JPH10197359A - Apparatus for diagnosing failure of thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermistor failure-diagnosing apparatus which can detect not only a shortcircuited state and an opened state, but an abnormality of a thermistor when the thermistor shows a constant resistance value at all times regardless of a temperature change. SOLUTION: The failure-diagnosing apparatus supplies a current to a thermistor 2 for a longer time than a normal temperature-sampling time, thereby letting the thermistor 2 generate heat by itself. Whether a resistance of the thermistor 2 changes or not during the heat generation time is detected by detecting a voltage VA/ D. Since it can be detected whether or not the resistance of the thermistor 2 changes, an abnormality of the thermistor when the thermistor shows a constant resistance value at all times is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermistor failure diagnosis apparatus.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional thermistor failure diagnosis apparatus. This failure diagnostic device is a microcomputer 56 having a current limiting resistor R52 connected between the thermistor 51 and a power supply, and an A / D port 55 connected to a connection point 53 between the resistor R52 and the thermistor 51. It is composed of The resistor R52 limits the current that always flows from the power supply to the thermistor 51 to prevent the thermistor 51 from overheating.

[0003] As shown in FIG.
The potential V _{A / D} of the A / D port 55 is sampled (Step S101). If the potential V _{A / D} is substantially equal to the power supply voltage Vcc (Step S102), it is determined that the thermistor 51 is open due to disconnection or the like. Then, it is determined that the thermistor 51 is abnormal, and the temperature sampling by the thermistor 51 is stopped (step S105).

On the other hand, the potential V _{A / D} is equal to the short-circuit potential Vss (≒ 0
V) (Step S103), the thermistor 5
1 is determined to be in a short circuit state, thermistor 51 is determined to be abnormal, and temperature sampling by thermistor 51 is stopped (step S105).

When the potential V _{A / D} is neither the power supply voltage Vcc nor the short-circuit potential Vss, it is determined that the thermistor 51 is normal (step S104), and temperature sampling is performed by the thermistor 51.

[0006]

However, the conventional thermistor failure diagnosis apparatus described above can detect an abnormality when the thermistor is open and an abnormality when the thermistor is short-circuited. It is not possible to detect an abnormality in which a constant value is shown regardless of a temperature change. As a specific example of such an abnormality, for example, when moisture such as water or water vapor enters the thermistor, the resistance value of the thermistor remains constant as described above.

As described above, when an abnormality occurs in which the resistance value of the thermistor remains constant, for example, when the air conditioner is operated based on the temperature detected by the thermistor, the air conditioner operates at the actual room temperature. Air-conditioning operation is performed based on the temperature different from the above. Therefore, as shown in FIG. 6, there is a possibility that excess or deficiency of cooling capacity or excess or deficiency of heating capacity occurs, a service call is made by a user, and a printed circuit board is replaced or normal parts other than the thermistor are replaced. There is.

For this reason, problems such as a long failure diagnosis time, a problem that even a normal part is replaced, and a problem of high cost for service occur.

An object of the present invention is to provide a thermistor failure diagnosis device capable of detecting not only a short-circuit state and an open state, but also an abnormality of a thermistor which always shows a constant resistance regardless of a temperature change. It is in.

[0010]

In order to achieve the above object, a failure diagnosis apparatus for a thermistor according to the first aspect of the present invention includes a switching element connected between the thermistor and a power supply, and a first element for measuring temperature. A switching control unit that turns on the switching element for a second period longer than the first period and turns on the switching element for self-heating of the thermistor; And a failure determination unit that determines whether the voltage across the thermistor has changed and determines whether the thermistor is normal or has failed.

According to the first aspect of the present invention, at the time of failure diagnosis, the switching control unit turns on the switching element only for the second period to cause the thermistor to self-heat, and the failure determination unit It is determined that the thermistor is normal when the voltage across the thermistor changes during period 2. On the other hand, when the voltage across the thermistor does not change during the second period, it is determined that the thermistor is abnormal.

[0012] The fact that the voltage across the thermistor does not change during the second period means that the thermistor is in a short-circuit state, the thermistor is in an open state, or the resistance value of the thermistor is constant despite the temperature rise This indicates that the state is either a constant state or a constant state.

Therefore, according to the present invention, it is possible to detect not only the short-circuit state and the open state of the thermistor, but also the abnormality of the thermistor which always shows a constant resistance regardless of the temperature change.

According to a second aspect of the present invention, in the thermistor failure diagnosis apparatus according to the first aspect, the switching control unit causes the thermistor to generate heat by itself.
After the end of the period, the switching element is turned off only for the third period and the thermistor cools, and then the switching element is turned on only for the first period to enable temperature sampling by measuring the voltage across the thermistor. It is characterized by doing.

According to the second aspect of the present invention, after the second period of the self-heating, the temperature sampling is performed after the thermistor is cooled only for the third period, so that the temperature sampling can be performed accurately.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows an embodiment of a failure diagnosis apparatus according to the present invention. This embodiment includes a microcomputer 1 as a switching control unit and a failure judgment unit, a transistor Q1 as a switching element, and a resistor R1. The microcomputer 1 has a general-purpose port Po and an A / D
Having a port _P P. Thermistor 2 is connected between the A / D port P _P and ground. The base of the transistor Q1 is connected to the general-purpose port Po, and the emitter of the transistor Q1 is connected to a power supply. The resistor R1 is connected between the collector and the A / D port P _P of the transistor Q1. The resistance value of the resistor R1 was set to a value smaller than the resistance value of the conventional current limiting resistor R51.

The operation of the fault diagnostic apparatus having the above configuration will be described with reference to the flowcharts shown in FIGS. This flowchart shows the operation of the microcomputer 1. First, in step S1, the general-purpose port Po is turned on, and the transistor Q1 is turned on only for the period T1. Then, a current flows through the thermistor 2 through the resistor R1. Then, the A / D port P _P appears a voltage V _{A / D} voltage drop of the thermistor 2. The microcomputer 1 samples this voltage V _{A / D} (step S
2), the change ΔV _{A / D of} the voltage V _{A / D} throughout the period T1
Is detected (step S3), and if it is determined that ΔV _{A / D} is substantially zero, it is determined that the thermistor 2 is abnormal (step S9). Examples of the abnormality include a case where the thermistor 2 is short-circuited, a case where the thermistor 2 is in an open state, and a case where the resistance value of the thermistor 2 is always constant irrespective of the temperature due to moisture penetration. is there.

In these cases, the voltage V from the thermistor 2
_{Since the} detected temperature obtained from the _{A / D} is erroneous, the operation of a predetermined device (for example, an air conditioner) based on the detected temperature is stopped. As shown in FIG. 2, when the thermistor 2 is normal, the period T1 is set to a sampling period during a normal temperature measurement so that the thermistor 2 generates heat and changes its resistance during the period T1. It is set longer than T2.

Therefore, if the voltage V _{A / D} changes and the change ΔV _{A / D} is clearly not zero as shown in a period T 1 in FIG. 2, the thermistor 2 is normal. Judge. Then, the general-purpose port Po is turned off (step S4), and the transistor Q1 is turned off for a predetermined cooling period. As a result, no current flows through the thermistor 2, and the thermistor 2 is naturally cooled (step S5). The cooling period may be set to a time corresponding to the self-heating value.

Next, the general-purpose port Po is turned on for a short period T2 shown in FIG. 2 (step S6), and the temperature is detected by detecting the voltage V _{A / D} determined by the resistance value of the thermistor 2 (FIG. 2). Step S7). This temperature sampling is performed at predetermined time intervals (steps S6 to S6).
S8).

As described above, according to this embodiment, the period T1 during which the thermistor 2 self-heats is set, and the quality of the thermistor 2 is determined based on whether or not the heat changes the resistance value of the thermistor 2. Therefore, it is possible to detect not only the short-circuit state and the open state of the thermistor, but also the abnormality of the thermistor which always shows a constant resistance regardless of the temperature change.

In this embodiment, after the self-heating period T1, the power supply to the thermistor 2 is stopped for a predetermined cooling period to cool the thermistor, and then the normal temperature sampling is performed. Can be executed.

In the above embodiment, the quality of the thermistor is determined by determining the gradient of the voltage V _{A / D} during the period T1 in FIG. 2 and comparing the gradient with a predetermined reference gradient. It may be.

[0025]

As is apparent from the above description, the failure diagnosis apparatus for a thermistor according to the first aspect of the present invention includes a switching element connected between the thermistor and a power supply, and the switching element for a first period during temperature measurement. While the element is turned on, the second time longer than the first period is used for failure diagnosis.
A switching control unit that turns on the switching element only during the period to self-heat the thermistor; and determines whether the voltage across the thermistor has changed during the second period to determine whether the thermistor is normal or faulty. A failure determination unit for determining whether

According to the first aspect of the present invention, at the time of failure diagnosis, the switching control section turns on the switching element for the second period to cause the thermistor to generate heat, and the failure determination section performs It is determined that the thermistor is normal when the voltage across the thermistor changes during period 2. On the other hand, when the voltage across the thermistor does not change during the second period, it is determined that the thermistor is abnormal.

The fact that the voltage across the thermistor does not change during the second period means that the thermistor is in a short-circuit state, the thermistor is in an open state, or the resistance value of the thermistor is constant despite the temperature rise. This indicates that the state is either a constant state or a constant state.

Therefore, according to the present invention, it is possible to detect not only the short-circuit state and the open state of the thermistor but also the abnormality of the thermistor which always shows a constant resistance regardless of the temperature change.

According to a second aspect of the present invention, in the failure diagnosis apparatus for a thermistor according to the first aspect, the switching control unit causes the thermistor to self-heat.
After the end of the period, the switching element is turned off only for the third period and the thermistor cools, and then the switching element is turned on only for the first period to enable temperature sampling by measuring the voltage across the thermistor. I do.

According to the second aspect of the present invention, the temperature sampling is performed after the thermistor is cooled for the third period after the second period of the self-heating, so that the temperature sampling can be performed accurately.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a thermistor failure diagnosis device according to an embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation of the embodiment.

FIG. 3 is a flowchart illustrating an abnormality detection operation of the embodiment.

FIG. 4 is a flowchart illustrating the normal operation of the embodiment.

FIG. 5 is a circuit diagram of a conventional thermistor failure diagnosis device.

FIG. 6 is a flowchart illustrating an example of a problem in a conventional example.

FIG. 7 is a flowchart illustrating an operation of a conventional example.

[Explanation of symbols]

1: microcomputer, 2: thermistor, Q1: transistor, R1: resistor, Po: general-purpose port, _PP : A /
D port, V _{A / D} ... voltage, ΔV _{A / D} ... change.

Claims (2)

[Claims] 1. A switching element (Q1) connected between a thermistor (2) and a power supply, and, during temperature measurement, the switching element (Q1) is turned on for a first period (T2), and a failure diagnosis is performed. Sometimes, the switching element (Q1) is turned on only for a second period (T1) longer than the first period (T2), and the thermistor is turned on.
(2) a switching control unit (1) for self-heating, and determining whether or not the voltage across the thermistor (2) has changed during the second period (T1). A failure diagnosis device for a thermistor, comprising: a failure determination unit (1) for determining whether the failure is normal or failure. 2. The failure diagnosis device for a thermistor according to claim 1, wherein the switching control section (1) causes the thermistor (2) to self-heat during the second period.
After the end of (T1), after the switching element (Q1) is turned off for the third period and the thermistor (2) cools,
A fault diagnosis device for a thermistor, characterized in that the switching element (Q1) is turned on for a first period (T2) to enable temperature sampling by measuring the voltage across the thermistor (2).