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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an engine mount for supporting an engine
or power plant in an engine compartment or the like, and more
particularly, to an engine mount which accommodates, rather than
suppresses, movement of the engine or power plant arising from torque
reactions and the like.
2. Description of the Prior Art
Power producing and power absorbing devices having rotating output and
input shafts must be supported in place within their respective
structures. Usually, the structure is a machine, and the task becomes both
supporting the device, and protecting the balance of the machine from
undesirable vibration or other forces originating within the device.
Examples of such devices which are power producers include internal
combustion engines and electric motors. Other examples, which encompass
power absorbing devices, include air compressors and air conditioning
compressors. The forces which originate from the device include torsional,
shearing, and axial forces, classified with respect to relationship of the
effective direction of the force to the device power input or output
shaft. The forces are of greater magnitude in devices having reciprocating
pistons, such as piston type internal combustion engines, and piston type
compressors, than in devices having pure rotational motion, such as
electric motors.
Another factor influencing the magnitude, frequency, and still other
characteristics of the undesirable forces is the number of pistons. A
single piston device creates the greatest undesirable forces, all other
factors being equal. This is because, for each full cycle to be completed,
and thus create forces counteracting other forces, two full revolutions of
the crankshaft must occur for a four stroke cycle, and one full revolution
for a two stroke cycle. As the number of pistons increases, the number of
offsetting forces increases for each full revolution, thus muting or
offsetting other forces.
In mounting such devices, the prior art generally attempts to address these
forces either by suppressing or absorbing them, or by transmitting them to
the machine. The latter approach is taken in those few instances wherein
power output is more important than longevity of the machine. Examples
include race cars, which frequently have engines solidly and unyieldingly
mounted to their chassis.
One consequence of this practice is to fatigue the drivers. Under racing
conditions, this may be acceptable, but in many other instances, it is
not. A motorized appliance, such as a chain saw, may be less desirable to
use, less safe, and usable for shorter periods of time, if it imposes this
burden on the user. The appliance may therefore provide reduced utility,
enjoy less success in the market, and suffer still other disadvantages.
Also, longevity of the device or of certain components will decrease, or
the power device may break loose from its associated structure, if
subjected to these forces, if the forces are not accommodated properly.
The prior art is replete with many specific situations and proposed
solutions, when considering motors and the like.
U.S. Pat. No. 5,221,192, issued to Christopher Heflin et al. on Jun. 22,
1993, exemplifies mounts providing solid rubber feet, and which have metal
studs embedded therein. It is a common practice within the air
conditioning industry to provide a resilient and elastic pad, in
combination with a bolt securing an air conditioning compressor to a
supporting structure. A signifcant problem presented by this arrangement,
and one addressed by the instant mount, is preventing the bolt from
transmitting destructive or undesirable forces from the compressor to the
supporting structure.
In U.S. Pat. No. 2,143,739, issued to John J. McCabe on Jan. 10, 1939, a
solid block of resilient material surrounds a bushing holding a shaft,
instead of a bolt. Shearing and torsional forces are thus resiliently
resisted and dissipated.
A pad and bolt type mount which avoids problems arising from the presence
of a single bolt passing entire through the pad is seen in U.S. Pat. No.
2,911,170, issued to Robert Galin et al. on Nov. 3, 1959. There are two
bolts arranged in line in place of one, each bolt having an enlarged head
embedded within the pad. The effect of a single through bolt is provided,
but additional flexure is accommodated by provision of two separate bolts,
each encased within the resilient pad.
A similar concept is shown in U.S. Pat. No. 2,292,536, issued to John J.
McCabe et al. on Aug. 11, 1942.
U.S. Pat. No. 3,018,990, issued to Alfred H. Muller on Jan. 30, 1962,
discloses a three point suspension system for an internal combustion
engine, employing three bearings of the bolt and pad type.
Bearing assemblies for bearing vertical loads, and for accommodating
occasional shear stresses are seen in U.S. Pat. Nos. 4,761,925, and
4,830,927, both issued to Yoshihide Fukahori et al. on Aug. 9, 1988, and
May 16, 1989, respectively. The subject bearing assemblies are directed to
support of buildings, and resisting earthquakes. The bearings both feature
laminations of rigid and elastic plates stacked in repeating patterns. The
stack is surrounded by a tubular member for imparting weather resistance.
In '927, plural bearings of high and low damping ability are arranged in
parallel to provide satisfactory ability to resist an actual earthquake.
The instant bearing both isolates its structure from a source of vibration
or injurious forces, and damps those forces.
An invention having similar purpose is shown in U.S. Pat. No. 4,887,788,
issued to Richard J. Fischer et al. on Dec. 19, 1989. A cylindrical
assembly of somewhat complicated internal arrangement of dissimilar
elastic, resilient materials is provided. Again, a tubular external member
provides environmental protection, and further adds reinforcing strength
to the assembly.
U.S. Pat. No. 5,035,395, issued to Brock R. Settlemier et al. on Jul. 30,
1991, describes a cradle assembly built up from components including two
stacks of elastic, resilient material.
U.S. Pat. No. 4,335,323, issued to Earl R. Kebbon et al. on Jun. 15, 1982,
illustrates a motor bearing opposing both shearing and axial loads imposed
upon the output shaft.
None of the above inventions and patents, taken either singly or in
combination, is seen to describe the instant invention as claimed.
SUMMARY OF THE INVENTION
Unlike all prior art examples of mounts, wherein the mount is solid
material throughout, although not necessarily of homogeneous composition,
the present invention suspends the mounted device such that torsional
movements, vibrations, and the like are allowed to proceed to the point of
self-cancellation. The instant mount neither suppresses nor passes
movement and vibration through to the surrounding structure.
Instead, the novel mount flexes to allow vibration, torsion, and other
movements, while exerting a small, elastic force urging the power
producing or utilizing device back to its original position. This is
acceptable since the cyclic dynamics of any selected device will tend on
its own to achieve an equilibrium, returning the device to its original
state. The novel mount thus accommodates, and does not dissipate or
distort, these forces.
The structure that enables this performance is an elastic, resilient tube
attached at one end to the device and at the other end to the supporting
chassis, arranged parallel to the power shaft of the device.
A section of rubber tubing serves adequately in the capacity of such a
mount. The mount is preferably secured to a disc at either end, one disc
being attached to the device, and the other disc being fixed to the
chassis. A disc enables supporting contact of the tube about the entire
periphery thereof, which arrangement leads to symmetrical construction and
constant dynamic performance throughout an entire shaft revolution. By
contrast, the member supporting the disc could be other than circular, or
could have a tube contacting surface which is discontinuous. In this
sense, discontinuous signifies that there are areas about the inner
circumference of the tube which are not in contact with the disc or its
counterpart.
Torsional forces enable the device to rotate about the axis of the power
shaft. Total displacement from a reference position may reach twenty-five
degrees of arc in either direction, for a total of fifty degrees of
rotation. This displacement is unheard of in conventional mounts. Yet the
self-equilibrating nature of constant rotary motion both returns the
device to its original rotational position, and also does not unduly
stress the mount.
Different mounting arrangements are possible. The device may be supported
fore and aft by two surrounding tubular mounts. Alternatively, one end of
the device may be supported against shearing forces by means other than
the novel mount, there being one novel mount on the other side of the
device.
Active resistance to forces other than torsional may be incorporated in the
novel mount. Axial forces in either direction may be accommodated by
elastic deflection of the tube, or may be augmented, as by internal solid
or even resilient blocks either surrounding the tube, or located within
the tube.
Shearing forces may be accommodated by a predetermined amount of sag of the
tube, or a separate solid or even resilient member may be provided to
augment resistance to shear.
Operation of the novel mount has proved successful. In a small scale trial,
a two stroke, gasoline engine intended for operating a chain saw,
manufactured by Sachs-Dolmar, has been satisfactorily suspended at one end
by a tube taken from a pneumatic tire inner tube. The inner tube was
supported on plywood discs of five and one half inch (14 cm) diameter and
three thirty-seconds of an inch (2.4 mm) thickness. The length of the tube
was two inches (5 cm). The engine, which weighs about five pounds (2.5
kg), operated at an output of 6.5 HP (5 kW) at 9,000 revolutions per
minute when placed in a model airplane, driving the propeller thereof.
Over one hundred hours of service free operation was achieved when this
phase of experimentation was ceased. Considerably greater operating times
without service may be possible. By contrast, a conventionally mounted
engine required repairs to correct for wear to linkage components and
servos after one hour's operation.
These results were corroborated by accelerometer tests performed on
another, small engine, in which the conventionally solid mounted engine
imposed forces of approximately 115 Gs upon the airframe, taken about two
inches from the crankshaft centerline. When this test was repeated after
employing the novel mounting scheme, forces imposed upon the airframe were
4-5 Gs.
Accordingly, it is a principal object of the invention to provide a mount
for a power producing or absorbing device having a rotating power shaft,
which mount attaches to both the device and to its chassis, and yieldingly
accommodates torsional forces.
It is another object of the invention to provide a mount which yieldingly
resists shear and axial forces.
It is a further object of the invention to provide a mount which is tubular
and parallel to the power shaft of the device.
Still another object of the invention is to provide a mount which is
resilient.
An additional object of the invention is to provide a mount which is
elastic.
It is again an object of the invention to provide a mount which
incorporates additional members resisting shearing forces.
Yet another object of the invention is to provide a mount which
incorporates additional members resisting axial forces.
It is an object of the invention to provide improved elements and
arrangements thereof in an apparatus for the purposes described which is
inexpensive, dependable and fully effective in accomplishing its intended
purposes.
These and other objects of the present invention will become readily
apparent upon further review of the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded, perspective view of the invention, with fragmentary
rendering of an associated engine and its chassis.
FIG. 2 is an environmental, side cross sectional view illustrating sag.
FIGS. 3, 4, and 5 are diagrammatic detail views illustrating permissible
limits of motor torsion accommodated by the novel mount.
FIG. 6 is an environmental, side cross sectional view of an alternative
embodiment of the invention, wherein a power shaft penetrates the novel
mount.
FIGS. 7 and 8 are side cross sectional views of alternative embodiments of
the invention wherein discs are designed to resist shearing forces.
FIG. 9 is a side cross sectional view of an alternative embodiment of the
invention having two tubes.
Similar reference characters denote corresponding features consistently
throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to FIG. 1 of the drawings, the novel mount 10 spans a power
device 12, such as an engine, and a member of the chassis 16 of a machine.
As employed herein, the term "appliance" will be understood to signify a
machine which either provides or absorbs rotary power. Power device 12
could, then, be a device such as an air compressor, for example.
Regardless of whether the power device provides or delivers power, it will
have a power input or output shaft 18, as is appropriate.
In its simplest form, mount 10 includes a flexible, resilient, preferably
elastic tube 20, and two end pieces, or discs. The end pieces serve to
anchor tube 20 at one end 22 to power device 12, and at the other end 24
to chassis 16. Discs, which are circular and flat, are a preferred
configuration, and this term will be employed to designate end pieces,
which of course may assume other configurations. Tube 20 is disposed
parallel to the axis of a power shaft (see FIG. 6) of power device.
As seen in FIG. 2, discs 26 and 28 are fixed to power device 12 and chassis
by fasteners 30. Tube 20, being flexible and resilient, is easily
installed over discs 26 and 28. Contact of tube 20 with discs 26, 28 takes
place between a peripheral surface 54 (see FIG. 1) of disc 26 or 28, and
the inside surface of tube 20.
The assembly comprising tube 20 and discs 26 and 28 will operate
satisfactorily with no further auxiliary structure in some applications.
However, where the height of the cylinder of tube 20 must be great, it is
possible to place spacers 33 inside tube 20. In this view, two spacers 33
are shown, there also being an antifriction washer 32, which prevents
plural spacers 33 from binding on one another. Washer 32 may be a hard,
smooth material, such as epoxy laid over a fiberglass base, and ground
smooth.
Spacers 33 limit axial compression, and may be dimensioned to resist
excessive sag of tube 20. Sag is illustrated in FIG. 2, occurring when one
disc 26 or 28 is lower than the other. This may arise from weight of power
device 12.
Spacers 33 are shown as solid, in the sense of being free of internal
voids, although voids would not change the performance of spacers 33. The
material selected may be rigid or resilient. Rigid material is
satisfactory in those applications wherein compressive forces are not
imposed on mount 10. To resist such forces, where present, without
imparting shock to power device 12, it may be desirable to manufacture at
least one spacer 33 from a resilient material.
Turning now to FIG. 6, an alternative embodiment of mount 10 is shown
wherein discs 26 and 28, and spacer 33, include respective central
openings 34,36 which are aligned with power shaft 18 of power device 12.
This arrangement enables power shaft 18 to pass through mount 10, in those
instances wherein it is desired to locate a mount 10 on the shaft side of
power device 12.
Regardless of whether sag and compression are counteracted, torsion of
power device 12 is accommodated by allowing it to pivot to a limited
degree about axis 38 of power shaft 18. As seen in FIGS. 3 and 4, about
twenty-five degrees of torsion is encountered to either side of a neutral
position. The neutral position signifies lack of torsion, indicated in
FIG. 5, by alignment of an arbitrary benchmark 40 located on power device
12 with another arbitrary benchmark 42 located on chassis 16.
Discs 26,28 may, of course, be configured to cooperate with one another,
spacers being unnecessary in this embodiment. This is shown in FIGS. 7 and
8. In the former view, discs 26 and 28 include frustoconical projection 44
and cooperating depression 46, which, when interfit, resist shearing
forces imposed on mount 10. Shearing forces include those forces having a
component perpendicular to axis 38.
FIG. 8 shows an arrangement wherein discs 26 and 28 still interfit, but
have a configuration including a stepped projection 48 and a cooperating
depression 50. Also shown in this view are bands 52 which may be placed
over tube 20. While resilience of tube 20 may provide satisfactory
engagement of discs 26,28, especially considering the tendency of tube 20
to constrict when subjected to elongation or torsion, engagement may be
augmented by bands 52. Bands 52 may be constructed as endless loops of
resilient material, adjustable bands such as screw operated clamps, as are
commonly employed to secure hoses in place, or still other types. Bands 52
constrict on tube 20 about peripheral surface 54 of discs 26,28.
In still another embodiment, illustrated in FIG. 9, plural tubes 20A,20B
are fitted to discs 26,28. This arrangement provides additional resilience
and strength within a tube 20 of limited length, while still accommodating
flexure thereof. Discs 26 and 28 have, in this embodiment, stepped
portions 56,58 of differing diameter to accept the two tubes 20A,20B.
It is to be understood that the present invention is not limited to the
embodiments described above, but encompasses any and all embodiments
within the scope of the following claims.
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