Blade tensioner and system for a chain

Details Blade tensioner and system for a chain Blade tensioner and system for a chain

2002-05-17

2004-10-26

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

C474S140000

Reexamination Certificate

active

06808467

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the field of blade tensioning. More particularly, the invention pertains to an improvement of the structure of a blade tensioner and a system that includes a blade tensioner that applies tension to the chain that drivingly connects the driven shaft within an engine to the driving shaft.
2. Description of Related Art
A blade tensioner has been used conventionally as the tensioner that applies tension to a chain. Generally, a blade tensioner consists principally of a resinous blade shoe having an arcuately curved chain sliding face, and metallic leaf spring-shaped blade springs that are disposed on the side opposite the chain sliding face of the blade shoe and that are used to exert a spring force on the blade shoe.
During chain operation, the chain travels while sliding along the chain sliding face of the blade shoe. At this time, the chain is subjected to compression loading as a result of the elastic resilience of the blade springs and the blade shoe, thereby tensioning the chain. When the chain slackens during operation, the blade springs, which deform elastically on the side where the radius of curvature increases, are subjected to return deformation on the side where the radius of curvature decreases, thereby causing the blade shoe to protrude into the chain side and take up the chain slack, so a constant, uniform tension is maintained in the chain.
There are numerous problems that arise involving how well the blade tensioner works. One such problem is damping efficiency. In an automobile engine, a blade tensioner as disclosed in prior art Japanese Patent Application Public Disclosure No. 2000-234656, and shown in
FIG. 1
, the blade tensioner (
100
) consists principally of the resinous blade shoe (
101
) having the arcuately curved chain sliding face (
101
a
), the metallic leaf spring-shaped blade springs (
102
) that are disposed on the side opposite the chain sliding face (
101
a
) of the blade shoe (
101
) and that are used to exert a spring force on the blade shoe (
101
), and the metallic support blade (
103
) that supports the blade shoe (
101
). Slots (
110
a
) and (
111
a
) are formed in the distal end portion (
110
) and the proximal end portion (
111
), respectively, of the blade shoe (
101
), and the ends of the blade springs (
102
) are inserted into and held within these slots. A pair of holes (
103
a
)(
103
b
), is formed in the support blade (
103
), and the support blade (
103
) is fastened within the engine by means of bolts inserted through these holes. The proximal end portion (
111
) of the blade shoe (
101
) is supported rotatably by the pin (
104
) fastened in the support plate (
103
). The lock washer (
105
) is installed on the pin (
104
). Support portion (
130
), which is equipped with the support face (
130
a
) that slidably support the distal end portion (
110
) of the blade shoe (
101
), is provided at the end of the support plate (
103
).
As shown in prior art
FIG. 2
, the blade spring (
102
) has a radius of curvature r
o
smaller than the radius of curvature of the blade shoe (
101
). However, after the blade spring is mounted in the blade shoe (
101
), and the blade tensioner is installed in the engine, the radius of curvature of the blade spring (
102
) changes from r
o
to R
o
(>r
o
). That is, the blade spring (
102
) is elastically deformed, which applies compression loading to the chain as a result of the elastic resilience equivalent to the amount of its elastic deformation, thereby maintaining the tension of the chain.
After the chain elongates during operation, the blade springs (
102
), which deformed elastically on the side where the radius of curvature increases in order to apply compression loading to the chain, are subjected to return deformation on the side where the radius of curvature decreases, as the result of the restoring force. Consequently, the chain sliding face (
101
a
) of the blade shoe (
101
) protrudes into the chain side, thereby taking up the chain slack.
Prior art
FIG. 3
shows an example of the application of the aforementioned blade tensioner to a timing chain used to drive an engine's overhead camshaft. In an engine's timing chain, the chain span generally is long because the center-to-center distance between the crankshaft and camshaft is long. As a result, the overall length of the blade shoe (
101
) also is long. Plus, the proximal end portion (
111
) of the blade shoe (
101
) is provided so as to rotate freely around point O, the center of the support shaft (
150
) fastened to the engine side. The distal end portion (
110
) is provided so as to slide freely along the linear support face (
160
) disposed on the engine side. Before the timing chain elongates, the distal end portion (
110
) of the blade shoe (
101
) contacts point A on the support face (
160
). When the timing chain elongates, the restoring force of the blade springs causes the blade shoe (
101
) to deform so that it protrudes toward the chain span side. As a result, as shown by the dashed line in
FIG. 2
, the proximal end portion (
111
) of the blade shoe (
101
) rotates around point O, and the distal end portion (
110
) slides along the support face (
160
), so the contact point on the support face (
160
) moves to point B.
At points D and E on the support face (
160
), the compression forces exerted by the chain on the blade shoe (
101
) as reactions to the compression loads applied by the blade shoe (
101
) to the chain are, respectively, F and F′. As for the, at point E the blade springs elastically deform as a result of the restoring force. This decreases the amount of elastic deformation, thereby also decreasing the compression load of the blade springs on the chain and results in the following inequality:
F>F′  (1)
Furthermore, as shown in prior art
FIG. 4
, at point D, the compression force F of the chain produces the bending moment M (=F×OA) that rotates the blade shoe around point O. Similarly, at point E, the compression force F′ produces the bending moment M′ (=F′×OB) that rotates the blade shoe around point O.
At points D and E, the compression forces F, F′ are decomposed into the direction parallel to the support face (
160
) and the direction orthogonal to the support face (
160
), and the angles formed by the directions in which the compression forces F, F′ are exerted and the directions orthogonal to the support face are labeled &thgr; and &thgr;′, respectively.
Of the compression force F at point D, F cos &thgr;, the component orthogonal to the support face, is in equilibrium with the normal force N of the support face (
160
). Plus, the compression force F, F sin &thgr;, the component parallel to the support face, is exerted in the direction that the blade shoe is slid along the support face (
160
). However, the force exerted against this F sin &thgr; is the frictional force &mgr;N (i.e., &mgr;Fcos &thgr;, where &mgr; is the coefficient of friction).
Similarly, of the compression force F′ at point E, F′ cos &thgr;′, the component orthogonal to the support face, is in equilibrium with the normal force N′ of the support face (
160
). Also, of the compression force F′, F′ sin &thgr;′, the component parallel to the support face, is exerted in the direction that the blade shoe is slid along the support face (
160
). The force exerted against this F′ sin &thgr;′ is the frictional force &mgr;N′ (i.e., &mgr;F′ cos &thgr;′).
Here &thgr;′>&thgr;, so
cos &thgr;′<cos &thgr;
Also, from (1),
F′<F
so
&mgr;F′ cos &thgr;′<&mgr;F cos &thgr;
Therefore,
&mgr;N′<&mgr;N  (2)
From (2), it is evident that the frictional force is less at point E than at point D.
However, when tension fluctuation and chain rattling during operation induce chord or harmonic vibration in the blade tensioner, each blade spring in the blade shoe

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