it can be a novolac phenolic resin or resol phenolic resin with a curing agent such as hexamethylenetetramine dissolved in methanol, methyl ethyl ketone, etc. Furthermore, to improve adhesion, these may be mixed with a novolac epoxy resin.

[0027] The preferred epoxy resin adhesive is a one-component epoxy adhesive that can be diluted with a solvent. After the solvent has evaporated, this one-component epoxy adhesive will become semi-cured on the slinger surface at an appropriate temperature and time, to the extent that it will not be washed away by the high-temperature, high-pressure molten resin during insert molding, and will become fully cured by the heat from the resin during insert molding and secondary heating.

[0028] Furthermore, in consideration of weather resistance, ferrite such as strontium ferrite is most suitable as the magnetic powder. In order to further improve the magnetic properties of the ferrite, lanthanum, cobalt, etc. may be mixed in, or part of the ferrite may be replaced with rare earth magnetic powder such as neodymium-iron-boron, samarium-cobalt, or samarium-iron.

[0029] As described above, the magnetic encoder 20 of the present invention can use, as at least a portion of the binder component of the plastic magnet material that forms the magnetic encoder 20, i.e., as the base resin of the binder that forms the magnetic pole-forming ring 21 of the magnetic encoder, PA10T, whose hard segment is made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, and a PA10T-based thermoplastic elastomer, whose soft segment is made of plant-derived dimer acid and plant-derived dimer diamine.

[0030] The above-mentioned 1,10-decanediamine is a plant-derived straight-chain diamine obtained through a unique manufacturing process using sebacic acid, whose main ingredient is castor oil obtained from castor bean seeds, etc.

[0031] Dimer acid, a softening ingredient, is made from vegetable oils such as linoleic acid and oleic acid, and is primarily composed of dibasic C36 dicarboxylic acid produced by the dimerization of C18 unsaturated fatty acids, with trace amounts of monobasic and tribasic acids. Dimer diamine, another softening ingredient, is also manufactured from dimer acid.

[0032] Furthermore, conventionally used soft segments of polyamide 12-based thermoplastic elastomers and the like contain block copolymers such as polyether, but the PA10T-based thermoplastic elastomer of the present invention does not contain such block copolymers, and therefore has excellent heat resistance stability.

[0033] As such, PA10T thermoplastic elastomers have significantly lower water absorption than polyamide 66, which is commonly used as a polyamide, so dimensional changes due to water absorption are very small and their excellent dimensional stability makes them very reliable.In addition, their low water absorption also ensures that they are resistant to snow-melting agents, which is required for magnetic encoders.

[0034] The molecular weight of the polyamide 10T-based thermoplastic elastomer described above is within a range that allows injection molding, specifically, a number average molecular weight of 13,000 to 28,000, and more preferably, in consideration of fatigue resistance and moldability, a number average molecular weight of 18,000 to 26,000. If the number average molecular weight is less than 13,000, the molecular weight is too low, resulting in poor fatigue resistance and low practicality. On the other hand, if the number average molecular weight exceeds 28,000, the melt viscosity becomes too high, making it difficult to precisely manufacture the magnetic encoder 20 by injection molding, which is undesirable.

[0035] In addition to polyamide 10T-based thermoplastic elastomer, PA10T, which is the hard segment of polyamide 10T-based thermoplastic elastomer and is made from plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, can also be used as a binder component. PA10T has the same molecular structure as the hard segment of polyamide 10T-based thermoplastic elastomer, so they are compatible with each other. Adding PA10T increases the tensile strength of the entire binder component, but reduces elongation and flexibility, so the amount added is limited to 80% by weight of the entire binder component.

[0036] Furthermore, it is preferable to add an iodide-based heat stabilizer or an amine-based antioxidant, either alone or in combination, to the binder resin as an additive to prevent deterioration due to heat during molding and use. As the amine-based antioxidant, aromatic amines such as N,N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenyldiamine, N,N'-di-2-naphthyl-p-phenylenediamine, N,N'-bis(1-methylheptyl)-p-phenylenediamine, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine can be suitably used. In addition, a secondary antioxidant such as 2-mercaptobenzimidazole or 2-mercaptomethylbenzimidazole may also be used in combination.

[0037] As described above, by applying a polyamide 10T-based thermoplastic elastomer, which has excellent heat resistance, low water absorption, and flexibility, to the resin material of the binder of the magnetic material of the magnetic encoder 20, it is possible to provide a magnetic encoder that has excellent heat shock resistance, is highly reliable, and can be used in a variety of environments, at low cost.

[0038] Furthermore, since the polyamide 10T-based thermoplastic elastomer of the present invention has a bio-content of 50% or more, it can be used to create a magnetic encoder that is more environmentally friendly than conventional polyamide 12-based thermoplastic elastomers that are made solely from petroleum-derived components and have a bio-content of 0%.

[0039] The present invention will be further described below with reference to examples of embodiments of the present invention and comparative examples. (Example of embodiment) The binder component composition of the magnetic material of the magnetic encoder is as shown in Table 1. The structure of a magnetic encoder is shown in Figures 2 and 3. The structure of the rolling bearing unit is as shown in Figures 1 and 4. [Magnetic encoder fabrication] Using resin pellets of the magnetic material made of the binder components shown in Table 1, a magnetic encoder can be manufactured by injection molding (tunnel gate) in a magnetic injection molding machine. The magnet fixing surface of the fixing member (slinger) is roughened, then coated with a phenolic adhesive, and after it is left in a semi-hardened state, it is molded and bonded using the heat of injection molding.

[0040] [Table 1]

[0041] Example 1 of the embodiment is a polyamide 10T-based thermoplastic elastomer ("Flexible Heat-Resistant Polyamide" manufactured by Unitika, unreinforced, average molecular weight unknown). Example 2 of the embodiment is a polyamide 10T-based thermoplastic elastomer ("Flexible Heat-Resistant Polyamide" manufactured by Unitika, unreinforced, average molecular weight unknown) + polyamide 10T ("Xecot (registered trademark)" XN400 manufactured by Unitika, unreinforced, average molecular weight unknown) in a weight ratio of 3:7. An example of a comparative form is a polyamide 12-based thermoplastic elastomer (UBEPAE1210U manufactured by Ube Industries, unreinforced, average molecular weight unknown) + polyamide 12 (UBESTA P3012U manufactured by Ube Industries, unreinforced powder product, average molecular weight unknown) in a weight ratio of 3:7. [Industrial Applicability]

[0042] The present invention can be applied to industrial machinery in general. [Explanation of symbols]

[0043] 10 Rolling bearing unit 11 Fixed ring (outer ring) 12 Rotating body (inner ring) 13 Rolling element (ball) 14 Cage 15 Sealing device 16 Sealing material 17 Fixing member (slinger) 20 Magnetic Encoder 21 Magnet section (magnetic pole forming ring)

Claims

1. A magnetic encoder comprising a fixed member that can be attached to a rotating body, and a substantially annular magnet portion that is attached to the fixed member and magnetized in multiple poles in the circumferential direction, The magnetic encoder is characterized in that the magnet portion is made of a magnetic material containing ferrite-based magnetic powder and a thermoplastic resin, the magnet portion is integrally joined to the fixing member made of a magnetic material, and the thermoplastic resin of the magnet portion includes PA10T, whose hard segment is made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid, and whose soft segment is made of plant-derived dimer acid and plant-derived dimer diamine.

2. 2. The magnetic encoder according to claim 1, wherein the thermoplastic resin contains PA10T, which is made of plant-derived 1,10-decanediamine and petroleum-derived terephthalic acid.

3. 3. The magnetic encoder according to claim 1, wherein the fixing member is made of a surface-roughened iron-based magnetic material.

4. 3. The magnetic encoder according to claim 1, wherein the magnetic powder contains at least strontium ferrite.

5. the magnet portion is integrally joined to the fixing member made of a magnetic material with an adhesive, 2. The magnetic encoder according to claim 1, wherein the adhesive is at least one selected from the group consisting of a phenol resin adhesive and an epoxy resin adhesive.

6. A rolling bearing unit comprising: a fixed ring; a rotating ring; a plurality of rolling elements arranged to be freely rollable in the circumferential direction between the fixed ring and the rotating ring; and a magnetic encoder according to claim 1 or 2, which is fixed to the rotating ring.

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