Piezoelectric device for converting pressure energy into electrical energy

Abstract

The invention relates to a device for converting pressure energy into electrical energy, comprising a cylindrical housing (1), said housing accommodating a piezoelectric transducer (6) and forming a pressure chamber (3), which receives a hydraulic medium (27), for applying pressure to the piezoelectric transducer. The piezoelectric transducer (6) is force-fittingly mounted between two concentric tubes (4, 5) held in a housing cover (2). The outer tube (4) is adjoined by a coaxial flow channel (14), which opens into the pressure chamber (3) by means of a diffuser (16) and which is fluidically connected, by means of radial flow openings (19), to an annular channel (18) which extends from the flow channel and concentrically surrounds the outer tube (4). The inner tube (5) has, on the side of the flow channel (14), a closure (21) which can be opened abruptly and has an upstream shock valve (22). The pressure chamber (3) which accommodates the two tubes (4, 5) together with the flow channel (14) and the annular channel (18) is filled, to a height covering the annular channel (18), with a hydraulic medium (27) which is acted upon by a highly pressurized gas cushion (28) filling the pressure chamber (3).

Description

[0001] Piezoelectric device for converting pressure energy into electrical energy

[0002] Technical field

[0003] The invention relates to a device for converting pressure energy into electrical energy with a cylindrical housing that accommodates a piezoelectric transducer made from a stack of coaxial piezoelectric rings and forms a pressure chamber containing a hydraulic medium for pressurizing the piezoelectric transducer.

[0004] State of the art

[0005] Piezoelectric transducers can be used to convert pressure energy into electrical energy. For this purpose, it is known (US 4,090,448 A) to arrange piezoelectric rings coaxially in a cylindrical housing and to apply pressure to this stack of piezoelectric rings either axially or radially with a hydraulic fluid in order to conduct the electrical energy generated in pulses via a spark gap between two electrodes. The expansion of the hydraulic fluid in a pressure chamber of the housing, due to heating and the evolution of vapor, is used to pressurize the piezoelectric rings.

[0006] To subject a piezoelectric transducer to pressure oscillations, it is also known (DE 10 2016 212 005 A1, DE 10 2016 212 015 A1) to provide a vibrating mass that is connected to the piezoelectric transducer via a hydraulic transmission device. Furthermore, it is known (EA 019 159 B1) to utilize the principle of a hydraulic ram for pressurizing piezoelectric transducers. Such a device comprises, on the inlet side, a tubular flow channel to which a cylindrical outlet chamber is connected coaxially, with an outlet valve located between the outlet chamber and the flow channel. On the outlet side, the flow channel is connected to an outlet having a shock valve, so that when the shock valve closes, the resulting shock wave opens the outlet valve against spring force and pressurizes the outlet chamber.The resulting pressure increase can be advantageously used to actuate a piezoelectric lining of the outlet chamber. However, a disadvantage is that this device can only be used in flowing water.

[0007] To avoid this disadvantage, it is known (EA 010732 B1, EA 020688 B1) to connect the inlet-side flow channel to an empty, closed container via a shock valve. This container is additionally sealed against the flow channel by a rupture disc. If the rupture disc is destroyed while the shock valve is open, a flow occurs within the flow channel into the open container. At sufficient flow velocities, this causes the shock valve to close, resulting in pressure conditions similar to those of a hydraulic ram. However, this requires that the device be installed in a sufficiently large volume of water, for example, in a body of still water.

[0008] To generate electrical energy using piezoelectric elements, it is also known (WO 2024 / 134015 A1) to utilize an electrohydraulic effect by which shock waves are generated in liquids by means of a short-term, intense electric arc ignited between two electrodes. For this purpose, a piezoelectric transducer in the form of a cylinder open at both ends and equipped with piezoelectric elements is provided in a pressure chamber completely filled with hydraulic fluid. This cylinder connects at one end face to a diffuser in which the electrodes required for discharging an electric arc are arranged.The shock wave generated during the arc discharge spreads on the one hand into the cylinder of the piezoelectric transducer and on the other hand in the opposite direction into the hydraulic pressure chamber, whereby a negative pressure results between these opposing shock waves, which can be used for resonance behavior, so that the firing sequence of the arcs can be adapted to a corresponding resonance behavior.

[0009] In order to make use of the energy absorbed by shock absorbers in motor vehicles, it is also known (GB 2 520646 A) to provide a damping cylinder completely filled with a hydraulic medium with piezo elements arranged in a ring around the cylinder wall, so that the pressure waves generated in the fluid when the piston provided in the damping cylinder is displaced can be used to actuate the piezo elements.

[0010] Description of the invention

[0011] The invention is therefore based on the objective of designing a device for converting pressure energy into electrical energy using a piezoelectric transducer in such a way that the principle of a hydraulic ram can be used to generate pressure oscillations without having to provide an underwater arrangement.

[0012] Starting from a device of the type described above, the invention solves the stated problem by arranging the piezoelectric rings forcefully between two concentric tubes held in a housing cover and supporting them axially between a cover-side abutment and a pressure ring on the opposite end of the two tubes, by connecting a coaxial flow channel to the outer tube which opens into the pressure chamber with a diffuser, and which is flow-connected via radial flow openings to an annular channel extending from the flow channel between the outer tube and a jacket extending over a partial length of the outer tube that concentrically surrounds the outer tube.that the inner pipe on the side of the flow channel has a snap-openable closure with an upstream shock valve, and that the pressure chamber accommodating the two pipes with the flow channel and the annular channel is filled with a hydraulic fluid at a height covering the annular channel, which is pressurized by a high-pressure gas cushion filling the pressure chamber above the hydraulic fluid.

[0013] To provide the hydrostatic pressure required for operating a hydraulic ram in still water, the hydraulic fluid in the closed pressure chamber of the housing is pressurized to a correspondingly high pressure by a highly compressed gas cushion, thus enabling the effect of a hydraulic ram to be utilized even within a closed housing. For this purpose, an inner tube, coaxial with the cylindrical housing, serves as an empty container equipped with a snap-open closure, upstream of which is a shock valve that is initially open.With the sudden opening of the inner tube, hydraulic fluid flows through the open shock valve into the inner tube at a high flow velocity due to the pressure difference between the pressure chamber and the inner, empty tube. The resulting forces cause the shock valve to close abruptly, triggering a water hammer with a pressure wave that propagates on one side into the flow channel coaxial with the inner tube and on the other side into the annular channel connected to the flow channel by radial flow openings. This annular channel extends between an outer tube enclosing the inner tube and a shell surrounding this outer tube, and, like the flow channel, terminates within the hydraulic fluid filling of the pressure chamber.This means that a negative pressure develops in the area of ​​the shock valve, which, in conjunction with the reflection conditions occurring in the opening area of ​​the flow channel and the annular channel, leads to an opposing pressure wave as the starting condition for a new shock wave. Since the piezoelectric transducer, in the form of a stack of coaxial piezoelectric rings, is held force-fit between the inner and the concentric outer tube, this transducer is subjected to pressure waves not only axially between the cover-side abutment and a pressure ring on the opposite, actuation-side end of the two tubes, but also radially between the two tubes.

[0014] This situation results in pressure-dependent elastic deformation of the walls of the annular channel and the flow channel, which, due to volume changes in the flow channel and the annular channel, generates additional hydraulic flows. The elastic behavior, effective under the high pressures of the gas cushion and the hydraulic pressure waves, interacts with the diffuser at the outlet of the flow channel to create flow conditions that, with careful adjustment of the design parameters, allow the vibrating system to exhibit oscillatory behavior in a resonance range with comparatively low damping.

[0015] Particularly simple design conditions for the instantly opening closure of the inner tube result when this closure incorporates a rupture disc. However, for resetting the device, a closure that can be re-closed is advantageous; magnetic closures, for example, are suitable for this purpose. The hydraulic fluid can be pressurized with a high-pressure gas cushion in a simple manner via a check valve, through which the pressure chamber of the housing can be connected to a high-pressure gas line.

[0016] To utilize the effect of a hydraulic ram, it is crucial that the shock valve closes abruptly upon reaching predetermined flow conditions. To meet these requirements with relatively simple design measures, the shock valve can incorporate a shearable stop to prevent it from opening. The shear forces required to shear off this stop are inherently defined by the design, ensuring that the shock valve closes as soon as the accelerating flow of the hydraulic fluid reaches a velocity that generates the shear forces necessary for closing the valve.

[0017] Brief description of the invention

[0018] The invention is illustrated in the drawing as an example. It shows

[0019] Fig. 1 shows a device according to the invention for converting pressure energy into electrical energy in a schematic axial section and the

[0020] Figs. 2 and 3 show this device in section in the area of ​​the shock valve, on one side with the shock valve open and on the other with the shock valve closed, on a larger scale.

[0021] Ways to implement the invention

[0022] The illustrated device for converting pressure energy into electrical energy comprises a vertical, cylindrical housing 1, which is closed at the top by a screwed-on lid 2 and forms a pressure chamber 3 into which two tubes 4, 5, held in the lid 2 and coaxial to the housing 1, project. These tubes 4, 5 accommodate a piezoelectric transducer 6 consisting of a stack of coaxial piezoelectric rings between them, with a force-fit connection between the two tubes 4, 5 and the piezoelectric rings being established in the radial direction by a dielectric inner lining 7 of the outer tube 4 and a dielectric outer lining 8 of the inner tube 5. In the axial direction, the piezoelectric transducer 6 is supported by a dielectric abutment 9 on the lid side and by a dielectric pressure ring 10 on the opposite end of the two tubes 4, 5.While the outer tube 4 is screwed directly into the cover 2, the inner tube 5 is held in place relative to the outer tube 4 by a screw insert 11, using a nut 12, wherein, according to the illustrated embodiment, the screw insert 11 forms an axial support for the abutment 9.

[0023] In the end of the outer tube 4 opposite the cover 2, a support sleeve 13 is provided for a flow channel 14 coaxial with the inner tube 5. This flow channel is formed by a connecting sleeve 15 to which a diffuser 16 is connected. A jacket 17, which surrounds the outer tube 4 at a distance, also connects to the support sleeve 13 to form an axial annular channel 18. This annular channel extends from a closed end in the region of the support sleeve 13 over a partial length of the outer tube 4 and opens into the pressure chamber 3 at an axial distance from the cover 2. A flow connection exists between the flow channel 14 and the annular channel 18 via radial flow openings 19 in the support sleeve 13 and in the connecting sleeve 15.

[0024] The inner tube 5 is closed at the lid end by a sealing plug 20 and at the opposite end by a snap-open closure 21. A shock valve 22 is located upstream of this closure 21, the valve body of which is designated 23 and, in the open position, allows a flow path 24 to the inner tube 5. According to the illustrated embodiment, the closure 21 has a piston 25 that is movable within the inner tube 5 and has a stop 26, e.g., formed by a rupture disc, which determines the closed position and which snaps the piston 25 open when the closure 21 is opened.

[0025] The pressure chamber 3 is partially filled with a hydraulic fluid 27, the level of which lies between the opening of the annular channel 18 and the cover 2. A high-pressure gas cushion 28 is provided in the pressure chamber 3 between the hydraulic fluid 27 and the cover 2, so that the hydraulic fluid 27 is subjected to a correspondingly high static pressure. The pressure chamber 3 is filled with the high-pressure gas via a check valve 29, through which the pressure chamber 3 can be connected to a high-pressure gas line. In contrast to the pressure chamber 3, the inner tube 5 between the sealing plug 20 and the closure 21 has a pressureless gas filling. This means that if the closure 21 is suddenly opened, for example by detonation of an explosive charge 30 and the associated destruction of the rupture disc forming the stop 26, which, with the shock valve 22 open as shown in Fig.2. The static hydraulic pressure acting on piston 25 displaces piston 25 within the inner tube 5, compressing the gas filling of the inner tube 5. The hydraulic fluid 27, flowing into the inner tube 5 under acceleration through the flow paths 24, exerts a closing force on the valve body 23, which, at a corresponding flow velocity, causes the shock valve 22 to close abruptly. For this purpose, the valve body 23 is provided with a shearable projection 31, which breaks off when the closing force specified by the design conditions is reached, releasing the valve body 23, which then abruptly closes the shock valve 22.

[0026] To put the device into operation, the instantly opening closure 21 must be actuated by detonating the explosive charge 30, as shown in the exemplary embodiment. This causes the bursting disc, which forms the stop 26 for the piston 25, to rupture, and the piston 25 is released. The hydrostatic pressure exerted on the piston 25 by the hydraulic fluid 27, which is loaded by the highly pressurized gas cushion 28, moves the piston 25 into the inner tube 5. Hydraulic fluid 27 flows in through the flow paths 24 of the shock valve 22 and compresses the initially unpressurized gas filling of the inner tube 5. When the accelerating hydraulic fluid 27 reaches a predetermined flow velocity, the closing force acting on the valve body 23 causes the projection 31 to shear off, resulting in the shock valve 22 closing instantly, as shown in Fig. 3.The resulting pressure waves propagate both into the flow channel 14 and through the radial flow openings 19 into the annular channel 18, whereby the piezoelectric transducer 6 is subjected not only to an axial pressure load from the pressure ring 10, but also to a radial pressure load from the outer tube 4. The electrical voltage generated in this way can be tapped off via an indicated electrical connection 32.

[0027] The large amplitudes of the pressure waves resulting from the comparatively high flow velocity when closing the shock valve 22 not only generate high electrical voltages, but also deform the structural components exposed to these pressure waves, in particular the connecting sleeve 15 in the area of ​​the flow channel 14 on the one hand and the casing on the other.

[0028] 17 and the outer tube 4 in the area of ​​the annular channel 18 on the other hand, elastic, which leads to additional hydraulic fluid flows due to the associated volume changes of the flow paths, which can be used advantageously for resonance vibrations of the hydraulic system acted upon by a high-tension gas cushion.

[0029] The pressure waves propagating on one side into the flow channel 14 and on the other side into the annular channel 18 cause a negative pressure in the area of ​​the shock valve 22, which, in conjunction with the reflection conditions in the opening area of ​​the annular channel 18 and the flow conditions in the area of ​​the diffuser 16 at the end of the flow channel 14, results in opposing pressure waves that relieve pressure in the flow channel 14 and the annular channel.

[0030] 18 result in pressure conditions in the area of ​​the shock valve 22 similar to the initial conditions when the shock valve 22 is closed. The high-frequency pressure oscillations with low damping that occur in the resonance range can thus be advantageously used to provide a high-frequency voltage with a comparatively large amplitude via the piezoelectric transducer 6.

Claims

Patent claims 1. Device for converting pressure energy into electrical energy with a cylindrical housing (1) which accommodates a piezoelectric transducer (6) made of a stack of coaxial piezoelectric rings and forms a pressure chamber (3) containing a hydraulic fluid (27) for pressurizing the piezoelectric transducer (6), characterized in that the piezoelectric rings are arranged force-fit between two concentric tubes (4, 5) held in a housing cover (2) and are supported axially between a cover-side abutment (9) and a pressure ring (10) on the opposite end of the two tubes (4, 5), in that a coaxial flow channel (14) opening into the pressure chamber (3) is connected to the outer tube (4) via a diffuser (16), which is connected by radial flow openings (19) to an annular channel (18) extending from the flow channel (14) between the outer tube (4) and a concentrically enclosing the outer tube (4),the outer tube (4) is fluid-connected to the outer tube (5), the inner tube (5) has a snap-openable closure (21) with an upstream shock valve (22) on the side of the flow channel (14), and the pressure chamber (3) accommodating the two tubes (4, 5) with the flow channel (14) and the annular channel (18) is filled with a hydraulic fluid (27) at a height covering the annular channel (18), which is pressurized by a high-pressure gas cushion (28) filling the pressure chamber (3) above the hydraulic fluid (27).

2. Device according to claim 1, characterized in that the suddenly opening closure (21) has a bursting disc.

3. Device according to claim 1 or 2, characterized in that the pressure chamber (3) can be connected to a high-pressure gas line by means of a check valve (29).

4. Device according to one of claims 1 to 3, characterized in that the shock valve (22) has a shearable projection (31) as a stop for the open position.

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