Electric motor

Abstract

To provide a magnetically induced motive force aligned in a movement direction by a greater component.SOLUTION: An electric motor has a stator having multiple stator poles with associated electrical windings, and a rotor having multiple rotor poles. The rotor has flux barriers between adjacent rotor poles, the flux barriers each having a material with an electrical conductivity higher than that of the rotor pole material. The flux barriers are electrically isolated from one another external to the ferromagnetic material. Eddy currents are induced in the flux barrier to cause destructive interference of an impending magnetic field, such that the flux barrier effectively acts to inhibit magnetic flux during motor operation, which in some cases will result in a repulsive force that will act to increase an induced motive force on the rotor poles.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 62 / 715,386, filed Aug. 7, 2018, the entire disclosure of which is incorporated herein by reference.

[0002] Technical Field The present invention relates to electric motors and the operation of such electric motors.

Background Art

[0003] Background Two ways in which the performance of an electric motor can be characterized are by their torque / force and their output. The output of a rotary motor is the product of the torque generated by the motor and the angular velocity of its output shaft. For a linear motor, the output is the product of the linear force and the velocity. Conventionally, there are two basic means for directly increasing motor performance: (1) increasing the size of the motor, and (2) generating a stronger magnetic field within the motor itself. While the ultimate size of the motor limits its particularly useful applications, increasing the magnetic field, and thereby increasing the electromagnetic force, can be important in enabling better motor performance and broader applications of motor technology. There is a need for new motor designs that provide acceptable high performance (e.g., high torque / force and output density) to enable applications with direct drive in a small package.

Summary of the Invention

Means for Solving the Problems

[0004] Summary Various aspects of the present invention feature an electric motor (motor) having a magnetic flux barrier disposed between passive poles to change the path of magnetic flux in order to provide a greater component of magnetically - induced power aligned with the direction of motion (to provide useful torque and / or linear force).

[0005] According to one aspect of the present invention, an electric motor has a stator having a plurality of stator poles and electrical windings associated with the stator poles, and a rotor having a plurality of rotor poles. The rotor is movable relative to the stator and defines a nominal gap between the stator poles and the rotor poles together with the stator. The rotor poles are stacks of layers of ferromagnetic material, at least on the surface of the rotor, separated from each other by an interface having a conductivity smaller than that of the ferromagnetic material. The rotor has a magnetic flux barrier between adjacent rotor poles, and the magnetic flux barriers each have a material having a higher conductivity than the ferromagnetic material. The magnetic flux barriers are electrically insulated from each other outside the ferromagnetic material.

[0006] As used herein, the term "electric motor" also includes a generator that generates electric power from mechanical force.

[0007] "Nominal gap" means the gap between the relative movement surfaces of the stator (or active magnetic component) poles and the rotor (or passive magnetic component) poles, across which magnetic flux extends during motor operation to induce a force on the rotor (or passive magnetic component). The term "active magnetic component" is used to refer to the part of the motor that includes the electrical windings associated with each magnetic permeability structure (magnetic flux is generated by the current flowing in the windings). The poles of the "active magnetic component" are called "active poles". The electrical windings will typically be held in a fixed relationship to the corresponding active poles. The wound stator is an example of an active magnetic component. Across the nominal gap within the passive magnetic component The term "passive magnetic component" is used to refer to the part of the motor in which motive force is induced by the magnetic flux generated by the active magnetic component to extend therein. The poles of the "passive magnetic component" are called "passive poles". The unwound rotor is an example of a passive magnetic component. The nominal gap can be axial, such as in an axial gap motor or a radial gap motor, and can be filled with air or other gas or even a liquid such as a refrigerant.

[0008] "Magnetic flux barrier" means a structure that defines at least one conductive path in which a current flow is induced by changing a magnetic field. Generally, eddy currents are induced within the magnetic flux barrier to cause a mutually canceling interference of the steep magnetic field, whereby the magnetic flux barrier effectively acts to suppress changes in magnetic flux during motor operation that result in a repulsive force that in some cases acts to increase the induced electromotive force on the passive pole.

[0009] "Conductivity" means the tendency of a material to conduct electricity. With respect to a structure such as a wire in which current flow is restricted to a main direction, "conductivity" means the conductivity in the main direction.

[0010] "Electrically insulated from each other" means that the ohmic resistance to the potential within the magnetic flux barrier is at least 10 times lower than the ohmic resistance between the magnetic flux barriers. The magnetic flux barriers being insulated from each other outside of a ferromagnetic object does not exclude the magnetic flux barriers being in a state of electrical communication through a layer of ferromagnetic material. In fact, in many cases, the magnetic flux barriers are electrically connected through a ferromagnetic material.

[0011] In some embodiments, at least some of the magnetic flux barriers each include a conductive band extending across a plurality of interfaces of a stack of layers.

[0012] "Conductivity" means that a material or structure has a conductivity that is at least as conductive as amorphous carbon at typical motor operating voltages or has a conductivity greater than 1000 Siemens / meter. Examples of conductive materials include silver, copper, aluminum, nickel, iron, and electromagnetic steel (either particle-oriented or not). Examples of non-conductive materials include unfilled resin, air, wood, and cotton. The term "insulating material" is used to refer to a material that is non-conductive, i.e., not conductive.

[0013] In some examples, the conductive band comprises, by mass fraction, at least 20%, in some cases 40% or in some cases 60% of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt. In some cases, each of the magnetic flux barriers having a conductive band also has a conductive layer of a material different from the conductive band and at least partially forms the outer surface of the rotor.

[0014] In some configurations, the conductive band comprises, by mass fraction, at least 1%, in some cases 5% or in some cases 15% of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes.

[0015] The conductive band may have or consist of discrete layers that extend parallel to the nominal gap and form an interface of intermediate layers of various materials. In some cases, one of the various materials comprises or consists essentially of copper, and another of the various materials comprises or consists essentially of nickel.

[0016] Often, the conductive band has an exposed surface facing the nominal gap.

[0017] In some motors, each of the magnetic flux barriers having a conductive band comprises at least two conductive bands that are electrically connected to each other at both ends of the stack of layers to form a conductive loop.

[0018] In some embodiments, at least some of the magnetic flux barriers each have a shape that includes two spaced-apart protrusions that extend away from the nominal gap and a surface layer that connects these two protrusions in a cross-section cut parallel to the ferromagnetic material layer of the stack of layers. The two protrusions can be disposed, for example, on both sides of a portion of the stack of ferromagnetic material layers.

[0019] In some embodiments, at least some of the magnetic flux barriers intersect a plurality of interfaces of the stack of layers and have an exposed surface that forms the surface of the rotor in the gap, with a constant width in the direction of relative movement between the rotor and the stator and a constant thickness perpendicular to the nominal gap, each having a conductive layer.

[0020] "Constant width" means that the layer has two edges but does not extend, for example, around the entire outer circumference of the rotor (or along the entire length of a linear passive magnetic component).

[0021] Similarly, "constant thickness" means that the layer extends to a limited depth but does not, for example, completely penetrate the rotor.

[0022] In some cases, the width of the layer is greater than twice the thickness of the layer, in some cases greater than five times, and in some cases greater than ten times.

[0023] In some motors, the layer is formed of a material having a skin depth of current greater than the layer thickness under motor operating conditions.

[0024] "Skin depth of current" means the depth from the surface of a conductor (where eddy currents induced by a changing magnetic field, especially at a given frequency, mainly flow). For a given material, the skin depth can be calculated as follows.

Equation

[0025] "Permeability" usually means the ability of a material to assist in the formation of a magnetic field. The permeability of a material can be determined according to ASTM A772. When a material is said to be "paramagnetic", it means that the material has a permeability of at least 1.3×10 -6 henries per meter.

[0026] In some examples, the layer is disposed within a channel defined by a ferromagnetic material and may be in electrical contact with the ferromagnetic material of a plurality of plates or all of the plates.

[0027] In some cases, the nominal gap is thinner in the layer than in the vicinity of the layer.

[0028] In some embodiments, each magnetic flux barrier includes a conductive material forming a loop centered on a core of a core material having a higher magnetic permeability (i.e., having a higher magnetic permeability) than the conductive material. In some cases, the core material is also ferromagnetic. For example, both the core material and the ferromagnetic material of the rotor pole may form adjacent portions of a stack of plates.

[0029] In some arrangements, the loop forms a part of the outer surface of the rotor bounding the nominal gap. The core may form a part of the outer surface of the rotor surrounded by the loop.

[0030] In some cases, the loop is disposed beneath the surface of the rotor bounding the nominal gap and including the edge of a layer of ferromagnetic material.

[0031] In some motors, the loop defines a capacitance that can be formed at discrete locations along the loop, such as by a non-conductive break within the loop.

[0032] The loop preferably has a resonance frequency within the propagable range of the ferromagnetic material.

[0033] The "propagable range" means a frequency range in which the magnetic permeability decreases by 10 dB or less with respect to the magnetic permeability at 60 hz as measured under static frequency conditions (e.g., by measuring the magnetic permeability of a given frequency over at least 5 cycles of an applied magnetic field).

[0034] In many motors, the interface between the layers of the stack consists of an oxidized surface of a ferromagnetic material. In some other motors, the interface includes a sheet of an insulating material, such as a sheet of resin film interleaved by ferromagnetic layers.

[0035] In many embodiments, the rotor is disposed within the stator. In some other embodiments, the rotor poles are disposed outside the stator poles.

[0036] In some motors, the nominal gap is a radial gap that is at least partially defined by the radially outer surface of the rotor. In some other motors, the nominal gap is an axial gap perpendicular to the axis of rotation of the rotor.

[0037] In some motors, each rotor pole (and / or each stator pole) has a plurality of teeth that define recesses therebetween.

[0038] In some embodiments, each stator pole has a flux shield that extends along both edges of the stator pole and is formed of a material having a higher conductivity than the material of the stator pole disposed between the flux shields.

[0039] According to another aspect of the present invention, a motor includes a passive magnetic component having a first surface defining a plurality of active poles having associated electrical windings, and a second surface movable in a first direction relative to the first surface to define a gap and spaced apart from the first surface. The second surface forms a series of spaced-apart passive poles of a first material that define slots therebetween, the slots extending at a non-zero angle in the first direction. Each slot includes a respective flux barrier of a second material that extends along the slot and forms a conductive path along the slot. The flux barriers are fixed to the first material within the slot and are connected to each other only through the first material.

[0040] In some embodiments, the slots extend perpendicular to the first direction (i.e., the non-zero angle is 90 degrees).

[0041] In some cases, the flux barriers fill the slots.

[0042] In some motors, the flux barriers contact (preferably electrically contact) the first material on both sides of the slot.

[0043] In some configurations, the flux barriers have an exposed surface that forms part of the second face.

[0044] In some motors, the passive poles include the edge surface regions of a stack of plates laminated such that the slots intersect some of the plates of the stack. Preferably, the second material of each flux barrier intersects some of the plates of the stack and / or contacts each of the plates of the stack directly.

[0045] The second material preferably has a higher conductivity than the first material.

[0046] In some examples, each of the flux barriers consists essentially of the second material.

[0047] In some cases, the second material contains at least 20% by mass fraction, in some cases 40% or in some cases 60% of an element or combination of elements selected from the group consisting of iron, nickel and cobalt.

[0048] In some examples, each of the flux barriers includes a conductive layer of the second material and a conductive layer of a third material that at least partially forms the outer surface of the rotor.

[0049] In some embodiments, the second material contains at least 1% by mass fraction, in some cases 5% or in some cases 15% of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene and carbon nanotubes.

[0050] In some configurations, each flux barrier includes a plurality of discrete layers that extend parallel to the nominal gap and form an interface of intermediate layers of various materials. In some examples, one of the various materials contains or is copper, and another of the various materials contains or is nickel.

[0051] In some embodiments, at least some of the magnetic flux barriers each have a cross-sectional shape including two spaced-apart protrusions extending away from a nominal gap and a surface layer connecting the two protrusions. In some cases, the magnetic flux barriers having this cross-sectional shape each further include a ferromagnetic material disposed between the two protrusions and under the surface layer.

[0052] In some cases, the second material of each magnetic flux barrier forms a conductive loop centered on the respective core of a core material having a higher magnetic permeability than the second material. The core material can be ferromagnetic. In some configurations, the core material and the first material form adjacent portions of a single stack of plates.

[0053] In some examples, the loop forms part of the outer surface of the rotor bounding the nominal gap. For example, the core can form part of the outer surface of the rotor surrounded by the loop.

[0054] In some motors, the loop bounds the nominal gap and is disposed under the surface of a passive magnetic component formed of the first material.

[0055] In some motors, the loop defines a capacitance that can be formed at discrete locations along the loop, such as by a non-conductive break in the loop.

[0056] The loop preferably has a resonance frequency within the propagation range of the first material.

[0057] In some embodiments, the active magnetic component is the stator of the motor and the passive magnetic component is the rotor of the motor. In some examples, the nominal gap is a radial gap at least partially delimited by the radially outer surface of the rotor. In some other examples, the nominal gap is an axial gap perpendicular to the axis of rotation of the rotor.

[0058] In some cases, each passive pole and / or each active pole has a plurality of teeth that define recesses therebetween.

[0059] In some cases, each active pole has a flux shielding portion that extends along both edges of the active pole, and the flux shielding portion is formed of a material having a higher conductivity than the material of the stator pole disposed between the flux shielding portions.

[0060] In some examples, the motor is a linear motor.

[0061] According to another aspect of the present invention, an electric motor includes an active magnetic component having a plurality of active poles associated with electric windings, and a movable passive magnetic component that is movable relative to the active magnetic component and has a plurality of passive poles of a ferromagnetic pole material. The active magnetic component and the passive magnetic component define a nominal magnetic gap therebetween between the active poles and the passive poles. The passive magnetic component has a flux barrier that connects adjacent passive poles of the passive magnetic component, and each flux barrier includes a conductive material different from the ferromagnetic pole material and defines at least one conductive path centered on a ferromagnetic core material. The flux barriers are electrically insulated from each other outside the pole material, and adjacent flux barriers are arranged such that each conductive path defined within the conductive material of one flux barrier does not surround a portion of the conductive path defined within the conductive material of the other flux barrier.

[0062] Preferably, the core material has a higher magnetic permeability than the conductive material.

[0063] In some cases, the core material and the pole material have the same material properties.

[0064] In some examples, the flux barrier extends into adjacent pole pairs.

[0065] In some motors, the flux barrier includes at least one loop of conductive material across the magnetically active extent of the passive magnetic component. In some cases, each flux barrier has a plurality of loops of conductive material that are insulated from each other outside the pole material and the core material, respectively.

[0066] In some embodiments, each magnetic flux barrier comprises at least 20% by mass fraction, in some cases 40% or in some cases 60%, of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt.

[0067] In some cases, each magnetic flux barrier comprises at least 1% by mass fraction, in some cases 5% or in some cases 15%, of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes.

[0068] In some examples, the core material is ferromagnetic. In some arrangements, the core material and the pole material include adjacent portions of a single stack of plates.

[0069] The loop forms part of the outer surface of a passive magnetic component that bounds the nominal gap in some motors. The core may form part of the outer surface of the passive magnetic component surrounded by the loop.

[0070] The loop may be disposed under the surface of a passive magnetic component that bounds the nominal gap and is formed of a first material.

[0071] In some cases, the loop has capacitances formed at discrete positions along the loop that define any capacitance.

[0072] Preferably, the loop has a resonance frequency within the propagation range of the first material.

[0073] In some embodiments, at least some of the magnetic flux barriers intersect a plurality of interfaces of the stack and have exposed surfaces that form the surface of the passive magnetic component in the gap, each having a constant width in the direction of relative movement between the passive magnetic component and the active magnetic component and a constant thickness perpendicular to the nominal gap.

[0074] In some applications, the width of the layer is greater than twice the thickness of the layer, in some cases greater than five times, and in some cases greater than ten times.

[0075] In some cases, the layer is formed of a material having a skin depth of current greater than the layer thickness.

[0076] The layer can be disposed within a channel defined by a first material.

[0077] In some cases, the nominal gap is thinner in the layer than in the vicinity of the layer.

[0078] In some motors, the active magnetic component is the stator of the motor and the passive magnetic component is the rotor of the motor. The nominal gap can be a radial gap at least partially delimited by the radially outer surface of the rotor or an axial gap perpendicular to the axis of rotation of the rotor.

[0079] In some embodiments, each passive magnetic component pole and / or each active magnetic component pole has a plurality of teeth that define a recess therebetween.

[0080] In some examples, each active magnetic component has a flux shield that extends along both edges of the pole and is formed of a material having a higher conductivity than the material of the active magnetic component disposed between the flux shields.

[0081] In some cases, the motor is a linear motor.

[0082] According to another aspect of the present invention, the electric motor includes a passive magnetic component having a first surface that defines a plurality of active poles associated with electrical windings, and a second surface that is movable relative to the first surface to define a gap and is spaced apart from the first surface. The second surface has a series of spaced-apart pole surface regions of a first material separated by inter-pole surface regions on the second surface. The passive magnetic component includes a second material that is conductive and has a low energy product, and a permeable material that defines internal paths connecting respective adjacent pairs of pole surface regions on both sides of each inter-pole surface region that are electrically insulated from each other outside the permeable material.

[0083] "Low energy product" means the property of a material having an energy product (B×H) of less than 100 kilojoules per cubic meter. It is also understood that the energy product is the product of the residual magnetism and the coercive force. Generally, the permanent magnet materials used in PM motors do not have a low energy product.

[0084] In some embodiments, the permeable material forms a stack of layers of ferromagnetic material that are separated from each other at least in the pole surface regions by an interface having a lower conductivity than the ferromagnetic material.

[0085] In some examples, the passive magnetic component includes bands of a third material, each band being under a respective inter-pole surface region within the passive magnetic component and extending across the current-suppressing interface. The third material can be, for example, iron, nickel, and cobalt or include them. Preferably, the third material has a higher magnetic permeability than the second material.

[0086] In some configurations, the second material extends between one side of the band and the edge of the layer of ferromagnetic material.

[0087] In some motors, the second material has a lower magnetic permeability than the first material.

[0088] In some embodiments, the second material of at least one of the inter-pole surface regions extends from the second surface into the passive magnetic component to an overall depth of about 1 to 50 mm, in some cases 2 to 25 mm or in some cases 5 to 15 mm.

[0089] In some configurations, the second material of at least one of the inter-pole surface regions has an extent in a first direction and extends from the second surface into the passive magnetic component to an overall depth that is 2 to 2000% (or in some cases 5 to 500% or in some cases 10 to 200%) of that extent.

[0090] In some cases, the second surface is movable relative to the first surface along the first direction, and the inter-pole surface regions are continuous in a second direction perpendicular to the first direction across the magnetically active extent of the pole surface regions.

[0091] In some motors, the ferromagnetic material forms a stack of layers of ferromagnetic material each extending in a first direction.

[0092] In some cases, the second material comprises or consists essentially of copper.

[0093] In some motors, the passive magnetic component is the rotor and the active magnetic component is the stator. The inter-pole surface regions and the pole surface regions may together form the cylindrical surface of the rotor, for example, the gap being the radial gap between the rotor and the stator. Or the inter-pole surface regions and the pole surface regions may together form the end face of the rotor, the gap being the axial gap between the rotor and the stator. In some cases, the end face is perpendicular to the axis of rotation of the rotor.

[0094] In some embodiments, the inter-pole surface regions each further include a ferromagnetic core material surrounded by the second material. In some cases, the core material is the same material as the first material.

[0095] In some examples, the pole surface region of the second face defines a slot therebetween, and the inter-pole surface region of the second face is formed by a second material disposed within the slot. Preferably, the slot extends at a non-zero angle (such as 90 degrees) with respect to the direction of relative movement between the first face and the second face. In some cases, the second material is fixed to the first material within the slot. In some examples, the slot is filled with the second material and / or the second material contacts the first material on both sides of the slot.

[0096] In some examples, the pole surface region includes an edge surface region of a stack of plates laminated such that the slots intersect some of the plates of the stack of plates. Preferably, the second material within each slot intersects some of the plates of the stack and / or directly contacts each of the plates of the stack.

[0097] The second material preferably has a higher conductivity than the first material.

[0098] In some motors, each of the inter-pole surface regions consists essentially of the second material.

[0099] The second material includes, in mass fraction, in some examples 20%, in some cases 40% or in some cases 60% of an element or combination of elements selected from the group consisting of iron, nickel and cobalt.

[0100] In some examples, the second material includes, in mass fraction, at least 1%, in some cases 5% or in some cases 15% of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene and carbon nanotubes.

[0101] In some embodiments, the inter-pole surface region includes the surface of a magnetic flux barrier disposed between the pole surface regions.

[0102] In some cases, each magnetic flux barrier has a discrete layer that extends parallel to the nominal gap and forms an interface of intermediate layers of various materials such as copper and nickel.

[0103] In some examples, at least some of the magnetic flux barriers each have a cross-sectional shape that includes two spaced-apart protrusions that extend away from the nominal gap and a surface layer that connects these two protrusions. For example, a ferromagnetic material is disposed between the two protrusions and under the surface layer.

[0104] In some configurations, the second material of each pole-to-pole surface region forms a conductive loop centered on the respective core of a core material having a higher magnetic permeability than the second material. In some cases, the core material is ferromagnetic. In some cases, the core material and the first material are adjacent parts of a single stack of plates. In some examples, the core forms part of a second face surrounded by the loop. The loop can be spaced apart from the second face and / or can define a capacitance. For example, the capacitance is formed at discrete positions along the loop. Preferably, the loop has a resonant frequency within the propagation range of the first material.

[0105] In some motors, each pole surface region (and / or each pole of the active magnetic component) has a plurality of teeth that define recesses therebetween.

[0106] In some examples, each pole of the active magnetic component has a magnetic flux shield that extends along both edges of the pole and is formed of a material having a higher conductivity than the material of the pole of the active magnetic component disposed between the magnetic flux shields.

[0107] In some cases, the motor is a linear motor.

[0108] According to another aspect of the present invention, an electric drive system includes a reluctance motor and a motor controller. The reluctance motor includes an active magnetic component defining a plurality of active poles associated with electric windings, and a passive magnetic component having a plurality of passive poles, being movable relative to the active magnetic component, and defining a nominal gap between the active poles and the passive poles together with the active magnetic component. The motor controller has a plurality of switches connected to respective electric windings or sets of windings of the active magnetic component, and is configured to (a) sequentially operate the switches for respective pole energization duty cycles to generate magnetic flux across the nominal gap between the active poles and the passive poles, and (b) pulse the current passing through the windings of the active poles during the energization duty cycle of each active pole, the pulsing including at least a series of three pulses during which the windings of adjacent active poles are not energized. The electric windings of the motor are configured such that the ratio of the maximum current to the minimum current passing through the energized windings of the active poles during current pulsing is at least 4:1.

[0109] In some embodiments, the motor controller is configured to pulse the current at a pulse frequency of 2 Hz to 1 MHz, in some cases 10 Hz to 20 kHz, and in some cases 100 Hz to 5 kHz during the energization duty cycle of each active pole.

[0110] In some examples, the motor controller is configured to maintain the pulse frequency at least up to a motor speed at which the energization duty cycle frequency for each active pole is at least one half of the pulse frequency during motor speed change.

[0111] For some applications, the motor controller is configured to pulse the current only at motor speeds below that corresponding to one pulse per energization duty cycle.

[0112] In some cases, at least one of the electric windings has a plurality of coils conductively connected in parallel and wound around a common core.

[0113] In some cases, at least one of the electrical windings is a winding of braided wire.

[0114] In some embodiments, the active magnetic component is the stator, and the passive magnetic component is a rotor that is movable relative to the stator by rotation about the rotor axis. The rotor can be disposed within the stator. The nominal gap can be, for example, a radial gap at least partially delimited by the radially outer surface of the rotor or an axial gap perpendicular to the rotor axis.

[0115] In some examples, the passive magnetic component further includes a magnetic flux barrier having a higher conductivity than the passive poles respectively between adjacent passive poles. The magnetic flux barriers are electrically insulated from each other outside the passive poles.

[0116] In some cases, the passive poles are formed by a stack of layers of a ferromagnetic material. At least some of the magnetic flux barriers can each include a conductive band that intersects a plurality of layers of the stack. The conductive band contains, in some cases at least 20%, in some cases 40% or in some cases 60% by mass fraction an element or combination of elements selected from the group consisting of iron, nickel and cobalt. Each of the magnetic flux barriers having a conductive band can further include a conductive layer of a material different from the conductive band and forming at least partially the outer surface of the passive magnetic component. In some examples, the conductive band contains, in some cases at least 1%, in some cases 5% or in some cases 15% by mass fraction an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene and carbon nanotubes. In some configurations, the conductive band has a discrete layer that extends parallel to the nominal gap and forms an interface of an intermediate layer of various materials (such as copper and nickel).

[0117] The conductive band can have an exposed surface facing the nominal gap.

[0118] In some cases, each of the magnetic flux barriers having a conductive band includes at least two conductive bands that are electrically connected to each other at both ends of the stack of layers to form a conductive loop.

[0119] In some embodiments, at least some of the magnetic flux barriers each have a shape that includes two spaced-apart protrusions extending away from a nominal gap and a surface layer connecting the two protrusions in a cross-section cut parallel to the layers of the stack. The two protrusions can be disposed on both sides of a portion of the stack.

[0120] In some configurations, at least some of the magnetic flux barriers intersect a plurality of layers of the stack and have an exposed surface that forms the surface of the passive magnetic component in the gap, and have a conductive layer with a constant width in the direction of relative movement between the passive magnetic component and the active magnetic component and a constant thickness perpendicular to the nominal gap, respectively. In some applications, the width of the layer is greater than twice the thickness of the layer, in some cases greater than five times, and in some cases greater than ten times.

[0121] The layer can be formed of a material having a current skin depth greater than the layer thickness and / or can be disposed within a channel defined by a permeable material. In some cases, the nominal gap is thinner in the layer than in the vicinity of the layer.

[0122] In some embodiments, each magnetic flux barrier includes a conductive material that forms a loop centered on a core of a core material that has a higher permeability than the conductive material. The core material can be ferromagnetic and / or the permeable materials of the core material and the passive pole can be adjacent portions of a laminated stack of plates.

[0123] In some cases, the loop forms a part of the outer surface of the passive magnetic component that bounds the nominal gap.

[0124] In some cases, the core forms a part of the outer surface of the passive magnetic component surrounded by the loop.

[0125] The loop can be disposed under the surface of the passive magnetic component that bounds the nominal gap and includes the edge of the layer of the stack.

[0126] In some examples, the loop defines a capacitance, such as a capacitance formed at discrete positions along the loop. Preferably, the loop has a resonance frequency within the propagation range of the ferromagnetic material of the passive pole.

[0127] In some embodiments, the passive magnetic component further includes a magnetic flux barrier connecting adjacent passive poles of the ferromagnetic pole material, the magnetic flux barrier having a conductive material different from the pole material respectively and defining at least one conductive path centered on the ferromagnetic core material. Preferably, the magnetic flux barriers are electrically insulated from each other outside the pole material, and adjacent magnetic flux barriers are arranged so as not to surround any part of any conductive path defined within the conductive material of one magnetic flux barrier by any conductive path defined within the conductive material of another magnetic flux barrier.

[0128] In some cases, each passive pole and / or each active pole has a plurality of teeth defining a recess therebetween.

[0129] In some examples, each active magnetic component has a magnetic flux shielding portion extending along both edges of the active pole, the magnetic flux shielding portion being formed of a material having a higher conductivity than the material of the active magnetic component disposed between the magnetic flux shielding portions.

[0130] In some applications, the ratio of the maximum current to the minimum current is at least 7:1. In some examples, the ratio of the maximum current to the minimum current is at least 10:1.

[0131] Another aspect of the present invention features a method of driving an electric motor. The method includes (a) energizing a first active pole of a series of active poles arranged along a gap between a series of active poles and a passive magnetic component having a series of passive poles arranged along the gap by pulsing a current through an electrical winding associated with the first active pole, the pulsing including a series of at least three pulses in which the windings of adjacent active poles of the series of active poles are not energized; (b) Pulsing the current through the electrical winding associated with the second active electrode of a series of active electrodes, wherein the pulsing includes at least three series of pulses during which the winding of the first active electrode is not energized, and passing a current through the electrical winding associated with the second active electrode according to a current waveform in which the ratio of the maximum current to the minimum current during the pulsing of the current through the electrical winding associated with the second active electrode is at least 4:1. And including.

[0132] In some examples, energizing the first active electrode includes pulsing the current at a pulse frequency of 2 Hz to 1 MHz, in some cases 10 Hz to 20 kHz, and in some cases 100 Hz to 5 kHz.

[0133] In some cases, energizing the first active electrode and then the second active electrode includes generating a first force between the first active electrode and the passive electrode across the air gap from the first active electrode and a second force between the second active electrode and the passive electrode across the air gap from the second active electrode.

[0134] In some examples, the first and second forces induce relative movement between the active electrode and the passive electrode. The relative movement can include movement of the passive magnetic component relative to the active electrode.

[0135] In some cases, the passive magnetic component is the rotor of a motor and the relative movement includes rotational movement of the rotor.

[0136] Some examples of the method include detecting the rotor speed and controlling the frequency of the pulsed current in response to the detected rotor speed.

[0137] Some examples also include maintaining the current pulse frequency at least up to a rotor speed at which the frequency at which each active electrode is energized is at least one-half of the pulse frequency during rotor speed change.

[0138] In some cases, the current is pulsed through the electrical windings associated with the first and second poles only at a rotor speed below that corresponding to one pulse per pole energization.

[0139] In some examples, the method includes energizing by pulsing a current passing through the electrical winding associated with a third active pole, which is disposed on the opposite side of the second active pole from the first active pole, after energizing the second active pole, the pulsing including a series of at least three pulses in which the windings of the first and second active poles are not energized.

[0140] In some embodiments, the method further includes re-energizing the first active pole by pulsing a current passing through the electrical winding associated with the first active pole after energizing the third active pole, and then re-energizing the second active pole by pulsing a current passing through the electrical winding associated with the second active pole, and then re-energizing the third active pole.

[0141] In some examples, pulsing a current passing through the electrical winding associated with the first active pole involves passing a current through the electrical winding associated with the first active pole according to a current waveform in which the ratio of the maximum current to the minimum current during the pulsing of the current passing through the electrical winding associated with the first active pole is at least 4:1 or in some cases at least 7:1.

[0142] In some examples, pulsing a current passing through the electrical winding associated with the first active pole involves pulsing a current passing through a plurality of coils that are conductively connected in parallel and wound around a common core. including pulsing.

[0143] In some cases, pulsing a current passing through the electrical winding associated with the first active pole involves operating a first switch to open and close between a voltage source and the electrical winding associated with the first active pole over a plurality of cycles.

[0144] In some embodiments, pulsing the current through the electrical winding associated with the first active pole generates eddy currents within a first magnetic flux barrier adjacent to the passive pole across the air gap from the first active pole, the magnetic flux barrier having a higher conductivity than the passive pole across the air gap.

[0145] In some examples, the passive magnetic component further includes a second magnetic flux barrier, the passive pole extending across the air gap from the first active pole being disposed between the first magnetic flux barrier and the second magnetic flux barrier, and the first magnetic flux barrier and the second magnetic flux barrier being electrically insulated from each other outside the passive pole.

[0146] In some cases, the passive pole is formed by a stack of layers of a permeable material.

[0147] In some examples, the eddy currents within the first magnetic flux barrier serve to deflect magnetic flux away from the first active pole.

[0148] In some configurations, the first magnetic flux barrier is disposed between the passive pole extending across the air gap from the first active pole and an adjacent passive pole, the magnetic flux barrier forming a loop of conductive material centered on a core of a core material having a higher permeability than the conductive material.

[0149] In some embodiments, the passive magnetic component further includes magnetic flux barriers between adjacent pairs of passive poles of a series of passive poles, the magnetic flux barriers each including a conductive material different from the material forming the passive poles and defining at least one conductive path centered on a permeable core material.

[0150] In some cases, the magnetic flux barriers are electrically insulated from each other outside the series of passive poles.

[0151] Adjacent magnetic flux barriers are preferably arranged such that no conductive path defined within the conductive material of one magnetic flux barrier encloses any portion of any conductive path defined within the conductive material of another magnetic flux barrier.

[0152] In some examples, the motor has flux shields that extend along both edges of each active pole and are formed of a material having a higher conductivity than the material of the active magnetic components disposed between the flux shields. In some cases, the flux shields extend into the gap between adjacent electrical windings. For example, the flux shields can extend from the air gap to the ferromagnetic yoke connecting adjacent active poles.

[0153] In some cases, the ratio of the maximum current to the minimum current is at least 7:1 or at least 10:1.

[0154] Some aspects of the present invention feature a flux barrier for improving the performance of an electric motor (e.g., increasing torque and output density). The flux barrier has a dynamic (or transient) diamagnetic property. By utilizing the flux barrier in the motor, a significant gain in torque can be achieved by directing the magnetic flux substantially tangentially. Here, the magnetic field is altered by redirecting the radial force (or normal force) along the tangential direction. That is, the average force vector during operation is substantially tangential. Here, the dominant force vector in conventional motor designs is inherently radial.

[0155] The permeability of the flux barrier can be controlled by adjusting the magnetic frequency of the eddy currents in the flux barrier (e.g., by pulsing the current through the electrical windings of the active poles). In this way, the electric motor can have significantly different magnetic properties at various magnetic frequencies. At low frequencies, the properties of the flux barrier are ferromagnetic, and from intermediate to high operating frequencies, the permeability of the flux barrier can be less than that of air, and the properties of the flux barrier are diamagnetic.

[0156] The present invention can also generate a high-reactance circuit in which the magnetic field is not spread through the electromagnetic cycle but is substantially reflected. This can reduce or eliminate magnetic flux fringing. Different from the conventional permanent magnet (PM) motor, almost zero magnetic flux spreads into the magnetic flux barrier in the motor designed according to the present invention, and demagnetization (coercive force) and overheating during operation can be avoided. Furthermore, the diamagnetic magnetic flux barrier does not generate a magnetic field during operation, and thus there is no magnetic field at all (not a magnetic field that exists in the reverse direction and then closes), so it behaves differently from a PM motor.

[0157] The present invention can be applied to various types of motors to improve their performance. The motor can be a radial-gap motor, or an axial-gap motor, or a linear motor. For example, the motor can be a switched reluctance motor (SRM), an induction motor (IM) or a permanent magnet motor (PM).

[0158] Various examples of the present invention disclosed herein can provide particularly high motor performance with significant torque / force and output density, and can be used not only in a stationary system but also to provide an essentially smooth and efficient output shaft power for propelling a vehicle. These design concepts can increase torque and output more efficiently by increasing the salient pole ratio of the motor itself, and avoid some of the conventional trade-offs that sacrifice one for the other. This motor can also achieve higher system efficiency during cycle operation for avoiding magnetic breakage that can occur with a permanent magnet motor under passive conditions.

[0159] Details of one or more embodiments of the present invention will be described in the accompanying drawings and in the following specification. Other features, objects, and advantages of the present invention will become apparent from the specification, the accompanying drawings, and the claims.

Brief Description of the Drawings

[0160] Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0161] Like reference numerals in the various figures indicate like elements.

[0162] Detailed Description Embodiments of the present disclosure provide systems, devices, and methods that use magnetic flux barriers to increase the performance of an electric motor. Various designs / configurations of the motor's magnetic flux barriers are presented and discussed. The magnetic flux barrier is configured to exhibit diamagnetic properties at the operating frequency such that magnetic flux passing through the magnetic gap between the active magnetic component (e.g., stator) and the passive magnetic component (e.g., rotor) is concentrated and redirected substantially tangentially, thereby increasing torque.

[0163] Exemplary Electric Drive System FIG. 1 shows an electric drive system 100 that includes an electric motor 102 and a motor controller 104 coupled to the electric motor 102. The motor controller 104 is configured to operate the electric motor 102 to drive a load 110. The load 110 can be a planetary gear set or another gear train such as an additional motor where multiple motors can be linked and operated in parallel.

[0164] The electric motor 102 has an output shaft 107 that is rotatable relative to the motor housing 105 (which is considered a reference for the rotation and other movements of the motor components). In use, the output shaft 107 can be coupled to a load 110 that can receive rotational power when the motor 102 is electrically activated by appropriate power and signals from the motor controller 104. The output shaft 107 can pass through the motor and be exposed at both ends. This means that rotational power can be transmitted at both ends of the motor. The housing 105 can be rotationally symmetric about the axis of rotation of the output shaft, but can have any outer shape and typically includes means for fixing the housing to other structures to prevent housing rotation during motor operation.

[0165] The electric motor 102 includes an active magnetic component 106 such as a stator and a passive magnetic component 108 such as a rotor. For illustrative purposes, hereinafter, the stator is used as a representative example of the active magnetic component and the rotor is used as a representative example of the passive magnetic component.

[0166] The rotor 108 is associated with the stator 106 and can be arranged within the stator 106, for example, in an interior rotor radial gap motor or parallel to the stator, for example, in an axial gap motor. As will be described in more detail below, the electrically active activity within the properly controlled stator 106 drives the movement of the rotor 108. The rotor 108 is rotatably coupled to the output shaft 107 such that any rotational component of the resulting rotor movement is transmitted to the output shaft 107, rotating the output shaft 107. The stator 106 is fixed to the motor 102 such that the rotor 108 moves about or parallel to the stator 106 during operation.

[0167] The stator 106 defines a plurality of stator poles having associated electrical windings, as shown in further detail in FIG. 4, and the rotor 108 includes a plurality of rotor poles. As shown in further detail in FIG. 5 below, the rotor 108 defines a nominal air gap with the stator 106 between the stator poles and the rotor poles. The rotor 108 is movable relative to the stator 106 along the direction of movement. As shown in FIG. 2, the stator 106 has a plurality of independently activatable windings 132 circumferentially spaced about the rotor 108. A plurality of adjacent windings 132 of the stator 106 can be activated simultaneously as a winding set, and the stator 106 can include a plurality of such multiple winding sets spaced about the stator 106. The motor 102 can also include a winding controller 130 having a set of switches 134 operable to activate the windings 132 of the stator 106. The switches 134 can be semiconductor switches (e.g., transistors such as metal oxide semiconductor field effect transistors (MOSFETs)). The winding controller 130 is coupled to the gates of the switches 134 and is operable to send respective control voltages to each switch 134. The control voltage can be a direct current (DC) voltage. The winding controller 130 can be present within the motor controller 104.

[0168] Although only three switches are shown in FIG. 2, it will be understood that the motor controller 104 may have switches for each stator pole or multiple switches for energizing a plurality of coils. Adjacent pole pairs may be wire-connected in series via a common switch. In such a case, the momentary high speed of the two moving rotors generates a slightly larger back electromotive force (EMF), i.e., a reverse EMF, compared to the slower poles, and instantaneously extracts a larger relative power, thereby providing additional acceleration and separation of relative speeds. Higher frequency excitation may reduce the influence of the low frequency harmonic ripple during operation. The switch 134 may be wire-connected in parallel to balance the relative speeds between the plurality of rotors in a nested configuration by using a parallel inductive load reactor. In some embodiments having a nested rotor configuration, the individual rotors within the system may be driven individually, and any harmonic frequency may be bypassed from one rotor to another by reducing the load on a given rotor. In some other embodiments, the rotors may be nested in pairs to provide a local balance of forces between the inner ring and the outer ring.

[0169] FIG. 2A shows another exemplary power switch 200 for an individual electrical winding 132. The power switch 200 may have an H-bridge circuit including four switching elements 202a, 202b, 202c, 202d with the electrical winding 132 centered in an H-shaped configuration. The switching elements 202a, 202b, 202c, 202d may be bipolar or FET transistors. Each switching element 202a, 202b, 202c, 202d may be coupled with its respective diode D1, D2, D3, D4. The diodes are called catch diodes and may be of the Schottky type. The upper end of the bridge is connected to a power source (e.g., battery Vbat), and the lower end is grounded. The gates of the switching elements may be coupled to a winding controller 130 operable to transmit respective control voltage signals to each switching element. The control voltage signal may be a DC voltage signal or an AC (alternating current) voltage signal.

[0170] The switching elements may be individually controlled by the controller 130 and may be turned on / off independently. In some cases, when switching elements 202a, 202d are turned on, the left lead of the stator is connected to a power source and the right lead is connected to ground. Current begins to flow through the stator, energizing the electrical winding 132 in a forward direction. In some cases, when switching elements 202b, 202c are turned on, the right lead of the stator is connected to a power source and the left lead is connected to ground. Current begins to flow through the stator, energizing the electrical winding 132 in a reverse direction. That is, by controlling the switching elements, the electrical winding 132 may be energized / activated in either of two directions.

[0171] The motor controller 104 (e.g., winding controller 130) may be configured to sequentially operate the switches 134 or 200 for each pole energization duty cycle to generate magnetic flux across the air gap between the stator poles and the rotor poles, as described in further detail in Figures 8A-8C. The switches may be controlled to sequentially energize the stator poles to generate a local attractive force that pulls on the rotor. Such sequential energization (or activation) may cause the rotor 108, output shaft 107, and load 110 to rotate.

[0172] As discussed in further detail below, various types and configurations of flux barriers may be implemented within the rotor 108 and / or stator 106. Flux barriers typically have diamagnetic properties greater than air during operation.

[0173] In some examples, the flux barriers are made of aluminum, copper, brass, silver, zinc, gold, pyrolytic graphite, It is made of a single material such as fight, bismuth, graphene, or carbon nanotubes. In some examples, ferromagnetic composite materials such as copper-iron, nickel-iron, lead-iron, brass-iron, silver-iron, zinc-iron, gold-iron, bismuth-iron, aluminum-iron, pyrolytic graphite-iron, graphene-iron, carbon nanotube-iron, or Alinco (aluminum-nickel-cobalt) alloy can be used as magnetic flux barriers and often have a higher conductivity than the ferromagnetic material (e.g., iron) that makes up the rotor poles. In some cases, the magnetic flux barrier (e.g., made of copper-iron) has a lower effective magnetic permeability than the ferromagnetic material. In some cases, the magnetic flux barrier (e.g., made of nickel-iron) has a higher effective magnetic permeability than the ferromagnetic material. In some examples, the magnetic flux barrier is constructed as a shielding pole of a conductive material that forms a loop centered on the core of a core material with a higher magnetic permeability than the conductive material. Due to the conductive material of the loop, the shielding pole can also have a higher effective conductivity than the core material (which can be, for example, iron).

[0174] Another material property of interest (referred to as the EMF shielding factor) is the quotient of conductivity and magnetic permeability (e.g., Siemens / Henry). The EMF shielding factors of two materials can be determined simultaneously by placing these equal-dimension samples on a non-conductive support such that the main plane of conduction of these equal-dimension samples (e.g., the orientation of the plane as experienced during operation in a magnetic system) is perpendicular to the magnetic field generated during the excitation of the Helmholtz coils, and then moving these samples between two parallel Helmholtz coils having a larger diameter than these samples. For a given excitation waveform (e.g., voltage, shape, frequency), the current in the Helmholtz coils will be proportional to the EMF shielding factor of the material between the coils such that an increase in the EMF shielding factor is observed as an increase in the current during a constant excitation.

[0175] As noted above and discussed in further detail below, the flux barriers are configured to be diamagnetic. The permeability of the flux barriers can be controlled by adjusting the magnetic frequency through the flux barriers. In this way, the motor can have significantly different magnetic properties at various magnetic frequencies. At low frequencies, the flux barriers can have a permeability at or near that of a ferromagnetic material, and at mid to high operating frequencies, the permeability of the flux barriers is preferably less than that of air and the properties of the flux barriers are diamagnetic.

[0176] As shown in further detail in Figures 9A-9C, the implementation of diamagnetic materials or structures within the rotor and / or stator may provide a means of improving the concentrated magnetic flux during operation of the motor. Specifically, when the stator and rotor poles are placed in a completely misaligned state, significant internal electromagnetic reflections (due to the diamagnetic properties of the flux barrier) significantly inhibit magnetic transmission through the flux barrier. The flux shielding can be significantly greater when the flux barrier is replaced with air slots between adjacent poles, as in some conventional motors. This diamagnetic shielding effectively causes the flux barrier to push the rotor while the reluctance of the electromagnetic poles pulls the rotor. This effect allows more energy to be produced from the motor system per cycle.

[0177] To operate the diamagnetic flux barrier at the operating frequency, as shown in FIG. 3, during the pole energization (magnetic pole energization) duty cycle of each active pole, the motor controller 104 is configured to pulse the current passing through the winding of the pole at a certain pulse frequency. Different from an induction motor that pulses each pole once in sequence at a low speed, the motor controller 104 pulse drives the current of a single pole multiple times at a low speed. Such multiple pulses to the same pole before pulse driving the subsequent pole constitute one energization duty cycle. In some examples, the motor controller pulses the current passing through the winding of the active pole during the energization duty cycle of the pole that includes a series of at least three pulses. During this series, the windings of adjacent active poles are not energized. The electrical circuit including the electrical winding of each pole is configured such that the ratio of the maximum current to the minimum current passing through the energized winding of the pole during current pulsing is at least 4:1, in some cases at least 7:1 or in some cases even 10:1. The minimum current passing through the winding between pulses can be as low as about zero. can be as low as about zero.

[0178] The pulsed current causes an alternating magnetic intensity (e.g., magnetic field) that induces eddy currents within the diamagnetic flux barrier. For a given flux barrier material, the higher the pulse frequency, the greater the eddy currents. The induced eddy currents generate a secondary magnetic field that opposes the applied alternating magnetic field, thereby generating a repulsive force. As shown in more detail in FIGS. 9A - 9C and FIG. 10, the repulsive force can concentrate and redirect approximately tangentially along the direction of relative motion between the rotor and the stator of the magnetic flux, thus increasing the force available to do work. Also, flux barriers having various materials or designs can have various diamagnetic properties. The higher the diamagnetic property of the flux barrier, the greater the eddy currents induced at a given magnetic (pulse) frequency. Therefore, the generated horizontal force is dependent on the magnetic frequency and the structure of the flux barrier, as will be discussed in more detail below with reference to FIG. 20.

[0179] The magnetic frequency (and the generated horizontal force) of the diamagnetic magnetic flux barrier is determined by the pulse frequency of the current passing through the windings of the poles during the energization duty cycle of each active pole. The pulse frequency is, for example, 2 Hz to 1 MHz in some cases, 10 Hz to 20 kHz in some cases, and 100 Hz to 5 kHz in some cases. In some cases, the motor controller is configured to maintain the pulse frequency at least up to a motor speed at which the energization duty cycle frequency for each active pole is at least one half of the pulse frequency during motor speed change. In some cases, the motor controller is configured to pulse the current only below a motor speed corresponding to one pulse per energization duty cycle. In some implementations, at least one of the electrical windings includes a plurality of coils that are conductively connected in parallel and wound around a common core. Such an electrical winding may have a low reactance that allows for a faster decay of the current between pulses.

[0180] Exemplary motor FIG. 4 shows an exemplary motor 400 including a stator 410 and a rotor 420. The motor 400, the stator 410, and the rotor 420 can be the electric motor 102, the stator 106, and the rotor 108 of FIG. 1, respectively. The motor 400 is a radial-gap motor such as a switched reluctance motor (SRM), and the rotor 420 is disposed within the stator 410. FIG. 5 is an enlarged view of a portion of FIG. 4.

[0181] The stator 410 features a series of circumferentially spaced stator poles 412, each including a stator core 414 and an associated electrical winding 416 surrounding the stator core 414. The stator 410 may have a plurality of stator protrusions that project, for example, from a stator back plate 402 (such as a yoke or back iron), thereby creating stator slots 418 and the stator core 414. Slots 418 exist between adjacent stator poles 412. The stator core 414 can be of one continuous piece or a combination of individual parts assembled within the motor. The continuous piece provides greater dimensional consistency with zero air tolerated within the stator assembly, while a series of discrete stator poles maintained in a mechanically aligned state by the stator housing may enable efficient manufacturing and assembly. The terminal ends of the stator protrusions are distributed, linear, or subordinate with respect to the stator protrusions and the back iron or yoke. In this example, the stator protrusions are linear, as shown in FIG. 5, and are stator protrusions of constant cross-section from the yoke to their distal ends in the air gap 430 defined between the stator 410 and the rotor 420.

[0182] The stator poles 412 enable electromagnetic transfer between the power electronics components and the stator core 414 and have electrical insulation between the pole windings. The electrical winding 416 can include conductive coils of wire such as insulated or enameled magnet wire or multiple welded conductive bands such as insulated copper tape. The electrical winding 416 can include windings of braided wire such as Litz wire. Litz wire can be used for high-frequency operation, and other configurations such as rectangular or flat wire can be used to increase the winding density and the skin effect. Each electrical winding 416 can include a plurality of coils that are conductively connected in parallel and wound around a common stator core 414.

[0183] The rotor 420 also has a series of circumferentially spaced rotor poles 422 that define slots 423 therebetween. The rotor 420 has a surface 402 that is movable relative to the surface 401 of the stator 410 in the direction of motion. The slots 423 extend at an angle other than zero (e.g., 90 degrees) relative to the direction of motion. The surface 402 of the rotor 420 is spaced from the surface 401 of the stator 410 to define an air gap 430 between the stator pole 412 and the rotor pole 422. It should be noted that the air gap 430 can be filled with a fluid other than air.

[0184] The air gap 430 can be maintained consistently during operation. In the motors described below, the stator pole 412 and the rotor pole 422 should maintain a non-zero air gap to prevent catastrophic damage resulting from contact of the rotor pole 422 with the stator pole 412. As shown in FIG. 5, the air gap 430 has a depth Dg perpendicular to the direction of motion. The depth Dg can be in the range of 0.05 to 2.0 millimeters (e.g., for motors having an output of less than 250 kilowatts (kW)). The rotor pole 422 can have a width W1 along the direction of motion, and the rotor slot 423 can have a width W2 along the direction of motion and a depth Ds perpendicular to the direction of motion. As will be discussed in more detail below, the dimensions of the air gap 430 can affect the horizontal force generated. In some examples, the slot 423 has a preferred depth Ds that is 50 to 500 times the depth (Dg) of the air gap 430 and a preferred width W2 at the surface 402 that is 25 to 100 times the depth Dg of the air gap 430. As will be discussed in more detail below, a flux barrier that can change the magnetic flux flow between the stator 410 and the rotor 420 and can modify the performance of the motor 400 can be disposed within the slot 423 between the rotor poles 422 and / or within the slot 418 between the stator poles 412. In this example, the flux barrier fills the slot. The dimensions of the air gap 430 and the slot 423 can affect the performance of the motor 400.

[0185] FIG. 6 is a perspective view of an exemplary stator core 600 made of a stack of ferromagnetic material laminations 601. The rotor core 600 can be used for the rotor 420 of FIG. 4. The laminations 601 are separated from each other at least at the surface of the rotor 600 by an interface 603 that has a lower conductivity than the ferromagnetic material. Thus, the interface is current suppressing compared to the ferromagnetic material of the laminations. In some cases, the interface 603 consists of an oxidized surface of the ferromagnetic material. For example, the ferromagnetic material can be iron (Fe), and the interface can be made of iron oxide (FeOX). In some cases, the interface 603 includes a sheet of insulator material that is alternately arranged with the ferromagnetic layers 601. For example, the sheet of insulator material can include a sheet of resin film.

[0186] The lamination 601 defines a rotor body 606 that has an axial hole 605 into which an output shaft (e.g., the output shaft 107 of FIG. 1) can be inserted and that can be movable with the rotor core 600. The lamination 601 also defines a series of spaced rotor poles 602 that project radially from the rotor body 606 and extend axially parallel to the axial hole 605. The projecting rotor poles 602 define slots 604 that extend axially parallel to the axial hole 605.

[0187] Exemplary flux barrier Various designs / configurations of flux barriers for electric motors including SRMs, axial-gap motors, and linear motors are presented and discussed below.

[0188] Exemplary flux barrier having a conductive band FIG. 7 shows an exemplary rotor 700 in which a flux barrier fills the slot between adjacent rotor poles. The rotor 700 can include the rotor core 600 of FIG. 6, and the rotor poles 702 can be the rotor poles 602 of FIG. 6. The rotor poles 702 can be of a stack of layers of ferromagnetic material separated from each other by an interface that has a lower conductivity than the ferromagnetic material.

[0189] Adjacent rotor poles 702 define slots (e.g., slot 604 in FIG. 6). The rotor 700 includes flux barriers 704 between adjacent rotor poles 702 and within the slots of adjacent rotor poles 702. The flux barriers 704 each have a conductivity higher than that of the ferromagnetic material. The flux barriers 704 are electrically insulated from each other outside the ferromagnetic material of the rotor 700, but may be electrically connected to each other through the rotor material.

[0190] As shown in FIG. 7, the flux barrier 704 may be in the form of a conductive band that extends along the axial direction of the rotor 700 (e.g., parallel to the axial hole 605 in FIG. 6) and intersects a plurality of interfaces of the stack of layers. In some examples, the conductive band is formed of a single material such as aluminum, copper, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, or carbon nanotubes. In some examples, the conductive band is a composite material such as copper-iron, nickel-iron, lead-iron, brass-iron, silver-iron, zinc-iron, gold-iron, bismuth-iron, aluminum-iron, pyrolytic graphite-iron, graphene-iron, carbon nanotube-iron, or an Alinco (aluminum-nickel-cobalt) alloy so that the conductive band (e.g., copper-iron) may have a conductivity higher than that of the ferromagnetic material of the rotor core. In some cases, the conductive band contains at least 1% by mass fraction, in some cases 5%, and in some cases 15% of an element selected from the group consisting of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, and carbon nanotubes. In some cases, the conductive band contains at least 20% by mass fraction, in some cases 40%, and in some cases 60% of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt. The rotor 700 may be fabricated by directly casting one or more materials of the flux barrier 704 into the slots such that the slots between the rotor poles 702 are filled with the flux barrier.

[0191] The rotor 700 having the flux barriers 704 within the slots between the rotor poles 702 can be used as the rotor 420 of FIG. 4 in a motor (e.g., the motor 400 of FIG. 4). The rotor 700, together with a stator (e.g., the stator 410 of FIG. 4), defines a nominal gap (e.g., the gap 630 of FIG. 6) between the stator poles and the rotor poles. The conductive band has an exposed surface facing the nominal gap. In many cases, the exposed surface of the conductive band forms a cylindrical surface together with the surface of the rotor poles.

[0192] Effect of the Flux Barrier FIGS. 8A - C and FIGS. 9A - C show the effect of the flux barriers on the magnetic flux between the stator poles and the rotor poles and passing through the nominal gap. FIGS. 8A - C show the magnetic flux without flux barriers (e.g., air filling the slots) between the rotor poles at the full non - alignment position (FIG. 8A), the 1 / 2 alignment position (FIG. 8B), and the full alignment position (FIG. 8C).

[0193] When the stator pole 802 (e.g., the stator pole 412 of FIG. 4) is energized, a magnetic field is generated and magnetic flux flows between the stator pole 802 and the rotor pole 804 (e.g., the rotor pole 422 of FIG. 4 or the rotor pole 602 of FIG. 6). The rotor pole 804 is movable relative to the stator pole 802 in a direction of motion parallel to the nominal gap 805 defined between the rotor pole 804 and the stator pole 802.

[0194] At the full non - alignment position, as shown in FIG. 8A, the magnetic flux 810 flows at an angle with respect to the direction of motion. A part of the magnetic flux 810 flows through the slot 803 adjacent to the stator pole 802 and filled with air and reaches the rotor pole 804, and a part of the magnetic flux 810 flows through the slot 806 adjacent to the rotor pole 804 and filled with air and reaches the rotor pole 804. At the 1 / 2 alignment position, as shown in FIG. 8B, the magnetic flux 820 has more parts passing through the nominal gap 805 and fewer parts passing through the stator slot 803 and the rotor slot 806. The angle between the magnetic flux 820 and the direction of motion becomes larger. At the alignment position, FIG. 8 As shown in C, the magnetic flux 830 flows through the rotor pole 804 in a substantially radial direction through the nominal gap 805. The angle between the magnetic flux 830 and the direction of motion is approximately 90 degrees.

[0195] Figures 9A - C show the same three relative rotor - stator positions, but the magnetic flux barriers fill the slots between adjacent rotor poles 904, and the rotor poles are in the fully non - aligned position (Figure 9A), the 1 / 2 - aligned position (Figure 9B), and the fully aligned position (Figure 9C). When the stator poles 902 are energized, a magnetic field is generated and the magnetic flux flows from the stator poles 902 to the rotor poles 904, and the rotor poles 904 and the stator poles 902 define the nominal gap 905.

[0196] In the non - aligned position, as shown in Figure 9A, the magnetic flux 910 flows at an angle with respect to the direction of motion. A part of the magnetic flux 910 flows through the slot 903 adjacent to the stator pole 902 to the rotor pole 904, and a part of the magnetic flux 910 flows through the magnetic flux barrier 906 filled in the slot adjacent to the rotor pole 904 to the rotor pole 904. However, compared with the magnetic flux 810 in Figure 8A, a part of the magnetic flux through the magnetic flux barrier 906 is greatly suppressed and deflected so that it extends more along the nominal gap 905 so that the magnetic flux 810 is concentrated and redirected more tangentially along the direction of motion. Similarly, in the 1 / 2 - aligned position, as shown in Figure 9B, the magnetic flux 920 is more concentrated compared with the magnetic flux 820 in Figure 8B, and in particular, a part of the magnetic flux through the magnetic flux barrier 906 is greatly suppressed and repelled. In the aligned position, as shown in Figure 9C, the magnetic flux 930 is similar to the magnetic flux 830 and flows through the rotor pole 904 substantially through the nominal gap 905.

[0197] At the operating magnetic frequency, the magnetic flux barrier exhibits diamagnetic properties to repel magnetic flux, thereby generating a repulsive force against the rotor poles. When the stator and rotor poles are arranged in a non-aligned state, significant internal electromagnetic reflection in the magnetic flux barrier changes the net direction of the magnetic flux between the poles. The shielding diamagnetic in the slot filled by the magnetic flux barrier effectively pushes the rotor in the desired direction of motion, while the magnetic attraction between the stator pole and the rotor pole pulls the rotor in the same direction. In this way, by using such a diamagnetic barrier, the vector of the magnetic field lines can be modified during the operation of the motor so that the radial force is approximately directed along the direction of motion. This increases the proportion of the magnetic induction force that serves to propel the rotor relative to the stator. This effect generates more useful kinetic energy per cycle from a given input energy from an electric drive system (e.g., the electric drive system 100 of FIG. 1). For example, when the rotor poles travel from a fully non-aligned position relative to the stator poles to a fully aligned position, the difference in the associated energy of the slots with magnetic flux barriers is much greater than the difference in the associated energy of slots without magnetic flux barriers such as air, and this can also well avoid the fringing magnetic field. In other words, the effective salient pole ratio is increased.

[0198] FIG. 10 shows the net magnetic induction forces with and without a magnetic flux barrier between adjacent poles. When the stator poles 1012 of the stator 1010 (e.g., the stator poles 412 of FIG. 4) are energized, a magnetic field is generated and magnetic flux flows from the stator poles 1012 to the rotor poles 1022 of the rotor 1020 (e.g., the rotor poles 422 of FIG. 4 or the rotor poles 602 of FIG. 6). The rotor 1020 is movable in the direction of motion relative to the stator 1010 and defines a nominal gap 1015 together with the stator 1010.

[0199] When only air exists in the slot 1024 between adjacent rotor poles 1022, the attractive force between the stator pole 1012 and the rotor pole 1022 causes a net instantaneous attractive force F0 at an angle θ0 with respect to the direction of motion. When a magnetic flux barrier 906 exists in the slot 1024 between adjacent rotor poles 1022 and / or in the slot 1014 between adjacent stator poles 1012, the attractive force between the stator pole 1012 and the rotor pole 1022 causes a net attractive force F1 at an angle θ1 with respect to the direction of motion. As discussed above with reference to FIGS. 9A and 9B, the magnetic flux barrier may exhibit diamagnetic properties to repel magnetic flux and effectively generate a repulsive force against the stator pole. As a result, the net attractive force F1 is redirected to have a larger component along the direction of motion. That is, F1cosθ1 > F0cosθ2, where F1 may be approximately the same as F0. When the rotor pole 1022 is in the fully non-aligned position, as shown in FIG. 9A, the angle is minimum and the horizontal force is maximum. When the rotor pole 1022 is in the 1 / 2 aligned position, as shown in FIG. 9B, there is a maximum change in reluctance and a maximum torque can be obtained.

[0200] Exemplary magnetic flux barrier having a conductive layer on a band FIG. 11 is a perspective view of another rotor 1100 having flux barriers 1104 in slots between adjacent rotor poles 1102. Similar to the rotor 700 of FIG. 7, the rotor poles 1102 are made of a stack of layers of ferromagnetic material separated from each other by interfaces that are less conductive than the ferromagnetic material. The interfaces can be current suppressing. Each flux barrier 1104 includes a conductive band 1108 that intersects a plurality of the interfaces and is electrically insulated from each other outside the ferromagnetic material. Different from the flux barrier 704 of the rotor 700 of FIG. 7, the flux barrier 1104 of the rotor 1100 additionally includes a conductive layer 1106 that covers the band 1108. The conductive layer 1106 is made of a material different from that of the conductive band 1108 and can have a higher conductivity than the conductive band 1108. In some examples, the band 1108 is made of iron, nickel, or cobalt, and the conductive layer 1106 is made of copper, aluminum, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, or carbon nanotubes. The rotor 1100 can be fabricated by casting the material of the conductive band 1108 into the slots of the rotor poles 1102 and depositing the conductive layer 1106 over the conductive band 1108 by plating or sputtering, etc.

[0201] The outer surface of the rotor 1100 and the outer surface of the stator 1120 define a nominal gap 1130 as shown in FIG. 12. The rotor 1100 is movable in the direction of motion with respect to the stator 1120. The conductive layer 1106 at least partially forms the outer surface of the rotor 1100. During operation, when the stator poles 1122 of the stator 1120 are energized by a pulsed current of a duty cycle as shown, for example, in FIG. 3, an alternating magnetic field is generated and a corresponding magnetic flux 1202 flows from the stator poles 1122 through the nominal gap 1130 to the rotor poles 1102. The pulsed magnetic field induces eddy currents 1204 in the conductive layer 1106 of the flux barrier 1104. The eddy currents 1204 can generate a secondary magnetic field that opposes the applied alternating magnetic field, as discussed above, thereby generating a repulsive force to change the net direction of the magnetic flux 1202.

[0202] The conductive layer 1106 has a constant width W in the direction of movement and a constant thickness T from the outer surface of the rotor 1100 along a direction perpendicular to the direction of movement (or the nominal gap 1130), and intersects a plurality of interfaces of the stack of layers. The width W of the layer 1106 is preferably greater than twice the thickness T of the layer 1106, in some cases greater than five times, and in some cases greater than ten times. The conductive strip 1108 can be of a thickness greater than that of the layer 1106.

[0203] In some examples, the thickness T of the layer 1106 is greater than the current skin depth of the material of the layer 1106 at a specific operating frequency such that the eddy current 1204 mainly flows in the skin of the layer 1106 between the outer surface and the skin depth and propagates over a long distance in the layer 1106 along the direction of movement in the direction of the adjacent rotor pole 1102. In this way, the magnetic flux 1202 can be more concentrated within the layer 1106 and redirected more tangentially to cause a greater horizontal force along the direction of movement.

[0204] Exemplary flux barriers having pairs of alternating layers FIG. 13 is a perspective view of another rotor 1300 having a flux barrier 1304 in the slot between adjacent rotor poles 1302. Similar to the rotor 1100 of FIG. 11, the rotor poles 1302 can be made of a stack of layers of ferromagnetic material separated from each other by interfaces having a lower conductivity than the ferromagnetic material. The flux barriers 1304 are electrically insulated from each other outside the ferromagnetic material of the rotor 1300. Different from the flux barriers 1104 of the rotor 1100 of FIG. 11, each flux barrier 1304 of the rotor 1300 is made of a plurality of pairs of alternating layers 1306, 1308 disposed in the slot between adjacent rotor poles 1302. The discrete layers 1306, 1308 extend parallel to the nominal gap and form intermediate layer interfaces of various materials. In a specific example, the layer 1306 is made of copper and the layer 1308 is made of nickel. The layer 1306 can have a higher conductivity than the layer 1308, and the layer 1308 can have a higher magnetic permeability than the layer 1306. The rotor 1300 can be fabricated by alternately depositing the layers 1306, 1308 in the slots between the rotor poles 1302.

[0205] As shown in FIG. 13A, each layer 1306 has a constant thickness T1 in a direction perpendicular to the nominal gap, and each layer 1308 has a constant thickness T2 in a direction perpendicular to the nominal gap. In some examples, the thickness T1 of layer 1306 is configured to be less than the current skin depth of the material of layer 1306 at a particular operating frequency, and the thickness T2 of layer 1308 is configured to be less than the current skin depth of the material of layer 1308 at a particular operating frequency. In this way, as shown in FIG. 13A, the magnetic flux 1310 flowing from the stator to the rotor 1300 can propagate through the plurality of layers 1306, 1308, generating eddy currents 1312 and thus a secondary magnetic field within the plurality of layers 1306, 1308.

[0206] Exemplary flux barrier with a shaded pole FIG. 14 is a perspective view of another rotor 1400 having a flux barrier 1404 in a slot between adjacent rotor poles 1402. Similar to the rotor 1100 of FIG. 11, the rotor poles 1402 are made of a laminated stack of layers of ferromagnetic material separated from each other by an interface having a lower conductivity than the ferromagnetic material. The interface can be current-suppressing. The flux barriers 1404 are electrically insulated from each other outside the ferromagnetic material. Different from the flux barrier 1104 of the rotor 1100 of FIG. 11 having a conductive layer on the band, the flux barrier 1404 of the rotor 1400 has a layer 1406 of conductive material surrounding a core 1408 of a core material within a slot between adjacent rotor poles 1402. The core material of the core 1408 can have a higher magnetic permeability than the conductive material of the layer 1406. The core 1408 can be of the same material as the rotor poles.

[0207] The layer 1406 includes three layer portions 1406a, 1406b, 1406c. The layer portion 1406a covers the inter-pole surface region between adjacent rotor poles 1402 and forms a portion of the outer surface of the rotor 1400. Each core 1408 is below the respective inter-pole surface region. The inter-pole surface region can be continuous in a direction perpendicular to the direction of motion across the fully magnetically active spread of the pole surface region of the rotor 1400. The layer portions 1406b, 1406c extend from the layer portion 1406a across the interface of the layer stack and between the adjacent rotor poles 1402 and the core 1408 of the flux barrier.

[0208] Similar to layer 1106 of FIG. 11, each of the layer portions 1406a, 1406b, 1406c may have a thickness greater than the current skin depth of the conductive material of layer 1406 such that the magnetic flux passing through layer portion 1406a is redirected more tangentially towards the adjacent rotor pole 1402 and the layer portions 1406b, 1406c serve to suppress or shield the magnetic flux between the pole and the core 1408. Layer portion 1406a has a constant width extending in the direction of motion. Layer portions 1406b, 1406c extend into the ferromagnetic material from the outer surface of the rotor 1400 to the full depth. The full depth is, for example, about 1 - 50 mm, in some cases about 2 - 25 mm, in some cases about 5 - 15 mm and 2 - 2000% of the width of layer portion 1406a, in some cases 5 - 500%, in some cases 10 - 200%.

[0209] The conductive material of layer 1406 may include copper. In some embodiments, the core material of core 1408 and the ferromagnetic material of rotor pole 1402 have the same material properties (e.g., made of iron). Core 1408 and rotor pole 1402 may be adjacent portions of a laminated stack of layers.

[0210] In some cases, the rotor 1400 may be fabricated by depositing a core material into the slots between adjacent poles of the rotor (e.g., rotor 600 of FIG. 6) to form a core 1408 having a gap between the pole 1402 and the adjacent core 1408, and then depositing a conductive material into the gap and within the top of the core 1408 to form layer 1406. In some cases, layers of shaped ferromagnetic material are aligned and laminated to form slots for receiving the conductive material, and then the conductive material is cast or otherwise deposited within the gap and over the top surface region to form the conductive layer 1406.

[0211] The magnetic flux barrier 1404 can be considered as a shading pole. Each shading pole can have the same dimensions as the rotor pole. Under low frequency or DC static conditions, there is little difference between the rotor pole and the shading pole, but under medium and high frequency operations, the magnetic resistance of the shading pole exceeds that of air, resulting in a higher torque density. Thus, by forming a shading pole between adjacent rotor poles, the vector of the magnetic field lines during the operation of the magnetic resistance poles (stator poles and rotor poles) can be uniquely modified such that the magnetic field is almost tangential. This enables the motor to utilize a radial force (or normal force or radial pressure) that can be an order of magnitude larger than the tangential force as the tangential force. The shading pole can also be extended to adjacent stator pole sets to further reduce the magnetic flux fringing characteristics of the motor.

[0212] FIG. 15 is a perspective view of another rotor 1500 having another example of a shading pole as a magnetic flux barrier 1504 between adjacent rotor poles 1502. Each magnetic flux barrier 1504 is made of a conductive loop 1506 centered on a permeable core 1508 between adjacent poles 1502. The loop 1506 can be a stack of thin layers of conductive material (e.g., a layer of copper separated by copper oxide, enamel, aluminum, or aluminum oxide), which are materials of similar permeability but less conductive. Similar to the rotor 1400 of FIG. 14, the rotor poles 1502 can be made of a laminated stack of layers of ferromagnetic material separated from each other by an interface with lower conductivity than the ferromagnetic material. The magnetic flux barrier 1504 forms an inter-pole surface region between the pole surface regions of the rotor poles 1502 and can thus be considered as a surface shading pole. The inter-pole surface region and the pole surface region define the outer surface (or end face) of the rotor 1500. Each core 1508 forms a part of the outer surface surrounded by the respective loop 1506. Each loop 1506 forms a part of the cylindrical outer surface of the rotor 1500 as shown in FIG. 15A.

[0213] Loop 1506 can be made of a conductive low-energy product. For example, loop 1506 can be made of copper. The material of core 1508 has a higher magnetic permeability than the material of loop 1506. The core material can be a ferromagnetic material (e.g., iron). The core material of core 1508 and the ferromagnetic material of rotor pole 1502 can be the same, such as at the adjacent part of the stack of layers. In some embodiments, rotor 1500 is formed by etching the region of the ferromagnetic material of the stack of layers according to the shape and position of loop 1506, and then depositing / casting a conductive material into the etched region to form loop 1506. Alternatively, the magnetic flux barrier can be formed of a conductive low-energy product disposed within core 1508 itself.

[0214] The conductive loops 1506 of magnetic flux barrier 1504 do not overlap and are electrically insulated from each other outside the ferromagnetic material. Magnetic flux barrier 1504 is connected to each other only through the ferromagnetic material. Magnetic flux barrier 1504 defines at least one conductive path (e.g., loop 1506) centered on the core material of core 1508. "Do not overlap" means that adjacent magnetic flux barriers 1504 are arranged so that any conductive path defined within the conductive material of one magnetic flux barrier does not enclose any portion of the conductive path defined within the conductive material of another magnetic flux barrier 1504.

[0215] As shown in FIG. 15, the loops 1506 of magnetic flux barrier 1504 can form a closed circuit made of a conductive material (e.g., copper). In some embodiments, the magnetic flux barrier can be formed as a shielding pole by an open loop of a conductive material. For example, FIG. 16 is a schematic diagram of another rotor 1600 having a magnetic flux barrier 1604 between adjacent rotor poles 1602. Magnetic flux barrier 1604 is similar to magnetic flux barrier 1504 of FIG. 15, except that magnetic flux barrier 1604 has an open loop 1606 having a break 1608 (e.g., a gap) as shown in FIG. 16.

[0216] The open loop 1606 can also be made of a conductive material (e.g., copper). The open loop 1606 defines capacitances that can be formed at discrete positions along the open loop 1606. For example, two opposing end faces of the open loop 1606 form a gap 1608, forming a capacitor. The open loop 1606 can be configured to have a resonance frequency within the propagation range of the ferromagnetic material (e.g., iron) of the rotor poles 1602 of the rotor 1600. In some embodiments, the rotor 1600 is formed by etching a region of ferromagnetic material according to the shape and position of the open loop 1606 and depositing / casting a conductive material within the etched region to obtain the loop 1606. The gap 1608 can be formed during the deposition of the conductive material and can be created by peeling or otherwise removing an elongated material to form each gap. Each capacitance gap 1608 preferably extends across at least one layer interface of the stack.

[0217] Exemplary flux barrier having a surface layer FIG. 17 is a perspective view of another rotor 1700 having a flux barrier 1704 between adjacent rotor poles 1702. Each flux barrier 1704 includes a conductive layer 1706 that forms an inter-pole surface region between adjacent poles 1702. Similar to the rotor 1500 of FIG. 15, the rotor poles 1702 can be made of a stack of layers of ferromagnetic material separated from each other by an interface having a lower conductivity than the ferromagnetic material. However, unlike the flux barrier 1504 of FIG. 15 having a conductive loop 1506, the conductive layer 1706 completely covers the inter-pole surface region and forms part of the outer surface of the rotor 1700. The conductive layer 1706 intersects almost all of the magnetically active plates of the stack and preferably contacts each of the plates of the stack directly.

[0218] The conductive layer 1706 can be formed under the outer surface, for example, by etching the ferromagnetic material of the stack of layers to form the inter-pole region and casting a conductive material into the inter-pole region.

[0219] FIG. 18 is a perspective view of another rotor 1800 having flux barriers 1804 between adjacent rotor poles 1802. Unlike the flux barriers 1704 of FIG. 17 having a conductive layer formed under the outer surface of the rotor 1700, each flux barrier 1804 includes a conductive layer 1806 formed on the cylindrical outer surface of the rotor 1800.

[0220] As shown in FIG. 19, the conductive layer 1806 has a thickness extending from the outer surface toward the nominal gap 1910 defined by the stator 1900 and the poles 1802 of the rotor 1800. The stator 1900 has an outer surface defining a plurality of stator poles 1902 having associated electrical windings 1904. Since the conductive layer 1806 is formed on the cylindrical outer surface of the rotor 1800, it is within the nominal gap 1910, making the clearance between the rotor and the stator lower at the conductive layer 1806 than in the vicinity of the layer 1806.

[0221] Effect of Flux Barrier Material / Configuration on Force FIG. 20 shows the forces generated by motors having various flux barriers (e.g., various materials / configurations) under a certain range of frequencies. Here, the force refers to the effective force parallel to the direction of motion in which the rotor is movable relative to the stator. The frequency refers to the magnetic frequency of the eddy currents induced in the flux barrier that can be controlled by the pulse frequency of the current energizing the stator poles of the stator.

[0222] Curve 2002 represents air as a passive material filling the slots between adjacent rotor poles, where the effective force remains constant over low frequencies and ultimately rapidly decays at high frequencies (e.g., beyond the core limit at point 2001). Curve 2004 behaves approximately as air at low frequencies but represents a single filling material (e.g., copper) as an increasing dynamic non-ferromagnetic flux barrier beyond the crossover frequency (at intersection 2005). Curve 2006 represents a shaded pole (e.g., a loop pole) as a dynamic ferromagnetic flux barrier, where at lower frequencies (e.g., below the crossover frequency), the effective force is lower than that due to air, while the effective force increases more rapidly and dramatically with frequency (e.g., beyond the crossover frequency) than that due to the straight non-ferromagnetic material (e.g., copper) filler represented by curve 2004. Along curve 2006, point 2003 indicates the magnetic resistance lower force limit of the conductive slot, point 2005 indicates the crossover frequency, and point 2007 indicates the airgap limited peak force.

[0223] To avoid the reduction of force at low speeds, the motor can be operated at a high magnetic frequency, for example, by pulsing the current through each pole winding at a low revolutions per minute (RPM), thereby increasing the output force. The reason the force of the shaded pole is lower than that of air at low frequencies can be largely attributed to the existence of alternating ferromagnetic flux paths that result in relative magnetic resistance asymmetry. At high frequencies, the motor is dominated by the relative inductive shading that occurs at the crossover frequency. This is the point 2005 where the salient pole ratio of the shaded pole is equal to that of air (effectively, the skin depth of the shaded pole is very similar to that of air). As the frequency increases, the salient pole ratio of the shaded pole continues to increase.

[0224] Curve 2012 represents a non-ferromagnetic superconductor as a straight fill material magnetic flux barrier, where a force gain greater than air is induced even at relatively low frequencies. In some cases, the magnetic flux barrier can be configured so that curves 2006 and / or intersection 2005 can be moved as far to the left as possible by adjusting, for example, the material ratio (e.g., the ratio of the conductive material of the loop to the ferromagnetic material of the core), the material itself, the layering of the material (e.g., a single material or a combination of materials), the orientation or geometry of the material layer with respect to the magnetic interface (e.g., depth, width, and relative proximity to the void). For example, even if the shielding pole of curve 2006 is made of a 10:90 ratio of copper and a rotor core, curve 2006 can become curve 2008 with a shielding pole made of a 66:33 ratio of copper and a rotor core.

[0225] In addition, the structure of the magnetic flux barrier can also affect the performance of the motor. When the magnetic flux barrier is made of pairs of alternating conductive layers and ferromagnetic layers (e.g., copper and nickel) (e.g., magnetic flux barrier 1304 in FIG. 13), the relationship between the generated force and frequency can be represented by curve 2010 closer to curve 2012 of the superconductor.

[0226] Exemplary magnetic flux barrier inside the rotor Figures 21 - 23 show another rotor 2100 having a magnetic flux barrier 2104 with a conductive element below the surface of a ferromagnetic rotor material. As shown in FIG. 22, the rotor body 2102 is made of a stack of laminations of ferromagnetic material. These laminations are separated from each other at least at the surface of the rotor by an interface that is less conductive than the ferromagnetic material. The interface can be current suppressing. The stack extends along its length and defines holes 2107 that intersect the interface.

[0227] As shown in FIG. 23, each magnetic flux barrier penetrates each layer of the stack to intersect each interface of the stack, and includes a conductive structure having at least two conductive bands 2110 (four are shown) that are electrically connected to each other at both ends of the stack by a conductive plate 2108 to form at least one conductive loop within the rotor. Each conductive band is inserted or cast into a corresponding longitudinal hole 2107 within the stack of rotor plates and can then be welded or soldered to the plate 2108. Referring back to FIG. 21, each conductive structure forms a magnetic flux barrier 2104 between two adjacent rotor poles 2106, together with the portion of the ferromagnetic plate that is between and directly surrounds the conductive bands.

[0228] FIGS. 24-26A show another rotor 2400 having a magnetic flux barrier 2410 with conductive elements within the ferromagnetic material of the rotor. Similar to the rotor 600 of FIG. 6, the rotor body 2402 can be made of a stack of laminations of ferromagnetic material. These laminations are separated from each other at least at the surface of the rotor by interfaces that have a lower conductivity than the ferromagnetic material. The interfaces can be current-suppressing. The rotor 2400 defines a central hole 2401 in the rotor body 2402. The hole 2401 can be similar to the hole 605 of FIG. 6, into which an output shaft (e.g., the output shaft 107 of FIG. 1) can be inserted and can be movable with the rotor 2400.

[0229] As shown in FIG. 25, the rotor body 2402 defines a series of spaced-apart rotor poles 2404 that form the outermost radial extent of the rotor body, and adjacent poles 2404 define slots 2406 therebetween. The rotor body 2402 also defines holes 2408 that extend parallel along its length.

[0230] Instead of filling the slots 2406 between adjacent rotor poles 2402, each of the flux barriers 2410 includes a conductive element that forms at least one loop across the magnetically active extent of the rotor body 2402 below the rotor surface. As shown in FIG. 26, the conductive structure of each flux barrier 2410 includes a plurality of loops 2412, 2414, 2416 of conductive material that are insulated from each other outside the ferromagnetic material of the rotor body 2402. As shown in FIG. 26A, each loop (e.g., loop 2416) includes at least two conductive bands 2418 that are electrically connected to each other at both ends of the stack by a conductive plate 2420. When assembled, each of the conductive bands extends along a corresponding hole 2408 in the rotor body, as shown in FIG. 25. The plate 2420 may have a curved shape with ends above the magnetically active extent of adjacent rotor poles 2404. The curved shape may be based on the shape of the slots 2406. Referring back to FIG. 24, the loops 2412, 2414, 2416 of the flux barriers 2410 may be arranged in series toward the slots 2406. In a sense, the conductive loop structure of each flux barrier extends into or across adjacent portions of adjacent rotor poles.

[0231] The flux barriers 2410 are electrically insulated from each other outside the ferromagnetic material. Adjacent flux barriers 2410 are preferably arranged such that no conductive path defined within the conductive material of one flux barrier encloses any portion of any conductive path defined within the conductive material of another flux barrier. The flux barriers 2410 may function as flux shields.

[0232] During operation, a transient electromagnetic field attempting to penetrate the ferromagnetic material surrounded by bands 2418, 2420 (and the outer band) can cause current to flow within these electric bands, and the resulting current can serve to effectively prevent the magnetic flux from penetrating the enclosed region. Next, the magnetic flux follows the narrow channels between segments 2416, 2414, 2412, resulting in a low magnetic resistance path with high magnetic resistance paths on both sides. The region surrounded by the magnetic flux barrier 2410 has magnetic propagation blocked, resulting in distinct low and high magnetic resistance paths. The force acts not in the air gap between the stator poles and the rotor poles, but rather in the shaded / unshaded regions within the rotor (such as those shown in FIG. 15). The interface between the enclosed core region and the unenclosed region can be considered a pseudo-core interface.

[0233] Exemplary magnetic flux barrier of a pole having a plurality of discrete teeth The toothed stator-rotor interface of a motor can be generated to maximize torque according to the surface area at the stator-rotor interface. Conventional motors are typically limited by their torque according to surface area due to relatively weak magnetic field interactions. A plurality of discrete teeth are included on each pole, and by effectively reducing the tooth pitch distance of the motor for the same pole, the number of cycles during which the pole can be energized for a given travel distance is increased. Specifically, by placing a plurality of teeth on a single pole, the force according to surface area can be increased.

[0234] Despite achieving a higher specified force for a given surface area, the higher output density in such designs can be limited due to significant leakage magnetic flux. One of the main sources of this leakage magnetic flux originates from the air in the slots that is generated between the teeth and gradually becomes smaller as the number of teeth increases. Therefore, in order to increase motor performance using a motor with multiple tooth poles, the increased specified force generated by increasing the number of teeth can be utilized at lower current loads. Under this approach, the motor maintains a relatively small number of total poles in the system, but the surface geometry on individual poles enables it to provide an increased number of switching cycles by allowing for more electrical cycles per pole arc. Specifically, a given specified force can be generated in a pole with a magnetomotive force (MMF) of 400 - 700 ampere - turns, while a typical pole would require an MMF of 3,000 - 4,000 ampere - turns to support the same force. The smaller ampere - turns require less space, which enables a motor that utilizes a multi - slot approach with proportionally smaller yokes and windings operated at high frequencies to achieve gains in torque, output, and torque density.

[0235] The relationship between the stator and rotor teeth is preferably in a ratio of 0.6:1 to 1.4:1, more preferably 0.8:1 to 1.2:1. For conventional slots, the tooth width relative to the air - gap ratio is preferably greater than 10:1, more preferably 30:1 to 100:1 for direct - drive traction applications, and 30:1 for applications requiring high speeds. For stator poles, the number of teeth per pole preferably falls within 20 - 90%, more preferably 40 - 80% of the number of teeth per pole that maximizes the force for a given air - gap.

[0236] For a given air gap, it is preferable to obtain the peak force with teeth less than the maximum integer (e.g., about 50 - 80% of the maximum). After the peak force, the force gain begins to asymptote and becomes relatively negligible. In a particular air gap of the motor design, more factors can be considered to optimize the force by the number of teeth per slot. For example, increased air slots can cause additional leakage flux and a reduction in saliency. Also, fewer and larger poles allow for a larger output density and handle higher current loads that lead to saturation. Further, as discussed below, the tooth slots can be filled with diamagnetic materials that can also affect motor performance.

[0237] For a given pole, the maximum inductance remains the same as the tooth dimension decreases and the number of teeth increases. However, the minimum inductance increases due to the permeability of the air in the slot becoming smaller. Thus, the total energy per cycle decreases as a result of the increase in the number of teeth per pole.

[0238] FIG. 27 shows a motor 2700 including a plurality of discrete teeth on each pole of the motor. The motor 2700 includes a stator 2710 and a rotor 2720. The outer surfaces of the stator 2710 and the rotor 2720 define an air gap 2715. The motor 2700 is similar to the motor 400 of FIG. 4 except that each stator pole 2712 of the stator 2710 includes a plurality of teeth 2714 having slots 2716 therebetween, and each rotor pole 2722 of the rotor 2720 includes a plurality of teeth 2724 having slots 2726 therebetween. Note that a slot 2718 may be present between adjacent stator poles 2712, while the rotor 2720 may include continuous alternating teeth 2724 and slots 2726 along the outer surface of the rotor 2720.

[0239] The flux barriers can be formed between adjacent rotor teeth 2724 and / or between adjacent stator teeth 2714. The flux barriers can be similar to the flux barrier 704 of FIG. 7, the flux barrier 1104 of FIG. 11, the flux barrier 1304 of FIG. 13, or the flux barrier 1404 of FIG. 14.

[0240] The flux barrier material can be a conductive material having a diamagnetic property greater than air during operation in order to increase the total energy per cycle. This generates a dynamic flux barrier. Using the impedance of the inductor to provide such diamagnetic properties results in a larger salient pole ratio during operation at low, intermediate, and high frequencies (e.g., 2 Hz to 1 MHz). As discussed above, this can be achieved by using the skin effect of all-metal single materials such as aluminum, copper, brass, silver, zinc, gold, pyrolytic graphite, bismuth, graphene, or carbon nanotubes, or more preferably superconductors. The superconductor can be operated at frequencies above 0.5 Hz, and copper can be operated at intermediate to high frequencies of 20 kHz to 1 MHz. In some other embodiments, copper-iron, nickel-iron, lead-iron, brass-iron, silver-iron, zinc-iron, gold-iron, bismuth-iron, aluminum-iron, pyrolytic graphite-iron, graphene-iron, carbon nanotube-iron, or Alinco (aluminum-nickel-cobalt) alloys, which can be operated at 100 Hz to 20 kHz, can be used. In some other embodiments, higher inductance fillers can be used to generate an equivalent impedance (such as constructing a loop pole or a shielding pole (e.g., a copper-shielded iron pole) at low frequencies). Such a combination of diamagnetic and ferromagnetic materials approximates the properties of a metamaterial. Structurally, as this slot filling begins to approximate a smooth and continuous surface on the rotor and stator faces and the tooth dimensions decrease, such a slot filling material can serve as a mechanical support to prevent physical deformation caused by the forces generated during operation.

[0241] As teeth become smaller at a given pole tip, the slots can be closer to each other, and the resulting leakage magnetic flux reduces both the salient pole ratio and the work per cycle (and thus torque). By replacing air with a material approximating a diamagnetic material (e.g., a single diamagnetic material or a combination of a diamagnetic material and a ferromagnetic material), it is possible to perform a process of increasing the number of motor teeth as an effective electromagnetic reduction, similar to a transmission. The energy per cycle, and thus torque, decreases as a result of increasing the number of teeth per pole for a given pole dimension, but torque and output density can be achieved by using a diamagnetic material to increase the salient pole ratio. In particular, a further advantage of a pole design or configuration with diamagnetic slot filling is that the magnetic field on a pole with a large number of teeth is generated in a single direction on a given pole, in contrast to a constant reversing magnetic field in a typical motor.

[0242] As discussed above in FIG. 20, at low frequencies, the generated effective force remains constant or flat with frequency because the diamagnetic magnetic flux barrier appears like air and thus has little or no effect. At intermediate to high frequencies, the flux shielding effect begins to dominate and the force continues to increase with increasing frequency. Thus, by filling the slots with a diamagnetic magnetic flux barrier, a lower drive current (and thus fewer windings) can be used, thus saving capital by using fewer wires and increasing efficiency by reducing resistive losses. Additionally, motor performance can be further improved by using a higher drive current (e.g., through saturation). Also, the slot depth affects the horizontal force generated. The resulting force can be substantially proportional to the depth of the slot along the direction perpendicular to the air gap.

[0243] Axial-gap motor with magnetic flux barriers FIG. 28 is a perspective view of an exemplary axial-gap motor 2800 having flux barriers between adjacent rotor poles. The axial-gap motor 2800 has a rotor 2804 disposed parallel to a stator 2802. The rotor 2804 defines a central hole 2801, and an output shaft can be disposed within the central hole 2801 such that the rotor 2804 can rotate with the output shaft.

[0244] The rotor 2804 is movable relative to the stator 2802 by rotation about the axis of rotation of the rotor (or the axis of rotation of the output shaft). The end face of the rotor 2804 is perpendicular to the axis of rotation of the rotor. The end face of the rotor 2804 is spaced from the end face of the stator 2802 along the axis of rotation to define a nominal gap 2803. The nominal gap 2803 is an axial gap between the end face of the stator 2802 and the end face of the rotor 2804 and along the axis of rotation of the rotor.

[0245] The stator 2802 defines a series of stator poles 2810 including stator pole cores 2812 surrounded by associated electrical windings 2814, respectively. The electrical windings 2814 of the stator 2802 are independently activatable and are circumferentially spaced about the stator. The rotor 2804 has a series of rotor poles 2820 having flux barriers 2830 therebetween. Each flux barrier 2830 has a conductive loop surrounding a core of a ferromagnetic material. The cores of the flux barriers, rotor poles, and rotor back plate can all be part of a series of ferromagnetic materials (e.g., formed by pressing and sintering powders). The conductive loop of the flux barrier can be, for example, a copper ring pressed onto the core.

[0246] FIGS. 29-32 show various views of a rotor 2900 of another axial-gap motor. The rotor 2900 has a flat active end face (facing a stator not shown) including pole surface regions forming rotor poles 2920 and inter-pole surface regions formed by flux barriers 2930 between the pole surface regions. In this example, the flux barrier 2930 is a shaded pole similar to the shaded pole 1404 of FIG. 14.

[0247] Each magnetic flux barrier 2930 includes a conductive material that forms a loop 2932 centered on the core 2934 of the core material. The core material has a higher magnetic permeability than the conductive material. The core material can be ferromagnetic. The core material of the core 2934 and the pole material of the rotor pole 2920 can be the same, and the core 2934 and the rotor pole 2920 form the entire continuous rotor body (e.g., of sintered iron powder). The conductive material of the magnetic flux barrier can be cast into the formed rotor core.

[0248] As shown in FIGS. 29 to 32, each loop 2932 includes five loop portions 2932a, 2932b, 2932c, 2932d, 2932e. The loop portion 2932a forms a part of the end face of the rotor 2900.

[0249] The loop portion 2932b extends to a spread having a certain depth along a direction parallel to the rotation axis and forms a part of the outer radial surface of the rotor 2900. The end face is perpendicular to the outer radial surface. The loop portion 2932c extends to a spread having a certain depth along a direction parallel to the rotation axis and forms a part of the inner radial surface of the rotor 2900. The depth of the loop portion 2932c can be the same as the depth of the loop portion 2932b.

[0250] The loop portions 2932d, 2932e extend radially from the inner radial surface of the rotor to the outer radial surface of the rotor to form a shielding wall between the adjacent rotor poles 2920 and the core 2934. The loop portions 2932d, 2932e also extend into the rotor body to a spread having a depth that can be the same as the depth of the loop portions 2932b, 2932c. Each of the loop portions can have a (preferably greater than the skin depth of the current of the conductive material of the loop 2932 at a specific operating frequency) consistent and identical thickness.

[0251] Stator with magnetic flux barrier The magnetic flux barrier can also be provided in the stator of the motor to further increase the performance.

[0252] FIG. 33 shows a stator 3300 having magnetic flux barriers 3320 disposed between stator poles 3310. The stator poles 3310 may be housed within a magnetically permeable yoke 3302 or may be magnetically permeable yokes. The stator poles 3310 may be connected to the yoke 3302. Each stator pole 3310 includes a stator core 3312 surrounded by an associated electrical winding 3314. The stator core 3312 (and yoke) may be made of a stack of layers of ferromagnetic material extending along a longitudinal axis. The layers are separated from each other by interfaces that are less electrically conductive than the ferromagnetic material. The stator core 3312 may be a stator spur that protrudes from the yoke 3302.

[0253] Each flux barrier 3320 forms a flux shield that extends along both edges of the stator pole 3310 and is formed of a material having a higher electrical conductivity than the ferromagnetic material of the stator core 3312. The flux barriers 3320 may extend into the gap between adjacent electrical windings 3314. As shown in FIG. 34, the flux barriers 3320 may extend from an air gap 3350 to a yoke 3302 that connects adjacent stator poles 3310. The air gap 3350 is defined between the two outer surfaces of the stator 3300 and the rotor 3400. The rotor 3400 includes a series of rotor poles 3410 having flux barriers 3420 therebetween, as discussed above.

[0254] 33 and 34, each stator core 3312 surrounded by electrical windings 3314 has an angular width W0 along the circumference of the stator 3300. The flux barriers 3320 extend into notches in the face of the stator core 3312 such that the angular width W1 of the stator core 3312 in the gap between the edges of adjacent flux barriers 3320 is less than the angular width W0 of the stator core 3312 surrounded by electrical windings 3314. That is, W1 <W0である。

[0255] FIG. 35 shows another stator 3500 having flux barriers 3520 disposed between stator poles 3510. Similar to the stator 3300 of FIGS. 33 - 34, each stator pole 3510 includes a stator core 3512 surrounded by an associated electrical winding 3514. The stator core 3512 can be stator protrusions protruding from a permeable yoke 3502, formed as a stack of permeable plates having current suppression interfaces. Each flux barrier 3520 is formed of a material having a higher conductivity than the material of the stator core 3512 and intersects the interfaces of the stack. As shown in FIG. 36, the flux barrier 3520 can extend from the air gap 3550 to the yoke 3502, connecting adjacent stator poles 3510 in the air gap 3550 defined between the stator 3500 and the rotor 3600. The rotor 3600 includes a series of rotor poles 3610 having flux barriers 3620 therebetween, as discussed above.

[0256] The motor 3500 differs from those of FIGS. 33 - 34 in that the angular width of the stator core is substantially constant from the air gap to the yoke 3502. That is, W0 = W1.

[0257] FIG. 37 shows another stator 3700 having flux barriers 3720 disposed between stator poles 3710. Similar to the stator 3300 of FIGS. 33 - 34, each stator pole 3710 includes a stator core 3712 surrounded by an associated electrical winding 3714. The stator core 3712 can be stator protrusions protruding from a permeable yoke 3702, having a stator core and a yoke formed as a stack of ferromagnetic plates having current suppression interfaces. Each flux barrier 3720 is formed of a conductive material and intersects at least most of the ferromagnetic plate interfaces of the stator core. As shown in FIG. 38, the flux barrier 3520 can extend from the inner surface of the stator 3700 to the yoke 3502 connecting adjacent stator poles 3710.

[0258] The stator core 3712 has longitudinal continuous tabs received within corresponding slots of the flux barriers 3720. After the windings are assembled on the core, the flux barriers can be inserted longitudinally and held in place by the tabs of the stator core, further securing the windings.

[0259] Linear motor having a flux barrier As discussed above, the flux barrier can be configured in a radial gap motor and an axial gap motor in which the rotor poles and / or the stator poles are arranged in the circumferential direction. Hereinafter, the rotor poles and / or a linear motor having a flux barrier in which the stator poles are arranged linearly and the relative movement between the stator and the rotor is along a straight line will be discussed.

[0260] Figs. 39 and 40 show an exemplary linear motor 3900 including a stator 3910 and a rotor 3950. The rotor 3950 is movable relative to the stator 3910 along the direction of movement and defines a nominal gap 3940 having a width perpendicular to the direction of movement together with the stator 3910.

[0261] The stator 3910 defines a series of stator poles 3920 that are arranged linearly along the direction of movement and are linearly connected by a permeable yoke or back plate 3902. Each stator pole 3920 includes a stator core 3922 surrounded by an associated electrical winding 3924. The stator core 3922 can be made of a stack of layers of ferromagnetic material each extending along the direction of movement. These layers are separated from each other by interfaces that are less conductive than the ferromagnetic material. The stator core 3922 can be a stator projection protruding from the yoke 3902. The stator projections define slots 3930 therebetween.

[0262] The rotor 3950 has a series of rotor poles 3960 therebetween with flux barriers 3970 and spaced along the direction of motion. The flux barriers 3970 can be shielding poles similar to the flux barrier 1504 in FIG. 15. Each flux barrier 3970 is made of a conductive loop 3972 centered on a permeable core 3974 between adjacent rotor poles 3960. The rotor poles 3960 can be made of a laminated stack of layers of ferromagnetic material separated from each other by interfaces with a conductivity lower than that of the ferromagnetic material. The flux barriers 3970 each have a flat outer surface parallel to the direction of motion, forming an inter-pole surface region between the pole surface regions of the rotor poles 3960. The inter-pole surface region and the pole surface regions define the outer surface (or end face) of the rotor 3950. Each core 3974 forms a part of the outer surface surrounded by the respective loop 3972. The loop 3972 can be made of a conductive low-energy product such as copper. The material of the core 3974 has a higher permeability than the material of the loop 3972. The material of the core 3974 and the ferromagnetic material of the rotor poles 3960 can be adjacent parts of the stack of layers. The loops 3972 of the flux barriers 3970 do not overlap and are electrically insulated from each other outside the ferromagnetic material. The flux barriers 3970 are electrically connected to each other only through the ferromagnetic material as much as possible.

[0263] FIGS. 41 and 42 show another exemplary linear motor 4100 including a stator 4110 and a rotor 4150, the stator 4110 and the rotor 4150 each having a plurality of tooth poles as described above with respect to FIG. 27, but the conductive material between the teeth forms loops. The rotor 4150 is movable relative to the stator 4110 along the direction of motion and defines a nominal gap 4440 having a width perpendicular to the direction of motion together with the stator 4110.

[0264] Similar to the stator 3910 of FIGS. 39 - 40, the stator 4110 defines a series of stator poles 4120 that are linearly arranged along the direction of movement and are linearly connected by a permeable yoke or backplate 4102. Each stator pole 4120 includes a stator core 4122 surrounded by an associated electrical winding 4124. The stator core 4122 can be made of a stack of layers of ferromagnetic material each extending along the direction of movement. These layers are separated from each other by interfaces that are less conductive than the ferromagnetic material. The stator core 4122 can be stator projections that project from the yoke 4102. The stator projections define slots 4130 therebetween. Different from the stator 3910, the stator poles 4120 (or stator cores 4122) include a plurality of teeth 4122a having slots 4122b therebetween at least on the outer surface of the stator poles 4120. As discussed above, the magnetic flux barriers are formed within the slots 4122b between the plurality of stator pole teeth 4122a. In the configuration shown, the material within the two left slots 4122b of each stator pole forms a loop around the left stator teeth 4122a, and the material within the two right slots forms a second loop around the right stator teeth 4122a. In this configuration, the two loops serve to shield magnetic flux penetration through the two outer stator pole teeth. Alternatively, a conductive material filling each of the tooth - to - tooth slots 4122b serves as a separate local magnetic flux reflector through the effect of eddy currents set up within the conductive material (without forming loops by the material of adjacent slots). As another alternative, each slot 4122b itself can include a shaded - pole magnetic flux barrier.

[0265] The rotor 4150 includes a series of rotor poles arranged linearly along the direction of motion. Each rotor pole includes a plurality of teeth 4160 having flux barriers 4170 within the slots between adjacent teeth 4160. Each flux barrier 4170 can be a shaded pole similar to the flux barrier 3970 of FIG. 39. Each flux barrier 4170 is made of a conductive loop 4172 centered on a permeable core 4174 between adjacent rotor pole teeth 4160. The loop 4172 can be made of a low-conductivity energy product. The core material of the core 4174 has a higher magnetic permeability than the material of the loop 4172. The core material of the core 4174 and the ferromagnetic material of the rotor pole 4160 can be adjacent parts of a stack of layers. The loops 4172 of the flux barriers 4170 do not overlap and are electrically insulated from each other outside the ferromagnetic material. The flux barriers 4170 can be connected to each other only through the ferromagnetic material.

[0266] Operation of a motor having a flux barrier The effect of the flux barrier can vary depending on the horizontal force at various frequencies. As shown in FIG. 20, the horizontal force can begin to increase when exceeding the cutoff frequency (e.g., 10 Hz), and the increase between the low frequency (e.g., 10 Hz) and the high frequency (e.g., 10 5 Hz) can exceed one order of magnitude. At high frequencies, the flux barrier can exhibit stronger diamagnetic properties to concentrate the magnetic flux toward the rotor pole and increase the component of the force along the direction of motion.

[0267] The effective force can also be affected by the operating conditions. Under saturation and at high frequencies, the flux barrier can exhibit stronger diamagnetic properties (compared to the unsaturated state) to concentrate the magnetic flux toward the rotor pole. The effective force can continue to increase as the frequency increases. For example, at high frequencies (e.g., 105 Hz), the horizontal force can increase by two orders of magnitude as the drive current increases from 10 ampere-turns (corresponding to unsaturated operating conditions) to 200 ampere-turns (corresponding to the saturated operating state).

[0268] As pointed out above, the number of teeth per pole can also affect the effective force. An increase in the number of teeth per pole can cause a gradual increase in force. However, when the gap dimension becomes larger (e.g., to 1.0 mm), the force can decrease as the number of teeth per pole increases.

[0269] Regarding the configuration with magnetic flux barriers, each pole set can be operated under pulsed-DC or pulsed-AC current.

[0270] This operation utilizes high inductance and low resistance magnetic flux barriers, resulting in a high reactance that is in phase with the magnetic field. As the magnetic field climbs the primary coil and the magnetoresistive teeth, the magnetic field is reflected through the shielding teeth, resulting in a high impedance to the magnetic field. This system can be operated via an alternating magnetic signal only through a 50% duty cycle (e.g., from the non-aligned position to the aligned position). Continuing over the duty cycle (e.g., from the non-aligned position to the aligned position) can generate reverse torque.

[0271] Higher reactance magnetic flux barriers can enable higher power factor systems that can generate torque more efficiently compared to conventional machines. A high reactance, high impedance magnetic flux barrier design can prevent almost all of the magnetic flux from entering the magnetic flux barrier over the entire operating cycle. In this way, the motor can benefit from the diamagnetic properties previously experienced only in superconducting motors over a wide range of temperatures (e.g., room temperature to high temperature). This may also be less sensitive to temperature compared to permanent magnet motors that tend to demagnetize above the critical temperature. This may also be less sensitive to temperature compared to permanent magnet motors that tend to demagnetize above the critical temperature.

[0272] The above-described motor having a flux barrier can be dynamically driven by a square-wave current. If the above-described motor is dynamically driven, the square wave can be used at a switching frequency that is relatively lower than that of an equivalent sine wave because the square wave induces a large reactance within the flux barrier while pulsating at a relatively low frequency (such as 50 Hz). This is due, in part, to the high percentage of harmonic values within the square wave as contrasted with the sine wave. This also reduces the switching losses required by the power electronics due to the high frequencies required by pulse-width modulation (PWM) switching. In such an operation, a relatively thin (e.g., 0.127 mm) lamination can be used to reduce eddy current losses in the iron core and at a low gauge (e.g., 0.2 mm), and even a Litz wire winding can be utilized within the primary coil to reduce skin effect losses within the core winding.

[0273] The above-described motor can also benefit from a higher winding efficiency of the coil. The typical slot fill ratio of the winding is 30 - 40% of a given slot area, but by utilizing casting techniques to fill the flux barriers within the slots between adjacent poles, the motor can utilize substantially all (e.g., 85 - 95%) of the slot volume of the flux barrier. This can reduce the total amount of wire required for the primary winding of the motor and thus enables the primary winding to use fewer turns of wire compared to a typical motor.

[0274] As pointed out above, filling the slots with a diamagnetic flux material presents a means of concentrating the flux during the operation of the motor. Specifically, when the stator and rotor are arranged in a non-aligned state, significant internal electromagnetic reflection impedes most of the magnetic propagation from the opposing pole surfaces. This diamagnetic shielding enables the magnetic field slots to effectively push the rotor, while the magnetic reluctance of the electromagnetic poles pulls the rotor. This effect enables more energy to be generated from the system per cycle, similar to the effect that permanent magnets can generate in some configurations.

[0275] This effect provides a significant advantage over permanent magnets that can be demagnetized by high eddy currents. This effect can be seen in the B-H curve that examines the retentivity of permanent magnets. In the motor described above, the high reactance flux barrier can approximate the permanent magnet in the opposite direction with infinite retentivity. Therefore, the flux barrier can reflect the applied magnetic field to achieve a magnetic field level that exceeds what can be achieved in a typical permanent magnet motor, and by generating a large back EMF, it can increase torque density, output density, and efficiency. Furthermore, while the permanent magnet is demagnetized at elevated temperatures as described above, the flux barrier can be constructed of materials that can withstand temperatures up to 100 degrees Fahrenheit higher than typical permanent magnets.

[0276] Furthermore, when the permanent magnet generates a constant magnetic field, a diamagnetic flux barrier dynamically exists in the transient state. This is advantageous for both efficiency and safety because the permanent magnet motor can generate detent torque, cogging torque, and braking torque that can sometimes be catastrophic due to the EMF that can be generated regardless of the power utilized. The motor described above can be controlled to inertially rotate effectively for an extended period with only losses from bearing resistance.

[0277] Furthermore, unlike an IM with an effective inductive load that generates a continuous current, the current within each flux barrier is allowed to return to nearly zero every cycle. The higher the operating frequency of the motor, the smaller the required current in each flux barrier to maintain reflection. Since the system is reactive, energy is either elastically returned to the rotor's kinetic energy or converted within each switching cycle.

[0278] The diamagnetic magnetic flux barrier filling can be adjusted dynamically during operation for a given application. Unlike air, the magnetic properties of the present system can be adjusted in both the amplitude of the magnetomotive force (MMF) and the frequency of the MMF at a given position. This enables real-time adaptation by weakening or strengthening the magnetic flux characteristics of the system by changing the switching frequency of the motor. This can change the back EMF on the primary coil, thereby enabling the motor to achieve a wider speed range than a conventional motor. Conventional motors have a fixed back EMF based on a fixed pole ratio used to change the magnitude of the magnetic field. The motor can change the magnitude of the magnetic field in addition to the activation frequency of the operation of the motor.

[0279] At high speeds, the motor can operate as a reactive magnetic resistance motor. In conventional SRM operation, the peak voltage is applied at the start of the non-alignment position of the stator and rotor (or stator-rotor teeth), and the current is rapidly increased until the stator and rotor (or stator-rotor teeth) reach the alignment point. At this point, a reverse voltage is applied and the current drops to zero. In the locked rotor (stall) state in a conventional SRM, the current is applied continuously rather than pulsed. In a motor with a magnetic flux barrier, during stall, the current is pulsed through the active coils. When the pole switching frequency exceeds the crossing frequency of the magnetic flux barrier during motor acceleration, each pole is excited by a single pulse.

[0280] Exemplary process Embodiments of the present disclosure provide a method of driving an electric motor. The electric motor can be the electric motor 102 of FIG. 1, and the method can be performed by a motor controller (e.g., the motor controller 104 of FIG. 1).

[0281] During operation, the motor controller energizes a first active pole of a series of active poles disposed along a gap between a passive magnetic component having a series of passive poles disposed along the gap and the gap, by pulsing a current through an electrical winding associated with the first active pole. The pulsed current includes a series of at least three pulses during which the windings of adjacent active poles of the series of active poles are not energized. Pulsing the current through the electrical winding associated with the first active pole causes current to pass through the electrical winding associated with the first active pole according to a current waveform in which the ratio of the maximum current to the minimum current during the pulsing of the current through the electrical winding associated with the first active pole is at least 4:1, 7:1 or even 10:1.

[0282] In some cases, the electrical winding associated with the first active pole includes a plurality of coils conductively connected in parallel with and wound around a common core. The motor controller may pulse the current through the plurality of coils conductively connected in parallel.

[0283] In some examples, the motor controller pulses the current through the electrical winding associated with the first active pole by operating a first switch to open and close within a plurality of cycles between a voltage source and the electrical winding associated with the first active pole. The first switch may be associated with and conductively coupled to the first active pole. The first switch may be switch 134 of FIG. 2 or power switch 200 of FIG. 2A.

[0284] After the first active pole is energized (by the plurality of current pulses), the motor controller energizes a second active pole of the series of active poles by pulsing the current through the electrical winding associated with the second active pole. The pulsed current of the second active pole includes a series of at least three pulses during which the winding of the first active pole is not energized, and causes current to pass through the electrical winding associated with the second active pole according to a current waveform. In the current waveform, the ratio of the maximum current to the minimum current during the pulsing of the current through the electrical winding associated with the second active pole is at least 4:1, 7:1 or even 10:1.

[0285] The first active pole can be energized by pulsing the current at a pulse frequency of 2 Hz to 1 MHz, in some cases 10 Hz to 20 kHz, and in some cases 100 Hz to 5 kHz. Energizing the first active pole and then the second active pole generates a first force between the first active pole and the passive pole across the air gap from the first active pole and a second force between the second active pole and the passive pole across the air gap from the second active pole. The first and second forces can induce relative movement between the active pole and the passive pole. The relative movement can include the movement of the passive magnetic component relative to the active pole.

[0286] In some examples, the passive magnetic component is the rotor of a motor, and the relative movement includes the rotation of the rotor. The motor controller can further detect the rotor speed and control the frequency of the pulsed current (or pulse frequency) according to the detected rotor speed. During rotor speed change, the motor controller can further maintain the current pulse frequency at least up to a rotor speed at which the frequency at which each active pole is energized is at least one half of the pulse frequency. The current can be pulsed only via the electrical windings associated with the first and second poles at a rotor speed less than that corresponding to one pulse per pole energization.

[0287] After energizing the second active pole, the motor controller can further energize a third active pole of a series of active poles disposed on the opposite side of the second active pole rather than the first active pole by pulsing the current passing through the electrical winding associated with the third active pole, including a series of at least three pulses during which the windings of the first and second active poles are not energized. After energizing the third active pole, the motor controller can re-energize the first active pole by pulsing the current passing through the electrical winding associated with the first active pole, and then re-energize the second active pole by pulsing the current passing through the electrical winding associated with the second active pole, and then re-energize the third active pole, and so on.

[0288] As pointed out above, the magnetic flux barrier can be implemented within a passive magnetic component. In some examples, by pulsing a current through an electrical winding associated with a first active pole, eddy currents are generated in a first magnetic flux barrier adjacent to a passive pole across a gap from the first active pole. The magnetic flux barrier has a higher conductivity than the passive pole across the gap. The passive magnetic component may further include a second magnetic flux barrier, and the passive pole extending across the gap from the first active pole is disposed between the first magnetic flux barrier and the second magnetic flux barrier. The first and second magnetic flux barriers are electrically insulated from each other outside the passive pole.

[0289] In some motors, the passive pole is formed by a stack of layers of a ferromagnetic material. The eddy currents in the first magnetic flux barrier serve to deflect magnetic flux away from the first active pole. In some examples, the first magnetic flux barrier is disposed between the passive pole extending across the gap from the first active pole and an adjacent passive pole, and the magnetic flux barrier forms a loop of a conductive material centered on a core of a core material that has a higher magnetic permeability than the conductive material.

[0290] In some cases, the passive magnetic component further includes a magnetic flux barrier between adjacent pairs of a series of passive poles, the magnetic flux barrier including a conductive material different from the material forming each passive pole and defining at least one conductive path centered on a ferromagnetic core material. The magnetic flux barriers are electrically insulated from each other outside the series of passive poles. Adjacent magnetic flux barriers may be arranged such that no portion of any conductive path defined within the conductive material of one magnetic flux barrier surrounds any portion of any conductive path defined within the conductive material of another magnetic flux barrier.

[0291] In some embodiments, the motor further includes a magnetic flux shield extending along both edges of each active pole, the magnetic flux shield being formed of a material having a higher conductivity than the material of the active magnetic component disposed between the magnetic flux shields. The magnetic flux shield may extend into a gap between adjacent electrical windings. The magnetic flux shield may extend from the gap to a ferromagnetic yoke connecting adjacent active poles.

[0292] Exemplary Cooling and Thermal Mitigation An electric motor can generate significant heat during operation (especially during high-frequency operation) and may require cooling. An active cooling system can be used to provide intermittent or continuous cooling of the surfaces by circulating a fluid refrigerant within the motor. The cooling system can be the cooling system as described in the continuing patent application U.S. Patent Application No. 62 / 675,207, entitled "Electric Motor," filed on March 23, 2018, which is hereby expressly incorporated by reference in its entirety.

[0293] Also, if the operating temperature is reduced, the efficiency and output of the magnetic flux barrier can increase for a given frequency. Typically, the operating conditions are from -80°C to 300°C. A refrigerant can be added to the motor system to further suppress the temperature and increase the diamagnetic properties of the magnetic flux barrier.

[0294] The refrigerant can be any conventional fluid used for heat mitigation. Under the operating conditions, the refrigerant can be a low-viscosity fluid within the range of 1 to 500 centipoise (such as water or motor oil that enables both high cooling efficiency and high rotational dynamics). The refrigerant not only provides braking of the vibrations generated during operation but also provides a restoring force to the harmonics generated at high rotational speeds.

[0295] Active cooling can enable a larger output density by providing a medium for absorbing heat from the electrical coils and mechanical contact surfaces. An active lubrication system can be used to provide intermittent or continuous lubrication of the surfaces by circulating a fluid lubricant within the motor. For example, a fluid pump can mechanically facilitate the flow of the lubricant from the fluid pump to the motor through a fluid line, and the lubricant can be discharged through a directional nozzle to provide active lubrication and / or fluid cooling at specific locations within the motor. Next, the fluid can gravitationally accumulate in an oil sump at the base of the motor and can reflux to the pump through a fluid line for recirculation. In this way, the motor rotor assembly can operate in a cold, non-immersed environment. Additionally, a portion of the lubricant can pass through a heat exchanger to add heat to or remove heat from the lubricant to modulate the temperature and / or viscosity of the lubricant to satisfy the special requirements of the application.

[0296] The refrigerant can be any conventional fluid used for heat mitigation. Under operating conditions, the refrigerant can be a low-viscosity fluid within the range of 1 to 500 centipoises (such as water or motor oil that enables both high cooling efficiency and high rotational dynamics). The refrigerant can not only provide braking of the vibrations generated during operation, but also provide a restoring force to the harmonics generated at high rotational speeds.

[0297] The motor can include a collection tray for gravitationally collecting the refrigerant released within the motor assembly and directing it back in the direction of the return fluid line.

[0298] The refrigerant system can have a fluid pump that provides a pressure gradient to the refrigerant to effect circulation within the fluid system. Such a pump can be a constant-displacement pump such as a rotary pump, or a variable-displacement pump such as a gear or piston pump. The pump can be operably connected to a mechanical or electrical power source and can be operated continuously or intermittently during motor operation. The wet sump active lubrication system can have a single fluid pump operably connected to the collection tray for circulating oil within the fluid line and within the cooling system. In this case, most of the oil supply is within the collection tray. Alternatively, a plurality of fluid pumps can be operated in a dry sump active cooling configuration where fluid from the collection tray is continuously pumped into a storage tank, preferably having a high height relative to its cross-sectional area, and a second pump can pump the fluid back to the motor under another controlled flow rate to complete the refrigerant circulation.

[0299] The refrigerant system can have one or more directional nozzles for guiding the refrigerant to a specific location within the motor assembly, for example, including stator poles therein.

[0300] Other embodiments Any of the motors described above can be controlled to generate electrical energy from kinetic energy (e.g., to apply a regenerative brake to the motor). This can be achieved by changing the timing of the excitation signal such that the stator current is pulsed at the point of minimum air gap (or even at a point slightly delayed from the point of minimum air gap) to generate a forward EMF during expansion. In this way, even if the motor cannot be mechanically backdriven by the torque applied to the output shaft, current is generated and directed to a storage portion within an associated battery, while a decelerating torque is applied to the rotor to slow down the motor.

[0301] Any of the motors described above can be controlled to generate electrical energy from kinetic energy (e.g., to apply a regenerative brake to the motor). This can be achieved by changing the timing of the compression wave such that the stator current is pulsed at the point of minimum air gap (or even at a point slightly delayed from the point of minimum air gap) to generate a forward EMF during expansion. In this way, even if the motor cannot be mechanically backdriven by the torque applied to the output shaft, current is generated and directed to a storage portion within an associated battery, while a decelerating torque is applied to the rotor to slow down the motor.

[0302] Although many examples have been described for illustrative purposes, the foregoing description is not intended to limit the scope of the invention as defined by the appended claims. Other examples and modifications within the scope of the following claims exist and will exist.

Claims

1. An electric motor, a stator having a plurality of stator poles and electrical windings associated with the stator poles; a rotor including a plurality of rotor poles; the rotor is movable relative to the stator and defines with the stator a nominal gap between the stator poles and the rotor poles, the rotor poles including a magnetically permeable pole material; each of the plurality of stator poles having flux shields extending along opposite edges of the stator pole, the flux shields being formed of a material having a higher electrical conductivity than a material of the stator poles disposed between the flux shields.

2. The electric motor of claim 1 , wherein each of the plurality of stator poles has a plurality of teeth defining recesses between each of the plurality of stator poles.

3. the rotor has flux barriers between adjacent rotor poles, each of the flux barriers including a second material having a conductivity different than a conductivity of the magnetically permeable pole material; The electric motor of claim 1 , wherein each of the flux barriers are insulated from one another outside of the plurality of rotor poles.

4. The electric motor of claim 1 , wherein the rotor is disposed inside the stator.

5. The electric motor of claim 1 , wherein the nominal gap is a radial gap bounded at least in part by a radially outer surface of the rotor.

6. 2. The electric motor of claim 1, wherein the nominal gap is an axial gap perpendicular to an axis of rotation of the rotor.

7. The electric motor of claim 1 , wherein each of the plurality of rotor poles has a plurality of teeth defining recesses between each of the plurality of rotor poles.

8. an active magnetic component having an associated electrical winding and a first surface defining a plurality of active poles; a passive magnetic component movable in a first direction relative to the first surface to define a gap and having a second surface spaced from the first surface; each of the plurality of active poles having a flux shield extending along opposite edges of the active pole, the flux shield being formed of a material having a higher electrical conductivity than a material of the stator poles disposed between the flux shields.

9. 9. The electric motor of claim 8, wherein the second surface forms a series of spaced apart passive poles of a first material defining slots therebetween, the slots extending at a non-zero angle in a first direction.

10. each of the slots includes a respective flux barrier including a second material extending along and forming a conductive path along each of the slots; 10. The electric motor of claim 9, wherein the flux barriers are secured to a first material in the slots and connected to each other only through the first material.

11. The electric motor of claim 10 , wherein the slots extend perpendicular to the first direction.

12. The electric motor of claim 10 , wherein the flux barrier fills the slot, the flux barrier contacting the first material on either side of the slot.

13. 11. The electric motor of claim 10, wherein the second material comprises at least 20%, in some cases 40%, or in some cases 60%, by weight percent, of an element or combination of elements selected from the group consisting of iron, nickel, and cobalt.

14. 9. The electric motor of claim 8, wherein the active magnetic component is a stator of the electric motor and the passive magnetic component is a rotor of the electric motor.

15. The electric motor of claim 14 , wherein a nominal gap is a radial gap bounded at least in part by a radially outer surface of the rotor.

16. 15. The electric motor of claim 14, wherein the nominal gap is the axial gap perpendicular to the axis of rotation of the rotor.

17. 9. The electric motor of claim 8, wherein each of the plurality of passive poles has a plurality of teeth defining a recess between each of the plurality of passive poles.

18. 9. The electric motor of claim 8, wherein each of the plurality of active poles has a plurality of teeth defining recesses between each of the plurality of active poles.

19. 9. The electric motor of claim 8, wherein the electric motor is a linear motor.

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