Control device for internal combustion engine

Abstract

To suppress deterioration of emission after starting an engine.SOLUTION: The control device 100 performs the air-fuel ratio control of the air-fuel mixture based on the output value of the downstream side air-fuel ratio sensor 20 until the period from when the engine is started to when the function of the oxygen storage ability is obtained in the catalyst 18 elapses. The control device 100 performs air-fuel ratio control of the air-fuel mixture based on the output value of the upstream side air-fuel ratio sensor 19 after a period from when the engine starting is started to when the function of the oxygen storage ability is obtained in the catalyst 18 has elapsed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The internal combustion engine described in Patent Document 1 includes a catalyst having oxygen storage capacity and provided in an exhaust passage, and an air-fuel ratio sensor provided upstream of the catalyst in the exhaust gas. A control device for this internal combustion engine controls the air-fuel ratio of the mixture based on the output value of the air-fuel ratio sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6075394 Summary of the Invention [Problem to be solved by the invention]

[0004] During the period from the start of engine startup to the completion of engine warm-up, the combustion state of the air-fuel mixture is unstable, and the amount of fuel adhering to the cylinders increases. As a result, the exhaust gas contains a large amount of unburned components. When these unburned components are present, the output value of the air-fuel ratio sensor deviates from the actual air-fuel ratio. If air-fuel ratio control is performed based on the output value of an air-fuel ratio sensor with such an output deviation, it is not possible to control the actual air-fuel ratio to the target value. This can result in a deterioration in emissions after engine startup. [Means for solving the problem]

[0005] The control device for an internal combustion engine that solves the above-mentioned problems is applied to an internal combustion engine that includes a catalyst that is provided in an exhaust passage and has oxygen storage capacity, an upstream air-fuel ratio sensor that is provided on the exhaust side upstream of the catalyst, and a downstream air-fuel ratio sensor that is provided on the exhaust side downstream of the catalyst, and performs air-fuel ratio control of the mixture of the internal combustion engine. This control device performs the air-fuel ratio control based on the output value of the downstream air-fuel ratio sensor until a predetermined period has elapsed after the engine start. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress deterioration of emissions after engine start. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an internal combustion engine and its peripheral structure to which an embodiment of a control device for an internal combustion engine according to the present invention is applied. [Figure 2] FIG. 2 is a flowchart showing the procedure of processing executed by the control device in the embodiment. [Figure 3] FIG. 3 is a flowchart showing the procedure of processing executed by the control device in the embodiment. [Figure 4] FIG. 4 is a flowchart showing the procedure of the process executed by the control device in the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of a control device for an internal combustion engine according to the present invention will be described below with reference to Figures 1 to 4. The internal combustion engine of this embodiment is assumed to be installed in a hybrid vehicle equipped with an internal combustion engine and an electric motor as the prime mover of the vehicle, but may also be installed in a vehicle equipped with only an internal combustion engine as the prime mover of the vehicle.

[0009] <Configuration of an internal combustion engine> As shown in FIG. 1, an intake passage 11 is connected to an internal combustion engine 10. A throttle valve 15 whose passage area is variable is provided in the intake passage 11, and the amount of air taken in through the air cleaner 14 is adjusted by controlling the opening of the throttle valve 15. The amount of air taken in, or the intake air amount GA, is detected by an air flow meter 16.

[0010] The air flowing through the intake passage 11 is mixed with fuel injected from a fuel injection valve 17, and then sent to the combustion chamber of the internal combustion engine 10 where it is combusted. An exhaust gas purification catalyst 18 for purifying components in the exhaust gas is provided in the exhaust passage 13, to which the exhaust gas generated by combustion in the combustion chamber is sent. The catalyst 18 is, for example, a three-way catalyst. When combustion is performed near the stoichiometric air-fuel ratio, the catalyst 18 oxidizes HC and CO in the exhaust gas and reduces NOx in the exhaust gas to purify the exhaust gas. The catalyst 18 also has an oxygen storage capacity, storing oxygen in the exhaust gas and releasing the stored oxygen into the exhaust gas. When the temperature of the catalyst 18 reaches or exceeds a predetermined activation temperature TH1, the catalyst 18 begins to purify the exhaust gas. When the temperature of the catalyst 18 reaches or exceeds a storage start temperature TH2, which is higher than the activation temperature TH1, the catalyst 18 begins to function as the oxygen storage capacity.

[0011] An upstream air-fuel ratio sensor 19 is provided on the exhaust upstream side of the catalyst 18. Also, a downstream air-fuel ratio sensor 20 is provided on the exhaust downstream side of the catalyst 18. The upstream air-fuel ratio sensor 19 and the downstream air-fuel ratio sensor 20 are well-known limiting current oxygen sensors. This limiting current oxygen sensor is a sensor that obtains 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. The limiting current oxygen sensor outputs a zero output current when the air-fuel ratio, which is closely related to the oxygen concentration in the exhaust gas, is the stoichiometric air-fuel ratio. Furthermore, as the air-fuel ratio becomes richer, the output current increases in the negative direction. As the air-fuel ratio becomes leaner, the output current increases in the positive direction. Therefore, the degree of leanness or richness of the air-fuel ratio upstream of the catalyst 18 can be detected based on the output value of the upstream air-fuel ratio sensor 19. Furthermore, the degree of leanness or richness of the air-fuel ratio downstream of the catalyst 18 can be detected based on the output value of the downstream air-fuel ratio sensor 20.

[0012] The upstream air-fuel ratio sensor 19 is provided with a heater 19h that heats the sensor element provided in the upstream air-fuel ratio sensor 19. The downstream air-fuel ratio sensor 20 is provided with a heater 20h that heats the sensor element provided in the downstream air-fuel ratio sensor 20.

[0013] The control device 100 controls the internal combustion engine 10, and operates operating parts of the internal combustion engine 10 such as the throttle valve 15, fuel injection valve 17, and spark plugs to control the torque, exhaust component ratio, and other control variables. The control device 100 is equipped with a CPU and memory composed of a ROM, RAM, and the like, and performs various controls by the CPU executing programs stored in the memory.

[0014] The control device 100 receives detection signals from an air flow meter 16, an upstream air-fuel ratio sensor 19, and a downstream air-fuel ratio sensor 20. The control device 100 also receives detection signals from various sensors, such as an accelerator sensor that detects the amount of accelerator pedal operation, a crank angle sensor 21 that detects the engine rotation speed NE, and a water temperature sensor 22 that detects the coolant temperature THW, which is the temperature of the coolant for the internal combustion engine 10. Various engine controls are then performed according to the operating conditions of the internal combustion engine 10 ascertained from the detection signals from these sensors.

[0015] The control device 100 acquires the impedance imp of the sensor element of the upstream air-fuel ratio sensor 19. Then, the control device 100 performs feedback control of the heater current, which is the current supplied to the heater 19h, so that the impedance imp becomes a predetermined reference value impb while the internal combustion engine 10 is operating.

[0016] Similarly, the control device 100 performs feedback control on the heater current of the heater 20h for the downstream air-fuel ratio sensor 20 so that the impedance of the sensor element of the downstream air-fuel ratio sensor 20 becomes a predetermined reference value while the internal combustion engine 10 is operating.

[0017] The control device 100 stops fuel injection from the fuel injection valve 17 when the vehicle is decelerating, for example, thereby executing a so-called fuel cut. <Air-fuel ratio control> During the period from the start of engine startup to the completion of engine warm-up, the combustion state of the air-fuel mixture is unstable, and the amount of fuel adhering to the cylinders increases. As a result, the exhaust gas contains a large amount of unburned components. The presence of these unburned components causes the output value of the air-fuel ratio sensor to deviate from the actual air-fuel ratio. For example, if the exhaust gas contains hydrocarbons as unburned components, the output value of the air-fuel ratio sensor will deviate leaner than the actual air-fuel ratio. Furthermore, if the exhaust gas contains hydrogen as an unburned component, the output value of the air-fuel ratio sensor will deviate richer than the actual air-fuel ratio. If known air-fuel ratio control is performed based on the output value of an air-fuel ratio sensor with such an output deviation, the actual air-fuel ratio cannot be controlled to the target value. This can lead to a deterioration in emissions after engine startup.

[0018] Therefore, in this embodiment, the air-fuel ratio control described below is executed. The control device 100 calculates a target air-fuel ratio AFt, which is a target value for the air-fuel ratio of the air-fuel mixture. The control device 100 refers to a preset air-fuel ratio conversion map to calculate the upstream air-fuel ratio AFf corresponding to the corrected upstream output value ILF2 obtained by correcting the upstream output value ILF, which is the output value of the upstream air-fuel ratio sensor 19. The corrected upstream output value ILF2 will be described later.

[0019] Furthermore, the control device 100 calculates the downstream air-fuel ratio AFr corresponding to the downstream output value ILR, which is the output value of the downstream air-fuel ratio sensor 20, by referring to a preset air-fuel ratio conversion map.

[0020] <First air-fuel ratio control> The control device 100 performs a first air-fuel ratio control that controls the air-fuel ratio of the mixture based on the downstream output value ILR until a predetermined period has elapsed since the engine start. In this embodiment, the predetermined period is the period from the start of the engine start until the catalyst 18 obtains its oxygen storage capacity.

[0021] As the first air-fuel ratio control, the control device 100 calculates a proportional term and an integral term and a derivative term as learned values ​​from the deviation between the target air-fuel ratio AFt and the downstream air-fuel ratio AFr, and a proportional gain, an integral gain, and a derivative gain that have been experimentally determined in advance. Then, PID control is performed to calculate a correction value for the currently set fuel injection amount of the fuel injector 17 from the sum of the proportional term, the integral term, and the derivative term. Note that instead of PID control, feedback control such as PI control that calculates the correction value based on the proportional term and the integral term may be performed.

[0022] The control device 100 then corrects the fuel injection amount using the calculated correction value. For example, when the downstream air-fuel ratio AFr is leaner than the target air-fuel ratio AFt, the fuel injection amount is corrected to be increased. On the other hand, when the downstream air-fuel ratio AFr is richer than the target air-fuel ratio AFt, the fuel injection amount is corrected to be decreased. By performing such feedback control of the air-fuel ratio, the downstream air-fuel ratio AFr is controlled to approach the target air-fuel ratio AFt.

[0023] <Second air-fuel ratio control> After the above-mentioned predetermined period has elapsed, the control device 100 performs second air-fuel ratio control to control the air-fuel ratio of the mixture based on the upstream-side output value ILF.

[0024] As the second air-fuel ratio control, the control device 100 calculates a proportional term and an integral term and a derivative term as learned values ​​from the deviation between the target air-fuel ratio AFt and the upstream air-fuel ratio AFf, and a proportional gain, an integral gain, and a derivative gain that have been experimentally determined in advance. Then, PID control is performed to calculate a correction value for the currently set fuel injection amount of the fuel injector 17 from the sum of the proportional term, the integral term, and the derivative term. Note that instead of PID control, feedback control such as PI control that calculates the correction value based on the proportional term and the integral term may be performed.

[0025] The control device 100 then corrects the fuel injection amount using the calculated correction value. For example, when the upstream air-fuel ratio AFf is leaner than the target air-fuel ratio AFt, the fuel injection amount is corrected to be increased. On the other hand, when the upstream air-fuel ratio AFf is richer than the target air-fuel ratio AFt, the fuel injection amount is corrected to be decreased. By carrying out such feedback control of the air-fuel ratio, the upstream air-fuel ratio AFf is controlled to approach the target air-fuel ratio AFt.

[0026] <Sub-air-fuel ratio control> When executing second air-fuel ratio control, the control device 100 also executes sub air-fuel ratio control. As the sub air-fuel ratio control, the control device 100 calculates a proportional term and an integral term and a derivative term as learned values ​​from the deviation between the sub target air-fuel ratio AFts and the downstream air-fuel ratio AFr, and a proportional gain, an integral gain, and a derivative gain that have been experimentally determined in advance. Then, PID control is executed to calculate a correction value for the currently set target air-fuel ratio AFt from the sum of the proportional term, the integral term, and the derivative term. Note that instead of PID control, feedback control such as PI control that calculates a correction value based on the proportional term and the integral term may be executed.

[0027] The control device 100 then corrects the target air-fuel ratio AFt using the calculated correction value. For example, if the downstream air-fuel ratio AFr is leaner than the sub-target air-fuel ratio AFts, the target air-fuel ratio AFt is corrected so that the target air-fuel ratio AFt changes to a richer value. On the other hand, if the downstream air-fuel ratio AFr is richer than the sub-target air-fuel ratio AFts, the target air-fuel ratio AFt is corrected so that the target air-fuel ratio AFt changes to a leaner value. The second air-fuel ratio control is then executed based on the corrected target air-fuel ratio AFt. By executing such sub-air-fuel ratio control, the oxygen storage capacity of the catalyst 18 can be appropriately achieved.

[0028] <Air-fuel ratio control switching> 2 shows the procedure of the process executed by the control device 100 to switch the air-fuel ratio control described above. Note that, hereinafter, the step number of each process is represented by a number preceded by "S."

[0029] When the process shown in FIG. 2 starts, the control device 100 determines whether an ignition switch (IGSW) provided in the vehicle is ON (S100). In the process of S100, when it is determined that the ignition switch is ON (S100: YES), the control device 100 starts energizing the heaters 19h and 20h provided in the air-fuel ratio sensors (S110). By energizing the heaters 19h and 20h, the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are activated early and become capable of detection even before the engine start is actually started.

[0030] Next, the control device 100 determines whether engine start has been initiated (S120). If it is determined that engine start has been initiated (S120: YES), the control device 100 calculates the catalyst temperature THsc (S130). The catalyst temperature THsc is the temperature of the catalyst 18, and is a value estimated by the control device 100. For example, the control device 100 calculates the catalyst temperature THsc based on the accumulated air amount since the start of engine start, the detection value of a sensor that detects the exhaust temperature, etc.

[0031] Next, the control device 100 determines whether or not the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detectable state (S140). In the processing of S140, the control device 100 determines that the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detectable state when, for example, the following conditions (a) and (b) are both established:

[0032] Condition (a): Neither the upstream side air-fuel ratio sensor 19 nor the downstream side air-fuel ratio sensor 20 is faulty. Condition (b): Both the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are activated.

[0033] If it is determined in the processing of S140 that the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detectable state (S140: YES), the control device 100 acquires the coolant temperature THW. Then, it is determined whether the acquired value is equal to or less than a threshold value THWref (S150). The threshold value THWref is a preset adaptive value. For example, when the internal combustion engine 10 is warming up and the coolant temperature THW is at a relatively high value, the combustion state of the air-fuel mixture is stable, and the output deviation of the air-fuel ratio sensor described above becomes small. Therefore, the maximum temperature of the coolant temperature THW at which the output deviation of the air-fuel ratio sensor is likely to occur may be set as the threshold value THWref.

[0034] In the process of S150, when it is determined that the coolant temperature THW is equal to or lower than the threshold value THWref (S150: YES), the control device 100 determines whether the current catalyst temperature THsc is lower than the above-mentioned storage start temperature TH2 (S160).

[0035] In the process of S160, when it is determined that the catalyst temperature THsc is lower than the storage start temperature TH2 (S160: YES), the control device 100 executes the above-described first air-fuel ratio control (S170).

[0036] On the other hand, if a negative determination is made in the processing of S150 above, or if a negative determination is made in the processing of S160 above, the control device 100 executes the second air-fuel ratio control and the sub air-fuel ratio control described above (S180).

[0037] When the process of S170 or the process of S180 is completed, or when a negative determination is made in any of the processes of S100, S120, and S140, the control device 100 terminates this process.

[0038] <Calculation of the correction value for correcting the upstream output value> FIG. 3 shows a procedure of a process that the control device 100 executes at each predetermined execution cycle to calculate the rate learning value KILG, which is a correction value for correcting the upstream output value ILF.

[0039] 3 starts, the control device 100 determines whether or not the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detectable state (S200). The process of S200 is the same as the process of S140 described above.

[0040] In the process of S200, when it is determined that the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detectable state (S200: YES), the control device 100 executes the process of S210.

[0041] In the process of S210, the control device 100 determines whether the above-mentioned fuel cut is currently being performed and whether the FC execution time is equal to or longer than a predetermined value α. The FC execution time is the time elapsed since the fuel cut started. The predetermined value α is a preset time from the start of the fuel cut until the value of the downstream output value ILR becomes stable.

[0042] In the processing of S210, if it is determined that fuel cut is being performed and the FC execution time is equal to or longer than the predetermined value α (S210: YES), the control device 100 acquires the upstream output value ILF and the downstream output value ILR (S220).

[0043] Next, the control device 100 calculates the output ratio KIL (S230). The output ratio KIL is a value used to correct the upstream output value ILF, and is calculated based on the difference between the upstream output value ILF and the downstream output value ILR. The control device 100 calculates a value by dividing the downstream output value ILR by the upstream output value ILF. Then, the control device 100 assigns the calculated value to the output ratio KIL (KIL=ILR / ILF).

[0044] Next, the control device 100 updates the ratio learning value KILG by smoothing the calculated output ratio KIL (S240). In the process of S240, the control device 100 calculates an updated value of the ratio learning value KILG based on, for example, the following equation (1).

[0045] Updated value of the ratio learning value KILG = (previous value of the ratio learning value KILG + currently calculated output ratio KIL) / 2 ... (1) The updated rate learning value KILG is stored in a memory (eg, a backup RAM) of the control device 100.

[0046] When the process of S240 is completed, the control device 100 ends this process in the current execution cycle. <Upstream output value correction and upstream air-fuel ratio calculation> FIG. 4 shows a procedure of processing that the control device 100 executes at each predetermined execution cycle to calculate the corrected upstream output value ILF2 obtained by correcting the upstream output value ILF and to calculate the upstream air-fuel ratio AFf.

[0047] 4 starts, the control device 100 determines whether or not the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detection-enabled state (S300). The processing of S300 is the same as the processing of S140 described above.

[0048] In the process of S300, when it is determined that the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 are in a detectable state (S300: YES), the control device 100 acquires the upstream side output value ILF (S310).

[0049] Next, the control device 100 calculates the corrected upstream output value ILF2 (S320). In the process of S320, the control device 100 reads the rate learning value KILG stored in memory, multiplies the read value by the upstream output value ILF, and assigns the result to the corrected upstream output value ILF2.

[0050] Next, the control device 100 calculates the upstream air-fuel ratio AFf based on the corrected upstream output value ILF2 (S330). In the processing of S330, the control device 100 calculates the upstream air-fuel ratio AFf corresponding to the corrected upstream output value ILF2 by referring to a preset air-fuel ratio conversion map, as described above.

[0051] When the process of S330 is completed, the control device 100 ends this process in the current execution cycle. <Actions and Effects of This Embodiment> (1) Even if unburned components such as HC and hydrogen gas are contained in the exhaust gas during the period from when engine start is initiated until engine warm-up is completed, the unburned components are purified as they pass through the catalyst 18. Therefore, the output value of the downstream air-fuel ratio sensor 20 provided on the exhaust downstream side of the catalyst 18 has a smaller output deviation due to unburned components than the output value of the upstream air-fuel ratio sensor 19 provided on the exhaust upstream side of the catalyst 18. Therefore, in this embodiment, a first air-fuel ratio control is implemented, which is air-fuel ratio control based on the output value of the downstream air-fuel ratio sensor 20 with a small output deviation, until a predetermined period has elapsed since engine start was initiated. Therefore, it is possible to suppress deterioration of emissions after engine start.

[0052] (2) When the catalyst 18 begins to function as an oxygen storage device, the catalyst 18 stores and releases oxygen, which may result in a period during which the output value of the downstream air-fuel ratio sensor 20 does not match the air-fuel ratio of the mixture. Furthermore, when the catalyst 18 begins to function as an oxygen storage device, a certain amount of time has passed since the engine started, so the combustion state of the mixture has improved and the amount of unburned components in the exhaust has decreased. Therefore, when the catalyst 18 begins to function as an oxygen storage device, the deviation in the output of the upstream air-fuel ratio sensor 19 becomes smaller.

[0053] Therefore, in this embodiment, the above-mentioned predetermined period is the period from when the engine start is initiated until the catalyst 18 obtains the oxygen storage capacity, and after the predetermined period has elapsed, the second air-fuel ratio control is carried out based on the output value of the upstream air-fuel ratio sensor 19.

[0054] In this case, during the period from when the engine start is initiated until the catalyst 18 obtains its oxygen storage capacity, a first air-fuel ratio control is implemented, which is air-fuel ratio control based on the output value of the downstream air-fuel ratio sensor 20. On the other hand, once the catalyst 18 obtains its oxygen storage capacity, a second air-fuel ratio control is implemented, which is air-fuel ratio control based on the output value of the upstream air-fuel ratio sensor 19. Therefore, it is possible to switch from air-fuel ratio control based on the output value of the downstream air-fuel ratio sensor 20 to air-fuel ratio control based on the output value of the upstream air-fuel ratio sensor 19 at an appropriate timing.

[0055] (3) The detection target of both the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 is the same fresh air when a fuel cut is being executed in the internal combustion engine 10. Therefore, the difference in the output values ​​of the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 when a fuel cut is being executed indicates an error in the output values ​​between the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20.

[0056] Therefore, in this embodiment, when a fuel cut is being executed in the internal combustion engine 10, the output value of the upstream side air-fuel ratio sensor 19 and the output value of the downstream side air-fuel ratio sensor 20 are acquired. Then, the output value of the upstream side air-fuel ratio sensor 19 is corrected using a ratio learned value KILG obtained by smoothing the output ratio KIL, which is a correction value calculated based on the difference between the acquired output value of the upstream side air-fuel ratio sensor 19 and the acquired output value of the downstream side air-fuel ratio sensor 20. Therefore, the error in the output values ​​between the upstream side air-fuel ratio sensor 19 and the downstream side air-fuel ratio sensor 20 can be reduced.

[0057] (4) In the present embodiment, the correction value for correcting the output value of the upstream air-fuel ratio sensor 19 is a value by which the output value of the upstream air-fuel ratio sensor 19 is multiplied, and is a value obtained by dividing the output value of the downstream air-fuel ratio sensor 20 by the output value of the upstream air-fuel ratio sensor 19. Therefore, the output value of the upstream air-fuel ratio sensor 19 can be corrected using the output value of the downstream air-fuel ratio sensor 20 as a reference.

[0058] <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.

[0059] The process of S110 shown in FIG. 2 may be omitted and the energization start timing of the heaters 19h and 20h may be set to another timing. The process of S150 shown in FIG. 2 may be omitted.

[0060] The process of S240 shown in Fig. 3 is omitted. In the process of S320 shown in Fig. 4, the corrected upstream output value ILF2 may be calculated by multiplying the upstream output value ILF by the output ratio KIL calculated in the process of S230 shown in Fig. 3 instead of the ratio learned value KILG.

[0061] The correction of the upstream output value ILF may be omitted by omitting the execution of the series of processes shown in Figures 3 and 4. Even in this case, actions and effects other than those of (3) and (4) above can be obtained.

[0062] The control device 100 is not limited to a device equipped with a CPU and memory and executing software processing. For example, the control device 100 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 100 may include a processing circuit having any of the following configurations (a) to (c): (a) a processing circuit equipped with one or more processing devices that execute all of the above processing according to a program and one or more program storage devices, such as ROM, that store the program; (b) a processing circuit equipped with one or more processing devices and one or more program storage devices that execute part of the above processing according to a program, and one or more dedicated hardware circuits that execute the remaining processing; (c) a processing circuit equipped with one or more dedicated hardware circuits that execute all of the above processing. Program storage devices, i.e., computer-readable media, include any available media that can be accessed by a general-purpose or dedicated computer. [Explanation of symbols]

[0063] 10...Internal combustion engine 11...Intake passage 13...Exhaust passage 14...Air cleaner 15...Throttle valve 16...Air flow meter 17...Fuel injection valve 18...Catalyst 19...Upstream air-fuel ratio sensor 19h...Heater 20...Downstream air-fuel ratio sensor 20h...Heater 21...Crank angle sensor 22...Water temperature sensor 100...Control device

Claims

1. A control device is applied to an internal combustion engine including a catalyst provided in an exhaust passage and having an oxygen storage capacity, an upstream air-fuel ratio sensor provided on the exhaust upstream side of the catalyst, and a downstream air-fuel ratio sensor provided on the exhaust downstream side of the catalyst, and performs air-fuel ratio control of an air-fuel mixture of the internal combustion engine, The air-fuel ratio control is carried out based on the output value of the downstream air-fuel ratio sensor until a predetermined period of time has elapsed since the engine start. Control device for internal combustion engines.

2. The predetermined period is a period from when the engine is started until the catalyst obtains the oxygen storage capacity, and after the predetermined period has elapsed, the air-fuel ratio control is performed based on the output value of the upstream air-fuel ratio sensor. The control device for an internal combustion engine according to claim 1.

3. When a fuel cut is being executed in the internal combustion engine, an output value of the upstream air-fuel ratio sensor and an output value of the downstream air-fuel ratio sensor are acquired, and The output value of the upstream air-fuel ratio sensor is corrected using a correction value calculated based on the difference between the acquired output value of the upstream air-fuel ratio sensor and the acquired output value of the downstream air-fuel ratio sensor. The control device for an internal combustion engine according to claim 1.

4. The correction value is a value by which the output value of the upstream air-fuel ratio sensor is multiplied, and is a value obtained by dividing the output value of the downstream air-fuel ratio sensor by the output value of the upstream air-fuel ratio sensor. The control device for an internal combustion engine according to claim 3.

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