JP2001146173A - Rear wheel steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear wheel steering system that can improve the straight- ahead stability of a vehicle via a simple structure and stably even after long- term use. SOLUTION: This rear wheel steering system comprises a substantially cylindrical housing 1, an electric motor (a brushless motor 3) for producing torque, a rotary member (nut member 15) rotatable via its support by a bearing 17 fixed in the housing and connection with the electric motor, and a movable memory (rod 19) that is shaped into a shaft with both ends coupled with the rear wheels of a vehicle, is provided with an externally threaded portion 19a adapted to engage an internally threaded portion 15a of the rotary member, is disposed against circumferential rotation and is axially movable to steer the rear wheels when the rotary member is rotated. Springy urging means 40 are disposed in the housing to urge a pressed portion 19d of the movable member between one end and the externally threaded portion thereof in a direction perpendicular to the axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rear wheel steering device for a vehicle.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Application Laid-Open No. 11-0207
As described in Japanese Patent Publication No. 13, a substantially cylindrical housing,
A motor that is housed in the housing and generates a rotational force, a substantially cylindrical rotating member that has an inner ring and an outer ring, is supported by a bearing fixed to the housing, and rotates by being connected to the motor, and a shaft. The rear wheel of the vehicle is connected at both ends and has a male threaded portion that meshes with a female threaded portion provided on the inner peripheral surface of the rotating member, and is arranged non-rotatably in the circumferential direction and moves in the axial direction by rotation of the rotating member. There is known a rear wheel steering device including a moving member that steers a rear wheel.

[0003] Such a rear wheel steering device transmits a rotational force to a rotating member by operating an electric motor, and converts the rotation of the rotating member into an axial displacement of a moving member.
It is an object of the present invention to steer a rear wheel of a vehicle connected to a moving member to improve running stability and the like of the vehicle.

In such a rear-wheel steering system, when the electric motor is not operated, for example, when traveling straight, the rear wheels, that is, moving members are input from the road surface (hereinafter referred to as "reverse") in order to improve the straight running stability and the like. It is desirable to set the connection play between the power transmission members disposed between the electric motor and the moving member as small as possible so as not to cause minute displacement due to “input”.

However, in the engagement between the internal thread of the rotary member and the external thread of the movable member for converting the rotational movement of the rotary member into the axial movement of the movable member, there is always a backlash due to the processing accuracy. This backlash causes connection play between the power transmission members, which is one of the causes of deteriorating the straight running stability and the like of the vehicle.

Means for reducing the backlash include improving the machining accuracy of the female thread and the male thread,
It is conceivable to selectively assemble a rotating member having a female thread portion and a moving member having a male thread portion. However, all of these means are not suitable for mass production and lead to an increase in production cost.

Therefore, in order to easily reduce the backlash without hindering mass productivity, the rear wheel steering device described in the above publication discloses a female screw portion of a rotating member and a male screw portion of a moving member that mesh with each other. Are arranged so as to be eccentric to each other by a predetermined amount, thereby minimizing the backlash between the two screw portions, that is, the connection play.

[0008]

However, in the rear wheel steering apparatus described in the above publication, the eccentricity between the rotating member having the female thread and the moving member having the male thread is reduced due to the variation in the dimensions of the components. If the amount of eccentricity is not stable and the amount of eccentricity is smaller than the specified range, the amount of backlash reduction will decrease. Conversely, if the amount of eccentricity is larger than the specified range, the contact pressure at the engagement of both will increase and the meshing resistance will decrease. There is a problem that the increase leads to an increase in the load on the electric motor.

Even when the amount of eccentricity is within the specified range, the use of the prolonged use causes wear on the bearing surface of the rotating member or the moving member, so that the amount of eccentricity gradually decreases, and the amount of backlash reduction is reduced. There was also a problem that it would decrease.

Further, from the viewpoint of setting the connection play between the power transmission members provided between the electric motor and the moving member to be as small as possible, the distance between the internal thread portion of the rotating member and the external thread portion of the moving member that mesh with each other is set. It is not enough to minimize the backlash of the bearing itself, and the axial backlash of the bearing itself that supports the rotating member remains, and the presence of such axial backlash in the bearing itself also reduces the straight running stability of the vehicle. Had become.

That is, when the moving member receives a reverse input from the road surface and receives a force in the axial direction, the input is transmitted from the male screw portion of the moving member to a rotating member having a female thread meshing with the moving member. Receives force in the direction. Since the rotating member is fixed by the bearing, the bearing also receives a force in the axial direction. Here, the bearing usually has an axial backlash itself for the sake of manufacturing convenience, improved durability, and the like, and the axial play of the bearing causes the moving member and, hence, the rear wheel to have an electric motor. Even during non-operation, a slight displacement is caused by the reverse input from the road surface. Therefore, the straight running stability of the vehicle is reduced due to the existence of the axial play of the bearing itself.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a simple structure and a rear wheel steering device capable of stably improving the straight running stability of a vehicle even after long-time use. It is an object to provide

[0013]

In order to solve the above-mentioned problems, an invention according to claim 1 is provided with a substantially cylindrical housing, an electric motor housed in the housing and generating a rotating force, and a motor inside the housing. A substantially cylindrical rotating member that is supported by a bearing fixed to the motor and rotates by being connected to the electric motor, and has a shaft shape, and rear wheels of the vehicle are connected to both ends, and among the rotating members, A male threaded portion meshed with a female threaded portion provided on the peripheral surface, and a moving member disposed non-rotatably in the circumferential direction, and moved in the axial direction by rotation of the rotating member to steer the rear wheel. In the rear wheel steering device, an elastic force urging unit that is provided between one end of the moving member and the male screw portion and that presses a pressed portion of the moving member in a direction perpendicular to the axial direction is provided in the housing. It was rear wheel steering apparatus, characterized in that the.

According to the first aspect of the present invention, the pressed portion of the moving member is pressed in a direction perpendicular to the axial direction by the elastic force of the elastic force urging means provided in the housing. The movable member having the portion is forcibly disposed eccentrically to a position where the movable member always contacts the rotating member having the female thread portion in a predetermined direction, and the backlash in the engagement of the two thread portions is minimized. Can be.

Further, since the movable member is always pressed with a predetermined load by the elastic force of the elastic force urging means and is forcibly decentered, the movable member is eccentric. There is no problem caused by the variation in the amount of eccentricity between the moving member and the rotating member due to the variation in the dimensions of each component.

Further, even if the bearing surface of the rotating member or the moving member is worn due to long-time use and the eccentricity of the moving member with respect to the rotating member changes, the moving member is urged by the elastic force urging means. The elastic force to be applied changes only by the elastic coefficient corresponding to the change in the amount of eccentricity. If the elastic coefficient of the elastic force urging means is set to be small, the elastic force applied to the moving member does not substantially change. Therefore, unlike the rear wheel steering device described in the above-mentioned publication, there is no problem that the backlash reduction amount decreases after long-time use.

Therefore, according to the first aspect of the present invention,
With a simple configuration and stable even after long-term use, the backlash in the engagement of both the male thread of the moving member and the female thread of the rotating member can be minimized, improving the straight running stability of the vehicle. It is possible to provide a rear wheel steering device that can be operated.

More preferably, as in the second aspect of the present invention, it is desirable that the elastic force urging means is configured to be able to adjust the pressing force by the elastic force. With this configuration, it is possible to freely adjust the elastic force for pressing the moving member in the direction perpendicular to the axial direction. In this case, the lower limit of the elastic force to be adjusted is the lower limit of the load necessary for forcibly eccentrically moving the moving member to a position where the moving member always contacts the rotating member in a predetermined direction. The upper limit is an upper limit of a range in which abnormal heat generation or the like does not occur in the drive circuit of the motor due to an increase in the load on the motor due to an increase in the contact pressure in the engagement between the male screw portion of the moving member and the female screw portion of the rotating member. It is desirable that

Further, as in the third aspect of the present invention, it is desirable that the pressed portion of the moving member is provided near the male screw portion in the axial direction. By providing the pressed portion of the moving member pressed by the elastic force urging means in the vicinity of the male screw portion, the backlash in the engagement between the male screw portion of the moving member and the female screw portion of the rotating member is more reliably minimized. can do.

According to a fourth aspect of the present invention, there is provided a substantially cylindrical housing, an electric motor housed in the housing and generating a rotational force, and an inner ring and an outer ring, which are fixed to the housing. A substantially cylindrical rotating member that is supported by bearings and rotates by being connected to the electric motor, and has a shaft shape, and rear wheels of the vehicle are connected to both ends, and are provided on an inner peripheral surface of the rotating member. A rear wheel steering device comprising: a male screw portion that meshes with a female screw portion, and a moving member that is arranged non-rotatably in the circumferential direction and that moves in the axial direction by rotation of the rotary member to steer the rear wheel. Wherein at least one of an inner ring and an outer ring of the bearing is press-fitted, and the inner ring or the outer ring is elastically deformed by the press-fitting to eliminate axial play of the bearing itself. And the steering apparatus.

According to the fourth aspect of the present invention, at least one of the inner ring and the outer ring of the bearing for supporting the substantially cylindrical rotating member is press-fitted, and the inner ring or the outer ring is elastically deformed by the press-fitting to thereby form a bearing. Since the axial play is eliminated, the play of the moving member in the axial direction caused by the play can be reduced, and the straight running stability of the vehicle can be improved. Further, by eliminating such backlash, the time from the start of driving of the electric motor to the start of displacement (steering) of the moving member and thus the rear wheel is shortened, and control accuracy of the rear wheel steering angle can be improved. .

Here, in the press-fitting, the axial play of the bearing is always maintained over the operating environment temperature range of the apparatus, even when the thermal expansion and contraction of the housing, the bearing, and the rotating member are considered. It is desirable to set the fitting dimensional relationship between the housing and the bearing and between the bearing and the rotating member so as to disappear.

According to a fifth aspect of the present invention, in the fourth aspect, an outer ring of the bearing is fixed to an inner peripheral surface of the housing, and an inner ring of the bearing is fixed to an outer peripheral surface of the rotating member. The rear wheel steering device is characterized in that the inner wheels are press-fitted.

According to the fifth aspect of the present invention, the outer race of the bearing is fixed to the inner peripheral surface of the housing, and the inner race of the bearing is fixed to the outer peripheral surface of the rotating member. It is possible to eliminate axial play.

Further, since at least the inner ring of the bearing is press-fitted, the reliability against excessive reverse input is improved. That is, in a conventional rear wheel steering device (for example, the device described in Japanese Patent Application Laid-Open No. H11-020713), the inner ring of the bearing and the outer peripheral surface of the rotating member are inserted and fitted to a locking member such as a snap ring. Since the rotating member is fixed in the axial direction, when an excessive reverse input occurs, only the locking member receives the axial load. However, the device according to claim 5 has a structure in which the load in the axial direction is also received by the press-fitting force of the two, and thus the reliability against excessive reverse input is improved by using the locking member together. .

According to a sixth aspect of the present invention, in any one of the first to third aspects, the bearing has an inner ring and an outer ring, and at least one of the inner ring and the outer ring of the bearing is press-fitted. The rear wheel steering device is characterized in that the inner ring or the outer ring is elastically deformed by the press-fitting to eliminate the axial play of the bearing itself. According to a seventh aspect of the present invention, in the sixth aspect, an outer ring of the bearing is fixed to an inner peripheral surface of the housing, and an inner ring of the bearing is fixed to an outer peripheral surface of the rotating member. The rear wheel steering device is characterized in that the inner wheel is press-fitted.

According to the sixth and seventh aspects of the invention, the backlash in the engagement between the male screw portion of the moving member and the female screw portion of the rotating member can be minimized, and the axial play of the moving member can be minimized. Can be reduced, and the straight running stability of the vehicle can be further improved.

[0028]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 1 is an axial sectional view of a rear wheel steering device according to the present invention. In FIG. 1, a housing 1 mainly includes a large-diameter cylindrical portion 1a, a conical portion 1b fitted to the large-diameter cylindrical portion 1a, and a small-diameter cylindrical portion 1c, which are connected and fixed to each other. . A brushless motor 3 (electric motor) is arranged in the large-diameter cylindrical portion 1a, and a hollow rotary shaft 5 as an output shaft is arranged so as to penetrate through the brushless motor 3.

The hollow rotary shaft 5 is rotatably supported on the inner peripheral portion of the small-diameter cylindrical portion 1c by a bearing 7 on the left side of FIG. The hollow rotary shaft 5 is rotatably supported on the inner peripheral portion of the large-diameter cylindrical portion 1a by a bearing 9 on the right side in FIG. The brushless motor 3
Are connected by a harness 11 to a power supply of a vehicle (not shown).

The hollow rotary shaft 5 forms a sun gear 5a at the right end in FIG. 1, and the sun gear 5a is connected to a planetary gear mechanism 13 installed in two stages in series.
Further, the output side at the subsequent stage of the planetary gear mechanism 13 is connected to a nut member 15 (rotating member). The nut member 15 is fixed to the large-diameter cylindrical portion 1 by a bearing 17 (bearing).
a is rotatably supported on the inner peripheral surface 1ab of the a. As a result, the rotational force of the brushless motor 3 is
, And is transmitted to the nut member 15 after being reduced by the planetary gear mechanism 13.

Here, the outer ring of the bearing 17 is press-fitted and fixed to the inner peripheral surface 1ab of the large-diameter cylindrical portion 1a.
Is also press-fitted and fixed to the outer peripheral surface of the nut member 15. Due to the elastic deformation of the outer ring and the inner ring of the bearing 17 due to the press-fitting, the initial axial play of the bearing 17 itself is eliminated. Further, the nut member 1
5 is fixed in the axial direction by the snap ring 30, but is also fixed in the axial direction by the press-fitting force between the inner ring of the bearing 17 and the nut member 15.
As described above, even when an excessive reverse input occurs, the occurrence of displacement of the nut member 15 in the axial direction is suppressed as much as possible, and reliability is improved.

The rod 19 (moving member) is connected to the housing 1 at a spline portion 19a provided at the right end in FIG.
Bearing 1 having splines provided in conical portion 1b
1 and is supported by the conical portion 1b so as to be slidable in the axial direction, and a sliding portion 19 provided at the left end in FIG.
b, the small-diameter cylindrical portion 1c is fitted with a bush 1ca formed of a low-friction material provided on the small-diameter cylindrical portion 1c.
c is slidably supported in the axial direction. As a result, the rod 19 is non-rotatably supported by the housing 1.

The rod 19 is approximately 1 /
A male screw portion 19c is provided at a portion having a length of 4, and meshes with a female screw portion 15a provided on the inner peripheral surface of the nut member 15. In addition, these male screw part 19c and female screw part 15
As for a, a so-called trapezoidal screw is adopted for convenience in processing and production. Thus, the rotational motion transmitted to the nut member 15 is transmitted as a linear motion of the rod 19.

The elastic force urging member 40 is disposed on the conical portion 1b of the housing 1. FIG. 2 is an enlarged view centering on the elastic force urging member 40 in FIG. As shown in FIG. 2, the elastic force urging member 40 includes a plug 48 screwed to the conical portion 1b of the housing 1 and a pressing member inserted into a recess of the plug 48 so as to be vertically slidable in FIG. 42, a spring 46 disposed in a space formed by the concave portion of the plug 48 and the concave portion of the pressing member 42 and urging the pressing member 42 upward with respect to the plug 48 in FIG. And an O-ring 44 for ensuring airtightness with the conical portion 1b of the housing 1.

FIG. 3 is a sectional view taken along line AA in FIG. 2. As shown in FIG. 2 and FIG. 3, the pressing member 42 urged upward in FIG. Presses the pressed portion 19d constituting a part of the rod 19 upward (in the direction perpendicular to the axial direction of the rod 19) in FIG. Pressing member 4
As shown in FIG. 3, the second end surface 42a has a shape corresponding to the cylindrical outer shape of the pressed portion 19d of the rod 19, and is configured to be in surface contact with the pressed portion 19d of the rod 19. . Thereby, the contact surface pressure between the pressing member 42 and the pressed portion 19d of the rod 19 can be reduced, and the amount of wear on both contact surfaces after long-time use can be reduced. In order to reduce the sliding resistance of the rod 19 with respect to the pressing member 42, it is desirable that the material of the pressing member 42 be a low friction material as in the case of the bush 1ca.

As described above, the end surface 42 of the pressing member 42
a presses the pressed portion 19 d of the rod 19 upward (in the direction perpendicular to the axial direction of the rod 19) in FIG. 2, the male screw portion 19 c of the rod 19 always moves against the female screw portion 15 a of the nut member 15 in FIG. In this case, the eccentric arrangement is forcibly arranged to the position where it comes into contact with the upper part, and the backlash (axial backlash) in the engagement of the two screw portions can be minimized. Also, the spring 15
Is set to a small value, the urging force of the spring 15 hardly changes even if the stroke of the pressing member 42 with respect to the plug 48 slightly changes. Therefore,
After long use, for example, the spline portion 19 of the rod 19
Even if the stroke of the pressing member 42 changes due to abrasion of the rod 19 and the eccentric amount of the rod 19 increases, the spring 46 can stably continue to apply a substantially constant pressing force to the rod. The above-mentioned backlash can be reduced stably even after long-time use. In order to eccentrically move the male screw portion 19c of the rod 19 to a position where the male screw portion 19c of the nut member 15 is securely contacted, the pressed portion 19d of the rod 19 is preferably set to a position as close as possible to the male screw portion 19c. Is desirable.

Since the plug 48 is screwed into the conical portion 1b of the housing 1, the position of the plug 48 in the vertical direction in FIG. 2 can be adjusted. Therefore, the elastic biasing force of the spring 46 can also be adjusted. The adjustment range of the elastic urging force is, as described above, the rod 1
The lower limit of the load necessary for forcibly eccentrically bringing the nut 9 into contact with the nut member 15 in a predetermined direction is defined as the lower limit, and the male screw portion 19c of the rod 19 and the female screw portion 15a of the nut member 15 It is preferable that the upper limit of the range in which abnormal heat generation or the like does not occur in the drive circuit of the brushless motor 3 due to an increase in the load of the brushless motor 3 due to an increase in the contact pressure in the engagement between the two.

The rod 19 has tie rods 23 at both ends thereof via universal joints 21a and 21b.
a, 23b and the tie rod 23
Each of a and 23b is connected to a rear wheel (not shown) of the vehicle.

As described above, with this configuration, the rotation of the brushless motor 3 is converted into the axial movement of the rod 19, and as a result, the rear wheels of the vehicle are steered. In the rear wheel steering device having such a configuration, as described above,
The axial play of the bearing 17 is eliminated by press-fitting, and the female thread portion 15a of the nut member 15 and the rod 1
When the brushless motor 3 is not operated, for example, when the vehicle travels straight, the axial play between the two screw portions is eliminated by eccentrically engaging the male screw portion 19c with the male screw portion 19c in the radial direction. The axial play can be minimized, and the straight running stability of the vehicle can be improved.

[0041]

As described above, according to the present invention,
It is possible to provide a rear-wheel steering device having a simple configuration and capable of stably improving the straight running stability of a vehicle even after long-time use.

[Brief description of the drawings]

FIG. 1 is an axial sectional view showing a rear wheel steering device according to an embodiment of the present invention.

FIG. 2 is an enlarged view mainly showing an elastic force urging member 40 in FIG.

FIG. 3 is a sectional view taken along line AA in FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Housing 1a Large diameter cylindrical part (housing), 1b Conical part (housing) 1c Small diameter cylindrical part (housing) 3 Brushless motor (motor) 15 Nut member (rotating member) 15a Female thread part 17 Bearing (bearing) 19 Rod (moving member) 19a male screw portion, 19d pressed portion 40 elastic force urging member

Claims (7)

[Claims] 1. A substantially cylindrical housing, an electric motor housed in the housing and generating a rotational force, and supported by a bearing fixed in the housing and connected to the electric motor. A rotating member having a substantially cylindrical shape that rotates, and having a shaft shape, a rear wheel of the vehicle is connected to both ends, and a male screw portion that meshes with a female thread portion provided on an inner peripheral surface of the rotating member is provided. A moving member that is disposed non-rotatably and moves in the axial direction by the rotation of the rotating member to steer the rear wheel; and a rear wheel steering device, wherein one end of the moving member and the male screw portion are interposed. A rear wheel steering device, wherein an elastic force urging means for pressing a pressed portion of the moving member in a direction perpendicular to the axial direction is provided in the housing. 2. The rear wheel steering device according to claim 1, wherein the elastic force urging means is configured to adjust the pressing force. 3. The rear wheel steering device according to claim 1, wherein the pressed portion of the moving member is provided near the male screw portion in the axial direction. 4. A motor having a substantially cylindrical housing, an electric motor housed in the housing and generating a rotational force, and a bearing having an inner ring and an outer ring fixed to the housing and supporting the electric motor. A substantially cylindrical rotating member that rotates by being connected to, and has an axial shape,
The rear wheels of the vehicle are connected to both ends, and are provided with a male screw portion that meshes with a female screw portion provided on the inner peripheral surface of the rotating member, and are arranged non-rotatably in the circumferential direction. And a moving member for moving the rear wheel to steer the rear wheel, wherein at least one of the inner ring and the outer ring of the bearing is press-fitted, and the inner ring or the outer ring is elastically deformed by the press-fitting. A rear wheel steering system wherein the axial play of the bearing itself is eliminated. 5. The bearing according to claim 4, wherein an outer ring of the bearing is fixed to an inner peripheral surface of the housing, an inner ring of the bearing is fixed to an outer peripheral surface of the rotating member, and at least an inner ring of the bearing is press-fitted. A rear wheel steering device characterized by the following. 6. The method according to claim 1, wherein
The bearing has an inner ring and an outer ring, and at least one of the inner ring and the outer ring of the bearing is press-fitted, and the inner ring or the outer ring is elastically deformed by the press-fitting to eliminate the axial play of the bearing itself. A rear wheel steering device characterized by being made to operate. 7. The bearing according to claim 6, wherein an outer ring of the bearing is fixed to an inner peripheral surface of the housing, an inner ring of the bearing is fixed to an outer peripheral surface of the rotating member, and at least the inner ring of the bearing is press-fitted. A rear wheel steering device characterized by the following.