Abstract:
A volumetric assembly includes: a roots-type supercharger device; a roots-type expander device; a first duct extending from the supercharger fluid inlet, the first duct supplying fluid to the roots-type supercharger device; and a second duct extending from the expander fluid outlet, the second duct directing fluid away from the roots-type expander device, wherein the first duct is positioned adjacent to the second duct, and wherein the first duct defines a first aperture and the second duct defines a second aperture, the first and second apertures being generally aligned; and a flexible membrane positioned between the first and second ducts in the first and second apertures, the flexible membrane sealing the first duct from the second duct, and the flexible membrane flexing as fluid flows within the first and second ducts to attenuate noise associated with the fluid flows.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application a Continuation of PCT/US2014/025790 filed on 13 Mar. 2014, which claims benefit of U.S. Patent Application Ser. No. 61/793,499 filed on 15 Mar. 2013 and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications. 
     
    
     BACKGROUND 
       [0002]    Roots-type devices are volumetric devices that output a fixed volume of fluid per rotation. In some instances, roots-type devices are used in supercharger systems as blowers to boost the pressure of fluid provided to a power source such as an internal combustion engine or a fuel cell. In other applications, the roots-type devices are used as expanders to extract energy from waste heat from a power source that would otherwise be wasted, such as an exhaust stream from a fuel cell, a working fluid that extracts heat from an internal combustion engine, or an exhaust fluid stream from an internal combustion engine. In all scenarios, there is noise associated with the passage of fluid through the roots-type devices. 
       SUMMARY 
       [0003]    In one aspect, a volumetric assembly includes: a roots-type supercharger device having at least two supercharger rotors, with each of the rotors having two or more lobes, the roots-type supercharger defining a supercharger fluid inlet and a supercharger fluid outlet; a roots-type expander device having at least two expander rotors, with each of the rotors having two or more lobes, the roots-type expander defining an expander fluid inlet and an expander fluid outlet; a first duct extending from the supercharger fluid inlet, the first duct supplying fluid to the roots-type supercharger device; and a second duct extending from the expander fluid outlet, the second duct directing fluid away from the roots-type expander device, wherein the first duct is positioned adjacent to the second duct, and wherein the first duct defines a first aperture and the second duct defines a second aperture, the first and second apertures being generally aligned; and a flexible membrane positioned between the first and second ducts in the first and second apertures, the flexible membrane sealing the first duct from the second duct, and the flexible membrane flexing as fluid flows within the first and second ducts to attenuate noise associated with the fluid flows. 
         [0004]    In another aspect, a system includes: a power source; and a volumetric assembly, the volumetric assembly including: a roots-type supercharger device having at least two supercharger rotors, with each of the rotors having two or more lobes, the roots-type supercharger defining a supercharger fluid inlet and a supercharger fluid outlet, the supercharger fluid outlet being connected to the power source to provide fluid for boosting the power source; a roots-type expander device having at least two expander rotors, with each of the rotors having two or more lobes, the roots-type supercharger defining an expander fluid inlet and an expander fluid outlet, the expander fluid inlet being coupled to a working fluid or an exhaust of the power source to provide fluid to the expander fluid inlet, and the roots-type expander device applying torque to the power source; a first duct extending from the supercharger fluid inlet, the first duct supplying fluid to the roots-type supercharger device; and a second duct extending from the expander fluid outlet, the second duct directing fluid away from the roots-type expander device, wherein the first duct is positioned adjacent to the second duct, and wherein the first duct defines a first aperture and the second duct defines a second aperture, the first and second apertures being generally aligned; and a flexible membrane positioned between the first and second ducts in the first and second apertures, the flexible membrane sealing the first duct from the second duct, and the flexible membrane flexing as fluid flows within the first and second ducts to attenuate noise associated with the fluid flows. 
         [0005]    In yet another aspect, a method of boosting a power plant and recovering energy from waste heat of the power plant includes: providing a roots-type supercharger device to boost the power plant, the roots-type supercharger having an inlet duct; providing a roots-type expander device to recover energy from the exhaust of the power plant, the roots-type expander device having an outlet duct; positioning the inlet duct adjacent to the outlet duct; and configuring a membrane positioned in an aperture between the inlet and outlet ducts to flex as pressure changes within the inlet and outlet ducts. 
         [0006]    The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic illustration of a system including a power plant and a volumetric device. 
           [0008]      FIG. 2  is a perspective view of an example volumetric supercharger device of the system of  FIG. 1 . 
           [0009]      FIG. 3  is a schematic illustration of rotors of the volumetric supercharger device of  FIG. 2 . 
           [0010]      FIG. 4  is a cross-sectional view of an example volumetric expander device of the system of  FIG. 1 . 
           [0011]      FIG. 5  is a schematic illustration of rotors of the volumetric expander device of  FIG. 4 . 
           [0012]      FIG. 6  is a perspective view of the volumetric assembly of  FIG. 1 . 
           [0013]      FIG. 7  is a schematic view of a portion of the volumetric assembly of  FIG. 6 . 
           [0014]      FIG. 8  is a schematic view of an example flexible member of the volumetric assembly of  FIG. 7 . 
           [0015]      FIG. 9  is a schematic illustration of another system. 
           [0016]      FIG. 10  is a schematic illustration of the noise cancellation operation of the system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,  FIG. 1  shows an example system  100  including a power source  102 , such as an internal combustion engine or a fuel cell, and a volumetric assembly  104  coupled thereto. 
         [0018]    The power source  102  is used to power various devices, such as a vehicle. In one embodiment, a fuel cell is used as the power source. 
         [0019]    The volumetric assembly  104  includes a volumetric supercharger device  110  and a volumetric expander device  112 . Both devices  110 ,  112  are roots-type devices. Roots-type devices are fixed displacement devices that output a fixed volume of fluid per rotation. 
         [0020]    Referring to  FIGS. 2-3 , in this example, the volumetric supercharger device  110  (sometimes referred to as a “supercharger” or “blower”) is used to pump fluid from the atmosphere to the power source  102 . The supercharger is used to boost a pressure of the fluid that is delivered to the power source  102 , increasing oxygen which allows more fuel. This enhances performance of the power source  102 . The same is true for a fuel cell, except the electrical output increases. 
         [0021]    The example volumetric supercharger device  110  includes two rotors  220 ,  222 . The rotors  220 ,  222  are helical in configuration and rotate relative to one another in a coordinated fashion. Fluid provided at a fluid inlet  210  of the volumetric supercharger device  110  is pumped by the volumetric supercharger device  110  and delivered via an outlet  212  to the power source  102 . Torque provided by the power source  102  or other external energy sources causes the volumetric supercharger device  110  to rotate. 
         [0022]    In this example, each of the rotors  220 ,  222  has four lobes  224 . These lobes  224  intermesh as the rotors  220 ,  222  spin to pump the fluid through the volumetric supercharger device  110 . More or fewer lobes can be used. 
         [0023]    One non-limiting example of a volumetric supercharger device is described in International Patent Application No. PCT/US12/40736 filed on Jun. 4, 2012, the entirety of which is hereby incorporated by reference. Other configurations are possible. 
         [0024]    Referring now to  FIGS. 4-5 , the example volumetric expander device  112  (sometimes referred to as an “expander”) includes two rotors  320 ,  322 . The rotors  320 ,  322  are helical in configuration and rotate relative to one another in a coordinated fashion. Fluid provided at a fluid inlet  310  of the volumetric expander device  112  causes the rotors  320 ,  322  to spin as the fluid moves through the volumetric expander device  112  to an outlet  312 . Typically, this fluid is derived from exhaust gases of the power source  102  and includes either exhaust gases or other fluids derived from a Rankine cycle. The use and operation of a volumetric expander in a Rankine cycle is described in published PCT International Patent Application WO 2013/130774, the entirety of which is incorporated by reference herein. Torque generated by the volumetric expander device  112  is delivered to the power source  102  or other components. 
         [0025]    In one design including a fuel cell, a compressor provides oxygen to the fuel cell stack. The higher the pressure, the greater the concentration of oxygen, so if the hydrogen fuel is increased to the fuel cell stack the amount of electricity generated increases. To recoup some of the energy used by the compressor in providing high pressure to the fuel cell stack, an expander can be used. The expander, which is attached directly to the roots compressor, controls the pressure built up in the fuel cell stack. 
         [0026]    In this example, each of the rotors  320 ,  322  has two lobes  324 . These lobes  324  intermesh as the rotors  320 ,  322  spin. More or fewer lobes can be used. 
         [0027]    One non-limiting example of a volumetric expander device is described in International Patent Application No. PCT/US13/28273 filed on Feb. 28, 2013, the entirety of which is hereby incorporated by reference. Other configurations are possible. 
         [0028]    Referring now to  FIGS. 6-8 , the volumetric assembly  104  is shown again. 
         [0029]    In this example, the fluid inlet  210  of the volumetric supercharger device  110  is connected to an inlet duct  510  that passes fluid through a passage  512  formed by the inlet duct  510  and into the volumetric supercharger device  110 . In addition, the fluid outlet  312  of the volumetric expander device  112  is connected to an outlet duct  520  so that fluid from the volumetric expander device  112  passes through a passage  522  as the fluid exits the volumetric expander device  112 . 
         [0030]    As shown in  FIGS. 7-8 , the ducts  510 ,  512  are positioned to converge so that the ducts  510 ,  512  abut one another. The duct  510  includes an aperture  516  and the duct  520  includes an aperture  526  that generally align with one another as the ducts  510 ,  512  abut. A flexible membrane  610  is positioned within these apertures  516 ,  526  to close the apertures  516 ,  526  so that fluid passing through the passage  512  does not mix with fluid passing through the passage  522 . 
         [0031]    In this example, the volumetric assembly  104  is controlled so that the pressure waves at the flexible membrane  610  are generally  180  degrees out of phase with each other. In other words, the volumetric supercharger device  110  and the volumetric expander device  112  are controlled so that the inlet pressure for the volumetric supercharger device  110  is generally  180  degrees out of phase with the outlet pressure for the volumetric expander device  112 . Referring to  FIG. 10 , schematic graphical depictions of the frequency and amplitude of the cyclical inlet pressure  1002  of the volumetric supercharger device  110  and the cyclical outlet pressure  1004  of the outlet pressure for the volumetric expander device  1112 . As can be seen, the inlet pressure  1002  is shown as being  180  degrees out of phase with the outlet pressure  1004 , wherein the inlet and outlet pressure  1002 ,  1004  have the same amplitude and frequency. The resulting additive combination of the inlet and outlet pressure  1002 ,  1004  is shown at pressure line  1006  which is shown as being completely flat as the inlet and outlet pressures  1002 ,  1004  completely cancel each other out. It is noted that pressure line  1006 , which is reflective of any remaining non-cancelled sound, may have a non-zero value where the inlet and outlet pressure  1002 ,  1004  do not completely cancel each other out. The addition of the oscillating inlet and outlet pressures  1002 ,  1004  will not cancel each other out completely if the amplitudes are different, if the frequency is different, and/or the phases are not fully out of phase with each other. Also, cancellation may not occur in certain instances where the supercharger rotors and the expander rotors have a different number of lobes. In one example, a four lobe compressor used in conjunction with a four lobe expander running at half the speed of the compressor will result in only half of the noise being cancelled if the pressure amplitudes are the same. 
         [0032]    In such a configuration, noise associated with the fluids flowing through the ducts  510 ,  520  can be attenuated. Specifically, some of the kinetic energy from the fluids flowing through one of the ducts  510 ,  520  is transferred to the other of the ducts  510 ,  520  through the flexible membrane at given periods of time to attenuate noise. 
         [0033]    In order to accomplish the attenuation, the number of lobes of the rotors for each volumetric device is equal if the speed (i.e., revolutions per minute) is equal. If one volumetric device runs more quickly than the other, then the number of lobes must be varied such that the ratio of the speed equals the ratio of the lobes. 
         [0034]    For example, in the depicted embodiment, the volumetric supercharger device  110  has four lobes  224  per rotor  220 ,  222 , and the volumetric expander device  112  has two lobes  324  per rotor  320 ,  322 . In such a configuration, the volumetric expander device  112  is run at twice the speed of the volumetric supercharger device  110   
         [0035]    The flexible member  610  is located near the volumetric assembly  104 , so that temperature and pressure in each of the ducts  510 ,  520  will generally be the same. This will make the wavelength at the pulsation frequency very close to the same in each of the ducts  510 ,  520 . 
         [0036]    The flexible membrane  610  is, in this example, capable of handling 1 to 2 psi pressure inputs and is generally acoustically transparent (i.e., has a high degree of flexibility) to allow as much communication between the ducts  510 ,  520  as possible. The material for the flexible membrane  610  is configured to be soft (flexible) but also be tough. One possible example of such as material is Mylar. Other polymeric materials can be used. 
         [0037]    The flexible member  610  can be configured with circumferential folds to allow for a large degree of motion. For example, the flexible member  610  includes folds  624  located at ends  622  of the flexible member  610  that are attached to the ducts  510 ,  520 . This allow for maximum flex for the flexible member  610  when mounted to the ducts  510 ,  520 . Other configurations are possible. 
         [0038]    Referring now to  FIG. 9 , an alternative example system  700  is shown. The system  700  can be used in conjunction with an internal combustion engine or a fuel cell, as described above. 
         [0039]    The system  700  includes an inlet  702  coupled to a roots expander. The inlet  702  leads into a main pipe  706 . The main pipe  706  is, in turn, connected to an outlet  704 . The path formed by  702 ,  706 ,  704  allows the fluid from the expander to flow therethrough. 
         [0040]    As shown, the main pipe  706  surrounds a second set of pipes. This second set of pipes includes an inlet pipe  710  and an outlet pipe  712 . The outlet pipe  712  is connected to the inlet of the roots compressor. 
         [0041]    Positioned between the inlet and outlet pipes  710 ,  712  is a flexible membrane  720 . This flexible membrane  720  functions in a similar manner to the flexible member  610  described above. By controlling the timing of the flow of fluids through the two passages (as described above), the flexible membrane  720  can provide noise cancelation benefits. 
         [0042]    Alternative designs can be used. For example, in one alternative embodiment, the ducts are located a distance apart, and a “Tee” duct or tube is run therebetween. One or more flexible membrane is positioned in the Tee duct to provide the acoustical performance. A length of the Tee duct can be varied to achieve the desired acoustical performance for a given application. For example, the length of the tube may be adjusted to adjust the distance from the source to the cancellation membrane to ensure that the pressures are 180 degrees out of phase. Other examples are possible. 
         [0043]    While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.