The disclosure of Japanese Patent Application No. 2013-192761 filed on Sep. 18, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a rotation angle detecting device that detects a rotation angle of a rotating body.
2. Description of Related Art
Brushless motors used in an electric power steering system and the like are controlled by supplying a current to a stator winding in accordance with a rotation angle of a rotor. In order to detect the rotation angle of the rotor, for example, a rotation angle detecting device shown in
A direction indicated by an arrow shown in
When the amplitudes (φ1, φ2 are regarded as the same value φ or when the signals V1, V2 are normalized so that each of the amplitudes is a predetermined specified value φ, the one output signal V1 is expressed by V1=φ·sin θ and the other output signal V2 is expressed by V2=φ·cos θ. Further, when φ is 1 (φ=1), the one output signal V1 is expressed by V1=sin θ, and the other output signal V2 is expressed by V2=cos θ. Accordingly, in order to simplify the description, the output signals V1, V2 of the respective magnetic sensors 111, 112 are expressed by V1=sin θ and V2=sin(θ+90)=cos θ, respectively.
The rotation angle θ of the rotor can be obtained on the basis of, for example, the following Expression (1) using the output signals V1, V2.
Japanese Patent Application Publication No. 2013-61346 (JP 2013-61346 A), Japanese Patent Application Publication No. 2010-101746 (JP 2010-101746 A), and Japanese Patent Application Publication No. 2007-322197 (JP 2007-322197 A) describe examples of the related art.
In the above-described rotation angle detecting device in the related art, when there is a failure in at least one of the magnetic sensors 111, 112, the rotation angle θ of the rotor 102 cannot be detected. Therefore, it is determined whether the magnetic sensors 111, 112 are normal on the basis of the following Expression (2), using the relation of sin2 θ+cos2 θ=1 (relation of V12+V22=1).
lower limit≦V12+V22≦upper limit (2)
The lower limit is set to, for example, 0.9, and the upper limit is set to, for example, 1.1. When Expression (2) is satisfied, it is determined that the magnetic sensors 111, 112 are normal. When Expression (2) is not satisfied, it is determined that there is a failure in at least one of the magnetic sensors 111, 112.
In a case where the two magnetic sensors are disposed at an interval of an electrical angle other than 90 degrees, if the angular interval is not an interval of an electrical angle of 180 degrees, it is possible to detect the rotation angle of the rotating body on the basis of the output signals of the two magnetic sensors. In this case, it is not possible to determine whether the magnetic sensors are normal using Expression (2).
An object of the invention is to provide a rotation angle detecting device that can determine whether two magnetic sensors are normal even in a case where the two magnetic sensors are disposed at an interval of an electrical angle other than 90 degrees.
According to an aspect of the invention, there is provided a rotation angle detecting device including a first magnetic sensor that outputs a first sinusoidal signal (V1) in accordance with rotation of a rotating body; and a second magnetic sensor that outputs a second sinusoidal signal (V2) in accordance with the rotation of the rotating body. A phase difference (α) between the first sinusoidal signal (V1) and the second sinusoidal signal (V2) is an electrical angle other than 90 degrees and 180 degrees. The rotation angle detecting device further includes a device that computes a rotation angle (θ) of the rotating body based on the first sinusoidal signal (V1) and the second sinusoidal signal (V2), and a determination device that determines whether both the first and second magnetic sensors are normal, or there is a failure in at least one of the first and second magnetic sensors, based on the first sinusoidal signal (V1), the second sinusoidal signal (V2), and the phase difference (α). The determination device is configured to determine that both the first and second magnetic sensors are normal when an expression (a) is satisfied, and to determine that there is a failure in at least one of the first and second magnetic sensors when the expression (a) is not satisfied, the expression (a) being
L≦X
12
≦U
X
12
=V
1
2
+V
2
2−2[1−2 sin2(α/2)]V1·V2−1+{1−2 sin2(α/2)}2, (a)
where L is a lower limit that is set in advance and that is smaller than 0, and U is an upper limit set in advance and that is larger than 0.
With the rotation angle detecting device according to the above-described aspect, even in the case where the two magnetic sensors are disposed at an interval of an electrical angle other than 90 degrees, it is possible to determine whether the magnetic sensors are normal.
The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
Hereinafter, embodiments in a case where the invention is applied to a rotation angle detecting device for detecting a rotation angle of a rotor of a brushless motor will be described in detail with reference to the accompanying drawings.
Three magnetic sensors 11, 12, 13 are disposed at intervals in a circumferential direction of the rotor 2, in the vicinity of the rotor 2. The three magnetic sensors 11, 12, 13 may be referred to as a first magnetic sensor 11, a second magnetic sensor 12, and a third magnetic sensor 13, respectively. For example, a sensor, which includes an element having electrical characteristics changing due to the action of a magnetic field, for example, a Hall element or a magnetoresistive element, can be used as the magnetic sensor.
The three magnetic sensors 11, 12, 13 are disposed on a concentric circle around the central axis of the rotor 2. In this embodiment, when an angular interval between two adjacent magnetic sensors is represented by an electrical angle, the three magnetic sensors 11, 12, 13 are disposed at equal angular intervals. The first magnetic sensor 11 and the second magnetic sensor 12 are disposed at an angular interval of α (electrical angle) degrees around the rotation center axis of the rotor 2. The first magnetic sensor 11 and the third magnetic sensor 13 are disposed at an angular interval of β (electrical angle) degrees larger than a degrees around the rotation center axis of the rotor 2. In this embodiment, α is set to 120 degrees, and β is set to 240 degrees. In this embodiment, the angular interval α between the second magnetic sensor 12 and the third magnetic sensor 13 and the angular interval α between the third magnetic sensor 13 and the first magnetic sensor 11 are both 120 degrees.
An angular interval θ between a reference position P of the rotor 2 shown in
When the amplitudes φ1, φ2, and φ3 are regarded as the same value φ or when the signals V1, V2, V3 are normalized so that each of the amplitudes is a predetermined specified value φ, the signals V1, V2, V3 are expressed by φ·sin θ, φ·sin(θ+α), and φ·sin(θ+β), respectively. When φ is 1 (φ=1), the signals V1, V2, V3 are expressed by sin θ, sin(θ+α), and sin(θ+β), respectively. Consequently, in the following description, the output signals V1, V2, V3 of the magnetic sensors 11, 12, 13 are expressed by V1=sin θ, V2=sin(θ+α)=sin(θ+120), and V3=sin(θ+β)=sin(θ+240), respectively.
The respective output signals V1, V2, V3 of the magnetic sensors 11, 12, 13 are input to a rotation angle computation device 20. The rotation angle computation device 20 computes the rotation angle θ of the rotor 2 on the basis of the respective output signals V1, V2, V3 of the magnetic sensors 11, 12, 13. The rotation angle computation device 20 is constituted by, for example, a microcomputer, and includes a CPU and memory (ROM, RAM, and the like). The rotation angle computation device 20 has a function of detecting a failure in the magnetic sensors 11, 12, 13 and a function of computing the rotation angle θ of the rotor 2 on the basis of output signals of two normal magnetic sensors.
The function of detecting a failure in the magnetic sensors will be described with reference to
A length of a straight line connecting the rotation center axis of the rotor 2 and the first magnetic sensor 11 is represented by A, a length of a straight line connecting the rotation center axis of the rotor 2 and the second magnetic sensor 12 is represented by B, and a length of a straight line connecting the first magnetic sensor 11 and the second magnetic sensor 12 is represented by C. When an angular interval between the reference position P for the rotation angle of the rotor 2 and the first magnetic sensor 11 is set to θ1 (equivalent to the rotor rotation angle θ in this embodiment) and an angular interval between the reference position P for the rotation angle of the rotor 2 and the second magnetic sensor 12 is set to θ2, the expressions of V1=sin θ1 and V2=sin θ2=sin(θ1+α) are established.
The following Expression (3) is established based on the cosine theorem.
A
2
+B
22AB cos(θ2−θ1)=C2 (3)
Since the magnetic sensors 11, 12 are disposed on the concentric circle around the central axis of the rotor 2, the expression of A=B is established. In addition, since a triangle having straight lines A, B, C as the three sides thereof is an isosceles triangle, the expression of C=2A sin(α/2) is established.
By substituting A=B and C=2A sin(α/2) into Expression (3), the following Expression (4) is obtained.
(cos θ2 cos θ1+sin θ2 sin θ1)=1−2 sin2(α/2) (4)
By transforming Expression (4), the following Expression (5) is obtained.
cos θ2 cos θ1={1−2 sin2(α/2)}−sin θ2 sin θ1 (5)
By squaring both sides of Expression (5), the following Expression (6) is obtained.
By substituting cos2 θ1=1−sin2 θ1 and cos2 θ2=1−sin2 θ2 into Expression (6), the following Expression (7) is obtained.
sin θ12+sin θ22−2{1−2 sin2(α/2)} sin θ1 sin θ2=1−{1−2 sin2(α/2)}2 (7)
By substituting sin θ1=V1 and sin θ2=V2 into Expression (7), the following Expression (8) is obtained.
V
1
2
+V
2
2−2{1−2 sin2(α/2)}V1·V2=1−{1−2 sin2(α/2)}2 (8)
Consequently, when a lower limit, which is set in advance, is represented by L (L<0) and an upper limit, which is set in advance, is represented by U (U>0), it is possible to determine whether the magnetic sensors 11, 12 are normal, on the basis of the following Expression (9).
L≦X
12
≦U
X
12
=V
1
2
+V
2
2−2{1−2 sin2(α/2)}V1·V2−1+{1−2 sin2(α/2)}2 (9)
When Expression (9) is satisfied, it is determined whether the magnetic sensors 11, 12 are normal. On the other hand, when Expression (9) is not satisfied, it is determined that there is a failure in at least one of the magnetic sensors 11, 12.
When it is determined whether the second and third magnetic sensors 12, 13 are normal on the basis of the output signal V2 of the second magnetic sensor 12 and the output signal V3 of the third magnetic sensor 13, it is possible to determine whether the magnetic sensors 12, 13 are normal on the basis of the following Expression (10).
L≦X
23
≦U
X
23
=V
2
2
+V
3
2−2{1−2 sin2(α/2)}V2·V3−1+{1−2 sin2(α/2)}2 (10)
When it is determined whether the first and third magnetic sensors 11, 13 are normal on the basis of the output signal V1 of the first magnetic sensor 11 and the output signal V3 of the third magnetic sensor 13, it is possible to determine whether the magnetic sensors 11, 13 are normal on the basis of the following Expression (11).
L≦X
31
≦U
X
31
=V
3
2
+V
1
2−2{1−2 sin2(α/2)}V3·V11+{1−2 sin2(α/2)}2 (11)
In this embodiment, since α is 120 degrees, X12, X23, X31 in Expressions (9), (10), (11) are expressed by the following Expressions (12), (13), (14), respectively.
X
12
=V
1
2
+V
2
2
+V
1
·V
2−0.75 (12)
X
23
=V
2
2
+V
3
2
+V2·V3−0.75 (13)
X
31
=V
3
2
+V
1
2
+V
3
·V
1−0.75 (14)
In this case, the lower limit U and the upper limit L are expressed by, for example, the following Expressions (15), (16).
L=−0.75×(γ/100) (15)
U=0.75×(γ/100) (16)
In Expressions (15), (16), γ denotes a value set in advance, and γ is set to, for example, 5.
A description will be made on a failure determination method in a case where N magnetic sensors are disposed at intervals on a concentric circle and an angular interval between the adjacent magnetic sensors is set so that a phase difference between output signals of the two adjacent magnetic sensors is 360/N degrees, N being a number equal to or larger than three. In this case, when an output signal of one magnetic sensor of the two adjacent magnetic sensors is represented by Va, an output signal of the other magnetic sensor is represented by Vb, a lower limit, which is set in advance, is represented by L (L<0), and an upper limit, which is set in advance, is represented by U (U>0), it is possible to determine whether the two adjacent magnetic sensors are normal on the basis of the following Expression (17).
L≦Xab≦U
Xab=Va
2
+Vb
2−2{1−2 sin2(180/N)}Va·Vb−1+{1−2 sin2(180/N)}2 (17)
Next, the function of computing a rotor rotation angle will be described. The rotation angle computation device 20 has a function of computing the rotor rotation angle θ on the basis of the first output signal V1 and the second output signal V2, a function of computing the rotor rotation angle θ on the basis of the first output signal V1 and the third output signal V3, and a function of computing the rotor rotation angle θ on the basis of the second output signal V2 and the third output signal V3.
The function of computing the rotor rotation angle θ on the basis of the first output signal V1 and the second output signal V2 will be described below. As described above, the expressions of V1=sin θ and V2=sin(θ+α) are established. Here, sin(θ+α) can be expanded as shown in the following Expression (18), based on the addition theorem.
sin(θ+α)=sin θ·cos α+cos θ·sin α (18)
It is possible to obtain the following Expression (19) using Expression (18).
The rotor rotation angle θ can be computed on the basis of the following Expression (20).
In this embodiment, α is 120 degrees (α=120 degrees).
The function of computing the rotor rotation angle θ on the basis of the first output signal V1 and the third output signal V3 will be described below. As described above, the expressions of V1=sin θ and V3=sin(θ+β) are established. Here, sin(θ+β) can be expanded as shown in the following Expression (21), based on the addition theorem.
sin(θ+β)=sin θ·cos β+cos θ·sin β (21)
It is possible to obtain the following Expression (22) using Expression (21).
The rotor rotation angle θ can be computed on the basis of the following Expression (23).
In this embodiment, β is 240 degrees (β=240 degrees).
The function of computing the rotor rotation angle θ on the basis of the second output signal V2 and the third output signal V3 will be described below. When the expression of Θ=(θ+α) is established, V2 is represented by the expression of V2=sin Θ and V3 is represented by the expression of V3=sin(Θ+α). Here, sin(Θ+α) can be expanded as shown in the following Expression (24), based on the addition theorem.
sin(Θ+α)=sin Θ·cos α+cos Θ·sin α (24)
It is possible to obtain the following Expression (25) using Expression (24).
The rotor rotation angle θ can be computed on the basis of the following Expression (26).
In this embodiment, α is 120 degrees (α=120 degrees).
A first failure flag F1 is a flag for storing a determination result that there is a failure in the first magnetic sensor 11, and is set (F1=1) when it is determined that there is a failure in the first magnetic sensor 11. A second failure flag F2 is a flag for storing a determination result that there is a failure in the second magnetic sensor 12, and is set (F2=1) when it is determined that there is a failure in the second magnetic sensor 12. A third failure flag F3 is a flag for storing a determination result that there is a failure in the third magnetic sensor 13, and is set (F3=1) when it is determined that there is a failure in the third magnetic sensor 13. When a power source for the rotation angle computation device 20 is turned on, all the flags F0, F1, F2, F3 are reset (F0=F1=F2=F3=0).
Referring to
The rotation angle computation device 20 determines whether the first failure flag F1 is in a set state (step S6). When the first failure flag F1 is in a reset state (F1=0) (step S6: NO), the rotation angle computation device 20 determines whether the second failure flag F2 is in a set state (step S7). When the second failure flag F2 is in a reset state (F2=0) (step S7: NO), the rotation angle computation device 20 determines whether X12 computed in step S3 satisfies the condition of L≦X12≦U (step S8).
When the condition of L≦X12≦U is satisfied (step S8: YES), the rotation angle computation device 20 determines that the first and second magnetic sensors 11, 12 are normal, and determines whether X31 computed in step S5 satisfies the condition of L≦X31≦U (step S9). When the condition of L≦X31≦U is satisfied (step S9: YES), the rotation angle computation device 20 determines that the first and third magnetic sensors 11, 13 are normal and proceeds to step S10. In step S10, the rotation angle computation device 20 computes the rotation angle θ on the basis of Expression (20), using the first output signal V1 and the second output signal V2. Then, the rotation angle computation device 20 terminates the processing in the present computation cycle. In step S10, the rotation angle computation device 20 may compute the rotation angle θ on the basis of Expression (23) or Expression (26).
When it is determined that the condition of L≦X31≦U is not satisfied in step S9 (step S9: NO), the rotation angle computation device 20 determines that there is a failure in the third magnetic sensor 13 as shown in
When the condition of L≦X23≦U is satisfied (step S13: YES), the rotation angle computation device 20 determines that there is a failure in the first magnetic sensor 11, and sets the first failure flag F1 (F1=1) (step S14). The rotation angle computation device 20 computes the rotation angle θ on the basis of Expression (26), using the second output signal V2 and the third output signal V3 (step S15). Then, the rotation angle computation device 20 terminates the processing in the present computation cycle.
When it is determined that the condition of L≦X23≦U is not satisfied in step S13 (step S13: NO), the rotation angle computation device 20 determines that there is a failure in the second magnetic sensor 12, and sets the second failure flag F2 (F2=1) (step S16). Then, the rotation angle computation device 20 terminates the processing in the present computation cycle. When it is determined that the third failure flag F3 is in the set state (F3=1) in step S12 (step S12: YES), the rotation angle computation device 20 determines that there is a failure in each of two or more magnetic sensors, and sets the rotation angle incomputable flag F0 (F0=1) (step S17). Then, the rotation angle computation device 20 terminates the processing in the present computation cycle.
When it is determined that the second failure flag F2 is in the set state (F2=1) in step S7 (see
When it is determined that the condition of L≦X31≦U is not satisfied in step S18 (step S18: NO), the rotation angle computation device 20 determines that there is a failure in each of two or more magnetic sensors, and sets the rotation angle incomputable flag F0 (F0=1) (step S20). Then, the rotation angle computation device 20 terminates the processing in the present computation cycle. When it is determined that the first failure flag F1 is in the set state (F1=1) in step S6 (see
When it is determined that the condition of L≦X23≦U is not satisfied in step S21 (step S21: NO), the rotation angle computation device 20 determines that there is a failure in each of two or more magnetic sensors, and sets the rotation angle incomputable flag F0 (F0=1) (step S23). Then, the rotation angle computation device 20 terminates the processing in the present computation cycle. When it is determined that the rotation angle incomputable flag F0 is in the set state (F0=1) in step S2 (see
In the above-described embodiment, even in the case where the angular interval between the two adjacent magnetic sensors is an interval of an electrical angle other than 90 degrees, it is possible to determine whether the two magnetic sensors are normal, or there is a failure in at least one of the magnetic sensors. In the above-described embodiment, even when there is a failure in any one of the three magnetic sensors 11, 12, 13, it is possible to compute the rotation angle θ of the rotor 2 on the basis of output signals of two other normal magnetic sensors.
Although the embodiment of the invention has been described, the invention can also be implemented in other embodiments. In the above-described embodiment, the angular interval between the adjacent magnetic sensors is an interval of an electrical angle of 120 degrees. However, the angular interval may be an interval of an electrical angle other than 120 degrees as long as the angular interval is an interval of an electrical angle other than 90 degrees and 180 degrees. In addition, all angular intervals between adjacent magnetic sensors may not be the same. In the above-described embodiment, three magnetic sensors may be provided. However, two magnetic sensors may be provided, or four or more magnetic sensors may be provided.
In the above-described embodiment, the first, second, and third output signals V1, V2, V3 are expressed by sin θ, sin(θ+α), and sin(θ+β), respectively. However, even when the first, second, and third output signals V1, V2, V3 are expressed by cos θ, cos(θ+α), and cos(θ+β), the invention can be applied. In the above-described embodiment, a pair of magnetic poles is provided in the rotor 2. However, two or more pairs of magnetic poles may be provided in the rotor 2.
The invention can also be applied to a case where a rotation angle of a rotating body other than a rotor of a brushless motor is detected.
Number | Date | Country | Kind |
---|---|---|---|
2013-192761 | Sep 2013 | JP | national |