JPS6323370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an intake system for a multi-cylinder engine equipped with a supercharger. This invention relates to something that prevents abnormal combustion in an engine.

(Prior Art) Conventionally, it has been known to provide a supercharger in the intake passage of an engine to supercharge the intake air, thereby increasing the filling efficiency of the intake air and increasing output.

In addition, as disclosed in Japanese Utility Model Publication No. 45-2321, a technique for obtaining a supercharging effect using intake pressure waves generated in the intake passage of an engine has conventionally been used in a single-cylinder engine to reduce the size of the intake pipe. Divided into two different passages, each with a separate intake port, the two intake passages are used when the engine is running at high speeds, and at low engine speeds, the intake passage that is at the later closing position is closed, allowing for early intake. By occluding the intake air, it is possible to obtain suitable charging efficiency over a wide range of engine speeds by utilizing the supercharging effect caused by the occlusion of the intake air at the maximum pressure of the intake air, which is a function of the intake pipe dimensions and engine speed. It has been proposed that However, this method is for a single-cylinder engine, and it is not clear how to use the intake pressure waves generated in the intake passage, its structure, and operation, and it cannot be put into practical use right away. It was hot.

By the way, in the above-mentioned supercharged engine, the intake air temperature increases due to the increase in intake pressure due to supercharging, so there is a problem that knocking is likely to occur in the engine's low-speed operating range, especially in the high-temperature, high-load, low-speed operating range. There is. Therefore, for example, in an engine equipped with an exhaust turbo supercharger, a waste gate valve is provided in the exhaust passage upstream of the turbine.
The intake pressure downstream of the blower (supercharger) is set by controlling the operation of the waste gate valve using the intake pressure (supercharging pressure) downstream of the blower, and allowing a portion of the exhaust gas to bypass the turbine and flow down. It is widely used to prevent the occurrence of knocking by maintaining a constant value so as not to exceed the value.

However, when the upper limit of supercharging pressure is regulated and controlled using a waste gate valve, etc., the exhaust pressure applied to the exhaust port is greater than the intake pressure (supercharging pressure) downstream of the supercharger in the engine high speed operating range. Become. Therefore, when the intake and exhaust air overlap, a large amount of high-temperature exhaust gas is brought into the combustion chamber from the exhaust passage, and a large amount of high-temperature exhaust gas is also carried from the combustion chamber to the intake passage or from the exhaust passage to the intake passage via the combustion chamber. As a result, there was a problem in that abnormal combustion such as premature engine ignition and knocking occurred.

(Object of the Invention) Therefore, in view of this point, the present invention provides intake characteristics of a supercharged engine as described above in an engine operating range where the exhaust pressure applied to the exhaust port is greater than the intake pressure downstream of the supercharger. It was discovered that when the intake port is opened, the intake air is compressed by the pressure of the residual exhaust gas in the combustion chamber, and a compression wave with a pressure equivalent to the above exhaust pressure is generated in the intake port part of the intake passage. Based on this, in a multi-cylinder engine with a supercharger, the compression wave at the time of opening of the intake port in one cylinder is determined by the compression wave at the time of opening of the intake port of one cylinder. This was done based on the fact that a supercharging effect can be effectively obtained (hereinafter referred to as the "exhaust interference effect") if the supercharging effect is applied (at the time of overlap). Due to the propagating compression waves of pressure that can counteract the exhaust pressure at the time of overlap, the amount of exhaust gas brought in and the amount of blowback when the intake and exhaust air overlap can be reduced even with a simple configuration by making slight design changes to the existing intake system. The purpose is to effectively prevent abnormal combustion in the engine.

(Structure of the Invention) The technical solution of the present invention to achieve this object is to adjust the length of the intake passage between each cylinder in the intake passage downstream of the supercharger in a multi-cylinder engine equipped with a supercharger. Compression waves that occur at the intake port of each cylinder when the intake port of each cylinder opens in an engine operating range where the stroke is the same for consecutive cylinders and the exhaust pressure acting on the exhaust port is greater than the intake pressure downstream of the supercharger. is set to propagate and perform supercharging immediately after the intake ports of other cylinders are opened the earliest after the intake ports of the cylinder are opened. As a result, due to the supercharging effect due to the so-called exhaust interference effect, in other words, when the intake and exhaust of the cylinder overlap, a compression wave at the time of opening with a pressure equal to the exhaust pressure propagates to the intake port, eliminating the pressure difference between the intake and exhaust. This suppresses the introduction of exhaust gas and blowback.

Here, the length L of the intake passage between cylinders to obtain the above exhaust interference effect is calculated by the following formula in the case of a 4-stroke reciprocating engine: L=(720/Z)×(60/360・N)×a...() is set to the value determined. In the above equation (), Z is the number of cylinders, and (720/Z) is the phase difference between consecutive cylinders in the intake stroke. It represents the rotation angle of the crankshaft required for propagation to immediately after the opening of the intake port of another cylinder, which opens the intake port earlier. Also, N is the engine rotation speed, and (60/360N) represents the time (seconds) required to rotate 1°. Further, a is the propagation velocity (sound velocity) of the pressure wave (compression wave). Note that the above equation () ignores the influence of the intake air flow on the propagation of pressure waves, but this is because the flow velocity is smaller than the speed of sound and causes almost no change in the length of the intake passage. .

(Effects of the Invention) Therefore, according to the present invention, in a multi-cylinder engine with a supercharger, supercharging is performed between each cylinder due to the exhaust interference effect in the engine high-speed operating range where the exhaust pressure is greater than the boost pressure. As a result, the amount of exhaust gas brought in and the amount blown back when the intake and exhaust systems overlap can be reduced even with a simple configuration by making slight design changes to the existing intake system, thereby reducing early ignition. Abnormal engine combustion such as pre-ignition and knocking can be effectively prevented, and the prevention can be easily and inexpensively implemented.

(Example) Hereinafter, an example as a specific example of the technical means of the present invention will be described based on the drawings.

FIGS. 1 and 2 show a first embodiment as a basic structural example in which the present invention is applied to a four-cylinder, four-cycle engine. In the same figure, 1A to 1D are the first to
It is the fourth cylinder, and 2 is a combustion chamber formed by the cylinder 3 and the piston 4 in each of the cylinders 1A to 1D.

Reference numeral 5 denotes a main intake passage whose one end opens to the atmosphere via an air cleaner 6 to supply intake air to each cylinder 1A to 1D, and an air flow meter 7 for detecting the intake air flow rate is provided in the main intake passage 5. A throttle valve 8 for controlling the amount of intake air is provided downstream of the air flow meter 7. The main intake passage 5 is branched into first to fourth intake passages 5a to 5d downstream of the throttle valve 8, and then connected to each of the cylinders 1A to 5d via intake ports 9, 9, .
It communicates with the combustion chambers 2, 2, . . . of 1D.

Each of the intake passages 5a to 5d is provided with electromagnetic valve type fuel injection nozzles 10, 10, . . . whose fuel injection amount is controlled according to the intake air flow rate based on the output of the air flow meter 7.

Further, a branch portion of the main intake passage 5 is located downstream of the throttle valve 8, and constitutes a communication passage 11 that communicates the first to fourth intake passages 5a to 5d with each other. The passage area Ac of the communication passage 11 is set to be equal to or larger than the minimum passage area A of each intake passage 5a to 5d (Ac≧A), so that pressure waves can be effectively propagated with less attenuation. I have to.
Although not shown in the figure, there is a connection between the throttle valve 8 of the main intake passage 5 and the branch part (communication passage 11) to prevent surging of intake air during transient operation such as during acceleration or deceleration of the engine. It is preferable to provide a surge tank with a predetermined volume to prevent surges and ensure good response of the fuel.

In addition, 12a to 12d each have first to first ends that communicate with the combustion chambers 2, 2, . . . of each cylinder 1A to 1D via exhaust ports 13, 13, . The downstream ends of each of the exhaust passages 12a to 12d are connected to the main exhaust passage 12 and then open to the atmosphere, and there is a passage in the middle of the main exhaust passage 12 for purifying the exhaust gas. A catalyst device 14 is provided. still,
15 is an intake valve that opens and closes the intake port 9, and 16 is an exhaust valve that opens and closes the exhaust port 13.

On the other hand, 17 is an exhaust turbo supercharger, and the supercharger 17 includes a turbine 17a disposed upstream of the catalyst device 14 in the main exhaust passage 12 and rotationally driven by the exhaust gas flow, and a main intake passage. The blower 17b is disposed between the air flow meter 7 of No. 5 and the throttle valve 8 and is driven by the turbine 17a, and the blower 17b directs intake air to each cylinder 1A.
It supercharges up to 1D.

Further, reference numeral 18 denotes a bypass passage which has one end opened upstream of the turbine 17a of the main exhaust passage 12 and the other end opened downstream of the turbine 17a to bypass the turbine 17a. A waste gate valve 19 is provided which is operated and controlled according to the intake pressure (supercharging pressure) in the main intake passage 5 of the engine. is opened to cause the exhaust gas flow to flow down through the bypass passage 18, bypassing the turbine 17a, thereby maintaining the supercharging pressure at a constant level so as not to exceed a set value. That is, as shown in FIG. 4, the supercharging pressure, that is, the intake pressure Pin downstream of the supercharger 17 (blower 17b), increases temporarily as the engine speed increases, even at a relatively steep slope, and then increases. ,
The characteristics are set such that when the rotation speed exceeds a predetermined value, the waste gate valve 19 is operated to maintain the set value. On the other hand, turbine 1
The exhaust pressure upstream of 7a, that is, the exhaust pressure Pex acting on the exhaust port 13, gradually increases as the engine speed increases, and when it exceeds a predetermined speed, the pressure becomes higher than the set upper limit supercharging pressure. show. Therefore, as shown in Fig. 4, the above intake pressure Pin
In the engine operating range where Pex is greater than the exhaust pressure Pex, for example, in the low engine speed region of 2000 to 4000 rpm, the exhaust pressure Pex is greater than the intake pressure.
There will be an engine operating range that is sufficiently larger than Pin, such as a high engine speed range of 5000 rpm or more.

In addition, the lengths of the intake passages 5a and 5d of the first cylinder 1A and the fourth cylinder 1D are set to be equal to _each other, and the lengths of the intake passages 5a and 5d of the first cylinder 1A and the fourth cylinder 1D are set to be equal to each other.
The intake passages 5b and 5c are also set to have the same length _l2 . Then, the passage length between adjacent cylinders in which the intake stroke in the ignition order of 1-3-4-2 is continuous, that is, the passage length between each cylinder and the earliest intake after the opening of the intake port 9 (opening of the intake valve 15) of the cylinder The length L of the intake passage through the communication passage 11 between the other cylinders in which the port 9 is opened is set to be the same, and the length L of the intake passage through the communication passage 11 is
When the path length of is lc, L=lc+l ₁ +l ₂ ,
It is set to a value determined by the above equation () so as to obtain an exhaust interference effect between the adjacent cylinders in an engine operating range where the exhaust pressure Pex is greater than the intake pressure Pin. Specifically, it is preferable to obtain the exhaust interference effect in a high rotation range where the exhaust pressure Pex is 200 mmHg or more higher than the intake pressure Pin, for example, 5000 to 7000 rpm, so the engine rotation speed N = 5000.
~7000rpm, and Z=4, sound speed a=376m/
s (at 80℃), and θ ₀ = 30, then from equation (), L
= 1.61~2.26m.

Next, the operation of the first embodiment will be explained with reference to FIG. 5. As shown in FIG. 4, the exhaust pressure Pex acting on the exhaust port 13 is changed to the intake pressure Pin ( engine operating range that is larger than the boost pressure (boost pressure), e.g. 5000 ~
In the engine high speed operation region of 7000 rpm, the above
From the relationship of Pex>Pin, when the intake port 9 of one cylinder, for example, the first cylinder 1A, is opened, the compression wave generated near the intake port 9 is generated between adjacent cylinders in the ignition order of 1-3-4-2. By setting the passage length L to a value determined by the above formula (), the intake port 9 of the third cylinder 1C, which is another cylinder, passes through the first intake passage 5a → the communication passage 11 → the third intake passage 5c. is effectively propagated immediately after opening. As a result, this opening compression wave forces intake air into the combustion chamber 2 from the intake port 9 of the third cylinder 1C at the beginning of the intake stroke, thereby performing supercharging (exhaust interference effect). Similarly, this exhaust interference effect changes from 3rd cylinder 1C to 4th cylinder 1D, and 4th cylinder 1D.
D → 2nd cylinder 1B, 2nd cylinder 1B → 1st cylinder 1A
The opening compression wave propagates to the intake port 9 of each cylinder at the beginning of the intake stroke, and supercharging is performed.

Therefore, due to the supercharging effect due to the exhaust interference effect between adjacent cylinders whose intake strokes are continuous, the intake stroke immediately after the opening of the intake port 9 of each cylinder, that is, the
When the exhaust overlaps, the intake pressure is the exhaust pressure
Due to the propagation of a compression wave at the opening with a pressure equal to Pex,
Since the pressure difference with the exhaust pressure Pex is almost eliminated, the amount of exhaust gas carried into the combustion chamber 2 and the amount blown back into the intake passages 5a to 5d are reduced. As a result, it is possible to effectively prevent the occurrence of abnormal engine combustion such as pre-ignition or knocking due to a large amount of high-temperature exhaust gas brought in or blown back.

In that case, the first to fourth intake passages 5a to 5, which are pressure wave propagation paths for obtaining an exhaust interference effect.
d and the communication passage 11 (branching part of the main intake passage 5) are located downstream of the throttle valve 8, so the pressure waves (compression waves) are not attenuated by the throttle valve 8, and the communication passage 11 is located downstream of the throttle valve 8. Passage area Ac
is greater than or equal to the minimum passage area A of each intake passage 5a to 5d, so that the resistance to the propagation of pressure waves is small;
Therefore, the above-mentioned exhaust interference effect can be effectively exerted.

Furthermore, the fuel injection nozzle 10 as a fuel supply device includes each intake passage 5a to 5d downstream of the communication passage 11.
Therefore, it is possible to prevent deterioration of fuel responsiveness due to an increase in the length of the intake passage and ensure good fuel responsiveness.

In addition, the supercharging effect due to the exhaust interference effect can be obtained by setting the passage length L between each cylinder 1A to 1D as described above, so a slight design change of the existing intake system is required, and the structure is extremely simple and therefore can be implemented easily and at low cost.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but also includes various other modifications. For example, although the first embodiment described above shows an example in which the present invention is applied to a four-cylinder four-stroke engine, the present invention can also be applied to various other multi-cylinder engines. For example, unlike the first embodiment, 4
Each cylinder 1A to 1 in a 4-cylinder engine
The first to fourth intake passages 5a to 5d, which communicate with D via the intake ports 9, may all be set to have the same length.

Further, FIG. 3 shows a second embodiment applied to an in-line six-cylinder four-stroke engine as an example of a modification (the same parts as in the first embodiment are given the same reference numerals and their explanations will be explained below). (omitted). In this example, intake passages 5a to 5f of each cylinder 1A to 1F
are branched downstream of the throttle valve 8 in the main intake passage 5 and communicated with each other through a communication passage 11', and are set to have equal lengths (note that they are two-dimensionally equal lengths in the figure, but the point is It suffices if the length is the same in three dimensions).
Further, the length L of the passage between adjacent cylinders in which the intake strokes in the ignition order of 1-5-3-6-2-4 are continuous is set equal to the value determined by the above equation (). Specifically, when Z=6 and other conditions are the same as in the case of 4 cylinders, L=1.07 to 1.50 m. Therefore, as shown in FIG. 6, the exhaust interference effect is as follows: 1st cylinder → 5th cylinder, 5th cylinder → 3rd cylinder, 3rd cylinder → 6th cylinder, 6th cylinder → 2nd cylinder,
It acts sequentially from the second cylinder to the fourth cylinder, and from the fourth cylinder to the first cylinder, supercharging the intake port 9 of each cylinder at the beginning of the intake stroke, thereby preventing abnormal combustion in the engine.

Further, although the above explanation has been made regarding a reciprocating engine, the present invention can of course be applied to a multi-cylinder rotary piston engine with a supercharger.
Especially in the case of a two-cylinder rotary piston engine, the phase difference between the cylinders is 180° and the length of the intake passage between the cylinders is L.
This is advantageous in terms of manufacturing design because the length can be shortened.

Furthermore, in each of the above embodiments, a single intake passage communicates with each cylinder via the intake port.
It can also be applied to systems where two intake passages, one for low load and one for high load, are communicated independently.
In this case, the length of the passage between the cylinders may be set so as to obtain an exhaust interference effect in either the low-load intake system or the high-load intake system. Preferably, the high-load intake passage is used for the low-load intake system. Since the area of the passage is larger than that of the passage and the attenuation of pressure waves can be kept small, it is advantageous to set it between cylinders in a high-load intake system.

Furthermore, in each of the above embodiments, the exhaust turbo supercharger 17 is used as the supercharger, but other various known superchargers such as a supercharging pump can be used.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIGS. 1 and 2 are an explanatory diagram of the overall configuration and a schematic diagram of the main parts of the first embodiment, and FIG. 3 is a diagram equivalent to FIG. 1 showing the second embodiment. , FIG. 4 is a diagram showing the characteristics of intake pressure and exhaust pressure with respect to engine speed, and FIGS. 5 and 6 are explanatory diagrams showing the mode of action of the exhaust interference effect in the first embodiment and the second embodiment, respectively. be. 1A to 1F...Cylinder, 5...Main intake passage, 5a to 5
f...Intake passage, 8...Throttle valve, 9...Intake port, 10...Fuel injection nozzle, 12...Main exhaust passage,
12a to 12f...exhaust passage, 13...exhaust port,
17...Exhaust turbo supercharger, 19...Waste gate valve.

Claims (1)

[Claims] 1. In a multi-cylinder engine equipped with an intake passage communicating with each cylinder via an intake port, an exhaust passage communicating with each cylinder via an exhaust port, and a supercharger provided in the intake passage, Engine operation in which the length of the intake passage between each cylinder downstream of the charger is made the same between cylinders with consecutive intake strokes, and the exhaust pressure acting on the exhaust port is greater than the intake pressure downstream of the supercharger. In the area, when the intake port of each cylinder opens, the compression wave generated in the intake port of that cylinder propagates immediately after the intake port of the other cylinder opens the earliest after the intake port of that cylinder opens, and supercharging is performed. An intake system for a multi-cylinder engine, which is characterized by being set to.