EP2668374A2

EP2668374A2 - Heat engine

Info

Publication number: EP2668374A2
Application number: EP12703950.1A
Authority: EP
Inventors: Walter Loidl
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-01-28
Filing date: 2012-01-05
Publication date: 2013-12-04
Anticipated expiration: 2032-01-05
Also published as: PL2668374T3; ES2551397T3; WO2012100275A2; AT510434B1; AT510434A4; EP2668374B1; WO2012100275A3

Abstract

Heat engine (1) having at least two cylinder/piston units (2-5) which in each case contain an expansion fluid (8) under a charging pressure, a device (16-20) for the individually controllable heat supply to the expansion fluid (8) of each cylinder/piston unit (2-5), and a control device (21) which controls the heat supply device (16-20), wherein the pistons (7) of the cylinder/piston units (2-5) are loaded by a common charging fluid (9), the charging fluid (8) is guided from the cylinder/piston units (2-5) via first non-return valves (12') to an inlet (11') and via second non-return valves (12'') which are directed in the opposite direction to an outlet (11'') of a hydraulic load (10), the control device (21) is equipped with a first pressure gauge (22'') for the pressure (p2) of the charging fluid (9) at the outlet (11'') of the load (10), and the control device (21) controls the heating and cooling phases of the heat supply device (16-20) at least depending on the measured outlet pressure (p2), in order to keep said pressure within a predetermined first range (P2,min, P2,max).

Description

Heat engine

The present invention relates to a heat engine, in particular for the low-temperature operation for the utilization of solar heat, waste heat from biological or industrial processes or the like, with:

at least two cylinder-piston units each containing a strain fluid under a biasing pressure, which changes its volume with a temperature change and thus moves the piston,

a device for individually controllable heat supply to the expansion fluid of each cylinder-piston unit, and

control means controlling the heat supply means for alternately heating and cooling each expansion fluid to thereby move the pistons,

wherein the piston of the cylinder-piston units are acted upon by a common biasing fluid, which exerts therein a biasing pressure on the respective expansion fluid.

Such a heat engine is known from WO 2009/082773. Effective expansion fluids often require a certain bias pressure to exhibit a significant coefficient of expansion in the desired operating temperature range. An example of this is liquid carbon dioxide, which under a pressure of about 60 - 70 bar when heated from 20 ° C to 30 ° C its volume changes by about 2.2 times.

In the heat engine known from WO 2009/082773, the common biasing fluid establishes a common, uniform biasing pressure in all of the cylinder-piston units by directly communicating with each other those cylinder chambers which face the cylinder chambers with the expansion fluids. The common biasing fluid achieves variable, dynamic coupling of the cylinder-piston units. In the known construction, the work of the cylinder-piston units is mechanically transferred to working pistons via piston rods. wear, which act on a common working fluid circulating in a hydraulic load circuit via check valves.

The invention has the aim of simplifying the decoupling of the work from the cylinder-piston units of a heat engine of the type mentioned initially and thus to further increase their efficiency.

This object is inventively achieved in that the biasing fluid is guided from the cylinder-piston units via first check valves to an input and via oppositely directed second check valves to an output of a hydraulic load in which it is subject to a pressure drop between input and output,

the control device is equipped with a first pressure gauge for the pressure of the biasing fluid at the outlet of the load, and

the control device controls the heating and cooling phases of the heat supply device at least in dependence on the measured output pressure in order to keep it within a predetermined first range,

wherein the expansion fluid contains liquid carbon dioxide and the lower range limit of said predetermined first range is greater than or equal to the condensing pressure of carbon dioxide at the operating temperature.

Liquid carbon dioxide is due to its high thermal expansion coefficient at room temperature, especially for operation of the heat engine in the low temperature range for the use of solar heat, waste heat from biological or industrial processes or the like. In addition, carbon dioxide resulting from combustion processes can be used for useful secondary recycling, in which it does not cause any greenhouse effect that is harmful to the environment. The heat engine of the invention thus also makes a contribution to the bypass-friendly C0 ₂ sequestration in the sense of a "Carbon Dioxide Capture and Storage" (CSS) process. The biasing fluid is used simultaneously as a working fluid and vice versa: By establishing two pressure levels in the biasing fluid, which are separated from each other via said check valves in the extension movement (high pressure) and retraction (low pressure) of the piston, a pressure difference can be obtained, which directly used for driving a hydraulic load and can be converted into mechanical work there. The control of the heating and cooling phases as a function of the measured output pressure of the hydraulic load see ensures that the biasing pressure reaches the required minimum biasing pressure for the operation of the expansion fluid at its low pressure level in any case. Said first predetermined range is selected so that its lower range limit is above the minimum biasing pressure of the expansion fluid.

A particularly advantageous embodiment of the heat engine of the invention has at least three cylinder piston units and is distinguished by the fact that the control device controls the number of cylinder-piston units which are in the heating phase at one time

Number of cylinder-piston units, which are in the cooling phase at the same time increases when the output pressure falls below the predetermined first range, and decreases when the output pressure exceeds the predetermined first range. This allows the operation to be adapted to extremely fluctuating environmental conditions. For example, in the low-temperature morning or evening hours of a solar system, approximately the same number of cylinder piston units can be operated in the heating and cooling phases, whereas in the midday heat few are rapidly heated

Cylinder-piston units face many slow-cooling cylinder-piston units.

According to a further feature of the invention, the fine adjustment control device can also shorten or lengthen each individual heating and / or cooling phase in order to control the output. gear pressure within the predetermined first range.

In a further advantageous embodiment of the invention, the control device is equipped with a second pressure gauge for the pressure of the biasing fluid at the input of the load and controls the heating and Abkühlphasen the heat supply device also in dependence on the measured input pressure to this within a predetermined second range to keep. Thus, e.g. the pressure difference for the hydraulic load can be controlled so that it corresponds to the pressure drop across the load or the work converted in the load is controlled by presetting the pressure difference.

Also, for controlling the output pressure, the controller may preferably increase the number of cylinder-piston units that are at a time in the heating phase against the number of cylinder-piston units that are in the cooling phase at the same time when the input pressure falls below given second range, and decrease when the input pressure exceeds the predetermined second range.

For fine adjustment of the output pressure control, the control device can also individually shorten or extend the heating and / or cooling phases in order to keep the inlet pressure within the predetermined second range.

Since the inlet pressure is always above the outlet pressure due to the pressure drop across the hydraulic load, it may be provided in a simplified embodiment that the first and second areas are equal, resulting in a minimum limit for the outlet pressure and a maximum limit for the inlet pressure.

Preferably, however, different control ranges are provided for the inlet pressure and the outlet pressure, ie the predetermined second area may be overlapping, then or at a distance from the first area, around individual minimum and maximum limits for the control of the inlet and outlet Building outlet pressures. Preferably, the two areas are at a distance from each other. Particularly preferably, the lower limit of the second range differs from the upper limit of the first range by approximately the pressure drop across the load, so that a minimum pressure difference can be guaranteed for the load.

The biasing fluid may be of any kind per se, for example compressed air. However, the biasing fluid is particularly preferably hydraulic fluid, resulting in a force-fitting and reliable pressure coupling. Preference is given to the input of the hydraulic load, a first elastic buffer and / or connected to the output of a second elastic buffer for the biasing fluid, so that short-term pressure fluctuations during switching operations or with tax-neungsungswendigen individual shortening or extensions of the heating and cooling phases temporarily absorbed can be.

The loading of the pistons with the biasing fluid can be carried out in various ways, for example by mechanical coupling of separate hydraulic biasing cylinders to the cylinder-piston units. The pistons of the cylinder-piston units are preferably designed as double-acting pistons, on one side of which the expansion fluid acts and on the other side of which the prestressing fluid acts, which results in a particularly simple construction.

A preferred embodiment of the invention is characterized in that the heat supply device for each cylinder-piston unit comprises a flowed through by a heat transfer medium heat exchanger, which is provided with a controlled by the control device check valve. By simply opening and closing the check valves, the times and durations of the heating phases can be specified, between which then the cooling phases arise.

The cooling phases can be accelerated if the heat supply device preferably also has a device for forced comprise cooling of the expansion fluids in the cooling phases. For this purpose, it is particularly favorable when the heat transfer medium is under pressure in the heating phase and the forced cooling device has a controllable pressure relief device for each heat exchanger. As a result, the heat transfer medium can be used simultaneously as a coolant, by causing it to cool down by releasing pressure.

Preferably, the pressure relief device comprises a negative pressure buffer, which can be connected via a controllable switching valve to the heat exchanger, whereby a sudden relaxation and thus particularly rapid cooling can be achieved.

Alternatively or additionally, the cylinder-piston units can be equipped with their own device for forced cooling of the expansion fluids in the cooling phases, which is controlled directly by the movement of their pistons. According to a particularly advantageous embodiment, such a forced cooling device for the cylinder-piston units comprises:

an auxiliary cylinder piston unit driven by the cylinder-piston unit and having at least one cylinder space,

a container in thermal communication with the expansion fluid having a vaporising agent,

wherein the container is connected via at least one by the piston movement of the cylinder-piston unit freewheelable check valve with said one cylinder chamber.

By appropriate control of the check valve can be achieved, for example, that during the heating and expansion of the expansion fluid - initially closed check valve - in the said one auxiliary cylinder chamber increasingly negative pressure, while the evaporation agent is compressed in the other auxiliary cylinder chamber at the same time. At the end of the expansion movement of the expansion fluid, the hitherto closed non-return valve is forcibly opened by appropriate control and the evaporation agent expands abruptly in the one auxiliary cylinder chamber, cools down thereby causing a forced cooling of the expansion fluid, which supports the retraction of the piston or accelerated. Preferably, provision is made for the container to be in fluid communication with the said one cylinder chamber of the auxiliary cylinder-piston unit via the other cylinder chamber and, downstream of it, the non-return valve.

In an alternative embodiment, the evaporation agent is compressed during the retraction movement of the cooling expansion fluid, remains in the extended state in the compressed state and then relaxes abruptly by the forced opening of the check valves in the end position of the extension movement. For this purpose, the container is preferably directly - i. not over the other cylinder space - via the check valve with said one cylinder space of the auxiliary cylinder piston unit in flow connection.

Preferably, the check valve is arranged directly in the piston of the auxiliary cylinder-piston unit and controlled by the striking of the piston in its one end position, resulting in a very compact design.

For the same reason, it is particularly beneficial if each

Cylinder-piston unit is axially assembled with its auxiliary cylinder-piston unit, with their pistons are connected to each other via a piston rod.

In this embodiment, it is preferably provided that the container is carried by the piston of the cylinder-piston unit and the flow connection from the container to the cylinder chamber (s) passes through the piston rod, resulting in a very compact construction and trouble-free integration of the forced cooling device using a minimum number - Moving parts achieved in the cylinder-piston units.

The invention will be explained in more detail with reference to embodiments illustrated in the accompanying drawings. In the drawings show:

Fig. 1 is a schematic diagram of a heat engine of the invention with four cylinder piston units; Figures 2a to 2c are timing diagrams of the control of the heat supply means and the resulting piston movements of the machine of Figure 1;

3 shows a block diagram of a practical embodiment of a heat engine according to the invention with two exemplary cylinder-piston units; and

4a and 4b are schematic diagrams of two different embodiments of cylinder-piston units with integrated auxiliary cylinder piston units as Zwangsabkühlein- direction.

Fig. 1 shows a heat engine 1 with four cylinder piston units 2-5. Each cylinder piston unit 2-5 has a cylinder 6 in which a piston 7 between a retracted position (shown at 2) and an extended position (shown at 5) can move.

The space 6 'in the cylinder 6 to the left side of each piston 7 is completely occupied by an expansion fluid 8. The expansion fluid 8 has a high coefficient of thermal expansion and expands when heated to move the piston 7 from the retracted to the extended position, or contracts as it cools to move the piston 7 back again. In the space 6 ', a mechanical stirring means (not shown) for the expansion fluid 8 can be arranged to improve the heat conduction therein.

In the example shown, the expansion fluid 8 is liquid

Carbon dioxide (C0 ₂ ), which at room temperature has a condensing pressure of about 65 bar. Liquid C0 ₂ shows in the range of 20 ° C to 30 ° C, a thermal expansion by about 2, 2 times. Instead of pure liquid carbon dioxide, it would also be possible to use mixtures of liquid carbon dioxide with substances other than expansion fluid 8.

In order to keep the C0 ₂ as expansion fluid 8 in its liquid state, the piston 7 is biased or biased with a biasing pressure greater than or equal to the condensing pressure in the direction of the expansion fluid 8. The biasing pressure is exerted by a biasing fluid 9 acting in the space 6 "to the right side of each piston 7, ie, the side of each piston 7 facing away from the expansion fluid 8. The biasing fluid 9 - preferably a hydraulic oil - circulates in all the cylinder-piston units 2-5 common hydraulic circuit, which includes a hydraulic load 10. The hydraulic load 10 is in for example a hydraulic motor with an input 11 'and an output 11 ", which is flowed through by the biasing fluid 9 and the kinetic energy of the biasing force 9 in mechanical work for an output shaft 11 ¹¹¹ converts. A pressure drop Δρ occurs between the input 11 'and the output 11 "of the load 10. Instead of a hydraulic motor, any other type of hydraulic load 10 which can be driven with a pressure gradient Δρ could also be used, as known in the art.

The biasing fluid 9 is led from the cylinder-piston units 2-5 via a set of first check valves 12 'and a first manifold 13' to the input 11 'of the load 10, and from its output 11 "via a second manifold 13" and a set second Check valves 12 "back to the cylinder chambers 6" of the cylinder-piston units 2 - 5. Each individual cylinder-piston unit 2 - 5 is thus a first, in the direction of the space 6 "to the input 11 'back and in the reverse direction blocking check valve 12' assigned, as well as a from the output 11 "to the room 6" out, in the reverse direction blocking second check valve 12 ".

When a piston 7 (arrow 14 ') is extended, the prestressing fluid 9 thus establishes a first pressure level pi at the inlet 11' of the load 10 (inlet pressure) via the first check valves 12 'and the first manifold 13', so to speak as "working fluid" Retraction of the piston 7 (arrow 14 ") closes the respective first check valve 12 'and opens the respective second check valve 12", so that the reduced by the pressure drop Δρ second pressure level p ₂ from the output 11 "of the load 10 (" output pressure ") via the second manifold 13 "into the respective back-acting cylinder piston units 2-5 and biased the expansion fluid 8.

The pressure of the biasing fluid 9 in the spaces 6 "of the cylinder-piston units 2 - 5 therefore oscillates between the input pressure (upper level) pi during extension (arrow 14 ') and the outlet pressure (lower level) p ₂ during retraction (arrow 14 "). As will be explained in more detail later, is ensured by appropriate pressure measuring and control devices that the lower pressure level, the output pressure p ₂ , the biasing fluid 9 in any phase of movement 14 ', 14 "the necessary operating pressure for the biasing fluid 9, eg the liquefaction pressure of liquid C0 ₂ , below and at the same time the desired or required pressure difference Δρ = Pi - P _{2 is maintained} at the load 10.

A first elastic intermediate store 15 'can be connected to the input 11' or the collecting line 13 ', for example a pressure container with gas filling and / or with an elastic membrane 15 in order to buffer short-term pressure fluctuations. Alternatively or additionally, it is also possible to connect a second such elastic intermediate store 15 "to the output 11" or the collecting line 13 ".

The heating of the expansion fluids 8 in the cylinder-piston units 2 - 5 is caused by means of a controllable heat supply means 16 - 20. In the example shown, the heat supply device 16 - 20 comprises a heat exchanger 16 for each cylinder-piston unit 2 - 5, which contacts the expansion fluid 8 in a heat-conducting manner and in which a heat transfer medium 17 circulates. The heat transfer medium 17 is e.g. heated by a solar panel 18 in a heat transfer circuit 19 (returns in Fig. 1 for the sake of clarity not shown).

The heat exchangers 16 may be of any type known in the art; Preferably, they are equipped with heat pipes for promoting the heat exchange and for the rapid and uniform distribution of the heat supplied in the expansion fluids 8. Each heat exchanger 16 is provided with a controllable check valve 20. The check valves 20 are alternately and intermittently opened by a central control means 21 to alternately heat and cool each cylinder-piston unit 2-5, thereby alternately expanding and contracting the expansion fluids 8 in the cylinders 6 and thus ultimately pushing the pistons 7 back and forth to move here. The piston movements are synchronized via the biasing fluid 9 circulating in the hydraulic circuit 10 - 13, in that the biasing fluid 9 flowing back from the outlet 11 'via the second check valves 12 "also assists and forces the retraction movement (arrow 14").

The control device 21 actuates the check valves 20 as a function of measured values of the inlet pressure pi and preferably also of the outlet pressure p ₂ which it receives from corresponding pressure gauges 22 ', 22 "which are connected to the inputs 11', 11" or their manifolds 13 ', A first, primary control target of the control device 21 is to keep the outlet pressure p ₂ within a first predetermined range P2, min _/ P2, max, which is determined in particular by the minimum biasing pressure for the expansion fluid 8, eg (temperature-dependent) about 50 - 60 bar with liquid carbon dioxide in the temperature range 20 - 50 ° C. In particular, the lower limit p ₂ , min of the first range is determined by the required minimum biasing pressure.

Further control objectives of the control device 21 may be that at the same time care is taken that the input pressure pi is within a predetermined (second) range Pi, min, Pi, max. The first and second regions may be identical or partially overlapping or immediately adjacent to or spaced apart, in which latter case the output pressure p _{2 is} in a lower region (pressure band) and the input pressure pi is in an upper region (pressure band) , With the latter embodiment, a minimum pressure difference or a minimum pressure drop Δρ = Pi - P _{2 are set} at the load 10, if such is required for the proper operation of the load 10, or the pressure difference for the load 10 are selectively varied, for example, to specify their energy conversion.

If the pressure drop Δρ at the load 10 is adjustable, ie the work of the load 10 can be controlled, the control device 21 can also control the pressure drop Δρ of the load 10 in further control targets, see optional control line ei. For example, the pressure ranges of input and output pressures pi, p ₂ that can be achieved on the basis of the current temperature conditions can be used to calculate a useful pressure difference pi-p ₂ and set this as the default for the pressure drop Δρ at the load 10.

The stated control objectives of the control device 21 are primarily with a control of the number of cylinder piston units 2 - 5, which are currently in the heating phase at a certain time, in relation to the number of those other cylinder piston units 2 - 5 , which are currently in the cooling phase at this time, achieved, as will now be explained in more detail with reference to FIG. 2.

In the upper timing diagrams of FIGS. 2a-2c, in each case the switching signals e ₂ -e _{5 of} the control device 21 for opening the shut-off valves 20 and in the lower timing diagrams the movements or paths s ₂ -s _{5 of} the pistons 7 of the cylinder Piston units 2 - 5 applied over time t.

FIG. 2 a shows a first operating state of the heat engine 1 for ambient conditions in which the cooling phase of the expansion fluid 8 is about three times as long as the heating phase, for example because the temperature of the heat transfer medium 17 is high and causes a rapid heating. The check valves 20 are cyclically opened for about a quarter of the stroke period, respectively. As can be seen, are located at a given time always a cylinder-piston unit 2-5 in the heating phase and three others in the cooling phase, ie the ratio of expanding cylinder-piston units 2-5 to contracting cylinder-piston units 2 - 5 is 1: 3 here.

2 b shows a second operating state of the heat engine 1, in which the check valves 20 are opened cyclically for a half-stroke period in each case. The ratio of cylinder-piston units 2-5 in the heating phase to cylinder-piston units 2-5 in the cooling phase here is 2: 2, which means approximately equal warm-up and cool-down phases, e.g. because of reduced heat, takes into account.

For example, decreases the temperature of the heat transfer medium

17 still further and thus further extends the heating phase, the control device 20 is in the third operating state of Fig. 2c, in which the ratio of cylinder piston units 2 - 5 in the heating phase to cylinder piston units 2 - 5 in the cooling phase. 3 : 1 is.

... The operating state Figure 2a, Figure 2b and Figure 2c is adjusted depending on the controller 21 by the output pressure p ₂ (and optionally also dependent on the input pressure p) falls below the output pressure p ₂ a predetermined lower Gren- ze p _2, min of its first range, in particular the liquefaction pressure of the expansion fluid 8 at the current operating temperature, the ratio of cylinder-piston units 2 - 5 in the heating phase to cylinder-piston units 2 - 5 is gradually increased in the cooling phase, eg 1: 3 -> 2: 2 -> 3: 1; If the output pressure p ₂ exceeds a predetermined upper limit p ₂ , _ma x, eg the condensing pressure plus a hysteresis threshold, then this ratio is successively reduced, eg 3: 1 -> 2: 2 -> 1: 3. As a further control target it can be taken into account that the inlet pressure pi is within its own second area i, _m i _n , P ₂ , max, or both areas are made coincidental, ie pi, _min = p ₂ , min and pi, _max = p ₂ , max, wherein the upper limit pi, _ma x = P ₂ , max, for example, is raised to the maximum permissible operating pressure of the heat engine.

When implementing the various control objectives of the control device 21, corresponding weightings can also be used and / or links between the regulatory objectives.

It will be appreciated that the discussed control may be extended to any number of cylinder-piston units 2-5, for example to 3, 5, 6, 7, 8, 12, 24, etc. cylinder-piston units. The more cylinder-piston units are available, the finer graduated the control can be done.

For fine adjustment, the control device 21 can additionally shorten or lengthen each individual heating or cooling phase, for example by offsetting the beginning ti of a heating phase and / or the beginning t _{2 of} a cooling phase or changing the duration t ₂ -ti. If heating or cooling phases of different cylinder-piston units 2 - 5 overlap in a short-term manner in a ratio (1: 3, 2: 2, 3: 1) that is greater or smaller than that selected with the aid of the aforementioned primary control, can corresponding short-term pressure fluctuations of the output pressure p ₂ and inlet pressure pi by means of the buffer 15 ', 15 "in the hydraulic circuit 10 - 13 are temporarily absorbed.

It should be noted that in a greatly simplified embodiment of the heat engine 1, which comprises only two cylinder piston units and thus allows only the single ratio 1: 1, the control device 21 can only perform the latter fine adjustment, with a corresponding restriction regarding exploitable operating conditions.

FIG. 3 shows a concrete realization and further development of the heat engine 1 of FIG. 1, wherein for the sake of clarity only two cylinder piston units 2, 3 are shown in place and the control device 21 with its measuring and control lines is not shown. However, it is understood that the embodiment shown in Fig. 3 can be extended to any number of cylinder-piston units. According to FIG. 3, a pump 23 conveys heat transfer medium 17, for example Refrigerant R 123 from Hoechst, from a supply 24 via a line 25 to the solar panel 18, from there via the line 19 and the check valves 20 to the heat exchangers 16, and There, via switching valves 26 and a return line 27 back to the reservoir 24. In the operating state shown in Fig. 3, the right check valve 20 is just opened and the left check valve 20 is closed, so that the right cylinder-piston unit 3 in the heating and Expansion phase and the left cylinder-piston unit 2 is in the cooling and contraction phase.

In order to accelerate the cooling phases, here the heat supply device 16-20 also comprises a device for forced cooling of the expansion fluids 8. The forced cooling device may be, for example, an optional feed path 28 for non-heated heat transfer medium 17, in order to provide it as shut-off valves 20 designed as a multi-way valve in the cooling phases in FIG to feed the heat exchanger 16. Alternatively, separate heat exchangers could be used for a separate cooling medium (not shown).

As shown, the forced cooling device preferably comprises a controllable pressure relief device which, after closing the shutoff valve 20, relaxes the heat transfer medium 17 which is still under the delivery pressure of the pump 23 via the switching valve 26 to a negative pressure intermediate store 29. The negative pressure in the vacuum buffer 29 is established via a suction line 30 from a Venturi -Ej ector 31 which is continuously fed via a line 32 by the pump 23 with heat transfer medium 17 in a circle. Due to the sudden expansion of the heat transfer medium 17 after the opening of the switching valve 26, the heat transfer medium 17 evaporates and thereby cools the expansion fluid 8 via the heat exchanger 16.

FIGS. 4a and 4b each show a further embodiment of a forced cooling device for the expansion fluids 8, which can be used alternatively or in addition to the aforementioned forced cooling device. The forced cooling device of FIGS. 4a and 4b is in each case integrated directly into one of the cylinder-piston units 2-5, and FIGS. 4a and 4b respectively show, by way of example, a cylinder-piston unit 2 equipped in this way.

In the embodiment of Fig. 4a, the cylinder-piston unit 2 is assembled with an auxiliary-cylinder-piston unit 40 which has a cylinder 41 and a piston 42. The piston 42 of the auxiliary cylinder-piston unit 41 is mechanically driven e.g. driven by a piston rod 43 of the piston movement of the cylinder-piston unit 2. For example, the cylinders 6 and 41 may be assembled together axially next to each other.

In the expansion fluid 8 of the cylinder-piston unit 2 protrudes in heat-conducting connection, a container 44 containing an evaporation means 45, which is in the operating position shown, for example up to a level 45 'liquid and above gaseous.

The interior of the container 44 is connected via a - formed here in the interior of the piston rod 43 - flow connection 46 with a cylinder chamber 47 of the auxiliary cylinder-piston unit 40 in flow communication. The opposite cylinder space 48 of the auxiliary cylinder-piston unit 40 is initially empty in the operating position shown in FIG. during the upward movement of the piston 42 is formed in the space 48 increasing negative pressure or - as far as the piston seals allow - vacuum.

The two chambers 47 and 48 on both sides of the piston 42 of the auxiliary cylinder-piston unit 40 are connected to one another via one or more check valves 49 in fluid communication. The check valves 49 are oriented to progressively compress the piston 42 as the negative pressure in the space 48 increases and the evaporation means 45 in the space 47, in the flow connection 46, and in the reservoir 44 progressively compresses is closed. As the expansion fluid 8 expands, the evaporation means 45 is thus compressed and progressively liquefied as the level 45 'rises while at the same time releasing negative pressure in the space 48.

The check valves 49 are now by the movement of the

Piston 42 controlled, u.zw. Forcibly open in their reverse direction when the piston 42 reaches its upper setting. For example, they are pushed open by corresponding pins or levers with which they strike against the inner end face of the cylinder 41. As a result, they are opened and the compressed, pressurized evaporation means 45 relaxes abruptly in the vacuum of the space 48, see arrows 50, whereby the evaporation means 45 abruptly cools. Through the heat-conductive connection of the container 44 to the expansion fluid 8 so that this is cooled abruptly and thus supports the cooling of the expansion fluid 8 and the retraction movement of the piston 7 and accelerated.

During the downward movement of the piston 42, the check valves 49 open in their forward direction, so that the evaporation agent 45 is again displaced from the space 48 in the space 47, in the flow connection 46 and in the container 44. When the piston 42 starts to move up again after reaching its down position, the check valves 49 close again and the process starts again. The compression, sudden relaxation (evaporation) and recompression of the evaporation agent 45 is a self-contained, closed cycle process, which positively supports the temperature circulation of the expansion fluid 8.

The embodiment of FIG. 4b differs from that of FIG. 4a in that the auxiliary cylinder-piston unit 40 has only one effective cylinder space 48, whereas the cylinder space 47 is open or unused, or eg additionally with a coolant (not shown) can be acted upon. The container 44 is here via the flow connection 46 and a deflection 46 'thereof in the piston 42 directly to the Cylinder chamber 48 in flow communication, wherein the check valve 49 in the flow connection 46, for example, the deflection 46 'acts, in the same manner as in Fig. 4a: During the downward movement of the pistons 7, 42 remaining from the last cycle in the space 48 evaporator 45 flows via the check valve 49 in the forward direction back into the container 44 and is compressed by the downward movement of the piston 42; during the upward movement of the pistons 7, 42, the check valve 49 closes and it comes again in the space 48 increasing negative pressure or vacuum until the piston 42 reaches its upper position and the valve 49, for example, by an end stop (not shown) pushed (Freed) is: The compressed in space 44 evaporation 45 relaxes abruptly on the freely controlled check valve 49 and the deflector 46 'in the space 48 (arrows 50), cools down and condenses until eg the level 45', whereby the Strain fluid 8 is forcibly cooled to support the now beginning retraction movement of the piston 7. The difference from the embodiment of FIG. 4a is therefore that in the embodiment of FIG. 4b the evaporation fluid 45 is compressed during the downward movement of the pistons 7, 42, whereas in the embodiment of FIG. 4a during the upward movement of the pistons 7, 42nd

In an alternative embodiment (not shown), the auxiliary cylinder-piston unit 40 or the components required for this cyclic process could also be constructed separately from the cylinder-piston unit 2 and coupled to it via corresponding flow connections and mechanical couplings.

The invention is not limited to the illustrated embodiments, but includes all variants and modifications that fall within the scope of the appended claims. Thus, for example, a larger number of cylinder-piston units could also be controlled in groups in groups in the same speed in order to control the circuit and control reducing effort; In this case, the cylinders 6 of a synchronizing group of cylinder-piston units could also share a common heat exchanger 16 and / or a common expansion fluid 8.

Claims

Claims:

1. heat engine (1), in particular for the low-temperature operation for the utilization of solar heat, waste heat from biological or industrial processes or the like., With:

at least two cylinder-piston units (2-5) each containing a biasing pressure under pressure expansion fluid (8) which changes its volume with a change in temperature and thus moves the piston (7),

a device (16-20) for individually controllable

Heat supply to the expansion fluid (8) of each cylinder-piston unit (2-5), and

control means (21) controlling the heat supply means (16-20) for alternately heating and cooling each expansion fluid (8) and thereby moving the pistons (7),

wherein the pistons (7) of the cylinder-piston units (2-5) are acted upon by a common biasing fluid (9) which applies therein a biasing pressure to the respective expansion fluid (8),

characterized in that the biasing fluid (9) from the cylinder-piston units (2-5) via first check valves (12 ') in a conventional manner to an input (11') and via oppositely directed second check valves (12 ") to a Output (11 ") of a hydraulic load (10) is guided, in which it is subject to a pressure drop (Δρ) between input and output (11 ', 11"),

the control device (21) is equipped with a first pressure gauge (22 ") for the pressure (p ₂ ) of the biasing fluid (9) at the outlet (11") of the load (10), and

the control device (21) controls the heating and cooling phases of the heat supply device (16-20) at least as a function of the measured output pressure (p ₂ ) in order to keep it within a predetermined first range (p2, min P2, max), wherein the expansion fluid (8) contains liquid carbon dioxide and the lower range limit (p ₂ , min) of said predetermined first range is greater than or equal to the condensing pressure of carbon dioxide at the operating temperature.

2. Heat engine according to claim 1 with at least three

Cylinder piston units (2-5), characterized in that the control means (21) the number of cylinder-piston units (2-5), which are at a time in the heating phase, compared to the number of cylinder-piston units, which at the same time in the cooling phase, increases when the output pressure (p ₂ ) falls below the predetermined first range (p2, min _/ P2, max), and decreases when the output pressure p ₂ exceeds the predetermined first range (p2, min _/ P2 , max).

3. Heat engine according to claim 1 or 2, characterized in that the control device (21) the heating and / or Abkühlphasen individually shortened or extended to the output pressure (p ₂ ) within the predetermined first range (p ₂ , min, P2, max).

4. Heat engine according to one of claims 1 to 3, characterized in that the control device (21) with a second pressure gauge (22 ') for the pressure (p) of the biasing fluid (9) at the input (11') of the load ( 10) and controls the heating and cooling phases of the heat supply means (16-20) also in dependence on the measured input pressure (pi) to keep it within a predetermined second range (pi, _min , pi, max).

5. Heat engine according to claim 4 with at least three cylinder-piston units, characterized in that the control device (21) the number of cylinder-piston units (2-5), which are at a time in the heating phase, compared to the number of cylinder Piston units (2 - 5), which are in the cooling phase at the same time, also increased when the input pressure (p) falls below the predetermined second range (pi, _m i _n , Pi, max), and also reduced, when the input pressure exceeds the predetermined second range (pi, _m in _# Pi, max).

6. Heat engine according to claim 4 or 5, characterized in that the control device (21) the heating and / or Abkühlphasen also individually shortened or extended to the input pressure (p) within the predetermined second range (pi, _m in, Pi, max).

7. Heat engine according to one of claims 4 to 6, characterized in that the first and the second region (p ₂ , min, P2, max, Pl, min, Pl, max) are the same.

A heat engine according to any one of claims 4 to 6, characterized in that the lower limit (pi, _m in) of the second region of the upper limit (p2, max) of the first region by about the pressure drop (Δρ) on the load (10 ) is different.

9. Heat engine according to one of claims 1 to 8, characterized in that at the input (11 ') of the hydraulic load (10), a first elastic buffer (15') for the biasing fluid (9) is turned on.

10. Heat engine according to one of claims 1 to 9, characterized in that at the output (11 ") of the hydraulic load (10), a second elastic buffer (15") for the biasing fluid (9) is turned on.

11. Heat engine according to one of claims 1 to 10, characterized in that the pistons (7) are double-acting piston, on one side of the expansion fluid (8) and on the other side of the biasing fluid (9) acts.

12. Heat engine according to one of claims 1 to 11, characterized in that the heat supply means (16 - 20) for each cylinder-piston unit (2-5) one of a heat transfer medium (17) through-flow heat exchanger (16), which with one of the control device (21) controlled shut-off valve (20) is provided.

13. Heat engine according to claim 12, characterized in that the heat exchangers (16) for forced cooling of the heat transfer medium (17) in each case with one of the Steuerein- direction (21) controlled pressure relief device (26, 29 - 32) are provided.

14. Heat engine according to claim 13, characterized in that the pressure relief device (26, 29 - 32) comprises a negative pressure buffer (29) which can be connected via a controllable switching valve (26) to the heat exchanger (16).

15. Heat engine according to one of claims 1 to 14, characterized in that the cylinder-piston units (2-5) are equipped with means (40-49) for forced cooling of the expansion fluids (8) in the cooling phases, which of the Movement of their pistons (7) is controlled.

A heat engine according to claim 15, characterized in that said forced cooling means (40-49) for each cylinder-piston unit (2-5) comprises:

one of the cylinder-piston unit (2-5) driven auxiliary cylinder-piston unit (40) having at least one cylinder chamber (48),

a container (44) in thermal conduction connection with the expansion fluid (8) with an evaporation means (45),

wherein the container (44) via at least one by the piston movement of the cylinder-piston unit (2-5) freely controllable check valve (49) with said one cylinder chamber (48) is connected.

17. Heat engine according to claim 16, characterized in that the container (44) via the other cylinder chamber (47) and this downstream of the check valve (49) with said one cylinder chamber (48) of the auxiliary cylinder Kolbenein- unit (40) in fluid communication.

18. Heat engine according to claim 16 or 17, characterized in that the check valve (49) directly in the piston (42) of the auxiliary cylinder-piston unit (40) and controlled by the abutment of the piston (42) in its one end position.

19. A heat engine according to any one of claims 16 to 18, characterized in that each cylinder-piston unit (2-5) is axially assembled with its auxiliary cylinder-piston unit (40), wherein its piston (7, 42) via a piston rod ( 43) are interconnected, and wherein preferably the container (44) from the piston (7) of the cylinder-piston unit (2-5) is supported.