JPH0247571B2 - - 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,
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; an auxiliary intake passage that branches from the main intake passage through an opening provided in 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 face approximately circumferentially with respect to the combustion chamber; and the above 2
The two intake ports are arranged on both sides of the center line of the main intake passage, and the opening where the auxiliary intake passage branches from the main intake passage has its center located at the center of the one intake port with respect to the center of the main intake passage. It is characterized by being biased toward the opposite side. According to this configuration of the present invention, in a low-load operating region where the on-off valve is closed, intake air is supplied only from the auxiliary intake passage. Since the auxiliary intake passage passes under the branch intake passage and opens into the intake port, the intake air flow is directed toward the combustion chamber at a relatively shallow angle, that is, at an angle close to perpendicular to the axis of the combustion chamber. The intake air flow is sent into the combustion chamber from only one intake port at a position offset laterally with respect to the axis of the combustion chamber, forming a strong swirl around the axis of 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 solid walls of the combustion chamber and is less likely to occur near the center. Therefore, based on the recognition that good combustion cannot be maintained in an engine with the spark plug placed near the center, a small diameter auxiliary intake passage is opened in each of the two intake ports, and a thin By blowing a high-speed flow symmetrically into the combustion chamber, the aim is to create intense turbulence near the center of the combustion chamber. Unlike such known intake devices, the present invention generates a strong swirl inside the combustion chamber by blowing a relatively wide high-speed reverse airflow in a direction biased to the axis of the combustion chamber. It is. In particular, in the present invention, the opening of the portion where the auxiliary intake port branches from the main intake passage is arranged with its center offset from the center of the main intake passage, and the direction of the deviation is in the direction of the opening where the auxiliary intake passage is connected. This is opposite to the direction of deflection of the intake port. Therefore, even if the outlet of the intake air from the auxiliary intake passage is formed to face the circumferential direction of the combustion chamber to increase the tendency for swirl to occur, there is no need to make an extreme bend in the auxiliary intake passage. It becomes possible to form an auxiliary intake passage with low intake resistance.

(Effects of the Invention) According to the present invention, since the auxiliary intake passage used in the low-load operation region branches from the bottom of the main intake passage, the auxiliary intake passage is located below the main intake passage and the auxiliary intake passage. Since this auxiliary intake passage is connected to one of the intake ports, it is possible to create a strong swirl inside the combustion chamber even with a relatively small intake air flow during low-load operation. can be formed and ensure combustion stability. Furthermore, the center of the opening of the part where the auxiliary intake passage branches off from the main intake passage is located on the opposite side of the center of the main intake passage from the intake port to which the auxiliary intake passage is connected. , even if the direction of the connection between the auxiliary intake passage and the intake port is oriented in the circumferential direction of the combustion chamber so that swirl is more likely to be formed,
There is no need to make extreme bends in the auxiliary intake passage,
It becomes possible to form an ideal auxiliary intake passage with low intake resistance. In addition, since the auxiliary intake passage branches off from the main intake passage at an uneven position as described above, the flow rate of the intake air passing through the multiple intake ports becomes uneven in the load region where the on-off valve begins to open.
As a result, it can be expected that a certain amount of swirl will be generated.

(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 combustion injection valve 23 is provided on the upstream side of the partition wall 14.
is arranged, and metered 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 1
2, the throttle valve 12 is closed in a low-load operating range where the opening degree of the throttle valve is relatively small, and is 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 . 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. No, but
The second intake port 6 also has a similar shape. On the other hand, since the auxiliary intake passage 20 opens to the first intake port 5 from below the main intake passage 11 and the first branch passage 15, it is oriented at a relatively shallow angle with respect to the combustion chamber 4. . Furthermore, since the first intake port 5 is arranged to be biased to one side with respect to the center line l of the cylinder bore 1a, the intake air jetted into the combustion chamber 4 at a shallow angle from the auxiliary intake passage 20 is directed within the combustion chamber 4. Generates a strong swirl in the horizontal plane.

In order to facilitate the generation of this swirl, it is desirable that the shape of the auxiliary intake passage 20 is formed so as to be oriented substantially tangentially to the peripheral wall of the cylinder bore 1a near the opening 21. In order to obtain such a shape, it is necessary to curve the auxiliary intake passage 20. However, as shown in Figure 1,
The auxiliary intake passage 20 has an opening 19 branching from the main intake passage 11 with its center pointing toward the main intake passage 11.
Since it is arranged on the side opposite to the first intake port 5, that is, on the side of the second intake port 6, with respect to the center of the , it is no longer necessary to give the auxiliary intake passage 20 an extreme bend, and as shown in FIG. 1, it is possible to form a relatively gentle flow path with little resistance.

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. As shown in FIG. 1, in this example,
An ignition plug 22 is attached to a portion of the cylinder head 2 where intake and exhaust ports are not formed, that is, a portion facing the first intake port 5 across the longitudinal centerline m of the cylinder block 1. Therefore, since the ignition plug 22 is located on the swirl locus formed by the intake air flow from the auxiliary intake passage 20, fresh air-fuel mixture is reliably supplied to the vicinity of the ignition plug 22, resulting in a good air-fuel mixture. Combustion occurs with ignitability.

When the throttle valve 12 is opened beyond a predetermined value as the engine load increases, the on-off valve 18 also begins to open. In an operating range where the opening degree of the on-off valve 18 is relatively small, a portion of the intake air is still supplied through the auxiliary intake passage 20. In this state, the auxiliary intake passage 20 opens only to the first intake port 5, and the opening 19 where the auxiliary intake passage 20 branches from the main intake passage 11 is biased toward the second intake port 6. Because of this position, the amount of intake air supplied to the combustion chamber 4 via the first intake port 5 is greater than the amount passing through the second intake port 6, and as a result, a certain amount of swirl is generated even in areas where the load is increased. can be formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an engine intake system according to an embodiment of the present invention, and FIG. 2 is a vertical sectional view of an engine embodying the present invention. 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 opening provided in the main intake passage upstream of the on-off valve so that the main intake passage branches off from the main intake passage and faces approximately circumferentially with respect to the combustion chamber. an auxiliary intake passage connected to one of the intake ports, the two intake ports are arranged on both sides of the center line of the main intake passage, and the opening where the auxiliary intake passage branches from the main intake passage is 1. An intake passage for an engine, wherein the center of the main intake passage is offset to a side opposite to the side where the one intake port is located with respect to the center of the main intake passage.