EP4144979A1 - Combustion engine with an element on the inner wall of a cylinder for scraping carbon residues - Google Patents

Abstract

1. Internal combustion engine with an element on the inner wall of the cylinder for scraping off oil carbon2. An internal combustion engine of a motor vehicle is described, with at least one working cylinder and a cylinder head closing the working cylinder, the working cylinder having a cylinder liner and/or a cylinder liner (1) and having at least one element in the area of the cylinder head that is suitable for removing any carbon that may form strip off

Description

The invention relates to an internal combustion engine with an element on the inner wall of the cylinder for scraping off oil carbon.

Out of DE 35 43 668 A1 an annular insert is known which protrudes from the head side of the cylinder liner. It narrows the inner diameter of the cylinder or cylinder liner and prevents carbon from coming into contact with the inner wall of the cylinder.

The DE 103 21 034 B3 shows a ring-shaped design that reduces the diameter as an insert in a groove or as an insert that protrudes beyond the cylinder liner on the head side and is inserted between the liner and the cylinder head without play. This is unsuitable for a large series, since the backlash-free use places increased demands on production and assembly.

In the DE 10 2011 012 507 B4 an embodiment is disclosed which projects beyond the cylinder barrel as an insert into which a groove is inserted. The insert narrows the area of the top dead center position through rotationally symmetrical and asymmetrical outer and inner contours of the ring element.

The object of the present invention is to avoid the disadvantages mentioned above and to create an internal combustion engine that consumes little oil and produces hardly any oil carbon, without having to accept disadvantages in terms of component rigidity.

According to the invention, this object is achieved by an internal combustion engine of the above type having the features characterized in claims 1 and 10 an internal combustion engine and a method with at least one element on the cylinder inner wall, which is worked into the cylinder inner wall in the corresponding TDC area of the top land of the piston by machining or an embossing/printing process and approximately performs the function of a fire ring. Advantageous configurations of the invention are contained in the further claims.

Knurls or knurls, sometimes also cords, are circumferential deviations in shape produced by means of knurling, which are embossed in a metal rotating body on the inner or outer surface. Knurls can make a workpiece easier to grip and thus prevent slipping, such as on a dumbbell handle. The knurling can take various forms and can be introduced either by milling, pressing or by embossing on a lathe.

Knurling and cording are two related manufacturing processes from the stamping group, which is part of pressure forming. In both processes, a round workpiece is pressed against a round tool and rolled so that both rotate. The profile of the tool is transferred to the workpiece. The elevations of the tool are pressed into the surface of the workpiece. Depending on whether knurls or cords (left-right knurls, cross knurls) are created, one speaks of knurling or cords.

For example, the handles or gripping surfaces of micrometers are often knurled to make them easier to grip than smooth surfaces.

Knurling used to emboss decorative elements or writing on the edge of a coin or medal used to make it difficult to file or trim coins because a filed area is immediately visible.

Another application is the creation of a serrated profile for a shaft-hub connection, e.g. B. for attaching a rotor core a shaft to transmit higher torques than with a shrink connection or knurled screw.

When knurling, a distinction is made between non-cutting knurling and cutting knurl milling. Depending on the process, the profile is pressed in with knurling wheels or milled on a knurling cutter. Special knurl milling tools can also be used on CNC lathes with driven tools in order to avoid re-clamping on other machines. Since the machining forces are lower when milling, it is mainly used for thin workpieces or on machining centers.

There are knurls in the following designs, RAA: knurl with axis-parallel grooves, RBL: left-hand knurl, RBR: right-hand knurl, RGE: left-right knurl, raised tips, also known as checkering, RGV: left-right knurl, deepened tips, RKE: cross knurl, raised tips , RKV: cross knurling, deepened tips, RTR: circular knurling (continuous). The profile angle is 90°, in special cases also 105°. The knurling is arranged in the end region of the inner wall on the cylinder head side at the level of the top dead center position of the corresponding piston top land piston.

Pistons for reciprocating engines are mostly made of cast aluminum alloys, occasionally also of cast iron. The blanks are cast in molds. The pistons for high-performance turbodiesel engines are also forged to improve performance and to reduce consumption and emissions through higher ignition pressures. The lateral surface, the valve pockets, the piston ring grooves and the piston pin bore are then machined.

Technologically, there are differences between diesel and petrol engine pistons due to the different combustion processes.

Diesel pistons are subject to higher thermal and mechanical loads and therefore have to be cast in the first piston ring groove Ring carriers made of austenitic cast iron ("Niresist") are reinforced to prevent the groove from chipping and material transfer to the ring due to micro-welding. In the case of very highly loaded pistons, brass bushings are stretched in the pin bore. Another characteristic feature of the pistons of direct injection diesel engines is the bottom bowl, in which the injected fuel is swirled and mixed with the air. Pistons that are subject to high thermal loads - especially racing, aircraft or turbo diesel engines - are often implemented with spray nozzles for the engine oil to cool the piston crown. The piston can be provided with a circumferential oil duct or only be cooled by spraying the crown. In slow-running large engines, the piston can also be cooled by circulation cooling. The medium is fed to the piston through a telescoping tube.

The wall thickness of pistons in petrol engines is thinner than in pistons in diesel engines, which allows higher engine speeds due to the lower weight. Hard anodizing can sometimes be used in the area of the first piston ring groove to reduce wear and tear and microwelding.

The piston crown has partially flat pockets to accommodate the valves protruding into the combustion chamber.

The piston has the following functional parts: the piston head, which is in contact with the medium. The piston crown is also referred to as the top land. The fire bridge follows. It extends from the piston crown to the upper piston ring groove. It protects the first piston ring from overheating. The ring game follows. Together with the other grooves and ring lands, the top land forms the so-called ring section. This is followed by the piston skirt or the piston skirt or the piston wall, the cylindrical component that fits into the cylinder bore with a small clearance and the piston pin with its bearing, which connects the piston to the connecting rod.

The piston skirt serves to guide the piston in the cylinder tube and is coated with a bonded coating on most pistons. In older designs, it often has a cast-in steel strip (control piston, “control plate”, “autothermic piston”) on the inside to control the increase in diameter when it is heated. To save weight, many high-speed four-stroke engines today have the piston skirt offset inwards on the sides (at the piston pin openings) ("box" piston).

The piston carries one or more grooves for the piston rings, the top one being the compression rings and at least one bottom one serving as an oil scraper ring. Most car pistons have two compression rings and one oil scraper ring. So-called two-ring pistons with only one compression ring are also used for racing engines. In the case of two-stroke engines, the piston skirts can also be provided with windows. In addition, most two-stroke pistons have locking pins in the piston ring grooves to prevent twisting and binding of the piston ring gaps in the cylinder timing windows. In the past there were two-stroke engines with nose pistons, which were supposed to improve gas exchange with cross scavenging. For about 90 years, reverse scavenging two-stroke engines have had a flat piston crown.

The knurling described above scrapes the resulting carbon and other combustion residues from the top land surfaces of the piston, so that when the piston moves downwards towards bottom dead center (BDC), this cannot damage the honing and wear is reduced. There are several design criteria such as B. Piston tilting tendency, top land play, top land zone, etc., which define the minimum height of the knurling. This design height (throw height) is generally smaller for aluminum pistons than for steel pistons. The higher elevation places special demands on the manufacturing process, since the materials used are rather unsuitable for the ejection. In addition, safety distances must be observed, e.g. B. Knurling to the first piston ring. The knurling is an integral ring element of a cylinder or cylinder liner, located at the level of the top dead center position of the corresponding piston on the inner wall of the cylinder or a cylinder liner faces the piston at TDC or its top land. The clearance between the knurling and the top land surface is greatly reduced by oblique grooves that are angled to the cylinder axis or the axis of the cylinder liner and narrow the dead center position between the top land zone and the first piston ring.

In the first step, the cylinder liner, pushed by hand onto a vise and clamped, is given a clearance and an inner chamfer. As described above, a knurled wheel (specially ground) in the embossing process creates the knurling on the head side, facing the inner wall and located in the area of the top dead center position of the corresponding piston crown piston. Then the smallest inner diameter is turned. The release plays an important role in the manufacturing process. Stamping into the cylinder liner leads to material transport. If there is no clearance, the sealing surface of the cylinder or cylinder liner may become uneven.

The knurling is worked into the inner wall of the cylinder or the cylinder liner by machining or a printing or embossing process at the level of the top dead center position of the corresponding piston. According to the invention, it is provided for the sustainable and reliable degradation of the resulting oil carbon and other combustion residues. The grooves of the knurling are raised and thus narrow the area and strip the carbon from the piston outer contour in the area between the piston crown and the first piston ring and counteract wear or the reduction of the honing. A deposit is only possible in a very thin, fine layer. In terms of manufacturing technology, knurling by knurling - the knurling process described above - can be used for large-scale production.

According to a preferred embodiment of the invention, the execution of the grooves of the knurling in the cylinder liner or the cylinder is angled arranged to the cylinder axis or axis of the cylinder liner.

The knurling of the cylinder liner or cylinder removes any carbon deposits and other conceivable residues from the top land of the piston. The knurling of the cylinder liner or cylinder does not end with the first piston ring, but maintains a minimum safety distance to prevent damage to the piston ring. The raised knurling of the cylinder liner or cylinder on the inside has a narrowing effect and reduces play in the top land area. This means that there is less space for oil carbon to form, since the inner diameter in the knurling area is smaller due to the raised grooves.

Fig. 1:

einen Ausschnitt einer Brennkraftmaschine, der die Rändelung einer Zylinderlaufbuchse und einen dazugehörigen Kolben zeigt,

Fig. 2:

einen Ausschnitt der Rändelung, der die Rillen zeigt.

The invention is explained in more detail below using an exemplary embodiment. Show in the drawing:

Figure 1:

a section of an internal combustion engine showing the knurling of a cylinder liner and an associated piston,

Figure 2:

a section of the knurling showing the grooves.

1 shows a section of an internal combustion engine with a cylinder liner 1, the embossed knurling 7 in the area of the dead center position of the corresponding piston 2 on the cylinder head side on its inner wall 6. The piston 2 has piston rings 3, a piston crown 4 and the top land zone 5, which extends from the piston crown 4 extends to the first piston ring 3. The constriction of the cylinder liner 1 in the area of the top dead center position of the corresponding piston begins with the knurling 7, as shown in detail in 2 you can see. Due to the raised knurling that the cylinder liner 1 has on its inner wall, the inner diameter in this area (OT) is smaller than in the rest of the cylinder or the cylinder liner 1. As a result, in the top land zone 5 there can be no or only carbon in a very small amount low Amount or settle in a very thin layer, which increases wear and can damage the cylinder barrel and honing in the up and down movement of the piston 2. The grooves 8 of the knurling 7 are arranged at an angle and have an angle to the axis of the cylinder or the cylinder liner 1. The knurling 7 is an integral part of the cylinder or the cylinder liner 1 and can be machined from the preferred material of the cylinder or the cylinder liner 1 . There are also methods of chipless knurling to attach the knurling 7 in the cylinder or in the cylinder liner.

2 shows an enlarged view of the knurling 7 in a section parallel to the axis; the individual grooves 8 can be seen as integral components of the cylinder or the cylinder liner 1.

Reference List

1

cylinder liner

2

Pistons

3

piston ring

4

piston crown

5

fire land zone

6

inner wall

7

knurling

8th

groove

Claims (10)

Internal combustion engine, in particular diesel engine, in particular of a motor vehicle, with at least one working cylinder and a cylinder head closing the working cylinder, the working cylinder having a cylinder liner and/or a cylinder liner (1) and which in the area of the cylinder head or the top dead center of the corresponding piston (2nd ) of the cylinder liner or the cylinder liner (1) has at least one element that is suitable for wiping off any carbon that may form. Internal combustion engine according to claim 1,
characterized in that the element which scrapes the carbon produced is raised towards the corresponding piston (2). Internal combustion engine according to claim 1 or 2,
characterized in that the element has at least one circumferential groove (8). Internal combustion engine according to claim 1 or 2,
characterized in that the element has at least one knurl (7). Internal combustion engine according to claim 3,
characterized in that the knurling, which the cylinder liner or the cylinder liner 1 has on its inner wall, is raised. Internal combustion engine according to one or more of the preceding claims,
characterized in that the inner diameter of the cylinder liner or the cylinder liner (1) in the area of the cylinder head - TDC of the corresponding piston - is smaller than in the rest of the cylinder or the cylinder liner (1) due to the element for scraping off the carbon. Internal combustion engine according to one or more of the preceding claims,
characterized in that the element consists of at least one circular circumferential groove. Internal combustion engine according to one or more of the preceding claims,
characterized in that the element consists of circumferential grooves arranged in a circle one above the other. Internal combustion engine according to one or more of the preceding claims,
characterized in that the element consists of an internal thread. Method for operating an internal combustion engine,
characterized in that an internal combustion engine according to one or more of the preceding claims is used.

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