GB2181867A - Method of controlling air-fuel ratio of air-fuel mixture for an internal combustion engine for vehicles - Google Patents

Abstract

When a vehicle enters a predetermined high and steady speed running condition (conditions 301, 302, 303) a basic fuel quantity factor KLSC is progressively decreased during time period TLSC until the air-fuel ratio is leaned to a value appropriate to the predetermined running condition. <IMAGE>

Description

SPECIFICATION Method of controlling air-fuel ratio of airfuel mixture for an internal combustion engine for vehicles This invention relates to a method of controlling the air-fuel ratio of a mixture being supplied to an internal combustion engine for vehicles, and more particularly to a method of this kind, which is adapted to improve fuel consumption when the vehicle is running at a steady high speed (high-speed cruising), while maintaining optimal driveability.

A fuel supply control system adapted for use with an internal combustion engine for vehicles, particularly a gasoline engine, has been proposed e.g. by Japanese Patent Provisional Publication (Kokai) No. 57-137633, which is adapted to determine the valve opening period of a fuel injection device for control of the fuel injection quantity, i.e. the air-fuel ratio of an air-fuel mixture being supplied to the engine, by first determining a basic value of the valve opening period as a function of engine rotational speed and intake pipe absolute pressure and then correcting the basic value through addition of constants and/or multiplication by coefficients, which are functions of engine rotational speed, intake pipe absolute pressure, engine cooling water temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.

On the other hand, it has also conventionally been carried out to lean an air-fuel mixture being supplied to the engine so as to make the air-fuel ratio of the mixture leaner than a stoichiometric mixture ratio, to thereby reduce the fuel consumption.

As one of such mixture-leaning methods, a method has been proposed by Japanese Provisional Patent Publication (Kokai) No. 59-539, which comprises defining beforehand a pluraiity of mixture-leaning operating regions by engine rotational speed and intake pipe absolute pressure as parameters indicative of engine operating conditions, and leaning the air-fuel ratio of the mixture to respective lean values appropriate to the mixture-leaning regions in which the engine is operating. According to this proposed method, the mixture-leaning regions include a particular high-speed running region of the vehicle where the vehicle speed is higher than a predetermined value (i.e. highspeed cruising outside a city or a town), and in which the mixture is leaned in order to improve fuel consumption.

However, a problem with this proposed method is that in carrying out such leaning of the mixture when the vehicle enters the particular high-speed running region, the basic valve opening period of the fuel injection valves (which corresponds to the basic fuel supply quantity) is multiplied by a fixed leaning coefficient, and as a result, the mixture is suddenly leaned to cause a sudden drop in engine torque, makjng the driver and the passengers feel uncomfortable. This sudden drop in engine torque is more conspicuous if the engine is installed in a vehicle designed with priority given to fuel economy, e.g. using the fixed mixture-leaning coefficient set to a small value, resulting in a greater shock.Another problem with the proposed method is that if the vehicle happens to enter the particular highspeed running region when it is being accelerated, the mixture is untimely leaned to cause a drop in the engine output to thereby spoil the engine accelerability.

It is the object of the invention to provide an air-fuel ratio control method for an internal combustion engine for vehicles, which is capable of curtailing fuel consumption by leaning the air-fuel mixture supplied to the engine when the vehicle has entered a particular highspeed running region without incurring a sudden change in engine torque and a sudden drop in engine output so that driveability and accelerability are not spoiled.

According to the invention, there is provided a method of controlling the air-fuel ratio of an air-fuel mixture being supplied to an internal combustion engine for use in a vehicle, to desired values appropriate to operating conditions of said engine. The method is characterized by comprising the following steps: (1) determining a basic fuel quantity to be supplied to the engine in dependence on operating conditions of the engine; (2) determining whether or not the vehicle is in a predetermined high and steady speed running condition; (3) measuring a time period elapsed from the moment the vehicle is determined to enter the predetermined high and steady speed running condition; and (4) progressively decreasing the basic fuel quantity in response to the measured elapsed time period, from the moment the vehicle is determined to enter the predetermined high and steady speed running condition until the air-fuel ratio of the air-fuel mixture becomes a desired value appropriate to the predetermined high and steady speed running condition.

Preferably, the basic fuel quantity is determined in terms of a basic fuel injection period of fuel injection means provided in the engine, the basic fuel injection period is multiplied by a coefficient which progressively decreases from an initial value of 1.0 to a predetermined value smaller than the initial value in response to the measured elapsed time period, from the moment the vehicle enters the predetermined high and steady speed running condition, and after the coefficient has decreased to the predetermined value the basic fuel injection period is multiplied by the coefficient decreased to the predetermined value as long as the vehicle is determined to be in the predetermined high and steady speed running condition.

Alternatively, the basic fuel quantity is determined in terms of the basic fuel injection period of fuel injection means provided in the engine, a variable is added to the basic fuel injection period, which progressively decreases from an initial value of zero to a predetermined negative value in response to the measured elapsed time period, from the moment the vehicle enters the predetermined high and steady speed running condition, and after the variable has decreased to the predetermined negative value the variable decreased to the predetermined negative value is added to the basic fuel injection period as long as the vehicle is determined to be in the predetermined high and steady speed running condition.

The above and other objects, features and advantages of the invention will become more apparent from the ensuing detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRA WINGS Figure 1 is a block diagram illustrating, by way of example, the whole arrangement of a fuel supply control system to which is applied a method according to the invention; Figure 2 is a block diagram illustrating the internal arrangement of an electronic control unit (ECU) appearing in Fig. 1; Figure 3 is a flowchart showing a mixtureleaning control manner including setting the value of a mixure-leaning coefficient KLSC, according to the method of the invention.

Figure 4 is a graph showing an Ne, PB-KLSC map for determining the value of coefficient KLSC; and Figure 5 is a graph showing a table of a mixture-leaning coefficient value XLSC plotted with respect to a timer count value TLSC.

DETAILED DESCRIPTION A method according to the invention will now be described in detail with reference to the drawings showing an embodiment thereof.

Referring first to Fig. 1, there is illustrated the whole arrangement of a fuel supply control system for internal combustion engines, to which a method according to the invention is applied. Reference numeral 1 designates an internal combustion engine which may be a four-cylinder type, for instance. An intake pipe 2 is connected to the engine 1; in the intake pipe is arranged a throttle valve 3, to which is connected a throttie valve opening (TH) sensor 4 for detecting its valve opening and converting same into an electrical signal which is supplied to an electronic control unit (hereinafter called "the ECU") 5.

Fuel injection valves 6 are arranged in the intake pipe 2 at locations between the engine 1 and the throttle valve 3, which correspond in number to the number of engine cylinders and are each arranged at a location slightly upstream of an intake valve, not shown, of a corresponding engine cylinder. These injection valves are connected to a fuel pump, not shown, and also 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.

On the other hand, an absolute pressure (PB) sensor 8 communicates through a conduit 7 with the interior of the intake pipe 2 at a location immediately downstream of the throttle valve 3. The absolute pressure (PB) sensor 8 is adapted to detect absolute pressure in the intake pipe 2 and applies an electrical signal indicative of the detected absolute pressure to the ECU 5.

An engine coolant temperature (TW) sensor 10, which may be formed of a thermistor or the like, is mounted on the cylinder block of the engine 1 in a manner embedded in the peripheral wall of an engine cylinder having its interior filled with cooling water, and is adapted to detect engine coolant temperature (TW) and applies an electrical signal indicativeof the detected engine coolant temperature to the ECU 5.

An engine rotational speed sensor (hereinafter called "the Ne sensor") 11 and a cylinder-discriminating sensor 12 are arranged in facing relation to a camshaft, not shown, of the engine 1 or a crankshaft of same, not shown. The former 11 is adapted to generate one pulse at one of particular crank angles of the engine each time the engine crankshaft rotates through 180 degrees, as a pulse of a top-dead-center position (TDC) signal, while the latter is adapted to generate one pulse at a particular crank angle of a particular engine cylinder. 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 cylinder block of the engine 1 for purifying ingredients HC, CO and NOx contained in the exhaust gases. An 02 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 indicative of the detected oxygen concentration to the ECU 5.

The ECU 5 operates in response to various engine operating parameter signals stated above, to determine operating conditions of the engine including mixture-leaning operating regions, and calculate the fuel injection period TOUT of the fuel injection valves 6 by the use of an equation given below, in accordance with the determined operating conditions of the engine.

TOUT=Ti x KLSC x K1 +K2 (1) where Ti represents a basic value of the valve opening period for the fuel injection valves 6, which corresponds to a basic fuel injection quantity and is determined from the engine rotational speed Ne and the intake pipe absolute pressure PB. KLSC respresents a correction coefficient which is set to a value less than 1.0 for leaning the air-fuel mixture when the vehicle is in a predetermined high-speed running region, as hereinafter explained in detail. K1 and K2 represent correction coefficients or correction variables which have their values calculated by respective predetermined equations on the basis of values of engine operating parameter signals supplied from the aforementioned various sensors, i.e. the throttle valve opening sensor 4, the absolute pressure (PB) sensor 8, the Ne sensor 11, the cylinder-discriminating sensor 12, and other parameter sensors, the equations being such that operating characteristics of the engine such as startability, emission characteristics, fuel consumption and accelerability are optimized.

The ECU 5 supplies driving signals to the fuel injection valves 6 to open same in response to the fuel injection period TOUT calculated as above.

Fig. 2 shows a circuit configuration within the ECU 5 in Fig. 1. An engine rotational speed (Ne) signal from the Ne sensor 11 is applied to a waveform shaper 501, wherein it has its pulse waveform shaped, and supplied to a central processing unit (hereinafter called "the CPU") 503, as the TDC signal, as well as to an Me value counter 502. The Me value counter 502 counts the interval of time between an immediately preceding pulse of the TDC signal and a present pulse of the same signal, which are inputted to the ECU 5 from the Ne sensor 11, and therefore its counted value Me corresponds to the reciprocal of the actual engine rotational speed Ne. The Me value counter 502 supplies the counted value Me to the CPU 503 via a data bus 510.

Respective output signals from the intake pipe absolute pressure (PB) sensor 8, the engine coolant temperature (TW) sensor 10, the 02 sensor 15, etc. have their voltage leveis shifted to a predetermined voltage level by a level shifter unit 504 and successively applied to an analog-to-digital converter 506 through a multiplexer 505. The analog-to-digital converter 506 successively converts into digital signals the analog output voltages from the aforementioned various sensors, and the resulting digital signals are supplied to the CPU 503 via the data bus 510.

Further connected to the CPU 503 via the data bus 510 are a read-only memory (hereinafter called "the ROM") 507, a random access memory (hereinafter called "the RAM") 508, and a driving circuit 509. The RAM 508 temporarily stores various calculated values from the CPU 503, while the ROM 507 stores control programs executed within the CPU 503, a map of the basic fuel injection period Ti for fuel injection valves 6, predetermined values of correction coefficients, a TLSC-XLSC table, hereinafter described, etc. The CPU 503 executes a Control program stored in the ROM 507 to calculate the fuel injection period TOUT for the fuel injection valves 6 in response to the various engine operating parameter signals, and supplies the calculated value of fuel injection period to the driving circuit 509 through the data bus 510.The driving circuit 509 supplies driving signals corresponding to the above calculated TOUT value to the fuel injection valves 6 to drive same.

Fig. 3 is a flowchart showing an example of a mixture-leaning control subroutine for setting the value of the mixure-leaning coefficient KLSC, according to the method of the invention, the subroutine being executed in synchronism with generation of TDC signal pulses. First, it is determined at step 301 whether or not the engine rotational speed Ne falls within a predetermined range (e.g.

2000-3000 rpm), or more specifically whether or not the count value Me corresponding to the interval between adjacent TDC signal pulses falls within a range defined by predetermined values MeLSCO and MeLSC1, which correspond to the extreme values of the predetermined range of the engine roational speed Ne. If the answer is Yes, it is then determined at step 302 whether or not the intake pipe absolute pressure PB falls within a range defined by predetermined values PBLSCO and PBLSC1 (e.g. 435 and 585 mmHg, respectively). If the answer is Yes, it is judged that the vehicle is running in a highspeed running region I defined in the Ne, PB KLSC map, shown in Fig. 4, wherein it is assumed that the vehicle is cruising at a high speed between predetermined values (e.g. 90 and 120 km/h).

If the answers to the questions of steps 301 and 302 are both affirmative, then it is determined at step 303 whether or not the engine coolant temperature TW is higher than a predetermined value TWLSC (e.g. 70"C). If the answer to the question of step 303 is Yes, that is, if the vehicle is cruising at a high speed and the engine temperature is so high that good combustion takes place, steps 306 through 310 are executed, as described later, to thereby determine the value of the mixtureleaning coefficient KLSC in order to effect leaning of the air-fuel mixture.

On the other hand, if the answers to the question of step 301 or 302 is negative, that is, if the vehicle is judged to be running in a region other than the high-speed cruising region I, in Fig. 4, or if the answer to the question of step 303 is negative, that is, if the engine temperature is not sufficiently high, the program proceeds to step 304 where a flag value FLSC is reset to 0, and then to step 305 where the mixture-leaning coefficient KLSC is set to 1.0 so as not to effect leaning of the mixture, and then the program terminates. The flag value FLSC is checked at step 307 during the next subroutine loop started by generation of the next TDC signal pulse to determine whether or not the flag FLSC was set to O in the last loop started by the immediately preceding TDC signal pulse.Since the flag value FLSC was reset to O in the last loop, the result of step 307 will be affirmative, that is, it is judged that mixture-leaning is not being effected.

If the answers to the questions at steps 301, 302, and 303 are all Yes, the program proceeds to step 306 to set the flag FLSC to 1 to indicate that mixture-leaning should be effected. At step 307 the answer will be Yes meaning that mixture-leaning is not being effected. Then, a TLSC timer is started at step 308, and the program proceeds to step 309.

The TLSC timer, which may be formed of a downcounter, for instance, has its initial count value TLSC set to a predetermined value tLSCG (e.g. 8 seconds) at step 308 when downcounting is started, and assumes a value O (e.g. 0 second) after the lapse of a time period corresponding to the count value tLSCG. If, on the other hand, the answer to the question at step 307 is. negative, the program directLy proceeds to step 309, skipping step 308.

At step 309 a value of the mixture-leaning coefficient XLSC is read from the TLSC-XLSC table in response to the count value TLSC assumed by the TLSC timer. The TLSC-XLSC table, shown in Fig. 5, is set such that the mixture-leaning coefficient XLSC decreases from 1.0 to a predetermined value XLSCG (e.g. 0.9) as the count value TLSC decreases from tLSCG to 0. Once the count value TLSC has been counted down to 0, it continues to assume 0 until step 308 is executed. The step 309 is followed by executing step 310 to set the mixture-leaning coefficient KLSC to the read value XLSC obtained at step 309.

Then the program terminates.

As described above, according to the invention, as soon as the vehicle enters the highspeed cruising region I while the engine coolant temperature is higher than the predetermined value TWLSC, the value of the mixtureleaning coefficient KLSC starts to be decreased from 1.0 and becomes equal to the predetermined value XLSCG when the predetermined time period tLSCG elapses, and thereafter it is maintained at the predetermined value XLSCG as long as the vehicle remains in the high-speed cruising region I. Therefore, it is possible to prevent a sudden torque change attributable to a sudden mixture-leaning conventionally effected when the vehicle enters the high-speed cruising region I.Further, by virtue of the gradual decrease of the coefficient KLSC, even if the vehicle temporarily enters the high-speed cruising region I during engine acceleration where high engine output is required, engine output is not spoiled because the mixture-leaning coefficient KLSC is not immediately set to the predetermined value XLSCG.

Since in the above embodiment the signals from the Ne sensor 11 and the absolute pressure (PB) sensor 8 are employed not only for determining the basic fuel injection period Ti, but also for determining whether the vehicle is running in the high-speed cruising region I, there is no need to use a special exclusive sensor for detecting the vehicle speed.

Although in the above embodiment, mixtureleaning is effected by means of the equation (1) wherein the basic fuel injection period Ti is multiplied by the mixture-leaning coefficient KLSC, it is also possible to effect mixtureleaning by means of the following equation (2) wherein the value Ti is decreased by a variable TLSC.

TOUT=Ti x K1 +K2+TLSC (2) where the variable TLSC is gradually decreased from 0 to a predetermined negative value as time elapses from the moment the engine enters the high-speed cruising region i until a predetermined time period elapses. Alternatively, it is also possible to effect mixture-leaning by means of the following equation (2) wherein a variable TLSC' is deducted from the value Ti.

TOUT= Ti x K1 + K2 - TLSC' (3) where the variable TLSC' is gradually increased from 0 to a predetermined positive value as time elapses from the moment the engine enters the high-speed cruising region I until a predetermined time period elapses.

Also, although in the above embodiment the mixture-leaning degree is progressively increased as the count value TLSC of the TLSC timer decreases, alternatively the mixture-leaning degree may be progressively increased by subtracting a predetermined value from the basic fuel injection period Ti each time a pulse of the TDC signal is generated, from the moment the vehicle enters the high and steady speed running condition until the air-fuel ratio of the mixture becomes a predetermined lean value.

Claims (8)

1. A method of controlling the air-fuel ratio of an air-fuel mixture being supplied to an internal combustion engine for use in a vehicle, to desired values appropriate to operating conditions of said engine, comprising the steps of: (1) determining a basic fuel quantity to be supplied to said engine in dependence on operating conditions of said engine; (2) determining whether or not said vehicle is in a predetermined high and steady speed running condition; (3) measuring a time period elapsed from the moment said vehicle is determined to enter said predetermined high and steady speed running condition; and (4) progressively decreasing said basic fuel quantity in response to the measured elapsed time period, from the moment said vehicle is determined to enter said predetermined high and steady speed running condition until the air-fuel ratio of said air-fuel mixture becomes a predetermined value appropriate to said predetermined high and steady speed running condition.

2. A method as claimed in claim 1, wherein said basic fuel quantity is determined in terms of a basic fuel injection period of fuel injection means provided in said engine, said basic fuel injection period is multiplied by a coefficient which progressively decreases from an initial value of 1.0 to a predetermined value smaller than said initial value in response to the measured elapsed time period, from the moment said vehicle enters said predetermined high and steady speed running condition, and after said coefficient has decreased to said predetermined value said basic fuel injection period is multiplied by said coefficient decreased to said predetermined value as long as said vehicle is determined to be in said predetermined high and steady speed running condition.

3. A method as claimed in Claim 1, wherein said basic fuel quantity is determined in terms of said basic fuel injection period of fuel injection means provided in said engine, a variable is added to said basic fuel injection period, which progressively decreases from an initial value of zero to a predetermined negative value in response to the measured elapsed time period, from the moment said vehicle enters said predetermined high and steady speed running condition, and after said variable has decreased to said negative predetermined value said variable decreased to said predetermined negative value is added to said basic fuel injection period as long as said vehicle is determined to be in said predetermined high and steady speed running condition.

4. A method as claimed in Claim 1, wherein said basic fuel quantity is determined in terms of said basic fuel injection period of fuel injection means provided in said engine, a variable is deducted from said basic fuel injection period, which progressively increases from an initial value of zero to a predetermined positive value in response to the measured elapsed time period, from the moment said vehicle enters said predetermined high and steady speed running condition, and after said variable has increased to said predetermined positive value said variable increased to said predetermined positive value is deducted from said basic fuel injection period as long as said vehicle is determined to be in said predetermined high and steady speed running condition.

5. A method as claimed in any preceding Claim, wherein said time period elapsed from the moment said vehicle is determined to enter said predetermined high and steady speed running condition is measured by timer means, and said basic fuel quantity is progressively decreased in response to the elapsed time period measured by said timer means, from the moment said vehicle is determined t6 enter said predetermined high and steady speed running condition until the elapsed time period measured by said timer means reaches a predetermined value.

6. A method as claimed in any of Claims 1 to 4, wherein said method is executed in synchronism with pulses of a signal generated at predetermined crank angles of said engine, and said basic fuel injection quantity is decreased by a predetermined value each time a pulse of said signal is generated, from the moment said vehicle is determined to enter said predetermined high and steady speed running condition until the air-fuel ratio of said air-fuel mixture becomes said predetermined value.

7. A method as claimed in any preceding Claim, wherein the rotational speed of said engine and absolute pressure in an intake passage of said engine are detected, said basic fuel quantity is determined based on the detected values of said engine rotational speed and said absolute pressure, and also whether or not said vehicle is in said predetermined high and steady speed running condition is determined based on the detected values of said engine rotational speed and said absolute pressure.

8. A method of controlling the air-fuel ratio of an air-fuel mixture being supplied to an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawings.