GB2394011A - Oil sealed rotary vane compressor - Google Patents

Abstract

An oil sealed rotary vane compressor with an air end 13, comprising a vertically oriented rotor 25 within a stator 33, and a drive end (12) the compressor being of modular construction such that the drive end and the air end are separable from each other.

Description

239401 1

ROTARY COMPRESSOR (5)

The present invention relates to a rotary compressor and is concerned with that type of compressor which is of oil sealed type, that is to say the type in which oil is injected into the compression space and is subsequently removed from the compressed gas, typically air, and then reused.

Various types of positive displacement oil sealed rotary compressors are known of which one is the so-called sliding vane eccentric rotor compressor in which a plurality of vanes are slideably accommodated in equispaced longitudinal slots formed in the periphery of a rotor which is mounted to rotate about an eccentric axis within a cylindrical stator. The outer edges of the vanes are maintained in contact with the inner surface of the stator and divide a crescent -

shaped space between the rotor and stator into a plurality, typically six or eight, of compression cells whose volume progressively increases and then decreases as the rotor rotates. An air inlet and outlet are positioned respectively each to communicate successively with each cell as its volume increases and when its volume has reached its minimum value. Oil is injected into each cell as its volume is increasing and serves not only to lubricate the vanes but also to form a seal between the vanes and the stator and between the vanes and the two end plates which close the ends of the stator. The oil serves also to remove the heat which is generated by virtue of friction and by virtue of the compression to which the air is subjected.

The vanes are maintained "in contact" with the stator by centrifugal force but they are in practice spaced from the stator by a small clearance gap which is occupied by oil which seals the gap.

Although rotary compressors of the aforedescribed type are reliable and efficient in operation, the increasing costs of materials used in their construction,

the energy for operating the compressor, and the cost associated with the floor space conventionally occupied by the compressor demand that attempts are made to improve upon these aspects of the currently known and available machines. Reduction of the cost of routine servicing and repair is also sought.

The present invention seeks to provide a rotary compressor which allows an improvement in at least one of the aforedescribed aspects.

According to one aspect of the present invention provides a rotary compressor of modular construction comprising a drive-end having a motor and an air-end having a rotor disposed within a stator the drive-end and air-end being separable from each other.

Preferably the drive-end and air-end are arranged in the vertical orientation and preferably the drive-end is disposed beneath the air-end.

The air-end may be secured to and be removable from the drive-end by bolts or the like.

Preferably the air-end comprises end flanges held together by tie rods.

Preferably the tie rods are disposed inwards of an outer housing which most preferably acts as a pressure vessel and surrounds the stator.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a rotary vane compressor in accordance with the present invention; Figure 2a is a perspective view of the compressor of Figure 1 in a partly assembled condition; Figure 2b is a perspective view of the rear of the compressor of Figure 1 in another part assembled condition;

Figures 3a to 3f are longitudinal sectional views of part of the compressor of Figure 1, each being taken in a different diametrical plane that contains the longitudinal access of the rotor / stator; and Figures 5 to 8 each show perspective views of the compressor in successive stages of assembly.

A rotary vane compressor 10 (see Figure 1) comprises a support structure 11 which has secured thereto a so-called compressor drive end 12 comprising an electric motor and a so-called air-end 13 comprising a rotary vane compressor.

The air-end 13 is supported vertically above the drive end and the airend is arranged to be selectively removable from the drive end and support structure 11 without the need to remove the motor from the support structure. A decorative and sound absorbing cover (not shown) is securable to the support structure 11 to enclose the electric motor and air-end.

The electric motor 13 is of a generally conventional construction and has an end face 15 (see Figure 2a) which supports a lower end face of the airend 13. The end face 15 of the motor is provided with 4 circumferentially spaced apertures 16 through which retention bolts extend in the assembly to engage with screw threaded apertures provided in the lower end face of the air-end 13.

These retention bolts are selectively removable when it is required to separate the air-end from the drive end.

In contrast to a conventional rotary vane compressor in which the rotor is of a substantially solid construction, in the present invention the electric motor has a long length shaft 17 extending therefrom to engage within a longitudinal bore which extends centrally through the rotor. The construction of the rotor shaft is described in more detail below.

The vertically extending portion 18 of the support structure houses electrical and other control components 19 (see Figure 1) and (as shown in

Figure 2b) a cooling fan 20 and heat exchanger 21 for cooling of oil which circulates through the air-end.

The construction of the air-end 13 will now be described in more detail.

The air-end 13 comprises a rotor 25 having a central bore 26 through which the motor shaft 17 extends. The bore 26 has a longitudinally extending groove 27 (see Figure 6), and the shaft 17 is provided with a short length slot 28 for location of a drive key 29 which engages with the groove 27 thereby to transmit drive from the motor to the rotor.

The rotor is provided in a manner known per se with six equispaced slots 30 which each accommodate a blade or vane 31. The outer edge of each blade 31 in use runs over the inner surface 32 of a stator 33 within which the rotor is mounted eccentrically. The vanes 31 may be of a type known per se but in this embodiment of the invention of a kind provided with obliquely extending surface grooves and profiled radially inner ends as described more specifically in our co-

pending UK patent applications of even date and entitled Rotary Sliding Vane Compressor (1) and Rotary Sliding Vane Compressor (2). The radially inner end of each of the slots 30 is profiled to correspond with the radially inner edge of each vane 31 as more specifically described in said co-pending applications.

The rotor and stator lie axially between upper and lower end flanges 34, 35. The lower end flange 35 is provided with oil seals 36, typically glass fibre reinforced PTFE lip seals. In use these serve to prevent oil escaping from within the air-end. To avoid the need carefully to machine or case harden the motor shaft, the shaft 17 carries a wear sleeve 37 for engagement by the seals 36. The sleeve is located axially between, at one end, a shoulder 38 at which the shaft 17 is stepped to reduce in diameter, and at the other end an annular recess 39 in the lower end face 40 of the rotor. The sleeve 37 is of non uniform internal

diameter. At an upper end it is a close fit around the shaft, to prevent flow of oil therebetween, and then at a position axially aligned with the lip seals it is of a slightly enlarged internal diameter. At the lower end of the wear sleeve the outer surface thereof is of a reduced diameter thereby to create a shoulder portion 41, that shoulder portion 41 providing an abutment to assist in ease of removal of the sleeve from around the shaft in the event of any need for replacement of the sleeve. The upper end flange 34 has a central spigot portion 45 which extends axially inwards towards the other end flange 35, and locates in an annular recess 46 in the upper end face of the rotor. The spigot portion 45 serves to maintain the rotor bore 26 aligned with centre line of the seals 36 when the air-end is separated from the motor shaft, and thus ensures that the rotor is maintained in the correct position ready for assembly or re-assembly with a motor shaft.

The air-end additionally comprises a cast top plate 50 and an extruded aluminium outer housing 51. The top plate 50 is maintained spaced above the central zone 52 of the upper end flange 34 by an outer annular sleeve portion 53 of said flange, and is sealed thereto by a seal 54 located in a groove 55 in the outer face of the portion 53. The outer housing 51 lies spaced radially outwards of and extends around the stator to define an annular chamber 56 therebetween.

The lower end flange 35 and top plate 50 are provided with radially outwardly facing grooves 57, 58 which accommodate seals 59, 60 whereby the annular chamber 56 is able to contain compressed gas at above atmospheric pressure.

The upper end flange 35 also has a radially outwardly facing groove 60' to contain a seal 61 which bears sealing against the inner surface of the outer housing 51.

The assembly of the top plate 50, upper and lower end flanges 34, 35, stator 33 and outer housing 51 are secured together axially by five uniformly

circumferentially spaced tie bars 65. Other embodiments of the invention may have a different number of tie bars and different circumferential spacing. The tie bars each locate in a screw threaded hole 63 in the lower end flange 35 and receive retention nuts 66 at their upper ends.

The upper end flange 34 is provided with five apertures 67 through which the tie bars 65 extend, and said apertures are of larger diameter than the tie bars whereby each aperture 67 provides an annular passage through which compressed gas may flow from the chamber 56 to an upper zone 68 (see Figure 3(c)). The upper zone 68 is surrounded by annular oil separator 69, this having a diameter greater than that of the stator bore. An earth strap 70 extends between the upper end flange 34 and the oil separator 69.

The chamber 56 contains an annular baffle 71 which in this embodiment is of a frustoconical shape. The upper end of the baffle is provided with apertures (not shown) whereby compressed air can pass from within the upper end of the baffle to aforedescribed passages 67. The lower end of the annular baffle 71 extends to a position close to the lower end flange 35 such that it is normally, In use of the compressor, below the level 72 of the sump oil.

Other constructional features of the compressor are described below in the context of an explanation of the manner in which the compressor operates.

Considering first the flow of lubricating and cooling oil, as aforedescribed, the oil lies generally in a sump the typical level of which is indicated at 72.

The upper end flange 35 is provided with an internal passage 80(b) (see Figure 3(e)) which communicates between the sump oil and a plurality of oil feed holes 81 that allow oil to flow from the passage 80 to the interface between the upper end of the rotor and confronting surface of the upper end flange 34, and also to the region of the aforedescribed spigot 45 and recess 46. The feed holes

81 are provided at a position at which the cell between neighbouring rotor vanes is relatively large, and thus at a low pressure. In consequence of the high pressure existing in the chamber 56 oil is forced via a vertically extending portion 80a of the passage 80, from the lower end of passage 80b that communicates with the sump. Oil entering at a low pressure zone between the rotor and stator provides lubrication and a fluid seal to the outer edges of the vanes and the inner surface of the stator, in addition to thin film lubrication between the axial ends of the rotor and confronting surfaces of the upper and lower end flanges 34, 35. Oil exits from between the rotor and stator either via oil relief pads, e.g. reed valves 84, or as an oil mist in the flow of compressed air exiting through an outlet 85 (see Figure 5) in the wall of the stator at the high pressure cell position.

That outlet leads into an angled tube 40 causes the flow of compressed air to enter the chamber 56 in a generally circumferential direction, thereby to cause the oil mist to impinge upon and flow around the inner surface of the frustoconical separator 71. Impinging oil mist is thereby collected by the separator and flows downwards to the sump.

The flow of air through the air-end is now described. Air enters through a conventional filter 86 into an upper chamber 87 for which it is drawn through a passage 88 into an intermediate chamber 89. The flow through the passage 88 is controlled in a manner per se by a servo controlled unloader valve 90 such that the flow rate of air drawn into the compressor is adjusted having regard to the user demand for compressed air.

From the chamber 89 air is drawn through apertures 91 in the upper end flange 34 to enter via an intake port or so-called intake "scroll" 91(a) a low pressure cell region 91(b) between vanes 31. In consequence of rotation of the vanes by the eccentrically mounted rotor, and reduction of volume of each cell, the air in each cell is compressed and then exits via the outlet 85 as

aforedescribed to enter the chamber 56. From the chamber 56 the air flows through the passages 67 to the region 68 and then radially outwards through the annular oil separator 69 to the outer annular cavity 93. From the cavity 93 it flows upwards and then radially outwards through the outlet port 94.

In addition to the afordescribed external connections, the air-end comprises oil inlet and outlet ports 92, 93 to enable oil in the sump to be circulated through and thereby cooled by the heat exchange 21.

It is to be understood that the aforedescribed compressor comprises features which do not need necessarily to be used in combination with one another, and aspects of the present invention are to be understood potentially to reside in individual features.

PLC/Jd - 02455

Claims (8)

1. A rotary compressor of modular construction comprising a drive-end having a motor and an air-end having a rotor disposed within a stator, the drive-end and air-end being separable from each other.

2. A rotary compressor in accordance with claim 1, wherein the drive-end and air-end are arranged in the vertical orientation.

3. A rotary compressor In accordance with claim 2, wherein drive-end Is disposed beneath the air-end.

4. A rotary compressor in accordance with any of claims 1 to 3, wherein the amend is secured to and removable from the drve-end by bolts or the like.

5. A rotary compressor In accordance with any of claims 1 to 4, wherein the air-end comprises end flanges held together by tie rods.

6. A rotary compressor in accordance with claim 5, wherein the tie rods are disposed inwards of an outer housing surrounding the stator.

7. A rotary compressor In accordance with claim 6, wherein the outer housing acts as a pressure vessel in surrounding the stator.

8. A rotary compressor substantially is herein described and depicted In Figures 1 to 8.