DE202020104923U1 - Cylinder unit with reduced top land - Google Patents

Abstract

Cylinder unit (1) for stationary gas engines in the displacement range from 1.8 to 2.2 liters per cylinder with a central mixture formation, which has a piston element (2) with a piston head (4) or a piston crown, a liner (3) and an annular Sealing element (6), the piston element (2) laterally, in the area of the piston head (4), a radially arranged groove (5) for receiving the sealing element (6) bounded towards the piston head (4) by a top land (7) , the top land (7) extending from the groove (5) to the piston head (4), characterized in that the liner (3) has an inner surface which extends from a first end to a second end of the liner (3 ), wherein the sealing element rests against the bushing in an area between the first end and the second end, has a constant radius on its inside along the stroke axis direction, by the height of the top land (7) and thus the distance of the groove (5) to To minimize the mounting of the sealing element (2) to the piston head (4) and thus the volume that is limited by the top land (7), sealing element (6) and liner (3) and extends to the combustion chamber end of the piston element (2).

Description

The invention relates to a cylinder unit for stationary gas engines in the displacement range from 1.8 to 2.2 liters per cylinder with a central mixture formation according to the preamble of claim 1.

From the DE 10 2018 205 673 A1 an internal combustion engine is known with an oscillating piston which can be moved in a cylinder and a stripping element which has the task of removing oil and soot particles from the cylinder jacket surface of the piston to the piston rings. For this purpose, the stripping element is arranged in such a way that it can loosen it mechanically. The stripping element is fixed against axial displacement by a shoulder in the bushing.

In contrast, the object of the invention is to propose a more efficient and more sustainable, and thus also more environmentally friendly, cylinder unit which at least partially improves the disadvantages of the prior art.

Based on a cylinder unit of the type mentioned in the introduction, this object is achieved by the features of claim 1. Advantageous embodiments and developments of the invention are possible through the measures mentioned in the subclaims.

Accordingly, a cylinder unit according to the invention is characterized in that the height of the top land and thus the distance of the groove for receiving the sealing element to the piston head or to the piston crown and thus the volume that is limited by the top land, sealing element and liner and up to the end of the combustion chamber Piston element is sufficient to be advantageously minimized.

The gas mixture in this volume is reached late by the ignition flame when igniting during the working cycle due to its position in the cylinder and is only partially or not converted at all and therefore contributes to useless raw material and energy consumption, i.e. it belongs to the so-called dead space of the cylinder. With a reduction in this volume, the efficiency and sustainability of an engine can be increased, because the volume effectively used for combustion is increased or optimized. This can be achieved by reducing the extent of the top land in the piston stroke direction and thus positioning the sealing element closer in the direction of the piston crown or a piston crown. From an environmental point of view, this has the advantage that less fuel has to be used to operate the engine. The reduced dead space also reduces the amount of unburned fuel emitted during the combustion cycle. The reduced methane slip therefore has a positive effect on the climate-damaging effectiveness of the engine exhaust, since methane has a high greenhouse effect, many times higher than, for example, carbon dioxide.

On the one hand, therefore, basically less methane than fuel, which was previously mixed externally in gaseous homogeneous form with the combustion air, is introduced into the piston and a higher proportion of it is burned so that much less methane is emitted in each cycle.

The liner ideally has a constant radius on its inside or its inner surface, which extends from a first to a second end of the liner, the sealing element in the area between the first and second end of the liner, along the stroke axis direction.

The uniform radius also results in a smaller surface and fewer edges on which particles can settle, which lead to greater and faster wear.

According to the design, a gap is formed between the piston element and the liner, so that the piston element can oscillate within the liner. The gas mixture to be burned is introduced into the combustion chamber on the piston bottom side. In order to avoid a spread of the fuel, here the gas mixture next to or even below the piston element and to avoid an expansion that occurs during the combustion, at least partially against the desired stroke direction, at least one sealing element, also called piston rings, is placed below the top land arranged that a spreading of the gas mixture is prevented by mechanical sealing.

Technically, this arrangement of the sealing element closer to the piston head in one embodiment of the invention is favored if the wiper element, as used in the prior art, is dispensed with. With a combination of a sealing element arranged closer to the piston head and a wiper element, the sealing element would either move permanently over the wiper element when the piston element oscillated or would always have to overcome the spatially arising step between the liner and wiper element, which is not structurally possible. With a permanent displacement of the sealing element to the level of the stripping element, the stripping element can be Purpose of scraping particles from the piston element no longer fulfilled, since the necessary mechanical contact with the piston element is not available.

In the case of a step to be overcome on the inner wall of the liner, the sealing element would have to bridge two different gap widths from piston element to liner or scraper element. In order to seal in both cases, the sealing element must be large enough to bridge the larger gap width, with the result that the sealing element is compressed during a piston stroke at the level of the stripping element. Such a high stress on the sealing element would lead to a much accelerated wear of it and thereby to a greatly increased risk of engine damage such as piston seizure.

In the prior art, the stripping element is arranged on the cylinder liner. In the case of an arrangement on a cylinder liner with a continuous radius within the meaning of the invention, the spatial expansion of the stripping element requires a larger gap between piston element and cylinder liner, which leads to an enlarged dead space and higher fuel consumption.

In the present exemplary embodiment of the invention, a stripping element is dispensed with. The combustion of gases greatly reduces the formation of soot compared to the combustion of liquid fuels, which is why a scraper element can be dispensed with without damaging the engine. Due to the fact that no liquid fuel is used, protection against oil drops is also not necessary.

The conversion of a diesel engine to the combustion of gas, in particular biogas, is technically easy to implement and economically feasible in the displacement range from 1.8 to 2.2 liters per cylinder. Furthermore, avoidance of the stripping element can be implemented at least in this displacement range.

The essentially cylindrical top land is preferably manufactured with a piston element stroke of 100 mm to 200 mm with an extension of 4-8 mm perpendicular to the radius, the height of the top land 5.5 mm and the stroke of the piston element 140-160 mm. Due to the greatly reduced height of the top land, the sealing element can be arranged much higher, with the result that the volume between the top land, sealing element and liner is significantly reduced.

It is also advantageous if the radial extension of the top land is designed in such a way that the cylinder unit has a gap between the top land and liner with a piston stroke / gap dimension ratio of 250: 1 - 350: 1, in particular 280: 1, 308: 1 and 320: 1. Since the top land and cylinder liner form the lateral boundaries of the damaged volume, a reduction in the distance between these two elements according to the above-mentioned conditions leads to a significant reduction in this volume.

An embodiment of the invention is shown in the drawing and is explained in more detail below with reference to the figures.

• 1 Teilausschnitt eines schematischen Aufbaus einer Zylindereinheit nach Stand der Technik mit Abstreifelement,
• 2 Teilausschnitt eines schematischen Aufbaus einer Zylindereinheit gemäß der Erfindung.

In detail shows:

• 1 Partial section of a schematic structure of a cylinder unit according to the prior art with a stripping element,
• 2 Partial section of a schematic structure of a cylinder unit according to the invention.

1 shows a schematic representation of a partial section of a cylinder unit 1 with a piston element 2 and a liner 3 . The piston element 2 points in the area of the piston crown 4th laterally a radial groove 5 for receiving a sealing element 6th on. This groove 5 is to the piston crown 4th through a top walkway 7th limited. The liner 3 points on its inner surface in the area of the top land 7th of the piston element a recess 8th to accommodate a scraper 9 on.

2 shows a schematic representation of a partial section of a cylinder unit 1 with a piston element 2 and a liner 3 . The piston element 2 points in the area of the piston crown 4th laterally a radial groove 5 for receiving a sealing element 6th on. This groove 5 is to the piston crown 4th through a top walkway 7th limited compared to the in 1 has a significantly reduced expansion in the stroke direction. The liner 3 shows, unlike in 1 , on their inside along the stroke axis direction, a constant radius, i.e. no indentation or bulge. Furthermore, compared to the prior art, no wiper element is provided, whereby the top land can be reduced in size and the sealing element can be attached closer to the piston crown. This also reduces the dead space of the engine, since the volume between the top land, cylinder liner and sealing element is reduced. At the same time, the effective volume is relatively enlarged, and a more efficient and environmentally friendly engine can be realized.

List of reference symbols

1

Cylinder unit

2

Piston element

3

Liner

4th

Piston crown

5

Groove

6th

Sealing element

7th

Top land

8th

Recess

9

Wiper element

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102018205673 A1 [0002]

Claims (4)

Cylinder unit (1) for stationary gas engines in the displacement range from 1.8 to 2.2 liters per cylinder with a central mixture formation, which has a piston element (2) with a piston head (4) or a piston crown, a liner (3) and an annular Sealing element (6), the piston element (2) laterally, in the area of the piston head (4), a radially arranged groove (5) for receiving the sealing element (6) bounded towards the piston head (4) by a top land (7) , the top land (7) extending from the groove (5) to the piston head (4), characterized in that the liner (3) has an inner surface which extends from a first end to a second end of the liner (3 ), wherein the sealing element rests against the bushing in an area between the first end and the second end, has a constant radius on its inside along the stroke axis direction, by the height of the top land (7) and thus the distance of the groove (5) z To accommodate the sealing element (2) to the piston head (4) and thus to minimize the volume which is limited by the top land (7), sealing element (6) and liner (3) and extends to the end of the piston element (2) on the combustion chamber side. Cylinder unit (1) according to one of the preceding claims, characterized in that the liner (3) has no stripping element (9). Cylinder unit (1) according to one of the preceding claims, characterized in that the substantially cylindrical top land (7) has an extension of 4 - 8 mm perpendicular to the radius, with a stroke of the piston element (2) of 100 mm to 200 mm , the height of the top land (7) preferably being 5.5 mm and the stroke of the piston element (2) being 140-160 mm. Cylinder unit (1) according to one of the preceding claims, characterized in that the top land (7) is designed in its radial extension in such a way that the cylinder unit (1) has a gap with a piston stroke between the top land (7) and the liner (3). Gap ratio of 250: 1 - 350: 1, in particular 280: 1, 308: 1 and 320: 1.

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