Scroll pump with isolation barrier

Scroll pumping apparatus includes a first scroll element and a second scroll element; a drive mechanism operatively coupled to the second scroll element for producing orbiting motion of the second scroll element relative to the first scroll element, the drive mechanism having an axis of rotation; and an isolation element to isolate a first volume and a second volume in the scroll pumping apparatus. The isolation element includes a first resilient annular member coupled, directly or indirectly, to the first scroll element, a second resilient annular member coupled, directly or indirectly, to the second scroll element, and a tubular member coupled between the first and second annular members.

FIELD OF THE INVENTION

This invention relates to scroll-type pumps and, more particularly, to devices and methods for isolation of the bearings and other lubricated components of such pumps from a working volume where compression and pumping of the fluid takes place.

BACKGROUND OF THE INVENTION

Scroll-type devices are well known in the field of vacuum pumps and compressors. In a scroll device, a movable spiral blade orbits with respect to a fixed spiral blade within a housing. The movable spiral blade is connected to an eccentric drive mechanism. The configuration of the scroll blades and their relative motion traps one or more volumes or “pockets” of a gas between the blades and moves the gas through the device. Most applications apply rotary power to pump the gas through the device. Other applications include expanders, which operate in reverse from compressors and extract power from the expansion of a pressurized gas.

A scroll pump includes stationary and orbiting scroll elements, and a drive mechanism. The stationary and orbiting scroll elements each include a scroll plate and a spiral scroll blade extending from the scroll plate. The scroll blades are intermeshed together to define interblade pockets. The drive mechanism produces orbiting motion of the orbiting scroll element relative to the stationary scroll element so as to cause the interblade pockets to move toward the pump outlet.

For proper function of the scroll pump, it is necessary to maintain a fixed angular relation, or synchronization, between the two scroll elements. Scroll pumps typically utilize one or more devices for synchronizing the intermeshed scroll blades. Each synchronizing device is coupled, directly or indirectly, between the stationary and orbiting scroll elements and is required to permit orbiting movement while preventing relative rotation of the scroll elements. In one prior art approach, disclosed in U.S. Pat. No. 801,182 issued Oct. 3, 1905, three crank mechanisms are connected between the orbiting and stationary scroll elements.

Oil-lubricated scroll devices are widely used as refrigerant compressors. Oil-lubricated scroll pumps have not been widely adopted for use as vacuum pumps, mainly because the cost of manufacturing a scroll pump is significantly higher than a comparably-sized, oil-lubricated vane pump. In cases where oil contamination is unacceptable, dry scroll pumps are used. Normally these pumps contain multiple rolling element bearings which require lubrication. One approach to lubrication is to use a low-vapor-pressure synthetic grease. However, some degree of contamination can still occur when the bearings are located within the vacuum space of the pump. In addition, the lubricating performance of such greases is generally inferior, and their cost higher, than equivalent petroleum greases.

Accordingly, methods have been devised to isolate the bearings from the pumping mechanism while still permitting the relative orbital motion of the fixed and moving scroll elements. U.S. Pat. No. 5,951,268, issued Sep. 14, 1999, describes the use of a flexible metal bellows for isolation of the running gear of a scroll pump, also relying on the bellows for synchronization of the scroll elements. The torsional load on the bellows due to its function in synchronization poses a risk of failure due to metal fatigue. U.S. Pat. No. 7,261,528, issued Aug. 28, 2007 to assignee of the present invention, describes the use of a rectangular flexible metal element for synchronization as well as to take axial loads, while using a bellows, rotatably mounted, for isolation.

Prior art use of tubular bellows for isolation requires that the bellows be of sufficient length to reduce the stresses in the bellows material below the fatigue life limit for the material. Increased bellows length increases the length of the pump, which may be unacceptable in many applications. Consequently, improved methods of isolating the running gear of a scroll pump from the vacuum space are needed.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, scroll pumping apparatus is provided. The scroll pumping apparatus comprises: a first scroll element and a second scroll element; a drive mechanism operatively coupled to the second scroll element for producing orbiting motion of the second scroll element relative to the first scroll element, the drive mechanism having an axis of rotation; and an isolation element to isolate a first volume and a second volume in the scroll pumping apparatus, the isolation element including a first resilient annular member coupled, directly or indirectly, to the first scroll element, a second resilient annular member coupled, directly or indirectly, to the second scroll element, and a tubular member coupled between the first and second annular members.

Isolation of the bearings and other contamination-generating components from the working volume of the pump is provided by an isolation element including two substantially annular members, joined by a tubular member. In the operation of the scroll pump, the annular members deflect to accommodate the lateral displacement of the orbiting scroll element with respect to the fixed scroll element.

In some embodiments, one or both ends of the isolation element is rotatably mounted to a respective mating component, and synchronization is provided by one or more separate synchronization devices. Thus the isolation element is not subjected to torsional stress.

In some embodiments, one or both of the annular members may be convoluted in a pattern of concentric circular convolutions to provide flexibility.

In some embodiments, the annular members of the isolation element may be joined by a short tubular bellows to provide additional flexibility.

In some embodiments, at least one of the annular members may include an elastomeric disk, of constant or non-constant section, to provide the desired flexibility.

In some embodiments, at least one of the annular members may include a dome-shaped element to provide the desired flexibility.

In some embodiments, both ends of the isolation element may be non-rotatably mounted, one end directly or indirectly coupled to the orbiting scroll element, and the other end directly or indirectly coupled to the pump housing or fixed scroll element, thus providing synchronization between the two scroll elements. In this case, although the isolation element is exposed to torsional stress, the complexity of the pump can be reduced as separate synchronization devices are not required.

According to a second aspect of the invention, a method is provided for operating scroll pumping apparatus of the type comprising a first scroll element and a second scroll element. The method comprises producing orbiting motion of the second scroll element relative to the first scroll element with respect to an axis of rotation; and isolating, using an isolation element, a first volume and a second volume in the scroll pumping apparatus during orbiting motion, the isolation element including a first resilient annular member coupled, directly or indirectly, to the first scroll element, a second resilient annular member coupled, directly or indirectly, to the second scroll element, and a tubular member coupled between the first and second annular members.

According to a third aspect of the invention, scroll pumping apparatus comprises a scroll set having an inlet and an outlet, the scroll set comprising a stationary scroll element including a stationary scroll blade and an orbiting scroll element including an orbiting scroll blade, wherein the stationary and orbiting scroll blades are intermeshed together to define one or more interblade pockets; a drive mechanism operatively coupled to the orbiting scroll element for producing orbiting motion of the orbiting scroll blade relative to the stationary scroll blade so as to cause the one or more interblade pockets to move toward the outlet, the drive mechanism having an axis of rotation; and an isolation element to isolate a first volume and a second volume in the scroll pumping apparatus, the isolation element including a first resilient annular member coupled, directly or indirectly, to the stationary scroll element, a second resilient annular member coupled, directly or indirectly, to the orbiting scroll element, and a tubular member coupled between the first and second annular members.

DETAILED DESCRIPTION OF THE INVENTION

A scroll pump in accordance with the prior art is shown inFIG. 1. A gas, typically air, is evacuated from a vacuum chamber or other equipment (not shown) connected to an inlet of the pump. A pump body includes a fixed scroll element1and a pump housing6. The pump includes an outlet13for exhaust of the gas being pumped.

The scroll pump includes a set of intermeshed, spiral-shaped scroll blades. The fixed scroll element1includes a stationary scroll blade11extending from a stationary scroll plate12. An orbiting scroll element2includes an orbiting scroll blade21extending from an orbiting scroll plate22. Scroll blades11and21extend axially toward each other and are intermeshed together to form interblade pockets31,32,33. Tip seals4, located in grooves at the tips of the scroll blades, provide sealing between the scroll blades. Orbiting motion of scroll blade21relative to scroll blade11produces a scroll-type pumping action of the gas entering the interblade pockets31,32,33between the scroll blades.

A drive mechanism for the scroll pump includes a motor (not shown) coupled through a crankshaft5to orbiting scroll element2. An end51of crankshaft5has an eccentric configuration with respect to the main part of crankshaft5and is mounted to orbiting scroll element2through an orbiting plate bearing set23. Crankshaft5is mounted to pump housing6through main bearings61,62. When the motor is energized, crankshaft5rotates in main bearings61,62. The eccentric configuration of crankshaft end51produces orbiting motion of scroll blade21relative to scroll blade11, thereby pumping gas from the inlet to outlet13.

The scroll pump may include a bellows assembly7coupled between a stationary component of the vacuum pump and the orbiting scroll element2so as to isolate a first volume8inside bellows assembly7and a second volume9outside bellows assembly7. In this prior art scroll pump, the bellows assembly7has a fixed connection at each end. Thus, any tendency of the orbiting scroll element2to rotate about its own center is inhibited by the torsional stiffness of bellows assembly7. Bellows assembly7is sealed to the stationary and moving components by seals (not shown). The bearings required to drive the pump are isolated from second volume9by bellows assembly7. Thus the vacuum space of second volume9is not contaminated by grease or oil as long as bellows assembly7and its end seals remain intact.

Another scroll pump in accordance with the prior art is shown inFIG. 2. In this case, bellows assembly7is mounted to orbiting scroll element2by a non-rotatable connection (not shown in detail). Bellows assembly7is mounted to the pump housing6by a rotatable connection including ring71and seal72. The bellows assembly being thus rotatably mounted, does not inhibit rotation of the orbiting scroll element about the pump axis.

Two supports24,25are mounted to orbiting scroll element2. Two more supports (not shown) are mounted to a stationary component of the pump housing6, located at 90 degrees from the two supports24,25mounted to the orbiting scroll element2. A substantially rectangular strip10is connected to supports24,25by clamping plate101and screws102. Similarly, strip10is connected to the other two supports on the pump housing by clamping plates and screws (not shown). As described in U.S. Pat. No. 7,261,528, flexible strip10thus resists the tendency of orbiting scroll element2to rotate about its own axis.

FIG. 3is a schematic cross-sectional diagram of a scroll pump in accordance with embodiments of the invention. Isolation between volumes8and9is provided by an isolation element11. Isolation element11has a fixed connection to orbiting scroll element2, and a seal is formed using sealing elements in accordance with standard practice. Isolation element11is mounted to pump housing6with a rotatable joint including a ring111and a seal112. The design of the fixed and rotatable connections of isolation element11to orbiting scroll element2and housing6is a matter of existing practice and is not relevant to the invention. It will be understood that a variety of seal designs can be employed within the scope of the invention. It will be understood that the rotatable joint may be made from isolation element11to orbiting scroll element2, and the fixed joint to housing6, within the scope of the invention.

Flexible band10is used for synchronization in the same way as inFIG. 2. It will be understood that other synchronization devices may be used within the scope of the invention.

Volume8inside the isolation element11, containing the bearings and rotating components of the pump, is separated from volume9outside the isolation element11, containing the vacuum space and the gas being pumped. The bearings required to drive the pump are isolated from volume9by isolation element11. Thus, contamination of the vacuum space by grease or oil cannot occur as long as isolation element11and its end seals remain intact.

FIG. 4is a schematic cross-sectional diagram of another scroll pump in accordance with embodiments of the invention. In this case, isolation element11is mounted in a non-rotatable fashion to both of orbiting scroll element2and pump housing6. Thus, any tendency of the orbiting scroll element2to rotate about its center is resisted by the torsional stiffness of isolation element11. Isolation element11is sealed to the stationary and moving components by seals (not shown). The bearings required to drive the pump are isolated from volume9by isolation element11. Thus contamination of the vacuum space by grease or oil cannot occur as long as isolation element11and its end seals remain intact. In this embodiment, additional synchronization devices are not required.

FIG. 5is a perspective cross-sectional view of an isolation element120in accordance with embodiments of the invention. Convoluted annular members122and124provide flexibility to accommodate lateral displacement. In applying the isolation element120to the scroll pump ofFIG. 3, at least one end of the isolation element120is rotatably mounted to the housing or the orbiting scroll element. The other end may have a fixed connection to the housing or the orbiting scroll element, or may be rotatably mounted. In the scroll pump ofFIG. 4, both ends of the isolation element have a fixed connection, one connection to the housing and one connection to the orbiting scroll element. Sealing and fixing of the ends of the isolation element to the fixed and moving components of the pump are effected by standard sealing and fixing methods. Details of such fixing and sealing methods are known to those skilled in the art.

A cross-sectional diagram of isolation element120ofFIG. 5is shown inFIG. 5A. First annular member122is sealed at its inside diameter to one end of the tubular member130, and second annular member124is sealed at its inside diameter to an opposite end of tubular member130. Annular members122and124are configured to be flexible and resilient to permit lateral and axial deformation, with the annular members returning to their original configurations when the deforming force is removed. In the embodiment ofFIGS. 5 and 5A, annular members122and124have concentric circular convolutions and may be formed, for example, of a thin metal. In the embodiment ofFIGS. 5 and 5A, tubular member130may be a thin metal tube. Tubular member130is shown as having a constant cross section, but may be formed with a non-constant cross section depending on the requirements of the scroll pump in which isolation element120is used. In particular, tubular member130may have a non-constant diameter along its length and/or may have a non-constant thickness along its length. The parameters of isolation element120, such as inside diameter, outside diameter, length, material thickness, and the like, depend on the application.

As shown inFIG. 5A, first annular member122is coupled to a first pump component140through a first seal142and second annular member124is coupled to a second pump component144through a second seal146. Pump components140and144undergo orbiting motion relative to each other during pump operation. For example, pump component140may be a fixed housing component, and pump component144may be an orbiting scroll element. As discussed below, seals142and146may be fixed seals or rotating seals.

Isolation element120is a sealed unit wherein first annular member122and second annular member124are sealed to tubular member130. In addition, first annular member122is sealed to pump component140, and second annular member124is sealed to pump component144. Accordingly, isolation element120provides isolation between a first volume150and a second volume152, while permitting relative movement of pump components140and144.

FIG. 6is a perspective cross-sectional view of an isolation element160in accordance with embodiments of the invention. A tubular member162of isolation element160includes a bellows section164between annular members122and124to provide additional flexibility in lateral displacement. It will be understood that it may be desired to eliminate one of the annular members. It will be further understood that the flexible tubular bellows section164may be located near either end, or in the middle, of the tubular member162of the isolation element. More than one tubular bellows section may be included in the tubular member162of the isolation element160, depending on the requirements of the application. One or more tubular bellows sections may be utilized in the tubular member of any of the embodiments described herein.

FIG. 7is a perspective cross-sectional view of an isolation element180in accordance with embodiments of the invention. Elastomeric disks190and192replace the annular members ofFIGS. 5 and 6to provide flexibility in lateral displacement. Center tube118may be of metal, a rigid plastic, or an elastomeric material. It will be understood that the elastomeric disks may replace one or both of the convoluted annular members in other embodiments of the invention.

FIG. 8is a perspective cross-sectional view of an isolation element200in accordance with embodiments of the invention. Dome-shaped members210and212replace the annular members ofFIGS. 5 and 6to provide flexibility in lateral displacement.

FIG. 9is a cross-sectional view of an isolation element400in accordance with embodiments of the invention. Isolation element400includes a first annular member402coupled through a seal404to a pump component406and a second annular member412coupled through a seal414to a pump component416. Annular members402and412are coupled to opposite ends of a tubular member420. In the embodiment ofFIG. 9, the first annular member402and the second annular member412have different outside diameters, with the respective diameters being selected according to the geometry of the scroll pump in which it is used. It will be understood that first annular member402can have a smaller outside diameter than second annular member412.

FIG. 10is a cross-sectional diagram of an isolation element450in accordance with embodiments of the invention. Isolation element450includes a first annular member452sealed to one end of a tubular member480and a second annular member462sealed to an opposite end of tubular member480. In the embodiment ofFIG. 10, first annular member452extends outwardly from tubular member480, and second annular member462extends inwardly from tubular member480. Tubular member480is sealed to the inside diameter of first annular member452and is sealed to the outside diameter of second annular member462. First annular member452is coupled through a seal454to a pump component456, and second annular member462is coupled through a seal464to a pump component466. The geometry of isolation element450is selected to according to the geometry of the scroll pump in which it is used.

FIG. 11is a cross-sectional diagram of an isolation element500in accordance with embodiments of the invention. In the isolation element500, a first annular member is sealed to one end of a tubular member530and a second annular member512is sealed to an opposite end of tubular member530. In the embodiment ofFIG. 11, tubular member530is sealed to the outside diameters of annular members502and512, and the annular members502and512extend inwardly from tubular member530. An inside diameter of first annular member502is coupled through a seal504to a pump component506, and an inside diameter of second annular member512is coupled through a seal514to a pump component516. As in previous cases, the geometry of isolation element500is selected according to the geometry of a scroll pump in which it is used.

Each of the disclosed isolation elements provides isolation between volumes within a scroll pump. The isolation element permits the lubricated and particle-generating components of the scroll pump, such as bearings and other rotating components, to be isolated from the working volume of the pump. The isolation element provides lateral and axial flexibility to accommodate the orbiting movement of the scroll pump, while providing isolation. It will be understood that the various configurations of the isolation element shown inFIGS. 9-11and described above can be applied to the isolation elements shown inFIGS. 5-8.

The first scroll element1and the second scroll element2can be any scroll elements known in the art or later developed. In general, second scroll element2describes orbiting motion relative to first scroll element1during operation of the scroll pump. The scroll elements1and2may be single-stage scroll elements or may have two or more stages. An example of a single-stage scroll pump is shown inFIGS. 3 and 4. A scroll pump having more than one stage is disclosed in U.S. Pat. No. 5,616,015, issued Apr. 1, 1997 to assignee of present invention. Each stage of the scroll pump may include one or more scroll blades. In some embodiments, the scroll elements1and2may include a stationary scroll element and an orbiting scroll element. In other embodiments, the scroll elements1and2may have a co-rotating configuration, as disclosed in U.S. Pat. No. 4,534,718, issued Aug. 13, 1985, wherein both scroll elements rotate and one scroll element describes orbiting motion relative to the other scroll element. The scroll pump may be oil-lubricated or dry (oil-free) and may operate as a vacuum pump or as a compressor.

In practical applications of the invention, other combinations of the essential features may be used than those illustrated.