JPH0988708A - Temperature sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect presence/absence of intermittence of a temperature sensor by eliminating a dedicated checker under ordinary temperature. SOLUTION: A voltage Vo of a common contact between an exhaust temperature sensor 12 and a voltage dividing resistance circuit 17 is input in a comparator 19 and compared with the reference voltage Vs (approximately 2.5V) so that an exhaust gas temperature alarm light 13 is lit on or off. The voltage dividing resistance circuit 17 is so constituted that an intermittence detecting resistance R1 (1.2MΩ) and a series circuit of a detecting resistance R2 (470Ω) and a transistor (Tr1) are connected in parallel to each other. In an ordinary time when a detection mode switch T1 is turned off, a CPU 14 turns on a transistor Tr1 by regarding an output terminal P1 as Lo level and when the detection mode switch T1 is turned on, it turns on a transistor Tr1 by regarding the output terminal P1 as Hi level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor circuit configured to detect a temperature of a detection target by a change in resistance value of a temperature sensor such as an exhaust temperature sensor of an automobile. The present invention relates to a temperature sensor circuit that enables diagnosis.

[0002]

For example, in a vehicle such as an automobile, an exhaust temperature sensor (CCO sensor) for detecting the exhaust temperature is provided, and the exhaust temperature rises abnormally (for example, 900 to 1).
Warning light (warning lamp)
Is lit to notify the user. Figure 10
1 shows a conventional sensor circuit 2 including an exhaust temperature sensor 1, which is connected in series with a voltage dividing resistor 3 and a voltage Vcc (for example, 5V) is applied between them. Then, the exhaust temperature sensor 1 and the partial pressure resistor 3
The voltage at the common connection point with is input to the inverting input terminal (−) of the comparator 4, and the reference voltage (about 2.5 V) is input to the non-inverting input terminal (+) of the comparator 4. Has become. In the figure, a portion surrounded by a chain double-dashed line is arranged in the engine control ECU, and its output terminal EGW is connected to a warning light lighting circuit (not shown).

Here, the exhaust gas temperature sensor 1 has the characteristics shown in FIG. 5, and the resistance value decreases as the exhaust gas temperature rises, and becomes about 431 Ω when 900 ° C. is detected, for example. . On the other hand, the resistance value of the voltage dividing resistor 3 is set to 470Ω, for example. As a result, when the temperature detected by the exhaust temperature sensor 1 exceeds 900 ° C., the output of the comparator 4 becomes Hi, an abnormality in the exhaust temperature is detected, and the exhaust temperature warning lamp inside the vehicle is turned on.

By the way, when the vehicle is shipped or inspected, an inspection (diagnosis) is made as to whether or not the exhaust temperature sensor 1 operates normally. In this case, since it takes a lot of time and effort to set the exhaust temperature sensor 1 to a high temperature of 900 ° C. at the time of inspection, generally, the dedicated checker 5 is used to set the exhaust temperature sensor 1 at a low temperature (normal temperature). The presence or absence of disconnection is being detected.

As shown in FIG. 10, the checker 5 is connected between both ends of the exhaust temperature sensor 1, and a built-in power source applies a predetermined voltage across the both ends to turn on the lamp 5a when energized. If there is an abnormality (disconnection),
The lamp 5a is turned off. With this,
If the exhaust temperature sensor 1 is not broken by the inspection by the checker 5, it is determined to be normal.

However, in the case of using the checker 5 to detect the presence / absence of disconnection of the exhaust gas temperature sensor 1, not only the labor of the inspection worker is required, but also the dedicated checker 5 is required and the vehicle side is required. However, there was a problem that the number of unnecessary parts such as connecting connectors and wires during actual traveling increased and the cost increased. It should be noted that in recent years, the number of vehicles that perform electronic control by a microcomputer has increased, and those equipped with a self-diagnosis function have been provided to prevent failures and improve safety. It is also necessary to enable self-diagnosis regarding the presence or absence.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a temperature sensor circuit capable of inspecting a temperature sensor for the presence or absence of a wire breakage at room temperature without requiring a dedicated checker. To provide.

[0008]

According to another aspect of the present invention, there is provided a temperature sensor circuit comprising: a temperature sensor whose resistance value changes depending on a detected temperature; and a voltage dividing means connected in series with the temperature sensor and having a resistance element. A voltage is applied to the temperature sensor and the temperature is detected based on the voltage at the common connection point between the temperature sensor and the voltage dividing means, and the resistance value of the voltage dividing means is normally measured at the time of detecting the temperature. A mode switching means for switching the temperature detection resistance value for the mode to a disconnection detection resistance value for an inspection mode different from that, and the resistance value of the voltage dividing means is switched to the disconnection detection resistance value by the mode switching means. And a disconnection determining means for determining whether or not the temperature sensor is disconnected based on the voltage at the common connection point.

At this time, if the temperature sensor is provided with an exhaust temperature sensor whose resistance value decreases as the exhaust temperature increases, the partial pressure is detected. The means includes a detection resistor having a small temperature detection resistance value, and a disconnection detection resistor having a sufficiently large disconnection detection resistance value inserted in parallel with the detection resistor, and the mode described above. The switching means can be configured to include a switch element that switches the energization of the resistors (the invention of claim 2).

In this case, the switch element is composed of a transistor and the mode switching means is a C for vehicle control.
The transistor can be configured to be turned on and off in response to a PU command signal (the invention of claim 3), and the switch element can also be configured to include a dedicated switch (claim 4). invention).

The disconnection determination means may be configured to include a comparison circuit for comparing the voltage at the common connection point with a reference voltage (invention of claim 5), or the voltage at the common connection point may be A / A / D converter for D conversion, and C for judging presence / absence of disconnection based on an output signal from the A / D converter
It can also be configured to include a PU (the invention of claim 6).

Further, the existing warning light is configured to be turned on according to the judgment result of the disconnection judging means (the invention of claim 7), or the judgment result data of the disconnection judging means is stored in a memory. The determination result data may be read from the memory (claim 8).
Invention).

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) First Embodiment First, a first embodiment in which the present invention is applied to a temperature sensor circuit for detecting whether or not there is an abnormality in exhaust temperature for a vehicle (claim 1,
2, 3, 5, 7) will be described with reference to FIGS.

FIG. 1 shows the entire structure of a temperature sensor circuit according to this embodiment. The temperature sensor circuit is arranged in a circuit main portion 11 and an exhaust gas purifying device portion arranged in an engine ECU of a vehicle. It is composed of an exhaust temperature sensor (CCO sensor) 12, which is a temperature sensor provided, an exhaust temperature warning lamp 13 and the like arranged on the instrument panel of the vehicle. Engine E
In the CU, a CPU 14 for controlling the engine etc.
Is provided.

The circuit main portion 11 is provided with connection terminals 15 and 16, and the exhaust temperature sensor 12 has one end connected to one connection terminal 15 and the other end connected to a ground terminal. As shown in FIG. 5, the exhaust gas temperature sensor 12 has a characteristic that the resistance value decreases as the exhaust gas temperature rises, and at room temperature (low temperature) when the engine is stopped, a high resistance value of about 1 MΩ, for example. And, for example, when 900 ° C. is detected, it becomes as low as about 431Ω. Further, the exhaust temperature warning lamp 13 is provided between the connection terminal 16 and the power supply terminal + Vb (for example, 14V).

Now, the circuit main portion 11 is constructed as follows. That is, the voltage dividing resistance circuit 17 as the voltage dividing means.
Is provided between a power supply terminal Vcc (for example, 5 V) and the connection terminal 15, and therefore the voltage dividing resistance circuit 17 and the exhaust temperature sensor 12 are connected in series, and a predetermined voltage (5 V) is applied between them. Is applied. The voltage dividing resistor circuit 17 includes a resistor R1 for detecting disconnection and a resistor R2 for detecting disconnection.
And a series circuit of a pnp-type transistor Tr1 which is a switching element, are connected in parallel. At this time,
The power supply terminal Vcc is connected to the emitter of the transistor Tr1 and the collector is connected to the detection resistor R2.

The resistance value of the detection resistor R2 (temperature detection resistance value) is, for example, 470Ω, and the resistance value of the disconnection detection resistor R1 (disconnection detection resistance value) is sufficiently larger, for example, 1.2 MΩ. It is said that. A protective diode 18 is provided in parallel with the transistor Tr1.

Two voltage dividing resistors R6 and R6 are provided between the output terminal P1 of the CPU 14 and the power supply terminal Vcc.
7 are connected in series, and the common connection point of the voltage dividing resistors R6 and R7 is connected to the base of the transistor Tr1. The output terminal P1 is connected to the ground terminal via the pull-down resistor R8. Now, as will be described later in detail, the output terminal P1 to Lo of the CPU 14
When a level signal is output, the transistor Tr1 is turned on, and when a Hi level signal is output from the output terminal P1, the transistor Tr1 is turned off.

The exhaust gas temperature sensor 12 is connected to the inverting input terminal (-) of the comparator 19 which constitutes a comparison circuit.
The voltage Vo at the common connection point (connection terminal 15) between the voltage dividing resistor circuit 17 and the voltage dividing resistor circuit 17 is input via the resistor R9. In addition, the voltage at the common connection point of the resistors R3 and R4 connected in series between the power supply terminal Vcc and the ground terminal is
The reference voltage Vs (about 2.5 V) is input to the non-inverting input terminal (+) of the comparator 19.
A feedback resistor R5 is connected between the output terminal of the comparator 19 and the non-inverting input terminal (+).
The output terminal of the comparator 19 is connected to the power supply terminal Vcc via the resistor R10. Also, the resistance R
The resistance values of 3, R4 and R5 are, for example, 1 kΩ and
It is set to 1.05 kΩ and 22.6 kΩ.

Further, the output terminal of the comparator 19 is connected to the base of a pnp type transistor Tr2, the emitter of the transistor Tr2 is connected to the power source terminal Vcc, and the collector is connected to the base of a pnp type transistor Tr3. Has been done. The base of the transistor Tr3 is connected to the ground terminal via the resistor R11.

The transistor Tr3 has an emitter connected to the power supply terminal Vcc and a collector npn.
-Shaped transistor Tr4 is connected to the base. Further, the base of the transistor Tr4 is connected to the ground terminal via the resistor R12. This transistor Tr
In 4, the emitter is connected to the ground terminal and the collector is connected to the connection terminal 16 via the resistor R13.

Thus, when the output terminal of the comparator 19 is at the Lo level, the transistor Tr2 is turned on, the transistor Tr3 is turned off, and the transistor Tr4 is turned on.
Is turned off, so that the exhaust temperature warning lamp 13 is not energized and turned off. When the output terminal of the comparator 19 becomes Hi level, contrary to the above, the transistor Tr2 is turned off, the transistor Tr3 is turned on, the transistor Tr4 is turned on, and the exhaust temperature warning lamp 13 is energized and lit. Is done.

On the other hand, one terminal of the inspection mode switch T1 is connected to the input terminal I1 of the CPU 14,
The other terminal of the inspection mode switch T1 is connected to the power supply terminal Vcc via the resistor R14. The input terminal I1 is connected to the ground terminal via the resistor R15. The inspection mode switch T1 is turned on and off (turned on when executing a diagnosis) by, for example, an existing terminal for exclusive use of the diagnosis.

In the normal state when the inspection mode switch T1 is off, the CPU 14 sets the output terminal P1 to Lo level to turn on the transistor Tr1 (normal mode), and the inspection mode switch T1 is turned on. In some cases, the output terminal P1 is set to Hi level to switch to the inspection mode in which the transistor Tr1 is turned off. Therefore, the inspection mode switches T1 and C
The PU 14 and the transistor Tr1 constitute a mode switching means.

Further, as will be described in detail in the following description of operation, by turning on and off the transistor Tr1,
The resistance value of the voltage dividing resistor circuit 17 connected in series with the exhaust temperature sensor 12 is switched. The exhaust temperature sensor 1 at this time is switched.
The voltage Vo at the common connection point between the voltage dividing resistor circuit 2 and the voltage dividing resistor circuit 17 is input to the inverting input terminal (−) of the comparator 19 via the resistor R9 and compared with the reference voltage Vs, so that the exhaust temperature in the normal mode is In the inspection mode, the exhaust temperature sensor 12 detects whether or not the exhaust temperature detected by the sensor 12 is abnormal.
It is possible to determine the presence or absence of disconnection. Therefore,
The disconnection judging means is composed of a comparison circuit including the comparator 19. Further, in the present embodiment, the result of the disconnection determination is output depending on whether the exhaust temperature warning lamp 13 is turned on or not.

Next, the operation of the above configuration will be described with reference to FIGS. As described above, when the vehicle is used normally, the inspection mode switch T1 is turned off, and the Lo level signal is output from the output terminal P1 of the CPU 14. At this time, the transistor Tr1 is on, and the voltage dividing resistance circuit 17 is in the normal mode in which the temperature detecting resistance value is set.

That is, in this normal mode, FIG.
As shown in (a) and FIGS. 3 and 4, the transistor T
Since r1 is turned on, the current i flows in the detection resistor R2 in the voltage dividing resistor circuit 17, and the resistance value is much larger than that of the detection resistor R2 (470Ω) provided in parallel with the current i. Almost no current flows through the disconnection detection resistor R1 having (1.2 MΩ). Therefore, the detection resistor R2 and the exhaust temperature sensor 12 are substantially connected in series, and a predetermined voltage Vcc is applied between them.
(5V) is applied. Then, the voltage Vo at the common connection point between the detection resistor R2 and the exhaust temperature sensor 12 passes through the resistor R9 and the inverting input terminal (−) of the comparator 19 is reached.
Is input to

The exhaust gas temperature sensor 12 has the characteristics shown in FIG. 5 and exhibits a high resistance value when the exhaust gas temperature is low, so that the voltage Vo at the common connection point becomes relatively large. , The input voltage to the comparator 19 is the reference voltage V
It is sufficiently larger than s. As a result, the output of the comparator 19 becomes Lo, and as a result, the exhaust temperature warning lamp 13
Remains off.

On the other hand, the exhaust temperature sensor 12 detects that the abnormal temperature (9
When a high temperature of 00 ° C. or higher is detected, the resistance value becomes extremely low (for example, 471Ω), the voltage Vo at the common connection point becomes small, and the input voltage to the comparator 19 becomes smaller than the reference voltage Vs. As a result, the comparator 1
The output of 9 becomes Hi, and as a result, the exhaust temperature warning lamp 13 is turned on. As described above, by monitoring the voltage Vo at the common connection point of the detection resistor R2 and the exhaust temperature sensor 12, it is possible to detect whether or not the exhaust temperature is abnormal.

On the other hand, at the time of inspection such as shipping of the vehicle, the switch T1 is turned on when the inspection operator performs a predetermined operation on the diagnostic-dedicated terminal or enters a diagnostic mode on the program. Like Then, as shown in FIGS. 3 and 4, the output terminal P1 of the CPU 14 is set to the Hi level and the transistor Tr1 is turned on.
Is turned off, and the voltage dividing resistance circuit 17 is switched to the inspection mode in which the resistance value for detecting disconnection is obtained.

That is, in this inspection mode, as shown in FIG.
As shown in (b), since the transistor Tr1 is turned off, in the voltage dividing resistor circuit 17, no current flows in the detection resistor R2, and the current i flows only in the disconnection detection resistor R1. Become. Therefore, the disconnection detection resistor R1
And the exhaust gas temperature sensor 12 are connected in series, and a predetermined voltage Vcc (5V) is applied between them.
Then, the voltage Vo at the common connection point of the disconnection detection resistor R1 and the exhaust temperature sensor 12 is transferred to the comparator 1 via the resistor R9.
9 is input to the inverting input terminal (-).

At this time, since the exhaust temperature sensor 12 is kept at room temperature (low temperature) during this inspection, the high resistance value (1
The resistance R1 for detecting disconnection
Since it also has a large resistance value (1.2 MΩ), the voltage Vo at the common connection point becomes small and the input voltage to the comparator 19 becomes smaller than the reference voltage Vs. As a result, the output of the comparator 19 becomes Hi, and as a result, the exhaust temperature warning lamp 13 is turned on.

On the other hand, at this time, if the exhaust temperature sensor 12 is disconnected, no current flows through the exhaust temperature sensor 12, so the voltage Vo at the common connection point becomes large (5 V), and the input to the comparator 19 is made. The voltage becomes higher than the reference voltage Vs. As a result, the output of the comparator 19 becomes Lo, and the exhaust temperature warning lamp 13 remains off.

As described above, during the inspection, when the exhaust temperature sensor 12 is normal (no disconnection) by monitoring the voltage Vo at the common connection point of the disconnection detection resistor R1 and the exhaust temperature sensor 12. When the exhaust temperature warning lamp 13 is turned on and the exhaust temperature sensor 12 is broken, the exhaust temperature warning lamp 13 is not turned on (remains off).
The inspector can easily see whether or not the exhaust temperature sensor 12 is broken by looking at the exhaust temperature warning lamp 13.
Note that FIG. 4 schematically shows the flow of processing when the above-described modes are executed.

As described above, according to the present embodiment, it is possible to detect whether or not the exhaust temperature sensor 12 is broken by simply providing the voltage dividing resistor circuit 17 whose resistance value can be switched and switching the resistance value. Therefore, unlike the conventional one in which the presence or absence of disconnection of the exhaust temperature sensor 12 is detected using the checker 5, at room temperature and without using the dedicated checker 5,
It has become possible to inspect whether the exhaust temperature sensor 12 is disconnected.

In this case, most of the circuit used for normal exhaust gas temperature detection can also be used for detecting disconnection of the exhaust gas temperature sensor 12, and only a few parts such as the resistor R1 for disconnection detection and the transistor Tr1 are added. Since it can be done with a simple circuit change, the existing CPU 14, the dedicated diagnosis terminal, and the existing exhaust temperature warning lamp 13 are used.
The configuration can be extremely simple and inexpensive. Further, the exhaust temperature sensor 12 can be detected for disconnection at a low temperature, and the checker 5 connection work and the like are not required, so that the inspection work requires little labor and can be performed by extremely simple work. Is.

(2) Second and Third Embodiments FIGS. 6 and 7 show the second and third embodiments (corresponding to claim 4) of the present invention, respectively, which correspond to the first embodiment.
It should be understood that this is a modification of the above embodiment, and instead of performing the mode switching by the command signal of the output terminal P1 of the CPU 14 in the first embodiment, the mode (the resistance value of the voltage dividing resistor circuit is changed by a dedicated switch. ) Is switched.

That is, the second embodiment shown in FIG. 6 has a voltage dividing resistor circuit 17 equivalent to that of the first embodiment, but has a circuit for turning the transistor Tr1 on and off. The switch T2 is inserted between the resistor R7 and the ground terminal in the electric path via the resistor R16.
As a result, by operating the switch T2,
The transistor Tr1 is switched on and off, and the normal mode and the inspection mode are switched.

In the third embodiment shown in FIG. 7, the voltage dividing resistor circuit 21, which is a voltage dividing means, is formed by connecting a series circuit of a detecting resistor R2 and a switch T3 and a disconnection detecting resistor R1 in parallel. The exhaust temperature sensor 12 is connected in series. As a result, when the switch T3 is operated, the resistance value of the voltage dividing resistor circuit 21 is also switched, and the normal mode and the inspection mode are switched.

According to the second and third embodiments, as in the first embodiment, the exhaust temperature sensor 12 is inspected for the presence or absence of wire breakage at room temperature without using the dedicated checker 5. It is possible to obtain the operation and effects such as the above, and in addition, it becomes possible to detect the disconnection without the CPU, and the invention can be applied to a vehicle having no CPU, for example.

(3) Fourth Embodiment FIGS. 8 and 9 show the fourth embodiment of the present invention (claims 1 and 2).
2, 3, 6, and 8), the same parts as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted, and the points different from the first embodiment will be mainly described below. explain.

In this embodiment, as shown in FIG.
Voltage dividing resistance circuit 17 connected in series with the exhaust temperature sensor 12
Is also provided with a resistor R1 for detecting disconnection, a resistor R2 for detection, a transistor Tr1 and the like.
4 is an output terminal P1 based on the inspection mode switch T1.
Is used to switch the transistor Tr1 on and off to switch the mode (resistance value of the voltage dividing resistor circuit 17). In this embodiment, the resistance value of the disconnection detection resistor R1 (disconnection detection resistance value) is set to 560 kΩ, and the resistance value of the detection resistor R2 (temperature detection resistance value) is set to 1 kΩ, for example. There is.

The voltage Vo at the common connection point (connection terminal 15) between the exhaust temperature sensor 12 and the voltage dividing resistance circuit 17 is input to the A / D converter 31 via the resistor R9. . The input terminal of the A / D converter 31 is further connected to the ground terminal via the capacitor C1. The output terminal of the A / D converter 31 is connected to the input terminal I2 of the CPU 14, and the voltage Vo is converted into a digital value and input to the CPU 14.

The output terminal P2 of the CPU 14 is pnp
-Type transistor Tr5 is connected to the base, the emitter of the transistor Tr5 is connected to the power supply terminal Vcc, and the collector is connected to the base of the npn-type transistor Tr6 via the resistor R18. The emitter of the transistor Tr6 is connected to the ground terminal and
The collector is connected to the connection terminal 16 and thus to the exhaust temperature warning lamp 13 via the resistor R19. Thus, when the output terminal P2 becomes Lo level, the exhaust temperature warning lamp 13 is turned on, and when the output terminal P2 becomes Hi level, the exhaust temperature warning lamp 13 is turned off.

Then, the CPU 14 compares the voltage Vo (digital value) input from the A / D converter 31 to the input terminal I2 with a preset threshold by the software configuration, and in the normal mode. In the above, the presence or absence of abnormality (high temperature) in the exhaust temperature is judged, and in the inspection mode, the presence or absence of disconnection of the exhaust temperature sensor 12 is judged. As shown in FIG. 9, at the output terminal P2, the Hi and Lo levels are switched according to the result of the determination.

Further, in this embodiment, the CPU 14
Is configured with a memory 32, and this memory 3
In 2, the judgment result of the disconnection detection in the inspection mode is stored. Then, the stored contents of the memory 32 are read by the output device 34 connectable via the connector 33 by using a diag code.

In the above structure, the operation as shown in FIG. 9 is executed. That is, during normal use of the vehicle, the inspection mode switch T1 is turned off, the output terminal P1 of the CPU 14 becomes Lo level, the transistor Tr1 is turned on, and the voltage dividing resistance circuit 17 becomes a temperature detecting resistance value. The mode is set. At this time, the resistance of the entire voltage dividing resistor circuit 17 is about 1 kΩ. Then, the voltage Vo at the common connection point of the voltage dividing resistance circuit 17 and the exhaust temperature sensor 12
Is input to the A / D converter 31 and is input to the input terminal I2 of the CPU 14 as a digital value.

At this time, if the exhaust temperature is abnormally high (900 ° C. or higher), the resistance of the exhaust temperature sensor 12 decreases to 431Ω and the voltage Vo decreases to about 1.5V. So C
The PU 14 determines whether the voltage Vo (digital value) is 1.5 V or less or 1.6 V or more. If the voltage Vo is 1.6 V or more, it is determined that the exhaust temperature is normal and the output terminal P2 is set to the Hi level. The exhaust temperature warning lamp 13 is turned off. On the other hand, 1.
If it is 5 V or less, it is determined that the exhaust temperature has become an abnormally high temperature, and the output terminal P2 is set to the Lo level, whereby the exhaust temperature warning lamp 13 is turned on.

On the other hand, in the inspection mode in which the inspection mode switch T1 is turned on, the output terminal P1 becomes Hi level and the transistor Tr1 is turned off, the resistance value of the voltage dividing resistor circuit 17 (disconnection detecting resistor R1) is 560 kΩ. It is said that At this time, if there is no disconnection of the exhaust temperature sensor 12 (1 MΩ at room temperature), the voltage Vo becomes about 3.2 V, and if the temperature rises a little, the voltage Vo falls a little lower than that. However, if the exhaust temperature sensor 12
If the disconnection occurs, the voltage Vo becomes 5V.

Therefore, the CPU 14 uses the A / D converter 31.
If the voltage Vo (digital value) output from is 3.2 V or less, it is determined to be normal and the output terminal P2 is set to the Lo level, whereby the exhaust temperature warning lamp 13 is turned on. On the other hand, if the voltage Vo is 5 V, it is determined that the wire is broken, the output terminal P2 is set to the Hi level, and the exhaust temperature warning lamp 13 remains off. At this time, the data of the detection result of the presence or absence of the disconnection of the exhaust temperature sensor 12 can be stored in the memory 32.

According to this embodiment, as in the first embodiment, it is possible to inspect the exhaust temperature sensor 12 for the presence or absence of disconnection at room temperature without using the dedicated checker 5. became. Then, in this embodiment, the CPU 1
4 indicates an exhaust temperature abnormality or an exhaust temperature sensor 1 based on the voltage Vo.
Since the presence or absence of disconnection of No. 2 is determined, it becomes possible to set an appropriate threshold value according to the mode, and the exhaust temperature warning lamp 13 can be arbitrarily set to be turned on and off. Is possible.

Moreover, it is possible to switch to the inspection mode by the operation of the inspection operator, and the CPU 14 can execute the self-diagnosis of the presence or absence of the disconnection of the exhaust temperature sensor 12 even when the vehicle is normally used. It will be possible. In this case, the self-diagnosis of the presence or absence of disconnection can be performed every time the CPU 14 is started up or every predetermined trip. At this time, it is not necessary to particularly notify by the exhaust temperature warning lamp 13, and the diagnosis result is stored in the memory 32. Then, the data may be read at the time of inspection of the vehicle.

The present invention is not limited to the above-described embodiments, and the resistance value of each resistor may be appropriately determined according to the characteristics of the temperature sensor, the overall circuit configuration, and the like. Further, the present invention is not limited to the detection of the disconnection of the exhaust temperature sensor of the automobile, but can be applied to the detection of the disconnection of various temperature sensors used for various purposes, etc. It is a thing.

[0054]

As is apparent from the above description, according to the temperature sensor circuit of the present invention, the temperature is detected based on the voltage at the common connection point between the temperature sensor and the voltage dividing means. The resistance value of the voltage dividing means, the mode switching means for switching from the temperature detection resistance value for the normal mode at the time of temperature detection to the disconnection detection resistance value for the inspection mode different from that, and the mode switching means Since the disconnection determination means for determining the presence / absence of disconnection of the temperature sensor based on the voltage at the common connection point when the resistance value of the pressure means is switched to the resistance value for disconnection detection is provided at room temperature and exclusively. It is possible to inspect whether or not the temperature sensor has a wire breakage while eliminating the need for a checker, which in turn makes the configuration extremely simple and inexpensive. Labor required for inspection work is one that exhibits an excellent practical effect that it is possible to dispense with an extremely simple work not applied most.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a temperature sensor circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a main part for explaining the operation.

FIG. 3 is a diagram for explaining the operation in each mode.

FIG. 4 is a flow chart schematically showing the operation in each mode.

FIG. 5 is a diagram showing characteristics of an exhaust temperature sensor.

FIG. 6 is a circuit configuration diagram of a main part showing a second embodiment of the present invention.

FIG. 7 is a circuit configuration diagram of a main part showing a third embodiment of the present invention.

FIG. 8 is a view corresponding to FIG. 1, showing a fourth embodiment of the present invention;

FIG. 9 is a view corresponding to FIG.

FIG. 10 is a circuit configuration diagram showing a conventional example.

[Explanation of symbols]

In the drawing, 11 is a circuit main part, 12 is an exhaust temperature sensor (temperature sensor), 13 is a warning light, 14 is a CPU, 17 and 21 are voltage dividing resistor circuits (voltage dividing means), 19 is a comparator (comparing circuit), 31 is an A / D converter, 32 is a memory, R1 is a resistance for disconnection detection, R2 is a detection resistance, Tr1 is a transistor, P1 and P2 are output terminals, I1 and I2 are input terminals, and T
1, T2 and T3 indicate inspection mode switches.

Claims (8)

[Claims] 1. A predetermined voltage is applied between a temperature sensor whose resistance value changes according to the detected temperature and a voltage dividing means connected in series with this temperature sensor and having a resistance element, whereby the temperature sensor and the voltage dividing means are connected to each other. Of detecting the temperature based on the voltage of the common connection point, the resistance value of the voltage dividing means, for the inspection mode different from the temperature detection resistance value for the normal mode at the time of detecting the temperature Mode switching means for switching to the resistance value for detecting disconnection, and disconnection of the temperature sensor based on the voltage at the common connection point when the resistance value of the voltage dividing means is switched to the resistance value for detecting disconnection by the mode switching means. A temperature sensor circuit, comprising: a disconnection determining means for determining the presence or absence of 2. A temperature sensor is provided to detect whether or not there is an abnormality in the exhaust temperature of the vehicle, and the temperature sensor is an exhaust temperature sensor whose resistance value decreases as the exhaust temperature increases, and the partial pressure The means includes a detection resistor having a small temperature detection resistance value, and a disconnection detection resistor having a sufficiently large disconnection detection resistance value inserted in parallel with the detection resistor, and 2. The temperature sensor circuit according to claim 1, wherein the mode switching means includes a switch element that switches the energization of the resistors. 3. The switch element comprises a transistor, and the mode switching means is configured to turn on and off the transistor according to a command signal from a CPU for vehicle control. Temperature sensor circuit. 4. The temperature sensor circuit according to claim 2, wherein the switch element comprises a dedicated switch. 5. The temperature sensor circuit according to claim 1, wherein the disconnection determination unit includes a comparison circuit that compares the voltage at the common connection point with a reference voltage. . 6. The disconnection determining means determines the presence / absence of disconnection based on an A / D converter that A / D converts the voltage at the common connection point and an output signal from the A / D converter.
The temperature sensor circuit according to claim 1, wherein the temperature sensor circuit includes U and U. 7. Depending on the judgment result of the disconnection judging means,
The temperature sensor circuit according to claim 1, wherein the temperature sensor circuit is configured to light an existing warning light. 8. The determination result data of the disconnection determination means is stored in a memory, and the determination result data can be read from the memory. Temperature sensor circuit.