JP7143032B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for controlling an air-fuel ratio by adjusting a fuel injection amount in an internal combustion engine.

In general, an exhaust passage of an internal combustion engine is equipped with a three-way catalyst that _oxidizes /reduces harmful substances HC, CO, and NOx contained in exhaust gas discharged from a cylinder to render them harmless. In order to efficiently _purify all of HC, CO, and NOx, the air-fuel ratio of the air-fuel mixture must be kept within a certain range near the stoichiometric air-fuel ratio called a window. For this reason, conventionally, O ₂ sensors are arranged upstream and downstream of the catalyst, respectively, and a double feedback loop is constructed using the output signals of these O ₂ sensors to feedback-control the air-fuel ratio.

The ECU (Electronic Control Unit), which governs the operation control of the internal combustion engine, applies a feedback correction that varies according to the air-fuel ratio of the gas flowing into the catalyst to the basic injection amount that is proportional to the amount of air (fresh air) taken into the cylinder. Multiplying the coefficient determines the amount of fuel injected from the injector.

As shown in FIG. 2, the ECU compares the output voltage of the front _O2 sensor, which detects the air-fuel ratio of the gas on the upstream side of the catalyst, with a judgment voltage value corresponding to the stoichiometric air-fuel ratio or an air-fuel ratio in the vicinity thereof, If the output voltage is higher than the judgment voltage value, it is judged that the air-fuel ratio is rich, and if it is lower than the judgment voltage value, it is judged that the air-fuel ratio is lean. However, when the output voltage of the front _O2 sensor fluctuates across the determination voltage value, the determination result of the air-fuel ratio is not immediately reversed, but the determination result is reversed after the elapse of the delay time. That is, when the output voltage of the front _O2 sensor switches from lean to rich (exceeds the judgment voltage value), it is judged that the air-fuel ratio has reversed from lean to rich after the rich judgment delay time TDR has elapsed. . In addition, when the output voltage of the front _O2 sensor switches from rich to lean (below the judgment voltage value), it is judged that the air-fuel ratio has reversed from rich to lean after the lean judgment delay time TDL has elapsed. .

The ECU increases or decreases the feedback correction coefficient FAF based on the determination result of the air-fuel ratio of the gas on the upstream side of the catalyst. Specifically, while the air-fuel ratio is determined to be rich, the feedback correction coefficient FAF is gradually decreased by the lean integral value KIM, while while the air-fuel ratio is determined to be lean, the feedback correction coefficient FAF is incremented by the rich integral value KIP.

The rich judgment delay time TDR and the lean judgment delay time TDL are set according to the air-fuel ratio of the gas downstream of the catalyst. As shown in FIGS. 3 and 4, the ECU compares the output voltage of the rear _O2 sensor that detects the air-fuel ratio of the gas downstream of the catalyst with the judgment voltage value, and if the output voltage is higher than the judgment voltage value, If the air-fuel ratio is lower than the judgment voltage value, the air-fuel ratio is judged to be lean. The longer the period in which the air-fuel ratio of the gas downstream of the catalyst is leaner, the longer the rich determination delay time TDR. Conversely, the longer the period in which the air-fuel ratio of the gas downstream of the catalyst is rich, the longer the lean determination delay time TDL. As a result, the control center of the air-fuel ratio feedback control that refers to the output voltage of the front O ₂ sensor, that is, the target to which the air-fuel ratio of the gas should be converged by the feedback control changes (see the following patent documents).

The output voltage of the rear _O2 sensor switches from rich to lean after oxygen has been stored to near the maximum oxygen storage capacity of the catalyst, resulting in an excess of oxygen in the catalyst. When the catalyst is filled with oxygen, it becomes difficult to reduce _NOx , and _NOx is easily discharged. On the other hand, the output voltage of the rear O ₂ sensor switches from lean to rich after most of the oxygen stored in the catalyst is consumed and the oxygen in the catalyst becomes deficient. When oxygen is insufficient in the catalyst, it becomes difficult to oxidize HC and CO, and these are likely to be discharged.

In short, there is a delay in the feedback that refers to the output signal of the rear O ₂ sensor, and the delay has caused a limit to the suppression of harmful substance emissions.

JP 2010-138791 A

SUMMARY OF THE INVENTION An intended object of the present invention is to further reduce the amount of harmful substances emitted from an internal combustion engine.

In order to solve the above-described problems, the present invention provides a control device for feedback-controlling the air-fuel ratio of gas flowing into an exhaust purification catalyst mounted in an exhaust passage of an internal combustion engine, wherein the amount of air sucked into the cylinder is , and the output signal of an air-fuel ratio sensor installed upstream of the catalyst in the exhaust passage. The target of the air-fuel ratio to be converged is changed by control, and when the output signal of the air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage exceeds the rich side threshold and indicates the air-fuel ratio rich, the deviation is reset to a predetermined value on the rich side , and/or when the output signal of an air-fuel ratio sensor installed downstream of the catalyst exceeds the threshold value on the lean side and indicates a lean air-fuel ratio, the deviation is reset to the rich side A control device for an internal combustion engine is configured to reset to a predetermined value on the lean side different from the predetermined value of . On the other hand, in addition to the deviation, the target air-fuel ratio to be converged by the feedback control is calculated based on the output signal of the air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage. , when the deviation between the target corresponding to the deviation and the target based on the output signal of the air-fuel ratio sensor downstream of the catalyst widens beyond a certain level, air-fuel ratio feedback control is performed using the latter target instead of the former target. shall be performed.

According to the present invention, it is possible to further reduce the amount of harmful substances emitted from an internal combustion engine.

1 is a diagram showing a schematic configuration of a vehicle internal combustion engine and a control device according to an embodiment of the present invention; FIG. FIG. 4 is a timing chart showing how air-fuel ratio feedback control is performed with reference to the output signal of an air-fuel ratio sensor on the upstream side of the catalyst; 5 is a graph illustrating the relationship between a control center correction amount FACF and delay times TDR and TDL; FIG. 5 is a timing chart showing how air-fuel ratio feedback control is performed with reference to the output signal of an air-fuel ratio sensor on the downstream side of the catalyst; FIG. 4 is a flowchart showing a procedure for calculating a control center correction amount FACF by the control device of the same embodiment; FIG. 4 is a timing chart illustrating transition of deviation Σ(ΔOS _n ) calculated by the control device of the embodiment;

One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of a vehicle internal combustion engine according to this embodiment. The internal combustion engine in this embodiment is a spark-ignited four-stroke engine, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). An injector 11 for injecting fuel is provided near the intake port of each cylinder 1 . A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1 . The spark plug 12 receives an induced voltage generated by an ignition coil and induces spark discharge between a center electrode and a ground electrode.

An intake passage 3 for supplying intake air 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 on the intake passage 3 from upstream.

An exhaust passage 4 for exhausting exhaust guides exhaust gas generated as a result of combustion of fuel in the cylinder 1 from an exhaust port of each cylinder 1 to the outside. 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 gas flowing through the exhaust passage 4 are installed upstream and downstream of the catalyst 41 in the exhaust passage 4 . Each of the air-fuel ratio sensors 43 and 44 may be an O ₂ sensor having an output characteristic that is non-linear with respect to the air-fuel ratio of the exhaust gas, or a linear A/F sensor having an output characteristic that is proportional to the air-fuel ratio of the exhaust gas. There may be. In this embodiment, each of the air-fuel ratio sensors 43 and 44 on the upstream side and downstream side of the catalyst 41 is assumed to be an O ₂ sensor that outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas. The characteristics of the output voltages f and g of the O ₂ sensors 43 and 44 show a large rate of change in output with respect to the air-fuel ratio in a certain range (window) near the stoichiometric air-fuel ratio, showing a steep slope. It draws a so-called Z characteristic curve that asymptotically approaches a low saturation value in the region and asymptotically approaches a high saturation value in the rich region where the air-fuel ratio is small.

The external EGR (Exhaust Gas Recirculation) device 2 realizes so-called high-pressure loop EGR, and includes an EGR passage 21 that communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3. , an EGR cooler 22 provided on the EGR passage 21 and an EGR valve 23 for opening and closing the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21 . The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33. As shown in FIG.

The ECU0, which is the control device for the internal combustion engine of this embodiment, is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like. The ECU 0 may be formed by connecting a plurality of ECUs or controllers so as to be able to communicate with each other via electric communication lines such as CAN (Controller Area Network).

The input interface of the ECU 0 receives a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft and the engine speed, and an accelerator pedal. or the opening of the throttle valve 32 as the accelerator opening (that is, the engine load factor required for the internal combustion engine), the accelerator opening signal c output from the sensor, the intake passage 3 (especially the surge tank 33 ), an intake air temperature/pressure signal d output from a temperature/pressure sensor that detects the intake air temperature and intake air pressure, a cooling water temperature signal e that is output from a water temperature sensor that detects a cooling water temperature that indicates the temperature of the internal combustion engine, An air-fuel ratio signal f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas on the upstream side of the catalyst 41, and an air-fuel ratio signal f that is output from an air-fuel ratio sensor 44 that detects the air-fuel ratio of the exhaust gas on the downstream side of the catalyst 41. A fuel ratio signal g, an atmospheric pressure signal h output from an atmospheric pressure sensor that detects the atmospheric pressure, and the like are input.

From the output interface of the ECU 0, an ignition signal i for the igniter 13 of the spark plug 12, a fuel injection signal j for the injector 11, an opening operation signal k for the throttle valve 32, and an opening degree for the EGR valve 23 It outputs an operation signal l and the like.

The processor of the ECU 0 interprets and executes a program stored in memory in advance, calculates operating parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various types of information a, b, c, d, e, f, g, and h necessary for controlling the operation of the internal combustion engine through an input interface, learns the engine speed, and injects into the cylinder 1. Estimate the amount of air (fresh air). Then, based on the engine speed, air amount, etc., various operations such as required fuel injection amount, fuel injection timing (including the number of fuel injections for one combustion), fuel injection pressure, required EGR rate, ignition timing, etc. Determine parameters. The ECU 0 applies various control signals i, j, k, l corresponding to the operating parameters through the output interface.

In determining the fuel injection amount, the ECU 0 first obtains the amount Ga of air taken into the cylinder 1, and is proportional to the intake air amount Ga (the theoretical air-fuel ratio or an air-fuel ratio in the vicinity thereof A basic amount TP of the fuel injection amount that can realize the fuel ratio is determined. The intake air amount Ga is estimated based on the engine speed and the intake pressure in the surge tank 33 . If necessary, the estimated value can be corrected according to intake air temperature, atmospheric pressure, and the like. If an airflow meter is installed in the intake passage 3, it is possible to directly measure the intake air amount Ga through the airflow meter.

Next, this basic injection amount TP is corrected with a feedback correction coefficient FAF determined according to the output signal f of the air-fuel ratio sensor 43 on the upstream side of the catalyst 41 . The feedback correction coefficient FAF is a positive number that increases and decreases around 1. Furthermore, the final fuel injection time (energization time for the injector 11) T is calculated in consideration of various correction coefficients K determined depending on the situation and the invalid injection time TAUV of the injector 11. The fuel injection time T is
T = TP x FAF x K + TAUV
becomes. Then, the signal j is input to the injector 11 for the fuel injection time T to open the injector 11 and inject the fuel.

Further, the ECU 0 executes a fuel cut to temporarily interrupt the fuel supply to the cylinder 1 according to the operating conditions. The ECU 0 cuts fuel, that is, stops fuel injection from the injector 11 when a predetermined fuel cut condition is satisfied. The ECU 0 determines that the fuel cut condition is satisfied at least when the amount of depression of the accelerator pedal is equal to or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed.

During the fuel cut, the throttle valve 32 is opened to an opening that does not depend on the depression amount (0 or close to 0) of the accelerator pedal. This operation is performed to reduce the pumping loss of the internal combustion engine during fuel cut and delay the deceleration of the engine rotation. The degree of opening of the throttle valve 32 at this time may be a constant value or may be increased or decreased according to the vehicle speed or the like.

Then, when a predetermined fuel cut end condition is satisfied, the ECU 0 ends the fuel cut, and restarts fuel injection (and ignition). The ECU 0 determines that the condition for terminating fuel cut is met when the amount of depression of the accelerator pedal exceeds a threshold, or when the engine speed drops to the fuel cut return speed.

It goes without saying that the throttle valve 32 is operated to an opening degree corresponding to the depression amount of the accelerator pedal after the fuel cut end condition is satisfied.

Hereinafter, the air-fuel ratio feedback control performed by the ECU 0 will be described in detail. The air-fuel ratio feedback control converges the air-fuel ratio of the air-fuel mixture charged in the cylinder 1, and thus 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. It maximizes the purification efficiency of harmful substances.

As shown in FIG. 2, the ECU 0 determines that the output voltage f of the front _O2 sensor 43, which is a sensor that detects the air-fuel ratio of the gas on the upstream side of the catalyst 41, corresponds to the stoichiometric air-fuel ratio or an air-fuel ratio in the vicinity thereof. If it is higher than the judgment voltage value, it is judged to be rich, and if it is lower than the judgment voltage value, it is judged to be lean. Then, the ECU 0 increases or decreases the feedback correction coefficient FAF based on the determination result of the air-fuel ratio of the gas on the upstream side of the catalyst 41 .

Specifically, the feedback correction coefficient FAF is reduced by the skip value RSM at the time when the determination result of the air-fuel ratio is reversed from lean to rich (when the following delay time TDR has elapsed). In addition, while it is determined that the air-fuel ratio is rich, the feedback correction coefficient FAF is gradually decreased by the lean integral value KIM per calculation cycle (control cycle). The calculation cycle period is equal to the period in which each cylinder 1 of the internal combustion engine undergoes a new cycle (a series of intake stroke-compression stroke-expansion stroke-exhaust stroke).

On the other hand, when the determination result of the air-fuel ratio is reversed from rich to lean (when the following delay time TDL has elapsed), the feedback correction coefficient FAF is increased by the skip value RSP. In addition, while it is determined that the air-fuel ratio is lean, the feedback correction coefficient FAF is gradually increased by the rich integral value KIP per calculation cycle.

When the feedback correction amount 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 becomes leaner. Conversely, when the feedback correction amount FAF increases, the amount of fuel injected 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 front _O2 sensor 43 fluctuates across the determination voltage value, the determination result of the air-fuel ratio of the gas on the upstream side of the catalyst 41 is not immediately reversed. After waiting for the elapse of , the judgment result is reversed. That is, when the output voltage f of the front _O2 sensor 43 switches from rich to lean (below the determination voltage value), it is determined that the air-fuel ratio has reversed from rich to lean after the lean determination delay time TDL has elapsed. . In addition, when the output voltage f of the front _O2 sensor 43 switches from lean to rich (exceeds the determination voltage value), it is determined that the air-fuel ratio has reversed from lean to rich after the rich determination delay time TDR has elapsed. .

The reason why the lean judgment delay time TDL and the rich judgment delay time TDR are provided is that when noise is mixed in the output signal f of the _O2 sensor 43, the lean/rich judgment result of the air-fuel ratio is reversed several times in a short period of time. This is intended to prevent chattering in which the fuel injection amount fluctuates.

The delay times TDL and TDR increase or decrease according to the control center correction amount FACF. FIG. 3 illustrates the relationship between the control center correction amount FACF and the delay times TDL and TDR. As the control center correction amount FACF increases, the lean determination delay time TDL (represented by the dashed line) is shortened and the rich determination delay time TDR (represented by the solid line) is extended. This delays the time at which the feedback correction coefficient FAF turns from increase to decrease, and hastens the time at which it turns from decrease to increase. As a result, the fuel injection amount increases on average, and the control center of the air-fuel ratio feedback control, in other words, the target air-fuel ratio of the gas to be converged by the feedback control shifts to the rich side.

Conversely, the lean determination delay time TDL is extended and the rich determination delay time TDR is shortened as the control center correction amount FACF becomes smaller. If so, the time at which the feedback correction coefficient FAF turns from increase to decrease is hastened, and the time at which it changes from decrease to increase is delayed. As a result, the fuel injection amount decreases on average, and the control center of the air-fuel ratio feedback control shifts to the lean side.

The ECU 0 also calculates the control center correction amount FACF during the air-fuel ratio feedback control. As shown in FIG. 5, the ECU 0 first subtracts the feedback correction coefficient FAF _n-1 calculated in the previous calculation cycle from the feedback correction coefficient FAF _n calculated in the current calculation cycle, and obtains the difference ΔFAF _n between the two. is obtained (step S1). n is a subscript representing an operation cycle.

Next, the ECU 0 obtains a value Σ(ΔFAF _n ) obtained by integrating ΔFAF _n calculated in a plurality of consecutive past calculation cycles (step S2).

Then, the ECU 0 obtains ΔOS _n shown in the following formula from the air amount Ga _n taken into the cylinder 1 and the integrated value Σ(ΔFAF _n ) of ΔFAF _n calculated in the current calculation cycle (step S3). .
ΔOS _n =−Gan×Σ(ΔFAF _n )/{1+Σ( _{ΔFAF n )} }
This ΔOS _n is an approximate value of the amount of change (increase or decrease) in the amount of oxygen stored in the catalyst 41 that increases or decreases as the gas discharged from the cylinder 1 flows into the catalyst 41 .

Further, a value Σ(ΔOS _n ) obtained by integrating ΔOS _n calculated in a plurality of consecutive past calculation cycles is obtained (step S4). This integrated value .SIGMA.(. _{DELTA.OS.sub.n} ) is a deviation indicating how much the amount of oxygen currently occluded by the catalyst 41 deviates from the desired target occluded amount. If the current oxygen storage amount in the catalyst 41 matches the target storage amount, the deviation Σ(ΔOS _n ) becomes zero. A positive value of the deviation Σ(ΔOS _n ) means that the oxygen storage amount in the catalyst 41 is greater than the target storage amount. Conversely, if the deviation Σ(ΔOS _n ) is a negative value, it means that the oxygen storage amount in the catalyst 41 is less than the target storage amount.

The target storage amount is desirably set to a value such that the oxidation reaction of the harmful substances HC and CO and the reduction reaction of NO _x in the catalyst 41 occur most efficiently. For example, the target storage amount is obtained by multiplying the maximum oxygen storage capacity of the catalyst 41 by a fixed ratio smaller than 1 (a value of about 0.5 to 0.6). The maximum oxygen storage capacity of the catalyst 41 gradually declines due to aging deterioration, but a specific method for estimating the maximum oxygen storage capacity is known as a diagnosis (self-diagnosis) function of the catalyst 41 (for example, Japanese Patent Laid-Open No. 2016 -070156, etc.), the explanation thereof is omitted here.

Thus, the ECU 0 adjusts the control center correction amount FACF according to whether the deviation Σ(ΔOS _n ) is positive or negative (steps S9 and S10). If the deviation Σ(ΔOS _n ) is a positive value, the control center correction amount FACF is increased (step S11) to change the control center of the air-fuel ratio feedback control to the rich side. If the deviation .SIGMA.(. _{DELTA.OS.sub.n} ) is a negative value, the control center correction amount FACF is made smaller (step S12) to shift the control center of the air-fuel ratio feedback control to the leaner side.

In steps S9 to S12, while the deviation Σ(ΔOS _n ) is a negative value, the control center correction amount FACF is gradually decreased by the lean integral value FACFKIM per operation cycle, while while the deviation Σ(ΔOS _n ) is a positive value, , the control center correction amount FACF can be gradually increased by the rich integration value FACFKIP per operation cycle. Alternatively, more simply, the control center correction amount FACF when the deviation Σ(ΔOS _n ) is a positive value is set to a value larger than that when the deviation Σ(ΔOS _n ) is 0, and the deviation Σ(ΔOS _n ) is a negative value, the control center correction amount FACF may be set to a value smaller than that when the deviation Σ(ΔOS _n ) is zero.

Of course, the above deviation Σ(ΔOS _n ) may contain an error. That is, the deviation Σ(ΔOS _n ) calculated through steps S1 to S4 may deviate from the deviation between the actual oxygen storage amount of the catalyst 41 and the target oxygen storage amount.

Therefore, when the output signal g of the rear _O2 sensor 44, which is a sensor that detects the air-fuel ratio of the gas on the downstream side of the catalyst 41, exceeds the rich-side threshold value and indicates that the air-fuel ratio is rich ( Step S5) and/or when the output signal g of the rear _O2 sensor 44 exceeds the lean side threshold value and indicates a lean air-fuel ratio (step S7), the calculated deviation Σ(ΔOS _n ) is reset. Yes (steps S6 and S8).

The threshold on the rich side is set to 0.85V, for example. When the output voltage g of the rear _O2 sensor 44 exceeds this threshold, it means that the oxygen stored in the catalyst 41 has run out and the air-fuel ratio of the gas flowing down from the catalyst 41 is excessively rich. . Therefore, as shown in _FIG . 6, when the output voltage g of the rear oxygen sensor 44 exceeds the rich side threshold (step S5), the ECU 0 stores the deviation Σ(ΔOS _n ) stored in the memory. It is reset to a value obtained by subtracting the current target storage amount from a predetermined value, eg, 0 (-target storage amount) (step S6). While the output voltage g of the rear O ₂ sensor 44 exceeds the rich side threshold, the deviation Σ(ΔOS _n ) is maintained at the predetermined value. After that, the control center correction amount FACF is adjusted (steps S10 and S12).

After the deviation Σ(ΔOS _n ) is reset to the predetermined value, if the output voltage g of the rear O ₂ sensor 44 decreases below the rich side threshold, the predetermined value is set as the initial value of the deviation Σ(ΔOS _n ). , and _{.DELTA.OS.sub.n} is added thereto, and the calculation of the deviation .SIGMA.(. _{DELTA.OS.sub.n} ) is restarted (steps S1 to S4).

The threshold on the lean side is set to 0.20 V, for example. When the output voltage g of the rear _O2 sensor 44 falls below this threshold, it means that oxygen is stored up to the maximum oxygen storage capacity of the catalyst 41 and the air-fuel ratio of the gas flowing down from the catalyst 41 is excessively lean. do. Therefore, when the output voltage g of the rear O ₂ sensor 44 falls below the lean-side threshold (step S7), the ECU 0 sets the deviation Σ (ΔOS _n ) stored in the memory to a predetermined value, for example, the current catalyst 41 is reset to a value obtained by subtracting the current target storage amount from the maximum oxygen storage capacity (step S8). During operation of the vehicle, fuel injection into cylinder ₁ of the internal combustion engine may occasionally be cut off for several seconds or more. It is not uncommon to fall below the threshold on the lean side. While the output voltage g of the rear O ₂ sensor 44 is below the lean side threshold, the deviation Σ(ΔOS _n ) is maintained at the predetermined value. After that, the control center correction amount FACF is adjusted (steps S10 and S11).

After the deviation Σ(ΔOS _n ) is reset to the predetermined value, if the output voltage g of the rear O ₂ sensor 44 increases to the lean side threshold or more, the predetermined value is set as the initial value of the deviation Σ(ΔOS _n ). , and _{.DELTA.OS.sub.n} is added thereto, and the calculation of the deviation .SIGMA.(. _{DELTA.OS.sub.n} ) is restarted (steps S1 to S4).

The ECU 0 repeats steps S1 through S12 each time a calculation cycle comes (each time any cylinder 1 enters a new cycle).

Incidentally, in conventional air-fuel ratio feedback control, the control center correction amount FACF is determined according to the output signal g of the air-fuel ratio sensor 44 on the downstream side of the catalyst 41 . That is, as shown in FIG. 4, the output voltage g of the rear O ₂ sensor 44 is compared with the judgment voltage value. If it is higher than the judgment voltage value, it is judged rich, and if it is lower than the judgment voltage value, it is judged lean. Note that this determination voltage value may not match the determination voltage value compared with the output signal f of the front O ₂ sensor 43 .

Then, based on the determination result of the air-fuel ratio of the gas on the downstream side of the catalyst 41, the control center correction amount FACF is increased or decreased. Specifically, while the air-fuel ratio is determined to be rich, the control center 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, The control center correction amount FACF is gradually increased by the rich integration value FACFKIP per calculation cycle. As described above, when the control center correction amount FACF decreases, the air-fuel ratio control center tends to lean, and when the control center correction amount FACF increases, the air-fuel ratio control center tends to rich.

In this embodiment, the controller 0 feedback-controls the air-fuel ratio of the gas flowing into the exhaust _purification catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine. And based on the output signal f of the air-fuel ratio sensor 43 installed upstream of the catalyst 41 in the exhaust passage 4, the deviation Σ (ΔOS _n ) between the amount of oxygen stored in the catalyst 41 and its target amount is estimated. A controller 0 for an internal combustion engine is configured to change the target air-fuel ratio to be converged by feedback control according to the deviation Σ(ΔOS _n ).

Further, the control device 0 of the present embodiment detects the deviation when the output signal g of the air-fuel ratio sensor 44 installed downstream of the catalyst 41 in the exhaust passage 4 exceeds the rich-side threshold value and indicates that the air-fuel ratio is rich. Σ(ΔOS _n ) is reset to a predetermined value and/or when the output signal g of the air-fuel ratio sensor 44 installed downstream of the catalyst 41 exceeds the lean side threshold value and indicates the air-fuel ratio lean. By resetting the deviation .SIGMA.(. _{DELTA.OS.sub.n} ) to a predetermined value, errors mixed in the deviation .SIGMA.(. _{DELTA.OS.sub.n} ) which is repeatedly calculated are eliminated.

According to this embodiment, the amount of oxygen currently occluded in the catalyst 41 can be converged to the desired target occluded amount. Therefore, it is possible to prevent the catalyst 41 from being filled with oxygen and discharging _NOx , and the catalyst 41 from lack of oxygen to discharge HC and CO, which is effective in improving emissions. The use of the _O2 sensor 43, which is cheaper than the linear A/F sensor, makes it possible to further reduce the emission of harmful substances, which is also advantageous in terms of cost.

The present invention is not limited to the embodiments detailed above. In the above-described embodiment, the control center correction amount FACF is adjusted according to the deviation Σ(ΔOS _n ) between the amount of oxygen stored in the catalyst 41 and the target amount of oxygen stored. I was changing my goals. However, instead of or together with this, a target value to be compared with the output signal f of the air-fuel ratio sensor 43 on the upstream side of the catalyst 41, in other words, a determination voltage to be compared with the output voltage f of the front O ₂ sensor 43 By adjusting the value itself, the target air-fuel ratio to be converged by feedback control may be changed. In this case, when the deviation Σ(ΔOS _n ) is a positive value, the determination voltage value is raised to shift the target value to the richer side, and when the deviation Σ(ΔOS _n ) is a negative value, the determination voltage value is increased. is lowered to shift the target value to the leaner side.

Further, in parallel with the calculation of the control center correction amount FACF based on the deviation Σ(ΔOS _n ) (without referring to the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41), the ECU 0, which is the control device for the internal combustion engine, conventionally It is also possible to calculate the control center correction amount FACF with reference to the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41, similar to the air-fuel ratio feedback control of . Each of these control center correction amounts indicates a target gas air-fuel ratio to be converged by feedback control.

Then, the divergence between the former control center correction amount FACF and the latter control center correction amount FACF spread beyond a certain level (the absolute value of the difference between the two became above a certain level, or the ratio of the two deviated from a certain range. (the ratio of both exceeds the upper limit of the range, or decreases beyond the lower limit of the range)), the latter control center correction amount FACF is used instead of the former control center correction amount FACF. It is conceivable to carry out air-fuel ratio feedback control using the air-fuel ratio sensor 44 downstream of the catalyst 41 , that is, to carry out feedback control to converge the air-fuel ratio to a target set based on the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 . Then, even if a large error temporarily enters the deviation Σ(ΔOS _n ), it is possible to appropriately avoid an increase in the amount of harmful substances discharged.

During the feedback control of the air-fuel ratio using the latter control center correction amount FACF, the output signal g of the air-fuel ratio sensor 44 exceeds the rich side threshold value and indicates a rich air-fuel ratio, and/or When the output signal g of the sensor 44 exceeds the lean side threshold value and indicates a lean air-fuel ratio, the deviation Σ(ΔOS _n ) is reset and the former control center correction amount FACF is used thereafter, that is, the deviation Σ It is possible to return to the feedback control that converges the air-fuel ratio to the target corresponding to (ΔOS _n ).

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

INDUSTRIAL APPLICABILITY The present invention can be applied to control of an internal combustion engine mounted on a vehicle.

0... Control unit (ECU)
REFERENCE SIGNS LIST 1 cylinder 11 injector 3 intake passage 4 exhaust passage 41 catalyst 43 air-fuel ratio sensor (O ₂ sensor) upstream of the catalyst
b... crank angle signal d... intake air temperature/intake pressure signal f... air-fuel ratio signal j... fuel injection signal

Claims (1)

A control device for feedback-controlling the air-fuel ratio of gas flowing into an exhaust purification catalyst mounted in an exhaust passage of an internal combustion engine,
Based on the amount of air taken into the cylinder and the output signal of an air-fuel ratio sensor installed upstream of the catalyst in the exhaust passage, the deviation between the amount of oxygen stored in the catalyst and its target amount is estimated. ,
According to the deviation, the air-fuel ratio target to be converged by feedback control is changed,
When the output signal of an air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage exceeds a rich-side threshold value to indicate that the air-fuel ratio is rich, the deviation is reset to a predetermined value on the rich side , or downstream of the catalyst. resetting the deviation to a predetermined value on the lean side different from the predetermined value on the rich side when the output signal of the air-fuel ratio sensor installed in the air-fuel ratio sensor exceeds the threshold value on the lean side and indicates the air-fuel ratio is lean ;
In parallel with the calculation of the target air-fuel ratio to be converged by the feedback control, based on the output signal of an air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage, separately from the deviation,
When the deviation between the target corresponding to the deviation and the target based on the output signal of the air-fuel ratio sensor downstream of the catalyst widens beyond a certain level, air-fuel ratio feedback control is performed using the latter target instead of the former target. A control device for an internal combustion engine to carry out .

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