JP2019167965A - Ball screw device and steering device - Google Patents

Abstract

To provide a ball screw device capable of suppressing occurrence of slipping between rolling balls kept into contact with each other even when the rolling balls of the ball screw device have a ball gathering state, reducing a load received by the rolling balls, and surely supporting the power to be transmitted, and a steering device using the ball screw device.SOLUTION: A ball screw device 40 includes large-diameter rolling balls 24a, intermediate-diameter rolling balls 24b having a diameter smaller than that of the large-diameter rolling balls 24a by first prescribed diameter difference α1, and small-diameter rolling balls 24c having a diameter smaller than that of the intermediate-diameter rolling balls 24b by second prescribed diameter difference α2. In a case when magnitude of power P to be transmitted is a first prescribed value P1 or less, the power P is transmitted only by the large-diameter rolling balls 24a on a rolling passage R1, and when the magnitude of the power P to be transmitted is over the first prescribed value P1, and a second prescribed value P2 or less, the power P is transmitted by the large-diameter rolling balls 24a and the intermediate-diameter rolling balls 24b on the rolling passage R1.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a ball screw device and a steering device.

  2. Description of the Related Art Conventionally, there is an automobile steering device that assists the operation of a rack shaft by operating a ball screw device with an electric motor and generating axial thrust on a rack shaft (rack shaft). In such a steering device, the rolling formed between the outer circumferential rolling groove formed on the outer circumferential surface of the rack shaft (screw shaft) and the inner circumferential rolling groove formed on the inner circumferential surface of the rolling element nut. A ball screw device in which the rack shaft and the rolling element nut are screwed together is formed by interposing a plurality of rolling balls having the same diameter in the path. At this time, all of the plurality of rolling balls formed with the same diameter function as load balls that receive a load when power is transmitted between the outer circumferential rolling groove and the inner circumferential rolling groove.

  In the above steering device, for example, when a steering operation such as a lane change on an expressway is repeated, a plurality of rolling balls that are aligned with a predetermined gap between each other in the rolling road are arranged. There is a case in which a gap between the rolling balls in a predetermined portion is clogged and the adjacent rolling balls come into contact with each other, so-called a so-called ball gathering state.

  In such a state, each adjacent rolling ball tries to rotate in the same direction according to the relative rotation of the rack shaft and the rolling element nut. Movement (rotation) occurs. For this reason, each rolling ball hinders the rotation of the opponent rolling ball that abuts. This increases the force required to operate the rack shaft in the axial direction, and may cause the driver to feel that the steering operation has become heavy. In addition, for an electric motor that rotates the rolling element nut and moves the rack shaft in the axial direction via the rolling balls, there is a possibility that the load increases and the power consumption increases.

  On the other hand, in the ball screw device described in Patent Document 1, spacer balls are arranged at a plurality of locations one by one in the middle of a plurality of rolling balls (load balls) provided in the ball screw device. The spacer ball is a ball having a diameter smaller than that of the load ball, and in Patent Document 1, a spacer ball formed with one kind of diameter is provided. Therefore, when the magnitude of the power transmitted between the outer circumferential rolling groove and the inner circumferential rolling groove (rolling path) is not more than a predetermined value, only the load ball has the outer circumferential rolling groove and the inner circumferential rolling groove. The spacer ball is disposed between the load balls in a rotatable state. Thereby, even if it comes to the state where the clearance gap between each rolling ball clogs and the adjacent rolling balls contact | abut in the rolling path of a ball screw apparatus, generation | occurrence | production of the slip between the rolling balls which contact | abut can be suppressed.

JP 2017-109624 A

  However, in Patent Document 1, the diameter of the spacer ball is one type. For this reason, when the magnitude of the power transmitted in the rolling path exceeds a preset first predetermined value, a plurality of load balls or outer circumferential rolling grooves (inner circumferential rolling grooves) are elastically deformed, and spacer balls Is in contact with the outer circumferential rolling groove and the inner circumferential rolling groove. Thereby, the spacer ball also functions as a load ball. For this reason, when the size of the power to be transmitted is larger than the first predetermined value, for example, when a ball crushing state occurs in a steering stop or the like when the vehicle is stopped, it functions as a spacer ball. Since there are no rolling balls, the steering operation may become heavy.

  The present invention has been made in view of the above problems, and even when the rolling ball of the ball screw device reaches a ball-striking state, the power transmitted in the rolling path is wide from a small region to a large region. Use of a ball screw device and a ball screw device that can suppress the occurrence of slip between the rolling balls abutting over a range and reduce the load applied to the rolling balls and reliably support the transmitted power. An object of the present invention is to provide a steering apparatus.

(1. Ball screw device)
In the ball screw device of the present invention, a screw shaft in which an outer peripheral rolling groove is formed in a spiral shape on the outer peripheral surface, and an inner peripheral rolling groove corresponding to the outer peripheral rolling groove is formed in a spiral shape on the inner peripheral surface. A rolling element nut, a spiral rolling path formed between the outer circumferential rolling groove and the inner circumferential rolling groove, and a continuous circulation connected to both ends of the rolling path together with the rolling path A connecting member having a connecting passage that forms a path; and a plurality of rolling balls that are arranged to roll in the circulation path. The plurality of rolling balls have a large diameter rolling ball, a medium diameter rolling ball having a diameter smaller than the large diameter rolling ball by a first predetermined diameter difference, and a diameter larger than that of the medium diameter rolling ball. A small-diameter rolling ball that is small by a difference of two predetermined diameters. And when the magnitude | size of the power transmitted between the said outer periphery rolling groove and the said inner periphery rolling groove is below a 1st predetermined value, only the said large diameter rolling ball is the said rolling path in the said rolling path. When the power is transmitted between the outer circumferential rolling groove and the inner circumferential rolling groove, and the magnitude of the transmitted power exceeds the first predetermined value and is equal to or less than a second predetermined value, In the rolling path, the large-diameter rolling ball and the medium-diameter rolling ball transmit the power.

  Thereby, when the magnitude of the power transmitted between the outer circumferential rolling groove and the inner circumferential rolling groove is equal to or less than the first predetermined value, only the large-diameter rolling ball is a load ball on the rolling path. Thus, power is transmitted between the outer peripheral rolling groove and the inner peripheral rolling groove, and the medium diameter rolling ball and the small diameter rolling ball do not transmit power. For this reason, even if the ball gathers in the rolling path and the large diameter rolling ball, the medium diameter rolling ball and the small diameter rolling ball come into contact with each other, the medium diameter rolling ball and the small diameter rolling ball are It is possible to satisfactorily suppress an increase in power transmitted as a spacer ball and transmitted. Thus, in the low load region where the magnitude of the power transmitted between the outer peripheral rolling groove and the inner peripheral rolling groove is not more than the first predetermined value, a small amount of load balls and many spacer balls are used. The increase in power during ball gathering is suppressed, and the relative rotation between the screw shaft and the rolling element nut is made smooth.

  In addition, when the magnitude of the power transmitted between the outer circumferential rolling groove and the inner circumferential rolling groove exceeds the first predetermined value and is equal to or smaller than the second predetermined value, The rolling ball becomes a load ball and transmits power together with the large-diameter rolling ball, and the small-diameter rolling ball does not transmit power. Thus, when the magnitude of the transmitted power exceeds the first predetermined value and is equal to or less than the second predetermined value, the medium-diameter rolling ball is added as a load ball. As described above, since the number of load balls increases, even if the transmitted power is a large power exceeding the first predetermined value, the power is reliably ensured by the medium-diameter rolling ball and the large-diameter rolling ball. Supported. At the same time, since the small-diameter rolling ball functions as a spacer ball, it is possible to satisfactorily suppress an increase in power transmitted between the outer peripheral rolling groove and the inner peripheral rolling groove.

(2. Steering device)
A steering device according to the present invention includes the ball screw device described above. As a result, the steering wheel can be smoothly steered when the magnitude of the power transmitted in the ball screw device is equal to or smaller than the first predetermined value and when it exceeds the first predetermined value and is equal to or smaller than the second predetermined value. A steering device is obtained.

1 is a schematic view showing an electric power steering apparatus according to the present invention. FIG. 2 is an enlarged cross-sectional view of a portion of the steering assist mechanism and the ball screw device of FIG. 1 according to the embodiment. It is a schematic diagram of a circulation path. It is a figure explaining the relationship between a rolling path and a rolling ball. It is a figure explaining a rolling element nut and a deflector. It is a figure explaining the structure of a rolling ball, and is a figure explaining the arrangement | sequence (1) of a rolling ball which concerns on this embodiment. It is a figure explaining the arrangement | sequence (3) of the rolling ball which concerns on this embodiment. It is a graph which shows the relationship between the steering load of a steering wheel, and a steering angle. It is a figure explaining the state of the rolling path and rolling ball in a low load area | region. It is a figure explaining the state of the rolling path and rolling ball in a medium load area | region. It is a figure explaining the state of the rolling path and rolling ball in a high load area | region. It is a figure explaining the arrangement | sequence (4) of the rolling ball which concerns on the modification 1. FIG. It is a figure explaining the arrangement | sequence (5) of the rolling ball which concerns on the modification 1. FIG. It is a figure explaining the arrangement | sequence (6) of the rolling ball which concerns on the modification 2. FIG. It is a figure explaining the arrangement | sequence (7) of the rolling ball which concerns on the modification 3. It is a figure explaining the arrangement | sequence (8) of the rolling ball which concerns on the other aspect of the modification 3.

<1. First embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an entire electric power steering apparatus illustrating a mode in which a ball screw device according to the present invention is applied to an electric power steering apparatus (corresponding to a steering apparatus) for a vehicle.

  The electric power steering device is a steering device that assists the steering force by the steering assist force. The ball screw device of the present invention can be applied to various devices to which the ball screw device can be applied, such as a four-wheel steering device, a rear wheel steering device, and a steer-by-wire device, in addition to the electric power steering device.

(1-1. Configuration of Steering Device 10)
The electric power steering device 10 (hereinafter referred to as the steering device 10) includes a steered shaft 20 (corresponding to a screw shaft of a ball screw device described later) coupled to a steered wheel (not shown) of the vehicle. It is a device that changes the direction of steered wheels (not shown) by reciprocating in the A direction (left-right direction in FIG. 1) that coincides with the axial direction.

  As shown in FIG. 1, the steering device 10 includes a housing 11, a steering wheel 12, a steering shaft 13, a torque detection device 14, an electric motor M (hereinafter referred to as a motor M), and the aforementioned steering shaft. 20, a steering assist mechanism 30, and a ball screw device 40.

  The housing 11 is a fixing member that is fixed to the vehicle. The housing 11 is formed in a cylindrical shape, and passes through the steered shaft 20 so as to be relatively movable in the A direction. The housing 11 includes a first housing 11a and a second housing 11b fixed to one end side (left side in FIG. 1) in the A direction of the first housing 11a.

  The steering wheel 12 is fixed to the end of the steering shaft 13 and is rotatably supported in the vehicle interior. The steering shaft 13 transmits torque applied to the steering wheel 12 by the driver's operation to the steered shaft 20.

  A pinion 13a constituting a rack and pinion mechanism is formed at the end of the steering shaft 13 on the steered shaft 20 side. The torque detection device 14 detects the torque applied to the steering shaft 13 based on the amount of twist of the steering shaft 13.

  The steered shaft 20 extends in the A direction. A rack 22 is formed on the steered shaft 20. The rack 22 meshes with the pinion 13a of the steering shaft 13, and constitutes a rack and pinion mechanism together with the pinion 13a. In the rack and pinion mechanism, the maximum axial force that can be transmitted between the steering shaft 13 and the steered shaft 20 is set based on the use of the steering device 10 or the like.

  Further, the steered shaft 20 is formed with a ball screw portion 23 at a position different from the rack 22. The ball screw portion 23 forms a ball screw device 40 together with a rolling element nut 21 described later, and a steering assist force is transmitted by the steering assist mechanism 30. Both ends of the steered shaft 20 are connected to left and right steered wheels (not shown) via unillustrated tie rods, knuckle arms, and the like, and the steered wheels are steered left and right by the axial movement of the steered shaft 20 in the A direction. Is done.

  The steering assist mechanism 30 is a mechanism that applies a steering assist force to the steered shaft 20 using the motor M as a drive source. The steering assist mechanism 30 includes a motor M, a control unit ECU that drives the motor M, and a driving force transmission mechanism 32. The motor M and the control unit ECU for driving the motor M are accommodated in a case 31 fixed to the first housing 11 a of the housing 11. The control unit ECU determines the steering assist torque based on the output signal of the torque detection device 14 and controls the output of the motor M.

  As shown in FIG. 2, the driving force transmission mechanism 32 includes a driving pulley 36, a driven pulley 34, and a toothed belt 35. The drive pulley 36 is attached to the output shaft 37 of the motor M. The output shaft 37 is disposed in parallel with the axis of the steered shaft 20. The driven pulley 34 is arranged on the outer peripheral side of the rolling element nut 21 so as to be integrally rotatable with the rolling element nut 21.

  One end side (the left side in FIG. 2) of the rolling element nut 21 in the A direction is rotatably supported by the inner peripheral surface 11b1 of the second housing 11b via a ball bearing 33. The toothed belt 35 is suspended from the drive pulley 36 and the driven pulley 34. The driving force transmission mechanism 32 transmits the rotational driving force generated by the motor M between the driving pulley 36 and the driven pulley 34 via the toothed belt 35.

(1-2. Ball screw device)
(1-2-1. Configuration of Ball Screw Device)
As shown in FIG. 2, the ball screw device 40 is mainly accommodated in the second housing 11b. The ball screw device 40 includes a steered shaft 20 (screw shaft), a ball screw portion 23 of the steered shaft 20, a rolling element nut 21 (corresponding to a nut), a connecting member 38, and a plurality of rolling balls 24. The ball screw portion 23 of the steered shaft 20 is formed by winding a plurality of outer peripheral rolling grooves 20 a formed in a spiral shape on the outer peripheral surface.

  The rolling element nut 21 is formed in a cylindrical shape, and is arranged coaxially with the ball screw portion 23 (steering shaft 20) on the outer peripheral side of the ball screw portion 23. The inner circumferential surface of the rolling element nut 21 is formed by winding a plurality of spirally, and includes an inner circumferential rolling groove 21a corresponding to the outer circumferential rolling groove 20a. The outer peripheral rolling groove 20a of the ball screw portion 23 and the inner peripheral rolling groove 21a of the rolling element nut 21 are arranged to face each other.

  A multi-row rolling path R1 on which a plurality of rolling balls 24 roll is formed between the outer circumferential rolling groove 20a and the inner circumferential rolling groove 21a (see the schematic diagram in FIG. 3). In addition, as shown in the schematic diagram of FIG. 3, the rolling path R1 is formed in a spiral shape from the A end to the B end. The outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a of the rolling path R1 are formed as shown in FIG. In the present embodiment, it is assumed that the outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a are both formed of a single R. However, the groove shape of the outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a is not limited to a single R shape, and may be a known single Gothic arch shape or the like.

  As described above, the plurality of rolling balls 24 are arranged to be able to roll in the multi-row rolling paths R1. Thereby, the outer peripheral rolling groove 20 a of the ball screw portion 23 (steering shaft 20) and the inner peripheral rolling groove 21 a of the rolling element nut 21 are screwed together via the plurality of rolling balls 24. As shown in FIG. 6, the plurality of rolling balls 24 include a plurality of large diameter rolling balls 24a, a plurality of medium diameter rolling balls 24b having a diameter smaller than the large diameter rolling balls 24a by a first predetermined diameter difference α1, and This is a ball group composed of a plurality of small-diameter rolling balls 24c whose diameter is smaller than the middle-diameter rolling ball 24b by a second predetermined diameter difference α2. The first predetermined diameter difference α1 and the second predetermined diameter difference α2 will be described in detail later.

  During the rotation of the ball screw in which the rolling element nut 21 and the steered shaft 20 (screw shaft) rotate relative to each other, a rolling function that functions as a load ball among the plurality of rolling balls 24 in the rolling path R1 shown in FIG. The moving ball (for example, the large diameter rolling ball 24a) is in contact with the point q on the groove surface of the inner peripheral rolling groove 21a and the point p on the groove surface of the outer peripheral rolling groove 20a. When the ball screw rotates, the power P is transmitted between the inner peripheral rolling groove 21a and the outer peripheral rolling groove 20a via the large-diameter rolling ball 24a.

  The connecting member 38 includes the rolling element nut 21 and the deflectors 51 and 52 described above. The connecting member 38 includes a connecting passage 43 that is connected to both ends (A end and B end in FIG. 3) of the rolling path R1 and forms a continuous circulation path 50 (see FIG. 3) together with the rolling path R1. The connecting passage 43 is a passage for the rolling ball 24 and is formed in the rolling element nut 21 and the deflectors 51 and 52.

  As shown in FIGS. 2 and 5, the rolling element nut 21 is formed with a pair of long mounting holes 41 and 42 that penetrate from the outer peripheral surface 21 b to the inner peripheral rolling groove 21 a on the inner peripheral surface. The pair of mounting holes 41 and 42 are connected to both ends (A end and B end) of the rolling path R1. Deflectors 51 and 52 are press-fitted into the pair of mounting holes 41 and 42, respectively. In addition, a communication groove 21 c that communicates with the pair of mounting holes 41 and 42 is formed on the outer peripheral surface 21 b of the rolling element nut 21. The communication groove 21c is formed in such a size that the large-diameter rolling ball 24a can roll.

  As shown in FIG. 2, the deflectors 51 and 52 are formed with through holes 51 a and 52 a that connect the A end and B end, which are both ends of the rolling path R <b> 1, and the communication groove 21 c. The deflectors 51 and 52 have rolling balls 24 (large diameter rolling balls 24a, medium diameter rolling balls 24b, and small diameter rolling balls 24c) that are scooped up from one end (A end or B end) of the rolling path R1. And has a function of leading to the communication groove 21c through the through holes 51a and 52a. The deflectors 51 and 52 have a function of discharging the rolling ball 24 in the communication groove 21c to the other end (B end or A end) of the rolling path R1 through the through holes 51a and 52a.

  As described above, the through-holes 51a and 52a of the deflectors 51 and 52 and the communication groove 21c of the rolling element nut 21 constitute the connecting passage 43 that short-circuits the A end and the B end of the rolling path R1 (see FIG. 2, see FIG. Thereby, the rolling ball 24 can be infinitely circulated in the circulation path 50 connected to the rolling path R <b> 1 via the connection path 43.

(1-2-2. Details of Rolling Ball 24)
As described above, the plurality of rolling balls 24 is a ball group including a plurality of large-diameter rolling balls 24a, a plurality of medium-diameter rolling balls 24b, and a plurality of small-diameter rolling balls 24c. In the present embodiment, when any three rolling balls that are continuously aligned are taken out of the plurality of rolling balls 24 that are aligned and arranged in a line in the circulation path 50, at least one of them is taken out. The rolling ball is a small diameter rolling ball 24c. Further, the three consecutively aligned rolling balls taken out include one large-diameter rolling ball 24a and one medium-diameter rolling ball 24b.

  Specifically, as shown in the schematic diagram of FIG. 6, the plurality of rolling balls 24 aligned in the circulation path 50 include a large-diameter rolling ball 24a (large), a medium-diameter rolling ball 24b (medium), and The small-diameter rolling balls 24c (small) are repeatedly arranged in the circulation path 50 in the order of arrangement (1) large → medium → small → large → medium → small. In the following description, when the arrangement order of the large diameter rolling balls 24a, the medium diameter rolling balls 24b, and the small diameter rolling balls 24c is described, only the large diameter rolling balls 24a are described as being large. The rolling ball 24b will be described only as medium, and the small-diameter rolling ball 24c will be described only as small. Further, when explaining the arrangement of the rolling balls 24, it is assumed that they are arranged from left to right in each figure.

  In the above, the arrangement (1) may be arranged in either direction in the circulation path 50. That is, in the direction opposite to the above-described arrangement direction, the arrangement (2) in the drawing may be arranged in the order of large → medium → small → large → medium → small → large → medium → small. Good. Further, the order of medium and large may be switched, and the arrangement (3) may be arranged in the order of medium → large → small → middle → large → small → middle → large → small... (See FIG. 7). Thereby, the number of each of the plurality of large-diameter rolling balls 24 a, the plurality of medium-diameter rolling balls 24 b and the plurality of small-diameter rolling balls 24 c arranged in the circulation path 50 is approximately the total number of the rolling balls 24. One-third is arranged.

  Further, in the above, between the plurality of rolling balls 24, the diameter φD1 (sphere diameter) of the plurality of large diameter rolling balls 24a and the diameter φD2 (sphere diameter) of the plurality of medium diameter rolling balls 24b. Is a first predetermined diameter difference α1 (α1 = φD1−φD2). The diameter difference between the diameter φD2 (sphere diameter) of the medium-diameter rolling ball 24b and the diameter φD3 (sphere diameter) of the small-diameter rolling ball 24c is the second predetermined diameter difference α2 (α2 = φD2). -ΦD3). The magnitudes of the first predetermined diameter difference α1 and the second predetermined diameter difference α2 are approximately several μm to several tens of μm.

  In the above description, the diameter φD1, the diameter φD2, and the diameter φD3 are the average sphere diameters in the respective groups of the rolling balls 24a, 24b, and 24c, respectively. At this time, the variation widths of the ball diameters of the rolling balls 24a, 24b, and 24c in each group are very small, and the individual ball diameters do not overlap between the groups of the rolling balls 24a, 24b, and 24c. Shall.

  The first predetermined diameter difference α1 indicates that when the magnitude of the power P to be transmitted in the rolling path R1 exceeds a first predetermined value P1 described later, the plurality of large-diameter rolling balls 24a are arranged on the inner circumferential rolling groove. It is equal to the amount of movement (elastic deformation) in the radial direction between 21a and the outer peripheral rolling groove 20a. The second predetermined diameter difference α2 is a plurality of values when the magnitude of the power P to be transmitted in the rolling path R1 exceeds a first predetermined value P1 and then a second predetermined value P2 described later. It is equal to the amount that the large-diameter rolling ball 24a and the medium-diameter rolling ball 24b move (elastically deform) relatively in the radial direction between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a.

  The first predetermined diameter difference α1 and the second predetermined diameter difference α2 are the first predetermined value P1, the second predetermined value P2, the number of the large diameter rolling balls 24a and the medium diameter rolling balls 24b, and the Young's modulus of each material. Etc. are set based on the above. The large-diameter rolling ball 24a, the medium-diameter rolling ball 24b, and the small-diameter rolling ball 24c are formed of an iron-based material such as stainless bearing steel, for example.

  In the above, the first predetermined value P1 and the second predetermined value P2 may be set assuming any situation. However, in the present embodiment, as an example, the first predetermined value P1 is set at a predetermined speed. This is set assuming frequent lane changes during driving. The second predetermined value P2 is set on the assumption that the steered wheels (not shown) are stationary when the vehicle is stopped.

  Therefore, the first predetermined value P1 and the second predetermined value P2 will be described based on the graph of FIG. Note that the diagrams G1 and G2 in the graph of FIG. 8 show the steering wheel 12 during normal times when the ball is not gathered (the road surface is a dry paved road and the steered wheels have a sufficiently deep tire groove). This is experimental data showing the relationship between the steering angle (steering angle) θ of the steering wheel 12 and the steering load Q when the steering wheel is steered. The diagrams G1 and G2 in FIG. 8 are graphs with different conditions of the vehicle speed V. The diagram G1 shows an example of data when the vehicle is traveling at a predetermined speed V (for example, 80 km / h), and the diagram G2 shows an example of data when the vehicle is stopped (V = 0).

  In the diagrams G1 and G2, the steering load Q when the steering wheel 12 is steered to the right from the position of the steering angle 0 deg is shown on the right side of the steering angle 0 deg and on the upper side of the diagrams G1 and G2. ing. Further, the steering load Q when the steering wheel 12 is steered in the left direction from the position of the steering angle 0 deg is shown on the left side of the steering angle 0 deg and below the diagrams G1 and G2.

  That is, in FIG. 8, the steering load Q when steering the steering wheel 12 in the right direction is positive, and the steering load Q when steering the steering wheel 12 in the left direction is negative. Further, the steering load Q decreases as the vehicle speed V increases, and the steering load Q increases as the vehicle speed V decreases.

  Further, in the graph of FIG. 8, the steering load Q of the steering wheel 12 is caused by the plurality of rolling balls 24 between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a when the ball screw device 40 is operated. What is necessary is just to consider that it is equal to the magnitude | size of the power P transmitted. Further, the diagram G1 merely illustrates data at a predetermined one speed, and the diagram is prepared for each vehicle speed V.

  Then, the inventor found that the steering load Q that the driver feels that the steering load of the steering wheel 12 is heavy when the vehicle is traveling straight ahead at a high speed (for example, 80 km / h), based on literature investigations and experiments. It was assumed that the steering load was when the steering angle θ1 exceeded ± 40 deg. Accordingly, in the diagram G1, ± 40 deg that is a point before the point exceeding ± 40 deg is selected, and the steering load Q1 at ± 40 deg is set as the first predetermined value P1. However, the steering angle θ1 of ± 40 deg is merely an example, and may be arbitrarily set to a desired angle.

  Further, the inventor found that the steering load Q that the driver feels that the steering load of the steering wheel 12 is heavy when the vehicle is stopped in a stationary state from the literature investigation and experiment, the steering angle θ2 is ± 300 deg. It was assumed that the steering load was exceeded. Therefore, ± 300 deg which is a point before the point exceeding ± 300 deg in the diagram G2 is selected, and the steering load Q2 at ± 300 deg is set as the second predetermined value P2. However, as described above, the steering angle θ2 is set to ± 300 deg to the last, and may be arbitrarily set to a desired angle.

  As described above, the first predetermined diameter difference α1, which is the difference between the diameter of the large diameter rolling ball 24a and the diameter of the medium diameter rolling ball 24b, and the diameter of the medium diameter rolling ball 24b and the small diameter rolling ball 24b. A second predetermined diameter difference α2 that is a difference in diameter from the diameter of the moving ball 24c is obtained by experiments or the like based on the first predetermined value P1 (steering load Q1) and the second predetermined value P2 (steering load Q2), respectively.

  That is, when the power P exceeding the first predetermined value P1 (steering load Q1) is transmitted between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a, the large-diameter rolling ball 24a, the inner circumferential rolling Large-diameter rolling that enables at least one member of the rolling groove 21a and the outer circumferential rolling groove 20a to be elastically deformed so that the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a abut on the medium-diameter rolling ball 24b. The diameter difference between the ball 24a and the medium diameter rolling ball 24b is obtained and set as the first predetermined diameter difference α1 (see FIG. 6).

  When the power P exceeding the second predetermined diameter difference α2 (steering load Q2) is transmitted between the inner peripheral rolling groove 21a and the outer peripheral rolling groove 20a, the large diameter rolling ball 24a, the medium diameter At least one member of the rolling ball 24b, the inner circumferential rolling groove 21a, and the outer circumferential rolling groove 20a is elastically deformed, and the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a are in contact with the small-diameter rolling ball 24c. The diameter difference between the medium diameter rolling ball 24b and the small diameter rolling ball 24c that can be obtained is obtained and set as the second predetermined diameter difference α2 (see FIG. 6).

(1-3. Action)
Next, the operation of the ball screw device 40 in the steering device 10 will be described. In the description, the power P transmitted between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a is divided into a case where it is in a low load region, a case where it is in a middle load region, and a case where it is in a high load region. To do. In all the states, it is assumed that at least a part of the rolling balls 24 arranged (accommodated) in the rolling path R1 is in a ball-striking state (see FIG. 6).

  Note that, for example, when the vehicle is traveling at a predetermined speed, the driver causes the steering wheel to steer left and right in small increments so that the plurality of rolling balls in the rolling path R1 approach each other. This is a known phenomenon that abuts in due course. Since the ball gathering is a known phenomenon, a detailed description thereof is omitted.

(1-3-1. Low load region)
First, the low load region will be described with reference to FIGS. The low load region refers to a region in a range up to a first predetermined value P1 (steering load Q1) among regions of power P transmitted between the inner peripheral rolling groove 21a and the outer peripheral rolling groove 20a ( (See FIG. 8). In the low load region, as shown in FIG. 9, in the rolling path R1, among the rolling balls 24 having three types of diameters, only the large-diameter rolling ball 24a has the inner circumferential rolling groove 21a and the outer circumferential rolling groove. 20a is contacted. That is, only the large-diameter rolling ball 24a becomes a load ball, and the power P is transmitted between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a. FIG. 9 is a diagram created based on the arrangement (1) of the rolling balls 24 described above.

  When the transmitted power P increases in the low load region, at least one member of the large-diameter rolling ball 24a, the inner circumferential rolling groove 21a, and the outer circumferential rolling groove 20a that receives the load is elastically deformed in the radial direction. To do. At this time, the diameter of the medium-diameter rolling ball 24b is formed smaller than the diameter of the large-diameter rolling ball 24a by a first predetermined diameter difference α1 set based on the first predetermined value P1. For this reason, until the power P exceeding the first predetermined value P1 (= steering load Q1) is applied between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a, the inner circumferential rolling groove 21a and the outer circumferential rolling groove 21a. The rolling groove 20a does not contact the medium diameter rolling ball 24b.

  As described above, in the low load region, the steering load Q is borne only by the large-diameter rolling balls 24a constituted by approximately one third of the total number of the plurality of rolling balls 24. Since this is an area, the steering load Q is not large and has sufficient durability.

  At the same time, in the low load region, a medium-diameter rolling ball 24b and a small-diameter rolling ball 24c that function as spacer balls are provided. That is, about 2/3 of the total number of the plurality of rolling balls 24 is the spacer ball. For this reason, when the ball screw device 40 is operated and the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a rotate relative to each other, even if the rolling ball 24 is in a ball-fed state, the medium-diameter rolling ball 24b and the small-diameter rolling ball 24b. The rolling ball 24c is allowed to idle and favorably suppresses an increase in the steering load Q of the steering wheel 12.

(1-3-2. Medium load region)
Next, the medium load region will be described with reference to FIGS. FIG. 10 is also a diagram created based on the above-described arrangement (1) of the rolling balls 24, as in FIG. The medium load region refers to the second predetermined value from the power exceeding the first predetermined value P1 (steering load Q1) in the region of the power P transmitted between the inner peripheral rolling groove 21a and the outer peripheral rolling groove 20a. A region formed in a range up to P2 (see FIG. 8). In the middle load region, as shown in FIG. 10, when the power P exceeds a first predetermined value P1 (steering load Q1), at least one of the large-diameter rolling ball 24a, the inner circumferential rolling groove 21a, and the outer circumferential rolling groove 20a. One member is elastically deformed in the radial direction, and the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a are in contact with the medium-diameter rolling ball 24b. Thereby, the medium-diameter rolling ball 24b functions as a load ball together with the large-diameter rolling ball 24a.

  Thereafter, at least one member of the large-diameter rolling ball 24a, the medium-diameter rolling ball 24b, the inner circumferential rolling groove 21a, and the outer circumferential rolling groove 20a that receives a load is elastically deformed in the radial direction, and the inner circumferential rolling groove 21a and the outer peripheral rolling groove 20a are displaced until just before contacting the small-diameter rolling ball 24c. That is, at least one member of the large-diameter rolling ball 24a, the medium-diameter rolling ball 24b, the inner circumferential rolling groove 21a, and the outer circumferential rolling groove 20a that receives a load is elastically deformed in the radial direction. The diameter of the ball 24c is formed to have a second predetermined diameter difference α2 with respect to the diameter of the medium diameter rolling ball 24b.

  For this reason, until the power P exceeding the second predetermined value P2 (= steering load Q2) is applied between the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a, the inner circumferential rolling groove 21a and the outer circumferential rolling groove 21a. The rolling groove 20a does not contact the small diameter rolling ball 24c. As described above, in the medium load region, the large-diameter rolling ball 24a is configured with approximately one third of the total number of the plurality of rolling balls 24, and is also configured with approximately one third. The intermediate rolling ball 24b bears a steering load Q up to a steering load Q2 (Q1 <Q2) larger than the steering load Q1, so that it has sufficient durability.

  At the same time, a small-diameter rolling ball 24c that functions as a spacer ball is provided in the medium load region. That is, approximately 1/3 of the total number of the rolling balls 24 is provided. For this reason, when the ball screw device 40 is operated and the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a rotate relative to each other, the small-diameter rolling ball 24c is allowed to move freely even if the rolling ball 24 is in a ball-fed state. This effectively suppresses an increase in the steering load Q of the rolling steering wheel 12.

(1-3-3. High load region)
Next, the high load region will be described with reference to FIGS. Note that FIG. 11 is also a diagram created based on the above-described arrangement (1) of the rolling balls 24 as in FIG. 9 and the head 10. The high load region is formed in a range of the power exceeding the second predetermined value P2 (steering load Q2) in the region of the power P transmitted between the inner peripheral rolling groove 21a and the outer peripheral rolling groove 20a. An area to be processed (see FIG. 8). In the high load region, as shown in FIG. 11, when the power P exceeds the second predetermined value P2 (steering load Q2), the large-diameter rolling ball 24a, the small-diameter rolling ball 24c, the inner peripheral rolling groove 21a, and the outer peripheral At least one member of the rolling groove 20a is elastically deformed in the radial direction, and the inner circumferential rolling groove 21a and the outer circumferential rolling groove 20a are in contact with the small-diameter rolling ball 24c.

  Thereby, the small diameter rolling ball 24c also functions as a load ball together with the medium diameter rolling ball 24b and the large diameter rolling ball 24a. That is, all of the rolling balls 24 function as load balls. Thereby, in the high load region, even a very large steering load Q exceeding the steering load Q2 can be favorably supported, and high durability can be obtained.

(1-4. Effects of First Embodiment)
According to the first embodiment, the plurality of rolling balls 24 include a large-diameter rolling ball 24a, a medium-diameter rolling ball 24b whose diameter is smaller than the large-diameter rolling ball 24a by a first predetermined diameter difference α1. A small-diameter rolling ball 24c having a diameter smaller than the middle-diameter rolling ball 24b by a second predetermined diameter difference α2.

  When the magnitude of the power P transmitted between the outer circumferential rolling groove 20a and the inner circumferential rolling groove 21a is equal to or less than the first predetermined value P1, only the large-diameter rolling ball 24a is on the outer circumference on the rolling path R1. When the power P is transmitted between the rolling groove 20a and the inner peripheral rolling groove 21a, and the magnitude of the transmitted power P exceeds the first predetermined value P1 and is equal to or less than the second predetermined value P2, In the rolling path R1, the large diameter rolling ball 24a and the medium diameter rolling ball 24b transmit the power P.

  Thereby, when the magnitude of the power P transmitted between the outer circumferential rolling groove 20a and the inner circumferential rolling groove 21a is equal to or less than the first predetermined value P1, the large-diameter rolling ball 24a in the rolling path R1. Only the load ball becomes a load ball, and power P is transmitted between the outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a, and the medium-diameter rolling ball 24b and the small-diameter rolling ball 24c do not transmit the power P. . For this reason, even if the ball gathering occurs in the rolling path R1, and the large diameter rolling ball 24a, the medium diameter rolling ball 24b, and the small diameter rolling ball 24c come into contact with each other, the medium diameter rolling ball 24b and It is possible to satisfactorily suppress the small-diameter rolling ball 24c from rolling as a spacer ball and increasing the transmitted power P.

  Thus, in a low load region where the magnitude of the power P transmitted between the outer peripheral rolling groove 20a and the inner peripheral rolling groove 21a is equal to or less than the first predetermined value P1, a small amount of load balls (large diameter The rolling balls 24a) and many spacer balls (medium-diameter rolling balls 24b and small-diameter rolling balls 24c) suppress an increase in power P at the time of ball gathering, and the rolling element nut 21 and the steering shaft 20 (screws) Smooth relative rotation with the shaft).

  Further, when the magnitude of the power P transmitted between the outer circumferential rolling groove 20a and the inner circumferential rolling groove 21a exceeds the first predetermined value P1 and is equal to or smaller than the second predetermined value P2, the rolling In the path R1, the medium-diameter rolling ball 24b serves as a load ball and transmits the power P together with the large-diameter rolling ball 24a, and the small-diameter rolling ball 24c does not transmit the power P.

  Thus, when the magnitude of the transmitted power P exceeds the first predetermined value P1 and is equal to or smaller than the second predetermined value P2, the medium-diameter rolling ball 24b is added as a load ball. Accordingly, since the number of load balls increases, even if the power P to be transmitted is a large power exceeding the first predetermined value P1, the power P is used for the medium-diameter rolling ball 24b and the large-diameter rolling ball 24a. Is surely supported by. At the same time, since the small-diameter rolling ball 24c functions as a spacer ball, the outer peripheral rolling groove 20a and the inner peripheral rolling groove even if the rolling ball 24 is moved in the rolling path R1. It is possible to satisfactorily suppress an increase in power P transmitted to and from 21a.

  In addition, according to the first embodiment, when the magnitude of the power P to be transmitted exceeds the second predetermined value P2 and enters the high load region, the large-diameter rolling ball 24a, the medium-diameter rolling ball in the rolling path R1. The moving ball 24b and the small diameter rolling ball 24c transmit power. As a result, the power P is reliably supported by the large-diameter rolling ball 24a, the medium-diameter rolling ball 24b, and the small-diameter rolling ball 24c, so that sufficient durability can be obtained.

  Further, according to the first embodiment, the steering device 10 includes the ball screw device 40. Thus, when the magnitude of the power P transmitted in the ball screw device 40 is equal to or less than the first predetermined value P1, and when the magnitude exceeds the first predetermined value P1 and equal to or less than the second predetermined value P2, the steering wheel 12 Can be smoothly steered.

<2. Modification of First Embodiment>
(2-1. Modification 1)
In the first embodiment, among the plurality of rolling balls 24 arranged in alignment in the circulation path 50, a plurality of large-diameter rolling balls 24a (large) and medium-diameter rolling balls 24b (medium ) And small-diameter rolling balls 24c (small) are arranged as follows: (1) Large → Medium → Small → Large → Medium → Small → Large → Medium → Small (or (3) Medium → Large → Small → Medium → Large → Small → Medium → Large → Small ...) However, it is not limited to this aspect.

  As a first modification of the first embodiment, the plurality of rolling balls 24 arranged in the circulation path 50 include at least one rolling ball out of the three rolling balls that are continuously aligned. If so, the other two rolling balls may be any rolling balls. That is, in the circulation path 50, an arrangement of a plurality of large-diameter rolling balls 24a (large), medium-diameter rolling balls 24b (medium), and small-diameter rolling balls 24c (small) is, for example, as shown in FIG. Arrangement (4) The arrangement may be repeated in the order of large → large → small → medium → medium → small → large → large → small. Further, as shown in FIG. 13, the arrangement (5) may be repeatedly arranged in the order of large → small → small → medium → small → small → large → small → small.

  When a plurality of rolling balls 24 are arranged in the arrangement order of the array (4), the same effect as in the first embodiment can be expected. Further, when the plurality of rolling balls 24 are arranged in the arrangement order of the array (5), the number of large-diameter rolling balls 24a and medium-diameter rolling balls 24b in the total number of the plurality of rolling balls 24. And the ratio of the number of small-diameter rolling balls 24c increases. For this reason, the number of load balls (large-diameter rolling balls 24a and medium-diameter rolling balls 24b) decreases in the low-load region and the medium-load region, thereby reducing the power P that can be transmitted. And preferably used. However, when arranged in the arrangement order of the array (5), the number of spacer balls (small-diameter rolling balls 24c) increases in the medium load region, so that the effect of reducing the increase in the steering load Q is improved.

(2-2. Modification 2)
As a second modification of the first embodiment, the ball screw device 40 includes any two rolling balls 24 that are continuously arranged among the plurality of rolling balls 24 that are arranged in the circulation path 50. You may arrange | position so that a ball may be equipped with the small diameter rolling ball 24c and one of the large diameter rolling ball 24a or the medium diameter rolling ball 24b. Specifically, the plurality of rolling balls 24 in the circulation path 50 include a plurality of large-diameter rolling balls 24a (large), medium-diameter rolling balls 24b (medium), and small-diameter rolling balls 24c (small), for example. As shown in FIG. 14, the arrangement (6) may be repeatedly arranged in the order of large → small → medium → small → large → small → medium → small → large.

  In this way, by arranging the plurality of rolling balls 24 in the arrangement order of the array (6), only the large-diameter rolling ball 24a becomes the load ball in the low load region, and the medium-diameter rolling ball 24b and the small-diameter rolling ball 24b. The rolling ball 24c becomes a spacer ball. Also in the medium load region, the large diameter rolling ball 24a and the medium diameter rolling ball 24b are load balls, and the small diameter rolling ball 24c is a spacer ball. Thereby, the effect similar to 1st embodiment is acquired.

  However, in the array (6) in the modified example 2, as in the array (5) in the modified example 1, the number of large-diameter rolling balls 24a and medium-diameter rolling balls 24b occupying the total number of the plurality of rolling balls 24. The ratio decreases, and the ratio of the number of small diameter rolling balls 24c increases. For this reason, the number of load balls (large-diameter rolling balls 24a and medium-diameter rolling balls 24b) decreases in the low-load region and the medium-load region, thereby reducing the power P that can be transmitted. And preferably used. However, when arranged in the arrangement order of the array (6), the number of spacer balls (small-diameter rolling balls 24c) increases in the low-load region and the medium-load region, so that the effect of reducing the increase in the steering load Q is reduced. Will improve.

(2-3. Modification 3)
As a third modification of the first embodiment, a plurality of rolling balls 24 may be arranged as follows. That is, in Modification 3, the plurality of rolling balls 24 arranged in the circulation path 50 is one of the four rolling balls that are continuously aligned, and one of them is a small-diameter rolling ball 24c. Each piece is one of the large-diameter rolling ball 24a and the medium-diameter rolling ball 24b. The remaining one is the other of the large diameter rolling ball 24a or the medium diameter rolling ball 24b. Further, the four rolling balls are configured by successively rolling balls having different diameters. That is, in the four rolling balls that are continuously aligned, the rolling balls having the same diameter are not continuously arranged.

  Therefore, in the modified example 3, the plurality of large-diameter rolling balls 24a (large), medium-diameter rolling balls 24b (medium), and small-diameter rolling balls 24c (small) in the circulation path 50 are, for example, large in the arrangement (7). It may be arranged in the order of → medium → large → small → large → medium → large → small → large → medium → large → small (see FIG. 15). As another mode, for example, the arrangement (8) is arranged in the order of large → medium → large → small → medium → large → medium → small → large → medium → large → small → medium → large → medium → small. (See FIG. 16).

  By arranging in such an arrangement order of the array (7) and the array (8), the ratio of the number of large-diameter rolling balls 24a or medium-diameter rolling balls 24b to the total number of the plurality of rolling balls 24 is as follows. The number of small diameter rolling balls 24c increases and the ratio of the number of small diameter rolling balls 24c decreases. For this reason, the number of load balls (large diameter rolling balls 24a and medium diameter rolling balls 24b) increases and the number of spacer balls (small diameter rolling balls 24c) decreases at least in the medium load region. It is preferable to consider and use.

<3. Other>
In the first embodiment, the ball screw device 40 according to the present invention is applied to the rack parallel type electric power steering device 10. However, it is not limited to this aspect. As another embodiment (not shown), the ball screw device 40 is, for example, a so-called rack direct type in which a rack shaft and a motor are arranged coaxially as described in JP 2011-105075 A, for example. You may apply to an electric steering device. A corresponding effect can be expected also by this.

  In the first embodiment, the circulation path 50 is formed by a multi-row, one-circulation path formed by the multi-row rolling paths R 1 and the single connection passage 43. However, this aspect is not limited. As another embodiment, a circulation path as disclosed in Japanese Patent Application Laid-Open No. 2006-020725 may be formed by a single-row single-circulation path configured by a single-row rolling path and a single connection passage. In this case, an arbitrary number of one line and one circulation path may be provided in the axial direction. A corresponding effect can be expected also by this.

  In the first embodiment, the connecting passage 43 of the connecting member 38 is formed inside the rolling element nut 21. However, the present invention is not limited to this mode, and the connecting passage may be configured by a known return tube system that is formed by attaching a tube or the like outside the rolling element nut 21. Moreover, you may comprise by the system which comprises a connection channel | path using a well-known top. Furthermore, in any case, the connecting passage may be configured by a known end cap method, a guide plate method, or the like. In any case, the same effect as in the above embodiment can be expected.

DESCRIPTION OF SYMBOLS 10; Electric power steering apparatus (steering apparatus), 11; Housing, 12; Steering wheel, 20; Steering shaft (screw axis), 20a; Outer periphery rolling groove, 21; Rolling element nut, 21a; 24; Rolling ball 24a; Large-diameter rolling ball 24b; Medium-diameter rolling ball 24c; Small-diameter rolling ball 38; Connecting member 40; Ball screw device 43 43 Connecting passage 50 50 Circulation path , P; power, P1; first predetermined value, P2; second predetermined value, α1; first predetermined diameter difference, α2; second predetermined diameter difference.

Claims (7)

A screw shaft in which an outer peripheral rolling groove is spirally formed on the outer peripheral surface;
A rolling element nut in which an inner circumferential rolling groove corresponding to the outer circumferential rolling groove is spirally formed on an inner circumferential surface;
A spiral rolling path formed between the outer circumferential rolling groove and the inner circumferential rolling groove;
A connecting member comprising a connecting passage connected to both ends of the rolling path to form a continuous circulation path together with the rolling path;
A plurality of rolling balls arranged to roll in the circulation path;
With
The plurality of rolling balls have a large diameter rolling ball, a medium diameter rolling ball having a diameter smaller than the large diameter rolling ball by a first predetermined diameter difference, and a diameter larger than that of the medium diameter rolling ball. A small-diameter rolling ball that is small by a difference of two predetermined diameters,
When the magnitude of power transmitted between the outer peripheral rolling groove and the inner peripheral rolling groove is equal to or less than a first predetermined value, only the large-diameter rolling ball is transferred to the outer peripheral rolling groove in the rolling path. Transmitting the power between the moving groove and the inner peripheral rolling groove,
When the magnitude of the power to be transmitted exceeds the first predetermined value and is equal to or less than the second predetermined value, the large-diameter rolling ball and the medium-diameter rolling ball are in the rolling path in the rolling path. A ball screw device that performs transmission.   When the magnitude of the power to be transmitted exceeds the second predetermined value, the large-diameter rolling ball, the medium-diameter rolling ball, and the small-diameter rolling ball transmit the power in the rolling path. The ball screw device according to claim 1, which is performed.   3. The plurality of rolling balls arranged in the circulation path, wherein at least one of the three rolling balls arranged in a row is the small-diameter rolling ball. Ball screw device.   4. The ball screw device according to claim 3, wherein the three rolling balls that are successively aligned include one of the large-diameter rolling ball and the medium-diameter rolling ball. 5.   In the plurality of rolling balls arranged in the circulation path, two rolling balls that are continuously arranged are one of the small-diameter rolling ball, the large-diameter rolling ball, and the medium-diameter rolling ball. The ball screw device according to claim 1, comprising: Among the plurality of rolling balls arranged in the circulation path, among the four rolling balls that are continuously aligned,
One is the small diameter rolling ball,
Two are one of the large diameter rolling ball or the medium diameter rolling ball,
One is the other of the large diameter rolling ball or the medium diameter rolling ball,
The ball screw device according to claim 1 or 2, wherein the four rolling balls are continuously aligned with rolling balls having different diameters.   A steering device comprising the ball screw device according to any one of claims 1 to 6.

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