EP0188742A2 - Heat engine - Google Patents

Abstract

In a heat engine, in particular a Stirling engine, comprising a displacement piston and a working piston, which are arranged coupled to one another in a housing that is linearly guided so as to be capable of oscillation, the gas space between the displacement piston and the working piston being connected to the gas space between the displacement piston and the housing via a Heater, cooler, regenerator arrangement is connected, and an external heat source can be connected, is provided to enable problem-free coupling of mechanical energy through the closed housing to the outside, that at least with the working piston (2) a magnetic or magnetizable , Within the housing (1) arranged coupling device (9, 15) is connected, and that a corresponding magnetic or magnetizable coupling device (8, 18) outside the housing (1) is movably mounted parallel to the piston path.

In order in particular to be able to control the vibration behavior of the working piston and displacement piston in each operating phase, it is further provided that a device for specifying the phase position between the working piston (2) and displacement piston (4) is formed by a magnetically coupled mechanical transmission, in particular a crankshaft transmission. In particular, it is provided that a rotational movement transmitted to the pistons is tapped from the translational movement of the pistons, the transmission devices serving for this purpose also being able to simultaneously determine the phase position of the pistons. The rotary movement of the pistons can be magnetically decoupled by means of the coupling devices according to the invention and transmitted directly to an output shaft.

Description

The invention relates to a heat engine according to the preamble of claim 1.

Such externally heated, regenerative heat engines have good prospects for a considerably wider spread in the future due to the low exhaust gas emissions, their very high achievable efficiency and their adaptability to a wide variety of heat sources. The Stirling engine is an example of this type of heat engine.

Although heat engines of this type work according to an ideal, reversible cycle, which runs between two isotherms and two isochors, and thus basically higher degrees of Carnot implementation can be achieved than with the much more widely used internal combustion engines, such machines have so far been able to do so for various reasons not yet widely enforced.

One problem is that the temperature of the heater head must be very high in order to achieve high efficiencies, and suitable materials have only recently been developed for this purpose. Another fundamental problem is that in order to achieve a good power density and correspondingly small, compact machines, the machine must be filled with high pressure helium or hydrogen. This leads to considerable difficulties, for example, in the known crankshaft spinning machines, since on the one hand the crankshaft seal is intended to prevent the working gas from diffusing out and on the other hand also the penetration of oil and lubricants from the gearbox into the interior of the machine. One approach to solving this problem was the invention of the free-piston Stirling engine (US Pat. No. Re. ₀ .176). Such an arrangement does not require a crankshaft, since both the working piston and the displacement piston oscillate freely gas or mechanically with a linear oscillation in the interior of a hermetically sealed pressure housing. A mass-spring resonance system is thus formed which is or should be coordinated via the dimensioning of the spring constants, mass and flow cross sections in such a way that the kinematics of the movement comes as close as possible to the ideal Stirling cycle.

With a free-piston machine of this type, the advantage over the crankshaft construction is that it is completely gas-tight, that is to say that there is no gas diffusion from the inside to the outside or oil from the outside to the inside. Furthermore, the structure, at least as far as the elementary components are concerned, is uncomplicated and accordingly enables a long service life. Ultimately, potentially one increased efficiency can be achieved because there is no crankshaft loss.

These advantages are offset by problems in the practical application of such a machine. Since the movement processes only take place inside the machine and there is no mechanical connection to the outside, additional devices that are to convert the oscillating movement of the working piston into electrical or thermal useful energy must also be accommodated inside the machine. This leads e.g. in addition to the fact that relatively expensive linear generators have to be used to generate electricity in comparison to commercially available rotating generators. Even greater problems arise when mechanical energy is to be decoupled as such. In this respect, attempts have been made to transmit the periodic pressure fluctuations inside the machine through a membrane to a hydraulic system. Another approach is to make the working piston so heavy that it has been used relative to the movable housing stand and the resulting housing movement to tap the energy of the linear vibration. In practice, both of the solutions mentioned lead to considerable technical complications, e.g. in the form of material problems when using a membrane or due to difficulties in converting the linear vibration movement of the housing into a rotary movement.

Another fundamental problem with free-piston machines is that such a mass-spring system is extremely difficult to analyze analytically. This includes in particular the question of piston centering around the central position and the phase angle between Displacement and working pistons. Measures such as the provision of gas overflow channels, gas intermediate stores, mechanical centering springs, etc. were taken to implement the theoretical specifications. All of these measures reduce the ideal efficiency, work only in narrowly limited control ranges and lead to deviations from the ideal Stirling cycle.

Proceeding from this, the object of the invention is to implement an externally heated, regenerative heat engine which combines the advantages of a free-piston and a crankshaft machine and largely avoids their respective disadvantages. In addition, according to the invention, a simple possibility of coupling mechanical energy out of a machine of the type in question is to be specified.

This object is achieved by the characterizing part of claim 1. The magnetic decoupling of the mechanical energy of the linearly oscillating working piston provided thereafter makes it possible to optimally design a free-piston engine without specific considerations in the design, e.g. regarding storage and choice of materials. The magnetically decoupled movement can be supplied externally through any known mechanical power transmission and conversion systems to any secondary units. If such secondary or sub-assemblies do not need rotating but linear movements, the decoupled linear vibration energy can be taken off directly. The magnetic decoupling also has the advantage that it acts as a slip clutch when overloads occur.

A particularly simple embodiment of the solution according to the invention is stated in claim 2. The magnets then arranged outside the housing can be designed both as permanent magnets and as electromagnets. No electrical cables have to be routed into the interior of the housing to supply electromagnets, since only soft iron parts are located there.

By designing the outer magnets as electromagnets and by providing an AC voltage source according to claim 3, a dynamic vibration effect can be exerted on the pistons to achieve an additional dynamic seal.

According to claim 5, a device for coordinating the phase position of the working and displacement pistons is advantageously provided. This device is preferably designed as a mechanical transmission, in particular as a crankshaft transmission.

This configuration makes it possible that the inner sequence of movements of the working and displacement pistons does not have to be freely oscillating, but rather is defined in accordance with a desired kinematics, that is to say in accordance with the selected, regenerative, externally heated, thermodynamic cycle. However, this ensures that the problems associated with free settling, for example with regard to centering, overshoot behavior in changing load ranges and other difficulties associated with the kinematics of the free-piston machine, are avoided. This leads to a substantial simplification of the free piston part while avoiding the conventionally required active and passive control systems. In order to implement the invention, mechanical phase coupling techniques that are sophisticated per se can be used, so that it is easily possible to implement such motors based on a basic type in very different performance classes.

According to the invention, the magnetic coupling devices and the downstream mechanical transmission are therefore used on the one hand to achieve optimal decoupling of the mechanical energy for further use, and on the other hand to impart a precisely defined phase position and a correspondingly coordinated vibration behavior to the oscillating piston by a mechanical transmission. This also avoids the difficulties of conventional free-piston machines that occurred in the start-up area and during load changes. All advantages of free-piston machines are thus achieved by avoiding the basic sealing problems, and on the other hand the problems typical of free-piston machines, which result from the complicated behavior of a freely oscillating system, are easily mastered.

The transmission device provided according to claim 7 allows, derived from the linear movement of the displacement piston and / or the working piston, to impart a rotary movement about its longitudinal axis to the latter. Such a rotary movement, in conjunction with the magnetic coupling devices described above, allows a combined translatory and rotary movement or a pure rotary movement for the drive on the outside of the housing to tap from secondary units. At the same time, the rotary movement achieves a dynamic sealing effect between the pistons and the inner wall of the housing.

The measure according to claim 8 ensures that the displacer piston and the working piston rotate with each other, but perform an independent linear movement.

The coupling means provided according to claim 9, which have a sinusoidal or cosine curve, allow the translational movement of the pistons to be converted into a rotary movement in a particularly simple manner.

By arranging the coupling means according to claim 10 it is achieved that these coupling means can also be used as the coupling devices provided according to claim 5 to achieve a defined phase position between the working and displacement pistons, with the setting of an exact sine wave. cosine relationship between the coupling means, which have a phase difference of ₀ ° 9 of the conventional phase difference is adjusted according to the one part of the displacer and on the other hand are assigned to the working pistons.

Instead of specifying a fixed phase position, the coupling means according to the invention make it possible to make it adjustable according to claim 11, ie by changing the angular position of the coupling means, for example by means of magnetic manipulators, the phase position between the working and displacement pistons can be adjusted be changed to certain operating modes or operating states.

Claim 12 specifies a particularly simple embodiment of the coupling means. The cam provided thereafter can be designed both as a sliding cam and can also be provided to reduce the friction that a wheel or a roller scans the guide curve. Another embodiment of the coupling means results from claim 13, wherein corresponding to the sinusoidal or cosine-shaped magnetisable or magnetic material provided thereafter, a magnetic or magnetisable coupling means interacting therewith, corresponding to a cam, is provided.

Further features, advantages and details of the invention result from the following description of a preferred embodiment with reference to the drawing.

• Fig.1a einen schematischen Schnitt durch eine erfindungsgemäße, nach dem Stirling-Prinzip arbeitende Freikolbenmaschine mit magnetischen Auskopplungseinrichtungen und nachgeschaltetem mechanischem Getriebe zur Veranschaulichung des Prinzips,
• Fig.lb einen Schnitt durch eine praktisch realisierte Ausführungsform gemäß Fig.la,
• Fig. 2 einen schematischen Schnitt, welcher die Entstehung der axialen Kraftübertragungskomponente veranschaulicht.
• Fig. 3 einen schematischen Längsschnitt durch eine Ausführungsform mit Kopplungs-Mitteln zur Erzeugung einer Drehbewegung der Kolben,
• Fig. 4 einen Querschnitt längs der Linie IV-IV in Fig. 3 und
• Fig. 5 eine Fig. 4 entsprechende Darstellung einer Ausführungsform mit mechanischen Kopplungs-Mitteln.

Show

• 1a shows a schematic section through a free-piston machine according to the invention, which works according to the Stirling principle, with magnetic decoupling devices and a downstream mechanical gear to illustrate the principle,
• Fig.lb a section through a practically realized embodiment according to Fig.la,
• Fig. 2 is a schematic section illustrating the formation of the axial power transmission component.
• 3 shows a schematic longitudinal section through an embodiment with coupling means for generating a rotary movement of the pistons,
• Fig. 4 shows a cross section along the line IV-IV in Fig. 3 and
• 5 shows a representation corresponding to FIG. 4 of an embodiment with mechanical coupling means.

Fig. 1 shows a housing 1, which is designed as a pressure cylinder. In this housing 1, a working piston 2 is arranged, which is mounted so that it can move up and down linearly via guide rings 3. Furthermore, a displacer 4 is arranged in the housing 1, which is likewise guided over the linkage 3. A heater 5, a regenerator 6 and a cooler 7 are arranged so that they have an interior 11, which is enclosed by the displacer 4, the working piston 2 and the housing 1, with an interior 12, which is between the housing 1 and the displacer 4 is included, connect. As is not shown in detail, the heater 5 is connected to an external heat source.

The displacer piston 4 is connected via a linkage 13 to a first inner coupling device 9, while the working piston 2 is connected via a linkage 14 to a second inner coupling device 15. Both coupling devices 9, 15 are designed as soft iron rings, which have grooves 16 and 17 open radially outwards.

The housing 1 or at least the housing area around the coupling devices 9, 15 is made of a non-magnetic material. For example, a plastic or a non-magnetic metal, such as eg aluminum or non-magnetic special steel. In the latter case, only certain eddy current losses have to be accepted when decoupling.

Corresponding coupling devices 8, 18 are arranged outside the housing 1 at the level of the coupling devices 9, 15. These coupling devices are each formed by an annular permanent magnet, which has inwardly open annular grooves 19 or 20. Instead of the permanent magnets shown for the sake of simplicity, appropriately designed electromagnets can also be used, it being equally possible to operate the electromagnets with direct current or with alternating current.

The outer coupling devices 8, 18 are each connected to a linkage 21 or 22, both linkages 21 and 22 being mounted so as to be movable independently of one another in the axial direction. The linkage 21 is connected via articulation points 23, 24 and the linkage 22 via articulation points 25, 26 to a mechanical transmission 10 designed as a crank mechanism. The mechanical transmission 1 ₀ , which is known as such from conventional Stirling engines, is shown only schematically in the drawing. The phase angle δ between working piston 2 and displacement piston 4 is predetermined by the choice of the angular position of the articulation points 24, 26. Due to the coupling between the transmission 10 and the working piston 2 or displacement piston 4, a fixed phase position is ensured both when starting and when load changes occur between working piston 2 and displacement piston 4. To achieve optimum efficiency, pistons 2, 4 and the gas paths or gas spaces are dimensioned so that that in the case of an ideal free swinging a phase angle δ, for example, would of 9 ₀ °, adjust, as it is dictated by the transmission lo. In this way, a particularly favorable efficiency is achieved, since the transmission 10 then only reacts to the phase position of the working piston 2 and displacement piston 4 in the critical areas. At the same time, the output shaft 27 of the transmission lo serves to drive downstream units, so that a very favorable decoupling of the mechanical energy from the displacer and working piston 4, 2 is achieved.

FIG. 2 shows how, due to the geometry of the outer and inner coupling devices 8, 9, which have annular grooves 2o and 17 that are open towards one another, an axial force component F is produced during an axial relative movement between the coupling devices 8 and 9, which component component achieves the desired coupling force represents. If the eddy current losses are neglected, i.e. if the housing 1, which only encases the cold part of the machine, is made of insulating plastic, there is a coupling force of approx. 8 ₀₀ Newton if one has an air gap induction of 0.5 Tesla and a piston diameter D of 25 cm with an air gap a of 1 cm. The computational consideration of eddy current losses when using a conductive housing 1, for example made of aluminum, shows that the losses to be considered are only minor.

Fig. 3 shows an embodiment in which derived from the oscillating translational movement of the working piston 2 'or the displacer 4', which is shown only schematically in the drawing are, a rotary movement (arrow 28) about the common longitudinal axis 29 is impressed on this piston. The graphic representation in FIG. 3 is limited to the explanation of the derivation of this rotary movement from the oscillatory movement along the axis 29.

In order to ensure that the working piston 2 'and displacement piston 4' rotate simultaneously and by the same amount, a connection 3o in the form of a mandrel is provided which engages with play in recesses 31 and 32 in the displacement piston 4 'and working piston 2', respectively , so that an unimpeded movement of these pistons in the axial direction is possible relative to each other. On the other hand, since the recesses 31, 32 or the connection 3o, i.e. the mandrel provided for this purpose, which in the exemplary embodiment is square in cross section, the pistons can only rotate together despite their free axial mobility.

As a coupling means between the linear movement and the rotary movement to be generated, the displacer 4 'has a cosine-shaped insert 33 made of magnetizable material, for example soft iron, while the working piston 2' has a corresponding insert 34 which is sinusoidal, ie relative to the insert 33 out of phase by 9 ₀ °. Magnets 35, 36 are attached to the housing wall, which interact with the inserts 33 and 34, respectively, so that the pistons 2 'and 4', respectively, during a longitudinal movement parallel to the axis 29 due to the magnetic force components described in connection with FIG. a continuous rotary movement is impressed in the direction of arrow 28. This rotary movement can take place via a magnetic coupling device are coupled, which in the exemplary embodiment is formed by the magnets 37, 38. An output shaft 39 can then be connected to the magnet arrangement 37 for driving secondary units.

4 that the outer magnets 35 (or 36) are arranged on an adjusting ring 41 which, as illustrated by the arrow 42, adjusts the angular position of the magnets 35 and 36 relative to the housing 4o and so that an adjustment of the phase angle 9 between the displacement piston 4 'and the working piston 23' is made possible.

5 shows an embodiment in which an adjusting ring 43 is provided in the interior of the housing wall 40. This setting ring 43 carries cams 44, at the front end of which rollers 45 are arranged. These rollers 45 engage in a sine or cosine ring groove 46 on the displacement piston or working piston and thus serve as coupling means for generating a rotary movement derived from the translatory movement of the piston. The magnet pairs 47 and 48 enable the angular position of the adjusting ring 4o to be fixed or changed, and thus in turn the phase angle δ between the working and displacement pistons.

Claims (15)

1. Heat engine, in particular a Stirling engine, comprising a displacement piston and a working piston, which are arranged coupled to one another in a linearly oscillating manner in a housing which is sealed off from the outside, the gas space between the displacement piston and working piston with the gas space between the displacement piston and the housing via a heater Cooler, regenerator arrangement is connected, and wherein an external heat source can be connected, characterized in that at least with the working piston (2) a magnetic or magnetizable coupling device (9, 15) arranged within the housing (1) is connected , and that a corresponding magnetic or magnetizable coupling device (8, 18) outside the housing (1) is movably mounted according to the piston path. 2. Heat engine according to claim 1, characterized in that the coupling device (9, 15) inside the housing (1) by a soft iron ring and the coupling device (8, 18) outside the housing (1) is formed by at least one magnet. 3. Heat engine according to claim 2, characterized in that the coupling device (9, 15) within the housing outwardly open annular grooves (16, 17) and the coupling device (8, 18) outside the housing (1) inwardly open ring grooves (19, 2 ₀ ). 4. Heat engine according to claim 2 or 3, characterized in that the coupling device (8, 18) arranged outside the housing (1) comprises an electromagnet which can be connected to an AC voltage source. 5. Heat engine according to one of claims 1 to 4, characterized in that both the working piston (2) and the displacement piston (4) with a coupling device (9, 15) is provided, the corresponding outer coupling devices (8, 18th ) are connected via a device specifying their mutual phase position. 6. Heat engine according to claim 5, characterized in that the device for specifying the phase position is a mechanical gear (1 ₀ ), in particular a crankshaft gear. 7. Heat engine according to one of claims 1 to 6, characterized by a at least one piston (2 'or 4') engaging transmission device for transmitting a rotational movement derived from the own linear movement of the pistons (2 'or 4') the pistons (2 'or 4') about their longitudinal axis (29). 8. Heat engine according to claim 7, characterized by a rotationally fixed, axially movable connection (3o) between the pistons (2 'or 4'). 9. Heat engine according to claim 7 or 8, characterized in that the transmission device by mechanical or magnetic, on the housing wall (4o) arranged first coupling means and corresponding with the piston or pistons (2 'or 4') connected second coupling means is formed, the first and / or second coupling means being sinusoidal or cosine-shaped. 1 ₀ . Heat engine according to one of claims 7 to 9, characterized in that the displacement piston (4 ') has sinusoidal coupling means and the working piston (2') has cosine-shaped coupling means relative thereto. 11. Heat engine according to one of claims 7 to lo, characterized in that the angular position of the first and / or second coupling means is adjustable. 12. Heat engine according to one of claims 7 to 11, characterized in that the sine or cosine coupling means through a groove (46) and the corresponding coupling means is formed by a cam (44) engaging in it. 13. Heat engine according to one of claims 7 to 12, characterized in that the sinusoidal or cosine-shaped coupling means through a along a piston (2 'or 4') or along the housing wall (4o) sinusoidal or cosine-shaped extending magnetic or magnetizable material (33) is formed.

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