SCREW COMPRESSOR FOR INTERNAL COMBUSTION ENGINES

Abstract: In a screw compressor, especially adapted for use as a supercharger for an internal combustion engine, a housing is composed of a barrel section (2) made from preferably aluminium and two end sections (3, 4), in which housing a pair of screw rotors (7, 8) are mounted. The end sections (3, 4) are provided with projections (29) inserted into the end portions of the barrel section (2) by forced fit between surfaces (30, 31) of the projections and the end portions of the barrel section and secured by screw joint.

Description: SCREW COMPRESSOR FOR INTERNAL COMBUSTION ENGINES. The present invention relates to a screw compressor, especially adapted for use as a super¬ charger for an internal combustion engine. Such a screw compressor comprises a housing, composed of a barrel section and two end sections, enclosing a working space provided with inlet and oudet ports and formed by two intersecting bores, and a pair of intermeshing rotors mounted in the housing, each rotor being provided with helical lands and intervening grooves. A screw compressor according to the invention is an improvement to earlier used super¬ chargers, e.g. turbo chargers which give a bad efficiency especially at low speed of the engine. A compressor according to the invention may suitably be driven by the crank shaft of the engine through a belt drive, which means that independent of the number of revolutions the compressor can always deliver a volume of air enough to fill the engine and having a pressure higher than the atmospheric one. Such feeding of pressurized air to the engine results in a higher power delivered. In a screw compressor it is essential that the barrel section and the end sections of the housing in mounted position has acceptable rigidity for the intermeshing rotors to act properly. Earlier known compressor housings have been produced from cast iron, which results in a rather heavy compressor partly due to the high density of iron, partly due to relatively thick walls. Such housing further requires a considerable amount of work to cut the housing to exact dimension (measure deviation .03 to .05 mm). Screw compressor housings have also been cast from aluminium. In order to obtain the necessary stability the barrel section and one end section are than cast as one unit. This means complicated bottom hole manufactue and thick walls. All those compressors are thus relatively heavy and bulky and thus unsuitable for mounting on the side of the engine. The aim of the present invention is to avoid the disadvantages mentioned above and to obtain a number of advantages in comparison with the earlier known screw rotor super¬ chargers. A screw compressor accordingto the invention is characterized in that the barrel section of the housing is produced by extrusion from a suitable material, preferably light metal, especially aluminium, and in that the end sections each is provided with a projection shaped correspondingly to the transverse section of the working space and inserted into the barrel section by forced fit. Furthermore an extruded housing needs considerably less and simpler adjustment. On the whole the extruded casing results in lower production cost. Furthermore an extruded barrel section can be cut into different lengths in order to achieve different swept volumes when using the same end sections. However, such an extruded barrel section is comparatively weak and needs strengthenings to obtain the necessary rigidity. This rigidity is obtained by the interconnection underpressure between the barrel section and the end section projections. The highest rigidity is obtained if the interconnected surfaces are cylindrical but it is also possible according to the invention that at least one of the interconnected surfaces is tapered. In a preferred embodiment of a compressor according to the invention the outlet port means is provided in a portion of the barrel section having flat surface. This flat surface can be produced by the extrusion which means a minimum of adjustment. The outlet ports can be cut out to a shape and size adapted to the desired internal compression ratio of the compressor. A preferred embodiment of the invention will now be described in connection with the drawings where: Fig. 1 shows a perspective view of a compressor housing, with barrel section and end sections separated from each other, Fig.2 shows a perspective view of a combined compressor and Fig. 3 shows a central longitudinal section through the compressor. As shown in the drawings the compressor comprises a housing 1, composed of a barrel section 2 and two end sections 3 and 4, respectively. The barrel section 2 comprises two bores 5 and 6, respectively, which intersect with each other. In the bores two rotors 7 and 8, respectively, are provided for rotation in opposite directions as the lands and grooves of the rotors intermesh within the intersecting portion of the bores 5, 6. The shafts of the rotors are mounted in the end sections 3, 4 in journals 11, 12 and 13, 14, respectively and the rotors are driven by belt 15, preferably from the crank shaft of the engine, and the drive is transferred to the rotors 7, 8 by gears 16 and 17, respectively. One end section 3 comprises three inlet openings 18 to each rotor for admittance of air and the barrel section 2 is provided with an outlet opening 19 for air from each rotor. Further¬ more each end section 3, 4 comprises radial projections 20 provided with holes 21 for bolts 22 to connect the barrel and end sections of the housing. The bolts pass through grooves 23 in the exterior of barrel section. Stillmore the end sections are provided with holes 24 in their intermediate portions for screws 25 fixed in the barrel section. The end section at the outlets 19 has cut away portions 26 to form channels to the outlet openings 19. As shown in the drawing the edge 27 of the opening 19 which is remote from the end section has a direction substantially the same as that of the land of the cooperating rotor. The characterizing feature of a compressor according to the invention is partly that the barrel section 2 is produced by extrusion of a suitable material, e.g. aluminium, partly that the projections 29 of the end sections 3, 4 pressed into barrel section by forced fit. By the extrusion a simple production of the barrel section blank in selective lengths and a cut is possible for adapting a suitable length for any application. As shown in the drawing one side 28 of the barrel section is plane and in this plane side the outlet ports 29 are cut out, e.g. by milling. Differently from earlier cast compressors flexibility is obtained with regard to the size of the outlets 19 and thus an adaption to the desired compression ratio. The shorter the outlet ports 19 are in longitudinal direction the higher compression ratio is obtained. The reason that barrel sections have not earlier been produced by extrusion in spite of those advantages is probably dependent upon the fact that the required stability of the compressor has not been obtained. By combining the extruded barrel section with end section which are forced into the barrel section by forced fit the required stability and rigidity is obtained. Furthermore the extrusion has facilitated a considerably thinner wall thickness resulting in a lower weight of the compressor. Forced fit has in the shown embodiment been obtained by providing the end sections with projections 29 the outer diameter 30 of which is somewhat larger than the inner diameter 31 of the bores 5, 6. In the shown embodiment the surfaces 30, 31 pressed together have straight cylindrical shape but it is possible to make at least one of those surfaces tapered. The end 3, 4 sections are preferably produced from the same material as the barrel section 2.

Claims: CLAIMS 1. A screw compressor, especially adapted for use as a supercharger for an internal combustion engine, comprising a housing composed of a barrel section (2), produced by extrusion from a suitable material, preferably light metal, especially aluminium, and two end sections (3, 4), enclosing a working space (5, 6) provided with inlet and outlet ports (18, 19) and formed by two intersecting bores (5, 6), and a pair of intermeshing rotors (7, 8) mounted in the housing, each rotor being provided with helical lands and intervening grooves, characterized in that each of the end sections (3, ) is provided with a projection (29) shaped correspondingly to the transverse section of the end portions of the barrel section (3, 4) and inserted into same by forced fit between surfaces (30, 31) of the projections (29) and the end portions of the barrel section (2). 2. A screw compressor according to claim 1, characterized in that said surfaces (30, 31) pressed together have straight cylindrical shape. 3. A screw compressor according to claim 1, characterized in that at least one of said surfaces (30, 31) pressed together is tapered. 4. A screw compressor according to any of claims 1-3, characterized in that the end sections (3, 4) and the barrel section (2) are produced from one and the same material. 5. A screw compressor according to any of claims 1-4, characterized in that said inlet port (18) is comprised in one of the end sections (3). 6. A screw compressor according to any of claims 1-5, characterized in that the outlet port (19) is located along a portion (28) of the barrel section which is designed to present a plane surface. 7. A screw compressor according to any of claims 1-6, characterized in that the length of the outlet port (19) in the longitudinal direction of the barrel section (2) is adapted to the desired internal compression ratio of the compressor.

Inventors: LINDBRANDT BENNY, LINDBRANDT, BENNY
Applicants: OPCON AUTOROTOR AB
Application year: 1990
Main classification: F01C21
IPC codes: F01C21, F02B33, F04C18