JP4491716B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by an electric motor.

A reduction gear is used in an electric power steering system (EPS) for automobiles. For example, in the column type EPS, the rotation of the output shaft of the electric motor is decelerated through the worm shaft and the worm wheel, so that the output of the electric motor is amplified and transmitted to the steering mechanism, and the steering operation is torque-assisted. Yes.
A moderate backlash is necessary for the meshing of the worm shaft and the worm wheel, but for example, when driving on a rough road, a rattling sound due to the backlash is generated due to reverse input from the road surface. There is.

  In order to prevent the occurrence of rattling noise, it is necessary to strictly adjust the amount of backlash generated between the worm shaft and the worm wheel within the range of machining accuracy of each component. Conventionally, when assembling the worm shaft and the worm wheel, each part is selected according to the degree of variation in dimensional accuracy, and the components having the appropriate combination accuracy are combined (so-called matching assembly). The work was very laborious and the manufacturing cost was high.

Even if the backlash is initially set to an appropriate range by matching assembly, the backlash may increase due to wear of the tooth portion due to a change over time, and noise may be generated.
Therefore, one end of the worm shaft is supported so as to be able to advance and retreat to the radial worm wheel side, and one end of the worm shaft is urged to the radial worm wheel side by the biasing means, so that the worm shaft and the rotation center of the worm wheel are It has been proposed to automatically adjust the distance (so-called center distance) to eliminate backlash (for example, Patent Document 1 and Patent Document 2).

On the other hand, there is provided an electric power steering device that supports the worm shaft so that the worm wheel can be deflected in the axial direction and biases the worm shaft in the axial direction of the worm wheel (for example, Patent Document 3).
JP 2002-37094 A JP 2002-67992 A JP 2001-108025 A

From the specifications of the teeth of the worm shaft and worm wheel, the direction of the driving reaction force that the worm shaft receives from the worm wheel when the drive is actually transmitted by the worm shaft and worm wheel is determined by the application of the biasing means. It is different from the trend direction. Therefore, an appropriate preload cannot be applied to the meshing portion of the worm shaft and the worm wheel.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering apparatus that can apply an appropriate preload to the meshing portion and suppress the generation of noise.

In order to solve the above problems, the present invention includes a transmission device for transmitting the power of an electric motor for assisting steering to a steering mechanism, and first and second urging members. A worm shaft connected to the output shaft of the motor and a worm wheel meshing with the worm shaft and connected to the steering mechanism, and the direction of the radial component of the driving reaction force received by the worm shaft from the worm wheel is the rotational direction of the worm shaft The first and second urging members are different in accordance with each of the first and second urging members, and a pair of main portions that form an end ring that surrounds the bearing that supports the worm shaft and a pair of end portions that extend from the pair of end portions of the main portion. And a single radial biasing portion extending from one of the pair of rotation regulating portions and disposed at a position corresponding to the direction of the radial component of the different driving reaction force. Including each The radial urging portions of the first and second urging members respectively attach worm shafts to the first and second urging directions that are opposite to the radial component directions of the different driving reaction forces. The respective rotation restricting portions of the first and second urging members restrict the rotation of the first and second urging members by engaging with the inner walls of the corresponding receiving recesses of the housing. The angles formed by the urging directions of the first and second urging members and the radial direction of the worm shaft toward the worm wheel are different from each other.

According to the present invention, when the worm shaft rotates to transmit the driving force to the worm wheel, the worm shaft rotates in the direction opposite to the direction in which the worm shaft actually receives the driving reaction force from the worm wheel. Since the bias is applied, an appropriate preload can be applied to the meshing portion of the worm shaft and the worm wheel, which can contribute to noise suppression.
The direction of the driving reaction force radial component of the upper Symbol worm shaft receives from the worm wheel, the phase depends on the direction of rotation of the worm shaft, said first and second biasing member, the phase different driving reaction Each includes a single radial biasing portion that biases the worm shaft in the opposite direction to the direction of the radial component of the force, so that the meshing portion of the worm shaft and worm wheel is engaged regardless of the rotational direction of the worm shaft. Appropriate preload can be applied.

Further, the respectively biasing direction of the first and second biasing members, the angle is different phases Rukoto the radial of the worm shaft toward the worm wheel side, the actual radial component of the driving reaction force Energizing in the direction corresponding to is substantially possible.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an electric power steering apparatus including a power transmission joint according to an embodiment of the present invention.
Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, As a steered shaft extending in the left-right direction of an automobile, having a pinion shaft 7 connected to the shaft 5 via a universal joint 6 and rack teeth 8a meshing with pinion teeth 7a provided in the vicinity of the end of the pinion shaft 7 Rack bar 8. The pinion shaft 7 and the rack bar 8 constitute a steering mechanism A including a rack and pinion mechanism.

The rack bar 8 is supported in a housing 9 fixed to the vehicle body so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding steering wheel 11 via a corresponding knuckle arm (not shown).
When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion teeth 7a and the rack teeth 8a. Thereby, steering of the steered wheel 11 is achieved.

The steering shaft 3 is divided into an input-side upper shaft 3 a that is continuous with the steering member 2 and an output-side lower shaft 3 b that is continuous with the pinion shaft 7. These upper and lower shafts 3 a and 3 b are connected via a torsion bar 12. Are connected to each other so as to be relatively rotatable on the same axis.
A torque sensor 13 is provided for detecting a steering torque based on the relative rotational displacement between the upper and lower shafts 3a and 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is obtained from an ECU (Electric Control Unit: electronic Control unit) 14. The ECU 14 drives and controls the steering assisting electric motor 16 via the drive circuit 15 based on a torque detection result or a vehicle speed detection result given from a vehicle speed sensor (not shown). The output rotation of the electric motor 16 is decelerated via the speed reducer 17 and transmitted to the pinion shaft 7 and converted into a linear motion of the rack bar 8 to assist steering.

The speed reducer 17 includes a worm shaft 18 that is rotationally driven by the electric motor 16 and a worm wheel 19 that meshes with the worm shaft 18 and is coupled to the lower shaft 3b of the steering shaft 3 so as to be integrally rotatable.
Referring to FIG. 2, worm shaft 18 is arranged coaxially with output shaft 20 of electric motor 16. The worm shaft 18 has first and second end portions 18a and 18b that are separated from each other in the axial length direction, and has a tooth portion 18c at an intermediate portion between the first and second end portions 18a and 18b.

  The worm wheel 19 is coupled to an intermediate portion in the axial direction of the lower shaft 3b of the steering shaft 3 so as to be integrally rotatable and immovable in the axial direction. The worm wheel 19 includes an annular cored bar 19a coupled to the lower shaft 3b so as to be integrally rotatable, and a synthetic resin member 19b surrounding the cored bar 19a and having teeth 19c formed on the outer periphery. The core metal 19a is inserted into the mold when the synthetic resin member 19b is molded with resin, for example.

The first end portion 18 a of the worm shaft 18 and the opposite end portion of the output shaft 20 of the electric motor 16 are connected to each other via a power transmission joint 21 so as to be able to transmit power.
The first and second end portions 18a and 18b of the worm shaft 18 are rotatably supported by the housing 17a of the speed reducer 17 via corresponding first and second bearings 22 and 23, respectively. The first and second bearings 22 and 23 are ball bearings, for example.

  Inner rings 24, 25 of the first and second bearings 22, 23 are fitted to the first and second end portions 18a, 18b of the worm shaft 18 so as to be integrally rotatable. The inner rings 24 and 25 are in contact with corresponding positioning step portions 18d and 18e of the worm shaft 18 which are opposite to each other. The outer rings 26 and 27 of the first and second bearings 22 and 23 are held in corresponding bearing holding holes 28 and 29 of the housing 17a of the speed reducer 17.

  The bearing holding hole 29 for the second bearing 23 is formed as a bias hole that can hold the second bearing 23 in a first radial direction R1 and a second radial direction R2 of the worm shaft 18 so as to be biasable. Has been. Between the inner peripheral surface of the bearing holding hole 29 and the outer peripheral surface of the outer ring 27 of the second bearing 23, an annular first biasing member 30 and a second biasing member 40 are interposed. The first urging member 30 urges the second bearing 23 in the first radial direction R1, and the second urging member 40 urges the second bearing 23 in the second radial direction R2.

Specifically, the first urging member 30 moves in the direction of the radial component F1 of the driving reaction force that the worm shaft 18 receives from the worm wheel 19 when the worm shaft 18 rotates in the first rotation direction C1. The second bearing 23 is urged in a first radial direction R1 (biasing direction) that is disposed at a corresponding position and is opposite to the direction of the radial component F1.
On the other hand, the second biasing member 40 corresponds to the direction of the radial component F2 of the driving reaction force that the worm shaft 18 receives from the worm wheel 19 when the worm shaft 18 rotates in the second rotation direction C2. The second bearing 23 is urged in a second radial direction R2 (biasing direction) which is the direction opposite to the direction of the radial component F2.

The angle P1 formed between the third radial direction R3 of the worm shaft 18 toward the center of the worm wheel 19 and the first radial direction R1 that is the biasing direction of the first biasing member 30 is, for example, 40 to 45 °. Set to range. Further, an angle P2 formed by the third radial direction R3 and the second radial direction R2, which is the biasing direction of the second biasing member 40, is set in a range of 75 to 80 °, for example.
The first and second urging members 30 and 40 are thin plate members formed of, for example, sheet metal. Referring to FIGS. 3 and 4 which are sectional views taken along line III-III in FIG. 2, the first urging member 30 includes a main body portion 31 having an end ring shape, and first and second main body portions 31. The first and second rotation restricting portions 32a and 32b respectively formed on the end portions 31a and 31b of the first and second radial restricting portions 33 including a cantilevered elastic tongue piece extending only from the first rotation restricting portion 32a. And an axially urging portion 34 formed of a plurality of inclined elastic tongue pieces formed on the side edge of the main body portion 61.

  The second urging member 40 is configured by eliminating the configuration of the axial urging portion 34 from the first urging member 30. Further, the second urging member 40 is used by being turned over so that the extending direction of the radial urging portion 33 is opposite to the first urging member 30. Since the second urging member 40 is the same as the first urging member 30 in other configurations, the same reference numerals are given to the drawings, and the description thereof is omitted.

Referring to FIG. 3, the radial urging portion 33 of the first urging member 30 is received by a first receiving recess 29 a formed in a part of the inner peripheral surface of the bearing holding hole 29, and The biasing force of the radial biasing portion 33 of the biasing member 30 biases the second end portion 18b of the worm shaft 18 through the second bearing 23 in the first radial direction R1 of the worm shaft 18. is doing.
The radial urging portion 33 of the second urging member 40 is received by a second receiving recess 29 b formed on a part of the inner peripheral surface of the bearing holding hole 29, and the second urging member 40. The urging force of the radial urging portion 33 urges the second end portion 18 b of the worm shaft 18 in the second radial direction R 2 of the worm shaft 18 via the second bearing 23. Thereby, the backlash between the worm shaft 18 and the worm wheel 19 is removed.

  The first receiving recess 29a has a pair of inner walls 29c and 29d that are opposed to each other in the circumferential direction of the bearing holding hole 29, and the rotation restricting portions 32a and 32b of the first urging member 30 correspond to the corresponding inner walls. By abutting on 29c and 29d, the rotation of the first urging member 30 in the circumferential direction of the bearing holding hole 29 is restricted. The same applies to the relationship between the pair of inner walls 29c, 29d provided in the second receiving recess 29b and the rotation restricting portions 32a, 32b of the second urging member 40.

Referring to FIG. 2, the axial urging portion 34 of the first urging member 30 is interposed between the end wall 17b of the housing 17a and the end surface of the outer ring 27 of the second bearing 23 opposed thereto. The worm shaft 18 is elastically biased toward the axial electric motor 16 through the second bearing 23 in a state received by the end wall 17b.
On the other hand, the outer ring 26 of the first bearing 22 is pressed against the positioning step 17c of the housing 17a by the preload adjusting and backlash adjusting screw members 36 screwed into the screw holes 35 connected to the corresponding bearing holding holes 28. And is positioned in the axial direction. Thereby, the urging force of the axial urging portion 34 contributes to applying preload to the first and second bearings 22 and 23 all together, and the backlash between the worm shaft 18 and the worm wheel 19 is eliminated. Will also contribute.

  Next, the power transmission joint 21 will be described in detail with reference to FIG. 5, which is a cross-sectional view taken along the line VV in FIG. 2, and FIG. 6, which is an exploded perspective view. First, referring to FIG. 2, the power transmission joint 21 includes a first engagement member 41 coupled to the output shaft 20 of the electric motor 16 so as to be integrally rotatable, and a worm shaft 18 as an input shaft of the speed reducer 17. Between the first and second engagement members 41 and 42, and a second engagement member 42 connected to the first end 18a of the first end portion 18a so as to be integrally rotatable. And an elastic member 43 that transmits torque. The first and second engaging members 41 and 42 are made of, for example, metal. The elastic member 43 is made of, for example, synthetic rubber or synthetic resin such as polyurethane.

Next, referring to FIGS. 5 and 6, the elastic member 43 includes an annular main body 44 and a plurality of engagement arms 45 extending in the radial direction from the main body 44. The plurality of engaging arms 45 are arranged at equal intervals in the circumferential direction X of the main body 44. Each engagement arm 45 has a pair of power transmission surfaces 46 facing each other in the circumferential direction X.
Referring to FIG. 6, the first and second engaging members 41, 42 are annular main portions 51, which form fitting holes 49, 50 for fitting the output shaft 20 and the worm shaft 18, respectively. 52 and a plurality of first and second engaging protrusions 55 and 56 formed to project from the opposing surfaces 53 and 54 of the main body portions 51 and 52, respectively.

The first and second engagement protrusions 55 and 56 of the first and second engagement members 41 and 42 are arranged at equal intervals in the circumferential direction of the corresponding main body portions 51 and 52, respectively.
In the assembled state of the power transmission joint 21, as shown in FIG. 5, the first and second engagement protrusions 55 and 56 of the first and second engagement members 41 and 42 are alternately arranged in the circumferential direction, The corresponding engagement protrusion 45 of the elastic member 43 is sandwiched between the first and second engagement protrusions 55 and 56 adjacent to each other in the circumferential direction. In other words, the first and second engaging protrusions 55 and 56 adjacent in the circumferential direction are engaged with each other with the corresponding engaging arm 45 of the elastic member 43 sandwiched in the circumferential direction.

As shown in FIGS. 5 and 6, the first and second engagement protrusions 55 and 56 include power transmission surfaces 57 and 58 of the corresponding engagement arm 45 of the elastic member 43, respectively.
According to the present embodiment, when the worm shaft 18 rotates and transmits the driving force to the worm wheel 19, the worm shaft 18 is opposite to the direction in which the driving reaction force from the worm wheel 19 is actually received. Since the worm shaft 18 is urged in the first radial direction R1 or the second radial direction R2, which is the direction of the above, an appropriate preload can be applied to the meshing portion of the worm shaft 18 and the worm wheel 19, and noise can be reduced. It can contribute to suppression.

  Further, the direction in which the worm shaft 18 actually receives the driving reaction force from the worm wheel differs depending on the rotation direction of the worm shaft 18, but in this embodiment, the worm shaft 18 and the worm wheel of the speed reducer 17. The first and second urging members 30 and 40 are arranged at positions that take into consideration the specifications of the 19 teeth and the rotational direction of the worm shaft 18. Therefore, an appropriate preload can be applied to the meshing portion of the worm shaft 18 and the worm wheel 19 regardless of the rotational direction of the worm shaft 18.

In order to adjust the backlash, when the second bearing 23 of the worm shaft 18 is supported so as to be deflectable in a predetermined deflection direction Y, a second direction in a direction crossing the deflection direction Y (for example, a direction orthogonal to the deflection direction Y) is used. It is preferable that the movement of the bearing 23 is restricted.
Therefore, as shown in FIG. 7, a bearing holding hole 291 made of a long hole can be used. The inner peripheral surface of the bearing holding hole 291 has a pair of semi-cylindrical surface portions 61 and 62 facing the deflection direction Y, and a pair of flat portions 63 that connect between the opposed end portions of the pair of semi-cylindrical surface portions 61 and 62, respectively. 64. The pair of semi-cylindrical surface portions 61 and 62 have their center positions 61a and 62a offset by a predetermined offset amount e1 in the biasing direction Y. The pair of flat portions 63 and 64 are parallel to the deflection direction Y.

  Further, instead of the pair of flat portions 63 and 64, as shown in FIG. 8, a pair of circular arcs having a center 65a at the center position between the center positions 61a and 62a of the pair of semi-cylindrical surface portions 61 and 62, respectively. It is good also as the bearing holding hole 292 using the parts 65 and 65. FIG. In this case, it becomes the center of so-called three points, and it becomes easy to process. Further, since the offset amount e1 is sufficiently small, the stepped portion formed at the connecting portion between each cross-section arcuate portion 65 and the pair of semi-cylindrical surface portions 61 and 62 is negligible (for example, 0.7 μm, 1 μm or less). .

  7 and FIG. 8, with respect to the biasing direction Y, the inner diameters of the bearing holding holes 291 and 292 are the outer diameter of the second bearing 23 and the plate thicknesses of the first and second urging members 30 and 40, respectively. , And a value obtained by adding a desired movable amount. Further, with respect to the direction Z perpendicular to the deflection direction Y, the outer diameter of the second bearing 23, the plate thickness of the first and second urging members 30, 40, and the assembly of the urging members 30, 40 are necessary. It is a value obtained by adding the minimum clearance.

  On the other hand, as shown in FIG. 9, recesses 66 and 67 are provided on the inner peripheral surface of the bearing holding hole 293 corresponding to the direction Z perpendicular to the biasing direction Y, and the bottoms of the recesses 66 and 67 are biased. A pair of engaging protrusions 68 and 69 that engage with the bottoms of the recesses 66 and 67 may be provided on the main body portion 31 of the biasing member 300, as a pair of guide portions parallel to the direction Y. good. In this case, as shown in FIG. 10, the engagement protrusions 68 and 69 may be formed by bulging with a sheet metal integral with the main body 31.

  In the embodiment shown in FIGS. 7, 8 and 9, by suppressing unnecessary movement (movement in directions other than the biasing direction Y) of the second end 18b of the worm shaft 18 and the second bearing 23. The durability of the urging member can be improved, and the occurrence of a hitting sound between the urging member and the housing 17a can be suppressed. Further, it is possible to suppress the increase in rotational torque and the occurrence of meshing sliding noise during rotation due to the above-described unnecessary movement.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing of the principal part of an electric power steering device. It is sectional drawing which follows the III-III line of FIG. It is a perspective view of the 1st and 2nd biasing member for urging | biasing the edge part of a worm shaft. It is sectional drawing which follows the VV line of FIG. It is a disassembled perspective view of a power transmission coupling. It is a schematic diagram which shows an example of a bearing holding hole. It is a schematic diagram which shows another example of a bearing holding hole. It is typical sectional drawing of the principal part of the electric power steering apparatus which shows the example of a change of a bearing holding hole and a biasing member. It is a perspective view of the principal part of the urging | biasing member of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering member 3 Steering shaft 5 Intermediate shaft 7 Pinion shaft 8 Rack bar 10 Tie rod 11 Steering wheel A Steering mechanism 16 Electric motor 17 Reduction gear 17a Housing 18 Worm shaft 19 Worm wheel 20 Output shaft 21 of electric motor Power transmission joint 29 Bearing holding holes 29a, 29b Receiving recess 30 First biasing member 31 Main portions 32a, 32b Rotation restricting portion 33 Radial biasing portion 34 Axial biasing portion 40 Second biasing member C1 First Rotational direction C2 Second rotational direction F1, F2 Radial direction component R1 of driving reaction force First radial direction (direction opposite to the radial direction component of driving reaction force, biasing direction)
R2 Second radial direction (the direction opposite to the direction of the radial component of the driving reaction force, biasing direction)
R3 Third radial direction (radial direction of the worm shaft toward the center of the worm wheel)
X circumferential direction Y biasing direction 291, 292, 293 bearing holding hole 300 biasing member

Claims (1)

A transmission device for transmitting the power of the steering assisting electric motor to the steering mechanism, and first and second urging members ;
The transmission device includes a worm shaft connected to the output shaft of the electric motor, and a worm wheel meshing with the worm shaft and connected to the steering mechanism.
The direction of the radial component of the driving reaction force that the worm shaft receives from the worm wheel differs depending on the rotational direction of the worm shaft,
The first and second urging members include a main part that forms an end ring surrounding a bearing that supports the worm shaft, a pair of rotation restricting parts that are respectively extended at a pair of end parts of the main part, Each including a single radial biasing portion extending from one of the pair of rotation restricting portions and arranged at a position corresponding to the direction of the radial component of the different driving reaction force,
The radial urging portions of the first and second urging members respectively attach worm shafts in first and second urging directions that are opposite directions of the radial components of the different driving reaction forces. Vigorously,
The respective rotation restricting portions of the first and second urging members restrict the rotation of the first and second urging members by engaging with the inner walls of the corresponding receiving recesses of the housing,
An electric power steering device characterized in that an angle formed by each of the urging directions of the first and second urging members and a radial direction of the worm shaft toward the worm wheel are different from each other .

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