The present disclosure is directed, in general, to gerotor compressors and expanders, and more specifically, to features that improve the performance of gerotor compressors and expanders.
A gerotor operates using inner and outer rotors that rotate about their respective axes within a housing. A drive mechanism synchronizes the rotors so that they do not touch. As the rotors rotate, teeth of the inner rotor and lobes of the outer rotor move relative to each other to create voids between the teeth of the inner rotor and the lobes of the outer rotor that open, reach a maximum volume, and then close. Fluid enters and leaves the voids through gaps (referred to as ports) between the lobes of the outer rotor.
The housing comprises four regions. A first of the four regions forms an inlet duct for the gerotor system. A second of the four regions forms an outlet duct for the gerotor system. The third and fourth of the four regions are located between the inlet duct region and the outlet duct region and have small clearances between inner and outer rotors and the housing. These two regions operate to prevent fluid flow around the outside of the outer rotor between the inlet duct and the outlet duct.
For a gerotor system operating as a compressor, input power to the drive mechanism drives the rotors. A fluid enters from the inlet duct of the housing through one or more intake ports as the void opens. Once the fluid is captured, the void volume decreases, causing the pressure of the fluid to increase. After a desired pressure (generated by the geometries of the two rotors) is achieved, the fluid exits through one or more outlet ports into the outlet duct of the housing.
For a gerotor system operating as an expander, high-pressure fluid enters from the inlet duct of the housing through one or more intake ports into a small void in the gerotor. The fluid is captured, and the fluid pressure operates on the rotors to cause the void volume to increase as the fluid pressure decreases. The expanding fluid causes the rotors to turn. After a desired pressure is achieved, the fluid exits through one or more outlet ports into the outlet duct of the housing. The rotation of the rotors produces output power from the gerotor drive mechanism.
Gerotor compressors and expanders have several advantages that apply to both gerotor compressors and expanders, such as the following:
No valves;
Low vibration;
Compact;
Efficient;
Tolerant of liquid;
Low manufacturing cost;
High pressure ratio per stage;
Rotational speed matches conventional engines, motors, and generators;
Low parts count;
Oil-free operation; and
Operates efficiently at varying speeds
According to a first embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The plurality of ports includes an inlet subset of ports and an outlet subset of ports. Fluid flows into the gerotor system through the inlet subset of ports and out of the gerotor system through the outlet subset of ports. The housing includes an inlet duct fluidly coupled with the inlet subset of ports and an outlet duct fluidly coupled with the outlet subset of ports. The inlet duct includes an input pipe and the outlet duct includes an outlet pipe. The inlet pipe is located on the inlet duct based upon a location of an inlet port in the inlet subset of ports having a highest inlet fluid velocity through the inlet port. The outlet pipe is located on the outlet duct based upon a location of an outlet port in the outlet subset of ports having a highest outlet fluid velocity through the outlet port.
According to a second embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The plurality of ports includes an inlet subset of ports and an outlet subset of ports. Fluid flows into the gerotor system through the inlet subset of ports and out of the gerotor system through the outlet subset of ports. The housing further includes an inlet duct fluidly coupled with the inlet subset of ports and an outlet duct fluidly coupled with the outlet subset of ports.
The inlet duct includes a plurality of inlet channel vanes that extend from an entrance end to a rotor end of the inlet duct. The inlet channel vanes form a plurality of inlet channels, which alter substantially identical velocities of fluid entering the inlet channels to a velocity at the rotor end that substantially matches a velocity of fluid through one or more corresponding inlet ports.
The outlet duct includes a plurality of outlet channel vanes extending from a rotor end to an exit end of the outlet duct. The outlet channel vanes form a plurality of outlet channels, each outlet channel configured to alter a velocity of fluid at the rotor end of the outlet channel that is determined by a velocity of fluid through one or more corresponding outlet ports to substantially identical velocities of fluid exiting the outlet channels.
According to a third embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The plurality of ports includes an inlet subset of ports and an outlet subset of ports. Fluid flows into the gerotor system through the inlet subset of ports and out of the gerotor system through the outlet subset of ports. The housing further includes an inlet duct fluidly coupled with the inlet subset of ports and an outlet duct fluidly coupled with the outlet subset of ports. The inlet duct includes an input pipe located at a first end of the inlet duct and the outlet duct includes an outlet pipe located at a first end of the outlet duct. A profile of a circumferential portion of the inlet duct varies from the first end to a second end of the inlet duct to alter fluid velocity vectors in the inlet duct to more closely match fluid velocity vectors passing through corresponding inlet ports. A profile of a circumferential portion of the outlet duct varies from the first end to a second end of the outlet duct to alter fluid velocity vectors passing through one or more outlet ports to substantially the same fluid velocity in the outlet pipe.
According to a fourth embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The outer rotor includes a plurality of lobe portions and at least one disk portion. The outer rotor further includes a feature on an inner surface of the outer rotor, where the feature is configured to reduce stress concentration in the bases of the lobe portions.
According to a fifth embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The outer rotor includes a plurality of lobe components and a plurality of disk components. Each lobe component is mounted to the disk components by at least one pin passing through at least one disk component into the lobe component.
According to a sixth embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The outer rotor includes a plurality of lobe components and a plurality of disk components, wherein the lobe components are hollow.
According to a seventh embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The outer rotor includes a plurality of lobe components and a plurality of disk components. An outer portion of each lobe component includes a first material and an inner portion of each lobe component includes a second material. The second material is a lighter material than the first material.
According to an eighth embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The outer rotor includes an outer surface having a region in proximity to a corresponding region of an inner surface of the housing. Either the outer rotor region or the housing region includes a labyrinth seal that is configured to reduce fluid leakage through a gap between the outer rotor region and the housing region.
According to a ninth embodiment of the present disclosure, a gerotor system includes an inner rotor, an outer rotor having a plurality of ports, and a housing. The inner rotor includes an outer face in proximity to a corresponding inner face of the housing. Either the inner rotor face or the housing face includes a labyrinth seal that is configured to reduce fluid leakage through a gap between the inner rotor face and the housing face.
Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.
For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
It should be understood at the outset that, although example embodiments are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or not. The present invention should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale.
For simplicity, this disclosure will focus on compressors; however, it should be understood that the disclosure applies equally as well to expanders. Further, it should be understood that a compressor and expander may be combined to form an engine, so the discussions below apply to engines as well.
While this disclosure discusses fluid flow into, within, and out of gerotors according to the disclosure, it will be understood that such fluids may comprise vapor or gas or a mixture of gas and fluid. Indeed, in gerotor operating as a compressor, a gas may enter the gerotor and be liquefied through compression.
The performance of gerotor compressors can be enhanced by incorporating features that accomplish the following:
reduce porting losses;
cut abradable coatings;
reduce deflection of outer-rotor lobes; and
reduce leakage through tight gaps.
Each feature will be discussed in more detail.
Reduce Porting Losses
In gerotor compressors, fluid enters through ports during an intake portion of a cycle and exits through other ports during a discharge portion of the cycle. Compared to the size of the ducts that carry fluid to and from the compressors, the size of the ports is relatively small; therefore, the fluid must accelerate to flow through the ports. The acceleration and subsequent deceleration may cause turbulence near the ports, which can reduce efficiency. Incorporating features that reduce turbulence can reduce porting losses.
The radial velocity vectors 108 and 110 through the ports are directly related to the rate of change of the rotating void volume. It should be noted that in addition to the radial velocity vector, there is also a circumferential velocity vector (not shown) that results from the rotation of the rotors. The circumferential velocity vector depends upon rotation rate of the inner rotor and outer rotor.
At the compressor inlet, the volume change is small at the 7 and 11 o'clock positions and is largest at the 9 o'clock position. The actual lengths of the radial velocity vectors shown in
At the compressor outlet, the volume change is small at the 1 o'clock position and is largest at the 3 o'clock position. The actual lengths of the radial velocity vectors shown in
To improve efficiency, fluid velocity through a port should more closely match the velocity in a duct external to the port. When there is a mismatch in fluid velocities, turbulence is generated, which converts kinetic energy into thermal energy and reduces efficiency. In addition, efficiency is improved when the direction of the velocity through the port matches that through ducts carrying fluid to or from the gerotor. The flow through a duct may be substantially radial; however, it should be noted that there is a circumferential component to the velocity vector, which reflects that fact that the inner rotor and outer rotor are rotating.
Because the port velocities are highest in the 3 and 9 o'clock positions, the compressor outlet and inlet pipes are located generally at the 3 and 9 o'clock positions, respectively. It should be noted that for a compressor having a compression ratio higher than the compressors shown in
To reduce losses, it is desirable that fluid direction in a duct more closely match a direction of fluid flow through the port. To satisfy this condition, an axis of the inlet and outlet pipes may be substantially aligned with dominant velocity vectors emanating from the outer rotor. As noted previously, the velocity vectors through the ports are not purely radial and have a circumferential component that results from rotor rotation. To improve efficiency, the axis of the inlet and outlet pipes may be aligned with the dominant velocity vectors through the ports, which includes both a radial and circumferential component.
To service the entire circumference of the fluid inlet, an inlet duct should extend from the 6 to the 12 o'clock positions. As a result, some of the fluid entering the compressor must flow in the circumferential direction. The gap between the outer rotor and the duct is defined by ensuring that at any angular position, the velocity of the fluid through the port (as illustrated in
Although
Similar to the inlet and outlet pipes described with reference to
Typically, fluid flow entering and exiting the compressor is not completely smooth and has pulses. The pulse frequency is N times the rotational rate of the outer rotor, where N is the number of ports in the outer rotor.
There are many ways to construct a resonant tuning section according to the disclosure.
The gerotor system 500 includes a converging section 520 and turning vanes 516. Additionally, the system 500 includes a diverging section 522 and turning vanes 518.
The inlet channels 740 and the outlet channels 742 are designed with the following considerations. At the entrance to the inlet duct 712, all fluid velocity vectors into the inlet duct 712 are substantially identical. As fluid flows along the inlet channels 740, the widths of the channels change so that, at the rotor end of the channels, magnitudes of the fluid velocities in the inlet channels 740 substantially match magnitudes of the fluid velocity through corresponding ports of outer rotor 704 (as explained above with reference to
Additionally, angles of the channels 740 in the inlet duct 712 vary so as to introduce circumferential components in the velocity of the incoming fluid that accommodate a rotational speed of the rotor 702 (as discussed with reference to
Inlet ducts 912A and 912B in this embodiment have rapidly converging profiles, while outlet ducts 914A and 914B have gradually diverging (e.g., conical) profiles. In other embodiments, an inlet duct may have a gradually converging profile and/or an outlet duct may have a rapidly diverging profile. To prevent flow separation, an angle less than about 7 degrees is preferred in such converging and diverging profiles.
Cut Abradable Coatings
To reduce leakage losses, a gerotor system should have small clearances between inner and outer rotors and the gerotor housing. During operation, the rotors are subjected to temperatures that cause the rotors to thermally expand. Should the rotors touch each other or the housing, damage can occur to the rotors and/or the housing.
To avoid damage when such contact occurs, it is desirable for one contacting element to have a hard surface, while the other contacting element has an abradable coating, such as molybdenum disulfide, polymers (e.g., porous epoxy), or soft metal (e.g., babbitt, brass, or copper). A particularly effective coating is nickel/graphite, which is applied via thermal spray. The nickel is porous with graphite-filled voids. If there is a large interference, the hard surface contacts the nickel/graphite coating and causes a portion of the coating to be removed. If there is a small interference, the hard surface contacts the nickel/graphite coating and pushes the nickel into the voids, thus displacing graphite.
When there is contact between the hard surface and the abradable coating, it is preferred that the hard surface be rough, such as can be obtained via sand blasting. The roughened surface accomplishes two objectives: (1) it acts like sand paper and helps remove the abradable coating, and (2) the resulting gap is roughened, which causes turbulence and thereby reduces flow through the gap.
The roughened surface works particularly well with softer coatings; however, with harder coatings (e.g., nickel/graphite), galling can occur. To avoid galling, the hard surface may incorporate cutting edges. Such cutting edges may include roughened edges, configured to leave the abradable coating roughened.
The cutting edges 1062 on the inner rotor 1002 may come into contact with mating surfaces on the outer rotor 1004 and/or the housing 1006. The mating surfaces have an abradable coating, as discussed above. The cutting edges 1062 are raised sufficiently high (preferably about 0.002 inch) from the upper and lower surfaces of the inner rotor 1002 that debris from the abradable coatings can be discharged, but not so high that significant dead volume is created between the inner rotor 1002 and the housing 1006.
The cutting edges 1060 on the outer rotor 1004 are located on the edges of the lobes. The mating surface of the housing 1006 has an abradable coating, as discussed above. The cutting edges are raised sufficiently high (preferably about 0.002 inch) from the surface of the outer rotor 1004 that debris from the abradable coatings can be discharged, but not so high that significant dead volume is created between the outer rotor 1004 and the housing 1006. A rake angle of the cutting edges 1060 is adjusted so that the cutting edge 1060 cuts the abradable coating, rather than smearing it, thereby reducing or preventing galling. Also, an open pocket 1064 is formed in the outer rotor 1004 in front of the cutting edge 1060, to collect debris generated from the abradable coating, which also reduces or prevents galling.
Reduce Deflection of Outer Rotor Lobes
The lobes of the outer rotor of a gerotor system bridge two discs that define the axial ends of the outer rotor. As the outer rotor spins, centrifugal forces act to deform it. Because the two discs are well supported in the radial direction, they do not undergo much deformation from centrifugal forces. In contrast, the lobes are not well supported in the radial direction and can deform significantly from centrifugal forces, particularly if the lobes bridge a long distance between the two discs.
If the disc and lobe are made from a single piece of material, then there are significant stress concentrations at the root of the lobe (the interface between the disc and lobe) as centrifugal forces are applied. If not addressed, such stress concentrations may cause cracks to form in the lobes of the outer rotor, which may lead to catastrophic failure. The chances of such failure can be reduced or eliminated by lowering the rotation rate of the outer rotor, however this solution may adversely affect compressor capacity.
To address stresses in the roots of the lobes of the outer rotor, a number of strategies may be deployed, as described below.
The outer rotor 1104 comprises components 1104A and 1104B that are joined like a “clam shell.” The component 1104A comprises disk/shoulder portion 1166A, fillet 1170A, and lobe portion 1168A. The component 1104B comprises disk/shoulder portion 1166B, fillet 1170B, and lobe portion 1168B. While components 1104A and 1104B are shown in
As may be seen in
To reduce or eliminate this effect, the fillets continue to the port region, as shown in View B. Components 1102A and 1102B are fabricated with the shoulder portions 1166A and 1166B in the port regions. The shoulder portions 1166A and 1166B continue the fillets 1170A and 1170B into the port regions of the outer rotor 1104, to mate with the rounded upper and lower edges of the inner rotor 1102, in order to reduce dead volume near the ports and improver the efficiency of a gerotor system utilizing the outer rotor 1104 and the inner rotor 1102.
The outer rotor 1204 comprises components 1204A and 1204B that are mechanically coupled to each other to form the contiguous outer rotor 1204. The component 1204A comprises undercut 1272A and lobe portion 1268A. The component 1204B comprises undercut 1272A and lobe portion 1268A. While the outer rotor 1204 is shown in
The outer rotor 1304 eliminates stresses in its lobes by forming the lobes 1376 as separate components from the disks 1374A and 1374B. Instead, because of centrifugal forces on the lobes 1376, the pins 1378A and 1378B are subjected to shear forces. To reduce centrifugal forces, the lobes 1376 may be constructed from lightweight materials, such as titanium whereas the discs 1374A and 1374B may be made from less expensive materials, such as steel. In a preferred embodiment, the lobes 1376 are constructed from materials that are both lightweight and stiff, such as carbon fiber composites or silicon carbide. To reduce the impact of centrifugal forces on the lobes of the outer rotor, the material property of interest for the lobes is the specific modulus, also known as the stiffness to weight ratio or specific stiffness.
The bolts 1480 pass completely through the disk 1474A, the lobe 1479, and the disk 1474B. As described for outer rotor 1304, shown in
The lobes 1576 and 1584 fit into pockets or recesses 1577 in the disks 1574A and 1574B. This design reduces stress on the bolts 1578 and 1580 by allowing some of the centrifugal force experienced by the lobes 1576 and 1584 to be resisted by forces on the sidewalls of the pockets 1577, in addition to forces on the bolts 1578 and 1580. Benefits and suitable elements of alternative embodiments as described with reference to
The lobes 1688 and 1690 are rounded and fit into rounded pockets or recesses 1687 in the disks 1686A and 1686B. A rounding profile of the recesses 1687 corresponds to a rounding profile of the lobes 1688 and 1690. As with the outer rotor 1504 described with reference to
Reduce Leakage Through Tight Gaps
As may be seen in
In the embodiments shown in
The outer faces of the outer rotor are coupled to bearings and gears, all of which are lubricated with oil that ultimately drains to a sump. Typically, the pressure in the oil sump is referenced to the compressor inlet (20 psia in this example), which is the lowest continuous pressure in the system. This strategy ensures that oil flows from the bearings and gears back to the sump. Temporarily, while a given void space is expanding and drawing gas into it, the pressure in the void space will drop below the compressor inlet pressure (for example 18 psia). During this temporary suction event, the void space could draw oil through the gaps into the void space. Generally, there is a desire to prevent the gas from being contaminated with oil, so this is an undesirable outcome. By ensuring that the farthest slot always has a slight pressure above the sump pressure, it ensures that gas leakage is always outward from the compression space and therefore oil cannot enter the compression space.
While the labyrinth seal is shown in
Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke paragraph 6 of 35 U.S.C. Section 112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.
The present application is related to U.S. Provisional Patent Application No. 61/940,293, which was filed on Feb. 14, 2014, and is entitled “Features that Improve the Performance of Gerotor Compressors and Expanders.” Provisional Patent No. 61/940,293 is hereby incorporated by reference into the present application as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent No. 61/940,293.
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3779674 | Eckerle | Dec 1973 | A |
4846642 | Nuber | Jul 1989 | A |
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20020187051 | Maier | Dec 2002 | A1 |
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20090220369 | Wiedenhoefer | Sep 2009 | A1 |
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Number | Date | Country | |
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20150267702 A1 | Sep 2015 | US |
Number | Date | Country | |
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61940293 | Feb 2014 | US |