Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Reexamination Certificate
1999-03-11
2001-07-10
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
C073S054350
Reexamination Certificate
active
06257051
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to viscometers used to measure or characterize the stress needed to shear a fluid at a given rate. In particular, this invention relates to viscometers for continuously monitoring changes in the viscosity of fluids used in or produced by a device or process including low-viscosity fluids such as engine lubricants, by monitoring the torque required to achieve differential rotation between two elements defining a flow path for the fluid there between. Such viscometers may be used for example in on-board systems to maintain the quality of engine lubricants which is essential to the proper operation and long service life of internal combustion engines or other equipment.
BACKGROUND OF THE INVENTION
One common form of viscometer comprises two coaxial cylinders (cylinder-in-cylinder) which are rotated relative to one another while measuring, either visually or electronically, the torque, or torque equivalent, required to achieve a differential rotation speed. The flow characteristics of the fluid can be determined by interposing the fluid in an annular gap between the cylinders and for a known differential rotational speed, measuring the torque, or torque equivalent. By factoring in the physical dimensions and the drag associated with bearings or seals of the viscometer that can affect torque measurement, the viscosity of the fluid can be calculated for a particular shear rate. Typically, a viscometer is driven at a single speed and the viscosity calculated at a single shear rate to allow relative comparison of fluids. However, if desired the viscometer can also be used to more fully characterize a fluid, by measuring torque over a range of differential rotational speeds.
In certain applications, viscometers are used to continuously monitor a fluid used in or produced by a device or process. The fluids can be either totally liquid or a liquid containing particulate. One method for using known coaxial cylinder viscometers in these applications is to put the viscometers in line with the fluid flow. Problems with this method include the complexity of designing the viscometers into the flow circuit, the difficulty in replacing components of the viscometers should failure occur, and accuracy issues should the fluid flow past the viscometers vary from a constant rate.
One way of overcoming some of the problems associated with mounting cylinder-in-cylinder viscometers in line with the flow path is to mount the viscometers outside the main flow path. In this arrangement, the outer cylinder of the viscometers is capped to form a cup-like structure with the inner cylinder or bob inside the cup. This allows the drive for the differential rotation to be mounted quite close to the rotating elements for a more compact design and also allows maintenance issues to be more easily addressed.
A problem with prior bob-in-cup viscometers used to continuously monitor a fluid used in or produced by a device or process is that a pump or other hardware is needed to control the fluid flow through the viscometers, which adds to the cost and complexity to using the viscometers. Another problem with prior bob-in-cup viscometers is that, when used to accurately measure low viscosity fluids containing particulate, particulate settling can occur resulting in inaccurate viscosity calculation. Thus, careful placement of prior bob-in-cup viscometers is critical to proper operation. Also, such viscometers are potentially subject to a number of possible sources of error due to unwanted friction and/or drag effects.
SUMMARY OF THE INVENTION
The present invention overcomes the above-noted and other shortcomings of prior bob-in-cup viscometers by providing a relatively simple way of continuously monitoring fluid viscosity without the cost and complexity of a pump or other hardware to maintain flow through the viscometers, and without the placement issues normally needed to prevent particulate settling when measuring particulate-containing low-viscosity fluids.
In accordance with one aspect of the invention, the viscometers are self pumping in order to maintain controlled fluid flow through the sections of the viscometers where the fluid flow properties are measured, essentially independent of flow rate of the fluid through its primary flow path. The self-pumping character of the viscometers is also a benefit in preventing particulate settling when used to accurately measure relatively low viscosity (e.g., 1 to 100 cSt.) fluids that may contain finely, relatively well-dispersed solids.
In accordance with another aspect of the invention, the viscometer bobs and cups are designed such that relative rotation between the two elements urges the fluid to flow through the viscometers due to a pressure differential caused by the rotation.
In accordance with another aspect of the invention, the flow through the viscometers is both controlled and sufficient to minimize or eliminate clogging due to any particulate settling from the fluid.
In accordance with another aspect of the invention, in one embodiment, the bob comprises a hollow cylinder closed at one end adjacent the closed end of the cup and open at the other end. Extending through the wall of the bob at a location near its closed end and facing a continuous wall of the cup are a plurality of discrete circumferentially spaced openings. Differential bob/cup rotation urges fluid from a volume outside the bob through the bob and out through the discrete openings in the bob wall for passage through an annular gap between the bob and cup and into a volume outside the cup.
In accordance with another aspect of the invention, in another embodiment, a plurality of discrete circumferentially spaced openings are provided in the wall of the cup near the closed end of the cup facing a continuous wall of the bob. Differential bob/cup rotation urges fluid from the volume outside the bob, through the annular gap between the cup and bob and out through the discrete openings of the cup wall to a volume outside the cup.
In accordance with another aspect of the invention, in another embodiment, the wall of the bob has discrete circumferentially spaced openings near one end facing a continuous wall of the cup, and the cup has discrete circumferentially spaced openings facing a continuous wall of the bob near the end of the bob that is opposite the end of the bob containing discrete openings. Differential bob/cup rotation urges fluid from a volume outside the bob through the discrete wall openings of the bob and annular gap between the bob and cup and out through the discrete openings in the cup to a volume outside the cup.
In accordance with another aspect of the invention, in another embodiment, the bob is a cylinder of finite side wall thickness open at both ends. Also, one of the open ends is spaced from the closed end of the cup an axial distance of between one half to five times the radial separation between the bob and cup, whereby differential bob/cup rotation urges fluid from a volume outside the bob through the bob, the separation between the end of the bob and closed end of the cup, and the annular gap between the bob and cup and into a volume outside the cup.
In accordance with another aspect of the invention, in another embodiment, a series of alternate coaxial cylinders of finite wall thickness are alternately supported by a pair of axially spaced end plates to provide alternate coaxial bobs and cups. One end plate has a central opening providing fluid communication between a volume outside the end plate and the center cylinder. Discrete circumferentially spaced openings are provided through the cylindrical wall of at least one bob/cup near its open end facing a continuous cylindrical wall of an adjacent cup/bob. Differential rotation of the end plates urges fluid from a volume outside the viscometer through the center cylinder and separations between the bob/cup cylinders and opposed end plates and through the circumferentially spaced openings in at least one bob/cup cylinder and the annular gaps between adjacent bob/cup cylinders and o
Boyle Frederick P.
Damm Klaus-Werner
Garvin Gary
George Herman F.
Heath Daniel H.
Esposito Michael F.
Gilbert Teresan W.
Politzer Jay L.
The Lubrizol Corporation
Williams Hezron
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