Abstract:
Apparatus for reducing fluid-borne noise in a hydraulic system that includes a housing that defines a hollow chamber, and inlet and outlet connections for in-line connecting the apparatus in a hydraulic fluid flow system. A resilient member is disposed within the housing and effectively divides the housing chamber into a first portion adjacent to the fluid inlet and outlet for receiving hydraulic fluid, and a second portion remote from the fluid inlet and outlet for containing gas under pressure. Pressure pulsations in the hydraulic fluid are reduced and at least partially absorbed by the combined effect of resiliency of the elastic member and compressibility of the contained gas.

Description:
[0001]    The present invention relates to suppression of fluid-borne noise in hydraulic or fluid handling systems, such as automotive power steering, power brake, air conditioning and fuel distribution systems.  
         BACKGROUND AND OBJECTS OF THE INVENTION  
         [0002]    There are many applications in industry and commerce where it is desirable to suppress fluid-borne noise in hydraulic power systems and other fluid handling systems. As an example, it is desirable to attenuate or suppress fluid-borne noise generated by the pump or fluid valving in automotive power steering, power brake, fuel distribution and air conditioning systems. It is also desirable to suppress compressor noise in domestic and commercial air conditioning systems. Fluid-borne noise can also be a problem in various industrial hydraulic systems where the fluid pressure pulses generate an audible and objectionable noise causing both wear and fatigue of system components, and which can also exceed OSHA requirements.  
           [0003]    The inherent design of fluid pumps, whether driven by an internal combustion engine, an electric motor or by fluid system valves, causes pressure fluctuations or pulses in the fluid line that generate fluid-borne noise. The pistons, gerotors, gears, vanes or other fluid displacement elements that pump the fluid cause pressure fluctuations, ripple or pulses within the fluid at a frequency that is dependent upon pump speed. The geometry and inherent characteristic of the pump can also be sources of fluid pressure fluctuations and vibrations. This fluid ripple can be a source of audible and objectionable noise, and can also excite components along its path (e.g., the steering gear in power steering) to cause them to become secondary generators of such noise.  
           [0004]    During normal operation of an automotive power steering system, for example, hydraulic fluid pressure can repetitively vary, and thereby generate a pressure-dependent wave form that can range substantially in amplitude between upper and lower limit values and induce system vibration. The frequency of such fluid-borne vibration can also vary substantially with the speed of the driving component (e.g., an engine) and other factors. It has been proposed to use expansible-type hoses as the fluid conductors in fluid systems in order to dampen and absorb such fluid-borne vibrations. These hoses typically consist of a tube of rubber or another elastomeric material, which is reinforced by braiding that consists of nylon or a similar material. The braiding may be disposed within the outer circumference of the tubing, or may be disposed within a layer of elastomeric material that is itself disposed around the outside of the tubing. The soft compressible elastic material of expansible hose expands upon pressure to absorb pressure fluctuations in the fluid. The strengthening braid also allows some degree of expansion when subjected to pressure.  
           [0005]    Expansible hoses are wide-band devices and, in principle, can respond to fluid vibrations over a wide frequency range. For satisfactory performance, there must be enough expansion capability in the elastomeric hose material to absorb the pressure fluctuations over the amplitude and frequency range encountered in the fluid system. However, this is possible only when the changes in volume flow rate associated with the pressure ripples are less than the volume expansion capability of the hose for the same change in hydraulic fluid pressure.  
           [0006]    Accordingly, to dampen the fluctuation even further, an attenuator in the form of a tuner conduit made of spirally constructed steel or nylon has been used within the hose. This tuner usually permits the fluid to flow from within its bore into the annulus or chamber formed between the tuner o.d. and the hose i.d. or bore. The fluid flowing in this annulus meets the fluid which is flowing inside the tuner bore at the downstream end of the tuner length.  
           [0007]    In a hydraulic fluid flow system, the pressurized hydraulic fluid output of the pump has both a mean pressure value and a pressure variation, pulsation or ripple. This fluid ripple acts as a dynamic force at a hydraulic bend, connection or end point, as does the steering gear in a power steering system. This dynamic force causes vibration of the fluid line itself and/or the structure connected to it. Vibrating surfaces cause audible and objectionable noise and are sources of discomfort in vehicles with hydraulic lines. In order to minimize this noise, the fluid pressure ripple has to be minimized or even eliminated. In current technology, hoses with tuners are being used on a trial and error basis to provide attenuation of the fluid ripple. Tuners are basically flexible conduit inserts that can be used coaxially inside a hose.  
           [0008]    It is recognized that there are two mechanisms that work to reduce such a ripple. The first is damping. The elastic hose lining and the fluid in the annular chamber (as well as expansion and contraction of the tuner conduit when made as an elastic structure) work conjointly as a damper to reduce the excitation of the ripple. Such damping is a mechanism that works for all frequencies. It is, therefore, referred to as broadband. The second mechanism is wave cancellation.  
           [0009]    Among the objects of the present invention are to provide apparatus for suppressing fluid-borne noise in hydraulic systems, such as automotive power steering, power brake, fuel distribution and air conditioning systems, that are economical to implement and reliable over an extended operating lifetime, where a hose system configuration can be employed in a variety of applications, and that are passive in operation and require no input of electrical or any other form of power.  
           [0010]    Further objects are to provide an improved system and apparatus offering increased flexibility of design, using conventional software that has been developed to simulate hydraulic lines with a traveling wave, and that utilize the phenomenon or mechanisms of fluid body and hose lines damping together with the phenomenon or mechanisms of fluid body and hose line damping together with the phenomena or mechanism of wave cancellation in order substantially to attenuate fluid ripple in the system as well as at the wave source (e.g., the pump) for particular frequencies found most objectionable in a given system and application. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention, together with additional objects, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:  
         [0012]    [0012]FIG. 1 is a schematic diagram of a fluid handling system equipped with improved fluid-borne noise suppression apparatus in accordance with a presently preferred embodiment of the invention;  
         [0013]    [0013]FIG. 2 is a sectional view on an enlarged scale of a portion of the system illustrated in FIG. 1;  
         [0014]    [0014]FIGS. 2A and 2B are sectional views that illustrate respective modifications to the embodiment of FIG. 2;  
         [0015]    [0015]FIG. 3 is a sectional view taken substantially along the line  3 - 3  in FIG. 2;  
         [0016]    FIGS.  4 - 9  are sectional views similar to that of FIG. 2 but showing respective additional modified embodiments of the invention;  
         [0017]    [0017]FIGS. 10 and 11 are sectional views that illustrate respective further embodiments of the invention;  
         [0018]    [0018]FIG. 12 is a sectional view that illustrates a further embodiment of the invention; and  
         [0019]    [0019]FIG. 13 is a sectional view that illustrates yet another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    [0020]FIG. 1 is a schematic diagram that illustrates a fluid handling system in the form of a hydraulically actuated power steering system  10 . Power steering system  10  includes a pump  12  for applying hydraulic fluid under pressure from a reservoir  14  through a closed-circuit fluid flow line  16  to a steering gear load  18 . Apparatus  20  (FIGS.  1 - 3 ) in accordance with the present invention is connected in fluid flow line  16 , between pump  12  and steering gear  18  in the schematic illustration of FIG. 1, for suppressing fluid-borne noise in the hydraulic fluid flowing through the system.  
         [0021]    Apparatus  20  includes a housing  22  of metal or plastic construction, preferably having an ovate longitudinal cross section (FIG. 2) and a circular transverse cross section in (FIG. 3). A fluid conduit or pipe  24 , also of metal or plastic construction, extends longitudinally through housing  22  for connection at opposed ends in fluid flow line  16 . Thus, fluid flowing through the closed path of system  10  flows through conduit  24  within housing  22 . Housing  22  thus defines an annular chamber  26  within the housing surrounding conduit  24 . Conduit  24  has at least one passage or hole  28 , preferably diametrically opposed passages  28  in the embodiment of FIGS.  2 - 3 , opening radially outwardly into chamber  26 .  
         [0022]    A hollow annular bladder  30  is disposed within chamber  26  surrounding conduit  24 . Bladder  30  is preferably secured to the inner surface of housing  22  spaced radially outwardly from conduit  24  and in spaced opposition to passages  28 , which in the illustrated embodiment are mid-way along the longitudinal dimension of housing  22 . A valve  32  (FIG. 3) is carried by bladder  30  and extends through housing  22  for selectively varying pressure of gas within the bladder.  
         [0023]    Fluid flowing through system  10  thus passes through conduit  24  within housing  22 . This fluid fills chamber  26  through passages  28 . Pressure pulsations within the fluid flow into chamber  26  and are damped by resilient compression of gas-filled bladder  30 . The composition of bladder  30  and the gas employed within the bladder may be selected depending upon application. For example, for automotive power steering applications, the bladder should be able to withstand temperatures up to 250° F. and pressures of up to 1,500 psi. Length and diameter of housing  22  and bladder  30  may be selected as a function of application. It is anticipated that, in some applications, bladder  30  will be fixed with gas at a desired pressure during the manufacturing process, and valve  32  will not be needed. It is also anticipated that the gas within bladder  30  will normally be air. Nitrogen is envisioned as a likely alternative in many applications.  
         [0024]    System  10  in FIG. 1 also preferably includes a noise-suppression tuner assembly  34 . Tuner assembly  34  is disclosed in greater detail in U.S. Application Ser. No.09/346,462 filed Jul. 1, 1999 and assigned to the assignee hereof. The disclosure of this copending application is incorporated herein by reference for purposes of background. In general, tuner assembly  34  includes a fluid conduit  36  connected at opposite ends in flow line  16 . A flexible inner tune  38  is coaxially mounted in conduit  36  and sized relative to conduit  36  to form a main conduit internally of tube  38  and an annular space between conduit  36  and tube  38 . A restrictor  39  is mounted in the annular space between tube  38  and conduit  36 , subdividing this annular space into axially adjacent annular sub-spaces. A multiplicity of apertures  41  open radially through tube  38  into the annular sub-spaces, each providing fluid communication to the annular sub-spaces. In this way, each of the annular subspaces serves as a fluid pulsation-absorption side-branch of tuner  34 .  
         [0025]    Apparatus  20  in accordance with the present invention acts as a Helmholz resonator to tune or cancel one particular frequency of fluid-borne noise or its harmonics. The fluid-filled portion of apparatus  20  also provides higher mass in the fluid system, which will help impede acceleration of pressure waves and minimize resulting vibration from the system.  
         [0026]    [0026]FIG. 2A illustrates a modification to the embodiment of FIG. 2, in which conduit  24  does not extend entirely through housing  22  as in the embodiment of FIG. 2, but rather forms spaced and separated inlet and outlet fittings  24   a  and  24   b  at opposed ends of housing  22 . Thus, all fluid flowing through housing  22  enters chamber  26 . FIG. 2B illustrates another modification to the embodiment of FIG. 2, in which opposed passages  28  in FIG. 2 are replaced by diametrically opposed elongated slots  28   a  that extend axially in the direction of conduit  24  and radially through the sidewall of the conduit.  
         [0027]    [0027]FIG. 4 illustrates an apparatus  32  for suppression of fluid-borne noise in accordance with another embodiment of the invention. Inlet and outlet fittings  24   a ,  24   b  are disposed in axial alignment at opposed ends of a housing  40 . An elongated resilient sleeve  34  extends between and is coupled to the opposed ends of fittings  24   a ,  24   b , being secured thereto by annular clamps  36 ,  38 . Sleeve  34  may be of suitable rubber or elastomeric composition. Thus, fluid flowing between inlet fitting  24   a  and outlet fitting  24   b  flows through resilient sleeve  34 . Housing  40  contains gas under pressure (e.g., air or nitrogen) exteriorally surrounding sleeve  34  (and fittings  24   a ,  24   b ). Thus, pressure fluctuations in fluid flowing through sleeve  34  expand the sleeve against the pressure of the surrounding gas, such that the combined effect of resiliency of sleeve  34  and compressibility of the gas reduces the amplitude of the fluid pressure fluctuations, and thus reduce fluid-borne noise.  
         [0028]    FIGS.  5 - 9  illustrate modifications to the embodiment of FIG. 4, in which like reference numerals indicate like components. In apparatus  42  of FIG. 5, conduit  24  extends entirely through housing  40 , and has a plurality of openings or passages  28  that extend radially through the wall of the conduit. Resilient sleeve  34  is externally secured to conduit  24  over openings  28 , being affixed to the conduit by clamps  36 , 38 . Once again, the interior of housing  40  surrounding conduit  24  and sleeve  34  is filled with gas under pressure. Thus, pressure fluctuations in fluid flowing through conduit  24  pass radially outwardly through openings  28 , and are absorbed by the combined effect of elasticity of sleeve  34  and compressibility of the gas within housing  40 , as previously discussed. The apparatus  44  of FIG. 6 is similar to that of FIG. 5, except that clamps  36 ,  38  in FIG. 5 are excluded. Sleeve  34  is secured to conduit  24  by elasticity of the sleeve, with addition of adhesive between the spaced ends of sleeve  34  and the opposing surface of conduit  24  if desired. Apparatus  46  in FIG. 7 is again similar to that of FIG. 5, except that circular openings or passages  28  in conduit (FIG. 5) are replaced by axially elongated slots  28   a.    
         [0029]    In the embodiments  48 ,  50  of FIGS. 8 and 9, the sleeve  34   a  is axially elongated as compared with sleeve  34  in FIGS.  4 - 7 , and is secured to conduit  24  by deformation of housing  40  over sleeve  34   a  around conduit  24 . That is, housing  40  in FIGS. 8 and 9 is of suitable malleable material, such as sheet metal, that is crimped or otherwise deformed over the axially spaced ends of sleeve  34   a  so as to secure both sleeve  34   a  and conduit  24  within housing  40 . (In the embodiments of FIGS.  4 - 7 , housing  46  is crimped or otherwise secured directly to conduit  24  or fittings  24   a ,  24   b .) Thus, in these embodiments, the axially spaced ends of sleeve  34   a  serve the additional function of sealing housing  40  to conduit  26 .  
         [0030]    [0030]FIG. 10 illustrates an apparatus  52  in accordance with another embodiment of the invention, in which a T-fitting  54  has axially aligned legs  53 ,  55  that provide for in-line connection to fluid line  16  (FIGS. 1 and 10), and a side leg  56  that is connected through the wall of a housing  58 . A rubber or elastomeric bladder  60  is secured by a clamp  62  to leg  56  within housing  58 . The volume of housing  58  surrounding bladder  60  contains gas under pressure fed thereto by a suitable valve (not shown). Thus, pressure fluctuations in the fluid flowing through line  16  are fed laterally into bladder  60 , and are absorbed by the combined effect of resiliency of bladder  60  and compressibility of the gas within housing  58 .  
         [0031]    [0031]FIG. 11 illustrates an apparatus  64  that is similar to that of FIG. 10, but in which bladder  60  contains gas under pressure rather than hydraulic fluid. That is, bladder  60  is coupled to a valve  72  that is carried by housing  58 . Housing  58  is again coupled to fluid line  16  by T-fitting  54 . Thus, the exterior of bladder  60  is engaged by hydraulic fluid fed to housing  58  by fitting  54 , while the interior of bladder  60  contains gas under pressure. Thus, as in the embodiment of FIGS.  1 - 3 , fluid pressure fluctuations are absorbed by the combined effect of resiliency of bladder  60  and compressibility of the gas contained within the bladder.  
         [0032]    [0032]FIG. 12 illustrates an apparatus  74 , in which an enclosure  76  is internally divided by a flexible diaphragm  78  of rubber or elastomeric composition. On one side of diaphragm  78 , enclosure  76  has an inlet fitting  80  and an outlet fitting  82  for in-line connection to fluid flow line  16 . Thus, the fluid flowing from outlet fitting  82  fills that portion of housing  76  on one side of diaphragm  78 . The opposing portion of housing  76  is filled with gas under pressure through a valve  72 .  
         [0033]    [0033]FIG. 13 illustrates an embodiment  84  that is similar to many respects to the embodiment  70  in FIG. 11. A T-coupling  86  is connected by a pipe  88  to a coupling  90 . Coupling  90  is connected to a fluid hose  16   a , and coupling  86  is connected by a second pipe  92  to fluid line  16  (FIG. 1). A pipe  94  extends laterally from coupling  86  to a coupling  96 , which connects to a hose  98 . The opposing end of hose  98  is closed by a coupling  100  that carries a valve for feeding gas (such as air) under pressure to a closed bladder  60 .  
         [0034]    In all of the disclosed embodiments, hydraulic fluid is separated from gas under pressure by a resilient member, such as a bladder, sleeve or diaphragm. In all embodiments, pressure fluctuations are absorbed, at least in part, by the combined effect of resiliency of the resilient member and compressibility of the gas. In the disclosed embodiments, the gas chamber may be either filled and sealed, as at the factory or at the time of installation, or may be coupled to dynamic gas pressure control means.  
         [0035]    There has thus been disclosed an apparatus for suppressing fluid-borne noise in a hydraulic system that fully satisfies all of the objects and aims previously set forth. Several alternative embodiments and associated modifications have been disclosed. Other modifications and variations will suggest themselves to persons of ordinary skill in the art. The present invention is intended to encompass all such modifications and variations as fall within the spirit and broad scope of the appended claims.