JP2002081351A - Controller of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an evaporative emission from being emitted into the atmosphere due to an increase of evaporation to an amount beyond the limit of adsorption by a canister by allowing the purge of large amount of evaporation purge within the range not causing the deterioration of drivability independently of a variation in characteristics of each engine. SOLUTION: In an controller of an engine performing the purge of evaporation by controlling the opening of a purge control valve 21 installed in a purge passage 19 allowing an intake passage to communicate with a fuel tank 18, an ECU12 judges the stability of the combustion state of an engine 1, and performs evaporation purge control according to the combustion state of the engine. When judging that the stability of the combustion state is high, the ECU12 performs the purge control for increasing the purge amount of evaporation. When judging that the stability of the combustion state is low, the ECU12 performs the purge control for lowering the purge amount of evaporation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an engine, and more particularly, to a process for purging evaporated fuel (evaporation) generated in a fuel tank or the like.

[0002]

2. Description of the Related Art Heretofore, in order to prevent an evaporator generated in a fuel tank or the like from being released into the atmosphere, the generated evaporator is temporarily adsorbed in a canister, and the adsorbed evaporator is passed through a purge control valve. A system for purging an intake system is known. For example, Japanese Patent Application Laid-Open No. 9-2135
Japanese Patent Publication No. 8 discloses a technique for correcting the opening of a purge control valve in accordance with a change in the engine speed. Specifically, during the duty control of the purge control valve, when the fluctuation amount of the engine speed is large within a predetermined engine rotation region, the operation cycle of the purge control valve is made shorter than before. As a result, it is possible to eliminate the occurrence of variations in the evaporation suction amount of each cylinder and to prevent the air-fuel ratio of a specific cylinder from becoming lean, thereby suppressing surge of the vehicle.

[0003]

By the way, the characteristics of the engine are affected by variations in the components of each engine and changes over time. Therefore, the maximum amount of the evaporative purge that can be tolerated within a range that does not cause deterioration in drivability varies from engine to engine. The above prior art,
There is no mention of performing a large amount of evaporative purge in consideration of the individual characteristics of the engine.

Accordingly, an object of the present invention is to enable a large amount of evaporative purging within a range that does not cause deterioration in drivability, regardless of variations in the characteristics of individual engines, and to reduce evaporative emissions by exceeding the adsorbed amount limit of the canister. Prevent release to the atmosphere.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an evaporative purge system by controlling an opening degree of a purge control valve provided in a purge passage connecting an intake passage and a fuel tank. The control apparatus for the engine includes a determination unit that determines the stability of the combustion state of the engine, and a control unit that controls the purge control valve. When the stability of the combustion state is determined to be high by the determination means, the control means performs purge control for increasing the evaporation purge amount. Further, when it is determined that the stability of the combustion state is low, the control means performs purge control for reducing the amount of the evaporative purge. Through such purge control, it is possible to perform a large amount of evaporative purge within a range that does not deteriorate the combustion state and combustibility of the engine, and it is possible to prevent evaporative emissions from being released to the atmosphere due to exceeding the adsorption limit of the canister. It can be reliably prevented.

Here, when performing the purge control for increasing the evaporative purge amount, the control means preferably controls the purge control valve to open. Further, when performing the purge control for reducing the evaporation purge amount, the control means preferably controls the purge control valve in the closing direction.

In the above arrangement, the control means includes:
It is preferable to perform the above-described purge control in an operation state in which the determination accuracy regarding the stability of the combustion state is high, typically, in an idling operation in a neutral shift position at a stop.

Further, a sensor for detecting the engine speed may be added to the above configuration. In this case, the determination means determines the stability of the combustion state based on the detected fluctuation amount of the engine speed.

Further, a sensor for detecting the combustion pressure of the cylinder may be added to the above configuration. In this case, the determining means
The stability of the combustion state is determined based on the detected fluctuation amount of the combustion pressure.

Further, a sensor for detecting the exhaust air-fuel ratio may be added to the above configuration. In this case, the determining means
The stability of the combustion state is determined based on the detected fluctuation amount of the air-fuel ratio.

[0011]

FIG. 1 is an overall configuration diagram showing an example of an engine to which the present invention can be applied. The engine 1 of the present embodiment is a normal intake system fuel injection engine. Each intake port of the engine 1 is provided with an intake valve 2 and each intake port communicates with an intake manifold 3. The intake manifold 3 is provided with an injector 7 for injecting fuel toward an intake passage formed therein. The injectors 7 are individually provided for the respective cylinders, and are supplied with fuel (gasoline) adjusted to a predetermined pressure through a fuel pipe communicating with the fuel tank 18. The discharge electrode of the ignition plug 6 faces the combustion chamber of the engine 1. Further, each exhaust port of the engine 1 is provided with an exhaust valve 4 and each exhaust port communicates with an exhaust manifold 5.

The flow rate of the air from which dust and the like in the atmosphere have been removed by the air cleaner 8 is controlled in accordance with the degree of opening of the electric throttle valve 10. This throttle valve 1
Numeral 0 is interposed in an intake passage between the air cleaner 8 and the air chamber 9, and its opening is adjusted by an electric motor. The engine control device 12 (hereinafter referred to as “ECU”) calculates a throttle opening based on an engine speed, a depression amount of an accelerator pedal 30 corresponding to an engine required load, and the like, and a throttle valve 10 via an electric motor.
Control. The intake air whose flow rate has been adjusted by the throttle valve 10 flows through the air chamber 9 and is mixed with fuel injected from the injector 7 in the intake manifold 3. The mixture thus formed flows into the combustion chamber of the engine 1 by opening the intake valve 2. Then, the ignition plug 6 ignites and burns the air-fuel mixture, thereby generating a driving force of the engine 1.

Exhaust gas generated by the combustion of the air-fuel mixture is discharged from the combustion chamber to an exhaust manifold 5 by opening an exhaust valve 4. This exhaust gas is converted into harmful components CO, HC, and the like in the exhaust gas by a catalytic converter 13 provided downstream of the exhaust manifold 5.
NOx is appropriately purified and discharged to the atmosphere via the muffler 15.

The engine speed (idle speed) during idle operation is controlled by an ISC valve 16 (idle speed control valve). The ISC valve 16 is interposed in a bypass passage 17 that communicates between the upstream side and the downstream side of the throttle valve 10.
Is controlled by At the time of the idling operation in which the throttle valve 10 is in the fully closed state, the opening degree of the ISC valve 16 is appropriately set to secure the amount of intake air necessary for performing the idling operation.

Evaporation generated inside the fuel tank 18 and the like is appropriately discharged to the air chamber 9 of the intake system via an evaporation purge system having the following configuration. That is, the upper part of the fuel tank 18 communicates with the air chamber 9 via the purge passage 19 for discharging the evaporative generated in the fuel tank 18. This purge passage 1
9 is provided with a canister 20 and a purge control valve 21. The canister 20 has an adsorbing portion made of activated carbon or the like for adsorbing the evaporator, and a lower portion thereof is provided with a fresh air inlet for introducing air. In addition,
In the present embodiment, the ECU 12 is used as the purge control valve 21.
The duty solenoid valve whose duty is controlled by the above is adopted, but an appropriate one such as a linear solenoid valve or a step motor type can be adopted.

The ECU 12 comprises a microcomputer, R
It is composed of an OM, a RAM, an input / output interface, etc., and receives sensor signals from various sensors.
The in-cylinder pressure sensor 22 is provided for each cylinder of the engine 1 and detects the combustion pressure Pe of the cylinder based on the sensor signal. The HC sensor 24 is a sensor that detects the amount of evaporation, and is provided in the purge passage 19.
The ECU 12 detects the concentration of hydrocarbon HC in the purge passage 19, that is, the evaporative concentration De based on the sensor signal from the sensor 24, and opens the purge control valve 21 appropriately according to the evaporative concentration De. The throttle sensor 25 is “ON” when the throttle opening sensor for detecting the throttle opening θt and the throttle valve 10 are fully closed.
And a built-in idle switch. The accelerator opening sensor 29 is a sensor for detecting an accelerator opening θa corresponding to the depression amount of the accelerator pedal 30. The engine speed sensor 26 is a sensor for calculating the engine speed Ne. For example, a crank angle sensor that generates an output pulse every time the crankshaft rotates a predetermined angle can be used. The cooling water temperature sensor 27
The sensor faces the cooling water passage of the engine 1 and detects a water temperature Te as the engine temperature. The air-fuel ratio sensor 28 is a sensor for detecting an air-fuel ratio A / F (air-fuel ratio) from exhaust gas flowing through an exhaust passage, and for example, a linear O2 sensor (oxygen sensor) can be used. Originally, the exhaust air-fuel ratio A / F calculated from the output signal of the air-fuel ratio sensor 28 (hereinafter, referred to as “air-fuel ratio A / F”)
Is equal to the target air-fuel ratio when there is no disturbance in the fuel injection amount (for example, when the evaporative purge is not performed). However, the actual air-fuel ratio does not match the target air-fuel ratio when the air-fuel ratio is affected by disturbance such as inflow of evaporative fuel into the intake system or aging. Therefore, air-fuel ratio feedback control is performed to converge the air-fuel ratio A / F to the target air-fuel ratio.

The ECU 12 is provided with a shift control device 31 (hereinafter referred to as "TCU") mainly composed of a microcomputer for controlling an automatic transmission (not shown).
Two-way communication is being performed. Thereby, the ECU 12
Data such as the operation position SR indicating the range (P, R, N, D range, etc.) selected by a select lever (not shown) is received from the TCU 31.

The ECU 12 calculates a fuel injection amount, a fuel injection timing, an ignition timing, and the like necessary for performing appropriate combustion according to a control program stored in the ROM, and controls the injector 7 and the ignition plug 6. Output a signal. Further, the ECU 12 controls the throttle valve 10 to secure a necessary intake air amount, and also controls the ISC valve 16 so that the idle speed becomes equivalent to the target idle speed Ntrg. further,
The ECU 12 outputs the duty signal DUTY to the purge control valve 21 so that the purge control valve 2
1 is duty-controlled.

FIG. 2 is a flowchart showing an execution routine of the evaporative purge according to the present embodiment. This routine is started by a periodic interruption at a predetermined interval (for example, 10 ms). When this routine is started, in step 1, the ECU 12 sets the operation position SR and the engine speed N
Read various signals such as e.

Next, in step 2, the operation position S
Based on R, it is determined whether or not the current select range is “N range”. If the range is set to a range other than the “N range”, the processing of this routine in the current cycle is ended, and the execution in the next cycle is awaited. On the other hand, in the case of “N range”, the process proceeds from step 2 to step 3.

In step 3, the throttle sensor 2
It is determined whether or not the idle switch built in 5 is “ON”. When a negative determination is made in step 3, that is, when the throttle valve 10 is not open and the valve is not idling, the process of this routine is temporarily terminated, and when an affirmative determination is made, the process proceeds to step 4.

In step 4, it is determined whether the vehicle speed で is 0 km / h. If the vehicle is running, the process of this routine is temporarily ended. If the vehicle is stopped, the evaporative purge control routine is called (step 5). That is, the evaporative purge control described in detail below
This is executed in the idle operation state of the N range when the vehicle is stopped. The combustion state of the engine can be detected most stably and accurately in this operating state. The following evaporative purge control can be performed during idling operation in the D range when the vehicle is stopped.

FIG. 3 is a flowchart showing an evaporative purge control routine. When this routine is called by the above-described evaporative purge execution determination routine, first, in step 11, it is determined whether or not the start timing of the evaporative purge control, that is, whether or not it is the first execution cycle immediately after this routine is called. . If an affirmative determination is made in step 11, step 12
If the determination is negative (second and subsequent execution cycles), the process proceeds to step S13.

In step 12, the duty ratio DUTY of the purge control valve 21 during idling is calculated with reference to the duty ratio calculation map shown in FIG. The duty ratio calculation map is a map in which an appropriate duty ratio DUTY is set for each opening ISC of the ISC valve 16 during idling operation based on a simulation or an experiment in advance. Has been memory. Duty ratio DUTY is IS
It is uniquely specified from the opening ISC of the C valve 16 and the opening ISC
Increases as. With the duty ratio DUTY calculated in this way, the purge control valve 21
Is determined. The opening IS of the ISC valve 16
Since C has a correlation with the idle speed, the duty ratio DUTY may be calculated using the target idle speed as a basic parameter. When the processing of step 12 ends, the processing of this routine ends once.

Once the duty ratio DUTY has been set in step 12, in subsequent execution cycles, step 1
The processes after 3 are executed. In step 13, an evaluation value required to evaluate the stability of the combustion state of the engine is calculated. This evaluation value can be typically calculated from the engine speed Ne, the combustion pressure Pe, the air-fuel ratio A / F, etc., according to a method described below.

(Method 1) Combustion by Engine Speed Ne
Fluctuations in the combustion state of the stability evaluation engine appear as fluctuations in the engine speed Ne. Therefore, during idle operation, which is an almost steady operating state, an evaluation value indicating the degree of fluctuation of the engine speed Ne is obtained, and this value is compared with a predetermined determination value to evaluate the stability of the combustion state. can do. FIG. 5 is an explanatory diagram of the in-cylinder pressure characteristics and the engine speed characteristics during the idling operation. In the case of a four-cylinder engine, the cylinders # 1 to # 4 performing the combustion stroke are driven at 180 ° CA according to the ignition order (# 1, # 3, # 2, # 4).
The combustion process does not overlap between adjacent cylinders in the ignition order. Therefore, during a period from immediately after the end of the combustion stroke of a certain cylinder to the start of the combustion stroke of the next cylinder, a section which is not affected by the combustion of each cylinder (therefore, suitable for the evaluation of combustion stability). ) Exists. Thus, for example, an engine rotation fluctuation amount (evaluation value) for each predetermined crank angle is calculated from a plurality of samples N # 1 to N # 4 appropriately extracted in this section, and this fluctuation amount is equal to or more than a predetermined determination value. When it has become, it is determined that the combustion stability has decreased (for example, Japanese Patent Laid-Open No.
Reference). Alternatively, the variance average of the sample may be used as the evaluation value in the same manner as (method 3) described later (the same applies to method 2).

(Method 2) Combustion stability by combustion pressure Pe
When the combustion state of the evaluation engine fluctuates, the combustion pressure Pe of the cylinder
(In-cylinder pressure) also changes. Therefore, during idling operation, an evaluation value indicating the degree of fluctuation of the combustion pressure Pe is obtained,
By comparing this value with a predetermined determination value, the stability of the combustion state can be evaluated. As shown in FIG. 5, a combustion pressure fluctuation amount (evaluation value) for each predetermined crank angle is calculated by using the cylinder pressures P # 1 to P # 4 during the idling operation as a sample. Then, when the amount of change becomes equal to or more than a predetermined determination value, it is determined that the combustion stability has decreased.

(Method 3) Combustion stability by air-fuel ratio A / F
Evaluation Figure 6 is an explanatory diagram of characteristics of the air-fuel ratio A / F. When performing air-fuel ratio feedback correction (PI control; proportional integral control), the air-fuel ratio A / F alternates between rich and lean with respect to the target air-fuel ratio. Here, when the combustion state deteriorates, the air-fuel ratio A / F becomes rough, and the oxygen consumption rate decreases due to the deterioration of the combustion state. At that time, the combustion state of all cylinders does not deteriorate uniformly, but the combustion state of a specific cylinder deteriorates. Further, the air-fuel ratio sensor 28 is provided immediately upstream of the three-way catalytic converter 13 where the exhaust from each cylinder joins, and thus detects the total air-fuel ratio. Therefore, when the combustion state deteriorates, the air-fuel ratio A / F detected by the air-fuel ratio sensor 28 has a spike-like output fluctuation on the lean side with respect to the normal state (thin line in FIG. 6) (thick line in FIG. 6). ). Therefore, by detecting the spike-like output fluctuation, it is determined that the combustion stability has decreased.

Specifically, an average air-fuel ratio A / Fave per unit time is calculated from the n air-fuel ratios A / F (n) detected by the air-fuel ratio sensor 28 according to, for example, a moving average shown by the following equation. I do. This unit time is determined by the execution cycle of the evaporative purge control routine and the sampling number n of the air-fuel ratio A / F. The sampling number n is determined by simulation or experiment to find a value suitable for capturing air-fuel ratio fluctuations.
The data is stored in the memory of the ECU 12 as fixed data.

[Equation 1] A / Fave = ΣA / F (n) / n

The thus calculated average air-fuel ratio A / Fa
From ve, an air-fuel ratio fluctuation value (A / F) w, which is an evaluation value of combustion stability, is calculated according to the variance average shown in the following equation. Then, when the air-fuel ratio fluctuation value (A / F) w is larger than a predetermined determination value (A / F) th, it is determined that the combustion stability has decreased.

(A / F) w = {({(A / F−A / Fave) ² / (n−1)}}

In step 14, it is determined whether the combustion stability is high by comparing the evaluation value calculated by the method described above with a predetermined determination value. If it is determined that the combustion stability is high, the process proceeds to step 15, where the duty ratio DUTY is set to a predetermined upper limit value DUTYmax in order to determine whether the current evaporative purge amount has reached the upper limit value (maximum allowable amount). Is also determined. If the determination in step 15 is affirmative, that is, if the combustion stability is high and the duty ratio DUTY is smaller than the upper limit value DUTYmax, the duty ratio DUTY is changed to the current value by the correction value α (α
> 0) is updated (step 16). That is, when it is determined that there is room to increase the evaporative purge amount on the combustion surface, the purge control valve 21 is controlled in the valve opening direction to act in a direction to increase the evaporative purge amount.

On the other hand, if a negative determination is made in step 15, that is, if the combustion stability is high and the duty ratio DUTY is equal to or greater than the upper limit value DUTYmax, the duty ratio DUTY is held at the upper limit value DUTYmax ( Step 1
7). That is, when it is determined that there is no room for increasing the evaporative purge amount on the combustion surface, the opening of the purge control valve 21 is fixed, and the evaporative purge amount is held.

On the other hand, if it is determined that the combustion stability is low, the process proceeds from step 14 to step 18. In this step 18, the duty ratio is determined in order to determine whether the current evaporative purge amount has reached the lower limit (minimum allowable amount).
It is determined whether DUTY is greater than a predetermined lower limit value DUTYmin. If the determination in step 18 is affirmative, that is, if the combustion stability is low and the duty ratio DUTY
Is greater than the lower limit value DUTYmax, the duty ratio DUTY
Is updated to a value obtained by subtracting the correction value α (α> 0) from the current value (step 19). That is, when it is determined that the combustion stability is reduced, the purge control valve 21
Is controlled in the valve closing direction to increase combustion stability.

On the other hand, if the determination in step 18 is negative, that is, if the combustion stability is low and the duty ratio is low.
If DUTY is equal to or less than the lower limit value DUTYmax, the duty ratio DUTY is held at the lower limit value DUTYmin (step 20). Thereby, the evaporation purge amount is also held.

As can be understood from the above description, in the engine control device according to the present embodiment, when it is determined that the combustion stability is high, it is determined that there is room for increasing the evaporation purge amount, and the purge control is performed. The valve 21 is controlled to open. Thus, the evaporative purge amount acts in the increasing direction. Conversely, when it is determined that the combustion stability is low, it is determined that the evaporation purge amount is too large, and the purge control valve 21 is controlled in the valve closing direction. As a result, the evaporative purge amount acts in a decreasing direction. Through such purge control, the maximum evaporative purge can be performed within a range that does not impair the combustion stability of the engine. Further, even if the characteristics of each engine are different due to variations in components of the engine or changes over time, it is possible to perform the maximum evaporative purge that matches the individual characteristics of each engine. And, by this maximum evaporation purge, it is possible to reliably prevent the evaporation from being released into the atmosphere due to exceeding the adsorption amount limit of the canister.

[0036]

As described above, according to the present invention, a large amount of evaporative purge can be performed irrespective of variations in individual engines within a range that does not cause deterioration of drivability.
It is possible to reliably prevent the evaporator from being released into the atmosphere due to exceeding the adsorption amount limit of the canister.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine according to an embodiment.

FIG. 2 is a flowchart showing a routine for determining execution of an evaporative purge.

FIG. 3 is a flowchart showing an evaporative purge control routine.

FIG. 4 is an explanatory diagram of a duty ratio calculation map.

FIG. 5 is an explanatory diagram of in-cylinder pressure characteristics and engine speed characteristics.

FIG. 6 is an explanatory diagram of air-fuel ratio characteristics.

[Explanation of symbols]

 1 engine, 12 engine control unit (ECU), 16 ISC valve, 17 bypass passage, 18 fuel tank, 19 purge passage, 20 canister, 21 purge control valve, 22 cylinder pressure sensor, 24 HC sensor, 25 throttle sensor, 26 engine Speed sensor, 28 air-fuel ratio sensor, 29 accelerator opening sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F02D 45/00 301 F02D 45/00 301L 362 362J 368 368G F term (reference) 3G044 BA03 BA11 BA28 CA06 CA16 CA18 EA03 EA19 EA23 EA36 EA37 EA42 EA43 FA20 FA27 FA30 FA38 GA02 GA08 GA22 GA27 3G084 BA06 BA09 BA27 CA03 CA07 DA28 EA11 EB08 EB12 EB22 EB25 EC06 FA05 FA06 FA10 FA20 FA21 FA26 FA29 FA34 FA38 3G093 AA01 DB01 DA05 DA05 DA06 EA07 EC01 FA04 FA11 FA14 FB01 FB02 3G301 HA14 JA21 KA07 KA28 LA04 MA01 NA01 NA08 NB15 NC02 ND02 ND17 ND41 NE01 NE06 NE16 NE17 NE19 PA11Z PA14Z PA15A PB09Z PB10Z PC01B PC01Z PD01B PD04PE02ZPZPE01 PE03 PE02Z

Claims (6)

[Claims] An engine control device for performing an evaporative purge by controlling an opening of a purge control valve provided in a purge passage that connects an intake passage and a fuel tank to determine a stability of a combustion state of the engine. When the stability of the combustion state is determined to be high by the determination means, the purge control for increasing the evaporative purge amount is performed, and when the stability of the combustion state is determined to be low, A control unit for performing purge control for reducing an evaporation purge amount. 2. The control means controls the purge control valve in an opening direction when performing a purge control for increasing an evaporative purge amount, and closes the purge control valve when performing a purge control for reducing an evaporative purge amount. The control device for an engine according to claim 1, wherein the control is performed in a direction. 3. The engine control device according to claim 1, wherein the purge control by the control means is performed during an idling operation at a stop neutral shift position. 4. A sensor for detecting an engine speed, wherein the determination means determines the stability of the combustion state based on a fluctuation amount of the engine speed detected by the sensor. The engine control device according to any one of claims 1 to 3. 5. A sensor for detecting a combustion pressure of a cylinder, wherein the determination means determines the stability of a combustion state based on a variation of the combustion pressure detected by the sensor. The engine control device according to any one of claims 1 to 3. 6. A sensor for detecting an exhaust air-fuel ratio, wherein said determining means determines the stability of the combustion state based on the amount of change in the air-fuel ratio detected by said sensor. An engine control device according to any one of claims 1 to 3.