JP2003247468A - Intake system for multi-cylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intake system for a multi-cylinder engine capable of improving torque characteristics in a middle speed range. <P>SOLUTION: The intake system for the multi-cylinder engines is constructed in such a manner that an air cleaner 46 is connected to a first and a second intake pipe 44, 45 connected, respectively, so as to provide communication with a first and a second cylinder having different firing intervals. A space A2, toward which an upstream end suction port 45b of the second intake pipe 45 connected to the second cylinder having a smaller firing interval is oriented, is made greater than a space A1, toward which an upstream end suction port 44b of the first intake pipe 44 connected to the first cylinder having a greater firing interval is oriented. <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 system for a multi-cylinder engine in which an intake passage for each cylinder connected to each cylinder is opened in an air cleaner.

[0002]

2. Description of the Related Art For example, a motorcycle may be equipped with a multi-cylinder engine configured to perform unequal-interval ignition by providing a 270-degree phase crankshaft, for example, from the viewpoint of improving traction performance. is there. In general, in an intake system used in a multi-cylinder engine of this type, an intake passage for each cylinder connected to each cylinder is opened in a common air cleaner.

[0003]

By the way, in the above-mentioned multi-cylinder engine in which unequal interval ignition is performed, although traction performance can be improved, there is a concern that valleys are likely to occur in the medium speed region in the torque characteristic. , Improvement in this regard is requested.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an intake system for a multi-cylinder engine which can suppress the occurrence of torque valleys in the medium speed range.

[0005]

According to a first aspect of the present invention, there is provided an intake system for a multi-cylinder engine in which an upstream end suction port of an intake passage connected to each cylinder is located in an air cleaner. Are configured to perform unequal-interval ignition, and the space in which the upstream end suction port of the intake passage of a small-interval cylinder with a small ignition interval is directed is the inlet end of the intake passage of a large-interval cylinder with a large ignition interval. The feature is that it is set larger than the space where the mouth is pointing.

According to a second aspect of the present invention, in the first aspect, the upstream end suction port of the intake passage for the small interval cylinder is directed substantially parallel to the air filter in the air cleaner, while the intake passage for the large interval cylinder is provided. It is characterized in that the upstream end suction port is oriented so as to obliquely face the air filter in the air cleaner.

According to a third aspect of the present invention, in an intake system for a multi-cylinder engine in which an upstream end suction port of an intake passage connected to each cylinder is located in an air cleaner, the cylinders of the engine perform unequal-interval ignition. And the upstream end inlet of the intake passage of the small interval cylinder with a small ignition interval and the upstream end inlet of the intake passage of the large interval cylinder with a large ignition interval. It is characterized in that they are arranged so as to be deviated in the direction, or that they are arranged so that the angle formed by the axis thereof and the flow direction of the intake air is different.

According to a fourth aspect of the present invention, in the third aspect, the upstream end suction port of the small-interval cylinder intake passage and the upstream end suction port of the large-interval cylinder intake passage are surfaces substantially parallel to the air filter. It is characterized by being placed at different positions inside.

According to a fifth aspect of the present invention, in the third aspect, the upstream end suction port of the intake passage for the small interval cylinder is directed substantially parallel to the air filter in the air cleaner, while the intake passage for the large interval cylinder is provided. It is characterized in that the upstream end suction port is oriented so as to obliquely face the air filter in the air cleaner.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the engine has a first ignition interval of 450 degrees.
It is characterized in that it is a 270-degree phase crank parallel two-cylinder engine including a cylinder (large-interval cylinder) and a second cylinder (small-interval cylinder) having an ignition interval of 270 degrees.

[0011]

According to the first aspect of the present invention, the space in which the upstream end suction port of the intake passage of the small-interval cylinder having a small ignition interval points is located in the upstream end suction port of the intake passage of the large-interval cylinder having a large ignition interval. Since it is set to be larger than the space in which the mouth is directed, a sufficient intake amount is secured even in the small-interval cylinder, and the occurrence of torque valleys in the medium speed range can be suppressed.

That is, in the case of the unequal-interval ignition engine, the effective intake time to the small-interval cylinder having the small ignition interval is shorter than the intake-capable time to the large-interval cylinder having the large ignition interval, so that the small-interval cylinder is supplied. The intake amount of is likely to be smaller than the intake amount to the large-interval cylinder. In the present invention, since the upstream end suction port of the intake passage of the small interval cylinder is directed toward the larger space, it becomes relatively easy to suck air into the intake passage of the small interval cylinder, and therefore the intake time Can be compensated for, and the difference with the intake air amount to the large-interval cylinder can be suppressed, and as a result, the occurrence of a torque valley can be suppressed especially in the medium speed range.

According to the invention of claim 2, the upstream end suction port of the intake passage for the small-interval cylinder is directed substantially parallel to the air filter in the air cleaner, while the upstream end suction port of the intake passage for the large-interval cylinder is introduced. Since the mouth is directed diagonally opposite the air filter in the air cleaner, it is possible to direct the upstream end suction port of the intake passage for the small-interval cylinder to a space larger than that for the large-interval cylinder with a simple configuration. Become.

According to the third aspect of the present invention, the upstream end suction port of the small-interval cylinder and the upstream end suction port of the large-interval cylinder are arranged such that their positions are deviated in the intake air flow direction, or
Or, since it is arranged so that the angle formed by the axis and the flow direction of intake air is different, intake air interference can be suppressed, air suction can be performed easily and reliably, and the intake amount to the small interval cylinder and the large interval cylinder can be reduced. It is possible to suppress the difference from the intake air amount, and as a result, it is possible to suppress the occurrence of a torque valley particularly in the medium speed range.

That is, in the case of an unequal-interval ignition engine, since the effective intake time differs depending on the cylinder, intake interference from adjacent cylinders is particularly likely to occur in the intake stroke of the small-interval cylinder. In the present invention, the position of the upstream suction port is offset in the flow direction of the intake air, or the angle between the axis and the flow direction of the intake air is made different, so that the above-mentioned intake interference can be suppressed.

According to the invention of claim 4, the upstream end suction port for the small-interval cylinder and the upstream end intake port for the large-interval cylinder are arranged at different positions in a plane substantially parallel to the air filter.
The upstream end suction ports can be deviated in the flow direction of the intake air with a simple structure. Further, in the invention of claim 5, the upstream end suction ports for the small-interval cylinders are oriented substantially parallel to the air filter, while the large intervals are provided. Since the cylinder upstream end suction port is oriented so as to face the air filter obliquely, the angle of the upstream end suction port with respect to the flow direction can be changed with a simple configuration.

According to a sixth aspect of the present invention, the engine includes a first cylinder having an ignition interval of 450 degrees (a large interval cylinder) and a second cylinder having an ignition interval of 270 degrees (a small interval cylinder) 270.
Since the engine is a two-cylinder engine with a parallel-phase crank, the configurations of claims 1 to 5 can be easily and reliably realized.

[0018]

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

1 to 7 are views for explaining an intake system for a multi-cylinder engine according to an embodiment of the present invention. FIG. 1 is a left side of a motorcycle provided with the intake system of the present embodiment. Fig. 2 is a sectional right side view of the intake device, Figs. 3, 4 and 5 are sectional left side views, rear views and bottom views of the air cleaner, respectively, and Figs. 6 and 7 are exhaust pipe left side views.
It is a top view. In the present embodiment, left and right, front and rear mean left and right, front and rear when viewed in a seated state.

In the figure, reference numeral 1 denotes a motorcycle to which the structure of this embodiment is applied, and a vehicle body frame 2 of the motorcycle 1 is connected to a head pipe (not shown) on the left,
A rear arm bracket 5 extending substantially vertically downward is connected to the rear ends of the pair of right tank rails 4, and left and right seat rails 6 extending obliquely upward toward the rear of the vehicle body are formed at the rear end portions of the left and right tank rails 4. It has a schematic structure in which is connected.

An engine 9 is mounted on the lower part of the left and right tank rails 4, a fuel tank (not shown) is mounted on the upper part, and the fuel tank is covered with a tank cover 10. A seat 11 is detachably arranged on the left and right seat rails 6.

A front fork 1 is attached to the head pipe.
A steering handle 14 is fixed to the upper end of the front fork 13, and a front wheel 15 is pivotally supported to the lower end. A rear arm 16 is pivotally supported between the left and right rear arm brackets 5 so as to be vertically swingable, and a rear wheel 17 is pivotally supported at the rear end of the rear arm 16.

A front cover 18 for covering the front, left and right sides of the steering handle 14 is provided on the front portion of the body frame 2.
And a headlight 22 is attached to the front cover 18. A rear body 23 that covers the upper portion of the rear wheel 17 is provided at the rear portion of the seat rail 6.

The engine 9 is a water-cooled 4-cycle parallel 2-cylinder engine, and is mounted with the cylinder axes of the first and second cylinders inclined forward. This engine 9 has 2
Having a 70-degree phase crankshaft, after the ignition of the first cylinder on the left side, when the crankshaft rotates 270 degrees, the second cylinder on the right side (small interval cylinder) is ignited, and the crankshaft after ignition of the second cylinder is It is configured to perform 270 ° → 450 ° unequal interval ignition in which the first cylinder (large interval cylinder) is again ignited when rotated by 450 °.

In the engine 9, the transmission gear case 9b is integrally connected to the rear portion of the crankcase 9a, the cylinder block 9c and the cylinder head 9d are laminated and fastened on the upper portion of the crankcase 9a, and the cylinder head 9d is fastened. It has a structure in which a head cover 9e is fastened, and pistons 19 are inserted and arranged in the first and second cylinders of the cylinder block 9c.
Is connected to a crankshaft (not shown) by a connecting rod 20.

The cylinder head 9d is formed with an intake port 9g and an exhaust port 9h which communicate with each cylinder. The intake port 9g forming a part of the intake passage extends substantially vertically upward and is led out to the rear wall of the cylinder head 9d.
The exhaust port 9h extends forward with a small curve and is led out to the front wall.

The cylinder head 9d is provided with an intake valve 24 for opening and closing the intake port opening 9g 'and an exhaust port opening 9h', and an exhaust valve 25. The intake valve 24 and the exhaust valve 25 respectively intake air. Cam shaft 24
a, the open / close drive is performed by the exhaust cam shaft 25a.

An exhaust device is connected to the front wall of the cylinder head 9d. That is, the first and second exhaust pipes 26 and 27 are connected to the connection ports of the left and right exhaust ports 9h, which are opened in the front wall of the cylinder head 9d, and the first exhaust pipe 26 is the first cylinder. In addition, the second exhaust pipe 27 communicates with the second cylinder.

Each of the exhaust pipes 26, 27 is bent vertically from the cylinder head 9d and extends vertically downwards 26a, 2 respectively.
7a, horizontal portions 26b and 27b extending substantially horizontally from the lower ends of the vertical portions 26a and 27a toward the rear of the vehicle, and the horizontal portions 26a and 27b.
b and 27b, there is an expanding portion 26c, 27c that expands outward from the rear end and extends diagonally upward and rearward of the vehicle. The rear end of each expanding portion 26c, 27c is followed by a rear portion. Mufflers 28 and 29 extending obliquely upward are connected. A catalyst (not shown) for purifying exhaust gas is arranged in each of the mufflers 28 and 29.

The lower portions of the vertical portions 26a and 27a are connected to each other by a connecting plate 30, and the expanded portions 26c and 2 are connected to each other.
The front ends of 7c are joined together by a portal bracket 31. The gate-shaped bracket 31 is bolted and fixed to the rear arm bracket 5. Further, exhaust sampling holes for measuring properties of exhaust gas are formed in front of the horizontal portions 26a, 27a, and are closed by plugs 33, 33.

Attachment members 28a and 29a are welded to the mufflers 28 and 29, respectively. The mounting members 28a and 29a are fixed to the rear arm bracket 5 and bolted to a stay member 5a extending rearward of the vehicle.

A connecting pipe 35 that connects the horizontal portions 26b and 27b to each other is bridged and joined to the central portion in the front-rear direction of the horizontal portions 26b and 27b. Exhaust gas from the first and second cylinders is connected to the second and first cylinders by this connecting pipe.
The exhaust pipes 27, 26 are designed to flow into each other.

A sensor insertion hole 26a is formed in the horizontal portion 26b of the first exhaust pipe 26 located on the left side of the vehicle, and the sensor insertion hole 26d is located near the downstream side of the connecting pipe 35. Specifically, it is formed on the downstream side of the connecting pipe 35 by about 50 mm.

A sensor main body 37a of an oxygen sensor 37 for detecting the oxygen concentration in the exhaust gas is inserted in the horizontal portion 26b, and the oxygen sensor 37 is attached to the mounting flange portion 3.
7c is fixed to the horizontal portion 26b with bolts 39. The detection portion 37b connected to the tip of the sensor body 37a faces the inside of the first exhaust pipe 26 through the sensor insertion hole 26d. Further, a guard plate 37d is arranged on the sensor body 37a so as to cover the lower side, and this is fixed to the flange portion 37c.

Here, the oxygen sensor 37 is arranged so as to incline obliquely upward toward the outside in the vehicle width direction, and is arranged in the projection plane below the engine 9 when viewed in the vehicle vertical direction. Further, the oxygen sensor 37 is on the side stand 41 side rotatably supported by the lower end portion of the rear arm bracket 5 on the left side of the vehicle between a storage position and a use position,
Further, it is arranged on the front side of the side stand 41.

As a result, the oxygen sensor 37 is arranged below the oxygen sensor 37 in the inconspicuous area surrounded by the guard plate 37d, above by the engine 9 and behind by the shaft supporting portion of the side stand 41, and flying stones are hard to hit. Has become. In this way, the oxygen sensor 37 is prevented from being damaged by external force or mischief.

When a side stand switch (not shown) for the purpose of controlling the ignition of the engine 9 is provided, the lead wire of the switch and the lead wire of the oxygen sensor 37 can be bundled and routed, and the appearance is neat. .

Further, an oil pan 9f accommodating an oil element (not shown) is detachably attached to the bottom of the engine 9, and the oil pan 9f is arranged so as to be offset to the right in the vehicle width direction. ing. Accordingly, the oxygen sensor 37 is arranged so as to be located on the opposite side of the oil pan 9f in the vehicle width direction.

Since the oxygen sensor 37 is connected and arranged in the vicinity of the downstream side of the connecting pipe 35 of the first exhaust pipe 26 communicating with the first cylinder as described above, not only the exhaust gas from the first cylinder but also the second cylinder is discharged. The oxygen concentration of the exhaust gas can be accurately detected. Therefore, one oxygen sensor 37 is sufficient even though it has two cylinders and two exhaust spaces 26 and 27, and the cost can be reduced.

Further, since the oxygen sensor 37 is arranged in the first exhaust pipe 26 connected to the first cylinder having a large ignition interval, the oxygen concentration of the exhaust gas from the first and second cylinders can be accurately measured also from this point. Can be detected. That is, the exhaust gas from the first cylinder surely comes into contact with the oxygen sensor 37 attached to the first exhaust pipe 26 on the first cylinder side, and the exhaust gas from the second cylinder also passes through the connecting pipe 35. Through oxygen sensor 37
Since it tends to flow to the side, the oxygen concentration of the exhaust gas from the second cylinder can also be detected accurately.

Furthermore, since the oxygen sensor 37 is arranged on the side stand 41 side and below the engine 9, the whole vehicle leans toward the oxygen sensor 37 side especially when the side stand 41 is used, so that the oxygen sensor 37 from the outside is used. It is possible to prevent the sensor 37 from being difficult to see, prevent the appearance from being deteriorated, and prevent damage due to mischief.

The oxygen sensor 37 is replaced with an oil pan 9f.
Since it is arranged on the opposite side in the vehicle width direction, the oxygen sensor 37 does not get in the way when the oil element in the oil pan 9f is replaced, the work can be performed easily, and the oxygen sensor 37 can be used during the work. Can be prevented from damaging.

An intake device is arranged on the rear wall of the cylinder head 9d. In this intake device, the first and second intake pipes 44, 45 are provided by interposing first and second throttle bodies 43, 43 at the connection ports of the left and right intake ports 9g opening on the rear wall of the cylinder head 9d. And an air cleaner 46 common to the first and second intake pipes 44 and 45.
It is configured to be connected. In addition, the intake port,
An intake passage is formed by the throttle body and the intake pipe.

A throttle valve 47 for changing the passage area is arranged in each throttle body 43. Further, a fuel injection valve 48 is mounted downstream of the throttle valve 47 of each throttle body 43, and a fuel injection port 48a of the fuel injection valve 48 is directed to a top wall portion in the intake port 9g. A fuel rail 49 is connected to each fuel injection valve 48.

The air cleaner 46 is arranged in the front cover 18 below the fuel tank, and the air filter 51 is interposed between the cleaner body 50 having a generally bowl shape and the lid member 52 is airtightly fastened by a plurality of screws 53. It has a fixed upper and lower split structure. The air filter 51 can be taken out by removing the screw 53 and opening the lid member 52. The inside of the air cleaner 46 is divided into a primary chamber 46a into which air is introduced and a secondary chamber 46b into which air filtered by the air filter 51 flows.

A primary chamber 46a is provided on the upper wall of the lid member 52.
An air inlet 52a for taking in air is formed toward the rear of the vehicle, and an opening / closing valve 55 that is driven to open / close by a diaphragm valve 54 is disposed in the air inlet 52a.

On the rear wall 50a of the cleaner body 50,
The first and second intake pipes 44 and 45 are connected. The first intake pipe 44 is connected to the first cylinder, and the second intake pipe 45 is connected to the second cylinder.
It communicates with the cylinder. The first and second intake pipes 44, 45
The downstream end openings 44a, 45a of the throttle body 4 are
3, 43, and each of the downstream end ports 44a,
45a are arranged at the same height position.

The upstream end suction ports 44b and 45b of the first and second intake pipes 44 and 45 extend from the rear wall 50a to the cleaner chamber 46.
protruding into b. The suction port 44 of the first intake pipe 44
b is opened upward and is oriented so as to diagonally face the air filter 51. On the other hand, the suction port 45b of the second intake pipe 45 is opened so as to be substantially parallel to the air filter 51. In this way, the space A2 in which the upstream end suction port 45b of the intake passage for the second cylinder, which is a small-interval cylinder with a small ignition interval, is directed, is upstream of the intake passage of the first cylinder, which is a large-interval cylinder with a large ignition interval. It is set to be larger than the space A1 in which the end suction port 44b is directed. Generally speaking, the space A1 means a space which is surrounded by the left end portion of the filter 51 in FIG. 2 and the upstream end suction port 44b and has a substantially triangular shape in FIG. 2, and the space A2 is the space in the filter 51. Figure 2
It means a space which is surrounded by the right side portion, the upstream end suction port 45b and the wall surface of the cleaner main body 50 and which has a substantially rectangular shape in FIG.

The second intake pipe 45 is formed so that the protruding length in the cleaner body 50 is longer than that of the first intake pipe 44. In this way, from the intake port opening 9g 'of the second cylinder, which is a small interval cylinder, to the second intake pipe 45
From the intake port opening 9g 'of the first cylinder of the large interval cylinder to the suction port 4 of the first intake pipe 44.
It is set longer than the intake passage length up to 4b.

In other words, the difference in the length of the intake passage means that the suction port 45b of the second intake passage and the suction port 44b of the first intake passage are offset from each other in the flow direction of the intake air. Specifically, the intake port 45b of the second intake passage is located upstream of the intake port 44b of the first intake passage in the flow direction of intake air.

In other words, the angle formed by the axis of the intake port 45b of the second intake passage and the direction of flow of the intake air passing through the air filter 51 (shown by the arrow a in FIG. 2) and the first intake passage. The angle between the axis of the suction port 44b and the flow direction of the intake air that has passed through the air filter 51 is set to a different value. Specifically, the axis of the intake port 45b of the second intake passage is substantially orthogonal to the flow direction of the intake air, while the axis of the intake port 44b of the first intake passage is the flow direction of the intake air. It is diagonally intersecting at about 45 degrees.

The operation and effect of this embodiment will be described.
According to the device of the present embodiment, by directing the upstream end suction port 45b of the intake passage of the second cylinder (small-interval cylinder) having a small ignition interval to be substantially parallel to the air filter 51, the suction port 4
The space A2 in which 5b is directed is set to be larger than the space A1 in which the upstream end suction port 44b of the intake passage of the first cylinder (a large-interval cylinder) having a large ignition interval is directed, so that a sufficient intake amount can be obtained even in the small-interval cylinder. This is ensured and the occurrence of torque valleys in the medium speed range can be suppressed.

As described above, in the case of an unequal-interval ignition engine, a substantial intake time to the second cylinder having a small ignition interval of 270 degrees is possible to intake to the first cylinder cylinder having a large ignition interval of 450 degrees. This is shorter than the time, and therefore the intake amount into the second cylinder tends to be smaller than the intake amount into the first cylinder. In the present embodiment, since the upstream end suction port 45b of the intake passage of the second cylinder is directed toward the larger space A2, it is easy to suck air, and thus the short intake time can be compensated. It is possible to reduce the difference from the intake air amount into the first cylinder, and as a result, it is possible to suppress the occurrence of a torque valley particularly in the medium speed range.

In order to secure the large space A2, the upstream end suction port 45b of the intake passage for the second cylinder is directed substantially parallel to the air filter 51 in the air cleaner, while the intake passage for the first cylinder is provided. Since the upstream end suction port 44b of the above is oriented diagonally opposite to the air filter 51 in the air cleaner, the upstream end suction port 45b of the intake passage for the small-interval cylinder has a space larger than that for the large-interval cylinder with a simple structure. It becomes possible to direct to A2.

Further, since the upstream end suction port 45b of the small interval cylinder and the upstream end suction port 44b of the large interval cylinder are arranged so that their positions are deviated in the flow direction of the intake air, the axis and the intake air Since it is arranged so that the angle formed by the flow direction is different, intake interference can be suppressed, air can be sucked easily and reliably, and the difference between the intake amount to the small interval cylinder and the intake amount to the large interval cylinder can be reduced. It is possible to suppress, and as a result, it is possible to suppress the occurrence of a torque valley particularly in the medium speed range.

That is, in the case of an unequal-interval ignition engine, since the effective intake time differs depending on the cylinder, intake interference from adjacent cylinders is particularly likely to occur in the intake stroke of the small-interval cylinder. In the present embodiment, in the plane substantially parallel to the air filter 51, the small-interval cylinder upstream end suction port 45b.
Is arranged on the upstream side of the upstream end suction port 44b for the large-interval cylinder, so that the upstream end suction ports 45b, 44b can be constructed with a simple structure.
The positions of the two can be deviated in the flow direction of the intake air, and as a result, the intake interference due to the intake air flow into each intake passage can be suppressed.

The small-interval cylinder upstream end suction port 45b is oriented substantially parallel to the air filter 51, while the large-interval cylinder upstream end suction port 44b is oriented obliquely opposite to the air filter 51. Due to the upstream end suction port 44
The angles of b and 45b with respect to the intake air flow direction can be changed.

Further, in the present embodiment, the protruding length of the second intake pipe 45 inside the air cleaner 46 is made longer than the protruding length of the first intake pipe 44 inside the air cleaner 46. The intake passage length can be made longer than the intake passage length to the first cylinder.

In this embodiment, the engine 9 is
Since a 270-degree phase crank parallel two-cylinder engine including a first cylinder (a large-interval cylinder) having an ignition interval of 450 degrees and a second cylinder (a small-interval cylinder) having an ignition interval of 270 degrees is used, the above-mentioned directing of the upstream suction port is performed. It is possible to easily and surely change the size of the space to be operated, shift the position of the upstream end suction port, change the angle of the suction port, etc., and improve the torque characteristic.

Although the parallel two-cylinder engine has been described in the above embodiment, the inventions of claims 1 to 5 can be applied to, for example, a V-type two-cylinder engine other than the above.

[Brief description of drawings]

FIG. 1 is a left side view of a motorcycle provided with an intake device according to an embodiment of the present invention.

FIG. 2 is a sectional right side view of the intake device.

FIG. 3 is a left side view of a cross section of an air cleaner of the intake device.

FIG. 4 is a rear view of the air cleaner.

FIG. 5 is a bottom view of the air cleaner.

FIG. 6 is a left side view of the exhaust pipe of the above embodiment.

FIG. 7 is a plan view of the exhaust pipe.

[Explanation of symbols]

9 engine 44b Upstream end suction port for large-interval cylinders 45b Upstream end suction port for small-interval cylinders 46 Air cleaner 51 filters A1 Space where the upstream suction port for large-interval cylinders points A2 Space where the upstream inlet for small-interval cylinders points

Claims (6)

[Claims] 1. An intake system for a multi-cylinder engine in which an upstream end suction port of an intake passage connected to each cylinder is located in an air cleaner, and the engine is configured such that each cylinder performs unequal interval ignition. In addition, the space where the upstream end suction port of the intake passage of the small interval cylinder with a small ignition interval is directed is set larger than the space where the upstream end intake port of the intake passage of the large interval cylinder with a large ignition interval is directed. Characteristic multi-cylinder engine intake device. 2. The intake passage for the small-interval cylinder has its upstream end suction port oriented substantially parallel to the air filter in the air cleaner, while the intake passage for the large-interval cylinder has its upstream end suction port. An intake device for a multi-cylinder engine, which is oriented so as to face the air filter diagonally in the air cleaner. 3. An intake system for a multi-cylinder engine in which an upstream end suction port of an intake passage connected to each cylinder is located in an air cleaner, and the cylinders of the engine are configured to perform non-uniform ignition. The positions of the upstream end intake port of the intake passage of the small interval cylinder with a small ignition interval and the upstream end intake port of the intake passage of the large interval cylinder with a large ignition interval are deviated in the intake flow direction. The intake device for a multi-cylinder engine, characterized in that it is arranged in such a manner that the axes thereof and the direction of the flow of intake air are different. 4. The upstream side intake port of the intake passage for the small interval cylinder and the upstream end intake port of the intake passage for the large interval cylinder at different positions in a plane substantially parallel to the air filter according to claim 3. An intake device for a multi-cylinder engine characterized by being arranged. 5. The intake passage for the small-interval cylinder has its upstream end suction port oriented substantially parallel to the air filter in the air cleaner, while the intake passage for the large-interval cylinder has its upstream end suction port. An intake device for a multi-cylinder engine, which is oriented so as to face the air filter diagonally in the air cleaner. 6. The engine according to claim 1, wherein the engine comprises a first cylinder (ignition interval cylinder) having an ignition interval of 450 degrees and a second cylinder (immediate interval cylinder) having an ignition interval of 270 degrees. An intake system for a multi-cylinder engine, which is a phase crankshaft parallel two-cylinder engine.