Apparatus and method for diagnosing deterioration of an engine exhaust system

Abstract

To provide a deterioration diagnostic device for an engine exhaust system capable of suppressing deterioration of an exhaust gas component due to a deterioration determination of an air-fuel ratio sensor and a catalyst.SOLUTION: A control unit 16 of a deterioration diagnostic device for an engine exhaust system includes: a time measurement section 32 measuring a first elapsed time from when a measurement value of an air-fuel ratio sensor 27 becomes below a predetermined first threshold value to when the measurement value becomes below a second threshold value on a lean side after a target air-fuel ratio is shifted to a lean region; a sensor deterioration determination section 34 determining deterioration of the air-fuel ratio sensor 27 on the basis of the first elapsed time; an integration section 33 determining integrated oxygen amount obtained by integrating oxygen amount occluded in a catalyst 25 before the measurement value obtained by the air-fuel ratio sensor 27 becomes below a predetermined third threshold value on the lean side of the second threshold value after the target air-fuel ratio is shifted to the lean region or a parameter corresponding to the integrated oxygen amount; and a catalyst deterioration determination section 35 determining deterioration of the catalyst 25 on the basis of the integrated oxygen amount or the parameter corresponding to the integrated oxygen amount.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an engine exhaust system deterioration diagnosis device and an engine exhaust system deterioration diagnosis method, and more particularly to an apparatus and method for diagnosing deterioration of an air-fuel ratio sensor and a catalyst in an engine exhaust system. [Background technology]

[0002] When a vehicle equipped with an engine is used for a long period of time, the catalyst provided in the exhaust path of the engine deteriorates, and therefore it is necessary to periodically diagnose whether the catalyst has deteriorated or not.

[0003] In a conventional catalyst deterioration diagnosis device, as described in Patent Document 1, for example, a target air-fuel ratio in air-fuel ratio feedback control is forcibly shifted to lean (i.e., the lean side region) to cause the catalyst to store oxygen, and the amount of oxygen stored in the catalyst is obtained until the measurement value of the air-fuel ratio sensor downstream of the catalyst reverses to the lean side. The deterioration of the oxygen storage capacity of the catalyst is detected by determining whether or not this stored oxygen amount is larger than a reference amount. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-329832 A Summary of the Invention [Problem to be solved by the invention]

[0005] While the deterioration diagnosis of the catalyst is performed as described above, the air-fuel ratio sensor provided in the exhaust path of the engine must also be periodically diagnosed for deterioration based on the change in the sensor output when the target air-fuel ratio is shifted to rich or lean.However, when the deterioration diagnosis device is used to perform deterioration diagnosis of the air-fuel ratio sensor and the catalyst, it is necessary to control the target air-fuel ratio to shift to rich or lean for each deterioration judgment of the air-fuel ratio sensor and the catalyst, which raises concerns that harmful components in the exhaust gas will increase and the exhaust gas components (EM) will deteriorate.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a deterioration diagnosis device for an engine exhaust system that can suppress the deterioration of exhaust gas components that accompanies the deterioration determination of an air-fuel ratio sensor and a catalyst. [Means for solving the problem]

[0007] The deterioration diagnosis device for an engine exhaust system of the present invention includes a catalyst arranged in an exhaust passage of an engine for purifying exhaust gas, an air-fuel ratio sensor arranged in the exhaust passage at a position downstream of the catalyst for measuring the air-fuel ratio of the exhaust gas, and a control unit for determining deterioration of the catalyst and the air-fuel ratio sensor, the control unit including an air-fuel ratio control unit for controlling a target air-fuel ratio of the engine to be either rich or lean, and a control unit for determining deterioration of the catalyst and the air-fuel ratio sensor after the air-fuel ratio control unit has shifted the target air-fuel ratio to lean and after the measurement value of the air-fuel ratio sensor falls below a predetermined first threshold. The catalyst deterioration determination unit includes a time measurement unit that measures a first elapsed time until the measurement value of the air-fuel ratio sensor falls below a predetermined second threshold that is set to be leaner than the first threshold; a sensor deterioration determination unit that determines deterioration of the air-fuel ratio sensor based on the first elapsed time; an integration unit that calculates an integrated oxygen amount obtained by integrating the amount of oxygen stored in the catalyst until the measurement value of the air-fuel ratio sensor falls below a predetermined third threshold that is set to be leaner than the second threshold after the target air-fuel ratio transitions to lean, or a parameter corresponding to the integrated oxygen amount; and a catalyst deterioration determination unit that determines deterioration of the catalyst based on the integrated oxygen amount or the parameter corresponding to the integrated oxygen amount.

[0008] In the deterioration diagnosis device of the present invention, the control unit has the above-mentioned configuration as a configuration capable of determining deterioration of the catalyst and the air-fuel ratio sensor in one lean period. In this configuration, after the air-fuel ratio control unit shifts the target air-fuel ratio to lean, the time measurement unit measures a first elapsed time from when the measurement value of the air-fuel ratio sensor falls below a predetermined first threshold to when it falls below a predetermined second threshold set to be leaner than the first threshold. The sensor deterioration determination unit determines deterioration of the air-fuel ratio sensor based on the first elapsed time. Meanwhile, the integration unit calculates an integrated oxygen amount by integrating the amount of oxygen stored in the catalyst until the measurement value of the air-fuel ratio sensor falls below a predetermined third threshold set to be leaner than the second threshold after the target air-fuel ratio shifts to lean, or calculates a parameter corresponding to the integrated oxygen amount. The catalyst deterioration determination unit determines deterioration of the catalyst based on the integrated oxygen amount or a parameter corresponding thereto.

[0009] In this configuration, since it is possible to set the period during which the air-fuel ratio sensor changes and the period during which oxygen is stored in the catalyst within the common lean period, it is possible to determine the deterioration of the air-fuel ratio sensor and the catalyst with a single shift to lean. As a result, it is possible to reduce the number of times that the air-fuel ratio is forcibly shifted to lean in order to determine the deterioration of the air-fuel ratio sensor and the catalyst, and to suppress the deterioration of exhaust gas components accompanying the determination of the deterioration of the air-fuel ratio sensor and the catalyst.

[0010] In the above-mentioned engine exhaust system deterioration diagnosis device, the integrating unit may integrate, as the parameter corresponding to the integrated oxygen amount, an amount of fuel consumption required to consume the oxygen stored in the catalyst after the air-fuel ratio control unit shifts the target air-fuel ratio from lean to rich, and the catalyst deterioration determination unit may determine deterioration of the catalyst based on the amount of fuel consumption corresponding to the integrated oxygen amount.

[0011] According to this configuration, the integrating unit integrates the fuel consumption amount required to consume the oxygen stored in the catalyst after the air-fuel ratio control unit shifts the target air-fuel ratio from lean to rich as a parameter corresponding to the integrated oxygen amount. This makes it possible to indirectly determine the integrated oxygen amount of the catalyst during the lean period by the fuel consumption amount that consumes the oxygen stored in the catalyst after the transition from lean to rich. Therefore, it becomes possible for the catalyst deterioration determining unit to determine the deterioration of the catalyst based on the fuel consumption amount corresponding to the integrated oxygen amount.

[0012] In the above-described deterioration diagnosis device for an engine exhaust system, it is preferable that the time measurement unit measures a second elapsed time from when the measurement value of the air-fuel ratio sensor exceeds the second threshold value to when it exceeds the first threshold value after the air-fuel ratio control unit shifts the target air-fuel ratio from lean to rich, and the sensor deterioration determination unit determines deterioration of the rich side of the air-fuel ratio sensor based on the second elapsed time.

[0013] According to this configuration, it is possible to determine not only the deterioration of the air-fuel ratio sensor on the lean side, but also the deterioration of the air-fuel ratio sensor on the rich side.

[0014] In the above-mentioned deterioration diagnosis device for the engine exhaust system, it is preferable that the sensor deterioration determination unit determines that the air-fuel ratio sensor is deteriorated when it determines that either one of the lean side judgment result and the rich side judgment result is deteriorated.

[0015] According to this configuration, if it is determined that either one of the lean side judgment result and the rich side judgment result is deteriorated, it is determined that the air-fuel ratio sensor is deteriorated, so that deterioration of the air-fuel ratio sensor can be determined more accurately.

[0016] The above-mentioned deterioration diagnosis device for an engine exhaust system is preferably applied to diagnosis of deterioration of the engine exhaust system of a hybrid vehicle having a motor as well as the engine as a drive source.

[0017] In a hybrid vehicle, the time during which the engine is not running and exhaust gas is not discharged, such as during deceleration, is longer than in a gasoline vehicle, and therefore the time during which deterioration diagnosis of the air-fuel ratio sensor and catalyst in the engine exhaust system can be performed is shorter while the vehicle is running. However, by using the deterioration diagnosis device described above, deterioration of the air-fuel ratio sensor and catalyst can be determined in a hybrid vehicle by shifting to lean once in a short period of time while the engine is running, and deterioration of exhaust gas components can be suppressed. As a result, hybrid vehicles can be driven in a more environmentally friendly manner.

[0018] The method for diagnosing deterioration of an engine exhaust system of the present invention is a method for diagnosing deterioration in an engine exhaust system including a catalyst disposed in an exhaust passage of an engine for purifying exhaust gas, and an air-fuel ratio sensor disposed in the exhaust passage at a position downstream of the catalyst for measuring the air-fuel ratio of the exhaust gas, the method including: a lean transition process for transitioning a target air-fuel ratio of the engine to lean; a time measurement process for measuring a first elapsed time from when a measurement value of the air-fuel ratio sensor falls below a first threshold value until it falls below a second threshold value set on the leaner side than the first threshold value, after the target air-fuel ratio transitions to lean; a sensor deterioration determination process for determining deterioration of the air-fuel ratio sensor based on the first elapsed time; an oxygen amount accumulation process for obtaining an integrated oxygen amount obtained by accumulating an amount of oxygen stored in the catalyst until the measurement value of the air-fuel ratio sensor falls below a predetermined third threshold value set on the leaner side than the second threshold value after the target air-fuel ratio transitions to lean, or a parameter corresponding to the integrated oxygen amount; and a catalyst deterioration determination process for determining deterioration of the catalyst based on the integrated oxygen amount or the parameter corresponding to the integrated oxygen amount.

[0019] According to this feature, since it is possible to set a period during which the air-fuel ratio sensor changes and a period during which oxygen is stored in the catalyst within the common lean period, it is possible to determine the deterioration of the air-fuel ratio sensor and the catalyst with a single shift to lean. As a result, it is possible to reduce the number of times that the air-fuel ratio is forcibly shifted to lean in order to determine the deterioration of the air-fuel ratio sensor and the catalyst, and to suppress the deterioration of the exhaust gas components. Effect of the Invention

[0020] According to the engine exhaust system deterioration diagnosis device and deterioration diagnosis method of the present invention, the number of times that the air-fuel ratio is forcibly shifted to a leaner state in order to determine the deterioration of the air-fuel ratio sensor and catalyst can be reduced, thereby suppressing the deterioration of exhaust gas components. [Brief description of the drawings]

[0021] [Figure 1]1 is a block diagram showing a schematic configuration of a hybrid vehicle to which a deterioration diagnosis device for an engine exhaust system according to a first embodiment of the present invention is applied. [Diagram 2] 2 is a block diagram showing the internal configuration of a controller shown in FIG. 1. [Diagram 3] 4 is a first half of a flowchart showing the procedure of a deterioration diagnosis method for an engine exhaust system according to a first embodiment. [Figure 4] 4 is a second half of the flowchart following the first half of the flowchart in FIG. 3. [Diagram 5] 5 is a diagnostic chart in the deterioration diagnostic method based on the flowcharts of FIGS. 3 and 4, in which both the rear air-fuel ratio sensor and the catalyst are normal. [Figure 6] 5 is a diagnostic chart showing a case where the rear air-fuel ratio sensor has deteriorated, in the deterioration diagnostic method based on the flowcharts of FIGS. [Figure 7] 5 is a diagnostic chart for when the catalyst has deteriorated in the deterioration diagnostic method based on the flowcharts of FIGS. 3 and 4. [Figure 8] 10 is a first half of a flowchart showing the steps of a deterioration diagnosis method for an engine exhaust system according to a second embodiment. [Figure 9] 9 is a second half of the flowchart following the first half of the flowchart in FIG. 8. [Figure 10] 10 is a diagnostic chart in the deterioration diagnostic method based on the flowcharts of FIGS. 8 and 9, in which both the rear air-fuel ratio sensor and the catalyst are normal. [Figure 11] 10 is a diagnostic chart showing a case where the rear air-fuel ratio sensor has deteriorated, in the deterioration diagnostic method based on the flowcharts of FIGS. [Figure 12] 10 is a diagnostic chart for when the catalyst has deteriorated, in the deterioration diagnostic method based on the flowcharts of FIGS. 8 and 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0023] (First embodiment) [Overall configuration of hybrid vehicle] Fig. 1 is a block diagram showing a schematic configuration of a hybrid vehicle to which an engine exhaust system deterioration diagnosis device according to the present invention is applied. The hybrid vehicle (hereinafter, referred to as HV vehicle) 1 shown in the figure includes an engine 2, a motor 4, a transmission 6, a clutch CL1, a differential gear 8, drive wheels 10, an inverter 12, a battery 14, and a controller 16. Both the engine 2 and the motor 4 generate driving force for running.

[0024] The engine 2 is an internal combustion engine that generates driving force by burning fuel, specifically, a gasoline engine that uses fuel mainly composed of gasoline. In the gasoline engine, the target air-fuel ratio is controlled to the stoichiometric air-fuel ratio during normal vehicle running, but the air-fuel ratio is varied to rich or lean when performing deterioration diagnosis of the catalyst 25 and the rear air-fuel ratio sensor 27 described later.

[0025] The intake passage 21 of the engine 2 is provided with a throttle valve 22 that adjusts the flow rate of air flowing through the intake passage 21, and an airflow sensor 23 that is disposed upstream of the throttle valve 22 and measures the airflow rate in the intake passage 21 upstream of the throttle valve 22.

[0026] Also, disposed in the exhaust passage 24 of the engine 2 are a catalyst 25 which purifies the exhaust gas discharged from the engine 2, and two air-fuel ratio sensors 26 and 27, namely, a linear air-fuel ratio sensor 26 which is disposed at a position upstream of the catalyst 25 and measures the air-fuel ratio of the exhaust gas at a position upstream of the catalyst 25, and a rear air-fuel ratio sensor 27 which is disposed at a position downstream of the catalyst 25 and measures the air-fuel ratio of the exhaust gas.

[0027] The catalyst 25 is composed of a three-way catalyst that purifies exhaust gas, and has the property of storing oxygen when the target air-fuel ratio is lean, and consuming the stored oxygen when the target air-fuel ratio is rich. In other words, when the catalyst 25 is in a normal state, it is possible to store a sufficient amount of oxygen, equal to or greater than a predetermined value, when the target air-fuel ratio is lean, but when the catalyst 25 is in a deteriorated state, it is not possible to store a sufficient amount of oxygen.

[0028] The rear air-fuel ratio sensor 27 is a sensor that corresponds to the air-fuel ratio sensor of the present invention. The rear air-fuel ratio sensor 27 may be any sensor that can measure the air-fuel ratio of the exhaust gas at a position downstream of the catalyst 25. For example, the rear air-fuel ratio sensor 27 may be an O 2 A sensor or the like is employed as the rear air-fuel ratio sensor 27.

[0029] The rear air-fuel ratio sensor 27 outputs the RO2 voltage in Fig. 5 as a measurement value of the air-fuel ratio of the exhaust gas. The magnitude of the RO2 voltage is, for example, 0 V when the target air-fuel ratio is lean and 1 V when it is rich, and shifts between 0 V and 1 V correspondingly when the air-fuel ratio is transitioning between lean and rich.

[0030] When the rear air-fuel ratio sensor 27 is in a normal state, when the target air-fuel ratio shifts to the lean or rich side, the measurement value of the rear air-fuel ratio sensor 27 (the RO2 voltage in FIG. 5) shifts quickly to the lean or rich side with good responsiveness in a short period of time. However, when the rear air-fuel ratio sensor 27 is in a deteriorated state, the responsiveness deteriorates and the time it takes to shift to the lean or rich side becomes longer.

[0031] The linear air-fuel ratio sensor 26, together with the rear air-fuel ratio sensor 27, is used for feedback control by an air-fuel ratio control unit 31 (described later) to keep a target air-fuel ratio at stoichiometric (theoretical air-fuel ratio) and for calculating the amount of oxygen stored in the catalyst 25. In addition, since the linear air-fuel ratio sensor 26 is disposed upstream of the catalyst 25 in the exhaust passage 24, it is also used for calculating the amount of oxygen stored in the catalyst 25.

[0032] The motor 4 is, for example, a three-phase AC synchronous motor generator, and generates driving force by receiving a supply of electric power stored in a battery 14. When the HV vehicle 1 decelerates, the motor 4 generates electric power by the rotational force transmitted from the drive wheels 10. In this case, a braking force corresponding to the electric power generated by the motor 4 acts on the drive wheels 10. The electric power generated by the power generation of the motor 4 is charged to the battery 14 via the inverter 12.

[0033] The engine 2 and the motor 4 are connected in series via a clutch CL1. The motor 4 is connected to a drive shaft of the drive wheels 10 via a transmission 6 and a differential gear 8. With this configuration, the engine 2 and the motor 4 can apply a driving force or a braking force to the drive wheels 10 via the transmission 6 etc.

[0034] The clutch CL1 connects and disconnects the output shaft (crank shaft) of the engine 2 and the rotating shaft (rotor shaft) of the motor 4. By connecting and disconnecting the output shaft and the rotating shaft, transmission and disconnection of torque between the engine 2 and the motor 4 is switched.

[0035] The transmission 6 has a function of changing the speed of rotation of the rotating shaft of the motor 4 and outputting the rotation, and in this example, a transmission with six forward speeds and one reverse speed is applied. The input shaft of the transmission 6 is connected to the rotating shaft of the motor 4, and the output shaft is connected to a differential gear 8 directly or indirectly via a drive shaft. When the clutch CL2 is disengaged (released), torque transmission between the input shaft and the output shaft is interrupted.

[0036] In this HV vehicle 1, when the clutch CL2 is engaged and the clutch CL1 is disengaged, only the driving force generated by the motor 4 is applied to the drive wheels 10 via the transmission 6 etc. On the other hand, when both clutches CL1 and CL2 are engaged, the driving forces of the engine 2 and the motor 4 are applied to the drive wheels 10 via the transmission 6 etc. At this time, when the motor 4 does not generate driving force (when the power supply to the motor 4 is cut off), only the driving force generated by the engine 2 is applied to the drive wheels 10 via the transmission 6 etc.

[0037] In other words, the HV vehicle 1 can run in any of the following modes: a mode in which it runs only using the driving force of the motor 4, a mode in which it runs only using the driving force of both the motor 4 and the engine 2, or a mode in which it runs only using the driving force of the engine 2.

[0038] The battery 14 is a chargeable and dischargeable secondary battery, and for example, a lithium ion battery or a nickel-metal hydride battery is used as the battery 14. The battery 14 supplies electric power to the battery 14 via the inverter 12, and also receives electric power generated by the motor 4 via the inverter 12 to store the electric power.

[0039] The inverter 12 converts between three-phase AC power and DC power. That is, when driving force is generated by the motor 4, the inverter 12 converts the DC power stored in the battery 14 into three-phase AC power and supplies it to the motor 4, and when three-phase AC power is generated by the motor 4, the inverter 12 converts the three-phase AC power into DC power and supplies it to the battery 14.

[0040] The controller 16 comprehensively controls the engine 2, inverter 12 (motor 4), transmission 6, clutch CL1, etc., so as to realize driving control of the HV vehicle 1 according to the driving conditions. The controller 16 is configured based on a well-known microcomputer, and includes a CPU (Central Processing Unit) that executes various programs, and memories such as ROM and RAM for storing programs and various data.

[0041] The controller 16 of this embodiment further has a function for determining deterioration of the catalyst 25 and the rear air-fuel ratio sensor 27, and is provided with a configuration shown in Fig. 2 (an air-fuel ratio control unit 31, a time measurement unit 32, an integrating unit 33, a sensor deterioration determination unit 34, and a catalyst deterioration determination unit 35) to realize this function. In other words, the controller 16 corresponds to the control unit of the present invention.

[0042] In other words, the engine exhaust system deterioration diagnosis device of this embodiment is composed of the above-mentioned catalyst 25, rear air-fuel ratio sensor 27, and controller 16, and overall is applied to diagnose deterioration of the engine exhaust system of the above-mentioned HV vehicle 1 which has a motor 4 together with an engine 2 as a driving source.

[0043] The controller 16 shown in FIG. 2 is configured to be able to determine the deterioration of the rear air-fuel ratio sensor 27 and the catalyst 25 by transitioning the target air-fuel ratio to lean once, and includes the above-mentioned air-fuel ratio control unit 31, a time measurement unit 32, an integrating unit 33, a sensor deterioration determination unit 34, and a catalyst deterioration determination unit 35.

[0044] The air-fuel ratio control unit 31 performs control to shift the target air-fuel ratio of the engine 2 to either rich or lean.

[0045] The time measurement unit 32 measures a first elapsed time β (see FIG. 5) from when the measurement value of the rear air-fuel ratio sensor 27 (specifically, the RO2 voltage in FIG. 5) falls below a predetermined first threshold value C until it falls below a predetermined second threshold value D that is set leaner than the first threshold value C after the air-fuel ratio control unit 31 shifts the target air-fuel ratio to lean.

[0046] The sensor deterioration determination unit 34 determines deterioration of the rear air-fuel ratio sensor 27 based on the first elapsed time β. For example, the sensor deterioration determination unit 34 determines the rear air-fuel ratio sensor 27 as normal when the first elapsed time β is below a threshold value β1, and determines the rear air-fuel ratio sensor 27 as deteriorated when the first elapsed time β is not below the threshold value β1 (i.e., when the first elapsed time β is equal to or greater than the threshold value β1).

[0047] The integrating unit 33 obtains an integrated oxygen amount α (see FIG. 5 ) by integrating the amount of oxygen stored in the catalyst 25 until the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below a predetermined third threshold B that is set to the leaner side than the second threshold D after the target air-fuel ratio shifts to the lean side. Note that the integrating unit 33 may obtain a parameter corresponding to the integrated oxygen amount α, for example, a fuel consumption amount ε, as in a second embodiment described later.

[0048] The catalyst deterioration determination unit 35 determines the deterioration of the catalyst 25 based on the integrated oxygen amount α. For example, the catalyst deterioration determination unit 35 determines that the catalyst 25 is normal when the integrated oxygen amount α exceeds a threshold value α1, and determines that the catalyst 25 is deteriorated when the integrated oxygen amount α does not exceed the threshold value α1 (i.e., when the integrated oxygen amount α is equal to or less than the threshold value α1). Note that the catalyst deterioration determination unit 35 may determine the deterioration of the catalyst 25 based on a parameter corresponding to the integrated oxygen amount α (for example, the fuel consumption amount ε) as in a second embodiment described later.

[0049] Moreover, the deterioration diagnosis device of this embodiment further has a function of determining deterioration of the rear air-fuel ratio sensor 27 on the rich side.

[0050] Specifically, the time measurement unit 32 measures the second elapsed time γ (see Figure 5) from when the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 exceeds the second threshold value D to when it exceeds the first threshold value C after the air-fuel ratio control unit 31 shifts the target air-fuel ratio from lean to rich.

[0051] In response to this, the sensor deterioration determination unit 34 determines deterioration on the rich side of the rear air-fuel ratio sensor 27 based on the second elapsed time γ. In the case of determining the rich side, similarly to the above-described determination on the lean side, the sensor deterioration determination unit 34 determines that the sensor is normal when the second elapsed time γ is below the threshold value γ1, and determines that the sensor is deteriorated when the second elapsed time γ is not below the threshold value γ1 (i.e., when the second elapsed time γ is equal to or greater than the threshold value γ1).

[0052] In addition, when the sensor deterioration determination unit 34 performs deterioration determination on both the lean side and the rich side as described above, it may determine that the rear air-fuel ratio sensor 27 is deteriorated if it determines that either one of the judgment results on the lean side or the judgment results on the rich side is deteriorated.

[0053] In the present invention, the deterioration determination of the rear air-fuel ratio sensor 27 needs to be performed at least on the lean side, and the rich side determination is not essential.

[0054] (Description of the engine exhaust system deterioration diagnosis method according to the first embodiment) <Outline of deterioration diagnosis method> When a deterioration diagnosis method is carried out using the deterioration determination device for an engine exhaust system configured as described above, the deterioration diagnosis method is carried out as follows.

[0055] That is, the degradation diagnosis method is roughly divided into the following five steps (1) to (5). (1) A lean transition process in which the target air-fuel ratio of engine 2 is transitioned to lean. (2) A time measurement process for measuring a first elapsed time β from when the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below the first threshold value C until it falls below a second threshold value D set leaner than the first threshold value C after the target air-fuel ratio transitions to lean. (3) A sensor deterioration determination process for determining deterioration of the rear air-fuel ratio sensor 27 based on the first elapsed time β. (4) An oxygen amount accumulation process in which, after the target air-fuel ratio has shifted to lean, the amount of oxygen stored in the catalyst 25 is accumulated until the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below a predetermined third threshold B that is set leaner than the second threshold D, to determine the accumulated oxygen amount α (or to determine a parameter corresponding to the accumulated oxygen amount α (fuel consumption amount ε, described later)). (5) A catalyst deterioration determination step for determining deterioration of the catalyst 25 based on the integrated oxygen amount α (or a parameter corresponding to the integrated oxygen amount α (fuel consumption amount ε, described later).

[0056] <Specific examples of deterioration diagnosis methods> Next, a specific example of the deterioration diagnosis method for the engine exhaust system of the first embodiment will be described in detail with reference to the flowcharts of Figures 3 and 4 and the normal state diagnosis chart of Figure 5. In this description, the rear air-fuel ratio sensor 27 will be referred to as the "RO2 sensor 27" as shown in Figures 3 to 5.

[0057] The controller 16 starts a deterioration diagnosis program periodically (or when a diagnosis start input signal is received by manual operation of the driver) when the HV vehicle 1 is running in a mode in which it runs using only the driving force of the engine 2.

[0058] When the deterioration diagnosis program is started, first, in step S1 of the flow chart of FIG. 3, the air-fuel ratio control section 31 of the controller 16 performs control to shift the target air-fuel ratio to the rich side.

[0059] Then, in step S2, the controller 16 waits until the measurement value of the RO2 sensor 27 (the RO2 voltage in FIG. 5) exceeds the reference voltage A. When the measurement value exceeds the reference voltage A, it becomes possible to consume all of the oxygen stored in the catalyst 25 and set the integrated oxygen amount α (see FIG. 5) to 0; in other words, it becomes possible to reset the integrated oxygen amount α to 0 before the lean transition.

[0060] After the measurement value (RO2 voltage) of the RO2 sensor 27 exceeds the reference voltage A, in step S3, the air-fuel ratio control unit 31 controls the target air-fuel ratio to shift to lean. Note that step S3 corresponds to the above-mentioned (1) lean shift process.

[0061] Then, in step S4, the integrating unit 33 starts to calculate the integrated oxygen amount α when the target air-fuel ratio is lean. The integrated oxygen amount α is found, for example, by multiplying the air flow rate obtained from the air flow sensor 23 by the difference between the air-fuel ratio (specifically, oxygen concentration) on the upstream side of the catalyst 25 obtained from the linear air-fuel ratio sensor 26 and the air-fuel ratio (specifically, oxygen concentration) on the downstream side of the catalyst 25 obtained from the RO2 sensor 27.

[0062] Then, in step S5, the controller 16 waits until the measurement value (RO2 voltage) of the RO2 sensor 27 falls below a first threshold value C, i.e., a reference voltage C.

[0063] When the voltage falls below the reference voltage C, in step S6, the time measurement unit 32 starts measuring the first elapsed time β (see FIG. 5).

[0064] After that, in step S7, the time measurement unit 32 of the controller 16 continues to measure the first elapsed time β until the measurement value (RO2 voltage) of the RO2 sensor 27 falls below the second threshold value D, that is, the reference voltage D.

[0065] When the measurement value (RO2 voltage) of the RO2 sensor 27 falls below the reference voltage D, in step S8, the time measurement unit 32 ends measurement of the first elapsed time β. The above steps S6 to S8 correspond to the above-mentioned (2) time measurement process.

[0066] Next, in step S9, the sensor deterioration determination unit 34 of the controller 16 determines whether the first elapsed time β falls below the threshold value β1 (see FIG. 5). If the sensor deterioration determination unit 34 determines that the first elapsed time β falls below the threshold value β1 (see FIG. 5), it determines that the RO2 sensor 27 is normal (i.e., the RO2 time constant is "normal") as in step S10, whereas if it determines that the first elapsed time β is not below the threshold value β1 (i.e., is equal to or greater than the threshold value β1), it determines that the RO2 sensor 27 has deteriorated (specifically, response deterioration) (i.e., the RO2 time constant is "deteriorated") as in step S11. The above steps S9 to S11 correspond to the above (3) sensor deterioration determination process.

[0067] Then, in step S12, the integrating unit 33 of the controller 16 continues integrating the integrated oxygen amount α until the measurement value (RO2 voltage) of the RO2 sensor 27 falls below the third threshold value B, i.e., the reference voltage B. Steps S4 and S12 as described above correspond to the above-mentioned (4) oxygen amount integration process.

[0068] When the measurement value (RO2 voltage) of the RO2 sensor 27 falls below the reference voltage B, in step S13, the catalyst deterioration determination unit 35 of the controller 16 determines whether or not the integrated oxygen amount α exceeds the threshold value α1 (see FIG. 5). When the catalyst deterioration determination unit 35 determines that the integrated oxygen amount α exceeds the threshold value α1 (see FIG. 5), it determines that the catalyst 25 is normal as in step S14, and when it determines that the integrated oxygen amount α does not exceed the threshold value α1 (see FIG. 5) (i.e., is equal to or less than the threshold value α1), it determines that the catalyst 25 is deteriorated (specifically, deteriorated in terms of oxygen storage capacity) as in step S15. The above steps S13 to S15 correspond to the above (5) catalyst deterioration determination process.

[0069] After the deterioration determination of the catalyst 25 is performed in the above steps S13 to S15, the deterioration determination of the rich side of the RO2 sensor 27 is performed as follows.

[0070] First, in step S16, the air-fuel ratio control section 31 controls the target air-fuel ratio to shift from lean to rich.

[0071] Then, in step S17, the controller 16 waits until the measurement value (RO2 voltage) of the RO2 sensor 27 exceeds the second threshold value D, that is, the reference voltage D.

[0072] When the voltage exceeds the reference voltage D, in step S18, the time measurement unit 32 starts measuring the second elapsed time γ (see FIG. 5).

[0073] After that, in step S19, the time measurement unit 32 of the controller 16 continues to measure the second elapsed time γ until the measurement value (RO2 voltage) of the RO2 sensor 27 exceeds the first threshold value C, that is, the reference voltage C.

[0074] When the measurement value (RO2 voltage) of the RO2 sensor 27 exceeds the reference voltage C, in step S20, the time measurement unit 32 ends measurement of the second elapsed time γ.

[0075] Next, in step S21, the sensor deterioration determination unit 34 of the controller 16 determines whether the second elapsed time γ falls below the threshold value γ1 (see FIG. 5). If the sensor deterioration determination unit 34 determines that the second elapsed time γ falls below the threshold value γ1 (see FIG. 5), it determines that the RO2 sensor 27 is normal (i.e., the RO2 time constant is "normal") as in step S22, whereas if it determines that the second elapsed time γ is not below the threshold value γ1 (see FIG. 5) (i.e., is equal to or greater than the threshold value γ1), it determines that the RO2 sensor 27 is deteriorated (i.e., the RO2 time constant is "deteriorated") as in step S23.

[0076] After performing the deterioration determination on the rich side of the RO2 sensor 27 in steps S21 to S23 described above, in step S24, the air-fuel ratio control unit 31 controls the target air-fuel ratio to be stoichiometric, thereby completing the series of programs of the deterioration diagnosis method.

[0077] In addition, when the RO2 sensor 27 is deteriorated on the lean side, the first elapsed time β does not fall below the threshold value β1, i.e., it is equal to or greater than the threshold value β1, as in steps S9 and S11 described above (see the dashed line of the first elapsed time β in FIG. 6). In addition, when the RO2 sensor 27 is deteriorated on the rich side, the second elapsed time γ does not fall below the threshold value γ1, i.e., it is equal to or greater than the threshold value γ1, as in steps S21 and S23 described above (see the dashed line of the second elapsed time γ in FIG. 6). In both cases of the lean side and the rich side, when the RO2 sensor 27 is deteriorated, as shown by the dashed line of the RO2 voltage in FIG. 6, it can be seen that the responsiveness of the RO2 sensor 27 to shift to the lean side or rich side becomes worse than that of the solid line in the normal state (the gradient of the curve becomes gentler, as shown by the dashed line of the RO2 voltage in FIG. 6). In addition, due to the effect of response degradation of the RO2 sensor 27, the transition control of the target air-fuel ratio between rich and lean also has a time lag, as shown by the dashed line of the target air-fuel ratio in FIG. 6, compared to the solid line in normal times.

[0078] Also, when the catalyst 25 is deteriorated, as in steps S13 and S15 above, the accumulated oxygen amount α does not exceed the threshold value α1, i.e., it is equal to or less than the threshold value α1 (see the dashed line of the accumulated oxygen amount α in FIG. 7). In this way, as the oxygen storage capacity of the catalyst 25 deteriorates, a time lag occurs in the rich-lean transition control of the target air-fuel ratio, as shown by the dashed line of the target air-fuel ratio in FIG. 7, compared to the solid line in the normal state. At the same time, a time lag occurs in the RO2 voltage, as shown by the dashed line of the RO2 voltage in FIG. 7, compared to the solid line in the normal state.

[0079] (Features of the first embodiment) (1) In the deterioration diagnosis device for the engine exhaust system of the first embodiment, the controller 16 has a configuration (air-fuel ratio control unit 31, time measurement unit 32, integrating unit 33, sensor deterioration determination unit 34, and catalyst deterioration determination unit 35) that can determine deterioration of the catalyst 25 and the rear air-fuel ratio sensor 27 in one lean period. In this configuration, after the air-fuel ratio control unit 31 shifts the target air-fuel ratio to lean, the time measurement unit 32 measures a first elapsed time β from when the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below a predetermined first threshold value C to when the measurement value falls below a predetermined second threshold value D set to be leaner than the first threshold value C. The sensor deterioration determination unit 34 determines deterioration of the rear air-fuel ratio sensor 27 based on the first elapsed time β. On the other hand, the integration unit 33 obtains an integrated oxygen amount α by integrating the amount of oxygen stored in the catalyst 25 after the target air-fuel ratio shifts to lean until the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below a predetermined third threshold B that is set to be leaner than the second threshold D. The catalyst deterioration determination unit 35 determines deterioration of the catalyst 25 based on the integrated oxygen amount α.

[0080] In addition, in correspondence with the above-mentioned deterioration diagnosis device, the deterioration diagnosis method for the engine exhaust system of the first embodiment includes the following steps (1) to (5): (1) a lean transition step for transitioning a target air-fuel ratio of the engine 2 to lean; (2) a time measurement step for measuring a first elapsed time β from when the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below a first threshold value C until it falls below a second threshold value D set to be leaner than the first threshold value C after the target air-fuel ratio transitions to lean; (3) a sensor deterioration determination step for determining deterioration of the rear air-fuel ratio sensor 27 based on the first elapsed time β; (4) an oxygen amount integration step for integrating the amount of oxygen stored in the catalyst 25 until the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 falls below a predetermined third threshold value B set to be leaner than the second threshold value D after the target air-fuel ratio transitions to lean to obtain an integrated oxygen amount α; and (5) a catalyst deterioration determination step for determining deterioration of the catalyst 25 based on the integrated oxygen amount α.

[0081] In the deterioration diagnosis device and deterioration diagnosis method as described above, it is possible to set, within the common lean period, the period during which the rear air-fuel ratio sensor 27 changes and the period during which oxygen is stored in the catalyst 25, so that it is possible to determine the deterioration of the rear air-fuel ratio sensor 27 and the catalyst 25 with a single shift to lean. As a result, it is possible to reduce the number of times that the air-fuel ratio is forcibly shifted to lean in order to determine the deterioration of the rear air-fuel ratio sensor 27 and the catalyst 25, and to suppress the deterioration of exhaust gas components accompanying the deterioration determination of the air-fuel ratio sensor and the catalyst.

[0082] (2) In the deterioration diagnosis device for an engine exhaust system of the first embodiment, a time measurement unit 32 measures a second elapsed time γ from when the measurement value (RO2 voltage) of the rear air-fuel ratio sensor 27 exceeds the second threshold value D until it exceeds the first threshold value C after the air-fuel ratio control unit 31 shifts the target air-fuel ratio from lean to rich. A sensor deterioration determination unit 34 determines deterioration of the rich side of the rear air-fuel ratio sensor 27 based on the second elapsed time γ.

[0083] According to this configuration, it is possible to determine not only the deterioration of the rear air-fuel ratio sensor 27 on the lean side, but also the deterioration of the rear air-fuel ratio sensor 27 on the rich side.

[0084] (3) In the deterioration diagnosis device for the engine exhaust system of the first embodiment, the sensor deterioration determination unit 34 may determine that the rear air-fuel ratio sensor 27 is deteriorated when it is determined that either one of the lean side judgment result and the rich side judgment result is deteriorated.

[0085] According to this configuration, if it is determined that either one of the lean side judgment result and the rich side judgment result is deteriorated, it is determined that the rear air-fuel ratio sensor 27 is deteriorated, so that it is possible to more accurately determine the deterioration of the rear air-fuel ratio sensor 27.

[0086] (4) The deterioration diagnosis device for an engine / exhaust system of the first embodiment is applied to perform deterioration diagnosis for an engine / exhaust system of an HV 1 that is equipped with an engine 2 and a motor 4 as drive sources.

[0087] In the HV vehicle 1, the time during which the engine is not running and exhaust gas is not discharged, such as during deceleration, is longer than in a gasoline vehicle, and so the time during which deterioration diagnosis of the rear air-fuel ratio sensor 27 and catalyst 25 of the engine exhaust system can be performed while the vehicle is running is shorter. However, by using the deterioration diagnosis device described above, it is possible to determine the deterioration of the rear air-fuel ratio sensor 27 and catalyst 25 in the HV vehicle 1 by shifting to lean once in a short period of time while the engine is running, and it is possible to suppress the deterioration of exhaust gas components. As a result, the HV vehicle 1 can be driven in a more environmentally friendly manner.

[0088] Although the deterioration diagnosis device of the above embodiment is applied to the deterioration diagnosis of the engine exhaust system of a hybrid vehicle 1, the present invention is not limited to this and can be applied to the deterioration diagnosis of the engine exhaust system of a gasoline vehicle equipped with only a gasoline engine.

[0089] Second embodiment In the deterioration diagnosis device of the above-described first embodiment, the accumulation unit 33 directly calculates the lean side accumulated oxygen amount α, and the catalyst deterioration judgment unit 35 judges the deterioration of the catalyst 25 based on the accumulated oxygen amount α, but the present invention is not limited to this.

[0090] In a degradation diagnosis device of a second embodiment described below, an integrating unit 33 may integrate, as a parameter corresponding to the integrated oxygen amount α, the fuel consumption amount required to consume the oxygen stored in the catalyst 25 after the air-fuel ratio control unit 31 shifts the target air-fuel ratio from lean to rich. In this case, a catalyst degradation determination unit 35 determines the degradation of the catalyst 25 based on the fuel consumption amount corresponding to the integrated oxygen amount α. Note that other configurations of the degradation diagnosis device of the second embodiment (specifically, the catalyst 25, the rear air-fuel ratio sensor 27, the air-fuel ratio control unit 31, the time measurement unit 32, and the sensor degradation determination unit 34) are common to the configurations of the degradation diagnosis device of the first embodiment, and therefore description thereof will be omitted.

[0091] In this configuration, the integrating unit 33 integrates the amount of fuel consumption required to consume the oxygen stored in the catalyst 25 after the air-fuel ratio control unit 31 shifts the target air-fuel ratio from lean to rich, as a parameter corresponding to the integrated oxygen amount α. This makes it possible to indirectly determine the integrated oxygen amount α of the catalyst 25 during the lean period from the amount of fuel consumption that consumes the oxygen stored in the catalyst 25 after the shift from lean to rich. Therefore, it becomes possible for the catalyst deterioration determining unit 35 to determine deterioration of the catalyst 25 based on the amount of fuel consumption corresponding to the integrated oxygen amount α.

[0092] (Description of engine exhaust system deterioration diagnosis method according to the second embodiment) As in the second embodiment, when determining deterioration of the catalyst 25 based on the fuel consumption amount corresponding to the accumulated oxygen amount α, it is possible to perform this together with the deterioration determination of the rear air-fuel ratio sensor 27 (RO2 sensor 27) during a series of rich-lean transitions by the following procedure.

[0093] <Specific examples of deterioration diagnosis methods> A specific example of the deterioration diagnosis method for an engine exhaust system according to the second embodiment will be described below in detail with reference to the flowcharts of Figures 8-9 and the normal state diagnosis chart of Figure 10. In this description as well, the rear air-fuel ratio sensor 27 will be referred to as the "RO2 sensor 27" as shown in Figures 8-10.

[0094] The flowcharts of FIGS. 8 and 9 are different from the flowcharts of FIGS. 3 and 4 above in the procedure for determining deterioration of the catalyst 25, but other procedures, such as the procedure for determining deterioration of the RO2 sensor 27, are common to both.

[0095] That is, when the deterioration diagnosis program is started, in steps S31 to S33 of the flowchart in FIG. 8, similar to steps S1 to S3 of the flowchart in FIG. 3 above, the target air-fuel ratio is controlled to transition to rich (step S31), the system waits until the RO2 voltage of the RO2 sensor 27 exceeds the reference voltage A (step S32), and the target air-fuel ratio is controlled to transition to lean (step S33).

[0096] 8, the integrating unit 33 starts to calculate the catalyst stored oxygen amount ε, which is the amount of oxygen stored in the catalyst 25 when the target air-fuel ratio is lean. The catalyst stored oxygen amount ε is calculated by a calculation method different from the integrated oxygen amount α of the first embodiment, for example, by using the air flow rate obtained from the air flow sensor 23, the air-fuel ratio (specifically, the oxygen concentration) upstream of the catalyst 25 obtained from the linear air-fuel ratio sensor 26, and other parameters.

[0097] 8, the same processes as steps S5 to S11 of the flowchart in FIG. 3 are performed to determine the deterioration of the RO2 sensor 27. That is, the RO2 sensor 27 waits until the RO2 voltage of the RO2 sensor 27 falls below a first threshold value C, i.e., a reference voltage C (step S35), and when the RO2 voltage of the RO2 sensor 27 falls below the reference voltage C, the measurement of the first elapsed time β (see FIG. 10) is started (step S36), and the measurement of the first elapsed time β is continued until the RO2 voltage of the RO2 sensor 27 falls below a second threshold value D, i.e., a reference voltage D (step S37), and when the RO2 voltage of the RO2 sensor 27 falls below the reference voltage D, the time measurement unit 32 ends the measurement of the first elapsed time β (step 38). Next, it is determined whether the first elapsed time β has fallen below a threshold value β1 (see FIG. 10) (step S39), and if it is determined that it has fallen below the threshold value, it is determined that the RO2 sensor 27 is normal (step S40). On the other hand, if it is determined that it has not fallen below the threshold value (i.e., it is equal to or greater than the threshold value β1), it is determined that the RO2 sensor 27 has deteriorated (step S41).

[0098] In step S42, the integrating unit 33 continues integrating the amount of oxygen occluded in the catalyst ε until the measurement value (RO2 voltage) of the RO2 sensor 27 falls below the third threshold value B, that is, the reference voltage B.

[0099] When the catalyst stored oxygen amount ε exceeds the reference value ε1 (when step S34 is Yes), in step S44 of FIG. 9, the air-fuel ratio control unit 31 controls the target air-fuel ratio to shift from lean to rich.

[0100] After the target air-fuel ratio shifts to the rich side, in step S45, the integrator 33 starts to calculate the fuel consumption amount δ required to consume the oxygen stored in the catalyst 25 as a parameter corresponding to the integrated oxygen amount. The fuel consumption amount δ is calculated, for example, by integrating the fuel injection amount set according to the operating state of the engine 2.

[0101] After that, in step S46, the integrating unit 33 continues integrating the fuel consumption amount δ until the RO2 voltage of the RO2 sensor 27 exceeds the third threshold value B, that is, the reference voltage B.

[0102] When the RO2 voltage of the RO2 sensor 27 exceeds the reference voltage B, the integrating unit 33 ends the calculation of the fuel consumption amount δ in step S47.

[0103] Next, in step S48, the catalyst deterioration determination unit 35 determines whether the fuel consumption amount δ has exceeded the threshold value δ1 (see FIG. 10). If the catalyst deterioration determination unit 35 determines that the fuel consumption amount δ has exceeded the threshold value δ1 (see FIG. 10), it determines that the catalyst 25 is normal, as in step S49, whereas if the catalyst deterioration determination unit 35 determines that the fuel consumption amount δ has not exceeded the threshold value δ1 (see FIG. 10) (i.e., is equal to or less than the threshold value δ1), it determines that the catalyst 25 has deteriorated (deteriorated in terms of oxygen storage capacity), as in step S50.

[0104] In the following steps S51 to S58, deterioration determination on the rich side of the RO2 sensor 27 is performed in the same manner as in steps S17 to S24 in FIG.

[0105] That is, the RO2 sensor 27 waits until the RO2 voltage of the RO2 sensor 27 exceeds the second threshold value D, i.e., the reference voltage D (step S51), and when the RO2 voltage of the RO2 sensor 27 exceeds the reference voltage D, measurement of the second elapsed time γ (see FIG. 10) is started (step S52), and measurement of the second elapsed time γ is continued until the RO2 voltage of the RO2 sensor 27 exceeds the first threshold value C, i.e., the reference voltage C (step S53), and when the RO2 voltage of the RO2 sensor 27 exceeds the reference voltage C, measurement of the second elapsed time γ is terminated (step S54). Next, it is determined whether the second elapsed time γ is below the threshold value γ1 (see FIG. 10) (step S55), and when it is determined that the second elapsed time γ is below the threshold value γ1, it is determined that the RO2 sensor 27 is normal (step S56), and when it is determined that the second elapsed time γ is not below the threshold value γ1 (i.e., it is equal to or greater than the threshold value γ1), it is determined that the RO2 sensor 27 is deteriorated (step S57). Thereafter, in step S58, the target air-fuel ratio is controlled to become stoichiometric, and the series of programs of the deterioration diagnosis method is completed.

[0106] In the deterioration diagnosis method shown in the flowcharts of FIGS. 8-9, as in the diagnosis method of FIGS. 3-4, when the RO2 sensor 27 is deteriorated on the lean side, the first elapsed time β becomes equal to or greater than the threshold value β1, as shown in FIG. 11 (see the dashed line of the first elapsed time β in FIG. 11). When the RO2 sensor 27 is deteriorated on the rich side, the second elapsed time γ becomes equal to or greater than the threshold value γ1 (see the dashed line of the second elapsed time γ in FIG. 11). When the RO2 sensor 27 is deteriorated in both the lean side and the rich side, as shown by the dashed line of the RO2 voltage in FIG. 11, the responsiveness of the RO2 sensor 27 to shift to the lean side or rich side becomes worse than that of the solid line in the normal state (as shown by the dashed line of the RO2 voltage in FIG. 11, the gradient of the curve becomes gentler).

[0107] Also, when the catalyst 25 is deteriorated, as in steps S48 and S50, the fuel consumption amount δ does not exceed the threshold value δ1, that is, it is equal to or less than the threshold value δ1 (see the dashed line of the fuel consumption amount δ in FIG. 12). That is, it is possible to indirectly know that the integrated oxygen amount corresponding to the fuel consumption amount δ is decreasing. In this way, as the oxygen storage capacity of the catalyst 25 deteriorates, a time lag occurs in the transition control between the rich and lean of the target air-fuel ratio, as shown by the dashed line of the target air-fuel ratio in FIG. 12, compared with the solid line in the normal state. At the same time, a time lag occurs in the RO2 voltage, as shown by the dashed line of the RO2 voltage in FIG. 12, compared with the solid line in the normal state. On the other hand, it can be seen that the catalyst storage oxygen amount ε stored in the catalyst 25 on the lean side reaches a predetermined reference value ε1, regardless of whether the catalyst 25 is normal or deteriorated, even when comparing the solid line in the normal state and the dashed line in the deteriorated state shown in FIG. 12.

[0108] That is, in the deterioration diagnosis device and deterioration diagnosis method of the second embodiment, deterioration of the catalyst 25 is determined based on the amount of fuel consumption required to consume the oxygen stored in the catalyst 25 on the rich side while ensuring the same deterioration determination conditions by setting the catalyst stored oxygen amount ε stored in the catalyst 25 on the lean side to a state where it has reached a predetermined reference value ε1. Therefore, since this deterioration determination of the catalyst 25 does not depend on the measurement value of the rear air-fuel ratio sensor 27, i.e., the RO2 voltage of the RO2 sensor 27, it is possible to accurately determine deterioration of the catalyst 25 without being affected by deterioration of the RO2 sensor 27, etc. [Explanation of symbols]

[0109] 1 Hybrid vehicles (HV vehicles) 2 Engine 16 Controller (control unit) 24 Exhaust passage 25 Catalyst 26 Linear air-fuel ratio sensor 27 Rear air-fuel ratio sensor (air-fuel ratio sensor) 31 Air-fuel ratio control unit 32 Time measurement section 33 Integration Section 34 Sensor deterioration determination unit 35 Catalyst deterioration determination section

Claims

1. A catalyst disposed in an exhaust passage of the engine for purifying exhaust gas; an air-fuel ratio sensor disposed in the exhaust passage at a position downstream of the catalyst for measuring an air-fuel ratio of the exhaust gas; a control unit for determining deterioration of the catalyst and the air-fuel ratio sensor; A deterioration diagnosis device for an engine exhaust system comprising: The control unit an air-fuel ratio control unit that controls the target air-fuel ratio of the engine to shift to either rich or lean; a time measurement unit that measures a first elapsed time from when a measurement value of the air-fuel ratio sensor falls below a predetermined first threshold value until the measurement value falls below a predetermined second threshold value that is set to be leaner than the first threshold value after the air-fuel ratio control unit shifts the target air-fuel ratio to lean; a sensor deterioration determination unit that determines deterioration of the air-fuel ratio sensor based on the first elapsed time; an integrating unit that calculates an integrated oxygen amount obtained by integrating an amount of oxygen stored in the catalyst until the measurement value of the air-fuel ratio sensor falls below a predetermined third threshold value that is set on the leaner side than the second threshold value after the target air-fuel ratio has shifted to the lean side, or a parameter corresponding to the integrated oxygen amount; a catalyst deterioration determination unit that determines deterioration of the catalyst based on the integrated oxygen amount or the parameter corresponding to the integrated oxygen amount; An engine exhaust system deterioration diagnosis device comprising:

2. 2. The engine exhaust system deterioration diagnosis device according to claim 1, the integrating unit integrates, as the parameter corresponding to the integrated oxygen amount, a fuel consumption amount required for consuming the oxygen stored in the catalyst after the air-fuel ratio control unit shifts the target air-fuel ratio from lean to rich, the catalyst deterioration determination unit determines deterioration of the catalyst based on the fuel consumption amount corresponding to the integrated oxygen amount.

1. An engine exhaust system deterioration diagnosis device comprising:

3. 3. The engine exhaust system deterioration diagnosis device according to claim 1, the time measurement unit measures a second elapsed time from when the measurement value of the air-fuel ratio sensor exceeds the second threshold value until when the measurement value exceeds the first threshold value after the air-fuel ratio control unit shifts the target air-fuel ratio from the lean to the rich, the sensor deterioration determination unit determines deterioration of the rich side of the air-fuel ratio sensor based on the second elapsed time.

1. An engine exhaust system deterioration diagnosis device comprising:

4. 4. The engine exhaust system deterioration diagnosis device according to claim 3, the sensor deterioration determination unit determines that the air-fuel ratio sensor is deteriorated when determining that either one of the lean side determination result and the rich side determination result is deteriorated. Characterized by An engine exhaust system deterioration diagnosis device.

5. The deterioration diagnosis device for an engine exhaust system according to any one of claims 1 to 4, The present invention is applied to a deterioration diagnosis of an engine exhaust system of a hybrid vehicle having a motor as well as the engine as a driving source.

1. An engine exhaust system deterioration diagnosis device comprising:

6. A catalyst disposed in an exhaust passage of the engine for purifying exhaust gas; an air-fuel ratio sensor disposed in the exhaust passage at a position downstream of the catalyst and measuring an air-fuel ratio of exhaust gas, comprising: a lean transition step for transitioning a target air-fuel ratio of the engine to a leaner air-fuel ratio; a time measurement step of measuring a first elapsed time from when a measurement value of the air-fuel ratio sensor falls below a first threshold value until the measurement value falls below a second threshold value set to be leaner than the first threshold value after the target air-fuel ratio has shifted to the lean side; a sensor deterioration determination step for determining deterioration of the air-fuel ratio sensor based on the first elapsed time; an oxygen amount integrating step for integrating the amount of oxygen stored in the catalyst until the measurement value of the air-fuel ratio sensor falls below a predetermined third threshold value set on the leaner side than the second threshold value after the target air-fuel ratio has shifted to the lean side, or for obtaining a parameter corresponding to the integrated oxygen amount; a catalyst deterioration determination step for determining deterioration of the catalyst based on the integrated oxygen amount or a parameter corresponding to the integrated oxygen amount; 1. A method for diagnosing deterioration of an engine exhaust system, comprising:

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