Hybrid ball bearing, particularly for refrigerant compressor

Abstract

A Hybrid ball bearing including an outer raceway, an inner raceway, and a plurality of balls arranged between the inner raceway and the outer raceway. The outer raceway and the inner raceway are made from bearing steel and have a first surface RMS roughness R.sub.q1. At least one ball of the plurality of balls is made from a ceramic material and has a second surface RMS roughness R.sub.q2. In a mint condition, the roughness of the raceways R.sub.q1 is 2 to 5 times higher than the roughness R.sub.q2 of the at least one ball, as well as a refrigerant compressor comprising such a hybrid ball bearing.

Claims

1. A hybrid ball bearing comprising an inner raceway and an outer raceway and a plurality of balls arranged therebetween, wherein the inner raceway and the outer raceway are made from bearing steel and have a first surface RMS roughness Rq1, and wherein at least one ball is made from a ceramic material and has a second surface RMS roughness Rq2, wherein the roughness Rq1 is 2 to 5 times higher than the roughness Rq2 of the at least one ball.

2. The hybrid ball bearing according to claim 1, wherein R.sub.SK1 is a skewness of the inner or outer raceway and R.sub.SK2 is a skewness of the at least one ball, Rq is a combined surface RMS of the raceways and balls, and a combined roughness skewness R.sub.sk of raceways and balls is R.sub.sk0, wherein R.sub.sk is defined as $R_{\mathrm{sk}}=\frac{R_{\mathrm{sk}1}{R}_{q1}^3+R_{\mathrm{sk}2}{R}_{q2}^3}{R_q^3}.$

3. The hybrid ball bearing according to claim 1, wherein R.sub.qx1 is a slope parameter of the inner or outer raceway, R.sub.qx2 is a slope parameter of the at least one ball, and a combined roughness slope parameter Rqx of raceways and balls is Rqx8 [mrad], wherein Rqx is defined as: $R_{\mathrm{qx}}=\frac{R_{\mathrm{qx}1}+R_{\mathrm{qx}2}}{2}.$

4. The hybrid ball bearing according to claim 1, wherein an osculation ranges between 1.02 and 1.1, wherein is defined as $=\frac{2r_{i,e}}{D_w},$ with r.sub.i,e being the raceway radius of the inner raceway or the outer raceway, and D.sub.w being the diameter of the ball.

5. The hybrid ball bearing according to claim 1, wherein at least one raceway is made from a hardened corrosion-resistant steel, having a corrosion resistance with a pitting potential of at least 25 mV higher than a stainless steel reference AISI 440C according to ASTM G61-86.

6. The hybrid ball bearing according to claim 1, wherein at least one ball is made from silicon nitride (Si3N4).

7. The hybrid ball bearing according to claim 1, wherein the balls are guided by means of a cage, which is made from a fiber-enforced material, a glass-fiber enforced PEEK or a carbon fiber material.

8. The hybrid ball bearing according claim 7, wherein the hybrid ball bearing is lubricated with pure refrigerant or a refrigerant/oil mixture forming an elasto-hydrodynamic lubricant film between the balls and the raceways.

9. The hybrid ball bearing according to claim 1, wherein the hybrid ball bearing is lubricated by means of an ultra-thin lubrication film arranged between the balls and the raceways, wherein the lubrication film thickness is less than 300 nm.

10. The hybrid ball bearing according to claim 1 wherein the hybrid ball bearing is integrated into a refrigerant compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The FIGURE shows:

(2) FIG. 1 presents a schematic drawing of a refrigerant compressor comprising a hybrid ball bearing according to the present invention.

DETAILED DESCRIPTION

(3) In the following same or similar functioning elements are indicated with the same reference numerals.

(4) FIG. 1 shows a sectional view of a refrigerant compressor 1 having an electric motor 2 which drives a shaft 4. The shaft 4 is radially supported by a set of hybrid roller bearings 10-1, 10-2, which are arranged on both sides of the motor 2. Further, the shaft 4 is axially and radially supported by a plurality of hybrid ball bearings 20-1, 20-2, 20-3. The hybrid ball bearings 20-1, 20-2, 20-3 are preferably angular contact ball bearings, which are enabled to support axial and/or radial forces, but may be any other type of ball bearing. The hybrid roller bearings 10-1, 10-2 may be any kind of roller bearing, e.g. a cylindrical roller bearing, a spherical roller bearing, a tapered roller bearing or a toroidal roller bearing or combinations thereof.

(5) Each hybrid roller bearing 10-1, 10-2 comprises an inner ring 12 having a raceway 13, an outer ring 14 having a raceway 15, and rollers 16 having raceway 17, which are arranged therebetween. The rollers 16 are further guided by means of a cage 18, which is preferably made from a glass-fiber enforced PEEK material. However, any other fiber-enforced material, e.g. a carbon fiber material, may be used for the cage.

(6) Analogously, each hybrid ball bearing 20-1, 20-2, 20-3 comprises an inner ring 22 having a raceway 23, an outer ring 24 having a raceway 25, and balls 26 having surfaces 27, arranged therebetween. Also, the balls 26 are guided by means of a cage 28, which is preferably made from a glass-fiber enforced PEEK material. However, any other fiber-enforced material e.g. a carbon fiber material, may be used for the cage.

(7) Further, it should be noted that the hybrid ball bearings shown in FIG. 1, have a contact angle of 25 to 30, but it is also possible to use hybrid ball bearings having contact angles in the range of 0 to 45. Optionally, the hybrid ball bearing and/or the hybrid roller bearing has an osculation , which ranges between 1.02 and 1.1, wherein is defined as =2r_(i,e)/D_w, with r.sub.i,e being the raceway radius of the inner raceway or the outer raceway, and Dw being the diameter of the ball. The proposed osculation gives a balance between low friction forces at the surface and high contact stresses, so bearing life is optimized.

(8) As is further shown in FIG. 1, the hybrid rolling bearings 10-1, 10-2, 20-1, 20-2, 20-3 are lubricated by lubrication means 30, 32, which are adapted to provide a lubricant to the hybrid rolling bearings 10-1, 10-2, 20-1, 20-2, 20-3. Since the device shown in FIG. 1 is a refrigerant compressor, it is preferred to use the refrigerant itself or a refrigerant/oil mixture as lubricant. This has proven to improve heat transfer in the condensers and the evaporator heat exchangers. Eliminating oil lubricant also eliminates the need for oil maintenance and oil cost.

(9) On the other hand, using pure refrigerant and/or a refrigerant/oil mixture as lubricant, leads to ultra-thin lubrications film thickness (UTFT) conditions due to the refrigerant providing an elasto-hydrodynamic lubrication film with a thickness of less than 200 nm. Since these applications work with very thin film thicknesses (e.g. less than 200 nm) any solid particle (debris, sand, oil soot, etc.) even the very small ones can produce damage in the contact surfaces and can modify the topography disrupting the film build-up capability of the original surface. Excessive contamination, which is also an issue in refrigerant lubricated rolling bearing, can also generate high friction forces that will hinder/block the rotation of the bearing and can produce fractures in the cage or seizure in the raceways and rolling elements.

(10) Thus, in order to improve the wear and fatigue life of hybrid rolling bearings used in the refrigerant compressor, it has already been common knowledge to use a hardened high nitrogen stainless steel, e.g. VC444 steel, and silicon nitride rolling elements for the hybrid rolling bearing.

(11) Additionally, the inventors have found that micropitting and corrosion induced wear of a hybrid ball bearing may be significantly reduced if the roughness's of the contacting surfaces of the hybrid ball bearing in mint conditions is engineered to be within predefined boundaries. It has been therefore proposed by the inventors to provide a hybrid ball baring 20-1, 20-2, 20-3, wherein the outer raceway 25 and the inner raceway 23 are made from bearing steel and have a first surface RMS roughness R.sub.q1, and wherein at least one ball 26 is made from a ceramic material and has a second surface RMS roughness R.sub.q2. Further it has been suggested that in mint conditions the roughness of the raceways R.sub.q1 is 2 to 5 times higher than the roughness R.sub.q2 of the at least one ball 26.

(12) The hybrid roller bearing 10-1, 10-2 may be any hybrid roller bearing known from the state of the art, but it is further preferred if the roughness's of the hybrid roller bearing are additionally engineered. Consequently, the outer raceway 15 and the inner raceway 13 of the hybrid roller bearings 10-1, 10-2 are also made from bearing steel and have a first surface RMS roughness R.sub.q1, and wherein at least one roller 16 is made from a ceramic material and has a second surface RMS roughness R.sub.q2. Further it has been suggested that in mint conditions the roughness of the raceways R.sub.q1 is 1.2 to 4 times higher than the roughness R.sub.q2 of the at least one roller 16.

(13) These predetermined roughnesses allow for avoiding any solid-to-solid contact even at mint conditions and under ultra-thin lubrications film operating conditions of the hybrid ball bearing.

(14) The steel used for the rings and the raceway is preferably a hardened corrosion resistant steel, e.g. VC444 steel. Another example is DIN X30CrMoN15-1 (AMS 5898). In general the hardened corrosion-resistant bearing steel for UTFT conditions refers to a bearing steel with an after-heat-treatment hardness HRC 58 and/or a fracture toughness of at least 14 MPa m (ASTM-E399-12). It is further preferred, if the corrosion resistance has a pitting potential bigger or equal to +25 mV higher than the stainless steel reference (AISI 440C) according to ASTM G61-86. After heat treatments the ring raceways 13, 15, 23, 25 are machined to dimensions, and the desired roughness is adjusted. The heat treatment usually comprises one of more of the following steps:

(15) Austenitising at 1000 C. to 1150 C.;

(16) Gas quench;

(17) Subzero treatment at 40 C. to 150 C.;

(18) Tempering to certain temperatures for different dimensional stability properties.

(19) Table 1 shows one example of the covered steel: DIN X30CrMoN15-1 (AMS 5898), compared with the reference steel AISI 440 C. It is further shown that different tempering temperatures give different dimensional stability properties for the same corrosion resistant steel.

(20) TABLE-US-00001 TABLE 1 Example of corrosion resistant steel parameters Pitting Potential relative to Steel reference, [mV] Tempering Hardness DIN +25 At 400 C. to 58 HRC X30CrMoN15-1 550 C. DIN +375 At 150 C. to 58 HRC X30CrMoN15-1 240 C. AISI 440C 0 Min. of 58 HRC ~204 C.

(21) The rolling elements, namely the rollers 16 and the balls 26 of the hybrid rolling bearings 10-1, 10-2, 20-1, 20-2, 20-3, are Silicon Nitride Balls (Si3N4): The rolling elements 16, 26 are made by most stringent ceramic quality control and grade and have to pass ASTM F2094 or ISO 26602 class I and II with rolling element grade equal or better than G10.

(22) Besides the roughness difference as mentioned above, the inventors have further found that it is preferred to adjust the combined roughness of raceways and rolling elements of the hybrid rolling bearings 10-1, 10-2, 20-1, 20-2, 20-3 used for applications operating under UTFT conditions to predetermined ranges. It has been proven that hybrid rolling bearings 10-1, 10-2, 20-1, 20-2, 20-3 having the roughness values as listed below are particularly resistant to corrosion induced wear even in UTFT conditions:

(23) For the hybrid ball bearings 20-1, 20-2, 20-3, the following values apply:

(24) The combined surface RMS roughness Rq of raceways and balls is:
R.sub.q410.sup.9(1000d.sub.m).sup.0.55 [meter], with R.sub.q={square root over (R.sub.q1.sup.2+R.sub.q2.sup.2)}.

(25) The combined roughness skewness R.sub.sk of raceways and balls is:

(26) $R_{\mathrm{sk}}0,\mathrm{with}{R}_{\mathrm{sk}}=\frac{R_{\mathrm{sk}1}{R}_{q1}^3+R_{\mathrm{sk}2}{R}_{q2}^3}{R_q^3}$

(27) The combined roughness slope parameter R.sub.qx of raceways and balls is:

(28) $R_{\mathrm{qx}}8\left[\mathrm{mrad}\right],\mathrm{wherein}{R}_{\mathrm{qx}}=\frac{R_{\mathrm{qx}1}+R_{\mathrm{qx}2}}{2}$

(29) For the hybrid roller bearings 10-1, 10-2, the following values apply:

(30) The combined surface RMS roughness R.sub.q of raceways and rollers is:
R.sub.q510.sup.8(1000d.sub.m).sup.0.2 [meter], with R.sub.q={square root over (R.sub.q1.sup.2+R.sub.q2.sup.2)}.

(31) The combined roughness skewness R.sub.sk of raceways and rollers is:

(32) $R_{\mathrm{sk}}0,\mathrm{with}{R}_{\mathrm{sk}}=\frac{R_{\mathrm{sk}1}{R}_{q1}^3+R_{\mathrm{sk}2}{R}_{q2}^3}{R_q^3}.$

(33) The combined roughness slope parameter R.sub.qx of raceways and rollers is:

(34) $R_{\mathrm{qx}}50\left[\mathrm{mrad}\right],\mathrm{wherein}{R}_{\mathrm{qx}}=\frac{R_{\mathrm{qx}1}+R_{\mathrm{qx}2}}{2}.$

(35) By providing at least a hybrid ball bearing 20-1, 20-2, 20-3 being engineered to have the above defined parameters, the ceramic balls reduce boundary frictions and optimize running-in. Further in poor lubrication and contamination conditions, the proposed ceramic balls delay the damage progression. In addition, the tight control of the composed roughness helps in the build-up of lubrication films and the improvement of running-in. The roughness of the raceways may be adapted by using appropriate honing and grinding processes. The roughness of the ceramic rolling elements may be adapted by using appropriate grinding and lapping processes using diamond abrasives.

REFERENCE NUMBERS

(36) 1 refrigerant compressor 2 electric motor 4 compressor shaft 10-1, 10-2 hybrid roller bearing 12 inner ring of the hybrid roller bearing 13 raceway of the inner ring of the hybrid roller bearing 14 outer ring of the hybrid roller bearing 15 raceway of the outer ring of the hybrid roller bearing 16 roller of the hybrid roller bearing 17 raceway of the roller of the hybrid roller bearing 18 cage of the hybrid roller bearing 20-1, 20-2, 20-3 hybrid ball bearing 22 inner ring of the hybrid ball bearing 23 raceway of the inner ring of the hybrid ball bearing 24 outer ring of the hybrid ball bearing 25 raceway of the outer ring of the hybrid ball bearing 26 balls of the hybrid ball bearing 27 surface of the balls of the hybrid ball bearing 28 cage of the hybrid ball bearing 30, 32 lubrications means