Friction gear transmission systems or components – Stepless ratio change – Driving and driven gears on nonlinear angularly related axes
Patent
1994-07-18
1996-11-19
Marmor, Charles A.
Friction gear transmission systems or components
Stepless ratio change
Driving and driven gears on nonlinear angularly related axes
476 53, F16H 1504
Patent
active
055757340
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a variable-speed drive, particularly for vehicles.
BACKGROUND ART
Known variable-speed drives normally comprise an input shaft, an output shaft, and a pair of conical bodies, each at least angularly integral with a respective shaft, and connected angularly to each other via the interposition of an intermediate element, the movement of which in relation to the conical bodies provides for varying the velocity ratio of the input and output shafts.
Depending on the application, the intermediate element is defined by a further rigid body, normally a cone or cylinder, or by a flexible element designed to cooperate with a lateral surface of the conical bodies.
In most applications in which a rigid body is used, at least part of the generating line of the body cooperates in sliding manner with part of the generating line of the conical bodies.
Though universally adopted, such a design presents a major functional drawback due to the variation in surface speed along the contacting portions of the generating lines resulting in relative slide between the contacting profiles, thus resulting in increased power loss due to friction and, consequently, in reduced efficiency of the variable-speed drive. Relative slide and, consequently, power loss may be reduced by reducing the length of the contacting portion of the generating line so that, at most, the rotary bodies contact at one point only.
Known design solutions for overcoming the above drawback are nevertheless unsatisfactory in terms of power transmission, which can only be increased by increasing the number of movable intermediate elements, thus resulting in an increase in the size and manufacturing cost of the drive.
The increase in cost is due to the fact that, according to the above solutions, one of the conical bodies must necessarily be axially mobile in relation to the other, thus requiring the use of self-compensating axial joints, i.e. capable of exerting predetermined axial pressure as a function of the torque on the conical drive body.
From DE-A-902 204 it is also known a solution wherein the conical bodies have conjugated curved side surfaces, which are kept in direct contact to each other by forcing means defined by an outer rigid ring axially movable in sliding contact with respect to the conical bodies. Even this solution is however not free from drawbacks, mainly consisting in the fact that the variable speed drive, in order to change the speed ratio between the input and output shafts by moving the ring axially, is to be provided with a friction device able to remove the load from the drive during the change speed operation; in this manner the drive cannot be employed as a continuous one despite the almost infinite speed ratios available.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a variable-speed drive designed to overcome the aforementioned drawbacks, and which, more specifically, provides for a high degree of mechanical efficiency and relatively high power transmission, while at the same time being straightforward in design and cheap to produce.
According to the present invention, there is provided a variable-speed drive for a vehicle, comprising a rotatable input shaft, at least one rotatable output shaft, and connecting means for connecting said input shaft to said output shaft, and enabling the velocity ratio of the shafts to be varied continuously, said connecting means comprising a first rotary drive element angularly secured to a first of said shafts and defined laterally by a first curved surface having a first radius of curvature, a plurality of second rotary drive elements angularly secured to a second of said shafts and arranged in a ring around said first rotary element, each said second rotary element being defined laterally on a side facing said first rotary element by a respective second curved lateral surface having a second radius of curvature; control means for effecting mutual engagement of said curved surface of said first rotary drive elem
REFERENCES:
patent: Re10968 (1888-11-01), Hoffman
patent: 958694 (1910-05-01), Cox
patent: 2526435 (1950-10-01), Teigman
patent: 3257857 (1966-06-01), Davin et al.
patent: 3910137 (1975-10-01), Nedeljkovitch
patent: 4841791 (1989-06-01), Lopez
Grabow Troy E.
Marmor Charles A.
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