JP2008121789A - Electric linear actuator - Google Patents

Abstract

An electric linear actuator is provided which has improved durability by suppressing the occurrence of indentation and peeling on a ball surface.
A housing, an electric motor that can be rotated forward and backward supported by the housing, a screw shaft that is rotatably supported by the housing and is driven to rotate by the electric motor, and its rotation is prevented. In an electric linear actuator comprising a nut member that engages with the screw shaft in a state of being displaced and displaces in the axial direction of the screw shaft as the screw shaft rotates, a sulfur-phosphorus extreme pressure agent that does not contain metal An electric linear actuator comprising a grease composition contained at a ratio of 0.1 to 5% by mass.
[Selection] Figure 1

Description

  The present invention relates to an electric linear actuator, for example, as a driving device for automatically switching a gear ratio of an automobile transmission or for automatically connecting / disconnecting a clutch, and more specifically, to extend the lubrication life. Regarding technology.

  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 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. The ball screw of the above-mentioned electric linear actuator has a ball (generally a steel ball) interposed between the screw shaft and the nut as a rolling element, so that friction loss during operation can be almost ignored. In addition to extremely high efficiency, it has features such as very little wear on the components because it does not slide in the relative rotation of the screw shaft and the nut. An all-ball type ball screw has a screw shaft with a male screw groove formed on its outer periphery, a nut with a female screw groove facing the male screw groove formed on its inner periphery, and a male screw groove and a female screw groove. 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 total ball type ball screw described above, when balls rolling in the same direction between both screw grooves come into contact with each other, relative sliding 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 an electric linear actuator that has improved durability by suppressing the occurrence of indentations and peeling on the ball surface.

In order to achieve the above object, the present invention provides the following electric linear actuator.
(1) A housing, an electric motor that can be rotated forward and backward supported by the housing, a screw shaft that is rotatably supported by the housing and is driven to rotate by the electric motor, and its rotation is prevented. An electric linear actuator comprising 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. An electric linear actuator comprising a grease composition containing 1 to 5% by mass.
(2) The electric linear as set forth in (1), wherein in the grease composition, the thickener is urea-based, and the sulfur-phosphorus extreme pressure agent is at least one of thiophosphate and thiophosphite. Actuator.

  Since the electric linear actuator according to the present invention encloses a grease composition containing a specific extreme pressure agent, indentation and peeling hardly occur on the ball surface of the ball screw, and load load, heat generation, vibration, etc. are large. Excellent durability even under severe conditions.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a half cut side view showing a first embodiment of an electric linear actuator according to the present invention. As shown in the drawing, an electric motor 2 that can freely rotate forward and backward is supported and fixed to one end portion (left end portion in FIG. 1) of a substantially cylindrical housing 1. Further, a portion near the proximal end of the middle portion of the screw shaft 3 is supported inside the middle portion of the housing 1 by a rolling bearing 4 capable of supporting a radial load and a thrust load, such as a deep groove type 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, the 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 engaged so as to be able to operate in reverse so that the nut member 14 can be displaced in the axial direction even when the electric motor 2 fails. I am letting. 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. 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. The foreign matter is prevented 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 intrusion. In order to improve the foreign matter intrusion prevention effect, 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 distal 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, since the cover 21 having elasticity is supported to the housing 1 so as to be slightly displaceable, the tip of the cover 21 is the output shaft member. 16 is smoothly followed. Therefore, the surface pressure of the sliding contact portion between the inner peripheral surface of the tip end portion 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.

  FIG. 2 shows a second embodiment of the electric linear actuator. 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.

  FIG. 3 shows a third embodiment of the electric linear actuator. 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.

  FIG. 4 shows a fourth embodiment of the electric linear actuator of the present invention. In the case of this example, an end plate 19 having an L-shaped cross section and an annular shape is fixed to the front end surface of the screw shaft 3 in which a ball screw groove is formed on the outer peripheral surface by bolts 20. 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 grease composition shown below is enclosed in the lubrication part of the electric linear actuator.

  The type of base oil of the grease composition is not limited, but mineral oils and synthetic lubricants can be suitably 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.

The kinematic viscosity of the base oil is preferably 10 to 200 mm ² / s at 40 ° C., more preferably from 20 to 150 mm ² / s. If the kinematic viscosity of the base oil is less than 10 mm ² / s (40 ° C.), the oil film becomes thin and durability and fretting wear become a problem. If it exceeds 200 mm ² / s (40 ° C.), the torque increases and the operability of the device is increased. It becomes a problem.

  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 urea system can be preferably used.

  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 grease composition is preferably in the range of 220 to 395, more preferably in the range of 265 to 350 in terms of penetration. If the penetration is less than 220, it becomes too hard to expect a sufficient lubricating effect, and if it exceeds 395, there is a risk of grease leakage.

To the grease composition, a sulfur-phosphorus extreme pressure agent not containing metal is added. This sulfur-phosphorus extreme pressure agent is a compound containing a phosphorus atom and a sulfur atom. In addition to a compound having both a phosphorus atom and a sulfur atom in the molecule, such as thiophosphate and thiophosphite, It includes a mixture of a compound having a phosphorus atom (phosphorus-based additive) and a compound having a sulfur atom in the molecule (sulfur-based additive). The thiophosphates have a basic structure of a thiophosphate ester, and examples thereof include triphenyl phosphorothioate (TPPT). Examples of the thiophosphites include organic trithiophosphites represented by the general formula “(RS) ₃ P; R is an alkyl group”, for example, tributyltrithiophosphite and tri (2-ethylhexyl) thiophosphite. Etc. These sulfur-phosphorus extreme pressure agents may be added in combination.

  The addition amount of the sulfur-phosphorus extreme pressure agent is 0.1 to 5% by mass, preferably 1 to 3% by mass, based on the total amount of grease. If the amount of sulfur-phosphorus extreme pressure agent added is less than 0.1% by mass, sufficient extreme pressure action cannot be imparted, and if it exceeds 5% by mass, not only the effect is saturated but also the thermal stability decreases and grease leaks. There is a risk of causing.

  You may add another additive to a grease composition as needed. For example, antioxidants such as amines such as phenyl-1-naphthylamine (PAN), phenols such as 2,6-di-t-dibutylphenol, sulfurs and dithiophosphates; alkali metals and alkaline earth metals Organic sulfonates, carboxylates, alkyl or alkenyl succinic acid derivatives such as alkyl or alkenyl succinic acid esters, rust inhibitors such as partial esters of polyhydric alcohols such as sulfitan monooleate; fatty acids and animal and vegetable oils Oil improvers; metal deactivators such as benzotriazole, etc. can be used alone or in combination. Moreover, these addition amount will not be restrict | limited especially if it is a range which does not impair the objective of this invention.

  The grease composition contains the above-mentioned components, but there are no restrictions on the manufacturing method thereof, and it can be prepared in the same manner as conventional grease. However, in general, a thickener is reacted in a base oil. After adding a sulfur-phosphorus extreme pressure agent and other additives to the base grease obtained in this way, the mixture is thoroughly kneaded with a roll mill or the like and mixed uniformly. Moreover, you may heat at the time of kneading | mixing.

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

(Examples 1-4, Comparative Examples 1-2)
According to the formulation shown in Table 1, six types of grease compositions A1 to A4 and B1 to B2 were prepared.

  Then, the grease composition is enclosed in the electric linear actuator of the first to fourth embodiments described above, the nut member is reciprocated along the screw shaft, and the number of cycles at the time when peeling or seizure occurs ( The number of reciprocating motions of the nut member) was determined. The results are shown in Table 2.

  From Table 2, in Examples 1 to 4 in which grease compositions A1 to A4 containing a specified amount of a sulfur-phosphorus extreme pressure agent according to the present invention were encapsulated, the occurrence of peeling or seizure was observed even after exceeding 1 million revolutions. I can't. On the other hand, in Comparative Example 1, since the grease composition B1 not containing a sulfur-phosphorus extreme pressure agent was enclosed, peeling or seizure occurred at an early stage. Further, as shown in Comparative Example 2, when the grease composition B2 containing the sulfur-phosphorus extreme pressure agent in excess of the specified amount is used, grease leakage occurs, seizure occurs early, and peeling occurs. It occurs early.

It is a half section side view showing a 1st embodiment of an electric linear actuator. It is a half section side view showing a 2nd embodiment of an electric linear actuator. It is sectional drawing which shows 3rd Embodiment of an electric linear actuator. It is a half part cutting side view showing the 4th example of an electric linear actuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing 2 Electric motor 3 Screw shaft 4 Rolling bearing 5 Outer ring 6 輪 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 Driven gear 32 Intermediate gears 33a and 33b Buffer ring 34 Worm 35 Worm wheel 36 Locking hole 37 Driven member 38 Projection

Claims (2)

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. An electric linear actuator comprising a nut member that engages with a screw shaft and displaces in the axial direction of the screw shaft as the screw shaft rotates.
An electric linear actuator comprising a grease composition containing 0.1 to 5% by mass of a sulfur-phosphorus extreme pressure agent containing no metal.   2. The electric linear actuator according to claim 1, wherein in the grease composition, the thickener is urea-based, and the sulfur-phosphorus extreme pressure agent is at least one of thiophosphate and thiophosphite.

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