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Viscous shear drives and methods using nanoparticles in the viscous mediumViscous shear drives and methods using nanoparticles in the viscous medium description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070163753, Viscous shear drives and methods using nanoparticles in the viscous medium. Brief Patent Description - Full Patent Description - Patent Application Claims
REFERENCE TO A RELATED APPLICATION AND PRIORITY CLAIM [0001]This application claims the priority of provisional patent application No. 60/759,278, filed Jan. 17, 2006 TECHNICAL FIELD OF THE INVENTION [0002]The present invention is directed to devices and methods in which a driving member transmits motion to a driven member through a viscous liquid medium that is subjected to shear stress due to relative motion between the members. [0003]A speed differential between the two members causes the liquid medium to develop a frictional drag regardless of whether the particular device is functioning as a clutch, a brake, or a force transmission device. The continuous generation of shearing stress in the motion-transmitting medium continuously generates internal heat. [0004]Although the present invention may be used advantageously in fluid coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a cooling fan of an internal combustion engine, and will be described in connection therewith. BACKGROUND OF THE INVENTION [0005]Fluid coupling devices of the viscous shear type have been popular for many years for controlling operation of engine-driven cooling fans ("fan drives") in motor vehicles. A typical viscous shear drive, when placed in an engaged condition, operates the fan at relatively higher speed to aid engine cooling by forcing more air through a radiator, and when cooling doesn't need to be aided, is placed in a disengaged condition where it transmits little or essentially no motion to the fan. [0006]A viscous fan drive in a motor vehicle engine cooling system uses a liquid medium, such as silicone, in order to create a drag friction between confronting surfaces of respective rotary components of the fan drive. One component, the driving component, is rotated by the engine, typically by a crankshaft-driven belt drive turning a sheave to which the one component is direct coupled. Rotation of the one component is imparted to the other component (the driven component) through the viscous medium. The fan is direct coupled to the other component. [0007]The amount of liquid permitted to flow between the confronting surfaces of the two components is controlled by a valve that normally is operated either closed or open, but may be operated to various intermediate positions by modulation or electronic control. At one limit of control, liquid is not allowed to flow between the surfaces whereas at an opposite limit liquid is allowed to flow. Presence of the liquid creates frictional forces related directly to the relative movement between the surfaces and sheer stresses in the fluid, consequently developing a torque or force that moves or drags the component to which the fan is direct coupled. Viscosity of the liquid determines the forces and speed of response. [0008]Examples of viscous clutches are found in U.S. Pat. No. 3,893,555, by Elmer; U.S. Pat. No. 4,004,668, by Blair; U.S. Pat. No. 6,032,775, by Martin, et al.; U.S. Pat. No. 6,530,748, by Light, et al; and U.S. Pat. No. 6,752,251, by May, et al. [0009]Fluid in a viscous drive heats up because of shear stress friction. That heat, sometimes called slip heat, is transferred to the relatively moving surfaces according to equations of heat transfer. One or both of the relatively moving surfaces may be coupled to a respective heat sink. Such heat sinks may have various shapes, textures, and/or fluid flow paths for dissipating the transferred heat. [0010]Slip heat develops at all non-zero speed differentials, but attains a maximum at a specific ratio of the speed of one surface to that of the other. [0011]Another type of fan drive uses a magnetorheological (MR) liquid as the coupling medium. While it too operates to create internal shear stresses, the shear strength, and hence the strength of coupling between the relatively moving surfaces is controlled by a magnetic field instead of by a valve controlling the amount of liquid available for contact between two surfaces. [0012]When the magnetic field applied to the medium is zero, the relative friction between the two surfaces is determined by initial viscosity of the fluid and that viscosity can be made relatively small. When the magnetic field is turned on, the fluid exerts a frictional effect proportional to the magnetic field; the greater the magnetic field, the greater the shear stress in the liquid between the moving surfaces. This fluid does not follow a viscous response curve since its shear stress is not proportional to the velocity differential between the surface speeds. However, the liquid must still dissipate heat generated as a function of the speed difference between the relatively moving surfaces. Heat generated by this process can cause instability of the MR fluid, leading to fluid destruction, and loss of control and/or malfunctioning of the fan drive. [0013]One means of controlling the effect of shear stress heating of the liquid medium is to turn off the drive when it overheats. But turning the drive off at a time when engine cooling needs to be aided by operating the fan would obviously be undesirable. What is desirable is to increase the useful lifetime of an MR fluid, increase the range of operating time, and generate a more efficient heat transfer from the liquid to external heat sinks. An example of an MR clutch is found in U.S. Pat. No. 6,585,092 by Smith et al. [0014]A relatively recent development in heat transfer technology is the use of nanofluids to increase the thermal conductivity of a liquid that transfers between a heat source and a heat sink. [0015]U.S. Pat. No. 6,221,275 by Choi, et al. describes certain nanofluids that can provide increased thermal conductivity to a heat transfer medium that is used merely to transfer heat more efficiently from a one surface to an opposite surface along the heat transfer path. [0016]U.S. Pat. No. 6,432,320 by Bonsignore, et al also teaches nanofluids for improved heat transfer, with the stated objective of transferring "heat from one body to another, typically from a heat source (e.g. a vehicle engine, boiler, computer chip, or refrigerator), to a heat sink, to effect cooling of the heat source, heating of the heat sink, or to remove unwanted heat generated by the heat source." [0017]U.S. Pat. No. 6,695,974 by Withers, et al. teaches a "novel fluid heat transfer agent suitable for use in a closed heat transfer system, for example, wherein energy is transferred between an evaporator and a condenser in heat exchange relationship" [0018]U.S. Pat. No. 6,858,157 by Davidson, et al. teaches the use of nanofluids to transfer heat from the coils of a transformer wound on an iron core through oil to the outside, surrounding volume. The major objective is to transfer heat from a heat source to a heat sink. Within the liquid, temperatures are generally equal to, or intermediate between, those of the heat source and the heat sink, i.e. the internal temperature in the fluid is always both less than the temperature of the heat source and greater than that of the heat sink. [0019]The common purpose in the various applications just summarized is to use an improved liquid to transfer heat from an external source to an external sink. SUMMARY OF THE INVENTION [0020]Unlike those various applications that are concerned with heat conduction properties of liquids for transferring heat through what amount to various forms of heat exchange structures or systems, a viscous shear drive requires a liquid that possesses the property of being able to transmit motion from a driving member to a driven member with some degree of efficiency. It has been accepted as inherent that heat will be generated internally of such a liquid. Consequently, liquids that are possess suitable motion-transmitting properties are essential to viscous shear drives. Continue reading about Viscous shear drives and methods using nanoparticles in the viscous medium... 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