JP2002364418A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain an oxygen adsorption quantity of an exhaust emission control catalyst at the optimal quantity, and to maintain the high exhaust emission control performance. SOLUTION: An initial value setting unit 21 sets the initial oxygen adsorption quantity value V0 when starting (restarting the operation) on the basis of the time passed after stopping the operation of the engine. An oxygen adsorption quantity computing unit 22 computes the oxygen adsorption quantity V on the basis of the initial value V0 and the oxygen adsorption change quantity Vb inside of the catalyst 12. A target air-fuel ratio setting unit 24 compares the oxygen adsorption quantity V with the optimal oxygen quantity set by an optimal oxygen adsorption quantity setting unit 23, and outputs a different thereof as a target air-fuel ratio, and an air-fuel ratio F/B control unit 25 controls the exhaust air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to a technique for controlling an amount of oxygen adsorbed on an exhaust purification catalyst to an optimum amount.

[0002]

2. Description of the Related Art Conventionally, an exhaust gas purifying catalyst is provided in an exhaust passage of an internal combustion engine, and the air-fuel mixture is evacuated in order to realize a high conversion by balancing oxidation and reduction in the exhaust gas purifying catalyst. 2. Description of the Related Art An exhaust gas purification system for an internal combustion engine that performs an air-fuel ratio feedback control that maintains a fuel ratio at a stoichiometric air-fuel ratio is known.

In this type of exhaust gas purification system, the amount of oxygen adsorbed on the catalyst greatly affects the conversion. That is,
If the amount of oxygen adsorbed by the catalyst exceeds the optimum value, CO, H
When the oxidation reaction of C is promoted, while the reduction reaction of NOx becomes slow, and conversely, when the amount of adsorbed oxygen becomes smaller than the optimum value, NO
While the reduction reaction of x is promoted, the oxidation reaction of CO and HC becomes dull.

[0004] In view of the above, there is known an air-fuel ratio control device that calculates the amount of oxygen adsorbed on a catalyst and controls the exhaust air-fuel ratio so that the calculated amount of oxygen adsorbed becomes an optimal value. See Japanese Unexamined Patent Publication No. Hei 10-184424.

[0005]

By the way, in the conventional air-fuel ratio control apparatus described above, the initial amount of oxygen adsorbed by the catalyst at the start of the engine is considered in consideration of the fact that the catalyst is exposed to the atmosphere while the operation of the engine is stopped. The maximum amount of oxygen that can absorb the value is set (maximum oxygen adsorption amount). However, when the maximum oxygen adsorption amount is set to the initial value as in the above-described conventional device, a difference may occur between the calculated oxygen adsorption amount and the actual oxygen adsorption amount,
As a result, there is a region where the exhaust is deteriorated.

That is, as shown in FIG. 6 (A), when a sufficient time has elapsed after the operation was stopped, the actual oxygen adsorption amount (solid line) was calculated because the catalyst adsorbed the maximum amount of oxygen. Although the measured oxygen adsorption amounts (broken lines) are almost the same, when the operation has been restarted before the amount of oxygen adsorbed on the catalyst reaches the maximum oxygen adsorption amount, the elapsed time after the operation stop is short, FIG.
As shown in (B), a difference occurs between the actual oxygen adsorption amount (solid line) and the calculated oxygen adsorption amount (dashed line). Too much control to reduce.

In this case, the fact that the amount of adsorbed oxygen is not at the optimum amount of oxygen means that the actual amount of adsorbed oxygen exceeds the optimum amount of oxygen (ie, becomes smaller than the optimum amount of oxygen) until the oxygen sensor on the downstream side of the catalyst. Therefore, even if the control of the exhaust air-fuel ratio is corrected immediately after the detection, there is a region where the amount of oxygen adsorbed by the catalyst deviates from the optimum amount of oxygen (shaded area in the figure), and the exhaust gas deteriorates. Resulting in.

The present invention has been made in view of the above problems, and accurately calculates the amount of oxygen adsorbed in the catalyst after the operation is stopped, and accurately estimates the amount of oxygen adsorbed in the catalyst at the start (initial value). The purpose is to maintain high exhaust gas purification efficiency.

[0009]

Therefore, the invention according to claim 1 calculates the amount of oxygen adsorbed on an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, and calculates the amount of adsorbed oxygen to a predetermined target value. An air-fuel ratio control device for an internal combustion engine that controls an exhaust air-fuel ratio so that the amount of oxygen adsorbed to the exhaust purification catalyst after the operation is stopped is calculated based on the elapsed time since the operation of the engine was stopped, An initial value of the amount of oxygen adsorbed at the time of starting is set based on the calculated amount of adsorbed oxygen after operation stop.

According to a second aspect of the present invention, the amount of oxygen adsorbed by the exhaust purification catalyst at the time of immediately preceding engine stop is stored, and the oxygen adsorbed amount after the operation is stopped is added to the oxygen adsorbed amount at the time of stop of the operation. The set value is set as an initial value of the oxygen adsorption amount at the time of restarting the operation. The invention according to claim 3 is characterized in that the oxygen adsorption amount after the stop of the operation is represented by a first-order delay with respect to the elapsed time from the stop of the operation of the engine.

The invention according to a fourth aspect is characterized in that a time constant of the oxygen adsorption amount after the operation is stopped is set based on an environmental temperature of the exhaust purification catalyst. The invention according to claim 5 is characterized in that a timer is provided, and the timer measures the elapsed time from the stop of the operation of the engine.

The invention according to claim 6 is characterized in that a cooling water temperature of the engine is detected, and an elapsed time from the stop of the operation of the engine is estimated based on the detected cooling water temperature of the engine.

[0013]

According to the first aspect of the present invention, the amount of oxygen adsorbed on the exhaust gas purification catalyst after the operation is stopped is calculated based on the elapsed time from the stop of the operation of the engine. Since the initial value of the amount of oxygen adsorbed at the time of startup is set based on the amount of oxygen adsorbed at the start, the air-fuel ratio control that keeps the optimal amount of oxygen adsorbed in the catalyst is started at the start of operation ( ), The amount of oxygen (initial value) adsorbed in the catalyst can be accurately calculated.

As a result, the accuracy of the air-fuel ratio control is improved, and the deterioration of the exhaust emission can be reliably prevented. According to the invention according to claim 2, it is easy and accurate to restart the operation by adding the oxygen adsorption amount after the operation stop to the oxygen adsorption amount of the exhaust purification catalyst immediately before the operation stop of the engine. The initial value of the oxygen adsorption amount can be set.

According to the third aspect of the invention, there is a limit to the amount of oxygen that can be adsorbed by the exhaust purification catalyst, and it is considered that the smaller the amount of adsorbed oxygen is, the easier it is to adsorb (the easier it is to adsorb). By expressing the oxygen adsorption amount after the stoppage of the operation as a first-order lag with respect to the elapsed time from the stoppage of the operation, it is possible to accurately express the amount using a simple equation.

According to the fourth aspect of the present invention, since the oxygen adsorption state of the exhaust purification catalyst changes depending on the temperature (of the catalyst itself), the time constant of the oxygen adsorption state expressed by the first-order lag is determined by the environmental temperature of the catalyst. , The oxygen adsorption amount after the operation is stopped can be calculated with higher accuracy. As the environmental temperature of the catalyst, any temperature representative of the environmental temperature of the catalyst portion when the operation is stopped may be used. In addition to the temperature of the catalyst itself, exhaust temperature, outside air temperature, intake air temperature and the like can be used.

According to the fifth aspect of the invention, the elapsed time from the stop of the operation of the engine is directly measured by the timer, and the amount of adsorbed oxygen in the catalyst after the stop of the operation can be calculated. According to the sixth aspect of the invention, by reading the temperature of the cooling water of the engine, it is possible to easily obtain the elapsed time from the stop of the operation of the engine with reference to, for example, a map.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of an internal combustion engine showing one embodiment of the present invention. In FIG. 1, an air flow meter 3 for detecting an intake air flow rate Qa is provided in an intake passage 2 of an engine 1, and an intake air amount Qa is controlled by a throttle valve 4.

Each cylinder of the engine 1 has a fuel injection valve (injector) 6 for injecting fuel into the combustion chamber 5, a combustion chamber 5
A spark plug 7 for performing spark ignition is provided therein, and a fuel mixture is formed by injecting fuel from the fuel injection valve 6 with respect to air sucked in through an intake valve 8, and the air-fuel mixture is formed. The fuel is compressed in the combustion chamber 5 and ignited by spark ignition by the spark plug 7.

An exhaust purification catalyst (hereinafter, simply referred to as a catalyst) 12 is interposed in the exhaust passage 10, and an air-fuel ratio sensor (hereinafter, an upstream air-fuel ratio sensor 11) is provided upstream and downstream of the catalyst 12, respectively. Downstream air-fuel ratio sensor 13). Exhaust gas of the engine 1 is discharged from the combustion chamber 5 to an exhaust passage 10 via an exhaust valve 9,
2 and are discharged into the atmosphere via a muffler (not shown).

The C / U 20 includes an upstream air-fuel ratio sensor 1
1. Signals from various sensors such as a downstream air-fuel ratio sensor 13, a crank angle sensor (not shown), a water temperature sensor (not shown) for detecting an engine coolant temperature Tw, and an air flow meter 3 are input. Note that the engine rotation speed Ne is
It is calculated based on a signal from the crank angle sensor. C
/ U20 sets the target exhaust air-fuel ratio (on the upstream side of the catalyst 12) by processing the various input signals in accordance with the control block diagram shown in the figure, and sets the injected fuel to be the target exhaust air-fuel ratio. Control the amount etc.

Hereinafter, the setting of the target exhaust air-fuel ratio according to the present embodiment will be described with reference to the control block diagram shown in FIG. The initial value setting unit 21 sets an initial value V0 of the oxygen adsorption amount of the catalyst 12. Specifically, the amount of oxygen adsorbed on the catalyst 12 after the engine is stopped is calculated (estimated), and the calculated oxygen adsorbed amount Va after the engine is stopped and the oxygen adsorption amount V (-1 immediately before the engine is stopped) are calculated. ) Is added to the initial value V0 of the amount of oxygen adsorbed on the catalyst 12 at the time of startup (when operation is resumed)
(= Va + V (-1)).

During the operation of the engine, the catalyst 1
Since the amount of oxygen adsorbed on the fuel cell 2 is controlled to be the optimum oxygen amount Vs, the initial value V0 may be simply set as the oxygen adsorption amount V (-1) = Vs after the engine is stopped. (V0 = Va + Vs). Here, the calculation of the oxygen adsorption amount Va after the engine is stopped will be described. In this embodiment,
After the engine is stopped, the gas exchange in the catalyst 12 proceeds at a constant rate, and the oxygen concentration changes in proportion to the elapsed time (see FIG. 2 (A)). Assuming that the amount is represented by the Langmuir type (see FIG. 2B), the oxygen adsorption amount Vs after the engine is stopped is calculated.

The Langmuir type is a well-known type of adsorption, in which (a) gas molecules are adsorbed on a predetermined surface of the adsorbent surface, and (b) one gas molecule is adsorbed on one adsorption site. (C) The energy state of the adsorbed molecule is constant even if there is no adsorbed molecule in the adjacent seat, and is expressed by equation (1). v = a · b · P / (1 + a · P) (1) where P: equilibrium pressure of gas phase, T: temperature, b: saturated adsorption amount,
a: Clausi from the relationship between P and T when the adsorption amount is constant
Isothermal heat of adsorption q _iso obtained by applying the us-Clapayron equation
And a = a ₀ exp (q _iso / RT) (a ₀ is a constant).

Then, as shown in FIG. 2C, the oxygen adsorption amount after the engine is stopped can be represented by a first-order lag with respect to the elapsed time. Therefore, the oxygen adsorption amount V after the engine is stopped is calculated by expressing the oxygen adsorption amount V after the engine is stopped as the equation (2), and measuring the elapsed time t after the engine is stopped. Va = K · (1−e ^{−t / T} ) (2) where K is a constant and T is a time constant, and a value obtained in advance by an experiment or the like is used. Further, a map set in advance may be referred to based on the elapsed time t.

Here, since the time constant T changes depending on the environmental temperature of the catalyst 12, an exhaust temperature sensor 14 or the like for detecting the exhaust temperature is disposed near the catalyst 12 (see FIG. 1). The time constant may be set based on the time constant (for example, the time constant T is set with reference to a table as shown in FIG. 3). According to this, the oxygen adsorption amount Va after the engine is stopped can be calculated (estimated) with higher accuracy.

Note that the exhaust temperature is an example representative of the environmental temperature of the catalyst 12, and the time constant T may be set based on the temperature of the catalyst itself, the outside air temperature, the intake air temperature and the like by the catalyst temperature sensor. . FIG. 4 is a time chart showing the state of the oxygen adsorption amount Va after the engine is stopped and the calculation of the oxygen adsorption amount Va.

As shown in the figure, when the engine stops, an engine stall flag is set, and counting by a timer is started. When the engine is restarted, the engine stall flag is cleared and the timer count ends. The timer count value at this time is read, and the oxygen adsorption amount Va after the engine is stopped is calculated by equation (2). Further, instead of the counting by the timer as described above, the engine cooling water temperature Tw may be detected, and the elapsed time t from the stop of the engine may be estimated based on the engine cooling water temperature Tw. this is,
This is based on the fact that the water temperature changes with the passage of time. For example, a table as shown in FIG. 5 is searched and estimated.

If the time during which the engine is stopped exceeds the predetermined value Ts, it is considered that the catalyst 12 is sufficiently exposed to the atmosphere and the maximum amount of oxygen that can be adsorbed on the catalyst 12 is adsorbed. , The maximum oxygen adsorption amount Vma of the catalyst 12
x is set as an initial value V0 of the oxygen adsorption amount. The oxygen adsorption amount calculation unit 22 calculates an oxygen adsorption amount V in the catalyst 12,
Remember.

Specifically, the initial value V0 of the amount of oxygen adsorbed set by the initial value setting means 21 is changed to the amount of change in the amount of oxygen adsorbed in the catalyst 12 after startup (after restart of operation) (change in adsorbed oxygen). The amount Vb is added to calculate the oxygen adsorption amount V in the catalyst 12 (V = V0 + Vb). Here, the adsorbed oxygen change amount Vb is, for example, determined by the upstream air-fuel ratio sensor 1.
1. Air-fuel ratio before catalyst λf (oxygen concentration) and air-fuel ratio after catalyst λr (oxygen concentration) detected by downstream air-fuel ratio sensor 13
From equation (3), the oxygen adsorption velocity ΔVb is calculated by
This is obtained by integration processing.

ΔVb = k · (λf−λr) (3) where k is a constant, and a predetermined value is set for each engine. At the time of starting, more oxygen than the optimum amount of oxygen is adsorbed.
Is usually a negative value. The above-described method of calculating the oxygen adsorption amount Vb after the start is an example, and may be calculated by another method.

The catalyst 12 when the engine is stopped
When the initial value is calculated in the initial value setting unit 21, the oxygen adsorption amount V in the inside is read out and used as the oxygen adsorption amount V (-1) when the engine is stopped (immediately before). The optimum oxygen adsorption amount setting unit 23 determines the operating state of the engine (engine load T
The optimum oxygen adsorption amount Vs in the catalyst 12 is set based on (p, engine rotation speed Ne, etc.). Here, the optimum oxygen adsorption amount Vs is (a range of) an oxygen adsorption amount at which the purification efficiency of the catalyst 12 is maximized. It is set to a relatively small value in an operating region where the operation is likely to occur.

The target air-fuel ratio setting unit 24 compares the oxygen adsorption amount V in the catalyst 12 calculated by the oxygen adsorption amount calculating unit 22 with the optimum oxygen adsorption amount Vs set by the optimum oxygen adsorption amount setting means 23. To calculate the difference, convert the difference into a target air-fuel ratio, and output it. The target air-fuel ratio is a target value of the exhaust air-fuel ratio detected by the upstream air-fuel ratio sensor 11.

Air-fuel ratio feedback (F / B) controller 2
Reference numeral 5 sets the injection fuel amount and the like based on the target air-fuel ratio (target λ) set by the target air-fuel ratio setting 24 and the actual air-fuel ratio (actual λ) detected by the A / F sensor 11. As described above, the amount of oxygen adsorbed in the catalyst 12 after the engine is stopped is calculated based on the elapsed time from the stop of the engine, and the calculated amount is used to set the initial value of the amount of oxygen adsorbed at the time of startup (when the operation is restarted). Thereby, the amount of oxygen adsorbed in the catalyst 12 at the time of starting the engine is accurately calculated (estimated).
Therefore, the amount of oxygen adsorbed in the catalyst 12 can be optimally controlled immediately after the start, and deterioration of exhaust gas can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing the amount of oxygen adsorbed on a catalyst after the engine is stopped.

FIG. 3 is a diagram showing an example of a table for setting a time constant of an oxygen adsorption amount after the engine is stopped.

FIG. 4 is a time chart for calculating an oxygen adsorption amount after the engine is stopped.

FIG. 5 is a diagram showing an example of a table for estimating an elapsed time since the engine was stopped.

FIG. 6 is a diagram showing a comparison between a calculated (estimated) value of an oxygen adsorption amount in a catalyst and an actual value in a conventional air-fuel ratio control device.

[Explanation of symbols]

 Reference Signs List 1 engine 2 intake passage 3 air flow meter 4 throttle valve 6 fuel injection valve 7 spark plug 8 intake valve 9 exhaust valve 10 exhaust passage 11 upstream air-fuel ratio sensor 12 exhaust purification catalyst 13 downstream air-fuel ratio sensor 20 control unit (C / U) 21) Initial value setting unit 22 Oxygen adsorption amount calculation unit 23 Optimum oxygen adsorption amount setting unit 24 Target air-fuel ratio setting unit 25 Air-fuel ratio F / B control unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G091 AA17 AB03 BA01 BA14 BA15 CB02 EA00 EA01 EA05 EA14 EA16 EA17 EA18 EA19 FA01 FA06 FB09 HA36 HA37 HA42 3G301 HA01 JA21 KA01 KA28 LA01 LB01 MA01 MA11 NA03 PE03 PZZZZ

Claims (6)

[Claims] An air-fuel ratio of an internal combustion engine that calculates an oxygen adsorption amount of an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine and controls the exhaust air-fuel ratio so that the oxygen adsorption amount becomes a predetermined target value. A control device that calculates an amount of oxygen adsorbed on the exhaust gas purification catalyst after the operation is stopped based on an elapsed time since the operation of the engine is stopped, and starts the engine based on the calculated amount of oxygen adsorption after the operation is stopped. An air-fuel ratio control device for an internal combustion engine, wherein an initial value of an oxygen adsorption amount at the time is set. 2. An oxygen adsorption amount of the exhaust gas purifying catalyst at the time of immediately preceding engine stoppage is stored, and the sum of the oxygen adsorption amount at the time of the stoppage of the engine and the oxygen adsorption amount after the stoppage of the engine is obtained.
2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the initial value of the oxygen adsorption amount at the time of restart of operation is set. 3. The internal combustion engine according to claim 1, wherein the amount of oxygen adsorbed after the stop of the operation is represented by a first-order delay with respect to an elapsed time from the stop of the operation of the engine. Fuel ratio control device. 4. The time constant of the amount of adsorbed oxygen after the operation is stopped is as follows:
4. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the air-fuel ratio is set based on an environmental temperature of the exhaust purification catalyst. 5. The air-fuel ratio control for an internal combustion engine according to claim 1, further comprising a timer, wherein the timer measures an elapsed time from a stop of the operation of the engine. apparatus. 6. The system according to claim 1, wherein a cooling water temperature of the engine is detected, and an elapsed time since the operation of the engine is stopped is estimated based on the detected cooling water temperature of the engine.
An air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 4.