Abstract:
A centrifuge is employed to continuously remove particulates from a fluid. In one embodiment, the centrifuge removes small particles of soot from lubricating oil of diesel engines. The fluid is introduced into the centrifuge through a distribution rotor so that vortexes are not propagated in the fluid. Laminar flow of the fluid down the sides of the outer rotor may contribute to the soot-removal effectiveness of the centrifuge.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to centrifuges and, more particularly, to centrifuges employed to remove particulates from lubricants. 
     Centrifuges have often been employed to remove various particulate contaminants from lubricating oil of internal combustion engines. The most common applications of centrifuges in this context have been in large diesel engines. Typically, lubricating oil of a large diesel engine may be continuously passed through a full flow filter and through a bypass centrifugal filter or centrifuge. While conventional centrifugal filters may be relatively costly, their cost is justified because engine life is improved when they are used. 
     Recent developments in environmental standards have introduced additional demands on filtering systems for diesel engine oil. Injector timing retardation is needed to meet more stringent air pollution standards. These demands result in increased production of carbon soot on the cylinder walls of an engine. Soot finds its way into the lubricating oil of the engine. Conventional full flow filters and conventional centrifugal filters do not adequately remove soot from the oil. Engine life is reduced in the presence of soot in the oil because the soot is abrasive and it reduces lubricating qualities of the oil. 
     Various efforts have been made to improve performance of centrifuges in attempts to introduce soot removal capabilities. Some examples of these efforts are illustrated in U.S. Pat. No. 6,019,717, issued Feb. 1, 2000 to P. K. Herman and U.S. Pat. No. 6,984,200 issued Jan. 10, 2006 to A. L. Samways. Each of these designs is directed to a problem of removing very small particles of soot, i.e., particles of about 1 to about 2 microns. Centrifuges separate particulates from fluids by exposing the particulates to centrifugal forces. Particulates with a density greater than the fluid are propelled radially outwardly through the fluid. But, in the case of soot particles suspended in oil, separation is difficult because soot particles have a density very close to oil. Consequently, very high centrifugal forces may be required to move the soot particles through oil. Typically centrifugal forces of about 10,000 g&#39;s may be needed. These high forces may be produced by rotating a centrifuge at very high speeds. Alternatively, the requisite high g forces may be produced within a centrifuge having a very large diameter. However, as a practical matter, it is desirable to limit the diameter of a centrifuge to diameter of about 7 to 10 inches to meet space limitation on a vehicle and to limit rotational inertial effects. Also there is a practical limitation on the rotational speed that can be imparted to a centrifuge. Speeds of about 10,000 to about 12,000 rpm represent the limits of the current state of the art. 
     In attempts to capture small soot particles within these practical speed and size parameters, prior art centrifuges employ complex and labyrinth-like oil passage pathways. As oil traverses these complex pathways, it remains in a centrifuge for a relatively long time. In other words, it has an extended “residence time”. It has heretofore been assumed that improved soot removal is directly related to increased residence time. 
     But, in various efforts to increase residence time, prior art centrifuges have employed oil passage pathways that introduce multiple changes in direction of flow of oil. Many of these changes in flow direction may be abrupt. As oil flow makes these abrupt changes in direction, vortices may be generated. These vortices may propagate throughout the entire mass of oil that may be present in a prior art centrifuge, resulting in oil flow that is turbulent in nature. Turbulence in oil flow may produce additional difficulty in removing small particles from the oil. Whenever any one particle is propelled outwardly by centrifugal force in a turbulent flow, there is a high probability that the particle will encounter a reverse flow of oil in a vortex. Such a reverse flow may propel the particle inwardly and thus cancel the desired effects of centrifugal force imparted by the centrifuge. Thus, the particle has a high probability of remaining suspended in the oil. 
     It can be seen that soot removal effectiveness of centrifuges in the present state of the art is bounded by various limiting conditions. First, there is a practical limit on a diameter of a centrifuge. Second, there is a practical limit on the rotational speed at which a centrifuge may be operated. And third, increased residence times may be attained at the cost of producing turbulent flow in a centrifuge. As described above, turbulent flow may offset or cancel any beneficial effects of increasing residence time. There has been no recognition in the prior art of a simple expedient to increase the soot removal effectiveness of centrifuges within the practical limits of centrifuge size and rotational speed. 
     As can be seen, there is a need for improvement of soot removal effectiveness in a practical centrifuge. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, an apparatus for extracting particulates from a fluid comprises a distribution rotor rotating with rotation of a spindle; a spindle passageway, inside the spindle, delivering the fluid to the distribution rotor; an outer rotor, rotating with rotation of the spindle, receiving the fluid expelled from the distribution rotor through centrifugal force, wherein the centrifugal force holds at least a portion of the particulates in the fluid to the outer rotor while the fluid may flow down an interior surface of the outer rotor. 
     In another aspect of the present invention, a centrifuge for extracting particulates from a fluid comprises a spindle, having a spindle passageway therewithin; a distribution rotor having distribution rotor channels, the distribution rotor channels fluidly communicating with the spindle passageway; and an outer rotor receiving fluid expelled from the distribution rotor channels through centrifugal force during rotation of the spindle, distribution rotor and outer rotor, wherein the centrifugal force holds at least a portion of the particulates in the fluid to the outer rotor while the fluid may flow down an interior surface of the outer rotor, and the portion of the particulates held to the outer rotor includes particulates having a size less than about 2 microns. 
     In still another aspect of the present invention, a method for removing particulates from a fluid comprises producing a flow of the fluid down an outer rotor of a centrifuge; and imparting centrifugal force on the fluid in a direction orthogonal to a direction of the flow of the fluid to capture the particulates from the fluid. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a centrifuge constructed in accordance with one embodiment of the present invention; 
         FIG. 2  is a cross sectional view of a portion of the centrifuge of  FIG. 1  taken along the line  2 - 2  showing various features in accordance with the present invention; 
         FIG. 3  is a cross sectional view of a centrifuge constructed in accordance with one embodiment of the present invention; 
         FIG. 4  is a cross sectional view of a centrifuge constructed in accordance with one embodiment of the present invention; 
         FIG. 5  is a computer image of the distribution rotor according to the embodiment of  FIG. 3 ; and 
         FIG. 6  is a flow chart of a method of collecting particulates from a fluid in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Broadly, the present invention may be useful in improving effectiveness of particulate removal of a centrifuge. More particularly, the present invention may provide a simple expedient to improve soot removal effectiveness that can be applied to a centrifuge that is operated and constructed within the bounds of practical size and speed of conventional centrifuges. 
     In contrast to prior art centrifuges, among other things, the present invention may provide a centrifuge that operates with a fluid flow therethrough which is laminar, i.e. non-turbulent. A desirable improvement of soot-removal effectiveness may achieved by constructing a centrifuge in an inventive configuration illustrated in  FIG. 1 . 
     Referring now to  FIG. 1 , there is shown a sectional view of a centrifuge  10 . The centrifuge  10  may be comprised of a spindle  12 , an outer rotor  14 , a housing  16 , a distribution rotor  18  and a driving device, such as a turbine (not shown). The driving device may rotate the spindle  12 , the outer rotor  14  and the distribution rotor  18  inside of the housing  16 . The driving device may rotate these components at a velocity of from about 5,000 revolutions per minute (rpm) to about 15,000 rpm, typically about 10,000 rpm. 
     A fluid (as indicated by an arrow  20 ) such as lubricating oil may be introduced under pressure into the spindle  12 . The fluid  20  may flow through a spindle passageway  12   a  and may exit the spindle passageway  12   a  at spindle exit ports  12   b . The fluid  20  may then continue into the distribution rotor  18  and proceed through distribution port channels  18   a  to distribution rotor exit ports  18   b . From here, the fluid may be expelled from the exit ports  18   b  to impinge upon the outer rotor  14 . The fluid may move down an inside  14   a  of the outer rotor  14 , through the force of gravity and/or pressure, with a substantially laminar flow. The fluid  20  may then proceed into the housing  16  through a return drain  16   b . As the fluid  20  flows through the centrifuge  10 , the fluid  20  may be subjected to centrifugal forces generated by rotation of the rotor  14  about a centrifuge axis  22 . The centrifugal forces are applied to the fluid  20  in a direction that is orthogonal to the axis  22 . 
     Referring to  FIG. 2 , there is shown cross sectional view of a portion of the centrifuge  10  of  FIG. 1  taken along the line  2 - 2 . In this view, the distribution rotor  18  has six distribution port channels  18   a  through which the fluid  20  may exit the spindle passageway  12   a . This configuration for the distribution rotor  18  is shown for example and is not meant to limit the scope of the present invention. Any number of distribution port channels  18   a  may be present to communicate fluid  20  from the spindle passageway  12   a  to the outer rotor  14 . 
     Referring now to  FIG. 3 , there is a cross sectional view of a centrifuge  30  constructed in accordance with one embodiment of the present invention. Similar to the centrifuge  10  of  FIG. 1 , the centrifuge  30  may comprise a spindle  32 , an outer rotor  34 , a housing  36 , a distribution rotor  38  and a driving device, such as a turbine (not shown). The driving device may rotate the spindle  32 , the outer rotor  34  and the distribution rotor  38  inside of the housing  36 . 
     The fluid (as indicated by arrow  20 ) such as lubricating oil may be introduced under pressure into the spindle  32 . The fluid  20  may flow through a spindle passageway  32   a  and may exit the spindle passageway  32   a  at spindle exit ports  32   b . The fluid  20  may then continue into the distribution rotor  38  and proceed through distribution port channels  38   a  to distribution rotor exit ports  38   b . From there, the fluid  20  may be expelled from the exit ports  38   b  to impinge upon the outer rotor  34 . The fluid may move down an inside  34   a  of the outer rotor  34 , through the force of gravity and/or pressure, with a substantially laminar flow. The distribution rotor  38  may have a conical inner structure  38   c  to guide the flow of the fluid  20 . The conical inner structure may have a larger diameter near distribution channels  38   a  in the distribution rotor  38  and a smaller diameter away from the distribution channels  38   a . The fluid  20  may then proceed into the housing  16  through a return drain  36   b . As the fluid  20  flows through the centrifuge  30 , the fluid  20  may be subjected to centrifugal forces generated by rotation of the rotor  34  about the centrifuge axis  22 . The centrifugal forces are applied to the fluid  20  in a direction that is orthogonal to the axis  22 . The embodiment of  FIG. 3  shows one example of soot collection in a cross-hatched portion  34   b  of the outer rotor  34 . 
     Referring now to  FIG. 4 , there is a cross sectional view of a centrifuge  40  constructed in accordance with one embodiment of the present invention. Similar to the centrifuge  10  of  FIG. 1 , the centrifuge  40  may comprise a spindle  42 , an outer rotor  44 , a housing  46 , a distribution rotor  48  and a driving device, such as a turbine (not shown). The driving device may rotate the spindle  42 , the outer rotor  44  and the distribution rotor  48  inside of the housing  46 . 
     The fluid (as indicated by arrow  20 ), such as lubricating oil, may be introduced under pressure into the spindle  42 . The fluid  20  may flow through a spindle passageway  42   a  and may exit the spindle passageway  42   a  at spindle exit ports  42   b . The fluid  20  may then continue into the distribution rotor  48  and proceed through distribution port channels  48   a  to distribution rotor exit ports  48   b . From there, the fluid  20  may be expelled from the exit ports  48   b  to impinge upon the outer rotor  44 . The fluid may move down an inside  44   a  of the outer rotor  44 , through the force of gravity and/or pressure, with a substantially laminar flow. The distribution rotor  48  may have a diameter D that is substantially constant along length L of the outer rotor  44 . This structure may result in an annular oil flow passage  49  that has a substantially constant width W throughout the flow passage  49 . 
     The fluid  20  may then proceed into the housing  46  through a return drain  46   b . As the fluid  20  flows through the centrifuge  40 , the fluid  20  may be subjected to centrifugal forces generated by rotation of the rotor  44  about the centrifuge axis  22 . The centrifugal forces are applied to the fluid  20  in a direction that is orthogonal to the axis  22 . The embodiment of  FIG. 4  shows one example of soot collection in a cross-hatched portion  44   b  of the outer rotor  44 . 
     Example 
     Referring to  FIG. 5 , there is shown a computer image of a distribution rotor  50  similar to the design of  FIG. 3 . The distribution rotor  50  was designed through a fluid dynamics computer simulation to determine the effectiveness of the centrifuge of the present invention. The distribution rotor  50  had four distribution channels  52  formed therein to allow fluid to move from a spindle passageway  54  to an outer rotor (not shown). The scale in  FIG. 5  shows the density of soot particles that may be collected in the outer rotor after 1852.11 ms of operation of the centrifuge of the present invention. 
     In this example, oil containing soot was flowed through the centrifuge at about 2 gallons per minute at a pressure of 50 psi and a temperature of 100° C. The distribution rotor  50  was rotated at an angular velocity of 10,000 rpm. The soot particle size varied from about 0.0666 microns to about 0.1971 microns. 
     This example shows that the centrifuge of the present invention is useful for soot removal, even soot particles that are relatively small (&lt;2 microns). In this context, engine wear from soot may be substantially reduced, as compared with the prior art. Soot particles larger than about 2 micrometers (μm) may be removed from lubrication systems with more conventional filtration devices. But conventional filtration systems typically may not control small particle soot accumulation at an equilibrium concentration. In prior art engines, small particle-soot removal lags behind soot production. There is a gradual buildup of small-particle soot until it becomes necessary to replace the lubricating oil with new oil that is free of soot. Typically, replacement is needed when soot concentration exceeds 1-2%. 
     The centrifuge of the present invention may extract small-particle soot at virtually the same rate that it is produced by the engine until an equilibrium concentration of about 1% or less is reached. After that point in time, the centrifuge of the present invention may control small-particle soot concentration at about 1% or less for an indefinite time. 
     The present invention may be considered a method for removing particulates from the fluid  20 . In that regard the method may be understood by referring to  FIG. 6 . In  FIG. 6 , a schematic diagram portrays various aspects of an inventive method  60 . In a step  62 , the fluid (e.g., fluid  20 ) with suspended particles therein may be continuously introduced into the centrifuge (e.g., centrifuge  10 ) as a laminar flow. In a step  64 , the fluid may be rotated to produce centrifugal forces on the suspended particles. In a step  66 , the fluid  20  may be continuously propelled axially in the centrifuge during rotation thereof. Laminar flow of the fluid may be maintained during the axial propelling of the fluid. In a step  68 , a portion of the suspended particles may be captured during passage of the fluid through the centrifuge. In a step  70  the fluid may be continuously removed from the centrifuge  10  in an amount that corresponds to an amount introduced in step  62 . 
     During performance of the method  60  it may be desirable to maintain a flow of the fluid so that a Reynolds number (Re) associated with the flow is about 1000 or less. A Reynolds Number less than 1000 is typically definitive of laminar, i.e., non-turbulent flow. For any particular fluid flow Re is a function of various parameters in accordance with the following expression:
 
 Re=ρVDe/μ 
 
     where
         μ=Absolute Viscosity of a fluid   ρ=Density of a fluid   V=Velocity of flow   De=Equivalent Hydraulic Diameter.
 
Additionally, it may be desirable to perform the rotating step  64  so that centrifugal forces equivalent to a centrifugal acceleration of about 10,000 g&#39;s are applied to the particles.
       

     The method  60  may be particularly useful for capturing small particles of soot that are suspended in lubricating oil of an engine. In that context, the method  60  may be advantageously performed by conducting the rotating step  304  at about 10,000 to about 12,000 rpm. Additionally, the method may be advantageously conducted by performing the capture step  68  at a radius of about 3 to about 5 inches from an axis of rotation of the centrifuge. When employed in this context, the method  60  may provide for an equilibrium concentration of about 1% or less of soot particles less than about 2 μm in an engine lubricating system with a capacity of about 40 liters. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.