JPS61234221A - Construction of combustion chamber in engine - Google Patents

Abstract

PURPOSE:To induct new charged air to be sufficiently sucked also to the side of a main combustion chamber from a high load use intake passage when the valve timing is overlapped, by opening the high load use intake passage to both the main combustion chamber and a squish zone. CONSTITUTION:An engine main unit 1 forms a combustion chamber 6 between a cylinder head 3 and the upper surface of a piston 5 further a main combustion chamber 8 in a head internal wall surface 3a by a recessed part 7. The recessed part 7 opens the first intake port 11 and the first exhaust port 13, and the other port is opened to a flat part being a squish zone excepting the recessed part 7. When the valve timing is overlapped in the end of an exhaust stroke in high loaded operation with a shutter valve 22 being opened, a large amount of new charged air is allowed to flow into the main combustion chamber 8 from a high load use intake passage 21 mainly through the first intake port 11. In this way, residual combustion gas in the main combustion chamber 8 is sufficiently scavenged in a short period.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for forming a compact main combustion chamber and squish zone between the inner wall surface of the cylinder head and the piston when the piston moves to top dead center. This relates to the structure of the combustion chamber of the engine.

(Prior Art) As a conventional combustion chamber structure of a four-cycle engine, there is one disclosed in, for example, Japanese Utility Model Application Laid-Open No. 59-17222. This publication describes that a recess is partially formed in the inner wall surface of the cylinder head to form a compact main combustion chamber between the recess and the upper surface of the piston when the piston is at top dead center, and A combustion chamber structure for a four-valve engine is disclosed in which a squish zone is formed between a portion of the inner wall surface other than the recess and the upper surface of the piston.

Moreover, in this combustion chamber structure, the low-load intake port and the first exhaust port are opened in the recess, and the high-load intake port and the second exhaust port are opened in a portion other than the four parts.

In an engine equipped with this type of combustion chamber structure, the main combustion chamber is compact, so the flame propagation distance within the main combustion chamber is shortened. Furthermore, at the end of the compression stroke, a squish flow is ejected from the squish zone into the main combustion chamber, creating turbulent flow within the main combustion chamber, thereby improving the flame propagation speed. As a result, even if the compression ratio is increased, knocking is less likely to occur and combustion efficiency can be improved. Moreover, when the compression ratio is increased, lean fuel can be burnt well and fuel efficiency can be improved.

Also, during low loads, new air-fuel mixture (hereinafter simply referred to as fresh air) is sucked into the main combustion chamber only from the low-load intake ports, while at high loads and high rotations, the low-load intake ports and high-load intake ports Since fresh air is sucked into the combustion chamber from the combustion chamber, the filling efficiency of fresh air is good during high loads.

(Problem to be solved by the invention) By the way, in such a four-stroke engine, the intake valve is opened at the end of the exhaust stroke when the exhaust valve is open, and the opening timing of the intake port overlaps with the opening timing of the exhaust port at the end. By doing so, fresh air is sucked into the combustion chamber to scavenge residual combustion gas in the main combustion chamber.

However, in the above-mentioned engine, the squish zone at the end of the exhaust stroke becomes very narrow, so even if fresh air is taken into the combustion chamber from the high-load intake port at the end of the exhaust stroke under high load, the narrow squish zone will become narrower. This results in air intake resistance, which is not very desirable in terms of scavenging residual combustion gas. In other words, during high loads, scavenging is mainly performed by fresh air from the low-load intake port, but this low-load intake port, that is, the low-load intake passage connected to it, accelerates the intake flow velocity or creates a swirl. Due to generation,
Passage resistance inevitably increases, and therefore there is a limit to not only the above-mentioned scavenging but also the improvement in filling efficiency under high loads.

Therefore, the present invention effectively generates swirl at low load without unnecessarily increasing intake resistance, and at the time of valve timing overlap at the end of the exhaust stroke at high load, from the high load intake passage to the combustion chamber. It is an object of the present invention to provide a combustion chamber structure for an engine that allows fresh air to flow into the main combustion chamber in a good manner and to sufficiently scavenge residual combustion gas in a main combustion chamber in a short period of time.

(Means and effects for solving the problem) In order to achieve the above-mentioned object, the present invention provides a high-load intake passage that opens into both the main combustion chamber and the squish zone, thereby improving the exhaust stroke during high-load conditions. When the valve timing overlaps in the final stage, fresh air from the high-load intake passage is sufficiently drawn into the compact main combustion chamber. Further, the intake port opening in the recess is used not only for supplying intake air during high loads but also for supplying intake air during low loads. in particular.

By forming a recess in a part of the inner wall surface of the cylinder head, when the piston moves to top dead center, a main combustion chamber is formed between the recess and the upper surface of the piston, and the inner wall surface of the head A squish zone is formed between a portion other than the recess and the upper surface of the piston, and a first intake port opened and closed by a first intake valve and at least one exhaust port opened and closed by an exhaust valve are opened in the four parts. A second intake port opened and closed by a second intake valve is opened in a portion other than the four parts of the inner wall surface of the head, and a high-load intake passage is provided with a shutter valve that is opened during high load. , an outlet end of a low-load intake passage that bypasses the shutter valve and has a smaller passage area than the high-load intake passage is communicated with the first intake port; The structure is as follows.

With this configuration, fresh air from the low-load intake passage is sucked into the combustion chamber from the first intake port when the load is low. Also, when the load is high, fresh air from the low-load intake passage is drawn into the combustion chamber from the first intake port, and the shutter valve opens to allow fresh air from the high-load intake passage to the first and second intake ports. It is inhaled into the combustion chamber through the port.

Moreover, when the valve timing overlaps at the end of the exhaust stroke under high load, the second
Fresh air is sucked into the squish zone through the intake port, but since the squish zone is narrow and has high intake resistance, fresh air from the high-load intake passage flows into the main combustion chamber through the first intake port. flows into. As a result, during high loads, residual combustion gas in the main combustion chamber is scavenged in a short time with a large amount of fresh air.

Furthermore, during the intake stroke, regardless of whether the load is low or high, the fresh air sucked into the recess from the first intake port generates a swirl in the combustion chamber that is favorable for combustion. On the other hand, at the end of the exhaust stroke, a squish flow is ejected from the squish zone into the main combustion chamber, forming a turbulent flow that is favorable for combustion within the main combustion chamber.

(Example) Hereinafter, an example of the present invention will be described based on the attached drawings.

In FIG. 1, 1 is an engine body, 2 is a cylinder block of the engine body 1, 3 is a cylinder head of the engine body 1, and a piston 5 is disposed in a cylinder 4.

A combustion chamber 6 is formed between the cylinder head 3 and the upper surface of the piston 5, and a recess 7 for forming a main combustion chamber is formed in the head inner wall surface 3a facing the combustion chamber 6 of the cylinder head 3. (Figures 1 to 3). This recessed portion 7 occupies approximately half of the head inner wall surface 3a, and is elongated in the engine width direction. As a result, when the piston 5 moves to the top dead center, a compact main combustion chamber 8 is formed between the recess 7 and the upper surface of the piston 5, and the flat part 9 other than the recess 7 of the head inner wall surface 3a and the piston As shown in FIG. 3, a squish zone 10 is formed between the upper surface of the cylindrical member 5 and the upper surface.

11 is a first intake port, 12 is a second intake port, 13
14 is a first exhaust port, and 14 is a second exhaust port, which are formed on the cylinder head 3. The first intake port 11 and the first exhaust port 13 are open at both ends of the recess 7 in the longitudinal direction, and the second intake port 12 is open adjacent to the first intake port 11 in the flat part 9. The exhaust port 14 is open adjacent to the first exhaust port 13 in the flat portion 9 . The first and second intake ports 11.12 are opened and closed by the first and second intake valves 15.1'6, and the first and second exhaust ports 13.14 are opened and closed by the first and second intake valves 15.1'6. Second
It is opened and closed by exhaust valves 17 and 18.

The cylinder head 3 and the intake pipe 19 connected to it include
A low-load intake passage 20 and a high-load intake passage 21 are formed so as to straddle these. The high-load intake passage 21 is branched into two at its downstream end, and the branch passages 21a and 21b are connected to the first and second intake ports 11.
Or it is connected to 12. In such a high-load intake passage 21, at a position slightly upstream of the branch part,
A shutter valve 22 is provided. This shutter valve 22
The valve is closed when the load is low, that is, fully closed or closed to a small opening, and is opened when the load is high. Further, the low-load intake passage 20 is branched from the bottom wall portion of the intake pipe 19 upstream of the shutter valve 22, bypasses the shutter valve 22, and has an outlet end 20a connected to the first intake port 11. It is communicated.

The low-load intake passage 20 has a passage area smaller than that of the branch passages 21a and 21b, and is designed so that a tangent to the cylinder 4 can generate a stronger swirl of intake air in the main combustion chamber 8. However, since the swirl-generating effect of the inner wall surface of the recess 7 for forming the main combustion chamber 8 can be fully expected, the directivity of the low-load intake passage 20 is not so strong. Not yet. Further, the downstream end of the partition wall 25 that partitions the low-load intake passage 20 and the high-load intake passage 21 is located considerably upstream of the intake valve 15, that is, a branch passage forming the high-load intake passage 21. 21a is the effective opening area of this partition wall 2.
5 so that it is not jammed as much as possible.

As a result, a sufficient effective opening area of the branch passage 21a constituting the high-load intake passage 21 is ensured.

Note that the first and second exhaust ports 13.14 are connected to the exhaust passage 23.
is connected to. Further, the spark plug 24 is disposed within the recess 7 approximately at the center of the head inner wall surface 3a.

Next, the operation of the above configuration will be explained.

First, during low load, since the shutter valve 22 is closed, all or most of the fresh air flows from the first intake port 11 into the recess 7 at high speed through the low-load intake passage 21, which has a small passage area. Inhaled. On the other hand, when the load is high, fresh air guided through the low-load intake passage 21 is sucked into the combustion chamber 6 from the first intake port 11, and the shutter valve 22 is opened to open the high-load intake passage 21. Fresh air guided through the combustion chamber 6 is drawn into the combustion chamber 6 from the first and second intake ports 11.12 via the branch passages 21a and 21b.

The fresh air supplied from the first intake port ll is transferred to the recess 7
flows along the inner wall of the combustion chamber 6, forming a swirl inside the combustion chamber 6. Furthermore, at the end of the exhaust stroke, fresh air is ejected from the squish zone 10 into the main combustion chamber 8 as a squish flow, forming a turbulent flow within the main combustion chamber 8. As a result, when fresh air in the main combustion chamber 8 is ignited by the spark plug 24, the flame is propagated throughout the main combustion chamber 8 at high speed.

Here, when the valve timing overlaps at the end of the exhaust stroke under high load, fresh air tries to be sucked into the squish zone 10 from the branch passage 21b of the high load intake passage 21 through the second intake port 12. . However, since the squish zone is narrow and the pressure is higher than that of the main combustion chamber 8, the fresh air from the high-load intake passage 21 is mainly transferred to the first intake port 11 from the branch passage 21a with a sufficient passage area. A large amount of air flows into the main combustion chamber 8 through the .

As a result, residual combustion gas in the main combustion chamber is sufficiently scavenged in a short period of time.

In the above embodiment, the case where two exhaust ports are provided has been explained, but the exhaust port 14 opened in the flat part 9 may be abolished and there are three valves. The exhaust port 14 may be opened into the recess 7.

(Effects of the Invention) As is clear from the above description, the present invention allows a large amount of fresh air from the high-load intake passage to be sucked into the main combustion chamber with low intake resistance when valve timing overlaps during high-load conditions. Therefore, fresh air can be easily taken into the combustion chamber from the high-load intake passage, and residual combustion gas in the main combustion chamber can be sufficiently scavenged in a short time.

In addition, since the intake passage for low loads is provided with a separate membrane, it is possible to effectively generate swirl especially at low loads. The passage area can be optimally set.

Of course, the low-load intake passage does not require a separate dedicated intake port, so the main combustion chamber can be kept as compact as the conventional one, and this type of combustion chamber The advantages of the structure can be fully utilized.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of an engine equipped with a combustion chamber structure according to the present invention. FIG. 2 is a bottom view of the cylinder head shown in FIG. 1. FIG. 3 is a cross-sectional view taken along the line ■-m in FIG. 2. l: Engine body 2 Niji cylinder block 3 Niji cylinder head 3a: Head inner wall surface 4: Cylinder 5: Piston 6: Combustion chamber 7: Recess 8: Main combustion chamber 9: Flat part 10 Varnishing zone 11: First intake port 12: Second intake port 13: First exhaust port 14: Second exhaust port 15: First intake valve 16: Second intake valve 17: First exhaust valve 18: First exhaust valve 20: Low load intake passage 20a: Outlet Eye end 21: High load intake passages 21a, 21b: Branch passage 22: Shutter valve Fig. 1 Fig. 2

Claims (1)

[Claims] (1) By forming a recess in a part of the inner wall surface of the cylinder head, when the piston moves to top dead center, a main combustion chamber is formed between the recess and the upper surface of the piston, and the head A squish zone is formed between a portion of the inner wall surface other than the recess and the upper surface of the piston, and the first intake port is opened and closed by the first intake valve and the at least one exhaust port is opened and closed by the exhaust valve. A high-load intake passage has a second intake port opened in the recess and opened and closed by a second intake valve, the second intake port is opened in a portion of the inner wall surface of the head other than the recess, and includes a shutter valve that is opened during high load. An outlet end of a low-load intake passage that communicates with both the first and second intake ports, bypasses the shutter valve, and has a passage area smaller than the high-load intake passage is connected to the first intake port. A combustion chamber structure of an engine, characterized in that the combustion chambers are in communication with each other.