JPH0649853Y2 - Exhaust port structure of 2-cycle internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an exhaust port structure of a two-cycle internal combustion engine equipped with an intake valve and an exhaust valve.

[Conventional technology and problems]

An intake valve and an exhaust valve are provided in a two-cycle internal combustion engine,
It has been proposed to improve the scavenging performance by opening the exhaust valve prior to the intake valve in the downward stroke of the piston to cause blowdown of the exhaust gas to promote introduction of fresh air into the cylinder bore. . In order to improve the fuel consumption rate at low engine speed and low load and to improve the output, the exhaust gas that flows back into the cylinder bore from the exhaust port after blowdown causes the swirling motion of the residual exhaust gas (swirl) around the axis of the cylinder bore. By the addition, the stratification of the fresh air portion near the spark plug and the high temperature exhaust gas portion in the cylinder bore below it is caused to occur, thereby improving the ignitability of the fresh air. For example, Japanese Patent Application No. 61-135054.

[Problems to be solved by the invention]

Since it is a two-cycle internal combustion engine, the period in which the intake valve and the exhaust valve are open at the same time inevitably becomes long. Therefore, the flow of exhaust gas flowing back from the exhaust port is affected by the flow of intake air introduced from the intake port,
It is difficult to obtain a suitable exhaust gas swirl. Therefore, the intended stratification cannot be obtained, and there is a problem of misfire at low rotation and low load.

It is an object of the present invention to provide an appropriate swirl when a backflow of exhaust gas after blowdown occurs in a two-cycle internal combustion engine equipped with an intake valve and an exhaust valve.

[Means for solving problems]

According to this invention, in a two-cycle internal combustion engine having an intake valve and an exhaust valve, two exhaust ports are divided from the intake side on a straight exhaust port and a bottom surface of a cylinder head branched from the straight exhaust port. It has a first ridge and a second ridge extending between a straight exhaust port opening in the tangential direction of the cylinder bore and an exhaust port branching therefrom, the first ridge extending the exhaust port. Separated from the intake side, the swirl flow of the backflow exhaust gas from the straight exhaust port is guided to the lower part of the cylinder bore, and the second ridge guides the backflow exhaust gas from the branched exhaust port toward the straight exhaust port. An exhaust port structure for an internal combustion engine is provided.

〔Example〕

In FIGS. 1, 2, 3, 4, 5, and 6, reference numeral 10 is a main body of an internal combustion engine, which includes a cylinder block 12, a cylinder bore 14, a crankshaft 15, a piston 16, a combustion chamber 17, and a cylinder head 18. And a spark plug 19. As shown in FIG. 4, the cylinder head 18 has two intake ports 20a, 20b and two exhaust ports 22a, 22b, and intake valves 24a, 24b for opening and closing the respective intake ports and exhaust ports, and an exhaust valve. It is a so-called four-valve type with high intake / exhaust efficiency including 26a and 26b. The intake valve and the exhaust valve are opened and closed by dedicated cams (not shown). Exhaust gas exhaust port 22 is used to cause backflow swirl of exhaust gas after blowdown at light engine load.
Of the a and 22b, the exhaust port 22b is the main exhaust port, and forms a straight line and opens in the tangential direction of the cylinder bore 14. On the other hand, the other exhaust port 22b is branched so as to be slightly curved as compared with the straight exhaust port 22b, and has a shape that should be called a modified Y shape.

In FIG. 4, a raised portion 30 is formed on the bottom surface of the cylinder head 18.
As shown in FIG. 1, its ridgeline 30 'extends substantially in the radial direction of the cylinder bore 14 and separates the intake port 20a, 20b side and the exhaust port 22a, 22b side. The raised portion 30 blocks the intake side and the exhaust side and prevents the two from interfering with each other to prevent blow-through of fresh air. This bump 30 is the electrode 19 of the spark plug 19.
The spark plug electrode 19a is curved so as not to interfere with it at a, and the spark plug electrode 19a is located on the intake port 20a, 20b side of the ridge plug 30 ', which allows fresh air near the spark plug electrode 19a. The stratification of is obtained. As shown in FIG. 4, the ridge 30 is composed of a first portion 30-1 having a low height and a second portion 30-2 functioning as a mask having a large height. As shown in FIG. 2, the first portion 30-1 is disposed between the opposing intake port 20b and exhaust port 22b. On the other hand, as shown in FIG. 4, the first second portion 30-2 is arranged between the opposing intake port 20a and exhaust port 22a. The second portion 30-2 of the ridge 30 is composed of two sides that are tapered with respect to its tip, and the side on the exhaust port 22a side is located on a substantially extended line of the outer peripheral surface of the valve seat of the exhaust valve 26a. The side on the intake port 20a side extends obliquely from the outer peripheral surface of the valve seat of the intake valve 24a. On the other hand the first of the uplift 30
The portion 30-1 is composed of both sides which are tapered with respect to its tip, but extends obliquely from the outer peripheral surface of the valve seat of the side exhaust valve 26b on the side of the exhaust port 22a, whereby the first side A difference in height of the ridge 30 is obtained between the portion 30-1 and the second portion 30-2.

In FIG. 5, a second ridge 31 which acts as a mask is provided between the exhaust ports 22a and 22b, the ridge of which is indicated by 31 'in FIG. The side of the raised portion 31 on the exhaust port 22a side extends obliquely from the outer peripheral surface of the valve seat of the exhaust valve 26a, and the side of the second exhaust port 22b side is located on the extension of the outer peripheral surface of the valve seat. There is.

In FIG. 6, the intake pipe 32 has a branch portion 33 to each cylinder, has an internal partition wall 33-1 inside thereof, two intake passages 34a, 34b are formed, and the intake port 20a, Connected to 20b. The effective size of the second intake passage 34b is larger than that of the first intake passage 34a, and the intake control valve 36 is installed. The intake control valve 36 of each cylinder is connected to an actuator 37 by link means 36 '. The actuator 37 is, for example, a diaphragm mechanism of negative pressure operation, and is switched between negative pressure and atmospheric pressure by a switching valve (not shown), and the intake control valve 36 opens and closes the intake passage 34b. Can be taken selectively. The intake control valve 36 is
As will be described later, it is closed at light load and opened at high load. Fuel injectors 38a, 38b are arranged in the intake passages 34a, 34b. 40a and 40b are reed valves, which are installed as necessary for controlling the reverse flow.

On the upstream side of the intake pipe 32, a mechanical supercharger 44, a throttle valve 46, an air flow meter 48, and an air cleaner 50 are sequentially arranged. The mechanical supercharger 44 is constituted by, for example, a roots pump or a vane pump, a drive shaft 44-1 thereof is provided with a pulley 44-2, and a belt 44-3 is connected to a pulley 15 'on the crankshaft 15. A bypass control valve 45 is installed in a bypass passage 44 'that bypasses the mechanical supercharger 44, and serves to adjust the intake pipe pressure.

In this embodiment, the exhaust manifold 54 is separately installed for each of the cylinder groups # 1 to # 3 and the cylinder groups # 4 to # 6. This grouping is
Ignition is made to alternate between these two groups. That is, in this embodiment, the ignition order is # 1, # 6, #
The order is 2, # 4, # 3, # 5. By grouping with alternate ignition, the exhaust pressure of one cylinder in the scavenging stroke is prevented from being influenced by the exhaust pressure of other cylinders. Cylinder groups # 1 to # 3, #
The exhaust manifolds 54 of the cylinder groups 4 to # 6 are connected to dedicated catalytic converters (which may also serve as a muffler or a dedicated muffler may be separately installed) 56.

The control circuit 60 controls the operation of the injectors 38a, 38b, and further controls the actuator 37, is configured as a microcomputer system, and is a fuel injection signal or an ignition signal according to signals from the air flow meter 48 and other sensors (not shown). Further, the operation signal of the intake control valve 36 is formed. The operation itself of the control circuit 60 is not directly related to the present invention, so its explanation is omitted.

FIG. 7 shows intake valves 24a, 24b and exhaust valves 26a, 26b in one cylinder determined by the profile and orientation of cams (not shown).
It shows the operation timing of. Exhaust valves 26a and 26b start to open at 80 ° before bottom dead center (BDC) and 40 after bottom dead center (BDC).
Closes at °. On the other hand, the intake valves 24a and 24b are at bottom dead center (BDC).
It begins to open at 60 ° in front and closes at 60 ° after bottom dead center (BDC). I indicates the fuel injection period, which starts after the intake valve is opened and ends slightly before bottom dead center (BDC).

Next, the combustion operation of a two-cycle internal combustion engine of the type having an intake valve and an exhaust valve, to which the present invention is applied, will be first outlined in outline, and then the characteristic operation of the present invention will be described. Intake control valve 36 during light engine load
Is closed and intake air is introduced into the engine only through the first intake passage 34a. In the process of lowering the piston 16, first, the exhaust valves 26a, 26b start to open at around 80 ° before bottom dead center (BDC). Therefore, exhaust gas is discharged from the combustion chamber to the exhaust ports 22a and 22b as indicated by arrow P in FIG. 8 (a), and so-called blowdown occurs, but this blowdown is weak and ends immediately. Then, when the piston 16 further descends, the inside of the cylinder bore 14 is weak but a negative pressure is generated, so that the exhaust gas flows backward toward the cylinder bore as indicated by an arrow Q due to the pressure difference between the exhaust ports 22a and 22b (see FIG. )). Then, due to the deformed Y-shape of the exhaust ports 26a, 26b, a swirl flow (swirl) of the residual exhaust gas is formed in the cylinder bore as shown by an arrow R. Around this time, the intake valve 24
Although a (24b also) starts to open, the introduction of fresh air does not substantially occur because the lift is still small and the throttle valve 46 is throttled. When the piston 16 descends further, the swirl of the exhaust gas continues, while the intake valve 24a,
Although the lift of 24b becomes large, since the intake control valve 36 is closed, fresh air is introduced from the intake passage 34 into the cylinder bore as shown by arrow S, while fresh air mixed with the injected fuel is swirled exhaust gas. When it gathers in the vicinity of the spark plug electrode above the portion (Fig. 8 (c)), the stratification is achieved.
Such a stratified state of the exhaust gas R and the fresh air S is maintained even when the piston reaches the bottom dead center (BDC) (Fig. 8 (d)). In (e), the intake valves 24a and 24b are closed, and blowback of fresh air is prevented. Then, the piston moves upward, but such a stratified state is maintained until the compression is completed, and the fresh air portion near the spark plug can be easily ignited.

In the high load state of the engine, the intake control valve 36 is opened. Therefore, the intake passage 34b which has been closed until now is opened. In FIG. 9, when the exhaust valves 26a, 26b are first opened in the process of lowering the piston 16, the exhaust gas in the cylinder bore 14 is discharged to the exhaust ports 22a, 22b by the blowdown P. By comparison, a large amount of exhaust gas is exhausted to the exhaust port (Fig. 9 (a).) By providing two exhaust valves, the required blowdown amount can be obtained even if the blowdown period is short. The opening timing of the exhaust valve can be relatively delayed, the expansion ratio is increased, and the output is improved.

The intake valves 24a, 24b start to open at the time of Fig. 9 (b),
This time, since the intake control valve 36 is open and the opening of the throttle valve 46 is large, the introduction of fresh air is performed as shown by the arrow T. At this time, fresh air is introduced from both of the intake ports 20a, 20b, the fresh air flows from the top to the bottom along the wall surface of the cylinder bore as indicated by arrow T, and the exhaust gas is exhausted by the exhaust port 22a, as indicated by arrow U. By letting it flow to 22b, so-called transverse scavenging is realized. At the time of Fig. 9 (c), the negative pressure component in the pressure wave pulse due to the strong blowdown appears, and the exhaust port 22
The a and 22b temporarily become negative pressure, and as a result, the introduction of the fresh air T into the cylinder bore is further promoted, and a part of the fresh air flows out to the exhaust ports 22a and 22b like V and is once stored. When the pressure of the exhaust ports 22a, 22b returns to the positive pressure, the stored fresh air flows back into the cylinder bore as indicated by arrow W, and swirl X of fresh air is generated (Fig. 9 (d)). As a result, turbulence occurs and flame spread after ignition is improved. 9th
The intake valves 24a and 24b have completed the closing at the time of the figure (e), and the blowback of fresh air is prevented.

In the operation of the two-cycle internal combustion engine to which the present invention described above is applied, the structure of the present invention can enhance the backflow swirl of exhaust gas after blowdown at the time of low engine load. That is, in FIG. 1, since the straight exhaust port 22b is opened in the tangential direction of the cylinder bore 14, the exhaust gas flow as shown by the arrow a at the time of exhaust backflow after blowdown (FIG. 8B). It has a tendency to cause a turning motion. The flow of backflow exhaust gas from the exhaust port 22b functions as a guide surface by the tapered side wall of the first portion 30-1 of the ridge 30, and the flow of exhaust gas flows in the cylinder bore as indicated by arrow a'in FIG. The swirl will be performed while pointing toward the bottom. First part 30-1 of the ridge 30
It also functions as a weir that restrains and holds the fresh air introduced from the intake port near the spark plug electrode, and as a result, the stratification action between the fresh air portion above the cylinder bore and the exhaust gas portion below the cylinder bore is achieved. To be achieved.

Exhaust gas from the straight exhaust port 22b As described above, in the process of generating the reverse flow swirl, the reverse flow of the exhaust also occurs from the other exhaust port 22a, but the exhaust port 22a is different from the main exhaust port 22b. The exhaust energy from the straight port 22b is slightly curved and the exhaust energy from the straight port 22b is high because the height of the portion 30-2 of the ridge 30 facing the exhaust port 22b is high to form a mask. Greater than In addition, a second raised portion 31 is formed between the exhaust port 22a and the exhaust port 22b, which extends from the straight port 22b to the curved port 2b.
The side 31-1 on the exhaust port 22a side of the second raised portion 31 serves as a mask for restricting the flow of exhaust gas toward the 2a side, and guides the exhaust gas from the curved port 22 toward the exhaust port 22b. Work as a guide. As a result, when viewed comprehensively,
A swirling motion of the exhaust gas in the directions a and a'of FIGS. 2 and 3 can be obtained. As a result, a good swirl motion of the exhaust gas after the blowdown as described in (b) of Fig. 8 is obtained, whereby the fresh air portion near the spark plug above the cylinder bore and the exhaust gas portion below the cylinder bore. And a good stratification effect can be achieved, and the ignition performance during low load operation can be improved.

〔effect〕

According to this invention, in a four-valve engine, two exhaust ports are provided, each having a straight exhaust port that opens in the tangential direction of the cylinder bore, and an exhaust port branched from this exhaust port. A first protrusion that separates the exhaust port from the intake side; and a second protrusion that extends between a straight exhaust port that opens in the tangential direction of the cylinder bore and an exhaust port that branches from the straight exhaust port, The exhaust port 22a, 22b is divided from the intake side by the raised portion 30 of No. 1, and the swirl flow of the backflow exhaust gas from the straight exhaust port 22b is guided to the lower part of the cylinder bore, and the second raised portion 31 is the branched exhaust gas. The reverse flow exhaust gas is guided from the port 22a to the straight port 22b so that it goes from the exhaust port 22a to the lower part of the cylinder bore as shown by a'in FIG. The swirl flow can be enhanced, and as a result, stratification in which the fresh air during the intake stroke is located above the exhaust gas portion below the cylinder bore is successfully achieved, and ignition performance during low load operation is improved. Effective to improve

[Brief description of drawings]

FIG. 1 is a cross-sectional view of one cylinder of the internal combustion engine of the present invention. FIG. 2 is a longitudinal sectional view of one cylinder of the internal combustion engine of the present invention, which is shown along the line II-II in FIG. FIG. 3 is a longitudinal sectional view of one cylinder of the internal combustion engine of the present invention, which is taken along the line III-III in FIG. FIG. 4 is a longitudinal section of one cylinder of the internal combustion engine of the present invention, which is shown along the line IV-IV in FIG. FIG. 5 is a longitudinal section of one cylinder of the internal combustion engine of the present invention, which is taken along the line VV of FIG. FIG. 6 is a schematic diagram of the overall configuration of the internal combustion engine of the present invention. FIG. 7 is an operation timing angle diagram of an intake valve and an exhaust valve of one cylinder in one cycle of the engine. FIG. 8 is a diagram for explaining a combustion operation in one cycle of a two-cycle internal combustion engine with an intake valve and an exhaust valve according to an embodiment of the present invention at a light load. FIG. 9 is a diagram for explaining a combustion operation in one cycle of a two-cycle internal combustion engine with an intake valve and an exhaust valve according to the embodiment of the present invention at a high load. 10 …… Engine body 17 …… Combustion chamber 20a, 20b …… Intake port 22a, 22b …… Exhaust port 24a, 24b …… Intake valve 26a, 26b …… Exhaust valve 30 …… First raised portion 30-1 …… First part 30-2 …… Second part 30 ′ …… Ridge line 31 …… Second raised portion 31 ′ …… Ridge line 32 …… Intake pipe 32-1, 32-2 …… Branch pipe part 32-3 …… Collecting pipe 36 ... Intake control valve 38a, 38b ... Fuel injector 41 ... Intake open / close valve 44 ... Mechanical supercharger 48 ... Air flow meter 54 ... Exhaust manifold 60 ... Control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI technical display location F02F 1/24 D 8503-3G (72) Inventor Toshio Tanahashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto Car Co., Ltd. (72) Inventor Hiroshi Noguchi 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd. (72) Inventor Toshio Ito 1 Toyota-cho, Toyota-shi, Aichi Toyota Auto Co., Ltd. (72) Inventor Toyoichi Umebana 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor: Kingo Horii Toyota City, Aichi Prefecture 1 Toyota Town Company, Toyota Motor Corporation (72) Inventor Takehiko Hirose Toyota City, Aichi Prefecture Toyota Town No. 1 Toyota Motor Corporation (56) References JP-A-52-104613 (JP, A) JP-A-53-56407 (JP A) Patent Akira 56-18019 (JP, A) JitsuHiraku Akira 58-20330 (JP, U)

Claims (1)

[Scope of utility model registration request] 1. A two-cycle internal combustion engine having an intake valve and an exhaust valve, which has two exhaust ports, a straight exhaust port and an exhaust port branched from the straight exhaust port, at the bottom surface of a cylinder head. A first ridge that separates the two exhaust ports from the intake side, and a second ridge that extends between the straight exhaust port and the exhaust port branching from the straight exhaust port. Separates the exhaust port from the intake side and guides the swirl flow of the backflow exhaust gas from the straight exhaust port to the lower part of the cylinder bore, and the second bulge is the backflow exhaust from the branched exhaust port toward the straight exhaust port. An exhaust port structure for an internal combustion engine, which guides gas.