JPH05333033A - Rotating speed detecting apparatus - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of a rotating speed detecting apparatus which detects the rotation with the use of a magnetoresistance element. CONSTITUTION:This rotating speed detecting apparatus is provided with a single magnetoresistance element 12, a magnetized rotary body 11 disposed confronting the element 12, and a power source VCC for applying a predetermined voltage to the element 12. The rotating speed of the rotary body 11 is detected by the change of the voltage at both ends of the magnetoresistance element 12. Moreover, a direct current component voltage control circuit 14 is provided so as to control the direct current component voltage of the change of the voltage at both ends of the element 12 to be in a predetermined ratio to the power source VCC (e.g. 1/2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation speed detecting device, and more particularly to a rotation speed detecting device for detecting rotation using a magnetoresistive element.

[0002]

2. Description of the Related Art There is a rotation speed detecting device as one of on-vehicle sensors. This rotation speed detection device is used to detect the rotation speed of an axle in an anti-brake system (ABS), for example.

Conventionally, there is a rotation speed detecting device of this type disclosed in Japanese Patent Laid-Open No. 62-66115. FIG. 8 shows the structure of the rotation speed detecting device disclosed in the publication. As shown in the figure, the rotation speed detection device 1 has two magnetoresistive elements 2 and 3, and each magnetoresistive element 2 and 3 is
Has a structure in which bridges are connected in a bridge shape. One end of the magnetoresistive element 2 is connected to the power supply V _CC , and the other end is connected to one end of the magnetoresistive element 3. In addition, the magnetoresistive element 3
The other end is grounded, and the output voltage is output from the output terminal 4 between the magnetoresistive elements 2 and 3. Incidentally, 5 is an amplifier for amplifying the output voltage.

The reason why the magnetic resistance elements 2 and 3 are connected in a bridge shape in the conventional rotation detecting device 1 as described above is as follows. That is, although the magnetoresistive elements 2 and 3 have good sensitivity, variations in resistance value are very large in a single element, and resistance temperature characteristics are also very large.
For example, it is known that the resistance value has a variation of 600 Ω to 4500 Ω, and the resistance temperature characteristic is such that the resistance value is reduced to 1/2 with a temperature change (increase) of 35 ° C.

Therefore, when a magnetoresistive element having such a variation in resistance value and a large resistance temperature characteristic is used as a single item, the deviation of the resistance value of the magnetoresistive element to be used, the environmental temperature to be used, and the magnetic field are used. The measurement value greatly changes depending on the strength, and the measurement accuracy decreases.

Therefore, the resistance-temperature characteristics of the magnetoresistive elements 2 and 3 are canceled by connecting the magnetoresistive elements 2 and 3 in a bridge shape, thereby improving the measurement accuracy.

[0007]

By connecting the magnetoresistive elements 2 and 3 in a bridge shape as described above, the resistance-temperature characteristics of the magnetoresistive elements 2 and 3 cancel each other out, and the measurement is performed depending on the ambient temperature to be used. It is possible to prevent the value from changing greatly.

However, if there is a variation in the initial resistance (resistance value when the applied magnetic field is zero) of the magnetoresistive elements 2 and 3, the magnetoresistive element for detecting the rotational speed (of the two magnetoresistive elements, There is a problem that the center of the amplitude of the voltage across one of the two) deviates from the center of the voltage applied to the bridge, the amplitude of the output voltage decreases, and the detection accuracy decreases.

Further, although the gear to be rotated is generally a gear made of a magnetic material, the two magnetoresistive elements 2,
In the rotational speed detecting device using 3, the two magnetoresistive elements 2 and 3 are connected to each other when one magnetoresistive element (for example, the magnetoresistive element 2) faces a mountain of the gear.
It is necessary to position the magnetoresistive elements 2 and 3 and the gear with high accuracy so that is opposed to the valley of the gear. However, in the case of a vehicle-mounted rotation speed detection device, the gears are arranged on the axle so that the shapes such as the outer diameter are different, and in order to position the magnetoresistive elements 2 and 3 and the gears with high accuracy, they are matched with the gear shape. There is a problem that a magnetoresistive element is required.

The present invention has been made in view of the above points. By using one magnetoresistive element and controlling the DC component voltage of the voltage change across the magnetoresistive element to a predetermined value, It is an object of the present invention to provide a rotation speed detection device that improves detection accuracy.

[0011]

FIG. 1 shows the principle of the present invention.

As shown in the figure, in order to solve the above-mentioned problems, in the present invention, a magnetic field generator (A1) and the magnetic field generator (A1) are provided.
1) A single magnetoresistive element (A2) is placed at a position affected by the magnetic flux generated by (1), and is placed opposite to the magnetoresistive element (A2) and is also placed on the rotating body (A3). The magnetic flux density changing part (A) that changes the magnetic flux density of the magnetic field applied to the magnetoresistive element (A2) at a cycle according to the rotation speed of this rotating body (A3).
4) and a voltage application unit (A5) for applying a predetermined voltage to the magnetoresistive element (A2), and detects the rotational speed of the rotating body (A3) from the voltage change at both ends of the magnetoresistive element (A2). In the rotation speed detecting device, the DC component voltage of the voltage change at both ends of the magnetoresistive element (A2) is a DC component so that the voltage has a predetermined ratio with respect to a predetermined voltage applied by the voltage applying unit (A5). It is characterized in that a DC component voltage control unit (A6) for controlling the voltage is provided.

[0013]

[Function] The DC component voltage control unit (A6) is a magnetoresistive element (A2).
The DC component voltage of the voltage change at both ends of the
The DC component voltage is controlled so that the voltage has a predetermined ratio with respect to the predetermined voltage applied in 5). Therefore, even if there is a variation in the initial resistance value of the magnetoresistive element (A2), the voltage applying section (A5) is always provided at both ends of the magnetoresistive element (A2).
The voltage of a predetermined ratio is applied to the predetermined voltage applied by. Therefore, the amplitude center of the output voltage can be set to a predetermined value regardless of variations in the initial resistance value of the magnetoresistive element (A2), and a large output voltage amplitude can be maintained at all times.

Further, since the DC component voltage control unit (A6) controls the DC component voltage of the voltage change at both ends of the magnetoresistive element (A2), it has no influence on the AC component which is the rotation detection signal. However, a highly accurate rotation speed detection signal can be obtained. Further, since the rotation speed can be detected by one magnetoresistive element (A2), the cost of the device can be reduced.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 2 shows a rotation speed detecting device 10 which is a first embodiment of the present invention. The rotation speed detection device 10 is used as a vehicle speed detection sensor in, for example, an in-vehicle ABS (Antilock Brake System).

In FIG. 1, reference numeral 11 is a rotating body made of a magnetic material, and the crests 11a of the formed teeth are magnetized to generate a magnetic field. Further, 12 is a magnetoresistive element, which is the rotational speed detecting device 10 according to the present invention.
Is configured to detect the rotation speed by one magnetoresistive element 12. The magnetoresistive element 12 is a rotating body 1.
It is arranged so as to face 1.

Therefore, the magnetic flux density of the magnetic field applied to the magnetoresistive element 12 increases as the crest 11a of the rotor 11 approaches the magnetoresistive element 12, and the valley 11b of the rotor 11 becomes the magnetoresistive element 12. As approaching, the magnetic flux density of the magnetic field applied to the magnetoresistive element 12 becomes smaller. In this way, the magnetic flux density of the magnetic field applied to the magnetoresistive element 12 changes as the rotating body 11 rotates. Magnetoresistive element 12
Has a property that its resistance value changes depending on the strength of the magnetic field, and changes the resistance value in response to the change in the magnetic flux density. Further, since the change in the magnetic flux density corresponds to the rotation speed of the rotating body 11, the rotation speed of the rotating body 11 can be detected by detecting the change in the resistance value of the magnetoresistive element 12. Reference numeral 13 in the drawing is a magnet, which is provided to give a magnetic bias to the magnetoresistive element 12.

Reference numeral 14 is a direct current component voltage control circuit which is a feature of the present invention, and is provided, for example, in an engine control unit (ECU) 15. The configuration of the DC component voltage control circuit 14 will be described below.

One end of the resistor R3 and the collector of the transistor Q1 are connected to the power source V _CC . The collector of the transistor Q2 is connected to the base of the transistor Q1, the other end of the resistor R3 is connected to the connection point 16 of the base and the collector, and the emitter of the transistor Q2 is grounded.

The emitter of the transistor Q1 is the ECU1
5 is connected to the signal input terminal 17 of the magnetoresistive element 12 provided in the outer case. One end of the magnetoresistive element 12 is connected to this signal input terminal 17, and the other end is connected to a ground terminal 18 also provided on the outer case of the ECU 15.

Resistors R1 and R2 forming a voltage dividing circuit are connected to a connection point 19 on the way from the emitter of the transistor Q1 to the signal input terminal 17, and the resistors R1 and R2 are connected in series. Together with the resistance R of the resistance R2
The side different from 1 and the connection side is grounded. The base of the transistor Q2 and the capacitor C are connected to the connection point 20 of the resistors R1 and R2. The side of the capacitor C different from the side connected to the connection point 20 is grounded. Further, a signal output terminal 21 is provided between the signal input terminal 17 and the connection point 19, and the rotation speed detection signal is output from the signal output terminal 21. Reference numeral 22 is an amplifier for signal amplification.

Next, the operation of the DC component voltage control circuit 14 will be described. The DC component voltage control circuit 14 having the above-mentioned configuration is a DC component constant voltage circuit, and the resistor R
By appropriately selecting the resistance values of R1 and R2, the voltage of the input signal terminal 17 is controlled so as to be stabilized at a voltage value that is approximately ½ of the voltage of the power supply V _CC .

Here, it is assumed that the resistance of the magnetoresistive element 12 varies and the initial resistance value of the magnetoresistive element 12 deviates from the predetermined resistance value (design resistance value). Now, a case where the voltage of the signal input terminal 17 increases due to the shift of the resistance value of the magnetoresistive element 12 in the increasing direction will be described as an example.

When the voltage of the signal input terminal 17 rises, the voltage of the connection point 20 also rises accordingly, and the transistor Q2
Base voltage rises. Further, as the base voltage of the transistor Q2 rises, the emitter current of the transistor Q2 increases, and along with this, the power source V _CC to the resistor R3.
The collector current flowing into the transistor Q2 via the transistor increases. As a result, the base voltage V of the transistor Q1
_C decreases, so that the DC component voltage control circuit 14 operates to decrease the voltage of the signal input terminal 17. Therefore, even if the resistance of the magnetoresistive element 12 varies, the voltage of the signal input terminal 17 has a predetermined value (approximately 1 / the voltage of the power supply V _CC ).
Voltage value of 2).

As described above, the DC component voltage control circuit 14
Since it functions as a DC component constant voltage circuit, it is possible to effectively eliminate the influence of variations in the resistance value of the magnetoresistive element 12. However, when the rotational speed of the rotating body 11 is detected, the magnetoresistive element 12 generates an AC waveform-like output signal corresponding to the change in the strength of the magnetic field applied from the rotating body 11. Since the AC waveform of this output signal is a voltage change component, in the configuration in which a known DC component constant voltage circuit is simply provided in place of the DC component voltage control circuit 14, the DC component constant voltage circuit is used to output a voltage change as an output signal. Also becomes a constant voltage, and the output signal is weakened.

Therefore, the DC component voltage control circuit 14 according to this embodiment is provided with an integrating circuit constituted by the resistor R1 and the capacitor C in the circuit. The time constant τ of this integrating circuit is represented by τ = R1 × C. Now, magnetoresistive element 1
When the input signal from 2 has a periodic fluctuation larger than the time constant τ (that is, when the frequency f of the input signal is small), the integration circuit does not function and the voltage at the connection point 20 (that is, the base of the transistor Q2). Since the voltage V _B ) changes in response to the voltage change of the output signal, the DC component voltage control circuit 14 acts to stabilize the voltage value V _A at the signal input terminal 17 as described above.

However, when the rotating speed of the rotating body 11 is high,
When the rolling speed is reached, the frequency of the input signal from the magnetoresistive element 12 is reduced.
Period fluctuation is smaller than time constant τ.
The frequency f of the signal becomes large). Therefore, the magnetoresistive element
The input signal waveform from 12 is integrated by the above integrating circuit.
Since the waveform becomes different, the base voltage V of the transistor Q2 _B
Becomes a constant value as the frequency f increases. to this
Therefore, the voltage V at the connection point 16_CLost control of
Therefore, the predetermined frequency f determined by the time constant of the integrating circuit
_cAt the above rotational speeds, fluctuations in the input signal are reduced.
The signal output terminal 21 has a high output.
Output signal can be taken out.

FIG. 3 shows a case where the frequency f of the AC magnetic field applied from the rotating body 11 to the magnetoresistive element 12 is gradually increased by gradually increasing the rotating speed of the rotating body 11 in the rotating speed detecting device 10. 3 shows a voltage waveform diagram in FIG.

As shown in the figure, the transistor Q2
The value of the base voltage V _B of the above converges as the frequency of the alternating magnetic field (which is equivalent to the rotation speed of the rotating body 11) approaches the predetermined frequency f _c , and becomes a constant voltage above f _c . .. Accordingly, in more than f _c voltage V _A at the signal input terminal 17 has a stable voltage waveform corresponding to the period variation of the input signal from the magnetic resistance element 12.

FIGS. 4 and 5 show the signal extraction terminal 1 with and without the integration circuit.
9 shows the output signal taken out of FIG. FIG. 4 shows an output signal when the integrating circuit is not provided.
Is an output signal when an integrating circuit is provided. still,
In each figure, (A) shows the output signal, and (B).
Indicates the base potential of the transistor Q2.

In the case of the configuration in which only the DC component constant voltage circuit is provided excluding the integrating circuit as shown in FIG. 4, the signal from the magnetoresistive element 12 is superposed on the base potential of Q2, and this signal is added to this signal. There is a corresponding variation. Further, the magnitude of the output signal is reduced by the action of the DC component constant voltage circuit and becomes a low output value of 0.08V _PP .

On the other hand, in the case of the DC component voltage control circuit 14 in which an integrating circuit is provided in the DC component constant voltage circuit, the base potential of Q2 is integrated and becomes a constant value, and the magnitude of the output signal is 0 because the DC component constant voltage circuit does not work.
46V _PP , which is a large value compared to the configuration shown in FIG. Therefore, it can be seen from FIGS. 4 and 5 that the DC component voltage control circuit 14 effectively outputs the AC wave-shaped input signal from the magnetoresistive element 12.

Further, FIG. 6A shows an output waveform in the case where a fixed resistance having a value equal to that of the magnetoresistive element 12 is arranged in a bridge shape with the magnetoresistive element 12 in place of the DC component voltage control circuit 14. FIG. 3B shows an output waveform by the rotation speed detecting device 20 according to the present invention. From the figure, compared with the configuration in which the fixed resistance is arranged in a bridge shape, the output of the rotation speed detection device 20 according to the present invention is slightly reduced (about 70%), but as described above, the variation of the resistance of the magnetoresistive element, In consideration of the temperature change and the change in the magnetic field strength during use, a fixed resistance bridge circuit can guarantee only about ⅕ of the output shown in FIG. 7A, so the circuit of the present invention maintains this level. Then, it is possible to obtain a high output that is three times or more as compared with the upper and lower limits of the variation of the magnetoresistive element.

As described above, the rotation speed detecting device 10
The DC component voltage control circuit 14 is provided, and the DC component voltage control circuit 14 is caused to function as a DC component constant voltage circuit to eliminate the influence of the variation in the resistance of the magnetoresistive element 12, and to provide the DC component constant voltage circuit. By combining the above-mentioned integrating circuit with the above, the direct current component constant voltage circuit does not reduce the output signal. Therefore, a high-output rotation speed detection signal can be obtained regardless of the resistance variation of the magnetoresistive element 12, so that the detection accuracy can be improved.

Further, the rotation speed detecting device 1 according to the present embodiment.
In the case of 0, the number of the magnetoresistive elements 12 can be set to one, so that the cost can be reduced as compared with a device having a conventional configuration in which two magnetoresistive elements are arranged. Further, the positioning of the rotating body 11 and the magnetoresistive element 12 is also performed by the rotating body 11
It suffices to position the crest 11a of the magnetic head so as to face the magnetoresistive element 12, and it is not necessary to position the other magnetoresistive element with the trough 11b of the rotating body 11 as in the conventional case, and the positioning work can be simplified. it can. Furthermore, since two wire harnesses that connect the magnetic resistance element 12 and the ECU 15 are sufficient, it is possible to reduce the number of wire harnesses by one as compared with the configuration in which two magnetic resistance elements are arranged.

FIG. 7 shows a rotation speed detecting device 30 which is a second embodiment of the present invention. The rotation speed detecting device 30 shown in the figure is the same as the DC component voltage control circuit 1 shown in the first embodiment.
In place of 4, the resistance value selection circuit 31 is provided. This rotation speed detection device 30 is also used as a vehicle speed detection sensor in, for example, an ABS mounted on a vehicle.

In the figure, reference numeral 32 denotes a magnetoresistive element, which is arranged to face a rotating body (not shown). Further, a magnet 33 for giving a magnetic bias is provided on the back of the magnetoresistive element 32.
Are arranged. Further, the resistance value selection circuit 31 includes a plurality of resistors having different resistance values (in this embodiment, 5 resistors R0 to R4 are used).
Individual), sample and hold circuit 41, switches SW1 to SW1
It is composed of SW4, comparators COMP1 to COMP4, and the like.

One end of the magnetoresistive element 32 has connection points 34-3.
Output terminal 4 via 8, capacitor C and operational amplifier 39
0, and the other end of the magnetoresistive element 32 is grounded. Further, the connection point 34 is connected to the power source V _CC through the resistor R _0.
And a sample and hold circuit 41 is connected to the connection point 34. Therefore, the magnetoresistive element 32 and the resistor R _{0 form} a bridge circuit, and the resistor R ₀
The resistance value of ₀ is selected to match the initial resistance value of the magnetoresistive element 32.

The resistors R1 to R4 are respectively connected in parallel with the resistor R0, and switches SW1 to SW4 are arranged between the respective connection points 35 to 38. The switches SW1 to SW4 are provided for a comparator COMP1 described later.
~ Opening and closing operations are performed by signals from COMP4 to connect the resistors R1 to R4 and the magnetoresistive element 32. The sample and hold circuit 41 is a circuit for sampling the voltage value of the connection point 34 connected to the magnetic resistance element 32 when a command signal comes in. As this command signal, for example, an IG signal from an ignition switch indicating that the engine has started is used.

The voltage value at the connection point 34 sampled by the sample-and-hold circuit 41 is calculated by each comparator COM.
It is supplied to P1 to COMP4. Each comparator COM
P1 to COMP4 have different threshold values, and when the voltage value of the connection point 34 supplied from the sample and hold circuit 41 is within the threshold value range, a comparator to which the threshold value is set (provisionally, Assuming that the comparator that has been set is COMP1, (described below) supplies a drive signal to the switch SW1 so that the switch SW1 is closed. Switch SW1
Is closed, the resistance R1 becomes the magnetoresistive element 32.
Therefore, the resistors forming the bridge circuit with the magnetoresistive element 32 are resistors R0 and R1. Therefore, the combined resistance value of the resistors forming the magnetic resistance element 32 and the bridge circuit is (R0 × R1) / (R0 + R1), and the switch S
The resistance value is different from the resistance value before W1 is closed.

By providing the resistance value selecting circuit 31 having the above-mentioned configuration, even when the resistance value of the magnetoresistive element 32 is varied and the values of the magnetoresistive element 32 and the resistance R0 are deviated, the resistance value of the magnetoresistive element 32 is changed. Each of the comparators COMP1 to COMP4 determines the voltage change of the connection point 34 caused by the value shift through the sample and hold circuit 41,
Resistors R1 to R4 connected to the magnetoresistive element 32 so that the voltage at the connection point 34 becomes approximately half the voltage value of the power supply V _CC.
Select.

As described above, even if the resistance value selection circuit 31 is provided in place of the DC component voltage control circuit 14 in the first embodiment, the same effect as in the first embodiment can be obtained, and the magnetic resistance can be obtained. Since the terminal voltage of the magnetoresistive element 32 can be controlled to be constant regardless of variations in the resistance value of the element 32,
Highly accurate rotation speed detection is possible.

In the above embodiment, the magnetoresistive element 1 is constructed by the DC component voltage circuit 14 and the resistance value selection circuit 31.
Although the configuration is such that the value of the voltage across both ends applied to the terminals 2 and 32 is approximately 1/2 of the voltage value of the power supply V _CC , the value of the voltage across the resistor is appropriately selected from the values of the resistors R1 and R2 in FIG. Therefore, by appropriately selecting the threshold values of COMP1 to COMP4 in FIG. 7, it is possible to set an arbitrary voltage value.

[0044]

As described above, according to the present invention, the DC component voltage control unit sets the DC component voltage of the voltage change at both ends of the magnetoresistive element to a predetermined ratio to the predetermined voltage applied by the voltage applying unit. Since the DC component voltage is controlled so that even if the initial resistance value of the magnetoresistive element varies,
A voltage of a predetermined ratio to the predetermined voltage applied by the voltage applying unit is always applied to both ends of the magnetoresistive element, and therefore the amplitude center of the output voltage is set to the predetermined value regardless of the variation in the initial resistance value of the magnetoresistive element. And has a feature that a large output voltage amplitude can always be maintained.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a circuit diagram of a rotation speed detecting device that is a first embodiment of the present invention.

FIG. 3 is a voltage waveform diagram of an output voltage and a base voltage of a transistor Q2.

FIG. 4 is a waveform diagram showing an output signal when an integrating circuit is not provided.

FIG. 5 is a waveform diagram showing an output signal when an integrating circuit is provided.

6A is an output waveform diagram when a fixed resistance is arranged in a bridge shape in place of the DC component voltage control circuit in the magnetoresistive element, and FIG. 6B is an output waveform by the rotation speed detection device according to the present invention. FIG.

FIG. 7 is a circuit diagram of a rotation speed detecting device that is a second embodiment of the present invention.

FIG. 8 is a diagram for explaining an example of a conventional rotation speed detection device.

[Explanation of symbols]

 10, 30 Rotational speed detection device 11 Rotating body 12, 32 Magnetoresistive element 13 Magnet 14 DC component voltage control circuit 15 ECU 16, 19, 20, 34-38 Signal input terminal 17 Signal input terminal 18 Earth terminal 21 Signal extraction terminal 22 Amplifier 31 Resistance value selection circuit 41 Sample and hold circuit

Claims (1)

[Claims] 1. A magnetic field generation section, a single magnetoresistive element arranged at a position affected by a magnetic flux generated by the magnetic field generation section, and a magnetic body arranged opposite to the magnetoresistive element and on a rotating body. A magnetic flux density changing unit that is provided and changes the magnetic flux density of the magnetic field applied to the magnetoresistive element at a cycle according to the rotation speed of the rotating body, and a voltage application that applies a predetermined voltage to the magnetoresistive element. A rotation speed detecting device for detecting the rotation speed of the rotating body from the voltage change at both ends of the magnetoresistive element, wherein the DC component voltage of the voltage change at both ends of the magnetoresistive element is
A rotation speed detecting device comprising a DC component voltage control unit for controlling the DC component voltage so that the voltage has a predetermined ratio to a predetermined voltage applied by the voltage applying unit.