WO2008102921A1

WO2008102921A1 - Vibration isolator using body springs

Info

Publication number: WO2008102921A1
Application number: PCT/KR2007/000894
Authority: WO
Inventors: Yang-Gyu Jei
Original assignee: Machinenow Co., Ltd.
Priority date: 2007-02-21
Filing date: 2007-02-21
Publication date: 2008-08-28

Abstract

The invention is a vibration isolator using body spring (BSD). The body springs of BSD support shaft load, and damping forces are resulted from the fluid flow between inner fluid spaces and friction forces between body spring tips and inner ring. Since body springs of BSD are one body of the outer ring, it has several advantages. The coincidence of the center of outer ring with the center of inner ring is easy, and body springs can sustain the axial loads of shaft. Whereas the damping forces of the squeeze film damper are resulted from the narrow fluid film, the damping forces of BSD are resulted from the fluid flow between large inner fluid spaces. BSD does not, therefore, requires additional oil circulating and cooling system. Since BSD can be used in a single unit, BSD is simple and cheap. BSD can be also used as fluid film bearing and vibration absorber.

Description

Vibration Isolator using Body Springs

[Technical Field]

Rotating machines can be easily found in industrial machines and household appliance To increase the operating efficiency per unit mass the rotating speed is being increased Because of high rotating speed, the vibration problems of rotating machinery become more serious The 80% of vibration problems of rotating machinery are resulted from mass unbalance The 15% of vibration problems are resulted from shaft misalignment and the 5% are resulted from the unstable vibrations of supporting bearings or seals

Complete balancing is not easy, and the unstable vibration of supporting bearing is not also easily controlled To overcome such vibration problems of rotating machinery, vibration dampers or vibration isolators are developed Here a new vibration isolator is invented to control of vibration problems of rotating machinery

[Background Art]

The bearings of a rotating shaft support loads, and also control vibrations Because of mass production, the price of rolling bearings is very cheap But the vibration damping capacity of rolling bearings is small, and the adjustment of the supporting stiffness of rolling bearings is not easy The sliding bearings which use the dynamic force of fluid film have high load capacity, and high vibration damping forces But in the sliding bearings oil circulating systems are required to lower the high temperature of the narrow fluid film In the rotating machine which is supported by sliding bearings, unstable vibrations occur at high rotating speed, and energy loss is significant.

To overcome the disadvantages of the low damping force and the adjustment difficulty of supporting stiffness of rolling bearings, several dampers were developed. In figure 1 the squeeze film damper which has very narrow fluid film is shown, and solid state damper which has elastic rubber between bearing and shaft is also shown.

Although the squeeze film damper may have high damping force, but the oil circulating system is required to lower the high fever of the narrow fluid film. It is also difficult to adjust the supporting stiffness of squeeze film damper(US patent 5,603,574, 5,513,917). The vibration damping force of solid state damper is not great, and the magnitudes of load capacity and supporting stiffness are limited.

To overcome the disadvantage of the squeeze film damper and solid state damper, we invented "Vibration Isolator using Leaf Springs (or Leaf

Spring Damper, LSD)" which was registered at several countries (Korea 10-0115437-0000, U.S.A 5,553,834, German DE 4420 596 C2, Austria AT 401 808B, Japan 2665312, China ZL 94108364). The research results of LSD were also published at several academic journals such as T.ASME, Journal of Vibration and Acoustics, 1999, Vol. 121 , pp. 343-350, and T.KSME, Section A, 1998, Vol.22, No.4, pp. 843-858. The applications of LSD got the mark of KT (Korea Technology).

Since LSD supports rotating shaft through several leaf springs, the supporting stiffness can be easily adjusted. Since the damping force of LSD is generated by the fluid flow between the inner fluid spaces, the big vibration damping force can be acquired. Because the inner fluid space of LSD is large, the oil circulating system to lower the high temperature of fluid film is not required Since LSD can be manufactured in single and simple product, LSD has the advantages of low price and simple installation

But LSD has several disadvantages Since the outer rιng(12) is supported by leaf spπngs(13), it is very difficulty to coincide the centers of the outer πng(12) with the center of the inner rιng(11) The coincidence of centers of outer and inner ring is very important in the alignment of rotating shaft In many rotating machineries the axial force always occurs because of axial fluid flow LSD can not also support the axial force When the dampers are installed at supporting bearings, the axial loading capacity of dampers is very important

[Disclosure of Invention]

The body spring damper (BSD) is invented to overcome the such several disadvantages of LSD

As shown in Figs 3~5, the several body spπngs(22), which are one body of the outer πng(21), support the inner πng(23) Since the rotating shaft is supported by several bearings, the alignment between bearings is important in the control of vibrations But in BSD the body sprιngs(22) are one body of the outer πng(21), it is easy to coincide the centers of outer rιng(21) with the center of inner rιng(23) BSD has the advantage of the easy adjustment of shaft alignment

Since body spπngs(22) are made of the same body of outer πng(21 ), it is easy to manufacture using lathe or milling machine The stiffness of the body sprιng(22) is easily controlled by the shape of boy spring And the body spring can also support the axial forces The inner fluid space(26) is formed by the body springs(22) and the side cover plates(24). The inner fluid spaces are filled with the working fluid. If the body spring has the shape which can not separate the inner fluid spaces, the intermediate elements(25) can be installed to separate the inner fluid spaces. If the relative motion occurs between the inner ring(23) and the outer ring(21 ), the fluid flow occurs due to the volume changes of the inner fluid spaces(26). The fluid in the inner fluid spaces(26) can flows through two channels. The one channel is the fluid passage(28) between the side cover plates and body springs(22) or intermediates elements(25). As shown in Fig.9 the other channel is the oil groove(32) on the side cover plate(24). By the fluid flow the vibration damping force is developed. The magnitude of the vibration damping force is controlled by the viscosity of fluid and the cross section area of the fluid passage(28) and the oil groove(32).

The another damping element is the friction between the tip of the body spring(22A) and the inner ring(23) in Figure 5. If the radius of the tip of body spring tip(22A) is smaller than the radius of the inner ring, the preload acts on the body springs. With the magnitude of the preload, the friction between the tip of the body spring and the inner ring varies. When the relative motion between the inner ring(23) and the outer ring(21) occurs, the relative motion between the body spring tip and the inner ring also occurs. Then the vibration damping forces are resulted from the friction. By experiments it is proved that the damping force resulted from the friction may be greater than the damping force resulted from the fluid flow between inner fluid spaces.

Since the inner fluid spaces(26) of BSD is sealed by the side cover plates(24) and sealing elements(27), there is no fluid loss. Since the magnitude of the inner fluid space is much greater than that of squeeze film dampers, the temperature of the working fluid is not so high. In BSD the oil circulating system is no required for oil cooling or oil feeding. Therefore BSD can be used in simple and single unit.

In the squeeze film dampers of KMS (US patent 5,603,574, 5,513,917) the damping forces are developed in the very narrow squeeze film spaces, and the high fever occurs. Therefore the oil circulating system for oil cooling is required. Whereas the inner fluid space of BSD is sealed by the side cover plates and sealing element, the fluid spaces of the squeeze film dampers of KMSis not sealed spaces. It is difficult for the squeeze film dampers of KMS to use in single and standard unit. The price of the squeeze film dampers of KMS is expensive. The squeeze film dampers of KMS is useful to use in fluid film bearings in which the oil circulating system is already installed.

The vibration characteristics of BSD are very similar to LSD. According to the vibration characteristics of LSD which were already published in several technical joumals(T.ASME, Journal of Vibration and Acoustics, 1999, Vol. 121 , pp. 343-350), the supporting stiffness and damping coefficients have linear and isotropic characteristics. There are no unstable vibration components in LSD. It is very easy to control the damping and stiffness forces. The damping force of BSD is higher than the damping forces of squeeze film damper or fluid film bearing.

[Best Mode for Carrying Out the Invention]

As shown in Fig.6 the invented vibration isolator, BSD, can be used in the vibration isolation of ball bearings instead of squeeze film dampers. BSD can be also used in the vibration control of non-rotating shaft. As shown in Fig.6, BSD does not require the auxiliary system such as oil cooling system. BSD can be used in single unit. If BSD is installed at the outer race of ball bearings, as shown in Fig.6, the various vibration occurred in rotating shafts can be controlled. In the rotating machinery design, the critical speeds of rotating shafts should not coincide with the rotating speeds. It is easier to control the stiffness of supporting bearings than the stiffness or inertia of the rotating shaft. But if the shaft is supported by ball bearings, it is difficult to adjust the stiffness of ball bearings. When the ball bearing is equipped with BSD, it is very easy to control the supporting stiffness.

When a rotor is passing its critical speed, very high vibrations occur. To control the high vibration at critical speeds, high damping forces are required. It is difficult to adjust the stiffness and damping forces of ball bearings. The stiffness of rolling bearings have almost fixed, and damping forces of rolling bearings are very small. If the vibration isolators using body springs (BSD) are applied, the easy adjustment of supporting stiffness and the achievement of high damping forces are possible. If BSD is installed at ball bearings, the vibration of rotating shaft can be easily controlled.

BSD can be applied for the vibration control of sliding bearings as well as ball bearings. The most serious problem of sliding bearings is the unstable vibration of oil whip occurring at high rotating speed. To overcome the unstable vibration of sliding bearings, various sliding bearings shown in Fig.7 are developed. Using the tilting pad bearing and flexural pivot bearing shown in Fig.7, the unstable vibration problem may be overcome. But high vibrations still occur at the critical speeds due to poor damping forces. If BSD is installed at sliding bearings, the stiffness can be easily controlled. And high damping forces can be obtained.

As shown in Fig.8, the inner ring(23) of BSD can be directly used as sliding bearing(30). In general the sliding bearings are operating at the bearing housing filled with oil. And if the body spring whose shape is shown in Fig.10 is used, the tip(22A) of the body spring can be directly used as sliding bearing. If the radius of the tip(22A) of the body spring is larger than the radius of the journal of rotating shaft, the fluid film exists between the tip(22A) and the journal(31A). As the journal rotates, the fluid pressure is developed in the wedge between the tip(22A) and the joumal(31A). With the developed pressure, the bearing can sustain the journal load.

When the inner ring(23) or the body spring tip(22A) is used as sliding bearing, the side cover plate(24) can be used as a thrust bearing as shown in Fig.9. If the radius of the joumal(31A) is larger than the radius of rotating shaft(31), and the spiral groove is carved at the side cover plate, then the fluid flow is induced in inward as the shaft rotates. With the fluid flow induced by the spiral groove, the hydrodynamic forces which can support the axial force are developed. If the fluid flow is induced in inward, the pressure in the wedge or inner fluid spaces becomes high. Then the high damping for the lateral vibrations is also resulted from the high pressure, and the vibration of the rotor becomes more stable.

Since the squeeze film damper of KMC (US patent 5,603,574, 5,513,917) does not have side cover plates, the damping forces resulted from fluid flow between inner fluid spaces can not be obtained.

The invention can be also used as vibration absorber. In Fig.11 , the basic concept of the vibration isolator using auxiliary inertia is shown. If the invention is used as damper, the outer ring is fixed at rigid housing. But the invention is used as vibration absorber, as shown in Fig.12, the outer ring and side cover plates are used as auxiliary inertia which is vibrating freely. If the inertia of vibration absorber has opposite phase to the inertia of the system, the vibration resulted from the inertia of the system are cancelled by the auxiliary inertia of vibration absorber.

The rubber vibration absorber used for the vibration control in the driving shaft of the automobile has several limitations. Since it made of rubber, the dynamic characteristics of rubber are varying because of the high fever of automobile engine. And the high vibration damping force can not be obtained. If the invention is used as the vibration absorber which is made of high temperature polymer, cheap vibration absorber having high damping forces and stable dynamic characteristics can be developed.

[Industrial Applicability]

The vibration isolator using body springs (BSD) can be applied at the high speed rotating machinery. For example, the turbocharger of automobile engine is rotating over 100,000rpm. The fluid film bearings used in turbocharger is being changed to ball bearings to reduce the energy loss and unstable vibration resulted from fluid film. But high damping forces are required at high rotating speed for the use of ball bearings. If the invention is applied, such problems can be easily solved.

The vibration isolator using body springs (BSD) can be applied at the vibration control of the spindle shaft of machine tools. For the high precision machining, the high stiffness and high damping force of bearings the supporting the spindle shaft are required. Whereas the damping force of hydrodynamic bearing is high, the supporting stiffness is not so high. Recently the hydrostatic bearings are applied to get high damping and stiffness forces. But the hydrostatic bearings require high pressure oil circulating and cooling system, and the energy loss is great. The current rubber vibration absorber used for the vibration controls of driving shaft of automobile engines has limited vibration damping forces, and the dynamic characteristics are changed with the high fever of engines. If the vibration isolator using body springs (BSD) can be used as the vibration absorber, then the high damping forces and stable dynamics characteristics can be obtained.

Claims

1. The vibration isolator using body springs consists of the body springs(22) which are one body of the outer ring(21) and support the shaft load through the inner ring(23), and the inner fluid spaces(26). which are composed by the side cover plates(24) and the body springs(22), producing the vibration damping forces resulted from the fluid flow through the oil passage(28) or the oil groove(23) connecting inner fluid spaces.

2. A vibration isolator using body springs(22) according to claim 1 , which has intermediate elements(25) between body springs in case of when the body springs(22) has the shape which can not separate the inner fluid spaces(26).

3. A vibration isolator using body springs according to claim 1 , which has oil groove(32) on the side cover plates(24) to control the fluid flow between the inner fluid spaces(26).

4. A vibration isolator using body springs according to claim 1 , which has vibration damping forces resulted from the friction between the inner ring(23) and the tip of body spring(22A), which can be controlled by the preload of the body spring tips on the inner ring

5. A vibration isolator using body springs according to claim 1 , in which ball bearing is installed.

6. A vibration isolator using body springs according to claim 1 , which can be used as vibration absorber in case of when the side cover plates(23) and outer ring(21 ) are used as auxiliary inertia

7. A vibration isolator using body springs according to claim 1 , the inner ring(23) or the body spring tips(22A) of which is used as fluid film bearing through the fluid pressure developed when the shaft journal(31A) rotates

8. A vibration isolator using body springs according to claim 7, the side cover plates(24) of which are used as the thrust bearings supporting the axial forces between the thrust journal(34) and side cover plates(24) when the radius of the shaft journal(31A) is greater than the radius of the rotating shaft(31 )