Abstract:
An energy attenuation method and apparatus for a system conveying liquid under pressure. The apparatus is disposed in a liquid conveying structure of the system and includes first and second outer hose conduits, each of which respectively defines an associated first and second tuning chamber each having an inlet end and an outlet end. A tubular conduit interconnects the two hose conduits such that the chambers communicate with one another via the tubular conduit. A first tuning tube of polymeric material is disposed in the first chamber and has a first end connected to the inlet end of the first chamber for receiving liquid therein and has a second open end that is spaced from the outlet end of the first chamber for emptying liquid into the first chamber. A second tuning tube of polymeric material is mounted in the second chamber and has a first end connected to the outlet of the second chamber for conveying liquid thereto and a second open end that is spaced from the inlet end of the second chamber for receiving liquid conveyed to the second chamber via the tubing conduit. Seven additional alternative embodiments of fluid noise attenuation systems are also disclosed.

Description:
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 OF THE INVENTION 
   There are many applications in industry and commerce where it is desirable, and in some cases required, 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 power steering, power brake, fuel distribution and air conditioning systems. 
   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 which generate fluid-borne noise. The pistons, rotors, 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. 
   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 magnitude or amplitude between the upper and lower limit values and induce system vibration. The frequency of such fluid-borne vibration also can vary substantially with the speed of the driving component (e.g., engine) and other factors. Therefore expansible-type hoses are often used 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 nylon or a similar material. The braiding or other reinforced member 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. 
   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. 
   In order to dampen the fluctuation even further, an attenuator in the form of a tuner conduit made of spirally constructed steel or smooth wall polymeric material, such as Teflon or nylon, also has been used within the hose. This tuner usually permits the fluid to flow, via clearances between the spiral tube or apertures in the tube, 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 and results in some reduction of the pressure pulsation and resultant noise and/or vibration. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with additional features and advantages thereof will be best understood from the following detailed description, appended claims and the accompanying drawings wherein: 
       FIG. 1  is a partially schematic and fragmentary view, and partially in longitudinal center section illustrating a representative fluid handling system equipped with an improved dual chamber pressure ripple attenuator conduit system for suppression of fluid-borne noise in accordance with one exemplary but preferred first embodiment of the invention applied to a power steering system. 
       FIG. 2  is a fragmentary longitudinal center section view of the inlet fitting subassembly of the first, upstream fluid tuning chamber of the  FIG. 1  system prior to crimping of the collar of this fitting subassembly. 
       FIG. 3  is an end view of an adapter shown by itself in  FIG. 4  and used in the inlet fitting subassembly of  FIG. 2 . 
       FIG. 4  is a longitudinal center section taken on the line  4 - 4  of  FIG. 3 . 
       FIGS. 5 ,  6 ,  7 ,  8 ,  9 ,  10  and  11  are partially schematic and fragmentary views, partially in longitudinal center section, illustrating respectively second, third, fourth, fifth, sixth, seventh and eighth embodiments of pressure ripple attenuator conduit systems for suppression of fluid-borne noise in accordance with the invention and also applied to a power steering system. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   First Embodiment 
   The fluid handling system illustrated in  FIG. 1  of the drawings is in the form of a hydraulically actuated power steering system  10  for a vehicle that incorporates a pair of serially coupled attenuator conduits in the form of fluid tuning chamber conduits  12  and  14 . The first chamber conduit  12  has an inlet fitting  16  (as described in more detail hereinafter with reference also to  FIGS. 2-4 ) suitably connected to the outlet end of a high-pressure metal conduit line  18  leading from a system power steering pump  20 . First chamber conduit  12  has an outlet fitting  22  connected by a separate tubular metal conduit  24  to an inlet fitting  26  of second chamber conduit  14 . It is to be understood that system  10  does not employ a restrictor as such or the equivalent thereof, inasmuch as a “restrictor” is a term used to refer to a device for separating a noise attenuating chamber or tube into two parts, and does not refer to a conduit for connecting two tuning chambers to each other, such as conduit  24 . 
   Both chamber conduits  12  and  14  are enveloped by a conventional volumetrically compliant elastomeric hose, the axially opposite open ends of a hose  28  of first chamber conduit  12  being respectively connected to associated inlet and outlet fittings  16  and  22  by conventional crimp collar shell fittings  30  and  32  respectively. Elastomeric hose  34  of second chamber conduit  14  is similarly connected at its axially opposite open ends to associated inlet and outlet fittings  26  and  36 , again hose  34  being coupled to these fittings by conventional crimp collar shell fittings  38  and  40  respectively. 
   First chamber conduit  12  has a hollow polymeric tuning tube  42  extending from inlet fitting  16  into the first tuning chamber  45  defined by the interior wall surface  44  of hose  28 , but has an open outlet end  43  that stops well short of the open entrance end  46  of outlet fitting  22 . Tuning tube  42  preferably has a right circular cylindrical constant diameter cross section and is made of Teflon material. It is to be noted that there are no bleed holes or other sidewall apertures in tuning tube  42 . It has been found that tuning tube  42  in first chamber  45  made of such polymeric material and without bleed holes provides optimum  14  wave side branch attenuation of pressure ripple. 
   The absence of bleed holes and the like in tube  42  also contributes to economy of manufacture and assembly. 
   Second chamber conduit  14  also has a polymeric tuning tube  50 , but, in accordance with a principal feature of the present invention, tube  50  extends from outlet fitting  36  into the tuning chamber  51  defined by hose  34 , and also stops well short of the open exit end  52  of inlet fitting  26  of chamber conduit  14 . A pair of bleed openings extend radially through the wall of tuning tube  50 , only one of such holes  54  being shown in  FIG. 1 , its companion hole (not shown) being located diametrically opposite hole  54 , if desired, or longitudinally staggered relative thereto. 
   Outlet fitting  36  of the second chamber  14  is suitably coupled to the high-pressure tubular conduit line  56  leading to a system load  58  and which, in the preferred embodiment, is a power steering gear. 
   Although the inlet and outlet fittings  16  and  36  in which the tuning tubes  42  and  50  are respectively secured may be of various forms of conventional constructions, it is presently preferred to employ the improved fitting  16  constructed as shown in more detail in  FIGS. 2 ,  3  and  4 .  FIG. 2  illustrates fitting  16  as a completed subassembly but for the crimping of collar  30 . As best seen in  FIGS. 3 and 4 , an improved form of adapter  100  is provided as a generally tubular piece having a through bore  102  and a nipple end  104  provided with annular barbs  106  and  108  having preferably a 7° and 15° taper respectively. Nipple  104  terminates at its inner end at a radially enlarged flange  110  and is adapted to telescopically receive the open upstream end of tuner tube  42  with a slight interference fit over the barbs  106  and  108 , with the end of the tube abutting flange  110  in assembly. Adapter  100  has a nose portion  112  extending from flange  110  to the upstream open end of the adapter that is provided with a beveled leading edge  114 . Nose  112  has a constant diameter cylindrical portion  116  that in turn leads into a 5° tapered portion  118  that terminates just short of flange  110  and is spaced therefrom by an annular external groove  120 . 
   Tube  18  is preformed to the extent of forming an inturned lip  122  at its open end and forming an annular bead stop  124  positioned to serve as a locating abutment for installing collar  30 . A steel reinforcing sleeve  126  is inserted with a slight press fit into tube  18  so as to be located as shown in  FIG. 2  relative to collar  30  in assembly. The end of sleeve  126  closest to tube lip  122  is dimensioned to slidably telescope onto nose portion  116  of adapter  100  with a press fit. 
   After collar  30  is telescoped onto tube  18  so as to abut stop bead  124 , another stop bead  130  is formed in tube  18  as shown in  FIG. 2  to capture the collar  30  in assembly on tube  18 . Adapter  100  is then telescopically inserted into the downstream end of tube  18 . As nose portion  112  of adapter  100  engages the tube bead  122  and then is progressively telescoped in tube  18 , the tapered portion  118  of adapter  100  causes bead  122  to expand slightly until the bead and adapter groove  120  are in registry, whereupon bead  122  snaps into groove  120  to lock adapter  100  in assembly in the downstream end of tube  18 . Concurrently nose portion  116  of adapter  100  telescopically enters into the downstream end of reinforcing sleeve  126  with a press fit. 
   The upstream end of tuning tube  42  is then inserted with a telescopic press fit onto nipple  104  of adapter  100 . To complete the assembly of fitting  16  in forming chamber conduit  12 , the end of hose  28  is inserted into the undeformed collar  30  in the annular space between tube  18  and the shell  132  of collar  30 . Collar sleeve  130  is then crimped to the form generally indicated in  FIG. 1  to complete the coupling of tube  18  with chamber conduit  12 , as indicated semi-schematically in  FIG. 1 . 
   Fittings  22  and  26  of tuning conduits  12  and  14  are of conventional crimp collar construction with associated steel reinforcing sleeves. 
   Outlet fitting  36  of the downstream second chamber conduit  14  is constructed in an identical manner to inlet fitting  16  described hereinabove, and tuning tube  50  is coupled to outlet tube  56  in like manner using another adapter  100 . 
   In one successful working first embodiment of the invention for automotive power steering applications, the following exemplary dimensional and material parameters were utilized: 
   
     
       
             
             
             
             
           
             
             
             
             
             
           
             
             
           
         
             
                 
                 
             
             
                 
               Metric 
               Inches 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               First Chamber Conduit 12: 
                 
                 
                 
                 
             
             
               Dimension A 
               425 
               mm 
               16.73 
               in 
             
             
               Dimension B 
               336 
               mm 
               13.23 
               in 
             
             
               Dimension C 
               298 
               mm 
               11.73 
               in 
             
             
               Dimension D 
               38 
               mm 
               1.50 
               in 
             
             
               Second Chamber Conduit 14: 
             
             
               Dimension E 
               264 
               mm 
               10.39 
               in. 
             
             
               Dimension F 
               175 
               mm 
               6.89 
               in 
             
             
               Dimension G 
               50 
               mm 
               1.97 
               in 
             
             
               Dimension H 
               7 
               mm 
               0.28 
               in 
             
             
               Dimension I 
               168 
               mm 
               6.61 
               in 
             
             
               Diameter of Bleed Holes 54 
               1.42 
               mm 
               056 
               in 
             
           
        
         
             
               Material of Hoses 28 and 34 
               DF 3907 
             
             
               Material of Tuning Tubes 42 and 50 
               ⅜ inch O.D.Teflon tubing 
             
             
                 
             
           
        
       
     
   
   It has been found that the use of tuning tube  42  in the first chamber conduit  12 , being made of polymeric material without an aperture in the tube for fluid bleed, functions or is operable to focus noise attenuation at specific frequencies. This is in contrast to both steel wound and apertured Teflon tubes that use fluid bleed-through from the tuning tube to aid in broadening noise attenuation. Thus, the elimination of the bleed hole in the first chamber tuning tube  42  provides greater attenuation of pressure ripple, and also reduces component manufacturing costs. 
   In the second chamber conduit  14 , the mounting of tuning tube  50 , having its inlet end  60  spaced from inlet fitting  26  and facing in the direction of the fluid feed from the power steering pump  20 , improves attenuation in the second tuning chamber  14  by using the damping characteristic of the second chamber hose material  34  in conjunction with the side branch tuning effect of apertured polymeric tuning tube  50 . 
   In order to evaluate the performance of the noise reduction capability of power steering system  10  of the invention, the same was compared to a prior production system of substantially identical construction except for a conventional assembly of a tuning tube in the second chamber having its inlet end coupled to the inlet fitting  26  and its outlet opening into the interior chamber of hose  34  and spaced 10 mm from the entrance to outlet fitting  36 . This production test control comparison system set-up also had a pair of diametrically opposite bleed holes (of the same dimension as bleed holes  54  set forth above) located in the first chamber tube at 50 mm from the interior end of inlet fitting  16 . The tuning tube in the second chamber of this comparison system also had the bleed holes  54  located 50 mm from the coupling of the inlet end of this second chamber tuning tube from the downstream or outlet end of inlet fitting  26 . All other dimensions and material parameters were the same as in the above-specified invention system  10 . Both systems were tested in a Chrysler RS Mini-van model year 2003 to perform NVH evaluations related to power steering “moan” and steering “grunt”. Interior sound pressure level measurements were acquired during specific vehicle operating conditions, which were at engine idle speed with and without steering effort applied. The vehicle was also subjectively evaluated for steering “grunt” and “shudder”. The results of the objective interior SPL measurements showed improvement in the power steering 10 th  and 20 th  order moan levels. 
   By subjective evaluation, the baseline test vehicle did not exhibit “shudder” or “grunt”. The evaluation of the test vehicle with the invention noise attenuation power steering system  10  showed no deterioration in the NVH performance level relative to “shudder” or “grunt”. 
   The conclusions developed from this testing were that the system  10  of the invention had lower “moan” levels than the aforementioned comparison pressure hose noise attenuation system, with no deterioration in “grunt” and “shudder” performance. Both the comparison pressure hose assembly and the invention pressure hose assembly are considered to be acceptable for production. 
   Thus, the aforementioned testing evaluation demonstrates that the improved sound attenuation system  10  of the invention represents an improvement both from the stand point of reduced manufacturing costs as well as improved performance in reducing power steering 10 th  and 20 th  order moan levels. 
   Second Embodiment 
     FIG. 5  illustrates a second embodiment system  200  of the invention wherein components identical to those described in the first embodiment of  FIGS. 1-4  are given like reference numerals and their description not repeated. It will be seen that the principal difference between the first and second embodiment systems  10  and  200  resides in the construction of the fluid tuning chamber conduit  12   a  employed in system  200 . Firstly, instead of having a hollow polymeric tuning tube  42  extending from the inlet fitting  16  into the first tuning chamber  45 , chamber conduit  12   a  of system  200  has a tuner conduit  202  extending from the outlet of chamber  45  in an upstream direction therein and has an open inlet end  204  facing upstream in chamber  45  and stopping well short of the inlet end of chamber  45 . Secondly, tuning tube  202  is constructed of spirally, (i.e., helically) wound steel ribbon material in a conventional manner instead of being made of smooth wall polymeric (e.g., Teflon) tubular material. 
   Tuning tube  202  is secured to the outlet of chamber conduit  12   a  by the components employed in the inlet fitting  16  of conduit  12  of first embodiment system  10 . The inlet to chamber conduit  12   a  uses the components of the outlet fitting  22  of chamber conduit  12  of system  10 . 
   The second chamber conduit  14   a  of system  200  is constructed the same as that in system  10 . However, it is to be noted that the bleed openings extending radially through the wall of tuning tube  50  (only one of such holes  54  being shown in  FIGS. 1 and 5 ) and located diametrically opposite one another (or if desired, longitudinally staggered relative to one another) are, again, optional features and may, if desired, be omitted, at least for certain applications, without significantly altering system performance. 
   Third Embodiment 
     FIG. 6  illustrates a third embodiment  300  of a hydraulically actuated power steering system for a vehicle also in accordance with the present invention. Again, those components previously described in conjunction with systems  10  and  200  are given identical reference numerals and their description not repeated. 
   It will be seen by comparing  FIGS. 5 and 6  that system  300  merely inverts 180° (figuratively speaking) the fluid tuning chamber  12   a  (end for end) so that spirally wound tuning cable  202  is attached to the inlet rather than the outlet end of chamber  12   b  and has its outlet end facing downstream and spaced from the outlet fitting  32  of chamber  12   b . Likewise, in system  300  the second chamber conduit  14  system  200  of  FIG. 5  is inverted 180° end for end to provide the second chamber conduit  14   b  of the system  300 . Thus, as shown in  FIG. 6 , the polymeric tuning tube  50  now is attached by a fitting  100  to the inlet of chamber  14   b , and has its outlet opening  60  facing downstream and spaced a suitable distance from the outlet of chamber  14   b.    
   Fourth Embodiment 
     FIG. 7  illustrates a fourth embodiment system  400  of a hydraulically actuated power steering system for a vehicle also in accordance with the present invention. Again, in system  400  those components identical to the components previously described in conjunction with systems  10 ,  200  and  300  of  FIGS. 1-6  are given like reference numerals and their description not repeated. 
   It will be seen that system  400  uses, for noise attenuation, just a single first chamber conduit  12   c  between pump  20  and load  58 . Thus, chamber conduit  12   c  has its inlet directly coupled via conduit line  18  to pump  20  and its outlet directly coupled via conduit line  24  to load  58 . Chamber conduit  12   c  of system  400  is constructed in a manner identical to chamber conduit  12   b  of system  300 , but in this configuration the outlet fitting  38  of chamber  14   b  now is used as an inlet fitting by being coupled via conduit line  18  to pump  20 . Similarly, the polymeric tuning tube  50  of chamber conduit  14   b  now serves in chamber conduit  12   c  as the outlet from interior chamber  51  and has its open end  60  facing upstream and spaced downstream of fitting  38  to receive fluid flow from interior chamber  51 . 
   Fifth Embodiment 
     FIG. 8  illustrates a fifth embodiment system  500  of a hydraulically actuated power steering system for a vehicle also in accordance with the present invention. Again, in system  400  those components identical to the components previously described in conjunction with systems  10 ,  200 ,  300  and/or  400  of  FIGS. 1-7  are given like reference numerals and their description not repeated. 
   It will be seen from  FIG. 8  that system  500 , like system  400 , utilizes a single tuning chamber  12   d  having a similar inlet fitting  38  connected via conduit line  18  to pump  20 , and having its outlet fitting  40  connected at its outlet end to load  58  via conduit line  24 . The imperforate polymeric tuning tube  50  is again mounted at its downstream end to fitting  100  of outlet fitting  40 . Tube  50  has its open upstream end  60  facing upstream of fluid flow-through chamber  12   d.    
   Chamber conduit  12   d  differs from chamber conduit  12   c  of system  400  in having a conventional crimp collar restrictor subassembly  502  affixed exteriorly and interiorly in the usual manner to hose  28  at a suitable location therealong, e.g., generally the midpoint between the inlet opening  52  and outlet opening  60  in chamber  12   d . The inner cylindrical restricting plug element  504  of restrictor subassembly  502  has the usual restricted through-passage  506  leading, in the upstream direction into a counterbore in which another imperforate polymeric tuning tube  508  is mounted. Tube  508  extends in an upstream direction to its open inlet end  510  that is spaced downstream from the outlet opening  52  of fitting  38 . Restrictor subassembly  502  thus subdivides hose  28  into two interior tuning chambers, namely, an upstream chamber  512  and a downstream chamber  514 . Inlet  510  of tube  508  thus opens into chamber  512 , whereas inlet  60  of tube  50  opens into chamber  514 . 
   Sixth Embodiment 
     FIG. 9  illustrates a sixth embodiment system  600  of a hydraulically actuated power steering system for a vehicle also in accordance with the present invention. Again, in system  600  those components identical to the components previously described in conjunction with systems  10 ,  200 ,  300 ,  400  and/or  500  of  FIGS. 1-8  are given like reference numerals and their description not repeated. 
   It will be seen that system  600 , like that of systems  400  and  500 , uses, for noise attenuation, just a single tuning chamber conduit  12   e  between pump  20  and load  58 . Thus, chamber conduit  12   e  has its inlet fitting  16  directly coupled via conduit line  18  to pump  20  and its outlet fitting  40  directly coupled via conduit line  24  to load  58 . 
   System  600  is characterized by having both an inlet tuning tube  42  and an outlet tuning tube  50  disposed in axially juxtaposed spaced apart relation in interior chamber  45 . The outlet  43  of inlet tube  42  faces the inlet  60  of outlet tube  50  and the tuning tubes are in fluid communication with one another via the unrestricted interior chamber  45  of hose  28 . Preferably chamber conduit  12   e  utilizes the inlet fitting  16  and inlet tuning tube  42  of system  10  at its upstream end, and utilizes at its downstream end the identical outlet construction, i.e., fitting  40  and tuning tube  50 , of the chamber conduit  14  of system  10 . 
   The operation and performance characteristics of system  600  differs from system embodiments  100 - 500 ,  700  and  800  in that this system  600  pressure hose and two tuning cable combination utilizes the full length of the hose energy absorbing capabilities along with the side branch attenuation of two tuners  42  and  50 . This system results in a fairly broad band of attenuation because of the large gap between tuners  42  and  50 . This type of broad band attenuation covers a wider band of attenuation even though the transmission loss is less as compared to a narrow band attenuator. This design provides an advantage where the pump speed varies considerably due to additional loading from the alternator (electrical), HVAC (ac compressor), and power steering loads. These additional loads can drastically affect engine and pump idle speeds. Although some vehicles have idle speed controllers to compensate for the additional loading, some vehicles do not. 
   Seventh Embodiment 
     FIG. 10  illustrates a seventh embodiment system  700  of a hydraulically actuated power steering system for a vehicle also in accordance with the present invention. Again, in system  700  those components identical to the components previously described in conjunction with systems  10 ,  200 ,  300 ,  400 ,  500  and/or  600  of  FIGS. 1-9  are given like reference numerals and their description not repeated. 
   It will be seen from  FIG. 10  that system  700  uses, for noise attenuation, just a single tuning chamber conduit  12   f  which preferably uses all of the components of tuning chamber  12  of  FIG. 1 , but is made axially longer to accommodate three additional components mounted within hose  28  between the outlet  43  of tuning tube  42  and the inlet  46  of outlet tube  22 . As shown semi-schematically in  FIG. 10 , these three additional components comprise three restrictor subassemblies  702 ,  704  and  706  constructed similar to restrictor subassembly  502  of system  500 . Each of these restrictor subassemblies  702 ,  704  and  706  has an associated imperforate polymeric tuning tube  708 ,  710  and  712  respectively mounted at its upstream end within an outlet counterbore of the associated restrictor plug element of each restrictor subassembly and having an open outlet end facing downstream. It will be understood that, for convenience, the scale of the hose  28  housing the restrictor subassemblies  702 ,  704  and  706  in  FIG. 10  is shown on a reduced scale relative to the remaining components illustrated in  FIG. 10 , it being understood that hose  28  has a constant outside diameter and inside diameter throughout its entire axial length between fittings  30  and  32 . 
   Eighth Embodiment 
     FIG. 11  illustrates an eighth embodiment system  800  of a hydraulically actuated power steering system for a vehicle also in accordance with the present invention. Again, in system  800  those components identical to the components previously described in conjunction with systems  10 ,  200 ,  300 ,  400 ,  500   600 , and  700  of  FIGS. 1-10  are given like reference numerals and their description not repeated. 
   It will be seen that system  800 , like that of system  10 , uses the serially coupled tuning chamber conduits  12  and  14 , with the output of pump  20  communicating via line  18  with the inlet  16  of chamber  12  and with the outlet of chamber  12  coupled by line  24  to the inlet  26  of chamber  14 . However, instead of coupling the output of chamber  14  directly to the load  58 , the outlet tube  36  is coupled via a tubular line  802  to the inlet of a third tuning chamber conduit  812  which is preferably identical in construction to chamber  12 . The outlet  22  of chamber  812  is then coupled via an output tubular conduit  824  to the load  58 . 
   It is to be understood that in systems  100 - 500 ,  700  and  800  each chamber (hose and tuner section) has a very specific attenuation characteristic. The chamber/tuners with no bleed, either by hole or cable winding, provide a high narrow band of fluid borne noise attenuation, even though the amount of attenuation is lower. When these two chambers, operable as specific noise filters, are placed in series, with any combination of filters, they thereby incorporate a given broad band attenuation with a specific narrow band frequency. The narrow band frequency is tuned for a specific pressure order of a pump. The lengths of each chamber/tuner will be dependent on the pump pressure pulsation frequencies. 
   Thus all of the noise attenuation hose designs of systems  100 - 500 ,  700  and  800  incorporate a broad and narrow band fluid borne noise filter. 
   Although the illustrated embodiments have been discussed in conjunction with conventional hydraulic power-assist vehicle steering systems commonly employed in automotive vehicles of current manufacture, the invention is by no means limited to such applications. Modifications and variations will readily suggest themselves to persons of ordinary skill in the art. The invention is therefore intended to embrace all such modifications and variations as fall within the spirit and broad scope of the appended claims.