Note: Descriptions are shown in the official language in which they were submitted.
~2~(~3~
TUNABLE VISCOUS SPRING MOUNT
Background of the Invention
_
The present invention relates generally to shock absorbers.
More particularly, it relates to shock absorbers of the type which
are mounted to vehicles and which use both an elastomeric shear
spring and the flow of fluid through a restricted orifice for
absorbing shock, structural leveling and energy dissipation.
As automobile design has tended to favor smaller, more energy-
efficient vehicles having reduced weight and engine power require-
mints, the resulting automobiles have been particularly subject to disadvantageous vibrational problems such as harder rides and en-
gone vibration detectable in the passenger compartment. These pro-
bless have arisen from such design factors as integral frame and
automobile cab construction whereby riding shocks to the frame are
directly transmitted to the passenger compartment. In addition, the
smaller engines are oftentimes inherently unbalanced and when they
are mounted to the integral frame they transmit their vibrations
directly to the cab. Such typical constructions generate several
types of vibration which are loosely segregated into low frequency,
high amplitude vibrations (i.e., a stationary car with the engine
idling or a moving car going over a bump) and high frequency, low
amplitude vibrations (i.e., the vibrations generated by a motor
operating at highway speeds being generally less than plus or minus
0.1 millimeter).
The theory of vibration transmissibility as it applies to en-
gone mounts seeks to generally provide high damping at low frequent
ales (up to 20 Ho) and low damping at high frequencies (above 20
Ho). Accordingly, various forms and types of engine mounts have
heretofore been suggested which provide substantial hydraulic damp-
in only above a predetermined amplitude of vibration oscillation.
These various forms and types of engine mounts have met with varying
degrees of success. It has been found that the defects present in
such prior engine mounts are such that the mounts are of limited en-
onomic and practical value.
A typical prior engine mount construction employs opposed
-- 1 --
Jo
lZ4~3346
armatures associated by an elastomeric member housing an hydraulic
fluid. The elastomeric member operates as a shear spring. A means
for partitioning the fluid chamber in the interior of the elicit-
metric shear spring is provided to segregate the interior into at
least two fluid chambers. The partition usually includes an oft-
flee for providing a restricted flow of fluid communication between
the chambers. A valve is associated with the restricted orifice to
clove the orifice upon a preselected prowar differential between
the fluid chamber. This prowar differential is generated a a
10 result of vibration or shock being incurred by the device.
A particular problem with such constructions is that they are
not susceptible for selective tuning to adjust the valve operation.
The valve possesses a natural frequency which defines one set of
operational characteristics of the engine mount only. Such an en-
15 gone mount will usually be designed for one particular type of vow-
ale structure and lacks the versatility to be applied for efficient
operation to a variety of vehicle designs.
Another problem with prior art engine mount constructions is
that the valve usually has only a single natural frequency which
; 20 affects the damping response identically both during mount come
Preston and rebound. Oftentimes it it highly desirable to have a
different operating ripen between compression and rebound to pro-
vise smoother vibration transmission or damping.
Yet another problem with prior art engine mounts occurs when
the valve seals fluid flow under a relatively high differential
pressure and pressure continues to increase in the fluid chambers.
Since the chambers have only limited means for relieving the pros-
sure differential, the mount can become undesirably stiff.
The present invention contemplates a new and improved device
30 which overcomes the above referred to problems and others to provide
a new viscous spring mount with a tunable flapper valve which is
simple in design, economical to manufacture, readily adaptable to a
plurality of vehicle types having a variety of structural and
dimensional characteristics, easy to tune and install and which
provide improved engine vibration isolation and damping.
-- 2 --
124(~346
Brief Summary of the Invention
In accordance with the present invention, there is provided a
viscous spring engine mount including a deflection amplitude and
frequency dependent flapper valve. The engine mount includes a
fluid flow restructure plate interposed between first and second
fluid chambers. The first fluid chamber includes a first wall port
lion generally defined by an elastomeric journal. The second fluid
chamber includes a second wall portion generally defined by an
elastomeric diaphragm. The restructure plate includes a main fluid
port and an auxiliary fluid port for communicating fluid between the
chambers. First and second elastomeric flaps are spaced from the
restructure plate and oppositely disposed about the main fluid port
whereby the flaps are selectively tensioned to seal the main fluid
port against fluid flow upon deflection of the flaps against the
port in response to a preselected shock amplitude and frequency to
the engine mount.
In accordance with another aspect of the present invention, the
elastomeric flaps comprise elongated bands including fastening means
for locating the bands a preselected clearance from the main fluid
port. The bands are sized to at least engage the port upon deflect
lion of the bands into engagement with the restructure plate.
In accordance with another aspect of the present invention, the
first and second flaps are tuned to have distinct natural
frequencies to effect a different damping response of the mount dun-
in compression than during rebound.
In accordance with a further aspect of the present invention,
the flaps are received in the first and second fluid chambers no-
spectively and each flap is free to deflect both away from and into
the port.
In accordance with still a further aspect of the present invent
lion the elastomeric diaphragm defining the second fluid chamber has
a central portion comprising a rigid and variable mass.
One benefit obtained by use of the present invention is an en-
gone mount which provides improved viscous spring damping.
Another benefit obtained from the present invention is an en-
- 3 -
12~3346
gone mount having an amplitude and frequency dependent hydraulic
valve which is selectively tunable to provide high or low damping at
a preselected vibrational amplitude and frequency.
Other benefits and advantages of the subject new engine mount
will become apparent to those skilled in the art upon a reading and
understanding of this specification.
Brief Description of the Drawings
The invention may take physical form in certain parts and en-
rangements of parts, the preferred embodiment of which will be de-
scribed in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:
FIGURE 1 is a cross-sectional view of an engine mount formed in
accordance with the present invention;
FIGURE 2 is a cross-sectional view of the engine mount of
FIGURE 1 rotated 90;
FIGURE 3 is a cross-sectional view taken along line 3-3 of
FIGURE l; and
FIGURE 4 is a cross-sectional view taken along line 4-4 of
FIGURE 1.
Detailed Description of the Invention
Referring now to the drawings wherein the showings are for
purposes of illustrating the preferred embodiment of the invention
only and not for purposes of limiting same, the figures show a vise
cows spring damper 10 particularly useful as an engine mount. The
25 damper 10 includes first and second opposed armatures 12, 14 which
are adapted for fastening to an engine and an automobile chassis
(not shown) respectively. The first armature 12 generally comprises
a piston including a first portion 16 preferably constructed of a
strong and durable material such as a metal, and a second portion 18
protruding therefrom comprising a threaded extension adapted for
fastening to an engine. A locating protrusion 20 is provided for
mating reception in a bore (not shown) for locking the piston 12
against rotational movement after assembly to the engine and frame.
The second armature 14 preferably comprises a metallic plate
defining a damper bottom wall and includes conventional fastening
-- 4 --
~z463346
means 24 for fastening the damper to an engine frame.
The side wall of the damper 10 comprises a cylindrically con-
figured annuls 26 and an elastomeric journal 28. Annuls 26 is
preferably constructed of a strong and durable material such as
steel and includes a flange 30 which is chemically bonded to the
journal 28. The elastomeric journal tapers from flange 30 towards
the piston 12 for attachment to the piston with conventional comma-
eel bonding techniques. The innermost end 34 of journal 28 come
proses an annular flange 34 engaging a shoulder 36 of flange 30.
lo Resting upon journal flange 34 is a partition plate 40 which sub-
staunchly divides the damper interior into a first fluid chamber 42
and a second fluid chamber 44. A conventional hydraulic fluid is
received in the fluid chambers. The partition plate 40 operates as
a means for fluid flow restriction between the first and second
fluid chambers to effect the viscous spring damping action of the
invention as will hereinafter be more fully discussed.
Interposed between the partition plate 40 and the second aroma-
lure 14 is an elastomeric diaphragm 50 which is positioned and
sealed at an annular bead 52 with a cylindrical ring 54. The bead
52 is compressed between plate 14 and ring 54 to define a select
lively pressurizable gas chamber 56. Preferably, a plate 58 forms a
top wall of the elastomeric diaphragm 50 to enhance the strength of
the diaphragm over this portion and to, more importantly, allow the
mass of the diaphragm to be varied. This construction causes
greater or lesser propensity for diaphragm 50 to oscillate at a
specific frequency. In particular, it facilitates diaphragm move-
mint and thus fluid flow near its natural frequency. This feature
is advantageous in providing optimum fluid damping at desired ire-
quench by the flap construction described hereinafter.
The general operation of communicating fluid chambers through a
means for fluid flow restriction in combination with a selectively
pressurizable gas chamber to provide an advantageous viscous spring
damper is more fully discussed in US. Patent No. 4,352,487.
; The partition plate 40 comprises an assembly having an elicit-
metric flap associated with a main fluid port that is spaced from the
- 5 -
clue
port a preselected distance and stressed to a preselected strain
whereby the flap exhibits a particular natural frequency. The flap
operates to seal the port upon amplitude deflection to the damper in
excess of a predetermined amount.
With particular reference to FIGURES 3 and 4, it may be seen
that partition plate 40 includes a main fluid port 64 and an axle-
cry fluid port 66. Main fluid port 64 may comprise a single aver-
lure or a plurality of fluid apertures. In the embodiment thus-
treated, two apertures are shown. It is important that the main
fluid port 64 provide a substantially greater fluid axis be-
tweet the fluid chambers than the auxiliary port 66. It has been
found that to operate as a proper viscous spring damper, the ratio
of the main port area that is sealed by the flap to the auxiliary
port cross-sectional area must be at least 5 to l, although when the
damper 10 is employed as an engine mounting assembly for present
size automobiles, the ratio preferably falls in the range of 40 to
50 to 1.
With continued reference to FIGURES 3 and 4, it may be seen
that auxiliary port 66 presents a tortuous flow path to fluid be-
tweet the fluid chambers. Fluid may enter the auxiliary port from the main fluid chamber only at a portion of the port channel 68
which is radially inner more than the elastomeric journal flange 34.
That portion of the auxiliary port which runs with the flange 34 is
sealed against the first fluid chamber 42 by the flange. Fluid from
the auxiliary port 66 is communicated to the second fluid chamber
from a portion of the port 66 cut in partition plate 40 that is open
to the second fluid chamber (FIGURE 4).
With reference to all the figures, associated with plate 40 are
first and second elastomeric flaps 74, 76 which are fastened to the
plate 40 at their terminal end portions with conventional fastening
means 78. The flaps 74, 76 comprise elastomeric bands which are opt
politely disposed about the main fluid port 64. The flaps are
selectively tensioned and selectively spaced from the plate 40
whereby the flaps operate to seal the main fluid port against fluid
flow upon deflection of the flaps against the port in response to a
-- 6 --
12~6~3~6
preselected shock amplitude and frequency to the damper lo. The
selective spacing 82 comprising the distance between the flap and
the plate allows fluid to freely pass through the main fluid port
until such time as the flap is urged or dragged into engagement with
the plate to seal the main fluid port 64. In addition, the greater
the tension placed upon the flaps 74, 76 the less susceptible the
flaps will be to deflection against the plate. It is a feature of
the present invention that each flap may be independently spaced and
stressed such that the flaps will possess distinct natural ire-
lo quenches. This permits the present invention to effect a different damping response on compression than on rebound.
More particularly, it may be seen that the first fluid chamber
42 includes a first wall portion defined by the elastomeric journal
28 which allows compression or expansion of first chamber 42 depend
dent upon forces applied to the damper lo Similarly, the second fluid chamber 44 includes a second wall portion defined by the
elastomeric diaphragm 50 to allow expansion and contraction of the
second fluid chamber in accordance with the expansion or contraction
of the diaphragm 50 and the gas chamber 56. Upon a compression
force being applied to the damper lo, fluid in the first fluid champ
bier 42 will be urged toward the second fluid chamber 44 through both
the main fluid port 64 and the auxiliary fluid port 66. Upon a
sufficient amplitude of shock or vibration to the damper lo, such
that the pressure in the first chamber 42 causes the first elicit-
metric flap 74 to be urged into engagement with the plate 40, thiamine fluid port will be sealed against fluid flow from the first
fluid chamber into the port 64 by first flap 74. The flaps are
sized to at least engage the port 64 upon deflection of the flaps
into engagement with the plate 40. Chile the first elastomeric flap
74 is thus urged into sealing engagement, the second elastomeric
flap 76 is being urged away from the partition plate 40 since the
pressure in the first fluid chamber is greater than the pressure in
the second fluid chamber. On the rebound from this deflection, the
opposite in deflection will occur to the flaps 74, 76. The fluid5 will be drawn from the second fluid chamber 44 towards the first
-- 7 --
lZ4~33~6
fluid chamber 42 and will urge the second elastomeric flap 76 toward
plate 40 while urging the first elastomeric flap 74 away from the
plate 40. When the first flap 74 is both spaced and tensioned dip-
fervently than the second flap 76, the amount of pressure different
trial which will cause the first flap 74 to seal the main fluid proton compression will be different from the amount of differential
pressure which will cause the second elastomeric flap 76 to seal the
main fluid port. This provides a selective and independent tuning
feature to the invention.
It is a common objective of mounting devices to provide a low
natural frequency for the suspended mass associated therewith (i.e.,
the engine) in order to most effectively isolate the vibrations
generated. This objective can result, however, in excessive de-
election of the suspended mass near its natural frequency if
insufficient damping is provided by the mount. The mount of the
present invention provides this desired damping by including ear
lately tunable flaps for sealing of main ports and by optimizing flow
characteristics by using an appropriate mass 58 as part of diaphragm
50.
Another design consideration of engine mounting assemblies
generally is that it is important to obtain low stiffness of the
mounting device at high frequency. The present invention limits the
stiffness of the device by substantially limiting the pressure which
may be exerted on the fluid chambers 74, 76. More particularly,
when the device 10 is subjected to a high amplitude deflection such
that there is a high pressure differential between the fluid champ
biers 42, 44 and the main fluid port 64 is sealed against fluid flow,
the elastomeric flaps 74, 76 may still deflect or bulge into the
fluid port 64 to expand the effective volume of the chamber beyond
i 30 plate 40. This bulging action limits the pressure of the chambers
and keeps the stiffness of the damper lower than if no bulging act
lion were free to occur.
The invention has been described with reference to the pro-
furred embodiment. Obviously, modifications and alterations will
occur to others upon the reading and understanding of the specific-
- 8 -
124~39~6
lion. It is my intention to include all such modifications and
alterations insofar as they come within the scope of the appended
claims or the equivalents thereof.
Having thus described my invention, I now claim:
