GB1599413A - Oil-injected rotary compressors - Google Patents

Description

(54) OIL-INJECTED ROTARY COMPRESSORS (71) We, COMPAIR INDUSTRIAL LIMITED, a British Company, of P.O. Box 7, Broomwade Works, High Wycombe, Buckinghamshire, HP13 5SF, COMPAIR CON STRUCTION AND MINING LIMITED, a British Company, of Holman Works, Camborne, Cornwall, ALEXANDER WILLIAM WRIGHT, a British Subject, of 4 Middlebrook Road, High Wycombe, Buckinghamshire and DERYK CARVETH, a British Subject, of Derwen, 32 Penware Parc, Camborne, Cornwall, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to oil-injected rotary compressors and more particularly to a method of draining oil from a transmission housing of such a compressor.

The invention provides a method of draining oil in an oil-injected rotary compressor comprising a compressor housing for rotor means and a transmission housing for a transmission for driving the rotor means, a shaft of the rotor means extending at one end through an inlet end wall of the compressor housing into the transmission housing and extending at its other end through an outlet end wall or the compressor housing, the method comprising supplying fluid pressure which is created in a region beyond the outlet end wall of the compressor housing by compressed working-fluid leaking around the shaft, to the transmission housing through a first duct and thereby driving oil from the transmission housing against the action of gravity on the oil through a second duct to a given region in the compressor housing where the pressure is lower than that in the said region beyond the outlet end wall.

The invention also provides an oil injected rotary compressor comprising a compressor housing for rotor means and a transmission housing for a transmission for driving the rotor means, a shaft of the rotor means extending at one end through an inlet end wall of the compressor housing into the transmission housing and extending at its other end through an outlet end wall of the compressor housing, said shaft having a fluid flow passage therearound for the leakage of compressed workingfluid to a region beyond the outlet end wall of the compressor housing, a first duct connecting said region to the transmission housing and a second duct, arranged for the flow of oil against the action of gravity on the oil and connecting the transmission housing to a given region in the compressor housing where the pressure is lower than that in the said region beyond the outlet end wall.

A preferred embodiment of an oil-injected rotary compressor according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through an embodiment of a rotary compressor according to the invention; and Figure 2 shows a modification to Figure 1.

Referring to Figure 1, an oil-injected meshing screw compressor 10 comprises a compressor housing i.e. a rotor housing 11 in which a main rotor i.e. a male screw rotor 12 is journalled in bearings 13, 14, 15. A gate rotor i.e. a female screw rotor (not shown) co-operating with the main rotor is also journalled in the housing 11 in known manner.

The main rotor shaft protrudes beyond the bearing 13 at the left-hand end of the compressor casing as viewed in the figure and the shaft extension 17 carries a toothed gear 18 which is keyed or otherwise secured to the shaft 17 for rotation therewith. The gear 18 is in mesh with a second gear 19 carried on a drive shaft 20, journalled in bearings 23, 24. Both gears 18, 19 are housed in a housing 22 for the gears, hereafter called the transmission housing, mounted on the compressor housing 11 and the drive shaft projects through an end wall of the transmission housing and is sealed with respect thereto by a shaft seal 25. The main rotor 12 is driven, in use, by a prime mover drivingly connected to the drive shaft 20.

In the use of the compressor 10, which is driven as described above, air (or other working fluid) passes through the compressor housing, while being compressed, from an inlet aperture 26 to an outlet aperture (not shown).

Compressed air is conveyed from the outlet aperture to a receiver (not shown) which also acts as a reservoir for lubricating oil for the compressor.

Oil from this reservoir is forced, by the pressure created in the receiver by the compressed air, back into the compressor housing via an oil inlet aperture 28.

Oil forced into the compressor housing through the apertures 28, enters a gallery 29 whence it passes into the space surrounding the rotors through a drilling 30. Further drillings 31, 32 in the compressor housing convey the oil to the bearings 14, 15 for lubrication thereof and a passage 34 leading from the top of the gallery 29 conveys oil to a second smaller gallery 35 in the transmission casing 22.

Oil from this second gallery 35 is conveyed by the pressure in the oil feed system through passages 36, 37 to an oil spray 38 to lubricate the gears 18, 19 and through passages 36, 39, 40 and 41 to lubricate the bearings 23, 24.

The space to the left of the bearings 23, 24 as viewed in Figure 1 communicates with the main part of the interior of the transmission housing by means of a drilling 43.

As can be seen in the Figure, the arrangement of the compressor 10 is such that the transmission housing 22 is underslung with respect to the compressor housing 11 so that the lowermost point of the transmission housing is some distance below the lowermost point of the compressor housing. This arrangement is largely dictated by the shape of a chassis on which the compressor 10 illustrated is to be mounted. It will be appreciated that, in use, the oil passing into the transmission housing 22 via the various passages described above for lubricating the gears 18, 19 and bearings 23, 24 will drain to the bottom of the transmission casing and will tend to collect in the region marked 45, so that if this oil were not removed, the oil level would eventually rise over at least part of the gear 19. This would be undesirable.

A passage 46 is provided in the transmission housing 22 connecting the region 45 to a gallery 47 which communicates with the rotor bore via a passage 48, but in view of the head difference between the oil level in the region 45 and the gallery 47, it is necessary to pressurise the transmission housing 22 in order to force the oil up the passage 46. The transmission housing is pressurised to some extent by compressed air entrained in the lubricating oil, but under some conditions (e.g. start-up) this pressurisation is only slight.

Such entrained air is inevitably present in the oil circulating in the compressor because of the mixing of oil and compressed air in the compressor itself and in the receiver.

Under certain conditions, this pressure is small as mentioned above and insufficient to force the collected oil up the passage 46. The necessary pressurisation of the transmission housing to drain the oil is achieved by a passage 50 connecting an aperture 51 in the transmission housing 22 with a space 52, at the right hand end of the bearings 14, 15 as viewed in the Figure, which is outside the compressor housing itself.

As already described above, oil under pressure lubricates the bearings 14, 15 and, in addition, there is a degree of leakage of oil and compressed air from the outlet end of the compressor housing past the seal 54 and around the bearings 14, 15. It is found in practice that the pressure in the region 52 (produced by the combination of oil pressure and air leakage) is of a sufficient order when applied to the transmission housing 22 via passage 50 to force oil up passage 46 and into reservoir 47. The oil level at 45 is then maintained such that the head difference between the oil level and the lowermost point of the compressor housing is equal to the pressure created in the transmission housing by the combined effec-t of the entrained air in the lubricating oil and the air fed through passage 50.In order to ensure that the region of the compressor housing to which this oil is returned is at a low pressure relative to the transmission housing, the passage 48 communicates with the rotor bore at a point immediately after the cut-off position of the main rotor.

A drain plug 55 is provided at the lowermost point of the transmission housing for draining surplus oil from the housing when the compressor is not in use.

Referring now to Figure 2, a modification of the compressor of Figure 1 is shown. Like reference numerals in Figure 2 indicate like parts to Figure 1.

In Figure 2, a further passage 56 opening into an orifice 57 connects the passage 50 to a position adjacent the meshing position of gears 18 and 19.

The passage 56 and orifice 57 conduct the oil and entrained air in passage 50 onto gear wheels 18 and 19, lubricating them before falling to region 45 of housing 22. The pressure in 22 created by the entrained and dissolved air coming out of suspension is sufficient to force oil up passage 46, 47, 48 against gravity and into the rotor bore.

By this means oil used to lubricate the bearings 14 and 15 is additionally used to lubricate gears 18 and 19 reducing the volume requirements of the oil flowing through passages 36, 37 and 38 or in most cases removing the need for it altogether. The system illustrated in Figure 2 has eliminated the high pressure oil spray 38.

Some advantages of a system such as described are that the total volumetric require ments of the lubrication system are reduced, the drainage oil is lifted into the rotor bores by leakage air which would otherwise be wasted, and no separate conduit is necessary to pressurise the transmission housing.

WHAT WE CLAIM IS: 1. A method of draining oil in an oil-injected rotary compressor comprising a compressor housing for rotor means and a transmission housing for a transmission for driving the rotor means, a shaft of the rotor means extending at one end through an inlet end wall of the compressor housing into the transmission housing and extending at its other end through an outlet end wall of the compressor housing, the method comprising supplying fluid pressure which is created in a region beyond the outlet end wall of the compressor housing by compressed working-fluid leaking around the shaft, to the transmission housing through a first duct and thereby - driving oil from the transmission housing against the action of gravity on the oil through a second duct to a given region in the compressor housing where the pressure is lower than that in the said region beyond the outlet end wall.

2. An oil injected rotary compressor comprising a compressor housing for rotor means and a transmission housing for a transmission for driving the rotor means, a shaft of the rotor means extending at one end through an inlet end wall of the compressor housing into the transmission housing and extending at its other end through an outlet end wall of the compressor housing, said shaft having a fluid flow passage therearound for the leakage of compressed working-fluid to a region beyond the outlet end wall of the compressor housing, a first duct connecting said region to the transmission housing and a second duct, arranged for the flow of oil against the action of gravity on the oil and connecting the transmission housing to a given region in the compressor housing where the pressure is lower than that in the said region beyond the outlet end wall.

3. A compressor as claimed in claim 2 in which said rotor means comprises a first main rotor and a second rotor and the second duct connects the lowermost part of the transmission housing to an aperture in a bore for the main rotor in the compressor housing which is isolated by the main rotor from the compressor inlet.

4. A compressor as claimed in claim 2 or claim 3 in which a first gear is fixed to the said one end of the shaft for driving the compressor, in mesh with a second gear connected to an outlet shaft of a prime mover and said first duct connects said region to a part of the transmission housing adjacent the meshing position of the first and second gears.

5. A method of draining oil in an oilinjected rotary compressor substantially as hereinbefore described with reference to the accompanying drawings.

6. An oil-injected rotary compressor substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. ments of the lubrication system are reduced, the drainage oil is lifted into the rotor bores by leakage air which would otherwise be wasted, and no separate conduit is necessary to pressurise the transmission housing. WHAT WE CLAIM IS:

1. A method of draining oil in an oil-injected rotary compressor comprising a compressor housing for rotor means and a transmission housing for a transmission for driving the rotor means, a shaft of the rotor means extending at one end through an inlet end wall of the compressor housing into the transmission housing and extending at its other end through an outlet end wall of the compressor housing, the method comprising supplying fluid pressure which is created in a region beyond the outlet end wall of the compressor housing by compressed working-fluid leaking around the shaft, to the transmission housing through a first duct and thereby - driving oil from the transmission housing against the action of gravity on the oil through a second duct to a given region in the compressor housing where the pressure is lower than that in the said region beyond the outlet end wall.

2. An oil injected rotary compressor comprising a compressor housing for rotor means and a transmission housing for a transmission for driving the rotor means, a shaft of the rotor means extending at one end through an inlet end wall of the compressor housing into the transmission housing and extending at its other end through an outlet end wall of the compressor housing, said shaft having a fluid flow passage therearound for the leakage of compressed working-fluid to a region beyond the outlet end wall of the compressor housing, a first duct connecting said region to the transmission housing and a second duct, arranged for the flow of oil against the action of gravity on the oil and connecting the transmission housing to a given region in the compressor housing where the pressure is lower than that in the said region beyond the outlet end wall.

3. A compressor as claimed in claim 2 in which said rotor means comprises a first main rotor and a second rotor and the second duct connects the lowermost part of the transmission housing to an aperture in a bore for the main rotor in the compressor housing which is isolated by the main rotor from the compressor inlet.

4. A compressor as claimed in claim 2 or claim 3 in which a first gear is fixed to the said one end of the shaft for driving the compressor, in mesh with a second gear connected to an outlet shaft of a prime mover and said first duct connects said region to a part of the transmission housing adjacent the meshing position of the first and second gears.

5. A method of draining oil in an oilinjected rotary compressor substantially as hereinbefore described with reference to the accompanying drawings.

6. An oil-injected rotary compressor substantially as hereinbefore described with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.