DE19909112A1 - Piston for a piston internal combustion engine - Google Patents

Abstract

The invention relates to a piston for a piston internal combustion engine with spark ignition or self-ignition, whereby the cylinders thereof are provided with gas outlets and inlets with controllable gas exchange valves and the respective gas inlets provide a flow direction for the gas flowing into each respective cylinder and said flow direction includes an at least partial turning movement that is directed around the cylinder axis. The inventive piston also comprises a piston bottom with a trough-shaped recess that is defined on the edge side by a squish area and that has at least two substantially radially aligned recessed interruptions in the region of at least partial areas.

Description

The main requirement for piston internal combustion engines, namely both piston internal combustion engines with spark ignition, as well with auto-ignition of the fuel mixture, are high speci performance, low pollutant emissions and low Fuel consumption. To fuel consumption at part load Lowering the range is useful, for example, for pistons internal combustion engines the operating point shift up to heavy loads while reducing the lifting volume (so-called downsizing).

For example for piston internal combustion engines with external ignition dung despite a smaller displacement compared to a conv tionally designed piston internal combustion engine the same torque To achieve ment and performance values, such in Displacement reduced piston internal combustion engines mostly with egg ner charging device, preferably an exhaust gas turbocharger, executed. With increasing degree of charging and thereby increasing the compression end pressures and end temperatures are growing at ei ner such piston engine the knock tendency. Out for this reason, supercharged engines are usually equipped with an egg operated at a lower compression ratio than ver comparable naturally aspirated engines. A low compression ratio is for the efficiency of the thermodynamic process ses unfavorable.

In order to solve this problem, such piston internal combustion engines are required machines have also been designed so that by an adjustable re displacement of the crankshaft a variable compression ratio ratio can be adjusted. This enables the Part load range with high compression ratio and lean Mixture and the full load range with stoichiometric mixture and low compression ratio to operate.  

To usual catalysts in such piston internal combustion To be able to use machines, the lean operation must Ignition timing / air ratio calibration can be selected so that the nitrogen oxide emission is low. But this starts Combustion process with very good lean running ability ahead.

From a thermodynamic point of view, a lean Be drive-wise and a high compression ratio for the Full load operation advantageous. To do this, the piston internal combustion seem to be designed so that it has a sufficient lean run has the ability to reduce nitrogen oxide emissions limit and on the other hand with intermittent operation to ensure sufficient distance from the lean running limit. In addition, for piston internal combustion engines with foreign ignition the knock tendency of conventional concepts can be reduced.

The known combustion chamber concepts required for this such lean burn engines are either 4-valve pistons internal combustion engines borrowed, such as for passenger cars be used with so-called tumble inlet channels are provided so that at the time of combustion the ge desired turbulence is present, or there is 2-valve col internal combustion engines with a so-called intake swirl work. In all cases, it is the shape of the focal The piston crown of the used space Piston as "smooth" as possible, d. H. without training fissures the, because such fissures for the combustion process in Combustion chamber can be assessed as unfavorable.

For piston internal combustion engines with auto-ignition, for example wise direct-injection diesel engines, is a high door bulence desirable to reduce soot emissions.

The invention has for its object a piston for to create a piston internal combustion engine, the at spark ignition systems a significantly reduced tendency to knock, a increased lean running ability and lower HC emissions,  and auto-ignition systems, especially diesel power substances, causes a reduction in soot emissions.

This problem is solved by a piston for a piston Internal combustion engine with spark or auto ignition, whose Zy linder with controllable gas exchange valves have passages and gas inlets, the gas inlets se the gas flowing into the respective cylinder Give direction of flow, which at least partially around Has twist aligned cylinder axis, with a Kol benboden, which has a trough-shaped depression, the is delimited on the edge by a squeeze surface and the we at least two ra at least essentially over partial areas dial-oriented, deepened interruptions. With Such a piston it is possible to adjust the swirl around the cylinder axis of the gas flowing into the cylinder, the more or less strong residual twist in a tum Blowing flow is present, especially that in a so-called called swirl inlet originally created, cylinder flow determined by the high inlet swirl with increasing upward movement of the piston over the ver deep interruptions in high turbulence, so not ge to implement directed cylinder flows. Even with one Guidance of the gas flowing into the cylinder in the form of a Tumble, there is often a residual twist, which with the inventive design effective in turbulence can be solved, so that here too with the onset of Combustion allows rapid flame progress. This also removes the risk of knocking the spark plugs Combustion chamber areas quickly reached from the flame front. On Another advantage is that the squeeze surfaces in Zy Reduced near the cinder wall and thus also the HC emission ver is reduced. The increase in turbulence in the wall area of the trough-shaped depression leads to a improved mixture formation and thus lower Ru emission.  

It is expedient if the interruptions in the crushing surface at most have a depth that corresponds to the depth of the trough corresponding deepening. Depending on the total ge design of the combustion chamber the transitions between the squeeze surfaces and the deep interruptions sharp-edged and / or be rounded. This can, for example se caused by the deepened interruptions as grooves with a rectangular cross-section or undulating in the course mig be executed.

It is also expedient if at least two are preferred diametrically opposed interruptions are provided, which are oriented essentially transversely to the gas inlet. This ensures that both in the inlet near Be range of the swirl flow as well as in the area away from the inlet Swirl flow in the upward movement of the directional cylinder channel flow is turbulently swirled, so that not only in the Area of the spark plug but also in the peripheral areas of the remaining squeeze areas there is a corresponding turbu lenz can train.

In a further embodiment of the invention it is provided that the trough-shaped depression and / or the interruptions ge arranged eccentrically in the piston crown opposite the piston axis are. Such an asymmetrical arrangement will Turbulence formation still supported.

In a further embodiment of the invention it is provided that the depth of the breaks is about 3 to 20% of the piston knife is. It is also useful if the width of the Interruptions and the diameter of the trough-shaped ver are dimensioned so that the squeeze area a total of et wa is 15 to 40% of the piston diameter.

In an embodiment of the invention, it is advantageous if the Interruptions are assigned to the gas exchange valves and such are dimensioned to be Ven effective clearance. This configuration is particularly for  Piston internal combustion engines advantageous, their gas exchange valves le with freely controllable actuators, for example in Form of hydraulic, pneumatic and / or electromagnetic table actuators are provided. Through freely controllable Actuators can actuate the gas exchange valves in to a high degree on an optimization of engine operation and / or the combustion process can be turned off. By inventing proper allocation of the interruptions in the squeeze area to the gas exchange valves with a reduced combustion chamber possible in the cylinder, at least a partial opening of the gas exchange to effect valves when the piston is still in the top dead center position.

The invention is based on schematic drawings of a Embodiment explained in more detail. Show it:

Fig. 1 is a plan view of a piston crown,

Fig. 2 shows a section according to line II-II in Fig. 1,

Fig. 3 is a plan view corresponding to FIG. 1 with modified interruptions in the squish area in the assignment for two gas exchange valves

Fig. 4 is a vertical section. the line IV-IV in Fig. 3,

Fig. 5 is a plan view of a piston crown with modified squeeze surface in the assignment for four gas exchange valves.

Fig. 1 shows a plan view of a substantially flat piston head, which is provided with a trough-shaped depression 1 . In the exemplary embodiment shown here, the depression 1 is circular-cylindrical, with a circular edge, the axis 2 of the depression 1 being displaced relative to the piston axis 3 in the direction of the spark plug 4 indicated here. The edge contour can also have a different course.

The recess 1 is delimited on the edge by a squeeze surface 5 which has radially aligned, recessed and interfering edges 6 forming interruptions 7 . The interfering edges 6 may be sharp-edged or rounded. The interruptions 7 not only have different widths here, but are also arranged asymmetrically with respect to the piston axis 3 on the piston head. In the example presented, the interruptions 7.1 which are displaced with respect to the cylinder axis 3 are made narrower than the transverse depressions 7.2 .

As shows the sectional representation according to FIG. 2, the depth T of the interruptions is 7 and dimensioned smaller than the depth of the muldenför-shaped recess 1 so that it is about 3 to 20% of the piston diameter. The width of the interruptions 7 is also such that the size of the squeeze surface 5, which is divided into four partial surfaces here, is between 15 and 40% of the piston surface, depending on the application.

In Fig. 1, the assignment of a swirl to Ga inlet 8 of the associated cylinder is indicated schematically. In the suction phase, ie during the downward movement of the piston and still at the beginning of its upward movement, a swirl flow results in the cylinder interior, as indicated by arrow 9 . This can be a swirl flow that is specifically generated by the alignment of the gas inlets or the residual swirl of the differently directed gas flow in the cylinder, for example a tumble flow. With increasing upward movement of the piston, however, this swirl flow 9 or the residual swirl is hampered by the ever increasing flow of the interfering edges 6 of the interruptions 7 in their free swirl movement and swirled in such a way that a distributing over the entire combustion chamber, not directed te turbulent Forms flow in the combustion chamber. Due to the side edges of the interruptions 7 delimited by the interfering edges 6 , part of the original swirl flow is deflected to a greater extent to the center of the combustion chamber and swirled here by the collision of several of these deflected partial flows and deflected again towards the cylinder wall, so that When the turbulent fuel-air mixture is ignited, the flame front can also spread quickly into the areas remote from the spark plug, thus reducing the risk of knocking.

In FIGS. 3 and 4 is a modified embodiment of the piston head described with reference to FIG. 1 for a piston internal combustion engine having two gas exchange valves shown. In these representations, the positions of the Gaseinlaßven valve 10 and the gas outlet valve 11 are shown.

The interruptions 7.1 shifted with respect to the cylinder axis 3 are dimensioned in their width so that the start of the opening movement of the gas exchange valves can be moved to a point in time at which the piston is still in the top dead center position. In this dimensioning, the interruptions 7 act for the range T their depth as valve clearance.

This concept can also be realized on piston internal combustion engines with four gas exchange valves per cylinder, ie two gas inlet valves 10 and two gas outlet valves 11 , as indicated in FIG. 5. In the embodiment shown here, the trough-shaped depression 1 is aligned coaxially with the cylinder axis 3 . An ignition device 4 , for example a spark plug, an ignition jet device in a gas engine or a fuel injection nozzle in a compression-ignition engine, opens into the combustion chamber in the region of the cylinder axis 3 . The depressions 7.1 and 7.2 can, as in turn, as shown in FIG. 5, be produced as millings of the squeezing surface 5 . By appropriate other guidance of the tool, however, the geometry of the interfering edges 6 can be changed so that, as shown, the interfering edges 6 of the interruptions are at least substantially radially aligned over at least part of their length, but also partially coaxially in the area of the clearance the gas exchange valves run.

Instead of the illustrated rectangular contour of the series of depressions 7 and pinch surfaces 5 , the arrangement can also have a wave-like contour. For example, an ellen-like contour can already be caused by the fact that the interfering edges 6 are more or less rounded and their transitions to the bottom surface of the recesses are also rounded. This can be modified to a "real" waveform.

Instead of a rectangular or wave contour, a sawtooth-like contour or a sequence of trapezoids formed by the sequence of the depressions 7 can also be provided. A change from sharp-edged and rounded interfering edges 6 can be useful.

Claims (10)

1. Piston for a piston internal combustion engine with spark or compression ignition, the cylinders with controllable Gaswechselven valves ( 10 , 11 ) provided gas outlets and gas inlets, the gas inlets ( 8 ) giving the gas flowing into the respective cylinder a direction of flow, at least partially has a twist aligned around the cylinder axis ( 3 ), with a piston head which has a trough-shaped depression which is delimited on the edge by a squeeze surface ( 5 ) and which has at least two deep interruptions which are at least substantially radially oriented at least over partial areas ( 7 ). 2. Piston according to claim 1, characterized in that the interruptions ( 7 ) of the squeeze surface ( 5 ) have at most a tie fe which corresponds to the depth of the trough-shaped depression ( 1 ). 3. Piston according to claim 1 or 2, characterized in that the interruptions ( 7 ) have radially oriented interference edges ( 6 ). 4. Piston according to one of claims 1 to 3, characterized in that at least the interference edges ( 6 ) are formed with sharp edges. 5. Piston according to one of claims 1 to 3, characterized in that at least the interfering edges ( 6 ) rounded out forms. 6. Piston according to claim 1 to 5, characterized in that at least two interruptions ( 7.1 ) are provided. 7. Piston according to one of claims 1 to 6, characterized in that the trough-shaped recess ( 1 ) and / or the interruptions ( 7 ) with respect to the piston axis ( 3 ) are arranged eccentrically in the piston crown. 8. Piston according to one of claims 1 to 7, characterized in that the depth T of the interruptions ( 7 ) is each et wa 3 to 20% of the piston diameter. 9. Piston according to one of claims 1 to 8, characterized in that the shape of the interruptions ( 7 ) and that of the trough-shaped recess ( 1 ) are dimensioned such that the sum of the squeezing surfaces ( 5 ) in total about 15 to 40% of Piston area is. 10. Piston according to one of claims 1 to 9, characterized in that the interruptions ( 7 ) are assigned to the gas exchange valves and are dimensioned so that they act as valve clearance for the range of their depth (T).