JP2008038652A - Misfire detection system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology enabling accurate detection of misfire of an internal combustion engine in a system detecting misfire of the internal combustion engine by comparing measurement values of air fuel ratio sensors and/or oxygen concentration sensors arranged before and after a catalyst. <P>SOLUTION: In the misfire detection system of the internal combustion engine provided with the first oxygen concentration sensor 7 provided in an exhaust passage in the upstream of the catalyst 6, the second oxygen concentration sensor 8 arranged in the downstream of the catalyst 6, and a detection means 10 detecting misfire of the internal combustion engine by comparing the measurement value of the first oxygen concentration sensor and measurement value of the second oxygen concentration sensor 8, passage ratio of unburned fuel composition of a cover 73 of the first oxygen concentration sensor 7 is set lower as compared to that of the cover 83 of the second oxygen concentration sensor 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a system for detecting misfire of an internal combustion engine.

As a technique for detecting misfire of an internal combustion engine, a technique for detecting misfire based on a difference in measured values of air-fuel ratio sensors arranged before and after a catalyst is known (see, for example, Patent Document 1).
JP-A-4-370350 Japanese Patent Publication No. 5-67766 JP 2001-289111 A JP 2004-316498 A

  Incidentally, in recent years, air-fuel ratio sensors and oxygen concentration sensors that can oxidize unburned fuel components have become widespread. When such an air-fuel ratio sensor or oxygen concentration sensor is arranged before and after the catalyst, it becomes difficult to detect misfire of the internal combustion engine by the above-described conventional technology.

  The present invention has been made in view of the above circumstances, and its purpose is to prevent misfire of an internal combustion engine by comparing measured values of air-fuel ratio sensors and / or oxygen concentration sensors arranged before and after the catalyst. An object of the present invention is to provide a technology capable of accurately detecting misfire of an internal combustion engine in a detection system.

  In order to solve the above-described problems, the present invention is a system for detecting misfire of an internal combustion engine based on the measured values of two oxygen concentration sensors arranged upstream and downstream of a catalyst. Compared to the oxygen concentration sensor downstream of the catalyst, the ability to oxidize unburned fuel components in the exhaust gas is reduced.

  Specifically, the catalyst disposed in the exhaust passage of the internal combustion engine, the first oxygen concentration sensor disposed in the exhaust passage upstream of the catalyst, the second oxygen concentration sensor disposed downstream of the catalyst, and the first A detection means for detecting misfiring of the internal combustion engine by comparing the measured value of the oxygen concentration sensor and the measured value of the second oxygen concentration sensor. The oxidation ability is made lower than the oxidation ability of the second oxygen concentration sensor.

The oxygen concentration sensor according to the present invention may be an air-fuel ratio sensor or an O ₂ sensor. The oxidizing ability of the first and second oxygen concentration sensors is mainly the ability to oxidize unburned fuel components in the exhaust.

  When the internal combustion engine misfires, the amount of unburned fuel components and oxygen contained in the exhaust gas increases. For this reason, when the internal combustion engine is misfired, the oxygen concentration upstream of the catalyst is significantly higher (lean) than when the internal combustion engine is not misfired.

  Further, since the unburned fuel component and oxygen in the exhaust cause an oxidation reaction in the catalyst, the oxygen concentration downstream of the catalyst hardly makes a difference between when the internal combustion engine misfires and when it does not misfire.

  Therefore, when the oxygen concentration upstream of the catalyst is higher (lean) than the oxygen concentration downstream of the catalyst, it can be considered that the internal combustion engine has misfired.

  By the way, if the first and second oxygen concentration sensors have the ability to oxidize unburned fuel components, the unburned fuel components and oxygen in the exhaust gas cause an oxidation reaction in the first oxygen concentration sensor.

  For this reason, even if the internal combustion engine is misfired, the measured value of the first oxygen concentration sensor is not significantly increased. As a result, when the internal combustion engine misfires, it is difficult for a clear difference to occur between the measured value of the first oxygen concentration sensor and the measured value of the second oxygen concentration sensor.

  Therefore, in the misfire detection system for an internal combustion engine according to the present invention, the oxidizing ability of the first oxygen concentration sensor is made lower than the oxidizing ability of the second oxygen concentration sensor.

  According to this configuration, when the internal combustion engine misfires, the unburned fuel component and oxygen in the exhaust gas hardly cause an oxidation reaction in the first oxygen concentration sensor. For this reason, a clear difference arises between the measured value of the first oxygen concentration sensor and the measured value of the second oxygen concentration sensor. As a result, the detection means can detect misfire of the internal combustion engine by comparing the measured values of the first and second oxygen concentration sensors.

  The oxygen concentration sensor includes a detection element for detecting the oxygen concentration and a cover that covers the detection element. A plurality of holes (flow holes) communicating the inside and outside of the cover are provided at a plurality of locations of the cover. An oxidation catalyst for oxidizing the unburned fuel component in the exhaust is provided near the detection element in the cover.

  As a method for reducing the oxidizing ability in the oxygen concentration sensor having such a configuration, a method for making it difficult for unburned fuel components in the exhaust to flow into the cover (reducing the passage rate of unburned fuel components) is exemplified. Can do.

  Since the unburned fuel component has a higher molecular weight than oxygen, the direction of movement cannot be rapidly changed. Therefore, when the flow holes are arranged at positions that do not face the flow direction of the exhaust, when the number of flow holes is reduced, or when the cross-sectional area of the flow holes is reduced, oxygen in the exhaust is not contained in the cover. The unburned fuel component in the exhaust gas is less likely to flow into the cover.

  Therefore, (1) the number of flow holes arranged in the first oxygen concentration sensor at a position facing the exhaust flow is less than that of the second oxygen concentration sensor, and (2) the number of flow holes of the first oxygen concentration sensor. Is less than that of the second oxygen concentration sensor, or (3) when the cross-sectional area of the flow hole of the first oxygen concentration sensor is made smaller than that of the second oxygen concentration sensor, the oxidizing ability of the first oxygen concentration sensor becomes the second oxygen. It becomes lower than the oxidizing ability of the concentration sensor.

  As another method for lowering the oxidizing ability of the first oxygen concentration sensor than that of the second oxygen concentration sensor, an adsorbent that adsorbs unburned fuel components is added only to the cover surface of the first oxygen concentration sensor. The method of doing can be illustrated.

  In the misfire detection system for an internal combustion engine according to the present invention, the detection means takes into account the amount of change in the catalyst temperature in addition to the comparison between the measurement value of the first oxygen concentration sensor and the measurement value of the second oxygen concentration sensor. You may make it detect misfire of an internal combustion engine.

  When the internal combustion engine misfires, a large amount of unburned fuel components are oxidized in the catalyst, so that the temperature of the catalyst increases significantly. Therefore, the detection means may consider that the internal combustion engine has misfired when the measured value of the first oxygen concentration sensor is higher than the measured value of the second oxygen concentration sensor and the amount of increase in the catalyst temperature is large. According to this method, the misfire detection accuracy can be increased.

  According to the present invention, in a system for detecting misfire of an internal combustion engine by comparing measured values of air-fuel ratio sensors and / or oxygen concentration sensors arranged before and after the catalyst, it is possible to accurately detect misfire of the internal combustion engine. It becomes possible.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a misfire detection system for an internal combustion engine according to the present invention.

  An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) having a plurality of cylinders 2. An intake passage 3 and an exhaust passage 4 are connected to the internal combustion engine 1. A compressor housing 50 and a turbine housing 51 of the centrifugal supercharger 5 are disposed in the intake passage 3 and the exhaust passage 4, respectively.

  An exhaust purification device 6 is disposed in the exhaust passage 4 downstream of the turbine housing 51. The exhaust purification device 6 is a device in which a catalyst is loaded in a casing. Examples of the catalyst include (1) an occlusion reduction type NOx catalyst, (2) an oxidation catalyst, (3) a particulate filter provided with an NOx storage reduction catalyst, or (4) a particulate filter provided with an oxidation catalyst. Etc. can be illustrated.

  An upstream air-fuel ratio sensor 7 is disposed in the exhaust passage 4 between the turbine housing 51 and the exhaust purification device 6. The upstream air-fuel ratio sensor 7 is an embodiment of the first oxygen concentration sensor according to the present invention.

  FIG. 2 is a cross-sectional view showing the configuration of the upstream air-fuel ratio sensor 7. The upstream air-fuel ratio sensor 7 includes a detection element 70 that outputs an electrical signal corresponding to the amount of oxygen in the exhaust gas. A catalyst layer 71 that oxidizes unburned fuel components in the exhaust is formed on a part or all of the surface of the detection element 70.

  The detection element 70 and the catalyst layer 71 described above are covered with double-structured covers 72 and 73 (hereinafter, the inner cover 72 of the two covers 72 and 73 is referred to as “inner cover 72”, and The outer cover 73 is referred to as an “outer cover 73”).

  The aforementioned inner cover 72 is provided with a plurality of flow holes 720 that communicate the inside and outside of the inner cover 72. The outer cover 73 described above is also provided with a plurality of flow holes 730 similar to the inner cover 72.

  Returning to FIG. 1, a downstream air-fuel ratio sensor 8 and an exhaust temperature sensor 9 are disposed in the exhaust passage 4 downstream of the exhaust purification device 6. The downstream air-fuel ratio sensor 8 is an embodiment of the second oxygen concentration sensor according to the present invention.

  FIG. 3 is a cross-sectional view showing the configuration of the downstream air-fuel ratio sensor 8. Similarly to the upstream air-fuel ratio sensor 7, the downstream air-fuel ratio sensor 8 also includes a detection element 80, a catalyst layer 81, an inner cover 82, and an outer cover 83. The inner cover 82 and the outer cover 83 have flow holes 820, 830 is provided.

  Output signals (measured values) from the upstream air-fuel ratio sensor 7, downstream air-fuel ratio sensor 8, and exhaust temperature sensor 9 are input to the ECU 10. The ECU 10 is an electronic control unit that performs various processes and controls based on measured values of the upstream air-fuel ratio sensor 7, the downstream air-fuel ratio sensor 8, the exhaust temperature sensor 9, and the like.

  For example, the ECU 10 performs misfire detection processing of the internal combustion engine 1 by comparing the measured value of the upstream air-fuel ratio sensor 7 with the measured value of the downstream air-fuel ratio sensor 8.

When the internal combustion engine 1 misfires, the amount of unburned fuel components (for example, hydrocarbon (HC), etc.) in the exhaust increases, and the amount of oxygen (O ₂ ) also increases.

  In this case, since the upstream air-fuel ratio sensor 7 detects a large amount of oxygen in the exhaust gas, the measured value of the upstream air-fuel ratio sensor 7 is the engine air-fuel ratio (ratio of fuel to air supplied to the internal combustion engine 1). (A lean value) (hereinafter, this phenomenon is referred to as “lean deviation”).

  On the other hand, the measured value of the downstream air-fuel ratio sensor 8 is substantially equal to the engine air-fuel ratio. This is because the unburned fuel component and oxygen in the exhaust cause an oxidation reaction by the catalyst of the exhaust purification device 6.

  Therefore, when the internal combustion engine 1 misfires, the measured value of the upstream air-fuel ratio sensor 7 is significantly leaner than the measured value of the downstream air-fuel ratio sensor 8.

  By the way, since the upstream air-fuel ratio sensor 7 includes the catalyst layer 71, it is difficult to cause a lean shift when the internal combustion engine 1 misfires. For this reason, even if the internal combustion engine 1 misfires, the difference between the measured value of the upstream air-fuel ratio sensor 7 and the measured value of the downstream air-fuel ratio sensor 8 becomes small, and the ECU 10 detects the misfire of the internal combustion engine 1. It may not be possible.

  Therefore, in the misfire detection system for the internal combustion engine of this embodiment, the oxidizing ability of the upstream air-fuel ratio sensor 7 is made lower than the oxidizing ability of the downstream air-fuel ratio sensor 8.

  If the oxidizing ability of the upstream air-fuel ratio sensor 7 is made lower than the oxidizing ability of the downstream air-fuel ratio sensor 8, the upstream air-fuel ratio sensor 7 is likely to cause a lean deviation and the downstream air-fuel ratio sensor 8 is less likely to cause a lean deviation. . For this reason, as the amount of the unburned fuel component contained in the exhaust gas increases, the difference between the measured value of the upstream air-fuel ratio sensor 7 and the measured value of the downstream air-fuel ratio sensor 8 increases.

  Therefore, when the internal combustion engine 1 misfires, a clear difference occurs between the measured value of the upstream air-fuel ratio sensor 7 and the measured value of the downstream air-fuel ratio sensor 8, and the ECU 10 accurately detects the misfire of the internal combustion engine 1. Can be detected.

  Hereinafter, a method for making the oxidizing ability of the upstream air-fuel ratio sensor 7 lower than the oxidizing ability of the downstream air-fuel ratio sensor 8 will be described.

  FIG. 4 is a front view of the upstream air-fuel ratio sensor 7 and the downstream air-fuel ratio sensor 8. 4A is a front view of the upstream air-fuel ratio sensor 7, and FIG. 4B is a front view of the downstream air-fuel ratio sensor 8.

  In FIG. 4, the number of flow holes 730 provided in the outer cover 73 of the upstream air-fuel ratio sensor 7 is smaller than the number of flow holes 830 provided in the outer cover 83 of the downstream air-fuel ratio sensor 8.

In this case, the unburned fuel component in the exhaust gas hardly flows into the outer cover 73 of the upstream air-fuel ratio sensor 7 and easily flows into the outer cover 83 of the downstream air-fuel ratio sensor 8. That is, the outer cover 73 of the upstream air-fuel ratio sensor 7 has a lower passage rate of unburned fuel components than the outer cover 83 of the downstream air-fuel ratio sensor 8.

  On the other hand, the oxygen in the exhaust gas has a lighter molecular weight than the unburned fuel component, and the direction of motion can be rapidly changed. Therefore, the outer cover 73 of the upstream air-fuel ratio sensor 7 and the outer cover of the downstream air-fuel ratio sensor 8 There is no significant difference in the oxygen passage rate between 83 and 83.

  Accordingly, when the internal combustion engine 1 misfires, a large amount of oxygen flows into the outer cover 73 of the upstream air-fuel ratio sensor 7 with almost no unburned fuel component flowing. As a result, the detection element 70 of the upstream air-fuel ratio sensor 7 is liable to cause a lean shift.

  On the other hand, since the unburned fuel component easily flows into the outer cover 83 of the downstream air-fuel ratio sensor 8, the unburned fuel component that could not be oxidized by the catalyst of the exhaust purification device 6 is oxidized by the catalyst layer 81. Become so. As a result, when the internal combustion engine 1 misfires, the detection element 80 of the downstream air-fuel ratio sensor 8 is unlikely to cause a lean shift.

  As described above, when the detection element 70 of the upstream air-fuel ratio sensor 7 is likely to cause a lean shift and the detection element 70 of the downstream air-fuel ratio sensor 8 is less likely to cause a lean shift, the upstream air Since the difference between the measured value of the fuel ratio sensor 7 and the measured value of the downstream air-fuel ratio sensor 8 becomes clear, the ECU 10 can accurately detect misfire of the internal combustion engine 1.

  In the present embodiment, as a method of making the unburned fuel component passage rate different between the outer cover 73 of the upstream air-fuel ratio sensor 7 and the outer cover 83 of the downstream air-fuel ratio sensor 8, the number of flow holes 730.830 Although the method of making these differ was illustrated, it is needless to say that the present invention is not limited to this.

  For example, the cross-sectional area of the flow hole 730 of the upstream air-fuel ratio sensor 7 may be made smaller than the cross-sectional area of the flow hole 830 of the downstream air-fuel ratio sensor 8. Further, the number of the flow holes 730 of the upstream air-fuel ratio sensor 7 may be made smaller than the number of the flow holes 830 of the downstream air-fuel ratio sensor 8 only in the portion directly facing the exhaust flow. Furthermore, in addition to the number of cross-sectional areas, the cross-sectional area may be different between the flow hole 730 of the upstream air-fuel ratio sensor 7 and the flow hole 830 of the downstream air-fuel ratio sensor 8.

  Further, instead of making the numbers and / or cross-sectional areas of the flow holes 730 and 830 of the outer covers 73 and 83 different, the numbers and / or cross-sectional areas of the flow holes 720 and 820 of the inner covers 72 and 82 may be made different. The relative positions of the flow holes 730 and 830 of the outer covers 73 and 83 and the flow holes 720 and 820 of the inner covers 72 and 82 may be different.

<Example 2>
Next, a second embodiment of the present invention will be described. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the first embodiment described above, the number and / or cross-sectional area of the flow holes 720, 820, 730, and 830 are used as a method of making the oxidizing ability of the upstream air-fuel ratio sensor 7 lower than the oxidizing ability of the downstream air-fuel ratio sensor 8. In this embodiment, an adsorption layer that adsorbs unburned fuel components on the surface of the outer cover 73 and / or the surface of the inner cover 72 is illustrated. An example of providing will be described.

When an adsorption layer for adsorbing unburned fuel components is provided on the surface of the outer cover 73 and / or the surface of the inner cover 72 of the upstream air-fuel ratio sensor 7, the unburned fuel components in the exhaust are converted to the upstream air-fuel ratio sensor 7. It becomes difficult to reach the catalyst layer 71. That is, the outer cover 73 and / or inner cover 72 of the upstream air-fuel ratio sensor 7 has a lower passage rate of unburned fuel components than the outer cover 83 and / or inner cover 82 of the downstream air-fuel ratio sensor 8. .

  Therefore, when the internal combustion engine 1 misfires, the difference between the measured value of the upstream air-fuel ratio sensor 7 and the measured value of the downstream air-fuel ratio sensor 8 becomes clear, so the ECU 10 detects the misfire of the internal combustion engine 1 with high accuracy. It becomes possible.

  The configurations of the first embodiment and the present embodiment described above can be combined as much as possible. In that case, the difference between the measured value of the upstream air-fuel ratio sensor 7 and the measured value of the downstream air-fuel ratio sensor 8 when the internal combustion engine 1 misfires is further clarified.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. It is sectional drawing which shows the structure of an upstream air fuel ratio sensor. It is sectional drawing which shows the structure of a downstream air-fuel-ratio sensor. (A) is a front view of an upstream air-fuel ratio sensor, (b) is a front view of a downstream air-fuel ratio sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Intake passage 4 ... Exhaust passage 5 ... Centrifugal supercharger (turbocharger)
6. Exhaust gas purification device (catalyst)
7: Upstream air-fuel ratio sensor (first oxygen concentration sensor)
8: Downstream air-fuel ratio sensor (second oxygen concentration sensor)
9 ... Exhaust temperature sensor 10 .... ECU (detection means)
70 ... Detection element 71 ... Catalyst layer 72 ... Inner cover 73 ... Outer cover 80 ... Detection element 81 ... Catalyst layer 82 ... Inner cover 83 .... Outer cover

Claims (5)

A catalyst disposed in the exhaust passage of the internal combustion engine;
A first oxygen concentration sensor disposed in an exhaust passage upstream of the catalyst;
A second oxygen concentration sensor disposed downstream of the catalyst;
Detecting means for detecting misfire of the internal combustion engine by comparing the measured value of the first oxygen concentration sensor and the measured value of the second oxygen concentration sensor;
In a misfire detection system for an internal combustion engine equipped with
A misfire detection system for an internal combustion engine, wherein an oxidizing ability of the first oxygen concentration sensor is made lower than an oxidizing ability of the second oxygen concentration sensor. 2. The first oxygen concentration sensor and the second oxygen concentration sensor according to claim 1, each including a detection element to which an oxidizing ability is added, and a cover that covers the detection element.
The internal combustion engine misfire detection system, wherein the cover of the first oxygen concentration sensor has a lower passage rate of unburned fuel components than the cover of the second oxygen concentration sensor. In Claim 2, the cover of the first oxygen concentration sensor and the second oxygen concentration sensor is provided with a flow hole through which exhaust enters and exits the cover,
The cover of the first oxygen concentration sensor has a smaller number of flow holes than the cover of the second oxygen concentration sensor, and is a misfire detection system for an internal combustion engine. In Claim 2, the cover of the first oxygen concentration sensor and the second oxygen concentration sensor is provided with a flow hole through which exhaust enters and exits the cover,
The misfire detection system for an internal combustion engine, wherein the cover of the first oxygen concentration sensor has a cross-sectional area of the flow hole smaller than that of the cover of the second oxygen concentration sensor.   The misfire detection system for an internal combustion engine according to claim 2, wherein an adsorbent that adsorbs an unburned fuel component is added to a surface of the cover of the first oxygen concentration sensor.

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