Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2000-12-11
2003-04-08
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
Reexamination Certificate
active
06543305
ABSTRACT:
BACKGROUND OF THE INVENTION
Transmission devices are gear trains that convert and transmit the power generated by a power source to comply with the load placed on the output shaft. Many prior art transmission devices, such as those commonly utilized in automobiles, require manual shifting among various gear ratios of the transmission. However, such transmissions are inherently inefficient due both to the loss of momentum caused by the removal of the power in order to change gears, and the inherent difficulty in determining the most efficient response to a load placed upon the output shaft.
A vast array of automatic transmissions are currently available. These transmissions do not require a manual determination of the most efficient response to a load placed upon the output shaft. In addition, they will typically reduce the time required to shift gears and, consequently, reduce the loss of momentum caused by the removal of power. Nonetheless, this loss of momentum, which is inherent in traditional automatic transmissions utilizing a variety of gear ratios, still results in a significant loss of power. In addition, the limited number of gear ratios available prevents these transmissions from achieving maximum efficiency.
In order to avoid momentum losses and attain maximum efficiency, it is desirable for a transmission to have a continuous, infinite range of gear ratios. Such a transmission would not require power to be removed in order to change gears and would be capable of efficiently responding to the various loads placed on the output shaft.
A number of United States Patents disclose continuous, or near-continuous, variable speed transmission. However, each has significant drawbacks. For example, U.S. Pat. No. 1,484,197 discloses a “change-speed transmission” that includes two conical wheels having teeth of uniform pitch throughout extending along the length of the cone and covering substantially one half of each conical surface. The cones are arranged to mesh with an intermediate wheel and are simultaneously rotated so that the teeth of one conical wheel move out of mesh with the intermediate wheel as the teeth of the other conical wheel move into mesh with the intermediate wheel. The gear ratio is varied by varying the position of the intermediate wheel relatively to the large and small diameters of the conical wheels.
This arrangement is successful at varying the gear ratio without loss of momentum. However, such a system creates inherently high shear stresses that severely limit its useful life. These shear stresses are explained by the fact that the circumference of the cylinder at its front and rear edges is the same, but these circumferences are forced to frictionally and rotatably engage with different-sized same, but these circumferences are forced to frictionally and rotatably engage with different-sized circumferences on the conical surface. As the wider portions of the conical surface travel faster that the narrower portions, the equal circumference of the cylinder respectively engages different-sized circumferences on the conical surface necessarily traveling at different speeds. This causes some portions of the cylinder to slip and rub against the faster conical portions resulting in shear forces.
U.S. Pat. Nos. 2,208,148 and 2,926,538 each describe a “change speed gear” having a plurality of stepped gears arranged side by side on a cone drum and a cylindrical control gear displaceable disposed along a line of the surface of the cone of stepped gears on the driving shaft. Each stepped gear is diametrically subdivided and the two halves of the toothed rim of each step are displaced relative to each other. The spaces between steps are subdivided and staggered and the widths of the spaces is equal to half the width of the teeth of the control gear. The difference in the number of teeth from step to step is divided by two such that the opposite spaces between the points of bisection of the displaced rim halves of all steps are aligned. In operation, the control gear is caused to change its position relative to the cone drum in a synchronized manner such that it moves from one gear to the next in a stepped motion.
As this system utilizes the same cylindrical type control gear as described above, it suffers that same shear stress problems. In addition, the averaged tooth arrangement disclosed in these patents creates both wear and shock on the gears when changing from one set of teeth to another. For this reason, it is useful only at very low speeds.
U.S. Pat. No. 2,234,653 describes a variable transmission having two shafts around which series of teeth are wound. Each series of teeth forms a helix of decreasing diameter, with the teeth of one shaft being aligned with a space between teeth on the other. A spur gear is mounted between the shafts and is dimensioned to engage teeth on both shafts. The movement of the spur gear upward or downward causes it to engage teeth on both shafts, then teeth on only one shaft, and then teeth on both shafts again, with each movement causing an instantaneous change in the gear ratio.
This system does not require power to be removed from the transmission and provides the desired variability. However, the cylindrical nature of the spur gear of the compensation member causes it to suffer from the same shear stress problems described above. In addition, the use of substantially straight teeth causes discontinuous contact between teeth resulting in rapid increases and decreases in stress during gear changes.
U.S. Pat. No. 2,697,365, titled “Power Transmission Equipment”, describes “a mechanism for producing positive infinitely variable speed changes in a power transmission system.” The mechanism includes “at least two conical gear members having uniformly spaced teeth generated in a constant lead spiral path on the conical surface of each of said conical gear members.” A compensation member, in the form of a spur gear, is interposed between, and engaged with, the conical members such that the axial position of the compensation member with respect to conical gear members determines the speed ratio obtained between the input and output members. In order to vary the speed ratio, the compensation member is disengaged from the conical members.
This system provides the desired variability. However, the cylindrical nature of the spur gear of the compensation member causes it to suffer from the same shear stress problems described above. In addition, the narrow tooth width required by this transmission decreases the overall strength of the teeth.
U.S. Pat. No. 2,875,628 describes a variable speed transmission that utilizes conical gears mounted in opposite relation to each other and each having sets of rigidly attached gear segments bounded by sets that are frictionally engaged with the rigidly attached segments. A spur gear is mounted between, and engaged with, the conical gears. The spur gear is adjustable upward and downward between the conical gears and shift gear ratios by moving from engagement with a rigidly attached gear segment to a frictionally engaged gear segment and then to the next rigidly attached gear segment.
This system is substantially continuous and provides an increased degree of variability. However, the cylindrical nature of the spur gear causes it to suffer from the same shear stress problems described above. Further, the lack of alignment between slopping and non-slipping teeth creates high stresses when going from a slipping portion to an adjacent non-slipping portion.
More recently, U.S. Pat. No. 5,407,399 describes a “variable speed friction transmission” A variable ratio friction transmission in which a straight sided cone and a roller are in frictional engagement. The roller moves over an element of the cone to change the speed ratio, and at all times stays parallel to itself and moves along a straight line axis. This axis passes through the apex of the cone at all times, but the cone is tilted about its apex to contact the roller or wheel as the ratio is changed.
This system is substantially continues and provide
Lawson, Philpot & Persson P.C.
Persson Michael J.
Wright Dirk
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