192 clutches and power-stop control – Field responsive frictional media type
Reexamination Certificate
2000-06-20
2001-11-20
Marmor, Charles A. (Department: 3681)
192 clutches and power-stop control
Field responsive frictional media type
C192S058400
Reexamination Certificate
active
06318531
ABSTRACT:
TECHNICAL FIELD
This invention relates to fluid clutches and more particularly to fluid clutches having a magnetorheological fluid (MRF) providing a torque transfer medium between the input and output members of the clutch.
BACKGROUND OF THE INVENTION
Many engine driven vehicles use an engine driven fan to provide cooling air flow across a radiator or heat transfer device to remove excess heat from the engine cooling fluid. The fan drive mechanism often has a fluid drive medium disposed between the input and output members of the clutch to control the fan speed relative to the speed of the engine. A viscous fluid, such as silicone, is generally used in these clutch mechanism. The torque capacity of the clutch is in part determined by the amount of viscous fluid filling the working chamber of the clutch. The amount of working fluid admitted to the working chamber is generally controlled by a thermostatic valve mechanism. The rotary speed of the input member of the clutch is equal to or directly proportional to the speed of the engine. As the engine cooling medium is elevated in temperature, the output member of the clutch, and therefore the fan, is increased in speed to increase the cooling air flow through the heat transfer device. These types of viscous fluid clutches are thermostatically controlled and require mechanisms for the admission and removal of the viscous fluid from the torque transfer area between the input and output members of the clutch. While these viscous clutches have performed adequately, there is a desire for more accurate fan speed control.
To provide a more controllable viscous fan clutch, it has been proposed that a magnetorheological fluid (MRF) be introduced between the input and output members of the clutch. The viscosity of the MRF can be controlled through the introduction of a magnetic field. As the viscosity of the MRF is increased, the torque transfer properties of the fluid are increased. Since the magnetic field can be controlled in intensity by a conventional electronic engine management system, the speed of the fan can be established more accurately for a given engine operating condition. Thus, a magnetorheological fluid clutch (MRC) will improve the efficiency of the engine cooling system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved magnetorheological viscous clutch.
The MRC has an input rotor hub with an annular cylindrical extension positioned in a cylindrical recess formed in one of the components of the clutch output. This establishes two working gaps between the input and output members of the clutch. The gaps are filled with a MRF. One of the output members, a coil housing, has an electromagnet secured therein and a front cover secured thereto. A steel sleeve is secured in the front cover as part of the electromagnetic circuit. The magnetic circuit includes the cylindrical extension of the input member and the MRF. The other of the output members, a nonmagnetic back cover, is attached to the front cover and has the fan attached thereto. The electromagnet is connected to an electrical circuit through slip rings and brushes on the coil housing.
In one aspect of the present invention, the input and output members of the clutch are supported for relative rotation by a bearing member that is shielded from the MRF storage cavity by a wall on the back cover of the output member. In another aspect of the present invention, the storage cavity has a sloping outer peripheral wall to direct MRF into the cylindrical working gaps between the input and output members of the MRC. In yet another aspect of the present invention, a plurality of wipers are disposed between the coil housing and the inner radial wall of the input hub and between the outer radial wall of the input hub and the back cover of the output member to prevent the accumulation and/or centrifugal packing of MRF in these areas.
In still another aspect of the present invention, a series of protrusions are formed on the cylindrical extension of the input member to cooperate with a radial wall on the front cover to prevent the accumulation and/or centrifugal packing of the iron particles of MRF in this area. In a further aspect of the present invention, a plurality of cooling fins are positioned on one radial face of the input member to assist the heat transfer from the working area to maintain the MRF cool. In a yet further aspect of the present invention, the input member and the output member cooperate to form two radially-spaced cylindrical working gaps with an inner cylindrical wall of each gap having a grooved surface to promote the circulation of fluid around the working gaps, reduce the occurrence of hot spots, and lessen the buildup of iron particles on the surfaces of the cylindrical walls.
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Kao Chi-Kuan
Moser George
Smith Anthony L.
Sommer Gordon
Usoro Patrick Benedict
General Motors Corporation
Grove George A.
Marmor Charles A.
Rodriguez Saul J.
Sedlar Jeffrey A.
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