JP2001073767A - Failure diagnosis device of thermostat in engine cooling system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent misjudgment on failure of thermostat when temperature of cooling water rises only slowly or rises rapidly. SOLUTION: This diagnosis device judges the followings as valve-opening failure when actual temperature of cooling water detected by water temperature sensor S1 is lower than that of specified valve-opening temperature of thermostat 5, after elapsing of high-load, high-speed operation for more than specified time. Or, it judges finally to be valve-opening failure when either the first failure judgment measure that temporarily judges valve-opening failure based on actual cooling water temperature by water temperature sensor S1, or the second failure judgement measure that temporarily judges as valve-opening failure when heat value ratio R=Qorh/Qig is bigger than the threshold value, after radiation volume Qorh from radiator 3 is calculated based on anticipated cooling water temperature according to operation of engine, and, on the other hand, heat intake volume Qig of cooling water from engine is calculated, judges as failure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermostat failure diagnosis system for an engine cooling system.

[0002]

2. Description of the Related Art In an engine cooling water system, a radiator and a thermostat (thermostat valve) are provided. The thermostat is opened and closed according to the temperature of the cooling water. The thermostat is opened when the cooling water of the engine is higher than a predetermined temperature (for example, 80 ° C.), and the cooling water circulates through the radiator by this opening. Cooling water is cooled by the radiator. Further, when the temperature of the cooling water is lower than the predetermined temperature, the thermostat is closed, and the cooling water flows by bypassing the radiator so that the temperature of the cooling water rises promptly. I have.

When the engine is started from a cold state in a state in which a valve opening failure (open sticking occurs) occurs in which the thermostat remains open while the thermostat is open, cooling water circulates through a radiator, and the temperature rises. It is not performed promptly, which is not preferable not only for promptly securing stable operation of the engine, but also unfavorable in terms of fuel efficiency and measures against exhaust gas.

[0004] In order to determine the failure of the thermostat to open, Japanese Patent Application Laid-Open No. 10-184433 discloses that when the actual temperature of the cooling water after a predetermined time has elapsed from the start of the engine is lower than the predetermined temperature, the cooling water is supplied to the radiator. It is disclosed that it is determined that the cooling of the thermostat has occurred, that is, that a thermostat valve opening failure has occurred.

[0005]

However, according to the above-mentioned publication, when the engine is started for a long time, such as idling, in which the amount of heat generated by the engine is extremely small, even if cooling by the radiator is not performed, Since the temperature of the cooling water does not rise so much, a situation in which a thermostat is erroneously determined to be a valve opening failure even though the valve opening failure has not occurred is likely to occur.

In order to prevent the erroneous determination as described above, the present applicant predicts the cooling water temperature from the operating state of the engine,
When the predicted temperature reaches the predetermined temperature, it is determined that a valve opening failure has occurred when the integrated value of the difference between the current predicted temperature and the actual cooling water temperature detected by the temperature sensor is equal to or greater than a predetermined value. Develop what you want. According to this determination method, even if the operation state in which the engine heat generation amount such as idling is small continues for a long time from the engine start, the time required for the predicted temperature to reach the predetermined temperature becomes longer, so that the erroneous determination of the valve opening failure is prevented. Will be.

However, in the above-described determination method using the predicted temperature, an operation state in which the cooling water temperature rises rapidly, for example, when the acceleration state on a steep uphill is continued for a long time immediately after the engine is started. If it continues, the predicted temperature will reach the predetermined temperature in a short time, and as a result, even if a valve opening failure has occurred, the above integrated value will be small, and it may be erroneously determined that the thermostat is normal. It turns out that there is.

The present invention has been made in view of the above circumstances, and has as its object to prevent erroneous determination that a valve opening failure has occurred when the cooling water temperature does not immediately rise. A thermostat failure diagnostic device in an engine cooling system that prevents misjudgment of normality when the cooling water temperature rises rapidly so that the thermostat valve opening failure can be more accurately determined. Is to provide.

[0009]

In order to achieve the above object, the present invention has a first solution as follows. That is, as described in claim 1 of the claims, the valve is opened when the cooling water of the engine reaches a predetermined temperature or higher to circulate the cooling water to the radiator, and the cooling water is lower than the predetermined temperature. In a thermostat failure diagnosis device in an engine cooling system having a thermostat that closes a valve and bypasses the radiator with the cooling water, a water temperature detecting unit that detects an actual temperature of the cooling water, and a high-load operation state of the engine. High load detecting means for detecting, high speed detecting means for detecting a high speed driving state of the vehicle,
When the high-load operation state and the high-speed operation state are continuously detected for a predetermined time or longer, when the actual water temperature detected by the water temperature detection means is lower than the valve opening temperature of the thermostat, the thermostat is opened. Failure determination means for determining that a valve failure has occurred.

In order to achieve the above object, the present invention is as follows as a second solution. That is, as described in claim 2 of the claims, the valve is opened when the cooling water of the engine reaches a predetermined temperature or higher to circulate the cooling water to the radiator, and the cooling water is lower than the predetermined temperature. When the valve is closed and the cooling water bypasses the radiator, the thermostat in the engine cooling system provided with the thermostat has a thermostat failure diagnosis apparatus, based on the actual cooling water temperature detected by the water temperature detecting means. Opening of the thermostat based on a relationship between an actual cooling water temperature detected by the water temperature detecting means and a predicted cooling water temperature calculated from an operation parameter indicating an operation state of the engine. And second failure determination means for determining a valve failure. Preferred embodiments based on the above solution are as described in Claims 3 and the following claims.

[0011]

According to the first aspect, one of the conditions for failure determination is that a high-load operation state in which the amount of heat generated by the engine is large is continued for a predetermined time or more, that is, the temperature of the cooling water is promptly increased. When it does not rise, the determination of the valve opening failure is not performed, so that a situation in which the valve opening failure is erroneously determined to be a failure is prevented. In addition, another condition for failure determination is that a high-speed operation state in which the engine is appropriately cooled by the running wind continues for a predetermined time or longer, that is, the cooling water temperature rises too quickly. Since the failure determination is not performed even in an operation state in which the valve is opened, it is possible to prevent a situation in which a valve opening failure is erroneously determined to be normal. As described above, the erroneous determination of the valve opening failure and the erroneous determination of the normal state are prevented, and the determination as to whether or not the valve opening failure is more accurate can be obtained.

According to the second aspect, the first failure determination method based on the actual cooling water temperature and the second failure determination based on the relationship between the actual cooling water temperature and the predicted temperature obtained based on the operating state of the engine. By performing both failure determinations with
A situation in which an erroneous determination is made by only one determination can be compensated for by the other determination, and the valve opening failure can be accurately determined as a whole.

According to the third aspect, a more specific one corresponding to the first aspect is provided as the first failure determination means. According to the fourth aspect, it is possible to determine that a valve opening failure has occurred even when a failure occurs in which the valve opening temperature at which the thermostat is actually opened is shifted to a temperature lower than a predetermined temperature set in advance. Will be possible. That is, the second
When the valve opening temperature is shifted to the lower temperature side as described above, the failure determination unit may erroneously determine that the valve is normal because the integrated value becomes smaller as a whole.
It is possible for the failure determination means to properly determine when there is a valve opening failure. According to the fifth aspect, it is preferable to reduce the chance of erroneously determining that the valve is normal even though the valve is open.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes an engine intended for an automobile. The outlet of a cooling water passage of the engine 1 is denoted by reference numeral 1a, and the inlet of the cooling water passage is denoted by reference numeral 1b. The outlet 1a is connected to a cooling water inlet 3a of the radiator 3 via a pipe 2. The cooling water outlet 3b of the radiator q3 is connected to a thermostat 5 via a pipe 4, and the thermostat 5 is connected to the cooling water inlet 1b of the engine 1 via a pipe 6. A pipe 7 that bypasses the radiator 3 with the pipe 2 and the thermostat 5
Connected through. Also, the pipe 2 and the pipe 6
The radiator 3 is connected to a pipe 8 that bypasses the pipe 7, and a heater core 9 is connected to the pipe 8. A pump 1 for supplying cooling water to the engine 1 is provided in the pipe 6.
0 is connected.

The thermostat 5 comprises a three-way switching valve. The thermostat 5 is opened when the temperature of the cooling water flowing through the thermostat 5 reaches a predetermined valve opening temperature (for example, 80 ° C.), and connects the pipe 6 to the pipe 4. The pipes 6 and 7 are shut off. As described above, when the thermostat 5 is opened, the high-temperature cooling water discharged from the engine 1 to the pipe 2 flows through the radiator 3 and is cooled there. 1 is supplied. In addition, thermostat 5
When the temperature of the cooling water flowing therethrough is lower than the predetermined temperature, the valve is closed to allow the pipe 6 to communicate with the pipe 7,
The pipes 6 and 4 are shut off (the flow state of the cooling water at this time is indicated by an arrow in FIG. 1). Thus, when the thermostat 5 is closed, the cooling water discharged from the engine 1 to the pipe 2 is circulated from the pipe 6 to the engine 1 through the pipe 7, that is, bypassing the radiator 3. .
When room heating is performed, a blower for performing heat exchange between the heater core 9 and room air is operated. However, when room heating is not performed, the passage of cooling water to the pipe 8 is prevented. An on-off valve may be provided.

FIG. 2 shows a control system for detecting (determining) a valve opening failure of the thermostat 5. In the figure, U is a control unit (controller) configured using a microcomputer. The control unit U receives signals from the various sensors S1 to S4. The sensor S1 detects the temperature of the cooling water, and is attached to the pipe 6 in order to detect the temperature of the cooling water passing through the thermostat 5 (the water temperature sensor S1 may be built in the thermostat 5). The sensor S2 detects the amount of intake air supplied to the engine 1, and detects the engine load. The sensor S3 detects the temperature of intake air supplied to the engine 1. The sensor S4 detects a vehicle speed. Control unit U
Determines the valve opening failure of the thermostat 5 based on the output from the sensor as described later. Then, when it is determined that a failure has occurred, the alarm 11 is activated.

Next, a method of determining a failure by the control unit U will be described with reference to the flowchart of FIG. 3. FIG. 3 corresponds to claim 1 in the claims. In the following description, Q indicates a step. First, the operation is started when the engine 1 is started, and the count value of the timer is initialized to zero. Then
In Q2, it is determined whether or not the engine load is at the time of a high load greater than a predetermined value. In the determination of Q2, YE
In the case of S, in Q3, it is determined whether or not the vehicle speed is higher than a predetermined vehicle speed. If the determination in Q3 is YES, the count value of the timer is counted up in Q4.

After Q4, in Q5, a predetermined time CH to be counted by the timer is set based on the cooling water temperature at the time of starting the engine. That is, even when the operating state of the engine and the vehicle is the same, the process of Q5 is performed in order to compensate for the difference in the degree of the temperature rise gradient of the coolant depending on the coolant temperature at that time. After Q5, in Q6, it is determined whether or not the timer count value is larger than a predetermined value (predetermined time) CH. Initially, the determination in Q6 is NO, and the process returns to Q2.

If the determination in Q6 is YES, in Q7, it is determined whether the predicted temperature of the cooling water predicted from the operating state of the engine 1 is higher than a predetermined temperature α.
In the embodiment, the predicted temperature of the cooling water is calculated by calculating a temperature rise for a predetermined short time using the engine load (for example, the intake air amount), the vehicle speed, and the intake air temperature as parameters. (The initial value of the predicted temperature is the actual cooling water temperature detected at the time of starting the engine). The predetermined temperature α is a temperature equal to or lower than the set valve opening temperature of the thermostat 5,
In the embodiment, the temperature is set near the valve opening temperature.

If YES in Q7, it is determined in Q8 whether the actual coolant temperature detected by the sensor S1 is lower (lower) than the predetermined temperature β. The predetermined temperature β is a temperature equal to or lower than the set valve opening temperature of the thermostat 5 and is set corresponding to the predetermined temperature α. In the embodiment, the predetermined temperature β is set to a temperature near the valve opening temperature and a temperature slightly lower than α (β is set to α
Can be set to the same value as.) If the determination in Q8 is NO, the actual cooling water temperature is sufficiently high, that is, the cooling by the radiator 3 is not being performed, and the thermostat 5 has a temperature considerably lower than the set valve opening temperature. Since it is a normal time when no valve opening failure has occurred, the valve is determined to be normal in Q9. Also, if the L determination in Q8 is YES, it is determined in Q10 that there is a valve opening failure,
At 11, the alarm 11 is activated.

If NO in Q2, or if Q2
If NO in the determination of 3, the timer count value is reset to 0 in each of Q12. As described above, the valve opening failure determination is set to be performed when the high load and the high vehicle speed continue for the predetermined time CH or more. The continuation of the high load and high vehicle speed state for a predetermined time or more includes the case where the total time obtained by integrating the high load and high vehicle speed time becomes the above predetermined time (the high load and high vehicle speed state is intermittent). In this case, Q1 in FIG.
Step 2 is unnecessary).

The flowcharts of FIGS. 4 and 5 show another method of judging a failure by the control unit U, and correspond to claim 2 in the claims. First,
In Q21 of FIG. 4, the predicted cooling water temperature is set as the actual cooling water temperature detected by the sensor S1. Thereafter, in Q22, the predicted cooling water temperature is calculated. This calculation is performed using the engine load, the vehicle speed, and the intake air temperature as parameters, similarly to the calculation of the predicted cooling water temperature in FIG.

In Q23, it is determined whether or not the actual cooling water temperature at the start of the engine is a considerably low temperature, for example, 35 degrees C. If the determination in Q23 is NO, it is determined that no failure determination is made, and the process is terminated. If YE is determined in Q23, it is determined in Q24 whether the temperature deviation obtained by subtracting the intake air temperature from the actual cooling water temperature at the time of starting the engine is a sufficiently small value, for example, 10 degrees C. When the determination in Q25 is NO, it is determined that no failure determination is made, and the process is terminated. In short, the processing of Q23 and Q25 is processing for not performing a failure determination when the engine 1 is once operated and the cooling water is at a considerably high temperature (to increase the cooling water temperature from almost the cold state). The failure judgment used is performed).

If the determination in Q25 is YES, in Q26, it is determined whether or not the predicted cooling water temperature is higher than a predetermined temperature set at about the middle temperature, for example, 40 ° C. If the determination in Q26 is NO, the process returns to Q22. If the determination in Q26 is YES, in Q27, the amount of heat radiation Qor from the radiator 3, as described later,
h is calculated. Next, in Q28, the heat receiving amount Qig of the cooling water from the engine 1 is calculated as described later. After Q28, in Q29, a heat amount ratio R, which is a ratio of the heat release amount Qorh to the heat reception amount Qig, is calculated. The larger the calorific value ratio R is, the higher the possibility that the cooling water is cooled by the radiator 3 is. After Q29, in Q30, it is determined whether or not the predicted cooling water temperature is lower than the set valve opening temperature of the thermostat 5 and is higher than a predetermined temperature (for example, 76 ° C.) set near the valve opening temperature. If the determination in Q30 is NO, the process returns to Q22.

When the determination in Q30 is YES, Q30 in FIG.
It moves to 41. In Q41, a threshold value α1 for failure determination is set based on the actual cooling water temperature at the time of starting the engine. Thereafter, in Q42, the heat quantity ratio R is:
It is determined whether or not it is larger than the determination threshold α1. If the determination in Q42 is YES, it is determined in Q43 that a valve opening failure has occurred, and in Q44, the alarm 11
Is activated.

If NO in Q42, in Q45, based on the actual cooling water temperature at the time of engine start,
A threshold value α2 for normality determination is set (α1> α
2). Thereafter, in Q46, it is determined whether or not the heat quantity ratio R is smaller than the determination threshold α2. If the determination in Q46 is YES, it is determined in Q47 that the valve-opening failure has not occurred and is normal. If the determination in Q46 is NO, it means that it is not possible to accurately determine whether a valve opening failure has occurred or is normal, and it is determined in Q48 that determination is impossible.

The setting of the determination threshold values α1 and α2 based on the actual cooling water temperature at the time of starting the engine has the same meaning as in the case of Q5 in FIG. It is compensated that it is changed according to the cooling water temperature at the start of the control.) In addition, the heat dissipation Q
The orh, the heat reception amount Qig, and the calculation method will be described in detail after a further control example shown in FIG. 6 is described.

FIG. 6 shows still another failure determination method by the control unit U, which has both the failure determination method of FIG. 3 and the failure determination methods of FIGS. 4 and 5. Corresponds to claim 5 in the range. In the following description, the failure determination method in FIG. 3 is referred to as an A method diagnosis, and the failure determination method in FIGS.
It is called a diagnostic method.

First, in Q51 of FIG. 6, it is determined whether or not the failure diagnosis of method A has been completed. This Q51
Is YES, the flag A is set to 1 in Q52 to indicate that the failure determination in the A method has been completed. After Q52, in Q54, it is determined whether or not the result of the failure determination in the A method is “normal”. If the determination in Q54 is NO, in Q58, it is finally determined that a failure (valve opening failure) has occurred.

If NO in Q51, Q53
After the flag A is reset to 0, the flow shifts to Q55. Also, when the determination of Q54 is YES, Q5
The processing is shifted to 5. In Q55, it is determined whether or not the failure determination in the B method has been completed. N in the judgment of Q55
In the case of O, the process returns to Q51. Also, YE is determined by the determination of Q55.
In the case of S, in Q56, it is determined whether or not the result of the failure determination in the B method is “normal”. If the determination in Q56 is NO, it is finally determined in Q58 that a failure (valve opening failure) has occurred.

If the determination in Q56 is YES, in Q57, it is determined whether or not the flag A is 1. If the determination in Q57 is NO, the process returns to Q51. If the determination in Q57 is YES, in Q59, it is finally determined that it is normal. Thus, in the control example of FIG.
Only when both the results of the failure determination in the A method and the B method are normal, it is finally determined to be normal, and when the result of at least one of the diagnosis methods is a failure, it is finally determined to be a failure. It has become.

Next, the heat amount ratio R between the heat release amount Qorh and the heat reception amount Qig used in the control examples of FIGS. 4 and 5 will be described.
As shown in equation (16) obtained as described later, the heat release amount Qorh is calculated based on the predicted cooling water temperature and the actual cooling water temperature, and the heat reception amount Qig indicates the operating state of the engine 1. It is calculated based on the operating parameters.

First, the algebraic sum of the amount of heat per unit time flowing into the cooling water is proportional to the product of the heat capacity of the cooling water and the rate of temperature rise per unit time. By applying this relationship to the cooling system model shown in FIG. 1, a differential form (basic expression of the cooling system heat model) as shown in the following equation (1) is obtained.

[0034]

(Equation 1)

Where C: specific heat of cooling water [Kcal / Kg · K] M: mass of cooling water [Kg] θe: temperature of cooling water [K] qig: per unit time of heat transfer from combustion gas to cooling water Qoe: Heat amount per unit time for transferring heat from the engine surface to the atmosphere [Kcal / s] qor: Heat amount per unit time for transferring heat from the radiator surface to the atmosphere [Kcal / s] qoh : Heat quantity per unit time transferred from the heater core surface to the atmosphere [Kcal / s]

The amount of heat per unit time and the total amount of heat transferred from the combustion gas of the engine 1 to the cooling water are determined according to the following equation (2) based on the calorific value of the fuel that has contributed to combustion among the supplied fuel. be able to.

[0037]

(Equation 2)

Rc: ratio of the amount of heat transferred to the cooling water of the amount of heat supplied to the combustion gas. Ηg: ratio of the amount of heat generated by the combustion gas that contributes to an increase in the temperature of the combustion gas. Γ: γ = λ (λ ≧ 1) ), Γ = 1 (when λ <1) λ: excess air ratio of combustion gas gf: fuel supply amount per unit time [Kg / s] Hu: low calorific value of fuel [Kcal / Kg]

The amount of heat per unit time and the total amount of heat transferred from the engine surface, the radiator surface, and the heater core surface into the atmosphere are represented by the formula (3) for the engine surface and the formula (4) for the radiator surface. As shown in the above, the surface of the heater core can be expressed as shown in Expression (5).

[0040]

(Equation 3)

Where, koe: thermal conductivity from the engine surface to the atmosphere vs: vehicle speed [Km / h] θae: atmosphere temperature on the engine surface [K]

[0042]

(Equation 4)

Where, kor: thermal conductivity from the radiator surface to the atmosphere θar: ambient temperature of the radiator [K]

[0044]

(Equation 5)

Where, oh: thermal conductivity from the heater core surface to the atmosphere voh: flow rate of the atmosphere passing through the heater core [Km /
h] θah: Atmospheric temperature of the heater core surface [K]

By substituting the equations (3) to (5) into the threshold (1), a differential form of the following equation (6) can be obtained.

[0047]

(Equation 6)

Here, since the purpose of practical use is to detect a valve opening failure in the valve closing region of the thermostat, the cooling system heat model covers the temperature below the valve opening temperature of the thermostat for simplicity. Further, in the current vehicle system, there is no input information for θae, θar, θah, and voh. Therefore, θae, θar, and θah are
It shall be replaced with the temperature of the intake air θia. Also, k
When oh (voh) is divided into a constant term at voh = 0 and an increment therefrom as in the following equation (7), each equation (8) to (1)
0).

[0049]

(Equation 7)

[0050]

(Equation 8)

[0051]

(Equation 9)

[0052]

(Equation 10)

Therefore, the following equation (11) is obtained from the equation (6).

[0054]

[Equation 11]

At present, it is unknown whether the thermostat 5 is operating normally, that is, qorh is unknown. If the cooling water temperature at this time is set as the actual cooling water temperature detected by the sensor S1 (θe = θea), the following equation (12) is obtained from the equation (11).

[0056]

(Equation 12)

Next, the thermostat 5 operates normally,
In addition, let it be assumed that the cooling water temperature when the blower fan for heating is not operating is unknown and θe = θep. In this case, since the route to the radiator 3 is considered to be disconnected and can be set as qorh = Qorh = 0, the expression (1)
From 1), the following equation (13) is obtained.

[0058]

(Equation 13)

The equation (12) is subtracted from the equation (13) to obtain qorh
The following equation (14) is obtained by rearranging

[0060]

[Equation 14]

By integrating both sides of equation (14), the following equation (1) is obtained.
It becomes like 5).

[0062]

(Equation 15)

Therefore, the heat quantity ratio R of Qorh to Qig is given by the following equation (16) according to the equations (15) and (2).

[0064]

(Equation 16)

In the above equation (16), the left side in the numerator is a term relating to the deviation between the current predicted cooling water temperature and the actual cooling water temperature, and the right side in the numerator is a term relating to the integrated value of the deviation between the two temperatures. (Integrated value of the value obtained by multiplying the vehicle speed). As described above, it is possible to calculate the heat release amount Qorh based on the predicted cooling water temperature and the actual cooling water temperature. The larger the heat amount ratio R is, the larger the heat release amount Q
Since orh is large, heat radiation from the radiator 3 (opening of the thermostat 5) is assumed.

The embodiment has been described above.
Each step (step group) shown in the chart or various members such as a sensor and a switch can be expressed by adding a name of a means to a higher-level expression of its function. Also, the flow
The function of each step (step group) shown in the chart can be expressed as a function of a function unit set in the control unit (controller) (the existence of a function unit). Of course, the objects of the present invention are not limited to those explicitly stated, but also implicitly include providing what is substantially preferred or expressed as advantages. Further, the present invention can be expressed as a failure determination method.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an engine cooling system.

FIG. 2 is a diagram showing a control system for performing a failure determination.

FIG. 3 is a flowchart illustrating a control example of the present invention.

FIG. 4 is a flowchart illustrating a control example of the present invention.

FIG. 5 is a flowchart illustrating a control example of the present invention.

FIG. 6 is a flowchart illustrating a control example of the present invention.

[Explanation of symbols]

 1: Engine 3: Radiator 5: Thermostat 10: Pump S1: Water temperature sensor S2: Intake air amount detection sensor S3: Intake temperature detection sensor S4: Vehicle speed sensor U: Control unit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Seiji Makimoto 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda F-term (reference) 2G087 AA27 BB01 BB27 CC25 EE18 3G084 BA33 CA01 CA04 CA09 DA27 EA07 EA11 EB22 EC01 EC04 FA00 FA02 FA05 FA07 FA20

Claims (5)

[Claims] The valve is opened to circulate the cooling water to the radiator when the cooling water of the engine becomes equal to or higher than a predetermined temperature. When the cooling water is lower than the predetermined temperature, the valve is closed to discharge the cooling water to the radiator. A thermostat failure diagnosis device for an engine cooling system provided with a thermostat for bypassing the engine; a water temperature detection means for detecting an actual temperature of the cooling water; a high load detection means for detecting a high load operation state of the engine; High-speed detection means for detecting an operation state; and when the high-load operation state and the high-speed operation state are continuously detected for a predetermined time or more, an actual water temperature detected by the water temperature detection means is a valve opening temperature of the thermostat. Failure determination means for determining that the thermostat is a valve opening failure when the temperature is lower than Thermostat failure diagnostic device. 2. The valve is opened to circulate the cooling water to the radiator when the cooling water of the engine has reached a predetermined temperature or higher. When the cooling water is lower than the predetermined temperature, the valve is closed to release the cooling water to the radiator. A failure diagnosis device for a thermostat in an engine cooling system provided with a thermostat for bypassing a temperature, wherein first failure determination means for determining a valve opening failure of the thermostat based on an actual cooling water temperature detected by water temperature detection means; A second failure determination unit configured to determine a valve opening failure of the thermostat based on a relationship between an actual cooling water temperature detected by the detection unit and a predicted cooling water temperature calculated from an operation parameter indicating an operation state of the engine; A diagnostic device for a thermostat in an engine cooling system, comprising: 3. The water temperature detection means according to claim 2, wherein the first failure judgment means detects the high load operation state of the engine and the high speed operation state of the vehicle continuously for a predetermined time or more. A thermostat in the engine cooling system, wherein when the actual water temperature is lower than the valve opening temperature of the thermostat, the thermostat is determined to have a valve opening failure. 4. A heat radiation amount calculating means according to claim 3, wherein said second failure judging means calculates a heat radiation amount from said radiator based on a relationship between said predicted temperature and an actual temperature; And a heat receiving amount calculating means for calculating a heat receiving amount from the engine based on the cooling water, and the thermostat is configured to determine a valve opening failure from a relationship between the heat releasing amount and the heat receiving amount. A fault diagnosis device for a thermostat in an engine cooling system. 5. The valve according to claim 2, wherein at least one of the first failure determination means and the second failure determination means determines that a valve opening failure has occurred. It is set so that it is finally determined to be normal only when it is determined that the valve is faulty, and only when both the first failure determination means and the second failure determination means determine normality. A thermostat failure diagnosis apparatus for an engine cooling system, characterized by the following.