JP3921898B2 - Multi-cylinder engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-cylinder engine, and more particularly to a multi-cylinder engine that reduces noise by fuel injected into a cylinder.
[0002]
[Prior art]
Engine noise, which is the main cause of noise from automobiles, includes combustion noise that is generated by combustion of the air-fuel mixture and mechanical noise that occurs when engine components such as piston and cylinder collide with each other or rub against each other. is there.
[0003]
Such engine sounds become louder as the engine speed increases and the sound quality changes. For this reason, unless engine noise is reduced, acceleration noise generated during acceleration not only becomes noise but also vibrations may become serious and cause a deterioration in driving feeling.
[0004]
In order to suppress the combustion noise of the engine, for example, it is conceivable to increase the rigidity of the engine. However, in that case, not only the production cost is high, but it is also necessary to increase the strength of the vehicle portion on which the engine is mounted. Therefore, the weight of the portion increases, and the weight balance of the entire vehicle cannot be achieved.
[0005]
In addition, as a means for suppressing combustion noise of the engine, for each cylinder in which the amount of change in the combustion pressure becomes a predetermined value or more during engine operation, the injection timing is retarded for each cylinder. Technology for suppressing noise generation (see Japanese Patent Application Laid-Open No. 59-37235) and so-called pilot injection in which a small amount of fuel is injected in advance prior to the main injection of fuel, and the injection timing is set to a specific cylinder A technique (refer to Japanese Patent Laid-Open No. 63-9657) for reducing vibration of the cylinder by shifting the cylinder is well known.
[0006]
However, the noise reduction techniques listed in these publications are techniques that must detect each time a cylinder that is actually generating noise among a plurality of cylinders, and perform noise suppression based on the detection result. . Therefore, since it is necessary to provide a detection device such as a sensor for every cylinder, the structure of the internal combustion engine becomes more complicated. In addition, since noise suppression can only be realized after confirming the generation of noise, a time lag has occurred between the generation of noise and the suppression of noise.
[0007]
The inventor of the present application conducted a noise experiment on a multi-cylinder diesel engine. I found out that it was going to be intense. And about the said specific cylinder, since the noise degree, ie, the frequency, was higher than the other cylinders, it discovered that the whole engine formed a specific vibration mode.
[0008]
[Problems to be solved by the invention]
The present invention has been invented based on the knowledge that in a multi-cylinder engine, the frequency of a specific cylinder is always higher than the frequency of other cylinders in a specific frequency band. The problem to be solved is to provide a multi-cylinder engine having a simple structure while reducing noise in view of the above situation.
[0009]
[Means for Solving the Problems]
The internal combustion engine of the present invention employs the following means in order to achieve the above object.
(1) A multi-cylinder engine of the present invention has an engine block in which a plurality of cylinders are arranged in series, and a multi-cylinder engine that generates noise when it vibrates in a specific frequency band during operation is unique to the multi-cylinder engine. For a specific cylinder that is specified in advance to be louder than other cylinders in the specific frequency band, the specific cylinder is set so as to slow combustion when there is vibration in the specific frequency band. It has fuel injection control means for performing fuel injection control to the cylinder.
[0010]
Here, the “specific frequency band” includes a frequency band of approximately 1 to 5 KHZ if the multi-cylinder engine is, for example, a 4-cylinder engine.
(2) Preferably, the multi-cylinder engine is an in-line multi-cylinder diesel engine having an even number of cylinders, and the specific cylinder is a central plurality of cylinders among cylinders arranged in series.
(3) The fuel injection control means performs main injection for injecting engine operating fuel into the cylinder and pilot injection for preventing ignition delay by injecting a smaller amount of fuel into the cylinder in advance prior to the main injection. It is preferable to include an injector to be performed and a control device for controlling the operation of the injector.
(4) When there is vibration in the specific frequency band, the control device preferably increases the execution amount of the pilot injection from the execution amount of normal injection for preventing ignition delay.
(5) The diesel engine includes a common rail that is a stock pressure chamber, and fuel injection is performed by the fuel injection control means at the pressure of the common rail. When there is vibration in the specific frequency band, the pressure of the common rail May be made lower than before.
(6) Preferably, the multi-cylinder engine is an in-line four-cylinder engine, and the specific cylinders are a second cylinder and a third cylinder.
[0011]
According to the present invention having such a configuration, the combustion of some specific cylinders is slowed down, and the noise of the entire engine is reduced accordingly. Moreover, the fuel injection control to the specific cylinder is performed so as to slow down the combustion of the specific cylinder, which is known in advance that noise is intense when there is vibration in a specific frequency band. It is not necessary to detect which cylinder has a strong vibration (noise). This eliminates the need for sensors and other detection devices. Therefore, the engine structure can be simplified accordingly.
[0012]
Moreover, since it is known in advance without detecting from which cylinder the noise is generated, the control can be performed without a time lag between the generation of the noise and the suppression of the noise. For this reason, noise reduction can be achieved efficiently.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
<Embodiment>
Embodiments according to the present invention will be described with reference to FIGS.
[0014]
The engine 1 shown in FIG. 1 is a diesel engine, for example, and shows a state when the engine 1 is viewed from above. In this embodiment, an in-line four-cylinder diesel engine in which the number of cylinders is four and these cylinders are arranged in series in the longitudinal direction of the engine block 1a is targeted. Reference numerals # 1 to # 4 denote the four cylinders.
[0015]
Reference numeral 6 denotes an edge of the engine 1. Since the present invention relates to engine vibration, for the sake of convenience, a phrase commonly used in a vibration system is applied to this edge and is referred to as clause 6.
[0016]
A two-dot chain line in FIG. 1 indicates a state in which the outline of the engine 1 is changed by this vibration when the engine 1 vibrates at a specific frequency band of approximately 1 to 5 KHZ, that is, a vibration mode M. In addition, this two-dot chain line indicates a change in the configuration of the engine 1 during vibration by comparing it with an engine outline (indicated by a solid line) when the engine 1 is not vibrating.
[0017]
The vibration mode M of the engine 1 will be described in detail.
The engine 1 warps outward in a bow shape (maximum) at the maximum vibration, and includes a center portion in the longitudinal direction of the engine, that is, a portion including # 2 and # 3 (more precisely, a portion between # 2 and # 3) It can be seen that 7 is the maximum amplitude position. Therefore, when the engine 1 is viewed from above when the engine 1 is in operation, the engine 1 is gradually narrowed at both ends and has a thick barrel shape at the center.
[0018]
The central part in the longitudinal direction of the engine is called an antinode with respect to the node 6 and is denoted by reference numeral 8. If "node" is defined as both ends that do not vibrate in the longitudinal direction of the engine, "antinode" can be defined as the maximum amplitude position of the bending mode with nodes at both longitudinal ends of the engine.
[0019]
Although not shown, as is well known, the diesel engine 1 includes a common rail that is a pressure accumulating chamber and an injector that injects fuel into the cylinder under the pressure of the common rail.
[0020]
The injector performs pilot injection to prevent ignition delay by injecting a smaller amount of fuel into the cylinder in advance prior to main injection, in addition to performing main injection for injecting engine operating fuel into the cylinder.
[0021]
In the past, it was known that when the engine vibrates in a specific frequency band, the vibration noise becomes noise. However, in other words, the engine 1 can have a belly at the center in the longitudinal direction of the engine. Even those skilled in the art have not understood that the vibration mode M is a cause of noise.
[0022]
As a result of diligent efforts, the inventor of the present application, even in the case of in-line even-cylinder diesel engines such as in-line 4-cylinder engines, even when each cylinder burns the same, The number of vibrations of the plurality of cylinders is higher than that of the other cylinders. Therefore, the portion between the central plurality of cylinders becomes an antinode, and it is experimentally determined that a vibration mode like the two-dot chain line shown in FIG. I found it.
[0023]
More specifically, in the case of an in-line four-cylinder diesel engine, when the engine frequency is approximately 1 to 5 KHZ, cylinders # 2 and # 3 have a higher frequency than cylinders # 1 and # 4, and , 6 are structurally difficult to vibrate, and therefore, the portion between the cylinders # 2 and # 3 becomes an antinode and the amplitude increases, that is, the noise is increased. Therefore, the cylinders # 2 and # 3 are referred to as specific specific cylinders of the engine 1 for convenience.
[0024]
And based on such knowledge, in the engine 1, when the vibration is in the frequency band of approximately 1 to 5 KHZ, the combustion to the cylinders # 2 and # 3 is made slow so that the combustion of the cylinders # 2 and # 3 becomes slow. Noise countermeasures are taken by providing fuel injection control means for performing fuel injection control.
[0025]
The fuel injection control means includes the injector and a central processing unit (hereinafter referred to as “CPU”) included in an engine control device (hereinafter referred to as “ECU”) that controls the operation of the injector.
[0026]
When there is vibration in a specific frequency band, the ECU increases the execution amount of pilot injection from the execution amount that is normally injected to prevent ignition delay. This increased amount is an amount that can smoothly shift from combustion by pilot injection to combustion by main injection.
[0027]
The amount that can be smoothly transferred will be described.
The amount of fuel for main injection is an amount commensurate with the amount of engine exhaust, but the amount of fuel for pilot injection is essentially an amount necessary to reduce ignition delay, for example. Therefore, there is usually a considerable difference between the injection amounts of the two.
[0028]
For this reason, the scale differs in the explosive force by the combustion by pilot injection, and the explosive force by the combustion by main injection. Therefore, when shifting from combustion by pilot injection to combustion by main injection, the pressure in the cylinder rises at a stretch and generates noise, but if the difference between the two is narrowed, that is, the amount of fuel injected by pilot injection When the explosion force in the combustion by the main injection is made closer to the explosion force in the combustion by the pilot injection, the pressure rise becomes slow and the noise is reduced.
[0029]
The increased amount differs depending on the engine displacement and the type of engine-equipped vehicle, and is obtained by experiments and calculations.
FIG. 2 shows a control routine for vibration prevention execution, which is stored in a read-only memory ROM included in the ECU.
[0030]
Then, it is called by the central processing unit CPU of the ECU as necessary.
When the process proceeds to this routine after the engine is started, the vibration prevention execution control routine determines whether or not the engine frequency is in a specific frequency band of approximately 1 to 5 KHZ in S101.
[0031]
If a positive determination is made in S101, the process proceeds to S102, and if a negative determination is made, this routine is terminated. This is because the present invention is for preventing noise when in a specific frequency band.
[0032]
In S102, pilot injection is performed to the specific cylinders # 2 and # 3 by the injector, and this routine ends. The injection amount is an amount increased from the normal pilot injection amount so that the transition from the combustion by the pilot injection to the combustion by the main injection can be smoothly performed as described above.
[0033]
3 and 4 are pressure-time diagrams in which the pressure levels of cylinders # 2 and # 3 are plotted on the vertical axis and time is plotted on the horizontal axis, in other words, the pressure waveform due to in-cylinder combustion in accordance with the time change. FIG.
[0034]
FIGS. 3 and 4 are comparison diagrams between the case where the present technology is not employed and the case where the present technology is employed for the cylinders # 2 and # 3, respectively. A state of a pressure change when main injection is continued after performing pilot injection to cylinders # 2 and # 3 when it is approximately 1 to 5 KHZ.
[0035]
4 shows that the pressure waveform of FIG. 4 showing the case where the present technology is adopted has a gentler inclination in the elliptical region A, and therefore, the combustion is slower in the cylinders # 2 and # 3. Thus, it can be seen that the combustion is smoothly shifted from the combustion by the pilot injection to the combustion by the main injection.
[0036]
FIG. 5 is a graph showing the effect of the present technology in comparison with the prior art. The sound pressure-frequency diagram is shown with the sound pressure levels # 2 and # 3 on the vertical axis and the frequency on the horizontal axis. It is.
A solid line A and a broken line B in FIG. 5 are a sound pressure graph line in the case of the conventional technique (before countermeasures) and a sound pressure graph line in the case of employing the present technique (after countermeasures), respectively.
[0037]
As is apparent from both graph lines, at approximately 1 to 5 KHZ, the broken line graph line B has a significantly lower sound pressure level than the solid line graph line A, that is, the noise is reduced. .
[0038]
Moreover, the inventor has clarified by experiments that the noise of the cylinders # 2 and # 3 becomes intense when the engine frequency is in the frequency band in the in-line four-cylinder engine 1, When the engine vibration becomes approximately 1 to 5 KHZ which is a specific frequency band, the above-described injection control may be performed so that the combustion of the cylinders # 2 and # 3 becomes slow. Therefore, there is no need for a sensor or other device for detecting which cylinder is vibrated (noise) as in the prior art. Therefore, the structure of the engine can be simplified accordingly.
[0039]
In addition, since it is known in advance without detecting from which cylinder the noise is generated, it can be controlled so that there is no time lag between the generation of the noise and the suppression of the noise. For this reason, noise reduction can be achieved efficiently.
[0040]
In this embodiment, the in-line four-cylinder engine is described. However, the present invention can be similarly applied to a multi-cylinder engine having an engine block in which a plurality of cylinders are arranged in series, such as an in-line six-cylinder engine. Of course.
[0041]
As another means for smoothly shifting from combustion by pilot injection to combustion by main injection, implementation by adjusting the pressure of a common rail provided as a pressure accumulation chamber in a diesel engine can be considered. That is, fuel injection by the fuel injection control means is executed with the pressure of the common rail, and when there is vibration in the specific frequency band, the pressure of the common rail is reduced more than before.
[0042]
The fuel that is pilot-injected is injected as fine particles under the pressure of the common rail. However, when the pressure of the common rail is decreased, the injected fuel is prevented from being atomized and becomes finer than usual. As a result, the ratio of contact with oxygen as a whole of the fuel is reduced, and as a result, combustion becomes slow and noise is reduced.
[0043]
【The invention's effect】
As described above, the multi-cylinder engine of the present invention has the following effects, for example.
[0044]
Since the combustion of some specific cylinders is slowed down, the noise of the entire engine is reduced accordingly. Moreover, when the engine frequency is in the specific frequency band for a specific cylinder that is known in advance to be noisy when the engine frequency is in the specific frequency band, the combustion for the specific cylinder should be slowed down. Since the fuel is injected into the specific cylinder, there is no need for a sensor or other device for detecting which cylinder is subject to intense vibration (noise) as in the prior art. Therefore, the engine structure can be simplified accordingly.
[0045]
In addition, since it is known in advance without detecting from which cylinder the noise is generated, there is no time lag between the generation of the noise and the suppression of the noise. For this reason, noise reduction can be achieved efficiently.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a multi-cylinder engine according to an embodiment of the present invention, in which vibration modes are also described.
FIG. 2 is a control routine for vibration prevention execution.
FIG. 3 is a pressure waveform diagram due to in-cylinder combustion according to a change in time, and is a diagram when the present invention is not applied (before countermeasures).
FIG. 4 is a pressure waveform diagram due to in-cylinder combustion according to a change in time, and is a diagram when the present invention is applied (after countermeasures).
FIG. 5 is a diagram showing the effect of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Inline 4 cylinder diesel engine 1a ... Engine block # 1- # 4 ... Cylinder 6 ... Node 8 ... Abdominal A ... Elliptical area M ... Vibration mode

Claims (6)

In a multi-cylinder engine having an engine block in which a plurality of cylinders are arranged in series and generating noise when vibrating in a specific frequency band during operation,
For a specific cylinder that is specific to this multi-cylinder engine and that is specified in advance to be louder than other cylinders in the specific frequency band, the combustion is slowed down when there is vibration in the specific frequency band. A multi-cylinder engine comprising fuel injection control means for performing fuel injection control to the specific cylinder. 2. The multi-cylinder engine according to claim 1, wherein the multi-cylinder engine is an in-line multi-cylinder diesel engine having an even number of cylinders, and the specific cylinder is a plurality of cylinders in a center among cylinders arranged in series. engine. The fuel injection control means includes a main injection for injecting engine operating fuel into the cylinder, and an injector for performing pilot injection for preventing ignition delay by injecting a smaller amount of fuel into the cylinder in advance prior to the main injection. The multi-cylinder engine according to claim 2, further comprising a control device that controls the operation of the injector. 4. The multi-cylinder according to claim 3, wherein when there is vibration in the specific frequency band, the control device increases the execution amount of the pilot injection more than the execution amount of normal injection for preventing ignition delay. engine. The diesel engine is provided with a common rail that is a stock pressure chamber, and fuel injection is performed by the fuel injection control means at the pressure of the common rail, and when there is vibration in the specific frequency band, the pressure of the common rail is increased up to that time. The multi-cylinder engine according to claim 1, wherein the multi-cylinder engine is lowered. The multi-cylinder engine according to any one of claims 1 to 5, wherein the multi-cylinder engine is an in-line four-cylinder engine, and the specific cylinders are a second cylinder and a third cylinder.

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