JPH07259609A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain an air-fuel ratio controller of an internal combustion engine, wherein roughness of the air-fuel ratio is small even if fuel properties of using fuel is largely changed. CONSTITUTION:An air-fuel ratio controller of an internal combustion engine is provided with an air-fuel ratio feedback control means, a learning value setting means for renewing and setting a learning value for correcting the fuel injection amount according to fluctuation of control condition in the air-fuel feedback control, a learning completion judging means 104, and a fuel injection amount control means for determining the suitable fuel injection amount to the engine after correcting the basic fuel injection amount by the air-fuel ratio feedback correction amount and the learning value. And it is provided with fuel property detecting means 101, 102 for detecting fuel property of using fuel, and a renewal time shortening control means 103 for shortening the time required to renew the learning value carried out by the learning value setting means when the change of fuel property is detected by the fuel property detecting means.

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 system for an internal combustion engine, and more particularly to an air-fuel ratio control system for an internal combustion engine in which a double air-fuel ratio sensor system and a deposit learning control system coexist.

[0002]

2. Description of the Related Art An internal combustion engine which is used for an air-fuel ratio sensor, for example, an O ₂ sensor, to generate an air-fuel ratio feedback correction amount for correcting a basic fuel injection amount determined by an operating state of an engine, and thereby feedback control the fuel injection amount. In an air-fuel ratio control system for an engine, in order to compensate for variations in the output characteristics of the O ₂ sensor, variations in fuel system parts such as fuel injection valves, and their changes over time or aging, a _second valve is provided downstream of the catalytic converter. A so-called double O ₂ sensor system is used in which the (sub) O ₂ sensor is provided and the air-fuel ratio feedback control is performed by the downstream O ₂ sensor in addition to the air-fuel ratio feedback control by the upstream (main) O ₂ sensor.

Further, in order to correct the control condition variation of the air-fuel ratio feedback control system due to the machine difference of the fuel system parts or the change over time or aging, the reference value of the air-fuel ratio feedback correction amount for each learning region based on the engine operating state. The air-fuel ratio learning control for correcting the deviation from is set, and the fuel injection amount is corrected by the air-fuel ratio learning value.

Further, in order to compensate for valve clearance, deposit adhesion to the injection port of the fuel injection valve, and characteristic changes due to deposit adhesion to the back surface of the cylinder intake valve, etc., a deposit learning is performed as a correction during transient (acceleration / deceleration). Controls are also implemented. Then, using the obtained deposit learning value, the fuel injection amount is increased (or decreased) and corrected, and the air-fuel ratio feedback control of the engine is executed stably and appropriately.

In addition, by recirculating a part of the exhaust gas into the intake mixture to lower the combustion temperature in the cylinder,
Exhaust gas recirculation (EG to reduce NO _x in exhaust gas
R) control is also implemented, and among them, a Kb type EGR that increases the EGR amount during high load acceleration has been adopted. By the way, when the double O ₂ sensor system and the deposit learning control system are combined,
The air-fuel ratio feedback control by the downstream (sub) O ₂ sensor is also performed during the transition when the deposit learning control is being executed. As a result, the air-fuel ratio feedback control by the downstream (sub) O ₂ sensor is performed on the upstream side of the catalyst. There is a problem that the fuel ratio changes, the deposit learning control becomes unstable, and erroneous learning of the deposit learning value occurs. Further, for example, when the rich skip amount (RSR) of the main air-fuel ratio feedback control is corrected by the sub O ₂ sensor, when the deposit learning control is executed during deceleration or acceleration depending on the magnitude of the O ₂ storage effect of the catalyst, There is a problem that the deposit learning value changes excessively. In order to solve such a problem, it has been proposed to prohibit the air-fuel ratio feedback control by the downstream O ₂ sensor until the deposit learning control is completed (JP-A-2-199).
249).

On the other hand, the roughness of the air-fuel ratio during acceleration / deceleration varies depending on the fuel used, and is larger in heavy or lighter than medium quality. Heavy fuel has a low volatility and a large amount of adhered to the wall surface, so it becomes lean during acceleration and becomes rich during deceleration (acceleration lean deceleration rich), and the air-fuel ratio becomes rough. Since the volatility is good and the amount of adhesion on the wall surface is small, the air-fuel ratio becomes rough due to acceleration rich deceleration lean. This air-fuel ratio roughening becomes the largest in the state where the deposit learning, and further the area learning when the above-mentioned air-fuel ratio learning control (area learning) for each area is also provided, are not completed.

FIG. 7 is a time chart for explaining the air-fuel ratio control characteristic at the time of transition. For example, when the fuel used changes from medium fuel to heavy fuel, the region learning and the deposit learning are still completed. If the sub-O ₂ sensor is activated with the activation determination permitted in the state where the air-fuel ratio is not activated, deceleration overrich occurs as shown by the air-fuel ratio change characteristic in the figure. This is sub lean because it is lean during acceleration.
_{The two} sensors also judge lean and increase the rich skip RSR to try to correct it rich, but immediately after the fuel is changed and the learning of the rich skip RSR is not completed, the correction amount becomes too large, And sub O
_This occurs because there is a response delay T in the exhaust gas determination of the _two sensors, and even if the base air-fuel ratio changes from lean to rich, it is not immediately determined to be rich.

For example, FIG. 8 is a time chart for explaining the air-fuel ratio control characteristic at the time of transition in which acceleration and deceleration are repeated. When the sub O ₂ sensor is operated before learning is completed, acceleration and deceleration are repeated. When such traveling is performed, the rich skip RSR diverges, and the air-fuel ratio (A / F) becomes over lean or over rich, which leads to deterioration of drivability and deterioration of emission.

[0009]

The above-mentioned tendency has a characteristic that the degree of overrich increases as the air-fuel ratio becomes rougher. Therefore, the operation of the sub-O ₂ sensor is stopped as proposed above. The actual situation is that there is only a measure to prevent it. However, when the fuel properties of the used fuel change, it takes time to complete the learning, so if the sub O ₂ sensor is stopped during that time,
The correction to the main air-fuel ratio feedback control is not performed, so that the controllability of the air-fuel ratio is deteriorated and the exhaust emission is deteriorated. That is, there is a problem that a highly accurate air-fuel ratio control system such as the double O ₂ sensor system cannot be fully utilized.

Further, in the case of the air-fuel ratio control apparatus for an internal combustion engine, which is also equipped with the above-mentioned EGR control system, particularly a system adopting the Kb type EGR that further increases at the time of high load acceleration, FIG. As shown by the air-fuel ratio and the EGR control characteristic of the throttle valve, for example, when the used fuel changes from light to heavy, and in a state where the region learning and the deposit learning due to the fuel change are not yet completed, the throttle valve Kb When acceleration is applied to the R port of a type EGR, there is a change from over lean to over rich as shown in the figure (when the fuel used changes from heavy to light, as indicated by the dotted line). The opposite is true), and a large amount of EGR is applied during acceleration lean, which deteriorates combustion, resulting in deterioration of drivability. It was also found.

Therefore, an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine in which the air-fuel ratio is less rough even if the fuel properties of the fuel used change greatly. More specifically,
The present invention relates to an air-fuel ratio feedback control that is configured so as not to cause air-fuel ratio roughening even if the fuel properties of the fuel used change significantly, and the air-fuel ratio of an internal combustion engine provided with learning control for correcting fluctuations in the control conditions. An object is to provide a fuel ratio control device.

Specifically, according to the present invention, in the double air-fuel ratio sensor system, when there is a change in the fuel property,
The operation of the sub air-fuel ratio sensor is stopped, the learning operation is sped up, and when the learning is completed, the operation of the sub air-fuel ratio sensor is enabled so that the air-fuel ratio does not become rough even if the fuel properties of the fuel used change significantly. An object is to provide an air-fuel ratio control device for an internal combustion engine.

Further, according to the present invention, when the fuel property changes, the EGR amount is reduced until the air-fuel ratio learning is completed so that the air-fuel ratio becomes rough even if the fuel property of the fuel used changes greatly. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine which has a small number.

[0014]

An air-fuel ratio control system for an internal combustion engine according to the present invention includes an air-fuel ratio feedback control means for generating an air-fuel ratio feedback correction amount for correcting a basic fuel injection amount according to an engine operating state, and an air-fuel ratio feedback control device. A learning value setting means for updating and setting a learning value for correcting the fuel injection amount according to a change in the control condition in the fuel ratio feedback control, and determining that the learning value updating by the learning value setting means is completed And learning completion determination means for permitting execution of other controls that affect the air-fuel ratio of the engine, and correct fuel injection to the engine by correcting the basic fuel injection amount with the air-fuel ratio feedback correction amount and the learning value. An air-fuel ratio control device for an internal combustion engine, comprising: a fuel injection amount control means for determining a fuel quantity; a fuel property detection means for detecting a fuel property of a used fuel; When a change in the fuel property is detected by means output, further configured to have an update time reduction control means for reducing the time required for updating of the learning value performed in the learned value setting means.

[0015]

According to the above construction, in the case of setting the learning value for correcting the fluctuation of the control condition in the air-fuel ratio feedback control, the fuel property detecting means and the update time shortening control means are provided to greatly change the fuel property. Only when the learning value is updated, the update speed of the learning value is increased, so that the learning update can be executed more accurately and other controls that affect the air-fuel ratio can be executed well.

[0016]

1 is a conceptual block diagram showing the outline of an example of a fuel injection control system for an internal combustion engine to which an air-fuel ratio control device for an internal combustion engine according to the present invention is applied. 1 is an internal combustion engine, 2 is an intake system, 3 is an exhaust system, 100 is fuel injection of the internal combustion engine 1,
An electronic control unit that controls ignition timing and other various controls. The internal combustion engine 1 includes a fuel injection valve 11 and a spark plug 12, and the fuel injection valve 11 is controlled by an injection timing and an injection time determined by an electronic control unit 100 based on inputs from various engine operating state detection sensors. The spark plug 12 is connected to the electronic control unit 100.
With reference to the detection output of the crank angle sensor 14 coupled to the distributor 13, the ignition control is performed via the igniter 15 and the distributor 13 at an ignition timing determined according to the engine operating state. These control algorithms may be known ones and are not limited to particular ones. Reference numeral 16 is an intake valve, 17 is an exhaust valve, and 18 is a cooling water temperature sensor.

The intake system 2 is provided with an air cleaner 21, a surge tank 22 and an intake pipe 23, and a throttle valve 24 disposed in the middle of the intake system 2 is interlocked with an accelerator pedal (not shown) so that intake air is supplied in response to a driving operation. An idling system 25 for determining the quantity and bypassing the throttle valve 24 is provided, and the electronic control unit 10
The bypass amount is adjusted under the control of 0, and the idling speed of the engine is controlled. In addition, 26 is an intake air temperature sensor, 2
Reference numeral 7 is a throttle opening sensor, and 28 is an intake pipe pressure sensor.

The exhaust system 3 includes an exhaust pipe 31 and a catalytic converter 32. The catalytic converter 32 purifies the exhaust gas, and the main O ₂ sensor 33 and the sub O ₂ sensor 34 are provided on the upstream side and the downstream side of the exhaust system 3. To detect the oxygen concentration in the exhaust gas and to make the detected output participate in the fuel injection amount determined by the electronic control unit 100, thereby feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine.

An exhaust gas recirculation (EGR) system 40 is provided between the exhaust system 3 and the intake system 2, and an EGR valve 41 for determining the EGR amount is controlled by an electronic control unit 100 via a flow control valve 42. Controlled. Note that 43
Is the E port and R provided on the throttle body
It is a switching valve that switches the negative pressure of the port. Further, a purge control system 50 for introducing vaporized fuel (vapor) into the intake system to perform combustion processing is provided, and a fuel tank 51 is provided.
The evaporated fuel from the above is adsorbed to the canister 52, and is purged at a predetermined time and amount via the purge valve 53 controlled by the electronic control unit 100. A vapor flowmeter 54 is provided in the vapor passage and a fuel temperature sensor 55 is provided in the fuel tank, and the electronic control unit 100 determines the fuel property of the fuel used based on the detected outputs.

FIG. 2 is a flow chart showing an example of software for realizing an embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention. For example, in the above-mentioned electronic control unit 100, periodically or at a predetermined crank angle. The main control loop for period control is interrupted and executed. First, in step 101, the fuel property of the used fuel is detected. Here, the fuel property is determined based on the detection outputs of the vapor flow meter 54 and the fuel temperature sensor 55 in FIG. 1 described above. That is, when the fuel temperature in the fuel tank is low and the vapor flow rate is high, it is determined that the fuel is a light fuel, and the fuel temperature is high.
When the vapor flow rate is small, it is determined that the fuel is heavy fuel. Other than those, it will be medium quality fuel. For detecting the fuel property, it is possible to use vapor measuring means such as RVP detection or fuel tank internal pressure detecting means.

Next, at step 102, it is judged if the fuel property is the same as before the engine is started (IG-ON). If the same (YES), the value learned previously is considered to be valid, and the routine proceeds to step 105, where the air-fuel ratio feedback control by the sub O ₂ sensor is operated, that is, the sub O ₂ operation permission is made. If different (NO), in step 103, the setting for speeding up the air-fuel ratio (A / F) learning is performed and the air-fuel ratio learning is executed. Then, in step 104, it is determined whether the air-fuel ratio learning is completed. Regarding the completion of the learning, it is necessary to determine that the later learning of the air-fuel ratio learning and the deposit learning has been completed, but here, the completion of the air-fuel ratio learning is determined.

As a method for judging the completion of learning,
For example, a learning completion determination counter is provided, and a determination time T _j for which each learning value X for area learning and deposit learning is constant.
If the variation is within Y% in the above period, that is, if the variation exceeds the determination time T _j and stays within X ± Y%, it can be considered to be completed. If these learnings are completed (YE
S), sub-O ₂ operation permission, if not completed (N
O), the operation of the sub-O _{2 is} prohibited, and the completion of these learning is awaited.

FIG. 3 is an explanatory diagram for explaining the flow of the operation of the embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, which is shown in comparison with the operation of the conventional apparatus. . When a change in the used fuel is detected after the engine is started, the main O ₂ will operate if the conditions are met, but the operation of the sub O ₂ will be stopped immediately. And sub-O until learning is completed
The operation stop of No. ₂ is continued, but in the case of the device according to the present invention, the operation stop of sub-O ₂ is shortened by the shortened period due to the speedup of learning, so that the air-fuel ratio roughness due to the stop of operation of sub-O ₂ is reduced. be able to.

FIG. 4 is a time chart of the air-fuel ratio feedback correction amount FAF for explaining the speed-up method of air-fuel ratio learning. When updating the air-fuel ratio learning, the average value FAF of the air-fuel ratio feedback correction amount FAF
A learning value update criterion ± A for AV is set, and when the reference value is exceeded, the air-fuel ratio learning value is updated. Therefore, by changing the reference value of the air-fuel ratio learning to a smaller value ± B, it is possible to speed up the air-fuel ratio learning. As one method for that, a map for learning speed-up (learning reference value ± B)
It is conceivable that the learning speed-up map is used to perform learning when the fuel property changes significantly, and when the learning is completed, the map is returned to the original determination reference value map.

FIG. 5 is a flow chart showing an example of software for realizing another embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention. For example, the electronic control unit 100 described above may have a regular or predetermined crank. At the corner, the main control loop of the period control is interrupted and executed. In this embodiment, when the fuel property changes, K
(B) EGR amount of b type EGR is adjusted. When the engine is started (IG-ON) in step 201, it is determined in step 202 whether the fuel property is heavy or light. To be done. If not (NO), that is, if it is a medium quality fuel, the routine proceeds to step 204, where E
Make the R port of GR conductive, that is, normal Kb
A type EGR operation is executed.

When the fuel used is either heavy or light (YES), it is determined in step 203 whether the air-fuel ratio learning is completed. If completed (YE
S), the normal Kb type EGR operation is executed, but during the period (NO) where it is not completed, the EGR R port is cut, that is, the high load acceleration shown by the hatching in FIG. 9 described above. The normal H type EGR operation is performed by eliminating the EGR increase amount at that time.

FIG. 6 is an explanatory diagram for explaining the flow of operation of another embodiment of the air-fuel ratio control system for an internal combustion engine according to the present invention with time. In the case of medium quality fuel, the negative pressure of the R port of EGR is conducted for normal operation regardless of engine start or fuel change, but in the case of heavy or light fuel, RGR of EGR is continued until learning is completed. The negative pressure in the port is cut to reduce the high load increase amount of EGR. As a result, it is possible to avoid the fluctuation of the air-fuel ratio up to the overlevel due to the fuel property change as shown in FIG.

In the embodiment described above, the operation of the sub O ₂ sensor system and the EGR system is controlled at the time of changing the fuel property. Needless to say, the present invention can be applied to other controls and processes that affect the air-fuel ratio when executed before completion of the fuel ratio learning and deposit learning, for example, execution of purge control.

[0029]

As described above, according to the air-fuel ratio control system for an internal combustion engine of the present invention, the learning value for correcting the fluctuation of the control condition in the air-fuel ratio feedback control,
For example, when setting the air-fuel ratio learning value and the deposit learning value, the learning update can be performed more accurately by increasing the learning update speed only when the fuel properties of the fuel used change significantly for those learning values. While executing, other controls that affect the air-fuel ratio, such as sub-O ₂
The operation of the system, increase / decrease of EGR, purge control, etc. can be executed well.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram showing an outline of an example of a fuel injection control system for an internal combustion engine to which an air-fuel ratio control device for an internal combustion engine according to the present invention is applied.

FIG. 2 is a flowchart showing an example of software for realizing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 3 is an explanatory diagram for explaining a temporal flow of the operation of the embodiment of the air-fuel ratio control device for the internal combustion engine according to the present invention.

FIG. 4 is a time chart of the air-fuel ratio feedback correction amount for explaining the speed-up method of air-fuel ratio learning.

FIG. 5 is a flowchart showing an example of software for realizing another embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 6 is an explanatory diagram for explaining a temporal flow of the operation of another embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 7 is a time chart for explaining the air-fuel ratio control characteristic during transition.

FIG. 8 is a time chart for explaining the air-fuel ratio control characteristic during a transition in which acceleration and deceleration are repeated.

FIG. 9 is a time chart for explaining the air-fuel ratio and EGR control characteristics during a transition.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake system 3 ... Exhaust system 11 ... Fuel injection valve 12 ... Spark plug 13 ... Distributor 14 ... Crank angle sensor 15 ... Igniter 16 ... Intake valve 17 ... Exhaust valve 18 ... Cooling water temperature sensor 21 ... Air cleaner 22 ... surge tank 22 23 ... intake pipe 23 24 ... throttle valve 25 ... idling system 26 ... intake air temperature sensor 27 ... throttle opening degree sensor 28 ... intake pipe pressure sensor 31 ... exhaust pipe 32 ... catalytic converter 33 ... main O ₂ sensor 34 ... sub O ₂ sensor 40 ... Exhaust gas recirculation (EGR) system 41 ... EGR valve 42 ... Flow control valve 43 ... Switching valve for switching negative pressure of E port and R port 50 ... Purge control system 51 ... Fuel tank 52 ... Canister 53 ... Purge valve 54 ... Vapor flowmeter 55 ... Fuel temperature Sensor 100 ... electronic control unit

Claims (1)

[Claims] 1. An air-fuel ratio feedback control means for generating an air-fuel ratio feedback correction amount for correcting a basic fuel injection amount according to an engine operating state, and a fuel injection amount is corrected according to a change in a control condition in the air-fuel ratio feedback control. A learning value setting means for updating and setting the learning value for setting the learning value, and determining that the learning value updating in the learning value setting means is completed, and another control affecting the air-fuel ratio of the engine. Learning completion determining means for permitting execution of the fuel injection amount, and fuel injection amount control means for correcting the basic fuel injection amount by the air-fuel ratio feedback correction amount and the learning value to determine an appropriate fuel injection amount to the engine. In the air-fuel ratio control device for an internal combustion engine, the fuel property detecting means for detecting the fuel property of the used fuel, and the change in the fuel property are detected by the fuel property detecting means. And when the air-fuel ratio control apparatus for an internal combustion engine further includes an update time reduction control means for reducing the time required for updating of the learning value performed in the learning value setting means.