JP2004251186A - Device for diagnosing failure of cooling water temperature sensor for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately determine failure of an engine water temperature sensor. <P>SOLUTION: This failure diagnosing device is provided with a sensor for detecting temperature of the cooling water for an internal combustion engine mounted on a vehicle, and a timer for determining whether a predetermined time has passed or not after starting the internal combustion engine. This failure diagnosing device computes a calorific value generated in the internal combustion engine on the basis of the fuel injection quantity of the internal combustion engine, and computes a cooling loss of the internal combustion engine on the basis of the computed calorific value. An effective calorific value is computed by subtracting the cooling loss from the calorific value, and the effective calorific value is added over the predetermined time. In the case where the effective added calorific values after the predetermined time passed are out of a predetermined range, when a change rate of the detection values of the sensor is smaller than a predetermined value, failure of the sensor is determined. The cooling loss can be corrected in response to the car speed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a failure diagnosis device that diagnoses a failure of a sensor that detects a temperature of cooling water of an internal combustion engine.
[0002]
[Prior art]
A radiator is mounted on a vehicle, and an internal combustion engine (hereinafter, referred to as an engine) is cooled by cooling water supplied from the radiator. The engine is provided with a sensor for detecting the temperature of the cooling water (hereinafter, referred to as an engine water temperature sensor). The temperature detected by the engine water temperature sensor is used for various controls of the engine. If the engine water temperature is not accurately detected, the engine cannot be properly controlled.
[0003]
One example of a method of detecting a failure of the engine water temperature sensor monitors a detection value of the engine water temperature sensor for a predetermined time. If the detected value changes beyond a predetermined range, it is determined that the sensor is normal. If the change in the detection value falls within the predetermined range, it is determined that the sensor has failed (for example, see Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-45851
[Problems to be solved by the invention]
Operation in which the engine water temperature hardly changes may be performed. When the engine in such a thermal equilibrium state is stopped and then restarted, if the same thermal equilibrium state operation is performed, the engine water temperature sensor may hardly change. According to the conventional method, in such a thermal equilibrium state, a normal engine water temperature sensor may be erroneously determined to be faulty.
[0006]
Therefore, there is a need for a failure diagnosis device that can more accurately determine the failure of the engine water temperature sensor even in the thermal equilibrium state.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a failure diagnosis device according to the present invention includes a sensor that detects a temperature of cooling water of an internal combustion engine mounted on a vehicle, and a timer that measures a predetermined time after the internal combustion engine starts. . The failure diagnosis device calculates the amount of heat generated by the internal combustion engine based on the fuel injection amount of the internal combustion engine. The cooling loss of the internal combustion engine is calculated based on the calorific value of the internal combustion engine. The effective heat amount is calculated by subtracting the cooling loss from the heat generation amount. The effective heat quantity is integrated over the above-mentioned predetermined time, and the effective integrated heat quantity is obtained. If the amount of change in the detection value of the sensor is smaller than the predetermined value when the effective integrated heat amount when the predetermined time has elapsed is outside the predetermined range, it is determined that the sensor has failed.
[0008]
According to the present invention, by calculating the cooling loss based on the calorific value, the cooling loss in the thermal equilibrium state can be accurately and easily calculated. Therefore, whether or not the engine is in a thermal equilibrium state can be accurately determined by checking whether or not the effective integrated heat amount is within a predetermined range. If the change in the engine water temperature is small when not in the thermal equilibrium state, it is determined that the engine water temperature sensor has failed. Therefore, it is possible to avoid erroneously determining that the normal engine water temperature sensor has failed.
[0009]
In one embodiment of the present invention, the failure diagnosis device further calculates a difference between the maximum value and the minimum value of the detection values of the sensor during the predetermined time. If the difference between the maximum value and the minimum value is smaller than a predetermined value when the effective accumulated heat amount when the predetermined time has elapsed is outside the predetermined range, it is determined that the sensor has failed.
[0010]
According to the present invention, by detecting the maximum value and the minimum value of the engine water temperature, the fluctuation range of the engine water temperature that can be detected by the engine water temperature sensor can be acquired more accurately. Therefore, a failure of the engine water temperature sensor can be detected more accurately.
[0011]
In one embodiment of the present invention, the cooling loss is corrected according to the speed of a vehicle equipped with the internal combustion engine. With the correction based on the vehicle speed, the cooling loss can be calculated more accurately.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall system configuration diagram of an internal combustion engine (hereinafter, referred to as “engine”) and a control device thereof according to an embodiment of the present invention.
[0013]
An electronic control unit (hereinafter, referred to as an “ECU”) 5 includes an input interface 5a for receiving data transmitted from each section of the vehicle, a CPU 5b for performing an operation for controlling each section of the vehicle, and a read-only memory (ROM). ) And a memory 5c having a random access memory (RAM), and an output interface 5d for sending a control signal to each part of the vehicle. The ROM of the memory 5c stores a program for controlling each part of the vehicle and various data. A program for implementing the failure diagnosis according to the present invention, and data and tables used when executing the program are stored in the ROM. The ROM may be a rewritable ROM such as an EEPROM. The RAM is provided with a work area for calculation by the CPU 5b. Data sent from each part of the vehicle and control signals sent to each part of the vehicle are temporarily stored in the RAM.
[0014]
The engine 1 is, for example, an engine having four cylinders. An intake pipe 2 is connected to the engine 1. A throttle valve 3 is provided upstream of the intake pipe 2. A throttle valve opening sensor (θTH) 4 connected to the throttle valve 3 supplies an electric signal corresponding to the opening of the throttle valve 3 to the ECU 5.
[0015]
A passage 21 that bypasses the throttle valve 3 is provided in the intake pipe 2. A bypass valve 22 for controlling the amount of air supplied to the engine 1 is provided in the bypass passage 21. The bypass valve 22 is driven according to a control signal from the ECU 5.
[0016]
The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2. The fuel injection valve 6 is connected to a fuel pump (not shown), and receives supply of fuel from a fuel tank (not shown) via the fuel pump. The fuel injection valve 6 is driven according to a control signal from the ECU 5.
[0017]
The intake pipe pressure (Pb) sensor 8 and the intake temperature (Ta) sensor 9 are provided on the intake pipe 2 downstream of the throttle valve 3. The intake pipe pressure Pb and the intake air temperature Ta detected by the Pb sensor 8 and the Ta sensor 9 are sent to the ECU 5, respectively.
[0018]
The engine water temperature (Tw) sensor 10 is attached to a cylinder wall (not shown) of the cylinder block of the engine 1 which is filled with cooling water. The temperature Tw of the engine cooling water detected by the Tw sensor 10 is sent to the ECU 5.
[0019]
The rotation speed (Ne) sensor 13 is mounted around a camshaft or a crankshaft (both not shown) of the engine 1. The Ne sensor 13 outputs a CRK signal pulse at a cycle of a crank angle (for example, 30 degrees) shorter than a cycle of a TDC signal pulse output at a crank angle related to the TDC position of the piston, for example. The CRK signal pulse is counted by the ECU 5, and the engine speed Ne is detected.
[0020]
An exhaust pipe 14 is connected to the downstream side of the engine 1. The engine 1 exhausts through an exhaust pipe 14. A catalyst device 15 provided in the exhaust pipe 14 purifies harmful components such as HC, CO, and NOx in the exhaust gas passing through the exhaust pipe 14.
[0021]
The wide area air-fuel ratio sensor (LAF) sensor 16 is provided upstream of the catalyst device 15. The LAF sensor 16 linearly detects the oxygen concentration in the exhaust gas in a wide air-fuel ratio range from lean to rich. The detected oxygen concentration is sent to the ECU 5.
[0022]
A vehicle speed (VP) sensor 17 is mounted near a drive shaft (not shown) of the vehicle on which the engine 1 is mounted, and outputs a pulse each time the wheel makes one revolution, and sends it to the ECU 5. The ECU 5 detects the vehicle speed based on the output of the VP sensor 17.
[0023]
The signal sent to the ECU 5 is passed to the input interface 5a, and is subjected to analog-digital conversion. The CPU 5b processes the converted digital signal according to a program stored in the memory 5c, and generates a control signal to be sent to an actuator of the vehicle. The output interface 5d sends these control signals to actuators of the bypass valve 22, the fuel injection valve 6, and other mechanical elements.
[0024]
There are two situations where the engine water temperature sensor hardly changes. The first case is when the engine water temperature sensor is fixed. Stiction indicates a condition in which the sensor does not respond to changes in engine water temperature and may occur, for example, due to a disconnection or short circuit. Sticking is a fault that is typically detected by the fault diagnostic device according to the present invention.
[0025]
The second is a case where the engine water temperature sensor is in a thermal equilibrium state even though it is normal. The thermal equilibrium state indicates a state in which the amount of heat generated by combustion in the engine and the cooling loss are in equilibrium. The cooling loss indicates, for example, the amount of heat lost by external factors such as wind and a heater. In the thermal equilibrium state, the effective heat quantity represented by "heat quantity-cooling loss" is almost zero, and thus the engine coolant temperature hardly fluctuates.
[0026]
According to the conventional method, when a situation where the engine water temperature hardly changes is detected, it is erroneously determined that the engine water temperature sensor has failed. However, according to the failure diagnosis device of the present invention, when such a small fluctuation range of the engine water temperature is detected, it is checked whether or not the engine is in a thermal equilibrium state. If it is determined that the engine is in the thermal equilibrium state, the failure determination for the engine coolant temperature sensor is suspended (or prohibited). Therefore, it is possible to avoid erroneously determining that the normal engine water temperature sensor is out of order.
[0027]
FIG. 2 shows a functional block diagram of a failure diagnosis device for an engine coolant temperature sensor according to one embodiment of the present invention. The functions represented by these functional block diagrams are typically realized by a computer program stored in the memory 5c (FIG. 1).
[0028]
The operating state detector 31 receives detection values from various sensors shown in FIG. The change amount detection unit 32 calculates a change amount of the detection value Tw of the engine water temperature sensor 10. The amount of change is calculated by the maximum value of | Tw-the minimum value of Tw. If the amount of change is larger than the first reference value, the diagnosis unit 33 determines that the engine coolant temperature sensor 10 is normal. This is because such a change does not occur if a failure (typically, sticking) occurs in the engine water temperature sensor.
[0029]
The timer 34 measures a predetermined time Ptime. Before the predetermined time Ptime has elapsed, the cooling loss CL is estimated by the cooling loss estimation block 35. The cooling loss estimation block 35 further includes function blocks 36 to 39.
[0030]
The first calorie calculating unit 36 calculates a calorific value Q per unit time generated by combustion in the engine. The heat quantity Q can be approximated by the fuel injection amount per unit time. The fuel injection amount per unit time is calculated by “basic fuel injection amount TIM × the number of injections per unit time”. Here, the basic fuel injection amount TIM indicates the amount of fuel injected at one time by the fuel injection valve 6 (FIG. 1), and is typically determined according to the engine speed NE and the intake pipe pressure PB. . The number of injections per unit time can be calculated based on the rotation speed NE. The unit time can be set to any appropriate value (for example, one TDC cycle).
[0031]
Depending on the vehicle, the calorific value Q may be further corrected by the intake pipe pressure PB or the like.
[0032]
Alternatively, the heat quantity Q may be calculated by another appropriate method. For example, the amount of heat Q may be calculated by detecting or estimating the amount of air supplied to the cylinder.
[0033]
The first integrator 37 integrates the heat quantity Q over a predetermined time Ptime to calculate an integrated heat quantity QTTL. The averaging unit 38 calculates an average amount of heat QAVE per unit time by dividing the integrated amount of heat QTTL by the predetermined time Ptime.
[0034]
The cooling loss calculator 39 calculates a cooling loss per unit time under the condition of a thermal equilibrium state. Since the thermal equilibrium state indicates that the heat generation amount and the cooling loss are substantially equal, the cooling loss CL can be approximated by the average heat amount QAVE. If the engine is in thermal equilibrium, the cooling loss CL is estimated with good accuracy.
[0035]
If the predetermined time Ptime has elapsed, the thermal equilibrium state block 40 determines whether the engine is in thermal equilibrium. The thermal equilibrium state block 40 further includes function blocks 41 to 43.
[0036]
The second calorie calculator 41 calculates the calorific value Q per unit time in the same manner as the first calorie calculator 36. The effective heat amount calculation unit 42 receives the cooling loss CL from the cooling loss estimation block 35. The effective heat amount calculation unit 42 calculates the effective heat amount by subtracting the cooling loss CL from the heat amount Q.
[0037]
The second integrator 43 adds the effective heat quantity (Q-CL) to the effective accumulated heat quantity QRF calculated in the previous cycle. When the engine is in a thermal equilibrium state, the effective heat quantity (Q-CL) has a value close to zero, and the effective accumulated heat quantity QRF hardly changes. Therefore, the fact that the effective integrated heat amount QRF falls within the predetermined range indicates that the thermal equilibrium state is established. In the thermal equilibrium state, an accurate failure determination cannot be made for the engine coolant temperature sensor 10, so the diagnosis unit 33 suspends (or inhibits) the failure determination.
[0038]
On the other hand, if the engine coolant temperature sensor 10 is actually fixed and is not in a thermal equilibrium state, a difference occurs between the average calorific value QAVE and the current calorific value Q (calculated by the second calorific value calculator 41). Since the cooling loss CL is approximated by the average heat quantity QAVE, the effective heat quantity (Q-CL) has a substantial value, and the effective integrated heat quantity QRF fluctuates beyond a predetermined range. In this case, the engine water temperature does not fluctuate even though it is not in the thermal equilibrium state, so the diagnosis unit 33 determines that the engine water temperature sensor 10 has failed.
[0039]
FIG. 3 is a diagram showing an example of the behavior of the failure diagnosis device according to the embodiment of the present invention in a thermal equilibrium state.
[0040]
In the previous operation cycle, the engine water temperature Tw is almost constant, which indicates that the engine is in a thermal equilibrium state. When the ignition switch is turned off at time t0, the engine stops. In response, engine water temperature Tw decreases.
[0041]
At time t1, the ignition switch is turned on again, and the current operation cycle is started. Since the engine is started, the engine water temperature Tw rises. From time t2, the engine coolant temperature Tw becomes substantially constant, and reaches a thermal equilibrium state.
[0042]
An average amount of heat QAVE is calculated over a predetermined time Ptime from the start of the engine, and the cooling loss CL is approximated by the average amount of heat QAVE. Preferably, the cooling loss CL is corrected by the vehicle speed VP.
[0043]
Since the engine coolant temperature Tw hardly fluctuates, there is a possibility that the engine has failed. Therefore, after the elapse of the predetermined period Ptime, it is determined whether or not the thermal equilibrium state exists. Since the effective integrated heat amount QRF calculated based on the effective heat amount (Q-CL) falls within a predetermined range defined by TRQ and TFQ, it is determined that the heat is in an equilibrium state. Therefore, the failure determination for the engine water temperature sensor 10 is suspended.
[0044]
According to the conventional method, in a thermal equilibrium state as shown in FIG. 3, it is determined that the engine water temperature sensor is stuck. According to the present invention, such erroneous determination can be avoided.
[0045]
A shaded area 43 indicates a fixed area. If the engine water temperature Tw fluctuates beyond the fixed region 43, the engine water temperature sensor 10 is determined to be normal.
[0046]
The detection value of the engine water temperature sensor is converted to a digital value. This digital value includes noise due to fluctuations in the ground voltage level and analog-digital conversion. It is preferable to set the width w of the fixed region 43 in consideration of such noise. In one embodiment of the present invention, the width w is represented by a predetermined number of bits (for example, 3 bits).
[0047]
As an example, it is assumed that the reference value TW0 of the engine coolant temperature has been converted to a digital value “3A”. The conversion can be performed based on a predetermined rule. The digital value that is three bits lower than the digital value “3A” is “37”. Thereafter, if an engine water temperature corresponding to a digital value smaller than the digital value “37” is detected, the engine water temperature sensor 10 is determined to be normal (for example, if the subsequently detected engine water temperature is “33”). , The amount of change from the reference value is 7 bits, which is larger than the width w (3 bits), so that the engine coolant temperature sensor is determined to be normal). By expressing the width w by the number of bits, the diagnostic processing executed by the ECU 5 can be simplified.
[0048]
When the width w of the fixed region 43 is represented by the number of bits, a rule for converting an analog temperature detection value into a digital value is defined in consideration of the width w. For example, when the width w is 3 bits and the change in the digital value is 3 bits or less, the digital value is assigned to the analog temperature detection value so that it can be reliably determined that the engine water temperature sensor has failed. Done.
[0049]
FIG. 4 is an example of a flowchart executed by the failure diagnosis device shown in FIG. The flowchart is executed at regular time intervals after the engine is started.
[0050]
In step S1, the current engine coolant temperature Tw is obtained from the engine coolant temperature sensor 10. In step S2, if the engine coolant temperature Tw is larger than the maximum value stored in the memory 5c (FIG. 1), the maximum value is updated with the engine coolant temperature Tw (S3). In step S4, if the engine coolant temperature Tw is smaller than the minimum value stored in the memory 5c, the minimum value is updated with the engine coolant temperature Tw (S5).
[0051]
In step S6, it is determined whether the deviation between the maximum value and the minimum value is larger than the first reference value. If the determination in step S6 is Yes, it indicates that the engine coolant temperature is fluctuating, and the engine coolant temperature sensor 10 determines that it is normal (S7).
[0052]
As described above, in one embodiment, the first reference value corresponds to the width w of the fixed region 43. The width w can be represented by the number of bits, for example, 3 bits. In this case, if the difference between the two digital values of the maximum and minimum values of the engine water temperature is larger than 3 bits, the engine water temperature sensor 10 is determined to be normal.
[0053]
If the determination in step S6 is No, the timer value is checked to determine whether a predetermined time Ptime has elapsed. The initial value of the timer is zero. Until the predetermined time Ptime has elapsed, the determination in step S8 is No, and in step S9, the timer value is incremented.
[0054]
In step S10, the calorific value Q per unit time is calculated based on the fuel injection amount per unit time, as described above. As an example, the unit time is set to a cycle time at which the flowchart is performed. When the cycle time is represented by S_Time, the heat quantity Q can be approximated by a value calculated according to “basic fuel injection amount TIM × rotation speed NE / S_time”.
[0055]
In step S11, the heat quantity Q calculated in step S10 is added to the previous accumulated heat quantity QTTL (k-1) to calculate the current accumulated heat quantity QTTL (k). Here, k is an identifier for identifying a cycle. In step S12, the average heat quantity QAVE is calculated by dividing the accumulated heat quantity QTTL (k) by the timer value.
[0056]
In step S13, the average vehicle speed VAVE is calculated. For example, the average vehicle speed VAVE can be calculated by dividing the integrated value of the vehicle speed VP detected by the vehicle speed sensor 17 by the timer value.
[0057]
In step S14, the cooling loss basic value CLBASE is calculated by dividing the average heat quantity QAVE by a vehicle speed correction value KVAVE corresponding to the average vehicle speed VAVE.
[0058]
FIG. 5 shows an example of a vehicle speed correction table stored in the memory 5c. By referring to the table based on the average vehicle speed VAVE, a vehicle speed correction value KVAVE corresponding to the average vehicle speed VAVE can be obtained.
[0059]
The average amount of heat in step S12 may be calculated using a moving average method. As an example, the average amount of heat QAVE (k) is represented by “(heat amount Q (k− (n−1)) + heat amount Q (k− (n−2)) +,..., + Heat amount Q (k)) / (cycle Time × n) ”. n is an arbitrary integer.
[0060]
In still another example, the average heat quantity QAVE (k) can be determined according to “(average heat quantity QAVE (k−1) × (n−1) + heat quantity Q (k)) / (cycle time × n)”. .
[0061]
Further, the average vehicle speed VAVE in step S13 may be obtained using such a moving average method.
[0062]
Referring back to FIG. 4, if the predetermined time Ptime has elapsed, the determination in step S8 becomes Yes. In step S15, the heat quantity Q (k) is calculated in the same manner as in step S10. In step S16, the cooling loss CL is calculated by multiplying the cooling loss basic value CLBASE by a vehicle speed correction coefficient KVAVE corresponding to the current vehicle speed VP (obtained from the vehicle speed sensor 17). The vehicle speed correction coefficient KVAVE can be obtained by referring to the table of FIG.
[0063]
In step S17, the effective integrated heat amount QRF (k) for the current cycle is calculated by adding the effective heat amount (Q-CL) to the effective integrated heat amount QRF (k-1) calculated in the previous cycle.
[0064]
In step S18, if the effective integrated heat amount QRF (k) is larger than the predetermined upper limit TRQ, it is determined that the vehicle is not in the thermal equilibrium state. Also, in step S19, if the effective integrated heat amount QRF (k) is smaller than a predetermined lower limit value TFQ, it is determined that there is no thermal equilibrium. In these cases, the engine water temperature Tw does not change even though it is not in the thermal equilibrium state, so it is determined that the engine water temperature sensor 10 has failed (S20).
[0065]
On the other hand, if the effective integrated heat amount QRF (k) is between the upper limit value TRQ and the lower limit value TFQ, it is determined that the engine is in a thermal equilibrium state, and the failure determination for the engine water temperature sensor 10 in this cycle is suspended. Alternatively, the failure diagnosis in the current operation cycle may be prohibited. Here, one operation cycle indicates a period from the start to the stop of the engine.
[0066]
In another embodiment, the upper limit TRQ and the lower limit TFQ can be obtained by referring to a predetermined table based on the first reference value. FIG. 6 shows an example of such a table.
[0067]
Depending on the characteristics of the engine water temperature sensor and the engine, the relationship between the engine water temperature and the amount of heat may not be proportional. For example, the amount of heat when the engine water temperature changes by 2 ° C. when the engine water temperature is around 100 ° C. may be different from the amount of heat when the engine water temperature changes by 2 ° C. when the engine water temperature is around 60 ° C. In such a case, the upper limit TRQ and the lower limit TFQ suitable for the current engine coolant temperature can be obtained by referring to the table shown in FIG. 6 based on the first reference value.
[0068]
For example, when the detected maximum value of the engine water temperature is high, the upper limit value TRQ1 and the lower limit value TFQ1 are obtained by referring to the curve 52, and when the detected maximum value of the engine water temperature is lower, the curve 51 is used. To obtain the upper limit value TRQ2 and the lower limit value TFQ2. When the detected maximum value of the engine water temperature falls between the engine water temperature set for the curve 51 and the engine water temperature set for the curve 52, the upper limit value TRQ is obtained by linear interpolation based on TRQ1 and TRQ2. , TFQ1 and TFQ2, the lower limit value TFQ can be obtained by linear interpolation.
[0069]
Alternatively, the table shown in FIG. 6 may be configured to be able to be referred to based on other values. For example, the table is configured such that the upper limit value TRQ and the lower limit value TFQ can be obtained by referring to the table based on the minimum value of the detected engine water temperature or the average value of the detected engine water temperature. be able to.
[0070]
The present invention can also be applied to a marine propulsion engine such as an outboard motor having a vertical crankshaft.
[0071]
【The invention's effect】
According to the present invention, even when the engine is in a thermal equilibrium state, it is possible to avoid erroneously determining a normal engine water temperature sensor as a failure.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an engine and a control device thereof according to an embodiment of the present invention.
FIG. 2 is a functional block diagram of an apparatus for diagnosing a failure of an engine water temperature sensor according to one embodiment of the present invention.
FIG. 3 is a diagram showing a behavior of the failure diagnosis device according to the embodiment of the present invention.
FIG. 4 is a flowchart for diagnosing a failure of an engine water temperature sensor according to one embodiment of the present invention.
FIG. 5 is a diagram showing a vehicle speed correction table according to one embodiment of the present invention.
FIG. 6 is a diagram showing a table for obtaining an upper limit value TRQ and a lower limit value TFQ of a heat quantity according to another embodiment of the present invention.
[Explanation of symbols]
1 Engine 5 ECU
9 Intake air temperature sensor 10 Engine water temperature sensor

Claims (3)

A sensor for detecting a temperature of cooling water of an internal combustion engine mounted on the vehicle,
A timer for measuring a predetermined time since the internal combustion engine is started,
Calorific value calculating means for calculating the amount of heat generated by the internal combustion engine based on the fuel injection amount of the internal combustion engine,
A cooling loss calculating unit that calculates a cooling loss of the internal combustion engine based on a calorific value of the internal combustion engine,
Subtracting the cooling loss from the heat generation amount, effective heat amount calculation means to calculate the effective heat amount,
Integrating means for integrating the effective heat amount for a predetermined time;
When the effective integrated heat amount when the predetermined time has elapsed is outside a predetermined range, if a change amount of a detection value of the sensor is smaller than a predetermined value, a determination unit that determines that the sensor has failed,
A failure diagnosis device comprising: Further comprising a deviation calculating means for calculating a difference between a maximum value and a minimum value of the detection values of the sensor during the predetermined time,
The determining means determines that the sensor has failed if the difference between the maximum value and the minimum value is smaller than a predetermined value when the effective accumulated heat amount at the time when the predetermined time has elapsed is outside a predetermined range. The fault diagnosis device according to claim 1. The failure diagnosis device according to claim 1, wherein the cooling loss is corrected according to a vehicle speed of a vehicle on which the internal combustion engine is mounted.

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