Diesel engine with high-pressure injection and charging function

Abstract

The invention relates to a diesel engine with a high-pressure injection and charging function [question for the inventor: which components define a "diesel engine" with the corresponding properties?] and / or a compression temperature of more than 700 °C and / or a combustion temperature of more than 1200 °C, a cylinder or a plurality of cylinders, each of which has a respective cylinder bore, a connecting rod which is paired with a respective cylinder, and a piston which is arranged in a respective cylinder bore and comprises an upper face, a lower face, and a circumferential surface with a nominal diameter, wherein the upper face is designed to receive pressure forces of a gas within the respective cylinder, the lower face has a connecting rod receiving area with an undercut which operates in a pulling direction and a pushing direction such that the connecting rod receiving area is designed to receive a thickened section of the respective connecting rod in a form-fitting manner and in a pivotal manner about a pivot axis, said thickened section corresponding to the receiving area, and the circumferential surface is designed to guide the piston in the respective cylinder bore along a movement axis, is equipped with a receiving area for a piston ring for sealing the piston off from the respective cylinder bore, and has a circumferential collar which protrudes from the upper face and has a height extending between the upper face and the receiving area for the piston ring. The invention additionally relates to a corresponding piston of a diesel engine.

Description

[0001] The invention relates to a diesel engine with high-pressure injection and turbocharging and / or a compression temperature of more than 700 °C and / or a combustion temperature of more than 1,200 °C, a cylinder or several cylinders with a respective cylinder bore, a connecting rod assigned to a respective cylinder and a piston arranged in the respective cylinder bore having a top surface, a bottom surface and a circumferential surface with a nominal diameter, wherein the top surface is designed to absorb pressure forces of a gas within the respective cylinder, and the bottom surface has a connecting rod receptacle with an undercut acting in a tensile and a compressive direction.such that the connecting rod receptacle is designed to receive a thickening of the respective connecting rod corresponding to the receptacle in a form-fitting manner and pivotable about a pivot axis, and the circumferential surface is designed to guide the piston in the respective cylinder bore along an axis of movement and with a receptacle for a piston ring for sealing the piston against the respective cylinder bore, and has a circumferential collar extending from the top with a height arranged between the top and the receptacle for the piston ring.

[0002] Diesel combustion engines have undergone extensive development. Modern diesel engines now utilize high-pressure fuel injection and forced induction, for example, with a compressor or turbocharger, resulting in correspondingly high compression and combustion temperatures and a significant increase in the power output relative to fuel consumption. This also reduces emissions. However, diesel engines are also reaching their technical limits, for example, regarding thermal management in the crankshaft assembly, particularly the pistons.The heat generated during combustion cannot be completely or quickly dissipated. Therefore, pistons in modern diesel engines must incorporate features to accommodate thermal expansion, such as ovality. They also often feature a pronounced "fire land," a recessed cross-section above the top piston ring extending towards the combustion chamber. This allows combustion heat to be directed laterally into the piston and thus reliably dissipated. This is particularly true for pistons with a conventional piston pin arrangement.

[0003] The purpose of the invention is to improve the state of the art.

[0004] The problem is solved by a diesel engine with high-pressure injection and turbocharging and / or a compression temperature of more than 700 °C and / or a combustion temperature of more than 1,200 °C, a cylinder or several cylinders with a respective cylinder bore, a connecting rod assigned to a respective cylinder and a piston arranged in the respective cylinder bore with a top, a bottom and a circumferential surface with a nominal diameter, wherein the top is designed to absorb pressure forces of a gas within the respective cylinder, the bottom has a connecting rod receptacle with an undercut acting in a tensile and a compressive direction,such that the connecting rod receptacle is designed to receive a thickening of the respective connecting rod corresponding to the receptacle in a form-fitting manner and pivotable about a pivot axis, and the circumferential surface is designed to guide the piston in the respective cylinder bore along an axis of movement and with a receptacle for a piston ring for sealing the piston against the respective cylinder bore, and has a circumferential collar extending from the top surface with a height arranged between the top surface and the receptacle for the piston ring, wherein a diameter of the circumferential collar is more than 98% of the nominal diameter of the circumferential surface.

[0005] Such a diesel engine has a piston which manages with a circumferential collar of almost the same size or the same size in relation to the nominal diameter of the circumferential surface, since in the described embodiment no pronounced fire bridge is necessary to keep the thermal management of the diesel engine within tolerable limits.

[0006] In this context, the following terms should be explained:

[0007] A "diesel engine" is an internal combustion engine, specifically a reciprocating piston engine, with compression ignition. In this process, injected fuel, for example, a petroleum product known as diesel fuel, is injected into a combustion chamber within a cylinder, particularly when the compression temperature has already been significantly increased by the compression of an air volume within the cylinder by a piston. This results in the self-ignition of the usually finely atomized fuel within the cylinder. In this context, the term "dieso-sotto engine" should also be mentioned, which operates on a hybrid principle between the diesel and Otto cycles with external ignition.Such a diesel engine features a "high-pressure injection" system, by means of which fuel, for example via a common rail or other arrangement, is injected into the combustion chamber at a typically very high injection pressure of, for example, over 1,000 bar. Likewise, such a diesel engine may have a "supercharger," whereby this supercharger is achieved by means of a compressor or a turbocharger, which, individually or in combination, forces air into the cylinder, thus achieving a higher cylinder filling and therefore a higher power output.

[0008] In this context, "compression temperature" is the temperature inside the cylinder reached when a piston in the crankshaft of a diesel engine compresses the intake air and prepares it for the combustion stroke. This compression process typically occurs immediately before the combustion stroke. In contrast, "combustion temperature" is the temperature reached when fuel is injected and the resulting combustion takes place.

[0009] A "cylinder bore" can, for example, be a cast and / or drilled bore within the engine block of an internal combustion engine, further refined by honing, for instance, creating a "cylinder." However, such a cylinder bore can also be a round or essentially round, open cavity in a steam engine, an expansion engine, or another type of power machine. The piston closes the cylinder bore at a final open end, so that pressure forces within the cylinder bore then act on the piston.

[0010] In a crankshaft drive, a connecting rod serves to mechanically connect a crankshaft to the reciprocating piston within the cylinder. The connecting rod is attached to the piston at a "head section," while a "foot section" connects to the head section via a "middle section," ensuring connection to an eccentric crankpin on the crankshaft. The head section has a thickened connection, and the foot section has a second connection for receiving the crankshaft.

[0011] A "piston" is a movable component which, together with a surrounding housing (in the case of a power engine, a "cylinder"), forms a closed cavity, the volume of which changes due to the movement of the piston within the cylinder. Such a principle can be implemented in various designs; in the present invention, a reciprocating piston movable up and down within a prismatically shaped cylinder is specifically described.

[0012] One "top" of such a piston is, for example, the piston crown, also known as the piston head, the area of ​​the piston that faces the combustion chamber in an internal combustion engine. This top surface, as illustrated by the example of the internal combustion engine, absorbs the pressure forces from the expanding, ignited gas mixture and thus transmits the forces necessary for the operation of the crank mechanism to the connecting rod and therefore to the crankshaft.

[0013] A "bottom side" is the side of the piston facing the connecting rod or connecting rod, in particular the side of the piston which has the connecting rod receptacle.

[0014] A "circumferential surface" is the area of ​​the piston that faces the cylinder bore in an internal combustion engine. The examples given refer to the standard design of a cylindrical piston, which is similar to a round disc, and the corresponding, essentially round, cylinder bore. However, other piston and cylinder bore shapes are also possible if technically feasible. The circumferential surface is also typically referred to as the piston skirt.

[0015] This circumferential surface has a so-called "nominal diameter", which, for example, denotes the desired diameter of the piston's circumferential surface.

[0016] A "gas" that exerts pressure forces can be a simple compressed gas, such as compressed air, or a gas produced by phase transition, such as superheated steam, or a gas mixture of, for example, ambient air and gasoline or diesel or another fuel, which exerts pressure forces through ignition, for example in a gasoline or diesel engine.

[0017] A "connecting rod receptacle" on the underside of the piston serves to hold a connecting rod in a tensile-resistant and pivotable manner, so that the piston together with the connecting rod in a so-called crank mechanism, i.e. for example in the case of a connecting rod mounted on a crankshaft, a force-fit connection of the piston to the crankshaft is established in such a way that the piston is force-fit to the connecting rod at the connecting rod receptacle.

[0018] An "undercut" refers to a design of a receptacle or part thereof in which a component, area, or sub-area prevents it from being pulled out in the direction of the force or enables the transmission of forces in a form-fit manner. Such an undercut can be the surface formed by a projection, which is then used by a component suspended or attached behind this undercut to transmit forces.

[0019] A "pivot axis" is, for example, the axis around which the connecting rod is rotatably or pivotably mounted on the piston. This pivot axis corresponds, for example, to the axis of the piston pin in the prior art.

[0020] A "thickening" of the connecting rod is an area that has a larger or wider cross-section or diameter than the preceding part of the connecting rod. In particular, such a thickening can serve, together with the undercut, especially with the surfaces formed by the undercut, to create a positive-locking, tensile- or compression-resistant connection.

[0021] An "axis of motion" describes an axis along which the piston moves, for example, during the rotation of a crankshaft. In particular, this axis of motion runs parallel to the central axis of a cylinder bore, although it is not a mathematically exact axis, but rather a corresponding direction with technically induced deviations.

[0022] A "piston ring" is a ring typically inserted into a circumferential groove of the respective piston, which acts as a sealing element between the piston and the cylinder bore. Such a piston ring is designed with different functions; in relation to the invention, the compression ring, usually located at the top and in direct contact with the combustion chamber in the cylinder, is meant here.

[0023] This piston ring serves to "seal" the piston, thus preventing the escape of combustion gases, in particular, past the piston into the cylinder bore towards the crankshaft of the internal combustion engine, especially the diesel engine.

[0024] A "circumferential collar" is a portion of the circumferential surface or a portion of the circumferential surface set off from the circumferential surface between the top surface and a receptacle, such as a ring groove, for the piston ring. This circumferential collar is also commonly known as a "fire land." The "diameter" of the circumferential collar is determined, for example, by a mean radius of the circumferential collar, i.e., a radius averaged using statistical methods across all points of the circumferential collar with respect to, for example, the axis of movement. Conversely, the nominal diameter of the circumferential surface can also be calculated in this way. The core of the invention lies in the fact that this circumferential collar, i.e., the fire land, ideally exhibits no radius difference compared to the circumferential surface beyond those inherent in the manufacturing process, meaning it can be manufactured, for example, in a single operation and setup.

[0025] To further simplify the manufacture of the diesel engine, in particular a piston for this diesel engine, the diameter of the circumferential collar is more than 99%, more than 99.5%, in particular more than 99.8% of the nominal diameter of the circumferential surface.

[0026] In one embodiment, the diameter of the circumferential collar is equal to the nominal diameter of the circumferential surface.

[0027] In this context, "equal" refers not only to mathematical equality but also to a technically determined equality. For example, when clamping a piston in a lathe to remove material in a defined manner to create the circumferential surface, the same tool setting with respect to radius is selected to produce both the circumferential surface and the circumferential collar. This significantly simplifies the manufacturing of the corresponding diesel engine, or rather, the corresponding piston.

[0028] To make the diesel engine more efficient and to further improve thermal management at the piston, the height of the circumferential collar along the axis of movement is less than 5%, less than 3%, less than 2%, and in particular less than 1% of the piston height.

[0029] This design results in a significantly flatter piston, with the top surface positioned closer to the piston ring. Combined with the connecting rod's thickened section for connection to an undercut in the piston, this design achieves excellent heat dissipation without requiring a pronounced piston crown. This, particularly in combination with the other previously mentioned features, offers the advantage of minimizing or eliminating combustion residues on the piston crown. Consequently, especially during alternating operation of the diesel engine between, for example, city and long-distance driving, this reduces damage caused by deposits being carried out of the cylinder, mechanical friction within the cylinder bore, or similar effects.

[0030] The piston's "height," and the related "height of the circumferential collar," describe the extension of the piston or its circumferential collar, respectively, along the axis of movement. The height of the circumferential collar is defined as the distance measured from, for example, an upper circumferential edge of the piston around its top surface to the uppermost piston ring. The piston's height, in particular, describes the distance between its top and bottom surfaces, whereby other parts of the piston, such as a piston skirt, may protrude above the bottom surface.

[0031] Such a "piston skirt", which refers to a tube-like extension of the piston towards the underside, i.e. towards the crankshaft, is designed to be particularly thin, resulting in a weight advantage and, ideally, greatly reducing thermal expansion.

[0032] In one embodiment, a radius of the circumferential surface, a radius of the circumferential collar, a radius of a nominal contour of the circumferential surface and / or a radius of the nominal contour of the circumferential collar has a deviation from a mean radius of the circumferential surface, mean radius of the circumferential collar, mean radius of the nominal contour of the circumferential surface and / or mean radius of the nominal contour of the circumferential collar of less than 1%, less than 0.5%, in particular less than 1‰.

[0033] This allows for a particularly round piston, enabling the diesel engine to be designed simply by using especially round, and therefore non-oval, pistons. In contrast to conventional diesel engines, where the piston must have an oval shape and different axes to accommodate thermal expansion, a diesel engine according to the invention thus requires very round pistons, which can be manufactured easily.

[0034] To further improve the piston's thermal expansion behavior, the piston is shaped such that a radially arranged, essentially planar first cross-sectional area extending through the axis of movement and a radially arranged, essentially planar second cross-sectional area extending through the axis of movement differ in size by less than 10%, less than 7%, less than 5%, and in particular by less than 2%. The reference point here is either the smallest cross-sectional area of ​​the respective comparison or an average cross-sectional area determined from any number of cross-sectional areas.

[0035] Thus, the corresponding cross-sectional areas of the piston are dimensioned in such a way that the thermal expansion behavior in different planes is identical or very similar, so that the piston can be used in the diesel engine over wide temperature ranges.

[0036] A corresponding "cross-sectional area" refers to a substantially flat surface that results from a conceptual cross-section of the piston along the axis of motion. This cross-sectional area is specified as an area measure, and the core of the invention lies in the fact that this cross-sectional area is equal to or similar to another cross-section rotated at an angle around the axis of motion.

[0037] In order to control thermal expansions more precisely, the piston is shaped such that a radially arranged, essentially flat first cross-sectional area extending through the axis of movement and a radially arranged, essentially flat second cross-sectional area extending through the axis of movement have sizes that differ from each other by less than 7%, less than 5% and / or less than 2%.

[0038] In this context, it should be noted that a first cross-sectional area and a second cross-sectional area can each denote arbitrary cross-sectional areas. For example, in one case, two cross-sectional areas with different reference axes, such as being perpendicular to each other, can be identical or similarly designed, so that, for instance, the thermal deformation behavior of the piston in the two principal directions is controlled. Likewise, the respective cross-sectional areas can be at any angle to each other, so that, in particular, a comparison of any cross-sectional areas around the circumference of the piston meets the aforementioned criteria.

[0039] In one embodiment, a piston skirt extending from the top to the bottom and / or beyond the bottom is arranged on the circumferential surface, wherein the piston skirt in particular has a radial thickness of less than 10%, less than 5% and / or less than 2% of a diameter of the piston.

[0040] Such a "piston skirt", which refers to a tube-like extension of the piston towards the underside, i.e. towards the crankshaft, is designed to be particularly thin-walled, resulting in a weight advantage and, ideally, a significant reduction in thermal expansion.

[0041] In order to compensate for the respective cross-sectional areas with respect to, for example, necessary thickenings and / or necessary parts of the piston, such as parts of the undercut, a compensation volume and / or several compensation volumes are arranged on the top and / or bottom, whereby a compensation for volume sections of the piston excluded from the respective cross-sectional area is created by means of the compensation volume and / or the compensation volumes.

[0042] Consequently, a corresponding compensation volume or volumes can be arranged in such a way that material of the piston is applied at a point where this is not technically necessary, so that the criteria of the size of different cross-sectional areas relative to each other are met.

[0043] In one embodiment, on the other hand, or additionally, a extraction volume and / or several extraction volumes can be excluded on the top and / or on the bottom, whereby a compensation for volume sections of the piston arranged on the respective cross-sectional area is created by means of the extraction volume and / or extraction volumes.

[0044] Thus, even in combination with corresponding compensation volumes, the extraction volumes can be used to compensate for corresponding surface areas.

[0045] A "compensation volume" describes an increase in volume, namely an additional amount of material applied, whereas a "removal volume" refers to a corresponding amount of material that is either absent or removed. For example, when casting a piston, an additional volume can be provided in the mold with respect to a corresponding removal volume, while a corresponding volume is removed from the mold with respect to a compensation volume. If the piston is manufactured using a machining process, for example, the corresponding compensation or removal volumes can be directly incorporated into a CNC milling program.

[0046] In order to influence the deformation behavior of the piston uniformly, several compensation volumes and / or several extraction volumes are arranged symmetrically to the axis of movement.

[0047] In one embodiment, the head region of the connecting rod has a first connection with a thickening for connecting a piston to a connecting rod receptacle of the piston, which has an undercut corresponding to the thickening, in a rotatable manner about the pivot axis, and the foot region has a second connection for receiving a crankshaft, and the head region is connected to the foot region via the central region, wherein the connecting rod has a lubricant guide connecting the second connection to the first connection in a fluid-carrying manner, so that a lubricant introduced into the lubricant guide at the second connection in the region of the crankshaft is guided through the lubricant guide to the first connection and the lubricant is available for lubricating and / or cooling the first connection.

[0048] Such an arrangement, with only a few modifications to known connecting rods, namely the provision of a lubricant guide along the connecting rod, ensures that the first connection between the connecting rod and the piston is reliably lubricated and / or cooled.

[0049] To simplify the design of the connecting rod, the lubrication system takes the form of a lubricant channel, which runs primarily along the central section. Such a lubricant channel can, for example, be a bore running along the central section of the connecting rod. Ideally, this ensures that only material in a neutral fiber of the bend-resistant central section passes through the channel, resulting in no or only negligible weakening of the connecting rod as a whole.

[0050] In one embodiment, the lubricant guide runs from a crankshaft eye associated with the second connection to the thickening, in particular from an inner surface of the crankshaft eye to the thickening.

[0051] With this embodiment of the invention, for example, a quantity of oil already present within a hollow crankshaft, and in particular under pressure, for lubricating the crankshaft bearing points in an engine housing, can be used to introduce it into the respective crankshaft bore. For this purpose, a corresponding bore or hole can be provided in the crankshaft bore or in a bearing shell inserted in the crankshaft bore, so that engine oil exiting under pressure from a crankshaft journal corresponding to the crankshaft bore can be introduced into the lubricant channel and drawn to thicken. Ultimately, the thickening, and thus the first connection between the connecting rod and piston, is reliably lubricated and cooled by means of the pressurized quantity of engine oil.

[0052] To enable particularly reliable and simple manufacturing of the connecting rod, the lubricant guide is introduced into the connecting rod by means of spark erosion and / or deep drilling.

[0053] This process, often simply called "electrical discharge machining" (EDM), can be used for high-precision material processing. The electrically conductive workpiece is immersed in a dielectric fluid and machined. An electrically conductive tool is brought close to the material, and the resulting voltage difference between the tool and the workpiece is used to generate sparks through localized discharge, primarily removing material from the workpiece.

[0054] In particular, in so-called die-sinking or drill EDM, a channel-like, eroded bore is created using a rod-shaped tool.

[0055] In contrast, "deep drilling" can be used as a special processing technique for drilling, whereby deep drilling is characterized by a drilling depth that is many times greater than the diameter.

[0056] In one embodiment, the lubricant guide on the thickening has a lubricant reservoir, wherein the lubricant reservoir is in particular introduced into an outer surface of the thickening and / or associated with the connecting rod receptacle.

[0057] This allows for a corresponding retention of lubricant, i.e., an additional amount of lubricant available in the area of ​​the thickening, and can also be used, for example, as a hydraulic cushion to prevent direct workpiece contact between an inner surface of the undercut and the outer surface of the thickening.

[0058] A "lubricant reservoir" can, for example, be provided as a depression in a surface of the thickening.

[0059] Similarly, a valve assembly can be assigned to this lubricant reservoir or another area of ​​the thickening. This valve assembly serves to control the flow of lubricant introduced into the lubricant guide at the second port in the area of ​​the crankshaft and guided through the lubricant guide to the first port by means of pivoting the thickening about the pivot axis.

[0060] Consequently, the amount of lubricant can be actively influenced by means of the valve device depending on the angular position of the pivoting of the thickening around the pivot axis, so that, for example, lubricating oil can only flow out when the connection between piston and connecting rod is unloaded or only slightly loaded.

[0061] The design of this valve device on the connecting rod can, analogously to the described valve device on the connecting rod, alternatively or additionally also be implemented as a synchronously acting valve device of a piston on the inner surface of the undercut according to a further aspect of the invention, such that a corresponding recess as a valve device is provided, for example, in this inner surface of the piston.

[0062] The invention will now be explained using exemplary embodiments. These will show... Figure 1 shows a schematic representation of a crank unit with a piston and a connecting rod in an isometric view; Figure 2 shows the piston of the crank unit. Figure 1 in a schematic side view, Figure 2b the piston in a schematic view from below, Figure 2c the piston of the Figure 2bin a sectional view AA, Figure 2 the piston in a bottom view with different section planes, Figure 3 the connecting rod of the Figure 1 in a schematic side view, Figure 3b the connecting rod in an isometric view, Figure 4 in a side view, partially cut away, an embodiment of a crank mechanism with a piston according to the invention and Figure 5 in a perspective view, partially cut away, an embodiment of a reciprocating internal combustion engine with a piston according to the invention.

[0063] A crank unit 101 comprises a piston 201 and a connecting rod 301. on.The crankshaft assembly 101 is part of a diesel engine (not shown), whereby the corresponding diesel engine can, for example, have four, six, or even eight of these crankshaft assemblies, with the respective pistons 201 being movably mounted along an axis of movement 281 within the corresponding cylinders. The connecting rod 301 is mounted around a crank axis 185 on the respective crankpin of a crankshaft 401 designed according to the number of cylinders. The diesel engine is, for example, configured as an inline four-cylinder, inline six-cylinder, or V8 engine. Each of these is a diesel engine with high-pressure injection for diesel fuel and turbocharging and / or supercharging, resulting in high combustion temperatures in the respective cylinder. Other designs can, of course, also be represented by the crankshaft assembly 101 in the corresponding number. The piston 101 is made of an aluminum alloy.

[0064] The connecting rod 301 is forged from steel and machined. It is pivotally mounted about a pivot axis 183 relative to the piston 201, so that during a complete rotation of the crankshaft (not shown), the crank axis 185 is guided in a circular motion. The piston 201 is moved up and down in the cylinder by means of the connecting rod 301, thus completing a full rotation of the crankshaft without mechanical obstruction. Gas pressure generated on a top surface 203 of the piston 201 by the combustion of, for example, injected diesel fuel, drives the piston 201, so that the engine operates according to the diesel principle. The injected diesel fuel is ignited by the compression of intake air in the cylinder. The compression temperature is over 700 °C, and the resulting combustion temperature is over 1,200 °C.The thermal influences on piston 201 are correspondingly high.

[0065] The piston 201 has, in addition to the surface 203 facing towards the combustion chamber in the cylinder, a circumferential surface 205 and a bottom surface 207. Within the top surface, a combustion chamber 241 with a conical cap 243 is arranged concentrically to the axis of movement 281, which widens the combustion chamber of the cylinder in the piston 201.

[0066] A predominant portion of the circumferential surface 205 forms a piston skirt, which is cylindrical towards the underside 207 and has thin walls. Starting from the top surface 203, the piston 201 has a narrow circumferential collar 221, which forms a gap between the top surface 203 and a first annular groove 223. A piston ring is arranged within this first annular groove 223 for sealing against the cylinder. Further towards the underside 207, an annular groove 225 and an annular groove 227 are arranged, with another piston ring inserted in the annular groove 225 as a sealing ring, and a piston ring in the annular groove 227 functioning as an oil scraper ring (piston rings not shown). Additionally, bores 229 are arranged in the annular groove 227, which facilitate the drainage of engine oil.

[0067] The circumferential collar 221 is known in diesel engines according to the prior art as a so-called "fire land" and in these engines is designed with a significantly smaller diameter than the circumferential surface of a piston. The circumferential collar 221, however, has a radius 282, which, within technical tolerances, is identical to a radius 284 of the circumferential surface 205. The piston 201 can thus be manufactured with respect to its cylindrical shape in a single setup and with a single adjustment on a lathe.

[0068] The circumferential collar 221 can be designed in this way because the usual function of a "fire bridge" in the prior art, namely additional heat dissipation via this fire bridge through a thinner diameter and thus access for the combustion gases in the piston 201, can be omitted. Further explanations are given below.

[0069] On its underside 207, the piston 201 has a receptacle 210 for the connecting rod 301. The receptacle 210 is essentially formed by an undercut 211, which has an inner surface 213 arranged concentrically around the pivot axis 183 and is bounded by an edge 217. To keep the undercut 211 accessible along the pivot axis 183 and to allow machining of the undercut 211 with the inner surface 213, the piston skirt 219 has a cutout 220 on both sides along the pivot axis 183. Through this cutout 220, the connecting rod 301 can be inserted into the piston 201, and a suitable tool for finishing the inner surface 213 can be inserted without obstruction during the prior machining of the piston 201.

[0070] Visible from the underside of piston 201 (see also Figure 2bThe piston 201 has different volumes. In addition to the volumes of the piston 201 directly dictated by technical requirements, namely the volume for forming the recess 210 with the undercut 211, the volume for the piston skirt 219, and corresponding volumes for creating smooth geometric transitions, the piston 201 has thickenings 231 arranged symmetrically to the axis of movement 281, pockets 233 also arranged symmetrically to the axis of movement 281, and additional thickenings 235 arranged symmetrically to the axis of movement 281 and in the direction of the pivot axis 183. The corresponding volumes of the thickenings 231, the pocket 233, and the thickenings 235 are selected such that arbitrary cross-sectional surfaces formed by the axis of movement 281, for example, cross-sectional surfaces along a cutting plane 271, a cutting plane 273, or a cutting plane 275 (see also Figure 2d), each with an area equal to, for example, 2% with respect to the smallest cross-sectional area of ​​the respective comparison. This geometric design ensures that the thermal expansion behavior of the piston 201 is nearly identical or even identical in different polar positions around the axis of movement 281. For this purpose, material is added at the thickening 231, material is subtracted at the pocket 233, and material is added at the thickening 235. Thus, for example, technically determined volumes, such as for the receptacle 210, are compensated accordingly in the respective cross-sectional planes. Similarly, a respective thickening 235 serves, for example, to at least partially compensate for the material missing at the cutout 220 in the piston skirt 219 to achieve corresponding cross-sectional areas. Other components are compensated analogously by subtracting or adding corresponding volumes of material from the piston 201.

[0071] Within the inner surface 213 of the undercut 211, annular grooves 215 are provided symmetrically to both sides of the pivot axis 183 and the axis of movement 281. Due to the shape of the undercut 211, these annular grooves are formed as partial annular grooves 215. Each annular groove 215 has a cross-section extending from a diameter 216 of the inner surface 213 to a diameter 218.

[0072] The connecting rod 301 has a connecting rod head 303, a central section 305, and a crankshaft connection 307. The connecting rod head is designed as a thickened section with a cylindrical outer surface 311. Taking necessary tolerances into account, the outer surface 311 corresponds to the diameter 216 of the inner surface 213 of the piston 201. Furthermore, chamfers 312 are arranged at the end regions of the thickened section in the direction of the pivot axis 183. Thus, the connecting rod head 303 can be inserted into the piston 201 along the pivot axis 183, forming a pivot joint with freedom of movement about the pivot axis 183.

[0073] The central section 305 connects the connecting rod head 303 to the crankshaft connection 307 and has a recess 306 on both sides along its extension between the connecting rod head 303 and the crankshaft connection 307, so that the central section 305 has a rigid cross-section corresponding to a double-T beam. Additionally, webs 315 with recesses 316 formed opposite the central section 305 are arranged such that the central section 305 is additionally rigidly connected to the crankshaft connection 307 while remaining as lightweight as possible.

[0074] The crankshaft connection 307 is formed approximately half from a section of the connecting rod 301 and a so-called cover 308, together forming the crankshaft eye 309, which is arranged concentrically around the crank axis 185. To create a low-friction, wear-resistant, and emergency-running connection to the crankshaft, the crankshaft eye 309 is provided with a bearing shell 321. The bearing shell is arranged in the crankshaft eye 309 in a rotationally fixed manner, so that the position of the bearing shell 321 relative to the connecting rod 301 is rotationally fixed.

[0075] Furthermore, the connecting rod 301 has a valve groove 341 on the outer surface 311 of the connecting rod head 303, which is connected to an outlet opening 343. The outlet opening 343 is part of an oil channel 345, which runs between the outlet opening 343 and an inlet opening 347 located within the crankshaft eye 309. The oil channel 345 is arranged in the neutral axis of the central region 305, so that the oil channel 345 causes minimal weakening of the central region 305, particularly against bending.

[0076] To mount the connecting rod 301 to the piston 201, the connecting rod head 303 is inserted into the undercut 211 along the pivot axis 183. An elastic retaining ring with a round wire cross-section is inserted within the annular groove 215, such that a portion of the retaining ring (not shown) extends into the cross-section of the undercut 211 formed by the inner surface 213. This retaining ring is then forced back into the annular groove by means of the chamfer 312 on the connecting rod head 303, the cross-section of the retaining ring being selected such that it can be positioned completely between the diameter 216 and the diameter 218.

[0077] The chamfer 312 thus facilitates the insertion of the connecting rod head 303 into the piston 201. Once the connecting rod head 303 is inserted completely symmetrically, a corresponding retaining ring springs back into its initial position and secures the connecting rod 301 to the connecting rod head 303 against unintentional removal along the pivot axis 183.

[0078] The function of the crank unit 101 with regard to the lubrication of the connection between the connecting rod head and the piston 201 in the undercut 211 is explained as follows:

[0079] Within the crankshaft (not shown), an oil channel running inside the crankshaft with corresponding outlet bores at the bearing points is provided for lubricating the respective bearing points. Likewise, the crankshaft has corresponding outlet bores for pressurized engine oil at the crankpins, which receive the respective connecting rod 301 around the crank axis 185. The engine oil is then held in a circumferential annular groove on the crankshaft and is forced through the inlet opening 347 into the oil channel 345 and on to the outlet opening 343. The outlet opening 343, together with the valve groove 341, creates an oil reservoir in which pressurized engine oil is available for lubricating the undercut 311.

[0080] Furthermore, the valve groove 341 serves to control the oil flow depending on the position of the crankshaft and the resulting position of the connecting rod 301 and the piston 201. When the piston 201 has reached top dead center or bottom dead center, the connecting rod 301 is essentially vertical within the cylinder bore along the axis of motion 281. In this state, the valve groove 341 is completely surrounded by the inner surface 213 of the undercut 211, so that no oil can escape through the valve groove 341. At this moment, for example, when the fuel ignites in the cylinder, reliable lubrication and ideal heat transfer between the piston 201 and the connecting rod 301 are ensured. Likewise, the oil cushion maintained in the oil reservoir further prevents direct material contact.

[0081] When the piston 201 is accelerated by the combustion gases, the crankshaft initially pivots by approximately 90°, deflecting the connecting rod 301. The valve groove 341 is dimensioned such that a portion of it is exposed at an edge 217 of the undercut 211. At this moment, pressurized engine oil, guided through the oil channel 345, can escape and thus also dissipate heat from the area of ​​the undercut 311. In this state, the connection between the connecting rod head 303 and the undercut 211 is subjected to relatively low stress, so the escape of engine oil can be advantageously utilized here, even if this results in less oil being available for lubrication.

[0082] When the crankshaft reaches bottom dead center (180°), the undercut 311 closes the valve groove 341. At this moment, the inertial forces of the piston 201 can again be absorbed with full oil pressure. At this point, further heat transfer to the engine oil occurs. At a crankshaft position of 270°, the oil pressure again dissipates heat from the open valve groove 341, which is released by the edge 217. Up to a crankshaft position of 360° (full angle, corresponding to 0°), the valve groove 341 is repeatedly closed by the edge 217, so that at top dead center, full oil pressure is again present at the connection point, allowing for renewed heat dissipation. This cycle is repeated with every crankshaft revolution, resulting in sufficient lubrication of the movement around the pivot axis 183 and optimized heat dissipation from the piston 201.

[0083] Figure 4 Figure 1 shows a partially cutaway side view of an embodiment of a crank mechanism according to the invention, wherein the crank mechanism comprises a piston 201 according to one of the embodiments described above, a corresponding connecting rod 301 – i.e., a crank unit 101 – and a crankshaft 401. The connecting rod 301 is coupled to the crankshaft 401 in the usual manner. The piston 201 is movable in a cylinder arrangement 501 along an axis of movement 281.

[0084] Figure 5Figure 1 shows a perspective and partially cutaway view – in a section – of an embodiment of a reciprocating internal combustion engine 601 in the form of a diesel engine with a cylinder arrangement 501 with four cylinders to form an inline four-cylinder engine and with pistons 201 and connecting rods 301 according to one of the above embodiments. Each piston 201 and one connecting rod 301 form a crank unit 101. The connecting rod 301 is coupled to a crankshaft 401.

[0085] In the Figures 4 and 5 For the sake of clarity, the "internal structure" of the piston 201 and the connecting rod 301 is not shown in the illustrated embodiments.

[0086] In this context, it should be noted that in all the embodiments of the diesel engine and the piston 201 described above, the geometric design of the piston 201, as outlined above, further optimizes heat dissipation. The central connection of the connecting rod 301 in the receptacle 210 of the piston 201 enables good heat conduction, thus eliminating the need for the "fire land" known from the prior art. Together with the simple geometry and uniform roundness of the piston 201, this allows for the production of a diesel engine that is both easy to manufacture and highly efficient.

[0087] As a result, the diesel engine can be operated with high combustion temperatures, thus enabling low-emission and efficient combustion, since good thermal management is ensured by the geometry of the piston 201, the compact design, the central heat dissipation into the connecting rod 301, and the controlled oil flow of the engine oil. Overall, the combination of piston 201 and connecting rod 301 according to the invention therefore has a very low weight and thus reduced moving masses. It should be noted that although this type of piston 201 and connecting rod 301 has been illustrated in the present example for a diesel engine with high-pressure injection and turbocharging, the corresponding arrangement of piston 201 and connecting rod 301 is also suitable for other reciprocating engines, for example, gasoline engines, supercharged engines, or gasoline engines. Reference symbol list

[0088] 101 Crank unit 183 Swivel axis 185 Crank axis 201 Piston 203 Top 205 Circumferential surface 207 Bottom 210 Receptacle 211 Undercut 213 Inner surface 215 Annular groove 216 Diameter 217 Edge 218 Diameter 219 Piston skirt 220 Cutout 221 Circumferential collar 223 Annular groove 225 Annular groove 227 Annular groove 229 Bore 231 Thickening 233 Pocket 235 Thickening 241 Combustion chamber 243 Spherical cap 261 Width 271 Cutting plane 273 Cutting plane 275 Cutting plane 281 Axis of movement 282 Radius 284 Radius 301 Connecting rod 303 Connecting rod head 305 Center area 306 Recess 307 Crankshaft connection 308 Cover 309 Crankshaft eye 311 Outer surface 312 Chamfer 315 Web 316 Recess 321 Bearing shell 341 Valve groove 343 Outlet opening 345 Oil channel 347 Inlet opening 401 Crankshaft 501 Cylinder arrangement 601 Reciprocating internal combustion engine

Claims

1. Diesel engine comprising a high-pressure injection and a supercharging and / or a compression temperature of more than 700°C and / or a combustion temperature of more than 1200°C, a cylinder or a plurality of cylinders, each having a respective cylinder bore, a connecting rod (301) associated with a respective cylinder, wherein the connecting rod (301) has a head region, a foot region and a middle region (305), wherein the head region is connected to the foot region via the middle region (305), and a piston (201) arranged in the respective cylinder bore, having an upper side (203), an underside (207) and a circumferential surface (205) having a nominal diameter (284), wherein the upper side (203) is configured for receiving pressure forces of a gas within the respective cylinder, characterized in that the underside (207) has a connecting-rod receptacle (210) which has an undercut (211) acting in a tensile and in a compressive direction, such that the connecting rod receptacle (210) is configured to receive, in a form-fitting manner and pivotable about a pivot axis (183), a thickened portion (303) in the head region of the respective connecting rod (301) that corresponds to the undercut (211) of the connecting-rod receptacle (210), the circumferential surface (205) is configured for guiding the piston (201) in the respective cylinder bore along an axis of movement (281) and is configured with a receptacle (223) for a piston ring for sealing the piston (201) with respect to the respective cylinder bore, and has a circumferential collar (221) extending from the upper side (203) and having a height arranged between the upper side (203) and the receptacle (223) for the piston ring, and wherein a diameter (282) of the circumferential collar (221) is more than 98% of the nominal diameter (284) of the circumferential surface (205).

2. Diesel engine according to claim 1, characterized in that the diameter (282) of the circumferential collar (221) is more than 99%, more than 99.5%, in particular more than 99.8%, of the nominal diameter (284) of the circumferential surface (205).

3. Diesel engine according to claim 1 or 2, characterized in that the diameter (282) of the circumferential collar (221) is equal to the nominal diameter (284) of the circumferential surface (205).

4. Diesel engine according to one of the preceding claims, characterized in that the height of the circumferential collar (221) along the axis of movement (281) is less than 5%, less than 3%, less than 2%, in particular less than 1%, of a height of the piston (201).

5. Diesel engine according to one of the preceding claims, characterized in that a radius of the circumferential surface (205), a radius of the circumferential collar (221), a radius of a nominal contour of the circumferential surface (205) and / or a radius of the nominal contour of the circumferential collar (221) has or have a deviation from a mean radius of the circumferential surface (205), a mean radius of the circumferential collar (221), a mean radius of the nominal contour of the circumferential surface (205) and / or a mean radius of the nominal contour of the circumferential collar (221) of less than 1%, less than 0.5%, in particular less than 1‰.

6. Diesel engine according to one of the preceding claims, characterized in that the piston (201) is shaped such that a first substantially planar cross-sectional area (271), arranged radially and extending through the axis of movement (281), and a second substantially planar cross-sectional area (273, 275), arranged radially and extending through the axis of movement, have sizes differing from one another by less than 10%, less than 7%, less than 5%, in particular less than 2%.

7. Diesel engine according to claim 6, characterized in that on the upper side (203) and / or on the underside (207) a compensation volume (231, 235) and / or a plurality of compensation volumes (231, 235) are arranged, wherein by means of the compensation volume (231, 235) and / or by means of the compensation volumes (231, 235), compensation is created for volume portions of the piston (201) removed at the respective cross-sectional area (271, 273, 275).

8. Diesel engine according to claim 6 or 7, characterized in that on the upper side (203) and / or on the underside (207) a deduction volume (233) and / or a plurality of deduction volumes (233) are recessed, wherein by means of the deduction volume (233) and / or by means of the deduction volumes (233), compensation is created for volume portions of the piston (201) arranged at the respective cross-sectional area (271, 273, 275).

9. Diesel engine according to one of the preceding claims, characterized in that the thickening (303) corresponding to the undercut (211) of the connecting-rod receptacle (210) has a first connection (303) for rotatably connecting the piston (201) about the pivot axis (183), the connecting rod (301) has a second connection (307) for receiving a crankshaft, and the middle region (305) connects the first connection (303) and / or the thickening (303) to the second connection (307), wherein the connecting rod (301) has a lubricant guide (343, 345, 347) fluid-conductingly connecting the second connection (307) to the first connection (303), such that lubricant introduced into the lubricant guide (343, 345, 347) at the second connection (307) in the region of the crankshaft is guided through the lubricant guide (343, 345, 347) to the first connection (303), and the lubricant is present for lubricating and / or cooling the first connection (303), wherein the lubricant guide (343, 345, 347) in particular has a lubricant channel (345), wherein the lubricant channel (345) in particular extends along the middle region (305).

10. Diesel engine according to claim 9, characterized in that the connecting-rod receptacle (210) has a control device for controlling a lubricant flow introduced into the lubricant guide (343, 345, 347) at the second connection (307) in the region of the crankshaft and guided through the lubricant guide (343, 345, 347) to the first connection (303), wherein in particular the control device has a control pocket introduced into an inner surface (213) of the undercut (211), or a plurality of control pockets introduced into an inner surface (213) of the undercut (211), such that in particular in the region of a top dead center and / or in the region of a bottom dead center of the piston (201) in the cylinder bore and / or of a substantially rectilinear arrangement of the connecting rod (301) with respect to an axis of movement (281) of the piston in the cylinder bore, the lubricant flow is limited or prevented.

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