LOW TORSIONAL STIFFNESS FLEXIBLE COUPLING

ACCOUPLEMENT SOUPLE A FAIBLE RIGIDITE TORSIONNELLE

English Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed is a flexible coupling which is characterized by low torsional
stiffness when a relatively low torque load is applied to the coupled shafts.
The coupling includes a plurality of variable stiffness torque transmitting
elements which permit low torsional stiffness at low torque but also permit the
coupling to operate at a relatively higher torque load.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROEPRTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An improved flexible coupling for transmitting torque between a
driving and driven shaft comprised of a hub means having outwardly extending
blade members, said hub being mounted on one of said shafts and a sleeve
element having inwardly extending blade members, said sleeve member being
mounted on the other of said shafts, said blades defining cavities for
containing elastomeric elements in compression for transmitting torque between
said shafts, the improvement comprising;
the elastomeric elements in compression in each of said cavities including
at least one element having a relatively low hardness and at least one element
having a comparable, relatively high hardness.
2. The coupling of claim 1 wherein said elastomeric elements in
compression in each cavity include one element of relatively low hardness
contained between two elements of relatively high hardness.
3. The coupling of claim 2 wherein the elements having a relatively high
hardness have a smaller diameter than the element having a relatively low
hardness.
4. The coupling of claim 3 wherein a pin member maintains the
concentricity of the elastomeric elements.

Description

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BACKGROUND OF THE INVENTION
This invention relates to flexible couplings by which torque is
transmitted between two shafts by means of elastomeric elements in compression
and, more particularly, to such a flexible coupling which has a low torsional
stiffness when a relatively low torque load is applied to the coupled shafts.
DESCRIPTION OF THE PRIOR ART
Flexible couplings for transmitting torque between misaligned driving and
driven shafts by means of elastomeric elements in compression are old and well
known in the arts, see US. Patent Nos. 2,764,003 and 2,873,590. Such
couplings have not only demonstrated the ability to compensate for misalignment
between the driving and driven shaft but also to protect the driving and driven
members from torsional shock loading and torsional vibration in most
applications. Use of such couplings in diesel marine drive systems has
presented a unique set of problems since the coupling must be designed to act
over a wide range of speeds and therefore over a wide range of torque, since in
marine propellers the torque is proportional to the square of the speed. It is
desirable to provide a torsional stiffness low enough to place the resonances
or critical speeds for a particular mode of torsion vibrations below minimum
operating speed. When the coupling used is designed to handle the highest
torque loadings at full speed, it is sometimes too stiff under low speed, low
torque conditions and torsional resonance may occur at the lower operating
speeds. This vibration can damage the propulsion system. However, if the
coupling used has a suitably low torsional stiffness, it often cannot handle
the high torque developed at higher speeds. This has led to numerous cases of
coupling and other drive component failure. Both vibration damage and coupling
failure are expensive in terms of repair parts and downtime.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing problems of the prior art by

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providing a coupling having low torsional stiffness at low torque loads but
also having sufficient stiffness to handle high torque loads. Each cavity
formed in part by the blades of the hub and sleeve of the coupling contains a
plurality of elastomeric elements of different harnesses. Under low torque
only the lower hardness elements are compressed resulting in a low torsional
stiffness. However, at high torque loadings the higher hardness elements also
become compressed and limit the torsional windup of the coupling so that the
lower hardness elements will not become overstrainecl.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side view, partially in section, of the coupling of the
present invention,
Figure 2 is a fragmentary and view of the coupling of Figure l; and
Figure 3 is an enlarged view of the portion of Figure 1 in section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Couplings by which torque is transmitted between two shafts by means of
elastomeric elements in compression are fully described in US. Patent Nos.
2,764,003 and 2,873,590.
Referring to Figures 1 and 2, the coupling of the present invention
generally designated lo is comprised of a hub 12 which has blades 14 that is
mounted on one of the pair of shafts to be rotated. In the preferred
embodiment, the hub 12 is made of cast ductile iron or cast steel. The sleeve
element 16 of the coupling which is mounted on the other shaft has blades 18
which in combination with blades 14, plate 20 and end plate 22 form the
cavities 24 which contain the elastomeric elements 26 and I The size of
blades 14 and 18 and the corresponding size of cavities 24 are design
considerations based on the use the coupling is to undergo. These design
considerations are well known and understood in the art and will not be
repeated here as they form no part of the present invention.

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Elastomeric elements 26 are made of a relatively hard, of approximately 75
dormitory, rubber and are placed on each side of an element 28 in each cavity
24. Element 28 is made of a softer rubber, of approximately 45 dormitory.
Elements 26 which is circular in cross section have a smaller diameter than the
diameter of element 28 and a pin 30 through elements 26 and 28 maintains their
concentricity. Pin 30 may be of metal or plastic or some other suitable
material. Under a low torque load only elements 28 would be compressed and the
coupling would have a low torsional stiffness; but as torque increased elements
26 would be compressed preventing overtraining of element 28.
While I have described a certain preferred embodiment of my invention, it
will be understood it may otherwise be embodied within the scope of the
following claims.