JP2009114387A - Lubricant composition and drive transmission mechanism and electric power steering device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant composition that can reduce abnormal sounds generating during rotation of a drive transmission mechanism of a reduction gear, a rotary bearing or a ball screw, without excessively increasing the rotation torque or without complicating the structure of the drive transmission mechanism or the like, and to provide a drive transmission mechanism and an electronic power steering device using the composition. <P>SOLUTION: The lubricant composition is prepared by mixing a base oil, a polymer and a thickening agent, and has an oil film thickness of not less than 10 nm and a complex elastic modulus of from 1 to 3.3 kPa. The reduction gear 18 as a drive transmission mechanism is charged with the lubricant composition. The electric power steering device 1 has the reduction gear assembled therein. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lubricant composition that can be suitably used for a drive transmission mechanism including a gear device, such as a reduction gear having a small gear and a large gear, a rolling bearing, a ball screw, and the like, and the lubricant. The present invention relates to a drive transmission mechanism filled with a composition, and an electric power steering device including the drive transmission mechanism.

  A reduction gear is used for an electric power steering device for an automobile. For example, in the column type EPS, the rotation of the electric motor is transmitted from the small gear such as the worm to the large gear such as the worm wheel in the speed reducer to reduce the rotational speed and amplify the output, and then apply it to the steering shaft. Thus, the steering operation is torque-assisted. Appropriate backlash is required for meshing the small gear and the large gear. However, if the backlash is too large, for example, when the rotation of both gears is reversed, or when the reaction force from the tire is input (kickback) by running on a bad road such as a stone pavement, A rattle sound (tooth rattling sound) may be generated due to the backlash, and if this is transmitted as noise in the passenger compartment, the driver is uncomfortable.

  For this reason, conventionally, so-called layered assembly has been adopted in which a combination of a small gear and a large gear is selected to assemble a reduction gear so that an appropriate backlash is achieved. Therefore, there has been a problem that the productivity of the electric power steering apparatus incorporating the reduction gear cannot be improved. In addition, if the backlash is excessively reduced, there has been a problem that the rotational torque of the reduction gear, and consequently the steering torque of the electric power steering device, excessively increases. Furthermore, even if the backlash was appropriate, it was not possible to suppress the fine vibration at the meshing portion between the small gear and the large gear and the accompanying meshing noise.

  Therefore, in order to solve these problems, the worm shaft is arranged so as to be biasable in the direction of the worm wheel, and the worm shaft is elastically biased toward the worm wheel by using a spring or the like. There has been proposed an electric power steering device that substantially eliminates backlash between the two (see Patent Document 1, etc.). However, in the above configuration, there is a problem that the manufacturing cost of the electric power steering apparatus increases because the structure of the speed reducer is complicated. Further, the generation of meshing noise due to micro vibrations at the meshing portion could not be suppressed.

  By increasing the surface accuracy of the tooth surface of the gear to suppress the occurrence of micro vibrations and the resulting meshing noise, and by increasing the viscosity of the base oil of the grease, the viscosity of the grease when flowing is increased. However, the so-called damping effect has been studied to suppress the generation of abnormal noise such as the meshing noise and rattle noise. However, the former configuration takes time and effort to manufacture the reduction gear and thus the electric power steering device. There is a problem that productivity is lowered and manufacturing cost is increased. In the latter configuration, there has been a problem that the rotational torque of the reduction gear, and hence the steering torque of the electric power steering device, excessively increases. Further, the solution to the contradictory problem of reducing the abnormal noise and suppressing the increase in torque has been demanded not only for gears such as a reduction gear but also for rolling bearings and ball screws, for example.

For example, in a rolling bearing, by increasing the viscosity of the grease base oil, the viscosity of the grease when flowing is increased, and the damping effect reduces the occurrence of rolling vibration and associated noise. However, the above method has a problem that the rotational torque of the rolling bearing is excessively increased. The same was true for the ball screw. Therefore, in order to suppress an increase in rotational torque of the grease, particularly at a low temperature, by blending a polymer such as cis-1,4-polyisoprene as a thickener while lowering the viscosity of the base oil itself. It has been studied to increase the viscosity of the grease as a whole during flow and reduce the occurrence of abnormal noise by the damping effect (see Patent Document 2).
JP 2000-43739 A JP 2000-328086 A

  However, as a result of investigations by the inventor, it is possible to reduce the noise and reduce the rotational torque by simply mixing a predetermined amount of polymer with a normal grease composition and adjusting the viscosity during flow to a predetermined range. It became clear that the inhibitory effect cannot be completely achieved. An object of the present invention is to reduce the noise generated during rotation of a drive transmission mechanism such as a speed reducer, a rolling bearing, a ball screw, etc. without excessively increasing the rotational torque, and to complicate the structure. It is another object of the present invention to provide a lubricant composition that can be reduced more than ever, a drive transmission mechanism and an electric power steering device using the same.

  In order to solve the above-mentioned problems, the inventor further examined the characteristics of a lubricant composition such as grease. As a result, as explained above, the thickness of the oil film formed by the lubricant composition in which the polymer as the thickener is blended with the base oil having a low viscosity is set within a predetermined range, and the lubricant composition If the complex elastic modulus indicating elasticity is set within a predetermined range among the viscoelastic properties of the object, the lubricant composition is given a good damping effect while suppressing an increase in rotational torque over a wide temperature range, and the speed is reduced. The present inventors have found that noise generated during rotation of a drive transmission mechanism such as a machine, or a rolling bearing, a ball screw, etc. can be reduced more than before, and the present invention has been completed. Accordingly, the present invention provides a lubricant composition comprising a base oil, a polymer and a thickener, having an oil film thickness of 10 nm or more and a complex elastic modulus of 1 KPa or more and 3.3 KPa or less. It is.

  As the polymer to be contained in the lubricant composition of the present invention, those having excellent durability and capable of maintaining the function as a thickener over a long period of time are preferably used. As the polymer, polyisoprene and polyester polyol are used. At least one selected from the group consisting of: Further, when the lubricant composition of the present invention is used for lubricating a gear constituting a gear device included in a drive transmission mechanism such as a speed reducer, the lubricant composition also includes buffer particles. It is preferable to contain. The buffer particles are interposed between the meshing portions of the gears meshing with each other, and function as a cushioning material to buffer the collision between the tooth surfaces of the two gears, thereby particularly reducing rattle noise. Thus, it is possible to more effectively reduce the noise generated when the drive transmission mechanism rotates.

  The buffer particles are preferably particles composed of at least one selected from the group consisting of a soft resin having rubber elasticity and rubber. The drive transmission mechanism of the present invention includes a gear device, and the region including the meshing portion of the gear constituting the gear device is filled with the lubricant composition of the present invention. This is preferable in that the steering torque of the power steering device can be sufficiently reduced. In addition, the electric power steering device of the present invention decelerates the output of the electric motor for assisting steering through the drive transmission mechanism and transmits the output to the steering mechanism. It is preferable at the point which can be reduced.

  According to the present invention, noise generated during rotation of a drive transmission mechanism such as a speed reducer, or a rolling bearing, a ball screw, and the like can be made without excessively increasing the rotational torque and complicating the structure. In addition, it is possible to provide a lubricant composition that can be reduced more than before, a drive transmission mechanism and an electric power steering device using the same.

<Lubricant composition>
The lubricant composition of the present invention comprises a base oil, a polymer, and a thickener, and has an oil film thickness of 10 nm or more and a complex elastic modulus of 1 KPa or more and 3.3 KPa or less. It is. In the present invention, the oil film thickness is limited to 10 nm or more because, if it is less than the above range, a good damping effect cannot be imparted to the lubricant composition, and abnormal noise cannot be effectively reduced. is there. The oil film thickness is preferably 500 nm or less even within the above range. A lubricant composition having an oil film thickness exceeding the above range has a viscosity that is too high, and may increase the rotational torque of a drive transmission mechanism, a rolling bearing, a ball screw, or the like. In the present invention, the oil film thickness of the lubricant composition is represented by a value measured by the following measuring method.

  That is, in a 25 ± 3 ° C. environment, a predetermined amount of a lubricant composition as a measurement target is supplied to the rolling contact surface between a glass plate and a 3/4 inch ball, and the ball is fed to 5N to 15N. The lubricant composition was measured by a light interference method by measuring the thickness of an oil film formed in contact with the glass plate under a load while applying a load at a rolling speed of 0.01 m / s. Oil film thickness. In the case where the lubricant composition contains buffer material particles, the oil film thickness is determined by using a composition comprising the remaining components (base oil, polymer, thickener, etc.) excluding the buffer material particles, It shall be expressed by the value measured by the measuring method.

  Further, in the present invention, the complex elastic modulus is limited to 1 KPa or more and 3.3 KPa or less, if less than the above range, it is not possible to give a good damping effect to the lubricant composition, This is because it cannot be effectively reduced. Moreover, when it exceeds the said range, it is because the viscosity of a lubricant composition is too high, and rotational torque, such as a drive transmission mechanism, a rolling bearing, and a ball screw, will raise excessively. In the present invention, the complex elastic modulus is expressed by a value measured by the following measurement method.

  That is, in an environment of 25 ± 3 ° C., a predetermined amount of the lubricant composition as a measurement object is a rotary type using a cone as a measurement jig, and the cone rotation is reversed forward and backward at a predetermined frequency. The elastic modulus of a rheometer having a vibration function to be vibrated and supplied to the cone (φ20 / 1 °) and measured by vibrating the cone under the condition of a frequency of 10 Hz is the complex elastic modulus of the lubricant composition. And When the lubricant composition contains buffer material particles, the complex elastic modulus is expressed by a value measured by the measuring method using the composition containing the buffer material particles.

The base oil constituting the lubricant composition is preferably a synthetic hydrocarbon oil [for example, poly α olefin oil (PAO)], but synthetic oil such as silicone oil, fluorine oil, ester oil, ether oil, mineral oil, etc. It can also be used. The base oils can be used alone or in combination of two or more. Further, as described above, it is preferable to use a base oil having a viscosity as low as possible in consideration of suppressing an increase in rotational torque in a wide temperature range, as described above. There is a possibility that the oil film thickness and the complex elastic modulus of the lubricant composition may not satisfy the above range. Therefore, considering these characteristics together, the base oil has a kinematic viscosity at 40 ° C. of 10 mm ² / s (40 ° C.) or more and 100 mm ² / s (40 ° C.) or less, particularly 20 mm ² / s (40 ° C. ) It is preferable to use one that is 40 mm ² / s (40 ° C.) or less.

  As the polymer, any of various polymers that can function as a thickener when combined with the base oil can be used. Particularly, when combined with a synthetic hydrocarbon oil such as PAO, durability is improved. As an excellent polymer that can maintain the function as a thickener over a long period of time, at least one selected from the group consisting of polyisoprene such as cis-1,4-polyisoprene and polyester polyol described above is available. Can be mentioned. In addition, as the polymer, when combined with a predetermined base oil, a polymer having a viscosity capable of constituting a lubricant composition in which the oil film thickness and the complex elastic modulus can satisfy the range described above is selected. Can be used.

Although the specific range is not particularly limited, when the base oil is combined with the base oil whose kinematic viscosity satisfies the preferred range described above, the oil film thickness and the complex elastic modulus are described above. In order to constitute a lubricant composition that can satisfy the range, the polymer has a kinematic viscosity at 40 ° C. of 1000 mm ² / s (40 ° C.) or more and 10000 mm ² / s (40 ° C.) or less, particularly 3000 mm ² / It is preferable to use one that is s (40 ° C.) or more and 7000 mm ² / s (40 ° C.) or less. Further, the content ratio of the polymer is not particularly limited, but the oil film thickness and the complex elastic modulus can satisfy the above-described ranges by combining a base oil and a polymer each having a kinematic viscosity that satisfies the above preferable range. In order to constitute the lubricant composition, the content of the polymer in the total amount of the base oil, the polymer and the thickener is preferably 20% by mass or more and 40% by mass or less.

  Examples of the thickener include various conventionally known thickeners such as a soap-based thickener, a urea-based thickener, an organic thickener, and an inorganic thickener. Among these, soap-type thickeners include metal soap-type thickeners such as aluminum soap, calcium soap, lithium soap and sodium soap, mixed soap-type thickeners such as lithium-calcium soap and sodium-calcium soap, aluminum Complex thickeners such as complex, calcium complex, and lithium complex sodium complex are listed, and lithium soap such as lithium stearate is particularly preferable.

  Examples of the urea thickener include polyurea, and examples of the organic thickener include polytetrafluoroethylene (PTFE) and sodium terephthalate. Further, examples of the inorganic thickener include organic bentonite, graphite, silica gel and the like. In addition, the lubricant composition may include a solid lubricant such as fluororesin (PTFE, etc.), molybdenum disulfide, graphite, polyolefin wax (including amide, etc.), phosphorus-based or sulfur-based extreme pressure as necessary. Additives, antioxidants such as tributylphenol and methylphenol, rust inhibitors, metal deactivators, viscosity index improvers, oiliness agents and the like may be added.

  The lubricant composition of the present invention may contain buffer particles as necessary. That is, when the lubricant composition of the present invention is used for lubrication of, for example, a rolling bearing or a ball screw, the lubricant is composed of only the components described above without including the buffer particles in the composition. It is preferred to constitute the composition. On the other hand, when the lubricant composition of the present invention is used for lubrication of gears constituting the gear device of a drive transmission mechanism including the gear device such as a reduction gear provided with a small gear and a large gear. In the composition, the buffer particles are included in the composition, so that the buffer particles are interposed in the meshing portions of the gears meshing with each other, and function as cushioning materials to buffer the collision between the tooth surfaces of both gears. In this way, particularly rattle noise can be reduced, and abnormal noise generated when the drive transmission mechanism rotates can be further effectively reduced.

  The cushioning material particle has a function to reduce the rattle noise by buffering the collision between the tooth surfaces of both gears as a cushioning material through the meshing portion of the gear constituting the gear device included in the drive transmission mechanism. In order to impart the above, any of various soft resin or rubber particles having rubber elasticity can be used. Examples of the soft resin on which the buffer material particles are based include polyolefin resin, polyamide resin, polyester resin, polyurethane resin, polyacetal resin, polyphenylene oxide resin, polyimide resin, and fluororesin.

  Examples of the rubber include oil-resistant rubbers such as ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), silicone rubber, and urethane rubber (U). Further, the buffer material particles may be formed using an oil-resistant thermoplastic elastomer such as olefin, urethane, polyester, polyamide, or fluorine. Among them, as a starting material that becomes a base of the repeating unit, buffer material particles made of a polyurethane resin synthesized by reacting a polyol, a crosslinking agent, and a polyisocyanate are preferable.

  The buffer material particles made of the polyurethane resin synthesize the polyurethane resin by reacting the liquid mixture of the components in a liquid dispersion in a non-aqueous dispersion medium that does not dissolve the components. It can be produced by a so-called dispersion polymerization method. According to the dispersion polymerization method, there is an advantage that it is possible to efficiently produce buffer material particles made of polyurethane resin having a uniform particle size while maintaining the spherical shape of the droplets dispersed in the dispersion medium. Further, as described above, there is an advantage that the elastic modulus and hardness of the buffer particles can be adjusted in an arbitrary range by adjusting the kind and content ratio of each component.

  The particle diameter of the buffer particles can be set to an optimum range according to the configuration of the gear device to be lubricated, particularly the backlash. In order to adjust the average particle size of the buffer particles produced by the dispersion polymerization method, the particle size of the droplets of the mixed liquid dispersed in the dispersion medium can be changed by changing the dispersion conditions and the like. That's fine. The shape of the buffer particles may be irregularly shaped or other shapes, but it improves the fluidity of the lubricant composition, improves the rolling property between the tooth surfaces, and improves the drive transmission mechanism. The spherical shape described above is preferable in consideration of the suppression of an increase in rotational torque, and hence the steering torque of the electric power steering device.

The elastic modulus of the soft resin or the like forming the buffer particles is, for example, 10 ⁻¹ MPa or more and 10 ⁴ MPa or less, particularly 5 × 10 ⁻¹ MPa or more and 10 ² within the temperature range of use of the lubricant composition. It is preferable that it is below MPa. If the elastic modulus is less than the above range, the effect of reducing the rattle noise by buffering the meshing impact of the gears constituting the gear device may not be sufficiently obtained, and the noise in the passenger compartment may not be sufficiently reduced. . In order to adjust the oil film thickness and the complex elastic modulus of the lubricant composition within the above ranges, for example, the type and content of the thickener, such as the type and viscosity of the base oil, the type of polymer, the viscosity, and the content ratio. What is necessary is just to adjust a kind, content rate, etc. of additives, such as a ratio, the elasticity modulus of a buffer material particle, a particle size, a shape, a content rate, a viscosity index improver, and an oiliness agent.

<Drive transmission mechanism and electric power steering device>
FIG. 1 is a schematic view of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 coupled to a steering member 2 such as a steering wheel so as to be integrally rotatable, and an intermediate coupled to the steering shaft 3 via a universal joint 4. A shaft 5, a pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6, and rack teeth 8 a that mesh with pinion teeth 7 a provided on the pinion shaft 7, extend in the left-right direction of the automobile. It has a rack bar 8 as a turning shaft. 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, the 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, and the steering wheel Twelve steering is achieved.

  The steering shaft 3 is divided into an input shaft 3a connected to the steering member 2 and an output shaft 3b connected to the pinion shaft 7. The two shafts 3a and 3b are relative to each other on the same axis via a torsion bar 13. It is mutually connected so that rotation is possible. Further, the torsion bar 13 is provided with a torque sensor 14 for detecting a steering torque from a relative rotational displacement amount between both the shafts 3a and 3b, and the torque detection result of the torque sensor 14 is an ECU (Electric Control). Unit: Electronic control unit) 15.

  The ECU 15 drives and controls the steering assist electric motor 17 via the drive circuit 16 based on a torque detection result, a vehicle speed detection result given from a vehicle speed sensor (not shown), and the like. Then, the output rotation of the electric motor 17 is decelerated via a reduction gear 18 as a drive transmission mechanism and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering. The speed reducer 18 includes a small gear 19 as an input shaft that is rotationally driven by an electric motor 17, and a large gear 20 that meshes with the small gear 19 and that is coupled to the output shaft 3 b of the steering shaft 3 so as to be integrally rotatable. The meshing portion of the small gear 19 and the large gear 20 is filled with the above-described lubricant composition of the present invention.

  Thereby, the meshing noise generated in the meshing portion of the small gear 19 and the large gear 20, the rattle noise, etc. without excessively increasing the rotational torque of the speed reducer 18 and the steering torque of the electric power steering device 1. Can be effectively reduced. The present invention is not limited to the embodiment described above. For example, examples of the gear device that can be lubricated by the lubricant composition of the present invention include the worm gear device including the worm and the worm wheel described above, as well as a helical gear, a spur gear, and the like. Examples thereof include a gear device including a gear meshed by rolling contact, a wave gear device, a cycloid gear device, and the like.

  The lubricant composition of the present invention is used for lubrication of various drive transmission mechanisms other than the speed reducer, which includes a gear device composed of two or more gears meshing with each other, or as described above, a rolling bearing. It can be used for lubricating various members such as a ball screw. For example, instead of the general electric power steering device shown in FIG. 1, a steering angle ratio variable mechanism that can continuously change the ratio of the steering angle of the steering member and the turning angle of the steered wheel according to the traveling vehicle speed. The lubricant composition of the present invention can also be used for lubricating the meshing portion of the gear constituting the VGRS of the electric power steering apparatus incorporating (VGRS). In addition, within the scope of the matters described in the claims of the present invention, the configuration of the drive transmission mechanism of the present invention can be applied to a drive transmission mechanism for a device other than an electric power steering device. Various changes can be made.

<Example 1>
(Preparation of grease)
A synthetic hydrocarbon oil having a kinematic viscosity (40 ° C.) of 30 mm ² / s as a base oil, and a cis-1,4-polyisoprene having a kinematic viscosity (40 ° C.) of 5000 mm ² / s as a polymer; Then, a lithium stearate thickener was mixed using a three-roll mill to prepare a grease having a polymer content of 30% by mass as a lubricant composition. With respect to the grease, when the oil film thickness was measured by the measurement method described above, it was 10 nm. Further, when the complex elastic modulus of the grease was measured by the measurement method described above, it was 2.50 KPa.

<Comparative example 1>
A grease was prepared in the same manner as in Example 1 except that cis-1,4-polyisoprene as a polymer was not blended. The grease had an oil film thickness of 5 nm and a complex elastic modulus of 0.70 KPa.
<Comparative Examples 2 and 3>
A grease was prepared in the same manner as in Example 1 except that the content ratio of cis-1,4-polyisoprene as a polymer was 10% by mass (Comparative Example 2) and 50% by mass (Comparative Example 3). The oil film thickness of the grease of Comparative Example 2 was 8 nm and the complex elastic modulus was 1.10 KPa, the oil film thickness of the grease of Comparative Example 3 was 50 nm, and the complex elastic modulus was 3.50 KPa.

<Example 2>
(Buffer material particles)
As the buffer material particles, a polyol, a cross-linking agent, and a polyisocyanate as starting materials that are the basis of the repeating unit constituting the polyurethane resin are dropped in a non-aqueous dispersion medium that does not dissolve each of the above components. Spherical particles made of the polyurethane resin were prepared by a dispersion polymerization method in which a polyurethane resin was synthesized by reacting in a dispersed state. The average particle diameter (volume average diameter) of the buffer material particles measured using a particle size distribution measuring apparatus using a laser diffraction / scattering method (registered trademark Microtrac manufactured by Nikkiso Co., Ltd.) was 1 μm. Moreover, the elastic modulus at 25 ° C. of the buffer particles measured by the following method was 12 MPa.

(Measurement of elastic modulus)
As shown in FIG. 2, the produced buffer material particles 101 are placed on a flat quartz base 102, and a quartz detection rod 103 having a flat tip surface is formed thereon. The base material when the buffer material particle 101 is compressed in the direction of the base 102 by applying a constant load F by the detection rod 103 in a state where the tip surface is in contact with the buffer material particle 101. The distance G between the surface of 102 and the tip surface of the detection rod 103 is measured, and from the measurement result, the formula (1):

〔式中、Ｒは緩衝材粒子１０１の圧縮前の半径、Ｓは、緩衝材粒子１０１の半径Ｒと、前記間隔Ｇとから、式(2)：

[In the formula, R is a radius of the buffer material particles 101 before compression, S is a radius R of the buffer material particles 101 and the gap G, and the formula (2):

によって求められる、緩衝材粒子１０１の圧縮変形量、Ｅは緩衝材粒子１０１の弾性率、νはポアソン比（＝０．４９）を示す。〕
に基づいて、緩衝材粒子１０１の弾性率Ｅを求める操作を実施（測定温度２５℃）して、前記測定温度における、緩衝材粒子１０１の弾性Ｅを求めた。

Is the amount of compressive deformation of the buffer material particles 101, E is the elastic modulus of the buffer material particles 101, and ν is the Poisson's ratio (= 0.49). ]
Based on the above, an operation for obtaining the elastic modulus E of the buffer material particles 101 was performed (measurement temperature 25 ° C.), and the elasticity E of the buffer material particles 101 at the measurement temperature was obtained.

(Preparation of grease)
A synthetic hydrocarbon oil having a kinematic viscosity (40 ° C.) of 30 mm ² / s as a base oil, and a cis-1,4-polyisoprene having a kinematic viscosity (40 ° C.) of 5000 mm ² / s as a polymer; While mixing with lithium stearate thickener using a three roll mill, the same base oil and the previously prepared buffer particles were added and mixed to prepare a grease as a lubricant composition did. In the grease, the content of the polymer in the total amount of each component excluding the buffer particles was 30% by mass, and the content of the buffer particles in the total amount of all components including the buffer particles was 20% by mass. It was. The oil film thickness of the grease was 10 nm, and the complex elastic modulus was 2.50 KPa.

<Examples 3 to 7, Comparative Examples 4 and 5>
As shown in Table 1, as the buffer material particles, those having different average particle diameters (volume average diameters) were used, and the lubricant was changed in the same manner as in Example 2 except that the content ratio of the buffer material particles was changed. A composition was prepared. The elastic modulus of each buffer material particle at 25 ° C. was 12 MPa. The oil film thickness and complex elastic modulus of each grease were as shown in Table 1.

<Real machine test>
The grease prepared in Examples 1 to 7 and Comparative Examples 1 to 4 is filled into a reduction gear composed of a worm gear device of the electric power steering apparatus shown in FIG. dB (A)] and steering torque (N · m) were measured. As the worm gear device, a combination of an iron-based metal worm 19 and a worm wheel 20 having teeth formed of a polyamide resin is used. The backlash was 2 '. Then, both measured values were evaluated according to the following criteria.

(Abnormal noise)
A: The measured value was 44 dB (A) or less. Extremely good noise reduction effect.
(Circle): The measured value exceeded 44 dB (A) and was 46 dB (A) or less. Good noise reduction effect.
X: The measured value exceeded 46 dB (A). Abnormal noise reduction effect.

(Steering torque)
A: The steering torque was 0.9 N · m or less. Very good steering torque suppression effect.
○: Steering torque exceeded 0.9 N · m and was 1.2 N · m or less. Good steering torque suppression effect.
X: The steering torque exceeded 1.2 N · m. Steering torque has increased.

  The results are shown in Table 1.

表１より、グリースの油膜厚さが１０ｎｍ以上で、かつ複素弾性率が１ＫＰａ以上、３．３ＫＰａ以下であるとき、減速機に発生する異音を、その回転トルクを過剰に上昇させることなく、効果的に低減できることが判った。

From Table 1, when the oil film thickness of the grease is 10 nm or more and the complex elastic modulus is 1 KPa or more and 3.3 KPa or less, the abnormal noise generated in the speed reducer can be increased without excessively increasing the rotational torque. It was found that it can be effectively reduced.

1 is a schematic view of an electric power steering apparatus according to an embodiment of the present invention. It is sectional drawing explaining the method of measuring the elasticity modulus of a buffer material particle.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 9 ... Steering mechanism, 17 ... Electric motor, 18 ... Reduction gear (drive transmission mechanism), 19 ... Small gear, 20 ... Large gear

Claims (6)

  A lubricant composition comprising a base oil, a polymer and a thickener, having an oil film thickness of 10 nm or more and a complex elastic modulus of 1 KPa or more and 3.3 KPa or less.   The lubricant composition according to claim 1, wherein the polymer is at least one selected from the group consisting of polyisoprene and polyester polyol.   The lubricant composition according to claim 1 or 2, further comprising buffer particles.   4. The lubricant composition according to claim 3, wherein the buffer material particles are particles made of at least one selected from the group consisting of a soft resin and rubber.   5. A drive transmission mechanism comprising a gear device, wherein a region including a meshing portion of a gear constituting the gear device is filled with the lubricant composition according to claim 1.   An electric power steering apparatus characterized in that the output of an electric motor for assisting steering is decelerated via the drive transmission mechanism according to claim 5 and transmitted to the steering mechanism.

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