JP5206221B2 - Method and system for controlling the fuel supply of an internal combustion engine - Google Patents

Description

The present invention relates to a method and system for controlling the fuel supply of an internal combustion engine.

In an engine, that is, an internal combustion engine, for exhaust gas purification, an exhaust gas purification catalyst is generally disposed in the exhaust passage. A three-way catalyst is used as the exhaust gas purification catalyst, and NOx, CO, It is also common to reduce HC. As described in Patent Document 1, in order to improve the purification efficiency of the three-way catalyst, the air-fuel ratio is fluctuated (vibrated) with the theoretical air-fuel ratio as a boundary. Further, in the engine, as described in Patent Document 2, the fuel injection amount is determined according to the intake air amount, and particularly from the viewpoint of exhaust gas purification by the exhaust gas purification catalyst, the exhaust air-fuel ratio is determined. In general, the fuel injection amount is determined so that becomes the stoichiometric air-fuel ratio.

JP 2007-239698 A JP 2007-303376 A

By the way, in a steady operation state of the engine, for example, in a state where the accelerator pedal depression amount of the automobile is substantially constant, the engine speed is constant or changes at a constant rate of change, so that the engine is stabilized. Desirable to be driven. In this steady operation state, when the engine speed increases, the filling amount decreases, so the fuel injection amount decreases, and the engine speed decreases. Conversely, when the engine speed decreases, the engine charge increases. Therefore, the fuel injection amount is increased and the engine speed is increased. Thus, the engine speed has converged to a constant engine speed (almost constant engine speed) or the rate of change has converged to a constant engine speed. Will be maintained.

On the other hand, in some engines, especially when the volume of the intake system is large or when a disturbance such as the introduction of EGR gas is received, the follow-up of the change in the charging amount is delayed with respect to the change in the engine speed in the steady operation state. (Generation of phase delay), the function of returning the engine speed to a constant speed or a constant rate of change (rotation restoring force) may be weakened. If the phase lag increases, in the extreme case, rotational fluctuations are also promoted.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method and a system for controlling the fuel supply of an internal combustion engine that can increase the rotational restoring force in a steady operation state. There is to do.

In order to achieve the object, the following solution is adopted in the method of the present invention. That is, as described in claim 1 in the claims,
A method for controlling fuel supply of an internal combustion engine in which a throttle valve for adjusting an intake air amount is disposed in an intake passage of an engine and an amount of fuel corresponding to the intake air amount is supplied.
A first step of detecting an intake air amount of the engine;
A second step of detecting a change in the required output;
In the first operating state in which the change in the required output detected in the second step is equal to or greater than a predetermined value, the amount of follow-up with the first follow-up degree with respect to the change in the intake air amount detected in the first step A third step of supplying fuel;
In the second operating state in which the change in the required output detected in the second step is less than the predetermined value, the change in the intake air amount detected in the first step is more than the first following degree. A fourth step of supplying an amount of fuel that follows with a small second following degree;
Bei to give a,
In the fourth step, the fuel supply amount per unit time is made constant even when the engine speed changes in the steady state where the throttle opening is constant in the second operating state.
It is Unishi. According to the above solution, in a steady operation state in which the change in the required output is less than the predetermined value, the followability of the supplied fuel amount to the change in the intake air amount is weakened, that is, in a direction in which the fuel supply amount becomes constant. By controlling the generated work of the engine to be substantially constant, the rotational restoring force can be increased. In particular, the rotational restoring force in a steady state where the throttle opening is constant can be sufficiently increased. On the other hand, at the time of acceleration such that the change in the required output in which the vibration due to the rotation fluctuation does not cause a problem becomes a predetermined value or more, the followability of the fuel supply with respect to the change in the intake air amount can be improved and the output responsiveness can be improved. .

Preferred embodiments based on the above solution are as described in claims 2 to 5 in the claims. That is,
In the second operating state, the fuel supply amount per unit time is set to be substantially constant (corresponding to claim 2). In this case, the function corresponding to claim 1 can be more fully exhibited by enhancing the function of making the generated work of the engine constant in the steady operation state.

  In the second operating state, when the engine speed decreases, the fuel supply amount for each cylinder cycle is increased (corresponding to claim 3). In this case, by adjusting the fuel supply amount, it is possible to more sufficiently improve the engine rotational resilience.

  In the second operating state, the average air-fuel ratio is made substantially the stoichiometric air-fuel ratio (corresponding to claim 4). This is preferable for exhaust gas purification.

A fifth step of detecting the exhaust air-fuel ratio;
A sixth step of feedback-controlling the fuel supply amount so that the exhaust air-fuel ratio detected in the fifth step becomes the stoichiometric air-fuel ratio;
Further comprising
The vibration frequency of the exhaust air-fuel ratio is lower than the vibration frequency of the intake air amount.
(Corresponding to claim 5). In this case, the air-fuel ratio feedback control is stably performed, and it is preferable for improving the engine rotation restoration property in the steady operation state.

In order to achieve the above object, the following solution is adopted in the system of the present invention. That is, as described in claim 6 in the claims,
A system for controlling the fuel supply of an internal combustion engine in which a throttle valve for adjusting the amount of intake air is disposed in an intake passage of the engine, and an amount of fuel corresponding to the amount of intake air is supplied.
Intake air amount detection means for detecting the intake air amount of the engine;
An output change detecting means for detecting a change in the required output;
In a first operating state in which the change in the required output detected by the output change detection means is equal to or greater than a predetermined value, the change in the intake air amount detected by the intake air amount detection means follows with a first follow-up degree. First fuel supply control means for supplying an amount of fuel;
In the second operating state in which the change in the required output detected by the first output change detection unit is less than the predetermined value, the first output is changed with respect to the change in the intake air amount detected by the intake air amount detection unit. A second fuel supply control means for supplying an amount of fuel to follow with a second follow-up degree smaller than the follow-up degree;
Bei to give a,
Further, the second fuel supply means is configured so that the fuel supply amount per unit time becomes constant even when the engine speed changes in the steady state where the throttle opening is constant in the second operating state. To control,
It is Unishi. According to the above solution, a system for realizing the control method according to claim 1 is provided.

According to the present invention, in an internal combustion engine that supplies an amount of fuel corresponding to the amount of intake air, it is possible to improve engine rotation recovery in a steady operation state, particularly in a steady state where the throttle opening is constant, and a large output increase. Both improvement in output responsiveness when requested can be satisfied.

In FIG. 1, E is an engine, particularly an automobile engine. In the embodiment, E is an in-line 4-cylinder spark ignition engine, and fuel is gasoline. FIG. 1 representatively shows one cylinder, and a combustion chamber 4 is defined by a cylinder 1, a cylinder head 2, and a piston 3 slidably fitted in the cylinder 1. A spark plug 5 is disposed facing the combustion chamber 4.

In the combustion chamber 4, two intake ports 10 and two exhaust ports 11 formed in the cylinder head 2 are opened. In FIG. 1, one of the two intake ports 10 and the two exhaust ports 11 is disposed in a direction perpendicular to the paper surface and is not depicted in FIG. 1. The intake port 10 is opened and closed by an intake valve 12, and the exhaust port 11 is opened and closed by an exhaust valve 13. A camshaft for driving the intake valve 12 to open and close is indicated by reference numeral 14, and a camshaft for driving the exhaust valve 13 to open and close is indicated by reference numeral 15. Each camshaft 14, 15 is linked to a crankshaft 16, and this crankshaft 16 is linked to the piston 3 via a connecting rod 17.

The intake port 10 in each cylinder is connected to a surge tank 21 via a branch intake passage 20. A common intake passage 22 is connected to the surge tank 21. An air cleaner 23 is disposed at the upstream end of the common intake passage 22. A throttle valve 24 is disposed in each branch intake passage 20, and a fuel injection valve 25 is disposed on the downstream side of the throttle valve 24. That is, although the fuel injection valve 25 is for port injection, it can also be a direct injection type in which fuel is directly injected into the combustion chamber 4.

On the other hand, the exhaust gas from the exhaust port 11 is discharged to the atmosphere through the exhaust passage 30. An exhaust gas purification device 31 made of, for example, a three-way catalyst is disposed in the exhaust passage 30. An air-fuel ratio sensor S4 is disposed in the exhaust passage 30 upstream of the exhaust gas purification device 31. In the embodiment, the air-fuel ratio sensor S4 is a linear sensor that can detect the air-fuel ratio continuously.

The exhaust passage 30 and each branch intake passage 20 are connected by an EGR passage 35. An EGR valve 36 is connected to the EGR passage 35.

In FIG. 2, U is a controller (control unit) configured using a microcomputer. The controller U controls the fuel injection valve 25 described above. Signals from various sensors S1 to S5 are input to the controller U. The sensor S1 detects the opening of the throttle valve 24, that is, the throttle opening. The sensor S2 detects the vehicle speed. The sensor S3 detects the engine speed. The sensor S4 detects the air-fuel ratio of the exhaust system as described above. The sensor S5 detects the intake air amount.

An outline of control by the controller U will be described. First, FIG. 3 shows changes in torque, output (horsepower), and fuel injection amount Qf with respect to fluctuations in the rotational speed ne in a steady operation state where the throttle opening is constant in an engine. . In FIG. 3, the α line is a torque change characteristic when the control according to the present invention is not executed, and the torque for canceling this change is weak with respect to the change in the engine speed ne (the rotation recovery property is weak). ). On the other hand, the β ray is a torque change characteristic when control (invention control) is performed so that the fuel injection amount Qf becomes constant, and the torque that cancels this change is strong against the change in the engine speed ne. It is a thing (strong rotation recovery).

In order to obtain a good rotational resilience such as the β ray, in the present invention, the fuel injection amount Qf per unit time is substantially constant (when the engine speed is substantially constant, the rate of change of the engine speed is almost constant). In a constant case, the rate of change of both fuel injections Qf is almost constant), and the degree of follow-up for changes in the intake air amount is lower than the degree of follow-up in the case of acceleration or the like. That is, by controlling the fuel injection amount Qf per unit time to be constant, the output becomes approximately constant, so that the torque increases when the rotational speed decreases, and the torque increases when the rotational speed increases. It becomes low, and the recoverability to the constant rotational speed becomes high. Such a characteristic that enhances the rotational resilience acts in real time, and thus is not affected by disturbance factors such as the volume of the intake system and the introduction of EGR gas into the intake system. Note that the control (expected control) so that the average fuel injection amount Qf is constant controls the fuel injection amount in inverse proportion to the engine speed.

FIG. 4 is a time chart showing the control of the present invention during steady operation in which the vehicle speed of the vehicle is substantially constant, as compared with the conventional case. The solid line shows the time when the control of the present invention is executed, and the average fuel Each of the injection amount Qf, the fuel injection amount for each cycle, and the rotational restoring force is shown by a conventional broken line. In the steady operation state, the air-fuel ratio is changed above and below the stoichiometric air-fuel ratio, and the average air-fuel ratio obtained by averaging the fluctuating air-fuel ratio becomes the stoichiometric air-fuel ratio.

In FIG. 4, since the vehicle speed is in a steady operation state where the vehicle speed is substantially constant, the vehicle speed Vs is substantially constant and the throttle opening TVO is also substantially constant. The engine speed ne causes a rotational fluctuation, and the filling amount ce at this time has a phase delay. Therefore, in the conventional system that determines the fuel injection amount based on the filling amount ce, as shown by the broken line, the fuel injection amount is adjusted based on the filling amount ce having a phase delay. Even when the number starts to decrease from a predetermined constant rotational speed, the fuel injection amount is continuously reduced because the filling amount is reduced, and the rotational resilience is low (bad, weak). End up. In other words, increasing the follow-up degree with respect to the change in the intake air amount means following the change in the filling amount. Restorability will be low.

In the control according to the present invention, in the steady operation state where the vehicle speed is substantially constant, the degree of follow-up of the change in the fuel injection amount with respect to the change in the filling amount ce is weakened by making the average fuel injection amount constant. More specifically, the fuel injection amount is changed following a change in the engine speed that does not substantially cause a phase delay. In a steady operation state where the engine speed changes at a substantially constant change rate, the change rate of the fuel injection amount per unit time is made substantially constant. Thereby, the same effect can be acquired by weakening the followable | trackability with respect to the change of filling amount.

Next, a specific control example of the present invention by the above-described controller U will be described with reference to a flowchart shown in FIG. 5 and a time chart shown in FIG. First, in Q1 of FIG. 5, it is determined whether or not a steady operation state is present. In Q1, for example, the condition that the amount of change in the throttle opening TVO is within a predetermined value (for example, ± 2%) and the amount of change in the vehicle speed Vs is within a predetermined value (for example, ± 1 km / h). When both are satisfied, it is determined that the vehicle is in a steady operation state. If NO is determined in Q1 or YES is determined in Q1 and the control of Q3 to Q11, which will be described later, is being executed and the steady operation state is not achieved, the process proceeds to Q12, which will be described later. (Determination of whether or not it is in a steady operation state is executed at predetermined timings by separate interrupt processing).

When the determination in Q1 is YES, the process proceeds to Q2, and control for making the fuel injection amount Qf per unit time constant (to make it constant) is started. Symbols or subscripts used in the following description have the following meanings.
“Δt” is a processing time interval, for example, 1 to 2 seconds.
“Qf” is the fuel injection amount per processing time Δt.
“A” is a correction constant of Qf for correcting the air-fuel ratio (inclination of increase or decrease).
“T” is the current time.
“End” is a subscript and indicates a value at the end of control.
“−1” is a subscript and indicates the value of the previous processing result.
“Tend-1” is the next processing start time and the end time of the previous control.
“Tsta” is the start time of each processing section.
“Qfo” indicates Qf at the start of processing.
“Ma” indicates an integrated value of the intake air amount.
“Mf” indicates an integrated value of the fuel injection amount.
“Ce” is the filling amount.
“Ne” is the engine speed.

On the premise of the above, an initial value is set in Q2. The initial value to be set is set as the section average fuel injection amount immediately before “Qfend”, which is the control target value in the current process, is determined to be in the steady operation state. The control constant “a” is set to zero. The processing time is set to “tend-1” (the current time is “t”).

After Q2, in Q3, “tend”, which is the current control end time, is set by adding “Δt” to the processing start time disclosure “tend-1”. Further, the initial value “Qfo” of the fuel injection amount is set as “Qfend”, the integrated air amount “Ma” is set to 0, and the integrated fuel injection amount “Mf” is set to 0.

After Q3, in Q4, the control fuel injection amount “Qf” is determined by adding a · (t−tstar) to the initial value “Qfo” (the initial value of “a” is set to 0) Therefore, there is no increase or decrease in the control fuel injection amount). The determined fuel injection amount “Qf” is injected from the fuel injection valve 25.

After Q4, in Q5, the accumulated air amount “Ma” and the accumulated fuel injection amount “Mf” are updated based on the formula shown in Q5. In the equation, “Ma” and “Mf” on the right side are the previous values, “ρ” is a unit mass, “Evol” indicates the in-cylinder volume (displacement), and “AFR” indicates the air-fuel ratio.

After Q5, at Q6, it is determined whether or not the current time “t” is greater than the end time “tend”. If NO in Q6, the current process interval time “Δt” has not elapsed, and the process returns to Q4. The setting of the control fuel injection amount in Q4 and Q5 and the update of “Ma” and “Mf” are executed for each combustion cycle.

When the determination in Q6 is YES, the end time “tend” is set (updated) to the current time “t”, and the final fuel injection amount Qfend is set to the current fuel injection amount “Qf” ( Updated).

After Q7, it is determined in Q8 whether or not the average air-fuel ratio obtained by dividing the cumulative intake air amount “Ma” by the cumulative fuel injection amount “Mf” is larger than the theoretical air-fuel ratio. If the determination in Q8 is YES, since the current position is on the lean side, the control constant “a” is set in Q9 as described later so that the rich direction is set. If NO in Q8, the control constant “a” is set as described later so as to be in the lean direction because it is currently on the rich side. Then, after Q9 or Q10, the control constant “a” is updated in Q11, and then the process proceeds to Q3 (control for the next processing period Δt is started).

The setting of the control constant “a” in Q9 is performed as follows, for example. In the following description, each symbol has the following meaning.
“AFRob” is the target air-fuel ratio, which in the embodiment is the theoretical air-fuel ratio (14.7).
“AFRoblr” is a target value at the time of lean to rich control (corresponding to Q9), and is an air-fuel ratio richer by, for example, “0.15” than the theoretical air-fuel ratio.
“AFRobrl” is a target value during rich to lean control (corresponding to Q10), and is an air-fuel ratio that is leaner by, for example, “0.15” than the theoretical air-fuel ratio.

Here, the theoretically required integrated fuel injection amount to be injected to obtain the target air-fuel ratio (theoretical air-fuel ratio) in the previous control (control during the period of “Δt”) is “Ma / AFRob”. The integrated injection amount actually injected is “Ma / AFRav” (“AFRav” is the calculated actual average air-fuel ratio). Therefore, the excess / deficiency amount ΔMf of the integrated fuel injection amount generated by the previous control is expressed by the following equation (1).

Formula (1)
ΔMf = Ma / AFRav−Ma / AFRob

Next, when the subscript “est” is shown as meaning the final predicted value in the next control period, the expected fuel amount is calculated when the predicted value of the intake air amount is “Maest” Further, when the control from lean to rich is performed (corresponding to Q9) as an example, the following equation (2) is obtained. Note that the predicted value “Maest” is set based on a change value before and after the previous processing time Δt.

Formula (2)
Required fuel amount = Maest / AFRoblr-ΔMf

On the other hand, the total fuel amount flowing from “Qfend” to “Qfend + a · Δt” (total fuel amount in the next processing period Δt) is expressed by the following equation (3).

Formula (3)
Total fuel amount = (Qfend + Qfend + a · Δt) · Δt / 2

In order for the total fuel amount to coincide with the required fuel amount, it is necessary to satisfy the following equation (4).

Formula (4)
Maest / AFRoblr−ΔMf = (Qfend + Qfend + a · Δt) · Δt / 2

From the above equation (4), the control constant “a” is expressed by the following equation (5).

Formula (5)
a = (Maest / AFRoblr−ΔMf−Qfend · Δt) · 2 // (Δt · Δt)

Formula (5) is transformed into Formula (6) below using Formula (2).

Formula (6)
a = (Maest / AFRoblr−Ma / AFRav + Ma / AFRob−Qfend · Δt) 2 / (Δt · Δt)

At the time of control from rich to lean in Q10, “AFRoblr” may be used in place of “AFRoblr” in the above equations.

In Q12, normal fuel injection amount control is executed. That is, for example, during acceleration that is not in a steady operation state, the fuel injection amount is determined based on the detected intake air amount (execution of fuel injection control with a high degree of follow-up against changes in the intake air amount). After Q12, the process returns to Q1.

As is clear from the above description, the processing for updating the control constant “a” in Q8 to Q11 is for air-fuel ratio feedback control based on the air-fuel ratio sensor S4. The process is performed after the process of Q6 is repeated a plurality of times (every process time Δt has elapsed). That is, the fuel injection amount control cycle is made larger than the air-fuel ratio control cycle, which is a control in which the vibration frequency of the air-fuel ratio sensor S4 is lower (smaller) than the vibration frequency of the intake air amount. As a result, fine control of the fuel injection amount can be performed while setting the average air-fuel ratio to the target air-fuel ratio. Moreover, this frequency becomes a frequency (for example, 1 Hz) lower than the resonance frequency (5-6 Hz) of the vehicle vibration system, and it is possible to completely eliminate the promotion of vehicle vibration.

Although the embodiments have been described above, the present invention is not limited to the embodiments, and appropriate modifications can be made within the scope of the claims. For example, in the steady operation state, the target air-fuel ratio is slightly changed between rich and lean with respect to the theoretical air-fuel ratio, but the target air-fuel ratio may be set to a constant value. The fuel used is not limited to gasoline, and any suitable fuel such as fuel in which gasoline is mixed with ethanol (including 100% ethanol fuel) can be used. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

The system diagram which shows an example of the engine to which this invention was applied. The block diagram which shows the example of a control system by this invention. Explanatory drawing which shows that a rotational restoring force is increased. The time chart which shows that a rotational restoring force is increased. The flowchart which shows the example of control of this invention. 6 is a time chart corresponding to the control example of FIG.

E: Engine 4: Combustion chamber 5: Spark plug 10: Intake port 11: Exhaust port 12: Intake valve 13: Exhaust valve 20: Intake passage 24: Throttle valve 25: Fuel injection valve 30: Exhaust passage 31: Exhaust gas purification catalyst S1: Sensor (throttle opening)
S2: Sensor (vehicle speed)
S3: Sensor (engine speed)
S4: Sensor (exhaust air / fuel ratio)
S5: Sensor (intake air amount)

Claims (6)

A method for controlling fuel supply of an internal combustion engine in which a throttle valve for adjusting an intake air amount is disposed in an intake passage of an engine and an amount of fuel corresponding to the intake air amount is supplied.
A first step of detecting an intake air amount of the engine;
A second step of detecting a change in the required output;
In the first operating state in which the change in the required output detected in the second step is equal to or greater than a predetermined value, the amount of follow-up with the first follow-up degree with respect to the change in the intake air amount detected in the first step A third step of supplying fuel;
In the second operating state in which the change in the required output detected in the second step is less than the predetermined value, the change in the intake air amount detected in the first step is more than the first following degree. A fourth step of supplying an amount of fuel that follows with a small second following degree;
Bei to give a,
In the fourth step, the fuel supply amount per unit time is made constant even when the engine speed changes in the steady state where the throttle opening is constant in the second operating state.
A method for controlling the fuel supply of an internal combustion engine. In claim 1,
A method for controlling fuel supply of an internal combustion engine, wherein the fuel supply amount per unit time is substantially constant in the second operating state. In claim 2,
A method for controlling fuel supply of an internal combustion engine, characterized in that, in the second operating state, when the engine speed decreases, the fuel supply amount for each cylinder cycle is increased. In any one of Claims 1 thru | or 3,
A method for controlling fuel supply of an internal combustion engine, characterized in that, in the second operating state, the average air-fuel ratio is substantially the stoichiometric air-fuel ratio. In claim 4,
A fifth step of detecting the exhaust air-fuel ratio;
A sixth step of feedback-controlling the fuel supply amount so that the exhaust air-fuel ratio detected in the fifth step becomes the stoichiometric air-fuel ratio;
Further comprising
A method for controlling fuel supply of an internal combustion engine, wherein an oscillation frequency of the exhaust air-fuel ratio is lower than an oscillation frequency of an intake air amount. A system for controlling the fuel supply of an internal combustion engine in which a throttle valve for adjusting the amount of intake air is disposed in an intake passage of the engine, and an amount of fuel corresponding to the amount of intake air is supplied.
Intake air amount detection means for detecting the intake air amount of the engine;
An output change detecting means for detecting a change in the required output;
In a first operating state in which the change in the required output detected by the output change detection means is equal to or greater than a predetermined value, the change in the intake air amount detected by the intake air amount detection means follows with a first follow-up degree. First fuel supply control means for supplying an amount of fuel;
In the second operating state in which the change in the required output detected by the first output change detection unit is less than the predetermined value, the first output is changed with respect to the change in the intake air amount detected by the intake air amount detection unit. A second fuel supply control means for supplying an amount of fuel to follow with a second follow-up degree smaller than the follow-up degree;
Bei to give a,
Further, the second fuel supply means is configured so that the fuel supply amount per unit time becomes constant even when the engine speed changes in the steady state where the throttle opening is constant in the second operating state. To control,
System for controlling the fuel supply of an internal combustion engine, wherein a call.

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