JP3950696B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus that generates a steering assist force by an electric motor.
[0002]
[Prior art and problems to be solved by the invention]
In the rack assist type electric power steering device, the rotation of the electric motor is decelerated through a pulley / belt mechanism, and then converted into an axial movement of the rack shaft through a ball screw mechanism that surrounds the rack shaft ( For example, see Japanese Patent Publication No. 4-28583.
In this case, since the belt is interposed in the power transmission path between the electric motor and the rack shaft, there is an advantage that impact load and vibration from the rack shaft are not transmitted to the electric motor.
[0003]
However, if the belt is excessively slack, the belt slips, which may cause malfunction and noise.
SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that can prevent malfunction and noise due to excessive slack of a belt.
[0004]
[Means for Solving the Problems and Effects of the Invention]
In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an electric motor that generates a steering assist force, a speed reduction mechanism that decelerates rotation of the electric motor, and an output rotation of the speed reduction mechanism that extends in the left-right direction of the vehicle. A conversion mechanism that converts the movement of the steering shaft in the axial direction, and the speed reduction mechanism includes an input pulley that is mounted on the same axis as the rotation shaft of the electric motor, an output pulley that is disposed so as to surround the steering shaft, and a belt for connecting the output pulley, seen including a tension adjusting mechanism for adjusting the tension of the belt, a first housing for housing the input pulley, said output pulley, second accommodating the converting mechanism and the steering shaft And the first and second housings have a cylindrical shape as a whole, and the first and second housings have mounting flanges so as to form a substantially Ω-shape when viewed from the end surface side. And second how Mounting flange of the ring are fastened to each other, the belt is characterized in that it is accommodated over the first and second housings.
In the present invention, by properly adjusting the belt tension, it is possible to prevent malfunction and noise due to excessive belt slack.
[0005]
According to a second aspect of the present invention, in the first aspect, the tension adjusting mechanism is a center-to-center distance changing mechanism that changes a distance between the shaft centers of the input pulley and the output pulley. In the present invention, the belt tension can be easily adjusted by changing the distance between the centers of the two pulleys.
According to a third aspect of the present invention, in the second aspect, the center distance changing mechanism includes a spacer interposed between the first housing that holds the input pulley and the second housing that holds the steering shaft. It is characterized by. In the present invention, the tension of the belt can be easily adjusted by adjusting the thickness of the spacer.
[0006]
According to a fourth aspect of the present invention, in the second aspect, the center distance changing mechanism can change the center distance between the first housing that holds the input pulley and the second housing that holds the steering shaft. It is characterized by including a guide mechanism for guiding relative movement in various directions. In the present invention, the belt tension can be easily adjusted by relatively moving both housings while maintaining parallelism between the shaft centers of both pulleys.
[0007]
According to a fifth aspect of the present invention, in the fourth aspect, the center distance changing mechanism further includes a screw capable of relatively driving the first and second housings in a direction guided by the guide mechanism. Is. In the present invention, the tension of the belt can be accurately adjusted by managing the tightening torque of the screw.
According to a sixth aspect of the present invention, in the fourth aspect of the invention, the center distance changing mechanism further includes an elastic member that relatively biases the first and second housings in a direction guided by the guide mechanism. To do. In the present invention, the belt is automatically maintained at an appropriate tension even when used for a long time.
[0008]
The invention according to claim 7 is the invention according to claim 2, wherein the center-to-center distance changing mechanism includes a circular hole formed in the fixed housing and a circular outer diameter portion supported by the circular hole so that the rotational position can be adjusted. And a circular eccentric hole having a center at a position deviated from the center of the circular outer diameter portion of the movable housing and for rotatably supporting the input pulley. In the present invention, the belt tension can be easily adjusted simply by rotating the movable housing in the circumferential direction of the circular hole.
[0009]
The invention according to claim 8 is characterized in that, in claim 7, the movable housing is integrally extended from the motor housing of the electric motor. In the present invention, the belt tension can be easily adjusted by simply rotating the motor housing in the circumferential direction.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering device (EPS) 1 includes a steering shaft 3 connected to a steering wheel 2 as a steering member, a pinion gear 4 provided at a tip portion of the steering shaft 3, and the pinion gear 4. And a rack shaft 6 as a steering shaft extending in the left-right direction of the vehicle.
[0011]
Tie rods 7 are coupled to both ends of the rack shaft 6, and each tie rod 7 is connected to a corresponding wheel 8 via a corresponding knuckle arm (not shown). When the steering wheel 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack shaft 6 along the left-right direction of the vehicle by the pinion gear 4 and the rack gear 5. Thereby, steering of the wheel 8 is achieved.
[0012]
The steering shaft 3 is divided into an input shaft 9 connected to the steering wheel 2 and an output shaft 10 connected to the pinion gear 4. These input and output shafts 9, 10 are mutually connected on the same axis via a torsion bar 11. It is connected.
A torque sensor 12 is provided for detecting a steering torque based on a relative rotational displacement amount between the input and output shafts 9 and 10 via the torsion bar 11, and a torque detection result of the torque sensor 12 is given to the control unit 13. The control unit 13 controls the voltage applied to the steering assisting electric motor 15 via the driver 14 based on the torque detection result, the vehicle speed detection result, and the like. The rotation of the rotating shaft 16 (see FIG. 2) of the electric motor 15 is decelerated via a speed reducing mechanism 17 including a pulley / belt mechanism. The output rotation of the speed reduction mechanism 17 is converted into the axial movement of the rack shaft 6 via the conversion mechanism 18 to assist the steering. The electric power steering apparatus 1 is a so-called rack assist type.
[0013]
2 is an enlarged view of a main part of the electric power steering apparatus 1, and FIG. 3 is a schematic cross-sectional view taken along the line III-III in FIG.
With reference to these drawings, the electric motor 15 is provided in a rack housing 19 as a second housing for accommodating the rack shaft 6. A motor housing 20 of the electric motor 15 is fixed to the rack housing 19 via a first housing 21 that holds an input pulley of the speed reduction mechanism 17.
[0014]
The first housing 21 has a cylindrical shape as a whole, and has a mounting flange 22 so as to form a substantially Ω shape when viewed from the end face side. The rack housing 19 as the second housing also has a mounting flange 23 opposite to the mounting flange 22 of the first housing 21, and a spacer 24 such as a shim is interposed between the mounting flanges 22, 23. Thus, both mounting flanges 22 and 23 are fastened to each other by screws 25. The screw 25 is screwed into the screw hole 23 a of the mounting flange 23 through the screw insertion hole 22 a of the mounting flange 22, for example.
[0015]
The feature of the present embodiment is that the distance between the first housing 21 and the second housing 19 is adjusted by adjusting the thickness of the spacer 24, whereby input and output pulleys 28 and 29 as will be described later. The tension adjustment of the belt 30 is achieved through the adjustment of the distance between the shaft centers 28a and 29a (center-to-center distance D). That is, the spacer 24 constitutes a center distance adjustment mechanism A as a tension adjustment mechanism.
[0016]
The speed reduction mechanism 17 has an input shaft 27 that is coaxially connected to the rotary shaft 16 of the electric motor 15 via a joint 26 that uses, for example, a spline, and a small diameter that can be integrally rotated at an axially intermediate portion of the input shaft 27. Input pulley 28, a large-diameter output pulley 29 disposed so as to surround the rack shaft 6 as a steering shaft, and a belt 30 wound around the input and output pulleys 28 and 29. The belt 30 is formed of, for example, a toothed belt (cogged belt), and the input pulley 28 is configured as a toothed pulley in which teeth that mesh with the toothed belt are formed on the outer periphery of the input shaft 27 at a uniform circumference. The output pulley 29 is similarly a toothed pulley.
[0017]
The input shaft 27 has first and second end portions 31 and 32, and the first and second end portions 31 and 32 are connected to the first housing 21 via corresponding bearings 33 and 34, respectively. It is rotatably supported by the corresponding support holes 35 and 36.
Further, the first end portion 31 of the input shaft 27 is connected to the rotary shaft 16 of the electric motor 15 through the joint 26 so as to be integrally rotatable.
The first housing 21 accommodates the connection housing 37 connected to the motor housing 20 so as to cover the portion where the rotating shaft 16 protrudes from the motor housing 20, and the main part of the speed reduction mechanism 17 in cooperation with the connection housing 37. And a reduction housing 39 for partitioning the accommodating chamber 38 to be provided.
[0018]
The connecting housing 37 has a cylindrical shape and houses the joint 26 therein. The connection housing 37 has a peripheral wall portion 40 and an end wall portion 41, and the end wall portion 41 is provided with the support hole 35.
The speed reduction housing 39 includes a peripheral wall portion 42 that is liquid-tightly fitted to the peripheral wall portion 40 of the connection housing 37, and an end wall portion 43. The support hole 36 is provided in the end wall portion 43. An input pulley 28 is accommodated in a storage chamber 38 defined by the connection housing 37 and the speed reduction housing 39. The mounting flange 22 is provided on both the connection housing 37 and the speed reduction housing 39.
[0019]
As the conversion mechanism 18 , for example, a ball screw mechanism or a bearing screw mechanism (see, for example, Japanese Patent Application Laid-Open No. 2000-46136) can be used to convert rotational motion into linear motion. In the present embodiment, description will be made in accordance with an example in which a ball screw mechanism is used. The conversion mechanism 18 includes a ball nut 44 as a rotating body surrounding the rack shaft 6.
The ball nut 44 is screwed into a ball screw groove 6 a formed in the middle of the rack shaft 6 via a ball 45, thereby constituting a conversion mechanism 18 . The ball nut 44 is rotatably supported by the rack housing 19 via a bearing 46. The output pulley 29 is fitted to the outer peripheral portion 47 of the ball nut 44 so as to be integrally rotatable. Specifically, the output pulley 29 is sandwiched between the stepped portion 48 formed on the outer peripheral portion 47 of the ball nut 44 and the fixing screw 50 screwed into the screw portion 49 of the outer peripheral portion 47, so that the output pulley 29 is fixed to the ball nut 44.
[0020]
According to the present embodiment, by adjusting the thickness of the spacer 24 made of shims or the like, the distance between the shaft centers 28a, 29a of the input and output pulleys 28, 29 (distance D between the centers) can be adjusted easily and inexpensively. it can. As a result, the tension of the belt 30 can be adjusted easily and inexpensively. The malfunction of the belt 30 and the generation of noise can be prevented.
Next, FIG. 4 shows another embodiment of the present invention. Referring to FIG. 4, the present embodiment differs from the embodiment of FIG. 3 in that the spacer 24 is eliminated and the first housing 21 holding the input pulley 28, the bearing 46 and the rack shaft 6 are provided. The rack housing 19 as the second housing holding the output pulley 29 is slid relative to each other in the lateral direction X along the mounting flanges 22 and 23, and the center distance D is set. The point is to adjust. The lateral direction X is a direction substantially orthogonal to the plane P including the axial centers 28a and 29a.
[0021]
In order to make this possible, the screw insertion holes 22b of the mounting flange 22 are formed as long holes in the lateral direction X, and both housings 19 in the lateral direction X are inserted through the screw insertion holes 22b made of the long holes. , 21 relative slides are guided. The point that a screw hole 23a that engages with the screw 25 is formed in the mounting member 23 is the same as the embodiment of FIG. A guide mechanism G as a center-to-center distance changing mechanism A is configured by the mounting flanges 22 and 23, the screws 25, and the screw insertion holes 22 b formed of long holes.
[0022]
In the present embodiment, since both the housings 21 and 19 are relatively slid in the lateral direction X, the tension of the belt 30 can be adjusted easily and inexpensively while saving space.
Next, FIG. 5 further shows another embodiment of the present invention. Referring to FIG. 5, the present embodiment is different from the embodiment of FIG. 4 in that in the embodiment of FIG. 4, both housings 21 and 19 are relatively slid along the lateral direction X. In the embodiment, the rack housing 19 and the connection housing 37A are relatively slid along the vertical direction Y to adjust the center distance D, and the rack housing 19 and the connection housing 37A are relatively aligned along the vertical direction Y. A single drive screw 51 for sliding is provided. The vertical direction Y is a direction substantially orthogonal to both the axis 28a and the axis 29a.
[0023]
Specifically, a guided portion 52 formed of an outward annular flange is provided on the peripheral wall portion 40 of the connection housing 37A, and an extending portion 53 extending in parallel to the input shaft 27 from the end wall portion 41 of the connection housing 37A is provided. Provide. Further, an end wall portion 54 extending in parallel to the end wall portion 43 of the speed reduction housing 39A is extended from the distal end of the extending portion 53, and a cylindrical portion 55 protruding in a stepped shape is formed on the end wall portion 54. A guided portion 56 is formed by the end surface of the cylindrical portion 55. The second end portion 32 of the input shaft 27 is rotatably supported by the inner peripheral surface 55a of the cylindrical portion 55 via the bearing 34.
[0024]
On the other hand, the speed reduction housing 39A is integrally formed as a part of the rack housing 19, and a guide portion 57 for guiding the guided portion 52 is formed in the rack housing and the speed reduction housing 39A. Further, a guide portion 58 made of, for example, a recess for guiding the guided portion 56 is formed on the end wall portion 43 of the deceleration housing 39A. A guided mechanism G is constituted by the guided portions 52 and 56 and the guiding portions 57 and 58. The drive screw 51 is screwed into the screw hole 60 of the extending portion 53 of the connection housing 37A through the screw insertion hole 59 of the peripheral wall portion 42 of the speed reduction housing 39A. The guide mechanism G and the drive screw 51 constitute a center distance changing mechanism A.
[0025]
According to the present embodiment, it is possible to easily and accurately adjust the tension of the belt 30 by managing the tightening torque of the drive screw 51, and to prevent malfunctions and noises associated with the belt 30. it can.
Next, FIG. 6 shows still another embodiment of the present invention. Referring to FIG. 6, the present embodiment is different from the embodiment of FIG. 5 in that the connection housing 39 </ b> A that holds the input pulley 28 by operating the single drive screw 51 in the embodiment of FIG. 5. And by pulling the motor housing 20, the center-to-center distance D is increased to increase the tension of the belt 30, but in the present embodiment, a pair of drive screws disposed on both sides of the belt 30 By pressing the connecting housing 39B that supports the first end portion 31 of the input shaft 27 and the support housing 61 that supports the second end portion 32 of the input shaft 27 along the vertical direction Y by operating 51a and 51b. The center distance D is increased to increase the tension of the belt 30.
[0026]
The connecting housing 37 </ b> B has a reduced diameter portion 62 and a large diameter portion 63 at the tip thereof, and the first end portion 31 of the input shaft 27 is supported by the large diameter portion 63 via the bearing 33. The large diameter portion 63 has a guided portion 64 composed of a pair of annular flanges.
The support housing 61 has a bottomed cylindrical shape and supports the second end portion 32 of the input shaft 27 via a bearing 34. A pair of guided portions 65 is constituted by the bottom portion of the support housing 61 and the annular flange.
[0027]
On the other hand, the speed reduction housing 39B is formed integrally with the rack housing 19, and has a pair of holding portions 66 and 67 having groove-shaped cross sections for holding the connection housing 39B and the support housing 61, respectively. Guide portions 68 and 69 for guiding the guided portions 64 and 65 are constituted by a pair of opposing wall portions of the holding portions 66 and 67, respectively. A guided mechanism G is constituted by the guided portions 64 and 65 and guide portions 68 and 69 for guiding the guided portions 64 and 65, and the guide mechanism G and the pair of drive screws 51a and 51b constitute a center-to-center distance adjusting mechanism A as a tension adjusting mechanism. It is configured.
[0028]
The pair of drive screws 51a and 51b are respectively screwed into screw holes 70 formed in the holding portions 66 and 67, and their tips are abutted against the large diameter portion 63 of the connection housing 37B and the outer peripheral surface of the support housing 61. .
According to the present embodiment, the input shaft 27 and the input pulley 28 can be accurately translated with respect to the shaft center 29 a of the output pulley 29 by the pair of drive screws 51 a and 51 b on both sides of the belt 30. . In the present embodiment, the center distance D may be adjusted by pulling the connecting housing 37B and the support housing 61 upward in FIG. 6 by the pair of drive screws 51a and 51b.
[0029]
7 and 8 show another embodiment of the present invention. With reference to FIGS. 7 and 8, the features of the present embodiment are as follows. That is, the circular hole 71 is provided in the fixed housing 39 </ b> C as a speed reduction housing formed integrally with the rack housing 19. A movable housing 72 that extends integrally from the motor housing 20 of the electric motor 15 has a circular outer diameter portion 73 that is rotatably fitted in the circular hole 71. The movable housing 71 has an eccentric hole 74 for rotatably supporting the first and second end portions 31 and 32 of the input shaft 27 via bearings 33 and 34. The center 74a of the eccentric hole 74 is eccentric from the axis 71a of the movable housing 71 (that is, the axis of the outer diameter portion 73).
[0030]
A center distance changing mechanism A as a tension adjusting mechanism is configured including the circular hole 71, the movable housing 72 and the eccentric hole 74. Further, a screw hole 77 is provided in one of the flange portions 75 and 76 of the fixed housing 39C and the movable housing 72 that are abutted with each other, and an arc-shaped screw insertion hole 78 is provided in the other, and the arc-shaped screw insertion hole 78 is provided. A fixing screw 79 is inserted into the screw hole 77, and the flange portions 75 and 76 of both housings 39C and 72 are fastened so that the rotational position can be adjusted.
[0031]
According to the present embodiment, by simply rotating the movable housing 72 together with the motor housing 20 of the electric motor 15, the shaft center 28 a of the input pulley 28 is moved away from the shaft center 29 a of the output pulley 29, and the center distance D is set. The tension of the belt 30 can be adjusted. Note that the movable housing 72 and the motor housing 20 may be configured separately.
FIG. 9 shows still another embodiment of the present invention. Referring to FIG. 9, the present embodiment is different from the embodiment of FIG. 6 in that a pair of elastic members 80 and 81 made of, for example, compression coil springs are used instead of the pair of drive screws 51a and 51b. These elastic members 80 and 81 elastically urge the connection housing 37B and the support housing 61 that support the first and second end portions 31 and 32 of the input shaft 27 along the longitudinal direction Y, The tension of 30 can be automatically adjusted to an appropriate value over a long period of time.
[0032]
The present invention is not limited to the above-described embodiments. For example, in each embodiment, the input and output pulleys 28 and 29 are formed of a synthetic resin such as polyacetal resin, so that the belt 30 The impact (vibration force) due to the meshing of the two may be reduced to further reduce the noise, and various other modifications can be made within the scope of the claims of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a main part of the electric power steering device.
3 is a cross-sectional view taken along line III-III in FIG.
FIG. 4 is a cross-sectional view of a main part of an electric power steering apparatus according to another embodiment of the present invention.
FIG. 5 is a cross-sectional view of a main part of an electric power steering apparatus according to still another embodiment of the present invention.
FIG. 6 is a cross-sectional view of a main part of an electric power steering apparatus according to still another embodiment of the present invention.
FIG. 7 is a cross-sectional view of a main part of an electric power steering apparatus according to still another embodiment of the present invention.
8 is a cross-sectional view taken along line VIII-VIII in FIG.
FIG. 9 is a cross-sectional view of yet another embodiment of the present invention.
[Explanation of symbols]
1 Electric power steering system (EPS)
2 Steering wheel (steering member)
6 Rack shaft (steering shaft)
6a Ball screw groove 15 Electric motor 16 Rotating shaft 17 Reduction mechanism 18 Conversion mechanism 19 Rack housing (second housing)
20 Motor housing 21 First housing 22, 23 Mounting flange 24 Spacer 25 Screw 27 Input shaft 28 Input pulley 29 Output pulley 28a, 29a Axle 30 Belt 37, 37A, 37B Connection housing 39, 39A, 39B Reduction housing 39C Fixed housing (Deceleration housing)
44 Ball nut 45 Ball 51 Drive screw 52, 56 Guide part 57, 58 Guide part 64, 65 Guide part 68, 69 Guide part 71 Circular hole 72 Movable housing 73 Outer diameter part 74 Eccentric hole 80, 81 Elastic member A Center Distance change mechanism D Center-to-center distance G Guide mechanism X Lateral direction (guided direction)
Y Longitudinal direction (guided direction)

Claims (8)

An electric motor that generates a steering assist force, a reduction mechanism that decelerates the rotation of the electric motor, and a conversion mechanism that converts the output rotation of the reduction mechanism into an axial movement of the steering shaft extending in the left-right direction of the vehicle,
The speed reduction mechanism adjusts the tension of the belt, an input pulley attached on the same axis as the rotating shaft of the electric motor, an output pulley arranged to surround the steering shaft, a belt connecting between the input and output pulleys, and the belt tension. look including a tension adjusting mechanism,
A first housing that houses the input pulley;
A second housing that houses the output pulley, the conversion mechanism, and the steering shaft;
The first and second housings are entirely cylindrical,
The first and second housings have mounting flanges so as to form a substantially Ω-shape when viewed from the end surface side.
The mounting flanges of the first and second housings are fastened together;
An electric power steering apparatus, wherein the belt is accommodated across the first and second housings .   2. The electric power steering apparatus according to claim 1, wherein the tension adjusting mechanism is a center-to-center distance changing mechanism that changes a center-to-center distance between the input pulley and the output pulley.   3. The electric power steering apparatus according to claim 2, wherein the center-to-center distance changing mechanism includes a spacer interposed between the first housing that holds the input pulley and the second housing that holds the steering shaft. .   3. The center distance changing mechanism according to claim 2, wherein the center distance changing mechanism guides the first housing holding the input pulley and the second housing holding the steering shaft to relatively move in a direction in which the center distance can be changed. An electric power steering apparatus including a guiding mechanism for performing the above operation.   5. The electric power steering apparatus according to claim 4, wherein the center distance changing mechanism further includes a screw capable of relatively driving the first and second housings in a direction guided by the guide mechanism.   5. The electric power steering apparatus according to claim 4, wherein the center-to-center distance changing mechanism further includes an elastic member that relatively biases the first and second housings in a direction guided by the guide mechanism.   3. The center distance changing mechanism according to claim 2, wherein the center-to-center distance changing mechanism includes a circular hole formed in the fixed housing, a movable housing having a circular outer diameter portion supported by the circular hole so that the rotational position can be adjusted, and the movable housing. An electric power steering device comprising a circular eccentric hole having a center at a position deviated from the center of the circular outer diameter portion and rotatably supporting the input pulley.   8. The electric power steering apparatus according to claim 7, wherein the movable housing is integrally extended from the motor housing of the electric motor.

Images