WO2003091556A1

WO2003091556A1 - Free-piston device provided with an electric linear drive

Info

Publication number: WO2003091556A1
Application number: PCT/EP2003/004199
Authority: WO
Inventors: Markus GRÄF; Martin Nedele; Jürgen Gräf
Original assignee: Deutsches Zentrum für Luft- und Raumfahrt e.V.
Priority date: 2002-04-25
Filing date: 2003-04-23
Publication date: 2003-11-06
Also published as: AU2003232496A1; JP2005524016A; JP4656840B2; DE10219549A1; EP1497542A1; DE10219549B4

Abstract

The invention relates to a universally applicable free-piston device with an electric linear drive (10, 40), comprising at least one piston receiving element (12) with at least one piston device (18) which is arranged in the piston receiving element (12) such that it can be displaced in a linear manner. The piston device (18) comprises a rotor device (46), and a stator device (48) is arranged on the piston receiving element (12). The at least one piston device (18) is driven by the action of a medium which expands in an expansion chamber (36, 38). According to the invention, the piston stroke can be variably adjusted by the linear drive (10, 40) in such a manner that the slack points of the displacement of the piston device (18) can be defined.

Description

DESCRIPTION

FREE PISTON DEVICE WITH ELECTRIC LINEAR DRIVE

The invention relates to a free piston device with an electric linear drive, comprising at least one piston receptacle with at least one piston device arranged to be linearly movable in the piston receptacle, the piston device comprising a rotor device and a stator device being arranged on the piston receptacle, and the at least one piston device under the action of Medium, which is expanding in an expansion space, can be driven.

Such a device is known for example from DE 22 17 194 C3.

With it, for example, chemical energy can be partly converted into mechanical energy via combustion, namely kinetic energy of a piston device, and this mechanical energy can then in turn be at least partly converted into electrical energy via the linear drive. By designing the piston movement as a free piston movement, pure linear mobility of the pistons can be achieved without the need for a crankshaft. Corresponding devices can be used, for example, as part of hybrid drives for motor vehicles and in particular in connection with serial hybrid concepts. They can also be used as a compact power generation unit to generate electricity or in connection with stationary applications such as combined heat and power plants.

Combustion devices with electrical generators are also known from US Pat. No. 6,199,519 B1, DE 31 03 432 AI, GDR patent No. 113 593, DE 43 44 915 AI or from the article "ADVANCED INTERNAL COMBUSTION ENGINE RESEARCH" by P. Van Blarigan , Proceedings of the 2000 DOE-Hydrogen Program Review.

Based on this, the object of the invention is to create a free-piston device with an electric linear drive of the type mentioned at the outset, which can be used universally.

This object is achieved according to the invention in the device mentioned at the outset in that the piston stroke can be variably adjusted via the linear drive in such a way that the dead centers of the movement of the piston device can be defined.

The fact that the piston stroke can be variably adjusted by corresponding electrical actuation of the linear drive means that the movement of the at least one piston device can be adjusted so that the optimal conditions prevail for the respective application. With a variable piston stroke, variable compression can be achieved; namely, the reversal points of the movement of a compressor piston of the piston device can be set in a targeted manner. This means that the device can be operated optimally in any load range.

At full load, for example, a large amount of gas must be drawn in. For combustion gases, for example, a large combustion chamber (as an expansion chamber) is therefore required, and thus a large piston stroke. In contrast, in partial load operation the intake volume is reduced and the volume is therefore reduced.

The linear drive can then also support the commissioning of the device, for example by controlling the initial compression via the linear drive.

The desired form of movement of the piston device can be set in a targeted manner via a control of the linear drive; the desired reversal point, the piston speed and the compression can each be set, so that improved part-load efficiency can be achieved, especially in part-load operation, since no throttle valve is necessary. The operating point of the device can thus be precisely determined by specifically specifying currents in the stator device.

In this way, an expansion chamber such as a combustion chamber can then be optimally adapted to the application, that is to say in particular the volume and the surface of the expansion chamber adapt specifically. This in turn results in extensive control and regulation options. It is thus possible to operate the device with different fuels or with expandable, non-combustible heat transfer media such as steam, which means that the device is suitable for a wide range of materials. It is also not necessary to change the device as such, that is to say the adaptation to a specific fuel such as vegetable oil or diesel (diesel principle) or normal or super gasoline (Otto principle) or hydrogen or natural gas can be carried out “online”, by adjusting the piston stroke accordingly, for example by applying current to the respective stator device.

It is even possible to implement a combined Otto-Diesel engine with the device according to the invention.

For example, it is also possible to switch between 2-stroke and 4-stroke operation.

A piston receptacle can have a constant inner diameter or a varying diameter and can, for example, be graduated. Several piston receptacles can be provided, whereby piston receptacles can be arranged in a packet-like or V-shaped manner.

It is possible to generate the expanding medium in the expansion space in different ways or to couple it into the expansion space. The expansion space can thus be a combustion space in which fuel combustion takes place and expanding fuel gases are generated in the process. It is also possible that the expansion space is a combustion chamber, in the fuel gases are coupled in, which expand in the combustion chamber. Furthermore, it is possible to couple a heat transfer medium such as steam into the expansion space, this heat transfer medium being generated externally or to which energy is supplied externally. This heat transfer medium then expands in the expansion space and causes a piston movement.

In particular, it is advantageous if the dead centers can be defined locally with respect to the piston receptacle, so that the compression of the system can be determined via a corresponding setting. It is then also advantageous if the dead centers for the movement of the piston device can be defined in time. This in turn also allows a movement of the at least one piston device to be set which has a constant period. This makes it possible, for example, to use pressure wave superchargers for a combustion chamber as an expansion chamber.

It is particularly advantageous if the movement of the piston device can be variably adjusted so that the location of the piston device can be defined at any time. As a special case, the piston speed is particularly adjustable. In this way, given appropriate specifications for the forms of movement of the at least one piston device, an optimal adaptation to the respective operating parameters of the device can be achieved via the linear drive, these operating parameters being determined in particular by the fuel used, by the load condition and further parameters.

Furthermore, it is advantageous if the top dead center and bottom dead center of the piston stroke of the piston device can be defined in order to be able to produce an optimal adaptation. In order to be able to set a variable piston stroke, the piston device delimits an expansion space at a first end and a space which is not an expansion space at an opposite end. This makes it possible to variably adjust the device by controlling the piston stroke.

In particular, the compression in the expansion space can be adjusted via the linear drive in order to optimize the system. As a result, an operating point of the system can be set variably.

In particular, the expansion space can then be adjusted, particularly with regard to volume and surface, in order to be able to produce the corresponding adaptation.

A control and / or regulating device is advantageously provided, by means of which the linear drive can be controlled electrically in such a way that a variable piston stroke can be set. This setting can be achieved in particular by controlling the current flow in the stator device. In this sense, the linear drive then also acts as a linear motor, via which the piston stroke and thus the reversal points or dead centers (TDC and TDC) of the piston movement can be set. In the case of a plurality of piston devices, each one can be assigned its own control and / or regulating device, or such a control and / or regulating device can control or regulate several piston devices. It is very particularly advantageous if a piston device comprises a first piston and an opposing second piston fixedly connected to it, the first piston delimiting the assigned expansion space. The first piston is the actual compressor piston, on which the expanding medium, such as expanding fuel gases, acts in order to move the piston device. The first piston is supported by the second piston. As a result, transverse forces are minimized, that is to say the piston device is prevented from tilting. This in turn ensures a defined, highly precise linear movement. In addition, the effort with regard to the lubrication between the piston and the inner wall of the cylinder can be kept low, since, due to the support of the compressor piston by the other piston in the pair of pistons, short piston shirts can be realized with a correspondingly reduced friction surface and then no oil pump has to be provided, but instead, for example, simple splash lubrication is sufficient. Furthermore, there is the possibility of using other materials such as ceramic materials or graphite for the pistons themselves, in addition to metallic materials, since a highly precise guidance can be formed with minimized friction losses, wherein only essentially pure pressure loads occur.

The concept according to the invention also makes it possible to dispense with the use of a cylinder head gasket, since the piston holder can be produced in one piece at least in the region of an expansion space.

A rotor device is arranged between the first piston and the second piston, which generates, for example, a magnetic field which is generated by a Relative movement relative to the stator device leads to a voltage induction, which in turn can then be tapped at the device. The rotor device and the stator device form the linear drive, which converts the kinetic energy of the piston device into electrical energy or conversely converts electrical energy into kinetic energy.

It is also advantageous if the non-expansion space for a piston device is designed as a spring-back space. Mechanical energy that is not decoupled from the linear drive can be absorbed via such a spring-back space during the combustion work cycle. The correspondingly stored energy can be used, for example, in a 2-cycle operation to compress a fuel-air mixture or in a 4-cycle operation to expel the exhaust gases.

A compressible element and / or medium is accommodated in the resilience space, which accordingly absorbs the mechanical energy and then releases it again. The compressible element can be a mechanical element and in particular a compression spring.

However, it is particularly advantageous if the compressible medium is a compressible fluid such as air. If it is then provided that the pressure in the resilience space can be adjusted and / or controlled and / or regulated, then the "elastic" properties of this medium can be set. In addition, a pump effect can then be achieved, for example with respect to the piston device, by controlling the pressure in the spring-back space in order to control and / or regulate the overflow of air. The air drawn in can then be pumped into the combustion chamber in a controlled manner.

It can also be provided that the pressure in the resilience space can be controlled and / or regulated so that a precompression function can be achieved via it. This increases the performance of the system, since pre-compression can take place.

A pump function, compression function or suction function can be implemented via a controllable / adjustable spring-back space. These respective functions can be used to control or regulate combustion processes. However, they can also be used for external purposes, for example to assist braking force when the device is used in a motor vehicle.

In order to enable such a control or regulation, the spring-back space is provided with at least one controllable inlet valve and at least one controllable outlet valve for the compressible medium. The valves are switched so that compression is possible with regard to the springback effect.

Furthermore, it is expedient if a first piston device and a second piston device are provided, which are arranged to be linearly movable, the piston devices each comprising and on a rotor device a stator device assigned to the respective rotor device is arranged in the piston receptacle. In particular, the piston devices are mutually oppositely movable. In this way, a mass balance can be carried out during the movement of the piston devices, so that the mechanical stability of the device can be optimized.

It is then advantageous if each piston device is assigned its own expansion space in order to be able to drive both piston devices using expanding medium such as combustion gases.

Furthermore, it is advantageous if the combustion chamber is formed between a piston in the respective piston device, which is facing away from the other piston device, and a piston receptacle facing the piston.

As a result, a variable piston stroke, as described above, can be set for both piston devices.

It can be provided that a further expansion space and in particular a combustion space is arranged between the two piston devices, this further expansion space being able to be operated in particular synchronously with the two outer expansion spaces (synchronous here essentially means push-pull). In this way, an increase in performance can be achieved.

It is particularly advantageous if the valve or valves for the gas exchange in an expansion space can be controlled and / or regulated and in particular electrically controlled via a control and / or regulating device and / or are adjustable. This enables an individual adjustment of all control times of the gas exchange, which significantly influence combustion properties, for example. This control or regulation, which can be carried out in particular via predefined software settings, then makes it possible to set an optimal operating point of the overall system even in the case of variable applications.

It is very particularly advantageous if inlet valves and / or outlet valves for an expansion space are arranged and designed such that a gas flow (inlet flow and / or outlet flow) can be formed essentially along an expansion chamber wall. In this way, reverse flushing can be implemented, in particular in 2-cycle operation, which makes the provision of inlet slots and outlet slots unnecessary. This in turn improves the exhaust gas quality and oil losses are minimized. The concept according to the invention results in a large number of possibilities for introducing fuel into the system. Power injection systems can also be used, and in particular direct injection systems for introducing fuel into the combustion chamber or combustion chambers.

In an advantageous variant of an embodiment, a charger is provided in order to control the gas exchange in an expansion space or the expansion spaces. The gas exchange can then be controlled with little energy expenditure.

In particular, the charger is a pressure wave charger or a Comprex charger, which can be operated with low power. In this way, pre-compression of the intake air can be achieved. Since the invention If the linear movement of the at least one piston device can be controlled in such a way that there is a constant period of oscillation of the piston movement at all possible operating points, a pressure wave charger can be used, which is dependent on constant periods with a small period spread.

In particular, the charger is connected to one or more expansion spaces for the respective piston devices in order to be able to carry out a correspondingly synchronized gas change with respect to the expansion spaces.

In a structurally simple embodiment, the piston devices are lubricated by splash lubrication.

It is also advantageous if a heating device is provided for preheating. As a result, the problems mentioned can be reduced in the case of a cold start in which friction losses occur, the exhaust gas quality is deteriorated and increased wear occurs.

In particular, windings of the stator device are used as heating elements, so that no increased design effort is required for this.

Advantageously, the rotor device comprises a plurality of magnetic elements, to which one or more flux guiding elements are assigned and in particular between which a flux guiding element is arranged in each case. In this way, the field lines of neighboring magnetic elements Concentrate, which in turn can optimize the power density of the system of the running device, that is, can assume high values. It is then also possible to use inexpensive magnetic elements with low remanence induction in order to still achieve a high power density.

The rotor device can be constructed in a structurally simple manner if the magnetic elements and the flow guide elements are seated on a piston rod, this piston rod then connecting the two pistons of the piston pair of a flow guide device.

Furthermore, it is expedient if the magnetic elements and the flux guiding elements are designed to be rotationally symmetrical with respect to an axis of the piston rod, so as to generate a defined induction voltage.

The magnetic elements and the flux guiding elements are advantageously arranged alternately in order to be able to generate high induction voltages during the movement of the rotor device relative to the stator device.

The flux guide elements are made of a magnetically conductive material such as iron or a magnetically conductive powder composite. The field lines of the adjacent magnetic elements can be concentrated by them so that they act as "field line collectors".

The magnetic elements can be permanent magnetic elements or electromagnetic elements. When electromagnetic elements are provided, the energy for operating these elements must be transferred to the rotor device. This can be done, for example, inductively or via slip rings. In principle, it is also possible to equip the rotor device with short-circuit rings in an asynchronous mode of operation, in which case this mode of operation corresponds to that of an asynchronous machine. It can also be provided that the rotor device is provided with a tooth structure with respect to a surface facing the stator device, or has such a tooth structure so that via corresponding different magnetic resistances (reluctance) of the magnetic circuit thus formed in the coils of the stator device by in-phase switching or coils a voltage is induced. Permanent magnets can also be used to increase the corresponding forces.

In an advantageous embodiment, the stator device and rotor device have different pole pitches, so that the force formation of the linear drive is not based on the fundamental waves of the stator current coating and rotor field, but the harmonics of the current coating produce the main force effect with the basic wave of the rotor field. In this way, the cross sections of inference yokes can be dimensioned smaller. In addition, the power density of the system can be increased significantly since it can be operated at higher frequencies, for example in the order of 500 Hz or higher.

It can be provided that additional secondary windings are provided with which electrical energy can be coupled out. About these secondary windings that meet a given energy requirement and a given

Voltage levels are adjusted, for example, an on-board electrical system Supply motor vehicle with electricity. The corresponding outlay for decoupling a corresponding current is low, a rectifier advantageously being arranged downstream of the secondary windings in order to generate a rectified current.

The linear drive can be single-phase or multi-phase.

In order to generate an induction voltage, a stator device comprises windings around the piston receptacle and in particular rotating main ring windings. Ring windings are particularly easy to wind. A voltage is induced in the windings in the stator device due to the relative movement between the stator device and the rotor device. The electrical ring energy is completely or largely coupled out or in through the main ring windings.

A synchronization device is advantageously provided, by means of which the movement of the two piston devices can be synchronized. This makes it possible to set the two piston devices in opposite directions with high accuracy, in order to achieve mass balancing with high accuracy.

In particular, the synchronization device then comprises secondary windings on the piston receptacle, the current flow of which can be individually controlled. If an asynchronicity of the two piston devices is then detected, the one that is running too fast can be controlled by appropriate control of the current flow Pistons are braked and / or the piston which is running too slowly is accelerated. With a synchronous movement, these secondary windings can be used, for example, to branch off electrical energy for an electrical system. The secondary windings can also be used for diagnostic purposes. In this way, for example, the introduction of fuel can be controlled in order to achieve synchronous operation with two or more piston devices.

It can also be provided that the synchronization device comprises secondary windings on the piston receptacle, which are assigned to the respective piston devices and are electrically connected to one another, so that a compensating current can flow between the secondary windings. The synchronization of the two piston devices is automatically regulated via this compensating current: if these move synchronously, no current flows. If these move asynchronously, then the compensating current generated slows down the piston device that is moving too quickly and accelerates the piston device that is running too slowly.

In particular, the current flow can be controlled electrically, so that, for example, a threshold value can be set, if it is exceeded a synchronization process must be carried out.

To support the synchronization of the two piston devices, it can be provided that the position of a piston device in the cylinder is detected by a control and / or regulating device from the voltage induced in the stator device. This allows you to be independent Detect the respective position of the piston device from a compensating current in order to also monitor the movement of these piston devices, for example.

It is also advantageous if a lubrication device for a piston device is designed such that the associated rotor device can be cooled with the lubricating oil. This minimizes the design effort for cooling the rotor device.

Furthermore, it is advantageous if cooling channels are arranged around the stator device and / or the piston receptacle, in particular in the region of an expansion space. The active components of the device can then be cooled via a corresponding cooling device, which comprises these cooling channels. However, usable heat can then also be coupled out via the cooling device, which heat can then be supplied to thermal applications such as, for example, vehicle heating or a combined heat and power plant. This in turn increases the overall effective efficiency of the system.

It can be provided that an expansion space is designed as a combustion space. Fuel gases then expand in such a combustion chamber. The combustion gases themselves can be generated in the combustion chamber by combustion processes taking place there, or can be generated externally and then coupled into the combustion chamber.

It is also possible for a heat transfer medium such as steam to relax in the expansion space. This heat transfer medium is preferably generated outside the expansion space or energy is supplied to the heat transfer medium outside the expansion space. For example, superheated steam is injected into an expansion room; the steam can relax there and cause a linear movement of the piston device. This in turn can be used to generate electricity. The heat generation and pressure increase takes place outside the expansion space. Various methods can be used to generate the heat transfer medium or to heat the heat transfer medium; for example, heating can take place via concentrated solar radiation, the solar radiation being concentrated via solar collectors. Heating or heat transfer can also take place via the combustion of solid, liquid or gaseous fuels. The heated heat transfer medium can be temporarily stored in a pressure vessel. According to the invention, this enables a free-piston steam engine to be designed which has a higher electrical efficiency than conventional steam engines. When using steam, for example, as the medium expanding in the expansion space, lubrication problems for the moving piston device are reduced, since in particular water lubrication of the piston device can be used.

It is expedient if a recooling device is provided for the medium discharged from the expansion space. This allows a cycle for the heat transfer medium with respect to the supply to the free piston device and the discharge from the free piston device to be realized. The following description of preferred embodiments serves in conjunction with the drawing to explain the invention in more detail. Show it:

Figure 1 is a schematic view of a first embodiment of a free piston device according to the invention with an electric linear drive, which is designed as a free piston combustion device;

Figure 2 shows a second embodiment of a device according to the invention;

Figure 3 shows a third embodiment of a device according to the invention;

Figure 4 schematically shows a combustion chamber;

Figure 5 shows a fourth embodiment of a device according to the invention;

Figure 6 shows a fifth embodiment of a device according to the invention and

FIG. 7 shows a sixth exemplary embodiment of a device according to the invention, which is designed as a free-piston steam engine. A first exemplary embodiment of a free-piston device (free-piston combustion device) according to the invention with an electric linear drive, which is designated as a whole in FIG. 1 by 10, comprises as the piston receptacle 12 a cylinder with a cylinder housing 14, in the interior 16 of which a first piston device 18 and a first one Piston device 18 spaced apart second piston device 20 are linearly displaceable.

The two piston devices 18 and 20 are essentially rotationally symmetrical with respect to an axis of symmetry 22 of the cylinder 12, at least with regard to their outer shape. The axes of the two piston devices 18 and 20 coincide with the axis of symmetry 22.

The first piston device 18 comprises a first piston 24a and a second piston 24b arranged at a distance from this first piston, these two pistons 24a and 24b being fixedly and in particular rigidly connected to one another via a piston rod 26. A pair of pistons is thereby formed.

The second piston device 20 is constructed identically with a first piston 28a, a second piston 28b and a piston rod 30 which is arranged between these two pistons 28a and 28b.

The second piston 24b of the first piston device 18 is the second piston

28b arranged facing the second piston device 20. The first piston 24a of the first piston device 18 is an end wall 32 of the Cylinder 12 is arranged facing, while the first piston 28a of the second piston device 20 is facing a wall 34 opposite the front wall 32 of the cylinder 12.

Between the respective first pistons 24a, 28a of the two piston devices 18, 20 and the facing cylinder wall 32 or 34, a combustion chamber with a combustion chamber 36, 38 is formed as an expansion chamber, in which combustion gases are expandable by the associated piston device (for the combustion chamber 36 the to drive the first piston device 18 and the second piston device 20) for the combustion chamber 38.

The dimensions of the respective combustion chambers with combustion chambers 36 and 38 are determined by the piston stroke of the respective piston devices 18 and 20, that is to say in particular the volume and surface are determined by the reversal point of the piston movement of the first pistons 24a and 28a.

The free-piston combustion device comprises an electric linear drive, designated as a whole by 40, which comprises a first part 42, which is assigned to the first piston device 18 and a second part 44, which is assigned to the second piston device 20.

The corresponding part 42 or 44 of the electric linear drive 40 in turn comprises a rotor device 46 which is arranged on the respective piston device 18 or 20. This rotor device 46 is moved with the piston device 18 or 20. Via a stator device 48, which is arranged on the cylinder 12 outside the cylinder housing 14, and in each case the Voltages are assigned to the first piston device 18 or the second piston device 20, voltages can then be induced in order to generate electrical energy.

The rotor device 46 comprises magnetic elements 50 and flux guide elements 52, which are arranged alternately on the associated piston rod 26 or 30.

The magnetic elements 50 can be permanent magnet elements which are in particular disc-shaped, rotationally symmetrical about the axis 22. These can also be electromagnetic elements which comprise corresponding windings arranged in particular concentrically about the axis 22. A corresponding device must then be provided in order to be able to transmit energy to these electromagnets. This can be done inductively, for example, or via slip rings.

A flux guide 52 is also disc-shaped and made of a material with high magnetic conductivity. For example, iron or magnetically conductive powder composite materials can be used.

Preferably, the magnetic elements 50, in particular if they are permanent magnets, and the flux-conducting elements 52 are designed such that they have a central opening with which they can be pushed onto the associated piston rod 26 or 30 during the production of the corresponding piston device 18 or 20 , The magnetic elements 50 are designed and in particular magnetized in such a way that the field lines of the adjacent magnetic elements 50 are concentrated in a flux guiding element 52, in order thus to increase the power density of the system. In particular, the magnetic elements 50 are arranged in parallel in such a way that the same poles point to one another.

It can also be provided that an outer surface of the respective rotor device 46 is designed such that it is tooth-shaped in a cross section comprising the axis 22 of an inner side facing a cylinder wall. The rotor device 46 has changing magnetic conductivities due to such a tooth structure, so that a propulsion for a piston device can be generated.

The stator device 48 comprises main ring windings 54, which is arranged around an outer wall of the cylinder 12. A voltage is induced in these ring windings upon relative movement of the magnetized rotor device 46, as a result of which electrical energy can be coupled out. A power generation device is then provided which is based on the principle of free piston guidance (linear mobility of the two piston devices 18 and 20).

The stroke of the two piston devices 18 and 20 can be controlled and / or regulated via a control and / or regulating device 56. In particular, such a control can be carried out that the location of the piston devices 18, 20 is fixed at any time. As a result, the reversal point of the piston movement of the first can be used as required Adjust pistons 24a and 28a so that the dimensions of the respective combustion chambers 36 and 38 can be adjusted. Appropriate control of the linear drive 40 allows the piston stroke to be set as a function of the load state, the compression to be set and the speed of the piston devices 18, 20 to be set, and thus the combustion chamber 36 or 38 to be set optimally depending on the load state. In particular, the volume of the combustion chambers 36, 38 and the respective surfaces of these combustion chambers 36 and 38 can then be adapted to the application. This local time-dependent adjustment of the piston stroke (position, compression, speed) can also be used to adapt to the fuel, i.e. a piston stroke distance and compression can be set, depending on whether for example diesel or vegetable oil (diesel principle) or gasoline, natural gas or hydrogen (Otto principle) is used as fuel. (The necessary ignition devices are not shown in the drawing.)

By specifically specifying currents in the stator device 48 and possibly in the rotor device 46, that is to say by controlling and / or regulating these currents, the associated piston device 18 or 20 can thus be influenced in its linear displaceability in order to determine the location of the reversal points of the piston movement to be able to precisely define the two piston devices 18, 20 in the external combustion chambers 36 and 38.

This makes it possible, for example, to set a correspondingly large piston stroke at full load, in which a large amount of air is required for the combustion chambers 36 and 38, while a reduced stroke can be set in the case of part-load operation with a reduced intake volume. The two piston devices 18 and 20 are arranged and designed so that they are in opposite directions. A spring-back space 58 is formed between its second pistons 24b and 28b, in which an elastic element or a compressible medium is accommodated.

For example, a compression spring can be arranged in the spring-back space 58, which at least partially absorbs the energy that was not decoupled from the linear drive 40 during a combustion work cycle. This stored energy can be used to compress the fuel-air mixture in a 2-stroke operation or to discharge the exhaust gases in a 4-stroke operation.

In particular, provision can be made for a granularly compressible fluid and in particular gas such as air to be accommodated in the spring-back space, which fluid just absorbs and releases the energy again.

It is provided that the pressure in the resilience space 58 can be controlled and / or regulated via one or more valves 60. The control and / or regulation of the valve or valves 60 is preferably carried out via the control and / or regulating device 56. Such a spring-back chamber 58, in which the pressure can be controlled, can also be used to pump a pump with respect to the two piston devices 18 and 20 to train. Appropriate valves 100 and 102 (see FIG. 2) allow controlled air to be pumped into combustion chambers 36 and 38. With correspondingly time-controlled closing of the valves 100 and 102, that is to say decoupling from the The spring back function (energy storage function) can be guaranteed in the environment. This control then takes place via the control and / or regulating device 56 synchronously with the timing of the combustion in the combustion chambers 36 and 38 (compare FIG. 2 with the combustion chambers 36 'and 38' there).

Each combustion chamber 36, 38 is provided with an electrically controllable outlet valve 62 and, in particular, an electrically controllable inlet valve 64, with a corresponding control taking place via the control and / or regulating device 56. This allows the intake of combustion chamber gases and the removal of combustion products to be controlled in a timely manner and, in particular, to be synchronized, for example in connection with the electrical actuation of the linear drive 40 by means of a corresponding electrical actuation device 66 and a possible pump function of the resilience space 58.

A suction line 68 leading into the corresponding combustion chamber 38 is connected to a charger 70. This suction line 68 is coupled to the combustion chamber 38 via an inlet valve 64.

An exhaust pipe 72 leads to the charger 70 via the outlet valve 62. The charger 70 itself has a supply 74 for intake air and a discharge 76 for exhaust gases.

A corresponding exhaust pipe 78 and a corresponding suction pipe 80 lead from the charger 70 to the other combustion chamber 36, with the coupling or decoupling is designed there in the same way as described with reference to the other combustion chamber 38.

The charger 70 is in particular a pressure wave charger (Comprex charger), in which the energy of the exhaust gas stream is used by the combustion chambers 36 and 38 to compress the charge air (intake air). In such a pressure wave supercharger, pressure waves and suction waves suck in and compress fresh air from the pulsating exhaust gases. This compression takes place in direct contact with the exhaust gases.

With the device according to the invention, a constantly oscillating displacement movement and, in particular, a collinearly opposing displacement movement of the two piston devices 18 and 20 can be formed. This in turn allows a constant oscillation of the discharged exhaust gases to be achieved, so that the gas exchange can be controlled and / or regulated via a charger. The advantage of a Comprex loader is that it requires very little energy.

The overall system of the charger 70 and movable piston devices 18 and 20 with their respective combustion chambers 36 and 38 can be designed precisely for an optimal operating point, which in turn can be designed for the charger 70, due to the constant period for the oscillating movement of these piston devices 18 and 20.

If a charger 70 is present, then the variant described above, in which the spring-back space 58 is used as a pump, is not implemented. It can also be provided that one or more secondary windings 82 are associated with the two piston devices 18, 20, respectively, around the cylinder. These are electrically separated from the main ring windings 54 of the respective stator device 48. The secondary windings 82 are arranged, for example, around the main ring windings 54 or lying next to them (in the axial extension of a ring winding axis of the main ring windings 54).

A further current can be coupled out via such secondary windings 82, for example to supply a 12V / 14V or a 36V / 42V electrical system of a motor vehicle with current. The number of turns is adapted accordingly. Such secondary windings 82 are preferably followed by a rectifier in order to be able to generate a rectified current accordingly.

Via secondary windings 82 (these can be the same secondary windings that are used to decouple an additional current or one provided separately therefrom), a synchronization of the two piston devices 18, 20 in their linear movement in the cylinder 12 can be achieved by means of a synchronization device. The synchronization device is included in the control and / or regulating device 56, at least with regard to its control and regulation part.

By switching the secondary windings 82 on and off in a targeted manner, depending on the position of the associated piston devices 18 and 20, a current can be generated or applied via which the assigned piston device 18 or 20 can be braked or accelerated. Asynchrony in the movement of the two piston devices 18, 20 can thereby be compensated for, in particular by braking the piston device which is running too fast.

During synchronous operation, these secondary windings 82 can then be used to generate electricity.

In particular, it can be provided that the respective secondary windings 82, which face the two piston devices 18 and 20, are electrically connected to one another. This is indicated in FIG. 1 by reference number 84. A compensating current can then flow between the respective secondary windings 82, which self-regulatingly synchronizes the movements of the two piston devices 18 and 20. The faster piston device is braked and the slower accelerated. A threshold value for this compensating current itself can be specified, for example, via the control and / or regulating device 56.

It can also be provided that a cooling device 86 comprising cooling channels 88 is arranged around the stator device 48 in order to cool the active components of the free-piston combustion device with linear drive 10; These active components include in particular the piston devices 18, 20, the cylinder 12 and the main ring windings 54.

It can also be provided that heat is extracted from the corresponding cooling device 86 and that this is used in thermal applications, for example for a vehicle heater or for a combined heat and power plant. The device according to the invention functions as follows:

Certain reversal points (UT and OT) of the two piston devices 18, 20 are set via the linear drive 40 by appropriate current application, in order thus to determine the volume and the surface of the respective combustion chambers 36 and 38. Furthermore, the speed of the piston devices 18, 20 and overall the compression are determined. This setting depends on the load (partial load or full load), the fuel (gasoline, natural gas, hydrogen, diesel, vegetable oil, etc.) and any other external parameters.

It can be provided that electrical preheating takes place for the start of the device and the cooling water of the cooling device 86 is also preheated. This preheating can take place via the linear drive 40 by using corresponding windings, for example the main ring windings 54, as heating elements. However, separate heating coils can also be provided.

The piston pairs 24a, 24b and 28a, 28b of the two piston devices 18 and 20 provide support for each piston device 18, 20, that is to say the pistons 24a, 24b and 28a, 28b of the piston pairs can be guided linearly without tilting.

In addition, the pistons 24b and 28b also serve to seal against the resilience space 58. As a linear drive, the reversal points of the movement of the two piston devices 18, 20 are (local and temporal) can be precisely specified, and therefore no throttle valve, which is otherwise responsible for throttle losses, is necessary for the air supply in part-load operation.

The intake of air and the removal of the exhaust gases can be controlled in a targeted manner by means of the valves 62 and 64 for the respective combustion chambers 36, 38. This can improve the efficiency of the overall system and improve the exhaust gas quality; an exact adjustment between the individual time-critical processes can take place through precise setting of the control times via points in time and the duration with regard to the gas change (flow through the valves 62, 64). Since the speed of the piston devices can also be controlled or regulated, even during the expansion process, the formation of exhaust gases can be influenced.

In particular, the inlet valve 64 is arranged and designed such that sucked-in air and resulting gas flows are guided along inner cylinder walls in order to obtain an optimized purging process for the gas exchange (see FIG. 4). For this purpose, the inlet valve 64 has, for example, a correspondingly designed guide plate 88 which ensures such a flow along. This is particularly necessary in 2-stroke operation to achieve reverse purging in the combustion chamber.

The intake and compression of air and the exhaust of exhaust gases is preferably carried out via a pressure wave charger 70.

During the movement of the piston devices 18, 20 due to the relative movement between the rotor device 46 and the stator device 48 induces a voltage in the latter, so that electrical energy is generated (i.e. mechanical energy is partially converted into electrical energy, the mechanical energy in turn resulting from a partial conversion into chemical energy due to the combustion).

Energy can be absorbed by the spring-back space 58, which is not decoupled from the linear drive 40 during the combustion work cycle.

The stator device 48 is cooled via the cooling device 86. The cooling device 86 also cools further parts of the cylinder 12 and, for example, the piston devices 18 and 20.

The pistons 24a, 24b, 28a, 28b are lubricated, for example, by simple splash lubrication, which means that no oil pump is required. The pistons then move in an oil bath which is swirled together by the movement in order to ensure an adequate supply of lubricating oil.

The pistons 24a, 24b, 28a, 28b can be produced with a minimized side surface facing the cylinder 12, that is to say the piston shirts can be made short, since correspondingly pairs of pistons with mutual support action are provided. Friction losses during the movement of the two piston devices 18 and 20 can thereby be minimized. As a result, the pistons 24a, 24b, 28a, 28b can also be produced from non-metallic materials such as ceramic materials or from graphite or, for example, glassy carbon. Such pistons can do without lubrication. This design is possible because essentially no transverse forces occur due to the mutual support of the piston pairs.

A high power density of the system can be achieved by the rotor device 46 according to the invention with alternating magnet elements 50 and flux guide elements 52, without having to use magnets with high remanence induction. In particular, high power densities can be achieved if the pole pitch in the rotor device and the stator device is different.

The linear drive 40 itself can have a single-phase, two-phase, three-phase or multi-phase structure.

The main ring windings 54 of the corresponding stator device 48 can be embedded in iron packets, for example, in order to achieve field guidance.

By means of the synchronization device, the two piston devices 18, 20, which can move in opposite directions, can be synchronized with one another, with self-regulation in particular being able to be carried out via a compensating current.

It can also be provided that the control and / or regulating device 56 evaluates position information of the two piston devices 18, 20 via the induced voltage; this evaluation is an evaluation of the relative position of the rotor device 46 to the associated stator device 48. For example, these detection results can then be used to improve the synchronization of the two piston devices 18 and 20. By providing additional windings in the stator device 48, the accuracy of the position determination can be increased.

The free-piston combustion device according to the invention can be operated, for example, in 2-stroke or 4-stroke operation.

In a second exemplary embodiment, which is designated 90 as a whole in FIG. 2, an overflow guide 92 is provided instead of a charger 70. The cylinder 12 itself is basically designed as described above, so that the same parts have the same reference numerals as in Figure 1, but with a dash.

A corresponding spring-back chamber 94 is coupled to a suction channel 96 and a suction channel 98 via corresponding valves 100 and 102, so that air can be sucked into the corresponding combustion chambers 36 'and 38' via these. The volume of the resilience chamber 94 is greater than the total volume of the two combustion chambers 36 ', 38' together in order to achieve a pre-compression of the intake air.

Otherwise, the device 90 functions exactly as described above. Intake air can be pre-compressed into spring-back space 94, which has a pump function, before it is pumped into combustion chambers 36 'and 38'.

In a third exemplary embodiment, which is designated as a whole in FIG. 3 by 104, a cylinder 106 is again provided, in which in turn two piston devices 108 and 110 are guided so as to be linearly displaceable. These are designed, as already described above, with respective piston pairs 112a, 112b and 114a, 114b. The pistons 112a and 114a are each arranged facing a respective front cylinder wall 116 and 118, while the two pistons 112b and 114b point to one another.

In contrast to the exemplary embodiments 10 and 90, the space between the two piston devices 108 and 110 is designed as a combustion chamber 120 in that an air / fuel mixture can be ignited accordingly.

For this purpose, this combustion chamber 120 is provided with an inlet valve 122 and an outlet valve 124. Fresh air is supplied to the combustion chamber 120 via the inlet valve and exhaust gas is discharged via the outlet valve 124.

A corresponding suction line 126 and a discharge line 128 is connected to a charger 130, which in turn, as already described with reference to the first exemplary embodiment, is connected to the outer combustion chambers 132 and 134 via respective suction lines 136 and exhaust gas discharge lines 138. Otherwise, the free-piston combustion device with a linear generator works as already described above. It is fundamentally possible for piston devices 140, 142 to be provided, between which a combustion chamber 144 is arranged (FIG. 5).

Each piston assembly 140, 142 in turn includes a pair of spaced pistons 146a, 146b and 148a, 148b, respectively.

It is now provided that a spring-back space 154, 156 is formed between the piston 146a and a facing cylinder wall 150 and the piston 148a and the facing cylinder wall 152, in which, for example, an elastic element 158, preferably a compression spring, is arranged.

In such a device, the energy that is not absorbed by a corresponding linear drive 160 during a combustion work cycle (during combustion in the combustion chamber 144) can then be stored separately for each piston device 140, 142, that is to say in an associated spring-back chamber 154 or 156. The linear drive 160 is basically of the same design as described above with reference to the linear drive 40.

In a fifth exemplary embodiment of a free-piston combustion device according to the invention with a linear drive, which is designated as a whole in FIG. 6 with 202, a piston receptacle 204 is provided, in which a single piston device 206 can be displaced linearly. Several such piston receptacles 204 can be interconnected, for example for power generation, in that they are stacked in a packet-like manner, for example, or two piston receptacles are each arranged in a V-shape. The piston device 206 in turn comprises a first piston 208 and an opposing second piston 210, which essentially serves to support the first piston 208. A piston rod 212 is arranged between these two pistons 208 and 210 and connects these two pistons 208 and 210 to one another.

A rotor device 214, which is designed as described above, is arranged between these two pistons 208 and 210 on the piston rod 212.

In turn, a stator device 216 configured as described above sits on the piston receptacle 204.

The first piston 208 faces an expansion space designed as a combustion chamber 218 and delimits it. This first piston 208 thus also directly experiences the pressure of the combustion gases expanding in the combustion chamber 218, which drive the piston device 206.

It is preferably provided that a thermal insulating element 220, for example a ceramic disk of the rotor device 214, is arranged on the first piston 208 in order to thermally isolate the combustion chamber 218 from the rotor device 214.

An exhaust line 224 leads from the combustion chamber 218 via a controllable outlet valve 222 to a charger 226. Furthermore, one leads from this bearing 226 Supply line 228 to the combustion chamber 218, into which it opens via a controllable inlet valve 230.

The charger 226 with its coupling to the combustion chamber 218 functions as already described above.

The second piston 210 faces a space 232, which is a non-combustion space. In particular, this is designed as a spring-back space in that a mechanical elastic element is arranged (not shown in FIG. 6) or in that a compressible medium such as air is arranged. In this case, controllable valves 234 are provided for controlling and / or regulating the pressure in this space 232 in order to be able to control the springback.

The device 202 according to the invention functions as described above with reference to the first exemplary embodiment, that is to say the piston movement can be variably adjusted via the control and regulating device 56.

The upper reversal point (OT) and the lower reversal point (UT) can be set, in particular spatially with respect to the piston receptacle 204 and can be set in time. Furthermore, the piston speed can be adjusted, and in turn the compression in the combustion chamber 218 can be adjusted. In particular, the setting takes place via a linear drive, which includes the rotor device 214 and the stator device 216. By adjusting the piston movement in such a way that the position of the first piston 208 is adjustable at least with respect to the point in time for reaching the upper reversal point and the lower reversal point and preferably such that the If the piston position of the first piston 208 can be defined in a defined manner at any time, the device can be variably adapted to different operating conditions or different operating parameters.

Free-piston combustion devices have been described above as exemplary embodiments for free-piston devices according to the invention. These can be used in particular as internal combustion engines.

It is also possible to implement a free-piston steam engine via the solution according to the invention, as will be described in more detail below.

In a sixth exemplary embodiment of a free-piston device according to the invention, which is designated as a whole in FIG. 7 by 300, a piston receptacle 302 comprises an interior 304 in which a piston device 306 is arranged so as to be linearly movable. The piston device 306 comprises a first piston 308 and an opposing second piston 310 connected to it.

The first piston 308 delimits an expansion space 312, in which a heat transfer medium such as steam can relax, a force being exerted on the first piston 308 and thus on the piston device 306 via this expansion of the heat transfer medium. The second piston 310 delimits a spring-back space 313, which is formed in the interior 304 of the piston receptacle 302 at the other end with respect to the expansion space 312. A rotor device 314, which moves with the piston device 306, is fixed to the piston device 306. A stator device 316 is fixed in place with respect to the piston receptacle 302.

The operation of such a drive device is basically the same as described above.

The heat transfer medium, which is in particular steam, is generated or heated outside the expansion space 312. For this purpose, a pressure vessel 318 is provided, for example, which is coupled to the expansion space 312 via an outlet 320. A line 322 for heat transfer medium is arranged between this outlet 320 and the expansion space 312.

The pressure vessel 318 can be heated by means of a heat source 324. The heat source itself can be heated by means of solar radiation or by means of fuels.

Heated heat transfer medium, such as superheated steam, is injected from the pressure vessel 318 into the expansion space 312 and can relax there. This leads to a piston movement on the piston device 306, as a result of which electrical energy can be generated. To couple the heat transfer medium into the expansion space, a corresponding valve 326 is arranged on it, which can be actuated mechanically or electrically. This allows the heat transfer medium supply to be controlled or regulated in a corresponding manner. At an outlet 328 of the expansion space 312 there is a further valve 330, via which the medium removal from the expansion space 312 can be controlled or regulated, this control taking place in particular coupled to the heat transfer medium supply.

The outlet 328 is connected via a line 330 to a recooling device 332, via which medium discharged from the expansion space 312 can be cooled. The medium that enters the recooling device 332 is under a lower pressure than the medium that exits the pressure vessel 318 and enters the expansion space 312 for expansion.

From the recooling device 332, medium such as steam can be fed via a line 334 into the pressure vessel 318, in order to be able to supply energy to the medium there, i.e. H. To be able to provide heat transfer medium for the expansion space 312.

A pump 336 is arranged in the line 334 in order to be able to convey the medium into the pressure vessel 318.

The pressure vessel 318 is preferably filled with steam.

Expansion of the steam introduced into the expansion space 312 under pressure causes the linear movement of the piston device 306, which in turn produces the electrical energy. The piston movement and the generation of the electrical energy takes place in the same way as described above. In such a free-piston steam engine, too, a plurality of piston devices and expansion spaces can be provided as described above.

It is also possible in a free-piston combustion device to supply combustion gases to a combustion chamber which have been generated externally and are then injected into the combustion chamber, which is delimited by the corresponding piston device.

Claims

EXPECTATIONS

1. Free-piston device with an electric linear drive (40), comprising at least one piston holder (12; 204) with at least one piston device (18; 20; 206) arranged linearly movable in the piston holder (12; 204), the piston device (18, 20; 206) comprises a rotor device (46; 214) and a stator device (48; 216) is arranged on the piston receptacle (12; 204) and the at least one piston device (18; 20; 206) under the action of a medium which is in a Expansion space (36; 38; 218; 312) expands, can be driven, so that the piston stroke can be variably adjusted via the linear drive (40) such that the dead center of the movement of the piston device (18; 20; 206) can be defined are.

2. Free piston device according to claim 1, characterized in that the dead centers locally with respect to the piston receptacle (12, 204; 302) can be defined.

3. Free piston device according to claim 1 or 2, characterized in that the dead centers for the movement of the piston device (18; 20; 206; 306) can be defined in time.

4. Free piston device according to one of the preceding claims, characterized in that the movement of the piston device (18; 20; 206; 306) is so variably adjustable that the location of the piston device (18; 20; 206; 306) can be defined at any time ,

5. Free piston device according to one of the preceding claims, characterized in that top dead center and / or bottom dead center of the piston stroke of the piston device (18; 20; 206; 306) can be defined.

6. Free piston device according to one of the preceding claims, characterized in that the piston device (18; 20; 206) delimits an expansion space (36; 38; 218; 312) at a first end and a space (58; 232; 318), which is not an expansion space.

7. Free piston device according to claim 6, characterized in that the compression in the expansion space (36; 38; 218; 312) via the linear drive (40) is adjustable.

8. Free piston device according to claim 6 or 7, characterized in that the expansion space (36; 38; 218; 312) is variably adjustable.

9. Free piston device according to one of claims 6 to 8, characterized in that the volume and surface of the expansion space (36; 38; 218; 312) are adjustable.

10. Free piston device according to one of the preceding claims, characterized in that a control and / or regulating device (56) is provided, via which the linear drive (40) can be electrically controlled so that a variable piston stroke is adjustable.

11. Free piston device according to one of the preceding claims, characterized in that a piston device (18; 20; 206; 306) has a first piston (24a; 28a; 208; 308) and an opposite second piston (24b; 28b; 210; 310).

12. Free piston device according to claim 11, characterized in that the rotor device (46; 214; 316) is arranged between the first piston (24a; 28a; 208; 308) and the second piston (24b; 28b; 210; 310).

13. Free piston device according to one of claims 6 to 12, characterized in that the non-expansion space (58; 232; 313), which is limited by the piston device (18; 20; 206; 306), as a spring-back space for the piston device (18 ; 20; 206; 306) is formed.

14. Free piston device according to claim 13, characterized in that a compressible element and / or medium is accommodated in the resilience space (58; 232; 313).

15. Free piston device according to claim 14, characterized in that the compressible element is a mechanically elastic element.

16. Free piston device according to claim 14, characterized in that the compressible medium is a compressible fluid.

17. Free piston device according to claim 14, characterized in that the pressure in the resilience space (58; 232; 313) is adjustable and / or controllable and / or adjustable.

18. Free piston device according to claim 17, characterized in that the pressure in the resilience space (58; 232; 313) can be controlled and / or regulated so that a pump function and / or compression function and / or suction function can be achieved via this.

19. Free piston device according to claim 17 or 18, characterized in that the pressure in the resilience space (58; 232; 313) is so controllable and / or regulatable that a pump effect with respect to a piston device (18; 20; 206; 306) can be achieved is.

20. Free piston device according to one of the preceding claims, comprising a first piston device (18) and a second piston device (20), which are arranged to be linearly movable, the piston devices (18, 20) each comprising a rotor device (46) and on the piston holder ( 12) a stator device (48) assigned to the respective rotor device (46) is arranged.

21. Free piston device according to claim 20, characterized in that two piston devices (18, 20) each have their own expansion space (36; 38) is assigned.

22. Free piston device according to claim 21, characterized in that the expansion space (36; 38) between a piston (24a; 28a) of the respective piston device (18; 20) which faces away from the other piston device (20; 18), and one Piston (24a; 28a) facing the piston receiving wall (32; 34) is formed.

23. Free piston device according to one of claims 20 to 22, characterized in that the two piston devices (18, 20) are movable in opposite directions to each other.

24. Free-piston device according to one of claims 20 to 23, characterized in that a further expansion space (120) is arranged between the two piston devices (108, 110).

25. Free piston device according to one of claims 20 to 23, characterized in that at least one spring-back space (58) is arranged between the two piston devices (18, 20).

26. Free piston device according to one of the preceding claims, characterized in that the valve or valves (62, 64; 326, 328) for the gas exchange in an expansion space (36; 38; 312) via a control and / or regulating device (56) are controllable and / or regulatable.

27. Free piston device according to claim 26, characterized in that the valve or valves (62, 64; 326, 328) for the gas exchange of an expansion space (36; 38; 312) are electrically controllable and / or adjustable.

28. Free piston device according to one of the preceding claims, characterized in that inlet valves (64) and / or outlet valves (62) for an expansion space (36; 38) are arranged and designed such that a gas flow can be formed essentially along an expansion chamber wall.

29. Free piston device according to one of the preceding claims, characterized in that at least one charger (70) is provided to control and / or regulate the gas exchange in an expansion space (36; 38) or the expansion spaces (36, 38).

30. Free piston device according to claim 29, characterized in that the charger is a pressure wave charger (70).

31. Free piston device according to claim 29 or 30, characterized in that the charger (70) is connected to one or more expansion spaces (36; 38) for the respective piston devices (18, 20).

32. Free-piston device according to one of the preceding claims, characterized in that a piston device (18; 20; 206) are lubricated by splash lubrication.

33. Free piston device according to one of the preceding claims, characterized in that a heating device is provided for preheating.

34. Free piston device according to claim 33, characterized in that windings of the stator device (48) are used as heating elements.

35. Free piston device according to one of the preceding claims, characterized in that the rotor device (46) comprises a plurality of magnetic elements (50), which one or more flux guide elements (52) are assigned.

36. Free piston device according to claim 35, characterized in that the magnetic elements (50) and the flux guide elements (52) sit on a piston rod (26; 30).

37. Free piston device according to claim 36, characterized in that the magnetic elements (50) and the flux guide elements (52) are rotationally symmetrical with respect to an axis (22) of the piston rod (26; 30).

38. Free piston device according to one of claims 35 to 37, characterized in that the magnetic elements (50) and flux guide elements (52) are arranged alternately.

39. free piston device according to one of claims 35 to 38, characterized in that the flux guide elements (52) are made of a magnetically conductive material.

40. free-piston device according to one of claims 35 to 39, characterized in that a flux guide element (52) is designed so that in this field lines of the adjacent magnetic elements (50) can be concentrated.

41. Free piston device according to one of claims 35 to 40, characterized in that the magnetic elements (50) are permanent magnet elements.

42. Free piston device according to one of claims 35 to 40, characterized in that the magnetic elements (50) are electromagnetic elements.

43. Free piston device according to one of the preceding claims, characterized in that a stator device (48) around the piston receptacle (12) comprises main ring windings (54).

44. Free piston device according to claim 43, characterized in that additional secondary windings (82) are provided, with which electrical energy can be coupled out.

45. free-piston device according to claim 44, characterized in that the secondary windings (82) is followed by a rectifier.

46. Free piston device according to one of claims 20 to 45, characterized in that a synchronization device is provided, by means of which the movement of the two piston devices (18, 20) can be synchronized.

47. Free piston device according to claim 46, characterized in that the synchronization device comprises secondary windings (82) on the piston receptacle (12), the flow of which is individually controllable.

48. free piston device according to claim 46 or 47, characterized in that the synchronization device comprises secondary windings (82) on the piston receptacle (12) which are associated with the respective piston devices (18, 20) and are electrically connected to one another, so that a compensating current between the Secondary windings (82) can flow.

49. free piston device according to claim 48, characterized in that the current flow is electrically controllable.

50. free piston device according to one of the preceding claims, characterized in that the position of a piston device (18; 20) in the piston receptacle (12) via a control and / or regulating device (56) is detected from an induced voltage.

51. Free piston device according to one of the preceding claims, characterized in that a lubricating device for a piston device is designed such that the associated rotor device (46) can be cooled with the lubricating oil.

52. Free piston device according to one of the preceding claims, characterized in that cooling channels (84) are arranged around the stator device (48).

53. Free piston device according to one of the preceding claims, characterized in that cooling channels are arranged around the piston receptacle (12).

54. Free piston device according to one of claims 13 to 53, characterized in that the resilience space (58) is provided with at least one controllable inlet valve and at least one controllable outlet valve for the compressible medium.

55. Free-piston device according to one of the preceding claims, characterized in that the rotor device (46) and the stator device (48) have different pole pitches.

56. Free piston device according to one of the preceding claims, characterized in that an expansion space is designed as a combustion space (36; 38; 218).

57. Free piston device according to claim 56, characterized in that in a combustion chamber (36; 38; 218) expand fuel gases.

58. Free piston device according to claim 57, characterized in that fuel gases are generated in the combustion chamber (36; 38; 218).

59. Free piston device according to claim 57, characterized in that fuel gases are generated externally and coupled into the combustion chamber.

60. Free piston device according to one of claims 1 to 55, characterized in that a heat transfer medium expands in an expansion space (312).

61. Free piston device according to claim 60, characterized in that the heat transfer medium is steam.

62. Free piston device according to claim 60 or 61, characterized in that the heat transfer medium is generated outside the expansion space (312) or the heat transfer medium outside the expansion space (312) is supplied with energy.

63. Free piston device according to one of claims 60 to 62, characterized in that a recooling device (332) is provided from the medium discharged from the expansion space.