JP2005299721A - Automobile ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automobile ball screw with a ball having smooth circulation to achieve less torque fluctuation, superior transmitting efficiency and higher strength and productivity. <P>SOLUTION: The ball screw 1 to be used for any kind of automobile actuator comprises a screw stem 2, a nut 3, and a ball 6 laid between screw grooves 4, 5 formed in the opposite faces of the screw stem 2 and the nut 3. A circulation form depends on a piece member 7. The screw groove 4 of the screw stem 2 is subjected to rolling forging. On a shoulder portion of the screw groove 4 of the screw stem 2, a chamfering portion 20 in a sectionally circular arc shape is formed at the same time with rolling forging. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ball screw for an automobile used for an actuator such as an electric power steering device and an automatic manual transmission (AMT).

2. Description of the Related Art Conventionally, a ball screw has been proposed in which a chamfered portion having an arcuate cross section is provided on a shoulder portion of a screw groove of a screw shaft (for example, Patent Document 1). This is to avoid the possibility of causing damage when the ball circulates while colliding with the shoulder of the thread groove at a high speed, thereby extending the life.
JP 2002-266976 A

The above-described conventional example is a device made for the characteristics required during high-speed operation of a ball screw used in a machine tool or a general industrial machine due to an increase in the speed of the machine.
In the application of ball screws for automobiles, characteristics different from those of machine tools and general industrial machines that are operated at high speed are required. That is, an apparatus that is directly operated by a human hand such as an electric power steering is required to operate with little torque fluctuation so as not to impair the steering feeling. In addition, when used as an actuator such as an automatic manual transmission (AMT) or an electric brake, it must be compatible with electronic control or have a high efficiency for obtaining a larger thrust, that is, no mechanical loss. Desired.
In addition, the ball screw for automobiles is strongly demanded for safety, and is further required to have excellent productivity for cost reduction.

  An object of the present invention is to provide a ball screw for an automobile in which the circulation of the ball is smooth, the torque fluctuation is small, the transmission efficiency is excellent, the strength and the productivity are excellent.

  The automotive ball screw of the present invention is a ball screw used in an automotive actuator, and is interposed between a screw shaft and a nut in which screw grooves for rolling the ball are opposed to each other, and the opposed screw grooves. And a thread groove of the screw shaft is formed by rolling, and a chamfer having an arc-shaped cross section is formed on a shoulder portion where the inner surface of the screw groove of the screw shaft is continuous with the outer surface of the screw shaft. The portion is formed by the rolling process.

According to the ball screw for automobiles of this configuration, since the chamfered portion having a circular cross section is formed on the shoulder portion of the screw groove of the screw shaft, the ball is circulated over the land portion between the screw grooves. Circulation is smooth, torque fluctuation is small, and transmission efficiency is excellent. If the chamfered portion is provided, the noise level is also reduced. Therefore, for example, in an automobile application where acoustic characteristics are required, such as an electric power steering device, the required characteristics can be satisfied.
Moreover, since this screw shaft is formed by rolling, it is excellent in productivity. In this case, in order to perform a cold rolling process using a roll die, by providing an arc-shaped section in a portion corresponding to the thread groove shoulder as a screw shaft product of the roll die, A chamfered portion having an arcuate cross section is formed. Thus, by providing a roll die with an arc-shaped section and rolling the chamfered portion of the shoulder at the same time as the thread groove, the material of the thread groove portion of the screw shaft is plastically flowed. When the meat swells, it is effective for preventing local concentration of force, preventing cracking, or reducing the amount of spring back and processing with high accuracy. By this rolling method, it is possible to easily form an arc-shaped chamfered portion of an arbitrary size on the shoulder of the screw groove of the screw shaft. Manufacturing is suitable for both cost and performance due to improved productivity.

  In consideration of this formability and operability when an actual ball screw is rotated, the radius of curvature of the arc-shaped chamfered portion may be in the range of 2.5 to 25% of the radius of the ball. preferable. If it exceeds 25%, the contact ellipse, which is the stress generation range of the inner surface of the thread groove generated by pressing the ball, increases the amount of interference with the chamfered portion of the thread groove, which may cause a short life. On the other hand, if it is less than 2.5%, the chamfered portion is too small, and various effects obtained by providing the chamfered portion cannot be sufficiently obtained.

  In addition, when using a threaded shaft that is rolled, it is indispensable to manage the shape of the seaming portion that is the material unsatisfied portion of the land portion. If the seaming part is large, the ball may fall when the ball gets over the land part, and the smooth operation is hindered. Therefore, it is important not only to provide a chamfered portion but also to manage the dimensions of the seaming portion. By making the seaming portion ½ or less of the axial length of the land portion, a smooth ball motion can be obtained.

The above-mentioned effects are particularly effective when the circulation type of the automobile ball screw according to the present invention is a piece type, that is, when a piece member that connects screw grooves of nuts is provided.
In the ball screw for automobiles, a piece type is often adopted as a circulation method because of the compactness of the nut and the feature that the circulation part can be arranged in the same manner when the nut rotates. In this circulation method, when the ball circulates, it circulates over the land portion of the screw shaft while being constrained by the space in the piece. For this reason, effects such as smoothing by effectively providing a chamfered portion having an arcuate cross section at the shoulder portion of the thread groove of the screw shaft and reducing the dimension of the seaming portion to 1/2 or less are effectively exhibited.

  The automotive ball screw according to the present invention is a ball screw used for an automotive actuator, wherein the threaded groove of the threaded shaft is rolled, and the inner surface of the threaded groove of the threaded shaft is outside the threaded shaft. Since the chamfered portion with a circular arc cross section is formed by the rolling process on the shoulder that continues to the radial surface, the ball circulation is smooth, torque fluctuation is small, transmission efficiency is excellent, and strength , And productivity is also excellent.

  A first embodiment of the present invention will be described with reference to FIGS. This ball screw 1 is a piece type ball screw used for an actuator for an automobile, and includes a screw shaft 2 and a nut 3, and screw grooves 4 and 5 formed on opposing surfaces of the screw shaft 2 and the nut 3. It consists of balls 6 interposed therebetween. The screw grooves 4 and 5 are spiral grooves that roll on the ball 6. The automobile actuator using the automobile ball screw 1 of this embodiment is used for an automatic manual transmission (AMT) of an automobile, but in addition to this, an electric power steering, a rear wheel steering device, an electric motor for an automobile. It may be used for a brake or the like.

  The nut 3 is provided with a piece member 7 as a part for circulating the ball 6. The piece member 7 is fitted into a fitting opening 8 formed in the nut 3 so as to penetrate the inner and outer surfaces, and one piece of connection for connecting adjacent circumferential portions of the helical thread groove 5 of the nut 3. It is a member in which the groove 9 is formed on the inner surface. By this connecting groove 9, a spiral ball rolling path formed between the screw shaft 2 and the threaded grooves 4 and 5 of the nut 3 becomes a circular path, and the ball 6 circulates and moves along this circular path. When the ball 6 passes through the connecting groove 9, the ball 6 gets over the thread of the screw groove 4 of the screw shaft 2.

  As shown in FIG. 4, the piece member 7 has a pair of wing portions 10 that engage with the thread grooves 5 of the nut 3 and a pair of crimping portions 11 that are fixed to the outer diameter portion of the nut 3. doing. The piece member 7 is fixed to the nut 3 by the engagement from the inner diameter side of the wing portion 10 and the caulking from the outer diameter side of the caulking portion 11.

  As shown in FIG. 3, the nut 3 has a pair of trunnion shaft portions 14 on the outer peripheral surface. The screw shaft 2 has a coupling fitting portion 13 at one end and a bearing fitting portion 15 at the other end.

  In such a piece-type automotive ball screw 1, in this embodiment, the thread groove 4 of the screw shaft 2 is formed by rolling. Further, as shown in FIG. 1B in an enlarged manner, a chamfered portion 20 having a circular arc cross section is formed on the shoulder portion where the inner surface 4a of the screw groove 4 of the screw shaft 2 continues to the outer surface 2a of the screw shaft. 4 are formed simultaneously by the rolling process.

The curvature radius r of the chamfered portion 20 is in the range of 2.5 to 25% of the radius R of the ball 6. In the land portion 21 formed of the outer diameter surface 2a between the adjacent screw grooves 4 of the screw shaft 2, a circumferential groove-shaped seaming portion 22 which is an unsatisfied portion of the material is generated by rolling. The axial length b of the seaming portion 22 is set to ½ or less of the axial length a of the land portion 21.
Since the chamfered portion 20 is provided, the axial length of the land portion 21 is the length when the chamfered portion 20 is omitted. In addition, the axial length b of the seaming portion 22 is a length between positions where dents start to be generated from the outer diameter surface of the land portion 21.

As shown in FIG. 5, the rolling process of the thread groove 4 of the screw shaft 2 is performed by sandwiching a round bar-shaped material W supported by a support base 34 so as to be rotatable and reciprocated between a pair of roll dies 35. This is done by rotating the die 35. The roll die 35 has a plurality of spiral ridges 35a for rolling on the outer peripheral surface.
As shown in FIG. 6, the chamfered portion 20 having a circular arc shape of the thread groove 4 in FIG. 1 is provided with a die portion 35 b having a circular arc shape corresponding to the chamfered portion 20 on the roll die 35. At the same time as the thread groove 4, it is rolled.

  According to the ball screw 1 for an automobile having this configuration, since the chamfered portion 20 having an arcuate cross section is formed on the shoulder portion of the screw groove 4 of the screw shaft 2, the ball 6 circulates over the land portion 20. The balls 6 are smoothly circulated, torque fluctuation is small, and transmission efficiency is excellent. That is, when the ball 6 passes through the piece member 7, it circulates over the land portion 20 while being restrained in the connecting groove 9 of the piece member 7. The movement of the ball 6 during the circulation is smoothly performed by the chamfer 20. When the chamfered portion 20 is provided, the noise level is also reduced. Therefore, for example, in an automobile application where acoustic characteristics are required, such as an electric power steering device, the required characteristics can be satisfied.

Moreover, since this screw shaft 2 is formed by rolling, it is excellent in productivity. In this case, the chamfered portion 20 is simultaneously formed with the screw groove 4 by providing the roll die 35 with the above-described arc-shaped mold portion 35b (FIG. 6) in a portion corresponding to the shoulder portion of the screw shaft product. It is formed. In this way, rolling the die chamfered portion 20 at the same time as the screw groove 4 while providing the roll die 35 with the circular arc-shaped mold portion 35 b becomes the screw groove 4 of the screw shaft 2. When the material of the part is plastically flowed and the meat is raised, it is effective to prevent local concentration of force, to prevent cracking, or to reduce the amount of springback and to perform processing accurately.
By this rolling method, it is possible to easily form an arc-shaped chamfered portion 20 having an arbitrary dimension on the shoulder of the screw groove of the screw shaft 2, and therefore in the processing of the screw shaft 2 of the automotive ball screw 1. The above rolling process is suitable for both performance and cost due to productivity improvement.

  In consideration of this formability and the operability when the actual ball screw 1 is rotated, the radius of curvature r of the chamfered portion 20 is in the range of 2.5 to 25% of the radius R of the ball 6. Is preferred. If it exceeds 25%, the contact ellipse P, which is the stress generation range of the inner surface of the thread groove caused by the ball 6 being pressed, increases the amount of interference with the chamfered portion 20 of the thread groove 4, and may cause a short life. There is. Moreover, if it is less than 2.5%, the chamfered portion 20 is too small, and various effects obtained by providing the chamfered portion 20 cannot be sufficiently obtained.

  In addition, when using the threaded shaft 2 that is rolled, it is essential to manage the shape of the seaming portion 22 that is an unsatisfied portion of the land portion 21. If the seaming portion 22 is large, the ball 6 may drop when the ball 6 gets over the land portion 21, and the smooth operation is hindered. Therefore, it is important not only to provide the chamfered portion 20 but also to manage the dimensions of the seaming portion 22. By making the seaming portion 22 to be 1/2 or less of the axial length a of the land portion 21, a smooth movement of the ball 6 can be obtained.

  7 to 9 show an example of a shift mechanism in an automatic manual transmission (AMT) using the ball screw 1 according to this embodiment. The shift mechanism 30 shifts, in other words, shift gears (not shown) by moving a plurality of arbitrary shift rails 32 installed in parallel in the housing 31 in the longitudinal direction (Y direction). ) Is switched. Each shift rail 32 has a notch 32a, and the shift finger 33 of FIG. 8 can be engaged therewith. By the engagement / disengagement of the shift finger 33, the shift rail 32 to be advanced / retreated is selected.

  The first motor 34 and the first ball screw 36 are used to move the shift finger 33 forward and backward for the selection. Further, the second motor 35 and the second ball screw 37 of FIG. 9 are used for the operation of swinging the shift finger 33 and moving the shift rail 32 forward and backward. As the first and second ball screws 36 and 37, the automotive ball screw 1 of the above embodiment is used. However, the first ball screw 36 does not have the trunnion shaft portion 14 for the nut 3 and is provided with the engagement groove 16.

  In FIG. 8, the first shaft member 38 is installed in the housing 31 so as to be able to advance and retreat, and a sleeve 39 is fitted to the outer periphery thereof so that it can only advance and retreat. The sleeve 39 can rotate integrally with the first shaft 38. The shift finger 34 is provided on the sleeve 39. The screw shaft 2 of the first ball screw 36 is disposed in parallel with the first shaft member 38 and is rotatably supported by the housing 31. One end of the screw shaft 2 is coupled to the output shaft of the first motor 34. It is connected via 40 so that rotation can be transmitted. The nut 3 of the ball screw 36 has an engagement groove 16, and an engagement piece 41 provided on the sleeve 39 engages with the groove 16 in the nut advance / retreat direction. For this engagement, when the screw shaft 2 of the ball screw 36 is rotated by the motor 34, the nut 3 is advanced and retracted, and the sleeve 39 and the shift finger 33 can be advanced and retracted together with the nut 3. By this advance and retreat, the shift finger 33 can be engaged with the notch 32a of any shift rail 32.

  In FIG. 9, the screw shaft 2 of the second ball screw 37 is rotatably installed on the housing 31 and is connected to the output shaft of the motor 35 via a coupling 42 so as to be able to transmit the rotation. The trunnion shaft portion 14 provided on the nut 3 of the ball screw 37 is engaged with an engagement notch 44 a provided on the lever 44. The lever 44 is integrally fixed to a rotation shaft 46 that is rotatably supported on the housing 31 by a support portion 45, and can swing forward and backward around the axis of the rotation shaft 46. When the screw shaft 2 of the second ball screw 37 is rotated by the second motor 35, the nut 3 advances and retracts, and the rotation shaft 46 is rotated together with the lever 44 by the advance and retreat of the nut 3. The rotation shaft 46 is provided in parallel with the first shaft 38 in FIG. 8, and the rotation can be transmitted to the first shaft 38 via a drive transmission means (not shown) such as a lever. . For this reason, the screw shaft 2 of the second ball screw 37 is rotated by the second motor 35, and the nut 3 is advanced and retracted thereby, via the lever 44, the rotating shaft 46, and the first shaft 38. Thus, the sleeve 39 is rotated. By the rotation of the sleeve 39, the shift rail 32 engaged with the shift finger 34 is advanced and retracted, and a switching operation of a transmission gear (not shown) can be performed.

  In the above embodiment, the circulation type of the automotive ball screw 1 is a piece type, but the present invention can be applied regardless of the circulation type. For example, an end cap type, a guide plate type, a return tube type, etc. It can also be applied to a ball screw.

(A) is a partially omitted sectional view of a ball screw according to an embodiment of the present invention, and (B) is a partially enlarged sectional view showing a screw shape of the screw shaft. It is a front view of the ball screw. It is a partial expansion perspective view of the land part of the screw shaft. (A)-(C) are the partial expanded views which respectively show the piece member fitting part of a nut, the longitudinal cross-sectional view of the piece member fitting part of the nut, and the schematic perspective view of the same piece member. It is a fracture front view of a rolling processing equipment. It is a partial enlarged front view of the roll die. It is a top view of the switching mechanism of the manual manual transmission using the ball screw. It is an AA line expanded sectional view of FIG. It is a BB line expanded sectional view of Drawing 8.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ball screw 2 ... Screw shaft 3 ... Nut 4, 5 ... Screw groove 6 ... Ball 7 ... Piece member 20 ... Chamfer part 21 ... Land part 22 ... Seaning part

Claims (4)

  A ball screw used in an actuator for an automobile, comprising: a screw shaft and a nut formed with opposing screw grooves for rolling the ball; and a plurality of balls interposed between the opposing screw grooves, The thread groove of the screw shaft is formed by rolling, and the chamfered portion having an arc-shaped cross section is formed by the rolling process on the shoulder portion where the inner surface of the screw groove of the screw shaft continues to the outer diameter surface of the screw shaft. An automotive ball screw characterized by the above.   The automotive ball screw according to claim 1, wherein a radius of curvature of the arc-shaped chamfered portion is in a range of 2.5 to 25% of a radius of the ball.   The automobile according to claim 1 or 2, wherein an axial length of a seaming portion generated by the rolling process in a land portion between screw grooves of the screw shaft is equal to or less than ½ of an axial length of the land portion. Ball screw.   4. The automotive ball screw according to claim 1, wherein the ball circulation type of the nut is a piece type provided with a piece member for connecting the screw grooves of the nut. 5.

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