JP2021169953A - Sensor signal generation device - Google Patents

Abstract

To provide a sensor signal generation device capable of preventing output of an incorrect sensor signal due to a precipitous change in a power supply voltage while securing electromagnetic noise resistance performance.SOLUTION: A sensor signal generation device 50 is connected to a sensor 70 in which current changes with a change in a physical quantity, and the sensor signal generation device outputs a sensor signal Ssns obtained by converting, to voltage, a sensor current Isns flowing through the sensor 70. A voltage application circuit 30 applies, to the sensor 70 via a voltage output terminal Vout, a power supply voltage Vcc input from a power supply 20 via a voltage input terminal Vin. A sensor signal generation circuit 40 is connected to the sensor 70 via the voltage output terminal Vout, and generates the sensor signal Ssns by converting the sensor current Isns to voltage. An inter-terminal capacitor 27 is connected between the voltage input terminal Vin and the voltage output terminal Vout, and suppresses transfer of variation of the power supply voltage Vcc to the sensor signal generation circuit 40.SELECTED DRAWING: Figure 2

Description

The present invention relates to a sensor signal generator.

Conventionally, a sensor signal generator that converts a current flowing through a sensor into a voltage and outputs it as a sensor signal is known.

For example, the sensor signal generator disclosed in Patent Document 1 is mounted on a vehicle and applies a power supply voltage input from a power supply to a wheel speed sensor via a voltage output terminal (Vout). The wheel speed sensor is composed of a magnetoresistive element, and the current corresponding to the applied power supply voltage changes with the change of the magnetic flux. The sensor signal generator converts the sensor current flowing through the wheel speed sensor into a voltage, and outputs a sensor signal corresponding to the rotation speed of the wheel from the signal output terminal (Sout).

Japanese Unexamined Patent Publication No. 2013-181946

In the device of Patent Document 1, a capacitor for preventing malfunction due to electromagnetic noise is provided between the voltage output terminal (Vout) and the ground. However, when a sudden fluctuation in the power supply voltage occurs, a charge / discharge current flows through this capacitor. Since the charge / discharge current and the sensor current cannot be distinguished from each other, an erroneous sensor signal may be output from the signal output terminal when the power supply voltage fluctuates.

The present invention has been created in view of the above points, and an object of the present invention is to generate a sensor signal that prevents an erroneous sensor signal from being output due to a steep fluctuation of the power supply voltage while ensuring electromagnetic noise resistance performance. To provide the equipment.

The sensor signal generator of the present invention is connected to a sensor (70) whose current changes with a change in physical quantity, and converts a sensor current (Isns), which is a current flowing through the sensor, into a voltage to obtain a sensor signal (Ssns). Output. This sensor signal generation device includes a voltage application circuit (30), a sensor signal generation circuit (40), and an inter-terminal capacitor (27).

The voltage application circuit applies the power supply voltage (Vcc) input from the power supply (20) via the voltage input terminal (Vin) to the sensor via the voltage output terminal (Vout). The sensor signal generation circuit is connected to the sensor via a voltage output terminal, converts the sensor current into a voltage, and generates a sensor signal. The inter-terminal capacitor is connected between the voltage input terminal and the voltage output terminal, and suppresses the fluctuation of the power supply voltage from being transmitted to the sensor signal generation circuit.

In the present invention, when a steep fluctuation of the power supply voltage occurs, a charge / discharge current flows through the inter-terminal capacitor connected between the voltage input terminal and the voltage output terminal, and the charge / discharge current is applied to the sensor signal generation circuit. It doesn't pass. Therefore, it is possible to prevent an erroneous sensor signal from being output from the signal output terminal when the power supply voltage fluctuates. Further, since the electromagnetic wave noise applied to the voltage output terminal is released to the voltage input terminal via the inter-terminal capacitor, the electromagnetic wave noise resistance performance can be ensured.

The schematic diagram of the vehicle to which the sensor signal generation device by one Embodiment is applied. A circuit diagram of a sensor signal generator according to an embodiment. (A) Comparative example, (b) Time chart for comparing sensor signals when the power supply voltage fluctuates according to the present embodiment.

(One Embodiment)
Hereinafter, an embodiment of the sensor signal generation device according to the present invention will be described with reference to the drawings. The sensor signal generator is connected to a sensor whose current changes with a change in physical quantity, and outputs a sensor signal obtained by converting the sensor current, which is the current flowing through the sensor, into a voltage. The sensor signal generation device of the present embodiment is applied as a device for generating a wheel rotation speed signal in a vehicle.

As shown in FIG. 1, for example, in a four-wheeled vehicle 90, the wheel speed sensors 701 are attached to the right front wheel (FR) 81, the left front wheel (FL) 82, the right rear wheel (RR) 83, and the left rear wheel (RL) 84, respectively. , 702, 703, 704 are provided. The braking control ECU 60 includes four sensor signal generators 501, 502, 503, 504 corresponding to each wheel speed sensor 701, 702, 703, 704.

Each wheel speed sensor 701-704 outputs a sensor current Isns1-Isns4 flowing through the wheel speed sensor 701-704 according to the rotation speed of each wheel 81-84 to the corresponding sensor signal generator 501-504. A power supply voltage Vcc is supplied from the power supply 20 to the sensor signal generator 501-504. The sensor signal generator 501-504 outputs a rotation speed signal as a sensor signal Ssns1-Ssns4 obtained by converting the sensor current Isns1-Isns4 into a voltage. The rotation speed signal is a pulse signal having a frequency corresponding to the rotation speed.

Since the configurations of the wheel speed sensors 701-704 and the sensor signal generators 501-504 in FIG. 1 are the same, the following are comprehensively referred to as "wheel speed sensor 70" and "sensor signal generator 50". .. Similarly, the symbols of the sensor current Isns1-Isns4 and the sensor signal Ssns1-Ssns4 are comprehensively referred to as "sensor current Isns" and "sensor signal Ssns". Further, the wheel speed sensor 70 is appropriately referred to as “sensor 70”.

Next, refer to FIG. First, the power supply 20 and the sensor 70 other than the sensor signal generator 50 will be described. The power source 20 is, for example, an in-vehicle battery having a standard voltage of about 14 [V] and a maximum voltage of about 20 [V]. The positive electrode of the power supply 20 is connected to the voltage input terminal Vin of the sensor signal generator 50, and the power supply voltage Vcc is applied to the sensor signal generator 50 via the voltage input terminal Vin. The negative electrode of the power supply 20 is grounded. Hereinafter, "grounded" specifically means that the vehicle is connected to the vehicle body.

The sensor 70 is an element in which the current flowing when a voltage is applied changes with a change in a physical quantity. Specifically, the sensor 70 of the present embodiment is a magnetoresistive element whose resistance value changes with a change in magnetic flux as a physical quantity. The sensor 70 is arranged so as to face the disk-shaped rotating body 75 that rotates together with the wheels in the axial direction. N poles and S poles are alternately magnetized in the circumferential direction of the rotating body 75, and the magnetic flux passing through the sensor 70 changes as the rotating body 75 rotates.

One end of the sensor 70 is connected to the voltage output terminal Vout of the sensor signal generator 50. The power supply voltage Vcc applied to the sensor signal generator 50 is applied to the sensor 70 via the voltage output terminal Vout. The other end of the sensor 70 is grounded.

Subsequently, the circuit configuration inside the sensor signal generation device 50 will be described. The sensor signal generation device 50 includes a voltage application circuit 30, a sensor signal generation circuit 40, and an inter-terminal capacitor 27. The voltage application circuit 30 and the sensor signal generation circuit 40 are integrally configured as an IC as in the prior art of Patent Document 1 (Japanese Unexamined Patent Publication No. 2013-181946). The inter-terminal capacitor 27 is mounted together on the board on which the IC is mounted. In FIG. 2, the frame of the alternate long and short dash line showing the sensor signal generator 50 means a substrate, and each terminal Vin, Vout, and Sout means a terminal of the substrate.

The voltage application circuit 30 applies the power supply voltage Vcc input from the power supply 20 via the voltage input terminal Vin to the sensor 70 via the voltage output terminal Vout. The sensor signal generation circuit 40 is connected to the sensor 70 via the voltage output terminal Vout, converts the sensor current Isns into a voltage, and generates the sensor signal Ssns.

The inter-terminal capacitor 27 is connected between the voltage input terminal Vin and the voltage output terminal Vout, and has a capacity of, for example, about several tens of nF. The inter-terminal capacitor 27 prevents malfunction due to electromagnetic noise applied to the voltage output terminal Vout. Further, the inter-terminal capacitor 27 suppresses the fluctuation of the power supply voltage Vcc from being transmitted to the sensor signal generation circuit 40 when the power supply voltage Vcc fluctuates sharply. The detailed action and effect will be described later.

The circuit configuration of the IC including the voltage application circuit 30 and the sensor signal generation circuit 40 is basically the same as that of the prior art of Patent Document 1. However, in this specification, some of the terms used in Patent Document 1 are changed, and the reference numerals are completely revised.

The voltage application circuit 30 includes a FET 31 and a drive circuit 35. The FET 31 switches between supplying or cutting off the supply of the power supply voltage Vcc to the sensor 70. The source of the FET 31 is connected to the voltage input terminal Vin. The drain of the FET 31 is connected to the current reduction circuit 41 of the sensor signal generation circuit 40. The gate of the FET 31 is connected to the drive circuit 35. The drive circuit 35 drives the FET 31 based on an external start signal and an overcurrent detection signal input from the overcurrent detection circuit 45 of the sensor signal generation circuit 40.

The sensor signal generation circuit 40 includes a current reduction circuit 41, a current-voltage conversion circuit 42, a filter circuit 43, a pulse waveform shaping circuit 44, and an overcurrent detection circuit 45.

The current reduction circuit 41 is composed of a current mirror circuit having a first FET 411 and a first FET 412. The source of the first FET 411 and the source of the second FET 412 are connected to the drain of the FET 31 of the voltage application circuit 30. The drain of the first FET 411 is connected to the voltage output terminal Vout, and the drain of the second FET 412 is connected to the current-voltage conversion circuit 42. The gate of the first FET 411 and the gate of the second FET 412 are connected to the voltage output terminal Vout.

The current-voltage conversion circuit 42 is composed of a resistor 423 having one end connected to the drain of the second FET 412 of the current reduction circuit 41 and the other end being grounded.

The filter circuit 43 has a resistor 433 and a filter capacitor 434. The voltage output by the current-voltage conversion circuit 42 is input to one end of the resistor 433. The other end of the resistor 433 is connected to the pulse waveform forming circuit 44 and the overcurrent detection circuit 45. One end of the filter capacitor 434 is connected to the other end of the resistor 433, and the other end of the filter capacitor 434 is grounded.

The pulse waveform forming circuit 44 includes a comparator 445 and a reference power supply 440. The comparator 445 compares the output voltage of the filter circuit 43 with the reference voltage Vref 4 of the reference power supply 440. The output terminal of the comparator 445 is connected to the signal output terminal Sout.

The overcurrent detection circuit 45 includes a comparator 455 and a reference power supply 450. The comparator 455 compares the output voltage of the filter circuit 43 with the reference voltage Vref 5 of the reference power supply 450. The output terminal of the comparator 455 is connected to the drive circuit 35 of the voltage application circuit 30.

Next, the operation of the rotation speed detection device will be described with reference to FIG. When the ignition switch of the vehicle is turned on and a start signal is input, the drive circuit 35 turns on the FET 31 of the voltage application circuit 30. When the FET 31 is turned on, the power supply voltage Vcc is applied to the sensor 70 via the voltage output terminal Vout. As a result, the sensor current Isns corresponding to the resistance value of the sensor 70 flows.

When the rotating body 75 rotates together with the wheels 81-84, the magnetic flux of the sensor 70 changes, and the resistance value of the sensor 70 also changes accordingly. Therefore, the sensor current Isns flowing through the sensor 70 changes according to the rotation of the wheels 81-84.

When the FET 31 of the voltage application circuit 30 is turned on, the same current as the sensor current Iss flows through the first FET 411 of the current reduction circuit 41. On the other hand, a reduced current Irdc smaller than that of the first FET 411, for example, (1/10) times, flows through the second FET 412. That is, the current reduction circuit 41 multiplies the sensor current Isns by "a predetermined multiple smaller than 1 time", for example, (1/10), and outputs the reduced current Irdc smaller than the sensor current Isns to the current-voltage conversion circuit 42.

The current-voltage conversion circuit 42 converts the reduced current Irdc output by the current reduction circuit 41 into a voltage and outputs it. The filter circuit 43 removes high frequency components as a low-pass filter.

The pulse waveform shaping circuit 44 shapes the output voltage waveform of the filter circuit 43 and outputs it as a sensor signal Ssns of the pulse waveform. The comparator 445 outputs a high level when the output voltage of the filter circuit 43 is larger than the reference voltage Vref4, and outputs a low level when the output voltage of the filter circuit 43 is equal to or less than the reference voltage Vref4. As a result, the sensor signal Ssns having a frequency corresponding to the rotation speed, which is formed into a pulse waveform, is output.

The overcurrent detection circuit 45 detects an overcurrent with respect to the current flowing through the FET 31 of the voltage application circuit 30 and the first FET 411 of the current reduction circuit 41 or the sensor current Iss based on the output voltage of the filter circuit 43. The comparator 455 outputs a high level indicating that an overcurrent is flowing when the output voltage of the filter circuit 43 is larger than the reference voltage Vref5. On the other hand, the comparator 455 outputs a low level indicating that no overcurrent is flowing when the output voltage of the filter circuit 43 is equal to or less than the reference voltage Vref5. The drive circuit 35 turns off the FET 31 when the output of the comparator 455 is at a high level, and protects the FET 31, 411 and the sensor 70 from overcurrent.

(Action effect)
FIG. 3 shows the simulation results of the pulse signal output when the power supply voltage fluctuates in the comparative example and the present embodiment. The configuration of the comparative example corresponds to the conventional technique of Patent Document 1, and a capacitor for preventing malfunction due to electromagnetic noise is provided between the voltage output terminal Vout and the ground. Assuming that the power supply voltage Vcc rises sharply from, for example, about 14 [V] to about 20 [V] at time tx, a charging current flows into the capacitor at this time. When the power supply voltage Vcc drops sharply, the discharge current flows out from the capacitor.

In the comparative example shown in FIG. 3A, the charging current of the capacitor affects the current flowing through the current reduction circuit 41 of the sensor signal generation circuit 40. Therefore, an erroneous pulse is superimposed on the sensor signal Ssns output from the signal output terminal Sout. This erroneous pulse causes a wheel speed detection error.

On the other hand, in the present embodiment shown in FIG. 3B, when the power supply voltage Vcc rises sharply at time tx, a charging current flows through the inter-terminal capacitor 27, but the charging current does not pass through the sensor signal generation circuit 40. Therefore, an erroneous pulse is not superimposed on the sensor signal Ssns output from the signal output terminal Sout. The same applies when the power supply voltage Vcc drops sharply and a discharge current flows through the inter-terminal capacitor 27. As described above, in the present embodiment, it is possible to prevent the charge / discharge current from flowing to the sensor signal generation circuit 40 when the power supply voltage fluctuates, and to prevent the erroneous sensor signal Ssns from being output from the signal output terminal Sout.

Further, in the present embodiment, the electromagnetic wave noise applied to the voltage output terminal Vout is released to the voltage input terminal Vin via the inter-terminal capacitor 27, so that the electromagnetic wave noise resistance performance can be ensured.

Further, as in the prior art of Patent Document 1, in the sensor signal generation circuit 40, the reduced current Irdc obtained by multiplying the sensor current Isns by a predetermined value smaller than 1 times by the current reducing circuit 41 is converted into a voltage by the current-voltage conversion circuit 42. NS. As a result, the permissible power of the resistor 423 constituting the current-voltage conversion circuit 42 can be suppressed, and the sensor signal generation circuit 40 can be miniaturized.

In addition, the sensor signal generation device 50 of the present embodiment is connected to the wheel speed sensor 70 that detects the rotation speed of the wheels, and outputs the sensor signal Ssns according to the rotation speed of the wheels. In general, the power supply voltage Vcc of an in-vehicle battery may fluctuate sharply. Further, it is important to improve the detection accuracy of the wheel speed from the viewpoint of improving the reliability of the vehicle braking control. Therefore, the sensor signal generation device 50 of the present embodiment is particularly effective when used as a wheel speed sensor signal generation device.

(Other embodiments)
(A) The sensor 70 is not limited to the magnetoresistive element, and may be a sensor of any principle in which the current changes with a change in some physical quantity. The application to which the sensor 70 is applied is not limited to the wheel speed sensor, and any application may be used. The sensor signal generator of the present invention is effective in a system in which the power supply voltage may change suddenly.

(B) When there is no demand for miniaturization of the sensor signal generation circuit 40, the sensor current Iss may be directly converted into a voltage without providing the current reduction circuit 41.

As described above, the present invention is not limited to such embodiments, and can be implemented in various embodiments without departing from the spirit of the present invention.

20 ... Power supply,
27 ... Capacitor between terminals,
30 ... Voltage application circuit,
40 ... Sensor signal generation circuit,
50 (501-504) ... Sensor signal generator,
70 (701-704) ... Wheel speed sensor (sensor).

Claims (3)

A sensor signal generator that is connected to a sensor (70) whose current changes with a change in physical quantity and outputs a sensor signal (Ssns) obtained by converting a sensor current (Isns), which is a current flowing through the sensor, into a voltage. ,
A voltage application circuit (30) that applies a power supply voltage (Vcc) input from a power supply (20) via a voltage input terminal (Vin) to the sensor via a voltage output terminal (Vout).
A sensor signal generation circuit (40) that is connected to the sensor via the voltage output terminal and converts the sensor current into a voltage to generate the sensor signal.
An inter-terminal capacitor (27) that is connected between the voltage input terminal and the voltage output terminal and suppresses fluctuations in the power supply voltage from being transmitted to the sensor signal generation circuit.
A sensor signal generator equipped with. The sensor signal generation circuit is
A current reduction circuit (41) that multiplies the sensor current by a predetermined value smaller than 1 time and outputs a reduction current (Irdc) smaller than the sensor current.
A current-voltage conversion circuit (42) that converts the reduced current into a voltage and outputs it.
The sensor signal generation device according to claim 1. The sensor signal generation device according to claim 1 or 2, which is connected to a wheel speed sensor that detects the rotation speed of wheels (81-84) as the sensor and outputs the sensor signal according to the rotation speed of the wheels.

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