JPS63140815A - Combustion chamber for gasoline engine - Google Patents

Abstract

PURPOSE:To improve the efficiency of combustion by forming a communicating path affording communication between a recess on the top of a piston and the top other than the recess. CONSTITUTION:A combustion chamber 6 is defined with a piston 1 provided on the top with a recess 5. An ignition plug 8 projecting from the lower surface of a cylinder head 4 is inserted in the recess 5 near the upper dead point of piston. A communicating path 9 affording communication between the recess 5 an the top other than said recess of piston is formed. Thus, fired combustion gas expands rapidly to the peripheral portion of piston through the communicating path 9 so that the efficiency of combustion can be improved.

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 four parts at the top of a piston.

[Prior Art] In a premixed Kallin engine that generates a combustion air-fuel mixture outside the cylinder, it is necessary to increase the combustion rate to improve combustion efficiency and to take precautions against knocking. Also,
It is also necessary to reduce unburned IC 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.

Great for reducing NOx in this type of engine! 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, resulting in N.

The amount of X generated increased. In order to suppress local increases in the 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 wall, and the cooling loss increases accordingly. This leads to the problem of increase. 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-mentioned problem of increased cooling loss, there is a problem that the provision of the swirl boat increases intake resistance in a high rotation range, resulting in a decrease in output.

In addition, there is an engine with a subchamber as a structure that is advantageous for reducing NOx, but the gas from the subchamber hits the wall of the combustion chamber with 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 Publication No. 13, 1983
0046@publication).

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 squish effect, it is necessary to widen the squish area, but in the conventional structure, when 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)
However, 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.

Also, for premixed gasoline engines (especially for supercharged engines), points are added to increase combustion efficiency.

If the fire timing is advanced, spontaneous combustion will occur at the end, causing 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, unburned HC at the end will inevitably increase IJ loss and worsen 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. In other words, 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 recess is narrowed relative to the inside of the recess. This structure is such that the spark plug, which is protruded from the lower surface of the cylinder head near the point, is inserted into the recess. 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. In addition, 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, reducing the occurrence of unburnt tC. .

[Problems to be Solved by the Invention] The present invention is based on the structure proposed by the applicant for the above-mentioned light, which narrows the opening of the recess to generate turbulent flow within the recess and improve the propagation speed of the jet flame. However, this provides another measure.

That is, an object of the present invention is to improve combustion efficiency and improve combustion efficiency by generating turbulence within the combustion chamber in a combustion chamber structure of a gasoline engine in which four parts are formed at the top of the piston and a spark plug is inserted into the recesses. The purpose of this invention is to enable single combustion, reduce NOx, and quickly propagate the flame ignited within the recess to the end of the top surface of the piston, thereby suppressing the occurrence of knocking.

[Means for Solving the Problems] The combustion chamber of the gasoline engine of the present invention that meets this purpose is formed by providing a recess at the top of the piston that opens toward the lower surface of the cylinder head, A combustion chamber for a gasoline engine in which a spark plug protruding from the lower surface of the cylinder head is inserted into a recess near the top dead center of the piston, and a communication passage is provided to communicate the inside of the recess with the top surface of the piston other than the recess. It consists of

Preferably, the axis of the communicating path is eccentric with respect to a line passing through the center of the recess. Further, only the inner surface of the recess at the top of the piston is made of ceramic.

[Function] In such a combustion chamber, during the compression stroke, a part of the flow compressed between the squish area of the piston and the lower surface of the cylinder head and directed toward the recess flows into the recess through the communication path. , the flow generates strong turbulence within the recessed combustion chamber. Therefore, uniform combustion is achieved,
The combustion effect is enhanced, lean combustion is also possible, and the generation of NOx is suppressed because there are no roughly localized high-temperature areas. During the expansion stroke, the combustion gas ignited within the recess flows backward through the communication passage, so that the flame is quickly transmitted to the end portion of the top surface of the piston, thereby suppressing the occurrence of knocking.

In addition, if the opening of the recess is narrowed, turbulent flow is generated due to the throttling effect, and the flame width velocity is further improved.

In addition, if the communication passage is made eccentric from the line passing through the center of the recess and opened into the recess, the flow flowing into the recess through the communication passage, or the combustion gas flowing out through the communication passage to the piston end. It becomes possible to impart a horizontal swirling component to the flow, resulting in more desirable turbulence and flame propagation.

Generally speaking, the strong turbulent flow inside the combustion chamber tends to increase heat loss through the combustion chamber wall surface, but if the inner wall surface of the recess is formed with a relatively thin ceramic layer, it is easy to insulate only the inside of the recess. This makes it possible to prevent problems caused by high heat around the piston (for example, the occurrence of knocking due to the high temperature of the piston, and the like), while also preventing an increase in cooling loss.

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

First Embodiment FIGS. 1 to 3 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 .

1 and 2 show the state when the piston 1 is at the top dead center, and a squish area 7 is formed between the top of the piston other than the recess 5 and the lower surface of the cylinder head 4. 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 four portions 5.

At the top of the piston 1, there is a communication passage 9 that extends obliquely and linearly and communicates between the top surface of the piston other than the recess 5 and the inside of the recess 5.
are provided around the recess 5. In this embodiment, the communication passages 9 are provided at eight locations equally spaced in the circumferential direction, and open at four locations each at the positions 1a corresponding to the intake and 1J1 air valves and at the other piston top surface positions 1b. There is.

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

During the compression stroke, a squish flow is generated between the top surface of the piston 1 and the lower surface of the cylinder head, as shown in FIG. It is directly flowed into the relatively lower part of the inside of 5. The flow from the communication path 9 causes strong turbulence within the recess 5, and the turbulence within the recess 5 achieves uniform combustion after ignition.

Therefore, combustion efficiency is increased and lean combustion becomes possible. In addition, NOx is also suppressed because uniform combustion prevents the occurrence of locally abnormally high temperatures.

During the expansion stroke after ignition, as shown in FIG. is guided directly to the top surface of the piston 1, and is guided to the end portion of the top surface of the piston.

Therefore, the flame jet that is rapidly combusted due to the turbulent flow quickly reaches the piston periphery through the communication passage 9, increasing the flame width velocity, realizing rapid combustion even at the end portion, and suppressing the occurrence of knocking. .

Second Embodiment Next, a second embodiment of the present invention is shown in FIGS. 6 and 7.

In this embodiment, provided at the top of the piston 11,
A communication path 13 between the piston top surface and the four parts 12 is arranged such that its axis is eccentric with respect to a line passing through the center of the recess 12. In other words, the communication path 13 is eccentric from the direction toward the center of the recess 12 and opens into the recess 12 .

In such a device, as shown in FIG. 8, when a part of the squish flow flows into the recess 12 through the communication passage 13, a horizontal swirling flow component is imparted to the inflow flow. The turbulent flow within the recess 12 and the squish flow flowing in from the opening side of the recess 12 are mixed better, and a further improvement in the combustion rate can be expected. Further, since a swirling flow component is also given to the flame jet that spreads from the inside of the recess 12 through the communication passage 13 during the expansion stroke, it becomes possible to quickly propagate the flame to every corner around the piston. Other configurations and operations are similar to those in the first embodiment, so in FIG. 8, the same reference numerals as in FIG. 1 are given to the parts corresponding to those in FIG. 1, and the explanation thereof will be omitted.

Third Embodiment Next, a third embodiment of the present invention is shown in FIGS. 9 and 10.

In this embodiment, only the inner surface of the four parts 22 formed at the top of the piston 21 is made of a relatively thin ceramic layer 23. This ceramic layer 23 is provided only on the inner surface of the recess 22, and is not provided on the other piston top surface and the lower surface of the cylinder head. Further, in this embodiment, the area of the opening 22a of the recess 22 is narrowed relative to the inside of the recess 22. The inside of the recess 22 and the top surface of the piston are communicated with each other by a communication passage 24 as in the first embodiment.

In this type of device, as shown in FIG. 11, even in the first half of the compression stroke, the airflow flowing into the four parts 22 is turbulent because the openings 22a of the four parts 22 are constricted. The air-fuel mixture is evenly stirred inside. In the latter half of the compression stroke, as shown in FIG. 12, a portion of the squishy flow compressed between the top surface of the piston and the bottom surface of the cylinder head flows into the fourth section 22 through the communication passage 24, and the squishy flow compresses between the top surface of the piston and the bottom surface of the cylinder head. 22
Strong turmoil occurs within. At this time, since the opening 22a is narrowed, the flow flowing in from the frontage 22a is naturally disturbed. Therefore, the turbulence caused by the throttle of the opening 22a is added to the turbulence caused by the flow from the communication path 24, resulting in stronger turbulence. As a result of generating strong turbulent flow within the combustion chamber, heat loss through the inner wall surface of the recess 22 tends to increase. However, by configuring the inner wall surface of the piston combustion chamber with ceramic, only the recess 22 is efficiently insulated and the heat loss is reduced. The amount of heat 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 four parts 22, heat is appropriately radiated from the peripheral part of the piston 2 to the cylinder block side, and abnormal heating of the peripheral part 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.

In the expansion stroke, as shown in FIG. 13, since the four openings 22a are narrowed, the combustion gas ignited within the recess 22 becomes a jet from the opening 22a and quickly flows around the piston. spread. Further, as in the above-described embodiment, since the combustion gas spreads around the piston through the communication passage 24, even more rapid flame propagation can be expected.

Other configurations and operations are similar to those in the first embodiment, so the eleventh embodiment
In the drawings to FIG. 13, parts corresponding to those in FIG. 1 are designated by the same reference numerals as in FIG. 1, and their explanations will be omitted.

[Effects of the Invention] As explained above, when using the combustion chamber of the gasoline engine of the present invention, a communication passage is provided that communicates the inside of the recess forming the combustion chamber at the top of the piston with the top of the piston other than the recess, During the compression stroke, part of the squish flow is guided into the recess through the communication path to generate strong turbulence within the recess, and during the expansion stroke, the combustion gas ignited within the recess quickly spreads through the communication path to the area around the piston. As a result, it is possible to shorten the combustion period, improve combustion efficiency, enable lean combustion, and reduce NOx, while also reliably suppressing the occurrence of knocking and significantly reducing the generation of unburned 1-IC. .

Furthermore, if the inner wall surface portion of the recess is made of ceramic, it is possible to prevent heat radiation (i) from the combustion chamber while preventing the piston periphery from becoming abnormally high 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 generate turbulent flow within the combustion chamber and improve flame propagation speed.

[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; FIG. 2 is a longitudinal sectional view of the device shown in FIG. 1 viewed from a right angle; FIG. 3 is a longitudinal sectional view of the device shown in FIG. 1. Figure 4 is a schematic diagram of the piston in the compression stroke of the device in Figure 1, Figure 5 is a schematic diagram of the device in Figure 1 in the expansion stroke, and Figure 6 is a schematic diagram of the device in the expansion stroke. A plan view of a piston in a combustion chamber of a gasoline engine according to a second embodiment of the present invention, FIG. 7 is a partial vertical cross-sectional view of the piston of FIG. 6 along line Vl-VI, and FIG. 8 is a second embodiment of the invention. FIG. 9 is a plan view of a piston in a combustion chamber of a gasoline engine according to a third embodiment of the present invention; FIG. 10 is a portion of the piston shown in FIG. 9 taken along line X-X. Fig. 11 is a longitudinal sectional view of the device of the third embodiment in the first half of the compression stroke, Fig. 12 is a longitudinal sectional view of the device of the third embodiment in the latter half of the compression stroke, and Fig. 13 is a longitudinal sectional view of the device of the third embodiment. This is a longitudinal cross-sectional view during the expansion stroke. 1.11.21...Piston 2...Cylinder block 3...
・・・・・・・・・Cylinder bore 4・・・・・・・・・
... Cylinder head 5.12.22 ... Recess 6, ... Combustion chamber 7 ... Squish area 8 ...
・・・・・・・・・Spark plug 9.13.24・・・Communication path 22a・・・・・・Recess opening 23・・・・・・ Ceramic layer Applicant: 1 person Toyota Motor Corporation Figure 1 Figure 2 Figure 5 Recess Figure 4 Figure 5 Figure 6 Figure 7 Figure 9 Figure 22 Recess Figure 10 '15 Cera (Tsuku layer)

Claims (4)

[Claims] (1) Gasoline in which a combustion chamber is formed by providing a recess opening toward the lower surface of the cylinder head at the top of the piston, and 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. 1. A combustion chamber for a gasoline engine, characterized in that the combustion chamber is provided with a communication path that communicates between a piston top surface other than the recess and the inside of the recess. (2) The combustion chamber for a gasoline engine according to claim 1, wherein the opening area of the opening of the recess is narrower than the inside of the recess. (3) The combustion chamber of a gasoline engine according to claim 1, wherein the axis of the communication passage is eccentric with respect to a line passing through the center of the recess. (4) The combustion chamber of 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.