Fault detection device and fault detection method

A fault detection device includes a wastegate valve, a control unit, a working gas amount computation section, and a determination section. The control unit obtains a rotational speed of an engine, a boost pressure, and an intake air temperature. The working gas amount computation section computes a computed value of a mass flow rate of working gas in the engine by using the rotational speed, the boost pressure, and the intake air temperature. The determination section determines that the wastegate valve has a fault when the computed value is not a normal value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/JP2013/075652 having an international filing date of Sep. 24, 2013, which designated the United States, which PCT application claimed the benefit of Japanese Patent Application No. 2012-223100 filed Oct. 5, 2012, the disclosures of each of which are incorporated herein by reference.

TECHNICAL FIELD

The techniques of the present disclosure relate to a fault detection device and a fault detection method for a wastegate valve.

BACKGROUND ART

A conventionally known turbocharger includes a turbine, a wastegate passage that bypasses the turbine, and a wastegate valve arranged in the wastegate passage. The wastegate valve opens the wastegate passage to reduce exhaust gas flowing into the turbine when the pressure of the exhaust gas exceeds a predetermined value.

A known example of a technique for detecting a fault of a wastegate valve is determining whether a detection value of a boost pressure exceeds a limit and indicating a fault when the detection value exceeds the limit (e.g., refer to Patent Document 1).

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

It is common that a boost pressure is detected as a different value even when a turbocharger is driven at the same rotational speed. Thus, to increase the accuracy of fault detection of a wastegate valve, there is still room for improvement in the aforementioned technique.

An object of the techniques of the present disclosure is to provide a fault detection device and a fault detection method that can detect a fault of a wastegate valve with great accuracy.

According to one aspect of the present invention to achieve the above objective, a fault detection device includes a wastegate valve, an acquisition section, a computation section, and a determination section. The acquisition section obtains a rotational speed of an engine, a boost pressure, and an intake air temperature. The computation section computes a computed value of a mass flow rate of working gas in the engine by using the rotational speed, the boost pressure, and the intake air temperature. The determination section determines that the wastegate valve has a fault when the computed value is not a normal value.

According to another aspect of the present invention to achieve the above objective, a fault detection method includes obtaining a rotational speed of an engine, a boost pressure, and an intake air temperature. The method includes computing a computed value of a mass flow rate of working gas by using the rotational speed, the boost pressure, and the intake air temperature. The method includes determining that a wastegate has a fault when the computed value is not a normal value.

According to these configurations, a mass flow rate of working gas is computed by using a boost pressure, an intake air temperature, and a rotational speed of the engine. A fault of the wastegate valve is determined based on the computed value. In other words, for detecting the fault of the wastegate valve, the intake air temperature is taken into account in addition to the boost pressure so that the fault of the wastegate valve is detected under the condition according to an ambient temperature. As a result, the fault of the wastegate valve is detected with great accuracy.

Preferably, the determination section uses data having the normal value that is set in accordance with an operation condition of the engine and determines that the wastegate valve has a fault when the computed value is not the normal value according to the operation condition.

According to this configuration, a fault of the wastegate valve is detected under the standard according to the operation condition of the engine. As a result, the fault of the wastegate valve is detected with great accuracy.

Preferably, the acquisition section obtains information indicating a control state of the wastegate valve. The determination section uses data having the normal value that is set for each control state in accordance with the operation condition and determines that the wastegate valve has a fault when the computed value is not the normal value, which is set in accordance with the operation condition.

According to this configuration, a fault is detected according to a control state of the wastegate valve, i.e., whether the wastegate valve is open or closed. Thus, the fault of the wastegate valve is detected with further great accuracy.

Preferably, the acquisition section obtains the rotational speed, the boost pressure, and the intake air temperature when a predetermined period has elapsed after the wastegate valve is switched between an open state and a closed state.

For example, even if the wastegate valve is switched from the closed state to the open state, rotation of the turbine affects the mass flow rate of working gas for a period of the inertial rotation of the turbine. In the period, the computed value of the working gas tends to be large. For this reason, if a fault is detected within a predetermined time after the wastegate valve is switched from the closed state to the open state under the same condition as in another period when the wastegate valve is in the open state, the wastegate valve is likely determined as having a fault. According to the configuration, fault detection is interrupted for the predetermined time after the wastegate valve is switched between the open state and the closed state. In other words, a fault is determined while the rotation of the turbine is stable compared to the rotation of the turbine immediately after the wastegate valve is switched between the open state and the closed state. Thus, a fault of the wastegate valve is detected with further great accuracy.

DETAILED DESCRIPTION OF THE PREFERRED EMOBIDMENTS

A fault detection device and a fault detection method according to one embodiment of the present invention will now be described with reference toFIGS. 1 to 3. First, the general structure of a diesel engine provided with a fault detection device will be described with reference toFIG. 1.

As shown inFIG. 1, a diesel engine10(hereinafter, referred to simply as an engine10) has a cylinder block11including in-line four cylinders12. Each of the cylinders12receives injection of fuel from a corresponding injector13. The cylinder block11is connected to an intake manifold14, which supplies intake air, which is working gas, to the cylinders12, and an exhaust manifold15, into which exhaust gas flows from the cylinders12.

The intake manifold14is connected to the upstream end of an intake passage16, to which an air cleaner (not shown) is attached. A compressor18of a turbocharger17is attached to the intake passage16. An intercooler19that cools intake air compressed by the compressor18is attached to a portion of the intake passage16, which is located downstream of the compressor18.

The exhaust manifold15is connected to an exhaust passage20. A turbine21is attached to the exhaust passage20and coupled to the compressor18. The exhaust manifold15and the exhaust passage20are connected to a wastegate passage22(hereinafter, referred to as a W/G (Waste Gate) passage22), which bypasses the turbine21.

A wastegate valve23(hereinafter, referred to as a W/G valve23) is attached to the W/G passage22and opens or closes the W/G passage22. A wastegate valve control section (hereinafter, referred to as a W/G valve control section24) controls opening or closing of the W/G valve23. The W/G valve control section24switches the W/G valve23between an open state and a closed state according to the rotational speed NE of the engine10and a fuel injection amount Qf. When the W/G valve23is in a closed state, exhaust gas in the exhaust manifold15flows into the turbine21. When the W/G valve23is in an open state, the exhaust gas in the exhaust manifold15bypasses the turbine21to flow into the exhaust passage20.

Various sensors are attached to the engine10and obtain information of the operation condition of the engine10. For example, a boost pressure sensor25is attached to a portion of the intake passage16that is located downstream of the compressor18. The boost pressure sensor25senses a boost pressure Pb at predetermined control intervals. The boost pressure Pb is the pressure of working gas that is compressed by the compressor18and flows in the intake passage16. An intake air temperature sensor26is attached to the intake manifold14. The intake air temperature sensor26senses an intake air temperature Tin at predetermined control intervals. The intake air temperature Tin is the temperature of working gas immediately before flowing into the cylinders12. The engine10is provided with a rotational speed detector27, which detects the rotational speed NE of the engine10. The rotational speed detector27detects the rotational speed of a crankshaft28to detect the rotational speed NE of the engine10at predetermined control intervals.

A fault detection device30, which detects a fault of the aforementioned W/G valve23, will now be described with reference toFIGS. 1 to 3. First, the electrical configuration of the fault detection device30will be described with reference toFIG. 1.

As shown inFIG. 1, the fault detection device30consists of a CPU, ROM, RAM, and the like and includes a control unit31for performing various computation and various settings and a memory32for storing various control programs and various data. The control unit31executes a fault detection process of detecting a fault of the W/G valve23based on the various control programs and the various data stored in the memory32.

The fault detection device30receives inputs of a detection signal indicating the boost pressure Pb from the boost pressure sensor25, a detection signal indicating the intake air temperature Tin from the intake air temperature sensor26, and a detection signal indicating the rotational speed NE of the engine10from the rotational speed detector27at predetermined control intervals. The fault detection device30also receives input of a control signal indicating the control state of the W/G valve23, i.e., whether the W/G valve23is open or closed, from the W/G valve control section24, which controls opening and closing of the W/G valve23, at predetermined control intervals. The fault detection device30also receives input of a signal indicating the fuel injection amount Qf from a fuel injection control section45at predetermined intervals. The fuel injection control section45controls the fuel injection amount Qf, which is an amount of fuel injected by the injectors13. The control unit31serves as an acquisition section and obtains the various information.

The control unit31has an open/closed flag setting section33that sets an open/closed flag F1, which indicates whether a wastegate valve is open or closed. When the W/G valve control section24inputs a control signal indicating that the W/G valve23is in the open state, the open/closed flag setting section33sets the open/closed flag F1to0. When the W/G valve control section24inputs a control signal indicating that the W/G valve23is in the closed state, the open/closed flag setting section33sets the open/closed flag F1to1.

The control unit31has a clock section34that measures a time period that has elapsed after the W/G valve23is switched between the open state and the closed state. The clock section34sets a count value C of a counter (not shown) to an initial value Ci when a control signal from the W/G valve control section24is changed and counts down the count value C at predetermined intervals. The control unit31continues the fault detection process of the W/G valve23when the count value C becomes0. When the W/G valve23is switched between the open state and the closed state, there is a transitional period immediately after the switching, which is a period for the turbine21to change the rotation to the rotation according to whether the W/G valve23is open or closed after the switching. The initial value Ci is a value for determining whether the transitional period has elapsed.

The control unit31has a working gas amount computation section35that computes a working gas amount, which is a mass flow rate of working gas supplied to the cylinders12. In the present embodiment, the working gas is intake air. The working gas amount computation section35computes a computed value Gc of the working gas amount by substituting the following values in the conditional equation, P×V=Gc×R×T. The working gas amount computation section35functions as a computation section for computing the computed value Gc.

P: the boost pressure Pb, which is a detection value by the boost pressure sensor25

V: a product of the rotational speed NE of the engine10and an exhaust amount D of the engine10

T: the intake air temperature Tin, which is a detection value by the intake air temperature sensor26

R: the gas constant

The control unit31has a reference value computation section36that computes a reference value Gs, which is an ideal amount of working gas according to the operation condition of the engine10, including whether the W/G valve23is open or closed. The reference value computation section36computes the reference value Gs of the working gas amount based on the rotational speed NE of the engine10, the fuel injection amount Qf, and reference data40stored in the memory32.

The reference data40is data created based on experiment results performed in advance for the engine10and having a corresponding reference value Gs provided according to the rotational speed NE of the engine10and the fuel injection amount Qf. The reference value computation section36selects a value from the reference data40according to the rotational speed NE of the engine10and the fuel injection amount Qf to compute the reference value Gs.

The control unit31has a threshold setting section37that sets a threshold Gt for a determination value Gj, which is the absolute value of a value obtained by subtracting the reference value Gs from the computed value Gc of the working gas amount. The threshold setting section37sets the threshold Gt based on the open/closed flag F1, the rotational speed NE of the engine10, the fuel injection amount Qf, and first threshold data41and second threshold data42stored in the memory32. The first threshold data41has the threshold Gt when the W/G valve23is controlled in the closed state, and the threshold Gt is set in accordance with the rotational speed NE and the fuel injection amount Qf. The second threshold data42has the threshold Gt when the W/G valve23is controlled in the open state, and the threshold Gt is set in accordance with the rotational speed NE and the fuel injection amount Qf.

The threshold Gt of each data41and42is a value provided based on experiment or simulation results performed in advance for the engine10, and the thermal influences to the W/G valve23and the W/G passage22are taken into account in the value. The threshold setting section37selects the first threshold data41or the second threshold data42according to the value of the open/closed flag F1and selects a threshold Gt from the selected threshold data according to the rotational speed NE and the fuel injection amount Qf to set the threshold Gt.

The control unit31has a determination section38that determines whether a fault has occurred in the W/G valve23. The determination section38computes the aforementioned determination value Gj and determines whether the determination value Gj is greater than or equal to the threshold Gt. The determination section38determines that a fault has occurred in the W/G valve23when the determination value Gj exceeds the threshold Gt. In other words, determination of whether the determination value Gj exceeds the threshold Gt corresponds to determination of whether the computed value Gc is a normal value (the reference value Gs). When the open/closed flag F1=0, the determination section38determines that the W/G valve23is in a first fault state, in which the W/G valve23is fixed in the open state. When the open/closed flag F1=1, the determination section38determines that the W/G valve23is in a second fault state, in which the W/G valve23is fixed in the closed state. When the determination value Gj is less than or equal to the threshold Gt, the determination section38determines that the W/G valve23operates normally.

The control unit31has a fault flag setting section39. When the determination section38determines the state of the W/G valve23, the fault flag setting section39sets a fault flag F2according to the determination result. The fault flag setting section39sets the fault flag F2to0when it is determined that the W/G valve23is in a normal state. The fault flag setting section39sets the fault flag F2to1when it is determined that the W/G valve23is in the first fault state. The fault flag setting section39sets the fault flag F2to2when it is determined that the W/G valve23is in the second fault state.

When the fault flag F2is set at1, the control unit31outputs a control signal indicating that the W/G valve23is in the first fault state to an alarm device46. When receiving input of the control signal, the alarm device46lights an alarm lamp46a, which indicates that the W/G valve23is in the first fault state, to notify a driver that the W/G valve23is in the first fault state.

When the fault flag F2is set at2, the control unit31outputs a control signal indicating that the W/G valve23is in the second fault state to the alarm device46. When receiving input of the control signal, the alarm device46lights an alarm lamp46b, which indicates that the W/G valve23is in the second fault state, to notify the driver that the W/G valve23is in the second fault state.

When the fault flag F2is set at1or2, the control unit31outputs an output limitation signal that indicates limiting the fuel injection amount Qf to the fuel injection control section45. When receiving input of the output limitation signal, the fuel injection control section45reduces the fuel injection amount Qf calculated according to the operation condition of the engine10at a predetermined ratio and controls the injector13to inject the reduced fuel injection amount Qf of fuel into the cylinders12.

After completing maintenance of the fault of the W/G valve23, an operator who has performed the maintenance sets the fault flag F2to0. The operator resets the lit alarm lamps46aand46bof the alarm device46and the output limitation by the fuel injection control section45.

The steps of the fault detection process executed by the fault detection device30will now be described with reference toFIG. 2. The fault detection process is repeatedly executed. As a process separated from the fault detection process described below, the control unit31performs setting and counting down of the count value C with the clock section34.

As shown inFIG. 2, when the fault detection process is started, the control unit31at the first step S11determines whether the fault flag F2is0, i.e., whether the W/G valve23operates normally. When the fault flag F2is1(step S11: NO), i.e., when a fault is already detected in the W/G valve23, the control unit31finishes the fault detection process.

When the fault flag F2is0(step S11: YES), the control unit31at the next step S12repeatedly determines whether the count value C of the clock section34is0. In other words, the control unit31at step S12determines whether the transitional period has elapsed after the control signal from the W/G valve control section24is changed.

When the count value C of the clock section34is0(step S12: YES), the control unit31at the next step S13obtains various information, which is the fuel injection amount Qf, the boost pressure Pb, the rotational speed NE of the engine10, and the intake air temperature Tin. In other words, the control unit31as an acquisition section obtains the rotational speed NE, the boost pressure Pb, and the intake air temperature Tin when a predetermined time has elapsed after the W/G valve23is switched between the open state and the closed state.

At the next step S14, the control unit31computes the computed value Gc of the working gas amount based on the boost pressure Pb, the rotational speed NE, and the intake air temperature Tin obtained at step S13. The control unit31also computes the reference value Gs of the working gas amount based on the fuel injection amount Qf and the rotational speed NE obtained at step S13and the reference data40stored in the memory32.

At the next step S15, the control unit31determines whether the open/closed flag F1is0. In other words, the control unit31at step S15determines whether the W/G valve23is controlled in the closed state.

When the open/closed flag F1is0(step S15: YES), the control unit31at the next step S16selects the first threshold data41as a threshold data for setting the threshold Gt. The control unit31also selects a value from the first threshold data41according to the fuel injection amount Qf and the rotational speed NE obtained at step S13, and sets the selected value as the threshold Gt. The control unit31at the next step S17then determines whether the determination value Gj, which is the difference between the computed value Gc and the reference value Gs, exceeds the threshold Gt set at step S16.

When the determination value Gj exceeds the threshold Gt (step S17: YES), the control unit31at the next step S18determines that the W/G valve23is in the first fault state, in which the W/G valve23is fixed in the open state, and sets the fault flag F2to1.

At the next step S19, the control unit31outputs an output limitation signal that indicates limiting the fuel injection amount Qf to the fuel injection control section45. The control unit31then outputs a control signal indicating that the W/G valve23is in the first fault state to the alarm device46and finishes a sequence of steps. When receiving input of the output limitation signal, the fuel injection control section45limits the fuel injection amount Qf. When receiving input of the control signal, the alarm device46lights the alarm lamp46ato notify the driver that the W/G valve23is in the first fault state.

In contrast, when the determination value Gj is less than or equal to the threshold Gt (step S17: NO), the control unit31at the next step S20determines that the W/G valve23operates normally, sets the fault flag F2to0, and finishes the sequence of steps.

When the open/closed flag F1at step S15is1(step S15: NO), the control unit31at the next step S21selects the second threshold data42as threshold data for setting the threshold Gt. The control unit31also selects a value from the second threshold data42according to the fuel injection amount Qf and the rotational speed NE obtained at step S13, and sets the selected value as the threshold Gt. The control unit31at the next step S22then determines whether the determination value Gj exceeds the threshold Gt set at step S21.

When the determination value Gj exceeds the threshold Gt (step S22: YES), the control unit31at the next step S23determines that the W/G valve23is in the second fault state, in which the W/G valve23is fixed in the closed state, and sets the fault flag F2to2.

When the fault flag F2is set at2, the control unit31moves to step S19and outputs an output limitation signal that indicates limiting the fuel injection amount Qf to the fuel injection control section45. The control unit31then outputs a control signal indicating that the W/G valve23is in the second fault state to the alarm device46and finishes the sequence of steps. When receiving input of the output limitation signal, the fuel injection control section45limits the fuel injection amount Qf. When receiving input of the control signal, the alarm device46lights the alarm lamp46bto notify the driver that the W/G valve23is in the second fault state.

In contrast, when the determination value Gj is less than or equal to the threshold Gt (step S22: NO), the control unit31moves to step S20, sets the fault flag F2to0, and finishes the sequence of steps.

Operation of the aforementioned fault detection device30will now be described with reference toFIG. 3.

The density of intake air changes depending on the environment such as ambient pressure and an ambient temperature. Thus, the mass flow rate varies even at the same volume flow rate. For this reason, even if intake air at the same volume flow rate is compressed by the compressor18with the same rotational speed, the boost pressure Pb, which is pressure after the compression, and the intake air temperature Tin, which is a temperature after the compression, vary depending on the environment.

In this regard, the aforementioned fault detection device30computes the working gas amount based on the boost pressure Pb, the intake air temperature Tin, and the rotational speed NE of the engine10, and detects a fault of the W/G valve23based on the computed value Gc. In other words, a fault of the W/G valve23is detected with the intake air temperature Tin in addition to the boost pressure Pb so that the intake air temperature Tin, i.e., an ambient temperature, is taken into account for the detection. As a result, compared to when a fault of the W/G valve23is detected only with the boost pressure Pb, the fault of the W/G valve23is detected with great accuracy.

For example, when the temperature of exhaust gas rises due to the large fuel injection amount Qf with the W/G valve23in the closed state, the thermally expanded W/G passage22and W/G valve23change a clearance between the W/G passage22and the W/G valve23. The change in the clearance changes a leak amount of exhaust gas in the W/G passage22. Similarly, even with the W/G valve23in the open state, the thermally expanded W/G passage22changes the flow path cross-sectional area of the W/G passage22, thereby changing the circulation amount of exhaust gas in the W/G passage22.

In this regard, the aforementioned fault detection device30selects the first threshold data41or the second threshold data42according to whether the W/G valve23is open or closed, and sets the threshold Gt provided in the selected threshold data as the threshold. The first threshold data41and the second threshold data42provide the threshold Gt according to the rotational speed NE and the fuel injection amount Qf, i.e., the threshold Gt taking account of the thermal expansion of the W/G valve23and the W/G passage22according to the operation condition of the engine10. In other words, the fault detection device30sets the threshold Gt while the open or closed state of the W/G valve23, the thermal influence to the W/G valve23, and the thermal influence to the W/G passage22are taken into account. As a result, a fault of the W/G valve23is detected with further great accuracy.

As shown inFIG. 3, when the rotational speed NE and the fuel injection amount Qf are increased as time elapses, the W/G valve23is switched from the closed state to the open state at time t1. Since a time period T between the time t1and time t2is a transitional period for which the turbine21has rotational inertia, the computed value Gc of working gas gradually decreases during the time period T. For this reason, the determination value Gj in the time period T is likely to be greater than the determination value Gj at time after the time t2. Thus, the W/G valve23is likely determined as having a fault.

Similarly, when the rotational speed NE and the fuel injection amount Qf are decreased as time elapses, the W/G valve23is switched from the open state to the closed state. A time period immediately after the switching is a transitional period for which the rotational speed of the turbine21that was stopped gradually increases. Thus, the computed value Gc of the working gas amount gradually increases during the period. For this reason, the determination value Gj in the period is also likely to increase, and the W/G valve23is likely determined as having a fault.

In this regard, when the W/G valve23is switched between the open state and the closed state, the aforementioned fault detection device30interrupts fault detection of the W/G valve23without obtaining various information until the count value C of the clock section34changes from an initial value Ci to0, i.e., until the transitional period elapses. This avoids erroneous detection of a fault due to the transitional period.

In the first fault state, in which the W/G valve23is fixed in the open state, oxygen is likely to be insufficient relative to the fuel injection amount Qf because a sufficient boost pressure cannot be obtained. Thus, it is a concern that non-burnt fuel contained in exhaust gas will increase so that the fuel efficiency is worsened. In the second fault state, in which the W/G valve23is fixed in the closed state, the exhaust pressure and the exhaust temperature in the exhaust manifold15are excessively increased, and the turbine21overruns.

In this regard, the aforementioned fault detection device30outputs an output limitation signal to the fuel injection control section45that limits the fuel injection amount Qf when a fault is detected in the W/G valve23. For this reason, non-burnt fuel contained in exhaust gas is reduced in the first fault state, and overrunning of the turbine21is avoided in the second fault state. In other words, failure caused by a fault of the W/G valve23is avoided by limiting the fuel injection amount Qf.

For example, when an air hose constituting the intake passage16is cracked, the first fault state is possibly determined even when the W/G valve23is not fixed in the open state. In this regard, the aforementioned fault detection device30detects a fault state by distinguishing between the first fault state, in which the W/G valve23is fixed in the open state, and the second fault state, in which the W/G valve23is fixed in the closed state. For this reason, it is easier to find out what causing the fault state by distinguishing the fault state of the W/G valve23when the fault state is determined in spite of the W/G valve23operating normally.

As described above, the fault detection device30and the fault detection method according to the above embodiment have the following advantages.

(1) A fault of the W/G valve23is detected while taking account of the intake air temperature Tin in addition to the boost pressure Pb. Thus, the fault of the W/G valve23is detected with great accuracy.

(2) The threshold Gt is set while taking account of whether the W/G valve23is open or closed, the thermal influence to the W/G valve23, and the thermal influence to the W/G passage22. Thus, a fault of the W/G valve23is detected with further great accuracy.

(3) Fault detection of the W/G valve23is interrupted until the transitional period elapses. Thus, erroneous detection of a fault due to the transitional period is avoidable.

(4) Failure caused by a fault of the W/G valve23is avoidable by limiting the fuel injection amount Qf.

(5) Distinction of a fault state between the first fault state and the second fault state makes it easier to find out the cause of a fault state when the fault state is determined in spite of the W/G valve23operating normally.

The above embodiment is modified in the following forms.

The fault detection device30does not necessarily need to output an output limitation signal to the fuel injection control section45when a fault is detected in the W/G valve23. In other words, even after the fault is detected in the W/G valve23, the fuel injection amount Qf does not necessarily need to be limited.

The fault detection device30may also detect a fault of the W/G valve23in the transitional period. In the configuration, it is preferable to store a third threshold data for providing a threshold in the transitional period in the memory32and set a threshold in the transitional period based on a third threshold data.

The threshold Gt may have a constant value regardless of whether the W/G valve23is open or closed.

The threshold Gt provided by the first threshold data41may be any value as long as the threshold Gt is set in accordance with the operation condition of the engine10. For example, the value may have a pattern of decreasing as the fuel injection amount Qf decreases. The threshold Gt provided by the first threshold data41may have a constant value regardless of the operation condition of the engine10. Similarly, the second threshold data42may be a value according to the operation condition of the engine10or may be a constant value regardless of the operation condition of the engine10.

The fault detection device30may have a range of working gas amounts in which a fault of the W/G valve23is determined and which is according to the fuel injection amount Qf and the rotational speed NE. Data for providing the range is stored in the memory32, and a fault is detected based on the data and the computed value Gc of a working gas amount. In other words, the fault detection device30may detect a fault of the W/G valve23without computing the determination value Gj but with the computed value Gc of the working gas amount.

A fault of the W/G valve23may be detected without distinguishing the fault state between the first fault state and the second fault state. When detecting a fault of the W/G valve23, only the first fault state may be detected, or only the second fault state may be detected.

An EGR passage may be provided for the engine10to circulate some of the exhaust gas through the intake passage16. In other words, working gas may be mixture of intake air and exhaust gas. In this case, it is preferable to compute the working gas while taking account of the pressure of the EGR passage, an EGR amount, and the like.

The fault detection device30may be one electronic control unit, or may consist of a plurality of electronic control units. The fault detection device30, the fuel injection control section45, and the W/G valve control section24may be included in one electronic control unit, or may be included in a plurality of electronic control units.

The engine provided with the fault detection device30may be a gasoline engine.