JP4679451B2 - Ball screw for automobile - Google Patents

Description

  The present invention relates to an automotive ball screw used for an electric power steering or an actuator of an automobile.

  The ball screw is composed of a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, and both opposing screw grooves. A plurality of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circulation path are used as, for example, a motion conversion mechanism that linearly moves the screw shaft by rotating the nut. ing.

  Generally, there are various types of ball screws having different ball circulation mechanisms, one of which is called a piece type. This piece-type ball screw has a threaded groove connection path, and a circulation piece member having a rolling path as a circulation path is mounted on a nut. The piece-type ball screw has an advantage that the configuration is relatively simple and the configuration can be made compact.

As an example of the piece-type ball screw, for example, there is one shown in Patent Document 1. In the actuator device of Patent Document 1, a piece type ball screw is used. In the nut constituting the piece type ball screw, piece holes for arranging the piece members are opened at two places in the front and rear in the axial direction. A pin hole for passing a pin shaft for rotatably locking the link member and the nut is formed between the circulating rows of nuts.
JP 2004-76824 A

  However, conventionally, when machining a piece hole, a tool for machining a piece hole is used, and when machining a pin hole, the tool is replaced with a tool for machining the pin hole. There was a hassle to replace. Therefore, the cycle time at the time of processing becomes longer, leading to an increase in cost.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an automotive ball screw that can reduce the cycle time during processing and can reduce the cost.

In order to achieve such an object, the present invention provides a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral thread groove formed on the inner peripheral surface. , A plurality of balls accommodated in a rolling path formed by opposing screw grooves, a circulating member mounted on the nut and having the rolling path as a circulation path, and a thrust transmission inserted into the nut the pin of use, in a ball screw having a, the nut, the pin hole for passing said pin, said circulation member circulation member bore is provided for placing, circulation member hole and these pin hole And are processed with the same tool and are formed with substantially the same dimensions.

  In the present invention, the pin hole and the circulation member hole are preferably circular holes having substantially the same diameter.

  Further, in the present invention, it is preferable that the pin hole and the circulation member hole are processed to a size obtained by feeding back a dimensional change after the heat treatment.

  Further, in the present invention, it is preferable that the processing of the pin hole and the circulation member hole is performed in the same process as the processing of the thread groove of the ball screw nut without changing the chuck.

According to the present invention, the pin hole and the circulation member hole is processed with the same tool, than have substantially the same diameter, the cycle time during pressure Engineering is shortened, the cost can be reduced. Further, since there is no need to replace the tool, there is no control position error associated with the tool replacement, and highly accurate machining can be performed.

  Further, according to the present invention, since the pin hole and the circulation member hole are circular holes having substantially the same diameter, they can be processed with the same drill or cutting tool.

  Further, according to the present invention, since the pin hole and the circulation member hole are processed to a size that feeds back the dimensional change after the heat treatment, the pin is inserted into the pin hole after the heat treatment, or the circulation member hole When the circulating member is inserted into the ring, it can be accurately inserted without error.

  In addition, according to the present invention, machining can be performed in the same process as the thread groove, and it is not necessary to change the chuck. Therefore, the cycle time at the time of machining is shortened, and the cost can be reduced.

A screw shaft having a spiral thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and a roller formed by both opposing screw grooves. In a ball screw comprising a plurality of balls accommodated in a movement path, a circulation member mounted on the nut and having the rolling path as a circulation path, and a thrust transmission pin inserted into the nut, said nut, a pin hole for passing said pin, said circulation member is circular member hole provided for placing and with these pin holes and circulation member hole is processed in the same tool, substantially the same It is formed with the dimension.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing an embodiment of an automotive ball screw according to the present invention, FIG. 1 (a) is a side view thereof, and FIG. 1 (b) is a front view of a ball screw nut. FIG. 2 is a view showing a ball screw nut, FIG. 2 (a) is a side view thereof, and FIG. 2 (b) is a front view thereof.

  The ball screw 1 includes a ball screw shaft 3 that is rotationally driven by an electric motor (not shown), and a ball screw nut 4 that is screwed onto the ball screw shaft 3 via a ball (not shown). The movement of the ball screw nut 4 in the axial direction is transmitted to the drive shaft 6 as a rotational movement through the swing link 5.

  At the left end of the ball screw shaft 3 in the figure, a coupling engaging portion 12 whose cross section is processed into a substantially square shape is formed. The coupling engaging portion 12 and a motor shaft of an electric motor (not shown) are rotatably connected by a coupling (not shown). By this coupling, the rotation of the motor shaft of the electric motor is transmitted to the ball screw shaft 3.

  A stepped portion 13 having a slightly larger diameter is formed on the right side of the drawing of the coupling engagement portion 12 of the ball screw shaft 3. The stepped portion 13 is press-fitted into the inner surface of a rolling bearing (not shown).

  On the right side of the stepped portion 13 of the ball screw shaft 3, a screw portion 15 having a spiral thread groove formed on the outer periphery is provided. A ball screw nut 4 having a substantially rectangular parallelepiped shape is screwed onto the screw portion 15 via a large number of balls (not shown). A spiral thread groove (not shown) on which the ball rolls is formed on the inner surface of the ball screw nut 4. Circulation member holes 22 and 22 are opened at two locations on the side surface of the ball screw nut 4, and piece members (circulation members) 8 and 8 for circulating the ball are fitted therein. When the motor shaft of the motor rotates, the ball screw shaft 3 connected through the coupling rotates. Then, the ball screw nut 4 moves on the spiral screw portion 15 in the left-right direction in the figure. In this example, a substantially rectangular parallelepiped ball screw nut has been described, but the present invention is not limited to this, and can be applied to, for example, a cylindrical ball screw nut.

  Pins 7 having a substantially cylindrical shape are press-fitted into both side surfaces of the ball screw nut 4. The pin 7 is fitted in a U-shaped notch 5 a at the tip of the swing link 5, and the axial movement of the ball screw nut 4 is driven as a rotational motion via the swing link 5. It is transmitted to the shaft 6.

  A stepped portion 16 having a slightly smaller diameter is formed on the right side of the screw portion 15 of the ball screw shaft 3. The stepped portion 16 is press-fitted into the inner surface of a rolling bearing (not shown). The rolling bearing is press-fitted into a housing (not shown). The ball screw shaft 3 is rotatably supported in the housing by the rolling bearing press-fitted into the stepped portion 13 and the rolling bearing press-fitted into the stepped portion 16.

  As shown in FIGS. 2A and 2B, a circular pin hole 21 into which the pin 7 is inserted is formed in a substantially central portion of both side surfaces of the ball screw nut 4. The pin holes 21 are provided so as to face both side surfaces of the ball screw nut 4. Further, two circular circulation member holes 22 and 22 for installing the piece members 8 and 8 are formed on both sides of the pin hole 21 on one side of the ball screw nut 4.

  In the present invention, the pin hole 21 and the circulation member hole 22 have the same diameter. When designing the pin hole 21 and the circulation member hole 22, first, the required strength is calculated from the use conditions and the like, and the diameter of the pin hole 21 is determined. On the other hand, the circulation member hole 22 into which the piece member 8 is inserted has a high degree of freedom that can be designed by the design operator, and can therefore have a diameter substantially the same as the size of the pin hole 21. Then, a dimensional change after the heat treatment is fed back, and a hole is drilled to a desired size after the heat treatment.

Next, the manufacturing method of the ball screw for cars concerning the present invention is explained.
FIG. 3 is a diagram showing a method for manufacturing a ball screw for automobiles according to the present invention. In FIG. 3, first, a predetermined inner diameter surface is formed by a drill or the like at the center of a cylindrical material (P1). Then, the outer diameter surface and inner diameter surface of the material are finished with a cutting tool (P2).

  Next, the ball rolling groove is cut by so-called point cutting (P3). With point cutting, a general-purpose tool whose cutting edge nose R is smaller than the radius of curvature of the thread groove is used. In this method, the entire thread groove is turned by sequentially shifting the shape in the arc direction.

  In the present invention, the pin hole 21 and the circulation member hole 22 are drilled in the same process as this cutting process without changing the chuck (P3). Specifically, first, the pin hole 21 and the circulation member hole 22 are prepared with the same drill. At this time, when processing the pin hole 21, a through hole is made in one side surface, a drill is inserted as it is, and a through hole is also formed in the other side surface. Next, the pin hole 21 and the circulation member hole 22 are formed in desired dimensions by boring using the same tool. Thereafter, if necessary, taper processing of the circulation member hole 22 is performed.

  Thus, since the pin hole 21 and the circulation member hole 22 can be formed with the same tool without changing the chuck, the time for changing the chuck or changing the tool is omitted, and there is one kind of tool. Therefore, it is possible to save the man-hours for tool management.

  Thereafter, a hardened layer is formed on the surface of the ball screw nut 4 in a range of 54 to 64 HRC by carburizing and tempering (P4). The surface hardening treatment by heat treatment is not limited to this, and tempering treatment or induction hardening may be used, or high-carbon chromium steel such as SUJ2 may be used as the material.

  Then, after the heat treatment, the ball rolling groove 2 is subjected to shot peening treatment (P5). In the present embodiment, steel beads having high hardness as well as specific gravity are used. Thereby, the scale by heat processing can be deleted, surface hardness can be improved, and surface hardness and surface compressive residual stress can be increased. In addition to the steel beads, the treatment may be performed with ceramic beads or glass beads.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The ball screw according to the present invention can be applied to an automotive ball screw used for an electric power steering or an actuator of an automobile.

It is a figure which shows embodiment of the ball screw for motor vehicles based on this invention, Fig.1 (a) is the side view, FIG.1 (b) is a front view of a ball screw nut. FIG. 2 is a view showing a ball screw nut, FIG. 2 (a) is a side view thereof, and FIG. 2 (b) is a front view thereof. It is a figure which shows the manufacturing method of the ball screw for motor vehicles based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ball screw 3 ... Ball screw shaft 4 ... Ball screw nut 5 ... Oscillation link 5a ... Cut-out part 6 ... Drive shaft 7 ... Pin 8 ... Piece member 12 .... Coupling engagement part 13 .... Stepped part 15 .... Screw part 16 .... Step part 21 ... Pin hole 22 .... Circulation member hole

Claims (4)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls housed in a rolling path formed by opposing screw grooves;
A circulating member mounted on the nut and having the rolling path as a circulation path;
A thrust transmission pin inserted into the nut;
In a ball screw with
Said nut, a pin hole for passing said pin, said circulation member is circular member hole provided for placing and with these pin holes and circulation member hole is processed in the same tool, substantially the same A ball screw characterized by being formed with the dimensions of   The ball screw according to claim 1, wherein the pin hole and the circulation member hole are circular holes having substantially the same diameter.   3. The ball screw according to claim 1, wherein the pin hole and the circulation member hole are processed to a size obtained by feeding back a dimensional change after heat treatment. The ball screw according to any one of claims 1 to 3, wherein the processing of the pin hole and the circulation member hole is performed in the same process as the processing of the thread groove of the ball screw nut without changing the chuck. .

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