Rotary Machines With Teardrop-Shaped Rotors

This application is a continuation of and claims priority benefits from U.S. patent application Ser. No. 18/346,234, filed Jul. 2, 2023, entitled “Pumps, Compressors, and Expanders with a Teardrop-Shaped Rotor”. The '234 application is a continuation of and claims priority benefits from International application No. PCT/CA2022/050021 filed on Jan. 7, 2022, entitled, “Rotary Machines With Teardrop-Shaped Rotors” which, in turn claims priority benefits from U.S. Provisional Patent Application Ser. No. 63/135,069 filed Jan. 8, 2021, entitled “Helical Trochoidal Rotary Machines With Improved Solids Handling”, and from U.S. Provisional Patent Application Ser. No. 63/144,200 filed Feb. 1, 2021, entitled “Rotary Machines With Teardrop-Shaped Rotors”.’

This application also claims priority from the '021, '069 and '200 applications. The '234, '021, '069 and '200 applications are incorporated by reference herein in their entireties.

The present invention relates to rotary positive displacement machines, where the machines are based on trochoidal geometry or offset trochoidal geometry and it is the inner profile of the stator that is hypotrochoidal or nearly hypotrochoidal in cross-section. In some embodiments the cross-sectional profile of the stator cavity is an ellipse or outwardly-offset ellipse, and the rotor has a teardrop-shaped cross-sectional profile. In some embodiments, the machines comprise a helical rotor that undergoes planetary motion relative to a helical stator. In some embodiments, the machines comprise a rotor seal.

Rotary machines, in which at least one rotor has planetary motion within a stator or housing, can be employed, for example, as positive displacement pumps, rotary compressors, vacuum pumps, expansion engines, and the like.

Pumps are devices that can move a working fluid from one place to another. There is a wide range of end uses for various types of pumps, including irrigation, fire-fighting, flood control, water supply, gasoline supply, refrigeration, chemical movement and sewage transfer. Rotary pumps are typically positive displacement pumps comprising a fixed housing, gears, cams, rotors, vanes and/or similar elements. Rotary pumps usually have close running clearances (only a small distance or gap between their moving and stationary parts), typically do not require suction or discharge valves, and are often lubricated only by the fluid being pumped.

A positive displacement pump moves fluid by trapping a volume of fluid in a chamber and forcing the trapped volume into a discharge pipe. Some positive displacement pumps employ an expanding chamber on the suction side and a decreasing chamber on the discharge side. Fluid flows into the pump intake as the chamber on the suction side expands, and the fluid flows out of the discharge pipe as the chamber collapses. The output volume is the same for each cycle of operation. An ideal positive displacement pump can produce the same flow rate at a given pump speed regardless of the discharge pressure.

Various classes of rotary machines are based on trochoidal geometries. Such rotary machines can comprise a rotor or stator whose cross-section is bounded by a certain family of curves, known as trochoids or trochoidal shapes. These include machines with the following configurations:

Thus, in these configurations, the rotor or stator is a trochoidal component, meaning it has a cross-sectional shape that is a trochoid.

Rotary machines where the rotor has a cross-sectional shape that is hypotrochoidal, and the stator cavity is shaped as an outer envelope of the rotor as it undergoes planetary motion are described in U.S. Pat. No. 10,087,758 which is incorporated by reference herein. Rotary machines with trochoidal geometries that comprise a helical rotor that undergoes planetary motion within a helical stator are described in U.S. Pat. Nos. 10,837,444 and 10,844,859 which are both incorporated by reference herein. In some embodiments, for example, with a rotor having an elliptical or near elliptical cross-section there are two, or at times three, sealing points between the rotor and stator as they move relative to each other, and every point of the rotor and stator surfaces are swept. The inverse apex of the stator cavity is a contact or sealing point, as are the two tips of the rotor. It has been found that an interference fit is not required for at least some pumps of this design, however in some embodiments an elastomeric stator is used. In other embodiments one or more seals are used (for example, at the inverse apex of the stator, and/or at the rotor tips) to improve the performance of the pump.

Generally, as used herein, an object is said to undergo “planetary motion” when it spins about one axis and orbits about another axis.

Rotary machines, such as those described above, can be designed for various applications including, for example, as pumps, compressors, and/or expansion engines. The design, configuration and operation of different rotary machines can offer particular advantages for certain applications.

Progressive cavity pumps (PCPs) are another type of rotary positive displacement machine that can offer advantages for certain applications. In PCPs, a rotor is disposed and rotates eccentrically within a helical stator cavity. The material to be pumped (typically a fluid) follows a helical path along the pump axis. The rotor is typically helical with a circular transverse cross-section displaced from the axis of the helix and defines a single-start thread. The corresponding stator cavity is a double helix (two-start thread) with the same thread direction as the rotor, and in transverse cross-section has an outline defined by a pair of spaced apart semi-circular ends joined by a pair of parallel sides. The pitch (the axial distance between adjacent threads) of the stator is the same as the pitch of the rotor, and the lead of the stator (the axial distance or advance for one complete turn) is twice that of the rotor.

In PCPs, the rotor generally seals tightly against the stator as it rotates within it, forming a series of discrete fixed-shape, constant-volume chambers between the rotor and stator. The fluid is moved along the length of the pump within the chambers as the rotor turns relative to the stator. The volumetric flow rate is proportional to the rotation rate. The discrete chambers taper down toward their ends and overlap with their neighbors, so that the flow area is substantially constant and in general, there is little or no flow pulsation caused by the arrival of chambers at the outlet. The shear rates are also typically low in PCPs in comparison to those in other types of pumps. In PCPs, where the rotor touches the stator, the contacting surfaces are generally traveling transversely relative to one another, so small areas of sliding contact occur. The rotor is typically formed of rigid material and the stator (or stator lining) of resilient or elastomeric material to facilitate sealing in the PCP. Elastomers are not generally thermally stable at high temperatures and they can react with or be degraded by some fluids. Therefore, for some applications an elastomeric stator cannot be used, and there is reliance on two metal surfaces sealing against each other. In such cases hard metals with good abrasion resistance are typically used for the rotor and stator, but wear and a lack of longevity can still be a problem. The location of most friction/wear in PCPs is generally where the rotor pockets into the end of the stator slot instantaneously contacting with great force the entire semi-circular rotor end into the half circular stator.

In a first set of embodiments, a rotary machine comprises a stator having a stator cavity and a rotor disposed within the stator cavity. The rotor has a helical profile, and a rotor axis, and a rotor shape in cross-section transverse to the rotor axis along at least a portion of a length of the rotor that is a teardrop shape. The stator cavity has a helical profile, a stator axis, and having a stator shape at any cross-section transverse to the stator axis along at least a portion of a length of the stator cavity that is an outer envelope formed when the teardrop rotor shape undergoes planetary motion. The rotary machine is configured so that, in operation of the rotary machine, the rotor undergoes planetary motion relative to the stator. In some embodiments the stator shape is an outwardly-offset ellipse. In other embodiments the stator shape is an ellipse.

In some embodiments of the first set of embodiments, the rotary machine includes a helical dynamic rotor seal mounted on the rotor.

In some embodiments of the first set of embodiments, the rotary machine has a geometry characterized by a radius R, an offset O and an eccentricity E, wherein E is the distance between the rotor axis and the stator axis, O is greater than zero, R is greater than E. In some embodiments where the stator shape is an outwardly-offset ellipse R+O=3E. In some where the stator shape is an outwardly-offset ellipse R+O>3E. In some embodiments where the stator shape is an ellipse R=3E. In some where the stator shape is an ellipse R>3E.

In some embodiments of the first set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the rotor spins about the rotor axis and orbits about the stator axis within the stator cavity. In some embodiments of the first set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the stator spins about the stator axis and orbits about the rotor axis. In some embodiments of the first set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the rotor spins about the rotor axis and the stator spins about the stator axis, and the rotor and stator are held at a fixed eccentricity in space.

In some embodiments of the first set of embodiments, rotary machine of is a multi-stage machine having a plurality of chambers between (and defined by) cooperating fluid-facing surfaces of the rotor and the stator. In some embodiments, each of the plurality of chambers has approximately the same volume. In some embodiments, each of the plurality of chambers has different dimensions. In some embodiments, each of the plurality of chambers has a different volume. In some embodiments, the pitch of the rotor and the stator varies along at least a portion of the length the rotor and stator, respectively. In some embodiments, rotor axis is inclined relative to the stator axis.

In some embodiments of the first set of embodiments, the rotary machine is a pump. In some embodiments of the first set of embodiments, the rotary machine is a compressor or an expander.

In a second set of embodiments, a rotary machine comprises a stator having a stator cavity and a rotor disposed within the stator cavity. The rotor has a rotor axis and a teardrop-shaped rotor cross sectional profile transverse to the rotor axis. The stator cavity has a stator axis, and a stator cross-sectional profile transverse to the stator axis that is an outwardly offset ellipse. The stator cross-sectional profile is an outer envelope formed when the teardrop-shaped rotor cross sectional profile undergoes planetary motion. The rotary machine is configured so that, in operation of the rotary machine, the rotor undergoes planetary motion relative to the stator.

In some embodiments of the second set of embodiments, the rotary machine further comprises a dynamic seal mounted on said rotor.

In some embodiments of the second set of embodiments, the rotary machine has a geometry characterized by a radius R, an offset O and an eccentricity E, wherein E is the distance between the rotor axis and the stator axis, O is greater than zero, R is greater than E. In some embodiments R+O=3E. In some embodiments R+O>3E.

In some embodiments of the second set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the rotor spins about the rotor axis and orbits about the stator axis within the stator cavity. In some embodiments of the second set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the stator spins about the stator axis and orbits about the rotor axis. In some embodiments of the second set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the rotor spins about the rotor axis and the stator spins about the stator axis, and the rotor and stator are held at a fixed eccentricity in space.

In some embodiments of the second set of embodiments, the rotary machine is a pump.

In a third set of embodiments, a rotary machine comprises a stator having a stator cavity and a rotor disposed within the stator cavity. The rotor has a rotor axis and a teardrop-shaped rotor cross sectional profile transverse to the rotor axis. The stator cavity has a stator axis, and a stator cross-sectional profile transverse to the stator axis that is an outwardly offset ellipse. The stator cross-sectional profile is an outer envelope formed when the teardrop-shaped rotor cross sectional profile undergoes planetary motion. The rotary machine is configured so that, in operation of the rotary machine, the rotor undergoes planetary motion relative to the stator. The rotary machine includes a dynamic rotor seal mounted on the rotor.

In some embodiments of the third set of embodiments the rotary machine has a geometry characterized by a radius R and an eccentricity E, wherein E is the distance between the rotor axis and the stator axis, R is greater than E. In some embodiments, R=3E. In some embodiments, R>3E.

In some embodiments of the third set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the rotor spins about the rotor axis and orbits about the stator axis within the stator cavity. In some embodiments of the third set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the stator spins about the stator axis and orbits about the rotor axis. In some embodiments of the third set of embodiments, the rotary machine is configured so that, in operation of the rotary machine, the rotor spins about the rotor axis and the stator spins about the stator axis, and the rotor and stator are held at a fixed eccentricity in space.

In some embodiments of the third set of embodiments, the rotary machine is a pump.

The present disclosure relates to, among other things, rotary machines in which a rotor undergoes planetary motion relative to a stator. This includes machines in which the stator is fixed (not moving) and the rotor spins about its longitudinal axis and orbits within the stator; machines in which the rotor is fixed and the stator spins and orbits; and machines in which the eccentric radius of the planetary motion is fixed and the rotor and stator both spin about their respective longitudinal axes. In some embodiments, the rotary machines are based on trochoidal geometries, and in some embodiments the rotary machines are based on offset trochoidal geometries, with the stator cavity having a hypotrochoidal geometry or offset hypotrochoidal geometry (in transverse cross-section, i.e. perpendicular to its axis).

A hypotrochoid is a roulette (or curve) traced by a point attached to a circle of radius r rolling (without slipping) around the inside of a fixed circle of radius L, where the point is at a distance d from the center of the interior circle. In some particular cases, an ellipse is formed when L=2r and d>r or d<r(d≠r).

shows ellipse. Ellipsecan represent the shape of a stator cavity in transverse cross-section. If the ellipse undergoes planetary motion, as if driven via a sun gear with radius r and a ring gear with radius 2r (arranged the same way as the circles of radius r and 2r used to generate the ellipse), the swept area from this motion of this ellipse is a limaçon with an inner loop, shown inas dashed line. The portion of limaçonthat falls within ellipse(shown as teardrop-shaped regionwith diagonal shading in) can define the transverse cross-sectional shape of a rotor. Regioncomes to a sharp point

By way of further explanation of this geometry,is a schematic diagram illustrating the profile generated by an ellipse (which can, for example, represent the cross-sectional shape of a stator cavity) as it undergoes planetary motion. Ellipse profiles-show various orientations of ellipseduring this motion. The outer envelope of profiles-, and all intervening profiles that could be generated by the motion of the ellipse, describe outer shape

Circleis the locus of the instantaneous center of rotation of the ellipse. Regionis a teardrop-shaped region having no ellipse profile lines falling within it. If ellipserepresents a stator cavity, regionrepresents a space that is never occupied by the stator itself during the planetary motion of the stator—it is always an open space. Hence a rotor having a teardrop-shaped cross-section (with pointed tip) can be disposed within such an elliptical stator cavity and can undergo planetary motion within the stator cavity.

As seen in, if ellipserepresented the cross-sectional shape of a stator cavity, and regionrepresented the cross-sectional shape of a rotor within that stator cavity, in this position of the rotor there are two separate chambers,and, between the rotor and stator within which there could be fluid. In some positions of the rotor relative to the stator there are three fluid chambers between the rotor and stator. When the rotor undergoes planetary motion relative to the stator, the fluid volume in both chambers is reduced and it is in this way that, with suitably placed inlets, outlets and/or other features, a rotary machine based on this geometry can pump a fluid and/or be used for other hydromechanical applications.

With this arrangement (assuming a contact fit between rotor and stator shapes) the tip of the rotor, represented by pointin, is in contact with the inner surface of the stator at all positions of the rotor as it undergoes planetary motion relative to the stator.

In some embodiments, rotary machines are based on a modification to the above-described geometry, as illustrated in the diagram shown in. Instead of being a true ellipse such as shown inas dashed line, the stator cavity transverse cross-sectional profile can be an offset ellipse, shown inas, generated by outwardly offsetting each point on an ellipse by a fixed distance or offset “O” measured perpendicular to a tangent to the ellipse at that point. With this offset applied, the resulting rotor shape(generated as described above) no longer comes to a sharp point at any part of its perimeter. Without the offset, the rotor shape is shown inwith dashed lineand has sharp tip. With the offset geometry, the tipof the rotor teardrop shape is more rounded.shows regionwhere a rotor seal can be mounted. A result of the offset geometry and having a more rounded region of the teardrop-shaped rotor surface being in contact with the stator, is that there tends to be less contact pressure between the components, and they are less susceptible to wear. Thus, offsetting both the stator and rotor profiles, as described, can broaden the sharp features to a more rounded profile, which reduces wear that tends to occur with sharp contact points.

In “straight” or “linear” embodiments of rotary machines having such an offset geometry, the transverse cross-sectional profile of the stator cavity is an outwardly-offset ellipse and the stator cavity is shaped as a prism where the base shape is the outwardly-offset ellipse; the rotor transverse cross-sectional profile is a teardrop with a rounded tip and the rotor is shaped as a prism where the base shape is the rounded teardrop.

andillustrate an embodiment of a rotor-stator assemblyfor a linear rotary machine. Rotorhas a teardrop-shaped profile, and is positioned inside statorwhere the transverse cross-sectional profile of stator cavityis an outwardly-offset ellipse. Rotor-stator assemblyincludes four fluid inlet/outlet ports or openingsformed in statorthat can be suitably configured so that the rotary machine can be used, for example, as a pump.

In some embodiments, the machine geometries described above are employed in rotary machines in which the rotor and stator transverse cross-sectional profiles are each swept along helical paths, the axes of those helices being the axes of rotation of those components in a reference frame in which both parts undergo simple rotary motion (the “centers” of those components). In these embodiments, the rotor and the stator cavity are twisted along their axes, rather than being straight or linear. The axes of the rotor and stator helices are offset from one another by a distance equal to the eccentricity (E) of the rotor.

Thus, in some embodiments the inner surface of a helical stator cavity is defined by an ellipse, or preferably an outwardly-offset ellipse, swept along a helical path, and a corresponding rotor is defined by sweeping the corresponding teardrop shape along a helical path with half the lead of the helical stator cavity. The helical rotor and corresponding stator have the same pitch. The rotor profile is a single-start helix, and so the pitch of the rotor is the same as the lead of the rotor. The stator profile is a double-start helical cavity, and so the lead of the rotor is half the lead of the stator.

As used herein, “pitch” is defined as the axial distance between adjacent threads (or crests or roots, for example, on a helix), and “lead” is defined as the axial distance or advance for one complete turn (360°). Pitch and lead are equal with single start helices; for multiple start helices the lead is the pitch multiplied by the number of starts.

For such machines, when a transverse cross-section is taken in any plane perpendicular to the axis of rotation (of the rotor and/or stator), the outer profile of the rotor and inner profile of the stator (that is, the cross-sectional shape of the rotor and the stator, respectively) is similar to those illustrated inand/or.

shows helical rotor, with teardrop-shaped transverse cross-section.is a side view of helical rotor, perpendicular to the longitudinal axis of helical rotor.shows a cross-sectional view of helical rotortaken in the direction of arrows A-A in.

andillustrate statorwith helical inner cavityhaving cross-sectional profilethat is an ellipse or an outwardly-offset ellipse. The outer surface of stator in this example is cylindrical.shows statorwith the dashed line indicating the stator cavity. In the illustrated embodiment, statorcorresponds to rotorof(in other words statorcan be used with rotor).

illustrates an embodiment of rotor-stator assemblywhere statorand rotorare similar to those illustrated inand, respectively. The inner surface of statordefines a helical stator cavityand a plurality of fluid chambersare defined between helical stator cavityand helical rotor. In the illustrated embodiment, the exterior surface of statoris cylindrical.is a side view of rotor-stator assembly.is a cross-sectional view taken in the direction of arrows A-A inand shows helical rotordisposed within helical stator cavitydefined by stator, with fluid chambersbetween rotorand stator.illustrates various transverse cross-sectional views of rotor-stator assemblytaken in the direction of arrows B-B, C-C and D-D in. In the illustrated embodiment. helical stator cavityhas a cross-sectional profile that is an ellipse or an outwardly-offset ellipse. As the cross-sections B-B, C-C and D-D progress along the axis of rotation of rotor, the cross-sectional profile of the rotor and stator progresses in a manner analogous to motion over time of rotorwithin or relative to helical stator cavity.

In embodiments of the rotary machines described herein that have a helical rotor and stator, as the rotor undergoes planetary motion relative to the stator, fluid chambers along the length of the machine can move fluid across a pressure differential (for example, from the low-pressure end of a pump to the high-pressure end) without the entire pressure differential across the machine acting across a single seal line. This is in contrast to linear (i.e. non-helicized) rotary machine embodiments where, for nearly all positions of the rotor relative to the stator, there are only two fluid chambers and a just single sealing point or region between the inlet and outlet of the pump. For example, see fluid chambersandand pointin.

One advantage of linear and/or helical rotary machines that are based on the geometries described herein is that the orbit speed of the rotor (relative to the stator) is reduced by a factor of two relative to some other rotary machines that are based on trochoidal geometry, and (like a PCP) they have a 1:1 spin/orbit rate ratio, rather than a 1:2 spin/orbit rate ratio. A reduced orbit speed can result in a reduction in centrifugal forces which can, in turn, reduce the magnitude of centrifugal forces that the associated hardware (for example, pump supports and drive rod) must tolerate. Rotor spin rate is the rate of rotation of the rotor about its axis and, in some embodiments, spinning the rotor is how the machine is driven. Orbit is the eccentric motion of the rotor relative to the stator which is generally more responsible for vibration. In at least some embodiments of machines where there is eccentric motion of the rotor and/or stator, a lower orbit rate is preferred (for a given pump output) because it typically results in reduced vibration. Vibration can limit the operational speed of some rotary machines.

In at least some embodiments of linear rotary machines described herein, as well as the rotor contacting the stator at the tip of the teardrop-shaped rotor, the rotor also contacts the stator on the base of the rotor (the opposite more rounded end) of the teardrop-shaped rotor. However, the contact between the base of the rotor and the stator is a rolling contact with little or no sliding contact and/or motion. Similarly, in at least some embodiments of helical rotary machines, there is rolling contact (rather than sliding contact) between this region of the helical rotor and the inner surface of the stator. This can result in reduced friction and less tendency for the parts to wear. In PCPs, and in some rotary machines that are based on trochoidal geometry, there is sliding contact between the rotor and the stator rather than rolling contact.

Yet another benefit of linear rotary machines and helical rotary machines that are based on the geometries described herein (for example, having a rotor with a teardrop-shaped cross-sectional profile and a stator cavity with a cross-sectional profile that is an ellipse or outwardly-offset ellipse) is that, in at least some embodiments, a single dynamic single seal can be used to reduce or prevent fluid slip between the rotor and stator. This is because there is a single point or continuous region of the rotor surface that is in contact or in close proximity with the stator during operation of the machine. Therefore, a dynamic a seal can be provided at the tip of the teardrop-shaped rotor (in linear embodiments) or along the helical crest of the single-start helical rotor (in helical embodiments).

In contrast, in conventional progressive cavity pumps there is no point or continuous region of constant contact between the rotor and the stator, so providing sealing between the rotor and stator can be more challenging. In machines where the rotor is a double-start helical rotor, typically two rotor seals would be used. Most rotary machines do not have a constantly contacting sealing point or region, so they require more seals or larger seal area. Some rotary machines do have a constantly contacting sealing point or region, but only on the stator. It is generally much easier to provide one or more seals on a rotor than inside the cavity of a stator, particularly in helical embodiments.