Blade tensioner with retaining pin and bracket

Details Blade tensioner with retaining pin and bracket Blade tensioner with retaining pin and bracket

1999-10-27

2001-05-29

Bucci, David A. (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

C474S109000, C474S140000

Reexamination Certificate

active

06238311

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a tensioners used with chain drives in automotive timing applications and more particularly to a blade-type tensioner which is provided mounted to a bracket and held in place by a retaining pin for shipping and convenient assembly to an engine.
Tensioning devices are used as a control device for a power transmission chain as the chain travels between a plurality of sprockets. Generally, it is important to impart and maintain a certain degree of tension to the chain to prevent noises or slippage. Prevention of slippage is especially important in the case of a chain driven camshaft in an internal combustion engine because slippage may alter the camshaft timing by several degrees, possibly causing damage. In the harsh environment in which an internal combustion engine operates, chain tension can vary between excessively high or low levels as a result of the wide variations in temperature and differences between the coefficients of linear expansion among the various parts of the engine, including the chain and the tensioner. Camshaft and crankshaft induced torsional vibration cause chain tension to vary considerably. This tension variation results in chain elongation. Moreover, wear of the chain components during prolonged use can cause elongation of the chain that results in a decrease in the tension of the chain.
Generally, blade-type tensioners use a spring blade interlocked under tension with a plastic shoe to provide tension to a chain. Before assembly into a operable tensioner the blade spring is preformed into an arcuate shape and the shoe is provided relatively flat. The shoe is constructed from a semi-rigid material which will deform or “creep” upon experiencing a load at high temperature. During assembly, the blade spring is flattened to correspond to the shape of the shoe and then interlocked with it. Because the semi-rigid shoe prevents the blade spring from returning to its original more arcuate shape, the blade spring applies a load to the shoe. After application of the tensioner to an engine, the heat from the engine, during operation, causes the temperature of the shoe to increase and become less rigid. The load from the blade spring causes the shoe to deform to a more arcuate shape. Through such deformation, tension is provided to a chain.
The chain tensioner is positioned to act against a free length of the chain between the sprocket gears. As the blade spring forces the shoe into a more arcuate shape, the apex of the shoe extends farther into the span of chain thereby increasing chain tension.
Typical blade-type chain tensioners have interlocked a blade spring to a shoe. For example, U.S. Pat. No. 3,490,302, to Turner et al., incorporated herein by reference, discloses a chain tensioner where the blade spring is mounted to mechanically interlock with, and thereby provide a load to, a shoe through a hole and pin combination. The blade spring continuously bears against the shoe.
Yet another structure for mounting a blade spring to a single shoe is disclosed in U.S. Pat. No. 5,055,088, to Cradduck et al., incorporated herein by reference. This reference discloses a blade-type tensioner which utilizes a plurality of blade springs interlocked with a plastic shoe through a passageway in the shoe and fastened using a split, or solid pin.
Unfortunately, the prior art blade-type tensioners have a drawback. Typically, blade-type tensioners are used in confined spaces and are supplied to engine assembly plants in a straight form for ease of assembly in the engine. In the prior art, the tensioner is fixed to a bracket in the flattened form by a retaining pin which passes between the blade spring and the shoe and engages a notch or slot formed in the shoe itself and further passes through a hole in the bracket fixing the blade tensioner in place. The formation of the notch in the shoe requires an additional manufacturing step and forms a potential weak spot in the shoe.
The prior art blade spring tensioner
10
is shown in
FIGS. 1-3
. The shoe
30
has a blade spring interconnected thereto, the blade spring including a pair of blade spring members
20
,
22
disposed along a bottom face
21
of the shoe
30
. One end of the blade spring is held by being inserted into a slot in the shoe. The other end of the blade spring has an opening
80
which is fitted over a projection
60
on the corresponding end of the shoe and is locked in place by a solid or split pin
50
passing crosswise through the projection
60
.
A slot
70
is formed near the center of the bottom face
21
of the shoe
30
adapted to receive a retaining pin
55
(shown in FIG.
2
). When the tensioner
10
is first mounted to the bracket
15
, the retaining pin
55
is passed through the tab
25
formed on the bracket
15
aligned with the slot
70
in the center portion of the shoe
30
and through a hole formed in the bracket, thus locking the shoe in place.
FIG. 3
illustrates the prior art blade tensioner
10
as applied to a generalized power transmission system including a driving sprocket
81
, a driven sprocket
82
and a chain
84
connecting the two sprockets. The blade tensioner
10
is mounted to the bracket
15
which, when mounted to the engine block
86
, directs the upper face
23
of the tensioner shoe
30
to tension the slack portion of the chain
84
. The bracket
15
includes a tab
25
spaced outward from the bracket face and located adjacent to the mid portion of the tensioner shoe
30
. The bracket
15
further includes a passive snubber
88
generally opposite the tensioner
10
and applied to the drive side of the chain.
The present invention is directed to a blade tensioner that addresses the problem of retaining the tensioner to the bracket by supplying a ready-to-use assembly that is easy and inexpensive to manufacture, simple to apply to an engine and results in a stronger tensioner.
SUMMARY OF THE INVENTION
The present invention is directed to a chain tensioner comprising a blade spring in interlocked association with a plastic shoe. The shoe includes a mechanism to securely retain the blade spring thereagainst and a further releasable mechanism to retain the tensioner in a retracted position when mounted upon on a bracket until the unit is installed in an engine timing system and released to permit operation.
In one embodiment, the bottom face at one end of the tensioner shoe has a knurl with a transverse bore for pivotal attachment to a pivot pin. A pair of longitudinal spring slots are formed in the knurl. The other end of the shoe has a protrusion on the bottom face. A bore is formed through the protrusion transverse to the longitudinal axis of the shoe. The bores of the knurl and the protrusion are parallel to each other. One end of the blade spring is inserted into the spring slots and the other end of the blade spring has an opening which fits over the protrusion. The blade spring is interlocked onto the shoe by a hollow roll pin located in the bore of the protrusion.
The interlocked shoe and blade spring are assembled to a bracket. The bracket includes a pivot pin extending from the face of the bracket for pivotal mounting of the first end of the shoe. The bracket also has a notched tab spaced outward from the bracket face and located adjacent the protrusion at the second or free end of the shoe. A retaining pin engages the notch in the tab and passes through the hollow roll pin thereby retaining the shoe to the bracket in a retracted state prior to application of the assembly to an engine. An integral passive snubber is attached to the bracket generally opposite the tensioner.
The advantages and features of the chain tensioner apparatus of the present invention will be better understood by reference to the embodiments which are hereafter presented and depicted by way of example in the following description taken in conjunction with the accompanying drawings in which like reference numbers are used to indicate like elements.


REFERENCES:
patent: 3490302 (1970-01-01), Turner
patent: 4798562 (1989-01-01), Matson et a

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