Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Tension adjuster has surface in sliding contact with belt
Reexamination Certificate
2000-05-17
2001-11-27
Green, Mary Ann (Department: 3682)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Tension adjuster has surface in sliding contact with belt
C474S122000
Reexamination Certificate
active
06322470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a chain tensioner system having a pair of arms. The arms are positioned outside opposite strands of chain in a power transmission system. The tensioner system causes the arms to travel inwardly towards a chain centerline which acts to simultaneously tension the two strands of a chain in an engine timing application.
Chain tensioning devices, such as hydraulic tensioners, are used as control devices for power transmission chains as the chain travels between a plurality of sprockets. In an automotive application, the tension of the chain can vary greatly due to the wide variation in the temperature and the linear expansion among the various parts of the engine. Moreover, wear to the chain components during prolonged use can produce a decrease in the tension of the chain. As a result, it is important to impart and maintain a certain degree of tension to the chain to prevent noise, slippage, or unmeshing of the chain with the sprocket teeth. It is especially important in the case of a chain-driven camshaft in an internal combustion engine to prevent the chain from slipping because the camshaft timing can be misaligned by several degrees, possibly rendering the engine inoperative or causing damage.
A hydraulic tensioner as used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921, which is incorporated herein by reference. Hydraulic chain tensioners typically have a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. A lever, arm or shoe is often used at the end of the plunger to assist in the tensioning of the chain. The hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through passages formed in the housing. The plunger is moved outward against the arm by the combined efforts of the hydraulic pressure and the spring force.
When the plunger tends to move in a reverse direction (inward) into the housing, typically a check valve is provided to restrict the flow of fluid from the chamber. In such a fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are easy in one direction (outward) but difficult in the reverse direction. In addition, rack and ratchet mechanisms, which are well known in the art are employed to provide a mechanical no-return function.
One example of a chain tensioner which uses a hydraulic tensioner and a pivoted lever to tension a chain is described in Sato et al., U.S. Pat. No. 5,318,482. Sato et al. show a conventional hydraulic tensioner with a plunger pressing a pivoted lever against a chain to impart an appropriate tension to the chain. The tensioner and single shoe arm of Sato et al. has limitations, however, in the amount of chain slack it can take up during the life of the chain. In addition, the single shoe arm of Sato et al. has limitations in its ability to absorb and damp cyclic vibrations in the chain during operation.
Conventional prior art tensioners which tension only one strand of chain, i.e., a single length of chain between two sprockets, in an engine timing application with long center distances between the sprockets have a common weakness. During operation of the engine, wear on the various chain parts causes the chain to lengthen. Taking up the resulting slack on one side of an engine timing system and not the other can cause the timing of the camshaft to change relative to the crankshaft. In some engine timing chain applications, the large center distances cause both sides of the chain span between sprockets to slacken as the chain wears and extends in length.
To address the above problems the present invention includes an actuator, in the form of a conventional hydraulic tensioner in combination with a pivoting lever. The lever has a pair of fixed pins on opposite sides of a central pivot bore. The fixed pins each carry an arm with each arm carrying an attached shoe. In combination, the shoes contact and act on separate strands of a common chain. This provides potentially double the operating take-up for a given range of tensioner operation as compared to a conventional hydraulic tensioner acting upon a single arm with an end pivot that acts on one chain strand.
When the present invention is used to tension separate strands of a single chain, vibrations which occur in one strand of chain tend to be cancelled when the energy of those vibrations are transferred to or combined with those in another strand through the pivoting tensioner. Further, when taking up chain slack in an engine timing application, the present invention minimizes the chance for changes in the timing between the crankshaft and the camshaft as the chain wears and slackens on both sides of the chain span between the sprockets.
SUMMARY OF THE INVENTION
The present invention provides a chain tensioner system which includes an actuator which may be a conventional hydraulic tensioner, in conjunction with a pivoting lever. The lever carries a pair of pivoting arms. The arms extend outside of and contact both lengths or strands of the span of chain between a pair of sprockets. Actuation of the tensioner against the lever causes rotation of the lever which causes inward motion of the arms. The inward motion of the arms causes tension to be imparted to both strands of the chain simultaneously.
One example of the chain tensioner system of the present invention includes a hydraulic actuator as described above and a pivoting lever. Alternately, the actuator may be a mechanical tensioner or any suitable mechanism which is capable of providing sufficient force and travel to act on the lever to provide an adjustment in tension of the chain. The chain has two opposite strands, spans or lengths that are the portions extending between the sprockets. The strand between the sprockets where the chain leaves a driven sprocket and enters a driving sprocket is typically the tight strand or side and the strand between the sprockets where the chain leaves the driving sprocket and enters the driven sprocket is typically the slack strand or side of the chain. However, in systems with large center distances, both sides of the chain evidence some slack.
The lever includes a first end which is located between the chain strands. In the center of the first end of the lever is a pivot bore. The pivot bore is a hole with a cylindrical sleeve or bushing through which a pivot pin, shaft or bolt is inserted and about which the lever may rotate. The pivot pin is attached to an engine block or a mounting surface. The pivot bore and pivot pin are centered on a centerline extending between the two sprockets.
A pair of fixed pins are attached near the periphery of the first end of the lever. The fixed pins are located in near alignment with the chain centerline and equally spaced apart on opposite sides of the pivot bore. A pair of arms, each with an attached plastic shoe, are mounted to and allowed to rotate on each of the fixed pins. The arms extend outside the strands of the chain such that the shoes are positioned to contact an outside portion of the chain. A first arm and associated shoe extend outside the slack strand and a second arm and shoe extend outside the tight strand of chain.
A first fixed pin which is mounted to the lever in a position generally below the pivot bore carries the first arm. The first arm extends outside the slack strand of the chain (assuming a pair of sprockets with a wrapped chain traveling in a clockwise direction). A second fixed pin which is mounted to the lever in a position generally above the pivot bore carries the second arm. The second arm extends outside of the tight strand of the chain.
A second end of the lever extends a distance from the first end of the lever and extends outside the loop of the chain. The second end of the lever has at least one contact surface. It should be understood that
Markley George L.
Wigsten Mark M.
Borg-Warner Inc.
Dziegielewski Greg
Green Mary Ann
Sidley Austin Brown & Wood
LandOfFree
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