Patent Publication Number: US-2007095603-A1

Title: Belt-type electric power steering apparatus

Description:
RELATED APPLICATION  
      This application claims convention priority to Korean patent application. No.  2005-0100983 filed on Oct. 25, 2005, the content of which is incorporated by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to a belt-type electric power steering apparatus. More particularly, the present invention relates to a belt-type electric power steering apparatus, in which a motor pulley housing and a gearbox housing are coupled by bolts and release of the bolts is prevented, thereby preventing the droop of the motor pulley housing.  
     DESCRIPTION OF THE PRIOR ART  
      Generally, hydraulic power steering apparatuses using hydraulic pressure of a hydraulic pump have been used as power steering apparatuses for vehicles. Since the 1990&#39;s, electric power steering apparatuses using an electric motor have been eventually popularized.  
      In a conventional hydraulic steering apparatus, a hydraulic pump, which is a power source assisting power for the hydraulic steering apparatus, is operated by an engine of a vehicle, and always consumes energy regardless of the rotation of a steering wheel. In an electric power steering apparatus, on the other hand, if a steering wheel rotates and generates torque, an electric motor which is operated by electric energy provides steering assistant power. Therefore, when the electric power steering apparatus is used, it is possible to improve energy efficiency in comparison with the hydraulic power steering apparatus.  
       FIG. 1  is a schematic view showing a configuration of a conventional electric power steering apparatus for a vehicle.  
      As shown in  FIG. 1 , the conventional electric power steering apparatus includes a steering system  100  extending from a steering wheel  101  to both wheels  108 , and an assistant power mechanism  120  for providing steering power.  
      The steering system  100  includes a steering shaft having an end connected to the steering wheel  101  to rotate along with the steering wheel  101 , and the other end connected to a pinion shaft  104  by a pair of universal joints  103 . Further, the pinion shaft  104  is connected to a rack bar  109  through a rack-pinion mechanism  105 , while both ends of the rack bar  109  are connected to both wheels of the vehicle by tie rods  106  and knuckle arms  107 , respectively.  
      The rack-pinion mechanism  105  has a pinion gear  111  mounted on the pinion shaft  104 , and a rack gear  112  mounted on a peripheral surface of one end of the rack bar  109  and engaged with the pinion gear  111 . When a driver operates the steering wheel  101 , torque is generated in the steering system  100  and causes the rack-pinion mechanism  105  and the tie rods  106  to steer the wheels  108 .  
      The assistant power mechanism  120  includes a torque sensor  121  for sensing torque applied to the steering wheel  101  by the driver, so as to output an electric signal in proportion to the sensed torque, an electronic control unit  123  for generating a control signal depending on the electric signal transmitted from the torque sensor  121 , an electric motor  130  for generating steering power according to the control signal transmitted from the electronic control unit  123 , and a belt-type power transmission apparatus  140  for transmitting the assistant power, generated by the electric motor  130 , to the rack bar  109  through the belt.  
      Accordingly, in the electric power steering apparatus, the torque generated by the rotation of the steering wheel  101  is transmitted through the rack-pinion mechanism  105  to the rack bar  109 . The assistant steering power which the electric motor  130  generates depending on the generated torque, is transmitted by the belt-type power transmission apparatus through a ball screw  150  to the rack bar  109 . In other words, the rack bar is moved along an axis thereof by the torque generated in the steering system  100  and the assistant power generated by the electric motor  130 .  
       FIG. 2  is a sectional view showing the conventional electric power steering apparatus for a vehicle.  
      As shown in  FIG. 2 , the conventional power steering apparatus for the vehicle includes the rack bar  109  extending across the vehicle and having the rack gear mounted on an outer peripheral surface thereof, the pinion shaft  104  having the pinion gear engaged with the rack gear, the ball screw unit  150  having balls  210 , a ball screw  203 , and a ball nut  205  engaged with the ball screw  203  through the balls  201 , the belt-type power transmission apparatus  140  connecting the ball nut  205  to the shaft  221  of the electric motor, and the electric motor  130 . Further, a motor pulley housing  240  encloses the electric motor and is fixed to a gearbox housing  250  by a bolt coupling.  
      The pinion shaft  104  is connected to the steering wheel through the steering shaft, and the rack bar  109  having the screw formed by a predetermined length at one end thereof is contained in a rack housing  223 .  
      The ball screw unit  150  includes the ball nut  205  formed to be coaxial with the rack bar  109  and enclosing the rack bar  109 , and the balls  201  arranged on the outer peripheral surface of the rack bar  109  and contacting the ball screw  203 . The ball nut  205  rotates as the motor shaft  221  rotates. A bearing  207  is interposed between the outer surface of the ball nut  205  and the inner surface of the rack housing  223  in order for the ball nut  205  to rotate smoothly.  
      The belt type power transmission apparatus  140  includes a belt  230  connecting the motor shaft  221  to the ball nut  205 , and transmits steering power generated from the electric motor  130  in proportion to the steering torque applied to the steering wheel to the rack bar  109  through the ball nut  205 . In other words, as the motor shaft  221  rotates, the ball nut  205  rotates by receiving the rotational force of the motor shaft  221  through the belt  230 . When the ball nut  205  rotates, the rack bar  109  straightly moves in a direction of the axis of the rack bar  109 .  
       FIG. 3  is a side view showing a motor pulley housing and gearbox housing for the conventional electric power steering apparatus of the vehicle.  
      The motor is fixed to the gearbox housing  250  by coupling the motor pulley housing  240  to the gearbox housing  250  using the bolts. During the steering of the wheels, the motor  221  rotates to operate the belt  230 , causing the ball nut  205  to rotate. Thus, the tension of the belt  230  is applied to the motor shaft  221  and the rack bar  109  provided with the ball nut  205  so that the force of the motor shaft  221  and the rack bar  109  pulls the motor shaft  221  and the rack bar  109  toward each other. The force concentrates on the bolt coupling portion of the pulley housing  240  and the gearbox housing  250  which is mechanically weakened. Further, during the steering of the wheels, the motor shaft  221  rotates while generating vibration and impact, etc. to cause loosening of the bolts. As a result, there is a disadvantage in that the motor shaft  221  moves in a direction to the rack bar  105  provided with the ball nut  205  so as to reduce the tension of the belt  230 , thereby causing noise between the belt  230  and the pulley, as well as damaging the belt  230 .  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a belt type electric power steering apparatus, which has the combination structure of the motor pulley housing capable of preventing loosening of the bolts and the deflection of the motor pulley housing when the motor pulley housing is coupled to a gearbox housing by means of bolts.  
      In order to accomplish an object of the present invention, there is provided a belt type electric power steering apparatus, the apparatus comprising: a gearbox housing enclosing a rack gear and a ball screw; a motor pulley housing coupled to the gearbox housing and enclosing an electric motor, a belt for transmitting rotational force of the electric motor to a rack bar, and locking washers interposed between bolt heads and the gearbox housing, for preventing loosening of bolts when the motor pulley housing is coupled to the gearbox housing. 
    
    
     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 schematic view showing a configuration of a conventional electric power steering apparatus for a vehicle;  
       FIG. 2  is a sectional view showing the conventional electric power steering apparatus for a vehicle;  
       FIG. 3  is a side view showing a motor pulley housing and a gearbox housing for the conventional electric power steering apparatus of the vehicle;  
       FIG. 4  is a partial sectional view of a portion marked by ellipse B in  FIG. 3 , according to the first embodiment of the present invention;  
       FIG. 5A  is a front view of a portion marked by ellipse B in  FIG. 3 , according to the second embodiment of the present invention;  
       FIG. 5B  is a side view of a portion marked by ellipse B in  FIG. 3 , according to the second embodiment of the present invention; and  
       FIG. 6  shows washers used for preventing loosening of bolts shown in  FIGS. 4 and 5 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, the embodiments 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, and so repetition of the description on the same or similar components will be omitted.  
       FIG. 4  is a partial sectional view of a portion marked by ellipse B in  FIG. 3 , according to the first embodiment of the present invention. In  FIG. 4 , the combination of a motor pulley housing  240  and a gearbox housing  250  by means of bolts is shown, in which a locking washer  430  is interposed between a bolt head  410  and the gearbox housing  250 .  
       FIG. 5A  is a front view of a portion marked by ellipse B in  FIG. 3 , according to the second embodiment of the present invention, and  FIG. 5B  is a side view of a portion marked by ellipse B in  FIG. 3 , according to the second embodiment of the present invention.  
      The tension of the belt  230  causes force to be applied to the motor pulley housing  240 , mounted on and fixed to the gearbox housing  250  by means of the bolts, in a direction marked by an arrow in  FIG. 5B . The first prominence  500  is formed at both edges of a guide hole  350  in order to prevent the movement of the motor pulley housing  240  in the direction marked by the arrow in  FIG. 5B . A block-shaped washer  510  is disposed between the bolt head  410  and the gearbox housing  250 , and has the second prominence  530  formed on a surface thereof, and a hole for the bolt formed at a center portion thereof. The locking washer  430  is interposed between the bolt head  410  and the block-shaped washer  510  so as to prevent movement of the motor pulley housing  240  by the first prominence  500  formed at both edges of the bolt guide hole  350  of the gearbox  250  and the second prominence  530  formed on the block-shaped washer  510 . Further, the locking washer  430  is interposed between the bolt head  410  and the block-shaped washer  510 , so as to prevent the bolt  400  from being loosened due to vibrations generated during the operation of the vehicle.  
       FIG. 6  shows washers used for preventing loosened of bolts shown in  FIGS. 4 and 5 B.  
      The washers are generally used to prevent the bolt head or nut from damaging the object to be coupled caused by the coupling force of the bolt or nut, or to prevent the coupled bolt or nut from being loosened by mechanical vibrations.  
      Doughnut-shaped plan washers made of a metal material are generally used as washers to prevent the damage of the material. Following washers, for example C-type spring washer  600  made by cutting a portion of a coil spring, a disc spring washer  610  with a disc shape, an inner tooth washer  620  with inner teeth formed on an inner periphery thereof, an outer tooth washer  630  with outer teeth formed on an outer periphery thereof, inner and outer tooth washer  640  with inner and outer teeth formed on inner and outer peripheries thereof, and a disc washer  650  with prominence formed on an outer periphery thereof, are mainly used as washers  40  to prevent the release of the bolts.  
      As described above, according to the present invention, the motor pulley housing is coupled to the gearbox housing by using the locking washers and the like, thereby making it possible to prevent the release of the bolts and the movement of the motor shaft to the rack bar with the ball nut. Thus, there is an advantage in that it is possible to prevent reduction of tension of the belt and the generation of noise, and prevent the damage to the belt in advance.  
      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.