Failure detecting apparatus for exhaust secondary air supply system

Abstract

In a V-type engine in which two air supply pipes are connected to banks thereof, respectively, two air-fuel ratio sensors are provided at positions downstream of the air supply pipes for producing outputs corresponding to the density of oxygen in exhaust emissions. When exhaust secondary air is supplied, differences between air-fuel ratio feedback correction factors calculated based on outputs of two air-fuel ratio sensors at a time and air-fuel feedback correction factors calculated at a time that is a time that results after a predetermined period of time has elapsed since the time are calculated. The differences so calculated are compared with a predetermined value, and, when the calculated differences do not exceed the predetermined value, the exhaust secondary air supply system is detected to fail.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a failure detecting apparatus for an exhaust secondary air supply system.

[0003] 2. Description of the Related Art

[0004] An exhaust secondary air supply system includes, for example, an air supply pipe connected to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine and an air pump. The exhaust secondary air supply system is intended to introduce secondary air from the air supply pipe into the exhaust system by driving the air pump so as to promote the combustion in the system to thereby reduce unburned constituents contained in exhaust gases.

[0005] In the exhaust secondary air supply system, since, in case there occurs a failure such as a damage to the air supply pipe, the expected function is not attained, various types of failure detecting methods have been proposed therefor, and a technique described in JP-A-5-26033 is disposed as an example.

[0006] In the technique described in the above-mentioned JP-A-5-26033, there is proposed an exhaust secondary air supply system including an air supply pipe connected to an air pump driven by an internal combustion engine for supplying secondary air to an upstream position of a catalytic converter and a control valve for controlling the opening of the air supply pipe so as to control the supply amount of secondary air. In this system, a failure of the exhaust secondary air supply system is detected by supplying secondary air intermittently in a predetermined diagnostic operating area to determine whether or not the output of an air-fuel ratio sensor (O2 sensor) disposed between an air supply position and the catalytic converter is reversed in response to the intermittent supplies.

[0007] In the related-art technique, in order to detect such a failure accurately, an output of the air-fuel ratio sensor resulting when the exhaust secondary air supply system operates normally needs to be verified through learning, which is troublesome, and there has been caused the inconvenience of the detection of a failure being delayed due to the necessity of such verification. The inconvenience becomes noticeable in particular, in the case of a V-type engine in which an exhaust system is provided for each bank.

SUMMARY OF THE INVENTION

[0008] Consequently, an object of the invention is to provide a failure detecting apparatus for an exhaust secondary air supply system which can resolve the drawback described above and detect the failure of the exhaust secondary air supply system easily and accurately.

[0009] With a view to attaining the object, according to a first aspect of the invention, there is provided a failure detecting apparatus for an exhaust secondary air supply system for supplying exhaust secondary air to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine, the failure detecting apparatus comprising:

[0010] an air-fuel ratio sensor for producing an output corresponding to a density of oxygen contained in exhaust gas flowing through the exhaust system; and a failure detecting section for comparing values obtained at different times based on outputs of the air-fuel ratio sensor when the exhaust secondary air is supplied so as to detect a failure of the exhaust secondary air supply system.

[0011] Since there is provided the failure detecting section for comparing values obtained at different times based on outputs of the air-fuel ratio sensor when the exhaust secondary air is supplied so as to detect a failure of the exhaust secondary air supply system, the failure of the exhaust secondary air supply system can be detected easily and accurately. In addition, since the necessity is obviated of doing the troublesome work in which the output of the air-fuel ratio sensor resulting when the exhaust secondary air supply system is normal is learned to be verified, there is no risk that the detection of the failure of the exhaust secondary air supply system is delayed. Furthermore, sine the failure detection is not such as to be implemented based on the output of the air-fuel ratio sensor when exhaust secondary air is supplied, in other words, based on the output of the air-fuel ratio sensor when the exhaust secondary air supply system is activated intermittently so as to supply exhaust secondary air intermittently, there is no risk that an erroneous failure detection results from the effect of an error caused by a difference in load of the internal combustion engine.

[0012] According to a second aspect of the invention, there is provided a failure detecting apparatus for an exhaust secondary air supply system as set forth in the first aspect of the invention, wherein the failure detecting section comprises a correction factor difference calculating section for calculating a difference between an air-fuel feedback correction factor calculated based on an output of the air-fuel ratio sensor at a time tn and an air-fuel feedback correction factor calculated at a time tn+m that is a time that results after a predetermined period of time m has elapsed since the time tn and a comparing section for comparing the difference so calculated with a predetermined value, so as to determine that the exhaust secondary air supply system fails when the calculated difference does not exceed the predetermined value.

[0013] Since a difference between an air-fuel feedback correction factor calculated based on an output of the air-fuel ratio sensor at a time tn and an air-fuel feedback correction factor calculated at a time tn+m that is a time that results after a predetermined period of time m has elapsed since the time tn is calculated so as to be compared with a predetermined value, whereby, when the calculated difference does not exceed the predetermined value, the exhaust secondary air supply system is detected to fail, the failure of the exhaust secondary air supply system can be detected more easily and accurately by setting the predetermined period of time appropriately or to, for example, a time that will be described below as a time needed for a change in the operating conditions such as load of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end.

[0014] According to a third aspect of the invention, there is provided a failure detecting apparatus for an exhaust secondary air supply system as set forth in the second aspect of the invention, wherein the predetermined period of time is set based on a time needed for a change in operating conditions of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end.

[0015] Since the predetermined period of time is set based on a time needed for a change in the operating conditions of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end, even when the air-fuel ratio sensor exhibits unexpected behaviors according to the change, an effect resulting from the unexpected behaviors can be avoided, whereby the failure of the exhaust secondary air supply system can be detected more easily and accurately.

[0016] According to a fourth aspect of the invention, there is provided a failure detecting apparatus for an exhaust secondary air supply system for supplying exhaust secondary air to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine, the failure detecting apparatus comprising:

[0017] a plurality of air supply pipes connected to the exhaust system of the internal combustion engine for supplying the exhaust secondary air, respectively;

[0018] a plurality of air-fuel ratio sensors disposed along the exhaust system at positions downstream of the plurality of air supply pipes for producing an output corresponding to a density of oxygen contained in exhaust emissions flowing through the exhaust system, respectively; and

[0019] a failure detecting section for comparing values with each other which are obtained based on the outputs of the plurality of air-fuel ratio sensors so as to detect a failure of the exhaust secondary air supply system.

[0020] Since there are provided the plurality of air-fuel ratio sensors disposed along the exhaust system at positions downstream of the plurality of air supply pipes for producing an output corresponding to the density of oxygen contained in exhaust emissions flowing through the exhaust system, respectively, and the failure detecting section for comparing values with each other which are obtained based on the outputs of the plurality of air-fuel ratio sensors so as to detect a failure of the exhaust secondary air supply system, the failure of the exhaust secondary air supply system can be detected easily and accurately. In addition, the necessity is obviated of doing the troublesome work in which the output of the air-fuel ratio sensor resulting when the exhaust secondary air supply system is normal is learned to be verified, and there is caused no inconvenience that the detection of the failure of the exhaust secondary air supply system is delayed. In addition, in a case where an air supply pipe is provided for each exhaust system of an engine such as a V-type engine which has an exhaust system on each bank, it is possible not only to detect the existence of a failure but also to detect which air supply pipe on the banks suffers from the failure when the failure is detected.

[0021] According to a fifth aspect of the invention, there is provided a failure detecting apparatus for an exhaust secondary air supply system as set forth in the fourth aspect of the invention, wherein the failure detecting section comprises a correction factor difference calculating section for calculating a difference between air-fuel ratio feedback correction factors calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors, and a comparing section for comparing the difference so calculated with a predetermined value, so as to determine that the exhaust secondary air supply system fails when the calculated difference exceeds the predetermined value.

[0022] Since the difference between the air-fuel ratio feedback correction factors calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors are compared with the predetermined value, whereby, when the calculated difference exceeds the predetermined value, the exhaust secondary air supply system is detected to fail, the failure of the exhaust secondary air supply system can be detected more easily and accurately.

[0023] According to a sixth aspect of the invention, there is provided a failure detecting apparatus for an exhaust secondary air supply system as set forth in the fourth aspect of the invention, wherein the internal combustion engine is a V-type engine, wherein the failure detecting apparatus comprises an air pump, and wherein the air supply pipe is connected to the air pump and is branched at an intermediate position along its length so as to be connected to banks of the V-type engine, respectively.

[0024] According to construction, in a V-type engine in which an air supply pipe is connected to each of banks thereof, the failure of an exhaust secondary air supply system can be detected easily and accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic view illustrating the overall construction of a failure detecting apparatus for an exhaust secondary air supply system according to an embodiment of the invention;

[0026] FIG. 2 is an explanatory perspective view showing in detail part of the apparatus shown in FIG. 1 including air supply pipes which are constituent components of the exhaust secondary air supply system;

[0027] FIG. 3 is a flowchart of an operation of the apparatus shown in FIG. 1;

[0028] FIG. 4 is a time chart explaining the operation of the apparatus shown in FIG. 3 which shows outputs of air-fuel ratio sensors (O2 sensors) resulting when no failure occurs in the exhaust secondary air supply system and air-fuel ratio feedback correction factors that are calculated based on the outputs;

[0029] FIG. 5 is a time chart explaining the operation of the apparatus shown in FIG. 3 which shows outputs of the air-fuel ratio sensors (O2 sensors) resulting when a failure occurs in the exhaust secondary air supply system and air-fuel ratio feedback correction factors that are calculated based on the outputs;

[0030] FIG. 6 is a flowchart, which is similar to that shown in FIG. 3, illustrating an operation of a failure detecting apparatus for an exhaust secondary air supply system according to a second embodiment of the invention; and

[0031] FIG. 7 is a flowchart of an operation of a failure detecting apparatus for an exhaust secondary air supply system according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, a failure detecting apparatus for an exhaust secondary air supply system according to embodiments of the invention will be described by reference to the accompanying drawings.

[0033] FIG. 1 is a schematic view showing the overall structure of a failure detecting apparatus for an exhaust secondary air supply system according to an embodiment of the invention.

[0034] In the same drawing, reference numeral 10 denotes a multi-cylinder internal combustion engine (hereinafter, referred to as an “engine”). The engine 10 is a four-cycle vee six-cylinder DOHC engine and has three cylinders 12 including cylinders numbers 1, 2 and 3 on a right bank 10R and three cylinders 12 including cylinders numbers 4, 5 and 6 on a left bank 10L.

[0035] In the engine 10, air taken in from an air cleaner 14 flows through an induction pipe 16 and reaches to intake ports of the respective cylinders via induction manifolds (not shown) while the flow rate of the air is being controlled by a throttle valve 20. Gasoline fuel is then injected from injectors (not shown) disposed at the intake ports. Thus, an air-fuel mixture so formed enters combustion chambers (not shown) of the respective cylinders when inlet valves (not shown) are opened and then burns when ignited by sparking plugs (not shown).

[0036] Exhaust emissions (exhaust gases) produced by combustion flow into exhaust manifolds 22 provided, respectively, on the left and right banks 10R, 10L when exhaust valves (not shown) are opened, merge at collecting portions, and thereafter flow through exhaust pipes 24 to the outside of the engine after harmful constituents have been removed at catalytic converters (of three-way type) 26.

[0037] An exhaust secondary air supply system 30 is provided at a position along the length of the exhaust system made up of the exhaust manifolds 22 and the exhaust pipes 24. The exhaust secondary air supply system 30 mainly includes an air supply pipe (a delivery pipe) 32 connected to a position upstream of the catalytic converters 26 along the exhaust system of the engine 10 and an air pump 34.

[0038] The induction pipe 16 is branched on an upstream side of the throttle valve 20, and a branch 16a connects to an intake side of the air pump 34 at the other end thereof. The air pump 34 connects to the air supply pipe 32 on an outlet side thereof. The air supply pipe 32 is branched via a cut-off valve 36 so as to be connected to the exhaust manifolds 22 on the left and right banks 10R, 10L, respectively. The air supply pipe disposed on the exhaust manifold 22 on the right bank 10R side is denoted as 32R, whereas the air supply pipe disposed on the exhaust manifold 22 on the left bank 10L side is denoted as 32L. Note that the air supply pipes 32R, 32L are constructed so as to have configurations which supply the same amount of air.

[0039] While the construction of the air supply pipe 32 is described in detail in FIG. 2, as shown in the drawing, flanges 32b are formed at distal ends of the air supply pipe 32 in the vicinity of openings 32a, whereby the air supply pipe 32 is connected to the exhaust manifolds 22 by being bolted to the exhaust manifolds 22 at the flanges 32b while aligning the openings 32a with holes (shown by broken lines in FIG. 1) 22a opened in the exhaust manifolds 22.

[0040] An electric motor 40 is connected to the air pump 34, whereby the air pump 34 is driven by virtue of the rotation of the electric motor 40 so as to suck in air taken in from the air cleaner 14 to thereby send air so sucked in to the air supply pipe 32 under pressure. The cut-off valve 36 includes a negative pressure diaphragm (not shown), so that the valve opens when a negative pressure is introduced via a negative pressure introducing mechanism, not shown, so as to supply pressurized air that has been introduced from an inlet opening 36a to the exhaust manifolds 22.

[0041] In FIG. 1, a crank angle sensor 42 is disposed in the vicinity of a rotational shaft (not shown) such as a crankshaft of the engine 10 for outputting a cylinder identifying signal, and the crank angle sensor 42 also outputs a TDC signal at a TDC position or in the vicinity thereof of each cylinder and a crank angle signal which results from the segmentation of the crank angle signal.

[0042] In addition, an absolute pressure sensor 44 is provided downstream of a position along the induction pipe 16 where the throttle valve 20 is disposed for outputting a signal corresponding to an induction manifold absolute pressure (an engine load) PBA, and a coolant temperature sensor 46 is disposed along a coolant passageway (not shown) of the engine 10 for outputting a signal corresponding to the engine coolant temperature TW.

[0043] Additionally, in the exhaust system, primary air-fuel ratio sensors 50 are disposed an upstream side of the catalytic converters 26 and secondary air-fuel ratio sensors 52 are disposed on a downstream side thereof, and the respective sensors output signals corresponding to the density of oxygen contained in exhaust emissions which flow through positions where those sensors are disposed, respectively (hereinafter, the sensors 50, 52 disposed on the right bank 10R are denoted as 50R, 52R, whereas the sensors disposed on the left bank 10L are denoted as 50L, 52L). The primary and secondary sensors are both an O2 sensor and output a signal which repeats reversals toward a rich direction and a lean direction across a value corresponding to a stoichiometric air-fuel ratio. Hereinafter, the primary air-fuel sensor 50 is referred to as a “PO2 sensor” and the secondary air-fuel sensor 52 is referred to as a “S02 sensor”.

[0044] Outputs of the group of sensors are sent to an ECU 54. The ECU 54 is made up of a microcomputer and not only counts crank angle signals inputted from the crank angle sensor 42 so as to detect an engine rotational speed NE but also calculates a fuel injection amount TI that is to be supplied to the engine 10 based on outputs of the sensors including the crank angle sensor 42 as will be expressed below.

TI=TIM×KO2×KTOTAL+TTOTAL

[0045] where, TIM is a base value that is obtained from the engine rotational speed NE and engine load (induction manifold absolute pressure)PBA through map retrieving. In addition, KO2 is an air-fuel ratio feedback correction factor that is determined based on a detected air-fuel ratio obtained from an output of the PO2 sensor and is calculated as will be expressed below. Hereinafter, n is a sample number of a discrete system or, to be more specific, a control cycle.

[0046] KO2(n)=KO2(n−1)-KO2I (in the case where a detected air-fuel ratio is rich);

[0047] KO2(n)=KO2(n−1)+KO2I (in the case where a detected air-fuel ratio is lean)

[0048] Namely, KO2 is determined by adding or subtracting the I (an integrating control term) to or from a deviation from a value corresponding to a stoichiometric air-fuel ratio (a center value between reversals). Note that KO2 is calculated for each bank based on outputs of the PO2 sensors 50R, 50L disposed on the left and right banks 10R, 10L, respectively. In addition, KO2 is controlled to be learned.

[0049] Additionally, KTOTAL is a correction factor in another multiplying format, and TTOTAL is a correction factor in an adding format. In addition, the fuel injection amount TI is shown as a valve opening time of the injector. Furthermore, the fuel injection amount TI is increased, for example, when the engine 10 is started.

[0050] The ECU 54 determines an ignition timing using the engine rotational speed NE and gives an instruction to energize the electric motor 40 for a predetermined period after the engine 10 has been started so as to drive the air pump 34 to supply exhaust secondary air to the exhaust system. Therefore, unburned constituents of fuel the amount of which is increased when the engine 10 is started are burned in the exhaust manifolds 22 and the exhaust pipes 24 downstream of the exhaust manifolds 22 to thereby be discharged into the atmosphere while heating the catalytic converters 26. Thus, the activation of the catalytic converters 26 is promoted and the discharge of unburned constituents to the atmosphere is reduced. In addition, the ECU 54 also detects the failure of the exhaust secondary air supply system 30.

[0051] Next, the operation of detecting the failure of the exhaust secondary air supply system 30 will be described.

[0052] FIG. 3 is a flowchart illustrating the operation.

[0053] To start the description of the flowchart, in step S10, whether or not it is in a monitor area (a failure detecting area) is determined. It is determined to be in a monitor area when the engine 10 is in the idling state or other steady-state operating conditions after the engine 10 is started and the warming up thereof is completed.

[0054] If denied in step 10, processes in the following steps are skipped, whereas if acknowledged, the flow proceeds to step S12, where whether or not the failure of the exhaust secondary air supply system 30 has been detected is determined. If acknowledged in step S12, too, processes in the following steps are skipped. Note that the processes in the following steps are also skipped, for example, if it is determined that the electric motor 40 does not fail but is heated excessively due to the excessive energization of the electric motor 40.

[0055] On the other hand, if denied in step S12, the flow proceeds to S14, where the air pump 34 is switched on, or the electric motor 40 is energized so as to activate the air pump 34, and the learning of the air-fuel feedback correction factor KO2 is prohibited. Namely, in order not to effect the originally desired air-fuel ratio feedback control through the artificial operation of air-fuel ratio for failure detection, the learning thereof is prohibited.

[0056] Next, the flow proceeds to S16, where, after a certain time (for example, from one to two seconds) has elapsed, air-fuel ratio feedback correction factors KO2 are calculated for the left and right banks from outputs of the PO2 sensors 50R, 50L on the left and right banks. Note that a correction factor calculated from an output of the PO2 sensor on the right bank is denoted as KO2R1 and that a correction factor calculated from an output of the PO2 sensor on the left bank is denoted as KO2L1. The time then is denoted as tn.

[0057] Next, the flow proceeds to S18, where air-fuel ratio feedback correction factors KO2 are calculated again for the left and right banks from outputs of the PO2 sensors 50R, 50L on the left and right banks at a time tn+m that is a time that results after a predetermined period of time m has elapsed since the time tn. A correction factor for the right bank calculated then is denoted as KO2R2 and that one for the left bank calculated then is denoted as KO2L2.

[0058] Next, the flow proceeds to S20, as shown in the drawing, whether or not differences exceed a predetermined value is determined which are obtained by subtracting the air-fuel ratio correction factors KO2R1, KO2L1 calculated at the time tn, respectively, from the air-fuel ratio feedback factors KO2R2, KO2L2 calculated at the time tn+m that is the time that results after the predetermined period of time m has elapsed since the time tn.

[0059] If acknowledged in S20, the flow proceeds to S22, where the air supply pipe 32 is determined (detected) to be normal, whereas if denied, or, to be more accurate, if denied regarding either or both of the KO2R, KO2L, the flow proceeds to S24, where the relevant air supply pipe 32R or 32L on the left and right banks is determined (detected) to fail.

[0060] Here, a description will be made by reference to FIGS. 4 and 5.

[0061] If the exhaust secondary air supply system 30 is normal, in FIG. 4, assuming that the air pump 34 starts driving at a time ta, the same amount of air is supplied to the exhaust manifolds 22 on the left and right banks and then flows through the exhaust pipes 24, and as a result of this, exhaust emissions get lean gradually at the positions where the PO2 sensors 50R, 50L are disposed. Consequently, values of the air-fuel ratio feedback correction factors KO2R, KO2L that are calculated based on detected values also gradually change so as to be corrected toward a rich direction, and differences between values at the time tn that is a time resulting immediately after the air pump is driven and values at the time tn+m are expanded to or over a certain value in conjunction with an increase in air amount during that time.

[0062] On the other hand, when the same amount of air is not supplied to the exhaust manifolds 22 on the left and right banks due to the occurrence of a failure of air leakage from either of the air supply pipes 32R, 32L on the left and right banks that is caused by a damage such as a crack made to the relevant air supply pipe 32R or 32L, the amount of air that flows through the exhaust pipes 24 comes to differ between the left and right banks.

[0063] For example, as shown in FIG. 5, when a failure such as one that has just been described above, the value of the air-fuel ratio feedback correction factor calculated based on the detected value of the PO2 sensor 50R does not show a predetermined change between the time tn and the time tn+m as shown in the same drawing.

[0064] Consequently, by setting the predetermined value appropriately and comparing the air-fuel ratio feedback correction factor calculated at the time tn and the air-fuel ratio feedback correction factor calculated at the time tn+m which is the time resulting after the predetermined period of time m has elapsed since the time tn for the left and right banks, it can be determined that a failure occurs in the exhaust secondary air supply system 30, the failure including, to be more accurately, those in which a damage such as a crack is caused to the air supply pipe 32R or 32L on the side where the difference does not exceed the predetermined value, the sealing at the connecting portion between the flange portion 32b of the relevant air supply pipe 32R or 32L and the corresponding exhaust manifold 22 is insufficient or the sealing at the connecting portion between the air pump 34 or the cut-off valve 36 and the air supply pipe 32 is insufficient.

[0065] Note that, here, the predetermined period of time is set based on a time needed for a change in operating conditions of the engine caused by an activation of the exhaust secondary air supply system 30 to come to an end. Namely, since the air pump 34 of the exhaust secondary air supply system 30 is driven by the electric motor 40, when the air pump 34 is driven, the operating conditions such as load of the engine 10 varies transiently due to a drastic increase in electric load. As a result, there is caused a risk that the behaviors of the air-fuel ratio are affected. To deal with this, the predetermined period of time is determined to be set based on the time needed for the change in the operating conditions to come to an end, or to be more specific, to be set to a time that is longer than the time needed for the change to come to an end. Therefore, the failure of the exhaust secondary air supply system 30 can be detected more accurately. Note that the air pump 34 is stopped after a second calculation has been completed.

[0066] Since the failure detecting apparatus according to this embodiment is constructed as has been described heretofore, the failure of the exhaust secondary air supply system 30 or, to be more specific, a failure such as a damage to the air supply pipe 32 can be detected more easily and accurately.

[0067] FIG. 6 is a flowchart illustrating an operation of detecting the failure of the exhaust secondary air supply system 30 according to a second embodiment of the invention.

[0068] To describe the flowchart, after processes from S100 to S106 which are similar to those of the first embodiment have been performed, the flow proceeds to S108, where air-fuel ratio feedback correction factors KO2 are calculated again from outputs of the PO2 sensors 50R, 50L of the left and right banks at a time tn+o which is a time resulting after a time o has elapsed since the time tn. As this occurs, a correction factor calculated for the right bank is denoted as KO2R2, and one for the left bank is denoted as KO2L2.

[0069] Next, the flow proceeds to S110, where air-fuel ratio feedback correction factors KO2 are calculated again for the left and right banks, respectively, from outputs of the PO2 sensors 50R, 50L of the left and right banks at a time tn+o+p which is a time resulting after a certain time p has elapsed since the time tn+o. A correction factor calculated for the right bank then is denoted as KO2R3 and one for the left bank is denoted as KO2L3. Note that the certain times o and p may be of the same length as that of the predetermined time m or may be a time which is shorter than the time m.

[0070] Next, the flow proceeds to S112, where, as shown in the drawing, it is determined whether or not differences exceed a predetermined value, respectively, which are obtained by subtracting the air-fuel feedback correction factors KO2R1, KO2L1 which result at the time tn from the air-fuel feedback correction factors KO2R2, KO2L2 which result at the time tn+o which is the time resulting after the predetermined period of time o has elapsed.

[0071] If denied in S112, or to be more accurate, if denied regarding either or both of KO2R, KO2L, the flow proceeds to S114, where the air supply pipe 32R or 32L on the relevant bank of the left and right banks is determined (detected) to fail, whereas if acknowledged in S112, the flow proceeds to S116, where it is determined whether or not differences exceed another predetermined value, respectively, which are obtained by subtracting the air-fuel feedback correction factors KO2R1, KO2L1 which result at the time tn from the air-fuel feedback correction factors KO2R3, KO2L3 which result at the time tn+o+p which is the time resulting after the predetermined period of time o+p has elapsed.

[0072] If acknowledged in S116 as well, then, the flow proceeds to S118, where the air supply pie 32 is determined (detected) to be normal, whereas if denied, or, denied regarding either or both of KO2R, KO2L, the flow proceeds to S114, the air supply pipe 32R or 32L on the relevant bank of the left and right banks is determined (detected) to fail.

[0073] Note that, in the above process, differences between outputs of the PO2 sensors 50R, 50L at the time tn and outputs thereof at the time tn+m may be obtained so that the differences so obtained are compared with the predetermined value that is set appropriately so as to detect a failure. In the specification, “Values obtained based on outputs of the air-fuel sensor” is meant to include not only air-fuel ratio feedback correction factors but also outputs themselves of the sensor.

[0074] In addition, while the predetermined value (and the second predetermined value) are set by selecting appropriately values that are good enough to determine a failure from the differences as is described above, for example, a difference between outputs of the PO2 sensors 50R, 50L when exhaust secondary air is not supplied may be learned, so that the predetermined value so set is corrected according to the learned value.

[0075] Additionally, While the time tn and the time tn+m that is the time resulting after the predetermined period of time has elapsed since the time tn are used for the air-fuel feedback correction factors KO2R, KO2L of the left and right banks, different times may be used between the left and right banks. Namely, the time tn and the time tn+m are used for the right bank, while a time tq and a time tq+r that is a time resulting after a predetermined period of time r has elapsed since the time tq may be used for the left bank.

[0076] As has been described heretofore, according to the embodiments, there is provided the failure detecting apparatus for the exhaust secondary air supply system 30 for supplying exhaust secondary air to the position upstream of the catalytic converter 26 disposed along the exhaust system of the internal combustion engine (engine) 10. The failure detecting apparatus comprises the air-fuel ratio sensors (the PO2sensors 50R, 50L) for producing outputs corresponding to the density of oxygen contained in exhaust gas flowing through the exhaust system, and the failure detecting section (the ECU 54, from S10 to S24) for comparing values obtained at the different times, that is, the time tn and the time tn+m based on the outputs of the air-fuel ratio sensors when the exhaust secondary air is supplied so as to detect the failure of the exhaust secondary air supply system.

[0077] To be more specific, the failure detecting section includes the correction factor difference calculating section (the ECU 54, from S16 to S18) for calculating the differences between the air-fuel feedback correction factors KO2R, KO2LKO2R1, KO2L1 calculated based on the outputs of the air-fuel ratio sensors at the time tn and the air-fuel feedback correction factors KO2R, KO2LKO2R2, KO2L2 calculated at the time tn+m that is the time that results after the predetermined period of time m has elapsed since the time tn and the comparing section (the ECU 54, S20) for comparing the differences so calculated with the predetermined value. Therefore, when the calculated differences do not exceed the predetermined value, the exhaust secondary air supply system is detected to fail.

[0078] In addition, the predetermined period of time m is set based on the time needed for the change in the operating conditions of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end.

[0079] FIG. 7 is a flowchart illustrating an operation of detecting the failure of the exhaust secondary air supply system 30 according to a third embodiment of the invention.

[0080] To start the description of the flowchart, in step S10′, whether or not it is in a monitor area (a failure detecting area) is determined. It is determined to be in a monitor area when the engine 10 is in the idling state or other steady-state operating conditions after the engine 10 is started and the warming up thereof is completed.

[0081] If denied in step 10′, processes in the following steps are skipped, whereas if acknowledged, the flow proceeds to step S12′, where whether or not the failure of the exhaust secondary air supply system 30 has been detected is determined. If acknowledged in step S12′, too, processes in the following steps are skipped. Note that the processes in the following steps are also skipped, for example, if it is determined that the electric motor 40 does not fail but is heated excessively due to the excessive energization of the electric motor 40.

[0082] On the other hand, if denied in step S12′, the flow proceeds to S14′, where the air pump 34 is switched on, or the electric motor 40 is energized so as to activate the air pump 34, and the learning of the air-fuel feedback correction factor KO2 is prohibited. Namely, in order not to effect the originally desired air-fuel ratio feedback control through the artificial operation of air-fuel ratio for failure detection, the learning thereof is prohibited.

[0083] Next, the flow proceeds to S16′, air-fuel feedback correction factors KO2 are calculated from outputs of the PO2 sensors 50R, 50L of the left and right banks. Note that a correction factor calculated from an output of the PO2 sensor on the right bank is denoted as KO2R and a correction factor calculated from an output of the PO2 sensor on the left bank is denoted as KO2L. Next, maximum values KO2RMAX and KO2LMAX are obtained, respectively.

[0084] Next, proceed to S18′, the maximum value of KO2LMAX so obtained is then subtracted from the maximum value of KO2RMAX so obtained, and a difference &Dgr;max is obtained in an absolute value.

[0085] Next, proceed to S20′, where the difference &Dgr;max obtained in an absolute value is then compared with a predetermined value, and whether or not the difference &Dgr;max exceeds the predetermined value is determined. If denied, then the flow proceeds to S22′, where the air supply pipe 32 is determined (detected) to be normal, whereas if acknowledged, the flow proceeds to S24′, where the air supply pipe 32 is determined (detected) to fail.

[0086] Here, to describe by reference to FIGS. 4 and 5, in the event that the exhaust secondary air supply system 30 is normal, assuming that the air pump 34 is started to be driven at a time ta in FIG. 4, the same amount of air is supplied to the exhaust manifolds 22 of the left and right banks and then flows through the exhaust pipes 24, as a result of which, exhaust gases become gradually lean at positions where the PO2 sensors 50R, 50L are disposed. Consequently, while values of air-fuel ratio feedback correction factors KO2R, KO2L that are calculated based on the values so detected change gradually as shown in the drawing to correct the lean exhaust gases to a rich direction, a difference between the maximum values becomes 0 or a minute number.

[0087] On the other hand, in the event that the same amount of air is not supplied to the exhaust manifolds 22 of the left and right banks due to there occurring a failure in which a damage such as a crack is caused in either of the air supply pipes 32R, 32L on the left and right banks to thereby cause a leakage of air therefrom, the amount of air flowing through the exhaust pipes 24 becomes difference between the left and right exhaust pipes.

[0088] For example, as shown in FIG. 5, assuming that a failure like one described above occurs in the air supply pipe on the right bank 10R, since the amount of air supplied becomes short, a change in value of the air-fuel ratio feedback correction factor KO2R calculated based on a detection value of the PO2 sensor 50R becomes smaller than a change in the air-fuel ratio feedback correction factor KO2L on the left bank 10L, and a difference between the two factors increases gradually to be maximum with the maximum value KO2LMAX.

[0089] Consequently, by comparing the difference &Dgr;max between the air-fuel ratio feedback correction factors KO2RMAX and KO2LMAX with the predetermined value while changing the predetermined value appropriately, it is possible to determine that there has occurred a failure in the exhaust secondary air supply system 30, the failure being defined more accurately as a failure in which a damage such as a crack is caused in the air supply pipe 32 which has the smaller maximum value (the smaller change in air-fuel ratio feedback correction factor), sealing at the connecting portion between the air pump 34, sealing at the connecting portion between the flange portion 32b of the air supply pipe 32 and the exhaust manifold 22 is insufficient, or the cut-off valve 36 and the air supply pipe 32 is insufficient.

[0090] Since the failure detecting apparatus according to the third embodiment of the invention is constructed as has been described above, the failure of the exhaust secondary air supply system 30, or to be more specific, a failure such as a damage to the air supply pipe can be detected easily and accurately.

[0091] Note that while, as has been described above, the predetermined value is set by selecting appropriately a value which is good enough to determined a failure from the difference, for example, a difference between outputs of the PO2 sensor 50R, 50L which results when exhaust secondary air is not supplied may be learned, so that the predetermined value set in accordance with the learned value may be corrected.

[0092] Note that while, in the above configuration, the failure is detected by obtaining the maximum values KO2MAX, KO2LMAX of the air-fuel ratio feedback correction factors of the left and right banks and then comparing the difference &Dgr;max between the maximum values with the predetermined value, the maximum values are not necessarily obtained in an strict fashion. For example, a maximum value may be obtained for one of the air-fuel feedback correction factors KO2R, KO2L, while a value just prior to the maximum value may be used for the other to calculate a difference between the two feedback correction factors for comparison with the predetermine value. Alternatively, values just prior to the maximum values may be used for both of the air-fuel feedback correction factors KO2R, KO2L to calculate a difference between the two feedback correction factors for comparison with the predetermine value.

[0093] Furthermore, a difference between outputs (or maximum values) of the PO2sensors 50R, 50L is obtained, and the difference may be compared with the predetermined value which is set appropriately so as to detect a failure. In this case, when the difference exceeds the predetermined value, a value toward the rich direction is outputted or the air supply pipe 32 on the PO2 sensor 50R or 50L side which indicates a reversal of output is regarded as failing.

[0094] As has been described above, according to the third embodiment, there is provided the failure detecting apparatus for an exhaust secondary air supply system 30 for supplying exhaust secondary air to a position upstream of the catalytic converter 26 disposed along the exhaust system (the exhaust manifolds 22, the exhaust pipes 24) of the internal combustion engine (the engine) 10. The failure detecting apparatus comprises a plurality of air supply pipes 32R, 32L connected to the exhaust system (the exhaust manifolds 22) of the internal combustion chamber for supplying the exhaust secondary air thereto, respectively, a plurality of air-fuel ratio sensors (the PO2 sensors 50R, 50L) disposed along the exhaust system (the exhaust pipes 24) at positions downstream of the plurality of air supply pipes for producing an output corresponding to the density of oxygen contained in exhaust emissions flowing through the exhaust system, respectively, and the failure detecting section (ECU 54, from S10 to S24) for comparing values with each other which are obtained based on the outputs of the plurality of air-fuel ratio sensors so as to detect a failure of the exhaust secondary air supply system.

[0095] To be more specific, the failure detecting section comprises the correction factor difference calculating section (ECU 54, S16, S18) for calculating a difference (to be more accurate, the difference &Dgr;max between the maximum values KO2RMAX and KO2LMAX) between air-fuel ratio feedback correction factors KO2R, KO2L calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors, and the comparing section (ECU 54, S20) for comparing the difference so calculated with the predetermined value. Therefore, when the calculated difference exceeds the predetermined value, the exhaust secondary air supply system is detected to fail.

[0096] In addition, the internal combustion engine is a V-type engine, the single air pump is provided, and the air pipe 32R, 32L is connected to the air pump and is branched at an intermediate position along the length thereof so as to be connected to the banks 10R, 10L of the V-type engine, respectively.

[0097] Note that while the first to third embodiments have been described by taking for example the construction in which the air supply pipes 32R, 32L are disposed on the left and right banks 10R, 10L of the V-type engine, respectively, and the PO2 sensors 50R, 50L are disposed downstream of the air supply pipes, respectively, the invention is not limited thereto and therefore equally applies to any engines other than V-type ones provided that the engine has a plurality of systems in its exhaust system with air supply pipes and air-fuel ratio sensors being disposed on the respective exhaust systems, respectively. In addition, while the O2 sensors are used as the air-fuel ratio sensors, the invention is not limited thereto and therefore any type of sensors may be used which is adapted for producing an output in proportion to the density of oxygen.

[0098] According to the first aspect of the invention, the failure of the exhaust secondary air supply system can be detected easily and accurately. In addition, since the necessity is obviated of doing the troublesome work in which the output of the air-fuel ratio sensor resulting when the exhaust secondary air supply system is normal is learned to be verified, there is no risk that the detection of the failure of the exhaust secondary air supply system is delayed. Furthermore, sine the failure detection is not such as to be implemented based on the output of the air-fuel ratio sensor when exhaust secondary air is supplied, in other words, based on the output of the air-fuel ratio sensor when the exhaust secondary air supply system is activated intermittently so as to supply exhaust secondary air intermittently, there is no risk that an erroneous failure detection results from the effect of an error caused by a difference in load of the internal combustion engine.

[0099] According to the second aspect of the invention, the failure of the exhaust secondary air supply system can be detected more easily and accurately by setting the predetermined period of time appropriately or to, for example, a time that will be described below as a time needed for a change in the operating conditions such as load of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end.

[0100] According to the third aspect of the invention, since the predetermined period of time is set based on a time needed for a change in the operating conditions of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end, even when the air-fuel ratio sensor exhibits unexpected behaviors according to the change, an effect resulting from the unexpected behaviors can be avoided, whereby the failure of the exhaust secondary air supply system can be detected more easily and accurately.

[0101] According to the fourth aspect of the invention, the failure of the exhaust secondary air supply system can be detected easily and accurately. In addition, the necessity is obviated of doing the troublesome work in which the output of the air-fuel ratio sensor resulting when the exhaust secondary air supply system is normal is learned to be verified, and there is caused no inconvenience that the detection of the failure of the exhaust secondary air supply system is delayed. In addition, in a case where an air supply pipe is provided for each exhaust system of an engine such as a V-type engine which has an exhaust system on each bank, it is possible not only to detect the existence of a failure but also to detect which air supply pipe on the banks suffers from the failure when the failure is detected.

[0102] According to the fifth aspect of the invention, the failure of the exhaust secondary air supply system can be detected more easily and accurately.

[0103] According to the sixth aspect of the invention, in a V-type engine in which an air supply pipe is connected to each of banks thereof, the failure of an exhaust secondary air supply system can be detected easily and accurately.

Claims

1. A failure detecting apparatus for an exhaust secondary air supply system for supplying exhaust secondary air to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine, the failure detecting apparatus comprising:

an air-fuel ratio sensor for producing an output corresponding to a density of oxygen contained in exhaust gas flowing through the exhaust system; and

a failure detecting section for comparing values obtained at different times based on outputs of the air-fuel ratio sensor when the exhaust secondary air is supplied so as to detect a failure of the exhaust secondary air supply system.

2. A failure detecting apparatus for an exhaust secondary air supply system as set forth in claim 1, wherein the failure detecting section comprises a correction factor difference calculating section for calculating a difference between an air-fuel feedback correction factor calculated based on an output of the air-fuel ratio sensor at a time tn and an air-fuel feedback correction factor calculated at a time tn+m that is a time that results after a predetermined period of time m has elapsed since the time tn and a comparing section for comparing the difference so calculated with a predetermined value, so as to determine that the exhaust secondary air supply system fails when the calculated difference does not exceed the predetermined value.

3. A failure detecting apparatus for an exhaust secondary air supply system as set forth in claim 2, wherein the predetermined period of time is set based on a time needed for a change in operating conditions of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end.

4. A failure detecting apparatus for an exhaust secondary air supply system for supplying exhaust secondary air to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine, the failure detecting apparatus comprising:

a plurality of air supply pipes connected to the exhaust system of the internal combustion engine for supplying the exhaust secondary air, respectively;

a plurality of air-fuel ratio sensors disposed along the exhaust system at positions downstream of the plurality of air supply pipes for producing an output corresponding to a density of oxygen contained in exhaust emissions flowing through the exhaust system, respectively; and

a failure detecting section for comparing values with each other which are obtained based on the outputs of the plurality of air-fuel ratio sensors so as to detect a failure of the exhaust secondary air supply system.

5. A failure detecting apparatus for an exhaust secondary air supply system as set forth in claim 4, wherein the failure detecting section comprises a correction factor difference calculating section for calculating a difference between air-fuel ratio feedback correction factors calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors, and a comparing section for comparing the difference so calculated with a predetermined value, so as to determine that the exhaust secondary air supply system fails when the calculated difference exceeds the predetermined value.

6. A failure detecting apparatus for an exhaust secondary air supply system as set forth in claim 4, wherein the internal combustion engine is a V-type engine, wherein the failure detecting apparatus comprises an air pump, and wherein the air supply pipe is connected to the air pump and is branched at an intermediate position along its length so as to be connected to banks of the V-type engine, respectively.

7. A failure detecting apparatus for an exhaust secondary air supply system as set forth in claim 5, wherein the correction factor difference calculating section calculates a difference between maximum values of air-fuel ratio feedback correction factors calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors.