Abstract:
To provide a rotation angle detector with high detecting accuracy for use in association with a steering wheel on a vehicle and the like, a rotation angle detector is constructed by providing a recess surrounding a shaft portion in a top face of a detecting member and extending a shaft support, formed on an upper cover, into the recess.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a rotation angle detector for use in detecting rotary angle of a steering wheel on a vehicle and the like.  
         BACKGROUND OF THE INVENTION  
         [0002]    With progress of higher-performance vehicles made in recent years, there have been proposed various rotation angle detectors (hereinafter called “RAD”) for detecting the rotary angle of a steering wheel (hereinafter called “SWH”). An example of such RAD is disclosed, for example, in Japanese Patent Non-examined Publication No. 2002-206910.  
           [0003]    A conventional art RAD will be described with reference to FIG. 5.  
           [0004]    On the circumference of rotating member  1 , there is formed spur gear portion  1 A. Rotating member  1  has engagement portion  1 B to engage the shaft of SWH (not shown) inserted in the center thereof. Insulative resin-made detecting member  2  has a substantially planar top face. Spur gear portion  2 A provided on the circumference of detecting member  2  is in mesh with spur gear portion  1 A on rotating member  1 . Detecting member  2  has a cylindrical columnar protrusion  2 B formed in the center of its underside. Protrusion  2 B has magnet  3  mounted at its end by such means as insert molding.  
           [0005]    Circular columnar shaft portion  4 , made of a metal, is fixed by insert molding or the like to the center, i.e., the rotation axis, of detecting member  2 , as projected upward.  
           [0006]    The axes of shaft portion  4  and magnet  3  are each arranged substantially in alignment with the axis of detecting member  2 .  
           [0007]    There are provided a plurality of wiring patterns (not shown) on both sides of wiring board  5  disposed substantially parallel to the underside of detecting member  2 . Further, magnetic sensor element  6  is mounted on the face opposite to detecting member  2 . Magnet  3  and magnetic sensor element  6  arranged opposite to each other constitute sensor means  7 .  
           [0008]    Further, there is provided wiring board  8  connected with wiring board  5  via lead wire  9 . On wiring board  8 , there is formed control means  10  constructed of electronic parts including a microcomputer. Control means  10  is connected to an electronic circuit (not shown) on the vehicle body by way of a connector (not shown).  
           [0009]    Further, cylindrical supporting member  11 , made of an insulative resin, is fixed on to the top face of wiring board  5 . Cylindrical supporting member  11 , while surrounding protrusion  2 B, supports the underside of detecting member  2  for rotation. Upper cover  12 , made of an insulative resin, has shaft support  12 A protruded downward from its underside, shaft support  12 A having a diameter slightly larger than the diameter of shaft portion  4  of detecting member  2 . Shaft portion  4  of detecting member  2  is inserted into shaft support  12 A to be supported thereby for rotation.  
           [0010]    Rotating member  1 , wiring board  5 , wiring board  8 , and the like are covered by insulative resin-made case  13 , insulative resin-made side cover  14 , and upper cover  12 , so that these are kept in place to configure RAD.  
           [0011]    As SWH is turned in the above described configuration, rotating member  1  is rotated accordingly. Following this rotation, detecting member  2  with its circumferential spur gear portion  2 A in mesh with circumferential spur gear portion  1 A of rotating member  1  also rotates taking, as the center of rotation, shaft portion  4 , which is supported by shaft support  12 A protruded from upper cover  12 . As detecting member  2  rotates, the magnetic field around magnet  3  mounted on the center of detecting member  2  changes. Then, the change in the magnetic field is detected by magnetic sensor element  6  and a detection signal with a substantially triangular waveform is output to control means  10 . Thus, it is arranged such that control means  10  detects the rotation angle of rotating member  1  on the basis of the number of waveforms and the voltage value of the detection signal from magnetic sensor element  6 . The angle of rotation of SWH can thus be detected. However, when such a conventional RAD is mounted on a vehicle, there are also placed other equipment or parts on top of RAD. Thereby, the height from the top face of detecting member  2  up to the top face of upper cover  12  is limited and, hence, length L 1  of shaft support  12 A formed between the top face of upper cover  12  and the top face of detecting member  2  becomes short. As a result, shaft portion  4  supported within shaft support  12 A tends to show play or looseness during the rotation.  
           [0012]    Such play or looseness causes undesirable rotational deflections to magnet  3  provided at the bottom end of detecting member  2 . Thus, conventional RAD is confronted with a problem that errors are liable to be produced in the detected angle of rotation.  
           [0013]    The present invention is addressed to such a problem in conventional art and it is an object of the invention to provide RAD with high detection accuracy.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention provides a rotation angle detector including a rotating member, a detecting member rotating in conjunction with rotation of the rotating member, a cover having a shaft support formed thereon for rotatably supporting a shaft portion of the detecting member, and sensor means for detecting rotation of the detecting member, in which the detecting member is provided with a recess surrounding the shaft portion and the shaft support formed on the cover is extended into the recess. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a sectional view of RAD according to an exemplary embodiment of the present invention.  
         [0016]    [0016]FIG. 2 is an exploded perspective view of RAD according to the embodiment of the invention.  
         [0017]    [0017]FIG. 3 is a voltage waveform diagram in RAD according to the embodiment of the invention.  
         [0018]    [0018]FIG. 4 is a method of detecting rotation angle in RAD according to the embodiment of the invention.  
         [0019]    [0019]FIG. 5 is a sectional view of conventional RAD. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    An exemplary embodiment of the present invention will be described with reference to the accompanying drawings.  
         [0021]    Component parts like those described in the section of background art will hereinafter be denoted by like reference numerals and detailed description of the same will be simplified. Further, the drawings are just schematic ones and not showing each position exactly.  
         [0022]    (Exemplary Embodiment)  
         [0023]    Rotating member  1  is made of an insulative resin such as polyoxymethylene (POM) and polyphenylene-sulfide (PPS). On the circumference of rotating member  1 , there is formed spur gear portion  1 A and, in the center portion of the same, there is provided engagement portion  1 B to engage the shaft of SWH (not shown) inserted therein.  
         [0024]    Insulative resin-made detecting member  21  is provided, on its circumference, with spur gear portion  21 A arranged in mesh with spur gear portion  1 A on rotating member  1 . Detecting member  21  is further provided with a cylindrical columnar protrusion  21 B in the center portion of its underside. At the end of protrusion  21 B, there is mounted magnet  3  by such means as insert molding.  
         [0025]    As magnet  3 , any type of permanent magnet can be used. For example, ferrite magnet, samarium magnet, and neodymium magnet can be preferably used. Circular-columnar shaft portion  22 , made of a metal, is fixed by insert molding or the like to the center position, i.e., the rotation axis of detecting member  21 , as projected upward. Further, in the top face of detecting member  21 , there is provided recess  21 C surrounding the periphery of shaft portion  22 . The axes of shaft portion  22  and magnet  3  are each arranged substantially in alignment with the axis of detecting member  21 . On a face opposite to detecting member  21 , there is disposed wiring board  5  with magnetic sensor element  6  mounted thereon. As magnetic sensor element  6 , such a magneto resistive element as InSb is preferably used.  
         [0026]    Magnet  3  and magnetic sensor element  6  arranged opposite to each other constitute sensor means  7 . Wiring board  8  having control means  10  thereon is connected to wiring board  5  via lead wire  9 . Control means  10  is connected to an electronic circuit (not shown) on the vehicle body through connector  23 . Further, cylindrical supporting member  24  made of an insulative resin such as POM and polybutylene-terephthalate (PBT) is fixed on to the top face of wiring board  5 . This cylindrical supporting member  24  is arranged to surround protrusion  21 B and supports the underside of detecting member  21  for rotation. Further, upper cover  25 , made of an insulative resin such as POM and PBT, is provided with shaft support  25 B protruding downward from its underside and having a through hole  25 A slightly larger in diameter than shaft portion  22  of detecting member  21 . This shaft portion  25 B is arranged to extend into recess  21 C provided in the top face of detecting member  21  until its end abuts on the bottom face of recess  21 C. Shaft portion  22  is inserted into shaft support  25 B to be supported thereby for rotation.  
         [0027]    Rotating member  1 , wiring board  5 , wiring board  8 , and the like are covered by insulative-resin-made case  13 , insulative-resin-made side cover  14 , and upper cover  12 , so that these are kept in place to configure RAD.  
         [0028]    As SWH is turned in the above described configuration, rotating member  1  is rotated accordingly. Following this rotation, detecting member  21 , with its circumferential spur gear portion  21 A in mesh with circumferential spur gear portion  1 A of rotating member  1 , also rotates taking shaft portion  22  as the center of rotation.  
         [0029]    At this time, length L 2  of shaft portion  22  supported by shaft support  25 B is made greater than length L 1  of that in the conventional art example shown in FIG. 5 by the depth dimension of recess  21 C into which shaft support  25 B is extended. Further, since the end of shaft support  25 B abuts on the bottom face of recess  21 C, detecting member  21  can be rotated with reduced play or undesirable rotational deflections.  
         [0030]    As detecting member  21  is rotated, magnet  3  mounted in the center of the same is also rotated. Changes in the magnetic field produced at this time are detected by magnetic sensor element  6 . Then, a detection signal cycling with a substantially triangular waveform gradually increasing, or decreasing, as shown in FIG. 3 is output to control means  10 . Where angles of rotation are indicated by negative numerals, the angles are that measured in the direction opposite to the direction in which the angles of rotation are indicated by positive numerals.  
         [0031]    Suppose now that the number of teeth of detecting member  21  is set to be, for example, one third of the number of teeth of rotating member  1  and magnetic sensor element  6  is adapted to detect one change in the magnetic field intensity every rotation of 180° of detecting member  21 . Then, detecting member  21  makes three rotations during one rotation of rotating member  1 , while, during one rotation of detecting member  21 , magnetic sensor element  6  detects two changes in the magnetic field intensity. Hence, six voltage waveforms in a substantially triangular shape are successively detected as the detection signal. More particularly, for a 60° rotation of rotating member  1 , one substantially-triangular voltage waveform is output from magnetic sensor element  6  and supplied to control means  10  as the detection signal. Then, control means  10 , first, counts the number of waveforms of the detection signal to thereby detect approximate angle of rotation of rotating member  1 . Then, the same detects the accurate angle of rotation of rotating member  1  from the voltage value. For example, in the case where the angle of rotation is θ as shown in the voltage waveform diagram of FIG. 4, then, first, the ordinal number of the waveforms counted from the base point at 0° is two, and hence it is detected that the angle of rotation is between 60° and 120°. Then, RAD is adapted to detect that the accurate angle of rotation is 90°, for example, based on voltage value v.  
         [0032]    In the present embodiment, as described above, while recess  21 C is provided in the upper face of detecting member  21  to surround shaft portion  22 , shaft support  25 B formed on upper cover  25  is extended into recess  21 C. Thus, shaft portion  22  of detecting member  21  can be supported by shaft support  25 B having an elongated span or dimension in the axial direction. As a result, play or undesirable deflections of shaft portion  22  occurring when it rotates within through hole  25 A can be reduced and undesired rotational deflections of magnet  3  provided at the end of detecting member  21  can also be reduced. Thus, it becomes possible to have a signal with small error detected by sensor means  7  and to obtain RAD having high detection accuracy.  
         [0033]    Further, since shaft portion  22  is supported by shaft support  25 B along its elongated axial span or dimension, the load applied to the inner periphery of through hole  25 A during rotation can be distributed.  
         [0034]    Consequently, wear and tear on the inner periphery of through hole  25 B due to rotation of shaft portion  22  can be reduced and hence the life of the product can be extended.  
         [0035]    As described above, according to the present invention, it becomes possible to provide RAD having undesirable rotational deflections of detecting member  21  reduced and capable of making highly accurate detection.