JP2005297647A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device having little change of resistance torque and noise. <P>SOLUTION: A link member 38 of a restriction mechanism 37 is equipped with a first slide contact part 41 slidably contacting to a peripheral surface 18d of a worm shaft 18, a second slide contact part 42 sliably contacting to a side surface 19c of a worm wheel 19, and a driven part 43. An annular switching part 40 of the side surface 19c of the worm wheel 19 displaces the link member 38 to a slide contact position slidably contacting to the worm shaft or the like to a separation position separating from the slide contact position slidably contacting to the worm shaft 18 or the like in collaboration with an energizing member 39. The worm shaft 18 and the worm wheel 19 are mutually linked through the link member 38 energized by the energized member 39. Fine vibration of the worm shaft 18 and the worm wheel 19 is mutually suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

A reduction gear is used in an electric power steering device for an automobile. For example, in the column type EPS, the rotation of the output shaft of the motor is decelerated via the worm shaft and the worm wheel, so that the output of the motor is amplified and transmitted to the steering mechanism to assist the steering operation with torque.
Moderate backlash is required for meshing of the worm shaft and worm wheel included in the reducer. For example, when driving on rough roads, rattling noise caused by backlash occurs due to reverse input from the road surface. There are things to do.

  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 with 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.
Further, when the worm wheel contains a synthetic resin, the backlash is clogged due to temperature expansion or swelling during use, and the resistance torque of the speed reducer may increase.

Therefore, it has been proposed to provide an elastic body at a position facing the rotation area of the worm on the outer peripheral side of the worm wheel (for example, Patent Document 1).
Further, it has been proposed that the worm and the worm wheel are always urged by a torsion coil spring relatively in one rotational direction in a no-load state (for example, Patent Document 2).

In this case, there is an advantage that troublesome assembly work such as matching assembly can be eliminated.
JP 2002-37100 A JP-A-9-164964

However, in Patent Document 1, the urging force of the elastic body always reaches the worm and the worm wheel.
Further, in Patent Document 2, there is a difference in noise prevention effect depending on whether the rotation direction of the worm shaft is the same or opposite to the biasing direction of the torsion coil spring.
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 device with little resistance torque change and noise.

  In order to solve the above-described problems, the present invention provides a drive gear coupled to an output shaft of an electric motor and a driven gear meshing with the drive gear in an electric power steering apparatus that assists steering by driving an electric motor according to an operation of a steering member. A reduction gear that includes a gear and decelerates the output rotation of the electric motor and transmits it to the steering mechanism, and a restriction mechanism that can restrict the relative displacement of the drive gear and the driven gear within a predetermined range including the steering angle midpoint. It is characterized by this.

  According to the present invention, the backlash between the drive gear and the driven gear can be reduced as much as possible during straight traveling, and the occurrence of rattling noise due to the backlash can be suppressed. Since the backlash is restricted only when necessary, the upper limit of the backlash between the gears can be increased. As a result, the conventional matching assembly can be abolished. Further, it is difficult to be affected by thermal expansion and swelling, and resistance torque and noise can be reduced.

  Further, in the present invention, the drive gear includes a worm shaft, the driven gear includes a worm wheel, and the restriction mechanism is separated from a sliding contact position in sliding contact with a side surface of the worm wheel and a peripheral surface of the worm shaft. A link member that is displaceable between the separation position and links the worm wheel and the worm shaft at the sliding contact position; an urging member that biases the link member toward the sliding contact position; There may be provided a switching portion provided in a ring shape on the side surface for switching the link member to the sliding contact position and the separation position.

In this case, the link member at the sliding contact position biased by the biasing member is in sliding contact with the worm wheel and the worm shaft, so that the worm wheel and the worm shaft are linked via the link member. Generation of noise can be reduced by mutually suppressing vibration.
Further, in the present invention, the switching portion includes a first portion for driving the link member to the separated position against the biasing member, and displacement of the link member to the sliding contact position by the biasing member. In some cases, the second portion is provided in a region corresponding to a predetermined range including the steering angle midpoint. In this case, the link member can be easily switched to the separation position or the sliding contact position by the first and second portions according to the rotational position of the worm shaft. As the first and second portions, a relatively projecting protrusion and a relatively recessed recess can be used, respectively.

  In the present invention, at least the first portion of the switching portion may include rubber or foamed resin attached to the side surface of the worm wheel. In this case, when switching from straight running to steering, the foaming resin or the like gradually elastically deforms, so that a damping effect can be obtained.

Preferred embodiments of the present invention will be described with reference to the accompanying 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 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 rack and pinion mechanism A as a steering 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 shaft 3a connected to the steering member 2 and an output shaft 3b connected to the pinion shaft 7. These input and output shafts 3a and 3b are on the same axis line via a torsion bar 12. They are connected to each other so as to be relatively rotatable.
A torque sensor 13 is provided for detecting a steering torque based on a relative rotational displacement amount between the input and output shafts 3a and 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is 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 output shaft 3b of the steering shaft 3, and further converted into a linear motion of the rack bar 8 via the pinion shaft 7, thereby assisting steering. .

The speed reducer 17 is a worm shaft 18 as a drive gear that is rotationally driven by the electric motor 16, and a worm wheel as a driven gear that meshes with the worm shaft 18 and is connected to the output shaft 3 b of the steering shaft 3 so as to be integrally rotatable. 19 is provided.
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 connected to an intermediate portion in the axial direction of the output 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 output 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.

A region including the tooth meshing portion B of the worm shaft 18 and the worm wheel 19 is filled with a lubricant such as grease. The first end 18a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are connected to each other coaxially via a cylindrical joint 21 so that power can be transmitted.
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. Each of the inner rings 24 and 25 is in contact with a corresponding positioning step portion of the worm shaft 18 opposite to each other. The outer ring 26 of the first bearing 22 is held in the bearing holding hole 27 of the housing 17a of the speed reducer 17 so as not to rotate. The outer ring 28 of the second bearing 23 is held in the bearing holding hole 29 of the housing 17a of the speed reducer 17 so as not to rotate.

  Further, the screw member 30 for adjusting the preload is screwed into the screw hole 31 formed continuously to the bearing holding hole 27, so that the preload is collectively applied to the first and second bearings 22, 23, and The outer ring 28 of the second bearing 23 contacts the annular positioning portion 32 of the end wall 17b of the housing 17a, whereby the worm shaft 18 is positioned in the axial direction. The screw member 30 after adjustment is fixed by the lock member 33.

One end portion 18 a of the worm shaft 18 and the output shaft 20 of the electric motor 16 are respectively fitted from the corresponding end portions of the joint 21 and coupled to the joint 21. One end 18a of the worm shaft 18 is coupled to the joint 21 by, for example, spline fitting, and the output shaft 20 of the electric motor 16 is coupled to the joint 21 by, for example, press fitting.
Next, referring to FIG. 3, the output shaft 3 b of the steering shaft 3 is rotatably supported by third and fourth bearings 34 and 35 disposed on both sides of the worm wheel 19. The third bearing 35 is held by a sensor housing 36 combined with the housing 17 a of the speed reducer 17, and the fourth bearing 35 is held by the housing 17 a of the speed reducer 17.

In the housing 17a of the speed reducer 17, a regulating mechanism 37 capable of regulating the relative displacement of the worm shaft 18 and the worm wheel 19 within a prescribed range including the steering angle midpoint with a prescribed regulating force is accommodated.
The restriction mechanism 37 includes a link member 38, an urging member 39 made of, for example, a compression coil spring, and a switching portion 40 provided on the side surface of the worm wheel 19.

  4 and 5, the link member 38 has, for example, a substantially rectangular parallelepiped shape, and is disposed along the radial direction of the worm wheel 19. The link member 38 includes a first surface 38a facing the peripheral surface 18d of the intermediate portion 18c of the worm shaft 18 and a side surface 19c of the synthetic resin member 19b of the worm wheel 19, and a second surface facing the first surface 38a. 38b. The first surface 38 a of the link member 38 is slidably contacted with a first sliding contact portion 41 slidably contacted with the peripheral surface of the intermediate portion 18 c of the worm shaft 18 and a side surface 19 c of the synthetic resin member 19 b of the worm wheel 19. A possible second slidable contact portion 42 and a driven portion 43 facing the switching portion 40 are provided.

  The link member 38 is guided so as to be movable along a direction X parallel to the output shaft 3b via a guide mechanism (not shown). That is, the link member 38 is guided so that it can be displaced along the direction X between the sliding contact position shown in FIG. 6 and the separation position shown in FIG. As shown in FIG. 4, the first and second sliding contact portions 41 and 42 of the link member 38 in the separated position are respectively the peripheral surface 18 d of the intermediate portion 18 c of the corresponding worm shaft 18 and the synthetic resin member of the worm wheel 19. It is separated from the side surface 19c of 19b. As shown in FIG. 6, the first and second slidable contact portions 41 and 42 of the link member 38 at the slidable contact position are respectively the peripheral surface 18d of the intermediate portion 18c of the corresponding worm shaft 18 and the synthetic resin of the worm wheel 19. It contacts the side surface 19c of the member 19b. Thereby, the link member 38 links the worm shaft 18 and the worm wheel 19 to each other, and suppresses the slight vibrations of the worm shaft 18 and the worm wheel 19.

4 and 6, the biasing member 39 is interposed between the second surface 38b of the link member 38 and the surface 17c of the housing 17a facing the second surface 38b. 39 biases the link member 38 to the sliding contact position along the direction X.
Referring to FIG. 7, the switching portion 40 is provided in an annular shape on the side surface 19 c of the synthetic resin member 19 b of the worm wheel 19, and the link member 38 is connected via the driven portion 43 in cooperation with the biasing member 39. It works to switch between the sliding contact position and the separation position. Specifically, the switching portion 40 includes a convex portion 44 as a first portion for driving the link member 38 to the separated position against the biasing member 39, and sliding of the link member 38 by the biasing member 39. It includes a recess 45 as a second part for allowing displacement to the contact position. The convex portion 44 and the concave portion 45 are integrally formed of a synthetic resin member 19b and a single member (for example, polyamide resin).

With reference to FIG. 7 and FIG. 8, an inclined portion 46 for connecting between the convex portion 44 and the concave portion 45 is provided. By the action of the inclined portion 46, the driven portion 43 of the link member 38 can smoothly transition from the concave portion 45 to the convex portion 44.
The concave portion 45 as the second portion is provided in a region Z corresponding to a predetermined range including the steering angle midpoint in the annular switching portion 40. The width Y of the link member 38 is set to be smaller than the circumferential length of the region Z. The concave portion 45 as the second portion may be flush with the main portion 19d of the side surface 19c of the synthetic resin member 19b of the worm wheel 19, but in this embodiment, the concave portion 45 is more than the main portion 19d of the side surface 19c. Is also prominent.

  According to the present embodiment, since the worm shaft 18 and the worm wheel 19 are linked to each other via the link member 38 during straight traveling, the backlash between the worm shaft 18 and the worm wheel 19 is minimized, and the worm Fine vibrations of the shaft 18 and the worm wheel 19 can be suppressed from each other. Thereby, generation | occurrence | production of the rattling sound resulting from a backlash can be suppressed.

  In addition, since the backlash is restricted only when necessary, the upper limit of the backlash of the worm shaft 18 and the worm wheel 19 can be set high. As a result, the conventional matching assembly can be abolished. Further, it is difficult to be affected by thermal expansion or swelling of the synthetic resin member 19b of the worm wheel 19, and resistance torque and noise can be reduced.

In addition, the position of the link member 38 can be easily switched between the sliding contact position and the separation position by a simple structure using the switching portion 40 provided on the side surface of the worm wheel 19.
As shown in FIG. 9, the convex portion 44A as the first portion of the switching portion 40A is flush with the main portion 19d of the side surface 19c of the worm wheel 19, and the concave portion 45A as the second portion is the main portion 19d. You may make it dent from.

  Further, as shown in FIG. 10, the switching portion 40 </ b> B may be formed of rubber or foamed resin and attached to the side surface 19 c of the worm wheel 19. In this case, when switching from straight running to steering, the foamed resin or the like is gradually elastically deformed so that a damping effect can be obtained. As a result, the link member 38 is lifted during gear rotation, and the drive There is an advantage that torque can be reduced and deterioration of steering wheel return can be suppressed. In addition, the convex part 44 as at least 1st part of the switching part 40B should just be formed with rubber | gum or foamed resin.

  Further, rubber or foam resin as a switching portion may be attached to the entire circumference of the side surface 19c of the worm wheel 19, and the protruding amount of the foam resin or the like from the side surface 19c of the worm wheel 19 may be uniform over the entire circumference. In this case, during straight running (non-steering), the link member 38 sinks into the foamed resin due to a static balance between the biasing force of the biasing member 39 and the elastic repulsion force of the foamed resin, etc. The shaft 18 and the worm wheel 19 are linked to each other. On the other hand, when the steering is started, the link member 38 is lifted against the urging member 39 by the action of the foamed resin or the like that moves relative to the link member 38, and the worm shaft 18 and the worm wheel 19 are mutually connected. The link is released.

  A bevel gear in which the drive gear and the driven gear mesh with each other may be used as the reduction gear. Further, the drive gear and the driven gear may be a helical gear or a hypoid gear.

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 schematic sectional drawing of a control mechanism, and the state which has the link member in a separation position is shown. It is a top view of a link member. It is a schematic sectional drawing of a control mechanism, and the state which has the link member in a sliding contact position is shown. It is a schematic side view of a worm wheel. It is sectional drawing of the principal part of a switching part. It is a side view of the worm wheel containing the switching part of another embodiment of this invention. It is sectional drawing of the principal part of the worm wheel of another embodiment of this invention.

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 Reducer 17a Housing 18 Worm shaft (drive gear)
18a First end portion 18b Second end portion 18c Intermediate portion 18d Peripheral surface 19 Worm wheel (driven gear)
19a Core 19b Synthetic resin member 19c Side surface 19d Main portion 37 Restriction mechanism 38 Link member 38a First surface 38b Second surface 39 Biasing member 40, 40A, 40B Switching portion 41 First sliding contact portion 42 Second Sliding portion 43 Driven portion 44, 44A Convex portion (first portion)
45, 45A Concave part (second part)
Z Area corresponding to a predetermined range including the steering angle midpoint

Claims (4)

In an electric power steering device that assists steering by driving an electric motor according to an operation of a steering member,
A reduction gear that includes a drive gear coupled to the output shaft of the electric motor and a driven gear that meshes with the drive gear, and that reduces the output rotation of the electric motor and transmits it to the steering mechanism;
An electric power steering apparatus comprising: a regulating mechanism capable of regulating relative displacement of the drive gear and the driven gear within a predetermined range including a steering angle midpoint. The drive gear includes a worm shaft, and the driven gear includes a worm wheel.
The regulating mechanism is freely displaceable between a sliding contact position that is in sliding contact with the side surface of the worm wheel and the peripheral surface of the worm shaft, and a separation position that is away from the sliding contact position. A link member to be
A biasing member that biases the link member to the sliding contact position;
An electric power steering apparatus comprising: a switching portion provided annularly on a side surface of the worm wheel for switching the link member to the sliding contact position and the separation position.   The switching unit according to claim 2, wherein the switching portion allows a first portion for driving the link member to the separation position against the biasing member, and allows the displacement of the link member to the sliding contact position by the biasing member. An electric power steering apparatus provided in a region corresponding to a predetermined range including a steering angle midpoint.   4. The electric power steering apparatus according to claim 2, wherein at least a first portion of the switching portion includes rubber or foamed resin attached to a side surface of the worm wheel.

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