Low-noise energy-saving roots pump and three-lobe rotor

Abstract

A low-noise energy-saving Roots pump. A pump body comprises a pump housing (11) and rotors. The pump housing (11) and two wall plates together define a pump cavity. A pair of rotors are arranged in parallel in the pump cavity. Backflow channels are arranged in the pump housing (11), so as to allow cooled airflow to flow into the pump cavity through the backflow channels, and the axes of the backflow channels are obliquely arranged relative to a line connecting the centers of the two rotors, so as to allow the cooled airflow to impact the rotors in the rotating directions of the rotors.

Description

A low-noise, energy-saving Roots pump and three-blade rotor Technical Field

[0001] The present invention belongs to the field of supercharging machinery, and in particular relates to a low-noise and energy-saving Roots pump and a three-blade rotor. Background Art

[0002] Roots pumps are characterized by no compression or lubrication within the pump chamber, enabling rapid startup within a wide pressure range, being insensitive to dust and steam, and having low service environment requirements. Therefore, they are widely used in fields such as petroleum, chemical engineering, mining, and manufacturing. As shown in Figure 22, the upper end of the pump housing 11c is provided with an air inlet 12 as the low-pressure end, and the lower end is provided with an exhaust port 13 as the high-pressure end. The two rotors rotate synchronously in opposite directions. At the moment when the base circle volume 16 formed by the rotor and the pump housing 11c is connected to the exhaust port 13, the high-pressure gas at the exhaust port 13 will instantly backflow into the base circle volume 16 in the direction indicated by the arrow m, generating very high noise and increasing energy consumption. Furthermore, due to the small gap between the rotors of the Roots pump, the pump body temperature rises during long-term operation, causing gap mismatch, leading to problems such as rotor interference or friction between the rotor blade peaks and the inner edge of the mechanism. Therefore, some technical solutions adopt a reflux cooling solution, which leads the cooled high-pressure gas from the exhaust port back to the pump chamber of the Roots pump to achieve cooling; in some vacuum pump solutions, a cooling port directly connected to the atmosphere is provided on the pump body to introduce external normal temperature airflow. For example, patent CN211525077U discloses a Roots pump with effective noise reduction. By controlling the structure and area of ​​the cooling port, the flow rate of the cooling gas entering the base circle volume is adjusted to achieve the function of reducing noise. However, the cooling airflow entering the pump chamber repeatedly causes radial impact on the rotor of the Roots pump, causing impact vibration of the entire machine and affecting the life of the entire machine; on the other hand, the kinetic energy of the cooling airflow is eventually dissipated in the form of noise and vibration, resulting in energy waste. Therefore, providing an improved low-noise and energy-saving Roots pump to improve the distribution of the reflux high-pressure cooling airflow has positive significance for increasing the service life of the Roots pump and optimizing energy consumption. Summary of the Invention

[0003] The present invention aims to provide a low-noise, energy-saving Roots pump to improve the distribution of return high-pressure cooling airflow. The present invention also provides a three-blade rotor.

[0004] According to an embodiment of one aspect of the present invention, a low-noise and energy-saving Roots pump is provided, comprising a pump body, wherein the pump body comprises a pump casing and a rotor, a wall panel is provided at each end of the pump casing, the pump casing and the two wall panels together form a pump chamber, and a pair of rotors are arranged in parallel in the pump chamber; it is characterized in that a return channel is provided on the pump casing to allow a cooling air flow to flow into the pump chamber through the return channel, and the axial center line of the return channel is inclined relative to the line connecting the centers of the rotors to allow the cooling air flow to impact the rotor along the direction of rotation of the rotor.

[0005] The tilted return flow channel deflects the cooling gas, preventing direct impact on the rotor shaft. Simultaneously, the cooling airflow impacts the rotor surface in the direction of rotation, providing a boost and reducing the energy consumption of the Roots pump. Furthermore, the cooled, high-pressure gas directly impacting the rotor improves its cooling efficiency.

[0006] Furthermore, in some embodiments, the rotor includes alternately arranged blade peaks and blade valleys, and the blade peaks and blade valleys are respectively configured as circular arcs with the center of the rotor as the center of the circle, and the arc length corresponding to the opening of the reflux channel around the center circumference of the rotor does not exceed the arc length of the blade peak, and the area of ​​the reflux channel controls the flow rate and speed of the reflux gas; the rotor profile between adjacent blade peaks of the rotor and the pump casing define a base circle volume for conveying the gas to be compressed, and the circumferential arc of the base circle volume relative to the center of the rotor is smaller than the arc formed by the reflux channel and the air inlet of the pump body relative to the center of the rotor, and the circumferential arc of the base circle volume relative to the center of the rotor is smaller than the arc formed by the reflux channel and the exhaust port of the pump body relative to the center of the rotor. The large arc of the blade peak can improve the air tightness of the rotor and reduce the leakage loss in the gap between the rotor and the pump casing during the operation of the Roots pump; by controlling the distance between adjacent blade peaks of the rotor and the angular relationship between the air inlet, the return channel opening and the air outlet of the pump casing, leakage in the return channel during the rotation of the rotor can be avoided, thereby reducing energy consumption and improving efficiency.

[0007] Furthermore, in some embodiments, the rotor is configured as an involute rotor, and the extended axis of the return flow channel is tangent to the rotor's base circle. The geometric properties of the involute dictate that the normal to the involute is tangent to the base circle. This tangent position of the extended axis of the return flow channel, i.e., the direction of the return flow channel's jet, to the base circle improves the efficiency of converting the impact force of the high-pressure airflow on the involute portion of the rotor into rotor torque, further improving the energy consumption of the Roots pump.

[0008] Furthermore, in some embodiments, a storage chamber is provided on the pump housing, and the reflux channel is connected between the storage chamber and the pump chamber; wherein the storage chamber is configured to be connected to the external atmosphere to introduce a cooling airflow from the external atmosphere; in other embodiments, the Roots pump further includes a reflux cooling device, which is provided downstream of the pump body and is used to cool the compressed gas discharged from the pump body. The reflux channel is connected to the reflux cooling device to allow partially cooled compressed gas discharged from the pump body to flow back to the pump chamber through the reflux channel via the storage chamber. The cooling gas can be pre-stored in the storage chamber and then sprayed into the pump chamber through the reflux channel. The provision of the storage chamber can simplify the structural design of the reflux channel, reducing its structural volume, while providing a stable gas source for the reflux channel, making the flow of the cooling gas smoother. For Roots pumps with direct exhaust to the atmosphere, the storage chamber is directly connected to the external atmosphere. Since the gas inhaled into the base circle volume is negative pressure gas, the pressure in the storage chamber is much higher than the base circle volume. The gas in the storage chamber can also be sprayed into the base circle volume at high speed to impact the rotor surface and drive the rotor to rotate.

[0009] Optionally, in some embodiments, the rotor is configured as a circular envelope rotor, and an extension line of the center line of the return flow channel is tangent to a circle formed by the center of the circular arc line in the circular envelope rotor around the center of the rotor.

[0010] Optionally, in some embodiments, the rotor is configured as a cycloid rotor, and an extension line of the center line of the return flow channel is tangent to the base circle of the cycloid.

[0011] Furthermore, in some embodiments, the rotor profile includes alternately arranged blade peaks and blade valleys, the involute is arranged between the blade peaks and the blade valleys, and smoothly transitions to the blade peaks and the blade valleys through a transition curve; the transition curve is configured as an arc line whose center falls on the rotor pitch circle.

[0012] Furthermore, in some embodiments, the rotor is configured as a two-lobed rotor or a three-lobed rotor.

[0013] According to another embodiment of the present invention, a three-lobed rotor is provided, which is used for the low-noise and energy-saving Roots pump provided in any of the above embodiments. The three-lobed rotor is configured as an involute rotor, and the meshing angle α of the involute part of the profile of the three-lobed rotor is P Satisfy cosα P =8(D / A-1) / π, the base circle radius of the involute is 0.5Acosα P, where D is the diameter of the tooth tip circle of the three-lobe rotor, and A is the center distance of the rotor. The three-lobe rotor's profile includes a blade peak, a meshing segment, and a blade valley. The blade peak is configured as an arc line with the center of the three-lobe rotor as the center and D as the diameter. The blade valley is configured as an arc line with the center of the three-lobe rotor as the center and 2A-D as the diameter. The central angle between each blade peak segment and each blade valley segment is 15°. The meshing segment is configured as an involute, and the maximum distance between the meshing segment and the center of the three-lobe rotor is The meshing section is smoothly connected to the blade peak and the blade valley respectively through a transition curve, and the transition curve is configured as an arc line with a center falling on the pitch circle of the three-blade rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG1 is a schematic structural diagram of a low-noise and energy-saving Roots pump in a first embodiment;

[0015] FIG2 is a schematic diagram of the rotor position of the low-noise and energy-saving Roots pump at the first working moment in the first embodiment;

[0016] FIG3 is a schematic diagram of the rotor position of the low-noise and energy-saving Roots pump at the second working moment in the first embodiment;

[0017] FIG4 is a schematic diagram of the rotor position of the low-noise and energy-saving Roots pump at the third working moment in the first embodiment;

[0018] 5 is a schematic diagram of the rotor position of the low-noise and energy-saving Roots pump at the fourth working moment in the first embodiment;

[0019] Figure 6 is a schematic diagram of the structure of a medium-low noise energy-saving Roots pump in a proportional manner;

[0020] FIG7 is a schematic diagram of the structure of a three-blade rotor in the first embodiment;

[0021] FIG8 is a schematic diagram of the fifth working moment position of the three-blade rotor in the first embodiment;

[0022] FIG9 is a schematic diagram of the sixth working instant position of the three-blade rotor in the first embodiment;

[0023] FIG10 is a schematic diagram of the position of the three-blade rotor at the seventh working moment in the first embodiment;

[0024] FIG11 is a schematic diagram of the eighth working moment position of the three-blade rotor in the first embodiment;

[0025] FIG12 is a schematic diagram of the third blade rotor position at the ninth working moment in the first embodiment;

[0026] FIG13 is a schematic structural diagram of a low-noise energy-saving Roots pump in a second embodiment;

[0027] FIG14 is a schematic structural diagram of a low-noise energy-saving Roots pump in a third embodiment;

[0028] FIG15 is a schematic structural diagram of a low-noise energy-saving Roots pump in a fourth embodiment;

[0029] FIG16 is a schematic structural diagram of a low-noise energy-saving Roots pump in a fifth embodiment;

[0030] FIG17 is a schematic structural diagram of a low-noise energy-saving Roots pump in a sixth embodiment;

[0031] FIG18 is a schematic diagram of the structure of the three-blade rotor in the fifth and sixth embodiments;

[0032] FIG19 is a schematic diagram of the structure of a circular arc three-blade rotor in the seventh embodiment;

[0033] FIG20 is a schematic diagram of the structure of a cycloid three-lobed rotor in the eighth embodiment;

[0034] FIG21 is a schematic structural diagram of a low-noise, energy-saving Roots pump that directly discharges air into the atmosphere according to a ninth embodiment;

[0035] Figure 22 is a schematic diagram of the structure of a Roots pump in a pair of proportions.

[0036] Meaning of the reference numerals: 11- pump housing; 11b- vacuum pump housing; 11c- pump housing; 12- air inlet; 13- exhaust port; 14- base circle volume; 15- base circle volume; 16- base circle volume; 20- cooling device; 21- reflux channel; 21a- left reflux channel; 21b- right reflux channel; 21c- reflux channel; 22- center axis of reflux channel; 23- cooling exhaust port; 24a- high-pressure air flow; 24c- high-pressure air flow; 25- high-pressure gas storage chamber; 30- three-leaf Rotor; 30a-left rotor; 30b-right rotor; 30c-rotor; 30d-two-leaf involute rotor; 30e-three-leaf involute rotor; 30f-three-leaf circular envelope rotor; 30g-three-leaf cycloid rotor; 31-base circle; 31d-base circle; 31e-base circle; 31f-arc center circle; 31g-base circle; 32-pitch circle; 32f-pitch circle; 33-involute end circle; 34-tooth top circle; 35-tooth root circle; 41-exhaust end muffler; 42-intake end muffler.

[0037] The purpose of the above-mentioned drawings is to provide a detailed explanation of the present invention so that those skilled in the art can understand the technical concepts of the present invention, and is not intended to limit the present invention. For the sake of simplicity, the above-mentioned drawings only schematically depict structures related to the technical features of the present invention and do not strictly depict the complete structure and all details according to actual scale. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below through specific embodiments with reference to the accompanying drawings.

[0039] Roots pumps offer fast start-up, high pumping speed, and high efficiency. As mechanical supercharging devices, they are widely used in the petroleum, chemical, and steel industries. Roots pumps rely on a pair of coupled rotors within the pump chamber to rotate synchronously and in opposite directions at high speed, driving and compressing the fluid within the pump to achieve pressurization. The gaps between the rotors and between the rotors and the pump chamber walls are very small, ensuring airtightness. Due to the small structural clearances of Roots pumps, the compressed gas during operation can cause a significant increase in temperature. For example, under some operating conditions, the pump casing temperature can reach 100°C-200°C when compressed air is used with a Roots pump. Under high-temperature conditions, the components of the Roots pump expand due to heat, causing changes in the gaps between the rotors and between the rotors and the pump casing. This thermal expansion reduces the gaps between the rotors and between the rotors and the pump casing. In severe cases, the rotors can even become stuck, damaging the Roots pump. In some technical solutions, the exhaust port of the Roots pump is equipped with a cooling device to reduce the temperature of the gas discharged by the Roots pump to a reasonable range. At the same time, some Roots pumps are equipped with a reflux cooling channel on the cooling device to guide the cooled compressed gas back to the base circle volume in the upstream pump chamber to achieve the purpose of cooling. At the same time, the pressure in the base circle volume is relatively low, and the kinetic energy of the refluxed compressed gas when rushing into the pump chamber can easily cause repeated radial impacts on the rotor, which is not conducive to the life of the rotor; at the same time, the compressed gas carries a high kinetic energy when rushing into the base circle volume at high speed. Under some working conditions, the air flow speed can exceed the speed of sound. Most of the kinetic energy of the compressed gas is eventually converted into noise, vibration and other forms of dissipation, and is not effectively utilized. Furthermore, the present invention has found in mass production practice that in existing solutions, when the Roots pump encounters a power outage during normal operation, the high-pressure gas at the exhaust port recoils against the rotor, which poses a risk of causing the rotor to reverse and collide and be damaged.

[0040] In order to solve the above problems, an embodiment of the present invention provides a low-noise and energy-saving Roots pump, which improves the distribution of the returning high-pressure cooling airflow in the pump cavity, thereby improving the reliability of the Roots pump and reducing the energy consumption and noise of the Roots pump.

[0041] In a first embodiment, the structure of a low-noise, energy-saving Roots pump is shown in Figure 1. The pump housing 11 is provided with an air inlet 12 at the top and an air outlet 13 at the bottom. The pump housing 11 and the left and right wall panels together form a pump chamber. The pump chamber houses a left rotor 30a and a right rotor 30b, which are arranged in parallel. The two rotors are coupled and rotate in opposite directions. As the left rotor 30a rotates counterclockwise and the right rotor 30b rotates clockwise, low-pressure gas input from the air inlet 12 is compressed in the base volume between the rotors and the pump housing, thereby increasing the gas pressure and causing the temperature to rise. To reduce the exhaust temperature, a cooling device 20 is further provided downstream of the air outlet 13. The cooling device 20 is internally provided with a liquid cooling line, and fins are provided on the outside of the liquid cooling line to increase the heat exchange area, thereby cooling the compressed gas. The cooled compressed gas is then discharged through the cooling outlet 23. The cooling outlet 23 can be discharged directly into the atmosphere or connected to a next-stage compression pump (such as another Roots pump or a diffusion pump) to further increase the gas pressure. The cooling device 20 provides a return gas path that directs some of the cooled compressed gas back into the base circular volume within the pump housing 11. The opening centers of the left and right return channels 21a, 21b are located on the line connecting the centers of the left and right rotors 30a, 30b. The central axes of the left and right return channels 21a, 21b are tilted along the rotational directions of the left and right rotors 30a, 30b, respectively. That is, the openings of the left and right return channels 21a, 21b are tilted toward the exhaust port 13. This ensures that the cooled high-pressure gas, when ejected along the return channel extension, impacts the rotor surface in the direction of rotor rotation.

[0042] In a preferred embodiment, the left and right rotors 30a, 30b are configured as involute rotors, with the meshing sections of the rotor profiles employing an involute structure. Specifically, an involute rotor is one involute profiled on either side of each rotor head. Accordingly, the extension of the return channel's central axis 22 is tangent to the involute's base circle 31. Specifically, the return channel's central axis 22 is located at the geometric center of the return channel's cross-section. The geometric properties of the involute indicate that the base circle tangent coincides with the involute normal, resulting in the highest kinetic energy transfer efficiency when high-pressure gas impacts the rotor's involute surface.

[0043] In various embodiments, the low-noise, energy-saving Roots pump can also utilize two, four, or more rotors. Due to the limitations of the rotor structure, the high-pressure gas propulsion efficiency of a two-rotor rotor is relatively low; while a rotor with more than four rotors is relatively complex, resulting in reduced area utilization.

[0044] In a preferred embodiment, the profile of the left rotor 30a and the right rotor 30b includes three groups of alternating peaks and troughs, with involutes arranged between the peaks and troughs and smoothly connected to the peaks and troughs via transition curves. Each peak segment and trough segment is configured as an arc line with the center of the rotor as the center of the circle. The arc line can increase the length of the small airtight gap formed between the left rotor 30a, the right rotor 30b and the pump housing 11, thereby reducing leakage losses. The transition curve between the tooth top / root arc line and the involute is configured as an arc line with the center falling on the rotor pitch circle. In a further preferred embodiment, the arc length of the peak segment arc line is not less than the corresponding arc length of the openings of the left return channel 21a and the right return channel 21b on the pump housing 11 along the rotor circumference, so that the peak segment can seal the opening of the return channel during rotor rotation, further improving the airtightness during operation of the Roots pump and improving energy efficiency. Taking the left reflux channel 21a as an example, when the left reflux channel 21a is configured as a uniform cylindrical tube body, when the tube diameter is d, the opening size of the left reflux channel 21a on the pump casing 11 is d / cosβ, where β is the inclination angle of the central axis of the left reflux channel 21a relative to the horizontal direction.

[0045] The low-noise, energy-saving Roots pump, shown in Figure 1, operates as follows. The left rotor 30a and left return flow channel 21a are analyzed. During the low-noise, energy-saving Roots pump's operation, the position shown in Figure 1 is used as the initial state. At this moment, the left rotor 30a and pump housing 11 define a base circle volume 14, separated from the air inlet 12. At the first instant of operation, the left rotor 30a rotates counterclockwise to the position shown in Figure 2. Driven by the left rotor 30a, the gas in the base circle volume 14 rotates counterclockwise with the left rotor 30a. Simultaneously, as the left rotor 30a rotates, the left return flow channel 21a connects with the base circle volume 14. High-pressure gas from the cooling device 20 begins to flow into the base circle volume 14 through the left return flow channel 21a, supercharging the low-pressure gas in the base circle volume and simultaneously impacting the left rotor 30a. At this point, the angle between the high-pressure gas and the left rotor surface is relatively small, resulting in a relatively small impact. The left rotor 30a continues to rotate counterclockwise to the second operating moment, at the position shown in Figure 3 . At this point, the high-pressure gas 24a ejected from the left return channel 21a impacts the involute portion of the left rotor 30a profile. The force vector of the impact is tangential to the base circle 31, and the impact force of the high-pressure gas 24a is converted to the maximum torque applied to the left rotor 30a. The left rotor 30a continues to rotate to the third operating moment, at the position shown in Figure 4 . At this point, the high-pressure gas impact point moves away from the involute portion. Simultaneously, due to the increased pressure in the base circle volume 14 and the reduced pressure differential in the left return channel 21a, as well as the increased distance between the opening of the left return channel 21a and the surface of the left rotor 30a, the impact of the high-pressure gas on the left rotor 30a is weakened. When the left rotor 30a rotates to the fourth working moment, its position is shown in Figure 5. The pressure difference between the base circle volume 14 and the left reflux channel 21a is further reduced, and the airflow impact effect is basically negligible. The base circle volume 14 is about to separate from the left reflux channel 21a and connect with the exhaust port 13. The gas in the base circle volume 14 will be mixed and compressed with the gas delivered by the right rotor 30b and discharged from the exhaust port 13, completing a working cycle.

[0046] In a comparative example, as shown in FIG6 , the reflux channel 21 c of the low-noise and energy-saving Roots pump is arranged horizontally, and the high-pressure gas 24 c ejected from the reflux channel 21 c impacts the surface of the rotor 30 c in a horizontal direction. Due to the structural limitations of the Roots pump rotor, the surface of the rotor 30c cannot form a plane that forms a large angle with the horizontal high-pressure gas 24c. A simple force analysis shows that the closer the opening position of the return channel 21c is to the line connecting the centers of the two rotors, the greater the radial impact of the high-pressure gas 24c on the rotor and the smaller the circumferential push. Increasing the angle between the high-pressure gas 24c and the surface of the rotor 30 by changing the position of the return channel 21c requires moving the opening position of the return channel 21c downward (as indicated by arrow 24d). However, at the position indicated by arrow 24d, while the high-pressure gas can form a nearly vertical position relative to the surface of the rotor 30c, the position of the return channel 21c is too close to the exhaust port 13, causing the return channel 21c to directly connect to the exhaust port 13 through the pump chamber at a specific working moment, causing the return channel 21c to lose the pressure difference with the pump chamber. Therefore, a return channel with a non-inclined structure cannot achieve the same optimization effect as the embodiment of the present invention.

[0047] In different embodiments, the structure of the low-noise and energy-saving Roots pump is not limited to the form provided in FIG1 . For example, the arrangement of the rotor in the low-noise and energy-saving Roots pump can be vertical, horizontal, or vertical axis; the rotor can be in a three-lobed form, a two-lobed form, a four-lobed form, or a more lobe form; the rotor shape can be in-line or spiral; in a preferred embodiment, the rotor adopts an involute rotor, and in other embodiments, a cycloid form or a circular envelope form can be adopted; in addition to the reflux cooling device 20 , a liquid cooling device for the rotor can be further provided; the opening structure of the reflux channel can adopt a straight cylindrical shape or a bell-mouth shape, and the reflux channel on each side can be provided with one opening, or a row of openings arranged in a straight line can be provided along the axial direction of the rotor. In some embodiments, the Roots pump is configured as a vacuum pump that discharges directly into the atmosphere, and the reflux cooling device can be omitted, and the reflux channel is directly connected to the atmosphere to form a cooling airflow at atmospheric pressure.

[0048] Another embodiment of the present invention provides a three-blade rotor, the profile structure of which is shown in Figure 7. One section of the profile AF is analyzed: it includes the peak section AB, the trough section EF, and the meshing section CD. The meshing section CD is smoothly connected to the peak section AB via the transition curve BC and to the trough section EF via the transition curve DE. The meshing section CD is an involute, and the radius of the base circle 31 of the involute is 0.5Acosα. P , α P is the involute meshing angle (pitch circle 32 meshing angle) and satisfies cosα P=8(D / A-1) / π, where D is the diameter of the three-lobe rotor outer circle (tooth tip circle 34), and A is the distance between the centers O of two three-lobe rotors. In the preferred embodiment, the peak segment AB and the valley segment EF are both arcs centered on the three-lobe rotor center O, with corresponding central angles of 15°. The peak segments AB and valley segments EF of two adjacent three-lobe rotors should be coupled to each other, so the peak segment AB has a diameter of D, and the valley segment EF has a diameter of 2A-D. The maximum distance between the involute of the meshing segment CD and the three-lobe rotor center O (i.e., the radius of the involute's termination circle 33) is In this state, the arc line BC with the intersection point O1 of OB and the three-blade rotor pitch circle 32 as the center and O1C as the radius is tangent to the blade peak section AB and the meshing section CD respectively, and the arc line DE with the intersection point O2 of the extended line of OE and the pitch circle 32 as the center and O2D as the radius is tangent to the meshing section CD and the blade valley section EF respectively, achieving a smooth transition of the profile. In one embodiment, the three-blade rotor center distance A is 330mm, the tooth tip circle diameter D is 450.6mm, and the pitch circle meshing angle α P The radius of the base circle 31 is 21°26'23.6", the radius of the involute end circle 33 is 153.58 mm, the radius of the involute end circle 33 is 195.29 mm, and the angle between the return channel center axis 22 of the return channel 21 and the line connecting the center points of the two rotors 30 is approximately 43°. In a preferred embodiment, the circumferential clearance between the rotor 30 and the pump housing 11 is set to 0.4 mm-0.5 mm, and the clearance between two adjacent rotors 30 is also set to 0.4 mm-0.5 mm.

[0049] In the low-noise, energy-saving Roots pump, the three-blade rotor shown in FIG7 operates as illustrated in FIG8 to FIG12 . For simplicity, only a portion of the pump housing 11 is shown in the figure, where the return channel centerline 22 of the return channel 21 is tangent to the base circle 31 of the rotor 30. Taking the fifth operating moment shown in FIG8 as the starting point for analysis, the position of the rotor 30 is shown in FIG8 . At this time, closed base circle volumes 14 and 15 are formed between the rotor 30 and the pump housing 11. The peak AB of the rotor 30 seals the orifice of the return channel 21, so that the base circle volumes 14 and 15 are neither connected to the air inlet 12 or exhaust port 13 of the pump housing 11, nor to the return channel 21. At the sixth operating moment shown in Figure 9 , rotor 30 rotates counterclockwise by a certain angle relative to Figure 8 . The peak AB of rotor 30 deviates from the orifice of return flow channel 21. The high-pressure airflow in return flow channel 21 enters base circle volume 14, creating a high-speed impact on transition curve BC of rotor 30. Force analysis shows that the impact force of the high-pressure, high-speed airflow on rotor 30 at this moment is approximately a force directed from the surface of transition curve BC toward point O1, and the torque increases with the rotation of rotor 30. At the seventh operating moment shown in Figure 10 , as rotor 30 rotates, the impact point of the high-pressure airflow in return flow channel 21 enters the range of the involute of meshing section CD. Compared to the eighth operating moment shown in Figure 11 , the geometric properties of the involute indicate that within section CD, the impact force vector of the high-pressure airflow remains tangential to base circle 31, resulting in the most efficient transfer of kinetic energy from the high-pressure airflow to rotor 30. At this time, base circle volume 15 is connected to exhaust port 13, and the gas therein is expelled from exhaust port 13 under the combined action of the two rotors. The rotor 30 continues to rotate counterclockwise until the ninth working moment as shown in FIG12 . At this time, the high-pressure airflow impacts the end point D of the meshing section CD. Due to the increase in the distance between the rotor 30 profile and the opening of the return channel 21 and the decrease in the pressure difference between the base circle volume 14 and the return channel 21, the impact of the high-pressure airflow gradually decreases. After the ninth working moment, the impact of the high-pressure airflow is almost negligible.

[0050] The geometric relationship between the rotor 30 and the pump housing 11 in the preferred embodiment will be further explained using the state shown in Figure 10 as an example. In the preferred embodiment, the radian of the base circular volume formed by the rotor 30 and the pump housing 11 relative to point O (the radian of the arc BG formed between the nearest endpoints of the peaks of two adjacent blade peaks) should be smaller than the radian between the return channel 21 and the air inlet 12 relative to point O (the radian of the arc S1S2) and the radian between the return channel 21 and the exhaust port 13 relative to point O (the radian of the arc S3S4). It is easy to understand that when the above relationship is met, at any given moment, the base circular volume 14 is connected to at most one of the air inlet 12, the return channel 21, or the exhaust port 13, thereby ensuring airtightness during operation of the Roots pump and improving operating efficiency.

[0051] The use of a three-lobed rotor 30, as shown in Figure 7, can, on the one hand, improve the airtightness of the AB section of the blade peak, reducing leakage losses during the operation of the Roots pump. On the other hand, it can utilize the high-pressure gas ejected from the return channel 21 to provide a boost to the rotor 30, reducing radial vibration of the rotor 30 while optimizing the energy consumption of the Roots pump. In special operating conditions, such as a sudden power outage, the high-pressure gas ejected from the return channel 21 can continue to impact the depowered rotor 30, delaying its reverse rotation. At the same time, the return channel 21 can balance the pressure difference between the base circle volume 14 and the exhaust port 13, further reducing the risk of rotor 30 reversing after a power outage and preventing damage to the rotor. Under normal operating conditions, the direct impact of high-pressure gas on the surface of the rotor 30 can further enhance the reflux cooling effect and further reduce the operating temperature of the rotor 30. In some embodiments, the high-pressure gas impact can reduce the energy consumption of the Roots pump by 2%-5%.

[0052] In different embodiments, according to the different structural design requirements and processing technology levels of the Roots pump, the three-blade rotor shown in Figure 7 can also adopt other structures. For example, the transition curves BC and DE can also be replaced by extended involutes or shortened involutes.

[0053] In a second embodiment, as shown in Figure 13, a low-noise, energy-saving Roots pump is configured as a direct-discharge atmospheric vacuum pump. The air inlet 12 is connected to the upstream flow channel, forming a negative pressure relative to atmospheric pressure. The exhaust port 13 discharges directly into the atmosphere. The return flow channel 21 is directly connected to the atmosphere, allowing external air to be injected into the base circle volume through the return flow channel 21 and impact the three-lobe rotor 30 to cool it. The center axis 22 of the return flow channel is tangent to the base circle 31 of the three-lobe rotor 30. An air inlet muffler 42 is connected upstream of the return flow channel 21 to reduce the noise generated by air entering the Roots pump; the exhaust port 13 is connected to the exhaust muffler 41 to reduce the noise generated when the gas is discharged to the atmosphere.

[0054] In the third embodiment, as shown in FIG14 , a low-noise and energy-saving Roots pump is equipped with a standard involute two-lobe rotor 30 d , and the central axis 22 of the return channel 21 of the return type is tangent to the base circle 31 d of the two-lobe rotor 30 d , so that the high-pressure cooling gas ejected from the return channel 21 impacts the surface of the two-lobe rotor 30 d , forming a driving effect.

[0055] In the fourth embodiment, as shown in FIG15 , the low-noise and energy-saving Roots pump is a vacuum pump, which adopts a two-lobe rotor 30 d , the return channel 21 is directly connected to the atmosphere, and the center axis 22 of the return channel is tangent to the base circle 31 d of the two-lobe rotor 30 d .

[0056] In the fifth embodiment, as shown in FIG16 , a low-noise and energy-saving Roots pump adopts a three-lobed involute rotor 30 e , wherein the peaks A′B′ of the three-lobed involute rotor 30 e are turned into large arcs to improve the airtightness between the three-lobed standard involute rotor 30 e and the pump housing 11 .

[0057] In the sixth embodiment, as shown in FIG17 , the low-noise and energy-saving Roots pump is a vacuum pump, which adopts a three-leaf standard involute rotor 30 e, wherein the large arc of the blade tip is also formed by turning the periphery of the impeller, and the center axis 22 of the reflux channel is tangent to the base circle 31 e of the three-leaf involute rotor 30 e.

[0058] The detailed structure of the three-lobe involute rotor 30e in the fifth and sixth embodiments is shown in Figure 18. Each rotor head is machined to form a large arc A'B' centered at O ​​to enhance airtightness. The arc A'B' extends 12°. The Roots pump's return channel axis 22 is tangential to the base circle 31e of the three-lobe involute rotor 30e (forming a 44.1° angle with the horizontal), enhancing the cooling airflow's propulsion effect on the three-lobe involute rotor.

[0059] In the seventh embodiment, a low-noise, energy-saving Roots pump utilizes a three-lobed circular envelope rotor 30f, as shown in Figure 19. The rotor pitch circle is 32f, where O3 is the center of the circular arc portion of the rotor head, O3M is the radius, and the arc line A"B" of the rotor lobe peak is a large arc centered at O, obtained by lathing to improve the airtightness between the rotor and the pump housing. The arc line A"B" has a radius of 12°. O3 is rotated about O to form the arc center circle 31f. The center axis 22 of the return flow channel of the low-noise, energy-saving Roots pump is arranged to be tangential to the arc center circle 31f (at an angle of 41.38° with respect to the horizontal) to enhance the cooling airflow's propulsion effect on the three-lobed circular envelope rotor 30f.

[0060] In the eighth embodiment, a low-noise, energy-saving Roots pump utilizes a three-lobed cycloid rotor 30g, as shown in Figure 20 . 31g represents the rotor's base circle (the generating circle of the cycloid). Arc lines A''B'' at the rotor's lobe peaks are large arcs obtained by turning with O as the center to improve airtightness between the rotor and the pump housing. Arc line A''B'' extends 12°. The center axis 22 of the return flow channel of the low-noise, energy-saving Roots pump is tangent to base circle 31g (forming an angle of 49.06° with the horizontal) to enhance the cooling airflow's propulsion of the three-lobed cycloid rotor 30g.

[0061] In the ninth embodiment, a low-noise, energy-saving Roots pump utilizes a three-lobed involute rotor 30, as shown in Figure 21. The central axis 22 of the return channel 21 is tangential to the base circle 31 of the rotor 30. The return channel 21 connects to the cooling exhaust port 23 via a high-pressure gas storage chamber 25, directing the cooled gas back in reverse flow. The high-pressure gas storage chamber 25 acts as a transition, simplifying the piping structure of the return channel and saving space. An exhaust muffler 41 is connected downstream of the cooling exhaust port 23 to reduce the exhaust noise of the Roots pump.

[0062] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent replacement of the involved component structures, as well as combination of implementation methods in different embodiments without causing structural or principle conflicts, all fall within the scope of protection of the present invention.

Claims

1. A low-noise, energy-saving Roots pump, comprising a pump body, the pump body comprising a pump casing and a rotor, the pump casing and two wall panels together forming a pump chamber, a pair of rotors being arranged in parallel in the pump chamber; characterized in that: A return flow channel is provided on the pump housing to allow the cooling air flow to flow into the pump chamber through the return flow channel. The axis of the return flow channel is inclined relative to the line connecting the centers of a pair of rotors to allow the cooling air flow to impact the rotor along the direction of rotation of the rotor.

2. The low-noise and energy-saving Roots pump according to claim 1 is characterized in that: The rotor includes alternately arranged blade peaks and blade valleys, the blade peaks and blade valleys are respectively configured as circular arcs with the center of the rotor as the center, the arc length of the opening of the reflux channel around the center of the rotor does not exceed the arc length of the blade peaks, and the area of ​​the reflux channel controls the flow rate and speed of the reflux gas; The rotor profile between adjacent blade peaks of the rotor and the pump casing define a base circle volume for conveying the gas to be compressed. The circumferential arc of the base circle volume relative to the center of the rotor is smaller than the arc formed by the reflux channel and the air inlet of the pump body relative to the center of the rotor. The circumferential arc of the base circle volume relative to the center of the rotor is smaller than the arc formed by the reflux channel and the exhaust port of the pump body relative to the center of the rotor.

3. The low-noise and energy-saving Roots pump according to claim 1 or 2, characterized in that: The rotor is configured as an involute rotor, and an extension line of a center line of the return flow channel is tangent to a base circle of the rotor along a rotation direction of the rotor.

4. The low-noise and energy-saving Roots pump according to claim 1 or 2, characterized in that: The pump housing is provided with a storage cavity, and the reflux channel is connected between the storage cavity and the pump cavity; in, The storage chamber is configured to be connected to the external atmosphere to introduce cooling airflow from the external atmosphere; or, The Roots pump also includes a reflux cooling device, which is arranged downstream of the pump body and is used to cool the compressed gas discharged from the pump body. The reflux channel is connected to the reflux cooling device to allow partially cooled compressed gas discharged from the pump body to flow back to the pump chamber through the reflux channel via the storage chamber.

5. The low-noise and energy-saving Roots pump according to claim 1 or 2, characterized in that: The rotor is configured as a circular envelope rotor, and the extension line of the center line of the return flow channel is tangent to the circle formed by the center of the tooth tip arc line in the circular envelope rotor around the center of the rotor along the rotation direction of the rotor.

6. The low-noise and energy-saving Roots pump according to claim 1 or 2, characterized in that: The rotor is configured as a cycloid rotor, and an extension line of a center line of the reflux channel is tangent to a base circle of the cycloid along a rotation direction of the rotor.

7. The low-noise and energy-saving Roots pump according to claim 3 is characterized in that: The rotor profile includes alternately arranged blade peaks and blade valleys, an involute is arranged between the blade peaks and the blade valleys, and smoothly transitions to the blade peaks and the blade valleys through a transition curve; the transition curve is configured as an arc line with a center falling on the rotor pitch circle.

8. The low-noise and energy-saving Roots pump according to claim 1 or 2, characterized in that: The rotor is configured as a two-lobed rotor or a three-lobed rotor.

9. A three-blade rotor, characterized in that: The three-lobed rotor is used for a low-noise and energy-saving Roots pump according to any one of claims 1 to 4 or 7 or 8, wherein the three-lobed rotor is configured as an involute rotor, and the meshing angle α of the involute part of the profile of the three-lobed rotor is P Satisfy cosα P =8(D / A-1) / π, the base circle radius of the involute is 0.5Acosα P , where D is the diameter of the tooth tip circle of the three-blade rotor, and A is the center distance of the rotor; The three-blade rotor has a profile including a blade peak, a meshing section and a blade valley, wherein The blade peak is configured as an arc line with the center of the three-blade rotor as the center and D as the diameter, and the blade valley is configured as an arc line with the center of the three-blade rotor as the center and 2A-D as the diameter. The central angle between each blade peak segment and the blade valley segment is 15°; The meshing section is configured as an involute, and the maximum distance between the meshing section and the center of the three-blade rotor is The meshing section is smoothly connected to the blade peak and the blade valley respectively through a transition curve, and the transition curve is configured as an arc line with a center falling on the pitch circle of the three-blade rotor.

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