Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Pulley or guide roll has eccentric mount for shifting or...
Reexamination Certificate
1999-03-12
2001-03-06
Wright, Dirk (Department: 3681)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Pulley or guide roll has eccentric mount for shifting or...
Reexamination Certificate
active
06196940
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to belt tensioners and more particularly to belt tensioners that can be easily and precisely installed in operative relation with a timing or drive belt.
Belt tensioners are well known in the prior art and have been used in many belt systems heretofore. A belt tensioner is a movable support structure that rotatably supports a portion of a belt in an engine or other mechanical system. A belt tensioner is movable to compensate for increases or decreases in belt path length due to wear and other factors to provide a constant belt tensioning force on a timing or drive belt.
A common type of conventional belt tensioner includes a fixed structure and a pivoted structure pivotally mounted on the fixed structure by a pivot assembly. The pivoted structure carries a belt-engaging pulley. A coil spring is mounted in surrounding relation to the pivot assembly and the ends of the spring are connected between the fixed and pivoted structures to bias the latter with respect to the former toward a position of maximum belt take-up. The spring biasing force decreases as the pivoted structure moves from a position of minimum belt take-up to a position of maximum belt take-up. Although the spring force varies within the range of movement provided, a substantially constant tension is maintained on the belt. The principles stated above can be appreciated from U.S. Pat. No. 4,473,362.
It is also known that when a belt tensioner is installed on an engine, the tensioner should be installed to apply a predetermined static tensioning force on the belt. On some belt tensioners, this is achieved by adjusting the same so that the pivoted structure that carries the pulley is positioned between two end stops that define the range of movement for the pivoted structure. A belt tensioner should maintain the proper belt tension level throughout the entire operational angular movement of the pivoted structure.
In accordance with prior art arrangements, during the adjustment or installation of the tensioner, an eccentric adjusting member forming part of the fixed structure is rotated to move an eccentric pivoted structure eccentrically disposed about the eccentric adjusting member. Rotating the eccentric adjusting member causes the eccentric pivoted structure to move into tensioning engagement with the belt. When the belt reaches a predetermined static tension, the opposing force upon continued rotation of the eccentric adjusting member causes the eccentric pivoted structure to move away from its stop in the belt engaging direction and into a position between the stops, wherein the belt tensioning pulley is disposed in a predetermined static tensioning relation to the belt. Such arrangements are proposed in U.S. Pat. No. 5,244,438, and UK Patent No. 2,249,152.
A shortcoming in the designs of these two patents is that they both disclose belt tensioners that provide an eccentric pivoted structure that is guided for movement on the eccentric adjusting member as the eccentric adjusting member is rotated to install the tensioner in tensioning relation with the belt. Thus, the eccentric pivoted structure and pulley mounted thereon follow a generally arcuate path when moving towards the belt and into tensioning engagement therewith. In addition, the spindle on which the pivoted structure is mounted and/or a base plate on which the eccentric adjusting member is mounted undergoes a connecting rod-type movement as the eccentric adjusting member is rotated. As a result of these movements, the base plate and/or pivot shaft may be installed out of alignment for proper tensioning of the belt when the mounting bolt is fixed and the eccentric adjusting member and pivot shaft are installed in there final, installed position.
U.S. Pat. No. 5,759,125 suggests a belt tensioner arrangement comprising a rigid support base having a longitudinal slot for allowing translational displacement of the support base to adjustably secure the support base to the vehicle engine. This movement is not restricted to an arcuate, connecting-rod type movement as with the two patents mentioned above, but is free to move in any direction as dictated by an externally applied force. This freedom of movement is no better or even worse than the connecting rod type arcuate movement with regard to proper alignment of the tensioner during installation. As with the two above-mentioned patents, the support base and/or pivot shaft in the '125 patent may be installed out of alignment for proper tensioning of the belt when the tensioner mounting bolt is eventually tightened and the tensioner is installed in its final position.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the problems found in the prior art belt tensioning devices by providing a belt tensioner that has an eccentric pivoted structure that is not guided on an inner eccentric adjusting member, but rather is mounted on a concentric spindle that is guided in a linear direction by a stud or bolt as the spindle is cammed towards the belt.
In accordance with this object, the present invention provides a belt tensioner for a motor vehicle engine, including a spindle portion, and an eccentric pivoted structure mounted for pivoted movement on the spindle portion. A rotatable pulley member is mounted for rotation on the eccentric pivoted structure, and a spring is constructed and arranged to bias the eccentric pivoted structure in a direction tending to force the rotatable pulley member into tensioning engagement with a belt trained about the pulley member. A force applying structure is constructed and arranged to force the spindle portion toward the belt against a counteracting belt load force applied by the belt to the rotatable pulley. Linear guiding structure is constructed and arranged to limit movement of the spindle portion to linear movement toward the belt during application of force by the force applying structure during installation of the belt tensioner.
The eccentric pivoted structure is mounted on a spindle portion that is concentric with respect to its internal bore, and is guided in a linear direction during installation of the tensioner.
In a preferred embodiment, the linear guiding structure includes a stud or bolt fixed to the engine frame that is received by the internal bore of the spindle portion. Because the interengagement or areas of contact between the stud or bolt and the tensioner is limited to a position above the belt centerline plane, the tilting forces applied by the belt to the tensioner during installation are counteracted. The counteracting force is enhanced because the points of engagement between the bolt or stud and rest of the tensioner is not limited to axial positions that are in axially overlapping relation with the spindle. Because the point of interengagement can be moved farther away from the pivot or bending point of the bolt or stud, the counteracting moment is greater than in prior art belt tensioner constructions.
In accordance with another object of the present invention, there is provided a method of installing a belt tensioner comprising a spindle portion. A pivoted structure is mounted on the spindle portion and a rotatable pulley member is mounted for rotation on the pivoted structure. A spring biases the pivoted structure in a direction tending to force the pulley member into tensioning engagement with a belt when the belt tensioner is installed on a motor vehicle engine. The method comprises mounting the belt tensioner on the motor vehicle engine with a relatively loose mounting bolt; moving the spindle portion in a substantially linear manner towards the belt so that the pulley is moved into forcible engagement with the belt so as to cause pivoting movement of the pivoted structure against the bias of the spring. After said tensioner is disposed in a predetermined tensioning relation with the belt, the mounting bolt is tightened so as to fix the pivot shaft in place.
Other objects and advantages of the present invention will be appreciated from the fol
Litens Automotive
Pillsbury Madison & Sutro LLP
Wright Dirk
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