Rack type electric power steering apparatus

A power steering system having the tensional force of a belt becomes higher as the distance between a motor shaft and a rack bar becomes larger because a second inclined portion of a support body passing through a guide hole is moved upwards along a first inclined portion to be inserted into a coupling recess, and accordingly, noise and damage to the belt can be prevented. If the support body is inserted into the coupling recess by a third inclined portion of a coupling recess and a motor housing is moved upwards, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger and, accordingly, noise and damage to the belt can be prevented.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2015-0004007, filed on Jan. 12, 2015, which is hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rack type electric power steering apparatus. More particularly, it relates to a rack type electric power steering apparatus in which the tensional force of a belt becomes higher as the distance between a motor shaft and a rack bar becomes larger because a second inclined portion of a support body passing through a guide hole is moved upwards along a first inclined portion to be inserted into a coupling recess, and accordingly, noise and damage to the belt can be prevented. Further, if the support body is inserted into a coupling recess by a third inclined portion of a coupling recess and a motor housing is moved upwards, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger, and accordingly, noise and damage to the belt can be prevented.

2. Description of the Prior Art

In general, a steering apparatus refers an apparatus that allows the driver to rotate a steering wheel to freely change the direction of travel of a vehicle, and is an apparatus that arbitrarily changes the center of rotation about which the front wheels are pivoted to help the driver drive the vehicle in a desired direction.

FIG. 1is a partially sectional view of a rack type electric power steering apparatus according to the related art.

As illustrated inFIG. 1, the rack type electric steering apparatus, according to the related art, includes a rack bar109that extends in a transverse direction of a vehicle and has a rack gear part on one side of an outer peripheral surface thereof, a pinion shaft104that has a pinion gear part that is engaged with the rack gear part, a ball screw part150that has balls201, a ball screw203, and a ball nut205engaged with the ball screw203via the balls201, a belt type transmission unit140that connects the ball nut205and a motor shaft221, a motor130, and a motor housing240that is fixed to a rack housing223through bolt coupling while surrounding the motor130.

The pinion shaft104is connected to a steering wheel through a steering shaft, and the rack bar109that has a screw of a predetermined length on one side of an outer surface thereof is installed within the rack housing223.

The ball screw part150includes a ball nut205, which is coaxially formed with the rack bar109and surrounds the rack bar109, and the balls201that make contact with the ball screw203formed on the outer surface of the rack bar109.

The ball nut205is rotated together with the motor shaft221as the motor shaft221is rotated, and a bearing207is provided between an outer peripheral surface of the ball nut205and an inner peripheral surface of the rack housing223for the smooth rotation of the ball nut205.

The belt type transmission unit140includes a belt230that connects the motor shaft221and the ball nut205, and transmits auxiliary power that is generated by the motor130to the rack bar109through the ball nut205in proportion to a steering torque applied to the steering wheel.

That is, as the motor shaft221is rotated, the ball nut205, which received a rotational force of the motor shaft221through the belt230, is also rotated, and as the ball nut205is rotated, the rack bar109is axially linearly moved according to the movements of the balls201and the ball screw203.

FIG. 2is a side view of a motor housing and a rack housing of the rack type electric power steering apparatus according to the related art.

The motor130is fixed by coupling the motor housing240surrounding the motor130and the rack housing223by means of bolts270.

If the motor shaft221drives the belt230while being rotated to rotate the ball nut205during a steering operation, a force that pulls the motor shaft221and a shaft of the rack bar109including the ball nut205towards each other is applied by a tensional force of the belt230.

Because the generated force is concentrated on a coupling portion of the bolts of the motor housing240and the rack housing223, which is most mechanically vulnerable, and the motor shaft221is moved towards the rack bar109that includes the ball nut205by a phenomenon in which the bolts300are released due to vibration and an impact occurring while the motor shaft221is rotated during a steering operation, the tensional force of the belt230decreases, noise occurs between the belt230and a driving pulley280or a driven pulley290, and the belt230is damaged.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the above-mentioned problems, and provides a rack type electric power steering apparatus in which the tensional force of a belt becomes higher as the distance between a motor shaft and a rack bar becomes larger because a second inclined portion of a support body passing through a guide hole is moved upwards along a first inclined portion to be inserted into a coupling recess, and accordingly, noise and damage to the belt can be prevented. Also, if the support body is inserted into a coupling recess by a third inclined portion of a coupling recess and a motor housing is moved upwards, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger and, accordingly, noise and damage to the belt can be prevented.

In order to achieve the object, there is provided a rack type electric power steering apparatus including: a rack housing that surrounds a rack bar coupled to a driven pulley, has a through-hole through which a motor shaft of a motor coupled to a driving pulley passes, has a guide hole that is spaced apart from the through-hole, and has a first inclined portion of which a cross-section in a direction in which the motor is coupled is changed; a motor housing to which the rack housing is coupled, on which the motor is mounted such that the motor shaft passes through the through-hole, and which has a coupling recess at a location corresponding to the guide hole; and a support body that passes through the guide hole to be coupled to the coupling recess and has a second inclined portion corresponding to the first inclined portion such that the driving pulley is moved away from the driven pulley when being coupled.

As described above, according to the present invention, because the second inclined portion of the support body passing through the guide hole is moved upwards along the first inclined portion to be inserted, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger, and accordingly, noise and damage to the belt can be prevented.

Furthermore, if the support body is inserted by the third inclined portion of the coupling recess and the motor housing is moved upwards, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger and, accordingly, noise and damage to the belt can be prevented.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the elements of the present invention, terms “first”, “second”, “A”, “B”, “(a)”, “(b)” and the like may be used. These terms are merely used to distinguish one structural element from other structural elements, and a property, an order, a sequence and the like of a corresponding structural element are not limited by the term. It should be noted that if it is described in the specification that one component is “connected,” “coupled” or “joined” to another component, a third component may be “connected,” “coupled,” and “joined” between the first and second components, although the first component may be directly connected, coupled or joined to the second component.

Unless otherwise mentioned in the detailed description of the present invention, the upper side ofFIG. 4will be described as an upper side, the lower side ofFIG. 4will be described as a lower side, the left side ofFIG. 4will be described as one side, and the right side ofFIG. 4will be described as an opposite side for the convenience of description.

FIG. 3is a side view of a motor housing and a rack housing of a rack type electric power steering apparatus according to a first embodiment of the present invention.FIG. 4is a front view of the motor housing and the rack housing of the rack type electric power steering apparatus according to the first embodiment of the present invention.FIG. 5is a perspective view illustrating a support body of the rack type electric power steering apparatus according to the first embodiment of the present invention.FIG. 6is a partially sectional view illustrating a process of coupling the support body to the rack housing and the motor housing in the rack type electric power steering apparatus according to the first embodiment of the present invention.FIG. 7is a partially sectional view illustrating a state in which the support body is coupled to the rack housing and the motor housing according to the first embodiment of the present invention.

Referring toFIGS. 3 to 7, in a detailed description of a feature structure of the first embodiment of the present invention, the rack type electric power steering apparatus, according to the first embodiment of the present invention, includes a rack housing320that surrounds a rack bar109coupled to a driven pulley290, has a through-hole380through which a motor shaft221of a motor130coupled to a driving pulley280passes in an axial direction of the rack bar109, and has a guide hole326that is spaced apart from the through-hole380, extending in the axial direction of the rack bar109, and having a first inclined portion324of which a cross-section is changed such that a vertical width thereof in a direction in which a motor130is coupled becomes narrower, a motor housing330to which the rack housing320is coupled, on which the motor130is mounted such that the motor shaft221passes through the through-hole380, and which has a coupling recess332at a location corresponding to the guide hole326, and a support body312that passes through the guide hole326to be coupled to the coupling recess332and has a second inclined portion314corresponding to the first inclined portion324such that the driving pulley280is moved away from the driven pulley290when being coupled.

A belt type transmission unit300includes a driving pulley280that is coupled to the motor shaft221, a driven pulley290that is coupled to a ball nut205, and a belt230that connects the driving pulley280and the driven pulley290, and auxiliary power that is generated by the motor130in proportion to a steering torque applied to a steering wheel is transmitted to the rack bar109through the ball nut205.

That is, the ball nut205that received a rotational force of the motor shaft221is also rotated by the belt230as the motor shaft221is rotated, and the rack bar109is axially linearly moved by balls and a ball screw as the ball nut205is rotated.

The rack housing320surrounds the rack bar109to which the driven pulley290is coupled, has a through-hole380through which the motor shaft221of the motor130to which the driving pulley280is coupled passes in the axial direction of the rack bar109, and has a guide hole326spaced apart from the through-hole380, extending in the axial direction of the rack bar109, and having a first inclined portion324of which a cross-section is changed such that a vertical width thereof in a direction in which a motor130is coupled becomes narrower.

Here, the through-hole380may be a slot such that a portion of the motor housing330is inserted into the slot and the motor shaft221is moved upwards and downwards.

The guide hole326has a first flat portion322extending from the first inclined portion324and having a constant vertical width in a direction in which the motor130is coupled.

That is, the guide hole326has a first flat portion322that has a constant vertical width on one side on which the motor130is coupled, and a first inclined portion324of which a vertical width becomes wider as it goes from the first flat portion322to an opposite side.

The guide hole326has the first inclined portion324on any one of the upper surface and the lower surface thereof, and a support body312that has a second inclined portion314corresponding to the first inclined portion324on any one of the upper surface and the lower surface thereof such that the support body312to correspond to the guide hole326is coupled to the guide hole326.

In the first embodiment of the present invention, because the first inclined portion324is formed on the lower surface of the guide hole326and the second inclined portion314is formed on the lower surface of the support body312such that the second inclined portion314of the support body312passing through the guide hole326is moved upwards along the first inclined portion324of the guide hole326to be inserted into the coupling recess332, the motor housing330is moved upwards such that the distance between the motor shaft221and the rack bar109becomes larger, increasing the tensional force of the belt230and, accordingly, preventing noise and damage to the belt230.

The motor130is coupled to the motor housing330surrounding the motor130by bolts.

The motor housing330is coupled to the rack housing320such that the motor130is mounted on the motor housing330and the motor shaft221passes through the through-hole380, and the coupling recess332is formed at a location corresponding to the guide hole326.

One or more slots390are formed in the rack housing320such that the driving pulley280that is coupled to the motor shaft221is moved away from the driven pulley290that is coupled to the rack bar109and one or more screw holes are formed in the motor housing330so that the tensional force of the belt230is adjusted by preliminarily coupling the bolts270to the screw holes after passing the bolts270through the slots390and moving the motor housing330upwards and downwards, and the motor housing330is fixed to the rack housing320by fastening the bolts270in the state in which the tensional force of the belt230is adjusted.

The coupling recess332has a third inclined portion334on the upper surface thereof such that a vertical width thereof becomes narrower as it goes towards a side on which the motor130is coupled.

Accordingly, if the support body312is inserted into the coupling recess332by the third inclined portion334of the coupling recess332and the motor housing330is moved upwards at the same time, the distance between the motor shaft221and the rack bar109becomes larger, increasing the tensional force of the belt230and, accordingly, preventing noise and damage to the belt230.

When the support body312passes through the guide hole326and is coupled to the coupling recess332, the second inclined portion314corresponding to the first inclined portion324is formed such that driving pulley280is moved away from the driven pulley290.

That is, the support body312has the second inclined portion314corresponding to the first inclined portion324of the guide hole326on any one of the upper surface and the lower surface thereof.

In addition, the support body312has a knob310that protrudes from an end in a direction in which a vertical width thereof becomes larger in an axial direction of the rack bar109.

In the rack type electric power steering apparatus, according to the first embodiment of the present invention, if the motor housing330is preliminarily coupled to the rack housing320as illustrated inFIG. 6Aand then the support body312is inserted into the guide hole326of the rack housing320as illustrated inFIG. 6B, the support body312having the second inclined portion314pushes the motor housing330upwards along the first inclined portion324of the rack housing320to be inserted into the guide hole326.

As illustrated inFIG. 6C, when the support body312is inserted and the motor housing330is moved upwards by the third inclined portion334of the motor housing330at the same time, and the tensional force of the belt230is increased in proportion to the distance h by which the motor housing330is moved along the inclined portion.

Accordingly, because the second inclined portion314of the support body312passing through the guide hole326is moved upwards along the first inclined portion324of the guide hole326and is inserted into the coupling recess332, the motor housing330is moved upwards and the distance between the motor shaft221and the rack bar109becomes larger, increasing the tensional force of the belt230and, accordingly, preventing noise and damage to the belt230.

If the support body312is inserted into the coupling recess332by the third inclined portion334of the coupling recess332and the motor housing330is moved upwards at the same time, the tensional force of the belt230increases as the distance between the motor shaft221and the rack bar109increases and, accordingly, noise and damage to the belt230can be prevented.

Here, as illustrated inFIG. 7, the inserted support body312may be fixed to the rack housing320through a fixing method such as bonding340, welding, or calking.

FIG. 8is a partially sectional view illustrating a process of coupling a support body to a rack housing and a motor housing in a rack type electric power steering apparatus according to a second embodiment of the present invention.

The second embodiment of the present invention is the same as the first embodiment of the present invention except for a guide hole426and a support body412, and thus only the structures and operations of the guide hole426and the support body412will be described.

As illustrated, in the rack type electric power steering apparatus, according to the second embodiment of the present invention, two or more first inclined portions424and two or more first flat portions422formed in the guide hole426are sequentially repeatedly formed inwards, and the support body412is configured such that second inclined portions414and second flat portions416are sequentially repeatedly formed to correspond to the first inclined portions424and the first flat portions422.

That is, in the guide hole426, a first flat portion422ahaving a constant vertical width is formed on one side in a direction in which the motor130is coupled, a first inclined portion424ais formed such that a vertical width thereof becomes larger as it goes from the first flat portion422ato an opposite side, and in turn, a first flat portion422bis formed from the first inclined portion424ato an opposite side and a first inclined portion424bis formed from the first flat portion422bto an opposite side such that a vertical width thereof becomes larger.

In the guide hole426, according to the embodiment of the present invention, three second inclined portions314and three first flat portions422are sequentially repeatedly formed, and also in the support body412corresponding to the guide hole426, three second inclined portions414and three second flat portions416are sequentially repeatedly formed.

That is, in the support body412, a second flat portion416ahaving a constant vertical width is formed on one side in a direction in which the motor130is coupled, a second inclined portion414ais formed such that a vertical width thereof becomes larger as it goes from the second flat portion416ato an opposite side, and in turn, a second flat portion416bis formed from the second inclined portion414ato an opposite side and a second inclined portion414bis formed such that a vertical width thereof becomes larger from the second flat portion416bto an opposite side.

In the guide hole426and the support body412formed in this way, because the inclined portions414and424and the flat portions416and422are repeatedly formed, the tensional force of the belt230can be adjusted in stages.

In the rack type electric power steering apparatus, according to the second embodiment of the present invention, if the motor housing430is preliminarily coupled to the rack housing420as illustrated inFIG. 8Aand then the support body412is inserted into the guide hole426of the rack housing420as illustrated inFIG. 8B, the support body412having the second inclined portions414pushes the motor housing430upwards along the first inclined portions424of the rack housing420to be inserted.

As illustrated inFIG. 8C, the support body412is inserted and the motor housing430is moved upwards by the third inclined portion434of the motor housing430, and the tensional force of the belt230is increased by the distance h by which the motor housing430is moved along the inclined portion.

Here, when the tensional force is high, a knob410of the support body412is pulled to fix the support body412to the rack housing420such that the upper second inclined portion414ais situated at the lower first inclined portion424band the upper second flat portion416ais situated at the lower first flat portion422b.

FIG. 9is a partially sectional view illustrating a state in which a support body is coupled to a rack housing and a motor housing in a rack type electric power steering apparatus according to a third embodiment of the present invention.

The third embodiment of the present invention is the same as the first embodiment of the present invention except for a guide hole526and a support body512, and thus, only the structures and operations of the guide hole526and the support body512will be described.

As illustrated inFIG. 9, the rack type electric power steering apparatus, according to the third embodiment of the present invention, further includes a fixing part528that is coupled to, or formed at, an end in a direction in which a vertical width of the guide hole526becomes larger, and a plug550that is coupled to the fixing part528while supporting the support body512.

That is, the fixing part528having a female screw portion560ais coupled to, or formed at, an end of the guide hole526in a direction in which a vertical end thereof becomes larger, and the plug550having a male screw portion560bis coupled to the female portion560aof the fixing part528to support the support body512.

Alternatively, a male screw portion may be formed in the fixing part528and a female screw portion may be formed in the plug550so that the plug550may be coupled to the fixing part528and the plug550may be press-fitted with the fixing part528.

Thereafter, a fixing recess510is formed on a surface of the support body512that faces the plug550, and a fixing boss552inserted into the fixing recess510is formed in the plug550.

Accordingly, because the fixing boss552of the plug550is inserted into the fixing recess510of the support body512, the support body512is supported by the rack housing520without being moved, thereby more firmly supporting the motor housing530.

Furthermore, because a coupling tool recess554is formed on a surface opposite to the surface on which the fixing boss552of the plug550is formed and a coupling tool is inserted into the coupling tool recess554to fix the plug550, the plug550is firmly fixed to the fixing part528.

As described above, according to the present invention, because the second inclined portion of the support body passing through the guide hole is moved upwards along the first inclined portion to be inserted into the coupling recess, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger, and accordingly, noise and damage to the belt can be prevented.

Furthermore, if the support body is inserted into the coupling recess by the third inclined portion of the coupling recess and the motor housing is moved upwards, the tensional force of the belt becomes higher as the distance between the motor shaft and the rack bar becomes larger and, accordingly, noise and damage to the belt can be prevented.

Even if it was described above that all of the components of an embodiment of the present invention are coupled as a single unit or coupled to be operated as a single unit, the present invention is not necessarily limited to such an embodiment. That is, at least two elements of all structural elements may be selectively joined and operate without departing from the scope of the present invention. Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. The scope of the present invention shall be construed on the basis of the accompanying claims in such a manner that all of the technical ideas included within the scope equivalent to the claims belong to the present invention.