1. Field of the Invention
The instant invention relates to multi-speed drives utilizing conical surfaces. More particularly, the instant invention relates to multi-speed drives utilizing opposed conical surfaces which are selectively engaged to vary output torque, output speed and output direction.
2. Technical Considerations and Prior Art
Most multi-speed drive mechanisms utilize a train of gears, an arrangement of belts and pulleys, or perhaps chains and sprockets. Since these mechanisms have many, well recognized drawbacks considerable effort has been expended over the years to improve them.
Considering gear drives first, gear drives necessarily involve sliding motion and therefore require lubrication. In addition, gear drives are noisy. Moreover precision gears are relatively expensive to manufacture and engineer due to their complex shape and due to the machining necessary for production. If a gear drive is utilized in a situation where it is desirable to limit torque, then a torque-limiting coupling or clutch must be used in combination with the drive. While it is possible to obtain a constant average torque output from a gear drive, there are always undulations in the output due to sliding action between the meshing gear teeth.
Most automotive gear drives are only about seventy five percent efficient in transmitting energy. While special drives having an efficiency on the order of ninety-five percent are available, they are very expensive and are generally not used for automotive applications. Furthermore, most automotive gear drives tend to be relatively heavy and consume considerable space. In automotive or vehicular applications, the relatively low efficiency of gear boxes, as well as their weight and size, results in design constraints which reduce overall efficiency and increase costs. In addition, in vehicles having a standard transmission, synchromeshing mechanisms are usually employed at extra cost and weight to insure smooth shifting. After a selected number of miles, the gear oil lubricant necessary to lubricate standard transmissions must be changed and used oil disposed of, which results in additional irritation and cost.
In many automotive applications, automatic transmissions utilizing fluid drives are now widely used as alternatives to gear boxes in order to spare the operator the inconvenience of manually shifting gears. However, the automatic transmissions currently on the market tend to be relatively expensive and are considerably less efficient than other gear boxes.
While transmissions which utilize belts and pulleys do not require lubrication, there is a tendency for the belts to stretch, slip and degrade due to friction between belts and pulleys. If the belts ride in grooves in the periphery of the pulleys, there is necessarily sliding contact between belts and grooves. Generally, belt transmissions have relatively limited longevity and reliability.
Chain and sprocket transmissions are perhaps a bit more predictable than belt transmissions; however, chain and sprocket transmissions require lubrication and are relatively noisy. Since they are not inherently torque-limiting, other mechanisms must be utilized if a torque-limiting feature is desired. Moreover, chain and sprocket mechanisms are relatively expensive to manufacture and are relatively inefficient.
In the past, in automotive applications, belts and pulleys and chains and sprockets have not been considered to be particularly desirable, and, in most applications, gear drives or fluid drives have been utilized. While belt drives may soon appear in the marketplace, they are still subject to the aforementioned limitations.
Friction drives which utilize cones have been experimented with for many years; however, cone drives have never been of great commercial significance because they wear quickly. Moreover, cone drives generally experience slippage which reduces their efficiency. Exemplary of a drive which utilizes conical surfaces is the drive of U.S. Pat. No. 4,161,890 in which a cone rotates on a stationary surface. However, the stationary surface is generally parallel to the axis of the cone, instead of being oriented at an angle thereto. Consequently, no appreciable torque escalation is accomplished. Moreover, the drive is essentially a friction drive with all of the drawbacks that usually accompany friction drives.
In view of the aforementioned considerations, there is a need for a new and improved multi-speed drive.