Abstract:
Disclosed are a rack-driven steering apparatus and a rack-driven auxiliary power steering apparatus including the same. The present invention can protect peripheral parts such as a motor for driving a nut pulley and an electronic control unit to improve durability when an excessive load reversely input from the outside is transmitted during an operation of a belt by the motor, and prevent a steering disabling state during a high speed travel of the vehicle, thereby providing a driver with a stable steering condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from and the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2011-0113702, filed on Nov. 3, 2011, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1.Field of the invention 
         [0003]    The present invention relates to a rack-driven steering apparatus and a rack-driven auxiliary power steering apparatus including the same, and more particularly to a rack-driven steering apparatus by which a steering force transmitted from the steering shaft to the rack bar can be transmitted more accurately and without loss, a separate rack bar supporting unit such as a support yoke and a yoke plug may not be employed, so that noise generated due to an increase of a gap caused by wear of the support yoke after the vehicle travels for a long time or generated by an impact reversely input from a road surface can be prevented and a comfortable steering feeling can be provided to the driver during the steering operation, and a rack-driven auxiliary power steering apparatus including the same. 
         [0004]    2. Description of the Prior Art 
         [0005]    As generally known in the art, a rack-driven auxiliary power steering apparatus includes a steering system extending from a steering wheel to two wheels, and an auxiliary power apparatus for supplying auxiliary steering power to the steering system. 
         [0006]      FIG. 1  is a partially sectional view schematically illustrating a general rack-driven auxiliary power steering apparatus, and  FIG. 2  is a sectional view schematically illustrating a portion of the general rack-driven auxiliary power steering apparatus. 
         [0007]    The general rack-driven auxiliary power steering apparatus includes a steering system  100  extending from a steering wheel  105  to two wheels  150 , and an auxiliary power apparatus  160  for supplying auxiliary steering power to the steering system  160 . 
         [0008]    The steering system  100  includes a steering shaft  110  an upper end of which is connected to the steering wheel  105  to be rotated together with the steering wheel  105  and a lower end of which is connected to a pinion shaft  120  via a pair of universal joints  115 . The pinion shaft  120  is connected to a rack bar  155  through a rack-pinion mechanism  135 , and opposite ends of the rack bar  155  are connected to the wheels  150  of the vehicle through tie rods  140  and knuckle arms  145 . 
         [0009]    In the rack-pinion mechanism  135 , a pinion gear  125  formed at a lower end of the pinion shaft  120  and a rack gear  130  formed at one side of an outer peripheral surface of the rack bar  155  are engaged with each other. 
         [0010]    The auxiliary power apparatus  160  includes a torque sensor  117  for detecting a steering torque applied to the steering wheel  105  by a driver and outputting an electric signal proportional to the detected steering torque, an electronic control unit (ECU) for generating a control signal based on the electric signal transferred from the torque sensor  117 , a motor  165  for generating auxiliary steering power based on the control signal transferred from the electronic control unit, and an auxiliary power unit  170  for transmitting the auxiliary power generated by the motor  165  via a belt  210 . 
         [0011]    A rack bar supporting unit according to the related art includes a pinion gear  125 , a rack bar  155 , a support yoke  260 , a spring  263 , and a yoke plug  265 . A rack-pinion type gearbox  210  converts a rotating force input from the steering shaft (not illustrated) as described above into linear movement. 
         [0012]    The rack bar  155  is engaged with the pinion gear  125  to convert rotation into linear movement, and a unit for supporting the rack bar  155  toward the pinion gear  125  is installed on a rear surface of the rack bar  155  so that the rack bar  155  and the pinion gear  125  can be smoothly engaged with each other. 
         [0013]    The unit for supporting the rack bar  155  includes a support yoke  260 , a spring  263 , and a yoke plug  265 , and the support yoke  260  is located on a rear side of the rack bar  155 , that is, at a side opposite to a surface where the rack gear  110  is formed, and is inserted into a cylinder  250  of the gearbox  130  to be moved in a forward/rearward direction perpendicular to the rack bar  155 . 
         [0014]    The support yoke  260  has a cylindrical shape to be slid forward and rearward in the cylinder  250 , and a front part of the support yoke  260  in contact with the rack bar  155  forms a semicircular recess to be attached to a rear side of the rack bar  155 . 
         [0015]    A spring  263  is disposed at a rear side of the support yoke  260  so that the rack bar  155  and the pinion gear  125  are attached to each other to effectively transmit a force, pushing the support yoke  260  with a predetermined pressure and compensating a gap generated between the rack bar  155  and the pinion gear  125 . 
         [0016]    The support yoke  260  frictionally slid with respect to a rear surface of the rack bar  155 , and is formed of a plastic softer than a general rack bar  155  to prevent the rack bar  155  from being worn out or generating noise due to friction. 
         [0017]    The spring  263  accommodated in a spring groove  220  applies a pressure so that the support yoke  260  and the rack bar  155  are attached to each other and is generally a coil spring, and a yoke plug  265  is located on a rear surface of the spring  263  to support the spring  263 . 
         [0018]    The yoke plug  265  supports the spring  263  to apply a pressure to the support yoke  260 . Screw threads and roots are formed in the yoke plug  265  to be fixedly coupled to the gearbox  210  and lock nuts  240  having threads and roots engaged with the threads and roots of the yoke plug  265 . 
         [0019]    However, in the rack-driven auxiliary power steering apparatus, an engaging force between the pinion gear and the rack gear is low due to a resilient deformation of the rack bar caused by a considerably long shape of the rack bar, making it essential to employ a rack bar supporting unit. 
         [0020]    Further, in the rack bar supporting unit according to the related art, if the support yoke is worn out to a degree, a gap is increased, making it difficult to properly support the rack bar. 
         [0021]    In addition, a rattle noise may be generated in the support yoke and the yoke plug due to an increase in a gap between the rack bar and the support yoke. 
         [0022]    Furthermore, impact noise may be generated as an impact load reversely input from a road surface is not absorbed when the vehicle travels on a rough road such as an unpaved road, and in severe cases, the support yoke or the yoke plug may be damaged. 
       SUMMARY OF THE INVENTION 
       [0023]    Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a rack-driven steering apparatus by which a steering force transmitted from the steering shaft to the rack bar can be transmitted more accurately and without loss, a separate rack bar supporting unit such as a support yoke and a yoke plug may not be employed, so that noise generated due to an increase of a gap caused by wear of the support yoke after the vehicle travels for a long time or generated by an impact reversely input from a road surface can be prevented and a comfortable steering feeling can be provided to the user during the steering operation, and a rack-driven auxiliary power steering apparatus including the same. 
         [0024]    In order to accomplish this object, there is provided a rack-driven steering apparatus including: a first gear provided at a lower end of a steering shaft; a ball nut having one end provided with a second gear engaged with the first gear and having a screw groove on an inner periphery surface thereof to transmit a steering force of the steering shaft to a rack bar; and a rack bar coupled to an inner side of the ball nut and having a second screw groove corresponding to the first screw groove on an outer peripheral surface thereof to be slid during rotation of the ball nut. 
         [0025]    In accordance with another aspect of the present invention, there is provided a rack-driven auxiliary power steering apparatus including: a first gear provided at a lower end of a steering shaft; a ball nut having one end provided with a second gear engaged with the first gear and having a first screw groove on an inner peripheral surface thereof to transmit a steering force of the steering shaft to a rack bar; a rack bar coupled to an inner side of the ball nut and having a second screw groove corresponding to the first screw groove on an outer peripheral surface thereof to be slid during rotation of the ball nut; a motor for generating an auxiliary steering force; and a nut pulley coupled to an outer peripheral surface of the ball nut such that the ball nut is rotated by a driving force of a belt driven by the motor, to transmit the auxiliary steering force. 
         [0026]    According to the present invention, a steering force transmitted from the steering shaft to the rack bar can be transmitted more accurately and without loss, a separate rack bar supporting unit such as a support yoke and a yoke plug may not be employed, so that noise generated due to an increase of a gap caused by wear of the support yoke after the vehicle travels for a long time or generated by an impact reversely input from a road surface can be prevented and a comfortable steering feeling can be provided to the user during the steering operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0028]      FIG. 1  is a partially sectional view schematically illustrating a general rack-driven auxiliary power steering apparatus; 
           [0029]      FIG. 2  is a sectional view schematically illustrating a portion of the general rack-driven auxiliary power steering apparatus; 
           [0030]      FIGS. 3 and 4  are sectional views illustrating portions of a rack-driven steering apparatus according to the present invention; 
           [0031]      FIG. 5  is a perspective view illustrating a portion of a rack-driven auxiliary power steering apparatus according to the present invention; and 
           [0032]      FIG. 6  is a sectional view of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same elements will be designated by the same reference numerals although they are shown in different drawings. Further, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. 
         [0034]    In addition, terms, such as first, second, A, B, (a), (b) or the like may be used herein when describing components of the present invention. Each of these terminologies is not used to define an essence, order or sequence of a corresponding component but used merely to distinguish the corresponding component from other component(s). 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. 
         [0035]      FIGS. 3 and 4  are sectional views illustrating portions of a rack-driven steering apparatus according to the present invention.  FIG. 5  is a perspective view illustrating a portion of a rack-driven auxiliary power steering apparatus according to the present invention.  FIG. 6  is a sectional view of  FIG. 5 . 
         [0036]    As illustrated in the drawings, the rack-driven steering apparatus according to the present invention includes: a first gear  307  provided at a lower end of a steering shaft  305 ; a ball nut  311  having one end provided with a second gear  309  engaged with the first gear  307  and having a screw groove  311   a  on an inner periphery surface thereof to transmit a steering force of the steering shaft  305  to a rack bar  303 ; and a rack bar  303  coupled to an inner side of the ball nut  311  and having a second screw groove  303   a  corresponding to the first screw groove  311   a  on an outer peripheral surface thereof to be slid during rotation of the ball nut  311 . 
         [0037]    The rack-driven auxiliary power steering apparatus according to the present invention includes: a first gear  307  provided at a lower end of a steering shaft  305 ; a ball nut  311  having one end provided with a second gear  309  engaged with the first gear  307  and having a first screw groove  311   a  on an inner peripheral surface thereof to transmit a steering force of the steering shaft  305  to a rack bar  303 ; a rack bar  303  coupled to an inner side of the ball nut  311  and having a second screw groove  303   a  corresponding to the first screw groove  311   a  on an outer peripheral surface thereof to be slid during rotation of the ball nut  311 ; a motor  320  for generating an auxiliary steering force; and a nut pulley  315  coupled to an outer peripheral surface of the ball nut  311  such that the ball nut  311  is rotated by a driving force of a belt  319  driven by the motor  320 , to transmit the auxiliary steering force. 
         [0038]    Unlike the related art where a pinion gear (see  125  of  FIG. 1 ) is engaged with a rack gear (see  130  of  FIG. 1 ) of a rack bar  303 , the first gear  307  provided at a lower end of the steering shaft  305  is spaced apart from the rack bar  303  by a predetermined distance, and an outer peripheral surface thereof, a diameter of which is expanded, is formed at a lower end of the steering shaft  305  to be inclined toward the steering shaft  305  and gear teeth are formed on the inclined outer peripheral surface of the first gear  307 . 
         [0039]    That is, the steering shaft  305  and the rack bar  303  are not coupled to each other and are installed at a predetermined angle to be spaced apart from each other, and the first gear  307  provided at a lower end of the steering shaft  305  is engaged with the second gear  309  of the ball nut  311  coupled to the rack bar  303  to transmit a rotating force of the steering shaft  305  to the ball nut  311 . 
         [0040]    Thus, an engaging force between the first gear  307  and the second gear  309  is enhanced, while improving power transmission performance without requiring a separate rack bar supporting unit including the support yoke (see  260  of  FIG. 2 ) and the yoke plug (see  265  of  FIG. 2 ) according to the related art. 
         [0041]    The first gear  307  may be separately formed to be coupled to the steering shaft  305  or a lower end of the steering shaft  305  may be machined to be integrally formed with the steering shaft  305 , and gear teeth of the first gear  307  are formed on the inclined outer peripheral surface of a lower end of the steering shaft  305  in a linear form in a direction of the steering shaft  305  or in a spiral form inclined at a predetermined angle. 
         [0042]    The ball nut  311  is coupled to the rack bar  303  via balls (not illustrated) to slide the rack bar  303  in the rack housing while rotating, and the nut pulley  315  for rotating the ball nut  311  and a bearing  313  for supporting rotation of the ball nut  311  are mounted to an outer peripheral surface of the ball nut  311 . 
         [0043]    A power transmitting structure for axially sliding the rack bar  303  to generate an auxiliary steering force is provided on an inner peripheral surface of the ball nut  311  and an outer peripheral surface of the rack bar  303 , and the power transmitting structure includes the second screw groove  303   a  formed on an outer peripheral surface of the rack bar  303  in a spiral form to have a semispherical or arc shape, balls (not illustrated) inserted thereinto, and the first screw groove  311   a  corresponding to the second screw groove  303   a  formed on an inner peripheral surface of the ball nut  311  in a spiral form to have a semispherical or arc shape. 
         [0044]    The ball nut  311  is a hollow tube having the first screw groove  311   a  on an inner peripheral surface thereof, and the bearing  313  is installed on an outer peripheral surface thereof to be supported by and fixed to the rack housing  301 . 
         [0045]    The second gear  309  engaged with the first gear  307  is provided at one end of the ball nut  311 , and the second gear  309  is formed at one end of the ball nut  311  to be inclined toward a center axis of the rack bar  303  and gear teeth are formed at the inclined end of the ball nut  311 . 
         [0046]    The second gear  309  may be separately formed to be coupled to one end of the ball nut  311  or one end of the ball nut  311  may be machined so that the second gear  309  is integrally formed with the ball nut  311 , and the second gear  309  is formed at the inclined end of the ball nut  311  of the second gear  309  in a linear form in a center axis direction of the rack bar  303  or in a spiral form inclined at a predetermined angle with respect to a center axis direction of the rack bar  303 . 
         [0047]    The first gear  307  and the second gear  309  may be bevel gears as the installation angles of the steering shaft  305  and the rack bar  303  are substantially perpendicular to each other. 
         [0048]    That is, bevel gears may be coupled to or integrally formed with a lower end of the steering shaft  305  and one end of the ball nut  311 . 
         [0049]    Meanwhile, the above-described rack-driven steering apparatus may further include an auxiliary power unit to constitute the rack-driven auxiliary power steering apparatus. 
         [0050]    That is, the rack-driven auxiliary power steering apparatus according to the present invention includes: a first gear  307  provided at a lower end of a steering shaft  305 ; a ball nut  311  having one end provided with a second gear  309  engaged with the first gear  307  and having a first screw groove  311   a  on an inner peripheral surface thereof to transmit a steering force of the steering shaft  305  to a rack bar  303 ; a rack bar  303  coupled to an inner side of the ball nut  311  and having a second screw groove  303   a  corresponding to the first screw groove  311   a  on an outer peripheral surface thereof to be slid during rotation of the ball nut  311 ; a motor  320  for generating an auxiliary steering force; and a nut pulley  315  coupled to an outer peripheral surface of the ball nut  311  such that the ball nut  311  is rotated by a driving force of a belt  319  driven by the motor  320 , to transmit the auxiliary steering force. 
         [0051]    Here, the auxiliary power unit includes a driving unit and a driven unit, and the driving unit includes a motor  320  controlled by an electronic control unit (ECU)  330 , a motor pulley  317  coupled to a shaft  321  of the motor  320 , and a belt  319 . 
         [0052]    The driven unit includes a ball nut  311  supporting the rack bar  303  in the rack housing  301  surrounding the rack bar  303 , and a nut pulley  315  coupled to an outer peripheral surface of the ball nut  311 . 
         [0053]    The motor pulley  317  connected to the motor  320 , and the nut pulley  315  connected to the rack bar  303  are disposed parallel to each other, the belt  319  is mounted on the motor pulley  317  and the nut pulley  315  to transmit a rotating force of the motor  320  to the rack bar  303  through the ball nut  311 , and the rack bar  303  is moved leftward and rightward by an operation of the ball nut  311  to generate an auxiliary steering force. 
         [0054]    The ball nut  311  is coupled to the rack bar  303  via balls to slide the rack bar  303  in the rack housing while rotating, and the nut pulley  315  for rotating the ball nut  311  and the bearing  313  for supporting rotation of the ball nut  311 , are mounted to an outer peripheral surface of the ball nut  311 . 
         [0055]    The above-described auxiliary power unit may further include: a torque sensor (see  117  of  FIG. 1 ) for outputting an electric signal proportional to a steering torque when a driver manipulates the steering wheel; and an electronic control unit  330  for generating an auxiliary steering control signal based on an electric signal transferred from the torque sensor to transmit the auxiliary steering control signal to the motor  320 . 
         [0056]    Thus, the torque sensor detects a steering torque generated when a driver manipulates the steering wheel, and the electronic control unit transmits the auxiliary steering control signal to the motor based on the steering torque to supplement a steering force of the driver. 
         [0057]    As described above, according to the present invention, a steering force transmitted from the steering shaft to the rack bar can be transmitted more accurately and without loss, a separate rack bar supporting unit such as a support yoke and a yoke plug may not be employed, so that noise generated due to an increase of a gap caused by wear of the support yoke after the vehicle travels for a long time or generated by an impact reversely input from a road surface can be prevented and a comfortable steering feeling can be provided to the user during the steering operation. 
         [0058]    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, among the components, one or more components may be selectively coupled to be operated as one or more units. 
         [0059]    In addition, since terms, such as “including,” “comprising,” and “having” mean that one or more corresponding components may exist unless they are specifically described to the contrary, it shall be construed that one or more other components can be included. All of the terminologies containing one or more technical or scientific terminologies have the same meanings that persons skilled in the art understand ordinarily unless they are not defined otherwise. A term ordinarily used like that defined by a dictionary shall be construed that it has a meaning equal to that in the context of a related description, and shall not be construed in an ideal or excessively formal meaning unless it is clearly defined in the present specification. 
         [0060]    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. Therefore, the embodiments disclosed in the present invention are intended to illustrate the scope of the technical idea of the present invention, and the scope of the present invention is not limited by the embodiment. 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.