JP4135422B2 - Manufacturing method of shaft provided with ball screw part - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for rolling a ball screw. In particular, the present invention relates to a technique for ensuring a long effective screw length of a ball screw.
[0002]
[Prior art]
FIG. 1 illustrates a shaft used in a power steering device of an automobile. A small-diameter cylindrical portion A, a ball screw portion B, and a rack tooth portion C are formed on the shaft in order from left to right in FIG. The rack tooth portion C of the shaft is meshed with a pinion provided at the lower end of the column shaft to constitute a rack and pinion mechanism. The ball screw portion B is accommodated in a ball screw nut that is rotated by a motor. When the driver operates the steering wheel, the column shaft rotates, and the shaft is reciprocated in the axial direction by the rack and pinion mechanism. As the shaft reciprocates, the wheels are steered. When the motor rotates the ball screw nut, the ball screw nut applies an axial force to the ball screw portion B, thereby assisting the reciprocation of the shaft.
This type of shaft is required to ensure a long effective screw length of the ball screw portion within a limited length.
[0003]
When manufacturing a shaft, an intermediate material in which a small diameter cylindrical portion A, a cylindrical portion for ball screw rolling having a larger diameter than the small diameter cylindrical portion A, and a rack tooth portion C are manufactured is manufactured. In this case, the rack tooth portion C is a non-rolled portion that is not rolled. Then, the ball screw rolling cylindrical portion of the intermediate material is through-feed rolled from the small diameter cylindrical portion A side to the rack tooth portion C side to complete the ball screw portion B.
[0004]
[Problems to be solved by the invention]
This will be described with reference to FIG. A roll die for rolling a ball screw by rolling a ball screw rolling cylindrical portion has a predetermined length in the axial direction. When the roll die rolls the ball screw rolling cylindrical portion from left to right in FIG. 2, the roll die must be stopped at a position where it does not interfere with the rack tooth portion C. When the roll die is stopped at a position where it does not interfere with the rack tooth portion C, the portion close to the rack tooth C of the cylindrical portion for ball screw rolling is rolled only by a part on the right side of the roll die, and is completely Not plastically deformed. For this reason, it is difficult to form a complete screw shape up to a position very close to the rack tooth portion C, and an incomplete screw portion having a length g1 on the side adjacent to the rack tooth portion C (rolling end side) ( Or an unprocessed area | region) will be formed. This is because the ball screw rolling cylindrical portion is released from elastic deformation when the roll die is retracted, and the outer diameter portion swells greatly. Therefore, there is a problem that the effective length of the ball screw (the length of the complete screw portion) remains at D1, and the length of the shaft is not fully utilized.
[0005]
Therefore, there is a need for a rolling technique that minimizes the length of the incomplete thread that is unavoidably formed on the rolling end side of the ball screw B. If the length of the incomplete thread portion can be shortened to g2, the effective length of the ball screw extends to D2. When the effective length of the ball screw is extended, the axial length of the shaft can be shortened, and the power steering device can be miniaturized.
[0006]
This invention is made | formed in view of said problem, and makes it a subject to implement | achieve the rolling technique which can shorten the length of the incomplete thread part which remains between a ball screw part and a rack tooth part. .
[0007]
[Means for solving the problem, operation and effect]
According to the first aspect of the present invention, the ball screw rolling cylindrical portion and the non-rolled portion are continuous, and the ball screw rolling cylindrical portion is separated from the non-rolled portion of the ball screw rolling cylindrical portion by a predetermined distance. Chamfered side truncated cone part that has an intermediate material that is larger in diameter than the screw bottom and smaller in diameter than the cylindrical part for ball screw rolling. It is a manufacturing method of a shaft provided with the ball screw part which carries out through feed rolling between the roll dies which have. In this manufacturing method, rolling of the intermediate material is started from the side that is not continuous with the non-rolled portion of the cylindrical portion for ball screw rolling . The boundary between the bite-side frustoconical portion and the cylindrical portion of the roll die, Ri position near to interfere with non-rolling unit after passing through the small diameter portion, the cylindrical portion of the roll-dies is non-rolling unit When the ball screw rolling cylindrical portion and the small diameter portion adjacent to each other are in contact with each other and the entire area of the small diameter portion is formed into a complete thread portion, the rolling is finished.
The intermediate material used in the above manufacturing method has a diameter larger than the thread bottom of the ball screw and a position larger than the non-rolled portion of the ball screw rolling cylinder portion by a predetermined distance than the ball screw rolling cylinder portion. It has a small diameter part. Since this small diameter portion is smaller in diameter than the ball screw rolling cylindrical portion, when rolling with a roll die, the amount that the roll die bites into the intermediate material is shallow, and the reaction force from the intermediate material is small. . In other words, the intermediate material is easily deformed plastically by rolling. A ball rolling surface that functions as a screw is formed. Further, since the small diameter portion is larger in diameter than the screw bottom of the ball screw, the screw bottom of the ball screw is surely formed by rolling with a roll die. Therefore, even if the rolling die finishes in a range where it does not interfere with the non-rolled portion, a complete screw is formed as close as possible to the non-rolled portion, and a long effective length of the ball screw can be secured. .
Here, the non-rolled portion means a portion where the ball screw of the shaft is not rolled, and includes a portion that cannot be rolled and a portion that cannot be rolled due to performance, for example, a rack tooth portion. The complete screw means a screw shape that can function as a ball screw.
[0008]
In the manufacturing method of the shaft provided with the ball screw portion described above, the boundary between the biting side truncated cone portion and the cylindrical portion of the roll die is at a position from passing through the small diameter portion of the intermediate material to interfering with the non-rolled portion. Ah it is, the cylindrical portion of the roll dies, in contact with both the ball screw rolling for the cylindrical portion and the small diameter portion adjacent to the non-rolling unit, the rolling at the time when the entire area of the small diameter portion is formed in the complete thread portion finish.
With this end the roll forming, can be the entire area of the small diameter portion in the complete thread portion, to increase the effective length of the ball screw.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 schematically illustrates a process in which the intermediate material 18 is subjected to through-feed rolling with a roll die 10 to complete a ball screw. The intermediate material 18 includes, in order from the left to the right in FIG. 3, a small-diameter cylindrical portion A, a ball screw rolling cylindrical portion 2 having a larger diameter than the small-diameter cylindrical portion A, and a screw bottom of the ball screw to be rolled. A small-diameter portion 6 having a large diameter and smaller than the cylindrical portion 2 for rolling a ball screw and a rack tooth portion C are continuous. With this configuration, the small diameter portion 6 is provided in the vicinity of the rack tooth portion C of the ball screw rolling cylinder portion 2. A tapered portion 4 is formed between the ball screw rolling cylinder portion 2 and the small diameter portion 6 so as to connect the two. Between the small diameter part 6 and the rack tooth part C, the taper part 8 which connects between these is formed.
[0013]
A pair of roll dies 10 exist on both sides of the intermediate material 18, but only one roll die 10 is illustrated in FIG. 3. The roll die 10 includes a cylindrical portion 14 and truncated cone portions 12 and 16 whose diameters are continuously reduced outward at both ends of the cylindrical portion 14. A spiral protrusion (not shown) for rolling the ball screw is formed on the outer periphery of the roll die 10.
The roll die 10 is driven by a drive mechanism (not shown) and rotates about its axis. The axial position of the roll die 10 is fixed. One of the roll dies 10 arranged on both sides of the intermediate material 18 is fixed in the direction perpendicular to the axis, whereas the other roll die 10 is movable in the direction perpendicular to the axis.
[0014]
A series of operations of through-feed rolling will be described with reference to the drawings.
As shown in FIG. 4, in the first operation S10 of through-feed rolling (hereinafter, “operation” is omitted and simply described as S10), the intermediate material 18 is placed at a predetermined position of the rolling device. It is thrown. In S12 following S10, a pair of roll dies 10 (hereinafter referred to as “roll dies R, L” in the description of FIG. 4) is driven, and rotation thereof is started. The roll die R is movable in the direction perpendicular to the axis, and the roll die L is fixed in the direction perpendicular to the axis. In S <b> 14, the roll die R starts to advance in the direction perpendicular to the axis of the roll die with respect to the intermediate material 18. When the roll die R starts to move forward, the distance between the roll die R and the roll die L approaches. In S16, the intermediate material 18 is sandwiched between the roll die R and the roll die L, and rolling of the ball screw is started. When the rolling of the ball screw is started, the intermediate material 18 rotates while being rolled, and is sent out in the axial direction.
[0015]
In S18, the roll die R advances to the advance end position. As roll die R advances to the forward end position, roll die R and roll die L are arranged to maintain a predetermined distance. In this state, the rolling of the intermediate material 18 is continued. In S20, it is detected that the intermediate material 18 has been sent to a predetermined position (a position to be described later, where the roll die 10 is separated from the intermediate material 18 in order to avoid interference with the rack tooth portion C). For this detection, for example, an optical sensor is used. When it is detected that the intermediate material 18 has been sent to a predetermined position, the roll die R starts to be retracted in S22. When the roll die R moves backward, the roll die R moves away from the intermediate material 18. In S24, the roll die R is retracted to the retracted end position. Then, in S26, the rotation of the roll dies R and L is stopped.
[0016]
3A of FIG. 3 has shown the position of the roll die 10 when the distance between roll dies starts approaching. 3B in FIG. 3 shows the roll die position when the rolling is almost finished and the distance between the roll dies 10 starts to separate. When the distance between the roll dies is separated from the position of 10B, the roll dies 10 and the rack tooth portions C do not interfere with each other.
Since the roll die 10 is separated from the intermediate material 18 in order to prevent the roll die 10 from interfering with the rack tooth portion C, the end of the ball screw rolling cylinder portion 2 on the small diameter portion 6 side and the small diameter portion 6 are separated. It is rolled only by part of the part 14. However, since the small diameter portion 6 has a smaller diameter than the ball screw rolling cylinder portion 2, the amount of the roll die 10 biting into the intermediate material 18 is shallow, and the reaction force from the intermediate material 18 is small. For this reason, the intermediate material 18 is easily plastically deformed by rolling, and the small diameter portion 6 is plastically deformed to form a ball rolling surface that functions as a ball screw. Moreover, since the small diameter portion 6 has a larger diameter than the screw bottom of the ball screw, the screw bottom of the ball screw is surely formed. When rolling is performed in this manner, the manufacturing limit of the complete thread portion can be shifted to the rack tooth portion C side, and the length of the incomplete thread portion can be suppressed to g2. Therefore, the effective length of the ball screw can be extended from D1 to D2, which is a limit in the conventional technology.
[0017]
Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
Further, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.
Therefore, it can also be configured as described below, for example.
[0018]
(1) The small diameter portion 6 of the intermediate material 18 is not limited to the shape shown in FIG. For example, a step may be provided as shown in FIG. As shown in FIG. 6, it may be tapered as a whole. As shown in FIG. 7, it may have a curved shape.
[0019]
(2) As shown in FIG. 8, the ball screw rolling cylindrical portion 2, the small diameter portion 6, and the non-rolling portion C of the intermediate material 18 are not continuous, and the ball screw rolling cylindrical portion 2 and the non-rolling cylindrical portion 2 are not connected. The rolling part C may be continuous, and the small diameter part 6 may be provided at a position away from the non-rolling part C of the cylindrical part 2 for ball screw rolling by a predetermined distance. Then, when performing through-feed rolling, the roll die 10 is separated from the roll die 10 at the position where the boundary between the cylindrical portion of the roll die 10 and the truncated cone portion 16 has completely passed through the small diameter portion 6 to complete the rolling. .
When through-feed rolling is performed in this manner, the entire area of the small diameter portion becomes a complete threaded portion, and the effective length of the ball screw can be further increased .
[Brief description of the drawings]
FIG. 1 illustrates an example of a shaft in which the present invention is preferably used.
FIG. 2 is a view for explaining a ball screw dimension of a shaft.
FIG. 3 shows a positional relationship of a roll die with respect to an intermediate material and a ball screw size.
FIG. 4 shows a series of operations of through-feed rolling.
FIG. 5 shows a modified example of a small diameter portion.
FIG. 6 Same as above.
FIG. 7 Same as above.
FIG. 8 shows a positional relationship of a roll die with respect to an intermediate material and a ball screw size.
[Explanation of symbols]
A: Small diameter cylindrical part B: Ball screw part C: Rack tooth part D1, D2: Effective length g1, g2 of ball screw: Length 2 of incomplete thread part: Cylindrical part 4 for ball screw rolling 4: Taper part 6 : Small diameter portion 8: Tapered portion 10: Roll die 12: Frustum portion 14: Column portion 16: Frustum portion 18: Intermediate material

Claims (1)

The ball screw rolling cylinder part and non-rolling part are continuous, and the ball screw rolling cylinder part has a larger diameter than the ball screw thread bottom and a ball screw at a position away from the non-rolling part of the ball screw rolling cylinder part. Rolling through an intermediate material having a smaller diameter part than the rolling cylinder part between the roll dies having a bite-side truncated cone part whose diameter decreases continuously outward from one end of the cylinder part. A manufacturing method of a shaft including a ball screw part to be manufactured,
Rolling of the intermediate material is started from the side that is not continuous with the non-rolled part of the cylindrical part for ball screw rolling, and the boundary between the biting side truncated cone part and the cylindrical part of the roll die passes through the small diameter part. position near to interfere with non-rolling unit from is, the cylindrical portion of the roll dies, in contact with both the ball screw rolling for the cylindrical portion and the small diameter portion adjacent to the non-rolling unit, the whole area of the small-diameter portion A manufacturing method of a shaft provided with a ball screw part , wherein rolling is completed when it is formed into a complete screw part .

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