JP2009074623A - Ball screw device and electric power steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw device which can allow the rocking motion of a ball nut with a slight sliding resistant, and further to provide an electric power steering system. <P>SOLUTION: Convex spherical surfaces 32a, 33a are provided on both end portion of the ball nut 21. Engaging members 31, 34 for rockably supporting the ball nut are arranged on both end portions in the axial direction of the ball nut in a rotary cylinder member 41. The engaging members have a plurality of engaging projections 31a, 34a which support the convex spherical surfaces and can elastically deform in the rocking direction of the ball nut. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ball screw device and an electric power steering device including the ball screw device.

  In general, an electric power steering apparatus includes a rack shaft that is moved in the axial direction by the rotation of a steering shaft, an electric motor that rotates the motor shaft based on a steering torque generated on the steering shaft, and a rotational movement of the motor shaft that is a rack shaft. And a ball screw device for converting the movement into the axial motion.

  By the way, in a rack coaxial electric power steering apparatus in which an electric motor is arranged coaxially with a rack shaft, for example, as described in Patent Document 1, a ball screw shaft is integrally provided on the rack shaft, and this ball A ball nut that is screwed onto the screw shaft via a rolling ball is integrally fixed to one end of the motor shaft by a tightening nut.

  In this type of electric power steering device, the rack screw strain due to manufacturing or the deflection of the rack shaft due to a large load from the outside exerts a heavy load on the ball screw device part. In addition, a so-called catching phenomenon occurs in which the torque temporarily increases during steering. For this reason, it is effective to make the rack shaft tiltable at the ball screw device portion.

Conventionally, the rack shaft is allowed to be inclined at the ball screw device portion. For example, as described in Patent Document 2, a ball nut screwed to the ball screw shaft is mounted on the rack housing by a spherical bearing. What is supported so as to be swingable with respect to the axis of the shaft is known.
JP 2006-131038 A Japanese Utility Model Publication No. 5-14939

  According to what is described in Patent Document 2 described above, a load in the shearing direction that is applied in accordance with the radial displacement of the rack shaft that occurs at the meshing portion between the pinion gear on one end side of the rack shaft and the rack portion. The ball nut is supported by the spherical bearing so that it can swing with respect to the rack housing even if the ball acts, so that the load in the shear direction is concentrated on the ball winding start and end of the ball screw device. As a result, there is an advantage that the ball can smoothly roll.

  However, in the device described in Patent Document 2, the ball nut of the ball screw device is supported by the spherical bearings (48, 49) that are slidably engaged with the annular members (46, 47) so as to be swingable. Therefore, there is a problem that it is difficult to smoothly swing the ball nut because the sliding frictional resistance of the spherical bearing is large.

  The present invention has been made in order to solve the above-described conventional problems, and provides a ball screw device and an electric power steering device that allow a ball nut to swing with a small sliding resistance. It is the purpose.

  In order to solve the above-mentioned problems, the ball screw device according to claim 1 is characterized in that a ball screw shaft in which a ball rolling groove is formed in a spiral shape on the outer peripheral surface, and a ball rolling groove in a spiral on the inner peripheral surface. A ball screw device comprising: a ball nut formed in a shape; wherein the ball nut is screwed onto the ball screw shaft via a circulating ball; and the ball nut is mounted in a rotating cylinder member with restricted axial movement. A convex spherical surface is provided at both axial end portions of the ball nut, and an engaging member that engages with the convex spherical surface and pivotally supports the ball nut at both axial end sides of the ball nut. The engaging member is disposed in the member, and the engaging member has a plurality of engaging protrusions that support the convex spherical surface and can be elastically deformed in the swinging direction of the ball nut.

  A feature of the invention of the ball screw device according to claim 2 is that, in claim 1, the engaging member is made of a synthetic resin.

  The invention of the ball screw device according to claim 3 is characterized in that, in claim 1 or claim 2, a large diameter portion having substantially the same diameter as the inner diameter of the rotary cylinder member is formed in the axial central portion of the ball nut. The large diameter portion is fitted to the inner periphery of the rotating cylinder member.

  The electric power steering device according to claim 4 is characterized in that a gear housing, a rack shaft that is inserted through the gear housing so as to be movable in the axial direction and is connected to an input shaft via a rack and pinion mechanism, and the rack An electric motor disposed coaxially with the shaft in the gear housing, a motor shaft rotated by the electric motor, and a ball screw device for converting the rotation of the motor shaft into the axial movement of the rack shaft In the electric power steering apparatus, the ball screw device includes a ball screw shaft in which a ball rolling groove is formed in a spiral shape on an outer peripheral surface, and a ball rolling groove formed in a spiral shape on an inner peripheral surface. A ball nut screwed through a circulation ball and mounted in the rotating cylinder member with restricted axial movement, A convex spherical surface is provided in the part, and an engaging member that engages with the convex spherical surface by allowing the ball nut to swing is disposed on both ends of the ball nut in the axial direction, The member is composed of a plurality of engaging protrusions that support the convex spherical surface and can be elastically deformed in the swinging direction of the ball nut.

  According to the invention of the ball screw device according to claim 1, the engagement of the ball nut, which is provided with convex spherical surfaces at both axial end portions thereof, is engaged with the convex spherical surface so as to swingably support the ball nut. The coupling member is disposed in the rotating cylinder member, and the engaging member has a plurality of engaging protrusions that support the convex spherical surface and can be elastically deformed in the swinging direction of the ball nut. The movement can be performed by elastic deformation of the engaging projections with almost no relative sliding between the engaging member and the convex spherical surface. As a result, the sliding frictional resistance during the swinging motion of the ball nut can be made extremely small, and the ball nut can be swung smoothly according to the strain and deflection of the rack shaft.

  According to the invention of the ball screw device according to the second aspect, since the engaging member is made of synthetic resin, it is possible to easily form an elastically deformable engaging protrusion.

  According to the invention of the ball screw device according to claim 3, the large-diameter portion that is substantially the same diameter as the inner diameter of the rotating cylinder member is formed at the axially central portion of the ball nut, and the large-diameter portion is formed on the inner periphery of the rotating cylinder member. Since they are fitted, the radial movement of the ball nut relative to the motor shaft can be limited while allowing the ball nut to swing.

  According to the invention of the electric power steering apparatus according to claim 4, the ball screw shaft in which the ball rolling groove is spirally formed on the outer peripheral surface, and the ball screw shaft in which the ball rolling groove is spirally formed on the inner peripheral surface. And a ball screw device constituted by a ball nut that is screwed through a circulating ball and mounted in a motor shaft so as to restrict axial movement, and is provided with convex spherical surfaces at both axial ends of the ball nut. An engaging member that engages with the convex spherical surface while allowing the ball nut to swing is disposed inside the motor shaft at both ends in the axial direction of the nut, and the engaging member supports the convex spherical surface and swings the ball nut. An electric power steering device having a ball screw device that can smoothly swing a ball nut in accordance with strain and deflection of a rack shaft because it is composed of a plurality of engaging protrusions that can be elastically deformed in the direction. It can be implemented.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an entire electric power steering apparatus 10 provided with a ball screw device according to the present embodiment. The electric power steering apparatus 10 extends in the left-right direction of a vehicle and is disposed in a housing 11. The housing 11 includes a pinion shaft 12 that is rotated by a steering wheel (not shown), a rack shaft 13 that has rack teeth 13 a that mesh with the pinion shaft 12, and an electric motor that is disposed coaxially with the rack shaft 13. A motor 14 and a ball screw device 15 that converts the rotational motion of the electric motor 14 into the axial motion of the rack shaft 13 are provided.

  The housing 11 includes a cylindrical motor housing 16 and hollow rack housings 17 and 18 that are coaxially fitted to both ends of the motor housing 16, and mounting portions 17 a and 18 a formed on the rack housings 17 and 18. It is designed to be supported by a vehicle body not shown.

  A rack shaft 13 is inserted into the housing 11 so as to be slidable in the axial direction, and both ends of the rack shaft 13 are connected to left and right steering wheels via tie rods. Is steered in the left-right direction.

  A ball screw shaft 20 constituting a ball screw device 15 is provided at one end of the rack shaft 13. As shown in FIG. 2, the ball screw device 15 includes a ball screw shaft 20 in which a ball rolling groove 20a is spirally formed on the outer peripheral surface, and a ball nut in which a ball rolling groove 21a is spirally formed on the inner peripheral surface. 21, a plurality of rolling balls 24 that roll in a ball raceway formed between a ball rolling groove 20 a of the ball screw shaft 20 and a ball rolling groove 21 a of the ball nut 21, and two adjacent balls It comprises a plurality of deflectors 25 that return the rolling balls 24 between the rolling grooves 20a and 21a. As will be described later, the ball nut 21 is swingably mounted in a motor shaft 41 that constitutes a rotor of the electric motor 14 with its axial movement and rotation being restricted. Thus, the rack shaft 13 is reciprocated in the axial direction together with the ball screw shaft 20 by forward and reverse rotation of the ball nut 21 by the motor shaft 41. The motor shaft 41 constitutes a rotating cylinder member in claims.

  Next, a configuration that allows the swinging motion of the ball nut 21 within the motor shaft 41 will be described with reference to FIGS.

  As shown in FIGS. 3 and 5, a nut housing portion 41a is formed at one end of the motor shaft 41, and the first engagement washer 31 and the first spherical washer are formed in the nut housing portion 41a from the bottom side. 32, ball nut 21, second spherical washer 33, and first engagement washer 34 are sequentially inserted on the same axis as the motor shaft 41, and are screwed into a screw hole formed at the open end of the motor shaft 41. The axial movement is regulated by the mating tightening nut 26.

  A key groove 21 a is formed on the outer periphery of the ball nut 21, and a key member 35 screwed to the motor shaft 41 is engaged with the key groove 21 a, whereby the ball nut 21 is prevented from rotating with respect to the motor shaft 41. Has been. A large-diameter portion 21b having substantially the same diameter as the inner diameter of the motor shaft 41 is formed at the axially central portion of the outer periphery of the ball nut 21, and both sides of the large-diameter portion 21b are connected to the outer periphery of the ball nut 21 and the motor shaft 41. A gap for allowing the ball nut 21 to swing is formed between the inner periphery and the inner periphery. As a result, the ball nut 21 is fitted in the motor shaft 41 at the center, and supported in a swingable manner with its radial movement restricted.

  Convex spherical surfaces 32 a and 33 a centering on the axis O of the ball nut 21 are respectively provided on the outer sides of the first and second spherical washers 32 and 33 disposed at both axial ends of the ball nut 21. The formed inner surfaces of the first and second spherical washers 32 and 33 are integrally joined to both end faces of the ball nut 21.

  The first and second engaging washers 31, 34 disposed on the outer sides of the first and second spherical washers 32, 33, respectively, center the first and second spherical washers 32, 33 about the axis O. As a plurality of elastically deformable needle-shaped engaging projections 31a and 34a that are supported so as to be swingable. A large number of engagement protrusions 31a, 34a are arranged with intervals in the circumferential direction and the radial direction of the engagement washers 31, 34, and the distal end portions of these engagement protrusions 31a, 34a are first and second The spherical washers 32 and 33 are aligned on a virtual spherical surface centered on the axis O so that they can be engaged with the spherical surfaces (convex spherical surfaces) 32a and 33a. The first and second engagement washers 31, 34 are made of, for example, synthetic resin, and can easily form a large number of needle-like engagement protrusions 31a, 34a by molding.

  As shown in detail in FIG. 4, the needle-like engaging protrusions 31a and 34a are arranged so that their axes are orthogonal to the spherical surfaces 32a and 33a of the first and second spherical washers 32 and 33. Thus, the engagement protrusions 31a and 34a have a large rigidity with respect to the axial direction of the ball nut 21, and with respect to the swinging direction of the first and second spherical washers 32 and 33 (the arrow direction in FIG. 4). Thus, it is configured to be easily elastically deformed.

  The ball nut 21 is swung by the ball screw shaft 20, the ball nut 21, the rolling ball 24, the first and second engaging washers 31, 34, the first and second spherical washers 32, 33, and the like. A ball screw device 15 that can allow movement is configured.

  According to the ball screw device 15 configured as described above, the swinging motion of the ball nut 21 causes the needle-like engagement protrusions 31a, 31 and 34 and the spherical washers 32 and 33 to slide relatively little with respect to each other. Since this can be performed by elastic deformation of 34a, the sliding frictional resistance during the swinging motion of the ball nut 21 can be made extremely small, and the ball nut 21 can be smoothly swung according to the strain and deflection of the rack shaft 13. Will be able to.

  The electric motor 14 applies an assist force in the axial direction to the ball screw shaft 20 (rack shaft 13) via the ball screw device 15, and includes a motor shaft 41 formed of a hollow rotor and a stator 42. Yes. The motor shaft 41 is rotatably supported by the housing 11 (motor housing 16 and rack housing 17) via bearings 43 and 44, and the ball screw shaft 20 is coaxially inserted into the hollow hole of the motor shaft 41. . A plurality of flat permanent magnets 45 are bonded to the outer periphery of the motor shaft 41, and a stator 42 is mounted on the inner periphery of the motor housing 16 so as to face the permanent magnet 45. The stator 42 includes a plurality of coils 46, and the motor shaft 41 is rotated by causing the magnetic flux generated by energizing the coils 46 to act on the permanent magnet 45.

  Next, the operation of the electric power steering apparatus 10 configured as described above will be described. When a steering wheel (not shown) is steered, steering torque is transmitted to an input shaft (not shown), and the rack shaft 13 is moved in the axial direction via a rack and pinion mechanism including the pinion shaft 12 and the rack teeth 13a.

  The steering torque applied to the input shaft is detected by a torque sensor (not shown), and the rotational position of the motor shaft 41 of the electric motor 14 is detected by a rotation angle detection sensor (not shown). The electric motor 14 is controlled based on the steering torque and the rotational position of the motor shaft 41, and an assist force is generated. The assist force generated by the electric motor 14 is converted into the axial movement of the rack shaft 13 by the ball screw device 15, and the steering force of the steering wheel by the driver is reduced.

  By the way, in the present embodiment, the ball screw device 15 is configured as shown in FIG. 3, so that the ball screw device 15 causes the ball nut 21 to oscillate with the engagement washers 31 and 34 and the spherical washer. 32 and 33 can be performed by elastic deformation of the needle-like engaging projections 31a and 34a without causing relative sliding. That is, as the ball nut 21 and the spherical washers 32, 33 swing, the needle-like engagement protrusions 31a, 34a of the engagement washers 31, 34 are elastically deformed as shown in FIG.

  Thereby, the sliding frictional resistance during the swinging motion of the ball nut 21 can be made extremely small, and the ball nut 21 can be smoothly swung according to the strain and deflection of the rack shaft 13.

  Moreover, the ball nut 21 is formed with a large-diameter portion 21b that is substantially the same diameter as the inner diameter of the motor shaft 41 at the axially central portion, and the large-diameter portion 21b is fitted to the inner periphery of the motor shaft 41, thereby The radial movement of the ball nut 21 relative to the motor shaft 41 can be limited while allowing the nut 21 to swing.

  Therefore, in a vehicle equipped with the electric power steering device 10 using the ball screw device 15 having such a configuration, the ball nut 21 can be smoothly swung according to the strain and deflection of the rack shaft 13, and the steering can be performed. A so-called catching phenomenon in which the torque temporarily increases sometimes can be accurately prevented, and the steering feeling can be improved.

  In the above-described embodiment, the large-diameter portion 21b formed at the axially central portion of the outer periphery of the ball nut 21 can restrict the movement of the ball nut 21 while allowing the ball nut 21 to swing. In the above, an example of fitting to the inner periphery of the motor shaft 41 has been described. However, a gap is formed between the outer periphery of the ball nut 21 and the inner periphery of the motor shaft 41 over the entire length of the ball nut 21 in the axial direction. In addition, the outer diameter of the ball nut 21 may be simply made smaller than the inner diameter of the motor shaft 41.

  In the above-described embodiment, the engagement washers 31 and 34 having a large number of needle-like engagement protrusions 31a and 34a are made of synthetic resin. However, the present invention is not necessarily limited to the synthetic resin, and is a spherical washer. Any material can be used as long as it can be elastically deformed in the swing direction of 32 and 33 (ball nut 21).

  In the above-described embodiment, the example in which the engagement protrusions 31a and 34a of the engagement washers 31 and 34 are needle-shaped has been described. However, the shape of the engagement protrusions 31a and 34a is the same as that of the spherical washers 32 and 33. Any shape that can be elastically deformed in the swinging direction may be a tooth shape or a rectangular shape.

  In the above-described embodiment, the spherical washers 32 and 33 are arranged between the both end portions of the ball nut 21 and the engaging washers 31 and 34. However, the spherical washers 32 and 33 and The ball nut 21 may be integrated, that is, a convex spherical surface may be formed at both ends of the ball nut 21.

  As described above, the present invention is not limited to the above-described embodiments, and various forms can be adopted without departing from the gist of the present invention described in the claims.

1 is an overall view of an electric power steering device including a ball screw device showing an embodiment of the present invention. It is sectional drawing which shows the ball screw apparatus cut | disconnected along 2-2 line | wire of FIG. It is a figure which shows the assembly | attachment state of the ball screw apparatus to a motor shaft. It is a principal part enlarged view of FIG. It is a figure which shows the decomposition | disassembly state of a ball screw apparatus. It is a figure which shows the operation state of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric power steering device, 13 ... Rack shaft, 14 ... Electric motor, 15 ... Ball screw device, 20 ... Ball screw shaft, 20a ... Ball rolling groove, 21 ... Ball nut, 21a ... Ball rolling groove, 21b ... large diameter part, 24 ... rolling ball, 26 ... clamping nut, 31, 34 ... engaging member (engaging washer), 31a, 34a ... engaging protrusion, 32, 33 ... spherical washer, 32a, 33a ... convex spherical surface 41 ... Motor shaft (rotating cylinder member).

Claims (4)

A ball screw shaft in which a ball rolling groove is spirally formed on the outer peripheral surface; and a ball nut in which a ball rolling groove is spirally formed on the inner peripheral surface. In the ball screw device, the ball nut is screwed through and the axial movement of the ball nut is restricted in the rotating cylinder member.
Convex spherical surfaces are provided at both axial end portions of the ball nut, and engaging members that engage the convex spherical surface and swingably support the ball nut are provided at both axial end sides of the ball nut. A ball screw device, wherein the engagement member has a plurality of engagement protrusions that support the convex spherical surface and are elastically deformable in a swinging direction of the ball nut.   2. The ball screw device according to claim 1, wherein the engaging member is made of a synthetic resin.   3. A large diameter portion having substantially the same diameter as the inner diameter of the rotating cylinder member is formed at an axially central portion of the ball nut, and the large diameter portion is fitted to the inner periphery of the rotating cylinder member. A ball screw device characterized by being combined. A gear housing, a rack shaft that is inserted in the gear housing so as to be movable in the axial direction and is connected to an input shaft via a rack and pinion mechanism, and an electric motor that is disposed coaxially with the rack shaft in the gear housing And an electric power steering apparatus comprising: a motor shaft rotated by the electric motor; and a ball screw device that converts the rotation of the motor shaft into an axial movement of the rack shaft.
The ball screw device has a ball screw shaft in which a ball rolling groove is formed in a spiral shape on an outer peripheral surface, and a ball rolling groove formed in a spiral shape on an inner peripheral surface and is screwed to the ball screw shaft via a circulating ball. And a ball nut mounted in the rotating cylinder member to restrict axial movement,
Convex spherical surfaces are provided at both axial ends of the ball nut, and engaging members that engage with the convex spherical surface are provided in the motor shaft at both axial ends of the ball nut to allow the ball nut to swing. The electric power steering apparatus according to claim 1, wherein the engaging member comprises a plurality of engaging protrusions that support the convex spherical surface and are elastically deformable in a swinging direction of the ball nut.

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