Friction gear transmission systems or components – Fluid control – Of toroidal transmission
Patent
1992-12-22
1994-05-31
Braun, Leslie A.
Friction gear transmission systems or components
Fluid control
Of toroidal transmission
476 40, F16H 1508
Patent
active
053165268
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to transmissions of the toroidal-race rolling-traction type. It relates in particular to ratio-varying components, or "variators", for such transmissions, the variators being of the kind in which each of a set of rollers transmitting traction between an input disc and an output disc is connected to hydraulic mechanism by which it is positioned, the roller position being a key factor in determining the transmitted ratio.
DESCRIPTION OF THE PRIOR ART
Variators of this type are well known art, and patent specifications GB-A-1395319, GB-B-2107009, EP-B-0078125 and EP-B-0133330 are some of many in which such a roller positioning system is illustrated and described. Each of those four specifications shows a set of three rollers transmitting traction between a rotatable input disc and a coaxial and control-rotating output disc, each roller being spaced from the others by 120.degree. of arc around the common axis of the discs. In each of the four specifications, the ratio transmitted from the input to the output disc by each roller is caused to vary by changing the position of that roller in a direction substantially tangential relative to the centre circle of the common torus presented by the input and output disc races. In each of the four quoted specifications, the mechanism for imparting that tangential movement to at least some of the rollers comprises pistons formed at opposite ends of the roller carriage--that is to say, the structure carrying the bearings on which the roller rotates--and moveable within hydraulic cylinders. Such a mechanism clearly requires many parts, because each of the two cylinders associated with each piston requires robust mechanism to maintain its position fixed, regardless of movement of the piston within it and of variations in the reaction between it and the piston. Furthermore each cylinder has to be connected to input and output hydraulic leads. Those leads, and their connections to the cylinders, must be substantial in order to withstand the fluid pressures to which they will be subjected, and the symmetrical disposition of the cylinders around the transmission axis means that the leads also will be disposed all around the circumference of the transmission, for instance cast within the transmission casing, or even possibly exposed. This creates a number of problems. For instance the cost of forming complex passages within a cast casing, the difficulty of making the joints to such passages oil-tight at high pressures, the need to maximise the diameter of all passages so as to minimise resistance to flow, the protection from damage of those parts if any of the passages are exposed, and the blocking of access for the assembling of the rollers and carriages.
It has also been proposed, for instance in patent specification GB-A-1600972, and in more detail in our U.S. patent application Ser. No. 07/689,774 (published as PCT International Publication No. WO90/05860) to control the tangential position and ratio angle of each roller by means of only a single piston-and-cylinder assembly located at only one of the ends of the roller carriage. For a typical set of three rollers this will clearly halve the number of cylinders, and thus diminish the problems of damage protection and access already referred to, but there is no teaching in either of those specifications that the three operating cylinders should be disposed otherwise than at intervals of 120.degree. of arc around the axis of the discs, just like the rollers themselves are. Substantial problems therefore remain.
SUMMARY OF THE INVENTION
The present invention is based on appreciating that if each roller is positioned by only a single hydraulic operating mechanism, as just described, it is possible to modify the disposition of the three mechanisms so that they all lie generally to one side only of the common axis of the discs, so potentially alleviating several of the problems already referred to. The invention applies particularly to variators, as shown in all the prior p
REFERENCES:
patent: 2076560 (1937-04-01), Hayes
patent: 3570317 (1971-03-01), Kraus
patent: 3828618 (1974-08-01), Sharpe et al.
patent: 5048359 (1991-09-01), Nakano
patent: 5067360 (1991-11-01), Nakano
Braun Leslie A.
Laub David W.
Torotrak (Development) Limited
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