JP4203939B2 - Ball screw device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw device configured to convert torque into a thrust between a nut member and a screw shaft, or to convert a thrust into torque.
[0002]
[Prior art]
The applicant of the present application has proposed a ball screw device as shown in Japanese Patent Application Laid-Open No. 2001-116095.
[0003]
The ball screw device described in this publication has a structure in which a nut member is supported via a rolling bearing with respect to a shaft body inserted through a central hole of a cylindrical screw shaft.
[0004]
In such a structure, in order to support the nut member arranged on the outer diameter side of the screw shaft with respect to the shaft body arranged on the inner diameter side of the screw shaft, a large-diameter cylinder is formed at one axial end of the nut member. A rolling bearing is interposed between the inner peripheral surface of the large-diameter cylindrical portion and the outer peripheral surface of the shaft body.
[0005]
[Problems to be solved by the invention]
In the above conventional example, due to the structure for supporting the nut member with respect to the shaft body, the dimension in the axial center direction becomes large, and the occupied space in the installation target of the ball screw device is restricted. In some cases, there is a problem that it cannot be used. There is room for improvement here.
[0006]
On the other hand, as shown in Japanese Patent Application No. 2001-310234, the applicant of the present application is a bracket such as a double cylinder that fits into the center hole of the screw shaft after being fitted on one end in the axial direction of the nut member. I am thinking of using If such a bracket is used, the dimension in the axial direction of the nut member does not have to be increased as in the conventional example, but there is room for improvement in the following points.
[0007]
That is, in the above-mentioned application, the bracket is manufactured by hot forging, or composite forging in which warm forging and cold forging are combined. Since the nut member is press-fitted and fitted to the inner peripheral surface of the cylindrical portion and positioned and fixed in the axial direction, it is necessary to process the bracket with high accuracy, and there is a concern that the manufacturing cost is high.
[0008]
In addition, as described above, when the nut member is press-fitted and fitted to the inner peripheral surface of the outer cylinder portion of the bracket, there is a possibility that the thread groove of the nut member may be distorted. I found out. However, if it does so, since the backlash of an axial direction will generate | occur | produce between a bracket and a nut member, it can be said that the means for positioning a nut member in an axial direction is needed separately.
[0009]
In view of such circumstances, the present invention provides a ball having a structure in which a nut member disposed on the outer diameter side of a screw shaft is supported via a bracket with respect to a shaft body inserted through a central hole of a cylindrical screw shaft. The purpose of the screw device is to facilitate the manufacture of the bracket mainly after shortening the dimension in the axial direction.
[0010]
[Means for Solving the Problems]
In the ball screw device of the present invention, as shown in claim 1, a plurality of balls are interposed between a screw groove provided on the inner peripheral surface of the nut member and a screw groove provided on the outer peripheral surface of the screw shaft, The torque is converted into thrust between the nut member and the screw shaft, or the thrust is converted into torque. The screw shaft is cylindrical, and the nut member is the center of the screw shaft. The shaft is inserted through the hole in a non-contact manner and is supported via a bracket, and the bracket is provided with a thick large-diameter portion that bulges radially outward at one shaft end of the cylindrical body. The nut member is concentrically covered at a predetermined interval on the outer diameter side of the body of the bracket, and one end of the nut member is an outer peripheral surface of the thick large diameter portion. And is fitted with a tightening allowance for centering The outer peripheral surface of the thick-walled large-diameter portion of the bracket is provided with a flange portion that is radially outwardly bulged on the one shaft end side, and is positioned on the outer peripheral surface of the thick-walled large-diameter portion. A convex portion is provided at a predetermined position on the circumference, and one thread groove of the nut member is provided continuously in the entire length of the inner peripheral surface. One end of the shaft is arranged, and one end of the screw groove of the nut member is phase-aligned with the convex portion of the thick-walled large-diameter portion. The nut member is positioned and fixed in the axial direction with respect to the bracket by inserting the screw thread (land portion) between the thread grooves of the nut member into the axial clearance between the convex part and the flange part. ing.
[0012]
According to a second aspect of the present invention, the ball screw device according to the first aspect is formed by integrally molding a resin gear on the outer peripheral surface of the nut member.
[0013]
According to a ball screw device of the present invention, as shown in claim 3 , in the above-described claim 1 or 2 , the screw shaft is not rotated with respect to the fixed portion and is not axially fixed, and the nut member and the bracket are When the shaft body is rotatably attached to the shaft body via a rolling bearing, and the shaft body is arranged to be movable in the axial direction, and when torque is applied to the nut member and the bracket The nut member, the bracket, and the shaft body are integrally moved along the screw shaft in the axial direction.
[0014]
In short, in the present invention, the bracket used for supporting the nut member disposed on the outer diameter side of the screw shaft with respect to the shaft body inserted through the center hole of the cylindrical screw shaft is described in the conventional example. As in the case of the heavy cylinder-shaped bracket, the overall axial dimension of the ball screw device can be shortened, and the upper half of the cross section has a simple L-shape, which facilitates manufacture. Moreover, since the tightening allowance of the centering is set for the fitting part between the nut member and the bracket, the thread groove of the nut member is not distorted as in the conventional example using the double cylinder bracket. That's it.
[0015]
In particular, by entering the threads of the nut member from the circumferential direction between the flange portion and the convex portion provided on the bracket, simple as to play without positioning and fixing the bracket and the nut member in the axial direction Since the structure is adopted, it is possible to manage the stop position during the expansion and contraction operation with high accuracy while avoiding unnecessary cost increase.
[0016]
In the invention of claim 2 , since the resin gear is provided on the nut member, torque can be transmitted between the nut member and the external device, and the gear is made of resin. It can be easily manufactured by insert molding or the like.
[0017]
In the invention of claim 3 , it is specified as a usage mode in which the nut member is moved forward and backward while rotating along the screw shaft, that is, a usage mode with a positive efficiency for converting torque into thrust.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described in detail with reference to the embodiments shown in the drawings.
[0019]
1 to 10 show an embodiment of the present invention. 1 is a longitudinal sectional view of the ball screw device, FIG. 2 is a longitudinal sectional view showing a state in which the nut member is moved in one axial direction from the state of FIG. 1, and FIG. 3 is an exploded perspective view of the ball screw device. 4 is a front view of the ball circulation path, FIG. 5 is a side view schematically showing the ball circulation path, FIG. 6 is a perspective view showing a state in which the nut member and the bracket are separated, and FIG. FIG. 8 is a plan view showing a coupling end stage between the nut member and the bracket, FIG. 9 is a perspective view showing a forced stop structure in the shrinking direction of the nut member, and FIG. FIG. 10 is a developed plan view showing a state where the notch of the bracket is engaged with the pin of the screw shaft.
[0020]
In the illustrated ball screw device 1, a nut member 2, a screw shaft 3, a plurality of balls 4, and a cage ring 5 are provided, and a ball 4 is interposed between opposing surfaces of the nut member 2 and the screw shaft 3. It is designed to circulate the group.
[0021]
The nut member 2 is formed with one screw groove 21 continuous from one shaft end to the other shaft end, and the screw shaft 3 has approximately two discontinuous windings in the middle region in the axial direction. Thread grooves 31a and 31b are formed. The screw groove 21 of the nut member 2 and the screw grooves 31a and 31b of the screw shaft 3 are set to have the same lead angle. The cross-sectional shapes of these screw grooves 21, 31a, 31b are gothic arc shapes, but they may be semicircular.
[0022]
By the way, in this embodiment, an overlap region having a predetermined length in the axial direction is secured in a maximum extension state where the nut member 2 and the screw shaft 3 are separated to the maximum, and about two turns of the screw shaft 3 are secured in the overlap region. The screw grooves 31a and 31b are set to be arranged, and the two-turn screw grooves 31a and 31b are set as independent closed loops, and the four groups of balls arranged in the two-turn screw grooves 31a and 31b in the closed loop are arranged. Each of them is circulated independently.
[0023]
Specifically, the two screw grooves 31a and 31b are individually closed loops in the thread (land portion) 32 existing between the two screw grooves 31a and 31b adjacent in the axial direction of the screw shaft 3. Ball circulation grooves 33 and 34 are provided. The two ball circulation grooves 33 and 34 individually connect the upstream side and the downstream side of the two-turn screw grooves 31a and 31b, respectively. The four groups are sunk to the inner diameter side so as to pass over the thread (land portion) 22 of the nut member 2 and return to the upstream side.
[0024]
The cage ring 5 holds the plurality of balls 4 so as to be rotatable by being spaced apart from each other at equal circumferential intervals. The retainer ring 5 is formed of a thin cylindrical member, and is provided with ball holes 51 having a long hole shape along the axial direction at several places on the circumference thereof. The balls 4 are stored one by one.
[0025]
The cage ring 5 is attached in a state where it is positioned so as to be substantially immovable in the axial direction with respect to the outer diameter side of the screw shaft 3 and is relatively rotatable. For this purpose, a reduced diameter portion 35 is provided on one axial end side of the screw shaft 3, and a radially inward flange 52 is provided on one end of the retainer ring 5, and held against the reduced diameter portion 35 of the screw shaft 3. The flange 52 of the device ring 5 is fitted, and the retaining ring 7 is engaged with the circumferential groove provided in the reduced diameter portion 35 of the screw shaft 3. However, the retaining ring 7 is attached to a position away from the step wall surface 36 that is formed at the boundary between the reduced diameter portion 35 of the screw shaft 3 and the portion where the screw groove 21 is formed. The flange 52 of the cage ring 5 is disposed with a slight play in the axial direction. As a result, the cage ring 5 is substantially immovable in the axial direction with respect to the screw shaft 3 and is allowed to rotate relatively.
[0026]
The nut member 2 is integrally coupled to the bracket 8. The bracket 8 is connected to a cylindrical shaft 11 in which a rotational power source such as a motor (not shown) is engaged via a reduction gear 10 and is inserted into the central hole of the cylindrical screw shaft 3 so as to be movable in the axial direction. It is supported via a rolling bearing 12. The screw shaft 3 is supported via a rolling bearing 14 with respect to a rotating shaft 13 that is spline-fitted to the inner diameter side of the cylindrical shaft 11. Although not shown, the rotary shaft 13 is supported so as to be axially stationary and rotatable with respect to a fixed part such as a case. In addition, a pair of flanges 15 and 16 whose opposing surfaces are tapered are provided on one end side in the axial direction of the cylindrical shaft 11 and the rotating shaft 13, and the opposing surfaces of the flanges 15 and 16 are arranged. The distance is adjusted in accordance with the reciprocation of the nut member 2 in the axial direction, so that the winding diameter of the belt 17 wound between the opposing surfaces of the flanges 15 and 16 is changed.
[0027]
This embodiment is characterized by the shape of the bracket 8 and the connecting structure of the nut member 2 to the bracket 8 and will be described in detail below.
[0028]
The bracket 8 is provided with a thick large-diameter portion 82 that bulges outward in the radial direction on one end side in the axial direction of a cylindrical body 81, and the upper half of the bracket 8 is substantially L-shaped. It is manufactured by cold forging a material (for example, JIS standard S20C). Further, on the outer peripheral surface of the thick-walled large-diameter portion 82, a flange 83 that bulges outward in the radial direction is provided at the end edge. Further, a predetermined circumferential position on the outer peripheral surface of the thick-walled large-diameter portion 82 A pin 84 as a convex portion is embedded in a state protruding from the head.
[0029]
As for the coupling of the nut member 2 to the bracket 8, the nut member 2 is arranged in a state of covering the outer diameter side of the body 81 of the bracket 8, and the axis of the nut member 2 with respect to the thick large-diameter portion 82 of the bracket 8. One end in the direction is externally fitted with a tightening margin (intermediate fit) that can be centered. At that time, as shown in FIG. 7, the phase of the pin 84 of the thick large-diameter portion 82 and the one open end of the thread groove of the nut member 2 are matched, and then one of the bracket 8 or the nut member 2 is rotated. However, when it is rotated by a predetermined angle, as shown in FIG. 8, the thread (land portion) 22 between the thread grooves 21 of the nut member 2 is formed in the axial clearance between the pin 84 and the flange 83. At this position, the nut member 2 is coupled to the bracket 8 while being positioned in the axial direction. Moreover, with such a positioning structure, not only the mounting phase of the screw groove 21 of the nut member 2 with respect to the bracket 8 can be easily managed, but also the bracket 8 and the nut member 2 can be coupled only at a predetermined phase. It becomes like this.
[0030]
An annular ridge 23 is provided on the outer peripheral surface of the nut member 2, and a resin gear 9 is formed integrally with the annular ridge 23. In addition, the spline 24 is formed in the outer peripheral surface of this cyclic | annular protruding part 23, and the gear 9 is prevented from rotating.
[0031]
The assembly procedure of the ball screw device 1 having such a configuration will be described. First, the nut member 2 is coupled to the bracket 8. Then, after attaching the cage ring 5 to the screw shaft 3, grease is applied to the ball pocket 51 of the cage ring 5 so as to fill the ball pocket 51. Insert the required number of balls 4. The grease here is urea grease having a viscosity that prevents the ball 4 from falling by its own weight, and the ball 4 is held in the ball pocket 51 with this grease. After that, the cage ring 5 is assembled in the nut member 2 coupled to the bracket 8 in a state where the cage ring 5 is not rotated with respect to the screw shaft 3.
[0032]
Next, the operation of the above-described ball screw device 1 will be described. First, when the bracket 8 and the nut member 2 are rotated by driving a motor (not shown), the nut member 2 itself is linearly moved along the screw shaft 3 toward one axial direction while rotating. For example, the state shown in FIG. 1 is changed to the state shown in FIG. On the other hand, when the motor is driven in the reverse rotation direction, the nut member 2 is moved toward the other axial direction while rotating in the opposite direction to the above, for example, from the state shown in FIG. 2 to the state shown in FIG. It becomes a state.
[0033]
Thus, by reciprocating the nut member 2 in the axial direction, the range in which the nut member 2 and the screw shaft 3 overlap in the axial direction changes in size, but the ball circulation grooves 33 and 34 in the screw shaft 3 change. As a result, the ball group 4 rolls and circulates while being guided by the cage ring 5 in the two-turn thread grooves 31a and 31b of the screw shaft 3 individually closed loops, thereby smoothly guiding the helical motion of the nut member 2. In addition, the phenomenon that the ball 4 comes out can be reliably prevented in the process in which the nut member 2 reciprocates within a predetermined movement stroke range.
[0034]
When the nut member 2 is moved in the contracting direction, the convex portion 18 with respect to the screw shaft 3 as shown in FIGS. 1, 2, and 9 in order to forcibly stop the nut member 2 at a predetermined limit position. Further, a notch 19 is provided with respect to a predetermined circumferential angle range on the inner peripheral surface of the thick-walled small-diameter portion 85 of the bracket 8 integrally coupled with the nut member 2. In this case, when the nut member 2 is moved in the shrinking direction, the notch 19 of the bracket 8 is moved from one end in the circumferential direction as shown in FIG. 10 as the nut member 2 approaches the predetermined stop position. Polymerization starts in the radial direction with respect to the convex portion 18 of the screw shaft 3, and finally the inner wall 19a at the other circumferential end of the notch 19 comes into contact with the peripheral surface of the convex portion 18 from the circumferential direction. As a result, the nut member 2 and the bracket 8 are physically forcibly stopped. In this state, the screw shaft 3 is slightly separated from the thick large-diameter portion 43 of the bracket 8 so as not to interfere.
[0035]
As described above, in this embodiment, the nut member 2 disposed on the outer diameter side of the screw shaft 3 is supported with respect to the tube shaft 11 inserted through the central hole of the cylindrical screw shaft 3. About the bracket 8, like the double cylinder-shaped bracket 8 described in the conventional example, the overall axial dimension of the ball screw device can be shortened, and the upper half of the cross section can be simplified to an L shape. Therefore, manufacturing becomes easy and it can contribute to reduction of manufacturing cost.
[0036]
In addition, since the fitting portion between the nut member 2 and the bracket 8 is set to a tightening allowance of about the centering, the nut member 2 is press-fitted and fitted to the inner periphery of the outer cylinder portion of the double cylinder bracket as in the conventional example. It is possible to reliably avoid the occurrence of distortion in the thread groove 21 of the nut member 2 as in the embodiment, which is advantageous in improving the smoothness of the expansion and contraction operation.
[0037]
Further, by inserting the screw thread 22 of the nut member 2 from the circumferential direction between the flange 83 provided on the bracket 8 and the pin 84, the bracket 8 and the nut member 2 are positioned and fixed without being displaced in the axial direction. Therefore, it is possible to manage the stop position during the expansion and contraction operation with high accuracy while avoiding unnecessary cost increase.
[0038]
In addition, this invention is not limited only to embodiment mentioned above, Various application and deformation | transformation can be considered.
[0039]
(1) In the above embodiment, by providing two ball circulation grooves 33 and 34 on the thread 32 of the screw shaft 3, each of the two winding groove grooves 31a and 31b adjacent in the axial direction is made an independent closed loop. Although the ball group 4 is configured to roll and circulate within the closed loop, the present invention can also be applied to a structure using a conventionally known circulating top. However, with the structure of the above-described embodiment, it is possible to eliminate a highly accurate part known as a circulating top in the past, and to save the trouble of forming a through hole for attaching the circulating top to the nut member 2 and the trouble of assembling the circulating top. In addition to contributing to the reduction of manufacturing costs, it is possible to avoid quality deterioration due to such misalignment, such as the necessity of aligning the ball circulation groove and the screw groove of the circulation top.
[0040]
(2) In the ball screw device 1 described in the above embodiment, one of the nut member 2 and the screw shaft 3 is used, or one of the nut member 2 and the screw shaft 3 is moved by rotating one of the nut member 2 and the screw shaft 3 in the axial direction. The other can be rotated by moving the shaft in the axial direction. The former usage pattern is referred to as normal efficiency for converting torque into thrust, and the latter usage pattern is referred to as reverse efficiency for converting thrust into torque. Hereinafter, four patterns (A-1 to A-4) according to the usage pattern at the normal efficiency and four patterns (B-1 to B-4) according to the usage pattern at the reverse efficiency will be described.
[0041]
(A-1) As explained in the above embodiment, the nut member 2 is moved in the axial direction while rotating. In this case, the nut member 2 may be rotationally driven while the screw shaft 3 is non-rotating and stationary in the axial direction.
[0042]
(A-2) The nut member 2 is moved in the axial direction without rotating. In this case, the screw shaft 3 is fixed in the axial direction, while the nut member 2 is not rotated, and the screw shaft 3 is driven to rotate.
[0043]
(A-3) The screw shaft 3 can be moved in the axial direction while rotating. In this case, the screw member 3 may be rotationally driven while the nut member 2 is non-rotating and stationary in the axial direction.
[0044]
(A-4) The screw shaft 3 is moved in the axial direction without rotating. In this case, the nut member 2 may be rotationally driven while the screw shaft 3 is not rotated and the nut member 2 is fixed in the axial direction.
[0045]
(B-1) The nut member 2 is rotated without moving in the axial direction. In this case, the nut member 2 is fixed in the axial direction, while the screw shaft 3 is not rotated, and the screw shaft 3 is moved in the axial direction.
[0046]
(B-2) The nut member 2 is rotated while being moved in the axial direction. In this case, the nut member 2 may be moved in the axial direction while keeping the screw shaft 3 stationary and non-rotating in the axial direction.
[0047]
(B-3) The screw shaft 3 is rotated without moving in the axial direction. In this case, the screw shaft 3 is fixed in the axial direction, while the nut member 2 is not rotated, and the nut member 2 is moved in the axial direction.
[0048]
(B-4) The screw shaft 3 is rotated while being moved in the axial direction. In this case, the screw member 3 may be moved in the axial direction while the nut member 2 is stationary and non-rotating in the axial direction.
[0049]
【The invention's effect】
The ball screw device according to the first to third aspects of the present invention is for supporting a nut member disposed on the outer diameter side of the screw shaft with respect to a shaft body inserted through the central hole of the cylindrical screw shaft. As for the bracket to be used, like the double cylindrical bracket described in the conventional example, the overall size of the ball screw device can be shortened in particular in the axial direction, and the upper half of the cross section has a simple L shape. Therefore, manufacture becomes easy. In addition, since the tightening allowance is set to about the center of the fitting part between the nut member and the bracket, there is no need to distort the thread groove of the nut member as in the conventional example using a double cylinder bracket. This is advantageous in improving the smoothness of the expansion and contraction operation.
[0050]
In particular, by entering the threads of the nut member from the circumferential direction between the flange portion and the convex portion provided on the bracket, simple as to play without positioning and fixing the bracket and the nut member in the axial direction Since the structure is adopted, it is possible to manage the stop position during the expansion and contraction operation with high accuracy while avoiding unnecessary cost increase.
[0051]
In the invention of claim 2 , since the resin gear is provided on the nut member, torque can be transmitted between the nut member and the external device, and the gear is made of resin. It can be easily manufactured by insert molding or the like, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a ball screw device according to the present invention. FIG. 2 is a longitudinal sectional view showing a state in which a nut member is moved in one axial direction from the state of FIG. FIG. 4 is a front view of the ball circulation path. FIG. 5 is a side view schematically showing the ball circulation path. FIG. 6 is a perspective view showing a state in which the nut member and the bracket are separated. Fig. 8 is a plan view showing the initial stage of coupling with the bracket. Fig. 8 is a plan view showing the stage when the nut member and the bracket are finished coupling. Fig. 9 is a perspective view showing a forced stop structure in the direction in which the nut member is contracted. Plane development showing how the bracket notch is engaged with the shaft pin [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ball screw device 2 Nut member 21 Nut member screw groove 3 Screw shaft 31a, 31b Screw shaft screw groove 4 Ball 8 Bracket 81 Bracket body 82 Bracket thick-walled diameter portion 83 Bracket flange 84 Bracket pin 9 Gear 11 Tube shaft 12 Rolling bearing

Claims (3)

A plurality of balls are interposed between a screw groove provided on the inner peripheral surface of the nut member and a screw groove provided on the outer peripheral surface of the screw shaft, and torque is converted into thrust between the nut member and the screw shaft. Or a ball screw device configured to convert thrust into torque,
The screw shaft has a cylindrical shape, and the nut member is supported via a bracket with respect to a shaft body that is inserted in a central hole of the screw shaft in a non-contact manner.
The bracket has a shape having a thick large-diameter portion that bulges radially outward at one axial end of a cylindrical body,
The nut member is concentrically covered with a predetermined interval on the outer diameter side of the body of the bracket, and the one shaft end of the nut member is centered with respect to the outer peripheral surface of the thick- walled large-diameter portion. It is externally fitted with a tightening allowance and is positioned and fixed in the axial direction,
On the outer peripheral surface of the thick-walled large-diameter portion of the bracket, a flange portion that bulges radially outward is provided on one shaft end side, and a convex portion is provided at a predetermined position on the outer peripheral surface of the thick-walled large-diameter portion. Provided,
Further, one thread groove of the nut member is continuously provided in the entire inner peripheral surface range,
The one end of the nut member is arranged with respect to the thick large-diameter portion of the bracket, and the one open end of the thread groove of the nut member is phase-matched with the convex portion of the thick large-diameter portion. Alternatively, one of the nut members is rotated by a predetermined angle, and the screw thread (land portion) between the thread grooves of the nut member is inserted into the axial clearance between the convex portion and the flange portion of the bracket. A ball screw device characterized in that the nut member is positioned and fixed in the axial direction. The ball screw device according to claim 1, wherein
A ball screw device, wherein a resin gear is integrally formed on an outer peripheral surface of the nut member. The ball screw device according to claim 1 or 2,
The screw shaft is non-rotating with respect to the fixed portion and is not axially fixed, and the nut member and the bracket are rotatably attached to the shaft body via a rolling bearing. Is arranged to be movable in the axial direction,
When torque is applied to the nut member and the bracket, the nut member, the bracket, and the shaft body are integrally moved along the screw shaft in the axial direction. A ball screw device characterized by the above.

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