JP2006194279A - Reduction gear and electric power steering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low noise reduction gear capable of keeping rotation torque low. <P>SOLUTION: Lubricant composition is filled in a zone including a meshing part A of a worm shaft 11 and a worm wheel 12 in the reduction gear 50. The lubricant composition includes lubricant and shock absorbing material particle of average particle diameter D1 which satisfies a condition 50μm<D1≤300μm. Antifriction bearings 34, 35 supporting the worm shaft 11 are of sealed types including a bearing seal sealing a gap between an outer ring and an inner ring. The bearing seal includes a rubber member including a seal lip slidingly abutting on an inner wall surface of an outer circumference groove of the inner ring. In surface characteristic expressed in a relation of wave length and amplitude obtained by performing Fourier transform of cross section curve of the sliding abutment surface of the seal lip, amplitude of wave length 30μm component is 0.3μm or more, preferably 0.5μm or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a speed reducer and an electric power steering apparatus using the same.

  A reduction gear is used for an electric power steering device for an automobile. For example, in a column type electric power steering device, the rotation of the electric motor is reduced by transmitting the rotation of the electric motor from a driving gear such as a worm to a driven gear such as a worm wheel, and the output is amplified and then applied to the column. Torque assists steering operation. Appropriate backlash is required for meshing between the drive gear and the driven gear as a reduction mechanism. However, rattling noise may occur due to backlash, for example, when the gear rotates forward or reverse, or when a reaction force from a tire is input while traveling on a rough road such as a stone pavement. If it is transmitted as noise in the passenger compartment, the driver will be uncomfortable.

For this reason, conventionally, the reduction gears are assembled by selecting the combination of the drive gear and the driven gear so as to achieve an appropriate backlash, so-called layered assembly, but this method has a problem that productivity is extremely low. is there. Further, even if the assembly is performed in layers, there is another problem that uneven steering torque occurs due to eccentricity of the shaft of the worm wheel.
The same problem exists not only in the speed reducer of the electric power steering apparatus but also in a general speed reducer having a small gear and a driven gear.

Therefore, for example, in a reduction gear of an electric power steering apparatus, the worm shaft can be biased toward the worm wheel, and backlash is reduced by providing a biasing means such as a spring body that biases the worm shaft in the biasing direction. It has been proposed to eliminate them (for example, see Patent Document 1).
On the other hand, it has been proposed to buffer the collision between the tooth surfaces of both gears at the meshing portion of the gears by adding buffer particles to the lubricant composition used for lubricating the gears of the reduction gear. (For example, refer to Patent Document 2).
JP 2000-43739 A (columns 0007 to 0009, FIG. 1) JP 2004-162018 A

However, the speed reducer disclosed in Patent Document 1 has a problem that the structure is extremely complicated and the manufacturing cost is increased.
Further, in the reduction gear of Patent Document 2, the buffer material particles added to the lubricant composition may enter the inside of the bearing that supports the drive gear and the driven gear, and in this case, the rotational torque of the bearing increases. There is a risk.

  An object of the present invention is to provide a speed reducer that can be kept inexpensive and low in noise, and that can maintain a low rotational torque, and an electric power steering apparatus using the same.

  The present invention relates to a reduction gear including a driving gear and a driven gear each supported by a bearing, and a lubricant composition is filled in a region including a meshing portion of the driving gear and the driven gear. And buffer material particles having an average particle diameter D1 of 50 μm <D1 ≦ 300 μm, and the bearing includes a bearing seal that seals between the outer ring and the inner ring, and the bearing seal is formed in an outer circumferential groove of the inner ring. It includes a rubber member having a seal lip that is in sliding contact with the wall surface.

  In the present invention, the buffer particles dispersed in the lubricant composition are interposed in the meshing portion of the drive gear and the driven gear to reduce the rattling noise by buffering the collision between the tooth surfaces of both gears. , Reducer noise caused by backlash can be reduced. Further, by simply adding buffer material particles to the lubricant, noise can be reduced at low cost without complicating the structure of the speed reducer.

  Furthermore, by using a bearing seal having a seal lip that is in sliding contact with the inner wall surface of the outer peripheral groove of the inner ring of the bearing, it is possible to reliably prevent the buffer material particles of the lubricant composition from entering the bearing. Therefore, the rotational resistance of the bearing can be kept low over a long period of time. Moreover, when the said buffer material particle is spherical, it is preferable at the point which can improve the fluidity | liquidity of a lubricant composition and can prevent the excessive raise of the resistance torque of a reduction gear.

The lubricant may be a semi-solid grease or a liquid lubricant.
When the lubricant is grease, the consistency of the lubricant composition to which the buffer particles are added is represented by NLGI (National Lubricating Grease Institute) number. 2-No. 000
It is preferable when used for a reduction gear.
When lubricating oil is used as the lubricant, the kinematic viscosity is 20 to 100 mm ² / s (4
0 ° C. is preferable for use in a reduction gear.

  On the other hand, when the seal lip is in sliding contact with the inner ring as described above, the inventor of the present application decreases the dynamic friction coefficient of the rubber of the bearing seal due to an increase in the sliding speed of the sliding contact surface, causing a stick-slip phenomenon, The knowledge that there is a possibility that the tip vibrates and a squeak noise may occur. Therefore, the seal lip includes a slidable contact surface that is in slidable contact with the inner wall surface of the outer peripheral groove of the inner ring, and in the surface property represented by the relationship between the wavelength and amplitude obtained by Fourier transform of the cross-sectional curve of the slidable contact surface, The amplitude of the 30 μm wavelength component is preferably 0.3 μm or more, and the amplitude of the 120 μm wavelength component is preferably 2.5 μm or less.

  That is, the sampled shape curve of the surface is regarded as a wave function, Fourier transformed, and frequency analysis is performed. By setting the amplitude of a relatively high-frequency (short cycle) component having a wavelength of 30 μm to 0.3 μm or more, a narrow and deep recess (high convexity) is given to the sliding surface. Thereby, the true contact part to the other party (sliding contact surface) can be reduced, and as a result, the static friction coefficient can be reduced and the track torque can be reduced. In addition, the degree of dependence of the friction coefficient on the sliding speed can be reduced to suppress the generation of squeal. On the other hand, if the amplitude of the relatively low frequency (long cycle) component having a wavelength of 120 μm exceeds 2.5 μm, the sealing function may become unstable, so 2.5 μm or less is preferable, more preferably 2 μm. It is as follows.

  Moreover, the electric power steering apparatus of the present invention is characterized in that the power of the electric motor is applied to the steering mechanism via the speed reducer. In this case, it is preferable at the point which can reduce the noise in a vehicle interior at low cost.

The present invention is described in detail below.
FIG. 1 is a schematic sectional view of an electric power steering apparatus according to an embodiment of the present invention. 2 is a cross-sectional view taken along the line II-II in FIG.
Referring to FIG. 1, in the electric power steering apparatus of this example, a first steering shaft 2 as an input shaft to which a steering wheel 1 is attached and a steering mechanism (not shown) such as a rack and pinion mechanism are connected. A second steering shaft 3 serving as an output shaft is coaxially connected via a torsion bar 4.

  The housing 5 that supports the first and second steering shafts 2 and 3 is made of, for example, an aluminum alloy and is attached to a vehicle body (not shown). The housing 5 includes a cylindrical sensor housing 6 and a cylindrical gear housing 7 that are fitted together. Specifically, the gear housing 7 is fitted with an annular step 7 a at the outer periphery of the lower end of the sensor housing 6 at the annular edge 7 a at the upper end. The gear housing 7 accommodates a worm gear mechanism 8 as a speed reduction mechanism, and the sensor housing 6 accommodates a torque sensor 9, a control board 10, and the like. The reduction gear 50 is configured by housing the worm gear mechanism 8 in the gear housing 7.

The worm gear mechanism 8 meshes with the worm wheel 12 as a driven gear that can rotate integrally with an axial intermediate portion of the second steering shaft 3 and is restricted from moving in the axial direction, and is shown in FIG. Thus, the worm shaft 11 as a drive gear connected to the rotating shaft 32 of the electric motor M via the spline joint 33 is provided.
Referring to FIG. 1 again, the worm wheel 12 is composed of an annular cored bar 12a coupled to the second steering shaft 3 so as to be integrally rotatable, and a tooth that surrounds the periphery of the cored bar 12a and forms teeth on the outer peripheral surface portion. And a resin member 12b. The cored bar 12a is inserted into a mold at the time of resin molding of the synthetic resin member 12b, for example.

The second steering shaft 3 is rotatably supported by first and second rolling bearings 13 and 14 that are disposed with the worm wheel 12 sandwiched between the upper and lower sides in the axial direction.
The outer ring 15 of the first rolling bearing 13 is fitted and held in a bearing holding hole 16 provided in the cylindrical projection 6 b at the lower end of the sensor housing 6. Further, the upper end surface of the outer ring 15 is in contact with the annular step portion 17, and movement in the axial direction with respect to the sensor housing 6 is restricted.

On the other hand, the inner ring 18 of the first rolling bearing 13 is fitted to the second steering shaft 3 by an interference fit. Further, the lower end surface of the inner ring 18 is in contact with the upper end surface of the core metal 12 a of the worm wheel 12.
The outer ring 19 of the second rolling bearing 14 is fitted and held in the bearing holding hole 20 of the gear housing 7. Further, the lower end surface of the outer ring 19 is in contact with the annular step portion 21, and movement in the axially downward direction with respect to the gear housing 7 is restricted.

  On the other hand, the inner ring 22 of the second rolling bearing 14 is attached to the second steering shaft 3 such that the inner ring 22 is integrally rotatable and the relative movement in the axial direction is restricted. Further, the inner ring 22 is sandwiched between a step portion 23 of the second steering shaft 3 and a nut 24 that is fastened to a screw portion of the second steering shaft 3. The torsion bar 4 passes through the first and second steering shafts 2 and 3. The upper end 4a of the torsion bar 4 is connected to the first steering shaft 2 by a connecting pin 25 so as to be integrally rotatable, and the lower end 4b is connected to the second steering shaft 3 by a connecting pin 26 so as to be integrally rotatable. The lower end of the second steering shaft 3 is connected to a steering mechanism such as a rack and pinion mechanism as described above via an intermediate shaft (not shown).

The connecting pin 25 connects the third steering shaft 27 disposed coaxially with the first steering shaft 2 so as to be integrally rotatable with the first steering shaft 2. The third steering shaft 27 passes through the tube 28 constituting the steering column.
The upper portion of the first steering shaft 2 is rotatably supported by the sensor housing 6 via a third rolling bearing 29 made of, for example, a needle roller bearing. The reduced diameter portion 30 at the lower part of the first steering shaft 2 and the hole 31 at the upper part of the second steering shaft 3 regulate the relative rotation of the first and second steering shafts 2 and 3 within a predetermined range. And a predetermined play in the rotational direction.

  Next, referring to FIG. 2, the worm shaft 11 is rotatably supported by fourth and fifth rolling bearings 34 and 35 held by the gear housing 7. Inner rings 36 and 37 of the fourth and fifth rolling bearings 34 and 35 are fitted in corresponding constricted portions of the worm shaft 11. The outer rings 38 and 39 are respectively held in bearing holding holes 40 and 41 of the gear housing 7.

  The gear housing 7 includes a portion 7 b that faces a part of the peripheral surface of the worm shaft 11 in the radial direction. Further, the outer ring 38 of the fourth rolling bearing 34 that supports the one end portion 11 a of the worm shaft 11 is positioned in contact with the stepped portion 42 of the gear housing 7. On the other hand, the movement of the inner ring 36 toward the other end portion 11 b is restricted by contacting the positioning step portion 43 of the worm shaft 11.

  Further, the inner ring 37 of the fifth rolling bearing 35 that supports the vicinity of the other end portion 11b (joint side end portion) of the worm shaft 11 is brought into contact with the positioning step portion 44 of the worm shaft 11 so as to move toward the one end portion 11a side. Movement is restricted. The outer ring 39 is urged toward the fourth rolling bearing 34 by a preload adjusting screw member 45. The screw member 45 is screwed into a screw hole 46 formed in the gear housing 7, thereby applying preload to the pair of rolling bearings 34 and 35 and positioning the worm shaft 11 in the axial direction. In order to fix the screw member 45 after the preload adjustment, a lock nut 47 is engaged with the screw member 45.

  The feature of the present embodiment is that a region containing at least the meshing part A of the worm shaft 11 and the worm wheel 12 in the gear housing 7 is filled with a lubricant composition in which buffer particles described later are dispersed. It is in. Further, the filled cushioning material particles enter the first and second rolling bearings 13 and 14 and the fourth and fifth rolling bearings 34 and 35 and have an adverse effect such as an increase in rotational resistance. In order to prevent this, a seal-type rolling bearing is used as these bearings. That is, it is a rolling bearing to which a bearing seal having a seal lip that contacts the inner ring is applied. The bearing seals do not necessarily have to be arranged at both ends of the rolling bearing, and the end of the rolling bearing on the side not facing the gear housing 7 may be a shield plate (sealing plate).

The lubricant composition may be filled only in the meshing part A, or may be filled in the entire periphery of the meshing part A and the worm shaft 11 or in the entire gear housing 7.
The lubricant composition includes the lubricant and the buffer particles as described above. Among these, the buffer particles need to have an average particle diameter D1 of 50 μm <D1 ≦ 300 μm.

  When the average particle diameter D1 of the buffer material particles is 50 μm or less, there is a limit to the effect of buffering the meshing impact between the driving gear and the driven gear to reduce the rattling noise, which can greatly reduce the noise of the reduction gear. Can not. Further, when the average particle diameter D1 exceeds 300 μm, there is a problem that the steering torque of the electric power steering apparatus increases or the noise of the speed reducer increases due to the generation of sliding noise.

Note that the average particle diameter of the buffer particles is preferably 100 μm or more even in the above range in consideration of further improving the effect of reducing the rattling noise. In consideration of more reliably preventing an increase in steering torque and generation of sliding noise, it is particularly preferably 200 μm or less even within the above range.
Various shapes such as a spherical shape, a granular shape, a flake shape, and a rod shape can be selected as the shape of the buffer material particles, but the spherical shape or the granular shape is preferable in consideration of the fluidity of the lubricant composition, and the spherical shape is particularly preferable.

As the buffer material for forming the buffer material particles, a material having a Young's modulus in the range of 0.1 to 10 ⁴ MPa is preferably used.
Since the Young's modulus of less than 0.1 MPa is too soft, the impact is absorbed through the meshing portion of the drive gear and the driven gear, thereby reducing the noise of the reducer by reducing the rattling noise. May not be sufficiently obtained. If the Young's modulus exceeds 10 ⁴ MPa, the steering torque of the electric power steering device may increase, or a sliding noise may be generated and the reduction gear noise may increase.

The Young's modulus of the buffer material forming the buffer material particles is preferably 0.5 MPa or more even in the above range in consideration of further improving the effect of reducing the rattling noise. In consideration of more reliably preventing an increase in steering torque and generation of sliding noise, it is particularly preferably 10 ² MPa or less even within the above range.
The other characteristics of the buffer material particles are not particularly limited, but the tensile strength of the buffer material forming the buffer material particles is preferably 1 to 50 MPa.

Further, the hardness of the buffer material forming the buffer material particles is preferably 10 or more in terms of Shore D hardness and 110 or less in terms of Rockwell hardness (R scale).
As the buffer material particles, any of various rubber or soft resin materials having rubber elasticity can be used.
Among these, examples of the soft resin include polyolefin resin, polyamide resin, polyester resin, polyacetal resin, polyphenylene oxide resin, polyimide resin, fluororesin, thermoplastic or curable (crosslinkable) urethane resin, and the like. Further, for example, olefin-based, urethane-based, polyester-based, polyamide-based, fluorine-based and other oil-resistant thermoplastic elastomers can be used.

On the other hand, examples of the rubber include ethylene propylene copolymer rubber (EPM), ethylene propylene diene copolymer rubber (EPDM), silicone rubber, urethane rubber (U) and the like.
However, in view of heat resistance, durability, etc., it is preferable to use spherical buffer material particles formed of a cured product of a curable urethane resin. Such buffer particles also have an advantage that Young's modulus, tensile strength, and hardness can be arbitrarily set by adjusting the degree of curing (degree of crosslinking) of the curable urethane resin.

The buffer particles are preferably blended at a ratio of 20 to 300 parts by weight with respect to 100 parts by weight of the lubricant.
If the blending ratio of the buffer particles is less than 20 parts by weight, the impact is absorbed by interposing the meshing portion of the drive gear and the driven gear, thereby reducing the noise of the reducer by reducing the rattling noise. May be insufficient. On the other hand, if it exceeds 300 parts by weight, the steering torque of the electric power steering device may increase, or the noise of the reduction gear may increase due to the generation of sliding noise.

The mixing ratio of the buffer particles to 100 parts by weight of the lubricant is preferably 25 parts by weight or more even in the above range in consideration of further improving the effect of reducing the rattling noise. In consideration of more reliably preventing an increase in steering torque and generation of sliding noise, it is particularly preferably 100 parts by weight or less even within the above range.
As the lubricant for dispersing the buffer material particles, either a liquid lubricating oil or a semi-solid grease may be used.

Among these, as the lubricating oil, the kinematic viscosity of ^{5~200mm 2 / s (40 ℃)} , especially 20 to 100 mm ² / s is preferable to use those which are (40 ° C.). As the lubricating oil, a synthetic hydrocarbon oil (for example, poly α-olefin oil) is preferable, but synthetic oils such as silicone oil, fluorine oil, ester oil, ether oil, and mineral oil can also be used. Lubricating oils can be used alone or in combination of two or more.

Lubricants include solid lubricants (molybdenum disulfide, graphite, PTFE, etc.), phosphorus-based and sulfur-based extreme pressure additives, antioxidants such as tributylphenol and methylphenol, rust inhibitors, Metal deactivators, viscosity index improvers, oiliness agents and the like may be added.
As one grease, the consistency as a lubricant composition to which buffer particles are added is represented by NLGI (National Lubricating Grease Institute) number. 2-No. 000, especially no. 2-No. It is preferable to use one that becomes 00.

The grease is formed by adding a thickener to the lubricating base oil as in the conventional case.
The lubricating base oil is preferably a synthetic hydrocarbon oil (for example, a polyalphaolefin oil), but synthetic oils such as silicone oil, fluorine oil, ester oil, and ether oil, mineral oil, and the like can also be used. The kinematic viscosity of the lubricating base oil is preferably 5 to 200 mm ² / s (40 ° C.), more preferably ^{20 to} 100 mm ² / s (40 ° C.).

As the thickener, various conventionally known thickeners (soap and non-soap) can be used.
In addition, greases may also contain solid lubricants (molybdenum disulfide, graphite, PTFE, etc.), phosphorus-based and sulfur-based extreme pressure additives, antioxidants such as tributylphenol and methylphenol, rust inhibitors, if necessary. Metal deactivators, viscosity index improvers, oiliness agents and the like may be added.

As the first rolling bearing 13, the second rolling bearing 14, the fourth rolling bearing 34, and the fifth rolling bearing 35, sealed rolling bearings having the same configuration are used. In FIGS. 1 and 2, the sealing structure of these bearings is schematically shown. Specifically, the bearing structure is similar to the structure of the first rolling bearing 13 shown as a representative in FIG. Yes.
Referring to FIG. 3, the first rolling bearing 13 is provided between the inner ring 18 as a rotating raceway ring, the outer ring 15 as a stationary raceway, and the inner ring 18 and the outer ring 15. A plurality of balls 54 as rolling elements, a retainer 55 for holding the balls 54, and a bearing seal 56 as a sealing device for sealing between the inner ring 18 and the outer ring 15 are provided. Grease is sealed inside the first rolling bearing 13.

The bearing seals 56 are respectively fixed to the inner circumferences of the pair of end portions of the outer ring 15 (only the bearing seal 56 on the side facing the gear housing 7 is shown in FIG. 3). A shield plate (sealing plate) may be used instead of the bearing seal 56 (not shown) on the side not facing the gear housing 7.
The bearing seal 56 includes an annular seal member 57 containing rubber and a cored bar 58 that is annular and has a substantially L-shaped cross section. The core metal 58 reinforces the seal member 57 by being vulcanized and bonded to the seal member 57.

  Examples of the rubber material included in the seal member 57 include silicone rubber, NBR (nitrile rubber), HNBR (hydrogenated nitrile rubber), ACM (acrylic rubber), and FKM (fluoro rubber). In consideration of the fact that it is used even under low temperature use conditions like an electric power steering device for automobiles, it is preferable to use silicone rubber or NBR.

The seal member 57 includes an inner peripheral portion 60 that faces a seal groove 59 as an outer peripheral groove at the end portion of the inner ring 18, and an outer peripheral portion 62 that is press-fitted into a mounting groove 61 as an inner peripheral groove at the end portion of the outer ring 15. . A seal lip 63 and first and second labyrinth forming lips 64 and 65 are formed on the inner peripheral portion 60 of the seal member 57.
The seal lip 13 protrudes inward in the axial direction at the inner peripheral edge of the seal member 57, and comes into sliding contact with the inner wall surface 59 a facing the axially outer side of the seal groove 59. The second labyrinth forming lip 65 is disposed on the radially outer side than the first labyrinth forming lip 64.

The first labyrinth forming lip 64 is formed in the vicinity of the inner peripheral edge of the seal member 57, and opposes in the vicinity of the surface of the seal groove 59 facing the outer diameter side. The first labyrinth forming lip 65 protrudes inward in the axial direction at a portion slightly outside the seal lip 63, and faces the corner between the seal groove 59 and the outer diameter of the inner ring 18. .
Referring to FIG. 3 and FIG. 4 which is an enlarged view of the main part of the bearing seal, the surface of the seal lip 63 includes a slidable contact surface 66 that slidably contacts the inner ring 18 in a region including the tip edge of the seal lip 63. The surface roughness of the region B (see FIG. 4) including at least the sliding contact surface 66 of the seal member 57 is set as follows.

  That is, in the surface properties expressed by the relationship between the wavelength and the amplitude obtained by Fourier transforming the cross-sectional curve of the sliding contact surface 66, the amplitude of the wavelength 30 μm component is 0.3 μm or more and the amplitude of the wavelength 120 μm component is 2 .5 μm or less. The cross-sectional curve can be obtained, for example, by binarizing scan data obtained by scanning a laser beam or imaging data using a laser beam in a predetermined area including a line for which a cross-sectional curve is to be obtained. Further, the cross-sectional shape obtained by a stylus type surface roughness measuring machine may be computerized to obtain a cross-sectional curve.

  By setting the amplitude of a relatively high-frequency (short cycle) component having a wavelength of 30 μm to 0.3 μm or more, a thin and deep recess (high convexity) is given to the sliding contact surface 66. Thereby, the true contact part to the other party (sliding contact surface 67) can be reduced, and as a result, the static friction coefficient can be reduced and the track torque can be reduced. In addition, the degree of dependence of the friction coefficient on the sliding speed can be reduced to suppress the generation of squeal.

Also, if the amplitude of the component with a wavelength of 30 μm is 0.5 μm or more, the real contact portion at the time of sliding contact can be made smaller by providing a narrower and deeper recess (high convexity) on the sliding contact surface. In addition, the coefficient of static friction can be made smaller, and the degree of dependence of the coefficient of friction on the sliding speed can be reduced to reliably prevent the generation of squealing noise.
If the amplitude of the relatively low frequency (long cycle) component having a wavelength of 120 μm exceeds 2.5 μm, the sealing function may become unstable, so 2.5 μm or less is preferable, and more preferably 2 μm or less. is there.

On the other hand, the inner wall surface 59 a of the seal groove 59 of the inner ring 18 is provided with a slidable contact surface 67 slidably contacting the slidable contact surface 66 of the seal lip 63 of the seal member 57, and at least the slidable surface of the inner wall surface 59 a of the seal groove 59 is provided. The surface roughness of the contact surface 67 is processed to be Rz 3.2 μm or less.
As a method of giving the above-mentioned unevenness to the sliding contact surface 66 of the seal lip 63, there is a method of roughening the surface by, for example, sandblasting or etching. Further, there is a method in which a part of the inner surface of the cavity of the mold is previously formed with unevenness by sandblasting or etching, and the unevenness is transferred to the sliding contact surface 66 of the seal member 57 as a molded product.

As described above, in the FFT analysis data, by setting the amplitude of the 30 μm wavelength component to 0.3 μm or more, more preferably 0.5 μm or more, the generation of squealing is suppressed or the generation of squeaking is prevented. can do.
Further, even if grease or lubricating oil as a lubricant composition flows into the sliding contact surface 66, the grease is collected in the narrow and deep concave portion, so that the intrusion into the first rolling bearing 13 is prevented. be able to. As a result, the friction torque can be kept low over a long period of time.

Further, by setting the amplitude of the wavelength 120 μm component to 2.5 μm or less, preferably 2 μm or less, it is possible to ensure a sealing function necessary for the bearing seal 56.
Further, by providing the sliding contact surface 66 with a deeper concave (higher convex) than the counterpart, the unevenness is deformed along with the sliding, and the true contact portion of the sliding contact surface 66 is gradually shifted from static friction to dynamic friction. Can do. Therefore, the apparent static friction coefficient can be reduced to reduce the orbital torque. In addition, the degree of dependence of the friction coefficient on the sliding speed can be reduced.

  The present invention is not limited to the above embodiment. For example, the configuration of the speed reducer of the present invention can be applied to a speed reducer for a device other than an electric power steering device, and various modifications are made within the scope of the matters described in the claims of the present invention. Can be applied.

Hereinafter, the present invention will be described in more detail based on examples.
Examples 1-6
To 100 parts by weight of grease obtained by adding a soap-based thickener to poly α-olefin oil, 200 parts by weight of spherical or granular buffer material particles having an average particle diameter of 120 μm made of a urethane-based thermoplastic elastomer are added and mixed uniformly. The consistency is represented by the NLGI number and No. A grease as a lubricant composition was prepared. The grease was filled in the speed reducer of the electric power steering apparatus shown in FIGS. 1 and 2 to obtain Examples 1 to 6.

In each of Examples 1 to 6, the first and second rolling bearings 13 and 14 and the fourth and fifth rolling bearings 34 and 35 were the same sealed type rolling bearings as shown in FIG. That is, a rolling bearing equipped with a bearing seal 56 having a seal lip 63 that is in sliding contact with the inner ring was used.
In Example 1, the process which roughens the sliding contact surface 66 of the bearing seal | sticker 56 used for the rolling bearing is not implemented.

  In Examples 2 to 6, the surface contact property 66 of the bearing seal 56 used in the rolling bearing is roughened, and the degree of roughening is variously changed, so that the surface properties of the slide contact surface 66 are different from each other. It was supposed to have. As the roughening process, a method was used in which the inner surface of the mold forming the seal lip 63 was roughened by sandblasting or blasting with glass beads, and the roughened shape was transferred to the sliding contact surface 66. The sand particle size and glass bead particle size were varied, and the degree of roughening was varied.

Comparative Examples 1 and 2
Comparative examples 1 and 2 were prepared by using the grease containing no buffer material particles as it was and filling the reduction gear of the electric power steering apparatus shown in FIGS.
In Comparative Example 1, the same sealed rolling bearing as shown in FIG. 3 was used for the first and second rolling bearings 13 and 14 and the fourth and fifth rolling bearings 34 and 35. The sliding contact surface 66 of the bearing seal 56 used in the rolling bearing is not roughened.

In Comparative Example 2, rolling bearings having no bearing seal were used for the first and second rolling bearings 13 and 14 and the fourth and fifth rolling bearings 34 and 35.
<Surface property measurement test>
Measuring apparatus Laser microscope: Lens magnification 20 times (0.95 μm / pixel)
Image: Horizontal 639 × Vertical 479 pixels, Brightness value 0-255 (256 gradations)
Measurement shape curve: 18 lines with a length of 550 pixels along the circumferential direction of the slidable contact surface at regular intervals from the inner circumference side to the outer circumference side of the seal member. FFT analysis: Hanning as window function Temperature: Room temperature
Derivation method A predetermined area of the sliding contact surface is imaged through a laser microscope, and the obtained image is binarized to obtain a binarized image representing unevenness by brightness, and then along the 18 measurement shape curves. Find the direction length and height. Subsequently, the shape of each measurement shape curve was subjected to FFT analysis, and an average value was obtained.

About Examples 1-6 and the comparative example 1, when the logarithmic display was carried out by making a wavelength into a horizontal axis and making an amplitude into a vertical axis | shaft, the result shown in FIG. 5 was obtained.
<Noise test and durability test>
In the reduction gears of Examples 1 to 6 and Comparative Examples 1 and 2, rattling noise was measured. In addition, when the rotation of the speed reducer was increased from a low speed to a high speed during the measurement, it was confirmed by human hearing whether or not an audible squeaking sound would occur.

After the noise test, the speed reducer was operated for 500 hours under the condition of a worm shaft speed of 250 rpm. After operation, the rolling bearings 13, 14, 34, and 35 were removed and disassembled, and it was confirmed with a microscope whether or not the buffer particles had entered the bearing.
The worm gear mechanism is a combination of an iron-based metal worm and a polyamide resin-based worm wheel. The backlash was 1 'and 4'. The results are shown in Table 1.

From Table 1, Examples 1 to 6 filled with the buffer material particles are 11 to 14 dB when the backlash is 1 ', and the backlash is 4' as compared with Comparative Examples 1 and 2 not filled with the buffer material particles. In some cases, it was confirmed that it has a significant effect of reducing rattling noise of 14 to 17 dB.
Also, regarding whether or not a squeal is generated when the speed of the speed reducer is increased during the noise test, in Table 1, ◎ indicates that no squeal is generated, and ◯ indicates the speed reducer 50. Indicates that no squeal is generated when the rotational speed of the worm shaft 11 exceeds 150 rpm, Δ indicates that no squeal is generated when the rotational speed of the worm shaft 11 exceeds 200 rpm, and □ indicates the rotation of the worm shaft 11. When the number exceeds 250 rpm, no squeal is generated.

In Examples 2 and 3 in which the amplitude of the component having a wavelength of 30 μm is 0.5 μm or more, no squeal occurred in the entire rotation speed range.
Further, in Examples 4 and 5 in which the amplitude of the component having a wavelength of 30 μm is in the range of 0.3 to 0.5 μm, a squealing sound was generated at a rotational speed of 150 rpm or less. No longer.

  In Test Example 6 in which the amplitude of the 30 μm wavelength component was 0.3 μm, a squealing sound was generated at a rotational speed of 200 rpm or less, but no squealing sound was generated at a rotational speed exceeding 200 rpm. On the other hand, in Example 1 and Comparative Example 1 in which the process of roughening the sliding contact surface was not performed, a squealing sound was generated at a rotational speed of 250 rpm or less. Examples 2-6 were able to demonstrate sufficient effect for noise reduction compared with comparative example 3. That is, when the roughness of the sliding surface is represented by a power spectrum, it has been found that the degree of influence on the frictional vibration can be clarified, and that the frictional vibration is converged particularly by increasing the amplitude component of the short wavelength.

Further, in Examples 1 to 6 using a sealed type rolling bearing having a seal lip that comes into contact with the inner ring, no intrusion of buffer material particles was observed in the rolling bearing after the durability test. Therefore, it was confirmed that the rolling bearing is not adversely affected by the buffer particles.
Next, the grease of Example 1 and Comparative Example 1 was filled in the actual reduction gear of the same electric power steering apparatus as described above, and the relationship between the steering angle and the torque was measured. The backlash was 4 '. The results are shown in FIG. Further, in FIG. 6A, the vicinity of the starting point where the steering angle is 0 ° and no torque is enlarged is shown in FIG. 6B. In these figures, the solid line is the result of Example 1, and the broken line is the result of Comparative Example 1.

6 (a) and 6 (b), in Comparative Example 1, there is a backlash region in the vicinity of the starting point because there is an idle running region in which no increase in torque corresponding to the increase in the steering angle is observed. I found out.
On the other hand, in Example 1, since the torque increases from the starting point in accordance with the increase in the steering angle and there is no idling region, there is substantially backlash due to the presence of the buffer particles. It turned out to be in the same state as not. As a result, it was confirmed that the noise can be greatly reduced by reducing the rattling noise as described above.
Examination of the particle diameter of the buffer particles As the buffer particles, spherical particles made of a cured product of a curable urethane resin (Young's modulus: 10 MPa) were used. The average particle diameter was changed in the range of 10 to 400 μm. Next, the above-mentioned buffer particles were blended at a blending ratio of 40 parts by weight with respect to 100 parts by weight of grease obtained by adding a soap-based thickener to poly-α-olefin oil to prepare a grease as a lubricant composition. Moreover, what did not mix | blend buffer material particle | grains was made into the average particle diameter of 0 micrometer.

Then, the grease was filled in the actual reduction gear of the electric power steering apparatus shown in FIGS. 1 and 2, and the rattling noise (dB) and the sliding noise (dB) were measured. The worm gear mechanism is a combination of an iron-based metal worm and a polyamide resin-based worm wheel.
(Gap sound)
In the measurement of the rattling noise, the backlash was 2 ′, 3.5 ′ and 5 ′. As for the reduction effect of the rattling noise, 55 dB is set as a threshold value, and when the measured rattling noise is less than this threshold value, the reduction effect is evaluated as good, and when the threshold noise exceeds the threshold value, the reduction effect is evaluated as poor did. The results are shown in FIG. The horizontal line (thick line) in the figure is the threshold value. The line-□-indicates the backlash 2 ',-▲-indicates the backlash 3.5', and-●-indicates the backlash 5 '.

From FIG. 7, when the backlash 2 'condition, the average particle size of the buffer material particles exceeds 50 μm, when the backlash 3.5 ′ condition is 80 μm or more, and when the backlash 5 ′ condition is 100 μm or more. In each case, a good effect of reducing rattling noise was obtained.
From these facts, it was confirmed that the average particle diameter of the buffer material particles needs to exceed 50 μm, and particularly preferably 100 μm or more.
(Sliding sound)
In the measurement of the sliding sound, the backlash was 2 ′. For the presence or absence of sliding sound, 55 dB is set as a threshold value. When the measured sliding sound is less than this threshold value, there is no sliding sound (good), and the sliding sound exceeds the threshold value. Evaluated as sound (bad). The results are shown in FIG. The horizontal line (thick line) in the figure is the threshold value.

From FIG. 8, it was found that the generation of sliding noise can be prevented when the average particle diameter of the buffer material particles is 300 μm or less. And from this, it was confirmed that the average particle diameter of the buffer material particles needs to be 300 μm or less.
Examination of Young's Modulus of Buffer Material Particles As the buffer material particles, spherical particles made of a cured product of a curable urethane resin having an average particle diameter of 150 μm were used. The Young's modulus of the cured product was changed in the range of 0.01 to 10 ⁵ MPa.

  Next, the above-mentioned buffer particles were blended at a blending ratio of 40 parts by weight with respect to 100 parts by weight of grease obtained by adding a soap-based thickener to poly-α-olefin oil to prepare a grease as a lubricant composition. And this grease was filled in the actual reduction gear of the same electric power steering apparatus as described above, and the rattling noise (dB) and the sliding noise (dB) were measured. All measurements were performed with a backlash 2 '. Further, the threshold value used as the evaluation reference was the same as described above.

The measurement result of the rattling sound is shown in FIG. 9, and the measurement result of the sliding sound is shown in FIG. From FIG. 9, when the Young's modulus of the cured product of the curable urethane resin as the buffer material forming the buffer material particles is 0.1 MPa or more, a good effect of reducing rattling noise was obtained. From this, it was confirmed that the Young's modulus of the buffer material forming the buffer material particles is preferably 0.1 MPa or more. Further, FIG. 10 indicates that the generation of sliding noise can be prevented when the Young's modulus of a cured product of a curable urethane resin as the buffer material for forming the buffer material particles is 10 ⁴ MPa or less. From this, it was confirmed that the Young's modulus of the buffer material forming the buffer material particles is preferably 10 ⁴ MPa or less.
Examination of the blending ratio of the buffer material particles As the buffer material particles, spherical particles having an average particle diameter of 150 μm made of a cured product of a curable urethane resin (Young's modulus: 10 MPa) were used.

Next, the blending ratio of the buffer particles is changed in the range of 0 to 50 parts by weight with respect to 100 parts by weight of the grease obtained by adding the soap-based thickener to the poly α-olefin oil to obtain a lubricant composition. A grease was prepared.
And this grease was filled in the actual reduction gear of the same electric power steering apparatus as described above, and the rattling noise (dB) was measured. The measurement was performed with a backlash 2 '. Further, the threshold value used as the evaluation reference was the same as described above.

  The measurement results are shown in FIG. From FIG. 11, when the blending ratio of the buffer material particles was 20 parts by weight or more with respect to 100 parts by weight of the grease, a good effect of reducing the rattling noise was obtained. From this, it was confirmed that the blending ratio of the buffer material particles is preferably 20 parts by weight or more.

1 is a schematic cross-sectional view of an electric power steering apparatus according to an embodiment of the present invention. It is sectional drawing which follows the II-II line of FIG. It is a schematic sectional drawing of the rolling bearing which supports a worm wheel. It is sectional drawing of the principal part of a bearing seal. In the embodiment of the present invention, it is a graph of surface properties represented by the relationship between the wavelength and amplitude obtained by Fourier transform of the cross-sectional curve of the sliding contact surface of the bearing seal of the rolling bearing, the horizontal axis is the wavelength, The vertical axis is the amplitude. FIG. 5A is a graph showing the result of measuring the relationship between the steering angle and the torque in the embodiment of the present invention, and FIG. 4B is an enlarged graph of the vicinity of the starting point of FIG. . In the Example of this invention, it is a graph which shows the result of having measured the relationship between the average particle diameter of buffer material particle | grains, and the rattling sound of the reduction gear of an electric power steering apparatus. In the Example of this invention, it is a graph which shows the result of having measured the relationship between the average particle diameter of buffer material particle | grains, and the sliding sound of the reduction gear of an electric power steering apparatus. In the Example of this invention, it is a graph which shows the result of having measured the relationship between the Young's modulus of the buffer material which forms buffer material particle | grains, and the rattling sound of the reduction gear of an electric power steering apparatus. In the Example of this invention, it is a graph which shows the result of having measured the relationship between the Young's modulus of the buffer material which forms buffer material particle | grains, and the sliding sound of the reduction gear of an electric power steering apparatus. In the Example of this invention, it is a graph which shows the result of having measured the relationship between the mixture ratio of a buffer material particle, and the rattling sound of the reduction gear of an electric power steering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 7 ... Gear housing, 8 ... Worm gear mechanism (deceleration mechanism), 11 ... Worm shaft (drive gear), 12 ... Worm wheel (driven gear), 13 ... 1st rolling bearing (bearing), 14 ... 2nd rolling bearing (Bearing), 15 ... outer ring, 18 ... inner ring, 34 ... fourth rolling bearing (bearing), 35 ... fifth rolling bearing (bearing), 50 ... reduction gear, A ... meshing part, M ... electric motor, 54 ... ball, 56 ... bearing seal, 57 ... sealing member (rubber member), 58 ... core metal,
59 ... Seal groove (outer peripheral groove), 59a ... inner wall surface, 60 ... inner peripheral part, 61 ... mounting groove, 62 ... outer peripheral part, 63 ... seal lip, 64 ... first labyrinth forming lip, 65 ... second Labyrinth forming lip, 66 ... sliding contact surface, 67 ... sliding contact surface

Claims (6)

In a reduction gear comprising a driving gear and a driven gear supported by bearings,
The region including the meshing portion of the drive gear and the driven gear is filled with the lubricant composition,
The lubricant composition includes a lubricant and buffer particles having an average particle diameter D1 of 50 μm <D1 ≦ 300 μm,
The bearing includes a bearing seal that seals between the outer ring and the inner ring,
The speed reducer according to claim 1, wherein the bearing seal includes a rubber member having a seal lip that is in sliding contact with the inner wall surface of the outer peripheral groove of the inner ring.   The speed reducer according to claim 1, wherein the buffer material particles are spherical.   In claim 1 or 2, grease is used as the lubricant, and the consistency in a state where buffer particles are added is represented by an NLGI number. 2-No. 000 reducer. The speed reducer according to claim 1 or 2, wherein a lubricating oil is used as the lubricant, and the kinematic viscosity is 5 to 200 mm ² / s (40 ° C). In any one of Claims 1 thru | or 4,
The seal lip includes a sliding contact surface that is in sliding contact with the inner wall surface of the outer peripheral groove of the inner ring,
In the surface properties expressed by the relationship between wavelength and amplitude obtained by Fourier transform of the cross section curve of the sliding surface, the amplitude of the 30 μm wavelength component is 0.3 μm or more and the amplitude of the 120 μm wavelength component is 2.5 μm. Reducer that is below. An electric power steering apparatus that applies power of an electric motor to a steering mechanism via the reduction gear according to any one of claims 1 to 5.

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