EP1126153A2 - Stirling engine - Google Patents

Abstract

The dual piston engine has a sealed cylinder (1) with a compression piston (7) on the cold cylinder side and an expansion piston (5) on the hot side. Each piston defines a chamber for the working gas between itself and the cylinder end, which is volume-adjusted by the piston stroke. Both chambers (11,12) are sealed against the chamber (16) between the pistons, which is used as a buffer chamber.

Description

The invention relates to a Stirling engine, working as a two-piston engine, consisting of a closed on all sides against the environment Cylinder whose ends are connected via a connection outside the cylinder have a cooler, a regenerator and a heater for the working gas and form a cold and a hot cylinder side, in the interior of which a compression piston on the cold side of the cylinder and an expansion piston are located on the hot cylinder side on a common axis that over Piston rods connected to an engine located outside the cylinder are and are driven out of phase with each other.

The Stirling engine is in the circle of thermodynamic machines So far, hardly implemented, although the implementation of the Stirling process is just the case offers enormous scope for design, like countless designs, IP applications, models, prototypes and small series versions demonstrate. There are many advantages over engines with internal combustion list: freedom in the choice of heat source, possible use of regenerative Energy, simple construction with few moving parts, no valves, high achievable efficiencies, lubricant-free constructions and long Maintenance intervals are just a few of them.

In order to achieve a high power density, the working gas is under Pressured. Variants with internal pressures of more than 100 bar are known. In addition, noble gases are used to reduce flow losses in the heater, cooler and regenerator. Monatomic gases, such as hydrogen or helium have proven to be effective in high-performance machines Working gases prevail over air.

The types of Stirling machines are essentially in the literature in the displacement machines (beta and gamma type), two-piston machines (Alpha type) and double-acting machines (Siemens type) divided (Lit .: Stirling machine technology, publisher Fritz Steimle, Müller Verlag Heidelberg, Stirling machines, Martin Werdich, Kuno Kübler, ÖKOBUCH, Staufen near Freiburg).

Displacement machines of the beta type have the advantage that the working piston and the displacer inexpensively arranged in a common cylinder are. In addition, the heat exchangers and the regenerator are usually centered around the cylinder, which is the prerequisite for one offers optimal gas flow. Essentially, only the working piston has to be be sealed towards the cylinder, which is due to the low temperatures the cold side of the cylinder is not a big problem. Furthermore, the Dead space losses due to the absence of manifolds or collectors are minimized become. This advantageously leads to the highest possible, efficiency-increasing Compression ratio.

Such designs have the disadvantage, however, that under the working piston there is a buffer space for the working gas under pressure got to. In many cases, the crankcase is used. High pressures however require an elaborate, pressure-resistant design of the entire housing, what the advantages of the compact design of the cylinder area who can minimize or even cancel the cost view. DE 196 12 616 A, DE 196 16 256 A and WO 99/04152 A show such arrangements.

To circumvent this disadvantage, use some explanations below the working piston has its own buffer space, which seals off from the crankcase is. The result is usually relatively long piston and displacement rods, that are freed from radial forces originating from the crank mechanism must therefore be equipped with cross-head guides or rhomboid gears are. The effort required for this is not insignificant, increasing the construction volume and thus reduces the chances of cost-effective production the machine.

With regard to buffer space, crankcase, rod seal and rod guides the same problem arises with two-piston machines of the type Alpha. In addition, such machines have the disadvantage that two separate ones Cylinders are required and two pistons must be sealed, one even on the hot side. The heat exchangers and the regenerator must be placed between the two cylinders, which is usually not without manifolds and collectors with the well-known disadvantages of a high Dead volume is possible. There are versions among the Alpha type machines known, which have arranged the cylinders in a V-shape. The angle between the cylinders are usually around 90 degrees. This arrangement allows use a simple crankshaft with only one crank pin to which the two connecting rods of the pistons are articulated. The angle between the cylinders is thus synonymous with the phase shift of the piston movements. The Advantages of the simple crank drive, however, are the high effort for the Arrangement of two cylinders and the seals to the pistons and Crankcase largely canceled. The power to weight ratio of the machine is unfavorable, no matter whether it is a pressure-free or pressurized Crankcase. The area of application is therefore essentially limited on stationary applications.

So far, remarkable results have been obtained with double-acting Stirling Earned machines of the type Siemens. Outputs of several hundred kW with a power-to-weight ratio that that of modern diesel engines is not inferior were achieved. The arrangement of these motors is characteristic of four double-acting cylinders, the piston movement of which is 90 Degree is out of phase. The hot side is opposite the Piston rod side of the cylinder. It is over the heater heat exchanger the regenerator and the radiator heat exchanger with the piston rod side of the next cylinder. The cylinders are of a total of four Heat exchanger-regenerator units chained together. The piston rods are either articulated to ordinary crankshafts via cross heads and connecting rods or via spherical bearings directly to a swashplate, parallel to the axis the piston rods. WO 99/01655 A shows such a machine that has already reached series maturity.

The disadvantages of the Siemens machine are essentially limited insists that four double-acting cylinders are required to function to reach. Furthermore, there are relatively large manifold and header volumes are required in the working gas path, which act as harmful dead volumes.

All engine versions considered so far have the same Disadvantage that the torque-generating forces of the working pistons are unfavorable take the internal course of the machine. The power of a working piston is transmitted to the crankshaft via the piston rod and the connecting rod. she closes over the main bearings of the crankshaft, the crankcase and the Cylinder again with the power source, the gas pressure. Such force profiles require fundamentally extremely stable and torsionally rigid components, e.g. Crankshaft, main bearing and crankcase.

Other types of Stirling machines are those with rotary pistons or vane compressors / motors as well as versions of free piston motors. Because of the large distance to the device according to the invention, it is not detailed.

The object of the invention is to create a Stirling engine at the outset mentioned type, which is characterized by a simple design and high operational reliability and low efficiency as well as a homogeneous Exhibits operational behavior.

The following description of the invention is for simplicity's sake aligned the Stirling engine, although they are equally used in Stirling chillers can be applied.

The task is performed on a machine of the type mentioned Kind basically solved in that each piston a variable by its strokes Space for the working gas between it and the respective cylinder end forms and that these spaces sealed against the space between the pistons are.

The inventive design of a Stirling engine avoids one Series of disadvantages of the recorded design variants on the other hand, advantages of individual construction methods. So it's a extremely simple construction with a cylinder similar to the beta type, at where the piston rods are passed through on the cold side. Both pistons move in the manner known for the beta type, namely out of phase by a crank angle of approximately 90 degrees. The main difference to a Beta Stirling engine is that instead of the displacer an expansion piston is arranged. The work process is the same as for a two-piston machine of the alpha type. Characteristic of the invention Training is that according to a preferred embodiment of the Compression piston leads the expansion piston by the phase angle.

In a development of the invention, the space between the pistons as Buffer space used.

According to a currently preferred embodiment, the pistons are for this pot-shaped and have different diameters, the Seals smaller pistons on the inside of the larger pistons. Usually the expansion piston will have the larger diameter and be longer than the compression piston. It is essentially only a functional dynamic piston seal is required.

The one already mentioned is located within the two pistons Buffer space for the compression and expansion phase of the process. The The largest part of the buffer volume is taken up by the space inside the expansion piston a, since this piston is advantageously relatively long to accommodate the high Reduce the temperature of the expansion room to the cold compression room to be able to keep the heat loss small. The whole Buffer space takes an average pressure, which is usually identical to that Boost pressure of the machine. Another buffer space is not necessary.

In a further embodiment of the device according to the invention both pistons have the same diameter. They slide along the cold surface of the cylinder and seal there. This shows the advantage Compared to known designs, especially in that no additional Measures must be taken to keep the cylinder tread in mind to cool for a long service life of the sliding surfaces and the piston rings. The cooler - heat exchanger is located in the area of this tread anyway and there is no need to create additional cold rooms for the cylinder cooling.

The placement of the two pistons within a cylinder simultaneous use of the buffer space created between the hollow pistons creates a significant saving in space and costs Alpha or beta or gamma machine types. As with known machine designs also, offers itself beyond that only the Cylinder under the high boost pressure required for power applications is set. In this case, the piston rods are sealed to one another and the compression piston rod against the cylinder guide bushing. Due to the design, the two sealing points can be fitted with long guide bushes be equipped with an accommodation of high quality seals facilitate.

The device according to the invention is also optional with one, the State of the art applicable pressurized gearbox applicable. The piston rod seals only need the differential pressures record between working and boost pressure and it's a rotating Seal required for the crankshaft leading to the outside. Such seals are available in a gas-tight version on the market. About that in addition, the known arrangement when used as a generator drive Generator in the pressure chamber possible.

Regardless of how the invention in terms of boost spaces is trained, there arises another more clearly, due to the design Advantage one. The forces of the two pistons are always the same or opposite directed. This fact can be derived simply from the fact that the Gas pressure in the hot cylinder side and in the cold cylinder side, respectively is the same and that the pressure in the cylinder sides during one revolution according to the behavior of the Stirling process between two reversal points fluctuates. The pressure in the cylinder sides is either greater, the same or less than the pressure in the buffer space inside the pistons. In the phase at which the cylinder pressure outweighs the buffer pressure, the piston forces act towards each other and vice versa when the buffer pressure is opposite the cylinder pressure predominates. The forces acting on the cylinder increase inside of this on. Only those are always opposed to the outside acting piston forces directed over the piston rods. These powers close z. B. when using a crank mechanism as an engine the connecting rods and crank pins of the crankshaft are short and theoretically exert no forces on the main bearings of the crankshaft and on the crankcase.

Practically, there remain residual forces caused by those leading out of the cylinder Surfaces of the piston rods are caused as well as inertia forces must also be intercepted by the main camps.

Further details and advantages of the subject matter of the invention the following description of the drawing.

Fig. 1

in stark schematisierter, vereinfachter Darstellungsweise eine erfindungsgemäße Maschine im Schnitt durch Kolben und Zylinder bei der Verwendung von zwei ineinanderlaufenden Kolben unterschiedlichen Durchmessers,

Fig. 2

in der Fig. 1 entsprechender Darstellungsweise eine Maschine mit Kolben gleichen Durchmessers, die entlang der kalten Seite des Zylinder gleiten und

Fig. 3

eine Ausführungsvariante zu Fig. 2 mit einer anderen Kolbenstangenführung.

The subject matter of the invention is illustrated in the drawing, for example. Show it

Fig. 1

in a highly schematic, simplified representation, a machine according to the invention in section through the piston and cylinder when using two pistons of different diameters running into one another,

Fig. 2

1 corresponding representation of a machine with pistons of the same diameter that slide along the cold side of the cylinder and

Fig. 3

an embodiment of Fig. 2 with a different piston rod guide.

In Fig. 1 the cylinder 1 is shown as a closed vessel, the is only broken through to the outside by the piston rod guide 9. The Cylinder 1 consists of a cold side 11 and a hot side 12. The two Rooms 11, 12 are by a cooler 2, a regenerator 3 and a heater 4 connected. Both the heater 4 and the cooler 2 are exemplary as Tubular heat exchanger drawn in the form that the cooler 2 with liquid is cooled and the heater 4 hot gases in an unspecified Form are fed. Both the cooler 2 and the heater 4 can also be designed differently, for example with fine ribs or fans.

An expansion piston is located within the hot side 12 of the cylinder 1 5, which is connected to a piston rod 6, which to the outside a crank mechanism 10 leads. There is a inside the cold cylinder side Compression piston 7, according to FIGS. 1 and 2, on a hollow piston rod 8 is attached, which leads to the crank mechanism 10 via connecting rods.

The illustration shows that the expansion piston 5 and the compression piston 7 are cup-shaped. According to Fig. 1, the expansion piston 5 has a larger diameter than the compression piston and the latter seals on the inner wall of the expansion piston 5. A piston seal 14 is the only working seal to separate the cylinder rooms 11, 12 and the buffer space 16. The expansion piston 5 carries on his lower end also a seal 15, which separates the hot cylinder side 12 caused by the cold cylinder side 11. There are none on this seal high demands, since it only causes the pressure difference has to be sealed by flow resistances in the heat exchangers 2, 3, 4.

The cooler 2 is advantageously designed such that the cooling water in a jacket around the cold side 11 of the cylinder 1, wherein both the cooler 2 and the cylinder wall of the cold cylinder side 11 flows around and is cooled. Due to the heat transfer is for the seals 15 and 14th a relatively cool operation is possible, which is the use of plastics enabled as piston seals. Shielding plates 13 also provide to ensure that the high temperature on the upper side of the expansion piston 5 acts, does not reach the inside of the compression piston 7.

The piston rods 6, 8 are connected to the crankshaft 10 of the connecting rods Articulated crank drive. To achieve symmetrical power transmission, is in the embodiment of FIGS. 1 and 2 here for the implementation of Piston rod 6 tubular piston rod 8 of the compression cylinder 7 articulated by means of two connecting rods to two crank pins of the crankshaft 10. 3 are for the compression piston 7 two diagonally with the same Piston rods arranged at a center distance and sealed off by 9a 8 available.

The crank pin for the compression cylinder 7 are opposite Crank pin for expansion cylinder 5 offset in a rotating circle by approx. 90 degrees. The picture to the left of the crankshaft 10 schematically shows the view of the crankshaft 10 from the left. In relation to the direction of rotation 17 it can be seen that the crank pin 7a for the compression piston 7 the crank pin 5a for the expansion piston 5 leads 90 degrees. Choosing a crankshaft 10 with is only three crank pins as a gear for the device according to the invention exemplary and useful for the functional explanation. They are just as good other constructions corresponding to the state of the art, e.g. on Rhombus engine as described in WO 99/04152 or engines as they are explained in DE 19722036 A1, DE 19616256 A1, WO 99/04153 A.

The handling of the Stirling process is now in 90-degree turning steps the crankshaft 10 explained. The drawn starting position is denoted by "0", the other positions correspond to the rotation angles "90", "180" and "270" defined. When considering the crank pins 5a, 7a in connection with the direction of rotation 17 can be seen that at this moment both pistons 5, 7 move down. The working gas is in the hot cylinder side 12 pushed and supplied heat. The pressure in cylinder 1 increases. In the Position "90" the expansion takes place. Both pistons 5, 7 move towards each other and do work. In the "180" position, both pistons 5 move, 7 upwards, the working gas is pushed into the cold cylinder side 11, doing so heat is dissipated. Finally, in the "270" position, it is understandable that both pistons 5, 7 move apart, compression takes place.

The process steps outlined are identical to those in a Stirling Alpha machine.

A further development of the idea according to the invention is shown in FIG. 2 and 3. Since the basic mode of operation is completely identical to that of Fig. 1, in the following description of Fig. 2 only on the executed difference to Fig. 1 received.

The compression piston 7 and the expansion piston 5 have the same diameter and slide one behind the other along the inner surface the cold cylinder side 11 of the cylinder 1. The cold cylinder side is advantageous 11 dimensioned in length so that both piston seals 14,15 along their Do not leave the cold cylinder area. The expansion piston 5 is on its bottom open. Its inner volume forms together with the volume above the compression cylinder 7, the buffer space 16. The relatively long Design of the expansion piston 5 ensures the formation of a sufficient Buffer space 16 that sufficient distance and shielding between the hot cylinder side 12 and the cold cylinder side 11 is present.

Claims (7)

Stirling engine, working as a two-piston engine, consisting of a cylinder (1) whose ends are closed on all sides against the environment a connection outside the cylinder (1) via a cooler (2), a regenerator (3) and a heater (4) for the working gas and form a cold and a hot cylinder side (11, 12), in the interior of which a compression piston (7) on the cold cylinder side (11) and an expansion piston (5) on the hot cylinder side (12) on a common axis located via piston rods (6, 8) with an outside of the cylinder (1) horizontal engine (10) are connected and out of phase with each other are driven, characterized in that each piston (5,7) one through his strokes variable space for the working gas between him and forms the respective cylinder end and that these spaces (11, 12) against the Space (16) between the pistons are sealed. Stirling engine according to claim 1, characterized in that the Piston rod bushing (9) attached to the cold side (11) of the cylinder (1) is. Stirling engine according to claim 1, characterized in that the Space between the pistons (5,7) is used as a buffer space (16). Stirling engine according to claim 1, 2 and 3, characterized in that the pistons (5,7) are cup-shaped and have different diameters have and that the smaller diameter piston on the inside of the larger piston seals (14) Stirling engine according to claim 1, 2 and, characterized in that both pistons (5,7) have the same diameter and along the cold one Slide and seal inside (11) of cylinder (1) Stirling engine according to claims 1-5, characterized in that the Compression piston (7) the expansion piston (5) based on the direction of rotation (17) advanced about 90 degrees. Stirling engine according to claims 1-6, characterized in that the Training as a refrigerator according to the Stirling principle.

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