JPH04132858A - Intake structure for engine - Google Patents

Abstract

PURPOSE:To improve ignitability of fuel-air mixture during low rotation running or low load running by providing two different intake ports different in the direction in which intake air flows in a cylinder. CONSTITUTION:In a compression stroke, after two intake ports 6 and 7 are closed, intake air in a combustion chamber 5 is compressed by a piston 4. Fuel is injected in intake air through a fuel injection valve 14 of the combustion chamber 5 to produce fuel-air mixture, and the fuel-air mixture is ignited by means of an ignition plug 15 for combustion. When, in an expansion stroke, the piston 4 is lowered to a given position, an exhaust valve 9 is opened, and combustion gas is exhausted in a combustion gas exhaust passage 20. When the piston 4 is further lowered to the vicinity of a bottom dead center, the two intake ports 6 and 7 are opened, intake air (fresh air) supercharged in the combustion chamber 5 through the two intake ports 6 and 7 is fed, and combustion gas remaining in the combustion chamber 5 is scavenged. This constitution improves ignitability of fuel-air mixture during low rotation running or low load running.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an intake structure for a two-stroke engine.

[Prior Art] In a conventional fuel-injected two-stroke engine, an intake port and an exhaust port open on the circumferential surface of the combustion chamber (the circumferential surface of the cylinder) near the bottom dead center, and both ports are opened by the side surface of the piston. It was meant to be opened and closed. Further, the injector was arranged directly facing the combustion chamber (see, for example, Japanese Patent Laid-Open No. 113820/1982). However, in such conventional fuel-injected two-stroke engines,
The upper part of the combustion chamber tends to become a dead space, so combustion gas remains in the combustion chamber, reducing volumetric efficiency. ■The heat load on the injector is high, reducing its durability. ■The fuel injection pressure of the injector increases. There was a problem in that the fuel was dispersed within the combustion chamber, resulting in poor ignitability of the air-fuel mixture at low rotation speeds or low loads.

Therefore, in order to solve the above-mentioned problem (2), a two-stroke engine has been proposed in which an exhaust port is opened on the ceiling surface (cylinder head) of a combustion chamber, and this exhaust port is opened and closed by an exhaust valve. In such a two-stroke engine, a so-called uniflow is formed in which both intake air and combustion gas flow unilaterally upward within the combustion chamber, so dead space is not generated and scavenging performance is improved.

[Problem to be solved by the invention] However, the inventors of the present application have solved the problem as shown in FIG.
A piston 102 is disposed within a cylinder 101, and an intake port 105 that communicates with an intake passage 106 is opened on the circumferential surface of the cylinder 101, while a combustion chamber 104 (cylinder 101)
Detailed information on the residual status of combustion gas for an upward flow uniflow two-stroke engine in which an exhaust port 107 communicating with an exhaust passage 109 opens on the ceiling surface 103 of the engine, and an exhaust valve 108 for opening and closing the exhaust port 107 is provided. An investigation revealed that near the bottom of the exhaust valve, near the upper periphery of the combustion chamber,
It has been found that combustion gas still remains in the shaded area S, such as near the center of the upper end surface of the piston and near the peripheral edge of the combustion chamber just above the intake port 105.

Further, in the conventional upward flow uniflow type two-stroke engine, the above-mentioned problems (1) and (2) have not been solved.

The present invention has been made in order to solve the above-mentioned conventional problems, and is capable of reliably scavenging air in the combustion chamber, increasing the durability of the injector, and at low speeds or low loads. An object of the present invention is to provide an upward flow uniflow two-stroke engine that can improve the ignitability of the air-fuel mixture.

[Means for Solving the Problems] In order to achieve the above object, the first invention has an intake port opened on the circumferential surface of the cylinder, and an exhaust port opened and closed on the ceiling surface of the cylinder that is opened and closed by an exhaust valve. , provides an intake structure for an engine of an upward flow uniflow type two-stroke engine, characterized in that two types of intake ports are provided with different intake air inflow directions into the cylinder.

In a second invention, in the first invention, two types of intake ports are arranged in the vertical direction, and the intake port arranged on the upper side is
To provide an intake structure for an engine, characterized in that the direction of intake air flowing into a cylinder is deviated upward from an intake port disposed below.

A third invention is based on the second invention, in which the engine is of a fuel injection type, a sub-injector is provided in the intake pipe directly connected to the intake port arranged on the upper side, and fuel is injected only from the sub-injector at low load. To provide an engine intake structure characterized by the following.

A fourth invention provides the intake structure for an engine according to the third invention, characterized in that during low load, fuel injection is performed after the exhaust valve is closed.

[Operations and Effects of the Invention] According to the first invention, the direction of inflow of intake air into the cylinder of each intake port can be individually directed to a region where combustion gas tends to remain. Therefore, the scavenging performance in the combustion chamber is improved, and the volumetric efficiency is increased.

According to the second invention, the same operation and effect as the first invention can be obtained.

Furthermore, since the intake port located on the upper side (hereinafter referred to as the upper intake port) is formed so that the direction of intake air flowing into the cylinder is deflected upward, the exhaust valve is particularly prone to retain combustion gas. Air is effectively scavenged near the bottom surface or at the upper periphery of the combustion chamber. In addition, the upper part of the combustion chamber is sufficiently filled with fresh air due to the flow of intake air rising within the combustion chamber.

Therefore, volumetric efficiency is increased. Additionally, cooling of the exhaust valve or cylinder head is promoted.

Here, when the injector is provided on the ceiling surface of the combustion chamber, the fuel particles injected from the injector collide with the intake air flowing in from the upper intake port, so that vaporization of the fuel is promoted. In addition, since the vaporized fuel tends to gather around the spark plug, the air-fuel mixture becomes stratified, and the ignitability of the air-fuel mixture at low rotation speeds or low loads is improved.

In addition, the intake port that is preferably located on the lower side (hereinafter referred to as
If this is called a lower intake port) and is opened horizontally or slightly downward, scavenging near the upper end of the piston can be promoted, and cooling of the piston can be promoted.

According to the third invention, the same operation and effect as the second invention can be obtained.

Furthermore, at low loads, fuel is supplied only from the upper intake port, so the fuel concentrates around the spark plugs, stratifying the mixture around the spark plugs, and igniting the mixture at low speeds or low loads. Sexuality is enhanced. In addition, under high load, fuel is injected from the main injector,
Of course, a nearly uniform air-fuel mixture is formed within the combustion chamber, increasing engine output.

Additionally, by installing the main injector in the intake system, it is possible to reduce the thermal load on the injector, reduce the fuel injection pressure, and ensure sufficient contact time (vaporization time) between the fuel and intake air. It can promote vaporization of fuel.

According to the fourth invention, the same operation and effect as the third invention can be obtained.

Furthermore, under low load conditions, fuel injection is performed after the exhaust valve is closed, which further promotes stratification and prevents fuel from leaking into the exhaust port.

[Example] Examples of the present invention will be specifically described below.

<First Example> Hereinafter, a first example of the invention according to claims 1 and 2 will be described.

As shown in FIG. 1, the two-stroke engine GE is provided with a cylinder block 1 and a cylinder head 2 fastened to the upper side of the cylinder block 1. As shown in FIG. A cylinder 3 is disposed within the cylinder block l, and a piston 4 is fitted into the cylinder 3 so that it can freely reciprocate in the cylinder axial direction between top dead center and bottom dead center. ing. Here, a combustion chamber 5 is defined by the lower end surface of the cylinder head 2, the inner peripheral surface of the cylinder 3, and the upper end surface of the piston 4.

At a position slightly above the upper end surface of the piston 4 at the bottom dead center position (FIG. 1 shows this state), a lower intake port 6 opens horizontally on the circumferential surface of the cylinder 3. An upper intake port 7 opens diagonally upward on the cylinder peripheral surface slightly above the lower intake port 6, as will be explained later. and both intake ports 6
．． 7 is adapted to be opened and closed by the side surface of the piston 4.

Further, an exhaust port 8 is opened on the ceiling surface of the combustion chamber 5 (lower surface of the cylinder head 2), and this exhaust port 8 is connected to an exhaust valve 9.
It is designed to be opened and closed by. The exhaust valve 9 is opened and closed at predetermined timing by an exhaust valve cam 13 attached to the camshaft 12 via the HLAII.

Here, in the stroke in which the piston 4 rises (hereinafter referred to as a compression stroke), after both intake ports 6.7 are closed, the intake air in the combustion chamber 5 is compressed by the piston 4, and the ceiling of the combustion chamber 5 is Fuel is injected into intake air from a fuel injection valve 14 provided on the surface to form an air-fuel mixture, and this air-fuel mixture is ignited and combusted by a spark plug 15.

In the stroke in which the piston 4 descends after the top dead center (hereinafter referred to as the expansion stroke), the piston 4 is pushed down by the pressure generated by the combustion of the air-fuel mixture, and this work is transferred via the connecting rod I6 and the crank pin 17. The rotational power of the crankshaft 18 is converted into rotational power. Further, in the expansion stroke, when the piston 4 descends to a predetermined position, the exhaust valve 9 is opened and combustion gas is discharged into the exhaust passage 20 via the exhaust port 8. When the piston 4 further descends to near the bottom dead center, both intake ports 6.7 are opened, and supercharged intake air (fresh air) is supplied from both intake ports 6.7 into the combustion chamber 5.
The combustion gas remaining inside is scavenged. At this time, both the intake air and the combustion gas form a uniflow that flows unidirectionally upward.

In order to supply intake air into the combustion chamber 5, an intake passage 21 is provided which communicates with both intake ports 6.7.The intake passage 21 is connected to an accelerator pedal (not shown) in order from the upstream side. A throttle valve 22 for supercharging intake air and a Roots-type supercharger 23 for supercharging intake air are interposed.

As shown in FIG. 2, the lower intake port 6, which has a relatively large opening area, opens in the horizontal direction. Therefore, the intake air flowing into the combustion chamber 5 from the lower intake port 6 basically crosses the inside of the combustion chamber 5 horizontally, collides with the inner peripheral surface of the opposite cylinder, and then forms an upward flow. It is supposed to be done.

On the other hand, the upper intake port 7 has a relatively small opening area, opens downward at an appropriate angle θ with respect to the vertically upward direction (cylinder axis direction), and opens toward the approximate center of the lower surface of the exhaust valve 9. It opens diagonally upward. Therefore, the intake air flowing into the combustion chamber 5 from the upper intake port 7 is
Basically, a flow is formed that crosses the inside of the combustion chamber 5 diagonally upward and collides with the lower surface of the exhaust valve 9.

The flow or behavior of intake air, fuel, and combustion gas in the expansion stroke and compression stroke will be described below with reference to FIGS. 2 and 4.

In the expansion stroke, as the piston 4 descends, the exhaust valve 9 (exhaust port 8) is first opened (curve CZ), and relatively high-pressure combustion gas in the combustion chamber 5 flows to the exhaust port 8 under its own pressure. and flows out into the exhaust passage 20.

Next, the upper intake port 7 is opened (curve G3), and intake air (fresh air) flows into the combustion chamber 5 from the + side intake port 7.

This intake air crosses the inside of the combustion chamber 5 obliquely upward and passes through the exhaust valve 9.
or the ceiling of the combustion chamber 5. At this time,
The vicinity of the lower surface of the exhaust valve 9 or the vicinity of the upper peripheral edge of the combustion chamber 5, where combustion gas tends to remain in the conventional two-stroke engine, is reliably scavenged. Moreover, cooling of the exhaust valve 9 is promoted, and its durability is enhanced.

When the piston 4 further descends, the lower intake port 6 is opened (curve G), and intake air flows into the combustion chamber 5 from the lower intake port 6. This intake air horizontally traverses the inside of the combustion chamber 5 along the upper end surface of the piston 4, collides with the inner peripheral surface of the opposite cylinder, and heads upward. At this time, scavenging is reliably performed near the center of the upper end surface of the piston 4 or near the lower peripheral edge of the combustion chamber 5, where combustion gas tends to remain in the conventional two-stroke engine. Further, cooling of the upper end surface of the piston 4 is promoted. Note that, at this time, the scavenging by the upper intake port 7 is of course continuing.

When the piston 4 begins to rise during the compression stroke after bottom dead center, the exhaust valve 9 (exhaust port 8) is closed (
Curve GO0 Note that fuel injection from the injector 14 is started at an appropriate time.

Next, the lower intake port 6 is closed (curve G2),
After this, the upper intake port 7 is open for a while (curve G3). In this way, during the period when only the upper intake port 7 is open, the supercharged intake air flowing into the combustion chamber 5 from the upper intake port 7 is pressed against the ceiling surface of the combustion chamber 5 by the upward flow, and the combustion The upper part of the chamber 5 is filled with intake air at a high density. At this time, the fuel particles injected downward from the injector 14 violently collide with the rising intake air, so that vaporization of the fuel particles is promoted. Since the vaporized fuel stays in the upper part of the combustion chamber 5 along with the rising intake air, a relatively rich air-fuel mixture is formed around the spark plug 15 (see Figure 1), and at low rotation speeds or low loads. The ignitability of the air-fuel mixture is improved.

When the piston 4 further rises, the upper intake port 7 is closed (curve G3).

Thereafter, when the piston 4 reaches near top dead center, the air-fuel mixture is ignited by the spark plug 15 (see Figure 1).
The piston 4 is pushed down by the pressure of the combustion gas, and the above-mentioned strokes are repeated.

As described above, according to the first embodiment, the air inside the combustion chamber 5 can be reliably scavenged, and the ignitability of the air-fuel mixture can be improved during low rotation or low load.

Second Embodiment> The second embodiment according to the invention of claims 3 to 4 will be described below, but since the second embodiment basically has the same configuration and function as the first embodiment, To avoid duplication, only the differences from the first embodiment will be explained.

As shown in FIG. 3, in the second embodiment, both intake ports 6
．． A main injector 32 is provided in the intake passage 2I on the upstream side of the branch to the main injector 7.

A sub-injector 31 is provided in the intake pipe 7a which is directly connected to the upper intake port 7 on the side of the upper intake port 7 from the branch part.

In this way, since both injectors 31 and 32 are installed in the intake system, the fuel injection pressure of both injectors 31 and 32 can be reduced. Also, both injectors 3
1.32 heat load is reduced and their durability is increased. Furthermore, since the contact time between the fuel and the intake air becomes longer, vaporization of the fuel is promoted.

In the above configuration, fuel is injected only from the sub-injector 31 during low rotation and low load. Fuel injection in this case is started immediately after the exhaust valve 9 (exhaust port 8) is closed. Therefore, at low engine speeds and low loads, the fuel concentrates in the upper part of the combustion chamber 5, the air-fuel mixture around the spark plug becomes stratified, and stratified combustion occurs, thereby improving ignition performance.

On the other hand, during high rotation and high load, the main injector 32
Fuel injection is performed only from the injectors 31 and 32 or from both injectors 31 and 32. In this case, the fuel injection angle is advanced within a range that does not cause fuel blow-through. Therefore, a substantially uniform air-fuel mixture is formed in the combustion chamber 5, and uniform mixed combustion is performed, so that the engine output is increased.

It goes without saying that the main injector may be provided on the ceiling surface (cylinder head) of the combustion chamber 5.

[Brief explanation of drawings]

FIG. 1 is an explanatory elevational cross-sectional view of a two-stroke engine showing a first embodiment of the present invention. FIG. 2 is a schematic diagram showing an elevational cross section around the combustion chamber of the engine shown in FIG. 1. FIG. 3 is a schematic diagram showing an elevational cross section around the combustion chamber of a two-stroke engine showing a second embodiment of the present invention. FIG. 4 is a diagram showing the characteristics of the opening/closing timing of the intake port and the opening/closing timing of the exhaust valve with respect to the crank angle. FIG. 5 is an explanatory elevational cross-sectional view of the vicinity of the combustion chamber of a conventional upward flow uniflow two-stroke engine. CE...Engine, ■...Cylinder block, 2.
... Cylinder head, 3... Cylinder, 4... Piston, 5... Combustion chamber, 6... Lower intake port, 7...
...Upper intake port, 7a...Intake pipe, 8...Exhaust port, 9...Exhaust valve, 14...Injector, 1
5... Spark plug, 21... Intake passage, 31...
Sub-injector, 32...main injector.

Claims (4)

[Claims] (1) In an upward flow uniflow two-stroke engine in which the intake port opens on the circumference of the cylinder and the exhaust port opens and closes on the ceiling of the cylinder, which is opened and closed by an exhaust valve, the direction of intake air flowing into the cylinder is different. An engine intake structure characterized by having two types of intake ports. (2) In the engine intake structure according to claim 1, the two types of intake ports are arranged in the vertical direction, and the intake port arranged on the upper side is arranged on the lower side in the direction of intake air flowing into the cylinder. An engine intake structure characterized by being formed so as to be deflected upward from the intake port. (3) In the engine intake structure according to claim 2, the engine is of a fuel injection type, and a sub-injector is provided in the intake pipe directly connected to the intake port arranged on the upper side,
An engine intake structure characterized in that fuel is injected only from a sub-injector at low loads. (4) The engine intake structure according to claim 3, wherein during low load, fuel injection is performed after the exhaust valve is closed.