JP7826083B2 - Cylinder head - Google Patents

Description

The present invention relates to cylinder heads for engines (internal combustion engines), and is particularly suited to cylinder heads that support lean burn and high EGR.

Gasoline engines are increasingly using lean burn and high EGR to improve fuel economy and reduce NOx emissions, but lean burn can easily reduce fuel ignition. Therefore, there is a demand for technology that can improve fuel ignition while increasing the air-fuel ratio, for example to 30 or more.

One method for ensuring combustion while increasing the fuel dilution rate is stratified charge combustion, and one method proposed in combination with stratified charge combustion is to provide a pre-chamber in the cylinder head, in which the flame generated in the pre-chamber is propagated to the mixture in the main combustion chamber.

As an example, Patent Document 1 discloses a system in which a downwardly-opening auxiliary chamber (central compartment) is formed by providing a downwardly-protruding annular wall in the center of a pent roof-shaped recess formed in a cylinder head, with an auxiliary intake port opening into the auxiliary chamber concentrically with its axis, and an ignition plug facing the side of the auxiliary chamber.

Japanese Patent Application Publication No. 07-229423

Generally, the pre-chamber is often bottomed, with a jet flame ejected from a hole in the bottom, but constructing the pre-chamber as an open type, as in Patent Document 1, has the advantages of high ignition response to the main air-fuel mixture and reliable scavenging of the pre-chamber.

However, in Patent Document 1, a protruding annular wall is installed inside the recess to form a pre-chamber, which can hinder the smooth flow of the main air-fuel mixture ejected from the main intake port, making it difficult to generate a tumble flow. There are also concerns that the annular wall may become a heat point during the combustion process, making it more likely to induce knocking. Furthermore, there is a possibility that the annular wall may melt due to heat or become damaged by explosive force, raising concerns that a serious situation such as a sudden engine shutdown could occur.

Furthermore, in Patent Document 1, the outlet of the auxiliary intake port opens concentrically with the pre-chamber, which means the auxiliary air-fuel mixture passes straight through the pre-chamber, resulting in insufficient flame generation within the pre-chamber, and as a result, there is concern that stratified charge combustion may be difficult to achieve.

The present invention was developed to improve this current situation.

The present invention includes various configurations, typical examples of which are specified in each claim. The invention of claim 1 is a generic concept,
"Having a combustion chamber recess that opens toward the cylinder bore of the cylinder block,
a main intake port that is opened and closed by a main intake valve to supply intake air, and an exhaust port that is opened and closed by an exhaust valve to discharge exhaust gas, are formed in the combustion chamber recess so as to be located on opposite sides as viewed from the crankshaft direction,
a pocket-shaped sub-chamber recessed upward from a top surface of the combustion chamber recess and having no injection hole is formed in the combustion chamber recess ,
a cylinder head in which an outlet of an auxiliary intake port opened and closed by a sliding auxiliary intake valve and an ignition plug are disposed on an upper bottom surface of the auxiliary intake chamber so as to be located on opposite sides of an axis of the auxiliary intake chamber,
The opening direction of the auxiliary intake port (the sliding direction of the auxiliary intake valve) is inclined upward and away from the axis of the sub-chamber .
The structure is as follows.

The invention of claim 2 is an embodiment of claim 1,
" The auxiliary chamber is formed in the cylinder head itself, and the spark plug is inclined upward and away from the axis of the auxiliary chamber ."
The structure is as follows.

The invention of claim 3 is an embodiment of claim 1 or 2,
"The auxiliary intake port is curved when viewed from the axial direction of the cylinder bore."
The structure is as follows.

The invention of claim 4 is any one of claims 1 to 3,
"Fuel injectors are provided in each of the main intake port and the auxiliary intake port, and the air-fuel ratio of the mixture in the auxiliary intake port is set to be richer than the air-fuel ratio of the mixture in the main intake port."
The structure is as follows.

In the present invention, the pre-chamber is formed as a pocket-like shape without a bottom plate in the combustion chamber recess provided in the cylinder head, so it does not obstruct the intake port flow ejected from the main intake port. Therefore, it does not adversely affect the generation of tumble flow or swirl flow, and does not hinder the stratification of the air-fuel mixture. Furthermore, because the pre-chamber does not become a heat point, it does not induce knocking, and there is no risk of melting due to heat or damage due to explosive force. Therefore, it is highly safe.

Furthermore, because the auxiliary intake port opens off-center to the inner periphery of the pre-chamber, it is possible to generate a swirl flow of the auxiliary mixture inside the pre-chamber, minimizing leakage of the auxiliary mixture and generating a strong flame in the pre-chamber. As a result, the stratified mixture generated in the main combustion chamber can be reliably ignited, ensuring stratified combustion. Therefore, stable operation can be achieved even with a lean mixture with an overall air-fuel ratio of 30 or more, which greatly contributes to lean burn and high EGR.

Furthermore, in the present invention, the auxiliary intake port and the spark plug are located on opposite sides, so they can be positioned without interfering with each other. Furthermore, the flow of auxiliary intake air is not obstructed by the spark plug electrode, which has the advantage of ensuring the generation of a swirl flow of auxiliary intake air in the pre-chamber.
Furthermore, in the present invention, the opening direction of the auxiliary intake port is tilted relative to the axis of the pre-chamber, and the guide function of the head of the auxiliary intake valve is utilized to direct the intake air toward the upper bottom of the pre-chamber, which is advantageous in that it further promotes the swirling of the auxiliary mixture inside the pre-chamber.

In the invention of claim 3, the auxiliary intake port is curved in plan view, which significantly improves the effect of converting the auxiliary intake air that is ejected in a straight line from the outlet of the auxiliary intake port into a swirling flow that flows along the inner surface of the auxiliary chamber (i.e., the effect of converting it into a swirl flow). As a result, this promotes the generation of a swirling initial flame, further improving the ignition ability of the main mixture. This therefore significantly contributes to the realization of stable stratified charge combustion.

By adopting the configuration of claim 4, the generation of an initial flame in the pre-chamber can be ensured, further contributing to lean burn and high EGR. Direct injection is one method of achieving stratified charge combustion, but direct injection injectors are expensive. In contrast, port injection injectors such as those described in claim 4 are less expensive than direct injection injectors, which also contributes to cost reduction.

1A is a diagram showing an embodiment, in which (A) is a partially cutaway bottom view of a cylinder head, and (B) is a cross-sectional view taken along the line BB of (A). FIG. 2 is a cross-sectional view taken along line II-II of FIG.

Next, an embodiment of the present invention will be described with reference to the drawings. This embodiment is applied to a multi-cylinder engine for an automobile. Below, the terms "front-rear" and "left-right" are used to specify directions; the front-rear direction is the crank axis direction, and the left-right direction is the direction perpendicular to the crank axis and the cylinder bore axis. The up-down direction is the axial direction of the cylinder bore.

(1) Description of Structure As shown in Figures 1(B) and 2, the engine has a cylinder block 2 in which a cylinder bore 1 is formed, and a cylinder head 4 fixed to the upper surface of the cylinder block 2 via a gasket 3, with a piston 5 slidably inserted into the cylinder bore 1. A connecting rod is connected to the piston 5 by a piston pin (neither is shown), and the connecting rod is connected to a crank pin (not shown).

The cylinder head 4 is formed with a downward recess (combustion chamber recess) 6 that opens toward the cylinder bore 1. The downward recess 6 is formed in a pent roof shape with a tapered surface, and is elongated in the front-to-rear direction when viewed from the bottom.

As shown in Figure 1(A), the cylinder head 4 is formed with a pair of main intake ports 7 and exhaust ports 8, one on the front and one on the back, that open toward the downward recess 6, and is also fitted with a main intake valve 9 that opens and closes the main intake port 7 and an exhaust valve 10 that opens and closes the exhaust port 8, which are slidably mounted thereon.

Approximately in the center of the downward recess 6 in the cylinder head 4, a pocket-shaped auxiliary chamber 11 is formed by hollowing out the downward recess 6 upward. The auxiliary chamber 11 is basically circular and is formed in the cylinder head 4 itself in an open style without any injection holes , with its depth being slightly smaller than its diameter. The auxiliary chamber 11 is formed with an auxiliary intake hollow 12 and an ignition plug hollow 13 that bulge symmetrically in the front-to-rear direction. The hollowed portions 12, 13 can also be called protrusions (or extensions) of the auxiliary chamber 11.

The outlet 14a of the auxiliary intake port 14 opens on the upper bottom surface of the auxiliary intake recess 12, and an auxiliary intake valve 15 that opens and closes the outlet 14a of the auxiliary intake port 14 is slidably attached to the cylinder head 4 via a bushing 16. The auxiliary intake valve 15 is biased in the closing direction by a spring (not shown), and is opened and closed by the intake camshaft.

Furthermore, the auxiliary intake valve 15 is inclined upward and away from the axis O of the cylinder bore in a cross-sectional view from the left and right (as shown in Figure 2). Therefore, the auxiliary intake recess 12 is also inclined with respect to the axis O of the sub-chamber 11. Therefore, the opening direction of the outlet 14a of the auxiliary intake port 14 is also inclined upward and away from the axis O of the cylinder bore 1 and the sub-chamber 11. Note that the auxiliary intake valve 15 can also be inclined with respect to the axis O of the cylinder bore 1 in a cross-sectional view from the front and rear.

As shown in Figure 1(A), the auxiliary intake port 14 has a main body portion 14b that is long in the left-right direction and is located between the pair of main intake ports 7, and an inclined portion 14c that bends in the front-rear direction from the tip of the main body portion 14b, with an outlet 14a provided at the tip of the inclined portion 14c. The inclined portion 14c also tapers toward the end. Therefore, the auxiliary intake port 14 has a herculean shape in plan view.

In the auxiliary intake port 14, the cross-sectional area of the main body 14b is the largest, but the cross-sectional area of the main body 14b is smaller than the cross-sectional area of one of the main intake ports 7. Therefore, the amount of intake air flowing through the auxiliary intake port 14 is much less than the amount of intake air flowing through the pair of main intake ports 7 (therefore, the majority of the intake air (air-fuel mixture) is supplied from the main intake port 7).

As shown in Figure 1(B), a main injector 17 is disposed in each of the pair of main intake ports 7, and an auxiliary injector 18 is disposed in the main body 14b of the auxiliary intake port 14. Needless to say, air is supplied to the main intake port 7 and auxiliary intake port 14 from a branch pipe in the surge tank.

As shown in Figure 2, the spark plug recess 13 is connected to a spark plug mounting hole 19, and a spark plug 20 is screwed into the spark plug mounting hole 19. The spark plug 20 has a center electrode 21 and a ground electrode 22, and the electrodes 21 and 22 are exposed downward from the upper bottom surface of the auxiliary chamber 11.

In this embodiment, the axis of the spark plug 20 (and the spark plug recess 13) is inclined relative to the axis O of the auxiliary intake chamber 11 (and the axis O of the cylinder bore 1) so that it moves away from the axis O in the front-to-rear direction as it goes up. Therefore, the auxiliary intake valve 15 and the spark plug 20 are inclined symmetrically on opposite front-to-rear sides across the axis O of the auxiliary intake chamber 11. Note that the reference numeral 23 in Figure 2 denotes a cooling water jacket.

(2) Summary This embodiment is configured as described above. During the intake stroke, intake air is sent from the main intake port 7 and the auxiliary intake port 14, and fuel is injected into each intake air. Then, during the combustion stroke, the air-fuel mixture filling the auxiliary combustion chamber 11 is ignited by the spark plug 20, and the initial flame generated in the auxiliary combustion chamber 11 propagates to the air-fuel mixture in the main combustion chamber, causing the entire mixture to combust.

In this case, the outlet 14a of the auxiliary intake port 14 is positioned offset toward one end of the auxiliary combustion chamber 11 in the front-to-rear direction, and as a result of the straightness of the intake air, a swirl flow of the auxiliary intake air (auxiliary air-fuel mixture) is generated inside the auxiliary combustion chamber 11, as shown by the arrow in Figure 1(A). As a result, the initial flame generated in the auxiliary combustion chamber 11 becomes a swirling flow and is ejected into the main combustion chamber, thereby enabling the flame to propagate effectively through the air-fuel mixture in the main combustion chamber.

Furthermore, by creating a swirling flow of the mixture in the auxiliary combustion chamber 11, the relatively rich mixture is prevented from diffusing into the main combustion chamber (the downward recess 6 and the cylinder bore 1) (the relatively rich mixture can be retained inside the auxiliary combustion chamber 11), making it possible to make the fuel lean overall while effectively utilizing the fuel and ensuring the generation of an initial flame.

In the main combustion chamber, the tumble flow is used to create a stratified air-fuel mixture, which is then ignited to achieve stratified combustion, ensuring reliable combustion even when the fuel is lean overall. In this embodiment, a strong initial flame can be propagated to the air-fuel mixture in the main combustion chamber, achieving stable stratified combustion. This allows for stable operation even with a lean air-fuel ratio of 30 or more, or in a high EGR state. As a result, thermal efficiency and fuel economy can be improved, while also contributing significantly to the reduction of NOx emissions.

In particular, bending the auxiliary intake port 14 in plan view, as in this embodiment, improves the effect of generating a swirling flow of the intake air (air-fuel mixture) ejected from the auxiliary intake port 14 around the axis of the auxiliary intake chamber 11, which is advantageous for generating a strong initial flame with excellent propagation properties.

Furthermore, as shown in Figure 2, the guide action of the head of the auxiliary intake valve 15 changes the direction of the mixture injected from the auxiliary intake port 14 in a direction intersecting the axis of the auxiliary intake valve 15, ensuring that the auxiliary intake (auxiliary mixture) becomes a swirling flow inside the auxiliary intake chamber 11. Therefore, to enhance swirling in the auxiliary intake chamber 11, it is preferable to maximize the ratio of the head outer diameter to the shaft diameter of the auxiliary intake valve 15. Furthermore, to enhance the guide function of the head, it is preferable to minimize the lift amount of the auxiliary intake valve 15.

As in this embodiment, tilting the auxiliary intake valve 15 relative to the axis O of the auxiliary intake chamber 11 makes it possible to use the guide function of the head of the auxiliary intake valve 15 to direct the intake air toward the upper bottom of the auxiliary intake chamber 11, which is advantageous in further promoting the swirling of the auxiliary air-fuel mixture inside the auxiliary intake chamber 11.

Regarding the opening and closing timing of the auxiliary intake valve 15, since the purpose of the auxiliary intake port 14 is to generate a strong initial flame, it is preferable to make the opening timing of the auxiliary intake valve 15 slower than that of the main intake valve 9, and to align the closing timing with that of the main intake valve 9.

Alternatively, by keeping the opening and closing timing the same as the main intake valve 9 and delaying the fuel injection timing by the auxiliary injector 18, it is possible to generate a strong initial flame while suppressing fuel diffusion. Furthermore, setting the mixture inside the auxiliary combustion chamber 11 to be richer than the mixture in the main combustion chamber is also preferable, as it ensures the generation of an initial flame in the auxiliary combustion chamber 11.

By appropriately combining the opening and closing timing of the auxiliary intake valve 15 and the timing and amount of fuel injected by the auxiliary injector 18, it is possible to generate a strong initial flame in the auxiliary combustion chamber 11.

The illustrated embodiment has been described above, but the present invention can be embodied in a variety of other ways. For example, in the illustrated embodiment, the auxiliary intake valve and spark plug are arranged symmetrically from front to back, but they may also be arranged symmetrically from left to right. Alternatively, they may be arranged with a 90° circumferential offset. The auxiliary chamber may also be formed into an elliptical shape.

The present invention can be embodied in a cylinder head, and therefore has industrial applicability.

1 Cylinder bore 2 Cylinder block 4 Cylinder head 5 Piston 6 Downward recess (cylinder head combustion chamber recess)
7 Main intake port 8 Exhaust port 9 Main intake valve 10 Exhaust valve 11 Sub-chamber 12 Auxiliary intake recess 13 Spark plug recess 14 Auxiliary intake port 17 Main injector 18 Auxiliary injector 19 Spark plug mounting hole 20 Spark plug

Claims (4)

a combustion chamber recess that opens toward the cylinder bore of the cylinder block;
a main intake port that is opened and closed by a main intake valve to supply intake air, and an exhaust port that is opened and closed by an exhaust valve to discharge exhaust gas, are formed in the combustion chamber recess so as to be located on opposite sides as viewed from the crankshaft direction,
a pocket-shaped sub-chamber recessed upward from a top surface of the combustion chamber recess and having no injection hole is formed in the combustion chamber recess ,
a cylinder head in which an outlet of an auxiliary intake port opened and closed by a sliding auxiliary intake valve and an ignition plug are disposed on an upper bottom surface of the auxiliary intake chamber so as to be located on opposite sides of an axis of the auxiliary intake chamber,
The opening direction of the auxiliary intake port is inclined upward and away from the axis of the sub-chamber.
Cylinder head. The sub-chamber is formed in the cylinder head itself, and the spark plug is inclined upward so as to move away from the axis of the sub-chamber.
2. The cylinder head according to claim 1. The auxiliary intake port is curved when viewed from the axial direction of the cylinder bore.
3. A cylinder head according to claim 1 or 2. a fuel injector is provided in each of the main intake port and the auxiliary intake port, and the air-fuel ratio of the mixture in the auxiliary intake port is set to be richer than the air-fuel ratio of the mixture in the main intake port;
A cylinder head according to any one of claims 1 to 3.