Internal combustion engine according to the opposed piston principle

Abstract

The invention relates to an internal combustion engine based on the opposed-piston principle, with an arrangement of two opposed pistons running in a cylinder with a common combustion chamber and equipped with piston rings, wherein the opposing pistons act on their own crankshafts via connecting rods and connecting rod bearings and eccentrics, and each of the two crankshafts has its own mechanical output, and the two outputs are each provided with a drive belt pulley, and the two drive belt pulleys are coupled via a drive belt and the piston movements are synchronized therewith, according to the preamble of claim 1.In order to further develop the aforementioned combustion engine in a compact design with high power density in such a way that it is designed to be resistant to high temperatures for the use of hydrogen and hydrogen-containing biofuels (biofuels) at high continuously available power, it is proposed according to the invention that the connecting rod bearings (8a, 8a') can be supplied with lubricant via a centrifugal disc (10, 10') also arranged on each crankshaft (5, 5') and an injector (9, 9') located in the immediate vicinity of the centrifugal disc (10, 10'), via which a drip or spray injection of lubricant can be carried out at adjustable cycle times, and that both the cylinder (2) and the piston rings (4, 4') of the pistons (3, 3') are made of a metallic material, while the pistons themselves are made of a carbon or carbon ceramic material.

Description

[0001] The invention relates to an internal combustion engine based on the opposed-piston principle, with an arrangement of two opposed pistons running in a cylinder with a common combustion chamber and equipped with piston rings, wherein the opposing pistons act on their own crankshafts via connecting rods and connecting rod bearings and eccentrics, and each of the two crankshafts has its own mechanical output, and the two outputs are each provided with a drive belt pulley, and the two drive belt pulleys are coupled via a drive belt and the piston movements are synchronized therewith, according to the preamble of claim 1.

[0002] Internal combustion engines based on the two-stroke opposed-piston principle are well-known and historically trace their origins back to the so-called Junkers engine. Two opposing pistons move within a single cylinder. The piston movements are precisely synchronized so that they converge simultaneously in one stroke, thus achieving enormous compression in the combustion chamber. It is crucial that their movements are perfectly synchronized and that ignition occurs at the exact moment of maximum compression. This engine type offers significant advantages in terms of the power-to-displacement ratio. Consequently, the engine is remarkably compact relative to its achievable power output.

[0003] An example of a precisely synchronized motor of this type is known from DE 10 2011 114 854 A1 and from US 2005 / 0274332 A1.

[0004] Considering the so-called eco-efficiency, there is a continuing trend towards electric drives in vehicles. A persistent problem is the limitation of electrical energy storage capacity in vehicles to achieve sufficient range even under less than ideal driving conditions and in winter conditions.

[0005] Regarding alternative fuels, it should be noted that not all conventional combustion engines can be converted to run on sustainable, renewable fuels without considerable effort. This applies to liquid fuels as well as gaseous fuels. These include biogas, but above all, hydrogen.

[0006] With regard to the already described high performance in terms of displacement and thus also in terms of the small-scale design of such engines, known measures for high-temperature resistant lubrication of such engines often fail.

[0007] Regarding engine lubrication in the piston-cylinder area, it is common practice in the prior art for the cylinder inner surfaces to be honed. This surface treatment affects the so-called tribological properties, reducing friction. However, after honing, the inner surface is not actually smooth, but rather exhibits a fine grooved structure, resembling a cross-hatch pattern. The use of lubricants, i.e., lubricating oils, increases friction. When using the aforementioned hydrogen-containing fuels, oil lubrication is disadvantageous or even impossible.

[0008] The invention is based on the objective of further developing the said combustion engine in a compact design with high power density in such a way that it is designed to be resistant to high temperatures for the use of hydrogen and hydrogen-containing biofuels at high available continuous power.

[0009] The problem set out is solved according to the invention in an internal combustion engine of the generic type by the characterizing features of claim 1.

[0010] Further advantageous embodiments are specified in dependent claims 2 to 10.

[0011] The core of the invention is that the connecting rod bearings can be supplied with lubricant via a centrifugal disc also arranged on each crankshaft and an injector located in the immediate vicinity of the centrifugal disc, via which a drip or spray injection of lubricant can be carried out at adjustable cycle times, and that both the cylinder and the piston rings of the pistons are made of a metal material, while the pistons themselves are made of a carbon or carbon ceramic material.

[0012] A conventional oil pan, such as that known from DE 10 2011 114 854 A1 for opposed-piston engines, into which moving parts of the crankshaft or eccentric must immerse, is omitted here. Instead, precisely positioned and metered lubrication is provided by injectors exactly where it is needed.

[0013] Since oxygen is also to be used when hydrogen is used as fuel, the use of oil lubrication in the combustion chamber is out of the question anyway.

[0014] The cylinder, or rather its inner wall, is made of steel, preferably the type used for high-strength hydraulic tubing. The pistons are made of carbon or carbon-ceramic material. The piston rings are also made of steel and, as usual, sit in circumferential grooves, the piston ring seats, on the piston. Lubrication in this area is achieved by the steel piston rings generating a fine abrasion of carbon dust in the groove of the carbon or carbon-ceramic piston (i.e., the piston ring seat). This dust then lubricates the steel piston rings against each other within the steel cylinder. A further, albeit very small, abrasion of carbon material, necessary only during startup, also lubricates the piston within the cylinder.Long-term and continuous operation tests have shown that this relatively low abrasion of the carbon material is sufficient to lubricate pistons with piston rings in the cylinder.

[0015] This lubrication effect remains active even after the engine is switched off and subsequently restarted.

[0016] In a further advantageous embodiment, it is specified that the centrifugal discs are each provided with a circumferential groove on the side supplied with lubricant by the injectors, into which the lubricant is injected, and that each groove is provided with at least one axial through-opening which aligns with a through-opening through the respective eccentric to the respective needle bearing of the connecting rod. In this way, the lubricant is metered directly to the required location.

[0017] In the area of ​​the connecting rod-crankshaft connection, i.e. the connecting rod bearings, injectors only provide lubrication as needed, localized to the lubrication required there.

[0018] Carbon or carbon-ceramic materials, e.g. materials with the designation FE 679, FE 709, FE 679 Q from the company Schunck Kohlenstofftechnik GmbH, Heuchelheim, Germany, can be used as starting materials for the aforementioned pistons.

[0019] The following material parameters of the carbon or carbon-ceramic materials are important for the implementation of the invention: - Bulk density from 1.75 to 1.98 (g / cm³<) - Porosity from 6 to 11 (%) - Flexural strength from 55 to 90 (MPa) - compressive strength from 145 to 245 (MPa) - modulus of elasticity 15 to 26 (GPa) - Coefficient of thermal expansion. 5.1 to 7.5 (10 -6< / K) - Rockwell hardness HR5 / 150 110 to 120 - thermal conductivity from 37 to 62 (W / mK) - Medium grain size from 8 to 12 (µm)

[0020] In an advantageous embodiment, the lubricant injection quantity is adjustable. This reduces the lubricant consumption to the actual necessary amount. Furthermore, it is advantageous that the cycle times between injections are adjustable. This also reduces the amount of lubricant and limits lubrication to the necessary areas.

[0021] In a further development, the lubricant can be a liquid lubricant, which includes lubricating oils, provided that this is limited to the connecting rod bearings.

[0022] Alternatively, the lubricant can consist of a dust-fine, dry, carbon-based lubricant. This is similar to a graphite powder, formed from the abrasion of the carbon or carbon-ceramic material, and does not need to be supplied externally.

[0023] In an advantageous embodiment, it is specified that the injectors for the lubricant are fed from a lubricant reservoir into which lubricant that can be returned from the said connecting rod bearing is returned.

[0024] In one design version, the lubricant for the connecting rod bearings can consist of a dust-fine, dry, carbon-based lubricant.

[0025] In a further advantageous embodiment, the bearings or bearing shells of the crankshafts can be made of carbon or carbon-ceramic material. The microfine abrasion that occurs at the beginning of operation effectively provides solid lubrication in this area. Since this type of lubrication is extremely temperature-resistant, fuels that operate at higher and therefore more efficient combustion temperatures can be used. This applies particularly to hydrogen and hydrogen-containing gas mixtures.

[0026] In a further specification, it is stated that the fuel used consists at least partially of hydrogen.

[0027] In a further advantageous embodiment, it is specified that the fuel consists of the two components hydrogen and oxygen, which can be introduced into the combustion chamber in gaseous form from two separate tanks.

[0028] One embodiment of the invention is shown in the drawing and described in more detail below.

[0029] It shows: Figure 1 : Perspective view of the internal combustion engine according to the invention Figure 2 : Slingshot disc Figure 3 : further illustration of the internal combustion engine

[0030] Figure 1Figure 1 shows a perspective view of the engine 1. Pistons 3, 3', acting as opposed pistons, are arranged within cylinder 2. These contain piston rings 4, 4' made of a carbon or carbon-ceramic material with the aforementioned specific material properties. In the preferred embodiment, the piston rings and the cylinder inner wall are made of steel.

[0031] The cylinder is made of steel suitable for hydraulic cylinders. The inner cylinder wall is polished accordingly.

[0032] For this purpose, for example, hydraulic pipes made of precision steel tubes according to DIN EN 10305-4 can be used very advantageously.

[0033] A particular aspect essential to the invention lies in the use of internally polished hydraulic tubes as cylinders for this engine according to the invention. In contrast to the cylinder inner surfaces used in the prior art, which are honed and thus have a grooved structure, the inner surfaces of the cylinder according to the invention are completely polished smooth. In the prior art, honing these surfaces is intended to increase the adhesion of lubricating oil.

[0034] The new type of lubrication in the piston-cylinder area is achieved entirely through the (short-term) abrasion of the carbon material. This is an important feature for the effects achieved in the combustion engine according to the invention, in conjunction with the lubrication via the finest abrasion of the carbon material already described above. Thus, not only is a honed cylinder inner surface unnecessary, but it would even be counterproductive in the present invention.

[0035] According to the invention, the two pistons 3, 3', which run as opposing pistons in cylinder 2, are made of carbon or carbon-ceramic material. One of the pistons runs on the crankshaft 5 via a piston-connecting rod-crankshaft connection, and the opposing piston runs on the crankshaft 5' accordingly. Both pistons compress the same compression chamber in cylinder 2.

[0036] The pistons 3, 3', which are not visible in detail, are known to be equipped with piston rings made of steel. These rings are seated in circumferential grooves around the pistons in so-called piston ring seats. During initial operation, the steel piston rings 4, 4' rub against the piston ring seats of the carbon or carbon-ceramic pistons 3, 3', producing a microfine abrasion of carbon dust that is deposited on the contacting friction surfaces. This condition is reached within a period of less than 0.5 seconds. From this moment on, the friction is so significantly reduced that virtually no further abrasion occurs. As the temperature continues to rise, friction and abrasion then adjust to the operating conditions.

[0037] The connecting rod connections engage eccentrics 8, 8' on the crankshafts 5, 5' on both sides of the internal combustion engine. On these same crankshafts, in addition to the connecting rod-crankshaft connection, the aforementioned centrifugal discs 10, 10' are arranged. These are supplied with injected lubricant by an injector 9, 9' on each piston shaft. For this purpose, the injectors are connected to lubricant reservoirs and pumps (not shown here), which supply minimally metered lubricant at adjustable cyclic intervals. The lubricant is supplied via at least one through-hole 12 in each of the centrifugal discs 10, 10', which extends with the further opening in the eccentric to the area of ​​the connecting rod needle bearings, thus creating a lubricant-locked connection from outside the eccentric, even as far as the connecting rod needle bearings 8a, 8a'.

[0038] This limits the lubrication required in the connecting rod area to the necessary minimum. Any dripping lubricant is collected, filtered if necessary, and returned to the injector(s) at each centrifugal disc.

[0039] In another embodiment, parts of the connecting rod and crankshaft bearings, i.e., bearing shells and / or bearing washers of the connecting rod-crankshaft connection, can be made of the aforementioned carbon or carbon-ceramic material. In this embodiment, this area would also be lubricated in the manner described above, with minimal wear of the mating surfaces. Optionally, in this case as well, the injectors can be configured so that the powdered wear particles are returned to the injectors.

[0040] The two opposing crankshafts 5, 5' are coupled to each other via drive belt pulleys 6 and 6' and a drive belt 7 to achieve precise, positively guided synchronization of both crankshafts. An adjustable idler pulley 14 allows the drive belt 7 to be adjusted for optimal, slip-free synchronization.

[0041] With regard to the aforementioned material data ranges of the carbon or carbon ceramic material, a preferred material with narrower material data ranges exists as follows: - Bulk density 1.95 to 196 (g / cm³<) - Porosity 6 to 8 (%) - Flexural strength from 85 to 90 (MPa) - compressive strength from 220 to 230 (MPa) - modulus of elasticity 15 to 17 (GPa) - Coefficient of thermal expansion. 7,4 (10 -6< / K) - Rockwell hardness HR5 / 150 120 - thermal conductivity from 58 to 62 (W / mK) - Medium grain size from 8 to 10 (µm)

[0042] It has been shown that carbon or carbon-ceramic materials with these specific material properties enable an internal combustion engine of the described new design, which achieves long service life, high robustness, smooth running and high performance when using hydrogen as fuel.

[0043] The engine according to the invention is equally suitable as a drive unit in all vehicles. The basic design can be expanded from the 2-piston version with one cylinder to any number of cylinders and a corresponding number of pistons.

[0044] In particular, the engine according to the invention is sophisticated and optimized for the use of hydrogen as fuel.

[0045] In conjunction with meeting the technological requirements for climate protection, significantly greater driving ranges are also achieved compared to purely electric drives. The lubricant injected via injector 9 is automatically guided through bore 12. The necessary forces for this are generated by the rotation of the crankshaft itself.

[0046] Figure 2 Figure 1 shows again the centrifugal discs 10, 10' mounted on both crankshafts 5 and 5'. These are each provided with a circumferential groove 11. Within the groove is at least one bore 12, which is oriented by the Figure 1 The injector shown, number 9, is supplied with lubricant. Thus, there are centrifugal discs on both crankshafts, through which the respective connecting rod-crankshaft connections are lubricated.

[0047] Figure 3Figure 1 shows once again the exact position of the centrifugal disc 10 on the crankshaft 5, and also the centrifugal disc and crankshaft opposite each other. The lubricant injected via the injector is guided through the respective opening 12 of each centrifugal disc 10. The necessary forces for this are generated by the rotation of the crankshaft itself. The opening 12 of each centrifugal disc 10 aligns with a further through-opening 12a in the eccentric 8 and opens into the needle bearing of the connecting rod 8a, where it provides precise lubrication. The through-opening 12a can also be reinforced by tubes pressed into it. The bearing 13 of the crankshaft 5 itself is a self-lubricating bearing in one possible embodiment. In another possible embodiment, at least the bearing shells can be made of carbon or carbon-ceramic material.All these details are designed identically on the side of the opposite crankshaft 5'.

[0048] The above-mentioned possible material, carbon or carbon ceramic material, can, for example, be a material in which carbon is introduced into an aluminum matrix or an aluminum oxide matrix, or sintered in by heat treatment. Position numbers

[0049] 1 Internal combustion engine 2 Cylinder 3, 3' Piston 4, 4' Piston rings 5, 5' Crankshaft 6, 6' Drive belt pulleys 7 Drive belt 8, 8' Crankshaft eccentric 8a, 8a' Connecting rod with needle bearings 9, 9' Injector 10, 10' Centrifugal disc 11, 11' Groove 12 Through-hole in centrifugal disc 12a' Aligned opening into the connecting rod needle bearing 13, 13' Crankshaft bearings (bearing shells) 14 Tensioner pulley

Claims

1. Internal combustion engine according to the opposed-piston principle, having an arrangement of two opposed pistons running in a cylinder with a common combustion chamber and equipped with piston rings, wherein each of the opposed pistons acts on a respective crankshaft via connecting rods and connecting rod bearings and eccentrics, and each of the two crankshafts has its own mechanical output, and the two outputs are each provided with a drive belt pulley, and the two drive belt pulleys are coupled via a drive belt and the piston movements are synchronised thereby, characterised in that the connecting rod bearings (8a, 8a') can be supplied with lubricant via a centrifugal disc (10, 10') that is also arranged on each crankshaft (5, 5') and via an injector (9, 9') in the direct vicinity of the centrifugal disc (10, 10'), via which a drip or spray injection of lubricant can be performed in adjustable cycle times, and that both the cylinder (2) and the piston rings (4, 4') of the pistons (3, 3') consist of a metal material, while the pistons themselves consist of a carbon or carbon-ceramics material.

2. Internal combustion engine according to the opposed-piston principle according to claim 1, characterised in that the centrifugal discs (10, 10') are each provided with a circumferentially introduced groove (11, 11') on the side subjected to lubricant by the injectors (9, 9'), into which the lubricant injection takes place, and that the grooves (11, 11') are each provided with at least one axial centrifugal disc passage opening (12, 12') which is aligned with an eccentrics passage opening (12a, 12a') through the respective eccentrics (8, 8') to the respective needle bearing of the connecting rods (8a, 8a').

3. Internal combustion engine according to the opposed-piston principle according to claim 1 or 2, characterised in that the cylinder (2) is a hydraulic cylinder having a polished inner surface.

4. Internal combustion engine according to the opposed-piston principle according to any one of claims 1 to 3, characterised in that the amount of lubricant to be injected is adjustable.

5. Internal combustion engine according to the opposed-piston principle according to any one of the preceding claims, characterised in that the lubricant is a liquid lubricant.

6. Internal combustion engine according to the opposed-piston principle according to claim 5, characterised in that injectors (9, 9') for the lubricant are fed from a lubricant reservoir, into which lubricant that can be fed back from said connecting rod bearings is fed back.

7. Internal combustion engine according to the opposed-piston principle according to claim 1 or 2, characterised in that the lubricant consists of an ultra-fine dry carbon-based lubricant.

8. Internal combustion engine according to the opposed-piston principle according to any one of the preceding claims, characterised in that the bearings or bearing shells of the crankshafts consist of carbon or a carbon-ceramic material.

9. Internal combustion engine according to the opposed-piston principle according to one or more of the preceding claims, characterised in that the fuel employed at least partially consists of hydrogen.

10. Internal combustion engine according to the opposed-piston principle according to any one of the preceding claims, characterised in that the fuel consists of the two components hydrogen and oxygen, which can be supplied in gaseous form and separately to the combustion chamber from two separate tanks.

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