JP4547601B2 - Reducer and electric power steering device using the same - Google Patents

Description

  The present invention relates to a reduction gear including a small gear and a large gear formed of one resin and the other metal, and an electric power steering apparatus including the reduction gear.

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. In recent years, in an electric power steering apparatus, considering reduction in noise and weight by reducing rattling noise, reduction in sliding resistance, etc., one of a small gear and a large gear of a reduction gear, more preferably Making large gears into resin is becoming common (see Patent Document 1).
JP 2002-54695 A (column 0002)

  Reduction gears are required to have low torque for the purpose of improving handle return performance and power transmission efficiency. In order to reduce the torque of the reducer, the role of a lubricant composition such as grease or lubricating oil that contributes to lubrication between the tooth surfaces of the large gear and the small gear as the friction surface is important. It is necessary to use a lubricant composition that can exhibit a stable effect in reducing friction in the widest possible temperature range.

  An object of the present invention is to provide a reduction gear having a small gear and a large gear, one of which is made of resin and the other of which is made of metal. An object of the present invention is to provide an electric power steering device having excellent power transmission efficiency.

In order to solve the above problems, a reduction gear according to the present invention includes a small gear and a large gear, one of which is made of resin and the other of which is made of metal, and a base oil and a hindered region in a region including meshing portions of both gears. The lubricant composition is filled with an ester.
In such a configuration, by adding a hindered ester to the lubricant composition, adhesion of the lubricant composition to the tooth surfaces of the large gear and the small gear formed with one resin and the other metal. Improve wettability, and always form a stable oil film that contributes to friction reduction over a wide temperature range with a lubricant composition in the gap between the tooth surfaces of the large gear and small gear, which are friction surfaces. Can do. For this reason, according to the present invention, a reduction gear including a small gear and a large gear formed by preventing the increase in torque due to running out of oil between tooth surfaces and forming one side with resin and the other with metal is more than ever. It is possible to further reduce the torque.

As the hindered ester to be added to the lubricant composition, neopentyl polyol fatty acid ester is preferably used. The amount of hindered ester added is preferably 7 to 12 % by weight in the total amount of the lubricant composition. Furthermore, it is preferable to use a synthetic hydrocarbon oil as the base oil of the lubricant composition.
The electric power steering device of the present invention is characterized in that the output of the steering assist motor is decelerated via the reducer and transmitted to the steering mechanism. Is preferable in that it can be improved.

The present invention is described in detail below.
<Lubricant composition>
In the speed reducer according to the present invention, the lubricant composition filled in the region including the meshing portion of the small gear and the large gear formed of one resin and the other metal is used as described above, the base oil and the hindered ester. Is included.

  Among these, as the hindered ester, pentaerythritol fatty acid ester having a structure in which fatty acid is esterified to all four hydroxyl groups of pentaerythritol, and fatty acid esterifying to all six hydroxyl groups of dipentaerythritol. Neopentyl polyol fatty acid ester containing dipentaerythritol fatty acid ester having a structure as a main component is preferable. Moreover, as a fatty acid which comprises neopentyl polyol fatty acid ester, C8-C30 fatty acids, such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, behenic acid, can be mentioned, for example.

The amount of hindered ester added is preferably 7 to 12 % by weight in the total amount of the lubricant composition. If the addition amount is less than 7 % by weight, the effect of improving the adhesion and wettability of the lubricant composition to the tooth surface and the like due to the addition of the hindered ester cannot be obtained sufficiently. There is a risk that the torque cannot be reduced .

Moreover, even if the addition amount exceeds 12% by weight, not only the effect of reducing the torque sufficiently to meet the addition amount is not obtained, but also the excessive hindered ester precipitates without completely dissolving in the base oil, and the lubricant composition As a result of reducing the fluidity of the object, there is a possibility that a stable oil film cannot be formed in the gap between the tooth surfaces of the large gear and the small gear, which are friction surfaces, and the reduction gear cannot be reduced in torque. In addition, since hindered esters are weak, they are aggressive to the resin, so if they are added excessively to the lubricant composition, the resin gear will wear rapidly before its preset life. There is also a risk of damage.

  The lubricant composition to which the hindered ester is added may be either a liquid lubricating oil or a semi-solid grease. Among these, lubricating oil is comprised by adding a predetermined amount of hindered ester to arbitrary base oil. As the base oil, various base oils such as synthetic oils such as ester-based synthetic oils, synthetic hydrocarbon oils, polyglycol-based synthetic oils, silicone-based synthetic oils, and fluorine-based synthetic oils and mineral oils can be used. Synthetic hydrocarbon oils such as α-olefin oil and polybutene oil are preferred.

  Synthetic hydrocarbon oils are less aggressive against resins compared to ester-based synthetic oils, etc., so they are excellent in terms of preventing the resin gears from being worn or damaged early, In addition to maintaining stable lubrication over a wide temperature range compared to mineral oil, etc., it is superior in lubrication performance compared to polyglycol-based synthetic oil and silicone-based synthetic oil, and is also cheaper than fluorine-based synthetic oil Has advantages.

The kinematic viscosity of the base oil is preferably 5 to 200 mm ² / s (40 ° C.), and more preferably ^{20 to} 100 mm ² / s (40 ° C.) when used for a speed reducer. 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.

The grease is also constituted by adding a predetermined amount of hindered ester and a thickener to an arbitrary base oil. As the base oil, the above-mentioned various synthetic oils and mineral oils can be used, but synthetic hydrocarbon oils such as poly-α-olefin oil and polybutene oil are also preferable for the same reason as described above. The kinematic viscosity of the base oil is again ^{5~200mm 2 / s (40 ℃)} , particularly to the ^{20~100mm 2 / s (40 ℃)} , preferred for use in the reduction gear.

  As the thickener, various conventionally known thickeners (soap and non-soap) can be used. In addition, greases may also contain solid lubricants (molybdenum disulfide, graphite, PTFE, etc.), phosphorous 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. The consistency of grease is represented by NLGI (National Lubricating Grease Institute) number. 3-No. 000, especially no. 2-No. It is preferably 220 to 475, particularly 265 to 430 in terms of the penetration specified by 00, Japanese Industrial Standard JIS K2220 5.3, when used for a reduction gear.

<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 the line II-II in FIG.
Referring to FIG. 1, in the electric power steering apparatus of this example, a first steering shaft 2 as an input shaft to which a steering wheel 1 is attached and a steering mechanism (not shown) such as a rack and pinion mechanism. 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.

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 resin member 12b surrounding the cored bar 12a and forming teeth on the outer peripheral surface portion. Yes. The core metal 12a is inserted into a mold when the resin member 12b is molded with resin, for example. And the metal core 12a and the resin member 12b are combined and integrated by the resin molding in the inserted state.

  As resin which forms the resin member 12b, conventionally well-known various resin can be used for the gears of a reduction gear. Examples of such resins include polyamide resins such as PA6, PA66, PA46, PA12, PA11, PA612, PA610, PA6T, PA9T, and MC (monomer casting) nylon, polyphenylene sulfide (PPS), polyetheretherketone (PEEK), Examples include polybutylene terephthalate (PBT), polyphthalamide (PPA), polyacetal (POM), and the like.

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

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

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

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

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

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

  Further, the inner ring 37 of the fifth rolling bearing 35 that supports the vicinity of the other end portion 11b (joint side end portion) of the worm shaft 11 is brought into contact with the positioning step portion 44 of the worm shaft 11 so as to move toward the one end portion 11a. 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 a 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.

  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 containing the hindered ester. 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.

Hereinafter, the present invention will be described in more detail based on examples.
Example 1
Polyalphaolefin oil as a base oil [kinematic viscosity 47.1 mm ² / s (40 ° C.)], neopentyl polyol fatty acid ester as a hindered ester [kinematic viscosity (40 ° C.): 40 to 51 mm ² / s, acid Value: 4.0 or less, hydroxyl value: 20 to 40, trade name Prover N-55 manufactured by Asahi Denka Kogyo Co., Ltd. was added to form the lubricating oil of Example 1. The amount of neopentyl polyol fatty acid ester added was 15% by weight in the total amount of the lubricating oil.

Comparative Example 1
The same polyalphaolefin oil used in Example 1 was used alone as a lubricating oil of Comparative Example 1 without adding the neopentyl polyol fatty acid ester.
The lubricating performance of the lubricating oils of Example 1 and Comparative Example 1 was evaluated using a pin-on-disk friction tester shown in FIG. In the apparatus shown in the figure, an upper pin PN and a lower plate PL formed of two kinds of materials whose lubrication performance is to be evaluated are brought into contact with the upper pin PN by applying a load as indicated by white arrows in the figure. In this state, when the lower plate PL is rotated about the rotation axis AX in the direction indicated by the solid line arrow in the drawing, the load applied to the upper pin PN in the direction indicated by the black arrow in the drawing is applied to the load cell. The friction coefficient is obtained from the measurement result.

  In this example, in order to evaluate the lubricating performance of the lubricating oil in a combination of a metal worm and a resin worm wheel, the upper pin PN is made of a bearing plate SUJ2, which is a general worm forming material, and the lower plate. The tip to be brought into contact with PL was formed into a spherical surface having a radius of 5 mm, and the lower plate PL was formed from MC nylon which is a general worm wheel forming material. The tip of the upper pin PN that is in contact with the lower plate PL was finished to have a center line average roughness Ra = 0.2 μm. Further, the surface of the lower plate PL with which the upper pin PN abuts was finished to have a center line average roughness Ra = 0.2 μm.

Then, with the lubricant of Example 1 or Comparative Example 1 applied on the lower plate PL, while applying a load of 9.8 N to the upper pin PN at a temperature of 25 ° C., the upper pin PN and the lower plate PL While rotating the lower plate PL so that the sliding speed of 1 mm / sec becomes 1 mm / sec, the load applied in the direction indicated by the black arrow in the figure was measured using a load cell to determine the friction coefficient.
The results are shown in Table 1. The table shows the relative value of the friction coefficient when the friction coefficient in Comparative Example 1 is 1.

From the table, it was found that by adding neopentyl polyol fatty acid ester as a hindered ester, the friction coefficient can be reduced by approximately 18.1%, and the lubricating performance of the lubricating oil can be improved.
Examples 2-5
The same neopentyl polyol fatty acid as used in Example 1 as a base oil and a poly-olefin oil [kinematic viscosity 48.0 mm ² / s (40 ° C.)] as a urea thickener and a hindered ester. The greases of Examples 2-5 were constructed by adding an ester. The amount of neopentyl polyol fatty acid ester added was 1% by weight (Example 2), 5% by weight (Example 3), 10% by weight (Example 4) and 15% by weight (Example 5) in the total amount of grease. It was.

Comparative Example 2
The grease of Comparative Example 2 was constructed in the same manner as in Examples 2 to 7 except that no neopentyl polyol fatty acid ester was added.
The lubricating performance of the greases of Examples 2 to 6 and Comparative Example 2 was evaluated using the same pin-on-disk friction tester as described above.

  The results are shown in Table 2 and FIG. In the table and the figure, relative values of the friction coefficient when the friction coefficient in Comparative Example 2 is set to 1 are shown. The table also shows the penetration of each grease.

  From the tables and figures, it was found that the friction coefficient can be reduced and the lubricating performance of grease can be improved by adding neopentyl polyol fatty acid ester as a hindered ester in the range of 0.1 to 15% by weight. From the results of Examples 2 to 5, it was found that the addition amount of neopentyl polyol fatty acid ester is preferably 1% by weight or more, particularly preferably 7% by weight or more. Furthermore, from the results of Examples 2 to 5, it was also found that the addition amount of neopentyl polyol fatty acid ester is preferably 12% by weight or less.

1 is a schematic cross-sectional view of an electric power steering apparatus according to an embodiment of the present invention. It is sectional drawing which follows the II-II line of FIG. In the Example of this invention, it is a perspective view explaining the outline | summary of the pin-on-disk type | mold friction tester used in order to evaluate the lubrication performance of a lubricant composition. It is a graph which shows the relationship between the addition amount of a hindered ester, and a friction coefficient in the grease manufactured by the Example and comparative example of this invention.

Explanation of symbols

11 Worm shaft (small gear)
12 Worm wheel (large gear)
50 Reducer M Electric motor

Claims (5)

  It is characterized by comprising a small gear and a large gear, one of which is made of resin and the other of which is made of metal. To reducer.   The speed reducer according to claim 1 filled with a lubricant composition using neopentyl polyol fatty acid ester as a hindered ester. The speed reducer according to claim 1, which is filled with a lubricant composition in which the amount of hindered ester added is 7 to 12 % by weight in the total amount of the lubricant composition.   The speed reducer according to claim 1, wherein a lubricant composition using a synthetic hydrocarbon oil is filled as the base oil.   An electric power steering apparatus characterized in that the output of a steering assist electric motor is decelerated and transmitted to a steering mechanism via the reduction gear according to any one of claims 1 to 4.

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