Abstract:
Disclosed is an EPS motor having a steering angle sensor for an electronic power steering system, wherein the EPS motor includes a housing, a bracket, a rotating shaft, a stator and a rotor, and the housing includes an upper housing having the stator and the rotor in an internal space thereof, the bracket coupled to an upper portion thereof, and the rotating shaft coupled to the upper housing to protrude downwards therefrom, and a lower housing disposed under the upper housing to receive the steering angle sensor therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2010-0131595, filed on Dec. 21, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to an electronic power steering system (EPS) for a vehicle and, more particularly, to an EPS motor having a steering angle sensor mounted to an electronic power steering system. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, an auxiliary steering system supported by additional power is used to ensure the steering stability of a vehicle. Conventionally, the auxiliary steering system uses a hydraulic pressure. However, recently, an electronic power steering system, which consumes less power and is excellent in accuracy, has been used. 
         [0006]    Such an electronic power steering system (EPS) controls the driving of a motor by an electronic control unit (ECU) depending on driving conditions detected by a vehicle speed sensor, a torque angle sensor and a torque sensor, thus ensuring stability in cornering of a vehicle and providing a rapid restoring force, and thereby allowing a driver to safely drive the vehicle. 
         [0007]      FIG. 1  is a schematic view showing the construction of a typical electronic power steering system. 
         [0008]    As shown in the drawing, the electronic power steering system includes a steering wheel  10 , a steering shaft  10   a,  an EPS motor  11 , a steering angle sensor  12  and an ECU  13 . 
         [0009]    The steering wheel  10  is rotated by a driver so as to change a direction of a vehicle. The steering wheel  10  is connected to the steering shaft  10   a.  If the driver rotates the steering wheel  10 , the steering shaft  10   a  rotates in the same direction as the steering wheel  10  in conjunction with the rotation of the steering wheel  10 . 
         [0010]    The EPS motor  11  is a motor that assists torque of the steering wheel  10  manipulated by a driver for steering, and enables the driver to more conveniently perform steering operation. Generally, the EPS motor  11  uses a brushless DC (BLDC) motor. The BLDC motor means a DC motor equipped with an electronic commutating device except for mechanical contact parts of the DC motor such as a brush or a commutator. A decelerator and a torque sensor (not shown) are coupled to an end of the EPS motor  11 . The torque sensor detects relative rotating displacement between an input shaft and an output shaft when the steering wheel  10  rotates, generates an electric signal based on the detected result, and thereafter transmits the signal to the ECU  13 . 
         [0011]    The steering angle sensor  12  is installed at a position around the steering wheel  10 , directly measures a rotating angle of the steering wheel  10  rotated by the driver&#39;s manipulation, and transmits a signal regarding the rotating angle to the ECU  13 . 
         [0012]    The ECU  13  electronically controls various drive sources of the electronic power steering system including the EPS motor  11 , based on data of a vehicle speed sensor (not shown), the torque sensor and the steering angle sensor  12 . 
         [0013]    However, the electronic power steering system constructed as described above is problematic in that the steering angle sensor  12  is mounted as a separate part, so that an additional space for installing the steering angle sensor  12  must be provided around the steering wheel  10 , thus causing inconvenience, and the number of assembling processes and the cost of parts are increased because of an increase in number of parts. 
       BRIEF SUMMARY 
       [0014]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an EPS motor, which is improved in structure to allow a sensor capable of detecting a steering angle to be installed in a housing of the EPS motor. 
         [0015]    In order to accomplish the above object, the present invention provides an EPS motor having a steering angle sensor for an electronic power steering system. The EPS motor includes a housing, a bracket, a rotating shaft, a stator and a rotor, and the housing comprises an upper housing including the stator and the rotor in an internal space thereof; the bracket coupled to an upper portion thereof, and the rotating shaft coupled to the upper housing to protrude downwards therefrom, and a lower housing disposed under the upper housing to receive the steering angle sensor therein. 
         [0016]    The lower housing may take a shape of a cylinder that is open at a top thereof, and may be coupled to a bottom surface of the upper housing. A wall surface of the lower housing may be formed integrally with the upper housing, and the bottom surface of the lower housing may be coupled with the substrate. 
         [0017]    Preferably, the steering angle sensor comprises a substrate mounted on a bottom surface of the lower housing, a worm gear formed on an outer circumference of the rotating shaft protruding from the upper housing, a worm wheel engaging with the worm gear, a first magnet member coupled to an end of the rotating shaft protruding from the upper housing, a second magnet member provided on the worm wheel, a first hall sensor provided at a position on the substrate corresponding to the first magnet member, and a second hall sensor spaced apart from the substrate by a predetermined distance and provided at a position corresponding to the second magnet member. 
         [0018]    Preferably, when a steering wheel is constructed to turn five times in total and a reduction gear ratio of an EPS reduction gear operated in conjunction with the rotating shaft connected to the steering wheel is 15:1, a reduction gear ratio of the worm gear formed on the rotating shaft to the worm wheel is 75:1. 
         [0019]    As apparent from the above description, according to the present invention, the steering angle sensor is integrated with the EPS motor, so that it is unnecessary to install a separate steering angle sensor, and thereby a degree of design freedom of the EPS can be increased. 
         [0020]    Further, the removal of the steering angle sensor leads to a reduction in cost of the EPS, thus enhancing price competitiveness and profitability of a product. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic view illustrating a typical electronic power steering system; and 
           [0022]      FIGS. 2 and 3  are sectional views schematically showing an EPS motor mounted to an electronic power steering system in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Hereinafter, an EPS motor having a steering angle sensor according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. 
         [0024]    As shown in  FIG. 2 , the EPS motor according to the present invention includes a housing  1 , a bracket  2 , a rotating shaft  3 , a stator  4 , and a rotor  5 . The housing  1  is characterized in that it is comprised of upper and lower housings  1   a  and  1   b,  and a steering angle sensor  100  is mounted to the lower housing  1   b.    
         [0025]    The upper and lower housings  1   a  and  1   b  may be integrated into a single body. Alternatively, the lower housing  1   b  may be provided separately from the upper housing  1   a,  and then may be coupled to a lower portion of the upper housing  1   a.    
         [0026]    The upper housing  1   a  takes a shape of a cylinder that is open at a top thereof. The stator  4  and the rotor  5  are installed in an internal space of the upper housing  1   a,  and the bracket  2  is coupled to an upper portion of the upper housing  1   a,  thus defining an external appearance of the EPS motor. Meanwhile, the rotating shaft  3  supporting the rotor  5  is installed along a central axis of the upper housing  1   a  to pass through a bottom surface of the upper housing  1   a.    
         [0027]    The lower housing  1   b  is disposed under the upper housing  1   b , and the steering angle sensor  100  is installed in the lower housing  1   b . A structure of the steering angle sensor  100  will be described later in more detail. As described above, the lower housing  1   b  takes a shape of a cylinder that is open at a top thereof, so that the lower housing  1   b  may be coupled to the bottom surface of the upper housing  1   a,  or a wall surface of the lower housing  1   b  may be integrated with the upper housing  1   a  and a bottom surface of the lower housing  1   b  may be coupled with a substrate  101  of the steering angle sensor  100  that will be described below. 
         [0028]    The rotating shaft  3  is rotatably supported at both ends thereof by the upper housing  1   a  and the bracket  2 . Preferably, a bearing  3   a  may be provided on a portion of the rotating shaft  3  supported by each of the upper housing  1   a  and the bracket  2 . Further, as described above, the rotating shaft  3  is coupled to the upper housing  1   a  to pass through the bottom surface thereof and protrude to an outside thereof beyond a predetermined length. 
         [0029]    The stator  4  is disposed on an inner circumference of the upper housing  1   a,  and is comprised of a core, a coil wound around the core, and an insulating material. Generally, a warm shrink fitting process is used to couple the stator  4  to the upper housing  1   a.  That is, if the upper housing  1   a  is heated to couple the stator  4  to the upper housing  1   a,  a metal material forming the upper housing  1   a  thermally expands, so that an inner diameter of the upper housing  1   a  increases. In this state, if the stator  4  is inserted into the upper housing  1   a  and the upper housing  1   a  is cooled, the upper housing  1   a  is shrunk and is in frictional contact with the stator  4 , so that the stator  4  can be supported on the inner circumference of the upper housing  1   a.    
         [0030]    The rotor  5  is mounted to an outer circumference of the rotating shaft  3 , and is disposed on a surface corresponding to the stator  4 . The rotor  5  includes a core and a magnet. 
         [0031]    Thus, if a current is applied to the stator  4 , the rotor  5  is rotated by electromagnetic interaction between the stator  4  and the rotor  5 , so that the rotating shaft  3  rotates in conjunction with the rotation of the rotor  5 . Since the rotating shaft  3  is connected to the steering shaft  10   a  (see  FIG. 1 ) via a reduction gear (not shown), the steering shaft  10   a  can also be rotated by the rotation of the rotating shaft  3 . Therefore, the EPS motor assists the rotation of the steering shaft  10   a  that rotates in conjunction with the steering wheel  10  as a driver rotates the steering wheel  10 . 
         [0032]    The steering angle sensor  100  functions to indirectly measure a steering angle of the steering wheel  10  rotated by a driver, and preferably includes the substrate  101 , a worm gear W 1 , a worm wheel W 2 , first and second magnet members M 1  and M 2 , and first and second hall sensors  110  and  120 . 
         [0033]    The first and second hall sensors  110  and  120  are installed at the substrate  101 . In the case of a structure where the lower housing  1   b  is coupled with the upper housing  1   a,  the substrate  101  is mounted on a bottom surface of the lower housing  1   a.  Meanwhile, in the case of a structure where the lower housing  1   b  is integrated with the upper housing  1   a,  the substrate  101  is coupled to close an opening of the lower housing  1   b  together with a cover means. 
         [0034]    The worm gear W 1  is formed on the outer circumference of the rotating shaft  3  protruding from the upper housing  1   a.    
         [0035]    The worm wheel W 2  is installed to be rotatable by a shaft member  102  connected to a wall surface of the lower housing  1   b,  and engages with the worm gear 
         [0036]    Meanwhile, the EPS reduction gear (not shown) operated in conjunction with the rotating shaft  3  usually has a reduction gear ratio of 15:1. The reduction gear ratio of 15:1 means that, when the EPS motor turns 15 times, the steering wheel  10  (see  FIG. 1 ) turns once. Thus, assuming that the steering wheel  10  turns left 2.5 times and turns right 2.5 times, so the steering wheel  10  turns 5 times in total, the EPS motor turns 75 times (5×15=75) when the steering wheel  10  turns 5 times. Therefore, a reduction gear ratio of the worm gear W 1  formed on the rotating shaft  3  and the worm wheel W 2  is 75:1, so that the worm wheel W 2  may turn 75 times per turn of the steering wheel  10  (see  FIG. 1 ). 
         [0037]    The first magnet member M 1  is provided on an end of the rotating shaft  3  protruding from the upper housing  1   a,  and the second magnet member M 2  is provided on the worm wheel W 2 . 
         [0038]    The first hall sensor  110  is located at a position on the substrate  101  to correspond to the first magnet member M 1 , and the second hall sensor  120  is located at a position on a support member  103  electrically connected to the substrate  101  to correspond to the second magnet member M 2 . 
         [0039]    Therefore, the first and second hall sensors  110  and  120  detect the first and second magnet members M 1  and M 2 , respectively. The first hall sensor  110  detects the rotation of the rotating shaft  3  supporting the rotor  5 , thus detecting precise motor rotating angle information, and the second hall sensor  120  detects a multiple turn of a motor. That is, the first hall sensor  110  is used to detect the rotating angle of the rotor  5  by detecting the rotation of the rotating shaft  3 , and the second hall sensor  120  is used to roughly detect the number of turns of the rotor  5 . 
         [0040]    As described above, the present invention is advantageous in that a steering angle sensor is integrally provided in a housing of an EPS motor, so that it is unnecessary to install a separate steering angle sensor, thus making it more convenient to assemble an electronic power steering system, and achieving a reduction in manufacturing cost owing to a reduction in number of parts. 
         [0041]    While the invention has been described in its preferred embodiments with reference to the accompanying drawings, it is to be understood that the invention is not limited thereto but may be variously embodied within the scope of the following claims.