Patent Publication Number: US-7708113-B1

Title: Variable frequency sound attenuator for rotating devices

Description:
FIELD OF THE INVENTION 
     Exemplary embodiments of the present invention are related to variable frequency noise attenuation for rotating devices and, more specifically, to a quarter wave tube having a variable length and volume. 
     BACKGROUND 
     The application of internal combustion engines, whether stationary or mobile, often requires significant noise, vibration and harshness (“NVH”) engineering to reduce naturally generated sound frequencies. Rotating devices installed in, or associated with, internal combustion engines are a common contributor to such noise. Rotating parts such as fan blades or supercharger lobes may generate sound that varies over a range of frequencies; primarily as a function of the rotational velocity of the component. Additionally, rotating components may also produce noise as they pass by stationary objects. 
     Under-hood and induction system noise associated with an automotive internal combustion engine is a target of significant NVH focus due to the desirability of providing a quiet and comfortable driving experience for the operator of the vehicle. Induction noise produced by the engine depends on the particular engine configuration and may be affected by such factors as the number of cylinders, and the volume and shape of the intake manifold, plenum and intake runners. The application of induction compression through the use of an engine driven supercharger, or an exhaust driven turbocharger, may also contribute substantially to under-hood noise. Other under-hood sound produced by the engine may be contributed by rotating accessory drives, associated accessories and fans for cooling the engine. 
     Quarter wave tubes produce a sound-canceling wave of a frequency that is tuned to a wavelength four times longer than the quarter wave tube. Quarter wave tubes are often used to reduce sound generated by engine induction systems, but are typically of a fixed length and are therefore limited to addressing specific frequencies. Noise of varying frequency or noise of several different orders, such as may be produced by variable-speed rotating components, may require the use of multiple quarter wave tubes or other sound attenuation solutions that can be costly, difficult to package and of limited effectiveness. 
     Accordingly, it is desirable to provide a sound attenuator such as a quarter wave tube that can attenuate varying sound frequencies that are generated by rotating devices. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment of the present invention, a variable frequency sound attenuation device is provided comprising a central portion rotatable about a first axis, a radial portion extending outwardly from the central portion, a chamber defined by the radial portion and having a closed first end and a second end opening outwardly of the radial portion and a second axis defined by the chamber and having a radial component. A piston is disposed within the chamber and is moveable along the second axis in response to a centrifugal force imparted on the piston by rotation of the central portion and the radial portion about the first axis. A biasing member, having a first end fixed within the chamber and a second end fixed to the piston, is configured to limit movement of the piston along the second axis. A variable length, quarter wave chamber is defined by the chamber, the second, open end of the chamber and the piston and has a variable frequency, sound attenuating length defined by the location of the piston along the second axis of the chamber. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which: 
         FIG. 1  is a schematic, plan view of an engine compartment of a motor vehicle; 
         FIG. 2  is a perspective view of an automotive supercharger; 
         FIG. 3  is perspective view of the interleaved rotors of the supercharger of  FIG. 2 ; 
         FIG. 4  is an enlarged view of one of the rotors of  FIG. 3 ; 
         FIG. 5  is a perspective view of a cooling fan assembly; 
         FIG. 6  is a partial enlarged view of a cooling fan blade of the cooling fan assembly of  FIG. 5  in a first mode of operation; and 
         FIG. 7  is a partial enlarged view of a cooling fan blade of the cooling fan assembly of  FIG. 5  in a second mode of operation. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In accordance with an exemplary embodiment of the present invention,  FIG. 1  illustrates an under-hood region  10  of a motor vehicle  12 . An internal combustion engine  14  may comprise one of a straight configuration, a v-configuration, a flat/boxer configuration or other know configuration without deviating from the scope of the invention. Additionally the internal combustion engine  14  may include any number of cylinders such as 3, 4, 5, 6, 8, 10 or 12 as are commonly used across a wide range of vehicle applications. A combustion air intake system, referred to generally as  16 , includes air induction conduits  18 , an air intake manifold  20  and, in the configuration shown in  FIG. 1 , a supercharger  22  for compressing combustion air prior to delivery to the intake manifold  20  and thereby enhancing the performance of the internal combustion engine  14 . 
     A cooling system  24  is configured to circulate a cooling medium, such as a mixture of glycol and water, through the internal combustion engine  14  to remove excess heat therefrom. The cooling system will typically include coolant hoses  26  that conduct coolant to and from a radiator  28 . The radiator  28  is generally associated with one or more cooling fans  30  which may be engine driven or electrically powered and are configured to force air over cooling fins (not shown) in the radiator  28  to thereby remove heat from the cooling medium flowing therethrough. 
     Referring now to  FIGS. 2 and 3 , in an exemplary embodiment the supercharger  22  may be a positive displacement, helical lobed supercharger that includes an axially extending housing  32  having an internal cavity  34  defined by a surrounding wall  36  and upstream and downstream end walls  38  and  40 , respectively. An inlet opening  42  in the upstream end wall  38  fluidly communicates the internal cavity  34  with a source of inlet air from the combustion air intake system  16 . An outlet opening  44  extends through the surrounding wall  36 , adjacent the downstream end wall  40  of the axially extending housing  32 , and communicates the internal cavity  34  with a pressurized side  46 ,  FIG. 1 , of the combustion air intake system  16 . Within the internal cavity  34  there are rotatably mounted a pair of supercharger rotors  48  and  50  each having a plurality of radially extending portions or lobes  52  and  54  with opposite helix angles. The rotor lobes  52  and  54  are interleaved when assembled into the internal cavity  34  of supercharger housing  32  to define, with the housing, a series of helical rotor chambers (not shown). In the exemplary embodiment illustrated, the radially extending rotor lobes  52  and  54  are twisted with equal and opposite helix angles. The direction of twist of rotor lobes  52  from the inlet opening  42  to the outlet opening  44  is counter-clockwise, while the direction of twist, or helical change, of the rotor lobes  54  is clockwise. An engine driven shaft (not shown) that may be belt, chain or gear driven, rotates the supercharger rotors  48 ,  50  on axially extending central portions or rotor shafts  56  and  57  that define rotor shaft axes  72  and  74 , respectively. As engine speed increases the rotational speed of the supercharger rotors  48 ,  50  will also increase, drawing an increasing volume of combustion intake air through the inlet opening  42 . The combustion air associated with the inlet opening  42  may be subject to pressure pulsations as a result of the rapid rotation of the rotor lobes  52 ,  54  as they index with the inlet opening  42 . 
     In an exemplary embodiment shown in detail in  FIGS. 3 and 4 , the radially extending rotor lobes  52  and  54  include hollow portions or chambers  58  that extend radially inwardly and axially, along a chamber axis  62 , within at least a portion of each lobe. The chambers  58  may follow any suitable inwardly axial path that promotes rotational balance of the rotors  48 ,  50 . The chambers  58  terminate through openings  60  adjacent the air inlet opening  42  associated with the upstream end wall  38  of the supercharger housing  32 . The hollow supercharger rotors  48 ,  50  may be produced using methods such as drilling following forming, investment casting, helical pull die-casting or other suitable method of manufacturing and are typically constructed of a metal alloy, ceramic or other suitable material which is capable of exhibiting durability in a high temperature, high pressure environment. The rotor lobe chambers  38  are effective at reducing the rotating inertia of the rotor lobes  52 ,  54 . 
     In an exemplary embodiment, the axes  62  of the rotor lobe chambers  58 ,  FIG. 4 , include both an axial component and a radial component with respect to the rotor shaft axes  72 ,  74 . A piston  64  is disposed in each rotor lobe chamber  58  and is configured for movement within the chamber along the chamber axis  62 . Biasing members such as springs  66  are disposed axially inwardly of each piston  64 . The springs are attached to the rotor lobes  52  and  54  adjacent to the closed inner ends  68  of the rotor lobe chambers  58  as well as to the pistons  64  to prevent egress of the pistons through chamber openings  60  during operation of the supercharger. The plurality of radially extending rotor lobes  52 ,  54 , the rotor lobe chambers  58  that terminate in openings  60  and the biased pistons  64  cooperate to define noise attenuation devices, or quarter wave tubes  70 . 
     In an exemplary embodiment, during operation of the internal combustion engine  14 , the engine driven central portions or rotor shafts  56 ,  57  rotate the supercharger rotors  48  and  50  and associated, radially extending rotor lobes  52  and  54 . As a result of the radial component in the axis  62  of each rotor lobe chamber  58 , relative to the axes  72 ,  74  of the rotor shafts  56  and  57 , each of the pistons  64  will be subject to an outwardly directed centrifugal force within the lobe chambers as the rotors spin. As a result of the radially outwardly directed force, the pistons  64  will move, against the bias of springs  66 , along the lobe chamber axes  62  towards the openings  60  of the lobe chambers  58 ,  FIGS. 3 and 4 . 
     The effect of the piston movement will be to shorten the length (“L”) of the quarter wave tubes  70 , resulting in a variable adjustment of the sound frequency attenuated by the quarter wave tubes based on the rotational speed of the engine  14  and associated rotational speed of the supercharger rotors  48  and  50 . More specifically, as the rotational speed increases, the frequencies attenuated are higher than those attenuated at lower rotational speeds. Such a variation allows the pressure pulsations resident at the inlet of the supercharger housing  32  to be effectively reduced as they vary based on the rotational speed of the supercharger rotors  48 ,  50 . A reduction in the rotational speed of the engine  14  and the supercharger rotors  48  and  50 , and a consequent reduction in the inertial forces acting on pistons  64 , will cause the biasing force of the springs  66  to retract the pistons  64  into the chambers  58  of the rotor lobes  52 ,  54  thereby increasing the length “L” of the quarter wave tubes  70 ; again resulting in a variable adjustment of the sound frequency attenuated based on the speed of the engine  14 . As radial force acting on the piston is proportional to the square of the speed, a spring  66  having a non-linear spring rate may be required to achieve desired tuning properties over a range of engine speed. In the alternative, if only two sound frequencies require attenuation, the springs  66  may be linear and a piston stop (not shown) that is positioned at a desired location along the length of the chamber  58  may be used to fix the length “L” of the tube, at speed. 
     Thus far, exemplary embodiments of the invention have been described with applicability to the rotating rotor lobes of a supercharger for an internal combustion engine. It should be apparent that the invention has other contemplated embodiments for variably reducing sound frequencies generated by rotating devices. Referring to  FIG. 5 , a fan shroud assembly  72  is shown for an automotive application such as that illustrated in  FIG. 1 . In the embodiment shown, the fan shroud assembly  72  includes two fans  30  mounted for rotation about fan motor axes  78  when powered by the electric motors  82 . In many vehicles with varying loads and operating environments, the electric motors may rotate the fans  30  at varying speeds depending upon the thermal energy that must be removed from the engine  14 . When little or no energy must be removed from the engine  14 , the fans may run at a low speed or may be turned off to reduce both the noise generated by the fans and to save energy. In vehicles having an engine driven cooling fan, the fan&#39;s rotational speed may vary constantly with the speed of the engine  14 . 
     When in operation, the fans  30  may be a significant source of generated sound especially as the plurality of radially extending portions or fan blades  84  pass stationary components such as the support brackets  86 . In an exemplary embodiment, and as illustrated in detail in  FIGS. 6 and 7 , a portion of each fan blade  84  (in this exemplary embodiment, the leading edge of the blade) defines a chamber  88  that extends radially outwardly from a location adjacent central portion or fan hub  90  to open adjacent the fan blade tip  92 . A piston  94  is disposed within each chamber  88  and is configured for axial movement within the chamber  88  along chamber axis  91 . Biasing members such as springs  96  are disposed in each of the chambers  88 , axially inwardly of each piston  94 . Each spring  96  is attached to its respective fan blade adjacent to the inner radial end  98  of the hollow chamber  88 , as well as to the piston  94  to prevent egress of the piston out of the hollow chamber  88  during rotation of the fans  30  about fan motor axis  78 . Spring  96  will have a spring rate selected to provide the desired retention and extension of the piston  94  that is necessary to achieve attenuation of the desired sound frequencies (i.e. to achieve the desired quarter-wave tuning). The fan blades  84 , comprising hollow chambers  88  terminating adjacent to the fan blade tips  92 , and including spring biased pistons  94 , define noise attenuation devices, or quarter wave tubes  100 . 
     During operation of the fans  30  the electric motors  82  rotate the central portions or fan hubs  90  and associated plurality of radial portions or fan blades  84  about fan motor axes  78 . As a result of centrifugal force generated by the rotation of the fan blades  84 , the pistons  94  will move radially outwardly against the bias of springs  96  and towards the fan blade tips  92 ,  FIG. 7 . The effect of the piston movement will be to shorten the length (“L”) of each quarter wave tube  100  resulting in variable adjustment of the sound frequency that is attenuated by the tubes based on the rotational speed of the fan(s)  30 . Such variation allows the sound generated by the rotation of the fans to be effectively reduced as the sound varies based on the rotational speed of the fan motors  82 . A reduction in rotational speed of the fan(s)  30 , and a resultant reduction in the radially outwardly directed centrifugal force imposed on pistons  94 , will allow the biasing force of the springs  96  to retract the pistons  94  into the hollow chambers  88  thereby increasing the length (“L”),  FIG. 6 , of the quarter wave tubes  100 ; again variably adjusting the sound frequency attenuated. As the radial force acting on the pistons  64  is proportional to the square of the speed, a spring having a non-linear spring rate may be required for specific tuning properties over a range of rotational speed. In the alternative, if only two sound frequencies require attenuation, the springs  66  may be linear and a piston stop (not shown), that is located at a desired position along the length of the hollow chamber  88 , may be used to fix the length of the tube, at speed. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the present application.