BR112019015639B1 - LINEAR ELECTRIC MACHINE - Google Patents

Abstract

A linear electrical machine (MEL) comprising a stator mounted in a housing, the housing and stator defining a work cylinder, a central core within the work cylinder and defining a cavity to house the intermediate cylindrical stator, a hollow actuator axially movable inside the working cylinder, extending into the cavity of the stator housing and forming an outer void space of the magnetic circuit between the activator and the stator, at least one fluid bearing between the central core and the activator providing a bearing gap, in which the central core is fixed axially with respect to the stator, in which the at least one fluid bearing provides coaxial location of the activator and the central core.

Description

[001] The present invention relates to a linear electric machine.

[002] These linear electrical machines can be used for various applications, including, among others, use as a linear generator with a free-piston engine, in which the combustion pressure acts on an activator to produce usable electrical current, the use as a gas expander, where a high pressure gas acts on an activator to produce usable electrical current, use as a gas compressor, where an electrical signal induces movement of an activator to pressurize a gas, the use in hydraulic systems, where actuator movement causes or is caused by the displacement of hydraulic fluid within a working chamber, and use as an actuator, where an electrical signal induces movement of an actuator to produce a desired acting effect.

[003] These actuators can be used in displacement and vibration testing systems, manufacturing operations and robotics. In displacement and vibration test system applications, the actuator can be used to apply a cyclic force or motion profile to a test subject. The test subject could be a sample of material, a discrete component, a subsystem assembly of components, or a complete product. The purpose of these tests may be to determine the durability of the test subject with the applied force or displacement function. Alternatively, tests may seek to characterize the test subject's response to the applied force or displacement function.

[004] The automotive industry makes extensive use of these test actuators for subassembly testing and complete product testing. The test actuator is typically arranged to support a vehicle or part of a vehicle, such as one or more wheels or suspension parts.

[005] In particular, in a vehicle testing application, the invention can be used as part of a vehicle testing system in a road simulator, in which each corner of a vehicle is typically supported by a separate actuator. Support can be provided directly to the vehicle's wheels or it can be provided to other components, such as a suspension part, an axle stub or support arms. Actuators can be applied to the vehicle body in certain situations. The movement of the actuators can then mimic vehicle movement on various road surfaces and other terrain. Therefore, the test environment is controlled, in which force or displacement application functions representing different driving speeds and road surface conditions can be applied to the vehicle. As examples, by varying the amplitude of a high-frequency displacement, a smoother or rougher road surface can be simulated. Alternatively, extreme loads can be applied to simulate potholes and other major road accidents. These tests can be used in vehicle development to reduce driving noise and ensure that the vehicle's suspension components are capable and durable enough for the intended range of driving conditions.

[006] Similarly, high-frequency displacements that characterize road loads at representative driving speeds are commonly used in servo-hydraulic systems as the basis for automotive test systems. In these systems, a hydraulic servo power pack generates a high pressure hydraulic fluid which is then sent to hydraulic actuators using one or more servo valves. These systems have several well-known drawbacks.

[007] First, the inertia of the hydraulic oil and servo-hydraulic power package components limits the practical frequency of road load functions that can be generated at approximately 150 Hz. This is well below the performance level required to represent accurately track road surface features representing features on a scale of 20mm and less, also being below actuation vibration frequencies known as excitation resonances in the vehicle structure which in turn produce undesirable noises within the vehicle interior. vehicle.

[008] Second, servo-hydraulic systems require expensive and dedicated infrastructure in the test facilities, which can be extremely bulky, and must also be located relatively close to the hydraulic actuators, to limit the inertia of oil movement within the system . Furthermore, this infrastructure requires special operation and maintenance expertise.

[009] Third, servo-hydraulic systems are huge energy consumers, making them expensive to operate and contributing to the carbon footprint of automotive development and manufacturing.

[0010] Fourth, hydraulic servo systems can be extremely noisy, making it difficult to differentiate between the noise produced due to the response of the test subject and the noise associated with the test actuator system itself.

[0011] As a result of these drawbacks, linear electromagnetic actuators are being adopted in place of hydraulic servo systems for certain automotive test applications and other test actuator applications. Linear electromagnetic actuators have the advantage of being more responsive, more compact, easier to operate and maintain, more efficient and less noisy.

[0012] In several of these systems, a spring and/or pneumatic cylinder are provided to allow the actuators described in the prior art to apply a static charge through or along the electrical activator of the machine and onto the test subject. This arrangement allows the force component attached to the actuator to be adjusted prior to operation to balance the test subject's weight and/or ensure the test subject is in the correct position prior to the start of the test.

[0013] US patent US7401520 discloses a complete system for testing a vehicle, comprising a plurality of equipment, each of the plurality of equipment comprising a frame for supporting at least a part of a wheel of a vehicle and a linear electromagnetic actuator at least partially contained within the frame, the linear electromagnetic actuator having a movable magnet and in use providing a substantially controlled vertical force to a vehicle wheel. Each of the devices is assembled to independently provide a substantially controlled vertical force on one of a plurality of supported vehicular wheels and a plurality of air springs (which are sometimes referred to as airbags) or alternatively mechanical springs (of group comprising a spiral spring, a torsion spring and a bundle of springs) which are provided to provide leveling of the supported vehicle.

[0014] This system has several drawbacks.

[0015] First, the requirement for a load-bearing mechanical connection between the airbag or the mechanical spring and the wheel plate or the electric machine driver adds inertial mass to the moving assembly. This additional inertia reduces the peak frequencies that the actuator is able to achieve for a given displacement.

[0016] Second, the use of a compliant member such as an airbag or mechanical spring introduces the possibility of generating undesirable resonances in the test actuator system, compromising the integrity of the actuation function that is applied to the test subject.

[0017] Third, the assembly taught by the US Patent US7401520 requires an unnecessary level of complexity in construction, due to the need to couple discrete sets of springs and electrical machines within each test actuator frame, resulting in greater cost and dimensions of the device in general.

[0018] The US patent US8844345 discloses equipment that provides movement to a test object, such as a motor vehicle in a controlled manner. Mounted thereon is a base with a linear electromagnetic motor having a first end and a second end, the first end being connected to the base. An air cylinder and piston combination has a first end and a second end, the first end connected to the base so that the cylinder and air piston combination is generally parallel to the linear electromagnetic motor. The second ends of the linear electromagnetic motor and pneumatic cylinder-piston combination are normally attached to a movable member, which is also attached to a support of the test object. A linear electromagnetic motor and pneumatic cylinder-piston combination control system the cylinder and pneumatic piston combination to support a substantial static load of the test object and the linear electromagnetic motor to provide controlled movement to the test object.

[0019] This system has several drawbacks similar to those previously described in relation to US Patent US7401520.

[0020] First, the requirement of a discrete combination of cylinder and pneumatic piston, the support and movable member of the load bearing for the test subject adds considerable inertial mass to the movable assembly. This additional inertia reduces the peak frequencies that the actuator is able to achieve for a given displacement.

[0021] Second, the use of the combination of cylinder and pneumatic piston, instead of an airbag or a mechanical spring, introduces friction due to the sliding seal between the cylinder and the pneumatic piston. This friction affects the net force that is applied to the test subject and can also result in wear and reduced actuator life.

[0022] Third, the assembly disclosed by US Patent US8844345 requires an unnecessary level of complexity in construction, due to the need to couple an electrical machine, a pneumatic cylinder, a member and mobile support for the test subject within each frame testing actuator, resulting in a higher cost and larger overall device dimensions.

[0023] Linear electrical machines may also include a working chamber in which a change in the volume of the working chamber causes movement of an activator, which then induces an electric current in one or more spirals, or in which movement of the activator caused by an electric current in one or more of the spirals causes a change in the volume of the working chamber. Examples of these systems include the use of a linear generator with a free piston engine, where the combustion pressure acts on an activator to produce usable electrical power, use as a gas expander, where a high pressure gas acts on an actuator for producing usable electrical power, use as a gas compressor, where an electrical signal induces movement in an actuator to pressurize a gas, use in hydraulic systems, where movement of the actuator causes or is caused by displacement hydraulic fluid inside the working chamber.

[0024] Many of the problems that are described above in relation to the use of the linear electric machine as an actuator are also present when using this device as a motor or generator acting on a fluid contained within the working chamber, and thus also obtained benefits similar. In particular, a linear generator with a free piston engine must effectively control the piston movement to obtain a consistent compression and expansion ratio desirable for efficient combustion and low emissions. The challenge of controlling the piston movement is widely recognized in the prior art, as the main challenge that must be solved before the free piston engine design can be successfully developed and commercialized. Linear electric machines are typically employed where free-piston machines can rarely achieve the desired level of motion control, because these machines have a large piston mass relative to the force that can be applied by the electric machine. This metric force or its reciprocal (force per unit of mobile mass), which is sometimes called the 'specific force', is the most important determinant of the motion control of the free-piston engine.

[0025] Good piston movement control performance is also essential in other applications that use the linear electric machine as a motor or generator acting on a fluid contained within the working chamber, including free piston gas expanders ( for example, within a waste heat recovery system from a Rankine cycle or refrigeration cycle), free piston gas compressors and free piston pumps, as the movement of the piston determines the pressure or displaced volume that is achieved at the end of the course. Therefore, any uncontrolled variation in the end of stroke position of the piston has a direct impact on the function of the device.

[0026] The present invention aims to solve one or more of the problems identified above.

[0027] According to the present invention, a linear electrical machine (MEL) is provided comprising a stator mounted in a housing, the housing and the stator defining a working cylinder, a central core inside the working cylinder and defining a cavity to house the intermediate cylindrical stator, an axially movable hollow activator within the working cylinder, extending into the interior of the stator housing cavity and forming an outer void space of the magnetic circuit between the activator and the stator, at least at least one curved portion or bearing between the central core and the activator providing coaxial location of the activator within the cavity of the stator housing, where the central core is fixed axially with respect to the stator.

[0028] The bearing or the curved part may be a fluid bearing, which could be a gas bearing, and which would typically be suitable for applications where the working cylinder contains a gas. Alternatively, the fluid bearing could be a hydrodynamic or hydrostatic bearing, which would typically be suitable for applications where the work cylinder contains a liquid. Where the specification refers to the use of a fluid bearing, this could be taken to mean any gas bearing, a hydrodynamic bearing and a hydrostatic bearing. The fluid bearing can provide the coaxial location of the activator and the central core.

[0029] Due to this assembly, and in particular the fluid bearing between the central core and the activator, there are no requirements for a greater length of the activator beyond the lower end of the stator, to remain coupled to an external fluid bearing below the stator , and the mass of the activator is therefore substantially reduced for the same electromagnetic force. In addition, to provide for the coaxial (and therefore concentric) location of the activator and central core, the fluid bearing also provides a reaction force to oppose any lateral loads that are generated by the stator of the linear electrical machine. The provision of a fluid bearing in the central core and within the upper and lower ends of the electrical machine stator reduces the length of the lateral load force transmission path between the stator and the fluid bearing. The transmission of lateral load force by the activator to the bearing positions can result in beam bending between the bearings or cantilever bending to either side of a single bearing. Such bending can result in non-concentric location between activator and central core and, by extension, non-concentric location between activator and stator and is therefore undesirable. Therefore, the assembly of the present invention reduces the requirement for greater activator mass to provide sufficient rigidity to the activator to limit activator bending under the action of lateral loads of the electrical machine stator. Therefore, the present invention can maintain the coaxial (and therefore concentric) relationship between the linear electrical machine stator and actuator with greater electrical machine force per unit of mobile mass than for alternative assemblies.

[0030] At least one of the fluid bearings is preferably mounted on the central core and operates on a bearing surface formed in the inner part of the hollow activator. The fluid bearing is typically a separate component, providing a flow of gas or liquid bearing fluid from a supply and into the bearing gap. The location of the fluid bearing in the fixed central core rather than in the activator prevents the additional mass of this component from contributing to the moving mass of the activator. The bearing shaft surface can be formed into the hollow activator frame and does not require the addition of a separate activator component. Therefore, this assembly allows the incorporation of a fluid bearing function to transmit the lateral loads generated by the electrical machine stator into the central core, while keeping the activator's moving mass to a minimum.

[0031] The at least one fluid bearing preferably defines a coaxial (and therefore concentric) location of the activator and the stator and the outer void space of the intermediate magnetic circuit. Therefore, this assembly allows the incorporation of a low friction fluid bearing function to accurately locate the activator with respect to the central core and the void space of the magnetic circuits, while keeping the activator's moving mass to a minimum.

[0032] A labyrinth-type seal can be used, in which the fluid flow and the pressure difference between the working chamber and the fluid bearing are controlled, by providing a series of annular channels in the activator. A labyrinth type seal is a non-contact seal that is commonly used in piston expander and compressor applications. The application of a labyrinth-type seal in the present invention eliminates the friction that would otherwise be associated with a contact seal, and it also removes the requirement for a separate fluid pressure relief feature between the fluid bearing and the chamber. of work.

[0033] The MEL may also comprise at least one working chamber and/or one preloaded chamber inside the working cylinder for applying a force to the activator. The working chamber and/or the preloaded chamber is preferably coaxial with the stator housing and bearing gap. By virtue of this assembly, the present invention allows for good integration of the working and/or preloaded chambers within the construction of the MEL and helps to reduce the overall size of the machine. The pre-charged chamber contains the fluid delivered at high pressure and which applies a net force to the activator. In the actuator setup, this helps to balance the test subject's weight and/or to ensure the test subject is in the correct position before testing begins. This close integration also eliminates the need for a separate mechanical element to provide a charge path between the working chamber and/or the pre-charged chamber and the activator, so that mobile mass is reduced.

[0034] The use of rigid wall elements for a preloaded chamber also avoids the use of compliant materials, such as those used in an airbag or mechanical spring. This reduces the impact of actuator system resonances that might otherwise affect the actuation function that is applied to the test subject.

[0035] This assembly also provides an actuator or MEL that is compact in size, especially in its width.

[0036] The provision of at least one fluid bearing provides a very low friction interface between the activator and the stator. This assembly offers low friction and mechanical wear, which are typically found in sliding contact bearings, and provides this benefit without the penalty of the reciprocating weight of rolling element bearings. Therefore, this assembly allows a higher frequency operation, due to the low inertia of the system. In addition, fluid bearings can form part of an effective non-contact pressure seal to conserve pressure in any working chamber without the friction associated with contact seals.

[0037] The invention relates to an empty space of the magnetic circuit. For the purpose of the invention, this term refers to a span in which the relative permeability is close to that of air. The gap may or may not contain air or another fluid. This usage is well known in the field of electrical machines.

[0038] One or more bearing shafts can be provided on each or both external and internal surfaces of the activator.

[0039] The preloaded chamber can act like a spring, in which the chamber has a non-zero spring rate, so that the preload force changes with the movement of the activator. In an alternative setup, the chamber can be mounted so that it has a zero spring rate. The pre-filled chamber may be provided with at least one conduit for regulating the pressure within the chamber. This conduit allows the pressure within the preloaded chamber to be regulated at a constant value, thus providing a zero spring rate assembly.

[0040] The electrical machine may be of the movable magnet type, in which the magnets are fixed to the movable activator. The moving magnet type machine offers a higher electrical machine force per unit of moving mass than other types of electrical machines. One embodiment uses a subtype of moving magnet machine commonly known as a slotted machine, in which the flux circuits are made by magnetically permeable materials and the magnetic flux is cut by current flowing in copper coils mounted in slots within this material.

[0041] An alternative subtype of moving magnet machine is commonly known as slotless machine, which offers a higher peak force and lower COGGING force, but with lower efficiency than slotted machine types. Alternative embodiments may use other established linear types of electrical machine, including flux switching machines and switched reluctance machines. These types of machines do not include magnets in the activator, allowing the activator to operate at the higher temperatures associated with Rankine cycle and internal combustion heat recovery applications without the risk of degradation of the magnetic materials and consequent impaired performance of the electrical machine.

[0042] The movement of the moving part of the end wall is preferably coaxial with the stator housing, which helps to minimize the width of the MEL. The empty space of the magnetic circuit is preferably cylindrical.

[0043] For an actuator, the mounting point of the test subject is preferably fixed to the activator, usually at its upper end. An anchor point may be provided instead of, or also as, a test subject mounting point. The anchor point is a location where the external element can be attached, attached or otherwise connected, whereas the test subject mounting point is a type of anchor point provided specifically for the purposes of transmitting the force to a test subject.

[0044] The fluid bearing preferably acts on a fluid bearing shaft on the inner surface of the activator. Alternatively or additionally, the fluid bearing acts on a fluid bearing shaft on the outer surface of the activator.

[0045] The MEL may further comprise an encoder connected to the activator, which typically detects one or more positions or speeds. The encoder can use at least one optical, magnetic or mechanical sensor. The encoder helps with actuator control by determining actuator position and/or speed.

[0046] At least one bearing span may have a plurality of axial channels extending through the arched cross-section arranged around the activator. The bearing span can either be cylindrical or have two or more arched sections.

[0047] The MEL includes a housing body containing one or more cooling channels. These cooling characteristics allow greater power from the electrical machine to be applied to the activator by removing the heat generated by the current flowing in the stator.

[0048] An example of the present invention will now be described with reference to the accompanying drawings, in which:

[0049] Figure 1 is a linear electrical machine (MEL) configured as an actuator showing the planes of section AA;

[0050] Figure 2 is an axial section AA through the midcourse of the MEL of Figure 1;

[0051] Figure 3 is an external view of an alternative MEL, showing the BB and CC section plans;

[0052] Figure 4 is an axial section BB through the MEL of Figure 3, showing a central core and an internal fluid bearing;

[0053] Figure 5 is a cross section BB showing inner and outer fluid bearings;

[0054] Figure 6 is a perpendicular section BB showing the top of the course or 'top dead center' position;

[0055] Figure 7 is a perpendicular section BB showing the bottom point of the stroke or 'bottom dead center center' position;

[0056] Figure 8 is an enlarged view of the perpendicular section AA showing the empty space of the magnetic circuit and the detail of the bearing shaft;

[0057] Figure 9 is a DC axial section showing the void space of the concentric magnetic circuit and the bearing span;

[0058] Figure 10 is an axial section CC showing an alternative assembly of internal fluid bearings;

[0059] Figure 11 is a BB section showing an alternative with central core and inner stator;

[0060] Figure 12 is an axial BB section showing another alternative assembly with an offset asymmetrical preloaded chamber;

[0061] Figure 13 is a perpendicular section BB showing another alternative with central core, inner and outer fluid bearings and activator fluid bearing;

[0062] Figure 14 is an enlarged view of cross-section BB showing in detail an exemplary embodiment of a labyrinth-type seal;

[0063] Figure 15 is an axial BB section showing an alternative assembly, in which the central core passes through the activator; It is

[0064] Figure 16 is an enlarged axial section BB, showing the use of the curved part.

[0065] Figure 1 is an external view of a first MEL operating as an actuator 10, having a movement axis 20 along which an activator moves (shown later) and the locations of various planes of other cross-sectional views.

[0066] Figure 2 shows the actuator 10 having a housing body 11. The housing body 11 is formed by a typically cylindrical wall 12 and end walls 13 defining a hollow interior. The interior has a stator 14, typically a tubular stator of a linear electric machine, which has a cylindrical bore 15 extending axially from one end 16 of the stator to the other end 17. Thus, the housing body and the stator define a cylinder working cylinder 53. A central core 34 is attached at least axially to the stator 14 within the working cylinder and, in this assembly, is attached to an attachment point of the central core 40 to the end wall 13. The upper end of the central core 34 is surrounded by a hollow activator 18, so that the activator slides on and off the central core 34.

[0067] The central core 34 and the stator define an intermediate stator housing cavity 51. The stator housing cavity is a cylindrical annular space within which the activator 18 is axially movable with respect to the stator 14. There is an outer void space of the magnetic circuit 21 (see Figure 9) between the activator and the stator. In this exemplary embodiment, the housing, and therefore the stator, are rigidly fixed and the actuator 18 moves within the stator 14 and over the central core.

[0068] A single elongated inner fluid bearing 35 is mounted in the central core and, in this example, no outer fluid bearing is provided in the housing body 11. The fluid bearing is substantially the same length as the stator 14, so that any lateral loads generated by the electric machine will be combined by an opposing force applied by the fluid bearing in the same axial position.

[0069] In an alternative example, the bearing can be replaced or supplemented by one or more curved parts 52, shown in Figure 16. This is particularly relevant in applications where the activator movement is small, typically less than 2 mm. These applications may include, among others, systems that apply a short motive signal, as in vehicle suspension systems to control the operating dynamics. In particular, given the typically limited height, any system that applies a damping force to a suspension system especially one mounted inside the vehicle. The curved portion may be in the form of a disc spring, a bundle of springs, a diaphragm or other elastic or flexible element between the central core and the actuator, and may or may not have axial holes or gaps. Other examples of curved portions are shown in US Patent 5,522,214. In both examples, the curved portion or fluid bearing retains radial motion of the actuator and provides coaxial location of the actuator within the stator housing cavity.

[0070] The chamber housing 28 defines the preloaded chamber 29. In this example, the chamber housing is inside the housing body and retained by the end wall 13. However, the chamber housing could form the end wall and it does not necessarily have to be inside the housing body 11. An opening 30 in the preloaded chamber is closed by an end 19a of the activator. Thus, the sliding movement of the activator changes the volume of the preloaded chamber. The pre-charged chamber is also provided with at least one conduit 47a through which pressurized fluid can be supplied to provide the necessary force for the activator. Chamber 29 contains a fluid which is typically a gas (although a liquid is also possible) supplied under high pressure and which applies a net force to activator 18 to balance the test subject's weight and/or ensure that the test subject is in the correct position before starting the test. Alternatively or additionally, an equivalent function of the preloaded chamber can be performed by the chamber 50 formed between the upper end of the central core 34 and the activator 18.

[0071] The sliding movement of the activator 18 inside the cylindrical stator hole 15 changes the volume of the preloaded chamber 29 and thus creates the same effect as a piston moving inside a cylinder. The working fluid in the pre-charged chamber 29 is preferably a compressible gas, however this fluid could also be an incompressible liquid, such as a hydraulic fluid which would move through the conduit 47a through the movement of the activator 18. This assembly leads to a better quality of the test subject's input signal as compared to airbag-type preloading systems, in which activator movement and the associated change in gas volume is accommodated by the changing shape of a conforming element, the conformance of which may result in unwanted system behavior, such as resonance or damping.

[0072] In any of the described examples, the preloaded chamber is formed by a side wall 29a, which may or may not be a cylindrical wall, a first end wall 29b typically formed by an inner surface of the end wall 13 or the housing 12 and which is fixed relative to the side wall 29a, the activator 18 and also to the outer surface of the central core 34. Therefore, the chamber 29 is generally annular. The preloaded chamber may not be a fully enclosed volume, and in addition to the conduit 47a other small gaps may exist between the activator 18, the central core 34 and the chamber housing 28. -loaded volume, any gaps are considered as integral parts of the surfaces 29a, 29b and 19a. One or more seals, for example polymeric gas seals, may be provided in this or any of the other examples to prevent significant leakage of pressurized fluid from the precharged chamber through these gaps.

[0073] The volume of the preloaded chamber 29 varies with activator movement. The first end wall 29b could also include a movable element that can vary the volume of the chamber preloaded with the activator. This construction is less due, rather, to the more complex control that would be required. Alternatively, or additionally, another wall element can be fitted to the actuator 18 to act as a movable part of the second end wall. Thus, the activator itself cannot define part of the preloaded chamber, but an additional element movable with the activator can. The preloaded chamber may have a uniform cross section along axis 20.

[0074] The upper end 19b of the actuator 18 extends from the upper end of the actuator 10, and is provided with an anchorage point 33. The anchorage point can be used for a test subject. The anchor point could be a flat plate or other surface onto which a test subject is positioned and held in place by its own weight, for example a vehicle resting on tires, each tire positioned in contact with an actuator. of test. Alternatively, the anchor point could include one or more attachment means for securely retaining the activator on the test subject or part of an external system to which a signal is applied. This can include one or more holes through the end of the activator.

[0075] In the preferred embodiment, an encoder body 32 is located in the central core and allows the encoder scale 31, mounted inside the upper end of the hollow actuator 18, to remain inside the actuator. In this example, the encoder is a position encoder and the encoder scale is a shaft, but the encoder scale could also be a flat surface and the encoder type could also be a speed/velocity encoder. The encoder body 32 is located inside the upper end of the central core 34, but can be located in any suitable place, providing information regarding the position and or speed/velocity of the actuator, to ensure that the actuator can be controlled.

[0076] Figure 3 is an external view of the linear electrical machine (MEL) 60, which could be operated as a generator having an axis of movement 20 along which an activator (shown later) moves and the locations of the BB planes and CC for other cross-sectional views. In subsequent Figures, the same reference numerals are used as in Figures 1 and 2 for equivalent components.

[0077] Figure 4 shows a cross-sectional view of the MEL 60. The MEL 60 is identical to the actuator 10, except for the addition of the working chamber 42 at the upper end, that is, the opposite end of the preloaded chamber 29, removing the test subject mounting point 33 and adding a conduit 47b that allows fluid communication into and out of the working chamber 42. The working chamber could be a combustion chamber of a combustion engine internal chamber, an expansion chamber for expanding a high-pressure gas or two-phase mixture to generate electrical energy, a compression chamber for pressurizing a gas or two-phase mixture using electrical energy, or a hydraulic chamber for receiving and displacing a hydraulic fluid or other liquid. The working chamber can act on activator 18 to generate motion, which then induces an electrical current in the stator coils 14.

[0078] Subsequent Figures all show the MEL 60, but any of the features disclosed there, other than those specific to the working chamber, would generally be applicable to the actuator of Figures 1 and 2. For example, any of the fluid bearing configurations could be used on actuator 10 as easily as on MEL 60.

[0079] A preloaded chamber 29 is provided to apply a controlled force to the activator 18 and, acting to oppose or balance any force that may be applied to the activator by the working fluid in the working chamber. That function of the preloaded chamber 29 is to store energy in the activator that has not been recovered by the electrical machine acting as a generator during the downward stroke of the activator away from its 'top dead center center position' (i.e. that is, the highest extension of its movement inside the working chamber 42). After the activator has reached its position from the center of bottom dead center, the return of its energy to the activator 18, obtained as a result of the preloaded chamber applying a force to the activator during its upward stroke away from the center of dead center bottom, allows the linear electrical machine to continue acting as a generator on the return stroke back toward top dead center center. The pressure of the fluid inside the precharged chamber 29 can be controlled by means of the precharged chamber conduit 47a, which, moreover, can allow the precharged working fluid to be displaced towards and against the direction of flow. pre-charged chamber when the volume of the pre-charged chamber varies with movement of the activator 18. The pre-charged chamber 29 can be filled with the same fluid that is used in the working chamber 42 (e.g., a cycle fluid Rankine in the case of a Rankine cycle gas expander application). Alternatively, the pre-charged chamber 29 can be filled with another fluid selected according to the application requirements, which can be a gas, a liquid or a two-phase mixture. If a gas is used as the precharged chamber fluid, the precharged chamber can act as a return chamber, in which the pressure of the working fluid gas rises when that of the precharged chamber volume decreases, resulting in a preloaded chamber peak force of, or around, a 'bottom dead centre' trigger position shown in Figure 7. This function of the preloaded chamber return chamber serves to reduce the time required to the activator stops and changes direction on the downstroke, thereby increasing the operating frequency and power density of a free piston engine, gas expander, or other device that uses the working chamber and precharged chamber.

[0080] Figure 5 shows an alternative bearing configuration, in which both an inner fluid bearing 35a and an outer fluid bearing 22a are provided. Multiple outer or inner fluid bearings could be provided if required.

[0081] Figures 6 and 7 illustrate the movement of the hollow activator 18 regardless of the fluid bearing configuration, between the top of the stroke or the 'top dead center center' position in Figure 6 to the bottom of the stroke or position from 'bottom dead center center' in Figure 7. At the top of the stroke in Figure 6, the lower end of activator 18 is substantially adjacent to the lower end of stator 14 and, in that position, the volume of precharged chamber 29 is at its maximum, and the volume of the working chamber 42 is at its minimum. In this assembly, and as a result of the inner fluid bearing 35, there is no requirement for an additional length of actuator beyond the lower end of the stator 17 to remain coupled to an outer fluid bearing, as may otherwise be required below the lower end. of the stator 17, and the mass of the activator 18 is thus substantially reduced for the same electromagnetic force. At the lower end of the stroke in Figure 7, the upper end of the activator 18 is just above the level of the upper fluid bearing 22a, although in practice the upper end may protrude more, or even be on a level with the upper end. of the fluid bearing 22a.

[0082] A greater detail of the inner bearing span 37 and the void space of the magnetic circuit 21 is shown in the views of Figures 8 and 9. Figure 8 also illustrates the location of an outer shaft 23 in the activator. This is the surface on which any external fluid bearing 22a acts. Also shown is an inner shaft surface 36, the surface upon which any inner fluid bearing 35 acts. The shaft surfaces are typically machined into the proper locations on the actuator and therefore do not require additional elements to be joined to the actuator for this purpose. purpose, and should typically not be provided unless a matching fluid bearing is used.

[0083] The activator is held in the coaxial position by the fluid bearing 35 which defines the inner gap of the bearing 37 between the outer surface of the fluid bearing 35 and one or more shafts 36 on the inner surface of the activator. If one or more outer fluid bearings 22a are also provided, the bearing gap between the inner surface of any outer fluid bearing 22a and the outer surface of the activator and the void space of the magnetic circuit 21 may be continuous. The relative sizes of any bearing span and any gaps in the magnetic circuit are dependent on the sizes of the activator, stator, and fluid bearings. The bearing gap is typically smaller than the magnetic circuit void space, so the magnetic circuit air gap thickness is more effectively controlled by the high radial stiffness of the fluid bearing.

[0084] Although fluid bearings (whether internal or external) are generally annular elements, having a porous structure, through which a gas or other fluid is supplied under pressure to provide a load-bearing function in the bearing span, any of the bearings 10, in which the fluid bearing is formed by a plurality of fluid bearing shoes 44 spaced around (for outer bearings) or within (for inner bearings) the shaft surface on which the bearing acts . Although two bearing shoes 44 are shown, three or four bearing shoes could be possible, and in fact, a greater number would also be possible, depending on the size of the actuator and the loads that the bearing shoes support. The bearing shoes are preferably equally spaced in order to provide an equal load on the activator and maintain coaxial positioning of the activator with respect to the stator. Fluid bearings could be formed from a generally porous material such as coal. Alternatively, fluid bearing porosity could also be provided by means of a set of discrete holes machined into one or more solid bearing components or bearing shoe components.

[0085] Figure 11 illustrates that the inner fluid bearing (whether with or without outer fluid bearings) could also be formed by two or more fluid bearings. In that example, the inner fluid bearing is replaced by an upper inner fluid bearing 35a and a lower inner fluid bearing 35b, and in addition, an outer fluid bearing 22a is also shown on top of the stator.

[0086] The division of the inner fluid bearing allows the intermediate axial space to be used, in this case, by the inclusion of an inner stator 38 mounted on the central core 34 to provide greater power to the electrical machine per unit of mobile mass of the activator. This significantly increases the dynamic performance of the actuator or MEL device acting in the working chamber. The inner stator 38 could be used in many different assemblies, for example with an upper inner fluid bearing and a lower outer fluid bearing (or vice versa), and not limited to the specific assembly shown in Figure 11.

[0087] Figure 12 shows that the preloaded chamber 29 need not have a uniform shape, nor does the preloaded chamber itself need to be coaxial with the rest of the actuator. The asymmetric displacement of the preloaded chamber 29 could be used in any of the assemblies in the previous Figures, which could result in the preloaded chamber having a non-uniform cross-section and/or a non-cylindrical sidewall.

[0088] Figure 13 shows another alternative configuration in which another internal fluid bearing 25 is provided in the activator 18 itself. The activator bearing 25 is mounted on the activator, being movable with the activator. Another bearing shaft surface 48 is formed on the inner surface of the working chamber 42 and a bearing gap is formed between the shaft surface 48 and the bearing actuator 25.

[0089] Figure 14 illustrates a labyrinth-type seal 46, in which the fluid flow and pressure difference between the working chamber 42 and the fluid bearing 35 is controlled by the provision of a series of annular channels 46a in the activator. A labyrinth type seal is a non-contact seal that is commonly used in piston expander and compressor applications. The use of a labyrinth-type seal in the present invention eliminates the friction that could be associated with a contact seal, and also removes the requirement for a separate vent between the fluid bearing and working chamber.

[0090] Figure 15 shows another variant, in which the central core 34 extends to the activator 18, so that the activator is a hollow tube, not being closed at either end. The central core is attached via attachment points 40 at both ends to the housing to maintain its radial and axial position within the MEL. The activator, in use, will slide up and down the central core. This assembly provides a more secure attachment for the central core in order to reduce the extent of cantilever bending of the central core which might otherwise result in concentricity between activator 19 and stator 14. This assembly allows the chamber to working chamber 42 and preloaded chamber 29 are equivalent in size and cross-sectional area, so that preloaded chamber 29 can alternatively serve as a second working chamber. Furthermore, this assembly reduces the area of the working chamber 42 acting on the piston and is therefore advantageous for high pressure working fluid applications. In these applications, the force that is applied by pressure from the working chamber to the end of the activator may, on the other hand, exceed the ability of the electric linear machine and the preloaded chamber to absorb the work applied by the working chamber during a single stroke. . Any of the previous bearing assemblies could be used in this variant.

Claims (14)

1. LINEAR ELECTRIC MACHINE (MEL) (60), characterized by comprising: a stator (14) mounted in a housing (28), the housing and the stator defining a working cylinder (53); a central core (34) within the working cylinder (53) and defining an intermediate cylindrical stator housing cavity (51); a hollow activator (18) axially movable with respect to the central core (34) inside the working cylinder (53), which extends into the interior of the stator housing cavity (51) and forms an outer void space of the magnetic circuit (21) between the activator (18) and the stator (14); at least one curved portion (52) or bearing between the central core (34) and the activator (18), providing coaxial location of the activator within the cavity of the stator housing (51); wherein the central core (34) is fixed axially with respect to the stator (14), further comprising at least one working chamber (42) inside the working cylinder (53) for applying a force to the activator (18) . 2. MACHINE, according to claim 1, characterized in that the curved part or bearing is a fluid bearing (35). 3. MACHINE, according to claim 2, characterized by the fluid bearing (35) providing the coaxial location of the activator (18) and the central core (34). 4. MACHINE according to claim 2 or 3, characterized in that at least one of the fluid bearings (35) is mounted on the central core (34) and operates on a bearing surface formed in the interior part of the hollow activator. 5. MACHINE according to any one of claims 2 to 4, characterized in that at least one fluid bearing (35) defines the coaxial location of the activator (18) and the stator (14) and the outer void space of the magnetic circuit (21 ) intermediary. 6. MACHINE according to any one of claims 1 to 5, characterized in that the working chamber (42) is coaxial with the stator housing and the bearing space. 7. MACHINE according to any one of claims 1 to 6, characterized in that it further comprises a labyrinth-type seal (46) between the activator (18) and the cylinder inside the working chamber (42). 8. MACHINE according to any one of claims 1 to 7, characterized in that each working chamber (42) is defined by a cylinder wall (12), a first fixed end wall (13) and a second end wall at least part of which is movable with the activator (18). 9. MACHINE according to any one of claims 1 to 8, characterized in that at least one of the working chambers (42) is a combustion chamber. 10. MACHINE according to any one of claims 6 to 9, characterized in that at least one of the working chambers (42) is a preloaded chamber (29). 11. MACHINE according to any one of claims 1 to 10, characterized in that the central core (34) includes one or more stator elements. 12. MACHINE according to claim 11, characterized in that it also comprises an empty space inside the magnetic circuit between the activator (18) and at least one of the stator elements in the central core (34). 13. MACHINE according to any one of claims 1 to 12, characterized in that the fluid bearing (35) is mounted on the activator (18) and operates on a bearing surface on the inner wall of the housing (28). 14. MACHINE according to claim 1, characterized in that the MEL is a moving magnet type machine, a slotless stator type machine, a flux switching type machine or a switched reluctance type machine.