阅读说明：本技术 具有噪音衰减通道的真空泵 (Vacuum pump with noise attenuation channel ) 是由 M.J.卢卡斯 T.霍拉米-佐伊 C.道塞特 J.B.塔米尼奥 G.隆巴尔 于 2019-12-20 设计创作，主要内容包括：真空罗茨鼓风机包括转子,所述转子能够旋转,以从入口捕获气体,并且进一步旋转,以从出口排放所捕获的气体。所捕获的气体被保持在形成在转子的凸叶与转子在其内旋转的相邻壳体之间的凹穴内。真空罗茨鼓风机包括压力释放系统,所述压力释放系统能够将压力释放气体输送到凹穴。压力释放系统包括音速通道,所述音速通道被构造为随着压力释放系统利用压力释放气体填充凹穴而产生阻塞流动状态。在一个形式中,压力释放气体可为冷却气体,但也设想了其它形式,例如,周围环境空气。(The vacuum roots blower includes a rotor that is rotatable to capture gas from an inlet and further rotated to discharge the captured gas from an outlet. The trapped gas is retained within pockets formed between the lobes of the rotor and the adjacent housing within which the rotor rotates. The vacuum roots blower includes a pressure relief system capable of delivering a pressure relief gas to the pockets. The pressure relief system includes a sonic passage configured to create a blocked flow condition as the pressure relief system fills the pocket with pressure relief gas. In one form, the pressure relief gas may be a cooling gas, but other forms, such as ambient air, are also contemplated.)

1. An apparatus, comprising:

a vacuum pump housing having an inlet configured to receive an incoming flow of compressible fluid, an outlet configured to receive an outgoing flow of compressible fluid, and a pressure relief channel having a pressure relief inlet intermediate the inlet and the outlet configured to provide an incoming flow of pressure relief fluid; and

a pair of intermeshing rotary members supported for complementary rotation within the vacuum pump housing, the rotary members and vacuum pump housing forming respective operative volumes therebetween, the operative volumes being rotatable with the rotary members, and wherein the operative volumes are alterable in dependence upon rotation of the rotary members, each of the respective operative volumes having the following regions: (1) open for inlet/closed for pressure relief channel/closed for outlet; (2) closed for inlet/open for pressure relief inlet/closed for outlet; and (3) closed for the inlet/closed for the pressure relief channel/open for the outlet;

wherein the pressure relief channel comprises a restriction in which the cross-sectional area is dimensioned to produce a sonic condition resulting in a choked flow condition of the restriction during at least a portion of when each of the respective operating volumes is in the region (2).

2. The apparatus of claim 1, wherein the pressure relief inlet is configured as an elongated inlet to the respective volume.

3. The apparatus of claim 2, wherein the restriction is a throat of a pinch-and-spread valve.

4. The apparatus of claim 2, wherein the pressure relief passage flows through a valve having a variable throat area, and wherein the pressure relief inlet is positioned between about 80 degrees and 140 degrees from the 12 o' clock position.

5. The apparatus of claim 4, wherein the region (2) occurs over an arc length of rotation of at least 35 degrees of one of the intermeshing rotating members.

6. The apparatus of claim 5, wherein region (2) occurs over an arc length of rotation of at least 60 degrees of one of the intermeshing rotating members, and wherein the restriction is a variable throat area.

7. The apparatus of claim 5, wherein the operating volume is at a pressure less than the static pressure in the outlet as the operating volume first transitions from region (2) to region (3), and wherein a flow path through the pressure relief channel to the pressure relief inlet is free of passive sound attenuating structures.

8. The apparatus of claim 5, wherein the vacuum pump housing further comprises a cooling air inlet disposed between the pressure relief channel and the outlet, and wherein the pressure relief channel is routable from a cooling air conduit that supplies cooling air to the cooling air inlet.

9. The apparatus of claim 5, wherein the pressure relief channel includes an end in fluid communication with ambient air such that the pressure relief channel is configured to convey ambient air, and wherein the vacuum pump housing is free of sound attenuating devices.

10. An apparatus, comprising:

a roots vacuum pump having a pair of counter-rotating rotors configured to be cooperatively engaged and rotate in engagement with each other to draw a vacuum, each of the pair of counter-rotating rotors having a plurality of respective lobes;

an inlet configured to provide a compressible fluid to a suction side of the roots vacuum pump;

an outlet positioned opposite the inlet and configured to flow the compressible fluid; and

a pair of pressure relief passages having respective openings into the roots vacuum pump, and disposed on opposite sides of the roots vacuum pump, and configured to provide a pressure relief fluid;

wherein each of the pair of counter-rotating rotors includes a pressure relief rotatable position in which adjacent lobes form a volume in fluid communication with a respective one of the pair of pressure relief passages and in which adjacent lobes obstruct fluid communication from either of the inlet and the outlet, each of the pair of pressure relief passages including a restriction sized to form a shockwave when pressure relief fluid flows toward the respective volume during operation of the Roots vacuum pump.

11. The apparatus of claim 10, wherein the pressure relief passage comprises a converging-diverging passage having a throat, the throat forming the restriction.

12. The apparatus as claimed in claim 10 wherein the pressure relief passage is in the form of an elongate opening in the roots vacuum pump, the elongate opening being in fluid communication with the volume when each of the pair of counter-rotating rotors is in a pressure relief rotatable position.

13. The apparatus of claim 12, wherein the restriction is a variable area restriction.

14. The apparatus as claimed in claim 13, wherein the volume is formed over an angular range of motion of adjacent lobes of at least 45 degrees, wherein the pressure relief passage is free of passive sound attenuating structures, and wherein the roots vacuum pump is coupled with a control system that is capable of automatically adjusting the variable area restriction.

15. The apparatus of claim 14, wherein the pressure relief rotatable position of adjacent lobes forms a volume open to the pressure relief passage when a trailing lobe of an adjacent lobe spans an angle between 5 and 15 degrees after the inlet is closed.

16. The apparatus as claimed in claim 12, further comprising a cooling gas inlet configured to provide cooling gas and positioned intermediate said outlet and said pressure relief passage, and wherein said respective openings permit fluid entry into said roots vacuum pump over an angular range of motion of said pair of counter-rotating rotors, and wherein said angular range of motion is at an arc position that obstructs fluid entry via said cooling gas inlet.

17. The apparatus of claim 12, wherein the pressure relief channel includes an opening to ambient such that ambient air acts as the pressure relief fluid flowing into the respective volume when each of the pair of counter-rotating rotors is in the pressure relief rotatable position.

18. The method comprises the following steps:

rotating a first rotor of a pair of intermeshing first and second rotors associated with a vacuum roots blower having an inlet and an outlet;

flowing a pressure relief fluid into a volume created between adjacent lobes of the first rotor as the first rotor passes through an opening from a pressure relief passage, the inlet and the outlet being blocked by adjacent lobes as the pressure relief fluid flows into the volume;

forming a shock wave in a restriction formed in the pressure relief passage; and

after the pressure relief fluid begins to flow, the flow of pressure relief fluid is stopped once the first rotor has traversed at least 45 degrees.

19. The method of claim 18, further comprising varying a cross-sectional area of the restriction during flow.

20. The method of claim 19, further comprising flowing fluid within the pressure relief channel directly to the opening without forming a sound attenuating chamber volume that is larger in cross-sectional area than the pressure relief channel.

Technical Field

The present invention relates generally to vacuum roots blowers and, more particularly, but not exclusively, to noise attenuation in vacuum roots blowers.

Background

Noise generated during operation of vacuum roots blowers is still an area of concern. Some existing systems have various disadvantages with respect to certain applications. Therefore, there remains a need for further contributions in this area of technology.

Disclosure of Invention

One embodiment of the present invention is a unique pressure relief system for a vacuum roots blower. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for attenuating noise in a vacuum roots blower. Other embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and drawings provided herein.

Drawings

FIG. 1 depicts a prior art embodiment of a vacuum Roots blower.

FIG. 2 depicts an embodiment of a vacuum Roots blower having a pressure relief system.

FIG. 3 depicts an embodiment of a vacuum Roots blower having a pressure relief system.

Fig. 4 illustrates the operation of the pressure relief system.

Fig. 5 illustrates the operation of the pressure relief system.

Fig. 6 illustrates the operation of the pressure relief system.

Fig. 7 illustrates the operation of the pressure relief system.

Fig. 8 illustrates the operation of the pressure relief system.

Fig. 9 illustrates the operation of the pressure relief system.

Fig. 10 illustrates the operation of the pressure relief system.

Fig. 11 illustrates the operation of the pressure relief system.

Fig. 12 illustrates the operation of the pressure relief system.

Fig. 13 illustrates the operation of the pressure relief system.

Fig. 14 illustrates the operation of the pressure relief system.

Fig. 15 illustrates the operation of the pressure relief system.

Fig. 16 illustrates the operation of the pressure relief system.

Fig. 17 illustrates the operation of the pressure relief system.

Fig. 18 illustrates the operation of the pressure relief system.

Fig. 19 illustrates the operation of the pressure relief system.

Fig. 20 illustrates the operation of the pressure relief system.

Fig. 21 illustrates the operation of the pressure relief system.

Fig. 22 illustrates the operation of the pressure relief system.

Fig. 23 illustrates the operation of the pressure relief system.

Fig. 24 illustrates the operation of the pressure relief system.

Fig. 25 illustrates the operation of the pressure relief system.

Fig. 26 illustrates the operation of the pressure relief system.

Fig. 27 illustrates the operation of the pressure relief system.

Fig. 28 illustrates the operation of the pressure relief system.

Fig. 29 illustrates the operation of the pressure relief system.

Fig. 30 illustrates the operation of the pressure relief system.

Fig. 31 shows an embodiment of the housing.

Fig. 32 illustrates an embodiment of a housing and valve member.

Detailed Description

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.

Referring to FIG. 1, a prior art vacuum Roots blower 50 is illustrated having an inlet 52 configured to supply fluid to a pair of intermeshing rotors 54 and 56, the combined rotation of the rotors 54 and 56 in turn delivering the fluid to an outlet 58 for discharge from the blower 50. The pair of intermeshing rotors 54 and 56 are located within a housing 57. In some forms, the rotors 54 and 56 include a two-dimensional cross-sectional profile that is then extruded along a third dimension (aligned with the axis of rotation). The vacuum blower 50 is configured to pull fluid from the inlet 52 and drive it toward the outlet 58. Some embodiments of the prior art vacuum blower also include a cool air inlet, such as cool air inlet 60 depicted in fig. 1. The cold air inlet serves to reduce the temperature of the air exiting the outlet 58, but not all prior art blowers 50 include a cold air inlet. It will be appreciated that any other suitable cooling gas may be used in addition to air. However, for ease of description, reference will be made to "cooling air" or "cold air," without intending to limit such fluids to atmospheric air components. Roots blowers (e.g., those described herein) find many applications in the industry because in some forms they are configured as oil-free devices. Some applications for roots blowers are in the food processing industry, in wastewater treatment plants, in pumping dry goods into tank trucks and in vacuum pumps used in street cleaning machines.

During the rotation sequence, the rotors 54 and 56 are configured to capture a pocket of fluid from the inlet 52 and rotate the pocket to a position to receive air from the cooling air inlet 60 or expose the pocket to the outlet 58 to complete the vacuum process from the inlet 52 to the outlet 58. Pockets are trapped between the lobes of each respective rotor and the housing surface surrounding the rotor, further description of which may be found in the following figures. When the trapped pockets are rotated into place and exposed to the cooling air inlet 60 or outlet 58, a transient or sudden influx of fluid may be experienced, which results in a rapid change in pressure. Such transient or sudden fluid surges may be caused by a relatively large pressure differential existing between any fluid trapped in the pockets and the pressurized fluid at the cooling air inlet 60 and/or outlet 58. Depending on the operating conditions, the higher pressure air from the cooling air inlet 60 or outlet 58 rushing into the trapped pockets may form shock waves or expansion waves or both, which may ring and otherwise cause noise. The formation of the shock wave may occur along the length of the rotor. Although the illustrated embodiment depicts respective rotors 54 and 56 having three lobes each, other embodiments may have a different number of lobes. For example, some embodiments may include four or five lobed rotors.

Turning now to fig. 2 and 3, embodiments of the present application include a pressure relief system 62 for providing pre-injection of fluid into the trapped pocket before the pocket reaches the outlet 58 (in those embodiments without the cooling air inlet 60) or the cooling air inlet 60 itself. The pre-injection of fluid into the rotating trapped pocket may help reduce the pressure differential between it and the outlet to a level where any noise generated by the influx of fluid is reduced and/or mitigated. In some forms, the pressure release may completely eliminate the difference in pressure.

Pressure relief system 62 may include pressure relief passages that flow pressure relief fluid from a fluid source and provide it to a trapped volume captured between the housing and the respective rotor. The illustrated embodiment depicts pressure relief system 62 as including a fluid relief passage from cooling air inlet 60, although other pressure relief fluid sources are contemplated. For example, the pressure relief fluid may originate from the surrounding environment, embodiments of which are described further below.

In the embodiment depicted in fig. 2, pressure relief system 62 includes vent 64, sonic passage 66, and injection port 68, but it will be understood that pressure relief system 62 may take on various shapes and sizes, and may not include all of the components depicted in fig. 2, as will be understood from the description herein. As the rotor 56 rotates to expose the low pressure trapped pockets to the charged pressure relief gas, the pressure relief system 62 is used to provide charging of the pressure relief gas from a source (e.g., cooling air 60) to one side of the vacuum ROOTS blower 50. While the depiction in FIG. 2 shows only one side of the pressure relief system, it will be understood that many embodiments will include a similar pressure relief system on the other side of the vacuum ROOTS blower 50 such that pressure relief gas is also provided to the rotors 54. Additionally, although the illustrated embodiment depicts only one pressure relief channel on each side, some embodiments may include more than one pressure relief channel on each side. For example, in those embodiments having four or five lobed rotors, additional pressure relief passages may be provided on each side to increase the chance and extent that fluid may be supplied to the pockets.

The cooling air inlet 60 may take the form of a single cooling fluid conduit including a bifurcation to direct cooling gas to either side of the vacuum roots blower 50. Such divergence may result in separate cooling air passages 70 to each side of the vacuum blower 50. The cooling air passage 70 leads to a cooling air injection port 72 located near an outlet 74. The cooling air injection ports 72 are generally located adjacent the outlet and serve to reduce the temperature of the fluid being pulled from the inlet 52 to the outlet 58 by the rotating action of the rotors 54 and 56. The openings 76 of the cooling air injection ports 72 may extend along all or a portion of the axial length of the rotors 54 and 56. The openings may further extend circumferentially around the interior of the housing 57 any of a variety of arc distances. In one form, the opening may be centered around the 6 o' clock position and extend over an arc length of 15 degrees, although other positions and ranges of arc lengths are contemplated herein.

As used herein, descriptions relating to clock positions (e.g., "6 o' clock") will be understood to refer to clock positions relative to the rotor 56 depicted in fig. 2 and 3, wherein the rotor rotates in a clockwise direction, as viewed from the perspective of fig. 2 and 3. It will be appreciated that the rotor 54 rotates in a counterclockwise direction, wherein a mirror image of the clock position can be readily determined. The 12 o' clock position will be understood to be a position determined by first drawing a reference line between an inlet side intersection 78 of the arc path swept by the rotors 54 and 56 and an outlet side intersection 80 of the arc path swept by the rotors 54 and 56. A second line is then drawn perpendicular to the reference line, the second line representing the 3 o 'clock-9 o' clock axis. The clock reference line is then plotted perpendicularly from the second line and offset from the reference line, wherein the clock reference line is plotted to locate the topmost and bottommost portions of the arc through which the rotor 56 travels. Although reference will be made herein to clock positions relative to the rotor 56, it will be understood that direct transformations may be made to determine the appropriate clock position of the rotor 54.

Instead of clock positions, angular measurements may also be used herein for reference. It will be understood that such angular measurements may be absolute or relative measurements, depending on the context, where the absolute angular measurement is referenced starting from the 12 o' clock position and progressing in a clockwise direction, as determined above. For the purpose of illustrating only a few non-limiting examples, 12 o' clock is the same as 0 degrees; 3 o' clock is same as 90 degrees; 6 o' clock is the same as 180 degrees, and so on.

The exhaust port 64 is configured to draw cooling air from the cooling air passage 70. Although the discharge openings 64 are shown as channels having rectangular cross-sections extending at high relative angles from the surface of the cooling air channel 70, other shapes and relative orientations are contemplated herein. As depicted, the drain 64 may extend along the entire width of the cooling air channel 70, although other shapes and sizes are also contemplated herein.

The cooling air injection port 68 is configured to provide air drawn by the exhaust port to a point for injection into the interior of the housing 57. Similar to the exhaust port 64, the cooling air injection port 68 is shown as a channel having a rectangular cross-section extending at a high relative angle from the surface of the housing 57. Other shapes and relative orientations are also contemplated herein. The cooling air injection ports 68 may extend any distance along the rotor 56, and in some forms may extend over less than the entire length of the rotor 56, as depicted in the illustrated embodiment. The port 68 may take on a variety of geometric cross-sectional shapes. In some forms, the ports 68 may be a plurality of openings generally converging in an elongated direction, each fed by one or more sonic channels 66, wherein such elongated direction may be along the length of the rotor. The opening of the injection port 68 may extend along an axial distance that is shorter than the axial length of the rotor.

The cooling air injection ports 68 may include an upstream edge formed in the housing 57 that begins at about the 4 o' clock position and extends over an arc length of 5 degrees, although other starting positions and degrees of opening are contemplated herein.

One or both of the exhaust port 64 and the cooling air injection port 68 may include various shapes including, but not limited to, triangular, perforated, and the like. Any suitable shape or shapes are contemplated to provide a suitable pre-injection rate.

Air drawn from cooling air passage 70 via vent 64 is provided to sonic passage 66, which sonic passage 66 is configured to create a choked flow condition. Sonic passage 66 generally includes a narrowed cross-section that creates a sonic choked flow condition. Such a narrowing section may be the throat of a converging-diverging (CD) nozzle, although other shapes are also contemplated. Depending on the flow conditions, which may change during the filling period of the pocket, resulting in a change in position during filling, shock waves may occur but need not occur in various positions in the CD nozzle. In one form, sonic passage 66 is a fixed geometry passage, but other embodiments may include a variable area sonic passage. In one such form, the cross-sectional area of sonic passage 66 may be adjusted in a manner similar to flow adjustment in a variable area valve. Thus, a valve handle may be provided wherein the user may vary the cross-sectional area of sonic passage 66. In other forms, the control system may be coupled to an actuator that is capable of varying the cross-sectional area of the sonic passage. Such actuators may be coupled to any suitable valve arrangement. The control system may be responsive to a sensor configured to detect sound or other vibrations. As will be appreciated, the sonic conditions present in the sonic passage limit the mass flow therethrough and serve to locate the shock waves in the sonic passage 66 away from physical interaction with the rotor 56.

The narrow portion of the passageway providing sonic passage 66 may take various forms in addition to those depicted in the example CD nozzle. For example, a narrowed portion or throat may be formed in the housing near an opening to the chamber (e.g., the opening of the injection port 68), where such opening is elongated in orientation. Accordingly, such embodiments may omit the extended channel 68 depicted as extending from one end of the sonic channel 66 to the housing, and instead include the sonic channel 66 as an elongated slit oriented in the rotor direction. Any changes to sonic passage 66 and/or injection port 68 may be supplied by any of a variety of pressure sources, whether ambient or via cooling air inlet 60. The area of the throat or throat will be understood to remain less than the area from which fluid is drawn from the fluid source (whether the cooling air inlet 60 or the ambient environment, etc.) to ensure that the air is accelerated to the sonic conditions required to form the choked flow.

There may be any number of passage configurations before the opening through which the port 68 injects gas into the interior of the rotor cavity. In one form, as shown, there is a pinch-and-spread valve (CD valve) positioned upstream of the pressure relief opening. In some embodiments, the CD valve may be a continuously contracting and continuously expanding valve, but in other forms the CD valve need not be smoothly continuous in the upstream or downstream sections. In some forms, the pressure relief opening may be a stepped transition, wherein an impingement is formed adjacent the outlet. In embodiments where sonic passage 66 is a Venturi (Venturi), some versions contemplate two or more sonic passages 66 connected in series with each other. Some embodiments may include venturi passages parallel to one another to provide fill gas to the common pocket as the rotor rotates. Instead of a venturi tube, a cylinder with a small diameter middle section may also be used.

The scale depicted in fig. 1-3 represents possible dimensions of the depicted apparatus. It will be understood that in other embodiments, other sizes and/or shapes/configurations of fig. 2-3 are possible.

Turning now to FIGS. 4-16 and 17-29, various calculations are shown comparing the operation of the prior art vacuum Roots blower 50 and the embodiment of the present application having a pressure relief system 62. On each page, the prior art Roots blower is shown on the bottom, while the vacuum Roots blower 50 embodiment of the present application is shown on the top. It will be appreciated that the views have been rotated relative to the configurations shown in figures 1-3. The inlet is shown on the left side of each blower, while the outlet and cooling air inlet are shown on the right side. Fig. 4-16 show pressure contours that begin at 0 degrees relative angle of the rotor in fig. 4 and progress through the rest of fig. 5-16 in 10 degree increments. Fig. 17-29 show mach contours that begin at 0 degrees relative angle of the rotor in fig. 17 and progress through the rest of fig. 18-29 in 10 degree increments. The angular measurements shown in fig. 4-29 are for ease of illustration and do not correspond exactly to the measurements provided herein with respect to the inlet and outlet positions, as will be understood in the context of this description. In other words, 0 degrees in fig. 4 does not correspond to the 12 o' clock position described above.

The 0 degree indication in fig. 4 shows a position where the rotor 56 will sweep past the inlet 52 and thereby close between adjacent lobes of the rotor 56 and form a pocket that will move to the outlet 58 upon further rotation of the rotor 56. Once the pockets are rotated to the outlet 58, any residual gas within the pockets may be vented and the process restarted, before the rotor 56 is rotated into intermeshing engagement with the rotor 54. It will be appreciated that in some modes of operation, the pocket may be at a pressure similar to the pressure of the gas at the outlet 74, while in other modes of operation, the pressure in the pocket may be lower than the pressure of the gas at the outlet 74. When the pressure in the pocket is lower than the pressure at the outlet 74, the gas filling process will take place into the pocket. Fig. 5 shows a position in which the pocket is closed from both the inlet 52 and the pressure relief injection port 68. Such intermediate positions between inlet 52 and port 68 are contemplated in many embodiments herein, but alternative embodiments are also contemplated. Fig. 6 depicts a rotational position of the rotor 56 in which the pocket is initially open to the injection port 68, wherein pressure relief gas may begin to fill into the pocket. Feature 82 shows a change in pressure through the fill port 68, indicating the fill process. Fig. 7 shows continued filling of the pocket by the pressure relief system 62.

Fig. 8-11 show the low pressure at the throat of sonic passage 66 as the gas reaches its mass flow rate limit through passage 66 due to the area ratio. Feature 84 shows the low pressure as a dark band region at the throat of sonic channel 66. The area at the throat of sonic passage 66 will be less than the area immediately upstream of the throat to ensure subsonic flow acceleration to cause flow blockage. Fig. 12-16 illustrate further rotation of rotor 56, wherein gas is filled into pockets, but no sonic conditions or impingement is created at the throat of sonic passage 66 due to the falling pressure differential between the pockets and injection ports 68 (as gas moves into the pockets). While in the illustrated embodiment, the sonic or impingement formation process is shown to occur from 40-70 degrees, it will be appreciated that such sonic or impingement formation may occur over a greater or lesser range depending on the initial pressure in the pocket, the relative area of the sonic passage 66 as compared to the initial area of flow (e.g., the initial upstream area of the sonic passage 66 when it takes the form of a CD nozzle), and the pressure at the initial area of flow. In some cases, the speed of sound or the impact formation may additionally depend on the rotor speed. In the case of a variable area sonic passage 66, the sonic velocity or impact formation may change as the cross-sectional area changes.

The 0 degree indication in fig. 17 shows a position where the rotor 56 will sweep past the inlet 52 and thereby close between adjacent lobes of the rotor 56 and form a pocket that will move to the outlet 58 upon further rotation of the rotor 56. Fig. 18 shows a position in which the pocket is closed from both the inlet 52 and the pressure relief injection port 68. Such intermediate positions between inlet 52 and port 68 are contemplated in many embodiments herein, but alternative embodiments are also contemplated. Fig. 19 depicts a rotational position of the rotor 56 in which the pocket is first open to the injection port 72, wherein pressure relief gas may begin to fill into the pocket. Feature 86 shows the change in velocity that occurs near the injection port 68, indicating the fill process. Fig. 20 shows continued filling of the pocket by the pressure relief system 62.

21-24 show sonic flow conditions at the throat of sonic passage 66, which may indicate impingement formation as the gas reaches its mass flow rate limit through passage 66 due to area ratio. The features 88 show sonic flow as a dark band region at the throat of the channel 66. Fig. 25-29 illustrate further rotation of rotor 56, wherein gas is filled into pockets, but no sonic or shock conditions are created at the throat of sonic passage 66 due to the falling pressure differential between the pockets and injection ports 68 (as gas moves into the pockets).

From the discussion above, as will be appreciated, the rotors 54 and 56 rotate through several zones that may be characterized by the location of their pockets and whether the pockets are in fluid communication with any corresponding channels (e.g., the inlet 52, the injection ports 68, and the outlet 74). Region (1) may be characterized as a pocket that is open to the inlet 52, closed to the pressure relief passage (e.g., injection port 68), and closed to the outlet 74. Region (2) may be characterized as a pocket that is closed to the inlet 52, open to a pressure relief inlet (e.g., port 68), and closed to the outlet 74. Region (3) may be characterized as a pocket that is closed to the inlet 52, closed to the pressure relief passage (e.g., port 68), and open to the outlet 74. In those embodiments having cooling air inlet 60, another region may be added, characterized by the pocket being closed to inlet 52, open to a pressure relief inlet (e.g., port 68), open to cooling air inlet 60, and closed to outlet 74. Such a region may be identified as region (2 a), wherein region (2) is further characterized by the pocket being closed to the cooling air inlet 60. Yet another area may be added characterized by the pocket being closed to the inlet 52, closed to the pressure relief inlet (e.g., port 68), open to the cooling air inlet 60, and open to the outlet 74. Such a region may be characterized as region (3 a), wherein region (3) is further characterized in that the pocket is closed to the cooling air inlet 60.

In one form, the vacuum roots blower 50 may be devoid of any passive sound attenuating structures on the pressure relief path side (e.g., the pressure relief system 62), such as dampers/foam/porous plates/or the like and/or any tube/chamber type mufflers or traps. In one non-limiting example, the blower 50 and/or the pressure relief system 62 may be devoid of a resonant chamber located immediately outside of the pressure relief inlet opening. An example of a resonant chamber that need not be used in embodiments of the present application is a double-walled chamber that forms a plenum volume that is larger in size than the passageways that supply fluid to and from the plenum. Examples of double-walled chambers include one in which one side of the wall is occupied by the rotor and the other side of the wall forms a chamber volume with the housing, wherein the chamber volume comprises a height and/or depth greater than the size of the pressure relief channel leading to the chamber. An example of a passive sound attenuating structure that may not be present in any of the embodiments of the present application may be found in U.S. patent No. 9,140,260 (e.g., a pulse capture chamber).

It will be appreciated that embodiments may provide, but need not provide, isolation of the pressure relief system 62 from the outlet 58 or for conduits leading from the outlet 58. The term "isolated" or "isolation" is intended to include situations where the pressure relief system 62 is not connected to form a bypass or other recirculation conduit flow path, wherein some amount of gas is drawn from the outlet 58 and circulated back through the pressure relief system 62. The term "isolated" or "isolation" does not include those situations in which the outlet vents to atmosphere and the pressure relief passage is connected to atmosphere.

In some embodiments, the travel arc length associated with the rotor 56 may be at least 35 degrees, wherein the pressure relief channel 62 provides gas into the pocket, and wherein over this arc length the pocket is sealed from the inlet 52 and outlet 58 by virtue of the position of the rotor within the volume (e.g., region (2)), while in other embodiments the travel arc length may be 40, 45, 50, 55, 60, 65, 70, and 75 degrees, and in some forms, may be up to 90 degrees. Different arc lengths of travel are contemplated depending on whether the rotor 56 is a three lobe or a four lobe rotor. It will be understood that the term "sealing" as used in this context includes situations where the rotor may not be in perfect contact along the entire surface, and instead may include elevations or other contact imperfections that allow a small to negligible amount of gas to leak past. Of course, it may also include those cases in which a perfect liquid-tight seal is formed.

The arc of travel associated with the rotor 56 is at least 10 degrees, may be 20 degrees, and in some forms may continue to larger angle rotations, such as those listed above in connection with arc lengths of fluid communication, where sonic conditions are present in the restriction (or opening in those embodiments that include a slot or other similar structure formed in the housing). Thus, the arc length of fluid communication from pressure relief system 62 to the pocket may be substantially consistent with the arc length associated with sonic conditions at the restriction (or opening), but is not necessarily consistent in all embodiments.

The position of the pressure relief system 62 to the upstream edge of the opening in the pocket (e.g., via port 68) may be anywhere between at least 60 degrees and at least 120 degrees from the 12 o' clock position, and may be higher in some forms. The pressure relief passage opening (e.g., through port 68) may be positioned up to a higher angle of 170 degrees. To illustrate only some non-limiting examples, the angular positions may be up to about 125, 130, 135, 140, 145, 150, 155, 160, 165, and 170 degrees.

FIG. 30 depicts a graphical view of pressure within a pocket versus rotational angle of the rotor. The y-axis represents the vacuum pressure within the pocket, with 0% at the top of the y-axis representing 0% vacuum and a lower level of the y-axis representing about 80% vacuum. The x-axis represents the range in which the rotor rotates. As can be seen in the graph, in this example embodiment, the pocket may be closed to the inlet at around 80 degrees, the pocket may be open to the pressure relief at around 100 degrees, and then the pocket may be open to the discharge port at around 160 degrees. Although the pressure rise (or vacuum loss) is shown as occurring in a linear fashion for convenience, no limitation is thereby intended or stated that such pressure rise needs to occur in this manner. As will be appreciated by those skilled in the art, some embodiments may have different pressure rise characteristics. The very rapid rise in pressure (or loss of vacuum) associated with the prior art devices is also shown on the figure.

Fig. 31 depicts an embodiment of the housing 57. Also shown are cooling air passages 70, outlets 58, and inlets 52. The injection port 68 is shown as an elongated opening.

Fig. 32 depicts a view of one embodiment of a housing 57, the housing 57 including injection ports 68 and sonic passage 66 on either side of an open interior into which the rotor is disposed. The injection port 68 on the bottom of the figure is in fluid communication with a valve member 90, which valve member 90 is movable in a direction along its elongated axis. Such a valve member 90 may be movable with the flow path to increase or decrease flow through the injection port 68. In the illustration of fig. 32, the valve member 90 is movable in a left or right direction and, in some forms, is insertable into the interior of the injection port 68. The valve member 90 may be operated manually or through the use of a controller and actuator, as discussed above. Although the illustration depicts only a single valve member 90 used in the lower injection port 68, other embodiments may include a valve member 90 in the upper injection port 68. The valve members 90 used in the flow path to provide fluid to the injection ports 68 may be the same or different.

The physical processes provided by the embodiments described herein are used to attenuate noise. Such physical processes may include the ability to dephase the noise signature (de-phase), for example, by capturing the noise within the pocket with a small throat. Sound may reflect around the throat and become attenuated. Among other additional and/or alternative physical processes, sonic conditions and the resulting fluid velocity through the pressure relief system may act to impede the transmission of noise upstream through sonic passage 66. For example, if a sonic condition occurs at the throat and the fluid accelerates further downstream of the throat toward the pocket as the CD nozzle spreads, then in the presence of such fluid flowing faster than sonic, noise generated within the pocket due to gas influx may not propagate upstream.

One aspect of the present application includes an apparatus comprising: a vacuum pump housing having an inlet configured to receive an incoming flow of a compressible fluid, an outlet configured to receive an outgoing flow of a compressible fluid, and a pressure relief channel having a pressure relief inlet intermediate the inlet and the outlet configured to provide an incoming flow of a pressure relief fluid, and a pair of intermeshing rotary members supported for complementary rotation within the vacuum pump housing, the rotary members and the vacuum pump housing forming respective operative volumes therebetween that rotate with the rotary members, and wherein the operative volumes are variable in accordance with rotation of the rotary members, each of the respective operative volumes having the following regions: (1) open for inlet/closed for pressure relief channel/closed for outlet; (2) closed for inlet/open for pressure relief inlet/closed for outlet; and (3) closed for the inlet/closed for the pressure relief channel/open for the outlet, wherein the pressure relief channel comprises a restriction in which the cross-sectional area is dimensioned to produce a sonic condition resulting in a choked flow condition of the restriction during at least a portion of when each of the respective operating volumes is in the region (2).

Features of the present application include wherein the pressure relief inlet is configured as an elongated inlet to the respective volume.

Another feature of the present application includes wherein the restriction is a throat of a pinch-and-spread valve.

Yet another feature of the present application includes wherein the pressure relief passage flows through a valve having a variable throat area, and wherein the pressure relief inlet is positioned between about 80 degrees and 140 degrees from the 12 o' clock position.

Other features of the present application include wherein the region (2) occurs over an arc length of rotation of at least 35 degrees of one of the intermeshing rotating members.

Other features of the present application include wherein the region (2) occurs over an arc length of rotation of at least 60 degrees of one of the intermeshing rotating members, and wherein the restriction is a variable throat area.

Other features of the present application include wherein the operating volume is at a pressure less than the static pressure in the outlet as the operating volume first transitions from region (2) to region (3), and wherein the flow path through the pressure relief channel to the pressure relief inlet is free of passive sound attenuating structures.

Other features of the present application include wherein the vacuum pump housing further comprises a cooling air inlet disposed between the pressure relief channel and the outlet, and wherein the pressure relief channel is routable from a cooling air duct that supplies cooling air to the cooling air inlet.

Other features of the present application include wherein the pressure relief channel includes an end in fluid communication with ambient air such that the pressure relief channel is configured to convey ambient air, and wherein the vacuum pump housing is free of sound attenuating devices.

Another aspect of the present application includes an apparatus comprising: a roots vacuum pump having a pair of counter-rotating rotors configured to be cooperatively engaged and rotate in engagement with each other to draw a vacuum, each of the pair of counter-rotating rotors having a plurality of respective lobes; an inlet configured to provide a compressible fluid to a suction side of the roots vacuum pump; an outlet positioned opposite the inlet and configured to flow a compressible fluid; and a pair of pressure relief passages having respective openings into the roots vacuum pump, and disposed on opposite sides of the roots vacuum pump, and configured to provide a pressure relief fluid, wherein each of the pair of counter-rotating rotors includes a pressure relief rotatable position in which an adjacent lobe forms a volume in fluid communication with a respective one of the pair of pressure relief passages, and in which the adjacent lobe obstructs fluid communication from either of the inlet and the outlet, each of the pair of pressure relief passages including a restriction sized to form a shockwave when the pressure relief fluid flows toward the respective volume during operation of the roots vacuum pump.

Features of the present application include wherein the pressure relief passage comprises a converging-diverging passage having a throat that forms the restriction.

Another feature of the present application includes wherein the pressure relief passage is in the form of an elongated opening in the roots vacuum pump, the elongated opening being in fluid communication with the volume when each of the pair of counter-rotating rotors is in the pressure relief rotatable position.

Yet another feature of the present application includes wherein the restriction is a variable area restriction.

Other features of the present application include wherein the volume is formed over an angular range of motion of at least 45 degrees of adjacent lobes, and wherein the pressure relief channel is free of passive sound attenuating structures.

Other features of the present application include wherein the pressure relief rotatable position of adjacent lobes forms a volume open to the pressure relief passage when the trailing lobe of the adjacent lobe spans an angle between 5 and 15 degrees after the inlet is closed.

Still other features of the present application include a cooling gas inlet configured to provide cooling gas and positioned intermediate the outlet and the pressure relief passage, and wherein the respective openings permit fluid to enter the roots vacuum pump over an angular range of motion of the pair of counter-rotating rotors, and wherein the angular range of motion is at an arc position that obstructs fluid entry via the cooling gas inlet.

Other features of the present application include wherein the pressure relief passage includes an opening to ambient such that ambient air acts as a pressure relief fluid flowing into the respective volume when each of the pair of counter-rotating rotors is in the pressure relief rotatable position.

Yet another aspect of the present application includes a method comprising: rotating a first rotor of a pair of intermeshing first and second rotors associated with a vacuum roots blower having an inlet and an outlet; flowing a pressure relief fluid into a volume created between adjacent lobes of the first rotor as the first rotor passes through the opening from the pressure relief passage, the inlet and outlet being blocked by the adjacent lobes as the pressure relief fluid flows into the volume; forming a shock wave in a restriction formed in the pressure relief passage; and stopping the flow of the pressure relief fluid once the first rotor has traversed at least 45 degrees after the pressure relief fluid begins to flow.

The features of the present application also include varying a cross-sectional area of the restriction during the flow.

Another feature of the present application further includes flowing fluid within the pressure relief channel directly to the opening without forming a sound attenuating chamber volume that is larger in cross-sectional area than the pressure relief channel.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. It should be understood that while the use of words such as preferred, preferably, preferred or more preferred in the description above indicate that the feature so described may be more desirable, this may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims, it is intended that when words such as "a," "an," "at least one," or "at least a portion" are used, the claims are not intended to be limited to only one item unless specifically stated to the contrary in the claims. When the phrases "at least a portion" and/or "a portion" are used, the object may include a portion and/or the entire object unless specifically stated to the contrary. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.