Abstract:
A rotation angle detecting device includes magnetic field forming members such as a permanent magnet and a yoke, a plurality of magnetic sensors disposed in the magnetic field to rotate relative to the magnetic field forming members to provide output signals that are 90 degrees in phase different from each other, a judgment level calculating circuit that provides a judgment level based on the output signals and judging circuit that judges the output signals normal if the judgment level is within a prescribed range and not normal if the judgment level is out of the prescribed range.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present application is based on and claims priority from Japanese Patent Applications 2005-305953, filed Oct. 20, 2005 and 2006-72136, filed Mar. 16, 2006, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a device for detecting a rotation angle of a rotating object. 
   2. Description of the Related Art 
   A rotation angle detecting device for detecting a rotation angle of a rotating object is well-known. For example, such a rotation angle detecting device is installed into an ignition device of an internal combustion engine to detect the rotation angle of an engine crank shaft. However, the internal combustion engine may fail if the rotation angle detecting device fails. 
   In order to prevent the above problem, JP-A-2002-104211 proposes to provide a rotation angle detecting device with an abnormality detecting function to be used for a motor-driven power steering system. This rotation angle detecting device includes a motor-rotation-angle sensor of a steering-shaft-driving motor and a steering-angle sensor of a steering shaft, so that the abnormality can be detected by comparing the motor-rotation-angle with the steering-angle. That is, in order to prevent the above-stated problem, the rotation angle detecting device disclosed in JP-A-2002-104211 necessitates a motor-rotation-angle sensor in addition to the steering-angle sensor. 
   SUMMARY OF THE INVENTION 
   Therefore, an object of the invention is to provide a rotation angle detecting device that does not necessitate the motor-rotation-angle sensor. 
   According to a feature of the invention, a rotation angle detecting device for detecting a rotation angle of a rotating object includes magnetic field generating means for providing magnetic field, sensing means for providing output signals that are 90 degrees in phase different from each other, a judgment level calculating means for providing a judgment level based on the output signals, the judgment level is within a prescribed range when the output signals are normal and out of the prescribed range when one of the output signals is not normal, and judging means for judging the judgment level normal or not normal. 
   Accordingly, an abnormality can be detected by calculation based on the output signals of the hall elements without providing additional detecting element. 
   In the above rotation angle detecting device the magnetic sensors are preferably disposed to have 90 degrees in angle to each other. 
   On the other hand, the magnetic sensors may be disposed to have an angle other than 90 degrees between them. In this case, the sensing means further includes converting means for converting sensor signals to the output signals that are 90 degrees in phase different from each other. 
   The output signals may be sinusoidal signals V 1 , V 2  that are respectively proportional to sine θ and cos θ, wherein θ is a rotation angle, and the judgment level D 1  is calculated from the following expression: D 1 =V 1   2 +V 2   2 . On the other hand, the judgment level may be calculated by adding differentiated or integrated values of the sinusoidal signals so as to become zero when the output signals are normal and not zero when one of the output signals is not normal. For example, the judgment level is calculated by the following expression: dV 1 /dθ+V 2 . 
   The plurality of magnetic sensors may be comprised of a plurality of pairs of magnetic sensors. In this case, the judging means judges the judgment level of each pair of the magnetic sensors normal or not normal, and the sensing means outputs the pair of output signals that are judged to be normal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a flow diagram showing a process of detecting an abnormality of a rotation angle detecting device according to the first embodiment of the invention; 
       FIG. 2  is a schematic diagram illustrating a rotation angle detecting device according to the first embodiment of the invention; 
       FIGS. 3A ,  3 B and  3 C are graphs showing relationship of the rotation angle with hall element&#39;s output signals, arithmetic angles and output angles; 
       FIG. 4  is a table showing levels of hall element&#39;s output signals and rotation angles; 
       FIG. 5  is a graph showing a relationship between a rotation angle and a judgment level D 1 ; 
       FIG. 6  is a flow diagram showing a process of detecting an abnormality of a rotation angle detecting device according to the second embodiment of the invention; 
       FIG. 7  is a graph showing a relationship between a rotation angle and a judgment level D 2  for the second embodiment; 
       FIG. 8  is a schematic diagram illustrating a rotation angle detecting device according to the third embodiment of the invention; 
       FIG. 9  is a graph showing a relationship between output signals of the rotation angle detecting device according to the third embodiment and other signals thereof; 
       FIG. 10  is a schematic diagram illustrating a rotation angle detecting device according to the fourth embodiment of the invention; 
       FIG. 11  is a table showing groups of elements and hall elements included in the respective groups of elements; 
       FIG. 12  is a flow diagram showing a process of detecting an abnormality of a rotation angle detecting device according to the fourth embodiment of the invention; 
       FIGS. 13A ,  13 B,  13 C,  13 D and  13 E are graphs showing relationships of the rotation angle with sensor signals, output signals and judgment levels; 
       FIG. 14  is a table for judging normality of pairs of hall elements; 
       FIG. 15  is a flow diagram showing a process of detecting an abnormality of a rotation angle detecting device according to the fifth embodiment of the invention; and 
       FIG. 16  is a table for judging normality of a group of hall elements. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Various embodiments of the present invention will be described with reference to the appended drawings. 
   A rotation angle detecting device  1  according to the first embodiment of the invention will be described with reference to  FIGS. 1–5 . 
   As shown in  FIG. 2 , the rotation angle detecting device  1  according to the first embodiment of the invention includes a cylindrical magnetic yoke  20 , a pair of arc-shaped permanent magnets  22 ,  24 , a magnetic sensor unit comprised of a pair of hall elements  30 ,  31 , a support member  50  and an ECU  90 . The yoke  20  and the permanent magnets  22 ,  24  form a magnetic field. The permanent magnets  22 ,  24  are fixed to the inner surface of the cylindrical yoke  20  spaced apart from each other at an angle of 180 degrees to form a magnetic field of a uniform magnetic flux density in the vicinity of the hall elements  30 ,  31 . 
   The hall element  30  and the other hole element  31  are fixed to the support member  50  along the rotation direction of the rotating object to have an angle of 90 degrees between them. In other words, they are disposed to be perpendicular to each other to form an L-shape. When the rotating object rotates, the hall elements  30  and  31  rotates relative to the yoke  20  and the permanent magnets  22 ,  24 . Accordingly, the hall element  30  and the another hall element  31  generate sinusoidal electric signals that are 90 degrees in phase different from each other. 
   Incidentally, the hall elements  30 ,  31  can be operated by a constant current source or a constant voltage source. The hall elements  30 ,  31  can be replaced by other magnetic sensors, such as magneto-resistance elements. 
   The ECU  90  includes a nonvolatile memory such as a flash memory that stores a rotation angle detection program, a volatile memory that temporarily stores the rotation angle detection program and various data and a CPU that executes the rotation angle detection program. 
   When the rotating objects rotates, the hall elements  30 ,  31  respectively generate sinusoidal output signals V 1 , V 2 , which are 90 degrees in phase different from each other, as shown in  FIG. 3A . That is, the hall element  30  generates a sine wave voltage output signal V 1 , and the hall element  31  generates a cosine wave voltage output signal V 2 . 
   Assuming that: the rotation angle is θ; 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 hole elements is I, the output signals V 1 , V 2  and the rotation angle θ can be expressed as follows.
 
 V 1 =kBI  sin θ  (1)
 
 V 2 =kBI  sin(θ−90)=− kBI  cos θ  (2)
 
   The ECU  90  executes the rotation angle detection program to detect the rotation angle of the rotating object based on the output signals V 1 , V 2 . The rotation angle detection program is executed whenever the rotation angle detecting device is operated. 
   At first, tan θ is calculated, and then an arithmetic angle θ is calculated as follows.
 
− V 1 /V 2=sin θ/cos θ=tan θ  (3)
 
θ=arc tan( V 1 /V 2)  (4)
 
   As shown in  FIG. 4 , the ECU  90  examines whether the sign of the output signals V 1 , V 2  is plus (+) or minus (−) to discriminate four ranges of the rotation angle in 360 degrees. The ECU  90  adds an offset angle to the arithmetic angle θ, which changes at a cycle of 180 degrees as shown in  FIG. 3B , based on the discrimination to obtain an output angle, which changes at a cycle of 360 degrees as shown in  FIG. 3C . 
   However, if any of the hall elements  30 ,  31  fails or is disconnected from the ECU  90 , the rotation angle detecting device  1  outputs an abnormal voltage signal. A CPU of the ECU  90  executes an abnormality detecting module that is included in the rotation angle detection program. 
   The abnormality detection by the ECU  90  is shown in  FIG. 1 . At step S 100 , a judgment level D 1  is calculated by the following expressions:
 
 D 1 =V 1 2   +V 2 2   =T 1(sin 2  θ+cos 2  θ)  (5)
 
 T 1 =k   2   B   2   I   2   (6)
 
   If the output signals of the hall elements  30 ,  31  are normal, T 1  is constant as shown in  FIG. 5 . On the other hand, T 1  changes if any output signal of the hall elements  30 ,  31  is not normal. 
   Subsequently, whether the judgment level D 1  is larger than T 1 −t1 and smaller than T 1 +t1 or not is examined at S 102 . Incidentally, the judgment level is stored in a flash memory of the ECU  90 . If the judgment level D 1  is not between T 1 −t1 and T 1 +t1, or the result of the examination is NO, the ECU  90  takes a countermeasure, such as displaying of an abnormality, at S 104 . 
   Thus, abnormality can be detected by calculation based on the output signals of the hall elements without providing additional detecting element. 
   A rotation angle detecting device  1  according to the second embodiment of the invention will be described with reference to  FIGS. 6 and 7 . The hardware of the rotation angle detecting device  1  is the same as that of the first embodiment. 
   The abnormality detection by the ECU  90  is shown in  FIG. 6 . At step S 200 , the output signal of the hall elements  30  is differentiated and the output signal of the hall element  31  is added thereto to obtain a judgment level D 2 . That is:
 
 D 2 =dV 1 /dθ+V 2 =kBI (cos θ−cos θ)=0  (7)
 
   If the output signals of the hall elements  30 ,  31  are normal, D 2  is zero as shown in  FIG. 7 . On the other hand, D 2  changes if any output signal of the hall elements  30 ,  31  is not normal. Incidentally, the judgment level D 2  can be obtained by addition or subtraction after one of the output signals V 1 , V 2  is differentiated or integrated an odd number of times more than the other. In other words, the judgment level D 2  is calculated by adding an nth differentiated value of the output signal V 1 , and an (n+1) th differentiated value of the output signal V 2  so that the sum becomes zero when both the output signals V 1 , V 2  are normal and does not become zero when any of the output signals V 1 , V 2  is not normal. 
   Subsequently, whether the judgment level D 2  is larger than −t1 and smaller than th or not is examined at S 202 . If the judgment level D 2  is not between −t1 and th, or the result of the examination is NO, the ECU  90  takes a countermeasure, such as displaying of an abnormality, at S 204 . 
   Thus, abnormality can be detected at a high accuracy. 
   A rotation angle detecting device  1  according to the third embodiment of the invention will be described with reference to  FIGS. 8 and 9 . 
   The rotation angle detecting device  1  according to the third embodiment of the invention includes a cylindrical magnetic yoke  20 , a pair of arc-shaped permanent magnets  22 ,  24 , a magnetic sensor unit composed of a pair of hall elements  30 ,  31 , a support member  50  and an ECU  90 . 
   The hall element  30  and the other hole element  31  are fixed to the support member  50  along the rotation direction of the rotating object to have an angle other than 90 degrees between them. 
   Assuming that the angles of the hall elements  30 ,  31  relative to the direction X are respectively θ1 and θ2, the sensor signals Vs 1 , Vs 2  and the rotation angle θ can be expressed as follows.
 
 Vs 1 =kBI  sin(θ+θ1)  (8)
 
 Vs 2 =kBI  sin(θ+θ2)  (9)
 
   These sensor signals Vs 1 , Vs 2  are converted into the following output signals V 1 , V 2  that are 90 degrees in phase different from each other.
 
 V 1 =Vs 1·sin θ2 −V 2·sin θ1  (10)
 
 V 2 =Vs 2·cos θ2 −V 2·cos θ1  (11)
 
   Thus, the output signals V 1 , V 2  have a sine-cosine relationship, as shown in  FIG. 9 . 
   Accordingly, the ECU  90  can calculate the judgment level D 1  or D 2  in the same manner as the first or the second embodiment. 
   A rotation angle detecting device  1  according to the fourth embodiment of the invention will be described with reference to  FIGS. 10–14 . 
   The rotation angle detecting device  1  according to the fourth embodiment of the invention includes a magnetic sensor unit composed of three hall elements  430 ,  431 ,  432  instead of a pair of hall elements  30 ,  31  of the third embodiment. Other components are the same as the third embodiment. 
   The hall element  430  has an angle of θ1 (e.g. 0 degree) relative to the direction X, the hall element  431  has an angle of θ2 (e.g. 40 degrees) relative to the direction X, and the hall element  432  has an angle of θ3 (e.g. 60 degrees) relative to the direction X, as shown in  FIG. 10 . 
   As shown in  FIG. 11 , the three hall elements  430 ,  431 ,  432  form three pairs P 1 , P 2 , P 3  of the hall elements. 
   These sensor signals Vs 1 , Vs 2 , Vs 3  are converted into the following output signals V 11 , V 12 , V 21 , V 22 , V 31 , V 32 , as shown in  FIG. 13B  and  FIG. 13D , in the same manner as that of the third embodiment at step S 400  shown in  FIG. 12 .
 
 V 11 =k ( Vs 1·sin θ2 −Vs 2·sin θ1)  (12)
 
 V 12 =k ( Vs 1·cos θ2 −Vs 2·cos θ1)  (13)
 
 V 21=1( Vs 2·sin θ3 −Vs 3·sin θ2)  (14)
 
 V 22=1( Vs 2·cos θ3 −Vs 3·cos θ2)  (15)
 
 V 31 =m ( Vs 3·sin θ1 −Vs 1·sin θ3)  (16)
 
 V 32 =m ( Vs 3·cos θ1 −Vs 1·cos θ3)  (17)
 
   In the above expressions, k, l, and m are coefficients to adjust the amplitude of the output signals V 11 , V 12 , V 21 , V 22 , V 31  and V 32 . 
   The ECU  90  calculate the judgment levels D 31 , D 32  and D 33  by the following expressions at S 402 .
 
 D 31 =V 11 2   +V 12 2   (18)
 
 D 32 =V 21 2   +V 22 2   (19)
 
 D 33 =V 31 2   +V 32 2   (20)
 
   Subsequently, whether the judgment levels D 31 , D 32 , D 33  are larger than T 3 −t1 and smaller than T 3 +t1 or not is examined at S 404 . 
   If the signals of the hall elements  430 ,  431 ,  432  are normal, the judgment level (e.g. D 33 ) is a constant T 3  as shown in  FIG. 13C . On the other hand, the judgment level changes if any output signal of the hall elements  430 ,  431 ,  432  is not normal, as shown in  FIG. 13E . If the judgment level D 31 , D 32  or D 33  is not between T 3 −t1 and T 3 +t1, or the result of the examination is NO, the ECU  90  takes a countermeasure, such as displaying of an abnormality. 
   Thereafter, at S 406 , the ECU  90  calculates a candidate output angle C 1  based on the output signals V 11  and V 12 , a candidate output angle C 2  based on the output signals V 21  and V 22  and a candidate output angle C 3  based on the output signals V 31  and V 32 , in the same manner as the first embodiment as to calculating an output angle. 
   Then, a normal pair is selected in a manner as shown in  FIG. 14  from the pairs P 1 , P 2 , P 3  at S 408 , and a candidate output angle C 1 , C 2  or C 3  that corresponds to the normal pair is provided as a normal output angle at S 410 . 
   With this embodiment, a correct output angle can be obtained even if one hall element fails. 
   Three hall elements can be disposed perpendicular to each other. In this case, it is not necessary to convert the sensor signals Vs 1 , Vs 2 , Vs 3  into the output signals. 
   A rotation angle detecting device  1  according to the fifth embodiment of the invention will be described with reference to  FIGS. 15 and 16 . 
   The rotation angle detecting device  1  according to the fifth embodiment of the invention is substantially the same as the fourth embodiment except for the process of rotation angle detecting operation. 
   The sensor signals Vs 1 , Vs 2 , Vs 3  are provided and converted into output signals at S 500 . The ECU  90  calculate the judgment levels at S 502 , which is compared with a constant to detect abnormality at S 504 . Thereafter, the ECU  90  calculates output angles based on the output signals, in the same manner as the fourth embodiment, so that a normal pair is selected from the pairs at S 506 , and an output angle that corresponds to a normal pair is provided as a normal output angle at S 508 . 
   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.