JP2021139340A - Internal combustion engine control device - Google Patents

Abstract

To further reduce an amount of a harmful substance discharged while an internal combustion engine is in operation.SOLUTION: An internal combustion engine control device detects an air-fuel ratio of gas passed through an exhaust purification catalyst installed in an exhaust passage of an internal combustion engine through an air-fuel ratio sensor and performs feedback control so that the air-fuel ratio converges to a target air-fuel ratio. The internal combustion engine control device also changes a correction amount considered in the target air-fuel ratio depending on a deterioration degree of the catalyst. Thus, the internal combustion engine control device can set the target air-fuel ratio for each operation region of the internal combustion engine with improved appropriateness and thereby curbing an increase in a discharge amount of a harmful substance with improved efficiency.SELECTED DRAWING: Figure 4

Description

The present invention relates to a control device for controlling an internal combustion engine mounted on a vehicle or the like.

Generally, the exhaust passage of an internal combustion engine is equipped with a three-way catalyst that oxidizes / reduces _{harmful substances HC, CO, and NO x contained in the exhaust gas discharged from the cylinder to make them harmless.} In order to efficiently purify all of HC, CO, and NO _x , it is necessary to keep the air-fuel ratio of the air-fuel mixture within a certain range near the theoretical air-fuel ratio called a window.

For this purpose, conventionally, air-fuel ratio sensors are arranged upstream and downstream of the catalyst in the exhaust passage, and a double feedback loop that refers to the output signals of the air-fuel ratio sensors is constructed to feedback-control the air-fuel ratio. There is. The ECU (Electronic Control Unit), which controls the operation of the internal combustion engine, has an air-fuel ratio (installed upstream of the catalyst) of the gas flowing into the catalyst to a basic injection amount proportional to the amount of air (fresh air) taken into the cylinder. The fuel injection amount from the injector is determined by multiplying the feedback correction coefficient that fluctuates according to the deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio (see, for example, the following patent documents).

Fluctuations in the air-fuel ratio of the gas discharged from the catalyst (the air-fuel ratio detected by the air-fuel ratio sensor installed downstream of the catalyst) are due to the fact that oxygen was occluded near the maximum oxygen storage capacity of the catalyst and oxygen became excessive. Or it indicates the fact that most of the oxygen occluded in the catalyst is consumed and oxygen is deficient. If the oxygen in the catalyst is filled, the reduction of the NO _x becomes difficult, NO _x is easily discharged. On the other hand, when oxygen is insufficient in the catalyst, it becomes difficult to oxidize HC and CO, and these are easily discharged. Correcting the air-fuel ratio of the gas flowing into the catalyst based on the air-fuel ratio of the gas discharged from the catalyst is very effective in suppressing the emission of harmful substances.

Japanese Unexamined Patent Publication No. 2010-138791

The maximum oxygen storage capacity of the catalyst gradually declines as it deteriorates over time. On the other hand, in the current control, the initial value of the target air-fuel ratio with respect to the air-fuel ratio of the gas flowing into the catalyst is uniformly determined according to the operating region of the internal combustion engine.

Therefore, there may be a time when the current atmosphere in the catalyst, in other words, the amount of oxygen occlusion, is not in a state suitable for oxidizing / reducing all of the _{harmful substances HC, CO, and NO x.} The atmosphere inside the catalyst is gradually improved by a feedback loop that refers to the output signal of the air-fuel ratio sensor downstream of the catalyst. As a result, corrections will be made in consideration of the degree of deterioration of the current catalyst, that is, the oxygen storage capacity, but there is a concern that the amount of harmful substances emitted will temporarily increase until the correction is completed.

The present invention has been made by paying attention to the above problems, and an object of the present invention is to further reduce the amount of harmful substances emitted during the operation of an internal combustion engine.

In the present invention, control is performed to detect the air-fuel ratio of the gas flowing through the exhaust gas purification catalyst mounted in the exhaust passage of the internal combustion engine via the air-fuel ratio sensor and perform feedback control to converge the air-fuel ratio to the target air-fuel ratio. The device comprises a control device for an internal combustion engine that changes a correction amount to be added to the target air-fuel ratio according to the degree of deterioration of the catalyst.

According to the present invention, the amount of harmful substances emitted during the operation of the internal combustion engine can be further reduced.

The figure which shows the schematic structure of the internal combustion engine and the control device in one Embodiment of this invention. The timing diagram which shows the content of the air-fuel ratio feedback control with reference to the output signal of the air-fuel ratio sensor upstream of a catalyst. The figure which illustrates the relationship between the correction amount FACF and the delay time TDR, TDL. A timing diagram showing the contents of air-fuel ratio feedback control with reference to the output signal of the air-fuel ratio sensor downstream of the catalyst. The timing diagram explaining the content of control by the control device of this embodiment.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle according to the present embodiment. The internal combustion engine of the present embodiment is a spark-ignition 4-stroke gasoline engine, and includes a plurality of cylinders 1 (for example, three cylinders, one of which is illustrated in FIG. 1). An injector 11 for injecting fuel toward the intake port is provided upstream of the intake valve of each cylinder 1 and in the vicinity of the intake port connected to each cylinder 1. Further, a spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives an induction voltage generated by the ignition coil and causes a spark discharge between the center electrode and the ground electrode. The ignition coil is integrally built in the coil case together with the igniter which is a semiconductor switching element.

The intake passage 3 for supplying intake air to the cylinder 1 takes in air from the outside and guides it to the intake port of each cylinder 1. An air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream on the intake passage 3.

The exhaust passage 4 for discharging the exhaust gas from the cylinder 1 guides the exhaust gas generated by burning the fuel in the cylinder 1 to the outside from the exhaust port of each cylinder 1. An exhaust manifold 42 and a three-way catalyst 41 for purifying exhaust gas are arranged on the exhaust passage 4.

Air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the gas flowing through the exhaust passage 4 are installed upstream and downstream of the catalyst 41 in the exhaust passage 4. The air-fuel ratio sensors 43 and 44 may be linear A / F sensors having output characteristics proportional to the air-fuel ratio of the exhaust gas, respectively, and are O ₂ sensors having output characteristics that are non-linear with respect to the air-fuel ratio of the exhaust gas. There may be. In this embodiment, a linear A / F sensor is assumed as the air-fuel ratio sensor 43 upstream of the catalyst 41, and an O _{2 sensor is assumed as the air-fuel ratio sensor 44 downstream of the catalyst 41.}

The output voltage f of the linear A / F sensor 43 becomes higher as the air-fuel ratio of the gas flowing into the catalyst 41 becomes leaner.

On the other hand, _{the output voltage g of the O 2} sensor 44 becomes lower as the air-fuel ratio of the gas flowing out from the catalyst 41 becomes leaner. In particular, in a certain range near the stoichiometric air-fuel ratio, the rate of change of the output with respect to the air-fuel ratio is large and shows a steep slope, and in the region where the air-fuel ratio is lean, it asymptotically approaches the low saturation value, and the air-fuel ratio is richer than that. In the region where is, a so-called Z characteristic curve that asymptotically approaches the high saturation value is drawn.

Incidentally, a catalyst for further exhaust gas purification (not shown) may be attached downstream of the catalyst 41 and the air-fuel ratio sensor 44 in the exhaust passage 4.

The exhaust gas recirculation device 2 opens and closes the external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, the EGR cooler 22 provided on the EGR passage 21, and the EGR passage 21 to open and close the EGR passage 21. The element is an EGR valve 23 that controls the flow rate of EGR gas flowing through the passage 21. The inlet of the EGR passage 21 is connected to a predetermined position downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined position (particularly, the surge tank 33 or the exhaust manifold 34) downstream of the throttle valve 32 in the intake passage 3.

The ECU 0, which is a control device for the internal combustion engine of the present embodiment, is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like. The ECU 0 may be a plurality of ECUs or controllers connected to each other so as to be able to communicate with each other via a telecommunication line such as CAN (Control Area Network).

The input interface of ECU0 has a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crank shaft of an internal combustion engine and the engine rotation speed. , Accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal by the driver or the opening of the throttle valve 32 as the accelerator opening (so to speak, the required engine load ratio or engine torque), the internal combustion engine The cooling water temperature signal d output from the water temperature sensor that detects the cooling water temperature, the intake air temperature in the intake passage 3 (particularly, the surge tank 33 or the intake manifold 34) and the intake air temperature output from the temperature / pressure sensor that detects the intake pressure. From the intake pressure signal e, the air-fuel ratio signal f output from the air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41, and the air-fuel ratio sensor 44 that detects the air-fuel ratio of the exhaust gas downstream of the catalyst 41. The output air-fuel ratio signal g, the cam angle signal h output from the cam angle sensor, and the like are input at a plurality of cam angles of the intake cam shaft.

From the output interface of ECU 0, ignition signal i for the igniter of the spark ignition device, fuel injection signal j for the injector 11, opening operation signal k for the throttle valve 32, and opening operation for the EGR valve 23. Outputs signal l and the like.

The processor of ECU 0 interprets and executes a program stored in the memory in advance, calculates an operation parameter, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, h necessary for the operation control of the internal combustion engine via the input interface, obtains the engine speed, and is sucked into the cylinder 1. Estimate the amount of air (fresh air). Then, based on the engine speed, intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, required EGR rate (or EGR gas amount), Various operating parameters such as ignition timing (including the number of spark ignitions per combustion), required EGR rate (or EGR gas amount), and the like are determined. The ECU 0 applies various control signals i, j, k, l corresponding to the operation parameters via the output interface.

When determining the fuel injection amount, the ECU 0 first obtains the amount of air sucked into the cylinder 1 and is proportional to the intake air amount (realizes the stoichiometric air-fuel ratio or an air-fuel ratio in the vicinity thereof according to the intake air amount). Determine the basic amount TP of the fuel injection amount (as possible). The intake air amount is the current engine speed, the current intake pressure in the surge tank 33 or the intake manifold 34, and the target phase angle of the intake valve opening / closing timing currently given from ECU 0 to the intake VVT (Variable Valve Timing) mechanism. Estimate based on etc. The estimated value of the intake air amount may be corrected according to the current intake air temperature, atmospheric pressure, and the like. This method of estimating the intake air amount is known.

Next, this basic injection amount TP is corrected by a feedback correction coefficient FAF according to the deviation between the air-fuel ratio of the gas flowing into the catalyst 41 and its target value, and various correction coefficients K determined according to environmental conditions and other conditions. .. The feedback correction coefficients FAF and K are positive numbers that increase or decrease around 1. Further, the final fuel injection time T, that is, the time for opening the injector 11, is calculated in consideration of the invalid injection time TAUV in which the fuel is not ejected even if the injector 11 is opened. The fuel injection time T is
T = TP x FAF x K + TAUV
Will be. The ECU 0 inputs a signal j to the injector 11 for the fuel injection time T, opens the injector 11 to inject fuel.

The air-fuel ratio feedback control converges the air-fuel ratio of the air-fuel mixture filled in the cylinder 1, and eventually the air-fuel ratio of the exhaust gas discharged from the cylinder 1 and led to the catalyst 41 to a desired target air-fuel ratio, and thus the catalyst 41. It maximizes the purification efficiency of harmful substances. The air-fuel ratio feedback correction coefficient FAF is determined based on the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41. As shown in FIG. 2, the ECU 0 compares the output voltage f of the air-fuel ratio sensor 43 that detects the air-fuel ratio of the gas upstream of the catalyst 41 with the determination voltage value corresponding to the target air-fuel ratio, and compares the output voltage f with the determination voltage value. If it is higher than, it is judged as lean, and if it is lower than the judgment voltage value, it is judged as rich. Then, the ECU 0 adjusts the feedback correction coefficient FAF by increasing or decreasing based on the determination result of the air-fuel ratio of the gas upstream of the catalyst 41.

Specifically, when the determination result of the air-fuel ratio of the gas upstream of the catalyst 41 is reversed from lean to rich (the following delay time TDR has elapsed), the feedback correction coefficient FAF is reduced by the skip value RSM. In addition, while it is determined that the air-fuel ratio is rich, the feedback correction coefficient FAF is gradually reduced by the lean integral value KIM per calculation cycle (control cycle). The cycle of the calculation cycle is equal to the cycle in which each cylinder 1 included in the internal combustion engine enters a new cycle (a series of intake stroke-compression stroke-expansion stroke-exhaust stroke). It is also conceivable that the absolute value of the lean integral value KIM is increased as the absolute value of the difference or ratio between the determination voltage value and the output voltage value f of the air-fuel ratio sensor 43 is larger.

On the other hand, when the determination result of the air-fuel ratio of the gas upstream of the catalyst 41 is reversed from rich to lean (the following delay time TDL has elapsed), the feedback correction coefficient FAF is increased by the skip value RSP. In addition, while determining that the air-fuel ratio is lean, the feedback correction coefficient FAF is incremented by the rich integral value KIP per calculation cycle. It is also conceivable that the absolute value of the rich integral value KIP is increased as the absolute value of the difference or ratio between the output voltage value f of the air-fuel ratio sensor 43 and the determination voltage value is larger.

When the feedback correction coefficient FAF multiplied by the basic injection amount TP decreases, the fuel injection amount by the injector 11 is reduced, and the air-fuel ratio of the air-fuel mixture tends toward lean. When the feedback correction coefficient FAF increases, the fuel injection amount by the injector 11 is increased, and the air-fuel ratio of the air-fuel mixture becomes rich.

However, when the output voltage f of the air-fuel ratio sensor 43 fluctuates so as to straddle the determination voltage value, the determination result of the air-fuel ratio of the gas upstream of the catalyst 41 is not immediately reversed, but the delay times TDL and TDR elapse. After waiting for, the judgment result is inverted. That is, when the output voltage f of the air-fuel ratio sensor 43 is switched from rich to lean (below the determination voltage value), it is determined that the air-fuel ratio is reversed from rich to lean after the lean determination delay time TDL has elapsed. Further, when the output voltage f of the air-fuel ratio sensor 43 is switched from lean to rich (exceeds the determination voltage value), it is determined that the air-fuel ratio is reversed from lean to rich after the rich determination delay time TDR has elapsed.

The lean determination delay time TDL and the rich determination delay time TDR are provided so that when noise is mixed in the output signal f of the air-fuel ratio sensor 43, the lean / rich determination result of the air-fuel ratio is inverted multiple times in a short period of time. The intention is to prevent chattering, which increases or decreases so that the fuel injection amount vibrates.

The delay times TDL and TDR increase or decrease according to the correction amount FACF. FIG. 3 illustrates the relationship between the correction amount FACF and the delay times TDL and TDR. In FIG. 3, the lean determination delay time TDL is represented by a broken line, and the rich determination delay time TDR is represented by a solid line. As the correction amount FACF becomes larger, the lean determination delay time TDL is shortened and the rich determination delay time TDR is extended. Then, the time when the feedback correction coefficient FAF changes from an increase to a decrease is delayed, and the time when the feedback correction coefficient FAF changes from a decrease to an increase is advanced. As a result, the fuel injection amount increases on average, and the target of the air-fuel ratio of the gas flowing into the catalyst 41 to be converged by the air-fuel ratio feedback control is displaced to the rich side.

On the contrary, as the correction amount FACF becomes smaller, the lean determination delay time TDL is extended and the rich determination delay time TDR is shortened. Then, the time when the feedback correction coefficient FAF changes from an increase to a decrease is advanced, and the time when the feedback correction coefficient FAF changes from a decrease to an increase is delayed. As a result, the fuel injection amount is reduced on average, and the target of the air-fuel ratio of the gas flowing into the catalyst 41 is displaced to the lean side.

The ECU 0 also calculates the above-mentioned correction amount FACF during the air-fuel ratio feedback control. As shown in FIG. 4, when calculating the correction amount FACF, the ECU 0 sets the output voltage g of the air-fuel ratio sensor 44 that detects the air-fuel ratio of the gas downstream of the catalyst 41 to the theoretical air-fuel ratio or a target air-fuel ratio in the vicinity thereof. Compared with the judgment voltage value corresponding to, if it is higher than the judgment voltage value, it is judged to be lean, and if it is lower than the judgment voltage value, it is judged to be rich. This determination voltage value does not always match the determination voltage value to be compared with the output signal f of the air-fuel ratio sensor 43. Then, the correction amount FACF is increased or decreased based on the determination result of the air-fuel ratio of the gas downstream of the catalyst 41.

Specifically, while it is determined that the air-fuel ratio of the gas downstream of the catalyst 41 is rich, the correction amount FACF is gradually reduced by the lean integral value FACFKIM per calculation cycle, while the air-fuel ratio is determined to be lean. During this period, the correction amount FACF is gradually increased by the rich integral value FACFKIP per calculation cycle. The absolute value of the lean integrated value FACFKIM may be increased as the absolute value of the difference or ratio between the determination voltage value and the output voltage value g of the air-fuel ratio sensor 44 is larger, and the absolute value of the rich integrated value FACFKIP may be increased. The larger the absolute value of the difference or ratio between the output voltage g of the air-fuel ratio sensor 44 and the determination voltage value, the larger the value may be. As described above, when the correction amount FACF decreases, the target air-fuel ratio of the gas flowing into the catalyst 41 tends toward lean, and when the correction amount FACF increases, the target air-fuel ratio of the gas flowing into the catalyst 41 tends toward richness. ..

During the operation of the internal combustion engine, the ECU 0 estimates the amount of oxygen currently occluded in the catalyst 41 at any time. The fuel injection amount at a certain point in the past is G _f (t), and the difference obtained by subtracting the theoretical air-fuel ratio from the measured air-fuel ratio detected via the air-fuel ratio sensor 43 at the same point t is ΔA / F (t) in the air. Assuming that the weight ratio of oxygen to the air-fuel ratio (≈0.23) is α, the oxygen occlusion OS of the catalyst 41 is set to
OS = α∫ {ΔA / F (t) × G _f (t)} dt
It can be obtained in the form of time integration as in. However, the oxygen storage capacity OS of the catalyst 41 does not exceed the maximum oxygen storage capacity of the catalyst 41.

ECU0 estimates the oxygen storage capacity of the current catalyst 41 as a diagnosis (self-diagnosis) function. For example, when the operation of the internal combustion engine and the vehicle is not adversely affected, the air-fuel ratio lean air-fuel mixture is supplied to the cylinder 1 to supply oxygen to the cylinder 1 from the state where oxygen is occluded to the full oxygen storage capacity of the catalyst 41. Perform active control to intentionally operate the air-fuel ratio rich. Then, the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 immediately indicates the air-fuel ratio rich, while the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 becomes the output signal f of the upstream air-fuel ratio sensor 43. It shows a rich air-fuel ratio with a delay. After the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 shows the air-fuel ratio rich (or after operating the air-fuel mixture to be air-fuel ratio rich), the output signal g of the air-fuel ratio sensor 44 downstream is rich in air-fuel ratio. This is because the oxygen occluded in the catalyst 41 is released until the above is shown to compensate for the lack of oxygen. If the stored oxygen amount OS of the catalyst 41 in this period (the amount of oxygen released from the catalyst 41, which is a negative value) is calculated, it becomes the maximum oxygen storage capacity of the catalyst 41.

Alternatively, active control in which the air-fuel ratio rich air-fuel mixture is supplied to the cylinder 1 of the internal combustion engine and oxygen is not occluded in the catalyst 41 at all, and the air-fuel ratio lean is intentionally operated from the air-fuel ratio supplied to the cylinder 1. To execute. Then, the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 immediately indicates the air-fuel ratio lean, while the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 becomes the output signal f of the upstream air-fuel ratio sensor 43. It shows a lean air-fuel ratio with a delay. After the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 indicates the air-fuel ratio lean (or after operating the air-fuel mixture to the air-fuel ratio lean), the output signal g of the air-fuel ratio sensor 44 downstream is the air-fuel ratio lean. This is because excess oxygen is adsorbed on the catalyst 41 until the above is shown. If the stored oxygen amount OS of the catalyst 41 in this period is calculated, it becomes the maximum oxygen storage capacity of the catalyst 41.

The oxygen storage capacity of the catalyst 41 gradually decreases with aging. Therefore, obtaining the oxygen storage capacity of the catalyst 41 is to estimate the degree of deterioration of the catalyst 41.

In the air-fuel ratio feedback control, the target air-fuel ratio of the gas discharged from the catalyst 41 is, in principle, constant. On the other hand, the target air-fuel ratio of the gas flowing into the catalyst 41 is not always constant. The ECU 0 of the present embodiment determines the target air-fuel ratio of the gas flowing into the catalyst 41 in consideration of the oxygen storage capacity of the current catalyst 41, in other words, the degree of aging deterioration of the catalyst 41.

More specifically, the target air-fuel ratio of the gas flowing into the catalyst 41 is set to the operating region of the internal combustion engine [engine speed, accelerator opening (or intake pressure (division of air) in the surge tank 33 or intake manifold 34). The base value according to the intake air amount or the fuel injection amount)] is multiplied by a coefficient (deterioration index) which is a correction amount according to the degree of deterioration of the catalyst 41.

In the memory of the ECU 0, map data that defines the relationship between the parameter indicating the operating area of the internal combustion engine and the base value of the target air-fuel ratio is stored in advance. The ECU 0 searches the map using the current operating area of the internal combustion engine as a key, and obtains the base value of the target air-fuel ratio.

As an example, when the operating region transitions to a higher rotation and / or higher load operating region, the base value of the target air-fuel ratio of the gas upstream of the catalyst 41 is on the rich side of the stoichiometric air-fuel ratio. It is biased to. If the air-fuel ratio sensor 43 is a linear A / F sensor 43, the base value of the determination voltage value to be compared with the output voltage f is lower than the voltage value corresponding to the theoretical air-fuel ratio.

In addition, the memory of the ECU 0 stores in advance map data that defines the relationship between the oxygen storage capacity that suggests the degree of deterioration of the catalyst 41 and the above-mentioned coefficient. The ECU 0 searches the map using the oxygen storage capacity of the current catalyst 41 as a key, and obtains a coefficient for multiplying the base value of the target air-fuel ratio by a correction amount.

In order to sufficiently oxidize / reduce all harmful substances HC, CO, and NO _{x in} the catalyst 41, the amount of oxygen stored in the catalyst 41 is 50% to 6% of the current maximum oxygen storage capacity of the catalyst 41. It is preferable to maintain the ratio. This is because if the amount of oxygen in the catalyst 41 is insufficient, the oxidation treatment of HC and CO becomes difficult, and if the amount of oxygen in the catalyst 41 is excessive, the reduction treatment of _{NO x becomes difficult.} Therefore, the correction amount according to the degree of deterioration of the catalyst 41 is determined so that the catalyst 41 can occlude about 50% to 60% of its maximum oxygen storage capacity. As for the tendency of the correction amount, the former case is better than the case where the catalyst 41 is new or has not deteriorated and has a large oxygen storage capacity, and the case where the catalyst 41 is deteriorated and the oxygen storage capacity is small. The target air-fuel ratio will be richer, and in the latter case, the target air-fuel ratio will be set to be leaner. If the air-fuel ratio sensor 43 upstream of the catalyst 41 is a linear A / F sensor, it is necessary to lower the determination voltage value to be compared with the output voltage f as the catalyst 41 deteriorates. The absolute value of the coefficient obtained by multiplying the base value by the correction amount becomes smaller as the deterioration of the catalyst 41 progresses.

FIG. 5 illustrates a pattern of air-fuel ratio feedback control by ECU 0. FIG. 5 shows a situation in a transitional period in which the accelerator opening is expanded by the driver to accelerate the engine speed. Further, the current catalyst 41 has not deteriorated and has a large oxygen storage capacity. In FIG. 5, the solid line represents the control by the ECU 0 of the present embodiment, and the broken line represents the conventional control.

In the conventional control, the initial value of the target air-fuel ratio of the gas upstream of the catalyst 41 is determined only by the operating region of the internal combustion engine at that time. Therefore, if the current oxygen storage capacity of the catalyst 41 is larger than expected, the oxygen in the catalyst 41 will continue to be excessive during the transitional period of acceleration, and the air-fuel ratio of the gas flowing downstream of the catalyst 41 will increase. _{There was a possibility that the harmful substance NO x} , which was temporarily leaner than the target air-fuel ratio and was not reduced even if it was temporary, was discharged downstream of the catalyst 41.

In the control by the ECU 0 of the present embodiment, in view of the fact that the oxygen storage capacity of the current catalyst 41 is still large, the target air-fuel ratio of the gas upstream of the catalyst 41 is corrected more richly as compared with the conventional control. As a result, excess oxygen in the catalyst 41 can be quickly purged by using it for the oxidation treatment of HC and CO in the transitional period of acceleration, and the air-fuel ratio of the gas flowing downstream of the catalyst 41 is maintained at the target air-fuel ratio. The amount of non-reduced harmful substance NO _x discharged downstream of the catalyst 41 can be reduced as compared with the conventional control.

In the present embodiment, the air-fuel ratio of the gas flowing through the exhaust gas purification catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine is detected via the air-fuel ratio sensor (linear A / F sensor) 43, and the air-fuel ratio (output) is detected. An internal combustion engine that performs feedback control for converging the voltage f) to the target air-fuel ratio (determined voltage value), and changes the correction amount to be added to the target air-fuel ratio according to the degree of deterioration of the catalyst 41. The control device of the engine was configured.

According to the present embodiment, it is possible to appropriately set the initial value of the target air-fuel ratio for each operating region of the internal combustion engine according to the degree of deterioration of the catalyst 41, and in particular, the operating region of the internal combustion engine has changed. It is possible to effectively suppress an increase in the emission of harmful substances.

The present invention is not limited to the embodiment described in detail above. In particular, the method for estimating the degree of deterioration of the catalyst 41 is not limited to that of the above-described embodiment. For example, after starting the stopped internal combustion engine, the amplitude of the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 is reduced to a predetermined value or less while the air-fuel ratio of the gas flowing into the catalyst 41 is increasing or decreasing. It is also possible to measure the elapsed time until the catalyst 41 is used, and to estimate that the longer the elapsed time is, the more the catalyst 41 is deteriorated.

Alternatively, it can be more simply estimated that the deterioration of the catalyst 41 progresses as the mileage of the vehicle and the cumulative number of revolutions of the internal combustion engine increase.

In addition, the specific configuration of each part can be variously modified without departing from the spirit of the present invention.

The present invention can be used for controlling an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
1 ... Cylinder 4 ... Exhaust passage 41 ... Catalyst 43 ... Air-fuel ratio sensor upstream of catalyst 44 ... Air-fuel ratio sensor downstream of catalyst f ... Output signal of air-fuel ratio sensor upstream of catalyst g ... Air-fuel ratio sensor downstream of catalyst Output signal

Claims (1)

It is a control device that detects the air-fuel ratio of the gas flowing through the exhaust gas purification catalyst installed in the exhaust passage of the internal combustion engine via the air-fuel ratio sensor and performs feedback control to converge the air-fuel ratio to the target air-fuel ratio. ,
A control device for an internal combustion engine that changes a correction amount to be added to the target air-fuel ratio according to the degree of deterioration of the catalyst.

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