DE102008030633B4 - Method for operating a free-piston device - Google Patents

Abstract

A method of operating a free piston device comprising at least one free piston engine with a linear electric drive, said at least one free piston engine having a piston device which is driven in a linear motion under the action of a medium expanding in an expansion space and by a return spring means exerts a return force, is moved back in an opposite direction, and wherein the piston device is coupled to the electric linear drive, in which a force profile of a force-displacement path for the piston device is given, the integral over a period of movement of the piston device corresponds to the usable work , which is convertible from electric linear drive into electrical energy.

Description

The The invention relates to a method for operating a free-piston device, which at least one free-piston engine with a linear electric drive wherein the at least one free-piston engine comprises a piston device which, under the action of a medium, is in an expansion space expanding, being driven in a linear motion and through a return spring device, which a restoring force exerts moved back in a reverse direction is, and wherein the piston means to the electric linear actuator is coupled.

Corresponding free piston devices are for example from the WO 03/091556 A1 and the EP 1 398 863 A1 known.

From the WO 2007/147789 A1 a method for operating a free-piston device is known in which the restoring force in the operation of the free-piston device is controlled and / or regulated by the desired value of at least one state variable of a gas in the resilience space is specified, the actual value is detected and at deviation from the target value at least approximately to the same is adjusted.

control and regulatory procedure for Free piston devices are described in the article "Free-Piston Diesel Engine Timing and Control - Towards Electronic Cam and Crankshaft "by T.A. Johansen et al., In IEEE Trans. Control Systems Technology, 10 (188-190), 2002, and "Dynamics and Control of a Free-Piston Diesel Engine "by T.A. Johansen et al., Proc. American Control Conference, Arlington, VA., 2001.

From the DE 43 44 915 A1 For example, a linear combustion engine generator is known in which two opposed pistons operating on a two-stroke principle bring a rotor with one or more coil-shaped pairs of magnetic poles into reciprocating linear motion and thereby generate electric current on the cylindrical stator in the windings.

From the DE 198 13 992 A1 is a free-piston internal combustion engine with electrical energy output known. It is a non-metallic, permanent magnetic piston provided in a cylinder, which is offset by combustion pressure in linear oscillatory movements. The energy extraction takes place inductively by arranged around the cylinder coils.

In the article "Comparison of gas spring variants with variable characteristic for a free-piston engine "of S.-E. Pohl and C. Ferrari, Research Engineering (2007) 71: Pages 181 to 188, gas spring variants are described, due to their adjustable spring characteristic for suitable for use in a free-piston engine.

Of the Invention is based on the object, a method of the initially to provide said type, by means of which in a free-piston device Set displacement and / or compression in a stable manner.

These The object is achieved according to the invention in the method mentioned solved, that predetermined a force profile of a force-displacement curve for the piston device becomes, its integral over a period of movement of the piston device of the usable Work corresponds to that of the electric linear drive in electrical Energy is convertible.

A Period of movement of the piston device is a complete cycle a movement starting from a starting point, where once the go through top dead center and the bottom dead center of the piston movement becomes. One period of a piston movement comprises in particular one Compression phase in the expansion space for the movement from the lower Dead center to top dead center and an expansion phase in the expansion space for the Movement from top dead center to bottom dead center. The starting point is basically any. For example, the starting point is the bottom dead center.

The Control strategy in the inventive solution is the piston device due to the acting forces in the expansion space and due to the restoring force "free" move allow. The force profile is thereby in its path-time dependence given, in principle while the piston movement of this force profile by a control intervention can be modified. The linear drive focuses on the application of force the piston device a reaction force, which accordingly affects the movement of the piston.

When Secondary condition when specifying the force profile must be the integral over the Force in a period of technically usable work in a period correspond. This technically usable work can be done by the linear drive be converted into electrical energy. This usable work can in principle be calculated if the dissipative energy is known or a similar approach for the loss energy is used.

at the solution according to the invention takes place the way-time dependence the piston movement is not regulated directly, that is it is no predetermined path-time curve for the piston movement is set, but the course of motion results as a consequence of the used force profile.

The used force profile is in particular to the appropriate application customized. For example, a hub and / or a compression set. The force profile can be optimized, for example, to this effect that, for example, the emission behavior in the expansion space positively influenced and / or the pressure in the expansion area defined (for example increased efficiency) is set and / or adjusted will that noise emission is minimized during the combustion process in the expansion space.

The inventive method let yourself insert when the free piston device with constant load or nearly constant load and in particular more consistent or nearly constant electrical power output operated becomes (stationary Business). in principle can also load changes consider (unsteady Business). It is basically possible, to switch to an active control, in which in particular the path-time curve of the piston movement via the linear drive regulating is given. In such an active control over the Linear drive is a direct reaction to a deviation of the Actual value of that Target value through change the parameter of the linear drive. In the solution according to the invention against it over the force profile, the application of force to the piston device over the Expansion space and the return spring device set directly.

at the solution according to the invention can be a corresponding control and Hierarchically build control device, wherein in the scheme a Separation between fast running processes (signal evaluations and Actuator control) and slower running control processes in the order of magnitude let the duration of a piston stroke perform.

Of the Piston stroke is the distance between the top dead center and the bottom dead center of a corresponding position of the piston device related to the expansion area. The displacement is the associated space, which is bounded by top dead center and bottom dead center. The compression is the (minimum) volume between an inside an end wall of a piston receiving, in which the piston device is arranged (cylinder wall) and the piston device, if this is positioned at top dead center. The compression ratio is The relationship from this minimum volume to a maximum volume at maximum Piston stroke.

Cheap is it, if in the specification of the force profile (the linear drive) of the Movement of the piston device solely by the application of force by the expanding medium and the restoring force of the return spring means is controlled without path-time control for the movement of the piston device. This results in a "thermodynamic" control, in which the electric linear drive is not used regulating becomes. In the solution according to the invention provides the linear drive a reaction force according to the force profile one. The flight movement of the piston device results derived from the given force profile. In an active control of the Linear drive, however, is the path-time course of the flight movement the piston device specified. As a direct reaction to a Deviation of an actual value from a target value at a certain value At the time the nominal force specification is changed by the linear drive. It then does not force the active control the piston device by the expanding medium and the restoring force set with predetermined force profile.

conveniently, To reset the piston movement, the restoring force, for example via a Gas spring and / or one or more parameters affecting the expansion of the medium in the expansion space. Thereby You can, for example, under the condition that the usable work the piston device corresponds to the decoupled electrical energy, to carry out a regulation to a constant setpoint stroke.

at an embodiment the expansion space is a combustion chamber and the piston device is caused by combustion gases, which form the expanding medium, driven.

Especially include parameters for the expansion space, which influence the piston movement and which can be adjusted at least one of the following parameters: one or more times at least one inlet opening, at least one inlet closing, at least one outlet opening, at least one outlet closure, one or more times of an injection of fuel or one or more times of ignition for a combustion, injection quantity, Gas mass in the expansion space.

parameter the return spring device, by soft the restoring force is adjustable, for example, pressure, temperature, maximum volume and minimum volume in a resilience space, in particular when the return spring means a gas spring is, spring characteristic for the restoring force, tension one Spring device, gas mass in the springback space.

One energetic state of the whole system is measured from (in particular thermodynamic) sizes in the expansion space and / or a resilience space the recoil device and position data of the piston device calculated. Especially a corresponding integral is calculated. In the solution according to the invention it basically possible, that the usable work required for a complete piston stroke movement was calculated to infer the useful work of a next period, if any can be assumed that a stationary operation is present. It can then from the determined usable work a corresponding regulation carried out be, for example, a defined target stroke and / or a set defined compression.

For example One or more models are used to determine work useful used to determine the dissipation energy. The system by the expansion of the expanding medium impressed mechanical Energy can not be complete be converted into electrical energy because dissipative losses available. Such irreversible energy losses do not contribute technically usable work and must be used accordingly in the determination the technically usable work from the integral over the force profile subtracted from. By using one or more appropriate Models leaves then calculate the technically usable work.

It can be provided that from the usable work, which for a period was calculated on the usable work of one or more temporally following piston strokes (within one period) closed becomes. By doing so leaves at a constant load or little variable load, the scheme Perform the piston movement in a simple manner. In particular, can be thereby easily adjust the force profile.

For example becomes a stroke of movement of the piston device in a certain Adjusted stroke range and / or a decoupling force of the electrical Set linear actuator in a certain range of force and / or A defined compression is set. By appropriate Presetting the force curve, this is possible in a simple manner.

For example can be reached at a regulation to a certain range of force be that exceeded a minimum force becomes or a maximum force not exceeded becomes. For example, it can also be based on a constant decoupling force be adjusted.

at an embodiment is at a constant lift and / or a constant compression and / or constant compression ratio regulated. The regulatory goal is to change the stroke of the movement the piston device between a bottom dead center and a to minimize top dead center or the compression change to minimize.

Especially becomes a force-distance dependence the force defines predetermined and / or varies, whereby the concrete dependence depends on the specific regulatory strategy.

It is also possible, for example, that a force profile is also modified within a period to for example, to allow adaptation to load changes or to optimize a specific control strategy. The force profile can basically time-dependent be modified.

In one embodiment, during a period of piston movement, the integral over the period is estimated, and optionally, the force profile is modified. From the data determined up to a certain point in time (in particular position of the piston device and thermodynamic variables), the integral over the period can be estimated. It can then be used to optimize the regulatory strategy, so necessary, the force profile can be modified to achieve the desired effects. For example, a force profile with a quantitatively or qualitatively different force-distance dependency can be used in order to allow an adaptation to the actual conditions. For example, it is possible to modify the force profile such that a compression lies in a defined value range. During a period can be intervened corrective. For example, in a compression phase, the compression is set to a desired value. This may be necessary, for example, if a combustion process is basically unsteady and can only be described with limited determinism, so that an exact prediction is not possible. Corrective intervention does not require exact predictability. In the solution according to the invention, the control intervention takes place via adaptation of the force profile and not via direct positioning of the piston device at a certain time on an actual position. If, for example, measurements prove that the compression is becoming too low, the amount of force is reduced so that less energy can be extracted via the linear drive. As a result, more compaction energy is available, which increases the compression and compression ratio.

Cheap is it when a compression set by means of the resilience space and / or is varied. Through a variable characteristic, for example one Gas spring may be the one in the resilience space stored energy amount and thus the for the compression phase the piston device available fixed energy. The example in a Gas spring stored energy, which for the provision of the piston device is used, is the sum of the (still to be coupled out) technically usable work, the compaction energy for a Expansion space and dissipation losses. The compaction energy from the expansion space is the integral of the compression force over the Way (compression energy). This is also the top dead center in Expansion space given; if less energy in the recoil device is stored, then there is only a small compression energy to disposal and this reduces the compression or the Compression ratio.

It is advantageous when it is possible to switch from one mode to another, in which the electric linear drive the course of movement of the piston device active and in particular in its path-time dependence sets. Thereby is a switch between "active" (regulatory) and "passive" (non-regulatory) operation the electric linear drive possible. This results in extended possibilities of use. For example can be used when switching to an active operation of the electric Linear drive, in which this actively influences the piston movement, in a simple and fast way to adapt to a load change respectively.

Especially the electric linear drive actively influences the course of the movement the piston device in a start phase and / or fault phase and / or transitional phase.

It has been considered favorable proved, if the regulation at least two hierarchically arranged Has levels, being in a first level on a time scale smaller than the duration of a piston stroke arranged on the free-piston engine Sensors emit signals and actuators activate the free-piston engine, in a second level, which is hierarchically superior to the first level is, a regulation calculation for the piston movement on the basis of the calculated usable Work of one or more preceding complete strokes of the piston device is performed, wherein between the first level and the second level a data exchange he follows. By doing so leaves to perform a separation between operations, must be reacted to immediately or evaluated immediately Need to become and events occurring on a slower time scale, namely the Time scale of a complete Piston strokes take place.

Especially in the second level, a control calculation for a following piston stroke based on the determination of usable work for one current and / or previous piston stroke. This can be easy on A parameter setting from the calculated usable energy if necessary, for the next or a subsequent piston stroke done.

It is also cheap if a third level is provided, that of the second level hierarchically superior is in which a surveillance performed the piston movement becomes. In the third level, for example, a sync the movement of several piston devices done or it can a surveillance and / or control of load changes.

Especially then takes place between the third level and the second level Data exchange.

The following description of preferred embodiments is in connection with the Drawings of the detailed explanation of the invention.

It demonstrate:

1 a schematic representation of a free piston device with a free-piston engine with electric linear drive;

2 a schematic representation of a hierarchically structured control / regulation device;

3 a schematic representation of a typical course of the speed as a function of time for the "free" movement of a piston device, wherein the position of a top dead center (OT _ex ) and bottom dead center (UT _ex ) is shown;

4 (a) bis (e) different possibilities for the course of an output force in dimensionless coordinates;

5 (a) to (c) further possibilities for the course of the outcoupling force in dimensionless coordinates with different energy distribution f _E with respect to an expansion phase and a compression phase;

6 schematically a section of a path-time curve of the piston device with excellent "event points";

7 (a) and (b) examples of different force profiles;

7 (c) schematically the time-dependent temperature profile in an expansion space in the force curves according to 7 (a) and (b);

8 (a) and (b) different force profiles;

8 (c) a pressure-volume diagram respectively for the force curves according to 8 (a) and (b);

9 (a) and (b) different force profiles;

9 (c) a pressure-volume diagram for the force courses according to 9 (a) and (b) (schematically).

An embodiment of a free piston device, which in 1 shown and there with 10 is designated comprises a free-piston engine 12 with electric linear drive 14 , It is basically the case that the free piston device 10 may comprise a plurality of free-piston engines with respective electric linear drive.

The free-piston engine 12 has a piston receptacle 16 which is cylindrical, for example, with a circular cross-section. The piston receiver 16 is through piston walls 18 limited.

In the piston receptacle 16 is a piston device 20 in a linear direction 22 movable. This linear direction is preferably parallel to an axis 24 the piston receiving 16 ,

The piston device 20 includes a first piston 26 , a second piston 28 and a connection device 30 which the first piston 26 and the second piston 28 connects with each other. The first piston 26 has a first piston surface 32 on which a first end wall 34 the piston receiving 16 is facing. Between the first piston surface 32 and the first end wall 34 is in the piston receptacle 16 an expansion area 36 educated. An expanding medium may be in the expansion space 36 a force on the first piston 26 exercise and thereby the piston device 20 in the linear direction 22 to drive in one movement.

The expansion space 36 has a variable volume, which is dependent on the position of the first piston 26 in relation to the first end wall 34 ,

In one embodiment, the expansion space is 36 a combustion chamber in which fuel can burn with oxidizer. The combustion gases then drive the piston device 20 at.

It is also possible in principle in the expansion room 36 a heat transfer medium expands while the piston device 20 drives.

The second piston 28 has a second piston surface 38 on which a second end wall 40 the piston receiving 16 is facing. The first end wall 34 and the second end wall 40 limit the piston intake 16 frontally. The first piston surface 32 and the second piston surface 38 are turned away from each other.

Between the second piston surface 38 and the second end wall 40 is a resilience space 42 educated. In the resilience space 42 is a springback device 44 added. This ensures that the piston device 20 by action on the second piston 28 towards the first end wall 34 is moved back.

In one embodiment, the return spring means 44 a compressible medium and in particular a gas. The return spring device 44 is then designed as a gas spring. (The recoil device 44 may in principle also have one or more mechanical springs.)

Due to the expanding medium, which is based on the first piston 26 acts, the piston device 20 in the direction of the second end wall 40 emotional. In the resilience space 42 which has a variable volume becomes the return spring means 44 compressed. It then exerts a restoring force on the piston device 20 out, which then this in the opposite direction on the first end wall 34 too moved.

The first piston 26 and the second piston 28 are at the edge opposite the piston receiver 16 sealed. Such a seal is associated with the second piston 28 by the reference numeral 46 indicated. This is the expansion space 36 and the resilience space 42 fluid-tightly separated. Further, there is a gap between the first piston 26 and the second piston 28 fluid-tight from the expansion space 36 and the resilience space 42 separated.

The first piston 26 and the second piston 28 are spaced from each other with intermediate connection means 30 , This is advantageously designed so that, with guaranteed structural rigidity, the mass of the moving piston device 20 is minimized.

The electric linear drive 14 comprises a rotor device 48 and a stator device 50 , The runner device 48 is between the first piston 26 and the second piston 28 at the connection device 30 arranged. It comprises a plurality of, for example, annular permanent magnets 52a . 52b etc., which are arranged with alternating polarity. With the linear movement of the piston device 20 moves the runner device 48 linear within the piston receptacle 16 outside the expansion area 36 and outside the resilience space 42 ,

The stator device 50 is arranged stationarily outside the piston receptacle. It comprises a plurality of windings 54 which the piston receiving 16 surrounded in the area in which the rotor device 48 is mobile.

By the movement of the rotor device 48 becomes a voltage on the stator 50 induced, which can be tapped. There is a (partial) conversion of mechanical energy into electrical energy. The electrical energy can be decoupled and used.

It is also possible, as in the WO 03/091556 A1 described, via a corresponding electrical loading of the stator 50 the movement of the piston device 20 to influence; the piston stroke can be controlled by the electric linear drive 14 set variably, so that the dead centers of movement of the piston device 20 are definable.

It is a control / regulation device 56 provided by which actuators of the free-piston device 10 can be controlled and sensor signals of the free-piston device 10 are evaluable. Furthermore, there is the control / regulation device 56 a control strategy and control strategy, which is implemented in hardware and / or software.

At the first end wall 34 is (at least) an inlet valve 58 for fuel and / or a fuel arranged material-oxidizer mixture and / or it is an inlet valve for oxidizer (in particular air) is provided. Furthermore, on the first end wall 34 (at least) an exhaust valve 60 arranged over which is consumed medium and in particular combustion exhaust gases from the expansion space 34 can be removed.

It can also be an injection device ( 61 ) may be provided for injecting fuel.

Furthermore, an ignition device 62 be provided (in 1 shown exaggeratedly for illustrative purposes) to form a fuel-oxidizer mixture in the expansion space 36 , which is then a combustion chamber, to be able to ignite.

Furthermore, the expansion area 36 a sensor device 64 assigned, over which one or more parameters are measurable. For example, the pressure in the expansion space 36 and / or the temperature measurable.

The control / regulation device 56 controls the intake valve (s) 58 , the exhaust valve 60 , the ignition device 62 and optionally an injection device. It can thereby be at one or more defined times, the one or more intake valves 58 open and close and / or the exhaust valves 60 can be opened and closed. Furthermore, fuel can be injected at a defined time and a fuel-oxidizer mixture can be ignited.

Signals of the sensor device 64 are sent to the control / regulation device 56 transmitted.

The control / regulation device 56 is also to the electric linear actuator 14 coupled, for example, optionally via the electric linear drive 14 the piston movement of the piston device 20 to be able to influence.

It is a sensor device 66 provided, which corresponding sensor signals of the control / regulating device 56 provides over which the instantaneous position of the piston device 20 in relation to the piston receiver 16 is measurable.

In one embodiment, the resilience space 42 if this is a gas spring chamber, a pressure accumulator 68 assigned. The accumulator 68 is with the resilience space 42 via a control valve 70 connected, which by the control / regulating device 56 is controllable. About the accumulator 68 is the pressure in the resilience space 42 for example, in a bottom dead center (UT _r ) of the piston device 20 in which this with the first piston 26 next to the first end wall 34 is, adjustable. It can be adjusted by the properties of the gas spring. In particular, a spring constant or spring characteristic can be set.

The accumulator 68 is filled with the appropriate springback medium or it is emptied. In particular, the pressure in the pressure accumulator can be 68 outside the piston receiver 16 to adjust. Accordingly, for example, a controllable three-two-way valve 72 intended. One way is a filling path for the accumulator 68 and a second way is a vent path. The three-way valve 72 is to the control / regulation device 56 coupled. A pump 73 is to an input of the three-way valve 72 connected.

The resilience space 42 are one or more sensors 74 assigned. In particular, a pressure sensor is provided. For example, a temperature sensor may also be provided. These represent their measured values of the control / regulation device 56 ready.

In 1 is by an arrow 76 schematically indicated that the control / regulating device 56 It is also possible to monitor, control and regulate other free-piston engines. For example, a further free-piston engine may be provided in order to obtain a mass balance with a corresponding arrangement of the piston device.

By a time-recurring expansion of medium in the expansion space 36 For example, by a time-repeating combustion of fuel, the piston device 20 driven in an oscillatory motion. The piston device moves between one with respect to the expansion space 36 bottom dead center (UT _ex ) and top dead center (OT _ex ). The bottom dead center is defined by the fact that the first piston 26 the largest distance to the first end wall 34 Has. The top dead center is defined by the fact that the first piston 26 the smallest distance to the first end wall 34 Has. In 3 are schematically shown below these dead points UT _ex and OT _ex . The deflection x refers to the distance from the first end wall 34 in the linear direction 22 , A piston stroke is the distance between top dead center and bottom dead center. This is denoted by S.

The control / regulation device 56 performs control operations and control operations hierarchically. She is in a first level 78 , a second level 80 and in a third level 82 divided. The third level 82 is the second level 80 parent and the second level 80 is the first level 78 superior.

On the first level 78 take place control operations and control operations, which are on a time scale, which are below the duration of a piston stroke. In the first level 78 find, for example, in an expansion space control device 84 Regulatory processes take place, which is the expansion of medium in the expansion space 36 and in particular combustion processes. These control operations include, in particular, the control of the intake valve (s) 58 , exhaust valve or exhaust valves 60 and the ignition device 62 and optionally the control or regulation of an injection device.

The expansion space control device 84 receives sensor signals of the sensor device 64 and uses these control processes and regulatory processes as a basis.

Furthermore, the first level includes 78 a linear drive control device 86 , which the linear drive 14 controls or regulates. By appropriate power supply of the stator 50 is this possible. The linear drive control device 86 receives signals from the sensor device 66 ,

Furthermore, the first level includes 78 a springback control device 88 , About this can be the control valve 70 control or regulate. The springback control device 88 includes signals from the sensor 74 ,

In the first level 78 becomes the free-piston engine 12 with electric linear drive 14 directly controlled or regulated. Actuators are activated (in 2 indicated by an arrowhead points to this) and sensor signals are received (in 2 indicated by the arrowhead pointing away from them).

In the second level 80 a control calculation takes place on a time scale which corresponds to the duration of one or more piston strokes. There is a kind of "integral" control calculation and then appropriate control. There is a data exchange between the first level 78 and the second level 80 ,

The third level 82 is the second level 80 superior. In the third level 82 For example, monitoring processes are performed and, for example, when multiple piston devices are present, synchronization operations can be performed.

The levels 78 . 80 and 82 work on different time scales. As a result, control processes can be structured hierarchically. In the first level 78 becomes the physical distance of the free-piston engine 12 with electric linear drive 14 directly influenced or there is a direct evaluation of sensor signals. In the second level 80 is, as will be described in more detail below, an event control and in particular control of the movement of the piston device 20 from one (complete) piston play to the next one. In the first level 78 There is an un indirect event control on the free-piston engine 12 with electric linear drive 14 ,

In the third level 82 For example, a load change adaptation takes place.

By the hierarchical structure allows the different time scales for control operations and control operations separate. Thereby can the regulatory operations be optimized.

According to the invention, the movement of the piston device 20 so regulated that the electric linear actuator 14 is not used regulating, that is no path-time control for the movement of the piston device 20 by the electric linear drive 14 he follows. (It is basically possible that via the electric linear drive 14 a defined movement form of the piston device 20 is given in their path-time dependence. For example, a sinusoidal course of the path x and the velocity v (as Derivation of the path over time).)

In the solution according to the invention, however, a "free" vibration of the piston device 20 allowed, which only by the expansion of the medium in the expansion space 36 and the restoring force in the springback space 42 and dissipative losses during movement. The usable work by the movement of the piston device 20 then essentially corresponds to that from the electrical linear device 14 decoupled electrical energy.

In 3 is schematically a course of movement indicated in the form of a velocity-time diagram for a complete movement of the first piston 26 from top dead center to bottom dead center to top dead center when top dead center is selected as the starting point. Typically, this course of motion is not exactly sinusoidal. In an expansion phase from top dead center to bottom dead center, the expansion accelerates the piston assembly 20 stronger than the restoring force in the springback space 42 the piston device 20 when moving from bottom dead center to top dead center (relative to the first piston 26 ) emotional. As a result, the time duration of a first phase of the piston movement (expansion phase) is shorter than the time duration of a second phase of the piston movement (compression phase or springback phase).

It it should be noted that, as will be explained in more detail below, the scheme so feasible is that the piston stroke S is fixed. This fixed piston stroke is then the size, up which is to be regulated.

According to the invention, it is provided that an adjustment process to a stationary operation and the stationary operation itself is performed so that the useful work of the piston device 20 by the electric linear drive 14 decoupled energy corresponds. It is basically possible that an intervention, for example, to specify starting conditions on the control / regulating device 56 is possible, in which the electric linear drive 14 is actively used and the piston device 20 in a certain position (by acting on the stator 50 ) is brought.

The usable work W _N per piston play is

It is composed of a contribution from the expansion area 36 (Pressure p _E ) and a contribution of the resilience space 42 (Pressure p _R ) and a Dissipationsbeitrag W _diss .

The over the electric linear drive 14 decoupled energy W _L is

F _L is the acting mechanical force, which corresponds to the decoupling force.

When the electric linear actuator 14 is operated as a purely electric generator, ie the electric linear drive 14 not regulating (purely passive) is operated and the piston device 20 their through the expansion of the medium in the expansion space 36 and is caused by the return spring force caused movement, then the usable work W _{N is} equal to that via the electric linear drive 14 decoupled energy W _L.

If the proportion W _{diss is} known or can be estimated, the usable work per piston stroke can be calculated. By specifying the conditions in the expansion area 36 in the springback room 42 can the usable work be adjusted to a certain extent.

The course of the force F _L is basically arbitrary with respect to a piston stroke as long as the condition W _L = W _{N is} fulfilled. There are therefore different specifications for the course of the force (for the force profile of the path dependence of the force) possible. In turn, a regulatory strategy can be implemented via these specifications.

A control strategy may be such that the piston stroke S is in a certain range of values and / or the force F _{L is} in a certain range of values and / or the compression is in a certain range of values and / or the compression ratio is in a certain range of values. In one embodiment, the control strategy is such that the piston stroke is fixed, ie the controlled variable is a fixed piston stroke S; there is a specification of the piston stroke S at a free movement of the Kol beneinrichtung 20 ,

In the 4 (a) to 4 (e) Possible predefinable force profiles are shown, which are related to a dimensionless coordinate χ (t), which is defined as

Where x (t _UT ) is the position of the first piston 26 at top dead center OT _ex and x (t) is the current piston position. The dimensionless force γ (t) is defined as γ (t) = F L (T) / F L, max (4)

The force F _{L, max} is defined as

Where k _{A is} an area factor.

By specifying the force profile of the force, a control can be carried out with the control strategy, a free movement of the piston device 20 to enable. The condition is W _N = W _L. The instantaneous desired force, which is the electric linear drive 14 is to decouple from the system is then selected according to a strategy, for example, to obtain a constant target stroke S.

Depending on the application, a corresponding force profile can be selected. Examples of force courses are in the 4 (a) to 4 (e) shown. These examples are symmetrical in terms of expansion and compression.

In 5 (a) is the force curve according to 4 (a) shown again. He can be moved ( 5 (b) and 5 (c) ). This corresponds to a different energy distribution to the expansion phase (f _E > 0.5) or to the compression phase (f _E <0.5). As mentioned above, the course of the decoupling force can be chosen so that the selected control strategy can be performed.

The intervention options in the control are in the corresponding control of the actuators of the free-piston engine 12 with electric linear drive 14 as above related to the first level 78 the hierarchical control and regulation described.

As in 6 indicated schematically, for example, a time of closing 90 the exhaust valve 60 and / or closing 92 of the inlet valve 58 be adjusted accordingly. Furthermore, for example, an injection start 94 be set. Furthermore, an ignition point 96 the ignition device 62 be set. Furthermore, a combustion end 98 to be influenced. Also opening 100 the exhaust valve 60 and an opening 102 of the inlet valve 58 can be set.

Furthermore, the conditions in the resilience space can be 42 for example, influence by pressure setting. About the accumulator 68 and the control valve 70 can be parameters of the return spring device 44 influence and adjust and if necessary adjust also in time dependence. For example, the return spring means 44 be stiffened or softened if necessary.

For example, by adjusting the pressure at bottom dead center UT _{r of} the resilience space 42 the compression can be adjusted or varied. A variable characteristic of the return spring means 44 influences the amount of stored energy and thus determines the energy available for a compression phase. This energy available for the compression phase is composed of that in the return spring device 44 stored energy for the upcoming recovery of the piston device 20 , the usable work to be coupled out in the compression phase, the compression energy for the expansion space 36 and dissipative losses together. It leaves you the top dead center OT _ex in the expansion space 36 to adjust. If less energy in the recoil device 44 is stored, then only a small compression energy is available and thus reduces the compression.

There is a corresponding control strategy in the second level 80 , It is closed from the useful work for a complete piston stroke on the next piston stroke. This assumption is correct when stationary operation or quasi-stationary operation is present, in which changes and in particular load changes are considerably slower than the duration of a piston stroke.

In the solution according to the invention, possibly starting from a starting phase, in which the electric linear drive 14 can be used regulating, for example, a control to a steady state operation in which the electric linear drive 14 not regulated as an electric generator is used. Both during the Einregelungsprozesses as well as in stationary (or quasi-stationary) operation corresponds to the useful work of the piston device 20 by the electric linear drive 14 decoupled electrical energy. The application of force to the piston device 20 through the expanding medium in the expansion space 36 and by the return spring force including dissipative losses determines the course of movement of the piston device 20 , The electric linear drive sets a reaction force according to the force profile and thus influences the trajectory of the piston device 20 ,

The restoring force and / or one or more parameters which the application of force to the first piston 26 determine (such as the in 6 displayed parameters) are set accordingly.

The regulation is a "thermodynamic" regulation. There are corresponding thermodynamic variables in the expansion space 36 and / or resilience space 42 adjusted to the "free" movement of the piston device 20 to obtain.

By the solution is it possible, for example, to adjust to a constant piston stroke S, d. H. on minimal changes adjust in the piston stroke.

In the 7 (a) and (b) are schematically different force profiles 104 and 106 and dimensionless coordinates. The force profile 104 belongs to an expansion phase 108a and a compression phase 108b , The area for the expansion phase 108a and for the compression phase 108b is equal to.

To the force profile 106 belongs to an expansion phase 110a and a compression phase 110b , The area of the expansion phase 110a is greater than the area of the compression phase 110b , The force profile 106 is chosen so that the piston movement in the expansion phase 110a slows down to when the piston device 20 by combustion processes in the expansion process 36 is driven. In 7 (c) is schematic that to the force profiles 104 and 106 associated cooling behavior of gases (cylinder gases) in the expansion space 36 shown. At the force profile 106 Cooling is slowed down as the piston movement during expansion by the force profile 106 is slowed down.

you sees that a corresponding cooling behavior over the used force profile can be adjusted. This in turn let yourself positively influence the emission behavior (for example, can be certain cooling curves adjust, with the cooling curves again determine particle formation).

In the 8 (a) and 8 (b) Further force profiles are shown, wherein the force profile according to 8 (a) the force profile 104 according to 7 (a) equivalent.

The force profile 112 according to 8 (b) is chosen so that the piston speed is greatly slowed in the area at and before the bottom dead center. Accordingly, the force profile 112 a waste 114 ,

The force profile 112 serves a combustion process in the expansion space 36 to approach a Gleichraumprozess having a high thermodynamic efficiency. In 8 (c) associated pV diagrams are shown (dependence of a pressure in the expansion space 36 [Cylinder pressure] depending on the volume). One recognizes the influence of the force profile 112 ,

In 9 (a) and (b) further force profiles are shown, the force profile according to 9 (a) the force profile 104 equivalent. The force profile 116 according to 9 (b) is chosen so that the noise emission during a combustion process is minimized. The noise emission is significantly increased by the pressure increase in the expansion space 36 certainly. The force profile 116 is chosen so that the piston device 20 is more accelerated after passing the top dead center. It should be avoided strong pressure gradients. Corresponding pV diagrams are in 9 (c) shown. It can be seen that the cylinder pressure at the force profile 116 leads to lower pressure gradients and thus to lower noise emission.

The Secondary condition is that the area over a Force profile over a period of movement of the usable energy piston device corresponds, which then over the electric linear drive can be coupled out as electrical energy is.

It is basically possible, that different requirements such as temperature behavior, noise etc. are taken into account when using the force profile.

The control / regulation device 56 has, for example, a database in which predetermined force profiles are stored and from which, depending on the application, the appropriate force profile is read out.

Basically the usable work during a period of piston movement from the useful work of a or several previous piston movement periods are estimated, to carry out a corresponding regulation. It can also be provided be that within a period of piston movement the usable Work for estimated this period becomes, in which the from the beginning to the period up to a certain one Date determined data used to work useful for the estimate the entire period. Optionally, the force profile is then modified to an optimized Regulation according to the selected To receive regulatory strategy.

Basically it so that when operating a free piston engine at full load the Hub (displacement) is greater as at partial load. At partial load, the displacement is reduced. By Adjustment of the stroke and / or compression according to the method of the invention let yourself according to the load conditions achieve optimized operation and it can be optimized electrical Disconnect energy.

By appropriate adjustment of the return spring device (for example, by increasing the pressure in a bottom dead center of a corresponding resilience space) let yourself a displacement adjustment in combination with the force profile adjustment carry out.

Claims (23)

Method for operating a free-piston device, which at least one free-piston engine with a linear electric drive wherein the at least one free-piston engine comprises a piston device which, under the action of a medium, is in an expansion space expanding, being driven in a linear motion and through a return spring device, which a restoring force exerts moved back in a reverse direction is, and wherein the piston means to the electric linear actuator is coupled, in which a force profile of a force-displacement curve for the piston device is given, whose integral over a period of a movement the piston device corresponds to the usable work, which of electric linear drive is convertible into electrical energy. Method according to claim 1, characterized in that that in the specification of the force profile of the movement of the piston device solely by the application of force by the expanding medium and the restoring force is controlled without path-time control for the movement of the piston device. Method according to claim 1 or 2, characterized that for adjusting the piston movement, the restoring force and / or a or several parameters indicating the expansion of the medium in the expansion space be adjusted. Method according to one of the preceding claims, characterized characterized in that the expansion space is a combustion chamber and the piston means by combustion gases, which the expanding Form medium, is driven. Method according to one of the preceding claims, characterized characterized in that parameters for the Expansion space, which influence the piston movement and which can be set to include at least one of the following parameters: one or more times of at least one inlet opening, Inlet closing, Auslassöffnens, Auslassschließens, Injection, ignition for one Combustion, injection quantity, gas mass in the expansion space. Method according to one of the preceding claims, characterized in that parameters of Spring return device, by which the restoring force is adjustable, at least one of the following parameters include: pressure, temperature, maximum volume, minimum volume in a resilience space, spring characteristic for the restoring force, bias of a spring device, gas mass in the resilience space. Method according to one of the preceding claims, characterized characterized in that an energetic state of measured sizes in the expansion space and / or a resilience space the recoil device and position data of the piston device is calculated. Method according to one of the preceding claims, characterized characterized in that to determine the usable work on or several models used to determine dissipation energy become. Method according to one of the preceding claims, characterized that characterized from the usable work, which for a period was calculated on the usable work of one or more temporally following piston strokes is closed. Method according to one of the preceding claims, characterized characterized in that a stroke of movement of the piston device in a certain stroke range and / or an output force of the electric linear drive in a certain force range and / or a compression in a certain compression area and / or the compression ratio is set in a specific compression ratio range. Method according to claim 10, characterized in that that at a constant lift and / or a constant compression and / or constant compression ratio is regulated. Method according to one of the preceding claims, characterized characterized in that a force-distance dependence of the force defines is specified and / or varied. Method according to claim 12, characterized in that that while a period of piston movement the integral over the period is estimated and optionally the force profile is modified. Method according to claim 13, characterized in that that the force profile is modified so that a compression is within a setpoint range. Method according to one of the preceding claims, characterized characterized in that a compression means of the resilience space adjusted and / or varied. Method according to one of the preceding claims, characterized characterized in that it is possible to switch from one or to a mode of operation, in which the electric linear drive the course of movement of the piston device active, and in particular in its path-time dependence sets. Method according to claim 16, characterized in that that in a starting phase and / or fault phase and / or transition phase the electric linear drive the movement pattern of the piston device in his way-time dependence active setting. Method according to one of the preceding claims, characterized characterized in that the control at least two hierarchically structured Has levels, wherein in a first level on a time scale smaller arranged as the duration of a piston stroke on the free-piston engine Sensors emit signals and actuators activate the free-piston engine, and in a second level hierarchically superior to the first level is, a regulation calculation for the piston movement on the basis of the calculated usable Work of one or more preceding full strokes of the piston device is performed, wherein between the first level and the second level a data exchange he follows. Method according to claim 18, characterized that in the second level a regulation calculation for a following piston stroke based on the determination of usable work for one current and / or previous piston stroke takes place. A method according to claim 18 or 19, characterized by a third level which is hierarchically superior to the second level is in which a surveillance performed the piston movement becomes. A method according to claim 20, characterized in that in the third level a Synchronisie tion of the movement of several piston devices takes place. Method according to claim 20 or 21, characterized that in the third level monitoring and / or control of load changes. Method according to one of claims 20 to 22, characterized that between the third level and the second level a data exchange he follows.