JP2004284407A - Electric power steering device - Google Patents

Abstract

In an electric power steering device, engagement between rack teeth and a pinion is eliminated to prevent a hitting sound (noise / vibration), and a play generating portion in a servo control system is reduced, thereby achieving a stable operation. It is an object of the present invention to provide a steering device capable of forming a servo control system, and in which a load is not unnecessarily applied to a ball joint to be used.
An electric power steering device includes a screw shaft, a support member, a casing, a rotating member, and an electric assist motor. The rotation is transmitted to the drive bevel gear portion 62, the driven bevel gear portion 52, and the female screw portion 51 by the electric assist motor 6, and moves the screw shaft 2 right and left. At this time, since the screw shaft 2 itself does not rotate, only the load for the lateral movement of the screw shaft 2 is applied to the link connecting portion 21 with the tie rod 91.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device having an Ackerman type link mechanism used for a steering device of an automobile.
[0002]
[Prior art]
2. Description of the Related Art A power steering device using a rack and pinion type gear device is widely used in a steering device of today's automobile. Particularly in recent years, power steering mechanisms, which were conventionally driven by hydraulic pressure, have been electrified for reasons such as “high mechanical efficiency”, “weight saving”, “layout advantage”, and “easy electronic control”. Tend to be.
[0003]
As the above-described electric power steering device, there are known several types, such as a column assist type, a pinion assist type, and a rack assist type, depending on the type of assisting the steering force. Both types have in common that a steering operation force of a driver is transmitted to a tie rod via a rack and pinion type gear device.
[0004]
In such a rack and pinion type steering device, a large load acts in the rack axial direction due to an impact load, for example, when a tire gets over unevenness of a road surface, and a bending moment acts on the rack. In addition, the rack is used while always receiving a vibrational axial load and bending moment due to the rotation of the tire, even if it is not a shock load.
[0005]
Therefore, when a rack and pinion type gear device is used as in a conventional electric power steering device, the meshing portion between the rack teeth and the pinion is used while constantly receiving an oscillating load from the road surface during traveling.
[0006]
The effect of the vibratory road surface input as described above is particularly noticeable when traveling on a road with large unevenness such as a stone pavement, especially when traveling on a smooth pavement road, When the influence is large, unpleasant noise or vibration called rattling noise may be generated from the meshing portion between the rack teeth and the pinion.
[0007]
As a conventional technique for suppressing a tapping sound and a vibration generated from a meshing portion between a rack tooth and a pinion, for example, Patent Literature 1 (JP-A-10-217985) and Patent Literature 2 (JP-A-2002-037090) Gazettes) are known.
[0008]
As a technique that does not use such a rack, for example, a steering mechanism driven by a ball screw mechanism as disclosed in Patent Document 3 (Japanese Patent Application Laid-Open No. 5-124524) is known. In this steering mechanism, the turning torque of the steering coming from the steering wheel is transmitted to a female screw (ball nut) integrated with the driven bevel gear and a male screw via a driving bevel gear and a driven bevel gear, and is converted into a linear motion of the output shaft. Is converted. On the other hand, the rotational output of the assist motor is transmitted and rotated to a worm, a worm wheel, a female spline, and a male spline that is fitted to the worm and integrated with the output shaft.
[0009]
As a result, a differential mechanism is formed, and the rotation of the drive bevel gear and the rotation of the worm appear in the form of axial movement of the output shaft. However, in this structure, the output shaft not only performs the originally required linear motion in the axial direction, but also rotates itself. For this reason, only the linear motion of the output shaft is transmitted to the tie rods provided for changing the directions of the left and right wheels, but it is necessary not to transmit this rotational motion. Ball joints are usually used for tie rods, and this function can be performed by the ball joints.However, the joints are used to carry both the rotation for steering link movement and the rotation of the output shaft itself. Therefore, it is not preferable from the viewpoint of durability and maintainability.
[0010]
2. Description of the Related Art In an assist type steering device (a so-called power steering device), a servo control system is configured, a torque applied to a steering wheel is detected, and a torque required for steering is assisted by a motor based on a result of the detection. . When the servo control system, particularly the mechanical transmission unit includes a play generation unit, the play makes the control extremely unstable. Therefore, the amount of this play and the place where it occurs must be minimized.
[0011]
In the steering device having the structure of Patent Document 3 described above, since a driving bevel gear, a driven bevel gear, a female screw worm, a worm wheel, a female spline, and a male spline are used, there are portions where mechanical loss occurs when transmitting force. In many cases, these transmission systems include a large amount of play, which is not preferable from the viewpoint of the stability of the servo control system.
[0012]
[Patent Document 1]
JP-A-10-217985 [Patent Document 2]
Japanese Patent Application Laid-Open No. 2002-037090 [Patent Document 3]
Japanese Patent Application Laid-Open No. 05-124524 (Japanese Patent No. 2690230)
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problem, and in an electric power steering device, engagement between a rack tooth and a pinion is eliminated to prevent hitting noise (noise / vibration) from being generated. It is an object of the present invention to provide a steering apparatus which can reduce a backlash generating portion in a servo control system and thereby form a stable servo control system and does not unnecessarily apply a load to a ball joint to be used.
[0014]
[Means for Solving the Problems]
The above problem is solved by the following means. That is, a first aspect of the present invention provides a screw shaft having a link connecting portion for linking to a tie rod at both ends thereof, a screw shaft having a male screw portion, the screw shaft being slidable in the axial direction and non-rotatable. A supporting member, a casing fixed to the supporting member, a rotating member having an internal thread portion screwed to the external thread portion, the rotating member being axially immovable and rotatably supported by the casing, and the casing. An electric power steering apparatus provided with an electric assist motor for driving the rotating member to rotate.
[0015]
According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the male screw portion and the female screw portion are screw-connected via a rollable ball to form a ball screw mechanism. An electric power steering apparatus characterized in that:
[0016]
According to a third aspect of the present invention, in the electric power steering apparatus according to the first or second aspect, the rotating member is coupled to the female screw portion via an elastic member. It is a steering device.
[0017]
According to a fourth aspect of the present invention, in the electric power steering apparatus according to the first to third aspects, the female screw portion is supported by the casing via a self-aligning roller bearing. Is an electric power steering device.
[0018]
According to a fifth aspect of the present invention, there is provided an electric power steering apparatus according to the first to fourth aspects, wherein the ball screw mechanism has three or more and six or less. It is a power steering device.
[0019]
A sixth aspect of the present invention is the electric power steering apparatus according to the first to fifth aspects, wherein the non-circular columnar portion of the screw shaft is slidably and non-rotatably fitted to the support member. An electric power steering apparatus comprising: a sliding member made of polytetrafluoroethylene having an inner surface complementary to the sliding member.
[0020]
According to a seventh aspect of the present invention, in the electric power steering apparatus according to the first to sixth aspects, the output shaft of the electric assist motor forms a stub shaft and a drive bevel gear portion is fixed. An electric power steering apparatus, which is engaged with a driven bevel gear provided in the rotating member.
[0021]
According to an eighth aspect of the present invention, in the electric power steering apparatus according to the first to sixth aspects, the output shaft of the electric assist motor is connected to an independent stub shaft via a speed reduction mechanism. The electric power steering apparatus is characterized in that a drive bevel gear portion of the stub shaft meshes with a driven bevel gear portion of the rotating member.
[0022]
A ninth aspect of the present invention is the electric power steering apparatus according to the seventh or eighth aspect, wherein the driven bevel gear portion and the drive bevel gear portion constitute a bevel gear bevel gear mechanism that can mesh with each other. An electric power steering apparatus characterized in that:
[0023]
A tenth aspect of the present invention is the electric power steering apparatus according to the ninth aspect, wherein one or both of the driven bevel gear portion and the drive bevel gear portion have a synthetic resin tooth surface. It is a power steering device.
[0024]
According to an eleventh aspect of the present invention, in the electric power steering apparatus according to the first to tenth aspects, a torque applied to a stub shaft constituted by an output shaft of the electric assist motor or an independent stub shaft is provided. The electric power steering device according to claim 1, further comprising a torque sensor for detecting a torque according to (1).
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment FIG. 1 is a schematic diagram showing an outline of an electric power steering device according to a first embodiment. The electric power steering device 1 includes a screw shaft 2, a support member 3, a casing 4, a rotating member 5, and an electric assist motor 6. The screw shaft 2 is provided with a link connecting portion 21 for linking with the tie rod 91 at both ends, and a non-circular columnar portion 22 and a male screw portion 23 are formed inside the both ends. The link connecting portion 21 is formed with a female portion of a ball joint, and engages with the male portion of the tie rod 91.
[0026]
The support member 3 is for fixing the entire electric power steering device 1 to a vehicle body (not shown), and a casing 4 is fixed to the support member 3 via a cylindrical portion 41. The screw shaft 2 passes through the support member 3, the cylindrical portion 41, and the casing 4.
[0027]
The rotating member 5 includes a female screw portion 51 and a driven bevel gear portion 52, and is supported in the casing 4 so as to be rotatable and immovable in the axial direction. The electric assist motor 6 is fixed to the outside of the casing 4, and a drive bevel gear unit 62 is fixed to an output shaft 61 in the casing 4. Since the drive bevel gear portion 62 is meshed with the driven bevel gear portion 52, the rotating member 5 can be driven to rotate by the electric assist motor 6. In the first embodiment, the output shaft 61 is the same as the stub shaft, that is, the stub shaft forms the shaft itself of the rotor 63 of the electric assist motor 6.
[0028]
A torque sensor 64 is provided on the output shaft 61 on the side opposite to the drive bevel gear unit 62, and detects torque applied from the steering wheel 92 to the stub shaft (in this case, the output shaft 61). The control device 8 calculates the magnitude and polarity of the driving power to be applied to the electric assist motor 6 based on the output of the torque sensor 64, and controls the calculated driving power, thereby assisting the driver's steering operation.
[0029]
Since the control device 8 only needs to be able to transmit and receive electric power and signals to and from the electric assist motor 6 and the torque sensor 64, even if it is mounted on the electric power steering device 1, it is fixed to another remote place, for example, a vehicle body. It may be done. Further, since the torque sensor 64 is interposed between the steering wheel 92 and the electric assist motor 6 and only needs to be able to detect the torque applied to the steering wheel 92, not only the electric power steering device 1 itself but also the steering wheel 92 Can be changed to be provided on an appropriate rotation transmission path leading to.
[0030]
FIG. 2 is an enlarged partial cross-sectional view showing the vicinity of the rotating member 5, the female screw portion 51, and the male screw portion 23. The male screw portion 23 and the female screw portion 51 are screw-connected via a rollable ball 511 to form a ball screw mechanism. Further, the rotating member 5 is connected to the female screw portion 51 via an elastic member 513. Have been. The main body of the rotating member 5 is supported by the casing 4 by a pair of ball bearings 514, and the female screw portion 51 is supported by the casing 4 via the self-aligning roller bearing 512.
[0031]
A force from a tie rod 91 is applied to the screw shaft 2 to apply a bending moment. Due to this bending deformation, the parallelism between the male screw portion 23 and the female screw portion 51 is slightly lost. When such a phenomenon occurs, an excessive load is applied to the biased ball 511, and the durability of the ball screw mechanism is reduced. The self-aligning roller bearing 512 allows the axial center of the female screw portion 51 to be inclined to some extent, and even when such a certain degree of bending occurs, the engagement between the male screw portion 23 and the female screw portion 51 performed via the ball 511 is maintained. This is to prevent damage.
[0032]
The elastic member 513 connecting the main body of the rotating member 5 and the female screw portion 51 is a flexible bush joint, and has a small inclination that the female screw portion 51 receives from the screw shaft 2 by deforming itself. The displacement is absorbed, and is prevented from being transmitted to the rotating member 5 main body. The elastic member 513 further prevents the transmission of vibration to the driven bevel gear portion 52 (described later) fixed to the rotating member 5 by absorbing the vibration of the tire received on the road surface, and thus has a curved bevel. It prevents the life of the gear mechanism from being impaired.
[0033]
In general, in a steering mechanism, a load acting in the axial direction of a tie rod is extremely large, and it is necessary to increase a lead when a screw shaft is used due to a relationship between a rotation amount of a steering wheel and a steering angle. On the other hand, thickening the screw shaft is limited because it is incompatible with the direction of reducing the weight of the vehicle body. Further, with a screw having a large lead, the surface pressure between the ball and the raceway surface is large, so that the load applied to the ball increases. For this reason, in the ball screw mechanism used in the present electric power steering device 1, a multi-start screw is employed.
[0034]
That is, a typical tie rod diameter is in the range of 20 mm to 35 mm. If a sufficient tie rod stroke (150 mm or more) is ensured in the range of the tie rod operation of 3.5 rotations or less of the steering wheel, the lead of the ball screw mechanism becomes large. If the number of ball screw mechanisms is less than three, the number of balls simultaneously contacting in one cross section is reduced, so that a sufficient load capacity cannot be secured. On the other hand, if the ball screw mechanism has more than six threads, the number of balls in the above sense increases, but the ball diameter becomes too small, so that sufficient load capacity cannot be secured from this point. Therefore, in the present invention, a ball screw mechanism composed of the male screw portion 23, the female screw portion 51, and the ball 511 employs three or more and six or less.
[0035]
When the screw shaft 2 is driven, it is necessary to prevent the screw shaft 2 from rotating due to the dynamic friction torque of the ball screw mechanism. For this reason, the sliding member 31 is fixed to the support member 3, and the screw shaft 2 is provided with a non-circular columnar portion 22. As shown in FIG. 3, the sliding member 31 has a non-circular inner surface 311, and the non-circular columnar portion 22 is slidably fitted to the inner surface 311, and the rotation of the screw shaft 2 is restricted by the non-circular shape. ing. The non-circular shape of the inner surface 311 and the non-circular columnar portion 22 can be, for example, a square. The material of the inner surface 311 of the sliding member 31 is preferably PTFE (polytetrafluoroethylene) which has a small coefficient of friction with the non-circular columnar portion 22 (steel) and can obtain sufficient strength.
[0036]
The drive bevel gear portion 62 and the driven bevel gear portion 52 constitute a bevel gear mechanism having a bend in the tooth trace direction, and one or both of the tooth surface portions (or the whole) are made of resin. Can be. The drive bevel gear portion 62 and the driven bevel gear portion 52 are inclined by an angle α that is appropriately deviated from a right angle. By providing the inclination angle α, the outer diameter of the driven bevel gear 52 can be reduced. Furthermore, the distance between the end (the lower end in FIG. 1) of the output shaft 61 (the stub shaft) and the female screw portion 51 can be increased, and the casing 4 has a ball for rotatingly supporting the output shaft 61. The bearing 611 can be provided with a margin. Thereby, the outer contour of the electric power steering device 1 can be made compact.
[0037]
By using the shafts of the two bevel gears (the drive bevel gear portion 62 and the driven bevel gear portion 52) as staggered shafts and using a hypoid bevel gear, the vertical outer diameter profile in FIG. 1 can be made more compact. It is.
[0038]
Second Embodiment FIG. 4 shows that an electric power steering apparatus 1 according to a second embodiment includes a screw shaft 2, a support member 3, a casing 4, a rotating member 5, and an electric assist motor 6, as in the first embodiment. However, only the arrangement of the electric assist motor 6 and the structure related thereto are different. Therefore, a duplicate description is avoided, and the description of the first embodiment is used.
[0039]
In the second embodiment, an independent stub shaft 66 that is not the same as the output shaft 61 is provided. One end of the stub shaft 66 is connected to a drive path leading to the steering wheel 92, and the other end of the stub shaft 66 is fixed to the drive bevel gear unit 62. The output shaft 61 of the electric assist motor 6 and the stub shaft 66 are connected by a motor reduction mechanism 65. In this example, the motor reduction mechanism 65 includes a spur gear 651 fixed to the output shaft 61 and a spur gear 652 meshed with the spur gear 651 and fixed to the stub shaft 66.
[0040]
Through the motor reduction mechanism 65, the electric assist motor 6 is directly connected and does not drive the drive bevel gear unit 62. Therefore, a small motor capable of producing only a relatively small output torque can be used for the electric assist motor 6. Instead of the spur gears 651 and 652, a combination of a worm and a worm wheel can be used for the motor reduction mechanism 65. In this case, a worm is fixed to the output shaft 61 of the assist motor 6, and a worm wheel is fixed to the stub shaft 66. In the motor deceleration mechanism 65, it is necessary to use a mechanism that generates as little play as possible.
[0041]
By selecting the type of the motor speed reduction mechanism 65, the degree of freedom in designing the electric power steering device 1 can be improved, and it is possible to meet more various requirements.
[0042]
According to the two embodiments described above, in any case, the screw shaft 2 does not rotate itself. For this reason, only the linear motion of the output shaft is transmitted to the tie rods provided for changing the directions of the left and right wheels, and the joint portion of the ball joint that forms the link mechanism with the tie rods is You will only be responsible for the load you receive from exercise. Thereby, durability and maintainability can be improved. Further, in the servo control system including the electric power steering device, since the play generation unit and the generation amount thereof can be reduced, it is possible to realize the stable servo control by suppressing the occurrence of the tapping sound.
[0043]
【The invention's effect】
As described above, according to the present invention, since the screw shaft does not rotate by itself, only the linear motion of the output shaft is transmitted to the tie rod provided for changing the direction of the left and right wheels, The joint portion of the ball joint that constitutes the link mechanism with the tie rods only bears the load received from the linear motion of the output shaft, and has the effect of improving durability and maintainability. Further, in the servo control system including the electric power steering device, since the play generation unit and the generation amount thereof can be reduced, there is an effect that it is possible to suppress occurrence of a tapping sound and realize stable servo control.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an outline of an electric power steering device according to a first embodiment.
FIG. 2 is an enlarged partial cross-sectional view showing the vicinity of a rotating member 5, a female screw portion 51, and a male screw portion 23.
FIG. 3 is a perspective view of a sliding member 31;
FIG. 4 is a schematic diagram showing an outline of an electric power steering device according to a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electric power steering device 2 Screw shaft 21 Link connection part 22 Non-circular columnar part 23 Male screw part 3 Support member 31 Sliding member 311 Inner surface 4 Casing 41 Cylindrical part 5 Rotating member 51 Female screw part 511 Ball 512 Self-aligning roller bearing 513 Elastic member 514 Ball bearing 52 Driven bevel gear 6 Electric assist motor 61 Output shaft 611 Ball bearing 62 Drive bevel gear 63 Rotor 64 Torque sensor 65 Motor reduction mechanisms 651, 652 Spur gear 66 Stub shaft 8 Control device 91 Tie rod 92 Steering wheel

Claims (11)

A screw shaft having a link connection portion for link connection to the tie rod at both ends thereof and having a male screw portion,
A support member that supports the screw shaft slidably in the axial direction and non-rotatably;
A casing fixed to the support member,
A rotating member having a female screw portion to be screwed with the male screw portion, and being rotatably supported by the casing so as to be axially immovable and rotatable;
An electric power steering device, comprising: an electric assist motor provided on the casing and configured to rotationally drive the rotating member. The electric power steering device according to claim 1,
An electric power steering apparatus, wherein the male screw portion and the female screw portion are screw-coupled via a rollable ball to form a ball screw mechanism. In the electric power steering device according to any one of claims 1 and 2,
The electric power steering device according to claim 1, wherein the rotating member is coupled to the female screw portion via an elastic member. In the electric power steering device according to any one of claims 1 to 3,
The electric power steering device according to claim 1, wherein the female screw portion is supported by the casing via a self-aligning roller bearing. In the electric power steering device according to any one of claims 1 to 4,
The electric power steering apparatus according to claim 1, wherein the ball screw mechanism has three or more and six or less. The electric power steering device according to any one of claims 1 to 5,
The support member includes a sliding member made of polytetrafluoroethylene having an inner surface complementary to the non-circular columnar portion of the screw shaft so that the non-circular columnar portion is slidably and non-rotatably fitted. A characteristic electric power steering device. In the electric power steering device according to any one of claims 1 to 6,
An electric power steering device, wherein an output shaft of the electric assist motor forms a stub shaft, and a drive bevel gear portion is fixed, and meshes with a driven bevel gear portion provided in the rotating member. In the electric power steering device according to any one of claims 1 to 6,
The output shaft of the electric assist motor is coupled to an independent stub shaft via a speed reduction mechanism, and the drive bevel gear portion of the stub shaft is meshed with a driven bevel gear portion of the rotating member. A characteristic electric power steering device. In the electric power steering device according to any one of claims 7 and 8,
The electric power steering device according to claim 1, wherein the driven bevel gear portion and the drive bevel gear portion form a bevel gear mechanism that can mesh with each other. The electric power steering device according to claim 9,
An electric power steering device, wherein one or both of the driven bevel gear portion and the drive bevel gear portion have a synthetic resin tooth surface. In the electric power steering device according to any one of claims 1 to 10,
An electric power steering device further comprising a torque sensor for detecting a torque applied to a stub shaft constituted by an output shaft of the electric assist motor or a torque applied to an independent stub shaft.

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