JPH11223127A - Spark ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark ignition type internal combustion engine to generate combustible air-fuel mixture around an ignition plug through rapid vaporization and mixture of fuel, fuel dispersing ability of fuel during high load and an air utilization factor are ensured with combustion stability during low load being ensured. SOLUTION: An ignition plug 30 is disposed approximately in the central position of a cylinder 24, and a combustion chamber 31 consists of a recess- shaped cavity 22 formed in the top surface of a piston 21. A fuel injection valve 23 is arranged away from the central axis of the cylinder 24. Fuel spray formed in a flat as seen from the jet nozzle 23a of a fuel injection valve 23, disposed in a state to incline based on the central axis of the cylinder 24, in the central axis direction along an jet axis, and in a fan-form shape as seen along the central axis of the cylinder is jetted so as to effect ignition and combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark ignition type internal combustion engine that draws air into a cylinder, compresses the intake air with a piston, and directly ignites and burns the fuel by directly injecting the fuel into the cylinder.

[0002]

2. Description of the Related Art In a conventional spark ignition engine, fuel is mainly supplied to an intake pipe by a carburetor or an injection valve, mixed with air in advance, and then sucked, ignited, and burned in a cylinder. Since the mixture is adjusted to a concentration within the flammable range, the load is usually adjusted by controlling the intake air amount, that is, by using a throttle valve. Therefore, work is required in the gas exchange process, and fuel efficiency is poor in a frequently used partial load, for example, in an automobile engine. Further, the specific heat ratio of the air-fuel mixture adjusted to the flammable range is small, which is disadvantageous in terms of thermal efficiency. On the other hand, a system has been proposed in which air is sucked, fuel is directly injected into a cylinder to ignite and burn (Japanese Utility Model Laid-Open No. 1-173416). this is,
At low load, fuel is injected at the end of the compression stroke and the spark plug 3
In this system, fuel is collected and burned to zero, and at high load, fuel is injected during an intake stroke, and fuel and air are mixed well to ignite and burn. In this case, since the load can be adjusted only by the fuel injection amount, the work in the gas exchange process becomes unnecessary, and the fuel efficiency is good even at the partial load. Further, since the ratio of air is high, the specific heat ratio is large, and the thermal efficiency is high.

[0003] However, it is difficult for this combustion method to produce a proper air-fuel mixture. That is, the fuel must be collected near the spark plug at low load, and the fuel must be dispersed at high load to prevent the rich mixture from collecting around the spark plug. If the air-fuel mixture around the spark plug is thick, it causes misfire, smoldering of the plug, generation of smoke, and the like. Also, unlike diesel,
Since combustion proceeds mainly by flame propagation, it is necessary to quickly vaporize and mix the fuel.

[0004]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art, in which fuel is quickly vaporized and mixed to form a combustible air-fuel mixture around a spark plug, and combustion stability at low load is reduced. It is an object of the present invention to provide a spark ignition type internal combustion engine capable of ensuring fuel dispersibility under high load and air utilization rate while maintaining performance.

[0005]

According to a first aspect of the present invention, there is provided a spark ignition type internal combustion engine in which fuel injected from a fuel injection valve into a combustion chamber is ignited by a spark plug. A spark plug is arranged at the center of the inner wall surface of the head and a fuel injection valve is arranged at a peripheral portion of the inner wall surface of the cylinder head, and a cavity is formed on the top surface of the piston from below the fuel injection valve to below the ignition plug, The cavity has a wall surface extending upward from the bottom surface of the cavity at an end of the cavity on the spark plug side and extending transversely to a plane including the fuel injection valve and the cylinder center axis, and the wall surface of the cavity is a piston top surface. Extends along an arc centered on a point in the cavity below the fuel injection valve, and the curvature of the cavity wall surface extending in the arc shape The radius is the same as or smaller than the distance from the injection port of the fuel injector to the cavity wall located below the spark plug, and the cavity wall is inclined so that the upper portion protrudes into the cavity. When viewed along the injection axis, the fuel injector sprays a flat fuel spray when viewed along the cylinder center axis, and forms a fan-shaped fuel spray when the engine is operating at a low load. .

In the second invention, in the first invention,
The vertical cross section of the cavity wall has an arc shape.

[0007] In the third invention, in the first invention,
The bottom surface of the cavity is formed flat.

[0008] In a fourth invention, in the first invention,
The fuel injection timing is advanced as the engine load increases.

According to a fifth aspect, in the first aspect,
The injection port of the fuel injection valve has a slit shape.

In the spark ignition type internal combustion engine according to the present invention, the fuel spray ejected from the injection valve has a flat shape when viewed along the injection axis and a fan shape when viewed along the cylinder center axis. By having a shape,
The fuel can be quickly dispersed in the cylinder. Since this flat fan-shaped spray easily entrains the surrounding air, when the fuel is injected in the compression stroke, the air heated to a high temperature by the compression is quickly taken in, and vaporization and mixing are quick. Further, the air entrained by the spray deprives the momentum of the spray, so that the flying speed of the spray is reduced and the spray length is shortened. Therefore, even if the injection timing is advanced, the fuel does not wet the cylinder wall, and conversely, even if the injection timing is delayed, the piston surface is not covered with the liquid film.

During low engine load operation, fuel spray is injected into the cavity on the top surface of the piston. This spray is easily guided to the spark plug and forms a combustible mixture. That is,
Since the spray spreads almost radially and collides with the cavity wall, the radius of curvature of the cavity wall at the position where the spray collides is (radius of curvature) ≦ (distance from the injection hole of the fuel injection valve to the inner wall of the cavity below the spark plug). If you do,
The collision angle of the spray becomes obtuse, and the spray opened in a fan shape gathers at the spark plug position, so that even a small amount of fuel can be efficiently burned. Further, since the upper part of the cavity wall is projected toward the inside of the cavity, the fuel does not flow out of the cavity. As a result, the flame does not extinguish and the combustion efficiency is good.

An embodiment of the present invention will be described below with reference to the drawings.

[0013]

1 to 4 show a first embodiment of the present invention.
In the fuel injection valve, the needle valve 1 is slidably fitted into a valve hole 6 formed in the base end face of the valve body 2.
A coil spring 5 is attached to the base end of the coil spring 5. A conical valve seat 8 is provided at the distal end of the valve hole 6 with which the conical distal end 7 of the needle valve 1 contacts, and a slit-shaped opening from the valve seat 8 to the distal end surface of the valve body 2. An injection hole 4 is provided. A sack portion 3 is provided between the slit-shaped injection hole 4 and the valve seat portion 8, and the needle valve 1 is provided.
An annular pressure chamber 12 is formed in the valve element 2 located around the boundary between the cylindrical main body and the conical tip 7. The distal end of the fuel supply passage 11 drilled at the base end of the valve body 2 is
It communicates with the outer peripheral surface of the pressure chamber 12. Needle valve 1 and valve body 2
An annular connection passage 13 connected to the pressure chamber 12 is provided therebetween. Needle valve 1 through fuel supply passage 11 and connection passage 13
When the pressure of the fuel acting on the tip 7 of the needle rises, the needle valve 1
Is disengaged from the valve seat portion 8 of the valve hole 6 against the coil spring 5.

For this reason, in the fuel injection valve according to the first embodiment, the pressure chamber 12 communicates with the injection hole 4 through the gap between the tip 7 of the needle valve 1 and the valve seat 8 of the valve hole 6. The valve is configured to open. The fuel is supplied to the slit-shaped injection hole 4 when the valve is opened by the fuel passage 11, the pressure chamber 12, the connection passage 13, and the gap between the distal end portion 7 of the needle valve 1 and the valve seat portion 8 of the valve hole 6. It constitutes a passage. The needle valve 1 can be directly lifted and opened using an electromagnetic force or the like in addition to the fuel pressure. Further, the slit-shaped injection hole 4 has an outer end 10 on the outer peripheral side of the valve body 2 and an inner peripheral side of the valve body 2, that is, an inner end 9 on the side of the sack portion 3, and the outer end 10 and the inner end 9 It is composed of a straight or arcuate passage.

Here, the inner end 9 of the slit-shaped injection hole 4
The range of the width W (distance between opposed sides) is 0.05 mm or more and the range of 0.
It is 24 mm or less. The optimal numerical range is from 0.06 mm to 0.20 mm. As a result, the fuel injected from the slit-shaped injection hole 4 becomes flat and fan-shaped, and as the liquid film moves away from the slit-shaped injection hole 4, its thickness decreases and the contact area with the surrounding air increases. The liquid film is torn off by the surrounding air, and rapidly changes to a fine spray. The average particle size ds of the spray obtained in this way
FIG. 5 shows the relationship between the width and the width W. As is apparent from FIG.
Becomes larger, the average particle size ds becomes larger. This is because the greater the width W, the greater the thickness of the injected fuel liquid film. FIG. 5 shows the results obtained from various experiments and the like. As is apparent from FIG.
When it exceeds mm, the average particle size ds of the spray increases rapidly. The width W at which the average particle diameter ds of the spray is maintained at a substantially uniform value is 0.06 mm or more and 0.20 mm or less.

Further, since the injection valve of the present invention has a large spray angle, there is an advantage that the spray length can be reduced as compared with the conventional hole nozzle. Since many spark ignition engines have a small cylinder diameter, the distance from the nozzle to the wall is short. The spray length should be appropriately short so as not to wet the wall with fuel. The spray grows with almost the same momentum. In the nozzle according to the first embodiment of the present invention, if the width W is determined, the momentum per unit spray angle is determined. Therefore, even if the spray angle is changed, the spray length does not change, but the spray length per flow rate is By increasing the spray angle, the spray length is reduced. Since the injection period is limited in the engine, the spray length per flow rate is important. FIG. 6 compares the spray length with a hole nozzle having the same flow rate. As the spray angle increases, the spray length decreases. For example, when the spray angle is set to 90 degrees, the spray length is less than half that of a conventional single-hole nozzle. It is 70% compared to a 5-hole nozzle. Here, it is compared with one fan-shaped spray, but it can be further shortened by providing a plurality of slits.

In the first embodiment of the present invention, such a fuel injection valve is provided in the internal combustion engine shown in FIGS. The internal combustion engine includes an intake port 27, an intake valve 28, a spark plug 30, an exhaust port (not shown), a cylinder head 25 equipped with an exhaust valve, and a cylinder 24 and a piston 21 reciprocally inserted into the cylinder 24. I have. A plurality of piston rings 29 are provided on the side surface of the piston 21 to prevent gas from flowing from the combustion chamber 31. The fuel injection valve 23 is attached to the cylinder head 25 on the intake valve 28 side so that the nozzle tip 23a is inclined substantially toward the cylinder center axis. The first embodiment has two intake valves, and the fuel injection valve 23 is located between the intake valves 28. The spray flow is flat in a plane including the central axis of the cylinder 24, in other words, flat when viewed along the injection axis, and in a plane substantially perpendicular to the central axis of the cylinder 24, in other words, in a fan shape. When viewed along the cylinder center axis, the fuel is ejected so as to expand in a fan shape.
Squirts slightly downward. The injection direction differs depending on the engine, but generally ranges from 20 degrees to 60 degrees below the cylinder.

On the top surface 21a of the piston 21, a cavity 2 having a nozzle tip 23a and a spark plug 30 at substantially both ends is provided.
2 is formed by opening it into the combustion chamber 31. Cavity 2
Reference numeral 2 denotes a compression top dead center, which is a depth at which the gap 30a of the ignition plug 30 is approximately at the center of the cylinder head 25 and the bottom surface of the cavity 22. The width of the cavity 22 is larger than the width of the spray projected on a plane perpendicular to the cylinder center axis when the spray tip reaches the center of the cylinder. That is, the spray in the space in the combustion chamber at this time is contained in the cavity 22 by the rise of the piston 21. Also,
As shown in FIG. 9, at least the spark plug 30 side of the wall surface of the cavity 22 has a concave curvature with respect to the cavity 22. The radius of curvature R is set to (radius of curvature R) ≦ (distance L from the injection hole of the fuel injection valve 23 to the cavity wall surface).

Air is compressed into the combustion chamber 31 in the compression stroke from the bottom dead center position where the piston 21 completes the intake to the top dead center. When fuel is ejected from the injection hole of the injection valve 23 in the compression process, the spray particles are flattened when projected onto a plane including the cylinder center axis and the nozzle 23a, as shown in FIG. When projected, they scatter in a fan shape and substantially symmetrically with respect to the spark plug 30. Since the fuel spreads rapidly after leaving the injection hole, the spray particles collide with the wall of the cylinder 24 at high speed,
The wall of No. 2 is not wet with a large amount of liquid spray. Also,
Because of its flat shape, it mixes quickly with the surrounding high-temperature air, so even if sensible heat or latent heat is taken for evaporation, the temperature of the mixture in the spray does not drop so much. The spray becomes a flow that winds upward and inward of the cavity 22 by the wall surface of the cavity 22. Combined with the rise of the piston 21, a combustible mixture is formed around the ignition plug 30 before the compression top dead center. The flame ignited by the ignition plug 30 burns by flame propagation.

At this time, due to the squish flow between the cavity 22 and the piston top surface 21a, the air-fuel mixture is contained in the cavity 22 and is prevented from scattering outside the combustion chamber.
The flame formed by the spark plug 30
Develop within. Therefore, there is no fear of misfiring or extinguishing. Furthermore, since the spray in the first embodiment of the present invention is a fan-shaped spray, the unevenness in concentration is small, and the flame propagation is not interrupted.
When the load is low and the load is small,
The injection timing is delayed, and the fuel is ignited before the fuel spreads.
On the other hand, when the load is high and the injection amount is high, the injection timing is advanced,
It is good to avoid that the rich air-fuel mixture collects too much in the spark plug 30.

In the internal combustion engine of the first embodiment, when the injection timing is delayed, as shown in FIGS. 9 and 10, the spray collides with the cavity 22 relatively early, but the spray is flat and the Since the bottom surface of the fan 22 has a fan-like shape, heat is effectively received from the piston 21 and the air, and vaporization and mixing can be performed quickly. Therefore, combustion in which the time from injection to ignition is shortened is possible. Further, if the curvature R of the cavity is set to (radius of curvature R) ≦ (distance L from the tip of the nozzle to the cavity wall surface), the fuel gathers at the spark plug 30 along the cavity wall surface of the curvature R, so that less fuel is used. Driving is possible.
On the other hand, when the injection timing is advanced, the spray of the first embodiment has a short spray length, so the time until collision with the cavity is long. However, since the spray is dispersed in a fan shape and is flat, Effective heat is obtained from the surrounding air, and there is no delay in evaporative mixing. Then, as shown in FIG. 11, the initially injected fuel collides with the cavity 22 and then diffuses in the air, so that a rich mixture is not collected in the ignition plug 30 and stable ignition is possible.

Further, when the load further increases and is close to the full load, it is possible to inject fuel not only in the compression stroke but also in the intake stroke. At this time, the spray length is short,
Since the spray has a low penetration force, even if the piston 21 goes down, it does not wet the wall surface of the cylinder 24 and is dispersed in the cylinder by the flow of the intake air, thereby increasing the air utilization.
In the internal combustion engine according to the first embodiment of the present invention, a stable combustible air-fuel mixture is formed in the ignition plug 30 regardless of the magnitude of the load as described above. Provides excellent performance as an internal combustion engine.

[Second Embodiment] In a second embodiment of the present invention, as shown in FIG. 12, the vertical wall surface of the cavity 22 has an R shape, and the piston top surface 21a protrudes from the inner wall of the cavity 22. It has a lip shape. Other fuel injection valve 23, spray shape, piston 2
1 and the like are the same as in the first embodiment.

In the second embodiment of the present invention having the above-described structure, the spray changes its direction after collision with the wall surface of the cavity 22 as in the first embodiment. Has a round shape (radius of curvature r ₁ ), so that the fuel flows in such a manner as to wind up toward the inside of the cavity 22. For this reason, the fuel is less likely to flow out of the cavity 22, and the flame after ignition is less likely to flow out of the cavity 22 to be cooled and extinguished. Also,
There is an advantage that the combustion period is shortened because strong turbulence is created in combination with the squish flow.

[Third Embodiment] In a third embodiment of the present invention, the cavity 22 has two stages, and FIGS.
As shown in FIG. 4, a cavity 22a is further formed inside a shallow cavity 22b. Other fuel injection valves 23, spray shapes, pistons 21 and the like are the same as those in the first embodiment.

When the cavity 22 according to the third embodiment of the present invention is used, the fuel can be more easily ignited when the load is low.
At high load, the fuel can be more diffused and burned. That is, if the injection timing is delayed at the time of the small injection amount as shown in FIGS. 15 and 16, the injected fuel enters the inner cavity 22b, is bent upward through the inner wall surface, and reaches the spark plug 30. Therefore, the fuel concentrates on the spark plug 30 without being excessively dispersed,
Ignition and combustion are possible with very little fuel. on the other hand,
When the load is high, the injection timing is advanced. Therefore, the fuel is
7, the outer large cavity 22 as shown in FIG.
b and the inner cavity 22a. The outer cavity 22b is bent upward and inward to reach the spark plug 30 as in the first embodiment.
The fuel a is bent downward and is dispersed in the cavity 22 without reaching the spark plug 30. As a result, a stable combustible air-fuel mixture is formed in the ignition plug 30 irrespective of the magnitude of the load, and excellent performance is provided, for example, as an automotive internal combustion engine having a large load variation.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a fuel injection valve according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing the fuel injection valve according to the first embodiment of the present invention.

FIG. 3 is a longitudinal sectional view showing a spray state of a fuel injection valve according to the first embodiment of the present invention.

FIG. 4 is a longitudinal sectional view showing a spray state of a fuel injection valve according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an average particle diameter and a width of a spray of a fuel injection valve in the first embodiment.

FIG. 6 is a diagram illustrating a relationship between a spray angle and a spray length ratio of a fuel injection valve according to the first embodiment.

FIG. 7 is a plan view showing the internal combustion engine according to the first embodiment.

FIG. 8 is a longitudinal sectional view showing the internal combustion engine according to the first embodiment.

FIG. 9 is a plan view showing a spray state of the internal combustion engine in the first embodiment.

FIG. 10 is a longitudinal sectional view showing a spray state of the internal combustion engine according to the first embodiment.

FIG. 11 is a longitudinal sectional view showing a spray state of the internal combustion engine according to the first embodiment.

FIG. 12 is a partial cross-sectional view of a piston in an internal combustion engine according to a second embodiment.

FIG. 13 is a plan view showing an internal combustion engine according to a third embodiment.

FIG. 14 is a longitudinal sectional view showing an internal combustion engine according to a third embodiment.

FIG. 15 is a plan view showing a spray state of an internal combustion engine according to a third embodiment.

FIG. 16 is a longitudinal sectional view showing a spray state of an internal combustion engine according to a third embodiment.

FIG. 17 is a plan view showing a spray state of an internal combustion engine according to a third embodiment.

FIG. 18 is a longitudinal sectional view showing a spray state of an internal combustion engine in a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Needle valve 2 ... Valve element 3 ... Sack part 4 ... Injection hole 5 ... Coil spring 6 ... Valve hole 7 ... Tip part 8 ... Valve seat 9 ... Inner end 10 ... Outer end 21 ... Piston 22, 22a, 22b ... Cavity 23 ... fuel injection valve 24 ... cylinder 30 ... spark plug 31 ... combustion chamber

Claims (5)

[Claims] In a spark ignition type internal combustion engine in which fuel injected from a fuel injection valve into a combustion chamber is ignited by an ignition plug, an ignition plug is disposed at a center portion of an inner wall surface of a cylinder head, and an inner wall surface of the cylinder head is provided. A fuel injection valve is arranged on the periphery of the piston, and a cavity is formed on the top surface of the piston from below the fuel injection valve to below the ignition plug, and the cavity is formed at the end of the cavity on the ignition plug side from the bottom surface of the cavity. A wall extending upward and extending transversely to a plane including the fuel injection valve and the cylinder center axis, and the wall surface of the cavity extends along the top surface of the piston around a point in the cavity below the fuel injection valve. The radius of curvature of the cavity wall surface extending in an arc shape is located below the spark plug from the injection hole of the fuel injection valve. The distance to the cavity wall surface is equal to or smaller than the cavity wall surface, and the cavity wall surface is inclined so that its upper part protrudes into the cavity, and when viewed from the fuel injection valve along the injection axis. A spark ignition type internal combustion engine in which a fan-shaped fuel spray is injected when it is flat and viewed along the cylinder center axis, and the fuel spray is injected into the cavity during low engine load operation. 2. The spark ignition type internal combustion engine according to claim 1, wherein a vertical cross-sectional shape of the cavity wall has an arc shape. 3. The spark ignition type internal combustion engine according to claim 1, wherein the bottom surface of the cavity is formed flat. 4. The spark ignition type internal combustion engine according to claim 1, wherein the fuel injection timing is advanced as the engine load increases. 5. The spark ignition type internal combustion engine according to claim 1, wherein the injection hole of the fuel injection valve has a slit shape.