Abstract:
A rotation angle detecting device that detects a rotation angle of a rotating object includes a permanent magnet that generates magnetic fields in response to rotation of the rotating object, a magnetic sensor, a first yoke and a second yoke. The magnetic sensor includes a pair of close integrated magnetic sensing elements, such as hall elements, disposed at a position around the permanent magnet so that one of the sensing elements senses magnetic field at a phase different from the other. The first yoke and the second yoke forms two magnetic paths crossing each other at the magnetic sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is based on and claims priority from Japanese Patent Application 2005-283939, filed Sep. 29, 2005, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a rotation angle detecting device that detects a rotation angle of an rotating object.  
         [0004]     2. Description of the Related Art  
         [0005]     Usually, a rotation angle of a rotating object is detected by a rotation angle detecting device that is constituted of a permanent magnet rotor linked with the rotating object, a pair of magnetic sensing elements that are respectively disposed around the permanent magnet rotor to be spaced apart from each other in the rotating direction, as disclosed in JP-A-2004-271495 or, its counterpart, US 2004/0164733 A1. When the rotating object rotates, the magnetic sensing elements detect a change in a magnetic field that is generated by the permanent magnet rotor, thereby providing signals relating to the rotation angle of the rotation object.  
         [0006]     Because the magnetic sensing elements are spaced apart in the rotating direction, it is difficult to accurately position the magnetic sensing elements. In other words, the angle formed between two magnetic sensing elements may not be a desired angle, the setting directions of two magnetic sensing elements may not be desired directions, or temperature difference between two magnetic sensing elements may arise. As a result, the magnetic sensing elements may generate signals that may cause an error in the rotation angle to be detected.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, an object of the invention is to provide an improved rotation angle detecting device that can accurately detect the rotation angle of a rotating object.  
         [0008]     Another object of the invention is to provide a new structure in which a pair of magnetic sensing elements is integrated into a single unit.  
         [0009]     According to a feature of the invention, a rotation angle detecting device includes field means for generating magnetic fields in response to rotation of a rotating object, a magnetic sensor including at least a pair of close integrated magnetic sensing elements disposed at a position around the field means so that one of the sensing elements senses magnetic field at a phase different from the other; and yoke means disposed around the field means for forming two magnetic paths crossing each other at the magnetic sensor.  
         [0010]     Because the two magnetic sensing elements are disposed very close to each other, it is possible to integrate them into a unit, so that the angle between the two elements and the setting directions thereof may be accurately formed. In addition, there is little temperature difference between two hall elements.  
         [0011]     In the above rotation angle detecting device, the magnetic sensor is preferably formed on a chip. The yoke means may include a plurality of first yokes disposed in a circumferential direction at gaps to form a first magnetic path and a second yoke disposed around the inner yokes to form a second magnetic path crossing the first magnetic path at one of the gaps, and the magnetic sensor is disposed in one of the gaps. The second yoke may have a projection projecting toward the magnetic sensor. Each of the gaps may have the same distance.  
         [0012]     Further, the above rotation angle detecting device may include another magnetic sensor that also includes a pair of close integrated magnetic sensing elements disposed at another position around the field means. One of the sensing elements is preferably disposed at an angle of 90 degrees to the other. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:  
         [0014]      FIG. 1A  is a cross-sectional plan view of a rotation angle detecting device according to the first embodiment of the invention;  
         [0015]      Fig. 1B  is a cross-sectional longitudinal view of the rotation angle detecting device according to the first embodiment cut along one-dot-chain line B-B in  FIG. 1A ;  
         [0016]      FIG. 2  is a schematic diagram illustrating a magnetic sensor unit;  
         [0017]      FIG. 3  is a graph showing a relationship between the rotation angle of the rotating object and the output signal of the magnetic sensor unit;  
         [0018]      FIG. 4  is a cross-sectional plan view of a rotation angle detecting device according to the second embodiment of the invention;  
         [0019]      FIG. 5  is a cross-sectional plan view of a rotation angle detecting device according to the third embodiment of the invention;  
         [0020]      FIG. 6  is a cross-sectional plan view of a rotation angle detecting device according to the fourth embodiment of the invention;  
         [0021]      FIG. 7  is a cross-sectional plan view of a rotation angle detecting device according to the fifth embodiment of the invention;  
         [0022]      FIG. 8  is a cross-sectional plan view of a rotation angle detecting device according to the sixth embodiment of the invention;  
         [0023]      FIG. 9A  is a cross-sectional plan view of a rotation angle detecting device according to the seventh embodiment of the invention;  
         [0024]      FIG. 9B  is a cross-sectional longitudinal view of the rotation angle detecting device according to the seventh embodiment cut along one-dot-chain line B-B in  FIG. 9A ;  
         [0025]      FIG. 10  is a cross-sectional longitudinal view of a rotation angle detecting device according to the eighth embodiment of the invention;  
         [0026]      FIG. 11  is a cross-sectional longitudinal view of a rotation angle detecting device according to the ninth embodiment of the invention; and  
         [0027]      FIG. 12  is a cross-sectional plan view of a rotation angle detecting device according to the tenth embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     The present invention will be described with reference to the appended drawings.  
         [0029]     A rotation angle detecting device according to the first embodiment of the invention will be described with reference to  FIGS. 1A-3 .  
         [0030]     As shown in  FIGS. 1A and 1B , a rotation angle detecting device  10  is set around a rotary shaft  12  that is linked with a rotating object (not shown). The rotation angle detecting device  10  is constituted of a ring-shaped permanent magnet  20 , four arc-shaped magnetic inner yokes  30 , a generally cylindrical magnetic outer yoke  40  and a magnetic sensor  50 .  
         [0031]     The ring-shaped permanent magnet  20  is magnetized to polarize in parallel with a radial direction thereof and fixed to the circumference of the rotary shaft  12 . The four inner yokes  30  are disposed around the permanent magnet  20  at equal intervals so that gaps  32  can be formed at intervals of 90 degrees. In other words, each of the gaps  32  is positioned around the permanent magnet  20  opposite to, or at  180  degrees from, another of the gaps  32 . The cylindrical outer yoke  40  is disposed around the inner yokes  30 . The outer yoke  40  has four projections  42  each of which projects toward one of the gaps  32 .  
         [0032]     The magnetic sensor  50  is a one-chip semiconductor element, which is disposed in one of the gaps  32  so as to confront one of the projections  42  and side surfaces of the inner yokes  30  that sandwich the magnetic sensor  50 . As shown in  FIG. 2 , the magnetic sensor  50  is constituted of a pair of hall elements  52  that are disposed perpendicular to each other to respectively sense magnetic flux densities of the magnetic field in directions perpendicular to each other, thereby detecting the direction of a composite magnetic field. In other words, the two hall elements  52  are disposed very close to each other. Accordingly, the angle of 90 degrees between the two hall elements  52 , and the setting directions thereof may be accurately formed. In addition, there is little temperature difference between two hall elements.  
         [0033]     The inner yokes  30  and the outer yoke  40  with one of the projections confronting the magnetic sensor  50  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees, as illustrated by broken lines.  
         [0034]     When a rotating object rotates and the rotary shaft  12  with the permanent magnet  20  rotates, the pair of hall elements  52  of the magnetic sensor  50  senses magnetic flux densities in the magnetic paths  200 ,  202  and provides output signals, which are a sine voltage signal and a cosine voltage signal, as shown in  FIG. 3 .  
         [0035]     Assuming that: the rotation angle is θ; the output signals of the magnetic sensor are Va, Vb; a coefficient that relates to the sensitivity of the magnetic sensor is k; the magnetic flux density of the composite magnetic field is B; and an amount of current supplied to the hall elements is I, the output signals Va, Vb and the rotation angle θ can be expressed as follows. 
 
 Va=kBI sin θ   (1) 
 
 Vb=kBI sin  (θ+90)= kBI cos θ   (2) 
 
 Va/Vb=sin θ/cos θ=tan θ   (3) 
 
θ=arctan ( Va/Vb )   (4) 
 
         [0036]     Thus, the rotation angle θ of the rotating object can be accurately detected.  
         [0037]     A rotation angle detecting device  60  according to the second embodiment will be described with reference to  FIG. 4 . Incidentally, the same reference numeral indicates the same or substantially the same part, portion or component hereafter.  
         [0038]     As shown in  FIG. 4 , one more magnetic sensor  50 ′ is disposed in another gap  32  that is located 180 degrees from the first magnetic sensor  50 . With this additional magnetic sensor  50 ′, a variation in the output signal of each of the magnetic sensors  50 ,  50 ′ can be easily corrected by combining the output signals of both magnetic sensor  50  and the magnetic sensor  50 ′. The additional magnetic sensor may be disposed in a gap other than 180 degrees from the first magnetic sensor  50 . Two or more additional sensor may be also used.  
         [0039]     A rotation angle detecting device  70  according to the third embodiment will be described with reference to  FIG. 5 .  
         [0040]     The rotation angle detecting device  70  is constituted of two pieces of arc-shaped inner yokes  72  and an outer yoke  76  having two projections  78  to provide a pair of gaps  74  so as to be positioned around the permanent magnet  20  opposite to, or at 180 degrees from, the other, instead of four pieces of arc-shaped inner yokes  30  of the first embodiment and the outer yoke  40  having four projections  42  thereof. The inner yokes  72  and the outer yoke  76  with one of the projections  78  confronting the magnetic sensor  50  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees, as illustrated by broken lines.  
         [0041]     It is easier to assemble the inner yokes  72  than the first embodiment.  
         [0042]     A rotation angle detecting device  80  according to the fourth embodiment will be described with reference to  FIG. 6 .  
         [0043]     The rotation angle detecting device  80  is constituted of two pieces of arc-shaped inner yokes  30 , each of which is the same as the inner yoke  30  of the first embodiment and an outer yoke  76  having two projections  78  to provide a gap  32  so as to be positioned around the permanent magnet  20  opposite to, or at 180 degrees from, the other. The inner yokes  30  and the outer yoke  76  with one of the projections  78  confronting the magnetic sensor  50  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees, as illustrated by broken lines.  
         [0044]     It is also easier to assemble the inner yokes  30  than the first embodiment.  
         [0045]     A rotation angle detecting device  90  according to the fifth embodiment will be described with reference to  FIG. 7 .  
         [0046]     The rotation angle detecting device  90  is constituted of a single piece of arc-shaped inner yoke  30  which is the same as the inner yoke  30  of the first embodiment and an outer yoke  76  having two projections  78  so as to be positioned around the permanent magnet  20  opposite to, or at 180 degrees from, the other. The inner yoke  30  and the outer yoke  76  with one of the projections  78  confronting the magnetic sensor  50  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees, as illustrated by broken lines.  
         [0047]     It is much easier to assemble the inner yokes  30  than the first embodiment.  
         [0048]     A rotation angle detecting device  100  according to the sixth embodiment will be described with reference to  FIG. 8 .  
         [0049]     The rotation angle detecting device  100  is constituted of four pieces of arc-shaped inner yokes  30  to provide four gaps  32  and a semi-cylindrical outer yoke  102  having three projections  104  positioned around the permanent magnet  20  at intervals of 90 degrees, instead of the cylindrical outer yoke  40  having four projections  42 . The inner yokes  30  and the outer yoke  102  with one of the projections  104  confronting the magnetic sensor  50  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees, as illustrated by broken lines.  
         [0050]     A rotation angle detecting device  110  according to the seventh embodiment will be described with reference to  FIGS. 9A and 9B .  
         [0051]     The rotation angle detecting device  110  is constituted of four pieces of arc-shaped inner yokes  30  to provide four gaps  32  and a cylindrical outer yoke  112  having a pair of projections  114  positioned around the permanent magnet  20  at intervals of 180 degrees. The inner yokes  30  and the outer yoke  112  with one of the projections  114  confronting the magnetic sensor  50  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees, as illustrated by broken lines in  FIG. 9A . The outer yoke  112  is made thinner than the inner yokes  30  to accommodate lead wires extending from the magnetic sensor  50 , as shown in  FIG. 9B .  
         [0052]     A rotation angle detecting device  120  according to the eighth embodiment will be described with reference to  FIG. 10 .  
         [0053]     The rotation angle detecting device  120  is constituted of four pieces of arc-shaped first yokes  122  positioned at a side of the permanent magnet  20  at intervals of 90 degrees to provide four gaps and a cylindrical second yoke  124  disposed at the side of the first yokes opposite the permanent magnet  20 . The second yoke has four projections  126  axially extending toward the gaps of the first yokes  122  at intervals of 90 degrees. The first yokes  122  and the second yoke  126  with one of the projections  126  confronting the magnetic sensor  50  form magnetic paths to cross each other at the sensor  50  at an angle of 90 degrees.  
         [0054]     Because the first and the second yokes are axially shifted from the permanent magnet  20 , the outside diameter of rotation angle detecting device can be reduced.  
         [0055]     A rotation angle detecting device  130  according to the ninth embodiment will be described with reference to  FIG. 11 .  
         [0056]     The rotation angle detecting device  130  is constituted of four pieces of arc-shaped first yokes  132  positioned around the permanent magnet  20  at intervals of 90 degrees to provide four gaps and a cylindrical second yoke  134  disposed at a side of the first yokes  132 . The second yoke  134  has four projections  136  axially extending toward the gaps of the first yokes  132  at intervals of 90 degrees. The first yokes  132  and the second yoke  134  with one of the projections  136  confronting the magnetic sensor  50  form magnetic paths to cross each other at the sensor  50  at an angle of 90 degrees.  
         [0057]     Because the second yokes are axially shifted from the permanent magnet  20 , the outside diameter of rotation angle detecting device can be reduced.  
         [0058]     A rotation angle detecting device  140  according to the tenth embodiment will be described with reference to  FIG. 12 .  
         [0059]     The rotation angle detecting device  140  is constituted of four pieces of arc-shaped inner yokes  142  positioned around the permanent magnet  20  at intervals of 90 degrees to provide four gaps  144 , four auxiliary yokes  160  disposed between the permanent magnet  20  and the inner yokes  142  to confront to one of the gaps  144  and a cylindrical outer yoke  150  disposed around the inner yokes  142 . The outer yoke  150  has four projections  152  axially extending toward the gaps of the inner yokes  142  at intervals of 90 degrees. The inner yokes  142 , the outer yoke  150  with one of the projections  152  confronting the magnetic sensor  50  and one a pair of auxiliary yokes  160  form magnetic paths  200 ,  202  to cross each other at the sensor  50  at an angle of 90 degrees.  
         [0060]     The auxiliary yokes  160  are effective to increase the strength of the magnetic field.  
         [0061]     In the above embodiments, a pair of hall elements  52  are disposed in a chip of the magnetic sensor  50  at an angle of 90 degrees to each other. The angle may be changed to an angle other than 90 degrees. The magnetic sensor  50  can be constituted of three or more hall elements or magneto-resistance elements.  
         [0062]     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.