JPH0217688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to an engine intake system, in particular, to open a plurality of intake ports such as two ports into a combustion chamber of the engine, and to open the same to each intake port. This invention relates to a type of intake device equipped with an intake valve that opens and closes.

(Prior art) Conventionally, in a reciprocating engine, two intake ports with approximately equal opening areas are opened for each combustion chamber to ensure a large opening area, and an intake passage formed in the cylinder head is By connecting each intake port at a large angle along the axial direction of the combustion chamber and allowing intake air to flow straight into the combustion chamber, the engine's filling efficiency is maximized and the engine output is increased. The intake structure is well known.

Such a two-port intake structure is advantageous in that it can achieve high output during high-load operation, but on the other hand, during low-load operation with a small amount of intake air, the intake air flow rate becomes weaker and combustibility decreases. In terms of fuel efficiency,
There is also a disadvantage in terms of emission.

In order to eliminate this drawback, a low-load intake passage and a high-load intake passage with a shutter valve interposed are connected to the above two intake ports, and the shutter valve is closed when the engine is operating at low load. , a device in which air is taken only from the low-load intake passage is known (for example, Japanese Patent Application Laid-Open No. 1989-1999)
(See Publication No. 44419).

However, such measures are not necessarily effective as low-load measures. In other words, it was originally designed to maximize the opening area of the two intake ports to achieve high output, so even if only one intake port is used, during extremely low load operation with a small amount of intake air, the opening area will be increased. The area is still too large to effectively improve the intake flow rate, and it is not possible to effectively form the swirl that is essential for improving combustibility.

It seems that such a problem can be solved by narrowing down the passage area of the low-load intake passage, as disclosed in Japanese Patent Laid-Open No. 56-146015, but in that case, the area of the high-load intake passage The original purpose of high output cannot be achieved unless the passage area is made very large, and if the passage area is actually increased, the imbalance with the passage area of the low-load intake passage increases, resulting in low-load A so-called switching shock occurs when switching from a low load to a high load, and when the load is high, intake air concentrates in the high load intake passage with less intake resistance, effectively increasing the output. There is a contradiction in that it is not possible to secure an effective intake passage area to achieve this goal. Furthermore, for the purpose of achieving high output, the port connection part of the intake passage is formed along the axial direction of the combustion chamber, as mentioned above, so by increasing the intake air velocity, the flow velocity within the combustion chamber can be increased. Even if a fast flow is generated, it is not generated as an effective swirl along the circumferential direction of the combustion chamber. Therefore, there is a problem in that this intake air flow is attenuated early in the compression stroke. However, if you restrict the low-load intake passage too much in an attempt to increase the flow velocity as much as possible, the load range that can be covered will be limited accordingly, and if you open the shutter valve in a relatively low load range, the high-load intake passage will also be able to handle the load. It becomes necessary to supply intake air. In that case, since the two intake ports are formed to face each other with respect to the horizontal center line of the combustion chamber, the intake flow taken in from the low-load intake port and the intake flow taken in from the high-load intake port are different. If the swirls collide with each other, the swirl is further weakened, if not eliminated, and it is difficult to ensure good combustibility due to the swirl.

As described above, restricting the low-load intake passage and the intake port connected thereto is not only inconsistent with the objective of achieving high output, but also causes various new problems.

The applicant aimed at increasing the output of the engine.
without substantially changing the intake port system.
In Japanese Patent Application No. 176,776/1987, we have already proposed an engine intake system equipped with an intake structure that can generate a swirl that is effective in improving combustibility within the combustion chamber during low-load operation of the engine. .

The proposed invention relates to an engine intake system in which a plurality of intake ports are opened to combustion chambers of an engine, and each intake port is opened and closed by an intake valve. An on-off valve is provided in the intake passageway, and the on-off valve is closed during low-load operation and opened during high-load operation, and the passage area of the intake passage is controlled to increase or decrease depending on the operating condition of the engine. The basic feature is that an auxiliary intake passage is provided, which branches from the bottom of the intake passage, is connected to any one of the intake ports, and has a passage area smaller than that of the intake passage.

That is, in this invention, during low-load operation of the engine when the on-off valve is closed, intake air flows exclusively through the auxiliary intake passage formed at the bottom side of the intake passage and flows through the engine at a high flow rate through the intake port to which this passage is connected. is supplied to the combustion chamber. In that case, since the auxiliary intake passage is formed at the bottom side of the intake passage, it necessarily forms a shallow angle with respect to the mating surface of the cylinder head and cylinder block, and the intake air flowing into the combustion chamber is It is possible to generate a swirl that rotates in the circumferential direction of the chamber, and during high-load engine operation when the on-off valve is opened, intake air is drawn in efficiently from multiple intake ports, ensuring the original high output. This is possible.

Therefore, according to the present invention, it is possible to improve combustibility during low-load operation, as well as improve fuel efficiency and emission performance, without sacrificing the original purpose of the two-intake port system, which is to increase engine output. However, there is still room for improvement.

One of them is the problem of the switching shock that may occur when switching from a low load to a high load as described above. In other words, while the on-off valve is opened from the low-load region where the auxiliary intake passage is used exclusively, when moving to the high-load region, a large amount of intake air flows into the combustion chamber from each intake port at once, so the charging amount decreases. increases rapidly, causing a kind of torque shock.

(Objective of the Invention) The object of the present invention is to expand the low load range that can be covered with the on-off valve closed while maintaining the swirl during low-load operation. The purpose of this is to prevent the above-mentioned switching shock by ensuring a sufficient amount of intake air to some extent when the valve is closed so as to minimize the intake air amount gap in the closed position.

(Structure of the Invention) Therefore, the present invention provides two intake ports, one of which opens into a combustion chamber, an intake passage whose branch ends branched downstream are respectively connected to each intake port, and the intake passage. Provided upstream from the branch of
An intake system for an engine having an on-off valve that is closed at low loads and opened at high loads, and an auxiliary intake passage that branches from an intake passage upstream of the on-off valve and is connected downstream to any one of the intake ports, The basic feature is that when the on-off valve is closed, an intake air supply means is provided for passing a predetermined amount of intake air from the intake port side end to which the auxiliary intake passage of the on-off valve is connected.

That is, in the present invention, even when the on-off valve is closed, intake air is secured not only from the auxiliary intake passage but also from the intake air supply means, so that a sufficient amount of intake air is secured and the load range that can be covered is expanded. be done.
Moreover, since this intake air supply means passes intake air at the end on the intake port side to which the auxiliary intake passage of the on-off valve is connected, the swirl is not weakened by interference or the like.

(Effects of the Invention) Therefore, according to the present invention, the load range that can be handled with the on-off valve closed can be expanded to the high load side while maintaining swirl performance, and switching shock can be effectively prevented. can do.

(Example) Hereinafter, an example of the present invention will be described in more detail.

As shown in FIG. 1, the combustion chamber 2 of one cylinder 1 of the engine E has first and second intake ports of approximately the same diameter, which are approximately symmetrical with respect to the center line l in the width direction of the cylinder block of the engine E. 4 and 5 are opened,
Exhaust ports 6 and 7 are located at positions facing the first and second intake ports 4 and 5 across the longitudinal center line m.
is opened.

The intake passage 8 that supplies intake air to the first and second intake ports 4 and 5 gradually branches within the cylinder head (see FIG. 2), and before the first and second intake ports 4 and 5, The branched intake passage 1 is divided into two by a partition wall 9 formed to protrude substantially along the width direction center line l.
0 and 11 are connected to the first and second intake ports 4 and 5, respectively. As shown in the figure, a shutter valve 1 is located upstream of the downstream branch point of the intake passage 8.
2 is interposed. Although this shutter valve 12 is not specifically shown, a well-known opening/closing control mechanism (for example, a link mechanism connected to a throttle valve) closes the intake passage 8 during low load operation of the engine E, and closes the intake passage 8 during high load operation. Its opening/closing is controlled so that it opens according to the load. On the upstream side of the shutter valve 12 in the intake passage 8, an upstream opening 13 of the auxiliary intake passage 13 is located toward the first intake port 4 with respect to the center line of the intake passage 8.
a is opened at the bottom wall of the intake passage 8. The auxiliary intake passage 13 has a downstream opening 13b that opens close to the first intake port 4, and is gently curved across the widthwise center line l, and is connected to the downstream opening 13a and the downstream opening 13a. 13b.
Shutter valve 1, as clearly shown in FIG.
2, an end on the side of the branch intake passage 10 to which the auxiliary intake passage 13 is connected is cut in a chord shape in the vertical direction to form a notch 12a.

Therefore, when the shutter valve 12 is fully closed, in addition to the auxiliary intake passage 13 that opens upstream of the shutter valve 12, the notch of the shutter valve 12 as shown by arrow A in FIG. 12
An intake passage passing through a is formed. The intake air flowing down along this intake passage A is divided into the branch intake passage 1
0 along the passage side wall 10a.

As specifically shown in FIG. 2, the auxiliary intake passage 13 is formed in a bottom wall 14 forming the bottom of the intake passage 8, and its downstream opening 13b is located at the upstream end of the partition wall 9, i.e. Branch intake passage 10,1
The first intake port 4 is located downstream of the first branch point and as close as possible to the first intake port 4 which is opened and closed by the intake valve 15. For this reason, the auxiliary intake passage 13
The entire amount of intake air flowing down flows into the combustion chamber 2 from the first intake port 4. The auxiliary intake passage 13 is a branch intake passage 10 that is curved in the axial direction of the cylinder 1 immediately upstream of the first intake port 4.
On the other hand, it intersects at a slight angle of inclination with respect to the mating surface C between the cylinder block 31 and the cylinder head 30, and therefore has a directionality in the circumferential direction of the combustion chamber 2. Become.

Slightly downstream of the upstream opening 13a of the auxiliary intake passage 13, a shutter valve 12 for opening and closing the intake passage 8 is provided so as to be inclined diagonally downward toward the downstream. A fuel injection valve 17 is attached to a mounting portion 16a provided in advance on the upper wall 16 of the intake passage 8. In this case, the fuel injection port 18 is connected to the shutter valve 1
It is set so as to be located slightly downstream of the rotation shaft 12b of No. 2 and on the center line of the intake passage 8.

Note that the intake valve 1 that opens and closes the first intake port 4
5. An intake valve (not shown) that opens and closes the second intake port 5 and an exhaust valve 1 that opens and closes the exhaust ports 6 and 7
9 (the other is not shown) are driven to open and close at predetermined timings synchronized with the rotation of the engine E by a well-known overhead cam mechanism 20.

Further, as shown in FIG. 1, the spark plug 21
is set in a portion where the first and second intake ports 4 and 5 and exhaust ports 6 and 7 are not provided, more specifically, in a central portion of the combustion chamber 2.

With the above configuration, during low-load operation when the shutter valve 12 is closed, intake air is supplied not only through the auxiliary intake passage 13 but also through the notch 12a of the shutter valve 12.

Therefore, while the amount of intake air that can be provided by the auxiliary intake passage 13 becomes saturated relatively quickly, since intake air also flows from the notch 12a, even when the shutter valve 12 is closed, The load range that can be covered can be expanded to the higher load side.

Moreover, the notch 12 of the shutter valve 12
As mentioned above, the intake air that passes through a flows down almost along the side wall 10a of the branched intake passage 10, and almost the entire amount flows into the combustion chamber 2 from the first intake port 4, so that it is combusted by the auxiliary intake passage 13. It does not disturb the swirl formed in chamber 2, but rather acts to strengthen it.

In other words, if the shutter valve 12 were simply opened to a low opening, the swirl would flow into the combustion chamber 2 from both the first and second intake ports 4 and 5 and collide, eliminating the swirl. In this embodiment, the load range that can be covered with the shutter valve 12 closed can be expanded, and a good swirl can be maintained within the expanded load range.

Furthermore, since the amount of intake air when the shutter valve 12 is closed can be secured so that the load range is expanded to the high load side, even if the shutter valve 12 is opened to a high load operation, the shutter valve 12 is opened, the rate of increase in intake air can be made relatively small, and so-called switching shocks can be reliably prevented.

During high-load operation when the shutter valve 12 is opened, sufficient intake air is supplied from the first and second intake ports 4 and 5, ensuring the high output inherent to the two ports.

In addition, in the above embodiment, the shutter valve 12
Although a notch 12a is provided in the cylinder head to form an intake passage when the shutter valve is closed, for example, a bypass passage that bypasses the end of the branched intake passage to which the auxiliary intake passage 13 of the shutter valve is connected may be provided in the cylinder head. Needless to say, it may be provided.

[Brief explanation of drawings]

FIG. 1 is an explanatory sectional view of a main part of an engine showing an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view taken in the - line direction of FIG. 2... Combustion chamber, 4, 5... First and second intake ports, 8... Intake passage, 10, 11... Branch intake passage, 12... Shutter valve, 12a... Notch, 13... ...Auxiliary intake passage, 14...Bottom wall, 1
5...Intake valve.

Claims (1)

[Claims] 1 Two intake ports, each opened and closed by an intake valve, are opened into one combustion chamber, and are opened and closed by an on-off valve that closes at low load and opens at high load, and are branched downstream of the on-off valve, with each branch end An intake passage connected to each of the intake ports, and an auxiliary intake passage branched from the intake passage upstream of the on-off valve and connected to one of the intake ports, An intake system for an engine, characterized in that an intake air supply means is provided for passing a predetermined amount of intake air from the end of the intake port connected to the intake passage when the on-off valve is closed.