Scroll pump

Abstract

The scroll pump includes an inlet and an outlet, a fixed scroll (120) that intermeshes with an orbiting scroll (130) to define a space therebetween for pumping fluid from the inlet to the outlet, a biasing device (170) configured to bias the orbiting scroll relative to the fixed scroll, a fluid recirculation path (190a) that extends through either the fixed scroll (130) or the orbiting scroll (120) from the space to the inlet, and a fluid recirculation valve (190b) disposed in the fluid recirculation path (190a), the fluid recirculation valve (190b) configured to allow fluid flow from the space through the fluid recirculation path (190a) to the inlet when in an open state and to prevent fluid flow through the fluid recirculation path (190a) when in a closed state, and configured to switch from the closed state to the open state when a pressure differential across the fluid recirculation valve (190b) is equal to or greater than a predetermined threshold.

Description

Technical Field

[0001] The present invention relates to a scroll pump.

Background Art

[0002] A scroll pump is a known type of pump used in various different industries for pumping fluids. A scroll pump operates by utilizing the relative movement of two meshing scrolls (known as a fixed scroll and a orbiting scroll) to pump fluid through the scroll pump.

[0003] One particular type of scroll pump uses a loaded shaft seal between the two scrolls. This load is typically provided by a spring that presses the two scrolls against each other via the shaft seal. It is generally desirable to improve the design of this type of scroll pump.

Summary of the Invention

Means for Solving the Problems

[0004] In a first aspect, a scroll pump is provided, the scroll pump comprising an inlet and an outlet, and a fixed scroll and an orbiting scroll that mesh with each other and define a space therebetween for pumping fluid from the inlet to the outlet through the scroll pump. The scroll pump further comprises a biasing device configured to bias the orbiting scroll relative to the fixed scroll, a fluid recirculation path extending through either the fixed scroll or the orbiting scroll from the space to the inlet, and a fluid recirculation valve disposed in the fluid recirculation path. When in an open state, the fluid recirculation valve is configured to permit flow of fluid from the space through the fluid recirculation path to the inlet. When in a closed state, the fluid recirculation valve is configured to block flow of fluid through the fluid recirculation path. The fluid recirculation valve is configured to switch from the closed state to the open state when a pressure difference across the fluid recirculation valve is equal to or greater than a predetermined threshold value.

[0005] The fixed scroll can include a first base and a first spiral wall extending from the first base. The swivel scroll can include a second base and a second spiral wall extending from the second base. The scroll pump can further include a first seal disposed between the first base and the second spiral wall. The scroll pump can further include a second seal disposed between the second base and the first spiral wall. The biasing device can be configured to bias the swivel scroll relative to the fixed scroll via the first seal and the second seal.

[0006] The first seal and / or the second seal can be formed at least in part from a polymeric material. The first seal and / or the second seal can be formed at least in part from polytetrafluoroethylene.

[0007] The first seal and / or the second seal can be a path seal.

[0008] The biasing device can include one or more springs.

[0009] The scroll pump can include a drive shaft configured to rotationally drive the swivel scroll. The biasing device can be configured to apply a force to the swivel scroll via the drive shaft. The biasing device can be configured to apply a force directly to a bearing that couples the swivel scroll to the drive shaft.

[0010] The fluid recirculation valve can be a check valve.

[0011] The scroll pump can further include a check valve disposed at the outlet of the scroll pump.

[0012] The predetermined threshold value can be between 100 mbar and 400 mbar. The predetermined threshold value can be between 200 mbar and 300 mbar. The predetermined threshold value can be 200 mbar.

[0013] The scroll pump can include an actuator and a drive shaft. The drive shaft is coupled to the orbiting scroll, and the actuator is configured to rotate the drive shaft to operate the drive shaft to orbitally drive the orbiting scroll. The fixed scroll is disposed between the actuator and the orbiting scroll.

[0014] The scroll pump can include an actuator and a drive shaft. The drive shaft is coupled to the orbiting scroll, and the actuator is configured to rotate the drive shaft to operate the drive shaft to orbitally drive the orbiting scroll. The orbiting scroll is disposed between the actuator and the fixed scroll.

[0015] In a second aspect, there is provided the use of the scroll pump of the first aspect for pumping a fluid.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

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Figure 5

Figure 6

Modes for Carrying Out the Invention

[0017] FIG. 1 is a schematic view showing a cross-section of a scroll pump 100 according to an embodiment (not to scale).

[0018] The scroll pump 100 includes a shell 110, a fixed scroll 120, a rotating scroll 130, a drive shaft 140, an actuator 150, a plurality of bearings 160, a biasing device 170, a first shaft seal 180a, a second shaft seal 180b, and a fluid recirculation mechanism 190.

[0019] In this embodiment, the shell 110 and the fixed scroll 120 together form the overall housing of the scroll pump 100, within which the remaining components of the scroll pump 100 are arranged. However, it should be understood that in other embodiments, the fixed scroll 120 does not form part of the overall housing of the scroll pump 100 and can instead be completely arranged within the overall housing.

[0020] The rotating scroll 130 is arranged within the overall housing of the scroll pump 100 and meshes with the fixed scroll 120. The rotating scroll 130 is configured to rotate relative to the fixed scroll 120 to pump fluid (e.g., gas) from an inlet (not shown) of the scroll pump 100 to an outlet (not shown) of the scroll pump 100. The scroll pump 100 can include a check valve (which may be referred to as an exhaust check valve) arranged at the outlet. The exhaust check valve is configured to prevent fluid from re-entering the scroll pump 100 when the scroll pump 100 is turned off. This results in reducing the amount of fluid that may return from the inlet of the scroll pump 100, which would otherwise cause an undesirable pressure increase in the system pumped by the scroll pump 100. Also, the exhaust check valve is configured to prevent exhaust fluid and / or air / oxygen, which may react with the pumped fluid, from entering the scroll pump 100.

[0021] The physical mechanism by which fluid is pumped by the rotation of the rotating scroll 130 relative to the fixed scroll 120 is well known and will not be described herein.

[0022] The fixed scroll 120 includes a first base 122 and a first spiral wall 124. The rotating scroll 130 includes a second base 132 and a second spiral wall 134. The first spiral wall 124 extends perpendicularly from the first base 122 toward the second base 132. The second spiral wall 134 extends perpendicularly from the second base 132 toward the first base 122. In this embodiment, the first base 122 and the first spiral wall 124 are integrally formed with each other. Also, in this embodiment, the second base 132 and the second spiral wall 134 are integrally formed with each other.

[0023] The first spiral wall 124 and the second spiral wall 134 are engaged with each other such that the end face of the first spiral wall 124 contacts the opposing face of the second shaft seal 180b, and the end face of the second spiral wall 134 contacts the opposing face of the first shaft seal 180a. In this way, the first shaft seal 180a, the first spiral wall 124, the second shaft seal 180b, and the second spiral wall 134 together define the space between the fixed and rotating scrolls 120, 130, and this space is used for the scroll pump 100 to pump fluid during operation. Each of the first and second spiral walls 124, 134 defines its respective spiral-shaped path between the turns or wraps of the spiral wall.

[0024] The drive shaft 140 is coupled to the orbiting scroll 130 and configured to rotate to drive the orbiting scroll 130 in an orbiting motion. The drive shaft 140 is disposed within the overall housing of the scroll pump 100. In this embodiment, the drive shaft 140 is coupled to the orbiting scroll 130 and the shell 110 via a plurality of bearings 160 that assist in the rotation of the drive shaft 140. In this embodiment, the drive shaft 140 extends through the fixed scroll 120, and the orbiting scroll 130 is attached to the end of the drive shaft 140. In this embodiment, the fixed scroll 120 is disposed between the actuator 150 and the orbiting scroll 130.

[0025] The actuator 150 (e.g., a motor) is coupled to the drive shaft 140 and configured to actuate the drive shaft 140 to rotate the drive shaft 140 and drive the orbiting scroll 130 in an orbiting motion. The actuator 150 is disposed within the overall housing of the scroll pump 100.

[0026] The plurality of bearings 160 mechanically couple the drive shaft 140 to the orbiting scroll 130 and the overall housing of the scroll pump 100, enabling the drive shaft 140 to rotate within the scroll pump 100 to drive the orbiting scroll 130. In this embodiment, the plurality of bearings 160 includes a bearing 160 disposed (and mechanically coupled) between the first end of the drive shaft 140 and the overall housing of the scroll pump 100, a bearing 160 disposed (and mechanically coupled) between the fixed scroll 120 and the drive shaft 140, and a bearing 160 disposed (and mechanically coupled) between the orbiting scroll 130 and the second end of the drive shaft 140 opposite the first end.

[0027] The biasing device 170 is configured to bias the fixed and swivel scrolls 120, 130 against each other. More specifically, the biasing device 170 is configured to bias the swivel scroll 130 toward the fixed scroll 120, and the swivel scroll 130 is axially loaded against the fixed scroll 120 via the first shaft seal 180a and the second shaft seal 180b. More specifically, the biasing is such that the end face of the first spiral wall 124 is pressed against the opposing face of the second shaft seal 180b, and the end face of the second spiral wall 134 is pressed against the opposing face of the first shaft seal 180a. Accordingly, the axial loads of the fixed and swivel scrolls 120, 130 are at least partially supported by the first and second shaft seals 180a, 180b. The axial loads caused by the biasing device 170 maintain the seal between the end faces of the first and second spiral walls 124, 134 and the respective opposing faces of the first and second shaft seals 180a, 180b. This tends to act to prevent unwanted leakage of fluid between different radially located portions of the space between the fixed and swivel scrolls 120, 130. In this embodiment, the biasing device 170 comprises a plurality of springs configured to exert a force on the swivel scroll 130 to bias the swivel scroll 130 toward the fixed scroll 120 via a plurality of bearings 160 and a drive shaft 140. Specifically, in this embodiment, the plurality of springs comprises a spring configured to exert a force on a bearing 160 disposed between a first end of the drive shaft 140 and the overall housing of the scroll pump 100, and a spring configured to exert a force on a bearing 160 disposed between the fixed scroll 120 and the drive shaft 140. However, in other embodiments, the biasing device 170 is composed of only one spring (e.g., any one of the springs described above).

[0028] The first and second shaft seals 180a, 180b are seals disposed in a path defined by the spiral walls 124, 134 of the fixed and orbiting scrolls 120, 130. These seals may also be referred to as path seals. Each of the first and second shaft seals 180a, 180b is a piece of spiral-shaped material sized to fit precisely within the path defined by the spiral walls 124, 134. The first shaft seal 180a is adjacent to the first base 122 and extends fully across the width of the path defined by the first spiral wall 124. The first shaft seal 180a is disposed between the second spiral wall 134 and the first base 122. The second shaft seal 180b is adjacent to the second base 132 and extends fully across the width of the path defined by the second spiral wall 134. The second shaft seal 180b is disposed between the first spiral wall 124 and the second base 132. In this embodiment, the first and second shaft seals 180a, 180b are both formed from polytetrafluoroethylene (PTFE). However, in general, one or both of the first and second shaft seals 180a, 180b can be formed from one or more other types of materials (e.g., other types of polymers that can be filled with carbon or glass to reduce wear).

[0029] The fluid recirculation mechanism 190 includes a fluid recirculation path 190a and a fluid recirculation valve 190b disposed in the fluid recirculation path 190a. In this embodiment, the fluid recirculation path 190a extends through the fixed scroll 120 from the space defined between the fixed and orbiting scrolls 120, 130 to the inlet of the scroll pump 100. More specifically, in this embodiment, the fluid recirculation path 190a extends through the first shaft seal 180a and the first base 122 of the fixed scroll 120. The fluid recirculation valve 190b is disposed within the fluid recirculation path 190a and is configured to allow the flow of fluid through the fluid recirculation path 190a when opened and to block the flow of fluid through the fluid recirculation path 190a when closed. When the fluid pressure difference across the fluid recirculation valve 190b is less than a predetermined threshold value, the fluid recirculation valve 190b is configured to be in a closed state. However, when the fluid pressure difference across the fluid recirculation valve 190b is equal to or greater than the predetermined threshold value, the fluid recirculation valve 190b is configured to switch from the closed state to the open state in order to allow fluid outflow from the space between the scrolls, thereby reducing the pressure within the space defined between the fixed and orbiting scrolls 120, 130. The threshold value is a value within the range of 100 mbar - 400 mbar. In a scroll pump as illustrated, tests have shown that 100 mbar is the lowest pressure difference that significantly and effectively reduces the lift-off force of the scrolls. Also, tests have shown that 400 mbar tends to be the highest pressure difference generated by a scroll pump of the type illustrated. Preferably, the threshold value is a value within the range of 200 mbar - 300 mbar. More preferably, the threshold value is 200 mbar.

[0030] The inlet of the fluid recirculation path 190a is fluidly connected to the space between the scrolls, the outlet of the fluid recirculation path 190a is fluidly connected to the inlet of the scroll pump 100, and the fluid recirculation valve 190b is disposed in the fluid recirculation path 190a between the inlet and the outlet of the fluid recirculation path 190a. When the fluid recirculation valve 190b is in the closed state, the fluid pressure difference across the fluid recirculation valve 190b is equal to the pressure difference between the pressure at the inlet to the fluid recirculation path 190a from the space between the scrolls and the pressure at the inlet of the scroll pump 100 (i.e., the pressure difference is equal to the pressure at the inlet to the fluid recirculation path 190a minus the pressure at the inlet of the scroll pump 100). Thus, the fluid recirculation valve 190b essentially functions as a blow-off valve that operates when necessary to relieve the high internal pressure of the scroll pump 100. In this embodiment, the fluid recirculation valve 190b is a spring-loaded check valve that utilizes an elastomer ball to seal the opening. However, it should be understood that generally any suitable type of valve can be used, such as a check valve that utilizes pads of different shapes to seal the opening.

[0031] FIG. 2 is a schematic view (not to scale) showing a cross-section of a scroll pump 100 according to another embodiment. The scroll pump 100 of FIG. 2 is the same as that described above with reference to FIG. 1, except that the fluid recirculation mechanism 190 is in the orbiting scroll 130 instead of the fixed scroll 120. More specifically, in this embodiment, the fluid recirculation path 190a extends through the orbiting scroll 130 from the space defined between the fixed and orbiting scrolls 120, 130 to the inlet of the scroll pump 100. Specifically, the fluid recirculation path 190a extends through the second shaft seal 180b and the second base 132 of the orbiting scroll 130.

[0032] FIG. 3 is a schematic view showing a cross section of a scroll pump 100 according to yet another embodiment (not to scale). The scroll pump 100 of FIG. 3 is the same as the scroll pump 100 described above with reference to FIG. 1, except that the fixed scroll 120 is disposed on the opposite side of the orbiting scroll 130. In other words, in the embodiment of FIG. 3, the orbiting scroll 130 is disposed between the actuator 150 and the fixed scroll 120, rather than the fixed scroll being disposed between the actuator 150 and the orbiting scroll 130. In this embodiment, the drive shaft 140 does not penetrate the fixed scroll 120.

[0033] FIG. 4 is a schematic view showing a cross section of a scroll pump 100 according to yet another embodiment (not to scale). The scroll pump 100 of FIG. 4 is the same as the scroll pump 100 described above with reference to FIG. 3, except that the fluid recirculation mechanism 190 is in the orbiting scroll 130 instead of the fixed scroll 120. More specifically, in this embodiment, the fluid recirculation path 190a extends through the orbiting scroll 130 from the space defined between the fixed and orbiting scrolls 120, 130 to the inlet of the scroll pump 100. Specifically, the fluid recirculation path 190a extends through the second shaft seal 180b and the second base 132 of the orbiting scroll 130.

[0034] FIG. 5 is a schematic view showing a cross section of a scroll pump 100 according to yet another embodiment (not to scale). The scroll pump 100 of FIG. 5 is the same as the scroll pump 100 described above with reference to FIG. 1, except that the biasing device 170 includes only one spring having one end attached to the drive shaft 140 and the other end attached to a bearing 160 that mechanically couples the orbiting scroll 130 to the drive shaft 140. In this embodiment, the biasing device 170 (specifically, the spring) is configured to apply a biasing force directly to the bearing 160 that mechanically couples the orbiting scroll 130 to the drive shaft 140. The biasing force acts to press the orbiting scroll 130 toward the fixed scroll 120 and biases both the fixed and orbiting scrolls 120, 130 together.

[0035] Figure 6 is a schematic view (not to scale) showing a further view of the scroll pump of FIG. 1. As shown, the inlet 300 of the fluid recirculation path 190a is disposed in the fixed scroll 120, passes through the fixed scroll 120, and extends from the space defined between the fixed and orbiting scrolls 120, 130 to the inlet 310 of the scroll pump 100. As shown, in this embodiment, the inlet 300 to the fluid recirculation path 190a is disposed at a position radially outside the centerline of the scroll pump 100 defined by the drive shaft 140. More specifically, the inlet 300 is disposed at a position such that there are three turns (or windings) of the spiral wall between the inlet and the centerline in the radial direction. However, in general, it should be understood that the inlet 300 can be disposed at other suitable positions on the scroll as long as it can provide the above-described function.

[0036] In scroll pumps of the above type, at various points in the operation of the scroll pump, there is a tendency for high internal pressures to exist in the space between the fixed scroll and the orbiting scroll (e.g., due to the fluctuating inlet pressure of the scroll pump, the fluctuating ambient exhaust pressure, and exposure to an exhaust check valve). These pressures act on the orbiting scroll and oppose the biasing device. If such high internal pressures overcome the biasing force by the biasing device, the orbiting scroll may be made to move away from the fixed scroll, and the spiral walls of the fixed scroll and the orbiting scroll no longer contact the opposing faces of the shaft seal (an effect called "lift-off"). This causes radial leakage and reduces the performance of the pump. Therefore, in order to prevent lift-off of the orbiting scroll, the biasing force by the biasing device tends to be high. This large axial load tends to lead to the use of large orbiting scroll bearings and a high wear rate of the shaft seal. However, in the scroll pump 100 described above, by using a fluid recirculation mechanism 190 to reduce the pressure in the space between the fixed and orbiting scrolls 120, 130, there is a tendency to advantageously prevent these above-mentioned problems. Specifically, the fluid recirculation mechanism 190 tends to enable the use of a biasing device 170 that applies a smaller biasing force to the orbiting scroll 130, and as a result, tends to enable the use of smaller orbiting scroll bearings and also tends to reduce the wear of the shaft seals 180a, 180b.

[0037] Furthermore, the presence of the fluid recirculation mechanism 190 tends to facilitate the use of an exhaust check valve. The reason is that the presence of the exhaust check valve tends to increase the pressure in the space between the scrolls, which tends to cause lift-off, but the presence of the fluid recirculation mechanism 190 counteracts this risk.

Explanation of Reference Numerals

[0038] 100 Scroll pump 110 Shell 120 Fixed scroll 122 First base 124 First spiral wall 130 Swivel scroll 132 Second base 134 Second spiral wall 140 Drive shaft 150 Actuator 160 Bearing 170 Biasing device 180a First shaft seal 180b Second shaft seal 190 Recirculation mechanism 190a Recirculation path 190b Recirculation valve 300 Inlet of the circulation path 310 Inlet

Claims

Claim 1 A scroll pump, comprising: an inlet and an outlet; a stationary scroll and a rotating scroll that mesh with each other and define a space therebetween for pumping fluid from the inlet to the outlet through the scroll pump, the stationary scroll and the rotating scroll; a biasing device configured to bias the rotating scroll relative to the stationary scroll; a fluid recirculation path separate from the biasing device, extending through either the stationary scroll or the rotating scroll from the space to the inlet; a fluid recirculation valve disposed in the fluid recirculation path; wherein when in an open state, the fluid recirculation valve is configured to permit fluid flow from the space through the fluid recirculation path to the inlet; when in a closed state, the fluid recirculation valve is configured to block fluid flow through the fluid recirculation path; the fluid recirculation valve is configured to switch from the closed state to the open state when a pressure difference across the fluid recirculation valve is equal to or greater than a predetermined threshold; the scroll pump includes a drive shaft configured to rotationally drive the rotating scroll, and the biasing device is configured to directly apply a force to a bearing that couples the rotating scroll to the drive shaft. Claim 2 The stationary scroll includes a first base and a first spiral wall extending from the first base. The rotating scroll includes a second base and a second spiral wall extending from the second base. The scroll pump further includes a first seal disposed between the first base and the second spiral wall. The scroll pump further includes a second seal disposed between the second base and the first spiral wall. The biasing device is configured to bias the rotating scroll relative to the stationary scroll via the first seal and the second seal. The scroll pump according to claim 1. Claim 3 The first seal and / or the second seal is at least partially formed of a polymer material. The scroll pump according to claim 2. Claim 4 The first seal and / or the second seal is a path seal. The scroll pump according to claim 2 or 3. Claim 5 The biasing device includes one or more springs, and the scroll pump according to any one of claims 1 to 4.

6. The scroll pump includes a drive shaft configured to rotationally drive the orbiting scroll, and the biasing device is configured to apply a force to the orbiting scroll via the drive shaft, and the scroll pump according to any one of claims 1 to 5.

7. The fluid recirculation valve is a check valve, and the scroll pump according to any one of claims 1 to 6.

8. The scroll pump further includes a check valve disposed at the outlet of the scroll pump, and the scroll pump according to any one of claims 1 to 7.

9. The predetermined threshold value is between 100 mbar and 400 mbar, and the scroll pump according to any one of claims 1 to 8.

10. The predetermined threshold value is between 200 mbar and 300 mbar, and the scroll pump according to claim 9.

11. The predetermined threshold value is 200 mbar, and the scroll pump according to claim 10.

12. The scroll pump includes an actuator and a drive shaft, the drive shaft is coupled to the orbiting scroll, the actuator is configured to operate the drive shaft to rotate the drive shaft to rotationally drive the orbiting scroll, and the fixed scroll is disposed between the actuator and the orbiting scroll, and the scroll pump according to any one of claims 1 to 11.

13. The scroll pump includes an actuator and a drive shaft, the drive shaft is coupled to the orbiting scroll, the actuator is configured to operate the drive shaft to rotate the drive shaft to rotationally drive the orbiting scroll, and the orbiting scroll is disposed between the actuator and the fixed scroll, and the scroll pump according to any one of claims 1 to 11.

14. Use of the scroll pump according to any one of claims 1 to 13 for pumping a fluid.

Images