Magnetic flux reduction circuit for mitigating main bearing current in electric motors and gearboxes

Abstract

A magnetic flux reduction circuit is provided for mitigating main bearing current in electric motors and gearboxes. An electric motor system includes: a stator connected to a housing of an electric motor; a main bearing connected to the housing; a main shaft rotating on the main bearing; a rotor mounted on the main shaft and rotating relative to the stator; and at least one of a magnetic flux reducing circuit element and a conductive rolling element arrangement disposed inside the main bearing and closer to the stator and the rotor than the main bearing, and reducing a bearing current flow through the main bearing.

Description

[0001] introduction Technical Field

[0002] The information provided in this section is for the purpose of generally presenting the context of the present disclosure. The work of the presently named inventors - to the extent it is described in this section, and aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither explicitly nor implicitly admitted to be prior art against the present disclosure.

[0003] The present disclosure relates to electric motors, and more particularly to circuits for reducing cyclic bearing currents (CBC), electrical discharge machining (EDM), and leakage currents in electric motors and gearboxes. Background Art

[0004] The electric machine may include an electric motor and a gearbox (or gearbox). A power source may supply a direct current (DC) voltage to an inverter, which converts the DC voltage into an alternating current (AC) voltage. The AC voltage drives the stator of the electric motor, which in turn rotates the rotor and shaft of the electric motor. The rotating shaft drives the gears of the gearbox. In a vehicle, the gearbox may be connected to one or more drive shafts for propelling the vehicle. Summary of the invention

[0005] An electric motor system is disclosed and includes: a stator connected to a housing of the electric motor; a main bearing connected to the housing; a main shaft rotating on the main bearing; a rotor mounted on the main shaft and rotating relative to the stator; and at least one of a magnetic flux reducing circuit element and a conductive rolling element device, which is disposed inside the main bearing and closer to the stator and the rotor than the main bearing, and reduces bearing current flow through the main bearing.

[0006] In other features, at least one of the magnetic flux reducing circuit element and the conductive rolling element arrangement includes at least two conductive rolling element arrangements.

[0007] In other features, at least one of the flux reducing circuit element and the conductive rolling element device includes a conductive bearing, brush, or spring in contact with the main shaft.

[0008] In other features, at least one of the flux reducing circuit element and the conductive rolling element device reduces or eliminates EDM bearing currents through the main bearing.

[0009] In other features, at least one of the flux reducing circuit element and the conductive rolling element device is disposed on the spindle.

[0010] In other features, at least one of the flux reducing circuit element and the conductive rolling element device is disposed within the spindle.

[0011] In other features, at least one of the magnetic flux reducing circuit element and the conductive rolling element device at least one of: i) operates as a shunt, and ii) reduces an amount of change in magnetic flux of the motor.

[0012] In other features, at least one of the flux reducing circuit element and the conductive rolling element device grounds the spindle.

[0013] In other features, at least one of the flux reducing circuit element and the conductive rolling element device has a lower impedance than one of the main bearings.

[0014] In other features, at least one of the magnetic flux reducing circuit element and the conductive rolling element device includes a conductive fluid.

[0015] In other features, at least one of the magnetic flux reducing circuit element and the conductive rolling element arrangement is preloaded.

[0016] In other features, at least one of the flux reducing circuit element and the conductive rolling element device has at least one of: a smaller inner diameter than one of the main bearings and a smaller outer diameter than one of the main bearings.

[0017] In other features, the motor system further includes at least one of a preload element and a conductive element extending from at least one of the flux reducing circuit element and the conductive rolling element device to a member of the housing.

[0018] In other features, the motor system further comprises a preload element that preloads at least one of the flux reduction circuit element and the conductive rolling element device. The preload element comprises at least one of a wire, a stranded and braided wire, a Litz wire, a strap, and a sliding spring.

[0019] In other features, at least one main bearing includes a stacked ball bearing arrangement.

[0020] In other features, the motor system further includes: a pair of temperature control elements disposed adjacent to the main bearing; a first set of fluid lines that circulate a first fluid through the pair of temperature control elements; another temperature control element disposed adjacent to at least one of the flux reducing circuit element and the conductive rolling element device; and a second set of fluid lines that circulate the first fluid or the second fluid through the other temperature control element, wherein the fluid flowing through the other temperature control element is hotter than the fluid flowing through the pair of temperature control elements.

[0021] In other features, the first set of fluid lines is not connected to, and is independent of, the second set of fluid lines.

[0022] In other features, an electric motor system is disclosed and includes: a stator connected to a housing of the electric motor; a main bearing connected to the housing; a main shaft rotating on the main bearing; a rotor mounted on the main shaft and rotating relative to the stator; and at least two magnetic flux reduction circuit elements, which are arranged outside the main bearing and farther away from the stator and the rotor than the main bearing, and reduce the flow of bearing current through the main bearing.

[0023] In other features, an electric motor system is disclosed and includes: a stator connected to a housing of the electric motor; a main bearing connected to the housing; a main shaft rotating on the main bearing; a rotor mounted on the main shaft and rotating relative to the stator; at least one of a magnetic flux reduction circuit element and a conductive rolling element device configured to reduce bearing current flow through the main bearing; a pair of temperature control elements disposed adjacent to the main bearing; a first set of fluid lines that circulate a first fluid through the pair of temperature control elements; another temperature control element disposed adjacent to at least one of the magnetic flux reduction circuit element and the conductive rolling element device; and a second set of fluid lines that circulate the first fluid or the second fluid through the other temperature control element. The fluid flowing through the other temperature control element is hotter than the fluid flowing through the pair of temperature control elements.

[0024] In other features, the motor system further includes: a pumping circuit configured to control the flow of a first fluid into and out of a first set of fluid lines, and to control the flow of a first fluid or a second fluid into and out of a second set of fluid lines; and a control module configured to control the operation of the pumping circuit to control the temperature of the main bearing and at least one of the flux reduction circuit element and the conductive rolling element device.

[0025] The present invention also includes the following scheme:

[0026] Solution 1. A motor system comprising:

[0027] a stator connected to the housing of the electric motor;

[0028] a main bearing connected to the housing;

[0029] a main shaft rotating on the main bearing;

[0030] a rotor mounted on the main shaft and rotating relative to the stator; and

[0031] At least one of a magnetic flux reducing circuit element and a conductive rolling element device is disposed inside the main bearing and closer to the stator and the rotor than the main bearing, and reduces a bearing current flowing through the main bearing.

[0032] Option 2. An electric motor system according to Option 1, wherein the at least one of the magnetic flux reducing circuit element and the conductive rolling element device includes at least two conductive rolling element devices.

[0033] Option 3. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device includes a conductive bearing, a brush or a spring in contact with the main shaft.

[0034] Option 4. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device reduces or eliminates the electrical discharge machining bearing current through the main bearing.

[0035] Option 5. The electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device is disposed on the main shaft.

[0036] Option 6. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device is disposed within the main shaft.

[0037] Option 7. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device performs at least one of the following: i) operates as a shunt, and ii) reduces the amount of change in the magnetic flux of the motor.

[0038] Option 8. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device grounds the main shaft.

[0039] Option 9. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device has a smaller impedance than one of the main bearings.

[0040] Option 10. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device includes a conductive fluid.

[0041] Option 11. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device is preloaded.

[0042] Option 12. An electric motor system according to Option 1, wherein at least one of the magnetic flux reducing circuit element and the conductive rolling element device has at least one of the following: i) a smaller inner diameter than one of the main bearings and ii) a smaller outer diameter than one of the main bearings.

[0043] Option 13. The electric motor system of Option 1 further comprises at least one of a preload element and a conductive element extending from the at least one of the magnetic flux reducing circuit element and the conductive rolling element device to a member of the housing.

[0044] Option 14. The motor system according to Option 13 also includes a preloading element, which preloads at least one of the magnetic flux reduction circuit element and the conductive rolling element device, wherein the preloading element includes at least one of a wire, a twisted and braided wire, a Litz wire, a belt and a sliding spring.

[0045] Embodiment 15. An electric motor system according to Embodiment 1, wherein at least one of the main bearings comprises a stacked ball bearing arrangement.

[0046] Solution 16. The motor system according to Solution 1, further comprising:

[0047] a pair of temperature control elements disposed adjacent to the main bearing;

[0048] a first set of fluid lines that circulate a first fluid through the pair of temperature control elements;

[0049] another temperature control element disposed adjacent said at least one of said magnetic flux reducing circuit element and said conductive rolling element means; and

[0050] A second set of fluid lines circulates the first fluid or the second fluid through the other temperature control element, wherein the fluid flowing through the other temperature control element is hotter than the fluid flowing through the pair of temperature control elements.

[0051] Embodiment 17. The electric motor system of Embodiment 16, wherein the first set of fluid lines is not connected to the second set of fluid lines and is independent of the second set of fluid lines.

[0052] Solution 18. A motor system comprising:

[0053] a stator connected to the housing of the electric motor;

[0054] a main bearing connected to the housing;

[0055] a main shaft rotating on the main bearing;

[0056] a rotor mounted on the main shaft and rotating relative to the stator; and

[0057] At least two magnetic flux reducing circuit elements are disposed outside the main bearing and farther from the stator and the rotor than the main bearing and reduce a bearing current flowing through the main bearing.

[0058] Solution 19. A motor system comprising:

[0059] a stator connected to the housing of the electric motor;

[0060] a main bearing connected to the housing;

[0061] a main shaft rotating on the main bearing;

[0062] a rotor mounted on the main shaft and rotating relative to the stator;

[0063] at least one of a magnetic flux reducing circuit element and an electrically conductive rolling element device configured to reduce a bearing current flow through the main bearing;

[0064] a pair of temperature control elements disposed adjacent to the main bearing;

[0065] a first set of fluid lines that circulate a first fluid through the pair of temperature control elements;

[0066] another temperature control element disposed adjacent said at least one of said magnetic flux reducing circuit element and said conductive rolling element means; and

[0067] A second set of fluid lines circulates the first fluid or the second fluid through the other temperature control element, wherein the fluid flowing through the other temperature control element is hotter than the fluid flowing through the pair of temperature control elements.

[0068] Embodiment 20. The electric motor system according to embodiment 16 further comprises:

[0069] a pumping circuit configured to control the flow of the first fluid into and out of the first set of fluid lines, and to control the flow of the first fluid or the second fluid into and out of the second set of fluid lines; and

[0070] A control module is configured to control operation of the pumping circuit to control the temperature of the main bearing and the at least one of the flux reducing circuit element and the conductive rolling element arrangement.

[0071] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The present disclosure will become more fully understood from the detailed description and accompanying drawings, in which:

[0073] Figure 1 is an example common mode voltage (CMV) signal;

[0074] Figure 2 is a cross-sectional side view of an example gearbox and motor showing the CBC, EDM bearing current, leakage current, and magnetic flux area associated with the CBC;

[0075] Figure 3 is a functional block diagram of a motor control system according to the present disclosure, including a cross-sectional side view of an example gearbox and a motor including a flux reduction circuit including flux reduction circuit elements disposed inside a main bearing of the motor;

[0076] Figure 4 is a functional block diagram of an electric motor system according to the present disclosure, including a cross-sectional side view of an example gearbox and electric motor including an electrically conductive rolling element arrangement disposed outside of a main bearing of the electric motor;

[0077] Figure 5 is a cross-sectional side view of an example gearbox including a high impedance gear and an electric motor including a flux reduction circuit according to the present disclosure;

[0078] Figure 6 is an impedance circuit according to the present disclosure that represents the impedance of the main bearing relative to the impedance of the flux reducing circuit element or the conductive rolling element device;

[0079] Figure 7 is a cross-sectional view of a stacked bearing arrangement according to the present disclosure;

[0080] Figure 8 is a cross-sectional view of a parallel temperature control circuit for independently controlling the temperature of a main bearing and a conductive rolling element device according to the present disclosure;

[0081] Fig. 9 is a cross-sectional view of a series temperature control circuit for controlling the temperature of a main bearing and a conductive rolling element device according to the present disclosure;

[0082] Fig.10 is a side cross-sectional view of a portion of an electric motor according to the present disclosure showing a support frame and a grounding device;

[0083] Fig.11 is a side cross-sectional view of a portion of an electric motor according to the present disclosure showing different preload elements and implementation locations for a conductive rolling element arrangement;

[0084] Fig.12 is a cross-sectional view of a portion of an electric motor including a conductive rolling element device and a preload element according to the present disclosure;

[0085] Fig.13 The present invention is a method of manufacturing a conductive rolling element device and a preloading element. Fig.12 A side cross-sectional view of another portion of the motor;

[0086] Fig.14 is a side cross-sectional view of a portion of an electric motor including a housing and a preload element including a wear resistant tip according to the present disclosure; and

[0087] Fig.15 is a functional block diagram of an electric motor system according to the present disclosure, including a cross-sectional side view of an example gearbox and electric motor including conductive rolling element arrangements disposed on the inner and outer surfaces of a motor shaft.

[0088] In the drawings, reference numerals may be repeated to identify similar and / or identical elements. DETAILED DESCRIPTION

[0089] The electric motor generally includes a stator, a rotor and a main shaft. The rotor is connected to the main shaft and rotates relative to the stator. The inverter converts the DC power into AC voltage and current to the coils of the stator to generate a magnetic field, which causes the rotor to rotate and thus the main shaft to rotate. As a byproduct, the stator is supplied with CMV and common mode current (CMC) via the inverter. The main shaft rotates on the main bearing located near the end of the main shaft.

[0090] The inverter performs switching operations to convert the DC power supply voltage into an AC power supply voltage that supplies the stator. Figure 1 As shown in , the CMV does not have a pure sinusoidal pattern, but rather a step-like (or "discontinuous") pattern due to the switching of the inverter. The rising and falling transitions of the CMV "steps" are called dV / dt (or the change in CMV over time). The change in CMV causes CMC, which in turn causes a change in flux (or dΦ / dt). CMC (or I CMC ) is equal to the motor parasitic capacitance and dV CMV Part of the CMC flows through the bearings and the rotor shaft and becomes the circulating bearing current (CBC), which is equal to the voltage Vshaft across the main shaft of the motor divided by the resistance Rshaft of the main shaft.

[0091] The magnetic flux appears over the area extending across the stator and across the motor between the main bearings, as Figure 2 as shown in . Figure 2A gearbox 200 and an electric motor 202 are shown. The electric motor 202 includes a stator 204, a rotor 206, and a main shaft 208 that rotates with the rotor 206. The area of ​​the magnetic flux is represented by an ellipse 210 and results in a voltage Vshaft measured across the main shaft 208 from a point at a first main bearing 212 to a point at a second main bearing 214. The voltage across the shaft Vshaft results in a circulating bearing current (CBC) represented by a dashed arrow 216 that flows through the main shaft 208, through the bearings 212, 214, and through the housing 218.

[0092] The EDM bearing current occurs due to the accumulated voltage on the main shaft 208. Unlike the CBC, the EDM bearing current occurs somewhat randomly and depends on how often a voltage threshold is exceeded for the main bearings 212, 214. The voltage threshold may refer to the voltage at which current begins to flow through the oil, lubricant, or grease of the main bearings 212, 214. The frequency of the CBC is the same as or proportional to the switching frequency of the current supplied to the stator 204. However, the frequency of the EDM bearing current is not the same as the switching frequency of the current supplied to the stator 204. The EDM bearing current is represented by arrows 220 and flows through the stator 204, the rotor 206, the housing 218, and the main bearings 212, 214.

[0093] The main shaft 208 is coupled to the shaft 222 of the gearbox 200 via a coupler 224 or via gears. The shaft 222 rotates on a bearing (e.g., bearing 226 is shown). The gearbox 200 and the motor 202 can be mounted on base plates 230, 232, which can be grounded as shown. Leakage current can occur from the stator 204 through the housing 218, the main bearing 212, the coupler 224 (or gear), the shafts 208, 222 and the bearing 226 to the base plate 230. This is represented by the dashed arrow 234. The leakage current can damage the gearbox bearing 226 and the gears of the gearbox 200, and can cause slotting of the gears.

[0094] The dV / dt instances that occur in the CMC due to inverter switching of the current supplied to the motor 202 cause micro discharges to occur between the bearing surfaces, i.e., between the surfaces of the ball bearing and the bearing seat (or race). These discharges may occur at a high frequency and may cause pitting, frosting, and grooves on the bearing surfaces. This results in damage to the bearing surfaces and causes increased running noise and reduced operating efficiency of the motor 202.

[0095] Bearing currents (including CBC and EDM bearing currents) are a challenging problem for electric machine systems including motors and / or generators. This applies to battery, hybrid and fuel cell electric vehicles (including cars, trains and ships), and also to wind turbines. Bearing currents can cause damage to motor bearings, gear bearings, gears and their lubricants, and lead to noise, vibration and harshness (NVH) problems, gear and bearing failures, motor and gearbox failures, and costly recalls.

[0096] The examples described herein include a magnetic flux reduction circuit and a conductive rolling element device that reduces the magnetic flux area, CBC, Vshaft, EDM bearing current, and leakage current of the motor and the corresponding gearbox. The examples include conductive bearing grounding elements and other grounding elements at various positions in the motor and gearbox, which alleviate CBC, EDM bearing current and leakage current. The examples also include a motor and gearbox impedance relationship for minimizing the current through the motor main bearing and the gearbox bearing. The examples also include a temperature control circuit for regulating the temperature of the main bearing, the magnetic flux reduction circuit element, and the conductive rolling element device. The conductive rolling element device may include bearings, brushes, clips, springs, slip rings, bearings without rolling elements but filled with conductive fluids, etc., which are in contact with rotating elements (such as rotating shafts or elements connected to the rotating shaft and rotating with the rotating shaft). The magnetic flux reduction circuit element includes a conductive rolling element device and other devices, such as i) elements that do not include rolling elements, such as ball bearings, and ii) elements disposed between the conductive rolling element device and other elements of the motor (e.g., the housing or other structural elements of the motor). Elements disposed between the conductive rolling element device and other elements of the motor may include: conductive rods, arms and / or structures; solid and / or woven sheets and / or wires; preload devices, such as springs; etc. The conductive rolling element device provides better conductivity and durability than carbon brushes or carbon rods. The conductive rolling element device may be grounded or ungrounded.

[0097] In one embodiment, a grounding element (including conductive bearings, conductive brushes and / or clips, slip rings, rotating devices, and / or conductive fluids) is implemented in the motor and / or corresponding gearbox to protect the motor bearings and / or gearbox bearings and gears from bearing currents and associated discharges. Examples include providing a grounding element with an impedance less than the impedance of the main bearings and / or gears to reduce current through the main bearings and gears. Lower impedance is provided by including a preloaded element; preloading the element; using conductive or low viscosity oil; reducing the thickness of the oil; mounting on a (internal or external) surface to mitigate skin effect; and / or providing an element with an increased or reduced contact area.

[0098] The flux reduction circuit elements may be located in various locations within the motor and corresponding gearbox. Each motor may have one or more flux reduction circuit elements. The flux reduction circuit elements may be mounted on one or both ends of the rotor shaft / gear shaft. The flux reduction circuit elements, which may be implemented on the grounding cable between the motor / drive unit and the vehicle ground, are more efficient and cost effective for bearing current reduction than inverter chokes. The flux reduction circuit elements i) reduce CBC by reducing dΦ / dt, ii) provide a shunt to shunt bearing currents, and iii) ground the main shaft of the motor to minimize and / or eliminate EDM bearing currents.

[0099] The examples disclosed herein are reliable and effective countermeasures to both CBC and EDM bearing currents. The examples provide improved bearing current shunting, reduction and grounding with reduced main bearing impedance, friction and wear.

[0100] Figure 3-Figure 15 The examples include various features. Some of these features are not shown in all drawings, but are applicable to all examples in these drawings.

[0101] Figure 3 A motor control system 300 is shown, which includes an example gearbox 302 and a motor 304, which includes a magnetic flux reduction circuit 306. The magnetic flux reduction circuit 306 includes one or more magnetic flux reduction circuit elements 308 (two are shown) that are disposed inside the motor main bearing 310. The motor 304 includes a stator 312, a rotor 314, and a main shaft 316. The stator 312 is mounted on a housing 318. The magnetic flux reduction circuit element 308 is implemented as an annular bearing in this example. The magnetic flux reduction circuit element 505 may also include or be other conductive devices, such as brushes, slip rings, clips, etc. The main bearing 310 is also annular. The main shaft 316 extends through the magnetic flux reduction circuit element 308 and the main bearing 310. Each of the magnetic flux reduction circuit element 308 and the main bearing 310 includes a pair of bearing seats (or races) and bearing balls carried on and between the races. The flux reduction circuit element 308 reduces the flux area of ​​the CBC and reduces, minimizes, and / or eliminates CMC and EDM bearing currents through the main bearing 310. The reduced flux area is represented by oval 320. The flux area that would be associated with the main bearing 310 if the flux reduction circuit element 308 was not included is represented by oval 322. Current through the flux reduction circuit element 308 is represented by arrow 324. Current through the main bearing 310, if any, is represented by arrow 326. The flux reduction circuit element 308 may be connected to the housing 318, a conductive member of the housing, and / or a conductive member extending from the housing, such as conductive member 327.

[0102] Gearbox 302 includes bearings 328 and shaft 329, which may be coupled to main shaft 316 directly or via two or more gears. Magnetic flux reducing circuit element 308 reduces and / or prevents leakage current from flowing through shaft 316, bearings 328, and housing 331 of gearbox 302.

[0103] The motor 304 may receive CMV and CMC from an inverter circuit 330, which receives power from a power source 332, such as a battery pack of the vehicle. A control module 334 controls and / or monitors the power source 332, controls the inverter circuit 330, and thus controls the operation of the motor 304. The CMV and CMC may be provided to the stator 312.

[0104] Figure 4 An electric motor system 400 is shown that includes an example gearbox 402 and an electric motor 404. The electric motor 404 includes one or more conductive rolling element devices 406 (two are shown) that are disposed outside of a main bearing 410 of the electric motor. The conductive rolling element devices 406 may alternatively be other conductive devices such as brushes, slip rings, clips, etc. The conductive rolling element devices 406 may be mounted to a plate 412 that is mounted to a housing 414 of the electric motor 404. The electric motor 404 includes a stator 416 and a rotor 418 that rotates with a main shaft 420. Bearing currents through the main bearing 410 are indicated by arrows 415. Bearing currents through the conductive rolling element devices 406 are indicated by arrows 417. By passing at least some of the bearing current through the conductive rolling element devices 406, the bearing currents through the main bearing 410 are reduced.

[0105] Figure 5 An example gearbox 500 is shown including a high impedance gear and a motor 502 including a magnetic flux reduction circuit 504 having a magnetic flux reduction circuit element 505. The magnetic flux reduction circuit element 505 may also include or be alternatively other conductive devices such as brushes, slip rings, clamps, etc. The gearbox 500 may include a first gear 506 connected to a main shaft 508 of the motor 502 via a first shaft 510 and / or a coupler 512. The gearbox 500 may also include a second gear 514 meshing with the first gear 506 and connected to a second shaft 516. The impedance of the gears 506, 514 and / or the shafts 510, 516 may be higher than the impedance of the main bearing 520 of the motor 502. This may include forming the gears 506, 514 and / or the shafts 510, 516 from a material(s) different than the material(s) of the main bearing 520 to have a higher impedance than the main bearing 520. This reduces the amount of leakage current that flows from the motor 502 and through the main bearing 520 and components of the gearbox 500 , such as the gears 506 , 514 and shafts 510 , 516 .

[0106] In one embodiment, shaft 516 includes one or more flux reducing circuit elements and / or conductive rolling element devices (e.g., flux reducing circuit element 505) that may be axially inboard or outboard of gear 514. One conductive rolling element device 530 is shown, which may be provided in addition to other (or main) bearings on shaft 516. Conductive rolling element device 530 may alternatively be one or more other conductive devices, such as brushes, slip rings, clips, etc. Although not shown, conductive rolling elements may be located on shaft 510, axially inboard and / or outboard of gear 514. Conductive rolling element devices located on shafts 510, 516 may be provided to minimize current flow through gears 506, 514, shaft 516, and / or other bearings on shaft 510 and / or shaft 516.

[0107] Figure 6 An impedance circuit 600 is shown, which represents the impedance 602, 604 of a main bearing (such as any main bearing mentioned herein), and the impedance 604 of a magnetic flux reduction circuit element or conductive rolling element device, respectively. The impedance of the main bearing can be greater than the impedance of the magnetic flux reduction circuit element and / or conductive rolling element device mentioned herein. This can be achieved by making the material of the main bearing have a higher impedance than the impedance of the conductive rolling element device. The impedances are connected in parallel. The magnetic flux reduction circuit element can have a current flow path that is shorter than the current flow path of the main bearing, resulting in a lower impedance. The lubricant, oil and / or grease of the main bearing can have a higher impedance than the conductive lubricant, oil and / or grease of the magnetic flux reduction circuit element and the conductive rolling element device. The impedance of the magnetic flux reduction circuit element has a reduced impedance at the frequency of the bearing current (for example, at 1.5 megahertz (MHz)). By providing a parallel arrangement, the bearing current is divided into a current passing through the main bearing and other currents passing through the magnetic flux reduction circuit element and the conductive rolling element device.

[0108] The impedance of a bearing comprising inner and outer races (or bearing seats) and bearing balls is based on the impedance of the inner and outer races, the impedance of the bearing balls or bearing rollers, and the impedance of the oil (or lubricant) layer between the races and the ball bearings. The oil (or lubricant) may coat the bearing balls. By reducing the radius of the races and the radius of each bearing ball or bearing roller, the impedance of the races and ball bearings is reduced. The capacitance is inversely proportional to the thickness of the oil coating.

[0109] In one embodiment, the main bearing impedance is minimized and contains a lubricant with low viscosity. In one embodiment, the main bearing includes a thicker oil film than the magnetic flux reduction circuit element and the conductive rolling element arrangement. In another embodiment, the magnetic flux reduction circuit element and the conductive rolling element arrangement are preloaded to reduce impedance. In another embodiment, the magnetic flux reduction circuit element and the conductive rolling element arrangement have a larger contact surface area than the main bearing to have a lower impedance than the main bearing.

[0110] Figure 7 A stacked bearing arrangement 700 is shown, which can be used in place of the main bearing arrangement shown in the other figures. The stacked bearing arrangement is provided as another example of how to increase the impedance of the main bearing to reduce the bearing current through the main bearing. The stacked bearing arrangement 700 includes an inner ring 702, an intermediate ring 704, and an outer ring 706. A first set of bearing balls or bearing rollers 708 is disposed between and rides on the tracks of the rings 702, 704. A second set of bearing balls 710 is disposed between and rides on the tracks of the rings 704, 706. The stacked bearing arrangement 700 can also be used to reduce gear currents (or leakage currents) to the gearbox. The stacked bearing arrangement 700 increases the impedance relative to the main bearing with a non-stacked arrangement to reduce the bearing current and gear current (if applicable) through the bearing. The stacked bearing arrangement 700 can also replace the bearings of the gearbox to reduce leakage currents into and / or through the gearbox. The bearing ball groups 708, 710 are radially stacked. The bearing ball sets 708, 710 may also be axially stacked.

[0111] Figure 8A parallel temperature control circuit 800 is shown for independently controlling the temperature of a main bearing 802 and a conductive rolling element device 806 of a motor 804. The motor 804 includes a stator 810 and a rotor 812, as well as a main shaft 814. The main bearing 802 has a corresponding temperature control element (e.g., a plate, ring, ring, etc.) 816. The conductive rolling element device 806 has a corresponding temperature control element (e.g., a plate, ring, ring, etc.) 818. The temperature control elements 816, 818 receive corresponding fluids from a pumping circuit 820, which may include one or more pumps, valves, flow controllers, etc. The pumping circuit 820 is controlled by a control module 822. A first fluid is supplied from the pumping circuit 820 to the temperature control element 816. A second fluid is supplied from the pumping circuit 820 to the temperature control element 818. The pumping circuit 820 is fluidly connected to a fluid source 821. In one embodiment, the first fluid is a coolant and is used to reduce the temperature of the element 816, and the second fluid is used to increase the temperature of the element 818. The control module 822 controls the temperature of the fluids so that the first fluid is cooler than the second fluid. Fluid line 824 connects the pumping circuit 820 to the element 816. Fluid line 826 connects the pumping circuit 820 to the element 818. The control module 822 can independently control the temperature of the fluids via a heating element 825 (e.g., a heater, a coil, etc.) and / or a cooling device 827 (e.g., a heat exchanger, a cold plate, etc.). The control module 822 can circulate the first fluid through the element 816, and then subsequently through the element 818, so that the fluid flowing through the element 818 is hotter than the fluid flowing through the element 816.

[0112] Although elements 816, 818 are shown on certain sides of the bearing 802 and the conductive rolling element device 806, elements 816, 818 may be on other sides of the bearing 802 and the conductive rolling element device 806. Likewise, the fluid flowing through element 816 and / or element 818 may also flow through shaft 814. The heating element 818 dilutes the oil lubricant in the conductive rolling element device 806, which reduces the impedance of the conductive rolling element device 806, thereby increasing the bearing current through the conductive rolling element device 806.

[0113] Fig. 9A series of temperature control circuits 900 are shown for controlling the temperature of a main bearing 902 and a conductive rolling element device 906 of a motor 904. The motor 904 includes a stator 910 and a rotor 912, as well as a main shaft 914. The main bearing 902 has a corresponding temperature control element (e.g., a plate, ring, ring, etc.) 916. The conductive rolling element device 906 has a corresponding temperature control element (e.g., a plate, ring, ring, etc.) 918. The temperature control elements 916, 918 receive corresponding fluids from a pumping circuit 920, which may include one or more pumps, valves, flow controllers, etc. The pumping circuit 920 is controlled by a control module 922. Fluid is supplied from the pumping circuit 920 to the temperature control element 916, and then from the element 916 to the element 918. The pumping circuit 920 is fluidly connected to a fluid source 921. Fluid line 924 is a supply line, and fluid line 926 is a return line. Control module 922 can independently control the temperature of the fluid via heating element 925 (eg, heater, coil, etc.) and / or cooling device 927 (eg, heat exchanger, cold plate, etc.) The fluid flowing through element 918 is hotter than the fluid flowing through element 916 .

[0114] Fig.10 A portion of an electric motor 1000 is shown illustrating a support frame 1002 and a grounding device 1004 connecting a magnetic flux reduction circuit element 1006 to a motor housing 1008. The magnetic flux reduction circuit element 1006 can be implemented as a conductive rolling element device. In the example shown, the magnetic flux reduction circuit element 1006 is disposed on a first shaft 1010, which is connected to a second shaft 1012. The shafts 1010, 1012 rotate relative to the support frame 1002 and the grounding device 1004. The frequency of the bearing current in the motor can be, for example, 1-10 MHz. High frequencies can cause a "skin effect" in which most of the current flowing through the wire is close to the outer surface of the wire and not close to the center (or core) of the wire. For this reason, the grounding device 1004 can be implemented as a twisted braided wire, Litz wire, wire tape, or a solid or braided sheet to increase the current flow between the magnetic flux reduction circuit element 1006 and the grounded housing 1008. This reduces the impedance of the grounding device 1004 and alleviates the skin effect.

[0115] The magnetic flux reduction circuit element 1006 can be implemented as and / or include a ball roller, a roller bearing, a needle bearing, a thrust bearing, a journal bearing, etc. The magnetic flux reduction circuit element 1006 can be preloaded and include a preload element. The preload element can be a bracket (such as bracket 1002), and / or can include a preload spring, a seal, etc. The magnetic flux reduction circuit element 1006 can include a conductive low-impedance lubricant. The magnetic flux reduction circuit element 1006 can be implemented as an unloaded conductive bearing for grounding and shunting the bearing current to ground. The bearing current is shunted to ground instead of flowing through the main bearing of the motor. By having the magnetic flux reduction circuit element 1006 on the shaft 1010 (or outer shaft), a shorter bearing current path is provided than when it is installed on, for example, the inner shaft 1012.

[0116] The grounding device (or wire) 1004 may be used in parallel with one or more other grounding elements, such as brushes or sliding clips. The brushes or sliding clips may also extend from the magnetic flux reducing circuit element 1006 to the housing 1008 and / or from the shaft 1010 to the housing 1008. One or more sliding clips may be used to press the magnetic flux reducing circuit element 1006 against the shaft 1010. This may be done to i) reduce the impedance of the series combination of the magnetic flux reducing circuit element 1006 and the sliding clip, and / or ii) handle displacement and load changes from different directions.

[0117] Fig.11 A portion 1100 of an electric motor is shown illustrating different preload elements of a conductive rolling element arrangement. The electric motor includes a housing (or casing) 1102, a first shaft 1104, a second shaft 1106, and a coupler 1108 mounted on the first shaft 1104. The housing 1102 includes a plurality of portions 1102A, 1102B, 1102C. The coupler 1108 is fixed to the first shaft 1104 and rotates with the first shaft 1104. Two main bearings 1110, 1112 are mounted on the coupler 1108. Although in Fig.111104 is not shown, but the first shaft 1104 can be rotated by the rotor of the motor. Conductive rolling element devices 1114, 1116, 1118, 1120 (which can be implemented as bearings) are shown, or can be conductive brushes and / or clips. Preload elements 1122, 1124, 1126 are respectively arranged between the conductive rolling element devices 1116, 1118, 1120 and the housing 1102. The preload elements 1122, 1124, 1126 can be implemented as springs, such as sliding springs, and can include wear-resistant tips 1130, 1132. The preload elements 1122, 1124, 1126 can be implemented as and / or include Litz wires, twisted and braided wires, straps, etc. Each of the conductive rolling element devices 1114, 1116, 1118, 1120 may include i) a preload spring and / or seal (two are indicated as 1140 on the conductive rolling element device 1114), and ii) a conductive lubricant, for example, between the bearing seat and the ball bearing. The preload provided by the preload elements 1122, 1124, 1126 reduces the impedance of the conductive rolling element devices 1116, 1118, 1120.

[0118] The conductive rolling element device 1114 can be arranged and pressed between and in contact with the housing 1102 and the first shaft 1104. The press fit can apply a preload to 1114, thereby reducing the oil film thickness between the seat and the rolling element. This reduces the impedance of the conductive rolling element device 1114. The conductive rolling element device 1114 has a smaller inner diameter than the main bearings 1110, 1112, and thus has a smaller inner radius than the main bearings 1110, 1112. This reduces the impedance of the conductive rolling element device 1114 compared to the main bearings 1110, 1112.

[0119] The conductive rolling element device 1120 can be disposed on the second shaft 1106, which can be a slower shaft than the shaft 1104. This reduces the oil film thickness of the conductive rolling element device 1120, so that the conductive rolling element device 1120 has a lower impedance than each of the main bearings 1110, 1112. The conductive rolling element device 1120 can be included and disposed next to and / or near the bearings of the gearbox to protect the bearings of the gearbox. The second shaft 1106 can be connected to the shaft of the gearbox.

[0120] Fig.12A portion 1200 of an electric motor including a preload element 1202 is shown. The preload element 1202 is disposed between a housing 1204 and a conductive rolling element device 1206. The conductive rolling element device 1206 may be disposed on a tube 1208. In another embodiment, the preload element 1202 is disposed between the conductive rolling element device 1206 and the tube 1208. The tube 1208 may be a shaft, a cooling tube, a heating tube, or other tube. The preload element 1202 may be implemented as a slip ring that slides along the rotation direction of the tube (or shaft) 1208. Fig.13 Shows Fig.12 Another part 1300 of the motor and the preload element 1202 are arranged between the housing 1204 and the conductive rolling element device 1206. The conductive rolling element device 1206 is arranged on the tube 1208.

[0121] exist Figure 11-13 In one embodiment, a preload element may be disposed between the conductive rolling element device and an upper portion of the corresponding housing so that, for example, if the corresponding shaft is struck or jerked upward, the amount of preload on the conductive rolling element device increases due to compression of the preload element. In one embodiment, a bearing preload is provided in opposite directions of the main bearing loading and slotting regions to compensate for changes in oil film thickness due to load or road vibrations. The thinner the main bearing oil film thickness becomes, the greater the bending of the preload clip is to reduce the oil film thickness of the conductive rolling element device, thereby also reducing the impedance of the conductive rolling element device.

[0122] Fig.14 A portion 1400 of an electric motor is shown including a housing 1402 and a preload element 1404 including a wear resistant tip 1406. The preload element 1404 is disposed between the housing 1402 and a tube 1408, such as a shaft, cooling tube, heating tube, etc. No conductive rolling element arrangement is included.

[0123] Fig.15An electric motor system 1500 is shown that includes an example gearbox 1502 and an electric motor 1504, the electric motor 1504 including a stator 1503, a rotor 1505, and conductive rolling element devices 1506, 1508, 1510 disposed on the inner and outer surfaces of a main shaft 1512 of the electric motor 1504. Although the conductive rolling element devices 1506, 1508, 1510 are disposed on the inner side of the main bearings 1514, 1516, the conductive rolling element devices 1506, 1508, 1510 may be loaded on the outer side of the main bearings 1514, 1516. As an example, the conductive rolling element device 1510 may be connected to the housing 1520 via a conductive rigid element 1522 (such as a bracket, a rod, a cooling pipe, a lubricant pipe, an inspection pipe, or a wiring pipe, etc.). The conductive rolling element device 1510 and / or its internal bearing seat is fixed and connected to the conductive rigid element 1522. The outer bearing seat of the conductive rolling element device 1510 is connected to the shaft 1512 and rotates with the shaft 1512.

[0124] Although one internal conductive rolling element device 1510 is shown, any number of conductive rolling element devices may be included. Furthermore, although the conductive rolling element device 1510 is disposed on the inside of the main bearing 1516, the conductive rolling element device 1510 may be disposed on the outside of the main bearing 1516 if the shaft 1512 extends to the outside of the main bearing 1516. Furthermore, the conductive rolling element device 1510 and / or other conductive rolling element devices may be included without the conductive rolling element devices 1506, 1508. By disposing the conductive rolling element devices 1506, 1508, 1510 on the inner and outer surfaces of the shaft 1512, the conductive rolling element devices 1506, 1508, 1510 address the skin effect associated with high frequency current passing through the shaft 1512, and most of the current flows near the inner and outer surfaces of the shaft 1512. Current flows through the devices 1506 , 1508 , 1510 and to or from the housing 1520 via, for example, components of the housing and / or components extending from the housing 1520 , such as the conductive components 1530 , 1532 and the conductive stiffness element 1522 .

[0125] The conductive rolling element device disclosed herein can be implemented as a grounded bearing, brush, clip, slip ring at various locations within and / or on the motor. The conductive rolling element device can be positioned to form a shorter current path and thereby have a reduced corresponding impedance path to shunt the bearing current. The conductive rolling element device can be implemented to ground the main bearing or rotor shaft to eliminate EDM bearing currents. The conductive rolling element device can be arranged to reduce the magnetic flux across the corresponding main bearing and the corresponding bearing current generated, wherein the voltage V applied to the motor rotor shaft is equal to dΦ / dt. The main shaft of the motor can be grounded via the conductive rolling element device to reduce CBC (or I BC ), where I BC is equal to Vshaft / Rshaft, where Rshaft is the resistance between points of the main shaft, such as from end to end, from main bearing to main bearing, and / or from conductive rolling element device to conductive rolling element device.

[0126] Examples disclosed herein include bearing current countermeasure (BCC) devices and elements, at least some of which include conductive devices (bearings, brushes, springs, etc.) at various motor and gearbox locations to achieve improved performance and reliability at reduced cost and power loss. The BCC devices and elements i) reduce the CBC of the main bearing by reducing dΦ / dt, ii) shunt the CBC and EDM bearing currents by providing a shunt, and iii) are implemented as part of a reduced impedance path to shunt the EDM bearing current away from the main bearing. At least some BCC devices and elements include conductive bearings with minimal electrical impedance to better mitigate the CBC and EDM bearing currents of the main bearing. This includes skin effect mitigation. The conductive bearings include conductive / low viscosity lubricants to reduce oil film thickness, bearing preloads, increase contact area and / or increase the number of rolling elements to increase the shunt of current away from the main bearing. Examples include grounded mounting locations to reduce the size and electrical impedance of the conductive bearings. Conductive bearings can be located on the drive end or non-drive end of the motor main shaft, on either end of the gearbox gear shaft, inside or outside the shaft, and / or directly on the shaft, cooling pipes, heating pipes, etc. to improve electrical and thermal performance. The conductive bearings can have an impedance less than the main bearings of the motor and the bearings of the gearbox. Examples also enable the addition of a smaller, low-cost AC choke to further reduce BC flowing through the main bearing.

[0127] In one embodiment, the main bearing of the electric motor disclosed herein operates as a high pass filter, and the flux reduction circuit element and the conductive rolling element device operate as a low pass filter. The cutoff frequency of the high pass filter can be at a frequency greater than the frequency of the bearing current. The cutoff frequency of the low pass filter can be greater than the frequency of the bearing current. For example, the high pass filter may not pass frequencies at or below 5 MHz. The low pass filter may pass frequencies at or below 5 MHZ. The flux reduction circuit element and the conductive rolling element device have reduced impedance to allow bearing current to pass through, which is different from the main bearing having a high impedance and allowing minimal or no bearing current to pass through it.

[0128] Preload as referred to herein may include axial and / or radial preload. Preload may be provided by rings, clips, springs, slip rings and / or by an installation process. For example, a magnetic flux reduction circuit element or conductive rolling element device may be press-fitted to provide a thin, low impedance element. The disclosed magnetic flux reduction circuit element and conductive rolling element device may include a lubricating oil film suitable for various speeds, loads, shocks, vibrations, displacements, fluid flow rates, viscosities, temperatures, etc.

[0129] Examples provide both motor and / or cooling and bearing current mitigation. Examples provide increased motor, gearbox and corresponding bearing life and provide a small size solution.

[0130] The foregoing description is merely illustrative in nature and is by no means intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be so limited, because other modifications will become apparent after studying the drawings, the specification and the following claims. It should be understood that, without changing the principles of the present disclosure, one or more steps in the method can be performed in different orders (or simultaneously). In addition, although each embodiment is described above as having certain features, any one or more of those features described with respect to any embodiment of the present disclosure can be implemented in any other embodiment and / or combined with the features of any other embodiment, even if the combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and the arrangement of one or more embodiments with each other is still within the scope of the present disclosure.

[0131] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaged," "coupled," "adjacent," "immediately adjacent," "on," "above," "below," and "disposed." Unless explicitly described as "direct," when describing a relationship between a first and a second element in the above disclosure, the relationship may be a direct relationship in which no other intervening elements exist between the first and second elements, but may also be an indirect relationship in which one or more intervening elements (either spatially or functionally) exist between the first and second elements. As used herein, the phrase "at least one of A, B, and C" should be interpreted to mean a logical (A or B or C) using a non-exclusive logical "or," and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

[0132] In the various figures, the direction of the arrows, as indicated by the arrow heads, generally indicates the flow of information (such as data or instructions) of interest to the illustration. For example, when element A and element B exchange various information, but the information transmitted from element A to element B is relevant to the illustration, the arrow may be directed from element A to element B. The unidirectional arrow does not imply that no other information is transmitted from element B to element A. In addition, for information sent from element A to element B, element B may send a request or receipt confirmation of the information to element A.

[0133] In this application, including the definitions below, the term "module" or the term "controller" may be replaced with the term "circuit". The term "module" may refer to, be part of, or include: an application specific integrated circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit; a digital, analog, or mixed analog / digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or grouped) that executes code; a memory circuit (shared, dedicated, or grouped) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system on a chip.

[0134] The module may include one or more interface circuits. In some examples, the interface circuit may include a wired or wireless interface connected to a local area network (LAN), the Internet, a wide area network (WAN), or a combination thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules connected via the interface circuit. For example, multiple modules may allow load balancing. In a further example, a server (also referred to as a remote or cloud) module may implement some functionality on behalf of a client module.

[0135] The term "code" as used above may include software, firmware, and / or microcode, and may refer to a program, a routine, a function, a class, a data structure, and / or an object. The term "shared processor circuit" covers a single processor circuit that executes some or all code from multiple modules. The term "group processor circuit" covers a processor circuit that executes some or all code from one or more modules in conjunction with an additional processor circuit. References to multiple processor circuits cover multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term "shared memory circuit" covers a single memory circuit that stores some or all code from multiple modules. The term "group memory circuit" covers a memory circuit that stores some or all code from one or more modules in conjunction with additional memory.

[0136] The term "memory circuit" is a subset of the term "computer-readable medium". The term "computer-readable medium" as used herein does not encompass transient electrical or electromagnetic signals propagated through a medium (such as on a carrier wave); therefore, the term "computer-readable medium" may be considered to be tangible and non-transitory. Non-limiting examples of non-transitory tangible computer-readable media are non-volatile memory circuits (such as flash memory circuits, erasable programmable read-only memory circuits, or mask read-only memory circuits), volatile memory circuits (such as static random access memory circuits or dynamic random access memory circuits), magnetic storage media (such as analog or digital magnetic tape or hard drives), and optical storage media (such as CDs, DVDs, or Blu-ray discs).

[0137] The apparatus and methods described in this application may be implemented in part or in whole by a special-purpose computer, which is created by configuring a general-purpose computer to perform one or more specific functions embodied in a computer program. The functional blocks, flow chart components and other elements described above serve as software specifications that can be transformed into computer programs by the routine work of skilled technicians or programmers.

[0138] The computer program includes processor executable instructions stored on at least one non-transitory tangible computer readable medium. The computer program may also include or rely on stored data. The computer program may include a basic input / output system (BIOS) that interacts with the hardware of the special-purpose computer, device drivers that interact with specific devices of the special-purpose computer, one or more operating systems, user applications, background services, background applications, etc.

[0139] A computer program may include: (i) descriptive text to be parsed, such as HTML (Hypertext Markup Language), XML (Extensible Markup Language), or JSON (JavaScript Object Notation), (ii) assembly code, (iii) target code generated by a compiler from source code, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. By way of example only, source code may be written using syntax from languages ​​including: C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Fortran, Perl, Pascal, Curl, OCaml, HTML5 (Hypertext Markup Language Version 5), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Visual Lua, MATLAB, SIMULINK, and

Claims

1. A motor system comprising: a stator connected to the housing of the electric motor; a main bearing connected to the housing; a main shaft rotating on the main bearing; a rotor mounted on the main shaft and rotating relative to the stator; and At least one of a magnetic flux reducing circuit element and a conductive rolling element device is disposed inside the main bearing and closer to the stator and the rotor than the main bearing, and reduces a bearing current flowing through the main bearing.

2. The electric motor system of claim 1, wherein the at least one of the magnetic flux reducing circuit element and the conductive rolling element arrangement comprises at least two conductive rolling element arrangements.

3. The electric motor system of claim 1, wherein the at least one of the magnetic flux reducing circuit element and the conductive rolling element device comprises a conductive bearing, a brush or a spring in contact with the main shaft.

4. The electric motor system of claim 1, wherein said at least one of said flux reducing circuit element and said conductive rolling element arrangement reduces or eliminates EDM bearing currents through said main bearing.

5. The electric motor system of claim 1, wherein the at least one of the magnetic flux reducing circuit element and the conductive rolling element device is disposed on the main shaft.

6. The electric motor system of claim 1, wherein the at least one of the flux reducing circuit element and the conductive rolling element device is disposed within the main shaft.

7. The electric motor system of claim 1, wherein the at least one of the magnetic flux reducing circuit element and the conductive rolling element device at least one of: i) operates as a shunt, and ii) reduces the amount of change in magnetic flux of the motor.

8. The electric motor system of claim 1 wherein said at least one of said flux reducing circuit element and said conductive rolling element arrangement grounds said main shaft.

9. The electric motor system of claim 1, wherein the at least one of the flux reducing circuit element and the conductive rolling element device has a smaller impedance than one of the main bearings.

10. The electric motor system of claim 1, wherein said at least one of said flux reducing circuit element and said conductive rolling element arrangement comprises a conductive fluid.

Images