JP7635744B2 - Pre-chamber engine - Google Patents

Description

This disclosure relates to a pre-chamber engine.

One example of an auxiliary combustion chamber engine is known from Patent Document 1. Patent Document 1 shows a technology that diffuses gases such as flames from the auxiliary combustion chamber (auxiliary chamber) to the main combustion chamber (main chamber) along a collision guide surface formed on the top surface of the piston, shortening the combustion speed in the main combustion chamber and improving thermal efficiency.

The shape of the collision guide surface shown in this Patent Document 1 is composed of an inclined surface and a stepped arc-shaped curved surface, and further, an upwardly curved surface is formed on the stepped arc-shaped curved surface so as to form a vertical swirling flow. It is shown that the gas ejected into the main combustion chamber strengthens the penetration of the ejection energy by the vertical swirling flow, and rides on the intake swirl to promote mixing in the main combustion chamber, increasing the combustion speed and improving thermal efficiency.

Japanese Patent Application Publication No. 6-307244

In a pre-chamber engine, which has a pre-chamber separated from the main chamber by a partition, a passageway formed in the partition that connects the main and pre-chambers, and a system (jet ignition system) that ignites the mixture in the pre-chamber by igniting the mixture in the main chamber so that the flame formed in the pre-chamber is ejected into the main chamber through the connecting passageway, a problem arises in that the flame (jet flame) that is formed in the pre-chamber and ejected into the main chamber through the connecting passageway collides with the cylinder inner wall surface and cylinder liner, which are at a lower temperature than the piston, increasing heat loss.

In addition, because the jet flame collides with the inner wall surface of the cylinder and the top surface of the piston, etc., and spreads, there is an issue that in the center of the main chamber (near the auxiliary chamber) where the flame does not collide with the wall surfaces, flame diffusion is difficult between the jet flames ejected from adjacent communication passages in the auxiliary chamber, resulting in slow combustion.

Meanwhile, the aforementioned Patent Document 1 shows that gas such as flame from the pre-chamber to the main chamber is diffused along a collision guide surface formed on the top surface of the piston, but the shape of this collision guide surface is inclined so that its height from the piston top surface is low in the central part of the main chamber (near the pre-chamber) and high in the peripheral part of the main chamber. For this reason, the flame from the pre-chamber is more likely to accumulate in the peripheral part than in the central part of the main chamber, making it difficult for the flame to diffuse within the main chamber.

The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a pre-chamber engine equipped with a jet ignition system in which the flame ejected from the pre-chamber is collided with a guide portion provided on the top surface of the piston, thereby diffusing the flame evenly within the main chamber and improving the combustion of the air-fuel mixture within the main chamber.

(1) In order to achieve the above object, at least one embodiment of the present disclosure provides an auxiliary chamber engine including a main chamber, an auxiliary chamber separated from the main chamber by a partition provided in a cylinder head, and a plurality of communication passages provided in the partition and communicating the main chamber with the auxiliary chamber, wherein a flame formed in the auxiliary chamber by ignition of a mixture in the auxiliary chamber is ejected into the main chamber via the plurality of communication passages to ignite the mixture in the main chamber, the engine comprising: a piston top surface including a plurality of convex guide parts having collision sides with which the flames ejected from each of the plurality of communication passages collide , the plurality of guide parts extending at an angle from the auxiliary chamber side toward an inner circumferential wall side of the cylinder in a plan view of the piston, the height of the plurality of guide parts decreasing with increasing distance from the auxiliary chamber, and the collision side of each of the plurality of guide parts inclining to one side in the circumferential direction with increasing distance from the auxiliary chamber in a plan view of the piston .

According to this configuration (1), the convex guide portion with which the flame collides extends at an angle from the auxiliary chamber side toward the cylinder inner wall side, so that the flame ejected from the auxiliary chamber does not collide directly with the cylinder inner wall or cylinder liner, but first collides with the guide portion, and is then guided to rotate circumferentially within the main chamber. This prevents the flame from directly colliding with the cylinder liner or cylinder inner wall, which are at a lower temperature than the piston, thereby preventing the flame from increasing its heat loss.

Furthermore, because the height of the guide section decreases as it moves away from the auxiliary chamber, i.e., as it approaches the cylinder inner wall, the flame tends to diffuse circumferentially near the cylinder inner wall without remaining between adjacent guide sections. This promotes combustion near the cylinder inner wall.

Furthermore, the flame ejected from the auxiliary chamber collides with the convex guide section and spreads near the collision section, promoting the spread of the flame in the center of the main chamber, which is closer to the auxiliary chamber. This promotes combustion in the center of the main chamber, which is closer to the auxiliary chamber.

As described above, the flame ejected from the auxiliary chamber is guided by a guide portion provided on the top surface of the piston, which prevents the heat loss of the flame from increasing and disperses the flame evenly within the main chamber, improving the combustion of the air-fuel mixture in the main chamber.

(2) In some embodiments, in a plan view of the piston, an angle between an extension line of the central axis of each of the plurality of communicating passages and a tangent line indicating the inclination direction of each of the plurality of guide portions at an intersection of the extension line and each of the plurality of guide portions, the tangent line facing the cylinder inner wall side, is an obtuse angle.

With this configuration (2), the flame that emerges from the auxiliary chamber and collides with the guide portion is guided in the main chamber toward the cylinder inner wall and swirls circumferentially within the main chamber.

(3) In some embodiments, in a plan view of the piston, the plurality of guide portions are curved toward one side in a circumferential direction as they become farther away from the sub chamber.

According to this configuration (3), since the guide portion is curved in the circumferential direction, the flame that collides with the guide portion is more strongly swirled in the circumferential direction within the main chamber.

(4) In some embodiments, in a plan view of the piston, the tip ends of the respective guide portions are positioned such that a straight line connecting a tip end of each of the respective guide portions and a center of the auxiliary chamber intersects with each of the adjacent guide portions.

According to this configuration (4), the tip of the guide part is positioned so that the straight line connecting the tip of the guide part and the center of the auxiliary chamber intersects with the adjacent guide part, so that a passage is formed between the adjacent guide parts, and the flame that hits the guide part is easily guided to the cylinder inner wall side through this passage between the guide parts.

(5) In some embodiments, in a plan view of the piston, the plurality of guide portions become thinner toward the tip portion on the cylinder inner wall side.

According to this configuration (5), the guide portion becomes thinner toward the tip, which makes it easier for the flame to diffuse in the circumferential direction near the cylinder inner wall without stagnating between adjacent guide portions. This promotes combustion near the cylinder inner wall. In addition, when combined with the guide portion having a height that decreases toward the tip, the flame diffusion near the cylinder inner wall is further promoted.

(6) In some embodiments, the piston may further include a sub-guide portion between adjacent guide portions in a plan view of the piston, the sub-guide portion extending at an angle from the auxiliary chamber side toward the cylinder inner circumferential wall side in the same direction as the plurality of guide portions.

According to this configuration (6), the sub-guide portion extends at an angle from the auxiliary chamber side toward the cylinder inner wall side in the same direction as the guide portion, so that the sub-guide portion can guide the flame after collision with the guide portion to the vicinity of the cylinder inner wall.

(7) In some embodiments, the height of each of the sub-guide sections is lower than the height of a position at which flame impinges on each of the plurality of guide sections from the communicating passage, and is formed lower than the height of the guide sections on both sides of the sub-guide section in the circumferential direction at the same radius from the center of the main chamber.

According to this configuration (7), the height of the sub-guide portion is lower than the height of the collision position of the flame from the communication passage, so the sub-guide portion does not impede the collision of the flame ejected from the communication passage with the guide portion. Furthermore, since the sub-guide portion is formed lower than the height of the guide portions on both sides of the sub-guide portion in the circumferential direction at the same radius from the center of the main chamber, the sub-guide portion does not impede the flame that tries to spread in the circumferential direction.

According to at least one embodiment of the present disclosure, by colliding the flame ejected from the auxiliary chamber with a guide portion provided on the top surface of the piston, it is possible to suppress an increase in heat loss of the flame and to distribute the flame evenly within the main chamber, thereby improving the combustion of the mixture in the main chamber.

1 is a schematic cross-sectional view showing a configuration around a combustion chamber of a pre-combustion chamber engine according to an embodiment of the present disclosure. FIG. FIG. 2 is a plan view of the piston top of the pre-chamber engine of FIG. 1 . FIG. 2 is a side view of the piston top of the pre-chamber engine of FIG. 1 . 3 is a schematic cross-sectional view taken along line AA in FIG. 2. FIG. 4 is a plan view of the piston top according to another embodiment, and corresponds to FIG. 2 . FIG. 6 is a side view of a piston top of the pre-chamber engine of the other embodiment of FIG. 5, and corresponds to FIG. 3.

The following describes an engine with a pre-chamber according to an embodiment of the present disclosure with reference to the drawings. This embodiment shows one aspect of the present disclosure, and is not intended to be limiting, and may be modified as desired within the scope of the technical concept of the present disclosure.

One embodiment of the present disclosure will be described with reference to Figures 1 to 4. Figure 1 is a schematic cross-sectional view showing the configuration around a combustion chamber 3 of a pre-chamber engine (hereinafter simply referred to as an engine) 1 according to one embodiment. The engine 1 includes a gasoline engine or a diesel engine, and has at least one cylinder.

As shown in FIG. 1, each cylinder has a cylinder 7 formed in a cylinder block 5, a piston 9 that reciprocates within the cylinder 7, and a cylinder head 11 fixed to the top of the cylinder block 5. The cylinder head 11 has an intake port 13 and an exhaust port 15 formed therein, and an intake valve 17 is provided in the intake port 13, and an exhaust valve 19 is provided in the exhaust port 15.

In addition, on the cylinder head 11 side of the cylinder 7, the combustion chamber 3 is partitioned by the cylinder inner wall 7a, the piston top surface 9a, and the cylinder head 11. A partition 25 is provided at the top 3a of the combustion chamber 3, partitioning the internal space of the combustion chamber 3 into a main chamber (main combustion chamber) 21 and an auxiliary chamber (auxiliary combustion chamber) 23. This partition 25 is arranged so as to cover an ignition plug 27 that is installed at or near the center of the cylinder at the top 3a of the combustion chamber 3 and discharges sparks into the combustion chamber 3. The internal space covered by the partition 25 in the combustion chamber 3 is the auxiliary chamber 23, and the space outside the partition 25 in the combustion chamber 3 is the main chamber 21.

Furthermore, a fuel injection valve 29 is installed on the cylinder inner wall 7a at the top of the cylinder 7, and the engine is configured as an in-cylinder injection engine (direct injection engine) that injects fuel directly into the cylinder 7. Note that in addition to the in-cylinder injection fuel injection valve 29, a port injection fuel injection valve that injects fuel into the intake port 13 may be added.

As shown in Figures 1 and 2, the partition wall 25 has multiple communication passages 31 that connect the main chamber 21 and the auxiliary chamber 23. A mixture of fuel and air in the main chamber 21 is introduced from the main chamber 21 to the auxiliary chamber 23 through some or all of the multiple communication passages 31, and the mixture is ignited in the auxiliary chamber 23 at a predetermined timing using the spark plug 27.

The flame formed by ignition in the auxiliary chamber 23 is jet-ejected into the main chamber 21 via multiple communication passages 31 to ignite the mixture in the main chamber 21 and promote combustion in the main chamber 21. This type of ignition system is called a jet ignition system, and is effective in igniting a lean mixture and promoting combustion, making it suitable for lean burn and large-volume EGR in the main chamber 21.

This embodiment shows a spark ignition engine using a spark plug 27, but it may also be a compression ignition engine using compression ignition.

Next, the guide portions 33 provided on the piston top surface 9a will be described. FIG. 2 is a plan view from above of the piston top, and as shown in FIG. 2, the piston top surface 9a is provided with the same number of convex guide portions 33 as the number of communicating passages 31, each having a collision side 37 against which the flames 35 ejected from the communicating passages 31 of the auxiliary chamber 23 collide. In FIG. 2, there are six communicating passages 31 and six guide portions 33. Note that the numbers of communicating passages 31 and guide portions 33 do not necessarily have to be the same, and the number of guide portions 33 may be fewer than the number of communicating passages 31.

Figure 3 shows a side view of the piston top, showing the state where flame 35 collides with the collision side 37 (collision point P). Thus, Figure 3 shows the state where the piston 9 is in a position near top dead center, where the spark plug 27 in the auxiliary chamber 23 ignites and flame 35 is ejected through the communication passage 31, and the ejected flame 35 collides with the collision side 37 of the guide portion 33.

The cross-sectional shape of the guide portion 33 along line A-A perpendicular to tangent line L2, which indicates the inclination direction of the guide portion 33 at collision point P in Figure 2, is formed into a gentle mountain shape as shown in Figure 4. That is, the apex 33a of the guide portion 33 is formed into a curved shape rather than an edge shape, and the flame 35 that collides with the collision side 37 flows smoothly over the apex 33a of the guide portion 33 to the side opposite the collision side 37 (flowing without peeling on the opposite side).

Furthermore, the guide portion 33 extends at an incline from the auxiliary chamber 23 side toward the cylinder inner wall 7a side in the plan view of the piston top in FIG. 2. This inclination shape may be linear or curved.

Furthermore, the height H of the guide portion 33 is formed to decrease as it moves away from the auxiliary chamber 23 toward the cylinder inner wall 7a, changing from the maximum height H1 of the guide portion 33 to the minimum height H2 (including zero) (see FIG. 3). The collision point P is located on the auxiliary chamber 23 side of the guide portion 33, so the height of the guide portion 33 decreases from the collision point P toward the cylinder inner wall 7a.

The height H of the guide portion 33 refers to the height from the piston top surface 9a to the top 33a of the guide portion 33 (see Figure 4).

As shown in FIG. 2, the angle θ between the extension line L1 of the central axis of the communication passage 31 and the tangent line L2 of the guide section 33 at the collision point P, which is the tangent line toward the cylinder inner wall 7a, is set to be an obtuse angle.

When an intake swirl flow is formed in the intake air flowing into the combustion chamber 3 from the intake port 13, it is preferable that the inclination direction of the guide portion 33 is inclined in the intake swirl flow direction so that the flame 35 is carried by the intake swirl flow and diffused into the combustion chamber 3.

According to the above embodiment, the convex guide portion 33 with which the flame 35 collides is inclined from the auxiliary chamber 23 side toward the cylinder inner wall 7a side, so that the flame 35 ejected from the auxiliary chamber 23 does not collide directly with the cylinder inner wall 7a or the cylinder liner, but first collides with the guide portion 33, and is then guided to rotate circumferentially within the main chamber 21.

In addition, the angle θ between the extension line L1 of the central axis of the communication passage 31 and the tangent line L2 indicating the inclination direction of the guide section 33 at the collision point P and the tangent line toward the cylinder inner wall 7a is set to be an obtuse angle, so that the flame 35 that collides with the collision side surface 37 of the guide section 33 is guided to move toward the cylinder inner wall 7a inside the main chamber 21 and to rotate circumferentially inside the main chamber 21.

In this way, the guide portion 33 suppresses the heat loss of the flame 35 that occurs when the flame 35 ejected from the auxiliary chamber 23 directly impinges on the cylinder liner or the cylinder inner wall 7a, which are at a lower temperature than the piston 9.

In addition, according to this embodiment, the height of the guide portion 33 decreases as it moves away from the auxiliary chamber 23, i.e., as it approaches the cylinder inner wall 7a, so that the flame 35 tends to diffuse in the circumferential direction near the cylinder inner wall 7a without remaining between adjacent guide portions 33. This promotes combustion near the cylinder inner wall 7a.

Furthermore, the flame 35 ejected from the auxiliary chamber 23 collides with the collision side 37 located on the auxiliary chamber 23 side of the convex guide portion 33, so that the flame 35 spreads near the collision portion, promoting the spread of the flame 35 on the central side of the main chamber 21 close to the auxiliary chamber 23. This promotes combustion on the central side of the main chamber 21.

Furthermore, the apex 33a of the cross-sectional shape of the guide part 33 perpendicular to the tangent line L2 of the guide part 33 at the collision point P has a curved shape rather than an edge shape, so the flame 35 that collides with the collision side 37 can flow smoothly over the apex 33a of the guide part 33 to the side opposite the collision side 37. This further promotes the diffusion of the flame 35 that collides with the collision point P toward the center of the main chamber 21.

As described above, by colliding the flame 35 ejected from the auxiliary chamber 23 with the guide portion 33 provided on the piston top surface 9a, it is possible to suppress an increase in heat loss of the flame 35, and to disperse the flame 35 evenly toward the center and periphery within the main chamber 21, thereby improving the combustion of the mixture within the main chamber 21.

In some embodiments, as shown in FIG. 2, in a plan view of the piston 9, the guide portion 33 curves in the circumferential direction as it moves away from the auxiliary chamber 23.

As such, because the guide portion 33 is curved in the circumferential direction, the flame 35 that collides with the guide portion 33 is strengthened in its circumferential swirl within the main chamber 21.

The length of the curved shape of the guide section 33 and the curvature of the curve do not have to be the same for all of the guide sections 33, and may be set taking into consideration the arrangement of the intake port 13 and exhaust port 15, as well as the flow of the mixture gas in the main chamber 21 due to the port opening area, etc.

In some embodiments, as shown in FIG. 2, in a plan view of the piston 9, the tip D of the guide portion 33 is positioned so that a straight line L3 connecting the tip D of the guide portion 33 in the extension direction (the tip of the center line of the guide portion 33) and the center C of the auxiliary chamber 23 intersects with an adjacent guide portion 33 (intersection point K).

In this way, the tip D of the guide part 33 is positioned to extend toward the cylinder inner wall 7a so that the straight line L3 connecting the tip D of the guide part 33 and the center C of the auxiliary chamber 23 intersects with the next adjacent guide part 33 (intersection K). This forms a passage 39 between the guide parts 33, and the flame 35 that collides with the collision side 37 of the guide part 33 flows toward the cylinder inner wall 7a along the passage 39 between the guide parts 33, making it easier for the flame 35 to be guided toward the cylinder inner wall 7a.

In some embodiments, in a plan view of the piston 9, the guide portion 33 becomes thinner toward the tip end on the cylinder inner wall 7a side.

By narrowing the guide portion 33 toward the tip, the flame 35 can easily diffuse in the circumferential direction near the cylinder inner wall 7a without remaining between adjacent guide portions 33. This further promotes combustion near the cylinder inner wall 7a. The shape of the guide portion 33 that narrows toward the tip, combined with the shape of the guide portion 33 that decreases in height toward the tip as already described, further promotes the diffusion of the flame 35 near the cylinder inner wall 7a.

Next, another embodiment will be described with reference to Figures 5 and 6. In comparison with the first embodiment, the other embodiment further includes a sub-guide portion 41 between adjacent guide portions 33, which extends at an incline in the same direction as the guide portion 33. In the other embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in Figures 5 and 6, a sub-guide section 41 is provided on the piston top surface 9a between adjacent guide sections 33, and extends in the same direction as the guide sections 33, at an angle from the auxiliary chamber 23 side toward the cylinder inner wall 7a side.

The height HS of this sub-guide section 41 (height from the piston top surface 9a to the top of the sub-guide section 41) is lower than the height HP (height from the piston top surface 9a to the collision point P) of the flame 35 on the collision side surface 37 of the guide section 33, and is formed lower than the height H of the guide sections 33 on both sides of the sub-guide section 41 in the circumferential direction at the same radius from the center of the main chamber 21.

The space between adjacent guide parts 33 refers to the space between adjacent guide parts 33 in the circumferential direction of the main chamber 21 in a plan view of the piston 9, and is sandwiched between a straight line L3 connecting a tip end D of the guide part 33 in the extension direction (tip end of the center line of the guide part 33) to the center C of the auxiliary chamber 23, and a straight line L4 connecting a base end B of the next adjacent guide part 33 in the extension direction (base end of the center line of the guide part 33) to the center C of the auxiliary chamber 23. At least a part of the sub-guide part 41 is provided between these adjacent guide parts 33.

In addition, while the height HS of the sub-guide portion 41 is shown as being constant from the base end to the tip end in FIG. 6, it may become lower toward the tip end. Also, the width of the sub-guide portion 41 in a plan view of the piston 9 may be the same from the base end to the tip end, or may become narrower toward the tip end.

According to the above other embodiment, the sub-guide portion 41 extends in the same direction as the guide portion 33, at an angle from the auxiliary chamber 23 side toward the cylinder inner wall 7a side, so that the sub-guide portion 41 can guide the flame 35 after collision with the collision side surface 37 of the guide portion 33 to the vicinity of the cylinder inner wall 7a.

Moreover, the height HS of the sub-guide portion 41 is lower than the height HP of the flame 35 at the collision point P, so it does not impede the collision of the flame 35 ejected from the auxiliary chamber 23 with the collision side surface 37.

Furthermore, the height HS of the sub-guide portion 41 is lower than the height H of the guide portions 33 on both sides of the sub-guide portion 41 in the circumferential direction at the same radius from the center of the main chamber 21, so there is no hindrance to the spread of the flame 35 that attempts to spread circumferentially within the main chamber 21 after colliding with the impact side 37 of the guide portion 33. In this way, by installing the sub-guide portion 41, the flame 35 that has collided with the impact side 37 can be efficiently guided to the vicinity of the cylinder inner wall 7a without impeding its spread in the circumferential direction.

1 Engine (pre-chamber engine)
3 Combustion chamber 3a Top of combustion chamber 5 Cylinder block 7 Cylinder 7a Cylinder inner peripheral wall 9 Piston 9a Piston top surface 11 Cylinder head 21 Main chamber 23 Auxiliary chamber 25 Partition wall 27 Ignition plug 31 Communication passage 33 Guide portion 33a Top of guide portion 35 Flame 37 Collision side surface 41 Sub-guide portion B Base end portion C of guide portion Center portion D of auxiliary chamber Tip portion θ Angle H between extension line of central axis of communication passage and tangent line at collision point P Height of guide portion H1 Maximum height H2 of guide portion Minimum height L1 of guide portion Extension line L2 of central axis of communication passage Tangent line L3 at collision point P Straight line L4 connecting tip portion of guide portion and auxiliary chamber center Straight line HS connecting base end portion of adjacent guide portion and auxiliary chamber center Height HP of sub-guide portion Height K of collision point P Intersection P of line L3 with adjacent next guide Collision point of flame

Claims (7)

1. A pre-chamber engine comprising: a main chamber; a pre-chamber separated from the main chamber by a partition wall provided in a cylinder head; and a plurality of communication passages provided in the partition wall for communicating between the main chamber and the pre-chamber, wherein a flame formed in the pre-chamber by ignition of an air-fuel mixture in the pre-chamber is ejected into the main chamber via the plurality of communication passages to ignite the air-fuel mixture in the main chamber,
a plurality of convex guide portions having collision sides on a piston top surface against which flames ejected from each of the plurality of communication passages collide;
the plurality of guide portions extend at an angle from the auxiliary chamber side toward a cylinder inner circumferential wall side in a plan view of the piston, the height of the plurality of guide portions decreases with increasing distance from the auxiliary chamber , and the collision side surface of each of the plurality of guide portions is inclined to one side in the circumferential direction with increasing distance from the auxiliary chamber in a plan view of the piston . 2. The engine with a separate chamber according to claim 1, wherein, in a plan view of the piston, an angle formed by an extension line of a central axis of each of the plurality of communicating passages and a tangent line indicating an inclination direction of each of the plurality of guide portions at an intersection of the extension line and each of the plurality of guide portions, the tangent line being a tangent line toward a cylinder inner wall side, is an obtuse angle. 3. The pre-chamber engine according to claim 1, wherein, in a plan view of the piston, the plurality of guide portions are curved toward one side in a circumferential direction as they move away from the pre-chamber. 4. The pre-chamber engine according to claim 1, wherein in a plan view of the piston, a tip end of each of the plurality of guide portions is positioned such that a straight line connecting a tip end of each of the plurality of guide portions and a center portion of the pre-chamber intersects with each of the plurality of adjacent guide portions. 5. The engine according to claim 1, wherein the plurality of guide portions are tapered toward a tip portion of the piston on an inner peripheral wall side of the cylinder in a plan view of the piston. 6. The pre-chamber engine according to claim 1, further comprising a sub-guide portion between adjacent guide portions in a plan view of the piston, the sub-guide portion extending obliquely from the pre-chamber side toward the cylinder inner circumferential wall side in the same direction as the plurality of guide portions. 7. The engine of claim 6 , wherein a height of each of the sub-guide portions is lower than a height of a position at which a flame impinges on each of the plurality of guide portions from the communicating passage, and is also lower than a height of the guide portions on both sides of the sub-guide portion in a circumferential direction at the same radius from the center of the main chamber.

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