DE19503852C2 - Air-fuel ratio control device and method for controlling the air-fuel ratio of an engine - Google Patents

Description

The invention relates to a fuel-air ratio rule device with the features of the preamble of the patent saying 1.

In a known control device of this type (JP 5-272 382 A) are measuring devices for measuring the fat and lean times separately for each bank and a correction device see which on the control device in the sense of an anglei the fat and lean times for both banks.  

In the example of a boxer engine with horizontally opposite lying, right and left cylinder banks with each meh Other cylinders are the suction system in the right and left Split inlet pipes downstream of the throttle valve, and the two intake or intake pipes are with the cylinders connected via an intake manifold. Are in the exhaust system if the cylinders of the right and the left bank with each right and left exhaust pipes via appropriate exhaust manifolds connected, and the right and left exhaust pipes are further combined into a single collecting tube, one end of which is connected to a muffler.

As an exhaust gas purification system for the engine described above a catalyst system is known, in each of which a catalyst in the left exhaust pipe and in the right exhaust pipe, as well as a Zu set catalyst are provided in the manifold. Also has a fuel-air ratio control system of the proposed Build an oxygen sensor in the right and left Exhaust pipe, the air-fuel ratio for each cylinder derbank based on the signals of the right and the left Oxygen sensor is determined to the appropriate force to determine the material injection quantity accordingly. With this sy the exhaust gas from the catalytic converters in the right and Left exhaust pipes cleaned, whereupon the exhaust gases, which come from the right and left cylinder banks, continue with of the additional catalyst downstream of the main catalysts getting cleaned.

In a fuel-air ratio control method according to Prior art described above, the fuel Air ratio regulated separately for each cylinder bank. If hence differences in the air-fuel ratio or in the Sensor output or in the sensor characteristics  between the right and left cylinder banks gen, both air-fuel ratios can be close to values the stoichiometric value can be regulated. The cleaning area Main catalyst conditions can be achieved with this method be optimized. However, if there is a difference between the off gears of the two oxygen sensors, the result is following difficulty. Since the exhaust gases from the right and lin ken exhaust pipes together upstream of the additional catalyst the cleaning condition or the tending tends to be quantified cleaning condition of the additional catalyst, a phase dif reference between the two oxygen sensor outputs conclude with the result that it is often impossible to find one to achieve sufficient cleaning effect.

As shown in curves (a) and (b) of FIG. 6, exhaust gases from the right and left exhaust pipes are supplied to the additional catalyst under the condition in the event of a phase difference between the outputs of the oxygen sensors of the right and left banks that the phases of the fat-lean states differ from each other. Consequently, the fat / lean conditions interfere with one another, so that, as is shown in curve (c) of FIG. 6 for the additional catalyst, no clear periodic fat / lean changes can be obtained, what leads to a deterioration in the cleaning function. Accordingly, in the catalytic converter system with a main catalytic converter for each cylinder bank and an additional catalytic converter for both cylinder banks (after collection), the fuel-air ratio of each of the three catalyzers must be regulated to an optimal periodic rich / lean state.

An example of the state of the art of a fuel Air ratio control system for one engine with several  Cylinder banks are disclosed in JP-POS 64-8332, in which the Air-fuel ratio of each cylinder group independent of back each other based on the oxygen sensor signal leadership is regulated. To avoid the difficulty Lich the phase difference in the air-fuel ratio between the corresponding cylinder groups is an additional auxiliary Oxygen sensor downstream of the exhaust gas collection section tubes arranged, and each feedback correction coefficient is corrected based on the auxiliary oxygen sensor output, such that the air-fuel ratio of the corresponding Cylinder groups can be compared.

As a second example of a known air-fuel ratio control system of an engine with several cylinder banks discloses JP-POS 3-26845 that three air-fuel ratio as in the first example, and that the air-fuel ratio of the two cylinders banks independently of each other based on each exit of the three fuel-air ratio sensors can be regulated. Fer ner is one of the banks on the exit of the auxiliary fuel Air ratio sensor set while the other bank ba based on the difference in air-fuel ratio is set between the two banks, so that the ge named difference between the two cylinder banks eliminated can be.

Also disclosed as a third example of a known force Substance-air ratio control system for an engine with several Cylinder banks the JP-GM-OS 63-79449 that a main force Substance-air ratio sensor in one of the exhaust pipes is that an auxiliary air-fuel ratio sensor in the Collector tube is provided and that the fuel air ver ratio of the two banks to the same  level based on the main air-fuel ratio Sensor signal are regulated and also based on the Auxiliary fuel-air ratio sensor signal to be corrected.

In the three control systems described last after the State of the art is an additional oxygen sensor in the collection tube provided so that the number of oxygen sensors he is high. Furthermore, in the first and the second case play the fuel-air ratio of the two cylinders benches independently of each other and so on the basis of the auxiliary Corrected oxygen sensor output that the difference of Air-fuel ratio between the cylinder banks eli can be mined. Therefore the control system is quite com plicated. Furthermore, in the third example, the two Air-fuel ratio of the two cylinder banks based regulated on the same control variable if the distribution of the Air-fuel ratio is not uniform. this leads to to the difficulty that the air-fuel ratio of the other bank cannot be adequately regulated.

To remedy these difficulties, it is the responsibility of the inventor dung, a fuel-air ratio control device for egg NEN engine with two banks of cylinders so that even with a difference in the outputs of the right and the left Oxygen sensor the use of an auxiliary oxygen sensor or of measuring devices for fat / lean times of the two Avoided benches and the cleaning effect of the in the collecting pipe provided catalyst can be improved.

To achieve this object, the invention provides a fuel Air ratio control device for an engine according to patent claim 1 before.  

It is preferred if the control device also the Features of claim 2.

The invention is based on schematic drawings conditions on an embodiment with further details ago explained. Show it:

Figure 1 is a block diagram of an entire fuel-air system of the invention.

Fig. 2 vibration diagram, which compares the outputs of the right and left oxygen sensors;

Fig. 3 is a flow chart of a control procedure for detecting a difference between two oxygen sensors;

Fig. 4 is a flow chart of a control procedure for setting a correction coefficient based on the difference between the two oxygen sensors;

Fig. 5 is a block diagram with a modification of the air-fuel ratio control system according to the invention, wherein a learning device is additionally provided, and

Fig. 6 is a vibration diagram showing the output signals of oxygen sensors, which are representative of rich-lean conditions of an additional catalyst in a fuel-air ratio control method according to the prior art.

With reference to FIG. 1, a system is for controlling a fuel-air ratio of a Boxer-engine described. The boxer engine 1 is in a right cylinder bank 2 with three cylinders (e.g. # 1, # 3 and # 5) and a left cylinder bank 3 with three cylinders (e.g. # 2, # 4 and # 6) divided. In the exhaust system, the corresponding cylinders of the right bank 2 communicate with a right exhaust pipe 5 via an exhaust manifold 4 and in the same way the corresponding cylinders of the left bank 3 communicate with a left exhaust pipe 7 via an exhaust manifold 6 . Furthermore, the right and left exhaust pipes 5 and 7 are connected to one another via a manifold 8 . Injectors 11 and 12 are arranged in the intake manifolds 9 and 10 of the right and left banks 2 , 3 for fuel injection.

The boxer engine has a triple catalytic converter system 20 . The catalytic system 20 comprises two main catalysts 21 and 22 , which are each arranged in the right and left exhaust pipes 5 and 7 upstream of the manifold 8 , and also an additional catalytic converter 23 in the manifold 8 in its downstream section from to form a two-stage catalytic system. Correspondingly, toxic components in the exhaust gas of the six cylinders of the right and left cylinder banks 2 and 3 can be cleaned by means of the three catalysts 21 to 23 .

In the air-fuel ratio control system, two oxygen sensors 25 and 26 are provided upstream of the main catalytic converters 21 and 22 of the right and left exhaust pipes 5 and 7 , respectively, in order to increase the air-fuel ratio (rich or lean) of the exhaust gas based on the oxygen concentration measure up. The corresponding outputs of the two oxygen sensors 25 and 26 form inputs of a control unit 30 for feedback control of the air-fuel ratios of the right and left cylinder banks 2 and 3 .

The principle of the fuel-air ratio feedback control is described below. If the fuel-air ratios of the right and left banks 2 and 3 are controlled simultaneously based on the output of only the right oxygen sensor 25 , the rich / lean change periods of the exhaust gases in the right and left exhaust pipes 5 and 7 synchronize with each other , And the same periodic rich / lean variation is clearly repeated in the ge collected in the manifold 8 exhaust gas, so that the cleaning condition for the set catalyst 23 is optimized. In this case, the air-fuel ratio of the right bank 2 in the vicinity of the stoichiometric air-fuel ratio value can be regulated by means of the right oxygen sensor 25 , so that the cleaning condition of the main catalytic converter 21 is also optimized.

If the output of the left oxygen sensor 26 is detected under the condition that the right oxygen sensor 25 detects the oxygen concentration at the stoichiometric air-fuel ratio, a difference in the air-fuel ratio between the two cylinder banks 2 and 3 can be based on a difference between the output signals of the two oxygen sensors 25 and 26 are discriminated. Therefore, if the air-fuel ratio of the left bank 3 is regulated based on the phase difference between the outputs of the two oxygen sensors 25 and 26 , it is also possible to roughly regulate the air-fuel ratio of the left bank 3 to the stoichiometric air-fuel ratio that the cleaning condition of the main catalyst 22 can be optimized.

Referring to FIG. 1, a control unit 30 determines the fuel injection amount, the ignition timings, etc. The control unit 30 includes a fuel-air ratio discriminating device 31 , a correction coefficient setting device 32 , a difference detecting device 33 , a correcting device 34 , a basic computing device 35 for calculating a basic injection pulse width, a computing device 36 for calculating the fuel injection pulse width for the right bank 2 and a computing device 37 for the fuel injection pulse width for the left bank 3 .

The output of the oxygen sensor 25 of the right bank 2 is input into the discriminating device 31 . After starting and warming up the engine 1 , the exhaust gas can be cleaned by means of the catalysts. Therefore, the discriminator 31 discriminates the rich / lean state of the exhaust gas based on the output signal of the right bank 2 oxygen sensor 25 . The result of discrimination is input to the correction coefficient setting device 32 . The correction coefficient setting device 32 sets an appropriate feedback correction coefficient LAMBDA for the air-fuel ratio according to the discrimination result. The outputs of the two oxygen sensors 25 and 26 of the right and left banks 2 , 3 are input into the difference detection device 33 . This device 33 detects a difference e between the two output signals of the two oxygen sensors 25 and 26 , that is, a difference in the rich / lean state between the two banks 2 and 3 based on the outputs of the two oxygen sensors 25 and 26 . The detected difference signal is entered into the correction device 34 . This correction device 34 determines a suitable correction coefficient Ke corre sponding to the detected difference between the two sensor signals, ie the difference in the air-fuel ratio between the two banks 2 and 3 .

Various engine operating conditions, such as the air intake amount detected by an air flow meter, the engine speed detected by a cure angle sensor, etc., are input to the computing device 35 for calculating the basic injection pulse width. The computing device 35 calculates a basic injection pulse width Tp based on the detected engine operating conditions. The calculated basic injection pulse width Tp and the feedback correction coefficient LAMBDA are input into the computing device 36 for calculating the fuel injection pulse width of the right bank. The computing device 36 calculates a corresponding fuel injection pulse width TiR using a different correction coefficient COEF as follows:

TiR = Tp × LAMBDA × COEF.

An injection signal of the calculated fuel injection pulse width TiR is output to the injector 11 of the right bank 2 .

Furthermore, the basic injection pulse width Tp, the feedback correction coefficient LAMBDA and the correction coefficient Ke are input to the computing device 37 for calculating the fuel injection pulse width of the left bank. The computing device 37 calculates a suitable fuel injection pulse-wide TiL using a further correction coefficient COEF as follows:

TiL = Tp × LAMBDA × Ke × COEF.

An injection signal with the calculated pulse width TiL is output to the injector 12 of the right bank 3 .

The operation of the air-fuel ratio control system according to the invention will now be described. When the engine is running, the exhaust gases of the right and left banks 2 and 3 flow through the right and left exhaust pipes 5 and 7 and thus through the main catalysts 21 and 22 of the catalyst system. Then the exhaust gases are collected from the right and left exhaust pipes in the manifold 8 . The collected gas mixture flows through the additional catalyst 23 . The oxygen concentrations in the exhaust pipes 5 and 7 are separately detected by the two oxygen sensors 25 and 26 in order to maintain the air-fuel ratios in the right and left cylinder banks, respectively.

The output of the oxygen sensor 25 of the right bank is now input into the discrimination device 31 of the control unit 30 . After the engine has warmed up, the exhaust gases can be cleaned by the catalytic converters, the discriminating device 31 discriminating the rich / lean state of the fuel based on the sensor outputs. Based on the discriminated rich / lean conditions, the correction coefficient setting device 32 sets a feedback correction coefficient LAMBDA of the fuel-air ratio. Based on the basic injection pulse width Tp, which was obtained from the computing device 35 , and the feedback correction coefficient LAMBDA, which was set by the correction coefficient setting device 32 , the computing device 36 calculates the fuel injection for the fuel injection pulse width of the right bank Pulse widths TiR = Tp × LAMBDA × COEF. Based on the basic injection pulse width Tp determined by the computing device 35 , the feedback correction coefficient LAMBDA obtained from the correction coefficient setting device 32 , and the correction coefficient Ke obtained from the correction device 34 , the Calculator 37 for the fuel injection pulse width of the left bank, the fuel injection pulse width TiL = Tp × LAMBDA × Ke × COEF.

Both, the calculated fuel injection pulse width re presenting injection signals are output to the injectors 11 and 12 , so that the fuel injection according to the engine operating conditions and the fuel-air ratio conditions of both banks 2 and 3 can be controlled.

Thus, the right bank 2 air-fuel ratio, as shown by the solid curve R in FIG. 2, can be feedback controlled, with a rich / lean variation repeating adjacent the stoichiometric air-fuel ratio. Therefore, if the exhaust gas from the right bank 2 is passed through the main catalyst 21 , toxic components can be effectively removed from the exhaust gas.

Under these circumstances, the fuel-air ratio of the left bank 3 is simultaneously controlled on the basis of the output signal from the oxygen sensor 25 of the right bank 2 so that the rich / lean variation of the left bank 3 with the corresponding variation of the right bank 2 syn chronized, as shown by the solid curve L in Fig. 2. As a result, the exhaust gas collected in the manifold 8 is passed through the additional catalyst 23 during a stable rich / lean period without disturbance through the rich / lean conditions of the two banks. Under these conditions, a sufficient catalytic effect can be obtained in the additional catalyst 23 , so that it is possible to effectively remove toxic components from the exhaust gases for exhaust gas purification.

In the system described above, the difference detection device 33 detects the difference of the air-fuel ratios of the two cylinder banks 2 and 3 based on the outputs of the two oxygen sensors 25 and 26 of the right and left banks 2 and 3 to the fuel-air ratio of the left bank 3 to correct. This correction control is described in detail below with reference to the flow charts of FIGS . 3 and 4.

The control unit 30 (hereinafter simply referred to as the controller) discriminates according to step S1 in FIG. 3 whether the output of the oxygen sensor 25 of the right bank 2 is inverted or not. If the sensor signal inverts or transitions from lean to lean according to point a or from rich to lean according to point b in Fig. 2, the controller discriminates that the sensor output is inverted. The displayed inverting criterion (stoichiometric value) of this inverting level can be replaced by a level at each intermediate point between the maximum fat state and the minimum lean state.

After discriminating the inverting state in step S1, the controller activates a timer (in step S2) and checks whether a predetermined time has elapsed after the sensor output has been inverted, in step S3. If "YES", the following steps are taken in order to prevent fluctuations which could be caused by correcting the fuel-air ratio immediately after inverting the sensor outputs. The controller detects the outputs of the two oxygen sensors 25 and 26 of both cylinder banks 2 and 3 in step S4. Based on the detected output signals, the controller discriminates the difference in air-fuel ratios of the right and left banks 2 and 3 in step S5.

If now the fuel-air ratio of the left bank 3 with respect to that of the right bank 2 deviates toward the lean side, as shown by the solid curve L in FIG. 2, the output of the oxygen sensor 26 is lean at both points a and b . If the sensor characteristic of the left bank 3 is the same as that of the right bank 2 , the air-fuel ratio of both banks 2 and 3 may be the same. If the sensor outputs have a difference despite the fact that both banks are regulated simultaneously only based on the output of the oxygen sensor 25 of the right bank 2 (eg in the case of "lean" at point a, but "rich" at point b) , this indicates an abnormality of the fuel system, so that it is also possible to use the differential detection as a diagnosis for the fuel system.

In step S5, in which the difference in the air-fuel ratio of the left bank 3 with respect to that of the right bank 2 is detected when the air-fuel ratio of the left bank 2 is the same as that of the right bank 2 (ie, that the initial values of the two oxygen sensors 25 and 26 are the same on the rich or lean side), the controller resets the timer in step S7 and ends the control procedure. Conversely, if the air-fuel ratio of the left bank 3 differs from that of the right bank 2 (ie, if the output value of one of the two oxygen sensors 25 , 26 is on the rich side and that of the other oxygen sensor is on the lean side), bil det the controller sets a correction coefficient Ke in step S6 and then resets the timer in step S7. Here, if the fuel-air ratio deviates toward the lean side as shown in the solid curve L in FIG. 2, the correction coefficient Ke is set to Ke <1.

Thus, when the correction coefficient Ke is set to Ke <1, the left bank 3 fuel injection pulse width TiL is calculated based on this correction coefficient Ke, and the injection signal is output with a fuel-air ratio value thus corrected.

In detail, as shown in FIG. 4 discriminates the regulator according to the set zen 1 (in step S11) whether this correction, the first correction after inverting the output of the oxygen sensor 25 of the right bank 2 is in accordance with step S12 of the correction coefficient Ke Ke <. In the case of "YES", the control increases the correction coefficient Ke with a large proportional increase rate (+ PR) to sharply correct the air-fuel ratio in step S13. In the case of "NO" in a second or more frequent correction, the controller increases the correction coefficient Ke with a small integral growth rate (+ I) to weakly or "smoothly" correct the air-fuel ratio in step S14.

In contrast, when the air-fuel ratio is shifted in phase to the rich side, and thus the correction coefficient is set to Ke <1, the control proceeds from step S11 to step S15 and on to steps S16 or S17 . The controller thus discriminates whether this correction is the first correction after inverting the output of the oxygen sensor 26 of the left bank 3 in accordance with step S15. In the case of "YES", the controller lowers the correction coefficient Ke with a large proportional decrease rate (-PR) to significantly or sharply correct the air-fuel ratio in step S16. In the case of "NO" after two or more times of correction, the controller lowers the correction coefficient Ke at a small integral rate (-I) to weakly or smoothly correct the air-fuel ratio in step S17.

Under these conditions, the air-fuel ratio of the left bank 3 , as shown by the dash-dotted curve L 'as shown in FIG. 2, is increasingly corrected to bring the fuel-air ratio of the bank 2 closer. Accordingly, if the exhaust gas of the left bank 3 is passed through the main catalyst 22 , the toxic components of the exhaust gas 12 can be effectively removed. As described above, in the catalyst system, the air-fuel ratios in the two main catalysts 21 and 22 for the right and left banks 2 and 3 , as well as for the additional catalyst 23 in the manifold 8 can be optimized, so that toxic Components in the exhaust gases can be removed most effectively by means of the two-stage cleaning, with the result that the overall efficiency of the cleaning is improved.

Fig. 5 shows a modification of the invention in which the air-fuel ratio is controlled by means of learning effects. This modification is based on the system of FIG. 1 with the exception that a fuel-air ratio learning device 40 is connected upstream of the correction coefficient setting device 32 and that a correction learning device 41 is connected upstream of the correction device 34 . The fuel-air ratio learning device 40 stores a learning map or table with values representative of the return correction coefficient LAMBDA for the air-fuel ratio representative of the various engine operating conditions (speed, load, etc.) in an updatable form. Thus, the feedback correction coefficient LAMBDA can be output based on a difference between the previous value and the current value, thereby further improving the responsiveness of the air-fuel ratio control.

The correction learning device 41 stores the difference correction coefficients Ke in the learning table, and the correction value is updated whenever the phase difference is corrected. During the correction, a learning process is carried out in such a way that an ongoing correction is carried out by multiplying the previous value by the updated value. It is therefore possible to minimize the fluctuations in the air-fuel ratio.

As described above, the air-fuel ratio nis control system and the method according to the invention for egg engine with right and left cylinder banks with one two-stage catalyst system with main catalysts and egg additional catalyst and one upstream in each exhaust pipe the oxygen sensor arranged from the main catalytic converter Air-fuel ratios of both banks starting simultaneously controlled by the output signal of only one oxygen sensor, and the fuel-air ratio of the other cylinder bank is calculated according to the difference between the outputs of the corrected both oxygen sensors. It is thus possible the fuel-air ratios of both banks based on the Difference between the two oxygen sensor outputs indicated measure to regulate. As a result, the cleaning capacity of the Additional catalyst in the manifold can be better used.

Furthermore, the fuel-air ratios of both banks can si multan based on the exit of one of the two Sauer  Substance sensors are controlled so that the control is simplified is. Since only two oxygen sensors are used, the Number of oxygen sensors reduced. Furthermore, ba based on the difference between the two oxygen sensors conclude their causes so that it is possible easily diagnose the fuel system.

In addition, if the air-fuel ratio control un ter exploitation of learning effects, this can Corrected bank air-fuel ratio based on who is correcting a currently learned correction coefficient the. This enables the fluctuations of the Air-fuel ratio.

Claims (2)

1. fuel / air ratio control device for an engine with a first cylinder bank ( 2 ) on one side of the engine, a second cylinder bank ( 3 ) on another side of the engine, a first inlet pipe ( 9 ) connected to the first cylinder bank, a two th, connected to the second cylinder bank inlet pipe ( 10 ), a first, to the first cylinder bank connected exhaust pipe ( 5 ) for exhausting gases from the first cylinder bank ( 2 ), a second, to the second bank connected exhaust pipe ( 7 ) for discharging gases from the second cylinder bank ( 3 ), a manifold ( 8 ) which is connected to the first and second exhaust pipes ( 5 , 7 ) to collect gases from these exhaust pipes, a first catalyst ( 21 ) in the first exhaust pipe ( 5 ) for cleaning the exhaust gases coming from the first cylinder bank ( 2 ), a second catalyst ( 22 ) in the second exhaust pipe ( 7 ) for cleaning the gases coming from the second bank ( 3 ), a Additional catalyst ( 23 ) in the manifold ( 8 ) for further cleaning of the exhaust gases coming from the first and second exhaust pipes, a first oxygen sensor ( 25 ) in the first exhaust pipe ( 5 ) between the first cylinder bank and the first catalytic converter for detection a first oxygen concentration in the first exhaust pipe and for emitting a first oxygen concentration signal, a second oxygen sensor ( 26 ) in the second exhaust pipe ( 7 ) between the second cylinder bank and the second catalyst for detecting a second oxygen concentration in the second exhaust pipe and for delivering a second oxygen concentration signal, a discriminating device ( 31 ) for the air / fuel ratio, which discriminates a fat / lean condition in the first exhaust pipe ( 5 ) and outputs a discrimination signal to the first oxygen concentration signal, one Korrekturkoeffizient- setting device (32) which, starting from the niersignal discrimi a R ckführ correction coefficient set for the air / fuel ratio (lambda), based on the discriminated rich / lean state, and outputs a Kor rektursignal, a first computing device (36) which, starting from the correction signal a it ste fuel injection pulse width (TIR) for the first cylinder bank ( 2 ) based on a basic injection pulse width (Tp) and the set feedback correction effi cient (LAMBDA) for the fuel / air ratio, and a second computing device ( 37 ) which generates a second fuel injection pulse width ( TiL) calculated for the second cylinder bank ( 3 ), characterized in that
a deviation detection device ( 33 ) detects a difference (e) between the fuel / air ratios of the first and second cylinder banks ( 2 , 3 ) and outputs a difference signal;
a correction device ( 34 ) based on the difference signal sets a correction coefficient (Ke) corresponding to the detected difference (e) and outputs a corrected difference signal; and
depending on the correction signal and the corrected difference signal, the second computing device ( 37 ) calculates the second fuel injection pulse width (TiL) based on a basic injection width signal (Tp) from a basic injection pulse width calculation device ( 35 ) in order to determine the fuel / air ratio at all To regulate the operating conditions of the engine to an optimal value. 2. Control device according to claim 1, characterized by:
a fuel-air ratio learning device ( 40 ) as part of the correction coefficient setting device ( 32 ) for storing and updating feedback correction coefficients (LAMBDA) for the air-fuel ratio determined according to various operating conditions and for outputting a differential correction coefficient between a previous value and a current value and
a correction learning device ( 41 ) as part of the correction device for storing and updating various correction coefficients (Ke) defined in accordance with the various operating conditions of the engine and for outputting a correction coefficient (Ke) based on the previous value.