Rotation angle detecting device

A rotation angle detecting device includes a magnetic member for providing a magnetic field, a magnetic sensor for sensing a change in the magnetic field when the magnetic member rotates relative to the magnetic sensor about a rotation axis. The magnetic sensor is disposed at a single position and includes a pair of sensor elements. The pair of sensor elements is disposed on an imaginary plane that is perpendicular to the rotation axis so that sensing surfaces of the sensor elements have 90 degrees in angle to each other and so that each of the sensing surfaces inclines by 45 degrees in angle to a line intersecting the rotation axis at right angles.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from Japanese Patent Application 2006-227680, filed Aug. 24, 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 rotation angle detecting device for detecting a rotation angle of a rotating object such as a crank shaft of an engine or a wheel of a vehicle.

2. Description of the Related Art

JP-2003-75108-A discloses a rotation angle detecting device. In such a rotation angle detecting device, a change in magnetic field caused by rotation of a permanent magnet rotor is detected by a pair of magnetic sensor elements for providing a pair of output signals. The output signals are converted into trigonometric functions to calculate the rotation angle of the rotating object.

Such a rotation angle detecting device has a difficulty in reducing its size because the pair of sensor elements is disposed distant from each other along the circumference of a permanent magnet rotor.

Further, it is difficult to accurately position the sensor elements around the permanent magnet rotor because of vibration when the rotation angle detecting device is installed into a motor vehicle or the like. As shown inFIG. 18, the magnetic flux density distribution around a permanent magnet rotor400is not uniform. Accordingly, one of the sensor elements may sense a change in the magnetic flux density that is different from the other sensor element if the sensor elements are not accurately positioned. Further, because such a sensor element changes its output signal as the temperature surrounding the sensor changes, the magnetic sensor may provide an inaccurate output signal if the temperature surrounding one of the sensor elements is different from the temperature surrounding the other sensor element.

If a pair of magnetic sensor elements412,412′ is integrated into a unit410that is disposed at a position around the permanent magnet rotor400as shown inFIG. 16, the size of the rotation angle detecting device can be reduced. In this case, the first sensor elements412is disposed so that the first sensor surface413thereof can be perpendicular to a line intersecting the rotation axis404of the permanent magnet rotor400at right angles and the second sensor element412′ is disposed so that the second sensor surface413′ thereof can be perpendicular to the first sensor surface413.

However, the sensor elements412,412′ provide output signals whose amplitude are different from each other as shown inFIG. 17when the permanent magnet rotor400rotates, because the sensor elements412,412′ are respectively disposed in the magnetic field of different magnetic flux density. Therefore, it is difficult to accurately convert the output signals to trigonometric functions.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a compact and accurate rotation angle detecting device.

According to a feature of the invention, a rotation angle detecting device includes a magnetic member for providing a magnetic field, a magnetic sensor for sensing a change in the magnetic field when the magnetic member rotates relative to the magnetic sensor about a rotation axis, in which: the magnetic sensor is disposed at a single position and includes a pair of sensor elements; the pair of sensor elements is disposed on an imaginary plane that is perpendicular to the rotation axis so that sensing surfaces of the sensor elements have 90 degrees in angle to each other; and each of the sensing surfaces inclines by 45 degrees in angle to a line intersecting the rotation axis at right angles.

Therefore, a compact rotation angle detecting device can be provided. Further, temperature difference between the pair of sensor elements can be minimized.

Even if the magnetic sensor is shifted from the permanent magnet rotor, the output signals of the pair of sensor elements equally change, so that the rotation angle can be detected accurately.

Assuming that maximum magnetic flux densities sensed by a magnetic sensor410that includes a pair of magnetic sensor elements412,412′ shown inFIG. 16are A and B, the magnetic flux densities B0x, B0y that are detected when a permanent magnet rotor400rotates by an angle θ relative to the magnetic sensor410are expressed as follows:
B0x=A×sin θ  (1)
B0y=A×cos θ  (2)

On the other hand, as shown inFIGS. 1A and 1Bfor example, the pair of sensor elements (e.g.22,22′) is disposed on an IC chip (e.g.20) that is placed on an imaginary plane perpendicular to the rotation axis (e.g.200) of the permanent magnet rotor (e.g.12) so that their sensing surfaces (e.g.23,23′) are disposed to have an angle of 90 degrees between each other and so that each of the sensing surfaces inclines by 45 degrees in angle to a line (e.g.202) intersecting the rotation axis (e.g.200) of the permanent magnet rotor at right angles.

The magnetic flux densities B1x, B1y that are sensed by a pair of magnetic sensor elements according to the present invention are expressed as follows:

It can be understood from the expressions (5) and (6) that even if the maximum values A, B of the output signals of the pair of magnetic sensor elements412,412′ of the magnetic sensor410shown inFIG. 16are different from each other, the maximum values of the output signals of the pair of magnetic sensor elements22,22′ of the magnetic sensor20according to the present invention are the same to each other (i.e. (A2+B2)/2)1/2). That is, the amplitudes of the output signals of the pair of sensor elements22,22′ are equal to each other.

According to another feature of the invention, the permanent magnet rotor is formed of a disk-shaped or cylindrical member.

According to another feature of the invention, a pair of magnetic sensor elements is integrally formed on a single chip. Therefore, the angle between the sensor surfaces of the sensor elements can be accurately set to 90 degrees in angle.

From the expression (5), the following expressions can be provided:
sin β=−B/(A2+B2)1/2(7)
cos β=A/(A2+B2)1/2(8)
therefore,
β=cos−1(A/(A2+B2)1/2)  (9)

and from the expression (6), the following expression can be provided:
sin γ=−B/(A2+B2)1/2(10)
cos γ=−A/(A2+B2)1/2(11)
therefore,
γ=cos−1(−A/(A2+B2)1/2)=180°−β  (12)

Thus, the phase difference (β−γ) between the output signals of the pair of magnetic sensor elements can be expressed as follows:
(β−γ)=(180°−β)=2×(β−90°)  (13)

As understood from the expression (13), the difference in phase between the output signals of two magnetic sensor elements is not equal to 90°. It is also understood from the expressions (9) and (12) that the phase difference (β−γ) in the structure shown inFIG. 16varies as the maximum values A, B change.

In the prior art structure shown inFIG. 16, the maximum values A, B of the magnetic flux densities that are detected by the pair of magnetic sensor elements412,412′ change if the position of the magnetic sensor410is shifted in a radial direction.

On the other hand, in the structure according to the invention, the maximum value of the magnetic flux density that is detected by each of the pair of magnetic sensor elements22,22′ does not change even if the position of the magnetic sensor is shifted in a radial direction.

According to another feature of the invention, each of the sensor elements is a Hall element.

According to another feature of the invention, the rotation angle detecting device further includes means for calculating a rotation angle of the rotating object by converting the output signals of the sensor elements to trigonometric functions. The means for calculating a rotation angle may adjust the phase difference between the output signals to 90 degrees in angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some preferred embodiments according to the present invention will be described with reference to the appended drawings.

A rotation angle detecting device10according to the first embodiment of the invention will be described with reference toFIGS. 1-8.

The rotation angle detecting device10is connected to a rotating object, such as an engine crank shaft or a steering wheel of a vehicle in order to detect the rotation angle of the crankshaft or the steering wheel. The rotation angle detecting device10includes a disk-shaped permanent magnet rotor12, a magnetic sensor (hereinafter referred to as the Hall IC)20, and an electronic control unit (hereinafter referred to as ECU)30. The permanent magnet rotor12is constructed of a pair of semicircular permanent magnets and a rotary shaft14that rotates about its rotation axis200. The permanent magnet rotor12is magnetized in a radial direction, as shown inFIG. 18.

The Hall IC20is disposed at a place around the circumference of the permanent magnet rotor12. The Hall IC20includes a pair of Hall elements22,22′ and the ECU30so as to provide the ECU with the output signals of the Hall elements22,22′. The ECU30may be separated form the Hall IC, however.

Each of the Hall elements22,22′ has a magnetic sensor surface23,23′ and is arranged to be placed on an imaginary plane that is perpendicular to the rotation axis200so that the magnetic sensor surface23inclines by 45 degrees in angle toward a normal line202that intersects the rotation axis200of the permanent magnet rotor12at right angles, as shown inFIGS. 1A,1B, and so that the magnetic sensor surfaces23of the pair of magnetic sensor elements22are positioned to have 90 degrees in angle between them. Therefore, the Hall elements23are disposed symmetric with respect to the normal line202.

The ECU30includes a CPU, a ROM, an EEPROM, etc. so that the ECU30can calculate a rotation angle of a rotating object from the output signals of the Hall IC20using a rotation angle calculation program that is stored in the EEPROM or the ROM.

A rotation angle of a rotating object is calculated from the output signals of the Hall elements in one of the following ways.

If the permanent magnet rotor12rotates relative to the Hall elements22,22′ of the Hall IC20by a rotation angle θ, magnetic flux densities B1x, B1y that are detected by the pair of Hall elements22,22′ are expressed from the expression (5), (6) and (12) as follows:
B1x=V×sin(θ+β)  (20)

wherein: V is a maximum value of the magnetic density detected by the magnetic sensor elements, or equal to ((A2+B2)/2)1/2.

Then, the following expression is provided from the expressions (22) and (23):

If the maximum flux densities A and B are measured beforehand, the rotation angle θ can be expressed as follows:
θ=−tan−1(−(B/A)×(B1x−B1y)/(B1x+B1y)  (30)

Since tan β=cot (90°−β), the expression (24) can be expressed as follows:
θ=tan−1(cot(90−β)×(B1x+B1y)/(B1x−B1y))  (40)

Assuming that the phase difference between the output signals of the pair of magnetic sensor elements22is α, then α=β−γ=−(180°−2β).

The following expression is provided from the expressions (40) and (41):

If the Hall IC20is shifted in a radial direction from the permanent magnet rotor12, the phase of each of the output signals300,312of the pair of Hall elements22,22′ varies as shown inFIG. 5. If the phase difference between two output signals increases to near 90 degrees in angle, the deviation of the rotation angle becomes smaller as shown inFIG. 8. In case that the phase difference is much smaller than 90 degrees in angle, the deviation of the rotation angle varies as shown inFIG. 6B. On the other hand, the deviation of the rotation angle is smaller than the former case, as shown inFIG. 7B, in case that the phase difference is 90 degrees in angle. Incidentally, broken lines inFIGS. 6A and 7Ashow the output signals of the Hall elements22when the Hall IC20is shifted.

In this case, the phase difference between the output signals of the Hall elements22is adjusted to 90 degrees in angle by using a map.

Thus, the rotation angle can be calculated by one of the above ways of calculation.

Temperature characteristics of the sensor elements are taken into account, the rotation angle can be calculated as follows.

Assuming that: (i) the magnetic flux densities detected by the magnetic sensor elements412,412′ shown inFIG. 16are B2x, B2y; (ii) the magnetic flux densities detected by the magnetic sensor elements22,22′ shown inFIG. 1are B3x, B3y; (iii) the phase angle of the magnetic sensor elements are β, γ; and (iv) the temperature characteristic coefficient of the magnetic sensor elements is k (t), the following expression can be formed from expression (1), (2), (5) and (6):

Then, the following expression is formed from the expression (52):
cos β3=A/(A2+B2)1/2

Therefore, the following expression can be formed from the expressions (8) and (9):
β3=cos−1(A/(A2+B2)1/2)=β  (54)

The following expression can be formed from the expression (53):
cos γ3=A/(A2+B2)1/2

Further, the following expression is formed from expressions (11) and (12):

It is understood from the expressions (52)-(55) that the phase angles of the output signals of the magnetic sensor elements22,22′ will not change although the amplitude of the output signals are multiplied by k (t). That is, the phase difference between the magnetic sensor elements22,22′ will not change.

The following expression can be formed from the expressions (5), (6) and (52)-(55):

If B1x and B1y in the expression (24) are respectively changed to B3x and B3y and the expressions (56) and (57) are substituted therefor, the rotation angle θ is expressed as follows:

Thus, even if the temperature surrounding the magnetic sensor elements change, the rotation angle θ will not change.

A rotation angle detecting device according to the second embodiment of the invention is shown inFIGS. 9A and 9B.

The rotation angle detecting device40includes a pair of Hall elements22,22′. Each of the Hall elements22,22′ has a magnetic sensor surface23or23′ and is arranged to be on an imaginary plane that is perpendicular to the rotation axis200of the permanent magnet rotor12so that each of the magnetic sensor surfaces23,23′ inclines by 45 degrees in angle toward a normal line202that intersects the rotation axis200at right angles and so that the magnetic sensor surfaces23of the pair of magnetic sensor elements22are positioned to have 90 degrees in angle between them. Therefore, the Hall elements23are disposed symmetric with respect to the line202.

However, the sensor surfaces23,23′ are arranged to face the permanent magnet rotor12, which is opposite to the sensor surfaces of the first embodiment.

A rotation angle detecting device according to the third embodiments of the invention will be described with reference toFIGS. 10A,10B.

As shown inFIGS. 10A and 10B, the rotation angle detecting device50includes a pair of Hall elements22,22′. Each of the Hall elements22,22′ has a magnetic sensor surface23or23′ and is arranged to be disposed on an imaginary plane that is perpendicular to the rotation axis200of the permanent magnet rotor12so that each of the magnetic sensor surfaces23,23′ inclines by 45 degrees in angle toward a line202that intersects the rotation axis200at right angles and so that the magnetic sensor surfaces23,23′ of the pair of magnetic sensor elements22,22′ are positioned to have 90 degrees in angle between them. However, the Hall elements23,23′ are disposed not symmetric with respect to the line202but disposed symmetric with respect to a line204that extends in parallel with a tangential line of the outer circumference of the permanent rotor12that intersects the line202at right angles.

A rotation angle detecting device60according to the fourth embodiment of the invention is shown inFIGS. 11A and 11B.

Each of the Hall elements22,22′ is disposed in the same manner as the fourth embodiment except that the sensor surfaces23,23′ are arranged to face in the opposite direction.

A rotation angle detecting device according to the fifth embodiment of the invention will be described with reference toFIGS. 12A and 12B.

The rotation angle detecting device70includes a pair of Hall elements22,22′. Each of the Hall elements22,22′ has a magnetic sensor surface23or23′ and is arranged to be disposed on an imaginary plane that is perpendicular to the rotation axis200of the permanent magnet rotor12so that each of the magnetic sensor surfaces23,23′ inclines by 45 degrees in angle toward the normal line202that intersects the rotation axis200at right angles and so that the magnetic sensor surfaces23,23′ of the pair of magnetic sensor elements22,22′ are positioned to have 90 degrees in angle between them. Therefore, the Hall elements23,23′ are disposed symmetric with respect to the line202. However, the Hall IC20is not disposed at a position around the permanent magnet rotor12but is disposed at a position above and within the circumference of the permanent magnet rotor12.

A rotation angle detecting device according to the sixth embodiment of the invention will be described with reference toFIG. 13.

The rotation angle detecting device80includes a pair of Hall elements22,22′ and a ring-shaped permanent magnet rotor82, which is different from the disk-shaped permanent magnet rotor12in that the magnet rotor82is constructed of a pair of arc-shaped permanent magnets. Each of the Hall elements22,22′ has a magnetic sensor surface23or23′ and is arranged to be disposed on an imaginary plane that is perpendicular to the rotation axis200of the permanent magnet rotor82so that each of the magnetic sensor surfaces23,23′ inclines by 45 degrees in angle toward the normal line202that intersects the rotation axis200at right angles and so that the magnetic sensor surfaces23,23′ of the pair of magnetic sensor elements22,22′ are positioned to have 90 degrees in angle between them. Therefore, the Hall elements23,23′ are disposed symmetric with respect to the line202.

A rotation angle detecting device according to the seventh embodiment of the invention will be described with reference toFIG. 14.

The rotation angle detecting device90has the same structure as the sixth embodiment except that the Hall IC20is disposed at a position above and within the circumference of the permanent magnet rotor82.

The Hall elements22,22′ can be formed separately. The ring-shaped permanent magnets82may be constructed of a pair of short bar-like permanent magnets and a pair of arc-shaped members that support the permanent magnets instead of the pair of arc-shaped permanent magnets.

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.