ROTOR PROVIDED WITH SHAFT PIVOTS

Abstract: The invention relates to a rotor (2, 3) provided with bearing trunnions (4, 5) and made of a material with limited strength properties, e.g. aluminum. At least one of the bearing trunnions (4) comprises, according to the invention, a concentric sleeve (20) made of steel at one end of the rotor. The inner end (21) of the sleeve (20) is radially attached to the rotor end (22) by a trunnion (4) protruding into the sleeve, or by a groove (40) in the rotor end (22), into which groove the end (21) of the sleeve protrudes, and the outer end of the sleeve (20) is kept by a screw (25, 27) screwed into the rotor (2, 3) and provided with a screw head (24) pressed axially in the direction towards the rotor end (22).

Description: ROTOR PROVIDED WITH SHAFT PIVOTS. The present invention relates to rotor provided with bearing trunnions, which rotor is of the type defined in the introduction of the attached claim 1. At rotors made of a material with limited strength properties in comparison to steel, some problems are involved in the provision of the bearing trunnions. If the bearing trunnions are made of the same material as the rotors and integrated with the rotors, e.g. of aluminum, magnesium, plastics or ceramic material, the bearing trunnions will get an unpractically large diameter and so also the bearings. This disadvantage is particularly obvious at journalling of the low pressure ends of the rotors in screw compressors provided with axial inlet ports, the design of which is restricted by bearing trunnions and bearing having a large diameter. The provision of axially positioned screws for reinforcing the bearing trunnions has been tested, but this has not been sufficient for avoiding harmful flexural stresses to the bearing trunnions. Steel shafts passing through especially plastic rotors have been used resulting in sufficient bending strength, but at the same time an increased rotor weight where low weight is desired. The object of the present invention is to achieve in a simple way rotors having bearing trunnions which have a comparatively small diameter but at the same time a great strength property, especially bending strength. This is achieved, according to the invention, by providing the rotor with the characteristics defined in claim 1. The outer layer of the bearing trunnion, hence, consists of a sleeve made of steel or a similar material having high strength properties and which can withstand high shearing stresses by the fact that its inner end is radially fixed to the rotor end by the outer end of the sleeve being hardly pressed in the direction towards the rotor end by a screw provided with a specially formed head and fixed to a threaded boring in the rotor end. The sleeve consists according to a preferred embodiment of the rotor according to the invention of the inner race of a radial bearing. For a suitable attachment of the inner end of the sleeve the rotor can be designed as stated in claims 3 and 4, and for a radial attachment of the outer end of the sleeve the rotor can be designed as stated in claim 5. The invention is described in further detail below with reference to the appended drawings, which show various embodiments of rotors according to the invention, and on which Fig.l is a side view of a screw compressor with housing, bearings and clutch shown in section, Fig.2 is a detail of Fig.l shown on a larger scale, and Fig.3 is a modification of the embodiment shown in Fig.2. Fig.l shows a screw compressor with a housing 1, in which a male rotor 2 and a female rotor 3 are journalled with bearing trunnions 4 and 5, respectively, in a low pressure end wall 6 and a high pressure end wall 7. Each bearing trunnion 5 is journalled in a combined thrust and radial bearing 8 whose inner race 9 together with a spacer sleeve 10 abut the bearing trunnion 5 and are kept pressed against the corresponding rotor end by a screw 11 screwed into the corresponding rotor 2,3 and having a head 12 that is pressing a synchronizing gear 13 and 14, respectively, against the inner races 9 of the bearings 8. The female rotor 3 and its synchronizing gear 14 are via a disc clutch 15 driven by a belt pulley 16 connected to said clutch. The journalling of the bearing trunnions 4 in the end wall 6 is shown most clearly in Fig.2. The bearing trunnion 4 is with close running fit enclosed by a steel sleeve 20, the inner end of which abuts the end surface 22 of the rotor 2 fixed in radial direction by the bearing trunnion 4. The outer end of the sleeve 20 protrudes beyond the end of the bearing trunnion 4 and abuts an annular, plane surface 23 of a head 24 of a screw 25 that extends through an axial boring 26 in the bearing trunnion 4 and with a threaded part 27 extends into a threaded boring 28. The head 24 of the screw is provided with a circular spacer 29 that extends into the outer end of the sleeve 20 for centering purposes. The sleeve 20 consists of the inner race of a radial bearing 30 having an outer race 31 abutting a cylindrical wall 32 in a cavity in the end wall 6. By the radial positioning of the sleeve 20 at the rotor end 22 by the inner part of the bearing trunnion 4 and the pressure of the screw head 24 against the outer end of the sleeve 20 and the centering of this by the circular spacer 29, shear stresses as well as flexural stresses acting on this part of the journalling of the rotor will be carried by the sleeve 20 and the axial pressure of the screw 25 against the sleeve 20. The diameter of the sleeve 20 accordingly can be essentially smaller than the diameter of a bearing trunnion made of e.g. aluminum. The bearing trunnion 4 in the sleeve 20 shown in Fig.2 is intended only for radial positioning of the inner end of the sleeve 20 with respect to the end of the rotor. Therefore, the bearing trunnion 4 can be made much shorter, which involves an essential material saving at the manufacturing of the rotor. It is even possible to completely spare the bearing trunnion if a positioning of the inner end 21 of the sleeve 20 can be achieved in another way. Such an embodiment is shown in Fig.3, which differs from the embodiment in Fig.2 in that the bearing trunnion 4 is eliminated and replaced by an annular groove 40 in the end surface 22 of the rotor 2, in which groove the inner end 21 of the sleeve 20 is situated and radially fixed. The journalling of the bearing trunnion 5 in Fig.l is carried out essentially in the same way as the journalling of the bearing trunnion 4 in Figs.l and 2. Instead of a sleeve 20 made in one piece and enclosing the bearing trunnion 4, the bearing trunnion 5 is positioned partly in the sleeve 10, partly in the inner race 9 of the bearing 8. At axial compression of these by the screw 11 the sleeve 10 and the inner race 9 will work like a single sleeve corresponding to the sleeve 20 of the bearing trunnion 4.

Claims: C L I M S 1. Rotor provided with bearing trunnions (4,5) and made of a material having limited strength properties, such as lightweight metal, characterized in that at least one (4) of the trunnions comprises a concentric sleeve (20) made of steel or a similar strong material, located at one end of the rotor and having an inner end (21) radially fixed by a guide means (4,40) at the end (22) of the rotor and an outer end positioned by a clamping surface (23) acted upon by a head (24) of a screw (25) that extends into a threaded boring (28) in the rotor end, and with the head (24) bears axially against the outer end of the sleeve (20) and keeps the sleeve (20) pressed against the rotor end (22) . 2. Rotor according to claim 1, characterized in that the sleeve (20) consists of the inner race of a radial bearing ( 30 ) . 3. Rotor according to claim 1 or 2, charcterized in that the guide means for the positioning of the inner end (21) of the sleeve (20) consists of a hollow trunnion (4) protruding from from the rotor end and having essentially the same outer diameter as the inner diameter of the sleeve (20). 4. Rotor as claimed in claim 1 or 2, characterized in that the guide means for the positioning of the inner end (21) of the sleeve (20) consists of an annular groove (40) in the rotor end into which groove the end portion (21) of the sleeve protrudes. 5. Rotor according to any of claims 1-4, characterized in that the under side of said screw head (24) is provided with a spacer (29) which with close alignment protrudes into the outer end of the sleeve (20) and faces said clamping surface (23) on the under side of the screw head (24).

Inventors: ENGLUND ARNOLD, ENGLUND, ARNOLD
Applicants: ENGLUND ARNOLD, LYSHOLM TECHN AB, ENGLUND, ARNOLD, LYSHOLM TECHNOLOGIES AB
Application year: 1997
Main classification: F04C29
IPC codes: F04C18, F04C29, F16C11, F16C19, F16C35, F16D1