Screw compressor with oil injection at multiple volume ratios

1. A compressor comprising:

a compressor housing;

a compression chamber defined by an inner bore and first and second ends of the compressor housing, the inner bore extending between the first and second ends of the compressor housing;

an inlet port upstream of the compression chamber;

a discharge port downstream of the compression chamber;

male and female screw rotors rotatably meshed together within the compression chamber, the male and female screw rotors operable for compressing a working fluid;

a compression pocket defined by a region in the compression chamber that is sealed from the inlet port and the discharge port;

a volume ratio defined within the compression pocket, the volume ratio varying between 1.0 at an entrance region proximate the first end of the compression chamber and a design maximum volume ratio at an exit region proximate the second end of the compression chamber;

a first lubricant injector in fluid communication with a first discharge orifice defined between the first and second ends and in the inner bore of the compressor housing, the first lubricant injector configured to inject lubricant into the compression chamber through the inner bore at a first volume ratio;

a second lubricant injector in fluid communication with a second discharge orifice defined between the first and second ends and in the inner bore of the compressor housing, the second lubricant injector configured to inject lubricant into the compression chamber through the inner bore at a second volume ratio, wherein the second volume ratio is larger than the first volume ratio; and

a main lubricant gallery formed in the compressor housing and a main lubricant inlet connected to the main lubricant gallery, the main lubricant inlet in fluid communication with a source of lubricant; wherein the first and second lubricant injectors are fluidly coupled with the main lubricant gallery through respective first and second axial galleries extending from the main lubricant gallery, the first and second lubricant injectors each define a passageway from the respective first and second axial galleries into the compression chamber to direct lubricant from the main lubricant inlet into the compression chamber.

2. The compressor of claim 1 further comprising a third lubricant injector configured to inject lubricant into the compression chamber at a third volume ratio different from the first and second volume ratios.

3. The compressor of claim 1 further comprising first and second injection ports extending through the housing at each of the first and second volume ratios.

4. The compressor of claim 3 , wherein the first injection port is positioned adjacent one of the male or female screw rotors and the second injection port is positioned adjacent the other of the male or female screw rotors.

5. The compressor of claim 1 , wherein the injected lubricant impinges onto one or both of the male and female screw rotors and mixes with the compressed working fluid in the compression chamber.

6. The compressor of claim 1 , wherein the main lubricant gallery extends across a width of the housing.

7. The compressor of claim 6 , wherein the main lubricant gallery is positioned proximate the second end of the housing adjacent the discharge port.

8. The compressor of claim 6 further comprising one or more lubricant injector ports extending from each of the first and second axial lubricant passages, respectively.

9. The compressor of claim 6 further comprising a connecting passageway extending between each of the first and second axial lubricant galleries and the main lubricant gallery.

10. A screw compressor comprising:

a compressor housing;

a compression chamber defined by an inner bore and first and second ends of the compressor housing, the inner bore extending between the first and second ends of the compressor housing;

an inlet port upstream of the compression chamber;

a discharge port downstream of the compression chamber;

male and female screw rotors rotatably meshed together within the compression chamber, the male and female screw rotors operable for compressing a working fluid;

a compression pocket defined by a region in the compression chamber that is sealed from the inlet port and the discharge port;

a first lubricant injector port in fluid communication with a first discharge orifice defined between the first and second ends and in the inner bore of the compressor housing, the first lubricant injector configured to inject lubricant into the compression chamber through the inner bore at a first volume ratio;

a second lubricant injector port in fluid communication with a second discharge orifice defined between the first and second ends and in the inner bore of the compressor housing, the second lubricant injector configured to inject lubricant into the compression chamber through the inner bore at a second volume ratio, wherein the second volume ratio is larger than the first volume ratio; and

a main lubricant gallery extending radially between the male and female rotors; and

first and second axial lubricant galleries formed in the compressor housing and extending from the main lubricant gallery to the first lubricant injector port and to the second lubricant injector port, respectively.

11. The screw compressor of claim 10 further comprising:

a third lubricant injector port configured to inject lubricant into the compression chamber at the first volume ratio; and

a fourth lubricant injector port configured to inject lubricant into the compression chamber at the second volume ratio.

12. The screw compressor of claim 11 , wherein lubricant from the third and fourth lubricant injector ports impinge on the other of the male screw rotor and female screw rotor, respectively and mixes with the compressed working fluid in the compression pocket.

13. The screw compressor of claim 11 wherein the main lubricant gallery extends across one end of the compressor housing.

14. The screw compressor of claim 13 , wherein the first and third injector ports extend directly from the main lubricant gallery.

15. The screw compressor of claim 13 , wherein the second and fourth injector ports extend from a distal end of the first and second axial lubricant galleries, respectively.

16. The screw compressor of claim 10 , wherein lubricant from the first and second lubricant injector ports impinge on the male screw rotor and the female screw rotor, respectively and mixes with the compressed working fluid in the compression pocket.

17. A method of operating a compressor comprising:

compressing a working fluid in a compression chamber with a meshed pair of male and female screw rotors, the compression chamber defined by an inner bore and two opposing ends of a compressor housing;

injecting lubricant through a first discharge orifice defined between the two opposing ends and in the inner bore of the compressor housing, the lubricant injected through the first discharge orifice into the compression chamber at a first volume ratio;

injecting lubricant through a second discharge orifice defined between the two opposing ends and in the inner bore of the compressor housing, the lubricant injected through the second discharge orifice into the compression chamber at a second volume ratio, the second volume ratio being greater than the first volume ratio;

wherein the injecting lubricant into the compression chamber at a first volume ratio includes flowing lubricant into a main lubricant gallery within the compressor housing which encloses the pair of male and female screw rotors, and subsequently flowing lubricant from the main lubricant gallery into an axial lubricant gallery also formed within the compressor housing, the axial lubricant gallery feeding a lubricant injector.

18. The method of claim 17 further comprising impinging the lubricant onto the male screw rotor and onto the female screw rotor at each of the first and second volume ratios in the compression chamber; and

mixing the lubricant with the working fluid at each of the first and second volume ratios in the compression chamber.