Electric motor

Abstract

To provide an electric motor which generates torque for smooth power transmission.SOLUTION: An electric motor has a stator mechanically coupled to a rotor by an oscillation traction joint, by that, during oscillation of the rotor with respect to the stator, a tilt axis of the rotor progresses about an axis of rotation of an output shaft. The rotor and a surface of the stator define a boundary of a dynamic gap, across which a magnetic field is produced by electrical activation of the motor to generate force between the rotor and the stator. The traction joint and the gap are arranged such that, in a plane containing the axis of rotation of the output shaft, the traction joint is angled with respect to a stator surface in contact with the gap. The rotor is connected to the output shaft by tiltable connection means such as a gimbal.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] Technical Field The present invention relates to electric motors and the operation of such motors. [Background technology]

[0002] background One way that an electric motor can be characterized is by its torque density (i.e., the torque achievable per unit motor volume). For many applications, especially those requiring high torque density, hydraulic motors have proven more practical, since high torque density is difficult to achieve with electric motors. A conventional motor has a stator with electromagnetic elements and a rotor that rotates with respect to the stator around a central axis of rotation. The stator and / or rotor are electrically actuated to generate a tangential magnetic force, which generates torque. In addition to the tangential force, electric motors also generate a normal force (sometimes called radial pressure) between the stator and rotor, which is the result of the magnetic force, and is greater in magnitude than the tangential force. In a typical motor, the radial pressure is carefully balanced across the rotor to prevent collisions between the stator and rotor. Some examples have attempted to harness the normal force by using a rotor that moves eccentrically. Summary of the Invention [Problem to be solved by the invention]

[0003] What is needed is a new motor design that utilizes, at least in part, radial pressure to generate torque with an acceptably smooth power transmission. [Means for solving the problem]

[0004] overview One aspect of the invention features an electric motor having an output shaft defining an axis of rotation, a rotor rotatably coupled to the output shaft, and a stator mechanically coupled to the rotor by a swinging traction joint, where the tilted axis of the rotor advances about the axis of rotation of the output shaft during swinging of the rotor relative to the stator. The rotor and stator surfaces define a dynamic gap in which electrical actuation of the motor generates a magnetic field to produce a force between the rotor and the stator. The traction joint and the gap are oriented in a plane containing the axis of rotation of the output shaft such that the traction joint is oblique with respect to a surface of the stator that borders the gap.

[0005] In some embodiments, the rotor is a first rotor, the stator is a first stator, and the swinging traction joint is a first swinging traction joint. The motor also includes a second rotor rotatably coupled to the output shaft and a second stator mechanically coupled to the second rotor by a second swinging traction joint, wherein a tilt axis of the second rotor advances during swinging of the second rotor relative to the second stator to define a conical surface with respect to the rotation axis of the output shaft. The surfaces of the second rotor and the second stator define a gap boundary in which a magnetic field is generated by electrical actuation of the motor to produce a force between the second rotor and the second stator.

[0006] In some examples, the first and second rotors are coupled to an output shaft such that during operation of the motor, the axes of the first and second rotors are inclined in opposite directions relative to the axis of rotation of the output shaft.

[0007] In some cases, the advancing first swing traction joint engagement point is in rotational alignment with the advancing second swing traction joint engagement point relative to the first stator.

[0008] The first and second rotors may be axially disposed between the first and second oscillating traction joints, or the first and second oscillating traction joints may be disposed between the first and second rotors.

[0009] In some motors, the rotor is rotatably coupled to the output shaft by a gimbal that defines two independent tilt axes perpendicular to each other and to the axis of rotation of the output shaft.

[0010] In some instances, the stator surface is cylindrical. In such cases, the rotor surface may be frusto-conical.

[0011] In many embodiments, the dynamic air gap is a radial air gap. By "radial" air gap is meant an air gap along the active magnetic flux path between the stator and rotor, where the path of least resistance across the gap is radial rather than axial or tangential with respect to the axis of rotation of the rotor. The air gap is dynamic in that it changes its size from point to point around the rotor and over time due to rotor wobble.

[0012] In some configurations, the stator has stator poles with windings associated therewith, and the radial air gap is radially interior to the stator poles. Preferably, at any one time during oscillation, the points of maximum traction engagement and minimum dynamic air gap of the traction joint are located on opposite sides of the axis of rotation.

[0013] In some other configurations, the stator has stator poles with windings associated therewith, and the radial air gap is radially on the anti-drive side of the stator poles. Preferably, at any one time during the swing, the point of maximum traction engagement of the traction joint is located on the same side of the output shaft as the instantaneous minimum dynamic air gap point.

[0014] In some embodiments, the traction interface features rotor teeth that mesh with stator teeth. In some cases, the rotor teeth include more teeth than the stator teeth. Preferably, there is a difference of one tooth between the total number of rotor teeth and stator teeth, such that one rocking movement of the rocking traction interface changes the rotational position of the rotor relative to the stator by one circumferential pitch of a tooth.

[0015] In some cases, the traction joint also features a tapered edge surface of the rotor that is arranged to roll against a tapered stop surface of the stator during rocking.

[0016] In some configurations, the stator includes a stator end cap that supports a bearing that receives the output shaft, the stator end cap featuring stator teeth.

[0017] In some instances, the traction joint features a resilient friction surface that is in rolling engagement with a reaction surface when subjected to a normal load.

[0018] In some configurations, the traction joint is radially on the non-drive side of the dynamic air gap. In other configurations, the traction joint is radially inboard of the dynamic air gap.

[0019] In some embodiments, the stator has a plurality of independently activatable windings spaced circumferentially around the rotor. The windings are activated sequentially prior to the forward swing traction joint engagement point to cause rotation of the rotor. The motor may also include a winding controller having switches operable to activate the stator windings.

[0020] In some configurations, multiple adjacent windings of the stator are simultaneously activatable as a winding group, and the stator includes multiple such winding groups spaced around the circumference of the stator.

[0021] In some embodiments, the stator has circumferentially spaced magnetic poles associated with the stator windings. The magnetic poles may be formed by axial stacking of laminations. Preferably, the laminations are formed to have a residual magnetic pole of at least 100 Gauss in the rotor for at least one minute after opening all stator windings. Such residual magnetic poles can, for example, help to retain rotor position after de-energization of the stator.

[0022] In some cases, the swinging traction joint is configured to rotationally advance the rotor relative to the stator a distance approximately equal to the pitch of the stator poles.

[0023] In some embodiments, the traction interface features a traction surface of the rotor that engages a stationary traction surface of the stator, the traction surface of the stator defining a stator pitch cone, the stator pitch cone angle being between 4 and 40 degrees. In some cases, the traction surface of the rotor defines a rotor pitch cone, the difference between the rotor pitch cone angle and the stator pitch cone angle being less than 10 degrees, preferably less than 7.5 degrees, and more preferably less than 5 degrees.

[0024] In some configurations, the rotor is disposed within the stator, e.g., between the stator poles, while in some other cases the rotor extends around the poles of the stator.

[0025] In some examples, the rotor has radially extending, circumferentially spaced teeth with a distal end face that interfaces with the dynamic air gap and may face radially outwardly toward the stator poles or may face radially inwardly toward the stator poles.

[0026] In some cases, the stator has circumferentially spaced poles associated with the stator windings. In some instances, each of the spaced teeth features a plurality of axially spaced tooth protrusions, and each stator pole features a plurality of axially spaced pole protrusions. Preferably, the tooth protrusions and pole protrusions are axially aligned at the minimum dynamic air gap point.

[0027] The rotor, in some embodiments, includes multiple laminations of ferromagnetic material adjacent the air gap.

[0028] In some cases, the swinging traction joint is lubricated. For example, the motor may include a flowable lubricant that is directed into the swinging traction joint by an oiling system. The motor, in some configurations, includes an active oiling system that includes a pump that causes a flow of lubricant to be directed to the swinging traction joint during operation of the motor. In some configurations, the output shaft defines an oiling port that is positioned to direct the flowable lubricant to the traction joint. The oiling port may be in fluid communication with an oiling channel, for example, defined by a gimbal on which the rotor is mounted.

[0029] Some motor configurations have an oiling rail with at least one nozzle positioned to spray lubricant from the rail to lubricate the traction joints.

[0030] Another aspect of the invention features an electric motor including an output shaft defining an axis of rotation, a rotor coupled to the output shaft at a tiltable connection means, and a stator disposed adjacent the rotor and defining a dynamic air gap. The stator has a plurality of windings each configured to generate a magnetic field to draw a respective side of the rotor toward the stator and to cause the rotor to oscillate relative to the stator in response to sequential activation of the plurality of windings to progressively tilt the tiltable connection means. The tiltable connection means features a gimbal positioned to transfer torque from the rotor to the output shaft.

[0031] In some embodiments, the rotor is a first rotor, the stator is a first stator, the dynamic air gap is a first dynamic air gap, and the tiltable connection means is a first tiltable connection means. The motor also includes a second rotor rotatably coupled to the output shaft and a second stator mechanically coupled to the second rotor by a second tiltable connection means characterized by a second gimbal configured to transfer torque from the second rotor to the output shaft. Surfaces of the second rotor and the second stator define a second dynamic air gap, between which a magnetic field is generated by electrical actuation of the motor to generate a force between the second rotor and the second stator.

[0032] In some cases, the first and second rotors are coupled to an output shaft such that, during operation of the motor, the axes of the first and second rotors are tilted in opposite directions relative to the axis of rotation of the output shaft.

[0033] In some arrangements, the advancing first dynamic air gap minimum position is rotationally aligned with the advancing second dynamic air gap minimum position relative to the first stator.

[0034] In some examples, the first stator is mechanically coupled to the first rotor by a first swing traction joint and the second stator is mechanically coupled to the second rotor by a second swing traction joint, and during swing of the rotors relative to the stator, the respective tilt axes of each rotor advance relative to the rotational axis of the output shaft. The first and second rotors may be axially disposed between the first and second swing traction joints, or, for example, the first and second swing traction joints are disposed between the first and second rotors.

[0035] In some cases, the stator surface is cylindrical, and the rotor surface may be frusto-conical.

[0036] In some motors, the dynamic air gap is a radial air gap. In some cases, the stator features stator poles associated with stator windings, and the radial air gap is radially inward of the stator poles. The stator may be mechanically coupled to the rotor by a swinging traction joint configured such that at any point during swing, the traction joint's maximum traction engagement point and minimum dynamic air gap point are located on opposite sides of the axis of rotation. In some other cases, the stator features stator poles associated with stator windings, and the radial air gap is radially on the anti-drive side of the stator poles. The stator may be mechanically coupled to the rotor by a swinging traction joint configured such that at any point during swing, the traction joint's maximum traction engagement point is located on the same side of the output shaft as the instantaneous minimum dynamic air gap point.

[0037] In some embodiments, the stator is mechanically coupled to the rotor by a rocking traction interface featuring rotor teeth that mesh with stator teeth. In some cases, the rotor teeth include more teeth than the stator teeth. Preferably, the total number of teeth in the rotor teeth and the stator teeth differ by one tooth, and each rocking motion of the rocking traction interface changes the rotational position of the rotor relative to the stator by a circumferential pitch of one tooth.

[0038] In some configurations, the traction joint also features a tapered edge surface of the rotor that is arranged to roll against a tapered stop surface of the stator during rocking.

[0039] Some examples of stators include a stator end cap that supports a bearing that supports the output shaft, the stator end cap featuring stator teeth.

[0040] The traction interface may be, for example, on the radially anti-driving side of the dynamic air gap or on the radially driving side of the dynamic air gap.

[0041] In some arrangements, the stator is mechanically coupled to the rotor by a rocking traction joint featuring resilient friction surfaces in rolling engagement with reaction surfaces under normal loads.

[0042] In some embodiments, multiple adjacent windings of the stator are simultaneously activatable as a winding group, and the stator includes multiple such multi-winding groups spaced around the periphery of the stator.

[0043] In some examples, the stator has circumferentially spaced magnetic poles associated with each stator winding, which may be formed by axial stacking of laminations.

[0044] In some embodiments, the stator is mechanically coupled to the rotor by a rocking traction joint featuring traction surfaces of the rotor engaging stationary traction surfaces of the stator, the traction surfaces of the stator defining a stator pitch cone, the stator pitch cone angle being between 4 and 40 degrees. Preferably, the traction surfaces of the rotor define a rotor pitch cone, the difference between the rotor pitch cone angle and the stator pitch cone angle being less than 10 degrees, more preferably less than 7.5 degrees, and even more preferably less than 5 degrees.

[0045] In some cases, the rotor features radially extending, circumferentially spaced teeth whose distal end faces abut the dynamic air gap. The distal end faces may, for example, face radially outward toward the stator poles or face radially inward toward the stator poles. In some configurations where the stator features circumferentially spaced poles associated with the stator windings, each of the spaced teeth has a number of axially spaced tooth protrusions, and each stator pole has a number of axially spaced pole protrusions. Preferably, the tooth protrusions and pole protrusions are axially aligned at the minimum dynamic air gap point.

[0046] In some instances, the rotor features multiple laminations of ferromagnetic material adjacent an air gap.

[0047] In some embodiments, the stator is mechanically coupled by a swinging traction joint, which is lubricated by an active lubrication system including a pump that causes a flow of lubricant to be directed to the swinging traction joint during operation of the motor. In some examples, the output shaft defines an lubrication port arranged to direct a flowable lubricant to the traction joint. The lubrication port may be in fluid communication with an lubrication channel defined, for example, by a gimbal. In some configurations, the motor includes an lubrication rail having at least one nozzle arranged to spray lubricant from the rail to lubricate the traction joint.

[0048] Another aspect of the invention features an electric motor that includes an output shaft defining an axis of rotation, a rotor coupled to the output shaft at a tiltable connection means, and a stator disposed adjacent the rotor to define a dynamic air gap. The stator has a plurality of windings each configured to generate a magnetic field to draw a respective side of the rotor toward the stator and to cause the rotor to oscillate relative to the stator in response to sequential activation of the plurality of windings and progressively tilt the tiltable connection means. The dynamic air gap is bounded by an outer circumferential surface of the rotor, and magnetic coupling between the rotor and the stator is primarily radial.

[0049] In some examples, the outer circumferential surface of the rotor is tapered.

[0050] In some embodiments, the rotor is a first rotor, the stator is a first stator, the dynamic air gap is a first dynamic air gap, the tiltable connection means is a first tiltable connection means, and the motor also features a second rotor rotatably coupled to the output shaft and a second stator mechanically coupled to the second rotor by the second tiltable connection means. Surfaces of the second rotor and the second stator define a second dynamic air gap within which a magnetic field is generated by electrical actuation of the motor, producing a force between the second rotor and the second stator.

[0051] In some configurations, the first and second rotors are coupled to an output shaft such that, during operation of the motor, the axes of the first and second rotors are oppositely tilted relative to the axis of rotation of the output shaft.

[0052] Preferably, the advancing first dynamic air gap minimum position is rotationally aligned with the advancing second dynamic air gap minimum position relative to the first stator.

[0053] In some embodiments, the first stator is mechanically coupled to the first rotor by a first swing traction joint and the second stator is mechanically coupled to the second rotor by a second swing traction joint, and the respective tilt axes of each rotor advance about the rotational axis of the output shaft during swing of the rotors relative to the stator. For example, the first and second rotors may be axially disposed between the first and second swing traction joints, or the first and second swing traction joints may be disposed between the first and second rotors.

[0054] In some instances where the stator includes stator poles associated with the stator windings, the radial air gap is radially interior to the stator poles. In cases where the stator is mechanically coupled to the rotor by a swinging traction joint, preferably the point of maximum traction engagement and minimum dynamic air gap of the traction joint at any one time during swing is located on opposite sides of the axis of rotation.

[0055] In some other instances where the stator includes stator poles associated with the stator windings, the radial air gap is radially on the anti-drive side of the stator poles. In cases where the stator is mechanically coupled to the rotor by a swing traction joint, preferably the point of maximum traction engagement of the traction joint at any one time during swing is located on the same side of the output shaft as the instantaneous minimum dynamic air gap point.

[0056] In some embodiments, the stator is mechanically coupled to the rotor by a rocking traction interface featuring rotor teeth that mesh with stator teeth. In some cases, the rotor teeth include more teeth than the stator teeth. Preferably, the total number of teeth on the rotor and stator teeth differ by one tooth, such that one rocking motion of the rocking traction interface changes the rotational position of the rotor relative to the stator by one circumferential pitch of a tooth.

[0057] In some instances, the traction joint also features a tapered edge surface of the rotor that is arranged to roll against a tapered stop surface of the stator during rocking. In some cases, the stator has a stator end cap that supports a bearing that supports the output shaft, and the stator end cap features stator teeth. The traction joint may be, for example, radially on the anti-drive side of the dynamic air gap or radially on the drive side of the dynamic air gap.

[0058] In some configurations, the stator is mechanically coupled to the rotor by a rocking traction joint that includes a resilient friction surface that is in rolling engagement with a reaction surface under normal load.

[0059] In some motors, multiple adjacent windings on the stator are capable of being activated simultaneously as a winding group, with the stator featuring multiple such winding groups spaced around the circumference of the stator.

[0060] In some embodiments where the stator is mechanically coupled to the rotor by a rocking traction joint featuring a traction surface of the rotor engaging a stationary traction surface of the stator, the traction surface of the stator defines a stator pitch cone, the stator pitch cone angle being between 4 and 40 degrees. Preferably, the traction surface of the rotor defines a rotor pitch cone, the difference between the rotor pitch cone angle and the stator pitch cone angle being less than 10 degrees, more preferably less than 7.5 degrees, and even more preferably less than 5 degrees.

[0061] In some arrangements, the rotor is disposed within the stator.

[0062] In some configurations, the rotor features radially extending, circumferentially spaced teeth whose distal end faces abut the dynamic air gap. The distal end faces may, for example, face radially outward toward the stator poles or radially inward toward the stator poles. In some cases where the stator features circumferentially spaced poles associated with the stator windings, each of the spaced teeth has a number of axially spaced tooth protrusions, and each stator pole has a number of axially spaced pole protrusions. Preferably, the tooth protrusions and pole protrusions are axially aligned with the minimum dynamic air gap point.

[0063] In some cases, the rotor has multiple laminations of ferromagnetic material adjacent the air gap.

[0064] In some configurations where the stator is mechanically coupled to the rotor by a swinging traction joint, the swinging traction joint is lubricated by an active lubrication system including a pump that causes a flow of lubricant to be directed to the swinging traction joint during operation of the motor. In some examples, the output shaft defines an oiling port positioned to direct a flowable lubricant to the traction joint. The motor may include an oiling rail having at least one nozzle positioned to spray lubricant from the rail to lubricate the traction joint.

[0065] In some examples, the rotor is rotationally coupled to the output shaft by a gimbal that defines two independent tilt axes perpendicular to each other and to the axis of rotation of the output shaft.

[0066] Yet another aspect of the invention features a method of operating an electric motor. The method includes actuating a first coil of a stator disposed adjacent to a rotor and defining a dynamic air gap with an outer circumferential surface of the rotor such that a magnetic coupling between the rotor and the stator is primarily radial, the rotor being coupled to an output shaft of the motor at a tiltable connection means. The method also includes actuating a second coil of the stator, the second coil being circumferentially spaced from the first coil, and thereafter actuating a third coil of the stator, the third coil being circumferentially spaced from both the first and second coils, the second coil being disposed between the first and third coils. Sequential actuation of the first, second, and third coils causes the rotor to oscillate about the output shaft axis, thereby rotating the output shaft.

[0067] In some examples, the rotor is a first rotor, the stator is a first stator, the dynamic air gap is a first dynamic air gap, the tiltable connection means is a first tiltable connection means, and the motor also features a second rotor rotatably coupled to the output shaft and a second stator mechanically coupled to the second rotor by the second tiltable connection means. The method includes sequentially actuating coils of the second stator to oscillate the second rotor about the output shaft axis, the first and second rotors transmitting cumulative torque.

[0068] In some cases, the first and second rotors are coupled to an output shaft such that, during operation of the motor, the axes of the first and second rotors are tilted in opposite directions relative to the axis of rotation of the output shaft.

[0069] In some examples, the second rotor and the second stator collectively define a second dynamic air gap, and during operation of the motor, a first advancing dynamic air gap minimum position is rotationally aligned with a second advancing dynamic air gap minimum position relative to the first stator.

[0070] In some cases, the first stator is mechanically coupled to the first rotor by a first swing traction joint and the second stator is mechanically coupled to the second rotor by a second swing traction joint, and as the rotors swing relative to the stator, the respective tilt axes of each rotor advance about the axis of rotation of the output shaft.

[0071] In some examples, each of the sequentially activated coils of the second stator is activated along with a respective coil of the first stator.

[0072] In some cases, the first, second, and third coils of the first stator and the sequentially activated coils of the second stator form jointly simultaneously activated coil pairs, each pair featuring both a coil of the first stator and a coil of the second stator that is circumferentially aligned with the coil of the first stator.

[0073] In some cases, activating the first coil of the stator includes simultaneously activating multiple circumferentially adjacent windings of the stator as a winding group that does not include the second coil or the third coil.

[0074] In some examples where the stator is mechanically coupled to the rotor by a swinging traction joint, the method also includes directing the flowable lubricant to the swinging traction joint during operation of the motor. Directing the flowable lubricant may include causing the lubricant to flow through an oiling port in the output shaft and / or spraying the lubricant from nozzles in an oiling rail in the motor.

[0075] As used herein, the term "electric motor" refers to electric motors and generators.

[0076] According to another aspect of the invention, an electric motor includes an orbital assembly having a first traction component disposed along a mechanical motion interface and operatively connected to a first magnetic component located along a magnetic motion interface. The motor also has a gimbal assembly including a plurality of gimbal rings connected via bearings about a rotational axis and operatively connecting the orbital assembly to an output shaft disposed along a central rotational axis, thereby providing a rotational degree of freedom. The motor also has a stationary assembly including a second traction component also disposed along the mechanical motion interface and operatively connected to a second magnetic component also disposed along the magnetic motion interface. The mechanical motion and magnetic motion interfaces are between different surfaces.

[0077] At least one magnetic component features a plurality of magnetic poles. An associated circuit is configured to electromagnetically activate the magnetic poles in a predetermined sequence. As a result of the electromagnetic activation, an eccentric magnetic force is generated between the first and second magnetic components, thereby eccentrically translating the track assembly relative to the stationary assembly about a virtual pivot point defined by the gimbal assembly. The compression (attractive force) between the first and second magnetic components is converted to a tangential thrust force through mechanical communication between the first and second traction components and transmitted to the output shaft through the gimbal assembly.

[0078] In some cases, the traction component of the track assembly is directly coupled to its magnetic component. For example, the traction component may feature gears attached directly to the rotor laminations. Or, it may be indirectly coupled to the magnetic component via a support plate. The support plate may provide low mass, structurally rigid, and geometrically consistent alignment between the track magnetic component, its associated traction component, and the gimbal assembly. Such a support plate may be manufactured from structurally suitable materials, such as alloy steel, carbon fiber composite, or aluminum alloy, by conventional techniques. In some applications, it may be structurally advantageous to incorporate the traction component into the support plate as a separate component. The support plate may also be directly coupled to the gimbal assembly to transmit torque while maintaining structural alignment. Although the support plate may include another component that may be operatively coupled to the gimbal ring, in some applications, it may be advantageous to incorporate the gimbal ring directly into the support plate as a separate component.

[0079] The components of the track assembly may be assembled using conventional techniques to achieve the desired structural rigidity and durability, such as fastening, welding, adhesive bonding, and mechanical interference bonding. The support plate may be coupled to the gimbal assembly using similar techniques, or, in the case of the support plate acting as a gimbal ring, the support plate may be operatively coupled to a second gimbal ring via a rotational bearing interface.

[0080] The traction components may be high friction soft materials such as rubber or urethane, rigid friction joints such as gears or traction rails, or may combine elements from multiple structures such as gears connected to a drive rail or rubber O-rings connected to a drive rail. The drive rail may define the travel limits of the orbiting rotor relative to the stator to provide consistent operation. Geared traction components may have an in-turned or circle-like tooth profile, straight or helical cuts, concave, convex, bevel cuts, or any combination thereof. The stator and rotor may each be coupled to a traction component, which may engage along a conical mating surface that rolls upon operation of the motor.

[0081] The motor may include one or more bearings coupling the output shaft and the stator housing. Such bearings may be plain, hydrodynamic, or rolling bearings, which may support radial, axial, or a combination thereof. The shaft bearings may also be multiple radial and thrust bearings supporting a combination of radial and axial loads. Tapered rolling bearings or angular bearings are preferred for automotive applications due to the anticipated shaft loads. The bearings may be permanently lubricated or require active lubrication.

[0082] One or both of the magnetic components may include a solid ferromagnetic material such as iron, iron alloy, iron oxide, alnico or magnetic material, a laminated ferromagnetic material such as laminated electric steel, iron cobalt steel, or amorphous alloy, or a solid composite material such as pressed powder metal core or sintered magnetic composite, or may feature a combination of such materials. The ferromagnetic material of the stator core may have low retentive strength and be considered magnetically soft, such as electric core iron, sintered magnetic composite, or soft magnetic material, or may have high retentive strength and be considered magnetically hard, such as alnico or hard magnetic material. A soft core material may allow efficient and fast sequential energization of the stator poles with relatively low hysteresis losses, while a hard core material may provide fixed positional stability of the rotor when no energization of the poles occurs. These materials may be patterned using conventional methods, such as machining, die stamping, laser cutting, or compression molding, and assembled as desired using conventional methods such as welding, crimping, fastening, or adhesive bonding.

[0083] The rotor core may be a ferromagnetic material arranged to provide a complementary magnetic outer surface that may facilitate magnetic communication with an excited stator. The rotor may be substantially uniform or may have slots to provide magnetic communication that allows for interference with the maximum radius of the rotor and the minimum radius of the stator. Alternatively, the outer surface may be substantially uniform. The surface may also be ground to a taper to provide a constant minimum air gap throughout the height of the rotor core during operation.

[0084] The gimbal assembly preferably provides a low friction torque transfer mechanism between the rotor core and the output shaft. The gimbal assembly may have a gimbal bearing in the form of a single row rolling bearing, a double row single rolling bearing, or a fluid or solid lubricated journal bearing. Double row rolling bearings, such as a single row needle bearing, may be used to even out wear on the bearing surfaces during operation.

[0085] The stator may include a stator core fixed to a stator housing to hold the stator core stationary during operation, a number of stator teeth that form a magnetic flux path with the stator core such that excitation of the poles increases the strength of the magnetic field in the stator core, and a housing traction plate that is coupled to the stator core by a direct mechanical connection or indirectly through the stator housing. The stator teeth may protrude from the stator yoke, or back-iron, thereby forming stator slots. The housing traction plate may also be used to support mechanical alignment between the orbiting rotor and the stator. The stator core may include one continuous material or a series of individual components. Although a continuous material may provide greater dimensional consistency, a series of individual stator poles held in mechanical alignment by the stator housing may allow for efficient manufacturing and assembly.

[0086] The stator may be on the drive side, the anti-drive side, or both the drive side and the anti-drive side. Multiple stator-rotor pole sets may be arranged concentrically with respect to each other so that during operation, forces resulting from electromagnetic excitation of multiple concentric, or nested, rotor poles are transferred to a gimbal assembly.

[0087] The stator poles allow electromagnetic communication between the power electronics and the stator core while providing electrical isolation. The stator poles may include coils of conductive wire, such as insulated or enamel-coated magnet wire, or multiple welded conductive rods, such as insulated copper rods. The stator housing provides structural support to the stator core during operation. The stator housing may be a direct mechanical extension of the stator core or a separate component.

[0088] The motors may be powered by a power electrical assembly controlled using conventional power electrical switches, which may be wired into a parallel drive to balance the relative speed between the two rotors in a dual rotor configuration by using parallel inductive load reactors.

[0089] The magnetic air gap of the motor is not consistent along the circumference of the rotor core. In the motor described below, the core material must maintain a non-zero air gap to prevent catastrophic damage resulting from the "wall" due to the complex three-dimensional orbital motion of the rotor core relative to the stator core. The air gap changes during operation of the motor and the interaction points may vary across the plane of the distance between the stator and rotor. However, a preferred minimum air gap may be, for example, 0.05 to 2.0 millimeters, more preferably 0.5 to 1.5 millimeters, and even more preferably 0.75 to 1 millimeter. It should be understood that the air gap may be filled with a fluid other than air.

[0090] The mechanical contact surfaces of the motor may be passively lubricated using conventional liquid lubricants such as gear oil, semi-solid lubricants such as grease, dry lubricants such as graphite or MoS2, or self-lubricating surfaces such as nylon or oil-impregnated metals.

[0091] Active lubrication may achieve higher power density by providing a medium that absorbs heat from electrical coils and mechanical contact surfaces. Active lubrication systems may be used to provide intermittent or continuous lubrication of surfaces by circulating a fluid lubricant through the motor. For example, a fluid pump may mechanically pump the fluid lubricant from the fluid pump through a fluid line to the motor where the lubricant may be discharged through a directional nozzle to provide active lubrication and / or fluid cooling to specific locations within the motor. The fluid may then be collected by gravity in an oil sump at the base of the motor and returned to the pump through a return fluid line for recirculation. In this manner, the motor rotor assembly may be lubricated and operated in a non-water-immersed environment. In addition, a portion of the lubricant may pass through a heat exchanger to add or remove heat from the lubricant to adjust the temperature and / or viscosity of the lubricant to suit the specific needs of each application.

[0092] The lubricant may be any conventional fluid used to lubricate mechanical contact surfaces. At operating conditions, the lubricant may be a low viscosity fluid in the range of 1-500 centipoise, such as motor oil, a medium viscosity fluid in the range of 500-2,000 centipoise, such as gear oil, or a high viscosity semi-fluid in the range of over 2,000 centipoise, such as grease. The lubricant may also be an aqueous fluid, which may or may not contain a lubricating material, such as sulfate-functionalized graphene.

[0093] The motor may include a collection pan that collects lubricant released within the motor assembly by gravity and directs it towards the return fluid line.

[0094] The lubrication system may include a fluid pump that provides a pressure gradient for the lubricant, causing it to circulate in the fluid system. Such a pump may be a fixed displacement pump, such as a rotary pump, or a variable displacement pump, such as a gear or piston pump. The pump may be operatively connected to a mechanical or electrical power source and may operate continuously or intermittently during operation of the motor. A wet sump active lubrication system may include one fluid pump that is operatively connected to a collection pan to circulate oil through the fluid lines in the system to be lubricated. In this case, the majority of the oil supply is in the collection pan. Alternatively, multiple fluid pumps may operate in a dry sump active lubrication configuration, where fluid from the collection pan is continuously pumped into a holding tank, preferably with a high height in relation to the cross-sectional area, and a second pump may pump fluid back to the motor at another controlled flow rate to complete the circulation of the lubricant.

[0095] The lubrication system may have one or more directional nozzles that direct lubricant to specific locations within the motor assembly, such as the traction plates, gimbal bearings, and stator poles.

[0096] The output shaft may provide input to additional gear trains, such as planetary gears.

[0097] The various embodiments of the invention disclosed herein can provide particularly high torque density and can be used to provide essentially smooth output shaft power for vehicle propulsion as well as in stationary systems. The design concept makes better use of normal, axial, and tangential forces to generate shaft power without some of the traditional trade-offs of utilizing one at the expense of the others.

[0098] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0099] Description of the drawings [Figure 1] FIG. 1 is a perspective view of a first example of an electric motor. [Diagram 2] FIG. 2 is a side view of the motor of FIG. [Diagram 3] FIG. 2 is a partial cross-sectional perspective view of the motor of FIG. 1 with non-rotating components cut away. [Figure 4] FIG. 4 is a side view of the cross section of FIG. 3, with the rotor tilted in a first direction. [Diagram 5] A second, oppositely tilted rotor is shown. [Figure 6] FIG. 2 is a schematic diagram of the operation of a wobbling rotor motor. [Figure 7] FIG. 2 is a cross-sectional view of the motor of FIG. [Figure 8] FIG. 1 is a schematic diagram of a motor controller including power switching. [Figure 9] FIG. 2 is a perspective view of the motor of FIG. 1 with the stator end cap removed. [Figure 10] FIG. [Figure 11A] The rotational advance of the rotor during one complete wobble cycle is shown continuously. [Figure 11B] The rotational advance of the rotor during one complete wobble cycle is shown continuously. [Figure 11C] The rotational advance of the rotor during one complete wobble cycle is shown continuously. [Figure 12] FIG. 13 is a cross-sectional view through the gimbal assembly of the alternative motor. [Figure 13] 12A is a cross-sectional view taken partially along line 12A-12A and partially along line 12B-12B of FIG. 12, showing the lubrication and cooling system. [Figure 14] FIG. 14 is an enlarged view of region 14 in FIG. [Figure 15] FIG. 2 is a partial cross-sectional perspective view of the motor of FIG. 1 including an oiling rail. [Figure 16] 3 shows a third example of another electric motor with a nominal stator angle of 30 degrees. [Figure 17] 4 shows a fourth example of another electric motor with a nominal stator angle of 20 degrees. [Figure 18] 1 shows an electric motor having a non-drive side traction joint. [Figure 19] 1 shows an electric motor having a non-drive side traction joint. [Figure 20] 1 shows an electric motor with a drive side traction joint. [Figure 21] 1 shows an electric motor with a drive side traction joint. [Figure 22] An outer rotor type gear stacked motor is shown. [Figure 23] An outer rotor type gear stacked motor is shown. [Figure 24] An inner rotor type gear stacked motor is shown. [Diagram 25] FIG. 25 is a top view of the motor of FIG. 24 with the housing end plates removed. [Figure 26] An outer rotor type segment gear laminated motor is shown. [Figure 27] Shows three-dimensional relative rotor / stator air gap surface motion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0100] Like reference symbols in the various drawings indicate like elements.

[0101] Detailed Description Referring initially to Figures 1 and 2, an electric motor 10 has an output shaft 12 rotatable relative to a motor housing 14, which is considered within this description as a reference for rotation and other motion of the motor components. In use, the output shaft 12 will be connected to another object to which the motor 12 applies a rotational force when electrically activated by appropriate power and signals. As can be seen in Figure 2, the output shaft 12 extends through the motor and is exposed at both ends, meaning that rotational force can be transmitted at both ends of the motor. The housing 14 is shown as being rotationally symmetric about the axis of rotation 16 of the output shaft 12, but may be of any geometry and will generally include means for securing the housing to another structure to prevent rotation of the housing during operation of the motor.

[0102] 3, motor 10 includes two rotors 18a and 18b, each associated with a stator. Rotor 18a is disposed within stator 20a, and rotor 18b is disposed within stator 20b. As will be explained in more detail below, electrical activity within stator 20a is appropriately controlled to drive the motion of rotor 18a, and similar electrical activity within stator 20b drives the motion of rotor 18b. Both rotors 18a and 18b are rotatably coupled to output shaft 12, such that any rotational components of the resulting rotor motion are transferred to output shaft 12, thereby rotating the output shaft. For ease of illustration, the bearings supporting the output shaft at each end of the motor have been omitted.

[0103] However, unlike conventional rotary electric motors, the motion of rotors 18a and 18b is not purely rotational. As described below, each rotor wobbles with respect to the stator, and this motion can be described as wobbling, in which the rotor rolls against the surface of the stator while the tilt axis of the rotor advances around the output shaft, sweeping a generally conical surface. The effective air gap between each rotor and its associated stator is generally radial, in that it is between the outer periphery of the rotor and the adjacent inner periphery of the stator, as in conventional radial gap motors. However, due to the rotor wobbling, the air gap in this motor is dynamic, i.e. it changes at any particular point around the rotor during the wobble cycle, as described below.

[0104] As can be seen in FIG. 3, rotor 18a carries teeth on its upper surface that engage rotor teeth 22 on the stationary end cap 24 of associated stator 20a. Rotor 18b has similar teeth (not visible in this view) that engage with teeth on the end cap of stator 20b. In this example, the meshing teeth form a rocking traction joint where the rocking rotor rocks on the stator and the engagement point advances around the rotor in synchronism with the advancement of the rotor tilt axis. This is called a traction joint because it serves to prevent rotational slip of the rotor relative to the stator. The rocking motion of the stator distributes the traction load to multiple teeth at once, with most of the teeth of the traction joint carrying the load at any one time. In some of the example figures, at least one third of the teeth are carrying torque at any one time. With circular teeth, half of the teeth may be loaded at any one time. In implementations that include teeth along the traction joint, the teeth mesh primarily axially; that is, the interface transfers axial loads or loads perpendicular to the magnetic air gap. Throughout this disclosure, examples of teeth meshing along the traction joint can be considered to mesh axially. Other examples of traction joints do not feature meshing teeth. In some implementations, the contact along such traction joints is primarily axial. In one alternative, the traction joint provides traction through metal-metal friction between rigid metal surfaces (such as occurs between a railroad wheel and a rail). The rail may be angled to increase the relative pressure, coated with a solid high friction material, such as elastomeric rubber or other elastomer, or utilize a friction fluid as used in some automotive continuously variable transmissions. The rail may be mechanically loaded only by the rotor, or may include a second mechanical preload. For the second mechanical preload, the delta angle between the stator and rotor is preferably greater than 10 degrees, otherwise the preload timing must be controlled and driven independently of the stator coils.

[0105] 4 and 5, each stator 20a and 20b features individually excitable windings or coils 26 associated with a ferromagnetic stator core 28. The core 28 may have, for example, a number of stator projections that may project from a stator yoke or back-iron, thereby creating the stator slots and poles. The stator core may be one continuous piece of material or a combination of individual components assembled into the motor. A continuous piece of material may provide greater dimensional consistency, while individual stator poles held in mechanical alignment by the stator housing may allow for efficient manufacturing and assembly. The termination of the stator projections may be diffuse, straight, or under-connected with respect to the stator projections and back-iron or yoke. In this example, the stator projections are straight and have a constant cross-sectional area from the yoke to its distal end in the air gap.

[0106] The outer circumferential surfaces of the rotors in this example are ground conically, while the inner surfaces of the rotors define a generally cylindrical surface. In FIG. 4, the upper rotor 18a is shown tilted to the left with respect to the output shaft 12, while the lower rotor 18b is tilted in the opposite direction. In this position, the air gap 28 between the rotor and stator face has a generally constant radial width along the axial length of the gap on the left side of each rotor in the figure, while on the right side of each rotor, the air gap varies along its length, decreasing toward the space between the rotors. The tilt axis 30 of the rotor 18a makes an angle of 4.34 degrees with respect to the stationary rotation axis 32 of the output shaft 12. As the rotor 18a wobbles and tilts progressively toward the different coils 26 of the stator 20a, its tilt axis 30 sweeps out a conical surface having an apex at A, the height A of the gimbal connection means 34 between the output shaft and the rotor 18a along the output shaft axis. In the tilted position shown, the air gap reluctance between the rotor and stator is lowest in the left coil 26 and highest in the right coil. The curved arrow shown across the left gap simply indicates that the coil slightly ahead of that position around the stator is energized to produce flux across the gap, while the coil on the opposite side of the stator is not energized. As will be explained further below, this creates a compression wave, i.e., a forward radial compression force, between the stator and rotor, causing the rotor to wobble. In the tilted position shown in FIG. 5, half way through the wobble cycle from the position shown in FIG. 4, the air gap reluctance between the rotor and stator is lowest in the right coil 26 and highest in the left coil. Rotor tilt is limited by rolling contact between the tapered stop surface 36 of each stator end cap and the tapered edge surface 38 of the adjacent rotor.

[0107] The relationship between the advancing compression wave and rotor wobble can be explained with respect to the simple model shown in FIG. 6. A flat disk 40 is attached to a rigid shaft 42, one end of which rests on a plane at point B. The disk and shaft are supported on the plane at points B and C by the end of the shaft and the edge of the disk. The disk can be made to roll on the plane by pushing down on the edge of the disk near contact point C, such as D. The same effect can be produced by pulling down the edge of the disk at D by the attractive force between the edge of the disk and the plane. Once the disk begins to roll, the rolling can be continued indefinitely by continuously pulling the disk towards the plane, always at a point just beyond the instantaneous contact point C, while the shaft 42 at contact point B remains stationary. The resulting rolling or wobbling motion would be, for example, the motion experienced by a child's toy top after it has stopped spinning upright. The edge of the disk rolls on the plane, not sliding. Similarly, the excitation of each coil of the stator generates a local attractive force that pulls on the rotor. By continuously energizing the coils leading (preferably 15-60 degrees beyond) the point of minimum radial air gap, the rotor can be made to oscillate like a tilted top, rolling against the resting surfaces of the stator end caps. However, an important difference between the operation of the simple model of Figure 6 and that of the motors of Figures 4 and 5 is that in the simple model, the compression or attraction occurs across the gap between the edge of the disk and the flat surface, bounded by the rolling surface itself. As the disk rolls around point B, the distance between the rolling edge of the disk and the flat surface changes by the distance at which the attraction between the edge of the disk and the flat surface comes into play. In this model, these are the same.

[0108] On the other hand, in the motor of Figures 4 and 5, the distance the rolling surface of the rotor travels during wobble is essentially axial, the maximum space between surfaces 36 and 38, which occurs when the effective air gap width is smallest, e.g., on the right side of Figure 5, and the gap in which the attractive compression forces operate (the magnetic air gap) is essentially radial. This causes the wobble to produce a much larger change in displacement at the rolling interface than the effective magnetic air gap. In this particular example, this allows the rotor to also be tilted, so that the rolling contact point is always on the opposite side of the rotor to the compression wave. By configuring the motor so that the rolling contact point and the compression wave are generally on opposite sides of the output shaft axis, smaller packaging and higher switching frequencies can be achieved due to the slower relative traction joint pitch speed. Conversely, by configuring the motor so that the rolling contact point and the compression wave advance generally on the same side of the output shaft axis (as in the example of the motor of Figures 20 and 21), a shorter mechanical load path is provided, which is advantageous in that it does not require the use of torsional force components through the gimbal.

[0109] Referring again to Figures 4 and 5, the axial and radial inertial forces caused by the mass acceleration of one of the rotors are balanced by those of the other rotor by the opposing oscillation of the two rotors. The oscillation is effectively symmetrical with respect to one another about a transverse plane that bisects the motor between the rotors. The forward magnetic engagement points of the two rotors are practically within 10 degrees of each other. Although generally balanced, there will always be a slight lag in one rotor compared to the other, and the power electronics will always accelerate the one moving slightly slower. Tolerance stack-ups in the gimbals, etc. may result in up to 3 degrees of slippage.

[0110] The gimbals 34a and 34b, which connect the rotors 18a and 18b, respectively, to the output shaft 12, are typically cross-axis gimbal assemblies having two rings, which transmit torque about the output shaft axis 32 while allowing 360 degrees of free tilt during rocking. To provide the necessary degrees of freedom, the output shaft is fixed to the inner ring of the gimbal by an inner cross pin (not visible in these figures), which is fixed to the rotor by a cross pin at a 90 degree angle to the inner pin. The fixed components are free to rotate about the pins on lubricated bearing surfaces.

[0111] 7, in this example, the stator end cap tapered stop surface 36 defines a stator cone angle β of 25.00 degrees relative to a normal to the output shaft axis, and the rotor tapered edge surface 38 defines a rotor cone angle γ of 22.83 degrees relative to a normal to the rotor tilt axis. The rotor tilt during operation is therefore + / - 2.17 degrees, which is just enough to allow indexing of tooth engagement between the rotor and stator during rocking. The tooth engagement, which is part of the traction interface between the rotor and stator, is characterized by rotor teeth 44 meshing with stator teeth 46. To effect rotational advancement of the rotor (and therefore the output shaft) relative to the stator, the number of teeth on the rotor's periphery is different from the number of teeth on the stator's periphery, so that as the rotor rolls around the stator during its rocking, the rotational indexing of the rotor is equal to the tooth pitch multiplied by the difference in the number of teeth. In this example, the stator end caps each have 59 teeth and the rotors each have 60 teeth, i.e., one more than the mating stator end cap. In other words, sequentially energizing the stator poles and creating a compression wave that completes one full rotation around the motor results in one complete oscillation cycle of the rotor, advancing the output shaft an amount of rotation equal to one tooth, or 6 degrees in this example.

[0112] The motor controller power electronics can be configured to sequentially energize the stator coils as in a reluctance motor. Figure 8 shows a simplified diagram of a suitable motor controller, with the processor 48 controlling the switches 50 to sequentially energize the stator poles 26a, 26b, and 26c. Referring also to Figure 9, such sequential activation causes the oscillation to advance in a clockwise direction about the rotor axis as the tilt axis looks down on the motor. Reversing the sequence causes the oscillation to advance in the opposite direction, meaning that the motor can be driven at full load in either direction. Although only three switches are shown in Figure 8, it should be understood that the motor controller would have one switch for each stator pole, i.e. 24 switches to energize the 24 coils shown in the stator arrangement of Figure 9. Referring again to Figure 5, the oscillation of the two rotors is symmetrical, so that the rotationally aligned pole pairs of the two stators can be excited together. In other words, the pole 26 shown on the leftmost side of the upper stator will be excited simultaneously and for the same duration as the pole 26 shown on the leftmost side of the lower stator. The rotationally aligned pole pairs of the two stators can therefore be excited in parallel through the same switch. For example, a motor controller for the twin stator motor shown in FIG. 9 would require a total of 24 switches. Alternatively, adjacent pole pairs may be wired in series through a common switch, but in such a case, the instantaneous faster of the two moving rotors will generate a slightly larger back EMF and instantaneously draw more relative power compared to the slower pole, thereby further accelerating and separating the relative speeds. In contrast, parallel wiring of adjacent poles of separate rotors may provide a negative feedback mechanism due to the parallel oscillating loads. In that sense, it can be considered self-balancing and can produce a smoother output torque with less potential for vibration.

[0113] With no current flowing through any of the motor stator poles, there is theoretically no internal motor force to hold the rotor in place. The stator laminations or core can be made from a ferromagnetic material with an appropriate degree of remanence so that the rotor remains most attracted to the most recently energized pole.

[0114] 10, the rotor's tapered edge surface 38 defines a frusto-conical surface that rolls around the mating tapered surface of the stator end cap during rotor rocking. In this example, the contact surface is on the non-drive side of the tooth, but in other examples it could be located on the drive side, or in some cases the teeth themselves could be designed for "zero gap" rolling such that the mating tooth profile itself limits rotor tilt. The mating teeth serve to react to torque transmitted from the rotor to the output shaft and could be of any suitable profile.

[0115] Referring again to FIG. 7, as previously mentioned, it is the tapered edge surface 38 that defines the rotor cone angle γ with an apex on the output shaft axis 32 at a height corresponding to the tilt center of the gimbal on which the rotor pivots. This apex E is referred to as the rotor focal point. The motor 10 has an operating radius Rw as the radial distance between the rotor axis 32 and the nominal radial location of the air gap 29 of about 75 mm, which is essentially half the inner diameter of the stator poles. The nominal overall diameter of the illustrated motor is 25 cm. The mirror plane 31 bisects the motor midway between the two rotors and is equally spaced a distance of about 19 mm from each focal point E. The two rotor / gimbal assemblies are essentially symmetrical to each other with respect to the mirror plane. The rotor focal point E can be identified by establishing the center of the rotor's wobbling motion on the central axis of the rotor gimbal assembly. Geometrically, the focal points are at the apexes of both the stator and rotor cones. These cone angles are used to derive many of the physical characteristics of the motor's geometry, including the tooth size, the angular distance the poles travel, the radial distance the poles travel, the wobble motion, and the angle of operation. These geometric relationships, as well as the gear ratio, are important in determining the overall geometry of the motor.

[0116] The dynamic nature of the air gap, as seen in this figure by comparing the air gap on the left side of the figure with the air gap on the right side of the figure, resulting from each rotor oscillation. As previously mentioned, the air gap changes dynamically during operation of the motor as the rotor oscillates relative to the stator about the central axis. During operation, the air gap at its minimum, i.e. when the rotor is in its closed position, is the point where maximum magnetic alignment between the stator and rotor occurs. The air gap at this minimum point may nominally be 0.25 mm laterally, but may vary across the intersecting plane. At this minimum air gap position, the teeth of the rotor at that circumferential position do not engage those of the stator, but are instead shifting. At that moment, the teeth 180 degrees away from that circumferential position are engaged and the air gap is at its maximum position. This maximum, i.e. when the rotor is in its open position, is the point where the magnetic alignment of the stator and rotor is at a minimum. Again, at this maximum air gap point, the teeth engage the traction interface. The air gap at this maximum point may be 6.86 mm center-to-center, of which 1.0 mm is the radial separation between the rotor and stator, and 6.60 mm is the longitudinal misalignment. For the embodiment described below in which the rotor laminations have teeth that face the air gap, these rotor lamination teeth are preferably aligned with the stator poles at the minimum air gap location, and are most misaligned with the poles at the maximum air gap location.

[0117] 11A-C show the rotor / shaft rotation resulting from one complete wobble cycle in succession. Starting with FIG. 11A, an index mark 60 is shown on the rotor face aligned with the cut edge of the stator end cap. The stator coils are activated in a sequence such that the compression wave advances 180 degrees around the stator and the rotor axis tilts through a similar 180 degree wobble or half a wobble cycle, after which the index mark in FIG. 11B indicates that the rotor has essentially rotated an amount equal to half a tooth pitch, or about 3 degrees in this case. After all of the stator coils have been activated to create a full 360 degree compression wave and a full rotor wobble is completed (FIG. 11C), the rotor and output shaft have rotated a total of one tooth pitch, or about 6 degrees. One complete wobble will move the rotor, for example, from the position shown in FIG. 4 to the position shown in FIG. 5 and back to the position shown in FIG. 4.

[0118] Electric motors can generate significant heat during operation and require cooling. Additionally, moving mechanical components and contacts can benefit from active lubrication, especially during operation at high frequencies. For some applications, separate fluids can be used for coolant and lubrication, e.g., water and oil, respectively. In other cases, a fluid, such as oil, can be used for both coolant and lubrication. In the following description, fluid can refer to coolant, lubrication, or both, as appropriate.

[0119] Referring now to Figure 12, the motor 14a has two rotors spaced apart along an output shaft, each of which is gimbal mounted. The cross-sectional view of Figure 12 is through one of the gimbal assemblies and shows a gimbal spindle 106 mounted on the shaft 12a. The spindle 106 defines an inner axle to which an inner gimbal ring 110 is mounted and pivots between two inner gimbal bearings 112a fixed in the inner gimbal ring 110. The inner gimbal ring 110 itself defines an outer axle perpendicular to the inner axle to which an outer gimbal ring 113 is mounted and pivots in two outer gimbal bearings 112b fixed in the outer gimbal ring 113. The gimbal bearings 112a, 112b are secured in holes in the spindle ring by locking rings and may have, for example, bronze, babbitt metal or other sliding wear surfaces, or roller elements.

[0120] Referring also to FIG. 13, the motor 10a is cooled and lubricated by fluid delivered into the motor through bores 102 in the motor output shaft 12a. In this view, a cross section through the left rotor is taken along line 12A-12A in FIG. 12, and a cross section of the right rotor is taken along line 12B-12B in FIG. 12, which is 90 degrees relative to that of the left rotor, to show both the inner and outer gimbal bearings 112a, 112b. Due to the relatively high frequency operation of the bearings in the gimbal assembly, active lubrication of the gimbal bearings can be achieved by forming cross bores in the output shaft and supplying fluid to these bearings via cross bore passages 104. Here, the inner ring 110 of the gimbal assembly can be supplied with fluid directly by orifices 108 through the gimbal spindle 106, while the outer ring 113 of the gimbal assembly can be supplied with fluid from orifices 114 through the outer gimbal bearing of the inner gimbal ring. The orifices may be of the metered type to prevent pooling of fluid which would cause losses at high speeds. Apertures 116 through the gimbal bearings allow radial flow out of the gimbal towards the stator windings. As shown in FIG. 14, a metered orifice plug 118 may be pivoted at the drive end of the radial passages 108 in the inner gimbal ring to direct a portion of the flow axially along a cross path 120 to the gear interface surface 122 and shaft bearing 124. A similar plug (not shown) may be provided at the output end of the channels 114 (FIG. 13) in the outer gimbal ring. Alternatively or in addition, grooves 124 may allow fluid to be delivered to the gear interface surface and bearings directly from the output shaft. The shaft bearing 125 may be sealed on its non-drive side or may allow flow to pass through the bearing and back to the sump.

[0121] 13, all of the lubricant / coolant fluid channeled through the output shaft 12a eventually drains into a reservoir 126, which opens onto the underside of the motor and may be structurally part of the stator housing. A pump 128 draws fluid 130 from the reservoir and delivers a continuous flow of fluid under pressure to the output shaft bore 102.

[0122] Referring now to FIG. 15, motor 10b has two compressed oiling / cooling rails 132 that are attached to the stator end plates and define a series of nozzles 134 that are directed toward the gear interface to continuously provide a mist or flow of fluid to lubricate and / or cool the traction control surfaces. The rails are fed by a pump (not shown) and the fluid is recirculated. The gear interface that rolls between the rotor and stator can be adjusted for different speeds, torques, and packaging constraints. Motor 10b of FIG. 16 is similar to motor 10 of FIG. 4, for example, but has higher stator and rotor cone angles of 30 and 28 degrees, respectively. The stator and rotor also have fewer teeth, 59 and 60, respectively, in this example, resulting in a lower electrical cycling frequency for a given output speed. The higher cone angle also reduces the dynamic load on the gimbal bearings at a given output speed. In contrast, the stator and rotor cone angles of motor 10c of FIG. 17 are 20 and 18 degrees, respectively, lower than motor 10 of FIG. 4. This configuration is particularly suitable for low RPM applications. The overall length of the resulting stator assembly is also reduced as a result. The rotor switching frequency and tilt envelope during operation depend on the number of teeth and the cone angle.

[0123] The relative locations of the rolling traction joint and the magnetic interface may vary. In the figures above, the traction joint is on the drive side of the magnetic interface in the direction of rotation and essentially on the non-drive side in the axial direction. Figures 18 and 19 show a motor 10d in which the traction joint 136 is radially on the non-drive side of the magnetic interface 138 and axially positioned on the non-drive side of the stator poles. The forward engagement point of the traction joint is also aligned with the forward minimum air gap location, so that the load path (between the torque input and torque output on the rotor) is advantageously short and does not cross the rotor. This allows the rotor to be designed with thinner wall thickness and lighter material, which may be more tolerant of deformation during heavy loads. Additionally, this design may result in a larger gear contact area, which results in lower gear pressure for a given electrical activation frequency, at the expense of a higher gear pitch speed.

[0124] 20 and 21 show a motor 10e with a stator traction surface on the axial drive side of the motor, on either side of a traction plate 140 fixed at its edge to the stator housing. This design allows for ease of construction and processing of the stator end plate. The traction plate may be formed from sintered steel or as a forging. The forward engagement points of the traction joints of both rotors are rotationally aligned so that any axial component of the load applied to the traction plate by one rotor is balanced with a similar load from the other rotor. This design may be particularly suitable for high torque operation with short load paths and low pitch speeds, and may reduce mechanical redundancy resulting from mounting two separate stator traction plates.

[0125] 22 and 23, motor 10f is both an outer rotor motor and a gear stacked motor. By outer rotor motor, we mean that the radial air gap between each stator-rotor pair is at the radially outer surface of the stator poles. Each rotor 200 is cup-shaped and extends around a corresponding stator 202, which is press-fit into an annular boss 204 of a corresponding clamshell housing cup 206. Each housing boss 204 carries stator teeth 46, which mesh with rotor teeth 44. Each rotor skirt carries a series of teeth 204, which extend radially inwardly towards the stator poles 208, defining the effective air gap 29. Configuring the rotor effective gap surface in this manner can provide several advantages. It may lower the maximum inductance of the magnetic circuit (when the active stator poles are aligned with adjacent rotor teeth), but it also lowers the minimum inductance (when the stator poles 208 are located between adjacent rotor teeth 204). Since the available work available from this motor varies with the difference between the maximum and minimum inductance, removing the ferromagnetic material between the rotor teeth may not significantly reduce the work available from the change in inductance, and it also significantly increases the surface area available for the flux path in gap 29, as well as providing weight savings.

[0126] Motor 10g of FIG. 24 also has gear lamination rotors 220a and 220b, but with an inner rotor configuration similar to that of motor 10 of FIG. 7. In this case, rotor teeth 204 face radially outwardly and define an air gap 29 with the inner surface of the stator. As shown in FIG. 25, the number of rotor lamination teeth 204 is the same as the number of rotor teeth 44, which is one more than the number of stator poles 222. In this example, there are 60 stator poles and 61 lamination teeth, which can be evenly divided into 2, 3, 4, 5, or even 6 poles.

[0127] In any of the motors described above, adjacent stator pole groups can be operated together and with the same magnetic orientation during operation of the motor. For example, in motor 10g shown in FIG. 25, the windings around each of poles 220a, 220b, and 220c can form one winding group 224 with all windings in the same direction, and the windings around each of poles 222d, 222e, and 222f can collectively form a second winding group 226. In operation, all of winding group 224 can be wired in parallel to one electrical switch, and all of winding group 226 can be wired in parallel to another electrical switch, so that pole groups 224 operate collectively and pole groups 226 operate collectively. The minimum inductance can also be lowered and the available work increased by operating adjacent poles simultaneously. Instead of surrounding each pole of a pole group with its own coil, a single coil can be wound around all of the poles of a group. Of course, when multiple stator poles are coupled together as an operating unit, the total number of stator poles should be an integer multiple of the number of poles in each group.

[0128] The maximum change in inductance during the motor's operating cycle can also be achieved by other structural modifications that further exploit the effective relative movement of the gap structure in the axial direction. Motor 10h of FIG. 26 is similar to motor 10f of FIG. 22, except that each stator pole 228 is subdivided to form three pole lobes 230 that are axially spaced apart and connected by a common back 232. Similarly, each rotor tooth 234 is subdivided to form three tooth lobes 236 that are axially spaced apart. At the minimum gap position (left side of the figure), the pole lobes are axially aligned with the tooth lobes. At the maximum gap position (right side of the figure), the tooth lobes are generally in maximum misalignment with the pole lobes, which greatly reduces the inductance. This example has three tooth lobes and three pole lobes, with the axial spaces between the tooth lobes and between the pole lobes having essentially the same axial dimensions as the central tooth lobe and central pole lobe, although other examples having two or four or more lobes on each rotor tooth and each pole lobe are envisioned. Preferably, the number of lobes on each pole is equal to the number of lobes on each stacked tooth.

[0129] The split pole / tooth configuration of FIG. 26 helps take advantage of the fact that in a wobbling rotor motor, the distance that the rotor structure in contact with the magnetic gap moves relative to the stator structure in contact with the magnetic cap is greater than just the radial displacement caused by the wobble. With reference to FIG. 27, point "F" represents the reference point of the rotor tooth 204 at the rotor's minimum gap position, and point "G" represents the same point of the rotor tooth at the rotor's next maximum gap position (i.e., after 1 / 2 wobble cycle). The length of line segment FG represents the total distance traveled during a half cycle, which is a compilation of the axial displacement 240, radial displacement 242, and tangential displacement 244. The axial subdivision of the rotor teeth and poles helps take advantage of the axial displacement 240 of the rotor teeth during wobble.

[0130] Any of the motors described above can be controlled to generate electrical energy from kinetic energy (e.g. to regeneratively brake the motor). This may be achieved by alternating the timing of the compression wave so that the stator current pulses at (or slightly delayed from) the point of minimum air gap to generate a forward EMF during expansion. In this way, a current can be generated and directed to be stored in an associated battery while a retarding torque is applied to the rotor to slow the motor down, but the motor cannot be mechanically backdriven by the torque applied to the output shaft.

[0131] Ferromagnetic lubricants such as magnetic fluids that may produce ferromagnetic compounds, ferromagnetic surface coatings such as cobalt plating, or surface treatments such as boriding may be used to reduce rolling friction and increase surface hardness. Hard ferromagnetic coatings may also support low surface roughness, mechanical polishing, and lower relatively high friction operation. These materials may be coated or added to the system using conventional methods.

[0132] Additional technical details of the motor design are described in pending patent application Ser. No. 15 / 549,659, entitled "High Torque Density Electric Motor and / or Generator," filed Aug. 8, 2017, the contents of which are incorporated by reference herein as if set forth in full.

[0133] While certain examples have been described for illustrative purposes, the above description is not intended to limit the scope of the invention as defined by the appended claims. There are other examples and modifications, both present and future, that are within the scope of the following claims.

Claims

1. an output shaft defining an axis of rotation; a first wobbling rotor coupled to the output shaft at a first tiltable connection; a first stator mechanically coupled to the first wobbling rotor by a first wobbling traction joint and disposed adjacent to the first wobbling rotor to define a first dynamic air gap, the first dynamic air gap being bounded by a first outer circumferential surface of the first wobbling rotor such that a magnetic coupling between the first wobbling rotor and the first stator is primarily radial; a second wobbling rotor coupled to the output shaft by a second tiltable connection; a second stator mechanically coupled to the second wobbling rotor by a second wobbling traction joint and disposed adjacent to the second wobbling rotor to define a second dynamic air gap, the second dynamic air gap being bounded by a second outer circumferential surface of the second wobbling rotor such that a magnetic coupling between the second wobbling rotor and the second stator is primarily radial; Equipped with the first stator includes a first plurality of windings, each winding configured to generate a first magnetic field to draw a respective side of the first wobble rotor toward the first stator and to cause the first wobble rotor to wobble relative to the first stator about an axis of rotation of the output shaft and to progressively tilt the first tiltable connection in response to sequential activation of the first plurality of windings; the second stator includes a second plurality of windings, each winding configured to generate a second magnetic field to draw a respective side of the second wobble rotor toward the second stator and to oscillate the second wobble rotor relative to the second stator about an axis of rotation of the output shaft and progressively tilt the second tiltable connection in response to sequential activation of the second plurality of windings; the sequential activation of the first plurality of windings of the first stator and the sequential activation of the second plurality of windings of the second stator transmit a cumulative torque to the first wobble rotor and the second wobble rotor to rotate the output shaft; an electric motor, the first point of engagement of the first swing traction joint being aligned with a first position of a minimum point of the first dynamic air gap;

2. During the oscillation of the first oscillating rotor with respect to the first stator, a first tilt axis of the first oscillating rotor advances around a rotation axis of the output shaft; the first rocking traction interface comprises a first set of rotor teeth configured to axially mesh with a first set of stator teeth at a first point of engagement; during the oscillation of the second wobble rotor relative to the second stator, a second tilt axis of the second wobble rotor advances about the axis of rotation of the output shaft; 2. The electric motor of claim 1, wherein the second rocking traction interface comprises a second set of rotor teeth configured to axially mesh with a second set of stator teeth at a second point of engagement.

3. 3. The electric motor of claim 2, wherein the output shaft defines an oiling port positioned to introduce a flowable lubricant to at least one of the first oscillating traction joint or the second oscillating traction joint during operation of the motor.

4. 3. The electric motor of claim 2, further comprising an active lubrication system comprising a pump such that a flow of lubricant is directed to at least one of the first oscillating traction joint or the second oscillating traction joint during operation of the motor.

5. the first oscillating traction joint and the first dynamic air gap are arranged in a first plane including an axis of rotation of the output shaft such that the first oscillating traction joint is inclined with respect to a stator surface of the first stator that defines a boundary of the first dynamic air gap; 3. The electric motor of claim 2, wherein the second oscillating traction joint and the second dynamic air gap are arranged in a second plane that includes an axis of rotation of the output shaft such that the second oscillating traction joint is inclined with respect to a stator surface of the second stator that defines a boundary of the second dynamic air gap.

6. the first set of rotor teeth comprises more teeth than the first set of stator teeth; or 3. The electric motor of claim 2, wherein there is a difference between a total number of teeth in the first set of rotor teeth and a total number of teeth in the first set of stator teeth of one tooth such that a single swing of the first swing traction joint changes the rotational position of the first swing rotor relative to the first stator by a circumferential pitch of one tooth.

7. 3. The electric motor of claim 2, wherein the first and second wobble rotors are coupled to the output shaft such that during operation of the motor, the first tilt axis of the first wobble rotor and the second tilt axis of the second wobble rotor are oppositely tilted with respect to an axis of rotation of the output shaft.

8. 3. The electric motor of claim 2, wherein a first advancing point of engagement of said first swinging traction joint is rotationally aligned with a second advancing point of engagement of said second swinging traction joint during operation of the motor.

9. the first swaying rotor and the second swaying rotor are axially disposed between the first swaying traction joint and the second swaying traction joint, or The electric motor of claim 2 , wherein the first and second swing traction joints are disposed between the first and second swing rotors.

10. 3. The electric motor of claim 2, wherein the first traction interface further comprises a tapered edge surface of the first wobbling rotor arranged to roll against a tapered stop surface of the first stator during wobble.

11. 3. The electric motor of claim 2, wherein the first wobbling rotor comprises radially extending, circumferentially spaced teeth having distal end faces that border the first dynamic air gap, and the first stator comprises circumferentially spaced poles associated with stator windings.

12. 3. The electric motor of claim 2, wherein each of the first and second wobble rotors is rotationally coupled to the output shaft by a respective gimbal.

13. The electric motor of claim 2 , wherein the first wobbling rotor is disposed within the first stator and the second wobbling rotor is disposed within the second stator.

14. The first plurality of windings of the first wobble rotor include: a first coil disposed adjacent the first wobbling rotor to define the first dynamic air gap; a second coil circumferentially spaced from the first coil; and a third coil circumferentially spaced from the first coil and the second coil, the second coil being disposed between the first coil and the third coil; and Equipped with The electric motor of claim 2 , wherein the sequential activation of the first plurality of windings includes activation of the first coil, the second coil, and the third coil, in that order.

15. 3. The electric motor of claim 2, wherein the sequentially activated coils of the first stator and the sequentially activated coils of the second stator together form simultaneously activated coil pairs, each pair characterized by both a coil of the first stator and a coil of the second stator circumferentially aligned with a coil of the first stator.

16. 1. An electric motor, comprising: an output shaft defining an axis of rotation; a wobble rotor connected to the output shaft; a stator mechanically coupled to the wobble rotor by a wobble traction joint, the tilt axis of the wobble rotor progressing around the rotation axis of the output shaft during wobble of the wobble rotor relative to the stator; Equipped with the surfaces of the wobbling rotor and the stator border a radial dynamic air gap in which a magnetic field is generated by electrical actuation of the electric motor to produce a force between the wobbling rotor and the stator; the oscillating traction joint and the radial dynamic air gap are arranged such that, in a plane containing the axis of rotation of the output shaft, the oscillating traction joint is inclined with respect to the stator defining the boundary of the radial dynamic air gap; the output shaft defines an oil port positioned to introduce a flowable lubricant to the swinging traction joint; an electric motor wherein the progressing point of engagement of said swing traction joint is aligned with the progressing position of the point of minimum of said radial dynamic air gap;

17. an active lubrication system including a pump for directing a flow of lubricant to the swinging traction joint during operation of the motor; 17. The electric motor of claim 16, wherein the oiling port is in fluid communication with an oiling channel defined by a gimbal on which the oscillating rotor is mounted.

18. 1. A method comprising:

1. An electric motor comprising: The electric motor is an output shaft defining an axis of rotation; a first wobbling rotor rotationally coupled to the output shaft; and a first stator mechanically coupled to the first wobbling rotor by a first wobbling traction joint, wherein surfaces of the first rotor and the first stator border a first radial dynamic air gap; a second wobbling rotor rotationally coupled to the output shaft; and a second stator mechanically coupled to the second wobbling rotor by a second wobbling traction joint, wherein surfaces of the second rotor and the second stator border a second radial dynamic air gap; Equipped with a progressive point of engagement of said first swing traction joint aligned with a progressive location of a minimum point of said first radial dynamic air gap; the electric motor is configured such that in a first plane including an axis of rotation of the output shaft, the first oscillating traction joint is inclined with respect to a surface of the first stator that defines a boundary of the first dynamic air gap, and the second oscillating traction joint and the second radial dynamic air gap are arranged such that in a second plane including an axis of rotation of the output shaft, the second oscillating traction joint is inclined with respect to a surface of the second stator that defines a boundary of the second dynamic air gap; operating the electric motor by activating the first stator, causing the first wobbler rotor to wobble relative to the first stator, generating a first magnetic field across the first radial dynamic air gap, thereby generating a first force between the first wobbler rotor and the first stator to rotate the output shaft, a first tilted axis of the first wobbler rotor advancing to define a first conical surface about the rotational axis of the output shaft, and activating the second stator, causing the second wobbler rotor to wobble relative to the second stator, generating a second magnetic field across the second radial dynamic air gap, thereby generating a second force between the second wobbler rotor and the second stator to rotate the output shaft, and a second tilted axis of the second wobbler rotor advancing to define a second conical surface about the rotational axis of the output shaft; The method includes:

19. 20. The method of claim 18, wherein during operation of the electric motor, a first advancing point of engagement of the first swinging traction joint is rotationally aligned with a second advancing point of engagement of the second swinging traction joint.

20. Operating the electric motor comprises:

20. The method of claim 18, comprising sequentially activating a first plurality of windings of the first stator and sequentially activating a second plurality of windings of the second stator to transmit cumulative torque to the first wobbling rotor and the second wobbling rotor to rotate the output shaft.

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