Patent Publication Number: US-2007095600-A1

Title: Belt-type transmission and electric power steering apparatus having the same

Description:
RELATED APPLICATION  
      This application claims priority to Korean Patent Application No. 2005-98474 filed on Oct. 19, 2005.  
     FIELD OF THE INVENTION  
      The present invention relates to a belt-type transmission and an electric power steering apparatus of an automobile having the same. More particularly, the present invention relates to a belt-type transmission having a tensioner arranged inside and in contact with a belt, which connects a drive shaft to a driven shaft, in order to adjust the tension of the belt without additional support structure for the tensioner, thereby reducing the number of parts and saving manufacturing cost, as well as an electric power steering apparatus of an automobile having the same.  
     BACKGROUND OF THE INVENTION  
      Although hydraulic power steering apparatuses which function by way of a hydraulic pump are generally used the a power steering apparatus of an automobile, the use of electric power steering apparatuses which function by way of an electric motor has been gradually on the rise since the 1990s.  
      A conventional hydraulic power steering apparatus has a hydraulic pump or a steering power source actuated by an engine, and thus consumes energy incessantly, irrespective of the rotation of a steering wheel. In an electric power steering apparatus, an electric motor supplies steering power in proportion to steering torque, when it is generated by the rotation of a steering wheel. Accordingly, the use of the electric power steering apparatus can enhance energy efficiency when it is used instead of the hydraulic power steering apparatus.  
       FIG. 1  is a diagram of a conventional electric power steering apparatus of an automobile.  
      As shown in  FIG. 1 , the electric power steering apparatus of an automobile generally includes a steering system  100  starting from a steering wheel  101  to both wheels  108 , as well as a steering power mechanism  120  for supplying steering power to the steering system  100 .  
      The steering system  100  includes a steering shaft  102  with the top connected to the steering wheel  101 , such that the steering shaft  102  can be rotated along with the steering wheel  101 . The steering shaft  102  is also connected at the bottom to a pinion shaft  104  via a pair of universal joints  103 . The pinion shaft  104  is connected to a rack bar  109  via a rack-pinion mechanism  105 , and both ends of the rack bar  109  are connected to the wheels  108  of the vehicle via tie rods  106  and knuckle arms  107 .  
      The rack-pinion mechanism  105  includes a pinion gear  111  and a rack gear  112  meshed with each other, in which the pinion gear  111  is provided at the bottom of the pinion shaft  104  and the rack gear  112  is formed on the rack bar  109 . The rack-pinion mechanism  105  converts the rotation of the pinion shaft  104  into the linear movement of the rack bar  109 . Accordingly, when a driver manipulates the steering wheel  101 , the pinion shaft  104  is rotated giving linear movement to the rack bar  109 , which in turn steers the wheels  108  via the tie rods  106  and the knuckle arms  107 .  
      The steering power mechanism  120  includes a torque sensor  121  for the detection of steering torque applied to the steering wheel by a driver. The torque sensor produces an electric signal in proportion to the detected steering torque. The steering power mechanism  120  also includes an Electronic Control Unit (ECU)  123  for generating a control signal in response to the electric signal from the torque sensor  121 ; a motor for generating steering power in response to the control signal from the ECM  123 ; and a belt-type transmission  140  for transmitting steering power from the motor  130  to the rack bar  109  via a belt.  
      Accordingly, the electric power steering apparatus is constructed so that the steering torque generated by the rotation of the steering wheel  101  is delivered to the rack bar  109  through the rack-pinion mechanism  105 ; and the steering power generated by the motor  130  in response to the steering torque is delivered to the rack bar  109  via the belt-type transmission  140 . That is, the steering torque generated by the steering system  100  is combined with the steering power generated by the motor  130  to make the rack bar  109  move along the axis.  
       FIG. 2  is a side-elevational view of a conventional electric power steering apparatus of an automobile, the illustration is partially in cross-section.  
      As shown in  FIG. 2 , the conventional electric power steering apparatus of an automobile includes a rack bar  109  extended across the vehicle with a rack gear formed on the outer periphery thereof, a pinion shaft  104  having a pinion gear meshed with the rack gear, a ball screw  210  having a ball nut  204  meshed with the ball screw  203  via balls  201 , a belt-type transmission  140  connecting the ball nut  205  to a motor shaft  221  and a motor  130 .  
      The pinion shaft  104  is connected to a steering wheel via a steering shaft, and the rack bar  109 , having a predetermined length of screw formed on the outer periphery, is received in a rack housing  223 . Furthermore, the rack housing  223  includes a first housing  225  in the rack gear side and a second housing  227  in the motor side.  
      The belt-type transmission  140  includes a belt for connecting the motor shaft  221  with the ball nut  205 . With the belt-type transmission  140 , steering power is generated by the motor  130  in proportion to steering torque applied to the steering wheel, and then is transmitted to the rack bar  109  via the ball nut  205 .  
      The belt-type transmission  140  is advantageous as it prevents any vibration or impact of the rack bar  109  from directly propagating to the motor  130 . However, as a drawback, change in belt tension caused by abrasion of the belt or pulley creates vibration in the belt, which in turn propagates to an automobile body making noises.  
      As an approach to overcome such a trouble in the art, a tensioner T which abuts against the outer surface of a belt is installed and adjusts the belt tension as shown in  FIG. 3 .  
      The tensioner T of the prior art includes a support protrusion  301  projected from a motor housing, a first support shaft  303  extended through the support protrusion  301 , a tensioner pulley  305  spaced from the support protrusion  301  at a predetermined distance, a second support protrusion  307  extended through the tensioner pulley  305 , a swing arm  309  connecting the first support shaft  303  to the second support shaft  307  and a torsion spring  311  pushing against the swing arm  309  in one direction.  
      The conventional tensioner T of this construction adjusts the tension of a belt  302  with the torsion spring  311 , which applies spring force to the swing arm  309  to push against the belt  302  from outside to inside.  
      However, there is a disadvantage in that the conventional approach needs a number of additional parts for the tensioner T, which complicates the fabrication process, and results in the increase of manufacturing cost.  
     SUMMARY OF THE INVENTION  
      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 arrange a tensioner inside and in contact with a belt in order to adjust the tension of the belt without the requirement of an additional support structure for the tensioner, thereby reducing the number of parts, simplifying the manufacturing process, and saving on manufacturing cost.  
      In order to accomplish this object, the invention provides a belt-type transmission including a rotatable drive shaft; a drive pulley coupled with the drive shaft; a rotatable driven shaft spaced from the drive shaft at a predetermined distance; a driven pulley coupled with the driven shaft; a belt connecting the drive shaft to the driven shaft; and a tensioner arranged inside and in contact with the belt.  
      In order to accomplish this object, the invention also provides an electric power steering apparatus of an automobile including a pinion shaft connected to a steering wheel of the vehicle, and having a pinion gear formed on one end; a rack bar connected to both wheels of the vehicle, and having a rack gear formed in one end part to mesh with the pinion gear and a ball screw formed in the other end part; a motor for generating steering power in proportion to steering torque generated by the steering wheel; a motor pulley coupled with a motor shaft of the motor; a ball nut meshing with the ball screw of the rack bar via a ball; a ball nut pulley provided on an outer periphery of the ball nut; a belt connecting the motor pulley to the ball nut pulley; and a tensioner arranged inside and in contact with the belt.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      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:  
       FIG. 1  is a diagram of a conventional electric power steering apparatus of an automobile;  
       FIG. 2  is a side-elevational view of a conventional electric power steering apparatus of an automobile, illustrating it partially in cross-section;  
       FIG. 3  is a cross-sectional view of a conventional tensioner;  
       FIG. 4  is a perspective view of a belt-type transmission according to a first embodiment of the invention;  
       FIG. 5  is a front elevational view of the belt-type transmission shown in  FIG. 4 ;  
       FIG. 6   a  is a diagram of an electric power steering apparatus of an automobile according to a second embodiment of the invention;  
       FIG. 6   b  is a magnified view of the electric power steering apparatus shown in  FIG. 6   a , whose illustration is partially in cross section; and  
       FIG. 7  is a cross-sectional view taken along the line A-A′ in  FIG. 6   b.   
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components throughout, and detailed description of well-known functions or components will be omitted since they may unnecessarily obscure the understanding of the invention.  
       FIG. 4  is a perspective view of a belt-type transmission according to a first embodiment of the invention, and  FIG. 5  is a front elevational view of the belt-type transmission shown in  FIG. 4 .  
      As shown in  FIGS. 4 and 5 , the belt-type electric power transmission according to the first embodiment of the invention includes a rotatable drive shaft  401 , a drive pulley  403  coupled with the drive shaft  401 , a rotatable driven shaft  402  spaced from the drive shaft  401  to a predetermined distance, a driven pulley  404  coupled with the driven shaft  402 , a belt  302  connecting the drive shaft  401  to the driven shaft  402  and a tensioner T abutting against the inner periphery of the belt  302 .  
      The drive shaft  401  is a cylindrical rotary shaft having a predetermined diameter, which delivers input rotational force to the driven shaft  402 . An actuator such as a motor is connected to the input side  405  of the drive shaft  401  to rotate the drive shaft  401 .  
      The drive pulley  403  is configured to surround the outer periphery of the output side  407  of the rotary shaft  401 , and the belt  302  moves in contact with the outer periphery of the drive pulley  403  to transmit rotational force from the drive shaft  401  to the driven shaft  402 . The drive pulley  403  may be provided integral to the drive shaft  401 , and protrusions may be formed on the outer periphery of the drive pulley  403  and the inner periphery of the belt  302  so that the belt  302  can have secure contact with the drive pulley  403 .  
      The driven shaft  402  functions to output rotational force delivered from the drive shaft  401 . The driven shaft  402  is spaced from the drive shaft  401  at a predetermined distance to receive rotational force from the drive shaft  401 .  
      The driven pulley  404  is configured to surround the outer periphery of the driven shaft  402 , and serves to deliver rotational force from the belt  302  to the driven shaft  402  as the belt  302  connected to the drive shaft  401  moves in contact with the outer periphery of the driven pulley  404 .  
      The belt  302  connects the drive shaft  401  to the driven shaft  402  to deliver rotational force from the drive shaft  401  to the driven shaft  402 . The belt  302  may be provided by one or more, and made of various materials such as metal and plastic. The belt  302  may also be provided on the inner periphery with protrusions that mesh with protrusions of the drive shaft  401  and/or the driven shaft  402 .  
      The tensioner T has a cylindrical configuration, in contact with the inner periphery of the belt  302 . The tensioner T may also be made hollow to reduce its weight. Preferably, the tensioner T has a diameter larger than the width of the belt  302  without making inside-contact with the tensioner T (herein the term “inside-contact” means that the tensioner T is arranged inside and in contact with the belt  302 ), such that the tensioner T installed inside the belt  302  can push against the inner periphery of the belt  302  to make the belt  302  tight.  
      As installed to contact the inner periphery of the belt  302 , the tensioner T can maintain a fixed position at all times owing to rotational force from both sides of the belt  302  that move in opposite direction. As a result, the tensioner T of this invention does not need additional support structure unlike conventional tensioners which are configured to contact the outside surface of the belt. Therefore, the invention can advantageously reduce the number of parts and simplify the manufacturing process, thereby saving manufacturing cost.  
      The tensioner T may also be made of elastic material such as plastic in order to cope with the loosening of the belt owing to the abrasion of the inner periphery of the belt  302  or the outer periphery of the tensioner T. Then, even though the belt  302  loosens owing to the abrasion, the elastic force of the tensioner T originating from its elasticity pushes the belt  302  outward so that the belt  302  can maintain its tension.  
       FIG. 6   a  is a diagram of an electric power steering apparatus of an automobile according to a second embodiment of the invention,  FIG. 6   b  is a magnified view of the electric power steering apparatus shown in  FIG. 6   a , whose illustration is partially in cross section, and  FIG. 7  is a cross-sectional view taken along the line A-A′ in  FIG. 6   b.    
      As shown in  FIGS. 6   a ,  6   b  and  7 , the electric power steering apparatus of an automobile according to the second embodiment of the invention includes a steering wheel  101  of an automobile, a pinion shaft  104  connected to the steering wheel  101 , having a pinion gear  111  formed at the bottom thereof, a rack bar  109  connected to both wheels  108  and having a rack gear  112 , which is formed at one part thereof and meshed with the pinion gear  111 , a motor  130  for generating steering power in proportion to steering torque generated by the steering wheel  101 , a motor pulley  601  coupled with the motor shaft  221 , a ball nut  205  meshed with a ball screw  203  of the back bar  109  via balls  201 , a ball nut pulley  602  arranged on the outer periphery of the ball nut  205 , a belt  302  connecting a motor pulley  601  to a ball nut pulley  602  and a tensioner T contacting the inner periphery of the belt  302 .  
      The pinion shaft  104  is connected to the steering wheel  101  via a steering shaft  102 , and the pinion gear  111  is formed at the bottom of the pinion shaft  104 .  
      The rack bar  109  is received in a rack housing, and connected at both ends to wheels  108  via tie rods  106  and knuckle arms  107 . The rack gear  112  is formed on one part of the rack bar  109 , and is meshed with the pinion gear  111 . Also, seals for preventing the leakage of lubricant are provided at predetermined portions of the rack bar  109  inside from the both ends.  
      The rack bar  109  receives, at one side, power from the motor shaft  221  via the belt  302 . In the outer periphery at the other side of the rack bar  109 , a spiral groove is extended to a predetermined length, forming the ball screw  203 .  
      The ball nut  205  meshes with the ball screw  203  via the balls  201 , surrounding the outer periphery of the rack bar  109 .  
      The ball nut pulley  602  is arranged on the outer periphery of the ball nut  205 , connecting the belt  302  to the ball nut  205 . The ball nut pulley  602  may also be made integral with the ball nut  205 . Furthermore, protrusions may be formed on the outer periphery of the ball nut pulley  602 .  
      The motor  130  includes a motor housing  611 , a cover  613  that closes an opened end of the motor housing  611 , a cylindrical stator  615  received in the motor housing  611 , a rotor  617  arranged inside the stator  615  and the motor shaft  221  which is coupled integrally with the rotor  617 .  
      The motor shaft  221  is arranged to be parallel with the rack bar  109 , with a left end  621  rotatably supported by a first bearing  623  installed in the motor housing  611  and a middle part rotatably supported by a second bearing  627  installed in the cover  613 . The cover  613  is also coupled with the motor housing  611  via bolts  629 .  
      The motor pulley  601  is arranged on a right end  628  of the motor shaft  221  and the belt  302  is connected to the motor pulley  601  so that steering power generated by the motor  130  can be transmitted to the rack bar  109 . The motor pulley  601  may be made integral with the motor shaft  221 . Furthermore, protrusions may be formed on the outer periphery of the motor pulley  601 .  
      The belt  302  connects the motor pulley  601  to the ball nut pulley  602  to transmit steering power from the motor  130  to the rack bar  109 . If necessary, protrusions may be formed on the inner periphery of the belt  302  to mesh with protrusions formed on the outer periphery of the motor pulley  601  or the ball nut pulley  602  so that the belt  302  can be driven in tight contact with the motor pulley  601  or the ball nut pulley  602 .  
      The tensioner T contacts the inner periphery of the belt  302  as in the first embodiment in order to push the belt  302  outward so that the belt  302  can maintain its tension.  
      Since other components have the same construction and operation as those of the first embodiment, the same reference signs are used to designate the same or similar components without detailed description thereof.  
      According to the present invention as described hereinbefore, the tensioner is provided inside and in contact with the belt without additional support structure in order to adjust belt tension. This as a result can advantageously reduce the number of parts and simplify manufacturing process, thereby saving manufacturing cost.  
      It is to be understood that while the present invention has been illustrated and described in relation to the preferred embodiments, such embodiments are illustrative only and that the present invention is in no event to be limited thereto. Rather, it is contemplated that modifications and variations embodying the principles of the present invention will no doubt occur to those skilled in the art. It is therefore contemplated and intended that the invention shall extend to all such modifications and variations and their equivalents as may incorporate the broad principles of this invention within the full spirit and scope of the claims appended hereto.