Patent Publication Number: US-2023159089-A1

Title: Rack assist type power sterring apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit and priority from Korean Patent Application No. 10-2021-0160385, filed in the Republic of Korea on Nov. 19, 2021, the entire contents of which are hereby incorporated by reference for all purposes as if fully set forth into the present application. 
     BACKGROUND 
     Field of the Disclosure 
     Embodiments of the present disclosure relate to a rack assist type power steering apparatus. More specifically, in the present embodiments, the nut pulley and bearing will not be separated from the ball nut, deformed or damaged even if the vehicle is continuously steered while driving. And the present embodiments prevent the slip of the nut pulley due to an impact transmitted from the road surface or an excessive load during operation, thereby transmitting accurate steering assistance force to the ball nut. 
     Description of the Related Art 
     A general rack assist type power steering apparatus includes a steering system that extends from the steering wheel to both road wheels and an auxiliary power mechanism that supplies steering assistance power to the steering system. 
     Such a conventional rack assist type power steering apparatus includes a motor controlled by an electronic control device, a motor pulley fixed to the motor shaft, a ball nut that combines with a rack bar through a ball, a return tube coupled to a ball nut and circulating the ball, a nut pulley coupled to the outer circumferential surface of the ball nut, a belt coupled to the motor pulley and the nut pulley. 
     However, this rack assist type power steering apparatus had problems in that the nut pulley or the bearing is detached, deformed or damaged due to the vibration generated by continuous steering while driving and the impact transmitted from the road surface. 
     In addition, this rack assist type power steering apparatus had problems in that the nut pulley slips due to an impact transmitted from the road surface or an excessive load during operation, so that the steering assistance power is lowered and the efficiency of power transmission is lowered, so that the accurate steering assistance force cannot be transmitted. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of the present disclosure provide a rack assist type power steering apparatus in which the nut pulley and bearing will not be separated from the ball nut, deformed or damaged even if the vehicle is continuously steered while driving. And the present embodiments prevent the slip of the nut pulley due to an impact transmitted from the road surface or an excessive load during operation, thereby transmitting accurate steering assistance force to the ball nut. 
     A rack assist type power steering apparatus according to the embodiments of the present disclosure may comprise a rack bar provided with an outer screw groove on an outer circumferential surface, a ball nut having an inner screw groove corresponding to the outer screw groove on an inner circumferential surface, and a bearing coupled to an outer circumferential surface, and a nut pulley provided with a belt coupling portion on an outer peripheral surface, and one end of an inner circumferential surface is provided with a support end coupled to an outer circumferential surface of the ball nut to support the bearing, and an other end of an inner circumferential surface is provided with an enlarged diameter portion which is stepped from the support end and increases in inner diameter. 
     According to the embodiments of the present disclosure, there is provided a rack assist type power steering apparatus in which the nut pulley and bearing will not be separated from the ball nut, deformed or damaged even if the vehicle is continuously steered while driving. And the present embodiment provides a rack assist type power steering apparatus capable of transmitting an accurate steering assist force to the ball nut by preventing slippage of the nut pulley due to an impact transmitted from the road surface or excessive load during operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a schematic view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure; 
         FIG.  2    is a perspective view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure; 
         FIGS.  3  and  4    are exploded perspective views illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure; 
         FIG.  5    is a perspective view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure; 
         FIGS.  6  and  7    are cross-sectional views illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure; 
         FIG.  8    is an exploded perspective view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure; 
         FIGS.  9  and  10    are cross-sectional views illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples or embodiments of the present disclosure, reference will be made to the accompanying drawings in which it is shown byway of illustration specific examples or embodiments that can be implemented, and in which the same reference numerals and signs can be used to designate the same or like components even when they are shown in different accompanying drawings from one another. Further, in the following description of examples or embodiments of the present disclosure, detailed descriptions of well-known functions and components incorporated herein will be omitted when it is determined that the description may make the subject matter in some embodiments of the present disclosure rather unclear. The terms such as “including”, “having”, “containing”, “constituting” “make up of”, and “formed of” used herein are generally intended to allow other components to be added unless the terms are used with the term “only”. As used herein, singular forms are intended to include plural forms unless the context clearly indicates otherwise. 
     Terms, such as “first”, “second”, “A”, “B”, “(A)”, or “(B)” may be used herein to describe elements of the disclosure. Each of these terms is not used to define essence, order, sequence, or number of elements etc., but is used merely to distinguish the corresponding element from other elements. 
     When it is mentioned that a first element “is connected or coupled to”, “contacts or overlaps” etc. a second element, it should be interpreted that, not only can the first element “be directly connected or coupled to” or “directly contact or overlap” the second element, but a third element can also be “interposed” between the first and second elements, or the first and second elements can “be connected or coupled to”, “contact or overlap”, etc. each other via a fourth element. Here, the second element may be included in at least one of two or more elements that “are connected or coupled to”, “contact or overlap”, etc. each other. 
     When time relative terms, such as “after,” “subsequent to,” “next,” “before,” and the like, are used to describe processes or operations of elements or configurations, or flows or steps in operating, processing, manufacturing methods, these terms may be used to describe non-consecutive or non-sequential processes or operations unless the term “directly” or “immediately” is used together. 
     In addition, when any dimensions, relative sizes etc. are mentioned, it should be considered that numerical values for an elements or features, or corresponding information (e.g., level, range, etc.) include a tolerance or error range that may be caused by various factors (e.g., process factors, internal or external impact, noise, etc.) even when a relevant description is not specified. Further, the term “may” fully encompasses all the meanings of the term “can”. 
       FIG.  1    is a schematic view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure;  FIG.  2    is a perspective view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure;  FIGS.  3  and  4    are exploded perspective views illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure;  FIG.  5    is a perspective view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure;  FIGS.  6  and  7    are cross-sectional views illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure;  FIG.  8    is an exploded perspective view illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure;  FIGS.  9  and  10    are cross-sectional views illustrating a rack assist type power steering apparatus according to the embodiments of the present disclosure. 
     Referring to  FIGS.  1  to  10   , a rack assist type power steering apparatus according to the embodiments of the present disclosure may include a rack bar  120  provided with an outer screw groove  120   a  on an outer circumferential surface, a ball nut  125  having an inner screw groove  127  corresponding to the outer screw groove  120   a  on an inner circumferential surface, and a bearing  140  coupled to an outer circumferential surface, and a nut pulley  130  provided with a belt coupling portion  131  on an outer peripheral surface, and one end of an inner circumferential surface is provided with a support end  133  coupled to an outer circumferential surface of the ball nut  125  to support the bearing  140 , and an other end of an inner circumferential surface is provided with an enlarged diameter portion  135  which is stepped from the support end  133  and increases in inner diameter. 
     In the rack assist type power steering apparatus according to the present embodiments, the torque sensor  103  is coupled to one side of the steering shafts  102  and  106  connected to the steering wheel  101 , and when the driver operates the steering wheel  101 , the electric signals received from the torque sensor  103 , the steering angle sensor  121 , the vehicle speed sensor  122 , etc. that detect it are sent to the motor  113  and steer the both side wheel  115  through the tie rod  119 . 
     In the rack assist type power steering apparatus according to the present embodiments, the upper steering shaft  102  is connected to the lower steering shaft  106  through the universal joint  104 , and steering is performed through the rack-and-pinion mechanism  116  including the pinion  108  and the rack gear  112 . 
     Here, the driving force of the motor  113  driven by the electronic controller  111  is transmitted to the ball nut  125  through the motor  113  and the belt  150 , and the rack bar  120  coupled to the ball nut  125  through the ball slides in the axial direction. And a tie rod  119  is coupled to both sides of the rack bar  120 , and the tie rod  119  is coupled to a knuckle arm  117  connected to the wheel  115  to steer the wheel  115 . 
     Then, the electrical signal generated from the torque sensor  103  is sent to the electronic controller  111 , and the electronic controller  111  controls the motor  113  based on the electric signals transmitted from the torque sensor  103  and the electric signals transmitted from the steering angle sensor  121  and the vehicle speed sensor  122  mounted on the vehicle. 
     A power transmission structure is provided on the inner circumferential surface of the ball nut  125  and the outer circumferential surface of the rack bar  120  to generate a steering assist force by sliding the rack bar  120  in the axial direction. This power transmission structure includes an outer screw groove  120   a  having a hemispherical or arc-shaped cross section on the outer circumferential surface of the rack bar  120  and formed in a spiral shape, a ball inserted therein, and an inner screw groove  125   a  having a hemispherical or arc-shaped cross section on the inner circumferential surface of the ball nut  125  to correspond to the outer circumferential screw groove  120   a  and spirally formed. 
     In the ball nut  125  having an inner screw groove  127  formed on the inner circumferential surface, several ball circulation holes  129  penetrating the inner circumferential and outer circumferential surfaces are spaced apart along the inner screw groove  127 . 
     Accordingly, the balls rolling along the inner screw groove  127  can be circulated through a circulation tube or an end cap coupled to the ball circulation hole  129 , and the bearing  140  supported by a rack housing is coupled to one side to support the rotation of the ball nut  125 . 
     The nut pulley  130  is provided on the outer peripheral side of the ball nut  125 , a belt coupling portion  131  is provided on the outer peripheral surface of the nut pulley  130 , and when the belt rotates, the nut pulley  130  rotates the ball nut  125  to linearly move the rack bar  120  left and right. 
     One end of the inner peripheral surface of the nut pulley  130  is provided with a support end  133  coupled to the other outer peripheral surface of the ball nut  125  to support the bearing  140 . The other end of the inner peripheral surface of the nut pulley  130  is provided with an enlarged diameter portion  135  that is stepped from the support end  133  and has an enlarged inner diameter. 
     A pulley screw portion  134  is formed on an inner peripheral surface of the support end  133  and a nut screw portion  128  is formed on an outer peripheral surface of the ball nut  125 , so that the pulley screw portion  134  is screwed with the nut screw portion  128 . 
     Further, the ball nut  125  has a fixing groove  124  formed on the outer peripheral surface of the other end to which the nut pulley  130  is coupled, so that the ball nut  125  is caulked and fixed with the end of the support end  133  of the nut pulley  130 . 
     The end of the support end  133  of the nut pulley  130  is formed at the same position in the axial direction as the end of the ball nut  125  or is formed to protrude more in the axial direction than the end of the ball nut  125 . 
     The caulking is performed by pressing the end of the support end  133  positioned above or below the fixing groove  124  in the drawing, which is the end of the support end  133  positioned opposite to the circumferential direction of the fixing groove  124  with a caulking tool and plastically deform it. And, it is fixed by filling the inside of the fixing groove  124  with the end of the support end  133 . 
     Therefore, when the ball nut  125  and the nut pulley  130  are combined, they are fixed to the fixing groove  124  so that the nut pulley  130  does not slip in the ball nut  125 . The driving force transmitted through the belt  150  can be accurately transmitted. 
     Here, the fixing grooves  124  may be one or more, and when two or more are provided, they are arranged at equal intervals in the circumferential direction of the ball nut  125 . Accordingly, it is possible to distribute the load applied to the caulking portion by equally distributing the positions at which the nut pulley  130  is fixed. 
     In the present embodiments, two fixing grooves  124  are provided and are arranged at equal intervals in the circumferential direction, and are shown as an example in a position facing each other in the radial direction. 
     And, the support end  133  is formed to protrude in the axial direction with a step difference in the radial direction from the belt coupling portion  131  to support one end of the inner race of the bearing  140  in the axial direction. 
     A tool coupling portion  137  to which a tool is coupled is formed on the outer peripheral surface of the support end  133 , so that when the nut pulley  130  is coupled to the ball nut  125 , a fastening tool is mounted on the tool coupling portion  137  to facilitate screw assembly. 
     And, on the outer peripheral surface of the ball nut  125 , a support protrusion  126  for supporting the other end of the inner ring of the bearing  140  in the axial direction is formed. Therefore when the nut pulley  130  is screwed to the ball nut  125 , one end of the inner ring of the bearing  140  is supported by the support end  133 , the other end of the bearing  140  is supported by the support protrusion  126  so that the bearing  140  is coupled without slipping at the fixed position. 
     In addition, as shown in  FIG.  7   , the ball nut  125  is provided with a fastening groove  128   a  formed in the circumferential direction on the outer peripheral surface of the other end to which the nut pulley  130  is coupled, the fastening member  150  may be coupled and fixed to the fastening groove  128   a.    
     Here, the fastening member  150  is formed in a ring shape with one side cut out and is coupled to the fastening groove  128   a  and supported by the end of the support end  133 , so that the nut pulley  130  is fixed so as not to move in the axial direction and prevents the screw from loosening. 
     In addition, as shown in  FIGS.  8  to  10   , the nut pulley  130  may have an inner peripheral surface of the support end  133  press-fitted to an outer peripheral surface of the ball nut  125 . 
     As shown in  FIG.  9   , the ball nut  125  has a fixing groove  124  formed on the outer peripheral surface of the other end of the ball nut  125  to which the nut pulley  130  is coupled, so that the end of the support end  133  of the nut pulley  130  maybe caulked and fixed. 
     Here, the fixing grooves  124  may be one or more, and when two or more are provided, they are arranged at equal intervals in the circumferential direction of the ball nut  125 . 
     And, as shown in  FIGS.  8  and  10   , ball nut  125  is provided with a fastening groove  128   a  formed in the circumferential direction on the outer peripheral surface of the other end to which the nut pulley  130  is coupled, and the fastening member  150  may be coupled to the fastening groove  128   a.    
     Here, as shown in  FIG.  8   , the fastening member  150  is formed in a ring shape with one side cut out, and the fastening member  150  is coupled to the fastening groove  128   a  and supported at the end of the support end  133 . 
     Accordingly, the nut pulley  130  is fixed so as not to move in the axial direction, and the slip of the nut pulley  130  is prevented. 
     In addition, the support end  133  is formed to protrude in the axial direction with a step difference in the radial direction from the belt coupling portion  131  to support one end of the inner race of the bearing  140  in the axial direction. A support protrusion  126  for axially supporting the other end of the inner race of the bearing  140  may be formed on the outer peripheral surface of the ball nut  125 . 
     Therefore, when the nut pulley  130  is press-fitted to the ball nut  125 , one end of the inner race of the bearing  140  is supported by the support end  133  and the other end of the bearing  140  is supported by the support protrusion  126 . Therefore the bearing  140  can be coupled without slipping at the position. 
     According to the embodiments of the present disclosure, there is provided a rack assist type power steering apparatus in which the nut pulley and bearing will not be separated from the ball nut, deformed or damaged even if the vehicle is continuously steered while driving. And the present embodiment provides a rack assist type power steering apparatus capable of transmitting an accurate steering assist force to the ball nut by preventing slippage of the nut pulley due to an impact transmitted from the road surface or excessive load during operation. 
     The above description has been presented to enable any person skilled in the art to make and use the technical idea of the present disclosure, and has been provided in the context of a particular application and its requirements. Various modifications, additions and substitutions to the described embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. The above description and the accompanying drawings provide an example of the technical idea of the present disclosure for illustrative purposes only. That is, the disclosed embodiments are intended to illustrate the scope of the technical idea of the present disclosure. Thus, the scope of the present disclosure is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the claims. The scope of protection of the present disclosure should be construed based on the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included within the scope of the present disclosure.