JPS63109222A - Combustion chamber of gasoline engine - Google Patents

Abstract

PURPOSE:To securely suppress the generation of knocking and reduce unburned HC by throttling the opening part of a recessed part which forms a combustion chamber on the top part of a piston while partially expanding said opening part of an intake valve side. CONSTITUTION:A combustion chamber 6 is formed by providing a recessed part 5 which is opened toward the bottom face side of a cylinder head 4 on the top part of a piston 1. The opening area of the opening part of the recessed part 5 is throttled with respect to the inside of the recessed part 5. In the vicinity of the top dead center of the piston 1, an ignition plug 8 which is projectingly provided on the bottom face of the cylinder head 4 is inserted into the recessed part 5. The opening part of the recessed part 5 is partially expanded on an intake valve 10a side. Thereby, the generation of knocking can be securely suppressed while greatly reducing the generation of unburned HC.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a combustion chamber of a gasoline engine formed by providing a recess at the top of a piston.

[Prior Art] In a premixed gasoline engine that generates a combustion mixture outside the cylinder, it is necessary to increase the combustion rate to improve the combustion efficiency, and to take precautions against knocking. Also,
It is also necessary to reduce unburned HC emissions as well as NOx.

With conventional rapid combustion technologies, such as multi-point ignition, there is a risk that the air-fuel mixture will burn too vigorously, resulting in NOx
could not be expected to reduce much.

In order to reduce NOx in this type of engine, a large amount of E
It is necessary to perform GR.

In addition, in conventional combustion chambers, there is no strong turbulence in the air-mixture flow within the combustion chamber, so when combustion efficiency is increased, the maximum combustion temperature partially increases, and N.

The amount of X generated increased. In order to suppress local increases in maximum combustion temperature, it is effective to create strong turbulence within the combustion chamber to stir it, but this increases the amount of heat that escapes to the outside of the combustion chamber through the combustion chamber walls, increasing cooling loss accordingly. This leads to the problem of As a structure for generating a strong swirl within a combustion chamber, a structure is known in which a swirl is generated by the cooperation of a swirl port outside the combustion chamber and a recess that forms the combustion chamber provided at the top of the piston (Japanese Patent Application Laid-Open No. 1983-1992). −
145808). However, with this structure, in addition to the above problem of increased cooling loss, the provision of the swirl boat increases intake resistance in a high rotation range, resulting in a decrease in output.

In addition, an engine with a pre-chamber is an advantageous structure for reducing NOx, but the gas from the pre-chamber hits the wall of the combustion chamber with great force, increasing the amount of heat that escapes to the outside of the piston through the wall.
There is a problem that cooling loss is increased.

As a structure for suppressing the amount of heat dissipated from the top of the piston and reducing cooling loss, a structure is known in which the wall of the recess provided at the top of the piston is made of ceramic to insulate the inside of the combustion chamber (Japanese Patent Publication No. 56-616 No. Publication, Utility Model Publication No. 59-13
Publication No. 0046).

However, these proposals only disclose the use of ceramics, and do not mention any relation to the air mixture flow within the combustion chamber.

Furthermore, it is well known that generating squish flow is effective in suppressing knocking and increasing combustion speed. However, in order to improve the effect of squish, it is necessary to widen the squish area, but in the conventional structure, if the squish area is widened, the quench area also becomes wide at the same time, resulting in an increase in unburned HC.

Also, multi-valve engines (for example, 4-valve engines)
In this case, since there is not much freedom in the shape of the combustion chamber, it is difficult to make the squish area itself large, and it is often difficult to improve the combustion improvement effect due to squish.

Furthermore, in the case of a premixed gasoline engine (particularly in the case of a supercharged engine), if the ignition timing is advanced in order to increase combustion efficiency, spontaneous combustion occurs at the end portion, resulting in knocking. In order to prevent this, attempts have been made to cool the end gas with squish or the like, or to supply the air-fuel mixture in layers. However, if this is done, the amount of unburned HC at the end portion will inevitably increase, which will worsen the exhaust gas. Moreover, retarding the ignition timing more than necessary will lead to deterioration of fuel efficiency.

In order to solve the various problems mentioned above, the following structure has been previously proposed by the present applicant, although the application has not yet been published. That is, in a premixed gasoline engine, a combustion chamber is formed by providing four parts at the top of the piston that open toward the lower surface of the cylinder head, and the opening area of the opening of the recess is narrowed relative to the inside of the recess. This structure is such that a spark plug protruding from the lower surface of the cylinder head is inserted into the recess near the top dead center of the piston. By constricting the concave opening, a wide squish area is achieved, suppressing knocking, and the constriction generates strong turbulence in the air-fuel mixture flowing into the combustion chamber, increasing combustion efficiency and reducing NOx. be done. Furthermore, in the post-ignition expansion stroke, the jet flame from the combustion chamber is sped up at the throttle section and rapidly propagated to every corner around the top of the piston, thereby reducing the generation of unburned HC.

[Problems to be Solved by the Invention] The present invention relates to a further improvement of the structure proposed by the present applicant for the above-mentioned light.

That is, the purpose of the present invention is to improve combustion efficiency and reduce NOx by generating turbulence, suppress knocking by a wide squish area, and improve flame propagation by using the combustion chamber structure of a premixed gasoline engine previously proposed by the applicant. In addition to reducing unburned HC emissions by improving the condition, almost all of the fuel is placed only in the combustion chamber and not supplied to the area around the piston and squish area, which further ensures the prevention of knocking and prevents the occurrence of knocking. The objective is to reduce fuel consumption.

[Means for Solving the Problems] The combustion chamber of the gasoline engine of the present invention that meets this purpose is a premixed gasoline engine that generates a combustion mixture outside the cylinder. A combustion chamber is formed by providing a recess that opens, and the opening area of the recess is narrowed relative to the inside of the recess, and the spark plug protruding from the lower surface of the cylinder head near the top dead center of the piston is inserted into the recess. It is inserted into the intake valve, and the four openings are partially expanded toward the intake valve side.

Preferably, only the inner surface of the recess at the top of the piston is made of ceramic.

(Function) In such a combustion chamber, the intake valve is opened during the intake stroke from just before the end of the exhaust stroke, and the air-fuel mixture is sucked into the cylinder. Since it is partially expanded toward this intake valve section, almost the entire amount of the air-fuel mixture taken in through the expanded section efficiently flows directly into the combustion chamber at the top of the piston. A squish flow is generated that flows toward the central combustion chamber, but this squish area is not supplied with air-fuel mixture or is supplied with a very lean air-fuel mixture, so knocking is reliably suppressed.In other words, By constricting the opening of the recess, a wide squish area is ensured, thereby obtaining a good squish flow, and in addition, by not supplying air-fuel mixture to the squish area, knocking is reliably prevented.

Further, during the compression stroke, airflow accompanying the squish flows into the piston combustion chamber, but since the opening of the recess is narrowed, a strong turbulent flow is generated within the combustion chamber. Since this turbulent flow within the combustion chamber is generated only by the combustion chamber structure without providing a swirl boat, the intake resistance is not increased by the turbulence generating structure even in a high rotation range.

Then, near the top dead center of the piston, the spark plug is inserted into the combustion chamber, and the turbulent air-fuel mixture in the combustion chamber is ignited, achieving uniform combustion within the combustion chamber and improving combustion efficiency. is increased, and the generation of NOx is suppressed.

During the expansion stroke, the jet flame ignited in the combustion chamber tries to spread, but since the four openings are narrowed, the flame propagation speed is increased in that part, and the flame does not spread rapidly even when directed toward the squish area. The air-fuel mixture that has spread to this area is also reliably combusted. Furthermore, since air-fuel mixture is not originally supplied to the squish area and the piston surrounding area, the generation of unburned HC is more reliably suppressed.

In addition, due to the strong turbulent flow inside the combustion chamber, heat loss through the combustion chamber wall surface tends to increase, but if the inner wall surface of the recess is formed with a relatively thin ceramic layer, it is possible to easily insulate only the inside of the recess. , Malfunctions due to high heat around the piston (
For example, it is possible to prevent the cooling loss from increasing while preventing the occurrence of knocking due to the heating of the portion, or the occurrence of knocking due to the heating of the portion.

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings.

1 to 4 show a combustion chamber of a gasoline engine according to a first embodiment of the present invention, and show a case where the present invention is applied to a four-valve engine.

In the figure, 1 indicates a so-called pent roof-shaped piston in which the top surface of the piston is not flat but roof-shaped, 2 is a cylinder block, 3 is a cylinder bore,
4 indicates a cylinder head. piston 1
A recess 5 that opens toward the lower surface of the cylinder head 4 is provided in the center of the top of the piston 1.
A combustion chamber 6 is formed between the top surface side of the cylinder head 4 and the lower surface of the cylinder head 4 .

In the fourth part 5, the opening area of the opening part 5a is narrowed compared to the inside of the recessed part. Therefore, the squish area 7 formed by the top surface of the piston and the lower surface of the cylinder head up to the recess opening 5a is wider than the conventional case where only a recess is provided.

1 and 2 show the state when the piston 1 is at the top dead center. The recess 5 and the spark plug 8 are arranged so that the spark plug 8 protrudes from the lower surface of the cylinder head and is inserted into the recess 5 near the top dead center of the piston 1 (for example, about 30 degrees in crank angle from the top dead center). The positional relationship is determined.

Therefore, at the top dead center of the piston 1, the ignition portion 8a of the spark plug 8 is completely located within the recess 5.

The inner surface of the four parts 5 is composed of a relatively thin ceramic layer 9. This ceramic layer 9 is provided only on the inner surface of the recess 5, and is not provided on the top surface of the piston or the lower surface of the cylinder head. However, although the ceramic layer 9 was provided in this embodiment, even if the ceramic layer 9 is not provided, knocking suppression, improvement of combustion efficiency, and NOx
And since the effect of reducing unburned IC can be obtained, it is not necessary.

As shown in FIGS. 1 and 3, the four openings 5a are
It is partially expanded toward the intake valve 10a side.

In this embodiment, this expanded portion 11 has two intake valves 10a.
, 10b, so that the opened intake valve 10a does not interfere with the piston 1 at the top dead center, as shown in FIG. It is adapted to project into the recess extension. The opening/closing timing of the intake valves 10a, 10b is as shown in FIG. 5, and the opening/closing timing of the intake valve 10b is delayed with respect to the opening/closing timing of the intake valve 10a.

In the figure, 12a and 12b represent exhaust valves, and 13 represents an intake boat.

The operation of the embodiment device configured as described above will be explained.

As shown in FIG. 5, the intake valve 10a is opened near top dead center at the end of the exhaust stroke, and closed during the intake stroke. The air-fuel mixture in the cylinder flows into the intake valve 10a. Since the opening 5a of the recess 5 forming the combustion chamber 6 is partially expanded toward the intake valve 10a, the air-fuel mixture flowing from the intake boat 13 efficiently flows directly into the recess 5 only.

The intake valve 10b is opened and closed at a later timing than the intake valve 10a. Substantially only air is taken in through this intake valve 10b. With the air-fuel mixture flowing into the recessed combustion chamber 6, air is introduced into the top surface of the piston and near the periphery of the piston through the intake valve 10b, so that a stratification of the air-fuel mixture is formed in the horizontal direction with respect to the cylinder. , a state = 12- is realized in which only air or a very lean mixture exists around the piston.

In this state, the compression stroke begins, and a squish flow occurs in the latter half of the compression stroke. As mentioned above, between this compression stroke and the ignition by the spark plug 8, only air or a very dilute mixture exists around the piston and in the squish area, so spontaneous ignition is suppressed and knocking occurs. or prevented.

As shown in FIG. 6, when the piston 1 is in the compression stroke, the concave opening 5a is narrowed to create a wide squish area, so a strong squish flow A of the air-fuel mixture is generated and flows into the combustion chamber 6. Strong turbulence B is generated in the airflow due to the constriction of the recess opening 5a. This turbulent flow is caused by the opening 5
Since it is generated by the throttling effect of a, it has nothing to do with the intake boat, and is generated without increasing intake resistance even in a high rotation range. Furthermore, by forming a wide squish area, the occurrence of knocking can be further suppressed.

When the piston 1 reaches the top dead center or its vicinity, the ignition plug 8 is inserted into the four part 5, as shown in FIG. . The air-fuel mixture is in a state of strong turbulence B and is combusted uniformly within the combustion chamber 6, so that the combustion temperature does not locally become abnormally high, and NOx is reduced. In addition, the flame is rapidly transmitted through the turbulent flow.

In the expansion stroke, as shown in FIG. 8, the jet flame C spreading from the inside of the recess 5 to the outside of the recess 5 increases in speed in this part because the four openings 5a are narrowed, and the jet flame C suddenly spreads from the inside of the recess 5 to the outside of the recess 5. do. Therefore, the combustion speed is increased, the combustion period is shortened, and the flame reaches every corner within the cylinder. Therefore, when this flame arrives, the unburned gas cooled in the wide squish area to prevent knocking is combusted, and the emission of unburned HC is suppressed.

In addition, as shown in No. 31 above, since only air or a very thin air-fuel mixture originally exists in the squish area or around the piston, there is no factor that causes unburned HC, or even if there is, the above-mentioned good flame propagation is not sufficient. The burner ensures reliable combustion and suppresses the generation of unburned IC.

Furthermore, as a result of generating strong turbulent flow within the combustion chamber 6, heat loss through the inner wall surface of the recess 5 tends to increase, but by constructing the inner wall surface of the piston combustion chamber with ceramic,
Only the inside of the recess 5 is efficiently insulated, and the amount of heat radiation can be suppressed.

As a result, an increase in cooling loss due to heat radiation from this portion is suppressed.

In this case, since no ceramic layer is provided except on the inner wall surface of the recess 5, heat is properly radiated from the peripheral portion of the piston 1 to the cylinder block side, and abnormal heating of the peripheral portion is prevented. Further, only the inside of the recess is heated to a high temperature, and the air-fuel mixture supplied to this portion is well atomized.

Next, a second embodiment of the present invention is shown in FIGS. 9 and 10. In this embodiment, the present invention is applied to a supercharged engine using a supercharger 21.

In the figure, 22 is an air cleaner, 23 is a throttle valve, and 24 is a surge tank, which is rotated by the driving force transmitted from the drive shaft 26 side to the intake pipe 25 on the downstream side of the surge tank 24. A supercharger 21 is provided. A pressure sensor 27 is provided in the intake pipe 25, and signals from the pressure sensor 27 and the crank angle sensor 28 are input to a computer 29. Based on this input signal, an injection control signal is sent from the computer 29 to the injector 30. FIG. 10 shows a schematic plan view, in which 33a shows the intake valve on the side where the recess 31 at the top of the piston 32 is expanded, 33b shows the other intake valve, and 34a and 34b show the exhaust valves.

In the device of this embodiment, fresh air (air) sucked into the air cleaner 22 is metered by the throttle valve 23, passes through the surge tank 24, and is sent to the supercharger 2.
1 to the intake pipe 25. The air guided here controls the fuel injection amount in the computer 29 using the pressure sensor 27 and the signal detected by the crank angle sensor 28 to detect the engine speed at that time, and sends it to the injector 30 as an injection signal. It will be done. The injected fuel then passes through the intake valve 33a and is supplied into the recess 31 at the top of the piston 32.

The opening/closing timing of the intake valves 33a and 33b at this time is as follows:
As shown in FIG. 5, one side is set to open a little earlier, making it easier to scavenge and cool the combustion chamber inside the piston. In particular, in this embodiment, since fresh air supercharged by the supercharger 21 is introduced into the combustion chamber at the beginning of the intake stroke, cooling of the piston surface and scavenging are performed powerfully and reliably. In addition, the fuel on the end portion of the bison surface disappears, making it possible to improve knock resistance and reduce unburned HC.

In addition, in order to further enhance the above effect, as shown in FIG.
It is also possible to make 2b into two systems, provide the supercharger 43 on the intake passage 42a side, and perform concentrated supercharging from one side.

[Effect of the invention] As explained above, when using the combustion chamber of the gasoline engine of the present invention, the four openings that form and cover the combustion chamber at the top of the piston are narrowed to generate strong (1) turbulent flow within the combustion chamber. The opening is partially expanded toward the intake valve side to allow the air-fuel mixture to flow directly into the recess, thereby shortening the combustion period, improving combustion efficiency, and reducing NOx.
Both reliable suppression of knocking and a significant reduction in unburned HC generation can be achieved.

Moreover, if the inner wall surface portion of the recess is made of ceramic, it is possible to suppress the amount of heat radiated from the combustion chamber while preventing the piston periphery from becoming abnormally high in temperature, and it is possible to suppress an increase in cooling loss.

The present invention is particularly suitable for use in multi-valve engines,
Within a limited degree of design freedom, it is possible to efficiently achieve mixed airflow only within the combustion chamber, generation of turbulent flow within the combustion chamber, wide squish area, and increased flame propagation speed.

Furthermore, if a supercharger or the like is provided in the intake system to introduce supercharged fresh air at the beginning of the intake stroke, the above-mentioned effects can be further enhanced.

[Brief explanation of the drawing]

1 is a longitudinal sectional view of a combustion chamber of a gasoline engine according to a first embodiment of the present invention, and is a longitudinal sectional view taken along line I-I in FIG. 3. FIG. 2 is a longitudinal sectional view of the device in FIG. 1. A vertical sectional view taken along the line ■-■ in Fig. 3, Fig. 3 is a plan view of the piston of the device shown in Fig. 1, Fig. 4 is a bottom view of the cylinder head side portion of the device shown in Fig. 1, and Fig. 5 is a diagram showing the relationship between the valve lift amount and crank angle showing the opening/closing timing of each valve in the device shown in FIG. 4, FIG. 6 is a schematic diagram of the compression stroke of the device shown in FIG. 2, and FIG. FIG. 8 is a schematic diagram of the device in the expansion stroke of the device shown in FIG. , Fig. 10 is a schematic plan view of the device shown in Fig. 9, and Fig. 11 is a schematic plan view of the device shown in Fig. 9.
FIG. 6 is a schematic plan view showing a modification of the device shown in the figure. 1...Piston 2...Cylinder block 3...
・・・・・・・・・Cylinder bore 4・・・・・・・・・
... Cylinder head 5 ...... Recessed portion 5a ... Opening 6 ...... Combustion chamber 7 ...・・・・・・・・・Squish area 8...
・・・・・・・・・Spark plug 9・・・・・・・・・・
...Ceramic layers 10a, 10b--Intake valve 11...Extended portions 12a, 12b...Exhaust valve 13...Intake boat 21.43・
...Supercharge Ja 22...
...Air cleaner 23...Throttle valve 24.41...Surge tank 27...Pressure sensor 28...・
......Crank angle sensor 29...
・・・・・・Computer 30・・・・・・・・・・・・
Injector 31...... Recess 32... Piston 33a, 33b
...Intake valve patent applicant Toyota Motor Corporation representative Patent attorney Presenter Benigumi (1 other person) = 21-

Claims (2)

[Claims] (1) In a premixed gasoline engine that generates a combustion mixture outside the cylinder, a combustion chamber is formed by providing a recess at the top of the piston that opens toward the lower surface of the cylinder head, and the opening area of the recess is narrowed into the recess, a spark plug protruding from the lower surface of the cylinder head near the top dead center of the piston is inserted into the recess, and the opening of the recess is partially expanded toward the intake valve side. The combustion chamber of a gasoline engine is characterized by: (2) The combustion chamber for a gasoline engine according to claim 1, wherein only the inner surface of the recess at the top of the piston is made of ceramic.