4,445,482 May 1, 1984

United States Patent [191

Hasegawa et al.

[54] AIR/FUEL RATION FEEDBACK CONTROL

SYSTEM ADAPTED TO OBTAIN STABLE

ENGINE OPERATION UNDER '

PARTICULAR ENGINE OPERATING CONDITIONS

[75] Inventors: Shumpei Hasegawa, Niiza; Noriyuki Kishi, Itabashi, both of Japan

Honda Gm

Kogyo Kabushiki

Kaisha, Tokyo, Japan

Appl. No.: 376,106

[22] Filed: May 7, 1982

[30]

Foreign Application Priority ‘Data

May 15, 1981 [JP] Japan ... .. 56-72991 [51] int. cm ... .. F02M 51/00; F02D 5/00 [52] us. 01. ... .. 123/489; 123/491; 123/493 Field of Search ... .. 123/489, 480, 478, 483, 123/491, 440

[73] Assignee:

[21]

[58]

[56]‘ References Cited U.S. PATENT DOCUMENTS

3,483,851 12/1969 Reichardt ... .. 123/491 4,354,238 10/1982 Manaka et a]. 123/489 4,359,993 11/1982 Carlson ... .. 123/493 4,383,515 5/1983 Higashiyama et a]. ... .. 123/489

4,445,482

May 1, 1984

[1 1]

[45]

Primary Examiner-Raymond A. Nelli Attorney, Agent, or Firm-Lyon & Lyon

[57]

Answer

An air/fuel ratio feedback control system adapted to control the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion engine, by the use of

a ?rst coef?cient having a value variable in response to actual exhaust gas concentration and at least one second

coef?cient having a value variable in dependence on the kind of a particular operating condition or region in

which the engine is operating. The control system is operable such that when the engine is operating in an

operating condition other than predetermined particu

lar operating conditions of the engine, the value of the

?rst coef?cient is varied in response to the output of an exhaust gas concentration sensor, and simultaneously

the value of the second coef?cient is held at a ?rst pre

determined value, and when the engine is operating in one of the predetermined particular operating condi

tions, the value of the second coef?cient is held at a second predetermined value, and simultaneously the value of the ?rst coef?cient at a third predetermined

value which is a mean value of values of the ?rst coef?

cient obtained when the engine is operating in the above

operating condition other than the particular operating conditions.

22 Claims, 18 Drawing Figures _

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, 4,445,482

I 1

AIR/FUEL RATION FEEDBACK CONTROL 7

SYSTEM ADAPTED TO, OBTAIN STABLE ENGINE

OPERATION UNDER PARTICULAR ENGINE

OPERATING CONDITIONS.

BACKGROUND OF THE INVENTION

This invention relates to an air/fuel ratio feedback

control system for performing by electronic means

feedback control of the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion en gine, and more particularly to an air/fuel ratio feedback control system of this kind, which is capable of posi

tively controlling the air/fuel ratio to a-predetermined

value best suited for a particular operating conditionof the engine when the engine is operating in the particular operating condition, to thereby achieve improved oper

ational stability and driveability of the engine. . A fuel supply control system adaptedfor use with an

internal combustion engine, particularly -,a‘igasoline.en- ' gine has been proposed e.g., by U.S. Pat. No; 3,483,851, which is adapted to determine the valve opening period

of a fuel quantity metering oradjusting means’for con

trol of the fuel injection quantity, i.e. theair/fuel ratio of an air/fuel mixture being supplied to the engine, by ?rst determining a basic value of the above. valve open ing period as a function of engine rpm and intakepipe absolute pressure and then adding to and/or multiply ing same by constants and/or coefficients being. dunc

tions of engine rpm, intake pipe absolute pressure, “en

gine temperature, throttle valve opening, ,exhaust vgas

ingredient concentration (oxygen concentration), etc.,

by electronic computing means. . . ~. -

Also, in. an engine having a three-way catalyst ar

ranged in its exhaust system, it is generally employed to control the air/fuel ratio of the mixture to a theoretical

_ mixture ratio in a feedback manner responsive to the

.output of an exhaust gas concentration sensor which

may be represented by’an Oz sensor, arranged in the exhaust system of the engine, to obtain the best conver-v

sion efficiency of unburned hydrocarbons, carbon mon

oxide and nitrous oxides in the exhaustgases emitted

from the engine. However, this feedback control based

upon the output of the exhaust gas sensor cannot be

applied when the engine is operating in a particular operating condition such as engine idle, wide-open

throttle where the air/fuel ratio of the mixture needs to be controlled to a value different from the theoretical

mixture ratio. _ . -

Therefore, in the case of applying the above exhaust gas concentration-based feedback to the aforemen tioned fuel supplycontrol system using coefficients,

etc., it is necessary to carry out open-loop control when

the engine is operating in such particular operating

condition, by using a coefficient having afpredeter

mined value corresponding to the particular operating condition, so as to achieve adesired predetermined

air/fuel ratio best suited for engine operating under the

above particular operating condition.

It is thus desirable that the predeterminedair/fuel ratio corresponding .to the particular operating condi tion canbe achieved with certainty by means of open

loop control. However, as a matter of fact, the actual air/fuel ratio can sometimes have a value different from

the desired predetermined value due to variations in the

performance of various sensors for detecting the operat ing condition of the engine and a system for controlling

or driving the fuel quantity‘ metering or adjusting

25 35 40 50 55 60

2

means. In such event, it is impossible to obtain required

operational stability and driveability of the engine.

OBJECT AND SUMMARY OF THE INVENTION

It is the object of the invention to provide an air/fuel

ratio feedback control system for use with an internal combustion engine, which is capable of controlling the air/fuel ratio of the mixture to a predetermined value or a value very close thereto corresponding to a particular operating condition of the engine, when the engine is operating in the above particular operating condition,

to thereby assure achievement of required operational

stability and driveability of the engine.

The present invention provides an air/fuel ratio feed

back control system f'or use with an internal combustion

engine, which is adapted to control the air/fuel ratio of

an air/fuel mixture being supplied to the engine, by the use of a ?rst coefficient having a value variable in re

sponse to the output of an exhaust gas concentration

sensor arranged in the exhaust system of the engine, and

at least one second coefficient having a value variable in

dependence on the kind of a’ particular operating condi

tion'in'which the engine is operating. The control sys

is characterized by including an electric‘ circuit

means which is operable such that when the engine is

operating in an operating condition (i.e. feedback con

trol region) other than predetermined particular operat ing conditions of the engine, the valuev of the first coeffi

cient is varied in response to the output of the exhaust gas concentration sensor, and simultaneously the value of the second coefficient is held at a first predetermined

value, and when the engine is operating in one of the

predetermined particular operating conditions, ‘the

value of the second coefficient is held at a second prede

termined value which is a mean value of‘ values of the first coef?cient obtained during engine operation under

the above operating condition, i.e. feedback control

region other than the particular operating conditions. -

Thus, during open-loop control under a particular oper ating condition of. the engine, the use of the ?rst coeffi

cient having its value held at the third predetermined or means value in addition to the second coefficient having

its value held at the second predetermined value makes

it possible to obtain an air/fuel ratio more closer to a desired air/fuel ratio best suited for engine‘ operation in the particular operating condition of the'engine, obtain

ing improved operational stability and driveability of

the engine. ' 1 I

Preferably, the above mean value at which the first

coefficient is to be held comprises a mean value of val

ues of the first coefficient each assumed immediately before or after a proportional term control action which

is performed during air/fuel ratio feedback1 control.

Also preferably, an up-to-date value of them: coef

ficient is used for calculation of the above'mean' value, each time it is obtained immediately before ‘or after each proportional term control action. Thus, a mean value of

the ?rst'coefficient can always be obtained which is an up-to-date value and which represents a mean value obtained at an instant when the actual air/fuel ratio of the mixture assumes a value most close to the theoreti cal mixture ratio, making it possible to carry out air/ fuel ratio control fully responsive to the present operating conditionof the engine, in an accurate manner. _

The above and other objects, features and advantages of the invention willbe more apparent from the ensuing

4,445,482

3

detailed description taken in connection with the ac companying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating the whole ar- 5 rangement of an air/fuel ratio feedback control system according to the present invention;

FIG. 2 is a block diagram illustrating a program for control of the valve opening periods TOUTM, TOUTS of the main injectors and the subinjector, which are

operated by an electronic control unit (ECU) in FIG. 1;

FIG. 3 is a timing chart showing the relationship between a cylinder-discriminating signal and a TDC

signal inputted to the ECU, and drive shgnals for the

main injectors and the subinjector, outputted from the ECU;

FIG. 4 is a ?ow chart showing a main program for

control of the basic valve opening periods TOUTM,

TOUTS;

FIGS. 5A and 5B illustrate a flow chart .showing a‘

subroutine for calculation of the value of “Oz-feedback

control” correction coefficient K02; _'

FIG. 6 is a view showing an Ne-Pi table for determin

ing a correction value Pi for correcting “Oz-feedback

control” correction coefficient K02; '

FIG. 7 is a graph showing a manner of detecting the

value of correction coefficient K01 by means of propor tional term control;

FIG. 8 is a graph showing a manner of applying correction coefficients to various operating conditions 30

of the engine;

FIGS. 9A and 9B illustrate a circuit diagram illustrat

ing the whole internal arrangement of the ECU, show

ing in detail a correction coefficient K02 calculating k

section; 35

FIG. 10 is a circuit diagram illustrating details of a

20

. lean/rich state comparator and part of a particular oper ating condition detecting circuit in FIG. 9;

FIG. 11 is a circuit diagram illustrating details of a K02 calculating circuit in FIG. 9;

FIG. 12 is a circuit diagram illustrating details of a

mean value calculating circuit in FIG. 9;

FIG. 13 is a circuit diagram illustrating details of another example of the KO; value calculating circuit in FIG. 9;

FIGS. 14A and 14B illustrate a circuit diagram illus

trating details of another example of the mean value calculating circuit in FIG. 9; and

FIG. 15 is a timing chart showing the relationship between various signals generated in the circuit of FIG.

14.

40

45

DETAILED DESCRIPTION

The present invention will now be described in detail

with reference to the drawings.

Referring ?rst to FIG. 1, there is illustrated the whole arrangement of a fuel supply control system for internal combustion engines, to which the present invention is

applicable. Reference numeral 1 designates an internal

combustion engine which may be a four-cylinder type, for instance. This engine 1 has main combustion chain’

bei's which may be four in number and sub combustion

chambers communicating with the main combustion chambers, none of which is shown. An intake pipe 2 is connected to the engine 1, which comprises a main

intake pipe communicating with each main combustion chamber, and a sub intake pipe with each sub combus

tion chamber, respectively, neither of which is shown.

55

65

4

Arranged across the intake pipe 2 is a throttle body 3

which accommodates a main throttle valve and a sub

throttle valve mounted in the main intake pipe and the

sub intake‘ pipe, respectively, for synchronous opera tion. Neither of the two throttle valves is shown. A throttle valve opening sensor 4 is connected to the main

throttle valve for detecting its valve opening and con

verting same into an electrical signal which is supplied to an electronic control unit (hereinafter called “ECU”)

5.

A fuel injection device 6 is arranged in the intake pipe

-2 at a location between the engine 1 and the throttle body 3, which comprises main injectors and a subinjec .tor, none of which is shown. The main injectors corre

spond in number to the engine cylinders and are each arranged in the main intake pipe at a location slightly

upstream of an intake valve, not shown, of a corre sponding engine cylinder, while the subinjector, which

is single in number,'is arranged in the sub intake pipe at

a location'slightly downstream of the sub throttle valve, for supplying fuel to all the'engine cylinders. The main

injectors and the subinjector are electrically connected to the ECU 5 in a manner having their valve opening

periods or fuel injection quantities controlled by signals supplied from the ECU 5. '

0n the other hand, an absolute pressure sensor 8

communicates through a conduit 7 with the interior of the main intake pipe'of the throttle body 3 at a location

‘immediately downstream of the main throttle valve.

The absolute pressure sensor 8 is adapted to detect absolute pressure in the intake pipe 2 and applies an

electrical signal indicative of detected absolute pressure

to the ECU S. An intake-air temperature sensor. 9 is

arranged in the intake pipe 2 at a location downstream of the absolute pressure sensor 8 and also electrically

connected‘ to the ECU 5 for supplying thereto an elec

trical signal indicative of detected intake-air tempera

ture. '

An engine temperature sensor 10, which may be

formed of a thermistor or the like, is mounted on the

main body of the engine 1 in a manner embedded in the peripheral wall of an engine cylinder having its interior

?lled with cooling water, an electrical output signal of which is supplied to the ECU 5.

An engine rpm sensor (hereinafter called “Ne sen sor”) 11 and a cylinder-discriminating ‘sensor 12 are

arranged in facing relation to a camsha?, not shown, of

the engine 1 or a crankshaft of - same, not shown. The former 11 is adapted to generate one pulse at a particu

lar crank angle each time the engine crankshaft rotates

through 180 degrees, i.e., upon generation of each pulse of the top-dead-center position (T DC) signal, while the

latter is adapted to generate one pulse at a particular

crank angle of a particular engine cylinder. The above

pulses generated by the sensors 11, 12 are supplied to

the ECU 5,

A three-way catalyst 14 is arranged in an exhaust pipe 13 extending from the main body of the engine 1 for purifying ingredients I-IC, CO and NOx contained in the

exhaust gases. An 0; sensor 15 is inserted in the exhaust

pipe 13 at a location upstream of the three-way catalyst 14 for detecting the concentration of oxygen‘ in the exhaust gases and supplying an electrical signal indica

tive of a detected concentration value to the ECU 5.

Further connected to the ECU '5 are a sensor 16 for

detecting atomospheric pressure and a starter switch 17

for actuating the starter, not shown, of the engine 1, respectively, for supplying an electrical signal indica