Hydraulic tensioner having a flexible blade arm

A chain tensioner system having a hydraulic tensioner and a tensioner arm with a spring blade. A hydraulic tensioner applies force against the end of the tensioner arm. The arm is pivotally supported at one end and supported by the tensioner piston at the other end. A blade spring into inserted into the plastic shoe to provide tension to the arm.

Reference is made to U.S. Pat. No. 5,653,652 entitled "Hydraulic Tensioning 
System With Dual Arm Blade," the subject matter of which relates to the 
present invention, and which is incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
This invention relates to tensioners used with chain drives in automotive 
timing applications and more particularly to a hydraulic tensioner having 
a blade-type tensioner arm. 
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 vibrations 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 chain tensioners use a blade spring interlocked under 
tension with a single shoe to provide tension to a chain. The blade spring 
is arcuate in shape and the shoe is relatively flat. The shoe is 
constructed from a semi-rigid material which will deform or "creep" upon 
experiencing a load at a high temperature. 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. 
During operation, as the heat from the engine 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 assembly 
is positioned along a free length of the chain between the sprockets. 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 
single shoe. For example, U.S. Pat. No. 3,490,302, to Turner et al., U.S. 
Pat. No. 4,921,472, to Young et al., and U.S. Pat. No. 5,055,088, to 
Cradduck et al., each disclose a blade-type tensioner having a blade 
spring mechanically interlocked with a shoe. U.S. Pat. No. 5,266,066, to 
White discloses a blade-type chain tensioner in which a blade spring is 
constructed from a simple rectangular metal band formed into an arcuate 
shape and interlocked within a pocket in a shoe to provide a load to the 
shoe. 
U.S. Pat. No. 5,462,493 addresses the limited arcuate range and oscillation 
problems of these single blade tensioners by providing two chain tensioner 
shoes in an overlapping configuration. One shoe imparts tension to the 
chain, while the other shoe damps the movement of the first shoe to reduce 
the oscillations. The overlapping shoe configuration also allows a greater 
range of arcuate movement so that the chain tensioner is able to meet the 
greater transverse movement associated with a longer center length timing 
chain. 
U.S. Pat. No. 5,653,652 provides for the two chain tensioner arms in an 
overlapping configuration, as referred to in U.S. Pat. No. 5,462,493, but 
also adds a hydraulic tensioner against the arms in order to provide a 
system with greater range of tensioning. 
One problem associated with the tensioning system of U.S. Pat. No. 
5,653,652, in certain types of timing chain configurations, is the set 
geometry provided by the system throughout its range of operation. 
Maintenance of contact between the chain and the tensioner arm is 
essential to maintain control of a chain system. In systems of fixed 
geometry, the contact area between these two elements (chain and tensioner 
arm) changes depending on the position or articulation of the tensioner 
arm. 
On chain systems with particularly short center distances, the fixed 
geometry is often such that the contact patch (or portion of the tensioner 
arm contacted by the chain) must be very short in any position of the 
tensioner so that the contact can be maintained throughout the life of the 
tensioner system as the patch moves along the arm due to wear over the 
life of the system. The present invention attempts to provide a longer 
contact patch throughout the life of the tensioner system since the 
tensioner arm can conform to the geometry of the chain strand at various 
positions. 
Another problem faced by systems of U.S. Pat. No. 5,653,652, in certain 
timing system configurations, arises due to slap or contact as the chain 
impacts the tensioner arm. Slap by the chain against the arm can cause 
pitting and material removal from the arm, which quickly leads to failure 
of the arm surface. The present invention provides a flexible arm that 
travels with and conforms to the path of the chain to minimize or 
eliminate impact in the form of slap or contact. 
SUMMARY OF THE INVENTION 
The present invention relates to a chain tensioner system having a blade 
style tensioner arm with a hydraulic tensioner. A tensioner is required on 
an automotive timing drive (chain or belt) to take up the slack as the 
chain wears and to take up chain stretch as the engine speed increases. 
The tensioner must be able to hold the force of the chain against the 
guide arm as the chain tension increases due to the cam and crank 
torsional oscillations. 
The present invention utilizes a hydraulic tensioner to apply force against 
the free end of the tensioner arm. In the system of the present invention, 
the arm is supported in two places, i.e., at the pivot point and against 
the tensioner piston. A blade spring is located inside the body of the 
tensioner arm. 
The tensioner of the present invention finds particular application in 
timing drives that have short center distances between shafts. 
Additionally, in balance shaft drives, often the chain is required to wrap 
the backside of a sprocket adjacent another sprocket. In such systems, it 
is difficult to package a traditional solid tensioner arm and maintain 
acceptable system geometry. The present invention utilizes a flexible 
plastic tensioner arm that includes a flat blade spring. The blade spring 
provides shape to the plastic as the temperature of the system increases 
and supplies a surface for which the hydraulic tensioner can be positioned 
against.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawings, FIG. 1 depicts a preferred embodiment of the 
system of the present invention having a hydraulic tensioner with a 
flexible tensioner arm with a blade spring. FIG. 1 shows an embodiment of 
the present invention installed adjacent to a chain 10, which is shown 
schematically. The chain includes two strands, 12, 14, which each contact 
opposite sides of the tensioner. 
The tensioning system of the present invention includes arm 16 and a 
hydraulic tensioner 20. One end 17 of the arm is pivotally attached to a 
support 22, which forms part of the tensioner housing. The center portion 
of the arm 16 is supported by upper portion 24 of the piston 26 of the 
hydraulic tensioner 20. The free end 19 of the arm 16 is supported by 
another housing support 28. 
The arm 16 is positioned so that its upper side 32 is against the underside 
34 of the chain strand 12. The bottom side 36 of the arm 16 is positioned 
against the upper side 24 of the tensioner piston. One end 17 of the arm 
16 has a single pivot about point 38, while the other end 19 is free and 
can slide along support 28. 
A conventional hydraulic tensioner of the prior art, which can be utilized 
with the system of the present invention, is shown in FIG. 4. Such a 
tensioner is also shown in Hunter U.S. Pat. No. 5,346,436, which is 
incorporated herein by reference. The hydraulic tensioner 20 includes a 
piston 26. The piston extends upward to apply pressure on the center 
portion and free end 19 of the arm 16. A tensioner 20, as shown, typically 
includes a housing 40 having a central bore 42 that forms a fluid chamber 
44 with the interior of the piston 26. The fluid chamber 44 is supplied 
with fluid through a passageway from a pressurized fluid source (not 
shown). The fluid source may be an oil pump or a reservoir. Fluid travels 
into the fluid chamber through a one-way check valve 45 (shown with ball 
47). Check valves are well-known in the tensioner art. A spring 46 
contacts the inside of the piston 26 causing the piston to be biased or 
move axially in a protruding or outward direction from the housing bore. 
The upper end 43 of the piston 26 contacts the arm 16 to provide tension 
on the arm which in turn applies tension along the chain strand 12. The 
second chain strand 14 travels along a stationary arm 48 or path at the 
bottom of the tensioner housing. 
The pivot point 38 of the arm 16 is the rotation point for the arm. The arm 
16 is pinned, or otherwise secured, against the engine at point 38. 
A blade, shown more clearly in FIG. 3, is inserted in arm 16. The flexible, 
metal blade increases the rigidity of the tensioner arm 16 also helps the 
plastic arm 16 maintain its shape. Preferably, the blade has a normally 
arcuate shape that imparts tension to the arm. 
FIGS. 1 and 2 depict one embodiment of the system of the present invention 
in an engine balance shaft system between two sprockets. The balance shaft 
system has a short center distance between the two crankshaft sprocket and 
balance shaft sprocket and thus requires a shortened tensioner to be 
inserted between the two chain strands 12, 14. 
The movement of the crankshaft sprocket 50, forces the chain 10 and the 
respective strands 12 and 14 into motion. One chain strand is the slack 
side while the other chain strand is the tight side. The tight side is the 
portion or span of chain that is in tension between the driving and the 
driven sprockets. The slack side is the portion of the chain that is 
leaving the driving sprocket and entering the driven sprocket. The piston 
and hydraulic tensioner are conventionally located on the slack side of 
the chain. 
In the embodiment shown in FIG. 1, the chain strand 12 wraps about a 
balance shaft sprocket 52. Alternately, the chain strands 12, 14 can be 
wrapped about two camshaft sprockets in a cam-to-cam drive of a dual 
overhead camshaft engine timing system. 
In operation, upon start-up, the piston of the hydraulic tensioner is 
biased outward by the spring, which causes the check valve to open to 
permit fluid to enter the fluid chamber. As the chain tightens, the inward 
force of the chain is balanced by the resisting force of the spring and 
hydraulic fluid that fills the chamber. Once the forces are relatively 
balanced, the check valve closes and no more fluid enters the chamber. The 
piston acts outwardly against the center or the free end of the tensioner 
arm. The tensioner arm pivots about the pivot point 38 and moves outward 
by the force of the piston. As the chain continues to move across the 
surface of the arm, the temperature of the arm increases, which causes the 
blade spring to bend and assist in maintaining tension in the chain. 
Those skilled in the art to which the invention pertains may make 
modifications and other embodiments employing the principles of this 
invention without departing from its spirit or essential characteristics, 
particularly upon the foregoing teachings. The described embodiments are 
to be considered in all respects only as illustrative and not restrictive, 
and the scope of the invention is, therefore, indicated by the appended 
claims rather than by the foregoing description. Consequently, while the 
invention has been described with reference to particular embodiments, 
modifications of structure, sequence, materials and the like would be 
apparent to those skilled in the art, yet still fall within the scope of 
the invention.