Bearing protection for inverter-driven motor

• US 20070201995A1
• Filed: 02/24/2006
• Published: 08/30/2007
• Est. Priority Date: 02/24/2006
• Status: Abandoned Application

• Current Assignee: Trane International Inc. (Trane Technologies plc)
• Original Assignee: American Standard Companies Incorporated (Ideal Standard International Topco SCA)
• Inventors: Harstad, Michael, Duga, Joel, Fiegen, Gregory, Sullivan, Brian, Kwiatkowski, James, Kotlarek, Peter, Heiden, Richard
• Application Number:
  US11/361,329
• Publication Number:
  US 20070201995A1
• Time in Patent Office: Days
• US Class Current: 417/423.120
• CPC Class Codes: F04D 29/023 especially adapted for elastic fluid pumps
• CPC Class Codes: F04D 29/0566 Ceramic bearing designs
• CPC Class Codes: F04D 29/059 Roller bearings
• CPC Class Codes: F05D 2300/21 Oxide ceramics
• CPC Class Codes: F05D 2300/2112 Aluminium oxides
• CPC Class Codes: F05D 2300/506 Hardness
• CPC Class Codes: F05D 2300/611 Coating
• CPC Class Codes: F16C 19/52 with devices affected by abnormal or undesired conditions

Abstract

A refrigerant motor/compressor employs both a serviceable shaft-grounding device and a ceramic coating to protect a rolling element bearing that could otherwise be damaged by high frequency induced common mode voltage and current originating from an inverter that includes a plurality of IGBTs (insulate gate bipolar transistors). The shaft-grounding device includes a stranded copper wire brush that rides against an axial end of the shaft and a high frequency stranded grounding wire that conducts the induced current away from the shaft. The shaft-grounding device is sized and positioned so that it can be momentarily removed for inspection without having to evacuate the refrigerant. The ceramic coating provides an electrical insulating surface on a bearing bracket and other parts that support the bearing. The coating comprises titanium dioxide and aluminum oxide to provide a surface that is sufficiently hard and tough to resist damage during assembly, thereby maintaining the coating'"'"'s integrity.

Claims

1. A compressor system powered by an AC voltage supply for compressing a refrigerant, comprising:

a compressor housing defining a suction inlet and a discharge outlet;

a motor housing extending from the compressor housing;

a bearing bracket extending from the motor housing;

a bearing having an outer periphery supported by the bearing bracket;

a shaft supported by the bearing and being rotatable about a rotational axis, the shaft includes an outboard end and an inboard end, the bearing is closer to the outboard end than to the inboard end;

a compressor element driven by the shaft and being rotatable relative to the compressor housing to force the refrigerant from the suction inlet to the discharge outlet, the compressor element is closer to the inboard end than to the outboard end; and

a minimally conductive coating disposed on the bearing bracket, the coating is between the bearing bracket and the bearing to provide electrical resistance therebetween, the coating is harder than the bearing bracket and the outer periphery of the bearing.

2. The compressor system of claim 1 wherein the minimally conductive coating is a ceramic coating including titanium dioxide and aluminum oxide.

3. The compressor system of claim 1, further comprising:

a seal ring attached to the bearing bracket, the seal ring includes a labyrinth seal in proximity to the shaft; and

a clamp ring attached to the bearing bracket, wherein the bearing is axially clamped between the seal ring and the clamp ring, and the ceramic coating is further disposed on the seal ring and the clamp ring.

4. The compressor system of claim 3, further comprising:

a rotor carried by the shaft, the rotor is closer to the outboard end than to the inboard end;

a stator disposed within the motor housing and encircling the rotor;

an inverter electrically coupled to the stator for driving the compressor element at various speeds, the inverter comprises a converter section for converting the AC voltage supply to DC voltage, and an inverter section electrically coupled to the converter section for converting the DC voltage to a variable frequency output that goes to the stator, at least one of the converter section and the inverter section includes a plurality of insulate gate bipolar transistors that can induce a common mode current in the shaft, wherein the common mode current at times exceeds one megahertz.

5. The compressor system of claim 4, further comprising:

a shaft-grounding device comprising a wire brush, a brush housing, and a spring, wherein;

a) the brush housing is coupled to the motor housing,

b) the wire brush is movable along a longitudinal centerline of the brush housing,

c) the spring urges the wire brush toward the outboard end of the shaft to create electrical continuity between the wire brush and the outboard end of the shaft,

d) the wire brush is electrically coupled to the brush housing, thereby establishing electrical continuity between the compressor housing and the outboard end of the shaft while the ceramic coating provides electrical resistance directly between the bearing and the bearing bracket.

6. The compressor system of claim 2, further comprising:

a shaft-grounding device comprising a wire brush, a brush housing, and a spring, wherein;

e) the brush housing is coupled to the motor housing,

f) the wire brush is movable along a longitudinal centerline of the brush housing,

g) the spring urges the wire brush toward the outboard end of the shaft to create electrical continuity between the wire brush and the outboard end of the shaft,

h) the wire brush is electrically coupled to the brush housing, thereby establishing electrical continuity between the compressor housing and the outboard end of the shaft while the ceramic coating provides electrical resistance directly between the bearing and the bearing bracket.

7. The compressor system of claim 6, wherein the longitudinal centerline and the rotational axis are substantially collinear.

8. The compressor system of claim 6, wherein the spring urges the wire brush to exert 4 to 20 ounces of force against the outboard end of the shaft.

9. The compressor system of claim 6, wherein the shaft-grounding device further comprises an anti-rotation element disposed within the brush housing, wherein the anti-rotation element limits relative rotational movement between the wire brush and the brush housing.

10. The compressor system of claim 6, wherein the shaft-grounding device further comprises a stranded grounding wire disposed within the brush housing for conveying the common mode current from the wire brush to the brush housing.

11. A compressor system powered by an AC voltage supply for compressing a refrigerant, comprising:

a compressor housing defining a suction inlet and a discharge outlet;

a motor housing attached to the compressor housing;

a bearing bracket attached to the motor housing;

a bearing supported by the bearing bracket;

a shaft supported by the bearing and being rotatable about a rotational axis, the shaft includes an outboard end and an inboard end, the bearing is closer to the outboard end than to the inboard end;

a compressor element driven by the shaft and being rotatable to force the refrigerant from the suction inlet to the discharge outlet, the compressor element is closer to the inboard end than to the outboard end;

an endplate spaced apart from the shaft, spaced apart from the bearing, and electrically coupled to the compressor housing;

a ceramic coating disposed on the bearing bracket, the ceramic coating is between the bearing bracket and the bearing; and

a shaft-grounding device comprising a wire brush, a brush housing, and a spring, wherein;

a) the brush housing is attached to the endplate,

b) the wire brush is movable along a longitudinal centerline of the brush housing,

c) the spring urges the wire brush toward the outboard end of the shaft to create electrical continuity between the wire brush and the outboard end of the shaft,

d) the wire brush is electrically coupled to the brush housing, and

e) the brush housing is electrically coupled to the endplate, thereby establishing electrical continuity between the compressor housing and the outboard end of the shaft while the ceramic coating provides electrical resistance directly between the bearing and the bearing bracket.

12. The compressor system of claim 11, further comprising:

a rotor carried by the shaft, the rotor is closer to the outboard end than to the inboard end;

a stator disposed within the motor housing and encircling the rotor;

an inverter electrically coupled to the stator for driving the compressor element at various speeds, the inverter comprises a converter section for converting the AC voltage supply to DC voltage, and an inverter section electrically coupled to the converter section for converting the DC voltage to a variable frequency output that goes to the stator, both the converter section and the inverter section include a plurality of insulate gate bipolar transistors that can induce a common mode current in the shaft, wherein the common mode current exceeds one megahertz.

13. The compressor system of claim 12, wherein the longitudinal centerline and the rotational axis are substantially collinear.

14. The compressor system of claim 12, wherein the spring urges the wire brush to exert 4 to 20 ounces of force against the outboard end of the shaft.

15. The compressor system of claim 12, wherein the shaft-grounding device further comprises an anti-rotation element disposed within the brush housing, wherein the anti-rotation element limits relative rotational movement between the wire brush and the brush housing.

16. The compressor system of claim 12, wherein the shaft-grounding device further comprises a grounding wire disposed within the brush housing for conveying the common mode current from the wire brush to the brush housing.

17. The compressor system of claim 12, further comprising:

a seal ring attached to the bearing bracket, the seal ring includes a labyrinth seal in proximity to the shaft; and

a clamp ring attached to the bearing bracket, wherein the bearing is axially clamped between the seal ring and the clamp ring, and the ceramic coating is further disposed on the seal ring and the clamp ring.

18. The compressor system of claim 12, wherein the ceramic coating is harder than the bearing bracket.

19. The compressor system of claim 12, wherein the ceramic coating is harder than an outer periphery of the bearing.

20. The compressor system of claim 12, wherein the ceramic coating includes titanium dioxide and aluminum oxide.

21. A compressor system powered by an AC voltage supply for compressing a refrigerant, comprising:

a compressor housing defining a suction inlet and a discharge outlet;

a motor housing adjacent to the compressor housing;

a bearing supported within the motor housing;

a shaft supported by the bearing and being rotatable about a rotational axis, the shaft includes an outboard end and an inboard end, the bearing is closer to the outboard end than to the inboard end;

a compressor element driven by the shaft and being rotatable to force the refrigerant from the suction inlet to the discharge outlet, the compressor element is closer to the inboard end than to the outboard end;

a rotor carried by the shaft, the rotor is closer to the outboard end than to the inboard end;

a stator disposed within the motor housing and encircling the rotor;

an inverter electrically coupled to the stator for driving the compressor element at various speeds, the inverter includes a plurality of insulate gate bipolar transistors that can induce a common mode current in the shaft, wherein the common mode current can exceed one megahertz; and

a shaft-grounding device comprising a wire brush, a brush housing, a spring, and a grounding wire, wherein;

a) the brush housing is electrically coupled to the motor housing,

b) the grounding wire electrically couples the wire brush to the brush housing;

c) the wire brush is movable along a substantially linear path, and

d) the spring is contained within the brush housing and urges the wire brush toward the outboard end of the shaft to create electrical continuity between the wire brush and the outboard end of the shaft.

22. The compressor system of claim 21, wherein the substantially linear path and the rotational axis are substantially collinear.

23. The compressor system of claim 21, wherein the spring urges the wire brush to exert 4 to 20 ounces of force against the outboard end of the shaft.

24. The compressor system of claim 21, wherein the shaft-grounding device further comprises an anti-rotation element disposed within the brush housing, wherein the anti-rotation element limits relative rotational movement between the wire brush and the brush housing.

25. The compressor system of claim 21 further including a bearing bracket supporting the bearing and a non-conductive coating on the bearing bracket.

26. A compressor system, comprising:

a motor housing having an interior containing a refrigerant and an exterior exposed to a surrounding atmosphere;

a compressor housing hermetically sealed to the motor housing;

an endplate extending from the motor housing;

a refrigerant disposed within the compressor housing and the motor housing;

a rolling element bearing inside the motor housing;

a journal bearing inside at least one of the motor housing and the compressor housing;

a shaft having an inboard end, an outboard end, and an intermediate section therebetween, wherein the rolling element bearing supports the outboard end, and the journal bearing supports the intermediate section;

a compressor element mounted to the inboard end of the shaft and being rotatable for compressing the refrigerant;

a shaft-grounding device extending into the opening of the endplate such that the shaft-grounding device is in electrical contact with the outboard end of the shaft and is exposed to the refrigerant and the surrounding atmosphere.

27. The compressor system of claim 26, further comprising a minimally conductive material interposed between the rolling element bearing and the motor housing.

28. The compressor system of claim 27 wherein the minimally conductive material is a ceramic coating, a metal oxide, or a silicon oxide.

29. The compressor system of claim 28, further comprising a rotor carried by the shaft between the rolling element bearing and the journal bearing, a stator encircling the rotor, an inverter powering the stator to rotate the rotor, the shaft, and the compressor element at various speeds, wherein the inverter includes a plurality of insulate gate bipolar transistors.

30. The compressor system of claim 26, wherein the endplate defines an opening whose cross-sectional area is less than 4 in² and wherein the opening of the endplate is a threaded hole that threadingly engages the shaft-grounding device.

31. A method of servicing a hermetically sealed compressor system that includes a motor housing exposed to a surrounding atmosphere, a shaft rotatable within the motor housing, a refrigerant disposed within the motor housing, and a shaft-grounding device that when properly installed is exposed to the refrigerant and the surrounding atmosphere and completes an electrical path between the shaft and the motor housing, the method comprising:

adjusting the temperature of the refrigerant until the refrigerant in the motor housing is at a pressure substantially equal to that of the surrounding atmosphere; and

removing the shaft-grounding device from within the motor housing while the pressure of the refrigerant is substantially equal to that of the surrounding atmosphere, thereby providing an opportunity to inspect the shaft-grounding device without having to evacuate the refrigerant from within the motor housing.

32. The method of claim 31, wherein the shaft-grounding device includes a spring, and the method of servicing a hermetically sealed compressor further comprises at least partially relaxing the spring upon removing the shaft-grounding device.