Intake system of multi-cylinder engine

An intake system of a V-engine provided with a surge tank arranged at a position higher than a cylinder head and divided in internal space into a top part and a bottom part. The surge tank has a plurality of intake tubes communicating the surge tank and intake ports, wherein intake tubes communicated with one cylinder bank of the V-engine are connected to the top part of the surge tank and intake tubes communicated with the other cylinder bank are connected to the bottom part of the surge tank. The surge tank is formed so that a front end of the top part is positioned further toward a rear side of the vehicle compared with the front end of the bottom part when the intake system is mounted to a V-engine mounted in the vehicle, whereby the height of the engine hood can be effectively lowered.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an intake system of a multi-cylinder engine.

2. Description of the Related Art

In a multi-cylinder engine provided with two cylinder banks each comprised of a plurality of cylinders, for example, a V-engine, it is necessary to arrange the surge tank above the engine for structural reasons. This is because with a V-engine, the intake ports are provided above the center of the structure and because the surge tank has to be arranged near the intake ports from the viewpoint of the intake efficiency or the layout of the intake pipe and exhaust pipe, etc.

In this way, since the surge tank is arranged above a V-engine, when placing the engine and the surge tank in the engine compartment, the position of the engine hood inevitably ends up becoming high. In particular, if also considering the need to provide a cushion material etc. between the engine hood and the tops of the engine body and the surge tank from the viewpoint of protecting pedestrians, the engine hood has to be positioned higher, and thus the possibility of changes in vehicle design is limited.

In general, from the viewpoint of securing the field of vision of the vehicle driver, the engine hood usually has to be made to incline downward toward the front of the vehicle. To make the height of the engine hood as a whole lower, it is necessary to make the height of the engine hood lower at the front region of the engine hood. In the intake system of the V-engine disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-121224, the surge tank is provided above the center of the two cylinder banks of the V-engine and facing throttle valves are provided at the two sides of the rear end of the surge tank. Due to this, it becomes possible to arrange the surge tank further to the rear. Further, the surge tank is formed so that its top surface is inclined downward toward the front of the vehicle when the surge tank is arranged above the center of the V-engine. By forming the surge tank in this way, the height of the engine hood is effectively made lower at the front region of the engine hood.

However, there is a surge tank which is divided in its internal space into a top part and a bottom part and provided with a partition between the top part and the bottom part. Further, in such a surge tank, the intake tubes connected to one cylinder bank of the V-engine are connected to the top part, while the intake tubes connected to the other cylinder bank are connected to the bottom part. Further, an opening communicating the top part and bottom part is provided at part of the partition in the surge tank. A valve for opening/closing the opening is provided in the opening. By operating this valve, the effective intake pipe length, which has an effect on the period of the intake pulsation occurring in the intake passage, is changed. It is possible to use this to raise the charging efficiency by the pulsation effect.

In this way, even when using a surge tank with an internal space divided into a top part and bottom part, the height of the engine hood has to be made lower. If however forming a surge tank so that its top surface inclines downward toward the front of the vehicle as described in Japanese Unexamined Patent Publication (Kokai) No. 4-121224, at the front region of the surge tank, the top part and bottom part of the surge tank end up becoming extremely thin. Therefore, in this case, it is difficult to make intake tubes branch from the sides of the top part and bottom part in the front region of the surge tank.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an intake system of a multi-cylinder engine effectively enabling the height of the engine hood to be made lower even when using a surge tank with an internal space divided into a top part and a bottom part.

In one embodiment of the present invention, there is provided an intake system of a multi-cylinder engine provided with two cylinder banks each comprised of a plurality of cylinders, provided with a surge tank arranged at a position higher than cylinder heads of the multi-cylinder engine when the intake system is attached to the multi-cylinder engine and divided in internal space into a top part and a bottom part and with pluralities of intake tubes communicating the surge tank and intake ports of said multi-cylinder engine; intake tubes communicated with one cylinder bank of the multi-cylinder engine being connected to the top part of the surge tank and intake tubes communicated with the other cylinder bank being connected to the bottom part of the surge tank; the surge tank being formed so that a front end of the top part is positioned further toward a rear side of the vehicle compared with a front end of the bottom part when the intake system is mounted to a multi-cylinder engine mounted in the vehicle.

According to this embodiment, the front end of the top part is formed positioned further to the rear of the vehicle compared with the front end of the bottom part. Therefore, in the front region of the surge tank, that is, the front region of the engine hood, there is only the bottom part of the surge tank. There is no top part. Accordingly, in this region, the height of the engine hood can be made lower.

Therefore, according to the present embodiment, it is possible to effectively make the height of the engine hood lower even when using a surge tank with an internal space divided into a top part and a bottom part.

Note that in the specification, “front” and “rear” means the front and rear of the vehicle in which the multi-cylinder engine is arranged. Further, “top” and “upper” and “bottom” and “lower” mean the top and upper and the bottom and lower in the vertical direction of the vehicle in which the multi-cylinder engine is arranged.

In another embodiment of the present invention, the top part and bottom part of the surge tank are connected to the same intake pipe at the upstream side of intake and the top part is given an angle with respect to the bottom part so that an angle between a direction of connection of the intake pipe to the top part and a direction of connection of intake tubes to the top part becomes larger than an angle between a direction of connection of the intake pipe to the bottom part and a direction of connection of intake tubes to the bottom part.

According to the present embodiment, since the angle between the direction of connection of the intake pipe to the top part of the surge tank (hereinafter referred to as the “intake pipe connection direction”) and the direction of connection of the intake tube to the top part (hereinafter referred to as the “intake tube connection direction”) is made large, the direction of flow of the intake gas from the intake pipe to the intake tubes through the top part of the surge tank will not change greatly and therefore the intake gas will more easily flow through the inside of the surge tank. That is, it is possible to reduce the intake resistance with respect to the intake gas.

Therefore, according to the present embodiment, by making the angle between the intake pipe connection direction and intake tube connection direction larger at the top part of the surge tank, it is possible to make the intake resistance with respect to the intake gas smaller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, an intake system of a multi-cylinder engine of the present invention will be explained with reference to the drawings.FIG. 1shows a vehicle mounting an intake system of a first embodiment of the present invention.

InFIG. 1,1indicates a vehicle mounting the intake system of the present invention,2an engine compartment in which the multi-cylinder engine is housed, and10an intake system of the present invention. The intake system10has an air cleaner11, an intake pipe12, a surge tank13, and a plurality of intake tubes14. The intake gas (intake air) passes through these and flows into the intake ports of the multi-cylinder engine. The intake pipe12is provided with a throttle valve15for adjusting the flow rate of the intake air flowing through the intake pipe12. In the specification, the front of the vehicle1, that is, the forward direction of the vehicle1, is described as the “front” (direction F inFIG. 1), while the rear of the vehicle1, that is, the reverse direction of the vehicle1, is described as the “rear” (direction R inFIG. 1). Further, the upward direction in the vertical direction of the vehicle1is described as “up” (direction U inFIG. 1), while the downward direction in the vertical direction of the vehicle1is described as “down” (direction D inFIG. 1).

FIG. 2toFIG. 5show an intake system10of a first embodiment mounted in a multi-cylinder engine. Here,FIG. 2is a partial plan view of the intake system10,FIG. 3is a partial front view of the intake system10, andFIG. 4andFIG. 5are partial side views of the intake system as seen from one side and the opposite side. In the illustrated embodiment, the case of using a six-cylinder V-engine, that is, an engine in which two cylinder banks each having three cylinders are arranged at a predetermined angle, is shown. Further, the engine3is mounted longitudinally in the engine compartment2, that is, is arranged so that the cylinders forming the cylinder banks31and32are arranged aligned in the front-rear direction. Note that the engine able to use the intake system10of the present invention is not limited to the above six-cylinder V-engine. The intake system10may be used for any engine so long as it is a multi-cylinder engine provided with two cylinder banks formed by pluralities of cylinders (for example, an eight-cylinder V-engine, a six-cylinder horizontally opposed engine, etc.).

As shown inFIG. 2toFIG. 5, the intake pipe12is branched into two branch pipes, that is, a top branch pipe17and bottom branch pipe18, at an intake pipe branch part16downstream of the throttle valve15. The top branch pipe17is positioned above the bottom branch pipe. The surge tank13is divided into two parts, that is, a top part13aand a bottom part13b, by a partition19(FIG. 4). The top part13ais positioned above the bottom part13b. The top part13ais connected to the top branch pipe17, while the bottom part13bis connected to the bottom branch pipe18. The top branch pipe17and the bottom branch pipe18are connected to the rear of the top part13aand the rear of the bottom part13brespectively. Further, the throttle valve15arranged in the intake pipe12is positioned above and behind the engine3. In this embodiment, the top part13aand the bottom part13bare not formed separately, but are formed integrally. However, the top part13aand the bottom part13bmay also be formed separately and then connected to form the surge tank13.

Further, the surge tank13is positioned above head covers33,34of the cylinder heads of the engine3. In particular, in this embodiment, the surge tank13is arranged above the head cover corresponding to one cylinder bank31of the engine3(hereinafter referred to as “the first cylinder bank”). The surge tank13is arranged at this position for the following reason. That is, in a V-engine, the intake ports have to be arranged at the center of the engine, structurally. The lengths of the intake tubes are set for optimally obtaining the pulsation effect explained later. Further, to evenly distribute the intake gas to the cylinders, it is necessary to make the lengths of the intake tubes uniform. If satisfying these conditions while connecting the surge tank to the intake ports positioned at the center of the engine, inevitably the surge tank becomes positioned above the head covers of the cylinder heads of the engine.

The partition19between the top part13aand bottom part13bof the surge tank13is provided with an opening20. Therefore, the opening20connects the top part13aand the bottom part13bthrough it. The opening20is provided with a valve21for opening and closing the opening20. Therefore, when the valve21is opened, the top part13aand bottom part13bare communicated with each other, while conversely when the valve21is closed, the top part13aand bottom part13bare not communicated.

The top part13aand bottom part13bof the surge tank13are each connected to three intake tubes141to146. The intake tubes141,143, and145connected to the top part13aare connected to the cylinders of the first cylinder bank31through the intake ports35provided at the cylinder heads, while the intake tubes142,144, and146connected to the bottom part13bare connected to the cylinders of the other cylinder bank32(hereinafter referred to as “the second cylinder bank”) than the first cylinder bank31through the intake ports36provided in the cylinder heads.

If designating the three cylinders of the first cylinder bank31the #1 cylinder, #3 cylinder, and #5 cylinder from the front to the rear, these cylinders are connected to a first intake tube141, a third intake tube143, and a fifth intake tube145. Further, if designating the three cylinders of the second cylinder bank32the #2 cylinder, #4 cylinder, and #6 cylinder from the front to the rear, these cylinders are connected to a second intake tube142, a fourth intake tube144, and a sixth intake tube146. Further, the intake pipe12connected to the surge tank13is positioned further to the rear than these intake tubes14near the part connecting with the surge tank13.

The valve21may be suitably operated to make effective use of the fluctuations in pressure in the intake passage (passage including intake tubes14, surge tank13, intake pipe12, etc.) to raise the efficiency of intake to the combustion chambers37of the engine3. The reason is as follows: That is, as methods for utilizing the fluctuations in pressure in an intake passage, there are the method of utilizing the pulsation effect occurring in the intake tubes14(inertial supercharging effect) and the method of utilizing the pulsation effect occurring in the passage from the intake tubes to the intake pipe branch part (resonant supercharging effect). The speed of the engine able to utilize these effects (hereinafter referred to as the “engine speed”) is limited. Further, the engine speed where resonant supercharging occurs is lower than the engine speed where inertial supercharging occurs.

The magnitude of the inertial supercharging effect and resonant supercharging effect is affected by the magnitude of the pulsation occurring in the surge tank. That is, the larger the volume of the surge tank or the greater the number of cylinders communicated with the surge tank, the weaker the pulsation occurring in the surge tank and consequently the stronger the inertial supercharging effect, but the weaker the resonant supercharging effect. In the present embodiment, by opening the valve21, the top part13aand the bottom part13bbecome communicated with each other and the two parts13aand13bfunction as a single surge tank. Consequently, compared with when the top part13aand bottom part13bfunction as separate surge tanks, the volume of the surge tank becomes substantially greater and the number of cylinders communicating with the surge tank becomes substantially greater, so the inertial supercharging effect becomes stronger. Conversely, by closing the valve21, the top part13aand the bottom part13bbecome separated and these parts13aand13bfunction as separate surge tanks. Therefore, the volume of each of the parts13aand13bbecomes smaller and the number of cylinders communicated with each of the parts13aand13bbecomes smaller, so the resonant supercharging effect is strengthened. Accordingly, as explained above, by operating the valve21in accordance with the engine speed, it is possible to effectively utilize the inertial supercharging effect and resonant supercharging effect and therefore the efficiency of intake to the combustion chambers37is raised.

However, from the viewpoint of increasing the degree of design freedom of the vehicle1and of securing the field of vision of the vehicle driver, it is necessary to lower the position of the engine hood4. In a V-engine3, the surge tank13is arranged at the top, so the height of the equipment in the engine compartment2(including the engine, intake system, etc., hereinafter referred to as the “engine equipment as a whole”) becomes high and inevitably the position of the engine hood4ends up becoming higher.

Therefore, to lower the position of the engine hood4, it is necessary to lower the height of the engine equipment as a whole in the region where the surge tank is arranged. In general, however, from the viewpoint of securing the field of vision of the vehicle driver, the engine hood4is inclined downward toward the front, so to make the height of the engine hood4as a whole lower, it is necessary to make the position of the engine equipment as a whole lower the further to the front. Consequently, it is necessary to lower the position of the top surface of the surge tank13in particular in the front region even at the surge tank13. Conversely, if lowering the position of the top surface of the surge tank13in the front region of the surge tank13, it is possible to lower the height of the engine hood4as a whole.

Therefore, in the first embodiment of the present invention, the surge tank13has its top part13ashifted to the rear compared with its bottom part13band has the top part13bnot completely overlapping the bottom part13b. Consequently, the front end22aof the top part13ais positioned further to the rear compared with the front end22bof the bottom part13b. Accordingly, at the front region23of the surge tank13, the surge tank13is formed by only the bottom part13b, so at that region23, the overall height of the surge tank13is lower than the region other than the front region23. Since the overall height of the surge tank13in the front region23is low, it is possible as a result to lower the height of the engine hood4as a whole.

This will be clear fromFIG. 4andFIG. 5as well. In these figures, the broken lines show the lower limit position at which the engine hood4can be disposed in the case of the present invention (more precisely, the lower limit position where the cushion material placed below the engine hood4can be arranged). As will be understood from these figures, at the front region23of the surge tank13, the engine hood4can be arranged at a low position. In particular,FIG. 4shows by the dot-dash lines the contours of the surge tank in the case if the top part were superposed on the bottom part of the surge tank even at the front region. Therefore, it is learned that according to the surge tank13of the present embodiment, the engine hood can be lowered to a position where it would otherwise end up interfering with the surge tank if arranging the top part over the bottom part.

Further, the top part13aof the surge tank13is formed to become gradually higher in height the further toward the rear. Along with this, the positions where the intake tubes141,143, and145are connected to the top part13aof the surge tank13become higher the further to the rear the intake tubes. On the other hand, the positions where these intake tubes141,143, and145are connected to the intake ports35of the engine3become the same in height. Therefore, the lengths in the vertical direction of the intake tubes141,143, and145connected to the top part13abecome longer the further to the rear the intake tubes. That is, as shown inFIG. 5, the lengths in the vertical direction of the intake tubes become longer in the order of141,143, and145.

On the other hand, the lengths in the horizontal direction of the intake tubes141,143, and145connected to the top part13abecome shorter the further to the rear the intake tubes. That is, as shown inFIG. 2, the lengths in the horizontal direction of the intake tubes become longer in the order of145,143, and141. This is due to the fact that the top part13ais shifted to the rear and thereby the distances between connecting points of the intake tubes141,143, and145to the top part13abecome shorter than the distances between the intake ports35to which these intake tubes141,143, and145are connected.

In this way, in the intake tubes141,143, and145connected to the top part13a, the further the intake tube to the rear, the longer its length in the vertical direction and the shorter its length in the horizontal direction, so as a result the lengths of the intake tubes141,143, and145connected to the top part13acan be made equal. Accordingly, it is possible to make the distribution of intake gas to the cylinders equal and to effectively utilize the pulsation effect occurring in the intake passage to obtain a high charging efficiency.

Further, the top part13aand bottom part13bof the surge tank13are not arranged in parallel. The top part13ais given an angle with respect to the bottom part13bin the horizontal direction. That is, the top part13ais shifted to be rotated by a predetermined angle toward the opposite side than the side where the intake tubes14are connected to the surge tank13along the axis near the point where the intake pipe12is connected to the surge tank13. Therefore, the angle θ between the direction by which the intake tubes14are connected to the top part13a(hereinafter referred to as the “intake tube connection direction”) and the direction in which the intake pipe12is connected to the top part13a(hereinafter referred to as the “intake pipe connection direction”) becomes larger than the angle between the intake tube connection direction to the bottom part13band the intake pipe connection direction to the bottom part13bfor the corresponding intake tubes (for example, the second intake tube142for the first intake tube141). Note that the intake pipe connection direction may be the direction in which the top branch pipe17is connected to the top part13aor the direction in which the top branch pipe17is branched at the intake pipe branch16.

In general, if the angle θ between the intake tube connection direction and the intake pipe connection direction to the surge tank13is small, the intake gas flowing from the intake pipe12to the surge tank13must flow through a sharp angle in the surge tank13in order to flow to the intake tubes14. That is, the angle of bending of the flowline of the intake gas in the surge tank13is small. Sharp bending of the flow of the intake gas results in intake resistance and invites a drop in the flow rate of the intake gas as a result.

As opposed to this, in the present embodiment, the angle θ between the intake tube connection direction and the intake pipe connection direction to the top part13aof the surge tank13is large, so the flow of the intake gas does not bend with a sharp angle and the bending angle of the flowline of the intake gas is large. Therefore, the intake resistance received by the intake gas due to bending of the flowline of the intake gas in the top part13abecomes relatively small.

Here, a comparison will be made of the flow rate of the intake gas to the cylinders when using a conventional type of intake system, that is, an intake system formed so that the top part of the surge tank completely overlaps the bottom part, and using an intake system of the present embodiment.FIG. 6shows the flow rates of intake gas to the cylinders (hereinafter referred to as “intake gas flow rate”) for the case of use of a conventional type of intake system and the case of use of an intake system of the present embodiment in the state with the valve21opened.

As will be understood fromFIG. 6, when using the intake system of the present embodiment, compared with when using a conventional type of intake system, the intake gas flow rate becomes greater in almost all of the cylinders. This is due to the small intake resistance received by the intake gas flowing through the top part13aof the surge tank13in the above way. Further, in the conventional type of intake system, there is fluctuation of the intake gas flow rate between cylinders. In particular, the intake gas flow rate tends to differ between odd number cylinders (cylinders of first cylinder bank) and even number cylinders (cylinders of second cylinder bank). This is believed to be because in the conventional type of intake system, the angle between the intake tube connection direction and intake pipe connection direction at the top part of the surge tank is smaller, by a large amount, than the angle between the intake tube connection direction and intake pipe connection direction at the bottom part of the surge tank, so the intake resistance received by the intake gas flowing through the top part of the surge tank becomes considerably larger than the intake resistance received by the intake gas flowing through the bottom part. As opposed to this, in the intake system of the present embodiment, it is believed that the angle between the intake tube connection direction and the intake pipe connection direction does not become that different between the top part13aand bottom part13bof the surge tank13, so fluctuation of the flow rate of intake air between the cylinders of the first cylinder bank31and cylinders of the second cylinder bank32is suppressed.

In this way, according to the first embodiment of the present invention, it is possible to maintain as is the large flow rate of intake air to the cylinders of the cylinder banks31and32and maintain the amounts of intake air substantially even among cylinders while lowering the height of the front region of the surge tank and thereby lower the attachment position of the engine hood.

Next, an intake system of a second embodiment of the present invention will be explained with reference toFIG. 7andFIG. 8.FIG. 7is a plan view similar toFIG. 2of the intake system40of the second embodiment, whileFIG. 8is a side view of the intake system40of the second embodiment. Note that in the following explanation, components similar to those of the first embodiment are assigned the same reference notations.

In the present embodiment, in the same way as the first embodiment, the case is shown of use of a six-cylinder V-engine5, but the embodiment may also be used for any multi-cylinder engine provided with two cylinder banks comprised of pluralities of cylinders (for example, an eight-cylinder V-engine, six-cylinder horizontally opposed engine, etc.) However, in this embodiment, unlike the first embodiment, the engine5is mounted transversely in the engine compartment2, that is, the cylinders forming the cylinder banks51and52are arranged aligned in the transverse direction (that is, a direction perpendicular to front-rear direction).

In the second embodiment, in the same way as the first embodiment, the surge tank43is divided in internal space into the two parts of the top part43aand bottom part43b. The top part43ais positioned above the bottom part43b, and the top part43aand bottom part43bare connected to the top branch pipe17and bottom branch pipe18, respectively. The top branch pipe17and the bottom branch pipe18are connected to the sides of the top part43aand the bottom part43b, respectively. Further, the top part43aand bottom part43bare formed integrally.

Further, the surge tank43is arranged above the head covers53corresponding to the cylinder bank (hereinafter referred to as the “third cylinder bank”)51positioned at the rear among the two cylinder banks51,52of the engine3. The top part43aand the bottom part43bof the surge tank43are each connected to three intake tubes441to446at the fronts. The intake tubes441,443, and445connected to the top part43aare communicated with the cylinders of the third cylinder bank51through the intake ports55, while the intake tubes442,443, and445connected to the bottom part43bare communicated with the cylinders of the cylinder bank (hereinafter referred to as the “fourth cylinder bank”)52separate from the third cylinder bank51through the intake ports56.

In the intake system of the second embodiment as well, in the same way as the intake system of the first embodiment, the surge tank43is formed with the top part43ashifted to the rear compared with the bottom part43band with the top part43anot completely overlapping the bottom part43b. Therefore, the front end45aof the top part43ais positioned more toward the rear compared with the front end45bof the bottom part43b. Accordingly, the surge tank43is comprised of only the bottom part43bat the front region46of the surge tank13, so the overall height of the surge tank43at the front region46is lower than the region other than the front region. Therefore, the height of the engine hood4as a whole can be lowered.

This is clear fromFIG. 8as well. In the figure, the broken line shows the lower limit position where the engine hood4can be arranged in the present invention in the same way as inFIG. 4andFIG. 5. As clear from this figure, it is possible to arrange the engine hood4at a low position in the front region46of the surge tank43. The dot-chain line in the figure shows the contours of the surge tank if arranging the top part over the bottom part of the surge tank in the front region as well. From this figure, according to the present embodiment, it is learned that it is possible to lower the engine hood down to a position which would end up interfering with the surge tank if arranging the top part over the bottom part.