Abstract:
In an expansion device for use in a working medium circuit, for performing a process sequence corresponding to that of a Clausius Rankine cycle or an Organic Rankine cycle, a working unit comprising two interleaved scroll elements is provided of which one is stationary whereas the other is supported for orbiting relative to the stationary scroll element so as to form separate expansion regions between the scrolls moving, upon orbiting of the movable scroll, from the center of the interleaved scroll elements circularly outwardly with increasing volumes in which a working medium admitted at the center can expand for driving the movable scroll element.

Description:
[0001]    This is a Continuation-In-Part application of pending international patent application PCT/EP2011/003764 filed Jul. 27, 2011 and claiming the priority of German patent application 10 2010 034 230.0 filed Aug, 7, 2011. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to an expansion device for use in a working medium circuit in which a working sequence corresponding to a Clausius-Rankine cycle can be carried out. The invention further relates to a method for operating such an expansion device. 
         [0003]    Internal combustion engines today have an efficiency level of up to 40 percent. The losses reside predominantly in heat transferred to a cooling medium and also in exhaust gas heat. 
         [0004]    The prior art resides in various methods and devices, by means of which electrical and/or mechanical energy is obtained from the exhaust gas heat and/or the cooling medium heat. 
         [0005]    By means of a Clausius Rankine cycle or an Organic Rankine cycle, thermal energy is converted into mechanical energy. An expansion device is normally arranged in such a Clausius Rankine cycle performed by axial piston machine or as a piston expander. 
         [0006]    It is the principal object of the present invention to provide an improved, in particular more energy-efficient, expansion device for use in a working medium circuit and an improved method for operating such an expansion device. 
       SUMMARY OF THE INVENTION 
       [0007]    In an expansion device for use in a working medium circuit, for performing a process sequence corresponding to that of a Clausius Rankine cycle or an Organic Rankine cycle, a working unit comprising two interleaved scroll elements is provided of which one is stationary whereas the other is supported for orbiting relative to the stationary scroll element so as to form separate expansion regions between the scrolls moving, upon orbiting of the movable scroll, from the center of the interleaved scroll elements circularly outwardly with increasing volumes in which a working medium admitted at the center can expand for driving the movable scroll element. The expansion ratio of the scroll-type working unit and/or a supply of working media to the scroll-type working unit can be changed. 
         [0008]    It is particularly advantageous that by means of the expansion device according to the invention a rotation movement, for example for driving an electric generator, can be directly provided. 
         [0009]    This rotation movement results in a low-vibration running of the expansion device, in particular in comparison with an alternating movement of a conventional piston expander, wherein the alternating movement must additionally be converted into a rotational movement for example via a gear device. 
         [0010]    The expansion device is characterized according to a particular embodiment by a fixed scroll element, a movable scroll element and an eccentric drive, wherein the fixed scroll element comprises a fixed scroll base plate and a fixed scroll spiral wall extending from the fixed scroll base plate, wherein the movable scroll element comprises a movable scroll base plate and a movable scroll spiral wall extending from the movable scroll base plate, and the movable scroll spiral wall and the fixed scroll spiral wall are in engagement with each other, so that they form at least one expansion region between the movable scroll element and the fixed scroll element. The movable scroll element can be moved circularly relative to the fixed scroll element by means of the eccentric drive and the size of the expansion region is changed during this circular movement along an expansion path. With such an expansion device, the number of components is advantageously reduced significantly in comparison with conventional expansion devices which are formed for example as an axial piston unit or as a piston expander. In particular the number of movable components is reduced. 
         [0011]    A working medium of the working medium circuit can advantageously be centrally supplied to the expansion device. 
         [0012]    According to an embodiment of the invention the working medium flowing in the working medium circuit can be supplied to the expansion device by means of a central inlet in the fixed scroll base plate. 
         [0013]    According to a further embodiment the working medium of the working medium circuit can be supplied to the expansion device by means of further inlets in the fixed scroll base plate along the expansion path. 
         [0014]    According to an advantageous embodiment the working medium of the working medium circuit can be fed to the expansion device with control and/or regulation by means of at least one cycle valve. 
         [0015]    According to an advantageous embodiment a separate cycle valve is assigned to each inlet in the fixed scroll base plate, wherein said cycle valve can advantageously be separately controlled and/or regulated. 
         [0016]    This variable supply of the working medium into the expansion device advantageously results in a variably adjustable pressure level of the working medium in the expansion device and a variably adjustable working medium throughput in the expansion device. 
         [0017]    This simple control and/or regulation of the working medium flow facilitates system design of the working medium circuit. 
         [0018]    An expansion pressure gradient within the expansion device is dependent upon the geometry of the scroll spiral walls. This geometry is thus purposefully adaptable in the design of the expansion device to the respective conditions in the working medium circuit. 
         [0019]    The scroll spiral walls are advantageously in the form of Archimedean spiral surfaces which are arranged displaced angularly by 180° relative to each other. 
         [0020]    It is thus possible with very simple means to vary the working medium flow in the working medium circuit and/or in the expansion device independently of a pump throughput of a pumping unit arranged in the working medium circuit. 
         [0021]    A pressure difference between a high pressure and a low pressure region, described hereinafter as an expansion gradient, of the working medium circuit can advantageously be reduced and/or adapted by means of an increase in the number of cycle valves arranged along the expansion path. 
         [0022]    Such a reduction results in numerous advantages. For example, through a simultaneous increase in the working medium throughput in the working medium circuit, overheating of the working medium can be avoided. 
         [0023]    Typically, a low expansion gradient is advantageous in the low engine load range, while a high expansion gradient is desirable in the high engine load range. By means of the expansion device, a particularly variable expansion of the working medium can be realized, whereby the working medium circuit and/or the expansion device is/are flexibly adaptable to changing heat energy inputs. 
         [0024]    During the process for operating an expansion device in a working medium circuit, wherein a process sequence is carried out within the working medium circuit, which process sequence corresponds to that of a Clausius Rankine cycle or an Organic Rankine cycle, according to the invention a movable scroll element is moved relative to a fixed scroll element by means of an eccentric drive in a circular movement so that the size of an expansion region formed between the movable scroll element and the fixed scroll element is changed during this eccentric drive movement along an expansion path. 
         [0025]    A working medium flow supplied to the expansion device is advantageously regulated and/or controlled by means of the separately or jointly actuated cycle valves. 
         [0026]    With this method, a variable expansion of the working medium in the expansion device is particularly advantageously facilitated. 
         [0027]    Therefore, virtually all the heat dissipation energy arising during operation of the internal combustion engine can be utilized in the working medium circuit and in the expansion device, whereby the expansion device can be adapted to heat dissipation energy quantities differing depending on the operating state. 
         [0028]    As an advantage of the invention, an increase in the degree of efficiency of the working medium circuit and the expansion device is achieved. By using the heat dissipation of the internal combustion engine, the degree of efficiency of the internal combustion engine is thereby further increased. 
         [0029]    The expansion device and the method for operating the expansion device can be used particularly advantageously within a given working medium circuit operated according to the principle of the Clausius Rankine cycle or the Organic Rankine cycle in order to achieve an optimized waste heat utilization of the internal combustion engine. 
         [0030]    The invention will become more readily apparent from the following description of an exemplary embodiment thereof with reference to the accompanying drawings: 
     
    
     
       Brief Description of Exemplary Embodiments 
         [0031]      FIG. 1  shows, schematically, a working medium circuit with expansion device, 
           [0032]      FIG. 2  shows, schematically, a variant of the expansion device, 
           [0033]      FIG. 3  shows, schematically, an alternative variant of the expansion device, and 
           [0034]      FIG. 4  shows schematically, an illustration of the sequence of the operatic of the expansion device. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0035]    Parts corresponding to each other are provided in all the drawings with the same reference numerals. 
         [0036]    The expansion device  1  is a part of a working medium circuit AK, in which a working medium AM is conveyed, and wherein a process sequence carried out in the working medium circuit AK corresponds to that of a so-called Clausius Rankine cycle or an Organic Rankine cycle, as shown in  FIG. 1 . 
         [0037]    This working medium circuit AK comprises a pumping unit F, a heat exchanger W, the expansion device  1  and a condenser K. 
         [0038]    In the process sequence of the Clausius Rankine cycle or the Organic Rankine cycle, the liquid working medium AM is supplied in a working medium flow circuit by the pressurizing unit F to the heat exchanger W. In the heat exchanger W, the liquid working medium AM is heated under constant pressure using the heat dissipation of an internal combustion engine in so that it evaporates. 
         [0039]    The heat exchanger W can thereby use—for example as an exhaust gas heat exchanger, exhaust gas recirculation heat exchanger and/or cooling medium heat exchanger—an exhaust gas heat and/or a heat of a cooling medium heat of the internal combustion engine in order to heat and evaporate the liquid working medium AM. 
         [0040]    The vaporized working medium AM under is fed high pressure to the expansion device  1  and is expanded in an adiabatic or virtually adiabatic expansion to a vapor AM of normal pressure. In the expansion device  1 , a kinetic energy of the vaporized working medium is thereby converted into a mechanical energy. 
         [0041]    For example the mechanical energy generated can be converted into electric energy if the expansion device  1  is coupled with an electric generator (not shown in further detail), This electric energy can be used for example to drive an electric motor (not shown in greater detail) which supplies additional power to the internal combustion engine. Alternatively, the mechanical energy produced by the expansion device  1  could be supplied directly to the internal combustion engine (not shown in greater detail) for the purpose of support. 
         [0042]    After expansion, the vaporized working medium AM is fed to the condenser K, in which the vaporized working medium AM is condensed isobarically or virtually isobarically by cooling and thus converted into a liquid state, and the liquid working medium AM is returned to the pressurizing unit F on the input side. 
         [0043]      FIG. 2  shows schematically an embodiment of the expansion device  1  according to the invention. 
         [0044]    The expansion device  1  is in the form of a scroll-type working unit, through which the working medium AM flowing in the working medium circuit AK can flow in the expansion direction. 
         [0045]    The expansion device  1  comprises a fixed scroll element  2  and a movable scroll element  3 . The fixed scroll element  2  has a round or disc-form fixed scroll base plate  4  and a fixed scroll spiral wall  5  which extends from the fixed scroll base plate  4  in the direction of the movable scroll element  3 . An inlet  6 . 1  is formed essentially in the middle of the fixed scroll base plate  4 , for example centrally, for admission of the working medium AM from the working medium circuit AK. 
         [0046]    The movable scroll element  3  has a round or disc-form movable scroll base plate  7  and a movable scroll spiral wall  8  which extends from the movable scroll base plate  7  in the direction of the fixed scroll element  2 . 
         [0047]    The scroll spiral walls  5  and  8  are thus formed as so-called Archimedean spiral surfaces which are arranged angularly displaced by 180° (clockwise) relative to each other. 
         [0048]    An expansion ratio within the expansion device  1 , which describes a pressure difference between a high pressure and a low pressure region of the expansion device  1 , depends upon the geometry of the scroll spiral walls  5  and  8 . This geometry can thus be purposefully adapted in the construction of the expansion device  1  to the respective conditions in the working medium circuit AK. 
         [0049]    The fixed scroll spiral wall  5  is in engagement with the movable scroll spiral wall  8  in such a way that it forms at least one expansion region  9 . 1  between the fixed scroll element  2  and the movable scroll element  3 . 
         [0050]    In dependence upon the geometry of the scroll spiral walls  5  and  8 , further expansion regions  9 . 2  to  9 . 5 , as shown in  FIGS. 3 and 4 , can be formed between the fixed scroll element  2  and the movable scroll element  3 . 
         [0051]    These expansion regions  9 . 1  to  9 . 4  can be changed in size and move in a manner to be described in further detail circularly along an expansion path between the scroll spiral walls  5  and  8 . 
         [0052]    The expansion path is the path defined by each expansion region  9 . 1  to  9 . 5  during an orbital movement of the movable scroll element  3  relative to the fixed scroll element  2 . 
         [0053]    An eccentric drive (not shown) is arranged on the movable scroll base plate  7 , said eccentric drive facilitating on the one hand a orbital movement of the movable scroll element  3  relative to the fixed scroll element  2  and on the other hand supplying a mechanical energy in the form of a rotation movement of a shaft (not shown) connected to the eccentric drive. 
         [0054]    The eccentric drive is advantageously formed in such a way that the movable scroll element  3  can be moved relative to the fixed scroll element  2  along a circle, wherein the movable scroll element  3  does not rotate. 
         [0055]    The working medium AM flowing in the working medium circuit AK can be fed to the expansion device  1  by means of the inlet  6 . 1 . A conventional cycle valve is assigned to this inlet  6 . 1  (not shown in greater detail), said cycle valve facilitating a control and/or regulation of the working medium flow which can be supplied to the expansion device  1 . 
         [0056]    By means of the two outlets  10 . 1  and  10 . 2 , the expanded working medium AM can be removed from the expansion device  1 . These outlets  10 . 1  and  10 . 2  are formed periodically, in dependence upon the orbital movement of the movable scroll element  3  relative to the fixed scroll element  2 , at the respective outer end  11 . 1  and  11 . 2  of the scroll spiral walls  5  and  8 . 
         [0057]      FIG. 3  shows, schematically, an alternative embodiment of the expansion device  1  according to the invention. 
         [0058]    Besides the inlet  6 . 1  described in  FIG. 1 , further inlets  6 . 2  to  6 . 5  are arranged in the fixed scroll base plate  4 . These inlets  6 . 2  to  6 . 5  are arranged along the expansion path in such a way that the expansion regions  9 . 1  to  9 . 5  can be accessed during their movement along the expansion path with working medium AM from the inlets  6 . 2  to  6 . 4 . 
         [0059]    A separate cycle valve is assigned to each inlet  6 . 1  to  6 . 5  (not shown in greater detail), By means of these separately or jointly actuated cycle valves, an individual control and/or regulation of a working medium flow which can be fed to the expansion device  1  by means of the inlets  6 . 1  to  6 . 5  is facilitated. 
         [0060]      FIG. 4  shows, schematically, an illustration of the sequence of the operation of the expansion device  1 . 
         [0061]    In order to illustrate the operating behavior of the expansion device  1 ,  FIG. 4  is shows the method steps S 1  to S 4  in a circular diagram. 
         [0062]    In method step S 1 , the centrally arranged expansion region  9 . 1  is filled by means of the inlet  6 . 1  under high pressure from the working medium circuit AK. The outlets  10 . 1  and  10 . 2  are closed. Further expansion regions  9 . 2  to  9 . 5  are formed between the scroll spiral walls  5  and  8  along the expansion path. 
         [0063]    By the expansion of the working medium AM and the resulting force acting on the scroll spiral walls  5  and  8 , the movable scroll spiral wall  8  and thus the movable scroll element  3  are triggered to carry out an orbital movement relative to the fixed scroll element. 
         [0064]    In the method step S 2 , this movement circling in clockwise direction is shown following a movement of the expansion regions of 90°. The expansion regions  9 . 1  to  9 . 3  have enlarged their volume in the process. This results in a pressure and/or temperature reduction of the working medium AM, hereinafter described as expansion. The expansion regions  9 . 4  and  9 . 5  have reached their greatest volume expansion and the outlets  10 . 1  and  10 . 2  are opened. The expanded working medium AM is fed through the outlets  10 . 1  and  10 . 2  to the working medium circuit AK and liquefied in the condenser K. 
         [0065]    In the method step S 3 , the orbital movement of the movable scroll element  3  is shown after a movement angle of 180°. The expansion regions  9 . 1  to  9 . 3  enlarge the volume during movement along the expansion path. The outlets  10 . 1  and  10 . 2  reach their greatest opening cross-section and thus support a backflow of the working medium AM into the working medium circuit AK. 
         [0066]    In the method step S 4 , the orbital movement of the movable scroll element  3  is shown after a movement angle of 270°. By the orbital movement of the movable scroll element  3  relative to the fixed scroll element  2 , a new expansion region  9 . 1 ′ has been formed while the expansion regions  9 . 1  to  9 . 3  become larger and continue their movement along the expansion path in the direction toward the outlets  10 . 1  and  10 . 2 . The outlets  10 . 1  and  10 . 2  are virtually completely closed and as a result the expansion regions  9 . 4  and  9 . 5  are eliminated in the further progression of the orbital movement of the movable scroll element  3 . 
         [0067]    After the completion of a full orbital movement of the movable scroll element  3  relative to the fixed scroll element  2 , the sequence begins again in the method step S 1 . 
         [0068]    With the force generated by the pressurized working medium AM and its expansion, a shaft (not shown) of the expansion device  1  is driven by means of the eccentric drive. An electric generator can thereby be directly driven by the expansion device  1 . 
         [0069]    This rotation movement of the shaft of the expansion device  1  advantageously results in a low-vibration running of the expansion device  1 . 
         [0070]    Further inlets  6 . 2  to  6 . 5  (not shown in further detail in  FIG. 4 ) can be arranged in the fixed scroll base plate  4  along the expansion path. By way of these additional inlets  6 . 2  to  6 . 5  additional expansion medium may be supplied to the expansion regions  9 . 1  to  9 . 5  during their circulation in the working medium circuit AL. 
         [0071]    A variably adjustable pressure level of the working medium AM in the expansion device  1  and/or a variably adjustable working medium throughput in the expansion device  1  advantageously result(s) from this variable introduction of the working medium AM into the expansion device  1 . 
         [0072]    This simple control and/or regulation of the working medium flow AM in the expansion device  1  advantageously facilitates a system design of the working medium circuit AK and the control and or regulation of the working medium circuit AK. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Expansion device 
           2  Fixed scroll element 
           3  Movable scroll element 
           4  Fixed scroll base plate 
           5  Fixed scroll spiral wall 
           6 . 1  to  6 . 5  Inlet 
           7  Movable scroll base plate 
           8  Movable scroll spiral wall 
           9 . 1  to  9 . 5  Expansion region 
           9 . 1 ′ Expansion region 
           10 . 1 ,  10 . 2  Outlet 
           11 . 1 ,  11 . 2  End 
         AK Working medium circuit 
         AM Working medium 
         F Pumping unit 
         K Condenser 
         S 1  to S 4  Method steps 
         W Heat exchanger