JP2768076B2 - Engine air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust system for an engine,
The present invention relates to an air-fuel ratio control device for an engine including an HC adsorption catalyst, a three-way catalyst, and an air-fuel ratio sensor in order from the upstream side.

[0002]

2. Description of the Related Art Conventionally, there has been an engine provided with a three-way catalyst in an exhaust system of an engine for purifying exhaust gas. In this case, in order to secure purification efficiency of the three-way catalyst, exhaust gas flowing into the three-way catalyst is required. It is necessary to vary the air-fuel ratio of the gas at a relatively short cycle near the stoichiometric air-fuel ratio (stoichio).
It provided an oxygen concentration sensor on the upstream side of the three-way catalyst (O ₂ sensor) is performed air-fuel ratio feedback control with less response delay.

On the other hand, recently, it has been required to reduce HC exhausted from an engine at a low temperature, and one of the measures is to use a Y-type zeolite, mordenite, or the like upstream of a three-way catalyst. A device provided with an HC adsorbent or an adsorption catalyst has been proposed (JP-A-2-7532).
No. 7).

[0004]

However, even with such an HC-adsorbing catalyst, other harmful components (eg, CO and NOx) and HC after the completion of warm-up are at least reduced to a conventional level. Efficiency is naturally required,
For this reason, even in a system having this HC adsorption catalyst, air-fuel ratio feedback control or some purification system that replaces it is necessary.

Therefore, considering a technique for performing the above-described air-fuel ratio feedback control in a system having the above-described HC adsorption catalyst, first, in order to secure the feedback responsiveness, it is necessary to use the HC adsorption catalyst. It is premised that an O ₂ sensor is provided on the upstream side. However, in a system having such an HC adsorbing catalyst, when the engine warms up and the temperature of the HC adsorbing catalyst exceeds a predetermined temperature, the engine is stopped. HC adsorbed on HC adsorption catalyst at low temperature
There are released, to become guided to the three-way catalyst, in a period of HC from the HC adsorption catalyst is released, that the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is grasped by the O ₂ sensor However, there is a problem that accurate feedback control of the air-fuel ratio becomes impossible.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been developed in view of the above.
It is an object of the present invention to provide an air-fuel ratio control device for an engine in which the air-fuel ratio of exhaust gas flowing into a three-way catalyst can be grasped even when the fuel is discharged, thereby enabling accurate air-fuel ratio control.

[0007]

According to a first aspect of the present invention, there is provided an air-fuel ratio control device for an engine according to the present invention, wherein an HC adsorbing catalyst, a three-way catalyst, and an air-fuel ratio sensor are arranged in the exhaust system of the engine in order from the upstream side. The fuel or intake air is supplied such that the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber is oscillated with a required period between the rich side and the lean side with respect to the stoichiometric air-fuel ratio. A control means for controlling at least one of the supply air-fuel mixture, and the supply air-fuel mixture set by the control means so as to vibrate so that the average value of the air-fuel ratio of the exhaust gas passing through the three-way catalyst is substantially close to stoichiometric. Correction means for correcting the average value of the air-fuel ratio of the engine based on the output of the air-fuel ratio sensor , and the engine is started in a low temperature state.
When the set time has elapsed since the engine started,
Is the temperature of the engine or the temperature of the HC adsorption catalyst.
When the temperature exceeds the fixed temperature, the supply
Limiting the mean value of the air-fuel ratio of the charge mixture to the lean side
And limiting means .

[0008]

[0009]

In the above-described air-fuel ratio control apparatus for an engine of the present invention, the control means sets the required period of the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber on the rich side and the lean side of the stoichiometric air-fuel ratio. At least one of the fuel and the intake air is controlled so as to be provided with vibration. At this time, the average value of the air-fuel ratio of the exhaust gas that has passed through the three-way catalyst is substantially in the vicinity of stoichio by the correction means. As described above, the average value of the air-fuel ratio of the supplied air-fuel mixture that is set in a vibrating manner by the control means is corrected based on the output of the air-fuel ratio sensor (claim 1).

When the engine is started in a low temperature state, the limiting means temporarily corrects the time from when the set time has elapsed since the start of the engine or when the temperature of the engine or the temperature of the HC adsorption catalyst exceeds the set temperature. The correction of the average value of the air-fuel ratio of the supplied air-fuel mixture to the lean side by the means is restricted (claim 1 ).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An air-fuel ratio control device for an engine according to an embodiment of the present invention will be described below with reference to the drawings.
Is a block diagram showing the overall configuration of the present apparatus, FIG. 2 is an overall configuration diagram of an engine system having the present apparatus, FIG. 3 is a control hardware block diagram of the present apparatus, and FIGS. FIG. 6 is a waveform chart for explaining the operation of the present apparatus.

The engine system having the present apparatus is as shown in FIGS. 1 and 2. As shown in these figures, an engine (internal combustion engine) EG is provided with an intake passage 2 and an exhaust passage leading to a combustion chamber 1 thereof. Having a passage 3 and an intake passage 2
The communication between the combustion chamber 1 and the combustion chamber 1 is controlled by an intake valve 4, and the communication between the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5.

In the intake passage 2, from the upstream side,
An air cleaner 6, a throttle valve 7, and an electromagnetic fuel injection valve (injector) 8 are provided. In the exhaust passage 3, in order from the upstream side, an HC adsorption catalyst 9A and a catalyst converter (three-way) for purifying exhaust gas. A catalyst 9 and a muffler (muffler) (not shown) are provided. In addition, the intake passage 2
Is provided with a surge tank 2a.

Here, the HC adsorption catalyst 9A is made of Y-type zeolite, mordenite, or the like, and adsorbs HC at a low temperature, and releases the adsorbed HC when the temperature rises.

Further, the injectors 8 are provided in the intake manifold portion by the number of cylinders. Now, assuming that the engine EG of this embodiment is an in-line four-cylinder engine, four injectors 8 are provided. That is, it can be said that the engine is a so-called multi-point fuel injection (MPI) type multi-cylinder engine.

The throttle valve 7 is connected to an accelerator pedal via a wire cable, so that the opening varies according to the amount of depression of the accelerator pedal. (I.e., an ISC motor) so that the opening of the throttle valve 7 can be changed without depressing the accelerator pedal during idling.

With this configuration, the air sucked through the air cleaner 6 according to the opening of the throttle valve 7 is mixed with the fuel from the injector 8 at the intake manifold so as to have an appropriate air-fuel ratio. By igniting the spark plug 35 at an appropriate timing, the fuel is burned to generate engine torque, and then the air-fuel mixture is discharged to the exhaust passage 3 as exhaust gas, and the mixture is exhausted by the HC adsorption catalyst 9A and the catalytic converter 9. CO, HC, N in
After the harmful components of Ox are purified, the muffler silences them and releases them to the atmosphere.

Further, various sensors are provided for controlling the engine EG. First, on the intake passage 2 side, an air flow sensor 11, which detects an intake air amount from Karman vortex information, an intake air temperature sensor 12, which detects an intake air temperature, and an atmospheric pressure sensor 13, which detects an atmospheric pressure, are provided at the portion where the air cleaner is provided. The throttle valve is provided with a potentiometer type throttle sensor 14 for detecting the opening of the throttle valve 7, an idle switch 15 for detecting an idling state, and the like.

On the exhaust passage 3 side, an oxygen concentration (O 2) in the exhaust gas is provided inside or downstream of the catalytic converter 9.
An oxygen concentration sensor 17 (hereinafter, simply referred to as an O ₂ sensor 17) is provided as an air-fuel ratio sensor for detecting ( ₂ concentration).

Further, as other sensors, a water temperature sensor 19 for detecting an engine cooling water temperature and a crank angle sensor 2 for detecting a crank angle as shown in FIGS.
1 (this crank angle sensor 21 also serves as a rotation speed sensor for detecting the engine speed) and a TDC sensor (cylinder determination sensor) 22 for detecting the top dead center of the first cylinder (reference cylinder) are provided in the distributor, respectively. Have been.

The detection signals from these sensors are input to an electronic control unit (ECU) 23.

The ECU 23 is also supplied with a voltage signal from a battery sensor 25 for detecting the voltage of the battery and a signal from a cranking switch 20 or an ignition switch (key switch) for detecting the starting time. I have.

The hardware configuration of the ECU 23 is as shown in FIG. 3. The ECU 23 has a CPU 27 as its main part.
Intake air temperature sensor 12, atmospheric pressure sensor 13, a throttle sensor 14, O ₂ sensor 17, water temperature sensor 19 and the input detection signal from the battery sensor 25 Interface 28
And an air flow sensor 11, a crank angle sensor 21, T
Detection signals from the DC sensor 22, the idle switch 15, the cranking switch 20, the ignition switch, and the like are input via the input interface 29.

Further, the CPU 27 has a ROM for storing program data and fixed value data via a bus line.
31, data is exchanged between a battery 32 and a battery backup RAM (not shown) which is backed up by holding the stored contents while the battery 32 is connected. Has become.

The data in the RAM 32 disappears and is reset when the ignition switch is turned off.

The fuel injection control signal based on the calculation result by the CPU 27 is supplied to the solenoid (injector solenoid) 8a (more precisely, the injector solenoid 8a) of the injector 8 via four injection drivers (injector drive circuits) 34. Transistor).

Focusing on fuel injection control (air-fuel ratio control), a control signal for fuel injection calculated by a method described later is output from the CPU 27 via the driver 34 to sequentially drive, for example, the four injectors 8. It is going to go.

For such fuel injection control (injector drive time control), the ECU 23 first
Basic driving time (basic pulse width) for injector 8
It has a basic pulse width setting means 51 as a basic drive time determining means for determining TB. And the engine 1 obtained from the engine speed N information from the crank angle sensor 21
The basic drive time TB is determined on the basis of the information on the intake air amount A / N per revolution.

Further, a forced modulation means 53 and a base air-fuel ratio setting means 54 are provided side by side, and outputs from the forced modulation means 53 and the base air-fuel ratio setting means 54 are selectively output by a switching means 55. It has become.

Here, the forcible modulating means 53 oscillates the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber 1 with a required period on the rich side and the lean side of the stoichiometric air-fuel ratio. The air-fuel ratio correction coefficient KAF (KAF = KAV + K
V1; KAV is for setting the average value of the air-fuel ratio of the supplied air-fuel mixture, and KV1 is for setting the air-fuel ratio variation having a required period.

The base air-fuel ratio setting means 54 provides an air-fuel ratio correction coefficient K corresponding to the engine speed N and the engine load A / N.
AF (= Kafo) is set.

When the engine cooling water temperature Tw is equal to or higher than a predetermined value Tw1 (this Tw1 is referred to as a feedback start water temperature) and is in a predetermined engine operating range (feedback zone; for example, an engine low / medium load zone), The output is switched to select the output from the forcible modulation means 53. If the engine cooling water temperature Tw is lower than the predetermined value Tw1 and is not in the predetermined engine operating range (feedback zone), the output from the base air-fuel ratio setting means 54 is selected. It is switched to do.

Further, the average value of the air-fuel ratio of the exhaust gas that has passed through the catalytic converter 9 is substantially in the vicinity of stoichiometry.
There is provided a base A / F correcting means 60 for correcting the average value of the air-fuel ratio of the supplied air-fuel mixture which is set by vibration by the forcible modulation means 53 based on the output of the O ₂ sensor 17.

When the engine is started in a low temperature state, the engine is temporarily started from the time when a set time has elapsed since the start of the engine or from the time when the temperature of the engine (engine cooling water temperature) or the temperature of the HC adsorption catalyst 9A exceeds the set temperature. A clip means 61 is provided as limiting means for limiting the correction of the average value of the air-fuel ratio of the supplied air-fuel mixture to the lean side by the base A / F correcting means 60.

Further, a warm-up increasing means 56 is provided as a water temperature correction means for setting a warm-up coefficient KWT (= Kwt) as a water temperature correction coefficient in accordance with the engine cooling water temperature Tw detected by the water temperature sensor 19. Intake air temperature sensor 1
A correction means 57 is provided for setting a correction coefficient K according to the intake air temperature detected in step 2, the atmospheric pressure detected by the atmospheric pressure sensor 13, and the like. A dead time correction means 58 for setting a dead time (invalid time) TD is also provided.

The basic pulse width setting means 51, the forced modulation means 53 or the base air-fuel ratio setting means 54, the warm-up increasing means 56, the correction means 57, and the dead time correction means 58
Of the injector 8 by adding the outputs from the
A pulse width setting means 59 for setting j (= TB × KAF × KWT × K + TD) is provided.

Next, the control procedure of the apparatus will be described with reference to the flowcharts of FIGS.

First, in step A1 of FIG. 4, the engine cooling water temperature Tw becomes Tw1 (feedback start water temperature).
It is determined whether or not it is lower. If it is, in step A2, the air-fuel ratio correction coefficient Ka is determined from the air-fuel ratio map according to A / N, N (A is the intake air amount and N is the engine speed).
fo is read out and set to KAF. Such setting of the air-fuel ratio correction coefficient Kafo is performed by the base air-fuel ratio correction means 54.

If it is determined in step A1 that the engine cooling water temperature Tw is equal to or higher than Tw1 (feedback start water temperature), it is determined in step A3 whether or not the engine is in a low-medium load engine operating range. A4
It is determined whether the O ₂ sensor output V is higher than the determination voltage Vs. Note that V may be an average value of the output of the O ₂ sensor during a required sampling period.

If V> Vs, that is, a rich state,
In step A5, the rich flag FR is set to 1 and V ≦ V
If it is s, that is, in the lean state, the rich flag FR is set to 0 in step A6. Then, after that, step A7
Then, the air-fuel ratio correction coefficient KAF is set to KAV + KV1. Here, KAV is an average value of the air-fuel ratio of the supplied air-fuel mixture, and KV1 is an air-fuel ratio variation having a required period.

Then, step A2 or step A7
Thereafter, in step A8, a water temperature correction coefficient Kwt is set in accordance with the engine cooling water temperature Tw, and this is set in KWT. The setting of the water temperature correction coefficient Kwt is performed by the warm-up increasing means 56.

After that, in step A9, other correction coefficients K and dead time TD are set, and then in step A10
After calculating the basic drive time TB, step A11
And the fuel injection time Tinj is set to TB × KAF × KWT × K
+ TD, and in step A12, this Ti
The injector 8 is driven according to nj.

Incidentally, the average value KAV and the variation KV1 of the air-fuel ratio used in step A7 are updated according to the flow shown in FIG.

That is, in step B1 of FIG. 5, it is first determined whether or not the count-up flag CUP is 1, and if so, the count value C is incremented by 1 in step B2. After the count value C is incremented in this way, in step B3, the count value C is changed to the maximum value C.
It is determined whether or not MAX has been reached. If not, the flag TO for checking the timing for updating the average value KAV is set to 0.
(Step B4), and the variation KV1 is updated (step B5). In this case, the variation KV1 is P + (Cβ /
CMAX). Here, P and β are constants.

When the count value C reaches the maximum value CMAX, TO is set to 1 and then CUP is set to 1 (steps B6 and B7).

On the other hand, if the count-up flag CUP is not 1 in step B1, the count value C is decremented by 1 in step B8. After decrementing the count value C in this way, it is determined in step B9 whether the count value C has reached the minimum value -CMAX,
Otherwise, the flag TO is set to 0 (step B1).
0), the variation KV1 is updated (step B11). In this case, the variation KV1 is obtained by (Cβ / CMAX) −P.

When the count value C reaches the minimum value -CMAX, TO is set to 1, and then CUP is set to 1 (steps B12 and B13).

The variation KV1 is updated in this manner. An example of a variation waveform of the variation KV1 is shown in FIG.
(C).

After the variation KV1 is updated in this way, it is then determined in step B14 whether the flag TO has become "1". That is, the count value C
Becomes maximum or minimum, then TO = 1, so
At this time, the average value KAV is updated as follows.

First, at step B15, the rich flag F
It is determined whether R is 1 or not. If FR = 1, that is, if the O ₂ sensor output V is larger than Vs (in a rich state)
Sets KAV = KAV-α, reduces the average value KAV, and shifts the KAV to the lean side (step B16).

Thereafter, at step B17, it is determined whether or not the KAV is smaller than a certain set value -KAVM1. If so, in step B18,
After setting KAV = -KAVM1, otherwise, the process of step B18 jumps to determine whether or not the HC adsorption catalyst 9A is in an engine operating state (specific operating state) where HC can be released (step S18). B19).

Here, in the following cases, it is determined that the vehicle is in the specific operation state. (1) For example, the engine cooling water temperature T as the engine temperature
w is between Tw2 (first engine temperature) and Tw3 (second engine temperature) higher than Tw2 (Tw1 <Tw2)
≦ Tw ≦ Tw3 <Tw4; Tw4 is the temperature after warm-up). (2) When the temperature Tc of the HC adsorption catalyst 9A is between Tc1 (first adsorption catalyst temperature) and Tc2 (second adsorption catalyst temperature) higher than Tc1 (Tc1 ≦ Tc ≦ Tc2). (3) From when the engine cooling water temperature Tw exceeds Tw2 (set engine temperature) to when the set time elapses. (4) From when the temperature Tc of the HC adsorption catalyst 9A exceeds Tc1 (set adsorption catalyst temperature) to when the set time elapses. (5) During the second set time t2 after the first set time t1 set according to the ambient temperature of the engine (at least one of the intake air temperature and the engine coolant temperature).

If it is determined in step B19 that the engine is in a specific operation state (an operation state in which HC can be released by the HC adsorption catalyst 9A), then in step B20, KA is determined.
V is another set value −KAVM2 (where 0 <KAVM2 <
KAVM1) is determined. If so, in step B21, KAV = -KAVM2
far. Thereby, the average value KA of the air-fuel ratio of the supply air-fuel mixture is obtained.
V is clipped to limit the correction of the average value KAV to the lean side.

In step B15, the rich flag F
If R is not 1, that is, if the O ₂ sensor output V is equal to or lower than Vs (in the lean state), KAV = KAV + α, the average value KAV is increased, and this KAV is shifted to the rich side (step). B22).

Thereafter, in step B23, it is determined whether or not the KAV is larger than the set value KAVM1. If not, return is performed, but if so, at step B24, KAV = KAVM1 is set, and the routine returns.

The average value KAV is updated in this manner. FIG. 6 shows a variation waveform example of the average value KAV.
(B). The output example of the O ₂ sensor is shown in FIG.
(A).

As described above, when the rich atmosphere in the three-way catalyst 9 due to the HC released from the HC adsorption catalyst 9A is detected by the O ₂ sensor 17, the base A / F correcting means 60 sets the median value of the forced modulation. Is gradually shifted to the lean side, so that the exhaust gas modulated near the stoichiometric portion always flows into the three-way catalyst 9, whereby the temperature rises and the HC adsorbed catalyst releases the adsorbed HC. However, good purification efficiency can be achieved.

Since the operating range of HC release is detected based on the water temperature and the like, and the clip value is set to the lean shift with respect to the median value of the forced modulation, the exhaust gas flowing into the three-way catalyst 9 due to HC release is emptied. Excessive leaning of the air-fuel ratio in the combustion chamber for maintaining the fuel ratio is prevented, so that drivability can be prevented from deteriorating.

If the main purpose is to increase the exhaust gas purification efficiency of the catalyst, steps B19 to B21 in FIG.
Can be omitted.

A three-way catalyst 9 having a heater can also be used. In this case, when the engine is started, power is supplied to the heater, and when the three-way catalyst 9 is warmed by exhaust heat, the heater is cut off. Is done.

[0061]

As described in detail above, according to the engine air-fuel ratio control apparatus of the present invention (claim 1), the HC adsorption catalyst, the three-way catalyst and the air In the case of a fuel ratio sensor, the fuel or the fuel is supplied such that the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber is provided with a required cycle on the rich side and the lean side with respect to the stoichiometric air-fuel ratio with a required period. A control means for controlling at least one of the intake air is provided, and the supply means vibrated by the control means so that the average value of the air-fuel ratio of the exhaust gas passing through the three-way catalyst is substantially in the vicinity of stoichiometry. Correcting means for correcting the average value of the air-fuel ratio of the air-fuel mixture based on the output of the air-fuel ratio sensor; and
The set time has passed since the engine started, or
Set the temperature of the engine or the temperature of the HC adsorption catalyst
The supply by the correction means temporarily from the point when the temperature is exceeded
Limiting the mean value of the air-fuel ratio of the mixture to the lean side
When the rich atmosphere in the three-way catalyst due to HC released from the HC adsorption catalyst is detected by the air-fuel ratio sensor, the median value of the forced modulation is gradually leaned. Side, so that the modulated exhaust gas always flows in the vicinity of stoichio into the three-way catalyst. As a result, even when the temperature rises and the HC adsorption catalyst releases the adsorbed HC, In addition to the advantages of achieving good purification efficiency , the HC
It is detected by the water temperature etc., and the
You can set a clip value for
The air-fuel ratio of exhaust gas flowing into the three-way catalyst due to HC release
The air-fuel ratio in the combustion chamber is excessively lean
And thus prevent deterioration of drivability.
There is an advantage that can be stopped.

[0062]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an apparatus according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an engine system having an apparatus according to an embodiment of the present invention.

FIG. 3 is a control hardware block diagram according to an embodiment of the present invention.

FIG. 4 is a flowchart illustrating the operation of one embodiment of the present invention.

FIG. 5 is a flowchart illustrating the operation of one embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the operation of one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Intake passage 2a Surge tank 3 Exhaust passage 4 Intake valve 5 Exhaust valve 6 Air cleaner 7 Throttle valve 8 Injector 8a Injector solenoid 9 Catalytic converter (three-way catalyst) 9A HC adsorption catalyst 11 Air flow sensor 12 Intake temperature sensor 13 Atmospheric pressure Sensor 14 Throttle sensor 15 Idle switch 17 O ₂ sensor (air-fuel ratio sensor) 19 Water temperature sensor 20 Cranking switch 21 Crank angle sensor 22 Cylinder discrimination sensor 23 Electronic control unit (ECU) 25 Battery sensor 27 CPU 28, 29 Input interface 30 A / D converter 31 ROM 32 RAM 34 Injection driver 35 Spark plug 51 Basic pulse width setting means 52 A / N calculation means 53 Forced modulation means 54 Base air-fuel ratio setting means 55 Switching means 56 Warm-up increasing means 57 Correcting means 58 Dead time correcting means 59 Pulse width setting means 60 Base A / F correcting means (Correcting means) 61 Clipping means (Limiting means)

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 41/14 310 F02D 45/00 368

Claims (1)

(57) [Claims] 1. An exhaust system of an engine is provided in order from an upstream side.
In an engine equipped with an HC adsorption catalyst, a three-way catalyst, and an air-fuel ratio sensor, the air-fuel ratio of the air-fuel mixture supplied to the engine combustion chamber has a required period between the rich side and the lean side of the stoichiometric air-fuel ratio. Control means for controlling at least one of fuel and intake air so as to be provided in an oscillating manner, and the control means such that the average value of the air-fuel ratio of the exhaust gas passing through the three-way catalyst is substantially in the vicinity of stoichio. Correction means for correcting the average value of the air-fuel ratio of the supplied air-fuel mixture which is set in an oscillating manner based on the output of the air-fuel ratio sensor , and when the engine is started in a low temperature state, the engine starts.
The set time has elapsed since the start of operation or the temperature of the engine
Or when the temperature of the HC adsorption catalyst exceeds the set temperature
From the air-fuel ratio of the supplied air-fuel mixture
An air-fuel ratio control device for an engine, comprising limiting means for limiting correction of an average value to a lean side .