Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Speed responsive
Reexamination Certificate
1999-10-02
2002-02-12
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
Speed responsive
Reexamination Certificate
active
06346056
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is an improvement, and method of using that improvement, to a family of belt-using, variable power transmission systems. Such systems include an endless belt power transmission system using pulleys, such as cone or tapered-face pulleys, with belt receiving surfaces formed by drive faces on axially movable, coaxially confronting members. Generally, such transmissions are called continuously variable transmissions, which will be referred to herein by the common abbreviation of “CVT.” More particularly, the variable power transmission systems using the improvement of the present invention axially move the confronting pulley surfaces in response to the centrifugal force produced by the rotational speed acting on a pivoted weight. The pivoted weight is a cam commonly called, and herein called, a camweight or a flyweight. The improvements of the present invention include improvements to the means of producing the centrifugal force so as to produce a more desirable side force on the belt as the shift ratio changes. The utility of the present invention extends to flyweight actuated devices not using belts.
DEFINITIONS
As used herein, “flyweight” and “camweight” are interchangeable.
A “conventional flyweight” consists of a symmetrical head surrounding a pivot axis (with a center) and one arm extending therefrom where the arm has a cam surface that, in operation, engages a roller or the like. The arm is sometimes described as being cantilevered.
FIGS. 1A and 1B
show examples of conventional flyweights. Characteristically, the head of a conventional flyweight, and its immediate vicinity, consists of an essentially symmetrical mass distribution radially from the center of the pivot axis. One manifestation of such symmetry would be an essentially constant radius from the center of the pivot to the outer edge of the head over approximately a semi-circle. Another manifestation of such symmetry would be the existence of an axis of symmetry extending essentially along the arm through the center of the pivot such that the distance to the outer edge of the head is approximately equal along pairs of radial lines emanating from the center of the pivot that have equal inclinations (angle) to the axis of symmetry.
A Ski-Doo type conventional flyweight is shown on FIG.
1
C. The Ski-Doo type conventional flyweight interchanges the cam surface and roller placing the roller on the arm and fixing the cam surface.
“Center-of-mass,” abbreviated herein as COM, is the centroid of the mass referred to. All masses have a COM. Because most of the mass of a conventional flyweight is contained in the arm and because of the symmetry of the head, the arm's COM is close to the COM of the entire conventional flyweight.
The “reference line” is the line that is normal to the rotational axis (which is usually the crankshaft center-line) and passes through the center of the pivot of the flyweight being discussed. “Shift ratio” is the ratio of the diameter of the belt passing over the secondary pulley to the diameter of the belt passing over the primary pulley. Shift ratio is also the ratio of the angular velocity of the primary pulley to the angular velocity of the secondary pulley when there is no slippage. Typically, shift ratios vary from about 3:1 (at low vehicle speed) to 0.8:1.
The “plumb line” of a flyweight is, as the name suggests, a plumb line dropped from the center of the pivot of a conventional flyweight that is statically suspended by the pivot while free to rotate about the pivot. It extends in both directions from the center of the pivot and is essentially the same as a line passing through the center of the pivot and the arm's COM. Note that the experimental method of determining the plumb line (just described) is only applicable to a conventional flyweight or a flyweight absent the mass supplements of the present invention. A flyweight according to the present invention shall have its plumb line determined after the removal of the mass concentrations of the present invention. Angles measured from the plumb line start at zero degrees for directions along the plumb line in the direction of the arm and increase in the direction of the cam surface on the arm. The shoulder of the preferred embodiment is preferably placed, integrally formed, or attached to a conventional flyweight so that the COM of the shoulder is within a 60 degree wide sector centered on the pivot's center and extending from 60 degrees from the plumb line to 120 degrees from the plumb line.
“Quadrants,” in a plane normal to the pivot's axis, are numbered from one to four increasing counterclockwise from a line segment that is normal to the plumb line and that extends from the pivot center on the side of the flyweight having the cam surface. Counterclockwise is a rotation from the line segment towards the head and clockwise is a rotation from the line segment towards the arm. It follows from the definitions that quadrant 1 encompasses 90 degrees from the plumb line to 180 degrees from the plumb line, that quadrant 2 encompasses 180 degrees from the plumb line to 270 degrees from the plumb line, that quadrant 3 encompasses from 270 degrees from the plumb line to zero degrees from the plumb line, and that quadrant 4 encompasses from zero degrees from the plumb line to 90 degrees from the plumb line. See FIG.
4
. For a conventional flyweight, most of the arm and the arm's cam surface are in the fourth quadrant.
Other definitions appear herein.
BACKGROUND
A conventional CVT has two tapered-faced pulleys interconnected with a belt of essentially fixed length. The sheaves of each pulley are able, under control, to move axially. One pulley's shaft is usually connected to the crankshaft of the engine. The system including a pulley, and its ancillary parts, that is connected to the engine is called the driving, driver, or primary clutch. The other pulley is connected through a linkage to the vehicle's drive train. It, and its ancillary parts, is called the driven or secondary clutch. Of necessity, when the sheaves of either pulley are close together, the associated belt must be located at a relatively large radius (distant from the axis of rotation) and when the sheaves of a pulley are far apart the associated belt must be located at a relatively small radius. It is also apparent that in a well designed system, because of the essentially fixed length of the belt, when the sheaves of one pulley are far apart then the sheaves of the other pulley must be close together. Larger shift ratios, characteristic of slower vehicle speeds, occur when the sheaves of the primary pulley are far apart and the sheaves of the secondary pulley are close together (rotational speed of the primary pulley is greater than the rotational speed of the secondary pulley). Smaller shift ratios, characteristic of high vehicle speed, occur when the sheaves of the primary pulley are close together and the sheaves of the secondary pulley are far apart (rotational speed of the primary pulley is less than the rotational speed of the secondary pulley).
Some of the ancillary parts of the primary clutch include a compression spring, or the like, tending to push the sheaves apart such that, at rest, the sheaves of the primary pulley have opened to allow the belt to lie close to the pulley's rotational axis, effecting a large shift ratio. Such a belt position at rest results in the engine having a desirable minimal load when starting. The force produced by this spring increases as the sheaves of the primary pulley get closer together (lower shift ratios) and further compress the spring. Additional ancillary parts of the primary clutch include a set of pivoting flyweights on the primary clutch pushing on a roller, or the like, linked such that the sheave spacing, and thus shift ratio, is responsive to speed and torque needs of the secondary clutch. In the known CVT systems, the net result of the spring and flyweights of the primary clutch includes:
enough primary pulley belt side force to al
Nouis Cynthia Lynn
Nouis Randy Gene
Bucci David A.
Charles Marcus
McLaughlin James C.
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