JP2010143284A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive electric power steering device having low noise. <P>SOLUTION: When an idler gear 35 starts to rotate by being driven by rotation of a driven gear 34 just after a steering member is reversed during stationary steering, the idler gear 35 receiving engaging reaction from the driven gear 34 is moved to a driving gear 33 side along a prescribed direction Z1 parallel to a line L1 for connecting rotation centers C1 and C2 of the driving gear 33 and the driven gear 34. Subsequently, when a tooth of the driving gear 33 starting rotation according to starting of an electric motor 23 runs after a tooth of the idler gear 35 and collides with the tooth of the idler gear 35, the collision is performed from a state of almost no backlash amount (in a state of the shortest entrance distance), and thereby energy of the collision is considerably reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus.

There is an electric power steering device that decelerates the output rotation of an electric motor through a parallel shaft gear mechanism having a driving gear, an idler gear, and a driven gear, and further converts it into an axial movement of the rack shaft using a ball screw mechanism.
In this type of electric power steering device, noise caused by backlash between gears becomes a problem.

Therefore, in this type of electric power steering apparatus, the idler gear is supported so as to be swingable around the rotation center of the drive gear by a support member that can swing around the rotation center of the drive gear, and the support member is supported by the biasing member. It has been proposed to provide a backlash removing mechanism that urges rotation (see, for example, Patent Document 1).
In the backlash removing mechanism, the idler gear is elastically biased to the driven gear by the biasing member, thereby removing the backlash between the idler gear and the driven gear.
JP 2007-15486 A

However, in Patent Document 1, it is necessary to provide a backlash removal mechanism including a swinging support member and a biasing member that biases the support member, and the structure is complicated. Therefore, the manufacturing cost is increased.
On the other hand, when the above-mentioned noise is to be reduced without providing a backlash removal mechanism as in Patent Document 1, it is necessary to manage the backlash between gears, for example, on the order of several tens of micrometers. For this purpose, it is necessary to strictly manage the positional accuracy and meshing accuracy of each gear, but such management is extremely difficult to perform in the mass production process.

  The present invention has been made in view of the above problems, and an object thereof is to provide an electric power steering device that is inexpensive and low noise.

  The inventor of the present application has paid attention to the fact that the noise is large when the handle is inverted during the stationary operation. That is, immediately after the steering wheel is reversed, the driven gear first rotates along with the reverse input from the steered shaft, and the idler gear starts to rotate following the rotation of the driven gear. At this stage, since the electric motor causing the response delay when the steering wheel is reversed has not started yet, the drive gear has not started to rotate, and therefore the backlash amount between the idler gear and the teeth of the drive gear is maximized. It has become.

  Thereafter, the electric motor is started, the drive gear starts to rotate slightly after the start of rotation of the idler gear, and the teeth of the drive gear collide with the teeth of the idler gear so as to follow the teeth of the idler gear. Since this collision starts from a state where the backlash amount between the teeth of the idler gear and the drive gear is the maximum (the state where the run-up distance is the longest), the energy of the collision is large, and the idler gear generates a large vibration. The inventor of the present application considered that this was the cause of the loud noise when the handle was reversed during the stationary operation.

  The present invention has been made on the basis of such knowledge, and the present invention relates to a mechanical steering mechanism that moves the steered shaft in the axial direction in accordance with the rotation operation of the steering member (2), and the electric motor (23). Including a rotary cylinder (31) driven via a speed reduction mechanism (24), and a motion conversion mechanism (25) for converting the rotation of the rotary cylinder into the axial direction (X1) of the steered shaft (10). The speed reduction mechanism includes a parallel shaft gear mechanism having a drive gear (33), an idler gear (35) and a driven gear (34) which are sequentially meshed, and is along the axial direction (Y1) of the support shaft (29) of the idler gear. When viewed from above, the support shaft (29) is supported so as to be movable in a predetermined direction (Z1) parallel to the line (L1) connecting the rotation centers (C1, C2) of the drive gear and the driven gear. It is characterized by being.

  In the present invention, when the idler gear starts to rotate following the rotation of the driven gear immediately after reversing the steering member at the time of stationary, the idler gear that receives the meshing reaction force from the driven gear rotates the rotation of the drive gear. It moves to the drive gear side along a predetermined direction parallel to the line connecting the center and the rotation center of the driven gear. As a result, the backlash amount between the teeth of the moved idler gear and the drive gear that has not yet started rotating can be made almost zero. Therefore, when the drive gear teeth that have started rotating with the start-up of the electric motor subsequently follow the idler gear teeth and collide with the idler gear teeth, there is almost no backlash (the shortest running distance). Therefore, the energy of the collision can be remarkably reduced, and as a result, it is possible to prevent the occurrence of vibration and noise during the reversing operation of the steering member at the time of stationary.

  On the other hand, when the drive gear and the idler gear mesh with each other first, the idler gear that receives the meshing reaction force from the drive gear moves to the driven gear side along the predetermined direction parallel to the line. Thereby, the backlash amount between the teeth of the idler gear and the driven gear can be made almost zero. Therefore, when the tooth of the driven gear that receives the reverse input from the road surface collides with the tooth of the idler gear, it collides from a state where there is almost no backlash (the state where the run-up distance is shortest). As a result, it is possible to prevent the occurrence of vibration and noise during reverse input from the road surface.

In general, the preferable backlash amount is about 100 μm to 150 μm, and therefore, the movable amount of the spindle of the idler gear in the long hole is, for example, about 80 μm to 120 μm.
The bearing includes a bearing (39, 40) that rotatably supports the spindle of the idler gear, and a support member (42, 43) having a long hole (46, 49) extending in the predetermined direction. The support member may be supported by the long hole of the support member so as to be movable in the predetermined direction (claim 2). In this case, while ensuring smooth rotation of the idler gear, the idler gear can be smoothly moved in the predetermined direction when necessary.

  Further, there may be provided a biasing member (65, 66) for biasing the bearing to the center position in the longitudinal direction of the long hole. In this case, the bearing that supports the idler gear support shaft can be prevented from freely moving in the long hole during straight traveling, so that the idler gear generates tooth contact vibration with each of the driving gear and the driven gear and generates noise. Can be prevented.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, an electric power steering apparatus 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, an intermediate A pinion shaft 7 connected to the shaft 5 via a universal joint 6 and a rack 9 that meshes with a pinion 8 provided in the vicinity of the end of the pinion shaft 7 are provided in the left-right direction of the automobile (corresponding to the axial direction X1). A rack shaft 10 is provided as an extending turning shaft. A rack and pinion mechanism including the pinion shaft 7 and the rack shaft 10 constitutes a steering mechanism 11 that moves the rack shaft 10 in the axial direction as the steering member 2 rotates.

  The rack shaft 10 is inserted into a housing 12 and a housing 36 that are fixed to the vehicle body and connected to each other, and is supported so as to be movable in the axial direction X1 via a double-row angular ball bearing 41 described later, a rack bush (not shown), or the like. Has been. A pair of end portions of the rack shaft 10 protrude outward from the housing 12 and the housing 36, respectively. A tie rod 14 is coupled to each of the pair of ends of the rack shaft 10 via a universal joint 13. Each tie rod 14 is connected to a corresponding steered wheel 16 via a corresponding knuckle arm 15.

When the steering member 2 is operated and the steering shaft 3 and the pinion shaft 7 are rotated, the rotation of the pinion shaft 7 is converted by the pinion 8 and the rack 9 into a linear motion in the axial direction X1 of the rack shaft 10. Thereby, the turning of the steered wheels 16 is achieved.
The pinion shaft 7 includes an input shaft 17 connected to the steering member 2 so as to be integrally rotatable with the intermediate shaft 5 and the steering shaft 3, an output shaft 18 provided with the pinion 8, and the input shaft 17 and the output shaft 18. And a torsion bar 19 which is connected to be coaxially rotatable. A cylindrical pinion housing 91 that accommodates the pinion shaft 7 is integrally formed in the housing 12 in an intersecting manner.

  A torque sensor 20 is provided for detecting a steering torque according to the relative rotation of the input shaft 17 and the output shaft 18 via the torsion bar 19. The torque detection result of the torque sensor 20 and the vehicle speed detection result from the vehicle speed sensor 21 are given to an ECU (Electronic Control Unit) 22. The ECU 22 drives and controls an electric motor 23 for generating a steering assist force as a steering force based on a torque detection result, a vehicle speed detection result, and the like.

  In addition, the electric power steering apparatus 1 includes a speed reduction mechanism 24 including a parallel shaft gear mechanism that reduces the rotation of the rotation shaft 26 of the electric motor 23, and a motion that converts the output rotation of the speed reduction mechanism 24 into the axial movement of the rack shaft 10. And a ball screw mechanism 25 as a conversion mechanism. The electric motor 23 applies an axial driving force to the rack shaft 10 via the speed reduction mechanism 24 and the ball screw mechanism 25, whereby steering is assisted.

The speed reduction mechanism 24 includes an input shaft 28 that is coaxially connected to the rotation shaft 26 of the electric motor 23 via a joint 27 and is rotatable together, and an idler gear support shaft 29 that is disposed in parallel with the input shaft 28. A screw shaft 30 as an output shaft arranged in parallel with the input shaft 28 is provided.
The screw shaft 30 is coaxially provided on a part of the rack shaft 10 as a steered shaft. The ball screw mechanism 25 is configured by the screw shaft 30, a ball nut 31 as a rotating cylinder surrounding the screw shaft 30, and a plurality of balls 32 interposed between the screw shaft 30 and the ball nut 31. . The ball nut 31 is engaged with the screw shaft 30 via a plurality of balls 32.

  The speed reduction mechanism 24 includes a drive gear 33 that can rotate with the input shaft 28, a driven gear 34 that can rotate with the ball nut 31, and the idler gear support shaft 29 with the drive gear 33. And an idler gear 35 that meshes with the drive gear 33 and the driven gear 34. Each of the drive gear 33, the driven gear 34, and the idler gear 35 may be configured by a spur gear or a helical gear.

  The speed reduction mechanism 24 and the ball screw mechanism 25 are accommodated in a cylindrical housing 36. The input shaft 28 is rotatably supported by a pair of bearings 37 and 38 held by a housing 36. The idler gear support shaft 29 is rotatably supported by a pair of bearings 39 and 40 held by a housing 36. A ball nut 31 that supports the screw shaft 30 via a ball 32 is rotatably supported by a double-row angular ball bearing 41 held by a housing 36.

The housing 36 includes a first housing 42 and a second housing 43 that are connected to each other. The housing 12 is connected to the first housing 42.
At least a part of the rack stopper 59 provided in the second housing 43 of the housing 36 is disposed radially inward of the driven gear 34. The rack stopper 59 restricts the amount of movement of the rack shaft 10 in the axial direction by contacting the universal joint 13 as a member that moves along with the rack shaft 10 (steering shaft).

  Further, a lock screw 57 for fixing the outer ring of the double-row angular ball bearing 41 held by the first housing 42 is provided. Even if the lock screw 57 is loosened, the amount of looseness of the lock screw 57 can be regulated by the end face of the second housing 43. As a result, interference between the lock screw 57 and the driven gear 34 can be prevented, and abnormal noise is generated. Try to prevent.

Referring to FIG. 2, a part of the driven gear 34 includes an annular protrusion 58 that protrudes from the other end of the ball nut 31. At least a part of the rack stopper 59 formed in the second housing 43 is disposed on the radially inner side of the protruding portion 58.
The rack stopper 59 is a stopper for restricting an axial stroke amount of the rack shaft 10 having the screw shaft 30. The housing (not shown) of the universal joint 13 (see FIG. 1) that connects the end of the rack shaft 10 and the tie rod 14 abuts against the stopper surface 60 of the rack stopper 59, so that the stroke amount of the rack shaft 10 is reduced. Being regulated.

An annular elastic member 62 is accommodated in an annular recess 61 formed in the stopper surface 60, and a part of the elastic member 62 protrudes from the stopper surface 60. Thereby, the elastic member 62 works so as to alleviate a collision sound when the housing of the universal joint 13 abuts against the stopper surface 60.
As shown in FIG. 2, the first and second housings 42 and 43 are fixed to each other by a fixing screw 44 in a state where the end surface 42 a of the first housing 42 and the end surface 43 a of the second housing 43 are abutted with each other. It is concluded.

  The double row angular ball bearing 41 includes an integrated outer ring 81, an inner ring unit 83 including a pair of inner rings 82 arranged in the axial direction, and two rows of balls 84. It corresponds to. Since this corresponds to back-to-back alignment, it is preferable because the load capacity against moment load can be increased. Instead of the double row angular ball bearing 41, for example, a back-to-back combined angular ball bearing may be used.

A circulator 70 for circulating the ball 84 in the raceway between the screw shaft 30 of the ball screw mechanism 25 and the ball nut 31 is disposed radially inward of the double-row angular ball bearing 41, and the rack shaft 10. The electric power steering device 1 is reduced in size with respect to the axial direction X1.
A bearing 37 that supports one end 28 a of the input shaft 28, a bearing 39 that supports one end 29 a of the idler gear support shaft 29, and a double-row angular ball bearing 41 that supports the ball nut 31 are held by the first housing 42. ing. Specifically, the bearing 37 is held in the bearing holding hole 45 of the first housing 42, the bearing 39 is held in the bearing holding hole 46 of the first housing 42 as a support member, and a double row angular ball bearing 41 is held in the bearing holding hole 47 of the first housing 42.

A bearing 38 that supports the other end 28b of the input shaft 28 is held in the bearing holding hole 48 of the second housing 43, and a bearing 40 that supports the other end 29b of the idler gear support shaft 29 is a first member as a support member. 2 is held in the bearing holding hole 49 of the housing 43.
A small diameter portion 50 is formed at one end of the ball nut 31, a small diameter portion 51 is formed at the other end of the ball nut 31, and a large diameter portion 52 is provided between the small diameter portion 50 and the small diameter portion 51. An inner ring unit 83 of the double-row angular ball bearing 41 is fitted into a holding recess 53 formed on the outer periphery of the large-diameter portion 52 of the ball nut 31. The large diameter portion 52 of the ball nut 31 has a positioning step 54 adjacent to one end of the holding recess 53.

A fixing nut 55 is fitted to a screw portion formed on the outer periphery of the small diameter portion 50. The inner ring unit 83 is sandwiched between the fixing nut 55 and the positioning step portion 54, whereby the axial movement of the inner ring unit 83 relative to the ball nut 31 is restricted.
In addition, the driven gear 34 is press-fitted into the outer periphery of the small-diameter portion 51, whereby the driven gear 34 is coupled to the ball nut 31 so as to be able to rotate along with the ball nut 31. The unit including the driven gear 34 and the ball nut 31 is supported in a cantilever manner only by the double-row angular ball bearing 41.

When the driven gear 34 is supported in a cantilever manner as described above, the alignment error of the driven gear 34 may increase. Therefore, it is preferable to provide crowning in the tooth line direction on the tooth surface of the driven gear 34. As a result, an increase in gear noise can be suppressed regardless of an increase in alignment error as described above.
The outer ring 81 of the double row angular ball bearing 41 is fitted in the bearing holding hole 47 of the first housing 42. A screw portion 56 is formed adjacent to the bearing holding hole 47 on the inner periphery of the first housing 42, and a lock screw 57 is fitted to the screw portion 56. An outer ring 81 is sandwiched and fixed between the lock screw 57 and the positioning step portion of the first housing 42.

  The lock screw 57 abuts on the end surface 81 a of the outer ring 81 of the double row angular ball bearing 41 to restrict axial movement of the double row angular ball bearing 41. The lock screw 57 is disposed between the driven gear 34 and the double-row angular ball bearing 41 in a direction parallel to the axial direction X1 of the rack shaft 10. With respect to the axial direction X1 of the rack shaft 10, the end surface 57a of the lock screw 57 and the end surface 43a of the second housing 43 are opposed to each other with a gap S1 provided therebetween.

  The main feature of the present embodiment is that when viewed along the axial direction Y1 (see FIG. 2) of the idler gear support shaft 29, as shown in FIGS. The bearings 39 and 40 that support the end portions are moved in a predetermined direction Z1 parallel to the line L1 connecting the rotation center C1 of the drive gear 33 and the rotation center C2 of the driven gear 34 by the corresponding bearing holding holes 46 and 49, respectively. It is in the point that it is supported.

Specifically, the first and second housings 42 and 43 as the support members are provided in the first and second housings 42 and 43, and the bearing holding holes 46 and 49 for holding the corresponding bearings 39 and 40 are elongated holes extending in the predetermined direction Z1. Is formed. The bearings 39 and 40 are supported by the long holes as the bearing holding holes 46 and 49 so as to be movable in the predetermined direction Z1.
As shown in FIGS. 4A and 4B, the outer rings 391 and 401 of the respective bearings 39 and 40 are fitted into the inner circumferences of the corresponding bearing holding holes 46 and 49, and the corresponding bearing holding holes are fitted. The rotation of the outer ring 391, 401 is regulated by 46, 49. In FIGS. 4 and 5, for the sake of easy understanding, the amount of the gap in the longitudinal direction between the bearings 39 and 40 and the corresponding bearing holding holes 46 and 49 is greatly shown. Is 80 μm to 120 μm. This is because the preferable backlash amount is about 100 μm to 150 μm, and therefore the movable amount of the idler gear support shaft 29 in the long hole is sufficient to be about 80 μm to 120 μm.

The inner rings 392 and 402 of the bearings 39 and 40 are fitted to the idler gear support shaft 29 so as to be able to rotate together. Each of the bearings 39 and 40 includes, for example, a ball bearing in which rolling elements 393 and 403 are interposed between the outer rings 391 and 401 and the inner rings 392 and 402.
In the present embodiment, immediately after the steering member 2 is reversed at the time of stationary, the driving force of the steering member 2 rotates the driven gear 34 via the pinion shaft 7, the rack shaft 10 and the ball screw mechanism 25. When the idler gear 35 starts to rotate following the rotation of the driven gear 34, the idler gear 35 that receives the meshing reaction force from the driven gear 34, as shown in FIG. It moves to the drive gear 33 side along a predetermined direction Z1 parallel to the line L1 connecting the rotation centers C2.

As a result, the distance between the rotation center C3 of the moved idler gear 35 and the rotation center C1 of the drive gear 33 that has not yet started rotating approaches, and the backlash amount between the teeth of the idler gear 35 and the drive gear 33 is almost zero. Can be.
Therefore, after that, when the teeth of the drive gear 33 that started rotating with the activation of the electric motor 23 follow the teeth of the idler gear 35 and collide with the teeth of the idler gear 35, there is almost no backlash amount (the running distance of the running distance). The collision energy can be remarkably reduced, and as a result, the vibration and noise during the reversing operation of the steering member 2 at the time of stationary are prevented in advance. be able to.

  On the other hand, when the drive gear 33 and the idler gear 35 mesh with each other first, the idler gear 35 that has received the meshing reaction force from the drive gear 33 moves toward the driven gear 34 along the predetermined direction Z1 as shown in FIG. Move to. Thereby, the backlash amount between the teeth of the idler gear 35 and the driven gear 34 can be made almost zero. Therefore, when the teeth of the driven gear 34 that have received reverse input from the road surface via the rack shaft 9 collide with the teeth of the idler gear 35, they collide from a state where there is almost no backlash (the state where the run-up distance is shortest). As a result, the energy of the collision can be remarkably reduced, and as a result, generation of vibration and noise at the time of reverse input can be prevented.

Since the bearings 39 and 40 are supported by the bearing holding holes 46 and 49 made of long holes so as to be movable in the predetermined direction Z1, the idler gear 35 can be smoothly moved in the predetermined direction Z1 when necessary while ensuring smooth rotation of the idler gear 35. Can be moved to.
The present invention is not limited to the above-described embodiment. For example, as shown in FIGS. 7A and 7B, bearings 39 and 40 that support the end portions of the idler gear support shaft 29 correspond to the corresponding bearings. A pair of urging members 65 and 66 that urge to the center position in the longitudinal direction of the long holes as the holding holes 46 and 49 may be provided. The pair of urging members 65 and 66 are disposed on both sides of the corresponding bearings 39 and 40 in the bearing holding holes 46 and 49, and urge the bearings 39 and 40 corresponding to each other in opposite directions.

  A part of each urging member 65, 66 is housed in a holding recess 67 provided at an end of the bearing holding hole 46, 47 in the predetermined direction Z1, and the remaining urging member 65, 66 is left. The portion protrudes from the holding recess 67 and contacts the outer rings 391 and 401 of the bearings 39 and 40. As each of the urging members 65 and 66, a compression coil spring may be used, or an elastic member such as a rod-shaped rubber may be used.

According to the present embodiment, it is possible to prevent the bearings 39, 40 supporting the idler gear support shaft 29 from freely moving in the bearing holding holes 46, 49 during straight traveling, so that the idler gear 35 is driven by the drive gear 33 and the driven gear. It is possible to prevent generation of noise due to tooth contact vibration with each gear 34.
In addition, various modifications can be made within the scope of the claims of the present invention.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is an expanded sectional view of the principal part of the electric power steering device of FIG. It is a typical side view which shows the positional relationship of each gear of a reduction mechanism, and has shown the state in which the bearing which supports an idler gear support shaft exists in the center position of the longitudinal direction of the long hole as a bearing holding hole. It is a partial cross section side view of the support structure of an idler gear spindle, (a) And (b) has shown the support structure of a pair of edge part of an idler gear spindle. It is a schematic side view showing the positional relationship of each gear of the speed reduction mechanism, and shows a state in which the idler gear is displaced toward the drive gear along a predetermined direction parallel to a line connecting the rotation centers of the drive gear and the driven gear. Show. It is a schematic side view showing the positional relationship of each gear of the speed reduction mechanism, and shows a state in which the idler gear is displaced toward the driven gear along a predetermined direction parallel to the line connecting the rotation centers of the driving gear and the driven gear. Show. It is a partial cross section side view of the support structure of the idler gear spindle of another embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering member, 3 ... Steering shaft, 7 ... Pinion shaft, 10 ... Rack shaft (steering shaft), 11 ... Steering mechanism, 23 ... Electric motor, 24 ... Deceleration mechanism (parallel shaft gear) Mechanism), 25 ... ball screw mechanism (motion conversion mechanism), 29 ... idler gear support shaft, 31 ... ball nut (rotary cylinder), 33 ... drive gear, 34 ... driven gear, 35 ... idler gear, 39, 40 ... bearing, 42 ... 1st housing (support member), 43 ... 2nd housing (support member), 46, 49 ... Bearing holding hole (long hole), C1 ... (drive gear) rotation center, C2 ... (driven gear) Center of rotation, C3... Center of rotation (of idler gear), L1... (Connecting between center of rotation of drive gear and driven gear) line, X1... (Axially turning shaft), Y1. , Z1 ... ( Parallel) predetermined direction to the line connecting the centers of rotation and the driven gear of the driven gear

Claims (3)

A mechanical steering mechanism that moves the steered shaft in the axial direction in accordance with the rotation operation of the steering member;
Including a rotating cylinder driven by an electric motor through a speed reduction mechanism, and converting the rotation of the rotating cylinder into an axial movement of a steered shaft,
The speed reduction mechanism includes a parallel shaft gear mechanism having a driving gear, an idler gear, and a driven gear that are sequentially meshed,
The support shaft is supported so as to be movable in a predetermined direction parallel to a line connecting the rotation centers of the drive gear and the driven gear when viewed along the axial direction of the support shaft of the idler gear. Electric power steering device. In claim 1, comprising a bearing that rotatably supports the support shaft, and a support member having a long hole extending in the predetermined direction,
The electric power steering apparatus, wherein the bearing is supported by the elongated hole of the support member so as to be movable in the predetermined direction.   3. The electric power steering apparatus according to claim 2, further comprising a biasing member that biases the bearing toward a central position in the longitudinal direction of the long hole.

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