JP4613509B2 - Rotational speed sensor - Google Patents

Description

  The present invention relates to a rotational speed sensor used in an automobile or the like.

  Conventionally, this type of rotational speed sensor has a circuit configuration as shown in FIG.

  In FIG. 8, 1 is an element part, and this element part 1 is constituted by connecting a pair of magnetoresistive elements 2 in series. Reference numeral 3 denotes an amplifying circuit. The amplifying circuit 3 amplifies output signals from the pair of magnetoresistive elements 2 in the element section 1 and includes a feedback resistor 4 and an operational amplifier 5. Reference numeral 6 denotes a voltage dividing circuit. The voltage dividing circuit 6 includes three resistors 7, and the voltage dividing circuit 6 generates two reference voltages. Reference numeral 8 is a comparison output circuit, and this comparison output circuit 8 is provided with two comparators 9 to which the output signal from the amplifier circuit 3 and the reference voltage generated by the voltage dividing circuit 6 are input. Comparison. An H level signal is output only when the output voltage from the amplifier circuit 3 is between two reference voltages generated by the voltage dividing circuit 6.

  Next, the operation of the conventional rotational speed sensor configured as described above will be described.

  The element unit 1 is disposed close to a rotating body (not shown) made of, for example, a magnetic material, and the magnetic flux density applied to the magnetoresistive element 2 changes according to the rotation of the rotating body (not shown). The fluctuation of the resistance value of the magnetoresistive element 2 that changes in accordance with the change of the magnetic flux density is input from the element unit 1 to the amplifier circuit 3 as the midpoint voltage of the magnetoresistive element 2. The feedback resistor 4 of the amplifier circuit 3 is composed of a resistor having a characteristic of a linear positive temperature coefficient. When the temperature rises, the amplification factor of the amplifier circuit 3 is increased, and the amplifier circuit 3 generates a temperature-compensated adjustment voltage. Is output. This adjusted voltage is input to two comparators 9 in the comparison output circuit 8 and compared with two reference voltages generated in the voltage dividing circuit 6, and the output voltage from the amplifier circuit 3 is generated in two voltages generated in the voltage dividing circuit 6. Only when the voltage is between the reference voltages, an H level signal is output.

  Here, for example, as shown in FIG. 9, when a filter is configured by connecting a capacitor 10 in parallel with the feedback resistor 4 of the amplifier circuit 3, a high-frequency component from an output signal from the element unit 1 in the amplifier circuit 3. Therefore, it is possible to provide a rotational speed sensor from which noise signals are removed.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
JP-A-11-303818

  However, in the above-described conventional configuration, the feedback resistor 4 of the amplifier circuit 3 is a temperature-sensitive resistor so as to improve temperature characteristics. Therefore, when the resistance value changes due to a change in ambient temperature, a capacitor provided in parallel with the feedback resistor 4 Therefore, there is a problem that the bandwidth of the signal from the element unit 1 to the comparison output circuit 8 fluctuates and the output characteristic of the rotation speed sensor deteriorates. Was.

  The present invention solves the above-mentioned conventional problems, and can improve the temperature characteristics, and even if the ambient temperature changes, the bandwidth of the signal leading from the element portion to the comparison output circuit is stable, An object of the present invention is to provide a rotation speed sensor capable of improving output characteristics.

  In order to achieve the above object, the present invention has the following configuration.

The invention according to claim 1 of the present invention includes a voltage dividing circuit, a resistor, a feedback resistor portion, and an input resistor portion, and a resistor provided on one end side is connected to a power supply voltage and provided on the other end side. A voltage dividing circuit is connected to the power supply voltage, and further, a reference voltage determining unit that forms a reference voltage by a midpoint potential of the input resistor unit and the feedback resistor unit, and at least two resistance values corresponding to the strength of the magnetic field Provided with a filter comprising an element part composed of a magnetoresistive element, and a capacitor provided in parallel with a feedback resistor that amplifies the output signal from this element part and passes only a specific frequency band of the output signal from the element part An amplifier, and a comparison output circuit provided with a comparator for comparing the reference voltage determined by the reference voltage determination unit and the output signal from the amplifier, and the comparator in the comparison output circuit By connecting a temperature sensing element in parallel with one of the resistors connected in series with the force resistor, the reference voltage input to the comparator due to temperature change is changed. The reference voltage input to the comparator due to temperature changes is changed by connecting a temperature sensing element in parallel with one of the resistors connected in series with the input resistance of the comparator in the output circuit. As a result, the reference voltage input to the comparator changes, and as a result, the hysteresis width in the hysteresis comparator changes due to the change in the reference voltage. Because the output signal from the voltage divider in the voltage decision unit is directly used as the reference voltage of the amplifier The resistance value of the temperature sensing element consisting of the thermistor can be changed in accordance with the change in the ambient temperature without changing the characteristics of the filter consisting of the capacitor, thereby improving the temperature characteristics. At the same time, even if the ambient temperature changes, the bandwidth of the signal from the element portion to the comparison output circuit can be stabilized.

As described above, the rotation speed sensor according to the present invention includes the voltage dividing circuit, the resistor, the feedback resistor unit, and the input resistor unit, and the resistor provided on one end side is connected to the power supply voltage and provided on the other end side. A voltage dividing circuit is connected to the power supply voltage, and further, a reference voltage determining unit that forms a reference voltage by a midpoint potential of the input resistor unit and the feedback resistor unit, and at least two resistance values corresponding to the strength of the magnetic field Provided with a filter comprising an element part composed of a magnetoresistive element, and a capacitor provided in parallel with a feedback resistor that amplifies the output signal from this element part and passes only a specific frequency band of the output signal from the element part An amplifier, and a comparison output circuit provided with a comparator that compares the reference voltage determined by the reference voltage determination unit with an output signal from the amplifier, and a comparator in the comparison output circuit By connecting a temperature sensing element in parallel with one of the resistors connected in series, the reference voltage input to the comparator due to temperature change is changed. The reference voltage input to the comparator due to temperature changes is changed by connecting a temperature sensing element in parallel with one of the resistors connected in series with the input resistance of the comparator in the comparison output circuit. The reference voltage input to the comparator changes according to the change, and thereby the hysteresis width in the hysteresis comparator changes due to the change in the reference voltage, so that the temperature characteristics of the element part can be corrected, The output signal from the voltage divider circuit in the reference voltage determination unit is directly used as the reference voltage of the amplifier. Therefore, it is possible to change the resistance value of the temperature sensing element consisting of the thermistor according to the change of the ambient temperature without changing the characteristics of the filter consisting of the capacitor, thereby improving the temperature characteristics. In addition, even if the ambient temperature changes, it is possible to provide a rotation speed sensor that can stabilize the bandwidth of a signal that passes from the element portion to the comparison output circuit.

  Hereinafter, the invention according to claims 1 to 3 of the present invention will be described using an embodiment.

  1 is a side sectional view of a rotation speed sensor according to an embodiment of the present invention, FIG. 2 is an exploded perspective view showing a state where a case is taken out from the rotation speed sensor, and FIG. 3 is a circuit diagram of the rotation speed sensor. .

  In FIGS. 1 to 3, reference numeral 11 denotes a case made of resin, and this case 11 is provided with a hollow portion 12 and a connector portion 13. Reference numeral 14 denotes a first inner case, and the first inner case 14 is inserted into the hollow portion 12 of the case 11. Reference numeral 15 denotes a second inner case. The second inner case 15 is inserted into the hollow portion 12 of the case 11 and has a hole portion 16. Reference numeral 17 denotes a magnet as a magnetism generating means, and the magnet 17 is inserted into the hole 16 of the second inner case 15. Reference numeral 18 denotes a circuit module. The circuit module 18 is sandwiched between the first inner case 14 and the second inner case 15. The circuit module 18 includes a first protection plate 19 and a second protection plate 20, and a lead frame 23 on which a processing circuit 22 including an element portion 21 and circuit components is mounted. The element unit 21 and the processing circuit 22 in the circuit module 18 have a circuit configuration as shown in FIG. The element unit 21 is configured by connecting a first magnetoresistive element 24 and a second magnetoresistive element 25 made of GMR in series. A power supply Vcc 26 is connected to one end of the first magnetoresistive element 24 and a voltage is applied thereto. One end of the second magnetoresistive element 25 is connected to the other end of the first magnetoresistive element 24, and The other end of the second magnetoresistive element 25 is grounded. The element unit 21 outputs a midpoint voltage Vs, which is an output voltage corresponding to the magnetic field sensed by itself, to the processing circuit 22. Reference numeral 27 denotes a voltage dividing circuit. One end of the voltage dividing circuit 27 is connected to the power source Vcc 26, a voltage is applied, and the other end is grounded, and the divided voltage Va is output.

  In the processing circuit 22, reference numeral 28 denotes a filter / amplifier circuit. The filter / amplifier circuit 28 includes a first capacitor 29, a first resistor 30, and an operational amplifier 31 that is an amplifier. The operational amplifier 31 inputs the output voltage Va from the voltage dividing circuit 27 to the non-inverting input terminal, and outputs the output signal from the element unit 21 to the inverting input terminal via the first capacitor 29 and the first resistor 30. You are typing. The filter / amplifier circuit 28 has a second resistor 32 and a second capacitor 33 as a filter connected in parallel with the operational amplifier 31. With these configurations, the filter / amplifier circuit 28 has an amplifying function for amplifying the output signal from the element unit 21 and a filter function for allowing only a specific frequency of the output signal from the element unit 21 to pass therethrough. .

  As described above, the filter / amplifier circuit 28 is a filter that is provided with the operational amplifier 31 that is an amplifier that amplifies the output signal from the element unit 21 and passes only a specific frequency band of the output signal from the element unit 21. Since the second capacitor 33 is provided, it is possible to stabilize the bandwidth of the signal from the element unit 21 to the comparison output circuit described later.

  Reference numeral 34 denotes a comparison output circuit. The comparison output circuit 34 is provided with a comparator 35, and an output signal from the filter / amplifier circuit 28 is input to the inverting input terminal of the comparator 35. The comparison output circuit 34 has a resistor 36, one end of which is connected to the power supply Vcc 26 and the other end is connected to the output terminal of the comparator 35. The comparison output circuit 34 has a feedback resistor unit 37 in the feedback unit of the comparator 35 and an input resistor unit 38 in the input unit. The input resistor unit 38 includes resistors 39 and 40 and a negative temperature. It is comprised with the temperature sensitive element 41 which consists of a thermistor which has a coefficient. The output voltage Vb from the voltage dividing circuit 27 is input to the input resistance unit 38. The reference voltage determining unit 42 includes a voltage dividing circuit 27, a resistor 36, a feedback resistor unit 37, and an input resistor unit 38, and the non-inverting output terminal of the comparator 35 is a reference determined by the reference voltage determining unit 42. A voltage is input. With these configurations, the comparison output circuit 34 forms a hysteresis comparator and outputs an H level or L level signal. And the output signal from the comparison output circuit 34 is output from the connector terminal of the connector part 13 welded with the circuit module.

  Next, a method for assembling the rotational speed sensor according to the embodiment of the present invention configured as described above will be described.

  First, after mounting the element portion 21 and the processing circuit 22 on the lead frame 23, the lead frame 23 is inserted and fixed between the first protective plate 19 and the second protective plate 20, and the circuit module 18 is mounted. Form.

  Next, after inserting the magnet 17 into the hole 16 of the second inner case 15, the circuit module 18 is sandwiched between the second inner case 15 in which the magnet 17 is inserted and the first inner case 14.

  Next, after fitting the first inner case 14, the second inner case 15, and the circuit module 18 into a mold (not shown) for forming the case 11, the first inner case 14 and the first inner case 14 The positions of the inner case 15 and the circuit module 18 are fixed by fixing pins (not shown) attached to a mold (not shown).

  Finally, while pulling out the fixing pin (not shown), the resin is poured into the mold (not shown) to form the case 11.

  Next, the operation of the rotational speed sensor according to the embodiment of the present invention configured as described above will be described.

  As shown in FIG. 4, the element unit 21 is disposed close to a gear-like rotating body 43 having, for example, a magnetic body, and according to the rotation of the rotating body 43, the first magnetoresistive element 24 and the second magnetoresistive element 24. The magnetic flux density applied to the magnetoresistive element 25 changes. Changes in the resistance values of the first magnetoresistive element 24 and the second magnetoresistive element 25 that change in accordance with the change in the magnetic flux density are caused by the first magnetoresistive element 24 and the second magnetoresistive element from the element portion 21. 25 is input to the filter / amplifier circuit 28 as a midpoint voltage. The filter / amplifier circuit 28 to which the output signal from the element unit 21 is input includes a first capacitor 29, a first resistor 30, an operational amplifier 31, a second resistor 32, and a second capacitor 33 to form a band pass filter. Therefore, a signal amplified by passing only a specific frequency band of the output signal from the element unit 21 is output and input to the comparison output circuit 34. The frequency band to be passed is expressed by (Equation 1).

  The comparison output circuit 34 outputs an H level signal if the output voltage from the filter / amplifier circuit 28 is lower than the reference voltage determined by the reference voltage determination unit 42, and outputs an L level signal if it is higher. In addition, since the comparison output circuit 34 forms a hysteresis comparator in which the hysteresis width changes due to a change in ambient temperature, it is possible to prevent erroneous detection such as chattering in the vicinity of the reference voltage.

  In addition, since the first magnetoresistive element 24 and the second magnetoresistive element 25 are made of GMR, the amplitude of the output voltage from the element portion 21 is large at a low temperature and has a temperature characteristic that changes small at a high temperature. . The comparison output circuit 34 corrects this temperature characteristic. In order to correct the temperature characteristic of the output signal from the element unit 21, it is necessary to change the width of the hysteresis in the comparison output circuit 34 in accordance with the change in the output signal amplitude from the element unit 21. Since the input resistor section 38 in the comparison output circuit 34 has a temperature sensing element 41 composed of a thermistor, the reference voltage input to the comparator 35 changes according to the ambient temperature change. Due to the change, the hysteresis width in the hysteresis comparator changes, and the temperature characteristics of the element unit 21 can be corrected.

  The change in the width of the hysteresis when the ambient temperature changes is expressed by (Equation 2).

  The resistance value of the feedback resistor unit 37 is 560 kΩ, the resistance value of the resistor 36 is 27 kΩ, the resistance value of the resistor 39 is 10 kΩ, the resistance value of the resistor 40 is 10 kΩ, the temperature sensitive element 41 composed of the thermistor is 10 kΩ at 25 ° C., B coefficient If the voltage Vb is 2.5 V, the resistance change due to the temperature change of the temperature sensing element 41 is based on the temperature on the horizontal axis and 25 ° C. on the vertical axis, as shown in FIG. It is expressed as a resistance change rate of the temperature sensitive element 41 made of the thermistor. Further, FIG. 6 illustrates a change in the combined resistance of the input resistance unit 38 when the ambient temperature changes as a temperature on the horizontal axis and a change in the combined resistance on the vertical axis. FIG. 6 shows that the value of the combined resistance decreases as the temperature increases.

  The reference voltage of the hysteresis comparator is expressed as (Equation 3).

  FIG. 7 shows the change when the temperature around the hysteresis width Vh of the comparison output circuit 34 changes. When the ambient temperature changes from −50 ° C. to + 150 ° C., the hysteresis width becomes 166 mV at −50 ° C. and 88 mV at 150 ° C., and can have a rate of change of about ± 30% based on 25 ° C. Thereby, the temperature characteristic of the output voltage from the element unit 21 can be corrected.

  That is, in the embodiment of the present invention, since the temperature sensitive element 41 made of the thermistor is provided in the input resistance part 38 in the reference voltage determining part 42, the characteristic of the filter made of the second capacitor 33 is varied. The resistance value of the temperature sensing element 41 made of the thermistor can be changed in accordance with the change in the ambient temperature in the absence of the temperature, thereby improving the temperature characteristics and changing the ambient temperature. This also has the effect that the bandwidth of the signal from the element unit 21 to the comparison output circuit 34 can be stabilized.

  In the embodiment of the present invention, the comparator 35, the feedback resistor unit 37, and the input resistor unit 38 constitute the comparison output circuit 34. Therefore, the comparison output circuit 34 has a hysteresis width. Since the temperature sensing element 41 formed of a thermistor is provided in the input resistance section 38 of the comparison output circuit 34, the hysteresis of the comparison output circuit 34 is caused by a change in resistance value due to a temperature change of the temperature sensing element 41. As a result, chattering in the vicinity of the reference voltage of the output signal can be prevented, and fluctuations in the output signal due to temperature changes in the element section 21 can be prevented. .

  In the above-described rotation speed sensor according to the embodiment of the present invention, a gear-shaped rotating body having a magnetic body is used as an object. However, the object is not necessarily a gear-shaped rotating body. It is possible to detect anything that changes the magnetic field.

  In the rotation speed sensor according to the embodiment of the present invention, the example in which the first magnetoresistive element 24 and the second magnetoresistive element 25 are connected in series has been described. However, the present invention is not necessarily limited thereto. Even when a plurality of magnetoresistive elements and resistors are connected in series or in parallel to form an element portion, the same effects as those of the embodiment of the present invention can be obtained.

  Further, in the rotation speed sensor according to the embodiment of the present invention, the temperature sensing element 41 made of the thermistor having a negative temperature coefficient is provided in the input resistance section 38. However, the temperature of the element section 21 or the magnetism generating means is provided. Depending on the characteristics, this may be replaced with a temperature sensing element having a positive temperature coefficient, and this temperature sensing element may be provided in the feedback resistance section 37 or both the input resistance section 38 and the feedback resistance section 37. May be provided.

  The rotational speed sensor according to the present invention can improve the temperature characteristics and can stabilize the bandwidth of the signal from the element section to the comparison output circuit even when the ambient temperature changes. And it is useful as a rotation speed sensor used for automobiles and the like.

1 is a side sectional view of a rotation speed sensor according to an embodiment of the present invention. The exploded perspective view which shows the state which removed the case from the rotation speed sensor Circuit diagram of the same rotation speed sensor Side sectional view showing the operating state of the rotation speed sensor A characteristic diagram showing the relationship between the temperature of the temperature sensing element and the rate of change in resistance value in the operating state of the rotation speed sensor Characteristic diagram showing the relationship between the combined resistance and temperature of the input resistance of the same rotation speed sensor Characteristic diagram showing the relationship between the hysteresis width and temperature of the comparison output section of the same rotation speed sensor Circuit diagram of conventional rotation speed sensor A circuit diagram showing a state where a filter is attached to an amplifier circuit in the same rotational speed sensor

21 element part 24,25 magnetoresistive element 31 operational amplifier (amplifier)
33 Second capacitor (filter)
34 Comparison Output Circuit 35 Comparator 37 Feedback Resistance Unit 38 Input Resistance Unit 41 Temperature Sensing Element 42 Reference Voltage Determination Unit

Claims (1)

A voltage divider circuit, a resistor, a feedback resistor unit, and an input resistor unit, and a resistor provided on one end side is connected to the power supply voltage, and a voltage divider circuit provided on the other end side is connected to the power supply voltage, and A reference voltage determining unit that forms a reference voltage by a midpoint potential between the input resistor unit and the feedback resistor unit; an element unit including at least two magnetoresistive elements that exhibit resistance values corresponding to the strength of the magnetic field; and An amplifier provided with a filter comprising a feedback resistor that amplifies the output signal from the element section and passes only a specific frequency band of the output signal from the element section and a capacitor provided in parallel, and determined by the reference voltage determining section A comparison output circuit provided with a comparator for comparing a reference voltage with an output signal from the amplifier, and a resistor in which an input resistance portion of the comparator in the comparison output circuit is connected in series On the other hand the rotational speed sensor configured to vary the reference voltage input to the comparator due to changes in temperature by connecting the temperature sensing element in parallel.

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