Abstract:
A detector of a rotation angle and torque is disclosed. First gear ( 1 ) and second gear ( 2 ) are coupled to input shaft ( 4 ) and output shaft ( 6 ) of a torsion-bar unit respectively. First magnet ( 20   a ) magnetized in a radius direction is rigidly mounted to first rotor ( 10 ) engaging with first gear ( 1 ). Second magnet ( 20   b ) magnetized in a radius direction is rigidly mounted to second rotor ( 16 ) engaging with second gear ( 3 ). Circuit board ( 15 ) is placed between first rotor ( 10 ) and second rotor ( 16 ). Circuit board ( 15 ) includes first magnetism detecting element ( 21   a ) on its first face confronting the first magnet ( 20   a ), and also includes second magnetism detecting element ( 21   b ) on its second face confronting the second magnet ( 20   b ).

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a detector, mounted to a torsion bar, for detecting a rotation angle and torque simultaneously. The detector of the present invention is used in a power steering of cars.  
       BACKGROUND ART  
       [0002]      FIG. 7  shows a conventional detector of a rotation angle and torque. Gear  32  is mounted to an input shaft (not shown) of a torsion bar. Gear  30  engaging with gear  32  includes circular-shaped code plate  29  having numbers of magnetic poles. Rotation of the input shaft entails code plate  29  to rotate. Magnetism detecting element  31  counts the number of magnetic poles rotating, thereby detecting a rotation angle of the input shaft. Gear  42  is mounted to an output shaft (not shown) of the torsion bar, and a rotation angle of the output shaft is detected in the same manner discussed above. When torque works to the torsion bar to produce torsion, comparison of the rotation angles between the input shaft and the output shaft will detect torque.  
         [0003]     However, obtaining a more accurate rotation angle requires code plate  29  to have more numbers of magnetic poles, so that the detector becomes bulky. Placement of magnetism detecting element  31  on code plate  29  along the radial direction also enlarges the detector.  
       DISCLOSURE OF THE INVENTION  
       [0004]     A detector of a rotation angle and torque of the present invention comprises the following elements:  
         [0005]     a first and a second gears;  
         [0006]     a first and a second rotors engaging with the first and the second gears respectively;  
         [0007]     a first and a second magnets rigidly mounted at the centers of the first and the second rotors respectively;  
         [0008]     a circuit board disposed between the first and the second rotors;  
         [0009]     a first magnetism detecting element disposed on a first face of the circuit board at a place confronting the first magnet;  
         [0010]     a second magnetism detecting element disposed on a second face of the circuit board at a place confronting the second magnet; and  
         [0011]     a housing accommodating the foregoing structural elements 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1A  shows a top view of a detector in accordance with a first exemplary embodiment of the present invention.  
         [0013]      FIG. 1B  shows a front sectional view of the detector shown in  FIG. 1 .  
         [0014]      FIG. 1C  shows a lateral sectional view of the detector shown in  FIG. 1 .  
         [0015]      FIG. 2  shows a perspective exploded view illustrating a structure of an arm of the detector shown in  FIG. 1 .  
         [0016]      FIG. 3  shows a perspective exploded view illustrating a structure of an arm.  
         [0017]      FIG. 4  shows a plan view illustrating a structure of another arm.  
         [0018]      FIG. 5A  shows a plan view of an arm stopper.  
         [0019]      FIG. 5B  shows a plan view of an arm brought into contact with the arm stopper.  
         [0020]      FIG. 6A  shows a sectional view illustrating a loose engagement between a first gear and a second gear.  
         [0021]      FIG. 6B  shows a sectional view illustrating a rotation stopper disposed between a first gear and a second gear.  
         [0022]      FIG. 7  shows a conventional detector of a rotation angle and torque. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]     Exemplary embodiments of the present invention are demonstrated hereinafter with reference to the accompanying drawings.  
         [0000]     Exemplary Embodiment 1  
         [0024]      FIGS. 1A, 1B  and  1 C show a top view, a front sectional view, and a lateral sectional view of a detector of a rotation angle and torque of the present invention.  
         [0025]     First gear  1  is fixed to input shaft  4  of torsion-bar unit  2  with screw  5 . Second gear  3  is fixed to output shaft  6  of torsion-bar unit  2  with screw  5 . A lower end of first gear  1  engages loosely with an upper end of second gear  3 . First gear  1  and second gear  3  are supported respectively by bearing  9  equipped to upper housing  7  and lower housing  8 , and accommodated in housings  7  and  8 .  
         [0026]     Input shaft  4  is fixed to an upper end of torsion bar  2   a  with spring-pin  2   b , and output shaft  6  is fixed to a lower end of torsion bar  2   a  with spring-pin  2   b . A lower end of input shaft  4  engages loosely with an upper end of output shaft  6 .  
         [0027]     Transmission of torque through torsion-bar unit  2  twists torsion bar  2   a , so that a difference in rotation angles between input shaft  4  and output shaft  6  is produced.  
         [0028]     First gear  1  engages with gear  11   a  of first rotor  10 , which is supported by bearing  14  of arm  13  mounted to upper housing  7  such that arm  13  can rotate on pivot  12 . Spring  19  has tensile force working on tip  17  of arm  13  and urging first rotor  10  mounted on arm  13  against first gear  1 , so that backlash of the gear can be reduced.  
         [0029]     Second gear  3  engages with gear  11   b  of second rotor  16 , which is disposed opposite to first rotor  10  with circuit board  15  in between, and is mounted on an arm in lower housing  8 . This arm has the same construction as arm  13 .  
         [0030]     First rotor  10  and second rotor  16  include first magnet  20   a  and second magnet  20   b  fixed at their centers respectively, and each one of the magnets has a magnetic field along the radial direction of the rotor. Both of magnets  20   a  and  20   b  are magnetized in one pole pair. Circuit board  15  is disposed between first rotor  10  and second rotor  16 , and board  15  has first magnetism detecting element  21   a  on its first face so that element  21   a  confronts first magnet  20   a . Board  15  also has second magnetism detecting element  21   b  on its second face so that element  21   b  confronts second magnet  20   b.    
         [0031]     Since circuit board  15  is equipped with first magnetism detecting element  21   a  and second one  21   b  on its both sides, so that board  15  can be accommodated in a compact space between upper and lower housings  7 ,  8 . This construction is thus effective to downsize the detector.  
         [0032]      FIG. 2  shows an exploded view of arm  13 . First rotor  10  having gear  11   a  is rotatably supported by bearing  14  between lower arm  13   a  and upper arm  13   b . As previously discussed, second rotor  16  having gear  11   b  is integrated into the arm which has the same construction as arm  13 .  
         [0033]     In  FIG. 1B , first magnetism detecting element  21   a  detects a change in the magnetic field of first magnet  20   a , so that a rotation angle of first rotor  10  can be detected. In a similar manner, second magnetism detecting element  21   b  detects a change in the magnetic field of second magnet  20   b , so that a rotation angle of second rotor  16  can be detected.  
         [0034]     Appropriate setting of the number of teeth of first gear  1 , second gear  3 , gear  11   a  of first rotor  10 , and gear  11   b  of second rotor  16  allows producing a relative change in respective rotation angles of first rotor  10  and second rotor  16 . This preparation thus allows detecting a rotation angle (absolute angle of multi-rotations) even if the rotation angle of input shaft  4  exceeds one rotation (360 degrees).  
         [0035]     When torsion bar  2   a  is twisted, and a relative angle change in the rotation angle occurs between input shaft  4  and output shaft  6 , the change amount in rotation is proportionate to torque working on torsion bar  2   a . Thus removal of a detection signal of an absolute rotation angle from detection signals supplied from first and second detecting elements  21   a  and  21   b  will find the torque working between the input and output shafts.  
         [0036]     In general, a change amount due to torsion in rotation of torsion bar  2   a  is as little as not more than  3  degrees, so that an engagement accuracy of teeth of gears becomes critical for improving a detection accuracy of detectors. As shown in  FIG. 1A , the detector of the present invention employs elastic member  19 , e.g. a spring, and this spring urges first rotor  10  (or second rotor  16 ) against first gear  1  (or second gear  3 ), thereby reducing an error accompanying backlash of the gear.  
         [0037]     As shown in  FIG. 2 , arm  13  supports first rotor  10  (or second rotor  16 ) with bearings on both the sides of the rotor, so that the force of elastic member  19  works on the teeth faces of first gear  1  (or second gear  3 ) at right angles. As a result, an error due to a slant of the gear can be prevented.  
         [0038]     A power steering device of cars uses the detector of the present invention, so that a rotation angle (absolute angle) and torque produced by operating the steering can be detected simultaneously with high accuracy, and the detector can be in a compact structure,  
         [0000]     Exemplary Embodiment 2  
         [0039]      FIG. 3  shows an exemplary embodiment of an arm of the detector of the present invention. Similar elements to the previous embodiment have the same reference marks and the descriptions thereof are omitted here. Arm  13  is formed from resin in one body and has space  22  as well as bearing  14  at its center for accommodating and supporting first rotor  10 . Thin-based section  23  is formed around bearing  14 . Since thin-based section  23  can be transformed against the elasticity of the resin for accommodating first rotor  10  in arm  13 , the construction of arm  13  of this second embodiment becomes so simple that arm  13  can be assembled in a short time.  
         [0040]      FIG. 4  shows another embodiment of the arm, for instance, arm  13  made from polyacetal resin has elastic slip  24  integrated therein. Elastic slip  24  urges first rotor  10 , mounted to arm  13  which can rotate around pivot  12 , against first gear  1 , thereby reducing an error accompanying backlash of the gear.  
         [0041]      FIGS. 5A and 5B  shows still another embodiment of the arm. Arm stopper  25  is formed on an inner face of upper case  7  near a tip of arm  13 . Space h ( FIG. 5A ) between arm stopper  25  and arm  13  is smaller than an intermeshing amount between gear  11   a  of first rotor  10  and first gear  1 . Thus even if arm  13  is moved by, e.g. vibrations, arm stopper  25  stops the move ( FIG. 25 ), so that the intermesh between gears is not come out. This structure allows preventing first magnet  20   a  of first rotor  10  from deviating from the rotating position initially set, thereby avoiding an accident. As a result, the reliability of the detector can be improved.  
         [0000]     Exemplary Embodiment 3  
         [0042]     As previously discussed, the lower end of first gear  1  loosely engages with the upper end of second gear  3  (ref.  FIG. 1C ).  FIG. 6A  shows a sectional view of this loose engagement. As shown in  FIG. 6B , rotation of first gear  1  with respect to second gear  3  causes a collision between these two gears at angle θ, thereby stopping the rotation. In other words, a shape of the loose engagement viewed from the sectional view constructs a rotation stopper which limits the rotation of first gear  1  and second gear  3  within a predetermined angle. The rotation stopper prevents torsion bar  2   a  from being twisted excessively. The rotation stopper is not limited to a shape shown in  FIG. 6 , and any shape as long as it can limit a relative rotation between input shaft  4  and output shaft  6  within a predetermined angle, it can produce a similar advantage to what is discussed above.  
       INDUSTRIAL APPLICABILITY  
       [0043]     The present invention provides a detector of a rotation angle and torque. This detector is suited to a power steering of cars.