JPS59224416A - Combustion chamber structure of engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The "Futsutsu" is a three-valve type equipped with valves that open and close a partial port, a secondary port, and an exhaust port that each independently open into the combustion chamber. This relates to the structure of the combustion chamber in the engine.

(Prior Art) Conventionally, as shown in, for example, Japanese Utility Model Application No. 53-106505, in a three-valve engine in which a part of the boat, a secondary port, and an exhaust port are opened in the combustion chamber of the engine, - A guide wall protruding into the combustion chamber is provided along a part of the outer circumference of the next boat, and this guide wall causes the intake air introduced into the combustion chamber from some ports to swirl in the circumferential direction of the combustion chamber to strengthen the swirl. Such a combustion chamber structure is known.

In the above combustion chamber structure, intake air is introduced only from a part of the boat in low speed or low load areas to improve the intake air flow velocity, and the guide wall strengthens the swirl, promoting vaporization and atomization of the fuel and increasing the combustion speed. At the same time, intake air is also introduced from the secondary port at high speed or high load ranges to improve output.

However, in the above-mentioned proposed structure, a guide wall is formed on the cylinder head wall partially around the outer periphery of the boat, and the guide wall restricts the inflow of intake air in one direction, and the intake air flows in the opposite direction to the guide wall. When the amount of intake air increases, the guide wall becomes an obstacle to the flow of intake air and increases intake resistance, which poses a problem of inhibiting full-throttle output characteristics.

In addition, there is also a known technology in which the bottom surface of the cylinder head protrudes into the cylinder bore to generate squish flow as the piston rises to improve the combustion speed. The squish flow is not designed with this in mind, and the squish flow is formed by the bottom surface of the protrusion that has a guide wall formed simply to generate swirl, and in some cases, the generated squish flow causes There is a risk of weakening the swirl, and there is a problem in that the combustibility has not been sufficiently improved in the entire combustion chamber including the vicinity of the secondary port remote from the spark plug.

(Object of the Invention) In view of the above circumstances, the present invention aims to generate squish flow without increasing intake resistance (generating swirl and weakening this swirl) by using some ports formed in the swirl port. It is an object of the present invention to provide a combustion chamber structure for an engine that allows flame to grow toward the secondary port side and improves combustibility throughout the combustion chamber.

(Structure of the Invention) The combustion chamber structure of the engine of the present invention includes a partial port that introduces intake air in the entire operating range of the engine, a secondary port that introduces intake air in the high speed or high load range, an exhaust port, and each of the above-mentioned ports. In a three-valve engine equipped with a port that opens and closes one port, the second boat is used as a swirl port that introduces intake air in the tangential direction of the cylinder bore, and the second port serves as a swirl port for introducing intake air from the next port. A spark plug is disposed directly downstream of a part of the port in the direction, and a protrusion protruding toward the center of the cylinder bore is formed on the back surface of the spark plug by the wall surface of the cylinder head forming a combustion chamber, and the lower surface of the protrusion This forms a squish flow that causes the combustion gas ignited by the spark plug to flow toward the opposite side of the cylinder bore when the piston rises, and is characterized by generating the squish flow in a direction that promotes swirl.

(Example) Hereinafter, the present invention will be explained in detail with reference to the drawings. In the engine shown in FIGS. 1 and 2, 1 is a cylinder block, 2 is a cylinder head, 3 is a piston, and
4 indicates a combustion chamber formed by the cylinder block 1, cylinder head 2, and piston 3.

5 is a partial boat for intake that opens into the combustion chamber 4, 6 is the same (secondary port for intake, 7 is an exhaust port for exhaust), - secondary boat 5 is an opening on one side of the cylinder head 2. The secondary port 6 communicates with a secondary intake passage 9 which also opens on one side of the cylinder head 2, and the exhaust port 7 communicates with an exhaust passage 10 which opens on the flat side of the cylinder head 2. ing.

A primary intake valve 1], a secondary intake valve 12, and an exhaust valve 13 are arranged in the secondary port 5, secondary port 6, and exhaust port 7, which are seated on respective valve seats.

Furthermore, 14 is a spark plug, which is part of port 5 in the combustion chamber A.
The electrode portion faces directly downstream in the inflow direction of the intake air.

The shape of the combustion chamber 4, that is, the shape of the bottom surface of the cylinder head 2, is shown by contour lines in FIG. 3, and as shown in cross section in FIGS. The pent roof has a so-called bent roof shape with slopes on both sides, with the ridge line (deepest part) being formed. Ports 5 and secondary ports 6 are partially opened on one slope of the pent roof, and the other side slopes. An exhaust port 7 is opened on the surface facing the secondary port 6, and a spark plug 14 is disposed facing the secondary port 5.

The above-mentioned next port 5 opens at a position offset from the center of the combustion chamber 4 when viewed in plan, and introduces intake air from the tangential direction of the cylinder bore C (outer diameter of the piston 3) to create a swirl A.
It is installed in the swirl port that generates. The primary intake passage 8 connected to the main port 5- has a downstream portion curved outward when viewed from above, and the primary intake passage 8 connects to the port 5-.
A large amount of the intake air flowing down flows outside the stem lla of the primary intake valve 11, and partially flows into the outer peripheral side of the cylinder bore C from the port 5, increasing the generation of swirl A, and furthermore, reducing the inflow angle on the vertical cross section as much as possible. The angle of inclination is set small so as to be close to horizontal, and the intake air flows toward the outer circumferential surface of the cylinder bore C, thereby ensuring the generation of swirl.

On the other hand, the secondary intake passage 9 connected to the secondary port 6 is set to have a larger inclination angle than the secondary intake passage 8 so as to allow intake air to flow in along the cylinder bore axis direction in the vertical section. The port 6 is formed as a so-called output port so as to suppress the generation of swirl and introduce intake air.

Furthermore, 15 indicates a valve operating mechanism that opens and closes the secondary intake valve 11, secondary intake valve 12, and exhaust valve 13 at predetermined timing. At the same time, a valve actuating device 19 that disables the opening/closing operation of the secondary intake valve 12 is attached. This valve actuating device 19 uses an operation cam 20 to move up and down the fulcrum position of the hydraulic tappet 18 that constitutes the rocking fulcrum of the rocker arm 17. When the valve actuating device 19 is actuated, the rocker arm 17 moves up and down the fulcrum of the camshaft 16. In response to movement, the secondary intake valve 12 swings about the point of contact with the secondary intake valve 12 as a fulcrum, and the secondary intake valve 12 is held in a closed state by a pulp spring 21.

FIG. 6 shows the opening/closing timing of some ports 5, secondary ports 6, and exhaust ports 7 by the secondary intake valve 11, secondary intake valve 12, and exhaust valve 13, and the exhaust port 7 is opened during the latter half of the explosion stroke. It opens near the bottom dead center and closes near the top dead center. On the other hand, the - secondary port 5 opens before and after the exhaust port 7 closes near the top dead center, closes near the bottom dead center in the latter half of the intake stroke, and the secondary port 6 partially opens earlier (opens later) than the port 5. The opening area of the large-diameter secondary port 6 in the fully open state is larger than that of the small-diameter partial port 5.

Further, the valve actuating device 19 is actuated according to the engine speed and torque (load), and as shown in FIG.
In the low rotation (low load) region ■, the secondary intake valve 12 is kept closed by the operation of the valve actuator [9], and the combustion chamber 4 is supplied with air from the partial port 5 opened by the primary intake valve 11. However, in the high rotation (high load) region ■, the valve actuating device 19 does not operate and the secondary intake valve 12 opens and closes according to the movement of the camshaft 16, In addition to a portion of the intake air introduced from the port 5, the intake air from the secondary intake passage 9 is supplied to the combustion chamber 4 through the port 6. In addition, the reason why the boundary line of the switching region in FIG. 7 is set to be inclined with respect to the rotation speed is because even when the engine speed is high, the amount of intake air is small in the region where the torque (load) is low. This is because a sufficient amount of intake air can be secured by supplying only the next boat 5.

On the other hand, a part of the wall surface of the cylinder head 2 forming the combustion chamber 4 extends from the vicinity of the secondary port 5 to the vicinity of the exhaust port 7 at the back of the spark plug 14.
A protrusion 22 is formed that protrudes toward the center. The protrusion 22 is configured to form a squish flow B by its lower surface 22a, which causes the combustion gas ignited by the ignition glove 14 to flow toward the opposite side (toward the center) of the cylinder bore when the piston 3 rises. The amount of protrusion of the protrusion 22 gradually increases from the vicinity of the port 5, reaches a maximum at the back of the spark plug 14, and gradually decreases toward the exhaust port 7.

Further, the side surface of the protrusion 22 is formed into a curved guide surface 22b that smoothly guides the intake air from the secondary port 5 in the tangential direction of the cylinder bore.

Further, the lower surface 22a of the protrusion 22 forming the squish flow
The angle of inclination from the side to the guide surface 22b is steep and steep in the part on the port 5 side (right side in FIG. 4) near the ridgeline (center line) of the combustion chamber 4, whereas In the portion on the 7 side (left side in FIG. 5), the angle becomes gentler due to the distance from the above-mentioned ridgeline. For this reason,
The squish flow B in each part of the protrusion 22 heads toward the secondary port 6 on the opposite side of the cylinder bore, but its strength varies in magnitude, and in the steeply angled portion on the - secondary port 5 side, the squish flow exits from the lower surface 22a. At times, the squish flow becomes dispersed and weakens, but in the case of a gentler angle section on the exhaust port 7 side, there is less dispersion when exiting from the lower surface 22a, and the squish flow becomes stronger, and as a whole, the squish flow tends toward the exhaust port 7 side. , - is formed to back up the swirl A by the next port 5 without weakening it.

In addition, on the wall surface of the cylinder head 2, there are auxiliary protrusions 23 that protrude inwardly into the cylinder bore C between the secondary port 5 and the secondary port 6 and between the secondary boat 6 and the exhaust port 7, respectively. and 24 are formed. A squish flow is also formed by this auxiliary protrusion 23 , 24 , but this is relatively weak and does not disturb the large intake flow. It has the effect of reducing the volume and reducing the amount of residual unburned gas.

In addition, the spark plug 14 is disposed near the upper protrusion 22, and the squish flow B caused by the protrusion 22 directly acts on the electrode part of the spark plug 14 and scavenges this electrode part together with the swirl A. Improves ignitability.

In the above configuration, when the intake air amount is small at low speed or in a low load range, the secondary intake valve 12 is closed by the valve actuating device 19, so that the combustion chamber 4 is supplied with a sw/l from only the port 5. The intake swirl A is smoothly guided in the tangential direction of the cylinder bore C by the guide surface 22b of the protruding portion 220, passes through the spark plug 14 immediately downstream, and flows toward the exhaust port 7. It curves and flows into the secondary port 6, forming a spiral swirl A as a whole. Further, as the piston 3 rises, the squish flow B is generated by the lower surface 22a of the protrusion 22 without obstructing the swirl A, and when the intake air is ignited by the spark plug 14 before the top dead center, the spark plug 1
The flame ignited by the squish flow B is pushed toward the center of the cylinder bore C, promoting the growth of the flame in the direction of the secondary port 6, and improving the combustion speed at a position away from the spark plug 14. Combustion performance is improved and torque increases.

Also, when there is a large amount of intake air at high speed or in a high load range, -
In addition to the secondary boat 5, intake air is also supplied from the secondary port 6, and the generation of swirl in the intake air supplied from the secondary port 6 is suppressed, the filling efficiency of the intake air is improved, and high output is obtained.

That is, as shown in the full-open curve shown in FIG. 7, in a state where the secondary intake valve 12 is closed at low rotation speeds and only a portion of the intake air is taken by the boat 5, intake air is supplied with a high flow rate of swirl A and squish flow B. The generation of combustibility improves and a large torque is obtained. However, while the intake air amount increases as the rotation speed increases, the intake air shortage occurs due to the narrow passage area, and the torque decreases. The torque decreases after exceeding the peak, but at this time the secondary intake valve 12 is opened and intake air starts being supplied from the secondary port 6, and the torque increases, resulting in good torque characteristics over the entire operating range. can get.

The intake air supply from the secondary port 6 is controlled by the valve actuating device 19, and as shown by the imaginary line in FIG. However, similarly to the operation of the valve actuating device 19, the on-off valve 25 may be opened and closed in a low speed or low load range to obtain the switching characteristics shown in FIG. Also,
This switching characteristic is performed mainly according to the engine speed as shown in Fig. 7, or it may be performed mainly according to engine load fluctuations, and in either case, when the intake air amount is small, Intake air is supplied only through port 5 to improve the flow velocity, and when the intake air amount increases, intake air is also supplied from secondary port 6 to increase the filling amount (and improve output).

[Brief Description of the Drawings] Fig. 1 is a vertical sectional view of the main parts of an engine according to an embodiment of the present invention, Fig. 2 is a bottom view of the cylinder head, and Fig. 3 shows the shape of the combustion chamber of the cylinder head in a contour view. Figure 111g4 is a sectional view taken along line IV-IV in Figure 3, Figure 5 is a sectional view taken along line V-V in Figure 3, and Figure 6 shows the opening and closing timing of each boat. FIG. 7 is a characteristic diagram showing a switching region between a partial port and a secondary port together with a fully open curve. 1... Cylinder block 2... Cylinder head 3... Piston 4... Fuel
Baking chamber 5...-Next port 6...Secondary port 7
...Exhaust boat 8...-Secondary intake passage 9...Secondary, intake passage 10...Exhaust passage 11...-
Secondary intake valve 12...Secondary intake valve 13...Exhaust valve 14.l.Spark plug 15...Valve mechanism 1
9...Valve actuator 22...Protruding portion 22a...
・Bottom surface 22b...Guidance surface 25
...Open/close valve A...Swirl B
...Squish flow C...Cylinder bore Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 7 Engine U3 rotation speed

Claims (2)

[Claims] (1) Three valves consisting of a primary port that introduces intake air in all engine operating ranges, a secondary port that introduces intake air in high speed or high load ranges, an exhaust port, and valves that open and close each of the above boats. In the second engine, the secondary port is a swirl boat that introduces intake air in a tangential direction of the cylinder bore, and a spark plug is disposed immediately downstream of the primary port in the swirl direction of the intake air introduced from the secondary port, On the wall surface of the cylinder head that forms the combustion chamber, a protrusion is formed on the back surface of the spark plug that protrudes toward the center of the cylinder bore, and the lower surface of the protrusion directs the combustion gas ignited by the spark plug when the piston rises toward the opposite side of the cylinder bore. An engine combustion chamber structure that is characterized by forming a squish flow that flows to the side. (2) The engine combustion chamber structure according to claim (1), wherein the protrusion has a curved surface that smoothly guides intake air from the next port in the tangential direction of the cylinder bore.