JP2008298107A - Ball screw and electric linear actuator having the ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw and an electric linear actuator having the ball screw, having heat resistance and grease resistance, and inexpensively improving durability. <P>SOLUTION: This electric linear actuator 1 has an electric motor 2, the ball screw 4 coaxially arranged at one end of a motor shaft 3, a rolling bearing 6 rotatably supporting the motor shaft 3 by a housing 5, a rolling bearing 9 fitted between the housing 5 and a nut 8 of the ball screw 4, and a seal 11 installed between the housing 5 and a screw shaft 10. The nut 8 is pressed in and fixed to the end of the motor shaft 3, and rotatably and axially immovably supported by the housing 5 via the rolling bearing 9. The screw shaft 10 is axially movably and nonrotatably supported. The seal 11 is constituted of boots composed of EPDM. The ball screw 4 is lubricated by grease composed of polyglycol-based base oil. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ball screw used for an actuator of an automobile and the like and an electric linear actuator provided with the same.

  In electric linear actuators used in various drive units of automobiles, a gear mechanism such as a trapezoidal screw or a rack and pinion is generally used as a mechanism for converting the rotary motion of the electric motor into a linear motion in the axial direction. Since these conversion mechanisms involve a sliding contact portion, the power loss is large, and it is necessary to increase the size of the electric motor and increase the power consumption. Therefore, a ball screw has been adopted as a more efficient actuator.

  The ball screw is composed of a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, and both opposing screw grooves. A large number of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circulation path are provided. For example, the screw shaft is linearly moved by rotating the nut.

  As an example of this, a ball screw as shown in FIG. 3 is known. This ball screw 50 is one moving member and a guide shaft (screw shaft) 51 in which a spiral ball groove 51a is formed on an inner peripheral surface serving as a guide surface thereof, and the other moving member, and A movable body (nut) 52 in which a spiral thread groove 52a facing the thread groove 51a is formed on the inner peripheral surface serving as the guide surface, and a rolling element interposed between the facing thread grooves so as to freely roll. A number of balls 53 and a tube-type circulation path 54 for circulating these balls 53 are provided.

  The tube-type circulation path 54 is formed by a tube having an approximately U-shaped outer shape, and the movable body 52 is connected to the movable body 52 through the movable body 52 through the movable body 52 in the tangential direction of both screw grooves 51a and 52a. It is inserted into the inner ball rolling space 56 and fixed to the outer periphery of the movable body 52 by a stopper 57. The ball 53 rolling in the spiral ball rolling space 56 moves around the screw grooves 51a and 52a a plurality of times, and is then scooped up at one end 54a of the tube-type circulation path 54 to be tube-type circulation. It is configured to repeat circulation through the path 54 and return from the other end (not shown) to the ball rolling space 56 in the movable body 52.

  In addition, grease is used to lubricate the ball screw 50. In order to prevent this grease from leaking to the outside and foreign matters such as rainwater and dust from entering the inside from the outside, a gap between the movable body 52 and the guide shaft 51 is used. A seal 58 is attached to the opening of the annular space formed in the.

In particular, in a ball screw 50 to which a high load is applied, such as an electric injection molding machine or an electric press machine, the balls 53 collide with each other and the surface thereof is scratched, causing backlash or peeling from the ball. Therefore, grease containing a base oil containing a specific aromatic thioether oil is used. Thereby, damage to the ball 53 is suppressed and the lubrication life is extended (for example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2004-324797

  In recent years, ethylene propylene rubber made of a terpolymer obtained by adding a small amount of a third component to a copolymer of ethylene and propylene, such as a seal 58 of the ball screw 50, and a rubber product such as an actuator of an automobile, so-called EPDM. In addition, a material in which this EPDM is added to a general-purpose resin such as polypropylene has been used. However, this EPDM has excellent heat resistance, ozone resistance, weather resistance, chemical resistance, and the like, but has poor grease resistance. Therefore, the EPDM is used as a seal 58 for the ball screw 50 that is in direct contact with the grease. If used, the seal 58 may deteriorate due to swelling (volume expansion). As a result, grease leaks and the durability of the ball screw 50 decreases, and there is a concern about contamination of the ball screw 50 around it.

The present invention has been made in view of such circumstances, and provides a ball screw having heat resistance and grease resistance, which is low in cost and improved in durability, and an electric linear actuator including the ball screw. With the goal.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a spiral thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft and spirally formed on the inner peripheral surface. And a plurality of balls accommodated in a rolling path formed by the opposing screw grooves, and a circulation member for infinite circulation of these balls, and with a predetermined grease. In the ball screw to be lubricated, the seal adjacent to the ball screw is formed of EPDM, and the grease is made of a polyglycol base oil.

  Thus, in a grease screw lubricated ball screw, the seal adjacent to the ball screw is formed of EPDM, and the grease is made of a polyglycol base oil, thereby preventing the seal from swelling and deteriorating. It is possible to provide a ball screw that is low in cost, excellent in heat resistance, and improved in durability.

  Preferably, as in the invention described in claim 2, if the organometallic extreme pressure agent, the solid lubricant, or a combination thereof is added to the grease, the lubricating auxiliary function can be exhibited. The lubrication performance of the ball screw is improved, and the durability of the ball screw can be further improved.

  According to a third aspect of the present invention, there is provided an electric motor, the ball screw according to the first or second aspect, coaxially disposed at one end of a hollow motor shaft, and a housing. A pair of rolling bearings for rotatably supporting the motor shaft, a rolling bearing fitted between the housing and a ball screw nut, and a housing and a screw shaft of the ball screw are mounted. The nut is press-fitted and fixed to the end portion of the motor shaft, and is rotatably supported by the housing via the rolling bearing and not axially movable. At the same time, the screw shaft is disposed on the motor shaft so as to be able to advance and retract, is supported so as to be axially movable and non-rotatable, and the seal is constituted by a boot made of EPDM.

  As described above, in the electric linear actuator, the nut is press-fitted and fixed to the end portion of the motor shaft, and is supported on the housing so as to be rotatable and non-movable in the axial direction via the rolling bearing. It is placed on the shaft so that it can move forwards and backwards, and it is supported so that it can move in the axial direction and cannot rotate, and the seal is made up of boots made of EPDM. In addition, it is possible to provide an electric linear actuator that can secure high performance, is low in cost, has excellent heat resistance, and has improved durability.

  According to a fourth aspect of the present invention, the circulating member is fitted into a piece window drilled in a body portion of the nut, the rolling path is used as a circulation path, and the nut is adjacent. If it is composed of a piece member with connecting grooves that connect between the thread grooves, a rolling bearing that rotatably supports the nut can be fitted to the outer periphery of the nut, and the space can be used effectively, and the device Can be made compact.

  According to a fifth aspect of the present invention, the piece window is formed in a circular cross section, the piece member is formed in a circular shape corresponding to the piece window, and the piece window is predetermined by boring. If it is configured with the finished surface of the size of, burrs can be prevented from being generated at the edge of the piece window in the screw groove, eliminating the need for burr removal processing and grinding the screw groove. It can be abolished and the cost can be reduced.

  According to a sixth aspect of the present invention, the rolling bearing for supporting the nut comprises a sealed type deep groove ball bearing having seals attached to both ends, the seal is formed of EPDM, and the rolling If the bearing is lubricated with grease made of a polyglycol base oil, it is possible to prevent the seal from swelling and deteriorating due to grease sealed inside or grease that has flowed out of the ball screw 4, and the rolling bearing Low cost, excellent heat resistance, and long life.

  The ball screw according to the present invention is opposed to a screw shaft having a helical thread groove formed on the outer peripheral surface, and a nut externally fitted to the screw shaft and having a helical thread groove formed on the inner peripheral surface. A ball screw having a plurality of balls accommodated in a rolling path formed by the two screw grooves and a circulating member for infinite circulation of these balls and being lubricated with a predetermined grease, adjacent to the ball screw The seal is molded with EPDM, and the grease is made of a polyglycol base oil, so that the seal is prevented from swelling and deteriorating, and it is excellent in heat resistance and low durability at low cost. A ball screw can be provided.

  An electric linear actuator according to the present invention includes: an electric motor; the ball screw according to claim 1 or 2 coaxially disposed at one end of a hollow motor shaft; and the motor relative to a housing. A pair of rolling bearings that rotatably support the shaft, a rolling bearing that is fitted between the housing and a nut of the ball screw, and a seal that is mounted between the housing and the screw shaft of the ball screw. In the electric linear actuator provided, the nut is press-fitted and fixed to an end portion of the motor shaft, and is rotatably supported on the housing via the rolling bearing so as not to be axially movable. Since the shaft is arranged to move forward and backward on the motor shaft, is supported so as to be axially movable and non-rotatable, and the seal is composed of a boot made of EPDM Boot is prevented from being deteriorated by swelling, can be ensured good sealability, excellent heat resistance at a low cost, it is possible to provide an electric linear actuator with improved durability.

  An electric motor, a ball screw coaxially disposed at one end of a hollow motor shaft, a pair of rolling bearings for rotatably supporting the motor shaft with respect to the housing, and nuts of the housing and the ball screw An electric linear actuator comprising a rolling bearing fitted between the housing and a seal mounted between the housing and a screw shaft of the ball screw, wherein the ball screw is press-fitted into an end of the motor shaft. A nut that is fixed, is rotatably supported via the rolling bearing with respect to the housing, and is supported so as not to move in the axial direction, and has a spiral thread groove formed on the inner peripheral surface, and is movable forward and backward with respect to the motor shaft. And a screw shaft that is axially movable and non-rotatably supported, and has a helical thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft. Yo A plurality of balls accommodated in the formed rolling path and a piece window bored in the trunk of the nut are fitted, and the rolling path is used as a circuit path, and between the adjacent screw grooves of the nut. And a piece member having a connecting groove formed therein, the seal is made of a boot made of EPDM, and the ball screw is made of a polyglycol base oil, and an organometallic extreme pressure agent or solid lubricant Lubricated with an agent or grease added in combination.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 is a longitudinal sectional view showing an electric linear actuator to which a ball screw according to the present invention is applied, FIG. 2A is a plan view showing the ball screw of FIG. 1, and FIG. 1B is a longitudinal section of FIG. FIG.

  An electric linear actuator 1 shown in FIG. 1 includes an electric motor 2, a ball screw 4 coaxially disposed at one end of a motor shaft 3 of the electric motor 2, and a motor shaft 3 with respect to housings 5a and 5b. A pair of rolling bearings 6 and 7 that are rotatably supported, a rolling bearing 9 that supports the nut 8 of the ball screw 4 with respect to the housing 5c, and the housing 5c and the screw shaft 10 of the ball screw 4 are mounted. And a boot (seal) 11.

  The electric motor 2 includes a stator 2a made of a permanent magnet fixed to the housing 5b, and a plurality of coils fixed to the outer periphery of the motor shaft 3 and opposed to the stator 2a via a predetermined radial clearance (air gap). A rotor 2b, a brush 2c attached to the housing 5a, and a commutator 2d that engages with the brush 2c, and constitutes a DC motor.

  The ball screw 4 is inserted into and fixed to one end of the motor shaft 3 through a cylindrical nut 8 and a large number of balls 12 inserted into the nut 8 so as to freely advance and retreat on the hollow motor shaft 3. The screw shaft 10 is provided. A flange 8b is formed on the outer periphery of one end of the nut 8, and an annular groove 8c is formed on the outer periphery of the other end, and the rolling bearing 9 is positioned and fixed by a retaining ring 13 and the flange 8b attached to the annular groove 8c. The nut 8 is supported by the housing 5c via the rolling bearing 9 so as to be rotatable and non-movable in the axial direction. On the other hand, a boot 11 which will be described later is mounted between the housing 5c and the screw shaft 10, and the screw shaft 10 is supported so as to be movable in the axial direction and non-rotatable.

  As shown in FIG. 2, the ball screw 4 includes a nut 8 in which a spiral thread groove 8a is formed on the inner peripheral surface, and a screw in which a spiral thread groove 10a corresponding to the screw groove 8a is formed on the outer peripheral surface. A number of balls 12 that are rotatably accommodated in a rolling path formed by the shaft 10, the nut 8 and the screw grooves 8 a and 10 a of the screw shaft 10, and a piece member 14 that serves as a circulation member for the balls 12, The piece type ball screw 4 is comprised. In this way, by adopting the piece-type ball screw 4, the rolling bearing 9 for rotatably supporting the nut 8 can be fitted to the outer periphery of the nut 8, and the space is effectively utilized to make the device compact. Can be achieved.

  The cylindrical nut 8 has a circular cross-section window 15 that penetrates the inner and outer peripheral surfaces and cuts out a part of the thread groove 8a, and has a substantially circular cross section corresponding to the piece window 15. The piece member 14 is fitted. A connecting groove 14a is formed on the inner side of the piece member 14 to connect adjacent ones of the screw grooves 8a, and the ball 12 rolls between the connecting groove 14a and the substantially one part of the screw groove 8a. Constitutes the road. A large number of balls 12 interposed between the screw grooves 8 a and 10 a in the rolling path roll along the screw grooves 8 a and 10 a, and are guided by the connecting groove 14 a of the piece member 14. After overcoming the thread, it returns to the adjacent thread groove 8a and rolls along the thread grooves 8a and 10a again.

  The connecting groove 14a of the piece member 14 is formed in a substantially S-shape so as to smoothly connect the adjacent thread grooves 8a, 8a of the nut 8. The depth of the connecting groove 14a is set to such a depth that the ball 12 can exceed the thread of the screw groove 10a in the screw shaft 10 in the connecting groove 14a.

  The cross-sectional shape of each thread groove 8a, 10a of the ball screw 4 may be a circular arc shape or a gothic arc shape, but here, the contact angle with the ball 12 can be increased and the axial clearance can be reduced. It has a Gothic arc shape that can be set. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The piece member 14 is made of a sintered alloy prepared by adjusting a metal powder into a plastic shape and molded by an injection molding machine. In this injection molding, first, metal powder and a binder made of plastic and wax are kneaded with a kneader, and the kneaded product is granulated into a pellet. The granulated pellets are supplied to a hopper of an injection molding machine, and are molded by so-called MIM (Metal Injection Molding) in which the pellets are pressed into a mold in a heated and melted state. A sintered alloy formed by such an MIM can be easily and accurately formed into a desired shape / dimension even if it has a high workability and a complicated shape.

  As the metal powder, materials that can be carburized and quenched later, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, Cr (chromium) is 1.1 wt%, Cu (copper) Exemplifies SCM415 which is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the rest is Fe (iron). Can do. The piece member 14 is hardened by carburizing and quenching so that the surface hardness is in the range of 30 to 40 HRC, and is provided with wear resistance.

  Although the piece windows 15 are provided one by one at both ends of the nut 8, in this embodiment, after the screw grooves 8a are finished by cutting, these piece windows 15 are rough-worked by drilling. The piece window 15 is finished by boring. As a result, it is possible to prevent burrs from being generated at the edge of the piece window 15 in the screw groove 8a, so that burr removal processing becomes unnecessary, and grinding of the screw groove 8a can be abolished. On the other hand, the thread groove 10a of the screw shaft 10 is formed by rolling. Thereby, the processing man-hour of the ball screw 4 can be reduced, the yield of the material can be improved, and the cost can be reduced.

  In FIG. 1, when the electric motor 2 is energized, the nut 8 rotates with the rotation of the motor shaft 3, and the screw shaft 10 is moved in the axial direction (left-right direction in the figure) by the rotation of the nut 8. That is, the ball screw 4 converts the rotational motion of the motor shaft 3 into the axial motion of the screw shaft 10 via the ball screw 4.

  Here, in the present embodiment, the rolling bearing 9 for supporting the nut 8 is formed of a sealed deep groove ball bearing having seals 9a attached to both ends, and the boot 11 and the seal 9a of the rolling bearing 9 are EPDM (ethylene propylene). Rubber). This EPDM is a terpolymer of ethylene, propylene and a diene monomer for crosslinking, and enables sulfur crosslinking (vulcanization) by copolymerizing a third component that is a non-conjugated diene monomer. In addition to heat resistance superior to rubber, it has low cost, ozone resistance, weather resistance, and chemical resistance equivalent to polyacrylic rubber. Specifically, vulcanized using 100 polymerization parts of ethylene / α-olefin / non-conjugated diene rubber copolymer (main component EPDM), 0.1 to 10 polymerization parts of sulfur, and 25 to 100 polymerization parts of carbon black. A boot 11 and a seal 9a are formed.

  On the other hand, grease is held in the nut 8 of the ball screw 4, and lubrication assists the ball screw 4 by this grease. In order to improve the grease resistance of the rubber component adjacent to the ball screw 4, here, the boot 11 made of EPDM and the seal 9a of the rolling bearing 9, grease made of a polyglycol base oil is used. . Further, like the ball screw 4, the rolling bearing 9 is lubricated with grease made of a polyglycol base oil. As a result, it is possible to provide the ball screw 4 that prevents the boot 11 and the seal 9a of the rolling bearing 9 from being swollen and deteriorated by the grease that has flowed out of the ball screw 4 and is improved in durability at low cost. In addition, the durability of the rolling bearing 9 adjacent to the ball screw 4 can be improved.

  Grease contains, for example, an antioxidant for high temperature use and various additives such as a rust preventive for rust prevention. As extreme pressure additives, organic molybdenum compounds such as molybdenum dithiophosphate and zinc dithiocarbamate An organometallic extreme pressure agent made of an organic zinc compound such as By including an extreme pressure additive that exhibits such a lubricating auxiliary function, the lubricating performance of the grease is improved, and the durability of the ball screw 4 can be further improved. In addition, examples of the extreme pressure additive include a solid lubricant such as a sulfur-phosphorus compound and PTFE, or a combination of these. The grease thickener is made of a non-soap urea compound such as polyurea. This improves the heat resistance of the grease, but other than this, a soap system such as a lithium complex may be used.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The ball screw according to the present invention can be applied as a ball screw used for an electric actuator of an automobile.

It is a longitudinal section showing an electric linear actuator to which a ball screw concerning the present invention is applied. (A) is a top view which shows the ball screw of FIG. (B) is a longitudinal cross-sectional view of (a). It is a longitudinal cross-sectional view which shows the conventional ball screw.

Explanation of symbols

1 ... Electric linear actuator 2 ... Electric motor 2a ... Stator 2b ... Rotor 2c ... Brush 2d ... Commutator 3 ...・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Motor shaft 4 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Ball screws 5, 5a, 5b, 5c, 5d ・ ・ Housings 6, 7, 9 ...・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Rolling bearing 8 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Nuts 8a, 10a ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Thread groove 8b ・ ・ ・ ・ ・ ・... Flange 8c ......... annular groove 9a ......... Seal 10 ......... screw Shaft 11 ... Boots 12 ... ········· Ball 13 ··················································· ... Connecting groove 15 ... Koma window 50 ... Ball screw 51 ... -Guide shaft 51a. 52a ... Thread groove 52 ... Movable body 53 ... Ball 54 ... ··································································································・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Ball rolling space 57 ・ ・ ・ ・ ・ ・ ・ ・ Stamp 58 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Seal

Claims (6)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls accommodated in rolling paths formed by the opposing thread grooves;
In a ball screw provided with a circulating member for infinite circulation of these balls and lubricated with a predetermined grease,
A ball screw, wherein a seal adjacent to the ball screw is formed of EPDM, and the grease is made of a polyglycol base oil.   The ball screw according to claim 1, wherein an organometallic extreme pressure agent, a solid lubricant, or a combination thereof is added to the grease. An electric motor;
The ball screw according to claim 1 or 2, which is coaxially disposed at one end of a hollow motor shaft,
A pair of rolling bearings for rotatably supporting the motor shaft with respect to the housing;
A rolling bearing fitted between the housing and a ball screw nut;
In the electric linear actuator provided with a seal mounted between the housing and the screw shaft of the ball screw,
The nut is press-fitted and fixed to an end portion of the motor shaft, and is rotatably supported on the housing via the rolling bearing and not axially movable.
An electric linear actuator characterized in that the screw shaft is arranged so as to be able to advance and retreat on the motor shaft, is supported so as to be axially movable and non-rotatable, and the seal is constituted by a boot made of EPDM.   The piece in which the circulating member is fitted into a piece window formed in the trunk portion of the nut, the rolling path is used as a circulation path, and a connecting groove for connecting between adjacent screw grooves of the nut is formed. The electric linear actuator according to claim 3, wherein the electric linear actuator is formed of a member.   The piece window is formed in a circular cross section, the piece member is formed in a circular cross section corresponding to the piece window, and the piece window is configured with a finished surface formed to a predetermined size by boring. The electric linear actuator according to claim 3 or 4.   The rolling bearing for supporting the nut is a sealed deep groove ball bearing with seals attached to both ends, the seal is formed of EPDM, and the rolling bearing is made of grease made of a polyglycol base oil. The electric linear actuator according to any one of claims 3 to 5, which is lubricated.

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