JP4567502B2 - Electric power steering device - Google Patents

Description

  The present invention relates to a technique for improving a rack and pinion type electric power steering apparatus.

In recent years, electric power steering devices have been frequently used in order to reduce the steering force of the steering wheel to give a comfortable steering feeling. In this type of electric power steering apparatus, a rack-and-pinion type technology has been developed in which an auxiliary torque corresponding to the steering torque is generated by an electric motor and this auxiliary torque is transmitted to the rack shaft of the steering system (for example, (See Patent Document 1).
JP 2002-321632 A

In the conventional electric power steering device according to Patent Document 1, a rack is formed on the front surface of one end portion of a rack shaft extending in the vehicle width direction, a pinion is meshed with the rack, and the rear surface side of the surface on which the rack of the rack shaft is formed. By attaching a rack guide that pushes out the back surface to the rack, one end of the rack shaft is supported by the pinion and the rack guide.
Such an electric power steering device further adopts a so-called three-point support structure in combination with the above-mentioned support by the pinion and the rack guide by supporting the other end portion and the intermediate portion of the rack shaft with bearings. Yes. Since the bearing that supports the other end portion and the intermediate portion of the rack shaft is slidably supported by the rack shaft, a plain bearing (also referred to as a sliding bearing or a bush) is generally employed.

  By the way, an electric power steering device mounted on a vehicle is often used in a wide range of temperatures from a low temperature to a high temperature. For this reason, a gap of a predetermined size is generally provided between the rack shaft and the flat bearing in consideration of a difference in thermal expansion between the rack shaft and the flat bearing. This gap increases at low temperatures and decreases at high temperatures.

  A torque obtained by adding an auxiliary torque generated by the electric motor in response to the steering torque generated by steering the steering handle, a so-called composite torque, is transmitted from the pinion shaft to the rack shaft via the rack and pinion mechanism. .

As described above, since there is a gap between the rack shaft and the plain bearing, when the rack is driven by the pinion, radial vibration is generated in the rack shaft due to the meshing action of both. obtain. In particular, there is a strong tendency to generate radial vibration due to the relationship between the pinion and rack tooth pressure angles.
Since an external force caused by a road surface reaction force further acts on the rack shaft, vibration is further promoted by this external force.

  As described above, the rack shaft is affected by both the relatively large combined torque and the external force caused by the road surface reaction force, so that vibration in the front-rear direction is likely to appear significantly. The vibration is transmitted to the vehicle interior via the steering handle, which causes noise in the vehicle interior. Further, if vibration is transmitted to the steering handle, it is not preferable in terms of steering feeling.

  An object of the present invention is to provide a technique capable of suppressing the vibration of the rack shaft during steering with a simple structure.

The invention according to claim 1 is an electric power steering apparatus in which a motor torque generated by an electric motor driven in accordance with a steering input is applied to a rack shaft, wherein a rack is formed at one end of the rack shaft. Then, a rackion that pushes the back surface is attached to the back side of the surface of the rack shaft that forms the rack, and a rack guide that supports one end of the rack shaft is supported by the pinion and the rack guide. the electric power steering apparatus for supporting a bearing with a predetermined clearance and the other end of, among the other end of the rack shaft, the position adjacent to the bearing, made of a material capable of elastic deformation supported by the elastic bearing, the inner diameter of the elastic bearing, a smaller diameter than the inner diameter of the bearing supporting the other end portion of the rack shaft, and a rack shaft in diameter can be slidably supported in the axial direction Characterized in that that.

The invention according to claim 2 is characterized in that the bearing is made of a metal material .

  The invention according to claim 3 is configured to transmit the steering torque and the motor torque directly from the pinion to the rack.

In the invention according to claim 1, the other end portion of the rack shaft, not only supported by a bearing having a gap, further, adjacent to the bearing, auxiliary made of a material capable of elastic deformation Since it is also supported by the elastic bearing, vibration of the rack shaft can be suppressed. For this reason, at the time of steering, vibration generated due to the meshing action of the pinion and the rack and vibration generated due to the influence of external force caused by the road surface reaction force can be suppressed.
Thus, the vibration of the rack shaft can be easily suppressed with a simple structure in which an auxiliary elastic bearing is added. When the vibration of the rack shaft is suppressed, the vibration of the steering wheel is also suppressed, so that the steering feeling is enhanced. In addition, since vibration transmitted to the vehicle interior via the steering handle can be suppressed, noise in the vehicle interior can be suppressed. Furthermore, since the vibration of the rack shaft is reduced, the wear of the rack and pinion mechanism can be reduced, and as a result, the durability of the electric power steering apparatus can be enhanced.
Moreover, an elastic bearing, since it is configured of a material capable of elastic deformation, even if thermal expansion difference between the rack shaft and the elastic bearing, it is possible that the elastic bearing is elastically deformed to absorb.

Further, in the invention according to claim 1 , the inner diameter of the elastic bearing is smaller than the inner diameter of the bearing supporting the other end portion of the rack shaft, and the diameter can support the rack shaft so as to be slidable in the axial direction. The vibration of the rack shaft can be further suppressed.
In the invention according to claim 2, the bearing is made of a metal material.

  According to the third aspect of the present invention, the steering torque and the motor torque generated by the electric motor are directly transmitted from the pinion to the rack. That is, the load on the rack and pinion mechanism is large and large vibrations are likely to occur. Even in the rack and pinion mechanism, vibration of the rack shaft can be easily suppressed by the auxiliary elastic bearing.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present invention.
The electric power steering apparatus 10 includes a steering system 20 that extends from a steering handle 21 of a vehicle to steering wheels (front wheels) 31 and 31 of the vehicle, and an auxiliary torque mechanism 40 that applies an auxiliary torque to the steering system 20.

In the steering system 20, a pinion shaft (input shaft) 24 is connected to a steering handle 21 via a steering shaft 22 and universal shaft joints 23, 23, and a rack shaft 26 is connected to the pinion shaft 24 via a rack and pinion mechanism 25. The left and right steering wheels 31, 31 are connected to both ends of the rack shaft 26 via ball joints 27, 27, tie rods 28, 28, and knuckles 29, 29.
The rack and pinion mechanism 25 includes a pinion 24 a formed on the pinion shaft 24 and a rack 26 a formed on the rack shaft 26.

  When the driver steers the steering handle 21, the left and right steering wheels 31, 31 can be steered by the steering torque via the rack and pinion mechanism 25, the rack shaft 26, and the left and right tie rods 28, 28.

The auxiliary torque mechanism 40 detects the steering torque of the steering system 20 applied to the steering handle 21 by the steering torque sensor 41, generates a control signal by the control unit 42 based on this torque detection signal, and generates the steering torque based on this control signal. Is generated by the electric motor 43, the auxiliary torque is transmitted to the pinion shaft 24 via the worm gear mechanism 44, and the auxiliary torque is transmitted from the pinion shaft 24 to the rack and pinion mechanism 25 of the steering system 20. This is the mechanism.
The steering wheels 31 and 31 can be steered by the rack shaft 26 by a combined torque obtained by adding the auxiliary torque of the electric motor 43 to the steering torque of the driver.

  As described above, the electric power steering apparatus 10 is configured to transmit all of the combined torque directly from the pinion 24a to the rack 26a.

  FIG. 2 is a front view of the electric power steering apparatus according to the present invention, and shows a left end portion and a right end portion in cross section. FIG. 2 shows that the rack shaft 26 is accommodated in a housing 51 extending in the vehicle width direction (left-right direction in the figure) so as to be slidable in the axial direction. The housing 51 includes an attachment portion 52 that is attached to a vehicle body (not shown). 32 and 32 are dust seal boots.

3 is a cross-sectional view taken along line 3-3 in FIG. 2 and shows a vertical cross-sectional structure of the electric power steering apparatus 10 including the rack guide 60.
In the electric power steering device 10, a pinion shaft 24, a rack and pinion mechanism 25, a steering torque sensor 41, and a worm gear mechanism 44 are housed in a housing 51, and an upper opening of the housing 51 is closed with a lid 54.
The housing 51 is set in a vertical orientation by rotatably supporting the upper end portion, the longitudinal center portion, and the lower end portion of the pinion shaft 24 via three upper and lower bearings 55 to 57, and the rack guide 60. Is provided.

  The rack guide 60 is a pressing unit that pushes out the back surface of the rack shaft 26 having the rack 26a. The rack guide 60 is a guide portion 61 that contacts the rack shaft 26 from the opposite side of the rack 26a. It consists of an adjustment bolt 63 that is pushed through (adjustment spring 62).

  The guide portion 61 can support the rack shaft 26 so as to be slidable in the axial direction while restricting the movement of the rack shaft 26 in the longitudinal direction of the pinion shaft 24. According to such a rack guide 60, a preload is applied to the rack 26a by the guide portion 61 by pressing the guide portion 61 with an appropriate pressing force via the compression spring 62 with the adjusting bolt 63 screwed into the housing 51. Thus, the rack 26a can be pressed against the pinion 24a. In the figure, 58 is an oil seal, 64 is a contact member for sliding the back surface of the rack shaft 26, and 65 is a lock nut.

4 is a cross-sectional view taken along line 4-4 of FIG. 3, and shows the relationship among the pinion shaft 24, the electric motor 43, and the worm gear mechanism 44. FIG.
The electric motor 43 is attached to the housing 51 with the motor shaft 43 a facing sideways, and the motor shaft 43 a extends into the housing 51.

The worm gear mechanism 44 is an auxiliary torque transmission mechanism that transmits auxiliary torque generated by the electric motor 43 to the pinion shaft 24, that is, a booster mechanism. More specifically, the worm gear mechanism 44 includes a worm shaft 46 connected to the motor shaft 43 a of the electric motor 43 via a coupling 45, a worm 47 formed on the worm shaft 46, and a worm wheel 48 meshed with the worm 47. Become. The worm wheel 48 is coupled to the pinion shaft 24.
As described above, the worm gear mechanism 44 is formed by meshing the worm wheel 48 on the steering system 20 (see FIG. 1) with the worm 47 on the electric motor 43 side.

  FIG. 4 shows that both ends of the horizontally extending worm shaft 46 are rotatably supported by the housing 51 via bearings 71 and 72 and a hollow eccentric sleeve 73. 74 and 75 are nuts. By simply rotating the eccentric sleeve 73, the backlash of the worm 47 with respect to the worm wheel 48 can be easily adjusted.

  Next, the support structure of the rack shaft 26 will be described with reference to FIGS. FIG. 5 is a schematic diagram of a rack shaft support structure according to the present invention, and is a schematic plan view in which the electric power steering apparatus 10 of FIG. 2 is combined with the system of FIG.

  As shown in FIGS. 2 and 5, the electric power steering apparatus 10 forms a rack 26a on the front or rear surface of one end portion of the rack shaft 26 extending in the vehicle width direction, and the pinion 24a is engaged with the rack 26a. A rack guide 60 that pushes the rear surface of the rack shaft 26 on which the rack 26a is formed is attached. The pinion 24a and the rack guide 60 support one end of the rack shaft 26 and the other end of the rack shaft 26. And the intermediate part of the rack shaft 26 are supported by bearings 81 and 82, respectively.

The bearing 81 at the other end is referred to as a first bearing 81, and the bearing 82 at an intermediate portion is referred to as a second bearing 82.
The first bearing 81 and the second bearing 82 are flat bearings having the same configuration and made of a metal material. “Plain bearing” is a bearing that supports a shaft with a surface, the surface and the shaft can perform a sliding motion, and supports a force in a direction perpendicular to the shaft, and is also referred to as a sliding bearing or a bush. Yes.

The first and second bearings 81 and 82 are configured to support the rack shaft 26 with a gap Sp having a predetermined size δ. As a result, the first and second bearings 81 and 82 support the rack shaft 26 so as to be slidable in the axial direction.
The reason for providing the gap Sp is as follows. The electric power steering device 10 mounted on a vehicle is often used in a wide range of temperatures from a low temperature to a high temperature. Accordingly, a gap Sp having a predetermined size δ is considered between the rack shaft 26 and the first and second bearings 81 and 82 in consideration of the difference in thermal expansion between the rack shaft 26 and the first and second bearings 81 and 82. Need to open. For this reason, a gap Sp is provided.

  Furthermore, the electric power steering device 10 is subjected to minute elastic deformation at a position adjacent to the first bearing 81 (for example, a position slightly closer to the shaft end than the first bearing 81) in the other end portion of the rack shaft 26. It is supported by an auxiliary bearing 83 made of possible materials. Hereinafter, the auxiliary bearing 83 is referred to as “elastic bearing 83”.

The elastic bearing 83 supports the rack shaft 26 without a gap and is slidable in the axial direction, and has the configuration of a flat bearing like the first and second bearings 81 and 82. That is, the inner diameter of the elastic bearing 83 is smaller than the inner diameters of the first and second bearings 81 and 82, and preferably has no gap with the rack shaft 26.
The material of the elastic bearing 83 is made of a material that can be absorbed by the elastic bearing 83 being elastically deformed when there is a difference in thermal expansion between the rack shaft 26 and the elastic bearing 83, for example, a resin material.

Here, in the vehicle width direction, the meshing center position of the pinion 24a and the rack 26a is P1 (hereinafter referred to as “pinion center P1”), and the center position of the first bearing 81 is P2 (hereinafter referred to as “first bearing center P2”). And the center position of the second bearing 82 is P3 (hereinafter referred to as “second bearing center P3”), and the center position of the elastic bearing 83 is referred to as P4 (hereinafter referred to as “third bearing center P4”). To do.
The second bearing center P3 is preferably at a substantially central position between the pinion center P1 and the first bearing center P2, but may be disposed between the centers P1 and P2.

Next, the operation of the support structure for the rack shaft 26 configured as described above will be described with reference to FIGS.
This support structure not only supports the other end portion of the rack shaft 26 by the first bearing 81 having the gap Sp, but also is made of a material adjacent to the first bearing 81 and capable of minute elastic deformation. Since it is also supported by the auxiliary elastic bearing 83, the vibration of the rack shaft 26 can be suppressed. For this reason, at the time of steering, vibration generated due to the meshing action of the pinion 24a and the rack 26a and vibration generated due to the influence of external force caused by the road surface reaction force can be suppressed.

  Thus, the vibration of the rack shaft 26 can be easily suppressed with a simple structure in which the auxiliary elastic bearing 83 is added. When the vibration of the rack shaft 26 is suppressed, the vibration of the steering handle 21 (see FIG. 1) is also suppressed, so that the steering feeling is enhanced. In addition, since vibration transmitted to the vehicle interior via the steering handle 21 is suppressed, noise in the vehicle interior can be suppressed. Furthermore, since the vibration of the rack shaft 26 is reduced, the wear of the rack and pinion mechanism 25 can be reduced, and as a result, the durability of the electric power steering apparatus 10 can be improved.

  Moreover, since the auxiliary elastic bearing 83 is made of a material capable of minute elastic deformation, even if there is a difference in thermal expansion between the rack shaft 26 and the auxiliary elastic bearing 83, the auxiliary elastic bearing 83 The bearing 83 can be elastically deformed and absorbed.

  Further, the inner diameter of the elastic bearing 83 is smaller than the inner diameters of the first and second bearings 81 and 82 (preferably, a diameter that does not have a gap between the rack shaft 26) and the rack shaft 26 is in the axial direction. Thus, the vibration of the rack shaft 26 can be further suppressed.

  Furthermore, the rack-and-pinion mechanism 25 is configured to transmit all of the combined torque obtained by adding the auxiliary torque to the steering torque directly from the pinion 24a to the rack 26a. Thus, vibration of the rack shaft 26 can be easily suppressed.

  Next, a modified example of the support structure for the rack shaft 26 will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected about the structure similar to the Example shown in the said FIG.2 and FIG.5, and the description is abbreviate | omitted.

  FIG. 6 is a schematic view of a rack shaft support structure (first modification) according to the present invention, and is shown corresponding to FIG. As shown in FIG. 6, the support structure of the rack shaft 26 of the first modification has a configuration in which the second bearing 82 (see FIG. 5) at the intermediate portion is eliminated.

  FIG. 7 is a schematic view of a rack shaft support structure (second modification) according to the present invention, and is shown in correspondence with FIG. As shown in FIG. 7, the support structure of the rack shaft 26 according to the second modification is configured such that a position adjacent to the second bearing 82 is supported by an elastic bearing 83 in the intermediate portion of the rack shaft 26.

  In the embodiment of the present invention, the electric power steering apparatus 10 applies to the rack shaft 26 the motor torque generated by the electric motor that is driven according to the steering input generated by steering the steering handle 21. Any configuration can be used.

  For example, only the steering torque generated by steering the steering handle 21 is applied from the pinion 24a to the rack 26a, and the auxiliary torque generated by the electric motor according to the steering torque is applied to the rack shaft 26 by a ball screw or the like. Can be configured.

  Further, the pinion shaft 24 and the rack shaft 26 are mechanically separated from the steering handle 21, and the electric motor generates motor torque according to the steering amount (steering input), and this motor torque is used as the pinion shaft 24 or the rack shaft 26. , The so-called steer-by-wire (abbreviated as “SBW”) configuration of the method of turning the wheels 31 and 31 can be achieved.

  In the embodiment of the present invention, the first and second bearings 81 and 82 are not limited to plain bearings, and may be needle bearings, for example.

  The electric power steering device according to the present invention is suitable for a device having a rack and pinion mechanism configured to transmit all of the combined torque obtained by adding the auxiliary torque to the steering torque directly from the pinion to the rack. .

1 is a schematic diagram of an electric power steering apparatus according to the present invention. 1 is a front view of an electric power steering apparatus according to the present invention. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2. FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. It is a schematic diagram of the rack shaft support structure according to the present invention. It is a schematic diagram of the rack shaft support structure (first modification) according to the present invention. It is a schematic diagram of the rack shaft support structure (second modification) according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering device, 21 ... Steering handle, 24 ... Pinion shaft, 24a ... Pinion, 25 ... Rack and pinion mechanism, 26 ... Rack shaft, 26a ... Rack, 43 ... Electric motor, 60 ... Rack guide, 81 ... Bearing (First bearing), 82 ... second bearing, 83 ... elastic bearing, Sp ... predetermined gap, δ ... size of the gap.

Claims (3)

An electric power steering apparatus configured to apply a motor torque generated by an electric motor driven in accordance with a steering input to a rack shaft, wherein a rack is formed at one end of the rack shaft, and a pinion is provided on the rack. A rack guide that pushes out the back surface is attached to the rear surface side of the surface of the rack shaft that meshes with the rack shaft, and one end portion of the rack shaft is supported by the pinion and the rack guide, and the other end portion of the rack shaft in the electric power steering apparatus for supporting a bearing with a predetermined clearance, of the other end portion of the rack shaft, an elastic bearing a position adjacent to the bearing made of a material capable of elastic deformation supported by, the inner diameter of the elastic bearing is smaller in diameter than the inner diameter of the bearing supporting the other end portion of the rack shaft, and the slide allowed the rack shaft in the axial direction An electric power steering device, characterized in that the diameter can be supported. The electric power steering apparatus according to claim 1 , wherein the bearing is made of a metal material .   3. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is configured to transmit the steering torque and the motor torque directly from the pinion to the rack.

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