192 clutches and power-stop control – Clutches – Fluent material
Patent
1985-11-22
1987-08-04
Krizmanich, George H.
192 clutches and power-stop control
Clutches
Fluent material
192 35, 192 54, 192 93A, 74711, F16D 3500, F16H 144
Patent
active
046839984
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a fluid friction clutch, especially for differential gears of motor vehicles employing a closed toroidal chamber comprising a cylindrical inner body having an access, a drum-shaped outer body arranged coaxially to said inner body and which can be rotated with respect to the inner body and with radial walls between the inner body and the outer body, the toroidal chamber containing plate sets engaging with one another, having a ring-shaped clutch plate encompassing the inner body, the clutch plate being arranged alternately successively and at a distance to one another, the clutch plates of a first plate set being in driving connection with the inner body and those of a second plate set being in driving connection with the outer body, the toroidal chamber having a sliding member affecting the plate spacing that can be axially moved and is developed as a rotating body.
Fluid friction clutches of this type are able to transfer torques and clutch torques as soon as the plate sets twist or rotate with respect to one another. The reason is the internal friction of the viscous medium. The higher the relative speed of the plate packets, the larger the moments that can be transferred. However, the transferrable torque is also reciprocal with respect to the plate spacing; thus it rises with decreasing spacing.
Because of this characteristic, fluid friction clutches are also suitable to be used as differential locks in differential gears of motor vehicles. In this case, one plate set, with respect to the drive, is connected with one output gear wheel, while the other plate set is either in driving connection with the differential cage or with the second output gear wheel. In this context, differential gears are meant which are installed between the two rear-axle shafts of a driving axle--thus so-called axle differentials--as well as those which are provided between two driving axles--combined with a transfer-gear box--of a four-wheel drive. The fluid clutches are either integrated into the structure of the differential gear or are combined with the differential gear as a separate unit.
A known fluid friction clutch for use in a motor vehicle is shown in U.S. Pat. No. 4,058,027. Actually two of such fluid clutches are disclosed which are separated from one another by a ring piston. Starting at a certain operating condition, one of the clutches also operates as a conventional friction clutch. When, in the case of this arrangement, the driving wheels rotate at different speeds, this causes the mentioned twisting or rotation of the plate sets in the differential gear. Because of the internal friction of the viscous medium, this twisting or rotation results in a rise in temperature which in turn causes a pressure rise in the toroidal chamber. In this case, the temperature rises the faster, the higher the differential speed between the plate sets. The rising pressure moves the ring piston in axial direction which, as a result, pushes the clutch plates together. The fluid friction clutch, as a result, can transfer an increasingly high torque which in reality has the effect of an increasingly strong locking of the differential gear. In the case of the known device therefore, by means of the temperature rise in the toroidal chamber, the differential gear is locked gradually as a function of the differential speed.
However, an increased temperature may be damaging to the viscous medium. It may in time lose its inherent qualities which are necessary for the perfect operation of the fluid friction clutch.
The known fluid friction clutches also have another disadvantage which occurs especially when they are provided in a differential gear for a four-wheel drive. During rapid driving, there will, as a rule, occur a difference of height of the body of the vehicle at the front axle and the rear axle. This causes differing dynamic wheel radii at the front and rear wheels with the result that the driving axles leading to the wheels must turn at differing speeds. In the differential gear which, in this case, is
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patent: 4462272 (1984-07-01), Roper
patent: 4576264 (1986-03-01), Lupo et al.
Cigdem Saffet
Lichnofsky Rudiger
Martin Harry
Bayerische Motoren Werke AG
Krizmanich George H.
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