DE102008030633A1 - Method for operating a free-piston device - Google Patents

Abstract

There is provided a method of operating a free piston device comprising at least one free piston engine with a linear electric drive, wherein the at least one free piston engine having a piston device which is driven in a linear motion under the action of a medium which expands in an expansion space a return spring, which exerts a restoring 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 curve for the piston device is given, its integral over a period of movement of the piston device corresponds to the usable work, which is convertible from the 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 has a restoring force exercises in a reverse direction, 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 is controlled and / or regulated during operation of the free-piston device 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 regulation methods for free piston devices are in the article "Free-Piston Diesel Engine Timing and Control - Towards Electronic Cam and Crankshaft" by TA Johansen et al., In IEEE Trans. Control Systems Technology, 10 (188-190), 2002 , and "Dynamics and Control of a Free-Piston Diesel Engine" by TA Johansen et al., In Proc. American Control Conference, Arlington, Va., 2001 , described.

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 a force profile of a force-displacement curve for the piston device is given, the 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 of bottom dead center to top dead center and an expansion phase in Expansion space for the movement from top dead center to 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 it is the piston device due to the forces acting in the expansion space and due to the restoring force "free" move allow. The force profile is thereby in its path-time dependence given, being basically during the piston movement this force profile can be modified by a control intervention can. The linear drive is based on the application of force to the piston device a reaction force corresponding to the movement of the piston affected.

When Secondary condition when specifying the force profile must be the integral over the power in a period of technically usable work in one 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 when the dissipative energy is known or a corresponding approach for the loss energy is used.

at the solution according to the invention takes place the path-time dependence of the piston movement is not direct regulated, that is, there is no predetermined path-time history set for the piston movement, but the course of movement arises as a consequence of the force profile used.

The force profile used is particularly adapted to the corresponding application. For example, a stroke and / or a compression is set. The force profile can be optimized, for example, to the effect that, for example, the emission behavior in the expansion space is positively influenced and / or the pressure in the expansion space defined (for example, for increased efficiency) is set and / or adjusted so that the noise emission during the combustion process in the expansion space is minimized.

The inventive method can be 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 operation). Basically leave also take into account load changes (transient operation). It is basically possible to switch to an active control in which in particular the path-time curve of the piston movement over the linear drive is prescribed regulating. In such an active Control via the linear drive is a direct reaction to a deviation of the actual value from the target value by change the parameter of the linear drive. In the inventive The solution, on the other hand, is the application of force via the force profile the piston device via the expansion space and the return spring means set directly.

at the solution of the invention leaves a corresponding control and regulation device hierarchically build up, whereby in the regulation a separation between fast ongoing processes (signal evaluation and actuator control) and slower regulatory processes of 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 bounded by top dead center and bottom one Dead center. The compression is the (minimal) volume between one 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 ratio of this minimum volume to one maximum volume at maximum piston stroke.

Cheap is it when when specifying the force profile (the linear drive) the course of movement of the piston device solely by the application of force by the expanding medium and the restoring force of Return spring device is controlled without path-time control for the movement of the piston device. It is done by it a "thermodynamic" control in which the electric linear drive is not used regulating. In the solution according to the invention provides the linear drive a reaction force according to the force profile. The flight movement the piston device is derived from the given Force profile. In an active control of the linear drive is against the path-time course of the flight movement of the piston device specified. In direct response to a deviation of an actual value from one Target value at a certain point in time becomes the target force specification changed by the linear drive. It will then be active Control does not force the piston device through the expanding medium and the restoring force with a predetermined Force profile adjusted.

conveniently, To reset the piston movement, the restoring force for example via a gas spring and / or one or more Parameters that influence the expansion of the medium in the expansion space, set. This can be done, for example, under the condition that the usable work of the piston device of the decoupled corresponds to electrical energy, a regulation to a constant target stroke carry out.

at In one embodiment, the expansion space is a combustion space and the piston device is characterized by combustion gases, which is the form expanding medium, driven.

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

parameter the return spring means, by which 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 is a gas spring, spring characteristic for the restoring force, tensioning of a spring device, Gas mass in the springback space.

An energetic state of the entire system is measured (in particular thermodynami ) variables in the expansion space and / or a resilience space of the return spring means and position data of the piston device calculated. In particular, a corresponding integral is calculated. In the solution according to the invention, it is possible in principle for the useful work, which has been calculated for a complete piston stroke movement, to conclude on the useful work of a next period, if it can be assumed that there is stationary operation. It can then be carried out from the determined usable work a corresponding regulation, for example, set a defined target stroke and / or a defined compression.

For example One or more models are used to determine work useful used to determine the dissipation energy. The system imprinted by the expansion of the expanding medium Mechanical energy can not be completely electrical Energy are converted because there are dissipative losses. Such irreversible energy losses do not contribute to the technically usable Work in and must be used in determining the technically usable work from the integral over the force profile subtracted from. By using one or more appropriate Models can then calculate the technically usable work.

It can be provided that from the usable work, which for a period has been calculated on the usable work of one or more several temporally following Kolbenhubbewegungen (within a Period) is closed. This can be maintained at the same Load or little variable load the regulation of the piston movement perform in a simple manner. In particular, lets 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 a minimum force is exceeded or a maximum force is not exceeded. It For example, it can also be adjusted to a constant decoupling force become.

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

Especially is defined a force-distance dependence of the force defined and / or varies, with the concrete dependence on depends on the specific regulatory strategy.

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

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 modified to optimize the control strategy, if necessary, the force profile 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, so that the compression and increase the compression ratio.

Cheap it is when a compression by means of the resilience space adjusted and / or varied. Through a variable characteristic For example, a gas spring can in the resilience space stored energy and thus affects the for the compression phase of the piston device available fixed energy. The example in a Gas spring stored energy, which is for the provision the piston device is used, results as the sum of (still to be coupled out) technically usable work, the compaction energy for an expansion space and dissipation losses. The compression energy from the expansion space is the integral of the Compression force over the way (compression energy). In order to is also given the top dead center in the expansion space; if less Energy is stored in the return spring device, then only a small compression energy is available 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 especially in its path-time dependence established. This is a switch between "active" (regulating) and "passive" (non-regulatory) operation of 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 proved favorable if the scheme at least has two hierarchically structured levels, wherein in a first Level on a time scale smaller than the duration of a piston stroke Sensors arranged on the free-piston engine deliver signals and actuators to drive the free piston engine, in a second level, which the is hierarchically superior to the first level, a control calculation for the piston movement on the basis of the calculated usable work of one or more previous complete ones Strokes of the piston device is carried out wherein between the first level and the second level a data exchange he follows. This can be a separation between operations that are immediately reacted to must or must be evaluated immediately and Events on a slower time scale, namely the time scale of a complete piston stroke take place.

Especially in the second level, a control calculation for a subsequent piston stroke based on the determination of usable Work for a current and / or previous piston stroke. Thereby can easily from the calculated usable energy one Parameter setting, if necessary, for the next or a subsequent piston stroke done.

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

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

The following description of preferred embodiments used in conjunction with the drawings for further explanation the invention. Show it:

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) to (e) different possibilities for the course of an outcoupling force in dimensions sen 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 where 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 arranged for fuel and / or a fuel-oxidizer mixture and / or 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 as well as the control of a Injector.

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. This allows the control 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 a derivative of the path over time) is given.)

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. This is the time duration of a first phase of Piston movement (expansion phase) smaller than the time duration of a second phase of the piston movement (compression phase or springback phase).

It It should be noted that, as explained in more detail below is, the scheme is feasible so that the piston stroke S is fixed. This fixed piston stroke is then the size, is to regulate on the.

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 within 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 piston device 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 For example, the solution is possible to regulate 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 force profile used can be adjusted. This in turn the emission behavior can be positively influenced (for example, you can set certain cooling curves, the cooling curves in turn the particle formation determine).

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 in 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 piston device corresponds to the usable energy, which then over the electric linear drive as electrical energy can be coupled out.

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

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 useful work during a period of the piston movement can be estimated from the useful work of one or more previous piston movement periods to achieve an ent to carry out the appropriate regulation. It can also be provided that, within a period of the piston movement, the useful work for this period is estimated, in which the data determined from the beginning to the period until a certain point in time are used in order to estimate the useful work for the entire period. Optionally, then the force profile is modified to obtain an optimized control according to the selected control strategy.

in principle it is such that when operating a free-piston engine at full load the stroke (displacement) is greater than at partial load. At partial load, the displacement is reduced. By adjusting the stroke and / or compaction according to the invention Method can be adjusted according to the load conditions achieve optimized operation and it can be optimized Disconnect electrical energy.

By corresponding adjustment of the return spring means (for example by increasing the pressure in a bottom dead center of a corresponding resilience space) can be a Displacement adjustment in combination with the force profile adjustment carry out.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 03/091556 A1 [0002, 0065]
• - EP 1398863 A1 [0002]
• WO 2007/147789 A1 [0003]

Cited non-patent literature

• - "Free-Piston Diesel Engine Timing and Control - Towards Electronic Cam and Crankshaft" by TA Johansen et al., In IEEE Trans. Control Systems Technology, 10 (188-190), 2002 [0004]
• "Dynamics and Control of a Free-Piston Diesel Engine" by TA Johansen et al., In Proc. American Control Conference, Arlington, Va., 2001 [0004]

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 has a restoring force exercises in a reverse direction, and wherein the piston means to the electric linear actuator coupled, in which a force profile of a force-displacement curve is given for the piston device whose 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. 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 one or more parameters governing the expansion of the medium in the expansion area. Method according to one of the preceding claims, characterized in that the expansion space is a combustion space is and the piston device by combustion gases, which is the form expanding medium, is driven. Method according to one of the preceding claims, characterized in that parameters for the expansion space, which affect the piston movement and which are adjusted include at least one of the following parameters: one or more Times of at least one inlet opening, inlet closing, Outlet opening, outlet closing, injection, Ignition for a combustion, injection quantity, Gas mass in the expansion space. Method according to one of the preceding claims, characterized in that parameters of the return spring means, by which the restoring force is adjustable, at least one of the following parameters: pressure, temperature, maximum volume, Minimum volume in a resilience space, spring characteristic for the restoring force, prestressing of a spring device, Gas mass in the springback space. Method according to one of the preceding claims, characterized in that an energetic state measured from Sizes in the expansion space and / or a resilience space the return spring means and position data of the piston means is calculated. Method according to one of the preceding claims, characterized in that for determining the usable work one or more models for the determination of dissipation energy be used. Method according to one of the preceding claims, characterized in that from the useful work, which for a period has been calculated on the usable work of one or more several temporally following Kolbenhubbewegungen is closed. Method according to one of the preceding claims, characterized in that a stroke of movement of the piston means 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 in a specific compression ratio range is set. 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 in that a force-distance dependence the force defined is specified and / or varied. Method according to claim 12, characterized in that that during a period of piston movement the integral over the period is estimated and, where appropriate, 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 in that a compression means of the resilience space adjusted and / or varied. Method according to one of the preceding claims, characterized in that it is switchable from one or on a mode of operation in which the electric linear drive the course of movement the piston device active, and in particular in its path-time dependence, established. 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 active in its path-time dependence. Method according to one of the preceding claims, characterized in that the control at least two hierarchically structured levels, wherein in a first level on a Time scale smaller than the duration of a piston stroke on the free-piston engine arranged sensors emit signals and actuators the free-piston engine control, and in a second level, which is hierarchically superior to the first level is, a control calculation for the piston movement below Based on the calculated usable work of one or more previous complete strokes of the piston device is performed, being between the first level and the second level is a data exchange. Method according to claim 18, characterized that in the second level a regulation calculation for a subsequent piston stroke based on the determination of usable Work for a current and / or previous piston stroke he follows. A method according to claim 18 or 19, characterized by a third level which is hierarchically superior to the second level in which a monitoring of the piston movement is performed becomes. Method according to claim 20, characterized in that that in the third level a synchronization of the movement of several piston devices takes place. Method according to claim 20 or 21, characterized that in the third level a monitoring and / or control of load changes is performed. Method according to one of claims 20 to 22, characterized in that between the third level and the second level is a data exchange.