EP2029859A1

EP2029859A1 - Free-piston device and method for operating a free-piston device

Info

Publication number: EP2029859A1
Application number: EP07730207A
Authority: EP
Inventors: Sven-Erik Pohl; Cornelius Ferrari
Original assignee: UMC Universal Motor Corp GmbH
Current assignee: UMC Universal Motor Corp GmbH
Priority date: 2006-06-20
Filing date: 2007-06-15
Publication date: 2009-03-04
Anticipated expiration: 2027-06-15
Also published as: CN101473106A; US20090101005A1; JP2009541635A; DE102006029532A1; RU2009101386A; WO2007147789A1; EP2029859B1

Abstract

The invention relates to a free-piston device comprising at least one piston cavity, in which at least one piston unit is mounted so that it can be displaced linearly. The piston unit or units can be driven by the action of a medium that expands in an expansion chamber. The piston cavity or cavities has/have a resilient-action chamber, which contains a compressible gas for exerting a restoring force on the piston unit or units and on which an actuator for controlling and/or regulating the restoring force during the operation of the free-piston device is mounted. The invention also relates to a method for operating a free-piston device.

Description

Free piston device and method for operating a free piston device

The invention relates to a free-piston device comprising at least one piston receptacle in which at least one piston device is arranged to be linearly movable, wherein the at least one piston device is drivable under the action of a medium which expands in an expansion space, and wherein the at least one piston receptacle has a resilience space in which a compressible gas for exerting a restoring force is received on the at least one piston device, and at least one actuator for controlling and / or regulating the restoring force, which is arranged on the resilience space.

The invention further relates to a method for operating a free-piston device, wherein at least one piston device, which is guided linearly movable in at least one piston seat, under the action of a medium which expands in an expansion space, is driven, and in which at least one piston device by a compressible gas which is received in a resilience space of the at least one piston seat, a restoring force is exerted.

By means of a free-piston device, for example, chemical energy via combustion can be partially converted into mechanical energy, namely kinetic energy of a piston device, and this mechanical energy is released then in turn at least partially convert into electrical energy via a linear drive. By designing the piston movement as a free-piston movement, it is possible to realize a pure linear mobility of the pistons without having to provide 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 for the generation of electricity or in connection with stationary application such as cogeneration units.

Free piston devices are known for example from GB 854 255 and DE 22 17 194 C3.

Combustion devices with electric generators are also known from US Pat. No. 6,199,519 Bl, DE 31 03 432 A1, DD R patent No. 113 593, DE 43 44 915 A1 or from the article "Advanced internal combustion engine research" by P. van Barrigan, Proceedings of the 2000 DOE Hydrogent Program Review.

From DE 102 19 549 B4 a free piston device with electric linear drive is known, which comprises at least one piston receptacle with at least one in the piston receiving linearly movable piston device, wherein the piston device comprises a rotor device and on the piston receiving a stator device is arranged. The at least one piston device is under the action of a medium, which in a Expansionsraum expands, driven, the piston stroke on the linear drive is variably adjustable so that the dead centers of movement of the piston device can be defined.

Another free-piston device with electric linear drive is described in WO 01/45977 A2.

From EP 1 398 863 A1 a free piston device is known in which a first displacement space, in which a piston is movable in the at least one piston device, on which the medium acts, and a second displacement space, in which the associated rotor device is movable, separate rooms are.

From DE 197 81 913 Tl a method for controlling the movement of a linear generator is known, wherein the linear generator is driven by an internal combustion engine with two aligned on an axis and oppositely arranged pistons. The current consumption is controlled so that a resistance force is obtained during a reciprocating cycle of the generator, which acts at least in the middle Hubbewegungsbereich the speed of movement of the generator substantially proportional to the generator. There are pressure sensors provided in the combustion chambers, wherein a control device triggers a device for igniting the mixture supplied to the combustion chambers when a predetermined pressure is reached.

A free piston device with electric linear drive is from the

DE 10 2004 062 440 B4. The free piston device has a Resilience space in which a gas is absorbed. At least one pressure sensor is provided on the resilience space with which the position and / or the speed of the piston device can be determined by measuring the pressure of the gas in the resilience space. By means of the measured pressure, a control and / or regulation of the free-piston device can thus be carried out, for example with regard to the injection of fuel into the expansion space, the ignition point of fuel in an expansion space and / or valves arranged on the expansion space.

Object of the present invention is to provide a free-piston device of the type mentioned, in which the free-piston device, in particular the movement of the at least one piston means in the at least one piston seat, in a simple manner is tunable.

This object is achieved in a generic free piston device according to the invention that the restoring force in the operation of the free piston device is controllable and / or regulated.

The gas received in the resilience space can at least partially absorb mechanical energy from the (at least one) piston device by being compressed by it. Conversely, by expansion, it can deliver energy to the at least one piston device and thereby provides, via the provisioned restoring force, for a return of the at least one piston device. Both during compression by the at least one piston device and during expansion, the gas taken up in the resilience space exerts a force on the piston device due to its own gas pressure. The force counteracts the compression by the piston device. The resilience space with the gas received therein thus has resilient properties and in particular forms a gas spring, wherein the restoring force is determined by the resilient properties of the resilience space. These are essentially determined by the way in which the gas is compressible by the piston device.

By means of the return spring arranged actuator, it is possible to control the restoring force emanating from the resilience space and / or to regulate. In this way, by means of the actuator influence can be taken as the gas in the resilience space is compressible by the piston device. As a result, the piston device can be influenced in its movement by adjusting the resilient properties of the resilience space. This makes it possible to tune the free-piston device in a simple manner. It is thereby possible to define an optimum operating point for the free-piston device in which, for example, the fuel is needed and / or the emission of pollutants is minimized. It is also conceivable to adapt the free-piston device to different fuels.

The at least one actuator can be designed in many ways, conceivable, for example, piston devices, flaps, control pins or the like.

The actuator may be self-controlled and / or regulated, for example by means of a control and / or regulating device.

According to the invention, the restoring force during operation of the free-piston device can be controlled and / or regulated. In this way, the free piston device is in Operation tunable. This makes it possible to adjust the operating point of the free-piston device without interrupting its operation. It can be provided that the control and / or regulation takes place according to a predetermined schedule. Such a flowchart may be deposited, for example, in a control and / or regulating device. It is also possible that during operation of the free-piston device one or more parameters are detected on the current operating state of the free-piston device, based on the control and / or regulation of the restoring force.

Preferably, the at least one actuator is movable. This makes it possible to perform the control and / or regulation of the restoring force in a structurally simple manner. For example, it can be provided that the at least one actuator displaces the gas absorbed in the resilience space by its movement.

It is advantageous if the at least one actuator is detectably movable, because this simplifies a need-based control and / or regulation of the restoring force. For example, the at least one actuator can be determined if no change of the restoring force should take place. This also allows a control and / or regulation in several and / or different sized steps.

Preferably, the at least one actuator is displaceable.

In particular, it can be provided that the displacement direction of the at least one actuator is parallel to the direction of movement of the at least one piston device. It is advantageous if the drive is assigned to the at least one actuator for movement. This makes it possible to precisely move and position the at least one actuator by means of the drive. The drive may be a mechanical and / or pneumatic and / or hydraulic and / or electric drive.

Preferably, the drive is controllable. This makes it possible to provide the drive with a signal from the outside and to effect a defined movement of the at least one actuator. For example, a control and / or regulating device may be provided for controlling the drive. The control and / or regulating device can control the drive, for example, according to a predetermined schedule or as a function of a signal supplied from the outside to the control and / or regulating device.

In an advantageous embodiment of the free-piston device according to the invention, at least one actuator is designed as a wall section delimiting the resilience space. This is a simple and robust way to form an actuator. The delimiting wall section may in this case be arranged on the piston receptacle, that is to say, for example, on a wall region of the piston receptacle. In particular, however, it is possible for the limiting wall section to be arranged in the interior of the at least one piston receptacle.

It is advantageous if the wall portion of an end face of the opposite at least one piston seat. As a result, the return spring force can be adjusted in a structurally simple manner. Very particularly preferred is an embodiment in which the wall portion is formed by a piston surface. A trained in this way wall section and thus also an actuator formed in this way has particularly favorable properties. The piston surface is preferably formed by a surface of a control piston, which is arranged in the piston receiving movable and in particular displaceable. The resilience space of the piston receptacle can be arranged between the piston surface and the piston device. This makes it possible to vary the gas volume in the resilience space (for example, based on a minimum gas volume or a maximum gas volume) by means of the control piston and in this way to change the resilient properties of the resilience space and thereby the restoring force. Furthermore, the direction of movement of the piston device and the direction of displacement of the control piston can run parallel to one another and, for example, parallel to an axis of symmetry of the piston receptacle.

It is favorable if at least one position sensor is provided, which cooperates with the at least one actuator. In this way, information about the position of the at least one actuator can be detected. It can be provided that the position sensor is arranged on the piston receptacle. It is also conceivable that it is located directly on the actuator. For example, the position sensor can be formed as an optical or mechanical sensor.

Preferably, the at least one position sensor is designed such that the position of the at least one actuator relative to the at least one Piston receptacle is detected. This allows in particular to control the position of the actuator relative to the piston receiving. Since the piston receptacle comprises the resilience space, the position of the actuator with respect to the resilience space is controllable in this way.

For a similar reason, namely preferably to control a movement of the actuator, it is advantageous if the at least one position sensor is designed so that a movement of the at least one actuator can be detected.

Preferably, a control and / or regulating device is provided, by means of which the free-piston device is controllable and / or controllable. For example, the control and / or regulating device can be used to control and / or regulate the injection of fuel into the expansion space, the ignition time of fuel in the expansion space and valves arranged on the expansion space for air intake or for the emission of exhaust gases.

It is advantageous if the restoring force is controllable and / or controllable by means of the at least one actuator via the control and / or regulating device. This allows, for example, the use of only one control and / or regulating device for the free-piston device.

It is particularly favorable if the restoring force can be controlled and / or regulated in accordance with a signal of a position sensor. This represents a simple one

Form of control and / or regulation of the restoring force. The position sensor, the control and / or regulating device, for example Provide information about the position and / or movement of the actuator of the free-piston device. This allows, for example, to control a drive via the control and / or regulating device in order to move the actuator or to stop an existing movement. As a result, the resilient properties of the resilience space and thus also the restoring force can be influenced, in particular controlled and / or regulated.

At least one pressure sensor is preferably arranged on the resilience space. This makes it possible to measure the pressure in the resilience space, that is to say the pressure of the gas absorbed in the return spring. For example, the pressure sensor may be arranged on an end face, in particular on an end wall, of the piston receptacle. The pressure of the gas in the resilience space is related to the restoring force applied to the piston by the gas. By means of the measuring signal of the pressure sensor, therefore, a statement about the restoring force can also be made.

It is advantageous if the at least one pressure sensor is designed such that the pressure in the resilience space can be measured in a time-resolved manner. This can also determine the change in pressure in the resilience space. In this way, the change in the restoring force can be determined.

It is advantageous if an electric linear drive is provided. As a result, electrical energy can be generated by means of the free-piston device. The electric linear drive can also be used to control and / or regulate the movement of the piston device, as described in US Pat

DE 102 19 549 B4, to which reference is expressly made. In particular, the at least one piston device then preferably comprises a rotor device, and a stator device is preferably arranged on the at least one piston receiver. The rotor device is magnetised. By movement of the piston device, an electrical voltage is induced in the stator device. Accordingly, can be acted upon by current application of the stator to the piston device.

In particular, it is favorable if the piston stroke can be variably adjusted via the linear drive such that the dead points of the movement of the at least one piston device can be defined. This is described in DE 102 19 549 B4, to which reference is expressly made.

The invention is further based on the object to improve the aforementioned method so that thus the free piston device, in particular the movement of the at least one piston device in the at least one piston seat, in operation is easily tuned.

This object is achieved in a generic method according to the invention in that the restoring force is controlled and / or regulated during operation of the free-piston device by the set value of at least one state size of the gas in the reset space is set, the actual value of at least one state variable is detected and at Deviation from the target value is at least approximately matched to the same.

The method according to the invention has the advantages already explained in connection with the free-piston device according to the invention. In particular, the restoring force is controlled and / or regulated during operation of the free-piston device. In this way, the free-piston device is tunable, in particular the movement of the (at least one) piston device in the (at least one) piston receptacle, without interrupting the operation of the free-piston device.

As already mentioned in connection with the explanation of the free piston device according to the invention, the force exerted by the gas restoring force with the pressure of the gas in relation. The gas pressure in this case represents a state variable of the gas. Further preferred state variables of the gas are, for example, the temperature, the volume and the number of particles in the gas, which is linked to the gas mass. These are in each case related to the gas pressure via the equation of state of a gas. In this way, for example, the temperature, the volume and the mass of the gas can be set in relation to the restoring force exerted by the gas on the piston device.

In the method according to the invention, the actual value of at least one state variable is detected and at least approximately matched to a predefinable setpoint value of at least one state variable. By means of the relationship between the restoring force and at least one state variable of the gas, it is possible in this way to carry out the control and / or regulation of the restoring force by controlling and / or regulating the actual value of at least one state variable.

It is particularly favorable if the pressure in the resilience space is measured in a time-resolved manner. The pressure in the resilience space corresponds to the pressure of the gas in the springback room. The pressure is a state variable whose setpoint can be specified. It can be determined by time-resolved measurement of the pressure, if the actual value of the pressure deviates from the nominal value.

It is possible that at least one actuator is moved. In particular, it can preferably be provided that a piston is displaced. By means of the movement of at least one actuator or a piston, it may be possible, for example, to displace gas in the resilience space so as to change its pressure. In this way, the restoring force can also be changed.

Preferably, the position of the at least one actuator or the piston is measured time-resolved. This provides, for example, the ability to quantitatively relate a pressure or pressure change of the gas to the position or movement of the at least one actuator or piston.

In a preferred method, the control and / or regulation of the restoring force via the adjustment of the gas mass in the resilience space. The gas mass can be increased or decreased. It is clearly linked to the number of particles in the gas, which is a state variable of the gas.

It is also favorable if the control and / or regulation of the return force is effected via the adjustment of the gas quantity in the resilience space. The amount of gas can be related for example via the gas density with the gas mass, which in turn is linked to the number of particles in the gas. It is particularly favorable if gas is supplied to the resilience space or if gas is removed from the resilience space. This makes it possible to adjust the gas mass and / or the amount of gas in the resilience space in a technically simple manner.

In particular, at least one valve is preferably actuated. By actuating the at least one valve, it is for example possible to open a gas line, so that gas is supplied to the resilience space or discharged from it. This makes it possible to adjust the gas mass and / or the gas quantity and the state variable associated with these variables, namely the particle number in the gas.

It is very particularly preferred if the pressure in the resilience space is controlled and / or regulated by means of a position of at least one actuator and / or a piston and / or by means of a position of at least one valve. In this way, the pressure is technically particularly easy to control and / or regulated.

As explained above, it is possible, for example, to move or displace at least one actuator or a piston, wherein the movement or the displacement can be detected by means of a position sensor. During the movement or displacement of gas can be displaced in the resilience space, so that thereby can change the pressure.

As mentioned, the state variables of a gas are not independent of each other, but linked together by the equation of state of the gas. For example, the pressure of a gas is proportional to the gas mass and inversely proportional to the amount of gas. This gives the possibility to express the gas mass and / or amount of gas by the gas pressure. If a valve arranged on the resilience space is actuated, then the gas mass and / or gas quantity in the resilience space and consequently also the pressure in the return space can be varied.

In the ways described, by means of the position of the valve and / or by means of the position of at least one actuator or a piston, the pressure in the resilience space can be controlled and / or regulated in a technically simple manner.

Preferably, in periodic operation of the free-piston device, the restoring force is controlled on a time scale greater than a working period and / or regulated. This reduces the technical complexity with which such a control and / or regulation is to be carried out. Preferably, the restoring force is controlled and / or regulated over at least three working periods.

The following description of preferred embodiments of the invention serves in conjunction with the drawings, the detailed explanation of the invention. Show it :

Figure 1: a schematic representation of an embodiment of a free piston device according to the invention, partially in section;

FIG. 2 shows a schematic representation of a free-piston device for carrying out the method according to the invention; and FIG. 3 shows a schematic pressure-time diagram for a compression chamber of a free-piston device according to FIG. 1 or FIG. 2.

An exemplary embodiment of a free-piston device according to the invention and in particular free-piston combustion device, which is shown in FIG. 1 and designated therein as 10, comprises a cylinder with a cylinder housing as the piston receptacle 12. The cylinder housing 14 has a first end wall 16, which has a first end side 18 of the piston receptacle 12 forms. Opposite the first end wall 16, the piston receptacle 12 is bounded by a second end wall 20, which forms a second end face 22 of the piston receptacle 12.

In an inner space 24 of the cylinder housing 14, a piston device 26 is positioned linearly displaceable. The piston device 26 is substantially rotationally symmetrical with respect to an axis 28 of the cylinder housing 14, at least with regard to its external shape. The direction of movement of the piston device 26 is parallel or coaxial with this axis 28.

The piston device 26 comprises a first piston 30 with a first piston surface 32, which faces the first end face 18. The piston device 26 further comprises a first piston 30 spaced second piston 34 having a second piston surface 36, which faces the second end face 22 of the piston seat 12. The second piston 34 essentially serves to support the first piston 30. The two

Pistons 30, 34 are connected via a holding structure 38 fixed and in particular rigidly connected to each other. As a result, a piston pair is formed on the piston device 26. The holding structure 38 includes, for example, a piston rod 40.

Between the first end face 18 of the piston receptacle 12 and the first piston 30, an expansion chamber with an expansion space 42 is formed. The expansion chamber is in particular a combustion chamber and the expansion space is a combustion chamber.

(In principle, it is also possible to expand in the expansion space a heat transfer medium, such as steam, which was generated outside the expansion space or to which energy was supplied outside the expansion space.) An example of a corresponding free piston device is disclosed in DE 102 19 549 B4 which is expressly referred to.)

In the expansion space 42, a medium is expandable to drive the piston device 26 in its linear movement. In the example of a combustion chamber, the expanding medium is fuel gases; These are generated in particular by a combustion process in the expansion space 42.

The dimensions of the expansion space 42 are determined by the piston stroke of the piston device 26, that is, the volume and the (inner) surface of the expansion space 42 are determined by the position of the first piston 30.

The expansion space 42 are one or more in particular electrically controllable inlet valves 44 and one or more in particular electrically controllable exhaust valves 46 assigned. The control of the (at least one) inlet valve 44 and the (at least one) outlet valve 46 via a control and / or regulating device 48. About the inlet valve 44 and the outlet valve 46, the intake of air and the discharge of particular combustion products can be targeted in time Taxes.

For example, a suction line 50 leading into the expansion space 42 is connected to a loader 52. The suction line 50 can be opened or closed by means of the (at least one) inlet valve 44.

Via the outlet valve 46, an exhaust pipe 54 leads to the loader 52. The loader 52 itself has a supply 56, in particular for intake air and a discharge 58 for exhaust gases.

The supercharger 52 may, for example, be a pressure wave supercharger in which the energy of the exhaust gas flow from the expansion space 42 is used to compress the charge air (intake air). With such a pressure wave loader, pressure waves and suction waves of the pulsating exhaust gases suck in fresh air and compress it. This compression takes place in direct contact with the exhaust gases.

During operation of the free-piston device 10, for example, a constant oscillating displacement movement of the piston device 26 takes place. This makes it possible to achieve a constant oscillation of the discharged exhaust gases, so that the gas exchange can be controlled and / or regulated via the supercharger 52. The advantage of a pressure wave loader is that it has only a small amount of energy. The total system of the supercharger 52 of the piston device 26 with its associated expansion space 42 can be due to the constant period for the oscillating movement of the piston device 26 interpret exactly to an optimal operating point, in turn, the charger 52 can be designed.

At least one pressure sensor 60 is arranged on the expansion space 42 in one embodiment. It is preferably a piezoelectric sensor. For example, the pressure sensor 60 is arranged on the first wall 16, which may have a recess in which the pressure sensor 60 is seated. The pressure sensor 60 is aligned with the first piston 30. In particular, an active sensor surface of the first piston surface 32 to.

The pressure in the expansion space 42 can be detected via the pressure sensor 60. In particular, it can be provided that the pressure in the expansion space 42 can be determined in a time-resolved manner via the pressure sensor 60.

In addition, a temperature sensor 62 can be provided on the expansion space 42, with which the temperature in the expansion space 42, preferably also time-resolved, can be determined.

The pressure sensor 60 and the temperature sensor 62 may be connected to the control and / or regulating device 48 via signal lines. As a result, they can transmit their signals to the control and / or regulating device 48. At the expansion space 42, an injection device 64 is further arranged. Fuel can be coupled into the expansion space 42 via this injection device 64. In this case, the injection device 64 can be controlled and / or regulated by the control and / or regulating device 48, for example.

Furthermore, an ignition device 66 is arranged on the expansion space 42, with which a fuel located in the expansion space 42 can be ignited. The ignition device 66 can also be controlled and / or regulated via the control and / or regulating device.

The free-piston device 10 comprises an electric linear drive, indicated as a whole by 68, which has a rotor device 70. The rotor device 70 is arranged on the piston device 26. It is moved with the piston device 26.

The electric linear drive 68 further comprises a stator device 72, which is arranged on the piston receptacle 12 outside of the cylinder housing 14. About them can induce voltages to generate electrical energy or it can be the piston device 26 influence accordingly.

The rotor device 70 comprises, for example, magnetic elements 74 and flux-conducting elements 76, which are arranged alternately on the holding structure 38 between the pistons 30 and 34. The holding structure 38 comprises, for example, a cylindrical carrier 78, on which the magnetic elements 74 and the flux-conducting elements 76 are seated. The cylindrical support 78 is held on the piston rod 40 and in particular integrally connected thereto. The connection takes place via radially extending, spaced strips or disks 80. The radial direction is perpendicular to the axial direction 28. The strips or disks 80 are spaced apart in the axial direction 28. As a result, a gap 82 is formed between adjacent strips or disks 80; The support structure 38 is thereby not made of a solid material, so that the mass of the piston device 26 is reduced compared to a production of a solid material.

The magnetic elements 74 may be permanent magnet elements, which are in particular disk-shaped rotationally symmetrical about the axis 28. In principle, it may also be electromagnetic elements which accordingly comprise, in particular, turns arranged concentrically about the axis 28. In this case, a corresponding device must be provided in order to be able to transmit energy to these electromagnetic elements. This can be done, for example, inductively or via slip rings.

The flux guides 76 are also disc-shaped and made of a high magnetic permeability material. For example, iron is used or magnetically permeable powder composite materials are used. The magnetic elements 74, in particular when it comes to permanent magnet elements, and the flux guide elements 76 are formed so that they have a central opening with which they can be pushed onto the carrier 78 during the production of the piston device 26.

The magnetic elements 74 are formed and in particular magnetized so that in a flux guide 76, the field lines of the adjacent magnetic elements 74 are concentrated, thus increasing the magnetic power seal of the system. In particular, the magnetic elements 74 are arranged in parallel so that equal poles of adjacent magnetic elements 74 assign each other.

It can also be provided that an outer surface of the rotor device 70 is designed so that it is designed tooth-shaped in a cross-section of the axis 28 of a cylinder wall facing inner side. As a result of such a tooth structure, the rotor device 70 has changing magnetic conductivities, via which a drive for the piston device 26 can be generated.

The stator device 72 comprises main ring windings 84, which are arranged outside the cylinder housing 14 surrounding this. In these main ring windings 84, a voltage is induced during relative movement of the magnetized rotor device 70, with electrical energy being able to be coupled out. It is thereby provided a power generating device, which is based on the principle of free piston guide (linear movement of the piston device 26). The stroke of the piston device 26 can be controlled and / or regulated via the control and / or regulating device 48. In particular, it is possible to carry out such a control / regulation that the location of the piston device 26 is fixed at any time. As a result, the point of reversal of the piston movement of the first piston 30 can be adjusted as required, in order in turn to be able to set the dimensions of the expansion space 42. By a corresponding control / regulation of the linear drive 68 so that the piston stroke can be adjusted depending on the load condition; Further, the compression can be adjusted, and it can adjust the speed of the piston device 26. This makes it possible to optimally set the expansion space 42 (in terms of volume and surface as well as volume change and surface change), depending on the load condition. In particular, this allows the volume of the expansion space 42 and the respective surface of the expansion space 42 to be adapted to the application.

Through the local-temporal adjustment of the piston stroke (position, compression, speed) can also be carried out an adjustment to the fuel used, d. H. a piston stroke and compression can be set, depending on whether, for example, a fuel such as diesel or vegetable oil is used with auto-ignition or a fuel such as gasoline, natural gas or hydrogen is used as fuel with ignition by an igniter.

By a specific specification of currents in the stator device 72 and, if appropriate, in the rotor device 70, ie by control and / or Regulating these currents, the piston device 26 can be influenced in its linear displaceability in order to be able to precisely determine the location of the reversal points of the piston movement of the piston device 26 for the expansion space 42.

As a result, for example, at full load, in which a large intake air is required for the expansion space 42, if this combustion is to take place, set a correspondingly large piston stroke, while at part load operation with reduced intake volume, a reduced stroke is adjustable.

It can also be provided that one or more secondary windings are arranged around the cylinder housing 14. These are electrically isolated from the main ring windings 84 of the stator device 72. The sub-windings are, for example, arranged around the main ring windings 84, that is to say they surround them. They can also be arranged next to main ring windings 84 (in particular in the axial extension of a ring winding axis of the main ring windings 84).

About such secondary windings, another power can be decoupled, for example, to provide a 12 V / 24 V or 36 V / 42 V electrical system of a motor vehicle with power. The number of turns of the secondary windings is adjusted accordingly. Such secondary windings are preferably followed by a rectifier in order to be able to generate a rectified current accordingly. It can also be provided that a cooling device 88 comprising cooling channels 86 is arranged around the stator device 72 in order to cool the active components of the free-piston device 10 (with linear drive 68); In particular, the piston device 26, the piston receptacle 12 and the main ring windings 84 belong to these active components.

It can also be provided that heat is coupled out of the corresponding cooling device 88 in order to use it in thermal engineering applications, for example for a vehicle heating system or a block heating plant.

Between the second piston 34 of the piston device 26 and the second end face 22 of the piston seat 12, a compression space in the form of a resilience space 90 is formed. The resilience space 90 does not occupy the entire volume of the cylinder housing 14 between the second piston surface 36 and the second end wall 20. The resilience space 90 is limited by the second piston surface 36, the walls of the cylinder housing 14 along wall portions 92 and 94 and a wall portion 96 which is formed by a piston surface 98 of a control piston 100.

The piston surface 98 in this case comprises the entire wall portion 96 of the resilience space 90. It forms an actuator of the free-piston device 10, whose operation will be explained in more detail below.

The piston surface 98 is positioned between the second piston surface 36 and the second end wall 20 of the piston receptacle 12. It lies opposite the second end face 22 and is in particular parallel to the second end wall 20 oriented. In this way, the piston surface 98 limits the resilience space 90 at the end, based on their orientation within the cylinder housing 14.

The resilience space 90 is formed in the piston receptacle 12 between the second piston 34 of the piston device 26 and the control piston 100, and limited in the longitudinal direction of the piston seat 12 of the second piston surface 36 of the second piston 34 and the piston surface 98 of the control piston 100.

In the resilience space 90 a compressible fluid is received, in particular a gas such as air.

The gas in the resilience space 90 can at least partially "elastically" absorb mechanical energy that was not coupled by the linear drive 68 during an expansion stroke of the piston device 26. This is done by compression of the gas by the piston device 26.

Conversely, the gas in the resilience space 90 can expand and in this way drive the piston 26 back. The stored energy may thus be used for compressing the fuel-air mixture in a two-stroke operation or for discharging the exhaust gases in a four-stroke operation, when combustion takes place in the expansion space 42 to produce the expanding medium.

The gas in the resilience space 90 thus forms a gas spring, which can absorb mechanical energy of the piston device 26 with high reversibility, and which can deliver energy to the piston device 26 by expansion. At the return spring space 90, a pressure sensor 102 is arranged, which is arranged on the piston surface 98 of the control piston 100. For example, the piston surface 98 has for this purpose a recess in which the pressure sensor 102 is arranged.

The pressure sensor 102 assigns the second piston surface 36 of the second piston 34, in particular with an active sensor surface.

In a variant of this exemplary embodiment, the pressure sensor can be arranged, for example, on one of the wall regions 92 or 94 between the second piston surface 36 and the piston surface 38.

Via the pressure sensor 102, the pressure in the resilience space 90 can be measured. In particular, the pressure can be measured by the pressure sensor 102 in a time-resolved manner. The pressure sensor 102 is preferably a piezoelectric sensor.

In addition, a temperature sensor 104 can be arranged on the resilience space 90, which, for example, can be arranged in a recess of the piston surface 98 of the control piston 100, similar to the pressure sensor 102.

By means of the temperature sensor 104, the temperature in the resilience space 90 can be measured. The pressure sensor 102 and the temperature sensor 104 can transmit their measuring signals to the control and / or regulating device 48 via signal lines.

The control piston 100 is movably mounted in the piston receptacle 12, in particular it is mounted in this linearly displaceable. In this way, the piston surface 98 in the cylinder housing 14 by means of the control piston 100 is movable and in particular linearly displaceable. The displacement direction is parallel or coaxial with the axis 28 and parallel to the direction of displacement of the piston device 26.

This gives the possibility to change the gas volume in the resilience space 90 for adjusting the restoring force of the gas spring; the minimum and the maximum gas volume can be changed, and in particular defined, adjusted. The gas volume is minimal when the piston assembly 26 is at its top dead center TDC with respect to the piston surface 98, and it is maximum when the piston assembly 26 is at its bottom dead center BDC with respect to the piston surface 98.

The control piston 100 is associated with a drive device 108. The control piston 100 is for this purpose via a holding device 106 with the drive means 108 in connection. The holding device 106 includes, for example, a piston rod 109, which can pass through the second end wall 20 of the piston receptacle 12. The holding device 106 may be designed to be rigid, as a result of which the control piston 100 can be moved in the piston receptacle 12 by means of the drive device 108 and, in particular, can be displaced linearly. The drive device 108 includes, for example, a hydraulic system for moving the control piston 100. Also conceivable, for example, are a pneumatic drive and / or an electric drive.

The control and / or regulating device 48 is connected to the drive device 108 via a control line so that it can be activated and, in particular, controlled by the control and / or regulating device 48. In this way, for example, the position of the control piston 100 by the control and / or regulating device 48 can be predetermined.

The free-piston device 10 has a position sensor 110 with which the position of the holding device 106 relative to the piston receptacle 12 can be detected. In this way, the position and a movement of the control piston 100 and thus also the piston surface 98 can be detected by the position sensor 110.

The position sensor 110 is arranged, for example, near the second end wall 20 of the cylinder housing 14, and an active sensor surface may be directed in the direction of the holding device 106. The position sensor 110 of the control and / or regulating device 48 can provide its measuring signal via a signal line.

Also conceivable is an arrangement of the position sensor 110, for example on the piston surface 98, wherein an active sensor surface can assign the second piston surface 36. In this case, the position sensor can be realized, for example, as an optical sensor. Also conceivable is a mechanically operating position sensor, which is mechanically coupled to the holding device 106, for example. The position sensor 110 may also be integrated into the drive device 108.

The resilience space 90 is closed gas-tight. The second piston 34 of the piston device 26 and the control piston 100 for this purpose include seals 112, for example in the form of polymer seals. These ensure a high tightness of the resilience space 90 even at high pressures of the gas inside.

On the control piston 100, in one embodiment, a gas line 114 is arranged, which may be guided, for example, in a bore of the control piston 100. The gas line 114 has an opening 116 which is arranged on the piston surface 98.

It can be provided that the gas line 114 can be opened and closed defined by means of a valve, not shown in the drawing. The resilience space 90 can then, for example, be in fluid-effective connection with a gas accumulator (not shown in the drawing).

The gas line 114 may be formed as a filling line for the resilience space 90. This gives the possibility to keep the amount of gas in the resilience space 90 constant.

Moreover, it is thereby possible to fill the resilience space 90 with gas for the first time during assembly of the free-piston device 10. Further examples of free-piston devices are disclosed in DE 102 19 549 B4 and in EP 1 398 863 A1. Reference is expressly made to these documents.

The free-piston device 10 according to the invention functions as follows:

Via the linear drive 68, certain reversal points (top dead center OT and bottom dead center UT) of the piston device 26 are adjusted by appropriate application of current in order to define the volume and the surface of the expansion space 42 and in particular of a combustion chamber. Furthermore, the speed of the piston device 26 is determined and overall the compression. This setting is made depending on the load (partial load or full load), fuel (gasoline, natural gas, hydrogen, diesel, vegetable oil, etc.) and any other external parameters.

It can be provided that for the start of the free-piston device 10, an electric preheating takes place and also the cooling water of the cooling device 88 is preheated. This preheating can take place via the linear drive 68 by using corresponding windings, for example the main ring windings 84, as heating elements. But it can also be provided own heating coils.

By the pair of pistons with the piston 30 and 34, a support of the piston device 26 is made, that is, the piston 30, 34 can be substantially linearly in the piston receiving 12 lead tilt-free. The pistons 30, 34 also serve to seal the expansion space with respect to the resilience space 90. By the linear drive 68, the reversal points of the movement of the piston device 26 locally and temporally exactly predeterminable. As a result, no throttle valve is necessary in part-load operation for an air supply, which is otherwise responsible for throttle losses.

By the inlet valve 44 and the outlet valve 46 for the expansion space 42, the suction of air and the discharge of the exhaust gases can be controlled specifically. As a result, the efficiency of the overall system and the quality of the exhaust gas can be improved; by precise adjustment of the timing over time and the duration in terms of gas exchange (flow through the inlet valve 44 and the exhaust valve 46) can take place a precise adjustment between the individual time-critical operations. Since the speed of the piston device 26 can also be controlled or regulated, even during the expansion process, the formation of exhaust gases can be influenced.

In particular, the inlet valve 44 is arranged and designed such that sucked air and resulting gas flows are guided along inner cylinder walls so as to obtain an optimized gas exchange rinsing process.

The suction and compression of air and the discharge of exhaust gases is preferably carried out via the loader 52.

It can be provided that the ignition of the medium in the expansion space 42 by the control and regulating device 48 in accordance with the signal one of the pressure sensors 60 or 102 can be controlled and / or regulated.

In particular, the valves 44, 46, the injection device 64 and / or the ignition device 66 can be controlled and regulated. This control and / or regulation can be carried out such that a substantially stoichiometric combustion in the expansion space 42 is possible. Such a control and / or regulation is disclosed for example in DE 10 2004 062 440 B4 of the same Applicant, to which reference is expressly made.

During the movement of the piston device 26, a voltage is induced in the latter due to the relative movement between the rotor device 70 and the stator device 72, so that electrical energy is generated: mechanical energy is partially converted to electrical energy, again the mechanical energy from a partial conversion chemical energy due to combustion.

Energy can be absorbed by the resilience space 90 that is not coupled out by the linear drive 68 during the combustion cycle, when combustion takes place in the expansion space 42. According to the invention makes it possible to adjust the properties of the resilience space 90 so that an optimal operating point is achieved even with temporal variations. This will be explained in detail below.

The stator device 72 is cooled via the cooling device 88. The cooling device 88 can also cool other parts of the piston receptacle 12 and, for example, the piston device 26. The pistons 30, 34 are lubricated for example via a simple splined lubrication, so that no oil pump is required. The pistons 30, 34 then move in an oil bath which is agitated by the agitation to ensure a sufficient lubrication oil supply.

The pistons 30, 34 can be produced with a minimized side surface facing the cylinder housing 14, that is to say piston covers can be made short, since the piston pair with the first piston 30 and the second piston 34 ensures a mutual supporting action. As a result, friction losses during the movement of the piston device 26 can be minimized.

In turn, this makes it possible to produce the pistons 30, 34 also from non-metallic materials such as ceramic materials or from graphite or, for example, glass fiber-reinforced carbon materials. Such pistons can do without lubrication.

The rotor device 70 with alternatingly arranged magnetic elements 74 and flux-conducting elements 76 makes it possible to achieve a high magnetic power density of the system. In particular, can be high

Achieve power densities when the pole pitch in the rotor device 70 and the stator device 72 is different.

As already mentioned, the gas in the resilience space 90 can absorb mechanical energy from the piston device 26 by being compressed by the piston device 26. In this case acts between the piston means 26, mediated by the second piston 34, and the gas in the resilience space 90, a force by means of which the gas is compressible by the piston means 26. Conversely, the gas in the resilience space 90 can deliver energy to the piston device 26 by expanding it and driving the piston device 26 in the direction of the end face 18 of the piston receptacle 12. Also in this case, a force acts between the gas and the second piston 34 of the piston device 26.

The gas in the resilience space 90 exerts at any time as a result of its gas pressure p a compression by the piston means 26 counteracting return force F on the piston device 26 from.

The restoring force F exerted by the gas is for example proportional to the pressure p of the gas. The proportionality constant is the area A, on which the restoring force F acts. The restoring force F can therefore be represented as a product p • A. This relationship between the return force F and the gas pressure p makes it possible to express the force exerted by the gas on the second piston 34 restoring force F by means of the gas pressure p. The gas pressure p corresponds to the internal pressure of the resilience space 90.

The free-piston device 10 has, as already mentioned, the actuator formed as a piston surface 98, with which the restoring force F can be controlled and / or regulated. The piston surface 98 in this case forms a wall portion 96 bounding the resilience space.

According to the above, the restoring force F can be controlled and / or regulated, for example, by the fact that the gas pressure p in the resilience space 90 can be controlled and / or regulated. The gas pressure p can be varied by adjusting the gas volume by moving and / or positioning the control piston 100, and thus in particular the piston surface 98 in the piston receptacle 12, and in particular adjusting the minimum and maximum gas volumes.

The gas pressure p can be measured by means of the pressure sensor 102 and provided to the control and / or regulating device 48. For example, the oscillation frequency of the piston device 26 during operation of the free piston device 10 in the order of 50 Hz. When using a piezoelectric sensor for the pressure sensor 102 can reach the necessary response time to measure the gas pressure p with sufficient accuracy and time resolved.

The control piston 100 and the actuator formed as a piston surface 98 can be moved by means of the drive means 108 and in particular move. In this way, the gas pressure p in the resilience space 90 is variable.

It can be provided that the control and / or regulating device 48 of the drive device 108 provides a control signal dependent on the gas pressure p. The drive device 108 may then perform the movement of the control piston 100 in response to the provided signal. In this way, the movement of the control piston is controllable and thus the gas pressure p in the resilience space 90 controllable. By means of the position sensor 110, the position of the holding device 106 and in this way the position and / or the movement of the piston surface 98, with respect to the piston receptacle 12 can be detected. The measurement signal of the position sensor 110 may be provided to the control and / or regulating device 48. This makes it possible to construct a control loop in which the gas pressure p is regulated as a function of the position and / or movement of the control piston 100.

Because the gas pressure p of the gas in the return spring space 90 can be controlled and / or regulated, the restoring force F exerted by the gas on the piston device 26 can thus also be controlled and / or regulated.

In particular, it is possible with the free-piston device 10 according to the invention to carry out the control and / or regulation of the restoring force F during operation of the free-piston device 10.

A schematic pressure-time diagram for the gas pressure p in the resilience space 90 is shown in FIG. 3. The gas pressure p in the resilience space 90 is shown schematically by the curve 118. The gas pressure p oscillates according to the oscillating movement of the _{piston device} 26 between a maximum pressure p _ma _einem and a minimum pressure p _min with a period T. The maximum pressure p _max is reached at top dead center OT of the piston device 26 with respect to the piston surface 98, and the minimum pressure p _min is reached at the bottom dead center UT of the piston _device 26 with respect to the piston surface 98. For example, it is possible to move the control piston and the piston surface 98 only within a time window ZF, which is arranged in time in the region of the bottom dead center UT. In this case, the piston device 26 is farthest from the piston surface 98, and the control piston 100 is movable with the least amount of force.

The control and / or regulation of the restoring force F exerted by the gas in the resilience space 90 on the piston device 26 makes it possible to tune the movement of the piston device 26. This makes it possible to set an optimum operating point of the free-piston device 10. At this optimum operating point, for example, the fuel may be required and / or the emission of pollutants may be minimized.

The regulation of the gas pressure p advantageously takes place over several, preferably at least three, periods T of the oscillation movement of the piston device 26. This reduces the technical requirements for the components of the free-piston device 10.

In a variant of this embodiment can be provided that does not move an entire, the resilience space 90 bounding wall. It is conceivable, for example, that moves only a certain wall portion of the resilience space 90 bounding wall to displace the gas in the resilience space 90.

By means of the free-piston device 10, it is possible to carry out a method according to the invention, in which the restoring force F is controlled and / or regulated during operation of the free-piston device 10, wherein the setpoint value at least one state variable of the gas in the resilience space 90 can be predetermined, the actual value of the at least one state variable is detected and, if it deviates from the desired value, it is at least approximated to the same.

The implementation of the method has already been explained above in the description of the operation of the free-piston device 10.

In this case, the gas pressure p in the resilience space 90 is used as the state variable of the gas, the desired value of which can be predetermined so that a specific operating point of the free-piston device 10 can be achieved. If the actual value of the gas pressure p deviates from the nominal value, then the control and / or regulating device 48 can activate the drive device 108, as a result of which the gas pressure p in the resilience space 90 can be controlled and / or regulated, as described above.

The nominal value of the gas pressure p may in this case be defined, for example, as a mean pressure during operation, or as a pressure at fixed times of operation of the free-piston device 10, for example the pressure p _max at the top dead center TDC or the pressure p _mm in the bottom Dead center UT (Figure 3).

Another free piston device for carrying out the method according to the invention is shown in FIG. 2 as a whole with the reference numeral 150. Basically, the same components as in the embodiment 10 are denoted by the same reference numerals. In the free-piston device 150, the piston device 26 is arranged displaceably in a piston receptacle 152. The piston housing 152 is formed by a cylinder housing 154. The cylinder housing 154 has a first end wall 156 which forms a first end face 158 of the piston housing 152. The first end wall 156 is opposed by a second end wall 160, which forms a second end face 162 of the piston receptacle 152.

The piston device 26 is positioned in an interior 164 of the cylinder housing 154.

Between the piston surface 36 of the piston 34 and the end wall 160, a compression space in the form of a resilience space 166 is formed. In the resilience space 166 is a compressible fluid, in particular a gas such as air, added.

The gas can be compressed by the movement of the piston device 26 and thereby at least partially absorb energy "elastically", which was not decoupled from the linear drive 68 during an expansion stroke. Accordingly, the gas in the resilience space 166 can release the energy, for example, by expanding and driving the piston device 26 in the direction of the end wall 156.

At the springback space 166, the pressure sensor 102 is arranged. For example, it is arranged on the second end wall 160. The second end wall 160 may have a recess for this purpose, in which the pressure sensor 102 is arranged. In particular, an active sensor surfaces of the piston surface 36 of the piston 34 may be facing. By means of the pressure sensor 102, the pressure in the resilience space 166 can be measured and, in particular, measured in a time-resolved manner.

It may further be provided that the temperature sensor 104 is arranged on the resilience space 166. By means of the temperature sensor 104, the temperature in the resilience space 166 can be detected.

The second end wall 160 has at least one opening, on which at least one valve is arranged. In particular, the end wall 160 has a first opening 168, which is associated with an inlet valve 170, and a second opening 172, which is associated with an outlet valve 174.

The first opening 168 of the resilience space 166 can be opened and closed by means of the inlet valve 170, and the second opening 172 of the resilience space 166 can accordingly be opened and closed by means of the outlet valve 174.

The intake valve 170 and the exhaust valve 174 may be controlled in time by the control and / or regulating device 48.

The inlet valve 170 and the outlet valve 174 may be magnetically and / or electrically and / or mechanically actuated. In particular, it can be valves with a short switching time, preferably up to a few milliseconds. Valves with a switching time of a few milliseconds are produced, for example, by the company "Lotus Engineering". A gas line, in particular a feed line 176, leads via the inlet valve 170 to a gas reservoir, for example a gas reservoir 178. With the inlet valve 170 open, a fluid-effective connection between the springback space 166 and the gas reservoir 178 can thereby be provided by the feed line 176.

In the supply line 176, a gas quantity sensor in the form of a volume flow sensor 180 is arranged. By means of the volume flow sensor 180, it is possible to detect a gas flowing through the supply line 176 amount of gas. The volume flow sensor 180 may provide its measurement signal to the control and / or regulating device 48 via a signal line.

It can be provided that the gas pressure in the gas reservoir 178 is greater than the gas pressure p in the resilience space 166. In this way, by opening the inlet valve 170, a certain amount of gas can flow from the gas reservoir 178 through the supply line 176 into the resilience space 166. This gas flow results from the pressure gradient between the gas pressure p in the return spring chamber 166 and the pressure in the gas reservoir 178. This quantity can be detected by means of the volumetric flow sensor 180 and communicated to the control and / or regulating device 48.

Via the outlet valve 174, a gas line, in particular a discharge line 182, leads from the resilience space 166 to a gas reservoir, for example a gas reservoir 184. With the outlet valve 174 open, a fluid-effective connection between the resilience space 166 and the gas reservoir 184 through the discharge line 182 can thereby result. It can be provided that a volume flow sensor 186 is arranged in the discharge line 182, which can detect a gas flowing through the discharge line 182 amount of gas. In particular, the volume flow sensor 186 of the control and / or regulating device 48 can provide its measuring signal via a signal line.

It is possible that the gas pressure in the gas reservoir 184 is less than the pressure in the springback 166. When opening the exhaust valve 174 flows due to the pressure gradient a certain amount of gas from the resilience space 166 through the discharge line 182 to the gas storage 184. The amount of gas can by means of the volume flow sensor 186 are detected and communicated to the control and / or regulating device 84.

It is thus possible, by opening the inlet valve 170 or the outlet valve 174, to remove gas from the resilience space 166 or to supply it to the resilience space 166. This makes it possible to adjust the gas mass and / or the amount of gas in the resilience space 166 by increasing or decreasing the gas mass and / or amount of gas.

For example, more gas can be supplied to the resilience space 166, so that the gas mass and the gas quantity in the resilience space 166 increase. Conversely, gas can be removed from the resilience space 166 so that the gas mass and the gas quantity in the resilience space 166 are reduced.

A variant of the free-piston device 150 has only one valve arranged on the return spring chamber 166, after the opening of which gas can be supplied to the return spring chamber 166 or removed therefrom. The method according to the invention can be carried out with the free-piston device 150 as follows:

As already explained, the restoring force F exerted by the gas in the resilience space 166 on the piston device 26 is proportional to the gas pressure p in the springback space 166. About this relationship, the restoring force F can be expressed by means of the gas pressure p.

In particular, it is possible to control the force exerted by the gas on the piston device 26 restoring force and / or to regulate by the gas pressure p in the spring back space 166 controlled and / or regulated.

The pressure p in the resilience space 166 here is a state variable of the gas. Its desired value can be predetermined and can be given for example by a desired operating point of the free-piston device 150. The set point may be a medium pressure, but it is also possible that it is a defined at fixed times during operation of the free-piston device 150 pressure.

The actual value of the pressure can be measured by means of the pressure sensor 102. The inventive method provides that the actual value is at least approximately equalized to the desired value.

According to the state equation of an ideal gas, the gas pressure p is proportional to the gas mass m of the gas. This makes it possible to adjust the gas pressure p (for example relative to a fixed position of the piston device 26) in the springback space 166 by means of the gas mass in the springback space 166. For example, the gas mass m in the resilience space 166 can be increased by opening the inlet valve 170 by flowing gas from the gas reservoir 178 through the supply line 176 into the resilience space 166. This increases the gas pressure in the resilience space 166.

The gas mass m in the resilience space 166 can be reduced by opening the exhaust valve 174; Gas flows from the resilience space 166 through the discharge line 182 into the gas reservoir 184. As a result, the gas pressure p in the resilience space 166 decreases.

It may be provided that the inlet valve 170 and / or the outlet valve 174 are opened and / or closed in a defined manner by the control and / or regulating device 48 in order to increase and / or reduce the gas mass m in the return spring chamber 166.

The gas pressure p can be measured in a time-resolved manner by means of the pressure sensor 102, wherein the measurement signal of the control and / or regulating device 48 can be provided. The control and / or regulating device 48 may open and / or close the inlet valve 170 and / or the outlet valve 174 as a function of the measuring signal of the pressure sensor 102. In this way, the gas mass in the resilience space 166 can be increased or decreased so long until the actual value of the gas pressure p in the resilience space 166 is at least approximately equalized to the desired value.

In this way it is possible to control and / or regulate the gas pressure p by means of the position of the inlet valve 170 and / or the outlet valve 174 via the control and / or regulating device 48. It can also be provided that the control and / or regulating device 48 evaluates which gas mass m is supplied to the resilience space 166 or removed from it when the inlet valve 170 or the outlet valve 174 is opened:

The gas mass m is, for example, proportional to the gas quantity, the proportionality factor being the gas density. The added or removed gas quantity can be detected by means of the volume flow sensors 180 or 186 and the corresponding measured values can be made available to the control and / or regulating device 48. This can then calculate the corresponding gas masses.

As a result of the relationship between the gas pressure p in the return spring chamber 166 and the force exerted by the gas on the piston means 26 and in particular the second piston 34 return force F is thereby also controlled and / or regulated. The control and / or regulation of the restoring force takes place during operation of the free-piston device 150.

In particular, it may be provided that the adjustment and / or control and / or regulation takes place only at certain times, for example within a time window ZF, which is arranged in terms of time at the bottom dead center UT of the piston device 26 relative to the second end wall 160 (FIG ). In this case, the gas pressure p in the _{resilience space} 166 is close to its minimum p _min . This makes it easier for the resilience space 166 to supply a certain amount of gas or to remove a certain amount of gas from it. By controlling and / or controlling the return force F exerted by the gas in the return spring chamber 166 on the piston device 26 and in particular the second piston 34, it is possible to change the state of movement of the piston device 26 defined. This allows an improved tuning of the free-piston device 150, in particular an adjustment of an optimal operating point of the same.

Claims

1. free piston device, comprising at least one piston receptacle (12) in which at least one piston device (26) is arranged linearly movable, wherein the at least one piston device (26) under the action of a medium which expands in an expansion space (42) is drivable , and wherein the at least one piston receptacle (12) has a resilience space (90) in which a compressible gas for applying a restoring force to the at least one piston means (26) is received, and at least one actuator (98) for controlling and / or Control of the restoring force, which is arranged on the resilience space (90), characterized in that the restoring force in the operation of the free-piston device (10) is controllable and / or regulated.

2. Free-piston device according to claim 1, characterized in that the at least one actuator (98) is movable.

3. free piston device according to claim 2, characterized in that the at least one actuator (98) is detectably movable.

4. free piston device according to claim 2 or 3, characterized in that the at least one actuator (98) is displaceable.

5. Free-piston device according to claim 4, characterized in that the displacement direction of the at least one actuator (98) is parallel to the direction of movement of the at least one piston device (26).

6. free piston device according to one of claims 2 to 5, characterized in that the at least one actuator (98) for movement, a drive (108) is associated.

7. free piston device according to claim 6, characterized in that the drive (108) is controllable.

8. free piston device according to one of the preceding claims, characterized in that at least one actuator (98) as a spring back space (90) limiting wall portion (96) is formed.

9. free piston device according to claim 8, characterized in that the wall portion (96) of an end face (22) of the at least one piston receptacle (12) opposite.

10. free piston device according to claim 8 or 9, characterized in that the wall portion (96) by a piston surface (98) is formed.

11. Free piston device according to one of the preceding claims, characterized in that at least one position sensor (110) is provided, which cooperates with the at least one actuator (98).

12. A free piston device according to claim 11, characterized in that the at least one position sensor (110) is formed so that the position of the at least one actuator (98) relative to the at least one piston receptacle (12) can be detected.

13. Free-piston device according to claim 11 or 12, characterized in that the at least one position sensor (110) is formed so that a movement of the at least one actuating member (98) can be detected.

14. Free-piston device according to one of the preceding claims, characterized in that a control and / or regulating device (48) is provided, by means of which the free-piston device (10) is controllable and / or controllable.

15. Free-piston device according to claim 14, characterized in that via the control and / or regulating device (48), the restoring force by means of the at least one actuator (98) is controllable and / or regulated.

16, free piston device according to claim 15, characterized in that the restoring force in accordance with a signal of a position sensor (110) is controllable and / or regulated.

17. Free piston device according to one of the preceding claims, characterized in that at least one pressure sensor (102) on the resilience space (90) is arranged.

18, free piston device according to claim 17, characterized in that the at least one pressure sensor (102) is formed so that so that the pressure in the resilience space (90) is time-resolved measurable.

19. Free-piston device according to one of the preceding claims, characterized in that an electric linear drive (68) is provided.

20. Free-piston device according to claim 19, characterized in that the at least one piston device (26) comprises a rotor device (70) and that a stator device (72) is arranged on the at least one piston receptacle (12).

21. Free-piston device according to claim 19 or 20, characterized in that the piston stroke via the linear drive (68) is variably adjustable such that the dead centers (TDC, UT) of the movement of the at least one piston device (26) are definable.

22. A method for operating a free-piston device, wherein at least one piston device, which is guided linearly movable in at least one piston receiving, under the action of a medium which expands in an expansion space, is driven, and in which the at least one piston device by a compressible Gas, which is accommodated in a resilience space of the at least one piston receptacle, a restoring force is exerted, characterized in that the restoring force is controlled and / or regulated during operation of the free-piston device by the setpoint value of at least one state size of the gas in the resilience space is predetermined the actual value of the at least one state variable is detected and, if it deviates from the desired value, it is at least approximately matched to it.

23. The method according to claim 22, characterized in that the pressure in the resilience space is measured time-resolved.

24. The method according to claim 22 or 23, characterized in that at least one actuator is moved.

25. The method according to claim 24, characterized in that a piston is moved.

26. The method according to claim 24 or 25, characterized in that the position of the at least one actuator or the piston is measured time-resolved.

27. The method according to any one of claims 22 to 26, characterized in that the control and / or regulation of the restoring force via the adjustment of the gas mass in the resilience space.

28. The method according to any one of claims 22 to 27, characterized in that the control and / or regulation of the restoring force via the adjustment of the amount of gas in the resilience space.

29. The method of claim 27 or 28, characterized in that gas is supplied to the resilience space or that gas is removed from the resilience space.

30. The method according to any one of claims 27 to 29, characterized in that at least one valve is actuated.

31. The method according to any one of claims 22 to 30, characterized in that the pressure in the resilience space by means of a position of at least one actuator or a piston and / or controlled by means of a position of at least one valve and / or regulated.

32. The method according to any one of claims 22 to 31, characterized in that during periodic operation of the free-piston device, the restoring force on a time scale greater than a working period, controlled and / or regulated.