WO2005005838A1

WO2005005838A1 - Rotary screw compressor with multiple stages

Info

Publication number: WO2005005838A1
Application number: PCT/IB2004/000128
Authority: WO
Inventors: Alexander Gorban
Original assignee: Elthom Enterprises Limited
Priority date: 2003-07-14
Filing date: 2004-01-15
Publication date: 2005-01-20

Abstract

A compressor comprises two series of screw elements, each series comprising an outer (5;15), an intermediate (6;16) and an inner screw element (7;17), all screw elements having profiled outer/inner surfaces. Working chambers adapted to transport a working medium are formed and moved upon rotation of the screw elements. Between the first and second series, a channel (18) is provided for transporting working medium from one side to the other one. The shapes of the screw elements are chosen in such a manner that, when they are synchronized, the working medium which is transported in the working chambers is compressed. In other words, the volume which can be transported in the first series.

Description

ROTARY SCREW COMPRESSOR WITH MULTIPLE STAGES

FIELD OF THE INVENTION The invention relates to a volume screw machine of rotary type acting as a compressor.

PRIOR ART Volume screw machines of rotary type comprise conjugated screw elements, namely a female (enclosing) screw element and a male (enclosed) screw element. The female screw element has an inner profiled surface (inner screw surface, female surface), and the male screw element has an outer profiled surface (outer screw surface, male surface). The screw surfaces are non-cylindrical and limit the elements radially. They are centred about axes which are parallel and which usually do not coincide, but are spaced apart by a length E (eccentricity). A rotary screw machine of three-dimensional type of that type is known from US 5,439,359, wherein a male element surrounded by a fixed female element is in planetary motion relative to the female element. The working chambers of internally conjugated rotary volume screw machines are formed by kinematic mechanisms consisting of these male and female curvilinear elements. The transformation of energy of a working substance, a liquid or a gas, is realized during expansion, displacement (pushing) compression, etc., for instance in rotary screw pumps, hydro(pneumatic) motors, compressors, vacuum pumps, internal and external combustion engines. That transformation of a motion is based on an interconnected rotary motion of male and female elements, making mechanical curvilinear contact with each other and forming closed working chambers for a working substance which performs an axial motion when a relative motion of conjugated elements in space is performed. In most cases, the screw surfaces have cycloidal (trochoidal) shapes as it is for example known from French patent FR-A-997957 and US 3,975,120. The transformation of a motion as used in motors has been described by V. Tiraspolskyi, "Hydraulical Downhole Motors in Drilling", the course of drilling, p.258-259, published by Edition TECHNIP, Paris. In the prior art, an interconnected motion of male and female elements is very often provided by a mechanism of synchronization. If the number of shape-forming arcs on a female element is more than that on a male element, the synchronization is ensured by self-meshing of these elements, i.e. without resorting to special synchronizing mechanisms. The effectiveness of the method of transforming a motion in the screw machines of the prior art is determined by the intensity of the thermodynamic processes taking place in the machine, and is characterized by the generalized parameter "angular cycle". The cycle is equal to a turn angle of any rotating element (male, female or synchronizing link) chosen as an element with an independent degree of freedom. The angular cycle is equal to a turn angle of a member with independent degree of freedom at which an overall period of variation of the cross section area (opening and closing) of the working chamber, formed by the male and female elements, takes place, as well as axial movement of the working chambers by one period Pm in the machines with an inner screw surface by one period Pf in the machines with an outer screw surface. Volume screw machines are desired for use in a variety of environments, for example for use as a compressor. The known methods of transforming a motion in volume screw machines of rotary type with conjugated elements of a curvilinear shape realised in the similar volume machines have the following drawbacks: - limited technical potential, because of an imperfect process of organizing a motion, failing to increase a quantity of angular cycles per one turn of the drive member with the independent degree of freedom; - limited specific power of similar screw machines; - limited efficiency; - existence of reactive forces on the fixed body of the machine. In all cases, the longitudinal axes of internally conjugated screw elements are parallel. Sometimes, they have eccentricity and some of them are movable. Either a planetary motion or a differential motion is SUMMARY OF THE INVENTION It is an object of the invention to solve the above-mentioned problems and to provide an improved rotary screw machine acting as a compressor. A compressor according to the invention comprises two series of rotary screw elements, each series comprising an outer enclosing screw element having a profiled inner surface, an intermediate screw element which is both enclosing and enclosed, having a profiled inner and a profiled outer surface, and an inner enclosed screw element having a profiled outer surface. An outer series of screw elements encloses an inner series of screw elements. Working chambers adapted to transport a working medium are formed in each series and moved upon rotation of at least one screw element in each series. There is, according to the invention, a channel provided, namely between said first and said second series in order to transport working medium from a working chamber formed by the first series on one side of the screw elements to a working chamber formed by the second series on the axially opposite side of the screw elements. In the invention, the rotary motion of the screw elements is synchronized, and the screw elements are shaped in such a manner that upon rotation, working medium which is transported in the working chambers formed by the first series of screw elements is compressed when being further transported in the working chambers formed by the second series of screw elements. That feature can be expressed in a different way: The volume which is transported per time unit in the working chambers formed by the first series of screw elements is higher than the volume transported in the second series of screw elements. The volume variation per one rotation of the shaft is higher in the first series than in the second series. A compression of the working medium is a result thereof. In a preferred embodiment of the compressor according to the invention, a mechanical synchronisation of the rotary motion of the screw elements is provided. In particular, rotors in each series can be mechanically coupled to each other and will thereby rotate with angular velocities (defined about coaxial longitudinal axes in each set) which have values characterized by a predetermined ratio (one with respect to the other one). The synchronization helps to optimize the function of the machine. In a preferred embodiment, the inner enclosed screw elements are rotors. Moreover, the outer enclosing screw elements may be contra- rotors which are driven contra-rotatively to the rotors, for example by means of synchronizing device which can be placed at the axial end of the screw elements. In order to have the volume screw machine used as a compressor, the working medium emanating from the working chambers formed by the second series of screw elements cannot be simply exhausted. Instead, that working medium has to be guided (or led) to the next stage. Preferably, a further stage comprising screw elements is provided to which the working medium is led. In a preferred version of the compressor according to the invention, a central (rotary) shaft is provided which is partially hollow, and the working medium emanating from the working chambers formed by the second series of screw elements, i.e. the compressed working medium, is led through the hollow shaft too (to the next stage of the volume screw machine). The next stage can be comprised of a second set of enclosing and enclosed screw elements forming working chambers, and the second set can be spaced apart from the first and second series of screw elements along a central axis of the compressor. Preferably, a rotary motion of a screw element in the second set (or both screw elements) is synchronized with a rotary motion in the first and/or second series. That synchronization can take place by mechanical coupling via the central rotary shaft. It can be supported or it can be caused by the working medium itself. It will then be the second set which comprises an outlet for exhausting of the compressed working medium, and not the second series of screw elements. The first stage comprised of the first and second series can comprise an inlet for suction of air into the working chambers formed by the first series of screw elements. That inlet should not be connected to the second series such that the working medium (air) enters the second series via the above- mentioned channel. BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more apparent from the description of a preferred embodiment thereof which is given below with respect to the drawing, in which Fig.l shows a longitudinal cross section of the compressor according to the invention, Fig.2 shows a cross section along the lines II-II in fig.l of the volume screw machine according to the invention, Fig.3 shows a cross section along the lines III-III of fig.l of the volume screw machine according to the invention, Fig.4 illustrates the principle how an end profile of a screw surface of anyone of the conjugated elements can be designed, Fig.5 presents an electronic CAD construction of a screw surface of the conjugated element having a symmetry order of n_m=4.

DESCRIPTION OF A PREFERRED EMBODIMENT A compressor according to the invention, which is shown in fig.l, comprises two different sets of conjugated elements, namely a first set 1 forming a kinematic differential mechanism intended for suction and for compressing of air and a second set 2 forming a planetary mechanism intended for compression of air. In other words, the compressor according to a preferred embodiment is a rotary screw machine in which a motion is transformed and in which a continuous-cyclic change of working substance potential energy takes place in synchronism to a process of passing that working substance through working chambers of the different sections. The volume screw machine therefore generates working substance energy. A synchronizer 11 is provided which is intended to support the operation of the set 1. It is to be noted that the single sets 1 and 2 of the volume screw machine according to the invention are spaced apart from each other along the central axis Z of the machine. In other words, the sets 1 and 2 do not surround each other. Rather, they are placed one behind the previous one, or, in other words, one in the line of the previous one. They are all centred about the central axis of the machine. The different sets are coupled by both a mechanical link and by the action of the gaseous working substance, i.e. a gaseous link. The mechanical link between the mechanisms 1 and 2 is provided by a common shaft 4 which is partially hollow and is further provided with a crank 10 attached thereto. Air can pass from the mechanism set 1 into the mechanism set 2 through the hollow portion of the shaft 4. The sets 1 and 2 together form the inventive rotary screw compressing machine (compressor) of volumetric type. The first set 1 comprises two series (groups) of conjugated elements, namely a first series of elements 5, 6 and 7 and a second series comprised of elements 15, 16 and 17. The details are as follows: The first set comprises first female elements 5 and 15 having an inner profiled surface 105 and 115, respectively, wherein these female elements 5 and 15 are centred about a fixed axis Z, the symmetry axis of the volume screw machine. The female elements 5 and 15 have a symmetry order of 6. In the following, the notion symmetry order relates to a rotational symmetry of an end surface of these elements. The first set further comprises second elements 6 and 16 which are both male and female, i.e. comprise both an outer trochoidal surface 216, 116 and an inner trochoidal surface 206, 106. They have a symmetry order of 5 and are centred about an own axis Oe and Oie, respectively. They execute a planetary motion. Synchronizer elements 7 and 17 having an outer profiled surface 207 and 217, respectively, with a symmetry order of 4 are further provided. Between these elements, working chambers 100, 300 on the one hand and 200 and 400 on the other hand are provided. Between the elements 5, 6 and 7 on the one hand and 15, 16 and 17 on the other hand, a channel 18 is provided such that air which is transported in the working chambers 100 and 200 can be returned to the (in fig.l) lower side of the volume screw machine and then be further transported in the working chambers 300 and 400. The second set 2 comprises only two conjugated elements, namely a female element 8 having an inner profiled surface 108 with a symmetry order of 3 which is also centred about the axis Z, and a male element having an outer profiled trochoidal surface 209 with a symmetry order of 2, which is centred about the axis Og and which executes a planetary motion. Working chambers 14 are formed between these elements. The set 1 shown in fig.l which forms a differential mechanism has the three degrees of freedom of the mechanical rotation of the elements 5, 6, 7 and 15, 16, 17. Two of these degrees are independent degrees of freedom of a rotation. The planetary kinematic mechanism of transforming a motion of set 2 shown in fig.l has the two degrees of freedom of mechanical rotation of the element 9. One degree thereof is an independent degree of freedom of a rotation. It is to be noted that all screw elements in the volume screw machine according to the invention have a particular well-defined shape d_m which is constructed in the following manner as explained with respect to fig.4 in which the profile d_m has a symmetry order of n_m=5: One starts with the construction of a hypocycloid l^~ which has the parametric form (dependent on parameter t): x(t)=E cos(n_m-l)t+E(n_m-l)cos t y(t)=E sin(n_m-l)t-E(n_m-l)sin t. Such hypocycloids l^~ of a symmetry order n_m, (n_m+l), (n_m+2), ... (n_m+i) are those curves which are described by a point A of a circle having the radius Oι_A=E and the centre O_E and which has been rolled (without sliding) along the inner surface of another circle with radii equal to En_m, E(n_m+1), E(n_m+2), ... E(n_m+i) having a centre O_m as it is shown in fig.l. The points where the point A contacts these circles are indicated at B, C, D, F, I. An equivalent way of constructing such a hypocycloid l^~ of a symmetry order n_m, (n_m+l), (n_m+2)_f ... (n_m-ι-i) is based on describing the curve the point A of circles with radii E(n_m-1), E(n_m+1), ... E(n_m+l+i) and centre O2 which roll (without sliding) along the inner surface of circles having radii equal to En_mf E(n_m+1), E(n_m+2), ... E(n_m-ι-2+i). The profile D_m used for the screw elements in the present invention is, starting from the hypocycloid r, obtained by rolling a circle with radius r₀ which is for example equal to 2E, r₀=FR=2E in fig.4, along the hypocycloid V, wherein during the rolling, the centre of that circle moves along the hypocycloid. If ro is chosen to vary monotonally along the z-axis (the axis perpendicular to the plane of the drawing in fig.l), one obtains for the profile D_m the parametric equations (dependent on parameter t): x(t)=E(cos[(n/(n+l))[arcsin(sin t)-t]]+n cos[(arcsin(sin t)-t)/(n+l)) +r₀(z)cos[arcsin(sin t)-(arcsin(sin t)-t)/(n+l)]; y(t)=E(sin[(n/(n+l))[arcsin(sin t)-t]]+n sin[(arcsin(sin t)-t)/(n+l)]) +r₀(z)sin[arcsin(sin t)-(arcsin(sin t)-t)/(n+l)]; wherein n=n_m-l or n=nrl. Fig.5 shows a three-dimensional representation of a screw element obtained by using the construction described above. All of the outer surfaces 217, 216, 207, 206, 209 of the male elements 17, 16, 7, 6, and 9 and all of the inner surfaces 105, 106, 115, 116, 108 of the female elements 5, 6, 15, 16, and 8, respectively, are radially limited by such non-cylindrical screw surfaces constructed as explained above. It is to be noted that the symmetry order of these surfaces increases from the interior to the exterior. In the second set, the screw element 9 has a symmetry order of 2, whereas the screw element 8 has a symmetry order of 3. In the first set 1, the innermost element 17, has a symmetry order of 4 and is surrounded by an element 16, with a symmetry order of 5 which itself is then surrounded by an element 15, having an inner profiled surface 115, with a symmetry order of 6. This series of symmetry orders is then repeated starting from the element 7 to the element 5. The elements 5, 7, 15, 17, are set such that they can rotate about the axis Z. The axes Oe, Oie, Og of the elements 6, 16,and 9, respectively, are movable. It is to be noted that the axis Oe has an eccentricity of Eι=E with respect to the central axis Z, and that the axis Oi6 has an eccentricity of -Ez (less than Ei) with respect to the central axis Z. These axes Oe and Oie are placed on a line traversing the central axis. During rotation, their spatial relationship remains conserved. In other words, if the eccentricities are chosen in such a manner as to obtain a statically balanced volume screw machine, the screw machine is also dynamically balanced. The elements 6, 16 and 9 are set in the machine such that they can execute a planetary motion about the axis Z. The elements 6, 16, are set between the elements 5, 7; 15, 17; respectively, without any additional means to start the rotors into a planetary motion. The rotor 9 is hinged on a crank 10 of shaft 4. In the differential mechanism 1 and the planetary mechanism 2, the links are set such as to make possible the performing of volume continuously-cyclic suction with compression in the set 1, compression with release of working substance in working chambers 14 of the set 2. An inlet 19 allows for suction of working medium (air) into the working chambers 100 and 200. The channel 18 serves to transport that working medium to the second series of screw elements 15 to 16. In a cavity 20 provided in the compressor, the compressed working medium (compressed air) can circulate and enter the hollow portion (channel) 21 of the rotary shaft 4. The air is then led to a further cavity 22 provided in the next stage, i.e. in set 2 from starting from which the air (which is compressed) can enter the working chambers 14 formed between the elements 8 and 9. When having reached the axial end of that set (stage) 2, the compressed air can be exhausted via the exhaust 23, possibly to the next stage of an engine in which the compressor shown in Fig. 1 is used. A cross section of the planetary mechanism 2 is shown in fig.3. The planetary mechanism 2 consists of the central fixed stator 8 and the planetary rotor-satellite 9, the crank 10 at the shaft 4. With fixed element 8, the planetary motion of the element 9 is defined by the following parameters:

degrees (i.e. for 3 chambers 14 volume variation per one rotation of the shaft 4 is given by 3*360/360=3). The total volume in set 2 is given by

for rotation of the shaft 4. In each set, the rotation of the female screw elements 8 about the central axis may be carried out. Alternatively, the element 8 may be stationary. A planetary motion of the male screw element 9 conjugated with the first one may be carried out with the help of the synchronizing coupling link-crank 10 or a third (male) conjugated screw element which is coaxial to the first one. Turning now to the first set, one can choose three kinds of state of the first group of elements 5, 6 and 7: a) The rotation (or state of immobility) of the first element 5 about the central fixed axis and the rotation (or state of immobility) of the third element (synchronizer) 7 about the central fixed axis, b) A revolution of the axis Oβ of the second element 6 about the fixed central axis, and c) Swivelling of the second element 6 with the help of the synchronizing coupling link (male conjugated screw element 7) which is coaxial to the first one. These three kinds of state can be (mechanically) synchronized each with the respective one of the second group of elements 15, 16 and 17 of the first set 1, comprising: d) The rotation (or state of immobility) of the first element 15 about the central fixed axis and the rotation of third element (synchronizer) 17 about the central fixed axis, e) A revolution of the axis Oι₆ of the second element 16 about the fixed central axis, and f) Swivelling of the second element 16. The differential motion (comprising a planetary motion of the elements 6 and 16 and a rotation of the elements 5, 15 and 7, 17) in the set 1 is defined by the following parameters: ω_r0(5, 15)= 1; £Uro(7, 17)="1; (&Vo(7, 17)-C->re(6, 16))/( _ro(5, 15)-^re(6, i6))= ns, 15/07, 17 and ω_re(o-6),

i5)ns, i5-ω_r0(7, i7)r⁾ , i7)/(ns, 15-117, ι₇)=(6+4)/(6-4)=5; (ω_s(6, i6)-ω_re(6, i6))/(ω_r0(5, i5)-ω_re(6,

is/n₆, ιe and ω_m(e,

5)(6/5)+5=0.2. The total volume of the working chambers 100, 300 driving a rotation of the shaft 4 is given by

and

Vτ(3oo)=6V3oo360/90=24V₃oo. The total volume of the working chambers 200 and 400 during a rotation of the shaft 4 is given by V_T(2oo)=5V₂oo360/75=24V2oo and

Vτ(3θθ)=5V₃oo360/75=24V₃oo. From the above, it is evident that in the case of a differential motion of the elements, the angular cycle may be varied by changing relative angular velocities of the motion of screw elements forming working chambers. The angular cycle can be 90 degrees in set 1 and 360 degrees in set 2. The direction of the axial motion of the working medium along the Z-axis in the chambers 100, 200 and 300, 400 is defined by the direction of revolution of the centres Q_, Oi6 of the elements 6, 16 in set 1. As mentioned above, to choose the same directions of working medium motion, the revolution of the centres 0₆, Oi6 is given the same direction. If one wanted to choose opposite directions of working medium motion in the chambers 100, 200 on the one hand and 300 and 400 on the other hand, the revolution of the centres Oβ, Oie should be made contrarotatively. The set 1 comprised of the groups of elements 5, 6, 7 and 15, 16 and 17 forms a section of suction and preliminary compression in which continuously-cyclic stepped air compression is carried out. The group of elements 8 and 9 in set 2 ensures final compression and working substance release (emission). The working chambers 100, 200 of suction in the differential mechanism 1 are formed by the outer series of conjugated elements 5, 6, 7 which are disposed coaxially to eccentricity in the inner cavities of each other. Preliminary compression is performed when air is pumped into the inner series of conjugated elements 15, 16, 17. The synchronizing device 11 serves for driving the elements-rotors 5, 7 and 15, 17 in set 1 into rotation in different directions with equal angular velocities, i.e. contrarotatively. Simultaneously, the shaft 4 of rotor 9 in set 2 is driven into rotation. The chambers of final compression 140 in the planetary mechanism 2 are formed by the elements 8 and 9, wherein element 9 is hinged to rotate by virtue of self-synchronization on the crank 10 of the shaft 4. The other element 8 is fixed. The interrelationship of the rotary motions of the elements 5, 7 and 15, 17 in set 1 and 9 in set 2 is ensured by a synchronization device 14 having a transmission ratio of 3, a hinged connection of the element 9 with the shaft 4 in set 2, and a mechanical connection of the elements 5 and 15 (hinged to rotate in fixed body 13) in 1 with the shaft 4 by virtue of the synchronizing device 11 which is an inverter of the rotary direction having a transmission ratio of -1. The element 8 (stator) in set is mechanically rigidly connected to the fixed body 13. In parallel to the provision of the synchronization of the rotation of the elements inside of the differential mechanism 1, a synchronization of a rotation between the groups of differential and planetary mechanism 1 on the one hand and 2 on the other hand may be ensured. It is also possible to synchronize the rotations of the elements of the planetary and the differential mechanism through alternation of the symmetry orders of the elements of all the groups in 1, 4 or 2. The choice of a number of transformation groups and the scheme of how the planetary and differential kinematic mechanisms are combined is determined by the required angular extent and a combination of the values of the axial movement periods of the working chambers in- between in these mechanisms. The operation of the compressor shown in fig.l is as follows: A gaseous constituent of a working substance of an engine (e.g., air) is inserted into the set 1 by an open left end surface 19 of the elements 15, 16 and 17 (where arrows are shown in fig.l) of the first group. Further, it is fed to an open left end surface of the elements 15, 16 and 17 of the second group via a channel (a clearance). The above-mentioned groups of elements 5, 6, 7 and 15, 16, 17 (together with the elements 8, 9) form a rotary screw air-compressor 1 of volumetric type. Through the channel 21 in shaft 4, compressed air is led away from the set 1 and delivered to an open left end surface 22 of the elements 8 and 9 of the combustion set 2, namely into the chamber 14. The ratio of compression is 8(Vioo+ ₂oo) ₄. The combustion chamber 14 is filled by the six air volumes from the compressor 1. When the shaft 4 rotates, the conjugated elements 5, 6, 7, 15, 16 and 17 in set 1 limit and move the working medium of the suction section 1 (6 chambers between the elements 5, 6 and 15, 16 and 5 chambers between the elements 6, 7 and 16, 17 along the axis Z) by moving their contacts of conjugation at the two independent degrees of freedom of contra-rotative motion of the elements 5, 7, 15, 17 in set 1 as defined by the unit 11. When the shaft 4 rotates, the conjugated elements 8 and 9 in set 2 limit and move the three working chambers 14 of the combustion section 2 along the Z-axis by moving their contacts of conjugation at one independent degree of freedom of rotary motion of the elements 9 in set 2 as defined by a crank of the shaft 4. The interconnected rotary motions about the main axis Z of the machine and about their own axes occur in the sets 1 and 2 with the three degrees of freedom of a mechanical rotation. In the engine of Fig.l, the mechanically connected rotors 5, 15 and the mechanically connected contra-rotors 7 and 17 rotate simultaneously about the Z-axis in opposite directions with the same relative velocities cθ(5, i5)=-l and cθ(₇, i7)=l- The relative angular velocity ω_re of a line of centres O₆-O-Oi₆ of the rotors 6 about the Z-axis relative to the velocity of the rotors 5, 7 is given by ω_re=5, wherein the relative angular velocity ω_S(₆, i₆) of the rotors-satellites 6, 16 about their axes O₆, Oie is given by ω_S(e, i6)=0.2. The complete compression degree k of the engine is the product of the compression degrees of the sets 1 and 2, k=k₁k₂=8(Vιoo+V₂oo)/Vi4. The compression ratio l<ι in set 1 is determined as being the relation of the sum of the products of the total volume of the six chambers between the elements 5, 6 and of the total volume of the five chambers between the elements 6, 7 to the sum of the products of the total volume of the six chambers between the elements 15, 16 and of the total volume of the five chambers between the elements 16, 17 by a number of cycles of volume variation during one turn of the shaft 4, namely: kι=24(V₁oo+V2oo)/[24(V3oo+V₄oo)3=(Vιoo+V2oo)/2(V₃oo+V-,oo). The compression ratio k₂ in the set 2 is given as being the relation of the sum of the products to a product, i.e. the first product of the total volume of the six chambers between the elements 15 and 16 in set 1 and the second product of the total volume of the five chambers between the elements 16 and 17 in the set 1 to the product of the total volume of the three combustion chambers between the elements 8 and 9 in set 2 during one turn of the shaft 4, namely: k2=24(V₃₀o+V₄oo)/3V₁₄o=8(V₃oo+V4oo)/Vi4. It is possible to obtain any compression ratio in the chamber 14 as required in different engines by choosing suitable relations of the geometrical volumes of the chambers in the sets 1 and 2. It is also possible to provide any compression mode, an adiabatic or polytrope compression mode. The realization of the chamber 14 of the two periods of birotative twist of the elements 8 and 9 permits to carry out the combustion of fuel/air mixture on axial gas transmission from one chamber into another at constant volume. Thereby, the thermodynamic efficiency of the engine is increased. The contra-rotative rotation of the output shafts 4 and 5 in the section 1 which are set up by the inverter 11 permits the connection of the engine with contra-rotative organs such as air propellers or water vanes, contra-rotative cutting members of mowing machines, saws, crushers and so on. A connection may also be realized with a counter- rotating turbine or main rotors of an aircraft and so on.

Claims

1. A compressor, comprising: Two series of series of screw elements (5, 6, 7; 15, 16, 17), each series comprising: - an outer enclosing screw element (5, 15) having a profiled inner surface (105, 115), - an intermediate screw element (6, 16) which is both enclosing and enclosed, having a profiled inner (106, 116) and a profiled outer (206, 216) surface, - an inner enclosed screw element (7, 17) having a profiled outer surface (207, 217) - wherein an outer series (5, 6, 7) encloses an inner series (15, 16, 17) of screw elements - wherein working chambers (100, 200, 300, 400) adapted to transport a working medium are formed and are transported upon rotation of a at least one screw element in each series, - wherein a channel (18) is provided between said first and second series in order to transport working medium from a working chamber (100, 200) formed by the first series of screw elements (5, 6, 7) on one side of the screw elements to a working chamber (300, 400) formed by the second series of screw elements (15, 16, 17) on the axially opposite side of the screw elements, and - wherein the rotary motion of the screw elements is synchronized, and wherein the screw elements are shaped in such a manner that upon rotation, working medium which is transported in the working chambers (100, 200) formed by the first series of screw elements (5, 6, 7) is compressed when being further transported into the working chambers (300, 400) formed by the second series of screw elements (15, 16, 17).

2. The compressor of claim 1, comprising a mechanical synchronization of the rotary motion of the screw elements.

3. The compressor of claim 2, wherein rotors (7, 17) in each series are mechanically coupled to each other, thereby rotating with identical angular velocities.

4. The compressor of claim 3, wherein the inner enclosed screw elements (7, 17) are rotors.

5. The compressor of claim 4, wherein the outer enclosing screw elements (5, 15) are contra- rotors driven contra-rotatively to the rotors (7, 17) by using a synchronizing device (11).

6. The compressor of any of the proceeding claims, comprising a central rotary shaft (4) which is partially hollow, such that working medium emanating from the working chambers (300, 400) formed by the second series of screw elements (15, 16, 17) is led through said hollow shaft.

7. The compressor of claim 6, comprising a second set (8, 9) of enclosing and enclosed screw elements forming working chambers (14) to which said working medium is led via said hollow shaft (4).

8. The compressor of claim 7, said second set (2) being spaced apart from the first and second series of screw elements (1) along a central axis of the compressor.

9. The compressor of claim 7 or 8, wherein a rotary motion of a screw element in the second set

(8, 9) is synchronized with a rotary motion in the first and/or second series.

10. The compressor of any of claims 7 to 9, said second set comprising an outlet (23) for exhausting of the compressed working medium.

11. The compressor of any of the proceeding claims, comprising an inlet (19) for suction of air into the working chambers (100, 200) formed by the first series of screw elements (5, 6,

7).