JP2561532B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an internal combustion engine (engine) for controlling the air-fuel ratio.

[Prior Art] Conventionally, as the air-fuel ratio control apparatus for an internal combustion engine, provided with a λ-type oxygen concentration sensor (O ₂ sensor) in the exhaust manifold as the upstream exhaust passage portion of the catalytic converter arranged partial, the O ₂ Paying attention to the fact that the sensor output changes from low to high or vice versa at the stoichiometric air-fuel ratio as a boundary, by feeding back this O ₂ sensor output, the air-fuel ratio will be close to the stoichiometric air-fuel ratio. The fuel ratio is controlled. Such air-fuel ratio feedback control is called so-called O ₂ feedback control.

Then, during such O ₂ feedback control, the O ₂ sensor output is compared with the on / off determination voltage (reference value), for example,
When the O ₂ sensor output is larger than this judgment voltage, it becomes lean, and conversely, when the O ₂ sensor output is smaller than this judgment voltage,
The air-fuel ratio control for enrichment is performed.

[Problems to be Solved by the Invention] However, in the conventional air-fuel ratio control device for an internal combustion engine, since the O ₂ sensor is provided in the upstream side exhaust passage portion of the catalyst arrangement portion, the result of the purifying action by the catalyst is related. There is a problem in that the information cannot be used at all, and as a result, variations in the output characteristics of the O ₂ sensor and characteristic deterioration of the catalyst purification capacity become the final exhaust gas characteristics.

Further, in the conventional air-fuel ratio control device for an internal combustion engine, its limit cycle frequency (when performing air-fuel ratio feedback control using the O ₂ sensor, the reciprocal of the cycle in which the O ₂ sensor or the feedback integral value is inverted) is It is difficult to set the limit cycle frequency that maximizes the catalyst purification efficiency because it is limited by the engine speed, operating conditions such as load, O ₂ sensor responsiveness, O ₂ sensor mounting position, etc. . Therefore, it is difficult to perform control so that the exhaust gas purification efficiency by the catalyst is maximized.

By the way, in Japanese Patent Laid-Open No. 52-81438, an air-fuel ratio deviation signal or an air-fuel ratio control signal is superposed with a high-frequency signal having an average value of zero to improve the conversion efficiency of a three-way catalyst to improve the exhaust purification performance. And a technique of setting the cycle of the superimposed high-frequency signal based on the engine speed.

The enzyme storage capacity of the catalyst depends on the exhaust gas flow rate, and the higher the exhaust gas flow rate, the more the capacity will be exceeded in a short time. Therefore, it is necessary to shorten the cycle of the superimposed high-frequency signal as the exhaust gas flow rate increases.

However, when the cycle of the superimposed high-frequency signal is set according to the engine speed as in this technique, the engine speed and the exhaust gas flow rate do not always have a one-to-one correspondence, so the exhaust gas flow rate There is a problem that the cycle of the high frequency signal cannot be changed according to the above, and the enzyme storage effect of the catalyst cannot be sufficiently exerted.

Further, JP-A-56-121831 discloses a technique for improving control response by superimposing a high-frequency vibration signal on an air-fuel ratio detection signal, and a cycle of the vibration signal as an injection command for a fuel injection system. Techniques for synchronizing are disclosed.

Synchronizing the cycle of the superimposed vibration signal with the injection command of the fuel injection system as in this technique means that the cycle depends on the engine speed as in the technique described in JP-A-52-84138. Is set in the fuel injection system in this manner, and even when the description is made in synchronization with the injection command of the fuel injection system, the cycle of the injection command and the exhaust gas flow rate do not necessarily have a one-to-one correspondence. Therefore, there is a problem that the cycle of the high-frequency signal cannot be changed according to the exhaust gas flow rate, and the oxygen storage effect of the catalyst cannot be sufficiently exerted.

The present invention is intended to solve such a problem, and it is assumed that the output of the exhaust gas component detection means such as the O ₂ sensor has received information regarding the result of the purification action of the catalyst, and the air-fuel ratio feedback The limit cycle frequency during control can be apparently increased so that the exhaust gas purification efficiency by the catalyst can be maximized while absorbing the variations in the output characteristics of the exhaust gas component detection means. Another object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine.

[Means for Solving the Problems] Therefore, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention according to claim 1 is provided with a catalyst provided in an exhaust system of the internal combustion engine and having a redox characteristic, and an inside of the catalyst. Alternatively, the exhaust gas component detection means provided in the exhaust system on the downstream side of the catalyst for rapidly changing the output in the vicinity of the stoichiometric air-fuel ratio and the intake air amount detection means for detecting the intake air amount of the internal combustion engine are provided. A first signal whose increase / decrease direction changes based on the output change of the gas component detection means and a period shorter than the output change cycle of the exhaust gas component detection means and set based on the intake air amount detected by the intake air amount detection means Signal forming means for forming a third signal by superimposing a second signal oscillating in a predetermined cycle, and an air-fuel ratio for controlling the air-fuel ratio of the combustion gas guided to the catalyst based on the third signal. With control means It is characterized in that the air-fuel ratio of the combustion gas introduced to the catalyst is oscillatingly given near the stoichiometric air-fuel ratio.

An air-fuel ratio control system for an internal combustion engine according to a second aspect of the present invention includes a first catalyst provided in an exhaust system of the internal combustion engine and having redox characteristics, and an exhaust system upstream of the first catalyst. An exhaust gas component detecting means which is provided in the exhaust gas component and whose output suddenly changes in the vicinity of the stoichiometric air-fuel ratio; and a second exhaust gas component detecting means which is provided around the exhaust gas component detecting means or in an upstream side exhaust system and which has a redox characteristic.
And an intake air amount detecting means for detecting the intake air amount of the internal combustion engine, and a first signal whose increasing / decreasing direction changes based on an output change of the exhaust gas component detecting means and the exhaust gas component detecting means A third signal which is shorter than the cycle of the output change of the means and which vibrates at a cycle set based on the intake air amount detected by the intake air amount detecting means;
Is provided, and an air-fuel ratio control means for controlling the air-fuel ratio of the combustion gas guided to the catalyst based on the third signal is provided. It is characterized in that it is configured so as to be given oscillatingly near the stoichiometric air-fuel ratio.

[Operation] In the air-fuel ratio control device for an internal combustion engine according to the first aspect of the present invention, the exhaust gas component detection means provided inside the catalyst or downstream of the catalyst, the output of which rapidly changes in the vicinity of the theoretical air-fuel ratio, is used. The first signal whose increase / decrease direction changes based on the output change and the cycle shorter than the output change cycle of the exhaust gas component detection means and set at the cycle set based on the intake air amount detected by the intake air amount detection means The air-fuel ratio of the combustion gas guided to the catalyst is controlled on the basis of the third signal obtained by superimposing the second signal on which the air-fuel ratio of the combustion gas guided to the catalyst is close to the theoretical air-fuel ratio. It is given vibrationally.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to the present invention as set forth in claim 2, the exhaust system is provided in the upstream exhaust system of the first catalyst and is surrounded by the second catalyst or is downstream of the second catalyst. A first signal whose increasing / decreasing direction changes based on the output change of the exhaust gas component detection means provided in the exhaust gas and the intake air amount detected by the intake air amount detection means that is shorter than the cycle of the output change of the exhaust gas component detection means. The air-fuel ratio of the combustion gas guided to the catalyst is controlled based on the third signal superposed with the second signal oscillating at the cycle set based on The air-fuel ratio is given oscillating near the stoichiometric air-fuel ratio.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIGS. 1 to 9 show an air-fuel ratio control apparatus for an internal combustion engine as an embodiment of the present invention, and FIG. FIG. 1B is a block diagram showing the fuel supply control system, FIG. 1B is a block diagram showing essential parts of the fuel supply control system, FIG. 2 is a block diagram mainly showing the hardware, and FIG. 3 is an overall configuration diagram showing the engine system. FIG. 4 is a flow chart for explaining the method of obtaining the correction coefficient for fuel supply control, FIG. 5 is a flow chart for explaining the solenoid valve driving routine, and FIG. 6 is a method for obtaining the correction coefficient for the high frequency component. 7 (a) to 7 (d) are waveform charts for explaining the action at the time of O ₂ feedback, and FIG. 8 is a view for explaining the O ₂ feedback zone. Is its air-fuel ratio Is a diagram for explaining the tendency of the high-frequency component data set value at the time of forced variation, FIGS. 10 and 11 show an air-fuel ratio control device for an internal combustion engine as another embodiment of the present invention.
FIG. 11 is an overall configuration diagram showing the engine system in correspondence with FIG. 3, FIG. 11 is a partial sectional view of the O ₂ sensor with a catalyst layer, and FIG. 12 is a further embodiment of the present invention. FIG. 3 is an overall configuration diagram showing an engine system having an air-fuel ratio control device for an internal combustion engine in correspondence with FIG. 3, and FIGS. 13 (a) to (d) are all operations of the device of the present invention during O ₂ feedback. 5 is another waveform diagram for explaining FIG.

Now, the engine system controlled by this device is as shown in FIG. 3, in which the engine (internal combustion engine) E is connected to the intake passage 2 communicating with the combustion chamber 1.
And an exhaust passage 3, and an intake passage 2 and a combustion chamber 1
Are controlled by an intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are controlled by an exhaust valve 5.

In addition, the intake passage 2 has an air cleaner in order from the upstream side.
6, throttle valve 7 and electromagnetic fuel injection valve (solenoid valve) 8
The exhaust passage 3 is provided with a catalytic converter (three-way catalyst) 9 for purifying exhaust gas and a muffler (silencer) (not shown) in order from the upstream side of the exhaust passage 3. Note that the intake passage 2 is provided with a surge tank.

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

Further, the throttle valve 7 is connected to the accelerator pedal via a wire cable, so that the opening degree changes according to the amount of depression of the accelerator pedal.
The opening / closing is also driven by a motor 10 so that the opening of the throttle valve 7 can be changed without pressing the accelerator pedal during idling.

With such a configuration, the air sucked through the air cleaner 6 according to the opening degree of the throttle valve 7 is mixed with the fuel from the solenoid valve 8 at the intake manifold portion so as to have an appropriate air-fuel ratio, and ignited in the combustion chamber 1. By igniting the plug 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. three harmful components of the NO _X after being purified, is silenced by the muffler adapted to be discharged to the atmosphere side.

Further, various sensors are provided to control the engine E. First, on the intake passage 2 side, an air flow sensor 11 as an intake air amount detecting means for detecting the intake air amount from the Karman vortex information, an intake temperature sensor 12 for detecting the intake air temperature, and an atmospheric pressure are provided in the air cleaner disposed portion. An atmospheric pressure sensor 13 for detecting is provided, and a position of the potentiometer-type throttle sensor 14 for detecting the opening of the throttle valve 7, an idle switch 15 for detecting an idling state, and an ISC motor 10 is provided in a portion where the throttle valve is arranged. A motor position sensor 16 for detecting

An O ₂ sensor 17 for detecting the oxygen concentration (O ₂ concentration) in the exhaust gas is provided inside the catalytic converter 9 on the exhaust passage 3 side (this catalytic converter 9 has a redox characteristic). . That is, this catalytic converter 9
Is divided into two catalytic parts 9A and 9B, and these catalytic parts 9A and 9B are
A and 9B are arranged in tandem.
The detection unit of the O ₂ sensor 17 is arranged between A and 9B. Here, since the O ₂ sensor 17 is preferably arranged at a position where the response delay does not deteriorate so much, the volume of the upstream catalyst portion 9A is set smaller than the volume of the downstream catalyst portion 9B. For example, assuming that the volume of the upstream catalyst section 9A is 200 cc, the volume of the downstream catalyst section 9B is set to approximately 800 cc. In addition, the catalyst part may be integrated without being divided into two parts. In this case, the O ₂ sensor 17 is embedded in the catalytic converter 9.

Further, the O ₂ sensor 17 is an application of the principle of a solid electrolyte oxygen concentration battery, and its output voltage has a characteristic that it changes rapidly near the stoichiometric air-fuel ratio, and the voltage on the lean side is lower than the stoichiometric air-fuel ratio. , The voltage on the rich side is higher than the stoichiometric air-fuel ratio. That is, the O ₂ sensor 17 is configured as a so-called λ type O ₂ sensor, and also constitutes an exhaust gas component detection unit which is provided inside the catalyst 9 and whose output changes rapidly near the stoichiometric air-fuel ratio.

Further, as other sensors, a water temperature sensor 19 for detecting the engine cooling water temperature and a vehicle speed sensor 20 for detecting the vehicle speed.
As shown in FIGS. 1 (a) and 2, a crank angle sensor 21 for detecting a crank angle (this crank angle sensor 21 is a rotation speed for detecting an engine rotation speed) is provided. A TDC sensor 22 for detecting the top dead center of the first cylinder (reference cylinder) is also provided in the distributor.

The detection signals from these sensors 11 to 22 are input to the electronic control unit (ECU) 23.

Note that a voltage signal from a battery sensor 25 that detects the voltage of the battery 24 and a signal from an ignition switch (key switch) 26 are also input to the ECU 23.

The hardware configuration of the ECU 23 is as shown in FIG. 2. The ECU 23 has a CPU 27 as its main part, and the CPU 27 is provided with the intake air temperature sensor 12 and the atmospheric pressure sensor 1.
3, detection signals from throttle sensor 14, O ₂ sensor 17, water temperature sensor 19 and battery sensor 25 are input interfaces
28 and the A / D converter 30 are input, and the idle sensor 15, the vehicle speed sensor 20 and the ignition switch 2 are input.
The detection signal from 6 is input through the input interface 29, and the air flow sensor 11, crank angle sensor 21 and T
The detection signal from the DC sensor 22 is directly input to the input port.

Further, the CPU 27 uses the bus line to store the program data and fixed value data in the ROM 31, the RAM 32 that is updated and sequentially rewritten, and the battery 24 that causes the battery 2
Battery backup RAM backed up by retaining its memory while 4 is connected
(BURAM) 33 is designed to exchange data.

The data in the RAM 32 is erased and reset when the ignition switch 26 is turned off.

Now, focusing on fuel injection control (air-fuel ratio control), CPU2
A fuel injection control signal calculated by a method described later is output from 7 through the driver 34, and four electromagnetic valves 8 are sequentially driven, for example.

And such fuel injection control (solenoid valve drive time control)
A functional block diagram for is shown in FIG. 1 (a). That is, when looking at this ECU 23 in terms of software, this ECU 23 shows that the basic drive time T for the solenoid valve 8
_The basic drive time determining means 35 for determining _B is provided. The basic drive time determining means 35 determines the engine 1 from the intake air amount Q information from the air flow sensor 11 and the engine speed Ne information from the crank angle sensor 21. Intake air volume per revolution
The Q / Ne information is obtained, and the basic drive time T _B is determined based on this information.

Further, an air-fuel ratio correction coefficient setting means (depending on the engine speed and load) for setting an air-fuel ratio correction coefficient K _AF1 corresponding to the engine speed and the engine load (the Q / Ne information has engine load information) from the map. Air-fuel ratio correction means) 36 and an air-fuel ratio correction coefficient for forcibly varying the air-fuel ratio at the time of O ₂ sensor feedback (the operating range in which O ₂ feedback is performed is the area indicated by the symbol FB in FIG. 8). K _FB
+ Kad) O ₂ sensor feedback correction means 37
Is provided, and these air-fuel ratio correction coefficient setting means 36
The O ₂ sensor feedback correction means 37 and the O ₂ sensor feedback correction means 37 are selectively selected by switching means 38 and 39 which are switched in conjunction with each other.

By the way, the O ₂ sensor feedback correction means 37 is configured by the following means. That is, the first
As shown in FIG. 2B, the O ₂ sensor feedback correction means 37 uses the first signal whose increase / decrease direction changes based on the output change of the O ₂ sensor 17 (in this case, the signal based on the feedback component K _FB is the first signal). The first signal generating means 45 for generating (1 signal) is provided, which is shorter than the output change cycle of the O ₂ sensor 17 and is set based on the intake air amount detected by the air flow sensor 11. Second signal generating means for generating a second signal (a signal based on the high frequency component or the forced vibration component Kad is the second signal) that vibrates at a different period (for example, about 10 to 17 hertz in terms of frequency) 46 and
The first signal from the first signal generating means 45 and the second signal from the second signal generating means 46 are superimposed to generate the signal of FIG. 3 (a signal corresponding to K _FB + Kad). 3 signal generating means (signal forming means) 47.

Focusing on the air-fuel ratio control by the O ₂ sensor feedback correction means 37, the air-fuel ratio of the combustion gas guided to the catalyst is controlled based on the third signal (K _FB + Kad) from the third signal generation means 47. However, at that time, the air-fuel ratio of the combustion gas guided to the catalyst 9 is controlled so as to be oscillated near the stoichiometric air-fuel ratio.

Here, according to the O ₂ sensor feedback correcting means 37 O ₂
Assuming that the output of the O ₂ sensor at the time of feedback is as shown in FIG. 7 (a), the air-fuel ratio correction coefficient portion (feedback component) K _FB based on the first signal has an integral gain I and a proportional gain Let P be I ± (P / 2),
7 (d), and the sudden ratio correction coefficient component (high frequency component) Kad based on the second signal is as shown in FIG. 7 (c), so the air-fuel ratio correction based on the third signal is performed. The coefficient (composite) K _AF + Kad is as shown in FIG. 7 (b).

Since the O ₂ sensor 17 is provided inside of the catalytic converter 9, the O ₂ sensor output frequency is compared to that provided an O ₂ sensor in the upstream of the catalytic converter 9 as in the prior art, is lower There is. Therefore, the frequency of the air-fuel ratio correction coefficient (feedback component) K _FB (limit cycle frequency) based on the first signal is also low.

Further, as shown in FIG. 1 (a), a cooling water temperature correction means 40 for setting a correction coefficient K _WT according to the engine cooling water temperature,
Intake temperature correction means 4 that sets the correction coefficient K _AT according to the intake temperature
1, atmospheric pressure correction means 42 that sets the correction coefficient K _AP according to the atmospheric pressure, acceleration increase correction means 43 that sets the correction coefficient K _AC for acceleration increase, dead time for correcting the drive time according to the battery voltage The dead time correction means 44 for setting (ineffective time) T _D is provided, and at the time of O ₂ feedback correction, the drive time T _INJ of the solenoid valve 8 is T _B × K _WT × K _AT × K
_AP × K _AC × (K _FB + Kad) + T _D , the solenoid valve 8 is driven at this time T _INJ , while the drive time T _INJ of the solenoid valve 8 is T _B × K except when O ₂ feedback correction is performed. _WT x K _AT x
With K _AP × K _AC × K _AF1 + T _D , this time T _INJ is the solenoid valve 8
Are driving.

By the way, the above correction coefficients K _WT , K _AT , K _AP , K _AC , K _AF (= K
_FB + Kad or K _AF1 ), especially the flow chart for _obtaining the air-fuel ratio correction coefficient K _AF is shown in Fig. 4. In this flow, first, in step a1, the correction coefficients K _WT , K _AT , K _AP, etc. After determining, the air-fuel ratio correction coefficient K _AF (= K _FB + Kad or K
_AF1 ) is determined. That is, in step a2 next to step a1, it is determined whether or not the condition for O ₂ feedback is satisfied, and if O ₂ feedback is OK, then in step a3, is the O ₂ sensor output larger than 0.5 volt? It will be judged. If it is small, the air-fuel ratio is lean, so the air-fuel ratio correction coefficient K _FB is made rich by setting I + (P / 2) (step a4). If it is large, the air-fuel ratio is rich, so the air-fuel ratio correction coefficient K Leaning (step a5) is performed by setting _FB to I- (P / 2).

Then, thereafter, in step a6, the high frequency component Kad is added, and the result is used as the air-fuel ratio correction coefficient K _AF .

By the way, the high frequency component Kad is generated as follows:
Although it becomes like the flowchart of the figure, the flowchart shown in this FIG.
It operates in preference to the routine shown. In this routine, first, in step c1, it is determined whether the frequency counter Kc is 0 or not. Since it is initially 0, the YES route is taken, and in step c2, the amplitude data Kn and frequency data Hz according to the operating state of the engine are set.

Note that this frequency data Hz directly functions as cycle data, but since the reciprocal is the frequency, it is called frequency data. Here, this data Hz is higher than the limit cycle frequency, and a value of, for example, about 30 to 50 (a value of about 10 to 17 in terms of frequency) can be selected.

In this case, the tendency of the amplitude and frequency of the high frequency component according to the operating state of the engine is set as shown in FIG. That is, when the engine speed Ne, the intake air intake amount Q, and Q / Ne become large, the amplitude and the frequency become large at first, and are set to saturate thereafter.

Further, the O ₂ feedback zone is a region as indicated by the symbol FB in FIG. 8, but this O ₂ feedback zone region is further divided into a plurality of zones, and the engine speed Ne or the intake air intake is divided for each zone. Amplitude Kn per quantity Q or Q / Ne
Alternatively, the data of the frequency Hz and the data of the frequency Hz may be associated and stored in the map (two-dimensional memory).

After that, in the next step c3, the amplitude value address K ₁ is set to Kn set in step c2, and in step c4, the flag N is set.
Is 1 or not. If N = 0, step
Take the NO route in c4, set N = 1 in step c5, then set Kad = K _{1 in} step c6, while if N = 1, take the YES route in step c4, and in step c7,
After setting N = 0, Kad = −K ₁ is set in step c8.
Then, after steps c6 and c8, the frequency data Hz set in step c2 is input to the frequency counter Kc (step c9).

When the frequency counter Kc is not 0 in step c1, Kc = Kc-1 is set in step c10, the value of the frequency counter Kc is decremented by 1, and the process returns.

Therefore, once the frequency data Hz is set in the frequency counter Kc, Kad = K ₁ or Kad = until Kc = 0.
When the value of −K ₁ is held and Kc = 0, the sign of Kad is inverted. As a result, a square wave having a frequency equivalent to the frequency set by the frequency data Hz and having an amplitude K ₁ [see the waveform in FIG. 7 (c)] can be obtained.

Therefore, the air-fuel ratio correction coefficient K obtained in step a6
_AF (= K _FB + Kad) is as shown in FIG. 7 (b), but at this time, due to the superimposed high frequency component Kad, even when the I gain becomes large at the time of enrichment,
Always cross the stoichiometric air-fuel ratio [see the alternate long and short dash line in FIG. 7 (b)] to the lean side [below the alternate long and short dash in FIG. 7 (b)] to reduce the I-gay when leaning. Even so, due to the superimposed high frequency component Kad, the stoichiometric air-fuel ratio is set to the rich side [above the one-dot chain line in FIG. 7 (b)]
The amplitude value of the high-frequency component Kad (corresponding to K ₁ ) is set so as to cross a little.

If the O ₂ feedback is not OK, the correction coefficient K _AF1 is read from the two-dimensional map in step a7 of FIG.

After the above steps a6 and a7, the correction coefficient K
From K _WT × K _AT × K _AP × K _AC × K _AF (step a
8).

In this way, the fuel supply control correction coefficient K is obtained.

Next, the control procedure for driving the solenoid valve is shown in the flow chart of FIG. 5. The flow chart shown in FIG. 5 is changed to the routine shown in FIG. 4 by interruption of the crank pulse at every 180 °. Operates with priority. In this routine, first in step b1, air quantity per cycle (Q / Ne) determined, in step b2, to determine the basic drive time T _B from the (Q / Ne), in step b3, the solenoid valve 8 Drive time T _INJ of T _B × K + T _D (K is the one obtained in Fig. 4)
Then, in step b4, this T _INJ is set in the injector driving timer, and in step b5, this timer is triggered. Then, when triggered in this way, fuel is injected only during the time T _INJ .

Further, the integral gain I is updated during such a fuel injection operation routine. That is, in step b6,
It is determined if O ₂ feedback is in progress, and if so, in step b7 it is determined whether the O ₂ sensor output is greater than 0.5 volts. If it is small, the air-fuel ratio is lean, so ΔI is added to the integral gain I to make it rich (step b8). If it is large, the air-fuel ratio is rich, so ΔI is subtracted from the integral gain I to make it lean ( Step b9).

On the other hand, if not in O ₂ feedback, step
At b10, the integral gain I is set to 1.0.

In this way, by updating the integral gain I for each crank pulse interruption, the update cycle of the integral gain I can be changed according to the engine speed.

Therefore, according to this embodiment, since the O ₂ sensor 17 is arranged inside the catalytic converter 9 as described above,
The air-fuel ratio can be controlled by using the information on the result of the purification action by the catalyst, which allows the air-fuel ratio to be controlled to the air-fuel ratio required by the catalyst without being affected by the variation in the output characteristics of the O ₂ sensor. Becomes

However, since the O ₂ sensor 17 is arranged inside the catalytic converter 9, the responsiveness of the O ₂ sensor 17 deteriorates, the limit cycle frequency becomes long, and if nothing is done as it is, the exhaust gas state However, in the present embodiment, the air-fuel ratio feedback component K _FB is modulated with a high frequency component Kad to the extent that the O ₂ sensor 17 does not respond, and the I gain is large at the time of enrichment. However, due to the superposed high frequency component Kad, the stoichiometric air-fuel ratio is always slightly crossed to the lean side, and at the time of leaning, even if the I gain becomes small, the superposed high frequency component Kad Thus, while slightly crossing the stoichiometric air-fuel ratio to the rich side, that is, while allowing the air-fuel ratio of the combustion gas guided to the catalyst to be given oscillating near the stoichiometric air-fuel ratio, Since it is made large, it is possible to approach the optimum air-fuel ratio fluctuation frequency for the catalytic converter 9 (the frequency at which the O ₂ storage effect of the catalyst is maximized), and as a result, the exhaust gas purification efficiency by the catalyst is increased. The maximum control can be performed and the exhaust gas state does not deteriorate.

Here, the O ₂ storage effect of the catalyst means the effect of storing O ₂ when the air-fuel ratio is lean and changing to a rich state, and then releasing the stored O ₂ for a while to promote the oxidation reaction. It has been confirmed that varying the air-fuel ratio at a required frequency higher than the limit cycle frequency will sufficiently exert the above O ₂ storage effect.

For the high frequency component Kad, the O ₂ sensor 17
Needless to say, the feedback from the O ₂ sensor 17 is performed at the limit cycle frequency, since does not respond.

The O ₂ sensor 17 may be arranged on the downstream side of the catalytic converter 9 as shown by the chain line in FIG.

Even in this case, the air-fuel ratio control using the information on the result of the purifying action by the catalyst 9 can be performed, whereby the air-fuel ratio required by the catalyst is not affected by the variation in the output characteristics of the O ₂ sensor. It becomes possible to control the fuel ratio.

Further, as shown in FIG. 10, an O ₂ sensor 17 may be provided on the upstream side of the catalytic converter 9 so that the O ₂ sensor 17 has a structure as shown in FIG. That is, the platinum electrode 17a on the exhaust passage side of the O ₂ sensor 17 is configured to be covered with the catalyst layer (three-way catalyst layer) 17d having the redox property. Reference numeral 17b in FIG. 11 is a platinum electrode on the atmosphere side, and 17c is a solid electrolyte portion containing ZrO ₂ or the like as a component.

Even in this case, the air-fuel ratio control using the information regarding the result of the purification action by the catalyst (in this case, the catalyst layer 17c) can be performed, and thus the air-fuel ratio can be controlled without being affected by the variation in the output characteristics of the O ₂ sensor. It is possible to control the fuel ratio to the air-fuel ratio required by the catalyst.

Further, as described above, do not be like that in the O ₂ sensor 17 provided a catalyst layer 17c, the O ₂ sensor 17 uses a conventional, but instead, as shown in FIG. 12, O ₂ sensor A second catalyst (three-way catalyst) 9'having a redox characteristic is provided separately from the catalytic converter (first catalyst) 9 on the upstream side of 17
May be provided.

Even in this case, the air-fuel ratio control can be performed using the information related to the result of the purifying action by the catalyst (in this case, the second catalyst 9 '), and thus the variation in the output characteristics of the O ₂ sensor is not affected. Thus, it becomes possible to control the air-fuel ratio to the air-fuel ratio required by the catalyst.

Incidentally, or the O ₂ sensor 17 disposed downstream of the catalytic converter 9, or provided with a catalyst layer 17c in the O ₂ sensor 17, separate from the catalytic converter 9 on the upstream side of the conventional ones similar to the O ₂ sensor 17 Even when the second catalyst 9'is provided, the air-fuel ratio feedback component K _FB is modulated with the high frequency component Kad to the extent that the O ₂ sensor 17 does not respond as in the above-described embodiment [Fig. 7]. (B)], the air-fuel ratio fluctuation frequency is increased. Therefore, in any case, the optimum air-fuel ratio fluctuation frequency for the catalytic converter 9 (the frequency at which the O ₂ storage effect of the catalyst is maximized) is achieved. ), And as a result, control that maximizes the exhaust gas purification efficiency by the catalyst can be performed.
The exhaust gas condition does not deteriorate.

In addition, at the time of enrichment, even if the I gain becomes large, due to the superimposed high frequency component Kad,
Although not always, at least for a certain period, the stoichiometric air-fuel ratio is slightly crossed to the lean side, and when leaning,
Even if the I gain becomes small, due to the superimposed high frequency component Kad, the stoichiometric air-fuel ratio is slightly crossed to the rich side for at least a certain period, that is, to the catalyst, even if not always. The high-frequency component Kad so that the air-fuel ratio of the burnt combustion gas is given oscillatingly near the stoichiometric air-fuel ratio
The amplitude value of (corresponding to K ₁ ) may be set. in this case,
Air-fuel ratio correction coefficient K _AF (= K obtained in step a6 of FIG. 4)
_FB + Kad) is as shown in Fig. 13 (b). In addition, in addition, the O ₂ sensor output at the time of O ₂ feedback by the O ₂ sensor feedback correction means 37 is as shown in FIG. 13A, and the air-fuel ratio correction coefficient component (feedback component) K based on the first signal is obtained. _AF is as shown in Fig. 13 (d),
The air-fuel ratio correction coefficient component (high frequency component) Kad based on the signal is as shown in FIG. 13 (c).

Further, as means for controlling the air-fuel ratio, in addition to controlling the fuel injection amount from the solenoid valve 8, the fuel supply amount from the electronic carburetor may be controlled, or the secondary air supply amount may be controlled.

[Effects of the Invention] As described in detail above, first, according to the air-fuel ratio control device for an internal combustion engine of the present invention as set forth in claim 1, the output is provided near the stoichiometric air-fuel ratio by being provided inside the catalyst or downstream of the catalyst. A first signal whose increasing / decreasing direction changes based on the output change of the exhaust gas component detecting means that changes abruptly, and an intake time shorter than the cycle of the output change of the exhaust gas component detecting means and detected by the intake air amount detecting means. On the basis of the third signal that is superimposed on the second signal that vibrates at the cycle set based on the amount of air,
The air-fuel ratio of the combustion gas guided to the catalyst is controlled, and the air-fuel ratio of the combustion gas guided to the catalyst is oscillatingly given in the vicinity of the theoretical air-fuel ratio. The information about the result of the above is received, and the limit cycle frequency at the time of air-fuel ratio feedback control can be apparently increased, which absorbs the variation in the output characteristics of the exhaust gas component detection means, while exhausting by the catalyst. There is an advantage that control can be performed so that the gas purification efficiency is maximized.

Further, by using a signal vibrating in a cycle set based on the intake air amount as the second signal which is a superposition signal, the second signal can be dealt with in response to a change in the oxygen storage capacity of the catalyst depending on the exhaust gas flow rate. It also has the advantage that the signal cycle can be changed and the oxygen storage effect of the catalyst can always be sufficiently exerted.

Further, in the air-fuel ratio control device for an internal combustion engine according to the present invention as set forth in claim 2, the exhaust system is provided in the upstream exhaust system of the first catalyst and is surrounded by the second catalyst or is downstream of the second catalyst. A first signal whose increasing / decreasing direction changes based on the output change of the exhaust gas component detection means, and the intake air shorter than the output change cycle of the exhaust gas component detection means and detected by the intake air amount detection means. The air-fuel ratio of the combustion gas guided to the catalyst is controlled based on the third signal obtained by superimposing the second signal oscillating at the cycle set based on the amount, and the air-fuel ratio of the combustion gas guided to the catalyst. Is provided in the vicinity of the stoichiometric air-fuel ratio in an oscillatory manner, the effect or advantage substantially the same as the effect or advantage obtained by the air-fuel ratio control device for an internal combustion engine according to the first aspect can be obtained.

[Brief description of drawings]

1 to 9 show an air-fuel ratio control system for an internal combustion engine as an embodiment of the present invention. FIG. 1 (a) is a block diagram showing its fuel supply control system, and FIG. 1 (b) is A block diagram of its essential parts, FIG. 2 is a block diagram mainly showing the hardware, FIG. 3 is an overall configuration diagram showing the engine system, and FIG. 4 is a method for obtaining a correction coefficient for fuel supply control. FIG. 5 is a flow chart for explaining the solenoid valve drive routine, FIG. 6 is a flow chart for explaining how to obtain the correction coefficient for the high frequency component, and FIGS. 7 (a) to 7 (d) are FIG. 8 is a waveform diagram for explaining the action at the time of O ₂ feedback, FIG. 8 is a diagram for explaining the O ₂ feedback zone, and FIG. 9 is for explaining the tendency of the high-frequency component data set value during the forced change of the air-fuel ratio. Is a diagram to 10 and 11 show an air-fuel ratio control system for an internal combustion engine as another embodiment of the present invention. FIG. 10 is an overall configuration diagram showing the engine system corresponding to FIG. 3, and FIG. FIG. 12 is a partial cross-sectional view of the O ₂ sensor with a catalyst layer, and FIG. 12 is an overall configuration showing an engine system having an air-fuel ratio control device for an internal combustion engine as still another embodiment of the present invention, corresponding to FIG. FIG. 13 is a diagram, and FIG.
(D) is another waveform diagram for explaining the operation of the device of the present invention during O ₂ feedback. 1 ... Combustion chamber, 2 ... Intake passage, 3 ... Exhaust passage, 4 ...
Intake valve, 5 exhaust valve, 6 air cleaner, 7
Throttle valve, 8 ... Solenoid valve, 9 ... Catalytic converter (first catalyst), 9A, 9B ... Catalytic part, 9 '... Second catalyst, 10 ... ISC motor, 11 ... Intake air amount Air flow sensor as detecting means, 12 ... Intake temperature sensor, 13 ... Atmospheric pressure sensor, 14 ... Throttle sensor, 15 ... Idle switch, 16 ... Motor position sensor, 17 ... O ₂ sensor, 17a, 17b ...... Platinum electrode, 17c ...... Solid electrolyte part, 17
d …… Catalyst layer, 19 …… Water temperature sensor, 20 …… Vehicle speed sensor, 2
1 …… Crank angle sensor, 22 …… TDC sensor, 23 …… Electronic control unit (ECU), 24 …… Battery, 25 …… Battery sensor, 26 …… Ignition switch (key switch), 27 …… CPU, 28 , 29 …… Input interface, 30…
… A / D converter, 31 …… ROM, 32 …… RAM, 33 …… Battery backup RAM (BURAM), 34 …… Driver, 35…
... basic drive time determining means, 36 ... air-fuel ratio correction coefficient setting means (engine-speed and air-fuel ratio correcting means according to load),
37 …… O ₂ sensor feedback correction means, 38,39 …… switching means, 40 …… cooling water temperature correction means, 41 …… intake air temperature correction means, 42 …… atmospheric pressure correction means, 43 …… acceleration increase correction means, 44 ... Dead time correcting means, 45 ... First signal generating means, 46 ... Second signal generating means, 47 ... Third signal generating means, E ... Engine.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masashi Chino 5-3-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Akira Takahashi 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Hideaki Katashiba 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Applied Equipment Research Laboratory (72) Minor Nishida 8th Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture No. 1-1 Mitsubishi Electric Co., Ltd. Applied Equipment Research Laboratory (72) Inventor Yasuyuki Makikawa 8-1-1 Tsukaguchihonmachi, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Co., Ltd. Applied Equipment Research Laboratory (56) Reference JP-A-52-81438 (JP, A) JP 56-121831 (JP, A) JP 54-17414 (JP, A) JP 63-271156 (JP, A) Actual development Sho 60-73819 (JP, U) Actual Kaisho 62 105345 (JP, U) JitsuHiraku Akira 61-189261 (JP, U) JitsuHiraku Akira 62-117220 (JP, U) JitsuHiraku Akira 60-15661 (JP, U) JitsuHiraku Akira 64-13219 (JP, U)

Claims (2)

(57) [Claims] 1. A catalyst provided in an exhaust system of an internal combustion engine and having a redox characteristic, and an exhaust gas component provided in the catalyst or in an exhaust system on the downstream side of the catalyst, the output of which rapidly changes near a stoichiometric air-fuel ratio. A first changer that has a detecting means and an intake air amount detecting means for detecting an intake air amount of the internal combustion engine, and the increasing / decreasing direction changes based on the output change of the exhaust gas component detecting means.
And a second signal which is shorter than the output change cycle of the exhaust gas component detection means and which oscillates at a cycle set based on the intake air amount detected by the intake air amount detection means. Is provided, and an air-fuel ratio control means for controlling the air-fuel ratio of the combustion gas guided to the catalyst based on the third signal is provided, and the emptying of the combustion gas guided to the catalyst is provided. An air-fuel ratio control device for an internal combustion engine, wherein the fuel ratio is configured to be oscillated near the stoichiometric air-fuel ratio. 2. A first catalyst which is provided in an exhaust system of an internal combustion engine and has a redox characteristic, and an upstream exhaust system of the first catalyst which is provided in an exhaust system and whose output suddenly changes in the vicinity of a theoretical air-fuel ratio. Exhaust gas component detecting means, a second catalyst provided around the exhaust gas component detecting means or in an upstream exhaust system and having redox characteristics, and an intake air amount detecting means for detecting an intake air amount of the internal combustion engine. A first signal whose increase / decrease direction changes based on the output change of the exhaust gas component detection means, and an intake shorter than the cycle of the output change of the exhaust gas component detection means and detected by the intake air amount detection means. A signal forming means for forming a third signal by superimposing a second signal vibrating in a cycle set based on the amount of air, and an air-fuel ratio of the combustion gas guided to the catalyst based on the third signal The air-fuel ratio control means for controlling is installed. It is in, wherein the air-fuel ratio of the combustion gas guided to the catalyst is configured as given vibrationally at the stoichiometric air-fuel ratio near the air-fuel ratio control apparatus for an internal combustion engine.