Abstract:
A load supporting structure of an electric booster type brake apparatus, includes: a housing including a rear housing member and a front housing member so as to define a receiving space therein; a ball screw shaft rotatably installed in the receiving space of the housing; a rotor installed at one side of the ball screw shaft so as to transmit torque; a first bearing installed between the rear housing member and one side of the rotor and configured to support a radial direction load due to a hydraulic reaction force; and a second bearing installed between the front housing member and the other side of the rotor and configured to support an axial direction load due to a hydraulic reaction force. Therefore, the number of components and the thickness of the housing are reduced, and therefore weight reduction of the electric booster type brake apparatus may be implemented.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0136007 filed in the Korean Intellectual Property Office on Nov. 28, 2012, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a load supporting structure of an electric booster type brake apparatus. 
       RELATED TECHNOLOGY 
       [0003]    In general, an electric booster type brake apparatus generates a front wheel brake pressure by driving a motor, generates a rear wheel brake pressure using a pedal effort, and implements mutual cooperative control. 
         [0004]    To do this, the electric booster type brake apparatus has a motor controlled by an electronic control unit (ECU) which recognizes a pedal stroke, and a front wheel master cylinder that is supplied with oil from an oil reservoir, for generating the front wheel brake pressure. The electric booster type brake apparatus has a rear wheel master cylinder that is supplied with oil from the oil reservoir by the pedal effort, for generating the rear wheel brake pressure. 
         [0005]    The electric booster type brake apparatus typically has a pedal simulator that provides a reaction force according to the pedal stroke to the pedal so as to allow the pedal effort to be sensed. 
         [0006]    A fail-safe function implemented by the electric booster type brake apparatus as described above typically performs a brake operation when an electric booster is failed, by applying multiple solenoid valves and supplying a hydraulic pressure flow to the master cylinder that generates a hydraulic pressure using the solenoid valves by the pedal. 
         [0007]    In more detail, referring to  FIGS. 1 to 3 , the electric booster type brake apparatus includes a motor  10  and a master cylinder (M/C)  20  for generating the front/rear wheel brake pressures, a sub master cylinder (sub M/C)  30  for the fail-safe function, a pedal simulator  40  for generating a pedal effort of a driver, two solenoid valves  50  including a first valve  51  and a second valve  52  for opening and closing flow paths, and the electronic control unit (ECU) for controlling a pedal stroke sensor and the motor. 
         [0008]    Referring to  FIGS. 2 and 3 , in an operation state of the electric booster type brake apparatus, the first valve  51  is opened and the second valve  52  is closed when a driver steps on a brake pedal. The pedal effort sensed by the driver is generated by a reaction force that is generated when a rubber and a spring of the pedal simulator  40  are compressed. 
         [0009]    Therefore, as illustrated in  FIG. 3 , the motor  10  rotates a ball screw  60  to move a piston  70  forward, and pressure generated at this time forms brake pressure in the master cylinder  20 . 
         [0010]      FIG. 4  is a view illustrating a load supporting structure of a motor of an electric booster type brake apparatus in the related art. 
         [0011]    Referring to  FIG. 4 , a rotor  11  and a torque connector  12  of the motor  10 , and the torque connector  12  and a ball screw shaft  13 , are formed in a spline type or in a hexagon shape, respectively, to transmit torque between the components, and are coupled by being fitted to each other. 
         [0012]    A protrusion  15  of a ball screw nut  14  is installed to be slidable with respect to a screw guide  16 . Therefore, the ball screw nut  14  moves forward to press the piston  70  when the motor  10  rotates. 
         [0013]    Therefore, a first bearing  17  installed on the rotor  11  supports a radial direction load, and a second bearing  18  supports the radial direction load and an axial direction load at the same time. 
         [0014]      FIG. 5  is a view illustrating an influence of a hydraulic reaction force of the master cylinder  20  on the load supporting structure of the electric booster type brake apparatus, when the electric booster type brake apparatus is operated. Here, the arrow illustrates an influence of the hydraulic reaction force of the master cylinder  20  on the load supporting structure of the electric booster type brake apparatus. 
         [0015]    In more detail, as illustrated in  FIG. 5 , the hydraulic reaction force is transmitted to the ball screw nut  14  that supports the piston  70 , and sequentially a load is applied to the ball screw shaft  13  coupled to the ball screw nut  14 . 
         [0016]    The load transmitted to the rotor  11  through the torque connector  12  that is installed to support the ball screw shaft  13  is finally supported by a rear housing member  19 - 1  of the motor  10  via the second bearing  18 . Here, as illustrated in  FIG. 6 , the rear housing member  19 - 1  is assembled and fastened to a front housing member  19 - 2  with a bolt so as to form a housing  19  having a receiving space therein. 
         [0017]    However, in a load supporting structure 2 of the electric booster type brake apparatus in the related art, because the rear housing member  19 - 1  supports the second bearing  18  that supports not only the radial direction load but the axial direction load, there is a problem in that the rear housing member  19 - 1  and the front housing member  19 - 2  need to be designed to have a large thickness in order to secure rigidity of the rear housing member  19 - 1  and the front housing member  19 - 2 , as illustrated in FIG. 
         [0018]    This design causes a weight increase when manufacturing a product according to the load supporting structure 2 of the electric booster type brake apparatus, a decrease in fuel efficiency of vehicles due to the weight increase, and an increase in manufacturing costs. 
         [0019]    Because the load supporting structure 2 of the electric booster type brake apparatus in the related art uses the torque connector  12 , a diameter of the rotor  11  needs to be large at the position where the rotor  11  is coupled to the second bearing  18 , as illustrated in  FIG. 8 . The second bearing  18  supports not only the radial direction load but the axial direction load and thus needs to have a high specification. As a result, in the load supporting structure 2 of the electric booster type brake apparatus in the related art, the second bearing  18  having a high specification and a large size is used, thereby causing an increase in manufacturing costs. 
         [0020]    Although the first bearing  17  supports only the radial direction load in the motor  10  and thus needs to have a substantially small size, there is a problem in that the bearing having a higher specification than requirement specifications needs to be chosen because the bearing having a size corresponding to an outer diameter of the rotor  11  needs to be used. 
       SUMMARY 
       [0021]    An aspect of the present invention has been made in an effort to provide a new load supporting structure of an electric booster type brake apparatus, capable of reducing a thickness of a housing of the electric booster type brake apparatus and reducing a specification of a bearing by changing a disposition or the like of a rotor supporting bearing installed in the electric booster type brake apparatus. 
         [0022]    An exemplary embodiment of the present invention provides a load supporting structure of an electric booster type brake apparatus, including: a housing including a rear housing member and a front housing member so as to have a receiving space therein; a ball screw shaft rotatably installed in the receiving space of the housing; a rotor installed at one side of the ball screw shaft so as to transmit torque; a first bearing installed between the rear housing member and one side of the rotor and configured to support a radial direction load due to a hydraulic reaction force; and a second bearing installed between the front housing member and the other side of the rotor and configured to support an axial direction load due to a hydraulic reaction force. 
         [0023]    One side of the rotor, which is bent in an axial direction, and the other side of the rotor, which is bent in a direction opposite to the direction in which the one side is bent, may be supported by the first bearing and the second bearing, respectively. 
         [0024]    The first bearing may be installed so that the radial direction load is applied to the rear housing member, and the second bearing may be installed so that the axial direction load is applied to the front housing member. 
         [0025]    Here, the front housing member may include an axial load supporting portion installed to have a thickness corresponding to the axial direction load supported by the second bearing. 
         [0026]    A diameter of the first bearing may be smaller than a diameter of the second bearing. 
         [0027]    In the load supporting structure of the electric booster type brake apparatus having the aforementioned configuration according to the exemplary embodiment of the present invention, the torque connector in the related art is removed, and a position of the bearing which supports the hydraulic reaction force is changed accordingly, thereby reducing the thickness of the housing. As a result, the number of components and the thickness of the housing are reduced, and therefore weight reduction of the electric booster type brake apparatus may be implemented and manufacturing costs may be reduced. 
         [0028]    As the disposition of the bearing which supports the hydraulic reaction force is changed, it is possible to use a bearing which meets an actual requirement specification of the load supporting structure of the electric booster type brake apparatus. 
         [0029]    The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a perspective view illustrating an electric booster type brake apparatus. 
           [0031]      FIG. 2  is a view illustrating a brake system of an electric booster type brake apparatus in the related art. 
           [0032]      FIG. 3  is a view illustrating a process in which brake pressure is generated in the electric booster type brake apparatus in the related art. 
           [0033]      FIG. 4  is a view illustrating a load supporting structure of a motor of the electric booster type brake apparatus in the related art. 
           [0034]      FIG. 5  is a view illustrating an influence of a hydraulic reaction force of a master cylinder on the load supporting structure of the electric booster type brake apparatus, when the electric booster type brake apparatus in the related art is operated. 
           [0035]      FIG. 6  is a view illustrating a state in which a front housing member and a rear housing member are coupled in the electric booster type brake apparatus. 
           [0036]      FIG. 7  is a cross-sectional view illustrating a cross section of a housing of the electric booster type brake apparatus in the related art. 
           [0037]      FIG. 8  is a perspective view illustrating a coupling relationship between a rotor, a first bearing, and a second bearing in the electric booster type brake apparatus in the related art. 
           [0038]      FIG. 9  is a view illustrating a load supporting structure of an electric booster type brake apparatus according to an exemplary embodiment of the present invention. 
           [0039]      FIG. 10  is a view illustrating an influence of a hydraulic reaction force on the load supporting structure of the electric booster type brake apparatus according to the exemplary embodiment of the present invention. 
           [0040]      FIG. 11  is a perspective view illustrating a coupling relationship between a rotor, a first bearing, and a second bearing in the electric booster type brake apparatus according to the exemplary embodiment of the present invention. 
       
    
    
       [0041]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0042]    In the figures, reference numbers refer to the same or equivalent parts of embodiments the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION 
       [0043]    Hereinafter, the exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings in order to clarify the solution to the technical problems of the present invention. However, to clearly describe the present invention, a description of the related art, which makes the subject matter of the present invention ambiguous, will be omitted. The terms described below are defined in consideration of each function in the present invention, and may be changed in accordance with the intention or the practice of a designer or a manufacturer. Therefore, the definition of the terms should be determined based on the contents disclosed in the entire specification. The elements denoted by the same reference numerals (drawing numbers) are the same elements through the specification. 
         [0044]    Hereinafter, a load supporting structure 1 of an electric booster type brake apparatus according to an exemplary embodiment of the present invention will be described. 
         [0045]      FIG. 9  is a view illustrating the load supporting structure 1 of the electric booster type brake apparatus according to an exemplary embodiment of the present invention. In more detail,  FIG. 9  relates to a load supporting structure of the above-described electric booster type brake apparatus, which relates to a motor. 
         [0046]    Referring to  FIG. 9 , the load supporting structure 1 of the electric booster type brake apparatus according to an exemplary embodiment of the present invention may include a housing  100  including a rear housing member  110  and a front housing member  120  so as to have a receiving space therein, a ball screw shaft  200 , a rotor  300 , a first bearing  400 , a second bearing  500 , and a ball screw nut  600 . 
         [0047]    Referring to  FIGS. 6 and 9 , the housing  100  is formed by assembling and fastening the rear housing member  110  and the front housing member  120  with a bolt or the like, and therefore the receiving space is formed in the housing  100 . 
         [0048]    The ball screw shaft  200  is rotatably installed in the receiving space of the housing  100 . As described above, the ball screw nut  600  moves forward when the motor rotates, and then the ball screw shaft  200  presses the aforementioned piston. 
         [0049]    Torque generated by the rotor  300  is directly transmitted to the ball screw shaft  200 . Here, the rotor  300  and the ball screw shaft  200  may be formed in a spline type or in a hexagon shape, respectively, to transmit torque, and may be coupled by being fitted to each other. Here, the spline type refers to a feature that is formed by directly cutting keys in multiple lines on the shaft in order to allow the shaft to slip. 
         [0050]    Therefore, referring to  FIG. 4 , the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention does not have the torque connector  12  which exists in the load supporting structure 2 of the electric booster type brake apparatus in the related art, which is installed between the ball screw shaft  200  and the rotor  300 , in comparison with the aforementioned load supporting structure 2 of the electric booster type brake apparatus in the related art. That is, because the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention does not have the torque connector, manufacturing costs thereof may be reduced. 
         [0051]    However, because a gap may be generated between the ball screw shaft  200  and the rotor  300  while being fitted to each other, the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention, of course, may compensate for the deviation caused by coaxiality. 
         [0052]    Hereinafter, a longitudinal direction of the ball screw shaft  200  is referred to as ‘an axial direction’, and a direction vertical to the axial direction is referred to as ‘a radial direction’. 
         [0053]    Referring to  FIGS. 9 to 10 , the first bearing  400  is installed between the rear housing member  110  and one side of the rotor  300 , and supports a radial direction load generated due to a hydraulic reaction force. Here, the arrow of  FIG. 10  illustrates an influence of a hydraulic reaction force generated due to main brake pressure, when the electric booster type brake apparatus is operated, on the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention. 
         [0054]    Because the first bearing  400  is installed between the rear housing member  110  and one side of the rotor  300 , the radial direction load applied to the first bearing  400  is supported by the rear housing member  110 . 
         [0055]    In more detail, referring to  FIG. 10 , the hydraulic reaction force causes a load to be applied to the ball screw shaft  200 , and the load is transmitted to the rotor  300 , which is coupled to the ball screw shaft  200  in a manner of spline or the like for transmitting torque. The load is finally supported by the rear housing member  110  via the first bearing  400 . 
         [0056]    As illustrated in  FIGS. 9 to 11 , the second bearing  500  is installed between the front housing member  120  and the other side of the rotor  300 , and supports an axial direction load generated due to the hydraulic reaction force. Because the second bearing  500  is installed between the front housing member  120  and the other side of the rotor  300 , the axial direction load applied to the second bearing  500  is supported by the front housing member  120 . 
         [0057]    In more detail, referring to  FIG. 10 , the hydraulic reaction force causes a load to be applied to the ball screw shaft  200 , and the load is transmitted to the rotor  300 , which is coupled to the ball screw shaft  200  in a manner of spline or the like for transmitting torque. The load is finally supported by the front housing member  120  via the second bearing  500 . 
         [0058]    Here, as illustrated in  FIGS. 9 to 11 , the rotor  300  is formed to have one side of the rotor  300  bent in the axial direction, and the other side of the rotor  300  which is bent in a direction opposite to the direction in which the one side is bent. 
         [0059]    As illustrated in  FIGS. 9 and 10 , the other side of the rotor  300 , which is supported by the second bearing  500 , may further include a vertical protrusion  310  so that the axial direction load may be easily applied to the second bearing  500 . 
         [0060]    Meanwhile, as illustrated in  FIGS. 9 and 10 , the front housing member  120  of the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention may include an axial load supporting portion  121  installed to have a predetermined thickness corresponding to the axial direction load. 
         [0061]    Therefore, when a high axial load is generated, the high axial load does not have an influence on the rigidity of the front housing member  120  in an area other than in the area of the axial load supporting portion  121  of the front housing member  120 . Accordingly, a thickness of the housing  100 , except for the axial load supporting portion  121 , may be further reduced compared to the load supporting structure 2 of the electric booster type brake apparatus in the related art, as illustrated in  FIG. 7 . 
         [0062]    Therefore, in the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention, because the second bearing  500  finally supports an axial load and the front housing member  120  supports the second bearing  500 , cross-sectional thicknesses of the rear housing member  110  and the front housing member  120  may be reduced, in comparison with the load supporting structure 2 of the electric booster type brake apparatus in the related art, as illustrated in  FIG. 4 . 
         [0063]    Because the cross-sectional thickness of the rear housing member  110  may be reduced, a size of the first bearing  400  may also be reduced corresponding to the cross-sectional thickness of the rear housing member  110 . 
         [0064]    Meanwhile, because the load supporting structure 2 of the electric booster type brake apparatus in the related art, as illustrated in  FIG. 4 , includes the torque connector  12 , an outer diameter of the rotor  11 , which corresponds to an outer diameter of the torque connector  12 , is also greater than an outer diameter of the rotor  300  of the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention. Therefore, the first bearing  17  of the load supporting structure 2 of the electric booster type brake apparatus in the related art, which supports a radial direction load, is required to have an exterior size greater than the size of an actual requirement specification, because of a large diameter of the rotor  11  of the load supporting structure 2 of the electric booster type brake apparatus in the related art. 
         [0065]    However, as illustrated in  FIG. 11 , as the first bearing  400  of the load supporting structure 1 of the electric booster type brake apparatus according to the exemplary embodiment of the present invention, which supports the radial direction load, a bearing, which meets an actual requirement specification, may be used. 
         [0066]    As described above, the exemplary embodiments have been described and illustrated in the drawings and the specification. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. Many changes, modifications, variations and other uses and applications of the present construction will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.