GB2162662A - Updating of adaptive mixture control system in I C engines - Google Patents

Abstract

An adaptive mixture control system including a first table for storing control coefficients for compensating for changes of the operating characteristics of devices such as fuel injectors and O2-sensors in an air-fuel ratio control system, and a second table for storing control coefficients for compensating for the change of the characteristic of an air-flow meter. Data in the first and second table are updated with values derived from the O2-sensor feedback signal when the engine is determined to be in a steady state. The amount of update at the first occasion may comprise half the values of the arithmetical average of the integral of the O2-sensor feedback signal, subsequent updates being increments or decrements of a fixed amount.

Description

SPECIFICATION Adaptive mixture control system The present invention relates to an air-fuel ratio control system for an automotive engine, and more particularly to an air- fuel ratio control system using an adaptive control system which can continually update data stored in a table of control coefficients for controlling the fuel supply in an electronic fuel-injection system.

In one known 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 decided by a fuel injector energisation time (injection pulse width). The basic injection pulse width (Tp) is obtained from the following formula.

Tp = K x Qh/N (1) where Qh is mass air flow, N is engine speed, and K is a constant.

The required 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 computing the desired injection pulse width.

T; = T, x (COEF) x a x K, (2) where COEF is a coefficient obtained by adding various correction or compensation coefficients such as coefficients on coolant temperature, fully open throttle position, engine load, etc., oe is a A correcting coefficient (the integral of the feedback signal of the O2-sensor provided in an exhaust passage), and K, is a correcting coefficient modified by a learning process (hereinafter called an adaptive control coefficient) for compensating for the change of characteristics of devices in the fuel control system such as injectors and the O2-sensor due to their progressive deterioration.The control coefficients relating to parameters such as coolant temperature and engine load, are obtained from look up tables in accordance with sensed information on operating conditions. The value of the adaptive control coefficient K, is obtained from a K,-table in accordance with engine load.

In addition, the performance of mass air flow meters or sensors for obtaining the mass air flow 0h may also deteriorate as time goes on. Accordingly, such changes of the operating characteristics should be corrected for.

The ignition timing of the engine is decided also by the mass air flow Qh and a table relating to the mass air flow and engine speed. In particular, if the mass air flow 0h increases, the amount of fuel increases and in addition ignition timing is advanced with decrease of the mass air flow. Accordingly, if a mass air flow meter deteriorates and fails to produce a proper output voltage, the air-fuel ratio of mixture supplied to the engine deviates from stoichiometry and improper ignition timing is set. For example, if the output voltage decreases owing to failure of the mass air flow meter, the ignition timing is advanced regardless of engine operating conditions. Such improper advance of timing will cause engine knock.

Accordingly the present invention seeks to provide a system which may properly control the airfuel ratio by updating control coefficient data relative to both the injector and mass air flow.

Accordingly the present invention provides an air-fuel ratio control system for an automotive engine in which the amount of fuel to be supplied to the engine is controlled adaptively by continually modifying a table of control coefficients.

An adaptive mixture control system according to the invention comprises at least one fuel injector, first means for detecting the amount of intake air, a first table for storing control coefficients for changes of the operating characteristics of devices in the air-fuel ratio control system, a second table for storing coefficients for compensating the change of the operating characteristic of the first means, an O2-sensor for detecting the concentration of exhaust gases of the engine and for producing a feedback signal dependent on the concentration, second means for updating the data in the first table with values derived from the feedback signal, and third means for updating the data in the second table with a value derived from the feedback signal.

Some embodiments 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 the system of the present invention; Figure 3a is an illustration showing a matrix of values for detecting the steady state of engine operation; Figures 3b and 3c show tables of adaptive control coefficients; Figure 4a shows the output voltage of an O2-sensor; Figure 4b shows the output voltage of an integrator; Figure 5 shows a linear interpolation for reading the table of Figure 3b; Figures 6a and 6b are illustrations for explaining the probability of updating; and Figures 7a and 7b are flowcharts showing the operation of the described embodiment of the present invention.

Referring to Figure 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 02sensor 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. 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 sensor 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 control the supply of 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 Figure 2, the microcomputer 15 comprises a microprocessor unit 27, ROM 29, RAM 30, RAM 31 with back-up, AID converter 32 and l/O interface 33. Output signals of O2-sensor 16, mass air flow meter 17 and throttle position sensor 18 are converted to digital signals by the AID converter 32 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 the control program to be described below.

In the preferred arrangement of the present invention, a Ka~ table for storing first control coefficients K, for devices in the fuel control system and a Q,-table for storing second control coefficients Q, for the mass air flow meter 17 are provided. Accordingly, the formula (2) is expressed as follows.

T, = Tp x (COEF) x a x (K, + 0,) (3) The adaptive control coefficients K, stored in a 0, are updated with data calculated during the steady state of engine operation. In such a system, the steady state is detected in terms of ranges of engine load and engine speed and persistence of a detected state. Figure 3a shows a matrix for the detection, 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 L0-L1, L,-L2, L2-L3, and L3-L4. Similarly, the engine speed is divided into four ranges.

In addition, the output voltage of the O2-sensor 16 cyclically changes through a reference voltage corresponding to a stoichiometric air-fuel ratio, as shown in Figure 4a. That is to say, the voltage changes between high and low voltages corresponding to rich and lean air-fuel mixtures. In this system, when the output voltage (feedback signal) of the O2-sensor continues during three cycles within one of sixteen divisions in the matrix, the engine is assumed to be in a steady state.

Figure 3b shows a K,-table for storing the adaptive control coefficients Q,, which is included in the RAM 31 of Figure 2. The K,-table is a two-dimensional table and has addresses a1, a2, a2, and a4 which are corresponding to engine load ranges L"- L1, L,-L2, L2-L3, and LsQ4. The 0,table is the same as the K,-table and has addresses b,, b2, b3 and b4.

All of the coefficients K, and Q, stored in K,-table and 0,table are initially set to the same value, that is the numerical value "I", since the fuel supply system is designed to provide as far as possible, the optimum amount of fuel without correction by the coefficients K, and 0,. However, automobiles cannot be manufactured with completely identical operating characteristics. Accordingly, the coefficients K, and Q, must be adaptively updated in each automobile, when it is actually used.

When the engine is started, the injection pulse width (Tj in the formula 3) is calculated as follows.

Since the temperature of the body of the O2-sensor 16 is low, the output voltage of the O2-sensor is very low. In such a state, the system is adapted to provide "1" as the value of the correcting coefficient. Thus, the computer calculates the injection pulse width (Tj) from mass air flow (0,), engine speed (N), (COEF), a, K, and Q. When the engine is warmed up and the O2-sensor becomes activated, an integral of the output voltage of the 2- sensor at a predetermined time is provided as the value of a. More particularly, the computer functions as an integrator, so that the output voltage of the O2-sensor is integrated. Figure 4b shows the output of the integrator.The system provides values of the integration at a predetermined interval (40ms). For example, in Figure 4b, integrals Ii, --- at times T#, Tt --- are provided. Accordingly, the amount of fuel is controlled in accordance with the feedback signal from the O2-sensor, which is represented by the integral.

The adaptive or learning function of the system operates as follows: when the steady state of engine operation is detected, the K,-table and Q-ta- ble are updated with a value relative to the feedback signal from the O2-sensor. The first updating is done with, for example, a half of the arithmetical average (A) of the maximum and minimum values in one cycle of the integration, for example the values of Imax and Imin of Figure 4b.

Thereafter, when the value of a is not 1, the K,-table is incremented or decremented with the minimum value (AA) which can be obtained in the computer. That is to say, the value of one bit is added to or subtracted from a BCD code representing the value A of the coefficient K, which has been rewritten at the first learning. Further, the 0,table is incremented or decremented with the minimum value (AA) in accordance with the result of this comparison.

In addition, the system has an electronic ignition timing control device 40 mounted on distributor 20 (Figure 1) for controlling the ignition timing dependent on the mass air flow 0.

The operation of the system will be described in more detail with reference to Figures 7a and 7b.

The learning program is started at predetermined intervals (40ms). During the first operation of the engine and the first occasion of driving the motor vehicle, the engine speed is detected at step 101. If the engine speed is within the range between N, and N4, the program proceeds to step 102. If the engine speed is out of the range, the program exits the routine at step 122. At step 102, the position of the row of the matrix of Figure 3a in which the detected engine speed is included is located and the position is stored in RAM 30. Thereafter, the program proceeds to step 103, where engine load is detected. If the engine load is within the range between L0 and L4, the program proceeds to step 104.

If the engine load is out of the range, the program exits the routine. Thereafter, the position of the column corresponding to the detected engine load is located in the matrix, and the position is stored in the RAM. Thus, the position of the division corresponding to the engine operating condition represented by engine speed and engine load is identified in the matrix, for example, division D1 is identified in Figure 3a. The program advances to step 105, where the position of the division is compared with the position of the division which was detected in the last learning cycle. However, since this is the first learning cycle, the comparison cannot be performed, and hence the program is terminated passing through steps 107 and 111. At step 107, the position of the division is stored in RAM 30.

At a subsequent learning cycle after the first one, the detected position is compared with the last stored position of the operating condition division at step 105. If the position of the division in the matrix is the same as at the last learning cycle, the program proceeds to 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 step 108, and if not, the program is terminated. At step 108, the number of the cycle of the output voltage is counted by a counter. If the counter counts up to, for example three, the program proceeds to step 110 from step 109. If the count does not reach three, the program is terminated. At the step 110, the counter is cleared and the program proceeds to step 122.

On the other hand, if the position of the division is not the same as at the last learning cycle, the program proceeds to step 107 from step 105, where the old position data is substituted by the new data. At step 111, the counter which has operated at step 108 in the last learning cycle is cleared.

At step 112, the arithmetical average A of maximum and minimum values of the integral of the output voltage of the O2-sensor at the third cycle of the output wave form is calculated and the value A is stored in the RAM. Thereafter, the program proceeds to step 113, where the address corresponding to the position of division is detected, for example, the address a2 corresponding to the division D, is detected and the address is stored in the RAM to set a flag. At step 114, the stored address is compared with the last stored address. Since, before the first learning step, no address has been stored, the program proceeds to step 115. At step 115, the adaptive control coefficient K, in the address of the Ka-table of Figure 3b is entirely updated with a half of the new value A that is the arithmetical average obtained at step 112.

At a subsequent learning step after the first updating, if the address detected at the process is the same as the last address, (the flag exists in the address) the program proceeds from step 114 to a step 116, where it is determined whether the value of a (the integral of the output of the O2-sensor) at the learning is greater than "1". If a is greater than "1", the program proceeds to a step 117, where the minimum unit hA (the value of one bit) is added to the learning control coefficient K, in the corresponding address. If a is not greater than "1", the program proceeds to a step 118, where it is determined whether a is less than "1". If a is less than "1", the minimum unit AA is subtracted from K, at a step 119.If a is not less than "1", which means that a is equal to "1", the program exits the updating routine. Thus, the updating operation continues until the value of the a becomes "1".

The program proceeds from steps 115,117 and 119 to step 120, which is the same as the step 113 in operation. Thus, the same programs as the above described programs are performed for updating the Q,-table at steps 121, 124, 125, 126, 127 and 128.

When the injection pulse width (T,) is calculated, the learning control coefficients K, and Q, are read out from the K,-table and Q,-table in accordance with the value of engine load L. However, values of K, and Q, are stored at intervals of loads. Fig. 5 shows an interpolation of the K,-table. At engine loads X1, X2, X3, and X4, updated values Y3 and Y4 (as coefficient K) are stored. When detected engine load does not coincide with the set loads X1 to X4, coefficient K, is obtained by linear interpolation.

For example, value Y of K, at engine load X is obtained by the following formula.

Y = ((X-X2) 1 (X4-X3)) x x (Y4-Y2) + Y2 Fig. 6a is a matrix pattern showing the updating probability over 50% and Fig. 6b is a pattern showing the probability over 70% by hatching divisions in the matrix. More particularly, in the hatched range in Fig. 6b, the updating occurs at a probability over 70%. From the figures it will be seen that the updating probability at extreme engine operating steady state, such as the state that low engine load at high engine speed and at high engine load at low engine speed, is very small. In addition, it is experienced that the difference between values of coefficient in adjacent speed ranges is small. Accordingly, it will be understood that the two-dimensional tables, in which a single data is stored at each address, is sufficient for performing the learning control of an engine.

In the system of the present invention, since a first table for storing correcting coefficients for fuel injectors and a second table for mass air flow are updated, exact air-fuel ratio control can be performed.

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 (3)

1. An adaptive mixture control system comprising at least one fuel injector, first means for detect ing the amount of intake air, a first table for storing control coefficients for changes of the operating characteristics of devices in the air-fuei ratio control system, a second table for storing coefficients for compensating the change of the operating characteristic of the first means, an O2-sensor for detecting the concentration of exhaust gases of the engine and for producing a feedback signal dependent on the concentration, second means for updating the data in the first table with values derived from the feedback signal, and third means for updating the data in the second table with a value derived from the feedback signal.

2. A system according to claim 1 further comprising fourth means for determining that engine operation is in a steady state in accordance with two variables of engine operation and for producing an output signal, each of the first and second tables being a two-dimensional table having addresses dependent on one of the two variables.

3. An adaptive air-fuel ratio control system according to claim 1 and substantially as herein described.