JP2006226314A - Piece type ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piece type ball screw capable of firmly fixing a piece member on a nut easily and quickly with good workability and of performing reliable fixing of the piece member at low cost. <P>SOLUTION: This piece type ball screw is provided with a ball screw shaft, a nut, a plurality of balls arranged in a rolling way formed between screw grooves opposing the ball screw shaft and the nut in a row and a plurality of piece members including a connection groove connecting the screw grooves of the nut. The piece member 4 is fitted in a piece window provided on the nut from a nut outer diameter side. A tapered shape rib part 4a of which projection height in a nut center side gets lower is provided with extending in a piece window depth direction on an outer circumference surface of the piece member 4 provided in parallel with an inner circumference surface of the piece window. The rib part 4a and the piece window inner circumference surface are projection-welded under a condition where the piece member 4 is fitted in the piece window. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a top-type ball screw used for an actuator for an automobile and other various devices.

  The top-type ball screw uses a top member having a connecting groove for connecting the screw grooves of nuts as a circulating member for circulating the ball. The top-type ball screw is excellent in compactness of the outer diameter of the nut, and the top member can be equally distributed in the circumferential direction, providing excellent dynamic balance when driven by nut rotation. Often done. In particular, in applications such as automobile actuators, the space-based restriction is large and the demand for compactness is strong, so the top ball screw is effective.

In the top-type ball screw, the top member is a member having a three-dimensional groove that circulates the ball as the connecting groove, and how this top member can be fixed with low cost and high reliability. Is important. That is, it is necessary to reliably fix the top member to the nut so that the top member does not fall off the nut due to the action of the radial force from the ball. For this reason, various fixing structures have been proposed.
For example, a top member is inserted into a top window provided on the nut from the outer diameter side of the nut, and the boundary portion between the top surface of the top member and the top surface of the top window is welded all around the contour of the top member by laser welding. Thus, there is one in which the top member is fixed (for example, Patent Document 1).

As another example, there has been proposed one in which a wing portion that engages with a thread groove of a nut is provided integrally with a top member and the top member is positioned with respect to the nut (for example, Patent Document 2).
JP 2003-28567 A JP 2001-132911 A

However, in the top-type ball screw disclosed in Patent Document 1, if the entire circumference of the top member is to be welded accurately, the cycle time becomes long and the cost increases. In addition, since there is a slight gap between the top window and the top member in order to insert the top member into the nut top window, the nut is inserted by indexing the nut in the circumferential direction prior to welding. A special holding jig is required to hold the top member so that it does not come out of the top window during work. Therefore, there is a problem that the work becomes complicated.
Further, in the case of the top ball screw disclosed in Patent Document 2, the shape of the top member is complicated and the wing portion needs to be formed with high accuracy, so that general sintering cannot be employed, and MIM ( It is necessary to form a top member by metal injection molding), resulting in an increase in cost.

  An object of the present invention is to provide a top-type ball screw that can fix a top member to a nut simply, quickly and firmly with good workability, and that can reliably fix the top member at a low cost. It is.

  The top type ball screw of the present invention includes a ball screw shaft, a nut, a plurality of balls arranged in a rolling path formed between the thread grooves facing the ball screw shaft and the nut, and the nut. A plurality of top members having connecting grooves for connecting the thread grooves, the top members being a top type ball screw fitted to the top window provided on the nut from the nut outer diameter side; A tapered rib portion having a lower protrusion height on the nut center side is provided on the outer peripheral surface of the top member provided in parallel with the inner peripheral surface so as to extend in the depth direction of the top window, and the rib portion and the top window are provided. It is characterized by projection welding the inner peripheral surface.

According to this structure, since the rib part was provided in the outer peripheral surface of the top member, the fitting part of the top member is limited to the partial rib part instead of the whole periphery of an outer peripheral surface. Therefore, strict dimensions between the top member and the top window are not required compared to the case of press-fitting a flat outer shape top member that does not have such a rib portion, and even if the press-fitting allowance is somewhat large, the top member is not required. The press-fit operation when press-fitting into the top window does not increase greatly, and the press-fit operation can be completed in a short cycle time. Further, the position of the top member can be fixed even if the press-fitting allowance is small. Since the rib portion has a tapered shape in which the protruding height on the nut center side is lowered, workability when inserting the top member into the top window from the outer diameter surface side of the nut is further improved.
In addition, as a final process for increasing the pull-out strength of the top member with respect to the top window, since projection welding is performed, a firm fixing strength can be obtained. In this case, because projection welding is adopted, the rib portion of the top member that comes into contact with the inner peripheral surface of the top window in the press-fitted state becomes a current application portion, and there is no need to separately provide a projection for welding. It is. In addition, because of projection welding, welding can be performed at a lower cost compared to all-around welding by laser welding.
Also in the manufacture of the top member, it is only necessary to provide the rib portion on the top member. Therefore, the shape is simple, the top member can be manufactured by general sintering, and can be manufactured at low cost.
For these reasons, the top member can be fixed to the nut easily, quickly and firmly with good workability, and the top member can be fixed with high reliability at low cost.

  In the present invention, the cross-sectional shape of the top member taken along a plane parallel to the nut axis may be an oval shape, and a plurality of the rib portions may be provided. When a plurality of rib portions of the top member are provided, the pressure input is dispersed when the top member is press-fitted into the top window, and the press-fitting can be easily performed.

The assembly method of the top type ball screw of the present invention is a method of assembling the top type ball screw of the present invention, and when the top member is inserted into the nut, it fits over the connecting groove of the top member and the thread groove of the nut. The top member is inserted to a position where the step between the connecting groove of the top member and the screw groove of the nut becomes zero using a jig to be inserted.
According to this assembling method, when the top member is inserted into the top of the nut, the jig is fitted over the connecting groove of the top member and the screw groove of the nut. It can be accurately inserted to the position where the step with the screw groove of the nut becomes zero. As a result, the ball connection between the connecting groove and the thread groove becomes extremely smooth, and a top type ball screw having excellent acoustic characteristics can be configured.
For example, when a top ball screw is used for EPS (electric power steering system), the step between the screw groove of the nut and the connecting groove of the top member is brought to zero as much as possible from the viewpoint of improving acoustic characteristics. is important. According to the assembling method of the present invention, such a demand can be satisfied.

The top type ball screw of the present invention includes a ball screw shaft, a nut, a plurality of balls arranged in a rolling path formed between the thread grooves facing the ball screw shaft and the nut, and the nut. A plurality of top members having connecting grooves for connecting the thread grooves, and the top member is a top type ball screw fitted to the top window provided on the nut from the nut outer diameter side. A tapered rib portion with a lower protrusion height on the nut center side extending in the depth direction of the top window is provided on the outer peripheral surface of the top member provided in parallel with the peripheral surface. Since the peripheral surface is projection-welded, the top member can be fastened to the nut simply, with good workability, and firmly, and the top member can be fixed with high reliability at low cost.
The assembly method of the top type ball screw of the present invention is a method of assembling the top type ball screw of the present invention, and when the top member is inserted into the nut, it fits over the connecting groove of the top member and the thread groove of the nut. The jig member is inserted until the step between the coupling groove of the top member and the screw groove of the nut becomes zero, so that the ball between the screw groove of the nut and the coupling groove of the top member is inserted. The connection becomes extremely smooth, and the acoustic characteristics can be improved and the vibration can be reduced.

  An embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the top ball screw includes a ball screw shaft 1, nuts 2, and a plurality of balls 3. The nut 2 is configured by attaching a top member 4 to a nut body 2a. The ball screw shaft 1 has a thread groove 5 on the outer periphery. The nut 2 has a screw groove 6 facing the screw shaft screw groove 5 on the inner periphery of a nut body 2a formed in a cylindrical shape. The ball 3 is arranged continuously to a rolling path 7 formed between the screw groove 5 of the ball screw shaft 1 and the screw groove 6 of the nut 2.

  The top member 4 is a member provided with an S-shaped connecting groove 8 for connecting adjacent ones of the screw grooves 6 of the nut 2, and the cross-sectional shape taken along a plane parallel to the nut axis is an oval shape. (That is, a shape composed of a pair of parallel straight lines and two arcs connecting both ends thereof). The thread groove 6 of the nut 2 is connected by the connection groove 8 to form a continuous circulation path of one turn. The depth of the connecting groove 8 is such that the ball 3 can exceed the thread of the screw groove 5 of the ball screw shaft 1 in the connecting groove 8. 2 shows a partial cross-sectional view of the nut 2, and FIGS. 3A and 3B show a perspective view and a side view of the top member 4. The nut body 2a is provided with a top window 11 penetrating the inner and outer peripheral surfaces, and the top member 4 is inserted into the top window 11 from the outer diameter side. The shape of the top window 11 is a shape in which the cross-sectional shape at an arbitrary position in the depth direction is constant, and the cross-sectional shape is an oval shape.

  The outer peripheral surface of the top member 4 is provided in parallel with the inner peripheral surface of the top window 11, and a tapered rib portion 4 a whose protruding height on the nut center side is lowered on the outer peripheral surface is the depth direction of the top window 11. A plurality of lines are provided so as to extend. Here, the number of the rib portions 4a is 4 to 6, but the number is not limited and can be appropriately set according to the size of the top member 4. In the example of FIG. 3, two rib portions 4 a are provided on each of a pair of parallel planar portions on the outer peripheral surface of the top member 11.

  The top member 4 is press-fitted and fitted by being inserted into the top window 11 of the nut body 2a from the outer surface side as shown in FIG. The top member 4 thus positioned is further welded and fixed to the nut body 2a. In this welding process, projection welding is used.

In the operation of inserting the top member 4 into the top window 11 of the nut body 2a, as shown by the crossing in FIG. 5, a jig that fits over the connecting groove 8 of the top member 4 and the thread groove 6 of the nut body 2a. 12 is arranged on the inner diameter side of the nut. The jig 12 has a convex cross section along the cross sectional shape of the connecting groove 8 and the screw groove 6. Both ends of the jig 12 are fitted into the thread groove 6 so as not to move on the nut body 2a, and the top member is moved to a position where the connecting groove 8 of the top member 4 contacts the jig 12 without a gap. 4 is inserted.
Thereby, the top member 4 can be accurately inserted to a position where the step between the connecting groove 8 and the thread groove 6 of the nut body 2a becomes zero.

  According to the top type ball screw having this configuration, a tapered rib portion 4a having a lower protrusion height on the nut center side is provided on the outer peripheral surface of the top member 4 so as to extend in the depth direction of the top window 11, and the top member Since the rib 4a and the inner peripheral surface of the top window 11 are projection welded after the 4 is press-fitted into the top window 11 and positioned, the top member 4 can be easily, quickly and firmly fixed with good workability. The top member 4 can be fixed with high reliability at a low cost.

That is, when a generally flat top member having no rib portion 4a is press-fitted into the top window 11, dimensional control becomes very difficult, and the space between the inner peripheral surface of the top window 11 and the outer peripheral surface of the top member is difficult. If there is a gap in the top, positioning of the top member becomes difficult. On the contrary, if the press-fitting allowance is too large, not only the top member cannot be inserted into the top window 11, but also an excessive tensile stress is applied to the nut body 2a, which may cause a crack.
On the other hand, when the rib portion 4a is provided on the outer peripheral surface of the top member 4 as in this embodiment, the fitting portion of the top member 4 is limited to the partial rib portion 4a, not the entire circumference of the outer peripheral surface. Therefore, the press-fit operation when press-fitting the top member 4 into the top window 11 does not increase, and the press-fit operation can be completed in a short cycle time. In addition, since a plurality of rib portions 4a are provided in a distributed manner in the circumferential direction of the top member 4, the pressure input is distributed and press-fitting can be easily performed.
Moreover, since the rib part 4a is made into the taper shape from which the protrusion height of the nut center side becomes low, workability | operativity in the case of inserting the top member 4 into the top window 11 from the outer-diameter surface side of the nut main body 2a is more. improves.

Further, as a final process for increasing the pull-out strength of the top member 4 with respect to the top window 11, projection welding is performed, so that a strong fixing strength can be obtained. In this case, the rib portion 4a of the top member 4 that is in contact with the inner peripheral surface of the top window 11 in the press-fitted state becomes the current application portion as it is. Therefore, there is no need to separately provide a projection for welding, which is reasonable. That is, the rib portion 4a serves both as a means for facilitating press-fitting and as a projection for projection welding, and a simple shape is sufficient.
Further, the shape of the top member 4 is not complicated unlike the case of the top member having the wing portion, and therefore, it can be easily formed by general sintering regardless of the MIM, and the cost can be reduced also in this respect.

  Further, when this top type ball screw is used for EPS (electric power steering), the acoustic characteristics are improved by making the step between the screw groove 6 of the nut 2 and the connecting groove 8 of the top member 4 as close as possible to zero. It is important from the viewpoint of improvement. In response to such a demand, as described above, in the assembly of the top ball screw, when the top member 4 is inserted into the top window 11 of the nut body 2a, the connecting groove 8 of the top member 4 and the nut body A jig 12 (FIG. 5) to be fitted over the thread groove 6 of 2a is disposed on the inner diameter side of the nut. Therefore, the top member 4 can be accurately inserted to a position where the step between the connecting groove 8 and the thread groove 6 of the nut body 2a becomes zero. As a result, the connection of the ball 3 between the connecting groove 8 and the thread groove 6 becomes extremely smooth, and a top ball screw having excellent acoustic characteristics can be configured.

(A) And (B) is the front view and sectional drawing of the top-type ball screw concerning one Embodiment of this invention. It is a fragmentary sectional view of the nut in the same top type ball screw. (A) And (B) is the perspective view and side view of the top member in the top type ball screw. It is an expanded sectional view which shows the attachment state to the nut of a top member. It is explanatory drawing of the operation | work which inserts a top member into a top window using a jig | tool.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ball screw shaft 2 ... Nut 2a ... Nut main body 3 ... Ball 4 ... Top member 4a ... Rib part 5 ... Screw groove 6 of a ball screw shaft ... Screw groove 7 of a nut ... Rolling path 8 ... Connecting groove 11 ... Top window 12 ... Jig

Claims (3)

A ball screw shaft, a nut, a plurality of balls arranged in series with a rolling path formed between screw threads facing the ball screw shaft and the nut, and a connecting groove for connecting the screw grooves of the nut to each other; A plurality of top members, the top member is a top type ball screw fitted to the top window provided in the nut from the nut outer diameter side,
On the outer peripheral surface of the top member provided in parallel with the inner peripheral surface of the top window, a tapered rib portion having a lower protrusion height on the nut center side is provided extending in the top window depth direction, and the rib A top-type ball screw characterized by projection welding the part and the inner peripheral surface of the top window.   The top-type ball screw according to claim 1, wherein a cross-sectional shape of the top member taken along a plane parallel to the nut axis is an oval shape and a plurality of the rib portions are provided.   A method for assembling the top ball screw according to claim 1 or 2, wherein a jig that fits between the connecting groove of the top member and the thread groove of the nut is used when the top member is inserted into the nut. An assembly method of a ball type ball screw, wherein the top member is inserted to a position where the step between the coupling groove of the top member and the screw groove of the nut becomes zero.

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