US20120164007A1

US20120164007A1 - Method and apparatus to attenuate vibrations from an air mover assembly

Info

Publication number: US20120164007A1
Application number: US12/978,224
Authority: US
Inventors: Eric T. Gamble; Kenton C. Green; Billy W. Medlin; Matthew L. Nickerson
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 2010-12-23
Filing date: 2010-12-23
Publication date: 2012-06-28

Abstract

A reduced-vibration air mover assembly comprises a first blade housing to support a first motor housing and a first motor through a first set of struts, the first motor rotatably coupled to a first blade, and a second blade housing to support a second motor housing and a second motor through a second set of struts, the second motor rotatably coupled to a second blade, and a layer of damping material having a first surface adhered to at least one of the first motor housing, the first set of struts and the first blade housing, and a second surface adhered to at least one of the second motor housing, the second set of struts and the second blade housing. A method of reducing vibration transfer to a computer chassis comprises adhesively securing a layer of damping material intermediate a first air mover and a second air mover.

Description

BACKGROUND

1. Field of the Invention
The present invention relates to a reduced-vibration air mover assembly for use in cooling a computer, and a method of reducing vibrations transferred from an air mover to a computer chassis.
2. Background of the Related Art
Computers are becoming lighter and smaller as consumers demand portability and compactness and as processor technology enables greater data processing capacity using fewer and smaller processors. As a computer chassis becomes smaller in size, a vibration producing component, such as an air mover, is necessarily positioned closer to a vibration-sensitive component such as a hard disk drive (HDD). HDDs are particularly sensitive to vibrations, and the performance of an HDD may be halved when exposed to vibrations.
Computers comprise processors that consume electrical power and produce heat. Air movers, such as axial rotary fans, are used to draw cooling air into the computer chassis and to move cooling air through the chassis to remove heat generated by processors and other components within the chassis. Moving a sufficient volume of cool air through the chassis will maintain the processors and other components within a favorable operating temperature range for optimal component performance and life. The use of adjacent and counter-rotating fans, arranged axially and in series one with the other, enables substantially increased air flow through a computer chassis to meet heightened heat removal demand. In counter-rotating fans, the rotation of the air moved from the blade of the first fan reacts on the blade of the second, counter-rotating fan to further contribute to head or pressure to move the air forward from the second fan. The first fan and the second, counter-rotating fan may be coupled one to the other in an air mover assembly that is installed in the computer chassis. Some air movers for computers provide a high-speed mode to further meet heat removal demand.
There are drawbacks to the use of air mover assemblies having counter-rotating fans and high-speed modes. As the number of fans increase, the vibrations produced by the fans are increased. As the rotational velocity of a given fan blade increases, the amplitude of vibrations transferred to the surrounding computer chassis generally increase exponentially with the increases in rotational velocity. Further, counter-rotating fans may exacerbate the magnitude of vibrations due to coincident imbalance and/or coincident harmonic vibration.
Fluid dynamics are an important consideration in designing a cooling system for a computer chassis. Cooling air flow is maximized by providing unobstructed air flow pathways both upstream and downstream of a rotating fan blade. For a compact computer chassis, unobstructed air flow pathways upstream and downstream of the fans require that the axis of the rotating fan blade be oriented within the chassis so that the direction of air flow from the rotating fan blade generally coincides with the direction of the length or the direction of the width of the chassis.
Most of the air moved through a chassis by a rotary fan blade is moved by the radially distal portion of the blade, and the rate of air moved by a rotary fan blade increases dramatically with increased blade diameter. However, increased blade diameter, like increased angular velocity, dramatically increases vibrations. Maximizing the blade diameter and maximizing the rotational speed of the fan blade are critical to maximizing air flow and to efficiently meeting heat removal demands, but the dramatically increased vibrations that result from the large diameter and the high rotational speed of a rotary fan blade are likely to impair the performance of a HDD positioned within the same computer chassis.
Vibration isolating systems may be used to prevent or reduce the magnitude of vibrations that are transferred to and within the computer chassis. The need for a vibration isolating system is, however, frustrated by the need to maximize heat removal capacity and the need to maximize rotary fan blade diameter.

BRIEF SUMMARY

One embodiment of the present invention provides an air mover assembly, comprising a first and second air movers with vibration damping material disposed there between. The first air mover has a first motor in a first motor housing to rotate a first blade in a first direction within a first blade housing that supports the first motor through a first plurality of struts, and the second air mover has a second motor in a second motor housing to rotate a second blade in a second direction opposite the first within a second blade housing that supports the second motor through a plurality of second struts. The first air mover and the second air mover are secured in axial alignment. The vibration damping material has a first surface secured to at least one of the first motor housing, the first blade housing and the first set of struts, and a second surface secured to at least one of the second motor housing, the second blade housing and the second set of struts.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view an embodiment of a layer of damping material formed for engaging the face of an air mover for a computer cooling system.

FIG. 2 is a perspective view of an embodiment of a first air mover to move air through a computer chassis.

FIG. 3 is a perspective view of an embodiment of a second, counter-rotating air mover having the layer of damping material of FIG. 1 adhered to the face of the second air mover.

FIG. 4 is a side elevation view of an embodiment of an air mover assembly comprising the first air mover of FIG. 2 assembled with the second air mover of FIG. 3 with the layer of vibration damping material of FIG. 1 secured there between.

FIG. 5A is a graph illustrating the amplitude of vibrations produced at maximum rotational velocity by an air mover assembly for moving air through a computer chassis and comprising a first air mover and a counter-rotating second air mover.

FIG. 5B is a graph illustrating the amplitude of vibrations produced at maximum rotational velocity by the same air mover assembly of FIG. 5A, except that a vibration damping layer is disposed between the first air mover and the counter-rotating second air mover.

DETAILED DESCRIPTION

An embodiment of the invention provides an air mover having a first fan comprising a first fan housing to support a first fan motor and a first fan blade through a first set of struts, a second fan comprising a second fan housing to support a second fan motor and a second fan blade through a second set of struts, and a layer of vibration dampening material having a first side adhesively coupled to the first set of struts and a second side adhesively coupled to the second set of struts.
In one embodiment of the invention, the vibration damping layer has a first surface that is adhesively secured to the face of the first fan, and a second surface that is adhesively secured to a face of the second fan, using an acrylic-based adhesive with high damping performance over a wide temperature range and a wide frequency range. One example of such an adhesive is an adhesive sold by Roush Industries as model RA960 damped viscoelastic adhesive.
In one embodiment of the invention, at least one strut of the first set of struts of the first fan comprises a groove to receive electrically conductive wires to deliver current to the first fan motor disposed centrally to the first set of struts. In another embodiment of the invention, at least one strut of the second set of struts of the second counter-rotating fan comprises a groove to receive electrically conductive wires to deliver current to the second fan motor disposed centrally to the second set of struts. In another embodiment of the invention, the at least one strut of the first set of struts and the at least one strut of the second set of struts are aligned one with the other so that the struts having the groove are abutted one against the other in an assembled configuration.
The vibration damping material is preferably a unitary member, but could include a plurality of discrete members secured between the first and second air movers. The vibration damping material may be either homogeneous, but may also be heterogeneous, such as including a plurality of layers having different polymer densities.
In various embodiments, use of the vibration damping material allows the first and second air movers to be secured in a computer chassis without a vibration isolation system coupling the first and second air movers to the computer chassis. Eliminating the use of a vibration isolation system about the perimeter of the air mover housing allows the use of a larger diameter air mover with the same space. However, the two air movers can be secured to the sheet metal chassis, or a frame or carrier that in turn is secured to the chassis, using screws. The two air movers or fans may be attached to each other with a plastic snap pin that is pushed through a hole in the flange of each fan and then expands to hold itself in position.
FIG. 1 is a perspective view an embodiment of a vibration damping material 20 formed for engaging the face of an air mover (see FIGS. 2 and 3) for a computer cooling system. The vibration damping material 20 is a thin sheet or layer comprising a center portion 26 coupled through a plurality of strut portions 24, 25, 27 to a peripheral portion 29. The vibration damping material 20 also comprises a plurality of voids or passages 22 to facilitate unimpeded air flow through the air mover assembly (see FIG. 4) into which the layer of damping material 20 is installed. The voids 22, strut portions 24, 25, 27, and the edge 28 may be customized to provide maximum damping by engaging a maximum amount of the faces (see FIG. 2) of the air movers without impeding or obstructing air flow through the passages or volutes of the air movers (see FIG. 2). The vibration damping material 20 has a first surface shown in FIG. 1 that may be referred to as side A and an opposing second surface that may be referred to as side B. In FIGS. 2-4, the reference numbers shown in FIG. 1 may be appended with an “A” or a “B” to uniquely identify the first and second surfaces.
FIG. 2 is a perspective view of an embodiment of a first air mover 10 to move air through a computer chassis. The face 10A of the air mover 10 comprises a motor housing 16 connected through a plurality of struts 14, 15, 17 to a flange portion 19. A motor (not shown) is provided within the motor housing 16 to rotate a fan blade 18 within the first air mover 10. A plurality of volutes 12 is provided through the face 10A adjacent the fan blade 18 to facilitate air flow across the fan blade 18 and through the first air mover 10. One strut 17 comprises a groove to receive a plurality of wires 11 to carry current to the motor (not shown) in the motor housing 16.
FIG. 3 is a perspective view of an embodiment of a second, counter-rotating air mover 30 having the layer of vibration damping material 20 of FIG. 1 disposed to generally cover the face 30A of the second, counter-rotating air mover 30. The air mover 30 will typically be identical to the air mover 10 of FIG. 1, but this is not a necessary condition. FIG. 3 reveals a first surface 20A of the layer of vibration damping material 20 and the second, opposite surface 20B (shown only at a temporarily folded back upper right hand corner) engages the face 30A of the second, counter-rotating air mover 30. The center portion 26 of the layer of vibration damping material 20 is illustrated in FIG. 3 as covering the motor housing 36 of the second, counter-rotating air mover 30, the strut portions 24, 25, 27 of the layer of vibration damping material 20 are illustrated as covering the struts 34, 35, 37 of the second, counter-rotating air mover 30, and the peripheral portion 29 of the layer of damping material 10 is illustrated as covering the flange portion 39 of the second, counter-rotating air mover 30. The strut portion 27 is noticeably larger (wider) than the other strut portions 24, 25 of the layer of vibration damping material 20 to cover the larger strut portion (see strut 17 in FIG. 14A) with the groove to receive the conductive wires that carry current to the motor (not shown) within the motor housing 16 (see FIG. 2).
FIG. 4 is a side elevation view of an air mover assembly 40 including the first air mover 10 of FIG. 2 axially aligned with the second, counter-rotating air mover 30 of FIG. 3. Specifically, the face 10A of the air mover 10 is directed toward the first face 30A of the second, counter-rotating air mover 30. The layer of vibration damping material 20 secured between the first air mover 10 and the second, counter-rotating air mover 30 dampens the vibrations produced by the air mover assembly 40 by absorbing and dissipating at least a portion of the vibrational energy produced by the activated air mover assembly 40. Upon activation of the air mover assembly 40, both air movers 10, will act to move air in the same direction so that air will flow through the air mover assembly 40 in the direction of arrow 42.
In one embodiment of the air mover assembly 40 of FIG. 4, the face 10A of the first air mover 10 is adhered to the first surface 20A of the layer of damping material 20 using an adhesive and the face 30A of the second, counter-rotating air mover 30 is adhered to the second, opposite surface 20B of the layer of damping material 20 using the adhesive to form and to maintain the air movers of the air mover assembly 40 in position one with the other. In an alternate embodiment, one or more fasteners 35 and 37 may be used to penetrate and to retain one or more of the flanges 19 of the first air mover 10 and one or more of the flanges 39 of the second, counter-rotating air mover 30 in a fixed relationship one with the other. Additional pieces of damping material may be used to fashion washers 35A and 37A disposed adjacent the fasteners 35 and 37.
In one embodiment, the face 10A of the first air mover 10 and the face 30A of the second, counter-rotating air mover 30 may be roughened or otherwise treated to promote adhesion and/or to increase friction between the faces 10A and 30A and the first surface 20A and second, opposite surface 20B of the layer of damping material 20.
It should be noted that the overall contribution of the layer of damping material 20 to the volume and/or size of the air mover assembly is very small and is wholly attributable to an increase in the size of the assembly in a direction of the arrow 42 which is directed from an unobstructed channel upstream of the air mover assembly 40 toward an unobstructed channel downstream of the air mover assembly 40. The amount of vibration attenuation obtained by this positioning of damping material, which will be discussed below in connection with FIGS. 5A and 5B, is beneficial to efforts to reduce the overall size of a computer chassis while maximizing air mover capacity to meet cooling demand.
FIG. 5A is an exemplary graph illustrating the amplitude of vibrations produced at maximum rotational velocity by an air mover assembly for moving air through a computer chassis and comprising a first air mover and a second, counter-rotating air mover, generally as illustrated in FIG. 4 but without the layer of vibration damping material. The y-axis is expressed in units of the logarithm (base 10) of power spectral density (“g”s of acceleration squared divided by the frequency width of the spectral line in Hz) of the two air movers running at maximum rotational velocity.
FIG. 5B is an exemplary graph illustrating the amplitude of vibrations using the same modes of measurement and produced at the maximum rotational velocity by an air mover assembly for moving air through a computer chassis and comprising a first air mover and a second, counter-rotating air mover of the air mover assembly of FIG. 4 with the layer of vibration damping material 20 disposed between the first air mover 10 and the second, counter-rotating air mover 30.
The results obtained using the present invention illustrate the effectiveness of damping using the disclosed apparatus and method. FIG. 5A illustrates that the number of vibration spectral peaks 44 exceeding 10 mPSD (mPSD=0.001×PSD, where PSD is the Power Spectral Density in units of g²/Hz) for the undamped air mover equals three, with one event 46 very close to the 10 mPSD threshold. FIG. 5B illustrates that the number of vibration spectral peaks exceeding 10 mPSD for the improved, damped air mover of the present invention equals zero, with one event 48 very close to the 10 mPSD threshold. It should be noted that the one event close to the 10 mPSD threshold for the improved air mover assembly is generally out of the range of normal operation for an air mover assembly. The root mean square 49A of the measured vibrations for the undamped air mover is 1.038 as compared to the substantially lower root means square 49B produced by the improved air mover assembly of 0.523. This substantial reduction in vibrations transferred from the air mover assembly to the computer chassis greatly benefits the overall efficiency of a hard disk drive (HDD) disposes within the same chassis as the air mover assembly, especially where the HDD is positioned near the air mover assembly or near a chassis component that is in direct physical contact with the air mover assembly. It should be understood that additional vibration reduction may be achievable by combining the use of the vibration damping material with the use of a vibration isolation system disposed about the periphery of the air mover assembly, but that approach consumes critically valuable space needed for increased blade diameter of the air mover components.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and/or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.
The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

1. An air mover assembly, comprising:

a first air mover having a first motor in a first motor housing to rotate a first blade in a first direction within a first blade housing that supports the first motor through a first plurality of struts;

a second air mover having a second motor in a second motor housing to rotate a second blade in a second direction opposite the first within a second blade housing that supports the second motor through a plurality of second struts, wherein the first air mover and the second air mover are secured in axial alignment; and

vibration damping material disposed between the first air mover and the second air mover, the vibration damping material having a first surface secured to at least one of the first motor housing, the first blade housing and the first set of struts, and a second surface secured to at least one of the second motor housing, the second blade housing and the second set of struts.

2. The air mover assembly of claim 1, wherein the vibration damping material has a first surface secured to the first motor housing, the first blade housing and the first set of struts and a second surface secured to the second motor housing, the second blade housing and the second set of struts.

3. The air mover assembly of claim 1, wherein the vibration damping material is a unitary member.

4. The air mover assembly of claim 1, wherein the vibration damping material includes a plurality of discrete members.

5. The air mover assembly of claim 1, wherein at least one of the first set of struts comprises a groove to receive a plurality of wires to conduct an electrical current to the first motor.

6. The air mover assembly of claim 1, wherein the first set of struts is aligned with the second set of struts.

7. The air mover assembly of claim 1, wherein the vibration damping material comprises polystyrene.

8. The air mover assembly of claim 7, wherein the layer of polystyrene has a thickness within the range from 0.006 to 0.014 inches.

9. The air mover assembly of claim 1, wherein the first surface of the layer of damping material is adhesively secured to a face of the first air mover using an acrylic-based damping adhesive and the second surface of the layer of damping material is adhesively secured to a face of the second, counter-rotating air mover using the acrylic-based damping adhesive.

10. The air mover assembly of claim 9, wherein the thickness of the acrylic-based damping adhesive is within the range from 0.001 to 0.004 inches.

11. The air mover assembly of claim 1, wherein the first set of struts are adhesively secured to a first surface of the vibration damping material and the second set of struts are adhesively secured to the second surface of the vibration damping material.

12. The air mover assembly of claim 2, wherein the vibration damping material is a unitary member.

13. The air mover assembly of claim 2, wherein the vibration damping material includes a plurality of discrete members.

14. The air mover assembly of claim 1, wherein the first and second air movers are secured in a computer chassis without a vibration isolation system coupling the first and second air movers to the computer chassis.

15. The air mover assembly of claim 2, wherein the vibration damping material is homogeneous.

16. The air mover assembly of claim 2, wherein the vibration damping material is heterogeneous.

17. The air mover assembly of claim 2, wherein the vibration damping material includes a plurality of layers.