JP2010007631A - Method and device for detecting failure of thermostat - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a failure of a thermostat with sufficient accuracy even during the operation of a heater for air conditioning. <P>SOLUTION: A device for detecting the failure of the thermostat 17 is provided with a heater operation determination means 22 for determining based on temperatures T1, T2 of cooling water detected by first and second water temperature sensors 11, 12 positioned at an upstream side and a downstream side of a heater core 13A whether the heater for air-conditioning 13 operates or not, a failure determination means 21 for determining based on at least one of the detected temperatures T1, T2 by both the temperature sensors 11, 12 whether the thermostat 17 fails or not, and a correction means 23 correcting a temperature of cooling water checked by the failure determination means 21 or a threshold Y for failure determination compared with it to a direction canceling effect of the heater 13 for air conditioning when the heater operation determination means 22 determines that the heater 13 for air conditioning operates. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a first cooling water passage in which a heater core of an air conditioning heater that uses heat of cooling water led out from an engine body is provided in the middle portion, and a branch portion extending from the first cooling water passage. An engine comprising: a second cooling water passage provided with a radiator for heat dissipation; and a thermostat that opens when the cooling water is at a predetermined temperature or higher and allows the cooling water to flow into the second cooling water passage from the first cooling water passage. The present invention relates to an apparatus and a method for detecting a failure of the thermostat in the cooling apparatus.

  Conventionally, as shown in Patent Document 1 below, in a thermostat failure detection device for an internal combustion engine that detects a failure of a thermostat provided in a cooling circulation path for cooling the internal combustion engine, the temperature of the cooling water when the thermostat is normal Is detected based on the water temperature at the start of the internal combustion engine, the elapsed time, etc., and the estimated cooling water temperature is compared with the actually measured actual water temperature to detect the failure of the thermostat. ing.

  However, when the heater core of the air conditioning heater (heating device) that uses the heat of the cooling water is provided in the middle of the cooling circulation path, the heat of the cooling water is taken away by the heater core. Otherwise, the failure of the thermostat cannot be accurately detected. Therefore, in the literature 1, for example, the following method is employed to prevent erroneous detection of a thermostat failure.

  First, the first method is to prevent erroneous detection of a thermostat failure by prohibiting the process of detecting the failure of the thermostat when it is determined that the air conditioning heater is operating. (Refer to claim 10 and paragraph 0074 of the same document).

Next, in the second method, even when the air conditioning heater is in operation, the cooling water temperature is not affected immediately after the start of the internal combustion engine and for a predetermined period thereafter (that is, the influence of the operation of the air conditioning heater is not affected). By detecting the deviation between the estimated value of the cooling water temperature and the actual water temperature at both timings, the failure of the thermostat is detected in consideration of the effect of the operation of the air conditioning heater. More specifically, in the second method, the deviation between the estimated value of the cooling water temperature and the actual water temperature is integrated over a predetermined period immediately after the start of the internal combustion engine, and the integrated value is compared with a predetermined threshold value to increase or decrease the magnitude. In addition to the determination (first determination process), the same process as described above is performed over a predetermined period thereafter (second determination process), and a thermostat failure is detected based on these two determination processes. (See Example 1 of the same document).
JP 2001-349218 A

  However, in the first method, since the failure of the thermostat cannot be detected during the operation of the air conditioning heater, the cooling water temperature of the internal combustion engine is appropriately set when the air conditioning heater continues to operate for a long period of time. There is a problem that failure of the thermostat, which plays an important role in maintaining, cannot be detected early.

  On the other hand, as in the second method, processing such as examining the deviation between the estimated value of the cooling water temperature and the actual water temperature is executed including immediately after the start of the internal combustion engine that is not affected by the heater operation. In this case, since the failure of the thermostat can be detected regardless of whether the air conditioning heater is operated, it is advantageous in that the delay in finding the failure as described above can be prevented. However, such a method is considered to have a problem in securing sufficient accuracy of thermostat failure detection.

  That is, immediately after the start of the internal combustion engine, which is thought to have no effect on the cooling water temperature due to the operation of the air conditioning heater, it is considered that the influence of the thermostat failure is quite small, so the thermostat failure has occurred. However, the deviation between the estimated value of the cooling water temperature and the actual water temperature may not appear clearly, and as a result, the thermostat may be overlooked.

  The present invention has been made in view of the above circumstances, and provides a thermostat failure detection device and a detection method capable of detecting a thermostat failure with sufficient accuracy even during operation of an air conditioning heater. With the goal.

  In order to solve the above-mentioned problems, the invention according to claim 1 of the present application includes a first cooling water channel provided with a heater core of an air conditioning heater that uses heat of cooling water derived from the engine main body in the middle. The second cooling water passage that extends so as to branch off from the first cooling water passage and is provided with a radiator for heat dissipation in the middle thereof, and opens when the cooling water is at a predetermined temperature or more, and opens from the first cooling water passage. A device for detecting a failure of the thermostat in a cooling device for an engine having a thermostat for allowing cooling water to flow into the second cooling water channel, the first water temperature detecting the temperature of the cooling water flowing from the engine body to the heater core. Detection means, second water temperature detection means for detecting the temperature of the cooling water flowing from the heater core to the engine body, and the temperature of the cooling water from the valve opening temperature of the thermostat When the engine is cold, the heater operation determining means for determining whether or not the air conditioning heater is operating based on the temperature of the cooling water detected by the both detecting means, and also when the engine is cold, Based on the temperature of the cooling water detected by at least one of the two detection means, a failure determination means for determining whether the thermostat has failed or not, and the air conditioning heater is operated by the heater operation determination means. Correction means for correcting the temperature of the cooling water checked by the failure determination means or the failure determination threshold value to be compared with this in a direction to cancel the influence of the operation of the air conditioning heater. It is characterized by comprising.

  According to the present invention, it is determined whether or not the air conditioning heater is operating based on the temperature of the cooling water detected upstream and downstream of the heater core, and the air conditioning heater is operating here. If determined, the temperature of the cooling water checked by the failure determination means for determining the failure of the thermostat or the failure determination threshold value compared with the temperature is corrected so as to cancel the influence of the operation of the air conditioning heater. As a result, even if the air conditioning heater is operating, it is possible to effectively prevent a malfunction of the thermostat due to a decrease in the temperature of the cooling water due to the influence, and the operation of the air conditioning heater can be prevented. Regardless of the presence or absence, a thermostat failure can always be detected with stable high accuracy.

  When the downstream end of the second cooling water channel is connected to the downstream side of the first cooling water channel by a predetermined distance from the heater core, the side closer to the outlet of the heater core than the connection portion, It is preferable that a second water temperature detecting means is provided (claim 2).

  According to this configuration, when the air conditioning heater is operated, the temperature of the cooling water lowered by the influence can be detected on the side closer to the outlet portion of the heater core. There is an advantage that it can be determined.

  The invention according to claim 3 of the present application includes a first cooling water channel provided with a heater core of an air conditioning heater that uses heat of cooling water derived from the engine body, and a branch from the first cooling water channel. And a second cooling water channel provided with a radiator for heat dissipation in the middle thereof, and when the cooling water is at a predetermined temperature or higher, the valve is opened to supply the cooling water from the first cooling water channel to the second cooling water channel. A method of detecting a failure of the thermostat in an engine cooling device having an inflow thermostat, wherein a temperature value is obtained from a first water temperature detecting means for detecting a temperature of cooling water flowing from the engine body to a heater core. A first step, a second step of acquiring a temperature value from a second water temperature detecting means for detecting the temperature of the cooling water flowing from the heater core to the engine body, and the cooling water And determining whether or not the air conditioning heater is operating based on the temperature of the cooling water detected by the two detection means when the engine is colder than the valve opening temperature of the thermostat. And a fourth step of determining whether or not the thermostat has failed based on the temperature of the cooling water detected by at least one of the detection means when the engine is cold. When it is determined in the third step that the air-conditioning heater is operating, the temperature of the cooling water checked in the fourth step or a failure determination threshold value compared with the temperature is determined as the air-conditioning The correction is made in a direction that cancels the influence of the heater operation.

  Even in the case of the present invention, the same effect as that of the invention according to the first aspect can be obtained.

  As described above, according to the thermostat failure detection apparatus and detection method of the present invention, it is possible to detect a thermostat failure with sufficient accuracy even during operation of the air conditioning heater.

  FIG. 1 is a diagram schematically showing an engine cooling device 1 to which a thermostat failure detection device according to the present invention is applied. The engine cooling device 1 shown in the figure includes a first cooling water passage 5 provided with a heater core 13A for heating the cooling water for heating, and for releasing the cooling water heat to the outside. The radiator 15 has the 2nd cooling water channel 6 provided in the middle part. The heater core 13A constitutes a part of an air conditioning heater 13 (heating device) that supplies warm air into the passenger compartment, and is provided as a heat exchanger for absorbing the heat of cooling water and using it for heating. It has been.

  The first cooling water passage 5 is disposed between the upstream side pipe 5A disposed between the engine body 3 and the inlet portion of the heater core 13A, and between the outlet portion of the heater core 13A and the engine body 3. The cooling water led out from the engine body 3 is supplied to the heater core 13A through the upstream pipe 5A and then returned to the engine body 3 through the downstream pipe 5B. It has become.

  A cooling water pump 19 for pumping the cooling water is provided in the middle of the downstream pipe 5B. When the engine starts, the cooling water is circulated by the operation of the cooling water pump 19, The engine body 3 is cooled by the circulating flow.

  The second cooling water passage 6 branches from the upstream piping 5A of the first cooling water passage 5 and extends to the inlet portion of the radiator 15, and extends from the outlet portion of the radiator 15 to extend the first cooling water. And a downstream pipe 6B connected to a middle portion of the downstream pipe 5B of the water channel 5.

  For the connecting portion S between the downstream pipe 6B of the second cooling water channel 6 and the downstream pipe 5B of the first cooling water channel 5, for example, a mechanical detection type using a bimetal or the like, or an electric detection type using a thermistor or the like. A thermostat 17 comprising a switching valve is provided.

  The thermostat 17 closes when the engine coolant temperature is lower than a predetermined temperature and closes the connection portion S, thereby cooling water between the first coolant channel 5 and the second coolant channel 6. It is configured to block the flow. And while the thermostat 17 is maintained in the valve-closed state in this way, the cooling water led out from the engine body 3 passes through the first cooling water passage 5 without being supplied to the radiator 15 side, and the heater core 13A. And then returned to the engine body 3.

  On the other hand, when the cooling water temperature of the engine becomes equal to or higher than the predetermined temperature, the thermostat 17 is opened and the connecting portion S is communicated, so that the cooling water between the first cooling water passage 5 and the second cooling water passage 6 is provided. The high-temperature cooling water led out from the engine body 3 branches from the first cooling water channel 5 and flows into the second cooling water channel 6. That is, the high-temperature cooling water led out from the engine body 3 is not only supplied to the heater core 13A through the first cooling water channel 5 but also to the radiator 15 through the second cooling water channel 6. After being cooled, it is returned to the engine body 3 again.

  A first water temperature sensor 11 (corresponding to the first water temperature detecting means according to the present invention) for detecting the temperature of the cooling water flowing from the engine body 3 to the heater core 13A is provided in the upstream side piping 5A of the first cooling water channel 5. The downstream pipe 5B is provided with a second water temperature sensor 12 (corresponding to the second water temperature detecting means according to the present invention) for detecting the temperature of the cooling water flowing from the heater core 13A to the engine body 3. It has been. Both the water temperature sensors 11 and 12 are electrically connected to the controller 20 for engine control, and the temperature of the cooling water detected by the both water temperature sensors 11 and 12 is input to the controller 20 as an electric signal. It is like that. The controller 20 is electrically connected to a crank angle sensor 25 for detecting a rotation angle of a crankshaft (not shown) of the engine body 3.

  FIG. 2 is a diagram showing the change over time of the detected temperatures by the first and second water temperature sensors 11 and 12. This figure shows the temperature change of the cooling water when the engine is cold started, and shows the state before the temperature of the cooling water reaches the valve opening temperature of the thermostat 17 (indicated by Ts in the figure). In this figure, T1 indicates the temperature of the cooling water detected by the first water temperature sensor 11, and T2 indicates the temperature of the cooling water detected by the second water temperature sensor 12. . Hereinafter, the detection temperature T1 detected by the first water temperature sensor 11 is referred to as a first detection temperature T1, and the detection temperature T2 detected by the second water temperature sensor 12 is referred to as a second detection temperature T2. Further, the values (both initial values of the detected temperatures) of the detected temperatures T1 and T2 at the time of starting the engine are T10 and T20.

  Specifically, in the graph of FIG. 2, four types of temperature lines classified according to the states of the air conditioning heater 13 and the thermostat 17 are shown as P, Q1, Q2, and R, respectively. Among these, the temperature line P represents the time change of the first and second detected temperatures T1 and T2 when the air conditioning heater 13 is inactive and the thermostat 17 is normal, and the temperature lines Q1 and Q2 are for air conditioning. Temporal changes in the first and second detection temperatures T1 and T2 when the heater 13 is operating and the thermostat 17 is normal, the temperature line R indicates the second detection when the thermostat 17 is out of order. The time change of temperature T2 is shown, respectively. The temperature line P is common to the first and second detection temperatures T1 and T2. This is because if the air-conditioning heater 13 is inactive, the cooling water temperature hardly changes before and after the heater core 13A, and the first detection temperature T1 and the second detection temperature T2 are substantially the same.

  Next, the failure diagnosis function of the controller 20 will be described with reference to the graph of FIG. The controller 20 includes a conventionally known CPU, various memories, and the like, and has a failure determination means 21, a heater operation determination means 22, and a correction means 23 as functional elements as shown in FIG.

  The failure determination means 21 is a cooling water detected by at least one of the first and second water temperature sensors 11 and 12 when the temperature of the cooling water is cold of the engine lower than the valve opening temperature of the thermostat 17. It is determined whether or not the thermostat 17 has failed based on the temperature (that is, at least one of the first and second detection temperatures T1 and T2). That is, when the engine is cold, the thermostat 17 should not normally open, but a failure (open failure) of the thermostat 17 occurs, and the thermostat 17 opens even though it is cold. Then, the cooling water derived from the engine body 3 flows into the radiator 15 that should not flow in, and therefore, as shown by the temperature line R in FIG. It becomes dull compared to the temperature line (P or Q1, Q2).

  Therefore, the failure determination means 21 checks the increase in the cooling water temperature after a predetermined time has elapsed from the time of starting the engine, based on the detection value of at least one of the first and second water temperature sensors 11 and 12. Thus, it is determined whether or not the thermostat 17 has failed. Although the failure detection of the thermostat 17 can be performed using either or both of the water temperature sensors 11 and 12, the second water temperature located downstream of the heater core 13A in this embodiment. A failure of the thermostat 17 is detected based on the detection value (second detection temperature T2) of the sensor 12.

  The heater operation determining means 22 is configured to detect the temperature of the cooling water (first and second detected temperatures T1 and T1) detected by the first and second water temperature sensors 11 and 12 located upstream and downstream of the heater core 13A. Based on T2), it is determined whether or not the air conditioning heater 13 is operating. That is, in the state where the air conditioning in the passenger compartment is heated and the air conditioning heater 13 is operating, the heat of the cooling water is taken away by the heater core 13A of the air conditioning heater 13, so that the temperature lines Q1 and Q2 in FIG. As shown, a predetermined temperature difference is generated between the first detection temperature T1 and the second detection temperature T2. Therefore, the heater operation determination means 22 determines whether or not the air conditioning heater 13 is operating by examining this temperature difference.

  When the heater operation determining means 22 determines that the air conditioning heater 13 is operating, the correcting means 23 is the temperature of the cooling water checked by the failure determining means 21 (second detection in this embodiment). The value of the temperature T2) is corrected so as to cancel the influence of the operation of the air conditioning heater 13. That is, when the air conditioning heater 13 is in operation, the value of the second detected temperature T2 is the value of the second detected temperature T2 because the heat absorbed by the heater core 13A of the air conditioning heater 13 is not operating. 2 (see the temperature line Q2 and the temperature line P in FIG. 2), the correction means 23 corrects the measured value to be added so as to cancel out the decrease in temperature.

  Next, a specific procedure of the control operation by the controller 20 configured as described above will be described based on the flowchart of FIG. When the ignition switch (not shown) is turned on and the power from the battery is supplied to the controller 20, and the flowchart of FIG. 3 starts, the controller 20 first starts based on the detection signal input from the crank angle sensor 25. Then, the current engine speed Ne is calculated, and it is determined whether or not the engine is started by determining whether or not the value is equal to or greater than a predetermined value Ne0 (for example, about 600 rpm). Is executed (step S1).

  When it is determined YES in step S1 and it is confirmed that the engine has started, the controller 20 determines the coolant temperature (second detected temperature) T2 detected by the second water temperature sensor 12 at this time. A process of reading and acquiring this as the second detected temperature T20 when the engine is started is executed (step S3).

  Next, the controller 20 determines whether or not the second detected temperature T2 input from the second water temperature sensor 12 is lower than the valve opening temperature Ts (see FIG. 2) of the thermostat 17 (step S5). When it is determined as YES and it is confirmed that T2 <Ts, that is, when it is confirmed that the engine is in a cold state, the built-in timer starts counting (step S7). Based on the count value, a process of determining whether or not the time t has elapsed since the engine start (step S9).

  On the other hand, if it is determined NO in step S5 and it is confirmed that T2 ≧ Ts, that is, if it is confirmed that the engine is in a warm state, the count value of the timer is reset (step S11), the flow ends without performing processing such as the operation determination of the air conditioning heater 13 as described later.

  When it is determined YES in step S9 and it is confirmed that the time t has elapsed since the engine start, the controller 20 detects the detected values input from the first and second water temperature sensors 11 and 12 at that time. Are read as first and second detection temperatures T1 and T2 at the time when the time t has passed (step S13), and the difference between the two detection temperatures T1 and T2 is greater than or equal to a predetermined threshold value X. By determining whether or not there is, a process for determining whether or not the air-conditioning heater 13 is operating is executed (step S15).

  That is, when the air conditioning heater 13 is in operation, a predetermined amount of heat is absorbed by the heater core 13A of the air conditioning heater 13, so that the time t has elapsed as shown by the temperature lines Q1 and Q2 in FIG. At that time, the value of the second detection temperature T2 (point c on the temperature line Q2) becomes lower than the value of the first detection temperature T1 (point b on the temperature line Q1). Therefore, the controller 20 checks whether or not the temperature difference between the detected temperatures T1 and T2 (ΔTx in the figure) is equal to or larger than a predetermined threshold value X to determine whether or not the air conditioning heater 13 is in operation. Determine. Specifically, the controller 20 determines that the air conditioning heater 13 is operating if the temperature difference ΔTx (= T1−T2) is equal to or greater than the threshold value X, and if the temperature difference ΔTx is smaller than the threshold value X, the air conditioning heater. It is determined that 13 is not activated (not activated). As described above, the determination process (step S15) here is executed by the heater operation determination unit 22 of the controller 20.

  If it is determined YES in step S15 and it is determined that the air conditioning heater 13 is operating, the controller 20 sets the air conditioning to the value of the second detected temperature T2 when the time t has elapsed. A process of adding the correction amount α in consideration of the temperature decrease due to the influence of the heater 13 is executed (step S17).

  That is, as can be seen from a comparison between the temperature line Q2 and the temperature line P in FIG. 2, when the time t has elapsed since the engine started, the value of the second detected temperature T2 when the heater is activated (on the temperature line Q2). The point c) is lower than the value of the second detected temperature T2 when the heater is not operated (point a on the temperature line P) by the amount of heat absorbed by the heater core 13A. When the controller 20 adds the correction amount α to the second detected temperature T2 detected by the second water temperature sensor 12 in order to cancel the decrease, the air conditioning heater 13 is not operated. A correction is made to raise the measured value to the temperature at which the temperature is expected to have been reached. The correction amount α may be a value determined in advance through experiments, calculations, or the like, or may be obtained empirically from the actual value of the cooling water temperature measured during the previous operation. Good. Further, as described above, the determination process (step S <b> 17) here is executed by the correction unit 23 of the controller 20.

  When the second detected temperature T2 is corrected in this way, the controller 20 determines the difference between the corrected temperature value T2 + α and the second detected temperature T20 at the time of engine start obtained in step S3, that is, (T2 + α ) -T20 is performed to determine whether or not the thermostat 17 is out of order by determining whether or not T20 is smaller than a predetermined threshold Y (step S19).

  That is, if the thermostat 17 is normal, the thermostat 17 is closed when the engine is cold, and the supply of the cooling water to the radiator 15 is stopped, so that the temperature of the cooling water rises relatively quickly. For this reason, when the time t has elapsed since the engine start, a sufficiently large temperature difference (ΔTy in the figure) is present between the temperature value T2 + α corrected in step S17 and the temperature T20 at the time of engine start. ) Should occur. Therefore, the controller 20 determines that the thermostat 17 is normal if the temperature difference ΔTy (= (T2 + α) −T20) is equal to or greater than the predetermined threshold Y, and conversely, if the temperature difference is smaller than the threshold Y, the thermostat 17 Determine that there is a failure. As described above, the determination process (step S19) here is executed by the failure determination means 21 of the controller 20.

  When it is determined YES in step S19 and it is determined that the thermostat 17 is malfunctioning, the controller 20 informs an occupant or the like that the thermostat 17 is malfunctioning on an instrument panel or the like in the passenger compartment. A process of operating a predetermined alarm device (for example, a warning lamp) provided is executed (step S21). On the other hand, if it is determined NO in step S19, the thermostat 17 is normal, and thus the series of flows is terminated without operating the alarm device.

  As described in steps S17 to S21 above, when the air conditioning heater 13 is operating (YES in step S15), the second detected temperature T2 detected by the second water temperature sensor 12 is the air conditioning heater. The increase is corrected by the influence of the operation of the heater 13, and the presence or absence of a failure of the thermostat 17 is determined based on the corrected detected temperature T2 + α. On the other hand, when it is determined NO in step S15 and it is confirmed that the air conditioning heater 13 is not operating, the controller 20 detects the second detected temperature T2 after the elapse of time t from the engine start, the engine 20 By determining whether or not the difference from the second detected temperature T20 at the time of starting, that is, T2−T20 is smaller than a predetermined threshold Y, it is determined whether or not the thermostat 17 has failed (step S23). That is, when the air-conditioning heater 13 is not operating, the detected temperature is not corrected as described above, and the failure determination of the thermostat 17 is performed by the second detected temperature T2 input from the second water temperature sensor 12. The value of is used as it is. And based on the result, processing, such as operating an alarm device (Step S21), is performed.

  As described above, the failure detection device for the thermostat 17 of the present embodiment is the first cooling water channel in which the heater core 13A of the air conditioning heater 13 that uses the heat of the cooling water derived from the engine body 3 is provided in the middle. 5 and the second cooling water passage 6 which extends so as to branch off from the first cooling water passage 5 and is provided with a radiator 15 for heat radiation in the middle thereof, and is opened when the cooling water is at a predetermined temperature or higher. A failure of the thermostat 17 in the engine cooling device 1 including a thermostat 17 for flowing cooling water from the first cooling water path 5 into the second cooling water path 6 is detected. The failure detection device for the thermostat 17 detects the temperature of the cooling water flowing from the engine body 3 to the heater core 13A and the temperature of the cooling water flowing from the heater core 13A to the engine body 3. The temperature of the cooling water detected by the water temperature sensors 11 and 12 (first and second) when the engine is cold when the temperature of the cooling water is lower than the valve opening temperature Ts of the thermostat 17 and the second water temperature sensor 12 to be detected. Based on the second detected temperature T1, T2), the heater operation determining means 22 for determining whether or not the air conditioning heater 13 is operating, and also the second water temperature sensor 12 when the engine is cold. Failure determination means 2 for determining whether or not the thermostat 17 has failed based on the temperature of the cooled cooling water (second detected temperature T2). When the heater operation determining means 22 determines that the air conditioning heater 13 is operating, the cooling water temperature (second detected temperature T2) checked by the failure determining means 21 is determined as the air conditioning. Correction means 23 for correcting in a direction to cancel the influence of the operation of the heater 13. According to the failure detection device for the thermostat 17 having such a configuration, there is an advantage that the failure of the thermostat 17 can be detected with sufficient accuracy even while the air conditioning heater 13 is in operation.

  That is, in the above embodiment, it is determined whether or not the air conditioning heater 13 is operating based on the first and second detected temperatures T1 and T2 detected on the upstream side and the downstream side of the heater core 13A. When it is determined that the air-conditioning heater 13 is in operation, the cooling water temperature (second detected temperature T2 in the above embodiment) that is checked by the failure determination means 21 that determines the failure of the thermostat 17 is used as the air-conditioner. Since the influence of the operation of the heater 13 is corrected in a direction that cancels out, the malfunction of the thermostat 17 is erroneously detected due to the temperature drop of the cooling water due to the influence even when the air conditioning heater 13 is operating. It is possible to effectively prevent the failure of the thermostat 17 with a stable and high accuracy at all times regardless of whether or not the air conditioning heater 13 is activated. That.

  Further, the temperature of the cooling water is detected by two water temperature sensors 11 and 12 provided on the upstream side and the downstream side of the heater core 13A, and based on the two detected temperatures (first and second detected temperatures T1 and T2). Thus, according to the above configuration in which the presence or absence of the operation of the air conditioning heater 13 is determined, there is an advantage that the operation of the air conditioning heater 13 can be detected with higher accuracy.

  That is, it is conceivable that the engine coolant temperature changes slightly due to the influence of other factors such as the outside air temperature, in addition to the influence due to the operation of the air conditioning heater 13, for example, a single water temperature sensor. If it is attempted to determine whether or not the air conditioning heater 13 is activated, the air conditioning heater 13 may be erroneously determined to be operating due to the influence of other factors as described above. For example, in Patent Document 1 described above, since a structure using such a single water temperature sensor is employed (see FIG. 1 and the like in the same document), it is possible to accurately determine whether or not the air conditioning heater 13 is activated. As a result, there is a possibility that a failure of the thermostat 17 is erroneously detected.

  On the other hand, in the above embodiment, by detecting the cooling water temperature on the upstream side and the downstream side of the heater core 13A, only the influence due to the operation of the air conditioning heater 13 is accurately based on the difference between the detected temperatures T1 and T2. Since it can be recognized, there is an advantage that the presence or absence of the operation of the air conditioning heater 13 can be determined with higher accuracy, and erroneous detection of a failure of the thermostat 17 can be more effectively prevented.

  In particular, in the above embodiment, the downstream end of the second cooling water channel 6 (that is, the outlet of the downstream pipe 6B) is connected to a position S that is a predetermined distance downstream of the heater core 13A in the first cooling water channel 5. Since the second water temperature sensor 12 is provided on the side closer to the outlet of the heater core 13A than the connection portion S, the temperature of the cooling water decreased due to the influence of the air conditioning heater 13 during operation. Can be detected on the side closer to the outlet of the heater core 13A, and the presence / absence of the operation of the air conditioning heater 13 can be determined with higher accuracy.

  In the above embodiment, if it is determined that the air conditioning heater 13 is in operation, the temperature detected by the second water temperature sensor 12 (second detection temperature) T2 is affected by the operation of the air conditioning heater 13. The correction amount α determined in consideration is added, and the difference between the corrected temperature value T2 + α and the second detected temperature T20 at the time of engine start, that is, (T2 + α) −T20 is determined from a predetermined threshold Y. The thermostat 17 is determined whether or not there is a failure (see steps S17 and S19 in FIG. 3), but instead of adding the correction amount α to the detected temperature T2, the failure is detected. The determination threshold Y may be corrected by the influence of the operation of the air conditioning heater 13, and the presence or absence of a failure of the thermostat 17 may be determined using the corrected threshold.

  Specifically, in order to correct the threshold value, a value obtained by subtracting the correction amount α from the original threshold value Y, that is, Y−α may be used as the corrected threshold value. Then, if the corrected threshold Y-α is Y ′, using this threshold Y ′, it is determined in step S19 whether or not the determination formula T2-T20 <Y ′ is satisfied. Similar to the above embodiment, it is possible to determine the presence or absence of a failure of the thermostat 17 with high accuracy after canceling the influence of the operation of the air conditioning heater 13.

  In the above embodiment, the first detection temperature T1 detected by the first water temperature sensor 11 that detects the temperature of the cooling water flowing upstream of the heater core 13A and the temperature of the cooling water flowing downstream of the heater core 13A are detected. The thermostat 17 is determined based on the second detection temperature T2 detected downstream of the heater core 13A out of the second detection temperature T2 detected by the second water temperature sensor 12. (Refer to steps S17, S19, and S23 in FIG. 3) It is naturally possible to make a failure determination of the thermostat 17 based on the first detected temperature T1 detected on the upstream side of the heater core 13A. As described above, when the failure determination of the thermostat 17 is performed based on the first detected temperature T1, only T2 and T20 in the processing formulas in steps S17, S19, and S23 of FIG. 3 are changed to T1 and T10. The general control flow is the same. Note that the behavior of the temperature value that appears when the thermostat 17 fails may be slightly different between the first detection temperature T1 and the second detection temperature T2, but in such a case, the correction amount α in step S17 Alternatively, the threshold value Y in steps S19 and S23 may be changed as necessary.

  Furthermore, it is possible to determine whether or not the thermostat 17 has failed based on both the detected temperatures T1 and T2. For example, when it is determined whether or not the rising width of the first detection temperature T1 and the rising width of the second detection temperature T2 from the start of the engine are smaller than a predetermined threshold, and both conditions are satisfied, It can be determined that the thermostat 17 has failed.

1 is a diagram schematically showing an engine cooling system to which a thermostat failure detection apparatus according to the present invention is applied. FIG. It is the temperature characteristic figure which showed the time change of the cooling water temperature according to the state of a heater core and a thermostat. It is a flowchart which shows the specific content of the control action performed by the failure detection apparatus of the said thermostat.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 (Engine) cooling device 3 Engine main body 5 1st cooling water channel 6 2nd cooling water channel 11 1st water temperature sensor (1st water temperature detection means)
12 2nd water temperature sensor (2nd water temperature detection means)
13A Heater core 15 Radiator 17 Thermostat 21 Failure determination means 22 Heater operation determination means 23 Correction means T1 First detection temperature (detection temperature by the first water temperature sensor)
T2 second detection temperature (detection temperature by the second water temperature sensor)
Ts (thermostat) valve opening temperature

Claims (3)

The heater core of the air conditioning heater that uses the heat of the cooling water led out from the engine body extends in a midway part so as to branch off from the first cooling water path, and in the middle part for heat dissipation An engine cooling apparatus comprising: a second cooling water passage provided with a radiator; and a thermostat that opens when the cooling water is at a predetermined temperature or higher and allows the cooling water to flow into the second cooling water passage from the first cooling water passage. An apparatus for detecting a failure of the thermostat,
First water temperature detection means for detecting the temperature of cooling water flowing from the engine body to the heater core;
Second water temperature detecting means for detecting the temperature of the cooling water flowing from the heater core to the engine body;
It is determined whether or not the air conditioning heater is operating based on the temperature of the cooling water detected by the both detection means when the temperature of the cooling water is lower than the valve opening temperature of the thermostat. Heater operation determining means;
Similarly, when the engine is cold, failure determination means for determining whether or not the thermostat has failed based on the temperature of the cooling water detected by at least one of the detection means.
When the heater operation determining means determines that the air conditioning heater is operating, the cooling water temperature checked by the failure determining means or the failure determination threshold value to be compared with the temperature is determined. A thermostat failure detection apparatus comprising: correction means for correcting in a direction to cancel the influence of the operation of the heater. In the thermostat failure detection device according to claim 1,
The downstream end of the second cooling water channel is connected to the downstream side of the first cooling water channel by a predetermined distance from the heater core, and the second water temperature is closer to the outlet of the heater core than the connection unit. A thermostat failure detection apparatus, characterized in that a detection means is provided. The heater core of the air conditioning heater that uses the heat of the cooling water led out from the engine body extends in a midway part so as to branch off from the first cooling water path, and in the middle part for heat dissipation An engine cooling apparatus comprising: a second cooling water passage provided with a radiator; and a thermostat that opens when the cooling water is at a predetermined temperature or higher and allows the cooling water to flow into the second cooling water passage from the first cooling water passage. A method of detecting a failure of the thermostat,
A first step of acquiring a temperature value from first water temperature detecting means for detecting a temperature of cooling water flowing from the engine body to the heater core;
A second step of acquiring a temperature value from a second water temperature detecting means for detecting the temperature of the cooling water flowing from the heater core to the engine body;
It is determined whether or not the air conditioning heater is operating based on the temperature of the cooling water detected by the both detection means when the temperature of the cooling water is lower than the valve opening temperature of the thermostat. A third step;
A fourth step of determining whether or not the thermostat has failed based on the temperature of the cooling water detected by at least one of the detection means when the engine is cold.
When it is determined in the third step that the air-conditioning heater is operating, the temperature of the cooling water checked in the fourth step or a failure determination threshold value compared with the temperature is determined as the air-conditioning A method for detecting a failure of a thermostat, wherein the influence of the operation of the heater is corrected in a direction to cancel the influence.

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