Patent Abstract:
Rotation detecting apparatus for detecting rotation of a magnetic rotor includes: a sensor chip having a magnetoresistive device; and a bias magnet. The magnetoresistive device is capable of detecting change of a magnetic vector near the sensor chip so that the rotation detecting apparatus detects the rotation of the magnetic rotor. The change of the magnetic vector is generated by the bias magnetic field and the rotation of the magnetic rotor. The bias magnet is disposed around the sensor chip so that a deflection angle of the magnetic vector is controllable.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based on Japanese Patent Applications No. 2004-196038 filed on Jul. 1, 2004, and No. 2004-327742 filed on Nov. 11, 2004, the disclosures of which are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to rotation detecting apparatus. 
   BACKGROUND OF THE INVENTION 
   A rotation detecting apparatus detects, for instance, revolutions of an engine mounted on a vehicle, and rotations of a rotator provided in a general-purpose machine. More specifically, the rotation detecting apparatus is capable of detecting rotation modes of the rotor by utilizing changes contained in resistance values of magnetic resistance elements. 
   Conventionally, as the above-described rotation detecting apparatus capable of detecting the rotations by utilizing the resistance value changes in the magnetic resistance elements, for example, a rotation detecting apparatus described in Japanese Laid-open Patent Application No. H07-333236 is known. 
   This rotation detecting apparatus includes a magnetic resistance element and a biasing magnet. The magnetic resistance element and the biasing magnet are stored into a case member. In this rotation detecting apparatus, a tip portion of the biasing magnet abuts against an inside bottom plane of the case member, and further, a tip portion of a molding member containing a magnetic sensor chip abuts against a projection portion formed on this inside bottom plane, so that such an “M-to-M distance” is determined, and this “M-to-M distance” corresponds to a distance between the magnetic resistance element and the biasing magnet. In other words, in this rotation angle detecting apparatus, deflection angles of the above-explained magnetic vectors which also contain a relationship with a rotor via a projected length of the projection portion formed on the inside bottom plane of the case member are optimized, namely, a sensing sensitivity as to the rotation angle detecting apparatus is optimized. 
   On the other hand, although the deflection angles of the magnetic vectors corresponding to the sensing sensitivity for the rotation detecting apparatus can be adjusted based upon the above-described M-to-M distance, the projected length of the projection portion formed on the case member must be changed in order to adjust this sensing sensitivity of the rotation detecting apparatus. As a result, in such a case that the above-explained M-to-M distance must be changed in view of unavoidable reasons and this distance change is caused by, for example, the shape of the rotor for the rotation detection mode, the case member itself must also be changed in view of the unavoidable reason. That is, for instance, parts numbers as to these changed case members must be increased, and also, a total number of metal molds must be unavoidably increased which are required to mold these changed case members. In an actual case, such an adjustment itself that the deflection angles of the magnetic vectors are adjusted only by changing the above-described M-to-M distance may cause some limitations. That is, a freedom of designing as to the rotation detecting apparatus is low, and the range for adjusting the deflection angles of the magnetic vectors is restricted in the practical field. 
   SUMMARY OF THE INVENTION 
   In view of the above-described problem, it is an object of the present invention to provide a rotation sensor having high sensing sensitivity and high degree of design freedom. 
   Rotation detecting apparatus for detecting rotation of a magnetic rotor includes: a sensor chip having a magnetoresistive device; and a bias magnet for applying bias magnetic field to the magnetoresistive device. The bias magnet and the sensor chip are integrated. The magnetoresistive device is capable of detecting change of a magnetic vector near the sensor chip on the basis of resistance change of the magnetoresistive device so that the rotation detecting apparatus detects the rotation of the magnetic rotor. The change of the magnetic vector is generated by the bias magnetic field and the rotation of the magnetic rotor. The bias magnet is disposed around the sensor chip so that a deflection angle of the magnetic vector is controllable. 
   The above apparatus can control the deflection angle of the magnetic vector so that the detection sensitivity of the rotation is improved. Further, the deflection angle of the magnetic vector can be controlled by the shape of the bias magnet so that the degree of design freedom becomes larger. 
   Preferably, the bias magnet includes a hollow portion having a groove, and the groove has a predetermined shape for providing control of the deflection angle of the magnetic vector. More preferably, the hollow portion of the bias magnet accommodates the sensor chip, and has a rectangular shape with a pair of wide sides. The wide sides of the hollow portion face the sensor chip, and are parallel to a surface of the sensor chip, the surface on which the magnetoresistive device is disposed, and the groove of the hollow portion extends in a longitudinal direction of the bias magnet. 
   Further, rotation detecting apparatus for detecting rotation of a magnetic rotor includes: a sensor chip having a magnetoresistive device; and a bias magnet for applying bias magnetic field to the magnetoresistive device. The bias magnet and the sensor chip are integrated in such a manner that the bias magnet is disposed around the sensor chip. The magnetoresistive device is capable of detecting change of a magnetic vector near the sensor chip on the basis of resistance change of the magnetoresistive device so that the rotation detecting apparatus detects the rotation of the magnetic rotor. The change of the magnetic vector is generated by the bias magnetic field and the rotation of the magnetic rotor. The bias magnet includes a hollow portion having a groove. The sensor chip is accommodated in the hollow portion of the bias magnet. The groove is disposed on an inner wall of the hollow portion. 
   The above apparatus can control the deflection angle of the magnetic vector so that the detection sensitivity of the rotation is improved. Further, the deflection angle of the magnetic vector can be controlled by the shape of the bias magnet so that the degree of design freedom becomes larger. 
   Further, rotation detecting apparatus for detecting rotation of a magnetic rotor includes: a sensor chip having a magnetoresistive device; and a bias magnet for applying bias magnetic field to the magnetoresistive device. The bias magnet and the sensor chip are integrated in such a manner that the bias magnet is disposed around the sensor chip. The magnetoresistive device is capable of detecting change of a magnetic vector near the sensor chip on the basis of resistance change of the magnetoresistive device so that the rotation detecting apparatus detects the rotation of the magnetic rotor. The change of the magnetic vector is generated by the bias magnetic field and the rotation of the magnetic rotor. The bias magnet includes a hollow portion. The sensor chip is accommodated in the hollow portion of the bias magnet. The hollow portion includes an inner wall, which faces the magnetoresistive device. The bias magnet has a low magnetic strength near the inner wall facing the magnetoresistive device, the low magnetic strength being lower than those of other positions of the bias magnet. 
   The above apparatus can control the deflection angle of the magnetic vector so that the detection sensitivity of the rotation is improved. Further, the deflection angle of the magnetic vector can be controlled by the shape of the bias magnet so that the degree of design freedom becomes larger. 
   Further, rotation detecting apparatus for detecting rotation of a magnetic rotor includes: a sensor chip having a magnetoresistive device; and a bias magnet for applying bias magnetic field to the magnetoresistive device. The bias magnet and the sensor chip are integrated in such a manner that the bias magnet is disposed around the sensor chip. The magnetoresistive device is capable of detecting change of a magnetic vector near the sensor chip on the basis of resistance change of the magnetoresistive device so that the rotation detecting apparatus detects the rotation of the magnetic rotor. The change of the magnetic vector is generated by the bias magnetic field and the rotation of the magnetic rotor. The bias magnet includes a hollow portion. The sensor chip is accommodated in the hollow portion of the bias magnet. The hollow portion includes an inner wall, which faces the magnetoresistive device. The bias magnet has a high magnetic strength portion near the inner wall not facing the magnetoresistive device, the high magnetic strength portion having high magnetic strength higher than those of other positions of the bias magnet. 
   The above apparatus can control the deflection angle of the magnetic vector so that the detection sensitivity of the rotation is improved. Further, the deflection angle of the magnetic vector can be controlled by the shape of the bias magnet so that the degree of design freedom becomes larger. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  is a cross sectional view showing rotation detecting apparatus according to a first embodiment of the present invention; 
       FIG. 2  is a plan view showing a biasing magnet of the apparatus according to the first embodiment; 
       FIG. 3  is a schematic cross sectional view showing the biasing magnet taken along line III—III in  FIG. 2 ; 
       FIGS. 4A and 4C  are plan view and side view showing a biasing magnet of the first simulation, and  FIG. 4B  is a schematic view showing a triangle groove of the biasing magnet of the first simulation, according to the first embodiment; 
       FIG. 5  is a schematic view explaining the first simulation, according to the first embodiment; 
       FIG. 6A  is a perspective view showing magnetic flux of the biasing magnet with no groove, and  FIG. 6B  is a perspective view showing magnetic flux of the biasing magnet with a groove, according to the first embodiment; 
       FIGS. 7A to 7C  are tables explaining results of the first simulation, according to the first embodiment; 
       FIG. 8  is a graph showing a relationship between a M-M distance and a deflection angle of a magnetic vector obtained by the first simulation, according to the first embodiment; 
       FIGS. 9A to 9E  are plan views showing a triangle groove of the biasing magnet of the second simulation, according to the first embodiment; 
       FIG. 10  is a graph explaining results of the second simulation, according to the first embodiment; 
       FIG. 11  is a perspective view showing a biasing magnet of the third simulation, according to the first embodiment; 
       FIG. 12  is a table explaining results of the third simulation, according to the first embodiment; 
       FIG. 13  is a perspective view showing a biasing magnet according to a first modification of the first embodiment; 
       FIG. 14  is a perspective view showing a biasing magnet according to a second modification of the first embodiment; 
       FIG. 15  is a table explaining results of a simulation of the biasing magnet shown in  FIGS. 13 and 14 , according to the first embodiment; 
       FIG. 16  is a plan view showing a biasing magnet according to a third modification of the first embodiment; 
       FIG. 17  is a schematic view explaining rotation detection by using rotation detecting apparatus according to a comparison of the first embodiment; 
       FIG. 18  is a cross sectional view showing the rotation detecting apparatus according to the comparison of the first embodiment; 
       FIG. 19  is a perspective view showing a bias magnet and a sensor chip in rotation detecting apparatus according to the second embodiment of the present invention; 
       FIG. 20  is a perspective view showing magnetic flux of a bias magnet, according to a comparison of the second embodiment; 
       FIG. 21  is a plan view showing the magnetic flux of the biasing magnet, according to the comparison of the second embodiment; 
       FIG. 22  is a perspective view showing magnetic flux of a biasing magnet, according to the second embodiment; 
       FIG. 23  is a plan view showing the magnetic flux of the biasing magnet, according to the second embodiment; 
       FIG. 24  is a graph showing a relationship between an air gap and a deflection angle of a magnetic vector obtained by the second embodiment and the comparison of the second embodiment; 
       FIG. 25  is a plan view showing manufacturing equipment of the biasing magnet, according to the second embodiment; 
       FIG. 26  is a cross sectional view showing the equipment taken along line XXVI—XXVI in  FIG. 25 ; 
       FIG. 27  is a cross sectional view explaining orientation of magnetic powder before the orientation is controlled, according to the second embodiment; 
       FIG. 28  is a cross sectional view explaining orientation of magnetic powder after the orientation is controlled, according to the second embodiment; 
       FIG. 29  is a perspective view showing magnetic flux of a bias magnet, according to a third embodiment of the present invention; 
       FIG. 30  is a plan view showing manufacturing equipment of the biasing magnet, according to the third embodiment; 
       FIG. 31  is a cross sectional view explaining orientation of magnetic powder after the orientation is controlled, according to the third embodiment; 
       FIG. 32  is a perspective view showing magnetic flux of a bias magnet, according to a modification of the third embodiment; and 
       FIG. 33  is a plan view showing manufacturing equipment of the biasing magnet, according to the modification of the third embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (First Embodiment) 
   The inventors have preliminary studied about rotation detecting apparatus as a comparison of a first embodiment of the present invention. The apparatus is capable of detecting rotations by utilizing resistance value changes in the magnetic resistance elements.  FIG. 17  indicates a flat-surface structure of a rotation detecting apparatus such as a crank angle sensor of an engine. 
   As shown in  FIG. 17 , in this rotation detecting apparatus, a sensor chip  11  has been arranged in such a manner that this sensor chip  11  is located opposite to a rotor “RT” which corresponds to an object to be detected. The sensor chip  11  has been equipped with a magnetic resistance element pair  1  which is constituted by two pieces of magnetic resistance elements MRE 1  and MRE 2 ; and also, another magnetic resistance element pair  2  which is constituted by two pieces of magnetic resistance elements MRE 3  and MRE 4 . Then, the sensor chip  11  has been manufactured in an integrated circuit form in combination with a processing circuit for this sensor chip  11 , and the integrated sensor chip member has been molded in an integral body by using a molding member  12 . Concretely, this rotation detecting apparatus owns the following structure. That is, the sensor chip  11  has been mounted on one end of a lead frame (not shown) inside the molding member  12 , and various terminals such as a power supply terminal T 1 , an output terminal T 2 , and a GND (ground) terminal T 3  have been conducted from the other end of the lead frame. Also, a biasing magnet  13  has been arranged in the vicinity of the sensor chip  11  in such a manner that this biasing magnet  13  surrounds the molding member  12 . The biasing magnet  13  applies biasing magnetic fields to both the above-described magnetic resistance element pairs  1  and  2 . Then, this biasing magnet  13  is made of a hollow cylindrical shape provided with a hollow portion  14  along a longitudinal direction of this biasing magnet  13 . While the molding member  12  has been stored in this hollow portion  14 , the biasing magnet  13  has been fixed at a predetermined position by using an adhesive agent, or the like. 
   In the rotation detecting apparatus constructed of the above-explained structure, when the rotor RT is rotated, changes contained in magnetic vectors which are generated in conjunction with the above-described biasing magnetic fields may be sensed as changes contained in resistance values of the respective magnetic, resistance elements MRE 1  to MRE 4 , and then, electric signals may be outputted from the sensor chip  11  in response to the sensed resistance value changes. That is, in this rotation detecting apparatus, changes contained in potentials at a center point between the magnetic resistance elements MRE 1  and MRE 2  of the magnetic resistance element pair  1  which constitutes a half bridge circuit, and also, in potentials at a center point between the magnetic resistance elements MRE 3  and MRE 4  of the magnetic resistance element pair  2  which similarly constitutes a half bridge circuit, are applied to the above-described processing circuit. In the processing circuit, various sorts of process operations such as a differential amplifying operation and a binary processing operation are carried out with respect to the potential changes, and thereafter, the process electric signals are derived from the output terminal T 2 . 
   Also, in the case that such a rotation detecting apparatus for detecting the rotation modes of the rotor is used in a practical field, both the molding member  12  which has molded the sensor chip  11  and the like, and the biasing magnet  13  are stored in a proper case member. In addition, while the entire rotation detecting apparatus has been stored in a resin case which may protect the respective terminals T 1  to T 3  in combination with this case member, the resultant resin case is mounted on an engine, and the like.  FIG. 18  indicates an example as to rotation detecting apparatus having the above-explained structure, which is mounted on an engine, and the like. 
   As indicated in  FIG. 18 , in such rotation detecting apparatus, both the molding member  12  and the biasing magnet  13  are stored into a case member  30  having a bottom-having cylindrical shape, and these members  12 ,  13 ,  30  are molded with a resin case  40  in an integral body. The molded resin case  40  is mounted on an engine, or the like. This resin case  40  may also function as a connecting connector which connects the own resin case  40  to an electronic control apparatus, and the like by a wiring manner. Also, the above-explained respective terminals T 1  to T 3  have been electrically connected to terminal conducting members  50   a  to  50   c , which also have terminals functioning as the above-described connector. These terminal conducting members  50   a  to  50   c  have been provided within the resin case  40  in an integral manner. Then, in this rotation detecting apparatus, a tip portion of the biasing magnet  13  abuts against an inside bottom plane of the case member  30 , and further, a tip portion of the molding member  12  containing the sensor chip  11  abuts against a projection portion  31  formed on this inside bottom plane, so that such an “M (i.e., MRE)-to-M (i.e., Magnet) distance” is determined, and this “M-to-M distance” corresponds to a distance between the magnetic resistance element pairs  1  and  2 , and the biasing magnet  13 . In other words, in this rotation angle detecting apparatus, deflection angles of the above-explained magnetic vectors which also contain a relationship with the rotor RT via a projected length of the projection portion  31  formed on the inside bottom plane of the case member  30  are optimized, namely, a sensing sensitivity as to the rotation angle detecting apparatus is optimized. 
   On the other hand, although the deflection angles of the magnetic vectors corresponding to the sensing sensitivity for the rotation detecting apparatus can be adjusted based upon the above-described M-to-M distance, as previously explained, the projected length of the projection portion  31  formed on the case member  30  must be changed in order to adjust this sensing sensitivity of the rotation detecting apparatus. As a result, in such a case that the above-explained M-to-M distance must be changed in view of unavoidable reasons and this distance change is caused by, for example, the shape of the rotor RT for the rotation detection mode, the case member  30  itself must also be changed in view of the unavoidable reason. That is, for instance, parts numbers as to these changed case members  30  must be increased, and also, a total number of metal molds must be unavoidably increased which are required to mold these changed case members  30 . In an actual case, such an adjustment itself that the deflection angles of the magnetic vectors are adjusted only by changing the above-described M-to-M distance may cause some limitations. That is, a freedom of designing as to the rotation detecting apparatus is low, and the range for adjusting the deflection angles of the magnetic vectors is restricted in the practical field. 
   As a result of experiments performed by the inventors of the present invention, the following facts could be confirmed: That is, the deflection angles of the above-described magnetic vectors are changed in conjunction with the rotations of the rotor in correspondence with the sectional shape of the hollow portion of the biasing magnet, into which the sensor chip is stored. Moreover, the deflection angles of the magnetic vectors, namely, the sensing sensitivity as this rotation detecting apparatus can be greatly improved, depending upon the sectional shape of the hollow portion. As a consequence, in accordance with the above-explained structure as the rotation detecting apparatus, while a relative positional relationship (for example, previously-explained “M-to-M” distance) among the magnetic resistance elements and the biasing magnet is not always changed, the deflection angles of the magnetic vectors which are give influences to the magnetic resistance elements can be adjusted by the sectional shape of the hollow portion. Not only the deflection angles of the magnetic vectors may be enlarged in the above-described manner, but also the improvement of the sensing sensitivity as the rotation detecting apparatus may be easily realized. Moreover, the deflection angles of the magnetic vectors may be basically adjusted by arranging the sectional shape of the hollow portion, so that the freedom degree as to designing of this rotation detecting apparatus may be largely improved. 
   Also, in this case, as the sectional shape of the hollow portion of the biasing magnet, for instance, in accordance with an inventive idea, such a shape may become advantageous that a groove has been formed in an inner side wall of the hollow portion of the above-described biasing magnet. This shape could also be confirmed by the experiments made by the inventors of the present invention. 
   Then, as this groove, for example, in accordance with an inventive idea, in such a case that the hollow portion of the biasing magnet has been formed in a substantially rectangular shape which corresponds to the sectional shape of the sensor chip, it may be effective to provide a groove in such a forming mode that this groove is elongated along a longitudinal direction of the biasing magnet with respect to an inner side wall of each of long edge sides of the hollow portion, which is located in parallel to and opposite to the arranging plane of the magnetic resistance elements in the sensor chip of the hollow portion. Moreover, in this case, in accordance with an inventive idea, since this groove is formed in the center portions of the inner side walls on the side of the respective long edges of the hollow portion, while the symmetrical characteristic as to the deflection angles of the magnetic vectors may be maintained, the deflection angles of the magnetic vectors can be easily adjusted, namely, can be readily enlarged. 
   It should be understood that, for example, in accordance with an inventive idea, as to a shape of the above-described groove, the below-mentioned shape can be employed: 
   (A) A groove is employed, the sectional shape of which is a triangular shape where a groove bottom portion constitutes a vertex. 
   Alternatively, in accordance with an inventive idea, as to a shape of the above-described groove, the below-mentioned shape can be employed: 
   (B) A groove is employed, the sectional shape of which is a semi-circular shape where a groove bottom portion constitutes an arc. Since the groove whose sectional shape is a triangular shape or semi-circular shape is employed, when the biasing magnet is molded by employing a metal mold, fluidity owned by a magnetic material within this metal mold can be hardly blocked by the groove. As a consequence, the magnetic material having better uniformity can be molded as the biasing magnet, as compared with that of such a case that a groove having another different shape is employed. Also, since these groove shapes are employed, the above-described adjusting operation as to the deflection angles of the magnetic vectors can be easily and firmly realized, which could also be confirmed by experiments made by the inventors of the present invention. 
   Referring now to  FIG. 1  to  FIG. 12 , a first embodiment mode for embodying a rotation detecting apparatus according to the present invention will be described. 
     FIG. 1  indicates an entire structure of the rotation detecting apparatus according to this embodiment mode. As indicated in  FIG. 1 , this rotation detecting apparatus has been arranged in a similar mode as represented in, for example,  FIG. 17 . That is, a molding member  12  containing a sensor chip  11  in which both the magnetic resistance element pairs  1  and  2  have been arranged in the similar mode, and a biasing magnet  13  which applies biasing magnetic fields to both the magnetic resistance element pairs  1  and  2  have been stored in a bottom-having cylindrical shaped case member  30 . This case member  30  has a projection portion  31 . Also, this case member  30  has been assembled in a resin case  40  in an integral body. The resin case  40  has been molded in such a manner that this resin case  40  may also function as a connecting connector which connects the own resin case  40  to an electronic control apparatus, and the like by a wiring manner. On the other hand, the above-explained respective terminals T 1  to T 3  have been electrically connected to terminal conducting members  50   a  to  50   c  which also have terminals functioning as the above-described connector. These terminal conducting members  50   a  to  50   c  have been provided within the resin case  40  in an integral body. However, in accordance with this embodiment mode, the above-described biasing magnet  13  has been manufactured with the following feature, as separately shown in a front view thereof of  FIG. 2 . That is, in this biasing magnet  13 , a triangular groove  17  has been formed in a center portion of an inner side wall on the side of each of long edges which are located parallel to and opposite to the arranging planes of the magnetic resistance element pairs  1  and  2  in the sensor chip  11 . Each of the triangular grooves  17  has been formed in such a triangular shape as viewed in a sectional plane thereof. In this triangular shape, a groove bottom portion constitutes a vertex. As apparent from also  FIG. 1 , this triangular groove  17  is elongated along the entire longitudinal direction of the above-explained biasing magnet  13 . 
     FIG. 3  is a perspective view for showing a sectional structure of the biasing magnet  13  in the case that such a biasing magnet.  13  is cut along a line III—III represented in  FIG. 2 . An internal shape of the above-described triangular groove  17  formed in this biasing magnet  13 , and an internal shape of a hollow portion  14  are illustratively shown in this drawing. 
   Next, a description is made of results of simulations which were performed by the inventors of the present invention as to the deflection angles of the above-described magnetic vectors which were changed, since the triangular grooves  17  were formed in the hollow portion  14  of the biasing magnet  13 . 
   The contents of the respective simulations are given as follows: That is, as a first simulation, in the biasing magnet  13  where the above-described triangular grooves  17  had been formed, an analyzing operation was carried out with respect to the deflection angles of the magnetic vectors in such a case that the previously explained “M-to-M distance” was changed. Also, as a second simulation, an analyzing operation was carried out with respect to the deflection angles of the magnetic vectors in the case that the shapes of the triangular grooves  17  were changed. Furthermore, as a third simulation, an analyzing operation was carried out with respect to the deflection angles of the magnetic vectors in the case that the lengths of the triangular grooves  17  were changed. Simulation conditions, simulated results, and the like will be subsequently described in detail according to the first to third simulations. 
   [First Simulation] 
   First, a description is made of an analyzing condition with respect to the above-explained first simulation. As shown in  FIGS. 4A to 4C , as the biasing magnet  13  which is employed in this analyzing operation, the below-mentioned biasing magnet was used. That is, dimensions of this biasing magnet  13  were given: a length of this biasing magnet  13  was “13.5 mm”; a lateral width thereof was “10.0 mm”; and a longitudinal width thereof was “9.0 mm.” In this biasing magnet  13 , such a hollow portion  14  was formed, the dimensions of which were given: a lateral width of the hollow portion  14  was “6.5 mm”; and a longitudinal width thereof was “2.6 mm.” Also, as the triangular grooves  17  which are formed in this hollow portion  14 , such a triangular groove as shown in  FIG. 4B  was used. That is, dimensions of this triangular groove  17  were given: a width “X” of the triangular groove  17  (namely, width of bottom edge) was “2.0 mm”; and a depth “Z” thereof was “0.8 mm.” Then, with employment of the above-described biasing magnet  13 , the analyzing operations are carried out in accordance with the following conditions: That is, as analyzing points for analyzing open degrees of the magnetic vectors which are required so as to calculate the above-explained deflection angles of the magnetic vectors, two sets of an analyzing point “IVA” and another analyzing point “IVB” are employed which correspond to positions where the above-described magnetic resistance element pairs  1  and  2  are actually arranged. Also, while distances between these two analyzing points IVA, IVB, and a rotor opposing plane  13   a  as an edge plane of the biasing magnet  13  are changed, namely M-to-M distances are changed, an analyzing operation is carried out as to how a deflection angle of a magnetic vector is represented with respect to each of the M-to-M distances. 
   On the other hand, as the rotor RT employed in this first analyzing operation, such a rotor “RT” having a shape indicated in  FIG. 5  was used. Then, open degrees of magnetic vectors at the above-described analyzing points “IVA” and “IVB” were analyzed when a point “VM” of a hill portion and another point “VC” of a valley portion were located opposite to the above-described rotation detecting apparatus while this rotor RT of  FIG. 5  was rotated. Both the point “VM” of the hill portion and the point “VC” of the valley portion have been formed on an outer peripheral portion of the rotor RT. Then, it is so assumed that deflection angles of magnetic vectors are calculated based upon such an angle difference between an open angle of the magnetic vectors at the analyzing points “IVA” and “IVB” when the rotation detecting apparatus is located opposite to the point “VC”, and another open angle of the magnetic vectors at the analyzing points “IVA” and “IVB” when the rotation detecting apparatus is located opposite to the point “VM.” It should also be understood that as indicated in this  FIG. 5 , a distance between a rotor opposing plane of the rotation detecting apparatus and a hill portion of the rotor RT is defined as “0.5 mm”, namely, an air gap “AG” is set to 0.5 mm. 
     FIGS. 7A to 7C  indicate results of this first simulation.  FIG. 7A  shows the simulation results obtained from such a biasing magnet  13  that the above-described triangular grooves  17  are not formed.  FIG. 7B  indicates the simulation results obtained from such a biasing magnet  13  that the above-explained triangular grooves  17  have been formed. 
   As apparent from these simulation results indicated in FIG.  7 A and  FIG. 7B , as to each of the M-to-M distances, although a magnetic sensitivity of the biasing magnet  13  where the triangular grooves  17  have been formed becomes lower than a magnetic sensitivity of such a biasing magnet  13  where the triangular grooves  17  have not been formed, a deflection angle of a magnetic vector of the first-mentioned biasing magnet  13  with the groove  17  exceeds a deflection angle of a magnetic vector of the last-mentioned biasing magnet  13  with no groove. By the way, as a factor causing the magnetic strength to be lowered, the below-mentioned reason may be conceived. That is, as to the biasing magnet  13  where the triangular grooves  17  have been formed, a volume of this biasing magnet  13  as the magnet is lowered by a volume of the triangular grooves  17 , as compared with such a biasing magnet  13  where the triangular grooves  17  are not formed. On the other hand, as a factor causing the deflection angle of the magnetic vector to be enlarged, the below-mentioned reason may be conceived. That is, since the magnetic strength is lowered, the deflectability as to the magnetic vector could be improved. It should also be understood that the following fact may also be conceived as one of these factors. That is, since the triangular grooves  17  are formed in the biasing magnet  13 , a generation mode as to magnetic fluxes (magnetic fields) generated from the biasing magnet  13  itself is changed. In other words, as indicated in  FIG. 6A , in the previously-explained biasing magnet  13  where no triangular grooves  17  are formed, which has been provided in the rotation detecting apparatus exemplified in  FIG. 18 , magnetic flux density (arrows of solid lines indicated in  FIG. 6A ) along the rotation direction of the rotor RT relatively becomes low, as compared with magnetic flux density (white-blanked arrows shown in  FIG. 6A ) along a direction which is located perpendicular to this rotation direction of the rotor RT. To the contrary, in the biasing magnet  13  where the triangular grooves  17  have been formed, as shown in  FIG. 6B , magnetic flux density (white-blanked arrows indicated in  FIG. 6B ) along the rotation direction of the rotor RT relatively becomes high, as compared with magnetic flux density (arrows of solid lines shown in  FIG. 6B ) along a direction which is located perpendicular to this rotation direction of the rotor RT. As a result of the high magnetic flux density, it can also be predicted that the deflection angles of the magnetic vectors may be enlarged. 
   Also, as apparent from a comparison made between values of areas which are surrounded by broken lines in  FIG. 7A  and  FIG. 7B , as to magnetic field strengths at the above-described point “VM”, a magnetic field strength of the biasing magnet  13  having no triangular grooves  17 , the M-to-M distance of which is “1.3 mm” becomes such a value of “−14.0 mT”, whereas a magnetic field strength of the biasing magnet  13  having the triangular grooves  17 , the M-to-M distance of which is “1.4 mm” becomes such a value of “−13.9 mT”, namely these magnetic field strengths at the point VM are substantially equal to each other. However, also even in this case, the deflection angle of the magnetic vector as to the biasing magnet  13  having no triangular grooves  17  is equal to “24.3 degrees”, whereas the deflection angle of the magnetic vector as to the biasing magnet  13  having the triangular grooves  17  is equal to “28.0 degrees”, resulting in an improvement of the deflection angle of the magnetic vector, while the adverse influence caused by the “M-to-M” distance can be mitigated. 
   On the other hand,  FIG. 7C  shows such a simulation result that the sensitivities of both the magnetic resistance element pairs  1  and  2  have been considered with respect to the magnetic strengths which have been acquired in  FIG. 7A  and  FIG. 7B . This simulation result of  FIG. 7C  is represented as a graph in  FIG. 8 . As indicated in  FIG. 8 , deflection angles of magnetic vectors as to the biasing magnet  13  where the triangular grooves  17  have been formed are enlarged over all of the M-to-M distances, as compared with deflection angles of magnetic vectors as to the biasing magnet  13  where the triangular grooves  17  have not been formed. For example, in the “M-to-M” distance of “1.3 mm” which corresponds to an area surrounded by a broken line of  FIG. 7C , a deflection angle of a magnetic vector as to the biasing magnet  13  where the triangular grooves  17  have been formed is enlarged approximately “1.35” times higher than a deflection angle of a magnetic vectors as to the biasing magnet  13  where the triangular grooves  17  have not been formed. 
   As previously explained, such a confirmation can be made. That is, since the triangular grooves  17  are formed in the hollow portion  14  of the biasing magnet  13 , this groove formation may give an extremely large merit in order to enlarge the deflection angles of the magnetic vectors. 
   [Second Simulation] 
   Next, a second simulation is explained. In this second simulation, analyzing operations were carried out as to deflection angles of the above-described magnetic vectors in such a case that a width “X”, and a depth “Z” as to a triangular groove  17  which will be formed in the hollow portion  14  were changed respectively. It should also be understood that other shapes of this biasing magnet  13  are made equal to those of the previously explained first simulation. 
     FIGS. 9A to 9E  shows shapes of triangular grooves  17  which constitute analysis objects in this second simulation. As represented in  FIGS. 9A to 9E , in this second simulation, 5 samples “S 1 ” to “S 5 ” were analyzed respectively. That is, as the samples “S 1 ” to “S 3 ”, the below-mentioned triangular grooves  17  have been employed, the widths “X” of which were “0.5 mm”; “1.0 mm”; and “1.5 mm”, and also, the depth “Z” of which was “0.5 mm.” Furthermore, as the samples “S 4 ” to “S 5 ”, the below-mentioned triangular grooves  17  have been employed, the depths “Z” of which were “1.0 mm”; and “1.5 mm”, and also, the width “X” of which was “1.0 mm.” It should also be understood that in this second simulation, the analyzing operations are carried out in such a case that the above-explained air gaps “AG” are three sorts of air gaps, namely, “0.5 mm”; “1.0 mm”; and “1.5 mm”, respectively. It should further be noted that as a shape of a rotor “RT”, the same shape as that of the first simulation is used. Further, the analyzing operations are carried out while the above-descried M-to-M distance is fixed to “1.3 mm.” 
     FIG. 10  is a graph for indicating results of this second simulation. The graph of  FIG. 10  clearly represents deflection angles of magnetic vectors as to the above-explained samples S 1  to S 5 , and in addition, a deflection angle of a magnetic vector as to a biasing magnet where the triangular groove  17  is not formed, for the sake of comparisons. As apparent from the simulation results with respect to the samples Si to S 3 , which are graphically indicated in  FIG. 10 , the wider the width “X” of the triangular groove  17  is widened, the larger the deflection angle of the magnetic vector is increased. Also, as apparent from the simulation results with respect to the samples S 2 , S 4 , and S 5 , which are graphically indicated in  FIG. 10 , the deeper the depth “Z” of the triangular groove  17  is increased, the larger the deflection angle of the magnetic vector is increased. It should also be noted that angles which are attached among the respective graphs indicative of simulation results of these samples S 1  to S 5  correspond to such values for indicating how the deflection angles of the magnetic vectors as to the respective samples S 1  to S 5  have been enlarged when the air gaps AG thereof are equal to “1.5 mm” with respect to the deflection angle of the magnetic vector of the biasing magnet where the triangular groove  17  is not formed when the air gap AG thereof is selected to be similarly “1.5 mm.” As also can be understood from these values, only as to the above-explained samples S 1  to S 5 , if the depth “Z” of the triangular groove  17  is made large (deeper), then the deflection angle of the magnetic vector may be furthermore enlarged, as compared with such a case that the width “X” of the triangular groove  17  is made larger (wider). 
   [Third Simulation] 
   Next, a third simulation is explained. In this third simulation, analyzing operations were carried out as to deflection angles of the above-described magnetic vectors in such a case that a length “L” as to a triangular groove  17  was changed as exemplified in  FIG. 11 , not in the case that the triangular grooves  17  were formed in the entire portion of the biasing magnet  13  along the longitudinal direction thereof. It should be noted that while other shapes of the biasing magnet  13  are made equal to those of the previous first simulation, analyzing operations were carried out in such a case that the above-explained air gaps “AG” were three sorts of air gaps, namely, “0.5 mm”; “1.0 mm”; and “1.5 mm”, respectively. It should also be noted that as a shape of a rotor “RT”, the same shape as that of the first simulation is used, and analyzing operations were carried out while the above-described M-to-M distance is fixed to “1.3 mm.” 
     FIG. 12  indicates results of this third simulation. As apparent from this  FIG. 12 , in any case that the air gap AG corresponds to “0.5 mm”, “1.0 mm”, and “1.5 mm”, since the triangular groove  17  having the length “L” is formed in the biasing magnet  13 , a deflection angle of a magnet vector is increased (see samples “U 2 ” to “U 5 ”), as compared with that of such a biasing magnet (namely, sample “U 1 ”) where the triangle groove  17  is not formed. However, a large change cannot be seen from deflection angles of magnetic vectors as to biasing magnets in which lengths “L” of triangle grooves  17  are longer than a certain length, concretely speaking, the lengths “L” become longer than “6.7 mm” of the sample U 3 . From the above-explained conditions, the following fact can be revealed: That is, in order that the triangular groove  17  is formed in the hollow portion  14  so as to enlarge the deflection angle of the magnetic vector, if such a triangular groove  17  having a certain length separated from the rotor opposing plane  13   a  of the biasing magnet  13  is formed in this hollow portion  14 , then the sufficiently enlarged deflection angle of the magnetic vector can be obtained. 
   Also, in this third simulation, an analyzing operation was carried out in the case that one triangular groove  17  has been formed only in any one of inner side walls on the long edge sides of the hollow portion  14 . In other words, as indicated as a sample U 6  in  FIG. 12 , in the case that one triangular groove  17  has been formed only in any one of inner side walls on the long edge sides of the follow portion  14 , a degree of enlarging a deflection angle of a magnetic vector thereof is lower than that of such a case that the triangular grooves  17  have been formed in the inner side walls on the side of the long edges of the hollow portion  14 . However, the deflection angle of the magnetic vector of the first-mentioned biasing magnet  13  is enlarged, as compared with that of the conventional biasing magnet  13  (sample U 1 ) where the triangular groove  17  is not formed. As apparent from the above-described simulation result, in order that the triangular grooves  17  are formed in the hollow portion  14  so as to enlarge the deflection angles of the magnetic vectors, there is a merit even in such a structure that one triangular groove  17  is formed only in one of these inner side walls of the hollow portion  14 . 
   These results obtained in the first to third simulations will now be summarized as follows: 
   (a) Since the triangular grooves  17  are formed in the hollow portion  14  of the biasing magnet  13 , the deflection angles of the magnetic vectors are enlarged. 
   (b) The wider the width “X” of the triangular groove  17  is widened, the larger the deflection angle of the magnetic vector is enlarged. 
   (c) The deeper the depth “Z” of the triangular groove  17  is increased, the larger the deflection angle of the magnetic vector is enlarged. 
   (d) As to the depth “Z” and the width “X” of the triangular groove  17 , there is an advantage that if the depth “Z” is made deeper, then the deflection angle of the magnetic vector may be further enlarged. 
   (e) If the triangular groove  17  owns a certain length separated from the rotor opposing plane  13   a  of the biasing magnet  13 , then a sufficiently large deflection angle of a magnetic vector may be obtained. Therefore, this triangular groove  17  is not always formed over the entire length of the biasing magnet  13 . 
   (f) Even when the triangular groove  17  is formed only in one of the inner side walls of the hollow portion  14 , the deflection angle of the magnetic vector may be enlarged. 
   As a consequence, in accordance with the above-described embodiment modes in which at least the above-explained structures (a) to (d) are employed, the below-mentioned effects can be achieved: 
   (1) While the relative positional relationship (for example, previously-explained “M-to-M” distance) among the magnetic resistance element pair  1 , the magnetic resistance element pair  2 , and the biasing magnet  13  is not always changed, the deflection angles of the magnetic vectors which are influenced to both the magnetic resistance element pairs  1  and  2  can be adjusted by the triangular grooves  17  formed in the hollow portion  14 . Not only the deflection angles of the magnetic vectors may be enlarged in the above-described manner, but also the improvement of the sensing sensitivity as the rotation detecting apparatus may be easily realized. Moreover, the deflection angles of the magnetic vectors may be basically adjusted by arranging the triangular grooves  17  of the hollow portion  14 , so that the freedom degree as to designing of this rotation detecting apparatus may be largely improved. 
   (2) Since the triangular grooves  17  are formed in the center portions of the inner side walls on the side of the long edges of the hollow portion  14 , while the symmetrical characteristic as to the deflection angles of the magnetic vectors may be maintained, the deflection angles of the magnetic vectors can be easily adjusted, namely, can be readily enlarged. 
   (3) Since the triangular groove  17  whose sectional shape becomes the triangular shape is employed as the groove to be formed in the hollow portion  14 , when the biasing magnet  13  is molded by employing a metal mold, fluidity owned by a magnetic material within this metal mold can be hardly blocked by the triangular groove  17 . As a consequence, the magnetic material having better uniformity can be molded as the biasing magnet, as compared with that of such a case that a groove having another different shape is employed. 
   It should also be understood that the rotation detecting apparatus of the above-described embodiment modes may be modified as follows: 
   That is, in the above-explained embodiment modes, the triangular grooves  17  have been formed in the entire portion of the biasing magnet  13  along the longitudinal direction. Alternatively, when the content of the summarized item (e) as to the simulation results is considered, the triangular groove  17  may be formed in such a way that this triangular groove  17  has a certain length (“6.7 mm”, in above example) separated from the rotor opposing plane  13   a  of the biasing magnet  13 . 
   Similarly, when the content of the summarized item (f) as to the simulation results is considered, the triangular groove  17  may be alternatively formed in such a way that this triangular groove  17  is formed only in one of the inner side walls which constitutes the hollow portion  14  of the biasing magnet  13 . 
   In the above-described embodiment modes, such a biasing magnet  13  that the triangular grooves  17  have been formed in the hollow portion  14  has been exemplified. Alternatively, instead of the above-described triangular grooves  17 , for instance, as shown in  FIG. 13  which corresponds to the previous drawing of  FIG. 3 , such a biasing magnet  13  may be alternatively employed in which a semi-circular groove  18  has been formed, and a groove bottom portion of this semi-circular groove  18  has been made in an arc shape. Also, similar to the above modification, as represented in  FIG. 14  which corresponds to the previous drawing of  FIG. 3 , such a biasing magnet  13  may be alternatively employed in which a rectangular groove  20  has been formed and a groove bottom portions of this rectangular groove  20  has been formed in a rectangular shape. Analyzed results of deflection angles of magnetic vectors as to either the biasing magnet  13  which has employed the semi-circular grooves  18  or the biasing magnet  13  which has employed the rectangular grooves  20  will now be explained with reference to  FIG. 15 . As represented in the analyzed results of  FIG. 15 , the deflection angles of the magnet vectors as to the biasing magnet  13  (sample V 1 ) where the semi-circular grooves  18  have been formed are also enlarged, as compared with the deflection angles of the magnetic vectors as to the biasing magnet (sample U 1  of  FIG. 12 ) where the triangular grooves  17  have not be formed. Moreover, a degree of the enlarged deflection angles becomes larger than that of such a biasing magnet (sample V 4 ) where the triangular grooves  17  having the same widths “X”, the same depths “Z”, and the lengths “L” have been formed. As a consequence, since the semi-circular grooves  18  are formed, the deflection angles of the magnetic vectors may be enlarged at the same degree, or higher degree than that of the above-explained triangular grooves  17 . In addition, the sensing sensitivity may be further improved. Also, in the case that this semi-circular groove  18  is employed in the biasing magnet  13 , similar to such a case that the above-described triangular groove  17  is employed in the biasing magnet  13 , there is a merit that fluidity of a magnet material used when this biasing magnet  13  is molded can be hardly blocked. On the other hand, the deflection angles of the magnet vectors as to the biasing magnets (samples V 2  and V 3 ) where the rectangular grooves  20  have been formed are also enlarged, as compared with the deflection angles of the magnetic vectors as to the biasing magnet (sample U 1  of  FIG. 12 ) where the triangular grooves  17  have not be formed. Then, in this case, more specifically, the depth “Z” of this rectangular groove  20  is made equal to, or deeper than the depths of other grooves, so that the following fact can be revealed from the analyzed results of  FIG. 15 . That is, an enlarging degree of the deflection angles of the magnetic vectors may become larger than the enlarging degrees of the deflection angles of the magnetic vectors as to the biasing magnet in which the triangular grooves  17 , or the semi-circular grooves  18  has been formed. As a consequence, as shapes of grooves, not only the above-explained triangular grooves  17 , but also the semi-circular grooves  18  and the rectangular grooves  20  may be properly employed. The Inventors of the present invention could confirm that the contents of the above-explained summarized items (a) to (f) with respect to the first to third simulation results may be similarly applied to these semi-circular grooves  18  and the rectangular grooves  20 . 
   In the above-described embodiment mode, such a biasing magnet  13  has been exemplified in which one of the triangular grooves  17  has been formed in each of the inner side walls of the hollow portion  14  on the side of the long edges thereof. For example, as shown in  FIG. 16 , such a biasing magnet  13  may be alternatively employed in which a plurality of triangular grooves  23  (for instance, three triangular grooves  22 ) have been formed in each of inner side walls thereof on he long edge side. Also in this alternative case the inventors of the present invention could confirm that similar operation effects to those of the above-described embodiment modes may be achieved. 
   Also, in the above-described embodiment mode, the triangular groove  17  has been formed in the center portion of the inner side wall of the hollow portion  14  on the long edge side. However, the position where this triangular groove  17  is formed may be alternatively selected to be any positions if these positions are located within the hollow portion  14 . In this alternative case, although the symmetrical characteristic as to the deflection angles of the magnetic vectors cannot be maintained, the deflection angles of the magnetic vectors may be easily adjusted, namely may be readily enlarged in a similar manner to that of the above-explained embodiment mode. 
   (Second Embodiment) 
   Prior to descriptions as to a second embodiment mode of a rotation detecting apparatus according to the present invention, a basic idea of the present invention will now be explained with reference to  FIG. 19  to  FIG. 21 . It should be understood that for the sake of easy understandings, such a conventional rotation detecting apparatus which employs a biasing magnet is employed as an example, and a portion of this biasing magnet is indicated in an enlarging manner. In this biasing magnet, magnetic field strengths have been substantially uniformly set over an entire peripheral portion of the own biasing magnet. For the sake of convenience, the same reference numerals shown in the previous drawing of  FIG. 17 , or  FIG. 18  will be employed as those for indicating the same, or similar structural elements indicated in  FIG. 19  to  FIG. 21 . 
     FIG. 19  shows a perspective structure of a sensor chip  11  and a biasing magnet  13  in an enlarging manner, which constitute the rotation detecting apparatus. As indicated in  FIG. 19 , the biasing magnet  13  has been formed in a hollow cylindrical shape and has been equipped with a hollow portion  14 , while a sectional shape of the hollow portion  14  along a direction perpendicular to a longitudinal direction of this biasing magnet  13  is made of a rectangular shape. The sensor chip  11  having magnetic resistance elements “MRE 1 ” to “MRE 4 ” has been stored into the hollow portion  14  in combination with a molding member  12 , so that a biasing magnetic field may be applied from the biasing magnet  13  with respect to the magnetic resistance elements MRE 1  to MRE 4  of this stored sensor chip  11 . It should also be noted that in this biasing magnet  13 , an edge plane  13   a  located opposite to the above-explained rotor has been magnetized as an “N pole”, whereas another edge plane located opposite to the edge plane  13   a  has been magnetized as an “S pole.” 
   While employing the enlarged perspective view of the biasing magnet  13 , conditions of magnetic fields which are generated from the biasing magnet  13  are illustratively shown in  FIG. 20 . For the sake of convenience, it should also be noted that in  FIG. 20 , magnetic fields on the side of long edges of the hollow portion  14  are represented by arrows denoted by 8 solid lines, and also, magnetic fields on the side of short edges of the hollow portion  14  are represented by arrows denoted by 2 solid lines. In the below-mentioned descriptions, high/low strengths of magnetic fields will be indicated based upon widthnesses of solid lines. However, as previously explained, since the magnetic field strengths of this biasing magnet  13  shown in  FIG. 20  are substantially equal to each other over the entire peripheral portion thereof, the above-explained magnetic fields may be represented by all of solid lines having the same widthness. As indicated in  FIG. 20 , in a single body of this biasing magnet  13 , magnetic fields generated from this single biasing magnet  13  are converged in a ring shape in such a mode that the magnetic fields are directed from the N pole to the S pole. However, when the tooth portion of the above-described rotor passes in opposite to the edge plane  13   a  of the biasing magnet  13 , magnetic vectors may be produced at this tooth portion in such a condition that the magnetic fields are drawn. Then, changes contained in angles of the produced magnetic vectors may be sensed by the magnetic resistance elements MRE 1  to MRE 4  as changes contained in resistance values. 
   On the other hand, in the above-described rotation detecting apparatus, the angle changes of the magnetic vectors which are produced when the above-explained rotor is rotated may be sensed as the changes contained in the resistance values of the above-described magnetic resistance elements MRE 1  to MRE 4 . In the case of the biasing magnet  13  shown in  FIG. 20 , all of the magnetic fields produced from this biasing magnet  13  may contribute to the generations of the above-explained magnetic vectors. As a consequence, in particular, the deflection angles of the magnetic vectors which are generated may also be limited by the magnetic fields produced on the side of the long edges of the hollow portion  14 . Referring now to  FIG. 21 , a detailed description is made of the above-described limitations as to the deflection angles of the magnetic vectors. 
     FIG. 21  illustratively shows conditions of magnetic fields which are produced from the biasing magnet  13  by employing a plane view of the biasing magnet  13  which is viewed from the side of the edge plane  13   a  located opposite to the above-explained rotor. As represented in  FIG. 21 , such magnetic fields which are produced from a portion “XXIA 1 ” and another portion “XXIA 2 ” on the side of the short edges of the hollow portion  14  are easily influenced by rotations of the rotor, if an attention is paid only to the magnetic fields which are generated from these portions XXIA 1  and XXIA 2 , then magnetic vectors may be readily deflected which are produced by these generated magnetic fields in conjunction with the rotations of the rotor. In other words, deflection angles thereof are largely maintained by the own deflection angles. To the contrary, magnetic fields which are generated from a portion XXIB 1  and another portion XXIB 2  on the side of the long edges of the hollow portion  14  are intersected perpendicular to the rotation direction of the rotor. As a result, components of such magnetic vectors which are produced by the magnetic fields generated from these portions XXIB 1  and XXIB 2  in conjunction with the rotations of the rotor may give such an effect that the easy deflections of the above-explained magnetic vectors which are produced by the magnetic fields generated from the portions XXIA 1  and XXIA 2  in conjunction with the rotation of the rotor may be blocked. In other words, if the magnetic field strengths of the magnetic fields can be lowered which are generated from the portions XXIB 1  and XXIB 2  on the side of the long edges of the hollow portion  14 , then an enlargement of the deflection angles of the above-explained magnetic vectors can be expected. 
     FIG. 22  to  FIG. 24  show a rotation detecting apparatus according to a second embodiment mode of the present invention, while the rotation detecting apparatus has been arranged based upon the above-described basic idea. Referring now to  FIG. 22  to  FIG. 24 , an arrangement of the rotation detecting apparatus according to this second embodiment mode will be described in detail. It should be noted that since a structure as the rotation detecting apparatus is basically identical to the above-described structure of the conventional rotation detecting apparatus, the same reference numerals shown in this conventional rotation detecting apparatus will be employed as those for denoting structural elements having the same, or similar functions, and thus, detailed descriptions thereof are omitted. 
     FIG. 22  illustratively indicates conditions of magnetic fields which are generated from a biasing magnet  13  employed in the rotation detecting apparatus according to the first embodiment mode, and this drawing corresponds to  FIG. 20 . As shown in  FIG. 22 , the biasing magnet  13  has been formed in a hollow cylindrical shape and has been provided with a hollow portion  14 . This hollow cylindrical shape of the biasing magnet  13  is not completely different from the shape of the conventional biasing magnet. A sectional shape of the hollow portion  14  is made in a substantially rectangular shape along a direction perpendicular to a longitudinal direction of the biasing magnet  13 . Also, a material for constructing the biasing magnet  13  is the same material as the conventional biasing magnet. However, this biasing magnet  13  owns the below-mentioned different point from the conventional biasing magnet whose the magnetic strengths have been substantially uniformly set. That is, in this biasing magnet  13 , magnetic strengths of biasing magnet portions which are located opposite to front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  in the sensor chip  11  (see  FIG. 19 ) stored in the hollow portion  14  have been selectively set to low magnetic field strengths from an edge plane  13   a  of this biasing magnet  13  to an opposing plane thereof. This edge plane  13   a  is located opposite to the rotor. As a consequence, among the magnetic fields generated from the biasing magnet  13 , the magnetic fields which are generated from the biasing magnet portions located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  are indicated by arrows made of narrow solid lines, as compared with magnetic fields which are generated from other portions of this biasing magnet  13 . 
     FIG. 23  illustratively shows conditions of magnetic fields which are produced from the biasing magnet  13  by employing a plan view of the biasing magnet  13  which is viewed from the side of the edge plane  13   a  located opposite to the above-explained rotor, which corresponds to the drawing of  FIG. 21 . As represented in  FIG. 23 , if an attention is paid to magnetic fields which are generated from a portion “XXIA 1 ” and another portion “XXIA 2 ” on the side of short edges of the hollow portion  14  within the biasing magnet  13 , similar to the previously explained biasing magnet  13  (see  FIG. 21 ), then magnetic vectors may be readily deflected which are produced by these generated magnetic fields in conjunction with the rotations of the rotor, and thus, deflection angles thereof are largely secured. To the contrary, within the biasing magnet  13 , field strengths of such magnetic fields which are generated from the biasing magnet portions located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4 , namely, field strengths of magnetic fields which are generated from a portion “XXIB 1 ” and another portion “XXIB 2 ” on the side of the long edges of the hollow portion  14  have been selectively set to low field strengths, which are different from those of the previously explained biasing magnet  13 . As a result, such magnetic vectors which are produced by the magnetic fields generated from these portions XXIB 1  and XXIB 2  in conjunction with the rotations of the rotor may be easily deflected, as compared with those produced from the previously explained biasing magnet  13 . Accordingly, such magnetic vectors may be suppressed which may block easy deflections of the above-described magnetic vectors which are produced by the magnetic fields generated from the portions XXIA 1  and XXIA 2  in conjunction with the rotation of the rotor. Then, as a consequence, the components of the magnetic vectors can be relatively strengthened, which are produced by the magnetic fields generated from this biasing magnet  13  in conjunction with the rotations of the rotor. 
     FIG. 24  represents a simulation result as to deflection angles of magnetic vectors which are produced from the magnetic fields generated from the biasing magnet  13  in conjunction with the rotations of the rotor, while the sensitivities of the magnetic resistance elements MRE 1  to MRE 4  have been considered. It should be understood that air gaps indicated in  FIG. 24  represent distances between the rotor and a rotor opposing plane of a rotation detecting apparatus in the case that this rotation detecting apparatus has been arranged as shown in  FIG. 18 . As apparent from this drawing, the deflection angles of the magnetic vectors produced in the case that the biasing magnet  13  is employed may exceed the simulation results about the magnetic vector deflection angles obtained in such a case that the conventional biasing magnet  13  is employed in substantially all of the air gaps. As a consequence, since the biasing magnet  13  is employed in which the magnetic field strengths of the portions located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  have been selectively set to the low magnetic field strengths, it is extremely effective so as to enlarge the deflection angles of the magnetic vectors. 
   Next, a method of manufacturing the above-explained biasing magnet  13  will now be explained with reference to  FIG. 25  to  FIG. 28 . 
   Normally, when a biasing magnet is manufactured, a molded body of a resin material which contains magnetic powder is formed, and then, this molded body of the resin material is magnetized. However, the above-explained biasing magnet  13  is featured by that the magnetic field strengths of the portions located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  have been selectively set to the low magnetic field strengths. As a consequence, in the below-indicated molding apparatus, while orientation modes of the magnetic powder contained in the above-described molded body are made different from each other, the above-explained magnetic field strengths are set in accordance with such differences in the orientation modes. Subsequently, the molding apparatus capable of executing such a molding step is described in detail. 
     FIG. 25  is a plan view for showing a molding apparatus  70  which forms the above-described molded body. As represented in  FIG. 25 , this molding apparatus  70  has been arranged by employing a molding die  72  which has a cavity  71  corresponding to the shape of the biasing magnet  13 . It should also be noted that this molding die  72  is manufactured by a non-magnetic material. Also, this molding apparatus  70  has been constituted by providing two sets of energizing coils  73  at upper and lower portions of the cavity  71 . These two energizing coils  73  may cover the cavity  71  except for such cavity portions corresponding to the above-described magnet portions XXIB 1  and XXIB 2 . 
     FIG. 26  is a sectional view for representing the molding apparatus  70  which is cut along a line XXVI—XXVI shown in  FIG. 25 . As indicated in  FIG. 26 , the molding die  72  is constituted by an upper die  72   a  and a lower die  72   b , and a molded body  74  is formed within the cavity  71  between the upper die  72   a  and the lower die  72   b . Two sets of the energizing coils  73  having the above-described modes have been arranged in each of the upper die  72   a  and the lower die  72   b.    
   Next, a description is made of the method for manufacturing the above-described biasing magnet  13  with employment of the molding apparatus  70  arranged in the above-described manner. 
   In other words, in the case that the biasing magnet  13  is manufactured by employing the above-described molding apparatus  70 , the below-mentioned manufacturing steps are executed: 
   (a) A resin material containing magnetic powder is injected into the cavity  71  of the molding die  72 . It should be understood that this injection of the resin material is carried out via a spool (not shown). 
   (b) While the respective energizing coils  73  are energized so as to apply proper magnetic fields with respect to the magnetic powder of the resin material filled in the cavity  71 , the orientation of the magnetic powder is controlled before the resin material is solidified. 
   (c) After the above-described resin material has been solidified as a molded body, the entire portion of this molded body is once demagnetized. 
   (d) Thereafter, a portion of the molded body, which is located opposite to the rotor, is magnetized as an “N pole”, whereas another portion of the molded body, which is located opposite to the first-mentioned portion, is magnetized as an “S pole” by using a magnetizing apparatus (not shown). 
   Now, a further detailed explanation is made of the above-explained manufacturing step (b).  FIG. 27  shows an orientation mode of the magnetic powder before the orientation of this magnetic powder is controlled with employment of a sectional diagram of the above-described forming apparatus  70  which is cut along a line XXVII—XXVII shown in  FIG. 25 . Also,  FIG. 28  indicates an orientation mode of the magnetic powder after the orientation of the magnetic powder has been controlled, and corresponds to the drawing of  FIG. 27 . It should also be noted that in  FIG. 27  and  FIG. 28 , in order to easily understand the orientation modes of the magnetic powder, the magnetic powder is displayed in an enlarging manner. As indicated in  FIG. 27 , under such a condition obtained before the energizing coils  73  are energized, orientation of magnetic powder MP present in the resin material is brought into unmatched condition. In contrast to this unmatched condition, when the respective energizing coils  73  are energized so that magnetic fields are produced around the respective energizing coils  73 , as indicated in  FIG. 28 , the orientation of the magnetic powder MP is controlled in correspondence with these generated magnetic fields. In other words, the orientation of the magnetic powder MP may be realized in such a way that the particles of the magnetic powder MP are directed to the respective energizing coils  73 . As a result, in the molded body which is manufactured by the molding apparatus  70 , orientation degrees of the magnetic powder MP of such portions thereof which correspond to the above-described magnet portions XXIB 1  and XXIB 2  are made lower, so that there is a difference in the orientation modes of the magnetic power MP within this molded body. Then, since the molded body having such different orientation modes is magnetized by way of the above-described manufacturing steps (c) and (d), the biasing magnet  13  which generates the previously explained magnetic fields shown in  FIG. 22  and  FIG. 23  can be manufactured. 
   Then, the above-described sensor chip  11  is stored in combination with the molding member  12  (see  FIG. 19 ) into the hollow portion  14  of the biasing magnet  13  which has been manufactured via the above-described manufacturing steps (a) to (d), and thereafter, the stored structural members are assembled with a case member, and the like, in an integral manner. As a result, the rotation detecting apparatus shown in  FIG. 18  may be manufactured. 
   In the above-described first embodiment mode, the below-listed effects can be achieved: 
   (1) The biasing magnet  13  has been formed in such a manner that the magnetic strengths of the biasing magnet portions (above-described portions XXIB 1  and XXIB 2 ) which are located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  have been selectively set to the low magnetic field strengths from the edge plane  13   a  of this biasing magnet  13  to the opposing plane thereof. As a consequence, the magnetic field strengths at the plane where the magnetic vectors are changed may be selectively set to the low magnetic field strengths. As a result, the components of the magnetic vectors can be relatively strengthened which are produced by the biasing magnetic fields generated from the biasing magnet  13  in conjunction of the rotations of the rotor. In other words, while a relative positional relationship (for example, previously-explained “M-to-M” distance) among the magnetic resistance elements MRE 1  to MRE 4  and the biasing magnet  13  is not always changed, the deflection angles of the magnetic vectors which give influences to the magnetic resistance elements MRE 1  to MRE 4  can be adjusted, and also, the improvement of the sensing sensitivity as the rotation detecting apparatus may be easily realized. 
   (2) While the biasing magnet  13  may be formed as the molded body of the resin material which contains the magnetic powder, the magnetic field strengths as to the portions which are located opposite to the front/rear planes of the magnetic resistance elements MRE 1  to MRE 4  are selectively set to the low magnetic field strengths in accordance with the differences in the orientation modes of the magnetic powder in the molded body. As a consequence, the above-explained magnetic field strengths can be simply set by suitably utilizing the structure as the above-explained molded body. Also, since the conventional magnet material may be directly utilized, increasing of the manufacturing cost may be suppressed. 
   (Third Embodiment) 
     FIG. 29  shows a rotation detecting apparatus according to a third embodiment mode of the present invention, while the rotation detecting apparatus has been arranged based upon the above-described basic idea. Referring now to  FIG. 29 , an arrangement of the rotation detecting apparatus according to this third embodiment mode will be described in detail. It should be noted that since a structure as the rotation detecting apparatus is basically identical to the above-described structure of the conventional rotation detecting apparatus, the same reference numerals shown in this conventional rotation detecting apparatus will be employed as those for denoting structural elements having the same, or similar functions, and thus, detailed descriptions thereof are omitted. 
     FIG. 29  illustratively indicates conditions of magnetic fields which are generated from a biasing magnet  13  employed in the rotation detecting apparatus according to the first embodiment mode, and this drawing corresponds to  FIG. 20 . As shown in  FIG. 29 , the biasing magnet  13  has been formed in a hollow cylindrical shape and has been provided with a hollow portion  14 . This hollow cylindrical shape of the biasing magnet  13  is not completely different from the shape of the conventional biasing magnet. A sectional shape of the hollow portion  14  is made in a substantially rectangular shape along a direction perpendicular to a longitudinal direction of the biasing magnet  13 . Also, a material for constructing the biasing magnet  13  is the same material as the conventional biasing magnet. However, this biasing magnet  13  owns the below-mentioned different point from the conventional biasing magnet. That is, in this biasing magnet  13 , magnetic strengths of biasing magnet portions which are located opposite to front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4 , namely magnetic strengths of magnetic fields as to the above-explained portions XXIB 1  and XXIB 2  (see  FIG. 21 ) have been selectively set to low magnetic field strengths from an edge plane  13   a  located opposite to the rotor up to such a position which covers the magnetic resistance elements MRE 1  to MRE 4  of the sensor chip  11 . As a consequence, the magnetic fields which are generated from the biasing magnet portions whose magnetic field strengths have been selectively set to the low magnetic field strengths are indicated by arrows made of narrow solid lines, as compared with magnetic fields which are generated from other portions of this biasing magnet  13 . 
   Then, if an attention is paid to magnetic fields which are generated from the portion “XXIA 1 ” and another portion “XXIA 2 ” (see  FIG. 21 ) on the side of the short edges of the hollow portion  14  within the biasing magnet  13 , similar to the previously explained biasing magnet  13  (see  FIG. 21 ), then magnetic vectors may be readily deflected which are produced by these generated magnetic fields in conjunction with the rotations of the rotor, and thus, deflection angles thereof are largely secured. To the contrary, within the biasing magnet  13 , field strengths of such magnetic fields which are generated from the portions XXIB 1  and XXIB 2  over the positions for covering the magnetic resistance elements MRE 1  to MRE 4  from the above-described edge plane  13   a  have been selectively set to low field strengths, which are different from those of the previously explained biasing magnet  13 . As a result, such magnetic vectors which are produced by the magnetic fields generated from these portions XXIB 1  and XXIB 2  in conjunction with the rotations of the rotor may be easily deflected, as compared with those produced from the previously explained biasing magnet  13 . Accordingly, such magnetic vectors may be suppressed which may block easy deflections of the above-described magnetic vectors which are produced by the magnetic fields generated from the portions XXIA 1  and XXIA 2  in conjunction with the rotations of the rotor. Then, as a consequence, the components of the magnetic vectors can be relatively strengthened, which are produced by the magnetic fields generated from this biasing magnet  13  in conjunction with the rotations of the rotor. 
   Next, a method of manufacturing the above-explained biasing magnet  13  will now be explained with reference to  FIG. 30  and  FIG. 31 . It should be understood that since the biasing magnet  13  is basically manufactured by way of the same manufacturing steps as those indicated in the above-described first embodiment mode, different points thereof will be mainly explained. 
     FIG. 30  shows a molding apparatus  70  for molding the above-explained biasing magnet  13 , and corresponds to the drawing of  FIG. 25 . As indicated in  FIG. 30 , this molding apparatus  70  has been arranged by employing a molding die  72  which has a cavity  71  corresponding to the shape of the biasing magnet  13 . It should also be noted that this molding die  72  is manufactured by a non-magnetic material. Then, two sets of energizing coils  73  have been arranged in an upper molding die  72   a  (see  FIG. 31 ) for constituting this molding die  72 , while these two energizing coils  73  may cover the cavity  71  except for such cavity portions corresponding to the above-described magnet portions XXIB 1  and XXIB 2 . To the contrary, an energizing coil  94  which covers the cavity  71  has been arranged in a lower molding die  72   b  (see  FIG. 31 ) which constitutes the molding die  72 . Thus, orientation of the above-explained magnetic powder may be controlled by operating these energizing coils  73  and energizing coil  94 . 
     FIG. 31  indicates an orientation mode of the magnetic powder after the orientation of the magnetic powder has been controlled, and corresponds to the drawing of  FIG. 28 . When the respective energizing coils  73  and  94  are energized so that magnetic fields are produced around the respective energizing coils  73  and  94 , as indicated in  FIG. 31 , the orientation of the magnetic powder MP is controlled in correspondence with these generated magnetic fields. In other words, the orientation of the magnetic powder MP may be realized in such a way that the particles of the magnetic powder MP are directed to the respective energizing coils  73  and  94 . As a result, in the molded body which is manufactured by the molding apparatus  70 , orientation degrees of the magnetic powder MP of such portions thereof which correspond to the above-described magnet portions XXIB 1  and XXIB 2  over the positions for covering the magnetic resistance elements MRE 1  to MRE 4  from the above-described edge plane  13   a  of the biasing magnet  13  are made lower, so that there is a difference in the orientation modes of the magnetic power MP within this molded body. Then, since the molded body having such different orientation modes is magnetized by way of the above-described manufacturing steps (c) and (d), the biasing magnet  13  which generates the previously explained magnetic fields shown in  FIG. 29  can be manufactured. 
   In accordance with the above-explained second embodiment mode, the below-mentioned effect can be obtained in addition to such effects which are equivalent to the above-explained effects (1) and (2) of the second embodiment modes. 
   (3) The biasing magnet  13  has been formed in such a manner that the magnetic strengths of the biasing magnet portions (above-described portions XXIB 1  and XXIB 2 ) which are located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  have been selectively set to the low magnetic field strengths from the edge plane  13   a  of this biasing magnet  13  which are located to the rotor over the positions which cover the magnetic resistance elements MRE 1  to MRE 4 . As a result, the orientation controls of the magnetic powder as to such portions except for the portions which are defined from the edge plane  13   a  located opposite to the rotor up to the positions which cover the magnetic resistance elements MRE 1  to MRE 4  may be realized in a similar control manner to the prior art, so that increasing of the manufacturing cost can be suppressed by applying the conventional molding die. 
   It should also be noted that the above-described respective embodiment modes may be alternatively modified so as to be carried out. 
   That is, in the second embodiment mode, the biasing magnet has been formed in such a manner that the magnetic strengths of the biasing magnet portions which are located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  have been selectively set to the low magnetic field strengths. Alternatively, only such a magnetic field strength as to a portion which is located opposite to the arranging plane of the magnetic resistance elements MRE 1  to MRE 4  may be selectively set to a low magnetic field strength. As a result, as indicated in  FIG. 32  corresponding to  FIG. 20  such a biasing magnet  13  may be realized in which the magnetic field generated from the portion which is located opposite to the arranging plane of the magnetic resistance elements MRE 1  to MRE 4  is illustratively represented by a solid line whose width is made narrower than that of other portion. Then, magnetic vectors may be easily deflected, as compared with those generated from the previously explained biasing magnet  13  (see  FIG. 21 ), while these magnetic vectors are produced from the magnetic field generated from the portion which is located opposite to the arranging plane of the magnetic resistance elements MRE 1  to MRE 4  of this biasing magnet  13  in conjunction with the rotations of the rotor. As a consequence, in such a case that only such a magnetic field strength as to the portion which is located opposite to the arranging plane of the magnetic resistance elements MRE 1  to MRE 4  is selectively set to the lower magnetic field strength, a similar effect to that of the first embodiment mode may also be achieved. It should be understood that when this biasing magnet  13  is manufactured, such a molding apparatus  70  as shown in  FIG. 33  corresponding to  FIG. 25  is employed. That is, this molding apparatus  70  has been arranged by employing a molding die  72  which has a cavity  71  corresponding to the shape of the biasing magnet  13 . It should also be noted that this molding die  72  is manufactured by a non-magnetic material. Also, this molding apparatus  70  has been constituted by providing two sets of energizing coils  113  at upper and lower portions of the cavity  71 . These two energizing coils  113  may cover the cavity  71  except for the portion which is located opposite to the arranging plane of the magnetic resistance elements MRE 1  to MRE 4 . A method for manufacturing the biasing magnet  13  by using this molding apparatus  70  is carried out in the same manner to that of the first embodiment mode. Also, the above-explained biasing magnet in which only such a magnetic field strength as to the portion which is located opposite to the arranging plane of the magnetic resistance elements MRE 1  to MRE 4  is selectively set to the low magnetic field strength, may also be employed as a modification of the second embodiment mode. 
   In the above-explained second embodiment mode, the orientation of the magnetic powder contained in the molded body has been controlled by employing this energizing coils  73 . Alternatively, a permanent magnet may be employed. In this alternative case, similar to the above-explained embodiment mode, the orientation of the magnetic powder may be alternatively controlled by using the magnetic fields generated from the permanent magnet. It should also be noted that such a permanent magnet may also be alternatively employed as a modification related to the second embodiment mode. 
   In each of the above-described embodiment modes, the magnetic field strengths as to the portions which are located opposite to the front/rear planes of the magnetic resistance elements MRE 1  to MRE 4  have been selectively set to the low magnetic field strengths. Alternatively, when such a magnetic field strength is set, for instance, these magnetic field setting operations may be carried out by utilizing demagnetization. In other words, such a biasing magnet whose magnetic field strengths have been substantially uniformly set may be molded by employing a molding apparatus similar to the conventional molding apparatus. Thereafter, magnetic field strengths as to the portions which are located opposite to the front/rear arranging planes of the magnetic resistance elements MRE 1  to MRE 4  may be selectively set to low magnetic field strengths by employing a demagnetizing device (not shown). Also, in this alternative case, such a biasing magnet which generates the magnetic fields as shown in  FIG. 22  and  FIG. 29  may be realized. 
   The above-described respective embodiment modes have described such a case of the biasing magnet  13  having the hollow portion  14 , the sectional shape of which has been made in the rectangular shape. Alternatively, even when a biasing magnet having a hollow portion made in another shape is employed, this biasing magnet may be similarly covered by the inventive idea of the present invention. Also, as to the biasing magnet itself, not only such a biasing magnet formed in a hollow cylindrical shape may be employed, but also a biasing magnet formed in another different shape may be employed. 
   Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.

Technology Classification (CPC): 6