Patent Publication Number: US-4733357-A

Title: Learning control system for controlling an automotive engine

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a system for controlling the operation of an automotive engine, and more particularly to a learning control system for updating data stored in a table for controlling the fuel supply in an electronic fuel-injection system. 
     In one type of electronic fuel-injection control, for example the publication Japanese Patent Application Laid Open No. 57-122135, 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 energization time (injection pulse width). Basic injection pulse width (T p ) can be obtained by the following formula. 
     
         T.sub.p =K×Q/N                                       (1) 
    
     where Q is mass air flow, N is engine speed, and K is a constant. 
     Desired injection pulse width (T i ) is obtained by correcting the basic injection pulse (T p ) with engine operating variables. The following is an example of a formula for computing the desired injection pulse width. 
     
         T.sub.i =T.sub.p ×(COEF)α×K.sub.a        ( 2) 
    
     Where COEF is a coefficient obtained by adding various correction or compensation coefficients such as coefficients of coolant temperature, full throttle open, engine load, etc., α is a λ correcting coefficient (the integral of the feedback signal of an O 2  -sensor provided in an exhaust passage), and K a  is a correcting coefficient by learning (hereinafter called the learning control coefficient). Coefficients, such as the coolant temperature coefficient and engine load, are obtained by looking them up in tables in accordance with sensed information. The value of the learning control coefficient K a  is obtained from a K a  -table in accordance with engine load. All of the coefficients K a  stored in the K a  -table are initially set to the same value, that is the number &#34;1&#34;. This is caused by the fact that the fuel supply system is to be designed to provide the most proper amount of fuel without the coefficient K a . However, very automobile can not be manufactured to have a desired function, resulting in the same result. Accordingly, the coefficient K a  should be updated by learning in every automobile when it is actually used. If the difference between the initial value &#34;1 &#34; and the updated value is large, hunting of the fuel injection system occurs. Heretofore, in order to prevent such a hunting, the initial value is incremented or decremented little by little until the value is entirely rewritten. Accordingly, a long time elapses before the value is updated, causing the delay of fuel control (FIG. 6a). 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a system which quickly operates to update a learning control coefficient and may prevent the hunting of a control system for a engine, such as an electronic fuel-injection system, whereby the engine operation can be properly controlled. 
     According to the present invention, there is provide provided a system for controlling an automotive engine by updated data, in which the data stored in a table is entirely updated the first time with an arithmetic average of feedback signal, and thereafter the data is incremented or decremented with a minimum storable value. 
     More particularly, the system comprises 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 in a state suitable for updating the data and for producing an output signal when this state occurs, third means for detecting the output signal of the second means, and for producing a first updating signal when the output signal of the second means did not exist before, and thereafter for producing second updating signals in accordance with the output signals of the second means. The arithmetic average of the data is updated with the feedback signal in accordance with the first updating signal, and thereafter the data is incremented or decremented with a minimum value in response to the second updating signal. The updating is continued until the feedback signal reaches a desired value. 
     In an aspect of the present invention, the second means comprises means for detecting a steady state of the engine operation for a predetermined period. 
     The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic illustration showing a system for controlling the operation of an internal combustion engine for a motor vehicle; 
     FIG. 2 is a block diagram of a microcomputer system used in a system of the present invention; 
     FIG. 3a is an illustration showing a matrix for detecting the steady state of engine operation; 
     FIG. 3b shows a table for learning control coefficients; 
     FIG. 4a shows the output voltage of an O 2  -sensor; 
     FIG. 4b shows the output voltage of an integrator; 
     FIG. 5 shows a linear interpolation for reading the table of FIG. 3b; 
     FIGS. 6a and 6b are graphs showing variations of learning control coefficients in a conventional system and a system of the present invention; 
     FIG. 7a and 7b are flowcharts showing the operation in an embodiment of the present invention; and 
     FIG. 8 is a flowchart of the operation in another embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 catalitic converter 6 and an O 2  -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 at 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 O 2  -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 the input signals and executes the hereinafter described process. 
     In the system of the present invention, the learning control coefficients K a  stored in a K a  -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 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 L 0  to L 4  on the X axis, and magnitudes of engine speed are set at five points N 0  to N 4  on the Y axis. Thus, the engine load is divided into four ranges, that is L 0  -L 1 , L 1  -L 2 , L 2  -L 3 , and L 3  -L 4 . Similarly, the engine speed is divided into four ranges. 
     On the other hand, the output voltage of the O 2  -sensor 16 cyclically changes through a reference voltage corresponding to a stoichiometric air-fuel ratio, as shown in FIG. 4a. Namely, 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 O 2  -sensor continues during three cycles within the same one of the sixteen divisions in the matrix, the engine is assumed to be in steady state. 
     FIG. 3b shows a K a  -table for storing the learning control coefficients K a , which is included in the RAM 31 of FIG. 2. The K a  -table has addresses a 1 , a 2 , a 3 , and a 4  which are corresponding to engine load ranges L 0  -L 1 , L 1  -L 2 , L 2  -L 3 , and L 3  -L 4 . As previously stated, each value stored in the table is &#34;1&#34; before driving a motor vehicle. 
     Explaining the calculation of the injection pulse width (T i  in formula 2) at starting of the engine, since the temperature of the body of the O 2  -sensor 16 is low, the output voltage of the O 2  -sensor is very low. In such a state, the system is adapted to provide &#34;1&#34; as the value of the correcting coefficient α. Thus, the computer calculates the injection pulse width (T i ) from mass air flow (Q), engine speed (N), (COEF), α and K a . When the engine is warmed up and the O 2  -sensor becomes activated, the integral of the output voltage of the O 2  -sensor at a predetermined time is provided as the value of α. More particularly, the computer has a function of an integrator, so that the output voltage of the O 2  -sensor is integrated. FIG. 4b shows the output of the integrator. The system provides values of the integration at a predetermined interval (40ms). For example, in FIG. 4b, integrals I 1 , I 2  --at times T 1 , T 2  --are provided. Accordingly, the amount of fuel is controlled in accordance with the feedback signal from the O 2  -sensor, which is represented by integral. 
     Explaining the learning operation, when steady state of engine operation is detected, the K a  -table is updated with a value relative to the feedback signal from the O 2  -sensor. The first updating is done with an arithmetical average (A) of maximum value and minimum value in one cycle of the integration, for example values of Imax and Imin of FIG. 4b. Thereafter, when the value of α is not 1, the K a  -table is incremented or decremented with a minimum value (ΔA) which can be obtained in the computer. Namely one bit is added to or subtracted from a BCD code representing the value A of the coefficient K a  which has been rewritten at the first learning. 
     The operation of the system will be described in more detail with reference to FIG. 7a, 7b. The learning program is started at a predetermined interval (40 ms). At 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 N 0  and N 4 , 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 L 0  and L 4 , 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 the division corresponding to the engine operating condition represented by engine speed and engine load is determined in the matrix, for example, division D 1  is determined in FIG. 3a. The program advances to a step 105, where the determined position of the division is compared with the division which has been detected at the last learning. However, since the present learning is the first, the comparison can not be performed, and hence the program is terminated passing through steps 107 and 111. At the step 107, the position of the division D 1  is stored in a RAM. 
     At a learning after the first learning, the detected position is compared with the last stored position of division at step 105. If the position of the division in the matrix is the same as the last learning, the program proceeds to a step 106, where the output voltage of O 2  -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 is terminated. 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 is terminated. 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, the arithmetical average A of maximum and minimum values of the integral of the output voltage of the O 2  -sensor at the third cycle of the output waveform 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 a 2  corresponding to the division D 1  is detected and the address is stored in a RAM to set a flag. At a step 114, the stored address is compared with the last stored address. Since, before the instant learning, no address wase stored, the program proceeds to a step 115. At step 115, the learning control coefficient K 2  in the address of the K a  -table of FIG. 3b is entirely updated with the new value A that is the arithmetical average obtained at step 112. 
     At a learning after the first updating, if the address detected at the process 114 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 α (the integral of the output of the O 2  -sensor) at the learning is greater than &#34;1&#34;. If the α is greater than &#34;1&#34;, the program proceeds to a step 117, where the minimum unit ΔA (one bit) is added to the learning control coefficient K a  in the corresponding address. If the α is less than &#34;1&#34;, the program proceeds to a step 118, where it is determined whether the α is less than &#34;1&#34;. If the α is less than &#34;1&#34;, the minimum unit ΔA is subtracted from K a  at a step 119. If the α is not less than &#34;1&#34;, which means that the α is &#34;1&#34;, the program exists the updating routine. Thus, the updating operation continues until the value of the α becomes &#34;1&#34;. 
     When the injection pulse width (T i ) is calculated, the learning control coefficient K a  is read out from the K a  -table in accordance with the value of engine load L. However, values of K a  are stored at intervals of loads. FIG. 5 shows an interpolation of the K a  -table. At engine loads X 1 , X 2 , X 3 , and X 4 , updated values Y 3  and Y 4   (as coefficient K a ) are stored. When the detected engine load does not coincide with the set loads X 1  to X 4 , coefficient K a  is obtained by linear interpolation. For example, value Y of k a  at engine load X is obtained by the following formula. 
     
         Y=((X-X.sub.3)/(X.sub.4 -X.sub.3))×(Y.sub.4-Y.sub.3)+Y.sub.3 
    
     Referring to FIG. 8 showing another updating routine, in the system, the first updating is stepwisely performed with a value smaller than the arithmetical average A until the value of the table reaches a value approximately equal to the desired value A. After the first updating, the updating of the table is performed in the same manner as the program of FIG. 7b. 
     More particularly, at step 114, if the flag does not exist in the address, the program proceeds to a step 115, where the learning control coefficient K a  is updated by a value dependent on the deviation of the feedback signal of the O 2  -sensor, for example a value V expressed by the following formula. 
     V=D×M+1, where D is the difference between the arithmetic average A and the desired value &#34;1&#34;, M is an arbitrary number less than &#34;1&#34;, for example, 0.2, 0.5 . . . At the next learning control operations, the program proceeds from step 114 to a step 120, where the number of the operation is counted up. At a step 121, the counted number is decided. When the number is smaller than three, the program proceeds to step 115, where the value V is added to the prior value. When the counter counts up to three, the program proceeds to the step 116, where the same operation as in FIG. 7b is performed. 
     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 system of the present invention, data in a table is largely updated by a value relative to the feedback signal at the first updating occurrence, and, after the first updating, the data is updated little by little as shown in FIG. 6b. Thus, the engine operation is properly controlled without hunting of the system. 
     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 without departing from the scope of the invention as set forth in the appended claims.