Machine element or mechanism – Mechanical movements – Rotary to intermittent unidirectional motion
Reexamination Certificate
2002-08-21
2004-10-26
Bucci, David A. (Department: 3682)
Machine element or mechanism
Mechanical movements
Rotary to intermittent unidirectional motion
C074S086000, C074S117000, C475S170000
Reexamination Certificate
active
06807878
ABSTRACT:
BACKGROUND OF INVENTION
A mechanical transmission device for modifying torque and speed of rotation from torque input to torque output, more particularly a device capable of modifying torque and speed of rotation in a continuously-variable fashion utilizing a set of levers that are unidirectionally rotatable about a first axis, in conjunction with an abaxial ring rotatable about a second axis, the second axis being itself rotatable about the first axis.
To expand the usefulness of rotary power sources, a variety of torque transmission and conversion devices have been developed. Of particular relevance to the device of this application are situations where it is desirable to greatly reduce the rotational speed of a power source in order to shift it into a useable range; where it is desirable to greatly increase the torque of the power source, whatever the speed; and/or where it is desirable to be able to vary the ratio between input and output rotational speed and torque.
Among the most energy-efficient variable transmission systems are the incrementally shiftable systems that employ multiple gears or chains and cogs, but these systems generally require an interruption in power during shifts, sometimes further requiring supplemental clutch devices and gear synchronizers, and where many ratios are required they can become complex, bulky, and difficult to manage. Continuously variable transmissions offer greater versatility and simplify shifting operations, but have tended to have shortcomings of their own which have limited their usefulness.
The hydraulic or electromotive drives, where a motor drives a pump or generator which then powers another motor, are among the most versatile continuously-variable drives. But they are typically massive and not very energy-efficient, so their use has mostly been restricted to heavy industry and high-load work and transport machinery. Also fluid and electricity is subject to leakage, and can behave as a compressible link, so hydraulic and electromotive drives tend to work poorly with low-speed power sources and the ratios between rotational input and rotational output can be unstable, varying with the load.
Limited-slip differential drives employ a split in the torque path with a brake or clutch or something to provide variable drag to select between paths having different ratios. Energy efficiency can be good when either path is fully selected, but there are frictional losses in all intermediate positions and the intermediate ratios tend to be unstable because the constancy of a given ratio is only as good as the proportionality between the friction and the power load.
Traction drives—where a ring, disk, or belt frictionally engages a disk, cone, or sphere at varying radii—have stable ratios throughout their range and are often more energy-efficient than limited-slip drives in the intermediate ratios, but the power is transmitted through a rolling frictional interface. This interface can slip if the shear load from the power exceeds the frictional grip, and it tends to be a focal point for polish, wear, heat buildup, and energy-loss problems.
Among the most efficient of the gear reduction drives are the planetary drives, in which a sun gear drives planetary gears within a ring gear, and where large reductions are desired, multiple stages are ganged together in series. Also reasonably efficient are the harmonic drives in which gears with nearly the same number of teeth are made to mesh either indirectly through rolling index gears traveling around the anchor and output gears or directly by physical deformation of one of the gears by rollers or such. Harmonic drives can achieve great speed reductions in a single stage, typically advancing the output gear only one or two teeth per revolution of the index gears or deformation rollers, but there is much sliding action between the teeth of harmonic drives and they often have flexible components in the load path, so they are poorly suited to high-load applications. Also, both planetary and harmonic drive systems have stable ratios, but they are fixed ratios which cannot be varied, so if multiple ratios are needed, multiple gearsets and changing mechanisms are also needed.
Worm drives are also effective speed reducers, but there is much friction in the interface between the screw and the gear it enmeshes, the output torque is both displaced from and not parallel to the input torque, and the reduction ratio of such drives is not variable.
Potentially some of the most energy-efficient of the continuously variable drives are the oscillation drives, where rotary power is converted to oscillating power and then back again to rotary power, and variable gearing is achieved by varying the amplitude of the oscillations. To have continuous power transmission, there must be at least two oscillating elements, each to take the load while the other is returning. Also, oscillation drives have tended to be not very compact. However, oscillation drives have reasonably stable ratios and they can entirely eliminate the frictional rolling interfaces that traction drives require, so the efficiency and durability can be quite good. The main design challenges of the oscillation drives have been to have the oscillating elements receive and deliver power as tangentially as possible to the rotary elements, and to have the input to output ratios remain highly consistent throughout each cycle, while keeping the total number of elements as few as possible.
The device of this application is a transmission with some, but not all, of the properties of a typical oscillation drive. As with many oscillation drives, rotary power an be supplied in either direction in order to produce output power in a single direction. Unlike with most oscillation drives however, true reciprocal motion in the various parts has been replaced with eccentric and intermittent rotary motion.
The objects of the transmission device here disclosed include a reasonably compact gear reduction transmission of simple, yet versatile, design which does not require exotic materials or manufacturing processes to build; having output torque that is co-axial with the input torque, in a ratio which can be steplessly varied from modest reduction to indefinitely high reduction without any interruption of power; including an integral neutral for zero transmission of power; operating with low friction so as to minimize wear, heat buildup, and power-loss problems; adaptable to high and low load applications; capable of utilizing slow or fast power sources that are either unidirectional or bidirectional in nature; and easily adaptable to provide unidirectional or bidirectional torque output.
Accordingly, this transmission device is thought to have numerous advantages over existing gear reduction systems. This device can match the continuous variability of hydraulic and electromotive transmissions, but unlike with those systems, any selected ratio will be quite stable independent of load, it should have better energy efficiency, and the effectiveness will not diminish even with power sources that have extremely slow rates of rotation. This device can match or exceed the variability of traction drives, but is not dependent upon a rolling frictional interface to transmit torque, so it should be able to handle higher loads without the slippage, heating, and wear problems. This device compares well against the efficiency and ratio stability of planetary, harmonic, and worm drives, but unlike those drives, the ratio between input and output rotation can be steplessly varied over a large range; it does not require multiple stages in series to achieve great gear reductions; and when compared to flexible harmonic drive systems, this should be more suitable for high-load situations.
A transmission with such properties can have applications in diverse areas including gear reductions for electrical motors, turbines, or other high speed rotary power sources where it is desirable to reduce the speed of rotation and have the output speed variable, for example so that the power source can op
Bucci David A.
Jackson & Walker, LLP
McAnulty Timothy
LandOfFree
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