GB1604097A

GB1604097A - Motor mountings

Info

Publication number: GB1604097A
Application number: GB22744/78A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1977-10-07
Filing date: 1978-05-25
Publication date: 1981-12-02
Also published as: IT1159919B; IT7828376A0; FR2405580A2; AU530688B2; JPS5454208A; DE2843749A1; FR2405580B2; AU3656778A

Description

(54) MOTOR MOUNTINGS (71) We, GENERAL ELECTRIC COMPANY, a corporation organised and existing under the laws of the State of New York, United States of America, of 1 River Road, Schenectady, 12305 State of New York, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is an improvement in, or modification of the invention described and claimed in our copending parent Application No. 23149/77 (Serial No. 1,577,356).

In our parent Application we describe and claim a motor mounting system in which mounting brackets are secured to an AC motor having a polar moment of inertia Ip measured in 1b-inches-seconds2, each bracket including a flat, radially extending arm and each of said arms an aperture, the apertures lying in different radial planes and the resulting cumulative effective spring constant of the brackets being less than 2.84.Ip.105 lb-inches per radian.

In accordance with one aspect of the present invention there is provided an AC induction motor having a torsional mode vibration isolating mounting arrangement, the motor having a polar moment of inertia Ip, measured in pound-inches-seconds2, and the mounting arrangement including at least two arms of different effective radial lengths, formed from sheet material, extending radially from the motor, the shape and/or thickness of each arm being selected such that the cumulative effective spring constant of the mounting arrangement, in pound-inches per radian, will be less than 2.84xIpx105; and so that arms of different radial length have generally equivalent torsional mode flexibility characteristics.

In accordance with another aspect of the present invention there is provided an electric AC induction motor having a mounting arrangement for isolating axial, torsional, radial, lateral, vertical tilting, and horizontal mode vibrations of the motor, the motor having a polar moment of inertia Ip expressed in 1b-inches-second2, and the mounting arrangement including a plurality of radially extending mounting lugs having a cumulative effective spring constant less than 2.84.Ip.105 1inches per radian, each lug having a circumferentially extending portion for attachment to a supporting structure, and each having a radially extending V-shaped portion as viewed in the circumferential direction with the free ends of the V-shaped portion being radially spaced apart; whereby radial mode vibrations are isolated due to relative flexing between the circumferentially and radially extending portions, torsional mode vibrations are isolated due to circumferential flexing of the radially extending portions, and vibrations of the other modes are isolated due to flexing and twisting movements permitted by the V-shaped configuration of the lugs.

By way of example only, examples of the different aspects of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevation, with parts removed and parts in section of a motor mounted in a Sirocco blower housing in accordance with one form of the present invention, Figure 2 is a front elevation of the motor mounting bracket shown in Figure 1, Figure 3 is a front elevation of a system including a motor mounting arrangement, with parts removed and parts in section, embodying another form of the invention; Figure 4 is an enlarged front elevation of part of the arrangement shown in Figure 3; Figure 5 is a view taken in the direction of lines 14-14 in Figure 3; Figures 6, 7, and 8 are side elevations of three different lugs that may be used in the arrangement of Figure 4; Figure 9 is a rear elevation of the lugs shown in Figures 6 7 and 8; Figure 10 is a view in the direction of lines 19-19 in Figure 9; and Figure 11 is a perspective view of a test stand that was used to measure the performance of systems such as that shown in Figure 3.

Figures 1 and 2 reveal a specific embodiment of the invention wherein a two lug, one piece mount 71 is fastened to the shell 72 of a motor 73 by means of screws 74, 76 that pass through holes 75 in the one-piece mount or bracket 71. In the embodiment of Figure 1, a uniformly flexible mount is provided, and yet the mount has unequal length lugs 77, 78 because of the logrithmic spiral form of the Sirocco blower housing 79.

The one piece bracket 71 was formed to fit halfway around the motor 73 and extend the unequal arms or projecting ends thereof generally radially out to the scroll wall 81. The ends 82, 83 of the arms 77, 78 have mounting screw holes 84 formed therein by means of which mounting screws 86 may mount the bracket 71 (and thus motor 73) to the housing 79.

The spring constant for the arm portions 77, 78 is made equal by adding a tuning hole in the otherwise stiffer arm as shown at 87.

Although a single hole 87 has been shown, it will be understood that the tuning means could be in the form of multiple apertures, cut outs along the edges 88, 89 of the arm 77, or in the form of reduced material thickness, although this latter approach would probably most easily be put into practice by making the arms 77, 78 separate and unconnected pieces.

In this regard, it will be apparent that two separate arms could be used instead of a single, one-piece bracket. The choice of which system to use normally should be made on the basis of producibility and cost; however, another approach to tuning the arm 77 would be to reduce the width of the arm 77, rather than simply notching it along the edges 88, 89.

This improved mounting system has two flexible arm portions of different radial length connected by a partial belly band section 91. In order to have uniform flexing about the axis of the motor, the spring constants of the arms are adjusted. In the illustrated form, the adjustment is accomplished by introducing a tuning hole in the shorter, stiffer arm thus reducing the moment of inertia of the cross-sectional area until the spring constants are equal.

With reference now to Figures 3 and 4, a vibration isolation mounting system is shown which not only isolates specific modes of vibration, but also does away with the need for a separate grounding lead and at the same time does not require the use of an elastomeric vibratidn isolator which could serve as an accelerator in the advent of a grease fire.

In Figure 3, a motor 96 (with parts broken away) has been illustrated wherein it is supported by means of a band or strap 97. As will be understood, the band 97 will be clamped onto the motor 96 by suitable clamping means such as a nut and bolt. A lug 98 has a motor end 95 thereof fastened to the band 97 by any suitable means although, depending upon the materials selected for use in making the lug 98, it may be desirable to spot weld the band and lug together. A radial portion 39 of the lug 98 extends radially from the motor and terminates at a right angle mounting portion 101. A stand-off spacer 102 is then interposed between the mounting portion 101 and a mounting ring 103 to provide room for flexing movement of the lug 98 in response to radial mode vibrations. Thus, during vibrations of the motor in a radial direction as indicated, for example, by the arrow "R", the bent portion 104 of the lug 98 will have room to deflect into the space 106. Similarly, the other lugs 98 that are used to support the motor 96 will also be free to vibrate radially.

Typically, radial vibration that might be caused by unbalance of a blower wheel attached to the shaft of the motor 96 and other rotating components will be isolated by the right angle mounting portions 101. The radial segment 99 of the lug 98 will isolate torque pulsations such as those that might be generated by the AC motor 96.

In addition, the radial portion 99 of the ug 98 has a special configuration which will allow the motor 96 to twist and the radial segment or portion 99 will dissipate the energy vibration introduced by a wobbly fan. The configuration of the radial segment 99 also provides a relatively long spring arm with a low spring constant in torsion that will fit a relatively confined radial space between the motor and mounting ring.

Figure 4 reveals the relationship between three lugs 98 and the band 97; while Figures 5 and 6-10 reveal specific constructional details and the specific configuration of the radial portion 99 of the lug 98.

In Figure 5, an arrow "W" has been applied to indicate the type of flexing or twisting motion that may be imparted to the motor 96 due to a wobbly fan. Moreover, the lug 98 has been shown in Figure 5 in a somewhat distorted form in order to emphasize the type of distortion or flexing that will take place in the lug 98 as a result of an unbalanced and wobbly movement of the motor induced by a wobbly fan.

Figure 6 is a side elevation of one of the lugs 98 and illustrates the "V" configuration of the radial portion 99 of lug 98.

Figure 9, on the other hand, is an end elevation taken by looking in the direction of lines 18-18 on Figure 6 while Figure 10 is a plan view of the lug 98 taken in the direction of lines 19-19 on Figure 9. The lug 98 was made from .018 inch thick steel and was dimensioned such that Figure 6 is essentially a full-scale representation thereof.

For purposes of reference, when modified lugs are considered hereinbelow in conjunction with Figures 7 and 8, it is noted that the offset dimension OS-1 for lug 98 was nominally about .234 inches. Moreover, the radius at the notch of the "V" was about 7/16 of an inch.

Figure 7 reveals a modified lug 108 made from .025 inch thick steel and differing from the lug 99 essentially in that the offset dimension OS1 is about .359 inches and the radius at the apex of the "V" is about 1/8 of an inch.

Two other modified lugs were also manufactured and tested and those lugs had the configuration as shown by the lug 109 in Figure 8. The other two lugs differed from each other in that a first one was made from .018 inch thick steel whereas a second one was made from .025 inch steel. Both of the lugs which corresponded to the lug 109 had an offset dimension OSI of nominally .419 inches and the radius at the apex of the "V" was nominally about 1/16 of an inch.

The lugs represented by Figures 6-8 were assembled with a band and fastened to a motor, then mounted to a mounting ring (as indicated for example by the mounting ring 103 in Figure 3) and the mounting ring was fastened to a test fixture illustrated as fixture 111 in Figure 11. The legs 112 of the fixture 111 were made from 3/4 inch square cold rolled steel and those legs in turn were 10 inches long and supported at the ends thereof by rubber grommets 114. Welded by means of small gussets 116 to the center of the legs 112 was a mounting plate 117, the mounting plate being formed from 1/4 inch cold rolled plate steel.

The mounting plate 117 had an overall dimension of 10 inches by 10 inches square and had a cut-out in the center thereof 7-1/2 inches diameter. A motor and blower wheel was then supported during a series of tests, by mounting arrangements that made use of the four different mounting lugs that have been described hereinabove in connection with Figures 6-8. The motor was energized with 60 cycle, 110 volt power and measurements were taken by placing an IRD displacement pickup at the points indicated by the arrows "A", "T", and "R" in order to detect axial, tangential, and radial vibrations respectively. The instrumentation used to determine the amount of vibration in the direction of the arrows "A", "T", and "R" included an IRD displacement pickup and vibration meter.

Data that was obtained showed that there was a substantial lowering of vibration (via displacement) in all six modes and particularly in the axial mode by comparison to a conventionally used mounting system which makes use of elastomeric rubber mounts. The other modes were torsional, radial, lateral, vertical tilting and horizontal tilting. Thus, the described mounting system dispenses with elastomeric vibration isolators while improving the vibration isolation characteristics.

Table II presents the test data obtained utilizing the intrumentation described hereinabove in connection with the test fixture of Figure 11 for five different mounting systems. The first mounting system utilized elastomeric vibration absorbers of a type utilized heretofore in the prior art, a mounting arrangement utilizing lugs as described hereinabove as lug 98, lugs as illustrated by lug 108, and two different sets of lugs corresponding to lug 109, one of which was made from .018 inch thick steel and the other of which was made from .025 inch thick steel.

During the test for which the data of Table II was obtained, the IRD displacement pickup was engaged at three different positions along the plate of the test fixture in order to obtain three different readings that are reproduced in Table II.

TABLE II MTG VOLTS RPM AXIAL RADIAL TANGENTIAL Prior Art 115 1685 1.87 1.81 1.95 lug 98 115 1655 11.0 2.2 .68 lug 108 115 1660 1.95 .23 .345 lug 109 115 1660 1.15 .31 .58 (.018 in.) lug 109 115 1650 .32 .48 .48 (.025 in.) It will be appreciated that the axial vibrations transmitted while utilizing the lug 98 generally were poorer than when using the lugs 108 and 109, and it is believed that this is due to the different radii used at the apex of the "V" or notch in each of the lugs (as compared more thoroughly hereinabove) and also due to the different dimensions of the offset dimension OS1. It is thus believed that it is preferable for the apex "V" to have a radius of less than 7/16 of an inch and the overall radial dimension of the lug is about 2.56 inches as illustrated and, further, it is believed that any dimension equivalent to the offset dimension OS1 should be greater than about .234 inches.

As described in more detail in our aforesaid parent application 23149/77 (Serial No.

1,577,356), the cumulative effective spring constant of the motor mounting brackets in each of the above described embodiments is less than 2.84.Ip. 105 Ib-inches per radian where Ip is the polar moment of inertia of the motor expressed in Ib-inches sec2.

WHAT WE CLAIM IS: 1. An AC induction motor having a torsional mode vibration isolating mounting arrangement, the motor having a polar moment of inertia Ip, measured in pound-inchesseconds2, and the mounting arrangement including at least two arms of different effective radial lengths, formed from sheet material, extending radially from the motor, the shape and/or thickness of each arm being selected such that the cumulative effective spring constant of the mounting arrangement, in pound-inches per radian, will be less than 2.84XIpX 105; and so that arms of different radial length have generally equivalent torsional mode flexibility characteristics.

2. A motor according to Claim 1, wherein at least two arms are interconnected by a partial belly band section, and wherein these arms and the belly band section are formed from a unitary strip of material.

3. A motor according to Claim 1, wherein at least one arm includes at least one aperture lying generally along a radially extending plane that contains a longitudinally extending neutral axis, and the or each aperture is generally symmetrical about one neutral axis, whereby the or each aperture provides the required flexibility without substantially reducing the strength of the respective arm in the axial direction.

4. A motor according to Claim 1, wherein at least one arm has an aperture located therein along the region of the arm subject to maximum deflection caused by torsional mode motor vibrations.

5. A motor according to Claim 1, wherein at least one of the arms has a motor end thereof tightly trapped against the motor by band means.

6. A motor according to Claim 5, wherein the band means and at least one arm interfit, one with another in a slotted arrangement.

7. An electric AC induction motor having a mounting arrangement for isolating axial, torsional, radial, lateral, vertical tilting, and horizontal mode vibrations of the motor, the motor having a polar moment of inertia Ip expressed in Ib-inches-seconds, and the mounting arrangement including a plurality of radially extending mounting lugs having a cumulative effective spring constant less than 2.84.Ip.105 1inches per radian, each lug having a circumferentially extending portion for attachment to a supporting structure, and each having a radially extending V-shaped portion as viewed in the circumferential direction with the free ends of the V-shaped portion being radially spaced apart; whereby

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. During the test for which the data of Table II was obtained, the IRD displacement pickup was engaged at three different positions along the plate of the test fixture in order to obtain three different readings that are reproduced in Table II. TABLE II MTG VOLTS RPM AXIAL RADIAL TANGENTIAL Prior Art 115 1685 1.87 1.81 1.95 lug 98 115 1655 11.0 2.2 .68 lug 108 115 1660 1.95 .23 .345 lug 109 115 1660 1.15 .31 .58 (.018 in.) lug 109 115 1650 .32 .48 .48 (.025 in.) It will be appreciated that the axial vibrations transmitted while utilizing the lug 98 generally were poorer than when using the lugs 108 and 109, and it is believed that this is due to the different radii used at the apex of the "V" or notch in each of the lugs (as compared more thoroughly hereinabove) and also due to the different dimensions of the offset dimension OS1. It is thus believed that it is preferable for the apex "V" to have a radius of less than 7/16 of an inch and the overall radial dimension of the lug is about 2.56 inches as illustrated and, further, it is believed that any dimension equivalent to the offset dimension OS1 should be greater than about .234 inches. As described in more detail in our aforesaid parent application 23149/77 (Serial No. 1,577,356), the cumulative effective spring constant of the motor mounting brackets in each of the above described embodiments is less than 2.84.Ip. 105 Ib-inches per radian where Ip is the polar moment of inertia of the motor expressed in Ib-inches sec2. WHAT WE CLAIM IS:

1. An AC induction motor having a torsional mode vibration isolating mounting arrangement, the motor having a polar moment of inertia Ip, measured in pound-inchesseconds2, and the mounting arrangement including at least two arms of different effective radial lengths, formed from sheet material, extending radially from the motor, the shape and/or thickness of each arm being selected such that the cumulative effective spring constant of the mounting arrangement, in pound-inches per radian, will be less than 2.84XIpX 105; and so that arms of different radial length have generally equivalent torsional mode flexibility characteristics.

radial mode vibrations are isolated due to relative flexing between the circumferentially and radially extending portions, torsional mode vibrations are isolated due to circumferential flexing of the radially extending portions, and vibrations of the other modes are isolated due to flexing and twisting movements permitted by the V-shaped configuration of the lugs.

8. A motor mounting arrangement substantially as hereinbefore described with reference to any one of the examples illustrated in the accompanying drawings.