JP2010111301A - Rack and pinion type steering device, and electric power steering device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rack and pinion type steering device reducing the bending moment applied to a farthest point tooth by reducing the height of the farthest point tooth of rack teeth to be engaged with a pinion tooth at the stroke end of a rack shaft, and an electric power steering device having the same. <P>SOLUTION: The rack and pinion type steering device includes a rack shaft 14 forming spiral rack teeth 14a, and a pinion shaft having spiral pinion teeth to be engaged with the rack teeth. The height of a farthest point tooth 14a1 of the rack teeth to be engaged with the pinion teeth at the stroke end of the rack shaft is set to be smaller than that of the other teeth. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rack and pinion type steering device used in a vehicle and an electric power steering device including the same.

  In a rack and pinion type steering device used in a vehicle, a pinion is rotated by operating a steering wheel, and a rack that meshes with the pinion is moved in the axial direction. And a steered wheel is steered via a tie rod by the axial movement of a rack. In this type of rack and pinion type steering device, in order to restrict the stroke end of the rack, the rack is forcibly stopped by contacting the housing. For this reason, a large bending stress is generated at the tooth base of the rack tooth located at the end of the rack tooth row due to the impact load generated by the forced stop of the rack. As what relaxes such a bending stress, what was described in patent document 1, for example is known.

In what is described in Patent Document 1, in order to relieve the bending stress generated at the base of the rack tooth at the endmost part, the tooth form of the rack tooth at the endmost part is changed to the tooth form of the rack tooth other than the end part. The bottom of the tooth profile groove is formed into a shallow tooth profile, or the bottom portion of the tooth profile groove is formed into a curved surface having a larger curvature radius than the tooth shape of the rack tooth other than the endmost portion.
JP 2006-96243 A

  However, in the thing of patent document 1, since it is necessary to form the tooth form of the rack tooth of the endmost part in the above-mentioned shape for every rack and pinion type steering device applied to each vehicle type, rack stroke etc. There is a problem that a rack shaft common to different vehicle types cannot be manufactured by a gear cutter or the like.

  In addition, in this type of rack and pinion type steering device, the rack teeth and the pinion teeth that mesh with the rack teeth are formed of a helical so that the meshing rate can be improved and the meshing noise can be reduced. For this reason, the meshing between the rack teeth and the pinion teeth at the stroke end of the rack shaft becomes an inclined tooth surface, and a rotational moment is applied to the rack shaft, so that the endmost tooth at the stroke end of the rack shaft is easily loaded. Become. Further, in the rack and pinion type steering apparatus having rack teeth and pinion teeth made of helical, the meshing length of the outermost teeth at the stroke end of the rack shaft is reduced. That is, at the stroke end of the rack shaft, as shown in FIG. 4, the meshing portion X0 of the rack teeth 14a and the pinion teeth 13a of the endmost teeth is meshed with the meshing portions X1 and X2 of the teeth excluding the endmost teeth. There may be a minimum relative to the length. In addition, the load is likely to concentrate on the smallest meshing portion of the end tooth due to the rotational moment applied to the rack shaft by the helical.

  The present invention has been made to solve the above-described conventional problems, and by reducing the height of the outermost tooth of the rack tooth that meshes with the pinion tooth at the stroke end of the rack shaft, It is an object of the present invention to provide a rack and pinion type steering device capable of relaxing an acting bending moment and an electric power steering device including the same.

  In order to solve the above-mentioned problem, the invention of the rack and pinion type steering apparatus according to claim 1 is characterized in that a rack shaft formed with helical rack teeth and a helical pinion engaged with the rack teeth. In a rack and pinion type steering apparatus having a pinion shaft formed with teeth, the height of the rack teeth that are engaged with the pinion teeth at the stroke end of the rack shaft is set to be higher than the tooth heights other than the furthest teeth. It is small.

  A feature of the invention of the rack and pinion type steering device according to claim 2 is that, in claim 1, the height of the endmost tooth is made small enough to reduce the bending moment acting on the endmost tooth.

  A feature of the rack and pinion type steering apparatus according to claim 3 is that, in claim 1, the height of the outermost tooth is made small to such an extent that the outermost tooth does not mesh with the pinion tooth.

  A feature of the electric power steering apparatus according to a fourth aspect is that the rack and pinion type steering apparatus according to any one of the first to third aspects is provided.

  According to the invention of the rack and pinion type steering device according to claim 1, the height of the outermost tooth of the rack tooth meshing with the pinion tooth at the stroke end of the rack shaft is made smaller than the tooth height other than the outermost tooth. The bending moment acting on the outermost tooth can be relaxed. Moreover, since the height of the rack teeth at the extreme end is reduced, after the common rack shaft is manufactured with a gear cutter, etc. The outermost teeth can be formed, and the manufacture of the rack shaft can be facilitated.

  According to the rack and pinion type steering device according to the second aspect of the invention, since the tooth height of the outermost tooth is made small enough to reduce the bending moment acting on the outermost tooth, the bending moment acting on the outermost tooth is reduced. Can be reduced.

  According to the rack and pinion type steering device of the third aspect of the present invention, since the tooth height of the outermost tooth is reduced to such an extent that the outermost tooth does not mesh with the pinion tooth, no bending moment is applied to the outermost tooth. The impact load at the stroke end of the rack shaft can be received by other teeth having a large meshing length.

  According to the electric power steering device of the present invention, the rack and pinion type steering device according to any one of claims 1 to 3 is provided, so that the bending moment acting on the endmost teeth is reduced. It is possible to alleviate or to prevent the bending moment from acting on the outermost teeth, and the durability of the electric power steering apparatus can be improved. In addition, since the rack teeth can be manufactured in which the tooth height of the endmost teeth is smaller than the rack shaft common to each vehicle type, the manufacture of the electric power steering device can be facilitated.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an electric power steering apparatus 10 including a rack and pinion type steering apparatus. In FIG. 1, an electric power steering apparatus 10 is, for example, a column assist type, and includes a steering shaft 12 coupled to a steering wheel 11, a pinion shaft 13 provided at a tip portion of the steering shaft 12, and a left-right direction of the vehicle. And a housing 15 for supporting the pinion shaft 13 and the rack shaft 14. The pinion shaft 13 is rotatably supported by the housing 15, and the rack shaft 14 is supported by the housing 15 so as to be linearly reciprocable. The pinion shaft 13 is formed with pinion teeth 13 a made of helical, and the rack shaft 14 is formed with rack teeth 14 a made of helical that mesh with the pinion teeth 13 a.

  Tie rods 16 are coupled to both ends of the rack shaft 14, and each tie rod 16 is connected to the steered wheels 17 via knuckle arms. Thereby, when the steering wheel 11 is operated and the steering shaft 12 is rotated, the rotation of the rack shaft 14 along the left-right direction of the vehicle is performed by the rack and pinion mechanism configured by the pinion shaft 13 and the rack shaft 14. Converted into a linear motion, the steered wheels 17 are steered.

  The steering shaft 12 is divided into a cylindrical first steering shaft 21 that is continuous with the steering wheel 11 and a second steering shaft 22 that is continuous with the pinion shaft 13. The first steering shaft 21 and the second steering shaft 22 are connected to a torsion bar. 23 are connected so as to be relatively rotatable by a predetermined angle on the same axis.

  Further, the electric power steering apparatus 10 is provided with a torque sensor 24 that detects a steering torque based on the relative rotation amount of the first steering shaft 21 and the second steering shaft 22, and the torque detection signal of the torque sensor 24 is a control unit. 25 is output. The control unit 25 controls the voltage applied to the steering assist electric motor 27 via the motor control unit 26 based on the torque detection signal. The rotation of the motor shaft of the electric motor 27 is transmitted to the second steering shaft 22 (pinion shaft 13) via the worm reduction mechanism 28, and steering is assisted.

  The rack shaft 14 is restricted in its stroke with respect to the housing 15, and when the rack shaft 14 reaches the stroke end, the end of the rack shaft 14 comes into contact with the housing 15 and the movement of the rack shaft 14 is forcibly stopped. It is like that.

  FIG. 2 shows a rack shaft 14 having rack teeth 14a. The rack shaft 14 includes rack teeth 14a having a predetermined tooth row so that the rack shaft 14 can be commonly applied to a plurality of vehicle types. That is, the rack shaft 14 has the number of teeth necessary for the rack shaft 14 to be able to make the maximum stroke among the vehicle types to which the rack shaft 14 is applied. The rack shaft 14 is manufactured in common for each vehicle type by gear cutting using a gear cutter or the like.

  The tooth height H1 of a tooth 14a1 (hereinafter referred to as the most end tooth) of the rack tooth 14a meshing with the pinion teeth 13a at the right stroke end and the left stroke end of the rack shaft 14 is shown in FIG. Thus, it is made small with respect to tooth height H0 of teeth other than the endmost tooth 14a1.

  That is, in the engagement of the rack teeth 14a and the pinion teeth 13a at the stroke end of the rack shaft 14, among the rack teeth 14a involved in the engagement, the teeth excluding the outermost teeth 14a1 of the rack teeth 14a are shown in FIG. As shown, while the meshing lengths of the meshing portions X1 and X2 are large, the meshing length X0 of the meshing portion is small in the outermost teeth 14a1, and may be minimal in some cases. In such a case, a large bending moment acts on the small meshing portion X0 of the outermost tooth 14a1 by rotating the rack shaft 18 by the helical.

  In order to prevent this, in the present embodiment, the tip of the outermost tooth 14a1 is scraped off by milling or the like, and the tooth height H1 is reduced so that other teeth having a large meshing length can be used. An impact load at the stroke end of the rack shaft 14 is received so that a large bending moment does not act on the outermost teeth 14a1.

  In this case, the bending stress acting on the outermost teeth 14a1 can be reduced by reducing the height H1 of the outermost teeth 14a1 of the rack teeth 14a to such an extent that the bending moment acting on the outermost teeth 14a1 can be reduced. it can. Alternatively, the height H1 of the outermost tooth 14a1 of the rack tooth 14a is largely cut off so that the outermost tooth 14a1 does not mesh with the pinion tooth 13a, so that no bending moment acts on the outermost tooth 14a1. Instead, impact loads can be applied to other teeth having a large meshing length. As a result, it is possible to reliably prevent the outermost teeth 14a1 from being damaged by the impact load, and it is possible to improve the durability of the rack and pinion type steering device, and hence the electric power steering device 10.

  Since the rack shaft 14 is manufactured in common for each vehicle type, the outermost teeth 14a1 of the rack teeth 14a meshing with the pinion teeth 13a at the stroke end of the rack shaft 14 are not necessarily rack teeth formed on the rack shaft 14. It changes according to the stroke of the rack shaft 14 instead of the teeth positioned at both ends of the rack 14.

  Next, the operation of the electric power steering apparatus 10 in the above-described embodiment will be described. When the steering wheel 11 is steered, steering torque is input to the pinion shaft 13 via the steering shaft 12. The steering torque input to the pinion shaft 13 is detected by the torque sensor 24, and the electric motor 27 is rotationally controlled based on the detected steering torque to generate a steering assist torque. The steering assist torque by the electric motor 27 is transmitted to the pinion shaft 13 via the worm reduction mechanism 28, and the rack shaft 14 is moved in the axial direction by the rotation of the pinion shaft 13. As the rack shaft 14 moves in the axial direction, the steered wheels 17 are steered through the tie rods 16 and the knuckle arms, and the steering force of the steering wheel 11 by the driver is reduced.

  By the way, when the end of the rack shaft 14 comes into contact with the housing 15 at the stroke end of the rack shaft 14 and is forcibly stopped, the end load tooth 14a1 of the rack tooth 14a that meshes with the pinion teeth 13a has an impact load. Causes a large bending moment. However, in the present embodiment, since the tooth height H1 of the outermost tooth 14a1 is made smaller than the tooth height H0 other than the outermost tooth 14a1, the bending moment acting on the outermost tooth 14a1 is reduced, or the outermost tooth It is possible to prevent the bending moment from acting on 14a1.

  As described above, in the rack and pinion type steering device of the present embodiment, the gear teeth of the rack teeth 14a are common to all teeth, and only the tooth height H1 of the outermost teeth 14a1 is smaller than the tooth heights H0 other than the outermost teeth 14a1. Therefore, after the rack shaft 14 common to each vehicle type is manufactured by a gear cutter or the like, the tooth height of the outermost teeth 14a1 of the rack teeth 14a is reduced by milling or the like, thereby reducing any tooth. The height H1 can be easily formed, and the rack shaft 14 can be easily manufactured.

  At this time, by reducing the height H1 of the outermost tooth 14a1 to such an extent that the bending moment acting on the outermost tooth 14a1 can be reduced, the bending moment acting on the outermost tooth 14a1 at the stroke end of the rack shaft 14 is reduced. be able to. Alternatively, by reducing the height H1 of the outermost tooth 14a1 to such an extent that the outermost tooth 14a1 does not mesh with the pinion tooth 13a, a bending moment is applied to the outermost tooth 14a1 with an unstable meshing length. It can be eliminated, and an impact load can be applied to other teeth having a large meshing length.

  In the above-described embodiment, the example in which the rack and pinion type steering device is applied to the column assist type electric power steering device 10 has been described. However, the present invention is not limited to the column assist type, and the electric power of the rack assist type or the like. It is also applicable to power steering devices.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the configurations described in the embodiments, and does not depart from the gist of the present invention described in the claims. It can take various forms.

1 is a schematic diagram of an electric power steering apparatus including a rack and pinion type steering apparatus according to an embodiment of the present invention. It is a figure which shows a rack axis | shaft. It is the enlarged view to which the 3A part and 3B part of FIG. 2 were expanded. It is a figure which shows the meshing state of the pinion tooth | gear and rack tooth in the stroke end of a rack shaft.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electric power steering device, 13 ... Pinion shaft, 13a ... Pinion tooth, 14 ... Rack shaft, 14a ... Rack tooth, 14a1 ... Endmost tooth, 15 ... Housing , H0, H1... Tooth length, X0, X1, X2.

Claims (4)

In a rack and pinion type steering apparatus comprising a rack shaft formed with helical teeth and a pinion shaft formed with helical pinions engaged with the rack teeth,
A rack-and-pinion type steering device, characterized in that the height of the outermost teeth of the rack teeth meshing with the pinion teeth at the stroke end of the rack shaft is made smaller than the height of the teeth other than the outermost teeth.   2. A rack and pinion type steering apparatus according to claim 1, wherein the height of the outermost tooth is made small enough to reduce the bending moment acting on the outermost tooth.   2. The rack and pinion type steering device according to claim 1, wherein a height of the outermost tooth is reduced to such an extent that the outermost tooth does not mesh with the pinion tooth. An electric power steering apparatus comprising the rack and pinion type steering apparatus according to any one of claims 1 to 3.

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