Method and apparatus for reducing noise in a roots-type blower

Abstract

A Roots-type blower comprises a housing defining a rotor chamber and an inlet and outlet to the rotor chamber. First and second rotors are mounted in the rotor chamber, each rotor defining a plurality of lobes, adjacent lobes and the housing cooperating to define gas transport chambers. The blower is configured so that a net flow rate of gas into a gas transport chamber is generally or approximately constant, whereby a change in gas pressure in the gas transport chamber is generally or approximately linear, as the gas transport chamber approaches the outlet. In one embodiment, this is accomplished by providing flow channels extending from the outlet towards the inlet, and from the inlet towards the outlet, corresponding to each rotor. The flow channels permit gas to flow from the high pressure outlet to a gas transport chamber and from the gas transport chamber to the low pressure inlet. The resulting amelioration of pressure spikes associated with flow back substantially reduces the operational noise level of the blower.

1 . A noise reducing configuration for a Roots-type blower comprising: 
 a housing defining a rotor chamber, said rotor chamber comprising having an inlet and an outlet;    a first and a second rotor rotatably mounted in said chamber, each rotor defining a plurality of lobes, adjacent lobes of each rotor cooperating with said housing to define at one or more times gas transport chambers, said rotors configured to move gas from said inlet via said gas transport chamber to said outlet; and    at least one outlet gas flow channel extending from said outlet along an inner surface of said housing at said rotor chamber in a direction opposite a direction of rotation of said rotor, said at least one outlet gas flow channel configured to permit gas to flow from said outlet into a gas transport chamber as said lobes of said rotor rotate towards said outlet, said at least one outlet gas flow channel configured so that a pressure of said gas in said chamber as said chamber moves towards said outlet changes at an approximately linear rate.    
   
   
       2 . The blower in accordance with  claim 1  including at least one outlet gas flow channel for each of said rotors, said outlet gas flow channel having a first end and a second end, said second end located at said outlet and said first end spaced therefrom in the direction opposite said direction of rotation of said rotor.  
   
   
       3 . The blower in accordance with  claim 1  wherein each outlet gas flow channel has a cross-sectional area which increases moving in the direction of the first end to the second end thereof.  
   
   
       4 . The blower in accordance with  claim 1  wherein said outlet gas flow channel has a cross-sectional area which increases non-linearly moving in the direction of the first end of the second end thereof.  
   
   
       5 . The blower in accordance with  claim 3  wherein said increase in area is associated with at least an increase in a depth of said channel.  
   
   
       6 . The blower in accordance with  claim 1  including at least one inlet flow channel corresponding to at least one of said rotors, said at least one inlet flow channel extending from said inlet along an inner surface of said rotor chamber in an opposite direction as the direction of rotation of said rotor, said inlet flow channel configured to permit gas to flow from a chamber to said inlet.  
   
   
       7 . The blower in accordance with  claim 1  wherein said Roots-type blower comprises part of a mechanical ventilator.  
   
   
       8 . The blower in accordance with  claim 1  wherein said rate of change of pressure of said gas varies from linearity by no more than about 10%.  
   
   
       9 . The blower in accordance with  claim 1  wherein said rate of change of pressure of said gas varies from linearity no more than about 5%.  
   
   
       10 . A noise reducing configuration for a Roots-type blower comprising: 
 a housing defining a rotor chamber, said rotor chamber having an inlet and an outlet;    a first and a second rotor rotatably mounted in said chamber, each rotor defining a plurality of lobes, adjacent lobes of each rotor cooperating with said housing to define at one or more times gas transport chambers, said rotors configured to move gas from said inlet via said gas transport chamber to said outlet; and    at least one outlet gas flow channel extending from said outlet along an inner surface of said housing in a direction opposite a direction of rotation of said rotor, said at least one outlet gas flow channel configured to permit gas to flow from said outlet into a gas transport chamber as said lobes of said rotor rotate towards said outlet, said at least one outlet gas flow channel configured so that a gas flow rate from said outlet into said gas transport chamber is approximately constant.    
   
   
       11 . The blower in accordance with  claim 10  including at least one outlet gas flow channel for each of said rotors, said outlet gas flow channel having a first end and a second end, said second end located at said outlet and said first end spaced therefrom in the direction opposite said direction of rotation of said rotor.  
   
   
       12 . The blower in accordance with  claim 10  wherein each outlet gas flow channel has a cross-sectional area which increases moving in the direction of the first end to the second end thereof.  
   
   
       13 . The blower in accordance with  claim 10  wherein said outlet gas flow channel has a cross-sectional area which increases non-linearly moving in the direction of the first end of the second end thereof.  
   
   
       14 . The blower in accordance with  claim 12  wherein said increase in area is associated with at least an increase in a depth of said channel.  
   
   
       15 . The blower in accordance with  claim 10  including at least one inlet flow channel corresponding to at least one of said rotors, said at least one inlet flow channel extending from said inlet along an inner surface of said rotor chamber in an opposite direction as the direction of rotation of said rotor, said inlet flow channel configured to permit gas to flow from a chamber to said inlet.  
   
   
       16 . The blower in accordance with  claim 10  wherein said Roots-type blower comprises part of a mechanical ventilator.  
   
   
       17 . The blower in accordance with  claim 10  wherein said gas flow rate changes by no more than about 10%.  
   
   
       18 . The blower in accordance with  claim 10  wherein said gas flow rate changes by no more than about 5%.  
   
   
       19 . A noise reducing configuration for a Roots-type blower comprising: 
 a housing defining a rotor chamber, said rotor chamber having an inlet and an outlet;    a first and a second rotor rotatably mounted in said chamber, each rotor defining a plurality of lobes, adjacent lobes of each rotor cooperating with said housing to define at one or more times gas transport chambers, said rotors configured to move gas from said inlet via said gas transport chambers to said outlet; and    at least one outlet gas flow channel extending from said outlet along an inner surface of said housing in a direction opposite to a direction of rotation of said rotor, said at least one outlet gas flow channel configured to permit gas to flow from said outlet into a gas transport chamber as said lobes of said rotor rotate towards said outlet, said at least one outlet gas flow channel defining a flow area which increases generally non-linearly towards the direction of said outlet.    
   
   
       20 . The blower in accordance with  claim 19  wherein a width of said at least one outlet gas flow channel is generally constant and a depth of said at least one channel increases non-linearly towards the direction of said outlet.  
   
   
       21 . The blower in accordance with  claim 19  including at least one outlet gas flow channel for each of said rotors, said outlet gas flow channel having a first end and a second end, said second end located at said outlet and said first end spaced therefrom in the direction opposite said direction of rotation of said rotor.  
   
   
       22 . The blower in accordance with  claim 19  wherein said increase in area is associated with at least an increase in a depth of said channel.  
   
   
       23 . The blower in accordance with  claim 19  including at least one inlet flow channel corresponding to at least one of said rotors, said at least one inlet flow channel extending from said inlet along an inner surface of said rotor chamber in an opposite direction as the direction of rotation of said rotor, said inlet flow channel configured to permit gas to flow from a chamber to said inlet.  
   
   
       24 . The blower in accordance with  claim 19  wherein said Roots-type blower comprises part of a mechanical ventilator.  
   
   
       25 . A noise reducing configuration for a Roots-type blower comprising: 
 a housing defining a rotor chamber, said rotor chamber having an inlet and an outlet;    a first and a second rotor rotatably mounted in said chamber, each rotor defining a plurality of lobes, adjacent lobes of each rotor cooperating with said housing to define at one or more times gas transport chambers, said rotors configured to move gas from said inlet via said gas transport chambers to said outlet;    at least one outlet gas flow channel corresponding to said first rotor, said at least one outlet gas flow channel extending from said outlet along an inner surface of said housing in a direction opposite a direction of rotation of said first rotor, said at least one outlet gas flow channel configured to permit gas to flow from said outlet into a gas transport chamber between two lobes of said first rotor as said lobes of said first rotor rotate towards said outlet;    at least one outlet gas flow channel corresponding to said second rotor, said at least one outlet gas flow channel extending from said outlet along an inner surface of said housing in a direction opposite a direction of rotation of second first rotor, said at least one outlet gas flow channel configured to permit gas to flow from said outlet into a gas transport chamber between two lobes of said second rotor as said lobes of said second rotor rotate towards said outlet;    at least one inlet gas flow channel corresponding to said first rotor, said at least one inlet gas flow channel extending from said inlet along an inner surface of said housing at said rotor chamber in a direction of rotation of said first rotor, said at least one inlet gas flow channel configured to permit gas to flow from said gas transport chamber between two lobes of said first rotor back to said inlet as said lobes of said first rotor rotate towards said outlet; and    at least one inlet gas flow channel corresponding to said second rotor, said at least one inlet gas flow channel extending from said inlet along an inner surface of said housing at said rotor chamber in a direction of rotation of said second rotor, said at least one inlet gas flow channel configured to permit gas to flow from said gas transport chamber between two lobes of said second rotor back to said inlet as said lobes of said second rotor rotate towards said outlet.    
   
   
       26 . The blower in accordance with  claim 25  wherein said inlet and outlet gas flow channels corresponding to said first and second rotors are configured such that a net rate of gas flow into said gas transport chambers is approximately constant.  
   
   
       27 . The blower in accordance with  claim 25  wherein said inlet and outlet gas flow channels corresponding to said first and second rotors are configured to cause an approximately linear rate of pressure change within said gas transport chambers.  
   
   
       28 . The blower in accordance with  claim 25  wherein said outlet gas flow channels corresponding to said first and second rotors have a cross-sectional area which increases generally non-linearly moving in the direction of said outlet.  
   
   
       29 . The blower in accordance with  claim 28  wherein said outlet gas flow channels corresponding to said first and second rotors have a cross-sectional area which increases continuously moving in the direction of said outlet.  
   
   
       30 . The blower in accordance with  claim 25  wherein said Roots-type blower comprises part of a mechanical ventilator.  
   
   
       31 . The blower in accordance with  claim 26  wherein said gas flow rate changes by no more than about 10%.  
   
   
       32 . The blower in accordance with  claim 26  wherein said gas flow rate changes by no more than about 5%.  
   
   
       33 . The blower in accordance with  claim 27  wherein said rate of change of pressure of said gas varies from linearity by no more than about 10%.  
   
   
       34 . The blower in accordance with  claim 26  wherein said rate of change of pressure of said gas varies from linearity changes by no more than about 5%.  
   
   
       35 . A method for configuring a gas flow path for providing a flow of gas between a port of a Roots-type blower and a gas transport chamber formed between lobes of at least one rotor of said blower, comprising the steps of: 
 selecting a length for said flow path;    selecting a desired gas transport chamber function that defines desired values of a characteristic of gas in said gas transport chamber as a function of rotor position;    selecting an area function that defines a cross-sectional area of said flow path along said length of said flow path;    calculating estimated values of said characteristic of said gas in said gas transport chamber corresponding to said area function;    comparing said estimated values to said desired values;    repeating said steps of selecting an area function, calculating estimated values, and comparing said estimated values to said desired values until said estimated values are approximately equal to said desired values.    
   
   
       36 . The method of  claim 35  wherein said length of said flow path comprises a taper angle.  
   
   
       37 . The method of  claim 36  wherein said rotor position is represented by a taper time.  
   
   
       38 . The method of  claim 35  wherein said characteristic of said gas in said gas transport chamber comprises a pressure of said gas.  
   
   
       39 . The method of  claim 38  wherein said desired gas transport chamber function comprises an approximately linear rate of change in pressure of gas in said gas transport chamber.  
   
   
       40 . The method of  claim 35  wherein said characteristic of said gas in said gas transport chamber comprises a flow rate of gas into said gas transport chamber.  
   
   
       41 . The method of  claim 40  wherein said desired gas transport chamber function comprises an approximately constant rate of gas flow to said gas transport chamber.  
   
   
       42 . The method of  claim 35  wherein said area function comprises a constant component and a variable component.  
   
   
       43 . The method of  claim 42  wherein said constant component comprises a leakage area.  
   
   
       44 . The method of  claim 42  wherein said variable component comprises a polynomial.  
   
   
       45 . The method of  claim 44  where said polynomial comprises a polynomial of the form Et 4 +Ft 7 +Gt 12  where “E,” “F,” and “G” are constants and wherein “t” is a normalized taper time.  
   
   
       46 . The method of  claim 45  wherein E equals approximately 0.007 in. 2 , F equals approximately 0.02 in. 2 , and G equals approximately 0.007 in. 2 .  
   
   
       47 . The method of  claim 45  wherein E equals approximately 0.001 in. 2 , F equals zero, and G equals approximately 0.001 in.  
   
   
       48 . The method of  claim 35  wherein said port comprises an outlet port of said blower.  
   
   
       49 . The method of  claim 35  wherein said port comprises an inlet port of said blower.  
   
   
       50 . The method of  claim 35  further comprising the step of configuring a gas flow channel that corresponds to said area function.  
   
   
       51 . The method of  claim 50  wherein said gas flow channel comprises a generally constant width.  
   
   
       52 . The method of  claim 51  wherein a depth of said gas flow channel increases along its length in a generally non-linear manner.  
   
   
       53 . The method of  claim 50  wherein said gas flow channel comprises an outlet flow channel.  
   
   
       54 . The method of  claim 50  wherein said gas flow channel comprises an inlet flow channel.  
   
   
       55 . The method of  claim 35  wherein said Roots-type blower comprises part of a mechanical ventilator.  
   
   
       56 . A method for configuring a gas flow path for providing a flow of gas between a port of a Roots-type blower and a gas transport chamber formed between lobes of at least one rotor of said blower, comprising the steps of: 
 selecting a length for said flow path;    selecting a desired gas transport chamber function that defines desired values of a characteristic of gas in said gas transport chamber as a function of rotor position;    selecting an initial incremental rotor position;    calculating an initial desired cross-sectional flow area corresponding to said gas transport chamber function at said initial incremental rotor position;    selecting a succeeding incremental rotor position;    calculating a succeeding desired cross-sectional flow area corresponding to said gas transport chamber function at said succeeding incremental rotor position;    repeating said steps of selecting a succeeding incremental rotor position and calculating a succeeding desired cross-sectional flow area for rotor positions traversing said length of said flow path.    
   
   
       57 . The method of  claim 56  wherein said length of said flow path comprises a taper angle.  
   
   
       58 . The method of  claim 57  wherein said rotor position is represented by a taper time.  
   
   
       59 . The method of  claim 56  wherein said characteristic of said gas in said gas transport chamber comprises a pressure of said gas.  
   
   
       60 . The method of  claim 59  wherein said desired gas transport chamber function comprises an approximately linear rate of change in pressure of gas in said gas transport chamber.  
   
   
       61 . The method of  claim 56  wherein said characteristic of said gas in said gas transport chamber comprises a flow rate of gas into said gas transport chamber.  
   
   
       62 . The method of  claim 61  wherein said desired gas transport chamber function comprises an approximately constant rate of gas flow to said gas transport chamber.  
   
   
       63 . The method of  claim 56  wherein said port comprises an outlet port of said blower.  
   
   
       64 . The method of  claim 56  wherein said port comprises an inlet port of said blower.  
   
   
       65 . The method of  claim 56  further comprising the step of configuring a gas flow channel that corresponds to said desired cross sectional flow areas.  
   
   
       66 . The method of  claim 65  wherein said gas flow channel comprises a generally constant width.  
   
   
       67 . The method of  claim 66  wherein a depth of said gas flow channel increases along its length in a generally non-linear manner.  
   
   
       68 . The method of  claim 65  wherein said gas flow channel comprises an outlet flow channel.  
   
   
       69 . The method of  claim 65  wherein said gas flow channel comprises an inlet flow channel.  
   
   
       70 . The method of  claim 56  wherein said Roots-type blower comprises part of a mechanical ventilator.