JP3801848B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle power steering apparatus using an electric motor.
[0002]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering equipment of a vehicle using an electric motor.
[0003]
[Problems to be solved by the invention]
In such an electric power steering device, a bearing is used to rotatably support the ball screw nut with respect to the housing. Such a bearing is disposed at both ends of the ball screw nut, but a restraining member is further provided to prevent the bearing from coming out of the ball screw nut.
[0004]
The holding member has a female screw that is screwed to a male screw formed on the outer periphery of the ball screw nut, and is prevented from falling off the bearing by being screwed to the ball screw nut.
[0005]
[Problems to be solved by the invention]
By the way, for example, in a general electric power steering apparatus, when the steering wheel is turned, the steering stopper finally comes into contact with the steering stopper, and further rotation is prevented. When the steering wheel is turned well, excessive contact of the steering stopper may occur. In such a case, there is a possibility that an impact force close to about 98.1 kN (10 tons) at maximum is generated on the rack shaft.
[0006]
When such a strong impact force is generated, the initial axial force of the restraining member that prevents the bearing from falling off the ball screw nut may be exceeded. However, if vibration during running is added to this, the restraining member may loosen. There is.
[0007]
In order to prevent the restraining member from loosening, if the restraining member is screwed into the ball screw nut with a strong torque to increase the initial axial force, the ball rolling path formed inside the ball screw nut will be deformed. The function of the ball screw nut may be impaired.
[0008]
On the other hand, how to adjust the play of the ball in the rolling path formed between the ball screw nut and the ball screw shaft is also a problem.
[0009]
In view of such problems, an object of the present invention is to provide an electric power steering device that is low in cost and excellent in impact resistance that can prevent a bearing from being removed from a ball screw nut.
[0010]
[Means for Solving the Problems]
The electric power steering apparatus of the first aspect of the present invention is
A housing;
A ball screw shaft extending through the housing and connected to a steering mechanism;
A motor having a rotor;
A ball screw nut that converts the rotational force of the rotor into an axial force and transmits it to the ball screw shaft;
A bearing that rotatably supports the ball screw nut with respect to the housing;
A holding member that holds the bearing against the ball screw nut by being screwed to the ball screw nut;
The restraining member can restrict relative rotation between the restraining member and the ball screw nut even when the screw portion screwed into the thread portion of the ball screw nut and the coupling force generated between the both screw portions are lost. Connecting means.
The electric power steering apparatus of the second aspect of the present invention is
A housing;
A ball screw shaft extending through the housing and connected to a steering mechanism;
A motor having a rotor;
A ball screw nut that converts the rotational force of the rotor into an axial force and transmits it to the ball screw shaft;
A bearing that rotatably supports the ball screw nut with respect to the housing;
A holding member that holds the bearing against the ball screw nut by being screwed to the ball screw nut;
The holding member has a connecting means capable of restricting relative rotation between the holding member and the ball screw nut by deforming at least a part of the thin portion toward the ball screw nut. .
[0011]
[Action]
An electric power steering apparatus according to a first aspect of the present invention includes a housing, a ball screw shaft extending through the housing and coupled to a steering mechanism, a motor having a rotor, and a rotational force of the rotor as an axis. The ball screw nut converted into a directional force and transmitted to the ball screw shaft, a bearing that rotatably supports the ball screw nut with respect to the housing, and the ball screw nut are screwed into the ball screw nut, whereby the ball A holding member that holds the bearing against the screw nut, and the holding member is screwed into the screw portion of the ball screw nut and the coupling force generated between both screw portions is lost. And a connecting means capable of restricting relative rotation between the restraining member and the ball screw nut. For example, when a large impact force is generated on the ball screw shaft when the steering stopper comes into contact, and the axial force of the restraining member against the bearing becomes zero, the restraining member is prevented from rotating. When the impact force disappears without loosening, a predetermined axial force can be applied to the bearing again.
An electric power steering apparatus according to a second aspect of the present invention includes a housing, a ball screw shaft extending through the housing and connected to a steering mechanism, a motor having a rotor, and a rotational force of the rotor as an axis. The ball screw nut converted into a directional force and transmitted to the ball screw shaft, a bearing that rotatably supports the ball screw nut with respect to the housing, and the ball screw nut are screwed into the ball screw nut, whereby the ball A restraining member that restrains the bearing against the screw nut, and the restraining member deforms at least a part of the thin portion toward the ball screw nut so that the restraining member and the ball screw nut And a connecting means capable of restricting relative rotation. Even when a large impact force is generated on the ball screw shaft during topper contact, and the axial force of the restraining member against the bearing becomes zero, the restraining member is prevented from rotating, so the restraining member is loosened. When the impact force disappears, a predetermined axial force can be applied to the bearing again.
[0012]
Further, it is preferable that the connecting means connect the holding member and the ball screw nut so as not to be relatively rotatable by using a shearing force of a resin material.
[0013]
Further, it is preferable that the connecting means connect the holding member and the ball screw nut so as not to be relatively rotatable by using a frictional force.
[0014]
Furthermore, since the holding member is adapted to adjust the backlash of the ball in the ball screw nut by being screwed to the ball screw nut, it is not necessary to provide a separate backlash removing means. An inexpensive electric power steering device is provided.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an electric power steering apparatus according to an embodiment of the present invention. In FIG. 1, the steering wheel 1 is connected to the upper end of a steering shaft 2.
[0016]
The lower end of the steering shaft 2 is connected to the upper end of the lower shaft 5 via the universal joint 4, and the lower end of the lower shaft 5 is connected to the upper end of the pinion shaft 7 via the universal joint 6. A pinion (not shown) is connected to the lower end of the pinion shaft 7, and the pinion meshes with the rack teeth of the ball screw shaft, that is, the rack shaft 22 (FIG. 2). In the rack housing 8 through which the rack shaft 22 is inserted, a rack shaft coaxial type five-phase rectangular wave drive brushless motor 23 is arranged in a manner described later.
[0017]
The torque sensor 3 is disposed in the vicinity of the pinion shaft 7 and detects the steering torque transmitted to the pinion shaft 7. The torque sensor 3 is configured to convert to a torsional angular displacement of a torsion bar (not shown) interposed between the pinion shafts 7 divided into two, for example, and to detect the torsional angular displacement magnetically or mechanically. Accordingly, when the operator steers the steering wheel 1, a torque detection signal Tv composed of an analog voltage corresponding to the magnitude and direction of the steering force is output to the controller 13.
[0018]
That is, for example, when the steering wheel 1 is in a neutral state, the torque sensor 3 outputs a predetermined neutral voltage as the torque detection signal Tv. When the voltage that increases from the neutral voltage according to the steering torque is counterclockwise, a voltage that decreases from the neutral voltage according to the steering torque at that time is output.
[0019]
A controller 13 is provided to drive and control the motor 23 to control the steering assist force to the steering system. The controller 13 is operated by being supplied with power from a vehicle-mounted battery 16. The negative electrode of the battery 16 is grounded, and the positive electrode is connected to the controller 13 via an ignition switch 14 and a fuse 15a for starting the engine, and is directly connected to the controller 13 via a fuse 15b. For example, the power supplied through the memory is used for memory backup. The controller 13 can drive and control the brushless motor 23 based on a torque detection signal Tv from the torque sensor 3 and a vehicle speed detection signal Vp from a vehicle speed sensor 17 disposed on an output shaft of a transmission (not shown), for example. it can.
[0020]
FIG. 2 is an axial cross-sectional view of the periphery of the rack shaft coaxial brushless motor according to the first embodiment. The housing, that is, the rack housing 8 is fixed to a vehicle body (not shown) by a bracket (not shown) . A rack shaft 22 is inserted into the rack housing 8, and the rack shaft 22 is connected to tie rods 9 (FIG. 1) and 10 at both ends thereof. The tie rods 9 and 10 are connected to a steering mechanism (not shown).
[0021]
A cylindrical stator 23b is fixed in the rack housing 8, and a coil 23a composed of a plurality of segments around which a part of the stator 23b is wound is provided. An elongated thin circular tubular rotor 23c is provided so as to be inserted through the stator 23b . A cylindrical driving magnet 23d is provided on the outer periphery of the rotor 23c so as to face the stator 23b . The drive magnet 23d is magnetized so as to alternately form N and S poles in the circumferential direction. The rack shaft 22 extends in the rotor 23c. The stator 23b , the coil 23a , the rotor 23c, and the driving magnet 23d constitute a brushless type electric motor 23.
[0022]
The rotor 23c is rotatably supported with respect to the rack housing 8 by a ball bearing 26 and a bearing (not shown). Although not shown, a phase detection rotor is attached to the outer periphery of the rotor 23c. This rotor is installed so as to have a certain correlation with the polarity in order to detect the polarity of the drive magnet 23d. This polarity phase is detected by a resolver R (FIG. 6) disposed adjacent to the position detection magnet, and an electrical signal indicating the polarity phase is output to the controller 13.
[0023]
The controller 13 sequentially supplies and distributes current to the segments of the coils 23a divided in the rotation direction, and as a result, the brushless motor 23 is driven and controlled to generate a predetermined rotation output.
[0024]
The left end of the rotor 23 c is connected to the right end of a substantially cylindrical ball screw nut 29. The ball screw nut 29 has a spiral inner thread groove 29 b on the inner side, and the inner thread groove 29 b forms a rolling path opposite to the outer thread groove 22 a formed on the left side of the rack shaft 22. A plurality of balls 30 are accommodated in the rolling path.
[0025]
The ball 30 is used to reduce the frictional force generated when the ball screw nut 29 and the rack shaft 22 rotate relative to each other. The ball screw nut 29 has a circulation path 29c, and the ball 30 can circulate through the circulation path 29c when the ball screw nut 29 rotates.
[0026]
The left end of the ball screw nut 29 is rotatably supported with respect to the rack housing 8 by an angular contact type ball bearing 25.
[0027]
3 is a view of the configuration of FIG. 2 taken along the line II-II and viewed in the direction of the arrow, and FIG. 4 is an enlarged view of an IV portion of the configuration of FIG. As shown in FIG. 4, a male screw 29 a is formed on the outer periphery of the left end of the ball screw nut 29. The cylindrical holding member 31 formed with the female screw 31 a that is screwed into the male screw 29 a has its right end in contact with the inner ring of the bearing 25.
[0028]
A thin tube portion 31b extending outward in the axial direction is formed at the end of the holding member 31 (left end in FIG. 4). As shown in FIG. 3, four notches 31c are formed on the outer periphery of the holding member 31 at equal intervals in the circumferential direction. The notch 31c is used when the holding member 31 is rotated by engaging a tool (not shown).
[0029]
Next, the operation of the present embodiment will be described with reference to the drawings. In FIG. 1, when the vehicle is running straight and no steering force is input from the steering wheel 1 to the rack shaft 22, the torque detection signal Tv output from the torque sensor 3 is zero or a low value. 13 does not rotationally drive the brushless motor 23. Therefore, this electric power steering apparatus is in a state where no auxiliary steering force is output.
[0030]
On the other hand, when the vehicle is about to turn a curve, the steering wheel 1 is steered and the steering force is transmitted to the rack shaft 22, so that the torque sensor 3 outputs a torque detection signal Tv corresponding to the steering torque. Then, in consideration of the detection signal Vp from the speed sensor 17, the controller 13 rotates the rotor 23c of the brushless motor 23 with an appropriate torque. When the rotor 23c rotates, the ball screw nut 29 also rotates, thereby moving the rack shaft 22 leftward or rightward to generate an auxiliary steering force.
[0031]
By the way, in order to prevent the ball bearing 25 from coming off from the ball screw nut 29, the restraining member 31 is screwed into the ball screw nut 29. In order to prevent the restraining member 31 from loosening, the initial axial force is increased. If the restraining member 31 is tightened with a torque that is as strong as possible, the circulation path 29c formed inside the ball screw nut 29 may be deformed and the function of the ball screw nut 29 may be impaired.
[0032]
With respect to such a problem, according to the present embodiment, the restraining member 31 is screwed into the ball screw nut 29 with a torque that does not deform the circulation path 29c and the like, and then the thin cylindrical portion 31b of the restraining member 31 is moved in the radial direction. And then deformed so as to be strongly pressed against the male screw portion 20a of the ball screw nut 29. As a result, the restraining member 31 is connected to the ball screw nut 29 so as not to rotate relative to the ball screw nut 29, and does not loosen even when a strong force is transmitted from the rack shaft 22. In the present embodiment, the caulking C constitutes a blocking means.
[0033]
On the other hand, the play of the ball 30 in the transfer path in the ball screw nut 29 can be easily adjusted using the present embodiment. For example, after the ball bearing 25 is assembled in the ball screw nut 29, the holding member 31 is screwed into the end of the ball screw nut 29, and the holding member 31 is rotated by a tool (not shown) until an appropriate preload is applied. .
[0034]
When an appropriate amount of preload is applied, the thin cylindrical portion 31b of the restraining member 31 is crimped (C) in the radial direction. As a result, the holding member 31 is connected to the ball screw nut 29 so as not to be rotatable relative to the ball screw nut 29, so that the play of the ball 30 in the ball screw nut 29 can be stably maintained.
[0035]
FIG. 5 is an end cross-sectional view of a ball screw nut showing a modification of the present embodiment. In FIG. 5, holes 131 a and 129 a that penetrate the holding member 131 and the ball screw nut 129 in the radial direction are formed. A thin tube portion is not formed on the holding member 131. Other points are the same as those in the above-described embodiment, and thus the description thereof is omitted.
[0036]
In the present modification, the holding member 131 is rotated to give an appropriate preload, and then the holes 131a and 129a are filled with the molten resin 132. When the resin 132 as the blocking means is solidified, the holding member 131 is fixed to the ball screw nut 129 , and even when a strong force is transmitted from the rack shaft 22 due to the shearing force and the frictional force. The looseness of the ball 30 in the ball screw nut 129 can be stably maintained.
[0037]
If it is desired to disassemble the ball bearing 25, the resin 132 shears when the restraining member 131 is rotated with a strong force, so that the restraining member 131 and the ball bearing 25 can be removed from the ball screw nut 129. When reassembling, the resin 132 may be removed from the holes 129a and 131a , and the assembly may be performed in a similar process.
[0038]
FIG. 6 is an axial cross-sectional view of the periphery of a rack shaft coaxial brushless motor by the electric power steering apparatus according to the second embodiment. In the present embodiment, only the configuration around the ball screw nut is different. Therefore, this configuration will be mainly described, and the same components as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted. . A rack housing 208 composed of a small diameter portion 208a and a large diameter portion 208b is fixed to a vehicle body (not shown) by a bracket (not shown). The rack shaft 22 is inserted into the large-diameter portion 208b of the rack housing 208, and the rack shaft 22 is connected to the tie rods 9 (FIG. 1) and 10 at both ends thereof. The tie rods 9 and 10 are connected to a steering mechanism (not shown).
[0039]
The rotor 123 c of the brushless motor 123 inserted through the rack housing 208 is supported by the bearing 226 so as to be rotatable with respect to the rack housing 208. The left end of the rotor 123c is engaged by the spline teeth with the right end of the substantially cylindrical ball screw nut 229, and both rotate integrally, but are relatively movable in the axial direction. It has become. Resin is applied to at least one of the tooth surfaces of the female spline 229d formed on the ball screw nut 229 (or the rotor 123c) and the male spline 123d formed on the rotor 123c (or the ball screw nut 229) for performing such coupling. By coating the resin coating, the resin coating absorbs the impact force when an impact force is applied such as when the steering stopper comes into contact, thereby preventing hitting sound. The ball screw nut 229 has a spiral inner thread groove 229b on the inner side, and the inner thread groove 229b forms a rolling path opposite to the outer thread groove 22a formed in the left portion of the rack shaft 22. A plurality of balls 30 are accommodated in the rolling path.
[0040]
The ball 30 is used to reduce the frictional force generated when the ball screw nut 229 and the rack shaft 22 rotate relative to each other. The ball screw nut 229 has a circulation path 229c therein, and the ball 30 can be circulated through the circulation path when the ball screw nut 229 rotates.
[0041]
An angular contact type bearing 251 that rotatably supports a ball screw nut 229 is disposed on the inner periphery of the small diameter portion 208 a of the rack housing 208 via a thin cylindrical sliding bush 231. The bearing 251 includes an outer ring 251a, a pair of inner rings 251b and 251c, and two rows of balls 251d disposed between the two rings.
[0042]
A pair of L-shaped metal cores 252a and 252b are arranged so as to abut against both ends of the outer ring 251a of the bearing 251, and a left metal core 252a and a spacer 252c attached to the small-diameter portion 208a A ring-shaped elastic member 235b is disposed between the left core metal 252b and a nut 233 that is screwed into the small-diameter portion 208a. .
[0043]
Inner rings 251 b and 251 c of the bearing 251 are attached to the ball screw nut 229 by a nut 227 screwed to the outer periphery of the left end of the ball screw nut 229.
[0044]
According to the present embodiment, the nut 227 is screwed into the ball screw nut 229 with a torque that does not deform the circulation path 229c and the like, and then the thin cylindrical portion 227b extending in the axial direction from the nut 227 is moved in the radial direction. It is crimped and deformed so as to be strongly pressed against the outer periphery of the ball screw nut 229. As a result, the nut 227 is connected to the ball screw nut 229 so as not to rotate relative to the ball screw nut 229, and does not loosen even when a strong force is transmitted from the rack shaft 22.
[0045]
According to the present embodiment, when a large impact force is generated on the rack shaft 22 as a ball screw shaft, for example, at the time of a steering stopper contact, the ball bush nut 229 together with the bearing 251 is assisted by the sliding bush 231. However, in this case, in addition to the effect of the resin coating of the spline teeth described above, the elastic members 235a and 235b can effectively absorb the impact force and suppress the occurrence of hitting sound and the like.
[0046]
The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the blocking means that achieves locking of the restraining member may be a filler that is applied between the male screw and the female screw to increase the frictional force between the screws.
[0047]
【The invention's effect】
According to the present invention, even when a large impact force is generated on the ball screw shaft , for example, when the steering stopper comes into contact, the rotation of the restraining member is prevented even when the axial force of the restraining member against the bearing becomes zero. Therefore, the restraining member does not loosen, and when the impact force disappears, a predetermined axial force can be applied to the bearing again.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an electric power steering apparatus according to a first embodiment.
FIG. 2 is a cross-sectional view in the axial direction around a rack shaft coaxial brushless motor according to the present embodiment;
3 is a view of the configuration of FIG. 2 taken along the line II-II and viewed in the direction of the arrows.
4 is an enlarged view showing an IV part of the configuration of FIG. 2. FIG.
FIG. 5 is an end cross-sectional view of a ball screw nut showing a modification of the embodiment.
FIG. 6 is a cross-sectional view in the axial direction of a periphery of a rack shaft coaxial brushless motor by an electric power steering apparatus according to a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Torque sensor 4, 6 Universal joint 5 Lower shaft 7 Pinion shaft 8 Rack housing 9, 10 Tie rod 13 Controller 14 Ignition switch 15a, 15b Fuse 16 Battery 17 Vehicle speed sensor 22 Rack shaft 23, 123 Brushless motor 25 , 26, 251 Ball bearing 29, 129 Ball screw nut 30 Ball 31, 23 Retaining member

Claims (20)

A housing;
A ball screw shaft extending through the housing and connected to a steering mechanism;
A motor having a rotor;
A ball screw nut that converts the rotational force of the rotor into an axial force and transmits it to the ball screw shaft;
A bearing that rotatably supports the ball screw nut with respect to the housing;
A holding member that holds the bearing against the ball screw nut by being screwed to the ball screw nut;
The restraining member can restrict relative rotation between the restraining member and the ball screw nut even when the screw portion screwed into the thread portion of the ball screw nut and the coupling force generated between the both screw portions are lost. An electric power steering apparatus having a connecting means.   2. The electric power steering apparatus according to claim 1, wherein the coupling unit restricts relative rotation between the holding member and the ball screw nut after the two screw portions are screwed together.   The connecting means restricts relative rotation between the restraining member and the ball screw nut using a shearing force of a resin material filled in a hole formed in and communicating with each of the restraining member and the ball screw nut. The electric power steering apparatus according to claim 1 or 2, wherein   The said connection means restrict | limits the relative rotation of the said suppression member and the said ball screw nut by deform | transforming at least one part of the said suppression member toward the said ball screw nut. The electric power steering device according to any one of the above.   5. The electric power according to claim 4, wherein relative rotation between the restraining member and the ball screw nut is limited by a frictional force acting between the deformed thin portion and the ball screw nut. Steering device.   6. The electric power steering apparatus according to claim 5, wherein the thin portion is a thin cylindrical portion.   The electric power steering apparatus according to any one of claims 1 to 6, wherein the holding member has a female screw portion, and the ball screw nut has a male screw portion screwed into the ball screw nut.   The electric power steering apparatus according to any one of claims 1 to 7, wherein the holding member is in contact with a bearing that rotatably supports the ball screw nut.   The electric power steering apparatus according to any one of claims 1 to 8, wherein the holding member is attached to the ball screw nut with a torque that does not deform the circulation path of the ball screw nut. .   The electric power steering device according to any one of claims 1 to 9, wherein an elastic member is disposed on a support portion of the ball screw nut.   The electric power steering apparatus according to any one of claims 1 to 10, wherein the holding member is provided with a portion for engaging a tool for rotating the holding member. A housing;
A ball screw shaft extending through the housing and connected to a steering mechanism;
A motor having a rotor;
A ball screw nut that converts the rotational force of the rotor into an axial force and transmits it to the ball screw shaft;
A bearing that rotatably supports the ball screw nut with respect to the housing;
A holding member that holds the bearing against the ball screw nut by being screwed to the ball screw nut;
The holding member has a connecting means capable of restricting relative rotation between the holding member and the ball screw nut by deforming at least a part of the thin portion toward the ball screw nut. Electric power steering device.   The electric motor according to claim 12, wherein relative rotation between the restraining member and the ball screw nut is limited by a frictional force acting between the deformed thin wall portion and the ball screw nut. Power steering device.   The electric power steering apparatus according to claim 12 or 13, wherein the thin portion is a thin cylindrical portion.   The electric power steering apparatus according to any one of claims 12 to 14, wherein a filler is applied to a screw portion of the holding member.   The electric power steering device according to any one of claims 12 to 15, wherein the holding member has a female screw portion, and the ball screw nut has a male screw portion screwed into the ball screw nut.   The electric power steering apparatus according to claim 12, wherein the holding member is in contact with a bearing that rotatably supports the ball screw nut.   The electric power steering apparatus according to any one of claims 12 to 17, wherein the restraining member is provided with a portion for engaging a tool for rotating the restraining member.   The electric power steering device according to any one of claims 12 to 18, wherein an elastic member is disposed on a support portion of the ball screw nut.   The said connection means restrict | limits the relative rotation between the said suppression member and the said ball screw nut by the part of the said suppression member deform | transformed toward the said ball screw nut. The electric power steering device according to any one of the above.

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