JPH0649737U - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] According to the switching between the lean air-fuel ratio operating region and the output air-fuel ratio operating region, the swirl control valve is opened / closed, or the fuel injection timing is changed. Suppress fluctuations in fuel ratio. Constitution: When the SCV 13 is opened / closed or the fuel injection timing is switched between early injection and intake synchronous injection in accordance with the switching of the target air-fuel ratio map according to the engine operating state, at the same time as the opening / closing of the SCV 13 is switched. Since the fuel injection amount is increased / decreased or corrected, or the fuel injection timing is gradually changed, it is possible to suppress a temporary change in the air-fuel ratio due to a change in the wall-flow fuel.
Therefore, it is possible to suppress the fluctuation of the in-cylinder pressure, the fluctuation of the engine output, the fuel consumption, and the deterioration of the exhaust gas harmful components.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an air-fuel ratio control device for an internal combustion engine. Specifically, the target air-fuel ratio is switched between a lean air-fuel ratio that is thinner than the stoichiometric air-fuel ratio and an output air-fuel ratio that is richer than the theoretical air-fuel ratio according to the engine operating conditions, and the swirl control valve is opened or closed accordingly. The present invention relates to an air-fuel ratio control device for an internal combustion engine, which suppresses a substantial fluctuation of the air-fuel ratio that occurs due to a difference in the amount of fuel deposited on the inner wall of the intake port when the fuel injection timing is switched.

[0002]

[Prior art]

 In recent years, a lean burn engine (lean burn engine) has been proposed in which combustion is performed at an air-fuel ratio (for example, 20 to 25) that is much larger than the theoretical air-fuel ratio for the purpose of improving fuel efficiency. In such a lean-burn engine, for example, when operating at low speed and low load, combustion is performed at the lean air-fuel ratio to improve fuel efficiency, reduce exhaust harmful substances, and improve output performance during acceleration and high load. By focusing on and switching to the air-fuel ratio (output air-fuel ratio) slightly smaller than the theoretical air-fuel ratio (rich side), we are aiming to improve fuel efficiency, reduce exhaust harmful substances and secure output performance.

On the other hand, a swirl control valve is provided in the intake system in order to secure the stability of ignition with respect to the air-fuel mixture of the lean air-fuel ratio and further activate the combustion. The swirl control is closed to generate a strong swirl in the cylinder to form an air-fuel mixture suitable for ignition near the spark plug, and to accelerate the flow of the air-fuel mixture to accelerate the flame propagation speed and activate combustion. In some cases, the lean burn was optimized. With this type, the intake air amount is large at high rotation speeds and high loads where combustion is performed at the output air-fuel ratio, and when the swirl control valve is closed, the intake resistance itself becomes large, and the resistance due to swirl also becomes large. The whirl control valve is opened to increase the suction efficiency and obtain the desired engine output.

[0004]

[Problems to be solved by the device]

 As described above, in the past, the swirl control valve was closed in the lean air-fuel ratio region and the swirl control valve was opened in the output air-fuel ratio region. Due to the difference in the amount of fuel (hereinafter referred to as wall-flow fuel) adhering to the inner wall of the intake system, such as air flow, the substance of the air-fuel mixture that flows into the cylinder when the swirl control valve is opened and closed is changed. The air-fuel ratio was fluctuating. In detail, when the swirl control valve is closed, the flow passage of the air-fuel mixture is increased because the passage area is narrowed, so that the mixture of fuel spray and air is activated, resulting in atomization of fuel spray and fog. As a result, the amount of wall-flow fuel formed as a result of the liquid fuel adhering to the inner wall of the intake system is small. On the contrary, when the swirl control valve is open, the passage area becomes large and the flow velocity of the air-fuel mixture becomes small.Therefore, each effect cannot be expected, and fuel in liquid form adheres to the inner wall of the intake system. As a result, the rate of fuel consumption increased and the amount of wall-flow fuel increased.

Therefore, as shown by the dotted line in FIG. 6, when the swirl control valve is switched from the closed state to the open state, a part of the injected fuel becomes wall-flow fuel and flows into the combustion chamber. As a result, the actual air-fuel ratio temporarily fluctuates toward the lean side. On the contrary, when the swirl control valve is switched from the open state to the open state, the wall flow fuel evaporates and is added to the injected fuel, so that the substantial air-fuel ratio is temporarily increased to the rich side. It was supposed to fluctuate.

As another example, in the lean air-fuel ratio region, intake synchronous injection that starts fuel injection within the opening period of the intake valve (injection end is set to about ATDC140deg) is performed, and in the output air-fuel ratio region, intake air injection is performed. In order to improve the ignition limit in the lean burn region, the fuel injection timing is switched to a large value so that the normal early injection is started before the valve is opened (the end of injection is set to about BTDC number deg). Some have been done. That is, in the case of early injection, the fuel injected before opening the intake valve receives heat in the intake port and is atomized. A mixture having a uniform concentration is easily formed. In this case, in the lean air-fuel ratio region, the air-fuel ratio near the spark plug, which is important for ignitability, becomes too lean, and the misfire limit is lowered. On the other hand, in the output air-fuel ratio region, the air-fuel ratio is relatively small and there is no problem in ignitability, so it is possible to effectively improve combustion by promoting mixing. Therefore, in the lean air-fuel ratio region, the fuel injection timing is switched to the intake synchronous injection to suppress atomization in the intake port and to supply a stratified mixture near the ignition plug that is easy to ignite. is there.

Even in such a case, as shown by the dotted line in FIG. 7, when the fuel injection timing is switched, the air-fuel ratio temporarily fluctuates due to the difference in the wall-flow fuel amount. That is, in the early injection, the atomization time is long in the intake port, so the atomization is promoted and the wall flow fuel amount is reduced. Conversely, in the intake synchronous injection, the fuel is atomized in the intake port. Since the time is short, the wall flow fuel amount is large.

[0008] The fluctuation of the air-fuel ratio as described above causes the fluctuation of the in-cylinder combustion pressure, which causes the fluctuation of the engine output, and further the deterioration of the fuel consumption and the exhaust harmful components. The present invention has been made in view of the above-mentioned problems, and switches the swirl control valve between open and close or sets the fuel injection timing according to the switching between the lean air-fuel ratio operating region and the output air-fuel ratio operating region. The purpose is to suppress the fluctuation of the air-fuel ratio due to the wall-flow fuel difference that occurs at the time, and to suppress the fluctuation of the engine output and further the deterioration of fuel consumption and emission harmful components.

[0009]

[Means for Solving the Problems]

 Therefore, the air-fuel ratio control device according to the first aspect of the present invention, as shown in FIG. 1, has a lean air-fuel ratio range in which the target air-fuel ratio is thinner than the stoichiometric air-fuel ratio, depending on the engine operating conditions. A target air-fuel ratio setting means A for switching and setting to a rich air-fuel ratio range, a swirl control valve installed in the engine intake system for controlling swirl generation in the cylinder, and the lean air-fuel ratio range according to the switching of the air-fuel ratio. In the case of, the swirl control valve is closed to strengthen the swirl, and the swirl control valve opening / closing control means B for controlling to open the swirl control valve in a denser air-fuel ratio range, and the air-fuel ratio control of the internal combustion engine. In the system, air-fuel generated due to the difference in the amount of fuel adhering to the inner wall of the intake port when the swirl control valve is opened or closed. And configure variations include fuel injection amount increase and decrease correction unit C to increase or decrease correcting the fuel injection amount to correct.

In the air-fuel ratio control device according to the second aspect of the present invention, as shown in FIG. 2, the target air-fuel ratio is set to a lean air-fuel ratio region thinner than the stoichiometric air-fuel ratio and an air-fuel ratio region richer than the theoretical air-fuel ratio according to the engine operating conditions. In an air-fuel ratio control device for an internal combustion engine, which includes a target air-fuel ratio setting means A for switching between and setting fuel injection timing setting means D for switching and setting fuel injection timing according to switching of the air-fuel ratio, and the fuel A fuel injection timing switching control unit E for gradually switching the fuel injection timing so as to correct the fluctuation of the air-fuel ratio caused by the difference in the amount of fuel adhering to the inner wall of the intake port when switching the injection timing. did.

[0011]

[Action]

 According to the configuration of the invention described in claim 1, when the target air-fuel ratio is switched between the lean air-fuel ratio region thinner than the stoichiometric air-fuel ratio and the air-fuel ratio region richer than the theoretical air-fuel ratio according to the engine operating conditions, It is possible to suppress the fluctuation of the air-fuel ratio due to the wall flow fuel difference in the intake port, which is caused by the opening / closing switching of the swirl control valve according to the switching of the air-fuel ratio.

According to the configuration of the invention as set forth in claim 2, the target air-fuel ratio is switched between the lean air-fuel ratio region thinner than the stoichiometric air-fuel ratio and the air-fuel ratio region richer than the theoretical air-fuel ratio according to the engine operating conditions. In this case, it is possible to suppress the fluctuation of the air-fuel ratio due to the wall flow fuel difference in the intake port caused by the setting change of the fuel injection timing according to the change of the air-fuel ratio.

[0013]

【Example】

 An embodiment of the present invention will be described below. In FIG. 3 showing the first embodiment, air is taken into the internal combustion engine 1 via a throttle valve 2, an intake manifold 3 and an intake valve 4. At each branch portion of the intake manifold 3, a fuel injection valve 5 is provided for each cylinder. The fuel injection valve 5 is an electromagnetic fuel injection valve which is energized by a built-in solenoid to open the valve and which is deenergized and closed, and energized by an injection pulse signal from a control unit 30 described later. The fuel is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator. The fuel is intermittently injected and supplied to the engine 1.

An ignition plug 6 is provided in each combustion chamber of the internal combustion engine 1 to ignite sparks to burn the air-fuel mixture. Then, the exhaust gas is discharged from the engine 1 through the exhaust valve 7, the exhaust manifold 8a, the exhaust pipe 8b, and the catalyst 9. Further, in the engine 1 of the present embodiment, a swirl control valve (hereinafter referred to as SCV) 13 is provided in the middle of the intake manifold 3. The SCV 13 is a butterfly-type throttle valve having a notch portion, and when the SCV 13 is closed to reduce the passage area, a high-velocity flow is generated to generate a strong swirl in the cylinder. As a result, it is possible to improve the ignitability and the flame propagation speed during lean combustion.

A diaphragm 14 is provided as an actuator that drives the SCV 13 to open and close. By controlling the introduction of the engine intake negative pressure into the pressure chamber of the diaphragm 14 by an electromagnetic three-way switching valve 15. Can open and close SCV13. A signal is sent from the control unit 30 to the three-way switching valve 15 so that the opening / closing control is performed according to switching between a lean air-fuel ratio region and an output air-fuel ratio region, which will be described later. Note that a motor may be used as an actuator that drives the SCV 13 to open and close.

By the way, the control unit 30 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input interface, and the like, receives output signals from various sensors, and will be described later. Thus, the fuel injection amount Ti by the fuel injection valve 5 is calculated, and the operation of the fuel injection valve 5 is controlled based on the fuel injection amount Ti. As the various sensors, an air flow meter 10 for detecting the intake air flow rate Q of the engine, a crank angle sensor 11 for extracting a rotation signal from a crankshaft, etc., and an empty space of the engine intake air-fuel mixture via the oxygen sensor concentration in the exhaust gas are used. An oxygen sensor 12 and the like for detecting the fuel ratio are provided.

The engine rotation speed Ne is calculated by measuring the period of the detection signal output from the crank angle sensor 11 for each predetermined crank angle or the number of detection signals generated within a predetermined time. Here, the CPU of the microcomputer incorporated in the control unit 30 has an air-fuel ratio map in which a target air-fuel ratio is set in advance according to the engine load represented by the basic fuel injection amount Tp and the engine rotation speed Ne. , The basic fuel injection amount Tp (= K × Q / Ne; K) based on the detected values of the intake air flow rate Q and the engine speed Ne in order to form the air-fuel mixture of the target air-fuel ratio stored in this air-fuel ratio map. Is calculated, and the final fuel injection amount Ti is calculated by applying various corrections (including air-fuel ratio feedback control using the oxygen sensor 12) to the basic fuel injection amount Tp according to engine operating conditions. . Then, an injection pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to each fuel injection valve 5 in synchronization with the intake stroke of each cylinder.

In the air-fuel ratio map, a lean air-fuel ratio (for example, 20 to 25) which is much larger than the theoretical air-fuel ratio (14.7) is set as the target air-fuel ratio in the low rotation speed and low load operation region. In the high rotation and high load operation regions other than the lean air-fuel ratio region, the theoretical air-fuel ratio or an output air-fuel ratio slightly smaller than the theoretical air-fuel ratio (for example, about 13) is set as the target air-fuel ratio. ing. Such a configuration corresponds to the target air-fuel ratio setting means.

By the way, the CPU of the microcomputer incorporated in the control unit 30 has an SCV opening / closing function which is set in advance to open / close the SCV according to the engine load represented by the basic fuel injection amount Tp and the engine speed Ne. A control map is set, and by referring to the SCV opening / closing control map, a signal is sent to the three-way switching valve 15 to open / close the SCV 13. That is, the SCV 13 is closed in the lean air-fuel ratio operation region, and the SCV 13 is opened in the output air-fuel ratio operation region. Such a configuration corresponds to the swirl control valve opening / closing control means.

Then, in order to prevent a change in the wall-flow fuel and a temporary change in the substantial air-fuel ratio due to the switching of the opening / closing of the SCV 13, the fuel injection amount Ti is changed by the change amount. Adjust to increase or decrease. For example, the SCV opening / closing correction coefficient S (= basic correction value × Ne correction value × load correction value × water temperature) is set based on each correction value that is preset and stored according to the engine operating state and the opening / closing switching direction of the SCV 13. (Correction value) is obtained, and the fuel injection amount Ti is increased / decreased to a corrected fuel injection amount Ti ′ (= Ti × S) for a predetermined time immediately after switching the opening / closing of the SCV 13. The predetermined time may be a certain fixed value, or may be set according to the driving condition or the like.

Here, the fuel injection amount increase / decrease correction control performed by the control unit 30 will be described based on the flowchart shown in FIG. Such control constitutes a fuel injection amount increase / decrease correction means. In step 1 (indicated as S1 in the figure; the same applies hereinafter), signals from various sensors are read by the control unit 30 to determine the basic fuel injection amount Tp, the engine speed Ne, and the like.

In step 2, based on the basic fuel injection amount Tp, the engine rotation speed Ne, etc., the SCV opening / closing control map stored in advance in the control unit 30 is referred to and whether or not the opening / closing switching condition of the SCV 13 is satisfied. To judge. If the opening / closing switching condition of the SCV 13 is satisfied, the process proceeds to step 3, and if the opening / closing switching condition of the SCV 13 is not satisfied, this flow ends.

In step 3, since the opening / closing switching condition of the SCV 13 is satisfied, the opening / closing switching of the SCV 13 is executed. Therefore, in order to suppress the air-fuel ratio variation due to the change in the wall flow fuel accompanying this, the fuel injection amount Ti is set to It needs to be corrected. Here, as described above, the SCV opening / closing correction coefficient S (= basic correction rate × Ne correction × load correction × water temperature correction) is obtained according to the opening / closing switching direction of the SCV 13, and the corrected fuel injection amount Ti ′ (= Ti × S) Ask for.

In step 4, a signal having a pulse width corresponding to the corrected fuel injection amount Ti ′ obtained in step 3 is sent to the fuel injection valve 5, and the increase / decrease correction is performed so that the substantial air-fuel ratio becomes the target air-fuel ratio. The injected fuel amount is injected and supplied to the engine. In step 5, it is determined whether or not the correction of the fuel injection amount has been performed for a predetermined time, and the correction of the fuel injection amount is continued before the predetermined time has elapsed, and after the predetermined time has elapsed, the present flow is executed. finish.

After that, the control returns to the normal air-fuel ratio control, and the fuel injection amount Ti according to the target air-fuel ratio is injected and supplied. According to the present embodiment, in the case where the SCV 13 is opened / closed in accordance with the switching between the lean air-fuel ratio operating region and the output air-fuel ratio operating region, the fuel injection amount is increased / decreased at the same time as the opening / closing switching. Therefore, it is possible to suppress a temporary change in the air-fuel ratio that accompanies a change in the wall flow fuel caused by the switching between the open and close states, and to suppress a change in the engine output, and further a deterioration in fuel consumption and harmful emission components.

Next, a second embodiment will be described. The second embodiment differs from the first embodiment shown in FIG. 3 in that the SCV 13 and the three-way switching valve 15 are not provided. Further, the SCV opening / closing control map of the first embodiment is not provided, and instead, the fuel injection timing setting map is provided in the second embodiment.

The fuel injection timing setting map is set and stored in the CPU of the microcomputer incorporated in the control unit 30, and the map is set in advance according to the engine load represented by the basic fuel injection amount Tp and the engine rotation speed Ne. In other words, the fuel injection timing is set so that the fuel injection timing is switched greatly according to the switching between the lean air-fuel ratio operation region and the output air-fuel ratio operation region. That is, as described above, the fuel injection timing is set so that the intake air synchronous injection is performed in the lean air-fuel ratio operation region, and the fuel injection timing is set such that the early injection is performed in the output air-fuel ratio operation region. Such a configuration corresponds to the fuel injection timing setting means.

Then, in order to prevent a change in the wall-flow fuel and a temporary change in the substantial air-fuel ratio when the setting of the fuel injection timing is changed, the change of the fuel injection timing is performed. It is done gradually. Other configurations are similar to those of the first embodiment, and detailed description thereof will be omitted. Here, the fuel injection timing switching control performed by the control unit 30 in the second embodiment will be described based on the flowchart shown in FIG. Such control constitutes fuel injection timing switching control means.

In step 11, signals from various sensors are read by the control unit 30, and the basic fuel injection amount Tp, the engine rotation speed Ne, etc. are obtained. In step 12, based on the basic fuel injection amount Tp, the engine rotation speed Ne, etc., the fuel injection timing setting map stored in advance in the control unit 30 is referred to and whether or not the fuel injection timing switching condition is satisfied is determined. to decide. If the switching condition is satisfied, the process proceeds to step 13, and if the switching condition is not satisfied, this flow is ended.

In step 13, it is necessary to switch the current fuel injection timing to the target fuel injection timing when the condition for switching the fuel injection timing is satisfied. Here, the change in the wall flow fuel due to the abrupt switching is performed. In consideration of the above, gradually switch over every X times. In this case, the switching is preferably performed within a predetermined time, but the above-mentioned predetermined time may be a certain fixed value or may be set according to the operating state and the like.

In step 14, it is determined whether or not the current fuel injection timing has reached the target fuel injection timing. If the target fuel injection timing has not come, the process returns to step 13 and the fuel injection timing is gradually changed. When the target fuel injection timing is reached, this flow is ended and normal air-fuel ratio control is performed.

According to the second embodiment, in the case where the fuel injection timing is largely switched according to the switching between the lean air-fuel ratio operating region and the output air-fuel ratio operating region, the switching of the fuel injection timing is gradually performed. Since this is done, it is possible to suppress temporary fluctuations in the air-fuel ratio due to changes in the wall-flow fuel that occur due to abrupt switching of the fuel injection timing, and it is possible to suppress fluctuations in engine output, fuel consumption, and harmful emission components. Deterioration can be suppressed.

In the present embodiment, the fuel injection timing is gradually changed to suppress the change in the wall flow fuel and prevent the air-fuel ratio from changing. Of course, the fuel injection amount may be increased or decreased when the fuel injection timing is switched, as in the embodiment. Further, when switching between the lean air-fuel ratio operating region and the output air-fuel ratio operating region, the first and second embodiments are also applied to the case where the SCV is opened and closed and the fuel injection timing is switched. Of course, it is also possible to suppress variations in the air-fuel ratio by appropriately combining the first embodiment and the second embodiment.

[0034]

As described above, according to the invention as set forth in claim 1, when the swirl control valve is opened and closed according to the switching between the lean air-fuel ratio operation region and the output air-fuel ratio operation region. In addition, since the fuel injection is increased / decreased at the same time as the opening / closing switching, it is possible to suppress the temporary change in the air-fuel ratio due to the change in the wall flow fuel caused by the opening / closing switching, and the fluctuation in the engine output, Further, it is possible to suppress deterioration of fuel efficiency and harmful components of exhaust gas.

According to the second aspect of the invention, when the fuel injection timing is switched in response to the switching between the lean air-fuel ratio operation region and the output air-fuel ratio operation region, the fuel injection timing is gradually switched. As a result, it is possible to suppress temporary fluctuations in the air-fuel ratio due to changes in the wall-flow fuel that occur due to abrupt switching of the fuel injection timing, and to fluctuate engine output, as well as fuel consumption and harmful emission components. Can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment according to the present invention.

FIG. 2 is a block diagram showing a second embodiment according to the present invention.

FIG. 3 is an overall configuration diagram of a first embodiment according to the present invention.

FIG. 4 is a flowchart showing a fuel injection amount increase / decrease correction control according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing a fuel injection timing temporary change control according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a change in air-fuel ratio due to switching of SCV opening / closing according to the first embodiment of the present invention.

FIG. 7 is a diagram showing fluctuations in the air-fuel ratio due to abrupt switching of fuel injection timing according to the second embodiment of the present invention.

[Explanation of symbols]

 1 Internal Combustion Engine 5 Fuel Injection Valve 10 Air Flow Meter 11 Crank Angle Sensor 13 Swirl Control Valve (SCV) 30 Control Unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 43/00 J 7536-3G U 7536-3G

Claims (2)

[Scope of utility model registration request] 1. A target air-fuel ratio setting means for switching and setting a target air-fuel ratio between a lean air-fuel ratio range thinner than a stoichiometric air-fuel ratio and an air-fuel ratio range richer than the theoretical air-fuel ratio according to engine operating conditions, and an engine intake system. And a swirl control valve for controlling swirl generation in the cylinder, and closes the swirl control valve in the lean air-fuel ratio region in response to the switching of the air-fuel ratio to strengthen the swirl, and swirl control in the richer air-fuel ratio region. In an air-fuel ratio control device for an internal combustion engine, which comprises a swirl control valve opening / closing control means for controlling the valve to open, a difference in the amount of fuel adhering to the inner wall of the intake port when switching the opening / closing of the swirl control valve. A fuel injection amount increase / decrease correction method for increasing / decreasing the fuel injection amount to correct the fluctuation of the air-fuel ratio that occurs. An air-fuel ratio control device for an internal combustion engine, characterized in that it is configured to include stages. 2. An internal combustion engine having a target air-fuel ratio setting means for switching and setting a target air-fuel ratio between a lean air-fuel ratio region thinner than a stoichiometric air-fuel ratio and an air-fuel ratio region richer than the stoichiometric air-fuel ratio in accordance with engine operating conditions. In the fuel ratio control device, fuel injection timing setting means for switching and setting the fuel injection timing according to the switching of the air-fuel ratio, and when the fuel injection timing is switched, it is caused by a difference in the amount of fuel adhering to the inner wall of the intake port. An air-fuel ratio control device for an internal combustion engine, comprising: a fuel injection timing switching control means for gradually switching the fuel injection timing to correct the fluctuation of the air-fuel ratio.