JPH09310635A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve exhaust emission by correcting an intake airfuel ratio so as to make an O2 storage rate in a target rate, estimating the O2 storage rate so as to make reducing speed of the O2 storage rate in a small level at the time of a rich condition more than that of increase speed of the O2 storage rage at the time of a lean condition. SOLUTION: A three-way catalyst (a catalytic converter) 12 having O2 storage action is arranged in the exhaust passage of an internal combustion engine, and an air-fuel ratio sensor 13 is arranged on an upstream side from the three- way catalyst 12. In a control unit 10, a deviation of a theoretical air-fuel ratio is calculated on the basis of the output of the air-fuel ratio sensor 13, and the storage rate of O2 stored in the three-way catalyst 12 on the basis of the air-fuel ratio deviation is estimated. An intake air-fuel ratio is controlled so as to make its estimated O2 storage rate in a prescribed target value. When the O2 storage rate is estimated, the O2 storage rate is increased at a change degree according to an air-fuel ratio deviation when an exhaust gas air-fuel ratio is in a lean condition, and the O2 storage rate is reduced when the ratio is in a rich condition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an air-fuel ratio control system for an internal combustion engine.

[0002]

2. Description of the Related Art A three-way catalyst is provided in an exhaust passage of an internal combustion engine, and an air-fuel ratio sensor provided in an exhaust passage upstream of the three-way catalyst detects the air-fuel ratio of the exhaust gas to detect the air-fuel ratio of the exhaust gas. The amount of O ₂ storage stored in the three-way catalyst is estimated based on the deviation ΔA / F from the theoretical air-fuel ratio, and the estimated value of this O ₂ storage amount is a target value (for example, the maximum O ₂ storage of the three-way catalyst). An internal combustion engine is known in which the intake air-fuel ratio is controlled so that the intake air-fuel ratio becomes about half (about half of the amount) (JP-A-6-249).
028). In the above device, if the deviation ΔA / F of the air-fuel ratio of the exhaust gas from the theoretical air-fuel ratio is equal, the amount of oxygen adsorbed by the three-way catalyst when lean and the amount of oxygen desorbed from the three-way catalyst when rich are obtained. The O ₂ storage amount is estimated as equal.

[0003]

However, in practice,
The desorption rate of oxygen desorbed from the three-way catalyst is lower than the adsorption rate of oxygen adsorbed on the three-way catalyst, that is, the oxygen desorbed from the three-way catalyst is shorter than the time required for oxygen to be adsorbed on the three-way catalyst. It takes a long time to release. Therefore, ΔA
Even if / F is equal, the desorption amount per unit time is smaller than the adsorption amount, and as a result, the O ₂ storage amount becomes larger than the target value, more oxygen is adsorbed, and lean exhaust gas becomes the catalyst. There is a problem that when it flows in, it cannot be sufficiently purified and the emission deteriorates.

In view of the above problems, the present invention accurately estimates the O ₂ storage amount, and based on the result, controls the intake air-fuel ratio so that the O ₂ storage amount stored in the three-way catalyst is always close to the target value. It is an object of the present invention to provide an air-fuel ratio control device that operates.

[0005]

According to the invention of claim 1, a three-way catalyst having an O ₂ storage function arranged in the exhaust passage of an internal combustion engine and an exhaust passage upstream of the three-way catalyst are provided. An air-fuel ratio sensor for detecting the exhaust gas air-fuel ratio, an air-fuel ratio deviation calculating means for calculating a deviation of the exhaust gas air-fuel ratio from the theoretical air-fuel ratio based on the output of the air-fuel ratio sensor, and the air-fuel ratio deviation calculating means and O ₂ storage amount estimating means but to estimate the O ₂ storage amount stored in the three-way catalyst based on a deviation from the stoichiometric air-fuel ratio calculated, O ₂ storage amount of the O ₂ storage amount estimating means estimated in advance An intake air-fuel ratio control means for controlling the intake air-fuel ratio so that the intake air-fuel ratio becomes a predetermined target value, and the O ₂ storage amount estimating means responds to a deviation from the theoretical air-fuel ratio when the exhaust gas air-fuel ratio is lean. Degree of change Together allowed to increase the O ₂ storage amount in the exhaust gas air-fuel ratio brought reduces the O ₂ storage amount change degree corresponding to a deviation from the stoichiometric air-fuel ratio at the time of the rich and the when the exhaust gas air-fuel ratio is lean There is provided an air-fuel ratio control device for an internal combustion engine that estimates the O ₂ storage amount by making the degree of change with respect to the deviation from the stoichiometric air-fuel ratio different when rich, and making the degree of change smaller when lean, as compared to when lean. It

[0006] In an air-fuel ratio control system for internal combustion engine formed in this manner, the O by ₂ storage amount estimating means, the O ₂ storage so that the exhaust gas air-fuel ratio O ₂ storage amount when the lean increases rapidly to estimate the amount, O ₂ exhaust gas air-fuel ratio to estimate the O ₂ storage amount as O ₂ storage amount when the rich decreases slowly, matching the change of the O ₂ storage amount in the actual three-way catalyst The amount of storage is estimated. And by inhalation the air-fuel ratio control means, the air-fuel ratio of the intake mixture as above O ₂ storage amount becomes the target O ₂ storage amount is controlled.

According to the invention of claim 2, the invention according to claim 1 is further provided with a catalyst temperature detecting means for detecting the temperature of the three-way catalyst, and the O ₂ storage amount estimating means is an exhaust gas according to the catalyst temperature. There is provided an air-fuel ratio control device for an internal combustion engine, which estimates the O ₂ storage amount by changing the difference in the degree of change between when the gas air-fuel ratio is rich and when it is lean.

In the air-fuel ratio control device for an internal combustion engine configured as described above, the O ₂ storage amount estimating means can make the difference in the degree of change of the O ₂ storage amount according to the temperature of the catalyst actually match. In consideration of this, the amount of O ₂ storage is estimated.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing an overall configuration of an embodiment when the present invention is applied to an internal combustion engine for automobiles. In FIG. 1, 1 is an internal combustion engine main body, 2a
Denotes an intake manifold connected to the intake port of each cylinder of the engine 1, and 11 denotes an exhaust manifold connected to the exhaust port of each cylinder.

The intake manifold 2a is connected to the intake passage 2 via a common surge tank 2b. Reference numeral 3 denotes an air flow meter for detecting an intake air amount of the engine 1. As the air flow meter 3, for example, a movable vane type having a built-in potentiometer is used, and generates a voltage signal proportional to the amount of intake air. Further, the intake passage 2 is provided with a throttle valve 16 having an opening degree according to a driver's operation amount of an accelerator pedal. Further, in the vicinity of the throttle valve 16, an idle state signal is generated when the throttle valve 16 is fully closed. A switch 17 is provided.

Reference numeral 7 is a fuel injection valve arranged near the intake port of each cylinder of the intake manifold 2a. The fuel injection valve 7 is provided with an engine control unit (hereinafter referred to as E)
The valve is opened in response to a signal from the CU 10 and pressurized fuel is injected for each intake port of each cylinder. Control of fuel injection from the fuel injection valve 7 will be described later. The exhaust manifold 11 is connected to the catalytic converter 12 via a common exhaust pipe. The catalytic converter 12 has a built-in three-way catalyst and can purify three components of HC, CO, and NO _x in the exhaust gas at the same time. An air-fuel ratio sensor 13 that generates a voltage signal according to the air-fuel ratio of the exhaust gas is provided on the upstream side of the catalytic converter 12, that is, at the collecting portion of the exhaust manifold 11. Is provided with an O ₂ sensor 15 that generates different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. The O ₂ sensor 15 is for determining the deterioration of the catalyst and is not always necessary in the present invention.

Further, the ignition distributor 4 of the engine 1 is provided with two crank angle sensors 5 and 6 for generating a pulse signal at every constant rotation of the engine crankshaft. In the present embodiment, the crank angle sensor 5 detects, for example, every time the specific cylinder reaches the compression top dead center (that is,
Outputs a pulse signal for reference position detection (every 20 ° CA)
The crank angle sensor 6 outputs a pulse signal for detecting a crank rotation angle, for example, every 30 ° CA.

The water jacket 8 of the cylinder block of the engine 1 is provided with a cooling water temperature sensor 9 for outputting an analog voltage corresponding to the engine cooling water temperature. E
The CU 10 includes, for example, an input / output interface 102,
A known digital computer in which a CPU 103, a ROM 104, and a RAM 105 are mutually connected by a bidirectional bus, and further, an AD converter 101, a backup RAM 106 that is directly connected to a power source and can retain stored contents even when an engine ignition switch is OFF, The clock generation circuit 107 and the like are provided.

The ECU 10 performs not only fuel injection control of the engine accompanied by air-fuel ratio control, which will be described later, but also ignition timing control and the like. In order to execute these controls, the ECU 10
An engine intake air amount signal from the air flow meter 3, a cooling water temperature signal from the cooling water temperature sensor 9, an air-fuel ratio signal from the air-fuel ratio sensor 13, a rich and lean signal from the O ₂ sensor 15 via the D converter 101. In addition to the pulse signals from the crank angle sensors 5 and 6 and the idle switch 1 via the input / output interface 102.
The idle signal or the like from 7 is input.

The engine intake air amount signal and the coolant temperature signal are fetched by an AD conversion routine executed every fixed crank time, and are stored in predetermined areas of the RAM 105 in the engine intake air amount data Q and the coolant temperature data THW, respectively.
Is stored as Every time the pulse signal of the crank angle sensor 6 is input, the engine rotation speed is calculated from the pulse interval by a routine (not shown) and stored in a predetermined area of the RAM 105 as engine rotation speed data Ne.

On the other hand, the ECU 10 is connected to the fuel injection valve 7 via the input / output interface circuit 102 and controls the fuel injection from the fuel injection valve 7. 108 in FIG.
Denoted by 109 and 110 are a down counter, a flip-flop, and a drive circuit for controlling the fuel injection time of the fuel injection valve 7, respectively. That is, when the execution fuel injection time TAU is calculated in the routine described later, the execution fuel injection time TAU is preset in the down counter 108, the flip-flop 109 is set, and the drive circuit 110 outputs the drive signal of the fuel injection valve 7. Output. As a result, the fuel injection valve 7 opens to start fuel injection. The down counter 108 counts the clock signal of the clock 107 and the flip-flop 109 is set when a preset time has elapsed, so that the drive circuit stops the drive signal of the fuel injection valve 7 and the fuel injection valve 7 is closed. To do. Therefore, the calculated execution fuel injection time T
The fuel injection valve 7 is opened for a time corresponding to the AU, and the fuel of the amount corresponding to the execution fuel injection time TAU is injected from the fuel injection valve 7 to the engine 1.

The above-mentioned execution fuel injection time TAU is obtained by correcting the basic fuel injection time calculated according to the operating conditions so that the O ₂ storage amount becomes a predetermined target value as described later. FIG. 2 is a flowchart of a routine for calculating the basic fuel injection amount time. This routine is executed by the ECU 10 at every constant crank angle (for example, 3
Every 60 ° CA). That is, in the routine of FIG. 2, the intake air amount data Q and the rotation speed data Ne are set to RA.
Read from a predetermined area of M105 (step 201),
The intake air amount Q / Ne per engine revolution is calculated (step 202), and the basic fuel injection time TAUB is calculated by the following formula (step 203). TAUB = α × Q / Ne Here, the basic fuel injection time TAUB is the fuel injection amount required to make the air-fuel mixture supplied to the combustion chamber the stoichiometric air-fuel ratio, and α is a constant.

Next, the control for correcting the O ₂ storage amount to the target value will be described. First, the O ₂ storage action of the catalyst which is the premise of the control will be described. The catalyst used in the present invention contains a component that occludes O ₂ such as ceria (Ce O ₂ ), and is occluded when the input gas (exhaust gas flowing into the catalytic converter) is richer than the theoretical air-fuel ratio. The exhausted O ₂ to oxidize HC and CO which are not completely combusted in the exhaust gas to make the output gas (exhaust gas flowing out from the catalytic converter) the theoretical air-fuel ratio, and conversely,
When the input gas is leaner than the stoichiometric air-fuel ratio, the excess O ₂ in the exhaust gas is stored to make the output gas the stoichiometric air-fuel ratio.

FIG. 3 is a diagram for explaining the above operation. O ₂ storage operation is not caused by the adsorption saturation of O ₂ in the T1 portion of FIG. 3, the air-fuel ratio of the gas leaving the air-fuel ratio of the incoming gases have the same but, O ₂ storage in the portion of the figure T2 Due to the action, the incoming gas is richer than the stoichiometric air-fuel ratio, but the outgoing gas is made to the stoichiometric air-fuel ratio. After that, all of the stored O ₂ is released at the portion T3, and the O ₂ storage action does not occur. Then, due to the O ₂ storage action, the incoming gas is leaner than the stoichiometric air-fuel ratio, but the outgoing gas is made the stoichiometric air-fuel ratio. If no O ₂ storage effect occurs, T
The air-fuel ratio of the incoming gas and the air-fuel ratio of the outgoing gas are the same in the portions of 2 and T4 as in the portions of T1 and T3.
Since the portion of T2 and T4 becomes the stoichiometric air-fuel ratio, the purification of the exhaust gas is improved by the O ₂ storage action.

[0020] Therefore, to estimate the O ₂ storage amount in order to effectively use the O ₂ storage operation, for example, as O ₂ before and after half of the maximum O ₂ storage capability of the catalyst is always stored in the catalyst, the engine A method of controlling the air-fuel ratio of the intake air-fuel mixture burned at 1 has been developed. here,
O ₂ to a storage amount control is performed to the front and rear half of its maximum O ₂ storage capability, abrupt disturbance (rich,
(Both on the lean side), exhaust gas with an air-fuel ratio that deviates from the stoichiometric air-fuel ratio enters the catalyst, but in that case, it is covered by the O ₂ storage function (adsorption and desorption of O ₂ ) of the above catalyst. This is to prevent deterioration of emission at the gas output level of the catalyst.

In the conventional technique, the control is performed as follows. That is, in FIG. 4, predetermined O ₂ is adsorbed in the catalyst at time t0, for example,
O ₂ before and after half of the maximum O ₂ storage capacity as the
There When adsorbed, if the disturbance is lean in the state shown by A in the inflow gas 4 occurs, to return to a predetermined O ₂ adsorption amount as the amount of O ₂ is increased to adsorb correspondingly In addition, the intake air-fuel mixture was adjusted so that the rich state shown by B appears in the incoming gas as much as the area A.

Therefore, in the prior art, the amount of O ₂ storage was estimated by the following equation regardless of whether the air-fuel ratio of the input gas is rich or lean. O ₂ storage amount = KO ₂ × ∫ {Ga × (ΔA / F) / (A / F)} × Δt (1) where KO _{2 is} the oxygen concentration ratio in the air, and Ga is the intake air amount (g / s), ΔA / F: deviation of the air-fuel ratio of the incoming gas from the theoretical air-fuel ratio, A / F: theoretical air-fuel ratio.

However, in reality, since the desorption rate of O ₂ is smaller than the adsorption rate, when the lean state indicated by A occurs as described above, the incoming gas is rich in the same area as that. The amount of adsorption will increase more than the predetermined amount if only the amount of adsorption is increased. As a result, when the lean exhaust gas flows in, the margin of the amount of O _{2 that} can be adsorbed in the catalyst becomes small, causing adsorption saturation of O ₂ and exhausting the exhaust gas in a lean state. .

Therefore, in the present invention, as shown in FIG. 5, the O ₂ storage amount is set to a predetermined target value (for example, the maximum O ₂ storage amount of the maximum O ₂ storage amount such that the rich area is larger than the lean area). Half). That is, B ′ = kA (k ≧ 1.0). Note that the O ₂ storage capacity also differs depending on the catalyst temperature, the difference between the adsorption rate and the desorption rate also differs, and the lower the catalyst temperature, the larger the difference. Therefore, as shown in FIG. In other words, a map in which the value of k becomes larger as the engine speed is detected, that is, when the engine speed is low and the load is low, is used, and k selected according to this map is used. However, the catalyst temperature may be directly detected, and k corresponding to the catalyst temperature may be stored in a map and used.

Therefore, in the present invention, the amount of O ₂ storage is estimated by classifying it according to the air-fuel ratio as follows. (I) Lean (ΔA / F> 0) O ₂ storage amount = KO ₂ × ∫ {Ga × (ΔA / F) / (A / F)} × Δt (2) (II) Rich ( ΔA / F <0) O ₂ storage amount = KO ₂ × ∫ {Ga × (ΔA / F) / k / (A / F)} × Δt (3) However, k is the value described above. (III) In the case of stoichiometric air-fuel ratio (ΔA / F = 0) The O ₂ storage amount is not changed.

FIG. 7 shows the current O ₂ based on the above.
It is a flowchart which estimates O2 (n) which is a storage amount, and is executed in a constant time interrupt routine. Therefore, while reading the necessary parameter k,
The deviation ΔA / F of the exhaust gas air-fuel ratio from the theoretical air-fuel ratio is calculated based on the air-fuel ratio signal from the air-fuel ratio sensor 13 (steps 71 to 72), and the exhaust gas air-fuel ratio is judged to be the theoretical air-fuel ratio from this deviation ΔA / F. If it is the theoretical air-fuel ratio,
_{Since the 2} storage amount does not change, the previous O ₂ storage amount of O ₂ (n-1) is left as it is, and if it is not the theoretical air-fuel ratio, it is similarly determined whether the exhaust gas air-fuel ratio is rich or lean, In the case of lean, the amount of change in the amount of O ₂ storage calculated based on the above equation (2), that is, KO ₂ ×
By adding Ga × a (ΔA / F) / (A / F) in a O ₂ storage amount of the previous O2 (n-1) ends, in the case of rich were calculated based on the above equations (3) O ₂ Change amount of storage amount, that is, KO ₂ × Ga × (ΔA / F) /
k / (A / F) is O2 which is the previous O ₂ storage amount
Add to (n-1) and end (steps 73 to 7)
7). Therefore, when rich, the O ₂ storage amount in the actual catalyst decreases at a slower rate than the rate at which the desorption rate increases slower than the adsorption rate,
Also in the above estimation calculation, since it is based on the equation (3) described above, than the speed increase of the O ₂ storage amount when the rich than the speed increase of the O ₂ storage amount in the case of lean, rich In the case of, the speed of reducing the amount of O ₂ storage is small, which corresponds to the actual change.

Next, FIG. 8 shows that the current O ₂ storage amount O ₂ (n) calculated above becomes the target O ₂ storage amount, that is, a predetermined target O 2 ₂ is a flowchart of a routine for comparing O2REF, which is _two storage amounts, and correcting the basic fuel injection time TAU (see FIG. 2) when O2 (n) and O2REF are different.

First, necessary parameters are read (step 81), and the target O ₂ storage amount O2REF and the current O ₂ storage amount O2 (n) are compared (step 8).
2, 84). Here, the target O ₂ storage amount O 2REF
Is a predetermined value, for example, half of the maximum O ₂ storage amount, as described above. And O2RE
If F = O2 (n), the basic fuel injection time TAUB is directly set to the execution fuel injection time TAU (step 83),
Lean exhaust gas is formed from the O ₂ storage amount be adsorbed further O ₂ have insufficient is what is required for the target O ₂ storage amount O2REF if O2REF> O2 (n) As described above, the basic fuel injection time TAUB is multiplied by KL (KL <1, for example, 14.25 / 14.5 when the stoichiometric air-fuel ratio is 14.5) to obtain the execution fuel injection time TAU (step 85), O
If 2REF <O2 (n), target O ₂ storage amount O
Since the amount of O ₂ storage exceeds the amount of ₂ REF and further desorption of O ₂ is required, KR (KR> 1) is added to the basic fuel injection time TAUB so that rich exhaust gas is formed. And, for example, the stoichiometric air-fuel ratio is 1
The value obtained by multiplying 4.5 by 14.75 / 14.5 etc. is set as the execution fuel injection time TAU (step 86).

[0029]

According to the present invention, when the intake air-fuel ratio is corrected so that the O ₂ storage amount becomes the target value,
₂ storage amount is performed estimation can not be directly measured but, O ₂ storage amount during the rich than the increase rate of the estimated actual O ₂ storage amount during the lean to suit changes in the O ₂ storage amount of the catalyst Since the decrease rate of is reduced, the estimation accuracy of the O ₂ storage amount is improved, that is, the control accuracy is improved, and the exhaust emission is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment in which the present invention is applied to an internal combustion engine for automobiles.

FIG. 2 is a flowchart of a routine for calculating a basic fuel injection time.

FIG. 3 is a diagram illustrating a concept of air-fuel ratio control using an O ₂ storage effect.

FIG. 4 is a diagram illustrating a concept of control for maintaining an O ₂ storage amount according to a conventional technique.

FIG. 5 is a diagram illustrating a concept of control for maintaining an O ₂ storage amount according to the present invention.

FIG. 6 is a map showing changes in coefficient k with respect to operating conditions.

FIG. 7 is a flowchart of a routine for calculating an O ₂ storage amount.

FIG. 8 is a flowchart of a routine for correcting the basic fuel injection time so that the O ₂ storage amount becomes a target value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine main body 10 ... ECU (engine control unit) 12 ... Catalytic converter 13 ... Air-fuel ratio sensor

Claims (2)

[Claims] 1. A three-way catalyst having an O ₂ storage function arranged in an exhaust passage of an internal combustion engine, and an air-fuel ratio sensor arranged in an exhaust passage upstream of the three-way catalyst for detecting an exhaust gas air-fuel ratio. An air-fuel ratio deviation calculating means for calculating a deviation of the exhaust gas air-fuel ratio from the stoichiometric air-fuel ratio based on the output of the air-fuel ratio sensor, and three based on the deviation from the stoichiometric air-fuel ratio calculated by the air-fuel ratio deviation calculating means. and O ₂ storage amount estimating means for estimating the O ₂ storage amount stored in the original catalyst, controlling the intake air as the O ₂ storage amount which the O ₂ storage amount estimation means has estimated the predetermined target value comprising a suction air-fuel ratio control means for said O ₂ storage amount estimating means, when the exhaust gas air-fuel ratio is allowed to increase the O ₂ storage amount change degree corresponding to a deviation from the stoichiometric air-fuel ratio when the lean Moni, the exhaust gas air-fuel ratio brought reduces the O ₂ storage amount change degree corresponding to a deviation from the stoichiometric air-fuel ratio at the time of the rich and the stoichiometric air-exhaust air-fuel ratio when the time and rich lean By changing the degree of change with respect to the deviation from the fuel ratio,
An air-fuel ratio control device for an internal combustion engine, which estimates the O ₂ storage amount by making the degree of change smaller when the engine is rich than when it is lean. 2. The catalyst temperature detecting means for detecting the temperature of the three-way catalyst is further provided, and the O ₂ storage amount estimating means is arranged depending on the catalyst temperature when the exhaust gas air-fuel ratio is rich or lean. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the O ₂ storage amount is estimated by changing the difference in the degree of change.