Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Load responsive tension adjuster or shifter
Reexamination Certificate
2001-11-07
2003-08-26
Hannon, Thomas R. (Department: 3682)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Load responsive tension adjuster or shifter
C474S103000, C474S110000
Reexamination Certificate
active
06609985
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to tensioners, which can be used with chain drives in automotive timing and power transmission applications, and, more particularly, to blade-type chain tensioners, with a vibration damping feature.
BACKGROUND OF THE INVENTION
Chain tensioning devices are used to control power transmission chains as the chain travels between a set of sprockets. Such chains usually have at least two separate strands, spans or lengths extending between the drive sprocket, such as a crankshaft sprocket, and the driven sprocket, such as a cam sprocket. The strand between the sprockets where the chain leaves the driven sprocket and enters the drive sprocket is frequently under tension as a result of the force imposed on the chain by the drive sprocket. The strand between the sprockets where the chain leaves the drive sprocket and enters the driven sprocket is frequently under reduced drive tension or slack due to the absence of driving force exerted on that strand. In systems with large center distances between the sprockets, both strands may evidence slack between the sprockets.
As a consequence, it is essential to the proper operation of the chain and sprocket system that a proper degree of engagement between the chain members and the sprockets is maintained during operation of the system. One aspect of maintaining such engagement of chain and sprocket is maintaining a proper degree of tension in the chain strands. The loss of chain tension can cause undesirable vibration and noise in the chain strands. The loss of chain tension also increases the possibility of chain slippage or unmeshing from the teeth of the sprocket, reducing engine efficiency and, in some instances, causing system failures. For example, it is especially important to prevent the chain from slipping in the case of a chain-driven camshaft in an internal combustion engine because misalignment of camshaft timing by several degrees can render the engine inoperative or cause damage to the engine.
The tension of the chain can vary due to wide variations in temperature and linear expansions among the various parts of an engine. Moreover, wear to the chain components during prolonged use also may produce a decrease in the chain tension. In addition, the intermittent stress placed on the chain devices in automotive applications due to variation in engine speed, engine load and other stress inducing occurrences can cause temporary and permanent chain tension.
To maintain tension in such transmission systems, tensioner devices have been used to push a tensioner member against the chain along a chain strand. Such transmission systems, typically press on the chain effective to mechanically deflect the strand path and impart the desired degree of tension on the chain. Current tensioner devices for performing this function include blade spring tensioners, which utilize one or more arcuate blade springs interlocked under tension with a relatively flat shoe made of plastic. The blade spring tensioner operates by permitting the chain to run across the plastic shoe. The spring blade(s) that is inserted within the shoe causes the shoe to creep or deform to a more arcuate shape as the shoe is heated, for example, from the contact of the shoe being driven across its surface. For example, U.S. Pat. No. 3,490,302 discloses such a chain tensioner where the blade spring is mounted to mechanically interlock with a shoe through a hole and pin combination. U.S. Pat. No. 4,921,472 discloses a blade spring tensioner having blade spring mechanically interlocked with a shoe through a passageway in the end of the shoe without the use of a pin. U.S. Pat. No. 5,266,066 discloses another blade spring chain tensioner in which a blade spring is constructed from a simple rectangular metal band formed in an arcuate shape and interlocked with a pocket in a shoe to provide a load to the shoe.
Unfortunately, the prior blade-type tensioners have certain drawbacks. For one, they are prone to prolonging oscillation of the chain. The harsh operating conditions of the engine induces varying tension in the chain. For instance, the cam shaft and crank shaft may induce torsional vibrations which cause chain tension to vary considerably. Moreover, abrupt tension variations may cause the chain to elongate in accordance with the chain stiffness. The blade spring reacts to the varying tension in the chain imparted by the torsional vibrations. Depending on the vibrational frequency, the spring force of the blade spring may react with a resonant vibration that establishes a prolonged oscillation of the chain. It is desirable to neutralize these inadvertent oscillations in the chain tensioning system as soon as possible and maintain a constant tension on the chain.
As one prior approach for addressing this oscillation problem, at least under certain limited conditions, U.S. Pat. No. 5,462,493 discloses a dual blade spring tensioner constructed of a pair of shoes in which one shoe is adapted to impart tension to a chain and overlaps the other shoe which is connected to a blade spring. The dual blade spring tensioner creates a passive mechanical damping feature by using the overlapping shoes to damp chain oscillations and vertical vibrations.
Despite these advances, the prior blade spring tensioning systems generally have found their applications limited to chain tensioning systems involving relatively short chain strands and low dynamic loads. More particularly, the prior blade spring tensioners generally have not performed as desired or needed on tensioning systems involving long strands or high dynamic loads, as they lack sufficient damping capability and/or offer inadequate tension control at system resonance in those more challenging environments for chain tensioning. Timing chains are subject to periodic tension inducement events in the engine, such as not only sprockets engaging the chain but also torque and cam engine vibrations transmitted through the engine block. The multiple forces acting on the tensioning system may accumulate or cancel, although some net vibrational frequency can and often does occur.
As a consequence, in chain tensioning systems involving long strands and/or high dynamic loads, hydraulic chain tensioner devices have been considered and used to provide dual functions of maintaining constant chain tension and dampening of chain movement. A hydraulic tensioner typically has a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. Hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through a check valve and passages formed in the housing of the device. The plunger may move outward against the chain, directly against a tensioner arm principally by an internal spring or similar structure and the plunger position is maintained in large part by hydraulic pressure within the housing. Such a hydraulic tensioner as used with a tensioner arm or shoe is shown in U.S. Pat. No. 5,967,921.
Regarding the mechanics of vibration damping with use of a hydraulic chain tensioner, as a chain traverses its path, it may vibrate or “kick” causing the chain to push against the tensioner arm. The force of the vibration or kick is transferred to the tensioner device causing the hydraulic plunger to move in a reverse direction away from the chain. This reverse movement is resisted by the hydraulic fluid in the chamber, as flow of the fluid out of the chamber is restricted by the check valve assembly. In this fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are relatively easy in one direction (toward the chain) but difficult in the reverse direction. In addition, rack and ratchet assemblies also may be employed to provide a mechanical no-return function.
Unfortunately, the hydraulic tensioners can be relatively expensive in comparison to conventional blade spring type chain tensioners. In addition, in some applications, the size and bulk of prior hydraulic tensioners can present difficulti
Patton Mark E.
Todd Kevin B.
Borg-Warner Inc.
Dziegielewicz David
Fitch Even Tabin & Flannery
Hannon Thomas R.
Johnson Vicky A.
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