JP2008115297A - Lubricant composition, reduction gear, and electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant composition which maintains noise reduction effectiveness over a long period of time when it is used for the lubricity of an intermeshing part between rollingly contact gears. <P>SOLUTION: The lubricant composition is filled into a region including an intermeshing part of a drive gear 21 and a driven gear 22 of a reduction gear 19. The lubricant composition comprises a lubricating oil as a lubricant and shock absorber particles having an average particle size of 300-500 μm. An average particle size of 300 μm or more provides marked effectiveness in reducing sliding sound. On the other hand, tooth hitting noise of the gears increases as the average particle size of the shock absorber particles is increased. Therefore, the average particle size of the shock absorber particles has been established in the above range. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  A reduction gear is used for an electric power steering apparatus for automobiles. 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 small gear such as a worm to a large gear such as a worm wheel, and the output is amplified. By giving, the steering operation is torque-assisted. Appropriate backlash is required for meshing of the small gear and the large gear as the speed 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 small gears and the large gears 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.

Therefore, it has been proposed to add buffer material particles to a lubricant composition used to lubricate the meshed portion of the worm and worm wheel (see, for example, Patent Document 1).
JP 2004-162018 A

In Patent Document 1 described above, when the teeth of the meshing portion of the worm and the worm wheel are brought into sliding contact with each other, the buffer material particles enter the meshing portion, and as a result, the backlash between the worm and the worm wheel is suppressed, and the noise is reduced. Is reduced.
By the way, the case where the rotating shaft of a steering shaft and an electric motor is arrange | positioned in parallel and the output of an electric motor is transmitted to the output shaft of a steering shaft via a parallel shaft gear mechanism is assumed. Since the rolling contact occurs in the meshing portion of the gear of the parallel shaft gear mechanism, the buffer material particles of Patent Document 1 may not withstand the contact load of the rolling contact portion and may break. As a result, the buffer material particles deteriorate early, and noise due to backlash is generated early. On the other hand, noise due to abnormal noise generated when the buffer particles are destroyed in the rolling contact portion is also a problem.

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 large gear that are in rolling contact with each other.
An object of the present invention is to provide a lubricant composition, a reduction gear, and an electric power steering device that can maintain a noise reduction effect over a long period of time when used for lubrication of meshing portions between gears that are in rolling contact. It is in.

It has been found that at the meshing portions of the gears that are in rolling contact with each other, it is highly possible that the buffer particles that contribute to the prevention of hitting sound will be crushed and destroyed at the rolling contact portion.
The present invention is based on such knowledge, and includes a lubricant used as a lubricant and buffer particles in a lubricant composition for lubricating a region including meshing portions of gears that are in rolling contact with each other. The lubricant composition is characterized in that the average particle diameter of the buffer particles is set in the range of 300 to 500 μm.

  If the average particle diameter of the said buffer material particle is set to the range of 300-500 micrometers, it is preferable at the point which can make both a sliding sound and a rattling sound (rattle sound) small. That is, it has been found that by setting the average particle diameter of the buffer material particles to 300 μm or more, there is a remarkable effect in reducing sliding noise. On the other hand, as the average particle size of the cushioning material particles increases, the rattling noise tends to increase. Therefore, the average particle diameter of the buffer material particles was set in the above range.

In addition, when the kinematic viscosity of the lubricating oil used as the lubricant is increased to lower the fluidity of the lubricating oil, the buffer particles are difficult to roll and enter the contact portion. As a result, the breakage of the buffer material particles at the rolling contact portion can be suppressed. Thereby, the noise prevention effect by a buffer material particle can be maintained over a long period of time. On the other hand, if the kinematic viscosity of the lubricating oil is increased when the particle diameter of the buffer material particles is 300 μm or more, the effect of reducing the rattling noise can be obtained, but the effect is saturated with respect to the reduction of the sliding noise. Further, if the kinematic viscosity of the lubricating oil becomes too high, there is a problem that the steering torque increases. Accordingly, considering the increase in steering torque in addition to rattling noise and sliding noise, it is preferable that the kinematic viscosity of the lubricating oil is 300 mm ² / s or more and is not too high.

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 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, and urethane rubber (U).
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 amount of the buffer material particles added is preferably 5 to 50% by weight of the lubricant. If the amount is less than 5% by weight, the noise reduction effect cannot be sufficiently obtained. If the amount exceeds 50% by weight, a problem of an increase in rotational torque occurs. Therefore, the above range is preferable.
The speed reducer of the present invention includes a small gear and a large gear, and is characterized in that the region including the meshing portion of both gears is filled with the above-described lubricant composition (claim 3). In this case, it is preferable in that noise such as rattling noise can be reduced at a low cost and the noise reduction effect can be maintained for a long time.

  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 (claim 4). 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.
<Lubricant composition>
As described above, the lubricant composition of the present invention contains lubricating oil as a lubricant and buffer particles. The average particle diameter of the buffer material particles is preferably set in the range of 300 to 500 μm.

  If the average particle diameter of the buffer material particles is set in the range of 300 to 500 μm, both the sliding noise and the rattling noise can be reduced. That is, by setting the average particle diameter of the buffer particles to 300 μm, there is a remarkable effect in reducing the sliding noise. On the other hand, as the average particle size of the buffer material particles increases, the rattle noise tends to increase. Therefore, the average particle diameter of the buffer material particles was set in the above range.

In addition, when the kinematic viscosity of the lubricating oil used as the lubricant is increased to lower the fluidity of the lubricating oil, the buffer particles are difficult to roll and enter the contact portion. As a result, the breakage of the buffer material particles at the rolling contact portion can be suppressed. Thereby, the noise prevention effect by a buffer material particle can be maintained over a long period of time. On the other hand, if the kinematic viscosity of the lubricating oil is increased when the particle diameter of the buffer material particles is 300 μm or more, the effect of reducing the rattling noise can be obtained, but the kinematic viscosity of the lubricating oil is increased to, for example, 1000 mm ² / s or higher. Even so, the effect is saturated with respect to the reduction of the sliding noise. Further, if the kinematic viscosity of the lubricating oil becomes too high, there is a problem that the steering torque increases. Accordingly, considering the increase in steering torque in addition to rattling noise and sliding noise, it is preferable that the kinematic viscosity of the lubricating oil is 300 mm ² / s or more and is not too high.

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.

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 by interposing the meshing portion of the small gear and the large 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.
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, and urethane rubber (U).
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 amount of the buffer material particles added is preferably 5 to 50% by weight of the lubricant. If the amount is less than 5% by weight, the impact of the meshing portion cannot be reduced, so that a sufficient noise reduction effect cannot be obtained. If the amount exceeds 50% by weight, the flow resistance of the particles increases and a problem of increased steering torque occurs. It is preferable to set in the range.
<Reduction gear and electric power steering device>
FIG. 1 is a schematic cross-sectional view of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering system (EPS) 1 includes a steering shaft 3 coupled to a steering member 2 such as a steering wheel so as to be integrally rotatable, and a universal joint 4 to the steering shaft 3. An intermediate shaft 5 connected via a pin, a pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6, and a rack tooth 8a meshing with a pinion tooth 7a provided on the pinion shaft 7. And a rack bar 8 as a steered shaft extending in the left-right direction.

  The pinion shaft 7 and the rack bar 8 constitute a steering mechanism 9 composed of a rack and pinion mechanism. The rack bar 8 is supported in a rack housing 10 fixed to the vehicle body so as to be linearly reciprocable via a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the rack housing 10, and tie rods 11 are coupled to the respective end portions. Each tie rod 11 is connected to a corresponding steering wheel 12 via a knuckle arm (not shown).

When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion teeth 7a and the rack teeth 8a. Thereby, steering of the steering wheel 12 is achieved.
The steering shaft 3 is divided into an input shaft 3 a connected to an attachment shaft 13 having a steering member 2 attached to one end thereof, and an output shaft 3 b connected to the pinion shaft 7. The input shaft 3a and the output shaft 3b are connected to each other via the torsion bar 14 so as to be relatively rotatable on the same axis. The lower end of the input shaft 3a is rotatably supported by the output shaft 3b via a slide bearing 15 such as a metal bush.

The upper end portion of the torsion bar 14, the upper end portion of the input shaft 3a, and the lower end portion of the mounting shaft 13 are connected to each other by a connecting member 16 made of, for example, a connecting pin so as to be integrally rotatable. Moreover, the lower end part of the torsion bar 14 is connected to the output shaft 3b so as to be integrally rotatable by a connecting member 17 made of a connecting pin, for example.
The output rotation of the electric motor 18 is transmitted to the pinion shaft 7 via the speed reducer 19 and further converted into a linear motion of the rack bar 8 to assist steering. The rotating shaft 20 of the electric motor 18 is disposed in parallel with the steering shaft 3.

  The reduction gear 19 is provided coaxially with the rotary shaft 20 of the electric motor 18 and is driven by the electric motor 18 as a small gear. The reduction gear 19 meshes with the driving gear 21 and can rotate integrally with the pinion shaft 7. And a driven gear 22 as a large gear to be connected. That is, the speed reducer 19 is configured by a parallel shaft gear mechanism, and the drive gear 21 and the driven field vehicle 22 are brought into contact with each other at the meshing portions of the teeth.

The drive gear 21 is integrally formed on the outer periphery of a shaft member 24 that is coaxially and rotatably connected to the rotary shaft 20 of the electric motor 18 via a joint 23.
In the gear housing 25 that houses the speed reducer 19, at least the meshing portions of the gears 21 and 22 are filled with a lubricant made of lubricating oil having a relatively high kinematic viscosity. The gear housing 25 is formed by combining a cylindrical first housing 25a and a cylindrical second housing 25b. The first housing 25a is combined with a third housing 26 constituting a part of the steering column, and a motor housing 27 is combined.

  The shaft member 24 in which the drive gear 21 is integrally formed is rotatably supported via a pair of rolling bearings 28 and 29 disposed on both sides of the drive gear 21 in the axial direction. Of the pair of rolling bearings 28 and 29, the outer ring of one rolling bearing 28 is held by a motor housing 27, and the outer ring of the other rolling bearing 28 is held by a second housing 25b.

  The output shaft 3b to which the driven gear 22 is attached so as to be integrally rotatable is rotatably supported by a pair of rolling bearings 30 and 31 disposed on both sides of the driven gear 22 therebetween. Of the pair of rolling bearings 30, 31, the outer ring of one rolling bearing 30 is held by the first housing 25a, and the outer ring of the other rolling bearing 31 is held by the second housing 25b. A known seal bearing is used for each of the rolling bearings 28 to 31.

  A torque sensor 32 is provided for detecting a steering torque based on the relative rotational displacement between the input and output shafts 3a and 3b via the torsion bar 14. Based on the steering torque detected by the torque sensor 32 and the vehicle speed detected by a vehicle speed sensor (not shown), the output torque of the electric motor 18 is adjusted, whereby the assist torque is adjusted.

In the gear housing 25, at least the meshing portions of the two gears 21 and 22 are filled with lubricating oil as a lubricant in which the above-mentioned buffer particles are dispersed. Lubricating oil may be filled only in the meshing portion, or may be filled in the entire periphery of the meshing portion and at least one of the gears, or in the entire gear housing 25.
The present invention is not limited to the above embodiment. For example, the configuration of the speed reducer according to the present invention can be applied to a speed reducer for a device other than the electric power steering device 1, and various modifications can be made within the scope of the matters described in the claims of the present invention. Changes can be made.

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 100 to 600 μm.
Next, the above-mentioned buffer particles were blended at a blending ratio of 20% by weight in a lubricating oil composed of a polyalphaolefin oil having a kinematic viscosity changed in the range of 50 to 5000 mm ² / s to obtain a lubricant composition.

Then, the lubricant composition was filled in the actual reduction gear of the electric power steering apparatus shown in FIG. 1, and the sliding noise (dB) and the rattling noise (dB) were measured. Both the drive gear 21 and the driven gear 22 are made of metal.
(Sliding sound)
In the measurement of the sliding sound, the backlash was 8 ′. The result is shown in FIG.

From FIG. 2, it was found that when the average particle diameter of the buffer material particles is 300 μm or more, there is a remarkable effect in reducing the sliding noise (see reference value). From this, it was confirmed that the average particle diameter of the buffer material particles needs to be 300 μm or more.
(Gap sound)
In the measurement of the rattling sound (rattle sound), the backlash was 8 ′. The result is shown in FIG.

As shown in FIG. 3, the increase in the particle size in each example where the average particle size is 300 μm or more and the kinematic viscosity is 1000 mm ² / s or more in which a remarkable effect was obtained in reducing the sliding noise of FIG. As a result, the rattle noise increases. Therefore, from the viewpoint of suppressing rattle noise, it has been found that the average particle size needs to be 500 μm or less (see standard value).

1 is a schematic cross-sectional view of an electric power steering device according to an embodiment of the present invention. In the Example of this invention, it is a graph which shows the result of having measured the relationship between the kinematic viscosity of lubricating oil, 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 average particle diameter of buffer material particle | grains, and the rattling sound of the reduction gear of an electric power steering apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 9 ... Steering mechanism, 18 ... Electric motor, 19 ... Reduction gear, 20 ... Rotating shaft, 21 ... Drive gear (small gear), 22 ... Driven gear (large gear), 25 ... Gear housing

Claims (3)

  In a lubricant composition for lubricating a region including meshing portions of gears that are in rolling contact with each other, the lubricant composition includes a lubricant used as a lubricant and buffer material particles, and the average particle size of the buffer material particles is 300 to A lubricant composition characterized by being set in a range of 500 μm.   A speed reducer comprising a small gear and a large gear, wherein the lubricant composition according to claim 1 or 2 is filled in a region including a meshing portion of both gears.   An electric power steering apparatus, wherein an output of an electric motor for assisting steering is transmitted to a steering mechanism via the reduction gear according to any one of claims 1 to 3.

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