SCROLL PUMP WITH OPTIMAL SPIRAL GEOMETRY

Description

[0001] The present invention relates to a scroll pump, in particular a scroll vacuum pump, according to the preamble of claim 1, as is known in its type, for example, from US 5 496 161 A. Further prior art can be found in the documents EP 3 751 143 A1, US 4 477 238 A, EP 3 153 708 B1 or EP 3 647 599 B1.

[0002] A scroll pump is a positive displacement pump sealed against atmospheric pressure that can be used, among other things, as a compressor. A scroll vacuum pump can be used to create a vacuum in a chamber connected to the gas inlet.

[0003] Scroll vacuum pumps are also known as spiral vacuum pumps or spiral conveying devices. The pumping principle underlying a scroll pump is generally known from the state of the art and will therefore only be briefly explained below.

[0004] A pumping stage of a scroll pump has two nested or inserted into one another, for example Archimedean spiral cylinders, which are also referred to simply as spirals below. Each spiral cylinder consists of at least one equidistant spiral wall with a support plate provided on one end face of the spiral wall, wherein the outer turns of the spiral cylinder, for example the two or three outermost turns of the spiral cylinder, can be formed by wall sections that are each at a constant distance from the center of the spirals in the circumferential direction. Even if these wall sections do not strictly speaking form spiral sections, in the context of the present invention they are nevertheless attributed to the spiral and referred to as turns thereof.

[0005] The spiral cylinders are inserted into each other in such a way that they engage without contact and enclose crescent-shaped or sickle-shaped volumes in sections. One of the two spirals is immobile or fixed in the pump housing, while the other spiral, along with its support plate, is moved along a circular path via an eccentric drive, which is why this spiral, together with its support plate, is also called an orbiter. The movable spiral thus performs a so-called centrally symmetric oscillation, which is also referred to as "wobbling" or "orbiting."A crescent-shaped volume enclosed between the spiral cylinders migrates increasingly inwards as the movable spiral orbits within the spirals, whereby process gas is conveyed by means of the migrat-ing volume from a radially outer gas inlet to a gas outlet located in the center of the spiral, which leads to a compression of the gas volume due to the decreasing gas volume.

[0006] In order to achieve the highest possible performance of the scroll pump, the axial gap between the spiral wall of one spiral cylinder and the carrier plate of the other spiral cylinder should be as small as possible, since otherwise the achievable ultimate pressure and the suction capacity will decrease due to backflow effects of process gas via the axial gap, whereas the required drive power will increase in an undesirable manner.

[0007] The size of the axial gaps in question depends fundamentally on permissible component tolerances, any bearing clearance, the tilt of the orbiter, and the thermal expansion of the spiral cylinders. Typically, the axial gaps are set to a constant value across the entire length of the respective spiral cylinder between its radially inner and outer ends. The thermal expansion of the respective spiral cylinder can be compensated for, if necessary, by a seal at the free end of the respective spiral wall.

[0008] However, particularly when the pump has reached its ultimate pressure, the heat generated by pump operation can only be dissipated insufficiently, which can lead to a temperature gradient developing, particularly in the movable spiral cylinder, between its radially outer end and its radially inner end. Likewise, the movable spiral cylinder as a whole can heat up more than the stationary spiral cylinder. Due to the resulting temperature gradient, the respective spiral cylinder or its spiral wall can expand to different extents between its radially inner and its radially outer end, so that the respective axial gap in the stationary operating state of the pump can exceed a permissible value in some areas and fall below a permissible value in others.Accordingly, in areas where the axial gap exceeds a permissible value, the process gas can flow back through the axial gap towards the suction side, which has a negative effect on the achievable ultimate pressure and the suction capacity of the pump.

[0009] The invention is therefore based on the object of minimizing temperature-related backflow losses of a scroll pump.

[0010] This object is achieved with a scroll pump, in particular with a scroll vacuum pump, having the features of claim 1.

[0011] If the wall heights of the spiral cylinders of a scroll pump are specified here, these height specifications refer to the cold state of the pump or to the nominal heights of the spiral walls with which they are manufactured.

[0012] The first wall height is measured from the first surface of the first support plate, from which the first wall protrudes, to the free end or wall head of the first wall. Similarly, the second wall height is measured from the second surface of the second support plate, from which the second wall protrudes, to the free end or wall head of the second wall.

[0013] According to an unclaimed embodiment, it can be provided that the first wall height and / or the second wall height is not constant or changes between its radially inner end and its radially outer end. In this unclaimed embodiment, it is thus provided that any temperature gradients that can arise along the wall of the respective spiral cylinder during operation of the scroll pump are compensated for by different wall heights. In particular, it is provided for this purpose that the respective spiral wall has a lower wall height in regions where it is warmer than in other regions. Warmer sections of the respective spiral wall can therefore expand more than less warm sections due to temperature, so that in the stationary operating state of the scroll pump, a substantially constant axial gap is established over the entire length of the respective spiral wall.In the stationary operating state of the scroll pump, the axial gap can therefore tend to reach its desired nominal dimension everywhere, so that no areas arise in which undesirably high backflow losses can occur due to the axial gap.

[0014] Further unclaimed embodiments will now be discussed below.

[0015] Thus, according to an unclaimed embodiment, it can be provided that the first wall height is lower at the inner end of the first spiral wall than at the outer end of the first spiral wall. Additionally or alternatively, it can be provided in a corresponding manner that the second wall height is lower at the inner end of the second spiral wall than at the outer end of the second spiral wall.

[0016] It has been recognized that during pumping operation of the scroll pump, a temperature gradient tends to develop in the respective spiral cylinder, increasing toward the inner end of the respective spiral wall. To compensate for this temperature increase toward the inner end of the respective spiral wall, it can be provided that the respective spiral wall height tends to be lower at the inner end of the respective spiral wall than at the outer end of the respective spiral wall.

[0017] In a spiral cylinder with a constant wall height, however, an axial gap would be formed at the radially outer end during steady-state operation that is larger than at the inner end of the spiral cylinder, so that process gas could undesirably flow back toward the pump inlet through the axial gap at the radially outer end. Because the spiral wall height increases toward the radially outer end of the respective spiral wall when the pump is cold, the lack of thermal expansion at the radially outer end is, in a sense, anticipated, so that an axial gap of the desired size also develops at the radially outer end of the spiral wall during steady-state operation.

[0018] According to a further unclaimed embodiment, it can be provided that the second wall height, i.e. that of the movable spiral cylinder, at the outer end of the second wall is less than the first wall height at the outer end of the first wall. Additionally or alternatively, it can be provided that the second wall height at the inner end of the second wall is less than the first wall height at the inner end of the first wall. In other words, the second spiral wall as a whole can have a lower wall height than the first spiral wall. It has been recognized that the heat from the stationary spiral cylinder can tend to be better dissipated than the heat from the movable spiral cylinder due to the contact with the housing of the scroll pump.To ensure equal axial clearances, the spiral wall of the movable spiral cylinder can be designed to be slightly lower overall than the spiral wall of the stationary spiral cylinder. This allows for essentially equal axial clearances at the free end of the movable spiral cylinder and the stationary spiral cylinder during stationary pumping operation.

[0019] According to a further unclaimed embodiment, it can be provided that the first wall height decreases continuously or steadily from the outer end of the first wall to the inner end of the first wall, without any jumps in the wall height being present between the inner end of the first wall and the outer end of the first wall. Additionally or alternatively, the second wall height can decrease continuously from the outer end of the second wall to the inner end of the second wall, so that here too there are no jumps in the wall height. If one considers the developed spiral wall, its shape corresponds to that of a trapezoid.

[0020] As an alternative to the previously described embodiment, in which the respective spiral wall corresponds to the shape of a trapezoid, it can be provided according to a further unclaimed embodiment that the first wall, between its outer end and its inner end, comprises at least one first wall section with a constant first wall height and at least one second wall section with a constant first wall height that differs from the constant first wall height of the first wall section of the first wall. Additionally or alternatively, it can be provided that the second wall, between its outer end and its inner end, also comprises at least one first wall section with a constant second wall height and at least one second section with a constant second wall height that differs from the constant first wall height of the first wall section of the second wall.In this case, it can be provided, for example, that the wall height of the first and / or second wall changes abruptly or in steps between the individual wall sections. Alternatively, it can be provided that the wall height of the first and / or second wall changes continuously or steadily between the individual wall sections, so that, for example, ramp-like additional wall sections can be provided between the individual wall sections, connecting the wall sections of different heights in a ramp-like manner.

[0021] For example, considering a spiral wall with a maximum wall height of 50 mm, the maximum height difference of the respective wall can be on the order of approximately 0.05 mm. Generally speaking, the maximum height difference of the first and / or second wall height can be 0.05 to 0.5%, preferably 0.1 to 0.3%, and particularly preferably 0.15 to 0.25% of the maximum first or second wall height, respectively, in order to compensate for the different thermal expansion behavior of the respective spiral wall along its length.

[0022] In the previously described unclaimed embodiments, it is provided that the first wall height and / or the second wall height changes between its inner end and its outer end in order to ensure that the respective axial gap can reach its desired nominal dimension everywhere in the stationary operating state of the scroll pump. In contrast to this, in order to achieve the desired nominal dimension of the respective axial gap, it is provided according to the invention that the first surface of the first carrier plate forms a first cavity or depression with a first depth that increases in the radial direction towards the center, and / or that the second surface of the second carrier plate forms a second cavity or depression with a second depth that increases in the radial direction towards the center, either continuously.The second wall can thus expand axially due to temperature changes without coming into contact with the axially adjacent support plate. Rather, an axial gap can be established in steady-state operation that has the desired nominal dimension throughout. It is not necessary for the first wall height and / or the second wall height to change between their inner and outer ends; rather, the invention can provide for the first wall height and / or the second wall height to be constant between their inner and outer ends.

[0023] In the event that the depth of the respective recess increases gradually in the radial direction, it can be provided according to a further embodiment that the first surface comprises a plurality of first circular ring surfaces located concentrically to one another, between which respective first depth jumps are present, and / or that the second surface comprises a plurality of second circular ring surfaces located concentrically to one another, between which respective second depth jumps are present.

[0024] According to a further embodiment, it can furthermore be provided that the number of wall sections of the first wall corresponds to the number of second annular surfaces, wherein it can be provided in particular that the second depth jumps are located in the radial direction approximately where the wall height of the first wall changes abruptly, and / or that the number of wall sections of the second wall corresponds to the number of first annular surfaces, wherein it can be provided in particular that the first depth jumps are located in the radial direction approximately where the wall height of the second wall changes abruptly.

[0025] In the following, the invention will now be described purely by way of example with reference to the drawings in which: Fig. 1 shows a conventional scroll vacuum pump in a sectional view; Fig. 2 shows a perspective view of the orbiter of the scroll vacuum pump of the Fig. 1shows; and Fig. 3 shows an embodiment of a spiral wall in a developed view, wherein the wall height is shown exaggerated; and Fig. 4 shows another embodiment of a spiral wall in a developed view, wherein the wall height is shown exaggerated.

[0026] The Fig. 1 shows a vacuum pump designed as a scroll pump 10. This comprises a first housing element 12 and a second housing element 14 connected to it via screws 15, which forms a support plate for a pump-active structure, namely a fixed spiral wall 16. The second housing element 14 thus forms a fixed spiral component of the scroll vacuum pump 10.

[0027] The spiral wall 16 interacts with a movable spiral wall 18, which, according to the perspective view of the Fig. 2extends circumferentially between an inner end 58 and an outer end 60. The same applies to the fixed spiral wall 16, which also extends between an inner end and an outer end.

[0028] The movable spiral wall 18 is formed on a movable support plate 20 and together with this forms the Fig. 2 Orbiter 21 of scroll vacuum pump 10, shown in perspective view, is driven eccentrically via an eccentric shaft 22 to generate a pumping effect. A process gas to be pumped is conveyed from an inlet 24, which is defined in the first housing element 12, to an outlet 26, which is defined in the second housing element 14.

[0029] The eccentric shaft 22 is driven by an electric motor 28 and supported by two roller bearings 30. The eccentric shaft 22 comprises an eccentric pin 32 arranged eccentrically to its rotational axis, which transmits its eccentric deflection to the movable spiral component 20 via another roller bearing 34.

[0030] To seal the drive, a seal in the form of a Fig. 1The bellows 36 is attached to the left-hand first end, the right-hand second end of which is attached to the housing base of the first housing element 12. The left-hand first end of the bellows 36 follows the deflection of the movable support plate 20. The bellows 36 surrounding the eccentric shaft 22 is flexible, but inherently torsionally rigid, and thus, due to the fact that it is attached to the support plate 20 on the one hand and to the first housing element 12 on the other, prevents the support plate 20 or the orbiter 21 from rotating about itself.

[0031] The scroll vacuum pump 10 further comprises a fan 38 for generating a cooling air flow 46. An air guide hood 40 is provided for this cooling air flow 46, to which the fan 38 is also attached. The air guide hood 40 and the housing elements 12 and 14 are shaped such that the cooling air flow 46 flows substantially around the entire pump housing, thus achieving good cooling performance.

[0032] The scroll vacuum pump 10 further comprises an electronics housing 42, in which a control device and power electronics components for driving the motor 28 are arranged. The electronics housing 42 also forms a base for the pump 10. A channel 44 is formed between the electronics housing 42 and the first housing element 12, through which the air flow 46 generated by the fan 38 is guided along the first housing element 12 and also along the electronics housing 42, so that both are effectively cooled.

[0033] As the representation of the Fig. 1can be removed, the movable spiral wall 18, which is also referred to here as the second wall 18, is formed integrally with the carrier plate 20, which forms a flat second surface 19 (see Fig. The wall height of the second wall 18 is measured from the flat second surface 19 of the second carrier plate 20 to the free end or wall head 50 of the second spiral wall 18. In a corresponding manner, the fixed spiral wall 16, which is also referred to here as the first wall 16, is formed integrally with the carrier plate 14 formed by the second housing element 14, the height of the first wall 16 being measured from the flat first surface 17 of this carrier plate 14 to the free end or wall head 52 of the first wall 16.

[0034] Between the free end 52 of the first spiral wall 16 and the support plate 20 of the second spiral wall 16, there is an axial gap 54, which should be as small as possible during pumping operation over the entire developed length of the first spiral wall 16. Similarly, between the free end 50 of the second spiral wall 18 and the support plate 14, which is formed by the second housing element 14, there is an axial gap 56, which should also be as small as possible.

[0035] To minimize the respective axial gap 54, 56 during stationary pumping operation, it is accordingly provided that the wall height H of the movable spiral wall 18 and / or that of the fixed spiral wall 18 changes between its inner end 58 and its outer end 60. In particular, it is provided that the respective spiral wall 16, 18 has a lower wall height in higher temperature regions than in colder temperature regions. Thus, the respective spiral wall 16, 18 can expand more in higher temperature regions to achieve the smallest possible axial gap 54, 56 than in colder regions.

[0036] Since the temperature of both spiral walls 16, 18 tends to increase in the direction of the inner end 58 of the respective spiral wall 16, 18 during stationary pumping operation, it is particularly provided that the height of the respective wall 16, 18 is somewhat lower at the inner end 58 of the respective wall 16, 18 than at the outer end 60 of the respective wall 16, 18. Since the movable spiral wall 18 tends to heat up more during pumping operation than the fixed wall 16, it can furthermore be provided that the movable wall 18 as a whole has a lower height than the fixed spiral wall 16, so that the movable spiral wall 18 can expand somewhat more due to temperature than the fixed spiral wall 16. In particular, it can be provided that the movable spiral wall 18 has a lower wall height H at both its inner end 58 and its outer end 60 than the fixed spiral wall 16 at the respective ends 58, 60.

[0037] Since the temperature increases during stationary pumping operation in the respective spiral wall 16, 18 towards the respective inner end 58, it can, according to the Fig. 3 In the embodiment shown, it can be provided in particular that the wall height H of the fixed spiral wall 16 or that of the movable spiral wall 18 decreases continuously from the respective outer end 60 to the inner end 58 of the respective spiral wall 16, 18. Thus, the higher the temperature becomes towards the inner end 58, the more the respective wall height H decreases, so that the respective spiral wall 16, 18 can expand more strongly in the axial direction as it approaches the inner end 58.

[0038] Alternatively, it may be used in accordance with the Fig. 4illustrated embodiment, it can be provided that the respective spiral wall 16, 18 has three wall sections 62, 64, 66, each with a different constant wall height H, wherein the wall height H decreases stepwise in the direction of the inner end 58 of the respective spiral wall 16, 18.

[0039] Alternatively, it may be used in accordance with the Fig. 4In the embodiment shown in dashed lines, it can be provided that the wall height H between the individual wall sections 62, 64, 66 changes continuously, so that the individual wall sections 62, 64, 66 are connected to one another via ramp sections 68 with a variable wall height H. Both in the embodiment with a suddenly changing wall height H and in the embodiment in which the individual wall sections 62, 64, 66 are connected to one another by ramp sections 68, the wall height H of the respective wall section is lower, the closer the respective wall section 62, 64, 66 is to the inner end 58 of the respective spiral wall 16, 18.

[0040] Since the height difference of the respective spiral wall 16, 18 between its inner end 58 and its outer end 60 is very small and not visible to the naked eye, the wall height H in the Fig. 3 and 4exaggerated. For example, the maximum height difference of the respective spiral wall 16, 18 can be only around 0.05 mm, which would not be visible to the naked eye with a spiral wall height H in the range of 10 to 50 mm. Although the maximum height difference of the respective spiral wall can also be slightly larger depending on the pump type, the maximum height difference is generally approximately 0.05 to 0.5%, preferably 0.1 to 0.3%, and particularly preferably 0.15 to 0.25% of the maximum height dimension of the respective spiral wall 16, 18.

[0041] According to the invention, in addition or alternatively to the embodiments of the Figures 3 and 4provided that the first surface 17 of the first carrier plate 14 forms a first cavity or depression 70 with a variable first depth T1, which increases in the radial direction towards the center of the first carrier plate 14, and / or that the second surface 19 of the second carrier plate 20 forms a second cavity or depression 72 with a variable second depth T2, which increases in the radial direction towards the center of the second carrier plate 20, as shown in the Figures 3 and 4 is indicated by a bold line L, which only illustrates the first or second surface 17, 19 of the respective support plates 14, 20.

[0042] According to Fig. 3 the first or second depth T1, T2 increases continuously towards the center of the respective carrier plate 14, 20, whereas the depth increase according to Fig. 4is carried out in two steps, which means that the first and second surfaces 17, 19 are formed by a plurality of concentrically arranged first circular ring surfaces 74, which are separated from each other by respective first depth steps. In particular, according to the representation of the Fig. 4 It can be provided that the number of wall sections 62, 64, 66 of the first wall 16 corresponds to the number of second annular surfaces 74, the second depth jumps being located in the radial direction at least approximately where the wall height H of the first wall 16 changes abruptly. In a corresponding manner, the number of wall sections 62, 64, 66 of the second wall 18 can correspond to the number of first annular surfaces 74, the first depth jumps being located in the radial direction at least approximately where the wall height H of the second wall 18 changes abruptly. List of reference symbols

[0043] 10Scroll vacuum pump 12First housing element 14Second housing element, carrier plate 15Screws 16Volt wall / volute 17First surface 18Volt wall / volute 19Second surface 20Carrier plate 21Orbiter 22Eccentric shaft 24Inlet 26Outlet 28Motor 30Rolling bearing 32Eccentric pin 34Rolling bearing 36Bellows 38Fan 40Air guide hood 42Electronics housing 44Duct 46Air flow 50Free end / wall head of 18 52Free end / wall head of 16 54Axial gap between 52 and 20 56Axial gap at 50 58Inner end 60Outer end 62First wall section 64Second wall section 66Third wall section 68Ramp sections 70First cavity, recess 72Second cavity, recess 74Annular surfaces HWall height T1variable depth of 70 T2variable depth of 72

Claims

1. A scroll pump, in particular a scroll vacuum pump (10), comprising a fixed-position spiral cylinder in the form of a first wall (16) having a first wall height (H), wherein the first wall (16) widens spirally from an inner end (58) to an outer end (60), and a movable spiral cylinder in the form of a second wall (18) having a second wall height (H) which widens spirally from an inner end (58) to an outer end (60) and which is nested with the spirally widening first wall (16), wherein the first wall (16) is provided at a first carrier plate (14) having a first surface, wherein the first wall height (H) extends from the first surface of the first carrier plate (14) up to the free end (52) of the first wall (16); and / or wherein the second wall (18) is provided at a second carrier plate (20) having a second surface, wherein the second wall height (H) extends from the second surface of the second carrier plate (20) up to the free end (50) of the second wall (18), characterized in that the first surface forms a first depression (70) having a first depth (T1) which increases continuously in the radial direction towards the center; and / or in that the second surface forms a second depression (72) having a second depth (T2) which increases continuously in the radial direction towards the center.

2. A scroll pump according to claim 1, characterized in that the first surface comprises a plurality of first circular ring surfaces (74) which are disposed concentrically to one another and between which there are respective first jumps in depth; and / or the second surface comprises a plurality of second circular ring surfaces (74) which are disposed concentrically to one another and between which there are respective second jumps in depth.

3. A scroll pump according to claim 2, characterized in that the number of wall sections (62, 64, 64) of the first wall (16) corresponds to the number of second circular ring surfaces (74), wherein it is in particular provided that the second jumps in depth are located in the radial direction where the wall height (H) of the first wall (16) changes abruptly; and / or the number of wall sections (62, 64, 64) of the second wall (18) corresponds to the number of first circular ring surfaces (74), with it in particular being provided that the first jumps in depth in the radial direction are located where the wall height (H) of the second wall (16) changes abruptly.