JP2007262895A - Failure diagnostic device for exhaust system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose an exhaust system failure without depending on an operating condition of an internal combustion engine. <P>SOLUTION: A device for diagnosing a failure of an exhaust system consisting of a first exhaust passage from a first cylinder group of an internal combustion engine, a first exhaust system including a first exhaust emission control means provided to the first exhaust passage, and a second exhaust system including a second exhaust passage from a second cylinder group of the internal combustion engine and a second exhaust emission control means provided to the second exhaust passage, detects the pressure difference (ΔP) between the first exhaust system and second exhaust system to determine that a failure occurs in either of the first or second exhaust system when the absolute value of the pressure difference is more than a prescribed threshold value (first and second determination values). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for diagnosing an exhaust system failure.

  Conventionally, a secondary air supply system is provided in an exhaust system of an internal combustion engine, and air (referred to as secondary air) is introduced upstream of a catalyst device provided in the exhaust system to reduce unburned components. It has been broken.

When a failure such as damage occurs in the exhaust system including the secondary air supply system, there is a possibility that the emission may be reduced. Therefore, a method for diagnosing the failure has been proposed. In Patent Document 1 below, in a secondary air supply system provided in a horizontally opposed four-cylinder engine, a difference between the maximum value and the minimum value of pressure pulsations in a passage for introducing secondary air is a predetermined threshold. In the following cases, it is determined that a failure has occurred because a leak or the like has occurred in the secondary air supply system and the pressure pulsation is smaller than the normal value.
Japanese Patent No. 3444458

  However, according to the above conventional method, the difference between the maximum value and the minimum value of the pressure pulsation varies according to the operating state of the internal combustion engine. In order to improve the accuracy of fault diagnosis, it is necessary to prepare a plurality of threshold values corresponding to various operating states. Alternatively, it is necessary to permit failure diagnosis only when a predetermined operating state is reached in accordance with a threshold value prepared in advance.

  One object of the present invention is to provide an apparatus capable of diagnosing whether or not a failure has occurred in an exhaust system including a secondary air supply system without depending on the operating state of the internal combustion engine.

  According to one aspect of the present invention, a first exhaust system including a first exhaust passage from the first cylinder group of the internal combustion engine and a first exhaust purification means provided in the first exhaust passage, and the internal combustion engine An apparatus for diagnosing a failure in an exhaust system having a second exhaust system including a second exhaust passage from the second cylinder group and a second exhaust purification means provided in the second exhaust passage includes the second exhaust system. A pressure difference detecting means for detecting a pressure difference between the first exhaust system and the second exhaust system; and if the absolute value of the pressure difference detected by the pressure difference detecting means is greater than a predetermined threshold value, the first and first Failure determination means for determining that there is a failure in any of the two exhaust systems.

  According to the present invention, since the failure is diagnosed based on the pressure difference between the first and second exhaust systems, the failure diagnosis can be performed without being limited to the operating state of the internal combustion engine. There is no need to set multiple thresholds according to various operating conditions.

  According to one embodiment of the present invention, the failure determination means further has a failure in the first exhaust system if the pressure difference detected by the pressure difference detection means is below a negative threshold value. If the pressure difference exceeds a positive threshold value, it is determined that there is a failure in the second exhaust system.

  According to the present invention, it can be determined which of the first and second exhaust systems has a failure.

  According to one embodiment of the present invention, the failure diagnosis apparatus further includes a first secondary air passage provided in the first exhaust system and connected between the intake passage communicating with the internal combustion engine and the first exhaust passage. A second secondary air passage provided in the second exhaust system and connected between the intake passage communicating with the internal combustion engine and the second exhaust passage; and a first secondary air passage provided from the intake passage. The first opening / closing means for opening / closing the flow of the air to the first exhaust passage and the second secondary air passage are provided for opening / closing the flow of the air from the intake passage to the second exhaust passage. An opening / closing means; and an opening / closing control means for controlling the first opening / closing means and the second opening / closing means. The pressure difference detection means is provided downstream of the first opening / closing means and the second opening / closing means, and is configured to detect a pressure difference between the first secondary air passage and the second secondary air passage. The failure determination means determines that the absolute value of the pressure difference detected by the pressure difference detection means is greater than a predetermined threshold when both the first and second opening / closing means are closed by the opening / closing control means. For example, it is determined that there is a failure in either the first exhaust system or the second exhaust system.

  According to the present invention, it is possible to determine which of the first and second exhaust systems including the first and second secondary air passages is defective by controlling the first and second opening / closing means. it can.

  According to one embodiment of the present invention, the failure diagnosis apparatus includes at least one air pump provided upstream of the first opening / closing means in the first secondary air passage and the second opening / closing means in the second secondary air passage. And an air pump control means for controlling the air pump. The air pump control means operates the air pump when the failure determination means does not determine that there is a failure in any of the first and second exhaust systems. The opening / closing control means opens one of the first and second opening / closing means in response to the operation of the air pump by the air pump control means. The failure determination means determines that there is a failure in both the first and second exhaust systems if the absolute value of the pressure difference detected by the pressure difference detection means is smaller than a predetermined threshold value.

  According to the present invention, it is possible to detect a case where there is a failure in both the first and second exhaust systems.

BEST MODE FOR CARRYING OUT THE INVENTION

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the overall configuration of an apparatus for diagnosing an exhaust system failure according to an embodiment of the present invention.

  The engine 10 is a multi-cylinder internal combustion engine (hereinafter referred to as an engine). In this embodiment, a four-cycle V-type six-cylinder DOHC engine is shown as an example. The engine 10 includes three cylinders (cylinders) 12 of # 1, # 2 and # 3 in the right bank 10R, and includes three cylinders 12 of # 4, # 5 and # 6 in the left bank 10L. .

  In the figure, the components provided for each bank are indicated by reference characters R and L. However, in the following description, it should be noted that with respect to matters common to the R component and the L component, the components are referred to only by reference numerals without the letters R and L.

  The air sucked from the air cleaner 14 reaches each cylinder 12 via the intake passage 16 and the intake manifold (not shown). The intake manifold is provided with an injector (not shown) for injecting fuel. The fuel / air mixture is taken into a combustion chamber (not shown) when an intake valve (not shown) of each cylinder 12 is opened, and is ignited and burned by a spark plug (not shown). . The amount of air introduced into each cylinder can be adjusted by the throttle valve 20.

  Exhaust gas generated by combustion in the cylinder is discharged to the exhaust manifold 22 when an exhaust valve (not shown) of the cylinder is opened. Thereafter, the exhaust gas flows into the exhaust passage 24 through the collecting portion of the exhaust manifold 22 and is removed from the engine after unwanted components are removed by the catalyst device 26.

  A secondary air supply device 30 is provided in the exhaust system including the exhaust passage 24 provided with the exhaust manifold 22 and the catalyst device 26. The secondary air supply device 30 includes an air supply pipe (delivery pipe) 32, an air valve 36, and an air pump 34 for the exhaust system of each bank. The secondary air supply device 30 is configured to supply the same amount of air for the two exhaust systems.

  The branch pipe 16a from which the intake passage 16 branches upstream of the throttle valve 20 is further branched and connected to the suction sides of the first and second air pumps 34R and 34L, respectively. The discharge sides of the first and second air pumps 34R and 34L are connected to the first and second air supply pipes 32R and 32L, respectively. The first and second air valves 36R and 36L are provided on the first and second air supply pipes 32R and 32L, respectively.

  When the first and second air pumps 34R and 34L are driven by an electric motor (not shown), the air sucked from the air cleaner 14 is sucked and the air is pumped to the corresponding air supply pipe 32. . The air valve 36 includes a negative pressure diaphragm and a reed valve (check valve), and opens when negative pressure is introduced through a negative pressure introduction mechanism (not shown). When the air valve 36 is opened, the air valve 36 introduces the air pressure-fed by the pump 34 from the suction port, and sends the air toward the exhaust manifold 22 through the exhaust port.

  The differential pressure sensor 37 includes an exhaust system pressure downstream of the first air valve 36R (referred to as a first pressure of the first exhaust system) and an exhaust system pressure downstream of the second air valve 36L (a second pressure). It is provided to detect a difference from the second pressure of the exhaust system). In this embodiment, the differential pressure sensor 37 is provided in a passage 38 communicating between the exhaust port of the first air valve 36R and the exhaust port of the second air valve 36L.

  Alternatively, as shown in FIG. 2, the differential pressure sensor 37 is connected to a position on the first air supply pipe 32R on the downstream side of the first air valve 36R and a first position on the downstream side of the second air valve 36L. You may provide on the channel | path 38 which connects a certain position on the 2nd air supply pipe | tube 32L.

  Further, in an alternative embodiment, a first pressure sensor is provided on the air supply pipe 32R downstream of the first air valve 36R, and a second pressure is provided on the air supply pipe 32L downstream of the second air valve 36L. A pressure sensor may be provided. The differential pressure can be obtained from the difference between the output of the first pressure sensor and the output of the second pressure sensor.

  The engine 10 is provided with a crank angle sensor 42 and generates a CRK signal and a TDC signal according to the rotation of a crankshaft (not shown). The CRK signal is output at every predetermined crank angle. The TDC signal is output at a crank angle related to the TDC position (top dead center) of an engine piston (not shown).

  An absolute pressure sensor 44 is provided downstream of the throttle valve 20 and outputs a signal corresponding to the absolute pressure (engine load) in the intake passage 16. Further, a water temperature sensor 46 is provided in the cooling water passage of the engine 10 and outputs a signal corresponding to the temperature of the engine cooling water.

  An atmospheric pressure sensor 48 is provided (or connected) to the ECU 54, and the atmospheric pressure sensor 48 outputs a signal corresponding to the atmospheric pressure.

  A first air-fuel ratio sensor 50 is provided upstream of the catalyst device 26, and a second air-fuel ratio sensor 52 is provided downstream of the catalyst device 26. Each air-fuel ratio sensor outputs a signal corresponding to the oxygen concentration in the exhaust gas.

  The outputs of these sensors are sent to an electronic control unit (hereinafter referred to as “ECU”) 54. The ECU 54 is a computer including a central processing unit (CPU) and a memory. The memory stores a computer program for realizing various controls of the vehicle and data necessary for executing the program.

  The ECU 54 calculates the engine speed based on the output from the crank angle sensor 42, calculates the fuel injection amount to be injected through the injector, and determines the ignition timing by the igniter.

  The ECU 54 issues an energization command to the electric motor, drives the air pump 34, and supplies secondary air to the corresponding exhaust system. As a result, unburned components of the fuel are combusted in the exhaust manifold 22 and the exhaust passage 24 downstream thereof, heating the catalyst device 26 and releasing it to the atmosphere. The activation of the catalyst device 26 is promoted, and the release of unburned components to the atmosphere is reduced.

  Further, the ECU 54 diagnoses a failure such as breakage in the exhaust system on the downstream side of the air valve 36 based on the output of the differential pressure sensor 37. This diagnostic method will be described below. According to one embodiment of the present invention, fault diagnosis includes first and second stages.

  With reference to (a) and (b) of FIG. 3, the failure diagnosis in the first stage according to one embodiment of the present invention will be described. In the first stage, the first and second air valves 36R and 36L are closed. After the stabilization waiting time T0 has elapsed, the value of the differential pressure sensor 37 is monitored over a predetermined determination time T1. Since the air valves 36R and 36L are closed, the first exhaust system downstream of the air valve 36R is in a state in which pressure from the exhaust gas is applied, as in the second exhaust system downstream of the air valve 36L. If there is no failure such as breakage in the first and second exhaust systems, as indicated by reference numerals 61 and 62, the first pressure of the first exhaust system and the second pressure of the second exhaust system Therefore, the value of the differential pressure sensor (first pressure-second pressure) changes in the vicinity of zero, as indicated by reference numeral 65.

  However, when a failure due to damage or the like occurs in the second exhaust system, the second pressure does not increase as indicated by reference numeral 71. Accordingly, the first pressure 61 is larger than the second pressure 71, and the value of the differential pressure sensor 37 takes a positive value as indicated by reference numeral 72. If the value of differential pressure sensor 37 exceeds a predetermined first determination value (indicated by reference numeral 73) having a positive value over failure determination time T1, it is determined that there is a failure in the second exhaust system. be able to.

  On the other hand, when a failure due to damage or the like occurs in the first exhaust system, as indicated by reference numeral 75, the first pressure does not increase. Therefore, the second pressure 62 becomes larger than the first pressure 75, and the value of the differential pressure sensor 37 takes a negative value as indicated by reference numeral 76. If the value of the differential pressure sensor 37 falls below a predetermined second determination value (indicated by reference numeral 77) having a negative value over the failure determination time T1, it is determined that there is a failure in the first exhaust system. be able to.

  FIG. 4 is a flowchart showing the first stage failure diagnosis process. In this embodiment, the processing is performed by the ECU 54 at predetermined time intervals after the engine is started.

  In step S <b> 1, the first determination value and the second determination value are corrected according to the atmospheric pressure detected by the atmospheric pressure sensor 48. This is because the atmospheric pressure may cause fluctuations in the differential pressure when a failure occurs.

  In step S2, the process waits for the stabilization waiting time T0 to elapse. In step S3, it is determined whether or not the differential pressure ΔP detected by the differential pressure sensor 37 is greater than a first determination value having a positive value. As shown in FIG. 3A, if the differential pressure ΔP is larger than the first determination value over the failure determination time T1 in step S4, the second exhaust system has a failure such as breakage in step S5. Judge that there is.

  If the determination in step S3 is No, it is determined in step S6 whether or not the differential pressure ΔP is lower than a second determination value having a negative value. As shown in FIG. 3B, in step S7, if the differential pressure ΔP is lower than the second determination value over the failure determination time T1, in step S8, there is a failure such as breakage in the first exhaust system. Judge that there is.

  Step S3 is the same as determining whether or not the absolute value of the differential pressure ΔP is greater than the first determination value, and step S6 includes determining that the absolute value of the differential pressure ΔP is the absolute value of the second determination value. Note that this is similar to determining whether it is greater than.

  Thus, in the first stage, it can be determined which of the first and second exhaust systems has failed. However, in the first stage, it is impossible to detect a state in which both the first and second exhaust systems have failed. To detect such a condition, the second stage can be implemented.

  With reference to FIGS. 5A and 5B, a second stage of failure diagnosis according to one embodiment of the present invention will be described. In the example shown in the figure, after the failure diagnosis in the first stage is completed (after the times T0 and T1 have elapsed), the failure diagnosis in the second stage is performed. In the second stage, one of the first and second air pumps is activated, and an air valve corresponding to the activated air pump is opened. In this example, the first air pump 34R is operated and the first air valve 36R is opened. After the stabilization waiting time T2 has elapsed, the value of the differential pressure sensor 37 is monitored over a predetermined failure determination time T3.

  If both the first and second exhaust systems are normal, the first pressure 81 of the first exhaust system is changed to the second pressure of the second exhaust system by the air pumped by the first air pump 34R. Higher than 82. The pressure difference between the two is large. As a result, the output of the differential pressure sensor 37 exceeds the third determination value (indicated by reference numeral 84) having a positive value over the determination time T3 as indicated by reference numeral 83.

  If there is a failure in both the first and second exhaust systems, as indicated by reference numeral 91, the first pressure is increased somewhat by the air pumped by the first air pump 34R, but there is a failure such as breakage. Therefore, the way to go up is small. Further, as indicated by reference numeral 92, the second pressure does not increase due to a failure such as breakage. The pressure difference between the two is small. As indicated by reference numeral 93, the output of the differential pressure sensor 37 cannot exceed the third determination value 84 over the failure determination time T3.

  Thus, it is possible to detect that both the first and second exhaust systems are out of order.

  In this example, after the determination time T3 has elapsed, the second air pump 34L is operated to open the second air valve 36L, and the failure diagnosis is completed. Note that this is not a necessary process for failure diagnosis.

  FIG. 6 is a flowchart showing the failure diagnosis process in the second stage. In this embodiment, the process is performed by the ECU 54 at predetermined time intervals after the first failure diagnosis is completed.

  In step S11, the third determination value is corrected according to the atmospheric pressure detected by the atmospheric pressure sensor 48. The reason is the same as described with reference to step S1 in FIG. In step S12, one of the first and second air pumps 34R and 34L is driven, and the air valve corresponding to the driven air pump is opened. In this embodiment, the first air pump 34R is driven to open the first air valve 36R. In step S13, the process waits for the stabilization waiting time T2 to elapse.

  In step S14, the absolute value of the differential pressure ΔP detected by the differential pressure sensor 37 is compared with a third determination value having a positive value. In step S15, if the absolute value of the differential pressure ΔP is greater than the third determination value over the determination time T3, both the first and second exhaust systems are normal as shown in FIG. Judgment is made (S16). In step S17, if the absolute value of the differential pressure ΔP is smaller than the third determination value over the determination time T3, a failure has occurred in both the first and second exhaust systems, as shown in FIG. 5B. It is determined that there is (S18).

  In step S19, the second air pump 34L is operated and the second air valve 36L is opened to complete the failure diagnosis.

  Alternatively, one air pump may be used. In this case, the discharge of the air pump can be switched between the first air supply pipe 32R and the second air supply pipe 32L.

  Note that pulsation may occur in the pressure of the exhaust system downstream of the air valve 36. In order to prevent the influence of pulsation, the output of the differential pressure sensor 37 may be filtered and a failure of the first and second exhaust systems may be diagnosed based on the filtered output. For example, filtering such as moving averages and low pass filters can be implemented.

The figure which shows schematically the structure of the apparatus which diagnoses the failure of an exhaust system according to one Example of this invention. The figure which shows the other example of arrangement | positioning of a differential pressure sensor according to one Example of this invention. The figure for demonstrating the 1st step of failure diagnosis according to one Example of this invention. The flowchart of the process of the 1st step of the failure diagnosis according to one Example of this invention. The figure for demonstrating the 2nd step of failure diagnosis according to one Example of this invention. The flowchart of the process of the 2nd step of failure diagnosis according to one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 16 Intake passage 22 Exhaust manifold 24 Exhaust passage 26 Catalytic device 30 Secondary air supply device 32 Air supply pipe 34 Air pump 36 Air valve 37 Differential pressure sensor

Claims (4)

A first exhaust system including a first exhaust passage from the first cylinder group of the internal combustion engine and a first exhaust purification means provided in the first exhaust passage; and a second exhaust system from the second cylinder group of the internal combustion engine. An exhaust system having a second exhaust system including an exhaust passage and a second exhaust purification means provided in the second exhaust passage;
Pressure difference detecting means for detecting a pressure difference between the first exhaust system and the second exhaust system;
Failure determination means for determining that there is a failure in any of the first and second exhaust systems if the absolute value of the pressure difference detected by the pressure difference detection means is greater than a predetermined threshold;
An apparatus comprising: The failure determination means further includes
If the pressure difference detected by the pressure difference detecting means is below a negative threshold value, it is determined that the first exhaust system has a failure, and the pressure difference exceeds the positive threshold value. If so, it is determined that there is a failure in the second exhaust system.
The apparatus of claim 1. An intake passage provided in the first exhaust system and communicating with the internal combustion engine; and a first secondary air passage connected between the first exhaust passage;
An intake passage provided in the second exhaust system and communicating with the internal combustion engine; a second secondary air passage connected between the second exhaust passage;
A first opening / closing means provided in the first secondary air passage, for opening and closing a flow of air from the intake passage to the first exhaust passage;
A second opening / closing means provided in the second secondary air passage, for opening and closing a flow of air from the intake passage to the second exhaust passage;
An opening / closing control means for controlling the first opening / closing means and the second opening / closing means,
The pressure difference detecting means is provided downstream of the first opening / closing means and the second opening / closing means, and is configured to detect a pressure difference between the first secondary air passage and the second secondary air passage. Has been
The failure determination means is configured such that an absolute value of a pressure difference detected by the pressure difference detection means when the first and second opening / closing means are both closed by the opening / closing control means. If greater than a threshold, the first exhaust system and the second exhaust system are configured to determine that there is a failure;
The apparatus according to claim 1 or 2. At least one air pump provided on the upstream side of the first opening and closing means in the first secondary air passage and the second opening and closing means in the second secondary air passage;
An air pump control means for controlling the air pump,
The air pump control means operates the air pump when the failure determination means does not determine that there is a failure in either of the first and second exhaust systems,
The opening / closing control means opens one of the first and second opening / closing means in response to the operation of the air pump by the air pump control means,
The failure determination unit determines that both the first and second exhaust systems have a failure if the absolute value of the pressure difference detected by the pressure difference detection unit is smaller than a predetermined threshold value.
The apparatus according to claim 1.

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