Fluid Transfer Device

Abstract

A positive displacement gear pump or gear hydraulic motor having at least a first rotor having first rotor teeth and a second rotor having second rotor teeth, the first rotor teeth meshing with the second rotor teeth. A first rotor chamber is defined between the first rotor teeth and a second rotor chamber is defined between the second rotor teeth. When the rotors mesh, the first rotor chamber, the second rotor chamber or both are sealed or substantially sealed to form what is referred to herein as a secondary chamber. Pressure fluctuations in the secondary chamber are released by internal flow passages in the first rotor, the second rotor or both, creating a fluid connection between the first rotor chamber and the second rotor chamber. The first rotor may be an internal gear rotor or both rotors may be external gear rotors.

Description

[Technical field]

[0001] Gear pumps and gear hydraulic motors [Background technology]

[0002] Gear pumps and gear hydraulic motors can form substantially enclosed chambers in their rotating parts that can vary in volume, leading to water hammer and turbulence. Summary of the Invention

[0003] A positive displacement fluid transfer device is provided that includes a housing defining an inlet flow path and an outlet flow path, a first rotor, and a second rotor. The first rotor is mounted for rotation within the housing about a first rotor axis and has first rotor tines and defines first rotor chambers at least partially between the first rotor tines, each first rotor chamber being defined at least partially by two first rotor tines of the first rotor tines. The second rotor is mounted for rotation within the housing about a second rotor axis parallel to the first rotor axis and has second rotor tines and defines second rotor chambers at least partially between the second rotor tines, each second rotor chamber being defined at least partially by two second tines of the second rotor tines. The first rotor tines and the second rotor tines are configured to mesh with each other at a meshing portion of the fluid transfer device. The first and second rotor tines come into mesh at an outlet portion of the device, where meshing of the first and second rotor tines reduces a collective volume of the first and second rotor chambers at the outlet portion of the device, and at least the first rotor chamber opens to an outlet flow path at the outlet portion of the device. The first and second rotor tines come out of mesh at an inlet portion of the device, where disengagement of the first and second rotor tines increases a collective volume of the first and second rotor chambers at the inlet portion of the device, and at least the first rotor chamber or at least the second rotor chamber opens to an inlet flow path at the inlet portion of the device. At least one of the first and second rotors defines an internal flow path arranged to connect the first rotor chamber to the second rotor chamber at at least a portion of the inlet portion, the meshing portion or the outlet portion of the device.

[0004] Various embodiments may include any one or more of the following configurations: one of the first rotor and the second rotor may be an outer rotor and the other of the first rotor and the second rotor may be an inner rotor, with the teeth of the outer rotor meshing with the teeth of the inner rotor as integral gear teeth. There may be a crescent seal between the inner and outer rotors. The crescent seal may seal the outer rotor teeth for volumetric displacement of fluid around the crescent seal in the first rotor chamber, seal the inner rotor teeth for volumetric displacement of fluid around the crescent seal in the second rotor chamber, or seal both the outer and inner rotor teeth. In cross section in a plane perpendicular to the outer rotor axis, the outer rotor teeth are shaped as fins with generally straight leading fin surfaces and generally straight trailing fin surfaces, and the inner rotor teeth are shaped as lobes with rounded leading lobe surfaces and rounded trailing lobe surfaces, the leading lobe surfaces being arranged to contact the trailing fin surfaces, and the trailing lobe surfaces being arranged to contact the leading fin surfaces. Other planes perpendicular to the outer rotor axis may have the same or different cross sections, where the leading and trailing directions are defined by the rotation of the rotors, and when the rotors mesh in an internal gear arrangement, the direction of rotation of the outer rotor is also the direction of rotation of the inner rotor. The number of outer rotor fins may be twice the number of inner rotor lobes. In cross section in the plane, the leading and trailing fin surfaces may be straight, and the leading and trailing lobe surfaces may be circular arcs.The first fin of the outer rotor fin may have a leading first fin surface of the leading fin surface that is parallel to a first radial line through the outer rotor axis and displaced in the trailing direction from the first radial line through the first radial line by a first displacement amount, an opposing fin of the outer rotor fin is rotationally symmetric to the first fin of the outer rotor fin, and a first lobe of the inner rotor lobe may have a trailing first lobe surface of the trailing lobe surface formed in a trailing leading shape, the trailing leading shape having a trailing leading radius substantially equal to or less than the first clearance value, i.e., the first displacement amount. The second fin of the outer rotor fin may have a trailing second fin surface of the trailing fin surface that is parallel to a second radial line through the outer rotor axis and displaced in the leading direction from the second radial line through the outer rotor axis by a second displacement amount, the second opposing fin of the outer rotor fin is rotationally symmetric with the second fin of the outer rotor fin, and the second lobe of the inner rotor lobe may have a leading second lobe surface of the leading lobe surface formed in a leading arc shape, the leading arc shape having a leading arc radius that is substantially equal to or less than the second clearance value, i.e., the second displacement amount. The first displacement amount is equal to the second displacement amount. For example, if the first lobe is a lobe, the trailing arc shape may be concentric with the leading arc shape and the leading first fin surface may be parallel to the trailing second fin surface. The outer rotor fins may be rotationally symmetric about the outer rotor, and the inner rotor lobes may be rotationally symmetric about the inner rotor.

[0005] In other embodiments, the first rotor tines and the second rotor tines may mesh as external gear tines.

[0006] In any of these embodiments, the internal flow passages may be in the first rotor tines, in the second rotor tines, or in the first and second rotor tines. In one example, the internal flow passages of the first rotor may be in every other first rotor lug, and the internal flow passages of the second rotor may be in every other second rotor lug. The positive displacement fluid transfer device may be arranged to direct fluid flow throughout the device substantially perpendicular to the first rotor axis. The positive displacement fluid transfer device may be configured to operate as a pump, with the inner rotor, the outer rotor, or both connected to a mechanical energy source to drive the pump. The positive displacement fluid transfer device may be configured to operate as a hydraulic motor, with fluid pressure driving the inner rotor, with the inner rotor connected to a mechanical energy receiver, or with fluid pressure driving the outer rotor, with the outer rotor connected to a mechanical energy receiver, or both.

[0007] These and other aspects of the devices and methods are set forth in the claims.

[0008] Embodiments will now be described with reference to the drawings, in which like reference numerals refer, by way of example, to like elements throughout. [Brief description of the drawings]

[0009] [Figure 1] 1 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device.

[0010] [Diagram 2] FIG. 2 is a pictorial view of the inner rotor of the embodiment shown in FIG. 1.

[0011] [Diagram 3] FIG. 3 is an axial cross-sectional view of the inner rotor of FIG. 2.

[0012] [Figure 4]1A-1C are side cross-sectional views of non-limiting embodiments of the disclosed fluid transfer devices including an outer rotor shaft that may be linked to an external device.

[0013] [Diagram 5] FIG. 2 is a cross-sectional view of the embodiment of FIG. 1 showing the angle between the position of Top Dead Center (TDC) and a point equidistant between the inlet and outlet.

[0014] [Figure 6] 1 is a pictorial diagram of a non-limiting embodiment of a fluid transfer device driven by or configured to drive an electric machine;

[0015] [Figure 7] FIG. 7 is a side cross-sectional view of the fluid transfer device shown in FIG. 6.

[0016] [Figure 8] FIG. 7 is a cutaway isometric view of the fluid transfer device shown in FIG. 6.

[0017] [Figure 9] 1A is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having fluid flow passages in the lobes of an inner rotor. FIG.

[0018] [Figure 10] 1A is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having fluid passages in the fins of an outer rotor. FIG.

[0019] [Figure 11] 1 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having fluid passages in the lobes of an inner rotor and in the fins of an outer rotor. FIG.

[0020] [Figure 12] FIG. 12 is a cross-sectional isometric view of the embodiment shown in FIG.

[0021] [Figure 13]FIG. 12 is a pictorial view of the outer rotor shown in FIG.

[0022] [Figure 14] 1 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having fluid flow passages located at the axial ends of an inner rotor. FIG.

[0023] [Figure 15] 1A-1D are schematic diagrams of geometric shapes used to construct non-limiting embodiments of fluid transfer devices.

[0024] [Figure 16] FIG. 2 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having three inner rotor lobes and fluid flow passages in the fins of an outer rotor.

[0025] [Figure 17] 17 is a pictorial view of the inner rotor, outer rotor, and crescent seal of the embodiment shown in FIG. 16.

[0026] [Figure 18] 1 is a pictorial diagram of an inner rotor as may be used in an embodiment of the disclosed fluid transfer device having fluid flow passages on both axial ends of the inner rotor.

[0027] [Figure 19] 1 is a schematic axial view of a non-limiting embodiment of a fluid transfer device having an inner rotor with leading and trailing surfaces defined by arcs of different diameters. FIG.

[0028] [Figure 20] 1 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having inner rotor teeth, the leading and trailing surfaces of the inner rotor teeth not defined by an arc, and having fluid flow paths within the inner rotor teeth.

[0029] [Figure 21]FIG. 2 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having inner rotor teeth, the leading and trailing surfaces of the inner rotor teeth not defined by an arc, and having a fluid flow passage within an inward projection of the outer rotor.

[0030] [Figure 22] FIG. 13 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having two external gear rotors with fluid passages within each tooth of each rotor.

[0031] [Diagram 23] FIG. 13 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having two external gear rotors with fluid flow passages in each tooth of only one rotor.

[0032] [Figure 24] FIG. 13 is an axial cross-sectional view of a non-limiting embodiment of a fluid transfer device having two external gear rotors with fluid flow passages in every other tooth of each rotor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Minor modifications may be made to the embodiments described herein without departing from what is recited in the claims.

[0034] Disclosed are designs for fluid transfer devices including at least a plurality of rotors and a housing, as well as methods for designing and constructing such devices. The structure of the device may be similar to that of a conventional positive displacement pump, but includes additional features designed to reduce the likelihood of fluid hammer or cavitation, which can be undesirable in such devices.

[0035] Sealing contact is defined in this disclosure as the area of ​​contact or sealing proximity between two rotors or between a rotor and a housing. Sealing proximity is defined in this disclosure as a gap of sufficient flow resistance to prevent excessive leakage.

[0036] The positive displacement device may include a housing and a first rotor and a second rotor having gear teeth that mesh with each other on at least a portion of the device. The positive displacement device may also be constructed with additional rotors, such additional rotors being within those disclosed herein. Either one of the two rotors in the pair of meshing rotors may be considered the first rotor and the second rotor. The first rotor is mounted for rotation within the housing about a first rotor axis, and the second rotor is mounted for rotation within the housing about a second rotor axis that is generally parallel to the first rotor axis. The term "teeth" is used to indicate that they mesh as gear teeth and does not necessarily imply a radially oriented structure. These devices may include devices where one rotor is an inner rotor located within another rotor, an outer rotor, and the outer rotor meshes with the inner rotor as an integral gear. Figures 1-21 disclose an embodiment according to the present disclosure having an inner rotor and an outer rotor. The positive displacement device may also include two external gear rotors that mesh in parallel. Figure 22 discloses an embodiment according to the present disclosure having two external gears arranged in parallel with meshing teeth as external gear teeth. The external gears are shown as being the same size but can be different sizes.

[0037] At a portion of the device away from meshing, the rotor may have a sealing contact with the housing for positive displacement of the fluid. As used herein, the term "housing" may include any element fixed within the housing, for example an insert mounted between the rotors, such as a crescent seal (also referred to as a crescent seal) in an internal gear configuration. Fluid may travel through the device in a first rotor chamber defined between the first rotor teeth and a second rotor chamber defined between the second rotor teeth. These chambers may be substantially closed and may be of constant volume in this portion of the device.

[0038] At the meshing portion of the device, the first rotor tines and the second rotor tines mesh with one another, which meshing will first be discussed with respect to how the tines move into and out of meshing.

[0039] The teeth of the first rotor enter into meshing with the teeth of the second chamber at the outlet portion of the device. The housing may define an outlet flow passage, with at least the first rotor chamber opening into the outlet flow passage in the outlet portion of the device. Here, we define the first rotor as a rotor having a chamber that opens directly to the outlet (i.e., not through a chamber of another rotor) in embodiments where only one rotor has a chamber that opens directly to the outlet. For example, in the particular internal gear example described below, only the outer rotor chamber may open directly to the outlet. In other embodiments (not shown), only the inner rotor chamber may open directly to the outlet. Also, both may open directly to the outlet, as shown in FIG. 22. When the teeth enter into meshing, this reduces the collective volume of the first rotor chamber and the second rotor as they move through the outlet portion of the device. At least in a portion of the outlet portion of the device, the first rotor chamber may open to the second rotor chamber without the additional configuration described below.

[0040] The teeth of the first rotor are disengaged from the teeth of the second rotor at the inlet portion of the device. The housing may define an inlet flow path, and at least the first rotor chamber or at least the second rotor chamber may open to the inlet flow path in the inlet portion of the device. If only the first rotor chamber opens directly to the outlet in the outlet portion, one or both of the first rotor chamber or the second rotor chamber may open to the inlet in the inlet portion, for example in an internal gear pump with a radially inward inlet and a radially outward outlet. In the specific example shown below, the first rotor chamber opens to the outlet. When the teeth go into unmesh, this reduces their collective volume as the first rotor chamber and the second rotor move through the inlet portion of the device. At least in the part of the inlet portion of the device, the first rotor chamber may open to the second rotor chamber without the additional configuration described below.

[0041] As the teeth move from the outlet portion to the inlet portion through the meshing portion, in the absence of additional configuration, the first rotor chamber may become sealed by the teeth of the second rotor, the second rotor chamber may be sealed by the teeth of the first rotor, or both. This may lead to water hammer or turbulence. Thus, it is proposed to connect the first and second rotor chambers using an internal flow passage defined by the first rotor, the second rotor, or both. As used herein, the term "internal" means internal to a non-axial bearing surface that interfaces with the other rotor. An embodiment such as that shown in FIG. 18 may have a flow passage on an axial surface, which in some embodiments may contact the end plate of the other rotor. In some cases, the internal flow passage may directly connect an otherwise unsealed chamber to an inlet or outlet, or may only indirectly connect to a chamber of the outer rotor via an inlet or outlet. In these cases, the term "connect" is used herein to encompass this indirect connection. The use of internal flow channels allows the tooth surfaces to press against each other with a high surface area, thereby improving the possibility of establishing and maintaining a fluid film to reduce contact stress. Further details are discussed below with respect to specific embodiments. In some implementations, one of the first rotor and the second rotor is an outer rotor, and the other of the first rotor and the second rotor is an inner rotor. The outer rotor teeth (outer rotor teeth) may be shaped as fins, for example, having a generally straight leading fin surface and a generally straight trailing fin surface. For convenience, the outer rotor teeth are referred to herein as fins, although non-fin shaped embodiments are also contemplated. The inner rotor teeth (inner rotor teeth) may be shaped as lobes, for example, including a rounded leading lobe surface and a rounded trailing lobe surface. For convenience, the inner rotor teeth are referred to herein as lobes, although non-lobed shaped embodiments are also contemplated.The terms "leading" and "trailing" are defined by the rotation of the outer rotor, which also corresponds to the direction of rotation of the inner rotor in the internal gear embodiment. The leading lobe surface is arranged to contact the trailing fin surface, and the trailing lobe surface is arranged to contact the leading fin surface. A crescent seal may be disposed between the inner and outer rotors. As the inner rotor lobes leave the area where they mesh with the outer rotor, they allow fluid from an inlet in the housing, which flows between the inner rotor lobes and between the outer rotor fins around the crescent seal, and is discharged to an outlet in the housing as the lobes re-enter the area where they mesh with the fins. The device may be operable as a pump, such that the inner or outer rotor is driven to induce a fluid flow, or as a hydraulic motor, such that the inner or outer rotor is driven by the fluid flow to rotate the shaft, or as either a pump or a hydraulic motor.

[0042] Fin and Lobe Shape

[0043] Throughout this specification, when a particular shape is described, e.g., a flat or rounded shape, this shape may occur in cross section in a plane perpendicular to the outer rotor axis. In cross sections in other planes perpendicular to the outer rotor axis, the same shape may exist (e.g., an arc corresponding to a cylindrical section surface), or may exist but be rotated (e.g., a helical shape, not shown), or there may be further variations, subject to any requirements for desired meshing. In some embodiments with fin-shaped outer rotor tines and lobe-shaped inner rotor tines, especially when the outer rotor fin count is twice the inner rotor lobes (2:1 embodiments), the fins and lobes may be more specifically shaped such that the leading and trailing fin surfaces are straight and the leading and trailing lobe surfaces are arcs. When the fin count is twice the lobes, there is a particular radius on the inner rotor where the portion of the inner rotor at this radius moves in a straight radial line relative to the outer rotor axis. By locating the center of the arc at this radius, the inner rotor lobe can maintain sealing contact with the straight surface of the outer rotor fin continuously for part of the rotor rotation. In a 2:1 embodiment, each lobe can contact two adjacent fins on one side and two adjacent fins on the other side, while a fin contacts two adjacent lobes and never contacts any other lobe. Thus, in principle, it is not required that the lobes be rotationally symmetrical with respect to each other, or that the fins be rotationally symmetrical with respect to each other (although each fin must be generally symmetrical with its opposite fin). For convenience, it is expected that rotational symmetry will generally be used. In the illustrated embodiment, the outer rotor fin is rotationally symmetrical about the outer rotor and the inner rotor lobe is rotationally symmetrical about the inner rotor. The leading surfaces of the fins and the corresponding trailing surfaces of the lobes may be related as follows and as shown in FIG. 15.The first fin 15040 of the outer rotor fin may have a leading first fin surface 15045 of the leading fin surface that is parallel to the trailing direction and displaced in the trailing direction from the first radial line 15050 through the outer rotor axis by a first displacement 15055. Note that the difference in location of the arc center 15000 relative to the lobe center 15060 of the first lobe 15070 is exaggerated so that the radial line 15055 does not appear parallel to the leading edge 15045. Also, in some embodiments, the fin surfaces of successive fins may be made parallel even if the arc centers are not concentric. In this case, the radial line 15050 may be moved to instead correspond to the path of movement of the lobe center 15060 relative to the outer rotor. Thus, to maintain continuous sealing contact between the leading first fin surface and the trailing first lobe surface over a portion of the rotation of the device, the trailing arc shape may have a trailing arc radius that is substantially equal to or less than a clearance value, such as clearance value 15065, i.e., the first displacement amount. Alternatively, the distance across the lobes 15070 may be configured to be substantially equal to or less than the clearance value, i.e., the sum of the first displacement values.

[0044] Similarly, the trailing surfaces of the fins and the corresponding leading surfaces of the lobes may be related as follows and as shown in FIG. 15. The second fin 15046 of the outer rotor fin may have a trailing second fin surface 15048 of the trailing fin surface that is parallel to a second radial line (not shown, but passing through the arc center 150155) and displaced in the leading direction from the second radial line through the outer rotor axis 15044 by a second displacement amount. The second radial line may correspond to the path of travel of the leading arc center 15015 of the first lobe 15070 relative to the outer rotor. Again, the difference in location of the arc center 15015 relative to the lobe center 15060 of the first lobe 15070 is exaggerated so that the radial line through the arc center 15015 does not appear to be parallel to the leading edge 15045 in this view. Also, in some embodiments, the fin surfaces of successive fins may be parallel even if the arc centers are not concentric. In this case, the radial line 15050 may be moved to correspond with the path of movement of the lobe center 15060 of the first lobe 15070 relative to the outer rotor. Thus, to maintain continuous sealing contact between the trailing first fin surface and the leading first lobe surface over a portion of the device's rotation, the trailing arc shape may have a leading arc radius that is substantially equal to or less than the first clearance value, i.e., the second displacement amount.

[0045] The second displacement amount may be equal to the first displacement amount or may be different from the first displacement amount. Thus, the leading and trailing surfaces may have different arc radii even on the same lobe. In most particular embodiments shown in the figures, the displacement amounts, and therefore the arc radii, are the same. Figure 19 shows an embodiment in which the displacement amounts are not equal.

[0046] In embodiments where the arc centers of the leading and trailing cylindrical section surfaces of the inner rotor are coincident, the contact path between the leading surface of the inner rotor lobe and the leading surface of the corresponding fin on the outer rotor may be parallel to the contact path between the leading surface of the lobe on the inner rotor and the leading surface of the corresponding fin on the outer rotor. Thus, considering one lobe as both the "first lobe" and the "second lobe" described above, the leading first fin surface is parallel to the trailing second fin surface in order to maintain a constant (possibly including zero) clearance when the trailing arc shape is concentric with the leading arc shape. In other embodiments, the arc centers of the leading and trailing cylindrical surfaces of the inner rotor may be non-coincident, or the leading and trailing cylindrical surfaces may be at different radii, as shown in FIG. 15. In some embodiments, the arc center may be at a particular radius from the axis of the inner rotor described above, such that a point at that radius moves in a straight radial line relative to the outer rotor. Thus, the cylindrical surfaces have continuous contact over a portion of the rotation of the inner rotor, and the outer rotor surfaces are parallel to a straight radial line along which the arc centre of the cylindrical surfaces travels, and are offset from such radial line by the radius of the cylindrical surfaces. If the leading and trailing surfaces of the inner rotor legs have non-coincident arc centres, the outer rotor fins contacting the inner rotor legs may have non-parallel straight surfaces, and if the leading and trailing surfaces of the inner rotor legs have different arc radii, the outer rotor fin surfaces may have correspondingly different offsets from the radius of the outer rotor. As noted above, the sealing surfaces of the outer rotor fins need not be parallel. Variations may be permitted, for example, the inner rotor sealing surface need not be perfectly cylindrical.

[0047] 15 illustrates a non-limiting example of how the geometry of the inner rotor 15020 may be derived. Arrow 15095 indicates a desired direction of rotation of the inner rotor 15020. The inner rotor 15020 has a leading edge 15030 and a trailing edge 15035. The leading edge 15030 may define an arc corresponding to a first circle 15010 having a first circle (and arc) center 15015. The trailing edge 15035 may define an arc corresponding to a second circle 15025 having a second circle (and arc) center 15000. In such embodiments, the outer rotor fin surfaces (not shown) that contact any given inner rotor leg may be non-parallel such that the surfaces are further away at a radius that defines a greater distance from the axis of the outer rotor; conversely, in another embodiment where the arc center of the trailing arc surface is in front of the arc center of the leading arc surface, the pair of outer rotor fin surfaces that contact any given inner rotor leg may be parallel.

[0048] Modifications such as these can be used to bias rotational forces on the outer rotor resulting from fluid pressure on the inner rotor, to increase the ratio of rolling to sliding contact between the inner rotor lobes and the outer rotor fins, or to achieve other desired effects. The lobes 19005 each have a leading surface 19010 and a trailing surface 19015 with a leading edge radius that is not equal to the trailing edge 19015. In this above-mentioned non-limiting embodiment, the radius of the trailing edge 19015 is greater than the radius of the leading edge 19010, but the radius of the leading edge 19010 can be configured to be greater than the trailing edge 19015. For reference, an outer rotor 19030 and crescent 19020 with radial fins 19025 are shown in FIG. An array of fluid paths 19035 are disposed within the lobes 19005 of the inner rotor 19000, spanning from the root between adjacent lobes to the outer diameter of said lobes 19005. For reference, arrows 19040 indicate the direction of rotation.

[0049] At least in embodiments having leading and trailing surfaces of concentric arcs of lobes and fin surfaces having equal radial extent, when the trailing surface of the inner rotor contacts or is in sealing proximity with the leading surface of the outer rotor, the leading surface of the outer rotor contacts or is in sealing proximity with the leading surface of the inner rotor to prevent a leakage path between the chambers.

[0050] Secondary Chamber

[0051] Fluid transfer devices as described above and conventional gear pumps generally form secondary chambers that may cause water hammer. In this specification, secondary chamber refers to an inner or outer rotor chamber that is substantially surrounded by the teeth of the other rotor in the rotational position of the device and is not connected to the inlet, outlet or chamber of the outer rotor except through the flow paths as described herein, particularly for the pressure reduction (relief) of the inner and outer chambers. For example, the gear pump of FIG. 20 has an outer rotor 20005 and an inner rotor 20010 and rotates in the direction indicated by the arrow 20040. The secondary chamber 20015 of the inner rotor chamber is formed in the area defined by the sealing contact between the leading edge of the inner rotor tooth 20025 and the outer rotor tooth 20030 and the sealing contact between the trailing edge of the inner rotor tooth 200335 and the outer rotor tooth.

[0052] Similarly, the gear pump shown in FIG. 22 has a first rotor 22005 rotating in the direction indicated by the arrow 22040 and a second rotor 22010 rotating in the direction indicated by the arrow 22045. The secondary chamber 22015 of the first rotor chamber is formed by a sealing contact between the leading edge of the first rotor outward projection 22020 and the second rotor outward projection 22025 and the trailing edge of the first rotor outward projection 22030 and the second rotor outward projection 22025. Pressure reduction (relief) is provided by a channel 22030 provided in both the inner rotor and the outer rotor. In other embodiments, such as shown in FIG. 23, the channel 220030 may be present in only one rotor. In other embodiments, such as shown in FIG. 24, the channel 220030 may be present in every second tooth of both rotors.

[0053] Other positive displacement fluidic devices having secondary chambers are described below.

[0054] Without the flow paths exiting these secondary chambers, fluid hammer or vacuum spikes will occur during certain operating conditions. In a non-limiting example shown in FIG. 20, the flow paths from the secondary chambers are located in the inner rotor outward projection and lead from the area between two adjacent inner rotor outward projections to the tip of the leading inner rotor outward projection. In another non-limiting example shown in FIG. 21, the flow paths 21005 from the secondary chambers, such as 21010, are located in the outer rotor inward projection, such as 21015, leading between the leading and trailing surfaces of the inward projection, which contact the inner rotor outward projection between the radially outer and radially inner contact surfaces. The device may be used with any of these flow paths or combinations thereof.

[0055] In a non-limiting example shown in Figure 9, a flow passage from a secondary chamber such as 10035 is disposed in the inner rotor lobe, leading from the area of ​​the junction between two adjacent inner rotor lobes to the tip of the trailing lobe. In another non-limiting example shown in Figure 10, a flow passage from a secondary chamber such as 12035 is disposed in the outer rotor fin, for example, leading between the leading and trailing surfaces of the fin that contact the inner rotor lobe between the radially outer and radially inner contact surfaces. The device may be used with any of these flow passages or a combination thereof.

[0056] In the non-limiting embodiment shown in FIG. 1, the rotary displacement device includes an outer rotor 110 and an inner rotor 105 that rotate and interact with each other to form a chamber (requires labeling), which decreases in overall volume as the inner and outer rotors intermesh with each other in the exhaust zone of the pump, and increases in overall volume in the intake zone of the pump. At full volume, the chamber may be divided into inner and outer portions by a crescent seal 170. In the non-limiting embodiment shown in FIGS. 1-14, the inner rotor has four radial projections and the outer rotor has eight radial projections. Many other lobe and fin counts may be used in the 2:1 ratio. The inventors anticipate that ratios other than 2:1 are also viable with other numbers of inner and outer rotor projections.

[0057] In the non-limiting embodiment shown in Figures 1-8, the inner rotor 105 rotates at half the speed of the outer rotor 110. The outer rotor 110 has radial projections 115 (referred to herein as outer rotor fins 115) having leading faces 120, 145 and trailing faces 140 that are parallel to but offset from a path of the center of a radius of the cylindrical sealing surface of the outer rotor 110. These offsets from the radial center point may be selected to accommodate the circumferential diameter of the rotor legs that extends between the contact arcs of the toe 125 and heel 130 of each inner rotor leg of the inner rotor leg 135. The leading and trailing offsets from the radius may be equal, for example. In other embodiments where the offsets from the radius are unequal, the leading and trailing edge diameters are also unequal. In other words, if these leading and trailing arcs are concentric, as in the non-limiting embodiment shown in Figures 1-8, the offset between the opposing outer rotor faces 120 is defined by the sum of the two radii of the opposing portions of the rotor legs that contact the aforementioned outer rotor faces 120. In addition to this offset, an offset is also added equal to the desired gap between the inner and outer rotors. This offset may be less than 0.001 or greater than 0.001 inches. 0.002 inches has been found to be an acceptable clearance for low to medium pressure pumping of low to high viscosity fluids. In this non-limiting embodiment, the inner rotor 105 rotates at half the speed of the outer rotor 110. The inner rotor 105 has half the number of lobes as the number of fins 115 on the outer rotor 110. The direction of rotation of the inner rotor 105 is indicated by arrow 160. The direction of rotation of the outer rotor 110 is indicated by arrow 165. The direction of inlet fluid flow is indicated by arrow 150. The direction of output fluid flow is indicated by arrow 155. In the non-limiting embodiment shown in FIG. 1 , a mating component 170 is positioned to interface between the sealing edge of the inner rotor 105 and the radial protrusion 115 of the outer rotor 110.

[0058] In this embodiment, the arc of the inner rotor tip 125 is concentric with the arc of the inner rotor heel 130 of the inner rotor foot 135, and the surfaces of both the tip 125 and heel 130 seal to the corresponding surfaces of the outer rotor 110. For clarity, the leading surface 125 of the inner rotor foot 135 seals to the trailing surface 140 of the outer rotor fin 115, and the trailing surface 130 of the inner rotor foot 135 seals to the leading surface 145 of the opposing outer rotor fin. The inner rotor 105 may have a two-piece construction where each of the two parts is generally a mirror image of the other for ease of manufacture. A non-limiting example of a rotor half 200 of such an inner rotor 105 is shown in FIG. 3. A one-piece inner rotor may also have these channels at one or both ends, rather than along the midplane.

[0059] An advantage of this geometry is the relatively long circumferential length of the outer rotor fins 115 around the OD (outer diameter) of the outer rotor 110. This is beneficial for structural reasons that add stiffness to the outer rotor 110, for example, providing ample area for both the bolt holes 180 for attaching the outer rotor ring 515 shown in FIG.

[0060] One objective that may be met by embodiments of this device is to reduce the resistance to fluid flow through the pump, especially when the pump is operated at high speeds, e.g., to achieve high power density, to operate within a more efficient range for the drive motor, or for other advantageous reasons. Low fluid flow resistance may be achieved by minimizing fluid directional changes in addition to minimizing fluid turbulence resulting from high speed fluid flow spikes. These high speed fluid flow spikes may be minimized by the disclosed geometry by reducing or eliminating areas where fluid must flow at high speeds through small gaps. In this exemplary pump of Figures 1-8, the cross-sectional areas of the fluid flow passages are approximately proportional to the volume of flow through those passages at any part of the cycle. In other words, the greater the volume of fluid flow through a passage, the larger the cross-sectional area of ​​said passage.

[0061] Another way to minimize flow resistance in this device is by minimizing the angular acceleration of the fluid as it passes from the inlet to the discharge of the pump. This may be done in several ways. The first way is by maintaining a high percentage of the fluid flow throughout the device substantially perpendicular to the first rotor axis. This may be done by minimizing the lateral flow of the fluid by drawing the fluid into and out of the rotor in a generally radial direction relative to the rotor chamber (or tangential to the housing). Another way to minimize the angular acceleration of the fluid is by having the fluid flow in and out of the same side of the pump in generally opposite directions. This generally involves drawing the fluid tangential to the inner and outer rotors, gradually turning the fluid with the outer and inner rotors 180°, and then these two fluid paths rejoining in a generally tangential manner as they leave the rotors and the pump.

[0062] To achieve low flow resistance, each secondary chamber (formed between two adjacent legs of the inner rotor and the fins on the outer rotor) must have a path to flow to the output port as it reduces volume. When it increases volume, the secondary chamber must also have a path to the inlet port. If this flow path does not exist, water hammer or vacuum spikes will occur. In this pump geometry, as shown in FIG. 3, a fluid flow path, indicated by arrows 205, is provided inside each leg 135 of the inner rotor 105 from the apex 210 between the two legs to the OD of the adjacent leg. Each passage 215 allows fluid to flow in the same direction from each apex to the OD of each leg adjacent to it. Then, the housing seal between the inlet and output port is shifted (or the position of the inner rotor shaft is shifted), so that the volume at TDC (including the volume at the OD of the leg at TDC and the volume in communication with it at the adjacent apex) is the smallest possible volume. In the exemplary embodiment of pump 500 shown in Figures 5-8, the angular shift of the inner rotor axis about the pump's main axis is 4.8 degrees. This offset is shown in Figure 5. Other angles can be used for other embodiments aimed at sealing the chamber to prevent fluid flow from the exhaust port to the intake port when the chamber is at its minimum volume. Additionally, other housing seal geometries may be utilized in embodiments where, for example, preventing leakage is important or non-essential or preventing fluid hammer is important or non-essential.

[0063] The embodiment shown in Figures 5-8 features an integrated motor 705 shown in Figures 6-8. In the embodiment shown in Figure 7, the motor 705 is used to power the inner rotor 105 via an input shaft 715. In this non-limiting embodiment, the outer rotor 110 is assembled to rotate within the lower housing 505 and is powered via an interaction between the inner rotor foot 135 and the outer rotor projection 115. In an alternative configuration (not shown), the outer rotor 110 may be arranged to be powered by the motor and the inner rotor 105 may be arranged to rotate about its axis relative to the upper housing 510. In another non-limiting example, the fluid flow provided to the energy transfer device may be used to generate mechanical power and output through the shaft of either the inner or outer rotor. If the electric machine is configured for use as a generator and coupled to a power generating shaft, electrical power may be generated from the fluid flow through the machine.

[0064] Teardrop outer rotor fin

[0065] In a non-limiting embodiment shown in FIG. 9, the radial projection 10010 of the outer rotor 10005 has a teardrop shape to reduce drag on the trailing edge 10040 of the radial projection 10010 of the outer rotor 10005. The leading edge of the radial projection 10010 of the outer rotor 10005 may also have a teardrop shape to reduce turbulence of the fluid flowing past the leading edge 10045 of the radial projection 10010. The direction of rotation of the inner rotor 10000 and the outer rotor 10005 is indicated by the arrow 10075. The housing 10065 may have a sleeve 10015 that seals the outer diameter of the outer rotor 10005. The sleeve 10015 may be made of a material with favorable wear and machinability characteristics, such as brass. The crescent 10060 may be made of a material with favorable wear and machinability characteristics, such as brass. The inlet port 10025 and exhaust port 10030 are also shown in Figure 9. The inlet port 10025 defines the point where the primary chamber opens to the inlet side of the pump, and the exhaust port 10030 defines the point where the primary chamber 10070 closes to the exhaust flow path of the pump. For reference, the secondary chamber 10035, the leading edge 10055 of the inner rotor 10000, and the trailing edge 10050 of the inner rotor 10000 are shown.

[0066] 10, the flow passage 12020 between the primary chamber 12065 and the secondary chamber 12035 is disposed through a radial protrusion 12010 of the outer rotor 12005. For reference, the inner rotor 12000, inlet port 12025, exhaust port 12030, and housing 12100 are shown.

[0067] In the non-limiting embodiment shown in FIG. 11, the flow passage 12020 between the primary chamber 12065 and the secondary chamber 12035 is disposed through the radial projection 12010 of the outer rotor 12005. This flow passage through the outer rotor fin is configured to allow sealing contact between the inner rotor tip and heel surfaces and the outer rotor fin to the outermost radial sealing location. The area outside the outer region of that is used as the flow passage inlet and outlet, leaving a large cross section at the widest part of the drop shape to provide fin stiffness, or a cross section wide enough for a bolt to pass through the fin if desired. In addition, the fluid passage 215 may be disposed within the radial projection 12090 of the inner rotor 12000. For reference, the crescent 12060, the inlet port 12025, and the exhaust port 12030 are shown. An isometric view of this aforementioned embodiment shown in FIG. 11 is also shown in FIG. 12 from a different perspective. Shown for reference are the inlet port 12025, exhaust port 12030, secondary chamber 12035, outer rotor 12005, housing sleeve 12015, crescent moon 12060, outer rotor radial projection 12010, primary chamber 12065, and inner rotor 12000. An isometric view of the outer rotor 12005 is shown in FIG. 13 showing the radial projection 12010, flow passage 12020, and outer rotor shaft 12110.

[0068] The non-limiting embodiment of FIG. 14 shows a simplified version of the fluid path 16005 located in the inner rotor 16020. The fluid path connects the secondary chamber 16025 to the outer diameter of the outer rotor 16065, thereby connecting the secondary chamber 16025 to the primary chamber 16030 to prevent water hammer. At top dead center, i.e., the position shown in FIG. 14, the end of the inner rotor radial projection 16015 extends all the way to the outer diameter of the outer rotor 16065. This may create a seal at the moment the machine is rotated to top dead center, but connects the secondary chamber 16025 to the primary chamber 16030 at the point of rotation directly clockwise or counterclockwise relative to top dead center. Another result of the radial projection of the inner rotor extending to the outer diameter of the outer rotor is a reduced cross-sectional area for fluid flow into the primary chamber 16030 when it opens to the inlet port 16035, as well as for fluid flow out of the primary chamber 16030 when it closes the outer port 16035. A further result of the radial projection of the inner rotor extending to the outer diameter of the outer rotor is a reduced cross-sectional area through which fluid can flow from the secondary chamber 16025 to the primary chamber 16030 when the volume of the secondary chamber 16025 is decreasing, as well as from the primary chamber 16030 to the secondary chamber 16025 when the volume of the secondary chamber 16025 is increasing. For example, the inner rotor shown in Figures 1-13 and 15-17 is designed with a smaller diameter to provide a gap between the outer diameter of the inner rotor radial projection at top dead center and the housing to provide a larger cross-sectional area into the primary chamber once the primary chamber opens to the inlet port and the chamber closes to the exhaust port, thereby resulting in reduced flow restriction. Similarly, the gap between the housing and the inner rotor lobes similarly reduces the flow restriction between the primary and secondary chambers. In this non-limiting embodiment, the crescent 16060 is formed as an integral part of the housing, rather than a separate part. However, the crescent 16060 can alternatively be a separate piece from the housing, and the housing and crescent are assembled together.Regardless of the assembly, stationary elements such as the crescent seal are considered part of the housing.

[0069] 18 illustrates a non-limiting embodiment in which a simplified inner rotor 18000 has a first array of fluid flow passages 18005 that span from a root between adjacent inner rotor radial projection lobes 18015 to an outer radius of the same inner rotor radial projection lobe 18015 on one axial side of the inner rotor 18005, and a second array of fluid flow passages 18010 on an opposing axial side of the inner rotor 18000 that are a mirror image of the first array of fluid flow passages. The axis of rotation 18020 of the inner rotor 18000 is shown in FIG. 18 for reference.

[0070] A three-lobed smaller crescent results in higher displacement

[0071] In one embodiment shown in Figures 16-17, an energy transfer machine includes an inner rotor with three lobes and an outer rotor with six fins. This is interchangeably referred to as a tri-lobe arrangement. Compared to a four-lobe design, the tri-lobe design allows for a smaller crescent outer diameter resulting in a higher theoretical maximum displacement than a four-lobe device for the same outer rotor diameter.

[0072] 3-lobe to 4-lobe contact ratio

[0073] Contact ratio is defined herein as the average number of contact points between a driven leading surface, such as leading surface 10055 in the non-limiting embodiment shown in FIG. 9 of the inner rotor 10000, and a driven trailing surface, such as trailing surface 10040 of the outer rotor 1005 shown in FIG. 9, as they rotate. In the disclosed embodiment devices, a ratio of 1 or greater ensures that there is always at least one contact point between the inner and outer rotors. Note that this presumes that once a driving surface stops contacting a driven surface, the driving surface does not regain contact with the driven surface until the next rotation. Similarly, contact ratio can be used to refer to the non-driven timing contact of a trailing surface, such as inner rotor trailing surface 10050 of the inner rotor 10000, and a leading surface, such as leading surface 10045 of the outer rotor 10005, which prevents the driven rotor from rotating faster than it is being driven, for example, during deceleration of the inner rotor 10000. As used herein, leading is used to describe a configuration that faces generally toward the direction of rotation and trailing is used to describe a configuration that faces generally away from the direction of rotation. For both the drive and timing surfaces, a contact ratio that is greater than or equal to 1 is contemplated by the inventors to provide for operation of the device without the need for external timing gears.

[0074] A four-lobe design provides a higher contact ratio than a three-lobe configuration. A higher contact ratio tends to provide a smoother engagement and may reduce noise.

[0075] In the embodiment shown in FIG. 16, the inner rotor 17070 is the driving rotor. This may be advantageous if an electric motor is used to power the inner rotor 17075 if the optimum speed of the motor is higher than the desired operating speed of the outer rotor 17075. For example, for a given power output, an electric motor may be most efficient at 1,000 RPM. If the desired operating speed of the outer rotor is 500 RPM, the inner rotor may be the driving rotor such that the electric motor may operate at its optimum speed of 1,000 RPM. Conversely, if the optimum speed of the outer rotor 17075 is similar to the optimum speed of the means powering the pump, the outer rotor 17075 may be the driving rotor. The inventors envision that other means may be used to drive the disclosed devices, such as, but not limited to, hydraulic motors, internal combustion engines, connected to the input of the disclosed devices via pumps, gears, or directly coupled methods or combinations of methods.

[0076] Secondary chamber in three lobes

[0077] In the non-limiting three-lobe design shown in FIGS. 15-17, the secondary chamber 17035 occurs in the area between the outer rotor radial projection 17010 and the root of the radial projection 17000 on the inner rotor 17000.

[0078] In the non-limiting embodiment shown in Figures 16-17, the radial projection of the outer rotor 17010 features a passage 17080 leading from the secondary chamber 17035 to the outer diameter of the outer rotor. This prevents water hammer from occurring, but does not introduce a leakage path from the inlet side of the pump to the discharge side of the pump at any point during the rotation of the two rotors. Figure 17 shows an isometric view of the inner rotor 17070, crescent 17060, housing 17015, and radial projection 17010 of the outer rotor. For reference, the direction of rotation is indicated by arrow 17095.

[0079] In the non-limiting example shown in FIG. 16 , the flow passage 17080 connecting the secondary chamber 17035 to the outer diameter of the outer rotor is positioned between two adjacent outer rotor surfaces, for example, between the inner trailing edge 17090 of the radial projection of the outer rotor and the inner leading edge 17085 of the radial projection of the outer rotor, in contact with the inner rotor lobe and leading to the outer diameter of the outer rotor 17075.

[0080] The drawings are semi-schematic and may lack certain elements such as bearings for simplicity.

[0081] In the claims, the term "comprises" is used in its inclusive sense and does not exclude other elements present. The infinitives "a" and "an" before a claim construct do not exclude more than one of the constructs present. Each individual construct described herein may be used in one or more embodiments and should not be construed as essential to all embodiments defined by the claims merely by virtue of its description herein.

Claims

1. a housing defining an inlet flow passage and an outlet flow passage; a first rotor mounted for rotation within the housing about a first rotor axis, the first rotor having first rotor tines and at least partially defining first rotor chambers between the first rotor tines, each first rotor chamber being at least partially defined by first rotor non-axial bearing surfaces of two first rotor tines of the first rotor tines; a second rotor mounted for rotation within the housing about a second rotor axis parallel to the first rotor axis, the second rotor having second rotor tines at least partially defining second rotor chambers between the second rotor tines, each second rotor chamber being at least partially defined by second rotor non-axial bearing surfaces of two second rotor tines of the second rotor tines.

1. A positive displacement fluid transfer device comprising: the first rotor tines and the second rotor tines are configured to mesh with one another at a meshing portion of the positive displacement fluid transfer device, and the first rotor non-axial bearing surface contacts the second rotor non-axial bearing surface when the first rotor tines mesh with the second rotor tines; the first rotor tines and the second rotor tines come into meshing at an outlet portion of the positive displacement fluid transfer device, the meshing of the first rotor tines and the second rotor tines reducing a combined volume of the first rotor chamber and the second rotor chamber in the outlet portion of the positive displacement fluid transfer device, and at least the first rotor chamber opening to the outlet flow passage in the outlet portion of the positive displacement fluid transfer device; the first rotor tines and the second rotor tines disengage at an inlet portion of the positive displacement fluid transfer device, the disengagement of the first rotor tines and the second rotor tines increasing the collective volume of the first rotor chamber and the second rotor chamber in the inlet portion of the positive displacement fluid transfer device, and at least the first rotor chamber or at least the second rotor chamber opening to the inlet flow passage in the inlet portion of the positive displacement fluid transfer device; at least one of the first rotor and the second rotor defines a flow passage, the flow passage being internal to the first rotor with respect to the first rotor non-axial bearing surface or internal to the second rotor with respect to the second rotor non-axial bearing surface, the flow passage being arranged to connect the first rotor chamber with the second rotor chamber at least in a portion of the inlet portion, the mating portion or the outlet portion of the positive displacement fluid transfer device; Positive displacement fluid transfer device.

2. 2. The positive displacement fluid transfer device of claim 1, wherein the first rotor is an outer rotor and the second rotor is an inner rotor, the teeth of the outer rotor (outer rotor teeth) meshing with the teeth of the inner rotor (inner rotor teeth) as internal gear teeth.

3. The positive displacement fluid transfer device of claim 2 further comprising a crescent seal between said inner rotor and said outer rotor.

4. 4. The positive displacement fluid transfer device of claim 3, wherein the crescent seal seals the outer rotor tooth for volumetric displacement of fluid about the crescent seal in the first rotor chamber.

5. 5. The positive displacement fluid transfer device of claim 3 or 4, wherein the crescent seal seals the inner rotor tooth for volumetric displacement of fluid around the crescent seal in the second rotor chamber.

6. 5. The positive displacement fluid transfer device of claim 3 or 4, wherein the rotation of the outer rotor defines a leading direction and a trailing direction, and wherein, at least in cross-section in a plane perpendicular to an outer rotor axis, the outer rotor tines are shaped as fins, the first rotor non-axial bearing surface includes a generally straight leading fin surface and a generally straight trailing fin surface, the inner rotor tines are shaped as lobes, and the second rotor non-axial bearing surface includes a rounded leading lobe surface and a rounded trailing lobe surface, the leading lobe surface being arranged in contact with the trailing fin surface and the trailing lobe surface being arranged in contact with the leading fin surface.

7. 7. The positive displacement fluid transfer device of claim 6, wherein the number of fins on the outer rotor (outer rotor fins) is twice the number of lobes on the inner rotor (inner rotor lobes).

8. 8. The positive displacement fluid transfer device of claim 7, wherein at least in cross section in said plane, said leading fin surface and said trailing fin surface are straight and said leading lobe surface and said trailing lobe surface are arcs.

9. 9. The positive displacement fluid transfer device of claim 8, wherein the outer rotor fin first fin has a leading first fin surface of the leading fin surface that is parallel to a first radial line through the outer rotor axis and displaced in the trailing direction from a first radial line through the outer rotor axis by a first displacement amount, an opposing fin of the outer rotor fin is rotationally symmetric with the first fin of the outer rotor fin, and a first lobe of the inner rotor lobe has a trailing first lobe surface of the trailing lobe surface formed in a trailing leading shape, the trailing leading shape having a trailing leading radius that is substantially equal to or less than a first clearance value, i.e., the first displacement amount.

10. 9. The positive displacement fluid transfer device of claim 8, wherein the second fin of the outer rotor fin has a trailing second fin surface of the trailing fin surface that is parallel to a second radial line through the outer rotor axis and displaced in the leading direction from a second radial line through the outer rotor axis by a second displacement amount, a second opposing fin of the outer rotor fin is rotationally symmetric with the second fin of the outer rotor fin, and a second lobe of the inner rotor lobe has a leading second lobe surface of the leading lobe surface formed in a leading arc shape, the leading arc shape having a leading arc radius that is substantially equal to a second clearance value, i.e., the second displacement amount, or less than or equal to a first clearance value, i.e., the first displacement amount.

11. The positive displacement fluid transfer device of claim 10 , wherein the first displacement amount is equal to the second displacement amount.

12. 11. The positive displacement fluid transfer device of claim 10, wherein the first lobe is the second lobe, the trailing arc shape is concentric with the leading arc shape, and the leading first fin surface is parallel to the trailing second fin surface.

13. 7. The positive displacement fluid transfer device of claim 6, wherein the outer rotor fins are rotationally symmetric about the outer rotor and the inner rotor lobes are rotationally symmetric about the inner rotor.

14. The positive displacement fluid transfer device of claim 1 , wherein the first rotor teeth and the second rotor teeth mesh as external gear teeth.

15. A positive displacement fluid transfer device according to any one of claims 1 to 4, wherein the flow passage is within the first rotor tine.

16. A positive displacement fluid transfer device according to any one of claims 1 to 4, wherein the flow passage is within the second rotor tine.

17. 5. The positive displacement fluid transfer device of claim 1, wherein the first rotor defines a first rotor flow passage of the flow path and the second rotor defines a second rotor flow passage of the flow path.

18. A volumetric fluid transfer device as described in claim 17, wherein the first rotor teeth and the second rotor teeth mesh as external gears, the first rotor flow passages are located within every other tooth of the first rotor teeth, and the second rotor flow passages are located within every other tooth of the second rotor teeth.

19. The positive displacement fluid transfer device of claim 1 , positioned to direct fluid flow through the positive displacement fluid transfer device substantially perpendicular to the first rotor axis.

20. 10. The positive displacement fluid transfer device of claim 1 configured to operate as a pump, the inner rotor being connected to a source of mechanical energy to drive the pump.

21. 10. The positive displacement fluid transfer device of claim 1 configured to operate as a pump, the outer rotor being connected to a source of mechanical energy for driving the pump.

22. 10. The positive displacement fluid transfer device of claim 1 configured to operate as a hydraulic motor, where fluid pressure drives the inner rotor, the inner rotor being connected to a mechanical energy receiver.

23. 10. The positive displacement fluid transfer device of claim 1 configured to operate as a hydraulic motor, wherein fluid pressure drives the outer rotor, the outer rotor being connected to a mechanical energy receiver.

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