Infinitely variable epicyclic transmissions

Details Infinitely variable epicyclic transmissions Infinitely variable epicyclic transmissions

2001-05-03

2002-12-24

Marmor, Charles A. (Department: 3681)

Planetary gear transmission systems or components

Nonplanetary variable speed or direction transmission...

Nonplanetary transmission is belt or chain gearing

C475S218000, C475S339000, C474S139000

Reexamination Certificate

active

06497634

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is generally concerned with power transmissions, particularly continuously variable transmissions, and more specifically transmissions for use in rotational machines requiring continuous, infinitely adjustable output speed and output torque while maintaining nearly constant rotational speed of the input prime mover.
2. Background Art
A continuously variable transmission suitable for automotive applications has been sought for nearly a century. It has even longer been recognized that pedal-driven vehicles would operate most efficiently if the propulsive ground wheel rotational speed were varied such that the input pedal rotational speed remains nearly constant, independent of the incline of the path. Tools designed to remove material in a manufacturing process (lathes, drills, mills, routers, and the like) often benefit from precise selection of the tool speed at the interface with the workpiece. For cost and power efficiency reasons, such tools typically are powered by synchronous electric motors. Both machine power sources (such as electric motors or internal combustion engines) and human propulsion operate most efficiently at fixed rotational speeds or within a limited range; however, the final application of the driving power usually requires a different or broader range of speeds. For all applications, whether for machine powered equipment or human powered vehicles, a transmission device combining the desirable characteristics of high torque capacity, high efficiency, compact size, light weight and competitive manufacturing cost has yet to be achieved.
3. Background Art
Currently, speed adjustment is normally accomplished by the use of control devices incorporating numerous selective discrete fixed ratio elements (usually gears).
Continuously variable speed control systems (transmissions) are an alternative means for speed adjustment, but tend to occupy large volumes, are heavy, often use some sort of belt system to adjust the speed, or use complicated ratchet and overriding clutch mechanisms. Most known continuous speed control systems offer the capability of producing adjustable speed in only one direction and require a clutch to uncouple the prime mover from the output. Generally, all known variable speed control systems have limited power transfer capabilities.
High power applications, usually involving a limited range of speed variation, such as in construction and agricultural equipment, are currently obtained using hydrostatic drives operating in low flow, high fluid pressure regimes, or hydraulic torque converters operating in high fluid flow, low pressure conditions, or limited slip differential transmissions, all of which suffer significant energy loss. Continuously variable transmissions have yet to be suitably integrated into high-speed/high-power applications such as standard motor vehicles. Continuously variable transmissions to date have yet to exceed the approximately 150 hp rating.
Infinitely Variable Versus Continuously Variable Transmission
Several devices have been proposed for achieving continuously variable output speed, some of which include infinitely variation capability. A “continuously variable” transmission is a transmission in which the ratio of output rotation speed to input rotation speed can be varied continuously from a first value to a second value, both values having the same algebraic sign. A continuously variable transmission may also include a discrete, usually separately actuated, reverse gear—having an algebraic sign different from the first and second value. An “infinitely variable” transmission is a transmission in which the ratio of output rotation speed to input rotation speed can be varied continuously from a first value to a second value—where the first and second values can have different algebraic signs. Thus, the “infinitely variable” transmission includes the “infinite” condition where the ratio of the input rotation speed to the output rotation speed is indeterminate, i.e., infinite. Thus “infinitely variable” transmissions may be characterized as a subset class of “continuously variable” transmissions, in that both classes have the capability to continuously control output speeds with generally fixed input rotational speed. However, infinitely variable transmissions offer a broader range of capability and applications due to their ability to drive output speeds to nearly zero while theoretically producing output torques approaching an infinite condition, limited only by the slip or load carrying capabilities of internal components.
Classes of Continuously/Infinitely Variable Transmissions
Both continuously variable and infinitely variable transmissions can be classified into five types.
The first type, which is the oldest and probably most extensively employed, includes two variable pitch pulleys connected by a belt with provision for varying the diameters of the pulleys and thus the speed ratio. While such devices are efficient, they characteristically are high in volume and weight, and have a limited range of speed variation. There have been at least two major improved variants to this basic dual variable pitch pulley concept. The power-limiting component in this design typically is either the belt reaching the limit of its tensile strength, or the friction between the belt and the pulley of smaller diameter. In a device disclosed in U.S. Pat. No. 3,720,113 to Van Dorne, the belt is changed from transferring torque via tension to transferring torque via compression. In the Van Dorne device, compression links are carried by a series of thin bands, the links conforming to each other to form a semi-rigid bar between the two variable pitch pulleys. The failure mode for the endless belt is changed from a tensile failure to one of buckling instability of the links, or material compression failure, both of which potentially allow a greater load than can be achieved by a tensile member. However, the speed adjustment range is limited.
A second major variant has been termed the Positive Infinitely Variable (PIV) variable speed drive used routinely in industrial applications. Within the definition used in this disclosure, the PIV is a misnomer because the speed control devices do not have a speed range where the output can be continuously varied to a negative algebraic sign. A feature of the PIV is the replacement of the belt by an endless chain, each link of the chain containing a series of transverse conforming rods that engage the edges of pulleys containing radial groves in the contact faces. This design eliminates slip between the endless belt-like member that transfers the torque and the mating variable pulley. While a speed variation range of as high as 6 is reported for such devices, the power ratings typically are below 30 hp.
A second type of continuously variable transmission includes single contact traction or friction drives using various schemes which rely on metal-to-metal rolling contact friction, sometimes using lubricant shear as the traction mechanism. Examples of such devices include cone on cone devices wherein two cones each of equal and opposite pitch are mated to contact at single points but in such a way that the summed circumference of the combined assembly is constant. Examples and variants of this type are shown in U.S. Pat. No. 4,392,394 to Hofbauer and U.S. Pat. No. 5,433,675 to Kraus.
Another example of continuously variable transmission is the ball and disc type. In this class of drive mechanism, the rotational axis for a ball element is usually at a substantially right angle to the rotational axis of a disc element. The ball element, which is constrained to have a surface of rotation, is positioned so that when it is pressed against the rotating disc element, the ball element is driven by the disc. By moving the ball element along a radius of the disc element, a variable speed drive can be obtained from the ball element. The efficiency of such mechanisms is highly dependent on the quality of contact between the two traction elemen

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