JP2006117827A - Electric linear actuator and grease composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric linear actuator and a grease composition which prevent impression and peel-off of ball surfaces and are durable even under severe conditions in use (heavy load, large heat generation, large vibration, etc). <P>SOLUTION: The grease composition which is composed of a base oil and a thickener added to it contains 1-10 mass% in total and 0.5-9.5 mass% individually of one or more kinds selected from carboxylic acids, carboxylic acid salts, ester compounds and amine compounds and antipeeling agent. The electric linear actuator is loaded with the grease composition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric linear actuator, for example, as a driving device for automatically changing the gear ratio of an automobile transmission or for automatically connecting and disconnecting a clutch. It is about technology to plan.

  2. Description of the Related Art Conventionally, an electric linear actuator that expands and contracts using an electric motor as a drive source and displaces various articles is known. For example, the nut member engaged with the screw shaft is displaced in the axial direction by the rotation of the screw shaft supported only in the housing by the forward and reverse electric motor supported by the housing. Then, an output shaft member having a base end portion coupled to the nut member and having a base end portion configured in a cylindrical shape is displaced in the axial direction (see Patent Documents 1 to 3). In each of these prior arts, the periphery of the base portion of the output shaft member is covered with a cylindrical cover to prevent foreign matter from entering the threaded portion between the screw shaft and the nut member. The outer peripheral surface of the output shaft member and the inner peripheral surface of the tip end portion of the cover are in sliding contact with each other. In addition, the ball screw of the electric linear actuator described above has a ball (generally a steel ball) interposed between the screw shaft and the nut as a rolling element, and friction loss during operation can be almost ignored. In addition to extremely high drive efficiency, it has features such as very little wear on components because the relative rotation between the screw shaft and the nut does not slide. A ball screw of the total ball type is provided between a male screw groove and a female screw groove, a screw shaft having a male screw groove formed on the outer periphery, a nut having a female screw groove facing the male screw groove formed on the inner periphery thereof, and And a circulation passage (tube, top, etc.) for circulating the ball from one end side to the other end side of the female screw groove formed in the nut. At the time of relative rotation between the screw shaft and the nut, the ball rolls with respect to both the male screw groove and the female screw groove and circulates from one end side to the other end side of the female screw groove through the circulation passage.

  By the way, in the above-mentioned total ball-shaped ball screw, when balls that roll in the same direction between both screw grooves come into contact with each other, relative slip occurs at the contact surface at twice the rolling speed. For this reason, when the drive speed of the ball screw is increased to improve the performance of the mechanical device, the ball surface is worn beyond the allowable limit in a relatively short time, or the ball or screw groove is seized due to frictional heat. There was a problem.

  In recent years, the use conditions of the ball screw have become more severe, and accordingly, indentation and peeling of the ball surface are likely to occur, and it is necessary to frequently replace the ball screw.

JP-A-8-322189 JP 9-327149 A US Pat. No. 5,669,264

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a grease composition and an electric actuator that improve the durability by suppressing the occurrence of indentation and peeling on the ball surface.

The above object is achieved by the grease composition and the electric linear actuator shown in the following (1) to (4).
(1) In a base grease obtained by blending a thickener with a base oil, a total of 1 to 10% by mass of two or more carboxylic acids and carboxylates, ester compounds, and amine compounds and 0.5% alone A grease composition containing 9.5% by mass and further containing a release agent.
(2) The grease composition as described in (1), wherein 1 to 10% by mass of metal dithiocarbamate is blended as the release agent.
(3) The grease composition according to (1), wherein 2 to 10% by mass of carbon black is blended as the release agent.
(4) A housing, a forward / reversible electric motor supported by the housing, a screw shaft which is rotatably supported by the housing and is driven to rotate by the electric motor, and its rotation is prevented. A nut member that engages with the screw shaft in a state and displaces in the axial direction of the screw shaft as the screw shaft rotates, and encloses the grease composition according to any one of (1) to (3) An electric linear actuator.

  The grease composition according to the present invention hardly causes indentation or peeling on the ball surface of the ball screw. Therefore, the grease composition according to the present invention and the electric linear actuator in which the grease composition is sealed can be used even under severe conditions such as large load load, heat generation, and vibration.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a half-cut side structure of an electric linear actuator according to the present invention as a first embodiment. An electric motor 2 that can freely rotate forward and backward is supported and fixed to one end (left end in FIG. 1) of a substantially cylindrical housing 1. Further, a portion near the proximal end of the screw shaft 3 inside the intermediate portion of the housing 1 is supported by a rolling bearing 4 capable of supporting a radial load and a thrust load, such as a deep groove ball bearing, so that only rotation is possible. Yes. The outer ring 5 constituting the rolling bearing 4 includes an inner surface (left side surface in FIG. 1) of the flange portion 6 formed inward on the intermediate inner surface of the housing 1 and an inner periphery of the housing 1. It is held between the stop ring 7 locked to the surface to prevent displacement in the axial direction. Further, an inner ring 8 constituting the rolling bearing 4 includes a step 9 formed at an intermediate portion of the screw shaft 3 and a stop ring locked to the outer peripheral surface of the base end portion (left end portion in FIG. 1) of the screw shaft 3. The inner ring 8 is prevented from being displaced in the axial direction with respect to the screw shaft 3. And the part which protruded from the said rolling bearing 4 in the base end part of the said screw shaft 3 and the output shaft 11 of the said electric motor 2 are couple | bonded by the coupling part 12 so that transmission of rotational force is possible. In the illustrated example, another rolling bearing 13 is also arranged around the coupling portion 12.

  A nut member 14 is screwed around the screw shaft 3. Therefore, the nut member 14 is displaced in the axial direction of the screw shaft 3 as the screw shaft 3 rotates if the rotation of the nut member 14 is prevented as described later. In the case of the electric linear actuator 15 of this example, the nut member 14 and the screw shaft 3 are all engaged so that they can be reversely operated so that the nut member 14 can be displaced in the axial direction even when the electric motor 2 fails. It is combined. For this purpose, the pitch (lead) between the internal thread formed on the inner peripheral surface of the nut member 14 and the external thread formed on the outer peripheral surface of the screw shaft 3 is increased. Further, a base end portion of a cylindrical output shaft member 16 is coupled to one end surface (right end surface in FIG. 1) of the nut member 14 by integrally forming the nut member 14 and the output shaft member 16. Yes.

  Further, an end plate 19 having a diameter larger than that of the screw shaft 3 is coupled and fixed to the portion of the tip end surface of the screw shaft 3 located inside the output shaft member 16 by a bolt 20. Therefore, the nut member 14 can be displaced in the axial direction only at a portion between the outer surface of the flange portion 6 (the right side surface in FIG. 1) and the end plate 19. FIG. 1 shows the nut member 14 in a neutral position, and in this state, between the both axial end surfaces of the nut member 14 and the outer surface of the flange 6 and the end plate 19, There is a gap (S / 2) that is 1/2 of the total stroke S. In the case of this example, the total stroke S is approximately 6 times (S≈6D) of the outer diameter (diameter to the top of the thread) D of the screw shaft 3.

  A through hole 17 for inserting a bolt or the like is formed at the tip of the output shaft member 16, and the output shaft member 16 is driven by an electric linear actuator 15 such as an input portion of an automobile transmission. It can be freely coupled to the driven member to be driven. Further, a portion closer to the inside tip of the output shaft member 16 and a portion closer to the middle than the through hole 17 is closed by a cap 18, and the screw shaft 3 and the nut member 14 are connected from the tip opening side of the output shaft member 16. It is intended to prevent foreign matter from entering the threaded portion.

  Further, a base end portion (left end portion in FIG. 1) is externally supported by a cover 21 on the outer peripheral surface of the distal end portion (right end portion in FIG. 1) of the housing 1. The cover 21 is formed in a tapered cylindrical shape by decreasing the outer diameter toward the tip (right end in FIG. 1) by injection molding or blow molding synthetic resin. Such a base 21 of the cover 21 is loosely fitted (slightly displaceable slightly) into a locking groove 23 formed on the outer peripheral surface of the distal end portion of the housing 1 with a protrusion 22 formed on the inner peripheral surface thereof. The housing 1 is coupled by being locked. In this state, the inner peripheral surface of the tip of the cover 21 is in sliding contact with or in close proximity to the outer peripheral surface of the output shaft member 16. Such a cover 21 is configured so that foreign matter is caught between the base end surface of the output shaft member 16 (left end surface in FIG. 1) and the front end surface of the housing 1 at the screwed portion between the screw shaft 3 and the nut member 14. Prevent entry. In order to improve the effect of preventing foreign matter entry, a plurality of concave grooves (or protrusions) are formed on the inner peripheral surface of the tip of the cover 21 over the entire circumference, and the inner peripheral surface of the tip of the cover 21 is formed. A labyrinth seal may be provided between the outer peripheral surface of the output shaft member 16 and the output shaft member 16.

  When the electric linear actuator 15 of this example configured as described above is used, the housing 1 is fixedly or swingably supported on a fixed portion (not shown) by using the mounting hole 24 or the like. Further, the tip end portion of the output shaft member 16 is coupled to a driven member (not shown) by a mounting member such as a bolt inserted through the through hole 17. In this state, the output shaft member 16 and the nut member 14 do not rotate regardless of the rotation of the screw shaft 3. Therefore, when the screw shaft 3 is rotated in a predetermined direction by the electric motor 2, the nut member 14 and the output shaft member 16 are displaced in the axial direction, and the driven member is displaced.

  In the case of the electric linear actuator 15 of this example, the cover 21 having elasticity is supported to the housing 1 so as to be slightly displaceable. Smoothly follows the member 16. Therefore, the surface pressure of the sliding contact portion between the inner peripheral surface of the tip end of the cover 21 and the outer peripheral surface of the output shaft member 16 is not partially increased. As a result, the resistance to the displacement of the nut member 14 based on the presence of the cover 21 can be kept small, and a highly efficient structure can be realized.

  Next, FIG. 2 shows a second embodiment of the present invention. In the case of this example, ball screw grooves are formed on the outer peripheral surface of the screw shaft 3 and the inner peripheral surface of the nut member 14, and a plurality of balls 25 are interposed between the two ball screw grooves. The ball screw mechanism 26 is configured. A circulation tube for circulating these balls 25 is not shown. The ball screw mechanism 26 can be operated in reverse even if the pitch of the ball screw grooves is reduced. Therefore, in the case of this example, this pitch is reduced so that a large output can be obtained for the ratio of the torque of the electric motor 2. For this reason, in order to ensure the required stroke, the number of rotations of the electric motor 2 increases. Therefore, the number of rotations is measured by the rotation detector 27, and the stroke can be measured from the number of rotations.

  Further, in the case of this example, the base end portion (left end portion in FIG. 2) of the bellows 28 is fitted on the outer peripheral surface of the front end portion (right end portion in FIG. 2) of the housing 1 and further suppressed by the band 29. I support it. The bellows 28 is configured to be stretchable by being formed in a bellows shape with rubber. The tip of such a bellows 28 is fitted on the outer peripheral surface of the output shaft member 16. In the case of this example, such a bellows 28 closes the gap between the base end surface of the output shaft member 16 (left end surface in FIG. 2) and the front end surface of the housing 1. The configuration and operation of the other parts are the same as in the case of the first example described above.

  Next, FIG. 3 shows a third embodiment of the present invention. In the case of the first example and the second example described above, the screw shaft and the electric motor are arranged concentrically with each other, whereas in the present example, the screw shaft 3 is electrically driven laterally. The motor 2 is provided in parallel to the screw shaft 3. Then, a drive gear 30 that can be driven to rotate by the output shaft 11 of the electric motor 2 and a driven gear 31 that is spline-engaged with the base end portion (left end portion in FIG. 3) of the screw shaft 3 are connected to an intermediate gear. The screw shaft 3 is rotatably driven by the electric motor 2.

  In the case of this example, the basic configuration and operation other than the arrangement of the electric motor 2 and the screw shaft 3 are substantially the same as those in the first example or the second example described above. This example is different from the first example or the second example in the following points. First of all, the outer side surface of the flange 6 formed on the inner peripheral surface of the housing 1 facing one end surface in the axial direction of the nut member 14 (the left end surface in FIG. 3), the axial direction of the nut member 14, etc. Buffer rings 33a and 33b are attached to the end face (the right end face in FIG. 3), respectively. Each of the buffer rings 33a and 33b receives the nut member 14 in a state where the nut member 14 is displaced to the end in the moving direction. Each of the buffer rings 33a and 33b is made of a material having a large internal loss, such as rubber. It is configured. A worm 34 having a large lead is formed at the base end portion (left end portion in FIG. 3) of the screw shaft 3, and the worm 34 and the worm wheel 35 are engaged with each other. A rotation detector (not shown in FIG. 3) is driven by the worm wheel 35 so that the number of rotations of the screw shaft 3 and the stroke of the nut member 14 can be measured.

  Next, FIG. 4 shows a fourth embodiment of the present invention. In the case of this example, a ring-shaped end plate 19 having an L-shaped cross section is fixed by a bolt 20 to the tip surface of the screw shaft 3 having a ball screw groove formed on the outer peripheral surface. A nut member 14 is provided around the screw shaft 3 via a ball screw mechanism 26 so as to be movable in the axial direction as the screw shaft 3 rotates. And between the front half part (right half part of FIG. 4) outer peripheral surface of the housing 1 and the one end part (left end part of FIG. 4) outer peripheral surface of the said nut member 14, and the other end part (FIG. 4 right end) Bellows 28a and 28b are spanned between the outer peripheral surface and the outer peripheral surface of the end plate 19, respectively. Further, the protrusions 38, 38 provided at the end of the driven member 37 are inserted into the locking holes 36, 36 provided at two positions on the diametrically opposite side of the outer peripheral surface of the intermediate part of the nut member 14. . Other configurations and operations are substantially the same as those of the second example described above. However, in the case of this example, since the stroke of the nut member 14 is small, a potentiometer for measuring the rotation speed of the electric motor 2 is omitted.

The above electric linear actuator encloses a grease composition described below.
Although the kind of base oil of the grease composition according to the present invention is not limited, mineral oil-based lubricating oil and synthetic lubricating oil can be preferably used. The mineral oil-based lubricating oil is not limited, and for example, paraffinic mineral oil, naphthenic mineral oil, and mixed oils thereof can be used. Synthetic lubricating oils are also not limited, but for example, synthetic hydrocarbon oils, ether oils, ester oils and fluorine oils can be used. Specifically, poly α-olefin oil or the like as the synthetic hydrocarbon oil, dialkyl diphenyl ether oil, alkyl triphenyl ether oil, alkyl tetraphenyl ether oil or the like as the ether oil, diester oil or neopentyl type as the ester oil. Examples include polyol ester oils, or complex ester oils, aromatic ester oils, and the like, and examples of fluoro oils include perfluoroether oil, fluorosilicone oil, chlorotrifluoroethylene oil, and fluorophosphazene oil. . These lubricating oils may be used alone or in appropriate combination of a plurality of types. Among these, considering lubricating performance and life at high temperatures and high speeds, it is preferable that a synthetic lubricating oil is contained, and it is particularly preferable that an ester oil and an ether oil are contained. Moreover, it is preferable that mineral oil type lubricating oil contains from a cost surface.
Incidentally, the kinematic viscosity of the base oil is preferably further 40~70mm ² / s in consideration of the low torque and durability is preferably 20 to 100 mm ² / s at 40 ° C..

  As the thickener, a material that is colloidally dispersed in the base oil to make the base oil semi-solid or solid may be used. Examples of such thickeners include lithium soaps, calcium soaps, sodium soaps, aluminum soaps, lithium complex soaps, calcium complex soaps, sodium complex soaps, barium complex soaps, aluminum complex soaps. And metal based soaps, bentonite, clay based inorganic compounds, monourea based, diurea based, triurea based, tetraurea based, urethane based, sodium terephthalate based organic compounds, and the like. Among these, a lithium soap system can be suitably used. One or more of these thickeners can be blended.

  The content of the thickener in the grease composition is preferably 3 to 40% by mass, more preferably 5 to 25% by mass. If it is less than 3% by mass, it is difficult to maintain the grease state, and if it exceeds 40% by mass, it becomes too hard to exhibit a sufficient lubrication state.

  Further, the consistency of the thickener is preferably in the range of 220 to 395, more preferably in the range of 265 to 350 in terms of the penetration. More preferably, it is in the range of 280 to 320 which is a blending consistency capable of automatic lubrication. If it is smaller than 220, it becomes too hard to expect a sufficient lubricating effect, and if it is larger than 395, it may leak from the linear motion device.

  The grease composition according to the present invention further contains two or more selected from carboxylic acids and carboxylates, ester compounds, and amine compounds. These compounds function as antioxidants or rust inhibitors. The content of the compound alone is 0.5 to 9.5% by mass, and the total is 1 to 10% by mass.

  As the amine compound, any aromatic amine compound used as an antioxidant for lubricating oil or resin can be used, and is not particularly limited, but α-naphthylamines and diphenylamines are preferable. Specifically, one or more aromatic amines selected from α-naphthylamines represented by the following general formula (I) and diphenylamines represented by the following general formula (II) are preferred. .

  In the formula, R1 represents a hydrogen atom or a group represented by the following general formula (A).

  In formula, R2 shows a hydrogen atom or a C1-C16 alkyl group.

  In the formula, R3 and R4 may be the same or different and each represents a hydrogen atom or an alkyl group having 1 to 16 carbon atoms.

First, the α-naphthylamines represented by the general formula (I) will be described.
In general formula (I), R1 is a hydrogen atom or a group represented by general formula (A), preferably a group represented by general formula (A). In the group represented by the general formula (A), R2 represents a hydrogen atom or a linear or branched alkyl group having 1 to 16 carbon atoms. Examples of the alkyl group represented by R2 include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, and the like. Group, pentadecyl group, hexadecyl group and the like (these alkyl groups may be linear or branched), among which a branched alkyl group having 8 to 16 carbon atoms is preferable.

Next, diphenylamines represented by the general formula (II) will be described.
R3 in the general formula (II) is a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, preferably an alkyl group having 1 to 16 carbon atoms. When one or both of R3 and R4 are hydrogen atoms, they may settle as sludge due to their own oxidation.
Examples of the alkyl group represented by R4 include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl Group, pentadecyl group, hexadecyl group and the like (these alkyl groups may be linear or branched), among which a branched alkyl group having 3 to 16 carbon atoms is preferable.

  In addition to the amine compounds represented by the above general formulas (I) and (II), Nn-butyl-p-aminophenol, 4,4-tetramethyl-diaminodiphenylmethane, N, N-disalicylidene Amine-based antioxidants such as -1,2-propylenediamine, alkoxyphenylamine, and partial amides of dibasic carboxylic acids can be used.

  Examples of carboxylic acids and carboxylic acid salts include stearic acid as monocarboxylic acid, alkyl or alkenyl succinic acid and derivatives thereof as dicarboxylic acid, naphthenic acid, abietic acid, lanolin fatty acid, calcium of alkenyl succinic acid, barium, magnesium, aluminum, Metal salts such as zinc and lead can be used. In particular, alkenyl succinic acid and zinc naphthenate are preferably used.

  Examples of the ester group include sorbitan monooleate, sorbitan trioleate, pentaerythritol monooleate, and succinic acid half ester as carboxylic acid partial esters of polyhydric alcohols. In particular, sorbitan monooleate and succinic acid half ester are preferably used.

  Furthermore, the grease composition according to the present invention contains a release agent. For example, metal dithiocarbamate such as ZnDTC may be added in an amount of 1 to 10% by mass (since it is an application with much sliding friction, it may be added slightly more). Metal dithiocarbamate also has an effect on extreme pressure. Carbon black can also be added as an anti-peeling agent. The effect of carbon black is described in detail in JP-A No. 2002-195277. However, when electricity is supplied with carbon black, generation of hydrogen ions due to electrolysis of water is suppressed, and white separation caused by hydrogen ions is suppressed. The average particle diameter of carbon black is preferably 10 to 300 nm, and the addition amount is preferably slightly larger 2 to 10% by mass in consideration of this field where there is much sliding friction as with ZnDTC.

  In addition to the above, extreme pressure agents such as phosphorus-based, zinc dithiophosphate, and organic molybdenum, oiliness improvers such as fatty acids and animal and vegetable oils, metal deactivators such as benzotriazole, etc., should not impair the purpose of the present invention. If necessary, it can be added as appropriate.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

  First, according to the blending ratio shown in Table 1, six types of grease compositions A1 to A4 and B1 to B2 were prepared.

  Next, the grease composition was sealed in the electric linear actuators of the first to fourth embodiments described above and driven, and a durability test was performed. The nut member is reciprocated along the screw shaft until peeling or seizure occurs, and the durability against delamination or seizure is determined by the number of cycles (number of reciprocating motions of the nut member) when peeling or seizure occurs. Evaluated. The evaluation results are shown in Table 2. In addition, the moving speed of the nut member in this durability test is 20 m / min.

  As can be seen from Table 2, the electric linear actuators of Examples 1 to 4 having the greases A1 to A4 can be driven up to about 1 million revolutions without causing separation or seizure. On the other hand, Comparative Example 1 is different from the component of the present invention in the rust preventive agent of the grease composition, and Comparative Example 2 contains neither a rust preventive agent nor a release agent. For this reason, separation and seizure occurred at a rotational speed less than half that of the example.

As described above, the grease composition according to the present invention contains a release agent in addition to the antioxidant and the rust preventive agent. Therefore, even if a low viscosity base oil having a kinematic viscosity of 100 mm ² / s or less is used, Seizure hardly occurs. Therefore, it is possible to realize a highly efficient electric linear actuator that can reduce torque.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a half cut side view showing a first embodiment of an electric linear actuator according to the present invention. It is a half part cutting side view showing the 2nd example of an electric linear actuator concerning the present invention. It is sectional drawing which shows 3rd Embodiment of the electrically driven linear actuator which concerns on this invention. It is a half part cutting side view showing the 4th example of an electric linear actuator concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing 2 Electric motor 3 Screw shaft 4 Rolling bearing 5 Outer ring 6 Ridge part 7 Stop ring 8 Inner ring 9 Step part 10 Stop ring 11 Output shaft 12 Coupling part 13 Rolling bearing 14 Nut member 15 Electric linear actuator 16 Output shaft member 17 Through hole 18 Cap 19 End plate 20 Bolt 21 Cover 22 Projection line 23 Locking groove 24 Mounting hole 25 Ball 26 Ball screw mechanism 27 Rotation detectors 28, 28a, 28b Bellows 29 Band 30 Drive gear 31 Drive gear 32 Intermediate gear 33a, 33b Buffer ring 34 Worm 35 Worm wheel 36 Locking hole 37 Driven member 38 Projection

Claims (4)

  A base grease obtained by blending a base oil with a thickener contains a total of 1 to 10% by mass of two or more carboxylic acids and carboxylates, ester compounds, and amine compounds and 0.5 to 9. A grease composition comprising 5% by mass and further containing a release agent.   2. The grease composition according to claim 1, wherein 1 to 10% by mass of metal dithiocarbamate is blended as the anti-peeling agent.   The grease composition according to claim 1, wherein 2 to 10% by mass of carbon black is blended as the release agent.   A housing, an electric motor capable of rotating forward and reversely supported by the housing, a screw shaft that is rotatably supported by the housing and is driven to rotate by the electric motor, and the rotation of the motor is prevented in its own rotation. A nut member that engages with the screw shaft and displaces in the axial direction of the screw shaft as the screw shaft rotates, and encloses the grease composition according to any one of claims 1, 2, and 3. Electric linear actuator.

Images