Friction gear transmission systems or components – With lubrication
Reexamination Certificate
2000-09-12
2001-08-14
Herrmann, Allan D. (Department: 3682)
Friction gear transmission systems or components
With lubrication
C092S052000, C092S11700R, C476S010000, C476S014000, C476S042000
Reexamination Certificate
active
06273839
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to continuously-variable-ratio transmissions (“CVT's”) of the toroidal-race rolling-traction type, and in particular to roller-control units of the kind by which the orientation of the traction-transmitting rollers may be controlled hydraulically, by means of the direct connection of the carriage of each roller to a piston, movable within a hydraulic cylinder connected to a controlled source of variable fluid pressure.
2. Discussion of Prior Art
Several patent publications of recent years, of which WO90/05860 is an example, describe toroidal-race transmissions in which direct connection of each roller to a piston subject to controlled hydraulic pressure suffices to maintain the angular orientation of each roller—and thus the ratio transmitted by it from an input disc—at the appropriate value at all times. The key to the efficacy of such an apparently simple method of roller control is that for any given combination of the essential parameters (operator demand, engine load and speed, final output speed etc.,) of the complete driveline of which the CVT is part, for each angular orientation that each roller may take up within its possible range of such orientations there will be a unique torque loading to which the roller will be subjected. A control system receives inputs representative of all the essential parameters, and sets up within the cylinder the appropriate hydraulic pressure to match the torque reaction associated with the desired orientation, so causing the roller to seek and hold that orientation.
One of the problems encountered in practice by CVT's, in which rollers are so controlled is that the length of the stroke that the piston must execute in order fully to control the roller is relatively long. Consequently, the housing for the piston/cylinder is of such a length that it can be difficult to install within the tight confines of, for example, an engine compartment.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a roller control unit for a continuously-variable-transmission of the toroidal-race rolling-traction type which at least reduces the above-mentioned problem.
Accordingly, the present invention provides a roller control unit for a continuously-variable-ration transmission of the toroidal-race rolling traction type, said roller control unit comprising:
a cylinder, having a cylinder wall and an end wall;
a piston, within the cylinder and to which the roller is connected for movement therewith; characterised by an axially extending shroud of variable length extending between the piston and the end wall, thereby to define in combination with the piston and cylinder a chamber for receiving hydraulic fluid, and in which the shroud comprises a telescopic shroud which in a first position of the piston is extended and in a second position of the piston is retracted.
Advantageously, the shroud comprises two or more axially extending tube sections, each section being slidable over the other between said first and second positions.
Preferably, said tube sections include endstops for engagement with corresponding endstops on an adjacent telescopic portion when in said fully extended position.
In one arrangement a first of said telescopic portions comprises an extension of the piston.
Advantageously, a second of said telescopic portions has at an end remote from said first telescopic portion an end stop for engagement with an end stop fixed relative to the cylinder.
Said cylinder may include an extension portion over which, in operation, said telescopic portion slides.
Advantageously, said end stop fixed relative to the cylinder comprises an end stop formed by or on said extension portion.
In one preferred arrangement the piston comprises a double action piston and the assembly includes a second shroud member extending between the piston and a second end wall of the cylinder, thereby to define a second hydraulic chamber for receiving hydraulic fluid.
Conveniently, one or more of said end stops comprises a circlip.
REFERENCES:
patent: 3828618 (1974-08-01), Sharpe et al.
patent: 5072811 (1991-12-01), Everhard
patent: 5564993 (1996-10-01), Robinson
patent: 5971885 (1999-10-01), Greenwood et al.
patent: 5971886 (1999-10-01), Yamamoto
patent: 5989150 (1999-11-01), Yamamoto
patent: 27 09 514 (1978-09-01), None
patent: 0 356 780 (1990-03-01), None
patent: 1287259 (1972-08-01), None
patent: 2 282 196 (1995-03-01), None
patent: WO 90/05860 (1990-05-01), None
Herrmann Allan D.
Nixon & Vanderhye P.C.
Torotrak (Development) Limited
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