JP2018146459A - Failure detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the accuracy of failure detection by a failure detection circuit.SOLUTION: A failure detection circuit 10 includes: an A/D converter 12 for converting a voltage to voltage digital values VAD and VBD; a first pressure divider 21A in which a first divided pressure VA, which is divided by a first temperature sensor 22A and a first resistor 23A, is acquired by the A/D converter 12; a second pressure divider 21B in which a second divided pressure VB, divided by a second temperature sensor 22B and a second resistor 23B, is acquired by the A/D converter 12; a temperature converter 14A for converting the values of the first divided pressure VA and the second divided pressure VB to the values of temperatures of a first temperature TA and a second temperature TB; and a failure detector 14B for detecting a failure when the difference between the first temperature TA and the second temperature TB is not smaller than a predetermined level. The first divided pressure VA is inclined to the temperature of the first temperature sensor 22A converted by the temperature converter 14A at a first inclination while the second divided pressure VB is inclined to the temperature of the second temperature sensor 22B at a second inclination, and the first and second inclinations are of opposite signs.SELECTED DRAWING: Figure 1

Description

  The present specification discloses a technique related to a failure detection circuit.

  Conventionally, a technique for detecting a failure based on signals from a plurality of temperature sensors is known. In the short-circuit fault device disclosed in Patent Document 1 below, the other end of the first resistor whose one end is connected to the reference power source is grounded via the first thermistor. The other end of the second resistor, which is connected to the reference power supply at one end, is grounded through the second thermistor. The first voltage divided by the first resistor and the first thermistor and the second voltage divided by the second resistor and the second thermistor are input to the MPU. The MPU detects a short-circuit failure by comparing the difference between the first voltage and the second voltage with a predetermined voltage.

JP 2008-164469 A

By the way, since the voltage divided by the resistor and the thermistor as in the above configuration is an analog signal, A / D conversion is performed inside or outside the MPU in order to convert it into a digital signal that can be processed inside the MPU. The structure for doing this is required. In the configuration of Patent Document 1, a short-circuit failure of the thermistor can be detected, but a failure caused by an abnormality of the A / D conversion unit for A / D conversion or an abnormality of the thermistor itself cannot be detected. There is a problem that failure detection with high accuracy cannot be performed.
The technique described in the present specification has been completed based on the above-described circumstances, and aims to increase the accuracy of failure detection.

  The failure detection circuit described in the present specification includes an A / D conversion unit that acquires a voltage and converts the voltage into a digital signal, a first temperature sensor, and a first resistor. A first voltage dividing unit obtained by the A / D converter by the first divided voltage divided by the temperature sensor and the first resistor, a second temperature sensor, and a second resistor. A second divided voltage obtained by the A / D converter and converted into the digital signal by the second divided voltage divided by the second temperature sensor and the second resistor; A temperature conversion unit that converts the values of the first divided voltage and the second divided voltage into a temperature value composed of a first temperature and a second temperature; and a difference between the first temperature and the second temperature. A failure detection unit that detects a failure when the temperature is equal to or greater than a predetermined value, and the temperature with respect to the temperature of the first temperature sensor converted by the temperature conversion unit The inclination of 1 minute voltage, wherein the inclination of said second divided voltage with respect to temperature of the second temperature sensor, positive and negative are opposite slope.

  According to this configuration, the slope of the first divided voltage with respect to the temperature of the first temperature sensor converted by the temperature conversion unit and the first divided voltage with respect to the temperature of the second temperature sensor converted by the temperature conversion unit. Since the positive and negative slopes are opposite to each other, the first voltage and the first temperature at the time of failure of the A / D converter and the temperature sensor are compared with the case where the slopes of the divided voltage voltages are the same. The temperature difference between the first temperature and the second temperature can be increased in accordance with the increase or decrease in the value of the two temperatures. When the temperature difference between the first temperature and the second temperature is increased, the failure detection unit can easily detect a failure using the temperature difference, so that the accuracy of failure detection can be increased.

The following embodiments are preferable as the embodiments of the technology described in this specification.
Arrangement of the first temperature sensor and the first resistor connected in series between the power supply side voltage and the ground, and the second connected in series between the power supply side voltage and the ground. The arrangement of the temperature sensor and the second resistor is opposite to the arrangement of the temperature sensor with respect to the resistance.
In this way, it becomes easy to disperse and arrange a plurality of temperature sensors, so that the circuit configuration can be simplified.

When the common change occurs in the increase / decrease in the values of the first divided voltage and the second divided voltage converted into the digital signal, the temperature conversion unit calculates the difference between the first temperature and the second temperature. Convert so that the difference is large.
In this way, an A / D drift failure occurs in the A / D converter, and a common change occurs in the increase and decrease of the values of the first divided voltage and the second divided voltage converted by the A / D converter. In some cases, the difference between the first temperature and the second temperature becomes large, and the failure detection unit can easily detect the failure, so that the accuracy of failure detection can be further improved.

The first temperature sensor and the second temperature sensor are arranged in an electrical junction box mounted on a path from a vehicle power source to a load.
In this way, the first temperature sensor and the second temperature sensor are both arranged in the electrical junction box, so that the temperature detected by the first temperature sensor and the second temperature sensor is usually large. Since the failure can be detected when the temperature difference occurs in an environment in which the temperature difference is unlikely to occur, the accuracy of failure detection can be improved.

  According to the technique described in this specification, it is possible to improve the accuracy of failure detection.

The figure which shows the failure detection circuit of embodiment The figure which shows the temperature-divided voltage (voltage digital value) characteristic of the temperature sensor The figure which shows the table of the correspondence of the voltage digital value of a divided voltage, and temperature. The figure which shows the movement of the set of the voltage digital value and temperature when AD drift failure arises in the A / D conversion part Flowchart showing microcomputer processing

<Embodiment>
The failure detection circuit 10 of this embodiment will be described with reference to FIGS.
The failure detection circuit 10 can be provided in an electrical connection box 30 mounted on a vehicle such as an automobile. The electrical junction box 30 is arranged on a path from an electric wire such as a battery to a load such as a motor or an electrical component, and performs conversion or control of power supplied to the load.

  As shown in FIG. 1, the failure detection circuit 10 includes a microcomputer 11, a first voltage dividing unit 21 </ b> A that divides a power supply side voltage Vcc (for example, 12 [V]) and outputs the divided voltage to the microcomputer 11, and a first voltage dividing unit. 21A, and a second voltage dividing unit 21B that divides the power supply side voltage Vcc and outputs the divided voltage to the microcomputer 11.

  The first voltage dividing unit 21A includes a first resistor 23A having one end connected to the power supply side voltage Vcc, a first temperature sensor 22A having one end connected to the first resistor 23A, and the other end grounded. Is provided. The first divided voltage VA divided by the first temperature sensor 22A and the first resistor 23A is output to the microcomputer 11. The second voltage dividing unit 21B includes a second temperature sensor 22B having one end connected to the power supply side voltage Vcc, a second resistor 23B having one end connected to the second temperature sensor 22B and the other end grounded. . The second divided voltage VB divided by the second temperature sensor 22B and the second resistor 23B is output to the microcomputer 11.

  The temperature sensors 22A and 22B are both NTC (Negative Temperature Coefficient) thermistors whose resistance decreases as the temperature rises. As a result, as shown in FIG. 2, the slope of the first divided voltage VA with respect to the temperature of the first temperature sensor 22A is a negative slope that falls to the right, and the second portion of the temperature with respect to the temperature of the second temperature sensor 22B. The slope of the voltage VB is a positive slope that rises to the right. In the present embodiment, the slope of the first divided voltage VA and the slope of the second divided voltage VB are substantially equal in absolute value, and the first divided voltage VA and the second divided voltage VB are Are set to intersect at 25 ° C. as a reference temperature (for example, normal temperature).

  As shown in FIG. 1, the microcomputer 11 includes an A / D conversion unit 12, a control unit 14, and a storage unit 13. The A / D converter 12 receives the first divided voltage VA and the second divided voltage VB, which are analog signals, converts them into voltage digital values VAD, VBD, which are digital signals, and outputs them to the controller 14. The control unit 14 includes a temperature conversion unit 14A that converts the values of the voltage digital value VAD and the voltage digital value VBD into a temperature value including the first temperature TA and the second temperature TB, and the first temperature TA and the second temperature. A failure detection unit 14B that detects a failure when the difference from TB is equal to or higher than a predetermined temperature.

  The storage unit 13 stores a reference temperature difference for determining failure as compared with the temperature difference TC between the first temperature TA and the second temperature TB. The reference temperature difference can be set to various values according to the external environment or the like, but is set to 10 ° C. in the present embodiment. As shown in FIG. 3, the storage unit 13 stores a table in which the voltage digital value VAD and the first temperature TA are associated with each other, and the voltage digital value VBD and the second temperature TB are associated with each other. . In this table, as shown in FIG. 4, when the voltage digital value VAD and the voltage digital value VBD both increase or decrease (a common change occurs) due to a drift failure or the like of the A / D converter 12 (FIG. 4). In this case, the voltage digital value increases from 2047 to 2400 due to drift failure), and the temperature TA and TB increase and decrease according to the voltage digital values VAD and VBD so that the difference between the first temperature TA and the second temperature TB increases. The direction is reversed.

Next, the processing of the microcomputer 11 will be described with reference to FIG.
When the first divided voltage VA and the second divided voltage VB are input to the A / D converter 12, as shown in FIG. 5, the A / D converter 12 has the first divided voltage VA and the second divided voltage VA. The voltage VB is converted into voltage digital values VAD and VBD (S1). Next, the temperature conversion unit 14A reads the table (FIG. 3) stored in the storage unit 13, converts the voltage digital value VAD to the first temperature TA using this table, and converts the voltage digital value VBD to the second temperature TB. (S2).

Next, the failure detection unit 14B calculates a temperature difference TC between the first temperature TA and the second temperature TB (S3). For example, when the first temperature TA = 45 ° C. and the second temperature TB = 5 ° C., the temperature difference TC = 30 ° C. Next, it is determined whether or not the temperature difference TC is larger than the reference temperature difference stored in the storage unit 13 = 10 ° C. (S4). When the temperature difference TC = 30 ° C., the temperature difference is larger than the reference temperature difference = 10 ° C. (“YES” in S4), so that an abnormality has occurred in the temperature sensors 22A, 22B, or the A / D conversion unit 12 Since there is a possibility that a drift failure has occurred, the failure detection unit 14B detects the failure and executes fail-safe processing (S5). In fail-safe processing, for example, by turning off the switch from the power source to the load such as in-vehicle electrical components to cut off the power supply to the load or controlling the engine so that it cannot be started, Make sure there are no malfunctions.
On the other hand, when the temperature difference TC is equal to or less than the reference temperature difference (10 ° C. or less) (“NO” in S4), it is normal (no failure is detected), so the failure detection unit 14B does nothing, The process ends.

According to this embodiment, the following operations and effects are achieved.
The failure detection circuit 10 has an A / D conversion unit 12 that acquires a voltage and converts the voltage into voltage digital values VAD and VBD (digital signals), a first temperature sensor 22A, and a first resistor 23A. The first voltage dividing unit 21A from which the first divided voltage VA divided by the first temperature sensor 22A and the first resistor 23A is acquired by the A / D conversion unit 12, and the second temperature sensor A second divided voltage VB obtained by the A / D converter 12 having a second divided voltage VB divided by the second temperature sensor 22B and the second resistor 23B. The pressure conversion unit 21B converts the values of the first divided voltage VA and the second divided voltage VB converted into the voltage digital values VAD and VBD into a temperature value composed of the first temperature TA and the second temperature TB. 14A and the difference between the first temperature TA and the second temperature TB is 10 ° C. or more (predetermined ), A slope of the first divided voltage VA with respect to the temperature of the first temperature sensor 22A converted by the temperature conversion unit 14A (about the first voltage division unit 21A). The slope of the temperature-divided voltage characteristic of the temperature sensor 22A) and the slope of the second divided voltage VB with respect to the temperature of the second temperature sensor 22B (the temperature-divided voltage characteristic of the temperature sensor 22B for the second voltage dividing section 21B). The slope of () is a slope opposite to positive and negative.

  In this way, the slope of the first divided voltage VA with respect to the temperature of the first temperature sensor 22A and the slope of the first divided voltage VA with respect to the temperature of the second temperature sensor 22B are opposite to each other. Therefore, compared with the case where the slopes of the divided voltages 22A and 22B are the same, the first divided voltage when an abnormality occurs in the A / D converter 12 and the temperature sensors 22A and 22B, etc. The temperature difference TC between the first temperature TA and the second temperature TB can be increased in accordance with the increase in VA and the second divided voltage VB. When the temperature difference TC between the first temperature TA and the second temperature TB increases, the failure detection unit 14B can easily detect a failure using the temperature difference TC, so that the accuracy of failure detection can be increased.

The first resistor 23A and the first temperature sensor 22A connected in series between the power supply side voltage Vcc and the ground, and the first resistor connected in series between the power supply side voltage Vcc and the ground. The arrangement of the temperature sensor 22B and the second resistor 23B is opposite to the arrangement of the temperature sensor with respect to the resistance.
In this way, it becomes easy to disperse and arrange the plurality of temperature sensors 22A and 22B, so that the circuit configuration can be simplified.

Further, the temperature conversion unit 14A determines that the first temperature TA and the first temperature TA when the common change occurs in the increase / decrease in the values of the first divided voltage VA and the second divided voltage VB converted into the voltage digital values VAD and VBD. Conversion is performed so that the difference from 2 temperature TB becomes large.
In this way, an A / D drift failure occurs in the A / D converter 12, and it is common to increase / decrease in the values of the first divided voltage VA and the second divided voltage VB converted by the A / D converter 12. When a change occurs, the difference between the first temperature TA and the second temperature TB becomes large and the failure detection unit 14B is less likely to detect a failure. Therefore, it is possible to further improve the accuracy of failure detection. .

The first temperature sensor 22A and the second temperature sensor 22B are arranged in an electrical junction box 30 mounted on a path from the power source of the vehicle to the load.
In this way, the first temperature sensor 22A and the second temperature sensor 22B are usually arranged by arranging the first temperature sensor 22A and the second temperature sensor 22B together in the electrical junction box 30. In an environment in which a large temperature difference is unlikely to occur in the temperature detected by, a failure can be detected when the temperature difference TC occurs, so that the accuracy of failure detection can be improved.

<Other embodiments>
The technology described in the present specification is not limited to the embodiments described with reference to the above description and the drawings. For example, the following embodiments are also included in the technical scope of the technology described in the present specification.
(1) Although temperature sensor 22A, 22B of the said embodiment was used as the NTC thermistor, it is not restricted to this, You may use another temperature sensor. For example, a PTC (Positive Temperature Coefficient) thermistor whose resistance value increases as the temperature increases may be used. Further, both a PTC thermistor and an NTC thermistor may be used. In this case, the PTC thermistor and the NTC thermistor may be connected to the same side (for example, both grounded) with respect to the resistor. Further, the slope of the first divided voltage VA and the slope of the first divided voltage VA are not limited to those shown in FIG. 2, and temperature sensors having different slopes can be used.

  (2) The point where the slope of the first divided voltage VA with respect to the temperature of the first temperature sensor 22A and the slope of the second divided voltage VB with respect to the temperature of the second temperature sensor 22B intersect is 25 ° C. However, the temperature is not limited to this, and other temperatures may be used.

  (3) The first divided voltage VA has a positive slope as a whole, and the second divided voltage VB has a negative slope as a whole. However, the slope is not limited to this. It may have a positive slope or a negative slope in the temperature range. The predetermined temperature range can be set to include a reference temperature (25 ° C.), for example.

  (4) Although the temperature conversion unit 14A converts the temperature using the table stored in the storage unit 13, the temperature conversion unit 14A is not limited thereto. For example, the temperatures TA and TB associated with the voltage digital values VAD and VBD may be converted by an approximate expression without using a table.

  (5) The failure detection circuit 10 is configured to be provided in the electrical connection box 30, but is not limited thereto, and a configuration in which a part or all of the failure detection circuit 10 is provided in addition to the electrical connection box 30 may be employed. . For example, the temperature sensors 22A and 22B may be configured to be provided in the battery and detect the temperature of the battery.

10: Failure detection circuit 11: Microcomputer 12: A / D conversion unit 13: Storage unit 14: Control unit 14A: Temperature conversion unit 14B: Failure detection unit 21A: First voltage dividing unit 21B: Second voltage dividing unit 22A: First 1st temperature sensor 22B: 2nd temperature sensor 23A: 1st resistance 23B: 2nd resistance 30: Electrical junction box TA: 1st temperature TB: 2nd temperature TC: Temperature difference VA: 1st divided voltage VAD : Voltage digital value (first divided voltage converted to digital signal)
VB: second divided voltage VBD: voltage digital value (second divided voltage converted into a digital signal)
Vcc: Power supply side voltage

Claims (4)

An A / D converter that obtains a voltage and converts the voltage into a digital signal;
A first temperature sensor and a first resistor, and a first divided voltage divided by the first temperature sensor and the first resistor is acquired by the A / D converter; 1 partial pressure section,
A second temperature sensor and a second resistor, and a second divided voltage divided by the second temperature sensor and the second resistor is acquired by the A / D converter; Two voltage dividers;
A temperature conversion unit that converts values of the first divided voltage and the second divided voltage converted into the digital signal into a temperature value composed of a first temperature and a second temperature;
A failure detection unit that detects a failure when a difference between the first temperature and the second temperature is equal to or greater than a predetermined value;
The inclination of the first divided voltage with respect to the temperature of the first temperature sensor converted by the temperature conversion unit is opposite to the inclination of the second divided voltage with respect to the temperature of the second temperature sensor. A fault detection circuit with a slope of. Arrangement of the first temperature sensor and the first resistor connected in series between the power supply side voltage and the ground, and the second connected in series between the power supply side voltage and the ground. 2. The failure detection circuit according to claim 1, wherein the arrangement of the temperature sensor and the second resistor is opposite to the arrangement of the temperature sensor with respect to the resistance. When the common change occurs in the increase / decrease in the values of the first divided voltage and the second divided voltage converted into the digital signal, the temperature conversion unit calculates the difference between the first temperature and the second temperature. The failure detection circuit according to claim 1, wherein the conversion is performed so that the difference becomes large. The said 1st temperature sensor and the said 2nd temperature sensor are distribute | arranged to the electrical junction box mounted in the path | route from the power supply of a vehicle to a load. Fault detection circuit.

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