Method of Controlling Operating Amounts of Operation Control Means for an Internal Combustion Engine

This invention relates to a method of controlling the operating amount of an operation control means for an internal combustion engine, and more particularly to a method of this kind which is adapted to correct the operating amount of such operation control means in a manner responsive to atmospheric pressure for improvement of the driveability of the engine over all operating regions of the engine inclusive of low load operating regions such as an idling region.

A method has been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos. 58-85337, 54-153929, and 58-88429, which determines a basic operating amount of operation control means for controlling the operation of the engine, such as a basic fuel injection amount to be supplied to the engine by a fuel supply quantity control system, a basic value of spark ignition timing to be controlled by an ignition timing control system, and a basic recirculation amount of exhaust gases to be controlled by an exhaust gas recirculation control system, in dependence on values of engine operating parameters indicative of the intake air quantity supplied to the engine, such as absolute pressure in the intake pipe of the engine downstream of a throttle valve therein and engine rotational speed, and corrects the basic operating amount thus determined in response to atmospheric pressure, to thereby set a desired operating amount for the operation control means with accuracy. The ground for correcting the operating amount in response to atmospheric pressure lies in that the back pressure or pressure of exhaust gases varies with a change in the atmospheric pressure to vary the quantity of air sucked into the engine cylinders per suction stroke even if absolute pressure in the intake pipe remains constant. However, while the engine is operating in a low load condition such as at idle, the intake pipe absolute pressure has a reduced rate of change relative to the lapse of time with respect to a rate of change in the engine rotational speed relative to the lapse of time. Therefore, according to the above proposed method of determining operating amounts of the operation control means in dependence on the intake pipe absolute pressure and the engine rotational speed (generally called "the speed density method", and hereinafter merely referred to as "the SD method"), it is difficult to set with accuracy an operating amount such as a fuel supply quantity in accordance with the state of condition of the engine, thus causing hunting of the engine rotation, during operation of the engine in such a low load condition. In view of the foregoing, a method (hereinafter merely called "the KMe method") has been proposed, e.g. by Japanese Patent Publication No. 52-6414, which is based upon the recognition that the quantity of intake air passing the throttle valve is not dependent upon either of pressure PBA in the intake pipe downstream of the throttle valve and pressure of the exhaust gases while the engine is operating in a particular low load condition wherein the ratio PBA/PA' of intake pipe pressure PBA downstream of the throttle valve to intake pipe pressure PA' upstream of the throttle valve is below a critical pressure ratio (=0.528) at which the intake air forms a sonic flow, and accordingly the quantity of intake air can be determined solely in dependence on the valve opening of the throttle valve, if the intake pipe pressure PA' upstream of the throttle valve remains constant. Therefore, this proposed method detects the valve opening of the throttle valve alone to thereby detect the quantity of intake air with accuracy while the engine is operating in the above-mentioned particular low load condition, and then sets an operating amount such as a fuel injection quantity on the basis of the detected value of the intake air quantity.

However, when the intake pipe pressure PA' upstream of the throttle valve assumes a value other than the standard atmospheric pressure, the KMe method is not appropriate to determine the operating amount with accuracy, requiring correction of the operating amount determined by the use of the KMe method, in response to the actual value of the pressure PA'.

It is the object of the invention to provide a method of controlling the operating amount of an operation control means for controlling an internal combustion engine, which employs both of the SD method and the KMe method for determining the operating amount, and is capable of correcting the values of operating amounts determined by these methods in response to atmospheric pressure, in respective appropriate manners to these methods, so as to set the operating amount with accuracy throughout the whole operating region of the engine inclusive of low load conditions of the engine such as an idling condition, thereby contributing to improvement of the driveability of the engine.

The present invention provides a method of controlling an operating amount of an operation control means for controlling the operation of an internal combustion engine having an intake passage, and an intake air quantity control means arranged in the intake passage for adjusting the opening area of the intake passage. The operating amount of the operation control means is controlled in a first arithmetic manner to a first desired value determined on the basis of a first operating parameter of the engine when the engine is operating in a predetermined operating condition, while it is controlled in a second arithmetic manner to a second desired value determined on the basis of a second operating parameter of the engine when the engine is operating in a condition other than the above predetermined operating condition.

The method according to the invention is characterized by comprising the following steps:

(1) detecting the pressure of intake air at a location upstream of the intake air quantity control means;

(2) when the engine is operating in the above predetermined operating condition, determining a first correction value appropriate to the first arithmetic manner, as a function of the detected value of the intake air pressure, correcting the first desired value of operating amount by the use of the determined first correction value, and controlling the operating amount of the operation control means to the corrected first desired value; and

(3) when the engine is operating in a condition other than the above predetermined operating condition, determining a second correction value appropriate to the second arithmetic manner, as a function of the detected value of the intake air pressure, correcting the second desired value of operating amount by the use of the determined second correction value, and controlling the operating amount of the operation control means to the corrected second desired value.

Preferably, the intake air pressure upstream of the intake air quantity control means is atmospheric pressure. Also preferably, the first operating parameter of the engine is the opening area of the intake passage which is adjusted by the intake air quantity control means, while the second operating parameter of the engine is pressure in the intake passage at a location downstream of the intake air quantity control means.

Further, preferably, the aforesaid predetermined operating condition of the engine is a low load operating condition of the engine. Also preferably, the aforesaid operation control means is a fuel supply quantity control means, wherein the aforesaid operating amount is the quantity of fuel being supplied to the engine by the fuel supply quantity control means.

Preferably, the first correction value is set to such a value that the first desired value of operating amount corrected by the same correction value decreases with a decrease in the atmospheric pressure, whereas the second correction value is set to such a value that the second desired value of operating amount corrected by the same correction value increases with a decrease in the atmospheric pressure.

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

FIG. 1 is a block diagram of the whole arrangement of a fuel injection control system for an internal combustion engine, to which is applied the method according to the present invention;

FIG. 2 is a block diagram of the interior construction of an electronic control unit (ECU) appearing in FIG. 1;

FIG. 3 is a flowchart showing a manner of calculating the valve opening period TOUT for the fuel injection valves;

FIG. 4 is a flowchart showing a manner of determining whether or not the engine is operating in a predetermined operating condition; and

FIG. 5 is a flowchart showing a manner of calculating an atmospheric pressure-dependent correction coefficient KPA.

The invention will now be described in detail with reference to the drawings showing an embodiment thereof.

As an example for correcting in dependence on atmospheric pressure an operating amount of an operation control means for an internal combustion engine, e.g. the fuel supply quantity, which is determined according to the SD method, a method has been disclosed in U.S. Ser. No. 424,404, now U.S. Pat. No. 4,481,929, which multiplies a basic fuel injection period Ti as the operating amount, determined as a function of intake passage absolute pressure and engine rotational speed, by the following correction coefficient KPA1: ##EQU1## where PA represents actual atmospheric pressure (absolute pressure), PA0 standard atmospheric pressure, .epsilon. the compression ratio, and .kappa. the ratio of specific heat of air, respectively. Calculation of the atmospheric pressure-dependent correction coefficient KPA1 value by the use of the above equation (1) is based upon the recognition that the quantity of air being sucked into the engine per suction cycle of same can be theoretically determined from the intake pipe absolute pressure PBA and the absolute pressure in the exhaust pipe which can be regarded as almost equal to the atmospheric pressure PA, and the fuel supply quantity may be varied at a rate equal to the ratio of the intake air quantity at the actual atmospheric pressure PA to the intake air quantity at the standard atmospheric pressure PA0.

When the relationship PA<PA0 stands in the equation (1), the KPA1 value of the atmospheric pressure-dependent coefficient KPA is larger than 1. So long as the intake pipe absolute pressure PBA remains the same, the quantity of intake air being sucked into the engine becomes larger at a high altitude where the atmospheric pressure PA is lower than the standard atmospheric pressure PA0, than at a lowland. Therefore, if the engine is supplied with a fuel quantity determined as a function of the intake pipe absolute pressure PBA and the engine rotational speed Ne in a low atmospheric pressure condition such as at high altitudes, it can result in a lean air/fuel mixture. However, such leaning of the mixture can be avoided by employing the above fuel increasing coefficient KPA1 value.

When the ratio (PBA/PA') of intake pipe pressure PBA downstream of the throttling portion such as a throttle valve to intake pipe pressure PA' upstream of the throttling portion is smaller than the critical pressure ratio (=0.528), intake air passing the throttling portion forms a sonic flow. The flow rate Ga(g/sec) of intake air can be expressed as follows: ##EQU2## where A represents equivalent opening area (mm.sup.2) of the throttling portion such as the throttle valve, C a correction coefficient having its value determined by configuration, etc. of the throttling portion, PA atmospheric pressure (PA=PA', mmHg), .kappa. the ratio of specific heat of air, R the gas constant of air, TAF the temperature (.degree.C.) of intake air immediately upstream of the throttling portion, and g the gravitational acceleration (m/sec.sup.2), respectively. So long as the intake air temperature TAF and the opening area A remain constant, the ratio of the flow rate of intake air Ga (in gravity or weight) under the actual atmospheric pressure PA to the flow rate of intake air Ga0 in gravity or weight under the standard atmospheric pressure PA0 can be expressed as follows: ##EQU3##

If the quantity of fuel being supplied to the engine is varied at a rate equal to the above ratio of flow rate of intake air, the resulting air/fuel ratio is maintained at a constant value. Therefore, the flow rate Gf of fuel can be determined from the flow rate Gf0 of same under the standard atmospheric pressure PA0 (=760 mmHg), as expressed by the following equation: ##EQU4##

Here, the atmospheric pressure-dependent correction coefficient KPA2 value can be theoretically expressed as follows: ##EQU5##

In practice, however, various errors resulting from configuration, etc. of the intake passage should be taken into account, and therefore the above equation can be expressed as follows: ##EQU6## where CPA represents a calibration variable which is determined experimentally.

According to the equation (3), when the relationship PA<760 mmHg stands, the correction coefficient KPA2 value is smaller than 1. Since according to the KMe method, the quantity of intake air is determined solely from the equivalent opening area A of the throttling portion in the intake passage with reference to the standard atmospheric pressure PA0, it decreases in proportion as the atmospheric pressure PA decreases such as at a high altitude where the atmospheric pressure PA is lower than the standard atmospheric pressure PA0. Therefore, if the fuel quantity is set in dependence on the above opening area A, the resulting air/fuel mixture becomes rich, in a manner reverse to the SD method. However, such enriching of the mixture can be avoided by employing the above correction coefficient KPA2 value.

FIG. 1 schematically illustrates the whole arrangement of a fuel injection control system for internal combustion engines, to which is applied the method according to the invention. In the figure, reference numeral 1 designates an internal combustion engine which may be a four-cylinder type. Connected to the engine 1 are an intake pipe 3 with its air intake end provided with an air cleaner 2 and an exhaust pipe 4. Arranged in the intake pipe 3 is a throttle valve 9, and an air passage 8 opens at one end 8a into the intake pipe 3 at a downstream side of the throttle valve 9 and communicates with the atmosphere through the other end. The air passage 8 has an air cleaner 7 provided at the other end opening in the atmosphere. Arranged across the air passage 8 is a supplementary air quantity control valve (hereinafter merely called "the control valve") 6 which is a normally closed type electromagnetic valve comprising a solenoid 6a and a valve body 6b disposed to open the air passage 8 when the solenoid 6a is energized, the solenoid 6a being electrically connected to an electronic control unit (hereinafter abbreviated as "the ECU") 5.

Fuel injection valves 10 are projected into the intake pipe 3 at a location between the engine 1 and the open end 8a of the air passage 8, and connected to a fuel pump, not shown, and also electrically connected to the ECU 5.

A throttle valve opening (.theta.TH) sensor 17 is connected to the throttle valve 9, while an intake air temperature (TA) sensor 11 and an intake pipe absolute pressure (PBA) sensor 12 are mounted in the intake pipe 3 at locations downstream of the open end 8a of the air passage 8. Further, the main body of the engine 1 is provided with an engine cooling water temperature (TW) sensor 13 and an engine rotational speed (Ne) sensor 14. These sensors are electrically connected to the ECU 5. Reference numeral 15 represents electrical devices such as headlights, a brake lamp, an electric motor for driving a radiator cooling fan. One terminal of each of these electrical devices 15 is electrically connected to the ECU 5 by way of a switch 16, while another terminal thereof is electrically connected to a battery 19. Reference numeral 18 designates an atmospheric pressure sensor also electrically connected to the ECU 5.

The operation of the fuel injection control system constructed as above will now be described.

The ECU 5 is supplied with signals indicative of operating parameter values of the engine from the throttle valve opening sensor 17, the intake air temperature sensor 11, the intake pipe absolute pressure sensor 12, the engine cooling water temperature sensor 13, the engine rotational speed sensor 14, and the atmospheric pressure sensor 18. The ECU 5 operates on these engine operating parameter signals and signals indicative of electrical loads from the electrical devices 15 to determine whether or not the engine is operating in an operating condition requiring the supply of supplementary air to the engine, and set a desired idling speed value. When the engine is determined to be operating in such supplementary air-supplying condition, the ECU 5 determines the quantity of supplementary air to be supplied to the engine in response to the difference between the set desired idling speed value and the actual engine rotational speed, so as to make the same difference zero, and thereby calculates a value of the valve opening duty DOUT ratio for the control valve 6 to drive the same valve with the calculated duty ratio.

The solenoid 6a of the control valve 6 is energized for a valve opening period of time corresponding to the calculated valve opening duty ratio DOUT to open the valve body 6b to open the air passage 8 so that a required quantity of air determined by the valve opening period of the valve 6 is supplied to the engine 1 through the air passage 8 and the intake pipe 3.

If the valve opening period for the control valve 6 is set to a larger value so as to increase the supplementary air quantity, an increased quantity of the mixture is supplied to the engine 1 to thereby increase its output so that the engine rotational speed increases. On the contrary, if the valve opening period is set to a smaller value, it results in a reduced mixture quantity and accordingly a decrease in the engine rotational speed. By controlling the supplementary air quantity, that is, the valve opening period for the control valve 6 in this manner, the engine rotational speed can be maintained at the desired idling speed value during idling operation of the engine.

On the other hand, the ECU 5 also operates on values of the aforementioned various engine operating parameter signals and in synchronism with generation of pulses of a TDC signal indicative of top-dead-center positions of the engine cylinders, which may be supplied from the engine rotational speed sensor 14, to calculate the fuel injection period TOUT for the fuel injection valves 10 by the use of the following equation:

where Ti represents a basic fuel injection period, which is determined according to the aforementioned SD method or the KMe method, selected depending upon whether or not the engine is operating in an operating region wherein a predetermined idling condition is fulfilled, as hereinafter described in detail.

In the above equation, K1 and K2 represent correction coefficients or correction variables which are calculated on the basis of values of engine operating parameter signals supplied from the aforementioned various sensors such as the engine cooling water temperature (TW) sensor 13, the throttle valve opening (.theta.TH) sensor 17, and the atmospheric pressure (PA) sensor 18. For instance, the correction coefficient K1 is calculated by the use of the following equation:

where KPA represents an atmospheric pressure-dependent correction coefficient, described in detail hereinafter, and KTW represents a coefficient for increasing the fuel supply quantity, which has its value determined in dependence on the engine cooling water temperature TW sensed by the engine cooling water temperature (TW) sensor 13, and KWOT a mixture-enriching coefficient applicable at wide-open-throttle operation of the engine and having a constant value, respectively.

The ECU 5 supplies the fuel injection valves 10 with driving signals corresponding to the fuel injection period TOUT calculated as above, to open the same valves.

FIG. 2 shows a circuit configuration within the ECU 5 in FIG. 1. An output signal from the engine speed (Ne) sensor 14 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 a preceding pulse of the TDC signal and a present pulse of same, inputted thereto from the Ne sensor 14, and therefore its counted value Me is proportional to the reciprocal of the actual engine speed Ne. The Me value counter 502 supplies the counted value Me to the CPU 503 via a data bus 510.

The respective output signals from the throttle valve opening (.theta.TH) sensor 17, the intake pipe absolute pressure (PBA) sensor 12, the engine cooling water temperature (TW) sensor 13, the atmospheric pressure (PA) sensor 18, etc., appearing in FIG. 1 have their voltage levels 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 analog output voltages from the aforementioned various sensors, and the resulting digital signals are supplied to the CPU 503 via the data bus 510.

On-off state signals supplied from the switches 16 of the electrical devices 15 in FIG. 1 are supplied to another level shifter unit 512 wherein the signals have their voltage levels shifted to a predetermined voltage level, and the level shifted signals are processed by a data input circuit 513 and applied to the CPU 503 through 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 driving circuits 509 and 511. The RAM 508 temporarily stores various calculated values from the CPU 503, while the ROM 507 stores a control program executed within the CPU 503, etc.

The CPU 503 operates in accordance with the control program stored in the ROM 507 to determine operating conditions of the engine on the basis of the engine operating parameter signals, as well as electrically loaded conditions of the engine on the basis of the on-off signals from the electrical devices 15, to calculate the valve opening duty ratio DOUT for the control valve 6 to a value corresponding to the determined loaded condition of the engine.

The CPU 503 supplies the driving circuit 511 with a control signal corresponding to the calculated valve opening duty ratio DOUT for the control valve 6, and then the driving circuit 511 operates on the control signal to apply a driving signal to the control valve 6 to drive same. The CPU 503 also operates on the various engine operating parmeter signals to calculate the valve opening period TOUT for the fuel injection valves 10, and supplies the driving circuit 509 with a control signal corresponding to the calculated valve opening period to cause same to apply driving signals to the fuel injection valves 10 to drive same.

FIG. 3 shows a manner of calculating the valve opening period TOUT for the fuel injection valves 10. First, in the step 1 of FIG. 3, it is determined whether or not is fulfilled a condition for applying the KMe method to calculation of the basic value Ti of the valve opening period 10 (hereinafter this condition will be called "the idle mode"). This determination as to fulfillment of the idle mode may be made by determining whether or not the engine is operating in a predetermined operating region as shown in the flowchart of FIG. 4, for instance. That is, in the step 1a of FIG. 4, it is determined whether or not the engine rotational speed Ne is lower than a predetermined value NIDL (e.g. 1,000 rpm). If the answer is negative or no, the program jumps to step 1d wherein a decision is rendered that the idle mode is not fulfilled. If the answer to the question at step 1a is affirmative or yes, the program proceeds to step 1b wherein it is determined whether or not the intake pipe absolute pressure PBA is lower than a predetermined reference value PBAC. The reference value PBAC is set at such a value as to determine whether or not the ratio (PBA/PA') of intake pipe absolute pressure PBA downstream of the throttle valve 9 to intake pipe absolute pressure PA' upstream of the throttle valve 9 is smaller than the critical pressure ratio (=0.528) at which the flow of intake air passing the throttle valve 9 forms a sonic flow. If the answer to the question of step 1b is negative or no, the fulfilment of the idle mode is negated at step 1d, while if the answer is affirmative, the program proceeds to step 1c to make a determination as to whether or not the valve opening .theta.TH of the throttle valve 9 is smaller than a predetermined value .theta.IDLH. That is, at a transition in engine operation from an idling condition with the throttle valve 9 in its substantially closed position to an accelerating condition with the throttle valve 9 rapidly opened, if this accelerating condition is detected solely from changes in the engine rotational speed and the intake pipe absolute pressure, there will occur a detection lag mainly due to the response lag of the absolute pressure sensor 12. Therefore, the throttle valve opening .theta.TH is employed to detect such accelerating condition. When such accelerating condition is detected by the throttle valve opening sensor 17, the SD method, hereinafter referred to, is applied to calculation of a proper accelerating increased fuel quantity for supply to the engine. If the answer to the question of step 1c is negative, it is decided that the idle mode is not then fulfilled. If all the answers to the questions of steps 1a through 1c are found affirmative at the same time, the program proceeds to step 1e to decide that the engine is operating in the idle mode.

Referring again to FIG. 3, if the determination at step 1 provides a negative answer, the SD method is employed to determine the basic fuel injection period value Ti at step 2. According to the SD method, a basic fuel injection period value Ti is selected from among a plurality of predetermined values stored in the ROM 507 within the ECU 5, which corresponds to a combination of detected values of intake pipe absolute pressure PBA and engine rotational speed Ne. The basic fuel injection period value Ti thus determined is applied to the aforegiven equation (4) together with the atmospheric pressure-dependent correction coefficient KPA forming part of the correction coefficients K1, to calculate the final fuel injection period TOUT, at step 4.

If the answer to the question of step 1 is affirmative, the program proceeds to step 3 to employ the KMe method for calculation of the basic fuel injection period Ti.

The basic fuel injection period Ti according to the KMe method is determined by the following equation:

where K(A) represents the equivalent opening area of the throttling portion in the intake passage, which is determined by the sum of the valve opening areas of the throttle valve 9 and the control valve 6. The valve opening areas of these valves 9, 6 may be obtained, respectively, from a value of the output signal from the throttle valve opening sensor 17 and a value of the valve opening duty ratio for the control valve 6 calculated by the CPU 503. In the equation (6), Me represents a time interval of generation of pulses of the TDC signal which is measured by the Me counter 502 in FIG. 2. The reason why the basic fuel injection period Ti can be determined by the use of the equation (6) above is as follows: The quantity of intake air passing the throttling portion of the intake passage per unit time is given solely as a function of the equivalent opening area of the throttling portion provided that the atmospheric pressure PA and the intake air temperature TAF remain constant, as endorsed by the equation (2). Further, the quantity of intake air sucked into an engine cylinder per suction stroke is proportional to the reciprocal of the engine rpm Ne, and accordingly to the Me value.

The basic fuel injection period value Ti thus determined is applied to the equation (4) to calculate the final fuel injection period TOUT, at step 4.

FIG. 5 shows a manner of calculating the atmospheric pressure-dependent correction coefficient KPA as part of the correction coefficients K1, appearing in the equation (5).

It is first determined in step 1 of FIG. 5 whether or not the engine is operating in the idle mode, as in step 1 of FIG. 3. If the answer is negative, the program proceeds to step 2 wherein the atmospheric pressure-dependent correction coefficient KPA1 is calculated by the use of the equation (1), to be applied to correction of the basic fuel injection period Ti determined according to the SD method. The coefficient KPA1 value thus determined is applied as the correction coefficient KPA to the equations (5) and (4), at step 3. If the answer to the question of step 1 is affirmative, the program proceeds to step 4 wherein the atmospheric pressure-dependent correction coefficient KPA2 is calculated by the use of the equation (3), to be applied to correction of the basic fuel injection period Ti determined according to the KMe method. The coefficient KPA2 value thus determined is applied as the correction coefficient KPA to the equations (5) and (4), at step 5.

The method according to the invention is not limited to control of the fuel supply quantity in a fuel supply control system for internal combustion engines as in the foregoing embodiment, but it may be applied to control of an operating amount of any operation control means for controlling the operation of an internal combustion engine, insofar as the operating amount is determined by the use of a parameter indicative of the intake air quantity. For instance, the method according to the invention may be applied to control of an operating amount of an ignition timing control system, and an exhaust gas recirculation control system.