GB2163276A - I.C. engine adaptive mixture control system having sensor failure compensation - Google Patents

Abstract

In an adaptive mixture control system which operates to update control coefficients stored in a table during steady state engine operation in accordance with a feedback signal, if failure of the signal sensing system occurs causing the updated data to exceeds a predetermined upper or lower limit value, all of the data items are rewritten with a predetermined fail safe 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 which continually updates data stored in a table of control coefficients.

In an adaptive control system, the updating of such data is normally carried out with new data obtained during the steady state of engine operation. Accordingly, means for determining whether the engine operation is in steady state is necessary. A conventional learning control system (for example U.S. Patent 4,309,971) has a matrix (two-dimensional lattice) comprising a plurality of divisions, each representing engine operating variables such as engine speed and engine load. When the values of the variables continue for a predetermined period of time in one of the divisions, it is determined that the engine is in a steady state. In addition, a threedimensional look-up table is provided, containing a matrix of values for determining the steady state. Data in the look-up table are updated with new data obtained during steady states.

In such a system if a sensor utilised for obtaining information for updating data deteriorates and fails to produce a proper output signal, the old data are replaced by incorrect data. In the case of an adaptive control system for controlling the air-fuel ration of fuel for a motor vehicle, an 02-sensor is employed for obtaining such information. If the 02-sensor does not produce a proper output signal, the driveability of the vehicle decreases and fuel consumption increases.

The present invention seeks to provide a system which reduces the problems caused by the failure of a sensor.

In a preferred embodiment of the present invention, the failure of a sensor is determined by the condition that the value of data in a look-up table exceeds a predetermined upper or lower limit value. When such a failure is detected, all of the data in the table are rewritten with a predetermined fail safe value.

Accordingly, the present invention, provides an adaptive mixture control system for an automotive engine comprising; a data table storing control coefficients; first means for detecting an operating condition of the engine and for producing a feedback signal dependent on the said condition; second means for updating the data in the table with a value or values derived from the feedback signal; third means for comparing the updated data with predetermined upper and lower limits; and fourth means for rewriting all of data in the table with a predetermined fail safe value, when the updated data exceeds the upper or lower limit.

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 present invention Figure 3a is an illustration showing a matrix for detecting the steady state of engine operation; Figure 3b shows a table for storing control coefficients; Figure 4a shows the output voltage of an 02-sensor; Figure 4b shows the output voltage of an integrator; Figure 5 shows a linear interpolation of the values in the table of Fig. 3b; Figures 6a and 6b are illustrations for explaining probability of updating; and Figures 7a and 7b are flowcharts showing the operation in 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 02-sensor 1 6 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 1 3 and pressure regulator 11. A solenoid operated valve 14 is provided in a bypass 1 2 around the throttle valve 5 so as to control engine speed at idling operation. A mass air flow meter 1 7 is provided on the intake pipe 2a and a throttle position sensor 1 8 is provided on the throttle body 3. A coolant temperature sensor 19 is mounted on the engine.Output signals of the meter 1 7 and sensors 18 and 1 9 are applied to a microcomputer 1 5. The microcomputer 1 5 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 1 5 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 02 sensor 16, mass air flow meter 1 7 and throttle position sensor 1 8 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 a control process to be described below.

In a system of this kind, the amount of fuel to be injected by the injector 4 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=KXQ/N (1) where Q is mass air flow, N is engine speed, and K is a constant.

The required injection pulse width (Tj) is obtained by correcting the basic injection pulse (Tp) in accordance with the engine operating variables. The following is an example of a formula for computing the desired injection pulse width.

T-TX(C0EF)XaX K3 (2) where COEF is a coefficient contained 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 the O2-sensor 16), and Ka is a variable correcting coefficient (hereinafter called an adaptive control coefficient). The required coefficients such as coolant temperature coefficient and engine load, are obtained by looking up tables in accordance with sensed information with respect to the engine operating conditions.

The adaptive control coefficients Ka stored in K3-table are updated with data calculated during the steady state of engine operation. The steady state is detected by engine operating conditions in predetermined ranges of engine load and engine speed and continuation of a detected state.

Fig. 3a shows a matrix of values for this 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 to five points No to N4 on the Y axis. Thus, the engine load is divided into four ranges, that is LO-L,, L1-L2, L2-L3, and L3 L4. Similarly, the engine speed is divided into four ranges.

The output voltage of the 02-sensor 1 6 changes cyclically 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 02-sensor continues for three successive cycles within one of sixteen divisions in the matrix, the engine is assumed to be in steady state.

Fig. 3b shows a K3-table for storing the learning control coefficients K3, which is included in the RAM 31 of Fig. 2. The K3-table is a two-dimensional table and has addresses a1, a2, a3, and a4 which correspond to engine load ranges L0-L1, L-L2, L2-L3 and L3-K4. All the coefficients Ka stored in the Ka table are initially set to the same value, that is the numerical value "1", since the fuel supply system is designed to provide as near as possible the correct amount of fuel without the coefficient Ka. However, every automobile cannot be manufactured to have a desired function, resulting in the same results.Accordingly, the coefficient Ka should be updated by learning at every automobile, when it is actually used.

When the engine is started, the calculation of the injection pulse width (Tin formula 2) takes place as follows: since the temperature of the body of the 02 sensor 1 6 is low, the output voltage of the 02-sensor is very low. In such a condition the system is adapted to provide '1' as the value of the correction coefficient a. Thus, the computer calculates the injection pulse width (Tj) from mass air flow (0), engine speed (N), (COEF), a and K3. When the engine is warmed up and the 02-sensor becomes activated, an integral of the output voltage of the 02-sensor at a predetermined time is provided at the value of a. More particularly, the computer includes the function of an integrator, so that the output voltage of the 02-sensor is integrated.Fig. 4b shows the output of the integrator. The system provides values of the integration at predetermined intervals (40ms). For example, in Fig. 4b, integrals 1" 12 ---at times T1, T2 ---are provided.

Accordingly, the amount of fuel is controlled in accordance with the feedback signal from the 02-sensor, which is represented by the integral.

The adaptive or "learning" process operates as follows: when the engine is determined to be operating in a steady state in one of the divisions of the matrix, the data in a corresponding address of the K3-table is updated with a value derived from the feedback signal from the 02- sensor. The first updating is done with an arithmetical average (A) of the maximum value and minimum values in one cycle of the integration, for example values of Imax and Imin of Fig. 4b.

Thereafter, when the value of a is not 1, the K3-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 substracted from, a BCD code representing the value A of the coefficient Ka which has been rewritten at the first learning.

The operation of the system will now be described in more detail with reference to Fig. 7. The learning program is started at a predetermined interval (40ms). During the first operation of the engine and the first time the motor vehicle is driven the engine speed is detected at step 101. If the engine speed is in a range between No and N4, the program proceeds to a step 1 02. If the engine is out of the range, the program exits the routine at a step 1 22. 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 to 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 identified in the matrix: for example, division D is identified in Fig. 3a. The program advances to a step 105, where the identified position of division is compared with the division which has been detected at the previous learning step. However, since this learning operation is the first one, 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 step after the first one, 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 that at the last learning step, the program proceeds to a step 106, where the output voltage of 02sensor 1 6 is detected. If the voltage changes from rich to lean and vice versa, the program progresses to a 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 from step 109 to step 1 10. If the count does not reach three, the program is terminated. At step 11 0, the counter is cleared and the program proceeds to step 112.

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, where the old data of the position is substituted by the new data. At the step 111, the counter which operated at step 108 of the last learning cycle is cleared.

At step 1 12, the arithmetical average A of the maximum and minimum values of the integral of the output voltage of the 02sensor 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 a step 114, the stored address is compared with the last stored address. Since, before the first learning step, no address is stored, the program proceeds to a step 11 5. At step 115, the learning control coefficient Ka in the address of the K3-table of Fig. 3b is entirely updated with the new value A that is the arithmetical average obtained at step 11 2.

After the updating of the table, the program proceeds to a step 1 16 where it is determined whether the correcting coefficient a is greater than "1". If a is greater than "1", which means that the value A written at the step 11 5 is small, the program proceeds to a step 11 7 where the difference D between the value A and the desired value "1" is obtained in order to obtain a value relative to the desired value "1".If the difference D is smaller than a predetermined lower limit, the program proceeds from a step 11 8 to a step 11 9. At the step 119, the failure of the 02sensor is indicated for example by a lamp, and all of data in the k3-table are rewritten with a predetermined fail safe value, for example "1". If the difference D is greater than the lower limit, the program terminates.

If the coefficient a is not greater than "1", it is determined whether the a is smaller than "1" at a step 1 20. If the a is smaller than "1", the sum S of the value A and the desired value "1" is calculated at a step 121. If the sum S is greater than a predetermined upper limit, the program proceeds from a step 1 24 to a step 1 23 where the failure of the 02sensor is indicated and all of the data in the k3-table are rewritten with the numerical value "1".

At a 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 11 4 to a step 125, where it is determined whether the value of a (the integral of the output of the 02sensor) at the learning is greater than "1". If a is greater than "1", the program proceeds to a step 126, where the minimum unit AA (the value of one bit) is added to the learning control coefficient Ka in the corresponding address. If a is not greater than "1", the program proceeds to a step 127, where it is determined whether a is less than "1". If a is less than "1", the minimum unit AA is subtracted from Ka at a step 128. If the 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 1 26 and 1 28 to step 116, and the same programs are performed as the above described programs.

When the injection pulse width (Tj) is calculated, the learning control coefficient Ka is read out from the K3-table in accordance with the value of engine load L. However, values of Ka are stored at intervals of loads. Fig. 5 shows an interpolation of the Ka-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 Ka is obtained by linear interpolation.

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

Y = ((X - X3)/(X4 - X3)) x (Y4 - Y3) Y3 Fig. 6 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 at 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 Ka in adjacent speed ranges is small. Accordingly, it will be understood that the two-dimensional table, in which a single item of data is stored at each address, is sufficient for performing the learning control of an engine.

Thus, in accordance with the present invention, the failure of a sensor is detected and fail safe operation is effected to properly maintain engine operation, until the failure is repaired.

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 mixture control system for an automotive engine comprising; a data table storing control coefficients; first means for detecting an operating condition of the engine and for producing a feedback signal dependent on the said condition; second means for updating the data in the table with a value or values derived from the feedback signal; third means for comparing the updated data with predetermined upper and lower limits; and fourth means for rewriting all of data in the table with a predetermined fail safe value, when the updated data exceeds the upper or lower limit.

2. A mixture control system according to claim 1 wherein the value derived from the feedback signal is equal to the value of the feedback signal.

3. A system according to claim 1 wherein the predetermined fail safe value is the numerical value 1.

4. An adaptive mixture control system according to claim 1 and substantially is herein described with reference to the accompanying drawings.