Linear compressor
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-02
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026052631_13082026_PF_FP_ABST
Abstract
Description
[0001] TITLE
[0002] LINEAR COMPRESSOR
[0003] TECHNICAL AREA
[0004] The present invention relates to a linear compressor, particularly for high-pressure applications, preferably for the compression of hydrogen. The invention also relates to a gas expander with a linear generator.
[0005] STATE OF THE ART
[0006] Compressors, also known as pressure compressors, are used to compress gases. High demands are placed on compressors for high-pressure applications, especially those with final pressures exceeding 200 bar and / or suction pressures exceeding 40 bar, in terms of leak tightness, pressure resistance, and durability. This also applies to compressors used with aggressive gases. Compressors for hydrogen applications, in particular, have a correspondingly complex design. Consequently, they are expensive to manufacture and require regular maintenance at short intervals.
[0007] Various types of compressors are known, such as piston compressors with a mechanically driven crank drive, metal diaphragm compressors with a hydraulic crank drive, or hydraulically driven piston compressors.
[0008] EP 0378967 A1 describes a reciprocating compressor for high-pressure applications with a piston guided in a dry-running cylinder housing. The piston is movable by means of a crankshaft of a crank drive. For this purpose, the piston is guided in a cylinder insert that provides a ring gap seal while allowing for a certain amount of leakage. The cylinder insert is made of a wear-resistant metallic or ceramic material. The piston has a head that is received in a recess of a connecting part of the drive. A ball is arranged in the recess so that the piston is held movable and with clearance within the recess.
[0009] DE 102022 001 448 A1 also discloses a piston compressor with a crank drive and a piston running dry in a cylinder. A stuffing box seals the annular gap between the piston and the cylinder, whereby a leakage flow of the compressed gas between the piston and the stuffing box is permitted.
[0010] Such dry-running piston compressors with a rotating crankshaft and corresponding crank mechanism are indeed suitable for high-pressure applications. However, the crank mechanisms require regular maintenance. Furthermore, they pose the risk of coming into contact with the gas being compressed, which can damage the material through corrosion or embrittlement.
[0011] In metal diaphragm compressors, the crank mechanism is better protected because the piston presses on hydraulic oil, which deforms a flexible metal diaphragm and thus compresses the gas. However, these compressors require a lot of space and consist of numerous parts. Furthermore, the service life of the seals and diaphragm is relatively short. Consequently, metal diaphragm compressors are expensive.
[0012] Hydraulically driven piston compressors have a hydraulic pump that moves the piston back and forth using hydraulic oil. These compressors are also prone to leaks and wear, so frequent maintenance and regular replacement of seals and components are necessary.
[0013] Reciprocating compressors with linear motors are known in the prior art, in particular linear compressors.
[0014] Linear motors are electric motors with electromagnets, i.e., with current-carrying coils and permanent magnets. By changing the direction of the current in the coils, a movable rotor can be moved in an axial direction relative to a stationary stator. In some embodiments, the coils are located in the stator or the permanent magnets in the rotor. In other embodiments, the arrangement is reversed. Linear motors with a circular cross-section are known, in which the stator forms a sleeve in which the rotor is guided and movable in the axial direction. In these embodiments, the stator and rotor are usually rotationally symmetrical. Linear motors exhibit less wear and therefore require less maintenance than hand-cranked drives. They are characterized by small dimensions, high dynamics, long travel distances, and high precision. Furthermore, they can transmit large forces.
[0015] EP 1 465328 A1 describes a linear motor with a primary part containing the coils and a secondary part equipped with the permanent magnets. The primary and secondary parts are arranged concentrically to each other. In one example, they are cylindrical with a round cross-section.
[0016] Linear compressors with linear motors feature a piston connected to the motor's rotor, which moves back and forth along the rotor's axis within a cylinder. The piston's movement draws gas from an intake side into a working chamber. The gas is compressed in the compression chamber and then expelled on a pressure side. Appropriate valves are present on both the intake and pressure sides. The working chamber is also called the compression chamber.
[0017] US 2015 / 0125323 A1 discloses a linear compressor with a linear motor. The compressor is intended for high-pressure applications, particularly with hydrogen. The rotor of the linear motor forms a free piston that extends through several compression chambers. Maintaining a tight seal between these chambers is difficult. This leads to high leakage rates between the compression chambers and increased wear of the piston seals. Since the operating pressures in the compression chambers change with seal wear, the mechanical stresses and the degree of compression also change. The stage pressure ratios, and thus the temperatures in the respective working chambers, can become unacceptably high, which can lead to hazardous and, depending on the type of gas being compressed, even explosive operating conditions.
[0018] EP 2242 168 A1 describes a linear generator for an automotive engine that converts gas pressure into mechanical motion. The cylindrical rotor is arranged concentrically within the cylindrical stator, with a sealing ring at each end of the rotor sealing against the inner wall of the stator.
[0019] EP 2 390990 A1 shows a linear motor with a stator and a rotor arranged concentrically with respect to the stator. Inside the stator is a replaceable bearing tube, which has the same length as the stator and has an internally located plain bearing in which the rotor is mounted for axial movement.
[0020] PRESENTATION OF THE INVENTION
[0021] It is an object of the invention to create a linear compressor, especially for high-pressure applications, which can be manufactured cost-effectively and allows for the longest possible maintenance intervals.
[0022] This problem is solved by a linear compressor with the features of claim 1.
[0023] The linear compressor according to the invention comprises a linear motor, a cylindrical opening, a piston, and a compression chamber. The compression chamber serves to compress a gas by means of the piston, which is movable back and forth within the cylindrical opening by the linear motor. The piston extends into the compression chamber at a first end. The linear motor has a housing that surrounds a stator and a rotor arranged in the stator. The piston is connected to or integrally formed with the rotor at a second end. The rotor and the piston are movable back and forth together in an axial direction relative to the stator to compress the gas in the compression chamber. The linear compressor has a compression body that is arranged outside the housing adjacent to it. The compression chamber is arranged within the compression body, and the piston projects from the housing into the compression body.
[0024] The device according to the invention is in principle a free-piston machine with a linear motor or linear generator and utilizes the corresponding advantages.
[0025] Thanks to the arrangement of the compression chamber in a compression body located outside the housing of the linear motor, the low maintenance requirements of the linear motor are also guaranteed in high-pressure applications and / or in applications with aggressive gases.
[0026] The separation of the compression chamber and linear motor, i.e., the modular design, also simplifies assembly and maintenance.
[0027] Preferably, an annular gap seal is provided to seal an annular gap between the piston and the cylindrical opening, allowing a gap leakage flow.
[0028] The use of an annular gap seal ensures that only small amounts of the gas to be compressed can enter the housing of the linear motor.
[0029] In other applications, instead of an annular gap seal, at least one piston seal is provided, which is arranged on the circumference of the piston and seals the sealing gap between the piston and the compression body.
[0030] Annular gap seals are particularly suitable for high pressures. Piston seals are particularly suitable for applications with compression pressures of less than 50 bar.
[0031] The annular gap seal is preferably a cylindrical sleeve with a precision bore through which a piston rod of the piston passes, the piston rod also having a diameter of as precise a diameter as possible. The annular gap seal allows laminar flow between the inner surface of the bore and the outer surface of the piston rod. The laminar flow depends on the Reynolds number. The Reynolds number depends on the kinematic viscosity of the gas, the gas velocity, and the size of the leakage gap between the channel and the piston rod. The gas velocity is cubed to the size of the leakage gap and cubed to the differential pressure. An advantage is that there is no contact pressure between the sleeve and the piston rod. The seal is achieved by restricting the flow.
[0032] The piston seal is preferably a sealing ring. The free end of the piston preferably has a larger diameter than the piston rod and forms a piston base. The at least one piston seal is preferably arranged in at least one groove on the circumference of the piston base. When using piston seals, the sealing gap between the piston and the compression body is typically large enough that the connection between the piston and the rotor is rigid and the piston does not touch the compression body.
[0033] Preferably, the cylindrical opening and the annular gap seal or piston seal are arranged within the compression body. The compression chamber forms part of the cylindrical opening. This optimizes the modular separation of the high-pressure area and the linear motor, ensuring shorter maintenance intervals or a virtually maintenance-free linear motor.
[0034] The compression body can be attached to the housing of the linear motor using known methods. Preferably, it is flanged on.
[0035] In preferred embodiments, the linear motor has a guide tube for guiding the rotor. Preferably, the guide tube forms an inner surface of the stator in which the rotor is guided. Preferably, the guide tube encapsulates the gas-carrying compression and drive chamber from the atmosphere and the current-carrying part of the stator.
[0036] Preferably, the guide tube extends over the entire range of motion of the rotor. The guide tube enables the use of a dry-running stator. Furthermore, the guide tube serves as a pressure-bearing tube, sealing the gas-pressurized drive chamber of the linear motor against the atmosphere and ensuring resistance to the gas pressure. The guide tube also seals the stator components against the drive chamber and thus against the gas.
[0037] Since the guide tube extends over the entire movement path of the runner, precise guidance of the passive part or runner is ensured concentrically to the active part or stator, thus minimizing radial electromagnetic forces.
[0038] The guide tube is preferably made of an electrically and magnetically non-conductive material with a low coefficient of friction and low thermal expansion. This prevents eddy currents and magnetic losses. Preferably, the guide tube consists of a technical ceramic, in particular aluminum oxide, silicon nitride, or zirconium oxide. High-performance plastics or fiber-reinforced plastics can also be used instead of or in combination with technical ceramics. The aforementioned materials and material composites can also be used for other internal and external guide sections, in particular for the rotor or piston. Preferably, components with guide sections have a coefficient of thermal expansion of less than 10 x 10⁻⁶. 6 1 / K on.
[0039] In preferred embodiments, the rotor and the guide tube are mutually seal-free. That is, neither the rotor nor the guide tube has any seals, in particular ring seals in the form of O-rings, that seal against each other. A gap is preferably provided between the rotor and the guide tube to ensure precise, centered, and friction-optimized movement of the rotor within the guide tube. This gap is preferably 10 to 20 µm in size.
[0040] Preferably, the stator forms a drive chamber in which the rotor is arranged to move back and forth. The rotor has a cavity and through-holes on both end faces. These through-holes connect the drive chamber to the cavity, preventing a differential pressure from building up within the drive chamber due to the rotor's movement. This is achieved by ensuring the through-holes are sufficiently large. The cavity in the rotor and the drive chamber also act as a compensation chamber for the gas flowing in through the leakage between the piston and the compression body or the annular gap seal. This compensation chamber is connected via the compression chamber to an intake line that leads into the compression body from the outside. All leakage within the compressor is thus contained. The pressure in the drive chamber is preferably identical to the compressor's intake pressure.The entire compression system is hermetically sealed and leak-free to the atmosphere. Furthermore, the pressure in the drive chamber is secured by the intake pressure control. This results in high safety and efficiency without gas losses.
[0041] Furthermore, a hollow design of the runner reduces its weight. This enables a high power density of the linear motor.
[0042] In other embodiments, the rotor is a compact component without a flow-through cavity. This offers the advantage, particularly in designs with a small rotor diameter, that the rotor's construction is simple and cost-effective, especially when the magnets are to be protected from the harmful effects of a surrounding gas, such as hydrogen, by means of a casing. Small rotor diameters are, in particular, diameters of less than 40 mm.
[0043] The stator and rotor are preferably rotationally symmetrical, i.e., with a round cross-section, and the rotor is arranged concentrically to the stator within the stator. This allows for high thrust forces, enabling the rotor to move back and forth at high frequencies. The piston can be rigidly connected to the rotor or integrally formed with it. Preferably, the piston and rotor are two separate components connected to each other. In preferred embodiments, the piston is held with clearance in the rotor. Preferably, it is pivotably mounted in the rotor. Movement of the piston transversely to the longitudinal axis of the linear motor, and thus to the direction of movement of the piston and rotor, compensates for manufacturing tolerances and thereby enables precise guidance of the piston within the annular gap seal.
[0044] The annular gap seal can be designed in various ways. Several solutions are known in the art, which are also suitable for high-pressure applications and applications with aggressive gases. Preferably, the annular gap seal is a cylindrical bushing arranged in an extension of the cylindrical opening. Preferably, it is a stuffing box. Preferably, the annular gap seal is maintenance-free. The piston is preferably sealed in the annular gap seal in a dry-running manner.
[0045] The circumferential leakage gap between the annular seal and the piston is typically between 2 m and 5 m. The size of the leakage gap, also called the sealing gap, influences the size of the leakage flow rate cubed. At high differential pressures and with a highly volatile gas such as hydrogen, a sealing gap of 2 to 3 m is optimal. However, changes in operating temperatures and high operating pressures during compressor operation, as well as manufacturing tolerances of the piston and annular seal, often prevent this optimal maximum value from being achieved.
[0046] This optimum should not be undercut. If the sealing gap becomes smaller than a minimum value, preferably 2 m, the piston can only be moved relative to the annular gap seal with increased thrust or not at all.
[0047] Annular gap seals are not wear-free due to the contacting and moving components, namely the bushing and the piston rod. The leakage gap increases over time due to wear, necessitating replacement of the piston and / or the bushing. In preferred embodiments, the linear compressor therefore has a control channel leading to the annular gap seal for controlled pressurization of the seal to adjust the leakage flow. Preferably, the geometry of the annular gap seal is altered by applying pressure to its outer diameter, thus precisely modifying the gap between the seal and the piston. This adjustable leakage rate makes it possible to maintain the sealing gap within a predetermined maximum and minimum value, thereby precisely controlling the leakage flow.This extends the intervals before the piston and / or the bushing need to be replaced.
[0048] Preferably, a control system is provided that includes monitoring of the linear drive's thrust force. The linear compressor's thrust force can be monitored, for example, by means of current and position control in the linear drive's servo controller. Alternatively or additionally, the gap leakage flow can be measured by continuously or at specific intervals measuring the gas flow from the drive chamber back into the compressor's intake line. This data can also be used for controlling the sealing gap. With very fast-moving pistons, it is advantageous to monitor and measure both the thrust force and the gap leakage flow.
[0049] The compression process generates heat, which should be continuously dissipated. Some embodiments utilize air cooling. However, cooling channels, preferably liquid cooling, are preferably provided within the compression body. In some embodiments, first cooling channels are provided for gas cooling and second air channels for liquid cooling.
[0050] Preferably, at least the area around the compression chamber is cooled. In preferred embodiments, the area around the annular gap seal is also cooled. In even more preferred embodiments, the area around the compression chamber, as well as approximately the entire area in which the piston moves within the compression body, is cooled. The linear motor is preferably also cooled, either with its own cooling system or with liquid cooling, as with the compression body. For example, a cooling system can be used that is integrated into the compressor or that is arranged separately from the compressor.
[0051] Compressors have suction-side or low-pressure-side inlet openings for the gas to be compressed and pressure-side or high-pressure-side outlet openings for the compressed gas. These inlet and outlet openings are preferably also arranged in the compression body, which preferably has recesses for receiving corresponding valves that close the inlet and outlet openings.
[0052] Thanks to the modular design of the linear compressor, it can be implemented in various versions.
[0053] In a first variant, it features a single linear motor, two pistons, and two compression chambers. One of the two compression chambers is located at each end face of the linear motor housing, with a piston projecting into each compression chamber. This results in the same linear motor operating two compression chambers, with two low-pressure inlets and two high-pressure outlets. The design does not necessarily have to be mirror-symmetrical. Different compression levels are possible.
[0054] In a second variant, the linear compressor comprises a single linear motor, a single piston, and a single compression element. A spring housing containing a mechanical spring, which is connected or operatively linked to the rotor, is arranged on the end face of the linear motor housing opposite the compression element.
[0055] In a third variant, the linear compressor comprises two linear motors, each with a housing and at least one piston, as well as at least two annular gap seals. The linear motors are arranged longitudinally, one behind the other. A compression body with a single compression chamber is positioned between the linear motors. One piston of each linear motor projects into this compression chamber with its first end, the annular gaps between each piston and the cylindrical openings of the compression body being sealed by the two annular gap seals. On the sides of the linear compressors opposite the central compression body, either another compression body or a spring body with a mechanical spring, as described above, is arranged.This arrangement has the advantage that the inertial forces cancel each other out when the two pistons move in opposite directions, thus balancing the inertial forces of the two rotors. This allows for the construction of large linear compressors with heavier rotors, which can nevertheless be operated with virtually no vibration.
[0056] Other variations are possible, for example, the use of more than two linear motors and a correspondingly larger number of compression chambers in series. In some embodiments, the rotor, or its active area, is longer than the stator, or its active area. This embodiment has the advantage that all energized stator coils always cover the active part of the rotor, thus generating a maximized linear force.
[0057] In other embodiments, the stator, or its active area, is longer than the rotor, or its active area. This embodiment has the advantage of minimizing the rotor mass.
[0058] Further embodiments are specified in the dependent claims.
[0059] The linear compressor according to the invention can also be used to generate electrical energy, i.e., as a free-piston machine with a linear generator. In this case, the linear motor serves as the linear generator. The compression modules are expansion modules, and the compression chambers are expansion chambers for the expansion of high-pressure gas introduced from the modules via the high-pressure-side valves. During expansion, the expanding gas moves the piston and thus the rotor, which induces a current in the stator coils. The expanded gas is released via the suction-side or low-pressure-side valve. The above description and the features of the dependent claims also apply here.
[0060] The object of the invention is preferably a fluid working machine for compressing or conveying fluids, in particular for compressing gases to high pressures, especially a linear compressor or a linear generator.
[0061] BRIEF DESCRIPTION OF THE DRAWINGS
[0062] Preferred embodiments of the invention are described below with reference to the drawings, which serve only for illustration and are not to be interpreted restrictively. The drawings show:
[0063] Figure 1 shows a longitudinal section through a linear compressor in a first embodiment according to the invention; Figure 2 shows the linear compressor according to Figure 1 on a smaller scale;
[0064] Figure 3 shows a cross-section through BB according to Figure 2;
[0065] Figure 4 shows a cross-section through CC according to Figure 2;
[0066] Figure 5 is an enlarged representation of section D according to Figure 2;
[0067] Figure 6 shows a variant of the linear compressor according to Figure 1, depicted in an enlarged section;
[0068] Figure 7 is an enlarged representation of section E according to Figure 2;
[0069] Figure 8 shows a schematic representation of a linear generator according to the invention as shown in Figure 1 in side view;
[0070] Figure 9 shows a longitudinal section through a linear compressor in a second embodiment according to the invention;
[0071] Figure 10 shows a longitudinal section through a linear compressor in a third embodiment according to the invention;
[0072] Figure 11 shows a longitudinal section through a linear compressor in a fourth embodiment according to the invention;
[0073] Figure 12 shows a longitudinal section through a linear compressor in a fifth embodiment according to the invention and
[0074] Figure 13 shows a longitudinal section through a linear compressor in a sixth embodiment according to the invention.
[0075] Identical or similar components or parts are identified by the same reference numerals. Unlabeled components or parts that are also recognizable and labeled in other figures correspond to the labeled components or parts. DESCRIPTION OF PREFERRED EXECUTIONS
[0076] Figures 1 and 2 show a linear compressor according to the invention in a first embodiment. It comprises an electric linear motor 100 and two compression modules 101. The two compression modules 101 are arranged on each end face of the linear motor 100.
[0077] The linear motor 100 has a primary part, i.e., a stator 1, and a secondary part, i.e., a rotor 2. The stator 1 and the rotor 2 are rotationally symmetrical, i.e., they have a circular cross-section. The rotor 2 is arranged concentrically to the stator 1 within the stator 1.
[0078] The stator 1 comprises an outer tube 10, or is surrounded by an outer tube 10, which is provided at both ends with an annular end plate 11. The end plates 11 and the outer tube 10 are made of a non-magnetic material. Together they form a housing. They are rigidly connected to each other at the outer diameter of the outer tube 10 by threaded rods and nuts (not shown). Current-carrying coils 12 and annular intermediate plates 13 and end plates 14, which guide the magnetic flux and are arranged between the coils 12, are arranged in a row inside the outer tube 10.
[0079] An inner tube, here called guide tube 16, is arranged concentrically to the outer tube 10 inside the latter over the entire length of the stator 1 and defines the intermediate plates 13 and the end plates 14. Between the intermediate plates 13 and the end plates 14, respectively, either an air gap 15 is present along the guide tube 16 or a support ring 17 is arranged. The support rings 17 are made of a magnetically and electrically non-conductive material. Support rings 17 are preferably used in applications with very high pressures in the drive chamber 90, i.e., more than 50 bar.
[0080] At such high pressures, some of the components, in particular the guide tube 16, outer tube 10, end plates 11, end plates 14 and intermediate plates 13, are preferably assembled by means of radial transition and press fits. This assembly bears the internal pressure of the drive chamber 90.
[0081] At pressures in the working space of less than 50 bar, the guide tube 16 is preferably designed so that it can bear the internal pressure alone without being connected to the surrounding components.
[0082] The guide tube 16 extends over the entire length of the stator 1. It is sealed against the inner circumference of the annular end plates 11. Corresponding first sealing rings are designated with the reference numeral 80. The sealing rings 80 seal the gas pressure in the drive chamber 90 from the interior of the stator 1.
[0083] The guide tube 16 is made of an electrically and magnetically non-conductive material. Preferably, its material is a technical ceramic, in particular aluminum oxide, silicon nitride, or zirconium oxide. Instead of, or in combination with, technical ceramics, high-performance plastics or fiber-reinforced plastics can also be used.
[0084] The rotor 2 has an outer sleeve 20 and an inner sleeve 21. The two sleeves 20, 21 each have a tube and a sealing ring on both end faces. When assembled accordingly and tightly welded, they form a double-walled tube with a tightly sealed annular space. Permanent magnets 22 are arranged in the annular space, spaced apart by spacer rings 23. These could be, for example, iron poles.
[0085] A round runner plate 24 is attached to both end faces of the double-walled tube, formed by the outer sleeve 20 and the inner sleeve 21. It has corresponding shoulders for receiving the ends of the double-walled tube 20, 21. The connection between the runner plates 24 and the double-walled tube 20, 21 is made, for example, by a press fit or an adhesive bond. Other connections, such as a screw connection, are also possible.
[0086] In this example, the circumferential surface of the rotor plates 24 projects slightly from the outer wall of the outer sleeve 20, so that it does not touch the guide tube 16. The rotor plates 24 form a small gap with the inner surface of the guide tube 16, preferably a minimum of 10 µm and a maximum of 30 µm. Thus, when the linear motor is actuated, the guide tube 16 moves the rotor plates 24 in an oscillating motion along the longitudinal axis L of the stator 1. The direction of movement of the rotor 2 is therefore along the longitudinal axis L. The control system necessary for actuating the linear motor and the power supply to the coils 12 are not shown in the figures. They correspond to the control systems for linear motors that are well known in the prior art. In the embodiment according to Figure 6, the surface of the rotor plates 24 is set back from the outer surface of the outer sleeve 20. Only the outer sleeve 20 is guided by the guide tube 16 when the runner 2 moves.
[0087] The guided surfaces of the runner plates 24 and / or the outer sleeve 20 are preferably made of an electrically and magnetically non-conductive material. Preferably, the material is a technical ceramic, in particular aluminum oxide, silicon nitride, or zirconium oxide. High-performance plastics or fiber-reinforced plastics can also be used instead of or in combination with technical ceramics.
[0088] The guided surfaces of the outer sleeve 20 and / or the runner plates 24 are preferably provided with a sliding layer, for example with PTFE (polytetrafluoroethylene). This is particularly relevant when the sliding surfaces of the guide tube and the runner 2 are in contact. In some embodiments, at least the guide tube 16 is provided with a sliding layer, for example made of PTFE.
[0089] The rotor plates 24 have at least one, preferably several, radially uniformly distributed through-openings 25 that lead into a cavity 28 of the rotor 2. The cavity 28 is formed by the rotor plates 24 and the double-walled tube 20, 21. It is preferably cylindrical. The through-openings thus connect the drive chamber 90, formed by the interior of the stator 1, with the cavity 28, formed by the interior of the rotor 2.
[0090] The rotor plates 24 also have a central recess 26 on their outwardly facing end face for receiving a piston head 30. This is clearly visible in Figure 5. The surface of the piston head 30 is preferably convex and rests against a flat base of the recess 26. The piston 3 passes through a retaining ring 27, which is preferably fixed to the rotor plate 24 by screws (not shown). This allows the piston 3 to move relative to the rotor 2 in directions transverse to the longitudinal axis L. Preferably, a clearance of approximately 50 pm in the direction of the longitudinal axis L is possible, meaning the piston 3 is fixed relative to the rotor 2 in the longitudinal direction but can move freely transversely.
[0091] Figure 6 shows a variant of this design. A rolling element 32, more precisely a ball, is arranged in the recess on a support. The piston head 31 is planar, allowing it to roll on the rolling element. Other known designs that also allow the piston 3 to be driven free from lateral forces can also be used.
[0092] On each side of the rotor 2, a piston 3 is connected to the corresponding rotor plate 24. The arrangement in this respect is preferably mirror-symmetrical with a mirror surface that runs centrally through the rotor 2.
[0093] The two pistons 3 each extend into one of the two compression modules 101. In single-stage compressors, the two compression modules 101 are preferably identical. Each compression module 101 has a solid compression body 4. In an air-cooled version, it has cooling fins, and in a liquid-cooled version, it has cooling channels, for example, water cooling channels 41 and gas cooling channels 42.
[0094] Each compression element 4 has a flange 44 for attachment to the adjacent side plate 11 of the linear motor 1. The connection is preferably made by screws (not shown) and is gas-tight. Corresponding secondary seals, preferably sealing rings, are indicated in the figures by reference numeral 81. The sealing rings 81 seal the gas pressure in the drive chamber against the atmosphere.
[0095] A through-hole within the compression body 4 is open at one end facing the linear motor 100 and closed at the other end, for example by means of a sealing plug 43. Alternatively, it is designed as a blind hole. The sealing plug 43 can also serve to accommodate sensors, for example for measuring compression pressure or piston position.
[0096] This bore forms a compression chamber 40. A bore, which serves to accommodate a suction-side or low-pressure-side compressor valve 60, leads from the outside to the compression chamber 40. A bore, which serves to accommodate a pressure-side compressor valve 61, leads from the compression chamber 40 to the outside. The valves 60 and 61 can also be arranged outside the compression body 4.
[0097] On the linear motor side, the bore widens outwards in two stages, forming a stepped recess. An annular gap seal, here an annular gap bushing 5, is arranged in this recess. The annular gap bushing 5 has a precise inner bore, the diameter of which is preferably 5 to 20 µm larger than the outer diameter of the piston 3. The piston 3 passes through the annular gap bushing 5 and projects into the subsequent bore section, which forms the compression chamber 40.
[0098] The difference between the inner diameter of the compression chamber 40 and the outer diameter of the piston 3 is preferably designed to be as small as possible, without the compression chamber 40 touching during the oscillating movement of the piston 3. Preferably, this difference in diameter is less than 100 pm.
[0099] During operation of the linear motor, the piston 3 moves in an oscillating manner in the annular gap bushing 5. Due to the oscillating movement of the free end of the piston in the compression chamber 40, gas is drawn in through the suction-side or low-pressure-side compressor valve 60, compressed and then released as high-pressure gas through the pressure-side compressor valve 61.
[0100] The annular gap bushing 5 is held gas-tight in the compression body 4, both from the drive chamber 90 and from the compression chamber 40. For this purpose, an annular fixing plate 50 is arranged in the widest section of the bore, which is preferably fixed to the compression body 4 with screws (not shown) and thereby secures the annular gap bushing 5. The inner diameter of the fixing plate 50 is selected such that it does not contact the piston 3.
[0101] The space at the outer diameter of the annular gap bushing 5 is connected to the gas pressure control valve port 62 via a control channel 45. Seals 82 and 83 seal this space against the drive chamber 90, and a seal 84 seals it against the compression chamber 40. Sealing rings (O-rings) are preferably used as seals.
[0102] The annular gap bushing 5 is made of a hard, wear-resistant material with a friction-optimized surface. Preferably, the bushing, in particular its guide section, has a coefficient of thermal expansion of preferably less than 10 x 10⁻⁶. 6 1 / K. Preferably, its material is a technical ceramic, in particular aluminum oxide, silicon nitride, or zirconium oxide. The inner and outer diameters of the bushing are manufactured with high precision. Preferably, the inner diameter is finished by precision honing and the outer diameter by precision grinding.
[0103] The piston 3 is guided and sealed by the annular gap bushing 5, leaving only a small annular leakage gap 46 between the annular gap bushing 5 and the piston 3. The circumferential leakage gap 46 is a few micrometers, preferably a minimum of 2 m and a maximum of 5 m.
[0104] Preferably, the leakage gap 46 within the annular gap bushing 5 can be selectively adjusted. For example, as can be seen in Figure 7, by means of a control channel 45 in the compression body 4. The control channel 45 leads from the gas pressure control valve connection 62 to the outer surface of the annular gap bushing 5. By means of a gas pressure control valve (not shown), a controlled gas pressure can be applied to the outer surface of the annular gap bushing 5, thereby selectively changing the volume or the inner diameter of the annular gap bushing 5 and thus the leakage gap 46 relative to the piston 3.
[0105] The control of the leakage gap 46, and thus the leakage flow of the gas to be compressed, can be achieved in various ways. For example, the thrust of the linear drive can be monitored by means of current and position control. Additionally, the leakage flow through the annular gap seal can also be measured. This leakage flow measurement preferably takes place in a connecting line V, which links the drive chamber 90 via the leakage flow connections 63 to an intake line A leading from the outside into the compression body 4. The intake line A and the connecting line V are shown schematically and with dashed lines in Figure 2.
[0106] Figure 9 shows a variant of this embodiment. Instead of a mirror-symmetrical structure with two compression modules 101, the compression module 101 with compression body 4 and annular gap bushing 5 described above is arranged on one end face of the linear motor 1. On the other end face of the linear motor 1, however, a spring housing 7 is attached by means of a flange 70. This connection is also gas-tight by means of first and second seals 80, 81.
[0107] The spring housing 7 has a recess 71 in which a mechanical spring, here a coil spring 72, is arranged. One end of the coil spring 72 is arranged in or connected to the recess 26 of the rotor plate 24. In the first embodiment, the gas in the opposing and alternately operating compression chambers acts as pneumatic springs so that the gas can expand sufficiently before the next intake cycle. In this example, the mechanical spring 72 serves this purpose. When the piston 3 moves to the left according to Figure 9, the spring 72 is relaxed; when it moves to the right, it is compressed.
[0108] Figure 10 shows another variant of the linear compressor. It features two linear motors 100, preferably of identical construction. At their outermost ends, they are each connected to identical compression modules 101. The description for the first embodiment also applies here. A central or middle compression module 102 is arranged between the two linear motors 100. It is constructed similarly to the compression modules 101 described previously. The difference is that the compression body 4 is longer, so that the through-bore at both ends has a stepped recess for receiving an annular gap seal, preferably again in the form of an annular gap bushing 5, with each of the two annular gap seals 5 being penetrated by a piston 3 of the two linear motors 100.The through-bore forms a compression chamber 40 between the free ends of the two pistons 3. The chamber is sized such that the two pistons 3 do not touch each other during counter-rotating operation. Preferably, the minimum distance between the two pistons 3 is in the range of 2% of the stroke of one piston 3. A suction-side (low-pressure-side) compressor valve 60 leads from the outside into the compression chamber 40, and a pressure-side compressor valve 61 leads from the compression chamber 40 to the outside. The two linear motors 10 are preferably operated such that the pistons 3 move in opposite directions within the central compression module 102.
[0109] The linear compressors described above can be used with the same design as gas expanders with a linear generator. Unlike the linear compressors, high-pressure gas flows into the compression chamber, which now serves as an expansion chamber. The overpressure moves the piston 3 and thus the rotor 2. The movement of the rotor 2 along the longitudinal axis L induces current in the coils 12 of the stator 1. The linear motor is thus operated as a linear generator. The expanded gas in the expansion chamber is discharged to the outside, and new high-pressure gas is admitted into the chamber.
[0110] If the piston engine is operated as a compressor, the compressor valves can be passive or actively controlled valves, e.g., solenoid valves. In the case of the gas expander, the inlet and outlet valves 60, 61 are preferably actively controlled valves, e.g., solenoid valves.
[0111] In the case of the gas expander, the timing of the valve opening and closing is analogous to that of compression. This timing is preferably determined by measuring the position of the rotor 2 and the gas pressure. The gas expansion drives the pistons 3 and thus the rotor 2.
[0112] Figure 8 shows a schematic representation of the embodiment of a gas expander described above.
[0113] Figure 11 shows another variant of the linear compressor for applications with compression pressures of less than 50 bar without annular gap seals. The linear compressor has the same construction as in the embodiments described above. However, it differs in that, instead of an annular gap bushing, the seal between the compression chamber 40 and the drive chamber 90 is provided by piston seals 33, which are arranged on the circumference of the piston 3 and seal the gap between the piston 3 and the compression body 4. The piston seals 33 are preferably piston sealing rings, for example, made of high-strength PTFE compounds. The piston seals 33 are pressed against the cylinder wall of the compression body 4 by the gas pressure in the compression chamber 40. The piston 3 preferably has a piston head 30, a piston rod that tapers with respect to the piston head, and a piston base 34 that has a larger diameter than the piston rod.The piston seals 33 are arranged in grooves on the circumference of the piston base 34 and slide along the inner diameter of the compression body 4.
[0114] When using piston seals 33, the sealing gap between piston 3 and compression body 4 is so large that the connection between piston 3 and rotor 2 can be rigid, with the piston 3 not touching the compression body 4.
[0115] The compression body 4 of the linear compressor according to Figure 11 can also be provided with gas or liquid cooling. In the illustrated variant, the compression body 4 is air-cooled. Corresponding cooling fins are designated with reference numeral 410. Figure 12 shows a further embodiment. It corresponds essentially to the first embodiment according to Figures 1 to 8. In contrast to the embodiments described above, however, the active area of the stator 1 is shorter than the active area of the rotor 2. The active area of the stator 1 and the rotor 2 are the areas in which the coils 12 and permanent magnets 22, respectively, are located. The rotor 2 again has an outer sleeve 20, and the stator 1 has an inner guide tube 16. The stator 1 and rotor 2 are in turn surrounded by a housing that has the outer tube 10, the annular end plates 11, and two second outer tubes 110.The two second outer tubes 110 form an extension of the end plates 11 on both sides of the arrangement and are connected to the flanges 44 at the end face.
[0116] In this embodiment, the guide tube 16 is therefore shorter than the outer sleeve 20. It preferably extends only over the active area of the stator 1 and terminates at the end plates 11, which adjoin the end plates 12 of the coil assembly 12. The guide tube 16 provides a gas-tight seal between the drive chamber 90 and the atmosphere, as well as against the electrically active part of the drive (not shown here). The corresponding seals are designated with reference numeral 80. The other seals shown in the embodiments according to Figures 1 to 11 and described above are also present, at least to the extent that they are shown in the figures but not labeled.
[0117] In this embodiment, the active area of the rotor is formed by permanent magnets 22 in the form of round disks, which are separated from each other by round spacer rings or round spacer disks 23. The active area of the rotor 2 is closed at its two end faces by at least one rotor plate 24 each and at its outer diameter by the outer sleeve 20.
[0118] The piston 3 is connected to the rotor 2 as described above. Preferably, it is pivotably connected to the rotor 2. Preferably, the rotor 2 again has the recess 26 and the retaining ring 27 for this purpose. Preferably, the piston 3 is connected to the rotor 2 with clearance.
[0119] The drive chamber 90 is connected to the intake line A via the connecting line V. In contrast to the first embodiment, the rotor 2 does not form a cavity 28, and therefore there are no through-openings 25. The connecting line V allows gas to flow back from the drive chamber 90 to the intake line A, so that excessive pressure does not build up in the drive chamber 90. Preferably, the pressure buildup in the drive chamber 90 is always less than ±10% of the nominal pressure in the drive chamber 90. This is achieved by appropriately dimensioning the drive chamber 90 and the connecting line V.
[0120] The embodiment according to Figure 13 essentially corresponds to the embodiment according to Figure 12. In this embodiment as well, the active area of the rotor 2 is longer than the active area of the stator 1.
[0121] In this variant, two guides 18 are provided to guide the outer sleeve 20 relative to the stator 1. The stator 1 preferably has a guide tube 16. Under normal operating conditions, the guide tube 16 is not in contact with the outer sleeve 20.
[0122] The two guides 18 are preferably arranged in the area of the end plates 11 or adjacent to these end plates 11 in the area of the second outer tubes 110 and thus outside the active area of the stator 1. They are preferably made of a high-strength and wear-resistant high-performance plastic, e.g. carbon fiber reinforced polyamide, or of a technical ceramic, e.g. zirconium oxide, which, in combination with the counter-running surface, has a low coefficient of friction.
[0123] In this embodiment, the active area of the rotor is formed by permanent magnets 22 in the form of annular disks, which are separated from each other by annular spacer rings 23. They form the cavity 28.
[0124] The active area of the runner 2 is closed off at its two end faces by at least one runner plate 24 each, at the outer diameter by the outer sleeve 20 and at the inner diameter, which defines the cavity 28, by the inner sleeve 21.
[0125] As in the first embodiment, through-holes 25 are provided which connect the cavity 28 with the drive chamber 90.
[0126] Preferably, the piston 3 is pivotably connected to the rotor 2, preferably with some clearance. The embodiments according to Figures 9, 10 and 11 can also be implemented with the stator-rotor arrangement according to Figures 12 and 13, i.e., with rotors 2 that are longer than the stators 1 and with flowable or non-flowable rotors 2.
[0127] The guidance of the runner 2 in Figure 13 can be implemented analogously to the embodiment shown in Figure 12. Conversely, the guidance of the runner 2 in the embodiment shown in Figure 12 can be implemented with two guides 18, as shown in Figure 13.
[0128] The linear compressor or gas expander according to the invention is cost-effective to manufacture and allows for the longest possible maintenance intervals. It also exhibits high efficiency and is suitable for use with high gas pressures and aggressive gases, particularly hydrogen. [REFERENCE SIGN LIST]
[0129] 1 Stator
[0130] 10 Outer pipe
[0131] 110 second outer pipe
[0132] 11 Front plate
[0133] 12 coils
[0134] 13 Intermediate plate
[0135] 14 End plate
[0136] 15 air gap
[0137] 16 guide tube
[0138] 17 Support ring
[0139] 18 Leadership
[0140] 2 runners
[0141] 20 outer sleeve
[0142] 21 Inner sleeve
[0143] 22 permanent magnet
[0144] 23 Spacer ring / spacer washer
[0145] 24 runner plate
[0146] 25 Through opening
[0147] 26 Exclusion
[0148] 27 Fixing ring
[0149] 28 Cavity
[0150] 3 pistons
[0151] 30 Piston head
[0152] 31 Piston head
[0153] 32 rolling elements
[0154] 33 Piston seal
[0155] 34 Piston base
[0156] 4 compression bodies
[0157] 40 compression chambers
[0158] 41 Water cooling channel
[0159] 410 cooling fins 42 gas cooling channel
[0160] 43 sealing plugs
[0161] 44 flange
[0162] 45 control channel
[0163] 46 Leakage gap
[0164] 5 ring gap bushing
[0165] 50 fixing plate
[0166] 60 low-pressure side compressor valve
[0167] 61 High-pressure side compressor valve
[0168] 62 Gas pressure control valve connection
[0169] 63 Leakage current connection / Connection of connecting line V to the suction line A
[0170] 7 Spring housings
[0171] 70 flange
[0172] 71 Exclusion
[0173] 72 spiral spring
[0174] 80 first seal
[0175] 81 second seal
[0176] 82 third seal
[0177] 83 fourth seal
[0178] 84 fifth seal
[0179] 90 Engine room
[0180] 100 linear motors
[0181] 101 Compression module
[0182] 102 mean compression modulus
[0183] A Intake manifold
[0184] L Longitudinal axis
[0185] V Connection line
Claims
26 PATENT CLAIMS 1. Linear compressor with a linear motor (100), a cylindrical opening, a piston (3), and a compression chamber (40) for compressing a gas by means of the piston (3), which can be moved back and forth in the cylindrical opening by means of the linear motor (100), wherein the piston (3) extends with a first end into the compression chamber (40), wherein the linear motor (100) has a housing (10, 11, 110) that surrounds a stator (1) and a rotor (2) arranged in the stator (1), wherein the piston (3) is connected to the rotor (2) at a second end or is integrally formed with it, wherein the rotor (2) and the piston (3) are jointly movable back and forth in an axial direction relative to the stator (1) in order to compress the gas in the compression chamber (40), characterized by that the linear compressor has a compression body (4) which is arranged outside the housing (10, 11, 110) adjacent to it, that the compression chamber (40) is arranged in the compression body (4), and that the piston (3) protrudes from the housing (10, 11, 110) into the compression body (4).
2. Linear compressor according to claim 1, wherein an annular gap seal (5) is provided to seal an annular gap between the piston (3) and the cylindrical opening, allowing a gap leakage flow.
3. Linear compressor according to claim 2, wherein the cylindrical opening and the annular gap seal (5) are arranged in the compression body (4) and wherein the compression chamber (40) is part of the cylindrical opening.
4. Linear compressor according to one of claims 2 or 3, wherein the annular gap seal (5) is a cylindrical bushing which is arranged in an extension of the cylindrical opening.
5. Linear compressor according to one of claims 2 to 4, wherein the linear compressor has a control channel (45) leading to the annular gap seal (5) for controlled pressurization of the annular gap seal (5) for adjusting the gap leakage current.
6. Linear compressor according to any one of claims 1 to 5, wherein the linear motor (100) has a guide tube (16) for guiding the rotor (2), wherein the guide tube (16) forms an inner surface of the stator (1) and wherein it extends over an entire movement path of the rotor (2).
7. Linear compressor according to claim 6, wherein the rotor (2) and guide tube (1) are mutually seal-free.
8. Linear compressor according to one of claims 1 to 7, wherein the stator (1) forms a drive chamber (90) in which the rotor (2) is arranged to be movable back and forth, wherein the rotor (2) has a cavity (28) and through-openings (25) on both end faces, wherein the through-openings (25) connect the drive chamber (90) with the cavity (28), whereby the cavity (28) acts as a compensating chamber.
9. Linear compressor according to any one of claims 1 to 7, wherein the rotor (2) is a compact component without a flowable cavity.
10. Linear compressor according to one of claims 1 to 9, wherein the piston (3) is held with clearance in the rotor (2).
11. Linear compressor according to one of claims 1 to 10, wherein the piston (3) is pivotably held in the rotor (2).
12. Linear compressor according to one of claims 1 to 11, wherein the compression body (4) has cooling channels (41, 42).
13. Linear compressor according to one of claims 1 to 12, wherein the compression body (4) has a low-pressure inlet opening and a high-pressure outlet opening.
14. Linear compressor according to one of claims 1 to 13, wherein a single linear motor (100), two pistons (3) and two compression bodies (4) are provided, wherein one of the two compression bodies (4) is arranged on each end face of the housing (10, 11, 110) of the linear motor (1) and wherein one piston (3) projects into each compression body (4).
15. Linear compressor according to one of claims 1 to 13, wherein a single linear motor (100), a piston (3) and a compression body (4) are provided, wherein a spring housing (7) with a mechanical spring (72) is arranged on the end face of the housing (10, 11, 110) of the linear motor (100) opposite the compression body (4), which is connected or operatively connected to the rotor (2).
16. Linear compressor according to any one of claims 1 to 15, insofar as referring back to claim 2, wherein two linear motors (100) each have a housing (10, 11, 110) and at least one piston (3) each, as well as at least two annular gap seals (5), wherein the linear motors (100) are arranged longitudinally one behind the other, wherein the compression body (4) is arranged between the linear motors (100), wherein one piston (3) of each linear motor (100) projects with its first ends into the compression chamber (40) and, wherein the annular gaps between each piston (3) and the cylindrical openings are sealed by means of the two annular gap seals (5).
17. Linear compressor according to claim 16, wherein on the end faces of the two housings (10, 11, 110) opposite the compression body (4) either a further compression body (4) is arranged, into which a further piston (3) from one of the two housings (10, 11, 110) projects, or a spring housing (7) with a mechanical spring (72) is arranged, wherein the spring (72) projects into the housing (10, 11, 110) and is connected or operatively connected to the end face of the rotor (2) arranged therein.
18. Linear compressor according to any one of claims 1 to 17, wherein the rotor (2) is longer than the stator (1).
19. Linear compressor according to any one of claims 1 to 17, wherein the stator (1) is longer than the rotor (2).29 20. Free-piston machine with a linear generator, wherein the free-piston machine has the features of the linear compressor according to any one of claims 1 to 19, wherein the linear motor serves as a linear generator and wherein the compression module and the compression chamber serve as an expansion module and expansion chamber respectively for the expansion of a high-pressure gas introduced into the expansion chamber for the purpose of moving the rotor by means of the piston.