Control device for internal combustion engine

Abstract

To suppress degradation of abnormality diagnostic precision of a sensor.SOLUTION: An internal combustion engine 10 includes: a catalyst 32 disposed on an exhaust passage 30; and a second air-fuel ratio sensor 88 disposed at an exhaust downstream side with respect to the catalyst 32 and detecting an air-fuel ratio of an exhaust gas. A control device 70 executes active control of the air-fuel ratio and executes an increase processing for increasing an intake air amount during the execution of the active control. The control device 70 executes a sensor diagnosis processing for determining presence or absence of abnormality in the second air-fuel ratio sensor 88 during the execution of the active control. In the sensor diagnosis processing, a period necessary for the integrated suction air amount calculated during the execution of the active control to reach a specified threshold value is regarded as a maximum execution period. The control device 70 executes a prohibition processing for prohibiting the increase processing of the suction air amount during the execution of the sensor diagnosis processing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] For example, the internal combustion engine described in Patent Document 1 is equipped with a catalyst and a filter in an exhaust passage. The engine performs active control to enrich the air-fuel ratio and increases the intake air amount to regenerate the filter. Furthermore, a diagnostic process to determine whether the catalyst has deteriorated is performed during active control.

[0003] The internal combustion engine described in Patent Document 2 is provided with a sensor that is disposed downstream of the catalyst in the exhaust gas and detects the air-fuel ratio of the exhaust gas. Then, a diagnostic process is performed to determine whether or not there is an abnormality in the sensor based on a change in the detected value of the sensor while the active control is being executed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-183672 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-209861 Summary of the Invention [Problem to be solved by the invention]

[0005] When the above-described sensor diagnostic process is performed, the execution period of the diagnostic process may be set to the period until the cumulative intake air volume calculated during active control reaches a specified threshold. In this case, when the above-described intake air volume increase process is performed, the time until the cumulative intake air volume reaches the threshold is shortened. As the time until the cumulative intake air volume reaches the threshold is shortened, the execution period of the sensor diagnostic process is shortened. If the execution period of the sensor diagnostic process is shortened, it becomes difficult to secure the time required for the sensor diagnosis, which may result in a decrease in the accuracy of the sensor abnormality diagnosis. [Means for solving the problem]

[0006] A control device for an internal combustion engine that solves the above problem is applied to an internal combustion engine that includes a catalyst provided in an exhaust passage and a sensor provided downstream of the catalyst to detect the air-fuel ratio of the exhaust. The control device performs active control of the air-fuel ratio and also performs an intake air amount increase process to increase the intake air amount during the active control. The control device also performs a sensor diagnosis process to determine whether or not there is an abnormality in the sensor during the active control. The sensor diagnosis process has a maximum execution period that is the period until the cumulative intake air amount calculated during the active control reaches a specified threshold. The control device then performs a prohibition process to prohibit the execution of the intake air amount increase process during the sensor diagnosis process. [Effects of the Invention]

[0007] According to the present invention, it is possible to prevent a decrease in the accuracy of the abnormality diagnosis of the sensor. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the configuration of an internal combustion engine, a drive system, and a control device according to an embodiment. [Figure 2] 4 is a flowchart showing the procedure of a process executed by the control device of the embodiment. [Figure 3]10 is a timing chart showing the operation of the embodiment, where (a) shows the execution state of active control, (b) shows the execution state of processing to increase the intake air amount, and (c) shows the change in the integrated intake air amount OSA during execution of active control. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of a control device for an internal combustion engine will be described with reference to the drawings. <Configuration of the internal combustion engine, drive system, and control device> As shown in FIG. 1, an internal combustion engine 10 has four cylinders, for example, cylinders #1 to #4. A throttle valve 14 is provided in an intake passage 12 of the internal combustion engine 10. A port injection valve 16 that injects fuel into an intake port 12a, which is a downstream portion of the intake passage 12, is provided in the intake port 12a. Air drawn into the intake passage 12 and fuel injected from the port injection valve 16 flow into a combustion chamber 20 when an intake valve 18 opens. Fuel is injected into the combustion chamber 20 from an in-cylinder injection valve 22. The air-fuel mixture in the combustion chamber 20 is combusted in response to spark discharge from an ignition plug 24. The combustion energy generated at this time is converted into rotational energy of a crankshaft 26.

[0010] The air-fuel mixture burned in the combustion chamber 20 is discharged as exhaust gas into an exhaust passage 30 when the exhaust valve 28 opens. A catalyst 32 having oxygen storage capacity is provided in the exhaust passage 30. When combustion is performed near the stoichiometric air-fuel ratio, this catalyst 32 oxidizes HC and CO in the exhaust gas and reduces NOx in the exhaust gas, thereby purifying the exhaust gas. A filter 34 that collects particulate matter in the exhaust gas is provided downstream of the catalyst 32. Note that the filter 34 in this embodiment supports a catalyst for purifying the exhaust gas.

[0011] A first air-fuel ratio sensor 87 is provided on the exhaust upstream side of the catalyst 32. The first air-fuel ratio sensor 87 is a sensor that detects an upstream air-fuel ratio AFf, which is the air-fuel ratio of the exhaust gas flowing into the catalyst 32. In addition, a second air-fuel ratio sensor 88 is provided on the exhaust downstream side of the catalyst 32. The second air-fuel ratio sensor 88 is a sensor that detects a downstream air-fuel ratio AFr, which is the air-fuel ratio of the exhaust gas after it has passed through the catalyst 32.

[0012] The first air-fuel ratio sensor 87 and the second air-fuel ratio sensor 88 are well-known limiting current oxygen sensors. These limiting current oxygen sensors are sensors that obtain an output current corresponding to the oxygen concentration in the exhaust gas by incorporating a ceramic layer known as a diffusion-controlling layer in the detection section of a concentration cell-type oxygen sensor. When the air-fuel ratio, which is closely related to the oxygen concentration in the exhaust gas, is the stoichiometric air-fuel ratio, the output current of the limiting current oxygen sensor is "0." Furthermore, as the air-fuel ratio becomes richer, the output current increases in the negative direction, and as the air-fuel ratio becomes leaner, the output current increases in the positive direction. Therefore, the degree to which the air-fuel ratio is lean or rich can be detected based on the outputs of these air-fuel ratio sensors.

[0013] The crankshaft 26 is mechanically connected to a carrier C of a planetary gear mechanism 50 that constitutes a power split device. A rotating shaft 52a of a first motor generator 52 is mechanically connected to a sun gear S of the planetary gear mechanism 50. A rotating shaft 54a of a second motor generator 54 and drive wheels 60 are mechanically connected to a ring gear R of the planetary gear mechanism 50. An AC voltage is applied to terminals of the first motor generator 52 by an inverter 56. An AC voltage is applied to terminals of the second motor generator 54 by an inverter 58.

[0014] The control device 70 controls the internal combustion engine 10, and operates operating parts of the internal combustion engine 10 such as the throttle valve 14, port injection valve 16, in-cylinder injection valve 22, and spark plug 24 to control the torque, exhaust gas component ratio, and other control variables. The control device 70 also controls the first motor-generator 52, and operates the inverter 56 to control the rotation speed, which is the control variable. The control device 70 also controls the second motor-generator 54, and operates the inverter 58 to control the torque, which is the control variable. Figure 1 shows operation signals MS1 to MS6 for the throttle valve 14, port injection valve 16, in-cylinder injection valve 22, spark plug 24, and inverters 56, 58, respectively.

[0015] The control device 70 references the intake air amount GA detected by the air flow meter 80 and the output signal Scr of the crank angle sensor 82 to control the control variable of the internal combustion engine 10. The control device 70 also references the coolant temperature THW, which is the temperature of the coolant for the internal combustion engine 10, detected by the water temperature sensor 86. The control device 70 also references the upstream air-fuel ratio AFf detected by the first air-fuel ratio sensor 87 and the downstream air-fuel ratio AFr detected by the second air-fuel ratio sensor 88. The control device 70 also references the output signal Sp of an output-side rotational angle sensor 89 that detects the rotational angle of the ring gear R. The control device 70 also references the output signal Sm1 of a first rotational angle sensor 90 that detects the rotational angle of the first motor-generator 52 to control the control variable of the first motor-generator 52. The control device 70 also references the output signal Sm2 of a second rotational angle sensor 92 that detects the rotational angle of the second motor-generator 54 to control the control variable of the second motor-generator 54. The control device 70 also refers to the accelerator operation amount ACCP, which is the amount of depression of the accelerator pedal detected by the accelerator sensor 94.

[0016] The control device 70 calculates the engine speed NE based on the output signal Scr of the crank angle sensor 82. The control device 70 also calculates the engine load factor KL based on the engine speed NE and the intake air amount GA. The engine load factor KL represents the ratio of the current amount of air flowing into the cylinder to the amount of air flowing into the cylinder when the internal combustion engine 10 is operating steadily under full load. The amount of air flowing into the cylinder is the amount of air flowing into each cylinder during the intake stroke. The control device 70 also calculates the vehicle speed SP of the vehicle equipped with the internal combustion engine 10 based on the output signal Sp of the output-side rotation angle sensor 89.

[0017] The control device 70 includes a CPU 72, a ROM 74, a storage device 75, and a peripheral circuit 76, which are capable of communicating with each other via a communication line 78. Here, the peripheral circuit 76 includes a circuit that generates a clock signal that regulates internal operations, a power supply circuit, a reset circuit, etc. The control device 70 controls the control amount by the CPU 72 executing a program stored in the ROM 74.

[0018] <Control and processing performed by the control device> The control device 70 controls the fuel injection of the port injection valves 16 and the in-cylinder injection valves 22. The control device 70 also controls the ignition timing of the spark plugs 24. The control device 70 also controls the air-fuel ratio of the mixture to a target air-fuel ratio AFt that is set based on the engine operating state. The control device 70 also calculates the required torque required for the vehicle to travel based on the accelerator operation amount ACCP and the vehicle speed SP. The control device 70 also controls the required output power Pe of the internal combustion engine 10 and the output torque of the first motor-generator 52 and the second motor-generator 54 so as to satisfy the required torque of the vehicle.

[0019] The control device 70 also calculates the deposition amount DPM, which is the amount of particulate matter trapped in the filter 34, based on the engine speed NE, the charging efficiency η, the coolant temperature THW, and the like. Then, it determines whether the deposition amount DPM is equal to or greater than a regeneration execution value DPMH. The regeneration execution value DPMH is set to a value at which the amount of particulate matter trapped in the filter 34 has increased and it is desired to remove the particulate matter. Then, when it is determined that the deposition amount DPM is equal to or greater than the regeneration execution value DPMH, the control device 70 makes a regeneration request to request the execution of regeneration control to remove the trapped particulate matter from the filter 34. Then, when the conditions for permitting the execution of regeneration control are met, the control device 70 executes regeneration control.

[0020] As this regeneration control, the control device 70 executes, for example, active control of the air-fuel ratio, processing to increase the intake air amount, and the like. Active control of the air-fuel ratio is a well-known control method that sets the target air-fuel ratio AFt of the mixture to an air-fuel ratio richer than the stoichiometric air-fuel ratio. When the air-fuel ratio of the mixture is set to an air-fuel ratio richer than the stoichiometric air-fuel ratio, the amount of unburned fuel contained in the combustion gas increases. This unburned fuel is oxidized in the catalyst 32, causing the temperature of the exhaust gas to rise. This heated exhaust gas flows into the filter 34, causing the temperature of the filter 34 to rise. When the temperature of the filter 34 rises in this way, the amount of particulate matter trapped in the filter 34 decreases, thereby causing the filter 34 to be regenerated.

[0021] The intake air amount increase process is a process for increasing the amount of intake air of the internal combustion engine 10 compared to when the intake air amount increase process is not executed. When the intake air amount is increased in this way, the output of the internal combustion engine 10 increases, and the exhaust temperature rises. This increase in exhaust temperature also causes the filter 34 to be regenerated. Note that the intake air amount increase process is executed when it is determined that there is no abnormality in the catalyst 32 in the catalyst diagnosis process described below, and when the sensor diagnosis process described below has been completed.

[0022] During active control, the control device 70 uses a known method to calculate the maximum oxygen storage amount Cmax of the catalyst 32. If the calculated maximum oxygen storage amount Cmax is equal to or greater than a specified threshold, the control device 70 determines that there is no abnormality in the catalyst 32, but if the maximum oxygen storage amount Cmax is less than the threshold, the control device 70 executes a catalyst diagnosis process to determine that there is an abnormality in the catalyst 32.

[0023] Furthermore, the control device 70 executes a sensor diagnostic process to diagnose whether or not the second air-fuel ratio sensor 88 is malfunctioning during active control. In this sensor diagnostic process, an integrated intake air amount OSA, which is an integrated value of the intake air amount since the start of active control, is calculated. If the downstream air-fuel ratio AFr, which is the detection value of the second air-fuel ratio sensor 88, indicates a value richer than the stoichiometric air-fuel ratio during the period until the integrated intake air amount OSA reaches a specified threshold value OSAref, the control device 70 determines that the second air-fuel ratio sensor 88 is malfunctioning. On the other hand, if the downstream air-fuel ratio AFr, which is the detection value of the second air-fuel ratio sensor 88, does not indicate a value richer than the stoichiometric air-fuel ratio during the period until the integrated intake air amount OSA reaches the specified threshold value OSAref, the control device 70 determines that the second air-fuel ratio sensor 88 is malfunctioning. In this way, the sensor diagnostic process is executed for a maximum period until the integrated intake air amount OSA, which is calculated during active control, reaches the threshold value OSAref. When it is determined whether or not there is an abnormality in the second air-fuel ratio sensor 88, the control device 70 completes the execution of the sensor diagnosis process.

[0024] The threshold value OSAref is a value of the integrated intake air amount OSA that can ensure the execution time TD of the sensor diagnosis process necessary to detect an abnormality in the second air-fuel ratio sensor 88 in just the right amount. If the value of the threshold value OSAref is too small, the execution time of the sensor diagnosis process will be insufficient. On the other hand, if the value of the threshold value OSAref is too large, the time until the sensor diagnosis process is completed will be excessively long. Therefore, an appropriate value that does not cause such inconvenience is set in advance for the threshold value OSAref.

[0025] <Procedure for prohibiting the increase in intake air volume> 2 shows the procedure for the process executed by the control device 70 to prohibit the intake air amount increase process described above until the sensor diagnosis process is completed. The process shown in FIG. 2 is realized by the CPU 72 executing a program stored in the ROM 74. The process shown in FIG. 2 is started by the control device 70 when the active control is being executed and various predetermined execution conditions that respectively permit the catalyst diagnosis process and the sensor diagnosis process are met. Note that, hereinafter, the step numbers of each process are represented by numbers preceded by "S."

[0026] When the series of processes shown in FIG. 2 is started, the control device 70 executes the prohibition process for prohibiting the process for increasing the intake air amount described above (S110). Next, the control device 70 starts calculating the cumulative intake air amount OSA (S120).

[0027] Next, the control device 70 executes the catalyst diagnostic process and the sensor diagnostic process (S130). Next, the control device 70 determines whether the cumulative intake air amount OSA is equal to or greater than the threshold value OSAref (S140). If it is determined that the cumulative intake air amount OSA is less than the threshold value OSAref, the control device 70 repeatedly executes the process of S140.

[0028] As time passes, the value of the cumulative intake air amount OSA increases, and when it is determined in the process of S140 that the cumulative intake air amount OSA is equal to or greater than the threshold value OSAref, the control device 70 completes the sensor diagnosis process (S150).Then, the control device 70 starts the process of increasing the intake air amount, which has been prohibited (S160), and ends this process.

[0029] Incidentally, when the intake air amount is increased at S160, the output of the internal combustion engine 10 increases. The control device 70 reduces the output torque of the second motor generator 54 by an amount corresponding to the increase in the output of the internal combustion engine 10, thereby suppressing changes in the torque required for vehicle running.

[0030] <Action and effect> The operation and effects of this embodiment will be described with reference to FIG. FIG. 3 illustrates changes in various values when the downstream air-fuel ratio AFr, which is the detected value of the second air-fuel ratio sensor 88, does not indicate a value richer than the stoichiometric air-fuel ratio during execution of active control, that is, when there is an abnormality in the second air-fuel ratio sensor 88.

[0031] 3(a) shows the active control state, FIG. 3(b) shows the intake air amount increase process execution state, and FIG. 3(c) shows the change in the integrated intake air amount OSA during the active control execution state.

[0032] At time t1, when active control is executed and the conditions for executing catalyst diagnostic processing and sensor diagnostic processing are met, the control device 70 starts the processing shown in Fig. 2. As a result, the catalyst diagnostic processing and sensor diagnostic processing are executed, and the value of the cumulative intake air amount OSA increases over time.

[0033] Then, when the cumulative intake air amount OSA reaches the threshold value OSAref at time t3, the execution of the sensor diagnostic process is completed. In this example, because there is an abnormality in the second air-fuel ratio sensor 88, the downstream air-fuel ratio AFr does not indicate a value richer than the stoichiometric air-fuel ratio during the period from time t1 to time t3, that is, within the execution time TD of the sensor diagnostic process. Therefore, at time t3, the control device 70 determines that there is an abnormality in the second air-fuel ratio sensor 88.

[0034] If the intake air amount increasing process is started at time t2 during the execution of the sensor diagnosis process, as indicated by the two-dot chain line L1, the cumulative intake air amount OSA increases at a faster rate after time t2, as indicated by the two-dot chain line L2. As a result, the cumulative intake air amount OSA reaches the threshold value OSAref in a shorter time, which may result in the sensor diagnosis process being terminated early before the execution time TD has elapsed.

[0035] In this regard, in this embodiment, the process for increasing the intake air amount is prohibited until the sensor diagnosis process is completed. In other words, the process for increasing the intake air amount is prohibited while the sensor diagnosis process is being executed. Therefore, it is possible to prevent the time required for the integrated intake air amount OSA to reach the threshold value OSAref from being shortened by executing the process for increasing the intake air amount. Therefore, it is possible to prevent a decrease in the accuracy of diagnosing an abnormality of the second air-fuel ratio sensor 88 due to a shortened execution period of the sensor diagnosis process.

[0036] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0037] The second air-fuel ratio sensor 88 may be a well-known concentration cell type oxygen sensor. This concentration cell type oxygen sensor produces an output of approximately 1 V when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and an output of approximately 0 V when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Furthermore, this sensor's output voltage changes significantly near the stoichiometric air-fuel ratio. Therefore, this oxygen sensor is capable of detecting whether the air-fuel ratio is lean or rich.

[0038] The filter 34 is not limited to a filter carrying a catalyst, but may be a filter alone. The control device is not limited to one equipped with a CPU 72 and a ROM 74 and executing software processing. For example, it may be equipped with a dedicated hardware circuit, such as an ASIC, that performs hardware processing on at least a portion of the software processing performed in the above embodiments. That is, the control device may have any of the following configurations (a) to (c): (a) equipped with a processing device that executes all of the above processing in accordance with a program, and a program storage device, such as a ROM, that stores the program; (b) equipped with a processing device and program storage device that executes part of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing; or (c) equipped with a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices equipped with a processing device and a program storage device, and multiple dedicated hardware circuits.

[0039] The vehicle is not limited to a series-parallel hybrid vehicle, but may be, for example, a parallel hybrid vehicle or a series hybrid vehicle. However, it is not limited to a hybrid vehicle, and may be, for example, a vehicle whose prime mover is only an internal combustion engine 10. Incidentally, in a vehicle whose prime mover is only an internal combustion engine 10, the increase in output of the internal combustion engine 10 that accompanies the execution of the intake air amount increase process may be offset by, for example, increasing the drive load of various accessories provided to the internal combustion engine 10. [Explanation of symbols]

[0040] 10...Internal combustion engine 12...Intake passage 12a...Intake port 14...Throttle valve 16...Port injection valve 18...Intake valve 20...Combustion chamber 22...In-cylinder injection valve 24...Spark plug 26...Crankshaft 28...Exhaust valve 30...Exhaust passage 32...Catalyst 34...Filter 50...Planetary gear mechanism 52...First motor generator 54...Second motor generator 56...Inverter 58...Inverter 60...Drive wheels 70...Control device 72...CPU 74...ROM 87...First air-fuel ratio sensor 88...Second air-fuel ratio sensor

Claims

1. The present invention is applied to an internal combustion engine including a catalyst provided in an exhaust passage and a sensor provided downstream of the catalyst to detect an air-fuel ratio of the exhaust, A control device that performs active control of an air-fuel ratio and also performs an increase process to increase an intake air amount during the execution of the active control, executes a sensor diagnosis process to determine whether or not there is an abnormality in the sensor during execution of the active control; the sensor diagnosis process is a process in which a maximum execution period is a period until an integrated intake air amount calculated during execution of the active control reaches a specified threshold value, A prohibition process is executed to prohibit the execution of the amount increase process while the sensor diagnosis process is being executed. Control device for internal combustion engines.

2. The threshold value is the integrated intake air amount corresponding to the time required to detect an abnormality in the sensor by the sensor diagnosis process. The control device for an internal combustion engine according to claim 1.

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