JP2006250282A - Ball screw device and electric power steering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw device in which each ball can roll smoothly without generating collision sound and the lifespan can be prolonged, and to provide an electric power steering employing the ball screw device. <P>SOLUTION: Ball rolling grooves are formed to make at least two rounds on both right and left sides of a nut, respectively. The distance between the centers of the right and left first-round ball rolling grooves which are adjacent to each other on their inner sides is set larger or smaller than the integral multiple of a pitch of a ball rolling groove of a screw shaft, and the distances between the centers of the ball rolling grooves on both the right and left sides are respectively set equal to the integral multiple of the pitch of the ball rolling groove of the screw shaft. Thus, pre-load is imposed to the balls between the ball rolling grooves on both the right and left sides of the nut and the ball rolling groove of the screw shaft. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ball screw device in which a ball circulates infinitely, and an electric power steering device to which the ball screw device is applied as a mechanism for transmitting auxiliary torque of an electric motor to a rack shaft.

  In an electric power steering device (electric power steering device), an auxiliary steering force based on an auxiliary torque of an electric motor is applied to a rack shaft that is provided between the left and right wheels and moves in the axial direction to steer the left and right wheels. In order to act, a ball screw device that converts rotational motion into linear motion is used.

  This ball screw device is configured by screwing a ball rolling groove formed on the outer periphery of the rack shaft and a ball rolling groove formed on the inner periphery of the nut member via a plurality of balls. In addition, the ball rolling grooves of the rack shaft and the nut member have respective centers at positions overlapped in the axial direction on the circumference where the rack shaft and the nut member are fitted, and from the outer diameter of the ball The ball has a cross-sectional shape formed by combining two arcs having a large curvature, and the ball is slightly close to zero with respect to each of the arc-shaped inner surfaces of the rack shaft and the ball rolling groove of the nut member. It is desirable to interpose so as to face each other with a gap.

  However, in order to perform such an interposition, high machining accuracy is required for the dimensions and shape of the ball, the cross-sectional shape and lead of the ball rolling groove, and the concentricity between the rack shaft and the nut member. There was a problem that the manufacturing cost of the was high.

  Therefore, as a ball screw device that can be processed with a certain degree of accuracy and smoothly rolls, for example, as shown in FIG. 8, a relatively large gap T between the inner surface of the ball rolling groove 51 and the outer peripheral surface of each ball 19. Some are set to ensure. According to this, each ball 19 rolls smoothly, but each ball 19 idles and collides between adjacent balls 19 due to vibrations propagated while the vehicle is running, generating an harsh collision sound. There was a problem of letting.

  As shown in FIG. 9, as a ball screw device, rolling is performed smoothly without generating such a collision sound, and an oversized ball 55 is used to give a preload to the ball rolling groove 53. There is something that is configured. However, although this can prevent the occurrence of a collision sound, there is a problem that the ball 55 is deformed and becomes multi-point contact with use, causing flaking and shortening the life of the ball screw device. It was.

Further, as shown in Patent Document 1, there is a case where the lead b of the female screw rail 20 on the inner periphery of the nut member 2 is formed larger than the lead a of the male screw rail 10 formed on the outer periphery of the rack shaft 1.
JP 2001-114117 A (page 6, FIG. 2, FIG. 3)

  According to this, the male thread rail 10 is formed with the same lead continuously by the lead a and the female thread rail 20 by the lead b. Therefore, when both rails are aligned in the axial direction at the central portion, the length of the lead The difference (ba) increases incrementally toward both ends, and the way the threaded rail hits the ball gradually increases. Therefore, abnormal heat generation, increased frictional moment, wear / deformation occur from such a strong contact point, and the life of the ball screw device is shortened.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problems, and each ball can smoothly roll without generating a collision sound, and can maintain a long life as a ball screw device. A screw device and an electric power steering device using the device are provided.

  In order to solve the above-described problem, the structural feature of the invention according to claim 1 is that a screw shaft having a spiral ball rolling groove on the outer peripheral surface and a spiral ball rolling groove on the inner peripheral surface. A plurality of nuts, and a plurality of balls respectively disposed in a raceway formed by opposing the ball rolling grooves of the screw shaft and the ball rolling grooves of the nuts. In a ball screw that connects a starting point and an ending point of a moving groove to endlessly circulate the ball in a substantially annular manner, a ball rolling groove having at least two turns is formed on each of the left and right sides of the nut. The distance between the centers of the first rolling ball rolling grooves adjacent on the inside of the right and left ball rolling grooves is larger or smaller than an integral multiple of the pitch of the ball rolling grooves of the screw shaft, and On both the left and right sides The distance between the centers of the ball rolling grooves of at least two or more turns provided is equal to an integral multiple of the pitch of the ball rolling grooves of the screw shaft, and the ball rolling grooves on the left and right sides of the nut and the screws Preload is applied to the ball between the ball rolling groove of the shaft.

  The structural feature of the invention according to claim 2 is that a screw shaft having a spiral ball rolling groove on the outer peripheral surface, a nut having a spiral ball rolling groove on the inner peripheral surface, and the screw shaft A ball screw comprising a ball rolling groove and a plurality of balls arranged in a track formed so as to face the ball rolling groove of the nut, wherein the lead of the ball rolling groove in the central portion of the nut is One or more rounds are formed longer or shorter than the ball rolling groove lead of the screw shaft, and the ball rolling groove lead at both ends of the nut and the ball rolling groove lead of the screw shaft. Is formed equally, and a preload is applied to the balls between the ball rolling grooves at both end portions of the nut and the ball rolling grooves of the screw shaft.

  The structural feature of the invention according to claim 3 is that the rotor of the electric motor formed in a hollow cylindrical shape, and a spiral ball rolling groove is formed on the inner peripheral surface, and the inner wall of the hollow hole of the rotor is concentric. A rack shaft provided with a screw shaft in which a spiral ball rolling groove is formed on a part of the outer peripheral surface, and the nut, the rack shaft, the nut, and the rack shaft are screwed together. An electric power steering apparatus comprising: a ball screw device comprising a plurality of balls to be driven; and a housing having a stator of the electric motor and rotatably supporting the rotor, the screw shaft of the ball screw device And the nut is the screw shaft and nut of the ball screw device according to claim 1 or 2.

  The structural feature of the invention according to claim 4 is that, in claim 3, the nut is formed integrally with the rotor.

  The structural feature of the invention according to claim 5 is that, in claim 3, an inner ring of a bearing for rotatably supporting the rotor on the housing is formed integrally with the rotor.

  In the invention according to claim 1, at least two or more turns of the ball rolling groove are formed on each of the left and right sides of the nut, and the center of the first rolling ball rolling grooves adjacent to each other inside the ball rolling grooves. The distance is formed larger or smaller than an integral multiple of the pitch of the ball rolling grooves of the screw shaft. As a result, when the nut and the screw shaft are screwed together, the nut with respect to the ball rolling groove of the screw shaft is increased by the distance between the centers of the ball rolling grooves of the first winding being increased or decreased. The ball rolling grooves are shifted in the axial direction toward the left and right ends of the nut or toward the central portion of the nut. Therefore, for example, when it is shifted toward the left and right ends of the nut, each ball in the ball rolling groove on one side of the nut is positioned at one point on the inner surface of the nut on the center side of the ball rolling groove. They contact each other, and contact with one point on the inner surface on the outer side in the axial direction with the ball rolling groove of the opposite screw shaft (so-called two-point contact). Each ball rolls on the left and right sides of the nut while applying a preload that pushes the nut toward each other from the left and right sides toward the center. On the other hand, when the above-described deviation occurs toward the central portion of the nut, each ball rolls while applying a preload that pushes the nut toward the left and right ends. Therefore, each ball rolls smoothly without contact in the ball rolling groove and with two-point contact. Furthermore, since the distance between the center of the ball rolling grooves on both the left and right sides formed two or more turns is equal to an integral multiple of the pitch of the ball rolling grooves on the screw shaft, the axial deviation is An equal shift occurs between the respective ball rolling grooves. Therefore, a preload is uniformly applied between each ball rolling groove and the ball.

  In the invention according to claim 2, the lead of the ball rolling groove in the central portion of the nut is formed longer or shorter by one or more turns than the lead of the ball rolling groove of the screw shaft, The ball rolling groove lead is formed equal to the ball rolling groove lead of the screw shaft. As a result, when the nut and the screw shaft are screwed together, the ball rolling groove of the nut is directed toward both ends of the nut or toward the central portion of the nut with respect to the ball rolling groove of the screw shaft. Deviation in direction. For this reason, for example, when they are displaced toward both ends of the nut, each ball in the rolling groove at each end of the nut comes into contact with one point on the inner surface of the nut at the center of the ball rolling groove. The ball rolling groove of the screw shaft is in contact with one point on the inner surface on the outer side in the axial direction (two-point contact). Each ball rolls at both ends of the nut while applying a preload that pushes the nut toward each other toward the central portion. On the other hand, when the above-described deviation occurs toward the central portion of the nut, each ball rolls while applying a preload that pushes the nut toward the opposite ends of the nut. Therefore, each ball rolls smoothly without contact in the ball rolling groove and with two-point contact. Further, the ball rolling grooves at both ends of the nut are formed by leads equal to the leads of the ball rolling grooves of the screw shaft, and the axial displacement is caused equally between all the opposing ball rolling grooves. Therefore, the hits of the balls against the opposing ball rolling grooves are equal, and the preload is uniformly applied. Accordingly, the preload can be easily set, and it is possible to prevent the preload from being applied more than necessary and to maintain the life of the ball screw device for a long time.

  In the invention according to claim 3, since the ball screw device according to claim 1 or 2 is used for an electric power steering device, the operation of the steering is smooth, and an impact sound is generated by vibration during running of the vehicle. There is nothing. Moreover, since each ball is given a uniform preload by two-point contact, it is possible to provide an electric power steering apparatus including a ball screw device that can maintain a long life.

  In the invention according to claim 4, since the nut of the ball screw device of the electric power steering apparatus is formed integrally with the rotor, the number of parts can be reduced and the accuracy of the assist mechanism to the rack shaft can be improved. Can do.

  In the invention according to claim 5, since the inner ring of the bearing for supporting the rotor of the electric power steering apparatus on the housing is formed integrally with the rotor, the production cost can be reduced by reducing the number of parts. Rotational accuracy can be improved.

  A ball screw device and an electric power steering device according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an electric power steering apparatus mounted on a vehicle body, and FIG. 2 is a cross-sectional view showing an embodiment of the electric power steering apparatus using a ball screw device. 3 and 4 are enlarged views showing the relationship between the threaded shaft of the rack shaft, balls and nuts in FIG.

  An electric power steering apparatus 1 includes a rack shaft 3, a ball screw mechanism 5, an input shaft 7, and an electric motor 9 mounted on an aluminum housing 2 that is attached to a vehicle body (not shown) that extends in the left-right direction of the vehicle. Etc. are assembled.

  The housing 2 is formed in an integral tubular shape as a whole by coaxially coupling the rack housing 16, the tube yoke housing 17, and the end housing 18 each formed in a tubular shape. The housing 2 is fixed to the vehicle body by a bracket or the like (not shown).

  As shown in FIG. 1, the rack shaft 3 inserted through the housing 2 is connected to the left and right steering wheels 10 via the tie rod 6 and the knuckle arm 8 respectively, and moves in the axial direction. The steered wheel 10 is steered. The rack shaft 3 has rack teeth 11 formed on one outer periphery, and the rack teeth 11 mesh with a pinion 13 carved at the tip of the input shaft 7 to which the steering torque is transmitted from the steering wheel 4. The rack shaft 3 is moved in the axial direction (left and right in the drawing) by the rotation of the pinion 13. As shown in FIG. 2, a screw shaft 15 constituting a male screw portion of the ball screw mechanism 5 is formed on the outer periphery of the rack shaft 3, and the screw shaft 15 has a helical shape on which a plurality of balls 19 roll. Ball rolling grooves 21 are formed. A nut 23 constituting an internal thread portion of the ball screw mechanism 5 is screwed to the screw shaft 15 via a plurality of balls 19. A spiral ball rolling groove 25 is formed in the nut 23, and a piece member 27 is fixed to an adjacent portion in the axial direction of the ball rolling groove 25. The top member 27 is formed with moving grooves 29 connecting the start and end of the adjacent ball rolling grooves 25, and each of the ball rolling grooves 25 is formed in a substantially annular infinite circulation by two turns on both the left and right sides. Forming a road.

  Further, as shown in FIG. 4 which is an enlarged view of the lower portion of the nut 23, the ball rolling groove 25 and the ball rolling groove 25 adjacent thereto are cut in the axial direction near the center of the nut 23 in the axial direction. The distance between the centers of curvature (a1 and a2) of the arc-shaped cross section (distance between the centers of adjacent ball rolling grooves 25) D1 is longer than the pitch P of the ball rolling grooves 21 of the screw shaft 15 by Δ. ing. According to this, when the nut 23 and the screw shaft 15 are screwed together, the ball rolling groove of the nut 23 is equal to the ball rolling groove 21 of the screw shaft 15 by Δ formed longer in the central portion of the nut 23. 25 is shifted in the axial direction toward the left and right ends of the nut 23. Due to this shift, each ball 19 in the ball rolling groove on both the left and right sides of the nut comes into contact with one point on the inner surface of the ball rolling groove 25 of the nut 23 on the central side of the nut, thereby rolling the ball of the screw shaft 15. The groove 21 is in contact with one point on the inner surface on the outer side in the axial direction (so-called two-point contact). Each ball 19 rolls on the left and right sides of the nut 23 while applying a preload that pushes the nut 23 toward the center from both the left and right sides. Further, in the endless circulation path formed by two turns on the left and right sides of the nut 23, the distance D2 between the centers of the ball rolling grooves 25 is formed to be equal to the pitch P of the ball rolling grooves 21 of the screw shaft 15, respectively. ing. Therefore, the deviation in the axial direction is generated as an equal deviation between all the opposing ball rolling grooves 21 and 25. Accordingly, the hits of the balls 19 against the opposing ball rolling grooves 21 and 25 are equal, and the preload is given uniformly.

  An input shaft 7 is assembled to the rack housing 16 so as to be rotatable and cannot be moved in the axial direction. The input shaft 7 has a universal joint, an intermediate shaft, a universal joint, and a steering shaft 45 at an outer end protruding from the rack housing 16. Etc., and is connected to the steering wheel 4. A pinion 13 is formed at the tip of the input shaft 7, and the pinion 13 meshes with the rack teeth 11 of the rack shaft 3.

  An electric motor 9 is assembled in the tube yoke housing 17, and the electric motor 9 includes a rotor 33 and a stator 35 formed in a hollow cylindrical shape. The rack shaft 3 is coaxially inserted into the hollow hole of the rotor 33, and the nut 23 is fitted on the inner periphery of the rotor 33 so as not to be relatively movable so as to rotate integrally with the rotor 33. A plurality of permanent magnets (not shown) are bonded to the outer periphery of the rotor 33, and a stator 35 having a plurality of coils is fixed to the inner periphery of the housing 2 so as to face the permanent magnets. The rotor 33 is rotatably supported on the tube yoke housing 17 by bearings 37 and 39 disposed on both sides of the stator 35. When the coil of the stator 35 is energized, the generated magnetic flux acts on the permanent magnet, and the rotor 33 rotates with the nut 23 to apply an axial assist force to the rack shaft 3. A rotation angle detection sensor 31 is provided on the inner periphery of the tube yoke housing 17 on the rack housing 16 side so that the rotational position of the rotor 33 can be detected.

  Further, as shown in FIG. 1, the electric motor 9 is electrically connected to the control circuit 41, and the control circuit 41 detects the steering torque generated by the operation of the steering wheel 4 and the rotation angle of the rotor 33. It is electrically connected to a rotation angle detection sensor 31 that detects. The torque sensor 43 is disposed between an operation shaft 45a and an operation shaft 45b constituting the steering shaft 45, and is configured to detect steering torque based on a relative angular displacement between the operation shaft 45a and the operation shaft 45b. . The control circuit 41 causes the electric motor 9 to generate a direction and a magnitude in which the auxiliary torque (assist force) should be applied according to the detection results of the torque sensor 43 and the rotation angle detection sensor 31.

  The operation of the electric power steering apparatus 1 configured as described above will be described below. When the steering wheel 4 is steered, steering torque is transmitted to the input shaft 7 via the steering shaft 45. The steering torque is converted into a steering force for moving the rack shaft 3 in the axial direction by a rack and pinion mechanism including the pinion 13 and the rack teeth 11.

  At this time, the torque sensor 43 detects the steering torque, and the rotation angle detection sensor 31 detects the rotational position of the rotor 33 of the electric motor 9, and the steering torque and the rotational position of the rotor 33 of the electric motor 9 are detected. Based on this, the control circuit 41 causes the electric motor 9 to generate auxiliary torque. This auxiliary torque is converted into an auxiliary steering force that assists the axial movement of the rack shaft 3 by the ball screw mechanism 5. Thereby, the steering force of the steering wheel 4 by the driver is reduced.

  Further, at this time, in the ball screw mechanism 5 in which the nut 23 together with the rotor 33 is rotated with respect to the rack shaft 3 by the electric motor 9, each ball 19 rolls while receiving a load, and the ball rolling grooves 21 and 25 and the top member Each circulation trajectory constituted by 27 moving grooves 29 is infinitely circulated. Each ball 19 is preloaded as described above, and smoothly rolls in a two-point contact without floating in the circulation track. Further, as described above, since each ball 19 has the same contact with the ball rolling grooves 21 and 25 and the preload is uniformly applied, the life of the ball screw mechanism 5 can be maintained long.

  In this embodiment, the distance between the centers of the adjacent ball rolling grooves 25 in the central portion of the nut 23 is longer than the pitch P of the ball rolling grooves of the screw shaft by Δ. The center distance corresponding to three pitches may be increased by Δ, for example.

  In this embodiment, the ball screw mechanism is formed with a plurality of so-called coma-type infinite circulation paths, but the present invention is not limited to this. For example, the start and end of the thread groove of the nut are arranged outside the nut. A return tube system in which a ball circulation path is formed by connecting with a tube along the axis, and a ball return groove provided along the axial direction of the nut with the ball guide groove of each end cap attached to both ends of the nut in the axial direction. An end cap type ball screw mechanism communicating with a passage may be used. In this case, the lead of the ball rolling groove in the central portion of the nut is formed longer or shorter than the lead of the ball rolling groove of the screw shaft for one or several turns, and the ball rolling groove at both end portions of the nut is formed. The lead of the moving groove and the lead of the ball rolling groove of the screw shaft are formed equally. Therefore, when the nut and the screw shaft are screwed together, the ball rolling groove of the nut with respect to the ball rolling groove of the screw shaft is shortened or shortened as described above at the central portion of the nut. A shift occurs in the axial direction toward both ends of the nut or toward the central portion of the nut. As a result, a preload is applied in the same manner as described above, and the ball rolls smoothly without contact and with two-point contact. Similarly, a uniform preload is applied to each ball.

  Next, a ball screw device and an electric power steering device according to a second embodiment of the present invention will be described below. In the electric power steering apparatus of this embodiment, as shown in FIG. 6, the nut 63 of the ball screw mechanism is formed integrally with the rotor 68 at one end inside the rotor 68 by cutting or grinding. . Other configurations are the same as those of the first embodiment.

  According to the electric power steering apparatus having the above configuration, since the nut 63 of the ball screw device is formed integrally with the rotor 68, the production cost can be reduced by reducing the number of parts, and the rack shaft 3 can be reduced. The accuracy of the assist mechanism can be improved.

  Next, a third embodiment of the ball screw device and the electric power steering apparatus according to the present invention will be described below. As shown in FIG. 7, the electric power steering apparatus according to the present embodiment is disposed on both sides of the stator 35 in the housing 2, and in the bearing 77 that supports the rotor 73, the inner ring 77 a of the bearing 77 is connected to the rotor 73. It is integrally formed. Other configurations are the same as those of the first embodiment.

  According to the electric power steering apparatus having the above configuration, since the inner ring 77a of the bearing 77 is formed integrally with the rotor 73, the production cost can be reduced by reducing the number of parts, and the rotational accuracy of the rotor can be improved. it can.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which mounted the electric power steering device which concerns on this invention in the vehicle body. A sectional view of an electric power steering device in a 1st embodiment. The enlarged view of the ball screw device. The enlarged view of the ball screw device. The figure which used the ball screw apparatus for the electric power steering device. The figure which used the ball screw apparatus in 2nd Embodiment for the electric power steering device. The figure which used the ball screw apparatus in 3rd Embodiment for the electric power steering device. The elements on larger scale of the conventional ball screw mechanism. The elements on larger scale of the conventional ball screw mechanism.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Housing, 3 ... Rack shaft, 5 ... Ball screw mechanism, 15 ... Screw shaft, 19 ... Ball, 21 ... Ball rolling groove, 23 ... Nut, 25 ... Ball rolling groove , 33 ... rotor, 37 ... bearing, 39 ... bearing, 63 ... nut, 68 ... rotor, 73 ... rotor, 77 ... bearing, 77a ... inner ring, D1, D2 ... distance between centers of ball rolling grooves.

Claims (5)

A screw shaft having a spiral ball rolling groove on the outer peripheral surface, a nut having a plurality of spiral ball rolling grooves on the inner peripheral surface, the ball rolling groove of the screw shaft, and each ball rolling of the nut Provided with a plurality of balls respectively arranged in a track formed so as to oppose the grooves, and connected to the start and end points of each ball rolling groove of the nut, and a plurality of infinitely circulating the balls in an endlessly circular manner In the ball screw as the circulation path,
At least two or more turns of the ball rolling groove are formed on each of the left and right sides of the nut, and the distance between the centers of the first rolling ball grooves adjacent on the inside of the ball rolling grooves on the left and right sides is a screw. The distance between the centers of at least two or more turns of the ball rolling groove formed on both the left and right sides is greater than or less than an integral multiple of the pitch of the ball rolling groove of the shaft. The ball screw device is formed to be equal to an integral multiple of the pitch of the nut, and a preload is applied to the ball between the ball rolling grooves on the left and right sides of the nut and the ball rolling grooves of the screw shaft. A screw shaft having a spiral ball rolling groove on the outer peripheral surface, a nut having a spiral ball rolling groove on the inner peripheral surface, the ball rolling groove of the screw shaft, and the ball rolling groove of the nut A ball screw having a plurality of balls arranged in a track formed opposite to each other,
The lead of the ball rolling groove in the central portion of the nut is formed longer or shorter than the lead of the ball rolling groove of the screw shaft for one or more rounds, and the ball rolling groove in both end portions of the nut And the ball rolling groove lead of the screw shaft are equally formed, and a preload is applied to the ball between the ball rolling groove at both end portions of the nut and the ball rolling groove of the screw shaft. A ball screw device characterized by that. A rotor of an electric motor formed in a hollow cylindrical shape, a spiral ball rolling groove formed on the inner peripheral surface, a nut provided concentrically on the inner wall of the hollow hole of the rotor, and a part of the outer peripheral surface A ball screw device comprising: a rack shaft provided with a screw shaft formed with a spiral ball rolling groove; and the nut, the rack shaft, and a plurality of balls for screwing the nut and the rack shaft together. An electric power steering apparatus comprising a housing having a stator of the electric motor and rotatably supporting the rotor;
The screw shaft and nut of the ball screw device according to claim 1 or 2, wherein the screw shaft and nut of the ball screw device are an electric power steering device.   4. The electric power steering apparatus according to claim 3, wherein the nut is formed integrally with the rotor.   4. The electric power steering apparatus according to claim 3, wherein an inner ring of a bearing for rotatably supporting the rotor on the housing is formed integrally with the rotor.

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