Engine system

Abstract

To provide an engine system which can efficiently and accurately determine the lowering of an oxygen occlusion discharge function.SOLUTION: An engine system 1 comprises a gasoline engine 2, an exhaust pipe 3, a three-dimensional catalyst 4, a front oxygen sensor 5, a rear oxygen sensor 6, an engine control unit 7 and a deterioration determination unit 8. When a time up until an increase of an oxygen concentration is detected by the rear oxygen sensor after a start of a fuel cut mode is shorter than a prescribed reference time, the deterioration determination unit 8 makes a first determination to determine that there is a risk of the deterioration of an oxygen occlusion discharge material. Then, the deterioration determination unit 8 makes a second determination to determine the deterioration of an oxygen occlusion discharge material only to the oxygen occlusion discharge material to which the first determination that there is the risk of the deterioration is made on the basis of an oxygen concentration detected by the rear oxygen sensor 6.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an engine system, specifically, an engine system including a gasoline engine and a three-way catalyst.

Background Art

[0002] The exhaust gas of a gasoline engine contains harmful components. Examples of harmful components include hydrocarbons (THC), carbon monoxide (CO), and nitrogen oxides (NOx). Harmful components are usually purified by a three-way catalyst (exhaust gas purification catalyst).

[0003] The three-way catalyst contains, for example, a noble metal as an active component. The purification activity of the three-way catalyst depends on the oxygen concentration of the exhaust gas. More specifically, the purification activity of the three-way catalyst is maximally exhibited in exhaust gas with a predetermined oxygen concentration when the air-fuel ratio of the gasoline engine is the stoichiometric ratio.

[0004] On the other hand, the required output of a gasoline engine varies. Therefore, it is difficult to maintain the stoichiometric ratio during the operation of a gasoline engine. Thus, during the operation of a gasoline engine, the air-fuel ratio in the lean operation mode (fuel-lean) and the air-fuel ratio in the rich operation mode (fuel-rich) are appropriately switched so as to straddle the stoichiometric ratio.

[0005] In such a case, since the air-fuel ratio of the gasoline engine is not the stoichiometric ratio, the oxygen concentration of the exhaust gas is excessive or insufficient, and the purification activity of the three-way catalyst is not maximally exhibited. Therefore, the three-way catalyst includes a material having an oxygen storage and release function (OSC function: Oxygen Storage Capasity), that is, an oxygen storage and release material (OSC material) to adjust the oxygen concentration of the exhaust gas.

[0006] The oxygen storage and release material absorbs oxygen from the exhaust gas when, for example, a gasoline engine is in lean operation mode (fuel lean) and there is an excess of oxygen in the exhaust gas. Conversely, the oxygen storage and release material releases the absorbed oxygen when, for example, a gasoline engine is in rich operation mode (fuel rich) and there is a shortage of oxygen in the exhaust gas. In this way, the oxygen storage and release material adjusts the oxygen concentration of the exhaust gas and improves the purification activity of the three-way catalyst 4.

[0007] On the other hand, the oxygen storage and release function of oxygen storage and release materials may decrease with use. In such cases, the purification activity of the three-way catalyst decreases. Therefore, it is required to determine the decrease in oxygen storage and release function and, if necessary, regenerate or replace the oxygen storage and release material.

[0008] As a device for determining a decrease in oxygen storage and release function, for example, the following catalyst degradation determination device has been proposed. This catalyst degradation determination device is equipped with a front oxygen sensor and a rear oxygen sensor installed in the engine's exhaust pipe. A voltage value that is approximately half the amplitude of the output signals of the front oxygen sensor and the rear oxygen sensor is set as a common reference value. When the engine's fuel cut-off occurs, the time from when the output of the front oxygen sensor falls below the reference value until the output of the rear oxygen sensor falls below the reference value is defined as the response delay time difference. Catalyst degradation is determined by comparing the response delay time difference with a predetermined degradation determination value (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 7-269330 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] On the other hand, as mentioned above, if catalyst degradation is determined solely by the response delay time difference of the rear oxygen sensor when the engine's fuel cut-off occurs, sufficient accuracy cannot be obtained.

[0011] More specifically, for example, with the method described above, depending on the setting of the degradation judgment value, it is possible to reliably determine that a catalyst is actually degraded, but it may also incorrectly determine that a catalyst is degraded even if it is not actually degraded.

[0012] This invention provides an engine system that can efficiently and accurately determine a decrease in oxygen storage and release function. [Means for solving the problem]

[0013] The present invention [1] comprises a gasoline engine, an exhaust pipe through which exhaust gas from the gasoline engine passes, a three-way catalytic converter interposed in the exhaust pipe and containing an oxygen storage and release material, a front oxygen sensor positioned upstream of the three-way catalytic converter in the gas flow direction and detecting the oxygen concentration of the exhaust gas, a rear oxygen sensor positioned downstream of the three-way catalytic converter in the gas flow direction and detecting the oxygen concentration of the exhaust gas, an engine control unit connected to the gasoline engine and controlling the operating mode of the gasoline engine, and a deterioration determination unit connected to the engine control unit, the front oxygen sensor and the rear oxygen sensor and determining the deterioration of the oxygen storage and release material based on the operating mode of the gasoline engine and the oxygen concentration of the exhaust gas, wherein the engine control unit sets the operating mode of the gasoline engine to a fuel cut mode, a rich inspection mode, etc. The system is selectively switchable between rich and lean inspection modes, and the deterioration determination unit first (1) operates the gasoline engine in the fuel cut mode via the engine control unit, and if the time from the start of the fuel cut mode until an increase in oxygen concentration is detected in the rear oxygen sensor is less than a predetermined standard value, it first determines that the oxygen storage and release material may be deteriorated, and then, only for the oxygen storage and release material that has been first determined to be potentially deteriorated, (2) operates the gasoline engine via the engine control unit so that the rich inspection mode and the lean inspection mode are repeated, and makes a second determination of the deterioration of the oxygen storage and release material based on the oxygen concentration detected in the rear oxygen sensor.

[0014] In the engine system described above, the degradation detection unit first operates the gasoline engine in fuel cut mode. The degradation detection unit then makes a preliminary determination of the degradation of the oxygen storage and release material based on the time elapsed from the start of fuel cut mode until an increase in oxygen concentration is detected by the rear oxygen sensor.

[0015] If the oxygen storage and release material is determined not to have deteriorated in the first determination, the determination process is terminated. On the other hand, if the oxygen storage and release material is determined to potentially have deteriorated in the first determination, the material is subjected to the second determination.

[0016] In the second assessment, the degradation assessment unit operates the gasoline engine so that it alternates between rich and lean test modes. The degradation assessment unit also makes a second assessment of the degradation of the oxygen storage and release material based on the oxygen concentration detected by the rear oxygen sensor.

[0017] Therefore, in the above engine system, the oxygen storage and release material is subjected to a second determination in addition to the first determination when specified. As a result, the deterioration of the oxygen storage and release function can be determined with greater accuracy compared to when the oxygen storage and release material is subjected to the first determination only.

[0018] Furthermore, in the engine system described above, if the oxygen storage and release material is determined not to have deteriorated in the first determination, the determination process is terminated. Therefore, compared to the case where the oxygen storage and release material is always subjected to the first and second determinations, the non-deterioration of the oxygen storage and release function can be determined more efficiently.

[0019] Furthermore, the second judgment involves repeatedly switching between rich and lean test modes, which may reduce fuel efficiency and exhaust gas purification efficiency. However, if the first judgment determines that the oxygen storage and release material has not deteriorated, and the judgment process is completed, the second judgment will not be performed, thus suppressing the decrease in fuel efficiency and exhaust gas purification efficiency.

[0020] The present invention [2] includes the engine system described in [1] above, wherein in the second determination, the deterioration determination unit (2a) operates the gasoline engine via the engine control unit so that the rich inspection mode and the lean inspection mode are repeated, and if the amount of change in oxygen concentration detected by the rear oxygen sensor exceeds a predetermined standard value, it makes a second a determination that the oxygen storage and release material may be deteriorated, and thereafter, only for the oxygen storage and release material that has been determined to be potentially deteriorated in second a, (2b) operates the gasoline engine via the engine control unit so that the rich inspection mode and the lean inspection mode are repeated, and if the difference between the timing of the change in oxygen concentration detected by the rear oxygen sensor and the timing of the change in oxygen concentration detected by the front oxygen sensor is less than a predetermined standard value, it makes a second b determination that the oxygen storage and release material is deteriorated.

[0021] In the engine system described above, the degradation detection unit operates the gasoline engine in the second a determination so that the rich test mode and lean test mode are alternated. The degradation detection unit also makes a second a determination if the amount of fluctuation in oxygen concentration detected by the rear oxygen sensor exceeds a predetermined standard value, indicating that the oxygen storage and release material may be degraded. Subsequently, in the engine system described above, only if a second a determination is made that the oxygen storage and release material may be degraded, the degradation detection unit operates the gasoline engine in the second b determination so that the rich test mode and lean test mode are alternated. The degradation detection unit also makes a second b determination if the difference between the timing of the fluctuation in oxygen concentration detected by the rear oxygen sensor and the timing of the fluctuation in oxygen concentration detected by the front oxygen sensor is less than a predetermined standard value.

[0022] Therefore, in the above engine system, since the oxygen storage and release material is used for both the second a determination and the second b determination, the deterioration of the oxygen storage and release function is determined more accurately than when the oxygen storage and release material is used for only one of the second a determination or the second b determination.

[0023] Also, in the above engine system, in the second a determination, when it is determined that the oxygen storage and release material has not deteriorated, the determination process ends. Therefore, the non-deterioration of the oxygen storage and release function is determined more efficiently than when the oxygen storage and release material is always used for both the second a determination and the second b determination.

[0024] Furthermore, in the above engine system, the oxygen storage and release material is subjected to the second b determination after the second a determination. And the degree of decrease in fuel efficiency and exhaust gas purification efficiency in the second a determination is milder than that in the second b determination. Therefore, in the above engine system, the oxygen storage and release material can suppress the decrease in fuel efficiency and exhaust gas purification efficiency compared to the case where the oxygen storage and release material is subjected to the second a determination after the second b determination.

Advantages of the Invention

[0025] According to the engine system of the present invention, the deterioration of the oxygen storage and release function of the oxygen storage and release material can be detected efficiently and accurately.

Brief Description of the Drawings

[0026] [Figure 1] FIG. 1 is a schematic diagram showing an embodiment of the engine system of the present invention. [Figure 2] FIG. 2 is a flowchart showing a flow for determining the deterioration of the oxygen storage and release material in the engine system shown in FIG. 1. [Figure 3]Figure 3A is a schematic diagram showing the time from the start of the fuel cut mode until an increase in oxygen concentration is detected by the rear oxygen sensor, assuming the oxygen storage and release material is not deteriorated. Figure 3B is a schematic diagram showing the time from the start of the fuel cut mode until an increase in oxygen concentration is detected by the rear oxygen sensor, assuming the oxygen storage and release material may be deteriorated. [Figure 4] Figure 4A is a schematic diagram showing the change in exhaust gas oxygen concentration detected by the rear oxygen sensor when the oxygen storage and release material is not deteriorated. Figure 3B is a schematic diagram showing the change in exhaust gas oxygen concentration detected by the rear oxygen sensor when the oxygen storage and release material may be deteriorated. [Modes for carrying out the invention]

[0027] 1. Overall configuration of the engine system In Figure 1, the engine system 1 is, for example, a power generation device mounted on an automobile. The engine system 1 comprises a gasoline engine 2, an exhaust pipe 3, a three-way catalytic converter 4, a front oxygen sensor 5, a rear oxygen sensor 6, an engine control unit 7, and a degradation detection unit 8.

[0028] Gasoline engine 2 is a known internal combustion engine. Gasoline engine 2 operates using a mixture of gasoline and air as fuel. In this mixture, the air-fuel ratio (A / F) is the value obtained by dividing the mass of air by the mass of gasoline. Examples of gasoline engine 2 include single-cylinder gasoline engines and multi-cylinder gasoline engines. Gasoline engine 2 has a known configuration. More specifically, gasoline engine 2 comprises a cylinder as a combustion chamber for fuel, a piston that moves up and down within the cylinder, a mixture supply system that supplies the mixture into the cylinder, and an ignition device that ignites the mixture. Gasoline engine 2 generates energy and exhaust gas by compressing and burning the mixture within the cylinder.

[0029] The exhaust pipe 3 is a pipe through which the exhaust gas of the gasoline engine 2 passes. The exhaust pipe 3 includes, for example, an exhaust manifold, an exhaust pipe, and a muffler. One end of the exhaust pipe 3 is connected to the gasoline engine 2 (cylinder). The other end of the exhaust pipe 3 is open to the atmosphere. The exhaust pipe 3 allows the exhaust gas generated in the cylinder to be released into the atmosphere. More specifically, a catalyst housing chamber 31 is formed in the middle of the flow direction of the exhaust pipe 3. A three-way catalyst 4 is housed in the catalyst housing chamber 31.

[0030] The three-way catalytic converter 4 is a catalyst that purifies harmful components contained in the exhaust gas of the gasoline engine 2. Examples of harmful components include hydrocarbons (HC), nitrogen oxides (NOx), and carbon monoxide (CO).

[0031] The three-way catalyst 4 includes, for example, a precious metal, a heat-resistant oxide, and an oxygen storage and release material. The precious metal is a metal that purifies harmful components contained in the exhaust gas. Examples of precious metals include platinum (Pt), rhodium (Rh), and palladium (Pd). The heat-resistant oxide is a carrier (metal carrier) that supports the precious metal. Examples of heat-resistant oxides include aluminum oxide, magnesium oxide, zirconium oxide, cerium oxide, and composite oxides thereof. These are used individually or in combination of two or more types. The oxygen storage and release material is a material (OSC material) that has an oxygen storage and release function (OSC function). The oxygen storage and release material is included in the three-way catalyst 4 to adjust the oxygen concentration of the exhaust gas. Examples of oxygen storage and release materials include ceria-zirconia composite oxide and magnesium-aluminum composite oxide. The oxygen storage and release material is also classified by its crystal structure. Examples of oxygen storage and release materials include perovskite-type composite oxides and spinel-type composite oxides. These can be used individually or in combination of two or more types. Heat-resistant oxides and oxygen storage and release materials may be used interchangeably, for example. That is, a heat-resistant oxide may be used as an oxygen storage and release material, or an oxygen storage and release material may be used as a heat-resistant oxide.

[0032] The three-way catalyst 4 is interposed in the exhaust pipe 3. More specifically, the three-way catalyst 4 is fixed on a catalyst support, for example, and housed in the catalyst housing chamber 31 of the exhaust pipe 3. Examples of catalyst supports include ceramic supports having a honeycomb structure.

[0033] The front oxygen sensor 5 is an oxygen sensor that detects the oxygen concentration of exhaust gas on the upstream side of the gas flow direction of the three-way catalytic converter 4. The front oxygen sensor 5 is located on the downstream side of the gas flow direction of the gasoline engine 2 and on the upstream side of the gas flow direction of the three-way catalytic converter 4. For example, the front oxygen sensor 5 may be a zirconia type oxygen sensor. The front oxygen sensor 5 detects the oxygen concentration of exhaust gas as a voltage, for example. The front oxygen sensor 5 is electrically connected to the engine control unit 7 and the degradation detection unit 8. As a result, the oxygen concentration of exhaust gas on the upstream side of the gas flow direction of the three-way catalytic converter 4 is input as an electrical signal to the engine control unit 7 and the degradation detection unit 8 (see dashed arrow in Figure 1).

[0034] The rear oxygen sensor 6 is an oxygen sensor that detects the oxygen concentration of the exhaust gas downstream of the three-way catalytic converter 4 in the gas flow direction. The rear oxygen sensor 6 is positioned downstream of the three-way catalytic converter 4 in the gas flow direction, and upstream of the downstream end of the exhaust pipe 3 in the gas flow direction. Examples of rear oxygen sensors 6 include zirconia type oxygen sensors. Preferably, the rear oxygen sensor 6 is an oxygen sensor of the same type as the front oxygen sensor 5. The rear oxygen sensor 6 detects the oxygen concentration of the exhaust gas as a voltage, for example. The rear oxygen sensor 6 is electrically connected to the degradation determination unit 8. As a result, the oxygen concentration of the exhaust gas downstream of the three-way catalytic converter 4 in the gas flow direction is input to the degradation determination unit 8 as an electrical signal (see dashed arrow in Figure 1).

[0035] The engine control unit 7 is a computer unit (e.g., an ECU: Electronic Control Unit) that performs electrical control of the engine system 1. The engine control unit 7 includes, for example, a calculation unit and a memory unit.

[0036] The engine control unit 7 is electrically connected to the gasoline engine 2 and the front oxygen sensor 5. The engine control unit 7 can control the operating mode of the gasoline engine 2 based on the oxygen concentration detected by the front oxygen sensor 5.

[0037] More specifically, the memory section of the engine control unit 7 contains an engine control program P1. The engine control program P1 allows for selective switching of the operating mode of the gasoline engine 2. For example, the engine control program P1 allows switching between a lean operating mode and a rich operating mode based on the oxygen concentration detected by the front oxygen sensor 5.

[0038] In addition, the rich operating mode is a mode in which the fuel mixture is burned in a state of excess fuel, where the air-fuel ratio (A / F) is lower than the stoichiometric air-fuel ratio. The lean operating mode is a mode in which the fuel mixture is burned in a state of excess fuel, where the air-fuel ratio (A / F) is higher than the stoichiometric air-fuel ratio.

[0039] The engine control program P1 switches the operating mode of the gasoline engine 2 between lean driving mode and rich driving mode, thereby enabling the air-fuel ratio of the gasoline engine 2 to be controlled to be close to the stoichiometric air-fuel ratio.

[0040] Furthermore, as will be explained in more detail later, the engine control program P1 allows the operating mode of the gasoline engine 2 to be selectively switched to one of the following: fuel cut mode, rich test mode, or lean test mode, separately from the rich driving mode and lean driving mode described above.

[0041] The degradation determination unit 8 is a computer unit (e.g., an ECU: Electronic Control Unit) that performs electrical control of the engine system 1. The degradation determination unit 8 includes, for example, a calculation unit and a memory unit.

[0042] The degradation detection unit 8 is electrically connected to the engine control unit 7, the front oxygen sensor 5, and the rear oxygen sensor 6. Based on the oxygen concentration detected by the front oxygen sensor 5 and the rear oxygen sensor 6, the degradation detection unit 8 can control the operating mode of the gasoline engine 2 via the engine control unit 7.

[0043] More specifically, the memory section of the degradation determination unit 8 is equipped with a degradation determination program P2. The degradation determination program P2, via the engine control unit 7 (engine control program P1), selectively switches the operating mode of the gasoline engine 2 to one of the following: fuel cut mode, rich inspection mode, or lean inspection mode.

[0044] The fuel cut mode is a mode that stops the supply of the air-fuel mixture to the gasoline engine 2. The rich test mode is a mode in which the air-fuel mixture is burned in a fuel-rich state where the air-fuel ratio (A / F) is lower than the stoichiometric air-fuel ratio, similar to the rich driving mode described above. However, the rich test mode is usually maintained for a longer period of time than the rich driving mode described above. The lean test mode is a mode in which the air-fuel mixture is burned in a fuel-lean state where the air-fuel ratio (A / F) is higher than the stoichiometric air-fuel ratio, similar to the lean driving mode described above. However, the lean test mode is usually maintained for a longer period of time than the lean driving mode described above.

[0045] Furthermore, as will be described in more detail later, the degradation judgment program P2 is capable of detecting the degradation of the oxygen storage and release material contained in the three-way catalyst 4 based on the operating mode of the gasoline engine 2 and the oxygen concentration of the exhaust gas.

[0046] Furthermore, although not shown in the diagram, the deterioration determination unit 8 is equipped with an optional notification device (not shown). The notification device (not shown) is, for example, a device for notifying the surroundings whether or not the oxygen storage and release material is deteriorating. Examples of notification devices (not shown) include a warning sound generating device and a warning image display device.

[0047] 2. Steady-state operation of the engine system In engine system 1, the operation of gasoline engine 2 causes the fuel-air mixture to burn, generating energy and exhaust gases. The operation of gasoline engine 2 is controlled by engine control system 7 (engine control program P1).

[0048] More specifically, when the engine system 1 is activated, a mixture of gasoline and air is first supplied into the cylinder under the control of the engine control unit 7 (engine control program P1). The mixture is compressed by the piston in the cylinder and ignited by the ignition device. As a result, the gasoline engine 2 generates energy and exhaust gas. The energy is used, for example, to power a vehicle equipped with the gasoline engine 2. Meanwhile, the exhaust gas is discharged from the gasoline engine 2 into the exhaust pipe 3, passes sequentially through the front oxygen sensor 5, the three-way catalytic converter 4, and the rear oxygen sensor 6, and is released into the atmosphere from the downstream end of the exhaust pipe 3.

[0049] The engine control unit 7 then controls the air-fuel ratio (A / F) of the fuel mixture in the gasoline engine 2 based on the oxygen concentration of the exhaust gas.

[0050] More specifically, in the engine system 1, the exhaust gas first comes into contact with the front oxygen sensor 5 upstream of the three-way catalytic converter 4 in the gas flow direction. The front oxygen sensor 5 detects the oxygen concentration of the exhaust gas before it comes into contact with the three-way catalytic converter 4. The oxygen concentration of the exhaust gas is measured, for example, as a voltage value. The oxygen concentration of the exhaust gas is then input as an electrical signal to the engine control unit 7 (engine control program P1) (see dashed arrow in Figure 1).

[0051] When the oxygen concentration of the exhaust gas is input to the engine control unit 7 (engine control program P1), the engine control unit 7 (engine control program P1) calculates the air-fuel ratio (A / F) of the air-fuel mixture used to generate the exhaust gas based on the oxygen concentration of the exhaust gas. The engine control unit 7 (engine control program P1) then determines whether the air-fuel ratio (A / F) of the air-fuel mixture used to generate the exhaust gas is high or low, and adjusts the fuel supply amount and air supply amount based on that determination.

[0052] More specifically, if the air-fuel ratio (A / F) of the mixture used to generate exhaust gas is higher than the desired air-fuel ratio (e.g., stoichiometric air-fuel ratio (A / F = 14.7)), (e.g., A / F > 14.7), the engine control unit 7 (engine control program P1) increases the proportion of fuel in the mixture and lowers the air-fuel ratio.

[0053] Furthermore, for example, if the air-fuel ratio (A / F) of the air-fuel mixture used to generate exhaust gas is lower than the desired air-fuel ratio (for example, the stoichiometric air-fuel ratio (A / F = 14.7)) (for example, A / F < 14.7), the engine control unit 7 (engine control program P1) reduces the proportion of fuel in the air-fuel mixture and increases the air-fuel ratio.

[0054] In this way, the engine control unit 7 (engine control program P1) provides feedback control of the air-fuel ratio (A / F) of the air-fuel mixture based on the oxygen concentration of the exhaust gas detected by the front oxygen sensor 5.

[0055] The exhaust gas, whose oxygen concentration has been detected by the front oxygen sensor 5, is then supplied to the catalyst housing chamber 31 and comes into contact with the three-way catalyst 4. The three-way catalyst 4 purifies (removes) harmful components from the exhaust gas.

[0056] The exhaust gas, purified of harmful components, is discharged from the catalyst containment chamber 31 and comes into contact with the rear oxygen sensor 6 downstream of the three-way catalyst 4 in the gas flow direction. The rear oxygen sensor 6 detects the oxygen concentration of the exhaust gas after it has come into contact with the three-way catalyst 4. The oxygen concentration of the exhaust gas is measured, for example, as a voltage value. The oxygen concentration of the exhaust gas is then input as an electrical signal to the degradation judgment unit 8 (degradation judgment program P2) (see dashed arrow in Figure 1). The exhaust gas is then released into the atmosphere from the downstream end of the exhaust pipe 3.

[0057] Then, the degradation determination unit 8 (degradation determination program P2) determines the degradation of the oxygen storage and release material contained in the three-way catalyst 4, as detailed below.

[0058] 3. Degradation Determination Flow Referring to Figure 2, the degradation determination flow of the oxygen storage and release material performed in the degradation determination unit 8 (degradation determination program P2) will be explained.

[0059] The degradation determination flow is started, for example, when a predetermined condition is met after the operation of gasoline engine 2 (for example, when the duration of operation of gasoline engine 2 exceeds a predetermined value).

[0060] In the degradation determination flow, as shown below, (1) the first determination process is executed (steps S1 to S6). Then, only if the first determination process determines that the oxygen storage and release material may be degraded, (2) the second determination process is executed (steps S7 to S20).

[0061] (1) First determination process When the first determination process (step S1) is executed, the degradation determination unit 8 (degradation determination program P2) first controls the gasoline engine 2 via the engine control unit 7 and operates the gasoline engine 2 in fuel cut mode (step S2).

[0062] More specifically, the degradation detection unit 8 may, for example, switch the operating mode of the gasoline engine 2 to the fuel cut mode at any time via the engine control unit 7. Alternatively, for example, the degradation detection unit 8 may wait for the timing when the engine control unit 7 switches the operating mode to the fuel cut mode during the normal operation of the gasoline engine 2.

[0063] Then, in the first determination process, the degradation determination unit 8 measures the time from when the fuel cut mode is started until an increase in oxygen concentration is detected by the rear oxygen sensor 6 (the time required for oxygen increase) (step S3).

[0064] In other words, when the gasoline engine 2 operates in fuel cut mode, the supply of the fuel-air mixture to the gasoline engine 2 is stopped. This means that the combustion of the fuel-air mixture within the gasoline engine 2 stops. As a result, the consumption of oxygen due to combustion stops. Consequently, the exhaust gas emitted from the gasoline engine 2 contains a relatively large amount of oxygen. In this case, the front oxygen sensor 5 detects the increase in oxygen concentration due to the start of the fuel cut mode. The exhaust gas is then supplied to the catalyst housing chamber 31.

[0065] In the catalyst chamber 31, the exhaust gas comes into contact with the three-way catalyst 4. For a while after the fuel cut mode is initiated, oxygen in the exhaust gas is absorbed by the oxygen storage and release material of the three-way catalyst 4. During this time, the rear oxygen sensor 6 does not detect an increase in oxygen concentration. When the fuel cut mode continues and the amount of oxygen supplied exceeds the oxygen storage capacity of the oxygen storage and release material, oxygen absorption by the oxygen storage and release material stops, and oxygen is discharged from the catalyst chamber 31. As a result, the rear oxygen sensor 6 detects an increase in oxygen concentration.

[0066] In such cases, if the oxygen storage and release material of the three-way catalyst 4 has not deteriorated, the oxygen storage capacity of the oxygen storage and release material is relatively large. Therefore, if the oxygen storage and release material of the three-way catalyst 4 has not deteriorated, the time from when the fuel cut mode is started until an increase in oxygen concentration is detected by the rear oxygen sensor 6 is relatively long, as shown in Figure 3A (see T1).

[0067] On the other hand, if the oxygen storage and release material of the three-way catalyst 4 is degraded, the oxygen storage capacity of the oxygen storage and release material is relatively small. Therefore, as shown in Figure 3B, if the oxygen storage and release material of the three-way catalyst 4 is degraded, the time from when the fuel cut mode is started until an increase in oxygen concentration is detected by the rear oxygen sensor 6 is relatively short (see T2).

[0068] Therefore, in the first determination process, the degradation determination unit 8 (degradation determination program P2) determines whether the time from when the fuel cut mode is started until an increase in oxygen concentration is detected by the rear oxygen sensor 6 is less than a predetermined standard value (step S4).

[0069] The predetermined reference value in the first judgment process (the time until an increase in oxygen concentration is detected) varies depending on the type of oxygen storage and release material. Preferably, when the oxygen storage and release material is used for the first time, the time from when the fuel cut mode is started until an increase in oxygen concentration is detected (see T1 in Figure 3A) and the reference value in the first judgment process are approximately the same.

[0070] Then, if the time until an increase in oxygen concentration is detected by the rear oxygen sensor 6 (time required for oxygen increase) is greater than or equal to a predetermined standard value (step S4; NO), the degradation determination unit 8 makes a first determination that there is no possibility that the oxygen storage and release material has deteriorated (i.e., the catalyst has not deteriorated) (step S5).

[0071] In the first determination, a state in which there is no possibility of deterioration of the oxygen storage and release material means a state in which it can be determined with almost certainty that the oxygen storage and release material has not deteriorated. In such a case, the deterioration determination unit 8 stops the deterioration determination flow (end).

[0072] On the other hand, if the time until an increase in oxygen concentration is detected by the rear oxygen sensor 6 (time required for oxygen increase) is less than a predetermined standard value (step S4; YES), the deterioration determination unit 8 makes a first determination that the oxygen storage and release material may be deteriorating (step S6).

[0073] In the first assessment, a state in which the oxygen storage and release material may be degraded means a state in which it is not possible to determine at that time whether the oxygen storage and release material is degraded or not.

[0074] In such cases, the deterioration determination unit 8 (deterioration determination program P2) performs the second determination process only on oxygen storage and release materials that have been first determined to be potentially deteriorated (step S7).

[0075] (2) Second determination process In the second determination process, the degradation determination unit 8 (degradation determination program P2) controls the gasoline engine 2 via the engine control unit 7, operating the gasoline engine 2 in rich operation mode and lean operation mode. That is, the degradation determination unit 8 (degradation determination program P2) operates the gasoline engine 2 so that the rich inspection mode and the lean inspection mode are repeated at a predetermined cycle. Then, the degradation determination unit 8 makes a second determination of the degradation of the oxygen storage and release material based on the oxygen concentration detected by the rear oxygen sensor 6.

[0076] More specifically, in the second determination process, (2a) the 2a determination process is executed as shown below (steps S8 to S13). Subsequently, if the 2a determination process determines that the oxygen storage and release material may be degraded, (2b) the 2b determination process is executed (steps S14 to S19).

[0077] (2a) Second a determination process In the 2a determination process, the deterioration determination unit 8 determines whether or not the oxygen storage and release material has deteriorated based on the amount of change in oxygen concentration detected by the rear oxygen sensor 6 (the height of the waveform in the oxygen concentration change graph).

[0078] More specifically, when the seconda determination process is executed (step S8), the deterioration determination unit 8 first operates the gasoline engine 2 via the engine control unit 7 so that the rich inspection mode and the lean inspection mode are repeated at a predetermined cycle (step S9).

[0079] Then, in the 2a judgment process, the degradation judgment unit 8 acquires a graph of the fluctuation of oxygen concentration detected by the rear oxygen sensor 6 (step S10).

[0080] In other words, when the gasoline engine 2 is operated so that the rich test mode and lean test mode are alternated, the oxygen concentration of the exhaust gas detected by the front oxygen sensor 5 fluctuates according to the switching of the operating mode.

[0081] For example, when gasoline engine 2 is operated in rich test mode (fuel mixture rich), a relatively large amount of oxygen is consumed in the combustion of the air-fuel mixture, resulting in a relatively low amount of oxygen in the exhaust gas. On the other hand, when gasoline engine 2 is operated in lean test mode (fuel mixture lean), relatively less oxygen is consumed in the combustion of the air-fuel mixture, resulting in a relatively high amount of oxygen in the exhaust gas. In other words, the oxygen concentration of the exhaust gas detected by the front oxygen sensor 5 fluctuates according to the switching of the operating mode.

[0082] In such cases, if the oxygen storage and release material of the three-way catalyst 4 has not deteriorated, a relatively large amount of oxygen will be absorbed and released by the oxygen storage and release material. In other words, when the gasoline engine 2 is operated in lean test mode (fuel lean), the exhaust gas contains a relatively large amount of oxygen, and the oxygen storage and release material absorbs this oxygen. Also, when the gasoline engine 2 is operated in rich test mode (fuel rich), the amount of oxygen in the exhaust gas decreases, so the oxygen storage and release material releases the absorbed oxygen.

[0083] Therefore, if the oxygen storage and release material of the three-way catalyst 4 is not deteriorated, the oxygen concentration of the exhaust gas is equalized within the catalyst chamber 31. As a result, the oxygen concentration of the exhaust gas detected by the rear oxygen sensor 6 does not fluctuate significantly depending on the operating mode switch. In other words, as shown in Figure 4A, if the oxygen storage and release material of the three-way catalyst 4 is not deteriorated, the amount of fluctuation in the oxygen concentration of the exhaust gas detected by the rear oxygen sensor 6 is relatively small (see H1), or the oxygen concentration of the exhaust gas detected by the rear oxygen sensor 6 is approximately constant (see dashed line).

[0084] On the other hand, if the oxygen storage and release material of the three-way catalytic converter 4 deteriorates, the amount of oxygen in and the amount of oxygen released by the oxygen storage and release material will be relatively low. In other words, when the gasoline engine 2 is operated in lean test mode (fuel lean), the amount of oxygen in the exhaust gas will be relatively high, but the oxygen storage and release material will not be able to store enough oxygen. Also, when the gasoline engine 2 is operated in rich test mode (fuel rich), the amount of oxygen in the exhaust gas will be relatively low, but the oxygen storage and release material will not be able to release enough oxygen. Therefore, if the oxygen storage and release material of the three-way catalytic converter 4 deteriorates, the oxygen concentration of the exhaust gas in the catalyst chamber 31 will not be sufficiently equalized. As a result, the oxygen concentration of the exhaust gas detected by the rear oxygen sensor 6 will fluctuate significantly depending on the switching of the operating mode. In other words, as shown in Figure 4B, when the oxygen storage and release material of the three-way catalytic converter 4 deteriorates, the amount of fluctuation in the oxygen concentration of the exhaust gas detected by the rear oxygen sensor 6 is relatively large (see H2).

[0085] Therefore, in the 2a determination process, the oxygen concentration fluctuation graph is referenced to determine whether the amount of fluctuation in oxygen concentration detected by the rear oxygen sensor 6 exceeds a predetermined standard value (step S11).

[0086] The predetermined reference value in the 2a judgment process (the amount of change in oxygen concentration detected by the rear oxygen sensor 6) varies depending on the type of oxygen storage and release material. Preferably, when the oxygen storage and release material is used for the first time, the amount of change in oxygen concentration detected by the rear oxygen sensor 6 (see H1 in Figure 4A) and the reference value in the 2a judgment process are approximately the same.

[0087] Then, if the amount of change in oxygen concentration detected by the rear oxygen sensor 6 is below a predetermined standard value (step S11; NO), the deterioration determination unit 8 makes a second a determination that there is no possibility that the oxygen storage and release material has deteriorated (i.e., the catalyst has not deteriorated) (step S12).

[0088] In the 2a determination, a state in which there is no possibility of deterioration of the oxygen storage and release material means a state in which it can be determined with almost certainty that the oxygen storage and release material has not deteriorated. In such a case, the deterioration determination unit 8 stops the deterioration determination flow (end).

[0089] On the other hand, if the amount of change in oxygen concentration detected by the rear oxygen sensor 6 exceeds a predetermined standard value (step S11; YES), the deterioration determination unit 8 makes a second a determination that the oxygen storage and release material may be deteriorating (step S13).

[0090] In the 2a assessment, a state in which the oxygen storage and release material may be degraded means a state in which it is not possible to determine at that time whether the oxygen storage and release material is degraded or not.

[0091] In such cases, the deterioration determination unit 8 performs the 2b determination process only on oxygen storage and release materials that have been determined to be potentially deteriorated in 2a (step S14).

[0092] (2b) Second b determination process In the 2b determination process, the degradation determination unit 8 determines whether or not the oxygen storage and release material has deteriorated based on the timing of the fluctuation in oxygen concentration detected by the rear oxygen sensor 6 (the phase of the waveform in the oxygen concentration fluctuation graph).

[0093] More specifically, when the second b determination process is executed (step S14), the deterioration determination unit 8 first operates the gasoline engine 2 via the engine control unit 7 so that the rich inspection mode and the lean inspection mode are repeated at a predetermined cycle (step S15).

[0094] Preferably, in order to observe the phase of the waveform in the oxygen concentration fluctuation graph more clearly, the repetition period between the rich test mode and the lean test mode in the 2b judgment process is set to be greater than the repetition period between the rich test mode and the lean test mode in the 2a judgment process. In other words, the length of the rich test mode in the 2b judgment process is set to be longer than the length of the rich test mode in the 2a judgment process. The length of the lean test mode in the 2b judgment process is set to be longer than the length of the lean test mode in the 2a judgment process.

[0095] Then, in the second b judgment process, the degradation judgment unit 8 acquires the fluctuation graph of oxygen concentration detected by the front oxygen sensor 5 and the fluctuation graph of oxygen concentration detected by the rear oxygen sensor 6, respectively (step S16).

[0096] In other words, as described above, when the gasoline engine 2 is operated so that the rich test mode and lean test mode are alternated, the oxygen concentration of the exhaust gas detected by the front oxygen sensor 5 fluctuates according to the switching of the operating mode.

[0097] Furthermore, as can be seen in Figures 4A and 4B, when the gasoline engine 2 operates in a manner that alternates between rich and lean test modes, the oxygen concentration of the exhaust gas detected by the rear oxygen sensor 6 may also fluctuate in accordance with the switching of the operating mode.

[0098] In such cases, if the oxygen storage and release material of the three-way catalyst 4 is not deteriorated, the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5 and the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 will differ significantly. In other words, if the oxygen storage and release material of the three-way catalyst 4 is not deteriorated, the oxygen storage and release material will sufficiently absorb and release oxygen depending on whether the exhaust gas contains a relatively large amount of oxygen or a relatively small amount of oxygen. Therefore, if the oxygen storage and release material of the three-way catalyst 4 is not deteriorated, the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 will lag significantly behind the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5.

[0099] On the other hand, if the oxygen storage and release material of the three-way catalyst 4 is deteriorated, the oxygen storage and release material will not adequately absorb and release oxygen, regardless of whether the exhaust gas contains a relatively large amount of oxygen or a relatively small amount of oxygen. Therefore, if the oxygen storage and release material of the three-way catalyst 4 is deteriorated, the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 will not differ significantly from the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5. For example, the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 will be approximately synchronized with the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5, except for the time required for the exhaust gas to pass through the catalyst chamber 31.

[0100] Therefore, in the 2b determination process, the fluctuation graph of oxygen concentration detected by the front oxygen sensor 5 and the fluctuation graph of oxygen concentration detected by the rear oxygen sensor 6 are referenced to determine whether the difference between the timing of the fluctuation of oxygen concentration detected by the rear oxygen sensor 6 and the timing of the fluctuation of oxygen concentration detected by the front oxygen sensor 5 is less than a predetermined standard value (step S17).

[0101] The predetermined reference value in the 2b judgment process (the difference between the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 and the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5) varies depending on the type of oxygen storage and release material. Preferably, when the oxygen storage and release material is used for the first time, the difference between the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 and the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5 and the reference value in the 2b judgment process are approximately the same.

[0102] Then, if the difference between the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 and the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5 is greater than or equal to a predetermined standard value (step S17; NO), the degradation determination unit 8 makes a second b determination that there is no possibility that the oxygen storage and release material has deteriorated (i.e., the catalyst has not deteriorated) (step S18).

[0103] In the 2b determination, a state in which there is no possibility of deterioration of the oxygen storage and release material means a state in which it can be determined with almost certainty that the oxygen storage and release material has not deteriorated. In such a case, the deterioration determination unit 8 stops the deterioration determination flow (end).

[0104] On the other hand, if the difference between the timing of the oxygen concentration fluctuation detected by the rear oxygen sensor 6 and the timing of the oxygen concentration fluctuation detected by the front oxygen sensor 5 is less than a predetermined standard value (step S17; YES), then the oxygen storage and release material is determined to be degraded (step S19).

[0105] In the 2b assessment, a state in which the oxygen storage and release material is deemed to be deteriorated means a state in which it can be judged with almost certainty that the oxygen storage and release material is deteriorated.

[0106] If the oxygen storage and release material is determined to be deteriorated, the deterioration determination unit 8 will notify the system that the oxygen storage and release material is deteriorated using a notification device (not shown) (step S20).

[0107] Furthermore, the degradation determination unit 8 stops the degradation determination flow (end). Subsequently, for example, when the gasoline engine 2 is stopped and then restarted, the degradation determination flow is started according to predetermined conditions (start).

[0108] 4. Effects In the engine system 1 described above, the degradation determination unit 8 first operates the gasoline engine 2 in fuel cut mode. The degradation determination unit 8 then makes a preliminary determination of the degradation of the oxygen storage and release material based on the time from when the fuel cut mode is started until an increase in oxygen concentration is detected by the rear oxygen sensor 6.

[0109] If the oxygen storage and release material is determined not to have deteriorated in the first determination, the determination process is terminated. On the other hand, if the oxygen storage and release material is determined to potentially have deteriorated in the first determination, the material is subjected to the second determination.

[0110] In the second determination, the degradation determination unit 8 operates the gasoline engine 2 so that the rich test mode and lean test mode are alternated. The degradation determination unit 8 also makes a second determination of the degradation of the oxygen storage and release material based on the oxygen concentration detected by the rear oxygen sensor 6.

[0111] Therefore, in the engine system 1 described above, the oxygen storage and release material is subjected to a second determination in addition to the first determination when predetermined conditions are met. As a result, the deterioration of the oxygen storage and release function is determined with greater accuracy compared to when the oxygen storage and release material is subjected to a first determination only.

[0112] Furthermore, in the engine system 1 described above, if the oxygen storage and release material is determined not to have deteriorated in the first determination, the determination process is terminated. Therefore, compared to the case where the oxygen storage and release material is always subjected to the first and second determinations, the non-deterioration of the oxygen storage and release function can be determined more efficiently.

[0113] Furthermore, the second judgment involves repeatedly switching between rich and lean test modes, which may reduce fuel efficiency and exhaust gas purification efficiency. However, if the first judgment determines that the oxygen storage and release material has not deteriorated, and the judgment process is completed, the second judgment will not be performed, thus suppressing the decrease in fuel efficiency and exhaust gas purification efficiency.

[0114] In particular, in the engine system 1 described above, the deterioration determination unit 8 operates the gasoline engine 2 in the second a determination so that the rich test mode and the lean test mode are repeated. Furthermore, if the amount of fluctuation in oxygen concentration detected by the rear oxygen sensor 6 exceeds a predetermined standard value, the deterioration determination unit 8 makes a second a determination that the oxygen storage and release material may be deteriorating. Subsequently, in the engine system 1, only if the second a determination is made that the oxygen storage and release material may be deteriorating, the deterioration determination unit 8 operates the gasoline engine 2 in the second b determination so that the rich test mode and the lean test mode are repeated. Furthermore, if the difference between the timing of the fluctuation in oxygen concentration detected by the rear oxygen sensor 6 and the timing of the fluctuation in oxygen concentration detected by the front oxygen sensor 5 is less than a predetermined standard value, the deterioration determination unit 8 makes a second b determination that the oxygen storage and release material is deteriorating.

[0115] Therefore, in the engine system 1 described above, the oxygen storage and release material is used for both the 2a and 2b determinations, so the deterioration of the oxygen storage and release function can be determined with greater accuracy compared to when the oxygen storage and release material is used for only either the 2a or 2b determination.

[0116] Furthermore, in the engine system 1 described above, if it is determined in the 2a determination that the oxygen storage and release material has not deteriorated, the determination process is terminated. Therefore, the non-deterioration of the oxygen storage and release function can be determined more efficiently compared to when the oxygen storage and release material is always subjected to the 2a and 2b determinations.

[0117] In addition, in the engine system 1 described above, in order to observe the phase of the waveform in the oxygen concentration fluctuation graph more clearly, the repetition period between the rich inspection mode and the lean inspection mode in the 2b judgment process is set to be greater than the repetition period between the rich inspection mode and the lean inspection mode in the 2a judgment process.

[0118] Therefore, the degree of decrease in fuel efficiency and exhaust gas purification efficiency in the 2b judgment is more severe than the degree of decrease in fuel efficiency and exhaust gas purification efficiency in the 2a judgment. In other words, the degree of decrease in fuel efficiency and exhaust gas purification efficiency in the 2a judgment is less severe than the degree of decrease in fuel efficiency and exhaust gas purification efficiency in the 2b judgment.

[0119] Therefore, in the engine system 1 described above, the oxygen storage and release material is first judged as 2a, and if necessary, judged as 2b after the 2a judgment. As a result, in the engine system 1 described above, the decrease in fuel efficiency and exhaust gas purification efficiency can be suppressed compared to the case where the oxygen storage and release material is judged as 2a after the 2b judgment.

[0120] 5. Variations In the above explanation, the second determination process is performed by first executing the second a determination process, followed by the second b determination process. However, for example, the second b determination process can be performed first, followed by the second a determination process. Also, for example, only the second a determination process can be performed, and the second b determination process can be omitted.

[0121] Furthermore, although the above description states that the degradation detection unit 8 is a separate computer unit from the engine control unit 7, the degradation detection unit 8 may be shared with the engine control unit 7. In other words, one computer unit may be used as both the engine control unit 7 and the degradation detection unit 8. [Explanation of Symbols]

[0122] 1. Engine System 2 Gasoline engine 3 Exhaust pipe 4 Three-way catalyst 5. Front oxygen sensor 6. Rear oxygen sensor 7. Engine control unit 8. Degradation detection unit

Claims

1. Gasoline engine, An exhaust pipe through which the exhaust gas of the aforementioned gasoline engine passes, A three-way catalyst containing an oxygen storage and release material is interposed in the exhaust pipe, A front oxygen sensor is positioned upstream of the three-way catalyst in the gas flow direction and detects the oxygen concentration of the exhaust gas. A rear oxygen sensor is positioned downstream of the three-way catalyst in the gas flow direction and detects the oxygen concentration of the exhaust gas. An engine control unit connected to the gasoline engine and controlling the operating mode of the gasoline engine, A deterioration determination unit is connected to the engine control unit, the front oxygen sensor, and the rear oxygen sensor, and determines the deterioration of the oxygen storage and release material based on the operating mode of the gasoline engine and the oxygen concentration of the exhaust gas. Equipped with, The aforementioned engine control unit is The operating mode of the aforementioned gasoline engine can be selectively switched to one of the following: fuel cut mode, rich test mode, or lean test mode. The aforementioned deterioration determination unit is first, (1) The gasoline engine is operated in the fuel cut mode via the engine control unit, and if the time from the start of the fuel cut mode until an increase in oxygen concentration is detected by the rear oxygen sensor is less than a predetermined standard value, a first determination is made that the oxygen storage and release material may be deteriorating. Next, Only if it is determined in the first determination that the oxygen storage and release material may be degraded, (2) An engine system that operates the gasoline engine via the engine control unit so that the rich inspection mode and the lean inspection mode are repeated, and makes a second determination of the deterioration of the oxygen storage and release material based on the oxygen concentration detected by the rear oxygen sensor.

2. In the second determination described above, the deterioration determination unit is (2a) The gasoline engine is operated via the engine control unit so that the rich test mode and the lean test mode are repeated, and if the amount of change in oxygen concentration detected by the rear oxygen sensor exceeds a predetermined standard value, the second determination a is made that the oxygen storage and release material may be deteriorating. after that, Only if it is determined in 2a that the oxygen storage and release material may be degraded, (2b) The engine system according to claim 1, wherein the gasoline engine is operated via the engine control unit so that the rich inspection mode and the lean inspection mode are repeated, and if the difference between the timing of the change in oxygen concentration detected by the rear oxygen sensor and the timing of the change in oxygen concentration detected by the front oxygen sensor is less than a predetermined reference value, the second b determination is made that the oxygen storage and release material is deteriorated.

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