Machine element or mechanism – Gearing – Teeth
Patent
1988-05-03
1989-09-19
Herrmann, Allan D.
Machine element or mechanism
Gearing
Teeth
74437, F16H 5508
Patent
active
048670022
DESCRIPTION:
BRIEF SUMMARY
Conventionally, the transmission of drive from one solid to another about their respective axes by means of toothing is limited to the special cases of cams, gearing, or other rack and pinion systems.
BACKGROUND OF THE INVENTION
In gearing, the pitch curve of each solid is a circle (as in cylindrical or conical gearing); in rack and pinion systems, the pitch curve of the rack is a circle of infinite radius. In most cases, the profiles of the teeth with which said solids are equipped are involutes to circles of constant diameter (or a straight line in the limiting case of a rack).
With such an arrangement, when one of the solids is subjected to uniform rotation, the other solid is driven with uniform rotation under good conditions concerning the arc of contact of the gearing, and the angle at which the teeth cooperate (optimum strength relative to transmission forces), and, in addition, is easy to make. The arrangement of the toothing thus corresponds to requirements for so-called standard toothing.
There are other types of toothing which are applied to non-circular pitch curves (in particular elliptical curves) in which uniform rotation of one of the solids gives rise to non-uniform rotation of the driven solid. However, the forms of toothing implemented do not satisfy standard criteria and as a result have not been applied in industry.
The present invention seeks to provide standard toothing in which each tooth is defined by a profile satisfying the conditions mentioned above, concerning arc of contact, ability to withstand the forces to be transmitted, and ease of cutting, even through the pitch curves thereof (which may be open or closed) are neither circles or nor straight lines, thereby providing non-uniform motion of the driven solid about its axis of rotation, said motion thus including stages of angular acceleration or deceleration for uniform motion of the driving solid.
SUMMARY OF THE INVENTION
More precisely, in a first aspect the present invention provides a tooth for coupling by meshing two solids which roll over each other along their respective pitch curves without sliding, said curves being other than entirely circular, the tooth being characterized in that the profile of its active surface is constituted by a flank portion (foot flank portion) situated inside the pitch curve and in the form of an involute of a circle determined for a given pressure angle, and by a face portion (head flank portion) outside the pitch curve and determined by calculation as a function of the pitch curve in such a manner that they instantaneous point of contact between the face portion (head flank portion) of the tooth and the flank portion (foot flank portion) of the co-operating tooth is situated on the tangent to the circle defining the flank portion (head flank portion) and passing through the instantaneous point of contact between the pitch curves, i.e. satisfying the envelope principle.
In a second aspect, the invention lies in toothing comprising a plurality of teeth as defined above about a pitch curve including at least one toothed arc following a logarithmic spiral.
In a variant embodiment of this toothing, the pitch curve comprises at least one elliptical toothed arc.
It may be observed in this respect that a particular embodiment of the invention lies in the presence of at least one circular arc in the pitch curve, where a circular arc is a special case either of a logarithmic spiral (having a right angle as its characteristic angle) or else of an ellipse (with the distance between the focuses being zero).
Toothing in accordance with the invention may also include a toothless arc of pitch curve between two toothed arc portions, said toothless are being tangential at its ends to the flank (foot flank) and face respectively of the teeth which it interconnects. This arc of the pitch curve may be an arc of a logarithmic spiral or of an ellipse.
Finally, in a third aspect, the present invention provides gearing fitted with toothing as defined above and in which each of the solids constituting the g
REFERENCES:
patent: 1142051 (1915-06-01), O'Connor
patent: 2447104 (1948-08-01), Trbojevich
patent: 2842977 (1958-07-01), Stibitz
patent: 2897765 (1959-08-01), Kitano
patent: 3753378 (1973-08-01), Bishop
patent: 4011764 (1977-03-01), Friedrichshafen
Product Engineering, 3-14-60, "Noncircular Gears", pp. 59-66.
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