JP2007192264A - Ball screw mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw mechanism whose long service lifetime is secured by being used in a state of suppressing an intersecting angle formed of an axial line of a screw shaft and that of a nut. <P>SOLUTION: The nut 104 is supported to a housing 101 via an elastic member 110 so as to be tiltable. When misalignment between an axial line of a hole 101b of the housing 101 loaded with a bearing 107 and that of a coupling shaft 102 occurs, the intersecting angle θ between the axial line of the nut 104 and that of the screw shaft 105 is restrained by allowing a tilt of the nut 104 to the housing 101 with the elastic deformation of the elastic member 110. Consequently, it is possible to achieve the long service lifetime of the ball screw mechanism by averaging the rolling element (ball) load distribution of the ball screw mechanism. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ball screw mechanism that is assembled to a general industrial machine or used in an automobile.

  In recent years, labor saving of vehicles and the like has progressed, and for example, a system has been developed in which a transmission, a parking brake, and the like of an automobile are performed not by hand but by the power of an electric motor. An electric actuator used for such an application may use a ball screw mechanism in order to convert the rotational motion transmitted from the electric motor into the axial motion with high efficiency.

Patent Document 1 discloses an electric transmission that is used to perform a shift by converting a rotational motion extracted from an electric motor into a linear motion via a ball screw mechanism.
JP 2004-52838 A JP 2004-19631 A

  By the way, in the transmission of Patent Document 1, the housing to which the motor is attached and the housing to which the ball screw mechanism is attached are provided separately, and thus a housing hole for sliding the connecting shaft and a housing hole for fixing the support bearing are provided. In such a case, the axes may be displaced due to a manufacturing error of the housing. This will be described with reference to the drawings.

  6 and 7 are diagrams illustrating an example of a transmission in which a housing to which an electric motor is attached and a housing to which a ball screw mechanism is attached are separated. In the figure, a hollow cylindrical connecting shaft 2 is arranged in an axial direction (left-right direction in the figure) and non-rotatable with respect to a hole 1 a of the housing 1. One end of the shift cable 3 is connected to the end (right end in the figure) of the connecting shaft 2 via a holder 2a. The other end of the shift cable 3 is connected to a shift fork of a transmission (not shown).

  A nut 4 is fixed to the inner periphery of the connecting shaft 2 so as to move integrally with the connecting shaft 2. A screw shaft 5 is inserted into the nut 4. A male screw groove is formed on the outer peripheral surface of the screw shaft 5, a female screw groove is formed on the inner peripheral surface of the nut 4, and a plurality of balls (in the spiral rolling path formed between the two screw grooves ( (Not shown) is arranged.

  A round shaft portion 5 a is formed on the left end side of the screw shaft 5 in the drawing, and the outer periphery thereof is rotatably supported by a bearing 7 that fits into the hole 10 a of the housing 1. The left end of the round shaft portion 5 a in the drawing is connected to the rotating shaft 9 a of the motor 9 via the coupling 8.

  When the operator operates a switch (not shown), the rotating shaft 9a of the motor 9 rotates, and the screw shaft 5 rotates accordingly. Since the rotational motion of the screw shaft 5 is converted into the axial motion of the nut 4, the connecting shaft 2 moves in the axial direction together with the nut 4, and the shift fork of the transmission (not shown) is moved via the shift cable 3. A predetermined shift operation can be performed.

  Here, in FIG. 6, the axis of the hole 10 a of the housing 1 for fixing the bearing 7 coincides with the axis of the screw shaft 5. However, due to the shape error of the housing or the like, a deviation Δ occurs between the axis A of the hole 10a and the axis B of the nut 4, and the screw shaft 5 may be inclined with respect to the nut 4 (FIG. 7). In such a case, a crossing angle θ occurs between the axis B of the nut 4 and the axis of the screw shaft 5C.

  FIG. 8 shows the life when the crossing angle θ is changed in a state where an axial load of 500 N is applied to a ball screw mechanism having a screw shaft diameter of 14 mm, a ball diameter of 3.175 mm, and a thread of 2.5 windings. It is a figure which shows the change of. As can be seen from FIG. 8, when the life when the crossing angle θ = 0 ° is 1, for example, when the crossing angle θ = 0.2 °, the life is greatly reduced to about 0.01.

  FIG. 9 is a diagram showing a distribution of a ratio (Q / Qmean) of the rolling element load Q when the intersection angle θ = 0.2 ° and the rolling element load average value Qmean when the intersection angle θ = 0 °. is there. According to FIG. 9, it can be seen that when the crossing angle θ = 0.2 °, a maximum load of 21 times is applied to the ball compared to when the crossing angle θ = 0 °. This significantly shortens the life of the ball screw mechanism. Therefore, it is desired to use the ball screw mechanism with the crossing angle θ as close to zero as possible.

  On the other hand, in FIG. 10 schematically illustrating an example of the apparatus of Patent Document 2, the nut 4 is held by the bearing 7 with respect to the hole 1a of the housing 1, and the stator 9A of the motor 9 is disposed on the inner peripheral surface of the housing 1. And the rotor 9B of the motor 9 is arrange | positioned on the outer peripheral surface of the nut 4 facing it. In such a configuration, since the nut 4 is disposed in the hole 1a via the bearing 7, no crossing angle θ is generated between the axis of the nut 4 and the axis of the screw shaft 5, but the motor 9 is incorporated. However, there is a problem that the cost becomes high.

  The present invention has been made in view of such problems of the prior art, and a ball screw mechanism that ensures a long life by using a state in which the angle of intersection between the axis of the screw shaft and the axis of the nut is suppressed. The purpose is to provide.

The ball screw mechanism of the present invention is
A housing;
A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut that is movable in the axial direction with respect to the housing, is arranged so as to surround the screw shaft, and has a female screw groove formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a rolling path formed between opposing screw grooves;
When there is a deviation between the axis of the hole for mounting the bearing that rotatably supports the screw shaft relative to the housing and the axis of the nut, the axis of the screw shaft and the axis of the nut The present invention is characterized in that suppression means for suppressing the formed intersection angle is provided.

  According to the ball screw mechanism of the present invention, when a deviation occurs between the axis of the hole for attaching the bearing that rotatably supports the screw shaft to the housing and the axis of the nut, the screw shaft Since the suppression means which suppresses the crossing angle which forms the axis of this and the axis of the said nut is provided, the long life of a ball screw mechanism is securable by suppressing the said crossing angle.

  When the restraining means is an elastic member disposed between the nut and the housing, the elastic member is elastically deformed, thereby allowing the nut to tilt with respect to the housing, thereby causing the intersection. Corners can be suppressed.

  When the elastic member is arranged so as to be movable in the axial direction of the nut relative to the nut or the housing, it is convenient when the nut is moved in the axial direction.

  When the restraining means includes a convex spherical surface formed on the outer peripheral surface of the nut that engages with the inner peripheral surface of the housing, the nut easily swings with respect to the housing, thereby the crossing. Corners can be suppressed.

  If the inner peripheral surface of the housing has a concave spherical surface corresponding to the spherical surface of the nut outer peripheral surface, the nut is easily swung by engaging the convex spherical surface with the concave spherical surface. Thus, the crossing angle can be suppressed.

  When the restraining means includes a convex spherical surface disposed between the housing and the nut that engages with the inner peripheral surface of the housing, the nut easily swings with respect to the housing, thereby The crossing angle can be suppressed.

  When the convex spherical surface is arranged so as to be movable in the axial direction of the nut with respect to the housing, it is convenient when the nut is moved in the axial direction.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side view of the ball screw mechanism according to the first embodiment, and FIG. 2 is a view of the configuration of FIG. 1 taken along line II-II and viewed in the direction of the arrow. In FIG. 2, the deviation between the axis of the housing hole to which the bearing is attached and the axis of the nut is exaggerated. Also, the motor is omitted.

  In FIG. 1, a hollow cylindrical connecting shaft 102 is disposed in a cylindrical hole 101a of the housing 101 so as to be movable in the axial direction (left-right direction in the drawing) and non-rotatable. One end of the shift cable 103 is connected to the end (right end in the figure) of the connecting shaft 102 via a holder 102a. The other end of the shift cable 103 is connected to a shift fork of a transmission (not shown).

  The outer periphery of a cylindrical resin elastic member 110 is bonded to the inner periphery of the connecting shaft 102, and the outer periphery of the nut 104 is bonded to the inner periphery of the elastic member 110. A screw shaft 105 is inserted into the nut 104. As shown in FIG. 2, a male screw groove 105 b is formed on the outer peripheral surface of the screw shaft 105, and a female screw groove 104 b is formed on the inner peripheral surface of the nut 104, and a helical shape formed between both screw grooves. A plurality of balls 111 are arranged in the rolling road. The nut 104 is provided with a top 112 that is a circulating member that circulates the ball 111 from one end of the rolling path to the other end during operation of the ball screw mechanism including the nut 104, the screw shaft 105, and the ball 111.

  In FIG. 1, a round shaft portion 105 a is formed on the left end side of the screw shaft 105, and the outer periphery thereof is rotatably supported by a bearing 107 attached to the hole 101 b of the housing 101. The left end of the round shaft portion 105a in the drawing is connected to the motor via a coupling (not shown).

  When the operator operates a switch (not shown), the rotating shaft of a motor (not shown) rotates, and the screw shaft 105 rotates accordingly. Since the rotational motion of the screw shaft 105 is efficiently converted into the axial motion of the nut 104 that cannot be rotated via the connecting shaft 102, the connecting shaft 102 to which the nut 104 is fixed can be moved in the axial direction. A predetermined shift operation can be performed by moving a shift fork of a transmission (not shown) via a shift cable 103 fixed to the connecting shaft 102.

  According to the present embodiment, the nut 104 is supported to be tiltable with respect to the housing 101 via the elastic member 110 as a restraining means, and therefore connected to the axis of the hole 101b of the housing 101 to which the bearing 107 is attached. When a deviation occurs between the shaft 102 and the shaft 102, the elastic member 110 is elastically deformed to allow the inclination of the nut 104 with respect to the housing 101, thereby causing a gap between the nut 104 and the screw shaft 105. Can be achieved by suppressing the crossing angle θ and averaging the rolling element (ball) load distribution of the ball screw mechanism.

  FIG. 3 is a side view of the ball screw mechanism according to the second embodiment. Also in FIG. 3, the deviation between the axis of the housing hole to which the bearing is attached and the axis of the nut are exaggerated. In FIG. 3, a hollow cylindrical connecting member 202 is disposed inside the cylindrical inner peripheral surface 201 a of a hollow housing 201 so as to be movable in the axial direction. The inner peripheral surface 202b of the connecting member 202 is a concave spherical surface having a radius R. On the other hand, the outer peripheral surface 204a of the nut 204 is a convex spherical surface having a radius R, and the nut 204 can swing with respect to the connecting member 202 by engaging the outer peripheral surface 204a with the inner peripheral surface 202b. It has a configuration. The nut 204 is provided with a non-rotating stopper (not shown) to prevent the housing 201 from rotating. One end of the shift cable 203 is connected to an end portion (right end in the figure) of the connecting shaft 202 via a holder 202a. The other end of the shift cable 203 is connected to a shift fork of a transmission (not shown). The spherical inner peripheral surface 202b and the outer peripheral surface 204a constitute a suppression means.

  A screw shaft 205 is inserted into the nut 204. A male screw groove is formed on the outer peripheral surface of the screw shaft 205, a female screw groove is formed on the inner peripheral surface of the nut 204, and a plurality of balls (in the spiral rolling path formed between the two screw grooves ( (Not shown) is arranged. The nut 204 is provided with a top 212 which is a circulating member that circulates the ball from one end of the rolling path to the other end during operation of the ball screw mechanism including the nut 204, the screw shaft 205, and the ball.

  A round shaft portion 205 a is formed on the left end side of the screw shaft 205 in the drawing, and the outer periphery thereof is rotatably supported by a bearing 207 attached to the hole 201 b of the housing 201. The left end of the round shaft portion 205a in the drawing is connected to the motor via a coupling (not shown).

  When the operator operates a switch (not shown), a rotating shaft of a motor (not shown) rotates, and the screw shaft 205 rotates accordingly. Since the rotational motion of the screw shaft 205 is efficiently converted into the axial motion of the nut 204 that is disabled to rotate through the connecting shaft 202, the connecting shaft 202 to which the nut 204 is fixed can be moved in the axial direction. A predetermined shift operation can be performed by moving a shift fork of a transmission (not shown) via a shift cable 203 fixed to the connecting shaft 202.

  According to the present embodiment, the nut 204 can swing relative to the connecting member 202 by the inner peripheral surface 202b and the outer peripheral surface 204a that are engaged with each other, and therefore the axis of the hole 201b of the housing 201 to which the bearing 207 is attached. And the axis of the connecting shaft 202 are shifted, the crossing angle θ between the axis of the nut 204 and the axis of the screw shaft 205 is suppressed by allowing the nut 204 to tilt with respect to the housing 201. A long life can be achieved by averaging the rolling element (ball) load distribution of the ball screw mechanism.

  FIG. 4 is a side view of the ball screw mechanism according to the third embodiment. Also in FIG. 4, the deviation between the axis of the housing hole to which the bearing is attached and the axis of the nut are exaggerated. In FIG. 4, a hollow cylindrical connecting shaft 302 is disposed in the hole 301 a of the housing 301 so as to be movable in the axial direction (left-right direction in the drawing) and non-rotatable. A cylindrical elastic member 310 is fitted and disposed between the housing 301 and the connecting shaft 302. The outer peripheral surface of the elastic member 310 is in contact with the inner peripheral surface of the housing 301, and slides with respect to the housing 301 as the connecting shaft 302 moves. One end of the shift cable 303 is connected to the end (right end in the figure) of the connecting shaft 302 via a holder 302a. The other end of the shift cable 303 is connected to a shift fork of a transmission (not shown). A nut 304 is fixed to the inner periphery of the connecting shaft 302.

  A screw shaft 305 is inserted into the nut 304. A male screw groove is formed on the outer peripheral surface of the screw shaft 305, a female screw groove is formed on the inner peripheral surface of the nut 304, and a plurality of balls (in the spiral rolling path formed between the two screw grooves ( (Not shown) is arranged. The nut 304 is provided with a top 312 that is a circulating member that circulates the ball from one end of the rolling path to the other end during operation of the ball screw mechanism including the nut 304, the screw shaft 305, and the ball.

  A round shaft portion 305 a is formed on the left end side of the screw shaft 305 in the drawing, and the outer periphery thereof is rotatably supported by a bearing 307 attached to the hole 301 b of the housing 301. The left end in the figure of the round shaft portion 305a is connected to the motor via a coupling (not shown).

  When the operator operates a switch (not shown), the rotation shaft of a motor (not shown) rotates, and the screw shaft 305 rotates accordingly. Since the rotational motion of the screw shaft 305 is efficiently converted into the axial motion of the nut 304 that is not allowed to rotate, the connecting shaft 302 to which the nut 304 is fixed can be moved in the axial direction. A predetermined shift operation can be performed by moving a shift fork of a transmission (not shown) via the connected shift cable 303.

  According to the present embodiment, the connecting shaft 302 to which the nut 304 is fixed with respect to the housing 301 is supported via the elastic member 310 as the restraining means, so that the axis of the bearing 307 and the axis of the nut 304 are When the displacement occurs between the shaft 304 and the screw shaft 305, the elastic member 310 is elastically deformed to allow the connection shaft 302 and the nut 304 to be inclined with respect to the housing 301. A long life can be achieved by suppressing the crossing angle θ and averaging the rolling element (ball) load distribution of the ball screw mechanism. Further, by using a low friction material such as PTFE for the elastic member 310, the resistance during movement can be reduced. Note that the elastic member 310 may be fixed to the housing 301 and the nut 304 may be slid relative thereto.

  FIG. 5 is a side view of the ball screw mechanism according to the third embodiment. Also in FIG. 5, the deviation between the axis of the housing hole to which the bearing is attached and the axis of the nut are exaggerated. In FIG. 5, a hollow cylindrical connecting shaft 402 is disposed in the hole 401 a of the housing 401 so as to be movable in the axial direction (left-right direction in the drawing) and non-rotatable. A convex spherical surface portion 402 b is formed on the outer periphery of the connecting shaft 402 and is in contact with the inner peripheral surface of the housing 401. One end of the shift cable 403 is connected to the end (right end in the figure) of the connecting shaft 402 via a holder 402a. The other end of the shift cable 403 is connected to a shift fork of a transmission (not shown). A nut 404 is fixed to the inner periphery of the connecting shaft 402.

  A screw shaft 405 is inserted into the nut 404. A male screw groove is formed on the outer peripheral surface of the screw shaft 405, a female screw groove is formed on the inner peripheral surface of the nut 404, and a plurality of balls (in the spiral rolling path formed between the two screw grooves ( (Not shown) is arranged. The nut 404 is provided with a top 412 that is a circulating member that circulates the ball from one end to the other end of the rolling path when the ball screw mechanism constituted by the nut 404, the screw shaft 405, and the ball is operated.

  A round shaft portion 405 a is formed on the left end side of the screw shaft 405 in the drawing, and the outer periphery thereof is rotatably supported by a bearing 407 attached to the hole 401 b of the housing 401. The left end of the round shaft portion 405a is connected to the motor via a coupling (not shown).

  When the operator operates a switch (not shown), the rotation shaft of a motor (not shown) rotates and the screw shaft 405 rotates accordingly. Since the rotational motion of the screw shaft 405 is efficiently converted into the axial motion of the nut 404 that is disabled from rotating, the connecting shaft 402 to which the nut 404 is fixed can be moved in the axial direction. A predetermined shift operation can be performed by moving a shift fork of a transmission (not shown) via the connected shift cable 403.

  According to the present embodiment, since the spherical surface portion 402b is in line contact with the inner peripheral surface of the housing 401, resistance during movement is reduced. Further, since the spherical portion 402b as the restraining means abuts against the inner peripheral surface of the housing 401, the connecting shaft 402 can be easily tilted with respect to the housing 401. When the deviation between the axis of the nut 404 and the axis of the nut 404 occurs, the inclination between the axis of the nut 404 and the axis of the screw shaft 405 is allowed by allowing the connecting shaft 402 and the nut 404 to tilt with respect to the housing 401. By suppressing the angle θ and averaging the rolling element (ball) load distribution of the ball screw mechanism, a long life can be achieved. If it is known that the hole 401b of the housing 401 for fixing the bearing 407 and the axis of the nut 404 are shifted in the vertical direction in the drawing, the spherical surface portion 402b may be a cylindrical surface. The hole 401a is preferably in the shape of a rectangular tube or the like having parallel surfaces that are in contact with the cylindrical surface at the top and bottom.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the ball screw mechanism of the present invention can be applied not only to a vehicle transmission but also to various machines.

It is a side view of the ball screw mechanism concerning a 1st embodiment. It is the figure which cut | disconnected the structure of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is a side view of the ball screw mechanism concerning a 2nd embodiment. It is a side view of the ball screw mechanism concerning a 3rd embodiment. It is a side view of the ball screw mechanism concerning a 4th embodiment. It is a figure which shows the example of the transmission which separated the housing which attaches an electric motor, and the housing which attaches a ball screw mechanism. It is a figure which shows the example of the transmission which separated the housing which attaches an electric motor, and the housing which attaches a ball screw mechanism. This shows the change in life when the crossing angle θ is changed in a state where an axial load of 500 N is applied to a ball screw mechanism having a screw shaft diameter of 14 mm, a ball diameter of 3.175 mm, and 2.5 turns and a row of thread grooves. FIG. It is a figure which shows distribution of ratio (Q / Qmean) of rolling element load Q when crossing angle (theta) = 0.2 degree and rolling element load average value Qmean when crossing angle (theta) = 0 degree. It is a figure which shows the example which incorporated the electric motor in the housing.

Explanation of symbols

101 Housing 101a Cylindrical hole 101b Hole 102 Connecting shaft 102a Holder 103 Shift cable 104 Nut 104b Female thread groove 105 Screw shaft 105a Round shaft part 105b Male thread groove 107 Bearing 110 Elastic member 111 Ball 112 Top 201 Housing 201a Cylindrical inner peripheral surface 201b Hole 202 Connection Shaft 202a Holder 202b Inner peripheral surface 203 Shift cable 204 Nut 204a Outer peripheral surface 205 Screw shaft 205a Round shaft portion 207 Bearing 212 Top 301 Housing 301a Hole 301b Hole 302 Connection shaft 302a Holder 303 Shift cable 304 Nut 305 Screw shaft 305a Round shaft portion 307 Bearing 310 Elastic member 312 Top 401 Housing 401a Hole 401b Hole 402 Connecting shaft 402a Holder 402b Spherical surface 403 Shift cable 404 Tsu DOO 405 threaded shaft 405a round shaft portion 407 bearing 412 pieces

Claims (7)

A housing;
A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut that is movable in the axial direction with respect to the housing, is arranged so as to surround the screw shaft, and has a female screw groove formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a rolling path formed between opposing screw grooves;
When there is a deviation between the axis of the hole for mounting the bearing that rotatably supports the screw shaft relative to the housing and the axis of the nut, the axis of the screw shaft and the axis of the nut A ball screw mechanism comprising a suppressing means for suppressing a crossing angle formed.   The ball screw mechanism according to claim 1, wherein the restraining means is an elastic member disposed between the nut and the housing.   The ball screw mechanism according to claim 2, wherein the elastic member is arranged to be movable in an axial direction of the nut with respect to the nut or the housing.   The ball screw mechanism according to claim 1, wherein the suppressing means includes a convex spherical surface formed on an outer peripheral surface of the nut that engages with an inner peripheral surface of the housing.   The ball screw mechanism according to claim 4, wherein the inner peripheral surface of the housing has a concave spherical surface corresponding to the spherical surface of the nut outer peripheral surface.   2. The ball screw mechanism according to claim 1, wherein the suppressing means includes a convex spherical surface disposed between the nut engaged with an inner peripheral surface of the housing and the housing. The ball screw mechanism according to claim 6, wherein the convex spherical surface is arranged so as to be movable in the axial direction of the nut with respect to the housing.

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