JP2000027718A - Air-fuel ratio control and evaporated fuel purge control device of lean-burn engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate influence by evaporated fuel on an air-fuel ratio by providing a fuel injection amount calculation means for calculating combustion injection amount from an injector by correcting basic fuel injection amount based on an evaporation coefficient and an air-fuel ratio feedback correction coefficient. SOLUTION: An evaporation correction coefficient is calculated from evaporated fuel concentration detected by an evaporation concentration sensor 73. A fuel injection amount calculation means calculates a final fuel injection pulse width based on a fuel injection amount calculating expression based on the evaporation correction coefficient. When a timer is started by prescribed timing, fuel calculated in a prescribed form is injected from an injector 12 by a driving pulse signal of a final fuel injection pulse width. At this time, evaporated fuel is purged as a mixed gas. Because purge flow rate of evaporated fuel from a CPC valve 18 is controlled so as to be a constant ratio for in-take air quantity, influence of the evaporated fuel on an air-fuel ratio is eliminated to surge a large quantity of evaporated fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control technique for a lean burn engine, and more particularly to an air-fuel ratio control technique for purging evaporated fuel generated in a fuel tank into an intake system of the engine. .

[0002]

2. Description of the Related Art Conventionally, there has been known a lean-van engine that improves combustion in a low-load and medium-load operation range and enables stable combustion at an air-fuel ratio thinner than the stoichiometric air-fuel ratio.
The lean-van engine improves theoretical thermal efficiency and reduces pumping loss, and achieves both improved fuel efficiency and reduced pollution. In this lean burn engine, the target air-fuel ratio during lean burn operation is set near a lean limit (surge limit, combustion limit). For this reason, when the actual air-fuel ratio deviates to the rich side from the target air-fuel ratio, knocking tends to occur, and when the actual air-fuel ratio deviates to the lean side, surge or misfire easily occurs. Accordingly, finer air-fuel ratio control is required, and a control method that takes into account the factors of the fuel disturbance in more detail is required.

On the other hand, vehicles such as automobiles are provided with an evaporative fuel purge system (evaporation purge system) in order to prevent fuel vapor generated in the fuel tank from being discharged into the atmosphere. This evaporative fuel purging system once adsorbs evaporative fuel to a canister, purges the intake system as an evaporative fuel mixture (hereinafter abbreviated as "evaporation") and burns it when a predetermined purge condition is satisfied. The leverage acts as a fuel disturbance. In particular, during lean-burn operation, the fuel ratio at the same air amount is lower than during operation at the stoichiometric air-fuel ratio, and thus the fuel is easily affected by evaporation.

[0004] For this reason, various systems have been proposed in the past in which the evaporative purge is considered when controlling the air-fuel ratio. For example, a method has been known in which a valve opening degree of a canister purge control valve (hereinafter abbreviated as CPC valve) interposed in a purge passage that connects a canister and an intake passage of an engine is switched to suppress the influence thereof. ing. In this case, the valve opening of the CPC valve is made different between the operation based on the stoichiometric air-fuel ratio and the lean burn operation, and when the operation mode is switched, the valve opening is switched to reduce the air-fuel ratio fluctuation immediately after the shift to the lean burn operation. Restrained.

However, as described above, the lean burn operation is performed over a wide range from a low load to a medium load operation range, and the target air-fuel ratio is controlled near the lean limit. It changes every moment for each operation area. Also, depending on the operating range, the target value may be an air-fuel ratio between the stoichiometric air-fuel ratio operation and the lean burn operation, or the timing of switching between the stoichiometric air-fuel ratio operation and the lean burn operation may change for each engine operating state. There are cases where it is done. In this case, the evaporative purge amount also needs to be relatively changed according to the change in the target air-fuel ratio.

On the other hand, in the system in which the purge amount is controlled by switching the valve opening as described above, the purge amount cannot be changed in accordance with the change in the target air-fuel ratio, and the air-fuel ratio fluctuation during lean burn operation is not possible. There is a problem of inviting. When the air-fuel ratio of the engine is controlled based on the output from an A / F sensor (air-fuel ratio sensor) provided in the exhaust system, it is possible to suppress the air-fuel ratio fluctuation to some extent by this feedback control. However, when the target air-fuel ratio changes every moment as in the case of the lean burn operation, the feedback control cannot sufficiently cope with the target air-fuel ratio, and there is a limit to the followability.

Therefore, the present applicant has filed Japanese Patent Application No. 9-26061.
In No. 9, in order to improve the accuracy of the air-fuel ratio control during the lean burn operation, a control method was proposed in which even if the evaporative fuel was purged, the influence of this on the air-fuel ratio control as a fuel disturbance was always in a constant rate state. I have. Here, the ratio between the flow rate of the evaporator and the amount of intake air (hereinafter referred to as the purge flow rate ratio) is made variable in accordance with the target air-fuel ratio, and the disturbance ratio exerted on the amount of fuel injected from the injector by the purged evaporator is calculated as the target air-fuel ratio. It is kept constant regardless of the fuel ratio. Thus, control followability is improved when air-fuel ratio feedback control is performed by the air-fuel ratio sensor or when combustion limit detection control is performed.

[0008]

Here, in the control system in which the purge flow ratio is variable as described above, the purge flow ratio is reduced during the lean burn operation. However,
If the amount of the evaporative purge is reduced, the interior of the canister is filled with the evaporative fuel. Therefore, it is necessary to secure the total amount of the evaporative fuel purge to a certain degree or more. For this reason, even in the case where the purge flow rate ratio is lowered (lean burn operation state), in order to enable purging of a large amount of evaporation, the basic average purge flow rate is set to be considerably high. It is necessary to keep.

However, during a high load region, particularly during lean burn operation, the suction pipe negative pressure becomes shallow, so that the amount of evaporative purge becomes small despite the large intake air amount.
Therefore, it is difficult to secure a target purge flow rate ratio in the entire operation range, no matter how large the capacity of the CPC valve. Further, there is a region where purging is impossible depending on the operation region. For this reason, a phenomenon occurs in which the target purge flow rate ratio is secured or not secured depending on the operation region, and the fuel disturbance ratio due to evaporation changes suddenly. Therefore, even when the air-fuel ratio feedback and the combustion limit detection control are performed, there is a problem that the control followability is deteriorated.

On the other hand, when changing the purge flow rate ratio, the target purge flow rate ratio is obtained based on the intake air amount detected by an air flow meter or the like. And
From this value, the target purge flow rate is calculated, and C
The evaporative purge amount is controlled by calculating the opening of the PC valve. However, as long as a detection value of a sensor such as an air flow meter is used for controlling the purge amount, a detection delay and a calculation delay including noise removal processing after sensing are inevitable. Further, when the CPC valve is operated, a response delay also occurs. Therefore, when such a control method is adopted, it is difficult to realize an optimum purge flow rate in real time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lean burn engine capable of correcting the fuel injection amount from an injector in consideration of the influence of fuel disturbance due to evaporation and improving control followability to a target air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control method and an air-fuel ratio control device.

[0012]

An air-fuel ratio control apparatus for a lean burn engine according to the present invention comprises a canister and a canister for adsorbing evaporative fuel generated in the fuel tank into an evaporative fuel purge passage communicating the fuel tank with an intake system. A canister purge control valve for controlling a purge amount of the evaporated fuel stored in the engine, and operating in a predetermined operation region at an air-fuel ratio smaller than the stoichiometric air-fuel ratio. The air-fuel ratio feedback correction coefficient is determined based on the detection value of the air-fuel ratio sensor provided in the system, and the basic fuel injection amount determined by the engine intake amount and the engine speed is corrected by the air-fuel ratio feedback correction coefficient. Air-fuel ratio control system for a lean burn engine that controls the amount of fuel supplied to A basic purge flow ratio calculating means for calculating a basic purge flow ratio which is a ratio between an evaporative fuel purge flow and an intake air amount during a stoichiometric air-fuel ratio operation, and a basic purge flow ratio and a target air-fuel ratio during a lean burn operation. Target purge flow ratio calculating means for calculating a target purge flow ratio of evaporative fuel to intake air amount; target purge flow rate calculating means for calculating a target purge flow rate of evaporative fuel from the target purge flow ratio and the intake air amount; Canister purge control valve opening calculating means for calculating the valve opening of the canister purge control valve based on the target purge flow rate,
An actual purge flow ratio calculation that calculates an actual purge flow ratio, which is a ratio between an actual evaporated fuel flow rate and an actual intake air amount, from the actual valve opening of the canister purge control valve and the intake air amount or the throttle valve opening. Means, an evaporation correction coefficient calculating means for calculating an evaporation correction coefficient for correcting the fuel injection amount from the injector according to the purge amount of the evaporated fuel, from the actual purge flow rate ratio and the evaporated fuel concentration, and an evaporation correction coefficient and an air-fuel ratio. Based on the feedback correction coefficient and
Fuel injection amount calculating means for calculating the fuel injection amount from the injector by correcting the basic fuel injection amount.

Thus, the fuel injection amount is feed-forward corrected irrespective of the state of the target purge flow rate,
Eliminate the effect of evaporation on the air-fuel ratio. Therefore, in addition to the control of the evaporative purge, the fuel injection amount is controlled in consideration of the amount of the evaporative purge, so that a large amount of evaporated fuel can be purged while maintaining high air-fuel ratio controllability.

An air-fuel ratio control device for a lean-burn engine according to the present invention is an air-fuel ratio control device for a lean-burn engine similar to that described above. A basic purge flow ratio calculating means for calculating a basic purge flow ratio, which is a ratio, and a target for calculating a target purge flow ratio of the evaporated fuel to the intake air amount based on the basic purge flow ratio and the target air-fuel ratio during the lean burn operation. Purge flow ratio calculating means; canister purge control valve opening calculating means for calculating the valve opening of the canister purge control valve from the target purge flow ratio and the opening of the throttle valve; and the actual valve of the canister purge control valve. From the opening and throttle valve opening, it is the ratio between the actual flow rate of fuel vapor and the actual intake air amount. An actual purge flow ratio calculating means for calculating a purge flow ratio, and an evaporative correction for calculating an evaporative correction coefficient for correcting the fuel injection amount from the injector according to the purge amount of the evaporative fuel from the actual purge flow ratio and the evaporative fuel concentration. It is characterized by comprising a coefficient calculating means and a fuel injection amount calculating means for correcting the basic fuel injection amount based on the evaporation correction coefficient and the air-fuel ratio feedback correction coefficient to calculate the fuel injection amount from the injector.

Further, an air-fuel ratio control apparatus for a lean burn engine according to the present invention is an air-fuel ratio control apparatus for a lean burn engine similar to that described above, wherein an air-fuel ratio flow rate and an intake air amount during a stoichiometric air-fuel ratio operation are determined. A basic purge flow ratio calculating means for calculating a basic purge flow ratio, which is a ratio, and a target for calculating a target purge flow ratio of the evaporated fuel to the intake air amount based on the basic purge flow ratio and the target air-fuel ratio during the lean burn operation. A purge flow ratio calculating means, a throttle valve opening calculating means for calculating an effective opening area of the throttle valve from an opening of the throttle valve, and a target purge flow ratio and an effective opening area of the throttle valve. A canister purge control valve opening calculating means for calculating a valve opening; An actual purge flow ratio calculating means for calculating an actual purge flow ratio which is a ratio between an actual flow rate of fuel vapor and an actual intake air amount from an actual valve opening of the trawl valve and a throttle valve opening; An evaporation correction coefficient calculating means for calculating an evaporation correction coefficient for correcting the fuel injection amount from the injector according to the purge amount of the evaporated fuel from the ratio and the evaporated fuel concentration, and based on the evaporation correction coefficient and the air-fuel ratio feedback correction coefficient. Fuel injection amount calculating means for correcting the basic fuel injection amount and calculating the fuel injection amount from the injector.

In addition, the air-fuel ratio control device for a lean-burn engine according to the present invention is the same air-fuel ratio control device for a lean-burn engine as described above, and is required to realize the torque required by the driver. Target air amount calculating means for calculating a target intake air amount of the throttle valve, throttle valve opening degree calculating means for calculating an opening degree of the throttle valve based on the target intake air amount, and an evaporative fuel purge flow rate during stoichiometric air-fuel ratio operation A basic purge flow ratio calculating means for calculating a basic purge flow ratio which is a ratio between the target purge air ratio and the target air-fuel ratio during the lean burn operation. A target purge flow ratio calculating means for calculating a flow ratio, and a target purge flow ratio of the evaporated fuel is calculated from the target purge flow ratio and the intake target air amount. Target purge flow rate calculation means, canister purge control valve opening degree calculation means for calculating the valve opening degree of the canister purge control valve based on the target purge flow rate, actual valve opening degree of the canister purge control valve and intake air amount or An actual purge flow ratio calculating means for calculating an actual purge flow ratio which is a ratio of an actual fuel vapor flow to an actual intake air flow from the throttle valve opening; and evaporating from the actual purge flow ratio and the evaporative fuel concentration. Evaporation correction coefficient calculating means for calculating an evaporation correction coefficient for correcting the fuel injection amount from the injector according to the fuel purge amount, and correcting the basic fuel injection amount based on the evaporation correction coefficient and the air-fuel ratio feedback correction coefficient. Fuel injection amount calculating means for calculating the amount of fuel injection from the injector. .

In this case, the canister purge control valve opening calculating means calculates the suction pipe pressure, the atmospheric pressure,
The effective opening area of the canister purge control valve may be calculated from the temperature of the fuel vapor mixture and the target purge flow rate, and the opening of the canister purge control valve may be calculated based on the effective opening area.

In addition, the actual purge flow ratio calculating means calculates the effective opening area of the canister purge control valve from the opening degree of the canister purge control valve and the effective opening area of the throttle valve obtained from the opening degree of the throttle valve. The actual purge flow rate ratio may be calculated. Further, the evaporation correction coefficient calculating means may estimate the fuel vapor concentration based on the air-fuel ratio feedback correction coefficient.

On the other hand, the evaporative fuel purge control device for a lean burn engine according to the present invention is stored in a canister for adsorbing evaporative fuel generated in the fuel tank and a canister in an evaporative fuel purge passage communicating the fuel tank with the intake system. A canister purge control valve for controlling a purge amount of the evaporated fuel, and an electronically controlled throttle for electrically controlling an intake air amount of the engine according to an operation state. An evaporative fuel purge control device for a lean burn engine that is operated at an air-fuel ratio thinner than the air-fuel ratio, the target calculating a target intake air amount of a throttle valve required to realize a torque required by a driver. Air amount calculation means, and throttle valve opening calculation for calculating the opening of the throttle valve based on the intake target air amount Means, a basic purge flow ratio calculating means for calculating a basic purge flow ratio, which is a ratio between an evaporative fuel purge flow and an intake air amount during a stoichiometric air-fuel ratio operation, and a basic purge flow ratio and a target air-fuel ratio during a lean burn operation. And based on
Target purge flow ratio calculating means for calculating a target purge flow rate ratio of the evaporated fuel to the intake air amount; target purge flow rate calculating means for calculating a target purge flow rate of the evaporated fuel from the target purge flow ratio and the intake target air amount. And a canister purge control valve opening calculating means for calculating the valve opening of the canister purge control valve based on the target purge flow rate.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of an engine control system, and FIG. 2 is a circuit configuration diagram of an electronic control system in an air-fuel ratio control device according to Embodiment 1 of the present invention. The air-fuel ratio control device of the present invention controls the purge flow rate of the evaporated fuel to be substantially constant with respect to the intake air amount in accordance with the change in the target air-fuel ratio in the lean burn engine, The fuel injection amount from the injector is corrected based on the concentration of the fuel vapor mixture to improve the control followability to the target air-fuel ratio.

In FIG. 1, reference numeral 1 denotes an engine. In FIG. 1, one cylinder of the engine 1 is shown as a representative. The engine 1 can select either combustion with a normal stoichiometric air-fuel ratio or lean burn (lean combustion) according to the operating state. Engine 1 cylinder head 1
An intake port 2 and an exhaust port 3 are formed in c. An intake valve 4 and an exhaust valve 5 are provided between these ports 2 and 3 and the combustion chamber 1a of the engine 1. The exhaust valve 5 is controlled by a cam 6 and a rocker arm 7, and the intake valve 4 Is opened and closed at a predetermined timing by a similar mechanism (not shown). In this case, the rotation angle of the cam 6 is detected by the cam angle sensor 31, and the data is transmitted to an electronic control unit (ECU) 40 described later.
Sent to

An intake passage 8 communicates with the intake port 2. A throttle valve 9 is provided in the intake passage 8, and an air chamber 70 is formed between the intake port 2 and the throttle valve 9. In the air chamber 70,
A pressure sensor 71 is provided so that the pressure in the intake passage 8 can be detected. An intake air temperature sensor 72 is provided downstream of the throttle valve 9 in the intake passage 8 so that the temperature in the intake passage 8 can be detected. An intake passage branches from the air chamber 70 to each cylinder.

The throttle valve 9 is further provided with a throttle opening sensor 32 for detecting a throttle opening. On the upstream side of the throttle valve 9,
An air flow meter 33 is attached, and detects a flow rate of air flowing in through the air cleaner 10.
It should be noted that an idle speed control valve (ISC valve) 24
Is provided so that the engine idling speed when the throttle valve 9 is fully closed can be adjusted.

The cylinder head 1c is provided with an ignition plug 11 whose tip is exposed to the combustion chamber 1a.
Further, in the combustion chamber 1a of each cylinder, an in-cylinder pressure sensor 74 for detecting the pressure in the combustion chamber is provided facing the combustion chamber 1a. Further, an injector 12 is located immediately upstream of the intake port 2. This injector 12 is connected to a fuel pipe 1 to which a fuel filter 27 is attached.
The fuel tank 14 is in communication with the fuel tank 14 through the fuel injection port 3, and injects fuel adjusted to a specified pressure into the intake port 2. The fuel pipe 13 has a return passage 2 connected to the fuel tank 14 via a fuel pressure regulator 25.
6 is provided, and excess fuel is appropriately stored in the fuel tank 14.
Is to be returned to.

A discharge passage 15 for discharging the fuel vapor generated in the fuel tank 14 extends from an upper portion of the fuel tank 14. The discharge passage 15 communicates with an upper portion of a canister 16 having an adsorbing portion 16a made of activated carbon or the like. The canister 16 is provided with a fresh air inlet 16b communicating with the atmosphere below the canister 16, and a mixture of fresh air from the fresh air inlet 16b and the evaporated fuel gas stored in the adsorption section 16a ( Fuel vapor mixture,
A purge passage 17 for guiding the evaporator extends further from the upper part thereof.

The purge passage 17 communicates with the intake passage 8 on the downstream side of the throttle valve 9.
A CPC valve 18 for controlling the evaporation flow rate is provided. As the CPC valve 18, a duty solenoid valve whose valve opening is controlled in proportion to the duty ratio of a drive pulse signal output from the ECU 40 described later is used. In this embodiment, the motor is fully closed when the duty ratio is 0%, that is, when the drive pulse signal is OFF, and is fully open when the duty ratio is 100%, that is, when continuous energization is performed. An evaporative concentration sensor 73 is provided between the CPC valve 18 and the intake passage 8 in the purge passage 17.
Evaporation concentration (evaporated fuel concentration) _{ev ev} can be detected.

In the cylinder block 1b of the engine 1,
A cooling water passage 19 is formed, in which a water temperature sensor 37 is attached. The crankshaft 20 of the engine 1 is provided with a crank angle sensor 38 opposed thereto. The crank angle sensor 38 detects the number of revolutions of the crankshaft 20 by passing through a protrusion 20 a provided on the crankshaft 20.

The exhaust port 3 is provided with an exhaust passage 21 communicating therewith, where an O ₂ sensor (air-fuel ratio sensor) is provided.
39 are attached. Further, a catalyst 22 and a muffler 23 are provided downstream of the O ₂ sensor 39. The detection data of the water temperature sensor 37 and a crank angle sensor 38, O ₂ sensor 39 is sent to the ECU 40.

On the other hand, as shown in FIG. 2, the ECU 40 includes a CPU 41, a ROM 42, a RAM 43, a backup RAM 44, a timer 45 and a microcomputer in which an I / O interface 46 is connected to each other via a bus line 47. , And its peripheral circuits. The O ₂ sensor 39 and the crank angle sensor 38
, And sends control signals to actuators such as the injector 12 and the CPC valve 18.

An O ₂ sensor 39 and a crank angle sensor 38 are connected to the I / O interface 46 via a waveform shaping circuit 48, respectively. Further, an air flow meter 33, a water temperature sensor 37, a fuel temperature sensor 36, a tank internal pressure sensor 34, a fuel remaining amount sensor 35, a pressure sensor 71,
The intake air temperature sensor 72 and the evaporation concentration sensor 73 are connected to the I / O interface 4 via the A / D converter 49, respectively.
6 is connected. Further, the I / O interface 46 includes the injector 12 and the CPC valve 18.
Are connected via the drive circuit 50.

The ROM 42 stores a control program and various control fixed data. The RAM 43 stores output signals to the sensors and switches after data processing, and data processed by the CPU 41. You.
In accordance with the control program stored in the ROM 42, the CPU 41 executes fuel injection control, evaporative purge control, air-fuel ratio control including these, ignition timing control, and the like. At this time, during the lean burn operation, the lean limit is detected based on the engine speed and the engine load, and when the lean limit is reached, the target air-fuel ratio is corrected to the rich side. On the other hand, when the lean limit has not been reached, the air-fuel ratio control for correcting the target air-fuel ratio to the lean side is performed. At this time, the air-fuel ratio control device controls the valve opening of the CPC valve 18 so that the effect of the purged fuel vapor on the air-fuel ratio is always constant, and the actual purge flow ratio is controlled. The fuel injection amount from the injector is corrected based on the calculated fuel concentration and the fuel vapor concentration, and the air-fuel ratio is controlled so as to become the target air-fuel ratio.

FIG. 3 is a block diagram showing a main configuration of the ECU 40. As shown in FIG. 3, various functional units are provided, including the engine operating region determining unit 51, and each unit will be described below in order while describing its function.

First, the ECU 40 has an engine operating region determining means 51 for determining whether the lean burn operating condition and the evaporative purge condition are satisfied based on various parameters such as the engine speed Ne indicating the engine operating condition.

Next, the ECU 40 calculates a basic purge flow ratio calculating means 52 for calculating a basic purge flow ratio PRTO indicating a ratio between a target value of the evaporative purge flow and an intake air amount at the time of the stoichiometric air-fuel ratio operation. Target equivalence ratio calculating means 53 for calculating a target air-fuel ratio. Also,
A target purge flow ratio calculating means 54 for obtaining a final target purge flow ratio PRATIO from the basic purge flow and the target air-fuel ratio is provided. Further, the target purge flow ratio PRAT
A target purge flow rate calculating means 55 for obtaining a target purge flow rate TPURGE from the IO and the intake air amount detected by the air flow meter 33; and a target purge flow rate TPURGE.
CPC valve opening calculating means 56 for determining the opening of the CPC valve 18 based on.

In addition, the ECU 40 calculates the throttle valve opening calculating means 5 for calculating the opening of the throttle valve 9 based on the data detected by the throttle opening sensor 32.
7 and an actual purge flow ratio calculating means 58 for calculating an actual purge flow ratio SPRATIO from the determined opening of the throttle valve 9 and the opening of the CPC valve 18. And
And evaporative concentration calculating means 61 for calculating a fuel vapor concentration chi _ev than the detection value of the evaporation concentration sensor 73, evaporation correction coefficient calculation means obtains the evaporative correction coefficient KEVAPO from the actual purge flow rate ratio SPRATIO the fuel vapor concentration chi _ev 59 and And a fuel injection amount calculating means 60 for determining a final fuel injection amount Ti which is a fuel amount finally injected from the injector 12 based on the obtained evaporation correction coefficient KEVAPO.

Therefore, the contents of each of the above means will be described.
The engine speed Ne calculated based on the output signals from the sensors and switches, the intake air amount Qa, the cooling water temperature Tw, the intake pipe pressure Pm, the combustion pressure P # i of each cylinder, the evaporative fuel concentration _evev, etc. The lean burn operation condition and the evaporated fuel purge condition are determined based on the above parameters.

Next, the basic purge flow ratio calculating means 52 calculates a basic purge flow ratio PRTO indicating the ratio between the target value of the purge flow and the intake air amount during the stoichiometric air-fuel ratio operation. In this case, the basic purge flow ratio PRTO is expressed by the following equation.

[0039]

(Equation 1)

In the above equation, PRTST is a correction coefficient at the start of purging, and has a value as shown in FIG. 4, and serves to gradually increase the evaporation amount until a predetermined purge flow ratio is reached.
That is, the ratio of the basic purge flow rate ratio PRTO is changed from 0 immediately after the lean condition is satisfied to 1 by the set value K ₀ every calculation cycle.
(100%).
Thus, the air-fuel ratio can be smoothly shifted without causing a rapid change in the air-fuel ratio at the start of the purge after the purge condition is satisfied.

Further, PRTCON is an evaporated fuel concentration corrected flow rate ratio (%), and sets the supply ratio of the evaporated fuel to the intake air amount Qa in accordance with the change in the evaporated fuel concentration _evev . Shows such a value. In the present embodiment, in the range of 2 to 0%, the higher the fuel vapor concentration _{ev ev} (the thicker), the lower the value, and the lower the fuel vapor concentration χ _ev (the lighter), the higher. Thus, the fuel disturbance due to the evaporation is suppressed to a predetermined ratio or less.

The basic purge flow rate ratio PRTO is calculated in the following procedure based on the purge start correction coefficient PRTST and the evaporated fuel concentration corrected flow rate ratio PRTCON. FIG. 6 is a flowchart showing a procedure for calculating the basic purge flow ratio PRTO.

The basic purge flow ratio setting routine shown in FIG. 6 is for setting the basic purge flow ratio PRTO of the evaporative fuel with respect to the intake air amount Qa corresponding to the change in the concentration of the evaporative fuel, and is executed at set intervals. .

First, in step S1, it is determined whether or not the fuel vapor purge condition is satisfied with reference to a determination value in a purge condition determination routine (not shown). In this purge condition determination routine, for example, a predetermined time (for example, 20 to 40 seconds) has elapsed after the engine has been started and the cooling water has been warmed up at or above the set temperature based on the elapsed time after the start and the coolant temperature Tw. In this state, it is determined that the purge condition is satisfied, and otherwise, it is determined that the purge condition is not satisfied.

When the purge condition is not satisfied, step S
The flow branches to 2 to clear the purge start correction coefficient PRTST, and then proceeds to step S7. On the other hand, when the purge condition is satisfied, the process proceeds to step S3. Then, referring to the value of the purge start correction coefficient PRTST, the process jumps to step S5 when PRTST = 1, and proceeds to step S4 when PRTST = 1. In step S4, updated with increased value set value T ₀ min purge start correction coefficient _{PRTST (PRTST ← PRTST + T 0} ).

When the process proceeds from step S3 or step S4 to step S5, the fuel vapor concentration _χev calculated based on the output signal of the evaporation concentration sensor 73 is read. Then, in step S6, based on the fuel vapor concentration _{ev ev} ,
With reference to the table having the above data with interpolation calculation, the evaporated fuel concentration corrected flow rate ratio PRTCON is set. In addition,
The evaporated fuel concentration χ _ev is directly detected from the concentration of the evaporated fuel actually purged by the evaporative concentration sensor 73, and also based on an air-fuel ratio feedback coefficient LAMBDA set based on the exhaust air-fuel ratio detected by the O ₂ sensor 39. May be estimated.

Thereafter, when the routine proceeds to step S7, the purge fuel concentration correction flow rate ratio PRTCON is set to the purge start correction coefficient P
The basic purge flow rate ratio PRTO is set after correction by RTST (PRTO ← PRTCON · PRTST), and the routine exits. Since the purge start correction coefficient PRTST when the purge condition is not satisfied is 0, the basic purge flow ratio PRTO at this time is set to 0.

Next, the target equivalence ratio calculating means 53 sets a target equivalence ratio (theoretical A / F / target A / F) KTG which sets the target air-fuel ratio during lean burn operation in comparison with the stoichiometric air-fuel ratio.
Set T. In this case, the target equivalent ratio KTGT is calculated in the following procedure. FIG. 7 is a flowchart showing a procedure for calculating the target equivalent ratio KTGT.

First, in step S21, a full opening increase coefficient KFULL is set based on the throttle valve opening, the basic fuel injection amount (basic fuel injection pulse width) Tp, or the engine speed Ne. This full opening increase coefficient KF
The ULL is set when the throttle valve opening is fully opened, when a high load state is detected based on the basic fuel injection amount Tp, or by referring to a table with interpolation calculation using the engine speed Ne as a parameter. Thus, in an operation state where high output is required, such as when the throttle valve is fully opened or during high load operation, the amount of fuel is increased and the output performance is improved. In addition,
KFULL = 0 is set when the throttle valve opening degree is other than the full open state and other than the high load operation. Therefore, the full opening increase coefficient KFULL during the lean burn operation is zero.

Subsequently, at step S22, a post-start increase coefficient KAS is set. The post-start increase coefficient KAS is
In order to ensure the stability of the engine speed immediately after the engine is started, it is set based on the cooling water temperature at the time of the start, etc., and is attenuated at every set time until it becomes 0 after the complete explosion. Therefore,
The fully-open increase coefficient KAS during the lean burn operation is zero.

Thereafter, at step S23, a water temperature increase coefficient KTW is set. The water temperature increase coefficient KTW is an increase coefficient for ensuring operability when the engine is cold, and is set based on the cooling water temperature Tw so that the lower the cooling water temperature Tw, the higher the fuel increase rate. Since the lean burn operation is performed after the completion of warm-up, the water temperature increase coefficient KTW becomes zero.

When the process proceeds to step S24, a target lean reduction coefficient setting subroutine is executed. FIG.
It is a flowchart which shows this target lean reduction coefficient setting subroutine. Here, first, in step S31, it is determined whether or not the lean burn operation condition is satisfied by a not-shown lean burn operation condition determination routine. In addition,
In the lean burn operation condition determination routine, for example, it is determined that the lean burn operation condition is satisfied under the following conditions.
That is, the elapsed time after the start of the engine has passed the set time (for example, 20 to 40 sec) or more, the engine operation range is in the low- to medium-load lean burn operation range, the warm-up has been completed, and the vehicle speed has been increased. Is a predetermined speed (for example,
When the speed is equal to or less than 120 km / h), it is determined that the lean burn operation condition is satisfied. Otherwise, it is determined that the lean burn operation condition is not satisfied.

If the lean burn condition is not satisfied in step S31, that is, if the engine is operating under the normal stoichiometric air-fuel ratio, the flow branches to step S32, where the lean shift correction coefficient KLNST is cleared, and the flow proceeds to step S35.
The lean shift correction coefficient KLNST is used to smoothly shift from the operation based on the stoichiometric air-fuel ratio to the lean burn operation without causing a sudden torque fluctuation.
As shown in FIG. 9, from the time when the lean condition is satisfied, the value is set to 1 by the set value K ₀ every calculation cycle (in this embodiment, the angle cycle).
(100%).

On the other hand, when it is determined in step S31 that the lean burn condition is satisfied, the process proceeds to step S33, and it is determined whether the lean transition correction coefficient KLNST has reached 1. If KLNST = 1, the process jumps to step S35, and if KLNST = 1, the process proceeds to step S34.

[0055] When the processing proceeds to step S34, and updated with the value obtained by adding the set value K ₀ at the time of correction coefficient KLNST lean transition,
Proceed to step S35. Then, steps S32 and S3
3 or the process proceeds from step S34 to step S35, based on the basic fuel injection amount Tp and the engine speed Ne, which are representatives of the engine load, and sets a basic lean decrease value KLNMAP with reference to a map with interpolation calculation. The basic lean decrease value KLNMAP is a basic value indicating how much the target air-fuel ratio A / F during lean burn operation is lean-corrected with respect to the stoichiometric air-fuel ratio. This value is an optimal value (1> KLNMAP ≧ 0) obtained in advance from an experiment or the like for each operation region specified by the engine speed Ne and the basic fuel injection amount Tp in a map as shown in FIG. Is stored. In addition, this basic lean weight loss value KLNM
AP is a value set for performing lean burn operation in a constant speed state from the low-speed low-load operation region to the medium-load operation region, and therefore, as shown in FIG. KLNMAP = 0 is set in the load operation region and the high load operation region.

Next, the routine proceeds to step S36, where the lean limit correction value K set in the lean limit correction value setting routine is set.
Read SURGE. FIGS. 11 and 12 are flowcharts showing a lean limit correction value setting routine during the lean burn operation.

As shown in FIG. 11, first, in step S4
In 1, it is determined whether or not the lean burn operation condition is satisfied.
The determination is made with reference to a determination value in a lean burn operation condition determination routine (not shown).

When the lean-burn operation condition is not satisfied, that is, when the operation state is based on the stoichiometric air-fuel ratio, step S4 is executed.
Proceed to 2. Then, all the combustion pressure data P1, P2,... Pn-1, Pn stored in the backup RAM 44 are cleared (Pn ← 0, Pn−1 ← 0, P2 ← 0,
P1 ← 0). Next, in step S43, the combustion pressure data count value N is cleared (N ← 0), and the routine exits.

On the other hand, if it is determined in step S41 that the lean burn operation condition is satisfied, the process proceeds to step S44, where the current combustion stroke cylinder #i is determined from the interrupt input of the cam pulse, and in step S45, the combustion stroke cylinder #i is determined. Is detected.

Next, in step S46, the first to (n-1) th combustion pressure data Pn to Pn-1 stored in the backup RAM 44 are sequentially incremented and updated, and the current combustion pressure P # i is incremented by one. The second combustion pressure data P1 is updated (Pn ← Pn−1, Pn−1 ← Pn−
2,... P3 ← P2, P1 ← P # i).

Then, in step S47, it is determined whether or not the count value of the combustion pressure data has reached the set number. If the count has reached, the process jumps to step S50, and if not, the process proceeds to step S48.

In step S48, the combustion pressure data count value N is counted up. Then, in a succeeding step S49, it is determined whether or not the combustion data count value N (N ≦ n) is equal to or more than a minimum number m (for example, 2) required for the calculation. N
If ≧ m, the process proceeds to step S50.

In step S50, the backup RAM
The average value (the average combustion pressure value) of the first to Nth combustion pressure data (the Nth combustion pressure data when N = n is determined in step S47 is Pn) stored in 44. ) Pave is calculated from the following equation.

[0064]

(Equation 2)

Subsequently, in step S51, the combustion pressure average value Pav of each of the first to Nth combustion pressure data is obtained.
dispersion value (combustion pressure dispersion value) P, which is the average deviation from e
sig is calculated from the following equation.

[0066]

(Equation 3)

Then, in step S52, the combustion pressure fluctuation rate Px is calculated from the ratio of the combustion pressure dispersion value Psig to the combustion pressure average value Pave (Px ← Psig /
Pave).

Thereafter, in step S53, a combustion state comparison reference value Pxs is set based on the engine operating state.
The combustion state comparison reference value Pxs is, for example, an engine speed Ne and a basic fuel injection amount T representative of the engine load.
It is set by referring to the map with interpolation calculation using p as a parameter. This map characteristic is, for example, as shown in FIG.
As shown in FIG. 3, a low value combustion state comparison reference value Pxs is stored in the low rotation low load operation region,
A combustion state comparison reference value Pxs having a gradually higher value is stored as the vehicle shifts to the high load operation region.

Next, in step S54, the combustion pressure fluctuation rate Px is compared with a combustion state comparison reference value Pxs.
Step S when the lean limit of ≤Pxs has not been reached
Go to 55. Then, the lean limit correction value KSURGE stored in the RAM 43 is updated with a value increased by the rich correction amount SURG1 (KSURGE ← KSURGE + S
URG1), exits the routine.

On the other hand, if it is determined in step S54 that the lean limit of Px> Pxs has been reached, the flow branches to S56. Then, the lean limit correction value stored in the RAM 43 is updated with a value reduced by the lean correction amount SURG2 (KSURGE ← KSURGE-SURG2), and the routine exits.

As a result, the lean limit correction value KSURGE stored in the RAM 43 is increased to a value at which the lean limit is reached, and is reduced to a value at which the lean limit is avoided when the lean limit is reached.

In this manner, the lean limit correction value KSUR
GE is obtained, and the value is read in S36, and the value is read in S36. Then, in step S37, a target lean reduction coefficient KLEAN for determining a target air-fuel ratio during lean burn operation is set. That is, the basic lean reduction value K set in S35
LNMAP is corrected by the lean shift correction coefficient KLNST and the lean limit correction value KSURGE to set a target lean reduction coefficient KLEAN (KLEAN ← KLN).
MAP / KLNST / KSURGE), and exit the routine.

When the target lean reduction coefficient setting subroutine is completed, the flow returns to FIG. 7 and proceeds to step S25 of the next target equivalent ratio setting routine. Then, this step S25
, The full opening increase coefficient KFULL, the start increase coefficient K
AS, water temperature increase coefficient KTW, target lean decrease coefficient KLE
The target equivalence ratio KTGT is set from the following equation based on AN, and the routine exits.

[0074]

(Equation 4)

In this case, since the fully-open increase coefficient KFULL, the increase coefficient after starting KAS, and the water temperature increase coefficient KTW during the lean burn operation are all 0 as described above, the target equivalent ratio K
TGT becomes KTGT ← 1-KLEAN. Therefore,
The target lean reduction coefficient KLEAN is a substantial parameter when setting the target air-fuel ratio A / F during lean burn operation.

The target purge flow ratio calculating means 54 obtains a target purge flow ratio PRATIO corresponding to the target air-fuel ratio from the basic purge flow ratio PRTO and the target equivalent ratio KTGT calculated as described above. FIG. 14 is a flowchart showing a target purge flow ratio setting routine for calculating the target purge flow ratio PRATIO.

This target purge flow ratio setting routine is executed at set intervals. First, the basic purge flow ratio PRTO is read in step S61, and the target equivalence ratio KTGT is read in step S62. Then, in step S63,
The target purge flow ratio PRATIO is set by correcting the basic purge flow ratio PRTO with the target equivalence ratio KTGT (PRAT
(IO ← PRTO / KTGT), exits the routine. When the fuel vapor purge condition is not satisfied, the target purge flow rate ratio PTO is set because the basic purge flow rate ratio PRTO is set.
RATIO is set to 0.

The target purge flow rate calculating means 55 calculates the target purge flow rate ratio PRATIO obtained as shown in FIG.
A target purge flow rate TPURGE corresponding to the target air-fuel ratio is determined. Then, the CPC valve opening calculating means 56 sets the opening of the CPC valve 18 based on the value, and operates the CPC valve 18. FIG. 15 shows the target purge flow rate TPU
It is the flowchart which showed the procedure which calculates | requires RGE and sets the CPC valve opening degree PVO.

The routine for setting the opening degree of the CPC valve shown in FIG. 15 is executed in each set cycle, and the target purge flow rate calculating means 55 firstly sets the air flow meter 3 in step S71.
The intake air amount Qa calculated based on the output signal of No. 3 is read. Next, in step S72, the target purge flow rate TPURGE of the evaporated fuel corresponding to the intake air quantity Qa is set by multiplying the intake air quantity Qa by the target purge flow rate ratio PRATIO calculated by the target purge flow rate ratio calculation means 54. (TPURGR ← Qa · PRATIO).

Next, the CPC valve opening calculating means 56
In step S73, the intake pipe pressure Pm calculated based on the output signal of the pressure sensor 71 is read. Then, in step S74, the intake pipe pressure Pm and the target purge flow rate TPUR
The opening degree PVO of the CPC valve 18 is set by referring to the map based on the GE with interpolation calculation.

As shown in FIG. 16, the map includes
As the intake pipe pressure Pm detected as an absolute value is lower (negative pressure is deeper) and the target purge flow rate TPURGE is smaller, a smaller valve opening PVO is stored. Further, the higher the intake pipe pressure Pm (the lower the negative pressure) and the greater the target purge flow rate TPURGE, the larger the valve opening PVO.
Is stored.

Then, in step S75, the calculated CP
A drive signal corresponding to the C-valve opening degree PVO is output to the CPC valve 18 and the routine exits. As a result, the purge flow rate of the fuel vapor stored in the canister 16 becomes CP
It is adjusted by the valve opening of the C valve 18. When the fuel vapor purge condition is not satisfied, the target purge flow ratio PR
Since ATIO is set to 0, the target purge flow rate T
PURGE is set to 0, and accordingly, the CPC valve opening PVO is set to 0.

On the other hand, the CPC valve opening PVO is
It can also be obtained from the pressure around the valve 18, the evaporation temperature, and the target purge flow rate TPURGE by using the orifice equation. That is, the CPC valve 18 is regarded as an orifice, and the flow rate of the compressible fluid can be calculated by the following equation by applying the formula.

[0084]

(Equation 5)

In the above equation, Qa is the mass flow rate of air passing through the CPC valve, C is the flow rate correction coefficient, A is the air passage area, κ
Is a specific heat ratio = 1.4, R is a gas constant of air, Pa is an atmospheric pressure, Ta is an atmospheric temperature as an intake air temperature, and KP is a correction coefficient. Note that the flow rate correction coefficient C is the engine speed Ne.
And a pressure ratio PR = Pm / Pa (Pm: intake pipe pressure). Note that KP takes the following value, and the result is stored in advance as a one-dimensional table of the pressure ratio PR.

[0086]

(Equation 6)

When this is applied to the CPC valve 18, the pressure sensor 7 provided downstream of the throttle valve 9 is considered.
1 to detect the intake pipe pressure Pm,
The pressure is the downstream pressure of the valve 18. Next, the atmospheric pressure Pa is estimated from the value of the pressure sensor 71 at the time of starting or when the throttle valve 9 is fully opened, and this is set as the upstream pressure of the CPC valve 18. Further, the intake air temperature Ta detected by the intake air temperature sensor 72 is used as the temperature of the purge evaporator, and this is regarded as the evaporator temperature. Further, the target purge flow rate TPURGE is set to C
The air mass flow rate Qa passing through the PC valve is defined as Qa. From these values, it is possible to determine the opening of the CPC valve 18 using the above-mentioned orifice equation. FIG. 17 is a functional block diagram of the CPC valve opening calculating means 56 when the opening of the CPC valve 18 is determined using the orifice equation.

As shown in FIG. 17, in this case, the CPC valve opening calculating means 56 calculates the intake pipe pressure Pm and the atmospheric pressure Pa
Ratio calculating means 81 for calculating the pressure ratio PR from the pressure ratio, a correction coefficient calculating means 82 for calculating the correction coefficient KP from the pressure ratio PR = Pm / Pa using a map, and an engine speed Ne.
And a flow rate correction coefficient calculating means 83 for calculating a flow rate correction coefficient C using a map from the pressure ratio PR. Further, there is provided a KF calculating means 84 for calculating K1 from the intake air temperature Ta and the atmospheric pressure Pa, and calculating KF from this and the correction coefficient KP. Further, an effective opening area calculation unit 85 for obtaining an air passage area A from the obtained KF, the target purge flow rate TPURGE, and the flow rate correction coefficient C to calculate an effective opening area of the CPC valve 18.
Having. In addition, from the effective opening area, an opening degree of the CPC valve 18 is calculated using a map as shown in FIG. 18, and an opening degree setting means 86 for setting the CPC valve opening degree PVO is provided. .

With this configuration, C for supplying the target purge flow rate TPURGE under the current conditions is obtained.
The opening of the PC valve 18 is set. When the effective opening area is calculated by the effective opening area calculation unit 85 to be equal to or larger than the effective opening area when the CPC valve 18 is fully opened, the CPC valve 18 is maintained at the full opening degree.

On the other hand, the actual purge flow rate ratio calculating means 58
From the actual flow rate of the PC valve 18 and the amount of air actually passing through the throttle valve 9, an actual purge flow rate ratio SPRATIO (SPRATIO = actual CPC valve flow rate / actual throttle valve passing air quantity), which is an actual purge flow rate ratio, is calculated. calculate.

In this case, the actual purge flow rate ratio calculating means 58
Is calculated from the CPC valve opening calculating means 56 to the CPC valve 1
The actual opening of the CPC valve 18 is obtained by applying the actual opening of the CPC valve 8 to the map shown in FIG. Then, using the orifice equation described above,
The actual flow rate of the C valve 18 is obtained. That is, CPC
The actual evaporation flow rate is obtained from the pressure around the valve 18 and the evaporation temperature. Note that the functional configuration for that is almost the same as that in FIG.

On the other hand, the amount of air actually passing through the throttle valve 9 is similarly calculated. That is, first, from the actual throttle opening detected by the throttle opening sensor 32, the actual throttle effective opening area is calculated using a map as shown in FIG. Next, from the pressures before and after the throttle valve 9 and the air temperature passing through the throttle valve 9, the actual amount of air passing through the throttle valve is obtained using the above-mentioned orifice equation. At this time, the pressure before and after the CPC valve 18 may be applied as the pressure before and after the throttle valve 9, and a value equal to the evaporation temperature may be applied as the temperature of the air passing through the throttle valve.

The actual amount of air passing through the throttle valve is the air flow meter 3 in the system shown in FIG.
3 means the intake air amount detected. Therefore, the actual purge flow rate ratio SPRATIO = actual CPC valve flow rate / Qa is calculated without using the detected value Qa of the air flow meter 33 instead of calculating the throttle effective opening area.
Can also be calculated as

Next, in the evaporation correction coefficient calculating means 59,
Based on the actual purge flow rate ratio SPRATIO determined in this manner, an evaporation correction coefficient KEVAPO for correcting the fuel injection amount from the injector 12 is calculated. Here, the final fuel injection amount (final fuel injection effective pulse width) Ti from the injector 12 is expressed by the following equation.

[0095]

(Equation 7)

Here, Tp is the basic injection pulse width, LAM
BDA is an air-fuel ratio feedback coefficient, and KBLRC is an air-fuel ratio learning correction coefficient. In this case, the evaporation correction coefficient KE
VAPO is expressed as follows using the evaporation concentration coefficient KEVPCON. The evaporation correction coefficient calculation means 59 calculates the actual purge flow rate ratio SPRATIO and the evaporation concentration coefficient KEVP.
An evaporation correction coefficient KEVAPO is calculated from CON.

[0097]

(Equation 8)

By the way, the evaporation concentration coefficient KEVPCON
Is calculated by subtracting the target equivalent ratio from the evaporation equivalent ratio. However, since the ratio of the evaporation equivalent is often equal to the target equivalent ratio, this may be represented by the evaporation equivalent ratio. Therefore, the evaporation concentration coefficient KEVPCO
N can be calculated from the evaporated fuel concentration χ _ev detected by the evaporation concentration sensor 73. Based on this, the evaporation correction coefficient calculating means 59 calculates the evaporation correction coefficient KEVAP.
O is calculated.

The evaporation concentration coefficient KEVPCON is
As described above, the evaporated fuel concentration か ら
_Although it is possible to detect and calculate _ev , the evaporative fuel concentration is estimated and calculated so that the correction control amount based on the air-fuel ratio feedback control based on the detection value of the O ₂ sensor 39 is reduced, and the evaporation concentration coefficient is calculated therefrom. It is also possible to estimate KEVPCON.

That is, in the state where the engine is operated and the evaporative purge is being performed, the first-order lag value n-LAMBDA of the air-fuel ratio feedback coefficient LAMBDA is calculated by the above-described fuel injection amount calculation formula. And the evaporative concentration coefficient KEVPCON can be estimated from the predetermined control value.

Here, the threshold value is set to LAMBDA. L1,
LAMBDA L2, LAMBDA H1, LAMBDA
H2, and the control value is KCON L1, KCON
L2, KCON H1, KCON Assuming H2,
Calculation of evaporation concentration coefficient KEVPCON is possible
It is.

[0102]

(Equation 9)

The fuel injection amount calculating means 60 calculates the final fuel injection pulse width Ti based on the evaporation correction coefficient KEVAPO calculated in this manner and the fuel injection amount calculation formula.
Is calculated. Then, the calculated final fuel injection pulse width T
A drive signal corresponding to i is output to the injector 12. As a result, the timer 45 is started at a predetermined timing, a drive pulse signal of the final fuel injection pulse width Ti is output to the injector 12 of the combustion stroke cylinder, and the predetermined fuel is injected from the injector 12.

At this time, if the evaporative purge condition is satisfied, the CPC valve 18 opens and the canister 16
Is purged into the air chamber 70 as an air-fuel mixture. In the air-fuel ratio control device according to the present invention, the purge flow rate of the evaporated fuel from the CPC valve 18 is
Based on the evaporated fuel concentration _{ev ev} and the target equivalence ratio KTGT that determines the target air-fuel ratio during lean burn operation, control is performed so as to be a constant rate with respect to the intake air amount. Therefore, during lean burn operation, even if the target air-fuel ratio changes in each operation region or operation state, the degree to which the evaporated fuel gives fuel disturbance to the air-fuel ratio control is always constant, and good air-fuel ratio controllability can be obtained. it can.

Further, since the air-fuel ratio does not fluctuate greatly even when the fuel vapor is purged, the air-fuel ratio feedback coefficient LAMBD set based on the output signal from the O ₂ sensor 39 is set.
It is possible to improve the convergence of A to the target air-fuel ratio and the followability when controlling the lean limit. Further, since the fuel vapor is purged at a constant rate, it is possible to prevent the occurrence of knocking, surge, and misfire even in the situation where the fuel vapor is purged to the maximum amount.

Furthermore, in the air-fuel ratio control device, the final fuel injection amount is determined by calculating the evaporation correction coefficient based on the actual purge flow ratio, so that the target fuel flow cannot be ensured. Thus, the fuel injection amount can be feed-forward corrected in the entire operation range.
Therefore, since the influence of the evaporated fuel on the air-fuel ratio can be eliminated, a large amount of evaporative purge can be performed while maintaining high air-fuel ratio controllability.

20 and 21 show the engine speed N
e and the target air-fuel ratio A / set for each operation region specified by the intake air amount per stroke or the throttle opening.
F and a target purge flow ratio PRATIO (%) when the basic purge flow ratio PRTO is set to 2%. FIG.
As shown at 0 and 21, in the lean burn operation region, the target purge flow rate ratio PRATIO that is substantially proportional to the target air-fuel ratio A / F is set.

(Embodiment 2) FIG. 22 is a block diagram showing a main configuration of functions related to air-fuel ratio control in an air-fuel ratio control device according to Embodiment 2 of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and the details are omitted.

The air-fuel ratio control device is a more simplified configuration of the air-fuel ratio control device of the first embodiment. That is, here, as shown in FIG.
Is obtained from the target purge flow ratio PRATIO and the opening of the throttle valve 9, so that the target purge flow calculating means 55 in FIG. 3 is omitted.

In this case, the throttle valve opening calculating means 57 calculates the actual effective opening area from the opening of the throttle valve 9. To calculate the effective opening area,
A table as shown in FIG. 19 is used. Next, C
In the PC valve opening calculating means 56, the throttle valve 9
Of the CPC valve 18 is calculated from the effective opening area of the CPC valve 18 and the target purge flow ratio PRATIO (CPC valve effective opening area = actual throttle effective opening area × P
RATIO). Then, after calculating the effective opening area of the CPC valve 18, the CP of the CPC valve 18 is calculated using the table of FIG.
The opening degree PVO of the C valve 18 is calculated.

On the other hand, in the air-fuel ratio control apparatus according to the second embodiment, the actual purge flow rate ratio calculating means 58 differs from the previous case in that the actual purge flow rate ratio SPRATIO Is calculated. Here, the actual purge flow rate ratio calculating means 58 first obtains the effective opening area from the opening degree PVO of the CPC valve 18 using the table of FIG. Next, the actual effective opening area of the throttle valve 9 obtained by the throttle valve opening calculating means 57 is read, and the ratio between the two is obtained to calculate the actual purge flow rate ratio SPRATI (SPRATI).
O = actual CPC valve effective opening area / actual throttle effective opening area). In addition, other configurations and actions are as follows.
This is the same as in the first embodiment.

As a result, it is not necessary to detect the pressures before and after the CPC valve 18 and the throttle valve 9 and the purge evaporating temperature (throttle passing air temperature) as in the first embodiment, and the configuration of the control device can be simplified. The cost can be reduced.

(Embodiment 3) FIG. 23 is a block diagram showing a main configuration of functions related to air-fuel ratio control in an air-fuel ratio control device according to Embodiment 3 of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and the details are omitted.

The air-fuel ratio control device is obtained by changing the throttle valve 9 in FIG. 1 to an electronic control throttle.
That is, in the control device of FIG. 23, a target torque calculating unit 62, a target air amount calculating unit 63, and a throttle valve opening calculating unit 64 are added instead of the throttle valve opening calculating unit 57 of FIG. Is similar to that of FIG.

Here, the target torque calculating means 62 calculates the torque required for the current driving condition from the detection values of the various sensors. In the control device, the basic target torque is first calculated by referring to a map from the accelerator opening and the engine speed operated by the driver,
The target torque value is calculated by adding a torque required to maintain a target idle rotation speed at the time of idling of the accelerator OFF and a torque required for driving auxiliary equipment.

The target air amount calculating means 63 calculates a throttle intake target air amount (hereinafter, abbreviated as a target air amount) required to realize the target torque. In the control device, the cylinder intake air amount required to achieve the target torque is obtained by referring to a map or the like, and the inverse chamber model (the relational expression between the cylinder intake air amount and the intake air amount passing through the throttle) is obtained from this value. ) Is used to determine the target air volume.

Then, the throttle valve opening calculating means 6
4 calculates the required opening degree of the throttle valve 9 from the value of the target air amount by using the orifice formula or referring to a map, and sends out a signal for driving the throttle valve 9.

On the other hand, the target purge flow rate TPURGE is determined by the target purge flow rate ratio PRATIO and the target air amount calculation means 63.
(TPURGE)
= Target air quantity x PRATIO). In this case, the control device first calculates the target intake air amount passing through the throttle valve, and drives the electronic control throttle and the CPC valve 18 based on this. Therefore, the actuators can be driven almost simultaneously. Therefore, since a response delay occurs between the actuators in a parallel state, it is possible to cancel each other's delay. In addition, it is possible to eliminate the influence of sensor detection delay or calculation delay that occurs when the air flow meter 33 detects the intake air amount, and thus it is possible to perform highly accurate evaporative purge control.

The present invention is not limited to the above embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, the target equivalent ratio K
Although the TGT is determined by the target equivalent ratio calculating means 53, the target equivalent ratio KTGT is also set when calculating the fuel injection amount in the fuel injection control. The value calculated by the fuel injection control system may be read.

In the above-described embodiment, the description has been made assuming that the air sucked into the engine is one that passes through the throttle valve 9 and one that passes through the CPC valve 18. 24 and other intake air passages are considered to be included in the throttle valve 9, and the above processing is performed.

[0122]

From the actual valve opening of the CPC control valve, the throttle valve opening and the intake air amount, the actual purge flow ratio, which is the ratio between the actual flow rate of fuel vapor and the actual intake air amount, is calculated. Since the final fuel injection amount is determined by calculating the evaporation correction coefficient based on the actual purge flow ratio, the fuel injection amount is corrected in the entire operation region by feed forward correction regardless of whether the target purge flow amount can be secured. can do. Therefore, since the influence of the evaporated fuel on the air-fuel ratio can be eliminated, a large amount of evaporative purge can be performed while maintaining high air-fuel ratio controllability.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an engine control system.

FIG. 2 is a circuit configuration diagram of an electronic control system in the air-fuel ratio control device according to the first embodiment of the present invention.

FIG. 3 is a block diagram illustrating a main configuration of an ECU.

FIG. 4 is an explanatory diagram showing a state of a purge start correction coefficient PRTST.

FIG. 5 is an explanatory diagram showing a state of a fuel vapor concentration corrected flow rate ratio PRTCON.

FIG. 6 is a flowchart showing a procedure for calculating a basic purge flow rate ratio PRTO.

FIG. 7 is a flowchart showing a procedure for calculating a target equivalent ratio KTGT.

FIG. 8 is a flowchart showing a target lean reduction coefficient setting subroutine.

FIG. 9 is an explanatory diagram showing a state of a lean transition-time correction coefficient KLNST.

FIG. 10 is an explanatory diagram (map) showing a state of a basic lean decrease value KLNMAP.

FIG. 11 is a flowchart illustrating a lean limit correction value setting routine during a lean burn operation.

FIG. 12 is a flowchart following FIG. 11 showing a lean limit correction value setting routine during lean burn operation.

FIG. 13 is an explanatory diagram (map) showing a state of a combustion state comparison reference value Pxs.

FIG. 14 is a flowchart showing a target purge flow ratio setting routine for calculating a target purge flow ratio PRATIO.

FIG. 15 is a graph showing a relationship between a target purge flow rate TPURGE and CPC.
It is the flowchart which showed the procedure which sets the valve opening degree PVO.

FIG. 16 is an explanatory diagram (map) showing a state of a CPC valve opening degree PVO.

FIG. 17 is a functional block diagram of a CPC valve opening calculating means when the opening of the CPC valve is determined using the orifice equation.

FIG. 18 is a map showing a relationship between the effective opening area of the CPC valve and the opening degree of the CPC valve.

FIG. 19 is a map showing the relationship between the effective opening area of the throttle valve and the throttle valve opening.

FIG. 20 is a map showing a target air-fuel ratio A / F set for each operation region specified by the engine speed Ne and the intake air amount per one stroke or the throttle opening.

FIG. 21 is a target purge flow ratio set for each operation region specified by the engine speed Ne and the intake air amount per stroke or the throttle opening when the basic purge flow ratio PRTO is set to 2%. It is a map which shows PRATIO (%).

FIG. 22 is a block diagram illustrating a main configuration of functions related to air-fuel ratio control in the air-fuel ratio control device according to the second embodiment of the present invention.

FIG. 23 is a block diagram illustrating a main configuration of functions related to air-fuel ratio control in an air-fuel ratio control device according to Embodiment 3 of the present invention.

[Explanation of symbols]

1 engine 8 an intake passage 9 a throttle valve 12 injector 16 canister 17 purge passage 18 CPC valve 32 throttle position sensor 33 air flow meter 39 O ₂ sensor 52 basic purge flow ratio calculating section 53 target equivalent ratio calculation unit 54 target purge flow rate calculating means 55 target purge flow rate calculation means 56 CPC valve opening degree calculation means 57 throttle valve opening degree calculation means 58 actual purge flow rate ratio calculation means 59 evaporation correction coefficient calculation means 60 fuel injection amount calculation means 61 evaporation concentration calculation means 62 target torque calculation means 63 Target air amount calculating means 64 Throttle valve opening calculating means 71 Pressure sensor 72 Intake air temperature sensor 73 Evaporation concentration sensor 74 In-cylinder pressure sensor KLNMAP Basic lean decrease value KSURGE Lean limit correction value KTGT eyes Equivalent ratio PR pressure ratio PRATIO target purge flow ratio PRTCON evaporative fuel concentration correction flow ratio PRTO basic purge flow ratio PRTST purge start correction coefficient PVO CPC valve opening Pa atmospheric pressure Pave average combustion pressure Pm intake pipe pressure Psig combustion pressure dispersion Value Px Combustion pressure fluctuation rate Pxs Combustion state comparison reference value Qa Intake air amount, CPC valve passing air mass flow rate SPRATIO Actual purge flow rate ratio SURG1 Rich correction amount SURG2 Lean correction amount TPURGE Target purge flow rate Ta Intake temperature (atmospheric temperature) Ti Final fuel Pulse width (final fuel injection amount) Tp Basic injection pulse width (basic fuel injection amount) Tw Cooling water temperature κ Specific heat ratio _{ev ev} Evaporated fuel concentration

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F02D 45/00 301 F02D 45/00 301G F-term (reference) 3G084 AA04 BA09 BA13 BA27 CA00 CA09 DA04 EB08 EB13 EC04 FA00 FA07 FA10 FA11 FA13 FA21 FA26 FA29 FA33 3G301 HA14 HA15 JA11 KA06 KA23 MA01 MA11 NA09 NC04 ND03 ND05 ND36 NE15 PA01Z PA07Z PA10Z PA11Z PB01Z PB09Z PC01Z PD02Z PE00Z PE03Z PE08Z PF00Z

Claims (8)

[Claims] A canister for adsorbing evaporative fuel generated in the fuel tank and a canister purge for controlling a purge amount of evaporative fuel stored in the canister in an evaporative fuel purge passage communicating the fuel tank with an intake system. A lean-burn engine that is provided with a control valve and is operated at an air-fuel ratio smaller than the stoichiometric air-fuel ratio in a predetermined operation region, determines an air-fuel ratio feedback correction coefficient based on a detection value of an air-fuel ratio sensor, and performs basic fuel injection. An air-fuel ratio control device for a lean burn engine that controls the amount of fuel supplied to the engine by correcting the amount by the air-fuel ratio feedback correction coefficient, wherein the ratio between the evaporated fuel purge flow rate and the intake air amount during stoichiometric air-fuel ratio operation is calculated. Basic purge flow ratio calculating means for calculating a basic purge flow ratio, and the basic purge flow ratio and lean A target purge flow ratio calculating means for calculating a target purge flow ratio of the evaporated fuel to the intake air amount based on the target air-fuel ratio during the lean operation, and a target of the evaporated fuel based on the target purge flow ratio and the intake air amount. Target purge flow rate calculating means for calculating a purge flow rate; canister purge control valve opening degree calculating means for calculating a valve opening degree of the canister purge control valve based on the target purge flow rate; and an actual valve of the canister purge control valve An actual purge flow ratio calculating means for calculating an actual purge flow ratio which is a ratio between an actual flow rate of the fuel vapor and an actual intake air amount from the opening and the intake air amount or the throttle valve opening; Correction unit that corrects the fuel injection amount from the injector according to the purge amount of the fuel vapor based on the fuel vapor concentration and the fuel vapor concentration. Evaporation correction coefficient calculating means for calculating, based on the evaporation correction coefficient and the air-fuel ratio feedback correction coefficient, a fuel injection amount calculating means for correcting the basic fuel injection amount and calculating a fuel injection amount from the injector. An air-fuel ratio control device for a lean burn engine, comprising: 2. A canister for adsorbing evaporative fuel generated in the fuel tank and a canister purge for controlling a purge amount of evaporative fuel stored in the canister in an evaporative fuel purge passage communicating the fuel tank with an intake system. A lean-burn engine that is provided with a control valve and is operated at an air-fuel ratio smaller than the stoichiometric air-fuel ratio in a predetermined operation region, determines an air-fuel ratio feedback correction coefficient based on a detection value of an air-fuel ratio sensor, and performs basic fuel injection. An air-fuel ratio control device for a lean burn engine that controls the amount of fuel supplied to the engine by correcting the amount by the air-fuel ratio feedback correction coefficient, wherein the ratio between the evaporated fuel purge flow rate and the intake air amount during stoichiometric air-fuel ratio operation is calculated. Basic purge flow ratio calculating means for calculating a basic purge flow ratio, and the basic purge flow ratio and lean A target purge flow ratio calculating means for calculating a target purge flow ratio of evaporative fuel to an intake air amount based on a target air-fuel ratio in a canister operation; and the canister based on the target purge flow ratio and a throttle valve opening. A canister purge control valve opening calculating means for calculating the valve opening of the purge control valve; and an actual flow rate of the fuel vapor and an actual intake air amount based on the actual valve opening and the throttle valve opening of the canister purge control valve. An actual purge flow rate ratio calculating means for calculating an actual purge flow rate ratio which is a ratio between the actual purge flow rate ratio and the evaporated fuel concentration, and an evaporator for correcting the fuel injection amount from the injector according to the purge amount of the evaporated fuel. An evaporation correction coefficient calculating means for calculating a correction coefficient, the evaporation correction coefficient and the air-fuel ratio feedback correction coefficient, Based on the air-fuel ratio control apparatus for a lean burn engine, characterized by having a fuel injection amount calculating means for correcting the basic fuel injection amount calculates the fuel injection quantity from the injector. 3. A canister for adsorbing evaporative fuel generated in the fuel tank and a canister purge for controlling a purge amount of evaporative fuel stored in the canister in an evaporative fuel purge passage communicating the fuel tank with an intake system. A lean-burn engine that is provided with a control valve and is operated at an air-fuel ratio smaller than the stoichiometric air-fuel ratio in a predetermined operation region, determines an air-fuel ratio feedback correction coefficient based on a detection value of an air-fuel ratio sensor, and performs basic fuel injection. An air-fuel ratio control device for a lean burn engine that controls the amount of fuel supplied to the engine by correcting the amount by the air-fuel ratio feedback correction coefficient, wherein the ratio between the evaporated fuel purge flow rate and the intake air amount during stoichiometric air-fuel ratio operation is calculated. Basic purge flow ratio calculating means for calculating a basic purge flow ratio, and the basic purge flow ratio and lean A target purge flow ratio calculating means for calculating a target purge flow ratio of evaporative fuel to an intake air amount based on a target air-fuel ratio at the time of engine operation, and a throttle for calculating an effective opening area of the throttle valve from the opening degree of the throttle valve. Valve opening calculating means; canister purge control valve opening calculating means for calculating the valve opening of the canister purge control valve from the target purge flow ratio and the effective opening area of the throttle valve; and the canister purge control valve An actual purge flow ratio calculating means for calculating an actual purge flow ratio which is a ratio between an actual flow rate of the evaporated fuel and an actual intake air amount from the actual valve opening and the throttle valve opening; From the fuel vapor concentration and the fuel vapor concentration, the fuel injection amount from the injector is compensated according to the fuel vapor purge amount. An evaporation correction coefficient calculating means for calculating an evaporation correction coefficient to be calculated, and a fuel injection for correcting the basic fuel injection amount to calculate a fuel injection amount from the injector based on the evaporation correction coefficient and the air-fuel ratio feedback correction coefficient. An air-fuel ratio control device for a lean burn engine, comprising: an amount calculating unit. 4. A canister for adsorbing evaporative fuel generated in the fuel tank and a canister purge for controlling a purge amount of evaporative fuel stored in the canister in an evaporative fuel purge passage communicating the fuel tank with an intake system. A control valve and an electronically controlled throttle for electrically controlling the intake air amount of the engine in accordance with the operating state of a lean burn engine that is operated at an air-fuel ratio smaller than the stoichiometric air-fuel ratio in a predetermined operation region. Determining an air-fuel ratio feedback correction coefficient based on the detection value of the air-fuel ratio sensor, and correcting the basic fuel injection amount with the air-fuel ratio feedback correction coefficient to control the amount of fuel supplied to the engine; A throttle valve that is required to achieve the torque required by the driver. Target air amount calculating means for calculating a target intake air amount of the throttle valve, throttle valve opening degree calculating means for calculating an opening degree of the throttle valve based on the target intake air amount, and an evaporative fuel purge flow rate during a stoichiometric air-fuel ratio operation. A basic purge flow ratio calculating means for calculating a basic purge flow ratio, which is a ratio between the target purge fuel ratio and the target air-fuel ratio during the lean burn operation. A target purge flow ratio calculating unit that calculates a purge flow ratio; a target purge flow ratio calculating unit that calculates a target purge flow amount of evaporative fuel from the target purge flow ratio and the intake target air amount; A canister purge control valve opening calculating means for calculating a valve opening of the canister purge control valve by using An actual purge flow ratio calculating means for calculating an actual purge flow ratio, which is a ratio between an actual flow rate of fuel vapor and an actual intake air amount, from an actual valve opening of the control valve and an intake air amount or a throttle valve opening. From the actual purge flow rate ratio and the evaporated fuel concentration, an evaporation correction coefficient calculating means for calculating an evaporation correction coefficient for correcting the fuel injection amount from the injector according to the purge amount of the evaporated fuel; and A fuel injection amount calculating means for correcting the basic fuel injection amount based on an air-fuel ratio feedback correction coefficient to calculate a fuel injection amount from an injector. 5. The air-fuel ratio control device for a lean burn engine according to claim 1, wherein said canister purge control valve opening calculating means includes: a suction pipe pressure;
An effective opening area of the canister purge control valve is calculated from an atmospheric pressure, a temperature of the fuel vapor mixture, and the target purge flow rate, and an opening degree of the canister purge control valve is calculated based on the effective opening area. An air-fuel ratio control device for a lean burn engine. 6. The air-fuel ratio control device for a lean burn engine according to claim 1, wherein the actual purge flow ratio calculating means obtains the actual purge flow ratio ratio from a valve opening of the canister purge control valve. An air-fuel ratio control apparatus for a lean burn engine, wherein an actual purge flow ratio is calculated from an effective opening area of a canister purge control valve and an effective opening area of a throttle valve obtained from a throttle valve opening. 7. The air-fuel ratio control device for a lean burn engine according to claim 1, wherein the evaporative correction coefficient calculating means is configured to calculate the fuel vapor based on the air-fuel ratio feedback correction coefficient. An air-fuel ratio control device for a lean burn engine, which estimates a concentration. 8. A canister for adsorbing evaporative fuel generated in the fuel tank and a canister purge for controlling a purge amount of evaporative fuel stored in the canister in an evaporative fuel purge passage communicating the fuel tank with the intake system. A control valve and an electronically controlled throttle for electrically controlling the amount of intake air of the engine in accordance with the operation state; a lean operation at a lower air-fuel ratio than the stoichiometric air-fuel ratio in a predetermined operation region. A fuel vapor purge control device for a burn engine, comprising: target air amount calculating means for calculating a target intake air amount of a throttle valve required to realize a torque required by a driver; A throttle valve opening calculating means for calculating an opening of the throttle valve based on the fuel vapor purge flow rate during stoichiometric air-fuel ratio operation; A basic purge flow ratio calculating means for calculating a basic purge flow ratio which is a ratio to the intake air amount; a target purge of evaporative fuel with respect to the intake air amount based on the basic purge flow ratio and a target air-fuel ratio during lean burn operation. A target purge flow rate calculating means for calculating a flow rate ratio; a target purge flow rate calculating means for calculating a target purge flow rate of evaporative fuel from the target purge flow rate ratio and the intake target air amount; and An evaporative fuel purge control device for a lean burn engine, comprising: a canister purge control valve opening calculating means for calculating a valve opening of the canister purge control valve.