JP2005023212A - Lubricant composition, speed reducer using it, and electric power steering apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant composition which can make noise lower than a conventional one irrespective of a backlash between a small gear and a large gear in their contact and without a complicated construction brought about; and a noise-low speed reducer using it and an electric power steering apparatus using the speed reducer. <P>SOLUTION: The lubricant composition comprises a buffering material particle BP as a lubricant agent, the particle having a double structure and an average particle size of 50-300μm, wherein the double structure is formed by coating the outer surface of an inner core BP1 made of a buffering material with an outer shell BP2 made of a softer buffering material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lubricant composition that can be suitably used for a speed reducer having a small gear such as a worm and a large gear such as a worm wheel, a speed reducer filled with the lubricant composition, and an electric motor including the speed reducer. The present invention relates to a power steering device.
[0002]
[Prior art]
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 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 and then applied to the column, thereby giving a steering operation. Torque assist.
Appropriate backlash is required for meshing between the small gear and the large gear as a reduction mechanism. However, for example, when the gear changes from forward rotation to reverse rotation, or when the reaction force from the tire is input after traveling on a bad road such as a stone pavement, a rattling sound is generated due to backlash. If these sounds are transmitted as noise in the passenger compartment, the driver is uncomfortable.
[0003]
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, for example, an electric power steering apparatus that can bias the worm shaft toward the worm wheel and eliminates backlash by providing a biasing means such as a spring body that biases the worm shaft in the biasing direction. Have been proposed (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP 2000-43739 A (columns 0007 to 0009, FIG. 1)
[0005]
[Problems to be solved by the invention]
However, the speed reducer disclosed in Patent Document 1 has a problem that the structure is extremely complicated and the manufacturing cost is increased.
Accordingly, an object of the present invention is to provide a lubricant composition capable of reducing noise, regardless of the size of backlash when a small gear and a large gear are combined, and without complicating the structure. It is an object to provide an object, a reduction gear with low noise by using the object, and an electric power steering device using the same.
[0006]
[Means for Solving the Problems]
The lubricant composition of the present invention comprises a lubricant,
Buffer material particles having a double structure in which the outer periphery of the inner core made of a buffer material is covered with an outer shell made of a softer buffer material, and having an average particle size of 50 to 300 μm;
It is characterized by including.
The inner core of the buffer material particles is preferably formed of a buffer material having a Young's modulus of 100 MPa or more, and the outer shell is preferably formed of a buffer material having a Young's modulus of less than 100 MPa.
[0007]
When grease is used as the lubricant, the consistency with the addition of the buffer particles is expressed by the NLGI number and No. 2-No. 00 is preferable.
Moreover, when using lubricating oil as a lubrication agent, it is preferable that the kinematic viscosity shall be 20-100 mm < ² > / s (40 degreeC).
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.
[0008]
Furthermore, the electric power steering device of the present invention is characterized in that the output of the steering assist motor is decelerated via the reduction gear and transmitted to the steering mechanism.
[0009]
【The invention's effect】
According to the present invention, the buffer particles dispersed in the lubricant composition are interposed in the meshing portion of the small gear and the large gear, thereby buffering the collision between the tooth surfaces of both gears, thereby reducing the noise. Can be reduced. In addition, the noise can be reduced at a low cost without complicating the structure of the speed reducer simply by adding the buffer particles to the lubricant.
[0010]
In addition, when fine particles such as buffer particles are blended in the lubricant, the flow is hindered to increase the viscosity, and the steering torque of the electric power steering device tends to increase.
However, in the buffer material particles having a double structure used in the present invention, the outer shell, which is softer than the inner core, works to reduce the meshing resistance of the gear during sliding, so that the steering torque is increased as described above. Can be suppressed.
[0011]
In addition, when using a single-layer structure formed of only the same relatively soft cushioning material as the outer shell, the cushioning material particles are crushed by the meshing between the small gear and the large gear. Therefore, the effect of reducing the noise described above cannot be obtained.
In order to obtain an effect of reducing noise while suppressing an increase in steering torque accompanying an increase in viscosity, the buffer material particles are maintained in a granular form without being completely crushed by the meshing between the small gear and the large gear. Therefore, the buffer particles need to have the above-mentioned double structure.
[0012]
In consideration of the fact that the inner core of the buffer particles sufficiently exhibits the effect of maintaining the granularity without being completely crushed by the meshing between the small gear and the large gear as described above, the buffer having a Young's modulus of 100 MPa or more is considered. It is preferable to form with a material.
Further, the outer shell may be softer than the inner core, but considering that the effect of suppressing the increase of the steering torque by further reducing the meshing resistance of the gear during sliding, the Young's modulus is less than 100 MPa. It is preferable to form with a buffer material.
[0013]
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 an NLGI (National Lubricating Grease Institute) number. 2-No. It is preferable to use 00 for use in a reduction gear.
In the case where the lubricant is a liquid lubricant, the kinematic viscosity is preferably 20 to 100 mm / s (40 ° C.) in the same manner for use in a reduction gear.
[0014]
Further, the speed reducer of the present invention includes a small gear and a large gear, and is preferably filled with the above-described lubricant composition in a region including a meshing portion of both gears, so that it is preferable in that noise caused by backlash can be reduced. .
Furthermore, the electric power steering device of the present invention decelerates the output of the steering assist motor via the speed reducer and transmits it to the steering mechanism, so that the noise in the passenger compartment can be reduced at low cost. preferable.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described below.
<Lubricant composition>
As described above, the lubricant composition of the present invention contains a lubricant and buffer material particles.
Among these, as the buffer material particles BP, those having a double structure in which the outer periphery of the inner core BP1 made of a buffer material is covered with an outer shell BP2 made of a softer buffer material as shown in FIG.
[0016]
Among the above, the inner core BP1 has a Young's modulus of 100 MPa or more in consideration of sufficiently exhibiting the effect of maintaining the granularity without being completely crushed by the meshing between the small gear and the large gear as described above. Is preferably formed. Further, considering that the effect of reducing noise by buffering the collision between the tooth surfaces of the two gears is interposed between the meshing portions of the small gear and the large gear, the buffer material forming the inner core BP1 The Young's modulus is preferably 10 ⁵ MPa or less even within the above range.
[0017]
As described above, the outer shell BP2 also has a Young's modulus of 100 MPa or less in consideration of further improving the effect of suppressing the increase in steering torque by reducing the meshing resistance of the gear during sliding. It is preferable to form with a buffer material. In addition, the Young's modulus of the buffer material forming the outer shell BP2 is particularly preferably 0.1 MPa or more even within the above range.
If the Young's modulus is less than 0.1 MPa, the outer shell BP2 becomes too soft, so that the noise is reduced by interposing the meshing portion of the small gear and the large gear to buffer the collision between the tooth surfaces of both gears. The effect may be insufficient. Further, the effect of reducing the backlash by interposing the meshing portion between the small gear and the large gear becomes insufficient, and there is a possibility that an uncomfortable feeling may be generated when the handle is operated.
[0018]
Examples of the buffer material forming the inner core BP1 and the outer shell BP2 include those made of various rubbers or soft resins having rubber elasticity.
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.
[0019]
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).
In order to make the outer shell BP2 softer than the inner core BP1, the inner core BP1 and the outer shell BP2 may be formed of two kinds of materials having different Young's modulus among the soft resin and rubber.
[0020]
Further, for example, the inner core BP1 and the outer shell BP2 are both formed of a curable urethane resin, and the degree of cross-linking of the inner core BP1 is made higher than that of the outer shell BP2, so that the outer shell BP2 is softer than the inner core BP1. The buffer particles BP having a structure can also be formed.
The average particle diameter _{D 2} of the buffer particles BP should be 50 to 300 [mu] m.
There is a possibility an average particle diameter D ₂ is not sufficient buffering action can be obtained with less than 50 [mu] m, when it exceeds 300μm the reverse is easily separated from the lubricant, a possibility that has not obtained a uniform lubricant composition is there. Note buffering action even more, given that improved, the average particle diameter D ₂ of the buffer particles BP is, 50 [mu] m or more even in the above-mentioned range, it is preferable in particular 100μm or more.
[0021]
The average particle diameter _{D 1} of the inner core BP1, the ratio _D 1 / _{D 2} between the average particle diameter _{D 2} of the buffer particles BP which is also the outside diameter of the outer shell BP2 is, and even a 1 / 3-1 / 2 preferable.
When the average particle diameter D ₁ of the inner core BP1 than this range is small, due to the nucleus BP1, there may not be obtained the effect of maintaining the particulate without being completely crushed by engagement between the small gear and the large gear, when the average particle diameter D ₁ of the inner core BP1 is large Conversely, relatively outside it becomes small thickness of the shell BP2, by the shell BP2, the steering torque by reducing the engagement resistance of the sliding time of the gear There is a possibility that the effect of suppressing the rise cannot be obtained.
[0022]
The shape of the buffer material particles BP can be selected from various shapes such as a spherical shape, a granular shape, a flake shape, and a rod shape. However, in consideration of the fluidity of the lubricant composition, the spherical shape shown in FIG. .
The buffer particles are preferably blended at a ratio of 20 to 200 parts by weight with respect to 100 parts by weight of the lubricant.
If the proportion of the buffer particles is less than 20 parts by weight, the buffering action by the buffer particles may be insufficient. Conversely, if it exceeds 200 parts by weight, the fluidity of the lubricant composition decreases, May not function as a lubricant.
[0023]
As the lubricant for dispersing the buffer material particles, either a liquid lubricating oil or a semi-solid grease may be used.
Among these, it is preferable to use a lubricating oil having a kinematic viscosity of 20 to 100 mm ² / s (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.
[0024]
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.
On the other hand, as grease, the consistency as a lubricant composition to which buffer particles are added is represented by an NLGI (National Lubricating Green Institute) number. 2-No. It is preferable to use one that becomes 00.
[0025]
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, a poly-α-olefin oil) is preferable, 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 ²⁰ to 100 mm ² / s (40 ° C.).
As the thickener, various conventionally known thickeners (soap and non-soap) can be used.
[0026]
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.
<Reduction gear and electric power steering device>
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 line II-II in FIG.
[0027]
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. A second steering shaft 3 as an output shaft to be connected 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 sensor housing 6 and a gear housing 7 that are fitted together. Specifically, the gear housing 7 has a cylindrical shape, and an annular edge portion 7 a at the upper end thereof is fitted into an annular step portion 6 a on the outer periphery of the lower end of the sensor housing 6. 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.
[0028]
The worm gear mechanism 8 is integrally rotated with an intermediate portion in the axial direction of the second steering shaft 3 and is restricted from moving in the axial direction. The worm gear mechanism 8 meshes with the worm wheel 12 and is connected to the rotary shaft 32 of the electric motor M. The worm shaft 11 (see FIG. 2) is connected via a spline joint 33.
Of these, the worm wheel 12 includes an annular cored bar 12a coupled to the second steering shaft 3 so as to be integrally rotatable, and a synthetic resin member 12b surrounding the cored bar 12a and forming teeth on the outer peripheral surface portion. ing. The cored bar 12a is inserted into a mold at the time of resin molding of the synthetic resin member 12b, for example.
[0029]
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.
[0030]
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.
[0031]
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. An 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 a 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).
[0032]
The connection 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.
[0033]
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.
[0034]
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.
[0035]
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. 47 is a lock nut engaged with the screw member 45 in order to fix the screw member 45 after the preload adjustment.
[0036]
In the gear housing 7, a region including at least the meshing portion A of the worm shaft 11 and the worm wheel 12 is filled with the above-described lubricant composition in which the buffer particles are dispersed. That is, the lubricant composition may be filled only in the meshing portion A, or may be filled in the entire periphery of the meshing portion A and the worm shaft 11 or in the entire gear housing 7.
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.
[Brief description of the drawings]
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 line II-II in FIG.
FIG. 3 is a cross-sectional view of a buffer material particle having a double structure contained in the lubricant composition of the present invention.
[Explanation of symbols]
BP Buffer material particles BP1 Inner core BP2 Outer shell A Engagement part M Electric motor 11 Worm shaft (small gear)
12 Worm wheel (large gear)
50 reducer

Claims (6)

A lubricant,
Buffer material particles having a double structure in which the outer periphery of the inner core made of a buffer material is covered with an outer shell made of a softer buffer material, and having an average particle size of 50 to 300 μm;
A lubricant composition comprising: The lubricant composition according to claim 1, wherein the inner core of the buffer material particles is formed of a buffer material having a Young's modulus of 100 MPa or more, and the outer shell is formed of a buffer material having a Young's modulus of less than 100 MPa. The consistency when no grease is used and grease is added as a lubricant is represented by an NLGI number. 2-No. The lubricant composition according to claim 1, wherein the lubricant composition is 00. The lubricant composition according to claim 1, wherein a lubricating oil is used as the lubricant and the kinematic viscosity is 20 to 100 mm ² / s (40 ° C.). A speed reducer comprising a small gear and a large gear, wherein the lubricant composition according to claim 1 is filled in a region including a meshing portion of both gears. An electric power steering apparatus characterized in that the output of a steering assist motor is decelerated via a reduction gear according to claim 5 and transmitted to a steering mechanism.

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