Torsional vibration isolating motor mounting system, mounting arrangement, assemblies including the same

Motor vibration isolating arrangements and systems using such arrangements are disclosed. In preferred arrangements, leaf spring mounting arms have low torsional spring constants and yet strength to withstand shipping and handling loads. The mounting member spring constants for axial, radial and tilting vibration modes are selected in specific forms so that the characteristic vibration transmissibility ratios for these modes are each close to unity, but so that torsional mode vibration transmissibility is substantially less than unity. In particularly preferred arrangements, sheet steel having a martensitic grain structure is utilized. In some forms, the motor shell constitutes one weldable member and a holding plate is weldable. The spring material is protected by heat sinking from being softening and weakened by conventional welding processes. The heat sinking members also contribute to a very strong fastening scheme.

BACKGROUND OF THE INVENTION 
The present invention relates generally to motor mounting systems, motor 
mounting arrangements, assemblies including the same, and flexible arms; 
and particularly those that are adapted for interconnecting a motor 
directly with a blower wheel and blower housing in a manner that provides 
improved isolation of torsional vibrations and yet also unfailingly 
provides stringent control of axial and tilting motor movements without 
excessively amplifying vibrations associated with such movements. 
In direct drive blower applications (for example those designed for 
furnaces and in room air conditioning applications), many different motor 
vibration isolation schemes have been used in an effort to reduce the 
noise caused by vibrations transmitted from the motor to the blower 
housing and any associated connected duct work; or to a support in an air 
conditioner. Predominant single phase induction motor torsional pulsations 
or vibrations having a frequency that is equal to or a multiple of twice 
the line frequency (for example 120 Hz for 60 Hz power supplies and 100 Hz 
for 50 Hz power supplies) are usually the source of the most objectionable 
noise in both of the above-mentioned applications and an effective but 
inexpensive noise isolation scheme for this vibration mode and frequencies 
is very much needed. 
Blower wheels supported within blower housings typically are dimensioned 
and positioned so that relatively close running tolerances are maintained 
between each wheel and housing in the interest of maximizing blower 
efficiency. In direct drive applications, a motor is suspended from the 
blower housing scroll and the motor shaft in turn supports and drives the 
blower wheel within the housing. This type of direct drive arrangement is 
very desirable because of its relative simplicity and economy as compared 
to other arrangements (e.g., those that require separated components such 
as belts, pulleys, separate blower wheel bearing systems and supports, 
etc.). However, with prior direct drive arrangements, it has been 
necessary to use complex and expensive mounting arms and related parts in 
order to generally satisfy the requisites of good torsional vibration 
isolation and acceptable control of other motor movement. 
It has long been known that motor vibrations or pulsations may be amplified 
during transmission to a blower housing, depending on the frequency of 
vibration and resonant frequency of the mounting system (or parts 
thereof). Thus, the resonant frequency of each part of such system should 
be considered in designing a mounting arrangement. However, direct drive 
blower motors also must be supported with sufficient stiffness or rigidity 
to prevent sagging or drooping of the motor and to prevent blower assembly 
damage from "shipping shock" tests or during actual shipping and handling. 
One primary problem exists because design efforts directed to minimizing 
the transmission of torsional mode vibrations may well increase the 
transmission of (or chance of amplification of) axial and tilting mode 
vibrations and may even excessively reduce the structural integrity of a 
given arrangement vis-a-vis shipping shock. 
Generally speaking, it would be preferable to completely isolate axial mode 
and tilting mode motor vibrations from a blower housing in direct drive 
applications. However, the need to rigidly support the motor and blower 
wheel, and thus maintain a predetermined running clearance between blower 
parts, has not permitted the use of connections between the motor and 
blower housing that are sufficiently "soft" to provide such complete 
isolation. 
Typical mobile home furnace blowers utilize motors rated at approximately 
373 watts (0.50 hp) or more and having a mass of 5.9 kg (13 pounds) or 
more. On the other hand, even heavier and more powerful motors often are 
used in typical residences, offices, and shop areas that utilize air 
moving blowers. The larger mass of such motors requires even more rigid 
mounting members for avoidance of tilting problems and shipping shock 
damage than would be the case with motors of smaller mass such as those 
used, for example, for window fan applications (typically these motors are 
rated at 75 watts or less and have a mass of 2.2 kg or less). 
Generally speaking, the larger the mass and power of the motor, the more 
difficult it is to resolve the abovementioned problems; and solutions 
applicable to small motor applications are not always applicable to 
arrangements involving larger motors. 
For example, many appliances that incorporate blower mounted motors are 
subjected to mechanical tests that simulate "shipping shock"-- i.e., 
conditions that might occur during handling and shipping of such 
appliances. These conditions could be bouncing onto a truck loading dock, 
rough railway transit, etc. The actual form of the tests may vary for 
different appliance manufacturers and for different types of appliances. 
However, one commonly used test procedure is spelled out in a test 
sequence specification of the "National Safe Transit Committee" (sponsored 
and coordinated by the Porcelain Enamel Institute, Inc.) for packaged 
products of one hundred pounds or more. This sequence involves vertically 
vibrating the packaged product for at least one hour at a frequency such 
that the product will momentarily leave the vibrating table or platform 
during the vibration cycle; and then permitting movement of the packaged 
product along an inclined plane until a face or edge of the package 
impacts against a backstop. This impact test may be carried out with a 
"Conbur Incline" testing device or other equipment producing equivalent 
results and a specified shock recorder. Of course, other tests may take 
place with an appliance unpackaged. In any event, however, after the 
selected test or test sequence, the appliance itself (e.g., a furnace) is 
inspected for damage, and such inspection usually involves close scrutiny 
of any electrical motors to determine that the shafts thereof and 
mountings therefor have not been deleteriously affected. 
Direct drive blower motors often are mounted so that the interface between 
the mounting means and the blower housing is located along or adjacent to 
a curved inlet or eye of the blower housing, such curved portion of the 
housing generally being less flexible and less apt to act as a sounding 
board for motor induced vibrations, and also being better able to 
withstand shipping shock that might tend to tear the motor from the 
housing. It thus would be desirable that any improved arrangements be such 
that attachment to a blower would be along the curved inlet thereof. 
In the past, one approach for mounting motors directly to blowers has 
involved the use of lugs that were fixed (for example by bolts or by 
welding) to a motor frame. In some applications utilizing this approach, 
the lugs were fixed (for example by bolting or welding) directly to a 
blower housing or scroll without grommets; and in others grommets have 
been used. In still other blower applications, such lugs have been 
interconnected with the motor by means of a strap or band. 
The general objectives of the mounting arrangements used heretofore have 
been to provide sufficient mounting rigidity to avoid excessive tilting 
and axial movement of the motor during operation and to withstand shipping 
shock, while also attempting to minimize the transmission of vibrations 
(particularly torsional mode vibrations) to the housing through the motor 
mounting members. Unfortunately, improvement of a given design for one of 
these characteristics frequently will have a negative affect on the other 
characteristics. In addition, it has sometimes been necessary to provide 
"internal packaging" for arrangements that are good noise suppressors. For 
example, temporary supplemental supports or pads may be provided in 
furnace blowers for transit purposes. These supports or pads then are 
discarded prior to putting the furnace (or other appliance) in operation. 
Thus, engineering compromises must be made even with the complex known 
mounting arrangements. 
A single member lug arm approach has long been recognized as a preferable 
form of direct drive motor mount (from a cost standpoint), but such 
approach simply has not been satisfactory in practice for direct drive 
blower applications vis-a-vis good torsional mode vibration isolation in 
combination with good mounting rigidity. For this reason, among others, it 
has been necessary to use relatively complex mounting arrangements for 
those applications where maximum isolation of torsional mode noise was to 
be provided as well as sufficient structural strength to meet shipping 
shock tests. For example, one prior arrangement has required the use of 
costly resilient hubs or cushion ring isolators along with a multitude of 
other different parts that have been assembled together to provide a 
costly and complex mounting arm assembly. 
One or two member lug mounts have also been devised that have been used 
with ultra-soft or ultra-resilient blower mounting pads or grommets. This 
particular type of approach, however, can create or aggravate still other 
problems such as those associated with: motor sag; reduced tilting mode 
resonant frequency with the result that such frequencies would fall into 
an amplification range; shipping and handling damage; and overcompression 
of the pads or grommets (due to the weight of the motor-blower wheel) 
accompanied with effective stiffening of such pads or grommets. 
Although a number of different design and performance criteria have been 
discussed hereinabove as illustrative of the complexity of the factors 
that must be satisfied with direct drive motor mounting arrangements, it 
will be understood that numerous other considerations may further confound 
the search for a desirable solution to the direct-mounted motor problems 
mentioned hereinabove. One of these, for example, is the possibility that 
a given motor mounting arrangement might have to support a motor with its 
shaft vertical, horizontal, or at some specified angle therebetween in 
different applications. 
Single member types of mounting arms or members for axial air flow fans 
have been shown in prior literature. For example, Anderson U.S. Pat. No. 
1,781,155 shows a motor that is supported by three substantially flat and 
straight supporting arms, the shaft of which supports a propeller type 
axial flow fan. Propeller or disc type fan mounting arrangements somewhat 
similar to Anderson's are also shown in Seyfried U.S. Pat. No. 1,873,343 
and Goettl U.S. Pat. No. 2,615,620. In Seyfried, leather, canvas, spring 
steel, and brass arms are mentioned; and in Goettl, curved arms having 
arcuate motor embracing portions are illustrated. 
Although it is desirable to utilize one piece mounting arms for direct 
drive blower motors, competitive economics would favor the permanent 
attachment of such arms to a motor shell during manufacture of the motor. 
However, for designs having very long arms, increased packaging costs and 
shipping costs due to increased package volume can offset the cost savings 
associated with single arm construction. Furthermore, while lengthy arms 
of the type shown by Seyfried, Anderson, etc. may be made from a choice of 
different materials (as described, for example, by Seyfried) and have 
satisfactory strength and torsional vibration transmissibility 
characteristics; prior attempts to utilize flat single member supports for 
direct drive blower motors have resulted in mounting arrangements having 
either unsatisfactory strength characteristics or unsatisfactory torsional 
vibration transmissibilities. 
To be more explicit, it can be assumed that the arms of Goettl, Seyfried, 
or Anderson (referred to hereinabove) would have sufficient strength to 
resist failure in either a tensile mode or buckling mode when supporting a 
propeller fan motor of given mass during a particular test. However, if 
those arms were shortened to permit mounting of the same motor in a blower 
housing inlet, even though the arms would still be sufficiently strong to 
not tear or buckle, the torsional mode vibration transmissibility of such 
arms would be objectionably increased. For example, an arm shortened from 
an effective radial extent of about 7.21 inches to an effective radial 
extent of about 2.2 inches would have a substantially greater 
transmissibility vis-a-vis 120 hz torsional mode vibrations. On the other 
hand, if the shortened arms were then further modified by being reduced in 
thickness and axial width in order to obtain a low transmissibility for 
torsional vibrations, their resistance to buckling would be reduced about 
69%, and their resistance to failure due to tensile stresses would be 
reduced about 88%. 
Accordingly, it would be desirable to provide new and improved motor 
mounting arrangements that include relatively short single member mounting 
arms, motors incorporating the same, and assemblies including the same 
that are low cost in terms of total material and total labor involved 
therewith, and yet that are at least satisfactory if not improved in terms 
of noise isolation and structural reliability. It would also be desirable 
to provide such arrangements that could be easily adapted for use with 
motors having different housing configurations or that are to be mounted 
with different shaft orientations; and systems including the same. 
Accordingly, it is a general object of the present invention to provide new 
and improved motor mounting systems, motor mounting arrangements and 
systems including the same whereby the above-mentioned and other problems 
may be solved. 
It is a more particular object of the present invention to provide a new 
and improved motor mounting system, motor mounting arrangement, and 
systems including the same, that has good resistance to shipping shock 
damage even without supplemental or internal packaging, a high degree of 
rigidity vis-a-vis axial and tilting mode vibrations, and low 
transmissibility for torsional mode vibrations. 
It is a further object of the present invention to provide new and improved 
motors and lug assemblies, that may be utilized to solve the 
above-mentioned and other problems, and that may be quickly and easily 
fastened to a blower or other type of housing. 
SUMMARY OF THE INVENTION 
In carrying out the above and other objects of the invention, in one 
preferred form thereof, I provide a new and improved motor mounting 
arrangement which includes single member lugs specifically designed so 
that the torsional mode resonant or natural frequency is less than twice 
the frequency of the motor power supply divided by the square root of two 
(.sqroot.2). 
Illustrated mounting arrangements are very "soft" (i.e., they have a low 
spring constant) with respect to torsional mode vibrations, are "stiff" 
with respect to axial and tilting mode vibrations, structurally reliable 
during shipping shock tests, and yet are readily deflectable torsionally 
for easy assembly with a blower housing. 
In specific forms illustrated herein, arrangements exemplifying the 
invention include lugs that are flexible in the torsional direction but 
strong and stiff in the axial and radial directions, thereby to prevent 
sag or tilt of a direct driven blower wheel and to successfully withstand 
shipping shock tests. 
In more preferred forms that are illustrated herein, arrangements embodying 
the invention include flexible members that are particularly adapted for 
pivotal mounting on a blower housing, i.e., that are particularly adapted 
to undergo at least limited oscillatory movement about the longitudinal 
axis of a fastener which attaches a mounting portion of such members to a 
blower housing. In these forms, short but strong mounting members are 
provided that also have low torsional mode vibration transmissibilities 
because of the flexibility of or "springiness" of such members, and also 
because such vibrations are utilized to oscillate the members about their 
pivotal mountings. 
The forms of the invention illustrated herein include flat mounting arms 
that have low torsional spring constants and yet have sufficient strength 
to withstand shipping and handling loads for motor and blower assemblies, 
and to permit all angle motor mounting. These arms have a unitary motor 
mounting pad and unitary housing mounting means which are a pad in one 
form and a tube in another. 
The spring constants of the mounting members for axial, radial and tilting 
vibration modes are selected so that the characteristic vibration 
transmissibility ratios for these modes are each close to unity. However, 
the characteristic torsional mode vibration transmissibility is 
substantially less than unity. In particularly preferred embodiments of 
the invention, high strength martensitic sheet steel is utilized to form 
the mounting members. 
In one approach that may be followed to produce systems and arrangements 
embodying the invention, lug members are formed from the selected material 
and then one end of these members is trapped between oppositely facing 
surfaces of fastening members to provide additional strength. In some 
forms, the motor shell constitutes one fastening member and a holding 
plate or pad is another fastening member. With these forms, it is 
preferred to capture the lug (e.g., with projections on one member that 
extend along cut-outs in the lug) against the motor shell and then 
projection weld the projections to the other member. This approach both 
protects the martensitic material from being softened and weakened during 
the welding process; and also provides a very strong fastening scheme that 
meets the rigors of shipping and handling as well as the rigors caused by 
prolonged vibration. The free end of the lug is specifically configured to 
prevent deformation and tearing at the base of the pad; and the lugs (even 
when fastened to a motor) are extremely easy to mount to a blower housing 
simply by deflecting the mounting arms (when necessary) with finger 
pressure so as to align holes in the mounting arms with previously 
provided holes in the blower housing. 
In accordance with another form of the invention, I trap the motor end of 
mounting arms between two pieces of steel that, when welded together, form 
a mounting block having a strap accommodating slot therein; and then tie 
or strap the assembled blocks and members to a motor shell. 
Important advantages are obtained by utilizing trapping means when 
assembling mounting arms to motor shells or motor shell embracing 
ligatures. For example, and in addition to preventing welding damage as 
referred to above, the trapping means may be utilized to reinforce a 
relatively weak and small motor mounting tab. By this means, mounting arm 
dimensions may be minimized to further reduce the torsional mode vibration 
transmissibilities thereof, even though the mounting tab for such an arm 
would likely be torn from the motor during shipping tests if it were to be 
riveted, bolted, or welded directly to the motor shell. 
Another important advantage of following yet another preferred procedure 
resides in reduced total assembly time and assembly procedure 
complexities. When carrying out this procedure, I support the shell and at 
least one reinforcing member, with a mounting arm tab sandwiched 
therebetween, at a welding station. Projections then are welded to the 
reinforcing member and/or shell to permanently assemble the shell, 
mounting arm, and reinforcing member. The shell, mounting arm, and any 
other parts assembled therewith then are treated (e.g., by phosphatizing 
and then painting) for appearance and corrosion or rust prevention 
purposes. Subsequently, a rotatable member is assembled with the shell of 
a stator and supported within the shell to form a complete motor. 
Generally the same procedures mentioned above may be followed when riveting 
or bolting a mounting arm to the shell, with the rivets or threaded 
fasteners (in lieu of welded projections) trapping the mounting arm tab 
between the motor shell and reinforcing means. 
The subject matter which I regard as my invention is set forth in the 
appended claims. The invention itself, however, together with further 
objects and advantages thereof may be better understood by referring to 
the following more detailed description taken in conjunction with the 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIGS. 1 and 2, there is illustrated a motor mounting system that 
includes a combination of a blower housing 36, a blower wheel 37 coupled 
in direct drive relationship with the shaft 38 of a single phase induction 
motor 39, and three torsionally flexible mounting arms 41, 42, 43. 
It will be appreciated that the motor is directly mounted to the blower 
housing 36 along the curved scroll 44 which defines an air inlet 46 at one 
side of the housing, the housing also having a second air inlet 47 
co-axial with inlet 46 and the rotational axis 48 of motor 39. 
Running clearances 49, 51 are provided between the blower wheel 37 and 
housing 36, and these clearances must be maintained during operation. The 
amount of clearance may vary from one blower assembly to another, but 
generally is kept as small as manufacturing tolerances (and a given 
mounting arrangement) will permit in order to minimize blower losses and 
thus maximize blower efficiencies. 
Vibrations are inherently generated during operation of motor 39. These 
vibrations have different modes, and four different vibrational modes have 
been denoted by arrows in FIGS. 1 and 2. With more specific reference to 
FIG. 2, the motor 37 tends to undergo an axial mode of vibration and thus 
tends to oscillate in the direction of the arrow 52. In addition, motor 37 
tends to vibrate radially as indicated by the arrow 53 and undergo tilting 
vibratory movement as represented by the arrow 54. For purposes of the 
present discussion, the tilting mode of vibration of motor 37 may be 
considered to be a rocking type of movement about the point 56. It will be 
understood, however, that radial and tilting mode vibrations may occur 
inplanes other than the vertical plane as represented in FIG. 2. 
With reference now to FIG. 1, arrow 58 represents the vibratory direction 
of movement of motor 39 due to torsional mode vibrations of motor 39 about 
its rotational axis 48 during operation thereof. 
Since motor 39 is mounted directly to the blower housing, it will be 
appreciated that all of the various modes of vibration of the motor may be 
transmitted directly to the housing 36. The housing 36, in turn, (and 
particularly the face 59) may then act as a sounding board and may amplify 
the vibrational sounds and noises transmitted thereto by the 
motor--depending on the transmissibility of the mounting arrangement for 
the different vibrational modes. Moreover, these sounds may be transmitted 
directly through duct work connected to housing 36 or by the air mass 
being moved by the blower wheel 37. 
Prior attempts (of which I am aware) at isolating motor induced vibrations 
from a blower housing have been directed at minimizing a plurality of the 
four different vibrational modes represented in FIGS. 1 and 2. However, it 
has long been known that some of the most objectionable noise transmitted 
to a blower housing are those vibrations associated with torsional mode 
vibrations. I have determined that good results can be obtained by 
minimizing the torsional mode resonant frequency so as to minimize the 
torsional mode transmissibility, and by concurrently increasing the 
resonant frequencies for modes of vibration other than torsional in order 
to establish transmissibilities for those modes as close to unity as is 
practical. Preferred forms of physical embodiments of the present 
invention discussed hereinbelow have been devised with this approach in 
mind. 
With reference to FIG. 2, it will be appreciated that whatever changes are 
made in the mounting arrangement there shown, the running tolerances 
represented at 49 and 51 must be observed in order to avoid mechanical 
interference between the blower wheel and blower housing during operation. 
Unfortunately, some prior effects directed at minimizing tilting, axial, 
and radial vibration modes have permitted the motor to sag or droop and 
thus have reduced, if not eliminated, those clearances. 
During shipping tests, the motor 31 will tend to move in at least the 
directions indicated by the arrows 52, 53, and 54, depending upon how the 
package is being tested. These forces are related to the mass of the motor 
39 and will either tend to buckle the radially extending mounting members 
41-43, or tend to cause failure in a tensile mode (for example by tearing 
one or more of these members from the blower housing or motor, by 
stretching one or more of them, or by actually fracturing due to tensile 
stresses). 
Three curves 61, 62, and 63 are shown in FIG. 3. These curves are referred 
to as general transmissibility curves and have been included herein for 
purposes of discussion. These curves will be familiar to persons skilled 
in the art but, for those less skilled, a more thorough understanding may 
be attained by referring to standard vibration analysis reference works. 
One such reference is a book entilted "Fundamentals of Vibration Analysis" 
by N. O. Myklestad, published by the McGraw-Hill Book Company in 1956, and 
assigned Library of Congress catalog number 55-11932. 
Considering only curve 61 for the moment, FIG. 3 represents the 
relationship between the transmissibility (defined as the ratio of the 
amplitude of the transmitted force to the driving force) of a given 
vibrating system to a ratio "r" which is defined as the ratio of the 
forcing frequency to the natural frequency of the system. If a system 
where to have an infinitely great natural or resonant frequency, "r" would 
approach zero, and the transmissibility of such system would be one, so 
the amplitude of forces transmitted by the system would be the same as the 
amplitude of the driving or exciting vibratory force. On the other hand, 
if the natural frequency of the system were an extremely small fraction of 
the forcing or driving frequency, the transmissibility would approach 
zero. 
The knee in the curve 61 in the vicinity of r=1 is related to the amount of 
damping in the system and the curves 61, 62, and 63 are each drawn for a 
different damping factor (this term is defined in the above referenced 
Myklestad book). More specifically, curve 61 is for a system where the 
damping factor is equal to 0.4; curve 62 is plotted for a damping factor 
of 0.2; and curve 63 is plotted for a damping factor of 0.1. 
In preferred physical embodiments of the present invention, motor 
supporting arrangements are designed so that the transmissibility of motor 
induced torsional mode vibrations to the blower housing is less than one 
and so that the ratio r is greater than .sqroot.2.0. On the other hand, 
these embodiments are designed so that the ratio r will be 0.3 or less for 
all vibrational modes other than torsional. Therefore, the 
transmissibility of the mounting arrangement with regard to axial mode, 
radial mode, and tilting mode vibrations will be close to unity. More 
specifically, preferred systems are devised to have natural frequencies in 
the axial, radial, and tilting modes that are at least 3 to 4 times 
greater than an expected fundamental forcing frequency so that the ratio r 
of forcing frequency to natural frequency for the component mounting arms 
for these modes will be no more than about 0.3 but preferably even less. 
Turning now to FIGS. 4 and 5, the spatial and geometric proportions and 
relationships of the blower housing 36, motor 39, and mounting arms 41-43 
will be described in more detail. It will be noted that in the preferred 
forms illustrated in FIGS. 4 and 5, the motor ends 64-66 of mounting arms 
41-43 are tightly fixed to the housing or shell 60 of the motor 39 to 
prevent being torn from the motor during rough shipping or handling (or 
tests simulating the same). The blower ends 71-73 of the arms 41-43 are 
fastened to the blower scroll 44 by means of self-tapping threaded 
fasteners 76-78. It will be noted however, that other types of fastening 
elements may be used. 
As will be understood, a pair of motor leads 67, 68 are provided which, 
when connected across a source of excitation voltage, will cause operation 
of the motor, it being noted that additional leads will be provided for 
multi-speed operation. Moreover, a grounding lead 69 is connected to the 
conductive housing of the motor and may be connected to the blower housing 
itself or any other suitable grounded structure. 
The fasteners 76-78 (see FIG. 4) are each tightened down against a grommet 
(such as the grommet 79) carried in an aperture in the blower end of each 
mounting arm. Although the fastener is drawn down against the grommet so 
as to hold the motor 39 rigidly in place with respect to movement in the 
tilting, axial, or radial modes; the blower ends of blower mounting pads 
71 of the arms 41-43 are held only loosely to the blower scroll 44 with 
respect to torsional mode movements. 
It will be noted that each blower mounting pad 71 is offset relative to the 
major, radially extending portion 81-83 of each mounting arm 41-43. Thus, 
the fastener accommodating aperture formed in the free or blower ends of 
the mounting arms is offset and each arm is capable of oscillating or 
pivoting about its fastener. Therefore, the fasteners 78 serve the purpose 
of holding the motor to the blower housing but also serve as pivot pins 
for the mounting arms. 
Reference is now made to FIG. 23 which clearly reveals, in phantom, the 
oscillatory movement of mounting arm 41 in response to torsional mode 
vibrations of motor 39 when it is mounted to the scroll 44 in the manner 
described hereinabove. It will be noted that the intermediate portion 81 
of mounting arm 41 is free to flex or bend in the manner of a leaf spring. 
This flexing is further enhanced by the freedom of the pad 71 to undergo 
pivotal movement relative to the mounting axis 86. 
With reference now to FIGS. 9 and 12, one means by which pivotal movement 
of the illustrated mounting arms may be encouraged will be described. FIG. 
9 reveals stiff spacing means in the form of a steel eyelet or sleeve 87 
which prevents gripping the mounting arm 41 so tightly with grommet 79 
that arm 41 will not be free to pivot about the axis 86 relative to the 
blower housing. 
FIG. 12 shows that one portion of the grommet 79 cushions the pad 71 and 
prevents it from making direct metal to metal contact with the housing. 
Metal to metal contact between the pad 71 and either the eyelet portions 
88 or 91, 87 or screw 77 also is prevented by another portion of the same 
grommet. Eyelet 87 includes a flange or shoulder 88 which conveniently 
provides a bearing surface for the head 89 of screw 77 (or a washer 
positioned thereunder when desired). With the arrangement illustrated in 
FIG. 12, the fastener 77 may be drawn down very tightly so that tubular 
portion 91 of eyelet 87 bears against scroll 44, and the motor thus is 
supported in a desired position without droop or sag. Moreover, with the 
arrangement illustrated in FIG. 12, the natural frequencies of the entire 
mounting system--vis-a-vis radial, tilting, and axial mode 
vibrations--will be very high with the result that a transmissibility 
approaching unity for each of these modes will be provided, this being one 
of the above stated objectives of structures embodying preferred forms of 
the invention. 
The axial length of the tubular portion 91 of the eyelet is selected in 
conjunction with the height of the grommet 79 so that the grommet 79 is 
not too tightly compressed in gripping relation with the blower pad 71 
even though screw 77 is drawn tightly against the eyelet 87. Thus, 
mounting arm 41 (as well as mounting arms 42 and 43 in FIG. 1) is able to 
oscillate about axis 86 during operation. 
Substantially improved results are obtained when mounting arrangements are 
made pursuant to FIGS. 4-12 of the drawings herein. While the combination 
of a leaf spring type single element mounting arm which is pivotal at its 
free end is important for obtaining the most desirable results, other 
structural criteria must also be provided for in order to provide an 
operative structure. 
Test results have shown that, for one arrangement substantially as shown in 
FIGS. 9 and 12, the natural frequency of such arrangement for torsional 
mode vibrations of 120 Hz is only about 26.6 Hz, which is quite desirable. 
On the other hand, when the grommet 79 was omitted for the same 
arrangement, and pad 77 was bolted tightly to the blower housing as 
illustrated in FIG. 13, the torsional mode natural frequency of the system 
for a forcing frequency of 120 Hz was about 33 Hz; and the motion of arm 
41 was then (it is believed) as illustrated in FIG. 24. Although the 
vibration isolation characteristics of the FIG. 13 arrangement were not as 
good as those of the FIG. 12 arrangement, the performance of a FIG. 13 
type of arrangement would still be sufficient for many applications 
presently being served by more complex and expensive prior art 
arrangements (e.g., by those of the type shown in FIGS. 25 and 26 herein). 
For small effective radial lengths (i.e., where the effective radial 
dimension L in FIG. 6 was 2.2 inches), mounting arrangements using 
mounting members configured exactly as shown in FIGS. 6-8 have failed 
during testing. More specifically, conventional cold rolled steel and 
conventional spring steels simply have not had suitable physical 
characteristics. However, short arms [i.e., arms with a length L of about 
3.5 inches (8.9 cm) or less] can be made to perform satisfactorily when 
they are fabricated from martensitic steel. Martensitic steel, as will be 
understood, is steel that has been specially processed to transform the 
microstructure of the material to martensite from, for example, austenite. 
This type of steel typically will have a tensile strength of from about 
130,000 psi to at least about 220,000 psi. It has now been determined that 
such material having a tensile strength of about 140,000 psi or more is 
well suited for use in practicing the present invention. More expensive 
alloy steels and stainless steels may also be used, provided they have a 
martensitic microstructure, but the use of such materials would represent 
a greater expense as compared to low carbon, alloy free, martensitic cold 
rolled steel. This more economical material is commercially available and 
may be purchased, for example, from Inland Steel Co. Another source of 
relatively inexpensive martensitic steel is the Athenia Steel Division, 
Division of the National-Standard Co. of Clifton, N.J. 
Review of FIG. 9 will quickly reveal that a better approach to utilizing 
the invention is to stamp a mounting arm blank and form (i.e., "blend") 
the ends thereof to establish the motor mounting tab and housing mounting 
means. Since low carbon steels (e.g., 0.25% or less carbon) generally are 
more easily formed than higher carbon (e.g., 0.50% or more carbon) steels, 
it is preferred to use a relatively low carbon steel such as that 
manufactured by Inland Steel Co. and marketed under the name "MartInsite" 
steel by that company. 
If the arms 41-43 were proportionately larger so that the length "L" (see 
FIG. 6) were much longer (e.g., 10 inches), conventional cold rolled steel 
could almost certainly be used satisfactorily, but it is emphasized that 
the present invention is addressed to those problem applications where 
short mounting arms must be used (e.g. where "L" is about four inches or 
less). 
Even when martensitic steel is utilized for lugs 41-43, other steps must be 
taken in order to ensure that the mounting arrangement is sufficiently 
strong (even though only marginally so in some cases) to meet the rigors 
of shipping tests. In order to provide the desired low torsional mode 
resonant frequencies that are needed, the arms 41-43 are formed of very 
thin material (e.g., about 0.035 of an inch or 0.9 mm); and the 
satisfactory attachment of such material to the shell of motor 39 is 
difficult to accomplish. For example, direct welding of motor holding 
means such as pad 65 to motor shell 102 would be convenient and 
inexpensive. However, the heat associated with welding can cause an 
undesirable transformation of the martensitic microstructure of arm 41. 
This type of change would be accompanied by a reduction in strength, and 
failure of arm 41 in the region of bend 156 or at the weld locations would 
occur. 
Thus, practical alternatives would be to utilize a structural adhesive, 
such as epoxy, to adhere pad 65 to shell 102, but care must be used to 
select an adhesive of sufficient strength to withstand all tests 
contemplated; and the adhesive must be hardenable in a conveniently short 
period of time at temperatures that are not so high that the 
above-mentioned martensitic microstructure is adversely affected. 
Another approach would be to use large headed bolts or screws (or 
conventional bolts with washers to increase the bearing area thereof) 
which would pass through holes in tab 65 and thread into bosses formed in 
shell 102 (similar to boss 119 in FIGS. 9 and 12), or into nuts. While 
this approach should be satisfactory, it would not be as economical as the 
preferred approach now to be described in conjunction with FIGS. 9-11. 
Initially, a mounting arm such as the arm 41 is positioned adjacent to the 
outer periphery of the shell 102. Thereafter, and while the mounting arm 
is held in a desired position relative to the shell, a reinforcing strap 
or plate 96 having a pair of projections 97, 98 thereon is positioned over 
the motor mounting pad. Locating means (shown as apertues 101 in FIGS. 
9-11) are defined by the motor mounting tab 65; and the projections 97, 98 
co-operate with such locating means to permanently hold the mounting arm 
41 in a fixed location on the shell 102. When the shell is about 0.050 
inch thick, and tab 65 is about 0.035 of an inch thick, the plate 98 
preferably is about 0.090 inch thick. This thickness of strap 96 prevents 
it from subsequently bending or buckling and also provides a mass that 
co-operates with the mass of shell 102 to provide heat sink means or heat 
transfer means that (it is believed) prevent adverse heat build-up and 
microstructure changes in the tab 65. 
One Preferred mode of carrying out the invention includes positioning a 
mounting arm (e.g., arm 41) adjacent to a motor shell, positioning a 
reinforcing plate adjacent to the mounting arm, and positioning projection 
means so that the projection means interfit with locating means defined by 
the tab 65 of the mounting arm. Thereafter, a welding electrode is 
relatively positioned adjacent to one side of the motor shell 102 and a 
second welding electrode is positioned adjacent to the reinforcing plate; 
and current is passed through the welding plate, projections, and the 
interface between the projections and the shell while the parts being 
welded are urged together so as to accomplish a weld along such interface 
(as best illustrated at 103, 104 in FIG. 11), and heat is transferred to 
the heat sink means to prevent substantial degradation of the 
microstructure of the tab 65. 
While round apertures 101 have been shown, it will be appreciated that 
notches rather than holes could be provided along the edges 104, 106 of 
the motor mounting pad 65. Other alternative arrangements of locating 
means will readily suggest themselves to persons skilled in the art and, 
accordingly, the forms illustrated herein should be considered for 
purposes of exemplification rather than limitation. 
My investigations have revealed that mounting arrangements retaining the 
suitable properties and characteristics mentioned above may also be 
provided even though parts thereof are not permanently fixed to the motor 
shell itself. For example, the arrangements shown in FIGS. 14-16 reveal 
that the invention may also be embodied in arrangements wherein a 
reinforcing plate 107 (including projections) that is substantially 
identical to the plate 96 may be welded to a notched backing or support 
plate 103, with the motor end or pad 112 of the mounting arm 108 
permanently trapped therebetween. The mounting arm 108 is virtually 
indentical to the mounting arm 41 described hereinabove and therefore 
further details thereof are not described herein. It is noted, however, 
that plate 103 and plate 107 constitute heat sink means for the FIG. 15 
embodiment; and that projections on plate 107 (or plate 103) tend to 
concentrate and localize welding heat in the same manner as projections 
97, 98 of FIG. 10. The band 109 is, as shown in FIG. 14, clamped about a 
motor 111. 
In a preferred mode of assembly, the plate 107 is positioned so that 
projection means thereon trap locating means in the mounting pad 112 
against plate 103. Thereafter, one electrode is positioned above the plate 
107 and another below the plate 103 whereupon the projections are welded 
to the other plate to permanently trap arm 112 and define a ligature 
accommodating notch or aperture 113. The ligature (such as strap 109) is 
then threaded through such notch, and thereafter fastened about a motor. 
Turning now to FIGS. 17-19, another embodiment of the invention will be 
described. In the structure there shown, a mounting arm 126 is provided 
with a motor pad 127 which has locating means 128, 129 (again in the form 
of apertures) that are used in conjunction with fastening the mounting arm 
to a motor or other structure. Rather than utilizing a flat offset blower 
pad, the blower end of the arm 126 is rolled into a tubular shape and 
welded upon itself at 132. Thereafter, a spacer sleeve 133, two washers 
134, 136, and rubber or other resilient material grommets 137, 138 are 
assembled therewith. Thereafter, a bolt, screw, or other suitable fastener 
is inserted through the center of the spacer sleeve to fasten the mounting 
arm to a blower housing. With the arrangement just described, the blower 
end of arm 126 is free to pivot about such fastener even though it is not 
offset in the manner described hereinabove in connection with FIG. 20. 
It will be noted that welding (at 132) of the martensitic material utilized 
for the arm 126 has just been indicated. Even though welding may alter the 
desirable martensitic characteristics of that portion of the arm 126 in 
the vicinity of the weld, the mounting arm still seems suitable for use 
because (it is believed) any changes in martensitic microstructure are 
probably localized near the location of weld 132 and this region of arm 
126 is not subjected to as great a stress as that portion closer to tab 
127. 
In FIGS. 20-22 three different elevations of a torsionally flexible 
mounting arm 161 have been shown. The arm 161 includes a blower end tab 
162 and motor tab 163 with projection accommodating apertures 164, 166 
therein. The tab 162 also has a hole 167 therein which can be used to 
accommodate a rubber grommet like the grommet 79 (of FIG. 12). Three or 
more arms 161 may be used in lieu of arms 41-43 and these shorter arms 161 
are of particular benefit for double shaft motor applications (such as 
room air conditioners) where the arm 161 would be fastened at the extreme 
end of a shell and mount the motor to a compartment wall rather than the 
eye of a blower. 
Prior to the present invention, many attempts have been made to provide 
direct mounted motors that would have suitable vibration transmissibility 
characteristics. Even though many efforts have been made in this 
direction, and much patented literature is available illustrating such 
efforts, two arrangements with which I am familiar that have most closely 
approached the desired characteristics are illustrated as prior art in 
FIGS. 25-28. 
FIGS. 27 and 28 illustrate a rather complex mounting structure which is 
assembled from a plurality of parts and fastened to a motor 174 by means 
of resilient end rings or hubs 175 that are carried by the motor end 
frames 176. The bracket assembly 177 then is mounted to a blower housing 
178 by means of a number of bolts 179, all as illustrated in FIG. 28. The 
performance of structures illustrated in FIGS. 27, 28 has been adopted by 
many persons in the industry as a standard of reference for good vibration 
isolation systems, and many in the industry have utilized the arrangement 
shown in FIG. 28. However, this approach is expensive, and in this regard 
it will be noted that a number of different arms 180, 181, 182 must be 
fabricated and then assembled with rings 175. In addition, a considerable 
amount of time and labor is involved in actually assembling this 
supporting structure 177 with the motor 174. 
A somewhat less expensive approach is illustrated in FIGS. 25 and 26 
wherein a wire type cage 183 is fabricated and then clamped with ligature 
means 184 to the outer periphery 185 of a motor 186. Relatively large 
resilient grommets or cushions 187 are then used to trap the ends of arm 
portions of the wire cage, and screws 189 are used to hold the entire 
structure on a blower housing 190. 
Surprisingly, arrangements embodying the present invention yield 
performance characteristics and overall noise transmission qualities that 
generally are as good, if not better in at least one respect for each 
given design, than the best state of the prior art direct drive motor 
mounting arrangements of which I am aware--including those of FIGS. 25-28. 
In addition to having surprisingly good performance, arrangements 
embodying the present invention can now be made at substantially less cost 
than the prior suitable arrangements. Accordingly, substantial benefits 
can result from use of the present invention. 
Accordingly, while I have now shown and described preferred and alternate 
embodiments of mounting arrangements, and methods of making the same (as 
well as components thereof); the disclosure contained herein should be 
construed as being exemplary, and the invention itself should be limited 
only by the scope of the claims that are appended hereto and that form 
part of my disclosure.