On-board rotational viscometers

Abstract

A viscometer for sensing or characterizing the stress required to shear a fluid at a given rate includes a pair of members coaxially mounted for relative rotation. Between the members is an annular gap defining a flow path for the fluid. The flow path is configured such that during differential rotation of the members, fluid is caused to flow through the annular gap that is a function of the differential rotation and the viscosity of the fluid. A sensor measures the torque or torque equivalent required to achieve such differential rotation between the members.

What is claimed is:  
     
         1 . A viscometer for measuring or characterizing the stress required to shear a fluid at a given rate comprising a pair of members coaxially mounted for relative rotation, an annular gap between said members defining a flow path for the fluid, a driver for producing such differential rotation, means within said flow path for causing fluid to flow through said gap during such differential rotation that is a function of the differential rate of rotation between said members and the viscosity of the fluid, and a sensor for measuring the torque or torque equivalent required to achieve such differential rotation between said members.  
     
     
         2 . The viscometer of    claim 1    wherein said means for causing fluid to flow through said gap comprises a plurality of circumferentially spaced discrete openings in one of said members through which the fluid flows to create a differential pressure causing the fluid to be pumped through said gap.  
     
     
         3 . The viscometer of    claim 2    wherein said discrete openings extend through a wall of one of said members and face a continuous wall of the other of said members.  
     
     
         4 . The viscometer of    claim 2    wherein one of said members comprises a cup and the other of said members comprises a bob coaxially mounted within said cup, said bob having a closed end adjacent a closed end of said cup.  
     
     
         5 . The viscometer of    claim 4    wherein said discrete openings extend through a wall of said bob adjacent said closed end of said bob and face a continuous wall of said cup.  
     
     
         6 . The viscometer of    claim 4    wherein said discrete openings extend through a wall of said cup adjacent said closed end of said cup and face a continuous wall of said bob.  
     
     
         7 . The viscometer of    claim 4    wherein said discrete openings extend through both a wall of said bob and a wall of said cup.  
     
     
         8 . The viscometer of    claim 7    wherein said discrete openings through said wall of said bob are adjacent said closed end of said bob and face a continuous wall of said cup, and said discrete openings through said wall of said cup are near an open end of said bob and face a continuous wall of said cup.  
     
     
         9 . The viscometer of    claim 7    wherein said discrete openings through said wall of said cup are adjacent said closed end of said cup and face a continuous wall of said bob, and said discrete openings through said wall of said bob are axially spaced from said discrete openings through said wall of said cup and face a continuous wall of said cup.  
     
     
         10 . The viscometer of    claim 1    wherein one of said members comprises a cup and the other of said members comprises a bob coaxially mounted within said cup with a separation between an inner end of said bob and a closed end of said cup that is between one half to five times the annular gap between said members, said bob having a longitudinal passage therethrough, whereby differential rotation of said bob and said cup causes fluid from a volume outside said bob to flow through said bob, through said separation between said bob and said cup and through said annular gap to a volume outside said cup.  
     
     
         11 . The viscometer of    claim 1    wherein said members are formed by coaxial cylinders on a pair of axially spaced end plates mounted for differential rotation, one of said end plates having a center opening providing fluid communication between a volume of fluid outside said one end plate and one of said cylinders.  
     
     
         12 . The viscometer of    claim 11    wherein each of said end plates has a plurality of alternate coaxial cylinders defining said gap there between.  
     
     
         13 . The viscometer of    claim 12    wherein said means for causing fluid to flow through said gap comprises a separation between at least one of said cylinders on one of said end plates and the other end plate that is between one half and five times said gap that creates a differential pressure causing the fluid to be pumped through said gap.  
     
     
         14 . The viscometer of    claim 12    wherein said means for causing fluid to flow through said gap comprises a plurality of circumferentially spaced discrete openings in at least one of said cylinders and facing a continuous wall of an adjacent cylinder through which the fluid flows creating a differential pressure causing the fluid to be pumped through said gap.  
     
     
         15 . The viscometer of    claim 1    wherein said members are axially symmetric but non-cylindrical, said members being shaped such that said annular gap increases as a function of the radius from a common axis of said members which creates a differential pressure causing fluid from a volume outside one of said members to flow through said one member and through said annular gap and into a volume outside the other of said members.  
     
     
         16 . The viscometer of    claim 1    wherein said members are axially symmetric but non-cylindrical, said members being shaped such that said annular gap remains the same as a function of the radius from a common axis of said members which creates a differential pressure causing fluid from a volume outside one of said members to flow through said one member and through said annular gap and into a volume outside the other of said members.  
     
     
         17 . The viscometer of    claim 1    wherein said driver comprises a motor, and a magnetic drive coupling between said motor and one of said members, the other of said members being relatively fixed, said magnetic drive coupling comprising a driving magnet rotatably driven by said motor, and a driven magnet driven by said driving magnet.  
     
     
         18 . The viscometer of    claim 17    wherein said other member comprises a cup, and said one member comprises a bob rotatably mounted within said cup, and said driving magnet surrounds said cup.  
     
     
         19 . The viscometer of    claim 18    wherein said driven magnet is carried by said bob within said cup.  
     
     
         20 . The viscometer of    claim 18    wherein said driven magnet forms said bob.  
     
     
         21 . The viscometer of    claim 17    wherein said other member comprises a cup fixedly mounted within a housing, said housing having a bore in coaxial alignment with an open end of said cup, and a hollow shaft rotatably mounted in said bore, said shaft extending into said cup, and said one member comprising a bob fixedly mounted on said shaft within said cup.  
     
     
         22 . The viscometer of    claim 1    wherein said one of said members comprises a cup having a closed end and an open end covered by a slotted cap, and the other of said members comprises a bob rotatably mounted on a bob shaft within said cup, said shaft having opposite ends received in bearing inserts in said cap and said closed end of said cup.  
     
     
         23 . The viscometer of    claim 1    wherein said one of said members comprises a cup, and the other of said members comprises a bob rotatably mounted within said cup, and said driver comprises an air motor, and a magnetic drive coupling between said motor and said bob, said magnetic drive coupling comprising a driving magnet rotatably driven by said air motor, and a driven magnet mounted in a recess in an inner end of said bob, said air motor including a motor housing containing a rotor through which regulated air pressure is supplied for driving said rotor and thus said bob through said magnetic drive coupling.  
     
     
         24 . The viscometer of    claim 22    wherein said cup has an externally threaded closed end for threaded receipt in an internally threaded bore in one end of said motor housing, and said one end of said motor housing has external threads for threaded engagement in an opening in a diagnostics chamber with said cup extending into said chamber.  
     
     
         25 . A viscometer for measuring or characterizing the stress required to shear a fluid at a given rate comprising a pair of members coaxially mounted for relative rotation, an annular gap between said members defining a flow path for the fluid, a driver for producing such differential rotation, and a sensor for measuring the torque or torque equivalent required to achieve such differential rotation between said members, said driver comprising a motor, and a magnetic drive coupling between said motor and one of said members, the other of said members being relatively fixed, said magnetic drive coupling comprising a driving magnet rotatably driven by said motor, and a driven magnet driven by said driving magnet, said other member comprising a cup fixedly mounted within a housing, said housing having a bore in coaxial alignment with an open end of said cup, and a hollow shaft rotatably mounted in said bore, said shaft extending into said cup, and said one member comprising a bob fixedly mounted on said shaft within said cup.  
     
     
         26 . The viscometer of    claim 24    wherein said driven magnet forms said bob within said cup.  
     
     
         27 . The viscometer of    claim 25    wherein said driving magnet surrounds said cup and said hollow shaft is rotatably mounted in said bore by bearing bushes without any end thrust location on said hollow shaft, whereby said driven magnet self-locates centrally within said cup in the magnetic field of said driving magnet.  
     
     
         28 . The viscometer of    claim 26    further comprising radial holes in said housing communicating with said bore between said bearing bushes to reduce any friction effect caused by fluid between said hollow shaft and said bore.  
     
     
         29 . The viscometer of    claim 24    wherein said bob is hollow and has a finite wall thickness, with a separation between an inner end of said bob and a closed end of said cup that is between one half to five times said annular gap between said members, whereby differential rotation of said bob within said cup causes fluid from a volume outside said bob to flow through said bob and said separation between said bob and said cup and through said annular gap between said bob and said cup and into a volume outside said cup.  
     
     
         30 . The viscometer of    claim 24    further comprising a diagnostics chamber containing a volume of the fluid, said chamber having an opening into which a portion of said housing containing said bore extends for flow of fluid from within said chamber through said viscometer and back to said chamber.  
     
     
         31 . The viscometer of    claim 29    wherein said motor comprises a precision electric motor.  
     
     
         32 . The viscometer of    claim 30    further comprising a locating plate on which said motor is mounted, and fasteners for securing said plate and said viscometer housing to said diagnostics chamber.  
     
     
         33 . The viscometer of    claim 31    further comprising a sleeve that is pressed against an outturned flange on said cup upon tightening said fasteners to clamp said cup to said housing.  
     
     
         34 . The viscometer of    claim 30    wherein said sensor includes means for monitoring motor speed and current variations which are calibrated against known viscosities to detect relatively small changes in the viscosity of the fluid over an expected viscosity measurement range.  
     
     
         35 . A viscometer for measuring or characterizing the stress required to shear a fluid at a given rate comprising a pair of members coaxially mounted for relative rotation, an annular gap between said members defining a flow path for the fluid, a driver for producing such differential rotation, and a sensor for measuring the torque or torque equivalent required to achieve such differential rotation between said members, said one of said members comprising a cup having a closed end and an open end covered by a slotted cap, and the other of said members comprising a bob rotatably mounted on a bob shaft within said cup, said shaft having opposite ends received in bearing inserts in said cap and said closed end of said cup, said bearing inserts being pressed into coaxial recesses in said cap and said closed end of said cup, said bearing inserts having half ball radiuses for seated engagement by the ends of said bob shaft, said ends of said bob shaft having radiuses that are slightly smaller than the radiuses of said bearing inserts, whereby said bob will move like a gyro within said bearing inserts with little effort required.  
     
     
         36 . The viscometer of    claim 34    wherein end play between said bob shaft and said bearing inserts is no more than 0.010 inch.  
     
     
         37 . A viscometer for measuring or characterizing the stress required to shear a fluid at a given rate comprising a pair of members coaxially mounted for relative rotation, an annular gap between said members defining a flow path for the fluid, a driver for producing such differential rotation, and a sensor for measuring the torque or torque equivalent required to achieve such differential rotation between said members, one of said members comprising a cup, and the other of said members comprising a bob rotatably mounted within said cup, and said driver comprising an air motor, and a magnetic drive coupling between said motor and said bob, said magnetic drive coupling comprising a driving magnet rotatably driven by said air motor, and a driven magnet mounted in a recess in an inner end of said bob, said cup having an externally threaded closed end for threaded receipt in an internally threaded bore in one end of said motor housing, and said one end of said motor housing having external threads for threaded engagement in an opening in a diagnostics chamber with said cup extending into said chamber, and a rotor shaft on which said rotor is rotatably mounted within said motor housing, said rotor shaft having an inner end extending coaxially into said bore in said motor housing, said driving magnet being mounted on said inner end of said rotor shaft for rotation by said air motor.  
     
     
         38 . The viscometer of    claim 36    further comprising a recess in said closed end of said cup into which said driving magnet on said inner end of said rotor shaft extends.  
     
     
         39 . The viscometer of    claim 36    wherein said sensor includes means for monitoring the regulated air pressure and RPMs of said rotor to determine the viscosity of the fluid.  
     
     
         40 . The viscometer of    claim 38    further comprising means for calibrating variations in the regulated air pressure and RPMs of said rotor against known viscosities to detect relatively small changes in viscosity of the fluid.