GB2168175A - Adaptive mixture control system - Google Patents

Abstract

An adaptive mixture control system updates data stored in a table of control coefficients at a steady state of engine operation in accordance with a feedback signal produced by a sensor only when the feedback signal A deviates from a predetermined reference range e.g. 0.99>/=A>/=1.01. The data is incremented or decremented with a suitable value.

Description

SPECIFICATION Adaptive mixture control system The present invention relates to a system for controlling the operation of an automotive engine, and more particularly to an adaptive control system for undating data stored in a table for controlling the fuel supply in an electronic fuel-injection system.

In one type of electronic fuel-injection control, the amount of fuel to be injected into the engine is determined in accordance with engine operating variables such as mass air flow, engine speed and engine load. The amount of fuel is determined by a fuel injector energisation time (injection pulse width). The basic injection pulse width (Tp) is obtained from the following formula: Tp=KXQ/N (1) where Q is a mass air flow, N is engine speed, and K is a constant.

The desired injection pulse width (T,) is obtained by correcting the basic injection pulse (Tp) with engine operating variables. The following is an example of a formula for determining the required injection pulse width.

T,=T,X(COEF)XaXK, (2) where COEF is a coefficient obtained by adding various correction or compensation coefficients such as coefficients of coolant temperature, fully open throttle position, engine load, etc., a is a a correcting coefficient (the integral of the feedback signal of an O2 sensor provided in an exhaust passage), and K, is a correction coefficient which is modified by a learning process (hereinafter called an adaptive control coefficient). The coefficients, such as coolant temperature coefficient and engine load, are obtained by looking up tables in accordance with sensed information. The value of the adaptive control coefficient K, is obtained from a K,-table in accordance with engine load.All of the coefficients K, stored in the K,-table are initially set to the same value, that is the number "1", so that the fuel supply system can provide the most suitable amount of fuel without the coefficient K. However, automobiles cannot be manufactured completely consistently. Accordingly, the coefficient K, is updated by an adaptive control system in each automobile, when it is actually used. The rewriting of the K,-table is performed in accordance with various variables such as the output of the O2-sensor, engine speed, engine load and others. In such a system, if the updated coefficient K, is rewritten in accordance with a small deviation of an input signal, which is caused, for example, by malfunction of a sensor or a small fluctuation of engine speed or engine load hunting occurs in the learning control system.

Accordingly, a proper amount of fuel cannot be supplied to the engine.

The present invention seeks to provide a system which reduces the occurrence of hunting in an adaptive control system.

Accordingly, the present invention provides a system for controlling an automotive engine by updated data, comprising a table for storing data, first means for detecting the operating condition of the engine and for producing a feedback signal dependent on the condition, second means for determining that the engine operating condition is appropriate for updating the data stored in the table and for producing a first output signal, third means for determining whether the feedback signal exceeds a predetermined range with respect to a desired value and for producing a second output signal, and fourth means responsive to the second output signal for incrementing or decrementing one of the data items.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic illustration showing a system for controlling the operation of an internal combustion engine for a motor vehicle; Figure 2 is a block diagram of a microcomputer system used in a system of the invention; Figure 3a is an illustration showing a matrix for detecting the steady state of engine operation; Figure 3b shows a table of adaptive control coefficients; Figure 4a shows the output voltage of an 02sensor; Figure 4b shows the output voltage of an integrator; Figure 5 shows a linear interpolation for reading the table of Fig. 3b; and Figures 6a and 6b are flowcharts showing the operation of an embodiment of the present invention.

Referring to Fig. 1, an internal combustion engine 1 for a motor vehicle is supplied with air through an air cleaner 2, intake pipe 2a, and throttle valve 5 in a throttle body 3, mixing with fuel injected from an injector 4. A three-way catalytic converter 6 and an O2-sensor 16 are provided in an exhaust passage 2b. An exhaust gas recirculation (EGR) valve 7 is provided in an EGR passage 8 in a well-known manner.

Fuel in a fuel tank 9 is supplied to the injector 4 by a fuel pump 10 through a filter 13 and pressure regulator 11. A solenoid operated valve 14 is provided in a bypass 12 around the throttle valve 5 so as to control engine speed during idling operation. A mass air flow meter 17 is provided on the intake pipe 2a and a throttle position sensor 18 is provided on the throttle body 3. A coolant temperature sensor 19 is mounted on the engine. Output signals of the meter 17 and sensors 18 and 19 are applied to a microcomputer 15. The microcomputer 15 is also applied with a crankangle signal from a crankangle sensor 21 mounted on a distributor 20 and a starter signal from a starter switch 23 which operates to turn on-off electric current from a battery 24. The system is further provided with an injector relay 25 and a fuel pump relay 26 for operating the injector 4 and fuel pump 10.

Referring to Fig. 2, the microcomputer 15 comprises a microprocessor unit 27, ROM 29, RAM 30, RAM 31 with back-up, A/D converter 32 and I/O interface 33. Output signals of O2-sensor 16, mass air flow meter 17 and throttle position sensor 18 are converted to digital signals and applied to the microprocessor unit 27 through a bus 28. Other signals are applied to the microprocessor unit 27 through I/O interface 33. The microprocessor manipulates input signals and executes hereinafter described process.

In the preferred embodiment of the present invention, the adaptive control coefficients K, stored in a K,-table are updated with data calculated during the steady state of engine operation.

Accordingly, the detection of the steady state is necessary. In the system, the steady state is decided by ranges of engine load and engine speed and continuation of a detected state.

Fig. 3a shows a matrix of detection values, which comprises, for example sixteen divisions defined by five row lines and five column lines. Magnitudes of engine load are set at five points L0 to L4 on the X axis, and magnitudes of engine speed are set at five points No to N4 on the Y axis. Thus, the engine load is divided into four ranges, that is Lo-L1 L,-L2, L2-L3, and L3-L4.

Similarly, the engine speed is divided into four ranges.

In operation, the output voltage of the 02-sensor 16 cyclically changes through a reference voltage corresponding to a stoichiometric air-fuel ratio, as shown in Fig. 4a. That is to say, the voltage changes between high and low voltages corresponding to rich and lean air-fuel mixtures.

In the system, when the output voltage (feedback signal) of the O2-sensor remains within one of the sixteen divisions in the matrix, for a continuous period of three cycles, the engine is assumed to be in steady state.

Fig. 3b shows a K,-table for storing the adaptive control coefficients K,, which is included in the RAM 31 of Fig. 2. The Ka-table has addresses al, a2, a3, and a4 which are corresponding to engine load ranges Lo-L1, Ll-L2, L2-L3, and L3-L4. As previously stated, each value stored in the tables is "1" before the vehicle is first driven.

On starting the engine the calculation of the injection pulse width (T, in formula (2)) proceeds as follows: since the temperature of the body of the 02sensor 16 is low the output voltage of the 02 sensor is very low. In such a state, the sytem is arranged to provide "1" as the value of correcting coefficient K,. Thus, the computer calculates the injection pulse width (T,) from mass air flow (Q), engine speed (N), (COEF), and K,. When the engine is warmed up and the O3-sensor becomes activated, a value relative to an integral of the output voltage of the O2-sensor is provided as a value of A. More particularly, the computer functions as an integrator, so that the output voltage of the O2-sensor is integrated. Fig. 4b shows the ouput of the integrator.The coefficient A is an arithmetical average of a maximum value Imax and a minimum value Imin.

The adaptive function operates as follows: when the value A deviates from a predetermined reference range (dead zone) in the steady state of engine operation, the K,-table is updated with the minimum value (hA) which can be obtained in the computer. That is to say the value of one bit is added to or subtracted from a BCD (Binary Coded Decimal) code representing the stored data. In this system, the desired value of A is "1". Accordingly, the reference range is a certain range with respect to the desired value "1", for example a range of + 1 % of "1".

The operation of the system will be described in more detail with reference to Figs. 6a and 6b. The adaptive program is started at a predetermined interval for example, (40ms). During the first operation of the engine and the first driving of the motor vehicle, engine speed is detected at step 101. If the engine speed is within the range between No and N4, the program proceeds to a step 102. If the engine speed is out of the range, the program exits the routine at a step 122. At step 102, the position of the row of the matrix of Fig. 3a in which the detected engine speed is included is detected and the position is stored in RAM 30. Thereafter, the program proceeds to a step 103, where engine load is detected. If the engine load is within the range between L0 and L4, the program proceeds to a step 104. If the engine load is out of the range, the program exits the routine. Thereafter, the position of column corresponding the detected engine load is detected in the matrix, and the position is stored in the RAM. Thus, the position of division corresponding to the engine operating condition represented by engine speed and engine load is decided in the matrix, for example, division D, is decided in Fig. 3a. The program advances to a step 105, where the decided position of division is compared with the division which has been detected at the last learning step. However, since this is the first learning step, the comparison cannot be performed, and hence the program exits the routine passing through steps 107 and 111. At the step 107, the position of division is stored in a RAM.

In a subsequent learning step, the detected position is compared with the last stored position of division at step 105. If the position of division in the matrix is the same as the last learning, the program proceeds to a step 106, where the output voltage of O2-sensor 16 is detected. If the voltage changes from rich to lean and vice versa, the program goes to a step 108, and if not, the program exits the routine. At the step 108, the number of the cycle of the output voltage is counted by a counter. If the counter counts up to three, the program proceeds to a step 110 from a step 109. If the count does not reach three, the program exits the routine. At the step 110, the counter is cleared and the program proceeds to a step 112.

On the other hand, if the position of the division is not the same as the last learning, the program proceeds to step 107, where the old data of the position is substituted with the new data. At the step 111, the counter which has operated at step 108 in the last learning is cleared.

At step 112, arithmetical average A of a maximum value and a minimum value of the integral of the output voltage of the O2-sensor during three cycles of the output wave form is calculated and the value A is stored in a RAM. Thereafter, the program proceeds to a step 113, where the address corresponding to the position of division is detected, for example, the address a2 corresponding to the division D1 is detected and the address is stored in a RAM.

Thereafter the program proceeds to a step 116, where it is determined whether the calculated value of A stored in the RAM is greater than "1.01". If the A is greater than "1.01", the program proceeds to a step 117, where the minimum unit AA (one bit) is added to the learning control coefficient K, in the corresponding address. If the A is less than "1.01", the program proceeds to a step 118, where it is determined whether the A is less than "0.99". If the A is less than "0.99", the minimum unit AA is substracted from K, at a step 119. If the A is not less than "0.99", which means that the A is approximate to "1", the program exits the updating routine. Thus, the updating operation continues until the value of the A converges to "1".

When the injection pulse width (T,) is calculated, the learning control coefficient K, is read out from the K,-table in accordance with the value of engine load L. However, values of K, are stored at intervals of loads. Fig. 5 shows an interpolation of the K,-table. At engine loads Xl, X2, X3, and X4, updated values Y3 and Y4 (as coefficient K,) are stored. Each of the loads is set at the middle value in each load range. When detected engine load does not coincide with the set loads X, to X4, coefficient K, is obtained by linear interpolation. For example, the value Y of K, at engine load X is obtained by the following formula.

Y=( (X-X3) /(X4-X3) )X(Y4-Y3)+Y3 Although the above described embodiments relate to fuel injection systems, the present invention can be applied to control systems other than the fuel injection system.

In accordance with the preferred arrangement of the present invention, a correction is applied only when a feedback signal deviates from a predetermined range (dead zone), so that hunting can be prevented.

While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made within the scope of the appended claims.

Claims (4)

1. An adaptive control system for an automotive engine by updated data, comprising: a table for storing control coefficients data; first means for detecting the operating condition of the engine and for producing a feedback signal dependent on the said condition; second means for determining that the engine operating condition is appropriate for updating the data stored in the table and for producing a first output signal; third means for determining whether the feedback signal exceeds a predetermined range with respect to a desired value and for producing a second output signal; and fourth means responsive to the said second output-signal for incrementing or decrementing one of the data items.

2. A system according to claim 1 wherein the second means comprises means for detecting a steady state of the engine operation for a predetermined period.

3. A system according to claim 1 wherein the first means includes a sensor for detecting the operating condition of the engine and the feedback signal is a value dependent upon the output of the sensor.

4. An adaptive control system substantially as herein described with reference to the accom panying drawings.