JP6519328B2 - Electric power steering device - Google Patents

Description

  According to the present invention, an electric power is transmitted by connecting a rack shaft screwed to a pinion shaft constituting a steering mechanism to a screw shaft of a ball screw mechanism and transmitting rotation of a motor to a nut of the ball screw mechanism via a reduction gear mechanism. It relates to a steering device.

In a rack and pinion type steering apparatus of a vehicle, a steering rotational force when steering a steering wheel is transmitted to a pinion shaft of the steering mechanism, converted into linear motion by a rack shaft screwed with the pinion shaft, and both ends of the rack shaft The steering wheel is transmitted to the turning wheel via a tie rod connected to the steering wheel, and the turning wheel is turned.
By connecting the rack shaft to a ball screw mechanism driven by an electric motor, an electric power steering apparatus can be configured (see, for example, Patent Document 1).

  The electric power steering apparatus of Patent Document 1 includes a drive pulley coaxially fixed to an output shaft of a motor, a driven pulley coaxially set to a nut of a ball screw mechanism, and an endless belt wound around the drive pulley and the driven pulley. The rotation mechanism of the output shaft of the motor is decelerated and transmitted to the nut through the drive pulley, the belt, and the driven pulley.

JP, 2013-24321, A

By the way, since the inertia of the nut, the drive pulley and the inertia of the driven pulley are large in this electric power steering apparatus of Patent Document 1, when the steering wheel is cut to the end and the rack shaft collides with the steering housing, a large impact load This may affect the screw shaft connected to the rack shaft.
Further, in the ball screw mechanism of Patent Document 1, a rolling element return passage for circulating rolling elements between the screw shaft of the ball screw mechanism and the screw groove of the nut is formed inside the nut. As it becomes larger, the inertia of the nut tends to increase.

  Therefore, the present invention has been made focusing on the unsolved problems of the above-described conventional example, and it is an object of the present invention to provide an electric power steering apparatus capable of reducing inertia.

  In order to achieve the above object, an electric power steering apparatus according to the present invention comprises a screw shaft having a screw groove formed on the outer peripheral surface, a nut having an inner peripheral surface and a screw groove corresponding to the screw groove of the screw shaft, A ball screw mechanism having a large number of rolling elements interposed in a helical track formed by a thread groove of a screw shaft and a thread groove of a nut, and a rolling element rolled to one end of the helical track to the other end of the helical track A rolling element circulation passage having a rolling element return passage to be circulated, a drive pulley coaxially fixed to the output shaft of the motor, a driven pulley having a larger diameter compared with the drive pulley coaxially fixed to the outer periphery of the nut A reduction mechanism for reducing rotation of an output shaft of a motor via a driving pulley, a belt and a driven pulley and transmitting the rotation to a nut, and an endless belt wound around a pulley and a driven pulley; The same shaft is connected, and the rack shaft is engaged with the pinion shaft that constitutes the steering mechanism. The driven pulley has an annular core metal coaxially fixed to the outer periphery of the nut. The driven pulley made of synthetic resin is integrally formed, and the rolling element circulating member is integrally formed on the inner circumferential side of the core metal, and the rolling element circulating member is a helical track of the rolling element circulating passage and rolling elements It was arranged at one axial end of the nut to guide the rolling elements between the return passages.

  According to the electric power steering apparatus according to the present invention, since the driven pulley made of synthetic resin is integrally formed on the core metal by injection molding or the like, the inertia can be reduced. In addition, the rolling element circulating member is integrally formed on the core metal, and the rolling element circulating member is disposed at one end of the nut in the axial direction by fixing the core metal to the outer periphery of the nut. The member for fixing the member becomes unnecessary.

FIG. 1 is a front view showing an embodiment of an electric power steering apparatus according to the present invention. It is a front view which shows the rack shaft applied to the electric-power-steering apparatus based on this invention. It is an expanded sectional view showing an important section of an electric power steering device concerning the present invention. It is the figure which showed the core metal which comprises the electric-power-steering apparatus based on this invention, the driven pulley integrally formed to this, and the rolling element circulation member from the axial direction. It is a perspective view which shows the metal core which comprises the electric-power-steering apparatus based on this invention, the driven pulley integrally formed to this, and a rolling element circulation member. It is a figure which shows the structure which fixes a metal core to a nut in the electric-power-steering apparatus based on this invention.

  Next, a first embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimension, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that parts having different dimensional relationships and ratios among the drawings are included.

In addition, the first embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention includes materials, shapes, and structures of component parts. , Arrangement, etc. are not specified to the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.
Hereinafter, an embodiment of an electric power steering apparatus according to a first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a front view showing the main part of the electric power steering apparatus according to the present invention, and FIG. 2 is a front view showing a rack shaft.
In the figure, reference numeral 1 denotes a steering gear mechanism, and the steering gear mechanism 1 includes a pinion mechanism 2 and a rack mechanism 3.
The pinion mechanism 2 includes a pinion shaft 5 rotatably supported by the pinion housing 4. The pinion shaft 5 is connected to a steering wheel via a steering shaft or the like (not shown). The rack mechanism 3 includes a rack shaft 7 slidably supported by the rack housing 6. The pinion shaft 5 and the rack shaft 7 are in mesh with each other, and the rotational force transmitted to the pinion shaft 5 is converted into a direct power by the rack shaft 7.

As shown in FIG. 2, the rack shaft 7 is a ball screw having a rack portion 8 with which the pinion shaft 5 meshes and a ball screw groove 9 a having a spiral gothic arc cross-sectional shape formed on the right side of the rack portion 8. An axis 9 is provided.
The electric power steering device 10 is disposed on the right end side of the rack shaft 7. The electric power steering apparatus 10 includes a ball screw mechanism 11, a steering assisting electric motor 12, and a speed reduction mechanism 13 connecting the ball screw mechanism 11 and the steering assisting electric motor 12.

As shown in FIG. 3, the ball screw mechanism 11 includes a ball screw nut 15 which is screwed to a ball screw groove 9 a of the ball screw shaft 9 of the rack shaft 7 via a ball 14.
The ball screw nut 15 is rotatably supported by a rolling bearing 17 accommodated in a bearing accommodating portion 16 formed at the right end in FIG. 1 of the rack housing 6.
The rolling bearing 17 is integrally assembled to the ball screw nut 15, and the inner ring 17a is connected to the inner ring 17a integrally formed with the ball screw nut 15, and the inner ring 17a via the ball 17b, and a bearing accommodating portion An outer ring 17 c fixed and supported at 16 is constructed.

  The steering assisting electric motor 12 is fixedly supported on the side of the pinion mechanism 2 of the motor support 18 integrally formed outward in the radial direction of the bearing accommodating portion 16 of the rack housing 6, and the rotation shaft 12 a is the motor support 18. It protrudes to the opposite side through the through-hole 18a formed in. The steering assisting electric motor 12 is rotationally driven by a motor control device 40 as shown in FIG. The motor control device 40 includes a torque sensor 40a that detects a steering torque input to a steering wheel (not shown) and a vehicle speed sensor 40b that detects a vehicle speed. The steering torque and the vehicle speed detected by the torque sensor 40a A steering assist torque command value is calculated based on the vehicle speed detected by the sensor 40b, and a motor drive current for causing the steering assist electric motor 12 to generate a necessary steering assist torque is determined based on the calculated steering assist torque command value. The motor drive current is output to the steering assisting electric motor 12.

  The reduction mechanism 13 includes a small diameter pulley 19 attached to the end of the rotary shaft 12a of the steering assisting electric motor 12, a large diameter pulley 20 integrally formed outward in the radial direction of the ball screw nut 15, and a small diameter. The timing belt 21 is wound around the pulley 19 and the large diameter pulley 20. A cover 22 is bolted, for example, to the bearing accommodating portion 16 and the motor support portion 18 so as to cover the small diameter pulley 19, the large diameter pulley 20, and the ball screw groove 9 a.

  In this electric power steering apparatus 10, the small diameter pulley 19 and the large diameter pulley 20 are respectively driven by the timing belt 21 by rotating the rotary shaft 12a of the steering assisting electric motor 12 clockwise as viewed from the left in FIG. Since the ball screw nut 15 is rotationally driven in a clockwise direction according to this, the ball screw shaft 9, that is, the rack shaft 7 is moved to the left, and conversely, the rotation of the steering assisting electric motor 12 The rack shaft 7 is moved to the right by rotationally driving the shaft 12a counterclockwise as viewed from the left. Further, the left end portion of the rack portion 8 of the rack shaft 7 and the right end portion of the ball screw shaft 9 are connected to turning wheels (not shown) via tie rods 23, respectively.

Here, as shown in FIG. 3, the ring-shaped core metal 25 that has passed the outer periphery of the ball screw nut 15 is coaxial with the ball screw nut 15 in a state in which it contacts the side surface 17 a 1 of the inner ring 17 a of the rolling bearing 17. It is fixed to
A large diameter pulley 20 made of synthetic resin and a rolling element circulating member 26 are integrally formed on the core metal 25 by injection molding or the like.

FIGS. 4 (a) and 4 (b) are views of the core metal 25 integrally formed with the large diameter pulley 20 made of synthetic resin and the rolling element circulating member 26, viewed from the axial direction, and FIG. 4 (a) is The large diameter pulley 20 protrudes in the front direction of the drawing with respect to the core metal 25 and the rolling element circulating member 26 is positioned inside the large diameter pulley 20. FIG. 4 (b) shows the core metal The back of 25 is shown.
A circular hole 25a is formed at an axial center position of the ring-shaped core metal 25, and a notch 25b is formed in a part of the periphery of the circular hole 25a.

A large diameter pulley 20 made of synthetic resin is integrally formed on the outermost periphery of the metal core 25 in a state where one end in the width direction is continuous.
An annular portion 27 made of a synthetic resin and a roll extending to the inner side of the annular portion 27 (inner side than the circular hole 25 a) are provided on the periphery of the circular hole 25 a of the core 25 located inside the large diameter pulley 20. The moving body circulation member 26 is integrally formed.

A cylindrical rolling element return member 28 is integrally formed on the rolling element circulating member 26. As shown in FIG. 5, the rolling element return member 28 extends along the axial direction of the core metal 25. The protrusion 25 is projected to the back side of the core metal 25 through the notch 25 b.
As shown in FIG. 6, the ball screw nut 15 constituting the ball screw mechanism 11 is formed with a ball screw groove 15a having a gothic arc cross-sectional shape in which the ball 14 spirally rolls on the inner peripheral surface.

Then, a spiral track is formed by the ball screw groove 9 a of the ball screw shaft 9 and the ball screw groove 15 a of the ball screw nut 15.
A rolling element circulating member mounting portion 29 is formed at the right end portion in the axial direction of the ball screw nut 15 by cutting out a part of the axially outermost ball screw groove 15a.
The rolling element circulating member 26 integrally formed on the core metal 25 is fitted into the rolling element circulating member mounting portion 29 to guide the ball 14 between the spiral track and the rolling element return passage described later. It has become.

Inside the rolling bearing 17, a circulation part (not shown) for guiding the ball 14 is formed between the spiral track and the rolling element return passage. And, on the side surface 17a1 of the inner ring 17a near the rolling element circulating member mounting portion 29 formed in the ball screw nut 15, a circulation hole 30 communicating with the aforementioned circulating portion is formed.
A plurality of screw holes 31 are formed in the side wall 17 a 1 of the rolling bearing 17 along the outer periphery of the ball screw nut 15. Further, through holes 32 are formed at a plurality of locations corresponding to the screw holes 31 formed in the side wall 17 a 1 at the periphery of the circular hole 25 a of the core metal 25.

  Then, the core metal 25 through which the circular hole 25 a passes through the outer periphery of the ball screw nut 15 abuts against the side wall 17 a 1 of the rolling bearing 17, passes the bolt 33 through the through hole 32 of the core metal 25, and enters the screw hole 31 of the side wall 17 a 1 By screwing in, the core metal 25 is fixed to the ball screw nut 15 via the rolling bearing 17. Although one bolt 33 is shown in FIG. 6, it is assumed that the bolt 33 is attached to all the corresponding screw holes 31 and through holes 32.

Here, when the core metal 25 abuts on the side wall 17 a 1 of the rolling bearing 17, the rolling element circulating member 26 integrally formed on the core metal 25 fits in the rolling element circulating member mounting portion 29 of the ball screw nut 15. Get stuck.
Furthermore, the tip of the rolling element return member 28 which is integrally formed on the rolling element circulating member 26 and which protrudes to the back surface side of the core metal 25 through the notch 25b is formed on the side wall 17a1 of the rolling bearing 17. Connected to the circulation hole 30 communicating with the circulation part. Thus, the rolling element return passage is formed by connecting the rolling element return member 28 and the circulation hole 30.

  Here, the screw shaft according to the present invention corresponds to the ball screw shaft 9, the nut according to the present invention corresponds to the ball screw nut 15, the rolling element according to the present invention corresponds to the ball 17b, and the drive according to the present invention The pulley corresponds to the small diameter pulley 19, the driven pulley according to the present invention corresponds to the large diameter pulley 20, the bearing side wall according to the present invention corresponds to the side wall 17 a 1 of the rolling bearing 17, and the bearing according to the present invention is the rolling bearing 17 The motor according to the present invention corresponds to the steering assisting electric motor 12.

Next, the effects of the electric power steering apparatus 10 of the first embodiment will be described.
In the first embodiment, since the large diameter pulley 20 made of synthetic resin is integrally formed on the core metal 25, it is possible to reduce the inertia.
The rolling element circulating member 26 is integrally formed on the core metal 25, and the rolling element circulating member 26 is a rolling element of the ball screw nut 15 by fixing the core metal 25 to the side wall 17 a 1 of the rolling bearing 17. Since it is mounted on the circulating member mounting portion 29, a member for fixing the rolling element circulating member 26 can be eliminated.

Further, since the cylindrical rolling element return member 28 constituting the rolling element return passage is integrally formed on the rolling element circulating member 26, a ball screw nut which has conventionally formed the rolling element return passage inside. Thus, the thickness of the ball screw nut 15 can be reduced, and the weight of the device can be reduced.
Further, the core metal 25 through which the circular hole 25a passes through the outer periphery of the ball screw nut 15 abuts against the side wall 17a1 of the rolling bearing 17, passes the bolt 33 through the through hole 32 of the core metal 25, and enters the screw hole 31 of the side wall 17a1. By screwing in, the core metal 25 is fixed to the ball screw nut 15 via the rolling bearing 17, and the arrangement of the large diameter pulley 20 and the rolling element circulating member 26 to the rolling element circulating member mounting portion 29 of the ball screw nut 15 Since the mounting is completed, the assembly efficiency of the device can be improved.

  Furthermore, when the core metal 25 is fixed to the ball screw nut 15 via the rolling bearing 17, the tip of the rolling element return member 28 integrally formed on the rolling element circulating member 26 is formed on the side wall 17a1 of the rolling bearing 17. Since the rolling element return passage is formed by connecting to the circulation hole 30, the assembly efficiency of the device can be further improved.

Reference Signs List 1 steering gear mechanism 2 pinion mechanism 3 rack mechanism 4 pinion housing 5 pinion shaft 6 rack housing 7 rack shaft 8 rack portion 9 ball screw shaft 9a ball screw groove 10 electric power steering device 11 ball screw mechanism 12 steering assist electric motor 13 deceleration Mechanism 14 Ball 15 Ball screw nut 15a Ball screw groove 16 Bearing accommodating portion 17 Rolling bearing 17a Inner ring 17a1 Side wall 17b Ball 17c Outer ring 18 Motor supporting portion 18a Through hole 19 Small diameter pulley 20 Large diameter pulley 21 Timing belt 22 Cover 23 Tie rod 25 Core metal 26 Rolling element circulating member 25a Circular hole 25b Notched portion 27 Annular portion 28 Rolling element returning member 29 Rolling element circulating member mounting portion 30 Hole for circulation 31 Screw hole 32 Through hole 33 Bolt 40 Motor control device 40a Torque sensor 40b Speed Sensor

Claims (5)

A screw shaft having a screw groove formed on the outer peripheral surface, a nut having a screw groove on the inner peripheral surface corresponding to the screw groove of the screw shaft, and the screw groove of the screw shaft and the screw groove of the nut A ball screw mechanism having a number of rolling elements interposed in a helical track;
A rolling element circulation passage having a rolling element return passage for circulating the rolling element rolled to one end of the spiral track to the other end of the spiral track;
A drive pulley coaxially fixed to the output shaft of the motor, a driven pulley having a larger diameter compared to the drive pulley coaxially fixed to the outer periphery of the nut, and an endless belt wound around the drive pulley and the driven pulley A reduction mechanism for reducing the speed of rotation of the output shaft of the motor via the drive pulley, the belt and the driven pulley and transmitting the rotation to the nut;
The screw shaft of the ball screw mechanism is connected, and a rack shaft screwed to a pinion shaft constituting the steering mechanism;
An annular core metal is coaxially fixed to the outer periphery of the nut, and the driven pulley made of synthetic resin is integrally formed on the outer periphery of the core metal, and a rolling element circulating member is formed on the inner periphery side of the core metal. Are integrally formed,
The rolling element circulating member is disposed at one axial end of the nut for guiding the rolling element between the spiral track of the rolling element circulating passage and the rolling element return passage. Electric power steering device.   2. The electric power steering apparatus according to claim 1, wherein a cylindrical rolling element return member constituting the rolling element return passage of the rolling element circulation passage is integrally formed on the rolling element circulation member. At the other axial end of the nut, a bearing for rotatably supporting the nut is integrally assembled, and inside the bearing, between the spiral track of the rolling element circulation passage and the rolling element return passage The other end side circulation part for guiding the rolling element is formed,
3. The electric power steering apparatus according to claim 2, wherein the rolling element return member is connected to a circulation hole of the other end side circulation portion which is open at a part of the bearing. The cored bar passing through the outer periphery of the nut abuts on a bearing side wall provided orthogonal to the axis of the bearing,
4. The cored bar according to claim 3, wherein the cored bar is fixed to the outer periphery of the nut by screwing a bolt having passed through the through hole formed in the cored bar into a screw hole formed in the bearing side wall. Electric power steering device.   The electric power steering apparatus according to claim 4, wherein a direction in which the circulation hole and the rolling element return member are connected corresponds to a direction in which the cored bar abuts on the bearing side wall.

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