192 clutches and power-stop control – Clutches – Automatic
Reexamination Certificate
1999-09-27
2001-03-06
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Automatic
C192S1030FA, C192S113210
Reexamination Certificate
active
06196368
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a power transmission unit having an input section and an output section and a hydraulic clutch which depends on the rotational speed difference, in which unit a hydrostatic displacement machine generates a pressure on the occurrence of a rotational speed difference between the input section and the output section, which pressure causes a reduction in the rotational speed difference, the displacement machine consisting of parts respectively drive-connected to the input section and the output section and one of the sections forming a housing containing the displacement machine, the displacement machine drawing in working fluid from a suction space.
Such power transmission units are more particularly used in drivetrains of motor vehicles, particularly four-wheel drive motor vehicles, either together with a differential gearbox, where the hydraulic clutch limits the differential effect, or for driving the second driven axle, the torque transmitted depending on the difference between wheel rotational speed and the drive shaft connected to the wheels of the other axle. The pressure generated by the displacement machine acts either on a clutch, preferably on a plate clutch, or by hindering the reactive motion of the displacement machine. The effect can be influenced by various valves, either automatically acting valves or externally actuated valves.
DESCRIPTION OF THE PRIOR ART
Such a power transmission unit is known from U.S. Pat. No. 5,709,627, in which the displacement machine draws in working fluid via a suction space from a sump provided at a lower level in an outer housing. In this arrangement, the suction space is bounded by a wall fastened to the stationary outer housing, which wall must be sealed relative to the rotating power transmission unit. If this seal leaks, even if only slightly—which it usually does—air is drawn in instead of the working fluid and this leads to further foaming of the working fluid (even a throttle valve at the outlet of the displacement machine leads to this) and hinders the build-up of the necessary pressure and, in addition, requires a non-return valve. Matters are made more difficult by the fact that the diameter of the seal must be large because of the suction space and the difference between the rotational speed of the output section and the outer housing is high. This produces very high sliding velocities and, in consequence, rapid wear of the seal.
SUMMARY OF THE INVENTION
The object of the invention is, therefore, to improve matters in such a way that the disadvantages quoted do not occur. The sealing problems are to be solved, and the build-up of pressure is not to be hindered by foaming, with the simplest possible construction and low system weight.
For this purpose and in accordance with the invention, the suction space is formed by a shell surrounding the housing and firmly connected to the latter in a fluid-tight manner, which shell is in fluid connection with the inside of the housing, and the suction space and the inside of the housing are completely filled with working fluid. The shell tightly surrounding the housing forms a hermetically closed suction space without seals and foaming cannot occur at all due to the complete filling. Due to the complete filling, the operational conditions (lubrication and heat removal) for the clutch plates are also optimum and no non-return valve is necessary. The number of parts and the installation volume is also smaller because no sump and no suction lines are required. The only seal still present, between the input section and the output section, has depending on the operating condition—a substantially smaller velocity difference (down to almost none) to deal with and its diameter is smaller.
The fluid connection with the inside of the housing is formed by at least one feed duct to the displacement machine and by drain ducts through which leakage and throttling fluid flows back into the suction space after passing through the plate clutch.
In a preferred embodiment, the suction space is connected to a chamber which is partially bounded by a flexible wall. By this means, a small positive pressure can be maintained within the appliance, which generally improves the action, permits a change to the characteristic and avoids the occurrence of a depression in the case of unfavorable heat dynamics. A depression could draw in air and external dirt and, in consequence, lead to damage to the small seal. The flexible wall is preferably a diaphragm but the shell itself could also be flexible. In the latter case, no separate chamber has to be provided.
In order to improve the cooling and the heat dynamics, the shell can have cooling ribs. If the shell consists of sheet metal, this simultaneously provides the flexible wall.
In a development of the invention, the suction space is connected to the inside of the housing by a duct in which a self-closing valve is provided. It is preferably an expanding material valve which, when it reaches a predetermined temperature, closes the duct. Such a valve closes without intervention from the outside if, in the case of overload, the temperature rises and exceeds a certain value. On cooling, it opens again.
REFERENCES:
patent: 4022272 (1977-05-01), Miller
patent: 5119923 (1992-06-01), Jonsson et al.
patent: 5632185 (1997-05-01), Gassmann
patent: 5709627 (1998-01-01), Teraoaka
patent: 5884739 (1999-03-01), Constantin
patent: 5967275 (1999-10-01), Gasch
patent: 5967285 (1999-10-01), Mohan et al.
Bachman & LaPointe P.C.
Bonck Rodney H.
Steyr-Daimler-Puch Fahrzeugtechnik AG & Co. KG
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