WO2011114234A1

WO2011114234A1 - Control system and control method of internal combustion engine

Info

Publication number: WO2011114234A1
Application number: PCT/IB2011/000730
Authority: WO
Inventors: Toru Sameshima
Original assignee: Toyota Jidosha Kabushiki Kaisha; Denso Corporation
Priority date: 2010-03-16
Filing date: 2011-03-16
Publication date: 2011-09-22
Also published as: JP2011190778A

Abstract

A control system of an internal combustion engine includes: a turbocharger (22) having a turbine (24) and a compressor (26); a waste gate valve (30) that regulates the amount of exhaust gas that bypasses the turbine (24); a valve control unit (50) that controls an opening of the waste gate valve (30); an exhaust temperature sensor (38) that detects an exhaust temperature downstream of the waste gate valve (30), and is located at a position where a detection value of the exhaust temperature increases as the opening of the waste gate valve (30) increases; and a failure detecting unit (50) that performs detection of a failure of the waste gate valve (30) based on the detection value of the exhaust temperature sensor (38), in a condition where the valve control unit (50) controls the opening of the waste gate valve (30) to a particular opening.

Description

CONTROL SYSTEM AND CONTROL METHOD OF INTERNAL COMBUSTION

ENGINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to control system and control method of an internal combustion engine, and more particularly to control system and control method of an internal combustion engine having a waste gate valve (WGV) that controls the boost pressure.

2. Description of the Related Art

[0002] As one example of the related art, a control system of an internal combustion engine having a waste gate valve (WGV) as described in, for example, Japanese Patent Application Publication No. 2009-287409 (JP-A-2009-287409) is known. The control system of the internal combustion engine is configured to detect the temperature (exhaust temperature) of exhaust gas, by means of an exhaust temperature sensor located in the vicinity of the WGV. When the exhaust temperature increases to an excessively high level, the system performs the control so that the exhaust temperature is reduced, thereby to suppress or prevent overheating of components, for example. Also, the control system of the internal combustion engine is configured to carry out deterioration diagnostic of the exhaust temperature sensor. More specifically, the WGV is initially brought into an open position while the engine is in an idling state, so that exhaust gas flows around the exhaust temperature sensor. Then, the actual exhaust temperature detected in this condition is compared with an exhaust temperature in an idling state, which has been obtained in advance by experiment, or the like, so as to make a diagnostic as to whether the sensor is deteriorated.

[0003] The above-described control system of the internal combustion engine is configured to perform a deterioration diagnostic of the exhaust temperature sensor, in a condition where the WGV is in the open position. However, in the above-described control system of the internal combustion engine, the occurrence of a failure in the WGV is not anticipated, and, if a failure occurs in the WGV, it becomes impossible to carry out deterioration diagnostic of the exhaust temperature sensor. Thus, there is room for improvement in the failure diagnostic function of the system including the WGV.

SUMMARY OF THE INVENTION

[0004] The invention provides a control system of an internal combustion engine which can detect a failure of a WGV with simple configuration, and improve the reliability without incurring a significant increase in cost.

[0005] A first aspect of the invention provides a control system of an internal combustion engine, including: a turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage, and operable to supercharge the internal combustion engine with intake air, utilizing an exhaust pressure; a waste gate valve that regulates the amount of exhaust gas that bypasses the turbine of the turbocharger; a valve control unit that controls an opening of the waste gate valve; an exhaust temperature sensor that detects an exhaust temperature downstream of the waste gate valve, and is located at a position where a detection value of the exhaust temperature increases as the opening of the waste gate valve increases; and a failure detecting unit that performs detection of a failure of the waste gate valve based on the detection value of the exhaust temperature sensor, in a condition where the valve control unit controls the opening of the waste gate valve to a particular opening.

[0006] According to the first aspect of the invention, the exhaust temperature sensor is located at the position where its detection value increases according to the opening of the WGV, so that a given relationship can be set or established between the opening of the WGV and the detection value of the exhaust temperature sensor. With this relationship stored as data, the system can detect the opening of the WGV based on the detection value of the exhaust temperature sensor. Accordingly, the failure detecting unit can easily detect a failure of the WGV based on the detection value of the exhaust temperature sensor, in a condition where the WGV is controlled to a particular opening. This eliminates the, need to provide an opening sensor, or the like, for the WGV, thus assuring improved reliability without incurring a significant increase in the cost of the system.

[0007] The control system of the internal combustion engine according to the first aspect of the invention may further include a first detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a first opening, as a first detection value, and a second detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a second opening, as a second detection value, and the failure detecting unit may perform the detection of the failure based on at least the first detection value and the second detection value.

[0008] The control system of the internal combustion engine according to the first aspect of the invention may further include a fully-closed-state detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the waste gate valve is controlled to a fully closed position or the vicinity thereof, as a fully-closed-state detection value, and a fully-open-state detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the waste gate valve is controlled to a fully open position or the vicinity thereof, as a fully-open-state detection value, and the failure detecting unit may perform the detection of the failure based on at least the fully-closed-state detection value and the fully-open-state detection value.

[0009] With the above arrangement, the failure detecting unit can detect a failure based on detection values at two different openings representing the fully closed position and the fully open position, thus assuring improved failure detection accuracy. In particular, failure detection is performed especially at the fully closed position and fully open position at which a failure, such as sticking, is likely to occur. Also, the use of the detection values obtained at the upper limit and lower limit of the operating range of the WGV makes it possible to have the detection value(s) reflect information on a failure that occurs at a certain intermediate opening, and thus detect a failure over the entire operating range with high sensitivity.

[0010] In the control system of the internal combustion engine as described above, the failure detecting unit may further include a valve closing determining unit that determines whether a valve closing operation of the waste gate valve is normal, based on a fully-closed-state reference value as a reference value of the detection value of the exhaust temperature sensor in the case where the waste gate valve is at or in the vicinity of the fully closed position, and the fully-closed-state detection value, and a valve opening determining unit that determines whether a valve opening operation of the waste gate valve is normal, based on a difference between the fully-closed-state detection value and the fully-open-state detection value, after the valve closing determining unit determines that the valve closing operation is normal.

[0011] With the above arrangement, the valve closing determining unit can determine whether the valve closing operation of the WGV is normal. Also, the valve opening determining unit can determine whether the valve opening operation of the WGV is normal. Accordingly an abnormality in the valve closing operation of the WGV (a failure in the open position) and an abnormality in the valve opening operation of the WGV (a failure in the closed position) are detected such that these abnormalities can be distinguished from each other. Consequently, detailed failure information can be obtained, and an appropriate countermeasure against a detected failure can be taken depending on the type of the failure, for example.

[0012] The control system of the internal combustion engine as described above may further include a reference value setting unit that variably sets the fully-closed-state reference value based on operating conditions of the internal combustion engine.

[0013] With the above arrangement, the reference value setting unit can set the fully-closed-state reference value to an appropriate value based on the operating conditions of the internal combustion engine. Thus, the possibility of erroneously detecting a failure due to change of the operating conditions of the internal combustion engine can be reduced or eliminated.

[0014] The control system of the internal combustion engine according to the first aspect of the invention may further include an in-cylinder pressure detecting unit that detects an in-cylinder pressure of the internal combustion engine, and a correcting unit that corrects the detection value of the exhaust temperature sensor based on the in-cylinder pressure detected by the in-cylinder pressure detecting unit.

[0015] With the above arrangement, even when an error occurs in the detection value of the exhaust temperature sensor, the correcting unit can correct the detection value to remove the error based on the in-cylinder pressure, and therefore, the accuracy of the detection value can be enhanced. Accordingly, the possibility of erroneously detecting a failure can be reduced or eliminated, and control at the time of a failure can be performed with increased accuracy.

[0016] In the control system of the internal combustion engine according to the first aspect of the invention, the exhaust temperature sensor may be located at a position downstream of the waste gate valve where the amount of exhaust gas that contacts the exhaust temperature sensor increases as the opening of the waste gate valve increases.

In this case, the waste gate valve may regulate the amount of exhaust gas flowing in a bypass passage provided in the exhaust passage so as to bypass the turbine of the turbocharger, and may include a plate valve body disposed in an opening end of the bypass passage. The plate valve body may be arranged to swing so as to control the opening of the waste gate valve, and the exhaust temperature sensor may be mounted on a wall of the exhaust passage downstream of the waste gate valve.

[0017] With the above arrangement, the exhaust temperature sensor can be located at the position where its detection value increases according to the opening of the

WGV.

[0018] The control system of the internal combustion engine according to the first aspect of the invention may further include an operating condition determining unit that determines whether operating conditions of the internal combustion engine are suitable for performing the detection of the failure. In this case, when the internal combustion engine is in steady-state operating conditions, and no failure occurs in the exhaust temperature sensor, the operating condition determining unit may determine that the operating conditions of the internal combustion engine are suitable for performing the detection of the failure. When the operating condition determining unit determines that the operating conditions of the internal combustion engine are suitable for performing the detection of the failure, the failure detection unit may perform the detection of the failure.

[0019] With the above arrangement, the operating condition determining unit can determine whether the operating conditions of the internal combustion engine are suitable for failure detection. It is thus possible to activate the failure detecting unit, depending on whether the operating conditions suitable for failure detection are achieved, and thus perform failure detection with stability.

[0020] A second aspect of the invention provides a control method of an internal combustion engine including a turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage, and operable to supercharge the internal combustion engine with intake air, utilizing an exhaust pressure, and a waste gate valve that regulates the amount of exhaust gas that bypasses the turbine of the turbocharger, which method includes: providing an exhaust temperature sensor that detects an exhaust temperature downstream of the waste gate valve, at a position where a detection value of the exhaust temperature increases as an opening of the waste gate valve increases, controlling the opening of the waste gate valve to a particular opening, and performing detection of a failure of the waste gate valve based on the detection value of the exhaust temperature sensor, in a condition where the opening of the waste gate valve is controlled to the particular opening.

[0021] According to the second aspect of the invention, it is possible to easily detect a failure of the WGV, and improve the reliability without incurring a significant increase in the cost of the system, as in the first aspect of the invention.

[0022] The control method of the internal combustion engine according to the second aspect of the invention may further include the steps of: obtaining a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a first opening, as a first detection value, and obtaining a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a second opening, as a second detection value, and the detection of the failure may be performed based on at least the first detection value and the second detection value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic diagram illustrating the overall system configuration of a first embodiment of the invention;

FIG. 2 is an external view of an exhaust system, showing the locations of a turbocharger, a waste gate valve, an exhaust temperature sensor, and so forth;

FIG. 3 is a view showing a characteristic curve indicative of the relationship between the opening of the waste gate valve and the detection value of the exhaust temperature sensor;

FIG. 4 shows map data used for setting a fully-closed-state reference value based on an engine speed and a load;

- FIG. 5 shows map data used for setting a fully-closed-state reference value based on a vehicle speed;

FIG. 6 is a flowchart of control executed by ECU in the first embodiment of the invention;

FIG. 7 is a schematic diagram illustrating the overall system configuration of a second embodiment of the invention;

FIG. 8 is a flowchart of control executed by ECU in the second embodiment of the invention;

SUBSTITUTE SHEET RULE 26 FIG. 9 is a flowchart of control executed by ECU;

FIG 10 is a flowchart of control executed by ECU;

FIG. 11 shows map data used for detecting a failed valve opening of a waste gate valve based on a fully-open-state detection value, in a third embodiment of the invention; and

FIGS. 12A and 12B are flowcharts of control executed by ECU in the third embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] First Embodiment Referring to FIG. 1 through FIG. 6, a first embodiment of the invention will be described. FIG. 1 is a schematic diagram illustrating the overall system configuration of the first embodiment of the invention. However, FIG. 1 schematically illustrates the overall configuration to facilitate explanation of the system, and the positional relationships among components, such as a WGV 30 and an exhaust temperature sensor 38 as described later, are not necessarily accurate.

[0025] The system of this embodiment includes an engine 10 as an internal combustion engine, and each cylinder of the engine 10 is provided with a fuel injection valve, intake valves and exhaust valves (none of which is shown in FIG. 1), and so forth. The engine 10 also includes an intake passage 12 through which intake air is drawn into each cylinder, and an exhaust passage 14 through which exhaust gas is discharged from each cylinder. An electronically controlled throttle valve 16 that controls the intake air amount and an intercooler 18 are disposed in the intake passage 12, and a catalyst 20 that cleans exhaust gas is disposed in the exhaust passage 14.

[0026] The engine 10 is also installed with a turbocharger 22 that supercharges the engine 10 with intake air, utilizing the exhaust pressure, and the turbocharger 22 includes a turbine 24 disposed in the exhaust passage 14, and a compressor 26 disposed in the intake passage 12. During operation of the turbocharger 22, the turbine 24 receives the exhaust pressure and rotates, thereby to drive the compressor 26, so that the compressor 26 compresses the intake air to a high pressure level (boost pressure), and supplies the compressed air into each cylinder. The engine 10 also includes a bypass passage 28 provided in the exhaust passage 14 so as to bypasses the turbine 24, and a waste gate valve (WGV) 30 that regulates the amount of exhaust gas that flows through the bypass passage 28. In the intake passage 12, an electromagnetically driven air bypass valve (ABV) 32 is provided which allows intake air to flow therethrough while bypassing the compressor 26.

[0027] Also, the system of this embodiment has a sensor system including a crank angle sensor 34, an intake pressure sensor 36, an exhaust temperature sensor 38, and a vehicle speed sensor 40, and an electronic control unit (ECU) 50 that controls operating conditions of the engine 10. The crank angle sensor 34 generates a signal that is in synchronization with rotation of the crankshaft of the engine 10, and the ECU 50 detects the engine speed and the crank angle based on the output signal. The intake pressure sensor 36 detects the pressure of the intake air as the intake pressure (or boost pressure), and the ECU 50 calculates the intake air amount or mass air flow of the engine 10 based on the intake pressure, and determine an operating condition of the turbocharger 22. The intake air amount may be detected by a flow-rate detection device, such as an air flow meter. The exhaust temperature sensor 38 detects the exhaust temperature at a location downstream of the WGV 30, and will be described in detail later. The vehicle speed sensor 40 detects the running speed of the vehicle in which the engine 10 is installed, as the vehicle speed S.

[0028] The sensor system also includes various sensors (such as a water temperature sensor that detects the temperature of an engine coolant, an accelerator pedal position sensor that detects the accelerator pedal position, and an air-fuel ratio sensor that detects the exhaust air-fuel ratio) which are needed for control of the vehicle or engine, in addition to the above-mentioned sensors 34 - 40, and these sensors are connected to the input side of the ECU 50. To the output side of the ECU 50 are connected various actuators, including the throttle valve 16, WGV 30, ABV 32, and fuel injection valves.

[0029] Then, the ECU 50 detects the operating information of the engine 10 through the sensor system, and drives each actuator based on the results of detection, thereby to control the engine operation. More specifically, the ECU 50 detects the engine speed NE and the crank angle based on the output of the crank angle sensor 34, and calculates the intake air amount or mass air flow based on the output of the intake pressure sensor 36. Also, the ECU 50 calculates the load (load factor) KL of the engine based on the engine speed NE, etc., and determines the fuel injection timing, etc. based on the detected crank angle. Then, the ECU 50 calculates the fuel injection amount based on the intake air amount, the load KL, etc., and drives the fuel injection valves at appropriate fuel injection timings. Also, the ECU 50 drives the WGV 30 based on the exhaust temperature and the intake pressure (boost pressure), for example, and executes boost pressure control for controlling the boost pressure to within an appropriate range.

[0030] Referring next to FIG. 2 and FIG. 3, the location and output characteristics of the exhaust temperature sensor 38 of this embodiment will be described. FIG. 2 is an external view of an exhaust system of the engine 10, showing the locations of the turbocharger, waste gate valve, exhaust temperature sensor, and so forth. In FIG. 2, only a portion of the turbocharger 22 on the turbine 24 side is illustrated. As shown in FIG. 2, the turbocharger 22, bypass passage 28 and the WGV 30 are assembled as an integral unit.

[0031] For example, the WGV 30 includes a plate valve body disposed swingably at an opening end of the bypass passage 28, and an actuator (not shown) for driving the valve body. In operation, the plate valve body swings according to a control signal transmitted from the ECU 50 to the actuator, so that the opening of the WGV 30 is controlled. With this control, the opening of the WGV 30 changes between a degree indicative of the fully closed position at which the WGV 30 closes or blocks the bypass passage 28, and a degree indicative of the fully open position at which the WGV 30 permits almost free flow of exhaust gas through the bypass passage 28. Under boost pressure control, the amount of exhaust gas that flows through the bypass passage 28 increases as the opening of the WGV 30 increases; as a result, the exhaust pressure that drives the turbine 24 is reduced, and the boost pressure of the intake air is reduced. For example, an electromagnetically driven solenoid, or an electric, mechanical, hydraulic or pneumatic motor, or the like, is used as the actuator of the WGV 30. In the example shown in FIG. 2, the WGV 30 is placed at the fully open position when it is inclined by an angle of about 45° from the opening end of the bypass passage 28.

[0032] In the meantime, the exhaust temperature sensor 38 is in the form of a general temperature sensor using a thermistor, for example, and is mounted on a wall of the exhaust passage 14 downstream of the WGV 30. The output of the exhaust temperature sensor 38 changes with a positive or negative correlation with change of the exhaust temperature. A temperature conversion map having data of the correlation between these parameters is stored in advance in the ECU 50. Accordingly, the ECU 50 detects the exhaust temperature, by converting the output of the sensor into a detection value of the exhaust temperature, referring to the temperature conversion map, based on the output of the exhaust temperature sensor 38.

[0033] Also, in this embodiment, the mounting position of the exhaust temperature sensor 38 is adjusted in advance, so that the amount of exhaust gas that contacts the exhaust temperature sensor 38 increases as the opening of the WGV 30 increases, for example. With the sensor thus positioned, the detection value of the exhaust temperature obtained by the exhaust temperature sensor 38 increases according to the opening of the WGV 30, as shown in FIG. 3. FIG. 3 shows a characteristic curve indicating the relationship between the opening of the waste gate valve and the detection value of the exhaust temperature sensor. The data shown in FIG. 3 indicates how the detection value of the exhaust temperature sensor 38 increases as the opening of the WGV 30 increases. With the exhaust temperature sensor 38 mounted at the position as described above, the amount of exhaust gas from which heat is transferred to the exhaust temperature sensor 38 increases as the opening of the WGV 30 increases, so that the characteristic as shown in FIG 3 can be obtained.

[0034] Since the characteristic as shown in FIG. 3 varies from one operating region of the engine to another region, map data, or the like, indicative of characteristics in the respective operating regions are stored in advance in the ECU 50. Accordingly, the ECU 50 can detect the opening of the WGV 30, by specifying an operating region in which the engine is operating, based on engine operation information, for example, and referring to the map data, based on the specified operating region and the detection value of the exhaust temperature sensor 38. Meanwhile, the detection value of the exhaust temperature sensor 38 also changes with the actual exhaust temperature. Therefore, the ECU 50 stores in advance a correction map used for correcting the detection value of the exhaust temperature sensor 38 in accordance with the opening of the WGV 30, for example. Using the correction map, the ECU 50 corrects the detection value of the sensor in accordance with the opening of the WGV 30, so as to obtain an accurate exhaust temperature.

[0035] The above-described detecting process is performed with accuracy, on the assumption that the WGV 30 and the exhaust temperature sensor 38 operate normally. To this end, the ECU 50 has a failure diagnostic function of detecting a short circuit, a break or disconnection, or the like, in the exhaust temperature sensor 38. The failure diagnostic function is generally known as a part of on-board diagnostics (OBD) of the ECU, for example. Also, the ECU 50 executes failure detection control as described below, so as to detect a failure of the WGV 30.

[0036] Initially, conditions under which the WGV failure detection control is executed will be described. In this embodiment, the ECU 50 is configured to execute failure detection control when all of the following conditions (1) through (4) are satisfied.

(1) The engine speed NE is within a specified range of O. E to PNE

corresponding to a low speed region.

(2) The engine load KL is within a specified range of CCKL to βκχ («.K.L^<KL<P L) corresponding to a low load region.

(3) The vehicle speed S is within a specified range of as to s (cts<S<Ps) corresponding to a low vehicle speed condition.

(4) No failure, such as a break, occurs in the exhaust temperature sensor 38.

[0037] These conditions are used for determining whether the operating conditions of the engine and the vehicle are suitable for performing failure detection control. Also, the above-indicated conditions (1) - (3) specify or define a certain steady-state operating region (steady-state operating conditions of the engine) in which the engine speed and load are low and the vehicle is running at a constant speed (including the case where the vehicle is stopped), and which is outside a supercharged operating region. In the steady-state operating region, the opening of the WGV 30 and the detection value of the exhaust temperature sensor 38 may meet the characteristic as shown in FIG. 3. The criteria values C NE, PNE, O L, KL, ots, β≤ of the respective conditions are easily obtained by experiment, or the like, and are stored in advance in the ECU 50. The above-indicated condition (4) is determined by the failure diagnostic function of the ECU 50.

[0038] In this regard, these conditions (1) - (4) are merely one example presented in this embodiment, and should not be interpreted to limit the present invention. In the following description, the above conditions (1) - (4) will be generically called "an execution condition of failure detection control". Accordingly, the execution condition of the failure detection control is satisfied when all of the conditions (1) - (4) are satisfied, and is not satisfied when one or more of these conditions is/are not satisfied. With the execution condition thus set, the failure detection control can be performed with stability only within the above-described steady-state operating region. In the failure detection control that is executed when the above execution condition is satisfied, the opening of the WGV 30 is initially controlled to a particular opening or openings. In this condition, a failure of the WGV 30 is detected by comparing the detection value of the exhaust temperature sensor 38 with a predetermined threshold corresponding to the particular opening. The failure detection control includes a valve closing determination process and a valve opening determination process, which will be described below.

[0039] The valve closing determination process is to determine whether the

WGV 30 is fully closed normally. In the determination process, a control signal for fully closing the WGV 30 is generated and input to the WGV 30, so that the WGV 30 is controlled to the fully closed position or the vicinity thereof (i.e., the opening of the WGV 30 is controlled to be equal to or close to a particular opening indicative of the fully closed position). In this condition, a detection value of the exhaust temperature sensor 38 is read as a fully-closed-state detection value ethtccl. Also, a fully-closed-state reference value kthtcgal is set by a method as will be described later, and an absolute value (|ethtccl-kthtcgal|) of a difference between the fully-closed-state detection value and the fully-closed-state reference value is calculated. The fully-closed-state reference value kthtcgal is a predetermined detection value (a reference value of the detection value of the exhaust temperature sensor 38) that should be obtained based on the output of the exhaust temperature sensor 38 when the WGV 30 is placed in the fully closed position or in the vicinity thereof, and may be easily obtained by experiment, or the like. In this connection, the phrase "the fully closed position or the vicinity thereof includes the true, fully closed position at which the opening of the WGV 30 is equal to zero, and the vicinity of the fully closed position represented by a minute degree of opening that may be regarded as a substantially fully closed position as viewed from the detection value of the exhaust temperature sensor 38.

[0040] The fully-closed-state reference value kthtcgal changes depending on the operating conditions of the engine and the vehicle, even in the steady- state operating region in which the above-indicated execution condition is satisfied. Therefore, map data as shown in FIG 4 is stored in advance in the ECU 50. FIG. 4 shows map data used for setting the fully-closed-state reference value based on the engine speed and the load. The ECU 50 sets the fully-closed-state reference value kthtcgal to an appropriate value (changes the fully-closed-state reference value kthtcgal), based on the engine speed NE and the load KL, with reference to the map data of FIG. 4. The map data shown in FIG. 4 is applied to, for example, a vehicle in which a manual transmission (MT) is installed. In a vehicle in which an automatic transmission (AT) is installed, and the fully-closed-state reference value kthtcgal may be set based on the vehicle speed, with reference to the map data of FIG. 5. Thus, FIG 5 is map data used for setting the fully-closed-state reference value based on the vehicle speed.

[0041] If the WGV 30 is fully closed normally according to the control signal, the fully-closed-state detection value ethtccl is substantially equal to the fully-closed-state reference value kthtcgal; therefore, the difference (|ethtccl-kthtcgal|) is equal to zero, or such a small value that only reflects an output error. Thus, in the valve closing determination process, the threshold T_A is set to a value that permits deviations from the fully-closed-state reference value kthtcgal, which are equivalent to output errors, and it is determined whether the difference (|ethtccl-kthtcgal|) is smaller than the threshold T_A. If an affirmative decision (YES) is made, it is determined that the valve closing operation of the WGV 30 is normal. If the difference (|ethtccl-kthtcgal|) is equal to or larger than the threshold TA, the WGV 30 is not fully closed due to some abnormality, even though the control signal for fully closing the WGV 30 has been generated and input to the WGV 30. In this case, it is determined that a failure to fully close (which will also be called "failure in the open position") occurs in the WGV 30.

[0042] The valve opening determination process is to determine whether the WGV 30 is fully opened normally, after it is determined in the above valve closing determination process that the valve closing operation is normal. In the valve opening determination process, a control signal for fully opening the WGV 30 is initially generated and input to the WGV 30, so that the WGV 30 is held at the fully open position or in the vicinity of thereof (i.e., the opening of the WGV 30 is controlled to be equal to or close to a particular opening indicative of the fully open position). In this condition, a detection value of the exhaust temperature sensor 38 is read as a fully-open-state detection value ethtcop, and an absolute value (|ethtcop-ethtccl|) of a difference between the fully-open-state detection value and the fully-closed-state detection value is calculated. In this connection, the phrase "the fully open position or the vicinity thereof includes the true, fully open position, and the vicinity of the fully open position represented by such a degree of opening that may be regarded as a substantially fully open position as viewed from the detection value of the exhaust temperature sensor 38.

[0043] At this time, it has been determined from the valve closing determination process that the fully-closed-state detection value ethtccl is a normal value. Accordingly, if the WGV 30 is fully opened normally according to the control signal, the above-indicated difference (|ethtcop-ethtccl|) is equal to a predetermined value corresponding to a difference between a predetermined detection value (a reference value of the detection value of the exhaust temperature sensor 38 at the time when the WGV 30 is fully opened) which should be obtained upon full opening, and the fully-closed-state reference value kthtcgal, or a value that deviates from the predetermined value only by a degree corresponding to an output error. Thus, in the valve opening determination process, the threshold TB is set to a value that permits deviations from the predetermined value, which are equivalent to output errors, and it is determined whether the difference (|ethtcop-ethtccl|) is larger than the threshold TB- If an affirmative decision (YES) is made, it is determined that the valve opening operation of the WGV 30 is normal. If the difference (|ethtcop-ethtccl|) is equal to or smaller than the threshold TB, the fully-open-state detection value ethtcop is smaller than a reference value corresponding to the normal fully open state, even though the control signal for fully opening the WGV 30 has been generated and input to the WGV 30, which means that the WGV 30 is not fully opened. In this case, a failure to fully open (which will also be called "failure in the closed position") occurs in the WGV 30.

[0044] Thus, according to this embodiment, it is possible to set or establish a given relationship between the opening of the WGV 30 and the detection value of the exhaust temperature sensor 38, by locating the exhaust temperature sensor 38 at a position where its detection value increases according to the opening of the WGV 30. With this relationship stored as data, the opening of the WGV 30 can be detected based on the detection value of the exhaust temperature sensor 38. Accordingly, the ECU 50 is able to easily detect a failure of the WGV 30, by controlling the WGV 30 to the particular openings (indicative of the fully closed position and the fully open position), and comparing respective detection values of the exhaust temperature sensor 38 with the thresholds corresponding to the particular openings in the above controlled conditions. This arrangement eliminates the need to install an opening sensor for the WGV 30, or the like, and thus improves the reliability without incurring a significant increase in the cost of the system.

[0045] Also, in this embodiment, a failure can be detected with enhanced accuracy, based on detection values at two different openings representing the fully closed position and the fully open position. In particular, failure detection is performed especially at the fully closed position and fully open position at which a failure, such as sticking, is likely to occur. Also, the use of the detection values obtained at the upper limit and lower limit of the operating range of the WGV 30 makes it possible to have the detection value(s) reflect information on a failure that occurs at a certain intermediate opening, and thus detect a failure over the entire operating range with high sensitivity.

[0046] Furthermore, it can be determined through the valve closing determination process whether the valve closing operation of the WGV 30 is normal. Also, it can be determined through the valve opening determination process whether the valve opening operation of the WGV 30 is normal. Accordingly, an abnormality in the valve closing operation of the WGV 30 (a failure in the open position) and an abnormality in the valve opening operation (a failure in the closed position) are detected such that these abnormalities can be distinguished from each other. Consequently, detailed failure information can be obtained, and an appropriate countermeasure against a detected failure can be taken depending on the type of the failure, for example.

[0047] FIG. 6 is a flowchart of a control routine executed by the ECU, in the first embodiment of the invention. The control routine illustrated in FIG. 6 is repeatedly executed during operation of the engine. In the routine of FIG. 6, the engine speed NE, load KL, vehicle speed S, detection value of the exhaust temperature sensor 38, and so forth are initially read or calculated (step 100). Then, it is determined whether the above-described execution condition of the failure detection control is satisfied (step 102), and the control ends if the execution condition is not satisfied.

[0048] If the execution condition of the failure detection control is satisfied, a control signal for controlling the WGV 30 to the fully closed position or the vicinity thereof is generated and output (step 104). Then, a fully-closed-state reference value kthtcgal is set based on the engine speed NE and the load KL, with reference to the map data of FIG. 4 (step 106). Also, a fully-closed-state detection value ethtccl is read (step 108). Then, a control signal for controlling the WGV 30 to the fully open position or the vicinity thereof is generated and output (step 110). Then, a fully-open-state detection value ethtcop is read (step 112).

[0049] In the next step, a difference (|ethtccl-kthtcgal|) between the fully-closed-state detection value ethtccl and the fully-closed-state reference value kthtcgal is calculated, and it is determined whether this difference is smaller than the threshold TA (step 114). Also, a difference between the fully-closed-state detection value ethtccl and the fully-open-state detection value ethtcop is calculated, and it is determined whether this difference is larger than the threshold TB (step 116). If affirmative decisions (YES) are made in both of the above steps 114, 116, it is determined that the WGV 30 is normal (step 118). If a negative decision (NO) is made in step 114, it is determined that a failure in the open position (i.e., a failure to fully close) occurs in the WGV 30 (step 120). If an affirmative decision (YES) is made in step 114, but a negative decision (NO) is made in step 116, it is determined that a failure in the closed position (i.e., a failure to fully open) occurs in the WGV 30 (step 122). When it is determined that a failure in the open position or a failure in the closed position occurs in the WGV 30, an alarm or warning device (such as MIL) that informs the operator of a failure of the WGV 30 may be activated.

[0050] In the first embodiment as described above, a portion of the ECU 50 which executes steps 104, 110 in FIG. 6 is a specific example of the valve control unit of the invention. Also, a portion of the ECU 50 which executes steps 104 - 122 is a specific example of the failure detecting unit of the invention, and a portion of the ECU 50 which executes step 108 is a specific example of the first detection value obtaining unit or the fully-closed-state detection value obtaining unit of the invention, while a portion of the ECU 50 which executes step 112 is a specific example of the second detection value obtaining unit or the fully-open-state detection value obtaining unit of the invention. Further, a portion of the ECU 50 which executes step 114 is a specific example of the valve closing determining unit of the invention, and a portion of the ECU 50 which executes step SI 16 is. a specific example of the valve opening determining unit of the invention, while a portion of the ECU 50 which executes 106 is a specific example of the reference value setting unit of the invention, and a portion of the ECU 50 which executes 102 is a specific example of the operating condition determining unit of the invention.

[0051] Second Embodiment Referring next to FIG. 7 through FIG. 10, a second embodiment of the invention will be described. In this embodiment, the system is configured to correct a detection value of the exhaust temperature sensor based on an in-cylinder pressure, and the configuration of the second embodiment is different in this point from that of the first embodiment. In the following description of the second embodiment, the same reference numerals as used in the first embodiment are assigned to the same constituent elements as those of the first embodiment, of which no further explanation will be provided.

[0052] FIG. 7 is a schematic diagram illustrating the overall system configuration of the second embodiment of the invention. As shown in FIG. 7, the system of this embodiment has substantially the same configuration as that of the first embodiment. However, the engine 10 is installed with an in-cylinder pressure sensor 60 that detects a pressure (which will be called "in-cylinder pressure") in each cylinder (only one cylinder with the in-cylinder pressure sensor 60 is shown in FIG. 7), and the in-cylinder pressure sensor 60 provides an in-cylinder pressure detecting unit of this embodiment. While the ECU 50 executes failure detection control similar to that of the first embodiment, the ECU 50 of the second embodiment further executes learning control to learn a deviation of the detection value of the exhaust temperature sensor 38 from an estimated value based on the in-cylinder pressure, and correction control to correct the detection value based on the result of learning.

[0053] Errors due to various factors may occur in detection values of the exhaust temperature sensor 38. Examples of the error factors include environmental factors, such as an outside-air temperature, individual differences among engines, variations in characteristics among cylinders, individual differences among exhaust temperature sensors 38, and a drift in the sensor output. In the learning control, therefore, the exhaust temperature is estimated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 60, and the amount of deviation (error) of the actual detection value from the estimated value is learned as a correction amount.

[0054] More specifically described, the in-cylinder pressure reflects a combustion condition of an air-fuel mixture in the cylinder, and therefore, there is a given correlation or relationship between the temperature of exhaust gas that has just been discharged from the cylinder, and the in-cylinder pressure. The exhaust gas discharged from the cylinder then reaches the location of the exhaust temperature sensor 38, after transmitting (dissipating) heat to surrounding structures, such as the exhaust passage 14 and the turbine 24. Therefore, there is a given correlation determined according to the heat capacities of the surrounding structures, etc., between the temperature of exhaust gas immediately after discharger thereof, and the exhaust temperature detected at the sensor position. In the ECU 50, data of the above-indicated two correlations, namely, data used for calculating the temperature of exhaust gas immediately after its discharge based on the in-cylinder pressure, and data used for calculating the exhaust temperature at the sensor position based on the temperature of exhaust gas immediately after its discharge, are stored in advance. These items of data are obtained by experiment or theoretical calculation, for example, under a condition that the WGV 30 is placed in the fully open position.

[0055] In the learning control, when certain learning conditions are satisfied, the temperature of exhaust gas immediately after its discharge is calculated from the in-cylinder pressure, based on the above-described correlation data, and an estimated value ethcps of the exhaust temperature at the sensor position is further calculated. In a condition where the WGV 30 is controlled to the fully open position or the vicinity thereof, a detection value (fully-open-state detection value ethtcop) of the exhaust temperature sensor 38 is read, and a difference (ethcps-ethtcop) between the detection value and the estimated value of the exhaust temperature ethcps is calculated as a correction amount ethtcfb. The correction amount ethtcfb is stored as a learned value in a nonvolatile memory, or the like, installed in the ECU 50. The above-mentioned learning conditions include a condition that the in-cylinder pressure 60 operates normally, in addition to the above-described execution condition of the failure detection control. Whether the in-cylinder pressure sensor 60 operates normally or not is determined through the failure diagnostic function of the ECU 50.

[0056] In the correction control, when the failure detection control is executed, the learned value of the correction amount ethtcfb is initially read from the memory of the ECU 50. Then, each time a detection value of the exhaust temperature sensor 38 is read, the detection value is corrected based on the correction amount ethtcfb. With this arrangement, even when an error occurs in the detection value of the exhaust temperature sensor 38, the error can be reduced or eliminated based on the in-cylinder pressure, and the accuracy of the detection value can be enhanced. Accordingly, the failure detection control is less likely to suffer from erroneous detection of a failure, or the like, and can be more precisely performed. Also, when the opening of the WGV 30 is detected based on the detection value of the exhaust temperature sensor 38, the detection accuracy can be improved.

[0057] FIG. 8 through FIG. 10 are flowcharts of control routines executed by the

ECU 50, in the second embodiment of the invention. The control routines illustrated in FIG. 8 - FIG. 10 are repeatedly executed during operation of the internal combustion engine. Initially, the routine of FIG. 8 will be described. In this routine, substantially the same operations as those of steps 100 — 108 of the first embodiment (FIG. 4) are performed in steps 200 - 208.

[0058] In the next stage, a learned value of the correction amount ethtcfb obtained by learning control (FIG. 9) is read (step 210), and the learned value is added to the fully-closed-state detection value ethtccl, so as to correct the fully-closed-state detection value ethtccl (step 212). In this manner, a. post-correction fully-closed-state detection value ethtccl2 is obtained. Then, a difference (|ethtccl2-kthtcgal|) between the post-correction fully-closed-state detection value ethtccl2 and the fully-closed-state reference value kthtcgal is calculated, and it is determined whether the difference is smaller than the threshold TA (step 214). If a negative decision (NO) is made in step 214, it is determined that a failure in the open position (or a failure to fully close) occurs (step 216), as in the first embodiment.

[0059] In the next stage, substantially the same valve opening determination process as that of the first embodiment is carried out in steps 218 - 228. In this case, too, a post-correction fully-open-state detection value ethtcop2 is calculated in step 222, by correcting the fully-open-state detection value ethtcop with the correction amount ethtcfb. Then, it is determined in step 224 whether a difference (|ethtcop2-ethtccl2|) between the post-correction fully-open-state detection value and the post-correction fully-closed-state detection value is larger than the threshold TB. In this manner, it can be determined whether the WGV 30 is normal, or a failure in the closed position (or a failure to fully open) occurs in the WGV 30 (steps 226, 228).

[0060] Referring next to FIG. 9, learning control will be explained. The routine illustrated in FIG. 9 is repeatedly executed independently of the routine illustrated in FIG. 8. In the routine illustrated in FIG. 9, it is initially determined whether the above-described learning conditions are satisfied (step 300). If a negative decision (NO) is made in step 300, the learning control ends. If the learning conditions are satisfied, an exhaust temperature estimated value ethcps is calculated by exhaust temperature estimation control (FIG. 10) (step 302). Also, a fully-open-state detection value ethtcop of the exhaust temperature sensor 38 is read (step S304). Then, a difference (ethcps-ethtcop) between the exhaust temperature estimated value and the fully-open-state detection value is calculated as a correction amount ethtcfb, and the correction amount ethtcfb is stored (step 306).

[0061] Referring next to FIG. 10, exhaust temperature estimation control will be explained. The routine illustrated in FIG. 10 is executed in step 302 of FIG. 9. In the routine illustrated in FIG. 10, an in-cylinder pressure detected by the in-cylinder pressure sensor 60 is read (step 400), and a temperature of exhaust gas immediately after discharge thereof is calculated based on the in-cylinder pressure (step 402). Then, an estimated value ethcps of the exhaust temperature at the sensor position is calculated based on the temperature of exhaust gas immediately after its discharge (step 404).

[0062] In the embodiment configured as described above, too, substantially the same effects as those of the first embodiment can be obtained. In this embodiment, in particular, the use of the in-cylinder pressure sensor 60 makes it possible to exclude the influences of error factors, by correcting the detection value of the exhaust temperature sensor 38, and thus improve the reliability of the system. Also, the correction amount ethtcfb can be obtained in advance through the learning control; therefore, the correction control can be started soon.

[0063] In the second embodiment as described above, a portion of the ECU 50 which executes steps 204, 218 in FIG. 8 is a specific example of the valve control unit of the invention. Also, a portion of the ECU 50 which executes steps 204 - 228 is a specific example of the failure detecting unit of the invention, and a portion of the ECU 50 which executes step 208 is a specific example of the first detection value obtaining unit or the fully-closed-state detection value obtaining unit of the invention, while a portion of the ECU 50 which executes step 220 is a specific example of the second detection value obtaining unit or the fully-open-state detection value obtaining unit of the invention. Further, a portion of the ECU 50 which executes step 214 is a specific example of the valve closing determining unit of the invention, and a portion of the ECU 50 which executes step 224 is a specific example of the valve opening determining unit of the invention, while a portion of the ECU 50 which executes step 206 is a specific example of the reference value setting unit of the invention, and a portion of the ECU 50 which executes step 202 is a specific example of the operating condition determining unit of the invention. Also, a portion of the ECU 50 which executes steps 210, 212, 222 and the routines of FIG. 9 and FIG. 10 is a specific example of the correcting unit of the invention.

[0064] Third Embodiment Referring next to FIG. 11, FIG. 12A, and FIG. 12B a third embodiment of the invention will be described. This embodiment adopts substantially the same configuration and control as those of the second embodiment (FIG. 7, FIG. 8). In addition, when it is determined that the WGV 30 has a failure in the closed position, the system of the third embodiment is configured to estimate the opening of the WGV 30 based on the exhaust temperature, and the configuration of the third embodiment is different in this point from that of the second embodiment. In this embodiment, the same reference numerals as used in the second embodiment are assigned to the same constituent elements, of which no further explanation will be provided.

[0065] As discussed above in connection with the first and second embodiments, when a failure in the closed position (i.e., a failure to fully open) occurs in the WGV 30, the fully-open-state detection value ethtcop, ethtcop2 becomes smaller than a reference value _'Corresponding to the normal, fully open state. In this case, it is anticipated that the WGV 30 is stopped at a certain intermediate opening; if the intermediate opening is smaller than a permissible limit, exhaust emissions may deteriorate depending on the operating conditions. Therefore, the system of this embodiment is configured to execute failed valve opening determination control.

[0066] In the failed valve opening determination control, when it is determined through the valve opening determination process that a failure in the closed position (i.e., a failure to fully open) occurs, the opening of the WGV 30 (which will be called "failed valve opening") ewgdeg is detected based on the fully-open-state detection value ethtcop, ethtcop2. Then, if the failed valve opening ewgdeg is smaller than a predetermined threshold Tc corresponding to the permissible limit, a warning device, such as MIL, is activated, to inform the operator of the failure. FIG. 11 shows map data used for detecting the failed valve opening of the WGV 30 based on the fully-open-state detection value. The map data is stored in advance in the ECU 50. Thus, the ECU 50 detects the failed valve opening ewgdeg based on the fully-open-state detection value ethtcop, ethtcop2, with reference to the above-indicated map data.

[0067] FIGS. 12A and 12B are a flowchart of a control routine executed by the ECU 50, in the third embodiment of the invention. The control routine illustrated in FIGS. 12A and 12B are used along with the routines of FIG. 9 and FIG. 10 of the second embodiment, and is repeatedly executed during operation of the internal combustion engine. In the routine of FIGS. 12A and 12B, substantially the same process as that of steps 200 - 226 of the second embodiment (FIG. 8) is carried out in steps 500 - 526. [0068] In the above-described process, if a negative decision (NO) is made in step S524, a failed valve opening ewgdeg is detected based on the fully-open-state detection value ethtcop2, with reference to the map data of FIG. 11 (step 528). Then, it is determined whether the failed valve opening ewgdeg is smaller than the above-indicated threshold Tc (step 530). If an affirmative decision (YES) is made in step 530, a warning device, such as MIL, is turned on (step 532). If a negative decision (NO) is made in step 530, it is determined that there is no fear of deterioration of exhaust emissions even though a failure in the closed position occurs in the WGV 30, and only the failure in the closed position is acknowledged (step 534).

[0069] In the third embodiment configured as described above, substantially the same effects as those of the first and second embodiments can be obtained. In this embodiment, in particular, when a failure in the closed position occurs, the failed valve opening determination control is executed, so that exhaust emissions are less likely or unlikely to further deteriorate upon occurrence of the failure, and an appropriate measure can be taken depending on the degree or seriousness of the failure.

[0070] In the third embodiment as described above, a portion of the ECU 50 which executes steps 504, 518 of FIGS. 12A and 12B is a specific example of the valve control unit of the invention. Also, a portion of the ECU 50 which executes steps 504 - 534 is a specific example of the failure detecting unit of the invention, and a portion of the ECU 50 which executes step 508 is a specific example of the first detection value obtaining unit or the fully-closed-state detection value obtaining unit of the invention, while a portion of the ECU 50 which executes step 520 is a specific example of the second detection value obtaining unit or the fully-open-state detection value obtaining unit of the invention. Further, a portion of the ECU 50 which executes step 514 is a specific example of the valve closing determining unit of the invention, and a portion of the ECU 50 which executes step 524 is a specific example of the valve opening determining unit of the invention, while a portion of the ECU 50 which executes step 506 is a specific example of the reference value setting unit of the invention, and a portion of the ECU 50 which executes step 502 is a specific example of the operating condition determining unit of the invention. Also, a portion of the ECU 50 which executes steps 510, 512, 522 is a specific example of the correcting unit of the invention.

[0071] While the third embodiment is provided by adding the failed valve opening determining control to the functions of the system of the second embodiment, the present invention is not limited to this arrangement, but the failed valve opening determining control may be added to the functions of the system of the first embodiment.

[0072] In the illustrated embodiments, the valve openings representing the fully closed position and the fully open position are used as the particular openings of the valve at which failure detection control is performed. However, the present invention is not limited to this arrangement, but intermediate openings other than those representing the fully closed position and fully open position may be used as particular openings.

Claims

CLAIMS:

1. A control system of an internal combustion engine, comprising:

a turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage, and operable to supercharge the internal combustion engine with intake air, utilizing an exhaust pressure; a waste gate valve that regulates the amount of exhaust gas that bypasses the turbine of the turbocharger;

a valve control unit that controls an opening of the waste gate valve;

an exhaust temperature sensor that detects an exhaust temperature downstream of the waste gate valve, and is located at a position where a detection value of the exhaust temperature increases as the opening of the waste gate valve increases; and

a failure detecting unit that performs detection of a failure of the waste gate valve based on the detection value of the exhaust temperature sensor, in a condition where the valve control unit controls the opening of the waste gate valve to a particular opening.

2. The control system according to claim 1, further comprising:

a first detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a first opening, as a first detection value; and

a second detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a second opening, as a second detection value; wherein

the failure detecting unit performs the detection of the failure based on at least the first detection value and the second detection value.

3. The control system according to claim 1 , further comprising:

a fully-closed-state detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the waste gate valve is controlled to a fully closed position or the vicinity thereof, as a fully-closed-state detection value; and a fully-open-state detection value obtaining unit that obtains a detection value of the exhaust temperature sensor in a condition where the waste gate valve is controlled to a fully open position or the vicinity thereof, as a fully-open-state detection value, wherein the failure detecting unit performs the detection of the failure based on at least the fully-closed-state detection value and the fully-open-state detection value.

4. The control system according to claim 3, wherein the failure detecting unit comprises:

a valve closing determining unit that determines whether a valve closing operation of the waste gate valve is normal, based on a fully-closed-state reference value as a reference value of the detection value of the exhaust temperature sensor in the case where the waste gate valve is at or in the vicinity of the fully closed position, and the fully-closed-state detection value; and

a valve opening determining unit that determines whether a valve opening operation of the waste gate valve is normal, based on a difference between the fully-closed-state detection value and the fully-open-state detection value, after the valve closing determining unit determines that the valve closing operation is normal.

5. The control system according to claim 4, further comprising a reference value setting unit that variably sets the fully-closed-state reference value based on operating conditions of the internal combustion engine.

6. The control system according to any one of claims 1 to 5, further comprising: an in-cylinder pressure detecting unit that detects an in-cylinder pressure of the internal combustion engine; and

a correcting unit that corrects the detection value of the exhaust temperature sensor based on the in-cylinder pressure detected by the in-cylinder pressure detecting unit.

7. The_.control system according to any one of claims 1 to 6, wherein the exhaust temperature sensor is located at a position downstream of the waste gate valve where the amount of exhaust gas that contacts the exhaust temperature sensor increases as the opening of the waste gate valve increases.

8. The control system according to claim 7, wherein:

the waste gate valve regulates the amount of exhaust gas flowing in a bypass passage provided in the exhaust passage so as to bypass the turbine of the turbocharger, and includes a plate valve body disposed in an opening end of the bypass passage, the plate valve body being arranged to swing so as to control the opening of the waste gate valve; and

the exhaust temperature sensor is mounted on a wall of the exhaust passage downstream of the waste gate valve.

9. The control system according to any one of claims 1 to 8, further comprising an operating condition determining unit that determines whether operating conditions of the internal combustion engine are suitable for performing the detection of the failure.

10. The control system according to claim 9, wherein:

when the internal combustion engine is in steady-state operating conditions, and no failure occurs in the exhaust temperature sensor, the operating condition determining unit determines that the operating conditions of the internal combustion engine are suitable for performing the detection of the failure; and

when the operating condition determining unit determines that the operating conditions of the internal combustion engine are suitable for performing the detection of the failure, the failure detection unit performs the detection of the failure.

11. A control method of an internal combustion engine including a turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage, and operable to supercharge the internal combustion engine with intake air, utilizing an exhaust pressure, and a waste gate valve that regulates the amount of exhaust gas that bypasses the turbine of the turbocharger comprising:

providing an exhaust temperature sensor that detects an exhaust temperature downstream of the waste gate valve, at a position where a detection value of the exhaust temperature increases as an opening of the waste gate valve increases;

controlling the opening of the waste gate valve to a particular opening; and performing detection of a failure of the waste gate valve based on the detection value of the exhaust temperature sensor, in a condition where the opening of the waste gate valve is controlled to the particular opening.

12. The control method according to claim 11 , further comprising:

obtaining a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a first opening, as a first detection value; and

obtaining a detection value of the exhaust temperature sensor in a condition where the opening of the waste gate valve is controlled to a second opening, as a second detection value; wherein

the detection of the failure is performed based on at least the first detection value and the second detection value.