JPS645059Y2 - - Google Patents

Description

[Detailed description of the invention] <Technical field> The present invention relates to a control device that performs feedback control of the air-fuel ratio based on a signal from an exhaust sensor in an internal combustion engine, and is particularly applicable to an exhaust pipe that is divided into two systems for each bank such as a V-type engine. This paper relates to improvements in control methods for devices equipped with exhaust sensors.

<Background Art> As a conventional control method of this type, for example,
There is something like the one shown in the figure (Reference: Nissan Motor Service Bulletin No. 476, Nissan President).
In the figure, the intake system of a V-type internal combustion engine 1 includes an air cleaner 2, an air flow meter 3, a throttle valve 4, an auxiliary air valve 5, an EGR (exhaust gas recirculation) control valve 6, and each cylinder in the left and right banks in the figure. Group fuel injector 7
It is equipped with A and 7B.

In addition, the exhaust system includes exhaust manifolds 8A and 8B connected to the cylinder groups of the left and right banks of the engine 1, respectively, and an exhaust pipe 10A with catalytic converters 9A and 9B interposed at the downstream ends of the exhaust manifolds 8A and 8B, respectively. , 10B are connected. Each exhaust pipe 10A,
The downstream ends of 10B are merged into one, and the muffler 11 is connected thereto. And exhaust manifold 8
Based on the signals from oxygen sensors 12A and 12B that detect the oxygen concentration in the exhaust gas, which are installed at the confluence of exhaust gases A and 8B, respectively, the air-fuel ratio λ becomes λ=
Feedback control is performed by setting the fuel injection amount so that it becomes 1.

FIG. 2 shows the characteristics of air-fuel ratio feedback control, which has been widely used in the past, and is controlled based on a signal from one oxygen sensor. Signal _a0 in the figure is an air-fuel ratio feedback correction coefficient that is multiplied by the basic injection amount of fuel set according to the engine operating conditions, and the detection signal of the oxygen sensor is the rich (lean) air-fuel ratio corresponding to the oxygen concentration in the exhaust. ) side to the lean (rich) side, it is set by so-called proportional-integral control, in which it is first decreased (increased) by a proportional amount P, and thereafter decreased (increased) by a minute integral amount I.
Also, a line is shown in the air-fuel ratio feedback correction coefficient α for which the air-fuel ratio λ=1 with respect to the control value.

In this case, the signal from the oxygen sensor indicates a rich state in interval T ₁ in the figure, and as fuel injection amount reduction control is performed during this period, the air-fuel ratio becomes λ = 1 at time t ₁ and is thereafter controlled in the direction of λ < 1. progresses, but by the time the oxygen sensor detects this state and the signal _b0 switches from the rich side to the lean side, exhaust gas with an oxygen concentration corresponding to the control result of the fuel control system has reached the oxygen sensor. Due to the wasted time Td until i.e. from t ₁ to time
The oxygen sensor detects a lean condition with a delay of Td,
From that point in time _t2 , fuel increase control is performed (reference document for control method: Japanese Patent Application Laid-Open No. 1983-91425).

In this way, in feedback control based on the signal from the oxygen sensor, the control amount is hunting mainly due to the presence of dead time Td and because the oxygen sensor is an ON/OFF type, but if the control gain is selected appropriately, Both the amplitude and period can be set to appropriate values, and there is no problem in practical use.

For this reason, in the case of the conventional V-type engine mentioned above, a control system is provided for each bank on the left and right banks to perform independent control, but this requires two independent control systems, which has the disadvantage of being expensive. . In addition, Japanese Patent Publication No. 52-
The conventional example disclosed in Japanese Patent No. 97024 also performs similar control. In the invention disclosed in the same publication, the left and right banks are controlled using one oxygen sensor, but this method cannot cope with changes over time in the dispersion of the left and right banks and changes due to operating conditions.

Therefore, in order to solve this problem, it may be possible to control the two banks with one control device based on the signals of the two oxygen sensors, but simply AND the two and output the same signal from both banks based on the common signal result. If control is performed by

That is, FIG. 3 shows the signals a ₁ and a ₂ of the air-fuel ratio feedback correction coefficient α in the left and right banks (both are controlled equally) and the corresponding signals of λ=1 when control is performed using the above method. It shows the position and characteristics of signals b ₁ and b ₂ from two oxygen sensors installed in the exhaust pipes connected to the left and right banks, respectively. In the figure, at time _t11 , both the signals b ₁ and b ₂ of the two oxygen sensors indicate richness, and the signals a ₁ and a ₂ of the air-fuel ratio feedback correction coefficient α reverse from increasing to decreasing, and the fuel injection amount control is activated. It will be done.

However, the air-fuel ratios of the left and right banks usually differ due to individual variations, and in this case, for example, one bank (in the figure, the bank corresponding to signal a ₁ is ahead of the other bank at time t ₁₂ ) Then, at time t ₁₄ , which is delayed by dead time Td from time t ₁₂ , the signal b ₂ of the oxygen sensor corresponding to the bank detects a lean state, but the signal of the other oxygen sensor It still indicates a rich condition, so control to reduce fuel is continued.

The other bank is at time t ₁₃ , slightly later than time t ₁₂ .
When λ=1 is reached, the oxygen sensor signal b ₂ detects a lean state at time t ₁₅ after a further delay of dead time Td.

At this time t ₁₅ the two oxygen sensor signals b ₁ , b ₂
Both indicate a lean state, so the control is switched to fuel increase control.

As a result of the delay in switching the control system due to the difference in the air-fuel ratio between the left and right banks, both the amplitude and period of hunting of the controlled variable greatly increase compared to the case shown in Fig. 2, and the exhaust characteristics and There was a risk that fuel efficiency would be adversely affected.

Also, since both banks are controlled by the same signal, the engine as a whole is controlled to λ = 1, but the air-fuel ratio of one bank is kept on the lean side, and the air-fuel ratio of the other bank is kept on the rich side. In this respect, there was a risk that exhaust characteristics and fuel efficiency would be adversely affected.

<Purpose of the invention> The present invention was devised in view of the above-mentioned conventional situation, and it creates a difference in the air-fuel ratio feedback control amount output to the two cylinder groups according to the difference in the signals from the two oxygen sensors. By doing so, it is possible to control the two cylinder groups to the same set air-fuel ratio,
It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that solves the above problems.

<Structure of the invention> For this reason, the present invention detects the oxygen concentration in the exhaust gas in each of the two exhaust pipes connected to the two cylinder groups, and detects the oxygen concentration in the exhaust gas depending on the size of the air-fuel ratio corresponding to the oxygen concentration in the exhaust gas. An air conditioner for an internal combustion engine that is equipped with an oxygen sensor that outputs two types of inverted signals, and performs feedback control to maintain the air-fuel ratio at a set value by increasing or decreasing the amount of fuel supplied based on the signals from these two oxygen sensors. The fuel ratio control device includes a signal discrimination means for discriminating signals from two oxygen sensors, and an air-fuel ratio output to two cylinder groups when the two oxygen sensors output different types of signals. Adding deviation to feedback control amount 2
In each cylinder group, a control amount correcting means is provided for performing correction control so that the difference between the air-fuel ratio feedback control amount and the control amount corresponding to the set air-fuel ratio is eliminated.

<Example> Hereinafter, an example of the present invention will be described. However, the configurations of the oxygen sensor and fuel supply system are the same as those shown in FIG. 1, and the same components will be described using the reference numerals given in the same figure.

FIG. 4 shows a control block diagram of the air-fuel ratio control device according to the present invention.

The basic injection amount calculation circuit 21 inputs the signal from the crank angle sensor 13 that detects the engine speed N and the signal from the air flow meter 3 that detects the intake air amount Q, and calculates the basic injection amount Tp as Tp=KQ. /N (K is a constant), and the signal S1 is calculated as 2, which will be described later.
The output signal is output to two multiplication circuits 25 and 27.

The signal discrimination circuit 22 includes two oxygen sensors 12
Input signals S2 and S3 from A and 12B, and
2 and S3 are both rich, S2 is rich and S3 is lean, S2 is lean and S3 is rich, and S2 and S3 are both lean. The determination signal S4 is output.

Air-fuel ratio feedback correction coefficient calculation circuit 23
calculates the air-fuel ratio feedback correction coefficient α in accordance with the discrimination signal S4 from the signal discrimination circuit 22, as will be described later. That is, as determined by the discrimination signal S4, both S2 and S3 are rich (lean).
If this is the case, the first time it is determined that this state has been switched, the air-fuel ratio feedback correction coefficient α is decreased (increased) by a proportional amount P from the previous value, and from the second time onward, it is decreased by a minute integral amount I. Decrease (increase).

The controlled amount correction circuit 24 includes oxygen sensors 12A, 1
As will be described later, a signal S6 for correcting the control amount of the air-fuel ratio feedback correction coefficient α of one bank, in this embodiment, the bank on the right side in FIG. 1, is input to the adding circuit 26. Output.

That is, when a deviation occurs in the air-fuel ratio λ with respect to the control value of the same air-fuel ratio feedback correction coefficient α due to individual variations between the left and right banks, one oxygen sensor has a large proportion of the rich period;
The other oxygen sensor has a larger proportion of the lean period.

In this case, the time at which the one oxygen sensor changes from lean to rich is earlier than the other oxygen sensor, and the time at which the oxygen sensor changes from rich to lean is delayed.

Therefore, when the control amount correction circuit 24 detects a difference in the reversal timing of the signals of the two oxygen sensors 12A and 12B, when inverting the control value of the air-fuel ratio feedback correction coefficient α, that is, the signal S2 of the two oxygen sensors, When both S3 become rich or lean, if the bank-side oxygen sensor 12B has a long rich period, the air-fuel ratio feedback correction coefficient of the same bank is given ±P by normal PI control as in the bank. A signal is output to decrease the predetermined amount Δα from the set value, and conversely, when the lean period is long, a signal is output to increase the predetermined amount Δα.

However, specifically, as described later, the addition circuit 2
In order to correct the value of the bank-side air-fuel ratio feedback correction coefficient α using the value of the bank-side air-fuel ratio feedback correction coefficient α as a reference in step 6, the control amount correction circuit 24 adjusts the predetermined amount Δα every time the control value is reversed. A signal corresponding to the integrated value is output.

The adder circuit 26 adds or subtracts the air-fuel ratio feedback correction coefficient α by a predetermined amount based on the signals S5 and S6, and outputs a signal S7 corresponding to the value α' to the second multiplier circuit 27.

The first multiplier circuit 25 multiplies the basic injection amount Tp by the air-fuel ratio feedback correction coefficient α based on the signals S1 and S5 to obtain the fuel injection amount Ti, and transmits the signal S8 to the first fuel injection valve drive circuit 28. Output to. The first fuel injection valve drive circuit 28 sends a drive pulse signal S9 having a pulse width corresponding to Ti to the fuel injection valves 7A attached to each cylinder on the bank side.
Output to.

The second multiplication circuit 27 multiplies the basic injection amount Tp and the corrected air-fuel ratio feedback correction coefficient α' based on the signals S1 and S7 to obtain the fuel injection amount Ti'.
The signal S10 is sent to the second fuel injection valve drive circuit 29.
Output to. The second fuel injection valve drive circuit 29 is
A drive pulse signal S11 corresponding to Ti' is output to the fuel injection valve 7B attached to each cylinder on the bank side.

Next, a series of control operations by such a control device will be explained with reference to the signal characteristic diagram shown in FIG.
At time t ₂₁ two oxygen sensors 12A, 12
Signals S2 and S3 of B both indicate a rich state,
Based on the signal from the signal discrimination circuit 22, the air-fuel ratio feedback correction coefficient calculation circuit 23 initially subtracts the value of the air-fuel ratio feedback correction coefficient α by a proportional amount P;
From the second time onwards, perform the calculation to subtract the integral by I,
The signal S5 is output.

As a result, the fuel injection amount output from the first fuel injection valve drive circuit 28 via the first multiplier circuit 25
The pulse width of the pulse signal S9 corresponding to Ti is reduced, the opening time of the fuel injection valve 7A on the bank I side is reduced, and the fuel injection amount is controlled to be reduced.

On the other hand, since the output of the bank side oxygen sensor 12B has already become rich at time _t20 before time _t21 , this deviation is detected and the control amount correction circuit 24
A signal S6 decreases the bank air-fuel ratio feedback coefficient α' by a predetermined amount Δα at time _t21 .
is output. As a result, the adder circuit 26 subtracts a predetermined amount from the bank air-fuel ratio feedback correction coefficient α to obtain the bank air-fuel ratio feedback coefficient α', and outputs the signal S7 to the second multiplier circuit 27.

The second multiplier circuit 27 calculates the fuel injection amount Ti' by integrating the basic injection amount Tp and the corrected air-fuel ratio feedback correction coefficient α', and sends the signal S10 to the second fuel injection valve drive circuit 29. A signal S11 having a pulse width corresponding to Ti' from the drive circuit 29 is output to the bank side fuel injection valve 7B.

In this way, the bank side fuel injection valve 7B
The amount of fuel injected from the bank is also controlled to decrease, but since the amount of decrease control is larger than that on the bank side, control is performed that slides toward the lean side.

Next, at time _t22 , the air-fuel ratio of the bank reaches λ=1, and at time _t24 , after the dead time Td has elapsed, the signal S2 of the oxygen sensor 7A is reversed from rich to lean, and at time _t23 , the bank's air-fuel ratio reaches λ=1. Air fuel ratio is λ=
1 and after the dead time Td has elapsed, at time _t25 , the signal S3 of the oxygen sensor 7B is reversed from rich to lean. Therefore, at time _t25 , the air-fuel ratio feedback correction coefficient calculation circuit 23 increases the air-fuel ratio feedback correction coefficient α by the proportional amount P, and thereafter performs calculations to increase the air-fuel ratio feedback correction coefficient α by the integral amount I, and outputs the signal S5. As a result, the multiplier circuit 25, the fuel injection valve drive circuit 2
8, the fuel injection amount from the bank side fuel injection valve 7A is switched to increase control.

On the other hand, the control amount correction circuit 24
Detecting the difference in the reversal timing of A and 12B, the bank side air-fuel ratio feedback correction coefficient α' is adjusted by a predetermined amount △
A signal S6 for decreasing α is output.

As a result, in the adding circuit 26, the air-fuel ratio feedback correction coefficient α' is increased by a control amount obtained by subtracting a predetermined amount Δα from the proportional amount P at time _t25 , and thereafter control is performed to increase it by an integral amount I.

Here, by increasing the amount of decrease in the air-fuel ratio feedback correction coefficient α on the bank side by Δα at time t ₂₁ , the time t ₂₃ at which λ=1 is reached is brought forward by that amount, and therefore the time t 23 between time t ₂₄ and t ₂₅ is The difference between the times t ₂₀ and t ₂₁ is reduced compared to the difference between the times t 20 and t 21 .

Also, by reducing the amount of increase in the air-fuel ratio feedback correction coefficient α' at time t ₂₅ by Δα, the time t ₂₆ at which λ=1 is reached in the bank is delayed by that amount and the time t ₂₇ at which λ=1 is reached in the bank. Since the deviation between the two oxygen sensors 12B and 12A detects these times t ₂₆ and t ₂₇ between the times t ₂₈ and t ₂₉ is shortened compared to the deviation between the times t ₂₄ and t ₂₅ . .

Thereafter, the same process is repeated, and the difference in the reversal timing of the signals S2 and S3 of the two oxygen sensors 12A and 12B is shortened, and at time _t30 they match within the allowable range, and in parallel with this, the air-fuel ratio of the bank The feedback correction coefficients α and α′ are the amplitude of hunting,
Control is performed so that the deviation amount from the air-fuel ratio λ=1 becomes equal while decreasing the period. In other words, the two banks are controlled to the same air-fuel ratio with approximately λ=1 as the control center without any variation.

In this way, the amplitude and period of the bank air-fuel ratio feedback correction coefficients α, α' can be reduced, and the air-fuel ratio can be controlled to the same level, thereby significantly improving both exhaust characteristics and fuel efficiency.

In addition, in this embodiment, when the control amount of the air-fuel ratio feedback correction coefficient α on the side where no correction is performed is limited to a predetermined range, the control margin is greater if the control center value is brought closer to the median value of the predetermined range. .
Therefore, by correcting the other air-fuel ratio feedback correction coefficient α', the bank to be corrected is selected so that the control center of the air-fuel ratio feedback correction coefficient α approaches the median value of the predetermined range. is desirable.

Furthermore, in this embodiment, when a deviation in the signal of the oxygen sensor is detected, one of the air-fuel ratio feedback correction coefficients is increased or decreased by a fixed value, but the correction amount is set in proportion to the amount of deviation. You can.

Furthermore, the air-fuel ratio feedback correction coefficients α and α' of the two systems may be both increased and decreased in opposite directions.

In addition, if one oxygen sensor fails, the amount of deviation between the air-fuel ratio feedback correction coefficients α and α' of the two systems is memorized at that time, and the conventional method is performed based on the signal from the normal oxygen sensor. If PI control is performed to set one air-fuel ratio feedback correction coefficient, and the other is set by adding the above-mentioned deviation amount to this, good control that absorbs variations between the two systems can be continued. In this case, if two systems of air-fuel ratio feedback correction coefficients are stored for each different operating state determined by the rotational speed, load, etc., better control can be achieved over all operating states.

<Effects of the invention> As explained above, according to the invention, two cylinder groups are brought to the same set air-fuel ratio by giving a deviation to the air-fuel ratio feedback control amount according to the type of signal output from the two oxygen sensors. Since the configuration is controlled, the amplitude and period of the hunting control amount are shortened, and the exhaust characteristics and fuel efficiency can be improved as much as possible.

In addition, compared to the case where two cylinder groups are controlled by completely independent control systems, the basic air-fuel ratio feedback control amount is set based on a common signal from the two oxygen sensors, and a predetermined amount is added or subtracted to this value. Since the configuration is such that the control amounts for two systems are set, the arithmetic circuits and the like can be shared, which is advantageous in terms of cost.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of mechanical components of an air-fuel ratio control device for an internal combustion engine, FIG. 2 is a characteristic diagram showing an example of air-fuel ratio feedback control based on a signal from one oxygen sensor, and FIG. Fig. 3 is a characteristic diagram showing an example of air-fuel ratio feedback control based on the signals of two oxygen sensors, Fig. 4 is a control block diagram showing an embodiment of the present invention, and Fig. 5 is a control characteristic diagram of the same embodiment. be. 1... V-type internal combustion engine, 7A, 7B... Fuel injection valve, 8A, 8B... Exhaust manifold, 12A,
12B... Oxygen sensor, 21... Basic injection amount calculation circuit, 22... Discrimination circuit, 23... Air-fuel ratio feedback correction coefficient calculation circuit, 24... Controlled amount correction circuit, 25, 27... Multiplication circuit, 26... ... Addition circuit, 28, 29 ... Fuel injection valve drive circuit, S1 ~
S9...Signal.

Claims (1)

[Scope of utility model registration request] Oxygen sensors are installed in the two exhaust pipe systems connected to the two cylinder groups, respectively, to detect the oxygen concentration in the exhaust gas and output two types of signals that are inverted depending on the size of the air-fuel ratio corresponding to the oxygen concentration in the exhaust gas. In an air-fuel ratio control device for an internal combustion engine that performs feedback control to maintain the air-fuel ratio at a set value by increasing or decreasing the amount of fuel supplied based on the signals from the two oxygen sensors, a signal discriminating means for discriminating between the two oxygen sensors; 2
Air-fuel ratio control for an internal combustion engine, characterized in that the air-fuel ratio control for an internal combustion engine is provided with a control amount correction means that performs correction control so that the difference between the air-fuel ratio feedback control amount and the control amount corresponding to a set air-fuel ratio in one cylinder group becomes equal. Device.