Connection piece connecting the housing of a drive unit to the housing of a compressor element

Abstract: Connection piece connecting the housing (4) of a drive unit (2) with the housing (5) of a compressor element (1), characterized in that it is provided with ribs (12) over at least a part of its wall, the height of which ribs is at least equal to one and a half time the thickness of the wall part upon which this rib is standing and the thickness of which, half the way up its height, is equal to at least half of the aforementioned thickness, whereby the ribs (12) form a pattern which divides the wall into adjacent wall segments (13), the first characteristic mode for bending of which has a resonant frequency which excludes excitation by all important excitation frequencies up to and including the highest of the compressor element (1).

Description: This invention relates to a connection piece for connecting the housing of a drive unit to the housing of a compressor element, more specifically a connection piece that is single-walled. Such connection pieces are used in compressor aggregates for connecting the mostly cast metal housing of a compressor element with the housing in which its drive unit is situated, for example, the housing of a motor. Due to constructive causes, these housings cannot be manufactured as one whole unit. In the connection piece, the coupling between the shaft or shafts of the rotor or rotors of the compressor element and the outgoing shaft or shafts of the drive unit is situated. In this connection piece, also a gearwheel transmission or another coupling transformer can be integrated. Compressor aggregates create a lot of noise. In order to restrict the noise level, vibration dampers are used for insulating the aggregate from the ground, and the framework is equipped with noise-restricting material. The channels through which ventilation air is sucked in are also acoustically treated. From US 3 263 521 A a transmission housing is known for change-speed transmissions of motor vehicles, which is realised with a double wall in order to strengthen the housing and reduce noise. Although these means already achieve a considerable noise dampening, the noise level of the compressor aggregate still is rather high. In an effort to further reduce this noise level, researches were made from which it became clear that considerable noise energy is created in the compressor element and, by the structural features of the whole aggregate, is transformed into undesired vibrations and noise. In particular, the resonant frequencies of the structure of this aggregate are evoked by the pulsation frequencies of this compressor element, which leads to the radiation of superfluous noise energy. It was noted that especially the connection piece between the housings of the compressor element and the drive unit are responsible for noise emission and transmission of vibrations and noise to the motor and to the support points of this connection piece. This invention aims at such a connection piece in which the noise radiation and transmission of vibrations are minimal, in such a manner that the noise emission of the compressor aggregate is reduced. This aim is achieved according to the invention in that the connection piece, on at least a part of its wall, is provided with ribs whereby the height of every rib is at least equal to one and a half time the thickness of the wall part upon which this rib is standing and of which the thickness, halfway up its height, is equal to at least half of the aforementioned thickness, whereby the ribs form a pattern which divides the wall into adjacent wall segments, the first characteristic mode for bending of which has a resonant frequency which excludes excitation by all important excitation frequencies up to and including the highest of the compressor element. Preferably, the ribs are provided on the connection piece in such a manner that the segments which are bordered by these ribs at least take up half of its wall. The ribs may be provided at the outer side or the inner side. The connection piece may be formed of a tubular part and two flanges at the extremities thereof, whereby, for example, at least the lateral flanks of this part are provided with ribs. With the intention of better showing the characteristics of the invention, hereafter, by way of example without any limitative character, several preferred forms of embodiment of a connection piece between a compressor element and a drive unit according to the invention are described, with reference to the accompanying drawings, wherein: figure 1 schematically represents a compressor aggregate with a connection piece according to the invention; figure 2, on a larger scale, represents a side eleational view of the connection piece of the comrpessor aggregate of figure 1; figure 3 represents a view according to arrow F3 in figure 2; figure 4 represents a view according to arrow F4 in figure 2; figure 5 represents a cross-section according to line V-V in figure 3; figure 6, on a larger scale, represents a cross-section according to line VI-VI in figure 2; figure 7 schematically represents a compressor aggregate analogous to figure 1, but in respect to another form of embodiment. In figure 1, a compressor aggregate is represented consisting of a compressor element 1, for example, a scroll compressor element with one rotor or a screw compressor element with two rotors, a drive unit 2 formed by an electric motor, and a connection piece 3 connecting the housing 4 of the drive unit 2 to the housing 5 of the compressor element 1 and in which the coupling 6 is situated between the outgoing shaft 7 of this drive unit 2 and a shaft 8 of a rotor of the compressor element 1. In the case that the compressor element 1 is a screw compressor and thus comprises two rotors, the shaft 8, by means of a gearwheel transmission, a belt transmission or another coupling transformer, can drive the shaft of a rotor. The connection piece 3 consists of a tubular part 9 with at one extremity a flange 10 for the fixation onto the housing 5 of the compressor element 1, and at the other, somewhat larger extremity a flange 11 for the fixation onto the housing 4 of the drive unit 2. The acousting energy created by the process of compression by a compressor element, is rather tonal and is a composition of deterministic signals. The lowest deterministic signal, the fundamental tone, is a sinus with a frequency equal to the rhythm with which the compressor elements sucks air from the environment and expels it into the outlet of the compressor element. The air is compressed in the compression chamber and expelled rather abruptly into the outlet, such that this process is not performed in a progressive manner. As a consequence, harmonic components of this fundamental tone are created. These harmonic components have a frequency which is an integral multiple of the basic frequency. Depending on a multitude of processes and geometric parameters, more or less harmonics are created and is their amplitude in respect to the fundamental tone important or not. This total tonal energy brings the housing 5 of the compressor element 1 and the flanged-on structures into vibrations which, each in its own manner, transform this energy into vibrations and noise. In order to restrict said vibrations, ribs 12 are provided on a part and preferably on more than half of the wall of the tubular part 9, according to a pattern which divides this outer side between the flanges 10 and 11 into adjacent wall segments 13. In the represented example, these ribs 12 are provided on the outer side of the aforementioned wall of the part 9, but they may also be situated at the inner side. These ribs 12 meet specific requirements. As represented in detail in figure 6, the height H or a rib 12 is at least one and a half time and, for example, two times the thickness D of the wall part upon which it is standing, and the width B, measured half the way up the height of this rib 12, is at least half of aforementioned thickness D and, for example, equal to this thickness. In consideration of the fact that the connection piece is a metal cast part, the ribs 12, due to casting-technical causes, are widening somewhat towards their basis. The top of the ribs 12 is rounded off, and the ribs 12 connect with a rounded part to the wall part upon which they are standing. The aforementioned pattern formed by the ribs 12 also meets specific requirements: namely, it has such a dense structure that the first characteristic mode for bending for each wall segment 13 has a resonant frequency which is such that no wall segment 13 can be excited by all important excitation frequencies up to and including the highest of the compressor element 1. The highest harmonic, in other words, the excitation component on highest frequency, then is no longer able to start the so-called breathing mode or first bending mode of any wall segment 13. As a result of this, this wall segment 13 cannot radiate any considerable noise. Each wall segment 13 will start vibrating when excited with a dynamic force. When the supplied vibration takes a frequency with one of the resonant frequencies of this wall segment 13, considerably more noise is radiated than the noise radiated by this wall segment for any other frequency. The characteristic mode is the manner in which a wall segment vibrates with one of its resonant frequencies and differs from resonant frequency to resonant frequency. The characteristic mode of the first resonant frequency is a typical bending mode, whereby the central point of the wall segment 13 performs an up-and-down movement and whereby all other points of this wall segment 13 perform a smaller movement which, however, is in phase with the movement of the central point. The first characteristic mode is also indicated as "breathing mode". Thus, the aforementioned pattern depends on the characteristics of the compressor element 1, such as the rotational speed and the rotor construction which exert an influence upon the excitation frequency of the compressor element 1. Most of the wall segments 13 may be provided with a groove 14 for the internal cooling of the connection piece 3. In the represented example, the ribs 12 and, thus, the wall segments 13 are present on the lateral flanks of the tubular part 9. The one lateral flank consists of parts forming an angle with each other. The upper side and the underside of part 9 have flat parts. With a lower one of such flat parts, the connection piece 3, with the intermediary of an elastic cushion 15, rests on a support 16, as represented in figure 1. In an analogous manner, the housing 4 of the drive unit 2 rests upon a second support point 17. It is obvious that the ribs 12 and, thus, the wall segments 13 can be situated also, or exclusively, at the upper and/or bottom side of the part 9. The flange 11 substantially extends outwardly in respect to the opening of the part 9 on the corresponding extremity of this part 9. This flange 11 shows four openings 18, provided with screw thread at the inside, for the fixation of the housing 4 thereupon by means of bolts. The flange 10, on the contrary, is asymmetrical in respect to the opening of the part 9 on the extremity concerned, in other words, the flange 10 protrudes outwardly at the lateral flank, and it protrudes inwardly at the other lateral flank. In this flange 10, openings 19 are provided for the fixation of the flange 10 at the housing 5 by means of bolts. The heretofore described connection piece 3 has a considerable reduction of the noise radiation as a consequence. The connection piece 3 must not necessarily be situated in the prolongation of the compressor element 1 and the drive unit 2. It can be situated, for example, next to, under or above this compressor element and this drive unit 2. In this case, the coupling 6 is formed by a transmission. Besides, in figure 7, a form of embodiment of a compressor aggregate is represented schematically, whereby the compressor element 1 and the drive unit 2 are not situated in their mutual prolongation and the connection piece 3 has an other form than described heretofore. In this form of embodiment, this connection piece 3 has the shape of a flat box in which the coupling 6, which is formed by a belt transmission, is situated. The compressor element 1 is fixed, by means of a flange and bolts, on top, on one side of this box. A shaft 8 of a rotor extends through an opening into the aforementioned side. The drive unit 2 is fixed in an analogous manner by means of a flange and bolts, at the lower end, on the other side of the connection piece 3. The outgoing shaft 7 extends through an opening into the last-mentioned side. On the lateral edge, as well as on the two aforementioned sides, next to the compressor element 1 and the drive unit 2, ribs 12 are provided which, thus, determine adjacent wall segments 13. As far as their dimensions as well as the pattern they are forming is concerned, the ribs 12 meet the same requirements as in the form of embodiment according to figures 1 to 6. In this case, too, the ribs 12 considerably reduce the noise radiation or transmission. In a variant, the compressor element 1 and the drive unit 2 may be situated above or next to each other at the same side of the connection piece 3. The present invention is in no way limited to the form of embodiment described heretofore and represented in the figures, on the contrary may such connection piece be realized in various variants without leaving the scope of the invention.

Claims: Connection piece for connecting the housing (4) of a drive unit 2) with the housing (5) of a compressor element (1), the connection piece being provided with ribs (12) over at least a part of its wall, the height of which ribs is at least equal to one and a half time the thickness of the wall part upon which this rib is standing and the thickness of which, half the way up its height, is equal to at least half of the aforementioned thickness, characterized in that said connection piece (3) is single-walled and in that the ribs (12) form a pattern which divides the wall into adjacent wall segments (13), the first characteristic mode for bending of which has a resonant frequency which excludes excitation by all important excitation frequencies up to and including the highest of the compressor element (1). Connection piece according to claim 1, characterized in that the ribs (12) are provided in such a manner that the segments (13) which are determined thereby take up at least half of the wall. Connection piece according to claim 1 or 2, characterized in that the ribs (12) are provided on the exterior side of the wall. Connection piece according to claim 1 or 2, characterized in that the ribs (12) are provided on the interior side of the wall. Connection piece according to any of the preceding claims, characterized in that it is formed of a tubular part (9) and two flanges (10 and 11) at the extremities. Connection piece according to claim 5, characterized in that the tubular part (9) is provided with ribs (12) at least on both lateral flanks. Connection piece according to any of the claims 1 to 4, characterized in that it forms a box, whereby the compressor element (1) and the drive unit (2) are fixed on the same side or on different sides of this box. Connection piece according to any of the preceding claims, characterized in that a coupling (6) is situated therein, in between an outgoing shaft (7) of the drive unit (2) and a shaft (8) of a rotor of the compressor element (1). Connection piece according to any of the preceding claims, characterized in that it has a part underneath with which it rests, by means of an elastic cushion (15), onto a support (16).

Inventors: BODART WILLY JOSEPH ROSA, PAUWELS RAPHAEL HENRI MARIA, VEYS PHILIP XAVIER JACQUES, BODART, WILLY JOSEPH ROSA, PAUWELS, RAPHAEL HENRI MARIA, VEYS, PHILIP XAVIER JACQUES
Applicants: ATLAS COPCO AIRPOWER NV, ATLAS COPCO AIRPOWER N.V.
Application year: 1998
Main classification: F04C29
IPC codes: F04D29, F04B53, F04C29