Diagnostic device

Abstract

To accurately diagnose deterioration of a catalyst.SOLUTION: A diagnostic system includes: a control section for resuming fuel supply to an engine in a rich atmosphere in which an air-fuel ratio is richer than a theoretical air-fuel ratio after fuel cut for stopping fuel supply to the engine; a calculation section for calculating oxygen consumption total amount that is total amount of oxygen consumption of a catalyst after resumption of the fuel supply to the engine; and a diagnosis section for diagnosing deterioration of the catalyst on the basis of the oxygen consumption total amount calculated by the calculation section. The calculation section calculates first oxygen consumption that is oxygen consumption before an air-fuel ratio detected by an air-fuel ratio sensor detecting an air-fuel ratio of exhaust gas flowing into the catalyst becomes richer than the theoretical air-fuel ratio on the basis of fuel injection amount, calculates second oxygen consumption that is oxygen consumption after the air-fuel ratio detected by the air-fuel ratio sensor becomes richer than the theoretical air-fuel ratio on the basis of the air-fuel ratio of exhaust gas, and calculates a total value of the first oxygen consumption and the second oxygen consumption as the oxygen consumption total amount.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a diagnostic apparatus.

Background Art

[0002] In recent years, techniques for diagnosing the deterioration of catalysts such as three-way catalysts provided in an exhaust passage connected to an engine have been proposed. For example, as disclosed in Patent Document 1, there is a method of diagnosing the deterioration of a catalyst by determining whether the oxygen storage capacity (OSC) of the catalyst has decreased.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a method of diagnosing deterioration focusing on the OSC of a catalyst, after fuel cut, the supply of fuel to the engine is restarted in a rich atmosphere, the total amount of oxygen consumption of the catalyst after the restart of fuel supply, which is the total amount of oxygen consumption, is calculated, and the deterioration of the catalyst is diagnosed based on the calculated total amount of oxygen consumption. In this case, when the calculated total amount of oxygen consumption is smaller than the assumed value, it is diagnosed that the catalyst is deteriorated.

[0005] Here, in the deterioration diagnosis and the like disclosed in Patent Document 1, the calculation start timing of the oxygen consumption amount is determined based on the detection result of an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas flowing into the catalyst. Specifically, the timing when the air-fuel ratio detected by the air-fuel ratio sensor switches from lean to rich is determined as the calculation start timing of the oxygen consumption amount, and the integrated value of the oxygen consumption amount per unit time at each time point after that time point is calculated as the total oxygen consumption amount. Therefore, when a response delay occurs in the air-fuel ratio sensor, the calculation start timing of the oxygen consumption amount is delayed, so the total calculated oxygen consumption amount becomes small, and the diagnostic accuracy of the deterioration diagnosis decreases.

[0006] Therefore, an object of the present invention is to provide a diagnostic device capable of accurately diagnosing the deterioration of a catalyst.

Means for Solving the Problems

[0007] In order to solve the above problems, a diagnostic device according to an embodiment of the present invention is a diagnostic device for a vehicle, comprising an engine, an exhaust passage connected to the engine, a catalyst provided in the exhaust passage, and an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas flowing into the catalyst, a control unit that resumes the supply of fuel to the engine in a rich atmosphere richer than the stoichiometric air-fuel ratio after a fuel cut that stops the supply of fuel to the engine, a calculation unit that calculates a total oxygen consumption amount, which is the total amount of oxygen consumption of the catalyst after the resumption of the supply of fuel to the engine, a diagnostic unit that diagnoses the deterioration of the catalyst based on the total oxygen consumption amount calculated by the calculation unit, and is provided with The calculation unit calculates a first oxygen consumption amount, which is the oxygen consumption amount before the air-fuel ratio detected by the air-fuel ratio sensor becomes richer than the stoichiometric air-fuel ratio, based on the fuel injection amount, Calculate a second oxygen consumption amount, which is the oxygen consumption amount after the air-fuel ratio detected by the air-fuel ratio sensor becomes richer than the stoichiometric air-fuel ratio, based on the air-fuel ratio of the exhaust gas. Calculate the total value of the first oxygen consumption amount and the second oxygen consumption amount as the total oxygen consumption amount.

Advantages of the Invention

[0008] According to the present invention, it becomes possible to accurately diagnose the deterioration of the catalyst.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The specific dimensions, materials, numerical values, etc. shown in such embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals to omit duplicate description, and elements not directly related to the present invention are not shown.

[0011] <Configuration of the Intake and Exhaust System> Referring to FIGS. 1 and 2, the configuration of the intake and exhaust system 1 according to an embodiment of the present invention will be described.

[0012] FIG. 1 is a schematic diagram showing a schematic configuration of the intake and exhaust system 1. The intake and exhaust system 1 is mounted on the vehicle 100. As shown in FIG. 1, the intake and exhaust system 1 includes an engine 10, an intake passage 20, an exhaust passage 30, and a diagnostic device 50.

[0013] The engine 10 is, for example, a spark ignition internal combustion engine. The engine 10 has one or a plurality of cylinders 11. In FIG. 1, only one cylinder 11 out of the plurality of cylinders 11 provided in the engine 10 is shown for ease of understanding. A piston 12 is slidably provided in the cylinder 11. A combustion chamber 13 is formed inside the cylinder 11. The combustion chamber 13 is partitioned by the inner surface of the cylinder 11 and the crown surface of the piston 12. An ignition plug 14 facing the combustion chamber 13 is provided in the cylinder 11. Further, a fuel injection valve 15 for injecting fuel toward the combustion chamber 13 is provided in the cylinder 11. An air-fuel mixture containing air and fuel is formed in the combustion chamber 13. The air-fuel mixture is ignited by the ignition plug 14 and burns. Thereby, the piston 12 in each cylinder 11 performs a linear reciprocating motion, and power is transmitted to a crankshaft connected to each piston 12.

[0014] Note that the fuel injection valve 15 is not limited to a type that directly injects fuel into the combustion chamber 13. For example, the fuel injection valve 15 may be provided in the intake passage 20 and inject fuel into the intake passage 20. In this case, the fuel is inhaled into the combustion chamber 13 together with the intake air.

[0015] Each combustion chamber 13 of the engine 10 communicates with the intake passage 20 via an intake port and communicates with the exhaust passage 30 via an exhaust port. An intake valve 16 capable of opening and closing the intake port and an exhaust valve 17 capable of opening and closing the exhaust port are provided in each cylinder 11. By driving the intake valve 16 and the exhaust valve 17, supply of intake air to the combustion chamber 13 and discharge of exhaust from the combustion chamber 13 are performed.

[0016] The intake passage 20 is connected to the engine 10 and is a passage through which the air supplied to the combustion chamber 13 of the engine 10 flows. An intake port (not shown) for taking in outside air from outside the vehicle 100 is provided at the upstream end of the intake passage 20. An air filter 21 is provided on the downstream side of the intake port in the intake passage 20. The air filter 21 removes foreign substances contained in the air flowing through the intake passage 20. A throttle valve 22 is provided on the downstream side of the air filter 21 in the intake passage 20. The throttle valve 22 adjusts the flow rate of the intake air sent to the engine 10 through the intake passage 20. The flow rate of the intake air sent to the engine 10 changes according to the opening degree of the throttle valve 22.

[0017] A surge tank 23 is provided on the downstream side of the throttle valve 22 in the intake passage 20. The intake air sent to the engine 10 is temporarily stored in the surge tank 23. An intake manifold (not shown) is provided on the downstream side of the surge tank 23 in the intake passage 20. The intake manifold branches toward each cylinder 11 of the engine 10 and is connected to the intake port of each cylinder 11.

[0018] In the intake passage 20, outside air is taken in from the intake port. The taken-in air passes through the air filter 21, then passes through the throttle valve 22 and the surge tank 23 in sequence, and is sent to the engine 10.

[0019] An air flow meter 24 is provided in the intake passage 20. The air flow meter 24 detects the intake air amount, which is the flow rate of the air inhaled into the intake passage 20 and flowing through the intake passage 20. The air flow meter 24 is provided, for example, between the air filter 21 and the throttle valve 22.

[0020] The exhaust passage 30 is connected to the engine 10 and is a passage through which the exhaust discharged from the combustion chamber 13 of the engine 10 flows. An exhaust port (not shown) for discharging the exhaust to the outside of the vehicle 100 is provided at the downstream end of the exhaust passage 30. An exhaust manifold (not shown) is provided in the exhaust passage 30. The exhaust manifold branches toward each cylinder 11 of the engine 10 and is connected to the exhaust port of each cylinder 11.

[0021] A catalyst 31 is provided on the downstream side of the exhaust manifold in the exhaust passage 30. The catalyst 31 is a three-way catalyst. The catalyst 31 oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust and reduces NOx in the exhaust to purify these harmful components into harmless water vapor (H2O), carbon dioxide (CO2), and nitrogen (N2). However, the catalyst 31 only needs to have at least the function of a three-way catalyst. For example, the catalyst 31 may have the function of a gasoline particulate filter (GPF) in addition to the function of a three-way catalyst.

[0022] In the exhaust passage 30, the exhaust discharged from the engine 10 passes through the catalyst 31 and is discharged from the exhaust port.

[0023] An air-fuel ratio sensor 32, a temperature sensor 33, and an oxygen sensor 34 are provided in the exhaust passage 30. The air-fuel ratio sensor 32 detects the air-fuel ratio of the exhaust flowing into the catalyst 31. The air-fuel ratio sensor 32 is provided upstream of the catalyst 31 in the exhaust passage 30. The temperature sensor 33 detects the temperature of the catalyst 31. The temperature sensor 33 is provided near the catalyst 31. The oxygen sensor 34 detects the oxygen concentration in the exhaust discharged from the catalyst 31. The oxygen sensor 34 is provided downstream of the catalyst 31 in the exhaust passage 30.

[0024] The vehicle 100 is provided with an accelerator opening sensor 41 and a vehicle speed sensor 42. The accelerator opening sensor 41 detects the accelerator opening corresponding to the operation amount of the accelerator operation by the driver. The vehicle speed sensor 42 detects the vehicle speed of the vehicle 100.

[0025] The diagnostic device 50 performs a deterioration diagnosis of the catalyst 31. The deterioration diagnosis means a series of processes for diagnosing the deterioration of the catalyst 31. Here, the catalyst 31 has an oxygen storage capacity (OSC). The OSC is realized by components such as ceria (CeO2) contained in the catalyst 31. The diagnostic device 50 performs a deterioration diagnosis focusing on the OSC of the catalyst 31. In the deterioration diagnosis by the diagnostic device 50, when the OSC of the catalyst 31 drops below the assumption, it is diagnosed that the catalyst 31 has deteriorated.

[0026] In a rich atmosphere richer than the stoichiometric air-fuel ratio, the purification efficiency of hydrocarbons (HC) and carbon monoxide (CO) by the catalyst 31 decreases. On the other hand, in a lean atmosphere leaner than the stoichiometric air-fuel ratio, the purification efficiency of NOx by the catalyst 31 decreases. Therefore, in order to balance the purification efficiency of hydrocarbons (HC) and carbon monoxide (CO) with the purification efficiency of NOx, it is necessary to control the air-fuel ratio of the exhaust gas flowing into the catalyst 31 near the stoichiometric air-fuel ratio. As described above, the catalyst 31 has an OSC. Therefore, in a rich atmosphere where oxygen is insufficient, oxygen is released from the catalyst 31. On the other hand, in a lean atmosphere where oxygen is excessive, oxygen is stored by the catalyst 31. Thereby, the air-fuel ratio of the exhaust gas flowing into the catalyst 31 is controlled near the stoichiometric air-fuel ratio.

[0027] The diagnostic device 50 includes one or more processors 51 and one or more memories 52 connected to the processor 51. The processor 51 includes, for example, a CPU (Central Processing Unit). The memory 52 includes, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory). The ROM is a storage element that stores programs and arithmetic parameters used by the CPU. The RAM is a storage element that temporarily stores data such as variables and parameters used in the processes executed by the CPU.

[0028] The diagnostic device 50 communicates with each device provided in the intake and exhaust system 1 (for example, ignition plug 14, fuel injection valve 15, throttle valve 22, air flow meter 24, air-fuel ratio sensor 32, temperature sensor 33, oxygen sensor 34, accelerator opening sensor 41, vehicle speed sensor 42, etc.). The communication between the diagnostic device 50 and each device is realized using, for example, CAN (Controller Area Network) communication.

[0029] FIG. 2 is a block diagram showing an example of the functional configuration of the diagnostic device 50. For example, as shown in FIG. 2, the diagnostic device 50 includes an acquisition unit 50a, a control unit 50b, a calculation unit 50c, and a diagnosis unit 50d. Note that various processes including the processes described below performed by the acquisition unit 50a, the control unit 50b, the calculation unit 50c, or the diagnosis unit 50d can be executed by the processor 51. Specifically, by the processor 51 executing the program stored in the memory 52, various processes are executed.

[0030] The acquisition unit 50a acquires various information used in the processes performed by the control unit 50b and the calculation unit 50c, and outputs it to the control unit 50b and the calculation unit 50c. For example, the acquisition unit 50a acquires information from the air flow meter 24, the air-fuel ratio sensor 32, the temperature sensor 33, the oxygen sensor 34, the accelerator opening sensor 41, and the vehicle speed sensor 42.

[0031] The control unit 50b controls the operation of each device in the intake and exhaust system 1. For example, the control unit 50b controls the ignition timing by the ignition plug 14. Also, for example, the control unit 50b controls the fuel injection timing and the fuel injection amount in the fuel injection by the fuel injection valve 15. The fuel injection amount is the injection amount of the fuel supplied to the engine 10. Also, for example, the control unit 50b controls the opening degree of the throttle valve 22.

[0032] Here, the control unit 50b executes a fuel cut that stops the supply of fuel to the engine 10 according to the driving state of the vehicle 100. For example, the control unit 50b executes the fuel cut when the vehicle 100 is decelerating and the accelerator opening is zero. Then, after the fuel cut, the control unit 50b executes catalyst neutralization control to resume the supply of fuel to the engine 10 in a rich atmosphere that is richer than the stoichiometric air-fuel ratio. The catalyst neutralization control is control for releasing oxygen from the catalyst 31 in which the oxygen storage amount has become excessive during the fuel cut. The deterioration diagnosis by the diagnostic device 50 is performed after the resumption of the supply of fuel to the engine 10. The deterioration diagnosis by the diagnostic device 50 is performed by the calculation unit 50c and the diagnostic unit 50d.

[0033] The calculation unit 50c calculates the total oxygen consumption amount, which is the total amount of oxygen consumption of the catalyst 31 after the resumption of the supply of fuel to the engine 10. The total oxygen consumption amount calculated by the calculation unit 50c is the total amount of oxygen released from the catalyst 31 by the catalyst neutralization control.

[0034] The diagnostic unit 50d diagnoses the deterioration of the catalyst 31 based on the total oxygen consumption amount calculated by the calculation unit 50c. Here, the total oxygen consumption amount calculated by the calculation unit 50c corresponds to the total amount of oxygen stored in the catalyst 31 during the fuel cut. Therefore, when the calculated total oxygen consumption amount is smaller than the assumed value, the diagnostic unit 50d determines that the OSC of the catalyst 31 has decreased more than expected and diagnoses that the catalyst 31 has deteriorated.

[0035] Note that the functions of the diagnostic device 50 according to the present embodiment may be divided into a plurality of devices, or a plurality of functions may be realized by one device. When the functions of the diagnostic device 50 are divided into a plurality of devices, the plurality of devices may be connected to each other via a communication bus such as CAN.

[0036] As described above, in the diagnostic device 50, the calculation unit 50c calculates the total amount of oxygen consumption of the catalyst 31 after the resumption of fuel supply to the engine 10. The diagnostic unit 50d diagnoses the deterioration of the catalyst 31 based on the total amount of oxygen consumption calculated by the calculation unit 50c. Here, in the diagnostic device 50 according to the present embodiment, by devising a method for calculating the total amount of oxygen consumption of the catalyst 31, it is possible to accurately diagnose the deterioration of the catalyst 31.

[0037] <Operation of Diagnostic Device> Subsequently, with reference to FIGS. 3 to 5, the operation of the diagnostic device 50 according to the embodiment of the present invention will be described.

[0038] FIG. 3 is a flowchart showing an example of the overall flow of processing performed by the diagnostic device 50. The control flow shown in FIG. 3 is repeatedly started at predetermined time intervals, for example, after completion.

[0039] When the control flow shown in FIG. 3 is started, first, in step S101, the diagnostic device 50 determines whether fuel cut is being executed. If it is determined that fuel cut is being executed (YES in step S101), the process proceeds to step S102. On the other hand, if it is determined that fuel cut is not being executed (NO in step S101), the control flow shown in FIG. 3 ends.

[0040] If it is determined YES in step S101, in step S102, the diagnostic device 50 determines whether the fuel cut has ended. If it is determined that the fuel cut has ended (YES in step S102), the process proceeds to step S103. On the other hand, if it is determined that the fuel cut has not ended (NO in step S102), step S102 is repeated.

[0041] If it is determined as YES in step S102, in step S103, the control unit 50b executes catalyst neutralization control. Thereby, the supply of fuel to the engine 10 is resumed in a rich atmosphere that is richer than the stoichiometric air-fuel ratio. Note that the control unit 50b can control the air-fuel ratio of the air-fuel mixture formed in the cylinder 11 of the engine 10, for example, by controlling the fuel injection amount and the opening degree of the throttle valve 22.

[0042] Next, in step S104, the diagnostic device 50 determines whether or not the deterioration diagnosis of the catalyst 31 has not been performed. Steps S105 to S108 described later correspond to the process of the deterioration diagnosis.

[0043] For example, the diagnostic device 50 performs the deterioration diagnosis once during the period from when the ignition switch is turned ON to when it is turned OFF. The diagnostic device 50 determines that the deterioration diagnosis has not been performed if the deterioration diagnosis has not been performed after the ignition switch was most recently turned ON. On the other hand, the diagnostic device 50 determines that the deterioration diagnosis has been performed if the deterioration diagnosis has already been performed after the ignition switch was most recently turned ON.

[0044] If it is determined that the deterioration diagnosis has not been performed (YES in step S104), the process proceeds to step S105. On the other hand, if it is determined that the deterioration diagnosis has been performed (NO in step S104), the control flow shown in FIG. 3 ends. Note that when it is determined as NO in step S104, the control unit 50b ends the catalyst neutralization control on the condition that the air-fuel ratio downstream of the catalyst 31 has become rich, in the same manner as the processes described later when it is determined as YES in step S104.

[0045] If it is determined as YES in step S104, in step S105, the calculation unit 50c calculates the total amount of oxygen consumption of the catalyst 31. Hereinafter, the process of calculating the total amount of oxygen consumption is also referred to as the calculation process.

[0046] FIG. 4 is a flowchart showing an example of the flow of the calculation process of the total oxygen consumption amount among the processes performed by the diagnostic device 50. The control flow shown in FIG. 4 corresponds to an example of the flow of the process in step S105 in the control flow shown in FIG. 3.

[0047] When the control flow shown in FIG. 4 is started, first, in step S201, the calculation unit 50c calculates the first oxygen consumption amount based on the fuel injection amount. The first oxygen consumption amount is the oxygen consumption amount before the air-fuel ratio detected by the air-fuel ratio sensor 32 becomes richer than the theoretical air-fuel ratio. In other words, the first oxygen consumption amount is the total amount of oxygen released from the catalyst 31 before the air-fuel ratio detected by the air-fuel ratio sensor 32 becomes richer than the theoretical air-fuel ratio. Even before the air-fuel ratio detected by the air-fuel ratio sensor 32 becomes richer than the theoretical air-fuel ratio, oxygen is released from the catalyst 31 during the execution of the catalyst neutralization control in which fuel is supplied to the engine 10 in a rich atmosphere.

[0048] As will be described later, step S201 is repeated until the upstream air-fuel ratio, which is the air-fuel ratio detected by the air-fuel ratio sensor 32, becomes rich. The upstream air-fuel ratio is the air-fuel ratio on the upstream side of the catalyst 31. That is, the upstream air-fuel ratio is the air-fuel ratio of the exhaust gas flowing into the catalyst 31. The upstream air-fuel ratio is obtained based on the detection result of the air-fuel ratio sensor 32.

[0049] In step S201, the calculation unit 50c integrates the oxygen consumption amount per unit time at each time point until the upstream air-fuel ratio becomes rich, and calculates the integrated value of the oxygen consumption amount per unit time at each time point as the first oxygen consumption amount.

[0050] The calculation unit 50c calculates the oxygen consumption per unit time at each point in time based on the fuel injection amount. The larger the fuel injection amount, the more the reaction in which the catalyst 31 releases oxygen is promoted. Therefore, for example, the calculation unit 50c calculates a larger value as the oxygen consumption per unit time at each point in time as the fuel injection amount is larger. Thus, by calculating the first oxygen consumption based on the fuel injection amount, the first oxygen consumption can be appropriately calculated. The fuel injection amount can be obtained based on various control command values determined by the control unit 50b.

[0051] Here, from the viewpoint of calculating the first oxygen consumption more accurately, it is preferable to calculate the first oxygen consumption based on the intake air amount in addition to the fuel injection amount. In this case, in calculating the first oxygen consumption, the calculation unit 50c calculates the oxygen consumption per unit time at each point in time based on the intake air amount. The larger the intake air amount, the more the reaction in which the catalyst 31 releases oxygen is promoted. Therefore, for example, the calculation unit 50c calculates a larger value as the oxygen consumption per unit time at each point in time as the intake air amount is larger. The intake air amount is obtained based on the detection result of the air flow meter 24.

[0052] Also, from the viewpoint of calculating the first oxygen consumption more accurately, it is preferable to calculate the first oxygen consumption based on the temperature of the catalyst 31 in addition to the fuel injection amount. In this case, in calculating the first oxygen consumption, the calculation unit 50c calculates the oxygen consumption per unit time at each point in time based on the temperature of the catalyst 31. The degree to which the reaction in which the catalyst 31 releases oxygen is promoted changes according to the temperature of the catalyst 31. The temperature of the catalyst 31 is obtained based on the detection result of the temperature sensor 33.

[0053] Next, in step S202, the calculation unit 50c determines whether the upstream air-fuel ratio has become rich. If it is determined that the upstream air-fuel ratio has become rich (YES in step S202), the process proceeds to step S203. On the other hand, if it is determined that the upstream air-fuel ratio has not become rich (NO in step S202), the process returns to step S201.

[0054] When it is determined as YES in step S202, in step S203, the calculation unit 50c calculates the second oxygen consumption amount based on the upstream air-fuel ratio. The second oxygen consumption amount is the oxygen consumption amount after the air-fuel ratio detected by the air-fuel ratio sensor 32 becomes richer than the theoretical air-fuel ratio. In other words, the second oxygen consumption amount is the total amount of oxygen released from the catalyst 31 after the air-fuel ratio detected by the air-fuel ratio sensor 32 becomes richer than the theoretical air-fuel ratio.

[0055] As will be described later, step S203 is repeated until the downstream air-fuel ratio becomes rich. The downstream air-fuel ratio is the air-fuel ratio on the downstream side of the catalyst 31. That is, the downstream air-fuel ratio is the air-fuel ratio of the exhaust gas discharged from the catalyst 31. Whether the downstream air-fuel ratio has become rich is determined based on the detection result of the oxygen sensor 34.

[0056] In step S203, the calculation unit 50c integrates the oxygen consumption amount per unit time at each time point until the downstream air-fuel ratio becomes rich, and calculates the integrated value of the oxygen consumption amount per unit time at each time point as the second oxygen consumption amount.

[0057] The calculation unit 50c calculates the oxygen consumption amount per unit time at each time point based on the upstream air-fuel ratio. The smaller the upstream air-fuel ratio, the larger the proportion of fuel in the exhaust gas flowing into the catalyst 31, so the reaction in which the catalyst 31 releases oxygen is promoted. Therefore, for example, the calculation unit 50c calculates a larger value as the oxygen consumption amount per unit time at each time point as the upstream air-fuel ratio is smaller. In this way, by calculating the second oxygen consumption amount based on the upstream air-fuel ratio, the second oxygen consumption amount can be calculated appropriately.

[0058] Here, from the viewpoint of calculating the second oxygen consumption more accurately, it is preferable to calculate the second oxygen consumption based on the intake air amount in addition to the upstream air-fuel ratio. In this case, in calculating the second oxygen consumption, the calculation unit 50c calculates the oxygen consumption per unit time at each time point based on the intake air amount. The larger the intake air amount, the more the reaction in which the catalyst 31 releases oxygen is promoted. Therefore, for example, the calculation unit 50c calculates a larger value as the oxygen consumption per unit time at each time point as the intake air amount is larger.

[0059] Also, from the viewpoint of calculating the second oxygen consumption more accurately, it is preferable to calculate the second oxygen consumption based on the temperature of the catalyst 31 in addition to the upstream air-fuel ratio. In this case, in calculating the second oxygen consumption, the calculation unit 50c calculates the oxygen consumption per unit time at each time point based on the temperature of the catalyst 31. The degree to which the reaction in which the catalyst 31 releases oxygen is promoted changes according to the temperature of the catalyst 31.

[0060] Next, in step S204, the calculation unit 50c determines whether the downstream air-fuel ratio has become rich. As described above, the calculation unit 50c can determine whether the downstream air-fuel ratio has become rich based on the detection result of the oxygen sensor 34. When it is determined that the downstream air-fuel ratio has become rich (YES in step S204), the process proceeds to step S205. On the other hand, when it is determined that the downstream air-fuel ratio has not become rich (NO in step S204), the process returns to step S203.

[0061] When it is determined YES in step S204, in step S205, the calculation unit 50c calculates the total value of the first oxygen consumption and the second oxygen consumption as the total oxygen consumption of the catalyst 31, and the control flow shown in FIG. 4 ends. Hereinafter, returning to FIG. 3, the description will continue.

[0062] Next to step S105, in step S106, the diagnosis unit 50d determines whether the total amount of oxygen consumption calculated by the calculation unit 50c is less than the threshold value. The threshold value is set to the total amount of oxygen consumption assumed during normal operation when the catalyst 31 is not deteriorated, or a value smaller than such a total amount of oxygen consumption.

[0063] If it is determined that the total amount of oxygen consumption calculated by the calculation unit 50c is less than the threshold value (YES in step S106), the process proceeds to step S107, and the diagnosis unit 50d diagnoses that the catalyst 31 is deteriorated. In this case, it is notified to the driver that the catalyst 31 is deteriorated. For example, the control unit 50b turns on a lamp in the vehicle 100 provided to notify the result of the deterioration diagnosis. Thereby, the driver can recognize that the catalyst 31 is deteriorated.

[0064] On the other hand, if it is determined that the total amount of oxygen consumption calculated by the calculation unit 50c is equal to or greater than the threshold value (NO in step S106), the process proceeds to step S108, and the diagnosis unit 50d diagnoses that the catalyst 31 is not deteriorated and is normal. In this case, for example, a lamp in the vehicle 100 provided to notify the result of the deterioration diagnosis does not light up.

[0065] Next to step S107 or step S108, in step S109, the control unit 50b ends the catalyst neutralization control, and the control flow shown in FIG. 3 ends.

[0066] FIG. 5 is a diagram showing an example of transitions of various state quantities in the deterioration diagnosis according to the present embodiment. In FIG. 5, transitions of a fuel cut flag, an upstream air-fuel ratio, a second oxygen consumption integrated value, a first oxygen consumption integrated value, and a downstream air-fuel ratio rich flag are shown as various state quantities. Note that in FIG. 5, the case where the air-fuel ratio sensor 32 is normal is indicated by a solid line, and the case where a response delay of the air-fuel ratio sensor 32 has occurred is indicated by a broken line.

[0067] The fuel cut flag becomes 1 when fuel cut is being executed, and becomes 0 when fuel cut is not being executed. The downstream air-fuel ratio rich flag becomes 1 when a detection result indicating that the downstream air-fuel ratio has become rich is output from the oxygen sensor 34, and becomes 0 when a detection result indicating that the downstream air-fuel ratio has become rich is not output from the oxygen sensor 34. The fuel cut flag and the downstream air-fuel ratio rich flag are stored, for example, in the storage element of the diagnostic device 50 and are rewritten by the diagnostic device 50.

[0068] The first oxygen consumption integrated value is the integrated value of the oxygen consumption at each time point in the calculation process of the first oxygen consumption. The second oxygen consumption integrated value is the integrated value of the oxygen consumption at each time point in the calculation process of the second oxygen consumption. In FIG. 5, the upstream air-fuel ratio is indicated by the λ value. Therefore, when the upstream air-fuel ratio in FIG. 5 is 1.0, the upstream air-fuel ratio becomes the stoichiometric air-fuel ratio.

[0069] In the example shown in FIG. 5, fuel cut is being executed before time point T1. Therefore, before time point T1, the upstream air-fuel ratio is lean. Also, before time point T1, the downstream air-fuel ratio is lean. At time point T1, the fuel cut ends and catalyst neutralization control is executed. Thereby, the supply of fuel to the engine 10 is restarted in a rich atmosphere richer than the stoichiometric air-fuel ratio. In the example of FIG. 5, the deterioration diagnosis of the catalyst 31 is performed after time point T1.

[0070] In the example of the solid line where the air-fuel ratio sensor 32 is normal, at time point T2 after time point T1, the upstream air-fuel ratio, which is the air-fuel ratio detected by the air-fuel ratio sensor 32, switches from lean to rich. Therefore, the calculation process of the first oxygen consumption is performed between time point T1 and time point T2. Thus, the integrated value of the oxygen consumption per unit time at each time point between time point T1 and time point T2 is calculated as the first oxygen consumption.

[0071] Then, at time point T4 after time point T2, the downstream air-fuel ratio switches from lean to rich. Therefore, between time point T2 and time point T4, the calculation process of the second oxygen consumption amount is performed. Thus, the integrated value of the oxygen consumption amount per unit time at each time point between time point T2 and time point T4 is calculated as the second oxygen consumption amount. During the period from time point T2 to time point T4, since the rich components in the exhaust gas are removed by the action of the catalyst 31, the downstream air-fuel ratio is lean. After that, the total value of the first oxygen consumption amount and the second oxygen consumption amount is calculated as the total oxygen consumption amount of the catalyst 31, and the deterioration of the catalyst 31 is diagnosed.

[0072] Here, there may be a response delay in the air-fuel ratio sensor 32. The response delay of the air-fuel ratio sensor 32 can be caused by various factors such as the change over time of the characteristics of the air-fuel ratio sensor 32 and the mounting accuracy of the air-fuel ratio sensor 32. In the example of the broken line where there is a response delay in the air-fuel ratio sensor 32, at time point T3 after time point T2, the upstream air-fuel ratio, which is the air-fuel ratio detected by the air-fuel ratio sensor 32, switches from lean to rich. Therefore, between time point T1 and time point T3, the calculation process of the first oxygen consumption amount is performed. Thus, the integrated value of the oxygen consumption amount per unit time at each time point between time point T1 and time point T3 is calculated as the first oxygen consumption amount.

[0073] Then, similar to the example of the solid line, at time point T4, the downstream air-fuel ratio switches from lean to rich. Therefore, between time point T3 and time point T4, the calculation process of the second oxygen consumption amount is performed. Thus, the integrated value of the oxygen consumption amount per unit time at each time point between time point T3 and time point T4 is calculated as the second oxygen consumption amount. After that, the total value of the first oxygen consumption amount and the second oxygen consumption amount is calculated as the total oxygen consumption amount of the catalyst 31, and the deterioration of the catalyst 31 is diagnosed.

[0074] Here, different from the present embodiment, when the upstream air-fuel ratio detected by the air-fuel ratio sensor 32 switches from lean to rich, the timing at which the calculation of the oxygen consumption starts is determined, and the integrated value of the oxygen consumption per unit time at each time point after that is calculated as the total amount of oxygen consumption of the catalyst 31. In this case, when the second oxygen consumption in the present embodiment is smaller than the assumed value, it is diagnosed that the catalyst 31 is deteriorated. However, as shown in FIG. 5, in the example of the broken line where there is a response delay in the air-fuel ratio sensor 32, compared with the example of the solid line where the air-fuel ratio sensor 32 is normal, the timing at which the calculation of the second oxygen consumption starts is delayed, so the calculated second oxygen consumption becomes smaller. Therefore, the diagnostic accuracy of the deterioration diagnosis decreases.

[0075] On the other hand, in the present embodiment, the first oxygen consumption, which is the oxygen consumption before the upstream air-fuel ratio becomes rich, and the second oxygen consumption, which is the oxygen consumption after the upstream air-fuel ratio becomes rich, are respectively calculated, and the total value of the first oxygen consumption and the second oxygen consumption is calculated as the total amount of oxygen consumption of the catalyst 31. Here, in the calculation process of the first oxygen consumption, although the upstream air-fuel ratio detected by the air-fuel ratio sensor 32 cannot be used, the first oxygen consumption can be appropriately calculated by calculating the first oxygen consumption based on the fuel injection amount. Also, in the calculation process of the second oxygen consumption, the second oxygen consumption can be appropriately calculated by calculating the second oxygen consumption based on the upstream air-fuel ratio. Therefore, regardless of whether there is a response delay in the air-fuel ratio sensor 32, the total amount of oxygen consumption of the catalyst 31 can be appropriately calculated. Thus, the deterioration of the catalyst 31 can be accurately diagnosed.

[0076] <Effect of the diagnostic device> Subsequently, the effect of the diagnostic device 50 according to the embodiment of the present invention will be described.

[0077] In the diagnostic apparatus 50 according to the present embodiment, the calculation unit 50c calculates a first oxygen consumption amount, which is the oxygen consumption amount before the upstream air-fuel ratio, which is the air-fuel ratio detected by the air-fuel ratio sensor 32, becomes richer than the stoichiometric air-fuel ratio, based on the fuel injection amount. Further, the calculation unit 50c calculates a second oxygen consumption amount, which is the oxygen consumption amount after the upstream air-fuel ratio, which is the air-fuel ratio detected by the air-fuel ratio sensor 32, becomes richer than the stoichiometric air-fuel ratio, based on the upstream air-fuel ratio. The calculation unit 50c calculates the total value of the first oxygen consumption amount and the second oxygen consumption amount as the total oxygen consumption amount of the catalyst 31. Thereby, regardless of whether or not there is a response delay in the air-fuel ratio sensor 32, the total oxygen consumption amount of the catalyst 31 can be appropriately calculated. Then, the diagnosis unit 50d diagnoses the deterioration of the catalyst 31 based on the total oxygen consumption amount of the catalyst 31 calculated by the calculation unit 50c. Therefore, the deterioration of the catalyst 31 can be accurately diagnosed.

[0078] Further, in the diagnostic apparatus 50 according to the present embodiment, it is preferable that the calculation unit 50c calculates the first oxygen consumption amount based on the intake air amount, which is the flow rate of the air inhaled into the intake air passage 20 connected to the engine 10, in addition to the fuel injection amount. Thereby, the first oxygen consumption amount can be accurately calculated according to the intake air amount. Therefore, the first oxygen consumption amount can be calculated more accurately. Therefore, the total oxygen consumption amount of the catalyst 31 can be calculated more accurately, so that the deterioration of the catalyst 31 can be diagnosed more accurately.

[0079] Further, in the diagnostic apparatus 50 according to the present embodiment, it is preferable that the calculation unit 50c calculates the first oxygen consumption amount based on the temperature of the catalyst 31 in addition to the fuel injection amount. Thereby, the first oxygen consumption amount can be accurately calculated according to the temperature of the catalyst 31. Therefore, the first oxygen consumption amount can be calculated more accurately. Therefore, the total oxygen consumption amount of the catalyst 31 can be calculated more accurately, so that the deterioration of the catalyst 31 can be diagnosed more accurately.

[0080] Further, in the diagnostic device 50 according to the present embodiment, it is preferable that the calculation unit 50c calculates the second oxygen consumption amount based on the intake air amount, which is the flow rate of the air inhaled into the intake air passage 20 connected to the engine 10, in addition to the upstream air-fuel ratio. Thereby, the second oxygen consumption amount can be accurately calculated according to the intake air amount. Therefore, the second oxygen consumption amount can be calculated more accurately. Thus, the total oxygen consumption amount of the catalyst 31 can be calculated more accurately, so that the deterioration of the catalyst 31 can be diagnosed more accurately.

[0081] Further, in the diagnostic device 50 according to the present embodiment, it is preferable that the calculation unit 50c calculates the second oxygen consumption amount based on the temperature of the catalyst 31, in addition to the upstream air-fuel ratio. Thereby, the second oxygen consumption amount can be accurately calculated according to the temperature of the catalyst 31. Therefore, the second oxygen consumption amount can be calculated more accurately. Thus, the total oxygen consumption amount of the catalyst 31 can be calculated more accurately, so that the deterioration of the catalyst 31 can be diagnosed more accurately.

[0082] As described above, the preferred embodiments of the present invention have been described with reference to the accompanying drawings. However, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications or corrections within the scope described in the claims also belong to the technical scope of the present invention.

[0083] For example, the processes described using flowcharts in this specification do not necessarily have to be executed in the order shown in the flowcharts. Also, additional processing steps may be adopted, and some processing steps may be omitted.

Explanation of Reference Numerals

[0084] 1 Intake and Exhaust System 10 Engine 20 Intake Air Passage 21 Air Filter 22 Throttle Valve 23 Surge Tank 24 Airflow Meter 30 Exhaust gas flow path 31 Catalyst 32 Air-fuel ratio sensor 33 Temperature sensor 34 Oxygen sensor 41 Accelerator opening sensor 42 Vehicle speed sensor 50 Diagnostic device 50a Acquisition unit 50b Control unit 50c Calculation unit 50d Diagnosis unit 51 Processor 52 Memory 100 Vehicle

Claims

1. A diagnostic device for a vehicle, comprising: an engine; an exhaust passage connected to the engine; a catalyst provided in the exhaust passage; and an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing into the catalyst, a control unit configured to resume supply of the fuel to the engine in a rich atmosphere richer than a stoichiometric air-fuel ratio after a fuel cut for stopping supply of the fuel to the engine, a calculation unit configured to calculate a total oxygen consumption amount, which is a total amount of oxygen consumption of the catalyst after resumption of supply of the fuel to the engine, and a diagnosis unit configured to diagnose deterioration of the catalyst based on the total oxygen consumption amount calculated by the calculation unit. The diagnostic device is provided with: The calculation unit: calculates a first oxygen consumption amount, which is the oxygen consumption amount before the air-fuel ratio detected by the air-fuel ratio sensor becomes richer than the stoichiometric air-fuel ratio, based on an injection amount of the fuel; calculates a second oxygen consumption amount, which is the oxygen consumption amount after the air-fuel ratio detected by the air-fuel ratio sensor becomes richer than the stoichiometric air-fuel ratio, based on the air-fuel ratio of the exhaust gas; and calculates a total value of the first oxygen consumption amount and the second oxygen consumption amount as the total oxygen consumption amount. Diagnostic device.

2. The calculation unit calculates the first oxygen consumption amount based on an intake air amount, which is a flow rate of air inhaled into an intake passage connected to the engine, in addition to the injection amount of the fuel. The diagnostic device according to claim 1.

3. The calculation unit calculates the first oxygen consumption amount based on the temperature of the catalyst, in addition to the injection amount of the fuel. The diagnostic device according to claim 1 or 2.

4. The calculation unit calculates the second oxygen consumption amount based on an intake air amount, which is a flow rate of air inhaled into an intake passage connected to the engine, in addition to the air-fuel ratio of the exhaust gas. The diagnostic device according to any one of claims 1 to 3.

5. The calculation unit calculates the second oxygen consumption amount based on the temperature of the catalyst, in addition to the air-fuel ratio of the exhaust gas. The diagnostic device according to any one of claims 1 to 4.

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