WO2005078269A1

WO2005078269A1 - Rotary screw machine of volumetric type for use as an external combustion engine

Info

Publication number: WO2005078269A1
Application number: PCT/IB2004/000195
Authority: WO
Inventors: Alexander Gorban
Original assignee: Elthom Enterprises Ltd
Current assignee: Elthom Enterprises Ltd
Priority date: 2004-01-15
Filing date: 2004-01-15
Publication date: 2005-08-25
Anticipated expiration: 2006-07-15

Abstract

Volume screw machine as an external combustion engine.A volume screw machine can be used as an engine in which external heat is transformed into mechanical energy. It has to comprise a compressor stage (18) and a detander stage (20) which both comprise at least two series of rotary screw elements, and wherein in each stage an outer series of rotary screw elements (5, 6, 7) encloses an inner series (15, 16, 17) of rotary screw elements. Intermediate to these two stages, a heat exchanger stage (19) is provided. At least one rotary screw element (17) in the compressor stage (18) and one rotary screw element (17) in the detander stage (20) are mechanically coupled to each other Preferably, a common central shaft (24) is used for that purpose.

Description

ROTARY SCREW MACHINE AS AN EXTERNAL COMBUSTION ENGINE

FIELD OF THE INVENTION The invention relates to a volume screw machine of rotary type for use as an external combustion engine.

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 and internal engines. In the present case, the transformation of energy shall take place in an external combustion engine. 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 P_m in the machines with an inner screw surface by one period P_f in the machines with an outer screw surface. 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 provided. SUMMARY OF THE INVENTION It is an object of the invention to solve the above-mentioned problems and to provide an improved volume screw machine for use as an external combustion engine. Such an improved volume screw machine comprises a compressor stage which comprises at least two series of rotary screw elements, wherein an outer series of rotary screw elements encloses an inner series of rotary screw elements, a detander stage comprising once again at least two series of rotary screw elements, wherein the same feature is provided, that an outer series of rotary screw elements encloses an inner series of rotary screw elements. Furthermore, the volume screw machine comprises an intermediate heat exchanger stage, and the volume screw machine works in such a manner that the at least one rotary screw element in the compressor stage and at least one rotary screw element in the detander stage are mechanically coupled to each other. In other words, a rotary motion in the compressor stage is synchronized with a rotary motion in the detander stage. Thereby, the thermo dynamic cycles defined by the motion of working chambers formed between the rotary screw elements can be well-defined in order to predetermine the thermodynamical properties of the volume screw machine. In a preferred embodiment of the volume screw machine according to the invention, each series in the compressor stage and/or in the detander stage (preferably in both of them in the same way) comprises an outer enclosing screw element having a profiled inner surface, and 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. In a further preferred embodiment, between the first and second series in the compressor stage and/or the detander stage (and once again preferably in both of them in the same way), a channel is provided in order to transport working medium from a working chamber formed in one of these series of rotary screw elements to a working chamber formed at the other one of these series of rotary screw elements. It is to be noted that in the compressor stage, the channel transports working medium from a working chamber formed in the outer series of rotary screw elements to the inner series of rotary screw elements, whereas in the detander stage, a channel transports working medium from an inner series of rotary screw elements to an outer series of rotary screw elements. In both of the compressor and/or the detander stages, a mechanical synchronization of the rotary motion of at least one screw element in each series to a corresponding one of the other series is provided. In other words, the relationship of the formation of working chambers in the first series and the formation of working chambers in the second series and the transport of working medium in these working chambers can be well-defined. Preferably, rotors in each series are mechanically coupled to each other, thereby rotating with identical angular velocities. The rotors are preferably the inner enclosed screw elements. The most simplest and therefore preferred way of coupling the rotary motions in the compressor and the detander stages is to use once again these rotors. In other words, the rotors in each series are coupled to each other, i.e. two rotors in the compressor stage and two rotors in the detander stage. The rotors in each stage can then be mechanically coupled via a common central shaft. Of course, this shaft can just be a rod which connects the inner enclosed screw elements of both stages and rotates with them. Regarding the working medium, in a preferred embodiment, the working medium emanating from the compressor stage is guided in a guiding tube surrounding the common central shaft to the detander stage. The heat exchanger stage comprises heat exchanger tube surrounding that guiding tube. Therefore, the heat exchanger stage is nothing else than a tube which provides enough space for a counter-flow installation. In order to provide a closed circuit for the transport of working medium in the volume screw machine, a pipe guiding working medium from an outlet of the detander stage to an inlet of the compressor stage (via these heat exchanger tubes) can be provided. For the volume screw machine to act as an external combustion engine, a heat supply to the detander stage on the one hand and a heat with the drawing means coupled to the compressor stage on the other hand have to be provided. 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 volume screw machine 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 illustrates the principle how an end profile of a screw surface of anyone of the conjugated elements can be designed, Fig.4 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 volume screw machine for use as an external combustion engine, i.e. an engine in which external heat is transformed into mechanical energy comprises, according to the invention a compressor stage 18, a detander stage 20 and an intermediate heat exchanger stage 19. Both the compressor stage 18 and the detander stage 20 comprise two series of rotary screw elements, namely a first series of rotary screw elements 5, 6, 7 and a second series of rotary screw elements 15, 16 and 17. Each series comprises an outer enclosing screw element (elements 5 and 15) having a profiled inner surface 105, 115, an intermediate screw element (elements 6 and 16) which is both enclosing and enclosed and which has a profiled inner (106, 116) and a profiled outer 206, 216 surface, as well as an inner enclosed screw element 7, 17 having a profiled outer surface 207, 217. Between the first and second series, a channel is provided which shall transport working medium from a working chamber 100, 200 formed in one of these series of rotary screw elements to a working chamber 300, 400 formed in the other one of these series of rotary screw elements. In the compressor, the channel transports working medium from the outer series of rotary screw elements (5, 6, 7) to the inner series of rotary screw elements (15, 16, 17), whereas in the detander, the channel transports working medium from the inner series of rotary screw elements 15, 16, 17 to the outer series of rotary screw elements 5, 6, 7. The working chambers 100, 200 formed by the outer series of rotary screw elements 5, 6, 7 in both the compressor and the detander stages provide a higher volume (per cycle of rotation) than those formed by the inner series of rotary screw elements 15, 16 and 17. It is to be noted that a mechanical synchronization of the rotary motion of the inner enclosed screw elements in each series to the corresponding one of the other series is provided. Namely, in each series the rotors 7, 17 are mechanically coupled and do thereby rotate with identical angular velocities. The formation of the working chambers is thereby solely defined by the shape of the screw elements. This will be explained in more detail below. According to the invention, the rotors 17 acting as inner enclosed screw elements in the inner series of rotary screw elements 15, 16, 17 in both the compressor 18 and the detander stages 20 are mechanically coupled via a common central shaft 24. In other words, the rotors 7 and 17 of the compressor stage are mechanically coupled to the rotors 7 and 17 of the detander stage and rotate with the same angular velocity. Working medium emanating from the compressor stage 18 is guided in a guiding tube surrounding the common central shaft 24 to the detander stage 20. That tube surrounding the common central shaft is long enough to be surrounded by heat exchanger tubes. In other words, heat exchanger tubes are wound around that guiding tube such that a counter-flowing working medium can be cooled while heating the working medium which is guided in the guiding tube. A closed circuit for the transport of working medium in the volume screw machine as shown in Fig. 1 is provided. Namely, a pipe guiding the working medium from an outlet of the detander stage 20 (via the heat exchanger tubes in the heat exchanger stage 19) is connected to an inlet of the compressor stage 18. In the detander stage there is a heat supply supplying heat QD, whereas from the compressor stage, heat Q_c can be withdrawn (by cooling). It is to be noted that the compressor stage 18 and the detander stage 20 are essentially of equal shape, i.e. have equal cross sections. This is in particular the case with the single screw elements: They have the same average radii and the same thicknesses. Both the first and the compressor 18 and detander 20 stages comprise two groups of conjugated elements, namely a first group of elements 5, 6 and 7 and a second group comprised of elements 15, 16 and 17. The details of their placement are as follows: As mentioned above, both the compressor and the detander stages comprise 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 O₆ and Oι₆, 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 chamber 100, 300 on the one hand and 200 and 400 on the other hand are provided between which working medium can be transported via a channel. The stages 18 and 20 shown in Fig.l form a differential mechanism having 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. 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.3 in which the profile D_m has a symmetry order of n_m=5: One starts with the construction of a hypocycloid I^" 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 r 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 equa l 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 I^" of a symmetry order n_m, (n_m+l), (n_m+2), ... (n_m+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_m, E(n_m+1), E(n_m+2), ... E(n_m+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 ro which is for example equal to 2E, ro=FR=2E in fig.4, along the hypocycloid V, wherein during the rolling, the centre of that circle moves along the hypocycloid. If r₀ 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)) +ro(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)]) +ro(z)sin[arcsin(sin t)-(arcsin(sin t)-t)/(n+l)]; wherein n=n_m-l or n=nrl. Fig.4 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, of the male elements 17, 16, 7, 6, and all of the inner surfaces 105, 106, 115, 116, of the female elements 5, 6, 15, 16, 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. Once again: In the stages 18 and 20, 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. Element 5 is rigidly connected to the body 13. The elements 5, 7, 15, 17, are set such that they can rotate about the axis Z. The axes O₆, Oι₆ of the elements 6, 16, respectively, are movable. It is to be noted that the axis O₆ has an eccentricity of Eι=E with respect to the central axis Z, and that the axis Oi6 has an eccentricity of - E₂ (less than Ei) with respect to the central axis Z. These axes 0₆ and O_i6 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 and 16 are set in the machine such that they can execute a planetary motion about the axis Z. The elements 6 and 16 are set between the elements 5, 7; 15, 17 respectively, without any additional means to start the rotors into a planetary motion. The differential motion (comprising a planetary motion of the elements 6 and 16 and a rotation of the elements 15, 15 and 17, 17) in the stages 18 and 20 is defined by the following parameters: ω_r0(5, i5)= 1; ω_r0(7, i7)=-l; (ω_r0(7, i7)-ω_re(6, i6))/(ω_r0(5, i5)-ω_re(6, i5/ri7, i7 and ω_re(o-6),

i5)ns, i5-ω_r0(7, i )ri7, i7)/(ns, i5^_ri7, i7)=(6+4)/(6-4)=5; (ω_S(6, i6)-ω_re(6, iδ))/(ω_r0(5, i5)-ω_re(6,

ls/nβ, ιe and ω_m(6,

i5)-ω_re(6, i6))(ns, ls/nβ, i6)+ω_re(6, i6)=(l- 5)(6/5)+5=0.2. The total volume of the working chambers 100, 30O driving a rotation of the shaft 4 is given by V_T(ioo)=6Vιoo360/90=24Vι₀o and Vτ(3θθ)=6V₃oo360/90=24V₃oo. The total volume of the working chambers 200 and 400 during a rotation of the shaft 4 is given by

and Vτ(3θθ)=5V₃oo360/75=24V₃oo. The direction of the axial motion of the working medium along the Z-axis in the chambers 100, 200 is defined by the direction of revolution of the centres O₆, Oι₆ of the elements 6, 16 in the stages 18 and 20. As mentioned above, to choose the same directions of working medium motion, the revolution of the centres O₆, 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 Oδ, Oi6 should be made contrarotatively. The stageδ comprised of the series of elements 5, 6, 7 and 15, 16 and 17 forms a section of suction and preliminary compression in which continuously-cyclic stepped working medium compression is carried out. The working chambers 100, 200 of suction in the differential mechanism 1 are formed by the outer group 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 group of conjugated elements 15, 16, 17. 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 basic information is that the engine is an external combustion engine performing a Stirling cycle. The compressor stage 18 compresses a working substance such as helium or hydrogen under pressure of 40 to 400 atmospheres esothermically. The heat exchanger stage 19 serves for isochoric heat exchange of parts of a working substance in that Stirling cycle. Finally, the working substance is esothermically expanded in the detander 20. The isochoric heat exchange takes place between working substance withdrawn from an output of the detander stage 20 and some part of a working substance output from the compressor stage 18. As mentioned above, external heat Q_D of any kind (e.g. heat of organic fuel combustion) is fed to the detander stage 20 in order to be transformed into work. Heat Qc is withdrawn (cooled) in the compressor stage 18. In the machine (which is shown in Fig. 1), the complete cycle of an axial movement of working chambers between inner elements 6, 7 and 16, 17 at the given symmetry orders of its element and at the given planetary scheme of the kinematic interaction, occurs in 144 angular degrees of rotation of the output shaft 4, i.e. 2.5 times per revolution, wherein the rotors 5, 15 are fixed and the relative angular velocity of the central rotors 7, 17 is taken to be -1. The relative angular velocity Ω_H of a line of the centers Oe-O-Oie of the rotors 6, 16 about the axis X with respect to the velocity of the rotors 7, 17 for this case, is determined by degration Ω_H=M₇/2=+2, wherein M₇=4 is the symmetry-order of the elements 7, 17. The relative angular velocity Ω₆ of the rotors 6, 16 about the axis O₆, Oiβ is determined by the expression Ω₆=(Ω_H-4)/5=-0.4. Instead of performing a Stirling cycle, it is also possible to provide the condition of constant pressure for the regenerative heat exchanger, i.e. to use an Ericson cycle.

Claims

1. A volume screw machine for use as an engine in which external heat is transformed into mechanical energy, comprising: - a compressor stage (18) comprising at least two series of rotary screw elements, wherein an outer series (5, 6, 7) of rotary screw elements encloses an inner series (15, 16, 17) of rotary screw elements, - a detander stage (20), comprising: at least two series of rotary screw elements, wherein an outer series of rotary screw elements (5, 6, 7) encloses an inner series of rotary screw elements (15, 16, 17), - an intermediate heat exchanger stage (19), wherein at least one rotary screw element (17) in the compressor stage and one rotary screw element in the detander stage are mechanically coupled to each other.

2. The volume screw machine according to claim 1, - wherein said compressor stage (18) and/or in said detander stage (20), each series comprises: - 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, and - an inner enclosed screw element (7, 17) having a profiled outer surface (207, 217).

3. The volume screw machine according to claim 2, wherein between such first and second series, a channel is provided in order to transport working medium from a working chamber formed in one of these series of rotary screw elements to a working chamber formed in the other one of these series of rotary screw elements.

4. The volume screw machine according to one of the preceding claims, wherein in said compressor stage (18) and/or said detander stage (20), a mechanical synchronization of the rotary motion of at least one screw element (7) in each series corresponding one (17) of another series is provided.

5. The volume screw machine of claim -4, wherein rotors (7, 17) in each series are mechanically coupled to each other, thereby rotating with identical angular velocities.

6. The volume screw machine of claim 5 with the features of claim 2, wherein the inner enclosed screw elements (17) are rotors.

7. The volume screw machine of any of the preceding claims with rotors (17) acting as inner enclosed screw elements in the inner series of rotary screw elements in both the compressor (18) and the detander (20) stage, wherein said rotors in each stage are mechanically coupled via a common central shaft (24).

8. The volume screw machine of claim 7, wherein working medium emanating from the compressor stage (18) is guided in a guiding tube surrounding said common central shaft (24) to the detander (20) stage, and wherein said heat exchanger stage (19) comprises heat exchanger tubes being wound around said guiding cube.

9. The volume screw machine of claim 8, comprising a pipe for guiding working medium from an outlet of said detander stage (20) to an inlet of said compressor stage (18) via said heat exchanger tubes, thereby providing a closed circuit for the transport of a working medium in the volume screw machine.

10. The volume screw machine according to one preceding claims, comprising a heat supply to the detander stage (20).

11. The volume screw machine of any of the preceding claims, comprising a heat withdrawing means coupled to the compressor stage (18).