Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2000-06-28
2001-11-27
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
Reexamination Certificate
active
06321613
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to variable ratio transmission and, in particular, it concerns a continuously variable transmission based on a conical arrangement of gear wheels.
Most conventional transmissions provide a relatively small number of discrete gear ratios between the rates of rotation of an input shaft and an output shaft. For example, in automotive applications, most vehicle gear boxes offer 3, 4 or at most 5 forward gear ratios to match road speed to a suitable engine speed. Although this number of gears is sufficient to bring the engine speed within its normal operative range, the matching of engine speed to road speed and desired power is typically very inefficient. For any given desired power output, an engine should optimally be run at a corresponding given engine speed. However, due to the very limited ratios available, the engine speed will almost always be either too low, resulting in less power than desired, or too high, resulting in energy wastage.
Theoretically, the engine speed mismatch could be reduced by providing more numerous, more closely spaced gear ratios. Since, however, each gear ratio is defined by the ratio of the numbers of gear teeth on two meshed gear wheels, each change of ratio requires disengagement of a first pair of gear wheels and engagement of another. Additional disengagement and slow re-engagement of a clutch is also required to allow matching of the new engine speed. As a result, the introduction of more frequent ratio changes would itself be highly disruptive to the operation of the transmission, causing corresponding lowering of efficiency.
In an attempt to improve efficiency and/or performance, various systems have been developed to provide a continuously variable transmission ratio, commonly referred to as “continuously variable transmissions” (CVT). These systems have abandoned the intermeshed gear wheel structure in favor of traction-based engagement which allows smooth ratio transitions without disengagement. Among the most prevalent examples of such systems are the Van-Doome belt or “V-belt”, and the toroidal traction drive.
Theoretically, because of correct matching of engine speed to the required power, CVT systems should be considerably more efficient than conventional fixed ratio transmissions. In practice, however, energy savings are small to non-existent. This is primarily due to major frictional losses and slippage which are generally inherent to traction-based systems.
There is therefore a need for a variable transmission based upon intermeshing gear wheels which would offer transition between different gear ratios without disrupting the driving engagement. Such a transmission would allow substantially unlimited numbers of gear wheels, thereby approaching near-optimal use of engine performance.
SUMMARY OF THE INVENTION
The present invention is a continuously variable transmission.
According to the teachings of the present invention there is provided, a variable ratio transmission for transferring torque between an input port and an output port, the variable ratio transmission comprising: (a) a first transmission shaft rotatable about a first axis and configured to provide a first of the input and output ports; (b) a series of at least two conical gear wheels of different sizes and having different numbers of gear teeth, each of the conical gear wheels being mounted upon, and rotationally coupled to, the first transmission shaft in such a manner as to define a predefined range of angular motion through which the conical gear can turn relative to the first transmission shaft about the first axis, the series together defining a conical external profile at an angle &thgr; to the first axis; (c) a second transmission shaft rotatable about a second axis and configured to provide a second of the input and output ports, the second axis being disposed at an angle &thgr; relative to the first axis; (d) a sliding gear wheel slidingly engaged with the second transmission shaft so as to rotate together with the second transmission shaft while being slidable in a direction parallel to the second axis, the sliding gear wheel being configured for driving engagement with any one of the conical gear wheels; and (e) an actuator associated with the sliding gear wheel and configured to displace the sliding gear wheel along the second transmission shaft parallel to the second axis between positions corresponding to selective engagement with each of the conical gears, thereby varying a drive ratio between the first and second transmission shafts.
According to a further feature of the present invention, the series of at least two conical gear wheels is implemented as a series of at least ten conical gear wheels.
According to a her feature of the present invention, the predefined range of angular motion through which a given one of the conical gears can turn relative to the first transmission shaft about the first axis is at least equal to an angular spacing of the gear teeth about the axis.
According to a further feature of the present invention, there are also provided a plurality of spring elements associated at least with the gear wheels and configured to bias the gear wheels to a predefined angular position within the predefined range of angular motion relative to the first transmission shaft.
According to a further feature of the present invention, the spring elements are configured to bias the gear wheels to an intermediate angular position within a middle third of the predefined range of angular motion.
According to a further feature of the present invention, there is also provided a controller operatively connected to the actuator for controlling displacement of the sliding gear wheel, wherein the series of conical gear wheels and the spring elements are configured such that, for a given pair of adjacent ones of the conical gear wheels, when a first of the pair of gear wheels is in the predefined angular position and a second of the pair of gear wheels is forced to an extreme of the predefined range of angular motion, gear teeth of the pair of conical gear wheels are substantially aligned in a changeover region defined angularly about the first axis relative to the first transmission shaft, the controller being configured to actuate the actuator to move the sliding gear wheel from engagement with the second gear wheel to the first gear wheel when the sliding gear wheel is engaged within the second gear wheel in the changeover region.
According to a further feature of the present invention, the actuator includes: (a) an elongated threaded bolt deployed parallel to the second transmission shaft; (b) a rider in threaded engagement with the elongated threaded bolt, the rider being mechanically linked to the sliding gear wheel; and (c) a drive unit deployed to rotate the elongated threaded bolt, thereby displacing the rider, and hence the sliding gear wheel, parallel to the second axis.
According to a further feature of the present invention, the gear teeth of the conical gear wheels are rounded at their axial extremes.
According to a further feature of the present invention, the gear teeth of the conical gear wheels are rounded at their radial extremes.
REFERENCES:
patent: 1111551 (1914-09-01), Adams
patent: 1508879 (1924-09-01), Healey
patent: 1817819 (1931-08-01), Healey
patent: 5653143 (1997-08-01), Langevin
Friedman Mark M.
Wright Dirk
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