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
2000-04-21
2001-11-27
Hannon, Thomas R. (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
C474S110000
Reexamination Certificate
active
06322469
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 device which tensions two separate strands of chain equally.
Chain tensioning devices, such as hydraulic tensioners and blade-type 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.
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 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) away from the chain, 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. An example of a check valve is shown in Dusinberre, II et al., U.S. Pat. No. 5,989,139, which is incorporated herein by reference. 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 arm of Sato et al. has certain 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 the ability to absorb and damp cyclic vibrations in the chain during operation.
An example of a blade-type tensioner which uses a plastic shoe biased by a blade spring is described in Turner et al., U.S. Pat. No. 3,490,302. Turner et al. show a blade spring mechanically interlocked to a plastic shoe. During operation of the engine, the spring causes the shoe to gradually assume a more arcuate shape which imparts tension to an associated chain or takes up increased slack as the chain wears. Due to the nature of the shoe, however, the tensioner has a slow reaction time in response to changes in chain tension and a limited ability to respond to cyclic vibrations.
Conventional prior art tensioners which tension only one strand of chain, i.e., the length of chain between two sprockets, in an engine timing application 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.
Other prior art chain tensioners impart a load to both strands of timing chain by a pair of pistons housed in a common housing located between the chain strands. However, the two pistons in these tensioners act independently and unequally upon the tight and slack strands of chain and fail to address the change of timing which occurs when one piston travels farther and takes up more slack on one side of the timing chain during operation and wear.
To address the above problems the present invention includes a single actuator operating two coupled shoes or wear faces simultaneously. The faces bear against two separate strands of the same 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 a pivot. When 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 multistrand tensioner. Further, when taking up chain slack in an engine timing application, the present invention helps prevent changes in the timing between the crankshaft and the camshaft during operation and as the chain wears and slackens.
SUMMARY OF THE INVENTION
The present invention provides a multistrand chain tensioner system which is designed to engage and tension two strands of chain simultaneously. The multistrand tensioner is preferably applied to a power transmission chain in an engine timing system but may be applied to a chain in any power transmission system.
The multistrand chain tensioner includes a single actuator and a pair of faces. The actuator may be a hydraulic tensioner or may be a spring based actuator, or the like. When the actuator is a hydraulic tensioner, the tensioner includes a housing with a bore. A piston or plunger is slidably disposed in the bore. The plunger is biased out from the bore by a piston spring disposed in a fluid chamber formed between the piston and housing. Pressurized fluid from an oil pump, or the like, enters the fluid chamber by way of a fluid passageway in the housing and also acts to bias the piston outwardly from the bore. The actuator may also be a simple coil or blade spring or a spring biased plunger.
A single actuator is housed within and fixed to a central anchoring or housing structure. The anchoring structure is fixed to the engine block by a plate mounting portion. A pair of parallel bars or rods pass through the central anchoring structure. The rods are free to slide through the structure. Tensioner arms are fastened securely to the end faces at the ends of the rods such that relative movement between the rods and the arms is prevented. A shoe or tensioner wear face is fixed to each arm by way of retention tabs, dovetail fittings or any suitable method. The faces are adapted to each contact a separate strand of the same chain.
The housing or anchoring structure is preferably located between strands of the chain and generally between the two sprockets about which the chain is wrapped. In operation, the actuator, which is located in the anchoring structure, produces an outward force upon one of the arms. The arm acted upon by the actuator is positioned inside the chain loop. Thus, the actuator forces the inside arm and inside face against an inside portion of a first strand of chain. The rods attached to the inside arm on one end are attached to an outside arm at an end opposite the inside arm. The rods act to pull the outside arm against an outside portion of a second strand of the chain.
REFERENCES:
patent: 3490302 (1970-01-01), Turner et al.
patent: 3964331 (1976-06-01), Olfield
patent: 4758207 (1988-07-01), Jepsen
patent: 4850934 (1989-07-01), Gibson, Jr. et al.
patent: 5055088 (1991-10-01), Cradduck et al.
patent: 5318482 (1994-06-01), Sato et al.
patent: 5597367 (1997-01-01), Trzmiel et al.
patent: 5797817 (1998-08-01), Senftleben et al.
patent: 5967922 (1999-09-01), Ullein et al.
patent: 5989139 (1999-11-01), Dusinberre, II et al.
patent: 6129644 (2000-09-01), Inoue
pate
Borg-Warner Inc.
Dziegielewski Greg
Hannon Thomas R.
McAnulty Timothy
Sidley Austin Brown & Wood
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