JP2006256414A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of further reducing rattles while securing smooth operation of a power conversion mechanism. <P>SOLUTION: An electric power steering device 10 is composed of a rack bar 1, an electric motor 40 and a power converting mechanism 20. The power converting mechanism 20 is a ball screw mechanism including a screw groove 21 spirally formed on the rack bar 1, and a ball screw nut 23 fitted thereinto through a ball 22 and rotated by the electric motor 40. In this electric power steering device 10, the front and rear ends of the ball screw nut 23 are made to elastically abut against a screw thread 1a on both sides of the screw groove 21, and separators 2a, 2b, 3a and 3b, as vibration attenuating members sliding against the screw thread 1a by rotation of the ball screw nut 23 are secured thereon. The separators 2a, 2b, 3a and 3b are separated around a rack bar axis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus.

  Patent Document 1 discloses a conventional electric power steering device. This electric power steering apparatus includes a rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, and an electric motor that rotationally drives the motor shaft based on the steering torque generated in the steering shaft. And a power conversion mechanism that converts the rotational motion of the motor shaft into a linear motion in the axial direction of the rack bar.

  The rack bar is a single bar. On one side of the rack bar, rack teeth are formed along the axial direction to mesh with a pinion that rotates by the rotational movement of the steering shaft. A power conversion mechanism is provided on the other side of the rack bar, and the rack bar and the power conversion mechanism can move relative to each other.

  The power conversion mechanism is a ball screw mechanism having a screw groove formed in a spiral shape on a rack bar, and a ball screw nut that engages with the screw groove via a ball and rotates by a motor shaft.

  The conventional electric power steering apparatus having such a configuration exhibits basic functions as described below, for example, by being mounted on an automobile.

  That is, when the operator steers, the electric motor rotates the motor shaft based on the steering torque generated on the steering shaft, thereby rotating the ball screw nut. For this reason, force is transmitted to the thread groove formed in the rack bar via the ball engaged with the ball screw nut, and the rotational motion is converted into a linear motion. For this reason, the rotational motion of the motor shaft is converted into a linear motion in the axial direction of the rack bar by the ball screw mechanism which is a power conversion mechanism, and assists the linear motion of the rack bar. Thus, this electric power steering apparatus can change the direction of the wheels without requiring an excessive operating force when the operator steers.

JP-A-11-334612

  By the way, since the need for improving the comfort of automobiles has been increasing in recent years, further reduction in noise has been demanded. In particular, when an automobile travels on an uneven road surface such as a cobblestone road, wheels vibrate, and noise (sounding sound) generated from an electric power steering device or a wheel suspension device due to the vibration is required to be reduced. Yes. This noise enters the vehicle and is sensed uncomfortable by the passenger, and is called rattle sound.

  Various reductions have been studied for the electric power steering system that is one of the causes of this rattle noise, but vibrations are generated from various locations, so improvement measures are not individually supported. Did not get. For this reason, the further improvement was calculated | required about reduction of a rattle sound.

  For example, in the electric power steering device of Patent Document 1, vibration damping members made of an elastic material are fixed to the front end and the rear end of a ball screw nut. The vibration attenuating member is elastically brought into contact with the thread groove and the thread on both sides of the thread groove by about 1 pitch or more, and is in sliding contact with the thread groove and the thread thread by the rotation of the ball screw nut. In this electric power steering apparatus, a retainer is provided on the outer periphery of the vibration damping member so that the elastic force exerted on the screw groove or the like by the vibration damping member is made constant by the retainer.

  For this reason, this electric power steering apparatus absorbs the vibration propagating from the rack bar to the ball screw nut when the vibration damping member is elastically deformed or generates a frictional force. This also suppresses the relative displacement of the gaps between the rack bar, the ball and the ball screw nut, thereby reducing the rattle noise caused by the collision between the rack bar, the ball and the ball screw nut.

  However, in this electric power steering apparatus, the vibration damping member circulates around the axis of the rack bar. More specifically, the vibration attenuating member has an annular shape having a convex portion that is substantially similar to the thread groove. The vibration damping member itself is firmly fixed to the ball screw nut.

  For this reason, in this electric power steering apparatus, since the vibration damping member is integrally slidably contacted with the thread groove and the screw thread in a large area, the sliding resistance between the rack bar and the vibration damping member becomes excessive. There was a fear.

  Further, in this electric power steering apparatus, since the vibration damping member is easily restrained in the thread groove, the vibration damping member corrects the position when the positional relationship between the rack bar and the vibration damping member is deviated. Difficult to deform. In particular, the electric power steering device avoids this tendency because the axis of the vibration damping member and the axis of the rack bar inevitably deviate within a tolerance due to variations in parts processing and assembly. I can't.

  For this reason, in this electric power steering device, there is a risk that the rotation failure of the ball screw nut is likely to occur and the operation of the power conversion mechanism cannot be performed smoothly.

  The present invention has been made in view of the above-described conventional situation, and provides an electric power steering device capable of further reducing rattle noise while ensuring smooth operation of a power conversion mechanism. Is a problem to be solved.

The electric power steering device according to the first aspect of the invention is a rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, and rotates the motor shaft based on the steering torque generated in the steering shaft. An electric motor for driving, and a power conversion mechanism for converting the rotational motion of the motor shaft into the linear motion in the axial direction of the rack bar,
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut is elastically abutted on the screw groove or a screw thread on both sides of the screw groove, and the screw groove or the screw thread slides by rotation of the ball screw nut. The contact damping member is fixed,
The vibration damping member includes a plurality of separated bodies separated around the axis of the rack bar.

  The electric power steering apparatus of the first invention having such a configuration exhibits basic functions as described below when mounted on an automobile, for example.

  That is, when the operator steers, the electric motor rotates the motor shaft based on the steering torque generated on the steering shaft, thereby rotating the ball screw nut. For this reason, force is transmitted to the thread groove formed in the rack bar via the ball engaged with the ball screw nut, and the rotational motion is converted into a linear motion. For this reason, the rotational motion of the motor shaft is converted into a linear motion in the axial direction of the rack bar by the ball screw mechanism which is a power conversion mechanism, and assists the linear motion of the rack bar. Thus, this electric power steering apparatus can change the direction of the wheels without requiring an excessive operating force when the operator steers.

  When an automobile equipped with such an electric power steering device travels on an uneven road surface such as a cobblestone road, the wheels vibrate finely vertically and horizontally in accordance with the uneven road surface. For this reason, the vibration of the wheel is transmitted to both ends of the rack bar of the electric power steering device via the tie rod. For this reason, the rack bar is vibrated in the axial direction and in a direction perpendicular to the axis by the vibration of the wheel, and accordingly, a ball in the thread groove of the rack bar and a ball screw nut engaged with the thread groove via the ball are also included. It will be vibrated.

  Here, in this electric power steering apparatus, a vibration damping member is fixed to at least one of the front end and the rear end of the ball screw nut. The vibration damping member elastically abuts on the thread groove or the thread on both sides of the thread groove, and comes into sliding contact with the thread groove or the thread by the rotation of the ball screw nut.

  For this reason, this electric power steering apparatus absorbs the vibration propagating from the rack bar to the ball screw nut when the vibration damping member is elastically deformed or generates a frictional force. This also suppresses the relative displacement of the gap between the rack bar, ball and ball screw nut, and can reduce rattle noise caused by collision between the rack bar, ball and ball screw nut.

  Further, in this electric power steering apparatus, the vibration damping member is composed of a plurality of separated bodies separated around the axis of the rack bar, so that there is a region that is not slidably contacted between the rack bar and the separated body. The area where the damping member is in sliding contact with the thread groove or the thread is smaller than the conventional one. For this reason, even if the vibration damping member of the present invention is elastically contacted by the same elastic force as that of the conventional one, the vibration damping member of the present invention has a smaller sliding resistance than that of the conventional one. And can be in sliding contact with each other.

  Further, in this electric power steering apparatus, there is a region that is not slidably contacted between the rack bar and the separated body, and as a result, each separated body does not restrain the rack bar too much, and each separated body is between itself. It can be deformed moderately toward the space. For this reason, in this electric power steering device, even if the positional relationship between the rack bar and the vibration damping member is deviated, the individual separators can be deformed so as to correct their positions.

  Therefore, the electric power steering apparatus according to the first aspect of the present invention is less likely to cause rotation failure of the ball screw nut, and thus can further reduce the rattle noise while ensuring a smooth operation of the power conversion mechanism.

  In the electric power steering apparatus according to the first aspect of the invention, it is preferable that the vibration damping member is in contact with only the thread.

  In this case, each separator constituting the vibration damping member is not brought into contact with the thread groove. For this reason, the surface that contacts the thread of each separator does not need to have a complicated shape like the contact surface of the vibration damping member of the conventional electric power steering device, and is substantially flat or outside the thread. A cylindrical surface substantially equal to the diameter may be used. For this reason, with regard to accuracy requirements when processing parts or assembling, even if each separator is displaced in a direction parallel to the axis, the state of contact with the screw thread hardly changes, and the ball screw nut rotates. There will be no adverse effects. For this reason, this electric power steering device can surely exhibit the effects of the first invention.

  In the electric power steering apparatus according to the first aspect of the present invention, it is preferable that the separators are arranged at equal angular intervals around the axis of the rack bar.

  In this case, since the individual separators are disposed so as not to bias the rack core, the force for biasing the rack bar does not easily act even when the ball screw nut rotates. ing. For this reason, this electric power steering device can achieve the effects of the first invention more reliably.

  In the electric power steering apparatus according to the first aspect of the present invention, it is preferable that the separate bodies are arranged at an angle of 180 ° around the axis of the rack bar.

  In this case, the effect of the present invention can be achieved while reducing the number of separators and reducing the frictional force caused by the vibration damping member slidingly contacting the thread.

  In the electric power steering apparatus according to the first aspect of the present invention, when each of the separated bodies is fixed to the front end and the rear end of the ball screw nut, each of the separated bodies fixed to the front end of the ball screw nut, and the ball screw It is preferable that each of the separated members fixed to the rear end of the nut is shifted by 90 ° or 270 ° around the axis of the rack bar.

  In this case, since the separating body constituting the vibration damping member elastically deforms or generates a frictional force at two locations apart from the front end and the rear end of the ball screw nut, vibration absorption, rack bar, The relative displacement of the gap between the ball and the ball screw nut can be suppressed more reliably. For this reason, this electric power steering device can achieve the effects of the first invention more reliably.

  The fact that each separator fixed to the front end and each separator fixed to the rear end are shifted by 90 ° or 270 ° around the axis of the rack bar means that the front and rear separators correspond to each other. To be compared.

  The vibration damping member according to the first aspect of the present invention may have various shapes such as a block shape such as a rectangular parallelepiped, a rod-like body, or a plate-like body. Various materials such as rubber, polyamide resin, Teflon (registered trademark) resin and the like can also be applied as the material of the vibration damping member.

The electric power steering device according to the second aspect of the invention is a rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, and rotates the motor shaft based on the steering torque generated in the steering shaft. An electric motor for driving, and a power conversion mechanism for converting the rotational motion of the motor shaft into the linear motion in the axial direction of the rack bar,
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut has a gap between the screw groove and abuts on the screw groove, and is in sliding contact with the screw groove by rotation of the ball screw nut. Is fixed,
The vibration damping member is levitated and supported by an urging force parallel to the axis of the rack bar.

  The electric power steering apparatus according to the second aspect of the invention is also mounted on an automobile and exhibits basic functions in the same manner as the electric power steering apparatus of the first aspect described above.

  Here, in this electric power steering apparatus, a vibration damping member is fixed to at least one of the front end and the rear end of the ball screw nut. The vibration attenuating member is in contact with the thread groove and is in sliding contact with the thread groove by the rotation of the ball screw nut.

  For this reason, this electric power steering apparatus absorbs the vibration propagating from the rack bar to the ball screw nut when the vibration damping member is elastically deformed or generates a frictional force. This also suppresses the relative displacement of the gap between the rack bar, ball and ball screw nut, and can reduce rattle noise caused by collision between the rack bar, ball and ball screw nut.

  Further, in this electric power steering apparatus, the vibration damping member has a gap between the screw groove and the vibration damping member is levitated and supported by an urging force parallel to the axis of the rack bar. For this reason, the vibration damping member is in sliding contact with the screw groove with a small area, and the sliding resistance between the rack bar and the vibration damping member is reduced.

  Further, in this electric power steering apparatus, since the vibration damping member has a gap between the screw groove, the vibration damping member does not restrain the rack bar too much, and the vibration damping member is It can be displaced moderately. Further, the levitation support acts so that the vibration damping member is displaced in the gap with the screw groove, and also acts to allow deviation of the axis of the vibration damping member relative to the rack bar. For this reason, in this electric power steering apparatus, even if the positional relationship between the rack bar and the vibration damping member is deviated, the vibration damping member can be displaced so as to correct its position.

  Therefore, the electric power steering apparatus according to the second aspect of the present invention is less likely to cause rotation failure of the ball screw nut, and thus can further reduce the rattle noise while ensuring a smooth operation of the power conversion mechanism.

  As the vibration damping member according to the second invention, various shapes such as a rod-like body, a plate-like body, or an arc to an annular body can be used. Various materials such as rubber, polyamide resin, Teflon (registered trademark) resin and the like can also be applied as the material of the vibration damping member.

  In addition, as a specific method of applying an urging force parallel to the axis of the rack bar to the vibration damping member, an elastic material such as a coil spring, a disc spring, or a rubber material is attached to a portion where the vibration damping member in the ball screw nut is fixed. The thing which interposes a body etc. are mentioned. Furthermore, an adjustment bolt or the like for adjusting the preload may be attached to the elastic body. By adjusting the degree of tightening of the adjusting bolt and compressing the elastic body to a predetermined length in advance, the urging force against the vibration damping member can be adjusted.

  In the electric power steering apparatus according to the second aspect of the present invention, it is preferable that the vibration damping member has an annular shape having a protrusion protruding into the thread groove.

  In this case, the vibration damping member comes into contact with the thread groove while circling around the axis of the rack bar. For this reason, the vibration damping member can be slidably contacted substantially uniformly around the axis of the rack bar, and the effect of the second aspect of the invention can be reliably exhibited.

An electric power steering device according to a third aspect of the invention is a rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, and rotates the motor shaft based on the steering torque generated in the steering shaft. An electric motor for driving, and a power conversion mechanism for converting the rotational motion of the motor shaft into the linear motion in the axial direction of the rack bar,
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut is provided with a vibration damping member that has a gap between the screw groove and abuts the screw groove, and is in sliding contact with the screw groove by the rotation of the ball screw nut. Fixed,
The vibration damping member is floated and supported by reverse biasing forces parallel to the axis of the rack bar and spaced from each other.

  The electric power steering apparatus according to the third aspect of the invention is also mounted on a vehicle and exhibits basic functions in the same manner as the electric power steering apparatus according to the first and second aspects of the invention.

  Here, in this electric power steering apparatus, a vibration damping member is fixed to at least one of the front end and the rear end of the ball screw nut. The vibration attenuating member is in contact with the thread groove and is in sliding contact with the thread groove by the rotation of the ball screw nut.

  For this reason, this electric power steering apparatus absorbs the vibration propagating from the rack bar to the ball screw nut when the vibration damping member is elastically deformed or generates a frictional force. This also suppresses the relative displacement of the gap between the rack bar, ball and ball screw nut, and can reduce rattle noise caused by collision between the rack bar, ball and ball screw nut.

  Further, in this electric power steering apparatus, the vibration damping member has a gap between the screw groove, and the vibration damping member is parallel to the axis of the rack bar and has a reverse biasing force spaced from each other. Supported by levitation. For this reason, the vibration damping member is in sliding contact with the screw groove with a small area, and the sliding resistance between the rack bar and the vibration damping member is reduced.

  Further, in this electric power steering apparatus, since the vibration damping member has a gap between the screw groove, the vibration damping member does not restrain the rack bar too much, and the vibration damping member is It can be displaced moderately. Further, the levitation support acts so that the vibration damping member is displaced in the gap with the screw groove, and also acts to allow deviation of the axis of the vibration damping member relative to the rack bar. For this reason, in this electric power steering apparatus, even if the positional relationship between the rack bar and the vibration damping member is deviated, the vibration damping member can be displaced so as to correct its position.

  In particular, the vibration attenuating member is slidably contacted with the thread groove by a reverse biasing force parallel to the axis of the rack bar and spaced from each other. More specifically, in this electric power steering apparatus, the vibration damping member is slidably contacted with the thread groove mainly by elastic deformation in the bending direction, such as twisting the thread groove. For this reason, even if the relative displacement between the rack bar and the vibration damping member increases, the displacement of the vibration damping member easily follows. Further, since the vibration damping member comes into contact with the screw threads on both sides of the thread groove, the vibration is absorbed in both directions of the screw threads, and the vibration damping effect is great.

  Therefore, the electric power steering device according to the third aspect of the present invention is less likely to cause rotation failure of the ball screw nut, and thus can further reduce the rattle noise while ensuring a smooth operation of the power conversion mechanism.

  The vibration damping member according to the third aspect of the invention can also have various shapes such as a rod-like body, a plate-like body, or an arc to an annular body. Various materials such as rubber, polyamide resin, Teflon (registered trademark) resin and the like can also be applied as the material of the vibration damping member.

  In addition, as a specific method of causing the biasing force in the opposite direction, which is parallel to the axis of the rack bar and spaced apart from each other, to act on the vibration damping member, as a part for fixing the vibration damping member in the ball screw nut, Examples include a coil spring, a disc spring, and an elastic member such as a rubber material. Furthermore, an adjustment bolt or the like for adjusting the preload may be attached to the elastic body. By adjusting the degree of tightening of the adjusting bolt and compressing the elastic body to a predetermined length in advance, the urging force against the vibration damping member can be adjusted.

  In the electric power steering apparatus according to a third aspect of the invention, it is preferable that the vibration damping member has an arc shape in which a central portion is located in the thread groove.

  In this case, the vibration damping member can be disposed in the space between the rack bar and the ball screw nut without increasing the outer diameter of the ball screw nut so much. For this reason, this electric power steering device can produce the effect of the third invention while suppressing an increase in size of the device.

An electric power steering device according to a fourth aspect of the present invention is a rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, and rotates the motor shaft based on the steering torque generated in the steering shaft. An electric motor for driving, and a power conversion mechanism for converting the rotational motion of the motor shaft into the linear motion in the axial direction of the rack bar,
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut is provided with a vibration damping member including a bearing that is eccentric with respect to the axial center of the rack bar at least exceeding the height of the thread groove crest,
The vibration damping member has an inner diameter that exceeds the outer diameter of the thread on both sides of the thread groove, and a part of the vibration damping member is provided in the thread groove and rolls the thread groove by the rotation of the ball screw nut. And an outer ring fixed to the ball screw nut and rolling the inner ring with a rolling element.

  The electric power steering apparatus according to the fourth aspect of the invention is also mounted on a vehicle and exhibits basic functions in the same manner as the electric power steering apparatus according to the first to third aspects of the invention.

  Here, in the electric power steering apparatus, at least one of the front end and the rear end of the ball screw nut is a vibration comprising a bearing that is eccentric with respect to the axis of the rack bar at least exceeding the height of the thread groove. A damping member is provided. This vibration damping member has an inner diameter that exceeds the outer diameter of the thread on both sides of the thread groove, a part of the inner ring that is provided in the thread groove and rolls with the thread groove by the rotation of the ball screw nut, and a ball screw. The outer ring is fixed to the nut and causes the inner ring to roll by a rolling element.

  For this reason, in this electric power steering apparatus, the inner ring of the vibration damping member rolls like a hula hoop with respect to the thread groove by the rotation of the ball screw nut. At this time, since the inner ring is related to the thread groove by rolling different from the sliding performed by the conventional vibration damping member, the resistance force becomes small. Since the thread groove is in contact with the ball screw nut via the vibration damping member including the inner ring, the rolling element, and the outer ring, the vibration of the thread groove is absorbed by these. Further, the relative displacement of the gaps between the rack bar, the ball and the ball screw nut is suppressed, and the rattle noise caused by the collision between the rack bar, the ball and the ball screw nut can be reduced.

  Therefore, the electric power steering device according to the fourth aspect of the present invention is less likely to cause rotation failure of the ball screw nut, and thus can further reduce the rattle noise while ensuring a smooth operation of the power conversion mechanism.

  The inner ring of the bearing as the vibration damping member according to the fourth aspect of the present invention may be made of a metal with a thread groove and a rolling surface, integrated with a rubber or resin ring, or with Teflon (registered trademark) resin. A resin coating such as the above may be applied.

  In the electric power steering apparatus according to a fourth aspect of the present invention, the inner ring has a gap between the screw groove and the outer ring is urged parallel to the rack bar axis or parallel to the rack bar axis. It is preferable that the buoyancy is supported by reverse biasing forces spaced apart from each other.

  In this case, the inner ring has a gap with the thread groove, and the outer ring is levitated and supported by an urging force parallel to the axis of the rack bar. For this reason, the inner ring rolls with a screw groove and a small area, and the rolling resistance between the rack bar and the inner ring is further reduced.

  In addition, since the inner ring has a gap with the thread groove, the vibration damping member does not restrain the rack bar too much, and the vibration damping member can be appropriately displaced by the gap with the thread groove. Further, the levitation support acts so that the inner ring is displaced in the gap with the thread groove, and also acts to allow a deviation of the axis of the vibration damping member relative to the rack bar. For this reason, in this electric power steering apparatus, even if the positional relationship between the rack bar and the vibration damping member is deviated, the vibration damping member can be displaced so as to correct its position.

  In particular, when the outer ring is floated and supported by reverse biasing forces that are parallel to the axis of the rack bar and spaced apart from each other, the inner ring is mainly threaded by displacement that squeezes the thread groove. Roll with grooves. For this reason, even if the relative displacement between the rack bar and the vibration damping member increases, the displacement of the vibration damping member easily follows. Further, since the inner ring rolls while contacting both side surfaces of the thread groove, vibration can be effectively absorbed in both directions parallel to the shaft core, and the vibration damping effect is great.

  As a specific method for applying an urging force parallel to the axis of the rack bar or reverse urging forces parallel to the axis of the rack bar and spaced apart from each other to the vibration damping member, Examples include an elastic body such as a coil spring, a disc spring, or a rubber material interposed in a portion where the vibration damping member is fixed. Furthermore, an adjustment bolt or the like for adjusting the preload may be attached to the elastic body. By adjusting the degree of tightening of the adjusting bolt and compressing the elastic body to a predetermined length in advance, the urging force against the vibration damping member can be adjusted.

  Hereinafter, with reference to the drawings, the first embodiment of the first invention, the second embodiment of the second invention, the third embodiment of the third invention, and the fourth embodiment of the fourth invention will be described below. 4 will be described.

  First, as shown in FIGS. 1 and 2, an electric power steering apparatus 10 according to a first embodiment will be described. The power steering device 10 includes a rack bar 1, an electric motor 40, and a power conversion mechanism 20.

  The rack bar 1 is a single rod-shaped body. On one side of the rack bar 1, rack teeth 8 that are integrally provided with a steering shaft (not shown) and mesh with a pinion 9 that is rotated by the rotation of the steering shaft are formed along the axial direction. Further, on the other side of the rack bar 1, a screw groove 21 constituting a power conversion mechanism 20 described later is formed in a spiral shape. The rack bar 1 converts the rotational motion of the steering shaft into a linear motion in the longitudinal direction, and can change the turning angle of a wheel (not shown) via a tie rod (not shown) connected to both ends 1L and 1R. It is like that.

  The power conversion mechanism 20 is a ball screw mechanism including a screw groove 21 formed in a spiral shape on the rack bar 1 and a ball screw nut 23 engaged with the screw groove 21 via a ball 22.

  The electric motor 40 includes an armature core 41 (coil, power supply terminal 44) installed in the housing 30, a cylindrical motor shaft 42 rotatably supported in the housing 30 via bearings 96 and 97, And a ring-shaped magnet 43 integrally attached to the outer cylindrical surface of the motor shaft 42. A ball screw nut 23 is fixed to the inner cylindrical surface of the motor shaft 42.

  As shown in FIG. 2, the ball screw nut 23 includes a main body 23 a located at the center of the ball screw nut 23, a separating body holder 23 b located at the front end of the ball screw nut 23, and a rear end of the ball screw nut 23. The lock nut 23c is positioned.

  The main body 23a has a cylindrical shape, and a spiral nut-side thread groove 24 is formed on the inner peripheral surface thereof. The outer peripheral surface of the main body 23a and the motor shaft 42 have a fitting structure, and the main body 23a is inserted into the motor shaft 42 so as to be in a predetermined position.

  As shown in FIGS. 2 and 4, the separating body holding body 23 b is also cylindrical, and separating bodies 3 a and 3 b as vibration damping members to be described later are fixed to the inner peripheral surface thereof. The outer peripheral surface of the separator holding body 23b and the motor shaft 42 have a fitting structure, and the separator holding body 23b is inserted into the motor shaft 42 before the main body 23a so as to be in a predetermined position. Has been.

  As shown in FIGS. 2 and 3, the lock nut 23 c is also cylindrical, and separators 2 a and 2 b as vibration damping members to be described later are fixed to the inner peripheral surface thereof. The lock nut 23c fixes the separator holding body 23b and the main body 23a to the motor shaft 42. A male screw 25a is processed on the outer peripheral surface of the lock nut 23c, and the inner peripheral surface of the motor shaft 42 is formed on the inner peripheral surface. The female screw 25b is processed, and the male screw 25a and the female screw 25b are screwed together. For this reason, after the separator holding body 23b and the main body 23a are inserted into the motor shaft 42, the lock nut 23c is screwed from one end of the motor shaft 42, whereby the separator holding body 23b and the main body 23a are attached to the motor shaft 42. Can be fixed.

  On the inner peripheral surface of the lock nut 23c, two separate bodies 2a and 2b arranged around the axis of the rack bar 1 at an angle of 180 ° are fixed. Each of the separators 2a and 2b is made of a resin and has a plate shape having a thickness that can exhibit a vibration absorbing function. Each separator 2a, 2b elastically abuts only on the thread 1a on both sides of the thread groove 21 and comes into sliding contact with the thread 1a on both sides of the thread groove 21 by the rotation of the ball screw nut 23. ing. At this time, the surfaces of the separators 2a and 2b that are in sliding contact with the thread 1a are simply flat surfaces because the separators 2a and 2b are plate-like.

  As shown in FIGS. 2 and 4, two separate bodies 3 a and 3 b arranged around the axis of the rack bar 1 at an angle of 180 ° are fixed to the inner peripheral surface of the separate body holder 23 b. ing. Each of the separators 3a and 3b is the same as the separators 2a and 2b fixed to the inner peripheral surface of the lock nut 23c, and is made of a resin and has a plate shape having a thickness that can exhibit a vibration absorbing function. There is no. Each of the separators 3a and 3b is also elastically brought into contact with only the screw threads 1a on both sides of the screw groove 21 and comes into sliding contact with the screw threads 1a on both sides of the screw groove 21 by the rotation of the ball screw nut 23. ing. At this time, the surfaces of the separators 3a and 3b that are in sliding contact with the thread 1a are simply flat surfaces because the separators 2a and 2b are plate-like.

  Separators 3a and 3b fixed to the inner peripheral surface of the separator holder 23b and separators 2a and 2b fixed to the inner peripheral surface of the lock nut 23c are 90 around the axis of the rack bar 1. ° Deviation. That is, in the cross-sectional views shown in FIGS. 2 to 4, the separators 2 a and 2 b are arranged above and below the rack bar 1, whereas the separators 3 a and 3 b are arranged on both side surfaces of the rack bar 1. Yes. For this reason, the separators 2 a, 2 b, 3 a, 3 b are arranged at intervals of 90 ° around the axis of the rack bar 1.

  The electric power steering apparatus 10 according to the first embodiment having the above-described configuration is mounted on an automobile and exhibits basic functions as described below.

  That is, when the operator operates the steering, the steering shaft rotates, the pinion 9 rotates, and the rack bar 1 moves linearly in the longitudinal direction. For this reason, the wheels are steered through the tie rods connected to the rack bar 1.

  At this time, in the power conversion mechanism 20 and the electric motor 40, during steering, a current controlled according to the steering torque is supplied from the power supply terminal 44 to the armature core 41, and between the armature core 41 and the magnet 43. The motor shaft 42 is rotationally driven by the action of electromagnetic force. Therefore, the ball screw nut 23 installed integrally with the motor shaft 42 also rotates at the same time, and axial driving force is transmitted to the rack bar 1 via the balls 22 and the screw grooves 21.

  Thus, the electric motor 40 rotationally drives the motor shaft 42 based on the steering torque generated in the steering shaft, and the power conversion mechanism 20 converts the rotational motion of the motor shaft 42 into a linear motion in the rack bar 1 axial direction. . For this reason, the electric motor 40 assists the linear motion of the rack bar 1. For this reason, when the pilot steers, the direction of the wheel can be changed without requiring an excessive operating force.

  When an automobile on which such an electric power steering device 10 is mounted travels on an uneven road surface such as a cobblestone road, the wheels vibrate finely vertically and horizontally in accordance with the uneven road surface. For this reason, the vibration of the wheel is transmitted to both ends of the rack bar 1 of the electric power steering apparatus 10 via the tie rod. For this reason, the rack bar 1 is vibrated in the axial direction and in the direction perpendicular to the axis by the vibration of the wheel, and accordingly, the ball 22 in the screw groove 21 of the rack bar 1 and the screw groove 21 are engaged via the ball 22. The ball screw nut 23 to be combined is also vibrated.

  Here, in the electric power steering apparatus 10, separators 2 a, 2 b, 3 a, 3 b as vibration damping members are fixed to the front end and the rear end of the ball screw nut 23. The separators 2 a, 2 b, 3 a, and 3 b are in elastic contact with the thread 1 a on both sides of the thread groove 21, and are in sliding contact with the thread 1 a by the rotation of the ball screw nut 23.

  For this reason, the electric power steering apparatus 10 absorbs vibrations propagating from the rack bar 1 to the ball screw nut 23 by elastically deforming the separators 2a, 2b, 3a, and 3b or generating a frictional force. Have been able to. This also suppresses the relative displacement of the gap between the rack bar 1, the ball 22 and the ball screw nut 23, and can reduce the rattle noise caused by the collision between the rack bar 1, the ball 22 and the ball screw nut 23. ing.

  Further, in this electric power steering apparatus 10, the vibration damping member is composed of four separators 2a, 2b, 3a, 3b separated around the axis of the rack bar 1, so that the rack bar 1 and the separators 2a, 2b are separated. There is a region that is not in sliding contact with 3a, 3b, and the area in which the vibration damping member is in sliding contact with the screw thread is smaller than in the conventional case. For this reason, even if the vibration damping member according to the first embodiment is elastically contacted by the same elastic force as the conventional one, the vibration damping member according to the first embodiment is smaller in sliding than the conventional one. The resistor can be in sliding contact with the rack bar 1.

  Further, in the electric power steering apparatus 10, there is a region that is not in sliding contact between the rack bar 1 and the separators 2a, 2b, 3a, and 3b, and as a result, each separator 2a, 2b, 3a, and 3b. However, the separators 2a, 2b, 3a, and 3b can be appropriately deformed toward the spaces between them. For this reason, in this electric power steering apparatus 10, even if the positional relationship between the rack bar 1 and each of the separators 2a, 2b, 3a, and 3b is deviated, the individual separators 2a, 2b, 3a, and 3b have their positions. Can be modified to correct.

  Therefore, in the electric power steering apparatus 10 according to the first embodiment, the rotation failure of the ball screw nut 23 is less likely to occur, and as a result, the rattling noise can be reduced while ensuring the smooth operation of the power conversion mechanism 20. It can be realized further.

  Further, in this electric power steering apparatus 10, each separator 2 a, 2 b, 3 a, 3 b is in contact with only the screw thread 1 a, and is not in contact with the screw groove 21. For this reason, the surface that contacts the thread 1a of each of the separators 2a, 2b, 3a, and 3b is not a complicated shape like the contact surface of the vibration damping member of the conventional electric power steering device, and is manufactured. It is an easy plane. For this reason, with respect to accuracy requirements at the time of processing and assembling of the parts, even if each separator 2a, 2b, 3a, 3b is displaced in a direction parallel to the axis of the rack bar 1, it is in contact with the thread 1a. Hardly changes and does not adversely affect the rotation of the ball screw nut 23. For this reason, the electric power steering apparatus 10 can reliably achieve the effects of the first invention.

  Further, in this electric power steering apparatus 10, the separators 2a, 2b, 3a, 3b are arranged at equal angular intervals around the axis of the rack bar 1, that is, at 90 ° intervals. The rotation of the screw nut 23 also makes it difficult for a force to bias the axis of the rack bar 1 to act. For this reason, this electric power steering device 10 can achieve the effects of the first invention more reliably.

  Further, in the electric power steering apparatus 10, the separators 2 a and 2 b fixed to the rear end of the ball screw nut 23 are arranged at an angle of 180 ° around the axis of the rack bar 1. The separators 3a and 3b fixed to the front end of the rack bar are also arranged at 180 ° around the axis of the rack bar 1, so that the number of the separators is reduced and the vibration damping member is threaded. The effect of the present invention can be achieved while further reducing the frictional force caused by sliding contact with la.

  Furthermore, in the electric power steering apparatus 10, the separators 2a and 2b fixed to the rear end of the ball screw nut 23 and the separators 3a and 3b fixed to the front end of the ball screw nut 23 1 and 90, the separators 2a and 2b and the separators 3a and 3b are elastically deformed or frictionally separated at two locations apart from the front end and the rear end of the ball screw nut 23. Can generate power. For this reason, the separators 2a, 2b3a, and 3b can more reliably perform vibration absorption and suppress relative displacement of the gaps between the rack bar 1, the ball 22, and the ball screw nut 23. For this reason, this electric power steering device 10 can achieve the effects of the first invention more reliably.

  As shown in FIGS. 5 to 7, the electric power steering apparatus 11 according to the second embodiment includes a ball screw nut 23 and a vibration damping member including a main body 23 a, a separator holding body 23 b, and a lock nut 23 c according to the first embodiment. The ball screw nut 23 is composed of a main body 23a and a lock nut 231c, and the vibration damping member 4 is levitated and supported by an urging force parallel to the axis of the rack bar 1 with respect to the separators 2a, 2b, 3a and 3b. Is different. Since other configurations are the same as those of the electric power steering apparatus 10 of the first embodiment, description thereof is omitted.

  As shown in FIGS. 5 to 7, the ball screw nut 23 includes a main body 23 a located at the front end of the ball screw nut 23 and a lock nut 231 c located at the rear end of the ball screw nut 23.

  The main body 23a has a cylindrical shape, and a spiral nut-side thread groove 24 is formed on the inner peripheral surface thereof. The outer peripheral surface of the main body 23a and the motor shaft 42 have a fitting structure, and the main body 23a is inserted into the motor shaft 42 so as to be in a predetermined position.

  The lock nut 231c is also cylindrical, and a vibration damping member 4 described later is fixed to the inner peripheral surface thereof. The lock nut 231c is configured to fix the main body 23a to the motor shaft 42. A male screw 25a is processed on the outer peripheral surface of the lock nut 231c, and a female screw 25b is processed on the inner peripheral surface of the motor shaft 42. These male screw 25a and female screw 25b are screwed together. For this reason, after the main body 23 a is inserted into the motor shaft 42, the main body 23 a can be fixed to the motor shaft 42 by screwing the lock nut 231 c from one end of the motor shaft 42.

  The vibration damping member 4 fixed to the inner peripheral surface of the lock nut 231c is made of resin and has an annular shape having a convex portion 4a protruding into the screw groove 21. The convex portion 4 a has a shape substantially similar to that of about one lead of the screw groove 21, and has a slight gap 4 b between the convex portion 4 a and the screw groove 21.

  The vibration damping member 4 is levitated and supported by a supporting elastic body 4c provided in a gap with the inner peripheral surface of the lock nut 231c. The supporting elastic body 4 c is made of soft rubber, and can displace the axial center of the annular vibration damping member 4 in accordance with the axial center of the rack bar 1. In addition, the vibration damping member 4 is configured to rotate integrally with the ball screw nut 23 by being locked by a detent pin 4d protruding from the lock nut 231c. Further, the vibration damping member 4 is loaded with an urging force parallel to the axis of the rack bar 1 by a pair of adjustment bolts 4e and a pressing rubber 4f arranged at 180 ° around the axis. . The pressing rubber 4f is previously compressed to a predetermined length by the adjusting bolt 4e, so that the urging force against the vibration damping member 4 can be adjusted.

  Thus, the vibration damping member 4 is lifted and supported by an urging force parallel to the axial center of the rack bar 1, thereby contacting the screw groove 21 with the gap 4 b between the screw groove 21 and the ball screw nut. By rotating 23, the screw groove 21 is brought into sliding contact.

  The electric power steering apparatus 11 according to the second embodiment having the above-described configuration is also mounted on an automobile and exhibits basic functions in the same manner as the electric power steering apparatus 10 according to the first embodiment.

  Here, in the electric power steering apparatus 11, the vibration damping member 4 is fixed to the rear end of the ball screw nut 23. The vibration attenuating member 4 is in contact with the thread groove 21 and is in sliding contact with the thread groove 21 by the rotation of the ball screw nut 23.

  For this reason, the electric power steering apparatus 11 can absorb the vibration propagating from the rack bar 1 to the ball screw nut 23 when the vibration damping member 4 is elastically deformed or generates a frictional force. Yes. This also suppresses the relative displacement of the gap between the rack bar 1, the ball 22 and the ball screw nut 23, and can reduce the rattle noise caused by the collision between the rack bar 1, the ball 22 and the ball screw nut 23. ing.

  Further, in this electric power steering apparatus 11, the vibration damping member 4 has a gap 4 b between the screw groove 21, and the vibration damping member 4 is levitated and supported by an urging force parallel to the axis of the rack bar 1. Yes. For this reason, the vibration damping member 4 is in sliding contact with the screw groove 21 in a small area, and the sliding resistance between the rack bar 1 and the vibration damping member 4 is reduced.

  Further, in this electric power steering apparatus 11, since the vibration damping member 4 has the gap 4 b between the screw groove 21, the vibration damping member 4 does not restrain the rack bar 1 excessively, and the vibration damping member 4. Can be appropriately displaced by the gap 4b with the screw groove 21. Further, the levitation support acts so that the vibration damping member 4 is displaced in the gap with the screw groove 21, and also acts to allow a deviation of the axis of the vibration damping member 4 with respect to the rack bar 1. For this reason, in this electric power steering apparatus 11, even if the positional relationship between the rack bar 1 and the vibration damping member 4 is deviated, the vibration damping member 4 can be displaced so as to correct the position.

  Therefore, the electric power steering apparatus 11 of the second embodiment is also less likely to cause the rotation failure of the ball screw nut 23, and as a result, the rattling noise can be reduced while ensuring the smooth operation of the power conversion mechanism 20. It can be realized further.

  Further, in this electric power steering apparatus 11, the vibration damping member 4 has an annular shape having a convex portion 4 a protruding into the thread groove 21, so that the vibration damping member 4 circulates around the axis of the rack bar 1. However, it can contact the thread groove 21. For this reason, the vibration damping member 4 can be slidably contacted substantially evenly around the axis of the rack bar 1, and the effect of the second aspect of the invention can be reliably exhibited.

  As shown in FIGS. 8 to 10, the electric power steering apparatus 12 according to the third embodiment includes a ball screw nut 23 including a main body 23 a, a separator holding body 23 b and 23 c, and a lock nut 23 c and vibration damping. The ball screw nut 23 is composed of a main body 23a and a lock nut 232c with respect to the separated bodies 2a, 2b, 3a, and 3b as members, and the vibration damping member 5 is parallel to the axis of the rack bar 1 and is spaced from each other. The difference is that it is lifted and supported by the reverse biasing force. Since other configurations are the same as those of the electric power steering apparatus 10 of the first embodiment, description thereof is omitted.

  As shown in FIGS. 8 to 10, the ball screw nut 23 includes a main body 23 a located at the front end of the ball screw nut 23 and a lock nut 232 c located at the rear end of the ball screw nut 23.

  The main body 23a has a cylindrical shape, and a spiral nut-side thread groove 24 is formed on the inner peripheral surface thereof. The outer peripheral surface of the main body 23a and the motor shaft 42 have a fitting structure, and the main body 23a is inserted into the motor shaft 42 so as to be in a predetermined position.

  The lock nut 232c is also cylindrical, and a vibration damping member 5 described later is fixed to the inner peripheral surface thereof. The lock nut 232c is configured to fix the main body 23a to the motor shaft 42. A male screw 25a is processed on the outer peripheral surface of the lock nut 232c, and a female screw 25b is processed on the inner peripheral surface of the motor shaft 42. These male screw 25a and female screw 25b are screwed together. For this reason, after the main body 23 a is inserted into the motor shaft 42, the main body 23 a can be fixed to the motor shaft 42 by screwing the lock nut 232 c from one end of the motor shaft 42.

  The vibration damping member 5 fixed to the inner peripheral surface of the lock nut 232c is made of resin and has an arc shape in which the central portion 5a is positioned in the screw groove 21. Since the vibration damping member 5 is arcuate, the vibration damping member 5 is disposed in the space between the rack bar 1 and the ball screw nut 23 without increasing the outer diameter of the ball screw nut 23 so much. Is possible. The central part 5 a of the arc located in the thread groove 21 has a slight gap 5 b between the center part 5 a and the thread groove 21.

  The vibration attenuating member 5 is levitated and supported by a supporting elastic body 5d provided in a gap with the inner peripheral surface of the lock nut 232c. The supporting elastic body 5d is made of soft rubber, and the vibration damping member 5 and the ball screw nut 23 are moved while the shaft core of the arc-shaped vibration damping member 5 is displaced in accordance with the shaft core of the rack bar 1. It is supported so that it can rotate together. Further, the vibration damping member 5 is a pair of adjustment bolts 5e and pressing rubber 5f disposed at both ends of the arcuate vibration damping member 5, and is opposite to each other in parallel to the axis of the rack bar 1 and at a distance from each other. The biasing force of the direction is loaded. The pressing rubber 5f is compressed in advance to a predetermined length by the adjusting bolt 5e, so that the urging force against the vibration damping member 5 can be adjusted. When the biasing force is applied to the vibration damping member 5 in this way, the central portion 5 a located in the screw groove 21 is deformed so as to be twisted in the screw groove 21 and abuts on both side surfaces of the screw groove 21. It is like that.

  Thus, the vibration damping member 5 is levitated and supported by reverse biasing forces parallel to the axis of the rack bar 1 and spaced apart from each other, whereby the gap 5b is formed between the central portion 5a and the screw groove 21. And is in contact with the thread groove 21 and is in sliding contact with the thread groove 21 by the rotation of the ball screw nut 23.

  The electric power steering device 12 according to the third embodiment having the above-described configuration is also mounted on the automobile and exhibits basic functions in the same manner as the electric power steering device 10 according to the first embodiment.

  Here, in the electric power steering apparatus 12, the vibration damping member 5 is fixed to the rear end of the ball screw nut 23. The vibration damping member 5 is in contact with the screw groove 21 and is in sliding contact with the screw groove 21 by the rotation of the ball screw nut 23.

  For this reason, the electric power steering device 12 can absorb the vibration propagating from the rack bar 1 to the ball screw nut 23 when the vibration damping member 5 is elastically deformed or generates a frictional force. Yes. This also suppresses the relative displacement of the gap between the rack bar 1, the ball 22 and the ball screw nut 23, and can reduce the rattle noise caused by the collision between the rack bar 1, the ball 22 and the ball screw nut 23. ing.

  Furthermore, in this electric power steering apparatus 12, the vibration damping member 5 has a gap 5b between the screw groove 21 and the vibration damping member 5 is parallel to the axis of the rack bar 1 and spaced from each other. It is supported by levitating force in the opposite direction. For this reason, the vibration damping member 5 is in sliding contact with the screw groove 21 in a small area, and the sliding resistance between the rack bar 1 and the vibration damping member 5 is small.

  Further, in this electric power steering device 12, since the vibration damping member 5 has the gap 5 b between the screw groove 21, the vibration damping member 5 does not restrain the rack bar 1 excessively, and the vibration damping member 5. However, the gap 5b with the screw groove 21 can be displaced moderately. Further, the levitation support acts so that the vibration damping member 5 is displaced in the gap 5 b with the screw groove 21, and also acts to allow deviation of the axis of the vibration damping member 5 from the rack bar 1. For this reason, in this electric power steering device 12, even if the positional relationship between the rack bar 1 and the vibration damping member 5 is deviated, the vibration damping member 5 can be displaced so as to correct the position.

  In particular, the vibration attenuating member 5 is slidably contacted with the screw groove 21 by biasing forces that are parallel to the axis of the rack bar 1 and spaced apart from each other. More specifically, in the electric power steering apparatus 12, the vibration damping member 5 is in sliding contact with the screw groove 21 mainly by the elastic deformation in the bending direction, such as twisting the screw groove 21. For this reason, even if the relative displacement between the rack bar 1 and the vibration damping member 5 increases, the displacement of the vibration damping member 5 easily follows. Further, since the vibration damping member 5 comes into contact with the screw threads on both sides of the thread groove 21, the vibration is absorbed in both directions of the screw threads, and the vibration damping effect is increased.

  Accordingly, the electric power steering device 12 of the third embodiment is also less likely to cause the rotation failure of the ball screw nut 23. As a result, the rattling noise can be reduced while ensuring the smooth operation of the power conversion mechanism 20. It can be realized further.

  Further, in this electric power steering apparatus 12, the vibration damping member 5 has an arc shape in which the central portion 5a is located in the screw groove 21, so that the outer diameter of the ball screw nut 23 is not increased so much. The vibration damping member 5 can be disposed in the space between the rack bar 1 and the ball screw nut 23. For this reason, this electric power steering device 12 can achieve the effects of the third invention while suppressing an increase in the size of the device.

  As shown in FIGS. 11 to 13, the electric power steering apparatus 13 according to the fourth embodiment includes a ball screw nut 23 and a vibration damping member including a main body 23 a, a separator holding body 23 b, and a lock nut 23 c according to the first embodiment. The separated parts 2a, 2b, 3a and 3b differ in that the ball screw nut 23 is composed of a main body 23a and a lock nut 233c, and the vibration damping member 6 is composed of a bearing which is eccentric. Since other configurations are the same as those of the electric power steering apparatus 10 of the first embodiment, description thereof is omitted.

  As shown in FIGS. 11 to 13, the ball screw nut 23 includes a main body 23 a located at the front end of the ball screw nut 23 and a lock nut 233 c located at the rear end of the ball screw nut 23.

  The main body 23a has a cylindrical shape, and a spiral nut-side thread groove 24 is formed on the inner peripheral surface thereof. The outer peripheral surface of the main body 23a and the motor shaft 42 have a fitting structure, and the main body 23a is inserted into the motor shaft 42 so as to be in a predetermined position.

  The lock nut 233c is also a stepped cylinder, and a vibration damping member 6 described later is fixed to the inner peripheral surface thereof. The lock nut 233c fixes the main body 23a to the motor shaft 42. A male screw 25a is processed on the outer peripheral surface of the lock nut 233c, and a female screw 25b is processed on the inner peripheral surface of the motor shaft 42. These male screw 25a and female screw 25b are screwed together. For this reason, after the main body 23 a is inserted into the motor shaft 42, the main body 23 a can be fixed to the motor shaft 42 by screwing the lock nut 233 c from one end of the motor shaft 42.

  The vibration damping member 6 fixed to the inner peripheral surface of the lock nut 233c has an outer ring 7a as a bearing that is eccentric with respect to the axis of the rack bar 1 at least beyond the height of the crest 1a of the thread groove 21, It consists of a moving body 7b and an inner ring 7c. The inner ring 7 c has an inner diameter that exceeds the outer diameter of the thread 1 a on both sides of the thread groove 21. A part 6 a of the inner ring 7 c is provided in the thread groove 21, and the thread groove 21 is formed by rotation of the ball screw nut 23. It is supposed to roll. The outer ring 7a rolls the inner ring 7c with the rolling elements 7b, and is provided so as to be rotatable integrally with the ball screw 23 while being eccentric with respect to the axis of the rack bar 1. The outer ring 7a, the rolling element 7b, and the inner ring 7c are made of steel, and in particular, the surface of the inner ring 7c that rolls with the thread groove 21 is coated with a resin. Further, the inner ring 7 c has a slight gap 6 b between a part 6 a of the inner ring 7 c and the screw groove 21.

  The outer ring 7a is levitated and supported by a supporting elastic body 6d provided in a gap with the inner peripheral surface of the lock nut 233c. The supporting elastic body 6 d is made of soft rubber, and the axial center of the outer ring 7 a that is eccentric with respect to the axial center of the rack bar 1 is displaced relative to the clearance between the rack bar 1 and the ball screw nut 23. The outer ring 7a is supported so as to be able to rotate integrally with the ball screw nut 23 while being displaced in accordance with. Further, the outer ring 7a is reversely arranged parallel to the axis of the rack bar 1 and spaced from each other by a pair of adjusting bolts 6e and a pressing rubber 6f arranged at 180 ° around the axis. The urging force is loaded. The pressing rubber 6f is compressed in advance to a predetermined length by the adjusting bolt 6e, so that the urging force against the outer ring 7a can be adjusted. When the urging force is applied to the outer ring 7 a in this way, a part 6 b of the inner ring 7 a provided in the thread groove 21 is displaced so as to be squeezed in the thread groove 21, so It comes to contact.

  In this way, the outer ring 8a is levitated and supported by reverse biasing forces parallel to the axis of the rack bar 1 and spaced from each other, whereby a part 6a of the inner ring 7c is spaced from the screw groove 21 by a gap 6b. And abuts against the thread groove 21, and rolls with the thread groove 21 by the rotation of the ball screw nut 23.

  The electric power steering apparatus 13 according to the fourth embodiment having the above-described configuration is also mounted on the automobile and exhibits basic functions in the same manner as the electric power steering apparatus 10 according to the first embodiment.

  Here, in the electric power steering apparatus 13, vibrations are formed at the rear end of the ball screw nut 23 from a bearing that is eccentric with respect to the axial center of the rack bar 1 at least beyond the height of the thread 1 a of the thread groove 21. A damping member 6 is provided. This vibration damping member 6 has an inner diameter that exceeds the outer diameter of the thread 1a on both sides of the thread groove 21, and a part of the vibration damping member 6 is provided in the thread groove 21. The inner ring 7c is fixed to the ball screw nut 23, and the outer ring 7a is rolled by the rolling element 7b.

  For this reason, in this electric power steering device 13, the inner ring 7 c of the vibration damping member 6 rolls like a hula hoop with respect to the screw groove 21 by the rotation of the ball screw nut 23. At this time, since the inner ring 7c is related to the screw groove 21 by rolling different from the sliding performed by the conventional vibration damping member, the resistance force is small. Since the screw groove 21 is in contact with the ball screw nut 23 via the vibration damping member 6 including the inner ring 7c, the rolling element 7b, and the outer ring 7a, the vibration of the screw groove 21 can be absorbed by these. . Further, the relative displacement of the gap between the rack bar 1, the ball 22 and the ball screw nut 23 can be suppressed, and as a result, the rattle noise caused by the collision between the rack bar 1, the ball 22 and the ball screw nut 23 is reduced. Have been able to.

  Accordingly, the electric power steering device 13 of the fourth embodiment is also less likely to cause the rotation failure of the ball screw nut 23, and as a result, the rattling noise can be reduced while ensuring the smooth operation of the power conversion mechanism 20. It can be realized further.

  Further, in this electric power steering apparatus 13, the inner ring 7c has a gap 6b between the inner ring 7c and the thread groove 21, and the outer ring 7a is attached in the opposite direction parallel to the axis of the rack bar 1 and spaced from each other. It is levitated and supported by forces.

  For this reason, the inner ring 7c can roll with a small area with the screw groove 21, and the rolling resistance between the rack bar 1 and the inner ring 7c is further reduced. Further, since the inner ring 7 c has the gap 7 b between the inner ring 7 c and the screw groove 21, the vibration damping member 6 does not restrain the rack bar 1 excessively, and the vibration damping member 6 is moderately held by the gap 6 b with the screw groove 21. Can be displaced. Further, the levitation support acts so that the inner ring 7 c is displaced in the gap 6 b with the screw groove 21, and also acts to allow deviation of the axis of the vibration damping member 6 with respect to the rack bar 1. For this reason, in this electric power steering device 13, even if the positional relationship between the rack bar 1 and the vibration damping member 6 deviates, the vibration damping member 6 can be displaced so as to correct the position.

  In particular, since the outer ring 7a is levitated and supported by reverse biasing forces that are parallel to the axial center of the rack bar 1 and spaced from each other, the inner ring 7c is mainly subject to displacement that squeezes the screw groove 21. Rolling with the thread groove 21. For this reason, even if the relative displacement between the rack bar 1 and the vibration damping member 6 increases, the displacement of the vibration damping member 6 can easily follow. Moreover, since the inner ring 7c rolls while contacting both side surfaces of the thread groove 21, vibration can be effectively absorbed in both directions parallel to the shaft core, and the vibration damping effect is great.

  In the above, the present invention has been described with reference to the first to fourth embodiments. However, the present invention is not limited to the first to fourth embodiments, and can be appropriately modified and applied without departing from the spirit of the present invention. Needless to say.

  The present invention is applicable to an electric power steering apparatus.

1 is a schematic cross-sectional view of an electric power steering device according to a first embodiment. 1 is an enlarged cross-sectional view of a main part of an electric power steering device according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view showing an AA cross section of FIG. 2 according to the electric power steering apparatus of the first embodiment. FIG. 3 is a cross-sectional view showing the BB cross section of FIG. 2 according to the electric power steering apparatus of the first embodiment. It is a principal part expanded sectional view of the electric power steering device of Example 2. FIG. FIG. 6 is a cross-sectional view taken along a line CC in FIG. 5 according to the electric power steering apparatus of the second embodiment. It is a principal part expanded sectional view of the electric power steering device of Example 2. FIG. FIG. 6 is an enlarged cross-sectional view of a main part of an electric power steering device according to a third embodiment. FIG. 9 is a cross-sectional view taken along the line DD in FIG. 8 according to the electric power steering apparatus of the third embodiment. FIG. 6 is an enlarged cross-sectional view of a main part of an electric power steering device according to a third embodiment. It is a principal part expanded sectional view of the electric power steering device of Example 4. FIG. 12 is a cross-sectional view showing an EE cross section of FIG. 11 according to the electric power steering apparatus of the fourth embodiment. It is a principal part expanded sectional view of the electric power steering device of Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rack bar 1a ... Thread 2a, 2b, 3a, 3b ... Separation body 4, 5, 6 ... Vibration damping member 5a ... Center part 6a ... Part of inner ring 7a, 7b, 7c ... Bearing (7a ... Outer ring, 7b ... rolling elements, 7c ... inner ring)
DESCRIPTION OF SYMBOLS 10, 11, 12, 13 ... Electric power steering apparatus 20 ... Power conversion mechanism 21 ... Screw groove 22 ... Ball 23 ... Ball screw nut 40 ... Electric motor 42 ... Motor shaft

Claims (11)

A rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, an electric motor that rotationally drives the motor shaft based on the steering torque generated in the steering shaft, A power conversion mechanism that converts rotational motion into linear motion in the axial direction of the rack bar;
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut is elastically abutted on the screw groove or a screw thread on both sides of the screw groove, and the screw groove or the screw thread slides by rotation of the ball screw nut. The contact damping member is fixed,
The electric power steering apparatus according to claim 1, wherein the vibration damping member comprises a plurality of separated bodies separated around the axis of the rack bar.   The electric power steering apparatus according to claim 1, wherein the vibration damping member is in contact with only the screw thread.   3. The electric power steering apparatus according to claim 1, wherein the separators are disposed at equal angular intervals around the axis of the rack bar.   4. The electric power steering apparatus according to claim 3, wherein each of the separated bodies is disposed at an angle of 180 ° around the axis of the rack bar.   When each of the separated bodies is fixed to the front end and the rear end of the ball screw nut, each of the separated bodies fixed to the front end of the ball screw nut, and each of the separated bodies fixed to the rear end of the ball screw nut The electric power steering apparatus according to claim 4, wherein the separated body is shifted by 90 ° or 270 ° around the axis of the rack bar. A rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, an electric motor that rotationally drives the motor shaft based on the steering torque generated in the steering shaft, A power conversion mechanism that converts rotational motion into linear motion in the axial direction of the rack bar;
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut has a gap between the screw groove and abuts on the screw groove, and is in sliding contact with the screw groove by rotation of the ball screw nut. Is fixed,
The electric power steering apparatus according to claim 1, wherein the vibration damping member is levitated and supported by an urging force parallel to the axis of the rack bar.   The electric power steering apparatus according to claim 6, wherein the vibration damping member has an annular shape having a protrusion protruding into the thread groove. A rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, an electric motor that rotationally drives the motor shaft based on the steering torque generated in the steering shaft, A power conversion mechanism that converts rotational motion into linear motion in the axial direction of the rack bar;
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut is provided with a vibration damping member that has a gap between the screw groove and abuts the screw groove, and is in sliding contact with the screw groove by the rotation of the ball screw nut. Fixed,
The electric power steering apparatus according to claim 1, wherein the vibration damping member is levitated and supported by reverse biasing forces parallel to the axis of the rack bar and spaced from each other.   9. The electric power steering apparatus according to claim 8, wherein the vibration damping member has an arc shape with a central portion located in the thread groove. A rack bar that changes the turning angle by converting the rotational motion of the steering shaft into a linear motion in the longitudinal direction, an electric motor that rotationally drives the motor shaft based on the steering torque generated in the steering shaft, A power conversion mechanism that converts rotational motion into linear motion in the axial direction of the rack bar;
Electric power that is a ball screw mechanism in which the power conversion mechanism has a screw groove formed spirally on the rack bar, and a ball screw nut that is engaged with the screw groove via a ball and is rotated by the motor shaft. In the steering device,
At least one of the front end and the rear end of the ball screw nut is provided with a vibration damping member including a bearing that is eccentric with respect to the axial center of the rack bar at least exceeding the height of the thread groove crest,
The vibration damping member has an inner diameter that exceeds the outer diameter of the thread on both sides of the thread groove, and a part of the vibration damping member is provided in the thread groove and rolls the thread groove by the rotation of the ball screw nut. And an outer ring which is fixed to the ball screw nut and causes the inner ring to roll with a rolling element.   The inner ring has a gap with the thread groove, and the outer ring has an urging force parallel to the axis of the rack bar or opposite directions parallel to the axis of the rack bar and spaced from each other. The electric power steering apparatus according to claim 10, wherein the electric power steering apparatus is supported by levitating force.

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