JP2704893B2 - Engine air-fuel ratio control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio control device for an engine having two fuel supply means installed at different locations.

(Prior Art) In an engine, in order to control an air-fuel ratio of an air-fuel mixture supplied to a combustion chamber to an optimum value, for example, as shown in Japanese Patent Application Laid-Open No. sensor for detecting the oxygen concentration (hereinafter, referred to as O ₂ sensor) is installed,
In some cases, the fuel supply amount is feedback-controlled in accordance with the output from the sensor. That is, when the residual oxygen concentration in the exhaust gas detected by the sensor is equal to or lower than a predetermined value, it is determined that the air-fuel mixture supplied to the combustion chamber is rich, and fuel such as a fuel injection valve provided in the intake passage is provided. The amount of fuel supplied by the supply means is reduced, and when the residual oxygen concentration in the exhaust gas is equal to or higher than a predetermined value, it is determined that the air-fuel mixture is lean, and the amount of fuel supplied by the fuel supply means is increased. The feedback control is performed so that the air-fuel ratio of the air-fuel mixture supplied to the fuel chamber is maintained at an optimum value (for example, air / fuel = 14.7).

On the other hand, Japanese Utility Model Laid-Open No. 60-102467 discloses an engine having a fuel injection valve at each of an upstream portion and a downstream portion of an intake passage. This is because, by selectively using the upstream and downstream fuel injection valves in accordance with the engine temperature, fuel supply or combustion is favorably performed both during and after the warm-up of the engine. It is like that.

In addition, it is conceivable to improve the responsiveness during acceleration by installing the fuel supply means in each of the upstream portion and the downstream portion of the intake passage. According to this, at least a first intake passage through which intake air passes at a low load and a second intake passage through which intake air is suppressed at a low load are provided as the intake passage, and the first intake passage and the second intake passage are provided. A first fuel supply means for supplying fuel downstream of the junction with the first fuel supply means, and a second fuel supply means for supplying fuel to the second intake passage. The capacity of the intake passage is made larger than the capacity of the intake passage from the first fuel supply means to the combustion chamber. In addition, at the time of a low load in which the intake air passes only through the first intake passage, fuel is supplied into the second intake passage by the second fuel supply means to form an air-fuel mixture in the second intake passage in advance. At the time of acceleration when the intake air is supplied from the second intake passage, the air-fuel mixture in the second intake passage is introduced into the combustion chamber prior to an increase in the amount of fuel supplied from the first fuel supply means. It improves responsiveness.

(Problems to be Solved by the Invention) By the way, when the fuel supply means is installed at different places as described above, how to control these fuel supply means when controlling the air-fuel ratio becomes an issue. That is, based on the output of the O ₂ sensor, both the fuel to the supply means for feedback controlling the control becomes remarkably complicated, stability control, cause reliability problems in that, also both the fuel supply means open If the control is performed by the control, the air-fuel ratio is not accurately controlled to the optimum value.

Therefore, the present invention is intended to control the air-fuel ratio accurately and stably without significantly complicating the control when the fuel supply means is installed at different places as described above. The task is to

(Means for Solving the Problems) In order to solve the above problems, an air-fuel ratio control device for an engine according to the present invention is characterized in that it is configured as follows.

That is, the invention according to claim 1 of the present application includes first and second fuel supply means as fuel supply means, one of which supplies fuel from an intake passage at a distance from the combustion chamber and the other of which supplies fuel. In an engine configured to supply fuel on the combustion chamber side, detection means for detecting a residual oxygen concentration in exhaust gas, and fuel supply on the combustion chamber side based on the residual oxygen concentration detected by the detection means. Means for controlling the amount of fuel supplied by the means by feedback control while controlling the amount of fuel supplied by the fuel supply means at a distance from the combustion chamber by open control. The smaller the ratio of the amount of fuel supplied from the fuel supply means on the combustion chamber side to the total amount of fuel supplied is the larger the control gain of the feedback control is. And butterflies.

Also, the invention according to claim 2 is a first intake passage through which intake air passes at least when the load is low, a second intake passage that suppresses the passage of intake air when the load is low, the first intake passage and the second intake passage. A first fuel supply means for supplying fuel to the combustion chamber side from the junction or a second fuel supply means for supplying fuel to the second intake passage; As in the present invention, detecting means for detecting the residual oxygen concentration in the exhaust gas, feedback control of the fuel supply amount by the first fuel supply means based on the residual oxygen concentration detected by the detecting means, and Control means for controlling the amount of fuel supplied by the fuel supply means by open control.

(Operation) According to the above configuration, first, in the case of the invention according to claim 1, control instability due to feedback control of both the first and second fuel supply units installed at different locations is avoided. In addition, since the fuel supply amount by the fuel supply means on the combustion chamber side close to the detection means for detecting the residual oxygen concentration in the exhaust gas is feedback-controlled, the air-fuel ratio is controlled with good responsiveness and with high accuracy. become. In this case, when the amount of fuel supply from the fuel supply means located farther from the combustion chamber is large, despite the fact that the amount of fuel supply from the fuel supply means on the combustion chamber side decreases, Since the gain of the feedback control is increased, the stability and responsiveness of the air-fuel ratio control are ensured.

According to the second aspect of the present invention, in addition to the operation of the first aspect of the present invention, at the time of a low load, fuel is supplied to the second intake passage by the fuel supplied from the second fuel supply means into the second intake passage. The air is stored, and the air-fuel mixture is quickly introduced into the combustion chamber during acceleration, so that the acceleration response from a low load region is improved.

(Examples) Hereinafter, examples of the present invention will be described. This embodiment is an embodiment common to the first and second aspects of the present invention.

First, the control system of this embodiment will be described with reference to FIG. 1. The engine 1 is provided with an intake passage 5 and an exhaust passage 6 which respectively communicate with a combustion chamber 4 via intake and exhaust valves 2 and 3.

In the intake passage 5, an air cleaner 7 and an air flow meter 8 are provided at an upstream end thereof, a surge tank 9 is provided at an intermediate portion thereof, and a throttle valve 10 is provided upstream of the surge tank 9. ing. Further, a bypass passage 11 is provided for communicating the upstream side of the throttle valve 10 and the downstream side of the surge tank 9, and an on-off valve 12 for controlling the opening and closing of the passage 11 is provided on the bypass passage 11. The intake valve 2 is located immediately downstream of the junction of the bypass passage 11 downstream of the surge tank in the intake passage 5.
The first fuel injection valve 13 is directed to the inside of the combustion chamber 4 through the
A second fuel injection valve 14 is provided between the throttle valve 10 and the surge tank 9 so as to point in the surge tank 9. Note that this second
Although one fuel injection valve 14 is provided, the first fuel injection valve 13 is provided for each cylinder, and is provided in the same number as the number of cylinders of the engine.

A control unit 20 for controlling the operation of the fuel injection valves 13, 14 and the like is provided. The control unit 20 includes an intake air amount signal a from the air flow meter 8 and a rotation sensor for detecting an engine speed. An engine speed signal b from the engine 21, a water temperature signal c from a water temperature sensor 22 for detecting the temperature of the engine cooling water, and a residual oxygen concentration in the exhaust gas which is provided in the exhaust passage 6.
The O ₂ signal d from the O ₂ sensor 23 is input. The control unit 20 outputs control signals e, f, and g to the first and second fuel injection valves 13, 14 and the bypass control valve 12, respectively, based on the input signals a to d. The control of the fuel injection amount from the second fuel injection valves 13 and 14 and the control of opening and closing of the on-off valve 12 are performed.
In that case, feedback control of the fuel injection amount is performed on the first fuel injection valve 13 based on the signal d from the O ₂ sensor 23 so that the air-fuel ratio converges to the target value. I have.

Next, the operation of the present embodiment will be described with reference to the flowchart of FIG. 2 showing the operation of the control unit 20.

First, the control unit 20, the airflow meter 8 shown in FIG. 1 in step S ₁ of the flow chart, the rotation sensor 21 receives a signal a~d from the water temperature sensor 22 and O ₂ sensor 23, these signals a~d intake air quantity shown, engine speed, engine coolant temperature and the residual oxygen concentration in the exhaust gas is read whether more than a predetermined value, then first in step S _2,
Calculating the basic pulse width T ₀ when injecting fuel from the second fuel injection valves 13 and 14. The basic pulse width T ₀ is equivalent to a load of the engine, it is set to a value corresponding to the intake air amount per intake stroke of each cylinder obtained from the above intake air amount and the engine speed.

Next, the control unit 20, in step S _3, it determines whether a condition for performing feedback control of the air-fuel ratio is satisfied. This condition is that the operating range with the basic pulse width T ₀ (engine load) and the engine speed as parameters belongs to a predetermined feedback zone set as a map in advance as shown in FIG. The water temperature is equal to or higher than a predetermined value, and the actual basic pulse width T ₀ , engine speed, water temperature, and the like are compared with these conditions.

Then, firstly, to describe the case where the feedback condition is not satisfied, in this case, the control unit 20 is configured to zero the feedback coefficient C _FB in step S _4, then the current operation region in step S ₅ It is determined whether the fuel injection belongs to the upper and lower injection zones set in the map of FIG. 3, that is, the region where fuel is injected from both the first and second fuel injection valves 13 and 14 in the downstream and upstream portions of the intake passage. Here, this vertical injection zone is set in a low-load low-speed region and is included in the above-mentioned feedback zone. When the engine water temperature is low, for example, the feedback condition is not satisfied. In some cases, the area outside the upper and lower injection zones is a downstream injection zone in which fuel is injected only from the first fuel injection valve 13 on the downstream side. Further, in this vertical injection zone, the on-off valve on the bypass passage 11 shown in FIG.
12 is opened, and intake air is supplied to the combustion chamber 4 by the bypass passage 11 and the opening of the throttle valve 10. More specifically, during idle operation, the ratio of intake air supplied through the opening of the bypass passage 11 and the throttle valve 10 is set to about 1: 1, and as the amount of intake air per hour increases, That is, as the throttle valve 10 is opened, the opening and closing valve 12 of the bypass passage 11 is controlled to be further opened.

Then, if it belongs to the upper and lower injection zone, to 1 vertical injection flag F ₀ in step S _6, if that does not belong to set the flag F ₀ at step S ₇ to 0.

Next, the control unit 20 determines the value of the flag F ₀ in step S _8, in the case of F ₀ = 0, whether immediately after the transition to the outside the zone from the upper and lower injection zone at step S ₉ determined, also in the case of F ₀ = 1, determines whether immediately after the transition from the outside of the upper and lower injection zone at step S ₁₀ into the zone, if immediately after any zone has migrated, step
To set the timer in S _11, S _12. This timer sets the feedback coefficient when executing the feedback control described later.
Used for C _FB correction.

And when it does not belong to the vertical injection zone (F ₀ = 0)
In step S _13, the first injection ratio, i.e. on set first, the ratio K of the injection quantity of the first injection valve 13 on the downstream side with respect to the total injection quantity of the second fuel injection valves 13 and 14 to 1.0 ,
Step Using this ratio K in S ₁₄ is calculated according to equation (1) described later of the first pulse width T _1, in step S _15, the control to drive the first fuel injection valve 13 in the pulse width T ₁ The signal e is output.

Also, if it belongs to the upper and lower injection zone (F ₀ = 1) is calculated based on the preset map the first injection ratio K in step S _16. As shown in FIG. 4, this map shows that in the upper and lower injection zones, the ratio K is higher on the high-load, higher-rotation side, in other words, the state (K = 1.0) in the downstream injection zone outside the zone. ). Then, in step S _17, and calculates according to equation (2) described later of the second pulse width T ₂ of the upstream side, in step S _18, to drive the second fuel injection valve 14 in the pulse width T ₂ The control signal f is output, and the step S
_14, first to calculate the pulse width T ₁ in step S _15, and outputs a control signal e to drive the first fuel injection valve 13 in the pulse width T _1.

The first and second pulse widths T ₁ and T ₂ are calculated according to the following equations.

_{T 1 = K (1 + C} 0 + C FB + C L1) T 0 + T V ... (1) T 2 = 4 (1-K) (1 + C 0 + C L2) T 0 + T V ... (2) where, C ₀ is This is a correction coefficient for performing the fuel injection amount increase correction during acceleration, the increase correction under high load, the water temperature correction, and the like.
C _L1, C _L2 is first obtained by the learning control described later, a learning value of the fuel injection amount of the second fuel injection valves 13 and 14, also T _V Starting the solenoid of the fuel injection valve 13, 14 This is the invalid injection time required to cause the injection. In addition,
The above description is for the case where the condition of the feedback control is not satisfied. In this case, the feedback coefficient C _FB in the equation (1) is zero.

On the other hand, when the feedback condition is determined as being satisfied in step S _3, the control unit
20 calculates P values constituting the feedback correction coefficient C _FB in step S ₁₉ (proportional term) and I value (integral term).

Here, the operation of the feedback control of the air-fuel ratio will be briefly described. As shown in FIG. 5, the output signal d from the O ₂ sensor 23 indicates that the residual oxygen concentration in the exhaust gas is equal to or higher than a predetermined value, Indicates that the air-fuel ratio is leaner than the target air-fuel ratio, the fuel injection amount is increased at a predetermined rate of change, and when the residual oxygen concentration indicated by the signal d from the sensor 23 falls below a predetermined value, The fuel injection amount when the air-fuel ratio changes to rich is reduced by a predetermined amount at once, and then gradually reduced at a predetermined change rate. Also,
As a result, when the air-fuel ratio turns lean again, the fuel injection amount is increased at once by a predetermined amount, and then gradually increased at a predetermined change rate, thereby maintaining the air-fuel ratio at the target air-fuel ratio. In this case, when the air-fuel ratio changes from lean to rich, and vice versa, the value that increases or decreases at once is the P value, and the rate of change when the amount gradually increases or decreases is the I value.

The control unit 20 calculates the P value and the I value based on a preset map shown in FIG. 6, and the map shows that the smaller the first injection ratio K, the more the P value and the I value. It is set to increase.

Next, the control unit 20 determines whether the timer is ON in step S _20, the timer in step S _11, S _12, operating between the upper and lower injection zone and said zone outside This is set when the area shifts, and before the set time elapses after the zone shift, step S ₂₁
Thus, the P value and the I value are increased and corrected, and the change in the injection amount accompanying the shift is performed quickly. Then, in step S _22, P value calculated as described above, to calculate a feedback coefficient C _FB using I value.

Thereafter, the control unit 20 determines whether or not a predetermined learning condition in step S ₂₃ is satisfied. The learning condition is, for example, that the engine water temperature is equal to or higher than a predetermined temperature that is higher than the feedback condition. Then, the learning condition if not satisfied, executes the steps S ₅ to S _18.

As a result, similarly to the case where the feedback condition is not satisfied, if the operating region is in the upper and lower injection zones, the first and second fuel injection valves 13 and 14 can be used to obtain the above-mentioned formula (1),
Fuels corresponding to the pulse widths T ₁ and T ₂ set according to (2) are respectively injected, and the fuel is injected only from the downstream first fuel injection valve 13 outside the upper and lower injection zones. . In particular, in the low-load low-speed vertical injection zone, the throttle valve 10 is in a substantially fully closed state and the intake air is mainly supplied to the combustion chamber 4 by the bypass passage 11, so that the fuel is injected from the second fuel injection valve 14. The fuel is stored in the surge tank 9 without being introduced into the combustion chamber 4, and an air-fuel mixture is formed in the surge tank 9. And at the next acceleration, the throttle valve
When 10 is opened and intake air is supplied from the valve 10 through the surge tank 9 to the combustion chamber 4, prior to the increase in the injection amount from the first fuel injection valve 13 accompanying the increase in the intake air amount, Thus, the air-fuel mixture stored in the surge tank 9 is quickly introduced into the combustion chamber 4, thereby improving the acceleration response from a low load region. In addition,
At the time of this acceleration, the operation region leaves the upper and lower injection zone, so that the fuel injection from the second fuel injection valve 14 upstream of the surge tank is stopped.

When the feedback condition is satisfied and the operation region belongs to the upper and lower injection zones, the pulse width T calculated from the first and second fuel injection valves 13 and 14 according to the above equations (1) and (2). _1, the amount of fuel corresponding to T ₂ is injected, in this case, the feedback coefficient C _FB calculated in step S ₂₂ are used only in the calculation of the pulse width T ₁ of the first fuel injection valve 13 Therefore, the feedback control of the fuel injection amount as shown in FIG. 5 according to the output from the O ₂ sensor 23 is performed only for the first fuel injection valve 13. Thus, first, the destabilization of the control when the feedback control for both the second fuel injection valve 13, 14 is avoided, performs feedback control for the first fuel injection valve 13 closer to the O ₂ sensor 23 Therefore, stable and accurate air-fuel ratio control is performed.

Further, the first fuel injection valve in the upper and lower injection zone
In the feedback control of 13, the first fuel injection valve
When the injection ratio K by 13 is small, the P value and the I value that constitute the feedback coefficient C _FB are increased.
Good control response can be obtained despite the small injection amount.

Next, description will be given of a case where a predetermined learning condition in step S ₂₃ is determined as that satisfied this case,
Control unit 20 operating region is determined whether belonging to the upper and lower injection zone at step S _24, when not belonging to the zone resets the vertical injection flag F ₀ to 0 in step S _25. Thus, the feedback control is performed only for the first fuel injection valve 13 as in the case where the learning condition is not satisfied. On the other hand, the learning condition is satisfied,
If the operating region belongs to the upper and lower injection zone, the learning control in step S26 and _subsequent steps is performed.

In this control, it first determines a first value of the learning completion flag F ₁ in step S _26, since the flag F ₁ is reset to the initial 0, this case, then step S ₂₇
Is executed, first, the upper and lower injection flag F ₀ is set to 0.
Thus, the next time the performance of step S _8, it can executes step S ₉ to S ₁₃ from the step S _8, the first injection ratio K is 1.0. That is, during the learning control of the first fuel injection valve 13, the fuel injection from the second fuel injection valve 14 is forcibly stopped. In this state, executing step S _28, to calculate a first learned value C _L1 used for feedback control of the first fuel injection valve 13. This learning value is calculated by reading a plurality of (even number) values of the increasing and decreasing inverting portions in the change of the injection amount of the first fuel injection valve 13 as shown in FIG. 5 and calculating the average value. Will be Then, if the learning of the injection quantity complete sets with, in 1 vertical injection flag F ₀ is set at step S ₂₉ to step S _30, the first learning completion running S ₃₁ flag F ₁ 1 Thus, the fuel injection by the second fuel injection valve 14 on the upstream side is restarted.

Further, when the first learning value C _L1 in this manner are calculated, and then executes step S ₃₂ from step S _26. In this case, the calculation of the second learning value C _L2 is not completed (F ₂ =
0), calculates the vertical injection learning value C _L0 in step S _33. This learning value C _L0 is the first learning value C _{L1 in a} state where fuel is being injected from both the first and second fuel injection valves 13 and 14.
Is calculated on the basis of the injection amount of the first fuel injection valve 13 in the same manner as in the calculation of.

Then, if the calculation of the learned value C _L0 is completed, and executes Step S ₃₅ from the step S _34, to calculate the second learning value C _L2 according the following equation (3).

C _L2 = C _L0 (1−K) / K (3) That is, the upper and lower injection learning value C _L0 obtained as described above.
Is used to determine the injection amount of the second fuel injection valve 14 using the first injection ratio K. In this case, the first fuel injection valve 13
It is assumed that the injection amount is set correctly since it is immediately after the calculation of the first learning value _CL1 .

When the first and second learning values C _L1 and C _L2 are calculated in this manner, the first fuel injection valve 13 is controlled by a small feedback coefficient C _{FB at the time} of feedback control. Therefore, the stability and accuracy of the fuel injection control are improved, and the injection amount of the second fuel injection valve 14 that does not perform the feedback control is set to an appropriate value.

(Effects of the Invention) As described above, according to the present invention, first and second fuel supply means are provided as fuel supply means, one of which supplies fuel from an intake passage at a distance from the combustion chamber, and the other. In the engine in which the fuel is supplied to the combustion chamber side, feedback control is performed only for the fuel supply means on the combustion chamber side. Therefore, the control of the air-fuel ratio is performed in a stable and accurate manner. In addition, the responsiveness of the control is improved particularly when the fuel supply amount by the fuel supply means on the fuel chamber side is small. According to the invention of claim 2, the stability and accuracy of the air-fuel ratio as described above are improved, and the acceleration response during acceleration from a low load region is improved.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a control system diagram of air-fuel ratio control, FIG. 2 is a flowchart showing this control operation, FIG. 3 is a map in which a control area is set, FIG. Is a map in which the characteristics of the first injection ratio in the upper and lower injection zones are set, FIG. 5 is a time chart showing a general control operation of the air-fuel ratio control, and FIG. 6 is a graph showing the P and I values constituting the feedback coefficient. It is a map in which characteristics are set. 1 ... engine, 4 ... combustion chamber, 5 ... intake passage, 9 ...
... second intake passage (surge tank), 10 ... throttle valve, 11 ... first intake passage (bypass passage), 13, 14 ...
... first and second fuel supply means (first and second fuel injection valves), 20
... Control means (control unit), 23 ... Remaining oxygen concentration detecting means (O ₂ sensor).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication F02M 69/00 360 F02M 69/00 320F (56) References JP-A-59-196947 (JP, A) JP-A-61-279746 (JP, A) JP-A-61-210250 (JP, A) JP-A-62-17329 (JP, A) JP-A-60-195348 (JP, A) JP-A-2- 5726 (JP, A) JP-A-2-130238 (JP, A) JP-A-2-49940 (JP, A) JP-A-61-16644 (JP, U)

Claims (2)

(57) [Claims] 1. A fuel supply means comprising first and second fuel supply means, one of which supplies fuel from an intake passage at a distance from the combustion chamber and the other of which supplies fuel on the combustion chamber side. An air-fuel ratio control device for an engine configured to supply the fuel, comprising: detecting means for detecting a residual oxygen concentration in exhaust gas; and supplying fuel to the combustion chamber based on the residual oxygen concentration detected by the detecting means. Control means for performing feedback control of the fuel supply amount by the means and controlling the fuel supply amount by the fuel supply means at a distance from the combustion chamber by open control, wherein the control means Wherein the smaller the ratio of the fuel supply amount from the fuel supply means on the combustion chamber side to the total fuel supply amount is, the larger the control gain of the feedback control is made. Air-fuel ratio control system of that engine. 2. A first passage through which intake air passes at least when the load is low.
An intake passage, a second intake passage in which passage of intake air is suppressed at a low load, and a junction of the first intake passage and the second intake passage or a first fuel for supplying fuel to a combustion chamber side from the junction. Supply means for supplying fuel to the second intake passage;
A fuel supply means, a detection means for detecting a residual oxygen concentration in the exhaust gas, and a feedback control of a fuel supply amount by the first fuel supply means based on the residual oxygen concentration detected by the detection means. An air-fuel ratio control device for an engine, further comprising control means for controlling the amount of fuel supplied by the second fuel supply means by open control.