JP3608486B2 - Multi-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-cylinder internal combustion engine.
[0002]
[Prior art]
A general multi-cylinder internal combustion engine has a fuel injection valve for each cylinder, and the fuel is injected into the intake port of each cylinder by each fuel injection valve. The fuel injection valve can perform intake asynchronous injection that completes fuel injection mainly before the intake stroke and intake synchronous injection that mainly injects fuel during the intake stroke.
[0003]
In the intake asynchronous injection, the fuel adhering to the wall surface of the intake port or the like can be vaporized by the intake air flow and introduced into the cylinder, so that it is easy to form an air-fuel mixture with good ignitability in the cylinder. On the other hand, it is necessary in anticipation that a relatively large amount of fuel adheres to the intake port when the intake pipe negative pressure is low, the amount of fuel adhering to the intake port is low, and the engine temperature is low, such as when starting the engine. You have to inject fuel that is significantly larger than the volume. Intake-synchronized injection allows most of the injected fuel to be introduced into the cylinder along with the intake air flow before adhering to the intake port wall surface, etc. Even when the engine is started, fuel that greatly exceeds the required amount is not required . However, since liquid fuel is mainly introduced into the cylinder, if the engine temperature is low, fuel vaporization is insufficient and it is difficult to form an air-fuel mixture with good ignitability.
[0004]
In Japanese Patent Laid-Open No. 9-32605, at the start of engine start, all the cylinders are set as intake asynchronous injection to form a good air-fuel mixture, thereby ensuring reliable ignition combustion. Is disclosed as a multi-cylinder internal combustion engine.
[0005]
[Problems to be solved by the invention]
In intake asynchronous injection at the time of engine startup, as described above, a relatively large amount of fuel remains on the intake port wall surface and the like. As a result, reliable startability is ensured by the above-described conventional technology. However, if the engine speed rapidly increases after the start (complete explosion) is completed and the negative pressure in the intake port rapidly increases, much of the attached fuel once The fuel is evaporated and introduced into the cylinder, and the air-fuel ratio becomes excessively rich, so that a large amount of unburned fuel is discharged. When the engine is started, the catalyst device provided in the exhaust system does not function sufficiently, so that this large amount of unburned fuel is released into the atmosphere without being sufficiently purified.
[0006]
Accordingly, an object of the present invention is to provide a multi-cylinder internal combustion engine that can ensure good engine startability and reduce the amount of unburned fuel discharged when the engine is started.
[0007]
[Means for Solving the Problems]
The multi-cylinder internal combustion engine according to claim 1 of the present invention starts engine starting by supplying fuel to only some cylinders by intake asynchronous injection and performing partial cylinder operation. When a predetermined engine operation state is obtained after the explosion is completed, fuel is supplied to the cylinders excluding the some cylinders by intake synchronous injection to perform all cylinder operation.
[0008]
The multi-cylinder internal combustion engine according to claim 2 according to the present invention is the multi-cylinder internal combustion engine according to claim 1, wherein the fuel supply to the cylinders excluding the some cylinders is from intake synchronous injection to intake asynchronous injection. It is characterized by migrating.
[0009]
The multi-cylinder internal combustion engine according to claim 3 according to the present invention is the multi-cylinder internal combustion engine according to claim 2, wherein the fuel supply to the cylinders excluding the some cylinders is performed from intake synchronous injection to fuel injection timing. It is characterized by being gradually advanced and shifted to intake asynchronous injection.
[0010]
The multi-cylinder internal combustion engine according to claim 4 according to the present invention is the multi-cylinder internal combustion engine according to claim 2 or 3, wherein fuel is supplied to the cylinders excluding the partial cylinders at an engine speed of idle rotation. It is characterized by shifting from the intake synchronous injection to the intake asynchronous injection until it becomes stable.
[0011]
A multi-cylinder internal combustion engine according to claim 5 according to the present invention is the multi-cylinder internal combustion engine according to any one of claims 1 to 4, wherein the predetermined engine operation state is an operation state corresponding to completion of engine start. It is characterized by being.
[0012]
A multi-cylinder internal combustion engine according to a sixth aspect of the present invention is the multi-cylinder internal combustion engine according to any one of the first to fifth aspects, wherein the predetermined engine operation state is not achieved within a set period from the start of engine start. The all-cylinder operation is performed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic longitudinal sectional view in a cylinder of a multi-cylinder internal combustion engine according to the present invention. In the figure, reference numeral 1 denotes an ignition plug disposed substantially at the center of the cylinder upper portion, and 2 denotes a piston. Reference numeral 3 denotes an intake port that communicates with the cylinder via the intake valve 4, and reference numeral 5 denotes an exhaust port that communicates with the cylinder via the exhaust valve 6. A fuel injection valve 7 is disposed in the intake port 3 of each cylinder.
[0014]
The fuel injection valve 7 performs the intake asynchronous injection that ends the fuel injection mainly before the intake stroke in a normal engine operation state. In the intake asynchronous injection, fuel is attached to the wall surface of the intake port 3 and the umbrella back of the intake valve 4 and the attached fuel is vaporized to some extent using the engine temperature, and the intake stroke is taken into the cylinder. When a flow occurs, it is also vaporized by this intake flow, and if the pressure in the intake port 1 becomes negative in the latter half of the intake stroke, vaporization is also promoted by this negative pressure. Thus, since the vaporized fuel is introduced into the cylinder, a sufficiently homogenous mixture can be formed in the cylinder, and good combustion can be realized.
[0015]
When such an intake asynchronous injection is carried out at the time of engine start, the first injected fuel is less fuel adhering to the intake port wall surface, the engine temperature is low, and the lower half of the intake stroke when cranking is low. In addition, since the negative pressure generated in the intake port is low, most of it remains attached to the wall surface of the intake port. Therefore, a large amount of fuel must be injected in anticipation of this. However, since vaporized fuel is mainly introduced into the cylinder, an air-fuel mixture with good ignitability is formed, and reliable startability is ensured.
[0016]
On the other hand, since a relatively large amount of fuel remains on the intake port wall surface or the like, when the engine speed increases rapidly after the start (complete explosion) is completed, the negative pressure in the intake port rapidly increases. Most of the adhered fuel is evaporated at a time and introduced into the cylinder, and the air-fuel ratio of the mixture becomes excessively rich, so that a large amount of unburned fuel is discharged. When the engine is started, the catalyst device provided in the exhaust system does not function sufficiently, so that a large amount of unburned fuel is discharged to the atmosphere without being sufficiently purified.
[0017]
In this embodiment, in order to solve this problem, the engine start is started by supplying fuel to only some cylinders by intake asynchronous injection and performing the partial cylinder operation. All cylinder operation is performed by supplying fuel to the cylinders except for by intake synchronous injection.
[0018]
In order to realize a relatively smooth operation in the partial cylinder operation, it is preferable that the operated partial cylinders are half of the cylinders whose ignition order is not continuous with each other. For example, in a four-cylinder internal combustion engine having an ignition order of # 1- # 3- # 4- # 2, there are # 1 cylinder and # 4 cylinder or # 2 cylinder and # 3 cylinder.
[0019]
FIG. 2 is a time chart showing the change in engine speed when the engine start is started only by the # 1 cylinder and the # 4 cylinder and the operation of the # 2 cylinder and the # 3 cylinder is started when the engine is in a predetermined engine operation state. FIG. 3 is a time chart showing the relationship of fuel injection timings between the # 1 cylinder and the # 3 cylinder. In FIG. 3, “exhaust” indicates an exhaust stroke, and “suction” indicates an intake stroke. Although the fuel injection timings of the # 4 cylinder and # 2 cylinder are omitted, the fuel injection timing of the # 4 cylinder is the same as that of the # 1 cylinder, and the fuel injection timing of the # 2 cylinder is the same as that of the # 3 cylinder. 2 and 3 will be described below.
[0020]
Cranking is started at time T0, and then intake asynchronous injection, for example, fuel injection in the exhaust stroke, is performed on the # 1 and # 4 cylinders. The first fuel injection amount A is an amount that greatly exceeds the required amount because most of the fuel injection amount A becomes fuel adhering to the intake port or the like. The fuel injection amount B after that remains part of the fuel adhering to the intake port or the like, but can be made almost necessary since a part of the previous adhering fuel is vaporized and introduced into the cylinder. .
[0021]
By the first fuel supply to the # 1 cylinder, combustion is started in the # 1 cylinder, and the engine speed starts to increase at time T1, which is the expansion stroke of the # 1 cylinder. Thereafter, combustion is repeated with # 4 cylinder, # 1 cylinder, and # 4 cylinder, and the engine speed continues to increase and reaches N1 at time T2. This engine speed N1 is a maximum speed that can be brought about by a predetermined fuel injection amount, fuel injection timing, and ignition timing during start-up in two cylinders, and cannot be further increased in two-cylinder operation. . Thus, the start is completed.
[0022]
Until the start is completed, in the # 1 cylinder and the # 4 cylinder, a good air-fuel mixture is formed in the cylinder by the intake asynchronous injection, and a reliable startability can be ensured. When the engine speed reaches N1, fuel is supplied to the # 2 and # 3 cylinders by intake synchronous injection. In the intake synchronous injection that mainly injects fuel during the intake stroke, most of the injected fuel can be introduced into the cylinder. Therefore, the initial fuel injection amount A ′ Compared to the fuel injection amount A, it can be reduced. However, in order to bring about reliable ignition combustion compared with the subsequent fuel injection amount B, the amount is slightly increased. The fuel injection amount B is the same as the fuel injection amount excluding the first intake asynchronous injection.
[0023]
Thus, the combustion in the # 3 cylinder is started, and the engine speed starts to increase from N1 at time T3 when the expansion stroke of the # 3 cylinder is reached. Thereafter, combustion is repeated with # 4 cylinder of intake asynchronous injection, # 2 cylinder of intake synchronous injection, and # 1 cylinder of intake asynchronous injection, and the engine speed is the maximum speed at the time of start in the two-cylinder operation at time T4. Similar to N1, the maximum rotational speed N2 in all-cylinder operation is reached.
[0024]
Immediately before reaching the maximum engine speed N2, the negative pressure in the intake port in the latter half of the intake stroke becomes very high. Since the adhering fuel is evaporated and introduced into the cylinder at one time, the combustion air-fuel ratio becomes excessively rich and a relatively large amount of unburned fuel is discharged. Since the fuel adhering to the wall surface is vaporized by the rise of the intake negative pressure even during time T2, the discharge of the unburned fuel is reduced as compared with the conventional case. Further, in the # 2 cylinder and the # 3 cylinder, the amount of fuel adhering to the intake port wall surface and the like by the intake synchronous injection is small, and thus the fuel air-fuel ratio does not become excessively rich, and unburned fuel The amount of discharge is small.
[0025]
In intake synchronous injection, when the engine temperature is low and the negative pressure in the intake port is low, such as when the engine is started, liquid fuel is mainly introduced into the cylinder. Fuel vaporization is insufficient and it is difficult to reliably ignite and burn. If misfire occurs, a large amount of unburned fuel is discharged. In this embodiment, in the # 2 cylinder and the # 3 cylinder, combustion is started by intake synchronous injection. At this time, the start is completed by the # 1 cylinder and the # 4 cylinder, and the intake air is increased as the engine speed increases. Since the negative pressure in the port is increased to some extent, the fuel vaporization state can be made relatively good, and reliable ignition combustion of the air-fuel mixture can be realized.
[0026]
Thus, according to the present embodiment, a relatively large amount of unburned fuel is discharged at time T4 from only the # 1 and # 3 cylinders that start combustion by intake air asynchronous injection. Compared to the case where a relatively large amount of unburned fuel is discharged, the amount of unburned fuel discharged can be sufficiently reduced. Further, as described above, good engine startability can be ensured.
[0027]
After reaching the maximum speed N2 at time T4, the fuel injection timing is gradually advanced in the # 2 and # 3 cylinders that have been performing the intake synchronous injection so far, and the fuel injection is started during the exhaust stroke. Thus, the fuel injection is terminated during the intake stroke. The fuel injected during the exhaust stroke adheres to the intake port wall surface, etc., but at this time, the engine temperature also rises, and the negative pressure in the intake port in the latter half of the intake stroke is high, so the adhering fuel is The fuel is vaporized well and introduced into the cylinder, and the fuel injected during the intake stroke is also easily vaporized by this negative pressure, and such fuel injection forms a relatively good mixture in the cylinder. be able to.
[0028]
The engine speed reaches the maximum engine speed N2 by the first amount of fuel increased in each cylinder, but thereafter gradually decreases and stabilizes at the idle engine speed N3 at time T5. The fuel injection of the # 2 cylinder and the # 3 cylinder is a complete intake asynchronous injection similar to the # 1 cylinder and the # 4 cylinder after the time T5. As described above, the intake asynchronous injection can achieve a good combustion because the fuel vaporization state of the air-fuel mixture becomes better than that of the intake synchronous injection. In the # 2 cylinder and the # 3 cylinder, by gradually advancing the fuel injection timing and shifting from intake synchronous injection to intake asynchronous injection, it is possible to gradually improve the combustion and realize an operation without a sense of incongruity. When the engine speed is stabilized at idle rotation, all cylinder operation is performed by intake asynchronous injection, and combustion in each cylinder becomes uniform, enabling stable idle rotation and subsequent good engine acceleration.
[0029]
Of course, the fuel supply to the # 2 and # 3 cylinders may be abruptly shifted from intake synchronous injection to intake asynchronous injection until the engine speed is stabilized at idle rotation. When shifting to the asynchronous injection, it is preferable to increase the amount of injected fuel in consideration of a part of the fuel adhering and remaining on the wall surface of the intake port.
[0030]
In this embodiment, when the fuel supply is started to the # 2 cylinder and the # 3 cylinder by the intake synchronous injection, that is, when the predetermined engine operation state in which the all cylinder operation is started, the engine speed is set to the # 1 cylinder and the # 1 cylinder. Immediately after reaching the maximum rotational speed N1 due to combustion of only # 4 cylinder. This time is the engine start completion time, and this time can be determined by monitoring the engine speed and reaching the preset N1. It can also be determined by monitoring the negative pressure in the intake port that changes in accordance with the engine speed. Further, it is also possible to use the fact that the change amount of the engine speed or the negative pressure change amount per unit time is detected and the change amount becomes smaller than the set value for this time determination.
[0031]
When starting with partial cylinder operation using # 1 and # 4 cylinders, the negative pressure in the intake port is relatively high, and the optimal operation start timing for cylinders # 2 and # 3 by intake synchronous injection is optimal. is there. However, this does not limit the present invention, and at least after the first explosion of the # 1 and # 4 cylinders, the negative pressure in the intake port is increased compared to the time of cranking, and the intake synchronous injection As a result, relatively good combustion can be achieved, and the amount of unburned fuel discharged from the entire cylinder can be reduced and good startability can be ensured. In addition, when a certain amount of time has elapsed since the start of the partial cylinder operation by the # 1 cylinder and the # 4 cylinder, the engine speed slightly decreases and the negative pressure in the intake port also decreases somewhat. Relatively good combustion is realized, and operation of the # 2 cylinder and # 3 cylinder by intake synchronous injection can be started.
[0032]
Thus, when it is determined by monitoring the engine speed or the negative pressure in the intake port that a predetermined predetermined engine operation state has been reached after the end of the initial explosion of some cylinders by intake asynchronous injection, It is sufficient to supply fuel to the cylinders other than the partial cylinders by intake synchronous injection to start all cylinder operation. However, due to poor fuel and other factors, some cylinder operation does not reach the predetermined engine operation state. It is also conceivable that all cylinder operation cannot be started. Therefore, it is preferable to forcibly start all-cylinder operation when a predetermined period has elapsed from the start of starting of some cylinders, even if the predetermined engine operation state is not reached.
[0033]
In the present embodiment, the intake synchronous injection to the # 2 cylinder and the # 3 cylinder is performed up to the maximum rotational speed N2 in the all cylinder operation. If the engine shifts to intake asynchronous injection before that time, fuel adheres to the wall surface of the intake port in the # 2 and # 3 cylinders before reaching the maximum engine speed N2, and when the engine reaches the maximum engine speed N2. This adhering fuel evaporates at a time, and the amount of unburned fuel discharged from these cylinders increases.
[0034]
However, if the intake synchronous injection is performed even once into the # 2 cylinder and the # 3 cylinder at the start of all cylinder operation, these cylinders until the maximum rotation speed N3 is achieved as compared with the case where the intake asynchronous injection is performed from the beginning. The amount of fuel adhering to the intake port wall surface and the like can be reduced, which makes it possible to reduce the amount of unburned fuel discharged from all cylinders when the engine is started.
[0035]
In the present embodiment, the fuel supply to the # 2 cylinder and the # 3 cylinder is shifted from the intake synchronous injection to the intake asynchronous injection. Of course, the intake synchronous injection is continued even when stabilized by idle rotation. You may do it. Further, the fuel supply to the # 1 cylinder and the # 4 cylinder needs to be the intake asynchronous injection at least until the completion of the first explosion in order to ensure startability, but thereafter, as the engine speed increases. Since the negative pressure in the intake port rises, relatively good fuel is possible as intake synchronous injection.
[0036]
Also, when starting all cylinder operation in a predetermined engine operation state, the fuel supply to the # 1 cylinder and # 4 cylinder is switched from intake asynchronous injection to intake synchronous injection, and all cylinders are operated by intake synchronous injection. May be. Thereafter, preferably, after reaching the maximum rotational speed N2 in the all-cylinder operation, all the cylinders may be gradually or suddenly changed from intake synchronous injection to intake asynchronous injection.
[0037]
In this way, reducing the number of cylinders and operation opportunities (number of injections) of intake asynchronous injection while ensuring engine startability is advantageous in reducing the amount of unburned fuel discharged at engine start. .
[0038]
In FIG. 3, in order to simplify the description, in the intake asynchronous injection of # 1 cylinder and the intake synchronous injection of # 3 cylinder, the fuel injection amount is increased (A and A ′) only for the first time, and thereafter Is the same fuel injection amount (B) in the intake asynchronous injection and the intake synchronous injection. Of course, in the intake asynchronous injection and the intake synchronous injection, the fuel injection amount may be gradually decreased after the first fuel increase. good. Further, the fuel injection amount after the first time may be made different between intake asynchronous injection and intake synchronous injection.
[0039]
【The invention's effect】
As described above, according to the multi-cylinder internal combustion engine of the present invention, the engine start is started by supplying the fuel to only some cylinders by the intake asynchronous injection and performing the partial cylinder operation. When a predetermined engine operation state is reached after completion, all cylinders are operated by supplying fuel to the cylinders excluding some cylinders by intake synchronous injection. As a result, in some cylinders, engine startability is ensured by good combustion by intake asynchronous injection, and in cylinders other than some cylinders, intake synchronization is achieved by the negative pressure generated in the intake port when the initial explosion of some cylinders is completed. Compared to intake asynchronous injection, it is possible to reduce the amount of fuel adhering to the intake port wall surface, etc., and increase the engine speed due to all-cylinder operation. Even if the negative pressure increases, the fuel adhering to the wall surface of the intake port evaporates at a time in some cylinders and the combustion air-fuel ratio becomes excessively rich, but this is only a part of all cylinders. In the cylinders other than the partial cylinders, the fuel air-fuel ratio does not become so rich, and it becomes possible to reduce the amount of unburned fuel discharged from all the cylinders when the engine is started.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view in a cylinder of a multi-cylinder internal combustion engine according to the present invention.
2 is a time chart showing changes in engine speed when the multi-cylinder internal combustion engine of FIG. 1 is started. FIG.
FIG. 3 is a time chart showing fuel injection when the multi-cylinder internal combustion engine is started in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Spark plug 3 ... Intake port 5 ... Exhaust port 7 ... Fuel injection valve

Claims (6)

When engine start is started by supplying fuel to only some cylinders by intake asynchronous injection and performing partial cylinder operation, when the predetermined engine operation state is reached after completion of the initial explosion of the partial cylinder, A multi-cylinder internal combustion engine characterized in that fuel is supplied to cylinders other than the partial cylinders by intake synchronous injection to perform all-cylinder operation. 2. The multi-cylinder internal combustion engine according to claim 1, wherein the fuel supply to the cylinders excluding the one part cylinder shifts from intake synchronous injection to intake asynchronous injection. 3. The multi-cylinder internal combustion engine according to claim 2, wherein the fuel supply to the cylinders excluding the some cylinders shifts from intake synchronous injection to intake asynchronous injection with the fuel injection timing gradually advanced. 4. The multi-cylinder internal combustion engine according to claim 2, wherein the fuel supply to the cylinders excluding the partial cylinders shifts from intake synchronous injection to intake asynchronous injection until the engine speed is stabilized at idle rotation. 5. organ. The multi-cylinder internal combustion engine according to any one of claims 1 to 4, wherein the predetermined engine operation state is an operation state corresponding to completion of engine start. The multi-cylinder internal combustion engine according to any one of claims 1 to 5, wherein the all-cylinder operation is performed when the predetermined engine operation state is not achieved within a set period from the start of engine start.

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