Abstract:
Apparatus ( 20 ) for testing the extent of contaminants in a fluid during a test period, comprises: a source (P s ) of pressurized fluid to be tested; a fluid sump (R); a first flow restriction (R 1 ) adapted to be supplied with fluid flow from the source, the first flow restriction being configured as an annular clearance between a first land ( 24 ) and a first bore ( 22 ) and being sized and arranged so as to be progressively occluded by contaminants in the fluid flow during said test period; a second flow restriction (R 2 ) arranged between the first flow restriction and said sump, the second flow restriction being configured as an annular clearance between a second land ( 55 ) and a second bore ( 22 ), the second flow restriction being substantially the same dimensionally as the first flow restriction so that the second flow restriction will not be occluded by contaminants passing through the first flow restriction and the pressure drops across each of the flow restrictions will be substantially equal at the beginning of a test period. In use, the improved apparatus performs an improved method.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to methods and apparatuses for sensing and determining the level of contaminants in a fluid, and, more particularly, to improved fluid contaminant measuring apparatuses and methods that closely simulate the physical conditions that such fluid will likely encounter in use.  
         BACKGROUND ART  
         [0002]    This invention provides a fluid contamination measuring apparatus that is closely related to the equipment described in British Patent Application No. 00 17 987.9, which is owned by the assignee of the present application. That system utilizes a contaminant sensing orifice that simulates the annular clearance between a closely-fitted valve spool land and its associated sleeve. The sensing orifice is itself defined between a valve spool land and a bore wall. The valve spool may be selectively moved in an axial direction to align the spool land with a sleeve recess of an enlarged diameter for flushing accumulated contaminant particles from the test orifice prior to the beginning of a test cycle.  
           [0003]    The testing technique of exposing an initially-clean test orifice to flow of a contaminated fluid and observing the effect of progressive attenuation of flow as contaminant particles accumulate in the test orifice has apparently been known for many years. Known measurement techniques appear to fall into two broad categories.  
           [0004]    In the first, the flow is directly measured, usually by means of a piston. This piston can be used to drive fluid through the test orifice, or to collect fluid passing through the test orifice. In either case, the piston displacement vs. time data enables flow through the orifice to be calculated. Examples of this type are shown in U.S. Pat. Nos. 4,663,966 and 4,495,799 (see FIG. 3 thereof).  
           [0005]    In the second category, the test orifice is connected in series with a source of pressurized fluid and a reference orifice having an impedance to flow similar to that of the test orifice. As the test orifice becomes progressively occluded by contaminants, the flow and the pressure drops across the series-connected restrictions will change, providing a basis for calibrating and determining the extent of contamination. An example of this type is shown in U.S. Pat. No. 4,495,799 (see FIGS. 1 and 2 thereof). The &#39;799 patent discloses an arrangement for passing pressurized fluid through an upstream reference orifice, described as a sharp-edged restriction having an opening much larger that the clearance of the annular test orifice, and then through the test orifice itself. A pressure sensing mechanism is then used to measure the pressure drop across the test orifice.  
           [0006]    A potential difficulty with this sort of apparatus is that the flow is laminar, and hence sensitive to changes in fluid viscosity and temperature. Pressure drops across the reference and test orifices can be expected to vary in several ways, even in the absence of a contaminant, and can introduce significant errors into the measurement. An attempt to deal with this shortcoming is shown in U.S. Pat. No. 4,685,066, in which a test filter (i.e., a porous disk, rather than an annular orifice) is arranged in series with a similar filter as a reference restriction. The upstream test filter will collect and accumulate particulate contamination, and the downstream filter will pass any particles that have passed through the test filter. Both elements will tend to have the same temperature sensitivity. Hence, that factor can be eliminated as a factor in the testing protocol.  
         DISCLOSURE OF THE INVENTION  
         [0007]    With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides improved methods and apparatuses for determining the extent of contaminants in a fluid.  
           [0008]    In one aspect, apparatus ( 20 ) for testing the extent of contaminants in a fluid during a test period, comprises: a source of pressurized fluid (P s ) to be tested; a fluid sump (R); a first flow restriction (R 1 ) adapted to be supplied with fluid flow from the source, the first flow restriction being configured as an annular clearance between a first land ( 24 ) and a first bore ( 22 ) and being sized and arranged so as to be progressively occluded by contaminants in the fluid flow during the test period; a second flow restriction (R 2 ) arranged between the first flow restriction and the sump, the second flow restriction being configured as an annular clearance between a second land ( 25 ) and a second bore ( 22 ), the second flow restriction being substantially the same dimensionally as the first flow restriction so that the second flow restriction will not be occluded by contaminants passing through the first flow restriction and the pressure drops across each of the flow restrictions will be substantially equal at the beginning of a test period.  
           [0009]    In this form, as the first flow restriction (R 1 ) becomes progressively occluded by contaminants in the fluid flow during the test period, the pressure drop across the first flow restriction will increase and the pressure drop across the second flow restriction (R 2 ) will decrease, such that the extent of contamination in the fluid will be indicated as a function of a change in pressure or as a change in the ratio of the pressure drops.  
           [0010]    The apparatus may include a pressure sensor ( 45 ) operatively arrange to measure the fluid pressure between the first and second flow restrictions, such that the extent of contamination in the fluid will be indicated as a function of a change in such sensed pressure.  
           [0011]    The flow restriction lands ( 24 ,  25 ) may be provided on a first valve spool ( 21 ) movably mounted in a first bore and adapted to be moved in one axial direction relative to the first bore to allow the flow restrictions to be flushed of contaminants prior to the commencement of a test period.  
           [0012]    In another aspect, the second land ( 61 ) may be provided on a second valve spool movably mounted in a second bore ( 63 ). This second flow restriction (R 2 ) may have a substantially-constant radial clearance and a variable axial length (L 2 ). The second flow restriction may have an impedance to flow that is a function of the extent to which the second land overlaps the second bore. The apparatus may further include a sensor ( 72 ) for sensing the length of the second flow restriction.  
           [0013]    The length of overlap (L 2 ) between the second land and the second bore may be arranged to be selectively increased during the test period so as to cause the pressure drop across the second flow restriction to be maintained substantially equal to the pressure across the first flow restriction as the first flow restriction becomes progressively occluded, such that the extent of contamination in the fluid will be indicated as a function of the length of the overlap.  
           [0014]    The second spool may be similarly adapted to be moved in one axial direction relative to the second bore to allow the second flow restriction to be flushed of contaminants prior to the commencement of a test period. The apparatus may include a regulator ( 56 ) operatively arranged to change the impedance of the second flow restriction so that the fluid pressure between the flow restrictions will remain substantially constant, such that the extent of contamination in the fluid will be indicated as a function of the change of impedance of the second flow restriction.  
           [0015]    In another aspect, the invention provides a method of testing the extent of contaminants in a fluid during a test period, comprising the steps of: providing a source of pressurized fluid to be tested; providing a fluid sump; providing a first flow restriction configured as an annular clearance between a first land and a first bore; causing fluid from the source to flow through the first flow restriction; progressively occluding the first flow restriction with contaminants in the fluid flowing therethrough; providing a second flow restriction between the first flow restriction and the sump, the second flow restriction being configured as an annular clearance between a second land and a second bore and being sized so as to not be occluded by contaminants passing through the first flow restriction; and monitoring the fluid pressure between the first and second flow restrictions; thereby to indicated the extent of contaminants in the source fluid as a function of the change in such monitored pressure during the test period.  
           [0016]    According to this method, accumulated contaminants may be removed or flushed from the first flow restriction prior to the beginning of the test period.  
           [0017]    In still another aspect, the invention provides a method of testing the extent of contaminants in a fluid during a test period, comprising the steps of: providing a source of pressurized fluid to be tested; providing a fluid sump; providing a first flow restriction configured as an annular clearance between a first land and a first bore; causing fluid from the source to flow through the first flow restriction; progressively occluding the first flow restriction with contaminants in the fluid flowing therethrough; providing a second flow restriction between the first flow restriction and the sump, the second flow restriction being configured as an annular clearance between a second land and a second bore; and varying the impedance of the second flow restriction as a function of the fluid pressure between the first and second flow restrictions; thereby to indicate the extent of contaminants in the source fluid as a function of the change in impedance of the second flow restriction during the test period.  
           [0018]    Accordingly, the general object of this invention is to provide improved apparatus for measuring the extent of contaminants in a fluid.  
           [0019]    Another object is to provide improved fluid contaminant testing apparatus which closely simulates the physical configuration of apparatus that will be encountered in use.  
           [0020]    Another object is to provide improved fluid contaminant testing apparatus in which the extent to contaminants is determined as a function of a change in pressure.  
           [0021]    Another object is to provide an improved fluid contaminant testing apparatus in which the extent of contaminants is determined as a function of position.  
           [0022]    Still another object is to provide improved methods for testing the level of contaminants in a fluid.  
           [0023]    These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings and the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a schematic view of a first form of the improved apparatus, showing means for measuring the pressure between the testing and reference orifices.  
         [0025]    [0025]FIG. 2 is a schematic view of a second form of the improved apparatus, showing a regulator for maintaining substantially constant the pressure between the testing and reference orifices. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.  
         [0027]    First Embodiment (FIG. 1)  
         [0028]    Referring now to the drawings, and, more particularly, to FIG. 1 thereof, the invention provides, in one aspect, an improved apparatus, generally indicated at  20 , for sensing the level or extent of contaminants in a fluid. Apparatus  20  is shown as broadly including a multi-lobed valve spool, generally indicated at  21 , which is mounted for sealed sliding axial movement within a cylindrical body bore  22 . Spool  21  is shown as having a leftward support land  23 , a test land  24 , a reference land  25 , and a rightward support land  26 . The various lands are connected by a common shaft  28 . The radial clearance between each outwardly-facing cylindrical surface of left and right support lands  23 ,  26  and the facing bore wall surface  22  is typically about one micron. The radial clearance between each outer cylindrical surface of the intermediate testing and reference lands  24 ,  25 , respectively, and the facing bore wall  22  may be on the order of five microns, depending on the expected size of the contaminant particles. A spring  29  is arranged in the spool right end chamber, and continuously urges the valve spool  21  to move leftwardly within bore  22  until a nose  30  at the left end of the spool abuts the rightwardly-facing wall of the spool left end chamber.  
         [0029]    A two-position solenoid valve, generally indicated at  31 , is shown as having a hydraulic portion  32  and an electrical actuator portion  33 . Pressurized fluid (containing contaminants) is arranged to be supplied from a source P s  via conduit  34  to solenoid port  35 . A conduit  36  communicates solenoid port  38  with the spool right end chamber containing spring  29 . Branch conduits  39  and  40  communicate conduit  34  with the spool left an end chamber and with the annular space between lobes  23  and  24 , respectively.  
         [0030]    The bore wall is shown as having a portion  41  of an enlarged diameter between lands  25  and  26 . This bore portion communicates with return R via a conduit  42 . Conduit  43  communicates conduit  42  with solenoid port  44 . A pressure gauge, labeled P i , is generally indicated at  45 . This pressure gauge is operatively arranged to normally measure the pressure between the testing and reference lands  24 ,  25 , respectively.  
         [0031]    At the beginning of a test cycle, the solenoid actuator  33  is operated so as to displace the solenoid&#39;s hydraulic section  32  to the alternative position. In this alternative position, the spool right end chamber communicates with return R via connected conduits  36 ,  43  and  42 . Supply pressure is provided to the spool left end chamber, and drives the valve spool  21  rightwardly such that the two lands  24 ,  25 , are arranged in the large-diameter portion  41  of the bore. This allows contaminants to be flushed from the orifices defined between the two lands and bore wall  22  prior to the commencement of a test cycle.  
         [0032]    Thereafter, solenoid  33  is operated to return its hydraulic section to the position shown in FIG. 1. Supply pressure will be provided to the spool right end chamber via communicating conduits  34 ,  36 . Supply pressure is continuously provided to the spool left end chamber via conduits  34 ,  39 . However, since the support lands  23 ,  26  have the same circular area, and are exposed to the same pressures in their respective end chambers, spring  29  will expand to urge the valve spool to move leftwardly until nose  30  abuts the end wall of the left spool end chamber.  
         [0033]    Fluid will then flow from the source through conduits  34 ,  40  to the annular space between left support land  23  and testing land  24 . Such fluid will then flow sequentially through the testing orifice defined between the testing land  24  and the bore wall, and through the reference orifice defined between reference land  25  and the bore wall, into the space between lands  25 ,  26 . From this chamber, fluid will flow to return via conduit  42 . The testing and reference lands  24 ,  25 , respectively, are carefully machined to be physically the same. That is to say that they have the same axial length and have the same outer dimension. Hence, the axial length and radial clearance of the two annular orifices (R 1 , R 2 ) defined between lands  24 ,  25  and bore wall  22  will be the same. At the beginning of each test cycle, the intermediate pressure determined by pressure sensor  45  will be one-half of the differential between the supply and return pressures.  
         [0034]    As flow continues during the test cycle, contaminants in the supplied fluid will begin to accumulate at the test orifice (R 1 ) between land  24  and bore wall  22 . Any contaminants that have passed through this orifice will necessarily pass through the second orifice defined between reference land  25  and bore wall  22  since the second orifice is geometrically the same as the first orifice. In effect, the first orifice acts as a filter that captures and accumulates contaminants in the test fluid. As the contaminants accumulate in the testing orifice, the pressure drop across this orifice will increase, the intermediate pressure determined by sensor  45  will decrease, and the pressure drop across the reference orifice (R 2 ) will similarly decrease. Thus, flow through the test and reference orifices is the same, and the apparatus shown in FIG. 1 is relatively insensitive to variations in fluid temperature and viscosity. The change in the intermediate pressure, or, better still, the change in the ratio of the intermediate pressure to the supply pressure (i.e., P i /P s ), therefore provides for an indication of the extent of contamination in the fluid.  
         [0035]    At the end of the test cycle, the solenoid may be operated to displace valve spool  21  so as to allow contaminants to be flushed from the reference orifice prior to the commencement of the next cycle.  
         [0036]    Second Embodiment (FIG. 2)  
         [0037]    A second embodiment of the improved apparatus is shown in FIG. 2. The improved apparatus, generally indicated at  50 , is shown as broadly including a main valve spool  51  slidably mounted within a main body bore  52 ; a solenoid valve  53  having an electrical section  54  and a hydraulic section  55 ; and a regulator, generally indicated at  56 .  
         [0038]    The valve spool is shown as including a leftward support land  58 , an intermediate sensing land  59  and a rightward support land  60 . The radial clearance between each left and right support land  58 ,  60 , respectively, and the facing bore wall  52  is typically on the order of one micron. As before, the radial clearance between intermediate sensing land  59  and the bore wall  52  is on the order of five microns. The various lobes are connected by a common stem  57 .  
         [0039]    Regulator  56  is shown as having a spool  61  and a displaceable piston  62  mounted within bores  63 ,  64 , respectively. More particularly, the regulator spool  61  is shown as having a leftward support land  65 , an intermediate stem  66 , an axially-elongated restricting land  68 , and a rightward support land  69 . Piston  62  is arranged in the smaller-diameter bore wall portion  64  of the body. This piston  62  has a leftward rounded nose  70  which is adapted to selectively engage the right end face of spool  61 . A rod  71  communicates the axial position of regulator spool  61  to a Linear Variable Differential Transformer (“LVDT”)  72 .  
         [0040]    Supply pressure is provided from a suitable source P s  to main spool left end chamber  73  and intermediate chamber  74  via conduit  75  and branch conduits  76 ,  78 , respectively. The main bore has a portion, indicated at  79 , of an enlarged diameter. The regulator right end chamber  81  communicates with main valve right end chamber  82  via conduits  83 ,  84 , and with the solenoid valve via conduit  85 . Conduit  86  communicates an enlarged-diameter portion  80  of regulator spool bore with the fluid return R. Branch conduit  88  communicates the regulator spool right end chamber with conduit  86  and the fluid return. Restricting land  68  is shown as having a leftward area A 1 . Piston  62  is shown as having a rightward area A 2 , which is one-half of area A 1 . Land  59  is shown as having an overlapped axial length of L 1 . The second orifice is shown as having an overlapped axial length L 2 , and an unoccluded radial clearance on the order of about five microns. As with the first embodiment, the radial clearances of the first and second orifices (R 1 , R 1 , respectively) are the same, but the length L 2  of the second orifice is variable. Conduit  89  communicates the space between lands  59 ,  60  with the space to the left of land  65 , which has scalloped cut-outs in its periphery to allow unrestricted fluid communication to the annular left end face of land  68 .  
         [0041]    At the beginning of a test cycle, solenoid  53  is operated to shift the main valve spool  51  rightwardly so that sensing land  59  is aligned with enlarged bore portion  79  so as to flush any contaminants from the testing orifice R 1  between sensing land  59  and bore wall  52 . After this has occurred, the solenoid and spool are returned to the position shown. Hence, fluid flows from the source via conduits  75 ,  78  to chamber  74  between lands  58 ,  59 , and through the sensing orifice R 1  defined between sensing land  59  and bore wall  52 , through conduit  89 , and through the overlapped portion of land  68  and bore wall  63 . From the enlarged-diameter portion, the fluid then flows via conduit  86  to the return. By virtue of the geometrical relationship between the end faces of the spools (i.e., A 2 =½A 1 ), the pressure in line  89  is continuously driven to equal one-half of the sum of the supply and return pressures [i.e., P 89 =(P s +R)/2]. In other words, the regulator spool will be driven by any force unbalance between the intermediate pressure on area A 1  and the supply pressure on reference piston area A 2  to a position where, at the start of a test, L 2  will equal L 1 . As the flow through the test orifice is reduced by contamination build-up, the intermediate pressure will tend to decrease, unbalancing the pressure forces on the regulator spool  61  and causing it to be moved axially within its body bore to increase the overlap L 2  of land  68 . As a result, the pressure drop across the second orifice with reduced flow will be maintained at approximately one-half of the supply pressure, and will thus equal the pressure drop across the test orifice. The position of second spool  61  relative to its bore is sensed and determined by LVDT  72 . Thus, in the second embodiment, the change with time of the regulator spool position signal can be used to calculate the level of contamination in the fluid.  
         [0042]    Modifications  
         [0043]    The present invention contemplates that many changes and modifications may be made. For example, while it is presently preferred to employ solenoids to selectively displace the valve spool within the body to allow flushing of contaminants from the orifice, other types of mechanisms could be substituted therefor. The various parts and components may be readily changed, as desired. For example, position sensing mechanisms other than a LVDT might alternatively be used. The bore wall may be provided in a body, or in a sleeve or bushing mounted on the body.  
         [0044]    Therefore, while two presently preferred forms of the improved contaminant sensing apparatus have been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.