Patent Publication Number: US-2017370523-A1

Title: Electrostatic oil ring, electrostatic oil ring assembly, and electrodynamic machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims benefit of U.S. Provisional Patent Application No. 62/106,289 filed 22 Jan. 2015 in the United States Patent and Trademark Office, the content of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of the present invention generally relate to an electrostatic oil ring, an electrostatic oil ring assembly, and an electric machine comprising an electrostatic oil ring assembly. 
     2. Description of the Related Art 
     An oil ring, also referred to as ring oiler, is a form of oil-lubrication system for bearings usually arranged in rotating machine, for example electrodynamic machines. An oil ring usually is a metal ring placed around a horizontal shaft adjacent to a bearing of a machine or engine. An oil sump is underneath the shaft and the oil ring is large enough to dip into the oil of the oil sump. As the shaft rotates, the ring is carried with the shaft. The oil ring then picks up some oil out of the oil sump and deposits the oil for example onto the shaft from where it flows sideways and lubricates the bearings, or directly onto the bearing. 
     Electrodynamic machines, such as horizontal shaft induction motors, have rotating shafts restrained by rolling element, hydrodynamic, or hydrostatic bearings. Hydrodynamic bearings can generate a self-sustaining pressurized lubricant liquid film interface between the bearing surface and the corresponding shaft journal. Lubricant forming the lubricant film needs to be refreshed to replace that which is inevitably squeezed out of the bearing/journal interface due to their relative rotation. Oil replenishment also conveniently transfers heat generated within the interface or by thermal gradient transfer between the surfaces away from the bearing, for example to a sump. For brevity, lubricant will hereafter be referred to as oil, as it is a commonly used industrial lubricant. 
     Induction motors oftentimes employ oil ring lubricated hydrodynamic bearings to support and constrain the rotating shaft. The hydrodynamic bearings are often contained in a bearing block portion of a bearing housing mounted on both axial ends of the motor. The bearing housing in cooperation with the motor housing forms an oil sump having a maximum fluid fill level below the motor shaft and bearing, so that the shaft does not come in direct contact with the sump oil. The bearing includes one or more axially or laterally restrained annular oil rings that capture the motor shaft journal within its inner cylindrical surface. The oil ring is in direct contact with the motor shaft journal at the ring&#39;s approximately 12 o&#39;clock upper position. The lower portion of the oil ring proximal its 6 o&#39;clock lower position is dipped into the oil within the sump. The oil ring can include a grooved or otherwise textured surface to enhance friction contact with the shaft journal. Motor shaft rotation imparts oil ring rotation. As the oil ring rotates, it carries and transports an oil film on its surface from the sump oil and deposits the oil into the bearing as the previously dipped portion rotates from its prior 6 o&#39;clock position to a new 12 o&#39;clock position in contact with the shaft journal. 
     An oil ring&#39;s oil transfer rate from the sump to the shaft journal bearing is a function of and proportional to shaft rotation speed. Under low RPM, high load conditions the oil rings may not be able to maintain a desired oil transfer rate from the sump to the bearing. Conversely, under high RPM conditions, oil may be slung off the ring due to centrifugal forces before a sufficient quantity can reach the bearing during the rotational trip from sump to bearing. 
     SUMMARY 
     Briefly described, aspects of the present invention relate to an electrostatic oil ring, an electrostatic oil ring assembly, and an electrodynamic machine, for example an induction motor, comprising an electrostatic oil ring assembly. 
     A first aspect of the present invention provides an electrostatic oil ring comprising an annular ring body with a surface, wherein at least a portion of the surface carries an electrostatic coating which electrostatically attracts lubricant in a lubricant reservoir when the oil ring passes through the lubricant reservoir. 
     A second aspect of the present invention provides an electrostatic oil ring assembly comprising a plurality of electrostatic oil rings, each oil ring comprising an annular ring body with a surface, wherein at least a portion of the surface carries an electrostatic coating which electrostatically attracts lubricant in a lubricant reservoir when the oil ring passes through the lubricant reservoir. 
     A third aspect of the present invention provides an electrodynamic machine comprising an internal lubricant reservoir; and at least one hydrodynamic bearing without a pressurized oil feed system, the hydrodynamic bearing comprising at least one oil ring in fluid communication with lubricant in the internal lubricant reservoir, the at least one oil ring comprising an annular ring body with a surface, wherein at least a portion of the surface carries an electrostatic coating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic perspective view of a bearing lubrication system as incorporated in an idealized exemplary induction motor, with the motor shown in phantom in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  illustrates a partial, axial, cross-sectional view of the bearing lubrication system focusing on an induction motor bearing housing in accordance with an exemplary embodiment of the present invention. 
         FIG. 3  illustrates a partial, radial, cross-sectional view of the bearing lubrication system of  FIG. 1  in accordance with an exemplary embodiment of the present invention. 
         FIG. 4  illustrates a schematic view of an induction motor incorporating the bearing lubrication system, showing the motor in a generally level, horizontal position in accordance with an exemplary embodiment of the present invention. 
         FIG. 5  illustrates a schematic view of an induction motor incorporating the bearing lubrication system, showing the motor in a rolled position about the shaft axis relative to the horizontal position of  FIG. 4  in accordance with an exemplary embodiment of the present invention. 
         FIG. 6  illustrates a schematic view of an induction motor incorporating the bearing lubrication system, coupled to a motor drive control, for varying lubrication system flow parameters in accordance with an exemplary embodiment of the present invention. 
         FIG. 7  illustrates a schematic 3-dimensional view of an oil ring, in accordance with an exemplary embodiment of the present invention. 
         FIG. 8  illustrates a schematic 2-dimensional view of a further embodiment of an oil ring in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     To facilitate an understanding of embodiments, principles, and features of the present invention, they are explained hereinafter with reference to implementation in illustrative embodiments. In particular, they are described in the context of an electrostatic oil ring, an electrostatic oil ring assembly, and an electric machine comprising an electrostatic oil ring assembly. Embodiments of the present invention, however, are not limited to use in the described devices or methods. 
     The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present invention. 
       FIG. 1  shows a schematic perspective view of a bearing lubrication system as incorporated in an idealized exemplary induction motor  10 , with the motor  10  shown in phantom, mounted on a deck surface  12 . The deck surface  12  may be stationary, for example and without limitation mounted to for example a factory building floor or in a moving object, which can be for example and without limitation a marine vessel, railroad locomotive, construction crane, or mining drag line. As illustrated, the motor  10  is shown in phantom line drawing, because its electrodynamic components are of conventional construction. 
     A motor shaft  15  of the induction motor  10  is supported by a bearing  25 , for example a hydrodynamic bearing.  FIG. 1  shows a pair of annular oil rings  30 . The induction motor  10  can comprise one or more oil rings  30 . Each oil ring  30  can be in direct contact with the motor shaft  15 , in particular a motor shaft journal at the ring&#39;s approximately 12 o&#39;clock upper position. The lower portion of the oil rings  30  at an approximate 6 o&#39;clock lower position is dipped into oil  35   a  within an internally defined oil sump  35 . It should be noted that the oil sump  35  and oil  35   a  are herein also referred to as lubricant reservoir  35  and lubricant  35   a.  A fill level  36  of the oil sump  35  is schematically depicted, and is below the lower 6 o&#39;clock surface of the rotating shaft  15  and bearing  25  so as not to whip or foam the oil  35   a,  or cause unwanted rotating drag on the shaft  15 . Rotation of the motor shaft  15  imparts rotation of the oil rings  30 . As the oil rings  30  rotate, they carry and transport an oil film on their surface from the oil sump  35  and deposit oil  35   a  into the bearing  25  as the previously dipped portion rotates from its prior 6 o&#39;clock position to a new 12 o&#39;clock position in contact with the shaft journal. The oil sump fill level  36  will flow to a horizontal level position under the influence of gravity, no matter what the relative orientation of the motor  10 . If the motor  10  is installed in a moving object, such as a ship with a rolling deck, it is likely at some rolling orientations that the oil rings  30  will not be dipped into internal oil sump  30 . 
     In an exemplary embodiment, a bearing lubrication system can provide a parallel oil delivery mechanism to the bearing  25 , and is complimentary to the existing installed oil delivery system comprising the oil rings  30 . As  FIG. 1  shows, the bearing lubrication system includes an oil sump pump  40 , herein also referred to as lubricant reservoir pump  40 , retained within the motor&#39;s existing internal oil sump  35 . The pump  40  may be conveniently electrically powered and have variable pumping capacity rates. Power for the pump  40  may be routed into the internal oil sump  35  through one of the existing fitting locations or a new aperture may be added in design revisions. The pump  40  has an oil intake  42 , herein also referred to as lubrication intake  42 , in communication with the oil  35   a  retained in the oil sump  35 . The oil intake  42  is oriented in the sump  35  in a position most likely to be below the oil fill line  36  under any or most foreseen motor orientations. The pump oil intake  42  can be mounted to the pump  40  with a two or three degree of motion swivel joint, so that it remains plumb with and below the oil fill line  36  during pump motion when installed on a moving object. Alternatively, for motor applications in moving objects, the pump oil intake  42  may be constructed with a check valve upstream of a smaller reserve supply of oil retained in the intake  42  if the intake loses continuous fluid communication with the oil  35   a  of the oil sump  35  by being above the sump oil fill line  36  during some transient orientations of the motor  10 . 
     The pump  40  generates a pressurized lubricant discharge that is routed through discharge line  44 , the distal outlet of which is oriented proximal the bearing  25 , so that the discharge is directed to cause oil  35   a  to contact directly or flow into the bearing  25  and shaft  15 , in particular a shaft journal interface/shaft bearing interface. The discharge line  44  may be constructed of any desired rigid or flexible pipe or tubing, and is fixed to the motor  10 , in particular to a housing of the motor  10 , by any chosen fastener or bracket structure familiar to those skilled in the art. An oil nozzle  45 , herein also referred to as lubricant nozzle  45 , or other fluid spray pattern regulating component may be coupled to the distal end of the discharge line  44  to alter the discharge spray pattern of the lubricant spray  50 . One skilled in the art may choose to substitute other components for the nozzle  45 , for example an orifice, pulsed injector or aerator, in order to achieve other desired oil spray patterns for a particular application 
       FIG. 2  is a partial, axial, cross-sectional view of the bearing lubrication system focusing on an induction motor bearing housing, and  FIG. 3  is a partial, radial, cross-sectional view of the bearing lubrication system of  FIG. 1 . As shown in  FIGS. 2-3 , the motor shaft  15  is retained in a bearing housing  20  that includes the bearing  25  and an air seal  27  which isolates for example oil from the electrodynamic components in an interior of the motor  10 . A pair of known elastomeric labyrinth seals  28  may flank the bearing  25  and corresponding journal surface of the shaft  15  to inhibit oil flow out of the bearing region axially along the shaft  15 , and to retain a reserve of oil for replenishment of the oil film formed between the bearing  25  and corresponding journal surfaces. As described before in connection with  FIG. 1 , the oil rings  30 , the oil sump  35  with fill level  36 , the pump  40  with intake  42 , the discharge line  44  with nozzle  45  and oil spray  50  are also illustrated in  FIGS. 2-3 . 
     In operation, the parallel or auxiliary lubrication system enables reliable lubrication (oil) distribution under any motor load or speed operating conditions, whether or not the existing oil rings  30  are in fluid communication with oil  35   a  in the motor&#39;s oil sump  35 . The electric sump pump  40  oil flow rate may be selectively adjusted based on anticipated motor operating parameters of the motor  10  or in reaction to sensed operating conditions. Unlike oil rings  30  alone that may not be able to deliver desired oil flow rates to the bearing  25  under low speed, high load or high speed operating conditions, the parallel electric sump pump  40  oil discharge flow rate through the pump nozzle  45  via the discharge line  44  may be adjusted as necessary to meet bearing operational needs. The sump pump  40  lubrication system assures reliable oil delivery to the bearings  25  when the motor  10  is operating in a moving vehicle, should the oil rings  30  lose contact with oil in the internal sump  35 . 
       FIG. 4  illustrates a schematic view of the induction motor  10  incorporating the bearing lubrication system, showing the motor  10  in a generally level, horizontal position.  FIG. 5  illustrates a schematic view of the induction motor  10  incorporating the bearing lubrication system, showing the motor  10  in a rolled position about the shaft axis relative to the horizontal position of  FIG. 4 . 
     In  FIG. 4 , the motor  10  is mounted on a deck, such as for example a ship deck  12 , in a generally horizontal position, as noted by the X-Y-Z horizontal reference axes. When the motor  10  is oriented horizontally, the lubricant fill line  36  is parallel with the deck  12 . One or more oil rings  30  are generally plumb with the deck  12  and are dipped into oil  35   a  below the fill line  36  of the oil sump  35 . The lubrication system is discharging oil spray  50  onto the bearing  25  in parallel with oil that is being deposited by the one or more oil rings  30 . If desired, the electric sump pump  40  may be de-energized, stopping the oil spray  50 , with the bearing  25  lubrication being supplied solely by the one or more oil rings  30 . 
     Referring now to  FIG. 5 , the deck  12  rolls and pitches, respectively, relative to the X-Y-Z horizontal reference axes. The oil rings  30  are not in continuous fluid communication with oil  35   a  in the oil sump  35  because they are above the fill line  36 . In such situations, the lubrication system maintains oil spray  50  on the bearings  25 , so that the bearings  25  receive the flow rate that they need for desired operational performance. 
       FIG. 6  illustrates a schematic view of an induction motor  10  incorporating the bearing lubrication system, coupled to a control unit  60 , for varying lubrication system flow parameters. In  FIG. 6 , the motor  10  is coupled to a known control unit  60 , herein also referred to as motor drive controller  60  via communications pathway  62  in known fashion. The motor drive controller  60  is capable of altering the motor operating parameters, such as speed, torque, and responses to varying loads on the motor  10 . Known drive controllers  60  are also capable of monitoring motor operating conditions such as stator winding current and temperature, oil sump temperature, etc. It is contemplated as part of the present invention that the electric oil sump motor  40  may be coupled to the motor drive controller  60 , so that the latter may vary the sump pump flow rate, pressure and operating cycle (i.e., continuous, fluctuating or intermittent operation) based on motor operating parameters or in reaction to sensed variations in motor operating parameters. 
     The lubrication system of the present invention may be incorporated in new induction motors or other electrodynamic machines that have hydrodynamic or rolling element bearings by installing the sump pump  40  and its oil intake  42  within the motor&#39;s existing oil sump, or externally installing the pump with its intake in communication with the motor&#39;s internal and/or external oil supply reservoir. The sump pump  40  discharge line  44  and nozzle may be located anywhere within or outside the motor housing that enables the nozzle to discharge oil spray  50  on the bearing  25 , so that lubricant is deposited where needed in the bearing. The lubrication system component sump pump  40  with intake  42 , discharge line  44  and nozzle  45  may be easily field- or shop-retrofitted into existing installed motors. 
       FIG. 7  is a schematic 3-dimensional view of an oil ring in accordance with an exemplary embodiment of the present invention. The exemplary oil ring  130  illustrated in  FIG. 7  may be used in machines or engines, for example electrodynamic machines such as electric motors or generators, for example induction motors, turbines and many other rotating machines, for example as described before in  FIGS. 1-6 . The oil ring  130  may be part of an oil ring assembly comprising a plurality of oil rings  130 , or may be an only oil ring  130  arranged in an electrodynamic machine. The electrodynamic machine can comprise additional lubrication systems as described before. 
     The oil ring  130  can comprise metal. As described previously, during operation of for example an induction motor  10  (see  FIG. 1 ), the oil ring  130  dips into oil sump  35  underneath the shaft  15  of the motor  10 . As the shaft  15  rotates, the ring  130  is carried with the shaft  15  of the motor  10 , and then picks up some oil  35   a  out of the oil sump  35  and deposits the oil  35   a  for example onto bearing(s)  25  and/or the shaft  15  of the induction motor  10 . But the oil  35   a  of the oil sump  35  presents a hydrodynamic resistance to the motion of the ring  130  which causes frictional losses. Additionally, the friction slows down the motion of the ring  130  thus limiting the rate at which the ring  130  is able to deliver oil  35   a  to the bearing(s)  25  and/or shaft  15 . 
     The oil ring  130  as illustrated in  FIG. 7  comprises an exemplary shape of a hollow cylinder. But the oil ring  130  can comprise many other designs, forms or shapes suitable for oil rings (see for example  FIG. 8 ). 
     The exemplary electrostatic oil ring  130  comprises an annular ring body  142  with an inner surface  132 , an outer surface  134 , and side surfaces  136  and  138 . The inner surface  132  is defined by an inner diameter and the outer surface  134  is defined by an outer diameter of the ring  130 . The inner surface  132  and the outer surface  134  are connected via the side surfaces  136  and  138 . At least a portion of one of the surfaces  132 ,  134 ,  136  and  138  comprises a electrostatic coating  140  that electrostatically attracts the machine oil  35   a  in the oil sump (lubricant reservoir)  35  when the ring  130  passes through the oil sump  35  such that a chemical bond, specifically an electron bond between electrons, of the oil ring  130 , specifically the coating  140 , and the oil  35   a  is formed thus improving lubrication, dampening, and/or temperature between the oil ring  130  and the electrodynamic machine  10 , in particular shaft  15  and/or bearings  25  of the machine  10 . 
     According to an exemplary embodiment, the oil ring  130  is coated with a material that interacts with the machine oil  35   a  on an electrostatic level, thus creating an electrostatic attraction between the oil  35   a  and the coating  140  allowing the oil ring  130  to collect and deliver more oil  35   a  from the oil sump  35  to the bearings  25 . 
     The triboelectric effect (also known as triboelectric charging) is a type of contact electrification in which certain materials become electrically charged after they come into frictive contact with a different material. The triboelectric series lists materials in order of the polarity of charge separation when they are touched with another object/material. 
     Relative positions of the machine oil  35   a  and the material of the coating  140  in the triboelectric series are such that when the materials, i.e., the machine oil  35   a  and the coating  140 , are rubbed together, they exchange electrons and a net charge is developed, causing an attractive force between the materials. As the oil ring  130  passes through the oil sump  35 , the coating  140  rubs against the oil  35   a  and creates an attractive charge that allows more oil  35   a  to be lifted by the ring  130 . 
     At least a portion or the complete outer surface  134 , the inner surface  132 , and side surfaces  136 ,  138  can comprise the coating  140 . According to  FIG. 7 , a portion of the outer surface  134  and a portion of the inner surface  134  comprise the coating  140 . In an alternative embodiment, the complete ring  130  can comprise the coating  140 , i.e. all the surfaces  132 ,  134 ,  136  and  138  are completely covered by the coating  140 . In a further alternative embodiment, the ring  130  consists of the material of the coating, i.e., can be for example manufactured from the material of the coating  140 . 
     The coating  140  of the oil ring  130  comprises for example a material with an appreciable difference in relative electro-negativity from machine oil (which is typically used as lubrication for rotating machines) in the triboelectric series, for example and without limitation Teflon®, PVC (Polyvinylchloride), and the like. According to the triboelectric series, machine oil comprises a positive charge affinity value of +29 nC/J. In contrast, PVC comprises a negative charge affinity value of −100 nC/J, and Teflon® comprises a negative charge affinity value of −190 nC/J. As the machine oil and the suggested coating materials comprise opposed charge affinity values, the materials will attract one another when the oil ring  130  is in motion and passes through the oil  35   a  in the oil sump  35 . One of ordinary skill in the art appreciates that many other materials comprising a negative charge affinity value distant to the positive charge affinity value of machine oil may be used. 
       FIG. 7  further illustrates gravitational force  102  to show the general arrangement of the oil ring  130 , particularly when arranged on a machine shaft. Rotation  104  is also shown; even though a clockwise rotation is shown, one skilled in the art can appreciate that a counter-clockwise rotation is possible. As illustrated, viscous force  106  is shown, and is generally in opposite to the gravitational force  102 . 
       FIG. 8  illustrates a schematic 2-dimensional view of a further embodiment of an oil ring. As noted before, an oil ring can comprise many different designs, shapes and forms.  FIG. 8  shows that the oil ring  150  comprises an annular ring body  152  in form of a torus with a closed surface  154  that is compact and without boundary. The oil ring  150  comprises electrostatic coating  156  distributed over the surface  154  of the ring  150 . As noted before, it is also possible that the complete surface  154  of the ring  150  comprises the coating  156 , or that the oil ring  150  is completely constructed from the material of the coating  156 . 
     The provided electrostatic oil ring  130 ,  150  and a corresponding oil ring assembly with a plurality of oil rings  130 ,  150  are a simple and inexpensive way to improve the bearing temperature performance in any electrodynamic machine utilizing oil rings. Further, by increasing the oil supply between the oil ring  130 ,  150  and a machine shaft, the lubrication can also decrease the overall temperature of the machine, as friction can be reduced. Further, because of damping provided by the additional oil, vibration in the machine can be reduced. Consequently, the overall performance of an electrodynamic machine is improved and, further, less repairs or shut downs are necessary. 
     While embodiments of the present invention have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.