JP6028708B2 - vehicle - Google Patents

Description

  The present invention relates to a vehicle, and more particularly to a vehicle having a function of performing a failure diagnosis of a thermostat provided in an engine cooling system.

  Generally, the engine cooling system is provided with a thermostat for adjusting the temperature of the cooling water by switching the cooling path. A technique for performing such a thermostat failure diagnosis is disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-207393 (Patent Document 1). In the technique disclosed in Patent Document 1, when the water temperature change rate is less than a predetermined value, the thermostat failure diagnosis process is prohibited.

JP 2005-207393 A JP 2003-176720 A

  In Patent Document 1, as described above, the thermostat failure diagnosis process is prohibited when the water temperature change rate is less than a predetermined value, but how to determine the calculation cycle (sampling cycle) of the water temperature change rate is as follows. No mention is made. For example, if the sampling period is lengthened, the followability to the water temperature change is deteriorated, and when the water temperature suddenly changes from increasing to decreasing, the timing for determining that the water temperature changing rate is less than a predetermined value (that is, thermostat failure diagnosis processing is prohibited) (Timing) is delayed, and there is a risk of misdiagnosis. Conversely, if the sampling period is shortened, it is likely to be affected by variations in the water temperature sensor, and the thermostat failure diagnosis process may be unnecessarily prohibited. However, Patent Document 1 does not mention any such problems and countermeasures.

  The present invention has been made to solve the above-described problems, and an object thereof is to appropriately suppress misdiagnosis due to thermostat failure diagnosis processing.

  A vehicle according to the present invention is a vehicle equipped with an engine for returning an engine cooling water channel formed inside the engine and cooling water discharged from the engine cooling water channel to the engine cooling water channel via a radiator. The temperature of the cooling water flowing through the radiator circulation passage, the bypass passage for returning the cooling water discharged from the engine cooling water passage to the engine cooling water passage without passing through the radiator, and the radiator circulation passage and the bypass passage Accordingly, the cooling water from the radiator circulation passage is shut off and the cooling water from the bypass passage is output to the engine cooling water passage, and the cooling water from the radiator circulation passage and the cooling water from the bypass passage are engine cooled. Thermostat that can be switched to either the open state that outputs to the water channel, and the cooling water in the engine cooling water channel An engine water temperature sensor that detects the temperature, a radiator water temperature sensor that detects the temperature of the cooling water in the radiator circulation passage, and a radiator circulation based on the leakage flow rate that flows through the radiator circulation passage and the output of the engine water temperature sensor when the thermostat is closed A controller that calculates an estimated value of the coolant temperature in the passage and performs a failure diagnosis process for diagnosing that the thermostat has failed when the output of the radiator water temperature sensor is larger than the calculated estimated value. The control device calculates when the first output change rate of the engine water temperature sensor calculated in the first sampling cycle is less than a first predetermined value that is a change rate when the engine water temperature sensor changes from increase to decrease, or in the second sampling cycle. When the second output change rate of the engine water temperature sensor is less than the second predetermined value, the thermostat failure diagnosis process is prohibited. The second sampling period is set to a value shorter than the first sampling period. The second predetermined value is set to a value smaller than the first predetermined value.

  According to such a configuration, even if the first output change rate of the engine water temperature sensor calculated in the first sampling period is larger than the first predetermined value, the engine water temperature sensor calculated in the second sampling period. When the second output change rate is less than the second predetermined value, thermostat failure diagnosis processing is prohibited. Here, the second sampling period is set to a value shorter than the first sampling period. Therefore, the second output change rate follows the output change of the engine water temperature sensor earlier than the first output change rate. As a result, it is possible to detect early that the output of the engine water temperature sensor has changed from an increase to a decrease based on the second output change rate, and appropriately prohibit the thermostat failure diagnosis process.

  Further, the second predetermined value is set to a value smaller than the first predetermined value. That is, in view of the fact that the second output change rate has a shorter sampling period than the first output change rate and is easily affected by variations in the water temperature sensor, the second predetermined value to be compared with the second output change rate is set to the first output change rate. A value smaller than the first predetermined value to be compared with the output change rate is set. Thereby, even if it is a case where the 2nd output change rate is used, it can control that failure diagnosis processing of a thermostat is prohibited unnecessarily by the influence of variation of a water temperature sensor.

  ADVANTAGE OF THE INVENTION According to this invention, the misdiagnosis by the thermostat failure diagnosis process can be suppressed appropriately.

It is a figure which shows the structure of a vehicle typically. It is a flowchart which shows the flow of a process of ECU. It is a flowchart which shows the detailed flow of diagnostic precondition determination. It is a figure which shows typically an example of the prohibition timing of a thermostat failure diagnosis process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a diagram schematically showing a configuration of a vehicle according to an embodiment of the present invention. Referring to FIG. 1, vehicle 100 includes an engine 20 and an engine cooling device 10 for cooling engine 20.

  The engine cooling device 10 includes an electric water pump (hereinafter also referred to as “electric pump”) 30, a radiator 40, a radiator circulation passage 50, a bypass passage 60, a thermostat 70, an engine-side cooling water temperature sensor 80, A radiator-side cooling water temperature sensor 90 and a control device (hereinafter also referred to as an ECU (Electronic Control Unit)) 200 are provided.

  The engine 20 has a water jacket 24 for cooling the engine 20 with cooling water. The water jacket 24 is formed around the cylinder of the engine 20 and constitutes a cooling water passage 25 through which the cooling water flows. The cooling water passage 25 is provided between the inlet portion 27 and the outlet portion 26, and sends out the cooling water from the inlet portion 27 from the outlet portion 26. The cooling water flowing in the cooling water channel 25 exchanges heat with the engine 20 to cool the engine 20. Thereby, the engine 20 is maintained at a temperature suitable for combustion.

  The electric pump 30 is a pump that is driven by an electric motor to circulate cooling water of the engine 20. The electric pump 30 is attached to the mounting side surface portion 22 of the engine body. The electric pump 30 delivers cooling water from the inlet 27 into the cooling water channel 25.

  The electric pump 30 is controlled to be driven and stopped by a control signal received from the ECU 200. Further, the electric pump 30 controls the discharge amount of the cooling water discharged from the electric pump 30 by a control signal received from the ECU 200.

  The outlet part 26 constitutes the branch part 120. The branch portion 120 is connected to the radiator circulation passage 50 and the bypass passage 60. The branch portion 120 divides the cooling water from the cooling water passage 25 into cooling water to the radiator circulation passage 50 and cooling water to the bypass passage 60.

  The radiator circulation passage 50 is a passage for circulating cooling water between the engine 20, the electric pump 30, and the radiator 40. The radiator circulation passage 50 includes pipes 50 a and 50 b and a radiator 40. The pipe 50 a is provided between the branch part 120 and the inlet part 42 of the radiator 40. The pipe 50 b is provided between the outlet portion 44 of the radiator 40 and the thermostat 70. The cooling water warmed by the engine 20 is cooled by passing through the radiator 40.

  The radiator 40 radiates the heat of the cooling water by exchanging heat between the cooling water flowing inside the radiator 40 and the outside air. The radiator 40 is provided with a cooling fan 46. The cooling fan 46 promotes heat exchange by blowing air and improves the heat dissipation efficiency of the cooling water in the radiator 40. The cooling water cooled by the radiator 40 is sent out from the outlet 44.

  The bypass passage 60 is a passage for circulating the coolant while bypassing the radiator 40. The bypass passage 60 includes pipes 60 a and 60 b and a thermal device 300. The pipe 60 a is provided between the branch part 120 and the thermal device 300. The pipe 60 b is provided between the thermal device 300 and the thermostat 70.

  The thermal apparatus 300 includes an EGR (Exhaust Gas Recirculation) cooler 28, a pipe 29, an exhaust heat recovery device 32, a heater 36, a throttle body 35, and an EGR valve 34.

  The EGR cooler 28 cools the EGR gas with cooling water. The exhaust heat recovery device 32 enhances startability at a low temperature by warming the cooling water by the heat of the exhaust gas. The throttle body 35 is prevented from sticking by being warmed by the cooling water. The EGR valve 34 is cooled by cooling water.

  The thermostat 70 is disposed in the junction 110 that joins the cooling water that has passed through the radiator circulation passage 50 and the cooling water that has passed through the bypass passage 60. The junction 110 is connected to the radiator 40 through the pipe 50b and is connected to the pipe 60b. Cooling water from the junction 110 is returned to the suction port of the electric pump 30.

  A valve body is provided inside the thermostat 70. The valve body of the thermostat 70 is configured to be switched between a closed state and an open state according to the temperature of the cooling water near the valve body.

  When the temperature of the cooling water near the valve body of the thermostat 70 is lower than a predetermined valve opening temperature (for example, about 70 ° C.), the valve body of the thermostat 70 is closed. In this case, the cooling water on the bypass passage 60 side passes through the thermostat 70 and is output to the water jacket 24. However, the cooling water on the radiator circulation passage 50 side is blocked from flowing in by the valve body, so Not output. As a result, the cooling water that has taken the heat of the engine 20 is returned to the engine 20 (water jacket 24) without being cooled by the radiator 40, so that the engine 20 is warmed up.

  On the other hand, when the temperature of the cooling water near the valve body of the thermostat 70 is equal to or higher than the above valve opening temperature, the valve body of the thermostat 70 is opened. In this case, the cooling water from the radiator circulation passage 50 and the cooling water from the bypass passage 60 pass through the thermostat 70 and are output to the water jacket 24. Moreover, the opening degree of a valve body is adjusted according to the temperature of a cooling water. Thereby, the mixing ratio of the cooling water from the radiator circulation passage 50 and the cooling water from the bypass passage 60 is adjusted, and the temperature of the cooling water passed through the water jacket 24 is kept at an appropriate temperature of the engine 20. It is.

  The engine-side cooling water temperature sensor 80 is provided in the branch part 120. The engine-side cooling water temperature sensor 80 detects the temperature of the cooling water delivered from the outlet 26 (hereinafter referred to as “engine outlet water temperature ECT” or simply “ECT”), and outputs the detection result (ECT detection value) to the ECU 200. To do. The engine-side cooling water temperature sensor 80 only needs to be provided in a path through which the cooling water is constantly circulated. For example, the engine-side cooling water temperature sensor 80 may be provided in the cooling water path 25.

  The radiator side cooling water temperature sensor 90 is provided in the pipe 50a. The radiator side cooling water temperature sensor 90 detects the temperature of the cooling water flowing in the pipe 50a of the radiator circulation passage 50 (hereinafter referred to as “radiator inlet water temperature RCT” or simply “RCT”), and the detection result (RCT detection value) is detected by the ECU 200. Output to. The radiator-side cooling water temperature sensor 90 only needs to be provided in the radiator circulation passage 50, and may be provided, for example, in the pipe 50b.

  In the vehicle 100 having the above-described configuration, if the thermostat 70 fails, the valve body does not open even if the coolant temperature near the valve body rises above the valve opening temperature, or the valve body is cooled. Even if the water temperature falls below the valve opening temperature, abnormalities such as an open failure that the valve body does not close occur. In a state where such a failure has occurred, the cooling water having an appropriate water temperature cannot be supplied to the cooling water passage 25 of the engine 20, and the operating efficiency of the engine 20 is reduced. For this reason, it is preferable to continuously perform failure diagnosis as to whether or not the thermostat 70 is functioning normally and find the failure early.

  Therefore, ECU 200 performs failure diagnosis of thermostat 70 based on the ECT detection value received from engine-side cooling water temperature sensor 80 and the RCT detection value received from radiator-side cooling water temperature sensor 90.

  In the water temperature region where the thermostat 70 is not originally opened (the water temperature region below the valve opening temperature), since the thermostat 70 is in a closed state, theoretically, the cooling water flows through the bypass passage 60 and the radiator circulation passage 50 is cooled. Water does not flow. Therefore, a difference of a predetermined value or more occurs between the ECT detection value and the RCT detection value. Therefore, when the temperature difference between the ECT detection value and the RCT detection value is less than a predetermined value in the water temperature region where the thermostat 70 is not originally opened, it is determined that the thermostat 70 is open, that is, the thermostat 70 is open. be able to.

  However, actually, even if the thermostat 70 is normally closed, if the water pressure in the radiator circulation passage 50 rises due to driving of the electric pump 30 or the like, the cooling water in the radiator circulation passage 50 is slightly transferred from the thermostat 70 to the cooling water passage 25. Leak out. In this case, although the thermostat 70 is in the closed state, an amount of cooling water corresponding to the leakage flow rate of the thermostat 70 flows into the radiator circulation passage 50 from the cooling water passage 25 and the cooling water in the radiator circulation passage 50. Due to the mixing, the radiator inlet water temperature RCT approaches the engine outlet water temperature ECT. Thereby, since the temperature difference between the ECT detection value and the RCT detection value becomes small, there is a possibility that the accuracy of the failure diagnosis is lowered.

  The ECU 200 according to the present embodiment performs failure diagnosis of the thermostat 70 in consideration of slight leakage of cooling water from the thermostat 70 even when the thermostat 70 is normal. Specifically, the ECU 200 calculates an estimated value of the radiator inlet water temperature RCT based on the ECT detection value and the leakage flow rate of the thermostat 70, and based on the comparison result between the calculated RCT estimated value and the RCT detection value. A process for diagnosing whether or not is an open fault (hereinafter also referred to as “thermostat open fault diagnosis process”) is performed.

  FIG. 2 is a flowchart showing a process flow when ECU 200 performs a thermostat open failure diagnosis process. This flowchart is repeatedly executed at a predetermined cycle while the ECU 200 is activated. The ECU 200 is activated by an IG on operation (operation for making the vehicle 100 runnable) by a user, and stopped by an IG off operation (an operation for making the vehicle 100 unrunnable) by a user. The This flowchart is realized by executing a program stored in advance in the ECU 200 at a predetermined cycle. Alternatively, for some steps, it is also possible to construct dedicated hardware (electronic circuit) and realize processing.

  In step (hereinafter, step is abbreviated as “S”) 10, ECU 200 is based on the ECT detection value received from engine-side cooling water temperature sensor 80 and the leakage flow rate that flows in radiator circulation passage 50 when thermostat 70 is in the closed state. Then, an estimated value (RCT estimated value) of the radiator inlet water temperature RCT is calculated.

  Specifically, ECU 200 can calculate the RCT estimated value using the following equation as an example.

RCT estimated value = (ECT detection value × leakage flow rate + RCT estimated value (previous value) × (pipe volume−leakage flow rate)) / pipe volume (1)
In equation (1), the RCT estimated value is calculated on the assumption that the cooling water of the ECT detection value and the cooling water of the RCT estimated value (previous value) are uniformly mixed according to the ratio of the leakage flow rate to the pipe volume. The

  Here, the leakage flow rate may be a fixed value determined in advance by an experimental result or the like, or may be a fluctuation value set to a larger value as the flow rate of the electric pump 30 increases, for example.

  The pipe volume is a volume of the pipe through which the cooling water from the engine side cooling water temperature sensor 80 to the radiator side cooling water temperature sensor 90 flows. In addition, the calculation accuracy can be improved by dividing the pipe line into an arbitrary number of areas and applying the formula (1) to each divided area.

  In S20, ECU 200 performs a process for determining whether or not a precondition for performing an open failure diagnosis process for thermostat 70 (hereinafter, also simply referred to as “diagnosis precondition”) is satisfied. Details of this process will be described later.

  In S30, ECU 200 determines whether or not to perform thermostat open failure diagnosis processing based on the processing result in S20.

  If it is not determined that the diagnosis precondition is satisfied in the process of S20 (NO in S30), ECU 200 ends the process without performing the thermostat open failure diagnosis process (the processes of S40 to S60). Let That is, the ECU 200 prohibits the thermostat open failure diagnosis process when the diagnosis precondition is not satisfied.

  On the other hand, when it is determined in step S20 that the diagnosis precondition is satisfied (YES in step S30), ECU 200 performs a thermostat open failure diagnosis process (steps S40 to S60).

  In S40, ECU 200 determines whether or not the RCT detection value received from radiator-side cooling water temperature sensor 90 is higher than the RCT estimated value calculated in S10.

  If the RCT detection value is higher than the RCT estimation value (YES in S40), ECU 200 determines that thermostat 70 is in the open failure state (S50).

  Conversely, when the RCT detection value is equal to or less than the RCT estimation value (NO in S40), ECU 200 determines that thermostat 70 is normal (S60).

  FIG. 3 is a flowchart showing a detailed flow of the process of S20 (diagnosis precondition determination) of FIG.

  In S21, ECU 200 determines whether or not the monitor precondition is satisfied. The monitor precondition is a condition set as a premise for monitoring (monitoring) the water temperature change rate in the processing of S22 and S23 described later. In the present embodiment, ECU 200 determines that the monitor precondition is satisfied when all of the following conditions (a) to (f) are satisfied.

(A) The thermostat failure diagnosis is not completed after the current IG ON operation.
(B) The ECT detection value is lower than the valve opening temperature (for example, 70 ° C.) of the thermostat 70.

(C) The ECT detection value at the time of engine start is included in the range of −10 ° C. to + 56 ° C.
(D) The engine is starting.

(E) A predetermined time (for example, 1 sec) has elapsed since the engine was started.
(F) The engine-side cooling water temperature sensor 80 and the radiator-side cooling water temperature sensor 90 are normal.

  Here, the condition (a) is based on the premise that the thermostat failure diagnosis is performed once during one trip (period after the IG ON operation until the next IG OFF operation) in the present embodiment. is there. Condition (b) is a condition for ensuring that the thermostat 70 is closed (if normal). Conditions (c) and (d) are conditions for ensuring that the ECT detection value increases in such a manner that a thermostat failure can be diagnosed after the engine is started. Condition (e) is a condition for eliminating the initial variation of the ECT detection value or the RCT detection value. The condition (f) is a condition for ensuring the reliability of the ECT detection value or the RCT detection value. The monitor precondition only needs to include at least the condition (b), and other conditions may be changed or deleted as necessary.

  In S22, ECU 200 determines whether the change rate of the ECT detection value calculated in the first sampling period (hereinafter also referred to as “first water temperature change rate ΔECT1” (unit: ° C./sec)) is less than predetermined value α. Determine whether or not. Here, the predetermined value α is a value (for example, 0.1 ° C./sec) set as a rate of change when the ECT detection value changes from increasing to decreasing.

  In S23, ECU 200 determines whether the change rate of the ECT detection value calculated in the second sampling period (hereinafter also referred to as “second water temperature change rate ΔECT2” (unit: ° C./sec)) is less than predetermined value β. Determine whether or not.

  Here, the second sampling period is set to a value shorter than the first sampling period. That is, the calculation cycle of the second water temperature change rate ΔECT2 is shorter than the calculation cycle of the first water temperature change rate ΔECT1. Further, the predetermined value β is set to a value (for example, 0 ° C./sec) smaller than the predetermined value α. The first water temperature change rate ΔECT1 and the second water temperature change rate ΔECT2 are separately calculated by the ECU 200.

  The ECU 200 detects the ECT detection value when the first water temperature change rate ΔECT1 is equal to or greater than the predetermined value α (NO at S22) and when the second water temperature change rate ΔECT2 is equal to or greater than the predetermined value β (NO at S23). It is determined that “diagnosis precondition is satisfied” (S24).

  On the other hand, when first water temperature change rate ΔECT1 is less than predetermined value α (NO in S22) or second water temperature change rate ΔECT2 is less than predetermined value β (NO in S23), ECU 200 detects ECT. Assuming that the value has changed from increasing to decreasing, it is determined that "diagnosis precondition is not satisfied" (S25).

  FIG. 4 is a diagram schematically illustrating an example of the prohibition timing of the thermostat failure diagnosis process when the engine outlet water temperature ECT changes from increasing to decreasing in the water temperature region below the valve opening temperature of the thermostat 70. FIG. 4 shows a case where the thermostat 70 is normally closed (no open failure).

  When the engine 20 is started with the thermostat 70 closed, the cooling water that has taken away the heat of the engine 20 is returned to the engine 20 (water jacket 24) through the bypass passage 60 without being cooled by the radiator 40. Therefore, the engine outlet water temperature ECT increases. At this time, as described above, the radiator inlet water temperature RCT does not increase theoretically, but actually, the radiator inlet water temperature RCT also increases so as to approach the engine outlet water temperature ECT due to the influence of the leakage flow rate of the thermostat 70. However, if the thermostat 70 is normal, the leakage flow rate is very small, so the radiator inlet water temperature RCT does not reach the engine outlet water temperature ECT. Therefore, while the engine outlet water temperature ECT is increasing, as shown before time t1 in FIG. 4, the state where the engine outlet water temperature ECT is higher than the radiator inlet water temperature RCT by a predetermined value or more is maintained.

  However, for example, when the heater 36 provided in the bypass passage 60 is turned on, the cooling water in the bypass passage 60 is cooled by heat exchange with the heater 36. Therefore, when the heat generation amount of the engine 20 is small, the engine outlet water temperature ECT may turn from increasing to decreasing as shown after time t1 in FIG. In such a case, even if the thermostat 70 is normal, the temperature difference between the engine outlet water temperature ECT and the radiator inlet water temperature RCT becomes small (time t1 to t3), and the radiator inlet water temperature RCT eventually becomes higher than the engine outlet water temperature ECT. Becomes higher (after time t3). In such a state, although the thermostat 70 is normal, the RCT detection value becomes higher than the RCT estimated value calculated in the process of S10 in FIG. 2, and therefore, the thermostat open failure determination process (S40 in FIG. 2). ˜S60), it is determined that “the RCT detection value is higher than the RCT estimated value” (YES in S40 in FIG. 2), and erroneously determined as “open failure state” (S50 in FIG. 2). That is, after the time t3, even if the thermostat 70 is normal, the RCT is higher than the ECT, so the “RCT detection value” is higher than the “RCT estimation value (estimated from the ECT detection value)”. It may be erroneously determined as an open failure.

  In order to suppress such erroneous determination, in the present embodiment, whether or not the ECT detection value has changed from increase to decrease is determined using “first water temperature change rate ΔECT1” having a long calculation cycle. When the determination is made using the “second water temperature change rate ΔECT2” having a short calculation cycle, and it is determined by at least one of the determinations that the ECT detection value has changed from an increase to a decrease, a thermostat open failure diagnosis process (S40 to S40 in FIG. 2) S60) is prohibited.

  The first water temperature change rate ΔECT1 having a long calculation cycle is not easily affected by variations in instantaneous values of ECT detection values. Therefore, by determining whether or not the ECT detection value has changed from increasing to decreasing based on “whether or not the first water temperature change rate ΔECT1 is less than the predetermined value α”, the thermostat open failure diagnosis process performs the variation in the ECT detection value. It is possible to suppress unnecessary prohibition due to the influence of

  On the other hand, since the first water temperature change rate ΔECT1 with a long calculation cycle has poor followability to the water temperature change, it cannot be detected at an early stage that the engine outlet water temperature ECT has actually changed suddenly from increasing to decreasing. Therefore, the timing for prohibiting the thermostat open failure diagnosis process may be delayed. In the example shown in FIG. 4, the time t4 when the first water temperature change rate ΔECT1 is determined to be less than the predetermined value α is after the time t3 when the RCT becomes higher than the ECT. In this case, during the period from time t3 to time t4, the first water temperature change rate ΔECT1 is not determined to be less than the predetermined value α although the RCT is higher than the ECT. Therefore, if only “first water temperature change rate ΔECT1” is used, the thermostat open failure diagnosis process is not prohibited during the period from the time t3 to the time t4 even though the RCT is higher than the ECT. There is a possibility that.

  However, in the present embodiment, even when it is determined that the first water temperature change rate ΔECT1 is not less than the predetermined value α, the second water temperature change rate ΔECT2 is determined to be less than the predetermined value β. The thermostat open failure diagnosis process is prohibited. Here, the second water temperature change rate ΔECT2 having a short calculation cycle follows the water temperature change earlier than the first water temperature change rate ΔECT1 having a long calculation cycle. Thereby, it can be detected early using 2nd water temperature change rate (DELTA) ECT2 that the ECT detection value changed from increase to decrease.

  Furthermore, in the present embodiment, when the second water temperature change rate ΔECT2 having a short calculation cycle is used, the second water temperature change rate ΔECT2 is compared with the second water temperature change rate ΔECT2 in view of being easily affected by variations in the ECT detection value. The predetermined value β is set to a value smaller than the predetermined value α compared with the first water temperature change rate ΔECT1. Thereby, even when the second water temperature change rate ΔECT2 is used, it is possible to suppress as much as possible that the thermostat failure diagnosis process is prohibited unnecessarily due to the influence of the variation in the ECT detection value.

  In the example shown in FIG. 4, the thermostat open failure diagnosis process is prohibited from time t2 when the second water temperature change rate ΔECT2 is less than the predetermined value β. That is, the thermostat open failure diagnosis process can be prohibited earlier than time t3 when RCT becomes higher than ECT. Furthermore, since the predetermined value β is set to a value smaller than the predetermined value α, the timing when the thermostat open failure diagnosis process is prohibited from time t1 when the second water temperature change rate ΔECT2 becomes less than the predetermined value α (time t2 ) Can be delayed. Thereby, it can suppress as much as possible that a thermostat failure diagnosis process is prohibited unnecessarily.

  As described above, the ECU 200 according to the present embodiment determines whether or not the ECT detection value has changed from increasing to decreasing depending on whether or not the first water temperature change rate ΔECT1 having a long calculation cycle is less than the predetermined value α. In addition, the determination is made based on whether or not the “second water temperature change rate ΔECT2” having a short calculation cycle is less than a predetermined value β (β <α). Then, when at least one of the determination results indicates that the ECT detection value has changed from increasing to decreasing, the ECU 200 prohibits the thermostat open failure diagnosis process. Therefore, it is possible to appropriately suppress erroneous diagnosis due to the thermostat failure diagnosis process.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Engine cooling device, 20 Engine, 22 Mounting side surface part, 24 Water jacket, 25 Cooling water channel, 26, 44 Outlet part, 27, 42 Inlet part, 28 Cooler, 29, 50a, 50b, 60a, 60b Piping, 30 Electric pump , 32 Exhaust heat recovery device, 34 EGR valve, 35 Throttle body, 36 Heater, 40 Radiator, 46 Cooling fan, 50 Radiator circulation passage, 60 Bypass passage, 70 Thermostat, 80 Engine side cooling water temperature sensor, 90 Radiator side cooling water temperature sensor , 100 vehicle, 110 junction part, 120 branch part, 200 ECU, 300 thermal equipment.

Claims (1)

A vehicle equipped with an engine,
An engine cooling water channel formed inside the engine;
A radiator circulation passage for returning cooling water discharged from the engine cooling water passage to the engine cooling water passage via a radiator;
A bypass passage for returning the cooling water discharged from the engine cooling water channel to the engine cooling water channel without passing through the radiator;
Connected to the radiator circulation passage and the bypass passage, and shuts off the cooling water from the radiator circulation passage according to the temperature of the cooling water flowing inside, and outputs the cooling water from the bypass passage to the engine cooling water passage A thermostat that can be switched between a closed state to be opened and an open state in which cooling water from the radiator circulation passage and cooling water from the bypass passage are output to the engine cooling water passage,
An engine water temperature sensor for detecting the temperature of the cooling water in the engine cooling water channel;
A radiator water temperature sensor for detecting a temperature of cooling water in the radiator circulation passage;
An estimated value of the cooling water temperature in the radiator circulation passage is calculated based on the leakage flow rate flowing through the radiator circulation passage in the closed state and the output of the engine water temperature sensor, and the estimated value A controller for performing a failure diagnosis process for diagnosing that the thermostat has failed when the output of the radiator water temperature sensor is large,
The control device, when the first output change rate of the engine water temperature sensor calculated in the first sampling period is less than a first predetermined value that is a change rate when turning from increase to decrease, or the second sampling period When the second output change rate of the engine water temperature sensor calculated in step S is less than a second predetermined value, prohibiting the failure diagnosis processing of the thermostat;
The second sampling period is set to a value shorter than the first sampling period,
The vehicle, wherein the second predetermined value is set to a value smaller than the first predetermined value.

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