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(11) | EP 3 480 460 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | VOLUMETRIC PUMP |
| (57) A volumetric pump (1) comprises a chamber (2) divided into a main sub-chamber (21)
and a secondary sub-chamber (22) by a first diaphragm (5) which is clamped in the
chamber (2). An inlet port (23) and an outlet port (24) are located in the main sub-chamber
(21), and a compensation port (26) is located in the secondary sub-chamber (22). A
linear actuator (6) is configured to cause a reciprocating movement in the first diaphragm
(5), thus causing a variation in the volume of the main sub-chamber (21). The pump
(1) also comprises a by-pass channel connecting a compensation port (26) located in
the secondary sub-chamber (22) with the inlet port (23) of the main sub-chamber (21).
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TECHNICAL FIELD
[0001] The invention refers to a mechanical pump for application in spacecraft, in particular in active thermal control systems, namely in Mechanically Pumped Driven Loops (MPDL) also known as Mechanically Pumped Loops (MPL).
STATE OF THE ART
[0002] The thermal control of spacecraft equipment is an important feature of the spacecraft overall functionality, being one of the main thermal loads the heat generated at the electronic components.
[0003] Spacecraft thermal control techniques can be classified as passive thermal control (PTC) or active thermal control (ATC). Passive thermal control does not involve moving parts and relies solely on conductive and radiative heat paths to achieve thermal management, using components such as heat pipes, coatings, multi-layer insulation (MLI), sun shields, radiating fins, etc. Active thermal control requires input power and is commonly used in applications involving high heat loads.
[0004] A mechanically pumped loop (MPL) is an active thermal control (ATC) technique that uses a pumping device (a centrifugal or positive displacement pump) to move a fluid within a closed hydraulic circuit (loop). The fluid absorbs heat from a source (components that dissipate heat) and transfers it to a sink (an external surface that rejects heat to space by radiation). Mechanically pumped loops can be categorized as single-phase loops or two-phase loops.
[0005] Mechanically Pumped Loops (MPL) are robust and reliable systems that provide efficient heat transfer capacity for relatively higher power dissipation requirements and wider temperature ranges than other techniques, along with other advantages such as the distribution flexibility and ease of integration into the spacecraft, predictable thermal performance and scalability. Moreover, the coolant can be selected to match the required thermal environment. Double-phase MPLs provide a more interesting thermal control mass budget when compared with the single-phase fluid loop as they are more weight-effective, being capable of achieving large heat transfer rates with much less pumping power that single-phase fluid loops.
[0006] Initial developments of MPLs for space use have implemented single-phase loops featuring centrifugal pumps. However, the output of a centrifugal pump fluctuates with the pressure variations; additionally, they have a very limited capability of dealing with high vapor volume fractions in the flow, which can lead to gas-locking of the pump can with the consequent loss of functionality. Therefore, centrifugal pumps are not suitable for double-phase loops since they are not self-priming, which are the current trends of the developments due to their higher heat transfer capacity and thermal stability.
[0007] Some solutions have been already proposed, such as the lobe pump FR 2824366 or the gear pump EP 2264317 B1. However, these rotary pumps sustain necessarily friction and wear (at the guiding of the shafts or the contact of the gears), compromising the durability of the pump. Rotary seals are also a critical component which is likely to fail in the long-term operation due to tribological issues. These limitations are common to all the positive displacement pumps of the rotary type, and similar issues preclude screw and piston pumps for long life spacecraft applications. The reciprocating pump proposed in US 6345963 B1 has potentially limited lifetime due to the intrinsic stress concentration of the metal bellows upon which it is based and the relatively large static pressures required; additionally, the vortex diode valves have shown very low efficiencies in general, which could be allowed, but cannot withstand full-gas flow, which is a stringent limitation on their use on an unmanned spacecraft.
[0008] Therefore, a reliable and durable mechanical pump would be desirable, in order to allow the application of MPL technology to high-capacity long-life applications, such as unmanned missions, serving telecommunications platforms, nuclear facilities, or any environment where reliability requirements are particularly high.
[0009] Diaphragm pumps are devices with no tribological issues due to dynamic seals or any other friction elements, so they offer some advantages with respect to the aforementioned documents. However, the linear actuators used in these devices cannot provide the required strokes against the high-pressure forces typical of the applications indicated above and for the long-life demanded, so the person skilled in the art would not be prompt to use any of these devices as a solution for this problem.
SUMMARY OF THE INVENTION
[0010] The invention provides a solution for this problem by means of a volumetric pump according to claim 1. Preferred embodiments of the invention are defined in dependent claims.
[0011] In a first inventive aspect, the invention provides a volumetric pump comprising
a chamber divided into a main sub-chamber and a secondary sub-chamber by a first diaphragm, the first diaphragm comprising a first face oriented towards the main sub-chamber, a second face opposite to the first face and oriented towards the secondary sub-chamber and an outer edge clamped to the chamber;
at least one inlet port and at least one outlet port being located in the main sub-chamber and being covered by at least one inlet valve and one outlet valve respectively;
a compensation port being located in the secondary sub-chamber, this compensation port being in fluid communication with the inlet port;
a linear actuator being configured to cause a reciprocating movement in the first diaphragm, thus causing a variation in the volume of the main sub-chamber.
[0012] The proposed invention improves the performance with respect to other volumetric pumps because of the absence of friction and dynamic seals, thereby increasing the reliability and extending its lifetime and being specially indicated for spacecraft applications, including unmanned missions.
[0013] Further, due to the compensation port located in the secondary sub-chamber, and being in fluid communication with the inlet port of the pump, the difference between the pressure at both sides of the diaphragm is only the differential pressure caused by the compression, but the diaphragm and, therefore, the actuator, have not to withstand the total fluid pressure. This also improves the lifetime of the pump.
[0014] The fact that the first diaphragm is clamped to the chamber does not exclude the possibility that both the first diaphragm and the chamber are manufactured together as a single part. This only makes reference to the fact that the diaphragm does not rotate or pivot with respect to the chamber, but the rotation is also restricted.
[0015] In some particular embodiments, the linear actuator is connected to the diaphragm by means of a coupling device.
[0018] The use of a compact high-force piezoelectric actuator operated at low frequencies allows a much easier control electronics than the typically used for the centrifugal pumps, the gear pump and the rotary lobe rotary brushless motor, thereby increasing the reliability and extending its lifetime.
[0019] In other particular embodiments, the linear actuator is a magnetostrictive actuator. These kind of actuators provide strokes in similar ranges to the piezoelectric actuators with lower actuation voltages and have potentially higher lifetimes since they are made of bulk material actuated electromagnetically.
[0020] In some particular embodiments, the first diaphragm has a central portion with a central thickness greater than the thickness in any point outside the central portion.
[0021] This central reinforcement of the diaphragm improves the efficiency of the pump, since it maximizes the volume displacement by limiting the diaphragm deformation.
[0022] In some particular embodiments,
the secondary sub-chamber is limited between the first diaphragm and a second diaphragm solidly attached to the first diaphragm by means of a rigid shank arranged coaxially with the linear actuator;
the linear actuator is located outside the chamber and in contact with the second diaphragm, so that when the linear actuator moves, it moves the second diaphragm and the solid connection between the second diaphragm and the first diaphragm by means of the rigid shank makes that the first diaphragm also moves.
[0023] This arrangement is a way of defining a secondary sub-chamber between two diaphragms, the linear actuator being configured to move the two diaphragms as a single piece, since they are solidly attached. The linear actuator is therefore kept outside the contact with the fluid, being a single way of preserving it from an aggressive environment.
[0024] In some particular embodiments, the second diaphragm has a lower surface than the first diaphragm.
[0025] These embodiments reduce the preload effect of the base pressure over the actuator, extending the working range of the actuators and allowing a higher life of the pump.
[0026] In some particular embodiments, the coupling device comprises a protective capsule around the linear actuator, the linear actuator being located inside the secondary sub-chamber, so that the linear actuator is adapted to move the first diaphragm without being in direct contact with the working fluid of the secondary sub-chamber.
[0027] This is an alternative way of achieving the isolation of the linear actuator. This improves its lifetime, since the working fluid may harm such a delicate part, especially in long term periods.
[0028] In some particular embodiments, the inlet and/or the outlet valve comprises
one clamped edge which is clamped to the main sub-chamber in the corresponding inlet or outlet port; and
a free end which allows the work fluid enter/exit the main sub-chamber by being flexed with respect to the clamped edge.
[0029] These embodiments are aimed for simplicity and reliability, since no electronic parts or controlled elements are present; the valves of these embodiments are passive valves, and are therefore less prone to be damaged.
[0030] In some embodiments, the inlet valve and/or the outlet valve is operated by a secondary piezoelectric actuator.
[0031] These embodiments are aimed for better performance, since the valve of these embodiments may be synchronized with the movement of the main actuator, not depending on fluid-dynamic effects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:
Figure 1 shows an exploded view of a first embodiment of a volumetric pump according to the invention.
Figure 2 shows a cross section of the volumetric pump of Figure 1.
Figure 3 shows a cross section of a second embodiment of a volumetric pump according to the invention.
Figures 4a and 4b show a cross section of the volumetric pump of Figure 2 in two different operative positions.
Figure 5 shows a detail of an inlet valve of a volumetric pump according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Figure 1 shows an exploded view of a first embodiment of a volumetric pump 1 according to the invention.
[0034] This volumetric pump 1 comprises
a chamber 2;
a first diaphragm 5 intended to divide the chamber 2 into two sub-chambers;
a second diaphragm 7 intended to provide a cover for the chamber 2;
an inlet port 23 and an outlet port 24;
an inlet valve 31 and an outlet valve 32, intended to cover the inlet 23 and outlet 24 ports;
a rigid shank 91 intended to be solidly attached to the first diaphragm 5 and to the second diaphragm 7, so that the first diaphragm 5, the second diaphragm 7 and the rigid shank 91 may constitute a single element; and
a linear actuator 6 intended to move the single element constituted by the first diaphragm 5, the second diaphragm 7 and the rigid shank 91.
[0035] The chamber 2 comprises a compensation port 26, intended to provide fluid communication between one of the sub-chambers and the inlet port 23.
[0036] Figure 2 provides a side cross section of such a volumetric pump 1. In this figure, the internal arrangement of each element may be seen.
[0037] As mentioned above, the chamber 2 is divided into a main sub-chamber 21 and a secondary sub-chamber 22 by means of the first diaphragm 5. The first diaphragm 5 has a first face 51 oriented towards the main sub-chamber 21 and a second face 52 opposite to the first face 51, being therefore oriented towards the secondary sub-chamber 22. An outer edge 53 of the first diaphragm 5 is clamped to the chamber, thus dividing the chamber 2 into a main sub-chamber 21 and a secondary sub-chamber 22.
[0038] Both the main sub-chamber 21 and the secondary sub-chamber 22 are intended to be full of working fluid, so the difference between the pressure in the first face 51 and the second face 52 of the first diaphragm 5 is only due to the differential pressure provided by the first diaphragm movement.
[0039] The inlet port 23, covered by the inlet valve 31, and the outlet port 24, covered by the outlet valve 32, are located in the main sub-chamber 21. The inlet port 23 is in fluid communication with the pump inlet 25, where the working fluid enters the pump system.
[0040] The first diaphragm 5 has a central portion 54 with a thickness which is greater than the thickness in any point outside the central portion 54.
[0041] A compensation port 26 located in the secondary sub-chamber 22 is intended to provide a fluid communication between the secondary sub-chamber 22 and the inlet port 23, so that the pressure at both sides of the first diaphragm 5 (i.e., in the main and secondary sub-chambers) is similar, and, as mentioned above, only differs due to the differential pressure provided by the first diaphragm movement.
[0042] In the embodiment shown in this figure, the secondary sub-chamber is limited between the first diaphragm 5 and a second diaphragm 7. This second diaphragm 7 is solidly attached to the first diaphragm 5 by means of a rigid shank 91, so that the first diaphragm 5, the shank 91 and the second diaphragm 5 constitute a single element. Both the first diaphragm 5 and the second diaphragm 7 are clamped to the inner wall of the chamber 2 in two different zones, thus limiting their movements.
[0043] The linear actuator 6 does not need to be isolated from the working fluid, since it is located outside the secondary sub-chamber 22. It contacts the second diaphragm 7 and, since this second diaphragm 7 constitutes a single element with the first diaphragm 5 by the solid attachment with the shank 91, the linear actuator 6 is able to move the first diaphragm 5 without a direct contact.
[0044] Figure 3 shows a cross section of a second embodiment, which has some differences with respect to the first embodiment shown in Figure 2.
[0045] In the embodiment shown in this figure, the chamber 2 is a closed cavity, and is divided into two sub-chambers by the first diaphragm. The linear actuator 6 is located inside the secondary sub-chamber 22, inside a protective capsule 92 which isolates the linear actuator 6 from the working fluid which fills the secondary sub-chamber 22. This protective capsule 92 does not prevent the linear actuator 6 from acting over the first diaphragm 5, transmitting the linear reciprocating movement thereto.
[0046] There is also a fluid connection between the secondary sub-chamber 22 and the inlet port 23 by means of the compensation port 26. This fluid communication makes the secondary sub-chamber 22, under the first diaphragm 5, have the same pressure as the inlet port 23, which is the base pressure. The pressure in the main sub-chamber 21 will oscillate around this base pressure, by adding or removing a differential pressure which is small compared with the base pressure. Hence, the first diaphragm 5 has a small pressure difference between their first and second faces.
[0047] Figures 4a and 4b show a cross section of the volumetric pump 1 of Figure 2, so that its operation may be observed. The embodiment shown in Figure 3 works in the same manner. The displacement of the first and second diaphragms 5, 7 has been exaggerated for the sake of understanding the working principle.
[0048] The inlet valve 31 and the outlet valve 32 are arranged to control the flow across the inlet port 23 and the outlet port 24 respectively.
[0049] The linear actuator 6 is arranged to cause an alternating displacement in the single element constituted by the first diaphragm 5, the rigid shank 91 and the second diaphragm 7, at an operation frequency, thus causing a variation in the volume comprised within the main sub-chamber 21, as may be observed in the difference between Figures 4a and 4b.
[0050] The variation of the volume comprised in the main sub-chamber 21 is caused by the elastic deformation of the first diaphragm 5, since the outer edge 53 thereof is clamped to the main chamber 2 and does not displace during this volume variation.
[0051] Figure 5 shows a detail of the inlet valve 31. The outlet valve has an analogue structure. In these figure, the following elements may be observed:
a clamped edge 311 which is clamped to the main sub-chamber 21 in the inlet port 23; and
a free end 312 which allows the work fluid enter the main sub-chamber 21 by being flexed with respect to the clamped edge 311.
[0052] In different embodiments, the valves 31 and/or 32 are operated by a secondary piezoelectric actuator instead.
[0053] In this text, the term "comprises" and its derivations (such as "comprising", etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.
[0054] The invention is obviously not limited to the specific embodiments described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.
a chamber (2) divided into a main sub-chamber (21) and a secondary sub-chamber (22) by a first diaphragm (5), the first diaphragm (5) comprising a first face (51) oriented towards the main sub-chamber (21) and a second face (52) opposite to the first face (51) and oriented towards the secondary sub-chamber (22) and an outer edge (53) being clamped in the chamber (2);
at least one inlet port (23) and at least one outlet port (24) being located in the main sub-chamber (21) and being covered by at least one inlet valve (31) and one outlet valve (32) respectively;
a compensation port (26) being located in the secondary sub-chamber (22), this compensation port (26) being in fluid communication with the inlet port (23);
a linear actuator (6) being configured to cause a reciprocating movement in the first diaphragm (5), thus causing a variation in the volume of the main sub-chamber (21).
the secondary sub-chamber (22) is limited between the first diaphragm (5) and a second diaphragm (7) solidly attached to the first diaphragm (5) by means of a rigid shank (91) arranged coaxially with the linear actuator (6);
the linear actuator (6) is located outside the chamber (2) and in contact with the second diaphragm (7), so that when the linear actuator (6) moves, it moves the second diaphragm (7) and the solid connection between the second diaphragm (7) and the first diaphragm (5) by means of the rigid shank (91) makes that the first diaphragm (5) also moves.
one clamped edge (311) which is clamped to the main sub-chamber (21) in the inlet port (23); and
a free end (312) which allows the work fluid enter the main sub-chamber (21) by being flexed with respect to the clamped edge (311).
one clamped edge (321) which is clamped to the main sub-chamber (21) in the outlet port (24); and
a free end (322) which allows the work fluid exit the main sub-chamber (21) by being flexed with respect to the clamped edge (321).
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description