JP2003329097A - Ball screw device and electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw device which works smoothly using a die member having a circulating passage of a tunnel shape for preventing a ball and a screw thread from coming in contact with and an electric power steering device which works smoothly by applying the ball screw device. <P>SOLUTION: In a ball screw mechanism 26 of the electric power steering device, the approximately annular circulating orbit on which the ball 70 circulates infinitely is composed of a ball rolling passage 68 in which a screw groove 34 of a rack shaft 12 and a ball rolling passage 68 of a ball screw nut 36 are formed opposing to each other, and a circulating groove 76 of a tunnel shape provided in the die member 74 and communicating approximately adjoining portion in the axial direction of the ball rolling passage 68. The die member 74 is comprised of a curved metal pipe 78 whose inside is the circulating passage 76 and a resinous cover 80 coating the outside of the pipe 78 and fitted into a setting hole 72 of the ball screw nut 36. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw device, and more particularly to a circulation orbit in which a large number of balls infinitely circulate in a substantially annular shape by connecting a portion of a ball rolling path that is substantially adjacent in the axial direction with a top member. The present invention relates to a so-called top-circulation ball screw device in which is formed.

The present invention also relates to an electric power steering apparatus to which the above ball screw device is applied as a mechanism for transmitting an auxiliary torque of an electric motor to a rack shaft.

[0003]

2. Description of the Related Art For example, in an electric power steering apparatus (electric power steering apparatus), an auxiliary electric motor is attached to a rack shaft that is provided between left and right wheels and moves axially to steer the left and right wheels. A ball screw device that converts a rotational motion into a linear motion is used to apply an auxiliary steering force based on a torque.

In such a ball screw device, a screw shaft having a thread groove formed on the outer peripheral portion and a nut having a thread groove formed on the inner peripheral portion are screwed together through a large number of balls. ing. Specifically, a large number of balls are arranged side by side so that they can roll while receiving a load in a spiral ball rolling path formed by opposing the screw groove of the screw shaft and the screw groove of the nut. A circulation path for infinitely circulating the large number of balls is provided on the nut side.

Thus, in the ball screw device, when the nut is driven to rotate, a large number of balls circulate indefinitely through the ball rolling path and the circulation path in accordance with the rotation, and the rotational force of the nut causes the mutual screw threads to rotate. The groove and the ball are smoothly converted into an axial moving force of the screw shaft, so that the screw shaft moves in the axial direction. Similarly, when the screw shaft is rotationally driven, the nut moves in the axial direction of the screw shaft, and when one of the nut and the screw shaft is moved in the axial direction of the screw shaft, the other rotates.

A ball screw device used in an electric power steering apparatus is a ball screw device in which a long circulation path is formed in an axial direction at a specific portion in a nut circumferential direction such as an end cap type or a return tube type. Compared to the device,
A so-called top-circulation ball screw device is used, which has a good weight balance with respect to the rotating shaft of the nut.

In the top-circulation ball screw device, top members (deflectors) each having a circulation groove as a circulation path are attached to a plurality of through holes that radially penetrate the nut. The circulation groove of each top member is open to the screw shaft (inner circumference of the nut) side, and is arranged so as to straddle the threads between the screw grooves that are adjacent to each other in the axial direction. The substantially adjacent portions are communicated so that one ball can pass through.

As a result, in the top-circulation type ball screw device, substantially circular circulation orbits (ball load rows for approximately one revolution of the spiral ball rolling path) in which the balls circulate infinitely are formed by the number of the tops. There is. And each top member (through hole),
Each of them is offset in the axial direction and arranged at equal intervals in the circumferential direction, so that unbalance during rotation is suppressed.

[0009]

However, in the conventional ball screw device as described above, the ball circulates between the circulation groove of the top member and the thread of the screw shaft.
In other words, since the ball circulates over the screw thread and circulates, the ball collides with the top member or the top of the screw thread and does not circulate smoothly, or the impact sound (noise) is generated due to the collision.
Sometimes occurred. In particular, in the screw shaft formed by rolling, a minute groove is formed at the top of the screw thread, and this groove has been a cause of hindering smooth circulation of the ball.

Further, in a structure in which a separator for preventing contact between adjacent balls is arranged between the balls,
The separator may come into contact with the threads and fall out from between the balls. Then, the dropped separator may be caught between the groove wall of the circulation groove of the top member and the screw thread and may be damaged.

Therefore, in the ball screw device described in Japanese Patent Laid-Open No. 2001-165274, a tunnel-shaped circulation path is provided in the top member so that the ball does not come into contact with the screw shaft (top of the screw thread). It adopts a circulating structure. However, in the ball screw device described in this publication, the top member is formed by combining a pair of halves divided along the circulation path. Therefore, when the pair of halves are combined, they are joined (projected) to each other. There was a problem that a step was generated in the hitting part.

The step in the radial direction of the circulation path is
It is formed inside the circulation path along the circulation path, which hinders the smooth circulation of the ball. In particular, in the configuration including the separator, the separator may be caught in the step, which may cause the separator to fall off between the balls or be damaged.

On the other hand, a step in the longitudinal direction of the top member,
That is, a step which shifts the positions of the ends of the pair of halves in the longitudinal direction lengthens the entire length of the top member and hinders the attachment of the top member to the through hole of the nut. If the through hole is made larger (longer) as a countermeasure against this, it violates the design requirement to reduce the step between the top member and the nut. That is, in order for the ball to smoothly enter and exit the circulation path of the top member, it is usually necessary to reduce the step difference between the nut and the top member. This increases the step (gap) between the top member and the top member, which hinders smooth ball circulation, that is, smooth operation of the ball screw device.

Further, in the ball screw device described in the above publication, the ball scooping portion is formed by squeezing the portions of the top member that are open to the screw shaft side at both ends of the circulation path toward the inner side of the circulation path into a substantially U shape. Although the ball scooping part is formed, the part along the opening edge part is sharpened to have an edge shape due to its function, and it is easy to cause abrasion due to scooping up of the ball, resulting in smoothness of the ball. There is a risk that it may hinder the circulation.

In view of the above facts, the present invention provides a ball screw device that operates smoothly by using a top member having a tunnel-shaped circulation path for preventing contact between a ball and a screw thread. Is the purpose of. A second object of the present invention is to obtain an electric power steering apparatus that includes the above ball screw device and operates smoothly.

[0016]

In order to achieve the first object, the ball screw device according to the invention of claim 1 is
It is formed in a tubular shape having a screw shaft having a thread groove on the outer peripheral portion and a screw groove which forms a spiral ball rolling path facing the screw groove on the inner peripheral portion, and relatively rotates the screw shaft. A nut that allows insertion, a plurality of balls that are arranged in the ball rolling path and roll while receiving a load due to the relative rotation, and a nut that is mounted in a mounting hole that penetrates the nut in a radial direction, A ball screw device provided with a top member provided with a circulation path that allows the balls to pass through portions substantially adjacent to each other in the axial direction of the ball rolling path such that one ball can pass therethrough, and circulates the ball in an infinite circle. The top member is a metal pipe that is curved corresponding to the ball rolling path and in which the tunnel-shaped circulation path is formed, and the mounting hole that covers the radially outer side of the pipe. To fix the pipe to the nut Constructed and a fat-made covering portion, and characterized in that.

According to another aspect of the ball screw device of the present invention, a plurality of balls are arranged side by side (in a row) in a spiral ball rolling path, and the balls are associated with relative rotation between the screw shaft and the nut. The ball rolling path and the circulation path of the top member attached to the nut, and infinitely circularly circulates. That is, a ball that has passed through approximately one turn of the spiral ball rolling path is returned to the original position by one round by the circulation path that communicates portions that are substantially adjacent to each other in the axial direction of the ball rolling path. As described above, the substantially circular circulation path in which the balls circulate infinitely is formed by the number of the top members (at least one).

Since the circulation path of the top member is a tunnel, the infinitely circulating ball does not come into contact with the top of the thread of the screw shaft and is smoothly affected by the shape of the thread. Then, as described above, it is restored for one lap.

Here, since the tunnel-shaped circulation path is formed by the metal pipe, no step is formed in the circulation path. Then, since the resin-made covering portion for covering the pipe is fitted into the mounting hole of the nut to fix the pipe to the nut, in other words, since the mounting portion to the nut is integrally formed, dimensional error is caused. In consideration of the above, it is not necessary to form the mounting hole in a large size, and the step between the top member and the nut can be suppressed to be small. With these,
The ball circulates smoothly and infinitely.

As described above, the ball screw device according to the first aspect of the invention operates smoothly by using the top member having the tunnel-shaped circulation path for preventing the contact between the ball and the screw thread.

Further, since the pipe is fixed to the nut through the resin-made covering portion, the vibration when the balls pass through the circulation path of the pipe is absorbed by the covering portion, and the noise is reduced. Further, since the circulation path that is curved and communicates with the ball rolling path can be formed by simple processing (bending) of the metal pipe, the manufacturing cost of the top member is reduced.

Furthermore, in the structure in which a separator for preventing contact between adjacent balls is arranged between the balls, there is no step in the circulation path as described above, and the step between the nut and the top member is small. The falling of the separator from between the balls is also prevented. Even if the separator falls off between the balls, the separator does not get caught between the top member and the screw thread because it passes through the tunnel-shaped circulation path.

A ball screw device according to a second aspect of the present invention is the ball screw device according to the first aspect, wherein the tip portion is arranged so as to be inserted into the thread groove of the screw shaft, and the ball is guided into the circulation path. It is characterized in that the guide convex portions are respectively provided on the screw shaft side edge portions of the openings located at both ends of the circulation path in the pipe.

In the ball screw device according to the second aspect of the present invention, the guide convex portion of the pipe guides the infinitely circulating ball into the circulation path, so that the ball circulates even more smoothly. The guide protrusion provided on the screw shaft side edge of the opening guides the ball into the circulation path with the tip of the guide protrusion inserted into the screw groove of the screw shaft. Unlike the conventional ball scooping portion, it is not necessary to form the edge portion, and wear or the like does not pose a problem. Therefore, while maintaining the function of smoothly circulating the ball as described above,
The ball screw device can have a long life and high speed rotation.

A ball screw device according to a third aspect of the present invention is the ball screw device according to the first or second aspect, wherein the pipe is constructed by combining half bodies divided into two along the longitudinal direction. The chamfered portion is formed on the inner surface side of the seam of the half body.

In the ball screw device according to the third aspect of the present invention, the pipe is constructed by combining two halves divided in the longitudinal direction, and the chamfered portion is formed on the inner surface side at the joint between the halves of the pipe. The ball circulates smoothly because there is no step on the inner peripheral surface (tunnel-shaped circulation path) of the pipe. Further, in the configuration including the separator, the separator circulates smoothly together with the balls.

Further, in order to achieve the first object, a ball screw device according to a fourth aspect of the invention is a screw shaft having a thread groove on an outer peripheral portion, and a spiral shape facing the thread groove. And a nut that is formed in a tubular shape having a thread groove that forms a ball rolling path in the inner peripheral portion thereof and that allows the screw shaft to be relatively rotatably inserted, and is arranged side by side in the ball rolling path, Accordingly, a plurality of balls that roll while receiving a load and a portion that is provided on the nut and that is substantially adjacent to the axial direction of the ball rolling path are communicated so as to allow passage of one ball, and the balls are substantially A top member provided with a tunnel-shaped circulation path for circularly circulating infinitely, and a screw shaft side edge portion of an opening located at both ends of the circulation path in the top member, respectively, and a tip portion thereof being the screw shaft. Insert the ball into the thread groove of the ball And a, and a guide protrusion lure into the circulation path.

In the ball screw device according to a fourth aspect of the present invention, a plurality of balls are arranged side by side (in a row) in a spiral ball rolling path, and the balls are associated with relative rotation between the screw shaft and the nut. The ball rolling path and the circulation path of the top member attached to the nut, and infinitely circularly circulates. That is, a ball that has passed through approximately one turn of the spiral ball rolling path is returned to the original position by one round by the circulation path that communicates portions that are substantially adjacent to each other in the axial direction of the ball rolling path. As described above, the substantially circular circulation path in which the balls circulate infinitely is formed by the number of the top members (at least one).

Further, since the circulation path of the top member is a tunnel shape, the infinitely circulating ball does not come into contact with the top of the thread of the screw shaft, and is smoothly affected by the shape of the thread and the like. Then, as described above, it is restored for one lap.

Here, since the guide convex portion of the spinning top member guides the infinitely circulating ball into the circulation path, the ball circulates more smoothly and infinitely. The guide protrusion provided on the screw shaft side edge of the opening guides the ball into the circulation path with the tip of the guide protrusion inserted into the screw groove of the screw shaft. Unlike the conventional ball scooping portion, it is not necessary to form the edge portion, and wear or the like does not pose a problem. Therefore, while maintaining the function of smoothly circulating the balls as described above, the life of the ball screw device and the speed of rotation can be increased.

As described above, the ball screw device according to the fourth aspect operates smoothly by using the top member having the tunnel-shaped circulation path for preventing the contact between the ball and the screw thread.

In order to achieve the second object, claim 5
An electric power steering apparatus according to the invention described above, a rack shaft provided with a rack along the axial direction, and a pinion that meshes with the rack and rotates by a steering torque to move the rack shaft in the axial direction. An electric power steering device connected to an electric motor, the steering force assisting means converting an auxiliary torque generated by the electric motor into a moving force in the axial direction of the rack shaft, The force assisting means is a ball screw device according to any one of claims 1 to 4, wherein a part of the rack shaft is used as the screw shaft and the nut is connected to the electric motor. , Is characterized.

In the electric power steering apparatus according to claim 5,
For example, when the pinion is rotated by the steering torque based on the operation (steering) of the steering wheel connected to the pinion, the rack shaft having the rack meshed with the pinion moves in the axial direction. At this time, the steering force assisting means connected to the electric motor converts the assisting torque of the electric motor into a moving force in the axial direction of the rack shaft to assist the axial movement of the rack shaft.
By this axial movement of the rack shaft, for example, the angle of the wheel connected to the rack shaft via the tie rod and the knuckle arm with respect to the vehicle body is changed (the wheel is steered).

Here, by providing a thread groove on the outer peripheral portion of the rack shaft so that the rack shaft serves as the screw shaft and the nut is connected to an electric motor, the steering force assisting means may be used. Since the ball screw device according to any one of items 1 to 4 is applied, the steering force assisting means is
Works smoothly.

As described above, the electric power steering apparatus according to the fifth aspect includes the ball screw apparatus according to any one of the first to fourth aspects, and operates smoothly.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION An electric power steering device 10 according to an embodiment of the present invention, and a ball as a ball screw device according to an embodiment of the present invention applied to the electric power steering device 10. The screw mechanism 26 will be described with reference to FIGS. 1 to 9.

FIG. 1 is a system diagram showing a schematic structure of an electric power steering apparatus 10 mounted on a vehicle body. As shown in these figures, the electric power steering apparatus 10
Includes a rack shaft 12 which is long in the vehicle width direction. Both ends of the rack shaft 12 are connected to left and right wheels (steering wheels) 18 via a tie rod 14 and a knuckle arm 16, respectively, and the wheels 18 are steered by moving in the axial direction. There is.

The rack shaft 12 has a rack and pinion mechanism 22 for transmitting a steering torque when operating (rotating) the steering wheel 20 and a steering force assist for transmitting an auxiliary torque generated by an electric motor 24 which is a brushless DC motor. A ball screw mechanism 26 as a means is arranged to move in the axial direction.

The rack and pinion mechanism 22 includes a rack 28 provided at one end of the rack shaft 12 in the axial direction.
And a pinion 30 that meshes with the rack 28. The pinion 30 is connected to the steering wheel 20 via a steering shaft 32. The rack-and-pinion mechanism 22 rotates the pinion 3 when the pinion 30 is rotated by the steering torque.
The rack shaft 12 having the rack 28 that meshes with 0 moves in the axial direction. In other words, the rack and pinion mechanism 22 is configured to convert the steering torque into a steering force (steering force) that moves the rack shaft 12 in the axial direction.

On the other hand, the ball screw mechanism 26 is screwed into the screw groove 34 provided on the other axial end of the rack shaft 12 and the screw groove 34 via a large number of balls 70 (described later), and the electric motor 24 And a ball screw nut 36 as a nut connected to. In the ball screw mechanism 26, when the ball screw nut 36 is rotated by the driving force (the auxiliary torque) of the electric motor 24,
The rack shaft 12 having a screw groove 34 that is screwed into the ball screw nut 36 is configured to move in the axial direction. In other words, the ball screw mechanism 26 is configured to convert the auxiliary torque generated by the electric motor 24 into an auxiliary steering force that assists the axial movement of the rack shaft 12. The detailed structure of the ball screw mechanism 26 will be described later.

The electric motor 24 is electrically connected to a control circuit 38, and the control circuit 38 is electrically connected to a torque sensor 40 which detects a steering torque generated by the operation of the steering wheel 20. The torque sensor 40 is disposed between the input shaft 32A and the output shaft 32B that form the steering shaft 32, and the input shaft 32
The steering torque is detected based on the relative angular displacement between A and the output shaft 32B (or each absolute angle thereof). The control circuit 38 causes the electric motor 24 to generate a detection result of the torque sensor 40, that is, an auxiliary torque having a direction and magnitude according to the steering torque (the electric motor 24).
Is driven to rotate).

As shown in the plan sectional view of FIG. 2, the rack shaft 12 described above has the housing 42.
And the housing 42 includes a rack and pinion mechanism 22, an electric motor 24, and a ball screw mechanism 2.
It houses six.

The housings 42 are tubular (tubular), respectively.
The rack housing 44, the tube yoke housing 46, and the end housing 48 formed in the above are coaxially coupled (for example, bolted) to each other to be integrally formed into a cylindrical shape. The housing 42 is
It is configured to be fixed to the vehicle body by a bracket or the like not shown.

The rack housing 44 is the housing 42.
The rack shaft 12 has an end portion on the rack 28 side, and has a pinion chamber 50 for accommodating the pinion 30 engaged with the rack 28. Pinion room 50
The pinion 30 arranged inside is rotatably supported by a bearing (not shown). A rack guide 52 is attached to the rack housing 44. One end of the rack guide 52 has a rack housing 44.
While being pressed by a spring (not shown) provided between the rack 28 and the other end, the other end contacts the back side of the rack 28 on the rack shaft 12 and maintains the meshing of the rack 28 with the pinion 30. ing.

The tube yoke housing 46 constitutes a substantially central portion of the housing 42, and an armature core 54 is fixed to an inner peripheral surface of the central portion in the axial direction thereof. The armature core 54 has a coil (both not shown) wound around a slot formed by being divided into a plurality in the circumferential direction,
A drive current is supplied to each coil via a terminal 54A.

Inside the armature core 54, a substantially cylindrical (hollow) motor shaft 56 is arranged. Both ends of the motor shaft 56 are rotatably supported by the bearings 58 and 60 with respect to the housing 42 with the rack shaft 12 inserted therein.
Further, a ring magnet 62 is bonded to the outer peripheral surface of the motor shaft 56 at a position corresponding to the armature core 54. As a result, the motor shaft 56 forms a magnetic path, and when power is supplied to the coil of the armature core 54 via the terminal 54A, the motor shaft 56
Is designed to rotate.

The tube yoke housing 4 described above
6, armature core 54 (coil, terminal 54A), motor shaft 56, ring magnet 62, bearing 58,
Reference numeral 60 constitutes the electric motor 24, and the electric motor 24 can be rotated forward and backward based on a control signal from the control circuit 38.

The end housing 48 is coupled to the end portion of the tube yoke housing 46 on the side opposite to the rack housing 44 as described above, and covers the end portion of the motor shaft 56 which partially projects into the inside thereof. .

A ball screw nut 36 constituting the ball screw mechanism 26 is mounted inside the end portion of the motor shaft 56 on the side of the end housing 48 by fitting or the like and is prevented from coming off by a lock nut 64. It is adapted to rotate integrally with the motor shaft 56.

The detailed structure of the ball screw mechanism 26 will be described below. As shown in the side sectional view of FIG. 3, in the ball screw mechanism 26, the screw groove 3 of the rack shaft 12 is
4 and the thread groove 66 of the ball screw nut 36 face each other to form a spiral ball rolling path 68. A large number of balls 70 are accommodated in the ball rolling path 68 so as to be rollable while receiving a load. That is, as described above, the ball screw nut 36 is screwed to the rack shaft 12 through the large number of balls 70.

Further, a separator 71 is arranged between a large number of balls 70 to prevent contact between adjacent balls 70. The separator 71 is a ball 7
The ball 70 is formed in a substantially ring shape having a diameter smaller than 0 and a thickness sufficiently smaller than the diameter of the ball 70. Part of the balls 70 adjacent to the recesses (not shown) provided on both sides in the axial direction are formed. The ball 70 is slidably inserted and held between the balls 70. A slight gap is provided between the ball 70 and the recess of the separator 71 in order to prevent unnecessary sliding between the ball 70 and the separator 71.

Further, as shown in FIGS. 4 and 5, the ball screw nut 36 has a thread 66A between the thread grooves 66.
A plurality of (four in the present embodiment) mounting holes 72 are formed by partially cutting out in the circumferential (spiral) direction and penetrating in the radial direction. The mounting holes 72 are elongated holes that are inclined with respect to the axial direction of the ball screw nut 36 and the lead angle direction of the screw groove 66, and are arranged so as to straddle the screw threads 34 </ b> A between the screw grooves 34. The mounting holes 72 are arranged along the spiral ball rolling path 68 while being offset by 90 °, and are offset in the axial direction and located at equal intervals in the circumferential direction.

A top member (deflector) 74 is attached to each attachment hole 72. Top member 74
Is formed substantially corresponding to the mounting hole 72 as a whole, and closes the mounting hole 72. The top member 74 has a tunnel-shaped circulation path 7 through which one ball 70 can pass.
6 is provided. As shown in FIGS. 6 (A) to 6 (C) in which the ball screw nut 36 is omitted, the circulation path 76 is formed in the thread groove 34 (ball rolling path 68) on both sides across the screw thread 34A. The ball 70 is opened and the portion substantially adjacent to the ball rolling path 68 in the axial direction is formed by the ball 70.
It is in communication so that it can pass through. The detailed configuration of the top member 74 will be described later.

As described above, in the ball screw mechanism 26, the ball rolling path 68 and the circulation path 76 are formed, and the ball 70 is infinitely circulated by the relative rotation of the rack shaft 12 and the ball screw nut 36. Of the ball rolling path 68) is formed (see FIG. 3). The same number of balls 70 and separators 71 are alternately arranged in each circulation orbit, and four ball load rows are configured to infinitely circulate in the circulation orbit. In the ball screw mechanism 26, since the top members 74 are arranged at equal intervals in the circumferential direction of the ball screw nut 36,
The ball screw nut 36 is configured to prevent unbalance during rotation driving.

Next, the detailed structure of the top member 74 will be described.
As shown in FIGS. 7A to 7D, the top member 7
4 is configured to include a metal pipe 78 and a resin-made covering portion 80 that covers the outside of the pipe 78 in the radial direction. The inside of the pipe 78 is the above-mentioned tunnel-shaped circulation path 76.
It is said that. 5 to 7, the covering portion 80 is shown by shading the drawings.

The pipe 78 is formed as shown in FIGS. 8A to 8D and 9 by bending and machining a metal pipe formed in a substantially cylindrical shape. There is. Specifically, the pipe 78 is divided into two halves 78A, 78 along the longitudinal direction shown in FIG.
It is configured by combining B. Also, each half 78
In the combined state of A and 78B, the chamfered portion 81 is provided on the inner peripheral surface side of the seam (butting portion) of each other.
A and 81B are formed. Like this, half 78
On the inner peripheral surface (circulation path 76) side of the pipe 78 configured by combining A and 78B, chamfered portions 81A and 81B (a V groove formed by a pair of chamfered portions) along the joint (longitudinal direction) thereof. ) Is formed, a step that hinders the smooth rolling of the ball 70 is not formed.

The pipe 78 in the state where the halves 78A and 78B are combined is formed in a substantially linear shape in plan view (when viewed from the outside in the radial direction when mounted on the ball screw nut 36), as shown in FIG. 8A. In addition, it is curved in an arc shape in a side view as shown in FIG. This curvature (curvature of the ball screw nut 36 in the mounted state as viewed in the axial direction) is determined by the screw groove 34, that is, the ball rolling path 68.
It is larger than the curvature of.

As shown in FIG. 8C, the circulation path 76
The openings 76A, 76B at both longitudinal ends of the pipe 78 are inclined as described above by cutting a part of the pipe wall of the pipe 78 from the side to the bottom (the side of the thread groove 34). The ball 70 is formed so as to be able to move forward and backward with respect to the circulation path 76 (that is, the pipe 78).

The pipe 78 is provided with guide convex portions 82 along the cutout opening edge portions. Each guide convex portion 82 has the above-mentioned openings 76A, 76A.
It is constituted by the pipe wall left uncut in B, and is located so as to intersect with the forward / backward direction of the ball 70. Specifically, each guide convex portion 82 is adapted to enter the adjacent thread groove 34 with the thread ridge 34A sandwiched therebetween in the mounted state by bending the pipe 78 as described above (FIG. 6). (A) and FIG. 6 (C)). In this state, each guide protrusion 82 is formed to have a substantially semicircular shape when viewed from the lead angle direction of the screw groove 34 (the shape projected in the lead angle direction). Also,
As described above, each of the guide protrusions 82 is formed by leaving the pipe wall uncut, so that each guide protrusion 82 is recessed on the ball 70 entry side.

As described above, the guide convex portion 82, which is the pipe wall of the curved pipe 78, has the ball rolling path 68 and the circulation path 7.
6 is connected with a gentle slope (the step on the circulation orbit is eliminated), and the infinitely circulating ball 70 is guided into the tunnel-shaped circulation path 76 inside the pipe 78. That is, the guide convex portion 82 of the pipe 78 and the circulation path 76 which are curved as described above form a locus that smoothly goes around the outside of the thread 34 on the inner surface of the pipe 78.

On the other hand, returning to FIG. 5 to FIG. 7, the covering portion 80 for covering the outside of the pipe 78 is the mounting hole 7 which is the above long hole.
It is formed so as to be able to fit in 2. Moreover, tongue portions 84 are respectively provided on both end portions in the longitudinal direction of the covering portion 80 along the outer surface opposite to the thread groove 34 side, and a part of the central portion on the outer surface side is formed into an arc shape. A pair of cutout recesses 86 is provided. This shape corresponds to the shape of a general top member having a conventional circulation groove.

The top member 74 is fitted (inserted) into the mounting hole 72 in the covering portion 80 and the tongue portions 84 are formed.
Is engaged with stepped portions (not shown) provided at both ends in the longitudinal direction of the mounting hole 72, and a screw head embedded in the ball screw nut 36 from the outside in the radial direction (all not shown).
It is fixed to the ball screw nut 36 by being pressed by. That is, the pipe 78 is fixed to the ball screw nut 36 via the covering portion 80 fitted in the mounting hole 72.

Next, the operation of this embodiment will be described.

In the electric power steering apparatus 10 having the above structure,
When the driver steers the steering wheel 20, the steering torque is converted into a steering force that moves the rack shaft 12 in the axial direction by the rack and pinion mechanism 22,
The rack shaft 12 moves in the axial direction, that is, the vehicle width direction.

At this time, the torque sensor 40 detects the steering torque, and the control circuit 38 causes the electric motor 24 to generate an auxiliary torque corresponding to the steering torque. This auxiliary torque is converted into an auxiliary steering force that assists the axial movement of the rack shaft 12 by the ball screw mechanism 26. As a result, the steering force of the steering wheel by the driver is reduced.

At this time, in the ball screw mechanism 26 in which the ball screw nut 36 rotates with respect to the rack shaft 12 by the electric motor 24, the balls 70 forming each ball load row receive a load (transmit torque).
While rolling, it infinitely circulates in each circulation orbit formed by the ball rolling path 68 and the circulation path 76 of each top member 74. Needless to say, the ball 70 located in the circulation path 76 is not loaded. Further, the adjacent balls 70 are prevented from contacting each other by the separator 71, so that the balls 70 roll smoothly without hindering the rolling of each other.

Since the circulation path 76 of the top member 74 has a tunnel shape, the infinitely circulating ball 70 does not come into contact with the top of the thread 34A of the rack shaft 12 and has a shape such as that of the thread 34A. Smoothly and quietly without being affected, the ball rolling path 68 is returned to its original position by about one lap.

Here, since the tunnel-shaped circulation path 76 is formed inside the pipe 78 in which the chamfered portions 81A and 81B are formed on the inner peripheral surface side at the joint of the pair of half bodies 78A and 78B, No step is formed in the circulation path 76. Then, the resin coating portion 80 for coating the pipe 78 is fitted into the mounting hole 72 of the ball screw nut 36 to fix the pipe 78 to the ball screw nut 36. Since the mounting portion is integrally formed of a resin material, it is not necessary to increase the size of the mounting hole 72 in consideration of a step (dimensional error) when assembling the two members as in the conventional case, and the top member 74 and the ball screw are not necessary. The step difference with the nut 36 can be kept small. As described above, the ball 70 circulates even more smoothly and infinitely.

That is, since the function of forming the tunnel-shaped circulation path 76 in the top member 74 (pipe 78) and the function of attaching the top member 74 to the ball screw nut 36 (covering portion 80) are separated, the circulation path 76 is separated. The top member 74 can be configured by using the pipe 78 that forms (defines) without any step and the covering portion 80 that does not need to enlarge the mounting hole 72.

Further, since the guide convex portion 82 of the pipe 78 guides the ball 70, which circulates infinitely, into the circulation path 76, the ball 70 circulates even more smoothly and infinitely. The guide protrusions 82 respectively provided on the screw shaft side edge portions of the openings 76A and 76B guide the balls 70 into the circulation path 76 with the tips thereof entering the screw grooves 34. It is not necessary to use the edge portion as the portion that comes into contact with 70, and wear or the like does not pose a problem. Therefore, it is possible to extend the life of the ball screw mechanism 26 and increase the rotation speed thereof, while maintaining the function of smoothly circulating the balls 70.

Further, the pipe 78 is covered with a resin covering portion 80.
Since the ball 70 is fixed to the ball screw nut 36 via the, the vibration when the ball 70 passes through the circulation path 76 of the pipe 78 is absorbed by the covering portion 80, and the noise is further reduced. Further, since the circulation path 76 can be formed by simple bending and machining of the metal pipe 78, the manufacturing cost of the top member 74 is reduced.

Furthermore, since there is no step in the circulation path 76 formed by the pipe 78 and the step between the ball screw nut 36 and the top member 74 is small as described above, the separator 71 is prevented from coming off from between the balls 70. To be done. Even if the separator 71 falls off between the balls, the separator 71 does not deviate from the ball load line because it passes through the tunnel-shaped circulation path 76. Therefore, the gap between the separators 71 and the balls 70 does not widen as the separators 71 drop out of the balls 70, and the separator 71 does not fall out of the balls 70 between the balls 70. Further, the separator 71 is also prevented from being caught between the top member 74 and the screw thread 34A.

As described above, in the ball screw mechanism 26 according to the present embodiment, the top member 74 having the tunnel-shaped circulation path 76 for preventing contact between the ball 70 and the screw thread 34A.
To work smoothly. Further, in the electric power steering apparatus 10 to which the ball screw mechanism 26 is applied, the ball screw mechanism 26 operates smoothly and the electric motor 24
The auxiliary torque of is smoothly transmitted to the rack shaft 12.

In the above embodiment, the ball screw mechanism 26 is provided with the top member 74 having the pipe 78 that is substantially linear in plan view, but the present invention is not limited to this, and for example, a ball The screw mechanism 26 may be configured to include a top member 90 according to the modified example shown in FIGS. 10 and 11. The top member 90 has a pipe 92 (see FIG. 11) that is curved in a substantially S shape with respect to its longitudinal direction, and a covering portion 94 that covers the radially outer side of the pipe 92 and fits into the mounting hole 72. Is configured.

Inside the pipe 92, there is provided a tunnel-shaped circulation path 96 corresponding to the pipe 92 and having a substantially S-shape in plan view. The screw groove 3 is formed in the openings 96A and 96B at both ends of the circulation path 96 in the pipe 92.
Guide protrusions 98 are provided along the four side edges. The guide protrusion 98 is similar to the guide protrusion 82 in the thread groove 34.
This is a configuration in which the ball 70 that enters and circulates infinitely is guided into the circulation path 96.

The pipe 92 is constructed by combining a pair of halves 92A, 92B divided into two along the longitudinal direction, and the inner peripheral surface (circulation path 96) at the joint between the halves 92A, 92B. The chamfered portion 99 is formed on the) side so that the circulation path 96 does not have a step that hinders the rolling of the ball 70. That is, like the circulation path 76 of the pipe 78, the circulation path 96 is formed without steps by simple bending and machining of the pipe 92 (there are more bending processes than the pipe 78, but the openings 96A, 96).
It is not necessary to cut out the side part of B). Although not shown, the chamfered portion 99 on the radially inner side of the pipe 92 is formed in the same manner as the chamfered portion 81A of the pipe 78. On the other hand, the covering portion 94 is formed in substantially the same manner as the covering portion 80, and has a tongue portion 84 and a concave portion 86.

The ball screw mechanism 26 (electric power steering apparatus 10) having the top member 90 described above also
The same operation and effect as the configuration including the top member 74 according to the above embodiment can be obtained.

In the above embodiment, the ball screw mechanism 26 is applied to the electric power steering apparatus 10. However, the present invention is not limited to this, and the ball screw mechanism 2 is not limited to this.
6 is any application for converting rotary motion into linear motion or converting linear motion into rotary motion (for example, machine tools)
May be used for.

Further, although the ball screw mechanism 26 is provided with the separator 71 in the above embodiment, the present invention is not limited to this, and the ball screw mechanism 26 is not provided with the separator 71. It goes without saying that it is also good. Note that FIG. 10C shows a structure without the separator 71.

Furthermore, in the above-described embodiment and modification, the top members 74 and 90 have a preferable structure having the guide protrusions 82 and 98, but the present invention is not limited to this.
The top members 74 and 90 may not have the guide protrusions 82 and 98. Further, the top members 74 and 90 are not limited to the preferable configuration in which the pipe 78 is formed by combining the pair of half bodies 78A and 78B and the pipe 92 is formed by combining the pair of half bodies 92A and 92B. The pipes 78 and 92 in which the circulation paths 76 and 96 are formed without steps by bending and machining a seamless pipe made of metal may be provided. in this case,
It goes without saying that the pipe 78 and the like need not have the chamfered portion 81A and the like. Further, the top members 74 and 90 are
The configuration having the guide protrusions 82 and 98 is not limited to the preferred configuration in which the outer side of the pipe 78 or the like is covered by the coating portion 80 or the like, and the pipe 78 or the like is 2 at the central portion in the longitudinal direction.
The structure may be divided, or the part that constitutes the circulation path 76 and the like such as the top member 74 and the part that fits into the mounting hole 72 may be formed integrally (or divided in each of the above directions). good.

[0081]

As described above, the ball screw device according to the present invention is excellent in that it smoothly operates by using the top member having the tunnel-shaped circulation path for preventing the contact between the ball and the screw thread. Have.

The electric power steering apparatus according to the present invention has the above-mentioned ball screw apparatus and has an excellent effect that it operates smoothly.

[Brief description of drawings]

FIG. 1 is a system diagram showing a schematic overall configuration of an electric power steering apparatus to which a ball screw mechanism according to an embodiment of the present invention is applied.

FIG. 2 is a plan sectional view showing an overall configuration of an electric power steering apparatus to which the ball screw mechanism according to the embodiment of the present invention is applied.

FIG. 3 is a sectional view of the ball screw mechanism according to the embodiment of the present invention.

FIG. 4 is a partially cutaway plan view of the ball screw mechanism according to the embodiment of the present invention.

FIG. 5 is a view of the top member constituting the ball screw mechanism according to the embodiment of the present invention as viewed from the inside of the ball screw nut.

6A and 6B are views showing the ball screw mechanism of the embodiment of the present invention with the ball screw nut showing the thread groove and the top member removed, and FIG. 6A is a front view and FIG. 6B is a plan view. ,
(C) is a side view.

FIG. 7 is a diagram showing a top member of a ball screw mechanism according to an embodiment of the present invention, (A) is a plan view, (B) is a front view, (C) is a bottom view, and (D) is a view. It is a side view.

FIG. 8 is a diagram showing a pipe constituting a top member of a ball screw mechanism according to an embodiment of the present invention, (A) is a plan view, (B) is a front view, and (C) is a bottom view. (D) is a side view.

FIG. 9 is a view of the pipe constituting the top member of the ball screw mechanism according to the embodiment of the present invention, which is divided along the longitudinal direction and viewed from the inside.

FIG. 10 is a view showing a screw groove of the ball screw mechanism according to the embodiment of the present invention and a top member according to a modified example with a ball screw nut removed, and (A) is a front view;
(B) is a plan view and (C) is a side view.

FIG. 11 is a view showing a top member according to a modified example which constitutes the ball screw mechanism according to the embodiment of the present invention,
(A) is a front view, (B) is a plan view, and (C) is a side view.

[Explanation of symbols]

10 Electric Power Steering Device 12 Rack Shaft (Screw Shaft) 24 Electric Motor 26 Ball Screw Mechanism (Ball Screw Device, Steering Force Aid Means) 28 Rack 30 Pinion 34 Screw Groove (Screw Groove of Screw Shaft) 34A Thread (Screw) Shaft thread) 36 Ball screw nut (nut) 66 Thread groove (thread groove of nut) 68 Ball rolling path 70 Ball 72 Mounting hole 74 Top member 76 Circulation path 76A, 76B Opening 78 Pipe 78A, 78B Half body 80 Cover 81A, 81B Chamfer 82 Guide convex 90 Top member 92 Pipe 92A, 92B Half 94 Cover 96 Circulation path 96A, 96B Opening 98 Guide convex 99 Chamfer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hajime Uemae             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F-term (reference) 3D033 CA02 CA05 CA16 CA21                 3J062 AA07 AB22 AC07 BA17 BA32                       CD06 CD43

Claims (5)

[Claims] 1. A cylindrical shape having a screw shaft provided with a thread groove on the outer peripheral portion and a thread groove on the inner peripheral portion, the thread groove facing the screw groove and forming a spiral ball rolling path, A nut that allows the screw shaft to relatively rotatably pass therethrough, a plurality of balls that are arranged side by side in the ball rolling path and that roll while receiving a load due to the relative rotation, and a mounting that radially penetrates the nut. Attached to the hole,
A ball screw provided with a top member provided with a circulation path for allowing one ball to pass through portions of the ball rolling path which are substantially adjacent to each other in the axial direction so as to circulate the ball in an infinite circle. In the device, the top member is a metal pipe that is curved corresponding to the ball rolling path and in which the tunnel-shaped circulation path is formed inside, and the attachment that covers the radially outer side of the pipe. A ball screw device, comprising: a resin-made covering portion that fits into a hole and fixes the pipe to the nut. 2. A guide convex portion, which is disposed with its tip portion inserted in a thread groove of the screw shaft and guides the ball into the circulation passage, has a screw at an opening portion located at both ends of the circulation passage in the pipe. The ball screw device according to claim 1, wherein the ball screw device is provided on each of the shaft side edge portions. 3. The pipe is configured by combining half bodies divided into two along the longitudinal direction, and a chamfered portion is formed on an inner surface side of a joint of the half bodies. The ball screw device according to claim 1 or 2. 4. A cylindrical shape having a screw shaft having a thread groove on an outer peripheral portion, and a screw groove facing the screw groove and forming a spiral ball rolling path on an inner peripheral portion, wherein: A nut that allows the screw shaft to be relatively rotatably inserted therein; a plurality of balls that are arranged side by side in the ball rolling path and that roll while receiving a load due to the relative rotation; A top member provided with a tunnel-shaped circulation path that allows the balls to pass through the portions substantially adjacent to each other in the axial direction of the path so as to pass through the ball infinitely in an annular shape, and the top member of the top member. Guide protrusions that are respectively provided on the screw shaft side edges of the openings located at both ends of the circulation path, and guide the balls into the circulation path by inserting the tip into the thread groove of the screw shaft. Ball screw device. 5. A rack shaft provided with a rack along the axial direction, a pinion meshed with the rack and rotating by a steering torque to move the rack shaft in the axial direction, the rack shaft being connected to an electric motor, An electric power steering apparatus comprising: a steering force assisting means for converting an assisting torque generated by an electric motor into a moving force in the axial direction of the rack shaft, wherein the steering force assisting means is the rack shaft. The ball screw device according to any one of claims 1 to 4, wherein a part of the screw shaft is used as the screw shaft and the nut is connected to the electric motor. Power steering device.