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 provided with piston rings, wherein the opposing pistons each act on their own 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 synchronized via this, according to the preamble of patent claim 1.

[0002] Internal combustion engines based on the two-stroke opposed-piston principle are well known and historically date back to the so-called Junkers engine. Two counter-rotating pistons run in a single cylinder. The piston movements are coordinated so that they converge simultaneously in one stroke, thus achieving enormous compression in the combustion chamber. Particular attention must be paid to ensuring that their movements are precisely synchronized and that ignition occurs at the precise moment of maximum compression. This type of engine offers enormous advantages in terms of the power-to-displacement ratio. The engine is therefore compact in size relative to its achievable power. An example of a precisely synchronized engine of this type is known from DE 10 2011 114 854 A1.

[0003] Considering so-called eco-efficiency, there is an unbroken trend toward electric drives in vehicles. The ongoing problem is the limitation of the storage capacity of electrical energy in vehicles in order to maintain sufficient ranges even under less than optimal driving conditions and during winter operation.

[0004] With regard to alternative fuels, it should be noted that not all conventional combustion engines can be converted to sustainable, renewable fuels without considerable effort. This applies to liquid fuels as well as gaseous fuels. These include biogas, but above all, hydrogen.

[0005] In relation to the already described high performance in terms of displacement and thus also in relation to the small construction of such engines, known measures for high-temperature-resistant lubrication of such engines often fail.

[0006] With regard to engine lubrication in the piston-cylinder area, it is common practice in the state of the art for the cylinder inner surfaces to be honed. This surface treatment affects the so-called tribological properties, reducing friction. In reality, however, the inner surface after honing is not smooth, but rather produces a fine grooved structure, similar to a cross-ground pattern. When using lubricants, i.e., lubricating oils, this structure is intended to increase the adhesion of oil-based lubricants. When using the aforementioned hydrogen-containing fuels, oil lubrication is disadvantageous or even impossible.

[0007] The invention is based on the object of further developing the said combustion engine with a compact design and high power density in such a way that it is designed for the use of hydrogen and hydrogen-containing biofuels (biofuels) with high continuous power available and is resistant to high temperatures.

[0008] The stated object is achieved according to the invention in an internal combustion engine of the generic type by the characterizing features of claim 1.

[0009] Further advantageous embodiments are specified in the dependent claims 2 to 11.

[0010] The core of the invention is that the connecting rod bearings can be supplied with lubricant via a centrifugal disc, which is 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 in 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.

[0011] An otherwise conventional oil pan, as known from DE 10 2011 114 854 A1 for opposed-piston engines, into which moving parts of the crankshaft or eccentric must be immersed, is eliminated. Instead, injector-controlled, precisely placed and metered lubrication is provided where needed.

[0012] Since oxygen is also to be used when hydrogen is used as a fuel, the use of oil lubrication in the combustion chamber is ruled out anyway.

[0013] The cylinder, or rather the inner cylinder wall, is made of steel, preferably steel as used for high-strength hydraulic pipes. The pistons are made of carbon or carbon-ceramic material. The piston rings are also made of steel and, as usual, lie in circumferential grooves, the piston ring seats, on the piston. Lubrication in this area is achieved by the steel piston rings creating a fine abrasion of carbon dust in the groove of the carbon or carbon-ceramic piston, i.e. the piston ring seat, which then lubricates the steel piston rings against each other in the steel cylinder. Further, albeit very slight, abrasion of the carbon material, which is only necessary at start-up, also lubricates the piston in 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.

[0014] This lubrication effect remains active even after the engine has been shut down and subsequently restarted.

[0015] In a further advantageous embodiment, the centrifugal discs are each provided with a circumferential groove on the side exposed to lubricant by the injectors, into which the lubricant is injected. The grooves are each provided with at least one axial through-hole, which is aligned with a through-hole through the respective eccentric to the respective needle bearing of the connecting rod. Thus, the lubricant is metered directly to the required location.

[0016] In the area of ​​the connecting rod-crankshaft connection, i.e. the connecting rod bearings, only lubrication is carried out via injectors, localized to the lubrication required there.

[0017] Carbon or carbon-ceramic materials, e.g. materials with the designation FE 679, FE 709, FE 679 Q from Schunck Kohlenstofftechnik GmbH, Heuchelheim, Germany, can be used as starting materials for the said pistons.

[0018] 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 / cm 3)< - Porosity from 6 to 11 (%) - Flexural strength from 55 to 90 (MPa) - Compressive strength from 145 to 245 (MPa) - Elastic modulus 15 to 26 (GPa) - Thermal expansion coefficient 5.1 to 7.5 (10 -6< / K) - Rockwell hardness HR5 / 150 110 to 120 - Thermal conductivity from 37 to 62 (W / mK) - Average grain size from 8 to 12 (µm)

[0019] In an advantageous embodiment, the lubricant injection quantity is adjustable. This reduces the use of lubricant to the actually necessary amount.

[0020] Another advantageous feature is that the cycle times between injections are adjustable. This also reduces the amount of lubricant required, while also limiting lubrication to the necessary areas.

[0021] In a further embodiment, 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, similar to graphite powder, which is formed from the abrasion of the carbon or carbon-ceramic material and does not require external input.

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

[0024] In one embodiment, 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. Microfine abrasion that occurs at the beginning of operation essentially acts as 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 embodiment, it is stated that the fuel used consists at least partly of hydrogen.

[0027] In a further advantageous embodiment, it is stated 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 and separately.

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

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

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

[0031] The cylinder is preferably made of steel, as used for hydraulic cylinders. The inner cylinder wall is polished accordingly.

[0032] For example, hydraulic pipes made of precision steel pipes DIN EN 10305-4 can be used very advantageously.

[0033] A particular aspect essential to the invention is the use of internally polished hydraulic tubes as cylinders for this engine according to the invention. In contrast to the cylinder interior surfaces used in the prior art, which are honed and thus exhibit a grooved structure, the interior surfaces of the cylinder according to the invention are polished completely 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 achieved effects in the combustion engine according to the invention, in conjunction with the lubrication via the finest abrasion of the carbon material described above. This not only eliminates the need for a honed inner cylinder surface, but would actually be counterproductive in the present invention.

[0035] According to the invention, the two pistons 3, 3', which act 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'. Both pistons compress the same compression chamber in cylinder 2.

[0036] Pistons 3, 3', not shown in detail, are known to be equipped with piston rings made of steel. These are known to be seated in circumferential grooves around the pistons in so-called piston ring seats. During initial commissioning, the steel piston rings 4, 4' rub against the piston ring seats of the carbon or carbon-ceramic pistons 3, 3', which are made of carbon or carbon-ceramic material, producing a microfine particle of carbon dust that deposits on the contacting friction surfaces. This state is reached within a period of < 0.5 seconds. From this moment on, friction is so drastically reduced that practically no further wear occurs. As the temperature continues to rise, friction and wear then adapt to the operating condition.

[0037] The connecting rod connections each engage eccentrics 8, 8' of the crankshafts 5, 5' on both sides of the internal combustion engine. On the same crankshafts, next to the connecting rod-crankshaft connection, the aforementioned flinger discs 10, 10' are arranged. These are each 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), through which minimally dosed lubricant is supplied at adjustable cyclical time intervals. Via the aforementioned at least one through-opening 12 in each of the flinger discs 10, 10', which, with the further opening in the eccentric, open into the area of ​​the needle bearings of the connecting rods, thereby creating a lubricant-tight connection from outside the eccentric, even up to the needle bearings of the connecting rods 8a, 8a'.

[0038] The lubrication required in the connecting rod area is thus limited to the necessary amount. Any dripping lubricant is collected, filtered if necessary, and fed back to the injector(s) on 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. Thus, in this exemplary embodiment, this area would also be lubricated in the manner described above, with minimal abrasion of the engaging surfaces. Optionally, in this case, the injectors can also be installed in such a way that the powdered abrasion is returned to the injectors.

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

[0041] With regard to the material data range of the carbon or carbon-ceramic material mentioned above, a preferred material with narrower material data ranges is as follows: - Bulk density 1.95 to 196 (g / cm 3)< - Porosity 6 to 8 (%) - Flexural strength from 85 to 90 (MPa) - Compressive strength from 220 to 230 (MPa) - Elastic modulus 15 to 17 (GPa) - Thermal expansion coefficient 7,4 (10 -6< / K) - Rockwell hardness HR5 / 150 120 - Thermal conductivity from 58 to 62 (W / mK) - Average grain size from 8 to 10 (µm)

[0042] It has been shown that carbon or carbon-ceramic materials with these specific material data enable a combustion engine of the new design described, 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 two-piston version with one cylinder to multiple cylinders and a corresponding number of pistons.

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

[0045] In conjunction with the technology's compliance with climate protection requirements, significantly greater ranges are also achieved compared to the use of purely electric drives. The lubricant injected via injector 9 is automatically passed through bore 12. The necessary forces are generated by the rotation of the crankshaft itself.

[0046] Figure 2 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 there is at least one bore 12, which is Figure 1 The injector 9 shown is supplied with lubricant. Thus, there are flinger discs on both crankshafts, through which the respective connecting rod-crankshaft connections are lubricated.

[0047] Figure 3shows once again the exact position of the flinger 10 on the crankshaft 5, correspondingly also the flinger and crankshaft opposite each other. The lubricant injected via the injector is passed through the respective opening 12 of the respective flinger 10. The forces required for this are generated by the rotation on the crankshaft itself. The opening 12 of the flinger 10 is aligned with another through-opening 12a in the eccentric 8 and opens into the needle bearing of the connecting rod 8a, where they provide precise lubrication. The through-opening 12a can also be reinforced by small 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 the same 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 by heat treatment. Position numbers

[0049] 1 Combustion engine 2 Cylinder 3, 3' Piston 4, 4' Piston rings 5, 5' Crankshaft 6, 6' Drive belt pulleys 7 Drive belt 8, 8' Eccentric of the crankshaft 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 in the needle bearing of the connecting rod 13, 13' Bearing (bearing shells) of the crankshaft 14 Tension pulley

Claims

1. An internal combustion engine operating on the opposed-piston principle, with an arrangement of two opposed pistons running in a cylinder with a common combustion chamber and provided with piston rings, wherein the opposing pistons act on their own crankshafts via connecting rods, 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 by this, characterized by thatthe connecting rod bearings (8a, 8a') can be supplied with lubricant via a centrifugal disc (10, 10') which is also arranged on each crankshaft (5, 5') and an injector (9, 9') which is located in the immediate vicinity of the centrifugal disc (10, 10'), via which a drip or spray injection of lubricant can be carried out 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 ceramic material.

2. Internal combustion engine according to the opposed piston principle, according to claim 1, characterized by thatthe centrifugal discs (10, 10') are each provided with a circumferential groove (11, 11') on the side supplied with lubricant by the injectors (9, 9'), into which the lubricant is injected, and the grooves (11, 11') are each provided with at least one axial through-opening (12, 12') which is aligned with a through-opening (12a, 12a') through the respective eccentric (8, 8') up 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, characterized by that the cylinder (2) is a hydraulic cylinder with a polished inner surface.

4. Internal combustion engine according to the opposed piston principle, according to one of claims 1 to 3, characterized by that the lubricant injection quantity is adjustable.

5. Internal combustion engine according to the opposed piston principle, according to one of claims 1 to 4 characterized by thatthe cycle times between injections are adjustable.

6. Internal combustion engine according to the opposed piston principle, according to one of the preceding claims, characterized by that the lubricant is liquid lubricant.

7. Internal combustion engine according to the opposed piston principle, according to one of the preceding claims characterized by that Injectors (9, 9') for the lubricant is fed from a lubricant reservoir into which recyclable lubricant is returned from said connecting rod bearing.

8. Internal combustion engine according to the opposed piston principle according to one of the preceding claims, characterized by that the lubricant consists of a dust-fine dry, carbon-based lubricant.

9. Internal combustion engine according to the opposed piston principle, according to one of the preceding claims, characterized by that the bearings or bearing shells of the crankshafts are made of carbon or carbon-ceramic material.

10. Internal combustion engine according to the opposed piston principle, according to one or more of the preceding claims, characterized by that the fuel used consists at least partly of hydrogen.

11. Internal combustion engine according to the opposed piston principle, according to one of the preceding claims, characterized by that the fuel consists of the two components hydrogen and oxygen, which are introduced into the combustion chamber in gaseous form from two separate tanks.

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