Method for controlling an internal combustion engine with fuel injection

Abstract: A future value is predicted based on time-serial data of measurement data heretofore available to attain high precision control of fuel injection of an engine, by providing: (1) an unit (12) for determining an accelera­ tion/deceleration level representing a magnitude of acceleration/deceleration of a vehicle based on a dis­ placement of a throttle opening degree in a predetermined time, (2) an unit (11) for predicting the future value by a digital advancing filter based on measurement data heretofore available, and (3) a correction unit (13) for calculating a measurement amount which is under or over when the predicting process is conducted, in accordance with the acceleration/deceleration level, and adding the calculated measurement value to said predicted value to calculate the future value of the measurement data. Where a table (53) for converting outputs of various sensors arranged around the engine etc. to physical amounts such as suction air amount, an unit (50, 201-204) for increasing the search speed for the table is provided.

Description: The invention relates to a method for controlling an internal combustion engine with fuel injection. In a prior art electric control apparatus e.g. disclosed in JP-A-63-253137, a fuel amount to be supplied in the next control step is determined based on a detected amount of suction air in the current control step. Hence, there exists an air amount detection error of approximately one control step. Therefore, it is difficult to keep the fuel supply amount at proper value and to control the air/fuel-ratio with a high precision. Further, since the air amount detection error is compensated by other treatments, the number of calculation steps increases. However, it is hard to implement such a control strategy with an existing 8-bit microcomputer because of a large resulting calculation load. US-A-4 424 568 discloses a control method for an internal combustion engine, directed to transient operations thereof. In order to increase the accuracy during transient operational conditions, the air amount and the engine revolution speed are predicted for the time of the actual fuel injection by extrapolation from past data. This prediction method, however, fails to present an accurate prediction when the operational conditions change quickly from a steady state operation and it does not include an input for the driver's intention, so that there occur problems with an over-reaction of the control system. DE-A-2 906 782 shows a method for damping vibrations caused by the engine. If such a vibration is detected, the injected fuel amount is changed accordingly. In order to influence the damping conditions, the first derivation of the engine revolution speed is determined and it is decided upon this determination, if a damping, i.e. an influence on the injected fuel amount, is necessary. Then the correction amount of the injected fuel is calculated as a function of this derivation. Looking at the changing rates of the engine revolution speed is, however, not sufficient for obtaining a high accuracy of the fuel injection, especially during transient operational conditions. EP-A-0 332 119 represents an Art. 54(3) EPC document and shows to dampen the longitudinal oscillation of a vehicle by detecting the longitudinal acceleration or the engine revolution speed and to differentiate these values. With the result of this differentiation a target opening degree of the throttle valve is determined and the same is controlled accordingly. This method is not applicable for obtaining a high precision prediction of the future value of an operational condition such as the intake air amount for determining an accurate actual fuel injection amount during operational conditions with a high changing rate. The object of the invention is to provide a method for controlling an internal combustion engine with fuel injection which realizes an increased accuracy of the engine control and determines future values of operational engine parameters. The object is solved according to the features of the independent claims. The dependent claims characterize advantageous features and developments of the invention. According to the invention, the future values of engine operational parameters, such as the suction air amount can be predicted and therewith it is possible to control the fuel injection amount and timing. The future values can be determined with an advancing filter based on measurement data heretofore available. When the measurement values change smoothly, a high precision prediction is attained. The correction steps can be performed in a correction unit which calculates a difference between a predicted future value obtained by the prediction process and a real future value. The prediction can be performed in an advancing filter, when the measurement data starts to change relatively fast from a steady state, and calculates the future value of the measurement data. Thus, the precision of the prediction at an early stage of transient period is assured. When this prediction method is applied to the prediction of the suction air amount of the engine, the suction air amount in one step advance can be predicted with high precision, and high precision control of the air/fuel-ratio is attained by controlling the fuel supply amount in accordance with the predicted value. Those operations are done by a microprogram. Ways of carrying out the invention are described in detail below with reference to drawings which illustrate only specific embodiments, in which: Fig. 1 shows a configuration of a future value prediction device for measurement data in accordance with the invention, Fig. 2 shows a configuration of the correction means shown in Fig. 1, Fig. 3 shows responses of air amount in an acceleration mode, Fig. 4 shows timing of the fuel injection and the suction stroke, Fig. 5 shows an overall configuration of a fuel injection control apparatus according to the invention, Fig. 6 shows a flow chart of a control program which predicts a suction air amount and determines a fuel supply amount based on the prediced amount. Fig. 1 shows a configuration of a device for predicting a future value of measurement data. It comprises an acceleration/deceleration level discrimination unit 12, a prediction unit 11 and a correction unit 13. Operations of the respective units are explained below. The prediction unit 11 predicts a future value by a digital advancing filter based on measurement data heretofore available. A prediction method by the advancing filter is preferably simple from a standpoint of processing by a microcomputer. Examples thereof are: (i) Predict a future value based on measurement value heretofore available on the assumption that an increment of measurement data per unit time (one-order differentiation of the measurement data by time) is held for a predetermined time period. (ii) Predict a future value based on measurement value heretofore available on the assumption that an increment of the above increment per unit time (two-order differentiation of the measurement data by time) is held for a predetermined time period. The prediction formulas in (i) and (ii) are expressed as follows. where S(i) (i = 1, 2, 3 ... k) is time-sequential date of the measurement values, Δt is a data sampling period, and S(k and) is a prediction value at a time k in advance of time T. The prediction unit predicts the future value based on the measurement values heretofore available by utilizing the formulas (10), (11) and (12). In the above method, the future value is predicted on the assumption that one-order or two-order differentiation of the measurement data is held. Alternatively, it may be possible to predict the future value on the assumption that n-order differentiation (n ≧ 3) of the measurement data is held. In order to predict the future value of the measurement data, the time period to the future point may be divided into several time frames and differentiations of the measurement data in different orders may be held in the respective time frames, for example, n-order differentiation of the measurement data is held in one time frame and m-order (m = n) differentiation of the measurement data is held in another time frame. For example, two-order differentiation of the measurement data is held at a current time k for a time frame up to time k+1, and one-order differentiation of the measurement data is held for a time frame advanced from the time k. In this case, a prediction formula for a measurement value at a time advanced by time T is given by S (k) = {2·S(k) - 3·S(k-1) + S(k-2)}· T Δt + S (13) where S(k): measurement data S andk: predicted value Δt: sampling period of measurement data. It is also possible to calculate a future value of the measurement data based on a sum-produkt mean value of the values predicted by at least two of the above prediction methods for the future value. The future value S and(k) of the measurement data is calculated by the following formula. where S and i (k) (i = 1, 2, 3 ... n): predicted values by the respective methods n: integer no smaller than 2 C₁: positive number Since the prediction process amplifies a noise (RF component) included in the measurement data, it is preferable not to conduct the prediction process in an unnecessary time period if immediate response of prediction is not required. Thus, if the immediate response of prediction is not required, the prediction means conducts the prediction process only in a transient state in which the measurement data varies, and in a steady state where the data is steady at a constant value, the prediction means do not conduct the prediction process but output the measurement data as it is. Where the immediate response of the prediction is required or where the amplification of the noise by the prediction process is to be avoided in the transient state in which the measurement data varies, the predicted value is passed through one-order or two-order low-pass filter represented by the following formulas of transfer function. or S: Laplacian operator The output of the filter is supplied to the prediction means as the future value of the measurement data. The constants S·ω n and T in the formulas (14) and (15) are selected such that a frequency component in the range defined below is eliminated. where Δt(sec) is the sampling period of the measurement data. The filters of the formulas (14) and (15) are utilized in the form of the following discrete formulas in the electronic control apparatus for the engine. where u(k): input to the filter y(k): output from the filter Δt: sampling period of the data A center difference is used to derive the formulas (14) and (15). The operation of the acceleration/deceleration level discrimination means is now explained. The acceleration/deceleration level discrimination means determines an acceleration or deceleration level representing a magnitude of the acceleration or deceleration of the vehicle based on a displacement Δϑ th of the throttle opening degree in a predetermined time. The acceleration or deceleration level may be set in the following manner. Where |Δϑ th | < m₁, it is regarded that it is not in the acceleration/deceleration status (acceleration/deceleration level 0). The acceleration/deceleration level discrimination means 12 discriminate the acceleration/deceleration level in accordance with the above formulas and send the result to the correction means 13. The operation of the correction means 13 is now explained. Fig. 2 shows a configuration of the correction means 13. The correction means 13 have a two-dimension map having an acceleration/deceleration level and an elapsed time from the start of the acceleration/deceleration on two axes. The map is looked up based on the determined acceleration/deceleration level and the elapsed time, and a time T to which the measurement data is to be advanced is multiplied to the looked-up value, and a measurement amount which is under or over when the prediction process is conducted is calculated. The output of the prediction unit 11 is added to the calculated measurement amount to produce a real future value of the measurement data a predetermined time ahead. Fig. 3 shows a response of suction air amount measurement value when an opening degree of the throttle valve is changed stepwise, a response when the above response is advanced by a desired time t₀, and a response when the response of the measurement value is advanced by the time t₀ by the prediction process. As seen from Fig. 3, when the measurement value starts to respond relatively fast from a steady state, the response of the desired time t₀ ahead cannot be exactly predicted by the prediction process for a certain time (several or several tens msec.) after the start of response. The correction unit compensates it. The differences between future values of the measurement data predicted by the prediction process and real future values of the measurement data are stored in the map for the respective acceleration/deceleration levels, and the measurement value produced by the prediction process is corrected by looking up the map so that the prediction precision in the early stage of the acceleration/deceleration is assured. The data of the map of Fig. 2 is calculated in the following manner. The throttle opening degree is changed at the acceleration level i from the steady operation state of the engine in which the throttle opening degree is maintained at a constant level, and an engine status amount which is a subjet of current prediction is measured. The response of the measurement value is represented by S₁(t), and a response when the above response is advanced by the time t₀ is represented by S₁(t + t₀). A response when the response S₁(t) is advanced by the prediction process is represented by S₂(t). Data D(t) of the acceleration level i of the map is calculated by the following formula: where t: time D(t) corresponds to unified correction amounts which represent a difference between the predicted and the real future amount when the prediction process is conducted to predict the measurement value of unit time ahead. Assuming that these amounts at the respective times are essentially proportional to the time to which the measurement data is to be advanced, the measurement amount can be used to predict the measurement value of the time T ahead by T·D(t). Namely, it is a product of the looked-up value of the two-dimension map and the time T. If the output of the prediction unit 11 is added to the product, the future value of the measurement data can be precisely predicted even if the response of the measurement data is relatively fast. In the above method, these measurement amounts, when the prediction process by the advancing filter is conducted, are stored in correlation with the acceleration/deceleration levels. In actual, it is affected by the engine rotating speed and the opening degree at the initial stage of the acceleration/deceleration. Accordingly, the rotating speed and the opening degree at the initial stage of the acceleration/deceleration may be introduced as the variables of a map to improve the correction precision. Construction and operation of a control system which applies the method for predicting the future value of the measurement data to the prediction of the suction air amount of the engine to control the fuel will be described in the following. An engine in which a cylinder inlet air amount is indirectly detected and the fuel is controlled based on the detected amount is considered. As described above, since the fuel supply amount in the next step is determined based on the detection value of the current air amount in the existing system, there is approximately one stroke of delay in the detection of the air amount and hence it is difficult to precisely control the air-to-fuel ratio. In order to solve the above problem, the detection value of the air amount to be used for the determination of the fuel supply amount is advanced by a time difference between the time at which the air amount is to be inherently detected, that is, the time at which the exact cylinder inlet air amount of the next step is to be detected and a time at which the air amount to be used for the determination of the fuel supply amount is to be detected. Since the time at which the air amount to be used for the determination of the fuel supply amount is detected is substantially equal to the fuel injection timing, the above time amount may be considered to be essentially within the range of the crank angle defined by the following formula, assuming that the fuel injection timing is ϑ i crank angle before a top dead center and a suction stroke is from ϑ s crank angle before the top dead center to ϑ e crank angle after the top dead center, as shown in Fig. 4. ϑ i - ϑ s ≦ ϑ d ≦ ϑ i + ϑ e (21) The above time difference T d (sec) is within the following range where N (rpm) is the engine rotating speed. The air amount at the time which is ahead by the time given by the formula (22) is predicted by the above prediction method and the fuel is controlled based on the predicted value. Thus, the delay in the detection of the air amount in the transient state is theoretically compensated and high precision control of the air-to-fuel ratio is attained. An overall configuration of the control system and an operation of a control program when the fuel control is done by a digital control unit are explained with refernce to Figs. 5 and 6. Fig. 5 shows an overall configuration of a fuel injection control apparatus which uses a speed density system (D jetronic system). A control unit 50 comprises a CPU 51, a ROM 52, a RAM 53, an I/O LSI 54, a timer 55 and a bus which electrically connects those elements. Signals from a throttle angle sensor 57, an internal pressure sensor 58, a coolant temperature sensor 59, a crank angle sensor 511 and an oxygen sensor 512 are supplied to the I/O LSI 54. The I/O LSI 53 sends a signal to a fuel injector 513. The I/O LSI 54 has an A/D converter and a D/A converter. The timer 55 issues an interruption request to the CPU 51 at a constant time interval, and the CPU 51 responds thereto to execute the control program stored in the ROM 52. Referring to Fig. 6, the operation of the control program which predicts the future value of the air amount detection value and determines the fuel amount based on the predicted value is explained. When an interruption request is issued at an interval of 10 msec., the output of the pressure sensor is A/D-converted in a step 501 to determine an internal pressure of a suction pipe. In a step 502, an engine rotating speed is determined based on a signal from the crank angle sensor 511. In a step 503, the data table stored in the RAM 53 is retrieved by using the engine rotating speed and the internal pressure of the suction pipe as parameters, to determine the engine suction air amount, which is stored into a predetermined address of the RAM 53. In a step 504, whether the vehicle is in the acceleration/deceleration state is determined by the method described above. If it is in the acceleration/deceleration state, the process proceeds to a step 505, and if not, the process proceeds to a step 509. In a step 505, the future value of the suction air amount which is ahead of the time of the formula (22) is predicted by the prediction process by the advancing filter, that is, by utilizing the formulas (10), (11), (12), (13) and (14) based on the suction air amount determined in the step 503, and the time-sequential data of the suction air amounts determined in the past interruptions and stored in the RAM 53. In the formulas (10) - (14), Δt represents the interruption period (10 msec.). In a step 506, the acceleration/deceleration level is determined based on the displacement of the throttle opening degree in the manner described above. In a step 507, the data table stored in the RAM 53 is looked up based on the acceleration/deceleration level and the elapsed time from the start of the acceleration/deceleration, and the looked-up value is multiplied by the time to which the suction air amount is to be advanced as shown in the formula (22) to calculate an air amount ΔQa which is under or over when the prediction process by the advancing filter is conducted. In a step 508, the air amount ΔQa which is under or over when the prediction process is conducted is added to the air amount Q anda' predicted by the advancing filter to calculate a true future value Q anda of the suction air amount which is ahead by the time given by the formula (22). The future value Q anda is calculated by Q a = Q a' + ΔQa (23) Finally, in a step 509 following to the step 504, a fuel injection pulse width T i corresponding to the fuel injection amount is calculated by the formula (24) based on the air amount Qa calculated in the step 503. In the step 509 following to the step 508, the fuel injection pulse width T i is calculated by the formula (25) based on the future value Q anda of the air amount determined by the step 508. where k : correction coefficient N : rotating speed T s : invalid injection time After the above steps, the process stands by until next interruption request is issued. In the above program, the suction air amount is predicted to determine the future value thereof. Alternatively, the time-serial data of the internal pressure of the suction pipe and the rotating speed may be stored, the future values of the internal pressure and the rotating speed may be determined from the time-serial data, and the data table may be looked up by the future values to determine the suction air amount so that the future value of the air amount is determined. The prediction may be done by the prediction unit described above or the prediction method shown in Fig. 1. The application to the engine of the speed density type has been described. The present invention is also applicable to the prediction of the air amount of a throttle speed type or a mass flow type (L jetronic system) which directly detects an electrical amount. In the throttle speed type which infers the suction air amount based mainly on the throttle opening degree and the rotating speed, the future value is not predicted based on the time-serial data of the inferred values of the air amount, but the future values of the throttle opening degree and the rotating speed are predicted and the suction air amount is inferred based on the predicted values to predict the future value of the air amount. In a MT (manual transmission) car, since the response of the engine rotating speed is much lower than the response of the throttle opening degree, the suction air amount may be inferred based on the future value of the throttle opening degree and the present value of the rotating speed. The prediction may be done by the prediction unit described above or the prediction method shown in Fig. 1. The method for controlling the fuel solely by the synchronous injecion based on the predicted air amount has been described. Alternatively, asynchronous injection may be used to control the fuel. By substituting the formula (4) to the formula (16), the following formula is derived. The above formula means that the pulse width of the synchronous injection is calculated by using the first term of the left side, and the pulse width of the asynchronous injection is calculated by using the second term of the left side. The pulse width T i of the synchronous injection may be calculated by the following formula based on the air amount predicted by the advancing filter, and the pulse width T i ' of the asynchronous injection may be calculated by the following formula based on the under prediction ΔQa of the air amount calculated for each acceleration/deceleration level. In the above method, the future value of the air amount for compensating the delay in the detection of the air amount is predicted. The delay in the detection of the air amount may also be compensated by applying the prediction method described above to the fundamental injection pulse width T p which is calculated by the control unit at the interval of 10 msec. In this case, the fundamental injection pulse width which is ahead of the time defined by the formula (22) is predicted based on the past data in the prediction method shown in Fig. 1, and the fuel injection pulse width T i is calculated by the following formula based on the predicted value T and p . T i = k · T p + T s (29) Since the delay in the detection of the air amount is compensated in this manner, the fundamental injection pulse width at the time at which the exact suction air amount in the next stroke is to be detected can be predicted so that the high precision control of the air-to-fuel ratio is attained.

Claims: Method for controlling an internal combustion engine with fuel injection, comprising the steps of: (A) Determining (step 503) the actual intake air amount Q a with the parameters intake pressure and rotational speed, (B) predicting (step 505) a future value of the intake air amount Q anda ' by a digital advancing filter using the actual and preceding intake air amounts stored in a RAM (53), (C) determining (step 506) an acceleration/deceleration level in the acceleration/deceleration level discrimination unit (12) based on the displacement Δϑ th of a throttle valve in a predetermined time, (D) determining a correction amount ΔQ a (step 507) on the basis of the acceleration/deceleration level, the elapsed time from the start of the acceleration/deceleration and the time to which the intake air amount is to be advanced, (E) correcting (step 508) the future value of the intake air amount Q and a ' in a correction unit (13) by adding the correction amount ΔQ a to gain a corrected future value of the intake air amount Q and a , and (F) controlling (step 509) the fuel injection based on the corrected future value of the intake air amount. Q and a . Method according to claim 1, characterized in that the actual intake air amount Q a is determined from a data table stored at a predetermined address in the RAM (35) (step 503). Method according to claim 1 or 2, characterized in that the correction of the predicted intake air amount Q and a ' is performed by reading a data table with unified correction amounts D(t) stored at a predetermined address in a RAM (35) with the acceleration/deceleration level and the elapsed time from the start of the acceleration/deceleration as parameters, and the unified correction amounts D(t) are multiplied with the time to which the intake air amount is to be advanced to gain the correction amounts ΔQ a (steps 507, 508). Method according to claims 1 - 3, characterized in that the correction of the predicted intake air amount Q and a ' is performed to compensate the error of the predicted intake air amounts Q and a ' obtained during the early stage of acceleration/deceleration. Method for controlling an internal combustion engine with fuel injection, comprising the steps of: (A) Predicting a future value of the manifold pressure by a digital advancing filter performing a n-th order differentiation using the actual and preceding manifold pressures stored in a RAM (35), (B) predicting a future value of the engine speed by a digital advancing filter performing a n-th order differentiation using the actual and preceding engine speeds stored in the RAM (35), (C) determining (step 506) an acceleration/deceleration level based on a displacement Δϑ th of a throttle valve in a predetermined time, (D) determining a correction amount for the future value of the manifold pressure on the basis of the acceleration/deceleration level, the elapsed time from the start of the acceleration/deceleration and the time to which the manifold pressure is to be advanced, (E) determining a correction amount for the future value of engine speed on the basis of the acceleration/deceleration level, the elapsed time from the start of the acceleration/deceleration and the time to which the engine speed is to be advanced, (F) correcting the future value of the manifold pressure by adding the correction amount for the future value of the manifold pressure to gain a corrected future value of the manifold pressure, (G) correcting the future value of the engine speed by adding the correction amount for the future value of the engine speed to gain a corrected future value of the engine speed, (H) determining the future value of the intake air amount Q and a with the parameters corrected future value of the manifold pressure and corrected future value of the engine speed and (I) controlling the fuel injection based on the future value of the intake air amount Q and a . Method according to claim 5, characterized in that the correction of the predicted manifold pressure is performed by reading a first data table with first unified correction amounts stored at a predetermined address in the RAM (35) with the acceleration/deceleration level and the elapsed time from the start of the acceleration/deceleration as parameters, the first unified correction amounts are multiplied with the time to which the manifold pressure is to be advanced to gain the correction amounts for the future value of the manifold pressure, the correction of the predicted engine speed is performed by reading a second data table with second unified correction amounts stored at another predetermined address in the RAM (35) with the acceleration/deceleration level and the elapsed time from the start of the acceleration/deceleration as parameters; and the second unified correction amounts are multiplied with the time to which the engine speed is to be advanced to gain the correction amounts for the future value of the engine speed. Method for controlling an internal combustion engine with fuel injection, comprising the steps of: (A) predicting a future value of the throttle angle by a digital advancing filter performing a n-th order differentiation using the actual and preceding throttle angles stored in a RAM (35), (B) predicting a future value of the engine speed by a digital advancing filter performing a n-th order differentiation using the actual and preceding engine speeds stored in the RAM (35), (C) determining (step 506) an acceleration/deceleration level based on a displacement Δϑ th of a throttle valve in a predetermined time, (D) determining a correction amount for the future value of the throttle angle on the basis of the acceleration/deceleration level, the elapsed time from the start of the acceleration/deceleration and the time to which the throttle angle is to be advanced, (E) determining a correction amount for the future value of the engine speed on the basis of the acceleration/deceleration level, the elapsed time from the start of the acceleration/deceleration and the time to which the engine speed is to be advanced, (F) correcting the future value of the throttle angle by adding the correction amount for the future value of the throttle angle to gain a corrected future value of the throttle angle, (G) correcting the future value of the engine speed by adding the correction amount for the future value of the engine speed to gain a corrected future value of the engine speed, (H) determining the future value of the intake air amount with the parameters corrected future value of the throttle angle and corrected future value of the engine speed and (I) controlling the fuel injection based on the future value of the intake air amount Q and a . Method according to claim 7, characterized in that the correction of the predicted throttle angle is performed by reading a first data table with first unified correction amounts D(t) stored at a predetermined address in a RAM (35) with the acceleration/deceleration level and the elapsed time from the start of the acceleration/deceleration as parameters, the first unified correction amounts D(t) are multiplied with the time to which the throttle angle is to be advanced to gain the correction amounts for the future value of the throttle angle. the correction of the predicted engine speed is performed by reading a second data table with second unified correction amounts stored at another predetermined address in the RAM (35) with the acceleration/deceleration level and the elapsed time from the start of the acceleration/deceleration as parameters, and the second unified correction amounts are multiplied with the time to which the engine speed is to be advanced to gain the correction amounts for the future value of the engine speed. Method according to claims 1 - 8, characterized in that a fuel injection timing is ϑ i degrees before a top dead center, a suction stroke reaches from ϑ s before the top dead center to ϑ e after the top dead center, and the time Td to which the intake air, the manifold pressure or the engine speed is to be advanced is within with N (rpm) as engine speed.

Inventors: FUNABASHI MOTOHISA, SEKOZAWA TERUJI, SHIOYA MAKOTO, TAKAHASHI SHINSUKE, FUNABASHI, MOTOHISA, SEKOZAWA, TERUJI, SHIOYA, MAKOTO, TAKAHASHI, SHINSUKE
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: F02D41
IPC codes: F02D41