JPH0247572B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine intake system, particularly an engine in which a plurality of intake ports are opened in one combustion chamber, and at least one of the intake ports is connected to an engine load. The present invention relates to an engine intake system of a type that has come to be selectively used depending on the type of engine.

(Prior art) Multiple intake ports are provided in the combustion chamber of the engine,
It is known to selectively use these intake ports depending on the engine load. For example, Tokukai Akira
In the engine disclosed in Japanese Patent No. 56-44419, a branch intake passage is connected to each of two intake ports formed in the cylinder head, and the branch intake passages are connected to a common main intake passage. One of the branch intake passages is provided with an on-off valve, and the main intake passage is provided with a throttle valve.The throttle valve and the on-off valve work together to prevent the throttle valve from opening beyond a certain degree. The on-off valve is designed to open when the In other words, one branch intake passage is closed by an on-off valve when the engine is operating at low load, so intake air is supplied at a relatively high flow rate only from the other branch intake passage, and during high load operation, intake air is supplied from both branches. It is supplied from the intake passage and can ensure a high filling amount. However, since the engine intake system described in this publication is intended to ensure a sufficient amount of intake air during high-load operation, the cross-sectional area of each branch intake passage is not formed so small. First, even if only one branch intake passage is used during low-load operation, the intake flow rate cannot be sufficiently increased in an operating region where the load is very small, such as during idling. In addition, the shape of the intake port is designed to introduce the intake air flow almost along the axial direction of the combustion chamber in order to ensure a high filling amount during high-load operation. Coupled with the fact that the area cannot be made very small, this makes it difficult to form a strong swirl inside the combustion chamber during low load operation.

Japanese Patent Laid-Open No. 55-25511 discloses that in an engine intake system having two intake ports, an auxiliary intake passage with a small cross-sectional area is opened in each intake port, and a thin air passage is opened from this auxiliary intake passage during low-load operation. Techniques have been disclosed for providing high-velocity intake air flow. The engine intake system described in this publication uses a high-speed intake air flow blown into the combustion chamber during low-load operation to form intense turbulence near the center of the combustion chamber, especially near the ignition plug, thereby scavenging air around the ignition plug. The aim is to promote stable combustion by increasing the flame propagation speed. However, with this intake system, although the auxiliary intake passage is effective in operating conditions where the engine load is very low, such as idling, in operating areas where the engine load increases even slightly, the auxiliary intake passage alone is insufficient. Since the amount of intake air cannot be secured,
It becomes necessary to open a branch intake passage that is continuous with each intake port. When the branch intake passage is opened even slightly in this way, the flow velocity of the intake air flow from the auxiliary intake passage decreases rapidly, and the turbulent flow within the combustion chamber is weakened. Therefore, this intake system cannot provide a satisfactorily stable combustion condition over a region where the engine load is slightly higher than the idling state to a medium load region.

(Objective of the Invention) The present invention provides an intake system in which a plurality of intake ports are opened in one combustion chamber to ensure a high filling amount of intake air during high-load operation, over a relatively wide range of low-load operation. It is an object of the present invention to form a strong swirl in a combustion chamber throughout the combustion chamber, thereby making it possible to obtain a good combustion state.

(Structure of the Invention) In order to achieve the above object, the present invention has the following structure. That is, the engine intake device according to the present invention includes two intake ports opening into the combustion chamber;
A branch intake passage connected to each of the two intake ports, a main intake passage connected to the upstream side of the branch intake passage, and an on-off valve provided in the main intake passage and opened during high-load operation; The main intake passage has an auxiliary intake passage that branches from the main intake passage on the upstream side of the on-off valve and is connected to one of the intake ports so as to face approximately circumferentially with respect to the combustion chamber. It is characterized in that the central axis is arranged so as to be biased toward the side of the intake port to which the auxiliary intake passage is connected.

According to the present invention, during low-load operation when the on-off valve is closed, intake air is supplied to the combustion chamber through the auxiliary intake passage. Since the auxiliary intake passage is formed to have a smaller cross-sectional area than the branch intake passage, a relatively high flow rate can be maintained even during low-load operation with a small intake air amount. Furthermore, since the auxiliary intake passage opens into one of the plurality of intake ports, intake air can be sent in a direction deviated from the center of the combustion chamber, and a strong swirl can be formed within the combustion chamber. In addition, by placing the center axis of the main intake passage off to the side of the intake port to which the auxiliary intake passage is connected, the flow of intake air from the main intake passage is assisted in the load range where the on-off valve begins to open. It shows a tendency to be biased toward the intake port connected to the intake passage, and in this load range, the intake flow from the auxiliary intake passage is also maintained to some extent, so the intake flow through the intake port connected to the auxiliary intake passage is The intake air flow will be larger than that from other intake ports, and a certain amount of swirl will be formed in the combustion chamber.

The intake system described in the above-mentioned Japanese Patent Application Laid-open No. 55-25511 has a configuration that generates swirl within the combustion chamber, and strong turbulence occurs along the peripheral wall of the combustion chamber and is less likely to occur near the center. Based on the recognition that good combustion cannot be maintained in an engine with the spark plug placed near the center, small-diameter auxiliary intake passages are opened in each of the two intake ports, and from these auxiliary intake passages a narrow high-speed By blowing the flow into the combustion chamber symmetrically, the aim is to create intense turbulence near the center of the combustion chamber. Unlike such known intake devices, the present invention forms a strong swirl inside the combustion chamber by blowing a relatively wide high-speed intake air flow in a direction biased to the axis of the combustion chamber. It is. In particular, in the present invention, by arranging the central axis of the main intake passage so as to be offset as described above, swirl can be generated in the combustion chamber even in a load range where the on-off valve begins to open.

(Effects of the Invention) In the present invention, as described above, the auxiliary intake passage for sending intake air to the combustion chamber during low load operation is
Since it is connected to one of the multiple intake ports,
Even during low-load operation with a small amount of intake air, it is possible to supply a relatively high-speed intake air flow in a direction deviated from the center of the combustion chamber, and a strong swirl can be formed within the combustion chamber. In addition, because the center axis of the main intake passage is biased toward the intake port to which the auxiliary intake passage is connected, a certain degree of swirl is generated within the combustion chamber even in the load range where the on-off valve begins to open. This makes it possible to obtain stable combustion conditions over a relatively wide range of low loads.

(Description of Examples) Referring to FIGS. 1 and 2, engine E
is a cylinder block 1 having a cylinder bore 1a.
The engine has a cylinder head 2 attached to the upper part of the cylinder block 1, and a piston 3 is disposed within the cylinder bore 1a so as to be able to reciprocate in the axial direction, thereby forming a combustion chamber 4 within the cylinder bore 1a. The cylinder head 2 has first and second intake ports 5, 6.
and an exhaust port 7 are formed, an intake valve 8 is formed in the first and second intake ports 5 and 6, and an exhaust port 7 is formed in the first and second intake ports 5 and 6, respectively.
An exhaust valve 9 is attached to the. Referring to FIG. 1, the first and second intake ports 5 and 6 have approximately the same diameter;
Cylinder center line l in the width direction of cylinder block 1
The exhaust port 7 is arranged at a position facing the second intake port 6 across the longitudinal centerline m of the cylinder block 1.

The intake system has a main intake passage 11 extending from an air cleaner 10, and a throttle valve 12 is disposed within the main intake passage 11. As shown in FIG. 1, the main intake passage 11 extends into the cylinder head 2.
In the vicinity of the intake ports 5 and 6, the first and second intake ports 5 and 6 are separated by a partition wall 14 formed substantially along the cylinder center line l in the width direction of the cylinder block, and communicate with the first and second intake ports 5 and 6, respectively. It constitutes second branch passages 15 and 16. Exhaust port 7
is connected to the exhaust passage 17 to constitute an exhaust system. This exhaust system may have a normal configuration. In the main intake passage 11, a fuel injection valve 23 is provided on the upstream side of the partition wall 14.
is arranged, and a predetermined amount of fuel is supplied to the combustion chamber 4 based on a signal corresponding to the engine operating conditions.

An on-off valve 18 is provided within the main intake passage 11 . This on-off valve 18 is, for example, a throttle valve 12.
The throttle valve 12 is configured to be closed in a low-load operation range where the opening degree of the throttle valve is relatively small, and to be opened when the throttle valve 12 is opened beyond a predetermined opening degree. An opening 19 is formed at the bottom of the main intake passage 11 slightly upstream of the on-off valve 18.
An auxiliary intake passage 20 is formed to extend below the main intake passage 11 from the main intake passage 11 . Auxiliary intake passage 20
is from the bottom of the main intake passage 11 to the first branch passage 15.
The opening 21 passes through the lower side of the opening 21 and is connected to the first intake port 5 .

A valve drive mechanism 25 for opening and closing the intake valve 8 and the exhaust valve 9 is arranged above the cylinder head 2. This valve drive mechanism 25 includes a camshaft 2 driven by an engine crankshaft (not shown).
6, and a cam 27 formed on the camshaft 26 and corresponding to each of the intake valve 8 and the exhaust valve 9. The cam 27 engages one end of a swinging arm 28 arranged to correspond to each of the intake valve 8 and the exhaust valve 9, and the other end of the swinging arm engages with a tappet 29 provided on the valve shaft of each valve. is engaged in.

As shown in FIGS. 1 and 3, the main intake passage 11 has a center axis 11a that is parallel to the cylinder block width direction, that is, the center axis 11a, and passes through the center of the cylinder bore.
It is arranged so as to be biased toward the intake port 5 side.
That is, the main intake passage 11 and the branch intake passage 15,
As shown in FIG. 3, the overlap with the branch intake passage 16 is greater than the overlap with the branch intake passage 15.

As shown in Fig. 2, the intake port 5 opens into the combustion chamber 4 at an angle close to the axial direction of the cylinder bore 1a in order to ensure a high filling amount during high-load operation. However, the second intake port 6 also has a similar shape. On the other hand, the auxiliary intake passage 20 includes the main intake passage 11 and the first branch passage 15.
Since it opens into the first intake port 5 from the lower side, it faces the combustion chamber 4 at a relatively shallow angle.

Furthermore, the first intake port 5 is connected to the cylinder bore 1
Since the combustion chamber 4 is arranged at a shallow angle from the auxiliary intake passage 20,
The intake air jetted out generates a strong swirl in the horizontal plane within the combustion chamber 4. In order to easily generate this swirl, the shape of the auxiliary intake passage 20 must be adjusted so that it is close to the opening 21 of the cylinder bore 1a.
It is preferable that the groove be formed so as to be oriented substantially tangentially to the peripheral wall of the tube.

In a low load region where the on-off valve 18 is closed, all intake air passing through the main intake passage 11 is guided from the opening 18 to the auxiliary intake passage 20, and is sent from the opening 21 through the first intake port 5 into the combustion chamber. Since the auxiliary intake passage 20 has a smaller cross-sectional area than each of the branch passages 15 and 16, a relatively high flow rate can be maintained even during low-load operation with a small intake air amount. Furthermore, since the auxiliary intake passage 20 is oriented in the circumferential direction of the cylinder bore 1a at a relatively shallow angle as described above, the intake air flow injected from the auxiliary intake passage 20 into the combustion chamber 4 is directed within the combustion chamber 4. to form a strong swirl. In a load range where the on-off valve 18 begins to open, the intake air flow in the main intake passage 11 begins to flow into the branch intake passages 15 and 16, and the flow rate of intake air passing through the auxiliary intake passage 20 decreases. However, as described above, the main intake passage 11 is arranged with its central axis 11a biased toward the first intake port 5, and the main intake passage 11 and the first
Since the overlap in the axial direction with the branch intake passage 15 is larger than the overlap with the second branch intake passage 16, the main intake passage 11 passes through the first branch intake passage 15 and the first
The intake air flow that reaches the intake port 5 is larger than the intake air flow that passes through the second branch intake passage 16 and reaches the second intake port 6. From this first branch intake passage 15 to the first
The intake air flow reaching the intake port 5 flows through the auxiliary intake passage 2.
0 and reaches the first intake port 5 to form an intake swirl in the combustion chamber 4.

In this example, the cylinder head 2 has a portion where the intake ports 5, 6 and the exhaust port 7 are not formed, that is, a portion facing the first intake port 5 across the longitudinal centerline m of the cylinder block 1. An ignition plug 22 is arranged at. This portion corresponds to the swirl trajectory caused by the intake air flow from the first intake port 5, and this arrangement ensures that the air around the spark plug 22 is scavenged and stable ignition and combustion can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of an engine intake system according to an embodiment of the present invention, FIG. 2 is a vertical sectional view of an engine embodying the present invention, and FIG. 3 is a schematic plan view of an engine intake system according to an embodiment of the present invention. FIG. 3 is a diagram showing an axial overlap between an intake passage and a branch intake passage. 1...Cylinder block, 1a...Cylinder bore,
2... Cylinder head, 3... Piston, 4... Combustion chamber, 5, 6... Intake port, 7... Exhaust port, 11
...Main intake passage, 15, 16...Branch intake passage, 18
...Opening/closing valve, 19...Opening, 20...Auxiliary intake passage.

Claims (1)

[Claims] 1. Two intake ports opening into the combustion chamber, a branch intake passage connected to each of the two intake ports, a main intake passage connected to the upstream side of the branch intake passage, and a main intake passage within the main intake passage. an on-off valve that is provided and opens during high-load operation; and an auxiliary intake port that branches from the main intake passage on an upstream side of the on-off valve and is connected to one of the intake ports so as to be oriented substantially circumferentially with respect to the combustion chamber. an intake passage, and the central axis of the main intake passage downstream of the on-off valve is parallel to the central axis and is on the side of the intake port connected to the auxiliary intake passage with respect to a line passing through the center of the cylinder bore. An engine intake device characterized by being arranged so as to be biased toward the center.