GB2509351A

GB2509351A - Air-fuel ratio control system

Info

Publication number: GB2509351A
Application number: GB1316952.9A
Authority: GB
Inventors: Shinji Fujita; Yuki Takano; Shinya Nakano; Satoko Sakiyama
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2012-09-28
Filing date: 2013-09-24
Publication date: 2014-07-02
Anticipated expiration: 2033-09-24
Also published as: JP5981827B2; GB201316952D0; JP2014070600A; GB2509351B; ITTO20130725A1

Abstract

An air-fuel ratio control system is provided that enables a prompt restoration ofair-fuel ratio control to a normal state after an injection of secondary air upstream of a catalyst, the cut of fuel injection, or deceleration leaning, and enables keeping emission performance high. At a stage at which the injection of secondary air is started or at a stage at which fuel cut control or deceleration leaning is performed, sliding mode control in a main body 100 of an air-fuel ratio controller is interrupted. Immediately after the injection of secondary air is finished or immediately after the fuel cut control or the deceleration leaning is finished, the air-fuel ratio control is made to shift to rich spike control in an open loop, and after the real air-fuel ratio (SVO2) transfers to the rich side, the sliding mode control in the main body 100 of the air-fuel ratio controller is resumed.

Description

AIR-FUEL RATIO CONTROL SYSTEM

The present invention relates to an air-fuel ratio control system, and in particular to an air-fuel ratio control system suitable for use in a vehicle (such as a motorcycle) with an internal combustion engine.

In an automobile system for decontaminating exhaust gas from an internal combustion engine (hereinafter "engine") by means of a catalytic device and exhausting it, it is desirable in view of environmental protection that the air-fuel ratio of exhaust gas of the engine is controlled to be an air-fuel ratio at which the exhaust gas decontamination capacity of the catalytic device is satisfactory.

A system that performs such air-fuel ratio control is disclosed in JP 3373724. In this document, the air-fuel ratio control system is configured so that a correction factor is superimposed on fuel injection quantity, so as to remove the lag of the injection quantity acquired based upon a fuel injection volume map (having engine speed, a throttle opening, vacuum and others as parameters) for determining the fuel injection quantity in the engine from target air-fuel ratio.

Specifically, an LAF sensor (a sensor that outputs a signal at a level proportional to the oxygen content of exhaust gas in a large range of the oxygen content (the air-fuel ratio) of exhaust gas) is installed upstream of a catalytic decontaminating device arranged in an exhaust pipe of the engine, and an oxygen sensor (an air-fuel ratio sensor) is installed downstream of the catalytic device. A predicted value of air-fuel ratio after catalysis is calculated using a detection value by the LAF sensor, and the correction factor is acquired using the predicted value by a sliding mode controller, for example.

As LAF sensors are expensive, there is a desire to do away with the LAF sensor installed upstream of the catalytic device, because of the cost reduction of the system and the limit of space for arrangement in a motorcycle and other vehicles.

However, as an output value (SVO2) of the oxygen sensor (to be a desired value of emission) converges on the desired value based upon the output value (SVO2) input to the sliding mode controller (SMC) which models the intake/exhaust of the engine, the air-fuel ratio before catalysis cannot be measured when no LAF sensor is installed upstream of the catalytic device; therefore, the prediction of the tolerance and the age deterioration of the engine and the injection error of a fuel injection valve in the modelled engine cannot be monitored, a predictable range of a predicted value of the output value (SVO2) is enlarged, and much time may be required for the convergence on the desired value by the sliding mode controller (SMC).

Besides, as gain in convergence by the sliding mode controller (SMC) also has a limit in adjustment, it is also conceivable that a predictive error of a predicted value of an output value (SVO2) cannot be eliminated and the output value (SVO2) cannot be converged on the desired value.

Depending upon the specifications of an internal combustion engine, a system may be installed in the exhaust pipe for injecting secondary air, upstream of a catalyst, to reduce the emission of exhaust gas. As the air-fuel ratio before entry into the catalyst varies when secondary air is injected, the sliding mode controller may have an effect upon the whole control system. Besides, generally, secondary air is set to supply sufficient air so as to enable secure combustion of residual fuel in the exhaust pipe unless special feedback is made. As a result, when secondary air is injected, the air-fuel ratio upstream of the catalyst is apt to be lean (oxygen is excessive). Therefore, when secondary air is injected, the quantity of oxygen stored in the catalyst readily increases immediately after the injection of secondary air and as a result, NO decontamination performance may be deteriorated.

Moreover, as air also flows into the catalyst when fuel injection is cut while a throttle valve is fully closed except the injection of secondary air, the quantity of oxygen stored in the catalyst increases and the same problem as that in the injection of secondary air occurs. Similarly, when deceleration leaning is made without cutting fuel from a viewpoint of protecting the catalyst, the quantity of oxygen stored in the catalyst also increases.

The present invention is made in view of such problems, and it is an object of at least the preferred embodiments of the present invention to provide an air-fuel ratio control system where air-fuel ratio can be optimized without installing an LAF sensor upstream of a catalytic device, the cost of the system can be reduced, the application of air-fuel ratio control to a motorcycle and others can be accelerated, and in addition, in the case of the injection of secondary air, fuel injection cut or deceleration leaning, air-fuel ratio control can be also promptly restored after restoration to a normal state from a control state of these, and emission performance can be kept high.

According to a first aspect of the present invention, there is provided an air-fuel ratio control system comprising: a basic fuel injection map that specifies fuel injection quantity to an engine based upon at least parameters of engine speed and throttle opening; air-fuel ratio sensing means which is provided downstream of a catalyst installed in an exhaust pipe of the engine and which senses air-fuel ratio; air-fuel ratio predicting means that predicts air-fuel ratio downstream of the catalyst; and correction factor calculating means that determines a correction factor for the fuel injection quantity based upon predicted air-fuel ratio from the air-fuel ratio predicting means by feedback control, wherein: the air-fuel ratio predicting means calculates the predicted air-fuel ratio based upon at least real air-fuel ratio from the air4uel ratio sensing means and a history of the correction factor; the air-fuel ratio control system has adaptive model correcting means that superimposes a second correction factor on the correction factor so as to make deviation between the real air-fuel ratio and the predicted air-fuel ratio which corresponds to the real air-fuel ratio and which is predicted in the past as a predictive error zero; a secondary air pulse induction system that injects secondary air into an exhaust path upstream of the catalyst is provided; the feedback control is interrupted at a stage at which the injection of secondary air is started; immediately after the injection of secondary air is finished, air4uel ratio control is made to shift to rich control in an open loop; and after the real air-fuel ratio transfers to a rich side, the feedback control is resumed.

With this arrangement, the quantity of oxygen stored in the catalyst as a result of the injection of secondary air can be reduced at an early stage by interrupting the feedback control after the injection of secondary air in the system in which the secondary air pulse induction system is installed, and performing rich injection control at the stage at which the injection of secondary air is finished. As a result, the interrupted feedback control can be restored at an early stage and emission performance can be kept high.

According to a second aspect of the present invention, there is provided an air-fuel ratio control system comprising: a basic fuel injection map that specifies fuel injection quantity to an engine based upon at least parameters of engine speed and throttle opening; air-fuel ratio sensing means which is provided downstream of a catalyst installed in an exhaust pipe of the engine and which senses air-fuel ratio; air-fuel ratio predicting means that predicts air-fuel ratio downstream of the catalyst; and correction factor calculating means that determines a correction factor for the fuel injection quantity based upon predicted air-fuel ratio from the air4uel ratio predicting means by feedback control, wherein: the air-fuel ratio predicting means calculates the predicted air-fuel ratio based upon at least real air-fuel ratio from the air-fuel ratio sensing means and a history of the correction factor; the air-fuel ratio control system has adaptive model correcting means that superimposes a second correction factor on the correction factor so as to make deviation between the real air-fuel ratio and the predicted air-fuel ratio which corresponds to the real air-fuel ratio and which is predicted in the past as a predictive error zero; the air4uel ratio control system has fuel cut control means that performs fuel injection halt control while the throttle opening is closed; when the fuel injection halt control by the fuel cut control means is started, the feedback control is interrupted; immediately after the fuel injection halt control by the fuel cut control means is finished, air-fuel ratio control is made to shift to rich control in an open loop; and after the real air-fuel ratio transfers to a rich side, the feedback control is resumed.

As air containing oxygen flows into the catalyst when fuel injection halt control is performed by the fuel cut control means by closing the throttle opening, the quantity of oxygen stored in the catalyst increases. However, with this arrangement, as the feedback control is interrupted when the fuel injection halt control by the fuel cut control means is started and rich injection control is performed at the stage at which the fuel injection halt control is finished, the quantity of oxygen stored in the catalyst by the intake of air containing oxygen according to the fuel injection halt control can be reduced at an early stage. As a result, the interrupted feedback control can be restored at an early stage and emission performance can be kept high.

According to a third aspect of the present invention, there is provided an air-fuel ratio control system comprising: a basic fuel injection map that specifies fuel injection quantity to an engine based upon at least parameters of engine speed and throttle opening; air-fuel ratio sensing means which is provided downstream of a catalyst installed in an exhaust pipe of the engine and which senses air-fuel ratio; air-fuel ratio predicting means that predicts air-fuel ratio downstream of the catalyst; and correction factor calculating means that determines a correction factor for the fuel injection quantity based upon predicted air-fuel ratio from the air-fuel ratio predicting means by feedback control, wherein: the air4uel ratio predicting means calculates the predicted air-fuel ratio based upon at least real air-fuel ratio from the air4uel ratio sensing means and a history of the correction factor; the air4uel ratio control system has adaptive model correcting means that superimposes a second correction factor on the correction factor so as to make deviation between the real air-fuel ratio and the predicted air-fuel ratio which corresponds to the real air-fuel ratio and which is predicted in the past as a predictive error zero; the air-fuel ratio control system has deceleration leaning control means that performs deceleration leaning: when the deceleration leaning by the deceleration leaning control means is started, the feedback control is interrupted; immediately after the deceleration leaning by the deceleration leaning control means is finished, air-fuel ratio control is made to shift to rich control in an open loop; and after the real air-fuel ratio transfers to a rich side, the feedback control is resumed.

Air containing oxygen flows into the catalyst as in the case of the fuel cut control when the deceleration leaning by the deceleration leaning control means is started, and so the quantity of oxygen stored in the catalyst increases. However, with this arrangement, as the feedback control is interrupted when the deceleration leaning by the deceleration leaning control means is started and rich injection control is performed at the stage at which the deceleration leaning is finished, the quantity of oxygen stored in the catalyst by the intake of air containing oxygen according to the deceleration leaning can be reduced at an early stage. As a result, the interrupted feedback control can be restored at an early stage and emission performance can be kept high.

Preferably, the feedback control is sliding mode control: and when the predictive error exceeds a preset threshold prior to resumption of the feedback control, PID control is performed so as to make an error between the real air-fuel ratio and a preset desired value zero.

Thus, when it is predicted that time is required for the convergence of sliding mode control by the injection of secondary air or fuel cut control or the intake of air containing oxygen according to the deceleration leaning, the convergence of the feedback control can be accelerated by first performing PID control at a stage at which the injection of secondary air is finished or at a stage at which the fuel cut control or the deceleration leaning is finished, and emission performance can be kept high.

In a further preferred form, the feedback control is resumed at a stage at which the predictive error is equal to or smaller than the preset threshold.

As the convergence of sliding mode control is secured when the predictive error is equal to or smaller than the threshold, emission performance can be kept high by resuming the feedback control.

Preferably, the air4uel ratio control system further comprises a controller that controls at least the correction factor calculating means and the adaptive model correcting means, wherein: the adaptive model correcting means is provided with predictive precision determining means that determines predictive precision based upon the predictive error; and when deterioration of the predictive precision is determined in the predictive precision determining means in the resumption of the feedback control, the PlO control is performed without using the air-fuel ratio predicting means so as to make the error between the real air-fuel ratio and the preset desired value zero.

With this arrangement, PID control is performed so that the error between the real air-fuel ratio and the preset desired value is made zero without using the air-fuel ratio predicting means when the deterioration of predictive precision is determined in the resumption of the feedback control. Thus, time until the predictive precision is secured can be more reduced, compared with a case in which the air-fuel ratio predicting means is used and emission performance can be kept high.

Preferably, the air1uel ratio control system further comprises a dedicated PID controller, wherein: the feedback control is the sliding mode control; and when the error between the real air-fuel ratio and the preset desired value exceeds the preset threshold prior to the resumption of the feedback control, the PID control is performed in the RID controller so as to make the error zero.

With this arrangement, PID control is performed using the dedicated RID controller so that the difference (the error) between the real air-fuel ratio and the desired value is made zero prior to the resumption of the feedback control, and the error can be converged on the threshold or less at a more early stage, compared with a case in which the predictive error in a main body of an air-fuel ratio controller is used, and normal sliding mode control (control in a first sliding mode controller) can be resumed at a more early stage. Thus, emission performance can be kept high.

Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. I is a perspective view showing an example of a motorcycle in which an air-fuel ratio control system according to the invention is installed; Fig. 2 is a block diagram showing an example of a control system of an engine of the motorcycle; Fig. 3 is a functional block diagram showing a configuration of an air-fuel ratio controller provided with a first air intake corresponding part; Fig. 4 is a control block diagram showing the configuration of the air-fuel ratio control system (the air-fuel ratio controller) in a first embodiment; Fig. 5 is a control block diagram showing a configuration of a main body of an air-fuel ratio controller in a comparative (prior art) example; Fig. 6 is an explanatory drawing showing a predictive model by a predictor; Fig. 7 is an explanatory drawing showing an operational concept of sliding mode control; Fig. 8 is a block diagram showing a configuration of an adaptive model corrector; Fig. 9 is a block diagram showing the specific configuration of the adaptive model corrector; Fig. 1 OA is a characteristic diagram showing a variation of output of an oxygen sensor for air-fuel ratio A/F and Fig. lOB is a characteristic diagram showing a variation of a first weighting component for real air-fuel ratio; Fig. hA is a characteristic diagram showing a variation of basic fuel injection quantity for a throttle opening and Fig. 11 B is a characteristic diagram showing a variation of a second weighting component for the throttle opening; Fig. 1 2A is a characteristic diagram showing a weighting function for engine speed NE and Fig. 12B is a characteristic diagram showing a weighting function for a throttle opening TH; Fig. 13 is an explanatory drawing for explaining a principle for acquiring a correction factor based upon predictive error corrected quantity; Fig. 14 is a control block diagram showing a configuration of a main body of an air-fuel ratio controller in a first alternative embodiment; Fig. 15 is a control block diagram showing a configuration of a main body of an air-fuel ratio controller in a second alternative embodiment; Fig. 16 is a control block diagram showing a configuration of a main body of an air-fuel ratio controller in a third alternative embodiment; Fig. 17 is a control block diagram showing a configuration of a main body of an air-fuel ratio controller in a fourth alternative embodiment; Fig. 18 is a control block diagram showing a configuration of a main body of an air-fuel ratio controller in a fifth alternative embodiment; Fig. 19 is a flowchart showing the processing operation of a first air intake corresponding part; Fig. 20 is a timing chart showing an execution period of the injection of secondary air or FC control or deceleration leaning, a rich spike control period (a residual oxygen processing period of a catalytic device), the variation of fuel injection quantity per unit time in rich spike control, the variation of the quantity of oxygen stored in the catalytic device, and the variation of an output value (SVO2) from the oxygen sensor; Fig. 21 is a functional block diagram showing a configuration of an air-fuel ratio controller provided with a second air intake corresponding part; and Fig. 22 is a flowchart showing the processing operation of the second air intake corresponding part.

Referring to Figs. ito 22, an embodiment in which an air-fuel ratio control system according to the present invention is applied to a motorcycle as an example vehicle will be described below.

First, the motorcycle 12 in which the air-fuel ratio control system 10 in this embodiment is mounted will be described, referring to Fig. 1.

The motorcycle 12 is configured by coupling the front 14 of a vehicle body and the rear 16 of the vehicle body via a low floor panel 18 as shown in Fig. 1. A handlebar 20 is turnably attached to the upper part of the front 14 of the vehicle body and a front wheel 22 is journaled to the lower part. A seat 24 is attached to the upper part of the rear 16 of the vehicle body and a rear wheel 26 is journaled to the lower part.

An intake pipe 30 and an exhaust pipe 32 are provided on an engine 28 of the motorcycle 12, as schematically shown in Fig. 2, and the intake pipe 30 is arranged between the engine 28 and an air cleaner 34. A throttle valve 38 is provided in a throttle body 36 provided to the intake pipe 30. A fuel injection valve is provided between the engine 28 and the throttle body 36 on the intake pipe 30.

The throttle valve 38 is turned according to the operation of a throttle grip 42 (see Fig. 1), and its turned quantity (an angle of the throttle valve 38) is detected by a throttle sensor 44. Air volume supplied to the engine 28 is varied by opening or closing the throttle valve 38 according to the operation of the throttle grip 42 by a rider.

A coolant temperature sensor 46 that detects the temperature of engine cooling water is provided on the engine 28, and a PB sensor 48 that detects intake air pressure (intake vacuum) is provided on the intake pipe 30. There are also provided a secondary air pulse induction system 1000 which is provided upstream of a catalytic device 50 installed in the exhaust pipe of the engine 28, and which takes air from the air cleaner 34 into the exhaust pipe as secondary air, and an oxygen sensor 52 (air-fuel ratio detection means) which is provided downstream of the catalytic device 50 installed in the exhaust pipe of the engine 28 and which detects air-fuel ratio downstream of the catalytic device 50. An oxygen content detected by the oxygen sensor 52 is equivalent to the real air-fuel ratio of exhaust gas after the exhaust gas passes through the catalytic device 50.

Furthermore, a vehicle speed sensor 56 that detects vehicle speed based upon the revolution speed of an output gear of reduction gears 54 is provided on the engine 28. A starter switch 58 is a switch for starting the engine 28 by the operation of an ignition key. Further, an atmospheric pressure sensor 60 is provided in a position remote from the intake pipe 30 of the air cleaner 34.

An engine control unit (ECU 62) is provided with an Al (secondary Air Injection) controller 1002, an FC (Fuel Cut) controller 1004, a deceleration leaning controller 1005, and an air-fuel ratio controller 1006 that functions as the air4uel ratio control system lOin this embodiment as shown in Fig. 3.

The Al controller 1002 drives the secondary air pulse induction system 1000 when a predetermined condition for taking in secondary air comes into effect, and takes air from the air cleaner 34 and injects it as secondary air upstream of the catalytic device 50 in the exhaust pipe 32. The Al controller 1002 outputs an Al initiation signal Sais prior to the initiation of the injection of secondary air or when the injection is initiated, and outputs an Al termination signal Saie when the injection of secondary air is finished.

The FC controller 1004 executes fuel cut control that interrupts the injection of fuel when a predetermined condition for such FC control, that a throttle opening is turned to zero (the throttle valve is fully closed), comes into effect. The FC controller 1004 outputs an FC control initiation signal Sfcs prior to the initiation of the execution of fuel cut control or when the execution is initiated, and outputs an FC control termination signal Sfce when the fuel cut control is finished.

The deceleration leaning controller 1005 executes deceleration leaning such that basic injection pulse width is decreased when a predetermined condition for deceleration leaning based upon the decrement of a throttle opening and the variation of intake pressure comes into effect. The deceleration leaning controller 1005 outputs a deceleration leaning initiation signal Srss prior to the initiation of the -10-execution of deceleration leaning or when the execution is initiated, and outputs a deceleration leaning termination signal Srse when the deceleration leaning is finished.

The air-fuel ratio controller 1006 is provided with a main body 100 of the air-fuel ratio controller, a basic fuel injection quantity calculating unit 116, and a first air intake corresponding part 1008A. The main body 100 of the air-fuel ratio controller is a main body of the controller using sliding mode control and will be described later.

The basic fuel injection quantity calculating unit 116 calculates basic fuel injection quantity TIMB by calculating a reference fuel injection quantity specified based upon engine speed NE, a throttle opening TH and intake air pressure PB using a basic fuel injection map 118, and correcting the reference fuel injection quantity according to the effective opening area of the throttle valve 38.

The basic fuel injection map 118 is provided with a first basic fuel injection map 118a based upon engine speed NE and a throttle opening TH, and a second basic fuel injection map 118b based upon the engine speed NE and intake air pressure PB. Accordingly, in the air-fuel ratio controller 1006, there is provided a map selector 142 that selects and indicates the basic fuel injection map to be used out of the first basic fuel injection map liSa and the second basic fuel injection map 118b, based upon engine speed NE and the throttle opening TM from a map for selection 140 in which indexes of the basic fuel injection map to be used are arrayed. In the map for selection 140, as shown in Fig. 7, an area in which the first basic fuel injection map 11 8a is to be used and an area in which the second basic fuel injection map 118b is to be used are arranged. The map selector 142 selects the basic fuel injection map to be used based upon input engine speed NE and an input throttle opening TH from the map for selection 140, and outputs a result of the selection Sa. When the engine speed NE is low, the probability that the first basic fuel injection map 118a is selected is high, and when the engine speed NE is high, the probability that the second basic fuel injection map 118b is selected is high.

Accordingly, the basic fuel injection quantity calculating unit 116 calculates the reference fuel injection quantity TIMB by calculating a reference fuel injection quantity specified based upon engine speed NE, a throttle opening TH and intake air pressure PB using the basic fuel injection map selected by the map selector 142, and correcting the reference fuel injection quantity according to the effective opening area of the throttle valve 38. The basic fuel injection quantity TIMB is corrected with target air-fuel ratio K02(k) from the main body 100 of the air4uel ratio controller and an environmental correction factor KECO based on coolant temperature, intake air temperature and atmospheric pressure and others, and is output as fuel injection time Tout.

The first air intake corresponding part 1008A includes an air-fuel ratio control halt requesting unit 1010, a rich spike controller 1012 and a resumption determining unit 1014.

The air-fuel ratio control halt requesting unit 1010 outputs a halt request signal Sg to the main body 100 of the air-fuel ratio controller, based on the input of an Al initiation signal Sais from the Al controller 1002 or an FC control initiation signal Sfcs from the FC controller 1004 or a deceleration leaning initiation signal Srss from the deceleration leaning controller 1005. A controller 126 in the main body 100 of the air-fuel ratio controller temporarily halts air-fuel ratio control based upon the input of a halt request signal Sg from the air-fuel ratio control halt requesting unit 1010.

The rich spike controller 1012 controls the fuel injection valve 40 based upon the input of an Al termination signal Saie from the Al controller 1002 or an FC control termination signal Sfce from the FC controller 1004 or a deceleration leaning termination signal Srse from the deceleration leaning controller 1005, and generates a rich spike (that is, temporarily performs rich injection with an air-fuel ratio at which fuel injection quantity is richer than normal, so as to reduce NO absorbed in the catalytic device) in a combustion chamber of the engine 28. In the rich spike control, fuel supply quantity according to a current output value (SVO2) of the oxygen sensor 52 is supplied to the combustion chamber of the engine 28 in unit time, referring to a rich spike map 1016 in which fuel supply quantity per unit time according to the output value (5V02) of the oxygen sensor 52 is registered.

The rich spike controller 1012 terminates the rich spike control when the output value (SVO2) of the oxygen sensor 52 transfers to the rich side.

The resumption determining unit 1014 outputs a control resumption signal Si to the main body 100 of the air-fuel ratio controller when the output value (SVO2)of the oxygen sensor 52 transfers to the rich side. The main body 100 of the air-fuel ratio controller resumes air-fuel ratio control based upon the input of the control resumption signal Si. The resumption of air-fuel ratio control in the main body 100 of the air-fuel ratio controller will be described later.

Next, the main body 100 of the air-fuel ratio controller will be described referring to Figs. 4to 18.

The main body 100 of the air-fuel ratio controller is provided with a predictor 102 (air-fuel ratio predicting means) that predicts air-fuel ratio downstream of the catalytic device 50, a first sliding mode controller 104 (correction factor calculating means) that determines a first correction factor DKO2OP(k) for fuel injection quantity based on the predicted air-fuel ratio DVPRE from the predictor 102, an identifier 106 that identifies parameters of the first sliding mode controller 104 and the predictor 102, and an air-fuel ratio reference value calculating unit 108 that calculates an air-fuel ratio reference value as shown in Fig. 4.

The operation of the predictor 102, the first sliding mode controller 104, the identifier 106 and the air-fuel ratio reference value calculating unit 108 will be described in comparison with a comparative prior art example shown in Fig. 5 (a main body 300 of an air-fuel ratio controller similar to the air-fuel ratio control system disclosed in JP 3373724).

First, the main body 300 of the air-fuel ratio controller in the comparative example shown in Fig. 5 assumes that an LAF sensor 110 (see a block shown by a broken line in Fig. 2) is installed upstream of the catalytic device 50, and the air-fuel ratio A]F(k) before catalysis is input from the LAF sensor 110.

The predictor 102 predicts dead time dt (air-fuel ratio (V02) after dead time elapses corresponding to distance from the fuel injection valve 40 to the oxygen sensor 52) from current time (k), so as to determine fuel injection quantity (target air-fuel ratio) downstream of the catalytic device 50.

In a predictive model by the predictor 102, output V3(k+dt)=Vpre(k) at the time of k+dt can be predicted from the following relational expression (1) if only air-fuel ratio CP1 before catalysis between time ta and time tb and the output V0 of the oxygen sensor 52 are acquired as shown in Fig. 6 when current time is k.

[Mathematical expression 1] 1/.

Vpre(k)= aix r',21'(k)+ a2x V0(k -+ pj x + cit -ci -However, as" ø" of "j 1-(dt-d-1)" cannot be observed at the time of k, a desired value () is used in place of it. In this case, V01(K) shows deviation between the output of the oxygen sensor 52 at the time of k and a desired value, and V0'(K-1) shows deviation between the output of the oxygen sensor 52 before the time of k by one unit time (a fixed time cycle) and a desired value. "cii", u2" and "f3j" are parameters determined by the identifier 106.

The first sliding mode controller 104 calculates injection quantity according to an error (predicted air-fuel ratio -desired value) of the model. Normally, sliding mode control, the concept of which is shown in Fig. 7, is a variable structure type feedback control method in which a switching line represented by a linear function having plural properties which are objects of control as variables is constructed beforehand, the properties are converged on the switching line at high speed by high gain control (an arrival mode)! and further, the properties are converged at required equilibrium points (converged points) on the switching line (a sliding mode), converging the properties on the switching line by so-called equivalent control input.

Such sliding mode control has an excellent characteristic that the properties can be stably converged at the equilibrium points on the switching line without being substantially influenced by disturbance and others once the plural properties which are the objects of control are converged on the switching line.

When a correction factor of air-fuel ratio of the engine 28 is calculated so as to stabilize the content of a specific component such as the oxygen content of exhaust gas downstream of the catalytic device 50 at a predetermined optimum value, the correction factor of air-fuel ratio is calculated so as to converge a value of the content of the specific component of exhaust gas downstream of the catalytic device 50 and its varying velocity respectively as properties of an exhaust system to be controlled for example at equilibrium points on the switching line (the points at which the value of the content and its varying velocity become predetermined optimum values and zero) using sliding mode control. When the correction factor of air-fuel ratio is acquired using the sliding mode control, the content of the specific component of exhaust gas downstream of the catalyst can be more precisely stabilized at the predetermined optimum value, compared with conventional type PID control and others.

A switching function and a control input arithmetic expression in the sliding mode control are as follows.

[Mathematical expression 2] [Switching function] c(k)= Jç(k)+ sv,;(k -i) (-i <s < o) [Control input arithmetic expression] ,(k)-u(k)+ u,.,3(k)+ u1,(k) Equivalent rule input Ueq(k) = bl(k) -al(k)) v01'(k)+ (s -a2(k))v; (k -i)} acquired from a conditional expression of Fc(k+1)=cr(k) j Arrival rule input cr(k) Adaptation rule input k In this case, lJeq(k) denotes equivalent rule input, Urch(k) denotes arrival rule input, U8(k) denotes adaptation rule input, and they are calculated in the following expression. Besides, in this case, V0'(k) and V01(k-1) denote errors of the model, V01'(k) denotes deviation between predicted air-fuel ratio at the time of k and a desired value, and V0'(k-1) denotes deviation between predicted air-fuel ratio before the time of k by one unit time (a fixed time cycle) and a desired value.

Krch and Kaap denote feedback gain and S denotes a switching function setting parameter.

The identifier 106 compensates predictive precision in the predictor 102 by correcting a model parameter of the predictor 102. Besides, the identifier adjusts parameters al(k), a2(k) and bl(k) in the first sliding mode controller 104 so as to minimize the deviation of V01'(k+1) calculated in the following model expression by adjusting the convergence velocity (feedback gain) to the switching line of o(k) according to the error of the model.

[Mathematical expression 3] v0,'(k+1) a1Q)xV/(k)+a2(k)xV0'(k_1)+b1(k)xØ,,7'(k_d) As a result, correlation between air-fuel ratio before catalysis cP, and V0 for target air-fuel ratio t0 is corrected by correcting the model parameters in the predictive expression.

The air-fuel ratio reference value calculating unit 108 calculates the air-fuel ratio reference value of the engine 28 specified based upon adaptation rule input U8d(k) from the first sliding mode controller 104 using a preset map.

Output from the first sliding mode controller 104, that is, control input Uop (DKO2OP(k)) to the exhaust system, is added to the air-fuel ratio reference value from the air-fuel ratio reference value calculating unit 108 in an adder 112, and the target air-fuel ratio K02(k) is acquired. The target air-fuel ratio KO2(k) is input to an adaptive controller 114 at the next stage. The adaptive controller 114 is a recurrence formula type controller that adaptively calculates a feedback correction factor KAF based upon air-fuel ratio t (AIF(k)) detected by the LAF sensor 110 and target air-fuel ratio t (K02(k)) in consideration of a change of operational status of the engine 28 and dynamic variation such as the variation of a property.

The basic fuel injection quantity calculating unit 116 acquires a reference fuel injection quantity specified based upon engine speed NE, a throttle opening TH and intake air pressure PB using the preset basic fuel injection map 118, and calculates basic fuel injection quantity TIMB by correcting the reference fuel injection quantity according to the effective opening area of the throttle valve. The basic fuel injection quantity TIMB is supplied to a multiplier 120, is corrected by a feedback correction factor KAF from the adaptive controller 114 and an environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others, and is output as fuel injection time Tout.

The main body 300 of the air-fuel ratio controller in the comparative example has a problem in that the expensive LAF sensor 110 is used, and so it cannot be applied to a motorcycle or other vehicle that has a limit in terms of the cost reduction of the system and space for arrangement. Then, in the main body 300 of the air-fuel ratio controller in the comparative example, as air-fuel ratio before catalysis 0 cannot be measured when no LAF sensor 110 is installed upstream of the catalytic device 50, the predictive precision of air-fuel ratio after catalysis may be deteriorated, the correction factor cannot be properly calculated when a great lag with theoretical air-fuel ratio is caused because of the dispersion of characteristics, the age deterioration and others of the engine 28 and the fuel injection valve 40, and it is estimated that it is difficult to optimize air-fuel ratio.

Thus, the main body 100 of the air-fuel ratio controller in this embodiment is provided with an adaptive model corrector 122 (adaptive model correcting means) that superimposes a second correction factor KTIMB on the first correction factor DKO2OP(k) so as to make a predictive error ERPRE(k) which is deviation between real air-fuel ratio SVO2(k) and predicted air-fuel ratio DVPRE(k-dt) zero, a second sliding mode/RID controller 124 that feedbacks so that an error between the real air-fuel ratio SVO2(k) and a preset desired value is made zero when predictive precision in the predictor 102 is deteriorated, a controller 126 that controls at least the first sliding mode controller 104 and the adaptive model corrector 122, and a switching arrangement 128 that switches between output on the side of the first sliding mode controller 104 and output on the side of the second sliding mode/RID controller 124 based upon an instruction from the controller 126 as shown in Fig. 4.

The switching arrangement 128 normally selects output on the side of the first sliding mode controller 104, and switches to output on the side of the second sliding mode/RID controller 124 based upon a switching instruction signal Sd from the controller 126.

The second sliding mode/RID controller 124 is provided with a second sliding mode control unit and a RID control unit, and one control unit is selected according to an instruction from the controller 126. In normal operation (except for a special situation such as the injection of secondary air, fuel cut control and deceleration leaning), one of the second sliding mode control unit or the RID control unit is selected according to the difference between an average of the transfer of the predictive error ERPRE(k) after filtering and a preset threshold. When the difference is greater than a preset selection reference value, the PID control unit is selected, and when the difference is equal to or smaller than the selection reference value, the second sliding mode control unit is selected. The selection reference value may also be determined as follows. That is, a degree of convergence (convergence time and others) on the difference by the second sliding mode control unit is grasped in an experiment and simulation beforehand; further, a range of the difference in which the degree of convergence has no effect on another control system is grasped, and the selection reference value is determined in the grasped range of the difference.

As the second sliding mode control unit is selected when the difference is equal to or smaller than the selection reference value and feedback control is made so as to make an error between real air-fuel ratio and a preset desired value zero, predictive precision can be secured at an early stage. Especially, as the PID control unit is selected when the difference exceeds the selection reference value, time until predictive precision is secured can be reduced more even if the difference is great.

Besides, the controller 126 selects the PID control unit based upon the termination of secondary air injection or the termination of fuel cut control or the input of a control resumption signal Si output from the resumption determining unit 1014 based upon the termination of deceleration leaning. Thus, even if the difference is great, time until predictive precision is secured can be more reduced.

That is, interrupted sliding mode control in the main body 100 of the air-fuel ratio controller can be restored at an early stage and emission performance can be maintained at a high level.

Further, the main body 100 of the air-fuel ratio controller is provided with a timing device 130 that delays predicted air4uel ratio DVPRE(k) from the predictor 102 by dead time dt, and a subtractor 132 that differentiates output DVPRE(k-dt) from the timing device 130 and real air-fuel ratio SVO2(k) from the oxygen sensor 52 to be predictive error ERPRE(k), and the predictive error ERPRE(k) from the subtractor 132 is supplied to the adaptive model corrector 122. 1' is incremented to the second correction factor KTIMB output from the adaptive model corrector 122 by an adder 134. The output of the adder 134 and the target air-fuel ratio K02(k) are multiplied by a multiplier 136, and the multiplied value is output as correction air-fuel ratio acquired by superimposing the second correction factor KTIMB on the target air-fuel ratio K02(k). The air-fuel ratio reference value is subtracted from the correction air-fuel ratio by a subtractor 138, and the subtracted value is input to the predictor 102 and the identifier 106.

The adaptive model corrector 122 is provided with a filtering unit 144 that first applies various filtering to a predictive error ERPRE(k)J a predictive precision determining unit 146 (predictive precision determining means) that determines predictive precision based upon the filtered predictive error ERPREQ), a first corrected quantity arithmetic unit 148a and a first correction factor arithmetic unit 1 50a respectively corresponding to the first basic fuel injection map 11 8a, and a second corrected quantity arithmetic unit 148b and a second correction factor arithmetic unit 15Db respectively corresponding to the second basic fuel injection map 11 8b as shown in Fig. 8.

The first corrected quantity arithmetic unit 148a feedbacks predictive error corrected quantity Bth(i, j) so that a predictive error ERFRE(k) in which a weight component based upon engine speed NE and a throttle opening TH is reflected is made zero at a fixed time cycle when the first basic fuel injection map 1 18a is selected by the map selector 142. For example, operation is started before time k by dead time dt, that is, at time (k-dt), the operation is performed at the fixed time cycle, and at the time k, predictive error corrected quantity OthlJ(k) is output.

Specifically, as shown in Fig. 9, the first corrected quantity arithmetic unit is provided with a weighting unit 152 that superimposes a first weighting component WSO2S(k) in which sensitivity for air-fuel ratio detected by the oxygen sensor 52 is reflected, a second weighting component Wtha(k-dt) in which the variation of values of the first basic fuel injection map I ISa for the variation of engine speed NE and a throttle opening TH is reflected, and a third weighting component WthlJ(k-dt) in which the first basic fuel injection map 11 Ba is made to correspond to plural areas sorted based upon the engine speed NE and the throttle opening TH, on the predictive error ERPRE(IK) at the fixed time cycle and acquires a correction model error EwlJ(k) corresponding to the plural areas, and a sliding mode control unit 154 that feedbacks respective predictive error corrected quantity OthlJ(k) corresponding to the plural areas so that correction model errors EwIJ(k) corresponding to the plural areas are made zero at the fixed time cycle.

To explain the first weighting component WSO2S(k), the output V0 of the oxygen sensor 52 has a nonlinear property for air-fuel ratio A/F as shown in Fig. -19- 1 DA. In areas Za and Zc, even if air-fuel ratio varies, the output V0 of the oxygen sensor 52 hardly varies. In the meantime, in an area Zb, the output V0 of the oxygen sensor 52 varies greatly according to a slight variation of air-fuel ratio NE.

In Fig. bA, a full line La shows a property of a new catalyst and a broken line Lb shows a property of the catalyst after age deterioration. When such properties are reflected in the correction model error EwIJ(k) as they are, there is a problem that a rapid change in the area Zb is input to the sliding mode control unit 154 and it takes much time to make the correction model error EwIJ(k) zero. Then, as shown in Fig. lOB, a value of weighting is reduced so that the rapid change is softened in the areaZb.

To explain the second weighting component Wtha, as to an output value SVO2 of the oxygen sensor 52, the greater the inclination of basic fuel injection quantity Tibs for the variation of a throttle opening TH is, the higher the probability that a predictive error ERPRE is caused by an error in the detection of the throttle opening TH is, as shown in Fig. hA. When the error is caused in the detection and a reference point of a value of basic fuel injection quantity in the basic fuel injection map shifts, the variation of air-fuel ratio increases as "a value acquired by dividing variation accompanied with the shift by the reference point" increases. Then, "a value acquired by dividing the inclination of the basic fuel injection quantity Tibs for the variation of a throttle opening TH by a value of the basic fuel injection quantity Tibs" is set as each engine speed NE. As a result, as shown in Fig. 113, when engine speed NE is high, the second weighting component Wtha is substantially the same even if a throttle opening TH is fully closed or is fully open, however, as engine speed NE gets low, the second weighting component Wtha increases as the throttle opening TH decreases.

The third weighting component WthLJ is a function such that a weighting value linearly decreases toward an adjacent vertex from each vertex of engine speed NE in the cases of 1000, 2000, 3000, 4500 (rpm) as to weighting functions for their engine speed as shown in Fig. 1 2A, for example. However, in Fig. 1 2A, when engine speed is 1000 rpm or less and is 4500 rpm or more, the weighting value is fixed. Similarly, as shown in Fig. 12B, weighting functions when a throttle opening TH is 10, 3°. 5°, 8° are such that a weighting value linearly decreases toward an adjacent vertex from each vertex of these throttle openings TH.

However, in Fig. 12B, when the throttle opening is 1° or less and is 8° or more, the weighting value is fixed.

-20 -The third weighting component WthiJ is acquired by multiplying weighting Wthn(i) in engine speed NE and weighting Wtht(j) in a throttle opening TH.

The sliding mode control unit 154 feedbacks predictive error corrected quantity GthlJ for an area in which the third weighting component WthlJ is larger than zero so that a correction model error EwIJ is zero and keeps the predictive error corrected quantity 8thlJ unupdated by making control input zero for an area in which the third weighting component WthlJ is zero.

The first correction factor arithmetic unit 1 50a acquires correction factors KTITHIJ corresponding to plural areas by superimposing the third weighting components WthlJ corresponding to the plural areas on predictive error corrected quantity BthlJ(k) corresponding to the plural areas at predetermined timing, adds all the correction factors, and acquires a second correction factor KTIMB. In this case, as all the correction factors are added, the third weighting component WthlJ shows weighting according to a position of the following point in an area including the point determined based upon engine speed NE and a throttle opening TH in the first basic fuel injection map I 18a. Accordingly, as shown in Fig. 13, plural areas are made by lattice points formed by 1000, 2000, 3000, 4500 (rpm) as engine speed and 1°, 30, 5°, 8° as the throttle opening and when a point determined by input engine speed NE and an input throttle opening TH is a point A, a correction factor corresponding to the point A is interpolated by correction factors at four points around the point A. In the meantime, the second corrected quantity arithmetic unit 148b feedbacks predictive error corrected quantity at the fixed time cycle so that a predictive error in which a weight component based upon engine speed NE and intake air pressure PB is reflected is zero when the second basic fuel injection map 11 8b is selected by the map selector 142. For example, before time k by dead time dt, that is, at time (k-dt), operation is started, the operation is performed at the fixed time cycle, and at the time k, predictive error corrected quantity BpblJ(k) is output.

As the specific configuration of the second corrected quantity arithmetic unit 148b is substantially the same as that of the first corrected quantity arithmetic unit 148a

shown in Fig. 9, the description is omitted.

The second correction factor arithmetic unit 15Db acquires correction factors corresponding to plural areas by superimposing the third weighting components corresponding to the plural areas on predictive error corrected quantity @pblJ(k) corresponding to the plural areas at predetermined timing, adds all the correction -21 -factors, and acquires a second correction factor KTIMB. As the specific configuration of the second correction factor arithmetic unit 1 SOb is also substantially the same as that of the first correction factor arithmetic unit 1 50a

shown in Fig. 9, the description is omitted.

The predictive precision determining unit 146 judges that predictive precision is deteriorated when a state in which the average of the transfer of the predictive error ERPRE(k) after filtering is larger than a preset threshold continues more than a set frequency, and outputs a predictive precision deterioration signal Sb. The predictive precision determining unit judges that predictive precision is secured when a state in which the average of the transfer of the predictive error after filtering is equal to or smaller than the preset threshold continues more than the set frequency, and outputs a predictive precision securement signal Sc. The predictive precision deterioration signal Sb and the predictive precision securement signal Sc are supplied to the controller 126.

The controller 126 temporarily halts processing by the first sliding mode controller 104 based on input of the predictive precision deterioration signal Sb (see Fig. 8) as shown in Fig. 4, temporarily halts the identifier 106, and reduces a cycle for activating the adaptive model corrector 122 the while. That is, a fixed time cycle for activating the first corrected quantity arithmetic unit 148a and the second corrected quantity arithmetic unit 148b is reduced.

Besides, the controller 126 outputs a switching instruction signal Sd to the switching arrangement 128 based on input of the predictive precision deterioration signal Sb. The switching arrangement 128 switches to output on the side of the second sliding mode/FID controller 124 based upon the input of the switching instruction signal Sd. The controller 126 also instructs the second sliding mode/PID controller 124 to start processing based upon the input of the predictive precision deterioration signal Sb. In this case, predicted air-fuel ratio from the predictor 102 is not used. In addition, the controller 126 selects either of the second sliding mode control unit or the PID control unit according to difference between the average of the transfer of the predictive error ERPRE(k) after filtering and the preset threshold as described above. When the difference is greater than the preset selection reference value, the RID control unit is selected, and when the difference is equal to or smaller than the selection reference value, the second sliding mode control unit is selected. Especially, the controller 126 forcibly selects the PID control unit based upon the input of a control resumption signal Si output from the resumption -22 -determining unit 1014 according to the termination of secondary air injection or the termination of fuel cut control or the termination of deceleration leaning. The second sliding mode/Plo controller 124 feedbacks so that an error between real air-fuel ratio (SVO2) and a preset desired value (for example, a fixed value showing an area of a stoichiometric amount of air) is zero. Output from the second sliding mode/PID controller 124 is supplied to the multiplier 120 via the switching arrangement 128. The basic fuel injection quantity calculating unit 116 calculates reference injection quantity specified based upon engine speed NE, a throttle opening TH and intake air pressure PB using the preset basic fuel injection map or the basic fuel injection map selected by the map selector 142, and calculates basic fuel injection quantity TIMB by correcting the reference fuel injection quantity according to the effective opening area of the throttle valve 38. The basic fuel injection quantity TIMB is corrected based upon output (target air-fuel ratio K02(k)) from the switching arrangement 128 and the environmental correction factor KECO determined based upon coolant temperature, intake air temperature, atmospheric pressure and others, and is output as fuel injection time Tout.

The temporary halt of the first sliding mode controller 104 and the identifier 106 may be also released by the output of a predictive precision securement signal Sc by the predictive precision determining unit 146, and may be also released after a predetermined time (time in which the securement of predictive precision is expected) elapses. In this case, as the supply of a switching instruction signal Sd from the controller 126 to the switching arrangement 128 is stopped, the switching arrangement 128 switches to output on the side of the first sliding mode controller 104. Besides, the controller 126 restores the fixed time cycle for activating the first corrected quantity arithmetic unit 148a and the second corrected quantity arithmetic unit 148b in the adaptive model corrector 122. Moreover, the controller 126 releases the temporary halt of the first sliding mode controller 104 and initializes a parameter of the identifier 106.

As described above, in the air-fuel ratio control system 10 (the air-fuel ratio controller 1006) in this embodiment, a value acquired by subtracting the air-fuel ratio reference value from a value acquired by superimposing the second correction factor KTIMB on the target air-fuel ratio KO2(k) is input to the predictor 102 and the identifier 106. That is, as predicted air-fuel ratio DVPRE(k) after dead time dt is output based upon the real air-fuel ratio SVO2(k) from the predictor 102, difference between the real air-fuel ratio SVO2(k) and the predicted air-fuel ratio DVPRE(k-dt) -23 -respectively temporally matched is input to the adaptive model corrector 122 as a predictive error ERPRE(k) by delaying the predicted air-fuel ratio DVPRE(k) by the dead time dt. The adaptive model corrector 122 superimposes the second correction factor KTIMB on the first correction factor DKO2OP(k) so that the predictive error ERPRE(k) is zero, the value is input to the predictor 102 and the identifier 106, and the value is reflected in processing in the predictor 102.

That is, the first correction factor DKO2OP(k) acquired by feedbacking so that deviation between predicted air-fuel ratio DVPRE(k) from the predictor 102 and target air-fuel ratio K02(k) is zero and the second correction factor KTIMB acquired by feedbacking so that the predictive error ERPRE(k) is zero are superimposed and its value is input to the predictor 102. Therefore, as the predictive precision of air-fuel ratio downstream of the catalytic device 50 can be secured even if the LAF sensor 110 heretofore installed upstream of the catalytic device 50 is removed, the air-fuel ratio of exhaust gas downstream of the catalytic device 50 can be converged on an optimum value, and as a result, the decontamination performance of the catalytic device 50 can be secured. Besides, even if the dispersion of the properties of the engine 28, the fuel injection valve 40 and others and an error of air-fuel ratio due to age deterioration and others are caused, the deterioration of predictive precision can be avoided. As described above, as the LAF sensor 110 can be omitted, a harness and an interface circuit of the ECU 62 respectively related to the LAF sensor 110 can be omitted, the cost of the system and the space for arrangement can be reduced, and the air-fuel ratio control system according to the present invention can be also readily applied to a vehicle having only little space for arrangement such as a motorcycle 12.

Normally, the LAF sensor 110 has to be maintained at a fixed temperature by a heater so as to secure satisfactory operating characteristics; however, in this embodiment, as the heater for the LAF sensor 110 can be also omitted, power consumption can be reduced and fuel economy can be enhanced.

Further, in this embodiment, as processing by the first sliding mode controller 104 is temporarily halted based upon the input of a predictive precision deterioration signal Sb, the constraint of a cycle in the adaptive model corrector 122 can be removed and the fixed time cycle for activating the first corrected quantity arithmetic unit 148a and the second corrected quantity arithmetic unit 148b can be reduced. Therefore, time until the predictive error ERPRE(k) is settled to zero can be reduced.

-24 -Furthermore, as processing in the second sliding mode/PID controller 124 is started based on input of a predictive precision deterioration signal Sb without using predicted air-fuel ratio DVPRE(k) from the predictor 102, fuel injection quantity is controlled so that real air-fuel ratio 5V02(k) approaches a predetermined desired value and predictive precision can be secured in short time.

In the following cases (a) to (c), air-fuel ratio downstream of the catalytic device 50 can be also converged on an optimum value at an early stage by such processing operation, and the deterioration of emission caused by the continuation of a state in which the air-fuel ratio of exhaust gas downstream of the catalytic device 50 cannot be converged on the optimum value can be avoided.

(a) The case that as an air-fuel ratioerror is caused due to the dispersion of the properties of the engine 28, the fuel injection valve 40 and others and age deterioration, a great predictive error that exceeds a range which can be adjusted by the predictor 102 is identified by the identifier 106 (b) The case that dynamic characteristics to be controlled rapidly vary (the variation in volume of exhaust gas by a change of an operating condition, the use of ethanol mixed fuel and others) (c) The case that the oxygen sensor 52 is located in a dead zone (an area in which the output of the oxygen sensor 52 hardly varies even if air4uel ratio varies) Furthermore, in this embodiment, as at a stage at which it is determined that predictive precision is secured, the cycle for activating the adaptive model corrector 122 is restored and the temporary halt of the first sliding mode controller 104 is released, the generation of the first correction factor DKO2OP(k) by the first sliding mode controller 104 is resumed at a stage at which predictive precision is secured, the predictive precision is further enhanced, and the optimization of air-fuel ratio downstream of the catalytic device 50 can be accelerated.

In this case, as parameters of the identifier 106 are initialized, the securement of predictive precision can be maintained by using initial values as identification parameters when predictive precision is secured or at a stage at which the securement of predictive precision is expected without using the identification parameters when predictive precision is deteriorated, and the optimization of air-fuel ratio downstream of the catalytic device 50 can be accelerated.

Furthermore, as the first corrected quantity arithmetic unit 148a of the adaptive model corrector 122 feedbacks predictive error corrected quantity OthlJ at the fixed time cycle so that a predictive error in which a weight component based upon engine speed NE and a throttle opening TH for the first basic fuel injection map 118a is reflected is zero and the second correction factor K11MB is calculated based upon the predictive error corrected quantity OthlJ at predetermined timing in the first correction factor arithmetic unit 150a, air-fuel ratio downstream of the catalytic device 50 can be optimized even if the LAF sensor 110 upstream of the catalytic device 50 is removed.

Especially, as predictive error corrected quantity BthlJ corresponding to plural area is feedbacked at the fixed time cycle so that the respective predictive error corrected quantity 8thlJ corresponding to the plural areas sorted in the first basic fuel injection map 118a based upon engine speed NE and a throttle opening TH is zero, correction factors KTITHIJ corresponding to the plural areas are calculated based upon the predictive error corrected quantity 6thlJ corresponding to the plural areas at predetermined timing, all the correction factors are added and the second correction factor KTIMB is acquired, the second correction factor KTIMB is a value acquired by correcting used map values using the correction factors KTITHIJ of the plural areas so that a predictive error ERRRE(k) is zero.

Accordingly, when the second correction factor KTIMB having such a characteristic is superimposed on the first correction factor DKO2OP, air-fuel ratio downstream of the catalytic device 50 can be optimized.

This is also similar as to the second corrected quantity arithmetic unit 148a and the second correction factor arithmetic unit 1 50b respectively corresponding to the second basic fuel injection map 11 8b.

In the above-mentioned example, the processing of the first sliding mode controller 104 and the identifier 106 is temporarily halted at the stage at which the deterioration of predictive precision is determined and the switching arrangement 128 switches to output from the second sliding mode/RID controller 124; however, for example, the processing of the first sliding mode controller 104 and the identifier 106 is temporarily halted based upon the input of a signal Se telling that an air-fuel ratio feedback condition from the ECU 62 comes into effect and the switching arrangement 128 may also switch to output from the second sliding mode/RID controller 124. In this case, when a predictive error is caused due to an operating condition or similar before the air-fuel ratio feedback condition comes into effect, the predictive error can be eliminated at an initial stage after the air-fuel ratio feedback condition comes into effect. After a predetermined time (a time in which the securement of predictive precision is expected) elapses after the input of the signal Se telling that the air-fuel ratio feedback condition comes into effect, the temporary halt may be also released.

Furthermore, as the cycle for activating the adaptive model corrector 122 is restored at a stage at which the preset time (the predetermined time) elapses after the deterioration of predictive precision is determined and the generation of the first correction factor DKO2OP(k) by the first sliding mode controller 104 is resumed at a stage at which the predictive precision is secured after the predetermined time elapses once or more when the temporary halt of the first sliding mode controller 104 is released, the predictive precision is further enhanced and the optimization of air-fuel ratio downstream of the catalytic device 50 can be accelerated. Predictive precision is secured by setting predetermined time for one tirrie as a time in which the securement of the predictive precision is expected when predetermined time for at least two times elapses.

Furthermore, when operation gain according to the correction factor of the adaptive model corrector 122 is set to be larger than normal gain, the similar effect can be also acquired in place of temporarily halting the processing of the first sliding mode controller 104 and the identifier 106 and reducing the cycle for activating the adaptive model corrector 122.

Next, the alternative embodiments of the above-mentioned main body 100 of the air-fuel ratio controller will be described referring to Figs. 14 to 18.

A main body boa of an air-fuel ratio controller in a first alternative embodiment as shown in Fig. 14 has a substantially similar configuration to that of the main body 100 of the air-fuel ratio controller; however, the main body lOOa is different in that target air-fuel ratio K02(k) from an adder 112 and a second correction factor KTIMB from an adaptive model corrector 122 are added in an adder 160. In this case, a value acquired by adding a first correction factor DKO2OP(k) and the second correction factor KTIMB is also input to a predictor 102 and an identifier 106. Accordingly, a similar effect to the main body 100 of the air-fuel ratio control system can be acquired.

A main body lOOb of an air-fuel ratio controller in a second alternative embodiment as shown in Fig. 15 has a substantially similar configuration to that of the main body 100 of the air-fuel ratio controller; however, the main body lOOb in the second variation is different in that target air-fuel ratio K02(k) is acquired by multiplying a value (KO2OP(k)) acquired by adding output from an adder 112 (a value (KO2OP(k) acquired by adding a first correction factor DKO2OP(k) from a -27 -first sliding mode controller 104 and an air4uel ratio reference value from an air-fuel ratio reference value calculating unit 108) and output (a value acquired by incrementing a second correction factor KTIMB by 1) from an adder 134 in an adder 162, without reflecting the second correction factor KTIMB in a predictor 102 and an identifier 106. In this case, as the second correction factor KTIMB is reflected in the output of a basic fuel injection quantity calculating unit 116, a similar effect to the main body 100 of the air-fuel ratio controller in this embodiment can be acquired.

A main body lOOc of an air-fuel ratio controller in a third alternative embodiment as shown in Fig. 16 has a substantially similar configuration to that of the main body 1 OOb of the air4uel ratio controller in the second alternative embodiment; however, the main body lOOc is different in that target air-fuel ratio K02(k) is acquired by adding output KO2SL(k) from an adder 112 and a second correction factor KTIMB from an adaptive model corrector 122 in an adder 164. In this case, as the second correction factor KTIMB is reflected in the output of a basic injection quantity calculating unit 116, a similar effect to the main body 100 of the air-fuel ratio controller in this embodiment can be also acquired.

A main body lOUd of an air-fuel ratio controller in a fourth alternative embodiment as shown in Fig. 17 has a substantially similar configuration to that of the main body 100 of the air-fuel ratio controller in this embodiment; however, a first switching arrangement 128a is installed between a predictor 102 and a first sliding mode controller 104, and a second switching arrangement 128b is installed on the output side of the first sliding mode controller 104. Normally, the predictor 102 is selected by the first switching arrangement 1 28a and output to the adder 112 is selected by the second switching arrangement 128b. Hereby, as predicted air-fuel ratio DVPRE(k) from the predictor 102 is input to the first sliding mode controller 104, a first correction factor DKO2OP(k) from the first sliding mode controller 104 is added to an air-fuel ratio reference value in the adder 112 and is output as target air-fuel ratio K02(k). In the meantime, when a switching instruction signal Sd is output from a controller 126, the first switching arrangement 1 28a selects the input of real air-fuel ratio SVO2(k) and the second switching arrangement 128b selects output to a multiplier 120. Hereby, the first sliding mode controller 104 feedbacks so that an error between the real air-fuel ratio (SVO2) and a preset desired value (for example, a fixed value showing an area of a stoichiometric amount of air) is zero. This output from the first sliding mode controller 104 is supplied to the multiplier 120 via the second switching arrangement 128b. Accordingly, in the -28 -tourth alternative embodiment, a similar effect to the main body 100 of the air-fuel ratio controller in this embodiment can be also acquired. Especially, according to the fourth alternative embodiment, a second sliding mode/PID controller 124 can be omitted and the configuration can be simplified.

A main body 100e of an air-fuel ratio controller in a fifth alternative embodiment as shown in Fig. 18 has substantially the same configuration as that of the main body 100 of the air-fuel ratio controller in this embodiment; however, the main body 1 OOe is different in that an LAF sensor 110 is installed upstream of a catalytic device 50, and the detected air-fuel ratio A/F(k) from the LAF sensor 110 is utilized. In this case, an adaptive controller 114 is installed between a switching arrangement 128 and a multiplier 120.

The deterioration of predictive precision caused by the shortage of the precision of a basic fuel injection map can be settled at an early stage by utilizing the LAF sensor 110. Naturally, as the main body 100 of the air-fuel ratio controller in this embodiment, the main body lOOa.of the air-fuel ratio controller in the first alternative embodiment to the main body lOUd of the air-fuel ratio controller in the fourth alternative embodiment, as the first correction factor DKO2OP(k) from the first sliding mode controller 104 and the second correction factor KTIMB from the adaptive model corrector 122 are superimposed and are input to the predictor 102 and the identifier 106, the deterioration of predictive precision can be settled at an early stage, however, the deterioration of predictive precision caused by the shortage of the precision of the basic fuel injection map 118 can be settled at an early stage by utilizing the LAF sensor 110.

The main body 100 of the air-fuel ratio controller in this embodiment and the various alternatives can be applied not only to the air-fuel ratio control of an engine, but also to a control system in which delay in transportation since control input till output is long and a predictor 102 is required to be configured.

Next, the processing operation of the first air intake corresponding part 1008A will be described with reference to a flowchart shown in Fig. 19.

First, in a step Si shown in Fig. 19, the air-fuel ratio control halt requesting unit 1010 determines whether the injection of secondary air is started or not. This determination is made depending upon whether an Al initiation signal Sais is input from the Al controller 1002 or not.

When the Al initiation signal Sais is input, the process proceeds to the next step S2, and the air-fuel ratio control halt requesting unit 1010 outputs a halt -29 -requesting signal S9 to the main body 100 of the air4uel ratio controller. The main body 100 of the air-fuel ratio controller temporarily halts air-fuel ratio control based upon the input of the halt requesting signal Sg.

Afterward, in a step S3, the rich spike controller 1012 waits for the termination of the injection of secondary air. That is, the rich spike controller waits until an Al termination signal Saie is input from the Ai controller 1002.

In the meantime, if it is determined in the step Si that no Al initiation signal Sais is input, the air-fuel ratio control halt requesting unit 1010 determines whether FC control is started or not in a step 54. This determination is made depending upon whether an FC control initiation signal Sfcs is input from the FC controller 1004 or not.

When the FC control initiation signal Sfcs is input, the process proceeds to the next step S5 and the air-fuel ratio control halt requesting unit 1010 outputs a halt requesting signal Sg to the main body 100 of the air-fuel ratio controller. The main body 100 of the air-fuel ratio controller temporarily halts air-fuel ratio control based upon the input of the halt requesting signal 5g.

Afterward, in a step 56, the rich spike controller loi2waitsforthe termination of the FC control. That is, the rich spike controller waits for the input of an FC control termination signal Sfce from the FC controller 1004.

If it is determined in the step 54, that no FC control initiation signal Sfcs is input, the air-fuel ratio control halt requesting unit 1010 determines whether deceleration leaning is started or not in a step Si. This determination is made depending upon whether a deceleration leaning initiation signal Srss is input from the deceleration leaning controller 1005 or not.

When the deceleration leaning initiation signal Srss is input, the process proceeds to the next step S8 and the air-fuel ratio control halt requesting unit 1010 outputs a halt request signal Sg to the main body 100 of the air-fuel ratio controller.

The main body 100 of the air4uel ratio controller temporarily halts air4uel ratio control based upon the input of the halt request signal Sg.

Afterward, in a step S9, the rich spike controller 1012 waits for the termination of deceleration leaning. That is, the rich spike controller waits for the input of a deceleration leaning termination signal Srse from the deceleration leaning controller 1005.

When the Al termination signal Saie is input in the step S3 or when the FC control termination signal Sfce is input in the step 56 or when the deceleration -30 -leaning termination signal Srse is input in the step 39, the process proceeds to the next step 310, the rich spike controller 1012 controls the fuel injection valve 40, and the rich spike controller applies rich spike control to the combustion chamber of the engine 28. In the rich spike control, the supplied quantity of fuel according to an output value (SVO2) of the oxygen sensor 52 at the current time is supplied to the combustion chamber of the engine 28 in unit time, referring to the rich spike map 1016. The rich spike control is made until the output value (SVO2) of the oxygen sensor 52 transfers to the rich side.

In a step Si 1, the resumption determining unit 1014 determines whether the output value (SVO2) of the oxygen sensor 52 has transferred to the rich side or not, and outputs a control resumption signal Si to the main body 100 of the air-fuel ratio controller at a stage at which the output value (SVO2) of the oxygen sensor 52 transfers on the rich side.

In a step S12, the main body 100 of the air-fuel ratio controller resumes air-fuel ratio control based upon the input of the control resumption signal Si.

The processing in steps Si to 312 will be described based upon a timing chart shown in Fig. 20. Fig. 20 shows an execution period Ta of the injection of secondary air or FC control or deceleration leaning, a rich spike control period Tb (a residual oxygen processing period of the catalytic device 50), the variation of fuel injection quantity per unit time in rich spike control, the variation (as a full line) of the quantity of oxygen stored in the catalytic device 50 and the variation (as a broken line) of the output value (SVO2) of the oxygen sensor.

First, at a time point ti, when the injection of secondary air (Al) or FC control or deceleration leaning is started, the real air-fuel ratio SVO2 shown by an output value of the oxygen sensor 52 transfers to the lean side and as a result, the quantity of oxygen stored in the catalytic device 50 gradually increases.

At a stage at which the quantity of oxygen stored in the catalyst reaches a maximum, the injection of secondary air (Al) or FC control or deceleration leaning is finished and at a termination time point t2, rich spike control, that is, the residual oxygen processing of the catalytic device 50, is performed. In the rich spike control, between the time point t2 and a time point t3, normally, fuel at a level to provide a very rich air-fuel ratio for a stoichiometric amount of air in a combustible area is injected (a high-concentration injection period TM). Accordingly, in the high-concentration injection period Tbl, the quantity of oxygen stored in the catalytic device 50 rapidly decreases. At a stage at which an output value SVO2 of the -31 -oxygen sensor 52 starts to gradually increase toward a stoichiometric level, injection quantity per unit time is gradually reduced. Between the time point t3 and a time point t4, normally, fuel at a level to provide a richer air-fuel ratio than the stoichiometric level in a range that has no effect upon output is injected (a low-concentration injection period Tb2). Accordingly, in the low-concentration injection period Tb2, the quantity of oxygen stored in the catalytic device 50 decreases more slowly than that in the high-concentration injection period Tbl. At a stage at which the output value 3V02 of the oxygen sensor 52 gradually approaches the stoichiometric level, fuel injection quantity per the unit time is gradually reduced.

At a stage at which an output value SVO2 of the oxygen sensor 52 transfers to the rich side, rich spike control is finished and feedback control in the main body of the air-fuel ratio controller is resumed.

The predictive precision determining unit 146 (see Fig. 8) in the main body of the air-fuel ratio controller that resumes control determines whether predictive precision by the predictor 102 is deteriorated or not in a step S13 shown in Fig. 19. That is, the predictive precision determining unit determines whether a state in which an average of the transfer of the predictive error ERPRE(k) after filtering is larger than the preset threshold continues more than the set frequency or not. When predictive precision by the predictor 102 is deteriorated, the process proceeds to a step S14, the controller 126 temporarily halts control in the first sliding mode controller 104, and the controller selects the PID control unit in the second sliding mode/PID controller 124. At this time, the switching arrangement 128 switches to output on the side of the second sliding mode/PID controller 124 according to the supply of a switching instruction signal Sd from the controller 126.

The PID control unit feedbacks so that an error between real air-fuel ratio (SVO2) and the preset desired value is zero. Hereby, output from the second sliding mode/PID controller 124 is supplied to the multiplier 120 via the switching arrangement 128. Hereby, the basic fuel injection quantity TIMB is corrected with output from the second sliding mode/PID controller 124 (in this case, the PID control unit) and the environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others, is output as fuel injection time Tout, and real air-fuel ratio SVO2 varies toward the desired value.

In the step S13, at a stage at which it is determined that predictive precision is secured, the process proceeds to a step 515 and the controller 126 resumes control in the first sliding mode controller 104. That is, the controller releases the -32 -temporary halt of the first sliding mode controller 104 and initializes the parameter of the identifier 106. Besides, the controller halts the supply of a switching instruction signal Sd to the switching arrangement 128. The switching arrangement 128 switches to output on the side of the first sliding mode controller 104. Hereby, the basic fuel injection quantity TIMB is corrected with output K02(k) from the first sliding mode controller 104 and the environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others and is output as fuel injection time Tout.

Afterward, at a stage at which feedback control in the first sliding mode controller 104 is resumed in the step 515 or when it is determined that deceleration leaning is not started in the step S7 (that is, when the injection of secondary air or fuel cut control or deceleration leaning is not made), the process proceeds to a step S16 and it is determined whether a request for the termination (the disconnection of power supply, a maintenance request and others) of the air-fuel ratio control system 10 is made or not. When no request for termination is made, processing after the step Si is repeated and at a stage at which a request for termination is made, processing operation in the air-fuel ratio control system lOis finished.

As described above, in the air-fuel ratio control system 10 in this embodiment, even if it is a system in which the secondary air pulse induction system 1000 is installed, the quantity of oxygen stored in the catalyst by the injection of secondary air can be reduced at an early stage by interrupting sliding mode control in the main body 100 of the air-fuel ratio controller after the injection of secondary air and executing rich injection control at a stage at which the injection of secondary air is finished. As a result, the interrupted sliding mode control is restored at an early stage and emission performance can be kept high.

When the halt of fuel injection is controlled by the FC controller 1004 by closing the throttle opening, the quantity of oxygen stored in the catalytic device 50 increases because air containing oxygen itself flows into the catalyst. However, in the air-fuel ratio control system 10 in this embodiment, as sliding mode control in the main body 100 of the air-fuel ratio controller is interrupted after fuel injection halt control by the FC controller 1004 and rich injection control is executed at a stage at which the fuel injection halt control is finished, the quantity of oxygen stored in the catalytic device 50 by the intake of air containing oxygen according to the fuel injection halt control can be reduced at an early stage. As a result, the interrupted sliding mode control can be restored at an early stage and emission performance can be kept high.

Besides, as air containing oxygen itself flows into the catalyst as in the case of the fuel cut control when deceleration leaning is started, the quantity of oxygen stored in the catalyst increases. However, according to the air-fuel ratio control system 10 in this embodiment, as feedback control is interrupted in deceleration leaning by the deceleration leaning controller 1005 and rich injection control is performed at a stage at which the deceleration leaning is finished, the quantity of oxygen stored in the catalyst by the intake of air containing oxygen according to the deceleration leaning can be reduced at an early stage. As a result, the interrupted feedback control is restored at an early stage and emission performance can be kept high.

Moreover, when it is predicted that time is required for convergence on sliding mode control by the injection of secondary air or fuel cut control or the intake of air containing oxygen according to the deceleration leaning, convergence on feedback control can be accelerated by first performing PID control at a stage at which the injection of secondary air is finished or at a stage at which fuel cut control or deceleration leaning is finished.

As the convergence on sliding mode control is secured when a predictive error is equal to or smaller than the threshold, emission performance can be kept high by resuming feedback control.

Especially, as PID control is made so that an error between real air-fuel ratio and the preset desired value is zero without using the predictor 102 when the deterioration of predictive precision is determined in the resumption of control in the main body 100 of the air-fuel ratio controller, time until predictive precision is secured can be more reduced than time when the predictor 102 is used and emission performance can be kept high.

Next, a second air intake corresponding part IOOBB will be described referring to Figs. 21 and 22.

The second air intake corresponding pad 1008B as shown in Fig. 21 has a substantially similar configuration to that of the first air intake corresponding part 1008A; however, the second air intake corresponding part 100BB is different from the first air intake corresponding part 1008A in that an error arithmetic unit 1018, a PID controller 1020 and a switching arrangement 1022 are further provided.

Besides, processing in the following units included in the second air intake -34 -corresponding part 1 008B is partially different from the processing in the air-fuel ratio control halt requesting unit 1010 and the resumption determining unit 1014.

That is, the air-fuel ratio control halt requesting unit 1010 outputs a halt request signal Sg to the main body 100 of the air-fuel ratio controller based upon the input of an Al initiation signal Sais from the Al controller 1002 or an FC control initiation signal Sfcs from the FC controller 1004 or a deceleration leaning initiation signal Srss from the deceleration leaning controller 1005, and outputs a first switching signal Shl to the switching arrangement 1022. The main body 100 of the air4uel ratio controller temporarily halts air-fuel ratio control based upon the input of the halt request signal Sg from the air-fuel ratio control halt requesting unit 1010.

Besides, the switching arrangement 1022 switches to output from the RID controller 1020 based upon the input of the first switching signal Shl.

The error arithmetic unit 1018 operates an error ERR between an output value (SVO2) of the oxygen sensor 52 at the current time and the preset desired value.

The RID controller 1020 executes RID control (feedback control) so that the error ERR acquired in the error arithmetic unit 1018 is zero. The output of the PID controller 1020 is input to the multiplier 120 via the switching arrangement 1022 as target air-fuel ratio K02(k). Hereby, the basic fuel injection quantity TIMB is corrected with the output from the RID controller 1020 and the environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others, is output as fuel injection time Tout, and an output value 5V02 of the oxygen sensor 52 varies toward the desired value.

The resumption determining unit 1014 compares the error ERR from the error arithmetic unit 1018 and the preset threshold, outputs a control resumption signal Si to the main body 100 of the air-fuel ratio controller at a stage at which the error ERR is equal to or smaller than the threshold, and outputs a second switching signal Sh2 to the switching arrangement 1022. The threshold may be the same as the threshold used in the predictive precision determining unit 146 in the main body 100 of the air-fuel ratio controller. The main body 100 of the air-fuel ratio controller resumes air-fuel ratio control based upon the input of the control resumption signal Si from the resumption determining unit 1014 and the switching arrangement 1022 switches to output from the main body 100 of the air-fuel ratio controller based upon the input of the second switching signal Sh2. Hereby, output from the main body 100 of the air-fuel ratio controller is input to the multiplier 120 via the switching -35 -arrangement 1022 as target air4uel ratio K02(k). That is, the basic fuel injection quantity TIMB is corrected with the output from the main body 100 of the air-fuel ratio controller and the environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others, and is output as fuel injection time Tout.

Next, processing operation of the second air intake corresponding part 1003B will be described with reference to a flowchart shown in Fig. 22.

First, in a step SlOl shown in Fig. 22, the air4uel ratio control halt requesting unit 1010 determines whether the injection of secondary air is started or not. This determination is made depending upon whether an Al initiation signal Sais from the Al controller 1002 is input or not.

When the Al initiation signal Sais is input, the process proceeds to the next step Si 021 the air-fuel ratio control halt requesting unit 1010 outputs a halt request signal Sg to the main body 100 of the air-fuel ratio controller, and the air-fuel ratio control halt requesting unit outputs a first switching signal Shi to the switching arrangement 1022. The main body 100 of the air-fuel ratio controller temporarily halts air-fuel ratio control based upon the input of the halt request signal Sg. The switching arrangement 1022 switches to output from the RD controller 1020 based upon the input of the first switching signal Shl.

Afterward, in a step Si 03, the rich spike controller 1012 waits for the termination of the injection of secondary air. That is, the rich spike controller waits for the input of an Al termination signal Saie from the Al controller 1002.

In the meantime, when it is determined that no Al initiation signal Sais is input in the step 5101, the air-fuel ratio control halt requesting unit 1010 determines whether FC control is started or not in a step S104. This determination is made depending upon whether an FC control initiation signal Sfcs is input from the FC controller 1004 or not.

When the EC control initiation signal Sfcs is input, the process proceeds to the next step 5105, the air-fuel ratio control halt requesting unit 1010 outputs a halt request signal Sg to the main body 100 of the air-fuel ratio controller, and the air-fuel ratio control halt requesting unit outputs a first switching signal Shi to the switching arrangement 1022.

Afterward, in a step S106, the rich spike controller 1012 waits for the termination of FC control. That is, the rich spike controller waits for the input of an FC control termination signal Sfce from the FC controller 1004.

When it is determined that no FC control initiation signal Stcs is input in the step S 104, the air-fuel ratio control halt requesting unit 1010 determines whether deceleration leaning is started or not in a step S107. This determination is made depending upon whether a deceleration leaning initiation signal Srss from the deceleration leaning controller 1005 is input or not.

When the deceleration leaning initiation signal Srss is input, the process proceeds to the next step 5108 and the air-fuel ratio control halt requesting unit 1010 outputs a halt request signal Sg to the main body 100 of the air-fuel ratio controller. The main body 100 of the air-fuel ratio controller temporarily halts air-fuel ratio control based upon the input of the halt request signal Sg.

Afterward, in a step S109, the rich spike controller 1012 waits forthe termination of deceleration leaning. That is, the rich spike controller waits for the input of a deceleration leaning termination signal Srse from the deceleration leaning controller 1005.

When the Al termination signal Saie is input in the step S103 or when the FC control termination signal Sfce is input in the step S106 or when the deceleration leaning termination signal Srse is input in the step 5109, the process proceeds to the next step 5110 and the rich spike controller 1012 controls the fuel injection valve 40 to generate a rich spike in the combustion chamber of the engine 28. The rich spike control supplies fuel of quantity according to an output value (SVO2) of the oxygen sensor 52 at the current time to the combustion chamber of the engine 28 in unit time1 referring to the rich spike map 1016. The rich spike control is continued until it is determined in a step 5111 that an output value (SVO2) of the oxygen sensor 52 has transferred to the rich side.

At a stage at which the output value of the oxygen sensor 52 transfer to the rich side, the process proceeds to a step 5112 and the error arithmetic unit 1018 calculates difference (an error) between an output value SVO2 of the oxygen sensor 52 at the current time and the desired value.

Afterward, in a step S113, the resumption determining unit 1014 determines whether control in the main body 100 of the air-fuel ratio controller is to be resumed or not. This determination is made depending upon whether the error is equal to or smaller than the threshold or not. When the error exceeds the threshold, the process proceeds to a step 5114 and the PID controller 1020 performs PID control so that the error is zero. The output of the RID controller 1020 is input to the multiplier 120 via the switching arrangement 1022 as target air-fuel ratio K02(k).

-37 -Hereby, the basic fuel injection quantity TIMB is corrected with the output from the PID controller 1020 and the environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others, is output as fuel injection time Tout, and an output value SVO2 of the oxygen sensor 52 varies toward the desired value.

In the step Si 13, at a stage at which it is determined that the error is equal to or smaller than the threshold, the process proceeds to the next step 5115, the resumption determining unit 1014 outputs a control resumption signal Si to the main body 100 of the air-fuel ratio controller, and outputs a second switching signal Sh2 to the switching arrangement 1022. The main body 100 of the air-fuel ratio controller resumes air-fuel ratio control based upon the input of the control resumption signal Si from the resumption determining unit 1014 and the switching arrangement 1022 switches to output from the main body 100 of the air-fuel ratio controller based upon the input of the second switching signal Sh2. Hereby, the output from the main body 100 of the air-fuel ratio controller is input to the multiplier via the switching arrangement 1022 as target air-fuel ratio K02(k). That is, the basic fuel injection quantity TIMB is corrected with the output from the main body of the air-fuel ratio controller and the environmental correction factor KECO based upon coolant temperature, intake air temperature, atmospheric pressure and others, and is output as fuel injection time Tout.

Afterward, at a stage at which feedback control in the first sliding mode F controller 104 is resumed in the step S115 or when it is determined that deceleration leaning is not started in the step S107 (that is, when the injection of secondary air, fuel cut control or deceleration leaning is not started), the process proceeds to a step 5116, and it is determined whether a request for the termination (the disconnection of power supply, a maintenance request and others) of the air-fuel ratio control system 10 is made or not. When no request for the termination is made, the processing after the step 5101 is repeated and ata stage at which the request for termination is made, processing operation in the air-fuel ratio control system 10 is finished.

As described above, in the air-fuel ratio control system 10 provided with the second air intake corresponding part 1 008B, RID control is performed so that difference (an error) between an output value SVO2 of the oxygen sensor 52 and the desired value is zero using the dedicated PID controller 1020 without using the second sliding mode/PID controller 124 in the main body 100 of the air-fuel ratio controller, and so the error can be converged on the threshold or less at an early stage without using a predictive precision determination routine (from the predictor 102 to the timing device 130, the filtering unit 144 in the adaptive model corrector 122 and the predictive precision determining unit 146) using a predictive error in the main body 100 of the air-fuel ratio controller, normal sliding mode control (control in the first sliding mode controller 104) can be resumed more early than in the case using the first air intake corresponding part 1008A, and emission performance can be kept high.

Besides, the second air intake corresponding part 10088 can be also applied to a configuration in which no second sliding mode/PID controller 124 is used as in the main body 1 OOd of the air-fuel ratio controller in the fourth alternative embodiment shown in Fig. 17, has high flexibility, and can be applied to various

specifications.

The air-fuel ratio control system aGcording to the present invention is not limited to the above-mentioned embodiments, and can naturally have various configurations unless the control system deviates from the scope of the present invention.

Claims

CLAIMS1. An air-fuel ratio control system comprising: a basic fuel injection map (118) that specifies fuel injection quantity to an engine (28) based upon at least parameters of engine speed and throttle opening; air-fuel ratio sensing means (52) which is provided downstream of a catalyst (50) installed in an exhaust pipe (32) of the engine (28) and which senses air-fuel ratio; air-fuel ratio predicting means (102) that predicts air-fuel ratio downstream of the catalyst (50); and correction factor calculating means (104) that determines a correction factor (DKO2OP) for the fuel injection quantity based upon predicted air-fuel ratio (DVPRE) from the air-fuel ratio predicting means (102) by feedback control, wherein: the air-fuel ratio predicting means (102) calculates the predicted air-fuel ratio (DVPRE) based upon at least real air-fuel ratio (5V02) from the air-fuel ratio sensing means (52) and a history of the correction factor (DKO2OP); the air-fuel ratio control system has adaptive model correcting means (122) that superimposes a second correction factor (KTIMB) on the correction factor (DKO2OP) so as to make deviation between the real air-fuel ratio (5V02) and the predicted air-fuel ratio (DVPRE) which corresponds to the real air-fuel ratio (SVO2) and which is predicted in the past as a predictive error (ERPRE) zero; a secondary air pulse induction system (1000) that injects secondary air into an exhaust path upstream of the catalyst (50) is provided; the feedback control is interrupted at a stage at which the injection of secondary air is started; immediately after the injection of secondary air is finished, air-fuel ratio control is made to shift to rich control in an open loop; and after the real air-fuel ratio (5V02) transfers to a rich side, the feedback control is resumed.
2. An air-fuel ratio control system comprising: a basic fuel injection map (118) that specifies fuel injection quantity to an engine (28) based upon at least parameters of engine speed and throttle opening; -40 -air-fuel ratio sensing means (52) which is provided downstream of a catalyst (50) installed in an exhaust pipe (32) of the engine (28) and which senses air-fuel ratio; air-fuel ratio predicting means (102) that predicts air-fuel ratio downstream of the catalyst (50); and correction factor calculating means (104) that determines a correction factor (DKO2OP) for the fuel injection quantity based upon predicted air-fuel ratio (DVFRE) from the air-fuel ratio predicting means (102) by feedback control, wherein: the air-fuel ratio predicting means (102) calculates the predicted air-fuel ratio (DVPRE) based upon at least real air-fuel ratio (SVO2) from the air-fuel ratio sensing means (52) and a history of the correction factor (DKO2OP); the air-fuel ratio control system has adaptive model correcting means (122) that superimposes a second correction factor (KTIMB) on the correction factor (DKO2OF) so as to make deviation between the real air-fuel ratio (SVO2) and the predicted air-fuel ratio (DVPRE) which corresponds to the real air-fuel ratio (SVO2) and which is predicted in the past as a predictive error (ERPRE) zero; the air4uel ratio control system has fuel cut control means (1004) that performs fuel injection halt control while the throttle opening is closed; when the fuel injection halt control by the fuel cut control means (1004) is started, the feedback control is interrupted; immediately after the fuel injection halt control by the fuel cut control means (1004) is finished, air-fuel ratio control is made to shift to rich control in an open loop; and after the real air-fuel ratio (SVO2) transfers to a rich side, the feedback control is resumed.
3. An air-fuel ratio control system comprising: a basic fuel injection map (118) that specifies fuel injection quantity to an engine (28) based upon at least parameters of engine speed and throttle opening; air-fuel ratio sensing means (52) which is provided downstream of a catalyst (50) installed in an exhaust pipe (32) of the engine (28) and which senses air-fuel ratio; air-fuel ratio predicting means (102) that predicts air-fuel ratio downstream of the catalyst (50); and correction factor calculating means (104) that determines a correction factor (DKO2OP) for the fuel injection quantity based upon predicted air-fuel ratio (DVPRE) from the air-fuel ratio predicting means (102) by feedback control, wherein: the air4uel ratio predicting means (102) calculates the predicted air-fuel ratio (DVPRE) based upon at least real air-fuel ratio (SVO2) from the air-fuel ratio sensing means (52) and a history of the correction factor (DKO2OP); the air4uel ratio control system has adaptive model correcting means (122) that superimposes a second correction factor (KTIMB) on the correction factor (DKO2OP) so as to make deviation between the real air-fuel ratio (SVO2) and the predicted air-fuel ratio (DVPRE) which corresponds to the real air4uel ratio (SVO2) and which is predicted in the past as a predictive error (ERPRE) zero; the air4uel ratio control system has deceleration leaning control means (1005) that performs deceleration leaning; when the deceleration leaning by the deceleration leaning control means (1005) is started, the feedback control is interrupted; immediately after the deceleration leaning by the deceleration leaning control means (1005) is finished, air-fuel ratio control is made to shift to rich control in an open loop; and after the real air-fuel ratio (SVO2) transfers to a rich side, the feedback control is resumed. F
4. The air-fuel ratio control system according to any one of Claims Ito 3, wherein: the feedback control is sliding mode control; and when the predictive error (ERPRE) exceeds a preset threshold prior to resumption of the feedback control, PID control is performed so as to make an error between the real air-fuel ratio (SVO2) and a preset desired value zero.
5. The air-fuel ratio control system according to Claim 4, wherein: the feedback control is resumed at a stage at which the predictive error (ERPRE) is equal to or smaller than the preset threshold.
6. The air-fuel ratio control system according to any one of Claims 1 to 3, comprising: -42 -a controller (126) that controls at least the correction factor calculating means (104) and the adaptive model correcting means (122), wherein: the adaptive model correcting means (122) is provided with predictive precision determining means (146) that determines predictive precision based upon the predictive error (ERPRE); and when deterioration of the predictive precision is determined in the predictive precision determining means (146) in the resumption of the feedback control, the PID control is performed without using the air-fuel ratio predicting means (102) so as to make the error between the real air-fuel ratio (SVO2) and the preset desired value zero.
7. The air-fuel ratio control system according to any one of Claims 1 to 3, further comprising: a dedicated PID controller (1020), wherein: the feedback control is the sliding mode control; and when the error between the real air4uel ratio (SVO2) and the preset desired value exceeds the preset threshold prior to the resumption of the feedback control, the PID control is performed in the PID controller (1020) so as to make the error zero.