JP2003193921A - Engine air intake device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress disagreeable noises attributable to the difference in frequency of the pressure pulsation caused by the difference in passage length by setting the passage length from a throttle valve to a suction passage to be substantially equal to each other while miniaturizing an air intake device. <P>SOLUTION: The length L2 between both ends 15a and 18a in the direction of the cylinder bank in second upstream end opening parts 15a-18a is set to be shorter than the length L3 between both ends in the direction of the cylinder bank in intake ports 8 opened in one side part of an engine unit 2 and arranged continuous in the direction. The length L1 between both ends 11a and 14a and 12a and 13a in the direction of the cylinder bank in first upstream opening parts 11a-14a is set to be shorter than the length L2 between both ends 15a and 18a in the direction of the cylinder bank in the second upstream opening parts 15a-18a. The first upstream end opening parts 11a, 12a and 13a and 14a partially overlapping each other are arranged substantially on the same circumference with respect to the second upstream end opening parts 16a and 17a located in the middle with respect to the direction of the cylinder bank. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake device for an engine having a variable intake system.

[0002]

2. Description of the Related Art Conventionally, an intake system for an engine is provided with a surge tank and a branch passage branched from the surge tank and connected to an intake port of each cylinder. Various techniques have been adopted for increasing intake air charging efficiency by utilizing dynamic supercharging effects such as inertial effects and resonance effects. Of this dynamic supercharging effect, the inertia effect is
When the negative pressure wave generated in each branch passage bounces off in the surge tank, the connection part of the surge tank and each branch passage becomes almost free end, the negative pressure wave is inverted to the positive pressure wave, and this positive pressure wave is transferred to the intake valve immediately before closing. By making it work, the intake charging efficiency is increased. The engine speed range in which the intake charging efficiency is enhanced by this inertial effect depends on the length of the branch passage, and it is effective to make it long in the low speed range and short in the high speed range.

By the way, in order to increase the intake charge efficiency in both the high speed operation state and the low speed operation state for the engine due to the inertial effect, the surge tank branches off from the surge tank and communicates with each cylinder of the engine and the surge tank. A technique has also been put into practical use in which two systems of branch passages, a high-speed passage and a high-speed passage communicating in the middle of the low-speed passage are branched so as to bypass the low-speed passage, by a rotary valve having a small intake flow resistance.

For example, as shown in FIGS. 26 and 27,
In the intake device described in Japanese Patent Application Laid-Open No. 10-89171, two openings 101, 102 for high speed and for low speed are formed so as to be separated from each other by a predetermined distance in the circumferential direction of the surge tank 100. Rotary valve 10 in which 102 is rotatably mounted in surge tank 100
It can be opened and closed with 3.

In the low speed operation state, as shown by the solid line arrow in FIG. 27, the intake air passes from the surge tank 103 through the opening 102 for low speed, and the intake passage for low speed 104 which makes about two laps around the outer peripheral portion of the surge tank 100, the common intake air. It is supplied to the intake port via the passage 105. On the other hand, in the high speed operation state, as shown in FIG.
As shown by the dotted line arrow 7 in FIG.
It is supplied to the intake port from 0 through the high speed opening 101 and the common intake passage 105.

Further, Japanese Patent No. 2824294 discloses that
A configuration is disclosed in which low-speed passages are bundled and connected to a surge tank, high-speed passages are bundled and connected to a surge tank, and branched into respective low-speed passages.

[0007]

In the intake device of the above publication, the high speed opening 101 and the low speed opening 102 are formed on the circumference of the surge tank 100 so as to be separated from each other, and the low speed operating state and the high speed operating state. When switching between the two, the rotary valve 103 is provided with two openings 101, 102.
However, since the opening area is temporarily narrowed at this time, the intake air is absorbed by the surge tank 1.
00 to low speed intake passage 104 or common intake passage 105
The resistance (hereinafter, referred to as intake air outflow resistance) at the time of flowing out to the intake air becomes large, and the intake charging efficiency decreases.

Further, in order to obtain a sufficient inertial effect in the low speed operation state, the low speed intake passage 104 needs to have a predetermined length or more. For this reason, the low-speed intake passage 104 is formed to have a passage length that makes approximately two rounds around the outer peripheral portion of the surge tank 100, and the length of the surge tank 100 in the cylinder column direction becomes large, so that the throttle valve to the intake port are extended over a plurality of cylinders. It is difficult to reduce the difference in the passage lengths between the cylinders, and the dynamic supercharging effect varies among the cylinders.

The present invention has been made in view of the above problems, and an object thereof is to make the passage size from the throttle valve to the intake passage substantially equal while miniaturizing the device, and to cause the difference in frequency of pressure pulsation due to the difference in passage length. An object of the present invention is to provide an intake system for an engine that suppresses unpleasant noise caused by the above, unifies the natural frequency between the low-speed intake passage and the high-speed intake passage, and makes the charging efficiency uniform.

[0010]

In order to solve the above-mentioned problems and to achieve the object, an intake system for an engine of the present invention branches from a collecting passage and opens at one side of an engine unit to form a cylinder row. A first passage communicating with the intake port of each cylinder arranged side by side in the direction; and a second passage branching from the collecting passage and communicating with the middle of the first passage so as to bypass at least the upstream side of the first passage. An intake system for an engine, comprising: a passage; and a variable intake mechanism capable of selectively changing a communication state between at least the collecting passage and the second passage according to an operating state of the engine. A cylinder in which the upstream end openings of the second passages that are set in the column direction and connected to the collecting passage are arranged side by side in the cylinder row direction, and the upstream end opening of the second passage that is connected to the collecting passage is arranged. The length between both ends in the direction of the cylinder is set shorter than the length between both ends in the direction of the cylinder row in each of the intake ports, and the upstream end opening of the first passage connected to the collecting passage is set in the direction of the cylinder row. The first passages are arranged side by side in the circumferential direction of the collecting passages, and the upstream end openings of the first passages are overlapped with each other in at least a part of the first passage, and the upstream end openings of the first passages are arranged between both end portions in the cylinder row direction. The length was set to be shorter than the length between both ends in the cylinder row direction of the upstream end opening of the second passage.

Further, preferably, the variable intake mechanism includes a hollow rotary valve which is arranged in the collecting passage and is rotatable around an axis of the collecting passage, and the upstream end opening of the second passage is provided. One in the cylinder row direction and the overlapping upstream end opening of the first passage are arranged at substantially the same position in the cylinder row direction, and the rotary valve has an outer peripheral portion at which the overlapping upstream end of the first passage is rotated. The opening and the second
An opening is formed to selectively open and close one of the upstream end openings of the passage.

[0012] Preferably, the upstream end opening of the first passage is arranged at substantially the same position in the circumferential direction as the upstream end opening of the second passage located in the middle in the cylinder row direction. There is.

Further, preferably, the first passage is formed so as to surround the collecting passage, and an upstream end opening thereof is connected to an outer peripheral portion of the collecting passage so as to communicate therewith.

Further, preferably, the first passage is set to an intake pipe length which is tuned to an intake characteristic in an engine low and medium rotation range, and the second passage is tuned to an intake inertia characteristic in an engine maximum rotation range. Set to long.

[0015]

As described above, according to the invention of claim 1, the axial direction of the collecting passage is set in the cylinder row direction, and the upstream end opening of the second passage connected to the collecting passage is arranged in the cylinder row direction. And the length between both ends in the cylinder row direction at the upstream end opening of the second passage connected to the collecting passage,
The length is set shorter than the length between both ends of each intake port in the cylinder row direction, and the upstream end opening of the first passage connected to the collecting passage is arranged side by side in the cylinder row direction and the circumferential direction of the collecting passage. The upstream end openings of the first passages arranged in the circumferential direction are overlapped with each other at least in part, and the length between the both ends in the cylinder row direction of the upstream end opening of the first passage is determined by the upstream end opening of the second passage. By setting it shorter than the length between both ends in the cylinder row direction, while making the device compact, the passage length from the throttle valve to the intake passage is made substantially equal, and due to the difference in frequency of pressure pulsation due to the difference in passage length. It is possible to suppress the unpleasant sound generated as a result, unify the natural frequencies of the low-speed intake passage and the high-speed intake passage, and make the filling efficiency uniform.

According to the second aspect of the present invention, the variable intake mechanism includes a hollow rotary valve which is disposed in the collecting passage and is rotatable around the axis of the collecting passage, and the upstream end opening of the second passage. No. 1 in the cylinder row direction and an overlapping upstream end opening of the first passage are arranged at substantially the same position in the cylinder row direction, and the outer peripheral portion of the rotary valve has its upstream end opening overlapping the first passage due to its rotation. By forming an opening that selectively opens and closes one of the upstream end openings of the second passage, it becomes possible to switch between a low speed operation state and a high speed operation state, and the intake charging efficiency in the low speed operation state can be improved. It is possible to improve.

According to the third aspect of the present invention, the upstream end opening of the first passage is located at substantially the same position in the circumferential direction as the upstream end opening of the second passage located in the middle in the cylinder row direction. With the arrangement, the opening of the rotary valve can be made common to switch between the low speed operation state and the high speed operation state, and it becomes easy to make the intake passage lengths substantially equal.

According to the fourth aspect of the present invention, the first passage is formed so as to surround the collecting passage, and the upstream end opening is connected to the outer peripheral portion of the collecting passage so as to communicate with each other. It becomes easy to make the passage lengths from the throttle valve to the intake passage substantially equal while reducing the size.

According to the fifth aspect of the present invention, the first passage is set to the intake pipe length which is tuned to the intake characteristic in the low and middle engine speed range, and the second passage is tuned to the intake inertia characteristic in the maximum engine speed range. By setting the intake air length to be longer, the intake passage length can be increased, and the intake charge efficiency in the low speed operation state can be improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The embodiment described below is an example in which the invention is applied to an intake device of an in-line four-cylinder engine for an automobile, but the present invention is, for example, within a range not departing from the gist of the invention. , The number of cylinders is not limited to 4 cylinders, V
The present invention can also be applied to a modified or modified version of the following embodiment so that it can be mounted on other engine types such as 6, V8, and horizontally opposed. [First Embodiment] First, an intake system for an engine according to a first embodiment of the present invention will be described.

In the following description, when viewed from the front of the engine of FIG. 1, the vertical direction of the plane of the drawing is the vertical direction of the vehicle body, the horizontal direction is the vehicle width direction (cylinder row direction), the front and back directions are the vehicle longitudinal direction, and similarly. In the plan view of the engine of FIG. 2, the front and back directions of the plane of the drawing are the vertical direction of the vehicle body, the left-right direction is the vehicle width direction (cylinder row direction), and the vertical direction is the vehicle front-back direction. One example is one horizontally placed in the width direction, but the present invention is not limited to this, and it goes without saying that the present invention is also applicable to one vertically placed in the front-rear direction of the vehicle body.

FIG. 1 is a front view of an engine air intake device according to a first embodiment of the present invention, FIG. 2 is a plan view of an engine air intake device according to a first embodiment of the present invention, and FIG. 3 is related to the present invention. FIG. 4 is a right side view of the engine intake system of the first embodiment, and FIG. 4 is a left side view of the engine intake system of the first embodiment of the present invention, respectively, showing an in-line 4-cylinder engine 1 (hereinafter referred to as engine 1). The engine unit 2 has a cylinder block 2a and a cylinder head 2b, and four first to fourth cylinders 3A to 3D arranged in series in the cylinder block 2a from the right side to the left side of the drawing. Is formed, the cylinder head 2b defines an upper end portion of each of the cylinders 3A to 3D, and a top surface portion 3a having two intake ports 8 and two exhaust ports 9 communicating with each of the cylinders 3A to 3D is formed. Done There. Each intake port 8 is provided with an intake valve 5 that opens and closes a port opening 8a that communicates with each cylinder 3A to 3D, and a valve guide that operates coaxially with a tangent line that is in contact with the axis of the intake port 8 at the port opening 8a. You will be guided at 5a. Similar to each intake port 8, each exhaust port 9 is provided with an exhaust valve 6 that opens and closes a port opening 9a communicating with each cylinder 3A to 3D, and a tangent line that is in contact with the axis of the exhaust port 9 at the port opening 9a. It is guided by the valve guide 6a so as to operate coaxially with.

In each of the cylinders 3A to 3D, a combustion chamber is formed by the top surface portion 3a, the piston 4, two intake valves 5 and two exhaust valves 6. The intake port 8 has an upstream portion of 1
In the book, it branches toward two intake valves 5 on the way.
The engine unit 2 is provided with an intake device 7 for introducing intake air into each of the cylinders 3A to 3D on one front side in the front-rear direction of the vehicle body, and the intake air introduced from the intake device 7 is By opening the intake valve 5 via the intake port 8, the respective cylinders 3A to 3D have a predetermined timing (for example, 3
(A->3C->3D-> 3B ignition order). <Intake Device> Next, the intake device 7 will be described.

As shown in FIGS. 1 to 4, the intake device 7
Is an intake pipe 23, a surge tank (collecting passage) 10,
Four first branch passages 11 to 14 branched from the outer peripheral portion of the surge tank 10 and respectively connected to the intake ports 8 of the four cylinders 3A to 3D, and a first branched passage 11 branched from the outer peripheral portion of the surge tank 10 are provided. The second branch passages 15 to 18 communicating with the first branch passages 11 to 14 so as to short-circuit the first branch passages 11 to 14, the surge tank 10, and the first branch passages 11 to 14 or the second branch passage 15 And a rotary valve (variable intake mechanism) 20 capable of selectively changing a communication state with each other in accordance with an operating state of the engine. The surge tank 10 and the first and second branch passages 11 to 1
8 is integrally formed of a material such as synthetic resin.

The surge tank 10 is formed in a hollow cylindrical shape whose axis extends horizontally in the left-right direction, is arranged near one side of the engine unit 2 in the longitudinal direction of the vehicle body, and the intake pipe is provided at the right end of the surge tank 10. A throttle body 24 is provided downstream of the intake pipe 23. The throttle body 24 has a built-in throttle valve 24a, and the opening degree of the throttle valve 24a changes according to the depression operation of an accelerator pedal or the operation of an electrically driven actuator, and the surge tank 10
The amount of intake air flowing in is adjusted. The length in the left-right direction of the surge tank 10 is formed to be shorter than the distance between the two intake ports 8 corresponding to the cylinders 3A and 3D at the left and right ends, respectively.

The first branch passages 11 to 14 are connected to the outer peripheral portion of the surge tank 10 at the first upstream end opening 11a to.
14a and the first pipe portions 11b to 11b extending in a straight line from the first upstream end openings 11a to 14a while extending obliquely upward to the engine unit 2 side and curving downward of the surge tank 10.
14b, second pipe portions 11c to 14c that linearly extend above the surge tank 10 while curving toward the engine unit 2 side below the surge tank 10, and bend toward the engine unit 2 side above the surge tank 10. To the intake port 8 that extends to the side of the engine 1
5 and the third pipe portions 11d to 14d connected to each other.

Further, the first pipe portions 11b to 14b which are curved from above the surge tank 10 and extend downward in the first branch passages 11 to 14 are formed so as to be arranged in a substantially planar shape in the cylinder row direction on the engine unit 2 side. Has been done.

Second pipe portions 11c to 14c extending upward from below the surge tank 10 in the first branch passages 11 to 14.
Are arranged in a substantially planar shape in the cylinder row direction on the side opposite to the engine unit 2 and are located at both ends of the cylinder row in the cylinder row direction.
The lower end positions P1 of the c and 14c are the second pipe portions 12c and 13c located at the center in the cylinder row direction when viewed from one side in the cylinder row direction.
Is arranged at a position higher than the lower end position P2.

The second branch passages 15 to 18 are connected to the outer peripheral portion of the surge tank 10 and have a second upstream end opening 15a to.
It slightly extends in a direction obliquely upward from 18a in a direction away from the engine unit 2, and joins in the middle of the straight line portion of the second pipe portions 11c to 14c of the first branch passages 11 to 14.

The first branch passages 11 to 14 are arranged so as to surround most of the outer circumference (about 4/5) of the surge tank 10, and the anti-engine unit 2 is provided in the second branch passages 15 to 18.
On the side, the second pipe parts 11c to 14c are connected to the surge tank 1
It is continuous linearly from the bottom of 0 to the top.

From the surge tank 10 to each of the four cylinders 3A
In order to make the passage length to the 3D intake port 8 equal,
First branch passage 1 corresponding to the two central cylinders 3B, 3C
Reference numerals 2 and 13 are first cylinders corresponding to the cylinders 3A and 3D at the left and right ends.
The surge tank 10 is arranged so as to extend downward from the branch passages 11 and 14 and curve upward to surround most of the outer circumference of the surge tank 10.

The first upstream end openings 11a to 14a are formed near the top of the outer peripheral portion of the surge tank 10. Of these four first upstream end openings 11a to 14a, the two first cylinders 3A and 3B on the right side correspond to the two first cylinders 3A and 3B.
The upstream end openings 11a and 12a are the second cylinder 3B from the right.
Corresponding to the second upstream end opening 16a and the surge tank 10
The two first upstream end opening / closing portions 13a, 14a corresponding to the two left cylinders 3C, 3D, which are formed on substantially the same circumference in the outer peripheral portion, correspond to the second cylinder 3C from the left. The second upstream end opening 17a and the outer peripheral portion of the surge tank 10 are formed on substantially the same circumference.

FIG. 5 shows the I-I of the intake system of the engine of FIG.
A cross-sectional view is shown showing the two first upstream end openings 11a on the right side,
The center line of 12a branches from one point on the outer circumference of the surge tank 10 and extends to form two first upstream end openings 11a, 12
a is formed so as to partially overlap in the substantially same circumferential direction. The two first upstream end openings 13a and 14a on the left side are formed similarly to the right side. That is, the four first upstream end openings 11a to 14a are formed close to each other in the vicinity of the central portion in the left-right direction of the surge tank 10, and from the throttle valve 24a to the four first upstream end openings 11a to 14a. The passage lengths are almost equal.

The second upstream end openings 15a to 18a of the second branch passages 15 to 18 are arranged side by side in the cylinder row direction with respect to the outer peripheral portion of the surge tank 10.

The four second upstream end openings 15a to 18a are arranged close to each other in the left-right direction so that the difference in passage length from the throttle valve 24a to the four second upstream end openings 15a to 18a becomes small. As described above, the length of the surge tank 10 in the left-right direction is shorter than the distance between the two intake ports 8 corresponding to the cylinders 3 at the left and right ends, respectively. 15
The difference in passage length from a to 18a is also small.

In the above structure, the first branch passages 11 to 1
4 is set to an intake pipe length that is tuned to the intake characteristic in the low and middle rotation range of the engine, and the first branch passage shorted by the second branch passages 15 to 18 is tuned to the intake inertia characteristic in the maximum rotation range of the engine. It is set to the intake length.

FIG. 10 is a development view of the rotary valve,
A cylinder in the intake port 8 in which the length L2 between the both ends 15a and 18a in the cylinder row direction of the second upstream end openings 15a to 18a is open to one side of the engine unit 2 and arranged side by side in the cylinder row direction. Length L3 between both ends in the row direction
It is set shorter.

Further, both end portions 11a, 14a and 12a in the cylinder row direction of the first upstream end openings 11a to 14a,
The length L1 between 13a is the second upstream end opening 15a-18.
It is set to be shorter than the length L2 between both ends 15a and 18a in the cylinder row direction of a.

The first upstream end openings 11a, 12a and 13a, 14 formed by partially overlapping each other.
“A” is arranged on substantially the same circumference with respect to the second upstream end openings 16a, 17a located in the middle in the cylinder row direction. <Variable intake mechanism> As shown in FIG.
The first upstream end openings 11a to 14a and the second upstream end openings 15a to 18a are respectively connected to the outer peripheral portion of the surge tank 10 so as to communicate with the internal space 22 of the surge tank 10, and four openings 10a and 10b, respectively. Are formed. In addition, inside the surge tank 10, the first upstream end openings 11a to 14a and the second upstream end openings 15a to 18a that overlap each other are provided.
Surge tank 1 to selectively open and close either
A rotary valve 20 is mounted which is rotatable around its axis 10c along the inner peripheral portion of 0.

FIG. 6 is a perspective view of the rotary valve. The rotary valve 20 made of a synthetic resin has a hollow cylindrical outer wall portion 20a extending in the left-right direction over the entire length and an end wall portion 20b closing the left end of the surge tank 10. And are integrally formed. The rotation of the rotary valve 20 causes the four openings 20d formed in the outer wall 20a in the direction of the axis 10c and the openings 10a and 10b formed in the outer peripheral portion of the surge tank 10 to communicate with each other. The end openings 11a to 14a and the second upstream end opening 15a to
Either 18a is selectively opened and closed.

The four openings 20d are formed by overlapping each other with the first upstream end openings 11a, 12a.
And the first upstream end opening 12a (13a) and the second upstream end opening, which are formed to have a width in the cylinder column direction and a length in the radial direction larger than the opening areas of 13a and 14a and are formed on substantially the same circumference. The first upstream end opening 11a is formed to have a radial length larger than the separation distance from the 16a (17a), and when the engine speed to be described later is between a low speed side operating state and a high speed side operating state. 14a and the second upstream end opening 15
Both a-18a form a partially open transient.

A pivot shaft portion 20c is provided at the center of the end wall portion 20b.
Is provided so that the pivot shaft portion 20c is rotatably supported.

The structure of the rotary valve 20 is not limited to the structure of the above embodiment, and various structures can be adopted.

As shown in FIGS. 1 and 2, a diaphragm type actuator 21 for rotatably driving the rotary valve 20 is arranged on the left side of the surge tank 10, and an output portion of the actuator 21 is a pivot shaft portion 20c. Are linked to. The actuator 21 has a general structure in which the negative pressure of the intake system introduced from the intake pipe by the negative pressure introduction pipe is applied to the diaphragm to drive the output section.

As shown in FIG. 7, in an operating state in which the engine speed is low, the opening 20d of the rotary valve 20 is located at the first upstream end openings 11a to 14a, and the internal space 22 of the surge tank 10 is located. And communicate with the second
The upstream end openings 15a-18a are closed.

On the other hand, as shown in FIG. 8, when the engine speed is in a high-speed operating state, the opening 20d of the rotary valve 20 is located at the second upstream end openings 15a-18a, and the inside of the surge tank 10 is in the open position. It communicates with the space 22 and closes the first upstream end openings 11a to 14a.

Further, as shown in FIG. 9, the opening 20d of the rotary valve 20 is located at the first upstream end opening 1 between the operating state in which the engine speed is on the low speed side and the operating state on the high speed side.
1a to 14a and the second upstream end openings 15a to 18a, and are in a transitional state in which they are both open.

Next, the operation of the intake device 7 will be described.

When the engine 1 is operating on the low speed side (operating state on the low speed rotation side), as shown in FIG. 7, the rotary valve 20 is rotationally driven by the actuator 21 as necessary, and the inside of the surge tank 10 is driven. The space 22 and the first upstream end openings 11a to 14a communicate with each other, and the second upstream end openings 15a to 18a are kept closed by the rotary valve 20. At this time, the intake air enters the intake port 8 from the surge tank 10 through the first upstream end openings 11a to 14a, the first pipe parts 11b to 14b, the second pipe parts 11c to 14c, and the third pipe parts 11d to 14d. Since it is filled and the passage length from the surge tank 10 to the intake port 8 becomes long, the intake filling efficiency in the low speed side operating state is enhanced by the inertial effect.

Further, the second pipe portions 11c to 14 in which the second branch passages 15 to 18 merge with the first branch passages 11 to 14, respectively.
Since c is continuous in a straight line, the passage resistance at this confluence portion becomes small, and it is possible to prevent the intake charge efficiency from decreasing.

On the other hand, when the engine 1 is operating at high speed (operating state on the high speed rotation side), as shown in FIG. 8, the rotary valve 20 is rotatably driven by the actuator 21 as required, and the surge tank 10 is rotated. Interior space 22
And the second upstream end openings 15a to 18a are communicated with each other, and the first upstream end openings 11a to 14a are held closed by the rotary valve 20. At this time, intake air is filled in the intake port 8 from the surge tank 10 through the second upstream end openings 15a to 18a and the second pipe portions 11c to 14c, and the passage length from the surge tank 10 to the intake port 8 is increased. Is shortened, the intake charging efficiency is increased in the high-speed side operating state due to the inertial effect.

Further, when the engine 1 switches from the low speed side operating state to the high speed side operating state, as shown in FIG. 9, the rotary valve 20 is rotatably driven by the actuator 21 as shown in FIG. End opening 11a
˜14a and the second upstream end openings 15a to 18a are both partially opened. At this time, the first upstream end openings 11a to 14a and the second upstream end openings 15a to 18a.
The sum of the areas of the open parts of a is the first upstream end opening 11
By setting the opening areas of a to 14a to be equal to or larger than the opening areas of the second upstream end openings 15a to 18a, the intake outflow resistance is reduced and the intake charging efficiency is prevented from decreasing. Can be suppressed to

According to the engine intake device 7 of the first embodiment described above, the following effects can be obtained.

A) When switching from the low speed side operating state to the high speed side operating state, the rotary valve 20 is provided with the first upstream end openings 11a to 14a and the second upstream end openings 15a to 15a.
18a, which is a transitional state in which the intake air outflow area is equal to or larger than the intake air outflow area in the low speed side operating state and the high speed side operating state. As a result, the intake charging efficiency at the time of switching can be minimized.

B) First upstream end openings 11a, 14a and 1
Since 2a and 13a are radially overlapped on the outer circumference of the surge tank 10 and are formed close to the center in the left-right direction, they are arranged so as to surround most of the outer circumference of the surge tank 10. The intake device 7 can be made compact while ensuring the length of the first branch passages 11 to 14 required to obtain the inertial effect in the low speed operation state, which is also advantageous in terms of installation space.

C) The length of the surge tank 10 in the left-right direction is made shorter than the distance between the two intake ports 8 corresponding to the cylinders 3A, 3D at the left and right ends, respectively, and the four first upstream end openings 11a ... Of the 14a, the two first upstream end openings 11a, 12a on the right side and the two first upstream end openings 13a, 14a on the left side are formed so as to partially overlap each other in the outer peripheral portion of the surge tank 10, and The two first
Since the upstream end openings 11a and 12a and the two left first upstream end openings 13a and 14a are also close to each other, the throttle valve 24a to the first upstream end openings 11a to 14a.
To the first branch passage 11
-14 and the second branch passages 15-18 are unified in natural frequency, and the charging efficiency can be made uniform.

Further, the two first branch passages 12 and 13 corresponding to the two central cylinders 3B and 3C are provided at the two left and right ends.
The first branch passages 11 and 14 corresponding to the three cylinders 3A and 3D
Since it curves further downward than the above, the passage lengths from the surge tank 10 to the intake port 8 in the four first branch passages 11 to 14 are substantially equal in the low speed side operating state. Therefore, in the four first branch passages 11 to 14, the passage lengths from the throttle valve 24a to the intake port 8 become substantially equal, and the difference in the frequency of pressure pulsation due to the difference in the passage lengths also becomes small. The unpleasant sound caused by the noise can be minimized in the low-speed operation state in which the noise of the engine 1 is small and the unpleasant sound has a large influence on the outside.

Also, the four second upstream end openings 15a-1
Since 8a is also formed close to the outer peripheral portion of the surge tank 10, the difference in passage length from the throttle valve 24a to the intake port 8 in the second branch passages 15 to 18 is small even in the high speed side operating state. Therefore, it is possible to suppress the unpleasant noise even in the high-speed operation state. In addition, since the volume of the surge tank 10 can be reduced, the response can be improved.

D) Since the rotary valve 20 is rotatably mounted on the surge tank 10, there is almost no space for disposing the rotary valve 20,
The intake device 7 can be made compact.

E) The second branch passages 15a to 18a linearly join the second pipe portions 11c to 14c of the first branch passages 11a to 14a in a straight line, so that the second branch passages 15a to 18a are joined in a low speed operation state. The passage resistance in the merging portion can be reduced, and the intake charging efficiency can be prevented from decreasing.
Further, since the third pipe portions 11d to 14d are also smoothly curved, it is possible to prevent the passage resistance from decreasing even in the high-speed side operating state, and to prevent the intake charging efficiency from decreasing.

F) The lower end positions P1 of the first branch passages 11 and 14 corresponding to the cylinders 3A and 3D at both ends in the cylinder row direction, when viewed from one side in the cylinder row direction, are the cylinders 3B and 3C at the center in the cylinder row direction.
By arranging the second branch passages 12 and 13 at a position higher than the lower end position P2 of the second branch passages 13 and 13, the passage lengths from the surge tank 10 to the respective cylinders are made substantially equal to each other, and the inertia effect is obtained in the low speed side operating region. Therefore, the torque can be improved. Further, since step spaces are formed at both ends in the cylinder row direction below the first branch passages 11 and 14, auxiliary machinery can be arranged in these spaces. [Second Embodiment] Next, an intake device for an engine according to a second embodiment of the present invention will be described.

The same elements as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. However, in the second embodiment,
A configuration in which the second branch passages 15 to 18 and the rotary valve 20 of the first embodiment are omitted can also be applied.

FIG. 11 is a front view of the engine air intake system of the second embodiment according to the present invention, FIG. 12 is a plan view of the engine air intake system of the second embodiment of the present invention, and FIG. 13 is related to the present invention. The right side view of the intake device of the engine of the second embodiment,
FIG. 14 is a sectional view taken along the line II-II of FIG. 13, and FIG. 15 is a view of the engine air intake device of the second embodiment according to the present invention seen from the engine unit side, respectively, and an engine air intake device 27 of the second embodiment is shown. The first branch passages 31 to 34 are provided so as to surround the surge tank 10 as in the first embodiment, and the first branch passages 31 to 34 are connected to the outer peripheral portion of the surge tank 10 at the first upstream end. Openings 31a to 34a
And the first pipe portions 31b to 34b that extend obliquely upward from the first upstream end openings 31a to 34a toward the engine unit 2 side and are curved and linearly extend downward of the surge tank 10.
And second pipe portions 31c to 34c linearly extending above the surge tank 10 while curving toward the engine unit 2 side below the surge tank 10, and curving toward the engine unit 2 side above the surge tank 10. Extension engine 1
The third pipe portions 31d to 34d are connected to the intake port 8 opening on the side surface of the casing via the mounting flange 25.

Further, as in the first embodiment, the second branch passages 15 to 18 are provided, and the second upstream end openings 15a to 18a connected to the outer peripheral portion of the surge tank 10 are away from the engine unit 2. To the second pipe portion 31c of the first branch passages 31 to 34 while curving obliquely upward to
It joins in the middle of the straight part of ~ 34c.

Second pipe portions 31c to 34c extending upward from below the surge tank 10 in the first branch passages 31 to 34.
Are arranged in a substantially planar shape in the cylinder row direction on the side opposite to the engine unit 2 and are located at both ends of the cylinder row in the cylinder row direction.
The lower end positions P1 of the c and 34c are the second pipe portions 32c and 33c located at the center in the cylinder row direction when viewed from one side in the cylinder row direction.
Is arranged at a position higher than the lower end position P2.

Further, the first pipe portions 31b to 34b, which are curved from above the surge tank 10 and extend downward in the first branch passages 31 to 34, are formed so as to be arranged in a substantially planar shape in the cylinder row direction on the engine unit 2 side. Has been done.

Of the first branch passages 31 to 34, the branch passages 31 and 34 located at both ends in the cylinder row direction have the first pipe portions 31b and 34b after branching from the surge tank 10 located at the center in the cylinder row direction. The first branch passages 32 and 33 are curved at a position higher than the first pipe portions 32b and 33b, and spread to both sides of the first branch passages 32 and 33 located in the center in the cylinder column direction and extend below the surge tank 10. .

Further, the first branch passages 31 and 34 corresponding to the cylinders 3A and 3D at both ends in the cylinder row direction overlap with each other in the cylinder row direction and branch upward from the surge tank 10.
Extending to the cylinders 3A and 3D via the common branch passage 30A,
The first branch passages 32 and 33 corresponding to the cylinders 3B and 3C at the center in the cylinder row direction overlap each other in the cylinder row direction and branch downward from the surge tank 10 to form the second common branch passage 30B.
To the cylinders 3B and 3C.

At the outer peripheral portion of the surge tank 10, a first common opening portion 30a is opened toward the first upstream end opening portions 31a and 34a corresponding to the cylinders 3A and 3D at both ends in the cylinder row direction.
And a second common opening 30b opening toward the first upstream end openings 32a, 33a corresponding to the cylinders 3B, 3C at the center of the cylinder row direction are formed, and the first and second common branch passages 3 are formed.
Intake air is introduced into each of the first branch passages 11 to 14 via 0A and 30B.

The first upstream end openings 31a to 34a are formed near the top of the outer peripheral portion of the surge tank 10. Of these four first upstream end openings 31a to 34a, the first upstream end openings 31a and 34a corresponding to the cylinders 3A and 3D at both ends in the cylinder row direction are close to each other in the cylinder row direction and are located in the center of the cylinder row direction. Cylinder 3 which is located in the center of the cylinder row
The first upstream end openings 32a and 33a corresponding to B and 3C are located closer to the surge tank 1 than the first upstream end openings 31a and 34a.
No. 1 that extends below 0 and is located at the center in the cylinder row direction
The upstream end openings 32a and 33a and the outer peripheral portion of the surge tank 10 overlap each other on substantially the same circumference, and the common branch passage 3
Forming 0. That is, the four first upstream end openings 3
1a to 34a are formed close to each other in the vicinity of the center of the surge tank 10 in the left-right direction, and the passage lengths from the throttle valve 24a to the four first upstream end openings 31a to 34a are substantially equal.

As shown in FIGS. 14 and 15, at least the first upstream end openings 31a and 34a of the first branch passages 31 and 34 corresponding to the cylinders 3A and 3D at both ends in the cylinder row direction and the cylinder at the center in the cylinder row direction. The first upstream end openings 32a, 33a of the first branch passages 32, 33 corresponding to 3B, 3C are inclined in the intake flow direction S1 of the surge tank 10 and surround the surge tank 10 in a spiral shape. Further, the flow passage cross-sectional shape of the first branch passages 31 to 34 is formed into a substantially parallelogram inclined in the intake flow direction of the surge tank 10.

Other than that, the structure of the rotary valve and the like is the same.

According to the engine intake system 27 of the second embodiment described above, the following effects can be obtained in addition to the effects of the first embodiment.

A) The lower end position P1 of the branch passages 31 and 34 corresponding to the cylinders 3A and 3D at both ends in the cylinder row direction, when viewed from one side in the cylinder row direction, is the cylinders 3B and 3C at the center in the cylinder row direction.
By arranging the second branch passages 32 and 33 at a position higher than the lower end position P2 of the second branch passages 33, the passage lengths from the surge tank 10 to the respective cylinders are made substantially equal to each other while the inertia effect is obtained in the low speed side operating region. Therefore, the torque can be improved. Further, as shown in FIG. 16 showing the front view of the engine 1, the engine can be downsized, and the first branch passages 31, 3
Since stepped spaces SP are formed at both ends of the lower four cylinders in the cylinder row direction, auxiliary equipment such as the starter motor 41 and the compressor 42 of the air conditioner can be arranged in this space SP.

Incidentally, in FIG. 16, the engine unit 2
Is a cylinder block 2a, a cylinder head 2b,
The head cover 2c and the oil pan 2d are provided, and the starter motor 41 meshes with the flywheel 43 to rotationally drive the crankshaft. An oil filter 44 is provided below the starter motor 41.

B) Since the first branch passages 31 to 34 are formed in the engine unit 2 side and the non-engine unit 2 side so as to be arranged substantially in the cylinder column direction, the size of the engine in the front-rear direction can be reduced. Further, as shown in FIG. 17 showing a right side view of the engine 1, a radiator unit 45 including a radiator and an electric fan arranged in the front of the engine room, and the engine unit 2 are arranged between the radiator unit 45 and the engine unit 2 in the front-rear direction of the vehicle body. A space for arrangement can be secured.

(C) At least the cylinders 3 at both ends in the cylinder row direction
First upstream end openings 31a and 34a of the first branch passages 31 and 34 corresponding to A and 3D, and a cylinder 3B at the center in the cylinder row direction,
Since the first upstream end openings 32a and 33a of the first branch passages 32 and 33 corresponding to 3C are inclined in the intake flow direction S1 of the surge tank 10, the first branch passages 31 from the surge tank 10 are separated from each other. It is possible to reduce the intake flow resistance to ~ 34.

(D) Since the flow passage cross-sectional shape of the first branch passages 31 to 34 is formed into a substantially parallelogram inclined in the intake air flow direction of the surge tank 10, the intake air is made to flow along the inner wall of the passage. , The secondary flow that becomes a spiral component due to the reflection of the intake air on the inner wall of the passage can be suppressed, the intake pressure loss can be reduced, and the average flow coefficient (Cf) can be increased. [Third Embodiment] Next, as an engine intake device according to a third embodiment of the present invention, the structure of the intake port 8 of the cylinder head 2b and the first branch passage 11 in the vicinity of the connection portion with the intake port 8 will be described. Structures 14 to 14 will be described.

The same elements as those in the first embodiment are designated by the same reference numerals and their explanations are omitted. However, in the third embodiment,
It can be applied to a combination with the intake device of the first or second embodiment or a combination with other different intake device configurations, and the second branch passages 15 to 18 and the rotary valve 20 of the first embodiment can be applied. The omitted configuration can also be applied.

FIG. 18 is a cross-sectional view in the lateral direction of the engine showing the engine air intake system of the third embodiment according to the present invention, FIG. 19 is an external view of a shutter valve, and FIG. 20 is a second embodiment according to the present invention. 21 is a plan view of the intake system of the engine of FIG. 21, FIG. 21 is a sectional view inside the passage when the shutter valve is opened, FIG. 22 is a sectional view inside the passage when the shutter valve is closed, and FIG.
XI-XXI sectional view, FIG. 24 shows IV-IV sectional view of FIG. 21, and FIG. 25 shows VV sectional view of FIG. 21, respectively, and the intake device 37 of the engine of the third embodiment has four cylinders 3A to.
The intake port 8 and the third pipe portions 11d to 1d of the first branch passages 11 to 14 connected to the intake port 8 obliquely upward from 3D.
4d extends to the upstream side. The upstream side of the first branch passages 11 to 14 (not shown) has the same structure as that of FIGS. 1 to 5.

Further, the passages 11 to 1 are provided in the first branch passages 11 to 14 (third pipe portions 11d to 14d) near the downstream end openings 11e to 14e connected to the intake port 8.
The shutter valve 51 that closes a part of the cross section of the flow passage of No. 4 to generate the tumble flow in the cylinder 3 has the first branch passages 11 to 14
Is rotatably supported by a shaft 52 that passes through the axis of and crosses the approximate center of the flow path cross section.

As shown in FIG. 19, the shutter valve 51 includes a lower half portion 51a which closes the flow passage cross section of the first branch passages 11 to 14 below the shaft 52 when fully closed, and a flow above the shaft 52 when fully closed. A lower half portion 51b is formed by cutting out a portion above the shaft 52 so as not to block the road cross section (bent in the downstream direction around the middle of the flow path cross section).

Then, the first branch passages 11 to 14 on the upstream side of the shutter valve 51 and the portion P of the intake port 8 on the downstream side which is not closed by the shutter valve 51.
The inner wall of No. 3 is formed in a substantially linear shape as compared with the conventional structure (dotted line portion P3 ′ in FIG. 18), and the first branch passages 11 to 14 on the upstream side and the intake port 8 on the downstream side sandwich the shutter valve 51. The part closed by the shutter valve 51 (see FIG.
8 is formed so as to bulge in the radial direction at the position where the shutter valve 51 is arranged, and the flow passage cross-sectional area of the first branch passages 11 to 14 at the position where the shutter valve 51 is arranged is defined by the shutter. It is formed to have a larger cross-sectional area of the flow path upstream and downstream of the valve 51.

Further, when viewed from one side of the engine in the cylinder row direction (the front and back direction of the paper surface in FIG. 18), the inclination angle θ2 of the first branch passages 11 to 14 is the intake port 8 at an angle.
Is larger than the inclination angle θ1 of.

The inner wall of the upper portion of the intake port 8 in which the valve guide 5a is disposed has a conventional structure in a section from the upstream side to the downstream side of the valve guide 5a (dotted line portion P in FIG. 18).
5 '), it is formed flat, and this flat portion P
5 is formed so as to reduce the flow passage area in the upper portion of the intake port 8 where the valve guide 5a is provided.

Further, the flow passage cross section from the vicinity of the branch portion in each intake port 8a, which branches into two and communicates with each cylinder 3A to 3D, to the throat portion P6 where the downstream flow passage area is narrowed is 2 The upper portion 8b, the side surface portion 8c, and the lower portion 8c on the side between the intake ports 8a that branch into two are formed in a flat and rectangular shape as compared with the conventional structure (dotted line portion 8a 'in FIG. 23). Anti-intake port 8 branching into
The side surface portion 8e is formed into a round shape on the intermediate side.

The cross-sectional shape of the intake port 8 in the section from the upstream to the downstream of the valve guide 5a is such that the inner wall of the upper portion is made substantially linear and the inner wall of the lower portion is inflated, and the first branch passages 11-14. The present invention can be applied by appropriately combining with the constitution in the vicinity of the connecting portion, but it is preferable to combine both constitutions.

According to the engine intake system of the third embodiment described above, the following effects can be obtained.

A) As shown in FIG. 19, the shutter valve 51 is notched at a portion above the shaft 52 so as not to close the flow passage cross section above the first branch passages 11 to 14 when fully closed, and the shutter valve 51 is not shown. By forming the first branch passages 11 to 14 on the upstream side and the inner wall of the part P3 of the intake port 8 on the downstream side, which is not closed by the shutter valve 51, with a substantially straight line across the 51, the intake flow resistance is reduced. When the shutter valve 51 is closed, the tumble flow can be strengthened by the intake flow along the inner wall above the passage, while the shutter valve 5
1, the inner walls of the first branch passages 11 to 14 on the upstream side and the portion of the intake port 8 on the downstream side that is closed by the shutter valve 51 are formed so as to bulge in the radial direction at the position where the shutter valve 51 is disposed. Since the flow passage cross-sectional areas of the first branch passages 11 to 14 at the arrangement position of the shutter valve 51 are formed larger than the flow passage cross-sectional areas of the upstream and downstream of the shutter valve 51, when the shutter valve 51 is opened. The tumble flow becomes weak and flow resistance can be reduced. With this configuration, an engine with low fuel consumption and high output can be obtained.

B) First branch passages 11 to 1 formed so as to surround the surge tank 10 in order to increase the passage length.
In 4, the tumble flow can be strengthened when the shutter valve 51 is closed while ensuring a high output when the shutter valve 51 is opened.

C) The inner wall of the upper portion of the intake port 8 in which the valve guide 5a is arranged is formed flat in the section from the upstream side to the downstream side of the valve guide 5a. Since it is formed so as to reduce the flow passage area of the upper portion of the intake port 8 provided, it is possible to suppress the attenuation of the flow due to the inner wall surface of the upper portion of the intake port 8.

D) Further, each cylinder 3A to 3 is branched into two.
The cross section of the flow passage from the vicinity of the branch portion of each intake port 8 communicating with D to the throat portion P6 at the downstream side where the flow passage area is narrowed has an upper portion 8b on the side between the two intake ports 8 branching. , Side portion 8c and lower portion 8d
Is formed into a flat and rectangular shape, and the side surface portion 8e is formed into a round shape on the side between the non-intake ports 8 that branch into the two, so that when the shutter valve 51 is opened, as shown in FIG. 25, while increasing the intake flow velocity along the upper portion 8b and the lower portion 8d of the flow passage section from the first branch passages 11 to 14 to each intake port 8 to secure high output, FIG.
As shown in FIG. 5, when the shutter valve 51 is closed, the intake flow velocity in the upper portion 8b of the flow passage section from the first branch passages 11 to 14 to each intake port 8 is increased to strengthen the tumble flow and enhance the intake charging efficiency. be able to.

[Brief description of drawings]

FIG. 1 is a front view of an intake device for an engine according to a first embodiment of the present invention.

FIG. 2 is a plan view of the intake device for the engine according to the first embodiment of the present invention.

FIG. 3 is a right side view of the intake device for the engine according to the first embodiment of the present invention.

FIG. 4 is a left side view of the intake device for the engine according to the first embodiment of the present invention.

5 is a cross-sectional view taken along the line I-I of FIG.

FIG. 6 is a perspective view of a rotary valve.

FIG. 7 is an enlarged view of a main part of FIG. 5 (low-speed side operating state).

FIG. 8 is an enlarged view of a main part of FIG. 5 (high-speed side operation state).

9 is an enlarged view of a main part (transient state) of FIG.

FIG. 10 is a development view of a rotary valve.

FIG. 11 is a front view of an intake device for an engine according to a second embodiment of the present invention.

FIG. 12 is a plan view of an intake device for an engine according to a second embodiment of the present invention.

FIG. 13 is a right side view of an intake device for an engine according to a second embodiment of the present invention.

14 is a sectional view taken along line II-II of FIG.

FIG. 15 is a view of an intake device for an engine according to a second embodiment of the present invention as viewed from the engine unit side.

FIG. 16 is a front view of an engine equipped with an intake system for an engine according to a second embodiment of the present invention.

FIG. 17 is a right side view of an engine equipped with an engine air intake system according to a second embodiment of the present invention.

FIG. 18 is a cross-sectional view in the lateral direction of the engine showing an intake device for an engine according to a third embodiment of the present invention.

FIG. 19 is an external view of a shutter valve.

FIG. 20 is a plan view of an intake device for an engine according to a second embodiment of the present invention.

FIG. 21 is a sectional view of the inside of the passage when the shutter valve is opened.

FIG. 22 is a sectional view of the inside of the passage when the shutter valve is closed.

23 is a sectional view taken along the line III-III in FIG.

FIG. 24 is a sectional view taken along the line IV-IV in FIG. 21.

25 is a cross-sectional view taken along line VV of FIG.

FIG. 26 is a vertical sectional view of a conventional intake device.

FIG. 27 is a diagram illustrating the operation of the conventional intake device.

[Explanation of symbols]

1 engine 2 engine units 2a cylinder block 2b cylinder head 2c head cover 2d oil pan 3A-3D cylinder 5 intake valve 6 exhaust valve 7,27,37 Intake device 8,8a intake port 9,9a Exhaust port 10 surge tank 10a, 10b, 30a, 30b openings 11-14, 31-34 First branch passage 11a-14a, 31a-34a 1st upstream end opening part 15-18 Second branch passage 15a to 18a Second upstream end opening 20 rotary valve 23 Intake pipe 24 Throttle body 24a throttle valve 30 common branch passages 41 Starter motor 42 Air conditioner compressor 43 flywheel 44 oil pan 45 radiator unit 51 shutter valve

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tatsuya Fujikawa             3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda             Within the corporation F-term (reference) 3G031 AA02 AA15 AA28 AB05 AB07                       AB08 AC01 AC03 AC04 AD08                       BA02 BA08 BA10 BA14 BB05                       DA30 DA34 DA38 EA02 EA08                       FA03 FA06 GA05 GA10 HA01                       HA04 HA08 HA09 HA10

Claims (5)

[Claims] 1. A first passage that branches from the collecting passage and communicates with an intake port of each cylinder that is open at one side of the engine unit and is arranged side by side in the cylinder row direction, and a branch from the collecting passage. The second passage communicating with the middle of the first passage so as to bypass at least the upstream side of the first passage, and at least the communication state of the collecting passage and the second passage is selectively selected according to the operating state of the engine. In the intake system of the engine, the intake passage of the engine is set to the cylinder row direction, and the upstream end opening of the second passage connected to the collection passage is arranged in the cylinder row direction. The length between the both ends in the cylinder row direction in the cylinder row direction in the upstream end opening of the second passage that is arranged side by side and is connected to the collecting passage is calculated from the length between the both ends in the cylinder row direction in each of the intake ports. Short The upstream end openings of the first passages connected to the collecting passages are arranged side by side in the cylinder row direction and the circumferential direction of the collecting passages, and the upstream end openings of the first passages are arranged in the circumferential direction. At least a portion is overlapped, and the length between both ends in the cylinder row direction at the upstream end opening of the first passage is set shorter than the length between both ends in the cylinder row direction at the upstream end opening of the second passage. The intake system for the engine, which is characterized by 2. The variable intake mechanism includes a hollow rotary valve that is disposed in the collecting passage and is rotatable around an axis of the collecting passage, and the upstream end opening of the second passage in the cylinder row direction. Of the first passage and the overlapping upstream end opening of the first passage are arranged at substantially the same position in the cylinder row direction, and the rotary valve has an outer peripheral portion with an overlapping upstream end opening of the first passage. The engine intake system according to claim 1, wherein an opening that selectively opens and closes one of the upstream end openings of the second passage is formed. 3. The upstream end opening of the first passage is arranged at substantially the same position in the circumferential direction as the upstream end opening of the second passage located in the middle in the cylinder row direction. The intake system for an engine according to claim 2, wherein the intake system is for an engine. 4. The first passage is formed so as to surround the collecting passage, and an upstream end opening of the first passage is connected to an outer peripheral portion of the collecting passage to communicate with each other. Engine intake system. 5. The first passage is set to an intake pipe length that is tuned to the intake characteristic in the low and medium rotation range of the engine, and the second passage is set to an intake length that is synchronized to the intake inertia characteristic in the maximum rotation range of the engine. The intake system for an engine according to any one of claims 1 to 4, wherein: