JPH0730698B2 - Multi-cylinder engine intake system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an intake system for a multi-cylinder engine, and more particularly to an intake system for a multi-cylinder engine configured to variably control a passage state of an intake passage according to an engine speed. Regarding the device.

(Prior Art) In recent years, in engines for automobiles and the like, it has been attempted to utilize the so-called intake inertia effect to increase the charging efficiency of intake air, thereby improving the engine output. The intake inertia effect is that a negative pressure wave generated near the intake port at the start of the intake stroke is propagated in the intake passage toward the upstream side and is reflected at the open end of the passage, which is a positive pressure wave. It is intended to increase the pushing action into the cylinder by utilizing the intake pressure vibration caused by the phenomenon that it is returned to the intake port, but this intake inertia effect is
The effect is exerted only when the natural frequency of the intake pressure vibration determined according to the length of the intake passage and the intake valve opening / closing cycle, that is, the engine speed are synchronized. Therefore, if the length of the intake passage is fixed to a fixed length,
The effective intake inertia effect is obtained only in a specific engine rotation range, and the intake charge efficiency cannot be improved over a wide operating range. Therefore, as a countermeasure against such a drawback, for example, in Japanese Patent Laid-Open No. 56-115819, the substantial length of the intake passage is shortened stepwise or steplessly as the engine speed increases. The configuration for changing the passage state is shown. However, the intake device shown in this publication forms a plurality of branch passages having different pipe lengths at the upstream end of the intake passage, and selectively opens these branch passages by operating a switching valve or the like. The length of the intake passage can be varied by changing the length of the intake passage, or by fitting a separate movable pipe at the upstream end of the intake pipe and sliding the movable pipe in the pipe length direction. Since the configuration is variable, particularly when applied to a multi-cylinder engine having a plurality of independent intake passages, there is a problem that the number of parts is significantly increased and the device becomes very complicated. For such problems,
A chamber having a required volume is communicated with each of the independent intake passages via an on-off valve, and the on-off valve is closed when the engine speed is in a low rotation range and the open-close valve is in a high rotation range. In the low rotation region, the upstream end of each independent intake passage (for example, a surge tank) acts as an atmosphere opening portion to lengthen the pipe length of the intake passage where the intake pressure vibration occurs, and also in the high rotation region. In the above, it is conceivable to shorten the pipe length of the intake passage in which the pressure vibration occurs by causing the communicating portion between the chamber and each independent intake passage to act as an atmosphere opening portion.

Therefore, in order to effectively utilize the intake inertia effect over a wide motion region by using such a method, the pipe length of the intake passage in which the intake pressure oscillation is generated corresponds to three stages, for example, three rotation regions of low, medium and high. In order to switch to three stages, each of the above independent intake passages must be provided with two chambers having a required volume, which causes an increase in the size of the intake device, an increase in weight, or a problem in installation space. Etc. will be invited. Further, in particular, in an engine configured to combine the upstream side of each of the above independent intake passages with an air flow meter and control the air-fuel ratio based on the output signal from the meter, the chamber as described above is used. If a plurality of air conditioners are provided, the volume of the intake passage on the downstream side of the air flow meter increases, and the responsiveness of the control deteriorates.

(Object of the Invention) The present invention addresses the above-mentioned problems relating to the intake system of an engine, and an overall intake system for a multi-cylinder engine that variably controls the substantial pipe length of the intake passage in accordance with the engine speed. (EN) An intake device which is compact and has a small number of parts and which can effectively utilize the intake inertia effect over a wide operating range. As a result, the problem of the installation space of the intake device is solved, the output torque is improved or equalized, and the volume of the intake passage is increased when various engine controls are performed based on the output signal of the air flow meter. The purpose is to prevent the control delay and the deterioration of responsiveness caused by the operation.

(Structure of the Invention) The present invention is characterized by having the following structure in order to achieve the above object.

That is, the branch passages of the cylinders whose ignition orders are not adjacent to each other and have a 360 ° crank angle phase are gathered into one independent intake passage on the upstream side, and these plural independent intake passages are further merged on the upstream side. In an intake system for a multi-cylinder engine having four or more even cylinders, a first communication passage having an expanded volume portion communicated with upstream portions of the plurality of independent intake passages via first opening / closing valves, respectively. A second communication passage that is provided on the downstream side of the communication passage and has no expanded volume portion that communicates with the downstream portions of the plurality of independent intake passages via the second opening / closing valve is provided. An opening / closing valve control means for opening / closing the first and second opening / closing valves is provided. The on-off valve control means closes both the first and second on-off valves when the engine speed is in the low speed range,
When in the middle rotation speed region, the first opening / closing valve is opened and the second opening / closing valve is closed, and in the high rotation speed region, both the first and second opening / closing valves are opened.

According to the above configuration, when the engine speed is in the low rotation speed range, that is, the opening / closing valve control means closes the first and second opening / closing valves so that the first communication passage and the second communication passage are connected to each other. When the independent intake passages are cut off, the upstream merging portion of each independent intake passage (the opening of each independent intake passage to the surge tank if a surge tank is provided) serves as the atmosphere opening portion. To work. Therefore, in this case, an intake pressure signal with a low natural frequency is generated in the long passage from the confluence portion to the combustion chamber, and this intake pressure vibration and the engine speed are in the low rotation range. The low-cycle intake valve opening / closing cycle (the number of times of opening / closing per unit time) is synchronized with this low rotation region.

Further, when the engine speed is in the middle rotation range, that is, when the upstream first opening / closing valve is opened and the respective independent intake passages and the first communication passages are communicated with each other, the first communication passages have the expanded volume portion. Therefore, the communication portion between the first communication passage and each independent intake passage acts as an atmosphere opening portion, whereby intake pressure vibration causes a relatively short passage portion from the communication portion to the combustion chamber. Will occur in. Therefore, the frequency of the intake pressure vibration occurring at this time is higher than that in the low rotation range, and the intake pressure vibration and the opening / closing cycle of the intake valve of a relatively high cycle are synchronized in the middle rotation range. become.

Furthermore, when the engine speed is in the high speed range, that is,
When the first and second communication passages and the respective independent intake passages are communicated with each other by opening both the first and second opening / closing valves, the second communication passage does not have an enlarged volume portion, The opening of the second communication passage to each independent intake passage functions as an atmosphere opening portion. This is because if only the second communication passage on the downstream side is opened while the first communication passage on the upstream side is blocked, the second communication passage on the downstream side is opened.
Since the communication passage does not have a sufficient volume, the communication portion between the second communication passage and the independent intake passage cannot serve as an atmosphere opening portion for reflecting the pressure wave. Since the first communication passage having the enlarged volume portion provided on the upstream side of the communication passage is also communicated with the independent intake passage at the same time,
This is based on the phenomenon that air can be replenished from the communication passage to the intake passage, which helps the communication portion of the second communication passage to act as a reflection point of the pressure wave. Further, even if a part of the pressure wave passes through the communication portion of the second communication passage, it does not reach the upstream side merging portion of each independent intake passage and is reliably reflected by the communication portion of the first communication passage. As a whole, the second communicating portion generally acts as a reflection point of the pressure wave. In this way, when the communication portion of the second communication passage on the downstream side acts as a reflection point of the pressure wave, intake pressure vibration occurs in a shorter passage portion from the communication portion to the combustion chamber. The frequency of the pressure vibration becomes higher than that in the middle rotation range, and the intake pressure vibration and the opening / closing cycle of the intake valve are synchronized in the high rotation range.

(Effects of the Invention) As described above, according to the intake system for a multi-cylinder engine according to the present invention, the independent intake air in which the branch passages of the cylinders whose ignition orders are not adjacent to each other and have a 360 ° crank angle phase are gathered on the upstream side. By connecting two communication passages to an upstream portion and a downstream portion of the passage and connecting or disconnecting these communication passages to or from the independent intake passages according to the engine speed, the low, medium, and high rotation regions are respectively provided. In the configuration in which the intake pressure oscillation and the opening / closing cycle of the intake valve are satisfactorily synchronized with each other, the communication passage provided on the downstream side of the two communication passages is not provided with an enlarged volume portion, and the communication passage is provided. Since the communicating part to the independent intake passage can be made to act as a reflection point of the pressure wave, that is, the atmosphere opening part, it is possible to effectively improve and equalize the intake inertia effect or output torque over a wide motion range. It is possible to reduce the size of the intake device while maintaining it. This solves the problem of the installation space or layout of the intake device, and increases the volume on the downstream side of the air flow meter, especially when various engine controls are performed based on the output value of the air flow meter. The resulting control delay or deterioration of responsiveness is suppressed to a minimum. In particular, according to the present invention, since the individual intake passages are such that the branch passages of the cylinders whose ignition orders are not adjacent to each other and have a 360 ° crank angle phase are assembled on the upstream side, one independent intake passage is provided. The intake strokes of the cylinders gathering in the passage do not overlap with each other in timing, and when the intake valve of one cylinder is open, the intake valves of the other cylinders are always closed. Therefore, the pressure wave generated in one cylinder is not affected by the opening of the intake valve in the other cylinder, and the positive pressure wave pushes the intake air, that is, the intake inertia effect is effective for each cylinder. Will be obtained.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIGS. 1 to 3 show the first embodiment of the present invention.
As shown in the figure, the intake device 2 of the engine 1 includes a main intake passage 5 having an upstream end connected to an air cleaner 3 and an air flow meter 4 for detecting an intake flow amount in the middle thereof, and a main intake passage 5 branched from the main intake passage 5. Two independent intake passages 6 ₁ , 6 ₂
And _one of the independent intake passages 6 ₁ and 6 ₂ is further branched from the independent intake passage 6 ₁ to form the second and third cylinders of the engine 1.
The second and third branch passages 8 ₂ and 8 _{3 respectively} communicating with the combustion chambers of 7 ₂ and 7 ₃ and the other independent intake passage 6 _{2 are} further branched to the first and fourth cylinders 7 ₁ and 7 ₄ of the engine 1. And the first and fourth branch passages 8 ₁ and 8 ₄ communicating with the respective combustion chambers. In that case, firing order in the first to fourth cylinders 7 _{1-7 4} of the engine 1, for example, the first
The cylinders 7 ₁ → the third cylinder 7 ₃ → the fourth cylinder 7 ₄ → the second cylinder 7 ₂ are arranged in this order, and therefore the ignition order is not adjacent and the second cylinder 7 ₂ and the second cylinder 7 ₂ which have a 360 ° crank angle phase. 3 and cylinder 7 ₃ is communicated to one of the independent intake passage 6 _1, also the first cylinder ₇₁ not adjacent to each other is also firing order and the fourth cylinder 7 ₄ is communicated with the other of the independent intake passage 6 ₂ It will be.

However, the intake device 2 has two independent intake passages.
The first communication passage 9 and the second communication passage 10 from the upstream side across 6 ₁ and 6 _2.
And are provided. Of these, the first communication passage 9 is
The interior is an enlarged volume having a required volume, and is communicated with the intermediate portion of the both independent intake passages 6 ₁ and 6 ₂ , and
First opening / closing valves 11 and 11 are respectively provided at the communication portions of the first communication passage 9 to both the independent intake passages 6 ₁ and 6 ₂ . On the other hand, the second communication passage 10 is a narrow passage having no enlarged volume inside, and communicates with the branch portions of the branch passages 8 ₁ to 8 ₄ downstream of the independent intake passages 6 ₁ and 6 _2. In addition, the second opening / closing valve 1 is provided in the communication portion of the second communication passage 10 to both the independent intake passages 6 ₁ , 6 ₂ .
2, 12 are arranged respectively. Further, in addition to the above configuration, the intake device 2 is provided with first and second actuators 13 and 14 for driving the first on-off valves 11 and 11 and the second on-off valves 12 and 12 to open and close, respectively. In addition, a control unit 16 is provided which receives the engine speed signal a from the engine speed sensor 15 and outputs the first and second drive signals b and c to the actuators 13 and 14, respectively. Then, the control unit 16 controls the predetermined first and second drive signals b, b according to the engine speed indicated by the engine speed signal a.
By outputting c, as shown in FIGS. 3 (I) and (II), when the engine speed is in the low speed region of the first set speed N ₁ or less, the first and second opening / closing valves 11 , 12 are both closed, and the first opening / closing valve 11 is opened and the second opening / closing valve 12 is closed in the middle rotation range from the first set speed N ₁ to the second set speed N _2. In addition, both the first and second opening / closing valves 11 and 12 are opened in the high rotation speed region of the second set rotation speed N ₂ or more.

Next, the operation of the first embodiment will be described.

When the engine 1 is operating, the intake air that is taken in from the air cleaner 3 in the intake device 2 and whose flow rate is detected by the air flow meter 4 when passing through the main intake passage 5 is:
It is distributed from the main intake passage 5 to the two independent intake passages 6 ₁ and 6 ₂ and is further supplied to the _first to fourth cylinders 7 _{1 to} 7 ₄ via the _first to _fourth branch passages 8 ₁ to 8 _4. Are distributed and supplied in the order of (first, third, fourth, second cylinder in this order).

In that case, the rotation speed signal a from the engine rotation sensor 15
When the engine speed detected on the basis of the engine speed is in the low speed range (the range of the first set speed N ₁ or less), the control unit 16 operates to close both the first and second on-off valves 11 and 12. Therefore, at the start of the intake stroke of the engine 1, that is, when the intake valve 17 shown in FIG. 2 is opened, the pressure wave generated in the intake port 18 and propagated toward the upstream side is divided into the branch passages 8 ₄ (8 _{The same} applies to ₁ to 8 ₃ ) and the independent intake passage 6 ₂ (6 ₁
The same applies to the above) and is reflected at the confluence position A of both independent intake passages 6 ₁ and 6 _{2 that} act as an atmosphere opening portion. Therefore,
The intake pressure vibration is generated as a vibration having a low natural frequency in the passage of the length L shown in the figure between the position A and the combustion chamber 19, and as a result, the intake pressure vibration and the intake valve 17 The opening / closing cycle, that is, the engine speed is synchronized with each other in the low speed region. By this tuning, an effective intake inertia effect is obtained, and as shown in FIG. 3 (III), the peak X ₁ occurs in the low rotation speed region in the characteristic of the intake charging efficiency, and this peak X ₁ or The output torque of the engine 1 in the low rotation speed region is increased by utilizing the characteristics in the vicinity.

Further, when the engine speed detected based on the engine speed signal a is in the medium speed range (the range from the first set speed N ₁ to the second set speed N ₂ ), the control unit 16 operates Due to the operation, only the first opening / closing valve 11 is opened, and the expanded volume portion of the _first communication passage 9 having a required volume is communicated with the independent intake passage 6 ₂ (6 ₁ ). The generated pressure wave is generated by the independent intake passage 6 ₂ (6 ₁ ) above.
Is reflected at the communication position B of the first communication passage 9 (hereinafter referred to as the first communication position). Therefore, in this case, the intake pressure vibration occurs in the short passage portion indicated by the length l ₁ , the natural frequency of the pressure vibration becomes higher than that in the low rotation region, and the intake pressure vibration and the intake air The opening / closing cycle of the valve 17 will be synchronized in the medium speed range of the engine speed. As a result, as shown in FIG. 3 (III), a peak X ₂ occurs in the characteristic of the intake charging efficiency in the middle rotation region, and by utilizing the characteristic of this peak X ₂ or the vicinity thereof, this middle rotation region Also in, the output torque is increased.

However, the engine speed is in the high speed range (second set speed
N ₂ or more), both the first and second on-off valves 11 and 12 are opened, and the first communication passage 9 having the expanded volume portion and the second communication passage having no expanded volume portion 10 and the independent intake passage 6 ₂ (6 ₁ ) are communicated with each other. In this case, although the second communication passage 10 does not have an enlarged volume, the intake port 18 pressure wave is propagated to the upstream side, a communication position to independent intake passage 6 ₂ of the second communication passage 10 (6 ₁₎ (hereinafter, second that communication position) are reflected by C. This is because the first and second on-off valves 11 and 12 are opened as described above, and the independent intake passage is separated from the expanded volume portion in the first communication passage 9.
Since it becomes possible to supplement 6 ₂ (6 ₁ ) with air, in other words, a phenomenon that occurs as if a sufficient volume is provided in the second communication passage 10 as well. Is. Therefore, only the second communication passage 10 is connected to the independent intake passage 6
Even if the second communication passage 10 is communicated with ₂ (6 ₁ ), the second communication position C does not act as a reflection point of the pressure wave because the second communication passage 10 does not have an enlarged volume. By connecting the second communication passage 10 with the first communication passage 9 to the independent intake passage 6 ₂ (6 ₁ ), it is possible to make the second communication position C act as a reflection point of the pressure wave. . Here, at this time, only a part of the pressure wave is at the second communication position C.
However, the pressure wave is not completely reflected at the first communication position B on the upstream side and does not reach the confluence position A on the upstream side. Can be viewed as being reflected at the second communication position C. When thus the second communication position C acts as a reflection point of the pressure wave, intake pressure vibration, a shorter length l ₂ of the passage portion than in the rotating region (multi-branched passages 8 ₁ 8 ₄ ), the natural frequency of the pressure vibration is further increased, and accordingly, the intake pressure vibration and the opening / closing cycle of the intake valve 17 are synchronized with each other in the high rotation speed region of the engine speed. By this tuning, a peak X ₃ is generated in the intake charge efficiency characteristic shown in FIG. 3 (III) in the high rotation region, and the characteristic in the peak X ₃ or in the vicinity thereof is utilized, so that in the high rotation region. Will also increase the output torque.
In this high rotation speed region, the ignition sequence (intake sequence)
Since the first and third branch passages 8 ₁ and 8 ₃ corresponding to the adjacent cylinders, for example, the first cylinder 7 ₁ and the third cylinder 7 ₃ are communicated via the second communication passage 10, The pressure wave generated in the intake port leading to the first cylinder 7 ₁ reaches the third cylinder 7 ₃ with good timing to further increase the action of pushing the intake air into the third cylinder 7 _3, and thus the intake port of each cylinder is increased. There is also an effect that the pressure wave generated in the positive influence sequentially on the cylinders in the next intake sequence. Further, the second and third cylinders 7 ₂ and 7 ₃ gathered in the independent intake passage 6 ₁ via the branch passages 8 ₂ and 8 ₃ and the independent intake passage 6
₂ to the branch passage 8 _1, 8 ₄ first is set via a fourth cylinder 7 _1, 7
No. ₄ is a cylinder that does not have the ignition order next to each other and has a 360 ° crank angle phase, so the intake strokes of these cylinders do not overlap in time, and the intake valve of one cylinder does not overlap. When 17 is open, the intake valve 17 of the other cylinder is always closed. Therefore, the pressure wave generated in one cylinder causes the intake valve in the other cylinder to
Not affected by the opening of 17,
The pushing action of the intake air by the positive pressure wave can be effectively obtained for each cylinder.

As described above, the control unit 16 is the first
By switching the open / closed states of the first and second on-off valves 11 and 12 to the states shown in FIGS. 3 (I) and (II) at the set rotation speed N ₁ and the second set rotation speed N ₂ , As shown in II), the intake charging efficiency is increased over a wide rotation range and a smoothed characteristic curve is obtained. Then, in particular, the second communication passage 12 having no expanded volume portion is connected to the independent intake passage 6 ₂ (6 ₁ ) together with the upstream side first communication passage 9 having an expanded volume portion, so that the second communication passage 12 can be connected in the high rotation region. Communication position C
Since it is possible to act as a reflection point of the pressure wave, the intake device 2 can be downsized and the air flow can be reduced compared to the case where the expanded volume portions are provided in both the first and second communication passages 9 and 12. When the fuel control or the like is performed based on the output value of the meter 4, the control delay and the like due to the increase in the volume on the downstream side of the meter 4 is suppressed to the minimum.

Next, a second embodiment of the present invention will be described based on the fourth to sixth aspects.

The intake device 21 of the engine 20 in this embodiment is provided with a surge tank 24 at the downstream end of a main intake passage 23 in which an air flow meter 22 is provided, and the surge tank 24
Two independent intake passages 25 ₁ and 25 ₂ branched from are respectively connected to an upper space 26 ₁ and a lower space 26 ₂ of a first communication passage 26 having an enlarged volume, and further, to the communication passage 26. Upper space 26 ₁
The 2nd and 3rd branch passages 27 ₂ and 27 3 branched from _2nd and _3rd have the ignition order next to each other and have a 360 ° clamp angle phase
Similarly, the first and fourth branch passages 27 ₁ and 27 _{4 which} are respectively connected to the cylinders 28 ₂ and 28 _{3 and which} are branched from the lower space 26 ₂ do not have the ignition order adjacent to each other and have a 360 ° crank angle phase. The second communication passage 29 which is connected to the _first and fourth cylinders 28 ₁ and 28 ₄ and which does not have an enlarged volume portion across these first to fourth branch passages 27 _{1 to} 27 ₄
Is provided. A first opening / closing valve 30 that connects and disconnects the upper space 26 ₁ and the lower space 26 ₂ is provided in the first communication passage 26, and the first communication passage 29 and the branch passages 27 _{1 to} 27 31 are respectively provided in the communicating portions with the fourth opening / closing valve _4, and the first opening / closing valve 30 and the second opening / closing valve 31 ... 31 are controlled by a control unit not shown in FIG. ) And (II), the opening and closing is controlled according to the engine speed.

That is, also in this embodiment, as in the first embodiment,
When the engine speed is in the low speed range (the range equal to or lower than the first set speed N ₁ ), both the first and second on-off valves 30 and 31 are closed, and intake pressure vibration with a low natural frequency causes intake air. Port 32 ...
E in the combustion chamber side 32 from the end portion E ... E of the independent intake passages 25 ₁ and 25 _{2 to} the surge tank 24 at the opening positions F, F in the passage of length L ', and when in the middle rotation region, 1 on-off valve 30
Only the valve is opened so that the intake pressure vibration of medium natural frequency is from the end portions E ... E of the intake ports 32 ... 32 to the opening positions G ... G from the branch passages 27 _{1 to} 27 ₂ to the first communication passage 26. Occurs in a passage of length l ₁ ′ of. Furthermore, when in the high rotation range,
By opening both the first and second on-off valves 30 and 31, the communication positions H ... H of the second communication passage 29 become the reflection points of the pressure wave and the high natural frequency is obtained, as in the above embodiment. 32 is generated in the passage of length l ₂ ′ from the end portions E ... E of the intake ports 32 ... 32 to the passage positions H ... H of the _second communication passage 29. As a result, the intake pressure oscillation and the opening / closing cycle of the intake valve 33 are well synchronized in each of the low, middle, and high regions, and as shown in FIG. ₁ , ₁ , ₂ and Y ₃ are generated respectively, and as a result, the intake charging efficiency is effectively increased over the entire rotation range and a smoothed characteristic curve is obtained.

As described above, also in this embodiment, the second communication passage 29 is provided.
Does not have an enlarged volume, but the communication position H
It is possible to make H act as a reflection point of the pressure wave in the high rotation region, and the intake device 21 is downsized. In this embodiment also, the independent intake passage
The second and third cylinders, which are gathered in 25 ₁ through branch passages 27 ₂ and 27 ₃
28 ₁ , 28 ₃ and the first and fourth cylinders 28 ₁ , 28 ₄ gathered in the independent intake passage 25 ₂ via the branch passages 27 ₁ , 27 ₄ do not have the ignition order adjacent to each other and 360 ° Since the cylinders have the crank angle phase, the action of pushing the intake air by the positive pressure wave can be effectively obtained for each cylinder.

[Brief description of drawings]

1 to 3 show a first embodiment of the present invention.
The figure is a schematic plan view of the intake system of the engine, FIG. 2 is a cross-sectional view taken along one of the independent intake passages and the fourth branch passage in FIG. 1, and FIGS. 3 (I), (II), ( III) is a characteristic diagram showing the opening / closing operation of the first opening / closing valve, a characteristic diagram showing the opening / closing operation of the second opening / closing valve, and a characteristic diagram of the intake charging efficiency showing the operation effect, respectively. Further, FIGS. 4 to 6 show a second embodiment of the present invention. FIG. 4 is a schematic plan view of the intake system of the engine, and FIG. 5 is from the surge tank to the second cylinder in FIG. 6A, 6B, 6C, 6D, 6E, 6F, 6E, 6F, 6I, 6I, 6I, 6I, 6I, 6I and 6I show characteristic diagrams showing the opening / closing operation of the first on-off valve and the opening / closing operation of the second on-off valve, respectively. FIG. 4 is a characteristic diagram and a characteristic diagram of intake air charging efficiency showing action and effect. 1,20 …… Engine, 2,21 …… Intake device, 6 ₁ , 6, ₂ , 25 ₁ , 25 ₂
...... Independent intake passage, 8 ₁ to 8 ₄ , 27 _{1 to} 27 ₄ …… Branch passage, 9,2
6 …… First communication passage, 10,29 …… Second communication passage, 11,30 …… First opening / closing valve, 12,31 …… Second opening / closing valve, A, 24 …… Confluence part (merging position, surge tank).

Claims (1)

[Claims] Claim: What is claimed is: 1. The branch passages of cylinders whose ignition orders are not adjacent to each other and which have a 360 ° crank angle phase are gathered into one independent intake passage on the upstream side, and the plurality of independent intake passages are provided on the upstream side. A first intake system for a multi-cylinder engine having four or more even-numbered cylinders joined together, the first intake system having an expanded volume section communicating with the upstream sections of the plurality of independent intake passages via first opening / closing valves, respectively. A communication passage; and a second communication passage that is provided on the downstream side of the communication passage and has no expanded volume portion that communicates with the downstream portions of the plurality of independent intake passages via the second on-off valve, respectively. When the engine speed is in the low speed range, the first and second opening / closing valves are closed, and when the engine speed is in the medium speed range, the first opening / closing valve is opened to the second speed.
When the on-off valve is closed and the engine is in the high rotation speed range,
An intake system for a multi-cylinder engine, comprising an opening / closing valve control means for opening the opening / closing valve.