JP4702623B2 - Reducer, electric power steering device and worm - Google Patents

Description

  The present invention relates to a speed reducer, an electric power steering apparatus using the speed reducer, and a worm used for the speed reducer.

  A reduction gear including a worm and a worm wheel that mesh with each other is used in an electric power steering apparatus for an automobile. For example, in a column-type electric power steering device, the output rotation of the electric motor is decelerated by transmitting it from the worm to the worm wheel in the reducer, and the output is amplified and then applied to the steering shaft to give torque assist to the steering operation. is doing. A moderate backlash is required for meshing of the worm and worm wheel included in the speed reducer.For example, when a reaction force from a tire is input on a rough road, a rattling sound is generated due to the backlash. When this occurs, if the sound is transmitted as noise to the passenger compartment, the driver is uncomfortable.

Therefore, for example, in a reduction gear of an electric power steering device, a worm and a worm wheel are added in a meshing region of the worm and the worm wheel by adding buffer particles to a lubricant composition used for lubricating a gear of the reduction gear. It has been proposed to buffer the collision between the tooth surfaces (see, for example, Patent Document 1).
On the other hand, a technique is disclosed in which a recess for storing a lubricant to be supplied to the meshing region of the gear is provided on the gear tooth surface as in Patent Document 2 or on the side surface of the gear as in Patent Document 3. ing.
JP 2004-162018 A JP-A-9-133199 JP-A-10-184863

However, when the reduction gear is used for a predetermined period, there is a problem that noise due to rattling noise is generated again.
An object of the present invention is to provide a reduction gear, an electric power steering device, and a worm that can reduce the generation of noise over a long period of time.

The inventor of the present application has obtained the knowledge that the buffer material particles are pulverized by long-term use, and the buffer effect cannot be achieved. In addition, it has been found that the most contributory part to the pulverization is not between the worm and the tooth surface of the worm wheel, but between the tooth tip surface of the worm wheel and the tooth bottom surface of the worm facing this. The present invention has been made on the basis of such knowledge, and includes a worm (20) and a worm wheel (21) that mesh with each other in the meshing region (A), and a lubricant in which buffer particles are added to at least the meshing region. In the speed reducer filled with the worm wheel, the tooth tip surface of the worm wheel and the tooth bottom surface of the worm at the center (A1) in the worm axial direction (65) of the tooth bottom surface (62) of the worm (20) at least in the meshing region. Provided is a reduction gear (14) characterized in that an escape groove (64) for allowing the lubricant to escape from a gap between the first and second lubricants extends in a spiral manner .

  The gap between the tooth tip surface of the worm wheel and the tooth bottom surface of the worm is the narrowest corresponding to the vicinity of the central portion in the axial direction of the tooth bottom surface of the worm. In the present invention, since the relief groove for the lubricant is provided in the axial central portion of the bottom surface of the worm, the buffer material particles of the lubricant are reliably prevented from being crushed in the meshing region between the worm and the worm wheel. it can. Thereby, deterioration of the lubricant due to use can be suppressed for a long period of time, and generation of noise can be reduced over a long period of time.

An electric power steering device characterized in that the power of the electric motor (M) is transmitted to the steering mechanism (4, 7) via the speed reducer is preferable (Claim 2). In this case, the deterioration of the lubricant can be suppressed for a long time, and the noise in the vehicle compartment can be reduced for a long time.
Furthermore, the worm used for the speed reducer includes a tooth bottom surface, and at least in the meshing region, a lubricant from a gap between a tooth tip surface of the worm wheel and a tooth bottom surface of the worm at a central portion of the tooth bottom surface in the worm axial direction. Preferably, the worm is characterized in that a relief groove (64) for escaping is provided in a spiral manner (Claim 3). In this case, since the deterioration of the lubricant can be suppressed for a long time, it is possible to reduce the sound caused by the backlash for a long time when meshing with the worm wheel.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram illustrating a schematic configuration of an electric power steering apparatus according to an embodiment to which a reduction gear according to an embodiment of the present invention is applied. Referring to FIG. 1, in the electric power steering apparatus 1, a first steering shaft 3 to which a steering member 2 such as a steering wheel is attached, and a second steering shaft 5 connected to a pinion shaft 4 are provided. Coaxially connected via a torsion bar 6. The rack teeth 7a of the rack bar 7 serving as a snake shaft extending in the left-right direction of the vehicle are engaged with the pinion teeth 4a formed in the vicinity of the end of the pinion shaft 4, and the rack and comprising the pinion shaft 4 and the rack bar 7 A steering mechanism is configured by the pinion mechanism.

The rack bar 7 is supported in a linearly reciprocating manner in a housing (not shown) fixed to the vehicle body, and tie rods 8 are coupled to both ends of the rack bar 7 protruding to the outside of the housing (not shown). Yes. Each tie rod 8 is connected to a corresponding steering wheel 10 via a corresponding knuckle arm 9.
The housing 11 that supports the first and second steering shafts 3 and 5 is made of, for example, an aluminum alloy, and is attached to a vehicle body (not shown). The housing 11 includes a sensor housing 12 and a cylindrical gear housing 13 that are fitted together. Specifically, the upper end 13 a of the gear housing 13 is fitted into the annular step portion 12 a on the outer periphery of the sensor housing 12. The gear housing 13 accommodates a reduction gear 14 composed of a worm gear mechanism, and the sensor housing 12 accommodates a torque sensor 15 and a control board 16.

  The speed reducer 14 is a worm wheel 21 that is integrally rotatable with an intermediate portion in the axial direction of the second steering shaft 5 and cannot be moved in the axial direction, and a rotating shaft 17 of the electric motor M as shown in FIG. And a worm 20 connected so as to be integrally rotatable through a joint mechanism such as a spline joint 18. In the gear housing 13, the worm 20 and the worm wheel 21 are engaged with each other in the engagement region A.

  The worm wheel 21 is connected to the second steering shaft 5 so as to be relatively non-rotatable, and surrounds the core metal 21a so as to be integrally rotatable with the core metal 21a and relatively non-rotatable. And a synthetic resin member 21b having a plurality of teeth 61 (see FIG. 3) formed on the outer periphery. The cored bar 21a is inserted into the mold when the synthetic resin member 21b is molded with resin, for example.

The second steering shaft 5 is rotatably supported by first and second rolling bearings 22 and 23 that are arranged with the worm wheel 21 sandwiched between the upper and lower sides in the axial direction.
The outer ring 24 of the first rolling bearing 22 is fitted and held in a bearing holding hole 25 provided in the cylindrical protrusion 12 b at the lower end of the sensor housing 12. The upper end surface of the outer ring 24 is in contact with the annular step portion 26, and the outer ring 24 is restricted from moving upward in the axial direction with respect to the sensor housing 12.

On the other hand, the inner ring 27 of the first rolling bearing 22 is fitted to the second steering shaft 5 by an interference fit. Further, the lower end surface of the inner ring 27 is in contact with the upper end surface of the core metal 21 a of the worm wheel 21.
The outer ring 28 of the second rolling bearing 23 is fitted in the bearing holding hole 29 of the gear housing 13. The lower end surface of the outer ring 28 is in contact with the annular step portion 30, and the outer ring 28 is restricted from moving downward in the axial direction with respect to the gear housing 13.

On the other hand, the inner ring 31 of the second rolling bearing 23 is attached to a state in which the inner ring 31 can rotate integrally with the second steering shaft 5 and the axial movement with respect to the second steering shaft 5 is restricted. Further, the inner ring 31 is sandwiched between a step portion 32 of the second steering shaft 5 and a nut 33 fastened to a screw portion of the second steering shaft 5.
The torsion bar 6 passes through the first and second steering shafts 3 and 5. An upper end 6 a of the torsion bar 6 is connected to the first steering shaft 3 by a connecting pin 34 so as to be rotatable integrally with the first steering shaft 3, and a lower end 6 b is connected to the second steering shaft 5 so as to be rotatable integrally with the second steering shaft 5. The lower end of the second steering shaft 5 is connected to the pinion shaft 4 via an intermediate shaft (not shown).

The connection pin 34 connects the third steering shaft 36 disposed coaxially with the first steering shaft 3 so as to be integrally rotatable with the first steering shaft 3. The third steering shaft 36 passes through a tube 37 constituting a steering column.
The upper portion of the first steering shaft 3 is rotatably supported by the sensor housing 12 via a third rolling bearing 38 made of, for example, a needle roller bearing. The reduced diameter portion 39 at the lower part of the first steering shaft 3 and the hole 40 at the upper part of the second steering shaft 5 regulate the relative rotation of the first and second steering shafts 3 and 5 within a predetermined range. And a predetermined play in the rotational direction.

  Next, referring to FIG. 2, the worm 20 is rotatably supported by fourth and fifth rolling bearings 43 and 44 held by the gear housing 13. Inner rings 45, 46 of the fourth and fifth rolling bearings 43, 44 are fitted into corresponding constricted portions of the worm 20. Further, the outer rings 47 and 48 are respectively held in bearing holding holes 49 and 50 of the gear housing 13.

  The gear housing 13 includes a portion 13 b that faces a part of the peripheral surface of the worm 20 in the radial direction. Further, the outer ring 47 of the fourth rolling bearing 43 that supports the one end 20 a of the worm 20 is positioned in contact with the step 51 of the gear housing 13. On the other hand, the movement of the inner ring 45 toward the other end 20b is restricted by contacting the positioning step 52 of the worm 20.

  Further, the inner ring 46 of the fifth rolling bearing 44 that supports the vicinity of the other end portion 20b (joint side end portion) of the worm 20 is brought into contact with the positioning step portion 54 of the worm 20 to move toward the one end portion 20a. It is regulated. The outer ring 48 is urged toward the fourth rolling bearing 43 by a preload adjusting screw member 55. The screw member 55 is screwed into a screw hole 56 formed in the gear housing 13, thereby applying a preload to the pair of rolling bearings 43 and 44 and positioning the worm 20 in the axial direction. A lock nut 57 is engaged with the screw member 55 to fix the screw member 55 after the preload adjustment.

In the gear housing 13, a region including the meshing region A of the worm 20 and the worm wheel 21 is filled with a lubricant in which buffer material particles are dispersed. The lubricant may be filled only in the meshing area A, or may be filled in the entire periphery of the meshing area A and the worm 20 or in the entire gear housing 13.
The above-described lubricant includes a lubricant and buffer material particles. 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 impact of meshing between the worm and the worm wheel to reduce the rattling noise, and the noise of the reduction gear cannot be significantly reduced. . Further, when the average particle diameter D1 exceeds 300 μm, there is a problem that the steering torque of the electric power steering device 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 area A between the worm and the worm wheel, 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 seal-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 material particles is less than 20 parts by weight, the impact is absorbed by interposing the meshing area A between the worm and the worm wheel, thereby reducing the noise of the reduction gear 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.
As the lubricating base 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. 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 can also contain solid lubricants (molybdenum disulfide, graphite, PTFE, etc.), phosphorus and sulfur extreme pressure additives, antioxidants such as tributylphenol and methylphenol, rust inhibitors, Metal deactivators, viscosity index improvers, oiliness agents and the like may be added.

FIG. 3 is an enlarged cross-sectional view of the meshing area A of FIG. FIG. 4 is a schematic view showing a main part of the worm.
3 and 4, the worm 20 includes a shaft 59 and a spiral worm tooth 60 that protrudes outward from the peripheral surface of the shaft 59. The worm tooth 60 defines a spiral tooth bottom surface 62 having a constant width in the axial direction on the peripheral surface of the shaft 59. In the meshing area A, the worm teeth 60 of the worm 20 and the plurality of teeth 61 of the worm wheel 21 are meshed. When the worm 20 rotates in a predetermined direction, the worm wheel 21 rotates in a corresponding direction (for example, a clockwise direction indicated by a white arrow in FIG. 3).

The shaft 59 of the worm 20 requires a minimum cross-sectional diameter of a predetermined value or more in terms of strength, whereas the distance between the centers of the worm 20 and the worm wheel 21 must be a predetermined value or less in terms of space. For this reason, in the meshing area A, the gap C between the tooth bottom surface 62 of the worm 20 and the tooth tip surface 63 of the tooth 61 of the worm wheel 21 is relatively small.
In a region corresponding to the meshing region A in the tooth bottom surface 62 of the worm 20, a lubricant relief groove 64 extending continuously in a spiral shape is provided. Even when the gap C is relatively small as described above, the lubricant intervening between the tooth tip surface 63 of the tooth 61 and the tooth bottom surface 62 of the worm 20 in the meshing region A escapes into the escape groove 64, so The buffer particles are not crushed.

  The relief groove 64 is formed at the center position A1 of the tooth bottom surface 62 in the worm axial direction 65. The width of the relief groove 64 is set to, for example, about 40% to 60% of the width W of the tooth bottom surface 62. The relief groove 64 needs to be provided in at least a region corresponding to the meshing region A of the tooth bottom surface 62 of the worm 20, and a range corresponding to, for example, two or three turns of the helical tooth bottom surface 62 (see FIG. 3 and FIG. 3). In FIG. 4, it is formed in 2 turns. The cross-sectional shape of the relief groove 64 is U-shaped as shown in FIG. 3, and the depth thereof is set to, for example, about 0.2 mm to 1.0 mm so that a sufficient amount of lubricant can flow.

  The gap C between the tooth tip surface 63 of the worm wheel 21 and the tooth bottom surface 62 of the worm 20 is the narrowest in the tooth bottom surface 62 of the worm 20 corresponding to the vicinity of the central position A1 in the worm axial direction 65. In the embodiment, since the relief groove 64 for the lubricant is provided at the central position A1 of the tooth bottom surface 62 in the worm axial direction 65, the buffer material particles of the lubricant are contained in the tooth tip surface 63 of the worm wheel 21 and the worm 20. Crushing between the tooth bottom surfaces 62 can be reliably prevented. Thereby, deterioration of a lubricant can be suppressed over a long period of time, and generation of noise can be reduced over a long period of time.

In the above embodiment, the relief groove 64 has been described as continuously extending in a spiral shape, but a plurality of longitudinal relief grooves are spaced at a predetermined interval along the central position A1 of the spiral tooth bottom surface 62. May be arranged intermittently.
Although the cross-sectional shape of the escape groove 64 has been described as being U-shaped in the above embodiment, the cross-sectional shape of the escape groove 64 may be a rectangle or a triangle.

Furthermore, although the case where the helical relief groove 64 for the lubricant is provided in the tooth bottom surface 62 of the worm 20 in the meshing region A has been described, the relief groove is the tip surface 63 of all the teeth 61 of the worm wheel 21. It is also possible to release the lubricant in the meshing area A by both the escape grooves.
The present invention is not limited to the contents of the above-described embodiment, and various modifications can be made within the scope of the claims.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment to which a gear concerning the present invention is applied. It is sectional drawing which follows the II-II line of FIG. It is an expanded sectional view of a meshing area. It is the schematic which shows the principal part of a worm | warm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 4 ... Pinion shaft (steering mechanism), 7 ... Rack (steering mechanism), 14 ... Reduction gear, 20 ... Worm, 21 ... Worm wheel, 61 ... Tooth, 63 ... Tooth surface, 64 ... Relief groove, 65 ... worm shaft direction, A ... engagement area, A1 ... center position (center portion), M ... electric motor

Claims (3)

In a speed reducer that includes a worm and a worm wheel that mesh with each other in a meshing region, and is filled with a lubricant to which buffer particles are added at least in the meshing region.
At least in the meshing region, an escape groove for spirally extending the lubricant from the gap between the tooth tip surface of the worm wheel and the tooth bottom surface of the worm is provided in the central portion of the worm tooth bottom surface in the worm axial direction. Reducer characterized by being.   An electric power steering device characterized in that the power of the electric motor is transmitted to the steering mechanism via the speed reducer according to claim 1. The worm used for the speed reducer according to claim 1, further comprising a tooth bottom surface, lubricated from a clearance between a tooth tip surface of the worm wheel and a tooth bottom surface of the worm at a central portion of the tooth bottom surface in the worm axial direction at least in a meshing region. A worm characterized in that an escape groove for releasing the agent is provided so as to extend spirally .

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