Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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C-3518
D~6,591
HYDRAULIC-ELASTOMERIC MOUNT
This invention relates to a hydraulic-
elastomeric mount and more particularly to the pro-
vision therein of a multi-function diaphragm.
In the typical mount such as used for
vehicle engines an elastomeric body is employed
made of natural or synthetic rubber. Such materials
have inherently low coefficients of damping and it
has been found that many of the vibratory inputs to
the vehicle would be better isolated if the engine
mounting system exhibited a higher coefficient of
~ damping. It is possible to provide an increased
damping coefficient by the selection of certain
rubber polymers and the use of additives but thus
far this has proven unsatisfactory because of
accompanying adverse affects on other properties
of the rubber. ~urthermore, this approach produces
large damping for all vibratory inputs regardless
of frequency or amplitude. Thus, there is a
major desire for a cost effective means of providing
increased damping that does not dictate the choice
of rubber used for the elastomeric body. Then there
is also the desire that the amount of damping be
controllable as to its magnitude for vibratory
inputs of vaxious frequencies and amplitudes,
Furthermore, the damping should be achieved in a
manner that does not compromise the many desired
features in the typical elastomeric mount design
and particularly those of major importance such as
specific stiffness ratios along the major axes and
specific configurations to suit packaging space
restrictions. Various mount designs have been
proposed adding hydraulic damping, however, they
are generally lacking in meeting all the desired
criteria and particularly that of damping
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controllability or are relatively complex and
difficult to manufacture while maintaining a high
degree of sealed integrity.
The hydraulic-elastomeric mount of the
present invention is a very simple, easy to manu-
facture design with excellent sealed integrity and
is adapted to be produced as a family of mounts
capable of providing a wide range of desired
characteristics to various degrees and without
compromising the desired vibration isolating
features available with just the elastomeric body.
The preferred embodiment comprises a pair of mounting
members interconnected by a hollow elastomeric body.
As adapted for use as a vehicle engine mount, one
of the mounting members is secured to the engine
while the other mounting member is secured to the
engine supporting structure of the vehicle. To
this arrangement is added an elastomeric diaphragm
that is configured so as to close the elastomeric
body and form therewith a closed cavity. A rigid
partition is then used to divide the cavity into a
primary chamber enclosed by the elastomeric body
and a secondary chamber enclosed by the diaphragm.
A liquid is contained in the chambers and the parti-
tion is provided with an orifice which interconnectsthe chambers. The liquid is thus forced to flow
at a restricted rate from the primary to the secondary
chamber upon contraction of the former and in the
opposite direction on expansion thereof to provide
a damping effect as the one mounting member vibrates
relative to the other. The diaphragm is further
configured so as to extend about and also over the
periphery of the partition and thereby form a seal
between the chambers and the exterior of the mount
as well as between the chambers. Moreover, the
diaphragm is configured to have a certain compliance
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at its rim permitting limited substantially free
or soft travel of the partition below a predetermined
vibration amplitude of one mounting member relative
to the other and to prevent such relative travel
above such amplitude so that flow through the orifice
to effect damping is dependent upon the predeter-
mined vibration amplitude.
Thus, in the present invention the
diaphragm is trifunctional in that in addition to
forming the secondary chamber, it also serves to
provide amplitude control and multiple sealing.
Furthermore, the total design is such that it
offers a wide family of mounts. This is accomplished
by the orifice being designed as a separate and
relatively movable part which mounts on the partition
with a limited free travel so as to permit small
inputs without damping for further amplitude control
as well as offer a selection of orifice diameter,
length and shape for various damping responsi~eness.
Further extension of the family is provided by
varying the compliance as well as the durometer of
the diaphragm as well as varying the wall thickness,
shape and durometer of the hollow elastomeric body
interconnecting the mounting members. Another
advantage is that the hollow elastomeric body can
be formed with a standard two-piece mold with no
loose cores using either injection or transfer
molding and with little excess rubber removal
required. Furthermore, assembly is simplified by the
formation of the orifice/ partition and diaphragm
as one subassembly and the molded formation of the
elastomeric body with one of the mounting members
and a retainer as a second subassembly which is
filled with the hydraulic fluid prior to final
assembly. At final assembly, the two subassemblies
are simply brought together and the retainer is
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then crimped or otherwise fixed to the remaining
other mounting member to retain all the mount parts
together.
These and other objects, advantages and
features of the present invention will become more
apparent from the following description and drawing
in which:
Figure 1 is a sectional view of one embodi-
ment of the hydraulic-elastomeric mount constructed
according to the present invention,
Figure 2 is a sectional view taken on
the line 2-2 in Figure 1.
Figure 3 is an exploded view of the mount
in Figure 1.
Figure 4 diagrammatically shows a mechanical
analogy of the hydraulic-elastomeric mount of the
present invention.
Figures 5 8 are graphs showing various
characteristics of the hydraulic-elastomeric mount
of the present invention (solid line curves)
compared with those of a typical conventional mount
having only an elastomeric body (dash line curVes).
Figures 9 and 10 are graphs showing
various characteristics of the hydraulic-elastomeric
invention of the present invention with hydraulic
fluid tsolid line curves) and without hydraulic
fluid (dash line curves).
Referring to Figures 1-3 there is shown
the hydraulic elastomeric mount according to
the present invention adapted for mounting an engine
in a vehicle. The mount has agenerally stepped
cylindrical shape and comprises a pair of stamped
sheet metal mounting members 10 and 12 which have
a circular cup and saucer shaped configuration
respectively. The mounting members 10 and 12 are
arranged with their concave sides facing each other
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and have a stud 14 and 15 respectively secured to
the center thereof and projecting outward therefrom
for attachment to an engine (not shown) and an
engine supporting member such as a frame or cradle
(not shown) of the vehicle. A hollow elastomeric
body 16 made of natural or synthetic rubber inter-
connects the mounting members 10 and 12 and to this
end, is molded about the cup-shaped mounting member
10 and to the interior of a stamped sheet metal
hollow retainer 18.
The elastomeric body 16 is configured
such that it essentially completely defines a hollow
cavity 20 therein covering the bottom 22 and both
sides of the cylindrical wall 24 of the mounting
member 10 and also the inner side of the cylindrical
wall 26 of the retainer 18, The elastomeric body 16
thus completely covers the head 27 of the stud 14
so as to positively prevent any possible leakage
therepast while also having extensive surface
attachment with both the mounting member 10 and the
retainer 18. Moreover, the mounting member 10
with its stuci 14, elastomeric body 16 and the
retainer 18 form a subassembly shown and designated
as 28 in Figure 3, It will be seen that the sub-
assembly 28 can thus be made with a conventionaltwo-piece mold without separate or loose core
pieces using either injection or transfer molding
and with little finishing such as flash rubber
removal required. And this includes the formation
of directional rate control effecting cavities or
voids within the elastomeric body itself. ~or
example, with diametrically oppositely located
cavities 29 as shown, the mount is provided with
a high or hard rate in one crosswise direction and
both a relatively soft or low rate at low amplitudes
and a non-linear high or hard rate at high amplitudes
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in a direction transverse thereto (vertical and
horizontal direction respectively as viewed from
the top in Figure 2), such difference in rates
being especially useful in isolating certain
combustion engine vibrations as is well known in
the art.
As shown in Figure 3, the retainer 18 of
subassembly 28 is initially formed with an unfolded
collar 30 having a scalloped edge 31 so as to receive
a second subassembly 32 comprising the other mounting
member 12, an elastomeric diaphragm 34 of natural
or synthetic rubber, a stamped sheet metal circular
dish-shaped partition 36 and an orifice member 37.
The elastomeric diaphragm 34 has a circular rim -
section 38 with a radially inwardly facing internalgroove 39 and the shoulder 40 on the side of the
groove opposite the spanning central portion 42 of
the diaphragm is flexible to receive the rim 44
of the partition 36. The partition rim 44 is thus
sandwiched as shown in Figure 1 between the shoulder
40 and the shoulder 46 on the opposite side of the
groove, the latter shoulder being formed integral
with and extending radially outward from the central
diaphragm portion 42 to join the latter with the
diaphragm rim portion 38. The partition 36 is
positioned with its concave side facing downwardly
and has a central aperture 48 therethrough into
which the orifice member 37 of elastomeric material
is adapted to be inserted and retained with a slip
fit. This slip fit permits limited free travel of
the orifice member 37 relative to the partition 36
in addition to limited substantially free or soft
travel of the latter provided by compliance of the
diaphragm rim 38 and these free travels operate to
prevent hydraulic damping below a predetermined low
amplitude as described in more detail later.
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The lower mounting member 12 with its
stud 15 is shaped with a collar 52 to receive the
rim 38 of the diaphragm 34 with the partition 36
in place and the orifice member 37 fitted to the
latter with such subassembly 32 then adapted to be
fit into the yet to be clinched collar 30 of the
retainer 18 of the other subassembly 28. In such
fit, the lower mounting member 12 is telescopically
received in the retainer collar 30 with the rim 38
of the diaphragm pressed therebetween whereafter
the scalloped edge 31 of the retainer is clinched
over the collar 52 on the lower mounting member to
retain all the mount parts together as shown in
Figure 1. In the assembly, the upper edge 60 of
the lower mounting member 12 engages the radial
shoulder 62 of the retainer collar to determine the
preload on the diaphragm rim 38 which plays an
important part in amplitude control as well as
sealing as w:ill be described in more detail later.
As seen in Figure 1, the elastomeric
diaphragm 34 closes the elastomeric body 16 so as
to form therewith a closed cavity generally desig-
nated as 64. Furthermore, the partition 36 divides
the cavity 64 into a primary chamber 66 enclosed
by the elastomeric body 16 and a secondary chamber
68 enclosed by the diaphragm 34. However, prior
to the closure of the cavity 64 at assembly, it is
substantially filled with a liquid such as a
commercial anti-freeze that will not freeze in
the environment of the intended usage. This
filling is readily accomplished by simply inverting
the subassembly 28 and filling to a certain level
69 in the retainer 18 (see Figure 3) such that the
secondary chamber 68 is then filled through the
orifice 70 on fitting and clamping of the sub-
assembly 32.
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The orifice member 37 has a central passage
70 of constant diameter extending centrally there-
through which interconnects the chambers 66 and 68
so as to permit the liquid in the primary chamber
to flow at a restricted rate into the secondary
chamber upon contraction of the primary chamber and
in the opposite direction on expansion thereof to
thereby provide a damping effect. Upon contraction
of the primary chamber 66, the wall section 72 of
the elastomeric body 16 extending angularly between
the mounting member 10 and the retainer 18 is caused
to bulge outwardly while the liquid therein is
forced to flow through the orifice 70 into the
chamber 68 to expand the latter as permitted by the
elasticity of the diaphragm's central portion 42.
Then on reversal in amplitude and resultantly
expansion of the primary chamber 66, the stretched
central diaphragm portion 42 retracts and thereby
contracts the secondary chamber 68 forcing the
liquid to flow back through the orifice into the
primary chamber to complete the cycle. To otherwise
permit free expansion and contraction of the
secondary chamber 68, the space between the diaphragm
34 and the lower mounting member 12 is vented to
atmosphere through a plurality of radial holes 73
formed in the latter. And because the diaphragm 34
is configured at its rim 38 to both extend around
and over the rim 44 of the partition 36, there may
be formed a seal not only between the chambers but
also a double seal between the chambers and the
exterior resulting in excellent sealed integrity
of the mount as will be described in more detail
later.
Moreover, the diaphragm rim 38 is configured
so as to permit limited substantially free or soft
travel of the partition 36 relative to the mounting
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members 10 and 12 below a predetermined low vibration
amplitude of one mounting member relative to the
other and to prevent such relative travel above
such amplitude so that flow through the orifice 70
to effect damping does not occur until such pre-
determined low vibration amplitude is exceeded.
Such free travel of the partition 36 is shown in
Figure 1 as being between the two phantom-line
positions and may be as much as + 1.0 mm depending
on the installation. This provides precise ampli-
tude control and is simply effected with a predeter-
mined compliance of the diaphragm rim 38 between the
sandwiching retainer 18 and mounting member 12. To
this end, the diaphragm rim 38 is free formed as-
shown in ~igure 3 so as to have oppositely facingannular sealing beads 74 at the outer perimeter.and
thinner but more radially extensive wall sections in
the groove shoulders 40 and 46 which sandwich the
partition riM 44. There is thus substantially
more compliance of the sealing beads 74 which flatten
at assembly to effect excellent sealing while the
partition capturing elastomeric wall sections 40
and 46 are preloaded to a predetermined extent
dependent on the amplitude responsiveness desired.
Furthermore as to sealing, there is provided in
addition to the face seal beads 74 an intermediate
radially projecting annular edge sealing bead 75.
The edge seal bead 75 has an interference fit with
the interior of the retainer collar 30 and thereby
cooperates with both of the face seal beads 74 to
provide double sealing between the chambers 66, 68
and atmosphere. On the other hand, the hydraulically
biased partition 36 is alternately pressed against
the elastomeric shoulders 40 and 46 of the diaphragm
so as to maintain tight sealing between the
chambers 66 and 68. For example, assuming that
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the primary chamber 66 is contracting and the hydraulic
pressure therein increasing, the partition 36 is
hydraulically pressed into very tight sealing contact
with the shoulder 46 while the other shoulder 40 is
relaxing with such partition movement and while the
double sealing provided by the sealing beads 74
and 75 remains unaffected because of the effective
isolation therefrom by reason of their radially
outward location relative to the partition. Then
when the secondary chamber 68 is contracting and
the hydraulic pressure therein increasing during
~ the remainder of each damping cycle, the partition
36 is hydraulically pressed into very tight sealing
contact with the shoulder 40 to thereby maintain
tightly sealed integrity between the chambers while
the other shoulder 46 relaxes and while double
sealing is maintained between the chambers and
atmosphere by the sealing beads 74 and 75. And
it will now be better appreciated that the earlier
described limited free travel of the orifice member
37 which is shown as being between the phantom~
line positions shown in Figure 1 operates to thus
effectively increase the displacement of the chamber
being contracted to thereby further delay damping
but not to the same extent possible with the much
larger displaceable chamber surface of the partition
36. To further aid in understanding the mount,
reference is now made to the mechanical analogy
thereof shown in Figure 4 and the graphs in
Figures 5-10.
In the mechanical analogy in Figure 4,
the elastomeric body 16 operating alone (no hydraulic
damping) has an inherent spring constant k and a
coefficient of damping c and in typical adaptation
without hydraulic damping for a typical vehicle
engine installation with the shape shown would
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produce the characteristics shown graphically in
dash line in Figures 5-8. For example, in Figure 5
wherein load is plotted against deflection, there
would normally be a distinct transition point
(feel) between a desired relatively soft rate over
a majority of the deflection range and a hard rate
in the remaining large deflection range. And because
the inherent damping characteristics of rubber are
relatively low and substantially constant there is
essentially no response of the damping to either
frequency as shown in Figure 6 or amplitude as
shown in Figure 7. And thus damping with just the
elastomeric body cannot be readily targeted to a
particularly troublesome frequency such as caused
by vehicle structure resonance nor can the damping
be readily strategically targeted for specific
amplitude response such as in the typical engine
installation wherein a small damping effect is
desired at low amplitude and high frequency of the
engine and a large damping effect is desired at
high amplitude and low frequency. Furthermore, the
rubber normally softens with increasing amplitude
and as a result the stiffness falls off therewith
as shown in Figure 8 whereas the reverse is desired
to assist in amplitude control.
Referring now back to the mechanical
analogy in Figure 4, the hydraulic damping arrange-
ment of the present invention adds to the elastomeric
body's spring stiffness k and coefficient of damping
c with what will be referred to as (1~ a wall bulge
stiffness k' resulting from the wall section 72,
(2) a diaphragm stiffness k" resulting from the
diaphragm central portion 42, (3) a coefficient of
damping c~ resulting from the primary and secondary
chambers 66 and 68 and connecting orifice 70, and
(4) free soft travel x resulting from primarily the
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12X4l318
compliance of the diaphragm rim 38 and secondarily
the slip fit of the orifice member 37. As shown in
the mechanical analogy, the wall bulge stiffness k'
is connected in series with both the diaphragm
stiffness k" and the orifice damping coefficient
c~ which are in turn both connected in series with
the free travel x. The improved result provided
by the coaction of all the mount elements is shown
in solid line in Figures 5-8. For example, as
shown in Figure 5, the deflection is now caused to
gradually increase with load throughout the
deflection range thereby avoiding any distinct
transition point and eliminating a distinct feel.
On the other hand, as shown in Figure 6 the net
effective damping with the hydraulic damping cl is
not relatively constant but bell-shaped over the
frequency range and by selection of the size of the
single orifice 70 and the stiffness k' and k" of
the body wall 72 and diaphragm midsection 42 may
be concentrat:ed or tuned at a specific frequency
so as to best diminish certain problemsome vibrations
in a particular installation. As shown in Figure 7
and with the effective damping no longer relatively
constant with amplitude or frequency and because
of the free soft travel x, only small damping is
provided at low amplitudes (high frequency) with
the damping thereafter increasing rapidly with
amplitude and substantially leveling off with large
damping at large amplitudes (low frequency~. The
very desirable advantage of minimum damping for small
amplitudes is made possible primarily by the free
soft travel of the partition 36 permitted by the
compliance of the diaphragm rim shoulders 40, 46 and
secondarily by the fluid displaced with the tele-
scoping motion of the orifice member 37 by reasonof its slip fit in the partition. And because of
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1~24~3~8
the added wall bulge stiffness k~ and diaphragm
stiffness k" coupled with the hydraulic damping
the net effective stiffness rather than falling
off with amplitude now increases with same as
shown in Figure 8.
Reference is now made to Figures 9 and 10
to further illustrate the improved performance
provided by the hydraulic-elastomeric mount of the
present invention. In Figures 9 and 10, loss angle
and dynamic rate are plotted respectively versus
amplitude comparing the mount with and without
hydraulic fluid. As can be seen in Figure 9 and
without hydraulic fluid, the loss angle as therein
defined increases gradually and very little with
amplitude whereas with the hydraulic fluid added
the loss angle desirably increases steeply with
amplitude and to a much greater extent (e.g. over
double) and thisoccurs in the lower half of the
amplitude range and thereafter remains relatively
constant. On the other hand and as shown in Figure
10, without hydraulic fluid the dynamic rate con-
tinues to decrease with amplitude whereas with
addition of the hydraulic fluid the dynamic rate
after initial fall off remains relatively constant.
The hydraulic elastomeric mount according
to the present invention is thus quite predictable
and may be readily adapted and tuned to meet a
specific application to give the desired spring
stiffness, coefficient of damping and resulting
dynamic rate calculated to best isolate a particular
set of vibration conditions. In other words, a
family of mounts is cost effectively offered with
selectability of such parameters as the durometer
of the rubber used in both the elastomeric body and
the diaphragm, the wall section thickness and angles
of the elastomeric body, the preload of the diaphragm
and the diameter, length and shape of the insertable
orifice.
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