JPH0862233A - Mr element-type rotary sensor - Google Patents

Abstract

PURPOSE: To make output level among a plurality of MR element-type rotary sensors constant. CONSTITUTION: A first MR element 104 and a second MR element 105 are laid out on one surface side and the other surface side of a slit circular plate of the MR element-type rotary sensor, respectively, the first and second MR elements 104 and 105 are held and first and second bias magnets 106 and 107 are laid out on the opposite side of a slit circular disc 103, the first MR element 104 and the second MR element 105 are connected in series, and then the potential is measured by a detection circuit 108.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slit disk having a plurality of slits for angle detection, an MR element arranged at a position facing the slit for angle detection of the slit disk, and the MR element. The present invention relates to an MR element type rotation sensor including a slit magnet and a bias magnet arranged on the opposite side of the slit disk.

[0002]

2. Description of the Related Art As a conventional rotation sensor, a bias magnetic field is applied by a bias magnet by rotating a slit disk having a plurality of angle detecting slits formed therein.
There is an MR element type rotation sensor that detects the amount of rotation of a rotating body by changing the resistance of the R element. This MR element type rotation sensor is used, for example, to detect the amount of rotation such as the number of rotations or the rotation angle of the cam shaft of the engine for controlling the engine in an automobile.

Now, the principle of rotation speed detection in the MR element type rotation sensor will be described with reference to FIGS. FIG. 7 is a magnetic flux density-resistance value characteristic diagram of the MR element, FIG.
Is a diagram showing the arrangement of the slit disk and the MR element, FIG. 9 is a basic detection circuit diagram, and FIG. 10 is a diagram showing the relationship between the resistance value change of the MR element and the output.

The MR element is a thin film element whose resistance value changes according to the magnetic flux density. FIG. 7 shows a state in which the resistance value of the MR element changes in accordance with the magnetic flux density applied in the film thickness direction. As shown in the figure, the MR element has a resistance value as the applied magnetic flux density B increases. It has the characteristic that R also becomes large.

In order to use this MR element as a detection element for a rotation sensor, as shown in FIG. 8, the angle detection slit 800 is formed on one surface side of a slit disk 801 for angle detection. Two MR elements 802 and 803 are arranged so as to face the slit 800. The bias magnet 804 for applying the bias magnetic field is connected to the MR element 80.
2, 803 are arranged on the back surface, and as shown in FIG. 9, two MR elements 802, 803 are connected in series and the midpoint potential thereof is measured.

In FIG. 8, when the slit disc 801 is rotated, the angle detecting slit 800 is moved to the MR element 80.
2, 803, the MR element 802,
The magnetic flux density applied to 803 changes. That is, the angle detecting slit 800 is the MR element 802 or 80.
3, the magnetic flux density B applied to the MR elements 802 and 803 is the smallest. On the contrary, the intermediate portion 805 of the angle detecting slits 800, 800 is the MR element 8
When it is opposite to 02 or 803, the magnetic flux density B becomes the largest. Here, when the difference between the maximum value and the minimum value of the magnetic flux density B is ΔB, the resistance value change ΔR of the MR element can be expressed by the following equation. Where R0 is the resistance value of the MR element when B = 0, μ is the magnetic permeability (electron mobility),
f is the shape factor of the MR element. ΔR = R0 ・ μ ・ f ・ ΔB

If the positional relationship between the distance l between the two MR elements 802 and 803 and the pitch L of the angle detecting slit 800 is 1 / L = 0.5, then each MR element 802
The resistance values Rc and Rd of 803 change as shown in FIG. Therefore, if the power supply voltage is Vcc, MR
The change amount Vp-p of the output voltage Vout of the element becomes Vp-p = Vcc · ΔR / (2R0 ′ + ΔR), and as shown in FIG.
A signal corresponding to the rotation of 1 is obtained. The MR element type rotation sensor is constructed by utilizing the above principle.

However, the slit disk 1101 shown in FIG.
When the distance d between the MR elements 1102 and 1103 changes, the value of the variation amount Vp-p of the output voltage Vout changes, as shown in FIG. For example, when the distance d = 1 mm and the value of the fluctuation amount Vp-p is 1, the distance d = 0.5.
In the case of mm, the value of the fluctuation amount Vp-p is about 1.9, and the distance d =
When the distance is 1.5 mm, the value of the fluctuation amount Vp-p is about 0.25. Therefore, the slit disk 1101 and the MR element 110
It is necessary to pay attention to the distance d from 2, 1103 when assembling.

Next, with reference to FIGS. 13 to 15, a specific structure of the conventional MR element type rotation sensor will be described. This MR element type rotation sensor shows an example in which it is attached to a cam shaft of an automobile engine. A shaft 1301 connected to a cam shaft (not shown) of the engine is rotatably supported by a housing 1302 by a bearing 1303. There is. A slit disk 1304 is fixed to the shaft 1301 by a shaft rotor 1305 so as to rotate integrally with the cam shaft. As shown in FIG. 14, a plurality of angle detecting slits 1 are provided on the outer peripheral portion of the slit disk 1304.
401 are formed at equal pitches. Slit disk 13
On one surface side of 04, two MR elements 1306, 13
07 are arranged. The MR elements 1306 and 130
7 is arranged so as to face the angle detecting slit 1401 so as to have a half pitch of the angle detecting slit 1401 when projected onto the slit disk 1304 as shown in FIG. A bias magnet 1308 for applying a bias magnetic field to the MR elements 1306 and 1307 is arranged on the back side of the MR elements 1306 and 1307. The two MR elements 1306 and 1307 are connected in series and connected to the detection circuit 1309. 1310 is the two MR elements 1306 and 1307, the bias magnet 13
08 and a detection circuit 1309 are built-in sensor units.

The slit disk 1304 is shown in FIG.
When rotated counterclockwise as shown in FIG.
6, the magnetic flux density passing through 1307 changes and the MR element 1
The resistance values of 306 and 1307 change. The MR element 1
A midpoint potential of 306 and 1307 is converted into a rectangular wave by a comparator and an angle signal is output.

[0011]

However, according to the conventional MR element type rotation sensor, two MR elements 130 are used.
Since 6 and 1307 are arranged on one surface side of the slit disc 1304, comparing the individual products, the air gap d (slit disc 130
4 and the MR elements 1306 and 1307) vary, resulting in different output levels among individual products.

The present invention has been made in view of the above, and an MR element type rotation sensor is formed by arranging MR elements on both sides of a slit disk, thereby making it possible to reduce the output level between individual products. The purpose is to keep it constant.

[0013]

In order to achieve the above-mentioned object, an MR element type rotation sensor according to the present invention has a slit disc formed with a plurality of angle detecting slits and an angle between the slit discs. An MR including an MR element arranged at a position facing a detection slit, and a bias magnet arranged on the opposite side of the slit disk with the MR element sandwiched therebetween.
In the element type rotation sensor, a first MR element arranged on one surface side of the slit disk and at a position facing the angle detecting slit, and the slit sandwiching the first MR element. A first bias magnet arranged on the opposite side of the disk, a second MR element arranged on the other surface side of the slit disk and at a position facing the angle detecting slit; A second bias magnet arranged on the opposite side of the slit disk with the second MR element sandwiched, the first MR element and the second MR element are connected in series to measure the midpoint potential. And measuring means.

[0014]

In the MR element type rotation sensor of the present invention, when the slit disk is rotated, the first MR element arranged on one surface side of the slit disk and the first MR element arranged on the other surface side. Since the angle detecting slits of the second MR element face each other, the first and second bias magnets are used by the first and second bias magnets.
The magnetic flux density applied to the R element changes, and the resistance value of each MR element changes. Since the first and second MR elements are connected in series and the midpoint potential is measured by the measuring means, even if the slit disk is biased to either MR element side,
It is possible to output a constant signal.

[0015]

Embodiments of an MR element type rotation sensor according to the present invention will be described below in detail with reference to the drawings. Figure 1 shows MR
2 is a vertical sectional front view of the element type rotation sensor. FIG. 2 is a plan view showing a positional relationship between the slit disk and the MR element. A shaft 100 connected to a rotating body (not shown) includes a housing 101, a bearing 102, and a bearing 102. It is rotatably supported by. A slit disk 103 is fixed to the shaft 100 by a shaft rotor 104 so as to rotate integrally. On the outer peripheral portion of the slit disk 103, a plurality of angle detecting slits 200 are formed at equal pitches as shown in FIG.

A first MR element 104 is arranged on one surface side of the slit disk 103 and at a position facing the angle detecting slit 200. The second MR element 105 is provided on the other surface side of the slit disk 103 and at a position facing the angle detecting slit 200.
Is arranged. The first and second MR elements 104,
The projections 105 are arranged so as to have a distance of a half pitch of the angle detection slits 200 when projected onto the slit disk 103. A first bias magnet 106 for applying a bias magnetic field to the MR element 104 is arranged on the opposite side of the slit disk 103 with the first MR element 104 interposed therebetween. Slit disk 10 sandwiching the second MR element 105
A second bias magnet 107 for applying a bias magnetic field to the MR element 105 is arranged on the side opposite to the No. 3. Then, the first and second MR elements 104 and 105 are connected in series and connected to the detection circuit 108 which is a measuring means.
First and second MR elements 104 and 105, bias magnet 1
06 and 107 and the detection circuit 108 are built in the sensor unit 109. The MR elements 104 and 10
The intervals between the five are arranged so that they are always constant.

FIG. 3 is a detection circuit diagram. In FIG.
A capacitor 300 is connected to the middle side of the first and second MR elements 104 and 105 connected in series, and a power source 301 is connected to one end side of the first MR element 104.
And the power source 301 are connected to the comparator 302.

The first and second MR elements 104 and 105 are
As described above, the thin film element whose resistance value changes according to the magnetic flux density, and is roughly classified into a semiconductor element and a ferromagnetic material. Among them, an MR element formed of an In-Sb semiconductor thin film is used as the element having the highest sensitivity. The slit disk 103 is often made of electromagnetic soft iron having a high magnetic permeability μ (μ = about 6000) and low cost. The bias magnets 106 and 107 have energy products BHmax. Large Nd-Fe-B magnet (BHm
ax. = 40 MGOe) is desirable. However, when the operating temperature range is wide, an Sm-Co magnet (BHmax. = 30 MGOe) having a small irreversible demagnetization and a small reversible temperature coefficient and a large energy product is desirable.

The operation of the above structure will be described in detail with reference to FIGS.

FIG. 4 is an enlarged view showing the positional relationship between the slit disk 103 and the MR elements 104 and 105. The distance between the slit disk 103 and the MR elements 104 and 105 is d.
1 and d2. Here, it is set so that d1 + d2 = constant (2 mm in the case described later). . FIG. 5 is a diagram showing an example of the variation of the magnetic flux density with respect to the distance from the slit disk and the characteristic of the bias magnetic flux.
FIG. 6 is a diagram showing an output state for each distance d1 between the slit disk 103 and the MR element 104. The distance d1 = 0.5 mm,
The output state is shown at 1.0 mm and 1.5 mm.

As a specific example, the bias magnet is 5 × 5 × 6.
When an Nd-Fe magnet of mm, a slit disk made of pure iron, and a pitch L of the angle detecting slits of 4.62 mm is used, the fluctuation amount of the magnetic flux density at the distance d from the slit disk, and The magnitude of the bias magnetic flux is shown in Fig. 5.
It changes as shown in.

The distance between the slit disk 103 and the MR elements 104 and 105 is originally designed to be d1 = d2 = 1 mm. However, if an error occurs at the time of assembly, the slit disk may have either MR element 104 or 1
Move to the 05 side.

Distance d1 = 0.5 mm (d2 = 1.5 m
m), the slit disk 103 is the first MR element 10
It is close to 4 and away from the second MR element 105. When the slit disk 103 is rotated in this state, as shown in FIG.
As shown in (a), the value of the magnetic flux density Ba sensed by the first MR element 104 near the slit disk 103 has a large amplitude, and the value of the magnetic flux density Bb sensed by the far second MR element 105 is: The amplitude is small. First and second MR element 10
Since the value of the magnetic flux density Ba on one side is very large with respect to the value of the magnetic flux density Bb on the other side, the midpoint potential Va in which 4, 105 are connected in series is as shown in FIG. The waveform is shifted upward without centering on Vcc / 2. Therefore, the midpoint potential Va is applied to the capacitor 300.
AC coupling is performed to cut the DC component, and the reference voltage Vcc / 2 generated by the power source 301 as shown in FIG.
Is converted to an output voltage Vb centered on. Its output voltage V
When b is given a hysteresis and converted into a rectangular wave by the comparator 302, a signal (output voltage) Vout can be obtained as shown in FIG.

Distance d1 = 1.0 mm (d2 = 1.0 m
In the case of m), since the slit disk 103 and the first and second MR elements 104 and 105 are equidistant, the values of the magnetic flux densities Ba and Bb felt by the respective MR elements 104 and 105 are
The amplitude is the same. The midpoint potential Va of each MR element 104, 105 is equal to the reference voltage Vcc as shown in FIG.
The waveform is centered on / 2. Also in this case, the midpoint potential Va is AC-coupled by the capacitor 300 to cut the DC component, and the output voltage Vb centered on the reference voltage Vcc / 2 generated by the power source 301 as shown in FIG. 6C.
Convert to. When the output voltage Vb is given a hysteresis and converted into a rectangular wave by the comparator 302, a signal (output voltage) Vout can be obtained as shown in FIG. 6D.

Distance d1 = 1.5 mm (d2 = 0.5 m
In the case of m), conversely to the above, the value of the magnetic flux density Ba sensed by the first MR element 104 far from the slit disc 103 is
The amplitude of the magnetic flux density Bb that the second MR element 105, which has a small amplitude and is close to, senses, is large (FIG. 6A). Therefore, the midpoint potential Va of the MR elements 104 and 105 is as shown in FIG.
As shown in (b), the waveform is shifted downward from the reference voltage Vcc / 2. Also in this case, the midpoint potential V
A is AC-coupled with the capacitor 300 to cut the DC component, and is converted into the output voltage Vb centered on the reference voltage Vcc / 2 generated by the power source 301 as shown in FIG. 6C. When the output voltage Vb is converted into a rectangular wave by the comparator 302 with a hysteresis, a signal (output voltage) Vout can be obtained as shown in FIG. 6D.

As described above, when the slit disk 103 is rotated, the angle detecting slit 200 is moved to the first and second M
Since it is opposed to the R elements 104 and 105, the magnetic flux density applied to each MR element 104 and 105 changes, and
The resistance values of the elements 104 and 105 change. Then, the midpoint potential Va of the first and second MR elements 104 and 105 is
The waveform is shifted to the upper or lower side with respect to the reference voltage Vcc / 2. However, when the DC component of the midpoint potential of the first and second MR elements 104 and 105 is cut by the capacitor 300 and the power source 301 and the rectangular wave is output by the comparator 302, the slit disk 103 is always rotated according to the rotation. A constant output signal is obtained.

Specifically, the bias magnet is 5 × 5 × 6 mm
In the case of using the Nd-Fe magnet of, the slit disc made of pure iron and the pitch L of the angle detecting slits being 4.62 mm, the value of the variation amount Vp-p of the midpoint potential Va is d
If 1 = d2 = 1 mm, then d1 = 0.5 m
In both cases of m and d2 = 1.5 mm, about 1.
3, the output did not change even if the value of the distance d1 between the slit disk 103 and the one MR element 104 changed due to the assembly error of the rotation sensor, and the rate of change became small.

Further, the MR element has a very large change in resistance value with respect to temperature (for example, M of In--Sb semiconductor thin film).
In the R element, assuming that the ambient temperature is 25 ° C as 1, it is about 7 at -40 ° C and about 0.2 at 150 ° C). However, if two MR elements are connected in series, the ambient temperature T
When a = T0, the midpoint potential Va can be expressed by the following equation. Va (T0) = Vcc × Ra (Ra + Rb)

When the ambient temperature Ta changes from T0 to T1, the resistance values Ra and Rb of the MR elements 104 and 105 become α times in accordance with the temperature coefficient peculiar to the substance. At this time, the midpoint potential Va (T1) can be calculated by the following equation. Va (T1) = Vcc × αRa (αRa + αRb) = Vcc × Ra (Ra + Rb) = Va (T0)

As described above, by connecting two MR elements in series and measuring the midpoint potential, the ambient temperature T
Even if a changes, the midpoint potential Va of each of the MR elements 104 and 105 does not change, so that the effect of temperature change can be canceled.

[0031]

As described above, according to the MR element type rotation sensor of the present invention, the first MR element arranged on one surface side of the slit disk and the other MR element type sensor are arranged on the other surface side. Since the angle detection slits of the second MR element face each other, the first and second M
The magnetic flux density applied to the R element changes, and the resistance value of each MR element changes. Since the first and second MR elements are connected in series and the midpoint potential is measured by the measuring means, even if the slit disk is biased to either MR element side,
It is possible to output a constant signal. Therefore, even if the assembly error occurs between the individual products and the distance between the first and second MR elements and the slit disk varies, the output level between the individual products can be kept constant. ， The influence of ambient temperature change can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view of an MR element type rotation sensor according to the present invention.

FIG. 2 is an enlarged plan view of a part of the MR element type rotation sensor according to the present invention.

FIG. 3 is a detection circuit diagram of an MR element type rotation sensor according to the present invention.

FIG. 4 is an enlarged view showing the positional relationship between the MR element and the slit disk of the MR element type rotation sensor according to the present invention.

FIG. 5 is a diagram showing an example of a variation amount of a magnetic flux density with respect to a distance from a slit disk and a characteristic of a bias magnetic flux of an MR element type rotation sensor according to the present invention.

FIG. 6 is a diagram showing an output state for each distance between the slit disk and the MR element of the MR element type rotation sensor according to the present invention.

FIG. 7 is a magnetic flux density-resistance value characteristic diagram of the MR element showing the rotation detection principle of the rotation sensor using the MR element.

FIG. 8 is a view showing a rotation detection principle of a rotation sensor using an MR element, showing an arrangement of a slit disk and an MR element.

FIG. 9 is a basic detection circuit diagram showing a rotation detection principle of a rotation sensor using an MR element.

FIG. 10 is a diagram showing a rotation detection principle of a rotation sensor using an MR element, showing a relationship between a change in resistance value of the MR element and an output.

FIG. 11 is an enlarged vertical sectional view for explaining the characteristics of the output fluctuation amount with respect to the distance between the MR element and the slit disk.

FIG. 12 is a diagram showing an example of a characteristic of an output variation amount with respect to a distance between an MR element and a slit disk.

FIG. 13 is a vertical sectional front view of a conventional example.

FIG. 14 is a front view of a slit disk.

FIG. 15 is an enlarged plan view of part of the conventional example.

[Explanation of symbols]

 103 Slit Disk 104 First MR Element 105 Second MR Element 106 First Bias Magnet 107 Second Bias Magnet 108 Detection Circuit as Measuring Means 200 Angle Detection Slit

Claims (1)

[Claims] 1. A slit disk having a plurality of angle detecting slits formed therein, an MR element arranged at a position facing the angle detecting slits of the slit disk, and the slit circle sandwiching the MR element. In an MR element type rotation sensor provided with a plate and a bias magnet arranged on the opposite side, a first element arranged on one surface side of the slit disk and at a position facing the angle detecting slit. An MR element, a first bias magnet disposed on the opposite side of the slit disk with the first MR element sandwiched between the MR element, the other surface side of the slit disk, and the angle detecting slit. A second MR element arranged at a position facing each other;
Measuring means for measuring the midpoint potential by connecting in series the second bias magnet arranged on the opposite side of the slit disk with the MR element sandwiched between the first MR element and the second MR element. An MR element type rotation sensor comprising: