Engine control device

Abstract

To provide an engine control device capable of properly performing abnormality diagnosis of an exhaust component while preventing a catalyst from becoming excessively high in temperature.SOLUTION: When an accelerator opening degree is less than a predetermined accelerator determination opening degree, a fuel cut for stopping fuel injection by a fuel supply device 11 is executed, and when a catalyst temperature specified by a catalyst temperature specifying device 100 is high during execution of the fuel cut, intake air amount increase control for controlling an intake air amount adjusting device 12 is executed so that an intake air amount becomes larger than when the catalyst temperature is low.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an engine control device. [Background technology]

[0002] A catalytic converter installed in the engine's exhaust passage to purify exhaust gas deteriorates when exposed to high temperatures. Therefore, in order to maintain good engine exhaust gas performance, it is necessary to prevent the catalytic converter from becoming excessively hot.

[0003] Patent document 1 discloses an engine that, in order to prevent the catalytic converter from overheating, increases the amount of air drawn into the combustion chamber during fuel cutoff (fuel cut), which stops the fuel supply to the combustion chamber, and introduces a large amount of air into the exhaust passage and ultimately the catalytic converter, thereby cooling the catalytic converter with that air. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-132185 Summary of the Invention [Problem to be solved by the invention]

[0005] In vehicle engines, it is necessary to diagnose whether various engine components are abnormal, specifically whether they have deteriorated or broken. Depending on the type of component, it may be necessary or preferable to perform the above diagnosis during a fuel cut. However, in the engine of Patent Document 1, the amount of air (i.e., exhaust gas) introduced into the exhaust passage increases when a fuel cut is initiated. Therefore, in such an engine, if the diagnosis of exhaust components installed in the portion through which exhaust gas passes is performed simply by cutting fuel, the increase in the amount of exhaust gas may affect the output of the exhaust components, making it possible to prevent an appropriate diagnosis of whether the exhaust components are abnormal.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an engine control device that can properly diagnose abnormalities in exhaust parts while preventing the catalyst from becoming excessively hot. [Means for solving the problem]

[0007] The engine control device according to the present invention is an engine control device provided in a vehicle equipped with an accelerator pedal, and includes an engine body having a combustion chamber formed therein, an exhaust passage and an intake passage respectively connected to the engine body, a fuel supply device that supplies fuel to the combustion chamber, an intake amount adjustment device that adjusts the intake amount which is the amount of air taken into the combustion chamber, a catalytic converter provided in the exhaust passage and purifying exhaust gas, a catalyst temperature specifying device that specifies the catalyst temperature which is the temperature of the catalytic converter, an accelerator opening detection device that detects the accelerator opening which is the opening of the accelerator pedal, and a control unit that controls the fuel supply device and the intake amount adjustment device, The unit performs a fuel cut to stop fuel injection by the fuel supply device when the accelerator opening detected by the accelerator opening detection device is less than a predetermined accelerator judgment opening, and when the fuel cut is performed and the catalyst temperature identified by the catalyst temperature identification device is high, performs intake amount increase control to control the intake amount adjustment device so that the intake amount is greater than when the catalyst temperature is low, and when the fuel cut is performed, performs an abnormality diagnosis to determine whether or not there is an abnormality in an exhaust part installed in a part through which exhaust gas passes, and prohibits the intake amount increase control while the abnormality diagnosis is being performed even when the fuel cut is performed (Claim 1).

[0008] According to the present invention, when the catalyst temperature is high, intake air volume increase control is implemented to increase the amount of air in the combustion chamber and therefore the amount of air introduced into the exhaust passage during fuel cut. Therefore, the timing of fuel cut can be used to cool the catalytic converter in the exhaust passage with a large amount of air, preventing the catalytic converter from overheating. Furthermore, the timing of fuel cut can be used to diagnose whether or not there is an abnormality in the exhaust components installed in the area through which exhaust gas passes.

[0009] Furthermore, in the present invention, even when a fuel cut is being performed, the intake air amount increase control is prohibited while an abnormality diagnosis is being performed to determine whether or not there is an abnormality in the exhaust parts. This prevents fluctuations in the amount of exhaust gas that occur when the intake air amount increase control is performed from affecting the results of the abnormality diagnosis. This allows for an appropriate diagnosis of whether or not the exhaust parts are normal.

[0010] In the above configuration, preferably, when the fuel cut is performed and the catalyst temperature is high, the control unit starts the intake amount increase control after the abnormality diagnosis is completed (claim 2).

[0011] This configuration prevents the intake air amount increase control from affecting the results of the abnormality diagnosis, while increasing the opportunities to execute the intake air amount increase control, i.e., to cool the catalytic converter. Therefore, it is possible to properly diagnose the exhaust components while reliably preventing the catalytic converter from overheating.

[0012] In the above configuration, preferably, the exhaust part includes an air-fuel ratio sensor provided in the exhaust passage for detecting the air-fuel ratio of the exhaust gas, and when the abnormality diagnosis is performed, the control unit diagnoses whether the air-fuel ratio sensor has deteriorated based on the output of the air-fuel ratio sensor at the start of the fuel cut (claim 3).

[0013] According to this configuration, it is possible to appropriately diagnose whether the air-fuel ratio sensor has deteriorated by utilizing the fact that the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor changes significantly when a fuel cut is started.

[0014] In the above configuration, preferably, the control unit prohibits the diagnosis of whether the air-fuel ratio sensor has deteriorated after the number of times that the control unit has diagnosed whether the air-fuel ratio sensor has deteriorated in one driving cycle reaches a predetermined number of determinations (claim 4).

[0015] This configuration allows the deterioration of the air-fuel ratio sensor to be diagnosed in each driving cycle, and prevents the intake air amount increase control from being reduced due to excessively frequent diagnosis. Therefore, it is possible to prevent the catalyst device from overheating while ensuring opportunities to diagnose the deterioration of the air-fuel ratio sensor.

[0016] In the above-described configuration, the air-fuel ratio sensor can be a sensor disposed in the exhaust passage downstream of the catalytic converter (claim 5).

[0017] In the above configuration, preferably, the air-fuel ratio sensor is a λ sensor that detects whether the state of the exhaust gas is in one of three states: a state in which the air-fuel ratio is the stoichiometric air-fuel ratio, a state in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio, or a state in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio (claim 6).

[0018] In the λ sensor configured as described above, the output changes relatively greatly when the air-fuel ratio of the exhaust gas changes. Therefore, if a λ sensor is used as the air-fuel ratio sensor and deterioration diagnosis is performed based on the change in the output of the air-fuel ratio sensor at the start of fuel cut, the deterioration diagnosis can be performed appropriately using the timing of fuel cut.

[0019] In the above configuration, preferably, the engine further includes an intake pressure sensor provided in the intake passage for detecting an intake pressure, which is the pressure of the intake air passing through the intake passage, and the exhaust parts include an EGR device having an EGR passage connecting the exhaust passage and the intake passage and an EGR valve for opening and closing the EGR passage, and when the abnormality diagnosis is performed, the control unit opens and closes the EGR valve and diagnoses whether or not the EGR device has malfunctioned based on a change in the intake pressure detected by the intake pressure sensor (claim 7).

[0020] When the EGR valve opens and closes appropriately, the flow rate of EGR gas, which is exhaust gas that passes through the EGR passage and flows back to the intake passage, changes, causing a change in intake pressure. Therefore, with this configuration, by diagnosing whether the EGR device is malfunctioning based on the change in intake pressure when the EGR valve opens and closes, it is possible to reliably diagnose whether the EGR valve is opening and closing appropriately, and ultimately whether the EGR device is malfunctioning. Furthermore, during fuel cut, even if the flow rate of EGR gas changes, it does not affect engine output, etc. Therefore, with this configuration, by diagnosing the EGR device using the timing of fuel cut, it is possible to reliably diagnose an abnormality in the EGR device while avoiding the diagnosis from affecting engine output, etc.

[0021] In the above configuration, preferably, the control unit prohibits diagnosing whether or not the EGR device is malfunctioning after the number of times that the control unit has diagnosed whether or not the EGR device is malfunctioning in one driving cycle reaches a predetermined number of determinations (claim 8).

[0022] This configuration allows the EGR device to be diagnosed for malfunction in each driving cycle, and prevents the intake air amount from being reduced due to excessively frequent diagnosis. Therefore, it is possible to prevent the catalyst device from overheating while ensuring opportunities to diagnose the EGR device for malfunction.

[0023] In the above configuration, when the fuel cut is not being performed and the catalyst temperature is high, the control unit limits the intake air amount to a predetermined upper limit intake air amount or less by the intake air amount adjusting device (claim 9).

[0024] According to this configuration, when fuel cut is not being performed and the catalyst temperature is high, the intake air volume is prevented from exceeding the upper intake air volume limit, thereby minimizing the combustion energy generated in the combustion chamber. This prevents the catalyst temperature from rising excessively. However, increasing the number of times the intake air volume is restricted increases the number of times engine output is restricted, which may result in a deterioration in vehicle drivability. In contrast, the present invention cools the catalyst device when fuel cut is performed as described above, thereby reducing the chances of the catalyst temperature rising excessively when fuel cut is not being performed. This prevents the catalyst temperature from rising excessively while suppressing a deterioration in drivability.

[0025] In the above-described configuration, the intake amount adjusting device may be a throttle valve provided in the intake passage for opening and closing the intake passage (claim 10). [Effects of the Invention]

[0026] As described above, the engine control device of the present invention can appropriately diagnose abnormalities in exhaust parts while preventing the catalyst from becoming excessively hot. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic configuration diagram of an engine system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a control block of the engine. [Figure 3] 4 is a flowchart showing the control contents executed by the PCM. [Figure 4] 4 is a time chart for explaining an outline of deterioration diagnosis of the rear O2 sensor. [Figure 5] 10 is a flowchart showing the contents of a deterioration diagnosis of a rear O2 sensor. [Figure 6] 10 is a flowchart showing a procedure for setting a catalyst protection flag. [Figure 7] 4 is a flowchart showing the contents of control performed by the PCM. [Figure 8] 10 is a flowchart showing the details of throttle control during non-FC. [Figure 9] 4 is a time chart showing the time changes of each parameter during fuel cut. [Figure 10] 4 is a time chart showing the time changes of each parameter during fuel cut. [Figure 11] 10 is a time chart for explaining an outline of a failure diagnosis of an EGR valve according to a second embodiment. [Figure 12] 10 is a flowchart showing the contents of a failure diagnosis of an EGR valve according to a second embodiment. [Figure 13] 10 is a time chart showing the time changes of each parameter during fuel cut according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028] (Overall configuration of the engine system) FIG. 1 is a schematic diagram showing a first preferred embodiment of an engine system E to which an engine control device according to a first embodiment of the present invention is applied. The engine system E includes an engine body 1 that is driven by a supply of fuel, and an intake passage 20 and an exhaust passage 30 connected to the engine body 1. The intake passage 20 is a passage through which intake air, which is air introduced into the engine body 1, flows. The exhaust passage 30 is a passage through which exhaust gas discharged from the engine body 1 flows. The engine system E is installed in a vehicle such as an automobile as a power source for driving the vehicle.

[0029] The engine body 1 is a multi-cylinder engine having a plurality of cylinders 2A (only one of which is shown in FIG. 1). In the first embodiment, the engine body 1 is a four-cylinder in-line engine, with the four cylinders 2A aligned in a direction perpendicular to the plane of the paper in FIG. 1. The engine body 1 includes a cylinder block 2 having the plurality of cylinders 2A formed therein, a cylinder head 3 attached to the upper surface of the cylinder block 2 so as to close the upper end openings of each cylinder 2A, and a plurality of pistons 4 housed in each cylinder 2A so as to be able to slide back and forth.

[0030] A combustion chamber 5 is defined above the piston 4 of each cylinder 2A. As will be described later, fuel is supplied to the combustion chamber 5. The mixture of the supplied fuel and air is burned in the combustion chamber 5, and the expansion force caused by the combustion causes the piston 4 to reciprocate up and down.

[0031] A crankshaft 13, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 2 (below the pistons 4). The crankshaft 13 is connected to the pistons 4 of each cylinder 2A via connecting rods. The crankshaft 13 rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 4.

[0032] A vehicle equipped with the engine system E is equipped with a multi-speed transmission as the transmission 60. The transmission 60 is also an automatic transmission, and the transmission 60 and the crankshaft 13 are connected via a torque converter and the like. The output of the engine body 1 is transmitted to the wheels 70 via the crankshaft 13, the torque converter, the transmission 60 and the like. In the first embodiment, the transmission 60 is a six-speed multi-speed transmission, and realizes six forward gears with different gear ratios.

[0033] A crank angle sensor SN1 is attached to the cylinder block 2. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 13, and the engine speed, which is the rotation speed of the crankshaft 13.

[0034] An intake port 6 and an exhaust port 7 that communicate with the combustion chamber 5 are formed in the cylinder head 3 for each cylinder 2A. The cylinder head 3 is also equipped with an intake valve 8 that opens and closes the opening of the intake port 6 on the combustion chamber 5 side, and an exhaust valve 9 that opens and closes the opening of the exhaust port 7 on the combustion chamber 5 side, for each cylinder 2A.

[0035] The cylinder head 3 is fitted with one injector 11 for each cylinder 2A that supplies fuel into the combustion chamber 5. The engine body 1 is a gasoline engine, and the injector 11 injects fuel, including gasoline, into the combustion chamber 5. The injector 11 injects fuel into the combustion chamber 5. The injector 11 is a side-injection fuel injection valve, and its tip faces the combustion chamber 5 from the inner circumferential surface of the combustion chamber 5. The cylinder head 3 is fitted with one spark plug 10 for each cylinder 2A that ignites the fuel-air mixture in the combustion chamber 5. The spark plug 10 is arranged so that its tip, including the spark plug, faces the inside of the combustion chamber 5 from near the center of the ceiling surface of the combustion chamber 5. The injector 11 corresponds to the "fuel supply device" of the present invention.

[0036] The intake passage 20 is connected to the cylinder head 3 so as to communicate with the intake port 6 of each cylinder 2A. In the intake passage 20, an air cleaner 21, a throttle valve 22, and a surge tank 23 are arranged in this order from the upstream side in the flow direction of intake air.

[0037] The air cleaner 21 is a filter that removes foreign matter from the intake air. The throttle valve 22 is a valve that opens and closes the intake passage 20. The amount of intake air flowing through the intake passage 20, and therefore the amount of air drawn into the combustion chamber 5, is changed depending on the opening of the throttle valve 22. The surge tank 23 is a tank that provides space for evenly distributing the intake air to each cylinder 2A. The throttle valve 22 corresponds to the "intake air amount adjustment device" of the present invention.

[0038] An air flow sensor SN2, an intake air temperature sensor SN3, and an intake air pressure sensor SN4 are arranged in the intake passage 20. The air flow sensor SN2 detects the intake air volume, which is the amount of air taken into each combustion chamber 5 through the intake passage 20. The intake air temperature sensor SN3 detects the intake air temperature, which is the temperature of the air flowing through the intake passage 20. The intake air pressure sensor SN4 detects the intake air pressure, which is the pressure inside the intake passage 20. The air flow sensor SN2 and the intake air temperature sensor SN3 are arranged near the air cleaner 21 and detect the flow rate and temperature of air passing through the intake passage 20 near the air cleaner 21, respectively. The intake air pressure sensor SN4 is arranged in the surge tank 23 and detects the pressure inside the surge tank 23.

[0039] The exhaust passage 30 is connected to the cylinder head 3 so as to communicate with the exhaust ports 7 of each cylinder 2A. A catalytic device 31 is disposed in the exhaust passage 30. The catalytic device 31 includes a catalyst and is a device that purifies exhaust gas by utilizing the action of the catalyst.

[0040] The catalytic device 31 incorporates a three-way catalyst. As a result, when the air-fuel ratio of the exhaust gas is at or near the stoichiometric air-fuel ratio, the catalytic device 31 oxidizes HC (hydrocarbons) and CO (carbon monoxide) while reducing NOx (nitrogen oxides). Here, the three-way catalyst has the property of storing oxygen. Therefore, when the exhaust gas contains a large amount of oxygen, the catalytic device 31 stores the oxygen. When the amount of stored oxygen is large, the catalytic device 31 is unable to sufficiently reduce NOx.

[0041] A front O2 sensor SN5 and a rear O2 sensor SN6 are disposed in the exhaust passage 30. The front O2 sensor SN5 detects the oxygen concentration and air-fuel ratio contained in the exhaust gas. The rear O2 sensor SN6 detects the air-fuel ratio of the exhaust gas. The front O2 sensor SN5 is attached to a portion of the exhaust passage 30 upstream of the catalytic converter 31 (in the direction of exhaust gas flow) and detects the oxygen concentration and air-fuel ratio of the exhaust gas flowing into the catalytic converter. In this embodiment, the front O2 sensor SN5 is disposed near the upstream end of the catalytic converter 31. The rear O2 sensor SN6 is attached to a portion of the exhaust passage 30 downstream of the catalytic converter 31 (in the direction of exhaust gas flow) and detects the air-fuel ratio of the exhaust gas flowing out of the catalytic converter 31. Here, no component capable of changing the air-fuel ratio, such as a catalyst, is disposed between the rear O2 sensor SN6 and the catalytic converter 31, and the rear air-fuel ratio detected by the rear O2 sensor SN6 is approximately equal to the air-fuel ratio in the catalytic converter 31. The rear O2 sensor SN6 corresponds to the "air-fuel ratio sensor" and "exhaust component" of the present invention.

[0042] In the following, the air-fuel ratio of the exhaust gas passing through the location where the front O2 sensor SN5 is installed, and that is upstream of the catalytic device 31, will be referred to as the front air-fuel ratio. Also, the air-fuel ratio of the exhaust gas passing through the location where the rear O2 sensor SN6 is installed, and that is downstream of the catalytic device 31, will be referred to as the rear air-fuel ratio. Also, in the following, a large / small air-fuel ratio will be referred to as lean / rich, and specifically, when the proportion of oxygen in the exhaust gas is high and the air-fuel ratio of the exhaust gas is large, it will be referred to as lean, and the opposite will be referred to as rich.

[0043] The front O2 sensor SN5 is a so-called linear O2 sensor that outputs a voltage proportional to the oxygen concentration and air-fuel ratio of the exhaust gas. Meanwhile, the rear O2 sensor SN6 is a so-called λ sensor that detects whether the exhaust gas is near the stoichiometric air-fuel ratio, leaner than the stoichiometric air-fuel ratio, or richer than the stoichiometric air-fuel ratio. Specifically, the output voltage of the rear O2 sensor SN6 is as shown in FIG. 2. Hereinafter, the output voltage of the rear O2 sensor SN6 will be referred to as the RO2 output voltage where appropriate. When the exhaust gas air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the RO2 output voltage is lower than a predetermined lean voltage. When the exhaust gas air-fuel ratio is richer than the stoichiometric air-fuel ratio, the RO2 output voltage is higher than a predetermined rich voltage. When the exhaust gas air-fuel ratio is stoichiometric, the RO2 output voltage is a stoichiometric voltage that is higher than the lean voltage and lower than the rich voltage. When the exhaust gas air-fuel ratio shifts from a leaner state to the stoichiometric air-fuel ratio, the RO2 output voltage increases from a voltage lower than the lean voltage through the lean voltage to the stoichiometric voltage. When the exhaust gas air-fuel ratio shifts from a richer state to the stoichiometric air-fuel ratio, the RO2 output voltage decreases from a voltage higher than the rich voltage through the rich voltage to the stoichiometric voltage.

[0044] In the first embodiment, the exhaust passage 30 is a so-called 4-2-1 type exhaust passage. That is, the exhaust passage 30 is configured such that four exhaust passages extending from the engine body 1 converge into two passages, which then converge into one downstream (in the flow direction of exhaust gas). The catalytic device 31, the front O2 sensor SN5, and the rear O2 sensor SN6 are all located downstream of the point where the exhaust passages converge into one passage.

[0045] The engine system E is provided with an EGR device 40. The EGR device 40 includes an EGR passage 41. The EGR passage 41 is a passage that connects the exhaust passage 30 and the intake passage 20 and recirculates EGR gas, which is a part of the exhaust gas, to the intake passage 20. The EGR passage 41 connects a portion of the exhaust passage 30 downstream of the catalytic device 31 (in the flow direction of the exhaust gas) with a portion of the intake passage 20 between the throttle valve 22 and the surge tank 23.

[0046] An EGR cooler 42 and an EGR valve 43 are provided in the EGR passage 41. The EGR cooler 42 cools the EGR gas flowing through the EGR passage 41 by heat exchange. The EGR valve 43 is a valve that opens and closes the EGR passage 41. The amount of EGR gas recirculated to the intake passage 20 is changed depending on the opening degree of the EGR valve 43. The EGR valve 43 is provided in the EGR passage 41 closer to the intake passage 20 than the EGR cooler 42.

[0047] (Control system) FIG. 3 is a functional block diagram showing the control system of the engine system E. The PCM 100 shown in this diagram is a device that is mounted on a vehicle and performs overall control of the engine system E. The PCM 100 is composed of a microcomputer that includes a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses. The PCM 100 corresponds to the "control unit" in this invention.

[0048] The PCM 100 is electrically connected to a crank angle sensor SN1, an air flow sensor SN2, an intake air temperature sensor SN3, an intake air pressure sensor SN4, a front O2 sensor SN5, and a rear O2 sensor SN6. Information detected by each of the sensors SN1 to SN6 is sequentially input to the PCM 100.

[0049] A vehicle equipped with the engine system E is equipped with an accelerator pedal 91 that is depressed by the driver, and an accelerator sensor SN7. The accelerator pedal 91 is an operating device for changing and adjusting the output of the engine main body 1 and, ultimately, the vehicle speed. The accelerator sensor SN7 detects the amount of depression of the accelerator pedal 91, i.e., the accelerator opening, which is the opening degree of the accelerator pedal 91. The accelerator opening is a parameter that is 0 (%) when the accelerator pedal 91 is not depressed and 100 (%) when the accelerator pedal 91 is at its maximum depression amount. The accelerator sensor SN7 corresponds to the "accelerator opening detection device" of the present invention.

[0050] The vehicle is equipped with a brake device 81, a brake pedal 82, and a brake sensor SN8. The brake device 81 is a device that applies braking force to the wheels 70 to brake the wheels 70. The brake pedal 82 is an operating means for switching between driving and stopping the brake device 81 and increasing or decreasing the braking force that the brake device 81 applies to the wheels 70. The brake pedal 82 is operated by the driver by depressing it. The brake sensor SN8 detects the amount of depression of the brake pedal 82, i.e., the brake opening degree, which is the opening degree of the brake pedal 82.

[0051] The vehicle is equipped with a vehicle speed sensor SN9 for detecting vehicle speed. The vehicle is provided with a start switch SW1 that is operated by the driver to start the engine main body 1. When a predetermined operation is performed on the start switch SW1, the switch turns to IG_ON, power is supplied to each part of the engine system E, and the engine main body 1 becomes startable. Furthermore, when a predetermined operation is performed on the start switch SW1 while the switch is in the IG_ON state, the switch turns to IG_OFF, power supply to each part of the engine system E is stopped, and the engine main body 1 becomes unable to start.

[0052] The PCM 100 sequentially receives information detected by the accelerator sensor SN7 and the brake sensor SN8, and a signal from the start switch SW1.

[0053] The PCM 100 controls each part of the engine system E while making various determinations and calculations based on input information from the sensors SN1 to SN9 and the start switch SW1. The PCM 100 is electrically connected to the spark plug 10, the injector 11, the throttle valve 22, the EGR valve 43, etc., and outputs control signals to these devices based on the results of the calculations.

[0054] The PCM 100 functionally includes a main control unit 101 and a diagnosis unit 102. The main control unit 101 controls the amount of intake air and the amount of fuel introduced into each combustion chamber 5. The diagnosis unit 102 performs abnormality diagnosis of the engine system E. In the first embodiment, the diagnosis unit 102 diagnoses whether the rear O2 sensor SN6 has deteriorated.

[0055] (Fuel cut and basic control during fuel cut) When a fuel cut condition is met, that is, the engine speed is higher than a predetermined idle speed and the accelerator opening is equal to or smaller than a predetermined accelerator judgment opening, the PCM 100 (main control unit 101) performs a fuel cut by stopping the drive of the injector 11 of each cylinder 2A and stopping fuel injection into each combustion chamber 5. The accelerator judgment opening is set to 0 (zero), i.e., an opening close to fully closed, and the fuel cut is essentially performed when the accelerator pedal 91 is not depressed (accelerator-off). During the fuel cut except when the intake amount increase control described below is being performed, the PCM 100 controls the throttle opening to a predetermined normal FC opening. The normal FC opening is 0 (zero), i.e., an opening close to fully closed, and is preset to an opening smaller (closed) than the throttle opening achieved when the fuel cut is not being performed. Furthermore, during the fuel cut except when the EGR valve failure diagnosis described below is being performed, the PCM 100 fully closes the EGR valve 43.

[0056] (Rear O2 sensor deterioration diagnosis) The abnormality diagnosis performed by the PCM 100 (diagnosis unit 102) will be described. As described above, in the first embodiment, the PCM 100 performs a deterioration diagnosis of the rear O2 sensor SN6 as an abnormality diagnosis. Hereinafter, the abnormality diagnosis performed by the PCM 100 will be referred to as a deterioration diagnosis of the rear O2 sensor SN6 as appropriate.

[0057] First, an overview of the deterioration diagnosis of the rear O2 sensor SN6 will be explained using Figure 4. Figure 4 is a time chart showing the time changes of the fuel cut flag, rear air-fuel ratio, and RO2 output voltage, which is the output voltage of the rear O2 sensor SN6. The fuel cut flag is a flag that is set to 1 when a fuel cut is implemented (described later) and is set to 0 when a fuel cut is not implemented.

[0058] When fuel cut is not being performed, the air-fuel ratio of the gas in the combustion chamber 5 and the exhaust gas is controlled to be close to the stoichiometric air-fuel ratio. On the other hand, when fuel cut is performed, the exhaust gas becomes almost entirely air. Therefore, when fuel cut is started, the air-fuel ratio of the exhaust gas becomes significantly leaner (larger) than close to the stoichiometric air-fuel ratio, and the RO2 output voltage drops. In the example of FIG. 4, fuel cut is started at time t1, and the RO2 output voltage drops accordingly.

[0059] In the graph of Figure 4, the solid line represents the RO2 output voltage when the rear O2 sensor SN6 is not degraded, and the dashed line represents the RO2 output voltage when the rear O2 sensor SN6 is degraded. As shown in this graph, the response speed of the rear O2 sensor SN6 decreases as it degrades, and the time dt2 required for the RO2 output voltage to drop from the predetermined first determination voltage V1 to the predetermined second determination voltage V2 when the sensor is degraded is longer than the time dt1 required when the sensor is not degraded. The PCM 100 utilizes this characteristic to determine the time required for the RO2 output voltage to drop from the predetermined first determination voltage V1 to the predetermined second determination voltage V2 after the fuel cutoff has started, and determines that the rear O2 sensor SN6 is degraded if the determined time is longer than a predetermined diagnostic time.

[0060] Fig. 5 is a flowchart showing the contents of the deterioration diagnosis of the rear O2 sensor SN6 performed by the PCM 100. Steps S1 to S14 shown in Fig. 5 are repeatedly performed at predetermined intervals while the IG_ON state is maintained.

[0061] First, the PCM 100 determines whether the diagnosis count, which is the number of times that the deterioration diagnosis of the rear O2 sensor SN6 has been performed, is less than a first determination count (step S1). The diagnosis count is the number of times that the deterioration diagnosis of the rear O2 sensor SN6 has been performed during the current driving cycle, and is the number of times that step S10 or step S11, which will be described later, has been performed. Note that a driving cycle is the period from when the IG_ON signal is turned on and the engine 1 can be started until when the IG_OFF signal is turned on and the engine 1 cannot be driven. Note that the above diagnosis count is reset to 0 when the IG_OFF signal is turned on. The first determination count is set in advance and stored in the PCM 100. In the first embodiment, the first determination count is set to 1, and in step S1, it is determined whether the diagnosis of the rear O2 sensor SN6 has been performed once since the IG_ON signal was turned on.

[0062] If the determination in step S1 is NO and the number of times the deterioration diagnosis of the rear O2 sensor SN6 has been performed is equal to or greater than the first determination number, the PCM 100 sets the diagnosis execution flag to 0 and resets the timer that was turned ON in step S6, which will be described later, to 0 (zero) (step S14). After step S14, the PCM 100 ends the process (returns to step S1) without performing steps S2 to S13. The diagnosis execution flag is a flag used in catalyst protection control, as will be described later, and is set to 1 while the deterioration diagnosis of the rear O2 sensor SN6 is being performed and is set to 0 at other times.

[0063] Here, whether the rear O2 sensor SN6 has deteriorated is determined in steps S10 and S11. Therefore, if the determination in step S1 is NO and the number of times the deterioration diagnosis of the rear O2 sensor SN6 has been performed is equal to or greater than the first determination number, the deterioration diagnosis of the rear O2 sensor SN6 is not performed thereafter (until IG_OFF is set). In other words, in the first embodiment, the number of times the deterioration diagnosis of the rear O2 sensor SN6 is performed during one driving cycle is limited to the diagnosis number.

[0064] On the other hand, if the determination in step S1 is YES and the number of times the deterioration diagnosis of the rear O2 sensor SN6 has been performed is less than the first determination number, the PCM 100 reads various information including the detected values ​​of the sensors SN1 to SN9 (step S2). In step S2, the PCM 100 reads at least the engine speed detected by the crank angle sensor SN1 and the accelerator opening detected by the accelerator sensor SN7.

[0065] Next, the PCM 100 determines whether a fuel cut is in progress (step S3). Specifically, the PCM 100 determines whether the above-described fuel cut condition is met and whether fuel injection from the injectors 11 of all cylinders 2A has stopped. If the determination in step S3 is NO, meaning that a fuel cut is not in progress, the PCM 100 proceeds to step S14, sets the diagnosis execution flag to 0, and ends the process (returns to step S1). On the other hand, if the determination in step S3 is YES, meaning that a fuel cut is in progress, the PCM 100 starts a deterioration diagnosis of the rear O2 sensor SN6 and sets the diagnosis execution flag indicating this to 1 (step S4).

[0066] After step S4, the PCM 100 determines whether the RO2 output voltage is equal to or lower than the first determination voltage V1 (step S5). The PCM 100 makes the determination in step S5 based on the RO2 output voltage read when step S5 is performed. If the determination in step S5 is NO, meaning that the RO2 output voltage is higher than the first determination voltage V1, the process ends (returns to step S1). On the other hand, if the RO2 output voltage is equal to or lower than the first determination voltage V1, the PCM 100 turns on the timer to measure time (step S6). Note that if the timer is already on, it remains on and continues to measure time.

[0067] After step S6, the PCM 100 determines whether the RO2 output voltage is equal to or lower than the second determination voltage V2 (step S7). The PCM 100 makes the determination in step S7 based on the RO2 output voltage read when step S7 is performed. If the determination in step S7 is NO and the RO2 output voltage has not decreased to the second determination voltage V2, the process ends (returns to step S1). On the other hand, if the determination in step S7 is YES and the RO2 output voltage is equal to or lower than the second determination voltage V2, the PCM 100 stops the timer (step S8). In this way, the PCM 100 measures the time from when the RO2 output voltage decreases to the first determination voltage V1 to when it decreases to the second determination voltage V2. Hereinafter, this time will be referred to as the voltage decrease time. The first determination voltage V1 is preset to a value lower than the stoichiometric voltage and higher than the lean voltage, and is stored in the PCM 100. The second determination voltage V2 is preset to a value smaller than the first determination voltage V1 and is stored in the PCM 100.

[0068] After step S8, the PCM 100 determines whether the voltage drop time is longer than a determination time (step S9). The determination time is preset and stored in the PCM 100. If the determination in step S9 is YES and the voltage drop time is longer than the determination time, the PCM 100 determines that the rear O2 sensor SN6 has deteriorated (step S10). On the other hand, if the determination in step S9 is NO and the voltage drop time is equal to or shorter than the determination time, the PCM 100 determines that the rear O2 sensor SN6 has not deteriorated and is normal (step S11).

[0069] After step S10 or step S11, the PCM 100 sets the diagnosis execution flag to 0 (step S12). After step S12, the PCM 100 counts up the number of times the deterioration diagnosis of the rear O2 sensor has been performed. That is, the PCM 100 adds 1 to the number of times the deterioration diagnosis of the rear O2 sensor has been performed. The PCM 100 also resets the timer to 0 (zero) and ends the process (return to step S1).

[0070] In this way, when the number of diagnoses of the rear O2 sensor SN6 is less than the first determination number, the deterioration diagnosis of the rear O2 sensor SN6 is performed from the start of fuel cut until the RO2 output voltage becomes equal to or less than the second determination voltage V2. During this period, that is, while the diagnosis of the rear O2 sensor SN6 is being performed, the diagnosis execution flag is set to 1; otherwise, the diagnosis execution flag is set to 0.

[0071] (Catalyst protection control) Next, the catalyst protection control performed by the PCM 100 to prevent the catalyst device 31 from overheating will be described.

[0072] (Catalyst temperature conditions) 6 is a flowchart showing the procedure for calculating the catalyst protection flag. Catalyst protection control is performed when the catalyst temperature, which is the temperature of the catalytic converter 31, is high. Specifically, catalyst protection control is performed when the catalyst temperature is equal to or higher than a first judgment temperature, and when the catalyst temperature has reached or exceeded the first judgment temperature but has not yet fallen below a second judgment temperature. The catalyst protection flag is a flag that indicates whether the conditions for performing this catalyst protection control are met.

[0073] Steps S51 to S56 shown in FIG. 6 are repeatedly performed at predetermined intervals while IG_ON is on. First, the PCM 100 reads various information, including the detected values ​​of sensors SN1 to SN9 (step S51). In step S51, the PCM 100 reads at least the intake air volume detected by the air flow sensor SN2, the engine speed detected by the crank angle sensor SN1, and the intake air temperature detected by the intake air temperature sensor SN3. Next, the PCM 100 estimates the catalyst temperature, which is the temperature of the catalytic converter 31 (step S52). Specifically, the PCM 100 estimates the temperature of the exhaust gas based on the intake air volume, the engine speed, the intake air temperature, the amount of fuel injected from the injector 11, and the like, and estimates the catalyst temperature based on the estimated exhaust gas temperature. In this embodiment, the PCM 100 determines the catalyst temperature in this way, and the PCM 100 corresponds to the "catalyst temperature determining device" in addition to the "control unit" of the present invention.

[0074] Next, the PCM 100 determines whether the catalyst temperature estimated in step S52 is equal to or higher than a first judgment temperature (step S53). The first judgment temperature is set in advance and stored in the PCM 100. The first judgment temperature is set to, for example, about 900°C. If the determination in step S53 is YES, meaning that the catalyst temperature is equal to or higher than the first judgment temperature, the PCM 100 sets a catalyst protection flag to 1 (step S54).

[0075] On the other hand, if the determination in step S53 is NO and the catalyst temperature is less than the first judgment temperature, the PCM 100 determines whether the conditions that the catalyst protection flag is 1 and the catalyst temperature is less than the second judgment temperature are met (step S55). If the determination in step S55 is NO and the catalyst protection flag is 0 or the catalyst temperature is equal to or greater than the second judgment temperature, the PCM 100 ends the process (returning to step S51). That is, the PCM 100 maintains the value of the catalyst protection flag at its current value. On the other hand, if the determination in step S55 is YES, the catalyst protection flag is 1, and the catalyst temperature is less than the second judgment temperature, that is, if the catalyst temperature becomes equal to or greater than the first judgment temperature and the catalyst protection flag is set to 1, and then the catalyst temperature drops to less than the second judgment temperature, the PCM 100 sets the catalyst protection flag to 0 (step S56) and ends the process (returning to step S51).

[0076] In this way, the catalyst protection flag is set to 1 when the catalyst temperature is equal to or higher than the first judgment temperature, or when the catalyst temperature has reached or exceeded the first judgment temperature but has not yet dropped below the second judgment temperature, and the conditions for implementing catalyst protection control are met. In other cases, when the conditions for implementing catalyst protection control are not met, the flag is set to 0. The catalyst protection flag is set to 0 when IG_OFF is selected.

[0077] (Fuel cut control) Fig. 7 is a flowchart showing control mainly performed during fuel cut by the PCM 100 (main control unit 101). Steps S61 to S100 shown in Fig. 7 are repeatedly performed at predetermined intervals while IG_ON.

[0078] First, the PCM 100 reads various information including the detected values ​​of the sensors SN1 to SN9 (step S61). In step S61, the PCM 100 reads at least the engine speed detected by the crank angle sensor SN1 and the accelerator opening detected by the accelerator sensor SN7.

[0079] Next, the PCM 100 determines whether or not a fuel cut is in progress (step S62). Specifically, the PCM 100 determines whether or not the above-described fuel cut condition is met and the fuel injection of the injectors 11 of all the cylinders 2A has stopped.

[0080] If the determination in step S62 is NO, meaning that fuel cut is not being performed, the PCM 100 performs non-FC throttle control (step S100). Non-FC throttle control is control of the throttle valve 22 that is performed during normal operation when fuel cut is not being performed. Non-FC throttle control will be described later. After performing step S100, the PCM 100 ends the process (returns to step S61).

[0081] If the determination in step S62 is YES and fuel cut is in progress, the PCM 100 determines whether the catalyst protection flag is 1 (step S63). In step S63, the determination is made using the catalyst protection flag that is calculated separately based on the catalyst temperature as described above.

[0082] If the determination in step S63 is NO and the catalyst protection flag is 0, the PCM 100 proceeds to step S66. In step S66, the PCM 100 sets the normal FC opening to the target throttle opening, which is the target value of the throttle opening. As described above, the normal FC opening is preset to an opening close to fully closed. After step S66, the PCM 100 proceeds to step S67.

[0083] If the determination in step S63 is YES and the catalyst protection flag is 1, the PCM 100 determines whether the diagnosis execution flag is 0 (step S64). That is, the PCM 100 determines whether a deterioration diagnosis of the rear O2 sensor SN6 is being performed.

[0084] If the determination in step S64 is NO and the diagnosis execution flag is 1, that is, if a deterioration diagnosis of the rear O2 sensor SN6 is being performed, the PCM 100 proceeds to step S66, sets the normal FC opening to the target throttle opening, and then proceeds to step S67.

[0085] If the determination in step S64 is YES and the diagnosis execution flag is 0, that is, if the deterioration diagnosis of the rear O2 sensor SN6 is not being performed, the PCM 100 proceeds to step S65 and performs intake amount increase control, which is one type of catalyst protection control.

[0086] The intake air amount increase control is a control for increasing the intake air amount, which is the amount of air taken into the combustion chamber 5. In step S65, the PCM 100 sets the target throttle opening to an opening that is larger (more open) than the normal FC opening. In steps S69 and S71, which will be described later, the throttle valve 22 is opened and closed so as to achieve the target throttle opening. Therefore, when the intake air amount increase control is performed, the intake air amount is increased compared to when the intake air amount increase control is not performed (when step S66 is performed). After step S65, the process proceeds to step S67.

[0087] In step S67, the PCM 100 opens and closes the throttle valve 22 so that the opening of the throttle valve 22 becomes the target throttle opening set in step S65 or step S66. For example, the PCM 100 identifies the current opening of the throttle valve 22 based on the drive current of the throttle valve 22, the output of a throttle valve opening sensor capable of detecting the opening of the throttle valve 22, etc., and drives the throttle valve 22 based on the current opening of the throttle valve 22 and the target throttle opening. After step S67, the PCM 100 ends the process (returns to step S61).

[0088] Returning to step S67, if the determination is NO and the catalyst protection flag is 0, the PCM 100 opens and closes the throttle valve 22 so that the throttle opening becomes the target throttle opening set in step S65 or step S66 (step S72). Here, in step S72, unlike steps S69 and S70, the opening and closing speed of the throttle valve 22 is not changed depending on the catalyst temperature, but is opened and closed at a predetermined speed. Note that even when step S72 is performed, if the target throttle opening and the current throttle opening match, the PCM 100 controls the throttle valve 22 to maintain that opening, and then ends the process (returning to step S61).

[0089] As described above, during fuel cut (determined YES in step S62), if the catalyst protection flag is 1 (determined YES in step S63), and if the diagnosis execution flag is 0 and deterioration diagnosis of the rear O2 sensor SN6 is not being performed (determined YES in step S64), intake air amount increase control is performed and the throttle opening is set to an opening greater than the normal FC opening. This increases the intake air amount compared to when the catalyst protection flag is 0 (determined NO in step S63). Also, during fuel cut, even if the catalyst protection flag is 1 (determined YES in step S63), if the diagnosis execution flag is 1 and deterioration diagnosis of the rear O2 sensor SN6 is being performed (determined NO in step S64), intake air amount increase control is prohibited and the throttle opening is controlled to the normal FC opening.

[0090] (Throttle control when not in FC mode) Next, the non-FC throttle control in step S100 will be described with reference to the flowchart in FIG.

[0091] When the non-FC throttle control is started, the PCM 100 first calculates a target torque, which is a target value of the engine torque (step S101). The PCM 100 calculates the target torque based on the accelerator opening detected by the accelerator sensor SN7, the vehicle speed detected by the vehicle speed sensor SN9, etc.

[0092] Next, the PCM 100 sets a target intake air amount, which is a target value of the intake air amount (step S102). The PCM 100 sets the target intake air amount based on the target torque, the engine speed detected by the crank angle sensor SN1, and the like.

[0093] Next, the PCM 100 determines whether the catalyst protection flag is 1 (step S103). If the determination in step S103 is YES and the catalyst protection flag is 1, the PCM 100 determines whether the target intake air amount set in step S102 is greater than the upper limit intake air amount (step S104). The upper limit intake air amount is set in advance and stored in the PCM 100. If the determination in step S104 is YES and the target intake air amount is greater than the upper limit intake air amount, the PCM 100 resets the target intake air amount to the upper limit intake air amount (step S105). That is, the target intake air amount is changed from the value set in step S102 to the upper limit intake air amount. After step S105, the PCM 100 proceeds to step S106.

[0094] On the other hand, if the judgment in step S103 is NO and the catalyst protection flag is 0, or if the target intake air volume set in step S102 is equal to or less than the upper limit intake air volume, PCM100 proceeds to step S106 without performing step S105, i.e., while maintaining the target intake air volume at the value set in step S102.

[0095] In step S106, the PCM 100 opens and closes the throttle valve 22 so as to achieve the target intake air amount set in step S102 or the target intake air amount reset to the upper limit intake air amount in step S105. When step S106 is performed, the non-FC throttle control ends.

[0096] As described above, when fuel cut is not being performed and the catalyst protection flag is 1, the PCM 100 performs control to limit the target intake air amount, and therefore the intake air amount, to an upper limit intake air amount or less, as one of catalyst protection controls.

[0097] (effect, etc.) Fig. 9 is a time chart that schematically shows the change over time of each parameter when fuel cut is initiated after the number of diagnoses of the rear O2 sensor SN6 has reached the first determination number and the catalyst flag is set to 1. From top to bottom, Fig. 9 shows charts of the catalyst protection flag, fuel cut flag, throttle opening, intake air amount, and catalyst temperature. In the charts of throttle opening, intake air amount, and catalyst temperature in Fig. 9, the dotted lines represent the throttle opening, intake air amount, and catalyst temperature according to a comparative example, and show the change over time of these when the throttle opening after fuel cut is set to the opening when the catalyst flag is set to 0, i.e., the normal FC opening, without performing intake air amount increase control.

[0098] In the example of FIG. 9 , fuel cut is initiated at time t11 with the catalyst protection flag set to 1. In the example of FIG. 9 , the number of diagnoses of the rear O2 sensor SN6 has already reached the first determination number, and deterioration diagnosis of the rear O2 sensor SN6 is not performed. Thus, in the example of FIG. 9 , in the first embodiment, when fuel cut is initiated at time t11, intake air amount increase control is performed and the throttle opening is set to a larger (opening) opening than the normal FC opening. On the other hand, in the comparative example, intake air amount increase control is not performed, and the throttle opening is controlled to the normal FC opening at time t11. As a result, as shown in the intake air amount chart of FIG. 9 , the intake air amount during fuel cut in the first embodiment is greater than that in the comparative example. Accordingly, in the first embodiment, more air flows into the catalytic converter 31, and the catalytic converter 31 is cooled more effectively by this air. Therefore, as shown in the catalyst temperature chart of FIG. 9 , in the first embodiment, the temperature of the catalytic converter 31 drops quickly after time t11.

[0099] As described above, in the first embodiment, when the catalyst protection flag is 1 and the catalyst temperature is high, the throttle opening and therefore the intake amount during fuel cut are made larger than when the catalyst protection flag is 0 and the catalyst temperature is low. Therefore, according to the embodiment, the timing of fuel cut can be used to cool the high-temperature catalytic device 31 with a large amount of air, thereby enabling the temperature to be reduced quickly. As described above, when the catalyst flag is 1 and the catalyst temperature is high, this means that the catalyst temperature is equal to or higher than the first judgment temperature, or that the catalyst temperature has once reached or exceeded the first judgment temperature but has not yet fallen below the second judgment temperature. When the catalyst flag is 0 and the catalyst temperature is low, this means that the catalyst temperature is lower than the second judgment temperature, or that the catalyst temperature has reached or exceeded the second judgment temperature but has not yet reached the first judgment temperature.

[0100] However, if the intake air amount increase control is performed while the deterioration diagnosis of the rear O2 sensor SN6 is being performed, an erroneous diagnosis of the rear O2 sensor SN6 may occur. This will be described in detail with reference to FIG. 10. FIG. 10 is a time chart that schematically illustrates the time variation of each parameter when the number of diagnoses of the rear O2 sensor SN6 has not reached the first determination number, the catalyst flag is set to 1, and a fuel cut is initiated at time t21. From top to bottom, FIG. 10 illustrates the following charts: catalyst protection flag, fuel cut flag, diagnosis execution flag, throttle opening, intake air amount, rear air-fuel ratio, and RO2 output voltage. In the charts of throttle opening, intake air amount, rear air-fuel ratio, and RO2 output voltage in FIG. 10, the dotted line indicates the time variation of each parameter in a comparative example in which the intake air amount increase control is not prohibited even while the deterioration diagnosis of the rear O2 sensor SN6 is being performed. In addition, in the chart of RO2 output voltage in FIG. 10, the solid line indicates the RO2 output voltage when the rear O2 sensor SN6 is not deteriorated in the first embodiment. In addition, the dashed line indicates the RO2 output voltage when the rear O2 sensor SN6 is not deteriorated and is normal in the comparative example, and the dashed line indicates the RO2 output voltage when the rear O2 sensor SN6 is deteriorated, that is, when it is malfunctioning, in the comparative example.

[0101] In the first embodiment, if a fuel cut is initiated when the number of diagnoses of the rear O2 sensor SN6 has not yet reached the first determination number, a deterioration diagnosis of the rear O2 sensor SN6 is initiated (the diagnosis execution flag is switched from 0 to 1). Also, in the first embodiment, even if the catalyst protection flag is 1, intake air amount increase control is prohibited while a deterioration diagnosis of the rear O2 sensor SN6 is being performed. As a result, in the first embodiment, at time t21, the throttle valve 12 is controlled so that its opening becomes the normal FC opening. By controlling the throttle opening to the normal FC opening, the intake air amount is significantly reduced after time t21.

[0102] On the other hand, in the comparative example, at time t21, deterioration diagnosis of the rear O2 sensor SN6 is started, and intake air amount increase control is performed, and the throttle valve 12 is controlled so that its opening is larger (more open) than the normal FC opening. In the comparative example, the intake air amount is also reduced after time t21, as in the first embodiment. However, in the comparative example, the throttle opening is controlled to a relatively large opening, so the reduction in the intake air amount is kept small.

[0103] When fuel cut starts at time t21 and fuel supply to the combustion chamber 5 is stopped, the rear air-fuel ratio gradually becomes leaner (larger) in both the first embodiment and the comparative example. However, in the first embodiment, after time t21, the intake air amount is significantly reduced along with the fuel amount. Therefore, in the first embodiment, after time t21, the rear air-fuel ratio changes relatively slowly. On the other hand, in the comparative example, the amount of fuel is reduced relatively more than the intake air amount, which is reduced by a small amount after time t21, so the rear air-fuel ratio rapidly becomes leaner.

[0104] As described above, when the rear O2 sensor SN6 deteriorates, the rate at which its output voltage (RO2 output voltage) decreases slows. However, as described above, in the comparative example, the rear air-fuel ratio itself rapidly becomes lean. Therefore, as shown by the two-dot chain line in FIG. 10, in the comparative example, even if the rear O2 sensor SN6 deteriorates, the rate at which the RO2 output voltage decreases does not slow down sufficiently. As a result, in the comparative example, there is a risk that the rear O2 sensor SN6 may be erroneously diagnosed as not having deteriorated, even though it has deteriorated.

[0105] Thus, if the intake air amount increase control is performed while the deterioration diagnosis of the rear O2 sensor SN6 is being performed, there is a risk that the deterioration diagnosis will not be performed appropriately. In contrast, in the first embodiment, the intake air amount increase control is prohibited while the deterioration diagnosis of the rear O2 sensor SN6 is being performed. Therefore, it is possible to avoid the deterioration diagnosis not being performed appropriately.

[0106] Furthermore, in the first embodiment, the intake air amount increase control is prohibited only while the deterioration diagnosis of the rear O2 sensor SN6 is being performed, and when the deterioration diagnosis of the rear O2 sensor SN6 is completed, the intake air amount increase control is initiated to increase the intake air amount. In the example of Fig. 10, when the deterioration diagnosis of the rear O2 sensor SN6 is completed as the RO2 output voltage drops to the second determination voltage V2 at time t22 (the diagnosis execution flag switches from 1 to 0), the intake air amount increase control is initiated to increase the throttle opening and the intake air amount. Therefore, according to the first embodiment, while preventing an erroneous diagnosis of deterioration of the rear O2 sensor SN6, there are more opportunities to perform the intake air amount increase control, i.e., to cool the catalytic device, and it is possible to more reliably prevent the catalytic device 31 from becoming excessively hot.

[0107] In the first embodiment, the deterioration of the rear O2 sensor SN6 is diagnosed based on the RO2 output voltage at the start of fuel cut, i.e., the output voltage of the rear O2 sensor SN6. Therefore, by utilizing the fact that the rear air-fuel ratio changes significantly at the start of fuel cut, it is possible to appropriately diagnose whether the rear O2 sensor SN6 has deteriorated.

[0108] In particular, the rear O2 sensor SN6 is a λ sensor whose output changes relatively significantly when the air-fuel ratio of the exhaust gas changes. Therefore, according to the first embodiment, deterioration of the rear O2 sensor can be appropriately diagnosed by utilizing the timing when the air-fuel ratio of the exhaust gas changes at the start of fuel cut.

[0109] In the first embodiment, the number of times the rear O2 sensor SN6 is diagnosed for deterioration during one driving cycle is limited to the diagnosis count. That is, after the number of times the rear O2 sensor SN6 is diagnosed for deterioration during one driving cycle reaches the diagnosis count, further diagnosis of the rear O2 sensor SN6 for deterioration is prohibited.

[0110] This allows the rear O2 sensor SN6 to be diagnosed for deterioration in each driving cycle, and prevents the intake air amount increase control from being reduced due to excessively frequent diagnosis. Therefore, the temperature of the catalytic converter 31 can be prevented from becoming excessively high while ensuring opportunities to diagnose the deterioration of the rear O2 sensor SN6.

[0111] Furthermore, in the first embodiment, when the catalyst protection flag is 1 and the catalyst temperature is high, the intake air amount is prevented from exceeding the upper intake air amount while fuel cut is not being performed, and the combustion energy generated in the combustion chamber is kept low. This makes it possible to more reliably prevent the catalyst temperature from becoming excessively high.

[0112] However, if the number of opportunities to restrict the intake air amount increases, the number of opportunities to restrict engine output also increases, which may result in a deterioration in vehicle drivability. In contrast, in the above embodiment, the catalytic converter 31 is cooled when a fuel cut is performed to prevent the temperature from rising excessively. This reduces the opportunities for the catalyst temperature to become high when a fuel cut is not performed, thereby suppressing a deterioration in vehicle drivability.

[0113] (Second embodiment) Next, an engine system according to a second embodiment to which an engine control device according to the present invention is applied will be described. In the first embodiment, the PCM 100 (diagnosis unit 102) performs a deterioration diagnosis of the rear O2 sensor SN6 as an abnormality diagnosis. In contrast, in the second embodiment, the PCM 100 (diagnosis unit 102) performs a fault diagnosis of the EGR device 40 as an abnormality diagnosis. Except for the content of this abnormality diagnosis, other configurations are substantially the same between the first and second embodiments. Therefore, the following mainly describes the abnormality diagnosis according to the second embodiment. Hereinafter, the abnormality diagnosis performed by the PCM 100 will be referred to as a fault diagnosis of the EGR device 40 where appropriate. The EGR device 40 includes an EGR passage 41 through which exhaust gas passes, and is provided in a portion through which exhaust gas passes. In the second embodiment, the EGR valve 43 corresponds to the "exhaust component" of the present invention.

[0114] (EGR valve failure diagnosis) An outline of the fault diagnosis of the EGR device 40 will be explained using Fig. 11. Fig. 11 shows the time variations of the throttle opening, the EGR opening which is the opening of the EGR valve 43, and the intake pressure which is the pressure inside the intake passage 20.

[0115] When the throttle opening is maintained at a constant value, the intake pressure changes depending on the opening / closing state of the EGR valve 43. Specifically, when the throttle opening is maintained at a constant value and the EGR valve 43 is fully closed and the EGR opening is maintained at 0 (zero), the intake pressure is maintained at a constant value, as shown by the dotted line in Figure 11. In contrast, when the EGR opening is increased from a state in which the throttle opening and EGR opening are maintained constant, and the EGR valve 43 is opened (at time t201), the intake pressure increases, as shown by the solid line in Figure 11. However, when the EGR valve 43 malfunctions, specifically, when the EGR valve 43 does not open properly despite receiving a command to open the EGR valve 43, or when the EGR passage 41 is clogged and EGR gas is not properly introduced into the intake passage 20, the intake pressure does not increase but remains at a value equivalent to the value before the command to open the valve was issued.

[0116] Using this, the PCM 100 issues a valve opening command to the EGR valve 43 with the throttle opening kept constant, and if the amount of change dP in the intake pressure generated at that time is equal to or greater than a predetermined determined pressure increase amount, the PCM 100 diagnoses that the EGR valve 43 is not malfunctioning and that the EGR passage 41 is not clogged, i.e., that the EGR device 40 is normal. On the other hand, if the amount of change in the intake pressure is less than the determined pressure increase amount, the PCM 100 diagnoses that the EGR valve 43 is malfunctioning or that the EGR passage 41 is clogged, i.e., that the EGR device 40 is malfunctioning.

[0117] Here, if the throttle opening is forcibly maintained at a constant opening while fuel is being supplied to the combustion chamber 5, the realized engine output may differ from the driver's intention, which is undesirable. Therefore, the PCM 100 diagnoses whether or not the EGR device 40 has failed while maintaining the throttle opening at a constant opening when a fuel cut is performed.

[0118] Fig. 12 is a flowchart showing the contents of the failure diagnosis of the EGR device 40 performed by the PCM 100. Steps S201 to S214 shown in Fig. 12 are repeatedly performed at predetermined intervals while the IG_ON state is maintained.

[0119] First, the PCM 100 determines whether the number of times the fault diagnosis of the EGR device 40 has been performed is less than a second determination number (step S201). The diagnosis number is the number of times that the fault diagnosis of the EGR device 40 has been performed during the current driving cycle, and is the number of times that step S208 or step S29, which will be described later, has been performed. Note that the above diagnosis number is reset to 0 when the IG_OFF is set. The second determination number is set in advance and stored in the PCM 100. In the second embodiment, the second determination number is set to 1, and in step S201, it is determined whether the fault diagnosis of the EGR device 40 has been performed once since the IG_ON was set.

[0120] If the determination in step S201 is NO and the number of times the failure diagnosis of the EGR device 40 has been performed is equal to or greater than the second determination number, the PCM 100 sets the diagnosis execution flag to 0 (step S214) and ends the process (returns to step S201) without performing steps S202 to S213. In the second embodiment, the diagnosis execution flag is set to 1 while the failure diagnosis of the EGR device 40 is being performed, and is set to 0 otherwise.

[0121] Here, whether or not the EGR device 40 has failed is determined in steps S209 and S210. Therefore, if the determination in step S201 is NO and the number of times the failure diagnosis of the EGR device 40 has been performed is equal to or greater than the second determination number, the failure diagnosis of the EGR device 40 is not performed thereafter (until IG_OFF is set). In other words, in the second embodiment, the number of times the failure diagnosis of the EGR device 40 is performed during one driving cycle is limited to the diagnosis number.

[0122] If the determination in step S201 is YES and the number of times the EGR device 40 has been diagnosed is less than the second determination number, the PCM 100 reads various information including the detected values ​​of the sensors SN1 to SN9 (step S202). In step S202, the PCM 100 reads at least the engine speed detected by the crank angle sensor SN1 and the accelerator opening detected by the accelerator sensor SN7.

[0123] Next, the PCM 100 determines whether or not fuel is being cut (step S203), similarly to step S3 in the flowchart of Fig. 5. If the determination in step S203 is NO, meaning that fuel is not being cut, the PCM 100 proceeds to step S204, sets the diagnosis execution flag to 0, and ends the process (returns to step S1). On the other hand, if the determination in step S203 is YES, meaning that fuel is being cut, the PCM 100 starts a fault diagnosis of the EGR device 40 and sets the diagnosis execution flag indicating this to 1 (step S204).

[0124] 7, and when a fuel cut is being performed and the diagnosis execution flag is 1, the intake amount increase control is not performed and the throttle opening is controlled to the normal FC opening. Also, when a fuel cut accompanied by the execution of a fault diagnosis of the EGR device 40 starts, the EGR valve 43 is fully closed, as in the case of the start of a normal fuel cut.

[0125] After step S204, the PCM 100 determines whether a predetermined first period has elapsed since the start of fuel cut (step S205). The first period is preset to a period longer than the period from when the opening degrees of the throttle valve 12 and the EGR valve 43 are changed until the fluctuation in the intake air pressure converges, and is stored in the PCM 100. If the determination in step S205 is NO, meaning that the first period has not yet elapsed since the start of fuel cut, the PCM 100 ends the processing (returns to step S201). On the other hand, if the determination in step S205 is YES, meaning that the time elapsed since the start of fuel cut is equal to or longer than the first period, the PCM 100 proceeds to step S206. That is, the PCM 100 waits for the first period to elapse since the start of fuel cut before executing step S206. In step S206, the PCM 100 opens the EGR valve 43. In the second embodiment, the EGR valve 43 is fully opened at this time.

[0126] Next, the PCM 100 determines whether a predetermined second period has elapsed since the EGR valve 43 was opened (step S207). The second period is preset to a period longer than the period from when the opening degree of the EGR valve 43 is changed until the fluctuation in the intake pressure converges, and is stored in the PCM 100. If the determination in step S207 is NO, meaning that the second period has not yet elapsed since the EGR valve 43 was opened, the PCM 100 ends the processing (returns to step S201). On the other hand, if the determination in step S207 is YES, meaning that the time elapsed since the EGR valve 43 was opened is equal to or longer than the second period, the PCM 100 proceeds to step S208. That is, the PCM 100 waits for the second period to elapse since the EGR valve 43 was opened, and then executes step S208.

[0127] In step S208, the PCM 100 determines whether the increase in intake pressure caused by the opening of the EGR valve 43 is less than a determined boost amount. Specifically, the PCM 100 calculates the increase in intake pressure by subtracting the intake pressure detected by the intake pressure sensor SN4 immediately before execution of step S206 from the intake pressure detected by the intake pressure sensor SN4 when step S208 is executed, and compares this with the determined boost amount. The determined boost amount is set in advance and stored in the PCM 100.

[0128] If the determination in step S208 is YES and the increase in intake pressure is less than the determined pressure increase amount, that is, if the intake pressure does not increase sufficiently even though the EGR valve 43 is changed from fully closed to fully open, the PCM 100 determines that the EGR device 40 is malfunctioning (step S209).On the other hand, if the determination in step S208 is NO and the increase in intake pressure is equal to or greater than the determined pressure increase amount, the PCM 100 determines that the EGR device 40 is normal and not malfunctioning (step S210).

[0129] After step S209 or step S210, the PCM 100 fully closes the EGR valve 43 again (step S211). The PCM 100 also sets the diagnosis execution flag to 0 (step S212). The PCM 100 also counts up the number of diagnoses of the EGR device 40 (step S213), and then ends the processing (return to step S201). This completes the failure diagnosis of the EGR device 40.

[0130] As described above, in the second embodiment, the abnormality diagnosis is performed by diagnosing whether or not there is a malfunction in the EGR device 40. In addition, in the second embodiment, the diagnosis execution flag is set to 1 during the period from the start of fuel cut to the end of the malfunction diagnosis of the EGR device 40, specifically, during the period from the start of fuel cut to the time when the EGR valve 43 is fully closed again, and the diagnosis execution flag is set to 0 at other times.

[0131] As described above, in the second embodiment, the PCM 100 also performs the same control as the control according to the first embodiment shown in the flowchart of FIG. 7. Therefore, in the second embodiment, even during fuel cut, the intake air amount increase control is prohibited while a fault diagnosis of the EGR device 40 is being performed and the diagnosis execution flag is set to 1. On the other hand, in the second embodiment, during fuel cut and while a fault diagnosis of the EGR device 40 is not being performed, the intake air amount increase control is performed and the intake air amount is limited to an upper limit intake air amount or less. As a result, according to the second embodiment, it is possible to prevent the catalytic converter 31 from overheating and to appropriately perform a fault diagnosis of the EGR device 40.

[0132] The fact that the second embodiment can appropriately perform a fault diagnosis of the EGR device 40 will be specifically described using the time chart of Fig. 13. Fig. 13 is a time chart showing the time changes of each parameter during fuel cut according to the second embodiment.

[0133] Fig. 13 is a time chart that schematically shows the change over time of each parameter when fuel cut is initiated at time t211 while the number of failure diagnoses of the EGR device 40 has not reached the second determination number and the catalyst flag is set to 1. From top to bottom, Fig. 13 shows charts for the catalyst protection flag, fuel cut flag, diagnosis execution flag, throttle opening, EGR opening, and intake pressure. In the charts of throttle opening and intake pressure in Fig. 13, the dotted lines indicate the change over time of each parameter in a comparative example in which intake amount increase control is performed while a failure diagnosis of the EGR device 40 is being performed.

[0134] In the second embodiment, the EGR failure diagnosis starts at time t211 (the diagnosis execution flag switches from 0 to 1), and the intake amount increase control is prohibited. As a result, in the second embodiment, at time t211, the throttle valve 12 is controlled so that its opening becomes the normal FC opening that is close to fully closed. Accordingly, after time t211, the intake pressure is significantly reduced.

[0135] On the other hand, in the comparative example, the intake amount increase control is performed when the fuel cut is started, so that the throttle opening is set to a larger (opening side) opening than the normal FC opening at time t211. Accordingly, in the comparative example, the intake pressure is maintained at a relatively high value even after time t211.

[0136] In both the second embodiment and the comparative example, the EGR valve 43 is fully closed at time t211 when fuel cut begins, and then opened at time t212, one hour after time t211. Accordingly, in both the second embodiment and the comparative example, the intake pressure increases. However, in the comparative example, the intake pressure is high before time t212. Therefore, the increase amount dP2 of the intake pressure in the comparative example is kept small. As described above, the PCM 100 determines that the EGR device 40 is malfunctioning when the increase amount of the intake pressure when the EGR valve 43 is open is less than the determined increase amount. Therefore, in the comparative example, even if the EGR device 40 is functioning normally, the increase amount dP2 of the intake pressure may be less than the determined increase amount, resulting in an erroneous determination that the EGR device 40 is malfunctioning. In contrast, in the above embodiment, if the EGR device 40 is functioning normally, the increase amount dP1 of the intake pressure when the EGR valve 43 is open is sufficiently large. Therefore, according to the above embodiment, it is possible to avoid erroneously determining that the EGR device 40 is abnormal when it is actually normal. In other words, according to the above embodiment, it is possible to appropriately perform a fault diagnosis of the EGR device 40. In the example of Fig. 13, the EGR fault diagnosis ends at time t213 after time t212, the EGR valve 43 is fully closed again, and the intake amount increase control is started to change the throttle opening from the normal FC opening to a more open opening.

[0137] Among the functions of the first embodiment described above, functions obtained by the configuration common to the second embodiment can also be obtained in the second embodiment.

[0138] (Variation) In the first embodiment, when the intake air amount increasing control is performed and when the control for limiting the intake air amount to an upper limit intake air amount is performed, the intake air amount is increased or decreased by increasing or decreasing the opening degree of the throttle valve 22. However, the device for increasing or decreasing the intake air amount is not limited to the throttle valve 22. For example, a variable valve mechanism capable of changing the opening and closing timing of the intake valve 8 may be provided in the device that drives the intake valve 8, and the intake air amount may be increased or decreased by changing the opening and closing timing of the intake valve 8.

[0139] In the above first embodiment, the catalyst protection control (intake air amount increase control and control to limit the intake air amount to or below the upper limit intake air amount) is described as being performed when the catalyst temperature is equal to or higher than the first judgment temperature, and when the catalyst temperature has become equal to or higher than the first judgment temperature but has not yet dropped below the second judgment temperature. However, the condition of when the catalyst temperature has become equal to or higher than the first judgment temperature but has not yet dropped below the second judgment temperature may be excluded from the conditions for performing catalyst protection control.

[0140] Furthermore, in the above first and second embodiments, a case was described in which, during a single fuel cut, intake volume increase control is started after the deterioration diagnosis of the rear O2 sensor SN6 or the failure diagnosis of the EGR device 40 is completed, but during a fuel cut in which the deterioration diagnosis of the rear O2 sensor SN6 or the failure diagnosis of the EGR device 40 is performed, the intake volume increase control may be prohibited until the fuel cut is completed.

[0141] Furthermore, the first and second embodiments may be combined to perform both a deterioration diagnosis of the rear O2 sensor SN6 and a failure diagnosis of the EGR device 40 during fuel cut. For example, the failure diagnosis of the EGR device 40 may be performed after the deterioration diagnosis of the rear O2 sensor SN6 is completed, and then the intake amount increase control may be started.

[0142] In the above embodiment, the exhaust components that are subject to abnormality diagnosis that is performed in priority over intake volume increase control during fuel cut and that are located in a section through which exhaust gas passes are described as the rear O2 sensor SN6 (first embodiment) and the EGR device 40 (second embodiment), but the above exhaust components are not limited to these.

[0143] In the above first embodiment, a case has been described in which the first determination count is 1, but the first determination count may be set to a value greater than 1. In addition, in the above second embodiment, a case has been described in which the second determination count is 1, but the second determination count may be set to a value greater than 1.

[0144] In the first embodiment, the catalytic device 31 includes a three-way catalyst as a catalyst, but the catalyst included in the catalytic device 31 is not limited to this. Also, in the first embodiment, the injector 11 is a side injection type, but the injection type of the injector 11 is not limited to this. Also, the case where fuel is injected directly into the combustion chamber 5 is described, but the fuel injection form is not limited to this. Also, the specific structure of the engine body 1, such as the number of cylinders, is not limited to the above. [Explanation of symbols]

[0145] 1 Engine body 5 Combustion chamber 11 Injector (fuel supply device) 20 Intake passage 22 Throttle valve (intake volume control device) 30 Exhaust passage 31 Catalytic converter 40 EGR device (exhaust part according to the second embodiment) 41 EGR passage 43 EGR valve 91 Accelerator pedal 100 PCM (control unit, catalyst temperature identification device) SN4 intake pressure sensor SN6 Rear O2 sensor (air-fuel ratio sensor, exhaust part related to the first embodiment) SN7 Accelerator sensor (accelerator opening detection device)

Claims

1. In a control device for an engine provided in a vehicle equipped with an accelerator pedal, an engine body in which a combustion chamber is formed; an exhaust passage and an intake passage, each connected to the engine body; a fuel supply device for supplying fuel to the combustion chamber; an intake air amount adjusting device that adjusts an intake air amount, which is the amount of air taken into the combustion chamber; a catalytic converter provided in the exhaust passage for purifying exhaust gas; a catalyst temperature specifying device for specifying a catalyst temperature, which is the temperature of the catalyst device; an accelerator opening detection device that detects an accelerator opening, which is the opening of the accelerator pedal; a control unit for controlling the fuel supply device and the intake air amount adjustment device, The control unit a fuel cut is performed to stop fuel injection by the fuel supply device when the accelerator opening detected by the accelerator opening detection device is less than a predetermined accelerator judgment opening; When the catalyst temperature specified by the catalyst temperature specifying device is high during the fuel cut, an intake amount increase control is performed to control the intake amount adjustment device so that the intake amount is larger than when the catalyst temperature is low, When the fuel cut is performed, an abnormality diagnosis is performed to determine whether or not an exhaust part provided in a portion through which exhaust gas passes is abnormal, The engine control device is characterized in that the intake amount increase control is prohibited while the abnormality diagnosis is being performed even when the fuel cut is being performed.

2. 2. The engine control device according to claim 1, 10. An engine control device according to claim 9, wherein the control unit starts the intake amount increase control after the abnormality diagnosis is completed if the catalyst temperature is high during the fuel cut.

3. 2. The engine control device according to claim 1, the exhaust component includes an air-fuel ratio sensor provided in the exhaust passage to detect an air-fuel ratio of the exhaust gas; When the abnormality diagnosis is performed, the control unit diagnoses whether the air-fuel ratio sensor has deteriorated based on an output of the air-fuel ratio sensor at the start of the fuel cut.

4. 4. The engine control device according to claim 3, the control unit prohibits a diagnosis of whether the air-fuel ratio sensor has deteriorated after the number of times that the control unit has diagnosed whether the air-fuel ratio sensor has deteriorated in one driving cycle reaches a predetermined number of determinations.

5. 4. The engine control device according to claim 3, 10. An engine control device, wherein the air-fuel ratio sensor is disposed in the exhaust passage downstream of the catalytic converter.

6. 4. The engine control device according to claim 3, an air-fuel ratio sensor that is a λ sensor that detects whether the state of the exhaust gas is in one of three states: a state in which the air-fuel ratio is the stoichiometric air-fuel ratio, a state in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio, or a state in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio;

7. 2. The engine control device according to claim 1, an intake pressure sensor provided in the intake passage to detect an intake pressure, which is the pressure of intake air passing through the intake passage; the exhaust part includes an EGR device including an EGR passage that connects the exhaust passage and the intake passage and an EGR valve that opens and closes the EGR passage; When the abnormality diagnosis is performed, the control unit opens and closes the EGR valve and diagnoses whether the EGR device has failed based on a change in intake pressure detected by the intake pressure sensor.

8. 8. The engine control device according to claim 7, The control unit prohibits further diagnosis of whether the EGR device is malfunctioning after the number of times the control unit diagnoses whether the EGR device is malfunctioning in a single driving cycle reaches a predetermined number of determinations.

9. 2. The engine control device according to claim 1, The control unit is configured to limit the intake air amount to a predetermined upper limit intake air amount or less by the intake air amount adjusting device when the catalyst temperature is high and the fuel cut is not being performed.

10. The engine control device according to any one of claims 1 to 9, 10. An engine control device, wherein the intake amount adjusting device is a throttle valve provided in the intake passage for opening and closing the intake passage.

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