GAS ROTARY SCREW COMPRESSOR

Abstract: A gas rotary screw compressor (1), in particular, for cooling gas suitable for low-power systems, the compressor having a casing (1a) having an intake conduit (6) and a delivery conduit (7); and the casing (1a) having, internally, a three-dimensional region shaped to follow the outer profile of the helical teeth (11b) of a male rotor (11) and the helical teeth (12b) of a female rotor (12), so as to define a first intake chamber (45) to minimize the load losses of the gas stream and so fill the casing (1a) with a maximum quantity of gas.

Description: GAS ROTARY SCREW COMPRESSOR TECHNICAL FIELD The present invention relates to a gas rotary screw compressor, m particular, for low-power air conditioning or refrigeration systems. BACKGROUND ART Rotary compressors normally comprise a casing housing a male rotor meshing with a female rotor. Such compressors, however, are used for handling large quantities of gas, m particular, cooling gas such as Freon. For low-power (3-7 HP) applications, reciprocating compressors have always been used on account of the problems encountered m adapting rotary compressors to low-power systems. One of the mam problems encountered when designing a rotary compressor for low-power, e.g. 3-7 HP, air conditioning or refrigeration systems is achieving optimum fill of the compressor to ensure an acceptable degree of efficiency. That is to say, difficulty is encountered in initiating the intake stage of compressors operating at fairly low male rotor rotation speeds; and, if severe load losses occur at the start of the intake stage - due to poor design of the conduits supplying gas to the rotors of the compressor - the gas expands. Both the above result in impairment of the fill factor of the compressor, which becomes more noticeable as the mass of gas being handled gets smaller. Moreover, if the gas supply conduits, the male and female rotors, and the gas/lubricant mixture discharge conduits are not designed properly, there is a danger the rotors may even operate like a fan and feed the gas, which should be aspirated, back to the supply conduits. DISCLOSURE OF INVENTION It is an object of the present invention to provide a gas rotary screw compressor designed to eliminate the aforementioned drawbacks. According to the present invention, there is provided a gas rotary screw compressor, in particular, for low-power air conditioning or refrigeration systems, as described and claimed in Claim 1. The gas compressed by the screw compressor could be any kind of gas, in particular, Freon or air. BRIEF DESCRIPTION OF THE DRAWINGS Two non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a side view of the compressor according to the present invention, which comprises three main bodies - in the example shown, a rotor body, a delivery body, and a lateral cover body - ideally defining an outer casing; Figure 2 shows a top plan view of the Figure 1 compressor; Figure 3 shows a front view, in the direction of arrow V : , of the Figure 1 compressor; Figure 4 shows, to a different scale, a longitudinal section A-A of the Figure 3 compressor; Figure 5 shows a side view of a male rotor forming part of the Figure 1 compressor; Figure 6 shows a front view, in the direction of arrow V 2 , of the male rotor in Figure 5; Figure 7 shows a side view of a female rotor forming part of the Figure 1 compressor; Figure 8 shows a front view, in the direction of arrow V 3 , of the female rotor in Figure 7; Figure 9 shows a longitudinal section A-A (not to scale) of the rotor body casing separated from the other two bodies; Figure 10 shows a front view (not to scale) of the Figure 9 rotor body casing; Figure 11 shows a cross section (not to scale) , along line B-B of the Figure 1 compressor, of the Figure 9 rotor body casing; Figure 12 shows the gap formed between the initially meshing ends of the male and female rotor teeth and a cusp on the inner surface of the rotor body casing; Figure 13 shows a top plan view of the delivery body; Figure 14 shows a front view, m the direction of arrow V 4 , of the Figure 13 delivery body; Figure 15 shows a cross section C-C of the Figure 14 delivery body; Figure 16 shows a side view of the lateral cover body; Figure 17 shows a longitudinal section D-D of the Figure 16 lateral cover body; Figure 18 shows a second embodiment of the compressor according to the present invention, m which s provided a separation chamber for knockout removal of the lubricating liquid from the gas; Figure 19 shows a longitudinal section E-E of the second embodiment in Figure 18. BEST MODE FOR CARRYING OUT THE INVENTION Number 1 m Figures 1-3 indicates a gas rotary screw compressor according to the present invention. In particular, compressor 1 is particularly suitable for compressing any cooling gas for low-power air conditioning or refrigeration systems Compressor 1 comprises an overall casing la and may be divided ideally into three bodies. More specifically, compressor 1 comprises a rotor body 2, a delivery body 3 and a lateral cover body 4, which are arranged in series and made integral with one another by mechanical fastening means. Figures 1-3 also show a shaft 5 for transmitting motion from a drive assembly (not shown) to rotary screw compressor 1; a gas intake conduit 6; a delivery conduit 7 for the compressed gas; and an injection conduit 8 for injecting a liquid lubricant for lubricating the rotors housed inside rotor body 2 and meshing as described in detail later on. The overall casing la comprises three external feet 9, which may be provided with respective internal threads by which to fasten compressor 1 as a whole to a supporting frame of any type (not shown) . As shown in more detail in Figures 4-8, rotor body 2 comprises a respective casing 10 which is' none other than a portion of overall casing la, and which houses a male rotor 11 and a female rotor 12. Male rotor 11 comprises a central body 11a (Figure 5) ; and a number of teeth lib formed integrally with central body 11a and which, in the example shown, are helical and five in number. In the embodiment shown, male rotor 11 is also formed integrally with shaft 5 and with a supporting shaft 13 at the opposite end of male rotor 11 to shaft 5. Each tooth lib of male rotor 11 has a passive side 14a and an active side 14b, and meshes, as described in detail later on, with a corresponding gap 15a (Figure 8) on female rotor 12. In the Figure 4-8 embodiment, the twist angle of each tooth lib is 310°, and the twist angle of each tooth 12b is (1.2x310°) . With reference to Figures 7 and 8, female rotor 12 is formed integrally with two supporting shafts 16 and 17 at opposite ends of female rotor 12, and also comprises a central body 12a on which are formed integrally a number of teeth 12b which, in the embodiment shown, are also helical, are six in number, and each adjacent pair of which defines a respective gap 15a. Gaps 15a are also six in number and, as stated, are engaged by teeth lib of male rotor 11 at the gas compression stage. Each tooth 12b of female rotor 12 also comprises a passive side 18a; and an active side 18b which contacts a corresponding active side 14b of a corresponding tooth lib on male rotor 11 at said compression stage. As shown in Figure 4, each of shafts 5, 13 formed integrally with male rotor 11 rests on a respective supporting member 19, 20 with a low coefficient of friction. Supporting member 19 is housed inside a respective seat 21 formed on the inner surface 22 of casing 10 of rotor body 2, while supporting member 20 is housed in a respective seat 23 formed in delivery body 3 (see also Figures 14, 15) . As shown in Figure 4, shafts 16, 17 supporting female rotor 12 are housed, at least partially, inside respective supporting members 24, 25 with a low coefficient of friction. Each supporting member 24, 25 is housed in a respective seat 26, 27; seat 26 is formed on the inner surface 22 of casing 10, and seat 27 in delivery body 3 (see also Figures 14, 15) . Shaft 5 has a keyway 5a for connection to a drive assembly (not shown) . The system is sealed by a first retaining ring 28 and a second retaining ring 29, both on the shaft 5 side. In addition to supporting member 20, shaft 13 is also supported by a pair of ball bearings 30, 31 housed in a seat 31a formed in lateral cover body 4 (Figures 16 and 17) . Bearings 30, 31 are gripped to each other and both against a face of delivery body 3 by an internally-threaded ring nut 32 screwed to a threaded end portion 33 of shaft 13. In addition to supporting member 25, shaft 17 supporting female rotor 12 is also supported by a ball bearing 34 housed in a seat 34a formed in lateral cover body 4 (Figures 16 and 17) . Bearing 34 is gripped against a surface of delivery body 3 by an internally threaded ring nut 36 screwed to a threaded end portion 37 of shaft 17. Ring nuts 33 and 36 are obviously also housed in respective seats 31a and 34a of body 4, together with respective bearings 30, 31 and 34. As shown in Figure 4, the three bodies 2, 3, 4 are made integral with one another by means of eight screws 38, only two of which are shown in Figure 4, and each of which comprises a head 38a and an at least partially threaded shank 38b. To connect bodies 2, 3, 4 to one another, the shank 38b of each screw 38 is first inserted through a corresponding through hole 39 formed in a connecting flange 40 of body 4 (Figures 16, 17), so that head 38a rests on the outer surface of flange 40; is inserted through a corresponding through hole 41 in body 4 (see also Figures 14, 15) ; and is then screwed inside a corresponding threaded dead hole 42 formed in casing 10 of body 2 (see also Figure 9) . Bodies 2, 3, 4 are thus packed tightly to one another as required. As shown in Figure 4, the two rotors 11, 12 have respective longitudinal axes Xi, X 2 of symmetry parallel to each other. Male rotor 11 has an outside diameter D em (Figures 5, 6) defining an outside circle enclosing the ends of teeth lib; and an inside diameter D r of an inner rolling circle defined at the bottom of the gaps defined by adjacent pairs of teeth lib. To enable male rotor 11 to mesh with female rotor 12, the outside diameter D e: - (Figures 7, 8) , defining a circle enclosing teeth 12b, of female rotor 12 is equal to rolling diameter D r , so that the ends of teeth 12b of female rotor 12 skim the bottom of the corresponding gaps defined by adjacent teeth lib on male rotor 11. In other words, as male rotor 11 meshes with female rotor 12, teeth lib of male rotor 11 engage corresponding gaps 15a on female rotor 12, and each active side 14b on male rotor 11 is gradually brought into contact with a corresponding active side 18b on female rotor 12 to transmit motion from male rotor 11 to female rotor 12. As stated, to ensure effective lubrication of the two meshing rotors 11, 12, a continuous stream of liquid lubricant is fed to rotor body 2 along conduit 8. Between the two rotors 11, 12 is defined a rolling line R 1 (Figure 4), which is simultaneously tangent to the circle of diameter D ef of female rotor 12, and to the rolling circle of diameter D r of male rotor 11. The outer surface of casing 10 of rotor body 2 has a flat portion 43 located at intake conduit 6 and having a number of threaded seats 44 by which to screw flat portion 43 easily to a connecting flange of a supply pipe (not shown) . As shown in Figures 2 and 3, an ideal plane P passes through the center C of intake conduit 6, perpendicularly to flat portion 43, is parallel to both axis X_ of male rotor 11 and axis X_ of female rotor 12, and contains, among other things, said rolling line The inner surface 22 of casing 10 of rotor body 2 has a three-dimensional region defining a first intake chamber 45 (see Figure 4) which, on the outside of casing 10, is m the form of a bulge defined laterally, and m projection, by two lines l 1 (Figures 1, 2) . In addition to inner surface 22, first intake chamber 45 is also defined inside casing 10 by an ideal compression plane P c (Figure 4) on which rest respective ends 46, 47 of male and female rotors 11, 12, and by the outer surfaces of rotors 11, 12 indicated, m projection, m Figure 9 by respective lines 1-, 1_ . First intake chamber 45 is substantially helical m shape, being so formed as to substantially reproduce the helical shape of teeth llr> and 12b, as shown by lines li, 1 2 on casing 10 (Figures 1, 2) . As shown m Figure 14, delivery body 3 comprises, on a face 49, a delivery outlet 48 which communicates hydraulically with delivery conduit 7 and is closed and opened periodically by the passage of respective ends 50, 51 of rotors 11, 12 (Figure 4) . The shape of delivery outlet 48 is determined m known manner on the basis of the geometry of rotors 11, 12; and the size of delivery outlet 48 m relation to that of intake conduit 6 depends on the type of gas compressed by compressor 1. Similarly, also as regards discharge of the compressed gas, compressor 1 may be likened to a two- stroke engine, the delivery outlet 48 of which is opened and closed cyclically by the passage m front of it of end 50 of rotor 11 and end 51 of rotor 12. Ends 50, 51 rest on face 49 of delivery body 3, so that rotors 11, 12 may be thought of as being confined between compression plane P ^ m body 2 at one end, and face 49 of body 3 at the other. In actual use, the gas flows into casing 10 along intake conduit 6 and m the form of threads substantially parallel to plane P; and, inside casing 10, the threads of gas are first parted by the action of rotors 11, 12 meshing and rotating m opposite directions to each other. After the threads are parted, which occurs at the connection of intake conduit 6 to inner surface 22 of casing 10, the cooling gas, entrained by the rotary movement of rotors 11 and 12, flows along portion 22a (Figures 4, 9) of surface 22. Rotors 11, 12 begin compressing the cooling gas at compression plane P c and, besides compressing it, also feed it, m the flow direction indicated by arrow F (Figure 4), to outlet 48 (Figure 14) and therefore to delivery conduit 7 communicating with a user device (not shown) . First intake chamber 45 is so formed as to accelerate the incoming cooling gas so that the gas itself initiates the desired pumping effect. The pumping effect is initiated on reaching a given number of revolutions, which depends on the type of cooling gas, and which, for commonly used cooling gases, is about 2500 rpm. As shown in Figures 9 and 11, first intake chamber 45 commences, on the rotor 11 side of compression plane P c , at a point Ci defined by an angle α. Angle α is obtained at ideal plane P c from a radius ri of a value substantially equal to D em /2 (Figures 5, 6) and joining axis Xi of rotor 11 (Figure 11) to a cusp 50a formed on inner surface 22 of casing 10 and extending longitudinally along the whole length of rotor body 2 in the direction of axes Xi, X?. For a 310° twist angle of helical teeth lib of rotor 11, angle α has been calculated to equal 70°. That is, for a 270° to 350° twist angle of teeth lib of rotor 11, angle α has been found to range between 50° and 80°. Similarly, on the rotor 12 side, first intake chamber 45 commences at a point C 2 defined, again at plane P c , by a given angle β, which is obtained from a radius r 2 of a value substantially equal to D ef /2, and therefore to D r /2, and joining axis X 2 of rotor 12 (Figure 11) to cusp 50a. For said twist angle (1.2x310°) of female rotor 12, angle β equals 55°. For a (1.2x270°) to (1.2x350°) twist angle of teeth 12b of rotor 12, angle β has been found to range between 45° and 65° . In addition to cusp 50a, the inner surface 22 of casing 10 also has a second cusp 51a (Figures 10, 11) opposite the first, and which extends longitudinally along only a portion of the length of rotor body 2, again in the direction of axes Xi, X . As shown in Figure 12, to avoid any cooling gas bypass areas which, in the case of low-power compressors 1, would cause the cooling gas to be fed back to intake conduit 6, the end edges of teeth lib and 12b are so formed as to minimize as far as possible a three-dimensional gap 52 between the end edges of teeth lib, 12b and cusp 50a or 51a. Starting from an ideal point I t located, in the Figure 12 plane, inside gap 52, and given the substantially bicylindrical shape of inner surface 22, the two-dimensional profiles of teeth lib, 12b may therefore be traced using known methods and subsequently developed in space. Moreover, for improved filling of casing 10, a second intake chamber 53 has inventively been provided on the opposite side of ideal compression plane P c with respect to first intake chamber 45. Part of the cooling gas admitted by conduit 6 is therefore fed to second intake chamber 53 and compressed m said flow direction indicated by arrow F (Figure 4 ) . To improve fill even further, second intake chamber 53 - which is substantially m the form of a pair of crossed rings - is so formed that its starting point C ^ m ideal plane P c is shifted by an angle γ obtained by rotating a radius r 3 - of a value substantially equal to D e ~,/2 - clockwise and perpendicularly to axis Xi of rotor 11 (Figure 11), so as to form, on the male rotor 11 side, a first delay region 53a to improve filling of body 2. Without first delay region 53a, the high rotation speeds of rotors 11, 12 could form low-pressure pockets inside body 2, so that the cooling gas is again fed towards intake conduit 6 as opposed to delivery conduit 7. In other words, first delay region 53a is defined angularly by angle ε between point C_ and point C 3 . For the same purpose, the end point d of second intake chamber 53 m plane P c is also shifted clockwise by an angle δ with respect to a radius r 4 perpendicular to axis X 2 of rotor 12 (Figure 11), so as to define a second delay region 53b defined by an angle λ which gives the distance between point C 2 and point C 4 . For an air compressor 1 - air being the most difficult gas to compress - tests have shown the best results to be obtained with an angle γ of 25° to 35°, and with an angle δ of 5° to 15° . The efficiency of rotary compressor 1 according to the present invention was found to range between 0.87 and 0.90, i.e. comparable with that of larger, higher- power rotary compressors. To minimize three-dimensional gap 52 as far as possible, teeth 12b of female rotor 12 are formed with a very small rounding radius. Also, to minimize the clearances between rotors 11, 12 and inner surface 22, active side 18b of each tooth 12b of female rotor 12 has a portion 54 (Figure 8) coated with low-friction material, such as TEFLON, deposited galvanically . Portion 54 ranges from 0.03 mm to 0.07 mm in thickness, and is defined in an annulus of a maximum diameter D max = 0.716 D era and a minimum diameter D m n = 0.65 D em . Male rotor 11, on the other hand, is ion bombarded with a titanium-nitride-based compound using a PVD (Physical Vapor Deposition) process to obtain an extremely hard outer surface. The mating of titanium-nitride-coated teeth lib and portions 54 of teeth 12b provides for reducing said clearances . Figures 18, 19 show an alternative embodiment to the one described with reference to Figures 1-17. Wherever possible, the same reference numbers as in the first embodiment are also used in the second. The main difference between the first and second embodiment lies in the flange of lateral cover body 3, which, in the second embodiment, is enlarged to connect a separating chamber 4a by which to separate the cooling gas from the liquid lubricant. In the second embodiment also, the cooling gas and the liquid lubricant are fed into casing 10 by intake conduit 6 and injection conduit 8 respectively. The cooling gas/liquid lubricant mixture compressed in rotor body 2 is fed to body 4 along delivery conduit 7 and a pipe 55 connected to the delivery conduit, and is fed into separation chamber 4a through an inlet 56 in a lateral wall of chamber 4a. Chamber 4a also has a delivery outlet 57 for the compressed gas separated at least partially from the liquid lubricant which, as a result of the swirl produced inside chamber 4a, settles by force of gravity on the bottom of chamber 4a. By means of a dip pipe 58 through a further outlet 59 in chamber 4a, the deposited liquid lubricant is fed back along a conduit 60 to injection conduit 8 and recirculated. A hole 62 with a screw cap 63 is provided at the bottom of chamber 4a to drain off the liquid lubricant. In the second embodiment in Figures 18 and 19, separating the liquid lubricant and the cooling gas immediately in chamber 4a and at compressor 1 greatly simplifies the cooling gas/liquid lubricant processing system downstream from compressor 1. The advantages of the present invention are as follows : - optimum filling of casing 10 of rotor body 2; reduction in the size of gaps 52 to prevent the cooling gas from being fed back to intake conduit 6; no clearance between rotors 11 and 12 or between rotors 11, 12 and the inner surface 22 of rotor body 2; 0.87 to 0.90 efficiency, comparable with that of larger rotary compressors; and as regards the second embodiment, immediate separation of the liquid lubricant and cooling gas at compressor 1, thus simplifying the cooling gas/liquid lubricant processing system downstream from compressor 1. Although the aforesaid desciption has been particularly focused on a cooling gas suitable for low- power systems, it is evident for a man skilled in the art to apply the teaching of the present invention to any screw compressor able to handle any kind of gas, in particular, air.

Claims: CLAIMS 1. A gas rotary screw compressor (1) comprising a casing (la) having an intake conduit (6) and a delivery conduit (7); said casing (la) also having an inner surface (22) and housing a male rotor with a longitudinal axis (Xi) of symmetry, and a female rotor (12) with a longitudinal axis (X 2 ) of symmetry; said male and female rotors (11, 12) having respective helical teeth (lib, 12b) ; and the compressor (1) being characterized in that: the meshing line (R of said male rotor (11) with said female rotor (12) substantially lies in a central plane (P) of said intake conduit (6); said plane (P) passing through the center (C) of said intake conduit (6) and being simultaneously parallel to said axes (Xi, X 2 ) ; and in that: at least one portion (22a) of the inner surface (22) of the casing (la) is shaped to follow the outer profile of said helical teeth (lib, 12b) so as to define a first intake chamber (45) to minimize, in said first intake chamber (45) , the load losses of the gas as the gas flows towards said male and female rotors (11, 12), and so fill said casing (la) with a maximum quantity of gas. 2. A compressor (1) as claimed in Claim 1, wherein said first intake chamber (45) follows the helical shape of said male and female rotors (11, 12) up to an ideal compression plane (P c ) inside said casing (la) . 3. A compressor (1) as claimed m Claim 2, wherein, on the male rotor (11) side, a point (C at which said first intake chamber (45) intersects said ideal compression plane (P = ) is separated by an angle (α) from a cusp (50a) on said inner surface (22) . 4. A compressor (1) as claimed m Claim 3, wherein, for a 270° to 350° twist angle of the teeth (lib) of the male rotor (11), sa d angle (α) ranges between 50° and 80° . 5. A compressor (1) as claimed m Claim 2, wherein, on the female rotor (12) side, a point (C 2 ) at which said first intake chamber (45) intersects said ideal compression plane (P c ) is separated by an angle (β) from a cusp (50a) on said inner surface (22) . 6. A compressor (1) as claimed m Claim 5, wherein, for a (1.2x270°) to (1.2x350°) twist angle of the teeth (12b) of the female rotor (12), said angle (β) ranges between 45° and 65°. 7. A compressor (1) as claimed m any one of Claims 2 to 6, wherein one end (46) of said male rotor (11) and one end (47) of said female rotor (12) rest on said ideal compression plane (P c ) . 8. A compressor (1) as claimed in Claim 7, wherein a second intake chamber (53) is also provided. 9. A compressor (1) as claimed m Claim 8, wherein said second intake chamber (53) is located behind said first intake chamber (45) with respect to said ideal compression plane (P c ) • 10. A compressor (1) as claimed in Claim 9, wherein projection of said second intake chamber (53) onto said ideal compression plane (P c ) defines a first point (C 3 ) and a second point (C 4 ) . 11. A compressor (1) as claimed in Claim 10, wherein said first point (C ) is separated by an angle (γ) from a radius (r 3 ) perpendicular to a longitudinal axis (X:) of symmetry of said male rotor (11) . 12. A compressor (1) as claimed in Claim 11, wherein said angle (γ) ranges between 25° and 35°. 13. A compressor (1) as claimed in Claim 10, wherein said second point (C 4 ) is separated by an angle (δ) from a radius (r 4 ) perpendicular to a longitudinal axis (X?) of symmetry of said female rotor (12) . 14. A compressor (1) as claimed in Claim 13, wherein said angle (δ) ranges between 5° and' 15°. 15. A compressor (1) as claimed in any one of the foregoing Claims, wherein said compressor (1) comprises a rotor body (2), a delivery body (3), and a lateral cover body (4) connected to one another by mechanical fastening means (38) . 16. A compressor (1) as claimed in Claim 15, wherein said rotor body (2) in turn comprises an injection conduit (8) for injecting a liquid lubricant. 17. A compressor (1) as claimed in Claim 15, wherein said male rotor (11) and said female rotor (12) are housed inside said rotor body (2) . 18. A compressor (1) as claimed in Claim 15, wherein said male rotor (11) is formed integrally with two respective shafts (5, 13) , and said female rotor (12) is formed integrally with two respective shafts (16, 17) . 19. A compressor (1) as claimed in Claim 18, wherein a first (5) of said shafts of the male rotor is supported by a first supporting member (19) with a low friction coefficient, while a second (13) of said shafts of the male rotor is supported by a second supporting member (20) with a low friction coefficient, and by a pair of bearings (30, 31) locked by means of a ring nut (32) . 20. A compressor (1) as claimed in Claim 19, wherein said first supporting member (19) is housed in a seat (21) inside the casing (10) of said' rotor body (2) ; said second supporting member (20) is housed in a seat (23) in said delivery body (3) ; and the pair of bearings (30, 31) and the ring nut (32) are housed in a seat (31a) in said lateral cover body (4) . 21. A compressor (1) as claimed in Claim 18, wherein a first (16) of said shafts of the female rotor is supported by a third supporting member (24) with a low coefficient of friction, while a second (17) of said shafts of the female rotor is supported by a fourth supporting member (25) with a low coefficient of friction, and by a bearing (34) locked by means of a ring nut (36) . 22. A compressor (1) as claimed in Claim 21, wherein said third supporting member (24) is housed in a seat (26) in the casing (10) of said rotor body (2) ; said fourth supporting member (25) is housed in a seat (27) in said delivery body (4); and the bearing (34) and the ring nut (36) are housed in a seat (34a) in said lateral cover body (4) . 23. A compressor (1) as claimed in any one of the foregoing Claims, wherein an active side (18b) of each tooth (12b) of said female rotor (12) is at least partially coated with a low-friction-coefficient material, such as TEFLON, deposited by means of a galvanic process. 24. A compressor (1) as claimed in any one of the foregoing Claims, wherein the teeth (lib) of said male rotor (11) are coated with a titanium-nitride-based compound deposited by a PVD method. 25. A compressor (1) as claimed in any one of the foregoing Claims, wherein the extension of a region (52), defined by any one tooth (lib) of the male rotor and any one tooth (12b) of the female rotor approaching one of the two cusps (50a, 51a) , is limited to prevent the formation of gas bypass regions. 26. A compressor (1) as claimed m any one of the foregoing Claims, wherein the outside diameter (D er ) of said female rotor (12) equals the rolling diameter (D r ) . 27. A compressor (1) as claimed m any one of Claims 15 to 26, wherein a chamber (4a) is provided for separating the liquid lubricant from the gas. 28. A compressor (1) as claimed m Claim 27, wherein the gas/liquid lubricant mixture is fed into said chamber (4a) through a lateral inlet (56) . 29. A compressor (1) as claimed m Claim 28, wherein the liquid lubricant deposited at the bottom of said chamber (4a) is recycled to said injection conduit (8) . 30. A compressor (1) as claimed m any one of the foregoing Claims, wherein said gas is a cooling gas, suitable, m particular, for low-power systems.

Inventors: DI BLASIO GABRIELE, TOMEI UMBERTO, VIGANO' DANILO, DI BLASIO, GABRIELE, TOMEI, UMBERTO, VIGANO', DANILO
Applicants: BLASIO GABRIELE DI, SAMPUTENSILI SPA, TOMEI UMBERTO, VIGANO DANILO, DI BLASIO, GABRIELE, SAMPUTENSILI S.P.A., TOMEI, UMBERTO, VIGANO', DANILO
Application year: 2000
Main classification: F04C18
IPC codes: F04C18, F04C29